Thermal Runaway Behavior of Li6PS5Cl Solid Electrolytes for LiNi0.8Co0.1Mn0.1O2 and LiFePO4 in All-Solid-State Batteries

Abstract

All-solid-state batteries (ASSBs) have received much attention because of their high energy density and safety. However, the safety of argyrodite-type Li₆PS₅Cl (LPSCl)-based ASSBs is still not assured because their thermal stability has been assessed under selected mild conditions. Herein, we introduce the poor thermal stability of LPSCl with Ni-rich layered oxide cathode materials as the trigger of thermal runaway. The charged composite cathode pellets containing Li_1–xNi_0.8Co_0.1Mn_0.1O₂ and LPSCl are explosively burned at 150 °C even in Ar. Moreover, the mechanical abuse gives rise to violent burning at room temperature. This is due to vigorous exothermic chemical reactions between delithiated Li_1–xNi_0.8Co_0.1Mn_0.1O₂ and LPSCl. However, LPSCl with LiFePO₄ exhibits excellent thermal stability, such as no violent exothermic reactions even at 350 °C. This is because LPSCl is metastable with delithiated Li_1–xFePO₄. Moreover, LiFePO₄ shows excellent electrochemical performance, such as a high reversible capacity of 141 mAh g^–1 and stable capacity retention over 1000 cycles, despite the fact that LiFePO₄ is known to be poorly electrochemically active for ASSBs. These findings provide fundamental insights to improve the thermal stability and electrochemical performance of LPSCl-based ASSBs.