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

Abstract

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 (O₂^2-) 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.