Comparative study of the electrochemical properties of LiNi0.5Mn1.5O4 doped by bivalent ions (Cu2+, Mg2+, and Zn2+)

The 5V-positive electrode materials LiNi0.45M0.05Mn1.5O4 (M = Cu, Mg and Zn) are synthesized via a thermopolymerization method. Scanning electron microscopy and X-ray diffraction analyses indicate that these doped LiNi0.45M0.05Mn1.5O4 samples remain their spinel structure with an octahedral morphology. According to the results of infrared spectroscopy, Cu2+ and Mg2+ ions take partially the place of Ni2+ ions and occupy the 4b sites of the P4(3)32 space group, while Zn2+ ions occupy the 8a sites of the Fd3m space group by displacing some Li+ ions originally at the 8a sites into the 16d sites. The LiNi0.45Cu0.05Mn1.5O4 and LiNi0.45Mg0.05Mn1.5O4 samples exhibit excellent rate performance with specific capacities of 98.3 and 92.4 mAh g(-1), respectively, at the charge-discharge rate of 10 C, while the LiNi0.5Mn1.5O4 sample delivers only 78.9 mAh g(-1) at 10 C. Besides, the LiNi0.45Cu0.05Mn1.5O4 and LiNi0.45Mg0.05Mn1.5O4 samples show good capacity retention at high temperature (55 A degrees C) with the capacities of 117.6 and 119.5 mAh g(-1), respectively, after 100 cycles at 1 C.