Materials are key to energy storage batteries. With experimental observations, theoretical research, and computational simulations, data-driven machine learning should provide a new paradigm for electrochemical energy storage material research and development. Its advantages include rapid capture of the complex structure-activity relationship between material composition, structure, process, and performance. In this study, the latest developments in employing machine learning in electrochemical energy storage materials are reviewed systematically from structured and unstructured data-driven perspectives. The material databases from China and abroad are summarized for electrochemical energy storage material use, and data collection and quality inspection problems are analyzed. Data-driven machine learning workflows and applications in electrochemical energy storage materials are demonstrated. They contain data collection, feature engineering, and machine learning modeling under structured data, and the model construction and application under unstructured data of graphics, representation images, and literature. Three principal contradictions and countermeasures faced by machine learning in electrochemical energy storage materials are highlighted: the contradiction and coordination of high-dimensional and small sample data, the contradiction and unity of model complexity and ease of use, and the contradiction and contradiction fusion between model learning results and expert experience. We highlighted that "Machine Learning Embedded with Domain Knowledge" construction should reconcile these contradictions. This review provides a reference for applying machine learning in electrochemical energy storage materials' design and performance optimization.

Cryogenic electron microscopy (cryo-EM), a powerful tool for the characterization of beam-sensitive materials, has been widely used in the life sciences and was awarded the Noble Prize in Chemistry in 2017. It was also used for the first time to visualize the nanostructure of lithium metal and yield some unprecedented results, attracting much attention and applications in the battery field. Cryo-treatment or low temperature can not only effectively alleviate the radiation damage produced by the high-energy electron beam, but it can also greatly reduce the reactivity and enhance the stability of the sample. Cryo-EM can provide structural information at the nano and even atomic scale. This review focuses on cryo-EM applications and achievements for Li metal batteries, including cryogenic focused ion beam-scanning electron microscopy (cryo-FIB-SEM) and cryogenic transmission electron microscopy (cryo-TEM). It will assist the audience in comprehending the benefits and essential role of cryo-EM in exploring the operating principle of batteries and illuminating material design. The plating and stripping behaviors of the Li metal, the nanostructure of the solid electrolyte interphase (SEI), the Li-storage mechanism of lithiophilic substrates, solid-solid interfaces in all-solid-state batteries, and cathode electrolyte interphase (CEI) are all applications of interest. Finally, we provide a perspective on the future technological development of cryo-EM as well as its potential application and opportunities in the battery field. The advancement of cryo-EM is expected to contribute to probing the structures of battery materials and interfaces, understanding the failure mechanisms, and thus facilitate the development of higher-energy and safer batteries.

Energy and the environment are important pillars behind the sustainable development of human society. Therefore, the future society requires efficient, economical, green, and safe electrochemical energy storage field to deal with global climate change and energy crisis. Thus, it is crucial to understand the electrochemical interface reaction mechanism to further guide the design of energy storage devices. Time-of-flight secondary ion mass spectrometry (ToF-SIMS), including ex situ and in situ methods, has emerged in recent energy electrochemical fields due to its ultra-high sensitivity, as well as temporal and spatial resolution. This review summarizes the latest developments and applications of ToF-SIMS in recent technologies of energy electrochemistry (e.g., lithium-ion, -sulfur, and lithium-oxygen batteries), with critically considering the technology-assisted revelation of the electrochemical reaction process and further design of better electrochemical energy storage systems. Finally, we also discussed the current challenges and future opportunities of ToF-SIMS, and advocated the widespread use of the technology to guide the design and innovation of future energy storage technologies.

