Energy storage is the key technology to support the development of new power system mainly based on renewable energy, energy revolution, construction of energy system and ensuring national energy supply security. During the period of 2016—2020, some projects had been supported by the national key R&D program "technology and equipment of smart grid". A series of research progresses have been achieved and some important demonstration projects have been performed. During the period of 2021—2025, both fundamental research and key technology in the direction of energy storage will be supported by the national key R&D program "technology of energy storage and smart grid". In this contribution, important progresses of energy storage projects during 2016—2020 and future plan during 2021—2025 will be briefly introduced.

The large-scale integration of new energy into the power grid during the past decade has posed challenges for the safe and stable operation of the power system. As a resource for flexible regulation, new forms of energy storage systems (ESS) support new energy consumption, the safe operation of the power grid, and enhanced control capabilities. As a result, its technology has rapidly advanced, allowing for the gradual integration, development, and application of power station systems ranging in size from one megawatt to one hundred megawatts. In this process, large-scale centralized ESS and wide area collaborative aggregation of distributed ESS are two application modes of the new types of large-scale ESS. This study primarily focuses on the application scenarios of large-scale new types of ESS on the power supply side and the power grid side; reviews the research progress of new types of ESS from three perspectives: application engineering, detection and evaluation, and standard formulation; discusses the technical development laws, phased achievements, and milestones over the past 10 years; and analyzes the existing problems and their root causes. Aiming at the application engineering, detection and evaluation, and standard formulation of the new type of ESS, the future key research directions, opportunities, and challenges are anticipated to serve as a reference for the large-scale application, standardized management, intelligent operation, safety, and quality enhancement of the new type of ESS.

Solid-state lithium batteries with solid electrolyte rather than traditional liquid organic electrolyte could employ high specific capacity cathodes and anodes, resulting in high energy density devices with high safety, which is consistent with the future development direction of power sources for electric vehicles and large-scale energy storage. To accelerate the practical application of both solid-state and all-solid-state lithium batteries with high energy density, high safety, and long service life, scientists from all over the world have done a lot of work and made many breakthroughs from 2011 to 2022. Herein, in view of the challenges and opportunities for solid-state lithium batteries, the research progress of solid-state lithium batteries in the last decade, including solid electrolyte materials, electrode/electrolyte interface regulation, and solid-state battery technology, was reviewed. Finally, possible research directions and development trends for solid-state lithium batteries are also discussed.

Thermal energy storage (TES) plays an important role in addressing the intermittency issue of renewable energy and enhancing energy utilization efficiency. This study focuses on recent progress in TES materials, devices, systems, and government policies. In terms of the TES materials, the formulation of composite TES materials (e.g., phase change and thermochemical materials) to improve material performance, molecular-scale simulation of the material properties, and the associated fabrication technologies have been summarized. Corrosion challenges of TES materials in practical applications were reviewed, especially high-temperature molten salt corrosion. Heat transfer enhancement measures of the slab type, packed bed, and tube-and-shell TES heat exchangers were discussed for TES devices. Besides, TES systems based on latent heat storage and thermal management, thermochemical heat storage, and liquid air energy storage, have been introduced. Finally, government policies of different countries to facilitate TES technology deployment were reported.

Renewable energy is gradually changing from auxiliary energy to dominant energy. The establishment of a new power system with "new energy and energy storage" as the main body puts forward new requirements for high-power, large-capacity, and long-term energy storage technology. Energy storage technology has the characteristics of intrinsic safety, long cycle life, recyclable electrolyte, good life cycle economy, and environmental friendliness. In recent years, it has received extensive attention from academia and industry. On the basis of the author's experience in the research, development and industrialization of flow battery energy storage technology, this paper reviews the development process of flow battery, and introduces the basic principle, performance characteristics and technology of vanadium flow battery energy storage technology. And the industrialization development status, combined with many years of high-power, large-capacity vanadium flow battery energy storage system engineering practical design experience, the modular design method of large-scale energy storage power station is clarified, the implementation of 5 MW/10 MWh vanadium flow battery energy storage system. The energy system industrialization project has been operating safely and stably for more than 9 years, and the energy conversion efficiency and energy storage capacity have not declined significantly. The practical application results fully verify the safety and reliability of the vanadium flow battery energy storage system. It has met the requirements of industrial application. According to the actual price of the megawatt-scale energy storage system in the third quarter of 2021 by the world's leading vanadium flow battery energy storage equipment, the price and life cycle economy of the vanadium flow battery energy storage system with different energy storage durations were analyzed, and it was pointed out that the focus of future research and development.

