Improved electrochemical performance of spinel-type LiMn1.90Mg0.05Si0.05O4 cathode materials synthesized by a citric acid-assisted sol–gel method

The spinel-type LiMn1.90Mg0.05Si0.05O4 cathode materials were successfully synthesized by a citric acid-assisted sol–gel method. The sintering parameters such as sintering temperature and sintering time were investigated, and the crystal structures, morphologies, and chemical compositions of synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS). The results indicate that all the co-doped samples synthesized at different calcination temperatures possess the cubic spinel structure of LiMn2O4 with space group of Fd-3m and the average particle size increases with the extending of sintering time. The electrochemical performance of synthesized samples was studied by galvanostatic charge–discharge tests and electrochemical impedance spectroscopy (EIS). Under the optimum sintering condition, the co-doped sample can deliver the initial discharge capacity of 136.2 mA h g−1 at 0.5 °C in the voltage range of 3.2–4.35 V with good capacity retention of 96.0 % after 100 cycles. When cycling at 55 °C, the optimal co-doped sample displays 91.3 % capacity retention after 20 cycles, compared to 58.6 % for the undoped sample. Most importantly, the addition of equimolar Mg2+ and Si4+ ions significantly enhances the rate performance, especially the capacity recovery performance as the charge–discharge rate restores to 0.2 from 10 °C.