Dual Cation Exchanged Poly(ionic liquid)s as Magnesium Conducting Electrolytes

Solid-state magnesium-ion conductors are desired for next-generation battery applications. Here we investigate magnesium conducting polymer electrolytes produced through dual cation exchange of a poly(ionic liquid) by mixing 1-butyl-3-methylimidazolium poly[4-styrenesulfonyl(trifluoromethanesulfonyl)imide] (BMIPSTFSI) with the magnesiated analogue Mg(PSTFSI)2. An ionic conductivity of 8.6 × 10–5 S cm–1 at 80 °C was achieved for the poly(ionic liquid), and conductivity did not significantly decrease with magnesium content up to 5 mol % Mg(PSTFSI)2 (3.8 × 10–5 S cm–1). The characteristic poly(ionic liquid) ion-to-ion correlation peak was observable via X-ray scattering at these low magnesium contents but disappeared at higher magnesium loadings. Polarization experiments were performed in Cu/Mg cells, resulting in sparse magnesium-rich particle-like deposits on the Cu electrode. With a lack of widespread deposition, however, either the magnesium electrodeposition or the magnesium stripping from the magnesium metal is unfavorable for this electrolyte.