Lithium-ion insertion kinetics of Nb-doped LiMn2O4 positive-electrode material

Nb-doped LiMn2O4 materials were synthesized by a solid state process, and the structure and kinetic performance were characterized by TG-DTA, XRD, SEM, CV, and EIS. TG-DTA shows that the decomposition reaction has almost completed and all reactions have finished at the temperature of 590 °C. XRD indicates that the all samples are in accordance with the standard spinel LiMn2O4. However, it can be found that little Nb5+ ions do not completely substitute Mn3+ ions of LiMn2−1.667xNbxO4 (x=0.02, 0.03, 0.04). SEM reveals that the average particle size of all samples is about 1 μm. CV exhibits that the improved reversibility and dynamic behaviors of LiMn2O4 can be attributed to the Nb doping. EIS demonstrates that Nb doping decreases the charge transfer resistance of LiMn2O4, and then reduces the cell impedance. Nb doping results in lower electrode polarization and a high lithium ion diffusion coefficient, and can effectively improve the kinetic performance of LiMn2O4.