Unveiling the Evolution of LiCoO₂ beyond 4.6 V

Abstract

The working mechanism of LiCoO2 beyond 4.6 V presents complicated issues: (1) the ambiguous multistructural evolutions, (2) the vague O-related anionic redox reactions (ARR) triggered by the overlap Co–O bands, and (3) the serious electrode–electrolyte interface stability challenges. The intricate relationship among them turns into a classic “chicken and egg” conundrum, leading to a confusing evolution process of LiCoO2. Herein, from an ingenious perspective combining stacking faults and nonhomogeneous delithiation, we originally demonstrate a series of intergrowth phase evolutions from O3 to O1, passing through the so-called H1-3 phase. Moreover, in sharp contrast to the O–O dimer formed in a traditional Li-rich layered cathode, a moderate and stable arrangement of oxidized lattice oxygen is unveiled as a manifestation of ARR in LiCoO2. Additionally, we clarify the nature that dehydrogenation and hydrolysis of electrolyte trigger the chain decompositions and intensify the surface degradation.