NOVELTY - The device comprises a positive electrode (973), a negative electrode (976), a third electrode (979) made of a material having specific surface area of 500 m2/g or larger, and an electrolyte. The negative electrode is sandwiched between the positive electrode and the third electrode. The positive electrode is sandwiched between the negative electrode and the third electrode. A main surface of the third electrode is formed perpendicular to a main surface of the positive electrode and a main surface of the negative electrode.    USE - The power storage device is useful in an electrical device (claimed) such as portable information terminals e.g. mobile phones, smartphones, laptop personal computers, portable music players, digital cameras, medical equipment, energy vehicles such as hybrid electric vehicles, electric vehicles, plug-in hybrid electric vehicles, display devices of TV, lighting devices, cordless phone handsets, pedometers, electronic notebooks, and calculators, where the power storage device comprises non-aqueous secondary batteries e.g. laminated lithium-ion secondary batteries, lithium-ion capacitors, and air cells.    ADVANTAGE - The device inhibits a decrease in the capacity of a power storage device by adjusting or rectifying an imbalance, which is caused by decomposition of an electrolyte solution at the negative electrode, in the amount of inserted and extracted carrier ions between the positive electrode and the negative electrode, and has reduced power consumption and improved reliability.    DETAILED DESCRIPTION - The device comprises a positive electrode (973), a negative electrode (976), a third electrode (979) made of a material having specific surface area of 500 m2/g or larger, and an electrolyte. The negative electrode is sandwiched between the positive electrode and the third electrode. The positive electrode is sandwiched between the negative electrode and the third electrode. A main surface of the third electrode is formed perpendicular to a main surface of the positive electrode and a main surface of the negative electrode. The device further comprises a fourth electrode made of a material having a specific surface area of 500 m2/g or larger. The positive electrode and the negative electrode are placed between the third electrode and the fourth electrode. INDEPENDENT CLAIMS are included for:    (1) an electrical device; and    (2) a method for charging a power storage device.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross-sectional view of a power storage device.    Positive electrode (973)    Negative electrode current collector (974)    Negative electrode (976)    Separator (977)    Third electrode. (979)