Materials for lithium-ion battery safety

Electrolytes for Multivalent Metal-Ion Batteries: Current Status and Future Prospect

Electrochemical energy storage has experienced unprecedented advancements in recent years and extensive discussions and reviews on the progress of multivalent metal-ion batteries have been made mainly from the aspect of electrode materials, but relatively little work comprehensively discusses and provides an outlook on the development of electrolytes in these systems. Under this circumstance, this Review will initially introduce different types of electrolytes in current multivalent metal-ion batteries and explain the basic ion conduction mechanisms, preparation methods, and pros and cons. On this basis, we will discuss in detail the research and development of electrolytes for multivalent metal-ion batteries in recent years, and finally, critical challenges and prospects for the application of electrolytes in multivalent metal-ion batteries will be put forward.

Perovskite-Type SrVO3 as High-Performance Anode Materials for Lithium-Ion Batteries

Perovskite-type oxides, characterized by excellent multifunctional physical and chemical properties, are widely used in ferroelectric, piezoelectric, energy conversion, and storage applications. It is shown here that the perovskite-type SrVO₃ can achieve excellent electrochemical performance as lithium-ion battery anodes thanks to its high electrically and ionically conductivity. Conducting additive-free SrVO₃ electrodes can deliver a high specific capacity of 324 mAh g^-1 at a safe and low average working potential of ≈0.9 V vs Li/Li⁺ together with excellent high-rate performance. A high areal capacity of ≈5.4 mAh cm^-2 is obtained using an ultrathick (≈120 μm) electrode. Moreover, the fully lithiated SrVO₃ electrode exhibits only 2.3% volume expansion that is explained by a simple solid-solution Li⁺ -storage mechanism, resulting in good cycling stability of the electrode. This study highlights the perovskite-type SrVO₃ as a promising Li⁺ -storage anode and provides opportunities for exploring a variety of perovskite oxides as next-generation metal-ion battery anodes.

Overcharge-Induced Phase Heterogeneity and Resultant Twin-Like Layer Deformation in Lithium Cobalt Oxide Cathode for Lithium-Ion Batteries

Overcharging is expected to be one of the solutions to overcome the current energy density limitation of lithium-ion battery cathodes, which will support the rapid growth of the battery market. However, high-voltage charging often poses a major safety threat including fatal incendiary incidents, limiting further application. Numerous researches are dedicated to the disadvantages of the overcharging process; nonetheless, the urgent demand for addressing failure mechanisms is still unfulfilled. Herein, it is revealed that overcharging induces phase heterogeneity into layered and cobalt oxide phases, and consequent "twin-like deformation" in lithium cobalt oxide. The interplay between the uncommon cobalt(III) oxide and the deformation is investigated by revealing the atomistic formation mechanism. Most importantly, abnormal cracking is discovered in the vicinity of the cobalt oxide where structural instability induces substantial contraction. In addition, surface degradation is widely observed in the crack boundary inside the particle. As unintentional overcharging can occur due to local imbalance in state-of-charge in severe operating conditions such as fast charging, the issues on overcharging should be emphasized to large extent and this study provides fundamental knowledge of overcharge by elucidating the crack development mechanism of layered cathodes, which is expected to broaden the horizon into high voltage operation.

Engineering by Cuts: How Kirigami Principle Enables Unique Mechanical Properties and Functionalities

Kirigami, the ancient art of paper cutting, has evolved into a design and fabrication framework to engineer multi-functional materials and structures at vastly different scales. By slit cutting with carefully designed geometries, desirable mechanical behaviors-such as accurate shape morphing, tunable auxetics, super-stretchability, buckling, and multistability-can be imparted to otherwise inflexible sheet materials. In addition, the kirigami sheet provides a versatile platform for embedding different electronic and responsive components, opening up avenues for building the next generations of metamaterials, sensors, and soft robotics. These promising potentials of kirigami-based engineering have inspired vigorous research activities over the past few years, generating many academic publications. Therefore, this review aims to provide insights into the recent advance in this vibrant field. In particular, this paper offers the first comprehensive survey of unique mechanical properties induced by kirigami cutting, their underlying physical principles, and their corresponding applications. The synergies between design methodologies, mechanics modeling, advanced fabrication, and material science will continue to mature this promising discipline.

Well-Defined Nanostructures by Block Copolymers and Mass Transport Applications in Energy Conversion

With the speedy progress in the research of nanomaterials, self-assembly technology has captured the high-profile interest of researchers because of its simplicity and ease of spontaneous formation of a stable ordered aggregation system. The self-assembly of block copolymers can be precisely regulated at the nanoscale to overcome the physical limits of conventional processing techniques. This bottom-up assembly strategy is simple, easy to control, and associated with high density and high order, which is of great significance for mass transportation through membrane materials. In this review, to investigate the regulation of block copolymer self-assembly structures, we systematically explored the factors that affect the self-assembly nanostructure. After discussing the formation of nanostructures of diverse block copolymers, this review highlights block copolymer-based mass transport membranes, which play the role of “energy enhancers” in concentration cells, fuel cells, and rechargeable batteries. We firmly believe that the introduction of block copolymers can facilitate the novel energy conversion to an entirely new plateau, and the research can inform a new generation of block copolymers for more promotion and improvement in new energy applications.

