Tuning the Solvation Structure in Aqueous Zinc Batteries to Maximize Zn-Ion Intercalation and Optimize Dendrite-Free Zinc Plating

Aqueous zinc batteries are recognized to suffer from H⁺/Zn²⁺ coinsertion in the cathode, but few approaches have been reported to suppress deleterious H⁺ intercalation. We realize this goal by tuning the solvation structure, using LiV₂(PO₄)₃ (LVP) as a model cathode. Phase conversion of LVP induced by H⁺ intercalation is observed in 4 m Zn(OTf)₂, whereas dominant Zn²⁺ insertion is confirmed in a ZnCl₂ water-in-salt electrolyte (WiSE). This disparity is ascribed to the complete absence of free water and a strong Zn²⁺–H₂O interaction in the latter that interrupts the H₂O hydrogen bonding network, thus suppressing H⁺ intercalation. On the basis of this strategy, a novel PEG-based hybrid electrolyte is designed to replace the corrosive ZnCl2 WiSE. This system exhibits an optimized Zn²⁺ solvation sheath with a similar low free water content, showing not only much better suppression of H⁺ intercalation but also highly reversible Zn plating/stripping with a CE of ~99.7% over 150 cycles.