PNNL

Abstract

Earth-abundant cathode materials are urgently needed to enable scaling of the Li-ion industry tomultiply TWh annual production, necessitating reconsideration of how good cathode materials canbe obtained. Irreversible transition metal migration and phase transformations in Li-ion cathodesare typically believed to be detrimental because they may trigger voltage hysteresis, poor kineticsand capacity degradation. Herein, we challenge this conventional consensus by reporting anunusual phase transformation from disordered Li- and Mn-rich rocksalts to a new phase (named d)which displays partial spinel-like ordering with short coherence length and exhibits high energydensity and rate capability. Unlike other Mn-based cathodes, the d phase exhibits almost no voltagefade upon cycling. We identify the driving force and kinetics of this in-situ cathode formation andestablish design guidelines for Li-rich, Mn-rich compositions that combine high energy density,high rate-capability, and good cyclability, thereby enabling Mn-based energy storage.