In recent years, stricter standards for lithium-ion batteries have been proposed due to the rapid development of portable electronic devices and new energy vehicles. LiNi x Co y Mn z O 2 (NCM, x + y + z = 1) has gradually become the mainstream of cathode materials for powering lithium-ion batteries due to its advantages of high energy density, long cycle life, and high reliability. Furthermore, the energy density of the NCM ternary battery is proportional to the nickel content. Promoting high nickel batteries will realize their lightweight property and high commercial value. This research initially summarizes the properties of polycrystalline and single crystal high nickel cathode materials. Then, the problems of high nickel single crystal cathode materials are emphasized from cation mixing, structural degradation, microcracks, surface side reactions, and thermal stability. Moreover, the coping strategies of coating, surface coating, and additives are discussed in detail. Finally, a summary of high nickel single crystal cathode materials is given, and future research directions are discussed.

Sodium-ion batteries (SIBs) are regarded as an important substitute for lithium-ion batteries (LIBs) due to their abundant and widespread raw material resources. The choice of the cathode has a great influence on the electrochemical performance of the battery, and Na3V2(PO4)3 (NVP) is one of the most promising cathodes for SIBs. Its special NASICON (Na superionic conductor) three-dimensional structure is conducive to achieving excellent structural and thermal stability during the charging and discharging process. Moreover, it has a flat sodiation/desodiation potential plateau and rapid sodium diffusion kinetics. However, the weak intrinsic conductivity limits its further application in the market. Fortunately, there are some strategies, like doping foreign ions, modifying the carbon coating, constructing NVP-based heterogeneous composite materials, and changing the morphology of NVP particles, that are powerful approaches to solve this problem. Herein, the structure and some modification strategies (i.e., foreign ion doping, carbon coating, and construction of NVP-based heterogeneous composite materials) of NVP are carefully reviewed. Finally, we summarized this paper and explored the future development of the NVP cathode.