Lithium metal batteries are considered next-generation rechargeable batteries owing to their ultrahigh energy density. However, during the charging/discharging process, the conversion mechanism and dendritic morphology of lithium metal anodes lead to huge and uneven internal volume modifications. Thus, lithium metal batteries experience more serious mechano-electrochemical problems compared with lithium-ion batteries, including lithium dendrite growth, lithium dendrite fracture and pulverization, solid electrolyte interphase (SEI) rupture, and electrolyte/separator mechanical failure. This review introduces the mechanical properties of lithium metal first, including elasticity, plasticity, and viscosity. Especially, the size effect of electrodeposited lithium is highlighted. Next, recent advances in mechano-electrochemical mechanisms in working lithium metal batteries are summarized. For the liquid electrolyte environment, the stress-driven lithium dendrite growth mechanism, interfacial (lithium metal and SEI, electrode and separator, and lithium metal and current collector) interaction mechanism, and external pressure regulation mechanism are presented. For the solid electrolyte environment, the ion transport impact from the solid-solid contact and interaction between the bulk/grain boundaries/voids of electrolytes and lithium metal are presented. Finally, the mechano-electrochemical mechanism in lithium metal batteries is summarized and the future development direction is prospected.

Lithium-ion batteries are being extensively used in numerous fields in terms of rapid reduction in production cost, which is primarily due to the technology development and effect of large-scale production. Several spent lithium-ion batteries will be generated, as their service life usually ranges from 6 to 8 years. The spent lithium-ion batteries, which generally contain rich energy metals and strategic elements, should be treated properly to avoid the waste of valuable energy element resources and environmental pollution. The recovery of cathodes that contain rich valuable metal elements has been intensively investigated and well-reviewed. As one of the four major materials of battery, electrolyte contains carbonate solvents and lithium hexafluorophosphate (LiPF₆) salt. It will be of both environmental protection and economic effectiveness once the spent electrolyte could be recovered and transformed into high-value products. This study will review the developed electrolyte recovery technologies and processes to efficiently improve the healthy development of the lithium-ion battery technique. Furthermore, its challenges and future development trends will also be summarized and prospected.

Room temperature sodium sulfur batteries are regarded as the next generation of large-scale energy storage systems because of its high energy density and the abundant resources of sodium and sulfur. Na₂S is a promising cathode material that possesses a high theoretical capacity (686 mAh/g), and is able to be coupled with non-sodium metal anode (e.g., hard carbon or Sn), which can get rid of the safety issues related to sodium metal. However, the electronically insulating nature and the poor reactivity of Na₂S, and its low kinetics conversion to polysulfides result in a large first-charge overpotential and poor cycle life, limiting their practical application. Herein, the fundamental knowledge and principle of storage sodium of Na₂S is detailed discussed. Additionally, recent reports on enhanced electrochemical performance strategies are comprehensively reviewed in detail with an emphasis on carbon-based Na₂S composite materials, Na₂S morphological structure design, Na₂S electrocatalytic mechanism, and device design. Finally, the perspectives are proposed on the future opportunities for Na₂S cathode material that are obstructing more practical Na₂S cathode based batteries.

Sodium-ion batteries (SIBs) are widely recognized as the best supplement to lithium-ion batteries in the field of large-scale energy storage applications. Hard carbons are the most practical anode materials for SIBs. However, the controversial sodium storage mechanism associated with the low-potential plateau and unknown structure-performance relationship of hard carbon anodes severely limits the commercialization of SIBs. This study summarizes the research progress and key challenges of different carbon anodes in SIBs and introduces the critical structural features of designing the ideal carbon anode. Then, inspired by our previous work on commercial carbon molecular sieves, we propose the ideal carbon model called "sieving carbons" The unique pore structure of sieving carbons, which we describe as a small pore mouth with a large pore stomach, and its impact on the sodium storage mechanism and properties are discussed in detail. Finally, the rational design principles for sieving carbon anodes with reversible and extensible low-voltage plateaus are discussed, as well as the opportunity and challenge of sieving carbons in promoting the commercialization of SIBs.

