Salt Anion Amphiphilicity-Activated Electrolyte Cosolvent Selection Strategy toward Durable Zn Metal Anode.

One effective solution to inhibit side reactions and Zn dendrite growth in aqueous Zn-ion batteries is to add a cosolvent into the Zn(CF 3 SO 3 ) 2 electrolyte, which has the potential to form a robust solid electrolyte interface composed of ZnF 2 and ZnS. Nevertheless, there is still a lack of discussion on a convenient selection method for cosolvents, which can directly reflect the interactions between solvent and solute to rationally design the electrolyte solvation structure. Herein, log P , where P is the octanol-water partition coefficient, a general parameter to describe the hydrophilicity and lipophilicity of chemicals, is proposed as a standard for selecting cosolvents for Zn(CF 3 SO 3 ) 2 electrolyte, which is demonstrated by testing seven different types of solvents. The solvent with a log P value similar to that of the salt anion CF 3 SO 3 - can interact with CF 3 SO 3 - , Zn 2+ , and H 2 O, leading to a reconstruction of the electrolyte solvation structure. To prove the concept, methyl acetate (MA) is demonstrated as an example due to its similar log P value to that of CF 3 SO 3 - . Both the experimental and theoretical results illustrate that MA molecules not only enter into the solvation shell of CF 3 SO 3 - but also coordinate with Zn 2+ or H 2 O, forming an MA and CF 3 SO 3 - involved core-shell solvation structure. The special solvation structure reduces H 2 O activity and contributes to forming an anion-induced ZnCO 3 -ZnF 2 -rich solid electrolyte interface. As a result, the Zn||Zn cell and Zn||NaV 3 O 8 ·1.5H 2 O cell with MA-involved electrolyte exhibit superior performances to that with the MA-free electrolyte. This work provides an insight into electrolyte design via salt anion chemistry for high-performance Zn batteries.