Ionic Switches with Positive Temperature Coefficient Enabled by Phase Separation within Hydrogel Electrolytes

Ionic switches with a positive temperature coefficient (PTC) effect are highly desirable in the fabrication of smart electrolytes for the safety protection of electrochemical energy devices. However, most of them encounter liquid leaking or volume shrinking problems, limiting their long-term and stable operations. Herein, a PTC-type ionic switch is introduced based on a poly(acrylic acid) (PAA) hydrogel soaked by calcium acetate (CaAc), with a resistance change of six times in maximum between the homogeneous and phase separated state. The PTC effect is owing to the strong phase separation upon heating where the ion transport is restricted. Such a hydrogel-based PTC-type ionic switch is in the solid state and isochoric during phase separation without leaking or shrinking issues. The influence of different CaAc soaking concentrations is investigated. A simplified model consisting of interconnected ion channels is proposed based on microstructure analysis. A smart supercapacitor is successfully demonstrated by this PTC ionic switch with a safety protection ability. The research here would provide a new pathway for the design and development of PTC-type ionic switches in the safety protection of electrochemical energy storage devices.

Pomegranate-Inspired Graphene Parcel Enables High-Performance Dendrite-Free Lithium Metal Anodes

Uncontrolled lithium dendrites seriously hinder the commercialization of lithium metal batteries in comparison to the durable lithium-ion batteries. Herein, inspired by squashy pomegranate structure, a novel loading strategy of metallic lithium (Li) is introduced to construct dendrite-free Li metal anodes through porous reduced graphene oxide/Au (PRGO/Au) composite microrods (MRs) as unique storage parcels. The abundant internal voids and robust host structure are capable of achieving high mass loading of Li metal and effectively alleviating the conceivable volume change during cycling, accompanied by the preferential selective plating/stripping of Li inside the graphene-based MRs with the embedded Au nanonuclei. As a result, the obtained PRGO/Au-Li anodes deliver a long-lifespan stable cycling up to 600 h with a high specific capacity of ≈2140 mA h g^-1 and voltage hysteresis as low as 20 mV in the absence of dendrites. The assembled full cells exhibit excellent rate capability and cycling stability. This work provides an alternative strategy to construct advanced high-energy-density lithium batteries via the unique 1D bioinspired graphene-based packaging strategy.

High-Performance and Highly Safe Solvate Ionic Liquid-Based Gel Polymer Electrolyte by Rapid UV-Curing for Lithium-Ion Batteries

Utilizing ionic liquids (ILs) with low flammability as the precursor component for a gel polymer electrolyte is a smart strategy out of safety concerns. Solvate ionic liquids (SILs) consist of equimolar lithium bis(trifluoromethylsulfonyl)imide and tetraglyme, alleviating the main problems of high viscosity and low Li⁺ conductivity of conventional ILs. In this study, within a very short time of 30 s, a SIL turns immobile using efficient and controllable UV-curing with an ethoxylated trimethylolpropane triacrylate (ETPTA) network, forming a homogeneous SIL-based gel polymer electrolyte (SGPE) with enhanced thermal stability (216 °C), robust mechanical strength (compression modulus: 1.701 MPa), and high ionic conductivity (0.63 mS cm^-1 at room temperature). A Li|SGPE|LiFePO₄ cell demonstrates high charge/discharge reversibility and cycling stability with a capacity retention rate of 99.7% after 750 cycles and an average Coulombic efficiency of 99.7%, owing to its excellent electrochemical compatibility with Li-metal. A close-contact electrode/electrolyte interface is formed by in situ curing of the electrolyte on the electrode surface, which enables the pouch full cell to work stably under the conditions of cutting/bending. In view of the excellent mechanical, thermal, and electrochemical performances of SGPE, it is believed to be a promising gel polymer electrolyte for constructing high-safety lithium-ion batteries (LIBs).

Ionization of Decamethylmanganocene: Insights from the DFT-Assisted Laser Spectroscopy

Metallocenes represent one of the most important classes of organometallics with wide prospects for practical use in various fields of chemistry, materials science, molecular electronics, and biomedicine. Many applications of these metal complexes are based on their ability to form molecular ions. We report the first results concerning the changes in the molecular and electronic structure of decamethylmanganocene, Cp*₂Mn, upon ionization provided by the high-resolution mass-analyzed threshold ionization (MATI) spectroscopy supported by DFT calculations. The precise ionization energy of Cp*₂Mn is determined as 5.349 ± 0.001 eV. The DFT modeling of the MATI spectrum shows that the main structural deformations accompanying the detachment of an electron consist in the elongation of the Mn-C bonds and a change in the Me out-of-plane bending angles. Surprisingly, the DFT calculations predict that most of the reduction in electron density (ED) upon ionization is associated with the hydrogen atoms of the substituents, despite the metal character of the ionized orbital. However, the ED difference isosurfaces reveal a complex mechanism of the charge redistribution involving also the carbon atoms of the molecule.

Proton Storage in Metallic H1.75MoO3 Nanobelts through the Grotthuss Mechanism

The proton, as the cationic form of the lightest element-H, is regarded as most ideal charge carrier in "rocking chair" batteries. However, current research on proton batteries is still at its infancy, and they usually deliver low capacity and suffer from severe acidic corrosion. Herein, electrochemically activated metallic H_1.75MoO₃ nanobelts are developed as a stable electrode for proton storage. The electrochemically pre-intercalated protons not only bond directly with the terminal O3 site via strong O-H bonds but also interact with the oxygens within the adjacent layers through hydrogen bonding, forming a hydrogen-bonding network in H_1.75MoO₃ nanobelts and enabling a diffusion-free Grotthuss mechanism as a result of its ultralow activation energy of ∼0.02 eV. To the best of our knowledge, this is the first reported inorganic electrode exhibiting Grotthuss mechanism-based proton storage. Additionally, the proton intercalation into MoO₃ with formation of H_1.75MoO₃ induces strong Jahn-Teller electron-phonon coupling, rendering a metallic state. As a consequence, the H_1.75MoO₃ shows an outstanding fast charging performance and maintains a capacity of 111 mAh/g at 2500 C, largely outperforming the state-of-art battery electrodes. More importantly, a symmetric proton ion full cell based on H_1.75MoO₃ was assembled and delivered an energy density of 14.7 Wh/kg at an ultrahigh power density of 12.7 kW/kg, which outperforms those of fast charging supercapacitors and lead-acid batteries.

