Na-ion batteries can meet the application requirements of being cost effective and having high safety in the field of energy storage due to the abundance of resources and their low cost, high energy conversion efficiency, long cycle life, low maintenance cost, and high level of safety. However, as a new chemical power system, Na-ion batteries have no related standard or specifications for their industrialization and marketing, which will seriously restrict the development of Na-ion battery technology. It is important to establish relevant national or industrial standards to standardize the inspection and quality of Na-ion batteries，regulate the market, and promote technological progress. In this article, we first introduce the situation concerning the global lithium and sodium resources. Then, we specify the characteristics and advantages, industrialization status, problems, and future development trends of Na-ion batteries， analyzing the current status of Na-ion battery standards worldwide and the reference standards or specifications of other batteries to point out the necessity of this exercise. Finally, we summarize the development history and reference significance of the standardization work done on lithium-ion batteries and suggest that the standard for Na-ion battery can be based on that of lithium-ion batteries, taking the characteristics of Na-ion batteries into account.

Sodium ion batteries are promising for large scale energy storage due to high abundance and low cost of sodium resources. So far, researchers have proposed several possible cathode and anode materials for sodium ion batteries. Electrolytes, serving as the media for redox reactions on cathode and anode, largely determine the electrode-electrolyte interfaces through the redox window, Na⁺ diffusion and migration, solvation structure of Na ions, and the coupled Na cation-anion-solvent (or solid framework) correlations etc. The electrolyte and interface play important roles in the thermodynamic and kinetics situations in sodium ion batteries, such as the electrode material stability, SEI formation, battery rate performance, thermal stability and cycling performance. In this work, we reviewed recent progresses in non-aqueous liquid and solid electrolytes for sodium ion batteries. The physicochemical properties of electrolytes and their remaining issues such as low ionic conductivity, narrow electrochemical window and poor stability of SEI layers are carefully discussed. The commercialization of sodium ion battery technology still requires development of functional and low-cost sodium ion battery electrolyte and comprehensive understanding the electrode-electrolyte interface properties.

Sodium-ion batteries have become a promising alternative energy storage device to lithium-ion batteries due to the abundance and low cost of sodium resources, especially for grid-scale energy storage systems. However, just like their lithium-ion batteries counterpart, sodium-ion batteries use a flammable liquid electrolyte as their ionic transportation medium, which inevitably leads to safety concerns. In this regard, solid electrolytes (SEs) can fundamentally resolve this issue due to their incombustibility. Besides, SEs can be paired with the metal anode directly, enhancing the energy density of the battery system. Compared to other types of SEs, inorganic SEs have attracted increasing attention owing to their high ionic conductivity, high ion transfer number, high mechanical properties, and excellent stability. However, in the practical application of all-solid-state sodium batteries, several inorganic SEs still face different difficulties such as low ionic conductivity and poor chemical/electrochemical stability. Therefore, the research and development of inorganic SEs is an important topic to realize the application of solid-state sodium batteries. In this paper, we introduce ion-migration mechanisms in solid materials and review the development of several of the most studied inorganic SEs: oxide, sulfide, and complex hydride electrolytes. Studies on solutions to enhance their ionic conductivity and chemical/electrochemical stability are discussed in detail, including the following aspects: enhancing ionic conductivity via ion doping; reducing the grain boundary resistance of NASICON-type SEs by controlling the chemical composition at the grain boundary or using a low-melting-point additive; solving the problem of the air sensitivity of sulfide-type SEs; developing new sulfide superionic conductors; and reducing the order-disorder phase transition temperature of complex hydride SEs and simultaneously increasing the ionic conductivity at room temperature. Finally, the key challenges and future developmental trends of SEs are summarized and discussed.

All-solid-state sodium-ion batteries consist of positive and negative electrodes and solid electrolytes. Solid electrolytes require not only high ionic conductivity but also a good electrolyteelectrode solid contact and interfacial stability. Of the diverse sodium-ion solid electrolytes, including oxides, sulfides, borohydrides, and polymers, sulfides are extremely attractive because of their advantages of high ionic conductivity and elastic modulus, good electrical contact with electrodes with cold-processing or solution coating, and broad temperature stability. In recent years, significant progress has been made concerning their ionic conductivity; however, their chemical stability and interfacial stability toward electrodes still requires in-depth study. In this study, the progress regarding sulfide-based sodium-ion solid electrolytes is reviewed, including preparation techniques, chemical structure, and ion transport. The mechanochemical synthesis, solid-state reaction, and solution synthesis methods are primarily discussed. The design strategies regarding the Na₃PS₄- and Na₃SbS₄-based ternary phase systems and the Na₁₁Sn₂PS₁₂- and Na₁₁Sn₂SbS₁₂-based quaternary phase systems are summarized. The influencing mechanism of cation- and anion-doping on Na⁺ vacancies/interstitials, Na⁺-lattice binding energy, lattice softening, Na⁺ distribution, and space groups is analyzed. In parallel, the interfacial performance between electrolytes and electrodes in all-solid-state batteries is reviewed, including the solidsolid contact between positive electrodes and electrolytes and the interfacial stability between negative electrodes and electrolytes. It is important to solve the interfacial issue that has arisen regarding sulfide solid electrolytes. Finally, some suggestions are presented for further investigations of sulfide-based sodium-ion solid electrolytes.

