(444d) Hydrated Eutectic Electrolytes for High Performance Rechargeable Zinc Batteries

Zinc has attracted significant interest as a promising anode material in aqueous rechargeable batteries, offering advantages such as high volumetric capacity (5857 mAhcm^-3 vs 2042 mAhcm^-3 for Li), low cost (2.4 USD.kg^-1 vs. 19.2 USD.kg^-1 for Li), and multiple electrons transfer capability (2e^- vs. 1e^- for Li). However, the intractable side reactions at the negative Zn anode and parasitic hydrogen evolution in the aqueous media hamper the technology unattainable for practical evaluations. Here, we present a hydrated eutectic electrolyte by combining hydrated Zn salt (ZnSO₄.7H₂O) with triethylamine hydrochloride. Eutectic formation between the two salts is attributed to Lewis acid-base interactions, facilitated by substantial charge delocalization exhibited by the SO₄^- anions, serving as a strong Lewis bases. The bipolar nature of H₂O readily interacts with the Zn⁺², forming an ion-conducting coordination complex, thereby suppressing the hydrogen evolution reaction (HER). The electrolyte offers a high electrochemical stability window (2.45V vs. Zn/Zn⁺²), wide liquid range suitable (T_liquid ³-20 ^oC), low vapor-pressure, environment insensitivity and the symmetrical Zn||Zn cell demonstrates excellent stability for >1000 hours at 0.1 mA/cm². When paired with V₂O₅, Zn exhibits a high discharge capacity of 270 mAh/g, and promising cyclability for >600 cycles. These results highlight its potential as an alternative to aqueous electrolytes for grid-level storage units.