Yuan Yang

We report the synthesis of a graphene-sulfur composite material by wrapping polyethyleneglycol (PEG) coated submicron sulfur particles with mildly oxidized graphene oxide sheets decorated by carbon black nanoparticles. The PEG and graphene coating layers are important to accommodating volume expansion of the coated sulfur particles during discharge, trapping soluble polysulfide intermediates and rendering the sulfur particles electrically conducting. The resulting graphene-sulfur composite showed high and stable specific capacities up to ~600mAh/g over more than 100 cycles, representing a promising cathode material for rechargeable lithium batteries with high energy density.

Sulphur is an attractive cathode material with a high specific capacity of 1,673 mAh g−1, but its rapid capacity decay owing to polysulphide dissolution presents a significant technical challenge. Despite much efforts in encapsulating sulphur particles with conducting materials to limit polysulphide dissolution, relatively little emphasis has been placed on dealing with the volumetric expansion of sulphur during lithiation, which will lead to cracking and fracture of the protective shell. Here, we demonstrate the design of a sulphur–TiO2 yolk–shell nanoarchitecture with internal void space to accommodate the volume expansion of sulphur, resulting in an intact TiO2 shell to minimize polysulphide dissolution. An initial specific capacity of 1,030 mAh g−1 at 0.5 C and Coulombic efficiency of 98.4% over 1,000 cycles are achieved. Most importantly, the capacity decay after 1,000 cycles is as small as 0.033% per cycle, which represents the best performance for long-cycle lithium–sulphur batteries so far. The practical performance of lithium–sulphur batteries is lower than expected because of polysulphide dissolution into the electrolyte over time. Sehet al. show that a yolk–shell nanoarchitecture is able to encapsulate sulphur cathode materials efficiently and thus allows over 1,000 charge/discharge cycles.

We developed two-step solution-phase reactions to form hybrid materials of Mn(3)O(4) nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Selective growth of Mn(3)O(4) nanoparticles on RGO sheets, in contrast to free particle growth in solution, allowed for the electrically insulating Mn(3)O(4) nanoparticles to be wired up to a current collector through the underlying conducting graphene network. The Mn(3)O(4) nanoparticles formed on RGO show a high specific capacity up to ∼900 mAh/g, near their theoretical capacity, with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn(3)O(4) nanoparticles grown atop. The Mn(3)O(4)/RGO hybrid could be a promising candidate material for a high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for the design and synthesis of battery electrodes based on highly insulating materials.

Rechargeable Li/S batteries have attracted significant attention lately due to their high specific energy and low cost. They are promising candidates for applications, including portable electronics, electric vehicles and grid-level energy storage. However, poor cycle life and low power capability are major technical obstacles. Various nanostructured sulfur cathodes have been developed to address these issues, as they provide greater resistance to pulverization, faster reaction kinetics and better trapping of soluble polysulfides. In this review, recent developments on nanostructured sulfur cathodes and mechanisms behind their operation are presented and discussed. Moreover, progress on novel characterization of sulfur cathodes is also summarized, as it has deepened the understanding of sulfur cathodes and will guide further rational design of sulfur electrodes.

Sulfur has a high specific capacity of 1673 mAh/g as lithium battery cathodes, but its rapid capacity fading due to polysulfides dissolution presents a significant challenge for practical applications. Here we report a hollow carbon nanofiber-encapsulated sulfur cathode for effective trapping of polysulfides and demonstrate experimentally high specific capacity and excellent electrochemical cycling of the cells. The hollow carbon nanofiber arrays were fabricated using anodic aluminum oxide (AAO) templates, through thermal carbonization of polystyrene. The AAO template also facilitates sulfur infusion into the hollow fibers and prevents sulfur from coating onto the exterior carbon wall. The high aspect ratio of the carbon nanofibers provides an ideal structure for trapping polysulfides, and the thin carbon wall allows rapid transport of lithium ions. The small dimension of these nanofibers provides a large surface area per unit mass for Li(2)S deposition during cycling and reduces pulverization of electrode materials due to volumetric expansion. A high specific capacity of about 730 mAh/g was observed at C/5 rate after 150 cycles of charge/discharge. The introduction of LiNO(3) additive to the electrolyte was shown to improve the Coulombic efficiency to over 99% at C/5. The results show that the hollow carbon nanofiber-encapsulated sulfur structure could be a promising cathode design for rechargeable Li/S batteries with high specific energy.

Passive daytime radiative cooling (PDRC) involves spontaneously cooling a surface by reflecting sunlight and radiating heat to the cold outer space. Current PDRC designs are promising alternatives to electrical cooling but are either inefficient or have limited applicability. We present a simple, inexpensive, and scalable phase inversion-based method for fabricating hierarchically porous poly(vinylidene fluoride-co-hexafluoropropene) [P(VdF-HFP)HP] coatings with excellent PDRC capability. High, substrate-independent hemispherical solar reflectances (0.96 ± 0.03) and long-wave infrared emittances (0.97 ± 0.02) allow for subambient temperature drops of ~6°C and cooling powers of ~96 watts per square meter (W m-2) under solar intensities of 890 and 750 W m-2, respectively. The performance equals or surpasses those of state-of-the-art PDRC designs, and the technique offers a paint-like simplicity.

Paper, invented more than 2,000 years ago and widely used today in our everyday lives, is explored in this study as a platform for energy-storage devices by integration with 1D nanomaterials. Here, we show that commercially available paper can be made highly conductive with a sheet resistance as low as 1 ohm per square (Omega/sq) by using simple solution processes to achieve conformal coating of single-walled carbon nanotube (CNT) and silver nanowire films. Compared with plastics, paper substrates can dramatically improve film adhesion, greatly simplify the coating process, and significantly lower the cost. Supercapacitors based on CNT-conductive paper show excellent performance. When only CNT mass is considered, a specific capacitance of 200 F/g, a specific energy of 30-47 Watt-hour/kilogram (Wh/kg), a specific power of 200,000 W/kg, and a stable cycling life over 40,000 cycles are achieved. These values are much better than those of devices on other flat substrates, such as plastics. Even in a case in which the weight of all of the dead components is considered, a specific energy of 7.5 Wh/kg is achieved. In addition, this conductive paper can be used as an excellent lightweight current collector in lithium-ion batteries to replace the existing metallic counterparts. This work suggests that our conductive paper can be a highly scalable and low-cost solution for high-performance energy storage devices.

MnO2 is considered one of the most promising pseudocapactive materials for high-performance supercapacitors given its high theoretical specific capacitance, low-cost, environmental benignity, and natural abundance. However, MnO2 electrodes often suffer from poor electronic and ionic conductivities, resulting in their limited performance in power density and cycling. Here we developed a "conductive wrapping" method to greatly improve the supercapacitor performance of graphene/MnO2-based nanostructured electrodes. By three-dimensional (3D) conductive wrapping of graphene/MnO2 nanostructures with carbon nanotubes or conducting polymer, specific capacitance of the electrodes (considering total mass of active materials) has substantially increased by ∼20% and ∼45%, respectively, with values as high as ∼380 F/g achieved. Moreover, these ternary composite electrodes have also exhibited excellent cycling performance with >95% capacitance retention over 3000 cycles. This 3D conductive wrapping approach represents an exciting direction for enhancing the device performance of metal oxide-based electrochemical supercapacitors and can be generalized for designing next-generation high-performance energy storage devices.

We introduce a novel design of carbon−silicon core−shell nanowires for high power and long life lithium battery electrodes. Amorphous silicon was coated onto carbon nanofibers to form a core−shell structure and the resulted core−shell nanowires showed great performance as anode material. Since carbon has a much smaller capacity compared to silicon, the carbon core experiences less structural stress or damage during lithium cycling and can function as a mechanical support and an efficient electron conducting pathway. These nanowires have a high charge storage capacity of ∼2000 mAh/g and good cycling life. They also have a high Coulmbic efficiency of 90% for the first cycle and 98−99.6% for the following cycles. A full cell composed of LiCoO2 cathode and carbon−silicon core−shell nanowire anode is also demonstrated. Significantly, using these core−shell nanowires we have obtained high mass loading and an area capacity of ∼4 mAh/cm2, which is comparable to commercial battery values.

Rechargeable lithium–sulfur (Li–S) batteries hold great potential for next-generation high-performance energy storage systems because of their high theoretical specific energy, low materials cost, and environmental safety. One of the major obstacles for its commercialization is the rapid capacity fading due to polysulfide dissolution and uncontrolled redeposition. Various porous carbon structures have been used to improve the performance of Li–S batteries, as polysulfides could be trapped inside the carbon matrix. However, polysulfides still diffuse out for a prolonged time if there is no effective capping layer surrounding the carbon/sulfur particles. Here we explore the application of conducting polymer to minimize the diffusion of polysulfides out of the mesoporous carbon matrix by coating poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) onto mesoporous carbon/sulfur particles. After surface coating, coulomb efficiency of the sulfur electrode was improved from 93% to 97%, and capacity decay was reduced from 40%/100 cycles to 15%/100 cycles. Moreover, the discharge capacity with the polymer coating was ∼10% higher than the bare counterpart, with an initial discharge capacity of 1140 mAh/g and a stable discharge capacity of >600 mAh/g after 150 cycles at C/5 rate. We believe that this conductive polymer coating method represents an exciting direction for enhancing the device performance of Li–S batteries and can be applicable to other electrode materials in lithium ion batteries.

There is a strong interest in thin, flexible energy storage devices to meet modern society needs for applications such as interactive packaging, radio frequency sensing, and consumer products. In this article, we report a new structure of thin, flexible Li-ion batteries using paper as separators and free-standing carbon nanotube thin films as both current collectors. The current collectors and Li-ion battery materials are integrated onto a single sheet of paper through a lamination process. The paper functions as both a mechanical substrate and separator membrane with lower impedance than commercial separators. The CNT film functions as a current collector for both the anode and the cathode with a low sheet resistance (∼5 Ohm/sq), lightweight (∼0.2 mg/cm2), and excellent flexibility. After packaging, the rechargeable Li-ion paper battery, despite being thin (∼300 μm), exhibits robust mechanical flexibility (capable of bending down to <6 mm) and a high energy density (108 mWh/g).

Silicon is a promising high-capacity anode material for lithium-ion batteries yet attaining long cycle life remains a significant challenge due to pulverization of the silicon and unstable solid-electrolyte interphase (SEI) formation during the electrochemical cycles. Despite significant advances in nanostructured Si electrodes, challenges including short cycle life and scalability hinder its widespread implementation. To address these challenges, we engineered an empty space between Si nanoparticles by encapsulating them in hollow carbon tubes. The synthesis process used low-cost Si nanoparticles and electrospinning methods, both of which can be easily scaled. The empty space around the Si nanoparticles allowed the electrode to successfully overcome these problems Our anode demonstrated a high gravimetric capacity (∼1000 mAh/g based on the total mass) and long cycle life (200 cycles with 90% capacity retention).

Tremendous effort has been put into developing viable lithium sulfur batteries, due to their high specific energy and relatively low cost. Despite recent progress in addressing the various problems of sulfur cathodes, lithium sulfur batteries still exhibit significant capacity decay over cycling. Herein, we identify a new capacity fading mechanism of the sulfur cathodes, relating to Li(x)S detachment from the carbon surface during the discharge process. This observation is confirmed by ex-situ transmission electron microscopy study and first-principles calculations. We demonstrate that this capacity fading mechanism can be overcome by introducing amphiphilic polymers to modify the carbon surface, rendering strong interactions between the nonpolar carbon and the polar Li(x)S clusters. The modified sulfur cathode show excellent cycling performance with specific capacity close to 1180 mAh/g at C/5 current rate. Capacity retention of 80% is achieved over 300 cycles at C/2.

Transparent electrodes, indespensible in displays and solar cells, are currently dominated by indium tin oxide (ITO) films although the high price of indium, brittleness of films, and high vacuum deposition are limiting their applications. Recently, solution-processed networks of nanostructures such as carbon nanotubes (CNTs), graphene, and silver nanowires have attracted great attention as replacements. A low junction resistance between nanostructures is important for decreasing the sheet resistance. However, the junction resistances between CNTs and boundry resistances between graphene nanostructures are too high. The aspect ratios of silver nanowires are limited to ∼100, and silver is relatively expensive. Here, we show high-performance transparent electrodes with copper nanofiber networks by a low-cost and scalable electrospinning process. Copper nanofibers have ultrahigh aspect ratios of up to 100000 and fused crossing points with ultralow junction resistances, which result in high transmitance at low sheet resistance, e.g., 90% at 50 Ω/sq. The copper nanofiber networks also show great flexibility and stretchabilty. Organic solar cells using copper nanowire networks as transparent electrodes have a power efficiency of 3.0%, comparable to devices made with ITO electrodes.