Owing to the low cost and abundance of sodium sources, sodium-ion batteries are considered one of the most competitive alternatives to lithium-ion batteries. However, the application of flammable organic liquid electrolytes in sodium ion batteries has potential safety hazards, including leakage, combustion, and even explosion. Due to its high safety, good stability, low cost, and environmental friendliness, NASICON-structured solid electrolytes can replace liquid electrolytes and separators to realize solid-state sodium batteries; this is becoming a new research hotspot in the field of energy storage. However, the ionic conductivity of NASICON-structured solid electrolytes needs to be further improved and high interface resistance between electrodes and solid electrolytes currently limit its further application. In this short review, the major crystalline structures and the sodium-ion migration mechanism of the NASICON-structured solid electrolyte are introduced and the main factors affecting the bulk conductivity and grain boundary conductivity are analyzed. Strategies to improve the bulk conductivity and grain boundary conductivity in recent years are summarized, showing that proper ion substitution and improvements in the phase purity and density are effective ways to improve the ionic conductivity. In addition, challenges for interface engineering and some interfacial modification methods in NASICON-structured solid electrolyte-based solid-state sodium batteries are presented, indicating that the exploration of novel modified materials and composite electrolytes is expected to further improve the interface properties. Finally, possible research directions and development trends of NASICON-structured solid electrolyte-based solid-state sodium batteries are discussed.

Recently, there has been rapid and profound progress with respect to the energy and power density of sodium-ion batteries. However, the conventional liquid organic electrolyte/separator system tends to evaporate and burst into flame, leading to wide concerns about its inherent low safety. To develop sodium ion batteries with high energy density and improved safety, solid electrolytes have gained attention, especially polymer-based electrolytes including solid and gel types. This article begins by reviewing the progress in fundamental mechanism and physical chemistry theoretical models for polymer electrolytes, followed by advancements in both solid and gel polymer electrolyte application in sodium ion batteries along with assessments of various material modification techniques, synthesis procedures, and novel material design. Based on the analysis, polymer electrolyte adopting oligomer, inorganic filler, and molecule design strategies are given for the successful conversion of a solid battery operation temperature from 90°C to room temperature or lower. A gel electrolyte relies on intermolecular forces and renders greater solvation effects for sodium salts, realizing quasi-solid batteries coupled with various electrodes generally at room temperature. In addition, a brief comment on hydrogel electrolytes concerning their great potential in aqueous sodium ion batteries is provided. Finally, an appeal is made concerning critical parameters, including volume and mass, in future reports, as well as a brief outlook concerning possible perspectives considering material design, and an in-situ polymer electrolyte technique in sodium ion batteries is proposed.

Sodium-ion batteries (SIBs) have been widely concerned by researchers because of their resource advantages and potential application in large-scale energy storage systems. The electrolyte is one of the core components of batteries, which plays roles of conducting ions and separating the cathode and anode electrodes. At present, the most commonly used organic liquid electrolyte has the shortcomings of flammability and easy to leakage, which brings great safety risks to the batteries and hinders the further development and application of SIBs. In this paper, the development strategies and research progress of improving electrolyte safety of SIBs are reviewed by summarizing the currently relevant reports. On the one hand, improvements and optimizations can be made on the basis of organic liquid electrolytes, such as the use of film-forming additives, flame retardant additives, or the use of high-concentration salt electrolytes; on the other hand, new electrolyte systems can be developed, such as aqueous electrolytes, ionic liquid electrolytes, all-solid-state electrolytes, and gel electrolytes etc. Advanced electrolytes are currently a research hotspot in the field of SIBs, in this article, the advantages and disadvantages of several advanced electrolytes and main challenges they faced have been analyzed and discussed. The application prospect of gel electrolytes in SIBs have been eminently introduced. Finally, the development trend of electrolytes for sodium ion batteries is prospected.

Low-cost and environmentally friendly sodium-ion batteries (SIBs) have great application prospects in the next generation of low-speed electric vehicle power and large-scale energy storage systems. The key to promoting the commercial application of SIBs is to develop electrode materials with excellent electrochemical performance and a low-cost. It is important to explore and fabricate appropriate high-performance SIB anodes. Compounds composed of oxygen/sulfur/selenium in group VI A as SIB anodes are low cost and environmentally friendly and have high theoretical capacity and safety, therefore attracting extensive attention from researchers. However, oxide/sulfide/selenide-anode materials cannot meet the rate performance demand due to their low electrical conductivity. In addition, the electrochemical cycling process is accompanied by a huge volume expansion, resulting in the crushing of the electrode, hindering the application of oxides/sulfides/selenides. Examining recent literature, this paper reviews the sodium storage mechanism of oxide/sulfide/selenide-anode materials and discusses their advantages and challenges. Some modification methods, such as composites with conductive carbon, structure control, and electrolyte improvement, are summarized as possible solutions to problems such as low conductivity, self-agglomeration, and sluggish kinetics. Finally, the development prospects of oxides/sulfides/selenides are forecasted for SIB anodes.

