Hydrothermal synthesis of Mg-doped LiMn2O4 spinel cathode materials with high cycling performance for lithium-ion batteries

Spinel LiMgxMn2-xO4 cathode materials were synthesised using a hydrothermal method, with the effects of doping Mg on the structure and electrochemical performance of LiMn2O4 subsequently investigated. It was found that no other hybrid phases existed in the LiMgxMn2-xO4 and that doped Mg cannot change the spinel lattice type of LiMn2O4. An appropriate Mg content was beneficial for improving the crystallinity and particle uniformity of the samples. The electrochemical performance of the LiMgxMn2−xO4 was assessed in the 2.9~4.3 V range, with the specific discharge capacity of the LiMn2O4 potentially reaching 139.9 mAh g−1 at 0.2 C, with a capacity retention rate of 63.76% after 100 cycles. Furthermore, the LiMn1.97Mg0.03O4 demonstrated an excellent cycling performance at both room temperature (25°C) and at a high temperature (55°C). At 25°C, the first specific discharge capacity was 124.3 mAh g−1 at 0.2 C, with a capacity retention rate of 94.29% after 100 cycles, while the specific discharge capacity can reach 94.8 mAh g−1 at 5 C and 74.0 mAh g−1 at 10 C. At 55°C, the initial specific discharge capacity was 125.6 mAh g−1 at 0.2 C, with a capacity retention rate of 85.43% after 100 cycles. The cyclic voltammogram curves and electrochemical impedance spectroscopy results indicated that, compared with the pristine LiMn2O4, the LiMn1.97Mg0.03O4 had a larger Li+-ion diffusion coefficient and smaller resistance during the charge–discharge process. Overall, the results indicated that Mg doping is beneficial in improving the electrochemical performance of spinel LiMn2O4.