Li2S is a high-capacity cathode material for lithium metal-free rechargeable batteries. It has a theoretical capacity of 1166 mAh/g, which is nearly 1 order of magnitude higher than traditional metal oxides/phosphates cathodes. However, Li2S is usually considered to be electrochemically inactive due to its high electronic resistivity and low lithium-ion diffusivity. In this paper, we discover that a large potential barrier (∼1 V) exists at the beginning of charging for Li2S. By applying a higher voltage cutoff, this barrier can be overcome and Li2S becomes active. Moreover, this barrier does not appear again in the following cycling. Subsequent cycling shows that the material behaves similar to common sulfur cathodes with high energy efficiency. The initial discharge capacity is greater than 800 mAh/g for even 10 μm Li2S particles. Moreover, after 10 cycles, the capacity is stabilized around 500–550 mAh/g with a capacity decay rate of only ∼0.25% per cycle. The origin of the initial barrier is found to be the phase nucleation of polysulfides, but the amplitude of barrier is mainly due to two factors: (a) charge transfer directly between Li2S and electrolyte without polysulfide and (b) lithium-ion diffusion in Li2S. These results demonstrate a simple and scalable approach to utilizing Li2S as the cathode material for rechargeable lithium-ion batteries with high specific energy.

Rechargeable lithium ion batteries are important energy storage devices; however, the specific energy of existing lithium ion batteries is still insufficient for many applications due to the limited specific charge capacity of the electrode materials. The recent development of sulfur/mesoporous carbon nanocomposite cathodes represents a particularly exciting advance, but in full battery cells, sulfur-based cathodes have to be paired with metallic lithium anodes as the lithium source, which can result in serious safety issues. Here we report a novel lithium metal-free battery consisting of a Li(2)S/mesoporous carbon composite cathode and a silicon nanowire anode. This new battery yields a theoretical specific energy of 1550 Wh kg(-1), which is four times that of the theoretical specific energy of existing lithium-ion batteries based on LiCoO(2) cathodes and graphite anodes (approximately 410 Wh kg(-1)). The nanostructured design of both electrodes assists in overcoming the issues associated with using sulfur compounds and silicon in lithium-ion batteries, including poor electrical conductivity, significant structural changes, and volume expansion. We have experimentally realized an initial discharge specific energy of 630 Wh kg(-1) based on the mass of the active electrode materials.

Spinel LiMn2O4 is a low-cost, environmentally friendly, and highly abundant material for Li-ion battery cathodes. Here, we report the hydrothermal synthesis of single-crystalline beta-MnO2 nanorods and their chemical conversion into free-standing single-crystalline LiMn2O4 nanorods using a simple solid-state reaction. The LiMn2O4 nanorods have an average diameter of 130 nm and length of 1.2 microm. Galvanostatic battery testing showed that LiMn2O4 nanorods have a high charge storage capacity at high power rates compared with commercially available powders. More than 85% of the initial charge storage capacity was maintained for over 100 cycles. The structural transformation studies showed that the Li ions intercalated into the cubic phase of the LiMn2O4 with a small change of lattice parameter, followed by the coexistence of two nearly identical cubic phases in the potential range of 3.5 to 4.3 V.

While MnO2 is a promising material for pseudocapacitor applications due to its high specific capacity and low cost, MnO2 electrodes suffer from their low electrical and ionic conductivities. In this article, we report a structure where MnO2 nanoflowers were conformally electrodeposited onto carbon nanotube (CNT)-enabled conductive textile fibers. Such nanostructures effectively decrease the ion diffusion and charge transport resistance in the electrode. For a given areal mass loading, the thickness of MnO2 on conductive textile fibers is much smaller than that on a flat metal substrate. Such a porous structure also allows a large mass loading, up to 8.3 mg/cm2, which leads to a high areal capacitance of 2.8 F/cm2 at a scan rate of 0.05 mV/s. Full cells were demonstrated, where the MnO2–CNT–textile was used as a positive electrode, reduced MnO2–CNT–textile as a negative electrode, and 0.5 M Na2SO4 in water as the electrolyte. The resulting pseudocapacitor shows promising results as a low-cost energy storage solution and an attractive wearable power.

Rechargeable lithium-sulfur (Li-S) batteries hold great potential for high-performance energy storage systems because they have a high theoretical specific energy, low cost, and are eco-friendly. However, the structural and morphological changes during electrochemical reactions are still not well understood. In this Article, these changes in Li-S batteries are studied in operando by X-ray diffraction and transmission X-ray microscopy. We show recrystallization of sulfur by the end of the charge cycle is dependent on the preparation technique of the sulfur cathode. On the other hand, it was found that crystalline Li(2)S does not form at the end of discharge for all sulfur cathodes studied. Furthermore, during cycling the bulk of soluble polysulfides remains trapped within the cathode matrix. Our results differ from previous ex situ results. This highlights the importance of in operando studies and suggests possible strategies to improve cycle life.

Replacing flammable organic liquid electrolytes with solid Li-ion conductors is a promising approach to realize safe rechargeable batteries with high energy density. Composite solid electrolytes, which are comprised of a polymer matrix with ceramic Li-ion conductors dispersed inside, are attractive, since they combine the flexibility of polymer electrolytes and high ionic conductivities of ceramic electrolytes. However, the high conductivity of ceramic fillers is largely compromised by the low conductivity of the matrix, especially when nanoparticles (NPs) are used. Therefore, optimizations of the geometry of ceramic fillers are critical to further enhance the conductivity of composite electrolytes. Here we report the vertically aligned and connected Li1+xAlxTi2-x(PO4)3 (LATP) NPs in the poly(ethylene oxide) (PEO) matrix to maximize the ionic conduction, while maintaining the flexibility of the composite. This vertically aligned structure can be fabricated by an ice-templating-based method, and its conductivity reaches 0.52 × 10-4 S/cm, which is 3.6 times that of the composite electrolyte with randomly dispersed LATP NPs. The composite electrolyte also shows enhanced thermal and electrochemical stability compared to the pure PEO electrolyte. This method opens a new approach to optimize ion conduction in composite solid electrolytes for next-generation rechargeable batteries.

Efficient and low-cost thermal energy-harvesting systems are needed to utilize the tremendous low-grade heat sources. Although thermoelectric devices are attractive, its efficiency is limited by the relatively low figure-of-merit and low-temperature differential. An alternative approach is to explore thermodynamic cycles. Thermogalvanic effect, the dependence of electrode potential on temperature, can construct such cycles. In one cycle, an electrochemical cell is charged at a temperature and then discharged at a different temperature with higher cell voltage, thereby converting heat to electricity. Here we report an electrochemical system using a copper hexacyanoferrate cathode and a Cu/Cu(2+) anode to convert heat into electricity. The electrode materials have low polarization, high charge capacity, moderate temperature coefficients and low specific heat. These features lead to a high heat-to-electricity energy conversion efficiency of 5.7% when cycled between 10 and 60 °C, opening a promising way to utilize low-grade heat.

We employ a MnCo2O4–graphene hybrid material as the cathode catalyst for Li–O2 batteries with a non-aqueous electrolyte. The hybrid is synthesized by direct nucleation and growth of MnCo2O4 nanoparticles on reduced graphene oxide, which controls the morphology, size and distribution of the oxide nanoparticles and renders strong covalent coupling between the oxide nanoparticles and the electrically conducting graphene substrate. The inherited excellent catalytic activity of the hybrid leads to lower overpotentials and longer cycle lives of Li–O2 cells than other catalysts including noble metals such as platinum. We also study the relationships between the charging–discharging performance of Li–O2 cells and the oxygen reduction and oxygen evolution activity of catalysts in both aqueous and non-aqueous solutions.

Sulfur is an exciting cathode material with high specific capacity of 1,673 mAh/g, more than five times the theoretical limits of its transition metal oxides counterpart. However, successful applications of sulfur cathode have been impeded by rapid capacity fading caused by multiple mechanisms, including large volume expansion during lithiation, dissolution of intermediate polysulfides, and low ionic/electronic conductivity. Tackling the sulfur cathode problems requires a multifaceted approach, which can simultaneously address the challenges mentioned above. Herein, we present a scalable, room temperature, one-step, bottom-up approach to fabricate monodisperse polymer (polyvinylpyrrolidone)-encapsulated hollow sulfur nanospheres for sulfur cathode, allowing unprecedented control over electrode design from nanoscale to macroscale. We demonstrate high specific discharge capacities at different current rates (1,179, 1,018, and 990 mAh/g at C/10, C/5, and C/2, respectively) and excellent capacity retention of 77.6% (at C/5) and 73.4% (at C/2) after 300 and 500 cycles, respectively. Over a long-term cycling of 1,000 cycles at C/2, a capacity decay as low as 0.046% per cycle and an average coulombic efficiency of 98.5% was achieved. In addition, a simple modification on the sulfur nanosphere surface with a layer of conducting polymer, poly(3,4-ethylenedioxythiophene), allows the sulfur cathode to achieve excellent high-rate capability, showing a high reversible capacity of 849 and 610 mAh/g at 2C and 4C, respectively.

Large-scale energy storage represents a key challenge for renewable energy and new systems with low cost, high energy density and long cycle life are desired. In this article, we develop a new lithium/polysulfide (Li/PS) semi-liquid battery for large-scale energy storage, with lithium polysulfide (Li2S8) in ether solvent as a catholyte and metallic lithium as an anode. Unlike previous work on Li/S batteries with discharge products such as solid state Li2S2 and Li2S, the catholyte is designed to cycle only in the range between sulfur and Li2S4. Consequently all detrimental effects due to the formation and volume expansion of solid Li2S2/Li2S are avoided. This novel strategy results in excellent cycle life and compatibility with flow battery design. The proof-of-concept Li/PS battery could reach a high energy density of 170 W h kg−1 and 190 W h L−1 for large scale storage at the solubility limit, while keeping the advantages of hybrid flow batteries. We demonstrated that, with a 5 M Li2S8 catholyte, energy densities of 97 W h kg−1 and 108 W h L−1 can be achieved. As the lithium surface is well passivated by LiNO3 additive in ether solvent, internal shuttle effect is largely eliminated and thus excellent performance over 2000 cycles is achieved with a constant capacity of 200 mA h g−1. This new system can operate without the expensive ion-selective membrane, and it is attractive for large-scale energy storage.

Jyotirmoy Mandal completed his PhD in Applied Physics at Columbia University in the City of New York and is currently a Schmidt Science Fellow and a postdoctoral researcher at University of California, Los Angeles. His research interests include low-cost optical designs for radiative cooling and solar heating, with a focus on applications in developing countries.Yuan Yang is an associate professor in the Department of Applied Physics and Applied Mathematics at Columbia University in the City of New York. His research interests include electrochemical energy storage and thermal energy management. Dr. Yang has published over 70 peer-reviewed journal articles, including in leading journals such as Science, Proceedings of the National Academy of Sciences, Advanced Materials, and Joule.Nanfang Yu is an associate professor in the Department of Applied Physics and Applied Mathematics at Columbia University in the City of New York. His research interests include mid-infrared and far-infrared optics, metamaterials, biophotonics, and biologically inspired flat optics. Dr. Yu’s research has been published in leading journals like Science, Nature Materials, Nature Nanotechnology, and Joule.Aaswath P. Raman is an assistant professor of Materials Science and Engineering at the University of California, Los Angeles (UCLA). He is also co-founder and chief scientific officer of SkyCool Systems, a startup commercializing radiative cooling technologies. Dr. Raman’s research interests include nanophotonics, metamaterials, radiative heat transfer, and energy applications, including radiative cooling. His works have been published in leading journals such as Nature, Nature Energy, Physical Review Letters, and Joule. Jyotirmoy Mandal completed his PhD in Applied Physics at Columbia University in the City of New York and is currently a Schmidt Science Fellow and a postdoctoral researcher at University of California, Los Angeles. His research interests include low-cost optical designs for radiative cooling and solar heating, with a focus on applications in developing countries. Yuan Yang is an associate professor in the Department of Applied Physics and Applied Mathematics at Columbia University in the City of New York. His research interests include electrochemical energy storage and thermal energy management. Dr. Yang has published over 70 peer-reviewed journal articles, including in leading journals such as Science, Proceedings of the National Academy of Sciences, Advanced Materials, and Joule. Nanfang Yu is an associate professor in the Department of Applied Physics and Applied Mathematics at Columbia University in the City of New York. His research interests include mid-infrared and far-infrared optics, metamaterials, biophotonics, and biologically inspired flat optics. Dr. Yu’s research has been published in leading journals like Science, Nature Materials, Nature Nanotechnology, and Joule. Aaswath P. Raman is an assistant professor of Materials Science and Engineering at the University of California, Los Angeles (UCLA). He is also co-founder and chief scientific officer of SkyCool Systems, a startup commercializing radiative cooling technologies. Dr. Raman’s research interests include nanophotonics, metamaterials, radiative heat transfer, and energy applications, including radiative cooling. His works have been published in leading journals such as Nature, Nature Energy, Physical Review Letters, and Joule.