Due to the abundance of sodium resources, sodium-ion batteries (SIBs), as rechargeable batteries, have received increasing attention, especially for large-scale energy storage systems. However, the development of SIBs is hindered by the lack of suitable host materials to reversibly insert/extract Na ions. Layered transition metal oxides (Na_xMO₂, M = Fe, Mn, Ni, Co, Cr and their combinations) are promising cathode materials for SIBs due to their high theoretical capacity and simple structure. Interlayer glide and phase transitions are more prone to occur in sodium transition metal layered oxides than in their lithium counterparts. In this review, recent progress on the structural evolution and electrochemical performance of Na_xMO₂ materials are summarized. The dependence of the battery performance (the cycle performance, rate performance, and energy efficiency) on the structural evolution are discussed. In addition, this review presents several strategies to alleviate this problem and points to next generation electrode materials for SIBs.

Na-ion batteries are regarded as a potential new rechargeable battery technology to replace lithium-ion batteries for large-scale energy storage applications in the future due to the rich abundance of Na sources and their low cost. Cathode materials, an important component of Na-ion batteries, determine the electrochemical performance of Na-ion batteries. Due to the large ionic radius of Na⁺ ions, developing cathode materials with stable structures and fast Na⁺ ion diffusion is still a significant challenge. Recently, many layered materials have been explored as cathodes with promising electrochemical performances, exhibiting great potential for application in Na-ion batteries. In this review, recently reported layered cathode materials are summarized and their Na storage mechanisms are carefully analyzed and discussed. Finally, perspectives on the future development of layered cathodes and their potential applications in Na-ion batteries are provided.

Sodium-ion batteries have potential applications in the field of electric bicycles, low-speed electric vehicles, and stationary energy storage due to the abundance and low cost of sodium resources. Of the various cathode materials proposed for sodium-ion batteries, vanadium (V)-based polyanionic compounds have become a research hotpot due to their high energy density, high power density, and stable structure. However, the low intrinsic conductivity and improper preparation method of such compounds impede their bulk electron and ion transfer, which limit the specific capacity, rate capability, and structure stability of these materials. In this review, starting from an analysis of the cell structure and sodium storage characteristics of several typical V-based polyanionic compounds, we review the charge transfer process, strategy for improving the kinetics, and progress in V-based polyanionic compounds from the perspective of the microstructure and mesoscopic electrode structure. Meanwhile, combined with a discussion of the practical applications of V-based polyanionic compounds, the important research directions to promote the further development of V-based polyanionic compounds are summarized.

The surging market of lithium-ion batteries has pushed up the price of lithium. Meanwhile, the lithium resources in the Earth's crust are scarce and unevenly distributed. Therefore, it is highly desirable to pursue alternatives to lithium-ion batteries. Sodium-ion batteries have attracted significant attention due to the abundant sodium resources and because sodium has similar chemical properties to lithium. Moreover, solid-state sodium batteries based on non-combustible inorganic solid electrolytes, which combine the advantages of high safety and low cost, are becoming promising energy storage devices in the field of large-scale energy storage. With considerable effort, electrolytes suitable for solid-state sodium batteries have been developed, including common β-Al₂O₃, NASICON-type, and sulfide solid electrolytes, as well as novel sodium-rich anti-perovskite and composite hydrides. The ionic conductivity of these solid electrolytes at ambient temperature can be enhanced to over 10^-3 S/cm by optimizing the synthetic conditions, element substitution, and structural manipulation approaches, making them fully capable of meeting practical requirements. However, the practical application of solid-state sodium batteries still faces challenges from the poor chemical or electrochemical compatibility between the electrolyte and cathode/anode materials and an inferior solid-solid interfacial contact. Here we summarize the opportunities and challenges encountered in the application of different types of solid electrolytes for solid-state sodium batteries and their corresponding solutions, then we discuss the possible development directions and trends of solid-state sodium batteries in the future.

Sodium ion battery is expected to be widely applied in the field of scalable energy storage due to its abundant sodium resources and relatively low cost. As electrode materials for sodium-ion battery, the transition metal oxides generally store sodium based on conversion reaction, which have high theoretical capacity and good application prospect. However, the electrochemical performance of traditional transition metal oxide electrodes is greatly limited by large volume change, poor cycle performance, voltage hysteresis, inferior rate performance and low initial coulombic efficiency. In order to overcome the above limitations, the active material is usually designed as a self-supported array electrode with a three-dimensional structure. With the advantages of large open space, suitable specific surface area, good conductivity, and close contact between active material and current collector, the 3D array electrode can significantly improve the performance of transition metal oxides when applied in sodium ion batteries. In the present work, the research advances of transition metal oxide micro-nano structured arrays for sodium-ion batteries in recent years have been reviewed, and the outlook has also been given.

