Delayed Phase Transition and Improved Cycling/Thermal Stability by Spinel LiNi_0.5Mn_1.5O₄ Modification for LiCoO₂ Cathode at High Voltages

Abstract

Increasing the upper cutoff voltage is capable of achieving higher charge capacity, whereas this strategy always causes a dramatic degradation of cycling and thermal stability. In this study, we first report spinel LiNi_0.5Mn_1.5O₄-modified LiCoO₂ (LiCoO₂@LiNi_0.5Mn_1.5O₄) as an outstanding cathode material. LiCoO₂@LiNi_0.5Mn_1.5O₄ retains capacity retention of 81.4% in a full cell between 4.45 and 3.00 V after 400 cycles at 0.5 C and is superior to 55.3% of pure LiCoO₂. In situ X-ray diffraction at an upper cutoff voltage of 4.75 V in combination with differential capacity curve reveals that the promoted cycling performance is ascribed to a delay of O3 → H1-3 → O1 phase transitions and a suppression of cobalt dissolution-induced side reactions. Moreover, LiNi_0.5Mn_1.5O₄ modification improves the thermal stability of LiCoO₂ by depressing the release of oxygen and the formation of cobalt dendrites.