Modulating the Spin State to Stabilize the Surface and Bulk Structure for Durable 4.6 V LiCoO2 Cathodes

Abstract

AbstractHigh‐voltage LiCoO2 (LCO) attracts great interest due to its high theoretical capacity, however, the aggravated oxygen redox, Co dissolution, and lattice degradation at high voltage potentially induce the instability of crystal structural and cathode–electrolyte interphase, and can ultimately lead to severe capacity fading. Herein, a design strategy of spin modulation is presented to stabilize the surface and bulk structure of the commercial LiCoO2 (C‐LCO). The prepared high‐spin state LiCoO2 via crystal field modulation elevates the Co─O band gap, suppresses the electronic compensation of oxygen at high voltage, and reduces the side reactions of reactive oxygen and dissolved Co ions with the electrolyte, which greatly restrains the irreversible phase transition from O3 to H1‐3 and the degeneration of cathode–electrolyte interphase. As a result, the spin‐modulated LiCoO2 shows significantly improved electrochemical performances including high discharge capacity, stable cycling behavior, and enhanced rate capability. This work based on spin modification by crystal field modulation can apply to other layered transition metal oxide cathodes, providing a new avenue for developing high‐energy–density cathodes.