Hydrated Deep Eutectic Electrolytes for High-Performance Zn-Ion Batteries Capable of Low-Temperature Operation

Aqueous Zn-ion batteries (ZIBs) are a promising energy storage technology due to their intrinsic safety, eco-friendliness, and cost-effectiveness. However, aqueous electrolytes generally induce parasitic interfacial reactions (e.g., dendrite growth and passivation) that degrade the Zn metal anode, shortening ZIBs lifespan. This study develops a novel hydrated deep eutectic electrolyte (DEE), containing sulfolane (SL) and Zn(ClO4)2·6H2O, to prevent water-induced deterioration. The strong coordination between SL and Zn2+ triggers the deep eutectic effect, extending the operating temperature window of the DEE. The unique water-in-DEE structure boosts ionic diffusion, promotes Zn2+ deposition, and reduces water reactivity, as revealed by in-depth simulations and experiments. The developed DEE suppresses dendrite formation, allowing the Zn\DEE\Zn symmetrical cells to cycle over thousands of hours without short-circuiting. With a polyaniline (PANI) cathode, Zn\DEE\PANI cells can cycle 2500 times with a capacity of 72 mAh g−1 at 3 A g−1 at room temperature and 500 times with 73 mAh g−1 at 0.3 A g−1 at −30 °C. The newly developed DEE significantly is a step forward for inexpensive, stable, and high-performance ZIBs.