Recent advances in Ni-rich layered oxide particle materials for lithium-ion batteries

Ni-rich layered oxides with chemical formula of LiNixCoyMnzO2 or LiNixCoyAlzO2 (x + y + z = 1, x ≥ 0.6) have been considered as promising cathode materials for lithium-ion batteries (LIBs) because of their high specific capacity (≥ 180 mAh g–1) and acceptable manufacture cost. However, the problems associated with high Ni content severely restrict their large-scale applications. In this review, we summarize the recent advances in Ni-rich layered oxide particle materials for LIBs. We begin with the introduction of the structure, redox mechanism, and problems of Ni-rich layered oxides, mainly including residual lithium compounds, gas evolution, rock-salt phase formation, microcrack of particles, dissolution of transition-metal ions, and thermal runaway. Then, four strategies (primary particle engineering, surface coating, doping, concentration gradient design) toward solving the problems of Ni-rich layered oxides will be systematically discussed with the emphasis on structure-performance relationships. To achieve satisfied comprehensive performance and accelerate large-scale applications of Ni-rich layered oxides, the combination of two or more strategies (particle engineering and surface/bulk stabilization techniques) with synergistic effects is necessary in future works. This review would promote further research and application of high-performance Ni-rich layered oxide particle materials for LIBs.