A study of structural, electrical and electrochemical properties of PVdF-HFP gel polymer electrolyte films for magnesium ion battery applications

New magnesium ion conducting polymer electrolyte films are developedand their experimental investigations are reported. The polymer electrolyte films arecomposed of various poly(vinylidene fluoride-co hexafluoropropylene):magnesium trifluoromethanesulfonate compositions (PVdF-HFP:Mg(Tf)2 in weight ratio) with different quantities of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid (EMITf). X-ray diffraction reveals that the pristine PVdF-HFP polymer film possesses a semi-crystalline structure and its amorphicity increases with increasing Mg(Tf)2 and EMITf concentrations. From thermal analysis, the melting temperature (Tm), relative crystallinity (χc) and thermal stability of the 90PVdF-HFP:10Mg(Tf)2 gel polymer electrolyte film doped with 40 wt.% EMITf are obtained as 112°C, 21.8% and 355°C, respectively. The room-temperature ionic conductivity of the gel polymer electrolyte film increases with increasing EMITf concentration and reaches a high value of approximately 4.63×10-3 S cm-1 at 40 wt.% EMITf due to its amorphicity increase and interconnected pore structure. For the 40 wt.% EMITf electrolyte film, the temperature dependence of ionic conductivity follows the Arrhenius relation with an activation energy of 0.35 eV. The electrochemical stability window of the 40 wt.% EMITf electrolyte film is determined as ~4.8 V. The findings from this study are promising and have great potential for practical ionic device applications, particularly in rechargeable magnesium ion batteries.