Delayed Phase Transition and Improved Cycling/Thermal Stability by Spinel LiNi0.5Mn1.5O4 Modification for LiCoO2 Cathode at High Voltages.

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 LiNi0.5Mn1.5O4-modified LiCoO2 (LiCoO2@LiNi0.5Mn1.5O4) as an outstanding cathode material. LiCoO2@LiNi0.5Mn1.5O4 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, LiNi0.5Mn1.5O4 modification improves the thermal stability of LiCoO2 by depressing the release of oxygen and the formation of cobalt dendrites.