High temperature phase transitions in solid state electrolytes

Solid state electrolyte (SSE) is the key component in all solid-state batteries (ASSBs). However, the high entropy and high enthalpy features make SSEs only stable at relevant high temperatures. When the temperature drops, a phase transition or decomposition would happen, resulting in much lower ionic conductivity. This limits the development and diversity of SSEs. Additionally, the decrease in ionic conductivity caused by phase transition also significantly affects the electrochemical performance of all solid-state batteries at low temperatures. Therefore, the study and regulation of phase transitions in SSEs are of great significance for the development of new SSEs and the improvement of the electrochemical performance of ASSBs at low temperatures. In this review, we mainly summarize the phase transitions in superionic conductors, techniques to determine such transitions, and methods to stabilize those metastable phases at room temperature. Additionally, we will give a possible experimental approach to new superionic conductors.