Enhancement of ionic conductivity and structural properties by 1‐butyl‐3‐methylimidazolium trifluoromethanesulfonate ionic liquid in poly(vinylidene fluoride–hexafluoropropylene)‐based polymer electrolytes

Polymer electrolytes (PEs) with poly(vinylidene fluoride–hexafluoropropylene) [P(VdF–HFP)] as the polymer host and doped with lithium trifluoromethanesulfonate (LiTf) and 1‐butyl‐3‐methylimidazolium trifluoromethanesulfonate (BMIMTf) were synthesized via a solution casting method. This P(VdF–HFP)/LiTf/BMIMTf‐based PE achieved about 1.8 ×10−3 S/cm at room temperature with 100 parts by weight (pbw) of BMIMTf. A discrepancy was observed when 25 pbw of BMIMTf was doped into the system and was related to the reactivity of Li+ and 1‐butyl‐3‐methylimidazolium cation (BMIM+), which could be corroborated with differential scanning calorimetry scans. Fourier transform infrared spectroscopy and X‐ray diffraction revealed the role of P(VdF–HFP) as merely a mechanical support with no direct interaction with BMIMTf. Photoluminescence was also used to detect structural alterations in the local environment of PE.