Large-scale energy storage is a pivotal part of the carbon neutrality and multi-energy complementation ecosystem, a bridge between clean energy and smart grid, and an important measure to ensure national energy security. The advanced secondary batteries are the key technology for large-scale energy storage. Sodium batteries based on oxide solid electrolytes (OSSBs), especially those with liquid metal sodium as the anode, are considered as one of the most promising and valuable grid-scale energy storage technologies owing to its high power density and abundant resources. However, there are still several shortcomings for OSSBs in terms of cycle stability, safety and cost, which prevent their practical applications. Importantly, strategies on how to effectively regulate the surface/interface electrochemical behavior of OSSBs and improve the energy storage performance while reducing the cost have become the focus of the current research. This review focuses on the research progress of OSSBs in recent years, mainly for the typical systems such as sodium-sulfur batteries and sodium-metal chloride batteries. We analyze the development of OSSBs from several key aspects, such as cost control, operating temperature reduction and application reliability optimization, and further propose the future prospects.

Compared with the current commercial lithium-ion batteries based on organic liquid electrolytes, solid-state lithium (Li) batteries using solid-state electrolytes hold great potential in improving safety and energy density, making them one of the important development directions for next-generation Li batteries. Among many solid-state electrolyte materials, Li₇La₃Zr₂O₁₂ (LLZO), a typical garnet-type solid electrolyte, has attracted extensive attention due to its high Li-ion conductivity and excellent chemical stability against lithium and wide electrochemical windows.However, the introduction of solid lithium lanthanum zirconium oxide (LLZO) causes many interfacial problems, such as noncontinuous physical contact, stress-strain, charge redistribution, and electrochemical instability. These problems affect the electrochemical performance of batteries and induce many new physical and chemical phenomena that require extensive exploration. In this review, from two perspectives of the external interface between the LLZO-based solid electrolyte and the electrode and the intrinsic interface inside the solid electrolyte and the composite electrode, the following topics are extensively discussed based on the research progress in our group and the frontier theoretical viewpoints in this field: First, the formation mechanism of lithium carbonate (Li₂CO₃) on the LLZO powder surface, its influence on electrochemical properties and the strategies to overcome this problem. Second, the effects of the internal interface regulation of LLZO-based electrolyte layers on the Li-ion conductivity and the electrochemical performance of the battery. Third, the characteristics of the LLZO/Li interface and the penetration growth of Li metal in LLZO-based ceramic electrolytes. The mechanism of Li infiltration and dendritic growth induced by the electric field, charge transfer, and stress-strain is also explicitly discussed. Fourth, existing problems of intrinsic interface inside the composite cathode and its integrated construction with the external interface against the solid electrolyte layer. By analyzing and summarizing the key science and technology of LLZO interfacial problems, this review inspires new insights into solving the critical problems of the garnet-type solid electrolyte/electrode interface and promoting the development of high-performance solid-state lithium batteries.

Flow batteries are regarded as a good contender for large-scale energy storage in grid applications. As flow battery technology has improved in the last decade, engineers now demand advanced modeling and simulation tools to assist the conventional experimental approaches to realize fast and efficient development of flow battery systems. In this study, recent advances in modeling and simulation of flow batteries are comprehensively reviewed, with a particular emphasis on numerical modeling and dynamic simulation of stack and module. Finally, future prospects for simulation technology for flow batteries are also discussed.

The popularization of electric vehicles is one of the main sources of demand for lithium-ion batteries. The charging performance of electric vehicles is an important parameter that affects the popularization process. With the same material system, a new charging strategy that replaces the traditional constant current and voltage charging strategy has attracted many researchers' attention in recent years. In addition, the new generation of battery management systems stipulates higher requirements for charging strategies. This article describes various optimized charging methods and their characteristics and applications. The research results show that, compared with the traditional constant current and voltage charging strategy, the optimized charging method can reduce charging time, improve charging performance, and effectively extend battery life. Finally, this article also proposes an outlook for the future optimization of charging strategies, hoping that online identification and real-time update of model parameters or the identification of characteristic signals through online methods will bring more powerful charging strategies.

