Revealing the quasi-solid-state electrolyte role on the thermal runaway behavior of lithium metal battery

Replacing flammable non-aqueous organic liquid electrolyte (LE) with high thermal stability solid-state electrolyte (SSE) is considered to overcome the safety issues in lithium metal batteries (LMBs). However, both inorganic solid-state batteries (SSBs) with high mechanical strength and thermal stability, as well as flexible polymer-based SSBs, are not proven to be inherently safe yet. Currently, the reliability of SSBs still require continuous scientific verification. In this work, quasi-solid-state electrolyte (QSE) with practical application prospects was prepared through in-situ polymerization method. The effects of QSE and LE on the thermal runaway behavior of LMBs were systematically compared from four levels: electrolyte, electrolyte/electrode interface, coin cells, and pouch cells. The results showed that higher thermal stability of QSE was conducive for improving the reliability of quasi-solid-state batteries (QSBs) under different abused conditions. The stable and dense solid electrolyte interface (SEI) in QSB could not only inhibit the severe side-reactions of LMBs during cycling at elevated temperature, but also enhance the decomposition temperature with dead lithium. QSE's lower reaction activity towards Li reduced the exothermic reaction inside the battery had been proven to increase the self-exothermic onset temperature and thermal runaway trigger temperature of LMBs, which promoted the safety performance of LMBs. Thus, this study revealed the thermal runaway mechanism of QSE in LMBs, and provided a theoretical guideline for safe QSBs design.