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

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 xMn2- xO4 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.