Water-modulated electrolyte enables the development of advanced low-temperature Zn-ion batteries

Abstract

Aqueous Zn-ion batteries face huge challenges at sub-zero temperatures due to electrolyte freezing and parasitic side reactions. Here, we present a low-temperature Zn-ion battery with a water-modulated Zn(BF₄)₂ electrolyte consisting of 1,3-dioxolane (DOL) and water in a 95 : 5 volume ratio. DOL was selected due to its low freezing point and ability to dissolve Zn(BF₄)₂ at high concentrations. A minimal water content is maintained to suppress ring-opening polymerisation of DOL, which prevents viscosity increment and conductivity losses, thereby preserving the electrolyte stability. By combining the computational simulations with experiments, the results show that DOL molecules disrupt the H-bond network of the remaining water and alter the Zn²⁺ solvation structure, which suppresses the hydrogen evolution reaction and facilitates dendrite-free Zn deposition even at low temperature. The water-modulated electrolyte exhibits excellent low-temperature performance. Specifically, the Zn‖MgVO full cell operates at −30 °C with over 90% capacity retention after 300 cycles at 1C, and it sustains over 2000 cycles at a high rate of 10C. This study confirms DOL modulation's key role in achieving hydrogen-free and dendrite-free Zn anodes, advancing understanding of intermolecular interactions in low-temperature electrolyte design.