Stabilizing Lattice Oxygen via Interfacial B–O Complexing for a 4.6 V LiCoO2 Cathode

Lithium cobalt oxide (LiCoO2) cathodes suffer serious structure instability when charged to high voltage (>4.5 V), including H1-3 phase transition, cobalt dissolution, and interfacial side reactions, which are closely related to the instability of surface lattice oxygen. Herein, an interfacial B–O complexing strategy was proposed to stabilize the surface lattice oxygen of LiCoO2 at 4.6 V, through the preferential coordination between derived products of the tris(pentafluorophenyl)borane electrolyte additive and LiCoO2. Combining a series of in situ and ex situ characterization methods with temporal and spatial resolution, it was revealed that the emergence of peroxy-like species (O22–) at high potentials is one of the origins of the instability of LiCoO2, which can be well inhibited thanks to interfacial B–O complexing. Thus, oxygen loss and interfacial side reactions can be drastically retarded, which consequently provides a more stable chemical environment for Co element, avoiding the dissolution and valence reduction of Co. Owing to the well-anchored Co and O elements, undesirable phase transition and local coordination structure change are suppressed, hence improving the capacity retention and rate performance of LiCoO2 at 4.6 V. This study provides an interfacial complexing strategy to stabilize the high-voltage LiCoO2 cathode.