Improving the green development of the whole society and realizing carbon peak and carbon neutrality are powerful driving forces for enhancing the adjustment of industrial structure and offer major strategic opportunities for the optimization and upgrading of industrial structure. This study combs the relevant data on the global production and sales of hydrogen energy and ammonia and the application fields, summarizes the crucial significance of China's development of renewable energy green hydrogen synthetic ammonia industry, extracts the fundamental conditions for China's development of green hydrogen synthetic ammonia industry from the energy base, crucial technologies, geographical distribution, and other factors, and analyzes technology roadmap, difficult challenges, technical developments and trends, competitiveness of various application scenarios, and the economy of green hydrogen synthetic ammonia. This study investigates the superior planning and development trend of China's green hydrogen synthetic ammonia industry and puts forward necessary suggestions for system guarantees and policies, to offer support for formulating the planning and policies of renewable energy green hydrogen synthetic ammonia industry. The research reveals that China has the fundamental conditions for the development of green hydrogen synthetic ammonia industry, and a detailed road map for the development and implementation of green hydrogen synthetic ammonia industry should be formulated as soon as possible. The study puts forward that China's green hydrogen synthetic ammonia industry is grouped into three steps. The primary task of the first stage (current—2025) is to enhance policy planning and technical level and give priority to the demonstration. The primary tasks of the second stage (2025—2030) are large-scale promotion, multifield support, and diversified application. The primary task of the third stage (2035—2050) is to improve the restructuring of the industrial structure and help attain double carbon target.

With the gradual expansion of lithium-ion battery applications in the field of new energy vehicles, endurance mileage has become a key factor restricting the development of new energy vehicles. Improving the energy density of lithium-ion batteries is an effective way to solve range anxiety. Owing to their high specific capacity, low cost, and relatively good safety, high-nickel ternary layered materials are now one of the most promising cathode candidates for the next high-specific energy lithium-ion batteries. However, increased nickel content significantly decreases ternary layered materials' cycling and thermal stability. In this regard, we first summarize the development process of cathode materials for lithium ion batteries and analyze the necessity of developing ternary layered materials for high nickel, after which the current challenges based on the research status of high nickel ternary layered cathode materials are systematically discussed. The failure mechanism of the material is comprehensively analyzed by considering cation mixing, structural degradation, microcracks, surface side reactions, and thermal stability. In addition, considering the problems of high nickel ternary layered materials, some effective and advanced improvement strategies, including surface coating, element doping, single-crystal structure, and concentration gradient design, are reviewed. The research progress of various improvement strategies and modification mechanisms is highlighted. Finally, we compare the characteristics of various improvement strategies. Based on the advantages of a single improvement strategy and the coupling effect of different improvement strategies, we look forward to the development direction of the improvement strategy for high nickel ternary layered materials and propose feasibility programs for the collaborative application of multiple improvement strategies.

Owing to their high energy density, low self-discharge rate, wide operating temperature range, and long cycle life, lithium-ion batteries are widely used in portable electronic equipment, electric vehicles, and energy storage. TiNb₂O₇ exhibits a much larger theoretical capacity (388 mAh/g). In the charging-discharging process, the volume change is small, and the generation of lithium dendrite can be avoided in the rapid charging process so that the battery has better safety and shorter charging time. Although TiNb₂O₇ is one of the most potential anode materials for lithium-ion batteries, its low electronic and ionic conductivities hinder its widespread application. TNO's structural characteristics, preparation methods, and modification strategies are discussed in this paper. The crystal structures and the mechanism of rapid lithium conduction are explained. Furthermore, several methods and their advantages for TNO preparation are introduced, including solid-state reaction, sol-gel, electrospinning, solvothermal, and template methods. In addition, the effects of nano, doping, defect, and composite on electron and charge conductivities, as well as the electrochemical performance of TNO, are emphatically analyzed. Nanocrystallization can shorten the diffusion path of lithium ions, the doping and introduction of oxygen vacancy can change the TiNb₂O₇ structure, the composite electrode can improve its conductivity, and different modification methods can effectively improve the rate performance and cycle stability of the electrode material, which is expected to make it a good application in high-power energy storage devices.

