Weakly solvating aqueous-based electrolyte facilitated by a soft co-solvent for extreme temperature operations of zinc-ion batteries

The aqueous zinc-ion battery (AZIB) is a promising option for grid-scale energy storage, but it faces challenges from parasitic water-related reactions and limited operational temperature range. Replacing H₂O molecules in the solvation sheath of Zn²⁺ with strongly solvating co-solvents can effectively suppress water-related side reactions. However, the excessive Zn²⁺-co-solvent interaction can cause a large activation energy of desolvation (E_a) and the decomposition of the co-solvent may introduce non-ionic conductive solid electrolyte interphase (SEI) species. Hence, we propose a weakly solvating electrolyte that adopts diethylene glycol dimethyl ether (G2) as a soft co-solvent. The G2 has a moderate Gutmann donor number (19 kcal mol⁻¹) and a low dielectric constant (7.4), which reduces the presence of water in the solvation sheath and enhances Zn²⁺-anion interaction. This electrolyte achieves an optimal E_a and a robust anion-derived SEI (ZnS-ZnSO₃-ZnF₂) on the zinc anode, allowing highly reversible Zn plating/stripping for over 7500 hours. The strong G2-H₂O interaction enables G2 to bind free H₂O and reconstruct the hydrogen bond network, which prevents water decomposition and widens the electrolyte's operational temperature range (−60 °C to 60 °C). The Zn//KV₁₂O_30−y·nH₂O (KVOH) full battery delivers a high-capacity retention of 91.2% following 8000 cycles at 5.0 A g⁻¹ at room temperature. It also achieves capacity retention of 82.9% over 4000 cycles (0.1 A g⁻¹) at −45 °C and 86.5% for 1200 cycles (5.0 A g⁻¹) at 60 °C, respectively. This work optimizes interface chemistry and temperature adaptability of AZIBs, offering guidance for designing weakly solvating aqueous-based electrolytes towards practical application. © 2024 The Royal Society of Chemistry.