Hydrophobic liquid electrolyte interphases for efficient aqueous zinc batteries

Expanding the electrochemical stability window of aqueous electrolyte solutions is a viable strategy to improve battery performance. Using water-in-salt aqueous electrolyte solutions, the solid electrolyte interphase formed on the negative electrode enables an electrochemical stability window up to 3.0 V, but this often reduces ionic conductivity and increases costs. Here, to circumvent these issues, we report the use of hydrophobic and electrode-philic ether-based additives in 3-molal aqueous zinc trifluoromethanesulfonate electrolyte solutions. These additives, characterized by a weak Zn-ion solvation capability, are soluble in the aqueous electrolyte solution at low concentrations (below 2 mol%). They can be adsorbed on both positive and negative electrode surfaces, inhibiting Zn dendrite growth, forming a liquid electrolyte interphase that extends the electrochemical stability window to 3.08 V, enabling high bulk ionic conductivity (about 54 mS cm^-1 at 25 °C) and ensuring the non-flammability of the aqueous electrolyte solution. This nanoengineered electrolyte approach enables a Zn||NaV₃O₈ single-layer pouch cell to operate 500 stable cycles (average Coulombic efficiency of 99.95%) with a specific discharge capacity retention of 80% at 500 mA g^-1 and 25 °C with a calculated initial specific energy of 132 Wh kg^-1 (based on the mass of the negative and positive electrode active materials).