The United States (US) government has listed advanced batteries as one of the four key product supply chains to maintain and enhance its economic competitiveness and achieve the goal of a clean energy transition. Recently, it has issued successive policies to support the development of a complete advanced battery industry chain in the country, increased investment in science and technology, and the construction of innovation platforms. Furthermore, enterprises have also increased their investment in the battery field. Therefore, this study introduces the US government's recent policies to support advanced battery technology and related industries, including the White House's 100-day assessment report on the safety of advanced battery supply chain, the Biden administration's establishment of battery-related provisions in the Infrastructure Investment and Job Act, the formulation of National Blueprint for Lithium Batteries 2021—2030, and the release of Energy Storage Grand Challenge Roadmap. This study also analyzes how the US government supported battery innovation and the construction of innovation platforms, including the establishment of technology research and development projects, such as energy storage, batteries, and advanced vehicles. Additionally, it further summarizes the US investment implementation plan and development trends in the advanced battery industry under policy support, including the increased investment of automobile enterprises in the battery industry, rapid growth of some American start-up battery enterprises, and increased investment in the battery supply chain. Finally, the impact of US advanced battery technology and industrial development on China's battery industry development is also analyzed, and policy suggestions are proposed for China to tackle these challenges.

Energy storage technology is the key to constructing new power systems and achieving "carbon neutrality." Flow batteries are ideal for energy storage due to their high safety, high reliability, long cycle life, and environmental safety. In this review article, we discuss the research progress in flow battery technologies, including traditional (e.g., iron-chromium, vanadium, and zinc-bromine flow batteries) and recent flow battery systems (e.g., bromine-based, quinone-based, phenazine-based, TEMPO-based, and methyl viologen [MV]?-based flow batteries). Furthermore, we systematically review these flow batteries according to their development and maturity and discuss their traits, challenges, and prospects. The bottlenecks for different types of flow battery technologies are also selectively analyzed. The future advancement and research directions of flow battery technologies are summarized by considering the practical requirements and development trends in flow battery technologies.

"Carbon peak" and "Carbon-neutrality" goals have accelerated the electrification goal of the transportation industry. Electric vehicles face severe range degradation and refrigerant selection problems due to low-temperature heating. Therefore, this paper summarizes the CO₂ heat pump air-conditioning technology and the entire vehicle thermal management system to improve the electric vehicle range. The advantages and disadvantages of four new refrigerants, R134a, R1234yf, R290, and CO_2, are analyzed. The characteristics of the basic transcritical CO₂ cycle system are introduced, and the optimization of the basic transcritical CO₂ cycle system is emphasized; it includes the transcritical CO₂ cycle system with a regenerator and with the technology of adding gas and increasing enthalpy. To apply heat pump air conditioning in electric vehicles, the working modes and characteristics of the direct heat pump with three heat exchanger systems and the secondary loop system are described. For the whole vehicle thermal management of CO₂ heat pump air conditioning, the requirements of the occupant compartment, power battery, and drive thermal motor management of electric vehicle are introduced. Finally, it is concluded that the CO₂ heat pump air conditioning system will effectively solve the serious problem of the battery range attenuation of electric vehicles in the winter and play a significant role in vehicle thermal management. At the same time, the problems of refrigeration, pressure resistance, sealing, control, and integration under high-temperature conditions require further exploration.

Advanced adiabatic compressed air energy storage technology has broad application prospects, as its life-cycle energy consumption and carbon dioxide emission research are of guiding significance for promoting energy storage technology development and policy formulation. A 10-MW advanced adiabatic compressed air energy storage system was the research object; a life cycle assessment model of the compressed air energy storage system was established; a life cycle inventory of each stage was conducted based on the actual unit, national standards, and reference literature; and the life-cycle energy consumption and carbon emissions of the system were analyzed. The research results showed that the life-cycle energy consumption and the life-cycle carbon emissions per kilowatt-hour of electricity generation were 5.65 MJ and 36.73 g, and the life-cycle net energy efficiency was 63.7%, from which energy consumption and carbon emissions accounted for the largest proportions in the operation phase, 99.2% and 90.5%, respectively; the heat storage, compression, and expansion systems accounted for a significantly high proportion of carbon emissions. Sensitivity analysis showed that system operating efficiency, system life, and gas storage time are important factors affecting life-cycle carbon emissions and that life-cycle energy consumption is more sensitive to system operation efficiency.

