Guangmin Zhou

We report a facile strategy to synthesize the nanocomposite of Co(3)O(4) nanoparticles anchored on conducting graphene as an advanced anode material for high-performance lithium-ion batteries. The Co(3)O(4) nanoparticles obtained are 10-30 nm in size and homogeneously anchor on graphene sheets as spacers to keep the neighboring sheets separated. This Co(3)O(4)/graphene nanocomposite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance, and good rate capability, highlighting the importance of the anchoring of nanoparticles on graphene sheets for maximum utilization of electrochemically active Co(3)O(4) nanoparticles and graphene for energy storage applications in high-performance lithium-ion batteries.

A well-organized flexible interleaved composite of graphene nanosheets (GNSs) decorated with Fe3O4 particles was synthesized through in situ reduction of iron hydroxide between GNSs. The GNS/Fe3O4 composite shows a reversible specific capacity approaching 1026 mA h g−1 after 30 cycles at 35 mA g−1 and 580 mAh g−1 after 100 cycles at 700 mA g−1as well as improved cyclic stability and excellent rate capability. The multifunctional features of the GNS/Fe3O4 composite are considered as follows: (i) GNSs play a “flexible confinement” function to enwrap Fe3O4 particles, which can compensate for the volume change of Fe3O4 and prevent the detachment and agglomeration of pulverized Fe3O4, thus extending the cycling life of the electrode; (ii) GNSs provide a large contact surface for individual dispersion of well-adhered Fe3O4 particles and act as an excellent conductive agent to provide a highway for electron transport, improving the accessible capacity; (iii) Fe3O4 particles separate GNSs and prevent their restacking thus improving the adsorption and immersion of electrolyte on the surface of electroactive material; and (iv) the porosity formed by lateral GNSs and Fe3O4 particles facilitates ion transportation. As a result, this unique laterally confined GNS/Fe3O4 composite can dramatically improve the cycling stability and the rate capability of Fe3O4 as an anode material for lithium ion batteries.

With the advent of flexible electronics, flexible lithium-ion batteries have attracted great attention as a promising power source in the emerging field of flexible and wearable electronic devices such as roll-up displays, touch screens, conformable active radio-frequency identification tags, wearable sensors and implantable medical devices. In this review, we summarize the recent research progress of flexible lithium-ion batteries, with special emphasis on electrode material selectivity and battery structural design. We begin with a brief introduction of flexible lithium-ion batteries and the current development of flexible solid-state electrolytes for applications in this field. This is followed by a detailed overview of the recent progress on flexible electrode materials based on carbon nanotubes, graphene, carbon cloth, conductive paper (cellulose), textiles and some other low-dimensional nanostructured materials. Then recently proposed prototypes of flexible cable/wire type, transparent and stretchable lithium-ion batteries are highlighted. The latest advances in the exploration of other flexible battery systems such as lithium–sulfur, Zn–C (MnO2) and sodium-ion batteries, as well as related electrode materials are included. Finally, the prospects and challenges toward the practical uses of flexible lithium-ion batteries in electronic devices are discussed.

Lithium-sulfur batteries have attracted attention due to their six-fold specific energy compared with conventional lithium-ion batteries. Dissolution of lithium polysulfides, volume expansion of sulfur and uncontrollable deposition of lithium sulfide are three of the main challenges for this technology. State-of-the-art sulfur cathodes based on metal-oxide nanostructures can suppress the shuttle-effect and enable controlled lithium sulfide deposition. However, a clear mechanistic understanding and corresponding selection criteria for the oxides are still lacking. Herein, various nonconductive metal-oxide nanoparticle-decorated carbon flakes are synthesized via a facile biotemplating method. The cathodes based on magnesium oxide, cerium oxide and lanthanum oxide show enhanced cycling performance. Adsorption experiments and theoretical calculations reveal that polysulfide capture by the oxides is via monolayered chemisorption. Moreover, we show that better surface diffusion leads to higher deposition efficiency of sulfide species on electrodes. Hence, oxide selection is proposed to balance optimization between sulfide-adsorption and diffusion on the oxides.

Abstract Hydrous ruthenium oxide (RuO 2 )/graphene sheet composites (ROGSCs) with different loadings of Ru are prepared by combining sol–gel and low‐temperature annealing processes. The graphene sheets (GSs) are well‐separated by fine RuO 2 particles (5–20 nm) and, simultaneously, the RuO 2 particles are anchored by the richly oxygen‐containing functional groups of reduced, chemically exfoliated GSs onto their surface. Benefits from the combined advantages of GSs and RuO 2 in such a unique structure are that the ROGSC‐based supercapacitors exhibit high specific capacitance (∼570 F g −1 for 38.3 wt% Ru loading), enhanced rate capability, excellent electrochemical stability (∼97.9% retention after 1000 cycles), and high energy density (20.1 Wh kg −1 ) at low operation rate (100 mA g −1 ) or high power density (10000 W kg −1 ) at a reasonable energy density (4.3 Wh kg −1 ). Interestingly, the total specific capacitance of ROGSCs is higher than the sum of specific capacitances of pure GSs and pure RuO 2 in their relative ratios, which is indicative of a positive synergistic effect of GSs and RuO 2 on the improvement of electrochemical performance. These findings demonstrate the importance and great potential of graphene‐based composites in the development of high‐performance energy‐storage systems.

Significance A series of metal sulfides were systematically investigated as polar hosts to reveal the key parameters correlated to the energy barriers and polysulfide adsorption capability in Li−S batteries. The investigation demonstrates that the catalyzing oxidation capability of metal sulfides is critical in reducing the energy barrier and contributing to the remarkably improved battery performance. Density functional theory simulation allows us to identify the mechanism for how binding energy and polysulfides trapping dominate the Li 2 S decomposition process and overall battery performance. The understanding can serve as a general guiding principle for the rational design and screening of advanced materials for high-energy Li−S batteries.

Graphene has been widely used to dramatically improve the capacity, rate capability, and cycling performance of nearly any electrode material for batteries. However, the binding between graphene and these electrode materials has not been clearly elucidated. Here we report oxygen bridges between graphene with oxygen functional groups and NiO from analysis by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy and confirm the conformation of oxygen bridges by the first-principles calculations. We found that NiO nanosheets (NiO NSs) are bonded strongly to graphene through oxygen bridges. The oxygen bridges mainly originate from the pinning of hydroxyl/epoxy groups from graphene on the Ni atoms of NiO NSs. The calculated adsorption energies (1.37 and 1.84 eV for graphene with hydroxyl and epoxy) of a Ni adatom on oxygenated graphene by binding with oxygen are comparable with that on graphene (1.26 eV). However, the calculated diffusion barriers of the Ni adatom on the oxygenated graphene surface (2.23 and 1.69 eV for graphene with hydroxyl and epoxy) are much larger than that on the graphene (0.19 eV). Therefore, the NiO NS is anchored strongly on the graphene through a C–O–Ni bridge, which allows a high reversible capacity and excellent rate performance. The easy binding/difficult dissociating characteristic of Ni adatoms on the oxygenated graphene facilitates fast electron hopping from graphene to NiO and thus the reversible lithiation and delithiation of NiO. We believe that the understanding of this oxygen bridge between graphene and NiO will lead to the development of other high-performance electrode materials.

Abstract Lithium–sulphur batteries with a high theoretical energy density are regarded as promising energy storage devices for electric vehicles and large-scale electricity storage. However, the low active material utilization, low sulphur loading and poor cycling stability restrict their practical applications. Herein, we present an effective strategy to obtain Li/polysulphide batteries with high-energy density and long-cyclic life using three-dimensional nitrogen/sulphur codoped graphene sponge electrodes. The nitrogen/sulphur codoped graphene sponge electrode provides enough space for a high sulphur loading, facilitates fast charge transfer and better immobilization of polysulphide ions. The hetero-doped nitrogen/sulphur sites are demonstrated to show strong binding energy and be capable of anchoring polysulphides based on first-principles calculations. As a result, a high specific capacity of 1,200 mAh g −1 at 0.2C rate, a high-rate capacity of 430 mAh g −1 at 2C rate and excellent cycling stability for 500 cycles with ∼0.078% capacity decay per cycle are achieved.

A unique sandwich structure is designed with pure sulfur between two graphene membranes, which are continuously produced over a large area, as a very simple but effective approach for the fabrication of Li–S batteries with ultrafast charge/discharge rates and long lifetimes.

Twinborn TiO₂–TiN heterostructures enable smooth trapping–diffusion–conversion of polysulfides and produce ultralong life lithium–sulfur batteries.

Abstract Lithium–sulfur (Li–S) battery has emerged as one of the most promising next‐generation energy‐storage systems. However, the shuttle effect greatly reduces the battery cycle life and sulfur utilization, which is great deterrent to its practical use. This paper reviews the tremendous efforts that are made to find a remedy for this problem, mostly through physical or chemical confinement of the lithium polysulfides (LiPSs). Intrinsically, this “confinement” has a relatively limited effect on improving the battery performance because in most cases, the LiPSs are “passively” blocked and cannot be reused. Thus, this strategy becomes less effective with a high sulfur loading and ultralong cycling. A more “positive” method that not only traps but also increases the subsequent conversion of LiPSs back to lithium sulfides is urgently needed to fundamentally solve the shuttle effect. Here, recent advances on catalytic effects in increasing the rate of conversion of soluble long‐chain LiPSs to insoluble short‐chain Li 2 S 2 /Li 2 S, and vice versa, are reviewed, and the roles of noble metals, metal oxides, metal sulfides, metal nitrides, and some metal‐free materials in this process are highlighted. Challenges and potential solutions for the design of catalytic cathodes and interlayers in Li–S battery are discussed in detail.

We review the development of carbon–sulfur composites and the application for Li–S batteries. Discussions are devoted to the synthesis approach of the various carbon–sulfur composites, the structural transformation of sulfur, the carbon–sulfur interaction and the impacts on electrochemical performances. Perspectives are summarized regarding the synthesis chemistry, electrochemistry and industrial production with particular emphasis on the structural optimization of carbon–sulfur composites.

Graphene-sulfur (G-S) hybrid materials with sulfur nanocrystals anchored on interconnected fibrous graphene are obtained by a facile one-pot strategy using a sulfur/carbon disulfide/alcohol mixed solution. The reduction of graphene oxide and the formation/binding of sulfur nanocrystals were integrated. The G-S hybrids exhibit a highly porous network structure constructed by fibrous graphene, many electrically conducting pathways, and easily tunable sulfur content, which can be cut and pressed into pellets to be directly used as lithium-sulfur battery cathodes without using a metal current-collector, binder, and conductive additive. The porous network and sulfur nanocrystals enable rapid ion transport and short Li(+) diffusion distance, the interconnected fibrous graphene provides highly conductive electron transport pathways, and the oxygen-containing (mainly hydroxyl/epoxide) groups show strong binding with polysulfides, preventing their dissolution into the electrolyte based on first-principles calculations. As a result, the G-S hybrids show a high capacity, an excellent high-rate performance, and a long life over 100 cycles. These results demonstrate the great potential of this unique hybrid structure as cathodes for high-performance lithium-sulfur batteries.

A flexible Li–S battery based on an integrated structure of sulfur and graphene on a separator is developed. The internal graphene current collector offers a continuous conductive pathway, a modified interface with sulfur, and a good barrier to and an effective reservoir for dissolved polysulfides, consequently improving the capacity and cyclic life of the Li–S battery. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Lithium-sulfur (Li-S) batteries have attracted great attention as next-generation high specific energy density storage devices. However, the low sulfur loading in the cathode for Li-S battery greatly offsets its advantage in high energy density and limits the practical applications of such battery concepts. Flexible energy storage devices are also becoming increasingly important for future applications but are limited by the lack of suitable lightweight electrode materials with robust electrochemical performance under cyclic mechanical strain. Here, we proposed an effective strategy to obtain flexible Li-S battery electrodes with high energy density, high power density, and long cyclic life by adopting graphene foam-based electrodes. Graphene foam can provide a highly electrically conductive network, robust mechanical support and sufficient space for a high sulfur loading. The sulfur loading in graphene foam-based electrodes can be tuned from 3.3 to 10.1 mg cm−2. The electrode with 10.1 mg cm−2 sulfur loading could deliver an extremely high areal capacity of 13.4 mAh cm−2, much higher than the commonly reported Li-S electrodes and commercially used lithium cobalt oxide cathode with a value of ~3–4 mAh cm−2. Meanwhile, the high sulfur-loaded electrodes retain a high rate performance with reversible capacities higher than 450 mAh g−1 under a large current density of 6 A g−1 and preserve stable cycling performance with ~0.07% capacity decay per cycle over 1000 cycles. These impressive results indicate that such electrodes could enable high performance, fast-charging, and flexible Li-S batteries that show stable performance over extended charge/discharge cycling.

Abstract The detrimental shuttle effect in lithium–sulfur batteries mainly results from the mobility of soluble polysulfide intermediates and their sluggish conversion kinetics. Herein, presented is a multifunctional catalyst with the merits of strong polysulfides adsorption ability, superior polysulfides conversion activity, high specific surface area, and electron conductivity by in situ crafting of the TiO 2 ‐MXene (Ti 3 C 2 T x ) heterostructures. The uniformly distributed TiO 2 on MXene sheets act as capturing centers to immobilize polysulfides, the hetero‐interface ensures rapid diffusion of anchored polysulfides from TiO 2 to MXene, and the oxygen‐terminated MXene surface is endowed with high catalytic activity toward polysulfide conversion. The improved lithium–sulfur batteries deliver 800 mAh g −1 at 2 C and an ultralow capacity decay of 0.028% per cycle over 1000 cycles at 2 C. Even with a high sulfur loading of 5.1 mg cm −2 , the capacity retention of 93% after 200 cycles is still maintained. This work sheds new insights into the design of high‐performance catalysts with manipulated chemical components and tailored surface chemistry to regulate polysulfides in Li–S batteries.

We report the template-directed synthesis of sulphur–carbon nanotubes and their use to form a membrane that is binder-free, highly conductive and flexible. This nanostructured membrane is used as a self-supporting cathode without metal current-collectors for Li-S batteries. The membrane cathode has a high electrical conductivity and renders a long life of sulphur of over 100 charge–discharge cycles. High discharge capacity of sulphur was attained at 712 mA h gsulphur−1 (23 wt% S) and 520 mA h gsulphur−1 (50 wt% S) at a high current density (6 A gsulphur−1). The overall capacity of the flexible cathode correspondingly reaches 163 mA h g−1 (23 wt% S) and 260 mA h g−1 (50 wt% S). These results demonstrate the great potential of this nanostructured flexible membrane as a cathode for Li-S batteries with fast charge–discharge performance and long life.

Batteries with high energy and power densities along with long cycle life and acceptable safety at an affordable cost are critical for large‐scale applications such as electric vehicles and smart grids, but is challenging. Lithium–sulfur (Li‐S) batteries are attractive in this regard due to their high energy density and the abundance of sulfur, but several hurdles such as poor cycle life and inferior sulfur utilization need to be overcome for them to be commercially viable. Li–S cells with high capacity and long cycle life with a dual‐confined flexible cathode configuration by encapsulating sulfur in nitrogen‐doped double‐shelled hollow carbon spheres followed by graphene wrapping are presented here. Sulfur/polysulfides are effectively immobilized in the cathode through physical confinement by the hollow spheres with porous shells and graphene wrapping as well as chemical binding between heteronitrogen atoms and polysulfides. This rationally designed free‐standing nanostructured sulfur cathode provides a well‐built 3D carbon conductive network without requiring binders, enabling a high initial discharge capacity of 1360 mA h g −1 at a current rate of C/5, excellent rate capability of 600 mA h g −1 at 2 C rate, and sustainable cycling stability for 200 cycles with nearly 100% Coulombic efficiency, suggesting its great promise for advanced Li–S batteries.