A two-step solution-phase synthesis led to LiMn0.75Fe0.25PO4 nanorods grown on graphene with superior electrical conductivity (see picture; rmGO=reduced mildly oxidized graphene oxide). The nanorod morphology is ideal for fast Li+ diffusion, with the diffusion path along the short radial direction (20–30 nm) of the nanorods. An ultrafast discharge performance for this hybrid cathode material is thus achieved. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by 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 sulfide (Li2S) is a promising cathode material for Li–S batteries with high capacity (theoretically 1166 mAh g–1) and can be paired with nonlithium–metal anodes to avoid potential safety issues. However, the cycle life of coarse Li2S particles suffers from poor electronic conductivity and polysulfide shuttling. Here, we develop a flexible slurryless nano-Li2S/reduced graphene oxide cathode paper (nano-Li2S/rGO paper) by simple drop-coating. The Li2S/rGO paper can be directly used as a free-standing and binder-free cathode without metal substrate, which leads to significant weight savings. It shows excellent rate capability (up to 7 C) and cycle life in coin cell tests due to the high electron conductivity, flexibility, and strong solvent absorbency of rGO paper. The Li2S particles that precipitate out of the solvent on rGO have diameters 25–50 nm, which is in contrast to the 3–5 μm coarse Li2S particles without rGO.

Transparent devices have recently attracted substantial attention. Various applications have been demonstrated, including displays, touch screens, and solar cells; however, transparent batteries, a key component in fully integrated transparent devices, have not yet been reported. As battery electrode materials are not transparent and have to be thick enough to store energy, the traditional approach of using thin films for transparent devices is not suitable. Here we demonstrate a grid-structured electrode to solve this dilemma, which is fabricated by a microfluidics-assisted method. The feature dimension in the electrode is below the resolution limit of human eyes, and, thus, the electrode appears transparent. Moreover, by aligning multiple electrodes together, the amount of energy stored increases readily without sacrificing the transparency. This results in a battery with energy density of 10 Wh/L at a transparency of 60%. The device is also flexible, further broadening their potential applications. The transparent device configuration also allows in situ Raman study of fundamental electrochemical reactions in batteries.

Solid-state Li-metal batteries are promising to improve both safety and energy density compared to conventional Li-ion batteries. However, various high-performance and low-cost solid electrolytes are incompatible with Li, which is indispensable for enhancing energy density. Here, we utilize a chemically inert and mechanically robust boron nitride (BN) film as the interfacial protection to preclude the reduction of Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte by Li, which is validated by in situ transmission electron microscopy. When combined with ∼1–2 μm PEO polymer electrolyte at the Li/BN interface, Li/Li symmetric cells show a cycle life of over 500 h at 0.3 mA·cm−2. In contrast, the same configuration with bare LATP dies after 81 h. The LiFePO4/LATP/BN/PEO/Li solid-state batteries show high capacity retention of 96.6% after 500 cycles. This study offers a general strategy to protect solid electrolytes that are unstable against Li and opens possibilities for adopting them in solid-state Li-metal batteries.

Solid electrolytes are crucial for the development of solid state batteries. Among different types of solid electrolytes, poly(ethylene oxide) (PEO)-based polymer electrolytes have attracted extensive attention owing to their excellent flexibility and easiness for processing. However, their relatively low ionic conductivities and electrochemical instability above 4 V limit their applications in batteries with high energy density. Herein, we prepared poly(vinylidene fluoride) (PVDF) polymer electrolytes with an organic plasticizer, which possesses compatibility with 4 V cathode and high ionic conductivity (1.2 × 10–4 S/cm) at room temperature. We also revealed the importance of plasticizer content to the ionic conductivity. To address weak mechanical strength of the PVDF electrolyte with plasticizer, we introduced palygorskite ((Mg,Al)2Si4O10(OH)) nanowires as a new ceramic filler to form composite solid electrolytes (CPE), which greatly enhances both stiffness and toughness of PVDF-based polymer electrolyte. With 5 wt % of palygorskite nanowires, not only does the elastic modulus of PVDF CPE increase from 9.0 to 96 MPa but also its yield stress is enhanced by 200%. Moreover, numerical modeling uncovers that the strong nanowire–polymer interaction and cross-linking network of nanowires are responsible for such significant enhancement in mechanically robustness. The addition of 5% palygorskite nanowires also enhances transference number of Li+ from 0.21 to 0.54 due to interaction between palygorskite and ClO4– ions. We further demonstrate full cells based on Li(Ni1/3Mn1/3Co1/3)O2 (NMC111) cathode, PVDF/palygorskite CPE, and lithium anode, which can be cycled over 200 times at 0.3 C, with 97% capacity retention. Moreover, the PVDF matrix is much less flammable than PEO electrolytes. Our work illustrates that the PVDF/palygorskite CPE is a promising electrolyte for solid state batteries.

Efficient and low-cost systems are needed to harvest the tremendous amount of energy stored in low-grade heat sources (<100 °C). Thermally regenerative electrochemical cycle (TREC) is an attractive approach which uses the temperature dependence of electrochemical cell voltage to construct a thermodynamic cycle for direct heat-to-electricity conversion. By varying temperature, an electrochemical cell is charged at a lower voltage than discharge, converting thermal energy to electricity. Most TREC systems still require external electricity for charging, which complicates system designs and limits their applications. Here, we demonstrate a charging-free TREC consisting of an inexpensive soluble Fe(CN)6(3-/4-) redox pair and solid Prussian blue particles as active materials for the two electrodes. In this system, the spontaneous directions of the full-cell reaction are opposite at low and high temperatures. Therefore, the two electrochemical processes at both low and high temperatures in a cycle are discharge. Heat-to-electricity conversion efficiency of 2.0% can be reached for the TREC operating between 20 and 60 °C. This charging-free TREC system may have potential application for harvesting low-grade heat from the environment, especially in remote areas.

Solar reflective and thermally emissive surfaces offer a sustainable way to cool objects under sunlight. However, white or silvery reflectance of these surfaces does not satisfy the need for color. Here, we present a paintable bilayer coating that simultaneously achieves color and radiative cooling. The bilayer comprises a thin, visible-absorptive layer atop a nonabsorptive, solar-scattering underlayer. The top layer absorbs appropriate visible wavelengths to show specific colors, while the underlayer maximizes the reflection of near-to-short wavelength infrared (NSWIR) light to reduce solar heating. Consequently, the bilayer attains higher NSWIR reflectance (by 0.1 to 0.51) compared with commercial paint monolayers of the same color and stays cooler by as much as 3.0° to 15.6°C under strong sunlight. High NSWIR reflectance of 0.89 is realized in the blue bilayer. The performances show that the bilayer paint design can achieve both color and efficient radiative cooling in a simple, inexpensive, and scalable manner.

Adaptive control of broadband light is essential for diverse applications including building energy management and light modulation. Here, we present porous polymer coatings (PPCs), whose optical transmittance changes upon reversible wetting with common liquids, as a platform for optical management from solar to thermal wavelengths. In the solar wavelengths, reduction in optical scattering upon wetting changes PPCs from reflective to transparent. For poly(vinylidene fluoride-co-hexafluoropropene) PPCs, this corresponds to solar and visible transmittance changes of up to 0.74 and 0.80, respectively. For infrared (IR) transparent polyethylene PPCs, wetting causes an “icehouse-to-greenhouse” transition where solar transparency rises but thermal IR transparency falls. These performances are either unprecedented or rival or surpass those of notable optical switching (e.g., electrochromic and thermochromic) paradigms, making PPCs promising for large-scale optical and thermal management. Specifically, switchable sub-ambient radiative cooling (by 3.2°C) and above-ambient solar heating (by 21.4°C), color-neutral daylighting, and thermal camouflage are demonstrated.

Flexible lithium-ion batteries (LIBs) can be seamlessly integrated into flexible devices, such as flexible displays, wearable devices, and smart cards, to provide power for steady operation under mechanical deformation. An ideal flexible battery should have high flexibility, high energy density, and high power density simultaneously, which are often in conflict with each other. In this Perspective, we analyze the flexible batteries based on structural designs from both the component level and device level. Recent progress in flexible LIBs, including advances in porous structures for battery components, superslim designs, topological architectures, and battery structures with decoupling concepts, is reviewed. In the end, perspectives on the future of flexible batteries are presented and discussed.

Visualization of ion transport in electrolytes provides fundamental understandings of electrolyte dynamics and electrolyte-electrode interactions. However, this is challenging because existing techniques are hard to capture low ionic concentrations and fast electrolyte dynamics. Here we show that stimulated Raman scattering microscopy offers required resolutions to address a long-lasting question: how does the lithium-ion concentration correlate to uneven lithium deposition? In this study, anions are used to represent lithium ions since their concentrations should not deviate for more than 0.1 mM, even near nanoelectrodes. A three-stage lithium deposition process is uncovered, corresponding to no depletion, partial depletion, and full depletion of lithium ions. Further analysis reveals a feedback mechanism between the lithium dendrite growth and heterogeneity of local ionic concentration, which can be suppressed by artificial solid electrolyte interphase. This study shows that stimulated Raman scattering microscopy is a powerful tool for the materials and energy field.

Interfacial issues commonly exist in solid-state batteries, and the microstructural complexity combines with the chemical heterogeneity to govern the local interfacial chemistry. The conventional wisdom suggests that "point-to-point" ion diffusion at the interface determines the ion transport kinetics. Here, we show that solid-solid ion transport kinetics are not only impacted by the physical interfacial contact but are also closely associated with the interior local environments within polycrystalline particles. In spite of the initial discrete interfacial contact, solid-state batteries may still display homogeneous lithium-ion transportation owing to the chemical potential force to achieve an ionic-electronic equilibrium. Nevertheless, once the interior local environment within secondary particle is disrupted upon cycling, it triggers charge distribution from homogeneity to heterogeneity and leads to fast capacity fading. Our work highlights the importance of interior local environment within polycrystalline particles for electrochemical reactions in solid-state batteries and provides crucial insights into underlying mechanism in interfacial transport.

Broadband electrochromism from visible to infrared wavelengths is attractive for applications like smart windows, thermal-camouflage, and temperature control. In this work, the broadband electrochromic properties of Li4Ti5O12 (LTO) and its suitability for infrared-camouflage and thermoregulation are investigated. Upon Li+ intercalation, LTO changes from a wide band-gap semiconductor to a metal, causing LTO nanoparticles on metal to transition from a super-broadband optical reflector to a solar absorber and thermal emitter. Large tunabilities of 0.74, 0.68 and 0.30 are observed for the solar reflectance, mid-wave infrared (MWIR) emittance and long-wave infrared (LWIR) emittance respectively. The values exceed, or are comparable to notable performances in the literature. A promising cycling stability is also observed. MWIR and LWIR thermography reveal that the emittance of LTO-based electrodes can be electrochemically tuned to conceal them amidst their environment. Moreover, under different sky conditions, LTO shows promising solar heating and sub-ambient radiative cooling capabilities depending on the degree of lithiation and device design. The demonstrated capabilities of LTO make LTO-based electrochromic devices highly promising for infrared-camouflage applications in the defense sector, and for thermoregulation in space and terrestrial environments.

