Testing of MnO2 Hybrid Aqueous Supercapacitors Under Extreme Climatic Conditions

Hybrid birnessite/carbon supercapacitor cells have been used to investigate the effect of the addition of ethylene glycol to aqueous neutral electrolytes on low temperature performance. The addition of progressively more ethylene glycol to the electrolyte resulted in a decrease in observed specific capacitance but enabled the operation of these predominantly aqueous systems at temperatures as low as -30 degrees C. At such low temperatures, specific capacitance of around 25 F g(-1) was observed with excellent cycling behavior. At lower levels of ethylene glycol and low temperatures, the electrolyte was found to freeze, with large increases in charge transfer and Warburg resistances (as measured by EIS) resulting in the failure of the cells to cycle.