Thermal stable polymer-based solid electrolytes: Design strategies and corresponding stable mechanisms for solid-state Li metal batteries

Compared to extensively used lithium-ion batteries (LIBs) with flammable carbonate-based organic liquid-electrolytes, lithium metal batteries (LMBs) with the combinations of solid-state electrolytes are considered one of the final schemes to replace traditional LIBs. However, solid polymer electrolytes or ceramic-polymer hybrid solid electrolytes can not qualify for flame retardancy for building safe battery systems. When the temperature reaches the melting point of polymers, the chain segment motion of the polymer backbone becomes vigorous, and lithium dendrites can easily penetrate polymer-based electrolytes. Meanwhile, the decomposition of solid electrolyte interphase and evaporation of liquid electrolytes are observed at the flammable test, which causes serious thermal runaway of the cells. In this review article, we summarize four integral parts (i.e., polymer regulation, additive modification, and preparation methods) that can elevate the thermal stability of polymer-based solid electrolytes and high-temperature operating abilities in LMBs. Analysis of various effective design strategies, critical parameters, and corresponding thermal stable mechanisms of polymer-based solid electrolytes are discussed. The fundamental challenges and developing trends for innovating thermal stable polymer-based solid electrolytes are presented for further investigation.