Lithium–sulfur batteries with high energy capacity are promising candidates for advanced energy storage. However, their applications are impeded by shuttling of soluble polysulfides and sluggish conversion kinetics with inferior rate performance and short cycling life. Here, single-atom materials are designed to accelerate polysulfide conversion for Li–S batteries. Nitrogen sites in the structure not only anchor polysulfides to alleviate the shuttle effect but also enable high loading of single-atom irons. Density functional theory calculations indicate that single-atom sites reduce the energy barrier of electrochemical reactions and thus improve the rate and cycling performances of batteries. The coin battery shows impressive energy storage properties, including a high reversible capacity of 1379 mAh g–1 at 0.1 C and a high rate capacity of 704 mAh g–1 at 5 C. The ratio of electrolyte dosage/energy density is as low as 5.5 g Ah1–. It exhibits excellent cycling performance with a capacity retention of 90% even after 200 cycles at 0.2 C.

Abstract Solid‐state lithium‐metal batteries with solid electrolytes are promising for next‐generation energy‐storage devices. However, it remains challenging to develop solid electrolytes that are both mechanically robust and strong against external mechanical load, due to the brittleness of ceramic electrolytes and the softness of polymer electrolytes. Herein, a nacre‐inspired design of ceramic/polymer solid composite electrolytes with a “brick‐and‐mortar” microstructure is proposed. The nacre‐like ceramic/polymer electrolyte (NCPE) simultaneously possesses a much higher fracture strain (1.1%) than pure ceramic electrolytes (0.13%) and a much larger ultimate flexural modulus (7.8 GPa) than pure polymer electrolytes (20 MPa). The electrochemical performance of NCPE is also much better than pure ceramic or polymer electrolytes, especially under mechanical load. A 5 × 5 cm 2 pouch cell with LAGP/poly(ether‐acrylate) NCPE exhibits stable cycling with a capacity retention of 95.6% over 100 cycles at room temperature, even undergoes a large point load of 10 N. In contrast, cells based on pure ceramic and pure polymer electrolyte show poor cycle life. The NCPE provides a new design for solid composite electrolyte and opens up new possibilities for future solid‐state lithium‐metal batteries and structural energy storage.

Passive daytime radiative cooling (PDRC) has drawn significant attention recently for electricity-free cooling. Porous polymers are attractive for PDRC since they have excellent performance and scalability. A fundamental question remaining is how PDRC performance depends on pore properties (e.g., radius, porosity), which is critical to guiding future structure designs. In this work, optical simulations are carried out to answer this question, and effects of pore size, porosity, and thickness are studied. We find that mixed nanopores (e.g., radii of 100 and 200 nm) have a much higher solar reflectance R̅solar (0.951) than the single-sized pores (0.811) at a thickness of 300 μm. With an Al substrate underneath, R̅solar, thermal emittance ε̅LWIR, and net cooling power Pcool reach 0.980, 0.984, and 72 W/m2, respectively, under a semihumid atmospheric condition. These simulation results provide a guide for designing high-performance porous coating for PDRC applications.

Abstract Passive daytime radiative cooling (PDRC) can realize electricity‐free cooling by reflecting sunlight and emitting heat to the cold space. Current PDRC designs often involve costly vacuum processing or a large quantity of harmful organic solvents. Aqueous and paint‐like processing is cost‐effective and environmentally benign, thereby highly attractive for green manufacturing of PDRC coatings. However, common polymers explored in PDRC are difficult to disperse in water, let alone forming porous structures for efficient cooling. Here, a simple “bottom‐up” ball milling approach to create uniform microassembly of poly(vinylidene fluoride‐ co ‐hexafluoropropene) nanoparticles is reported. The micro‐ and nanopores among secondary particles and primary particles substantially enhance light scattering and results in excellent PDRC performance. A high solar reflectance of 0.94 and high emittance of 0.97 are achieved, making the coating 3.3 and 1.7 °C cooler than commercial white paints and the ambient temperature, under a high solar flux of ≈1100 W m −2 . More importantly, the volatile organic compound content in the aqueous paint is only 71 g L −1 . This satisfies the general regulatory requirements, which are critical to sustainability and practical applications.

The development of light-weight batteries has a great potential value for mobile applications, including electric vehicles and electric aircraft. Along with increasing energy density, another strategy for reducing battery weight is to endow energy storage devices with multifunctionality – e.g., creating an energy storage device that is able to bear structural loads and act as a replacement for structural components such that the weight of the overall system is reduced. This type of batteries is commonly referred to as “structural batteries”. Two general methods have been explored to develop structural batteries: (1) integrating batteries with light and strong external reinforcements, and (2) introducing multifunctional materials as battery components to make energy storage devices themselves structurally robust. In this review, we discuss the fundamental rules of design and basic requirements of structural batteries, summarize the progress made to date in this field, examine potential avenues and sources of inspiration for future research, and touch upon challenges remaining in this field such as safety, costs, and performance stability. Though more fundamental and technical research is needed to promote wide practical application, structural batteries show the potential to significantly improve the performance of electric vehicles and devices.

Copper nanofiber networks, which possess the advantages of low cost, moderate flexibility, small sheet resistance, and high transmittance, are one of the most promising candidates to replace indium tin oxide films as the premier transparent electrode. However, the chemical activity of copper nanofibers causes a substantial increase in the sheet resistance after thermal oxidation or chemical corrosion of the nanofibers. In this work, we utilize atomic layer deposition to coat a passivation layer of aluminum-doped zinc oxide (AZO) and aluminum oxide onto electrospun copper nanofibers and remarkably enhance their durability. Our AZO–copper nanofibers show resistance increase of remarkably only 10% after thermal oxidation at 160 °C in dry air and 80 °C in humid air with 80% relative humidity, whereas bare copper nanofibers quickly become insulating. In addition, the coating and baking of the acidic PEDOT:PSS layer on our fibers increases the sheet resistance of bare copper nanofibers by 6 orders of magnitude, while the AZO–Cu nanofibers show an 18% increase.

Efficient and low-cost systems are desired to harvest the tremendous amount of energy stored in low-grade heat sources (< 100 °C).An attractive approach is the thermally regenerative electrochemical cycle (TREC), which uses the dependence of electrode potential on temperature to construct a thermodynamic cycle for direct heat-toelectricity conversion.By varying the temperature, an electrochemical cell is charged at a lower voltage than discharged; thus, thermal energy is converted to electricity.Recently a Prussian blue-based system with high efficiency has been demonstrated.However, the use of an ion-selective membrane in this system raises concerns about the overall cost,

The rational construction of battery electrode architecture that offers both high energy and power densities on a gravimetric and volumetric basis is a critical concern but achieving this aim is beset by many fundamental and practical challenges. Here we report a new sea urchin-like NiCoO2@C composite electrode architecture composed of NiCoO2 nanosheets grown on hollow concave carbon disks. Such a unique structural design not only preserves all the advantages of hollow structures but also increases the packing density of the active materials. NiCoO2 nanosheets grown on carbon disks promote a high utilization of active materials in redox reactions by reducing the path length for Li+ ions and for electron transfer. Meanwhile, the hollow concave carbon not only reduces the volume change, but also improves the volumetric energy density of the entire composite electrode. As a result, the nanocomposites exhibit superior electrochemical performance measured in terms of high capacity/capacitance, stable cycling performance and good rate capability in both Li-ion battery and supercapacitor applications. Such nanostructured composite electrode may also have great potential for application in other electrochemical devices.

A galvanic displacement reaction-based, room-temperature "dip-and-dry" technique is demonstrated for fabricating selectively solar-absorbing plasmonic nanostructure-coated foils (PNFs). The technique, which allows for facile tuning of the PNFs' spectral reflectance to suit different radiative and thermal environments, yields PNFs which exhibit excellent, wide-angle solar absorptance (0.96 at 15{\deg}, to 0.97 at 35{\deg}, to 0.79 at 80{\deg}) and low hemispherical thermal emittance (0.10) without the aid of antireflection coatings. The thermal emittance is on par with those of notable selective solar absorbers (SSAs) in the literature, while the wide-angle solar absorptance surpasses those of previously reported SSAs with comparable optical selectivities. In addition, the PNFs show promising mechanical and thermal stabilities at temperatures of up to 200{\deg}C. Along with the performance of the PNFs, the simplicity, inexpensiveness and environment-friendliness of the "dip-and-dry" technique makes it an appealing alternative to current methods for fabricating selective solar absorbers.

We develop supercapacitor (SC) devices with large per-area capacitances by utilizing three-dimensional (3D) porous substrates. Carbon nanofibers (CNFs) functioning as active SC electrodes are grown on 3D nickel foam. The 3D porous substrates facilitate a mass loading of active electrodes and per-area capacitance as large as 60 mg/cm2 and 1.2 F/cm2, respectively. We optimize SC performance by developing an annealing-free CNF growth process that minimizes undesirable nickel carbide formation. Superior per-area capacitances described here suggest that 3D porous substrates are useful in various energy storage devices in which per-area performance is critical.

Successful strategies for stabilizing electrodeposition of reactive metals, including lithium, sodium, and aluminum are a requirement for safe, high‐energy electrochemical storage technologies that utilize these metals as anodes. Unstable deposition produces high‐surface area dendritic structures at the anode/electrolyte interface, which causes premature cell failure by complex physical and chemical processes that have presented formidable barriers to progress. Here, it is reported that hybrid electrolytes created by infusing conventional liquid electrolytes into nanoporous membranes provide exceptional ability to stabilize Li. Electrochemical cells based on γ‐Al 2 O 3 ceramics with pore diameters below a cut‐off value above 200 nm exhibit long‐term stability even at a current density of 3 mA cm −2 . The effect is not limited to ceramics; similar large enhancements in stability are observed for polypropylene membranes with less monodisperse pores below 450 nm. These findings are critically assessed using theories for ion rectification and electrodeposition reactions in porous solids and show that the source of stable electrodeposition in nanoporous electrolytes is fundamental.

Abstract The rapid development of flexible and wearable electronics proposes the persistent requirements of high‐performance flexible batteries. Much progress has been achieved recently, but how to obtain remarkable flexibility and high energy density simultaneously remains a great challenge. Here, a facile and scalable approach to fabricate spine‐like flexible lithium‐ion batteries is reported. A thick, rigid segment to store energy through winding the electrodes corresponds to the vertebra of animals, while a thin, unwound, and flexible part acts as marrow to interconnect all vertebra‐like stacks together, providing excellent flexibility for the whole battery. As the volume of the rigid electrode part is significantly larger than the flexible interconnection, the energy density of such a flexible battery can be over 85% of that in conventional packing. A nonoptimized flexible cell with an energy density of 242 Wh L −1 is demonstrated with packaging considered, which is 86.1% of a standard prismatic cell using the same components. The cell also successfully survives a harsh dynamic mechanical load test due to this rational bioinspired design. Mechanical simulation results uncover the underlying mechanism: the maximum strain in the reported design (≈0.08%) is markedly smaller than traditional stacked cells (≈1.1%). This new approach offers great promise for applications in flexible devices.

Tremendous low-grade heat (i.e., <130 °C) exists in solar thermal, geothermal, and industrial waste heat. Efficient conversion of low-grade heat to electricity can recover these wasted resources and reduce energy consumption and carbon footprint. Along with thermoelectrics and thermogalvanic cells, thermally regenerative electrochemical cycle (TREC) has attracted wide attention recently, because it has a high temperature coefficient (>1 mV/K), high efficiency, and low cost. In TREC, conversion to electricity is realized by charging–discharging an electrochemical cell at different temperatures. In this Perspective, we will discuss the principle of TREC and recent progress, such as new material systems and mechanisms. More importantly, we will give our opinions on the challenges and future directions of this field, including fundamental understanding, material design, and system engineering.