Full-cell cycling of a high density silicon-majority anode with 2× volumetric capacity of graphite and a stabilized coulombic efficiency exceeding 99.9%.

Lithium–sulfur (Li–S) batteries are promising next-generation energy storage technologies due to their high theoretical energy density, environmental friendliness, and low cost. However, low conductivity of sulfur species, dissolution of polysulfides, poor conversion from sulfur reduction, and lithium sulfide (Li2S) oxidation reactions during discharge–charge processes hinder their practical applications. Herein, under the guidance of density functional theory calculations, we have successfully synthesized large-scale single atom vanadium catalysts seeded on graphene to achieve high sulfur content (80 wt % sulfur), fast kinetic (a capacity of 645 mAh g–1 at 3 C rate), and long-life Li–S batteries. Both forward (sulfur reduction) and reverse reactions (Li2S oxidation) are significantly improved by the single atom catalysts. This finding is confirmed by experimental results and consistent with theoretical calculations. The ability of single metal atoms to effectively trap the dissolved lithium polysulfides (LiPSs) and catalytically convert the LiPSs/Li2S during cycling significantly improved sulfur utilization, rate capability, and cycling life. Our work demonstrates an efficient design pathway for single atom catalysts and provides solutions for the development of high energy/power density Li–S batteries.

Significant increases in the energy density of batteries must be achieved by exploring new materials and cell configurations. Lithium metal and lithiated silicon are two promising high-capacity anode materials. Unfortunately, both of these anodes require a reliable passivating layer to survive the serious environmental corrosion during handling and cycling. Here we developed a surface fluorination process to form a homogeneous and dense LiF coating on reactive anode materials, with in situ generated fluorine gas, by using a fluoropolymer, CYTOP, as the precursor. The process is effectively a "reaction in the beaker", avoiding direct handling of highly toxic fluorine gas. For lithium metal, this LiF coating serves as a chemically stable and mechanically strong interphase, which minimizes the corrosion reaction with carbonate electrolytes and suppresses dendrite formation, enabling dendrite-free and stable cycling over 300 cycles with current densities up to 5 mA/cm2. Lithiated silicon can serve as either a pre-lithiation additive for existing lithium-ion batteries or a replacement for lithium metal in Li-O2 and Li-S batteries. However, lithiated silicon reacts vigorously with the standard slurry solvent N-methyl-2-pyrrolidinone (NMP), indicating it is not compatible with the real battery fabrication process. With the protection of crystalline and dense LiF coating, LixSi can be processed in anhydrous NMP with a high capacity of 2504 mAh/g. With low solubility of LiF in water, this protection layer also allows LixSi to be stable in humid air (∼40% relative humidity). Therefore, this facile surface fluorination process brings huge benefit to both the existing lithium-ion batteries and next-generation lithium metal batteries.

An all solid-state lithium-ion battery with high energy density and high safety is a promising solution for a next-generation energy storage system. High interface resistance of the electrodes and poor ion conductivity of solid-state electrolytes are two main challenges for solid-state batteries, which require operation at elevated temperatures of 60–90 °C. Herein, we report the facile synthesis of Al3+/Nb5+ codoped cubic Li7La3Zr2O12 (LLZO) nanoparticles and LLZO nanoparticle-decorated porous carbon foam (LLZO@C) by the one-step Pechini sol–gel method. The LLZO nanoparticle-filled poly(ethylene oxide) electrolyte shows improved conductivity compared with filler-free samples. The sulfur composite cathode based on LLZO@C can deliver an attractive specific capacity of >900 mAh g–1 at the human body temperature 37 °C and a high capacity of 1210 and 1556 mAh g–1 at 50 and 70 °C, respectively. In addition, the solid-state Li–S batteries exhibit high Coulombic efficiency and show remarkably stable cycling performance.

Research on lithium (Li) metal chemistry has been rapidly gaining momentum nowadays not only because of the appealing high theoretical capacity, but also its indispensable role in the next-generation Li-S and Li-air batteries. However, two root problems of Li metal, namely high reactivity and infinite relative volume change during cycling, bring about numerous other challenges that impede its practical applications. In the past, extensive studies have targeted these two root causes by either improving interfacial stability or constructing a stable host. However, efficient surface passivation on three-dimensional (3D) Li is still absent. Here, we develop a conformal LiF coating technique on Li surface with commercial Freon R134a as the reagent. In contrast to solid/liquid reagents, gaseous Freon exhibits not only nontoxicity and well-controlled reactivity, but also much better permeability that enables a uniform LiF coating even on 3D Li. By applying a LiF coating onto 3D layered Li-reduced graphene oxide (Li-rGO) electrodes, highly reduced side reactions and enhanced cycling stability without overpotential augment for over 200 cycles were proven in symmetric cells. Furthermore, Li-S cells with LiF protected Li-rGO exhibit significantly improved cyclability and Coulombic efficiency, while excellent rate capability (∼800 mAh g-1 at 2 C) can still be retained.

Developing high-capacity anodes is a must to improve the energy density of lithium batteries for electric vehicle applications. Alloy anodes are one promising option, but without pre-stored lithium, the overall energy density is limited by the low-capacity lithium metal oxide cathodes. Recently, lithium metal has been revived as a high-capacity anode, but faces several challenges owing to its high reactivity and uncontrolled dendrite growth. Here, we show a series of Li-containing foils inheriting the desirable properties of alloy anodes and pure metal anodes. They consist of densely packed LixM (M = Si, Sn, or Al) nanoparticles encapsulated by large graphene sheets. With the protection of graphene sheets, the large and freestanding LixM/graphene foils are stable in different air conditions. With fully expanded LixSi confined in the highly conductive and chemically stable graphene matrix, this LixSi/graphene foil maintains a stable structure and cyclability in half cells (400 cycles with 98% capacity retention). This foil is also paired with high-capacity Li-free V2O5 and sulfur cathodes to achieve stable full-cell cycling.

The lithium–sulfur (Li–S) battery is one of the most promising battery systems due to its high theoretical energy density and low cost. Despite impressive progress in its development, there has been a lack of comprehensive analyses of key performance parameters affecting the energy density of Li–S batteries. Here, we analyse the potential causes of energy loss during battery operations. We identify two key descriptors (Rweight and Renergy) that represent the mass- and energy-level compromise of the full-cell energy density, respectively. A formulation for energy density calculations is proposed based on critical parameters, including sulfur mass loading, sulfur mass ratio, electrolyte/sulfur ratio and negative-to-positive electrode material ratio. The current progress of Ah-level Li–S batteries is also summarized and analysed. Finally, future research directions, targets and prospects for designing practical high-performance Li–S batteries are proposed. Li–S batteries are a promising next-generation storage technology and the assessment of their performance is critical for their development. Here the authors analyse key Li–S cell parameters, formulate the energy density calculation and discuss design targets for practical applications.

Bismuth vanadate (BiVO4) has been widely regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting because of its low cost, its high stability against photocorrosion, and its relatively narrow band gap of 2.4 eV. However, the achieved performance of the BiVO4 photoanode remains unsatisfactory to date because its short carrier diffusion length restricts the total thickness of the BiVO4 film required for sufficient light absorption. We addressed the issue by deposition of nanoporous Mo-doped BiVO4 (Mo:BiVO4) on an engineered cone-shaped nanostructure, in which the Mo:BiVO4 layer with a larger effective thickness maintains highly efficient charge separation and high light absorption capability, which can be further enhanced by multiple light scattering in the nanocone structure. As a result, the nanocone/Mo:BiVO4/Fe(Ni)OOH photoanode exhibits a high water-splitting photocurrent of 5.82 ± 0.36 mA cm(-2) at 1.23 V versus the reversible hydrogen electrode under 1-sun illumination. We also demonstrate that the PEC cell in tandem with a single perovskite solar cell exhibits unassisted water splitting with a solar-to-hydrogen conversion efficiency of up to 6.2%.

A three-dimensional (3D) hierarchical porous graphene macrostructure coupled with uniformly distributed α-Fe2O3 nano-particles (denoted Fe-PGM) was designed as a sulfur host in a lithium-sulfur battery, and was prepared by a hydrothermal method. In this hybrid structure, the α-Fe2O3 nano-particles are proved to not only strongly interact with the polysulfides, but more importantly, chemically promote their transformation to insoluble species during the charge/discharge process, working as chemical barriers for the shuttling of the lithium polysulfides (LiPSs). Therefore, together with 3D hierarchical porous structure facilitating fast electron/ion transfer, Fe-PGM as a sulfur host in a cathode contributes to a high rate performance (565 mAh g−1 at a high rate of 5 C relative to 1571 mAh g−1 at 0.3 C) as well as long cyclic stability (an ultralow capacity fading rate of 0.049% per cycle over 1000 cycles at the high current rate of 5 C).