Due to its high capacity, low cost, and environmental safety, layered oxide O₃-NaNi_1/3Mn_1/3Fe_1/3O₂ is one of the most promising cathode medium recently. However, its complicated phase transitions during the charge-discharge process lead to inferior electrochemical properties. In this study, we report a synergetic modification method to simultaneously increase the rate capacity and cycling stability of the O₃-NaNi_1/3Mn_1/3Fe_1/3O₂ cathode medium by utilizing B₂O₃-coating and B³⁺ doping. The B₂O₃-coated NaNi_1/3Fe_1/3Mn_1/3O₂ cathode was prepared using the ball milling method. Materials with different B₂O₃ contents were prepared and characterized using X-ray diffractometer, scanning electron microscope, transmission electron microscopy, and electrochemical examinations. The best performing compound was obtained when 2% B₂O₃ coating was utilized. B₂O₃ was uniformly distributed between NaNi_1/3Fe_1/3Mn_1/3O₂ particles, and the preparation process did not change the crystal structure of NaNi_1/3Fe_1/3Mn_1/3O₂. Furthermore, the charge-discharge curves indicated that the capacity retention of 2% B₂O₃-coated samples was enhanced from 78% to 87% after 200 cycles. B₂O₃-coated NaNi_1/3Mn_1/3Fe_1/3O₂ also exhibited remarkable rate capability (99 mAh/g at a high rate of 10 C, compared to 75 mAh/g for the pristine). These results indicated that the proposed approach is an effective and reliable surface modification strategy for reinforcing the electrochemical properties of layered oxide materials for sodium-ion batteries.

Studying the swelling force of Si-based anodes for the next generation of high energy lithium-ion batteries is crucial. In this study, we assembled 60-Ah large pouch batteries with commercialized SiO _x /Graphite and NCM811 cathode, tested their cycle life and swelling force increase, and studied the relevant mechanisms and strategies for reducing the swelling force. The structure of SiO _x was a 3～5 nm Si core distributed in amorphous SiO₂, and the specific capacity of SiO _x in the first cycle was 1380 mAh/g and the first columbic efficiency was ca. 75%. The swelling force increase during the first cycle was 7320 N, which was 4 times higher than that of graphite-based batteries. The cycling tests under different ambient temperatures showed high temperature-dependent tendency. At 25 ℃, 45 ℃, and 60 ℃, the cycle numbers were 980, 850, and 500, corresponding to 70% SOH, with the maximum swelling force being 25107, 25490, and 23667 N, respectively. The root cause for the swelling force increase was the solid electrolyte interface growth and thickening with repeated electrochemical cycles. The compression curve was applied to sorting appropriate cushion that can accommodate the swelling force. The results showed that polyurethane cushion had the best compression properties, reducing the swelling force by 50%. This study provides a foundation for using SiO _x in large-scale lithium-ion batteries.

Electrochemical impedance spectroscopy (EIS) contains rich information about the battery state of health (SOH). However, due to the correlation of EIS data at different frequencies, the SOH estimation model constructed from the whole frequency range of EIS data may have poor performance and high complexity. Therefore, this study proposes an SOH estimation method with feature selection and Gaussian process regression by combining sequential forward search and cross-validation to seek the feature set. A level diagram method was adopted to formulate model performance evaluation indicators based on the number of features and the estimation error, which aimed to balance model complexity and model estimation accuracy. A public dataset was used to validate the proposed method, and the results showed that the proposed model with feature selection could achieve higher accuracy and less time for the EIS test than the model constructed from the whole frequency range of EIS data. This study provides theoretical and technical support for applying EIS to online SOH estimation.

This study explores a time-sharing heating system using an electric boiler, which is a high-density composite phase change material. By combining the variation law of the load coefficient of heating in winter with outdoor ambient temperature, the optimization design of the heat storage device of the time-sharing heating system was performed, and the optimization principle of the time-sharing heating system was proposed. Considering the demonstration project of urban heating as an example, the time-sharing and proportion heating system could save the boiler room's space by 31%, initial investment by 33%, and operating cost by 46%. Furthermore, the power load of the boiler room can be reduced and pressure of power capacity can be increased, compared with the traditional direct-heat electric boiler. The heating load analysis revealed that the time-sharing heating system could heat peak regulation and equipment reserve function in extremely cold weather.