A Minireview on the Regeneration of NCM Cathode Material Directly from Spent Lithium-Ion Batteries with Different Cathode Chemistries

Research on the regeneration of cathode materials of spent lithium-ion batteries for resource reclamation and environmental protection is attracting more and more attention today. However, the majority of studies on recycling lithium-ion batteries (LIBs) placed the emphasis only on recovering target metals, such as Co, Ni, and Li, from the cathode materials, or how to recycle spent LIBs by conventional means. Effective reclamation strategies (e.g., pyrometallurgical technologies, hydrometallurgy techniques, and biological strategies) have been used in research on recycling used LIBs. Nevertheless, none of the existing reviews of regenerating cathode materials from waste LIBs elucidated the strategies to regenerate lithium nickel manganese cobalt oxide (NCM or LiNixCoyMnzO2) cathode materials directly from spent LIBs containing other than NCM cathodes but, at the same time, frequently used commercial cathode materials such as LiCoO2 (LCO), LiFePO4 (LFP), LiMn2O4 (LMO), etc. or from spent mixed cathode materials. This review showcases the strategies and techniques for regenerating LiNixCoyMnzO2 cathode active materials directly from some commonly used and different types of mixed-cathode materials. The article summarizes the various technologies and processes of regenerating LiNixCoyMnzO2 cathode active materials directly from some individual cathode materials and the mixed-cathode scraps of spent LIBs without their preliminary separation. In the meantime, the economic benefits and diverse synthetic routes of regenerating LiNixCoyMnzO2 cathode materials reported in the literature are analyzed systematically. This minireview can lay guidance and a theoretical basis for restoring LiNixCoyMnzO2 cathode materials.

Ethynyl and Furyl Functionalized Porphyrin Complexes as New Organic Cathodes Enabling High Power Density and Long-Term Cycling Stability

Organic cathode materials have recently attracted abundant attention due to their flexible structural tunability and recyclability. However, the low intrinsic electrical conductivity and high solubility in electrolytes of organic electrode materials have significantly limited their practical application. Herein, we present [5,15-bis(ethynyl)-10,20-difurylporphinato] copper(II) (CuDEOP) as a new cathode for rechargeable organic lithium batteries (ROLBs). The combination of both ethynyl and furyl groups of the CuDEOP cathode with a nanorod structure renders it with enhanced structural stability and an extended delocalized π-electron system to deliver excellent cycling stability (capacity retention of 76% after 6000 cycles) and a high power density (16 kW kg^-1). The furyl electroactive groups participate in charge storage contribution to achieve a reversible six-electron-transfer redox reaction in a specific voltage range. The mechanism characterizations indicate that the nitrogen atoms on the porphyrin ring act as active sites to alternatively store both PF₆^- anions and Li⁺ cations, and the charge storage process is a pseudocapacitive-dominated reaction. This observation will offer a new avenue for designing functionalized molecules for electrochemical energy-storage (EES) systems.

Two-Dimensional Black Phosphorus: Preparation, Passivation and Lithium-Ion Battery Applications

As a new type of single element direct-bandgap semiconductor, black phosphorus (BP) shows many excellent characteristics due to its unique two-dimensional (2D) structure, which has great potential in the fields of optoelectronics, biology, sensing, information, and so on. In recent years, a series of physical and chemical methods have been developed to modify the surface of 2D BP to inhibit its contact with water and oxygen and improve the stability and physical properties of 2D BP. By doping and coating other materials, the stability of BP applied in the anode of a lithium-ion battery was improved. In this work, the preparation, passivation, and lithium-ion battery applications of two-dimensional black phosphorus are summarized and reviewed. Firstly, a variety of BP preparation methods are summarized. Secondly, starting from the environmental instability of BP, different passivation technologies are compared. Thirdly, the applications of BP in energy storage are introduced, especially the application of BP-based materials in lithium-ion batteries. Finally, based on preparation, surface functionalization, and lithium-ion battery of 2D BP, the current research status and possible future development direction are put forward.

Advancing chemical hazard assessment with decision analysis: A case study on lithium-ion and redox flow batteries used for energy storage

Batteries are important for promoting renewable energy, but, like most engineered products, they contain multiple hazardous materials. The purpose of this study is to evaluate industrial-scale batteries using GreenScreen® for Safer Chemicals, an established chemical hazard assessment (CHA) framework, and to develop a systematic, transparent methodology to quantify the CHA results, harmonize them, and aggregate them into single-value hazard scores, which can facilitate quantitative comparison and a robust evaluation of data gaps, inconsistencies, and uncertainty through the implementation of carefully selected scenarios and stochastic multicriteria acceptability analysis (SMAA). Using multiple authoritative toxicity data sources, six battery products are evaluated: three lithium-ion batteries (lithium iron phosphate, lithium nickel cobalt manganese hydroxide, and lithium manganese oxide), and three redox flow batteries (vanadium redox, zinc-bromine, and all-iron). The CHA results indicate that many materials in these batteries, including reagents and intermediates, inherently exhibit high hazard; therefore, safer materials should be identified and considered in future designs. The scenario analysis and SMAA, combined, provide a quantitative evaluation framework to support the decision-making needed to compare alternative technologies. Thus, this study highlights specific strategies to reduce the use of hazardous materials in complex engineered products before they are widely used in this rapidly-expanding industry sector.

