Depth-dependent valence stratification driven by oxygen redox in lithium-rich layered oxide
Jin Zhang, Qinchao Wang, Shaofeng Li, Zhisen Jiang, Sha Tan, Xuelong Wang, Kai Zhang, Qingxi Yuan, Sang‐Jun Lee, Charles J. Titus, K. D. Irwin, Dennis Nordlund, Jun‐Sik Lee, P. Pianetta, Xiqian Yu, Xianghui Xiao, Xiao‐Qing Yang, Enyuan Hu, Yijin Liu
Abstract
Abstract Lithium-rich nickel-manganese-cobalt (LirNMC) layered material is a promising cathode for lithium-ion batteries thanks to its large energy density enabled by coexisting cation and anion redox activities. It however suffers from a voltage decay upon cycling, urging for an in-depth understanding of the particle-level structure and chemical complexity. In this work, we investigate the Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 particles morphologically, compositionally, and chemically in three-dimensions. While the composition is generally uniform throughout the particle, the charging induces a strong depth dependency in transition metal valence. Such a valence stratification phenomenon is attributed to the nature of oxygen redox which is very likely mostly associated with Mn. The depth-dependent chemistry could be modulated by the particles’ core-multi-shell morphology, suggesting a structural-chemical interplay. These findings highlight the possibility of introducing a chemical gradient to address the oxygen-loss-induced voltage fade in LirNMC layered materials.