An anti-freezing pure inorganic electrolyte for long cycle life aqueous sodium-ion batteries at -40 °C

Aqueous electrolytes have the great application potential for sodium-ion batteries owing to eco-friendliness, high-safety, and low cost. However, the high freezing point of common aqueous electrolytes greatly limits the normal operation of aqueous sodium-ion batteries (ASIBs) at low temperatures. Herein, MnCl2<middle dot>4H(2)O is introduced into NaCl solution to form the hybrid NaCl/MnCl2<middle dot>4H(2)O electrolyte to expand the application scope of ASIBs. Due to the strong interaction between Mn2+ and water molecules, the hydrogen bond network in water is damaged on a large scale. Thus, the hybrid electrolyte maintains a liquid state and has a high ionic conductivity (2.44 mS cm(-1)) at -50 degrees C. When used the optimized hybrid inorganic electrolyte, the pure inorganic compositions full battery assembled with Na2CoFe(CN)(6) cathode and active carbon anode delivers a high specific capacity of 54.0 mAh g(-1) at -40 degrees C under 1 C (1 C = 150 mA g(-1)). Excitingly, when tested at -40 degrees C under 10 C, the battery can achieve an ultra-long cycle stability of 10,000 cycles with a capacity retention of similar to 99 %. Significantly, this work opens a new path to explore the ASIBs with superior electrochemical performance at low temperatures.