A Stable Solid Polymer Electrolyte for Lithium Metal Battery with Electronically Conductive Fillers.

Electronic conduction in solid-polymer electrolytes is generally not desired, which causes leakage of electrons or energy loss, and the electronically conductive domains at electrode-electrolyte interfaces can lead to continuous decomposition of electrolytes and shorting issues. However, it is noticed in this work that in an insulating matrix, the conductive domains at certain aspects could also have positive effects on the electrolyte performance with proper control. This work evaluates the limitation and benefits of electronically conductive domains in a solid-polymer electrolyte system and discusses the approach to improve the electrolyte physicochemical properties with densified local electric field distribution, enhanced bulk dielectric property, and charge transfer. By deliberately introducing the conductive domains in a regular solid-polymer electrolyte, stable cycle life, low overpotential, and promising full cell performance could be achieved.

Reversible Al Metal Anodes Enabled by Amorphization for Aqueous Aluminum Batteries.

Aqueous aluminum metal batteries (AMBs) are regarded as one of the most sustainable energy storage systems among post-lithium-ion candidates, which is attributable to their highest theoretical volumetric capacity, inherent safe operation, and low cost. Yet, the development of aqueous AMBs is plagued by the incapable aluminum plating in an aqueous solution and severe parasitic reactions, which results in the limited discharge voltage, thus making the development of aqueous AMBs unsuccessful so far. Here, we demonstrate that amorphization is an effective strategy to tackle these critical issues of a metallic Al anode by shifting the reduction potential for Al deposition. The amorphous aluminum (a-Al) interfacial layer is triggered by an in situ lithium-ion alloying/dealloying process on a metallic Al substrate with low strength. Unveiled by experimental and theoretical investigations, the amorphous structure greatly lowers the Al nucleation energy barrier, which forces the Al deposition competitive to the electron-stealing hydrogen evolution reaction (HER). Simultaneously, the inhibited HER mitigates the passivation, promoting interfacial ion transfer kinetics and enabling steady aluminum plating/stripping for 800 h in the symmetric cell. The resultant multiple full cells using Al@a-Al anodes deliver approximately a 0.6 V increase in the discharge voltage plateau compared to that of bare Al-based cells, which far outperform all reported aqueous AMBs. In both symmetric cells and full cells, the excellent electrochemical performances are achieved in a noncorrosive, low-cost, and fluorine-free Al2(SO4)3 electrolyte, which is ecofriendly and can be easily adapted for sustainable large-scale applications. This work brings an intriguing picture of the design of metallic anodes for reversible and high-voltage AMBs.

A General Strategy of Anion-Rich High-Concentration Polymeric Interlayer for High-Voltage, All-Solid-State Batteries.

All-solid-state batteries are promising energy storage systems as a power source for future electric applications. However, the solid electrolytes have suffered from oxidative vulnerability at the catalytic cathode's surface, particularly at the high-voltage charging process. The poor charge transport and the contact issue at the electrolyte/electrode interface also hamper fully utilizing high-energy-density batteries. In this work, a general design of a high-concentration polymeric interlayer is developed. The interactions between a number of anions in the high-salt-concentration and the polymer chain's functional groups have shown outstanding physicochemical properties, including the rich solvation sites and conductive nanochannels, which Li+ ions can coordinate to or conduct through. The high-concentration polymeric interlayer is also highly resistant to oxidation (up to 5 V) that leads to significant improvement in cycle life with various cathodes, including LiNi1/3Co1/3Mn1/3O2, LiCoO2 and LiFePO4, demonstrating a high Coulombic efficiency over 99.9%.

Revealing the Solid-State Electrolyte Interfacial Stability Model with Na-K Liquid Alloy.

