As an important energy storage technology, sodium sulfur battery has GWh-class installed capacity in the global energy storage market. However, its safety problem has become a major factor restricting its further development. This paper first introduces the structure, operating principle and commercial development status of sodium sulfur battery, and then in view of the potential danger of this battery, proposes the resolution strategies based on the cell level and the module level. The strategies of toughening solid electrolyte, reducing local current density, enhancing thermal mechanical stability of sealing materials, anti-corrosion of cell shell, thermal management and fire source isolation of the battery incubator are analyzed. The research and development of materials and structure designs involving these strategies are reviewed, and the future research directions of sodium sulfur battery on low temperature type and high temperature flow type are presented finally.

In the process of Li-ion cell formation, a part of the active lithium from the cathode is consumed to form a solid-electrolyte interphase layer on the anode surface, resulting in an irreversible capacity loss. Especially in the case of adding high-capacity silicon-based anode materials to graphite, this kind of active lithium loss leads to an extremely low-first cycle coulomb efficiency and battery capacity. The problem can be effectively solved via the compensation of active lithium. The various ways used to supply active lithium are mainly divided into two categories: anode and cathode prelithiations. Anode prelithiation methods include physical mixing and chemical, self-discharge, and electrochemical pre-lithiations. The physical mixing lithiation method involves the addition of lithium metal powder to the anode or plate lithium metal foil to the anode surface, whereas the solution containing sacrificial lithium-rich compounds, such as butyl lithium, is used to prelithiate the anode in the case of chemical lithiation. Self-discharge lithiation is accomplished by the contact between the anode and lithium metal in the electrolyte. For electrochemical prelithiation, lithium metal is introduced into the battery as the third electrode, and the prelithiation is completed by discharging the anode. In the case of cathode prelithiation, sacrificial lithium-rich compounds with a high irreversible capacity are added to the cathode. Sacrificial lithium-rich compounds can be divided into binary lithium-containing compounds, such as Li₂O, Li₂O₂, and Li₂S; ternary lithium-containing compounds, including Li₆CoO₄ and Li₅FeO₄; organic lithium-containing compounds represented by Li₂DHBN and Li₂C₂O₄. The prelithiation technology can not only increase the capacity of lithium-ion cells but also benefit its cycling performances, especially for cells with silicon-containing anode. In this paper, the recent developments of lithium prelithiation technology are summarized, and several of our own works are introduced. The application prospect of lithium prelithiation technology is also forecasted.

Alloy-type materials are promising anode materials for lithium/sodium ion batteries owing to their high specific capacity and suitable lithium/sodium intercalation potential. Compared with the control of the morphology and structure of alloy materials, micron alloy materials are more cost effective. This article reviews the research progress in optimizing electrolyte to stabilize micro-alloy materials, and reveals the relationship between volume effect and the stability of micro-alloy electrodes. In the traditional electrolyte system, the volume expansion causes the alloy electrode exposed the fresh interface, which leading the fast decomposition of the electrolyte, but the volume effect is only a phenomenon, not the root cause of the failure of the alloy material. The decomposition of electrolyte can form an electronically insulating SEI on the surface of the pulverized alloy material (leading the alloy material lack of electrical contact), this is the root cause of the failure. At the same time, this article also compares the difference between the alloy electrodes in lithium storage and sodium storage, where sodium ions have lower desolvation energy than lithium ions, which makes it easy to complete the desolvation process at the interface of alloy electrodes. Also, the absolute potential of the alloying reaction between sodium ions and the alloy electrode is higher. These two advantages can improve the stability of the electrolyte (reducing the reduction and decomposition of the electrolyte), so based on the sodium storage mechanism of micron alloy electrode, the choice of electrolyte is wider. At the same time, this article also looks forward to the development direction of using electrolyte to stabilize micron alloy electrodes: increasing the voltage resistance window of ether solvents, and developing high-voltage lithium (sodium) ion full batteries based on the micron alloy electrodes.

Sulfide is one of the most promising solid electrolytes to realize all-solid-state batteries for its superior ionic conductivity and excellent mechanical properties. The Si-based anode with a high theoretical specific capacity (3759 mA·h/g, ～10 times that of graphite) is a promising candidate to further increase the energy density of sulfide all-solid-state for wide applications. Moreover, the combination of Si-based anode and sulfide solid electrolyte can be used to improve the interfacial solid-solid contact and ion transportation using mechanically soft sulfides to accommodate huge volume expansion of silicon-based anodes, thus achieving a high capacity and suppressing repetitive the solid-electrolyte-interphase formation to realize long-cycle high-energy density batteries. However, despite the promising advantages of Si-based anode sulfide all-solid-state batteries, effective characterization methods and in-depth understanding of basic scientific issues in this field are still missing, presenting poor full-battery performance, fast decay of capacity, and low energy density. This paper summarizes the related work/progress in this field and elaborates the three types of Si-based anode sulfide all-solid-state batteries (pellet, wet coating, and thin film). Moreover, the key factors influencing battery performances, such as Si particle size, external stress, appropriate cut-off voltage, and Young's modulus of sulfide electrolytes, are comprehensively analyzed. Finally, the current problems and challenges in this field are proposed for its benign development in the future.

All-solid-state lithium batteries, with good safety, long life and high energy, are an emerging option for next-generation technologies on the road to a green energy storage device. All-solid-state lithium batteries are prepared with all-solid electrode and all-solid electrolyte without liquid additives. Therefore, the electrode preparation and assembly of all solid-state lithium batteries are quite different from those of existing liquid lithium batteries. Here we summarize the typical assembly approaches of prototype all-solid-state batteries using oxide, sulfide, or polymer as solid electrolytes, providing reference for all-solid-state battery researchers.In this paper, the electrode preparation and assembly technology with the corresponding performance characteristics of several typical all-solid-state lithium batteries are reviewed in detail. The structure, cathode preparation methods, anode modification methods and battery assembly methods of oxide, sulfide and polymer solid electrolyte are summarized and analyzed respectively. Finally, some suggestions on the laboratory development and assembly methods of all solid state lithium batteries are given.

