Preparation of co-doped spherical spinel LiMn2O4 cathode materials for Li-ion batteries

Surface cobalt doping and bulk yttrium doping were combined to improve the cycling stability of spherical spinel LiMn2O4 at elevated temperature (55 °C). The cobalt surface doping was more effective than cobalt bulk doping at the same doping level, because the surface cobalt doping prevents more efficiently manganese from dissolving in electrolyte. At yttrium doping level of 5%, doped spinel LiMn2O4 had specific capacity in excess of 130 mAh g−1 and 120 mAh g−1 at first cycle and at 100th cycle, respectively, at 25 °C. Doping of yttrium enhanced the activity of manganese in spinel LiMn2O4, leading to both increase of specific capacity and decrease of cycleability, because the active manganese easily dissolved into electrolyte during cycling. Moreover, the raise of the temperature led to an intensive dissolution of manganese and poor performance at elevated temperature when yttrium doped. The dissolution could be effectively inhibited by cobalt surface doping. 0.5% yttrium bulk and 0.5% cobalt surface co-doped spherical spinel LiMn2O4 had the excellent performance, and its initial specific capacities are 118 mAh g−1 and 110 mAh g−1 at 25 °C and 55 °C, respectively, and its 50th cycle specific capacities remained to be 114 mAh g−1 and 91 mAh g−1 at 25 °C and 55 °C, respectively.