In recent years, reversible redox activities of both transition-metal (TM) cations and oxygen anions were found to be feasible in a number of Li-excess transition-metal oxides, enabling significant enhancement in charge storage capacity of lithium-ion battery (LIB) cathodes. [1-2] Most high-capacity cathode materials reported in the literature are either layer-structured similar to the well-studied Li- and Mn-rich (LMR) oxides, or cation-disordered rock-salts. For the layered LMR, repeated cycling at high voltages is known to cause significant voltage and capacity fade, hysteresis, and impedance rise. Understanding the origin of these issues has been on-going for well over a decade, and various degradation mechanisms have been proposed. [3-4] Likewise, obtaining high capacity in cation-disordered rock-salt oxides often comes at the expense of cycling stability that becomes progressively worse with either deeper oxidation of oxygen at higher potential or extended cycling involving oxygen redox. It is unclear, however, what properties and/or processes may have caused the performance issues in this newer class of cathode materials with 3D Li migration pathways. In this presentation, we use cation-disordered Li1.3Nb0.3Mn0.4O2 (LNMO), a compound recently reported to have an impressive discharge capacity of ca. 300 mAh/g at 60 oC [5], as a baseline system to investigate the chemical and structural origins of performance deterioration in this class of cathode materials. Degradation mechanisms as well as design strategies to balanced capacity and stability will be discussed.

Understanding performance degradation in Li-rich cation-disordered rocksalt cathodes

2019 Fall National Meeting

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