Solid-state lithium-sulfur (Li-S) batteries replace the traditional liquid electrolyte system with solid-state electrolyte, which is expected to solve the serious problems of the shuttle effect of polysulfide, the side reaction between lithium metal and liquid electrolyte, poor safety performance in liquid electrolyte-based Li-S batteries. However, solid-state Li-S batteries still face great challenges in terms of the selection of solid-state electrolyte and electrode/electrolyte interfaces. Herein, we review recently studies on the applications of sulfide solid electrolyte and polymer matrix electrolyte, and analyze the electrode/electrolyte interfacial contact issues in the solid-state Li-S batteries. The (electro-)chemical stabilization approaches to solve the intrinsic defects in sulfide solid electrolytes, and the properties of organic polymer electrolytes and ionic conductivity enhancement methods are detailedly summarized. We also demonstrate the intrinsic properties buried in the electrode/electrolyte interfaces that limit the capacity delivering. Recently reported corresponding approaches to suppress these serious problems are further reviewed, especially related to the sluggish reaction kinetics on the interfaces. In the last section, we point out that intrinsic defects of different electrolytes should be addressed critically, and it is of great significance for the practical application of solid-state Li-S batteries to further study the interface transport mechanism and design the electrode/electrolyte interface structure reasonably in practice.

Due to its high energy density, high safety, wide working temperature range, and long service life, solid-state lithium metal battery has been one of the important development directions of next-generation lithium batteries. As a typical oxide solid electrolyte, Li₇La₃Zr₂O₁₂ (LLZO) presents high lithium-ion conductivity, wide electrochemical window, high mechanical strength, and good thermal stability. Thus, LLZO solid-state lithium metal batteries have attracted significant attention in academic and industrial fields. However, the possible formation of lithium dendrite through the solid electrolyte and the large interface resistance between electrolyte and electrode limit severely its practical deployment. These issues are correlated with the microstructural characteristics of LLZO electrolyte, the chemical and electrochemical compatibility between cathode and LLZO, the solid contact at the cathode/electrolyte interface, and the wettability of lithium anode with LLZO electrolyte. This study reviews the reported advancements and summaries the strategies to solve these problems. For the cathode, the compatibility between the positive electrode and LLZO, and interface resistance can be improved by means of the surface coating of the cathode active particles, the construction of 3D electrolyte interface, the introduction of a flexible polymer or gel electrolyte as interlayer, and composition of positive active particles with flexible or viscous ionic conductive materials. For the anode interface, eliminating the lithium carbonate on the surface of LLZO electrolyte, introducing reactive or flexible intermediate layer, and modulating the lithium anode composition can improve the wettability of lithium to LLZO electrolyte; thus, reducing the interface resistance. Finally, the future research direction and perspective of LLZO-based solid-state battery is proposed.

Among various energy storage devices, rechargeable ion batteries (RIBs) have been commercialized in portable electronic devices, electric vehicles, etc., thanks to their advantages of excellent reversibility, long lifespan, high safety and easy-to-operate property. With the shortage of lithium and cobalt resources and the promotion of renewable energy sources, high efficient RIBs with low-cost and environmental friendly merit are urgently required, whereas their developments are limited by the lack of suitable cathode materials. Compared with other candidates, polyanionic compounds have shown virtues of diversity, structural fruitfulness, adjustable working potential and great stability, and therefore are promising cathode materials for promoting the application of next-generation RIBs. In this paper, polyanion cathode materials are systematically classified into phosphate, sulfate, single polyanion and mixed polyanion, and the crystal structure and electrochemical properties of various cathode materials are introduced in detail with LiFePO₄, Na₃V₂(PO₄)₃, NaVPO₄F, Na₂Fe₂(SO₄)₃, Li₂FeSiO₄, etc. as the representative compounds. The research progress of various kinds of polyanionic cathode materials is reviewed, and the research achievements of coating, doping and nanocrystallization of the materials are briefly summarized. Finally, the bottleneck in the development of polyanionic cathode materials, i.e., low electronic conductivity, is discussed, and the corresponding solutions are proposed.

With the rapid development of manufacturing technology, portable electronic devices are developing in the direction of stretchability, light weight, miniaturization, and intelligence, and stretchable electronic devices that can stretch, bend, and fold have emerged. Different from ordinary supercapacitors, stretchable all-solid supercapacitors have stronger anti-deformation ability, and have received widespread attention for potential applications in the fields of wear and medical treatment. This paper summarizes the research and development status of stretchable all-solid supercapacitors by discussing recent related literatures. It briefly introduces all solid-state supercapacitors, focusing on stretchable gel electrolytes, including three systems of hydrogel, organic gel and ion gel electrolytes. At the same time, it also focuses on the research status of stretchable electrodes, including stretchable electrodes based on gels, based on elastic substrates and based on structural design. Some challenges and future development directions that stretchable all-solid supercapacitors still need to face in the future are discussed, and the research focus of stretchable all-solid supercapacitors is to improve energy density, practicability and versatility. It is hoped that more innovative research will be stimulated to promote the development and practical application of stretchable supercapacitors.

Compared with the traditional liquid lithium-ion battery, a solid-state lithium battery (SSLB) uses a solid electrolyte instead of an organic electrolyte to greatly improve safety and energy density, which can effectively reduce safety risks of electric vehicles and relieve users' anxiety. A solid electrolyte is one of the core elements of SSLB and serves as the electronic insulator and ionic conductor. However, several problems, such as the low ionic conductivity, large interface impedance, and poor interface stability, exist with the use of this electrolyte. Based on the discussion of relevant literatures, the ionic conduction mechanism, and the research progress of sulfide solid electrolyte, oxide solid electrolyte, polymer solid electrolyte, and composite solid-electrolyte SSLB, the main problems and solutions of these four solid electrolytes were mainly reviewed and discussed in this work. For the improvement of ionic conductivity, the methods for adjusting the composition of solid electrolytes were introduced. As for the improvement of the interface, this work introduced the idea of interface design and manufacturing process. The comprehensive analysis showed that the performance of solid electrolytes can be effectively improved through doping and coating modification, exploration of the advanced interface research and diagnosis technology, and guidance of interface design with an excellent lithium-ion transport capacity, and innovation and optimization of the process. Finally, the industrialization processes of solid-state lithium batteries in domestic and foreign key enterprises were listed, and the future application prospect of solid-state lithium batteries was analyzed and prospected.

