Capacity loss of lithium manganese oxide spinel in LiPF6/ethylene carbonate-dimethyl carbonate electrolytes

The stability of lithium manganese oxide spinel in LiPF6/EC:DMC (ethylene c arbonate-dimethyl carbonate) based electrolytes has been investigated at di fferent states of charge and at temperatures between 21 and 55 degrees C. R eversible capacity loss due to reinsertion of lithium takes place at all st ates of charge and temperature. This reaction can proceed to the extent of inserting more than one Li per Mn2O4 at 55 degrees C resulting in the forma tion of tetragonal Li1+xMn2O4. The second process, irreversible capacity lo ss due to dissolution of the cathode, makes little contribution to capacity loss in highly charged electrodes, but has an effect comparable to reinser tion in discharged electrodes. (C) 1999 The Electrochemical Society. S0013- 4651(98)06-038-8. All rights reserved.