Cr₈O₂₁ is considered as a potential cathode material due to its high specific capacity and low cost. However, Cr₈O₂₁ can be only applied in primary batteries due to the large first-cycle irreversible capacity and the poor cycle stability. Currently, Cr₈O₂₁ is usually synthesized under high pressure or normal pressure under oxygen atmosphere. This procedure is dangerous and prone to generate impurity. Herein, the pure-phase Cr₈O₂₁ was prepared by two-step pyrolysis of CrO₃ under air atmosphere. The electrochemical performance of the as-prepared Cr₈O₂₁ cathode was investigated. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were used to investigate the electrochemical reaction mechanism of Cr₈O₂₁. The as-prepared Cr₈O₂₁ delivers a high initial discharge specific capacity of 400.4 mAh/g and a specific energy of 1218 Wh/kg at 0.1 C. The reversible specific capacity is 304.4 mAh/g and a reversible capacity retention of 88.7% is achieved after 100 cycles, exhibiting good electrochemical performance and cycling stability. The crystal structure of Cr₈O₂₁ consists of two [CrO₆] sublattice units and one [CrO₄] sublattice unit, in hich the [CrO₄] is located between the two [CrO₆] sublattice units. XPS tests reveal that the redox reaction of Cr₈O₂₁ involving three-electron transfer between Cr⁶⁺ and Cr³⁺ occurs during charging and discharging process. XRD tests indicate that the sublattice of [CrO₄] in Cr₈O₂₁ transfer to amorphous after the intercalation of Li-ions which corresponding to the first plateau at the initial discharge curve. Furthermore, at the second discharge plateau, the microcrystals of LiCrO₂ are generated. During the subsequent cycling, LiCrO₂ is electrochemically oxidized and reduced reversibly, suggesting the good rechargeable capability of Cr₈O₂₁.

The tubular ZEBRA battery (also called sodium-metal chloride battery) has extensive prospects in grid energy storage, backup power supply, and extreme environment applications, and has been commercially exhibited. However, enhancing its cycle stability performance is still the focus of the next-generation ZEBRA battery. Determining the state of health (SOH) is crucial to forecasting the cycle stability of the ZEBRA battery. Based on the analysis of the cathode particle characteristics, long cycle performance curves, and voltage relaxation curves of the tubular cell, we discovered that the ZEBRA battery would go through three distinct performance stages, namely, early activation, performance stabilization, and later performance aging stage. By observing the modifications in the voltage relaxation curves, we could judge the performance stage and obtain the ZEBRA battery's SOH. Based on the judgment, changing the composition of the cathode could reduce the activation time, and improve the long cycle stability of the battery.

Blast furnace slag (BFS) is a very affordable matrix material, and carbonates (Na₂CO₃ and K₂CO₃) are promising phase change materials for high-temperature applications; however, carbonates react with BFS when it is in the molten state. A two-step approach was created as a result to solve this problem. First, carbonate was used to modify BFS so that it can no longer react with carbonate; second, a hybrid sintering method was used to create form-stable phase change materials (FSPCMs). After thermal cycling, the obtained K₂CO₃/KMBS FSPCMs exhibited better shape preservation than Na₂CO₃/NMBS FSPCMs. Further tests revealed that K₂CO₃ and KMBS were chemically compatible. The measurement was consistent with the calculated value, and the latent heat of K₂CO₃/KMBS FSPCMs gradually increased with the increase in K₂CO₃ content. At the mass ratio of 4∶6 (40K₂CO₃/60KMBS), the latent heat is 94.8 kJ/kg, and the thermal stability is the best.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 4634 papers online from Jun. 1, 2022 to Jul. 31, 2022. 100 of them were selected to be highlighted. High-nickel ternary layered oxides and Li-rich cathode materials are still under extensive investigations of the influences of doping and interface modifications on their electrochemical performances and surface and bulk evolution of structures under prolong cycling. For alloying mechanism anode materials, such as silicon-based composite materials, many researchers pay attention to the binders. Large efforts were devoted to design the three-dimensional structure electrode, interface modification, and inhomogeneity plating of lithium metal anode. The researches of solid-state electrolytes are mainly focused on synthesis, doping, structure design and stability of pre-existing materials and developing new materials, whereas liquid electrolytes are improved by the optimal design of solvents and lithium salts for different battery systems and adding different additives. For solid-state batteries, the studies are mainly focused on the improvement of ionic and electronic conductivity in cathodes. To suppress the "shuttle effect" of Li-S battery, composite sulfur cathode with high ion/electron conductive matrix and functional binders are studied. Other relevant works are also presented to the design of electrode structure and manufactural SEI. There are a few papers for the characterization techniques are on lithium deposition, volume change of silicon-based anode materials and oxygen release of ternary layered materials. Furthermore, theoretical calculations are done to understand the stability of solid electrolytes and the interface of solid state electrolyte/Li.