In China, the goals of "peak carbon dioxide emissions" and "carbon neutrality" were proposed in December 2020. As a result, industrial and energy structures must be optimized and improved battery technology, developed. The electrode could represent the working mechanism and the corresponding evolution of electrochemical systems during battery operation. The inhomogeneity of the electrode process in a single battery becomes increasingly obvious as the energy density and size of batteries rise. However, in terms of space and time, the challenges apply to multi-scale, multi-level, multi-process, multi-step, and multi-field coupling issues in electrochemical batteries. In this review, we will focus on the electrode process of batteries with different active ions as well as related processes such as liquid mass transfer, surface charge electron transfer, and solid phase diffusion. The influences of voltage, overpotential, diffusion coefficient, and geometric parameters on battery design have been analyzed in typical examples of high energy-density batteries, high-power-density batteries, and long-life cycle batteries. Furthermore, the impact of the electrode process inhomogeneity mechanism on battery performance has been discussed. We examine the electrode processes of lithium-ion batteries and Al batteries using various types of in-situ characterization technologies from different manufacturers based on visualization and quantitative analysis. The findings may be used to better understand the electrode process, which can help with material design and structure optimization. The existing scientific and technical challenges are also analyzed by establishing the relationship between the electrode process and battery performance. Existing scientific and technical issues are also analyzed, promising a platform for rational design and manufacture of high-performance batteries.

Understanding the structure-activity relationship of electrochemical energy storage system will greatly promote the discovery and regulation of new phenomena and new properties in electrode materials. However, no single technology can clarify all the problems of complex interface reactions in the electrochemical system. Only by observing from multiple perspectives can we see the buried interface and the evolution process under working conditions. Many energy storage materials are rich in transition metal elements, and their magnetic properties are closely related to lattice structure, electronic energy band and electrochemical performance. Therefore, magnetometry can reveal structural phase transition and local electron distribution changes of energy materials, analyze the mechanism of physical and chemical reactions, and guide material design. Focusing on magnetic characterization technology for energy storage, this paper firstly discusses the technical principle of magnetometry, and then summarizes the research progress of magnetometry in studying the structural characteristics of electrode materials and characterizing the reaction process, especially introduces the unique advantages of in-situ magnetometry in monitoring the magnetic changes in real time and illustrating the reaction mechanism. Comprehensive analysis shows that in-situ magnetometry technology can characterize the charge transfer in electrochemical reactions with high sensitivity and rapid response, which provides a new idea for revealing the electrochemical reactions at complex interfaces and has broad application prospects in energy storage science. This paper is helpful to understand the important value of magnetometry technique in the research of battery materials and further promote the development of magnetometry technique in the field of energy storage.

Lithium-ion batteries have been widely applied in portable electronics due to their high energy densities. However, their potential applications in electric vehicles and grid energy storage call for higher energy density. It is a critical challenge to develop the next-generation electrochemical energy storage devices. Synchrotron X-ray imaging techniques are currently catching increasing attention due to their intrinsic advantages, including non-destructiveness, chemically responsiveness, elementally sensitivity, and high penetrability to enable operando investigation of a real battery. Based on the derived nano-tomography techniques, it can provide 3D morphological information including thousands of slice morphologies from the bulk to the surface. Combined with X-ray absorption spectroscopy, X-ray imaging can even present chemical and phase mapping information, including the oxidation state, local environment, etc., with sub-30 nm spatial resolution, which addresses the issues that we only obtain as averaged information in traditional X-ray absorption spectroscopy. Through an operando charging/discharging setup, X-ray imaging enables the study of the correlation between the morphology change and the chemical evolution (mapping) under different states of charge and cycling. In addition, X-ray imaging breaks up the size limit of nanoscale samples for the in-situ transmission electron microscope imaging, which enables a large, thick sample with a broad field of view, truly uncovering the behavior inside a real battery system. We will discuss a few major X-ray imaging technologies, including X-ray projection imaging, transmission X-ray microscopy, scanning transmission X-ray microscopy, tender and soft X-ray imaging, and coherent diffraction imaging. Researchers can choose from various X-ray imaging techniques with different working principles based on research goals and sample specifications. With the X-ray imaging techniques, we can obtain the morphology, phase, lattice and strain information of energy materials in both 2D and 3D in an intuitive way. In addition, with the high-penetration X-rays and the high-brilliance synchrotron sources, operando/in-situ experiments can be designed to track the qualitative and quantitative changes of the samples during operation. We expect this review can broaden readers' view on X-ray imaging techniques and inspire new ideas and possibilities in energy materials research.

