An objective is to provide a novel aqueous electrolytic solution constituting an aqueous power storage device that stably operates even at a high voltage.

An electrolytic solution for a power storage device contains water as a solvent and has a composition in which an amount of the solvent is not greater than 4 mol with respect to 1 mol of an alkali metal salt.

An energy storage device can include a cathode, an anode, and a separator between the cathode and the anode, where the anode and/or electrode includes an electrode film having a super-fibrillized binder material and carbon. The electrode film can have a reduced quantity of the binder material while maintaining desired mechanical and/or electrical properties. A process for fabricating the electrode film may include a fibrillization process using reduced speed and/or increased process pressure such that fibrillization of the binder material can be increased. The electrode film may include an electrical conductivity promoting additive to facilitate decreased equivalent series resistance performance. Increasing fibrillization of the binder material may facilitate formation of thinner electrode films, such as dry electrode films.

Graphene electrodes-based supercapacitors are in demand due to superior electrochemical characteristics. However, commercial applications have been limited by inferior electrode cycle life. A method to fabricate highly efficient supercapacitor electrodes using pristine graphene sheets vertically-stacked and electrically connected to the carbon fibers which results in vertically-aligned graphene-carbon fiber nanostructure is disclosed. The vertically-aligned graphene-carbon fiber electrode prepared by electrophoretic deposition possesses a mesoporous three-dimensional architecture which enabled faster and efficient electrolyte-ion diffusion with a specific capacitance of 333.3 F g.sup.−1. The electrodes have electrochemical cycling stability of more than 100,000 cycles with 100% capacitance retention. Apart from the electrochemical double layer charge storage, the oxygen-containing surface moieties and α-Ni(OH).sub.2 present on the graphene sheets enhance the charge storage by faradaic reactions. This enables the assembled device to provide a gravimetric energy density of 76 W h kg.sup.−1 with a 100% capacitance retention even after 1,000 bending cycles.

Graphene electrodes-based supercapacitors are in demand due to superior electrochemical characteristics. However, commercial applications have been limited by inferior electrode cycle life. A method to fabricate highly efficient supercapacitor electrodes using pristine graphene sheets vertically-stacked and electrically connected to the carbon fibers which results in vertically-aligned graphene-carbon fiber nanostructure is disclosed. The vertically-aligned graphene-carbon fiber electrode prepared by electrophoretic deposition possesses a mesoporous three-dimensional architecture which enabled faster and efficient electrolyte-ion diffusion with a specific capacitance of 333.3 F g.sup.−1. The electrodes have electrochemical cycling stability of more than 100,000 cycles with 100% capacitance retention. Apart from the electrochemical double layer charge storage, the oxygen-containing surface moieties and α-Ni(OH).sub.2 present on the graphene sheets enhance the charge storage by faradaic reactions. This enables the assembled device to provide a gravimetric energy density of 76 W h kg.sup.−1 with a 100% capacitance retention even after 1,000 bending cycles.

An asymmetric nanocomposite supercapacitor and a method of making the asymmetric nanocomposite supercapacitor. The asymmetric nanocomposite supercapacitor includes a negative electrode with monoclinic tungsten oxide (m-WO.sub.3) nanoplates, and a binding compound coated on one face of a substrate, and a positive electrode with a carbonaceous material and a binding compound coated on one face of a substrate. Where the face of the positive electrode and the face of the negative electrode coated with the carbonaceous material and m-WO.sub.3 nanoplates, respectively, are separated by and in direct contact with a porous separator.

A negative active material includes a carbon material. The carbon material satisfies the following relationship: 6<Gr/K<16, Gr is a graphitization degree of the carbon material, measured by means of X-ray diffraction; and K is a ratio Id/Ig of a peak intensity Id of the carbon material at a wavenumber of 1250 cm.sup.−1 to 1650 cm.sup.−1 to a peak intensity Ig of the carbon material at a wavenumber of 1500 cm.sup.−1 to 1650 cm.sup.−1, and is measured by using Raman spectroscopy, and K is 0.06 to 0.15. The negative active material according to this application can significantly improve an energy density, cycle performance, and rate performance of the electrochemical device.

An electrochemical device includes a pair of electrodes and an electrolytic solution. At least one of the pair of electrodes contains porous carbon particles. In a pore distribution of the porous carbon particles, an integrated volume B is more than or equal to 0.15 cm.sup.3/g and an integrated volume C is less than or equal to 0.25 cm.sup.3/g. The integrated volume B is an integrated volume of pores each having a pore diameter of more than or equal to 20 Å and less than or equal to 60 Å. The integrated volume C is an integrated volume of pores each having a pore diameter of more than 60 Å and less than or equal to 500 Å.

An electrode for an electrochemical device includes porous carbon particles. In a pore distribution of the porous carbon particles, a ratio B/A of an integrated volume B to an integrated volume A ranges from 1 to 1.5, inclusive. The integrated volume A is an integrated volume of pores each having a pore diameter of more than or equal to 1 nm and less than 2 nm. The integrated volume B is an integrated volume of pores each having a pore diameter of more than or equal to 2 nm and less than or equal to 50 nm. A volume-based particle diameter frequency distribution of the porous carbon particles has a first peak and a second peak. A particle diameter corresponding to the second peak is larger than a particle diameter corresponding to the first peak.

An electrode for an electrochemical device includes porous carbon particles. In a pore distribution of the porous carbon particles, a ratio B/A of an integrated volume B to an integrated volume A ranges from 1 to 1.5, inclusive. The integrated volume A is an integrated volume of pores each having a pore diameter of more than or equal to 1 nm and less than 2 nm. The integrated volume B is an integrated volume of pores each having a pore diameter of more than or equal to 2 nm and less than or equal to 50 nm. A volume-based particle diameter frequency distribution of the porous carbon particles has a first peak and a second peak. A particle diameter corresponding to the second peak is larger than a particle diameter corresponding to the first peak.

A method for manufacturing composites in which the nanosize of a carbon material and a metal compound can be maintained as the final product is realized to provide a superior electrode material. A treatment of increasing the functional groups possessed by a carbon material is performed in advance. Then, a metal compound precursor is supported on a carbon material by separately performing a treatment of adsorbing one of source materials of the metal compound to the functional groups of the carbon material having increased functional groups and a treatment of reacting the adsorbed source material of the metal compound with the rest of the source materials on the carbon material to produce a metal compound precursor on the carbon material. Finally, a lithium source is introduced and calcined.