Role of Interfaces in Solid-State Batteries

Solid-state batteries (SSBs) are considered as one of the most promising candidates for the next-generation energy-storage technology, because they simultaneously exhibit high safety, high energy density, and wide operating temperature range. The replacement of liquid electrolytes with solid electrolytes produces numerous solid-solid interfaces within the SSBs. A thorough understanding on the roles of these interfaces is indispensable for the rational performance optimization. In this review, the interface issues in the SSBs, including internal buried interfaces within solid electrolytes and composite electrodes, and planar interfaces between electrodes and solid electrolyte separators or current collectors are discussed. The challenges and future directions on the investigation and optimization of these solid-solid interfaces for the production of the SSBs are also assessed.

Improving the Ionic Conductivity of PEGDMA-Based Polymer Electrolytes by Reducing the Interfacial Resistance for LIBs

Polymer electrolytes (PEs) based on poly(ethylene oxide) (PEO) have gained increasing interest in lithium-ion batteries (LIBs) and are expected to solve the safety issue of commercial liquid electrolytes due to their excellent thermal and mechanical stability, suppression of lithium dendrites and shortened battery assembly process. However, challenges, such as high interfacial resistance between electrolyte and electrodes and poor ionic conductivity (σ) at room temperature (RT), still limit the use of PEO-based PEs. In this work, an in situ PEO-based polymer electrolyte consisting of polyethylene glycol dimethacrylate (PEGDMA) 1000, lithium bis(fluorosulfonyl)imide (LiFSI) and DMF is cured on a LiFePO4 (LFP) cathode to address the above-mentioned issues. As a result, optimized PE shows a promising σ and lithium-ion transference number (tLi+) of 6.13 × 10-4 S cm-1 and 0.63 at RT and excellent thermal stability up to 136 °C. Moreover, the LiFePO4//Li cell assembled by in situ PE exhibits superior discharge capacity (141 mAh g-1) at 0.1 C, favorable Coulombic efficiency (97.6%) after 100 cycles and promising rate performance. This work contributes to modifying PEO-based PE to force the interfacial contact between the electrolyte and the electrode and to improve LIBs' performance.

Priority and Prospect of Sulfide-Based Solid-Electrolyte Membrane

All-solid-state lithium batteries (ASSLBs) employing sulfide solid electrolytes (SEs) promise sustainable energy storage systems with energy-dense integration and critical intrinsic safety, yet they still require cost-effective manufacturing and the integration of thin membrane-based SE separators into large-format cells to achieve scalable deployment. This review, based on an overview of sulfide SE materials, is expounded on why implementing a thin membrane-based separator is the priority for mass production of ASSLBs and critical criteria for capturing a high-quality thin sulfide SE membrane are identified. Moreover, from the aspects of material availability, membrane processing, and cell integration, the major challenges and associated strategies are described to meet these criteria throughout the whole manufacturing chain to provide a realistic assessment of the current status of sulfide SE membranes. Finally, future directions and prospects for scalable and manufacturable sulfide SE membranes for ASSLBs are presented.

Formation of Nanochannels Using Polypropylene and Acetylcellulose for Stable Separators

In this study, a polymer separator with enhanced thermal stability is prepared to solve the problem of thermal durability of lithium-ion battery separators. This separator is manufactured by coating a solution of acetyl cellulose and glycerin on polypropylene. The added glycerin reacts with the acetyl cellulose chains, helping the chains become flexible, and promotes the formation of many pores in the acetyl cellulose. To improve the thermal stability of the separator, a mixed solution of acetyl cellulose and glycerin was coated twice on the PP membrane film. Water pressure is applied using a water treatment equipment to partially connect the pores of a small size in each layer and for the interaction between the PP and acetyl cellulose. SEM is used to observe the shape, size, and quantity of pores. TGA and FT-IR are used to observe the interactions. Average water flux data of the separators is 1.42 LMH and the decomposition temperature increases by about 60 °C compared to the neat acetyl cellulose. It is confirmed that there is an interaction with PP between the functional groups of acetyl cellulose.

Concentrated Electrolytes Enabling Stable Aqueous Ammonium-Ion Batteries

Rechargeable aqueous batteries are promising devices for large-scale energy-storage applications because of their low-cost, inherent safety, and environmental friendliness. Among them, aqueous ammonium-ion (NH₄ ⁺ ) batteries (AAIB) are currently emerging owing to the fast diffusion kinetics of NH₄ ⁺ . Nevertheless, it is still a challenge to obtain stable AAIB with relatively high output potential, considering the instability of many electrode materials in an aqueous environment. Herein, a cell based on a concentrated (5.8 m) aqueous (NH₄ )₂ SO₄ electrolyte, ammonium copper hexacyanoferrate (N-CuHCF) as the positive electrode (cathode), and 3,4,9,10-perylene-bis(dicarboximide) (PTCDI) as the negative electrode (anode) is reported. The solvation structure, electrochemical properties, as well as the electrode-electrolyte interface and interphase are systematically investigated by the combination of theoretical and experimental methods. The results indicate a remarkable cycling performance of the low-cost rocking-chair AAIB, which offers a capacity retention of ≈72% after 1000 cycles and an average output potential of ≈1.0 V.

Synthesis and Electrochemical Performance of the Orthorhombic V2O5·nH2O Nanorods as Cathodes for Aqueous Zinc Batteries

Aqueous zinc-ion batteries offer the greatest promise as an alternative technology for low-cost and high-safety energy storage. However, the development of high-performance cathode materials and their compatibility with aqueous electrolytes are major obstacles to their practical applications. Herein, we report the synthesis of orthorhombic V₂O₅·nH₂O nanorods as cathodes for aqueous zinc batteries. As a result, the electrode delivers a reversible capacity as high as 320 mAh g⁻¹ at 1.0 A g⁻¹ and long-term cycling stability in a wide window of 0.2 to 1.8 V using a mild ZnSO₄ aqueous electrolyte. The superior performance can be attributed to the improved stability of materials, inhibited electrolyte decomposition and facilitated charge transfer kinetics of such materials for aqueous zinc storage. Furthermore, a full cell using microsized Zn powder as an anode within capacity-balancing design exhibits high capacity and stable cycling performance, proving the feasibility of these materials for practical application.

