In Situ Co-O Bond Reinforcement of the Artificial Cathode Electrolyte Interphase in Highly Delithiated LiCoO2 for High-Energy-Density Applications

Highly delithiated LiCoO₂ has high specific capacity (>200 mAh g^-1); however, its degradation behavior causes it to have poor electrochemical performance and thermal instability. The degradation of highly delithiated LiCoO₂ is mainly induced by oxygen vacancy migration and weakening of oxygen-related interactions, which result in pitting corrosion and fault formation on the surface. In this research, a coupling agent, namely, 3-aminopropyltriethoxysilane (APTES), was grafted onto the surface of LiCoO₂ to form a cross-linking structure. Through the aza-Michael addition reaction, an oligomer formed from barbituric acid and bisphenol a diglycidyl ether diacrylate were reacted with the cross-linking APTES to form an artificial cathode electrolyte interphase (ACEI). The highly delithiated LiCoO₂ containing the ACEI had considerably less degradation on the surface of the bulk material caused by oxygen release. The formation of the O1 phase was prevented in high delithiation and high-temperature operations. This research revealed that the ACEI reinforced the Co-O bond, which is crucial in preventing gas evolution and O1 phase formation. In addition, the ACEI prevents direct contact between the electrolyte and highly active surface of LiCoO₂, thereby preventing the formation of a thick and high impedance traditional cathode electrolyte interphase. According to the present results, highly delithiated LiCoO₂ containing the ACEI exhibited outstanding cycle retention and capacity at 55 °C as well as low heat capacity release in the fully delithiated state. The ACEI considerably protected and maintained the electrochemical performance of highly delithiated LiCoO₂, which is suitable for high-energy-density applications, such as electric vehicles and power tools.