To improve the rate capability of hard carbon (HC), the corresponding hierarchical porous morphology was designed and the metal organic framework (ZIF-8) was selected as a precursor, and the hierarchical pore structure was adjusted via the addition of BiCl₃. The results show that the synthesized hierarchical structure of HC electrodes can effectively improve the diffusion of Na ions. The synthesized hierarchical porous hard carbon can achieve a high reversible capacity of 225 mA·h/g and 177 mA·h/g at different currents of 2 A/g and 5 A/g, respectively, based on the optimized micro- and macro-pores. Furthermore, a relationship between the hierarchical porous structure (with micro- and macro-pores) and the sodium storage process was discussed. It is indicated that the micro-pores prefer to facilitate the sodium-ion diffusion in a plateau region, while the meso-pores prefer to provide more defect sites to enhance the adsorption of sodium ions, consequently improving the sodium storage capacity.

Boron (B)-doped LiNi_0.6Co_0.2Mn_0.2O₂ cathode materials were prepared by oxalate co-precipitation and subsequent heat treatment. The effects of doping with different boron sources (B₂O₃, H₃BO₃ and LiBO₂) on the morphology, structure and electrochemical properties of the materials were investigated. The X-ray diffracation and Rietveld refinement revealed that the B element was successfully doped into the material lattice. The electrochemical performance characterization showed that the doping effect of B₂O₃ was the best, with excellent rate performance (the specific discharge capacity was 145.1 mA·h/g at 5 C) and long-term cycle stability (the capacity retention ratio was 84.5% after 300 cycles at 1 C). The enhanced electrochemical performance is attributed to the fact that boron doping effectively reduces the surface residual lithium compound, enhances the structural stability of the material, effectively inhibits the voltage drop and improve the polarization phenomenon, and reduces the charge transfer resistance, thus inhibiting the capacity decay and achieving excellent electrochemical performance.

The composite polymer solid electrolytes (CPE) were prepared by a solution-casting and hot-pressing method. Na-β-Al₂O₃ and g-C₃N₄ particles were incorporated into a polyoxyethylene and polycaprolactone blended polymer electrolyte to obtain the CPE. The microstructures, chemical and electrochemical properties of the composite electrolytes were investigated. The composite electrolyte with a high conductivity at room temperature, a high voltage stability, and a dendrite suppression capability is obtained via optimizing the mass ratio of each component, especially g-C₃N₄. At 50 ℃, the symmetric cells with metallic Na electrodes exhibit a good long-term cycling stability at a current density of 0.1 mA/cm². The all-solid-state cells with Na₃V₂(PO₄)₃@C positive electrode and Na/C composite negative electrode maintain a specific capacity of about 107 mA·h/g at 0.2 C.

Na₁₁Sn₂PS₁₂ solid electrolytes were synthesized by a high-temperature quenching method, and the structures as well as electrochemical performance were investigated. A Na₁₁Sn₂PS₁₂ phase with a certain amount of impurity can be obtained in quenching process. The content of impurity phase in the quenching precursors annealed at 430 ℃ decreases and the room-temperature ionic conductivity enhances from 0.34×10^-4 S/cm to 6.26×10^-4 S/cm. In addition, a prepared Na₁₁Sn₂PS₁₂ possesses a low activation energy of 0.27 eV and an electronic conductivity of 2.25×10^-8 S/cm, and an electrochemistry stability window between 0.8 V and 2.8 V. Also, Na₁₁Sn₂PS₁₂ is used in all-solid-state sodium batteries, showing good electrochemical performances.

A hammer-like Co₃O₄ was firstly prepared by using metal-organic framework-74 as a template, and then compounded with elemental Ag to fabricate a highly active catalyst with an improved electronic conductivity. The Li-O₂ battery with this prepared catalyst has a specific discharge capacity of 13 945 mA·h/g at a current density of 100 mA/g. Even at a high current density of 1 000 mA/g, the battery can still maintain a specific discharge capacity of 4 476.3 mA·h/g, indicating that it has an excellent rate performance. Also, the cycle performance is greatly improved. For the limited specific capacity of 1 000 mA·h/g at the current density of 500 mA/g, the battery with Ag/Co₃O₄ catalyst can be used for 195 cycles, while that with Co₃O₄ catalyst can be used for only 42 cycles.

