Upgrading low-temperature cycling stability of hybrid Na–air batteries via sodium biphenyl modification

Abstract

Na–air batteries offer advantages such as high theoretical energy density and abundant precursor resources. Owing to the low first ionization energy of sodium ions, Na–air batteries have more competitive low-temperature performance compared to similar batteries. However, at low temperatures, Na–air batteries continue to encounter critical challenges, including safety risks associated with dendrite growth during cycling and increased interfacial impedance induced by the elevated viscosity of the electrolyte. Herein, a strategy is proposed to improve battery safety and ensure stable operation of the battery at low temperature, preparing a liquid anode with low voltage gap and high safety by dissolving metallic sodium and biphenyl in ethylene glycol dimethyl ether solvent, and adding antifreeze additives to the liquid system to improve the low-temperature cycle performance of the battery. The prepared liquid anode reacts mildly with water, while leveraging the low viscosity and weak solvation properties of 1,3-dioxolane, enabling the assembled hybrid Na–air battery to maintain a low voltage gap of 0.54 V at −30 °C and to cycle stably for over 750 cycles. This work offers a viable strategy for developing batteries with high safety and stability at low temperatures, and provides a valuable reference for the design of batteries operating under extreme conditions.