Tensile Property and Corrosion Performance of Ag Microalloying of Al-Cu Alloys for Positive Electrode Current Collectors of Li-Ion Batteries

The development of a current collector for Li-ion batteries is of great significance for improving the performance of Li-ion batteries. Tensile property and corrosion performance of the positive electrode current collectors are an indispensable prerequisite for the realization of high-performance Li-ion batteries. In our study, the effects of Ag alloying on the microscopic structure, electrical conductivity, tensile property and corrosion resistance of Al-xCu (x = 0.1–0.15%) alloy foils were investigated. Moderate Ag addition on the Al-Cu alloy could reduce the size of second phases and promote the formation of second phases. The tensile strength of the Al-0.1Cu-0.1Ag alloy was higher than that of the Al-0.1Cu alloy at both room and high temperatures. All of the alloy foils demonstrated high electrical conductivity around 58% ICAS. The corrosion potential and corrosion current density of the Al-0.1Cu alloy were demonstrated by Tafel polarization to be −873 mV and 37.12 μA/cm², respectively. However, the Al-0.1Cu-0.1Ag alloy showed enhanced corrosion resistance after the Ag element was added to the Al-0.1Cu alloy, and the Al-0.1Cu-0.1Ag alloy had a greater positive corrosion potential of −721 mV and a lower corrosion current density of 1.52 μA/cm², which suggests that the Ag element could significantly improve the corrosion resistance of the Al-Cu alloy.

Fast magnesium ion conducting isopropylamine magnesium borohydride enhanced by hydrophobic interactions

New materials for the next generation of electrochemical energy storage devices such as batteries are of extreme importance. Here we investigate the structure, ionic conductivity and thermal properties of isopropylamine magnesium borohydride based composites with different compositions, Mg(BH₄)₂·x(CH₃)₂CHNH₂, x = 0.5, 0.9, 1.25, 1.5, 1.75, 2.5, 3.1. Three new compounds are discovered, x = 1, 2, and 3 and the monoclinic structure of Mg(BH₄)₂·2(CH₃)₂CHNH₂ (P2₁/c) is investigated in detail. This structure consists of neutral complexes [Mg(BH₄)₂((CH₃)₂CHNH₂)₂] di-hydrogen bonded to form layers and these layers are connected by hydrophobic interactions via the isopropyl moieties. The orthorhombic unit cell of Mg(BH₄)₂·(CH₃)₂CHNH₂ was also determined, a = 9.78, b = 12.17 and c = 17.24 Å. In general, the samples are thermally stable up to 50 °C where they started to become softer, and at 70 °C isopropylamine release and melting started. The highest Mg²⁺ ionic conductivity was that of Mg(BH₄)₂·1.5(CH₃)₂CHNH₂, σ(Mg²⁺) = 2.7 × 10^-4 S cm^-1 at 45 °C, with an activation energy of E_A = 1.22 eV. Furthermore, reversible stripping/plating of Mg was displayed at 45 °C, with an oxidative stability of 1.2 V vs. Mg/Mg²⁺. The addition of MgO nanoparticles (75 wt%) improves the mechanical and thermal stability, and decreases the activation energy, to E_A = 0.56 eV. Thereby the Mg²⁺ conductivity is increased at low temperature. This suggests that the hydrophobic interactions contribute to the high ionic conductivity in the solid state, which opens a new avenue for design and discovery of electrolyte materials.

Heterogeneity and Nanostructure of Superconcentrated LiTFSI-EmimTFSI Hybrid Aqueous Electrolytes: Beyond the 21 m Limit of Water-in-Salt Electrolyte

Ionic liquids such as EmimTFSI (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide) have been found to improve the solubility of LiTFSI salt in water-in-salt electrolyte (WiSE) from 21 to 60 m. However, the molecular origin of such enhancement in the solubility is still unknown. In the present work, we elucidate the microscopic structures of LiTFSI-EmimTFSI-based hybrid aqueous electrolytes and compare them with the structure of LiTFSI-based WiSE using molecular dynamics simulations. Our analysis reveals the presence of alternating water-rich clusters and TFSI-rich extended domains in the WiSE. In these clusters and domains, the Li⁺ ions reside such that the total number of oxygen atoms around them is conserved to four, where water contributes about three oxygen atoms. The addition of EmimTFSI in the WiSE results in removal of water from the nearest-neighbor solvation shell of TFSI^- ions but not from the Li⁺ ions. Significant structural changes are observed when LiTFSI salt is further added to LiTFSI-EmimTFSI aqueous solution. In both the hybrid electrolytes, water and Emim⁺ cations are found to avoid each other. The simulated X-ray scattering structure factor reveals the presence of larger length-scale heterogeneity in the most concentrated solution of the hybrid aqueous electrolyte. We observe that this nanoscale heterogeneity originates from a water-TFSI-Emim-TFSI-water-TFSI-Emim-TFSI-like arrangement in which Li⁺ ions are dispersed such that the coordination number of oxygen atoms around them is enhanced to five, wherein the major contribution comes from the TFSI^- ions. We envision that the enhanced LiTFSI solubility originates from the replacement of water molecules with TFSI^- ions in the first solvation shell of Li⁺ ions.

