A Highly Conductive Gel Polymer Electrolyte for Li-Mg Hybrid Batteries

Compared to lithium-ion batteries, lithium-magnesium hybrid batteries (LMIBs) provide high capacity and increased safety at a lower cost. However, their development has been hamstrung by a dependence on toxic and corrosive liquid electrolytes. To remove this roadblock, we fabricated a hybrid gel polymer electrolyte ( hGPE) composed of lithium bis-(trifluoromethylsulfonyl)imide (LiTFSI) and magnesium bis-(trifluoromethylsulfonyl)imide [Mg(TFSI)(2)] salts, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid (IL), and poly(vinylidene fluoride-co-hexafluoropropylene), with an ionic conductivity of 3.2 mS/cm and excellent electrochemical stability. Ion dynamics within the hGPE were evaluated by dielectric analysis: ion transport within the hGPE is found to differ fundamentally from that of bulk IL solutions. We propose that the confinement of the IL within the polymer matrix induces aggregation at the pore center, leaving a pathway of high mobility at the pore edge. We then demonstrate the first proof-of-concept quasi-solid-state LMIB, with a high initial capacity of 141.5 mAh/g and Coulombic efficiencies above 90%.