Sodium-ion batteries (SIBs), considered as potential supplement to lithium-ion batteries (LIBs), have been widely studied in recent years. Among all types of cathode materials, layered oxide material is the most promising kind and has been verified in 100 kW·h Sodium-ion battery energy storage station. However, it still suffers the disadvantages of high alkalinity and poor cycling performance. Benefited from the experience of gradient distribution design in ternary cathode materials for LIBs, liquid coating method was adopted to prepare manganese-rich shell coated layered oxide cathode material, so as to reduce the residue alkaline in the surface, to enhance the material process property during battery fabrication and to improve the electrochemical performance. Materials with different Mn contents were prepared and characterized by scanning electron microscope (SEM) and electrochemical examinations. The best performance is obtained when 1%Mn coating is utilized. The X-ray diffraction (XRD) results show that O3 structure (space group: R-3m) is maintained after coating. Moreover, the residual alkaline is reduced with calculated pH decreased from 11.74 to 11.33, proving the effectiveness of our design. At the same time, material with 1% Mn coating has the best electrochemical performance within the voltage of 2.5～4 V. The rate capability improved from 85.4% to 90.4% at 1 C rate after coating and the capacity retention after 100 cycles is also enhanced from 81.5% to 90.5%. In this paper, the Mn-rich shell coated positive electrode materials is studied comprehensively, which verifies the effect of our design and provides a new idea for the design of surface modified positive electrode materials.

With the widespread application of lithium-ion batteries (LIBs) in many energy storage fields, spent LIBs are being produced in large quantities. Discarding LIBs without any treatment causes great harm to the natural environment on which human beings rely for survival and is a waste of resources. In this paper, we collect lithium manganate cathodes from spent LIBs as the main raw materials. Via a combination of ball milling and high temperature sintering, the sodium-ion battery (SIB) cathode material Li_0.25Na_0.6MnO₂ (LNMO) is successfully synthesized; its electrochemical performance, kinetic characteristics, and the phase transition process caused by ion de-insertion are then studied. The results show that LNMO has a high specific capacity (131.5 mA·h/g) and an excellent rate performance (97.9% capacity retention). The apparent ion diffusion coefficient of the electrode is on the order of 10^-12 cm²/s, showing a fast ion de-insertion ability and kinetic process, which is one of the main reasons for its excellent rate performance. Recycling spent lithium manganate materials and applying them to the next generation of low cost SIBs has the dual significance of simultaneously achieving the effective recycling of spent LIBs and finding a source of raw SIBs materials.

VOPO₄·2H₂O is thought to be a promising cathode material for sodium-ion batteries (SIBs) owing to its typical two-dimensional layered structure, which facilitates rapid sodium transportation. Here, a cathode constructed of VOPO₄·2H₂O nanosheets (thickness: ~10 nm) was successfully prepared via a simple hydrothermal method. The corresponding morphology and electrochemical properties of the cathode were systematically analyzed. The as-prepared VOPO₄·2H₂O nanosheets were very uniform, and when used as the SIB cathode, it displayed an excellent electrochemical performance including high reversible specific capacity, excellent rate capability and good cycling stability. For example, the VOPO₄·2H₂O nanosheet cathode showed a high average operating voltage of 3.5 V and a reversible capacity of 130 mA·h/g at a rate of 0.05 C. Even at a high rate of 5 C, the cathode could still obtain a capacity of 70 mA·h/g and a retention of 77% was maintained after 400 cycles. This outstanding sodium storage performance is primarily due to the advantages of its unique nanosheet structure, which promotes rapid sodium diffusion.

Sodium-ion batteries (SIBs) are attractive for large-scale energy storage due to the abundance and low cost of sodium resources. However, cathode materials with single transition metal redox have limited capacity, hindering their further application. Recently, layered transition metal oxides have shown high specific capacity owning to the redox of transition metals and oxygen and have emerged as a new path to optimize the electrochemical performance of cathodes. Therefore, it is important to investigate the special structure and evolution mechanism in anionic redox reaction. In this study, the formation mechanism and structural regulation in anionic redox reaction are presented. This review is expected to offer a reference for designing high-performance cathode materials in SIBs.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 3632 papers online from Jun. 1, 2020 to Jul. 31, 2020. 100 of them were selected to be highlighted. Layered oxide cathode including Ni-rich oxides and lithium cobalt oxide are still under extensive investigations for studying the influences of doping and coating on their electrochemical performances, and the synthesis of single-crystal materials. Large efforts were devoted to optimize and design the electrode structure of silicon-based and lithium metal anode materials, aiming to buffer detrimental volume change and regulate the deposition of Li. The researches of solid state electrolytes mainly focuses on developing new materials and understanding the mechanism of Li⁺ transport, while liquid electrolytes mainly focuses on the optimal design of solvents, lithium salts and development of different additives The researches that work on Solid-State battery and Lithium-Sulfur battery involve mainly the development of 3D composite cathode. The evolution of electrode microstructure and electrochemical properties are investigated by using in-situ and ex-situ technologies. There are a few papers related to the theoretical works, too.