Few-layer black phosphorus (BP) nanosheets that are clean and of high quality, are efficiently produced by exfoliating bulk BP crystals, which are prepared by a scalable gas-phase catalytic transformation method in water. They are stable enough in water for further processing and applications. As an example, these BP nanosheets are combined with graphene to give high-performance flexible lithium-ion batteries. Atomically thin black phosphorus (BP) has recently attracted a great deal of interest because of its unique electronic and optical properties and a wide range of promising applications. It has a tunable direct bandgap bridging the energy gap between semimetallic graphene and various large-bandgap transition metal dichalcogenides (TMDCs),1, 2 a high carrier mobility,3 good current saturation characteristics,4 and in-plane anisotropic properties,5 which open up applications for it in electronics and optoelectronics such as high-performance radio-frequency6 and logic transistors,4 near- and mid-infrared photodetectors and modulators,7 mid-infrared polarizers and polarization sensors,8 and plasmonic devices.9 It has also been predicted to have negative Poisson's ratio,10 anomalous elastic properties,11 and high thermoelectric figure of merit.12 In addition, BP is a very promising high-specific-capacity electrode material for lithium ion batteries (LIBs) and sodium ion batteries.13, 14 Mechanical exfoliation of bulk BP was the first method to be developed and is currently still the main method of preparing atomically thin BP sheets that have high structural and electronic quality suitable for fundamental studies as well as electronic and optoelectronic devices, however, the yield is very low. For many important classes of applications, such as battery electrodes, printed electronics, and solar cells, large-scale production of defect-free atomically thin BP in a processable form such as liquid suspensions, inks, or dispersions is urgently required. Very recently, several groups have reported the production of few-layer BP nanosheets in dispersion form by liquid-phase exfoliation of bulk BP in appropriate solvents.15, 16 However, the solvents used for exfoliation have a high boiling point (N-methyl-2-pyrrolidone (NMP), ca. 204 °C; dimethyl formamide (DMF), ca. 153 °C; dimethyl sulfoxide (DMSO), ca. 189 °C; N-cyclohexyl-2-pyrrolidone (CHP), ca. 154 °C at 7 mm Hg), so they are difficult to remove when BP nanosheets are processed in films or composites, especially considering the low stability of BP nanosheets. Such solvent residuals cover the surface of BP nanosheets and inevitably limit the utilization of their intrinsic properties in applications. In addition, scalable synthesis of high-quality bulk BP with high efficiency is also challenging, although it is the prerequisite for large-scale production of BP nanosheets. Several methods have been developed for the production of bulk BP, including heating white phosphorus under high pressure,17 transforming white phosphorus in mercury18 or liquid bismuth,19 and transformation of red phosphorus using high-energy mechanical milling at ambient conditions.13 However, these methods either use toxic chemicals or complex apparatuses, or are time-consuming, or only give small BP crystals or BP nanoparticles. Compared to these methods, the recently developed mineralizer-assisted gas-phase transformation method shows a great potential to efficiently produce large-size BP crystals under simple and safe conditions.20, 21 Here, we report the synthesis of centimeter-size bulk BP crystals by an efficient mineralizer-assisted gas-phase transformation method and scalable clean production of few-layer BP nanosheets by exfoliating these BP crystals in water, utilizing the hydrophilic nature of BP. The bulk BP crystals show high purity and high quality, with a mobility of ca. 242 cm2 V−1 s−1 and current on/off ratio of ca. 5000 at room temperature for their few-layer counterparts made by mechanical exfoliation, and can be efficiently exfoliated in water to yield a few-layer BP nanosheet dispersion with high concentration. The BP nanosheets retain the high quality of the bulk crystals, have very high crystallinity, and are free of impurities and stable enough in water for further processing and applications. As an example, we demonstrate the use of these BP nanosheets for paper-like high-performance flexible LIB electrodes by combining them with highly conductive graphene sheets, which show a high specific capacity of 501 mAh g−1, excellent rate capability, and prolonged cycling performance at a current density of 500 mA g−1. The Experimental Section gives details of the synthesis of large-size high-quality BP crystals using the mineralizer-assisted gas-phase transformation method. Figure 1a shows a 3 mm-sized BP crystal, and BP crystals as large as 6 mm can also be obtained (Figure S1, Supporting Information). Energy dispersive X-ray spectroscopy (EDS) measurements show that the sample is composed of only P element without any other elements being observed (Figure S2, Supporting Information). Atomic absorption spectroscopy (AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) measurements further indicate that the purity of the BP crystal is higher than 99.8 at%, and therefore it can be directly used without purification. X-ray diffraction (XRD) measurements confirm that the samples are BP crystals with high crystallinity (Figure 1b). As reported previously, both good crystallinity and high purity are very important for keeping BP stable in air.17 Therefore, our BP crystals show a high thermal stability; they can endure temperatures of as high as ca. 400 °C in air (Figure S3, Supporting Information). To further confirm the high quality of the BP crystals, we fabricated monolayer to few-layer BP flakes by mechanical exfoliation and measured their Raman spectra and electronic transport properties (Figure 1c–f). Atomic force microscopy (AFM) measurements show that each BP flake has uniform thickness and a smooth surface (Figure 1d), indicating that the bulk BP crystals have a well-defined layered structure and can be easily exfoliated. As shown in Figure 1e, all the BP flakes show three Raman peaks between 300 and 500 cm−1: (365 cm−1), B2g (442 cm−1), and (470 cm−1).22 Note that these peaks have small widths of ca. 1.9, 3.1, and 2.5 cm−1, respectively, indicating the high quality of the samples. As previously reported,23 the intensity ratio of the peak to Si peak (ca. 521 cm−1) increases linearly with the thickness for samples less than 15 nm thick (Figure 1e, and Figures S4, S5, Supporting Information), which allows the thickness of the BP flakes to be identified. Figure 1f shows the room temperature transport property of a 10 nm-thick few-layer BP-based field-effect transistor (FET) with a back gate on heavily doped silicon wafer covered with 285 nm SiO2. The extracted field-effect hole mobility can reach 242 cm2 V−1 s−1 with an on/off current ratio of ca. 5 × 103. It is worth noting that this transport property is comparable to those of BP flakes with the same thickness reported so far,3, 4 further confirming the high quality of the bulk BP crystals prepared by the scalable mineralizer-assisted gas-phase transformation method. Similar to graphene oxide, BP sheets are highly hydrophilic, which allows good dispersion in water without the use of any surfactant or solvents such as DMF, NMP, DMSO, or CHP. Therefore, we directly exfoliated bulk BP crystals in water by sonication, which gives a homogeneous BP nanosheet dispersion (Figure 2a).The color of the dispersion changes from light yellow to light black as the concentration is increased. The Tyndall effect was observed in the BP nanosheet dispersion (inset of Figure 2b), indicating the colloidal nature of the dispersion. We further used UV-vis absorption spectroscopy to characterize the dispersion (Figure S6, Supporting Information). It is worth noting that the absorbance divided by cell length (A/l) at wavelength λ = 684 nm shows a perfect linear relationship with the concentration (C) (Figure 2b). This behavior is consistent with the Lambert–Beer law, A/l = αC, yielding an absorption coefficient of α = 2767 L g−1 m−1. Such consistence suggests the good dispersion of BP nanosheets in water. It is well recognized that high-concentration dispersions are highly desirable for various practical applications. We systematically studied the influence of sonication power (Ps), initial BP concentration (Ci), and sonication time (ts) on the concentration of the dispersed BP nanosheets in water. The speed of centrifugation was fixed at 2500 revolutions per minute (rpm). As shown in Figure 2c–e, the concentration of dispersed BP nanosheets increases linearly with increasing Ps and ts. Considering that high sonication power might severely break the P–P bonds, a low Ps no more than 380 W was used in our exfoliation experiments. Compared to other parameters, Ci has a much stronger influence on the concentration of BP nanosheets. The concentration increases more than 17 times when Ci increases from 1 to 6 mg mL−1. BP nanosheet dispersion with a concentration as high as ca. 0.4 mg mL−1 can be obtained for Ci= 6 mg mL−1, Ps = 380 W, and ts = 300 min, which corresponds to a yield of 6.7 wt%. The yield can be further improved to ca. 30 wt% by recycling the sediment 4 times. Figure 2f shows 1 L BP nanosheet dispersion with a concentration of 0.17 mg mL−1. AFM measurements (Figure S7, Supporting Information) indicate that the mean thickness of BP nanosheets is ca. 9.4 nm (corresponding to ca. 18 layers) for a centrifugation speed of 2500 rpm (Figure 2g), while it is reduced to ca. 5.2 nm (corresponding to ca. 10 layers) when the centrifugation speed is increased to 5000 rpm (Figure 2h). We used X-ray photoelectron spectroscopy (XPS) and XRD to characterize the chemical composition and structure of the original bulk BP crystals and the BP nanosheets obtained. Both samples show a strong BP XPS peak at ca. 130 eV with a very tiny oxidized phosphorus (POx) sub-band (ca. 134 eV), indicating that no strong oxidation occurred during the exfoliation process in water (Figure S8, Supporting Information). The POx sub-band is attributed to weak oxidation of the BP surface in the presence of oxygen. Moreover, both samples show sharp XRD peaks, indicating that the BP nanosheets retain the high crystallinity of the bulk BP crystals (Figure S9, Supporting Information). In addition, it is worth noting that the BP nanosheets show some additional small XRD peaks that are absent in the bulk BP crystals (Figure S9). This suggests that the BP nanosheets are randomly distributed without preferential orientation when they are exfoliated from bulk BP crystals. We further used transmission electron microscopy (TEM) to characterize the detailed crystal structure of the BP nanosheets obtained. As shown in Figure 3a and Figure S10 (Supporting Information), the BP nanosheets are very thin and ca. 200 nm in lateral size (Figure 3a). The lattice constants extracted from the diffraction pattern (inset of Figure 3a) are 3.36 Å and 4.43 Å, which are consistent with those of bulk BP.24 Figure 3b shows a scanning TEM (STEM) high angle annular dark field (HAADF) image of two BP nanosheets. The corresponding EDS elemental mapping (Figure 3c) and EDS spectrum (Figure S11, Supporting Information) show that the nanosheets are composed of uniform P element without obvious O element being detected. High-resolution TEM (HRTEM) images show that the nanosheets are very clean, without visible impurities or defects, and have perfect orthogonally symmetric structure (Figure 3d). These results indicate that the exfoliated BP nanosheets produced by sonication in water retain the high quality of the original bulk BP crystals, which is consistent with the XPS and XRD measurements. Previous studies have shown that the exfoliated BP nanosheets degrade under ambient conditions, reacting in the presence of water or oxygen.25 In particular, it was found that water is predominantly responsible for the degradation process of BP nanosheets. Considering the use of water during our exfoliation process, it is necessary to estimate the stability of our BP nanosheets before further processing and applications. To do this, 1 L of BP nanosheet dispersion was sealed in a glass bottle and the absorbance at λ = 684 nm was recorded as a function of time. It is worth noting that only ca. 10 wt% of the BP nanosheets was dissolved after one week, and still ca. 60 wt% of the nanosheets was left even after eight weeks (Figure S12, Supporting Infomration). These results indicate that our BP nanosheets are stable enough in water for further processing and applications, which is different from the previous observations.25 We suggest that the high stability of our BP nanosheets can be attributed to their intrinsic high crystallinity and high purity, as shown above, as well as the oxygen-isolated measurement conditions. It can be clearly seen from Figure S13 (Supporting Information) that the presence of oxygen can greatly enhance the degradation of BP nanosheets immersed in water. These experimental observations are consistent with recent theoretical calculations,26 which show that water prefers to attach to the surface of BP through hydrogen but does not interact directly with the pristine lattice of BP; however, water will interact with BP once it has been oxidized. Therefore, the BP nanosheet dispersion should be stored in oxygen-isolated containers such as sealed bottles after preparation. The mass production of high-quality clean BP nanosheets opens up the possibility of applications beyond electronic and optoelectronic devices. It is well known that BP is an attractive anode material with an ultrahigh theoretical specific capacity of 2596 mAh g−1 (about 7 times that of the commonly used graphite anode material), which, however, faces many challenges, such as rapid capacity decay owing to the low electrical conductivity and severe volume variation during the lithiation/delithiation processes.13 Considering the excellent electrical conductivity of graphene and the two-dimensional flexible characteristic of both graphene and BP nanosheets,27, 28 we designed layer-structured flexible BP nanosheet–graphene (BP-G) hybrid paper as an anode, which not only solves the above problems but also provides a great potential for use in flexible energy storage devices. In addition, it is worth noting that no inactive metallic current collector, other binders, and conductive additives are used in this hybrid anode, therefore, it is also expected that the energy density of the whole electrode can be greatly improved. The BP-G hybrid paper was fabricated by vacuum filtration of a mixed dispersion of graphene sheets and few-layer BP nanosheets (see the Experimental Section). The graphene sheets, produced by an intercalation–exfoliation method, have a thickness of less than 10 layers and a lateral size of 1–5 μm.28 Importantly, these graphene sheets are almost free of oxygen functional groups and defects, and have a very high electrical conductivity of ca. 1000 S cm−1.28 As shown in Figure S14 (Supporting Information), the electrical conductivity of the hybrid electrode increases with the loading amount of graphene sheets. On the other hand, to make full use of the high specific capacity of BP and increase the mass specific/volumetric capacity of the LIBs, the amount of graphene sheets should be kept as low as possible on the condition that the conductivity is high enough. Considering the balance of the electrical conductivity and specific capacity of the hybrid electrode, therefore, 20 wt% graphene sheets and 80 wt% BP nanosheets were used in our experiments to fabricate the BP-G hybrid electrode. As shown in Figure 4a, the BP-G hybrid paper is mechanically robust and can be bent through nearly 180° without breaking, indicating its great potential for use as an electrode in future flexible energy storage devices.29 Both the top-view (Figure 4b) and cross-sectional view SEM images (Figure 4c) of the paper show that all the graphene and BP sheets are closely contacted in a face-to-face manner because of their two-dimensional structure, which can be further confirmed by TEM observations and EDS elemental mapping (Figure 4d–f). Such good contact together with the excellent electrical conductivity of graphene sheets enables a rapid electron transport between BP nanosheets. In addition, the very small size of BP nanosheets and the hierarchical open porous structure of BP-G hybrid papers lead to a short diffusion length of lithium ions and large electrode–electrolyte contact area. The big difference in lateral size (about 10 times difference) implies that the small BP nanosheets can be wrapped by large graphene sheets in the hybrid paper, and therefore, their volume expansion can be accommodated. As a result, the BP-G hybrid paper is expected to have a greatly improved rate capability and cycling stability compared to the BP nanosheets themselves. We also tried to fabricate flexible BP nanoparticle–G hybrid paper (Supporting Information), however, the hybrid paper obtained is very brittle and could hardly be peeled off from the filter membrane because the BP nanoparticles are sparsely dispersed on the surface of graphene without intimate contact (Figure S15, Supporting Information). It readily broke into small pieces during attempts to peel it off (Figure S15). This further demonstrates the advantages of combining different two-dimensional materials together to form a sheet-on-sheet structure for flexible electrochemical energy storage applications. The electrochemical lithium storage behaviors of the BP nanosheet, G paper, and BP-G hybrid paper anodes were examined by discharge/charge voltage profiles at a constant current of 100 mA g−1 as shown in Figure 4g. In the second discharge curve, two typical voltage plateaus are found around 0.63 and 0.25 V for the BP-G hybrid paper electrode, which are ascribed to the transformation from elemental P to LixP and finally to Li3P.13 In the charge curve, two plateaus, located at about 1.35 and 1.55 V, are found, which respectively originate from the reverse reaction for the formation of LixP and P from Li3P.13 In contrast, only one short plateau appears at around 0.25 V for the BP nanosheet electrode, and a declined slope below 0.5 V for the graphene paper electrode. Moreover, the voltage gap between discharge and charge potentials for BP and G paper electrodes are much larger than for the BP-G hybrid paper electrode, exhibiting higher overpotential. We characterized the BP nanosheets after the first cycle, and found that they had changed from crystalline state to amorphous state (Figures S16 and S17, Supporting Information), which are similar to those observed in red phosphorus–graphene composites.30, 31 However, it is worth noting that the amorphous BP is still well dispersed and adhered to the graphene without noticeable disconnection. These results confirm that the excellent electrical conductivity of graphene and the good contact between graphene and BP sheets significantly promote the reaction kinetics of the electrode, which can also be verified by the following rate capability tests. As shown in Figure 4h, the BP-G hybrid paper electrode delivers a high specific capacity of 920 mAh g−1 at a current density of 100 mA g−1, based on the total mass of the electrode, which is much higher than those of BP nanosheets (180 mAh g−1) and G paper electrodes (435 mAh g−1) based on the total mass of the electrode and the theoretical capacity of graphite (372 mAh g−1).32, 33 Moreover, this capacity is also much higher than the total sum (231 mAh g−1) of the individual capacity contributions of BP nanosheets (180 × 80% = 144 mAh g−1) and graphene (435 × 20% = 87 mAh g−1) based on their mass ratio in the hybrid, suggesting a synergistic effect between graphene and BP nanosheets that improves the electrochemical performance (Figure S18, Supporting Information). The volumetric capacity is another important concern for practical application of a BP nanosheet-based anode. After the binder and metal current collector had been replaced with lightweight graphene sheets, the volumetric capacity and volumetric energy density of the BP-G hybrid paper reached 1030 mAh cm−3 and 1571 Wh L−1, respectively, which are comparable or even superior to the other reported values for high volumetric capacity lithium battery anodes.34-36 When the discharge/charge current density is increased to 500 mA g−1 or even 2500 mA g−1, the BP-G paper electrode still shows high specific capacities of 501 and 141 mAh g−1, which are comparable to those previously reported,37, 38 implying the good reversibility of the BP-G hybrid paper electrode at high current density. In contrast, the G paper electrode drops dramatically to below 200 mAh g−1 and the BP nanosheet electrode fails to function at a current density of 500 mA g−1. Moreover, when the current density is changed from 2500 mA g−1 back to 500 mA g−1, the BP-G electrode recovers its capacity of 502 mAh g−1, indicating the good rate capability and structural stability. More importantly, the BP-G hybrid paper electrode shows excellent prolonged cycle performance at moderate current density. When cycled at 500 mA g−1 over 500 cycles, it could still deliver a capacity of 402 mAh g−1 with an average Coulombic efficiency approaching 100% (Figure 4i). This means that the capacity retention is 80.2% and the capacity decay rate is as low as 0.04% per cycle, which makes BP-G hybrid paper attractive and promising as a high capacity/energy anode material with long cycle life. Based on the above structure analyses, the excellent cycling stability and rate capability of BP-G hybrid paper electrode can be attributed to the good contact between graphene and BP nanosheets, favorable charge-transport pathway, short diffusion length of lithium ions, large electrode–electrolyte contact area, and the effective confinement of BP by graphene wrapping. In conclusion, using a scalable mineralizer-assisted gas-phase transformation method, we have prepared centimeter-size high-quality BP crystals that show a mobility of ca. 242 cm2 V−1 s−1 and current on/off ratio of ca. 5000 at room temperature for few-layer samples obtained by mechanical exfoliation. With these high-quality BP crystals as starting materials, we demonstrated the scalable clean production of BP nanosheets by liquid exfoliation in water, utilizing the hydrophilic nature of BP. It was found that the BP crystals can be efficiently exfoliated in water to yield a few-layer BP nanosheet dispersion with a high concentration. Moreover, the BP nanosheets retain the high quality of their bulk crystals, and are free of impurities and stable enough in water for further processing and applications. As an example, we demonstrated the use of these BP nanosheets for high-performance flexible paper-like LIB electrodes by combining them with highly conductive graphene sheets, which shows a high specific capacity of 501 mAh g−1, excellent rate capability, and prolonged cycling performance at a current density of 500 mA g−1. Synthesis of Large-Size BP Crystals: Red phosphorus (900 mg), AuSn alloy (360 mg), and SnI4 (18 mg) were first sealed in a quartz ampoule (13 cm in length and 15 mm in diameter) evacuated to a pressure lower than 10−3 mbar. Then the sealed ampoule was placed horizontally in the reaction zone of a tube furnace (Lindberg Blue M (TF55035KC-1)) and heated to 650 °C within 1 h. After being kept at 650 °C for 24 h, the ampoule was cooled to 500 °C at a rate of 40 °C h−1, and then cooled to room temperature after being held at 500 °C for at least 30 min. During the above synthesis process, large BP crystals (about 860 mg) were formed on the cold end of the ampoule. By prolonging the reaction time we could achieve almost full conversion. Finally, the large BP crystals were picked out and washed with toluene to remove the residual mineralizer, followed by water and acetone washing. Preparation of Few-Layer BP Nanosheet Dispersion: The BP crystals obtained were first ground to BP powders, and then the powders were dispersed in deionized water (20 mL) with an initial concentration of 1–10 mg mL−1 by tip sonication (Scientz-IID ultrasonic homogenizer, P0 = 950 W, output power: 0.1P0–0.5P0) for 30–300 min. After the dispersion had settled for 12 h, the supernatant was decanted and then centrifuged at 1500–5000 rpm for 30 min (TGL-16C, Shanghai Anting Scientific Instrument Factory). Finally, the resulting BP nanosheet dispersion (supernatant) was collected for further structural characterization and LIB applications. Structural Characterizations: The morphology and crystallinity of the large-size BP crystals were characterized by SEM/EDS (Nova NanoSEM 430, 10 kV/5 kV) and XRD (D-MAX/2400 using Cu Kα radiation). The purity of the bulk BP crystals was characterized by AAS (Z2300, Hitachi) and ICP-AES (PE8300, PerkinElmer). The structure of the few-layer BP flakes made by mechanical exfoliation was characterized by optical microscopy using a Nikon ECLIPSE LV100D and Raman spectroscopy using a LabRAM HR800 (632.8 nm He-Ne laser, spot size ca. 1 μm2, 100× objective lens). The thermal stability was measured from 30 °C to 600 °C at a heating rate of 10 °C min−1 in air or Ar using a Netzsch-STA 449C, and the electrical properties were measured under high vacuum (10−5 torr) at room temperature using a Keithley 4200 semiconductor parameter analyzer. The absorption of BP nanosheet dispersions was measured using a UV-vis absorption spectrometer (JACSO V-550). The thicknesses of the few-layer BP nanosheets exfoliated in water were measured using AFM (Nanoscope IIIa). The detailed chemical compositions of bulk BP crystals and BP nanosheets were characterized by XPS with an ESCALAB250 (150 W, spot size 500 mm) using Al Kα radiation; all spectra were calibrated to the binding energy of adventitious carbon (284.8 eV). Their detailed structure was characterized by TEM (JEOL JEM 2010, 200 kV), STEM (FEI Tecnai F30, 300 kV), and HRTEM (FEI Titan3 G2 60–300 S/TEM, fitted with two CEOS Cs aberration correctors and monochromator, 60 kV). AFM samples were prepared by dropping the BP nanosheet dispersion onto SiO2/Si substrates followed by drying on a hot plate and acetone washing. TEM samples were prepared by directly dropping the BP nanosheet dispersion onto carbon grids (230 mesh) followed by acetone washing. Fabrication of BP-G Hybrid Paper and G Paper and Electrochemical Measurements: The electrochemical properties of BP nanosheets, G paper, and BP-G hybrid paper as anode materials in half cells were evaluated by a galvanostatic charge/discharge technique. The BP-G hybrid paper and G paper were fabricated by vacuum filtration. The few-layer BP nanosheet dispersion was first filtered, washed with ethanol, and dried overnight at 60 °C in vacuum. Then the mixture of the obtained BP nanosheet powder (80 wt%) and few-layer graphene powder made by the intercalation–exfoliation method (20 wt%) or pure few-layer graphene powder was dispersed in NMP, followed by tip-sonication (190 W, 60 min) and vacuum filtration. After being washed with ethanol and drying overnight at 100 °C in vacuum, the BP-G hybrid paper or G paper was peeled off from the filter membrane. The obtained BP-G hybrid paper or G paper was directly used as the anode, and lithium-metal foil was used as the counter and reference electrodes, which were separated by Celgard 2400 separator. The mass loading of BP-G paper or G paper was 1–1.5 mg cm−2, and the capacity was calculated based on the total mass of the electrode. The BP nanosheet electrode was prepared by mixing 70 wt% BP powder with 20 wt% conductive carbon black (super P) as a conducting agent and 10 wt% polyvinylidene fluoride dissolved in NMP as a binder to form a slurry, which was then coated onto a copper foil and dried under vacuum at 100 °C for 12 h. The foil was shaped into a circular disk with a diameter of 12 mm and finally dried in a vacuum oven at 120 °C for 6 h. The total mass of the electrode was about 1.3–1.7 mg, and the geometrical area of the electrode was 1.13 cm2. Coin cells (size 2032) were assembled in an argon-filled glove box with the BP nanosheet electrode or G paper electrode or BP-G hybrid paper electrode, and a mixture of 1 M LiPF6 in ethylene carbonate, dimethyl carbonate, and ethylmethyl carbonate (1:1:1 vol) as the electrolyte. Charge/discharge measurements were carried out galvanostatically at various current densities over a voltage range of 0.001 to 3 V (vs. Li+/Li0) using a battery testing system (LAND CT2001A). L.C. and G.M.Z. contributed equally to this work. This work was supported by the National Natural Science Foundation of China (Nos. 51325205, 51290273, 51221264, and 51172240) and the Chinese Academy of Sciences (Nos. KGZD-EW-303–1 and KGZD-EW-T06). As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Abstract Accelerated conversion by catalysis is a promising way to inhibit shuttling of soluble polysulfides in lithium–sulfur (Li–S) batteries, but most of the reported catalysts work only for one direction sulfur reaction (reduction or oxidation), which is still not a root solution since fast cycled use of sulfur species is not finally realized. A bidirectional catalyst design, oxide–sulfide heterostructure, is proposed to accelerate both reduction of soluble polysulfides and oxidation of insoluble discharge products (e.g., Li 2 S), indicating a fundamental way for improving both the cycling stability and sulfur utilization. Typically, a TiO 2 –Ni 3 S 2 heterostructure is prepared by in situ growing TiO 2 nanoparticles on Ni 3 S 2 surface and the intimately bonded interfaces are the key for bidirectional catalysis. For reduction, TiO 2 traps while Ni 3 S 2 catalytically converts polysulfides. For oxidation, TiO 2 and Ni 3 S 2 both show catalytic activity for Li 2 S dissolution, refreshing the catalyst surface. The produced sulfur cathode with TiO 2 –Ni 3 S 2 delivers a low capacity decay of 0.038% per cycle for 900 cycles at 0.5C and specially, with a sulfur loading of 3.9 mg cm −2 , achieves a high capacity retention of 65% over 500 cycles at 0.3C. This work unlocks how a bidirectional catalyst works for boosting Li–S batteries approaching practical uses.

