Optimizing Li-Excess Cation-Disordered Rocksalt Cathode Design Through Partial Li Deficiency

摘要

Li-excess disordered rocksalts (DRXs) are emerging as promising cathodematerials for Li-ion batteries due to their ability to use earth-abundant transitionmetals. In this work, a new strategy based on partial Li deficiency engineeringis introduced to optimize the overall electrochemical performance ofDRX cathodes. Specifically, by using Mn-based DRX as a proof-of-concept, itis demonstrated that the introduction of cation vacancies during synthesis(e.g., Li_(1.3)-xMn~(2+)_(0.4-x)Mn~(3+)_xNb_(0.3)O_(1.6)F_(0.4), x = 0, 0.2, and 0.4) improves both thedischarge capacity and rate performance due to the more favored short-rangeorder in the presence of Mn~(3+). Density functional theory calculations andMonte Carlo simulations, in combination with spectroscopic tools, revealthat introducing 10 vacancies (Li_(1.1)Mn~(2+)_(0.2)Mn~(3+)_(0.2)Nb_(0.3)O_(1.6)F_(0.4)) enables bothMn~(2+)/Mn~(3+) redox and excellent Li percolation. However, a more aggressivevacancy doping (e.g., 20 vacancies in Li_(0.9)Mn~(3+)_(0.4)Nb_(0.3)O_(1.6)F_(0.4)) impairsperformance because it induces phase separation between an Mn-rich and aLi-rich phase.