Interface Engineering to Boost Thermal Safety of Microsized Silicon Anodes in Lithium-Ion Batteries

Battery safety is vital to the application of lithium-ion batteries (LIBs), especially for high energy density cells applied in electric vehicles. As an anode material with high theoretical capacity and natural abundance, Si has received extensive attention for LIBs. However, it suffers from severe electrode pulverization during cycling due to large volume changes and an unstable solid electrolyte interphase (SEI), resulting in accelerated capacity fading and even safety hazards. Therefore, safe and long-term cycling of Si-based anodes, especially under high-temperature cycling, is highly challenging for state-of-the-art high-energy LIBs. The thermal behavior of SEI is crucial for a high safety battery as the decomposition of SEI is the first step in thermal runaway. Here, highly reversible and thermotolerant microsized Si anodes for safe LIBs are demonstrated. Comprehensive electrochemical/mechanical/thermochemical behaviors of the SEI are systematically investigated. The rational design of robust SEI endows the Si-based cells with long-term durability at elevated temperatures and superior thermal safety. This work paves the way for designing industrial-scale, low-cost, microsized Si anodes with applications in next-generation LIBs with high energy densities and high safety.

Understanding of the Electrochemical Behavior of Lithium at Bilayer-Patched Epitaxial Graphene/4H-SiC

Novel two-dimensional materials (2DMs) with balanced electrical conductivity and lithium (Li) storage capacity are desirable for next-generation rechargeable batteries as they may serve as high-performance anodes, improving output battery characteristics. Gaining an advanced understanding of the electrochemical behavior of lithium at the electrode surface and the changes in interior structure of 2DM-based electrodes caused by lithiation is a key component in the long-term process of the implementation of new electrodes into to a realistic device. Here, we showcase the advantages of bilayer-patched epitaxial graphene on 4H-SiC (0001) as a possible anode material in lithium-ion batteries. The presence of bilayer graphene patches is beneficial for the overall lithiation process because it results in enhanced quantum capacitance of the electrode and provides extra intercalation paths. By performing cyclic voltammetry and chronoamperometry measurements, we shed light on the redox behavior of lithium at the bilayer-patched epitaxial graphene electrode and find that the early-stage growth of lithium is governed by the instantaneous nucleation mechanism. The results also demonstrate the fast lithium-ion transport (~4.7-5.6 × 10-7 cm2∙s-1) to the bilayer-patched epitaxial graphene electrode. Raman measurements complemented by in-depth statistical analysis and density functional theory calculations enable us to comprehend the lithiation effect on the properties of bilayer-patched epitaxial graphene and ascribe the lithium intercalation-induced Raman G peak splitting to the disparity between graphene layers. The current results are helpful for further advancement of the design of graphene-based electrodes with targeted performance.

Interface and electronic structure engineering induced Prussian blue analogues with ultra-stable capability for aqueous NH4+ storage

Aqueous ammonium ion batteries (AAIBs) are considered potential energy storage solutions due to their faster kinetics, eco-friendliness, and high safety. Yet, appropriate electrode material for AAIBs is in continual investigation. Here, Prussian blue analogues (PBAs), Na_0.73Ni[Fe(CN)₆]_0.88, are applied by a covalent bond assisted engineering with in situ polyaniline (PANI) polymerization. The synthesized PANI/Na_0.73Ni[Fe(CN)₆]_0.88 hybrid (PNFF) inherited the advantages of the high conductivity of PANI and the stability of PBAs. The content of PANI had an effect on the electrochemical performance of PNFF. When served as cathode for AAIBs, the as-prepared PNFF-60 (PNFF with adjusted PANI content) delivers an enhanced reversible capacity of 92.5 mA h g^-1 at 100 mA g^-1 after 200 cycles. Even at a high current density of 2000 mA g^-1, 95.2% capacity retention (1000 cycles) can be achieved by PNFF-60. The ammonium storage mechanism of PNFF-60 is fully investigated by in situ Raman and ex situ XPS/FTIR analysis. Moreover, an aqueous NH⁴⁺ full cell is assembled by coupling the polyimide@MXene (PI@MXene) anode, exhibiting durable cycling stability. This work adds to the understanding of constructing PBAs-based hybrid electrodes for ammonium ion storage devices.

Carbon-Based Modification Materials for Lithium-ion Battery Cathodes: Advances and Perspectives

Lithium-ion batteries (LIBs) have attracted great attention as an advanced power source and energy-storage device for years due to their high energy densities. With rapid growing demands for large reversible capacity, high safety, and long-period stability of LIBs, more explorations have been focused on the development of high-performance cathode materials in recent decades. Carbon-based materials are one of the most promising cathode modification materials for LIBs due to their high electrical conductivity, large surface area, and structural mechanical stability. This feature review systematically outlines the significant advances of carbon-based materials for LIBs. The commonly used synthetic methods and recent research advances of cathode materials with carbon coatings are first represented. Then, the recent achievements and challenges of carbon-based materials in LiCoO2, LiNixCoyAl1-x-yO2, and LiFePO4 cathode materials are summarized. In addition, the influence of different carbon-based nanostructures, including CNT-based networks and graphene-based architectures, on the performance of cathode materials is also discussed. Finally, we summarize the challenges and perspectives of carbon-based materials on the cathode material design for LIBs.

