Structures, issues, and optimization strategies of Ni-rich and Co-low cathode materials for lithium-ion battery

•The main issues of cathode materials can be summarized as microcracks, residual lithium compounds, and cation mixing.•Surface coating, elemental doping, electrolyte modification and crystal structure engineering can improve the electrochemical performance of cathode materials.•It is still difficult to meet the requirements of long cycle stability and battery safety by adopting a single modification strategy.•A comprehensive modification strategy has become a hot spot.