Inhibition of oxygen release and stabilization of the bulk structure of lithium-rich layered oxides by strong Mo–O covalent binding

Abstract

Lithium-rich layered oxides (LLOs) are highly promising materials for next-generation lithium-ion batteries. However, the irreversible oxygen release during charging and discharging can cause severe interfacial side reactions and unfavorable phase transitions, leading to capacity and voltage drops continuously, which is the root cause of deterioration in the performance of LLOs. In this study, an effective modification strategy of constructing strong covalent Mo–O bonds is proposed to change the local coordination environment of oxygen in LLOs and thus inhibits the release of lattice oxygen during cycling. It improves the migration barrier of transition metal elements, suppresses Mn reduction during the cycling process, prevents the occurrence of phase transition from layered to spinel, and plays a role in stabilizing the crystal structure. Moreover, lattice oxygen fixation prevents the release of O⁻/O₂ⁿ⁻ (0 < n < 4) species into the electrolyte that leads to undesirable interfacial reactions, and reduces the generation of a series of unfavorable film-forming organics, such as ROCO₂Li and ROLi. In this regard, a stable and highly ion-conductive cathode electrolyte interphase is formed on the surface of LLOs. The electrochemical results indicated that the cycling stability of the modified LLOs was significantly improved.