Under the considerations of superior ionic conductivities, excellent stable interphase with lithium metal anode, and low cost, lithium-stuffed garnets have been recognized as one of the most promising solid-state lithium electrolytes. Research on garnets and their composite electrolytes inspired the battery community over the past 10 years. However, the exploration of the unique morphologies of garnet-type electrolytes derived from new synthesis methods has received hardly any attention thus far, although the morphologies of garnet electrolytes are important for their applications in solid polymer electrolytes. Herein, we report a solvothermal method to synthesize a unique nanostructured garnet-type electrolyte, viz. cubic three-dimensional petaloid garnet electrolytes. Uniform aluminum-lanthanum-zirconium glycerate solid spheres are first synthesized as precursors and subsequently chemically transformed into three-dimensional petaloid garnet electrolytes. A composite solid polymer electrolyte containing 10% three-dimensional petaloid garnet exhibits a practically useful conductivity of 5.59 × 10^-5 S·cm^-1 at 25 ℃. For comparison, a composite solid polymer electrolyte containing 10% garnet nanoparticle shows a conductivity of 1.45 × 10^-5 S·cm^-1. This finding provides a strategy to explore superionic conductors.

Garnet-type electrolyte-based solid-state lithium metal batteries have attracted the attention of researchers due to their advantages of high energy density, high safety and long cycle life. However, there is huge interfacial impedance between garnet-type electrolyte and lithium anode, which seriously impedes the normal operation of the cell. To solve this problem, a bit of liquid electrolyte is introduced into the interface between garnet-type electrolyte and lithium anode in this work, which obviously reduces the interfacial resistance, and makes the solid-state lithium symmetric cells cycle normally. Furthermore, the morphology composition, interfacial resistance and cycle stability of the interface layer between garnet-type electrolyte and lithium anode are studied by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The research results show that liquid electrolyte greatly decreases the interface resistance, especially at 80 ℃, the values are as low as 1.89 Ω·cm² and 3.24 Ω·cm² before and after cycling, respectively.

All-solid-state lithium batteries with metal sulfide pyrite (FeS₂) as cathode can achieve a high reversible specific capacity. However, the large stress/strain and poor solid-solid contact during cycling seriously impedes the electrochemical performances of all-solid-state lithium batteries. In this work, Co-doped FeS₂ nanoparticles are synthesized by the solvothermal method, and the Li₇P₃S₁₁ solid electrolytes are in-situ coated on the surface of Co_0.1Fe_0.9S₂ nanoparticles to form Co_0.1Fe_0.9S₂@Li₇P₃S₁₁ nanocomposite materials. The doping of the transition metal Co can improve the electrochemical reaction kinetics of FeS₂, and the in-situ coating of Li₇P₃S₁₁ solid electrolyte can further improve the solid-solid contact and lithium-ion transportation at the interface, which results in excellent electrochemical performances of the all-solid-state lithium batteries. Transmission electron microscopy observation confirms that Li₇P₃S₁₁ solid electrolyte is coated on the surface of Co_0.1Fe_0.9S₂ nanoparticles. Electrochemical performance tests show that the coating of Li₇P₃S₁₁ solid electrolyte can effectively improve the specific capacity and cycling stability of FeS₂-based all-solid-state lithium batteries. The Co_0.1Fe_0.9S₂@Li₇P₃S₁₁ composite cathode delivers a high discharge capacity of 882.1 mA·h/g at 200 mA g^-1 and maintains a value of 670.9 mA·h/g after 100 cycles. This work can promote the application of metal sulfide cathode materials for all-solid-state lithium batteries and provide experimental evidence for the development of all-solid-state lithium batteries with a higher energy density.

The fast ionic conductive inorganic particles of Na₃Zr₂Si₂PO₁₂ (NZSPO) were introduced into polypropylene fine (PAN) nanofibers and used to form the three-dimensional fiber network-reinforced bicontinuous solid electrolyte composites of NZSPO/PAN-[PEO-NaTFST] via the electrospinning method. When the mass ration of NZSPO∶PAN was regulated at 2∶1, a maximum ionic conductivity at room temperature arrived at 3.38×10^-5 s/cm, and its electrochemical stability window can be expanded to 4.4 V. Na₃V₂(PO₄)₃ and metal Na were adopted as the cathode and anode to assemble an all solid-state sodium-on battery. The reversible capacity of the first cycle was 109.7 mA·h·g^-1, which can be maintained at 84.5 mA·h·g^-1 after 200 cycles with a high coulomb efficiency near 100% at 0.1 C. Differential scanning calorimetry curves confirmed that the NZSPO-PAN composite fiber can inhibit the crystallization of PEO polymer and accelerate the process of ion transport kinetics at low temperatures.

Aqueous zinc-ion batteries (AZIBs) are an attractive choice for large-scale energy storage in the future. However, suitable cathode materials for Zn²⁺ storage are lacking. This work finds that the cathode material Na₃V₂(PO₄)₃ (NVP) with the natrium super ionic conductor (NASICON) structure can achieve efficient Zn²⁺ storage and ultralong-cycle performance in high-concentration electrolytes. In this paper, a simple sol-gel method is used to prepare a uniform carbon-coated NVP. With the help of X-ray diffraction, scanning electron microscopy, constant current charge-discharge, and other characterization test methods, the structure, morphology, and performance of the NVP materials when used as cathode for AZIBs are analyzed. Additionally, the effects of different concentrations of electrolytes on the electrochemical performances are studied. The results show that NVP materials can provide high-capacity storage, excellent rate performance, and long-cycle life as the electrolyte concentration increases. After 1000 cycles at a high current density of 2000 mA·g^-1, the capacity retention rate is still 77.8%, and the coulombic efficiency per cycle of the material is close to 100%. Furthermore, the kinetic process of the NVP electrode is explored through cyclic voltammetry and galvanostatic intermittent titration technique. Experiments prove that these excellent electrochemical performances can be attributed to the stable and open NASICON framework and excellent kinetic behavior.

