Enhancement of the electrochemical performance of the spinel structure LiNi0.5-xGaxMn1.5O4 cathode material by Ga doping

A sol-gel method was adopted to obtain LiNi 0.5-x Ga x Mn 1.5 O 4 ( x  = 0, 0.04, 0.06, 0.08, 0.1) samples. The effect of Ga doping on LiNi 0.5 Mn 1.5 O 4 and its optimum content were investigated, and the electrochemical properties at room temperature and at a high temperature were discussed. The structural, morphological, and vibrational features of LiNi 0.5-x Ga x Mn 1.5 O 4 ( x  = 0, 0.04, 0.06, 0.08, 0.1) compounds were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). The XRD results demonstrate that all samples have a disordered spinel structure with a space group of Fd3m, and Ga doping restrains the formation of the Li x Ni 1-x O secondary phase. FT-IR analysis reveals that Ga doping increases the degree of cation disorder. The SEM results reveal that all samples possess a fine spinel octahedron crystal. The electrochemical performance of the samples was investigated by galvanostatic charge/discharge tests, dQ/dV plots, and electrochemical impedance spectroscopy (EIS). The LiNi 0.44 Ga 0.06 Mn 1.5 O 4 sample with the optimum content shows a superior rate performance and cycle stability after Ga doping, especially at a high discharge rate and high temperature. In addition, the LiNi 0.44 Ga 0.06 Mn 1.5 O 4 sample retained 98.3% of its initial capacity of 115.7 mAhg −1 at the 3 C discharge rate after 100 cycles, whereas the pristine sample delivered a discharge capacity of 87.3 mAhg −1 at 3 C with a capacity retention of 80% at the 100th cycle. Compared with the pristine material, the LiNi 0.44 Ga 0.06 Mn 1.5 O 4 sample showed a high capacity retention from 74 to 98.4% after 50 cycles at a 1 C discharge rate and 55 °C.