Lithium-ion batteries (LIBs) are widely used due to their advantages of high energy density and low environmental pollution. However, there are still some problems that cannot be ignored, i.e., degradation of the electrochemical performance and poor thermal stability due to the deterioration of the structure of the electrode materials. Therefore, modification of the electrode materials is still a current research focus for LIBs. Based on the unique advantages of niobium (Nb), introducing Nb into LIBs as a positive doping material can increase the electronic conductivity, improve stability, expand the insertion/extraction channel of Li⁺, and reduce the degree of cation mixing. In addition, the introduction of Nb into LIBs as a negative active material, via Nb oxide or Nb-based composite oxides, also results in excellent electrochemical performance. In solid electrolytes, Nb is not only the main doping element of Li₇La₃Zr₂O₁₂ but also the main component element of Li₅La₃Nb₂O₁₂. This paper discusses the recent literature and summarizes and analyzes the application of Nb in LIBs, with an emphasis on the doping mechanism and associated applications in positive material, negative material, and solid electrolytes for LIBs. For positive LIB materials, the research status of Nb in unitary, binary, ternary, lithium-rich, and polyanionic materials is introduced. For negative materials, the research progress of Nb oxide and Nb-based oxide anode materials as new negative materials is highlighted. In solid LIB electrolytes, the doping and application of Nb are introduced. Finally, the industrial application prospects and feasibility of Nb-modified electrode materials are analyzed. A comprehensive analysis shows that the research scope of Nb in lithium battery series is increasingly extensive as are its applications. It is believed that Nb will play a more important role in the field of lithium batteries in the future.

Lithium-sulfur (Li-S) batteries have attracted tremendous attention due to their high energy density, low cost, and environmental friendliness. However, the integration of intrinsic low conductivity (S/Li2S) and shuttle effects (polysulfides) may confine the utilization of active sulfur and cause serious volume expansion of active sites, therefore leading to a rapid capacity decrease during long-term cycles. In recent years, some publications have suggested that elemental sulfur could be fused at high temperature to form linear chain sulfur fragments and subsequently form organic sulfur copolymers via high temperature cyclization, which is considered an effective strategy to cope with the poor cyclic stability of the traditional Li-S system. In this review, first, we examine the reaction mechanisms and shortcomings of traditional Li-S batteries. Then, we review the synthesis methods, lithium storage mechanism, research progress of various active groups (nitrile, unsaturated hydrocarbon, thiol group, and micro-molecule organosulfide) and molten sulfur, list the dis/advantages of organosulfur polymer systems, and suggest strategies and outlooks according to scientific views. In summary, organic sulfur copolymers can efficiently reduce the shuttle effects of traditional C/S batteries, due to the whole/partial active sulfur fragment integrated into the cathode. Such organic sulfur copolymers may simultaneously achieve high sulfur loading and long cycling stability.

A nanostructured coating with conductive carbon is an effective way to improve the electrochemical performance of conversion-type materials. In this study, a three-dimensional porous sandwich-type structure constructed using interconnected two-dimensional N,P-co-doped carbon sheets with a composite of SnS₂ nanoparticles embedded in a carbon matrix is proposed. The resulting unique porous structure with large specific surface and structural stability is capable of facilitating ion/electron transportation and providing more active sites to adsorb more Na⁺, while the ultra-fine SnS₂ nanoparticles can accommodate the stress change accompanying the volume expansion and contribute to reducing the Na⁺ diffusion length. The composite electrode demonstrates superior stability, as well as an excellent rate capability. A kinetic analysis demonstrates enhanced surface pseudocapacitive behavior benefiting from the structural design and ultra-fine nanoparticles, which are the two main factors leading to its outstanding performance.

The widespread application of lithium-ion batteries greatly improves peoples’ quality of life. However, due to the use of flammable organic liquid electrolytes, there is a safety risk with traditional lithium-ion batteries and their energy density is limited. The development of all-solid-state batteries using solid electrolytes is expected to solve these problems. With high ionic conductivity, good environmental stability, and mild synthesis conditions, the NASICON-structured solid electrolyte Li_1+xAl_xTi_2-x(PO₄)₃ (LATP, 0≤x≤0.5) is a fairly promising solid electrolyte. This paper first reviews the progress of LATP according to four aspects: Its crystal structure, ionic diffusion mechanism, synthetic methods, and methods to improve its ionic conductivity. In addition, with the electrochemical instability and high interface impedance of the LATP solid electrolyte against electrode active materials limiting its application in all-solid-state lithium batteries, the solutions to these key issues are summarized in the second part of the paper. Finally, it is emphasized that interface problems are the main challenge limiting the application of LATP solid electrolytes in all-solid-state batteries, necessitating the development of better strategies to further optimize the interface between LATP and electrode active materials.