As a new emerging electrochemical energy storage device, lithium-ion batteries (LIBs) show excellent value in consumer electronics, transportation power systems, and grid energy storage. However, there are occasional safety accidents during LIB commercialization, affecting large-scale applications. This study reviews crucial research methods for battery safety based on three research scales: material, cell, and system, including experimental methods based on physical samples and simulation methods based on computer numerical models. The basic principles of these methods are introduced, and applicable scenarios and functions are demonstrated through typical cases. The relationship between experimental and simulation methods is discussed. Representative methods are introduced, such as thermal analysis and in situ temperature-dependent characterization of materials, accelerating rate calorimetry, and numerical cell simulation. Based on a systematic review of multiscale research strategies, the research on lithium battery safety in each scale should be conducted jointly. The safety research of the next-generation lithium battery, such as solid-state and lithium metal batteries, is prospected. The safety research of these systems is in an early stage, and research on the material and cell is a crucial topic currently.

With the widespread use of lithium-ion batteries, the issue of thermal safety of lithium-ion batteries has become increasingly prominent. Compared with the costly and destructive experimental methods, modeling simulation has become an important tool for thermal safety research of Li-ion batteries due to its advantages of economy, safety and speed. In this paper, the latest lithium-ion battery models and their applications in thermal safety design are reviewed in three scales: microscopic modeling, single-cell modeling, and cell pack modeling. The applications of density flooding theory and molecular dynamics simulations in the regulation of lithium dendrite growth and safe design of electrolyte in Li-ion batteries, the application of single-cell modeling coupled with thermal equations, and the study of Li-ion battery group thermal modeling in optimizing the thermal management system of batteries are highlighted. Finally, the defects of the existing thermal models for Li-ion batteries are summarized, and the future research methods for Li-ion battery thermal models are prospected.

Monte Carlo (MC) simulation, on the basis of probability and statistics theory, was proposed by Von Neumann et al. in 1940s. As an important numerical method, MC simulation has been used to investigate thermodynamic and kinetic properties of ionic conductors. However, there exists a large improvable space for the MC simulation in the calculation accuracy, simulation efficiency and simulation process automation. In this work, through systematic analysis of the Hamiltonian model in MC simulation (For example, based on bond-valence theory or cluster expansion, the configuration energy is given by fitting the neighbors interaction parameters that can always be obtained by first principles calculations of representative small supercells) and the evolution model (For example, configuration evolution based on the assumption of single-ion jump mode) of material structure, a set of MC simulation paradigms for analyzing the ion transport and phase transition characteristics of ionic conductors are extracted, and the corresponding semi-automatic simulation codes are given which can be used for predicting the respective dependences of the ionic conductivity and the occupancy of the migrated ions in the garnet-structured ionic conductor with the lithium ion concentration. To expand the application of MC simulation in the research of ionic conductor, we further analyze its applications in the typical thermodynamic and kinetic properties calculations of electrochemical energy storage materials which includes anode and cathode materials, electrolytes and the related interfaces, including the ionic diffusion problems, the distribution characteristics of migrated ions and the evolution of related interface. Finally, the current challenges faced by MC methods are prospected and the possible solutions are presented, including: ① Accurately capturing all possible events (such as single-ion hop and two-ion cooperation hop) and their descriptions (such as the Hamiltonian calculations); ② Searching for efficient algorithm to accurately find the evolution trajectory of the system; ③ Accurately obtaining the corresponding actual time in the MC simulation.

