STUDIES ON LI-MN-O SPINEL SYSTEM (OBTAINED FROM MELT-IMPREGNATION METHOD) AS A CATHODE FOR 4 V LITHIUM BATTERIES .4. HIGH AND LOW-TEMPERATURE PERFORMANCE OF LIMN2O4

The cycling profile of an Li/1 M LiPF6 + ethylene carbonate/dimethyl c arbonate (1:2 in volume)/LiMn2O4 cell is examined at various operating temperatures (0, 25 and 50 degrees C). The capacity fades faster on c ycling at a high operating temperature than that at a low one. It is f ound that the two-phase structure in a high-voltage region is very sen sitive to the working temperature. This two-phase structure can be sta bly maintained for lithium-ion insertion/extraction at a low temperatu re in the high voltage region, while it is effectively forced to trans form to a more stable one-phase structure at high temperatures. The ca pacity loss at high operating temperature is due to the following fact ors: (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 decom poses on the electrode.