The development of anode materials with high specific capacitance and wide voltage is a valid approach to increase the energy density of quasi-solid asymmetric supercapacitors. Herein, nitrogen-doped amorphous vanadium oxide arrays are constructed on the surface of a carbon cloth by means of the hydrothermal reaction and subsequent interaction with ammonia. Compared with the undoped one, the nitrogen-doped amorphous vanadium oxide delivers a high specific capacitance of 432.2 F·g^-1 at -0.9～0 V with an excellent cycling stability and maintains a value of 203.3 F·g^-1 when the current density increases to 10 A·g^-1. When assembling into a quasi-solid asymmetric supercapacitor with a MnO₂@CC positive-electrode and PVA/LiCl gel-electrolyte membrane, the device shows a remarkably improved energy density of 50.5 W·h·kg^-1 at a power density of 475 W·kg^-1. The excellent electrochemical performance can be mainly attributed to its unique nanostructure. The amorphization induces vanadium oxide to expose more reactive sites, whereas nitrogen doping greatly improves the intrinsic conductivity with reduced polarization during the electrochemical process, hence significantly enhancing the specific capacitance and reaction kinetics.

The WO₃ is a typical cathodic electrochromic material, which colors in the reduction (cation intercalation) state and fades in the oxidation (cation deintercalation) state. However, Prussian blue (PB) is a typical anodic electrochromic material, which colors in the oxidation (cation de-intercalation) state and fades in the reduction (cation intercalation) state. The electrochromic-supercapacitor was constructed based on the WO₃ and PB films due to the matched color changes for WO₃ and PB films under different ion-storage states. The WO₃ and PB composite films were prepared on the surface of transparent conductive glasses using the pulsed laser deposition and electro-deposition methods. The symmetric electrochromic-supercapacitor was fabricated using WO₃ and PB composite films as electrodes. The results showed that the WO₃/PB composite film presents superior cycling stability with the areal capacitance retention of 83.8% after 200 cycles. In addition, the supercapacitor presents an optical contrast of 53.2% between the total coloring and bleaching states at 650 nm, which is ascribed to the synergetic color changes for WO₃ and PB films under different voltages. Such supercapacitor exhibits different color changes under different charge-discharge states; thus, realizing the indication of energy-storage states through color changes. Our work pushes the combination of electrochromism and energy storage, leading to the visualization of energy-storage states for supercapacitors.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 2566 papers online from Feb. 1, 2021 to Mar. 31, 2021. 100 of them were selected to be highlighted. Studies on layered-oxide cathode material foucus on doping, surface coating, preparation of precursors and structural evolution with cycling, among which, investigation on high-nickel ternary layered oxides attracts large attention. Volume expansion and subsequent problems is the focus of silicon-based anode materials, and research is mainly on coating of silicon particles, fabricating composite silicon-based anodes and microstructure control. Other anodes such as lithium metal, graphite and oxide electrode are also involved. Among them, researchs on the interface of lithium and design of three-dimensional structure anode are the main topic. As for solid state electrolytes, investigations mainly include the synthesis, doping and analyses of sulfide, oxide and polymer-oxide composite solid electrolyte. In terms of liquid electrolyte, electrolytes and additives for high-voltage ternary layered oxide cathodes and metal lithium anodes, regulation for positive/negative interface layers, and the performance improvement of graphite and silicon anodes is developed. For solid-state batteries, the preparation and design of composite positive electrodes, surface modification of active materials, and lithium metal/solid electrolyte interface are the main contents. To suppress the “shuttle effect” of Li-S battery, composite sulfur cathode based on catalysis, high ion/electronic conductive matrix, and other battery technologies are developed. The characterization analysis part covers lithium metal deposition, the volume expansion of graphite and silicon anodes, microstructure, dissolved transition metal elements and gas generation of cathode. Degraded interface contact in solid-state batteries, the deposition and peeling of lithium anodes, and the stability of the electrode interface is involved in theoretical simulation work part. The interface related studies involve SEI and the visual characterization in solid-state and liquid batteries mainly.

Lithium (Li) metal anode is a highly promising candidate for next-generation high-energy-density batteries, leading the future development of batteries to satisfy the ever-growing demand of energy storage. However, the uncontrollable reaction happens easily when ultrahigh active metallic lithium is exposed to the ambient environment, induce deterioration of electrochemical properties or even severe safety issues such as fire, combustion, explosion. The stabilization (passivation) of Li is of great significance to the safety and simplicity of industrial application. This review first briefly introduces the corrosion mechanism of lithium metal in air and suggests that the uncontrolled reaction of lithium metal with a variety of substances is an important cause of application safety problems. It then introduces the progress of lithium metal anode passivation technology from three aspects, including: i. physical protection by ex-situ physical coating such as ALD, MLD, magnetron sputtering and vacuum coating and spin coating; ii. lithium surface treatment by in-situ surface chemistry to produce protective layers such as lithium alloys, inorganic compounds, solid electrolytes and organic compounds; iii. architecture design to obtain a stable lithium metal anode. The advantages and disadvantages of each method are also analysed in relation to their process principles. Afterwards, the passivation mechanism and recent progress of application such as pre-lithiation, lithium-based batteries in conventional electrolyte systems and all-solid-state lithium batteries in energy storage are discussed. Finally, we propose some possible perspectives of lithium metal anode passivation technology in terms of addressing issues such as high costs and overall environmental protection.

The reference electrode test method has a wide range of applications in lithium-ion batteries. Herein, we introduce the production of several types of conventional reference electrodes, including Swagelok method, implant of reference electrode, and in-situ deposition. We also introduce the applications of lithium reference electrodes in lithium-ion batteries, such as the test of electrode potential, separation analysis in the electrochemical impedance spectroscopy of electrodes, the interface reactions between electrodes and electrolytes, and the decision of fast charging boundaries of batteries. We believe that the reference electrode can still be improved in the following aspects: lifetime, implantation position, and the convenience and operability of implantation. Thus, reference electrodes can find more applications in commercial batteries.

Anode materials are an important part of lithium-ion batteries. However, the current commercial lithium-ion battery anode materials have a low energy storage density, which is insufficient to satisfy the needs of the development of social productivity. Therefore, new high-capacity lithium-ion anode materials must be developed. Among the numerous candidate materials, transition-metal-oxide anode materials have attracted considerable attention due to their large theoretical capacity and excellent lithium storage performance. However, the application of transition-metal-oxide anode materials is limited by their low conductivity, poor cycle, and rate performances. To improve the electrochemical performance of transition-metal-oxide anode materials, researchers had conducted a number of research and achieved certain progress. This paper reviews the related achievements in recent years. The modification and optimization of transition-metal-oxide materials are described from two aspects: modification of transition-metal-oxide materials (morphology and size control, composite with other good performance materials) and preparation of new metal oxide anode materials (binary metal oxides). The key factors affecting the lithium storage performance of the materials are also discussed. The analysis shows that the nanomaterials are beneficial to slowing down the pulverization and prolonging the life cycle of the material. The synergistic effect can be achieved through combining with other materials to compensate its own defects. The binary metal oxide is an important topic in the research of transition-metal-oxide anode materials. Finally, the development prospect of transition-metal-oxide anode materials is prospected.

