Progress and perspective of high-voltage lithium cobalt oxide in lithium-ion batteries

Lithium cobalt oxide (LiCoO2, LCO) dominates in 3C (computer, communication, and consumer) electronics-based batteries with the merits of extraordinary volumetric and gravimetric energy density, high-voltage plateau, and facile synthesis. Currently, the demand for lightweight and longer standby smart portable electronic products drives the development of the upper cut-off voltage of LCO-based batteries to further improve the energy density. However, several challenges, including irreversible structural transformation, surface degradation, cobalt dissolution and oxygen evolution along with detrimental side reactions with the electrolyte remain with charging to a high cut-off voltage (>4.2 V vs. Li/Li+), resulting in rapid capacity decay and safety issues. Based on the degradation mechanisms and latest advances of the high-voltage LCO, this review summarizes modification strategies in view of the LCO structure, artificial interface design and electrolytes optimization. Meanwhile, many advanced characterization and monitoring techniques utilized to clarify the structural and interfacial evolution of LCO during charge/discharge process are critically emphasized. Moreover, the perspectives in terms of integrating multiple modification strategies, applying gel and solid-state electrolytes, optimizing the recovery process and scalable production are presented.