Stepwise Dopant Selection Process for High-Nickel Layered Oxide Cathodes

Abstract

NCM-based lithium layered oxides (LiNi1–x–yCoxMnyO2) have become prevalent cathode materials in state-of-the-art lithium-ion batteries. Higher energy densities can be achieved in these materials by systematically increasing the nickel content; however, this approach commonly results in inferior cycle stability. The poor cycle retention of high-nickel NCM cathodes is generally attributed to chemo-mechanical degradation (e.g., intergranular microcracks), vulnerability to oxygen-gas evolution, and the accompanying rocksalt phase formation via cation mixing. Herein, the feasibility of doping strategies is examined to mitigate these issues and effective dopants for high-nickel NCM cathodes are theoretically identified through a stepwise pruning process based on density functional theory calculations. Specifically, a sequential three-step screening process is conducted for 38 potential dopants to scrutinize their effectiveness in mitigating chemo-mechanical lattice stress, oxygen evolution, and cation mixing at charged states. Using this process, promising dopant species are selected rationally and a silicon-doped LiNi0.92Co0.04Mn0.04O2 cathode is synthesized, which exhibits suppressed lattice expansion/contraction, fewer intergranular microcracks, and reduced rocksalt formation on the surface compared with its undoped counterpart, leading to superior electrochemical performance. Moreover, a comprehensive map of dopants regarding their potential applicability is presented, providing rational guidance for an effective doping strategy for high-nickel NCM cathodes. © 2022 Wiley-VCH GmbH