NOVELTY - An electrical device has an electric power generating element (21) containing positive electrode obtained by forming positive electrode active material layer (13) containing positive electrode active material, and negative electrode obtained by forming negative electrode active material layer (15) containing negative electrode active material, and separator impregnated with electrolyte solution. The positive electrode active material comprises solid solution of positive electrode active material comprising complex oxide (I) of lithium, nickel, manganese and cobalt.    USE - Electrical device e.g. lithium-ion secondary battery (claimed) for driving power supply and auxiliary power supply. Uses include but are not limited to electric vehicle, hybrid electric vehicle, passenger car, bus, trucks, fuel cell vehicle, electric train, mobile telephone and notebook personal computer.    ADVANTAGE - The electrical device has excellent durability, long-term reliability and high cycle characteristics.    DETAILED DESCRIPTION - An electrical device has an electric power generating element containing positive electrode obtained by forming positive electrode active material layer containing positive electrode active material in the surface of positive electrode electrical power collector (11), and negative electrode obtained by forming negative electrode active material layer containing negative electrode active material on the surface of negative electrode power collector, and separator impregnated with electrolyte solution. The negative electrode active material comprises alpha (silicon material) and beta (carbon material). The silicon material is silicon-containing alloy, and siloxane (SiOx, where x is number of oxygen atoms satisfying the valence of silicon) comprising mixture of amorphous silicon dioxide particles and silicon particles, alpha + beta is 80-98, alpha is 3-40, and beta is 40-95. The positive electrode active material comprises e(solid solution of positive electrode active material), where e is 80-98 wt.%. The solid solution of positive electrode active material comprises lithium-nickel-manganese-cobalt complex oxide of formula: Li1.5(NiaMnbCoc(Li)d)Oz (I), where z is number of oxygen atoms, a+b+c+d is 1.5, d is 0.1-0.4, and a+b+c is 1.1-14. The electrolyte solution comprises 1,5,2,4-dioxadithiane-2,2,4,4-tetroxide and difluoro lithium phosphate.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional schematic view of nonaqueous electrolyte lithium-ion secondary battery.    Laminate-type battery (10)    Positive electrode electrical power collector (11)    Positive electrode active material layer (13)    Negative electrode active material layer (15)    Electric power generating element (21)