As an important part of electrochemical energy storage system, electrolyte is one of the key factors to determine the battery capacity, support the energy storage and cycle stability of supercapacitor. As a new kind of soft functional materials, ionic liquids are widely used in electrochemical energy storage components, such as lithium batteries and supercapacitors, and gradually become one of the best substitutes for traditional organic electrolytes because of their high conductivity, wide electrochemical window, good thermal stability and no significant vapor pressure. At present, the design and research of ionic liquid electrolytes mostly use experimental test method, which has large search range, high cost, and it is difficult to accurately obtain a deep understanding of its dynamic structure, formation mechanism and action mechanism at the nano and micro level. Therefore, this review aims to summarize the related progress of ionic liquid electrolyte in simulation calculation. Firstly, according to different simulation scales, three simulation methods for ionic liquid electrolytes are introduced, and their advantages and disadvantages are discussed. Secondly, according to the different components of ionic liquid in electrolytes, the simulation research status of ionic liquid in battery and supercapacitor are reviewed respectively. Finally, the future challenges and development direction of ionic liquid electrolytes are discussed, in order to provide a new research idea for the simulation of electrolytes.

Electrochemical impedance spectroscopy (EIS) is a powerful electrochemical method from which many fundamental processes in the research system can be characterized, such as charge transfer, double-layer charging, and mass transport. Effective EIS analysis requires reasonable models. Typical models include equivalent circuit and physical models. This paper introduces three methods for solving physical EIS models, including analytical solutions, the time-space method, and the frequency-space method. We take a Faradaic electrochemical interface with diffusion-controlled mass transport as an example, deduce the analytical solution, introduce the time- and frequency-space methods to solve EIS numerically, and compare the results of different methods. Then, taking the typical metal-ion deposition reaction in rechargeable batteries as an example, we provide the analytical EIS solution at the potential of zero charges and compare the two numerical methods' accuracy. We compare the EIS results of metal ions with different valences. Our results show the frequency-space method's accuracy is higher than the time-space method and can be used as a first choice for the numerical EIS solution. When maintaining other parameters, the EIS of ions with high valence is smaller than ions with low valence. Finally, we summarize and compare the advantages and disadvantages of the above three methods. This study's results can be a guide to the physical EIS model and can be used to analyze the EIS results of the metal-ion deposition reaction.

The solid electrolyte interphase is a critical but little understood part of a battery. Robust solid electrolyte interphase is the key component to facilitate high-energy-density batteries. However, due to the solid electrolyte interface's complexity, its experimental characterization and structural resolution are extremely challenging. Recently, atomic level multiscale simulations have provided new tools for understanding and resolving solid electrolyte interfaces. This paper summarizes simulation techniques for studying solid electrolyte interfaces. It focuses on micromesoscopic (<100 nm) scale simulation methods, especially quantum chemical methods for electrochemical simulations, reaction force field methods for large-scale chemical reaction simulations, and specific applications of these new techniques in studying the initial reactions and dynamic evolution of solid electrolyte interfaces in batteries. With the steady improvement of computer hardware and theoretical algorithms, multiscale theoretical simulations will provide the theoretical basis for high-energy-density battery development and intelligent manufacturing.

Rechargeable batteries are common in key national strategic development fields, such as electric vehicles, due to their high-energy density and high-cycle stability. During repeated charging and discharging, the uneven deposition of metal ions will lead to dendrite growth on the electrode surface, the reduction of reversible capacity and internal short circuit. Dendrite formation is an extremely complex process, which involves many disciplines such as electrochemistry, thermodynamics, kinetics and crystallography. And it is affected by multiple factors such as charging conditions, compressive stress, battery composition, temperature, magnetic field and so on. This paper systematically summarizes the theoretical models involved in dendrite nucleation and growth, comprehensively reviews the phase-field simulations in battery dendrites. The effects of charging condition, stress, external pressure and ion distribution on dendrite growth are discussed, and the research paradigm of electrochemical phase-field simulation in the field of battery dendrite is given. Subsequently, we apply an electrochemical phase-field model to investigate the influence of separator surface coating on ion distribution and dendrite growth uniformity. This work provides a theoretical basis for the design of dendrite inhibiting separator. Finally, the shortcomings of current phase-field simulations and future research directions are pointed out.