Application of advanced anode and cathode materials in commercial lithium-ion batteries is attracting attention due to their high capacity. Silicon (Si)/graphite anodes and nickel (Ni)-rich lithium nickel manganese cobalt oxide with layered structures have been paired in commercial 18650 high energy density cells (∼270 Wh/kg). It is crucial to investigate the cell performance and the aging behavior of this commercial cell. In this study, we present commercial cell degradation mechanisms by comparing fresh and aged electrodes, including changes of crystal structure, morphology, elemental composition, and electrochemical properties. The quantitative analysis was done based on dV/dQ incremental capacity analysis of 18650 cells. To determine the amount of cyclable lithium ions (Li+) and active material loss, the lithiation and delithiation capacity were compared for fresh and aged electrodes in half coin cells. Results showed that even with 5% (by mass) of Si added in the anode, cracks occurred across the anode leading to contact loss and thickening of the solid electrolyte interphase (SEI) layer. Additionally, the average fluorine (F) ratio of the aged anodes was higher compared to that of the fresh anodes. More severely, the F content on the Si aggregations on aged anodes increased to as high as 5 times that of the fresh anode, indicating SEI growth, especially on Si particles. Solid 7Li nuclear magnetic resonance results showed no detectable Li metal deposition on the aged anode. On the cathode side, cracks on the primary particle interfaces contributed to cathode material loss, contact loss, and impedance rise. Therefore, Li+ loss into the thickened SEI layer, particle cracking, and impedance rise are the main reasons behind cell degradation.

Solid polymer electrolytes (SPEs) are attractive for next-generation energy storage, because they are more thermally stable compared to conventional liquid electrolytes and simpler for scalable manufacturing than ceramic electrolytes. However, there is a growing body of research suggesting that the interfacial instabilities between SPEs and other battery components (e.g., electrodes and electrolyte fillers) hinder their practical applications. This Perspective highlights the degradation mechanisms at these interfaces revealed by recent works, especially in lithium/4 V cathode systems with high energy density. We also review recent progresses on mitigating such instabilities and provide perspectives on how to further understand and address these issues, such as advanced characterizations and simulations, which deliver a valuable guide for future studies to accelerate the development of SPEs-based solid-state batteries.

An important requirement of battery anodes is the processing step involving the formation of the solid electrolyte interphase (SEI) in the initial cycle, which consumes a significant portion of active lithium ions. This step is more critical in nanostructured anodes with high specific capacity, such as Si and Sn, due to their high surface area and large volume change. Prelithiation presents a viable approach to address such loss. However, the stability of prelithiation reagents is a big issue due to their low potential and high chemical reactivity toward O2 and moisture. Very limited amount of prelithiation agents survive in ambient air. In this research, we describe the development of a trilayer structure of active material/polymer/lithium anode, which is stable in ambient air (10-30% relative humidity) for a period that is sufficient to manufacture anode materials. The polymer layer protects lithium against O2 and moisture, and it is stable in coating active materials. The polymer layer is gradually dissolved in the battery electrolyte, and active materials contact with lithium to form lithiated anode. This trilayer-structure not only renders electrodes stable in ambient air but also leads to uniform lithiation. Moreover, the degree of prelithiation could vary from compensating SEI to fully lithiated anode. With this strategy, we have achieved high initial Coulombic efficiency of 99.7% in graphite anodes, and over 100% in silicon nanoparticles anodes. The cycling performance of lithiated anodes is comparable or better than those not lithiated. We also demonstrate a Li4Ti5O12/lithiated graphite cell with stable cycling performance. The trilayer structure represents a new prelithiation method to enhance performance of Li-ion batteries.

Traditional polyolefin separators are widely used in lithium-ion batteries. However, they are subject to thermal shrinkage which may lead to failure at elevated temperatures, ascribed intrinsically to their low melting point. And besides, recycling of spent lithium-ion batteries mainly focuses on precious metals, like cobalt, while other components such as separators are usually burnt or buried underground, causing severe hazards for the local environment, such as “white pollution”. Therefore, to solve the aforementioned problems, we incorporated attapulgite (ATP) nanofibers, a natural mineral, into sodium alginate (SA), a biodegradable polysaccharide extracted from brown algae, through a phase inversion process, whereby a porous separator was prepared. The resulting SA/ATP separator is endowed with high thermal and chemical stability, enhanced retardancy to fire, and excellent wettability with commercial liquid electrolyte (420% uptake). Attractive cycling stability (82% capacity retention after 700 cycles) and rate capability (115 mAh g−1 at 5 C) in LiFePO4/Li cells are achieved with such separator, additionally. Moreover, as both ingredients are nontoxic, this eco-friendly separator can degrade in soil without inducing any contamination. This work offers a viable choice to process a thermally stable, eco-friendly separator and open up new possibilities to improve the safety of batteries while alleviating the “white pollution”.

Very high hydroxide conductivity in a robust anion exchange membrane due to very low tortuosity, with two distinct water regimes.

Graphitic carbon nitride is an ordered two-dimensional stability. However, its bulk structure with low electrical conductivity (less than 1 S cm–1) restricts the applications in electrochemical energy storage. This is because conventional synthesis methods lack effective thickness control, and the excessive nitrogen doping (∼50%) leads to poor electrical conductivity. Here, we report an ultrathin conductive graphitic carbon nitride assembly (thickness of ∼1.0 nm) through graphene-templated van der Waals epitaxial strategy with high electrical conductivity (12.2 S cm–1), narrow pore-size distribution (5.3 nm), large surface area (724.9 m2 g–1), and appropriate nitrogen doping level (18.29%). The ultra-thin structure with nitrogen doping provided numerous channels and active sites for effective ion transportation and storage, while the graphene layers acted as micro current collectors; subsequently, it exhibits high energy storage capability of 936 mF cm–2 at 1 mA cm–2 with excellent stability of over 10 000 cycles. Moreover, the all-solid-state supercapacitors showed an ultra-high energy density of 281.3 μWh cm–2 at 1 mA cm–2 with high rate capability, Coulombic efficiency, and flexibility. This work represents a general framework for the bottom-up synthesis of ultrathin 2D materials, which may promote the application of graphitic carbon nitride in energy storage.

Efficient low-grade heat recovery can help to reduce greenhouse gas emission as over 70% of primary energy input is wasted as heat, but current technologies to fulfill the heat-to-electricity conversion are still far from optimum. Here we report a direct thermal charging cell, using asymmetric electrodes of a graphene oxide/platinum nanoparticles cathode and a polyaniline anode in Fe2+/Fe3+ redox electrolyte via isothermal heating operation. When heated, the cell generates voltage via a temperature-induced pseudocapacitive effect of graphene oxide and a thermogalvanic effect of Fe2+/Fe3+, and then discharges continuously by oxidizing polyaniline and reducing Fe3+ under isothermal heating till Fe3+ depletion. The cell can be self-regenerated when cooled down. Direct thermal charging cells attain a temperature coefficient of 5.0 mV K-1 and heat-to-electricity conversion efficiency of 2.8% at 70 °C (21.4% of Carnot efficiency) and 3.52% at 90 °C (19.7% of Carnot efficiency), outperforming other thermoelectrochemical and thermoelectric systems.

By storing energy from electrochemical processes at the electrode surface, pseudocapacitors bridge the performance gap between electrostatic double-layer capacitors and batteries. In this context, molecular design offers the exciting possibility to create tunable and inexpensive organic electroactive materials. Here we describe a porous structure composed of perylene diimide and triptycene subunits and demonstrate its remarkable performance as a pseudocapacitor electrode material. The material exhibits capacitance values as high as 350 F/g at 0.2 A/g as well as excellent stability over 10 000 cycles. Moreover, we can alter the performance of the material, from battery-like (storing more charge at low rates) to capacitor-like (faster charge cycling), by modifying the structure of the pores via flow photocyclization. Organic materials capable of stable electron accepting pseudocapacitor behavior are rare and the capacitance values presented here are among the highest reported. More broadly, this work establishes molecular design and synthesis as a powerful approach for creating tunable energy storage materials.

cis,cis-Muconic acid is an unsaturated dicarboxylic acid that can be produced in high yields via biological conversion of sugars and lignin-derived aromatic compounds. Muconic acid is often targeted as an intermediate to direct replacement monomers such as adipic or terephthalic acid. However, the alkene groups in muconic acid provide incentive for its direct use in polymers, for example, in the synthesis of unsaturated polyester resins. Here, biologically derived muconic acid is incorporated into polyesters via condensation polymerization using the homologous series of poly(ethylene succinate), poly(propylene succinate), poly(butylene succinate), and poly(hexylene succinate). Additionally, dimethyl cis,cis-muconate is synthesized and subsequently incorporated into poly(butylene succinate). NMR measurements demonstrate that alkene bonds are present in the polymer backbones. In all cases, the glass transition temperatures are increased whereas the melting and degradation temperatures are decreased. In the case of poly(butylene succinate), utilization of neat muconic acid yields substoichiometric incorporation consistent with a tapered copolymer structure, whereas the muconate diester exhibits stoichiometric incorporation and a random copolymer structure based on thermal and mechanical properties. Prototypical fiberglass panels were produced by infusing a mixture of low molecular weight poly(butylene succinate-co-muconate) and styrene into a woven glass mat and thermally initiating polymerization resulting in thermoset composites with shear moduli in excess of 30 GPa, a value typical of commercial composites. The increased glass transition temperatures with increasing mucconic incorporation leads to improved composites properties. We find that the molecular tunability of poly(butylene succinate-co-muconate) as a tapered or random copolymer enables the tunability of composite properties. Overall, this study demonstrates the utility of muconic acid as a monomer suitable for direct use in commercial composites.

Thermal management is critical to improving battery performance and suppressing thermal runaway. Besides developing external cooling technologies, it is important to understand and control thermal transport inside batteries. In this paper, heat transfer inside batteries is first analyzed and the thermal conductivity of each component is measured. The results show that low thermal conductivity of the separator is one major barrier for heat transfer in Li-ion batteries. To improve thermal conductivity of the separator, a hierarchical nano/micro-Al2O3/polymer separator is prepared with thermal conductivity of ~1 W m−1 K−1, representing an enhancement of 5× compared to commercial polyethylene-based separators. Modeling has been performed to understand mechanism behind the enhancement of thermal conductivity, which suggests that addition of nanoparticles significantly reduces thickness of polymer coating on micron-sized Al2O3 particles and thus increase the thermal conductivity of the composite separator. This Al2O3-based separator also has similar ionic conductivity with commercial polymer separators. Such composite separator may have potential applications in developing batteries with better performance and safety.

Poly (ethylene oxide) (PEO) polymer electrolytes are promising candidates for next-generation rechargeable lithium batteries. However, the poor interfacial stability between 4 V cathodes and PEO electrolytes impedes their applications in 4 V lithium batteries with high energy density. Here, we demonstrate a facile and effective strategy to enhance the interfacial stability by the synergy of Li1.5Al0.5Ge1.5(PO4)3 (LAGP) coating on the cathode surface, and salt combination in the electrolyte, even with a cut-off voltage of 4.25–4.4 V vs. Li+/Li. Nano-LAGP coated Li|PEO|LiCoO2 cell delivers stable cycling with a capacity retention of 81.9%/400 cycles and 84.7%/200 cycles at 60 °C when charged to 4.25 and 4.3 V in pure polyether electrolyte, respectively. Steady cycling is also demonstrated at room temperature and with LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode. This work offers a viable and scalable approach to improve the stability between PEO electrolytes and 4 V cathodes and open up new possibilities for practical application of 4 V lithium metal batteries.

Abstract Passive daytime radiative cooling (PDRC) dissipates terrestrial heat to the extremely cold outer space without using any energy input or producing pollution. It has the potential to simultaneously alleviate the two major problems of energy crisis and global warming. In this review, we summarize general strategies implemented for achieving PDRC and various applications of PDRC technologies. We first introduce heat transfer processes involved in PDRC, including radiative and nonradiative heat transfer processes, to evaluate the PDRC performance. Subsequently, we summarize the general material designs used for controlling PDRC performance, such as tuning the thermal mid‐infrared emittance and solar reflectance. Finally, we discuss the diverse applications of PDRC technologies to overcome problems in space cooling, solar cell cooling, water harvesting, and electricity generation. image

High-performance stretchable batteries are key components for stretchable devices. However, it is challenging to have both high stretchability and high energy density simultaneously. Herein, we report a design of accordion-like stretchable lithium ion batteries, where the rigid energy storage units are connected by wrinkled and stretchable components. Simulation results show that such accordion-like design and the tape/metal/tape sandwiched structure reduces maximum stress of Al foil in the structure from 31.2 MPa to only 17.1 MPa, which significantly enhance the cell stability. Meanwhile, as the volume of rigid segments are larger than the stretchable part, such design can achieve stretchability of 29% while maintaining 77% (233 Wh L−1) of volumetric energy density of that in conventional packing. Experimentally, the cell shows a high capacity retention of 95.4% even after stretching by 22% for 10,000 times, bending for 20,000 times, and 100 cycles at 0.5 C. It also provides steady power output during continuous dynamic mechanical tests. The corresponding average discharge voltage is only reduced by 1 mV. This accordion-like battery provides an alternative strategy to design stretchable batteries for stretchable devices.