Solid Li-ion electrolytes used in all-solid-state lithium-ion batteries (LIBs) are being considered to replace conventional liquid electrolytes that have leakage, flammability, and poor chemical stability issues, which represents one major challenge and opportunity for next-generation high-energy-density batteries. However, the low mobility of lithium ions in solid electrolytes limits their practical applications. Here, we report a solid composite polymer electrolyte with Y2O3-doped ZrO2 (YSZ) nanowires that are enriched with positive-charged oxygen vacancies. The morphologies and ionic conductivities have been studied systemically according to concentration of Y2O3 dopant in the nanowires. In comparison to the conventional filler-free electrolyte with a conductivity of 3.62 × 10-7 S cm-1, the composite polymer electrolytes with the YSZ nanowires show much higher ionic conductivity. It indicates that incorporation of 7 mol % of Y2O3-doped ZrO2 nanowires results in the highest ionic conductivity of 1.07 × 10-5 S cm-1 at 30 °C. This conductivity enhancement originates from the positive-charged oxygen vacancies on the surfaces of the nanowires that could associate with anions and then release more Li ions. Our work demonstrates a composite polymer electrolyte with oxygen-ion conductive nanowires that could address the challenges of all-solid-state LIBs.

Nanomaterials provide many desirable properties for electrochemical energy storage devices due to their nanoscale size effect, which could be significantly different from bulk or micron-sized materials. Particularly, confined dimensions play important roles in determining the properties of nanomaterials, such as the kinetics of ion diffusion, the magnitude of strain/stress, and the utilization of active materials. Nanowires, as one of the representative one-dimensional nanomaterials, have great capability for realizing a variety of applications in the fields of energy storage since they could maintain electron transport along the long axis and have a confinement effect across the diameter. In this review, we give a systematic overview of the state-of-the-art research progress on nanowires for electrochemical energy storage, from rational design and synthesis, in situ structural characterizations, to several important applications in energy storage including lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, and supercapacitors. The problems and limitations in electrochemical energy storage and the advantages in utilizing nanowires to address the issues and improve the device performance are pointed out. At the end, we also discuss the challenges and demonstrate the prospective for the future development of advanced nanowire-based energy storage devices.

A microporous-mesoporous carbon with graphitic structure was developed as a matrix for the sulfur cathode of a Li-S cell using a mixed carbonate electrolyte. Sulfur was selectively introduced into the carbon micropores by a melt adsorption-solvent extraction strategy. The micropores act as solvent-restricted reactors for sulfur lithiation that promise long cycle stability. The mesopores remain unfilled and provide an ion migration pathway, while the graphitic structure contributes significantly to low-resistance electron transfer. The selective distribution of sulfur in micropores was characterized by X-ray photoelectron spectroscopy (XPS), nitrogen cryosorption analysis, transmission electron microscopy (TEM), X-ray powder diffraction and Raman spectroscopy. The high-rate stable lithiation-delithiation of the carbon-sulfur cathode was evaluated using galvanostatic charge-discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. The cathode is able to operate reversibly over 800 cycles with a 1.8 C discharge-recharge rate. This integration of a micropore reactor, a mesopore ion reservoir, and a graphitic electron conductor represents a generalized strategy to be adopted in research on advanced sulfur cathodes.

ConspectusThe development of next-generation lithium-based rechargeable batteries with high energy density, low cost, and improved safety is a great challenge with profound technological significance for portable electronics, electric vehicles, and grid-scale energy storage. Specifically, advanced lithium battery chemistries call for a paradigm shift to electrodes with high Li to host ratio based on a conversion or alloying mechanism, where the increased capacity is often accompanied by drastic volumetric changes, significant bond breaking, limited electronic/ionic conductivity, and unstable electrode/electrolyte interphase.Fortunately, the rapid progress of nanotechnology over the past decade has been offering battery researchers effective means to tackle some of the most pressing issues for next-generation battery chemistries. The major applications of nanotechnology in batteries can be summarized as follows: First, by reduction of the dimensions of the electrode materials, the cracking threshold of the material upon lithiation can be overcome, at the same time facilitating electron/ion transport within the electrode. Second, nanotechnology also provides powerful methods to generate various surface-coating and functionalization layers on electrode materials, protecting them from side reactions in the battery environment. Finally, nanotechnology gives people the flexibility to engineer each and every single component within a battery (separator, current collector, etc.), bringing novel functions to batteries that are unachievable by conventional methods.Thus, this Account aims to highlight the crucial role of nanotechnology in advanced battery systems. Because of the limited space, we will mainly assess representative examples of rational nanomaterials design with complexity for silicon and lithium metal anodes, which have shown great promise in constraining their large volume changes and the repeated solid–electrolyte interphase formation during cycling. Noticeably, the roadmap delineating the gradual improvement of silicon anodes with a span of 11 generations of materials designs developed in our group is discussed in order to reflect how nanotechnology could guide battery research step by step toward practical applications. Subsequently, we summarize efforts to construct nanostructured composite sulfur cathodes with improved electronic conductivity and effective soluble species encapsulation for maximizing the utilization of active material, cycle life, and system efficiency. We emphasize carbon-based materials and, importantly, materials with polar surfaces for sulfur entrapment. We then briefly discuss nanomaterials strategies to improve the ionic conductivity of solid polymer electrolytes by means of incorporating high-surface-area and, importantly, high-aspect-ratio secondary-phase fillers for continuous, low-tortuosity ionic transport pathways. Finally, critical innovations that have been brought to the area of grid-scale energy storage and battery safety by nanotechnology are also succinctly reviewed.

Considerable research efforts have been devoted to the lithium–sulfur battery due to its advantages such as high theoretical capacity, high energy density, and low cost. However, the shuttle effect and the irreversible deposition of Li2S result in severe capacity decay and low Coulombic efficiency. Herein, we discovered that the transition metal phosphides cannot only trap the soluble polysulfides but also effectively catalyze the decomposition of Li2S to improve the utilization of active materials. Compared with the cathodes without transition metal phosphides, the cathodes based on Ni2P, Co2P, and Fe2P all exhibit higher reversible capacity and improved cycling performance. The Ni2P-added electrode delivers capacities of 1165, 1024, 912, 870, and 812 mAh g–1 at 0.1, 0.2, 0.5, 1.0, and 2.0 C, respectively, and high capacity retention of 96% after 300 cycles at 0.2 C. Even with a high sulfur mass loading of 3.4 mg cm–2, the capacity retention remains 90.3% after 400 cycles at 0.5 C. Both density functional theory calculations and electrochemical tests reveal that the transition metal phosphides show higher adsorption energies and lower dissociation energies of Li2S than those of carbon materials.

The increasing demand for electric vehicles and large-scale smart grids has aroused great interest in developing high energy density storage devices. Lithium–sulfur (Li–S) battery has attracted much attention owing to its high theoretical energy density and abundance, but many challenges such as rapid capacity fade and low sulfur loading and utilization have impeded its practical use. Here, we present a free-standing TiO2 nanowire/graphene hybrid membrane for Li/dissolved polysulfide batteries with high capacity and long cycling life. Graphene membrane with high electrical conductivity is used as a current collector to effectively reduce the internal resistance in the sulfur cathode and physically immobilize the dissolved lithium polysulfides. The TiO2 nanowires introduced into the graphene membrane offer a hierarchical composite structure, in which the TiO2 nanowires not only have strong chemical binding with the lithium polysulfides, but also show a strong catalytic effect for polysulfide reduction and oxidation, promoting a fast redox reaction kinetics with high capacity and low voltage polarization. This hybrid electrode delivers a high specific capacity of 1327 mA h g−1 at 0.2 C rate, a Coulombic efficiency approaching 100%, high-rate performance of 850 mA h g−1 at 2 C rate, and long cyclic stability with a capacity of 1053 mA h g−1 at 0.2 C rate over 200 cycles, demonstrating great prospect for application in high energy Li–S batteries.

Abstract The lithium–sulfur (Li–S) battery is considered a promising candidate for the next generation of energy storage system due to its high specific energy density and low cost of raw materials. However, the practical application of Li–S batteries is severely limited by several weaknesses such as the shuttle effect of polysulfides and the insulation of the electrochemical products of sulfur and Li 2 S/Li 2 S 2 . Here, by doping nitrogen and integrating highly dispersed cobalt catalysts, a porous carbon nanocage derived from glucose adsorbed metal–organic framework is developed as the host for a sulfur cathode. This host structure combines the reported positive effects, including high conductivity, high sulfur loading, effective stress release, fast lithium‐ion kinetics, fast interface charge transport, fast redox of Li 2 S n , and strong physical/chemical absorption, achieving a long cycle life (86% of capacity retention at 1C within 500 cycles) and high rate performance (600 mAh g −1 at 5C) for a Li–S battery. By combining experiments and density functional theoretical calculations, it is demonstrated that the well‐dispersed cobalt clusters play an important role in greatly improving the diffusion dynamics of lithium, and enhance the absorption and conversion capability of polysulfides in the host structure.

Abstract The lithium–sulfur (Li–S) battery is a next generation high energy density battery, but its practical application is hindered by the poor cycling stability derived from the severe shuttling of lithium polysulfides (LiPSs). Catalysis is a promising way to solve this problem, but the rational design of relevant catalysts is still hard to achieve. This paper reports the WS 2 –WO 3 heterostructures prepared by in situ sulfurization of WO 3 , and by controlling the sulfurization degree, the structure is controlled, which balances the trapping ability (by WO 3 ) and catalytic activity (by WS 2 ) toward LiPSs. As a result, the WS 2 –WO 3 heterostructures effectively accelerate LiPS conversion and improve sulfur utilization. The Li–S battery with 5 wt% WS 2 –WO 3 heterostructures as additives in the cathode shows an excellent rate performance and good cycling stability, revealing a 0.06% capacity decay each cycle over 500 cycles at 0.5 C. By building an interlayer with such heterostructure‐added graphenes, the battery with a high sulfur loading of 5 mg cm −2 still shows a high capacity retention of 86.1% after 300 cycles at 0.5 C. This work provides a rational way to prepare the metal oxide–sulfide heterostructures with an optimized structure to enhance the performance of Li–S batteries.

Abstract Single‐atom metal catalysts (SACs) are used as sulfur cathode additives to promote battery performance, although the material selection and mechanism that govern the catalytic activity remain unclear. It is shown that d‐p orbital hybridization between the single‐atom metal and the sulfur species can be used as a descriptor for understanding the catalytic activity of SACs in Li–S batteries. Transition metals with a lower atomic number are found, like Ti, to have fewer filled anti‐bonding states, which effectively bind lithium polysulfides (LiPSs) and catalyze their electrochemical reaction. A series of single‐atom metal catalysts (Me = Mn, Cu, Cr, Ti) embedded in three‐dimensional (3D) electrodes are prepared by a controllable nitrogen coordination approach. Among them, the single‐atom Ti‐embedded electrode has the lowest electrochemical barrier to LiPSs reduction/Li 2 S oxidation and the highest catalytic activity, matching well with the theoretical calculations. By virtue of the highly active catalytic center of single‐atom Ti on the conductive transport network, high sulfur utilization is achieved with a low catalyst loading (1 wt.%) and a high area‐sulfur loading (8 mg cm −2 ). With good mechanical stability for bending, these 3D electrodes are suitable for fabricating bendable/foldable Li–S batteries for wearable electronics.

