Electrolytes for Zn Batteries: Deep Eutectic Solvents in Polymer Gels

Gel polymer electrolytes composed of deep eutectic solvent Acetamide₄:Zn(TFSI)₂ and poly(ethylene oxide) (PEO) are prepared using a fast, solvent-free procedure. The effect of the PEO molecular weight and its concentration on the physicochemical and electrochemical properties of the electrolytes are studied. Gels prepared with ultra-high molecular weight PEO present pseudo-solid behavior and ionic conductivity even higher than that of the original liquid electrolyte. A decrease in the dendritic growth in soft gels with PEO contents up to 1 wt. % is demonstrated. The changes in the chemical structure of the electrolyte produced by the strong interactions between ethylene oxide units and Zn²⁺ have also been studied. The addition of PEO takes the electrolyte out of its original eutectic composition, producing blend crystallization. However, it is possible to retain the eutectic point of the electrolyte in a gel form if the addition of PEO is accompanied by the reduction of acetamide.