Quantifying Degradation Parameters of Single-Crystalline Ni-Rich Cathodes in Lithium-Ion Batteries.

作者：Wengao Zhao, Kuan Wang, Xinming Fan, F. Ren, Xie-Yu Xu, Yangyang Liu, Shi-Zhao Xiong, Xiangsi Liu, Zhengfeng Zhang, Mayan Si, Ruizhuo Zhang, W. van den Bergh, Pengfei Yan, C. Battaglia, T. Brezesinski, Yong Yang · 发表于：Angewandte Chemie · 年份：2023 · DOI：10.1002/anie.202305281 · 被引用次数：35 · 研究领域：Medicine

Single-crystal LiNi1-x-yCoxMnyO2 (SC-NCM, x + y + z = 1) cathodes are renowned for their high structural stability and reduced accumulation of adverse side products during long-term cycling. While advances have been made using SC-NCM cathode materials, careful studies of cathode degradation mechanisms are scarce. Herein, we employed quasi single-crystalline LiNi0.65Co0.15Mn0.20O2 (SC-NCM65) to test the relationship between cycling performance and material degradation for different charge cutoff potentials. The Li/SC-NCM65 cells showed >77% capacity retention below 4.6 V vs. Li+/Li after 400 cycles and revealed a significant decay to 56% for 4.7 V cutoff. We demonstrate that the SC-NCM65 degradation is due to accumulation of rock-salt (NiO) species at the particle surface rather than intragranular cracking or side reactions with the electrolyte. The NiO-type layer formation is also responsible for the strongly increased impedance and transition-metal dissolution. Notably, the capacity loss is found to have a linear relationship with the thickness of the rock-salt surface layer. Density functional theory and COMSOL Multiphysics modelling analysis further indicate that the charge-transfer kinetics is decisive, as the lower lithium diffusivity of the NiO phase hinders charge transport from the surface to the bulk.