Ideal pseudocapacitive behavior of alpha-MnO2 electrodes over a potential range of 3 V is found in lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)-doped butylmethylpyrrolidinium-dicyanamide (BMP-DCA) ionic liquid (IL), which is non-flammable and has a decomposition temperature of as high as similar to 300 degrees C. Accordingly, this electrolyte is promising for high-energy, high-power, and high-safety supercapacitor applications. The addition of 0.01 M LiTFSI in the IL improves the oxide capacitance from 90 F g(-1) to 120 F g(-1), which is due to the incorporated Li+ ions promoting Mn valent state variation (between trivalent and tetravalent) during charge discharge. However, excessive LiTFSI doping causes a capacitance decay due to reduced electrolyte ionic conductivity. In situ X-ray absorption spectroscopy is used to investigate the energy storage mechanism. A capacitance activation process of alpha-MnO2 in the Li+-doped BMP-DCA IL is found. (C) 2013 Elsevier B.V. All rights reserved.