The fundamental factor determining the performance of solid-state ionic devices is their ionic conductivity. Ion conduction in inorganic solid electrolytes involves migration in the grain bulk and across the grain boundary, which is correlated with the structure of the point defect. The various point defects and their influence on grain bulk conductivity are elucidated here, as well as the grain boundary space-charge layer and the derived characteristics of grain boundary conduction. The content would provide some guidance in the design of solid electrolytes with high ionic conductivity.

Since lithium ion batteries gradually entered the market for electric vehicles and smart grids, mechanics, as one of the intrinsic characteristics of materials, has attracted an increasing amount of interest from the entire community. The current challenge in power batteries and energy-storage batteries is mechanics-induced deterioration, which is required to operate for thousands of cycles, and correspondingly active particles experiencing thousands of periods of periodic inflation and shrinkage. Based on our research results, we will discuss the mechanism of mechanics-induced degradation for layer-structured cathodes and possible solutions. First, we'll go through the fundamentals of mechanics investigation. During cycling, the crystalline deformation of active materials is classified as the elastic deformation, and internal stress can be estimated using the Hookean Equation. Then, we return to the "damage-fracture" model of mechanical-induced degradation. Internal stress in the model would generate more and more defects, finally leading to fractures where electrolytes permeate the bulk and react, causing the cyclic stability to drop. Finally, we describe effective solutions for mitigating the influence of particles' mechanics-induced degradation, with a focus on reducing lattice variation and constructing robust surface layers. The ablation of lattice change reduces particle stress by removing the stain, whereas the surface tough shell layer prevents electrolyte permeating into the fractured bulk. In general, the mechanics-induced degradation of active materials is unavoidable, although its influence can be delayed or lessened with the appropriate strategies.

Carbon-coated SiO_x composite anodes with different drying temperatures and binding systems, including poly(vinylidene fluoride) (PVDF), polymerized styrene butadiene rubber/carboxymethyl cellulose (SBR/CMC), and sodium alginate (SA), were prepared. Their quasi-static tensile and interfacial tensile-shear properties were thoroughly tested. The results showed that when the drying temperature increases, the elastic modulus, tensile strength, and interface tensile-shear strength of the active layer of each binding system gradually decrease. Among them, the ratio of tensile strength to elastic modulus of electrodes containing SBR/CMC is the highest. Additionally, its tensile-shear strength is also relatively less affected by temperature. The ratio of tensile strength to elastic modulus of electrodes with SBR/CMC is better suited for high-temperature drying than SA and PVDF systems.

With the proliferation of clean and sustainable energy applications and the rapid growth in the electric vehicle industry, increasing opportunities for advanced energy storage/conversion technologies and devices are being created than ever before. With the virtue of high-energy-density, environmental friendliness, security, and cost-effectiveness, rechargeable zinc-air batteries (ZAB) are among the most promising metal-air batteries. Furthermore, zinc used in zinc-air batteries has abundant resources, is cheap, has a moderate energy density, and has high reduction potential. Nevertheless, during recharging, the redox reaction's kinetics on the air cathode is exceptionally sluggish, resulting in a large super potential for the cell, rendering them challenging for commercial application in ZABs. Zeolite imidazolium-based metal-organic framework (ZIF)-derived catalysts can facilitate the oxygen reaction significantly. We review recent advances in ZIF-derived materials used as cathode catalysts in ZAB. We first summarize several vital ZIF-derived materials for ZAB applications, including ZIF-derived metal nitride electrocatalysts, ZIF-derived metal oxide electrocatalysts, ZIF-derived S/P/B doping and ZIF-derived nonmetallic carbon catalysts. Further, the advantages and disadvantages of these ZIF-derived catalysts are discussed. Finally, some perspectives are provided on the challenges and development of advanced ZIF-derived catalysts for ZAB.

