Effect of Co3+ Doping on Crystal Structure and Electrochemical Properties of Spinel LiMn2O4 Cathode Material

To inhibit the influence of structural distortion caused by the Jahn–Teller effect on LiMn2O4 (LMO), the spinel LMO doped with cobalt ions is prepared by a simple solid-state calcining method. The effects of different cobalt doping amounts on the structure and electrochemical properties of LMO are investigated. The XRD refinement results show that Co3+ successfully enters the lattice of LMO, and its spinel structure is not changed. Due to the smaller radius of Co3+ and the larger bond energy, the unit cell of the LMO material shrinks, and the spinel structure is more stable. The initial capacity of the material decreases with the increase of Co doping content, but the cycle performance is significantly improved. Impressively, when Co doped at x = 0.04, the initial discharge specific capacity of the LMO-0.04 sample is 115.5 mAh·g–1 at 0.1C, and the capacity retention rate is still 81.04% after 500 cycles. The cycle times are much higher than that of the pure LMO sample. Additionally, the diffusion coefficient of Li+ calculated by the Randles–Sevcik equation shows that the doping of Co3+ significantly improves the mobility of Li+ compared with pure LMO. Hence, Co3+ doping can effectively inhibit the structural distortion caused by the Jahn–Teller effect and improve the electrochemical performance of LMO.