Spinel LiMn₂O₄ Electrode in Room Temperature Molten Salt

抄録

Room Temperature Molten Salt (RTMS) based on 1-methyl-3-ethylimidazolium chloride/AlCl₃/LiAlCl₄ is recently shown to provide a promising medium for lithium battery due to its high current capability and inertness towards active material. In the present work, the electrochemical properties of a Li_xMn₂O₄ electrode in RTMS, the most commonly used positive electrode material, were investigated by cyclic voltammetry, coulometric titration and constant current cycling. From cyclic voltammetric studies, the Li_xMn₂O₄ electrode in RTMS was found to exhibit the same electrochemical behavior as in other non-aqueous electrolytes. However, a new and very large irreversible anodic peak was found due to the insertion of AlCl₄⁻ into the carbon current collector. During coulometric studies, coulombic efficiencies greater than 96% were obtained at composition close to x = 1 in Li_xMn₂O₄. However, for Range I (0 < x < l), a rapid decrease in coulombic efficiency was observed at x less than 0.6. For Range II (1 < x < 2), close to 86% of the electrode material could be used. Thus, Range II was selected for battery application. For cycling at Range I, greater than 95% cycling efficiencies were obtained up to insertion/extraction capacities of 60 mAh/g, whereas at Range II, 98% cycling efficiencies at the first 20 cycles were obtained up to 120 mAh/g. The difference was attributed to the irreversible insertion of AlCl₄⁻ anions into the carbon current collector at high anodic potential and hence less lithium was extracted from the Li_xMn₂O₄ electrode in 0 < x < 1. The electrochemical performance of the LiMn₂O₄ electrode as positive electrode material for secondary lithium battery at different lithium insertion in RTMS was discussed in the light of the results obtained.