The growing family of MXenes, i.e., layered transition metal carbides and/or nitrides, has become an important candidate of electrode materials for new-concept energy storage devices due to their unique properties. Presently, the most widely studied MXenes material is Ti₃C₂T _x, which was etched from the MAX phase ceramic material Ti₃AlC₂ by the Gogotsi team of Drexel University. Herein, proceeding from our exploration of the lithium storage performance of Ti₃C₂T _x /SnO₂, the novel preparation methods of MXenes with different microstructures were reviewed. Afterward, several main energy storage mechanisms of MXenes were discussed. The literature showed that two-dimensional MXenes with accordion or clay-like structures are mainly prepared with HF or LiF + HCl as etchants. Reducing the stack of 2D nanosheets and forming an alternate alignment structure effectively improves the electrochemical performance of 2D MXenes. Meanwhile, the template method is mainly used to prepare three-dimensional MXenes and their composites. In addition to inhibiting the accumulation of nanosheets, 3D MXenes have abundant micron channels, which is beneficial to the diffusion of electrolytes and the transport of carriers. Coupled with their excellent electrical conductivity (≈10⁵ S/cm), low lithium-ion diffusion energy barrier, and unique metal ion adsorption characteristics, we believe that 3D MXenes have great potential to become an ideal active material or electrode of secondary batteries. Finally, the opportunities and challenges of MXenes' series energy storage materials were presented.

Solid-electrolyte interphase (SEI) largely affect the safety, cycle life, and rate capability of the Li (ion) batteries. Improving the mechanical properties, e.g. Young's modulus, of SEI helps to withstand the damages caused by volume changes of the electrode material resulted from lithium-ion intercalation/deintercalation. Atomic Force Microscopy (AFM) nanoindentation affords as an effective way to obtain both the morphology and Young's modulus of a specified area of a sample. However, in order to calculate the precise Young's modulus with statistical significance, a mass of forces curves from various areas of the samples are usually needed, which makes this method laborious. Recently, the newly-developed Amplitude Modulation-Frequency Modulation mode (AM-FM mode) of AFM has been reported as an efficient approach to measure the Young's modulus of materials, which provides both the morphology graph and Young's modulus map at the same time in several minutes. Since the development of AM-FM mode is still in its early stage, herein we studied the feasibility of applicating this technique in the SEI research. First, we demonstrated AM-FM can be applied on rapidly distinguishing materials with different Young's modulus on one sample. Then we found that the tip radius parameter in this mode has a huge impact on the Young's modulus value. We evaluated the accuracy of AM-FM as a quantitative method to quickly characterize Young's modulus of a studied sample by using standard materials with known Young's modulus. It turned out that the Young's modulus of studied samples obtained by AM-FM still needed to be further improved. To conclude, in this work we demonstrated that AM-FM method is a novel technique for quickly distinguishing different materials on one sample, after further improvement it could probably be used for quickly measuring the Young's modulus of SEI.

When preparing precursors, materials with various morphologies can be obtained by controlling different reaction conditions. Notably, the ammonia condition significantly affects morphology. Herein, high-nickel ternary precursor materials with different morphologies were prepared under different ammonia conditions. It was found that the precursor prepared under low-ammonia condition had fine whiskers on the surface, dense internal structure, and branching-like external structure. After sintering the precursor material, the primary particles still grew radially, and more slender than in other conditions. After fabricating the button battery, the capacity reached 210.3 mA·h/g at 0.2 C discharge, and the first charge-discharge efficiency reached 93.05%, with excellent cycle and rate performance. Herein, the discharge capacity of the device increased by 3% compared with the same ratio of commercial devices. The morphology control method provides a new idea for the large-scale preparation of high specific capacity ternary cathode materials.