Lithium‐sulfur (Li‐S) batteries are being considered as the next‐generation high‐energy‐storage system due to their high theoretical energy density. However, the use of a lithium‐metal anode poses serious safety concerns due to lithium dendrite formation, which causes short‐circuiting, and possible explosions of the cell. One feasible way to address this issue is to pair a fully lithiated lithium sulfide (Li 2 S) cathode with lithium metal‐free anodes. However, bulk Li 2 S particles face the challenges of having a large activation barrier during the initial charge, low active‐material utilization, poor electrical conductivity, and fast capacity fade, preventing their practical utility. Here, the development of a self‐supported, high capacity, long‐life cathode material is presented for Li‐S batteries by coating Li 2 S onto doped graphene aerogels via a simple liquid infiltration–evaporation coating method. The resultant cathodes are able to lower the initial charge voltage barrier and attain a high specific capacity, good rate capability, and excellent cycling stability. The improved performance can be attributed to the (i) cross‐linked, porous graphene network enabling fast electron/ion transfer, (ii) coated Li 2 S on graphene with high utilization and a reduced energy barrier, and (iii) doped heteroatoms with a strong binding affinity toward Li 2 S/lithium polysulfides with reduced polysulfide dissolution based on first‐principles calculations.

As a low dimensional crystal, graphene attracts great attention as heat dissipation material due to its unique thermal transfer property exceeding the limit of bulk graphite. In this contribution, flexible graphene–carbon fiber composite paper is fabricated by depositing graphene oxide into the carbon fiber precursor followed by carbonization. In this full‐carbon architecture, scaffold of one‐dimensional carbon fiber is employed as the structural component to reinforce the mechanical strength, while the hierarchically arranged two‐dimensional graphene in the framework provides a convenient pathway for in‐plane acoustic phonon transmission. The as‐obtained hierarchical carbon/carbon composite paper possesses ultra‐high in‐plane thermal conductivity of 977 W m −1 K −1 and favorable tensile strength of 15.3 MPa. The combined mechanical and thermal performances make the material highly desirable as lateral heat spreader for next‐generation commercial portable electronics.

Lithium-metal batteries (LMBs) are considered as promising next-generation batteries due to their high energy density. However, commercial carbonate electrolytes cannot be used in LMBs due to their poor compatibility with the lithium-metal anode and detrimental hydrogen fluoride (HF) generation by lithium hexafluorophosphate decomposition. By introducing lithium nitrate additive and a small amount of tetramethylurea as a multifunctional cosolvent to a commercial carbonate electrolyte, NO3- , which is usually insoluble, can be introduced into the solvation structure of Li+ to form a conductive and stable solid electrolyte interface. At the same time, HF generation is suppressed by manipulating the solvation structure and a scavenging effect. As a result, the Coulombic efficiency (CE) of Li||Cu half cells using the designed carbonate electrolyte can reach 98.19% at room temperature and 96.14% at low temperature (-15 °C), and Li||LiFePO4 cells deliver a high capacity retention of 94.9% with a high CE of 99.6% after 550 cycles. This work provides a simple and effective way to extend the use of commercial carbonate electrolytes for next-generation battery systems.

A common issue plaguing battery anodes is the large consumption of lithium in the initial cycle as a result of the formation of a solid electrolyte interphase followed by gradual loss in subsequent cycles. It presents a need for prelithiation to compensate for the loss. However, anode prelithiation faces the challenge of high chemical reactivity because of the low anode potential. Previous efforts have produced prelithiated Si nanoparticles with dry air stability, which cannot be stabilized under ambient air. Here, we developed a one-pot metallurgical process to synthesize LixSi/Li2O composites by using low-cost SiO or SiO2 as the starting material. The resulting composites consist of homogeneously dispersed LixSi nanodomains embedded in a highly crystalline Li2O matrix, providing the composite excellent stability even in ambient air with 40% relative humidity. The composites are readily mixed with various anode materials to achieve high first cycle Coulombic efficiency (CE) of >100% or serve as an excellent anode material by itself with stable cyclability and consistently high CEs (99.81% at the seventh cycle and ∼99.87% for subsequent cycles). Therefore, LixSi/Li2O composites achieved balanced reactivity and stability, promising a significant boost to lithium ion batteries.

Lithium-sulfur (Li-S) batteries are regarded as promising next-generation high energy density storage devices for both portable electronics and electric vehicles due to their high energy density, low cost, and environmental friendliness. However, there remain some issues yet to be fully addressed with the main challenges stemming from the ionically insulating nature of sulfur and the dissolution of polysulfides in electrolyte with subsequent parasitic reactions leading to low sulfur utilization and poor cycle life. The high flammability of sulfur is another serious safety concern which has hindered its further application. Herein, an aqueous inorganic polymer, ammonium polyphosphate (APP), has been developed as a novel multifunctional binder to address the above issues. The strong binding affinity of the main chain of APP with lithium polysulfides blocks diffusion of polysulfide anions and inhibits their shuttling effect. The coupling of APP with Li ion facilitates ion transfer and promotes the kinetics of the cathode reaction. Moreover, APP can serve as a flame retardant, thus significantly reducing the flammability of the sulfur cathode. In addition, the aqueous characteristic of the binder avoids the use of toxic organic solvents, thus significantly improving safety. As a result, a high rate capacity of 520 mAh g-1 at 4 C and excellent cycling stability of ∼0.038% capacity decay per cycle at 0.5 C for 400 cycles are achieved based on this binder. This work offers a feasible and effective strategy for employing APP as an efficient multifunctional binder toward building next-generation high energy density Li-S batteries.

Lithium polysulfide (LiPS) shuttling is one of the main obstacles hindering the practical use of lithium-sulfur (Li-S) batteries. Constructing an interlayer composed of carbon or noncarbon materials on separator is a promising way to restrain the LiPS shuttling, but such a layer always hinders the Li ion diffusion and is hard to realize the reuse of the captured LiPSs. In this study, an in-plane heterostructure constructed by graphene and titanium carbide (TiC) was prepared by directly using graphene as a template and the carbon source to react with TiCl4 under thermal treatment. In this process, graphene was partially transformed into TiC forming such a heterostructure, which is benefit to reducing the Li ion and electron diffusion barrier. Moreover, the TiC has strong affinity towards LiPSs and high conductivity. Thus, the in-plane heterostructures filtered on a separator as a coating layer effectively blocks the shuttle of LiPSs and greatly improves the sulfur utilization and cycling performance, indicating a promising way to promote the practical applications of high performance Li-S batteries.

Lithium-sulfur batteries have a high theoretical energy density of 2500 Wh/kg and are promising candidates for meeting future energy storage demands. However, dissolution of the intermediate polysulfide species into the electrolyte remains as a major challenge, causing fast capacity degradation in Li-S batteries. Many recent studies have reported various materials such as metal oxides and sulfides that interact strongly with polysulfide species and can alleviate the dissolution problem, though little work has focused on quantitative comparison of different materials under equivalent conditions. Here, we establish a standard procedure to quantitatively compare the polysulfide adsorption capability of candidate materials. We found that an order of magnitude of difference is evident between poor adsorption materials such as carbon black and strong adsorption materials such as V2O5 and MnO2. We elucidate different adsorption mechanisms may be present and probe possible adsorption species. We expect our work will provide a useful strategy to screen for suitable candidate materials and valuable information for rational design of long cycle life Li-S batteries.

A 3D graphene cage with a thin layer of electrodeposited nickel phosphosulfide for Li2S impregnation, using ternary nickel phosphosulphide as a highly conductive coating layer for stabilized polysulfide chemistry, is accomplished by the combination of theoretical and experimental studies. The 3D interconnected graphene cage structure leads to high capacity, good rate capability and excellent cycling stability in a Li2S cathode.

Lithium metal anodes with high energy density are important for further development of next-generation batteries. However, inhomogeneous Li deposition and dendrite growth hinder their practical utilization. 3D current collectors are widely investigated to suppress dendrite growth, but they usually occupy a large volume and increase the weight of the system, hence decreasing the energy density. Additionally, the nonuniform distribution of Li ions results in low utilization of the porous structure. A lightweight, 3D Cu nanowire current collector with a phosphidation gradient is reported to balance the lithiophilicity with conductivity of the electrode. The phosphide gradient with good lithiophilicity and high ionic conductivity enables dense nucleation of Li and its steady deposition in the porous structure, realizing a high pore utilization. Specifically, the homogenous deposition of Li leads to the formation of an oriented texture on the electrode surface at high capacities. A high mass loading (≈44 wt%) of Li with a capacity of 3 mAh cm-2 and a high average Coulombic efficiency of 97.3% are achieved. A lifespan of 300 h in a symmetrical cell is obtained at 2 mA cm-2 , implying great potential to stabilize lithium metal.

Next-generation batteries based on conversion reactions, including aqueous metal-air batteries, nonaqueous alkali metal-O2 and -CO2 batteries, alkali metal-chalcogen batteries, and alkali metal-ion batteries have attracted great interest. However, their use is restricted by inefficient reversible conversion of active agents. Developing bifunctional catalysts to accelerate the conversion reaction kinetics in both discharge and charge processes is urgently needed. Graphene-, or graphene-like carbon-supported atomically dispersed metal catalysts (G-ADMCs) have been demonstrated to show excellent activity in various electrocatalytic reactions, making them promising candidates. Different from G-ADMCs for catalysis, which only require high activity in one direction, G-ADMCs for rechargeable batteries should provide high activity in both discharging and charging. This review provides guidance for the design and fabrication of bifunctional G-ADMCs for next-generation rechargeable batteries based on conversion reactions. The key challenges that prevent their reversible conversion, the origin of the activity of bifunctional G-ADMCs, and the current design principles of bifunctional G-ADMCs for highly reversible conversion, have been analyzed and highlighted for each conversion-type battery. Finally, a summary and outlook on the development of bifunctional G-ADMC materials for next-generation batteries with a high energy density and excellent energy efficiency are given.

Abstract Realizing long cycling stability under a high sulfur loading is an essential requirement for the practical use of lithium–sulfur (Li–S) batteries. Here, a lamellar aerogel composed of Ti 3 C 2 T x MXene/carbon nanotube (CNT) sandwiches is prepared by unidirectional freeze‐drying to boost the cycling stability of high sulfur loading batteries. The produced materials are denoted parallel‐aligned MXene/CNT (PA‐MXene/CNT) due to the unique parallel‐aligned structure. The lamellae of MXene/CNT/MXene sandwich form multiple physical barriers, coupled with chemical trapping and catalytic activity of MXenes, effectively suppressing lithium polysulfide (LiPS) shuttling under high sulfur loading, and more importantly, substantially improving the LiPS confinement ability of 3D hosts free of micro‐ and mesopores. The assembled Li–S battery delivers a high capacity of 712 mAh g −1 with a sulfur loading of 7 mg cm −2 , and a superior cycling stability with 0.025% capacity decay per cycle over 800 cycles at 0.5 C. Even with sulfur loading of 10 mg cm −2 , a high areal capacity of above 6 mAh cm −2 is obtained after 300 cycles. This work presents a typical example for the rational design of a high sulfur loading host, which is critical for the practical use of Li–S batteries

Abstract Sodium‐ion batteries (SIBs) based on conversion‐type metal sulfide (MS) anodes have attracted extraordinary attention due to relatively high capacity and intrinsic safety. The highly reversible conversion of M/Na 2 S to pristine MS in charge plays a vital role with regard to the electrochemical performance. Here, taking conventional MoS 2 as an example, guided by theoretical simulations, a catalyst of iron single atoms on nitrogen‐doped graphene (SAFe@NG) is selected and first used as a substrate to facilitate the reaction kinetics of MoS 2 in the discharging process. In the following charging process, using a combination of spectroscopy and microscopy, it is demonstrated that the SAFe@NG catalyst enables an efficient reversible conversion reaction of Mo/Na 2 S→NaMoS 2 →MoS 2 . Moreover, theoretical simulations reveal that the reversible conversion mechanism shows favorable formation energy barrier and reaction kinetics, in which SAFe@NG with the Fe–N 4 coordination center facilitates the uniform dispersion of Na 2 S/Mo and the decomposition of Na 2 S and NaMoS 2 . Therefore, efficient reversible conversion reaction MoS 2 ↔NaMoS 2 ↔Mo/Na 2 S is enabled by the SAFe@NG catalyst. This work contributes new avenues for designing conversion‐type materials with an efficient reversible mechanism.

A nonflammable electrolyte has been designed to enhance the interfacial stability and electrochemical kinetics for lithium metal batteries. As a result, Li||NCM811 cells show stable cycling stability at an ultrahigh cut-off voltage of 4.8 V.

Lithium cobalt oxide (LiCoO2) is the most widely used cathode materials for smart phones and laptop batteries. With the rapid development of portable electronics, more than 100,000 tons of spent lithium-ion batteries (LIBs) are produced every year. Conventional battery recycling processes including pyrometallurgical and hydrometallurgical processes mainly aim at extracting valuable metallic components from spent LIB cathodes, which requires high temperature reduction and/or acid/alkali chemicals to destroy covalent bond in cathodes and convert them into atoms for further extraction. The former leads to high energy consumption and the latter produces a lot of wastewater, which not only increases cost, but also damages our environment. Moreover, traditional recycling starts from spent battery cathodes and ends up with lithium/cobalt salts, which is unsustainable. Herein, a different recycling strategy to directly convert degraded LiCoO2 into high-voltage LiCoO2 cathode materials was proposed, featuring a closed-loop and green procedure. The directly-converted LiCoO2 from spent cathodes exhibits excellent cyclability at 4.5 V with a high capacity retention of 97.4% after 100 cycles, even superior than pristine LiCoO2. The recovery efficiencies of lithium and cobalt reach 91.3% and 93.5%, respectively, and the energy consumption could be greatly reduced since the roasting temperature was dropped below 400 °C with the assistance of ammonium sulfate. Due to the utilization of low-cost reagents and water as the leaching agent, the potential benefit of the recovery process was estimated to reach 6.94 $/kg cell.

Two-dimensional transition metal dichalcogenides (TMDCs) show great potential as efficient catalysts for Li-CO2 batteries. However, the basal plane engineering on TMDCs toward bifunctional catalysts for Li-CO2 batteries is still poorly understood. In this work, density functional theory calculations reveal that nucleophilic N dopants and electrophilic S vacancies in the ReS2 plane tailor the interactions with Li atoms and C/O atoms in intermediates, respectively. The electrophilic and nucleophilic dual centers show suitable adsorption with all intermediates during discharge and charge, resulting in a small energy barrier for the rate-determining step. Thus, an efficient bifunctional catalyst is produced toward Li-CO2 batteries. As a result, the optimal catalyst achieves an ultrasmall voltage gap of 0.66 V and an ultrahigh energy efficiency of 81.1% at 20 μA cm-2, which is superior to those of previous catalysts under similar conditions. The introduction of electrophilic and nucleophilic dual centers provides new avenues for designing excellent bifunctional catalysts for Li-CO2 batteries.

SignificanceIn recent years, lithium-ion batteries (LIBs) have been widely applied in electric vehicles as energy storage devices. However, it is a great challenge to deal with the large number of spent LIBs. In this work, we employ a rapid thermal radiation method to convert the spent LIBs into highly efficient bifunctional NiMnCo-activated carbon (NiMnCo-AC) catalysts for zinc-air batteries (ZABs). The obtained NiMnCo-AC catalyst shows excellent electrochemical performance in ZABs due to the unique core-shell structure, with face-centered cubic Ni in the core and spinel NiMnCoO4 in the shell. This work provides an economical and environment-friendly approach to recycling the spent LIBs and converting them into novel energy storage devices.

