An ultralow-temperature aqueous zinc-ion battery

The freezing of aqueous electrolytes severely limits the operation of aqueous zinc-ion batteries (AZIBs) in low-temperature conditions owing to the terrible ion conductivity and interface kinetics. Here, a 4 M Zn(BF₄)₂electrolyte with a low freezing point (−122 °C) and high ion conductivity (1.47 mS cm⁻¹at −70 °C) is developed for AZIBs. Comprehensive analyses, including spectroscopic measurement and theoretical calculation, demonstrate that introducing BF₄⁻anions can break the hydrogen-bond networks in original water molecules by the formation of OH⋯F hydrogen bonds, resulting in an ultralow freezing point. The 4 M Zn(BF₄)₂-based electrolyte enables the Zn//tetrachlorobenzoquinone (TCBQ) battery to exhibit excellent electrochemical performance in the wide temperature range of 25 to −95 °C, achieving a high discharge capacity of 63.5 mA h g⁻¹and energy density of 76.2 W h kg⁻¹at a record-breaking temperature of −95 °C. This work provides a simple and green strategy to design high-performance AZIBs at low-temperature conditions.