Lithium is considered a battery anode material with high theoretical energy. However, the growth of lithium dendrites can connect the positive and negative poles, causing disasters, such as explosions. Therefore, the inhibition of lithium dendrite is essential to improve the safety of lithium metal batteries. Herein, the dendrite morphology and temperature field distribution under different initial conditions are studied by coupling the nonlinear phase-field model with a thermal model. As the reaction progresses, the temperature of the lithium dendrite region exceeds that of the electrolyte region due to exothermic reaction, and a temperature gradient is formed at the interface between the lithium dendrite and electrolyte region. Then, the morphology characteristics of lithium dendrites at different temperatures were studied and the inhibition effect was quantified. It was found that the lower the temperature, the longer the lithium dendrites, the more the number of lithium dendrites, and the more the side branches are generated during charging, and thus the more likely "dead lithium" is formed during discharge. The dendrite length and morphology at different charging frequencies were analyzed by changing the frequency of the pulse current. The results show that a 5 ms pulse followed by a 10 ms rest period is the appropriate frequency for restraining lithium dendrites, and a relatively uniform deposition surface can be obtained at this frequency. By investigating the average dendrites growth rate under different overpotential and diffusion coefficients, a dimensionless number Da is introduced to illustrate the competition between diffusion and electrode reaction. It can be concluded that reducing the difference between the reaction and diffusion rates is a necessary condition for restraining lithium dendrites.

Aqueous zinc-ion batteries have a high energy density, good stability, and high safety factor; as a double transition metal oxide, NiCo₂O₄ has excellent electrical conductivity and electrochemical activity. Therefore, herein, NiCo₂O₄ was novelly used as a novel cathode material for aqueous zinc-ion batteries. The solid spinel NiCo₂O₄ material was prepared by the sol-gel and calcination heat methods. Using scanning electron microscopy, transmission electron microscope, energy dispersive spectroscopy, and electrochemical technology, the morphology and electrochemical properties of the cathode material of the new aqueous zinc-ion batteries were analyzed. The results show that the spinel NiCo₂O₄ material has excellent purity and crystallinity, and the particles are evenly dispersed without agglomeration and impurity. Moreover, it has good and stable charge-discharge performance. At a current density of 100 mA·g^-1, the initial specific discharge capacity of the electrode is 92 mA·h·g^-1, 60 mA·h·g^-1 after 100 cycles, and 44 mA·h·g^-1 after 200 cycles. However, when the current density is high, the specific capacitance of the NiCo₂O₄ electrode decreases by 27 mA·h·g^-1, which has irreversible impact damage to a certain extent. This study highlights that NiCo₂O₄ material improves the performance of aqueous zinc-ion batteries, which can guide the future design of aqueous zinc-ion batteries.

Presently, the high value-added utilization of low-cost petroleum asphalt faces great challenges. Herein, based on the high carbon content of asphalt, an S-doping porous carbon (SPC) framework structure was successfully prepared using a NaHCO₃ template. Afterward, a three-dimensional structure was prepared by the in situ growth of MoS₂ nanosheets on the surface of the SPC using MoCl₅ and sublimated sulfur as the molybdenum and sulfur sources. The as-formed material achieves a good contact between MoS₂ and the carbon substrate, and its interlaced structure can greatly improve the electron transfer rate and shorten the transmission path of Li⁺ and e^-. Additionally, its porous structure provides abundant reactive sites for Li⁺. When tested as lithium anode, the material obtains a high specific capacity of 1069 mA·h·g^-1 after 400 cycles. This work may provide a new idea for the high value-added utilization of low-cost petroleum asphalt.

