Butylmethylpyrrolidinium–dicyanamide (BMP–DCA) ionic liquid (IL), which enables the pseudocapacitive behavior of a MnO₂ electrode, performing over a wide potential range of 3 V, is considered to be a promising electrolyte for supercapacitors. Various additives are doped in this IL electrolyte in attempt to further improve the electrochemical performance of MnO₂; NaDCA is found to be the most effective. An appropriate concentration (∼0.01 M) of NaDCA in the IL can optimize the capacitance of the MnO₂ electrode; the values are 100 and 125 F g⁻¹ at 25 and 50 °C, respectively. The NaDCA-doped IL is superior to traditional aqueous electrolytes for high-energy, high-power, elevated-temperature, and long-life MnO₂ supercapacitor applications.