Due to the limited non-renewable energy resources, the use of renewable energy is greatly affected by the environment, and it is imperative to develop a new generation of energy storage and conversion systems. Potassium ion batteries are very likely to become the next generation of large-scale commercial energy storage systems due to their advantages such as high energy density and low cost. Prussian blue analogues have attracted great attention due to their open three-dimensional frame structure and the ability to quickly deintercalate potassium ions. Derivatives synthesized with it as a template have been extensively studied. Based on the investigation of relative literature, this review introduces the structure of potassium ion batteries and Prussian blue analogs and their derivatives in detail, summarizes the advantages of potassium ion batteries, Prussian blue analogs and their derivatives, reviews the current status of the application of materials in potassium ion batteries, and give a detailed introduction to the performance of the cathode and anode materials. For cathode materials, it mainly introduces iron-based, manganese-based, other types and partial substitution of Prussian blue analogs and related modification strategies, focusing on the analysis of the charge and discharge mechanism of different types of materials; for anode materials, the Prussian blue derivatives through carbon modificated strategies are introduced, and the advantages and disadvantages of the traditional carbon anode materials are briefly summarized for comparison. Comprehensive analysis shows that through exploring synthetic methods, adopting partial substitution, introducing low-dimensional structures and other strategies, it is expected to enhance the future applications of Prussian blue analogs and their derivatives in potassium ion batteries.

Sodium sulfate decahydrate is a popular inorganic hydrated salt phase change material because of its suitable phase change temperature (32.4 ℃), high latent heat of phase change value (>200 J/g), low price, wide source, safety and non-toxicity. However, there are problems such as large subcooling, severe phase separation and leakage in the application process. This paper reviews the research progress in recent years to solve the above problems, the preparation of eutectic salt phase change materials and related applications, and makes the following outlook on the subsequent research directions: in terms of reducing the subcooling degree, use of borax, preparation of eutectic salts or addition of external field perturbation to improve subcooling; in terms of suppressing phase separation, highly thermally conductive porous materials can be used to adsorb phase change materials, and the method of preparing stereotyped phase change materials by vacuum impregnation can be used to improve or eliminate the phase separation phenomenon; in terms of eutectic salt materials, binary phase diagrams can be drawn to find new eutectic phase change materials for research, especially organic phase change materials that are currently less combined; in terms of applications, focus on researching and broadening the scope of application in conjunction with sodium decahydrate sulfate phase change energy storage devices and systems.

Pouch-type gel Li-ion batteries were fabricated by in-situ polymerization and constructed from a LiCoO₂ cathode, a graphite anode, a ceramics-coated polyethylene separator, and a gel electrolyte that was dispersed in between. Electrochemical tests showed that the battery using the gel electrolyte exhibited comparable capacity and cycling stability compared with that using the liquid electrolyte. The differential scanning calorimeter tests indicated that the gel electrolyte exhibited an improved thermal stability toward LiCoO₂ and graphite than the liquid electrolyte. The hot-plate and accelerating rate calorimetry tests suggested that the safety property of the battery can be enhanced using gel electrolytes instead of liquid electrolytes. An ultrathin pouch battery was also fabricated by in-situ polymerization, and it showed good flexibility and can still operate after folding and cutting.

The latent heat per unit volume of sodium acetate trihydrate is about twice compared with that of paraffin wax at the same melting point. However, sodium acetate trihydrate has the disadvantages of phase separation and high subcooling, which limit its application. A thermal cycling device using a semiconductor thermoelectric cooling module was designed to shorten the cycle period and improve the experimental efficiency of experiments to study the stability of sodium acetate trihydrate. In the investigation of the stability of subcooling, a thermal cycling test was performed for 500 times on a sodium acetate trihydrate composite by adding disodium hydrogen phosphate dodecahydrate and nanoalumina as nucleating agents and sodium carboxymethyl cellulose as thickening agent. Experimental results show that this composite can nucleate effectively after 500 cycles and maintain a relatively stable supercooling. In the investigation of latent heat stability, the analysis of the phase diagram of sodium acetate trihydrate showed that the low solubility of anhydrous sodium acetate in water is the main reason for its phase separation. The content of disodium hydrogen phosphate dodecahydrate was increased to reduce the ratio of anhydrous sodium acetate to the bound water to reduce the latent heat loss of the composite phase-change material appropriately. The results showed that the average subcooling degree of the composite phase-change material was 5～8 ℃ under a high number of cycles, and the latent heat of phase change retained similar values. The results in this paper can be helpful for the application of sodium acetate trihydrate, and thermal cycling setup using thermoelectric modules can be used for the studies of other phase-change materials.

With the growing demand for cold chain logistics, convenient and fast cold chain transportation has been developed rapidly. As the core technology required for cold chain transportation, phase change cold storage technology is receiving more and more attention for it can improve energy utilization efficiency and provide a stable low-temperature environment required for cold chain transportation, and the key to its practical application is phase change energy storage material. This paper reviewed the development status of the cold chain logistics industry, introduced the classification of phase change energy storage materials used in cold chain transportation and their advantages and disadvantages, and summarized the methods and principles of phase change energy storage materials performance regulation; at the same time, it introduced the applications of various new phase change energy storage agents in food transportation and vaccine transportation; finally, it pointed out that the preparation of phase change energy storage materials with high cold storage capacity and stable cycling performance and the expansion of their applications are the focus of future research.

