Studies on Li-Mn-O spinel system (obtained from melt-impregnation method) as a cathode for 4 V lithium batteries Part IV. High and low temperature performance of LiMn_2O_4

摘要

The cycling profile of an Li/1 M LiPF_6 + ethylene carbonate/dimethyl carbonate (1:2 in volume)/LiMn_2O_4 cell is examined at various operating temperatures (0, 25 and 50℃). The capacity fades faster on cycling at a high operating temperature than that at a low one. It is found that the two-phase structure in a high-voltage region is very sensitive to the working temperature. This two-phase structure can be stably maintained for lithium-ion insertion/extraction at a low temperature in the high-voltage region, while it is effectively forced to transform to amore stable one-phase structure at high temperatures. The capacity loss at high operating temperature is due to the following factors: (i) an unstable two-phase structure co-exists in the high-voltage region for lithium-ion insertion/extraction; (ii) Mn slowly dissolves in the electrolyte solution, and (iii) the electrolyte solution decomposes on the electrode.