Nonflammable highly-fluorinated polymer electrolytes with enhanced interfacial compatibility for dendrite-free lithium metal batteries

Abstract

Conventional liquid electrolytes applied in lithium-ion batteries suffer from high flammability, lithium dendrites and leakage. Gel polymer electrolytes (GPEs) are promising alternative electrolytes owing to their high ionic conductivities and enhanced safeties. Nevertheless, the flammable plasticizers of GPEs still bring safety hazards for the batteries. To address these issues, nonflammable highly-fluorinated quasi-solid-state polymer electrolytes (ED@PVDF) with ultrahigh ionic conductivities, excellent flame-retardant properties and superior cycling stability are developed. ED@PVDF possesses three-dimensional polymeric network within the framework of electrospun PVDF fibers, which is fabricated by thiol-ene click reaction. Highly-fluorinated carbonates (fluoroethylene carbonate and methyl 2,2,2-trifluoroethyl carbonate) are employed as plasticizers for ED@PVDF to improve flame-retardant property and enhance compatibility with anodes. Nonflammable ED@PVDF exhibits remarkable flame resistance, the highest ionic conductivity (4.41 mS cm−1 at 30 °C) among the nonflammable polymer electrolytes and wide electrochemical windows (5.6 V). ED@PVDF can promote the generation of LiF-rich solid electrolyte interphase and effectively restrain dendrite growth on Li metal anodes. ED@PVDF endows LiFePO4 cells with outstanding rate capability (specific capacity of 123.8 mAh g−1 at 5C rate) and superior cycling stability (capacity retention of 81.4% over 1000 cycles).