Poly(Ionic Liquid)‐Based Composite Gel Electrolyte for Lithium Batteries

Abstract Composite gel polymer electrolyte (cGPE) containing a poly(ionic liquid) (PIL) polymer, imidazolium cation‐based ionic liquid as a solvent, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as salt, and glass fillers with various concentrations have been developed and tested in lithium batteries. cGPEs with 1 wt% glass filler shows the highest ionic conductivity and lithium‐ion transference number with 25 % and 18.18 % improvement compared to gel polymer electrolyte (GPE), respectively. Raman results show that the improvement is due to the improved ion‐pair dissociation of LiTFSI, which causes improvement of Li + mobility. Cyclic charge‐discharge studies using binder‐free LiFePO 4 /C cathode and lithium anode for 100 cycles at various C‐rates and at a fixed rate of C/2 for 300 cycles show superior performances compared to other cGPEs and GPE. Electrochemical impedance spectroscopy and scanning electron microscopy confirm uniform deposition of reaction products on the cathode surface, which improves the charge‐transfer reactions and hence improves cyclic performances for cGPE‐1 cells with increasing cycles.