Zinc-air battery is a special fuel cell that uses oxygen in the air as a cathode reactive material. It has the advantages of high theoretical energy density, safety and portability, and green and pollution-free. It is one of the ideal power supplies for flexible wearable optoelectronic products. Electrochemical oxygen reduction reaction (ORR) and oxygen precipitation reaction (OER) play a vital role in the performance of zinc-air batteries. At present, noble metal Pt has the highest ORR catalytic activity in alkaline media, and Ir and Ru and their oxides have excellent OER catalytic activity. However, the high cost, scarcity, and bifunctional catalytic activity of a single precious metal catalyst have severely limited its commercial activity. It is important to develop non-precious metal bifunctional catalysts with catalytic performance equivalent to that of precious metal catalysts. Based on the research achievements of non-noble metal cathode catalysts for zinc-air batteries at home and abroad in recent years, this paper reviews in detail the research of non-metal heteroatomic doped carbon materials, transition metal matrix composites, transition metal compounds, metal-organic frames and their derivatives as cathode catalysts. The preparation methods of different materials and the effect mechanism of zinc-air battery performance enhancement are introduced in detail. It is concluded that the reasonable control of the size, morphology, and structure of non-precious metal bifunctional cathode catalysts can improve the performance of zinc-air batteries and is expected to replace precious metal catalysts. Finally, the current zinc-air battery non-noble metal cathode catalysts, including a summary on the problems existing in the development of the future should study the theory of electrochemical reaction, high development intrinsic catalytic activity of the composite catalyst and improve the air electrode structure three directions, is expected to achieve the commercial development of zinc-air battery non-noble metal cathode catalyst.

The electrode plates of lithium-ion batteries are the most important parts of the cell. An increase in the number of electrode plate layers can increase the capacity of the battery but also causes heat generation accumulation inside the battery and blocks heat dissipation externally, which ultimately threatens the safety of the battery. In this study, a three-dimensional layered electrochemical-thermal model is proposed for a 10 A·h lithium iron phosphate battery. The influence of the number of electrode plates on the heat accumulation effect is first analyzed theoretically, and then a temperature distribution validation is conducted to ensure the accuracy of the model. Subsequently, the effect of the number of electrode plates on the temperature distribution is investigated. The discharge rate and the number of electrode plate layers are both considered to examine the heat accumulation effect of lithium ion battery. The design basis of the number of electrode plate layers is ultimately provided. The results show that the heat accumulation effect is strengthened with the increase in the number of electrode plate layers, leading to a temperature increase of the battery. In addition, there is a larger temperature gradient in the direction perpendicular to the electrode plate. With the increase in the rate and number of electrode plate layers, the temperature of the tabs becomes higher than that of the cell and the high temperature region gradually concentrates in the tabs; therefore, the dissipation of the tabs is considered. In addition, the temperature deviation also increases as the discharge rate increases; the temperature deviation increases by approximately 11.2 times when the rate increases from 3 C to 10 C. Therefore, if the strategy of fast chargingdischarge is implemented for the battery, the number of electrode plates of the battery should not be too large to avoid an uneven distribution of the internal thermo-electrochemical properties caused by the excessive temperature differences in the battery, which eventually leads to high local temperatures or capacity degradation.

Li-ion battery is one of the most promising technologies in the field of grid power storage; however, fire safety issues hinder their large-scale application. This paper reviews the current literature referring to the safety status of Li-ion battery energy storage from the perspective of thermal runaway propagation theory, extinguishing agents, firefighting equipment, and relevant standards. The shortcomings of existing methods of fire prevention are pointed out, and the safety advantages of prefabricated container energy storage are summarized. Finally, the technical requirements and the emerging trends are discussed.

The frequent safety accidents of lithium-ion batteries have put forward higher safety requirements for battery manufacturers. Using the adiabatic environment provided by ARC, the 23 A·h soft-package NCM523 power lithium battery has been studied. During thermal runaway, thermal characteristic parameters change, temperature field distribution, and the evolution of thermal runaway. The thermal runaway trigger temperature of a 25% SOC battery is 22.68 ℃ lower than that of a 75% SOC battery. The maximum temperature T_m of a 75% SOC battery is 70.07 ℃ higher than that of a 25% SOC battery. The maximum temperature rise rate is 111.37 ℃/min. That is to say, the chemical reaction exotherm of the 75% SOC battery during thermal runaway is more severe and the thermal runaway is more destructive. During thermal runaway, the maximum temperature of the positive and negative electrodes of the 25% SOC battery are 385.5 ℃ and 342.7 ℃， respectively, and the positive temperature of the battery is higher than the negative temperature of 42.8 ℃; the maximum temperatures of the positive and negative electrodes of the 75% SOC battery are 508.8 ℃ and 365.8 ℃, respectively. The positive temperature of the battery is 143 ℃ higher than the negative temperature. The 25% SOC battery bulges obviously at 119.75 ℃; at 339.35 ℃, the battery generates a lot of thick smoke, the battery does not explode, and the damage is more serious after thermal runaway. The battery started to produce heat to the maximum temperature of thermal runaway, which took 5.125 h. When the 75% SOC battery is 171.06 ℃, a wide bulge appears near the positive electrode; after 4.77 min, a large amount of smoke is emitted between the positive and negative electrodes of the battery; within 1s, the battery emits flame, and the battery occurs The explosion, the combustion caused by the explosion lasted about 6.4 s, and the battery started to generate heat to the maximum temperature of thermal runaway for a total of 6.715 h.

