Tailoring Zn²⁺ Solvation for Dendrite-Free and High-Efficiency Aqueous Zinc Batteries

Aqueous zinc-metal batteries (ZMBs) offer high capacity, intrinsic safety, and low cost but remain challenged by dendrite growth, hydrogen evolution, and interfacial instability. Here, we develop a solvation-engineered hybrid electrolyte comprising 3 M Zn(OTf)₂ in water, methanol, and dimethyl sulfoxide (3:1:1, v/v/v). Methanol disrupts the hydrogen-bond network, while DMSO stabilizes Zn²⁺ coordination, collectively forming a unique solvation structure as confirmed by isothermal titration calorimetry, density functional theory, and Raman spectroscopy. This environment promotes preferential triflate anion decomposition, yielding an in situ fluorine-rich solid electrolyte interphase (SEI) that passivates zinc, reduces water activity, and suppresses hydrogen evolution. As a result, Zn||Zn cells cycle stably for over 4000 h at 0.5 mA cm^-2, Zn||Cu cells achieve 99.8% coulombic efficiency over 2000 cycles, and Zn||MnO₂ cells deliver > 150 mAh g^-1 at 1C with sustained cathode stability. This work demonstrates a simple, scalable solvation-engineering strategy that stabilizes zinc interfaces without complex additives or highly concentrated electrolytes, advancing the practical deployment of aqueous ZMBs.