[BMIM]BF ₄-modified PVDF-HFP composite polymer electrolyte for high-performance solid-state lithium metal battery

Abstract

In this work, we demonstrated a novel non-flammable composite polymer electrolyte, which can be applied for high-performance solid-state lithium 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), Al ₂O ₃ particles and [BMIM]BF ₄. 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|LiFePO ₄ 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.