In the inspection of the internal conductor of the solid heat storage device, it was found that problems such as the deformation of the conductor, the self-short circuit, and the breakdown of the component due to the electromagnetic force of the heat transfer conductor under the high temperature situation, which seriously affect the safety of heat storage. In order to study the electromagnetic distribution and force of the electric heating element in the heat storage hole, this article focuses on the electromagnetic analysis and calculation of the 800 ℃ high-voltage electric heating element structure optimization design to ensure the reasonable distribution of electromagnetic field under high voltage. A three-dimensional finite element calculation model was established for the spiral and wave-shaped electric heating elements, the magnetic density distribution of the two models was analyzed, and the bending structure of the wave-shaped electric heating element was optimized. The influence of different voltages and different wave distances on the magnetic density spatial distribution of flat-angle wave elements is analyzed. Research shows that the magnetic density distribution of the wave-shaped electric heating elements in the two structures is more reasonable; The optimized flat-angle design can effectively reduce the internal and external breakdown of the component. The voltage only has an effect on the magnetic density value of the heating element, and the large wave pitch can effectively reduce the magnetic density distribution. While proving the feasibility of the proposed electric heating element model, this article also has a good guiding value for heat storage safety.

An outlet volute has a direct and non-negligible influence on the overall performance and working range of a centrifugal compressor. The complete three-dimensional turbulent internal flow of the outlet volute can cause a circumferential pressure distortion at the inlet of the volute, which directly affects the flow stability of the upstream components. In this paper, the multi-objective optimization design of the centrifugal compressor volute of a compressed-air energy storage system was performed, and a parameterized design method of variable cross-sectional shape was proposed. With the total pressure loss coefficient and static pressure recovery coefficient as optimization target variables, using multiple control surfaces and control points to control the cross-sectional shape of the centrifugal compressor volute and combining the optimal Latin hypercube experimental design method and the full three-dimensional computational fluid dynamics numerical method to generate the sample space, the second-generation non-dominated sorting genetic algorithm was used for multi-objective optimization of the Kriging approximation model, and an optimization platform and an optimization method were established. The results show that the optimized cross-section shape can reduce the shear stress in the vortex center and cause the uniform distribution of the meridional velocity in the outlet volute. In the design point, the overall isentropic efficiency and pressure ratio of the optimal design increased by 0.45% and 0.36%, respectively. Compared with the initial model, the volute with an optimized cross-sectional shape can improve the overall performance of the centrifugal compressor effectively. This research promotes the application of numerical optimization design method in the outlet volute of a centrifugal compressor and provides a reference for the optimal design of centrifugal compressors with high performance and low total pressure loss.

Two models of hollow flywheel with variable thickness are established to analyze their stress characteristics. The stress characteristics of the two models are analyzed using ANSYS Workbench. By increasing the flange height of the two rotor models, the variation law of flywheel stress and flywheel deformation is studied. Seven suitable flange heights are selected to analyze the change trend of stress in the direction of flywheel radius under the selected flange height, and the maximum stress and maximum deformation of the two flywheel models are compared. The results showed that the maximum radial stress, maximum circumferential stress, and maximum axial stress of the two flywheel models reach stable values at the flange height of 60 mm, 60 mm, and 80 mm, respectively. The maximum stresses of Model 1 are 65%, 13.3%, and 430% higher than those of Model 2, and the deformation is 43.89% lower than that of Model 2. Under the same moment of inertia, the stress stable values of Model 1 are 54.3%, 44.4%, and 1420% higher than those of Model 2. During the same conditions, using flywheel Model 1 can better reduce the deformation of flywheel; using flywheel Model 2 can better reduce the stress of flywheel. The research results can provide a reference for the design of energy storage flywheels with long cylinder structures.

Based on the power supply system of oil field, this paper studies the problem of insufficient power response of generator in the case of frequent load increase and decrease and large load shock value. Based on the technical characteristics of the energy storage flywheel, the power demand of the winch is compensated by the energy storage flywheel. Aiming at the existing problems, this paper carries out the objective optimization design and proposes a power slope distribution regulation scheme for winch, and builds a specific experimental platform for verification. Experimental results show that, input flywheel makes the power curve of the generator better smooth, reduces the power input of the unit about 500kW, improves fuel efficiency and power quality, at the same time, the potential energy of the drilling process is recycled,the effect of energy conservation and emission reduction is achieved.

Among the popular electrochemical energy storage components, supercapacitors are attractive in engineering applications because of their favorable characteristics of high power density and less working limitations. An integrated three-port converter is proposed in this paper to give full play to the supercapacitor and reduce the overall cost. On the one hand, the supercapacitor energy storage port is connected to the input port through a bidirectional Cuk converter, which can meet the voltage fluctuation requirements brought by the wide voltage operation characteristics of the supercapacitor and obtain continuous and small ripple port current. On the other hand, both the supercapacitor and the input port are connected to the output port through the boost-half-bridge converter. Because the components used in the boost-half-bridge converter are well multiplexed with the bidirectional Cuk converter, fewer components are required, contributing to lower cost. According to the power relationship between the input and output ports, the proposed integrated three-port converter has four operating modes. In these modes, the working principle of the proposed converter is basically similar, except for the value and direction of the port current, which has a good consistency. In this paper, the operation principle of the converter is analyzed in detail, and voltage gain between the three ports and voltage/current stresses of the components are derived. Finally, a simulation model is built to verify the effectiveness of the proposed converter working in four modes. This study helps promote the application of integrated three-port converters in supercapacitor energy storage systems, which may be further popularized.

Adsorption heat storage is a heat storage method with high-heat storage density and low-heat loss. Zeolite-liquid water adsorption heat storage system with zeolite particles, as heat storage medium, has the advantages of a simple system, good circulation performance, and high efficiency. In this study, the characteristics of the discharge process in the zeolite-liquid water adsorption heat storage system were investigated. The two-dimensional axisymmetric convection heat transfer model of the reactor was established using Fluent. The influence of the inlet velocity, reactor aspect ratio, and particle size on the water temperature at the outlet during the discharge process was analyzed. The results showed that the maximum temperature rise of 70 ℃ can be obtained during the system's discharge process under the present calculation conditions. The smaller the inlet velocity, the larger the temperature rise, and the larger the ratio of height to diameter, the larger the temperature rise. When the aspect ratio exceeds 1.5, the temperature rise will not increase with the increase in aspect ratio. Besides, the smaller the particle size, the higher the reaction rate, and the higher the temperature rise, the more favorable it is for zeolite to fully react with water. This study improves the mechanism of the solid-liquid adsorption process and provides theoretical guidance for the design and application of the zeolite-liquid water adsorption heat storage system.

