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

• The prepared electrolyte has sound mechanical flexibility and thermal stability.
• The 40 wt.% EMITf gel polymer electrolyte exhibits a high amorphicity.
• The room-temperature ionic conductivity reaches ∼4.63 × 10−3 S cm−1 at EMITf = 40 wt.%.
• The electrochemical stability window is ∼4.8 V for the 40 wt.% EMITf electrolyte.

New magnesium ion conducting polymer electrolyte films are developed and their experimental investigations are reported. The polymer electrolyte films are composed 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.

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