Advancing anti-freezing hydrogel electrolyte based on deep eutectic solvent for wide temperature range aqueous zinc-ion battery

Abstract

Hydrogels based on Deep Eutectic Solvents (DES) demonstrate remarkable anti-freezing, resilience, and toughness, presenting a promising avenue to the operation of aqueous zinc-ion batteries under extreme conditions. A gel electrolyte capable of operating over a wide temperature range is developed based on a DES comprising 1 mol/kg (m) Zn(ClO₄)₂ + 3.5 m Mg(ClO₄)₂. Spectral characterization confirms the synergistic influence of both anions and cations on the freezing point of the DES. With four hydrogen bond (HB) acceptors, Mg²⁺ exhibits strong electrostatic attraction towards the O atoms of H₂O, while ClO₄⁻ forms numerous HBs with H₂O molecules. This dual interaction allows for precise adjustment of the chemical environment around the H and O atoms of H₂O, resulting in an exceptionally low freezing point of -116.92 °C for the DES. The gel electrolyte derived from this DES demonstrates an impressive ionic conductivity of 0.285 mS/cm at -70 °C. Leveraging its excellent low-temperature performance and compatibility with a zinc anode, the flexible Zn-Mn battery constructed with this electrolyte exhibits robust electrochemical performance at low temperatures. Specifically, at -70 °C, it achieves a high specific capacity of 76.83 mAh/g, displays excellent rate capability, and maintains stable cycling performance. Moreover, the Zn-Mn battery operates reliably across a broad temperature range from -70 to 80 °C. This study presents innovative insights for advancing Zn-Mn batteries capable of efficient operation across diverse environmental conditions, thereby opening new avenues for their development.