Ionic liquid mediated magnesium ion conduction in poly(ethylene oxide) based polymer electrolyte

Magnesium ion conduction in poly(ethylene oxide) (PEO) based polymer electrolyte incorporated with room temperature ionic liquid (RTIL) is reported. The electrolyte films comprise the PEO complexed with magnesium trifluoromethanesulfonate (or magnesium triflate) added with different amount of ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf). The polymer electrolyte with ∼50 wt.% of ionic liquid offers a maximum electrical conductivity of ∼5.6 × 10−4 S cm−1 at room temperature (∼25 °C) with improved thermal and electrochemical stabilities. The Mg2+ ion conduction in the PEO-complex is confirmed from cyclic voltammetry, impedance and transport number measurements. A significant increase in the Mg2+ ion transport number (tMg2+tMg2+) is observed with increasing content of the ionic liquid in PEO–Mg salt complex and the maximum value is obtained to be ∼0.45 for ∼50 wt.% of ionic liquid. The interaction of imidazolium cations with ether oxygen of PEO, as evidenced from FTIR and Raman studies, play an important role in the substantial enhancement in the tMg2+tMg2+ value.

Research highlights
► We have studied the effect of ionic liquid (IL) addition on the properties of PEO–Mg salt electrolyte.
► The results indicate the PEO–Mg salt-IL system a thermally and electro-chemically stable film.
► The addition of IL in PEO–Mg triflate system results in enhancement in Mg2+ ion transport number.
► Interaction of imidazolium cations with PEO plays important role in Mg2+ ion conduction.