Electrochemical performance and thermal stability of GaF3-coated LiNi0.5Mn1.5O4 as 5 V cathode materials for lithium ion batteries

LiNi0.5Mn1.5O4 coated with various amounts of GaF3 were prepared and investigated as cathode materials for lithium ion batteries. The sample was characterized by X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy (EDX). The results indicated that the electrochemical performance of LiNi0.5Mn1.5O4 was effectively improved by the GaF3 coating. The 0.5 wt% GaF3-coated LiNi0.5Mn1.5O4 delivered a discharge capacity of 97 mAh g−1 at 20 C (3000 mA g−1), while the pristine sample only yielded 80 mAh g−1 at 10 C. Meanwhile, the 0.5 wt% GaF3-coated LiNi0.5Mn1.5O4 exhibited an obviously better cycle life than the bare sample at 60 °C, delivering a discharge capacity of 120.4 mAh g−1 after 300 cycles, 82.9 % of its initial discharge capacity, while the pristine only gave 75 mAh g−1. At 0.1 C, the self-discharge of 0.5 wt% GaF3-coated LiNi0.5Mn1.5O4 is about 3.4 %, while the pristine is about 10.2 % after a 5-day rest at room temperature. Furthermore, GaF3 coating greatly reduced the self-heating rate and improved the thermal stability of LiNi0.5Mn1.5O4. These improvements were attributed to the GaF3 layer not only increasing the electronic conductivity of the LiNi0.5Mn1.5O4 but also effectively suppressing the reaction between the LiNi0.5Mn1.5O4 and the electrolytes, which reduced the charge-transfer impedance and the dissolution of Ni and Mn during cycling.