Improved Electrochemical Performances of LiCoO₂ at Elevated Voltage and Temperature with an In Situ Formed Spinel Coating Layer

Abstract

Although various cathode materials have been explored to improve the energy density of lithium-ion batteries, LiCoO₂ is still the first choice for 3C consumer electronics due to the high tap density and high volumetric energy density. However, only 0.5 mol of lithium ions can be extracted from LiCoO₂ to avoid side reactions and irreversible structure change, which typically occur at high voltage (>4.2 V). To improve the electrochemical performances of the LiCoO₂ cathode material at high cut-off voltage and elevated temperature for higher energy density, an in situ formed spinel interfacial coating layer of LiCo _xMn_{2- x}O₄ is achieved by the reaction of the surface region of the LiCoO₂ host. The capacity retention of the modified LiCoO₂ cycled at a high voltage of 4.5 V is significantly increased from 15.5 to 82.0% after 300 cycles at room temperature, due to the stable spinel interfacial inhibiting interfacial reactions between LiCoO₂ and the electrolyte as confirmed by impedance spectroscopy. We further demonstrated that LiCoO₂ with the spinel interfacial layer also exhibits an excellent cycling stability at a high temperature of 45 °C.