[BMIM]BF4-modified PVDF-HFP composite polymer electrolyte for high-performance solid-state lithium metal battery

Abstract

Solid-state polymer electrolytes are regarded as promising candidates to suppress the growth of lithium dendrite and settle the inflammable issues of organic-liquid electrolytes. However, solid-state polymer electrolytes still cannot meet the requirements of high mechanical strength, satisfactory ionic conductivity and extended electrochemical window at room temperature. To solve these issues, a novel ionic liquid composite polymer electrolyte (ILCPE) was synthesized via solvent tape-casting technique, consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based composite polymer electrolytes, filled with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Al₂O₃ particles and [BMIM]BF₄. With good fire resistance and excellent mechanical performances, the ILCPE exhibits an improved electrochemical stability window of 5.6 V versus Li/Li⁺ potential, as well as a high ionic conductivity of 5.26 × 10⁻³ S cm⁻¹ at 25 °C. The Li|ILCPE|Li symmetric battery can operate stably for more than 800 h. At 2C rate, Li|ILCPE|LiFePO₄ cell delivered a high specific discharge capacity of 156.5 mA h g⁻¹ and 130 mA h g⁻¹ at 55 °C and 25 °C, respectively, and obtained high capacity retention of 95.5% after 300 charge–discharge cycles at 25 °C.