Improvement of electrochemical properties of Ca₃Co₄O₉ as anode materials for lithium-ion batteries by Cr doping

Electrochemical performance of the misfit-layered Ca₃Co₄O₉ and Ca₃Co_3.9Cr_0.1O₉ anode material for lithium-ion batteries were investigated. The single phase of Ca₃Co₄O₉ and Ca₃Co_3.9Cr_0.1O₉ powders were successfully synthesized by the thermal hydro-decomposition method. Both samples showed plate-like particle morphology. The particle size of the doped sample was almost twice larger than the size of Ca₃Co₄O₉. By doping Cr, the electrochemical properties of Ca₃Co_3.9Cr_0.1O₉ were considerably improved compared to the undoped sample. The specific capacity of the doped sample increased with the number of cycle. After 100 cycles, the specific capacities of the undoped and doped sample were 280 and 513 mAh.g⁻¹, respectively, showing an increase of over 80 %. The high rate performance of the doped sample was also improved. The cyclic voltammetry measurements showed the enhanced reactivity, and the electrochemical impedance spectroscopy showed the reduced resistivity of the Cr-doped anode. The better electrochemical properties of Ca₃Co_3.9Cr_0.1O₉ were attributed to the formation of CoO, the enhanced reactivity, the good electrical conduction, and the reduction in volume changing.