Interaction between Zn2+ cations and n-methyl-2-pyrrolidone in ionic liquid-based Gel Polymer Electrolytes for Zn batteries

Zinc-based batteries have been extensively used due to their numerous advantages. Currently, several research groups focus their investigation mainly on Zn/air batteries, because of their highly specific energy, and the named Zinc-ion batteries (ZIBs), as most viable candidates for replacing Li-ion batteries. However, these batteries usually include alkaline aqueous electrolytes, which present several inconveniences. Use of gel polymer electrolytes  instead of conventional alkaline aqueous ones is considered a possible way to solve these problems. In our laboratory we prepare ionic liquid-based gel polymer electrolytes, trapping zinc triflate salt together with an ionic liquid into a polymer host, PVdF-HFP. Besides, presence of n-methyl-2-pyrrolidone into the gel polymer electrolytes turns out to be a key factor due to the interaction between Zn²⁺ cations and carbonyl groups of the n-methyl-2-pyrrolidone, as it has been confirmed by ATR-FTIR. It should be noted that cation transport number measurements confirm that this interaction improves the Zn²⁺ transport inside the gel polymer electrolytes. Remarkable electrical and electrochemical properties obtained reveal these gel polymer electrolytes as excellent candidates to be used in zinc batteries. Thus, we have probed these ionic liquid-based gel polymer electrolytes in Zn/MnO₂ batteries, resulting specific capacities of 125 mAh g^-1. Therefore, these gel polymer electrolytes may break through to the development of new Zn/air batteries in the near future.