The reaction of charged cathodes with nonaqueous solvents and electrolytes -: II.: LiMn2O4 charged to 4.2 V

The thermal decomposition of LiMn2O4 charged to 4.2 V was studied using a combination of accelerating rate calorimetry and X-ray diffraction. The electrolyte and solvent were removed from the surface of the electrode using a rinsing procedure. Then electrode samples were either heated dry with solvent added or with electrolyte added. The dry electrode was determined to convert from the lambda -MnO2 structure to the beta -MnO2 structure upon exposure to elevated temperatures (below 300 degreesC). In the presence of solvent, there is solvent oxidation and reduction to MnO. The reaction of LixMn(2)O(4) with xM LiPF6/EC:DEC (0 < x < 1.5) was also studied. The reactivity increases as the salt concentration increases. These experiments point the way to safer lithium-ion cells using LiMn2O4, since electrodes in electrolytes with lower concentrations of LiPF6 than, for example, 1 M, demonstrate improved thermal behavior. (C) 2001 The Electrochemical Society.