In this work, the Na-K liquid alloy with a charge selective interfacial layer is developed to achieve an impressively long cycling life with small overpotential on a sodium super-ionic conductor solid-state electrolyte (NASICON SSE). With this unique multi-cation system as the platform, we further propose a unique model that contains a chemical decomposition domain and a kinetic decomposition domain for the interfacial stability model. Based on this model, two charge selection mechanisms are proposed with dynamic chemical kinetic equilibrium and electrochemical kinetics as the manners of control, respectively, and both are validated by the electrochemical measurements with microscopic and spectroscopic characterizations. This study provides an effective design for high-energy-density solid-state battery with alkali Na-K anode, but also presents a novel approach to understand the interfacial chemical processes that could inspire and guide future designs.

Three-dimensional mesostructures as high-temperature growth templates, electronic cellular scaffolds, and self-propelled microrobots.

Recent work demonstrates that processes of stress release in prestrained elastomeric substrates can guide the assembly of sophisticated 3D micro/nanostructures in advanced materials. Reported application examples include soft electronic components, tunable electromagnetic and optical devices, vibrational metrology platforms, and other unusual technologies, each enabled by uniquely engineered 3D architectures. A significant disadvantage of these systems is that the elastomeric substrates, while essential to the assembly process, can impose significant engineering constraints in terms of operating temperatures and levels of dimensional stability; they also prevent the realization of 3D structures in freestanding forms. Here, we introduce concepts in interfacial photopolymerization, nonlinear mechanics, and physical transfer that bypass these limitations. The results enable 3D mesostructures in fully or partially freestanding forms, with additional capabilities in integration onto nearly any class of substrate, from planar, hard inorganic materials to textured, soft biological tissues, all via mechanisms quantitatively described by theoretical modeling. Illustrations of these ideas include their use in 3D structures as frameworks for templated growth of organized lamellae from AgCl-KCl eutectics and of atomic layers of WSe2 from vapor-phase precursors, as open-architecture electronic scaffolds for formation of dorsal root ganglion (DRG) neural networks, and as catalyst supports for propulsive systems in 3D microswimmers with geometrically controlled dynamics. Taken together, these methodologies establish a set of enabling options in 3D micro/nanomanufacturing that lie outside of the scope of existing alternatives.

In Situ Formation of Liquid Metals via Galvanic Replacement Reaction to Build Dendrite-Free Alkali-Metal-Ion Batteries.

Galvanic replacement reactions have been studied as a versatile route to synthesize nanostructured alloys. However, the galvanic replacement chemistry of alkali metals has rarely been explored. A protective interphase layer will be formed outside templates when the redox potential exceeds the potential windows of nonaqueous solutions, and the complex interfacial chemistry remains elusive. Here, we demonstrate the formation of room-temperature liquid metal alloys of Na and K via galvanic replacement reaction. The fundamentals of the reaction at such low potentials are investigated via a combined experimental and computational method, which uncovers the critical role of solid-electrolyte interphase in regulating the migration of Na ions and thus the alloying reaction kinetics. With in situ formed NaK liquid alloys as an anode, the dendritic growth of alkali metals can be eliminated thanks to the deformable and self-healing features of liquid metals. The proof-of-concept battery delivers reasonable electrochemical performance, confirming the generality of this in situ approach and design principle for next-generation dendrite-free batteries.

Biredox Eutectic Electrolytes Derived from Organic Redox-Active Molecules: High-Energy Storage Systems.

One promising candidate for high-energy storage systems is the nonaqueous redox flow battery (NARFB). However, their application is limited by low solubility of redox-active materials and poor performance at high current density. Reported here is a new strategy, a biredox eutectic, as the sole electrolyte for NARFB to achieve a significantly higher concentration of redox-active materials and enhance the cell performance. Without other auxiliary solvents, the biredox eutectic electrolyte is formed directly by the molecular interactions between two different redox-active molecules. Such a unique electrolyte possesses high concentration with low viscosity (3.5 m, for N-butylphthalimide and 1,1-dimethylferrocene system) and a relatively high working voltage of 1.8 V, enabling high capacity and energy density of NARFB. The resulting high-performance NARFB demonstrates that the biredox eutectic based strategy is potentially promising for low-cost and high-energy storage systems.

