Reviewing failure mechanisms and modification strategies in stabilizing high-voltage LiCoO2 cathodes beyond 4.55V

Lithium cobalt oxide (LiCoO2 or LCO) is undoubtedly one of the best commercial cathode materials for Lithium-ion batteries (LIBs). High energy density, excellent cycle life, and long-term reliability make it most attractive for the growing electronics market. The working voltages in LCO have been raised to achieve greater energy density that can fulfill fast charging and portable electronics consumer needs. Yet, charging beyond 4.4 V inevitably decreases the cathode stability, resulting in poor performance. Several factors cause operational issues in LCO at high voltages, particularly surface degradation, unfavorable side reactions, and irreversible phase transitions. These detrimental phenomena are aggravated by the increased charging voltage, leading to rapid capacity decay and early cell failure. Our review summarizes the failure mechanisms and mitigation strategies adopted recently to stabilize LCO at high cutoff voltages. We begin our discussions with the crystal structure analysis of LCO, describe the possible degradation phenomena and modification routes, and finally examine the prospects and challenges of LCO-based research in all-solid-state batteries (ASSBs).