Abstract: An object is to increase the amount of ions capable of entering and leaving a positive electrode active material in an ion battery so that the capacity of the battery is increased. When a solid solution including alkali metal oxide having electrical conductivity less than or equal to 10?10 S/cm and including alkali metal with a valence of 2 or more, and alkali metal oxide having electrical conductivity greater than or equal to 1×10?6 S/cm and less than or equal to 3×10?6 S/cm is used as a positive electrode active material in an ion battery, the amount of ions capable of entering and leaving the positive electrode active material is increased, so that the capacity of the battery is increased.

Abstract: An object is to provide a power storage device with high discharge capacity and high energy density. The power storage device includes a positive electrode in which a positive electrode active material is formed over a positive electrode current collector; and a negative electrode which faces the positive electrode with an electrolyte interposed therebetween. The positive electrode active material includes a film-form first region which includes a compound containing lithium and nickel; and a film-form second region which includes a compound containing lithium and one or more of iron, manganese, and cobalt, but not containing nickel. The first region is covered with the second region. Since a superficial portion of the positive electrode active material does not contain nickel, nickel is not in contact with an electrolyte solution; thus, generation of a catalyst effect of nickel can be suppressed, and a high discharge potential of nickel can be utilized.

Abstract: An object is to provide a power storage device with high discharge capacity and high energy density. The power storage device includes a positive electrode in which a positive electrode active material is formed over a positive electrode current collector; and a negative electrode which faces the positive electrode with an electrolyte interposed therebetween. The positive electrode active material includes a film-form first region which includes a compound containing lithium and nickel; and a film-form second region which includes a compound containing lithium and one or more of iron, manganese, and cobalt, but not containing nickel. The first region is covered with the second region. Since a superficial portion of the positive electrode active material does not contain nickel, nickel is not in contact with an electrolyte solution; thus, generation of a catalyst effect of nickel can be suppressed, and a high discharge potential of nickel can be utilized.

Abstract: A power storage device including a positive electrode having a positive electrode active material and a positive electrode current collector; and a negative electrode which faces the positive electrode with an electrolyte provided between the negative electrode and the positive electrode is provided. The positive electrode active material includes a first region which includes a phosphate compound containing lithium and nickel; and a second region which covers the first region and includes a compound containing lithium and one or more of iron, manganese, and cobalt, but not containing nickel. Since the entire superficial portion of a particle of the positive electrode active material does not contain nickel, nickel is not in contact with an electrolyte solution; thus, generation of a catalyst effect of nickel can be suppressed, and a high discharge potential of nickel can be utilized.

Abstract: A power storage device includes a positive electrode including a positive electrode current collector and a positive electrode active material having an olivine structure which is represented by a structural formula LiFexMe1-xPO4 (Me=Mn, Ni, or Co) (x is greater than 0 and less than 1) over the positive electrode current collector, or a power storage device includes a positive electrode including a positive electrode current collector and a positive electrode active material, and a negative electrode which faces the positive electrode through an electrolyte, where discharging capacitance is greater than or equal to 150 mAh/g and energy density per unit weight is higher than or equal to 500 mWh/g.

Abstract: A power storage device comprising a positive electrode which includes in a positive electrode active material layer, lithium iron phosphate particles whose surface is supported by a carbon material and whose half width of the X-ray diffraction peak is less than or equal to 0.17°, or greater than or equal to 0.13° and less than or equal to 0.165? or whose particle size is greater than or equal to 20 nm and less than 50 nm or greater than or equal to 30 nm and less than 40 nm; or a method for manufacturing a power storage device comprising the steps of mixing the lithium iron phosphate particles, a conduction auxiliary agent, and a binder so as to be a paste, and applying the paste on a current collector, thereby manufacturing a positive electrode.

Abstract: An object is to increase the amount of ions capable of entering and leaving a positive electrode active material in an ion battery so that the capacity of the battery is increased. When a solid solution including alkali metal oxide having electrical conductivity less than or equal to 10?10 S/cm and including alkali metal with a valence of 2 or more, and alkali metal oxide having electrical conductivity greater than or equal to 1×10?6 S/cm and less than or equal to 3×10?6 S/cm is used as a positive electrode active material in an ion battery, the amount of ions capable of entering and leaving the positive electrode active material is increased, so that the capacity of the battery is increased.

Abstract: A capacitor having stable characteristics and an improved energy density while sufficiently ensuring a bonding strength between the polarizable electrode layer and the current collector is provided. A buffer layer including a ratio of 60 wt % to 90 wt %, preferably 70 wt % to 80 wt %, of carbon nanofiber or carbon nanotube, is formed over the current collector. Then, by forming a polarizable electrode layer over the aforesaid buffer layer, a pair of electrodes are obtained in which, the buffer layer and the polarizable electrode layer are stacked in this order over the current collector. Additionally, a capacitor is formed with the above-mentioned pair of electrodes by opposing the polarizable electrode layers to each other so as to be facing one another with a separator sandwiched therebetween in an electrolyte solution.