Fast Li-ion transport and nonflammable double-layered polymer electrolyte for high-performance Li-metal batteries

Solid-polymer-electrolyte-based Li-metal batteries (LMBs) are touted as emerging future technologies owing to their excellent resistance to leakage, high energy density, safety, and flexible design. Herein, we prepare a double-layered polymer electrolyte with self-extinguishing properties and enhanced ionic conductivity by utilizing decabromodiphenyl ethane and zeolite additives. Higher concentrations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are found to help reduce interface resistance, thereby improving Li⁺ conductivity as a result of the existence of free Li cations and TFSI⁻ anions. This cutting-edge electrolyte achieves a ionic conductivity of 1.2 mS cm⁻¹ at an operating temperature of 60 °C and maintains voltage stability at up to 5.2 V. Moreover, incorporating LiTFSI at 60 % relative to poly ethylene oxide decreases the generation of LiF on the surface, thereby improving stability. An electrochemical cell designed with a LiFePO₄ cathode exhibits an initial capacity of 156.6 mAh g⁻¹, an exceptional capacity retention of 94.3 %, and a highly stable Coulombic efficiency of 98.2 % over 250 cycles at a rate of 1 C. This research paves the way for advancements in solid polymer electrolytes for LMBs, offering a promising strategy to enhance their electrochemical performance and fire safety.