Joseph Wild is a PhD student in the Materials Science and Engineering program at Columbia University. He obtained his MEng in Mechanical Engineering from Imperial College London in 2020. His research mainly focuses on lithium-ion batteries, with an emphasis on advanced materials, modeling, and degradation diagnostics.Rishav Choudhury is a master’s student in the Materials Science and Engineering program at Columbia University. He obtained his BSE in Materials Science and Engineering from the University of Michigan, Ann Arbor in 2020. His research mainly focuses on solid-state batteries with a focus on interfacial stability.Yuan Yang is currently an associate professor of materials science in the department of applied physics and applied mathematics at Columbia University. He received his PhD at Stanford University in 2012. Dr. Yang’s research interests include advanced energy storage and thermal energy management. He has published more than 80 papers with a total citation over 20,000 times and an H-index of 46. Dr. Yang is a Scialog fellow on Advanced Energy Storage and a Web of Science Highly Cited Researcher in 2020. He has won a Young Innovator Award by Nano Research and an Emerging Investigators Award by Journal of Materials Chemistry A. Joseph Wild is a PhD student in the Materials Science and Engineering program at Columbia University. He obtained his MEng in Mechanical Engineering from Imperial College London in 2020. His research mainly focuses on lithium-ion batteries, with an emphasis on advanced materials, modeling, and degradation diagnostics. Rishav Choudhury is a master’s student in the Materials Science and Engineering program at Columbia University. He obtained his BSE in Materials Science and Engineering from the University of Michigan, Ann Arbor in 2020. His research mainly focuses on solid-state batteries with a focus on interfacial stability. Yuan Yang is currently an associate professor of materials science in the department of applied physics and applied mathematics at Columbia University. He received his PhD at Stanford University in 2012. Dr. Yang’s research interests include advanced energy storage and thermal energy management. He has published more than 80 papers with a total citation over 20,000 times and an H-index of 46. Dr. Yang is a Scialog fellow on Advanced Energy Storage and a Web of Science Highly Cited Researcher in 2020. He has won a Young Innovator Award by Nano Research and an Emerging Investigators Award by Journal of Materials Chemistry A.

Abstract In recent decades, extensive nanomaterials and related techniques have been proposed to achieve high capacities surpassing conventional battery electrodes. Nevertheless, most of them show low mass loadings and areal capacities, which deteriorates the cell‐level energy densities and increases cost after the consideration of inactive components in batteries. Achieving high‐areal‐capacity is essential for those advanced materials to move out of laboratories and into practical applications, yet remains challenging due to the decreased mechanical properties and sluggish electrochemical kinetics at elevated mass loadings. In this paper, the previously reported strategies for promoting areal lithium storage performance, including material‐level designs, electrode‐level architecture optimization, and novel manufacturing techniques are reviewed. Sodium‐ion battery electrodes are discussed subsequently, emphatically on its difference with those for lithium storage. Pouch‐cell‐level energy densities based on high‐areal‐capacity electrodes with different thicknesses are also estimated. For each category of these strategies, working principles, advantages, and possible problems are analyzed, with typical examples presented in detail and a summary table comparing the structures and achieved performance. Finally, the features of the high‐areal‐capacity electrodes demonstrated in this review are concluded, and overlooked issues and potential research directions in this field are summarized.

We report here an iterative synthesis of long helical perylene diimide (hPDI[n]) nanoribbons with a length up to 16 fused benzene rings. These contorted, ladder-type conjugated, and atomically precise nanoribbons show great potential as organic fast-charging and long-lifetime battery cathodes. By tuning the length of the hPDI[n] oligomers, we can simultaneously modulate the electrical conductivity and ionic diffusivity of the material. The length of the ladders adjusts both the conjugation for electron transport and the contortion for lithium-ion transport. The longest oligomer, hPDI[6], when fabricated as the cathode in lithium batteries, features both high electrical conductivity and high ionic diffusivity. This electrode material exhibits a high power density and can be charged in less than 1 min to 66% of its maximum capacity. Remarkably, this material also has exceptional cycling stability and can operate for up to 10,000 charging-discharging cycles without any appreciable capacity decay. The design principles described here chart a clear path for organic battery electrodes that are sustainable, fast-charging, and long lasting.

In this paper, GO-TiO2/PVDF composite ultrafiltration membranes were prepared for slightly polluted ground water treatment with high efficiency and low energy consumption. The TiO2 nanoparticles solidly loaded on GO reduced the agglomeration between GO sheets, and the grafting of GO-TiO2 nanocomposites by polyethylene glycol (PEG), partially grafted onto the surface of TiO2 nanoparticles, prevented the agglomeration between TiO2 nanoparticles. GO-TiO2 was used as an additive to prepare GO-TiO2/PVDF composite ultrafiltration membrane by non-solvent induced precipitation phase separation method, and the fouling resistance and hydrophilicity of the membrane were improved. The structure and morphology of the composite ultrafiltration membranes were characterized using FTIR, SEM and contact angle testers, and the water flux and fouling resistance of the composite ultrafiltration membranes were evaluated using the ultrafiltration method, and investigate the effectiveness of the composite ultrafiltration membranes in treating slightly polluted ground water. The 0.05% GO-TiO2/PVDF composite ultrafiltration membrane has better hydrophilicity and fouling resistance, with a pure water flux of 280.3 L/(m2·h), 2.1 times higher than that of the PVDF membrane. In an experiment using GO-TiO2/PVDF composite ultrafiltration membrane to filter campus lake water, the removal rates of COD, DOC and aromatic compounds (UV254) were increased by 15.8%, 54.2% and 55.4% respectively compared to using PVDF membrane, and the GO-TiO2/PVDF composite ultrafiltration membrane has excellent filtration effect for slightly polluted ground water.

Directional freezing is an efficient approach to design anisotropic materials with surface void and well-defined aligned channels along the freezing direction for charge transmission and ion diffusion. Herein, poly(vinyl alcohol) (PVA)/bacterial cellulose (BC)/MXene (PBM) composite aerogels are prepared via directional freezing. The aligned porous architecture of PBM not only enables uniform loading and high accessibility of PPy through the aerogel network, but also ensures efficient penetration and fast transport of electrolytes. The as-prepared PPy@PVA/BC/MXene (PPy@PBM) aerogel based supercapacitors show a high areal specific capacitance of 3948 mF cm−2 at 0.47 mA cm−2, a desirable energy density 178 μWh cm−2 at a power density of 951 μW cm−2 and excellent cycling stability (120% capacitance retention after 10,000 cycles). In addition, the PPy@PBM aerogels demonstrate high sensitivity (313.2 kPa−1 in 200 to 3000 Pa pressure range), ultralow detection limit (<1 Pa) and fast response (79 ms) as pressure sensors. This study proposes an efficient approach to prepare porous composite aerogels for supercapacitor electrodes and pressure sensors.

This paper presents single nanostructure devices as a powerful new diagnostic tool for batteries with LiMn2O4 nanorod materials as an example. LiMn2O4 and Al-doped LiMn2O4 nanorods were synthesized by a two-step method that combines hydrothermal synthesis of β-MnO2 nanorods and a solid state reaction to convert them to LiMn2O4 nanorods. λ-MnO2 nanorods were also prepared by acid treatment of LiMn2O4 nanorods. The effect of electrolyte etching on these LiMn2O4-related nanorods is investigated by both SEM and single-nanorod transport measurement, and this is the first time that the transport properties of this material have been studied at the level of an individual single-crystalline particle. Experiments show that Al dopants reduce the dissolution of Mn3+ ions significantly and make the LiAl0.1Mn1.9O4 nanorods much more stable than LiMn2O4 against electrolyte etching, which is reflected by the magnification of both size shrinkage and conductance decrease. These results correlate well with the better cycling performance of Al-doped LiMn2O4 in our Li-ion battery tests: LiAl0.1Mn1.9O4 nanorods achieve 96% capacity retention after 100 cycles at 1C rate at room temperature, and 80% at 60 °C, whereas LiMn2O4 shows worse retention of 91% at room temperature, and 69% at 60 °C. Moreover, temperature-dependent I−V measurements indicate that the sharp electronic resistance increase due to charge ordering transition at 290 K does not appear in our LiMn2O4 nanorod samples, suggesting good battery performance at low temperature.

Eine zweistufige Lösungsphasensynthese ergab LiMn0.75Fe0.25PO4-Nanostäbe auf Graphen mit verbesserter elektrischer Leitfähigkeit (siehe Bild; rmGO=reduziertes, milde oxidiertes Graphenoxid). Die Nanostabmorphologie eignet sich ideal für eine schnelle Li+-Diffusion entlang der kurzen radialen Richtung (20–30 nm) der Nanostäbe. Dies führt zu einer ultraschnellen Entladeleistung dieses Hybrid-Kathodenmaterials. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by 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.

This paper presents a systematic investigation on the controlled synthesis of wurtzite aluminum nitride (AlN) one-dimensional (1D) nanostructures in a chemical vapor deposition (CVD) system using Al and NH3 as starting materials. By controlling reaction temperature and NH3 flow, nanostructures with manifold morphologies including nanoneedles, branched nanoneedles, short nanorods, slim nanorods, and nanofences were synthesized with high yield and selectivity. The correlation between experiment parameters and product morphologies was interpreted by a surface diffusion based model. Moreover, electrical properties of a single nanoneedle were studied for the first time, in which typical semiconductor characteristics were observed. Silicon was speculated to incorporate into the AlN nanoneedle from silicon substrates during the synthesis, which served as an n-type donor and was responsible for the observed electrical behavior.

A carbon nanotube (CNT)–textile–Pt cathode for aqueous-cathode microbial fuel cells (MFCs) was prepared by electrochemically depositing Pt nanoparticles on a CNT–textile. An MFC equipped with a CNT–textile–Pt cathode revealed a 2.14-fold maximum power density with only 19.3% Pt loading, compared to that with a commercial Pt coated carbon cloth cathode.

The morphology and anion transport of an α-C modified imidazolium functionalized anion exchange membrane, 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl)imidazolium functionalized polyphenylene oxide (with ion exchange capacity {IEC} = 1.53 or 1.82 mequiv/g), were studied in detail. The novel cation is less susceptible to OH– attack (0% degradation) compared to unsubstituted imidazolium functionalized polyphenylene oxide (25% degradation) after 24 h at 80 °C in 1 M KOH. The two different IEC materials (with the same protected cation) show interesting differences in membrane performance. From AFM and SAXS under humid conditions, the domain sizes of the membrane change, which impact the transport properties. The lower IEC sample showed a smaller tortuosity and, thus, needs a longer diffusion time for the water molecules to be fully hindered inside the hydrophobic clusters, which is confirmed by water self-diffusion measurements from pulsed field gradient NMR. From conductivity and diffusion measurements, the higher IEC sample exhibited Vogel–Tammann–Fulcher behavior, thus indicating that the polymer chain’s movement dominates the transport. However, the lower IEC sample exhibited the linear Arrhenius behavior signifying water-mediated transport. The maximum Cl– conductivity observed was 23 mS/cm at 95% RH and 90 °C.

Electrical double layer capacitors (EDLCs) are usually charged by applying a potential difference across the positive and negative electrodes. In this paper, we demonstrated that EDLCs can be charged by heating. An open circuit voltage of 80-300 mV has been observed by heating the supercapacitor to 65 °C. The charge generated at high temperature can be stored in the device after its returning to the room temperature, thus allowing the lighting up of LEDs by connecting the "thermally charged" supercapacitors in a series. The underlying mechanism is related to a thermo-electrochemical process that enhances the kinetics of Faradaic process at the electrode surface (e.g., surface redox reaction of functional group, or chemical adsorption/desorption of electrolyte ions) at higher temperature. Effects of "thermal charging" times, activation voltage, rate, and times on "thermally charged" voltage are studied and possible mechanisms are discussed.

