Patent attributes
A lithium ion secondary battery is provided. The battery includes a positive electrode having at least a cathode active material and a binder, a negative electrode, an electrolyte, and a separator which are arranged between the positive electrode and the negative electrode, and in which an open circuit voltage per unit cell in a full charging state lies within (4.25V≦voltage≦6.00V). The cathode active material includes either a lithium-cobalt composite oxide expressed by a general formula: LiaCo1-xMexO2-b (Me denotes metal elements of at least one, two or more kinds selected from V, Cu, Zr, Zn, Mg, Al, and Fe; 0.9≦a≦1.1; 0≦x=0.3; and −0.1≦b≦0.1) or a lithium-cobalt-nickel-manganese oxide expressed by a general formula: LiaNi1-x-y-zCoxMnyMezO2-b (0.9≦a≦1.1; 0<x<0.4; 0<y<0.4; 0<z<0.3; and −0.1≦b≦0.1). The binder includes a polyacrylonitrile resin.
