Engineering Surface Oxygen Vacancies Buffer Achieving Ultrahigh-Voltage LiCoO₂.

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• High-energy lithium-ion batteries (LIBs) require higher operating voltages (≥4.6 V) for increased energy density.
• Elevated voltages in LiCoO2 (LCO) cause lattice oxygen release, leading to surface degradation and increased interfacial resistance due to electrolyte reactions.

Purpose of the Study:

• To engineer the surface of LiCoO2 to withstand higher operating voltages.
• To mitigate surface degradation and enhance the electrochemical performance of LCO-based LIBs.

Main Methods:

• Introduced lanthanum molybdate (La2Mo2O9, LMO) with 41% oxygen vacancies onto the LCO surface by regulating annealing temperature.
• Utilized La and Mo ions as an "oxygen anchor" to stabilize LCO surface oxygen via robust La-O and Mo-O bonds.
• Leveraged LMO's oxygen vacancies to capture released oxygen from bulk LCO in situ.

Main Results:

• Successfully stabilized the LCO surface structure at high operating voltages.
• Mitigated interfacial side reactions between the electrolyte and LCO material.
• Achieved 86.2% capacity retention in a half-cell after 100 cycles at 4.6 V and 1C.
• Demonstrated 90% capacity retention in a full cell after 450 cycles.

Conclusions:

• Surface engineering with LMO effectively stabilizes LCO at high voltages by anchoring oxygen and capturing released oxygen.
• This approach significantly alleviates structural degradation and enhances the electrochemical performance and cycle life of LCO-based LIBs.