Abstract:

Spinel powders of Li_1.035Co_xMn_1.965-xO₄ (x=0-0.100) systems were synthesized by a simple wet chemical process with post heat-treatment. X-ray diffraction (XRD) patterns reveal that the Co doping does not affect the Fd3m space group of the cathode materials. Scanning electron microscope (SEM) images show that the Li_1.035Co_xMn_1.965-xO₄ cathode materials have a uniform and nearly cubic morphology with a narrow size distribution. Transmission electron microscope (TEM) results demonstrate that the Li_1.035Co_0.035Mn_1.930O₄ powder has a good crystalline state. The electrochemical testing results indicate that the prepared Co-doped Li_1.035Co_xMn_1.965-xO₄ samples show a better cycling ability and rate capability at room temperature than that of Co-free Li_1.035Mn_1.965O₄. In particular, the Li_1.035 Co_0.035Mn_1.930O₄ sample delivers a reversible specific capacity of 113 mAh/g in 1^st cycle and retains 93.8% of its initial capacity after 100 cycles at 0.5C rate. When discharging at 4C rate, the Li_1.035Co_0.035Mn_1.930O₄ powder maintains 86 mAh/g, which is 76.1% of the reversible capacity at 0.5C. Comparatively, the Li_1.035Mn_1.965O₄ powder maintains only 64.8% of its reversible capacity at 0.5C discharge rate. The electrochemical impedance spectroscopy results show that Co ion doping can enhance the electrical conductivity and the Li-ion diffusion coefficient. These results indicate a superior cycling and rate performance compared with the pristine one.

Key words: lithium ion batteries, Co doping, hydrothermal method, spinel lithium manganese oxide