Although electrochemical double layer capacitors (EDLCs) have high specific power, their specific energy is rather low. To address this issue, a composite material between EDLC-type N-doped graphene aerogel (N-rGO(ae)) with an N-doped content of ca. 8 at% and pseudocapacitor-type mixed-valence manganese oxide (MnOx) nanoparticles with a diameter of <20 nm was synthesized and used as the electrode material of hybrid supercapacitors. In addition, a new electrolyte of ionic liquid electrolyte 1-butyl-1-methylpyrrolidinium dicyanamide ([BMP][DCA]) with a redox additive (K-4[Fe(CN)(6)]) was employed to further improve the performance of the hybrid supercapacitor. The as-fabricated supercapacitor exhibits an excellent specific energy and power of 44.7 Wh kg(-1) and 4551.4 W kg(-1), respectively. In situ electrochemical X-ray absorption spectroscopy (XAS) was also used to investigate the charge storage mechanism of the mixed-valence MnOx in the composite. Interestingly, with the presence of redox additive in the electrolytes, a wide oxidation state variation range of Mn in the MnOx/N-rGO(ae) composite can be observed indicating high redox activities and confirming the faradaic charge transfer interaction between redox additive and MnOx. Furthermore, the in situ XAS result also confirms the reversibility of the redox reaction of MnOx showing that the hybrid supercapacitor using the ionic liquid electrolyte with a redox additive in this work may be practically used in high-energy applications. (C) 2018 Elsevier Ltd. All rights reserved.