The role of dopants in mitigating the chemo-mechanical degradation of Ni-rich cathode: A critical review

Abstract

Ni-rich cathodes are more promising candidates to the increasing demand for high capacity and the ability to operate at high voltages. However, the high Ni content creates a trade-off between energy density and cycling stability, mainly caused by the chemo-mechanical degradation. Oxygen evolution, cation mixing, rock salt formation, phase transition, and crack formation contribute to the degradation process. To overcome this problem, strategies such as doping, surface coating, and core-shell structures have been employed. The advantage of doping is to engineer the cathode surface, structure, and particle morphology simultaneously. This review aims to summarize recent advances in understanding chemo-mechanical degradation mechanism and the role of different dopants in enhancing the thermal stability and overall electrochemical performance. The pinning and pillaring effects of dopants on suppressing oxygen evolution, cation mixing, and phase transition are introduced. It is found that the higher ionic radii enable dopants to reside on cathode particles, preserving the particle surface and refining particle morphology to suppress crack formation. Finally, the effect of doping on Li ion diffusion, rate capability, and long-term stability are discussed.