A mechanically driven form of Kirigami as a route to 3D mesostructures in micro/nanomembranes.

Assembly of 3D micro/nanostructures in advanced functional materials has important implications across broad areas of technology. Existing approaches are compatible, however, only with narrow classes of materials and/or 3D geometries. This paper introduces ideas for a form of Kirigami that allows precise, mechanically driven assembly of 3D mesostructures of diverse materials from 2D micro/nanomembranes with strategically designed geometries and patterns of cuts. Theoretical and experimental studies demonstrate applicability of the methods across length scales from macro to nano, in materials ranging from monocrystalline silicon to plastic, with levels of topographical complexity that significantly exceed those that can be achieved using other approaches. A broad set of examples includes 3D silicon mesostructures and hybrid nanomembrane-nanoribbon systems, including heterogeneous combinations with polymers and metals, with critical dimensions that range from 100 nm to 30 mm. A 3D mechanically tunable optical transmission window provides an application example of this Kirigami process, enabled by theoretically guided design.

Guided Formation of 3D Helical Mesostructures by Mechanical Buckling: Analytical Modeling and Experimental Validation.

Three-dimensional (3D) helical mesostructures are attractive for applications in a broad range of microsystem technologies, due to their mechanical and electromagnetic properties as stretchable interconnects, radio frequency antennas and others. Controlled compressive buckling of 2D serpentine-shaped ribbons provides a strategy to formation of such structures in wide ranging classes of materials (from soft polymers to brittle inorganic semiconductors) and length scales (from nanometer to centimeter), with an ability for automated, parallel assembly over large areas. The underlying relations between the helical configurations and fabrication parameters require a relevant theory as the basis of design for practical applications. Here, we present an analytic model of compressive buckling in serpentine microstructures, based on the minimization of total strain energy that results from various forms of spatially dependent deformations. Experiments at micro- and millimeter-scales, together with finite element analyses (FEA), were exploited to examine the validity of developed model. The theoretical analyses shed light on general scaling laws in terms of three groups of fabrication parameters (related to loading, material and 2D geometry), including a negligible effect of material parameters and a square root dependence of primary displacements on the compressive strain. Furthermore, analytic solutions were obtained for the key physical quantities (e.g., displacement, curvature and maximum strain). A demonstrative example illustrates how to leverage the analytic solutions in choosing the various design parameters, such that brittle fracture or plastic yield can be avoided in the assembly process.

Controlled mechanical buckling for origami-inspired construction of 3D microstructures in advanced materials.

Origami is a topic of rapidly growing interest in both the scientific and engineering research communities due to its promising potential in a broad range of applications. Previous assembly approaches of origami structures at the micro/nanoscale are constrained by the applicable classes of materials, topologies and/or capability of control over the transformation. Here, we introduce an approach that exploits controlled mechanical buckling for autonomic origami assembly of 3D structures across material classes from soft polymers to brittle inorganic semiconductors, and length scales from nanometers to centimeters. This approach relies on a spatial variation of thickness in the initial 2D structures as an effective strategy to produce engineered folding creases during the compressive buckling process. The elastic nature of the assembly scheme enables active, deterministic control over intermediate states in the 2D to 3D transformation in a continuous and reversible manner. Demonstrations include a broad set of 3D structures formed through unidirectional, bidirectional, and even hierarchical folding, with examples ranging from half cylindrical columns and fish scales, to cubic boxes, pyramids, starfish, paper fans, skew tooth structures, and to amusing system-level examples of soccer balls, model houses, cars, and multi-floor textured buildings.

Cryo-Electron Microscopy Reveals Na Infiltration into Separator Pore Free-Volume as a Degradation Mechanism in Na Anode:Liquid Electrolyte Electrochemical Cells.

