A Dual Salt/Dual Solvent Electrolyte Enables Ultrahigh Utilization of Zinc Metal Anode for Aqueous Batteries

Rechargeable aqueous zinc batteries are promising in next-generation sustainable energy storage. However, the low zinc (Zn) metal anode reversibility and utilization in aqueous electrolytes due to Zn corrosion and poor Zn²⁺ deposition kinetics significantly hinder the development of Zn-ion batteries. Here, a dual salt/dual solvent electrolyte composed of Zn(BF₄)₂/Zn(Ac)₂ in water/TEGDME (tetraethylene glycol dimethyl ether) solvents to achieve reversible Zn anode at an ultrahigh depth of discharge (DOD) is developed. An "inner co-salt and outer co-solvent" synergistic effect in this unique dual salt/dual solvent system is revealed. Experimental results and theoretical calculations provide evidence that the ether co-solvent inhibits water activity by forming hydrogen bonding with the water and coordination effects with the proton in the outer Zn²⁺ solvation structure. Meanwhile, the anion of zinc acetate co-salt enters the inner Zn²⁺ solvation structure, thereby accelerating the desolvation kinetics. Strikingly, based on the electrolyte design, the zinc anode shows high reversibility at an ultrahigh utilization of 60% DOD with 99.80% Coulombic efficiency and 9.39 mAh cm^-2 high capacity. The results far exceed the performance reported in electrolyte design work recently. The work provides fundamental insights into inner co-salt and outer co-solvent synergistic regulation in multifunctional electrolytes for reversible aqueous metal-ion batteries.