Thermal Stability of Various Cathode Materials against Li6.25Al0.25La3Zr2O12 Electrolyte

Thermal stability of LiCoO2, LiMn2O4 and LiFePO4 with Li6.25Al0.25La3Zr2O12(Al-LLZ) solid electrolyte was investigated at 300-800 degrees C. In the case of LiCoO2/Al-LLZ mixture, the XRD patterns and charge-discharge behavior did not change after the heat treatment at 800 degrees C. In contrast, the formation of impurities and degradation of cathode performance were observed for LiMn2O4/Al-LLZ mixture and LiFePO4/Al-LLZ mixture. The decomposition of Al-LLZ and the formation of some impurities were observed from 600 degrees C for LiMn2O4/Al-LLZ mixture, leading to decrease in the discharge capacity. In the case of LiFePO4/Al-LLZ mixture, the decomposition of both materials was started at 400 degrees C. These results indicate that the limit of heat treatment temperature for the formation of electrode/solid electrolyte system strongly depends on the kind of electrode material. (C) The Electrochemical Society of Japan, All rights reserved.