A random copolymer, tris(2,4,6-trimethoxyphenyl) phosphonium functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO–TPQP) was cast from three different solvents: dimethyl sulfoxide (DMSO), ethyl lactate, or a 41:59 vol% mixture of DMSO and ethyl lactate. Solvents were selected via analysis of the Hansen solubility parameters to vary the phase separation of the polymer in the films. An optimized mixture of DMSO and ethyl lactate chosen for film fabrication and this film was contrasted with films cast from the neat constituent solvents. Atomic force microscopy identified domains from nanometer to tens of nanometer sizes, while the light microscopy showed features on the order of micron. SAXS revealed a cation scattering peak with a d-spacing from 7 to 15 Å. Trends in conductivity and water diffusion for the membranes vary depending on the solvent from which they are cast. The mixed solvent cast membrane shows a linear Arrhenius behavior indicating fully dissociated cationic/anionic groups, and has the highest bromide conductivity of 3 mS/cm at 95% RH, 90 °C. The ethyl lactate cast membrane shows a linear Arrhenius relation in conductivity, but a Vogel–Tamman–Fulcher behavior in its water self-diffusion. While water increases bromide dissociation, water and bromide transport in these films seems to be decoupled. This is particularly true for the film cast from ethyl lactate.

Abstract Broadband high reflectance in nature is often the result of randomly, three-dimensionally structured materials. This study explores unique optical properties associated with one-dimensional nanostructures discovered in silk cocoon fibers of the comet moth, Argema mittrei . The fibers are populated with a high density of air voids randomly distributed across the fiber cross-section but are invariant along the fiber. These filamentary air voids strongly scatter light in the solar spectrum. A single silk fiber measuring ~50 μm thick can reflect 66% of incoming solar radiation, and this, together with the fibers’ high emissivity of 0.88 in the mid-infrared range, allows the cocoon to act as an efficient radiative-cooling device. Drawing inspiration from these natural radiative-cooling fibers, biomimetic nanostructured fibers based on both regenerated silk fibroin and polyvinylidene difluoride are fabricated through wet spinning. Optical characterization shows that these fibers exhibit exceptional optical properties for radiative-cooling applications: nanostructured regenerated silk fibers provide a solar reflectivity of 0.73 and a thermal emissivity of 0.90, and nanostructured polyvinylidene difluoride fibers provide a solar reflectivity of 0.93 and a thermal emissivity of 0.91. The filamentary air voids lead to highly directional scattering, giving the fibers a highly reflective sheen, but more interestingly, they enable guided optical modes to propagate along the fibers through transverse Anderson localization. This discovery opens up the possibility of using wild silkmoth fibers as a biocompatible and bioresorbable material for optical signal and image transport.

Abstract Flexible batteries, seamlessly compatible with flexible and wearable electronics, attract a great deal of research attention. Current designs of flexible batteries struggle to meet one of the most extreme yet common deformation scenarios in practice, folding, while retaining high energy density. Inspired by origami folding, a novel strategy to fabricate zigzag‐like lithium ion batteries with superior foldability is proposed. The battery structure could approach zero‐gap between two adjacent energy storage segments, achieving an energy density that is 96.4% of that in a conventional stacking cell. A foldable battery thus fabricated demonstrates an energy density of 275 Wh L −1 and is resilient to fatigue over 45 000 dynamic cycles with a folding angle of 130°, while retaining stable electrochemical performance. Additionally, the power stability and resilience to nail shorting of the foldable battery are also examined.

This manuscript presents a working redox battery in organic media that possesses remarkable cycling stability. The redox molecules have a solubility over 1 mol electrons/liter, and a cell with 0.4 M electron concentration is demonstrated with steady performance >450 cycles (>74 days). Such a concentration is among the highest values reported in redox flow batteries with organic electrolytes. The average Coulombic efficiency of this cell during cycling is 99.868%. The stability of the cell approaches the level necessary for a long lifetime nonaqueous redox flow battery. For the membrane, we employ a low cost size exclusion cellulose membrane. With this membrane, we couple the preparation of nanoscale macromolecular electrolytes to successfully avoid active material crossover. We show that this cellulose-based membrane can support high voltages in excess of 3 V and extreme temperatures (−20 to 110 °C). These extremes in temperature and voltage are not possible with aqueous systems. Most importantly, the nanoscale macromolecular platforms we present here for our electrolytes can be readily tuned through derivatization to realize the promise of organic redox flow batteries.

A membrane using heterpolyacids as the protogenic group can solve the chemical durability issue of polymer electrolyte fuel cells.

A chemically stable copolymer [poly(2,6 dimethyl 1,4 phenylene oxide)-b-poly(vinyl benzyl trimethyl ammonium)] with two ion exchange capacities, 3.2 and 2.9 meq g−1, was prepared as anion exchange membranes (AEM-3.2 and AEM-2.9). These materials showed high OH− conductivities of 138 mS.cm−1 and 106 mS.cm−1, for AEM-3.2 and AEM-2.9 respectively, at 60°C, and 95% RH. The OH− conductivity = 45 mS.cm−1 for AEM-3.2 at 60% RH and 60°C in the absence of CO2. Amongst the ions studied, only OH− is fully dissociated at high RH. The lower Ea = 10–13 kJ.mol−1 for OH− compared to F− ∼ 20 kJ.mol−1 in conductivity measurements, and of H2O from self-diffusion coefficients suggests the presence of a Grotthuss hopping transport mechanism in OH− transport. PGSE-NMR of H2O and F− show that the membranes have low tortuosity, 1.8 and 1.2, and high water self-diffusion coefficients, 0.66 and 0.26 × 10−5 cm2.s−1, for AEM-3.2 and AEM-2.9 respectively. SAXS and TEM show that the membrane has several different sized water environments, ca. 62 nm, 20 nm, and 3.5 nm. The low water uptake, λ = 9–12, reduced swelling, and high OH− conductivity, with no chemical degradation over two weeks, suggests that the membrane is a strong candidate for electrochemical applications.

LiCoO2 (LCO) possess a high theoretical specific capacity of 274 mAh g−1, and currently LCO charged to 4.48 ​V with a capacity of ~190–195 mAh g−1 is penetrating the commercial markets. Scalable strategies to further enhance the performance of LCO are highly attractive. Here, we develop a scalable ball-milling and sintering method to tackle this long-standing challenge by modifying LCO surface with only 1.5–3.5% ceramic solid electrolyte nanoparticles, specifically Li1.5Al0.5Ge1.5(PO4)3 (LAGP) as an example. Consequently, the atomic-to-meso multiscale structural stabilities have been significantly improved, even with a high cut-off voltage of 4.5 ​V vs. Li/Li+, leading to excellent electrochemical stabilities. The nano-LAGP modified Li|LCO cell exhibits high discharge capacity of 196 mAh g−1 at 0.1 ​C, capacity retention of 88% over 400 cycles, and remarkably enhanced rate capability (163 mAh g−1 at 6 ​C). These results show significant improvement compared to the Li|LCO cells. The as-prepared graphite|LAGP-LCO full cells also show steady cycling with 80.4% capacity retention after 200 cycles with a voltage cut-off of 4.45 ​V. This work provides a simple and scalable approach to achieve stable cycling of LCO at high voltage with high energy density.

Suppressing lithium dendrites in carbonate electrolyte remains a grand challenge for high voltage lithium metal batteries. The role of adhesion between the interfacial layer and the lithium metal in controlling lithium growth is often overlooked. Here, we find that the adhesion energy significantly influences lithium dendrite growth by the phase-field simulations, and LiAl is an attractive material with strong adhesion with lithium metal by density functional theory (DFT) calculations. Then a simple solution process is developed to form conformal nanostructured LiAl interfacial layer on the lithium metal surface. With the nanostructured LiAl alloy-based interfacial layer, the Li/Li symmetric cell can be cycled stably for more than 1100 times at 5 mA/cm2, 1 mAh/cm2 with a low overpotential of 170 mV. For the LiNi1/3Co1/3Mn1/3O2/Li full cell, this interfacial layer improves the capacity retention from 59.8% to 88.7% for 120 cycles at 1 C rate, and for the LiFePO4/Li system, the modified lithium anode also improves capacity retention from 79.5% to 99.4% after 150 cycles. This study represents a new approach to enhance the performance of lithium anode for rechargeable batteries with high voltage and high energy density.

Abstract Structural batteries are attractive for weight reduction in vehicles, such as cars and airplanes, which requires batteries to have both excellent mechanical properties and electrochemical performance. This work develops a scalable and feasible tree‐root‐like lamination at the electrode/separator interface, which effectively transfers load between different layers of battery components and thus dramatically enhances the flexural modulus of pouch cells from 0.28 to 3.1 GPa. The underlying mechanism is also analyzed by finite element simulations. Meanwhile, the interfacial lamination has a limited effect on the electrochemical performance of Li‐ion cells. A graphite/LiNi 0.5 Mn 0.3 Co 0.2 O 2 full cell with such interfacial lamination delivers a steady discharge capacity of 148.6 mAh g −1 at C /2 and 95.5% retention after 500 cycles. Moreover, the specific energy only decreases by 3%, which is the smallest reduction reported so far in structural batteries. A prototype of “electric wings” is also demonstrated, which allows an aircraft model to fly steadily. This work illustrates that engineering interfacial adhesion is an effective and scalable approach to develop structural batteries with excellent mechanical and electrochemical properties.

It is widely accepted that concentration polarization in liquid electrolytes promotes whisker growth during metal deposition, and therefore, high salt concentration is favored. Here, we report unexpected opposite behaviors in solid polymer electrolytes: concentration polarization can induce phase transformation in a polyethylene oxide (PEO) electrolyte, forming a new PEO-rich but salt-/plasticizer-poor phase at the lithium/electrolyte interface, as unveiled by stimulated Raman scattering microscopy. The new phase has a significantly higher Young’s modulus (∼1–3 GPa) than a bulk polymer electrolyte (<1 MPa). We hereby propose a design rule for PEO electrolytes: their compositions should be near the boundary between single-phase and two-phase regions in the phase diagram so that the applied current can induce the formation of a mechanically rigid PEO-rich phase to suppress lithium whiskers. LiFePO4/PEO/Li cells with concentration-polarization-induced phase transformation can be reversibly cycled 100 times, while cells without such transformation fail within 10 cycles, demonstrating the effectiveness of this strategy.

Phosphorus-incorporated three-dimensionally ordered macroporous carbons (P-3DOMCs) are synthesized by a colloidal crystal templating strategy with polystyrene spheres as the templates and phenolic resol containing phosphoric acid (PA) as the carbon source. The textural properties and the surface chemistry have been investigated by scanning electron microscopy, nitrogen sorption, and X-ray photoelectron spectra. The content of PA in phenolic resol plays a critical role in the morphology and textural properties of the resulting P-3DOMCs. Using 0.18 g of PA helps to achieve more pronounced 3D-network structure. The carbon materials are employed as supercapacitor electrodes in 6 M KOH aqueous solution, and the cyclic voltammetry and galvanostatic charge–discharge results indicate that they possess higher specific capacitances and retentions than the corresponding phosphorus-free counterpart and the commercial activated carbon. The easy ion transport, large ion-accessible surface area and effective heteroatom functional groups of the 3DOM nanoarchitecture render the carbon material a promising candidate for supercapacitor application.

The surface structure and adjacent interior of commercially available silicon nanopowder (np-Si) was studied using multinuclear, solid-state NMR spectroscopy. The results are consistent with an overall picture in which the bulk of the np-Si interior consists of highly ordered ("crystalline") silicon atoms, each bound tetrahedrally to four other silicon atoms. From a combination of ¹H, 29Si and ²H magic-angle-spinning (MAS) NMR results and quantum mechanical 29Si chemical shift calculations, silicon atoms on the surface of "as-received" np-Si were found to exist in a variety of chemical structures, with apparent populations in the order (a) (Si-O-)₃Si-H > (b) (Si-O-)₃SiOH > (c) (HO-)nSi(Si)m(-OSi)4-m-n ≈ (d) (Si-O-)₂Si(H)OH > (e) (Si-O-)₂Si(-OH)₂ > (f) (Si-O-)₄Si, where Si stands for a surface silicon atom and Si represents another silicon atom that is attached to Si by either a Si-Si bond or a Si-O-Si linkage. The relative populations of each of these structures can be modified by chemical treatment, including with O₂ gas at elevated temperature. A deliberately oxidized sample displays an increased population of (Si-O-)₃Si-H, as well as (Si-O-)₃SiOH sites. Considerable heterogeneity of some surface structures was observed. A combination of ¹H and ²H MAS experiments provide evidence for a substantial population of silanol (Si-OH) moieties, some of which are not readily H-exchangeable, along with the dominant Si-H sites, on the surface of "as-received" np-Si; the silanol moieties are enhanced by deliberate oxidation. An extension of the DEPTH background suppression method is also demonstrated that permits measurement of the T₂ relaxation parameter simultaneously with background suppression.