Batteries utilizing a sodium (Na) metal anode with a liquid electrolyte are promising for affordable large-scale energy storage. However, a deep understanding of the intrinsic degradation mechanisms is limited by challenges in accessing the buried interfaces. Here, cryogenic electron microscopy of intact electrode:separator:electrode stacks is performed and degradation and failure of symmetric Na||Na coin cells occurs through the infiltration of Na metal through the pores of the separator rather than by mechanical puncturing by dendrites is revealed. It is shown the interior structure of the cell (electrode:separator:electrode) must be preserved and deconstructing the cell into different layers for characterization results in artifacts. In intact cell stacks, minimal liquid is found between the electrodes and separator, leading to intimate electrode:separator interfaces. After electrochemical cycling, Na infiltrates into the pore free-volume, growing through the separator to create electrical shorts and degradation. The Na infiltration occurs at interfacial regions devoid of solid-electrolyte interphase (SEI), revealing SEI plays an important role in preventing Na from growing into the separator by being a physical barrier that the plated Na cannot penetrate. These results shed new light on the fundamental failure mechanisms in Na batteries and demonstrate the importance of preserving the cell structure and buried interfaces.

Preparative separation of iridoid glucosides and crocins from Gardeniae Fructus using sequential macroporous resin column chromatography and evaluation of their anti-inflammatory and antioxidant activities.

Iridoid glycosides (geniposide (GP), genipin-1-gentiobioside (GB), etc.) and crocins (crocin Ⅰ (CR1), crocin Ⅱ(CR2), etc.) are two main bioactive components in Gardeniae Fructus (GF), which is a famous traditional Chinese medicine. Iridoid glycosides exhibit many activities and are used to manufacture gardenia blue pigment for the food industry. Crocins are rare natural water-soluble carotenoids that are often used as food colorants. A sequential macroporous resin column chromatography technology composed of HC-500B and HC-900B resins was developed to selectively separate iridoid glucosides and crocins from GF. The adsorption of GP on HC-900B resin was an exothermic process. The adsorption of CR1 on HC-500B resin was an endothermic process. The two kinds of components were completely separated by a sequential resin column. GB and GP were mainly found in product 1 (P1) with purities of 11.38% and 46.83%, respectively, while CR1 and CR2 were mainly found in product 2 (P2) with purities of 12.32% and 1.40%, respectively. The recovery yields of all the compounds were more than 80%. The above results showed that sequential resin column chromatography technology achieved high selectivity and recovery yields. GF extract, P1 and P2 could significantly inhibit the secretion of nitric oxide (NO), tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) in lipopolysaccharide (LPS)-induced RAW264.7 cells, indicating that iridoid glycosides and crocins provide a greater contribution to the anti-inflammatory activity of GF. At the same time, compared to the GF extract and P1, P2 exhibited stronger scavenging activities against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radicals, indicating that crocins may provide a significant contribution to the antioxidant activity of GF.

Design Principles and Applications of Next-Generation High-Energy-Density Batteries Based on Liquid Metals.

Increasing need for the renewable energy supply accelerated the thriving studies of Li-ion batteries, whereas if the high-energy-density Li as well as alkali metals should be adopted as battery electrodes is still under fierce debate for safety concerns. Recently, a group of low-melting temperature metals and alloys that are in liquid phase at or near room-temperature are being reported for battery applications, by which the battery energy could be improved without significant dendrite issue. Besides the dendrite-free feature, liquid metals can also promise various high-energy-density battery designs on the basis of unique materials properties. In this review, the design principles for liquid metals-based batteries from mechanical, electrochemical, and thermodynamical aspects are provided. With the understanding of the theoretical basis, currently reported relevant designs are summarized and analyzed focusing on the working mechanism, effectiveness evaluation, and novel application. An overview of the state-of-the-art liquid metal battery developments and future prospects is also provided in the end as a reference for further research explorations.

Next-Generation Liquid Metal Batteries Based on the Chemistry of Fusible Alloys.