The increasing demand for wearable electronic devices necessitates flexible batteries with high stability and desirable energy density. Flexible lithium–sulfur batteries (FLSBs) have been increasingly studied due to their high theoretical energy density through the multielectron chemistry of low-cost sulfur. However, the implementation of FLSBs is challenged by several obstacles, including their low practical energy density, short life, and poor flexibility. Various graphene-based materials have been applied to address these issues. Graphene, with good conductivity and flexibility, exhibits synergistic effects with other active/catalytic/flexible materials to form multifunctional graphene-based materials, which play a pivotal role in FLSBs. This review summarizes the recent progress of graphene-based materials that have been used as various FLSB components, including cathodes, interlayers, and anodes. Particular attention is focused on the precise nanostructures, graphene efficacy, interfacial effects, and battery layout for realizing FLSBs with good flexibility, energy density, and cycling stability.

Abstract Traditional recycling processes of LiCoO2 rely on destructive decomposition, requiring high-temperature roasting or acid leaching to extract valuable Li and Co, which have significant environmental and economic concerns. Herein, a direct repairing method for degraded LiCoO2 using a LiCl–CH4N2O deep eutectic solvent (DES) was established. The DES is not used to dissolve LiCoO2 but directly serves as a carrier for the selective replenishment of lithium and cobalt. Replenishment of lithium restores LiCoO2 at different states of charge to a capacity of 130 mAh/g (at 0.1 C rate), while replenishing the cobalt increases the capacity retention rate of 90% after 100 cycles, which is comparable to pristine LiCoO2. The DES is collected and reused multiple times with a high repair efficiency. This process reduces energy consumption by 37.1% and greenhouse gas emissions by 34.8% compared with the current production process of LiCoO2, demonstrating excellent environmental and economic viability.

Abstract Wearable electronics require lightweight and flexible batteries, of which lithium‐sulfur (Li‐S) batteries are of great interest due to their high gravimetric energy density. Nevertheless, flexible Li‐S batteries have unsatisfactory electrochemical performance owing to electrode fracture during repeated bending, the volume change of sulfur species and the severe shuttle effect. Binders play essential roles in these batteries but have always lacked attention. Herein, a self‐healing polyvinylpyrrolidone‐polyethyleneimine (PVP‐PEI) binder cross‐linked by hydrogen bonds, which also regulates polysulfide redox kinetics, is reported. The dynamic hydrogen‐bonding networks repair the cracks and ensure the integrity of the electrode while numerous polar groups such as CO and ‐NH 2 suppress the shuttle effect by immobilizing polysulfides. Therefore, Li‐S batteries with the PVP‐PEI binder exhibit excellent cycling stability (a capacity decay rate of 0.0718% per cycle at 1 C after 450 cycles), an outstanding areal capacity of 7.67 mAh cm −2 even under a high sulfur loading (7.1 mg cm −2 ) and relatively lean electrolyte conditions ( E / S ratio = 8 µL mg −1 ). Flexible Li‐S pouch cells using the PVP‐PEI binder show a stable performance for 140 cycles and a favorable capacity retention of over 95% after 2800 bending cycles, confirming its application potential in high‐performance flexible Li‐S batteries.

The recycling of spent lithium-ion batteries is an effective approach to alleviating environmental concerns and promoting resource conservation. LiFePO4 batteries have been widely used in electric vehicles and energy storage stations. Currently, lithium loss, resulting in formation of Fe(III) phase, is mainly responsible for the capacity fade of LiFePO4 cathode. Another factor is poor electrical conductivity that limits its rate capability. Here, we report the use of a multifunctional organic lithium salt (3,4-dihydroxybenzonitrile dilithium) to restore spent LiFePO4 cathode by direct regeneration. The degraded LiFePO4 particles are well coupled with the functional groups of the organic lithium salt, so that lithium fills vacancies and cyano groups create a reductive atmosphere to inhibit Fe(III) phase. At the same time, pyrolysis of the salt produces an amorphous conductive carbon layer that coats the LiFePO4 particles, which improves Li-ion and electron transfer kinetics. The restored LiFePO4 cathode shows good cycling stability and rate performance (a high capacity retention of 88% after 400 cycles at 5 C). This lithium salt can also be used to recover degraded transition metal oxide-based cathodes. A techno-economic analysis suggests that this strategy has higher environmental and economic benefits, compared with the traditional recycling methods.

Recycling spent lithium-ion batteries (LIBs) is promising for resource reuse and environmental conservation but suffers from complex processing and loss of embedded value of spent LIBs in conventional metallurgy-based recycling routes. Herein, we selected a eutectic LiI-LiOH salt with the lowest eutectic point among binary eutectic lithium salt systems to provide a Li-rich molten environment, not only offering excess lithium but benefiting ion diffusion compared with that in the solid environment. Hence, the highly degraded LiNi0.5Co0.2Mn0.3O2 in spent LIBs which suffers high Li-deficiency and serious structural defects with harmful phase transitions is directly regenerated. A facile one-step heating strategy in the presence of a combination of the eutectic lithium salt and Co2O3 and MnO2 additives not only simplifies the recycling process but also endows the cathode materials with lithium supplementation and structural ordering, which contributes to a restoration of the capacity and stable cycling performance. In particular, this eutectic salt with a low eutectic point helps decrease the temperature and time of the direct recycling process and shows good adaptability for other layer oxide cathode materials (LiCoO2 and LiNi0.6Co0.2Mn0.2O2) in spent LIBs with varying cathode chemistry. As such, the feasibility of the direct recycling route is improved and broadened with simple and efficient processing, providing an idea for energy-saving cathode regeneration in future LIB recycling.

As one of the CO2 capture and utilization technologies, Li-CO2 batteries have attracted special interest in the application of carbon neutral. However, the design and fabrication of a low-cost high-efficiency cathode catalyst for reversible Li2CO3 formation and decomposition remains challenging. Here, guided by theoretical calculations, CO2 was utilized to activate the catalytic activity of conventional nitrogen-doped graphene, in which pyridinic-N and pyrrolic-N have a high total content (72.65%) and have a high catalytic activity in both CO2 reduction and evolution reactions, thus activating the reversible conversion of Li2CO3 formation and decomposition. As a result, the designed cathode has a low voltage gap of 2.13 V at 1200 mA g–1 and long-life cycling stability with a small increase in the voltage gap of 0.12 V after 170 cycles at 500 mA g–1. Our work suggests a way to design metal-free catalysts with high activity that can be used to activate the performance of Li-CO2 batteries.

Lithium-sulfur (Li-S) batteries with high energy density have been considered one kind of promising next-generation energy storage system. However, the shuttling effect of polysulfides caused by the intrinsic sluggish reaction kinetics severely hinders their commercialization. The catalytic effect, a powerful solution towards polysulfides shuttling by accelerating the conversion of polysulfides, has aroused great attention. Numerous catalysts have been developed and proved to have catalytic effects in the past years. More importantly, many advanced in-situ characterization technologies and electronic structure analyses have been combined to study the “black box” of the catalytic process, which promotes the practical application of Li-S batteries entering a new stage. In this review, instead of summarizing recent achievements in catalyst materials and structural designs, the key issues that how to observe, understand, design, and use catalytic effect in Li-S batteries are systematically discussed. In-situ techniques are summarized to see the actual catalytic process. Band theory is applied to understand the electronic structure, thus deciphering design principles and strategies of catalytic effect. Subsequently, how to use the catalytic effect to realize Ah-level Li-S pouch cells is analyzed. Last, we propose a research paradigm for catalytic effect, which will enlighten the future development of Li-S batteries and other next-generation batteries based on conversion reactions.

The overuse and exploitation of fossil fuels has triggered the energy crisis and caused tremendous issues for the society. Lithium-ion batteries (LIBs), as one of the most important renewable energy storage technologies, have experienced booming progress, especially with the drastic growth of electric vehicles. To avoid massive mineral mining and the opening of new mines, battery recycling to extract valuable species from spent LIBs is essential for the development of renewable energy. Therefore, LIBs recycling needs to be widely promoted/applied and the advanced recycling technology with low energy consumption, low emission, and green reagents needs to be highlighted. In this review, the necessity for battery recycling is first discussed from several different aspects. Second, the various LIBs recycling technologies that are currently used, such as pyrometallurgical and hydrometallurgical methods, are summarized and evaluated. Then, based on the challenges of the above recycling methods, the authors look further forward to some of the cutting-edge recycling technologies, such as direct repair and regeneration. In addition, the authors also discuss the prospects of selected recycling strategies for next-generation LIBs such as solid-state Li-metal batteries. Finally, overall conclusions and future perspectives for the sustainability of energy storage devices are presented in the last chapter.

Zinc-based flow batteries have attracted tremendous attention owing to their outstanding advantages of high theoretical gravimetric capacity, low electrochemical potential, rich abundance, and low cost of metallic zinc. Among which, zinc-iron (Zn/Fe) flow batteries show great promise for grid-scale energy storage. However, they still face challenges associated with the corrosive and environmental pollution of acid and alkaline electrolytes, hydrolysis reactions of iron species, poor reversibility and stability of Zn/Zn2+ redox couple. In this work, bromide ions are used to stabilize zinc ions via complexation interactions in the cost-effective and eco-friendly neutral electrolyte. Cyclic voltammetry results reveal that the redox reversibility between Zn and stabilized Zn2+ is greatly improved. The results of spectrum characterizations and density functional theory calculations verify that the formation of Zn[Brn(H2O)6-n]2-n (1 ≤ n ≤4, n is integer.) ions accounts for the increased electrochemical reversibility of Zn/Zn2+pair. Moreover, to overcome the bottleneck of slow kinetics of the coordination interactions between Zn2+ and Br−, ZnBr2 is judiciously selected as the electrolyte additive to promote the complexation process. Adopting K3Fe(CN)6 as the positive redox species to pair with the zinc anode with ZnBr2 modified electrolyte, the proposed neutral Zn/Fe flow batteries deliver excellent efficiencies and superior cycling stability over 2000 cycles (356 h), shedding light on their great potential for large scale energy storage.

The quasi-intercalation reaction mechanism in solid-state Li–SPAN batteries leads to fast reaction kinetics and small volume change.

The recycling of lithium-ion batteries is important due to limited metallic resources and environmental protection. However, most current studies aim at only extracting valuable components from cathode materials, and the lithium in the anode is usually ignored due to its low concentration. Herein, we develop an integrated recycling strategy for both cathode and anode materials. Batteries are disassembled, and lithium in lithiated graphite is extracted in water and converted to Li2CO3 after absorbing CO2 from the air, which is then used for the direct regeneration of LiCoO2 and LiNi0.5Mn0.3Co0.2O2, while the degraded graphite is regenerated by the delithiation and activation. LiCoO2 with different degrees of failure can retrieve a capacity of 130 mAh/g, while degraded graphite can realize a capacity of 370 mAh/g after regeneration, values which are comparable to commercial materials. Importantly, no external lithium salt is necessary, and water is the only reagent used during regeneration of the cathode material.

The advent of 5G and the Internet of Things has spawned a demand for wearable electronic devices. However, the lack of a suitable flexible energy storage system has become the "Achilles' Heel" of wearable electronic devices. Additional problems during the transformation of the battery structure from conventional to flexible also present a severe challenge to the battery design. Flexible Zn-based batteries, including Zn-ion batteries and Zn-air batteries, have long been considered promising candidates due to their high safety, eco-efficiency, substantial reserve, and low cost. In the past decade, researchers have come up with elaborate designs for each portion of flexible Zn-based batteries to improve the ionic conductivities, mechanical properties, environment adaptabilities, and scalable productions. It would be helpful to summarize the reported strategies and compare their pros and cons to facilitate further research toward the commercialization of flexible Zn-based batteries. In this review, the current progress in developing flexible Zn-based batteries is comprehensively reviewed, including their electrolytes, cathodes, and anodes, and discussed in terms of their synthesis, characterization, and performance validation. By clarifying the challenges in flexible Zn-based battery design, we summarize the methodology from previous investigations and propose challenges for future development. In the end, a research paradigm of Zn-based batteries is summarized to fit the burgeoning requirement of wearable electronic devices in an iterative process, which will benefit the future development of Zn-based batteries.

The sluggish redox kinetics of sulfur and the uncontrollable growth of lithium dendrites are two main challenges that impede the practical applications of lithium-sulfur (Li-S) batteries. In this study, a multifunctional host with vacancy-rich MoSSe vertically grown on reduced graphene oxide aerogels (MoSSe/rGO) is designed as the host material for both sulfur and lithium. The embedding of Se into a MoS2 lattice is introduced to improve the inherent conductivity and generate abundant anion vacancies to endow the 3D conductive graphene based aerogels with specific sulfiphilicity-lithiophilicity. As a result, the assembled Li-S batteries based on MoSSe/rGO exhibit greatly improved capacity and cycling stability and can be operated under a lean electrolyte (4.8 μL mg-1) and a high sulfur loading (6.5 mg cm-2), achieving a high energy density. This study presents a unique method to unlock the catalysis capability and improve the inherent lithiophilicity by heteroatom doping and defect chemistry for kinetics-enhanced and dendrite-free Li-S batteries.

Flexible Zn-air batteries (FZABs) have significant potentials as efficient energy storage devices for wearable electronics because of their safeties and high energy-to-cost ratios. However, their application is limited by their short cycle lives, low discharge capacities per cycle, and high charge/discharge polarizations. Accordingly, herein, a poly(sodium acrylate)-polyvinyl alcohol (PANa-PVA)-ionic liquid (IL) hydrogel (PANa-PVA-IL) is prepared using a hygroscopic IL, 1-ethyl-3-methylimidazolium chloride, as an additive for twin-chain PANa-PVA. PANa-PVA-IL exhibits a high conductivity of 306.9 mS cm-1 and a water uptake of 2515 wt% at room temperature. Moreover, a low-cost bifunctional catalyst, namely, Co9 S8 nanoparticles anchored on N- and S-co-doped activated carbon black pearls 2000 (Co9 S8 -NSABP), is synthesized, which demonstrates a low O2 reversibility potential gap of 0.629 V. FZABs based on PANa-PVA-IL and Co9 S8 -NSABP demonstrate high discharge capacities of 1.67 mAh cm-2 per cycle and long cycle lives of 330 h. Large-scale flexible rechargeable Zn-air pouch cells exhibit total capacities of 1.03 Ah and energy densities of 246 Wh kgcell-1 . This study provides new information about hydrogels with high ionic conductivities and water uptakes and should facilitate the application of FZABs in wearable electronics.

New methods for recycling lithium-ion batteries (LIBs) are needed because traditional recycling methods are based on battery pulverization, which requires pre-treatment of tedious and non-eco-friendly discharging and results in low efficiency and high waste generation in post-treatment. Separating the components of recycled LIB cells followed by reuse or conversion of individual components could minimize material cross-contamination while avoiding excessive consumption of energy and chemicals. However, disposing of charged LIB cells is hazardous due to the high reactivity of lithiated graphite towards cathode materials and air, and the toxicity and flammability of the electrolytes. Here we demonstrate that the disassembly of charged jellyroll LIB cells in water with a single main step reveals no emissions from the cells and near perfect recycling efficiencies that exceed the targets of the US Department of Energy and Batteries Europe. The precise non-destructive mechanical method separates the components from jellyroll cell in water, avoiding both uncontrollable reactions from the anode and burning of the electrolyte, while allowing only a limited fraction of the anode lithium to react with water. Recycling in this way allows the recovery of materials with a value of ∼7.14 $ kg−1 cell, which is higher than that of physical separation (∼5.40 $ kg−1 cell) and much greater than the overall revenue achieved using element extraction methods (<1.00 $ kg−1 cell). The precise separation method could thus facilitate the establishment of a circular economy within the LIB industry and build a strong bridge between academia and the battery recycling industry.