Enabling Scalable Polymer Electrolyte with Synergetic Ion Conductive Channels via a Two Stage Rheology Tuning UV Polymerization Strategy

Lithium metal batteries with polyethylene oxide (PEO) electrolytes are considered as one of the ideal candidates for next generation power sources. However, the low ambient operation capability and conventional solvent-based fabrication process of PEO limit their large-scale application. In this work, a comb-like quasi-solid polymer electrolyte (QPE) reinforced with polyethylene glycol terephthalate nonwoven is fabricated. Combining the density functional theory calculation analysis and polymer structure design, optimized and synergized ion conductive channels are established by copolymerization of tetrahydrofurfuryl acrylate and introduction of plasticizer tetramethyl urea. Additionally, a unique two-stage solventless UV polymerization strategy is utilized for rheology tuning and electrolyte fabrication. Compared with the conventional one-step UV process, this strategy is ideally suited for the roll-to-roll continuous coating fabrication process with environmental friendliness. The fabricated QPE exhibits high ionic conductivity of 0.40 mS cm^-1 and Li⁺ transference number (t = 0.77) at room temperature. LiFePO₄ //Li batteries are assembled to evaluate battery performance, which deliver excellent discharge capacity (144.9 mAh g^-1 at 0.5 C) and cycling stability (with the retention rate 94.5% at 0.5 C after 200 cycles) at room temperature. The results demonstrate that it has high potential for solid-state lithium metal batteries.

Lithium Bromide-Induced Organic-Rich Cathode/Electrolyte Interphase for High-Voltage and Flame-Retardant All-Solid-State Lithium Batteries

Poly(ethylene oxide) (PEO)-based solid electrolyte suffers from limited anodic stability and an intrinsic flammable issue, hindering the achievement of high energy density and safe all-solid-state lithium batteries. Herein, we surprisingly found out that a bromine-rich additive, decabromodiphenyl ethane (DBDPE), could be preferably oxidized at an elevated voltage and decompose to lithium bromide at an elevated potential followed by inducing an organic-rich cathode/electrolyte interphase (CEI) on NCM811 surface, enabling both high-voltage resistance (up to 4.5 V) and flame-retardancy for the PEO-based electrolyte. On the basis of this novel solid electrolyte, all-solid-state Li/NCM811 batteries deliver an average reversible capacity of 151.4 mAh g^-1 over the first 150 cycles with high capacity retention (83.0%) and high average Coulombic efficiency (99.7%) even at a 4.5 V cutoff voltage with a unprecedented flame-retardant properties. In view of these exploration, our studies revealed the critical role of LiBr in inducing an organic-rich thin and uniform CEI passivating layer with enhanced lithium ion surface diffusion and high-voltage resistant properties, which provides a new protocol for the further design of a high-voltage PEO-based all-solid-state electrolyte.

Recent Advances of Carbon Materials in Anodes for Aqueous Zinc Ion Batteries

Carbon-based materials have been successfully applied in the zinc ion batteries to improve the energy storage capability and durability of zinc anodes. In this review, four types of carbon materials (conventional carbons, fiber-like carbons, carbon nanotubes, graphene and other 2D carbon materials) are introduced based on the electrode preparation, physicochemical property and battery performance. Several modification strategies are also illustrated, such as heteroatom doping, hierarchical design and metal/carbon composites. Besides the discussion of existing issues of zinc anodes, the structure-performance relationships are analyzed in depth. Finally, conclusive remarks of this review are summarized and prospects of the future improvement are proposed.

Search for New Anode Materials for High Performance Li-Ion Batteries

Owing to an unmatched combination of power and energy density along with cyclic stability, the Li-ion battery has qualified itself to be the highest performing rechargeable battery. Taking both transportable and stationary energy storage requirements into consideration, Li-ion batteries indeed stand tall in comparison to any other existing rechargeable battery technologies. However, graphite, which is still one of the best performing Li-ion anodes, has specific drawbacks in fulfilling the ever-increasing energy and power density requirements of the modern world. Therefore, further research on alternative anode materials is absolutely essential. Equally important is the search for and enhanced use of right earth abundant materials for battery electrodes so as to bring down the costs of the battery systems. In this spotlight article, we discuss the current research progress in the area of alternative anode materials for Li-ion battery, putting our own research work over the past several years into perspective. Starting from conversion anode systems like oxides and sulfides, to insertion cum alloying systems like transition metal carbides, to molecularly engineered open framework systems like metal organic frameworks (MOFs), covalent organic frameworks (COFs), and organic-inorganic hybrid perovskites (OIHPs), this spotlight provides a complete essence of the recent developments in the area of alternative anodes. The possible and potential impact of these new anode materials is detailed and discussed here.

Oxygen Plasma Modified Carbon Cloth with C=O Zincophilic Sites as a Stable Host for Zinc Metal Anodes

Aqueous zinc-ion batteries (ZIBs) are currently receiving widespread attention due to their merits of environmental-friendly properties, high safety, and low cost. However, the absence of stable zinc metal anodes severely restricts their potential applications. In this work, we demonstrate a simple oxygen plasma treatment method to modify the surface state of carbon cloth to construct an ideal substrate for zinc deposition to solve the dendrite growth problem of zinc anodes. The plasma treated carbon cloth (PTCC) electrode has lower nucleation overpotential and uniformly distributed C=O zincophilic nucleation sites, facilitating the uniform nucleation and subsequent homogeneous deposition of zinc. Benefiting from the superior properties of PTCC substrate, the enhanced zinc anodes demonstrate low voltage hysteresis (about 25 mV) and stable zinc plating/stripping behaviors (over 530 h lifespan) at 0.5 mA cm^-2 with 15% depth of discharge (DOD). Besides, an extended cycling lifespan of 480 h can also be achieved at very high DOD of 60%. The potential application of the enhanced zinc anode is also confirmed in Zn|V₁₀O₂₄·12H₂O full cell. The cells with Zn@PTCC electrode demonstrate remarkable rate capability and excellent cycling stability (95.0% capacity retention after 500 cycles).

