Cost attractive hydrogel electrolyte for low temperature aqueous sodium ion batteries

摘要

Low temperature tolerance of aqueous sodium ion batteries (ASIBs) represents a high challenge, eventhough ASIBs are attractive for large scale energy-storage application due to their high safety, low cost and environmental friendliness. For the first time, this work reports a Na2SO4-SiO2 hydrogel type electrolyte operated at low temperature as -30 degrees C using fumed silica as the gel matrix and methyl alcohol as the anti-freezing additive. Due to the inter-molecular bonding between SiO2 and Na2SO4, the precipitation of Na2SO4 and the continue growth of the Na2SO4 grain in supersaturated electrolyte is highly suppressed at low temperature. The Na2SO4-SiO2 hydrogel electrolyte possesses a high ionic conductivity as 0.070 mS cm(-1) at -30 degrees C. An aqueous sodium ion cell with the as-proposed SiO2-Na2SO4 hydrogel electrolyte has been developed based on active carbon (AC) as the cathode and carbon coated NaTi2(PO4)(3) (NTP@C) as the anode. At -30 degrees C, the cell possesses a reversible capacity of 61.8 mAh g(-1) (based on NTP@C) at a current density as 0.13 A g(-1) (0.13 mA cm(-2)) with a high cycling stability. This work provides a new path for the development of aqueous sodium ion batteries for low temperature operation.