Phase change material (PCM)-based thermal management systems have the advantages of no extra energy consumption, a simple system structure, and good temperature uniformity compared to air-cooled, liquid-cooled, and heat pipe thermal management systems. The battery arrangement and spacing have a large impact on the heat dissipation performance of the module, and there is little research on improving the performance of PCM-based thermal management systems via improving the module structure. An electrochemical-thermal coupling model was developed based on the finite element method. The accuracy of the model was verified via experiments. The numerical method was used to study the effects of parallel, staggered, and crossed arrangements and the cell spacing on the thermal management performance. For rectangular cylindrical battery modules, compared to non-parallel arrangements, the parallel arrangement can improve the utilization of phase change materials and the heat dissipation effect of a system. During the discharge process, the highest temperature of the battery generally increases and there is a decelerating increase process. The smaller the battery spacing, the higher the maximum temperature of the battery. The maximum temperature difference of the batteries shows a rising-falling-rising trend. The temperature difference and drop during the rising-falling process is positively correlated with the battery spacing, and when the maximum temperature difference rises again, it is inversely proportional to the battery spacing. The average phase change ratio starts to increase from the phase change start time. The smaller the battery spacing, the earlier the phase change occurs and the larger the average phase change ratio. For rectangular phase change material-based cylindrical battery thermal management systems, the optimal battery spacing is between 4 mm and 5 mm.

Safety issues are an important topic concerning lithium-ion battery energy storage systems. Exploring the causes of safety accidents and conducting intensive research on evaluations and early warnings of the safety status, as well as management and control and the prevention of safety accidents, have great significance. Based on the investigation report released on safety accidents that recently occurred in South Korea, we carefully analyzed four aspects of the factors involved, namely, the battery itself, the external excitation sources, the environment and operating conditions, and the related management systems, to examine the underlying mechanisms triggering and furthering the safety accidents. We discuss the interactions in-between the above four aspects. Moreover, we summarize these experiences and draw lessons from them, as well as propose research and development directions for the safety management of lithium-ion battery energy storage systems.

Studies on the estimation of the battery power state of charge (SOC) are primarily based on the charge and discharge data of a single cell under ideal experimental conditions, which may not correspond to the actual complex and variable driving conditions. In response to this problem, relying on the National Big Data Alliance of New Energy Vehicles and using data-driven methods, the transient, dynamic, and driving behavior and aging, dynamic, time-varying, and mileage features were derived. Using the method of stacking fusion and integration learning based on feature combination, an SOC estimation of the battery power discharge process under actual complex and variable working conditions was conducted. A reference XGBoost Model 0 based on transient features, five XGBoost Models (1, 2, 3, 5, and 6) based on feature combination, and a Linear Model 4 were constructed for comparison and analysis. Comparing Models 1-6 with the reference Model 0, the mean absolute error (MAE) and mean square error (MSE) of the stacked fusion model (stacked model) based on feature combination were the smallest, 0.39 and 0.32, respectively, which compared to Model 0, decreased by 38% and 46%, respectively; meanwhile, the coefficient of determination was the highest, reaching 0.9995, which was an increase of 2% compared to Model 0. The generalization ability of the stacked model also performed well, and the average and standard deviation of its accuracy reached 98.89% and 0.03%, respectively. Comparing Models 5 and 6 and the reference Model 0, it can be seen that, as the feature dimension increases, the MAE and MSE of the model decreases, the coefficient of determination increases, and the performance of the model improves. This study helps promote the application of data-driven methods in the estimation of the SOC of power batteries and provides guidance and a reference for the estimation of the SOC of actual electric vehicles.

Supercapacitor energy storage devices are used to realize the regenerative braking energy absorption functions in rail transit projects. These devices can be effectively used to solve the problem that the inverter feedback-type energy-saving device transmits the regenerative energy to the 110-kV main substation. Based on the train operation parameters in the actual project, mechanical and electrical analyses of the train-braking process are conducted. Further, an overall designs scheme of the energy-saving device with capacitor energy storage is proposed. The energy-storage-type energy-saving device includes a two-way chopper and a supercapacitor bank. The main circuit of the chopper adopts a staggered parallel two-way buck-boost circuit, and the supercapacitor bank adopts a series and parallel scheme. According to the voltage and current requirements of the energy storage device, several series and parallel configurations are designed for a supercapacitor bank. Based on the train model, rectifier unit, and energy storage device, a control strategy is designed for the chopper circuit in the energy storage device to realize energy storage during train braking and energy release during traction. Finally, the pulse-width modulator rectifier in its power-source mode is used as the train simulation source to simulate the traction and braking processes of the train. The control strategy of the chopper circuit and the charging and discharging characteristics of the supercapacitor are verified through experiments. Results show that the control strategy of the chopper circuit and the capacity configuration scheme of the power bank of the energy storage scheme satisfy the requirements of the source device.