As a green energy storage device, supercapacitors have attracted much attention due to their high power density, low cost, and excellent environmental protection compared to secondary energy storage batteries. Electrode materials, electrolytes, and diaphragms affect the electrochemical performance of supercapacitors. Herein, we synthesize Co₃O₄ nanoleaves derived from metal-organic framework structure by a simple hydrothermal route. The prepared product shows a porous structure. By optimizing the solution concentration and reaction time, the electrode material delivers a specific capacitance of 156 F·g^-1 at a current density of 0.5 A·g^-1. After 6000 cycles, the device retained 80% of the initial capacity. An assembled device delivers a power density of 22.5 W·kg^-1 at an energy density of 157.5 W·h·kg^-1. Even after 8000 cycles, it still possesses an excellent specific capacity.

Herein, a shape-stable molten salt-based composite phase change material with low melting temperature and large temperature range was fabricated by cold compression-hot sintering approach and investigated. A eutectic quaternary nitrate of Ca(NO₃)₂-KNO₃-NaNO₃-NaNO₂ is used as the phase change material (PCM), and halloysite and graphite are respectively employed as the structure supporting material and thermal conductivity enhancer. Several characterizations, including differential scanning calorimetry, laser thermal conductivity test, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy were conducted to investigate the microstructure, chemical compatibility, and thermal properties of the composite. The results show that a fairly low melting point about 91.3 ℃ and relatively high decomposition temperature of 627.5 ℃ were observed, giving the composite a large energy storage density exceeding 630.15 kJ/kg at a temperature range of 25—625 ℃. For the composite containing 10% graphite, the material's thermal conductivity can be increased by 44.8% from 0.58 to 1.18 W·(m·K)^-1. Due to the special hollow structure of the halloysite nanotube, the molten salt can be absorbed by the halloysite, and hence the issues of salt corrosion, leakage, and decomposition can be effectively addressed. No chemical reaction occurs among the salt, halloysite, and graphite, including good chemical stability achieved in the composite. After 100 heating-cooling cycles, the fluctuation of the phase change temperature and latent heat is less than 3.5%, demonstrating the excellent cycling stability of the composites. The present results indicate that such salt-based composite with low melting temperature and high thermal performance could be an effective alternative to organic-based PCMs used in low-mid thermal energy storage systems.

Research and development progress on energy storage technologies of China in 2021 is reviewed in this paper. By reviewing and analyzing three aspects of research and development including fundamental study, technical research, integration and demonstration, the progress on major energy storage technologies is summarized including hydro pumped energy storage, compressed air energy storage, flywheel, lead battery, lithium-ion battery, flow battery, sodium-ion battery, supercapacitor, new technologies, integration technology, fire-control and safety technology. The results indicate that extensive improvements of China's energy storage technologies have been achieved during 2021 in terms of all the three aspects. China is now the most active country in energy storage fundamental study and also one of the core countries of technical research and demonstration.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 3795 papers online from Dec. 1, 2021 to Jan. 31, 2022. 100 of them were selected to be highlighted. Layered oxide cathode including Ni-rich oxides and lithium-rich materials, are still under extensive investigations for the modification of doping and coating. Large efforts were devoted to design the three-dimensional structure electrode, interface modification, and inhomogeneity plating of lithium metal anode. For alloying mechanism anode materials, beside 3D structure design, many researchers pay attention to the binders. The researches of solid-state electrolytes mainly focused on synthesis, doping, structure design and stability of pre-existing materials and developing new materials, whereas liquid electrolytes mainly focused on the optimal design of solvents and lithium salts for different battery systems and testing different additives. For solid-state batteries, more papers are related to the design of composite cathode and the modification of interfaces. The works for lithium-sulfur batteries are mainly focused on improving the activity of sulfur and suppressing the "shuttle effect". The characterizations include the investigations on Li deposition, interfacial reaction, and structure of cathode materials under high current density. Furthermore, there are theoretical works for the conductivity solid electrolyte with doping, the analyses of interfacial stress, and the interfacial stability of solid state batteries. Prelithiation of electrodes are also studied in few papers.