Abstract Solid‐state lithium–sulfur (Li–S) batteries using gel polymer electrolytes have attracted much attention owing to their higher safety compared to liquid electrolytes and lower interfacial resistance compared to ceramic electrolytes. However, except for their unsatisfactory lithium‐ion conductivity, relatively low mechanical strength, the unavoidable polysulfide shuttling in gel polymer electrolytes still limits their development. This work designed a poly(ethylene oxide)‐polyacrylonitrile (PEO‐PAN) copolymer membrane electrolyte, in which PAN fibers act as both a filler and crosslinker. This structure not only provides improved ionic conductivity, high mechanical strength, and lithium dendrite blocking ability, it also inhibits polysulfide shuttling as a result of strong polysulfide adsorption by the CNO functional groups formed during the PEO and PAN crosslinking process, which improves the safety, cycling stability and rate capability when used in Li–S batteries. A more than 96% capacity retention after 1000 bend cycles of the flexible battery is also achieved because of the high flexibility and high bonding strength of this electrolyte.

Abstract A large amount of spent LiFePO 4 (LFP) has been produced in recent years because it is one of the most widely used cathode materials for electric vehicles. The traditional hydrometallurgical and pyrometallurgical recycling methods are doubted because of the economic and environmental benefits; the direct regeneration method is considered a promising way to recycle spent LFP. However, the performance of regenerated LFP by direct recycling is not ideal due to the migration of Fe ions during cycling and irreversible phase transition caused by sluggish Li + diffusion. The key to addressing the challenge is to immobilize Fe atoms in the lattice and improve the Li + migration capability during cycling. In this work, spent LFP is regenerated by using environmentally friendly ethanol, and its cycling stability is promoted by elevating the d‐band center of Fe atoms via construction of a heterogeneous interface between LFP and nitrogen‐doped carbon. The FeO bonding is strengthened and the migration of Fe ions during cycling is suppressed due to the elevated d‐band center. The Li + diffusion kinetics in the regenerated LFP are improved, leading to an excellent reversibility of the phase transition. Therefore, the regenerated LFP exhibits an ultrastable cycling performance at a high rate of 10 C with ≈80% capacity retention after 1000 cycles.

Zinc-air batteries (ZABs) with high energy density and safety are promising as next-generation energy storage systems, while their applications are severely hindered by the sluggish reaction kinetic of air cathodes. Developing a bifunctional catalyst with high activity and durability is an effective strategy to address the above challenges. Herein, a Co3O4/Mn3O4 nanohybrid with heterointerfaces is designed as advanced cathode catalyst for ZABs. Density functional theory calculations show the heterogeneous interface between Co3O4/Mn3O4 can improve the dynamics of carrier transport and thus enhancing the catalytic activity and durability. The Co3O4/Mn3O4 catalyst anchored on reduced graphene oxide (rGO) exhibits high oxygen reduction reaction (ORR) activity with a half-wave potential of 0.86 V, and excellent oxygen evolution reaction (OER) activity with the potential of 1.59 V at 10 mA cm−2, which are comparable to the commercial noble metal catalysts. The improved ORR/OER catalytic activity is ascribed to the synergistic effect of heterointerfaces between Co3O4 and Mn3O4 as well as the improved conductivity and contact area of oxygen/catalysts/electrolytes three-phase interface by rGO. Furthermore, a home-made ZAB based on Co3O4/Mn3O4/rGO shows a high open circuit voltage of 1.54 V, a large power density of 194.6 mW cm−2 and good long-term cycling stability of nearly 400 h at 5 mA cm−2, which affords a promising bifunctional oxygen catalyst for rechargeable ZABs.

Flexible lithium-sulfur (Li-S) batteries with high mechanical compliance and energy density are highly desired. This manuscript reported that large-area freestanding MXene (Ti3C2Tx) film has been obtained through a scalable drop-casting method, significantly improving adhesion to the sulfur layer under the continuously bent. Titanium oxide anchored on holey Ti3C2Tx (TiO2/H-Ti3C2Tx) was also produced by the well-controlled oxidation of few-layer Ti3C2Tx, which greatly facilitates lithium ion transport as well as prevents the shuttling of lithium polysulfides. Therefore, the obtained sandwich electrode has demonstrated a high capacity of 740 mAh g-1 at 2 C and a high capacity retention of 81% at 1 C after 500 cycles. Flexible Li-S batteries based on this sandwich electrode have a capacity retention as high as 95% after bending 500 times. This work provides effective design strategies of MXene for flexible batteries and wearable electronics.

Lithium metal batteries (LMBs) are considered promising candidates for next-generation battery systems due to their high energy density. However, commercialized carbonate electrolytes cannot be used in LMBs due to their poor compatibility with lithium metal anodes. While increasing cut-off voltage is an effective way to boost the energy density of LMBs, conventional ethylene carbonate-based electrolytes undergo a number of side reactions at high voltages. It is therefore critical to upgrade conventional carbonate electrolytes, the performance of which is highly influenced by the solvation structure of lithium ions (Li+ ). This review provides a comprehensive overview of the strategies to regulate the solvation structure of Li+ in carbonate electrolytes for LMBs by better understanding the science behind the Li+ solvation structure and Li+ behavior. Different strategies are systematically compared to help select better electrolytes for specific applications. The remaining scientific and technical problems are pointed out, and directions for future research on carbonate electrolytes for LMBs are proposed.

Abstract The operation of traditional aqueous-electrolyte zinc-ion batteries is adversely affected by the uncontrollable growth of zinc dendrites and the occurrence of side reactions. These problems can be avoided by the development of functional hydrogel electrolytes as replacements for aqueous electrolytes. However, the mechanism by which most hydrogel electrolytes inhibit the growth of zinc dendrites on a zinc anode has not been investigated in detail, and there is a lack of a large-scale recovery method for mainstream hydrogel electrolytes. In this paper, we describe the development of a recyclable and biodegradable hydrogel electrolyte based on natural biomaterials, namely chitosan and polyaspartic acid. The distinctive adsorptivity and inducibility of chitosan and polyaspartic acid in the hydrogel electrolyte triggers a double coupling network and an associated synergistic inhibition mechanism, thereby effectively inhibiting the side reactions on the zinc anode. In addition, this hydrogel electrolyte played a crucial role in an aqueous acid-based Zinc/MnO 2 battery, by maintaining its interior two-electron redox reaction and inhibiting the formation of zinc dendrites. Furthermore, the sustainable biomass-based hydrogel electrolyte is biodegradable, and could be recovered from the Zinc/MnO 2 battery for subsequent recycling.

The recycling of spent lithium-ion batteries (LIBs) has become a necessity for recovering valuable resources and protecting the environment to support sustainable development. We report the design of a highly efficient CoFe/C catalyst by combining the Co and Fe wastes from spent LIBs with sawdust-derived carbon, which were cathode materials in zinc–air batteries (ZABs). As a result of the electrostatic attraction between the Co3+/Fe3+ cations and the hydroxyl groups in sawdust, CoFe nanoparticles are uniformly dispersed in the CoFe/C catalyst after annealing. The Fe atoms in the CoFe nanoparticles are all isolated into single sites by the Co atoms, which redistribute the electrons in the CoFe/C catalyst. The catalyst produced a Pt-like dissociative mechanism, contributing to an excellent oxygen reduction reaction performance. After assembly in ZABs, the CoFe/C catalyst cathode exhibits a long cycling stability of 350 h and an impressive power density of 199.2 mW cm–2. The CoFe/C catalyst cathode has also been used in flexible ZABs to power LEDs or charge a mobile phone. The work combines spent LIBs with sawdust to fabricate high-performance catalysts, which could reduce environmental pollution and realize high economic value.

Abstract Li metal is the ultimate choice for the anode in next‐generation high energy density rechargeable batteries. However, undesired dendrite growth, dead Li formation, and a large volume change of the lithium metal anode lead to severe safety hazards such as short‐circuiting, fire, or even explosion. Graphene oxide (GO) in large areas has been prepared as the Li metal host via a continuous centrifugal casting method. Aligned microchannels are then fabricated in it by a simple punching method using 3D printed templates. The GO matrix effectively regulates the lithium plating/stripping behavior while the aligned channels uniformly distributes the Li‐ion flux and provides short Li‐ion diffusion paths. The Li/ holey GO composite is flexible with a controllable thickness from 50 to 150 µm, which corresponds to capacities from 9.881 to 27.601 mAh cm −2 . As a result, the anode has a low overpotential of 30 mV after 100 h, a high capacity of ≈3538 mAh g −1 (91.4% of the theoretical capacity), and a superior rate ability of up to 50 C with a LiFePO 4 cathode. The holey GO/Li electrode is also paired with other cathodes and used in pouch cells, indicating its suitability for various high‐energy battery systems.

The development of flexible zinc-air batteries (FZABs) has attracted broad attention in the field of wearable electronic devices. Gel electrolyte is one of the most important components in FZABs, which is urgent to be optimized to match with Zn anode and adapt to severe climates. In this work, a polarized gel electrolyte of polyacrylamide-sodium citric (PAM-SC) is designed for FZABs, in which the SC molecules contain large amount of polarized -COO- functional groups. The polarized -COO- groups can form an electrical field between gel electrolyte and Zn anode to suppress Zn dendrite growth. Besides, the -COO- groups in PAM-SC can fix H2 O molecules, which prevents water from freezing and evaporating. The polarized PAM-SC hydrogel delivers a high ionic conductivity of 324.68 mS cm-1 and water retention of 96.85 % after being exposed for 96 h. FZABs with the PAM-SC gel electrolyte exhibit long cycling life of 700 cycles at -40 °C, showing the application prospect under extreme conditions.

Lithium cobalt oxide (LCO) is widely used in Li-ion batteries due to its high volumetric energy density, which is generally charged to 4.3 V. Lifting the cut-off voltage of LCO from 4.3 V to 4.7 V will increase the specific capacity from 150 to 230 mAh g-1 with a significant improvement of 53%. However, LCO suffers serious problems of H1-3/O1 phase transformation, unstable interface between cathode and electrolyte, and irreversible oxygen redox reaction at 4.7 V. Herein, interface stabilization and band structure modification are proposed to strengthen the crystal structure of LCO for stable cycling of LCO at an ultrahigh voltage of 4.7 V. Gradient distribution of magnesium and uniform doping of nickel in Li layers inhibit the harmful phase transitions of LCO, while uniform LiMgx Ni1-x PO4 coating stabilizes the LCO-electrolyte interface during cycles. Moreover, the modified band structure improves the oxygen redox reaction reversibility and electrochemical performance of the modified LCO. As a result, the modified LCO has a high capacity retention of 78% after 200 cycles at 4.7 V in the half cell and 63% after 500 cycles at 4.6 V in the full cell. This work makes the capacity of LCO one step closer to its theoretical specific capacity.

Lithium-sulfur (Li-S) batteries are considered as one of the most promising candidates to achieve an energy density of 500 Wh kg⁻1 . However, the challenges of shuttle effect, sluggish sulfur conversion kinetics, and lithium-dendrite growth severely obstruct their practical implementation. Herein, multiscale V2 C MXene (VC) with a spherical confinement structure is designed as a high-efficiency bifunctional promotor for the evolution of sulfur and lithium species in Li-S batteries. Combining synchrotron X-ray 3D nano-computed tomography (X-ray 3D nano-CT), small-angle neutron scattering (SANS), and first-principle calculations, it is revealed that the activity of VC can be maximized by tuning the scale, and the as-attained functions are conducted as follows: (i) the VC acts as the efficient lithium polysulfide (LiPS) scavenger due to the large number of active sites; (ii) the VC exhibits significantly improved electrocatalytic function for the Li2 S nucleation and decomposition reaction kinetics owing to the scale effect; and (iii) the VC can regulate the dynamic behavior of Li-ions and thus stabilize the lithium plating/stripping effectively on account of the unique ion-sieving effect.

Lithium-based rechargeable batteries have dominated the energy storage field and attracted considerable research interest due to their excellent electrochemical performance. As indispensable and ubiquitous components, electrolytes play a pivotal role in not only transporting lithium ions, but also expanding the electrochemical stable potential window, suppressing the side reactions, and manipulating the redox mechanism, all of which are closely associated with the behavior of solvation chemistry in electrolytes. Thus, comprehensively understanding the solvation chemistry in electrolytes is of significant importance. Here we critically reviewed the development of electrolytes in various lithium-based rechargeable batteries including lithium-metal batteries (LMBs), nonaqueous lithium-ion batteries (LIBs), lithium-sulfur batteries (LSBs), lithium-oxygen batteries (LOBs), and aqueous lithium-ion batteries (ALIBs), and emphasized the effects of interactions between cations, anions, and solvents on solvation chemistry, and functions of solvation chemistry in different types of electrolytes (strong solvating electrolytes, moderate solvating electrolytes, and weak solvating electrolytes) on the electrochemical performance and redox mechanism in the abovementioned rechargeable batteries. Specifically, the significant effects of solvation chemistry on the stability of electrode-electrolyte interphases, suppression of lithium dendrites in LMBs, inhibition of the co-intercalation of solvents in LIBs, improvement of anodic stability at high cut-off voltages in LMBs, LIBs and ALIBs, regulation of redox pathways in LSBs and LOBs, and inhibition of hydrogen/oxygen evolution reactions in LOBs are thoroughly summarized. Finally, the review concludes with a prospective outlook, where practical issues of electrolytes, advanced in situ/operando techniques to illustrate the mechanism of solvation chemistry, and advanced theoretical calculation and simulation techniques such as "material knowledge informed machine learning" and "artificial intelligence (AI) + big data" driven strategies for high-performance electrolytes have been proposed.

A conventional two-electrode rechargeable zinc-air battery (RZAB) has two major problems: 1) opposing requirements for the oxygen reduction (ORR) and oxygen evolution (OER) reactions from the catalyst at the air cathode; and 2) zinc-dendrite formation, hydrogen generation, and zinc corrosion at the zinc anode. To tackle these problems, a three-electrode RZAB (T-RZAB) including a hydrophobic discharge cathode, a hydrophilic charge cathode, and a zinc-free anode is developed. The decoupled cathodes enable fast ORR and OER kinetics, and avoid oxidization of the ORR catalyst. The zinc-free anode using tin-coated copper foam that induces the growth of (002)Zn planes, suppresses hydrogen evolution, and prevents Zn corrosion. As a result, the T-RZABs have a high discharge capacity per cycle of 800 mAh cm-2 , a low voltage gap between the discharge/charge platforms of 0.66 V, and an ultralong cycle life of 5220 h at a current density of 10 mA cm-2 . A large T-RZAB with a discharge capacity of 10 Ah per cycle with no obvious degradation after cycling for 1000 h is developed. Finally, a T-RZAB pack that has an energy density of 151.8 Wh kg-1 and a low cost of 46.7 US dollars kWh-1 is assembled.

Recycling spent lithium-ion batteries (LIBs) has become an urgent task to address the issues of resource shortage and potential environmental pollution. However, direct recycling of the spent LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode is challenging because the strong electrostatic repulsion from a transition metal octahedron in the lithium layer provided by the rock salt/spinel phase that is formed on the surface of the cycled cathode severely disrupts Li+ transport, which restrains lithium replenishment during regeneration, resulting in the regenerated cathode with inferior capacity and cycling performance. Here, we propose the topotactic transformation of the stable rock salt/spinel phase into Ni0.5Co0.2Mn0.3(OH)2 and then back to the NCM523 cathode. As a result, a topotactic relithiation reaction with low migration barriers occurs with facile Li+ transport in a channel (from one octahedral site to another, passing through a tetrahedral intermediate) with weakened electrostatic repulsion, which greatly improves lithium replenishment during regeneration. In addition, the proposed method can be extended to repair spent NCM523 black mass, spent LiNi0.6Co0.2Mn0.2O2, and spent LiCoO2 cathodes, whose electrochemical performance after regeneration is comparable to that of the commercial pristine cathodes. This work demonstrates a fast topotactic relithiation process during regeneration by modifying Li+ transport channels, providing a unique perspective on the regeneration of spent LIB cathodes.

