Structure and Electrochemical Performances of Co-Substituted LiCo_xLi_(x-y)Mn_(2-x)O_4 Cathode Materials for the Rechargeable Lithium Ion Batteries

摘要

Spinel LiMn_2O_4 and Co, Li co-substituted LiCo_xLi_(x-y)Mn_(2-x)O_4 (x = 0.20; y = 0.05, 0.10 and 0.15) cathode materials were synthesized by sol-gel technique using lithium acetate, manganese acetate, cobalt acetate and tartaric acid as the starting materials. The effect of Co, Li substitution on the structure and surface morphology of LiCo_xLi_(x-y)Mn_(2-x)O_4 has been examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The materials for all the compositions have exhibited a phase pure cubic spinel structures from the XRD analysis. The crystallinity and average particle size of the synthesized materials were decreased by the substitution of Co, Li. The electrochemical properties of the assembled LiCo_xLi_(x-y)Mn_(2-x)O_4/Li/LiPF_6 cells were evaluated for charge/discharge studies at different rates and electrochemical impedance measurements. This co-substituted LiMn_2O_4 has improved specific capacity and capacity retention over pure spinel LiMn_2O_4. The co-substitution of LiMn_2O_4 cathode material has increases cyclability; however, the discharge capacity reduces. Among all the compositions, LiCo_(0.10)Li_(0.10-)Mn_(1.80)O_4 cathode has improved the structural stability and excellent electrochemical performances of the rechargeable lithium-ion batteries.