Exceptional Cycling Performance Enabled by Local Structural Rearrangements in Disordered Rocksalt Cathodes

摘要

The capacity of lithium transition-metal (TM) oxide cathodes is directly linkedto the magnitude and accessibility of the redox reservoir associated with TMcations and/or oxygen anions, which traditionally decreases with cycling asa result of chemical, structural, or mechanical fatigue. Here, it is shown thata capacity increase over 125 can be achieved upon cycling of high-energyMn- and F-rich cation-disordered rocksalt oxyfluoride cathodes. This studyreveals that in Li_(1.2)Mn_(0.7)Nb_(0.1)O_(1.8)F_(0.2), repeated Li extraction/reinsertionutilizing Mn~(3+)/Mn~(4+) redox along with some degree of O-redox participationleads to local structural rearrangements and formation of domains withoff-stoichiometry spinel-like features. The effective integration of theselocal “structure-domains” within the cubic disordered rocksalt frameworkpromotes better Li diffusion and improves material utilization, consequentlyincreased capacity upon cycling. This study provides important new insightsinto materials design strategies to further exploit the rich compositional andstructural space of Mn chemistry for developing sustainable, high-energycathode materials.