Interfacial doping engineering has been considered a promising strategy to improve the reaction kinetics of 2D heterostructures in sodium-ion batteries (SIBs). Much attention has been paid to the enhancement mechanism of reaction kinetics of pristine heterostructures during discharge, whereas less attention has been given to the optimization of reaction kinetics of discharged products during charge. Therefore, there is an urgent need for systematic understanding and design guide for interfacial doping engineering of 2D heterostructures to achieve good bidirectional reaction kinetics. In this paper, interfacial doping engineering is designed by the guidance of theoretical calculation, a new interface composed of Co-doped MoS2 (Co-MoS2) and N-doped graphene (NG) has excellent electrical conductivity and Na+ adsorption ability during discharge. Moreover, the revealed Na2S-Mo(Co)/NG interface is greatly beneficial to the dispersion, adsorption, and decomposition of Na2S and the overall electrical conductivity during charge. The good bidirectional reaction kinetics of Co-MoS2/NG interfaces in cobalt-doped MoS2 anchored on three-dimensional nitrogen-doped carbon (Co-MoS2/3DNC) composites have been systematically demonstrated by electrochemical characterization technologies. Therefore, an efficient reversible conversion reaction is enabled by the Co-MoS2/NG interfaces. The Co-MoS2/3DNC shows good rate performance and excellent long-term cycling stability of 1500 cycles at the current density of 1 A g−1. This work provides new insight into designing interfacial doping engineering for highly reversible and durable conversion-type composite anodes.

High-voltage lithium metal batteries (LMBs) pose severe challenges for the matching of electrolytes with aggressive electrodes, especially at low temperatures. Here, we report a rational modification of the Li+ solvation structure to extend the voltage and temperature operating ranges of conventional electrolytes. Ion-ion and ion-dipole interactions as well as the electrochemical window of solvents were tailored to improve oxidation stability and de-solvation kinetics of the electrolyte. Meanwhile, robust and elastic B and F-rich interphases are formed on both electrodes. Such optimization enables Li||LiNi0.5 Mn1.5 O4 cells (90.2 % retention after 400 cycles) and Li||LiNi0.6 Co0.2 Mn0.2 O2 (NCM622) cells (74.0 % retention after 200 cycles) to cycle stably at an ultra-high voltage of 4.9 V. Moreover, NCM622 cells deliver a considerable capacity of 143.5 mAh g-1 at -20 °C, showing great potential for practical uses. The proposed strategy sheds light on further optimization for high-voltage LMBs.

Lithium metal is a desirable anode for high-energy density lithium–sulfur (Li–S) batteries. However, its reliability is severely limited by dendrite growth and side reactions with polysulfides, which are yet challenging to solve simultaneously. Herein, we report a protective layer that works the same way as the ion-permselective cell membrane, yielding a corrosion-resistant and dendrite-free Li metal anode specially for Li–S batteries. A self-limited assembly of octadecylamine together with Al3+ ions on a Li metal anode surface produces a dense, stable yet thin layer with ionic conductive Al–Li alloy uniformly embedded in it, which prevents the passage of polysulfides but regulates the penetrated Li ion flux for uniform Li deposition. As a result, the assembled batteries show excellent cycling stability even with a high sulfur-loaded cathode, suggesting a straightforward but promising strategy to stabilize highly active anodes for practical applications.

Sluggish CO 2 reduction reaction (CO 2 RR) and evolution reaction (CO 2 ER) kinetics at cathodes seriously hamper the applications of Li-CO 2 batteries, which have attracted vast attention as one kind of promising carbon-neutral technology. Two-dimensional transition metal dichalcogenides (TMDs) have shown great potential as the bidirectional catalysts for CO 2 redox, but how to achieve a high exposure of dual active sites of TMDs with CO 2 RR/CO 2 ER activities remains a challenge. Herein, a bidirectional catalyst that vertically growing MoS 2 on Co 9 S 8 supported by carbon paper (V-MoS 2 /Co 9 S 8 @CP) has been designed with abundant edge as active sites for both CO 2 RR and CO 2 ER, improves the interfacial conductivity, and modulates the electron transportation pathway along the basal planes. As evidenced by the outstanding energy efficiency of 81.2% and ultra-small voltage gap of 0.68 V at 20 μA cm −2 , Li-CO 2 batteries with V-MoS 2 /Co 9 S 8 @CP show superior performance compared with horizontally growing MoS 2 on Co 9 S 8 (H-MoS 2 /Co 9 S 8 @CP), MoS 2 @CP, and Co 9 S 8 @CP. Density functional theory calculations help reveal the relationship between performance and structure and demonstrate the synergistic effect between MoS 2 edge sites and Co 9 S 8 . This work provides an avenue to understand and realize rationally designed electronic contact of TMDs with specified crystal facets, but more importantly, provides a feasible guide for the design of high-performance cathodic catalyst materials in Li-CO 2 batteries.

Composite-polymer-electrolytes (CPEs) embedded with advanced filler materials offer great promise for fast and preferential Li+ conduction. The filler surface chemistry determines the interaction with electrolyte molecules and thus critically regulates the Li+ behaviors at the interfaces. Herein, we probe into the role of electrolyte/filler interfaces (EFI) in CPEs and promote Li+ conduction by introducing an unsaturated coordination Prussian blue analog (UCPBA) filler. Combining scanning transmission X-ray microscope stack imaging studies and first-principle calculations, fast Li+ conduction is revealed only achievable at a chemically stable EFI, which can be established by the unsaturated Co-O coordination in UCPBA to circumvent the side reactions. Moreover, the as-exposed Lewis-acid metal centers in UCPBA efficiently attract the Lewis-base anions of Li salts, which facilitates the Li+ disassociation and enhances its transference number (tLi+). Attributed to these superiorities, the obtained CPEs realize high room-temperature ionic conductivity up to 0.36 mS cm-1 and tLi+ of 0.6, enabling an excellent cyclability of lithium metal electrodes over 4,000 h as well as remarkable capacity retention of 97.6% over 180 cycles at 0.5 C for solid-state lithium-sulfur batteries. This work highlights the crucial role of EFI chemistry in developing highly conductive CPEs and high-performance solid-state batteries.

Solid polymer electrolytes (SPEs) are promising substitutes for current flammable liquid electrolytes to achieve high-safety and high-energy-density lithium metal batteries. Polyethylene oxide (PEO) based solid polymer electrolytes have attracted increasing attention because of their excellent flexibility, manufacturability, light weight, and low-cost processing, while they often suffer from low ionic conductivity at room temperature, low lithium transference number and unsatisfactory interfacial resistance, which largely restrain their practical application. Herein, two-dimensional holey silica nanosheets (2D-HSN) as the fillers, together with LiNO3 as the electrolyte additive, are introduced in a PEO/poly(vinylidene fiuoride-co-hexafluoropropylene) (PVDF-HFP) blended polymer matrix to obtain a SPE. The incorporation of HSN filler creates supplementary channels for lithium ion migration and lowers the crystallinity of the polymer, thereby facilitating the movement of lithium ions. The HSN-based SPE demonstrates higher ionic conductivity up to 3.7 × 10−4 S cm−1 at 30 °C, larger Li+ transference number close to 0.34, and more stable lithium plating/stripping than that without the fillers, and HSN can promote the formation of more stable solid electrolyte interphase (SEI) layer. The as-assembled LiFePO4||Li batteries deliver a high specific capacity of 159 mA h g−1 with the capacity retention of 95.5% after 200 cycles at 30 °C, as well as superior rate performance and cycling stability compared to that using the blank SPE.

Abstract Aqueous zinc batteries possess intrinsic safety and cost-effectiveness, but dendrite growth and side reactions of zinc anodes hinder their practical application. Here, we propose the extended substrate screening strategy for stabilizing zinc anodes and verify its availability (d substrate : d Zn(002) = 1: 1→d substrate : d Zn(002) =n:1, n = 1, 2). From a series of calculated phyllosilicates satisfying d substrate ≈ 2d Zn(002) , we select vermiculite, which has the lowest lattice mismatch (0.38%) reported so far, as the model to confirm the effectiveness of “2d Zn(002) ” substrates for zinc anodes protection. Then, we develop a monolayer porous vermiculite through a large-scale and green preparation as a functional coating for zinc electrodes. Unique “planting Zn(002) seeds” mechanism for “2d Zn(002) ” substrates is revealed to induce the oriented growth of zinc deposits. Additionally, the coating effectively inhibits side reactions and promotes zinc ion transport. Consequently, the modified symmetric cells operate stably for over 300 h at a high current density of 50 mA cm −2 . This work extends the substrate screening strategy and advances the understanding of zinc nucleation mechanism, paving the way for realizing high-rate and stable zinc-metal batteries.

An Fe2O3/single-walled carbon nanotube (Fe2O3/SWCNT) membrane with high Fe2O3 loading (88.0 wt%) is prepared by oxidizing a flow-assembled Fe/SWCNT membrane. The Fe2O3/SWCNT membrane can be used as a flexible, binder-free and current-collector-free anode in lithium ion batteries, which shows a high reversible capacity of 1243 mA h g−1 at a current density of 50 mA g−1 and an excellent cyclic stability over 90 cycles at 500 mA g−1. The superior electrochemical performance of the Fe2O3/SWCNT electrode can be attributed to the structural characteristics of the SWCNT network and the uniformly distributed Fe2O3 nanoparticles (5–10 nm). The nanosized Fe2O3 has a short lithium ion diffusion length and minimal volume change during lithiation–delithiation. The high loading ratio of Fe2O3 nanoparticles renders the high capacity. The highly conducting interwoven SWCNT network not only facilitates electron conduction but also buffers the strain applied to Fe2O3 nanoparticles during the lithiation and delithiation. These results demonstrate the great potential of this hybrid membrane anode for high-performance flexible lithium ion batteries.

Lithium–sulfur (LiS) battery, as a high energy-density storage system, has attracted great attention for next generation rechargeable battery applications. However, the fast capacity decay caused by lithium polysulfides (LiPSs) dissolution impedes its prospect for commercialization. In this work, nitrogen-doped graphene, as a chemical immobilizer, was designed to bind LiPSs and stabilize sulfur in the cathode for high performance LiS batteries. The incorporated nitrogen dopants in the graphene network were found to have a strong binding effect on the LiPSs to improve electrochemical stability and promote fast electrochemical reaction kinetics. As a result, the nitrogen doped graphene-based sulfur electrode could deliver an initial capacity of ∼1200 mAh g−1 at 0.3 A g−1, and exhibit good capacity retention with only 0.05% capacity decay per cycle after 300 cycles at 0.75 A g−1.

Abstract Flexible energy‐storage devices have attracted growing attention with the fast development of bendable electronic systems. Thus, the search for reliable electrodes with both high mechanical flexibility and excellent electron and lithium‐ion conductivity has become an urgent task. Carbon‐coated nanostructures of Li 4 Ti 5 O 12 (LTO) have important applications in high‐performance lithium ion batteries (LIBs). However, these materials still need to be mixed with a binder and carbon black and pressed onto metal substrates or, alternatively, by be deposited onto a conductive substrate before they are assembled into batteries, which makes the batteries less flexible and have a low energy density. Herein, a simple and scalable process to fabricate LTO nanosheets with a N‐doped carbon coating is reported. This can be assembled into a film which can be used as a binder‐free and flexible electrode for LIBs that does not require any current collectors. Such a flexible electrode has a long life. More significantly, it exhibits an excellent rate capability due to the thin carbon coating and porous nanosheet structures, which produces a highly conductive pathway for electrons and fast transport channels for lithium ions.

Using an aberration-corrected transmission electron microscope, we observed the oxygen vacancies, profiled the concentration in the SnO2−δ nanocrystals on an atomic scale, and estimated the amount of oxygen vacancies to be ca. 3.3 atom%. The SnO2−δ nanocrystals show much improved initial Coulombic efficiency, rate capability and specific capacity compared with stoichiometric SnO2 when used as an anode material for lithium ion batteries.

Electrochemical intercalation of ions into the van der Waals gap of two-dimensional (2D) layered materials is a promising low-temperature synthesis strategy to tune their physical and chemical properties. It is widely believed that ions prefer intercalation into the van der Waals gap through the edges of the 2D flake, which generally causes wrinkling and distortion. Here we demonstrate that the ions can also intercalate through the top surface of few-layer MoS2 and this type of intercalation is more reversible and stable compared to the intercalation through the edges. Density functional theory calculations show that this intercalation is enabled by the existence of natural defects in exfoliated MoS2 flakes. Furthermore, we reveal that sealed-edge MoS2 allows intercalation of small alkali metal ions (e.g., Li+ and Na+) and rejects large ions (e.g., K+). These findings imply potential applications in developing functional 2D-material-based devices with high tunability and ion selectivity.

Nitrogen-doped microporous carbon spheres (NPCSs) with a high surface area (1958 m2 g−1), large micropore volume and a high nitrogen content were synthesized by a simple one-step polymerization and subsequent ZnCl2 activation. The NPCSs can host a large number of small sulfur molecules, and restrict the reaction between the carbonate-based electrolytes and polysulfides. As a result, the NPCSs-sulfur (NPCSS) cathode exhibits excellent cyclic stability (initial capacity of 1382 mAh g−1 and 1002 mAh g−1 after 200 cycles at 0.3 C) and high rate performance (645 mAh g−1 at 3 C) even using the conventional carbonate-based electrolytes, demonstrating its potential use in long-life, safe lithium-sulfur batteries.

In lithium-sulfur (Li-S) chemistry, the electrically/ionically insulating nature of sulfur and Li2S leads to sluggish electron/ion transfer kinetics for sulfur species conversion. Sulfur and Li2S are recognized as solid at room temperature, and solid-liquid phase transitions are the limiting steps in Li-S batteries. Here, we visualize the distinct sulfur growth behaviors on Al, carbon, Ni current collectors and demonstrate that (i) liquid sulfur generated on Ni provides higher reversible capacity, faster kinetics, and better cycling life compared to solid sulfur; and (ii) Ni facilitates the phase transition (e.g., Li2S decomposition). Accordingly, light-weight, 3D Ni-based current collector is designed to control the deposition and catalytic conversion of sulfur species toward high-performance Li-S batteries. This work provides insights on the critical role of the current collector in determining the physical state of sulfur and elucidates the correlation between sulfur state and battery performance, which will advance electrode designs in high-energy Li-S batteries.

One of the most attractive research areas in lithium-ion batteries (LIBs) is to design elaborate nanostructure of the electrode, which has been considered as keys to solve the problems such as the low energy density, slow lithium ion and electron transport, and the large volume change of electrode materials during cycling processes. Here, mesoporous Co3O4 with controllable structures was directly grown on a graphene membrane by hydrothermal reaction followed by annealing treatment, and used as an integrated anode in LIBs without using metallic current collector, binder and conductive additive. The light graphene membrane as current collector with high electrical conductivity and stability contributes to the high energy density of LIBs. A mesoporous structure with enough space is beneficial to lithium ion diffusion and strain buffer of Co3O4 during discharge/charge processes, rendering the electrodes high performance. The integrated electrode shows good rate capability and impressive cycling stability without capacity loss over 500 cycles under a high current density of 500 mA g−1.