To achieve high energy and power densities, we developed a highvoltage 2.5 V electrochemical pseudo-capacitor with a maximum energy density of 304 W h kg À1 based on MnO 2 nanowires electrodeposited on nickel foam as electrode with a novel Li-ion quasiionic liquid as electrolyte.

Co(II), Sn(II), V(III), Ni(II), Mn(II), and Ru(III) species in ureabased quasi-ILs were investigated using cyclic voltammograms and X-ray absorption near-edge structure (XANES) spectra. The excellent pseudocapacitive characteristics of MnO 2 -graphene nanocomposite electrodes in ILs, associated with the large variation of Mn oxidation state during charge and discharge cycles, were also elucidated using in situ XANES spectra.Room temperature ionic liquids (RTILs) are extensively employed in diverse devices for energy storage, such as lithium secondary batteries and electric double-layer capacitors because of their unique physical and chemical properties; these include being nonvolatile, nonflammable, low toxicity, stable thermally and electrochemically, highly conductive, having wide electrochemical windows and a varied combination of cations and anions. [1][2][3][4][5][6][7][8] The wide electrochemical window of an IL enables the electrodeposition of active elements that are difficult to reduce in aqueous solutions. 2 Some organic solvents, including propylene carbonate (PC) and diethyl carbonate, have already found practical application in contemporary electronic devices, such as in mobile telephones and portable computers, but all these organic solvents have potential drawbacks according to safety concerns about their flammable and volatile nature that can lead to explosions or incendiary accidents. Furthermore, lithium anodes with a high theoretical discharge capacity (3860 mA h g 21 ) are unusable in such solvents because of dendritic lithium deposition during the charging cycle. From a point of view of practical application, it is of great interest to seek ILs with satisfactory solubility, modest cost, small viscosity and wide potential windows. RTIL (or molten-salt) electrolytes based on urea-based mixtures have been extensively investigated since 2003. 9-14 Especially, the complex systems based on urea-ChCl (choline chloride 10,14 ) or urea-EMIC (1-ethyl-3-methylimidazolium chloride 9 ) were considered to be promising electrolytes for electrochemical behavior because of their facile, environmentally friendly preparation without organic solvents, large ionic conductivity, satisfactory solubility and modest