Abstract
A new route for the preparation of nickel and cobalt substituted spinel cathode materials (LiMn(1.95)Co(0.025)Ni(0.025)O₄ and Li(1.1)Mn(1.95)Co(0.025)Ni(0.025)O₄) by freeze-drying of acetate precursors followed by heat treatment was suggested in the present work. The experimental conditions for the preparation single-phase material with small particle size were optimized. Single-phase spinel was formed by low-temperature annealing at 700 °C. For discharge rate 0.2 C, the reversible capacities 109 and 112 mAh g(−1) were obtained for LiMn(1.95)Co(0.025)Ni(0.025)O₄ and Li(1.1)Mn(1.95)Co(0.025)Ni(0.025)O₄, respectively. A good cycle performance and capacity retention about 90% after 30 cycles at discharge rate 0.2⁻4 C were observed for the materials cycled from 3 to 4.6 V vs. Li/Li⁺. Under the same conditions pure LiMn₂O₄ cathode materials represent a reversible capacity 94 mAh g(−1) and a capacity retention about 80%. Two independent experimental techniques (cyclic voltammetry at different scan rates and electrochemical impedance spectroscopy) were used in order to investigate the diffusion kinetics of lithium. This study shows that the partial substitution of Mn in LiMn₂O₄ with small amounts of Ni and Co allows the cyclability and the performance of LiMn₂O₄-based cathode materials to be improved.