With a long cycle life, high rate capability, and facile cell fabrication, liquid metal batteries are regarded as a promising energy storage technology to achieve better utilization of intermittent renewable energy sources. Nevertheless, conventional liquid metal batteries need to be operated at relatively high temperatures (>240 °C) to maintain molten-state electrodes and high conductivity of electrolytes. Intermediate and room-temperature liquid metal batteries, circumventing complex thermal management as well as issues related to sealing and corrosion, are emerging as a novel energy system for widespread implementation. In this Outlook, we elaborate the appealing features of fusible alloys-based liquid metals for energy storage devices and describe the metallurgical fundamentals, cost, and safety analysis of fusible alloys. Recent advances are discussed covering the rational screening of metallic alloys, interfacial engineering on the electrodes, and design of advanced electrolytes. In the end, we provide perspectives on current challenges and future opportunities in this field. This outlook not only aims to provide a design principle for high performance liquid metal batteries, but also inspires further development of novel energy systems beyond conventional solid-state batteries and high-temperature batteries.

Low-Temperature Multielement Fusible Alloy-Based Molten Sodium Batteries for Grid-Scale Energy Storage.

The sustainable future of modern society relies on the development of advanced energy systems. Alkali metals, such as Li, Na, and K, are promising to construct high-energy-density batteries to complement the fast-growing implementation of renewable sources. The stripping/deposition of alkali metals is compromised by serious dendrite growth, which can be intrinsically eliminated by using molten alkali metal anodes. Up to now, most of the conventional molten alkali metal-based batteries need to be operated at high temperatures. To decrease the operating temperature, we extended the battery chemistry to multielement alloys, which provide more flexibility for wide selection and rational screening of cost-effective and fusible metallic electrodes. On the basis of an integrated experimental and theoretical study, the depressed melting point and enhanced interfacial compatibility are elucidated. The proof-of-concept molten sodium battery enabled by the Bi-Pb-Sn fusible alloy not only circumvents the use of costly Ga and In elements but also delivers attractive performance at 100 °C, holding great promise for grid-scale energy storage.

Redistributing Li-Ion Flux by Parallelly Aligned Holey Nanosheets for Dendrite-Free Li Metal Anodes.

Li metal is the most ideal anode material to assemble rechargeable batteries with high energy density. However, nonuniform Li-ion flux during repeated Li plating and stripping leads to continuous Li dendrite growth and dead Li formation, which causes safety risks and short lifetime and thus impedes the commercialization of Li metal batteries. Here, parallelly aligned holey nanosheets on a Li metal anode are reported to simultaneously redistribute the Li-ion flux in the electrolyte and in the solid-electrolyte interphase, which allows uniform Li-ion distribution as well as fast Li-ion diffusion for reversible Li plating and stripping. With holey MgO nanosheets as an example, the protected Li anodes achieve Coulombic efficiency of ≈99% and ultralong-term reversible Li plating/stripping over 2500 h at a high current density of 10 mA cm-2 . A full-cell battery, using the protected anode, a 4 V Li-ion cathode, and a commercial carbonate electrolyte, shows capacity retention of 90.9% after 500 cycles.

A Ternary Hybrid-Cation Room-Temperature Liquid Metal Battery and Interfacial Selection Mechanism Study.

The dendrite-free sodium-potassium (Na-K) liquid alloy composed of two alkali metals is one of the ideal alternatives for Li metal as an anode material while maintaining large capacity, low potential, and high abundance. However, Na- or K-ion batteries have limited cathode materials that can deliver stably large capacity. Combining advantages of both, a hybrid-cation liquid metal battery is designed for a Li-ion-insertion-based cathode to deliver stable high capacity using a Na-K liquid anode to avoid dendrites. The mechanical property of the Na-K alloy is confirmed by simulation and experimental characterization, which leads to stable cycling performance. The charge carrier selection principle in this ternary hybrid-cation system is investigated, showing consistency with the proposed interfacial layer formation and ion distribution mechanism for the electrochemical process as well as the good stability. With Li ions contributing stable cycling as the cathode charge carrier, the K ion working as charge carrier on the anode, and Na as the medium to liquefy K metal, such a ternary hybrid battery system not only inherits the rich battery chemistry of Li-insertion cathodes but also broadens the understanding of alkali metal alloys and hybrid-ion battery chemistry.

