Universal strategy of Ca2+-mediated antifreeze electrolyte for ultralow-temperature aqueous Zinc-Ion batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) are considered as the promising candidate for energy storage due to high safety, eco-friendliness, and low-cost. However, the operation in extreme cold environments remains a critical challenge for applications. Herein we propose a universal design strategy of anti-freezing electrolyte using Ca²⁺ mediation for regulating hydrogen bond (HB) network and solvation structure. The Zn(ClO₄)₂ electrolyte with CaCl₂ additive achieves an ultralow freezing point (-60.66 °C) and high ionic conductivity (1.79 mS cm^-1 at -60 °C). Molecular dynamics simulations reveal the Ca²⁺-induced the regulation of HBs and competitive hydration, which reduces Zn²⁺coordination numbers from 5.75 to 4.69. This optimization lowers energy barriers for rapid reaction kinetics, enabling long-term cycling stability (>1100 h for Zn||Zn), high Coulombic efficiency (99.61 % over 600 cycles for Zn||Cu), and 70.62 % capacity retention after 350 cycles in full cells at -60 °C. Remarkably, this strategy is applicable to various systems such as Zn(ClO₄)₂, Zn(BF₄)₂, ZnCl₂, and Zn(OTf)₂, where freezing points drops >40 °C and all achieve long-term lifespan at -55 °C. It is expected that our work provides a universal framework for ultralow-temperature energy storage.