Anion-Type Solvation Structure Enables Freeze-Tolerant Aqueous Zinc-Vanadium Batteries.

Abstract

Aqueous zinc batteries represent a promising solution for large-scale energy storage, offering inherent safety and cost advantages. However, their subzero operation is fundamentally constrained by severely retarded reaction kinetics of Zn²⁺. Herein, to construct high-performance, freeze-tolerant aqueous zinc-vanadium batteries, 2-methyltetrahydrofuran (2-MeTHF) with weak coordination and dissociation capacity is introduced as a functional co-solvent to reconstruct Zn²⁺ solvation structures from water-dominated ([Zn(H₂O)₆]²⁺) to anion-dominated ([Zn(H₂O)₂(OTf^-)₄]^2-) in 1 M Zn(OTf)₂. The as-constructed anion-type solvation configuration creates low-barrier desolvation/migration ion channels and anion-rich interface, leading to key improvements in bulk Zn²⁺ ion transport and interfacial stability, benefiting both the anodic and cathodic chemistry. Substantial improvement of Zn plating/stripping reversibility, contributed by promoted Zn-diffusion kinetics and OTf^--derived robust protective interphase, is obtained from 25 to -20 °C, while long-term structure integrity of NaV₃O₈∙1.5H₂O cathode, attributed to the prohibition of H₂O-driven degradation and dissolution issues, is also effectively maintained. Consequently, even at -20 °C, where the pure aqueous electrolyte hardly works, the Zn||NaV₃O₈∙1.5H₂O assembled in 2-MeTHF-containing electrolyte still presents long-term cycling durability up to 8000 cycles at 5 A g^-1, with negligible capacity decay throughout the test. This work highlights the significant role of anion-type solvation of Zn²⁺ in achieving wide-temperature aqueous zinc batteries.