Engineering Surface Oxygen Vacancies Buffer Achieving Ultrahigh-Voltage LiCoO₂

Applying higher operating voltage (≥4.6 V) to elevate the energy density of LiCoO₂ (LCO) is essential for achieving high-energy lithium-ion batteries (LIBs). However, a higher working voltage would induce lattice oxygen release, resulting in the surface structure transition from the initial layered to a disordered phase. Furthermore, direct contact between the electrolyte and LCO material could lead to serious surface side reactions, resulting in severely enhanced interfacial resistance. Herein, by regulating the annealing temperature, we first introduced La₂Mo₂O₉ (LMO) with sufficient oxygen vacancies (41%) to engineer the LCO surface. Specially, the La and Mo ions with high bonding energy with oxygen could form robust La-O and Mo-O bonds with LCO surface oxygen, acting as an "oxygen anchor" to stabilize the oxygen. Furthermore, the abundant oxygen vacancies in the LMO buffer could in situ capture and reserve the possible released oxygen from bulk LCO. Therefore, the reaction involving oxygen species with the electrolyte is effectively mitigated, thus validly alleviating the structure degradation and elevating the electrochemical performance, enabling the half-cell to showcase 86.2% capacity retention after 100 cycles under 4.6 V and 1C, and a full cell could also achieve excellent capacity retention (90%) after 450 cycles.