Lithium battery energy storage cabin is the core component of the energy storage system, which stores a large number of batteries. Once a serious accident occurs, it is easy to burn the whole battery cabin. If the operation data of the system and battery stack at the time of the accident cannot be obtained, it will bring difficulties to the accident analysis. In this paper, the possible faults and abnormal conditions of lithium battery energy storage cabin are comprehensively studied and analyzed, and a scheme of lithium battery energy storage cabin operation status information acquisition system is proposed. The scheme can record the operation status information in real time, and quickly start the recording when the abnormal conditions occur in the energy storage cabin, save the data, so as to provide technical support for the accident analysis of energy storage system.

Domestic fuel cell cogenerated heat and power technology is a field with broad development prospects for fuel cell application technology. The proton exchange membrane fuel cell (PEMFC) consumes the chemical energy of the fuel during operation. In addition to converting part of the chemical energy into electrical energy, the rest of the chemical energy is lost in the form of heat. If this part of the heat cannot be used reasonably and effectively, it will decrease the energy utilization rate of the system and an unsafe operation of the fuel cell simultaneously. Under the premise of normal power generation, a water-cooled PEMFC cogeneration scheme was proposed to recover and utilize the heat generated during the operation of the PEMFC. The heat generated by the stack is taken out by the cooling liquid, and the high temperature cooling liquid after heat absorption is exchanged with the normal temperature tap water in the heat exchanger. The water tank is used to store hot water to realize heat recovery and utilization. Based on the Matlab/Simulink software platform, a fuel cell cogenerated heat and power system simulation model is established, which consists of a stack model, a radiator model, and a hot water storage tank model. Besides, a control strategy of the system in different working modes and a fuzzy PID controller for stack temperature control are designed. The results showed that a good dynamic response and anti-interference performance using fuzzy PID controller can be obtained. The simulation results also showed that the maximum-combined heat and power efficiency of the system within the power load range is about 83%, which meets the daily heating and electricity demand of the family and improves the energy utilization rate.

The estimation methods of state-of-charge (SOC) for lithium-ion batteries are reviewed. SOC is used to characterize the remaining capacity of the battery in the current cycle, which is also an important indicator of battery management in electric vehicles. When an accurate estimation of SOC is obtained, batteries would avoid bad working conditions, such as a run with low capacity, ensure that the battery always runs in a safe-state. Thus, the battery efficiency was improved and the life-time was prolonged. The common estimation methods of SOC are introduced and compared. The ampere-hour integration method is the simplest. However, it is an open-loop estimation system; thus, the estimation error is unable to correct itself. The open-circuit voltage method is used to estimate SOC based on the corresponding relationship between the open-circuit voltage and SOC. The need for long-standing time to obtain stable voltage values makes this method unsuitable for on-line estimation. The Kalman filter family method is a combination of ampere-hour integration and open-circuit voltage, which is suitable for on-line estimation. The system observation value error is used to correct the state estimation. When an appropriate battery model is established, high estimation accuracy can be obtained. The data-driven method needs long-term historical data to build a database. The advantages and disadvantages of these methods and the improvement scheme are summarized. Based on the above analyses, combined with the limitations and challenges of the SOC estimation algorithm in practice, the future research direction of on-line SOC estimation for lithium-ion batteries is presented.

With the lithium cobalt oxide battery as the research object, to solve the problem of the ineffective prediction of the state of charge (SOC) due to drastic changes in the battery current under complex working conditions, we established a double-layer unscented Kalman filter (DLUKF) architecture based on accurate parameters to estimate the value of SOC accurately. First, the functional relationship and characteristic curve between the open circuit voltage and SOC of the battery in the second-order circuit model were obtained from the experimental data of hybrid pulse power characteristics. Second, the recursive least squares method was applied to accurately identify the unknown variables in the model online to enhance the adaptive learning capability in the process of model identification and solve the problem of inaccurate model parameter estimation. Finally, the unknown variables in the model were identified accurately based on the output value of the model. Then, the DLUKF algorithm was used to realize the prediction of SOC fast to solve the problem of inaccurate estimation and large error of a single UKF algorithm in a strong nonlinear system. This paper compared the DLUKF algorithm with the single UKF algorithm under UDDS and FUDS conditions. The SOC curve, SOC error curve, terminal voltage curve, and terminal voltage error curve estimated by the two algorithms were compared. The results showed that the average error of DLUKF algorithm was lower than that of UKF algorithm, and when comparing predictions, the result of DLUKF algorithm was more accurate.

An improved ant colony optimization algorithm (IACO)-optimized particle filter (PF) is proposed for battery state of charge (SOC) estimation, and it is used to solve the particle depletion problem caused by the traditional particle filter algorithm SOC estimation. The ants replace the particles and reposition them before the update step to solve the particle depletion problem by increasing the diversity of the particles. Combined with the second-order Thevenin battery equivalent model, the state and observation equations required by the algorithm are obtained, and parameter identification is then performed in accordance with the pulse discharge experiment. The IACO-PF and PF algorithms are used to estimate the SOC under pulse discharge and DST operating conditions. The experimental results show that the lithium battery SOC estimation result based on the IACO-PF algorithm is more effective and accurate than the traditional PF algorithm.

The thermal effect of lithium-ion battery on the working process will affect its temperature and electrochemical performance and its safety and service life. For the design of battery thermal management systems, the change rule of thermal characteristics and heat generation mechanism of batteries in the process of discharge must be analyzed and the interaction of different properties of heat generation inside the battery under the temperature change be evaluated. Therefore, in this paper, an electrochemical thermal coupling model based on dynamic parameter response is established for nickel-rich ternary lithium-ion battery. The 0.3 and 1 C discharge and temperature rise experiments are conducted at 0°C and 40°C, respectively. The verification results showed that the coupling model has good accuracy and reliability and can accurately analyze the thermal characteristics of the battery. Based on the verified model, the temperature rise characteristics of Ni-rich Li-ion batteries under different discharge rates, ambient temperatures, and heat exchange environments are studied, and the internal heat generation mechanism and heating characteristics of the battery are further analyzed. The results revealed that the total heat production of the battery increases rapidly with the increase in the discharge rate, and the internal temperature inhomogeneity of the battery is aggravated. The large difference of the entropy heat coefficient between the positive and negative electrodes increases the heat production of the positive-electrode region and makes that of the negative electrode gentler. The research results can provide guidance for the thermal performance evaluation of lithium-ion battery and the design of the thermal management system of battery packs.