Despite recent advances in the understanding of fundamental cancer biology, cancer remains the second most common cause of death in the United States. One of the primary factors indicative of high cancer morbidity and mortality and aggressive cancer phenotypes is tumors with a low extracellular pH (pHe). Thus, the ability to measure tumor pHe in vivo using noninvasive and accurate techniques that also provide high spatiotemporal resolution has become increasingly important and is of great interest to researchers and clinicians. In an effort to develop a pH-responsive magnetic resonance imaging (MRI) contrast agent (CA) that has the potential to be used to measure tumor pHe, well-defined pH-responsive polymers, synthesized via reversible addition–fragmentation chain transfer polymerization, were attached to the surface of gadolinium-based nanoparticles (GdNPs) via a "grafting to" method after reduction of the thiocarbonylthio end groups. The successful modification of the GdNPs was verified by transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and dynamic light scattering. The performance of the pH-responsive polymer modified GdNPs was then evaluated for potential use as smart MRI CAs via monitoring the relaxivity changes with changing environmental pH. The results suggested that the pH-responsive polymers can be used to effectively modify the GdNPs surface to prepare a smart contrast agent for MRI.

Lithium metal anode has great potential for high-energy-density lithium batteries due to its high theoretical capacity, but its practical applications are limited by the uncontrollable growth of lithium dendrites. In this work, we fabricate a facile 3D porous polymer structure with one-step phase inversion method and verify the structure by Stimulated Raman Scattering Microscopy. Such 3D porous structure leads to uniform lithium plating and striping, improving the electrochemical performance remarkably. In Li/Cu cell tests, the porous structure modified Cu delivers high Coulombic Efficiency (CE) of 96% after 240 cycles at 1 mA/cm2, while bare Cu drops to less than 20% after 42 cycles. As for Li/Li cell tests, it delivers stable cycling over 1275 cycles with only 200 mV over potential at 3 mA/cm2 and 1 mAh/cm2 in Li/Li cells. At as high as 4 mA/cm2, it delivers more than 200 cycles with less than 200 mV. With PVdF-HFP interfacial layer, it could hold up to 4 mAh/cm2, it delivers more than 110 hours at 4 mA/cm2 and 4 mAh/cm2. The as-assembled LiFePO4/porous polymer/lithium full cell shows stable capacity around 153 mAh/g and no obvious voltage polarization over 350 cycles at 0.5 C. The stable cycling performance can be attributed to the lower current density from the large specific surface area of as-deposited lithium in porous polymer matrix and confined dendrite growth path in 3D porous structure.

With the advance of personal and customized fabrication techniques, the capability to embed information in physical objects becomes evermore crucial. We present LayerCode , a tagging scheme that embeds a carefully designed barcode pattern in 3D printed objects as a deliberate byproduct of the 3D printing process. The LayerCode concept is inspired by the structural resemblance between the parallel black and white bars of the standard barcode and the universal layer-by-layer approach of 3D printing. We introduce an encoding algorithm that enables the 3D printing layers to carry information without altering the object geometry. We also introduce a decoding algorithm that reads the LayerCode tag of a physical object by just taking a photo. The physical deployment of LayerCode tags is realized on various types of 3D printers, including Fused Deposition Modeling printers as well as Stereolithography based printers. Each offers its own advantages and tradeoffs. We show that LayerCode tags can work on complex, nontrivial shapes, on which all previous tagging mechanisms may fail. To evaluate LayerCode thoroughly, we further stress test it with a large dataset of complex shapes using virtual rendering. Among 4,835 tested shapes, we successfully encode and decode on more than 99% of the shapes.

β-amyloid 1-40 oligomers (Aβ40O) is considered to be one of the important biomarkers for the diagnosis and treatment of Alzheimer's disease (AD). To explore a method with excellent performance is favorable for measuring the low concentration of Aβ40O in AD patients. Here, we developed a simple and fast method with a double stranded DNA (dsDNA)/graphene oxide (GO) based sensor, which was a fluorescent probe for a highly sensitive detection of Aβ40O down to 0.1 nM with a linear detectable range from 0.1 nM to 40 nM. The proposed sensor effectively reduced non-specific adsorption and improved the specificity of detection because of the covalent conjugation of a binding DNA (bDNA) containing Aβ40O-targeting aptamer (AptAβ) onto GO surface, as well as the optimization of the number of mismatch base pairs of dsDNA. Moreover, AD patients and healthy persons were distinguished by this present method. All advantages of this method are exactly what the clinical detection of AD biomarkers need. This novel aptasensor might pave a way towards the early diagnosis of AD.

There is a critical need for higher performing proton exchange membranes for electrochemical energy conversion devices that would enable higher temperature and drier operating conditions to be utilized. A novel approach is to utilize multiacid side chains in a perfluorinated polymer, maintaining the mechanical properties of the material, while dramatically increasing the ion-exchange capacity; however, as we show in this paper, the more complex side chain gives rise to unexpected physical phenomena in the material. We have thoroughly investigated a doubly functionalized perfluorosulfonic imide acid side chain perfluorinated polymer (PFIA), the simplest of many possible multiacid side chains currently being developed. The material is compared to its simpler perfluorosulfonic acid (PFSA) analogue via a battery of characterization and modeling investigations. The doubly functional side chain profoundly influences the properties of the PFIA polymer as it gives rise to both inter- and intraside chain interactions. These affect the nature of thermal decomposition of the material but, more importantly, force the backbone of the polymer into an unusually highly ordered more crystalline configuration. Under water saturated conditions, the PFIA has the same proton conductivity as the PFSA material, indicating that the additional proton does not contribute to the ionic conductivity, but the PFIA shows higher proton conductivity at lower RH conditions owing to dynamic changes in its local molecular environment. A transition is observed between 30 and 60 °C, indicating an order/disorder transition that is not present in the PFSA analogue. The mechanism of proton transport in the PFIA is due to more delocalized protons and more flexible side chains with better-dispersed, smaller water clusters forming the hydrophilic domains than in the PFSA analogue.

Passive daytime radiative cooling (PDRC) is an electricity-free method for cooling terrestrial entities. In PDRC, a surface has a solar reflectance of nearly 1 to avoid solar heating and a high emittance close to 1 in the long-wavelength infrared (LWIR) transparent window of the atmosphere (wavelength λ = 8–13 μm) for radiating heat to the cold sky. This allows the surface to passively achieve sub-ambient cooling. PDRC requires careful tuning of optical reflectance in the wide optical spectrum, and various strategies have been proposed in the last decade, some of which are under commercialization. PDRC can be used in a variety of applications, such as building envelopes, containers, and vehicles. This perspective describes the principle and applications of various PDRC strategies and analyzes the cost, and economic and environmental consequences. Potential challenges and possible future directions are also discussed.

The development of structural batteries has been obstructed by the intrinsically low mechanical strength of battery materials inside. Here, we propose a multifunctional structural battery platform by deploying electrodeposition-like reactions to prepare for conformally-coated electrodes, together with carbon fabrics as the skeleton to endow them with mechanical robustness. As a proof of concept, the Li/S battery system based on the electrodeposition-like mechanism was introduced into the structural batteries for the first time. The Young's modulus of optimized sulfur and lithium electrodes reach 9.2 ± 1.2 GPa and 4.5 ± 0.6 GPa, respectively, 5–20 times higher than conventional electrodes. Additionally, a thermally stable composite separator combining boron nitride nanofiller with PVdF polymer (BN/PVdF) is rationally designed, which possesses high compressive strength over 180 MPa. The structural cell integrated with these structural components delivered an excellent lifespan under compression up to 20 MPa for 20 cycles at 0.2 C. Moreover, the structural Li/S cell in pouch configuration displays better resistance to mechanical deformation when compared to the regular Li/S cell. This work provides valuable insight into structural batteries with high energy density.

<h2>Summary</h2> Stimulated Raman scattering (SRS) is a nonlinear Raman scattering process that can amplify Raman scattering by up to 10⁸ times under modern microscopy configuration. SRS microscopy has emerged as a powerful chemical imaging technique due to its high chemical, spatial, and temporal resolution. While SRS microscopy was originally designed for biomedical applications, it has drawn increasingly more attention from the materials science community in recent years. The high-speed and high-chemical sensitivity of SRS are attractive for both high-throughput material characterizations and capturing transient dynamics in chemical transport and reactions. It has been explored in various topics, such as 2D materials, energy storage and conversion, and polymerizations with great success. In this review, we discuss principles, instrumentation, and current applications of SRS microscopy in materials science, followed by our perspectives on future exciting topics to be studied by SRS microscopy.

Nickel-rich layered transition metal oxide is limited by the poor structural stability during cycling as cathode materials for next-generation lithium-based automotive batteries. In the past, the poor electrochemical performance was mainly attributed to cracks and formation of rock-salt phase on the particle surface at high potentials. Rarely is the effect of bulk phase structure evolution on properties discussed. Here, we report a bulk oxygen release induced dynamic accumulative electrochemical–mechanical coupling failure mechanism. Domain-like rock salt phases are generated due to the oxygen release and transition metals migration in the bulk region of LiNi0.6Co0.2Mn0.2O2 (NCM622) particles at the first cycle high cutoff voltage. Then, reversible compressive/tensile lattice strain alternately dominate around the domain boundary and accumulate with cycling, leading to capacity fading and becoming the origin of intracrystalline cracks. The results suggest that, in addition to the side effects from the surface, the structural transformation of the bulk plays an important role in the capacity fading. The stabilization of lattice oxygen in bulk region is a feasible solution to suppress the structural transition and the inhomogeneous stress distribution.

We studied the effect of pressure on LiMn2O4 commercial powders and well-characterized nanorods using angle-dispersive synchrotron X-ray diffraction (XRD) in diamond anvil cells and found that spinel LiMn2O4 is extremely sensitive to deviatoric stress induced by external applied pressure. Under nonhydrostatic conditions, bulk LiMn2O4 underwent an irreversible phase transformation at pressures as low as 0.4 GPa from a cubic Fd-3m to tetragonal I41/amd structure driven by the Jahn–Teller effect. In contrast, bulk LiMn2O4 under hydrostatic conditions experienced a reversible structural transformation beginning at approximately 11 GPa. Well-characterized LiMn2O4 nanorods with an average diameter of 100–150 nm and an average length of 1–2 μm were investigated under the same experimental conditions and showed a similar structural behavior as the bulk material confirming that LiMn2O4 displays an extremely sensitive structural response to deviatoric stress. Scanning electron microscope (SEM) images of the samples especially the nanorods that were recovered from high pressure demonstrated a link between the changing morphology of the materials and the origin of the phase transition. We also found that nanostructured materials can accommodate more stress compared to their bulk counterparts. Our comparative study of bulk and nanorod LiMn2O4 improves our understanding of their fundamental structural and mechanical properties, which can provide guidance for applied battery technology. In addition, LiMn2O4 represents a strongly correlated system, whose structural, electronic, and magnetic properties at high pressure are of broad interest for fundamental chemistry and condensed matter physics.

Gilsonite is a natural fossil resource, similar to a petroleum asphalt high in asphaltenes. Asphaltenes are a class of organic compounds operationally defined based on their solubility in organic solvents, and as a result there is wide range of potential compositions and structures that can fit into this class. Specific compounds are challenging to propose due to its complexity. A sample of the asphaltene derived from the Gilsonite deposit was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy. The high intensity of the 1600 cm−1 infrared peak, which corresponds to a CC stretching vibrational mode of the aromatic carbons also found prevalent in other asphaltenes, is likely a characteristic asphaltene feature. The high intensity can be explained by the stack structure and/or by polycyclic aromatic infrared transitions with a high dipole moment derivative. The nanosize stack structure was validated by the electron microscope and diffraction patterns, giving inter-sheet distances of 2.54 and 3.77 Å. Complementary calculations using density functional theory suggest a specific island-type polycyclic aromatic molecular model, with the calculated vibrational modes consistent with all of the characteristic peaks in the infrared spectrum. The method combining theoretical and experimental can be extended for more specific asphaltene molecular structure identifications.