Gradient chaotropic regulation of Zn2+ solvation chemistry for low-temperature zinc metal batteries.

Aqueous zinc-ion batteries have emerged as a promising system for safe and sustainable energy storage. However, their practical application is hindered by detrimental interfacial side reactions and inadequate low-temperature performance. Herein, we report the design of a gradient chaotropic ionic liquid (IL)-based aqueous electrolyte (Emim⁺-TFA⁻/OTf⁻-Zn2+-H2O), which can simultaneously fulfil the conflicting demands of dendrite-free zinc deposition and low-temperature operation. By forming an antifreeze electrolyte with a hydrophobic yet salt-philic interface, the proposed formulation overcomes the limitations of conventional IL-based systems that rely on H2O-lean compositions, complex additives, or elaborate solvent mixtures. Thus, the assembled zinc-ion cells exhibit improved zinc plating/stripping stability. At a current density of 0.1 mA cm-2 and 0.1 mAh cm-2, the Zn | |Zn symmetric cells endure prolonged zinc plating/stripping, exceeding 13,000 h at -30 °C and 6690 h at -40 °C. In full cells, Zn | |VO2@VO maintains nearly 100% capacity retention over 3500 cycles at 0.2 A g-1 and -40 °C. This gradient chaotropic Zn2+ electrolyte design provides a versatile platform for effective antifreeze Zn2+ solvation chemistry and accelerated interfacial ion transport, enabling high-performance zinc batteries in subzero environments.