The direct measurement of the state of charge (SOC) for lithium-ion batteries, whose physical characteristics or the electrochemical characteristics are highly complex, presents difficulty. Methods, such as deep neural networks, have recently received wide attention and have been exploited to estimate battery SOC. To improve the estimation performance of SOC, capture accurately the interior dynamic characteristics of the batteries, and alleviate the vanishing and exploding gradient problem in neural networks, in this paper, we introduce a bidirectional learning strategy and develop two specific methods, i.e., the estimation of the SOC with the bidirectional long short-term memory (Bi-LSTM) networks and the bidirectional gated recurrent unit (Bi-GRU) networks. Both the proposed bidirectional networks consist of three parts: the input, hidden, and output layers. The input layer accepts the sequence of measurements, such as the voltages, currents, and temperatures. The hidden layer consists of two LSTM/GRU sub-layers; one processes the forward information, and the other processes the backward information to learn the input-output sequence mapping form the context of the sequence. The output layer outputs the learned SOC. Python, TensorFlow, and Keras are used to develop the concrete models, and the resultant ones are tested and analyzed on the benchmark data sets, where three temperature and nine working conditions are considered. The results show that the proposed bidirectional learning methods can outperform their competitors, with higher accuracy and better robustness. Being different from the idea of constructing battery equivalent models, the proposed method is data-driven and intends to estimate SOC with easily obtainable measurements, such as the voltages, currents, and temperatures, and provides a potential method for SOC estimation.

In recent years, the lithium iron phosphate battery (LIB) has been widely used in energy storage and power transformation systems because of its advantages of good stability and high reliability. With the purpose of investigating the fire risk of LIB with large capacity, the thermal abuse test of the 228 A·h LIB is conducted through the fire test platform. The combustion process and heat generation law of the LIB were systematically studied, as well the fire characteristics of the battery with different state of charge (SOCs) were compared and analyzed. The result indicates that the combustion behavior of the battery can be roughly divided into several stages: the first jet flame, stable combustion, multiple jet lame and extinguishing stages. Further, the combustion behavior will further accelerate the temperature rise, and the internal short circuit for the battery with higher SOC will cause the rapid temperature rise. The battery with high SOC shows intense combustion behavior while the corresponding burning time will be shorter, which is specifically reflected in the higher temperature, heat release rate (HRR) and heat of combustion. In addition, the venting time is earlier than the voltage drops although the high temperature will result in the slight attenuation of the battery. The results in this work can provide theoretical and technical support for the safety design and fire prevention and control technology of lithium-ion battery systems in the fields of energy storage and transformer substation system.

The change of concentration of lithium-ion in the liquid phase between the cathode and anode was monitored through the potential of battery, cathode, and anode with different charge and discharge rates using a three-electrode battery in this article. The trend of concentration variation of lithium-ion in liquid phase between the cathode and anode was also investigated using a three-electrode battery with different layers separator. The apparent chemical diffusion coefficient of the cathode and anode in a three-electrode battery was tested by GITT. The results are as follows: the concentration change of lithium-ion in the liquid phase between the cathode and anode during charging and discharging is related to the potential of an anode (vs. Li), and the concentration of lithium-ion in the liquid phase between the cathode and anode during charging is larger than the discharging. During charging, the higher the rate, the larger the concentration of lithium-ion in the liquid phase between the cathode and anode, and the opposite for discharging. Increasing the diffusion path by increasing the number of separator layers between the cathode and anode, the concentration of lithium-ion in the liquid phase between the cathode and anode decreases with the increase in layers, and the changing trend of the concentration of lithium-ion in the liquid phase remains unchanged. However, the concentration of lithium-ion in the liquid phase near the side of the cathode and anode is still different. The apparent chemical diffusion coefficient of lithium-ion in cathode (3.57×10^-9～5.63×10^-8 cm²·s^-1) is greater than that in the anode (1.16×10^-10～8.21×10^-8 cm²·s^-1). The trend of the diffusion coefficient of lithium-ion in an anode is related to the potential of an anode (vs. Li). The results showed that the deintercalation rate of lithium-ion in cathode is faster than that in anode, and the concentration change of lithium-ion in the liquid phase between the cathode and anode was controlled by the anode.

Based on the core collection database of Web of Science, the research about lithium secondary batteries was visually analyzed by the software Cite Space. The results showed that the research history of lithium secondary batteries can be divided into three stages, namely, the initial, steady growth, and rapid growth stages. The main research force changed constantly in Japan, the USA, China, France, and South Korea. More countries are joining this research, and countries are collaborating more closely. For the synthesis of battery materials with a high energy density and safety performance, the exploration of new electrode materials and technologies for structural performance optimization is an important research topic. The studies on electrodes for lithium secondary batteries are focused on layered oxides, spinel, and polyanionic materials for cathodes, and carbon, silicon for anodes and solid-state electrolyte. The selection of positive-electrode doping elements, the combination of novel technologies (such as nanometer and porous, among others), and emerging high-performance materials are important development directions for lithium secondary batteries.

Energy storage technology, which is the key technology to promote the adjustment of energy structure in China and even in the world, can solve the problems in the process of clean and renewable energy utilization such as low energy density, intermittently and large fluctuation. With the rapid development of the energy storage industry, the demand for high-level talents in energy storage technology has been skyrocketing. Energy storage technology involves the knowledge of power engineering and engineering thermophysics, electrical engineering, materials science and engineering, chemical engineering and technology, and has strong interdisciplinary, which brings great difficulty to the cultivation of talents in the field of energy storage. Aiming at solving serious shortage of high-level talents in energy storage technology, this paper carries out experimental teaching practice and exploration of interdisciplinary top-notch innovative talents training for energy storage technology. Taking China University of Mining and Technology as an example, the measures and methods to cultivate the innovative ability of top-notch talents in energy storage technology through interdisciplinary experimental teaching are introduced in this paper: strengthening the interdisciplinary basic knowledge of energy storage by adding specialized courses in energy storage technology, establishing a multidisciplinary team of energy storage technology innovation instructors and collaborative education through the manufature, teaching and research by relying on the high-level innovation platform of energy storage technology, etc. The results and quality of the training are analyzed, which provides some references for the cultivation of top innovative talents in the energy storage technology industry.