Improvement of Float Charge Durability for LiCoO2 Electrodes under High Voltage and Storage Temperature by Suppressing O1-Phase Transition

To produce electronic devices with high functionality and longer operating times, the energy density of lithium-ion batteries (LIBs) has to be increased while maintaining a long battery life and high reliability. The energy density of LIBs can be increased by increasing the charge cut-off voltage. The float charge durability of LIBs containing LiCoO2 under high voltage is one of the most important issues in practical use. The leakage current during float charge conditions is caused by the O1 phase transition of LiCoO2. In this study, metal-substituted lithium cobalt oxides, LiCo1-xMxO2 (M = Co, Ni, Al, Mg, and Zr), were investigated to suppress degradation during float charge conditions. When Ni was substituted for Co at an amount of 5%, the float charge durability improved more than 4 times compared to bare-LiCoO2 without lowering the energy density. According to the structural analysis, we proposed the mechanism for improving float charge durability by LiCo1-xNixO2; Ni ions partially migrate to the lithium layer and then stabilize the O3 structure. This Ni ions substitution in LiCoO2 greatly contributes to extending life and the safety of high energy density LIBs containing layered positive materials.