Development of Mn oxide supercapacitors incorporating ionic liquid (IL) electrolytes was attempted. The experimental results indicate the possibility of achieving pseudocapacitive performance of Mn oxide in ILs without involving protons and alkali cations, thus opening a route of developing electrolytes for oxide-based pseudocapacitors. In 1-ethyl-3-methylimidazolium-dicyanamide aprotic IL, Mn oxide can exhibit a specific capacitance of 72 F/g in a potential window of 2 V. Due to high ionic conductivity, large electrochemical windows, excellent thermal stability, and nonflammability of the IL, a high-voltage and long-life energy storage system is successfully proposed.