Plastic crystal-incorporated magnesium ion conducting gel polymer electrolyte for battery application

Abstract

Studies on a novel composition of magnesium ion conducting gel polymer electrolyte (GPE), comprising a solution of Mg-salt, magnesium trifluoromethanesulfonate (Mg-triflate or $\hbox {Mg(Tf)}_{2})$ in a plastic crystal succinonitrile (SN), entrapped in a host polymer poly(vinylidenefluoride–hexafluoropropylene) (PVdF–HFP) was reported. Small amount of an ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf) was added to stabilize the GPE composition. The electrolyte possesses excellent dimensional integrity in the form of free-standing thick film, which offers the ionic conductivity of $4 \times 10^{-3} \hbox { S } \hbox {cm}^{-1}$ at room temperature ${\sim }26{^{\circ }}\hbox {C}$. The electrochemical potential window of the electrolyte, observed from the linear sweep voltammetry, is determined to be ${\sim }4.1 \hbox { V}$. The magnesium ion conduction in the GPE film is confirmed from cyclic voltammetry, electrochemical impedance spectroscopy and dc polarization techniques. Different structural, thermal and electrochemical studies demonstrate the promising characteristics of the polymer film, suitable as electrolyte in rechargeable magnesium batteries. The potential of the GPE as electrolyte/separator was ascertained by fabricating a prototype magnesium battery of the configuration Mg:graphite composite $\hbox {anode}/\hbox {GPE}/\hbox {MnO}_{2}$-cathode. The specific discharge capacity of $40 \hbox { mAh g}^{-1}$ (with respect to the $\hbox {MnO}_{2}$ cathode material) was obtained at the first discharge. The cell shows charge–discharge performance for eight cycles with a substantial fading in capacity.