Room-Temperature All-Liquid-Metal Batteries Based on Fusible Alloys with Regulated Interfacial Chemistry and Wetting.

Liquid metal batteries are regarded as potential electrochemical systems for stationary energy storage. Currently, all reported liquid metal batteries need to be operated at temperatures above 240 °C to maintain the metallic electrodes in a molten state. Here, an unprecedented room-temperature liquid metal battery employing a sodium-potassium (Na-K) alloy anode and gallium (Ga)-based alloy cathodes is demonstrated. Compared with lead (Pb)- and mercury (Hg)-based liquid metal electrodes, the nontoxic Ga alloys maintain high environmental benignity. On the basis of improved wetting and stabilized interfacial chemistry, such liquid metal batteries deliver stable cycling performance and negligible self-discharge. Different from the conventional interphase between a typical solid electrode and a liquid electrolyte, the interphase between a liquid metal and a liquid electrolyte is directly visualized via advanced 3D chemical analysis. Insights into this new type of liquid electrode/electrolyte interphase reveal its important role in regulating charge carriers and stabilizing the redox chemistry. With facile cell fabrication, simplified battery structures, high safety, and low maintenance costs, room-temperature liquid metal batteries not only show great prospects for widespread applications, but also offer a pathway toward developing innovative energy-storage devices beyond conventional solid-state batteries or high-temperature batteries.

Reversible redox chemistry in azobenzene-based organic molecules for high-capacity and long-life nonaqueous redox flow batteries.

Redox-active organic molecules have drawn extensive interests in redox flow batteries (RFBs) as promising active materials, but employing them in nonaqueous systems is far limited in terms of useable capacity and cycling stability. Here we introduce azobenzene-based organic compounds as new active materials to realize high-performance nonaqueous RFBs with long cycling life and high capacity. It is capable to achieve a stable long cycling with a low capacity decay of 0.014% per cycle and 0.16% per day over 1000 cycles. The stable cycling under a high concentration of 1 M is also realized, delivering a high reversible capacity of ~46 Ah L-1. The unique lithium-coupled redox chemistry accompanied with a voltage increase is observed and revealed by experimental characterization and theoretical simulation. With the reversible redox activity of azo group in π-conjugated structures, azobenzene-based molecules represent a class of promising redox-active organics for potential grid-scale energy storage systems.

Phenothiazine-Based Organic Catholyte for High-Capacity and Long-Life Aqueous Redox Flow Batteries.

Redox-active organic materials have been considered as one of the most promising "green" candidates for aqueous redox flow batteries (RFBs) due to the natural abundance, structural diversity, and high tailorability. However, many reported organic molecules are employed in the anode, and molecules with highly reversible capacity for the cathode are limited. Here, a class of heteroaromatic phenothiazine derivatives is reported as promising positive materials for aqueous RFBs. Among these derivatives, methylene blue (MB) possesses high reversibility with extremely fast redox kinetics (electron-transfer rate constant of 0.32 cm s-1 ), excellent stability in both neutral and reduced states, and high solubility in an acetic-acid-water solvent, leading to a high reversible capacity of ≈71 Ah L-1 . Symmetric RFBs based on MB electrolyte demonstrate remarkable stability with no capacity decay over 1200 cycles. Even concentrated MB catholyte (1.5 m) is still able to deliver stable capacity over hundreds of cycles in a full cell system. The impressive cell performance validates the practicability of MB for large-scale electrical energy storage.