Lithium-rich cathode materials are regarded as one of the most promising candidates for high energy lithium-ion batteries delivering reversible capacity of 300 mA·h/g, which are better than the commercial cathode materials. However, some drawbacks of lithium-rich cathode materials (i.e., low initial Coulombic efficiency, voltage decay and capacity decay) affect the practical application. In this review, we represented recent studies on two types lithium-rich cathode materials, i.e. lithium-rich Mn-based cathode materials and lithium-rich cation disordered cathode materials, introduced the crystal structure, cation redox and anion redox mechanisms of these lithium-rich cathode materials in detail, discussed the drawbacks of the materials and some sources of these drawbacks, and summarized the performance improvement, thus providing the theoretical guidance and technical support for future research of lithium-rich cathode materials.

The safety and cycling stability issues of lithium-ion battery as a prevalent electrochemical energy storage device have attracted much recent attention. Lithium plating on the anode material is a common failure reason of lithium-ion battery, thus becoming a hot research area in industry. However, some common detection methods are not applied for the batteries due to the closed packed structure. Therefore, the detection of lithium plating becomes a problem in the lithium-ion battery industry. To address this issue, this review represented recent progress on lithium plating detection methods via the following aspects, i.e., building special in-situ cells, prediction according to external properties, and measurement of new physical parameters. In addition, the future developing trend was also prospected.

Lithium-ion capacitor has structure of consisting of the battery-type anode and capacitor-type cathode, thus having a enabling high energy density and a high power density. This capacitor expected to become the next generation of new energy storage devices. The kinetic mismatch between the Faradaic battery-type anode and capacitive cathode is a great challenge for lithium-ion capacitors. Therefore, researchers have developed a variety of high-rate lithium-ion battery materials. Among these materials, vanadium-based materials are considered as ideal anode materials for lithium-ion capacitor due to their low cost, large specific capacity, and superior rate performance. This review summarized recent work on the optimization strategies of several vanadium-based anode materials, i.e. Li₃VO₄, VN and Li₃V₂O_5. In addition, the future directions in the application of vanadium-based anode materials for lithium-ion capacitor were also proposed.

Solid-state lithium batteries with solid electrolytes are expected to enhance the battery safety and energy density as one of the most promising next-generation batteries. Among various solid-state electrolytes, sulfide solid electrolyte is considered as promising candidate due to its ultra-high ionic conductivity. However, its large-scale production is restricted due to its fragility and difficulty in processing, which affects its application in solid-state batteries. Recent work indicates that the flexibility of solid electrolytes can be realized via introducing flexible polymers or supporting frameworks in solid electrolytes membranes, constituting a solution to the embrittlement challenge in large-scale and thin-film electrolyte preparations. Therefore, developing flexible solid electrolytes is one of the important strategies to promote the industrialization of solid-state batteries. This review introduced the physical/chemical properties and development of sulfide solid electrolytes, summarized the related research work on polymer self-supporting method and flexible skeleton-supporting method in the flexibility of solid electrolytes, and discussed the technical characteristics and advantages/disadvantages of wet/dry processes in the flexible sulfide solid electrolyte preparation, respectively. In addition, the future development aspects were also given to promote the practical application of solid-state lithium batteries.

Compared with conventional organic liquid electrolyte batteries, all-solid-state batteries for next-generation energy storage have attracted recent attention due to their advantages of high safety, high energy density and long cycle life. Organic-inorganic composite solid electrolytes as the most promising electrolyte systems have some advantages of inorganic solid electrolytes with a high strength, a high stability and a high ionic conductivity, and some advantages of solid polymer electrolytes for softness and easy processing as well. This review introduced the fundamentals of Li-ion solid-state electrolytes, and discussed some problems of organic-inorganic composite solid electrolytes (i.e., ionic conductivity, solid-solid interface, electrochemical window and compatibility between organic and inorganic compounds) and optimization strategies. In addition, some challenges and future development on organic-inorganic composite solid electrolytes were also described.