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

Abstract

A sol-gel method was adopted to obtain LiNi0.5-xGaxMn1.5O4 (x = 0, 0.04, 0.06, 0.08, 0.1) samples. The effect of Ga doping on LiNi0.5Mn1.5O4 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 LiNi0.5-xGaxMn1.5O4 (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 LixNi1-xO 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 LiNi0.44Ga0.06Mn1.5O4 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 LiNi0.44Ga0.06Mn1.5O4 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 LiNi0.44Ga0.06Mn1.5O4 sample showed a high capacity retention from 74 to 98.4% after 50 cycles at a 1 C discharge rate and 55 °C.