Revealing the Accelerated Capacity Decay of a High-Voltage LiCoO₂ upon Harsh Charging Procedure

In practical applications, LiCoO2 (LCO) cathode is usually charged with a constant current plus constant voltage (CC+CV) procedure to obtain higher capacity delivery. However, the harsh condition upon CC+CV procedure causes the accelerated capacity decay of LCO. Herein, the fading mechanism of LCO cycling upon CC+CV procedure at 4.6 V versus Li/Li+ is first revealed. Comparing with a pure CC charging, the accelerated capacity decay of LCO upon CC+CV procedure is attributed to both the bulk and surface structure damages: i) the CV charging triggers more H1-3 phase separation, leading to the generation of lattice dislocations, curved Co-O layers, and ultimately the bulk microcracks inside the LCO particles; ii) upon cycle, the CV charging causes more side reactions and more surface structure collapse issues, including forming thick surface phase transition layer (PTL), causing more Co dissolution, forming thick and loose CEI layer, etc., which seriously increases the charge transfer resistance and reduces the interface Li+ transport kinetics. This work provides a new insight into the fading mechanism, and shows a new pathway for designing more advanced LCO cathodes.