China is speeding up the construction of a clean, low-carbon, safe and efficient energy system. The remarkable feature is to promote the rapid development of new energy installation. However, with the continuous increase of new energy installation, the random fluctuation of its output has brought huge peak regulation pressure to the power balance, and has become the main factor restricting the high proportion of new energy consumption. At the same time, due to the weak support of power electronic equipment of new energy, the security and stability of high proportion of new energy power system is also facing great challenges. Combined with the characteristics of new energy distribution, as well as the regulation demand brought by its rapid growth, this paper puts forward the analysis principle of enhancing power system regulation capacity and allocating energy storage; Combined with the safe operation requirements of UHV power grid, the role of energy storage in improving the security of UHV power grid is analyzed. The GW level energy storage is configured in the receiving end power grid to participate in the power grid frequency safety control, which can effectively reduce the impact of power imbalance, reduce the amplitude of system frequency drop, improve the frequency recovery characteristics, and ensure the frequency stability of the system. Comprehensive analysis shows that promoting the application of GW level electrochemical energy storage and building a more flexible and efficient power system can not only effectively promote the healthy development and efficient utilization of new energy, but also effectively guarantee the safe and stable operation of the power system with high proportion of new energy and high proportion of power electronic equipment. The pilot application of electrochemical energy storage in power system has gained a lot of experience, which lays a good foundation for the next large-scale application.

Mathematical models for predicting lithium battery lives are complex, prone to over-fitting, and have poor generalization; accordingly, a time series decomposition-integration model (EEMD-GSGRU) based on Ensemble Empirical Mode Decomposition (EEMD) and Gated Recurrent Unit (GRU) with Grid Search (GS) is proposed. In this model, the lithium battery capacity data are first decomposed into the trend factor with a large total proportion and the error factor with a small total proportion. Then, the decomposed time series are predicted for GRU and combined for a real-time rolling prediction. Finally, GS is used to search the network parameters and Adam optimization is used to update the network weight of the GRU. Using a lithium battery dataset provided by NASA for the model, the superiority of the EEMD-GSGRU model is proved in comparison to other algorithms. It is shown that the EEMD-GSGRU model improves the accuracy of the lithium battery life prediction.

This study focuses on the research of Chinese city application readiness status and improvement countermeasures of fuel cell logistics vehicles (FCLVs), which have become the vehicles with the largest scale of promotion and the highest degree of commercialization among all three fuel cell vehicle (FCV) types. The study is done from the perspective of hydrogen energy terminal consumption and based on summarizing the practical path and development trend of the promotion and application of FCVs in China. First, the study introduces main vehicle models and application scenarios of FCLVs, and investigates and compares the application status and key influencing factors of some representative Chinese cities from all four kinds of the country’s city-classes. Second, five dimensions including local conditions, policy environments, supporting facilities, vehicle operation and maintenance, as well as market promotion and their sub-level factors are constructed into the evaluating index system for city readiness of FCLVs by using methods of AHP, gray correlation, and Delphi. Deploying the established evaluation model, readiness of typical cities such as Shanghai and Foshan are measured and analyzed. The result shows that the overall level of city readiness of FCLV application in China is not high. Among the four classes of cities, the prefecture-level cities are the most active but the provincial capital cities are the weakest. Common challenges behind the low city readiness include intensive but weakly-targeted and implementable policies, and low expandable market promotion mode. Countermeasures and suggestions for different kinds of cities are put forward to improve their readiness of FCLV application, including optimization of the selection strategy of appropriate matching FCLV models with application scenarios, usage of renewable energy for hydrogen production according to local conditions and acceleration of the layout and construction of hydrogenation stations, enhancement of supporting policies such as the right of way and parking of FCLVs, and support of business model innovation and innovative operators.

Aiming at the problem of particle dilution in traditional particle filter (PF) estimations of the state of charge (SOC), an improved bat algorithm (IBA) is proposed to optimize the PF algorithm to estimate the SOC. The particles are represented as bat individuals, which imitate the predatory process of a bat population and solve the problem of particle dilution in PF technology. The theoretical model of the battery state space is built using a second-order Thevenin battery model, and the relevant parameters of the battery are identified. The SOC estimation experiment is carried out based on the IBA-PF algorithm and the standard PF algorithm under pulse current operating conditions and dynamic stress test operating conditions. The experimental results show that, compared to the traditional PF algorithm, the estimation accuracy of the lithium battery SOC based on IBA-PF is within 2%, which indicates good adaptability and stability for non-linear and non-Gaussian SOC estimations of lithium batteries.