Hydrotropic solubilization of zinc acetates for sustainable aqueous battery electrolytes

Among the more sustainable battery chemistries, the aqueous zinc system is receiving renewed interest. To accelerate the practical applications of this promising technology, an effective strategy is to deploy high salt concentration electrolytes that could address the critical technical barriers, notably hydrogen evolution reaction and dendrite growth at the anode side. However, the state-of-the-art recipes are either zinc-ion deficient or halogen salt dependent, both of which unfortunately create extra challenges. Here we show a highly concentrated aqueous electrolyte formula utilizing zinc acetate, an otherwise poorly water-soluble but cheap and eco-friendly salt. The unprecedented solubility (up to 23 m) is a result of the introduction of hydrotropic agents that transform the acetate anion ligands to a hydrophilic coordination structure. All three hydrotropic agents including potassium acetate, urea and acetamide are effective in constructing highly concentrated zinc acetate electrolytes with which the assembled Zn//pyrene-4,5,9,10-tetraone full cell retains 70% of its initial capacity after 4,000 cycles. This work provides a unique opportunity to design high-performance electrolytes for applications in the wide battery space. The authors deploy a hydrotropic solubilization strategy turning an otherwise poorly water-soluble acetate into a salt for a high-concentration aqueous electrolyte that features low cost and environmental sustainability and enables good performance of zinc batteries.