Synthesis and Characterization of Gel Polymer Electrolyte Based on Epoxy Group via Cationic Ring-Open Polymerization for Lithium-Ion Battery

The polymer electrolytes are considered to be an alternative to liquid electrolytes for lithium-ion batteries because of their high thermal stability, flexibility, and wide applications. However, the polymer electrolytes have low ionic conductivity at room temperature due to the interfacial contact issue and the growing of lithium dendrites between the electrolytes/electrodes. In this study, we prepared gel polymer electrolytes (GPEs) through an in situ thermal-induced cationic ring-opening strategy, using LiFSI as an initiator. As-synthesized GPEs were characterized with a series of technologies. The as-synthesized PNDGE 1.5 presented good thermal stability (up to 150 °C), low glass transition temperature (Tg < −40 °C), high ionic conductivity (>10−4 S/cm), and good interfacial contact with the cell components and comparable anodic oxidation voltage (4.0 V). In addition, PNGDE 1.5 exhibited a discharge capacity of 131 mAh/g after 50 cycles at 0.2 C and had a 92% level of coulombic efficiency. Herein, these results can contribute to developing of new polymer electrolytes and offer the possibility of good compatibility through the in situ technique for Li-ion batteries.

Data-driven prediction of battery failure for electric vehicles

Despite great progress in battery safety modeling, accurately predicting the evolution of multiphysics systems is extremely challenging. The question on how to ensure safety of billions of automotive batteries during their lifetime remains unanswered. In this study, we overcome the challenge by developing machine learning techniques based on the recorded data that are uploaded to the cloud. Using charging voltage and temperature curves from early cycles that are yet to exhibit symptoms of battery failure, we apply data-driven models to both predict and classify the sample data by health condition based on the observational, empirical, physical, and statistical understanding of the multiscale systems. The best well-integrated machine learning models achieve a verified classification accuracy of 96.3% (exhibiting an increase of 20.4% from initial model) and an average misclassification test error of 7.7%. Our findings highlight the need for cloud-based artificial intelligence technology tailored to robustly and accurately predict battery failure in real-world applications.

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A well-integrated machine learning technique is applied to failure prediction

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A cloud-based closed-loop framework is established for real-world EV applications

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Cloud-based AI solution is based on an in-depth analysis of the field data

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Both electrochemical and statistical feature engineering are established

Thermal Decomposition Characteristics of PEO/LiBF4/LAGP Composite Electrolytes

Lithium-based batteries with improved safety performance are highly desired. At present, most safety hazard is the consequence of the ignition and flammability of organic liquid electrolytes. Dry ceramic-polymer composite electrolytes are attractive for their merits of non-flammability, reduced gas release, and thermal stability, in addition to their mechanical strength and flexibility. We recently fabricated free-standing solid composite electrolytes made up of polyethylene oxide (PEO), LiBF4 salt, and Li1+xAlxGe2−x(PO4)3 (LAGP). This study is focused on analyzing the impacts of LAGP on the thermal decomposition characteristics in the series of PEO/LiBF4/LAGP composite membranes. It is found that the appropriate amount of LAGP can (1) significantly reduce the organic solvent trapped in the polymer network and (2) increase the peak temperature corresponding to the thermal degradation of the PEO/LiBF4 complex. In the presence of LAGP, although the peak temperature related to the degradation of free PEO is reduced, the portion of free PEO, as well as its decomposition rate, is effectively reduced, resulting in slower gas release.

From room temperature to harsh temperature applications: Fundamentals and perspectives on electrolytes in zinc metal batteries

As one of the most competitive candidates for the next-generation energy storage systems, the emerging rechargeable zinc metal battery (ZMB) is inevitably influenced by beyond-room-temperature conditions, resulting in inferior performances. Although much attention has been paid to evaluating the performance of ZMBs under extreme temperatures in recent years, most academic electrolyte research has not provided adequate information about physical properties or practical testing protocols of their electrolytes, making it difficult to assess their true performance. The growing interest in ZMBs is calling for in-depth research on electrolyte behavior under harsh practical conditions, which has not been systematically reviewed yet. Hence, in this review, we first showcase the fundamentals behind the failure of ZMBs in terms of temperature influence and then present a comprehensive understanding of the current electrolyte strategies to improve battery performance at harsh temperatures. Last, we offer perspectives on the advance of ZMB electrolytes toward industrial application.

Boosting Zn||I2 Battery's Performance by Coating a Zeolite-Based Cation-Exchange Protecting Layer

High-performance Zn||I₂ batteries were established by coating zeolite protecting layers. The Zn²⁺-conductive layer suppresses I₃^- shuttling, Zn corrosion/dendrite growth. The Zeolite-Zn||I₂ batteries achieve long lifespan (91.92% capacity retention after 5600 cycles), high coulombic efficiencies (99.76% in average) and large capacity (203-196 mAh g^-1 at 0.2 A g^-1) simultaneously. The intrinsically safe Zn||I₂ battery, one of the leading candidates aiming to replace traditional Pb-acid batteries, is still seriously suffering from short shelf and cycling lifespan, due to the uncontrolled I₃^--shuttling and dynamic parasitic reactions on Zn anodes. Considering the fact that almost all these detrimental processes terminate on the surfaces of Zn anodes, modifying Zn anodes' surface with protecting layers should be one of the most straightforward and thorough approaches to restrain these processes. Herein, a facile zeolite-based cation-exchange protecting layer is designed to comprehensively suppress the unfavored parasitic reactions on the Zn anodes. The negatively-charged cavities in the zeolite lattice provide highly accessible migration channels for Zn²⁺, while blocking anions and electrolyte from passing through. This low-cost cation-exchange protecting layer can simultaneously suppress self-discharge, anode corrosion/passivation, and Zn dendrite growth, awarding the Zn||I₂ batteries with ultra-long cycle life (91.92% capacity retention after 5600 cycles at 2 A g^-1), high coulombic efficiencies (99.76% in average) and large capacity (203-196 mAh g^-1 at 0.2 A g^-1). This work provides a highly affordable approach for the construction of high-performance Zn-I₂ aqueous batteries.