Thermal Stability of Various Cathode Materials against Li<sub>6.25</sub>Al<sub>0.25</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub> Electrolyte

Abstract

Thermal stability of LiCoO 2 , LiMn 2 O 4 and LiFePO 4 with Li 6.25 Al 0.25 La 3 Zr 2 O 12 (Al-LLZ) solid electrolyte was investigated at 300-800C. In the case of LiCoO 2 /Al-LLZ mixture, the XRD patterns and charge-discharge behavior did not change after the heat treatment at 800C. In contrast, the formation of impurities and degradation of cathode performance were observed for LiMn 2 O 4 /Al-LLZ mixture and LiFePO 4 /Al-LLZ mixture. The decomposition of Al-LLZ and the formation of some impurities were observed from 600C for LiMn 2 O 4 /Al-LLZ mixture, leading to decrease in the discharge capacity. In the case of LiFePO 4 /Al-LLZ mixture, the decomposition of both materials was started at 400C. 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.