Patent ID: 7759007

Claim:
A lithium ion secondary battery comprising: a positive electrode comprising a cathode active material and a binder; a negative electrode; an electrolyte; and a separator which is arranged between said positive electrode and said negative electrode, wherein an open circuit voltage per unit cell in a fully charged state lies within a range from 4.25V or more to 6.00V or less, wherein said cathode active material contains either a lithium-cobalt composite oxide expressed by a general formula: Li a Co 1-x Me x O 2-b in which Me denotes metal elements of at least one kind or two or more kinds selected from vanadium V, copper Cu, zirconium Zr, zinc Zn, magnesium Mg, aluminum Al, and iron Fe; a is set to a value of 0.9≦a≦1.1; x is set to a value of 0≦x≦0.3; and b is set to a value of −0.1≦b≦0.1, or a lithium-cobalt-nickel-manganese oxide expressed by a general formula: Li a Ni 1-x-y-z Co x Mn y Me z O 2-b in which Me denotes metal elements of at least one kind or two or more kinds selected from vanadium V, copper Cu, zirconium Zr, zinc Zn, magnesium Mg, aluminum Al, and iron Fe; a is set to a value of 0.9≦a≦1.1; x is set to a value of 0<x<0.4; y is set to a value of 0<y<0.4; z is set to a value of 0<z<0.3; and b is set to a value of −0.1≦b≦0.1, and wherein said binder contains a polyacrylonitrile resin, and wherein said polyacrylonitrile resin includes an ester group.