Patent ID: 7745042

Claim:
A lithium ion secondary battery, comprising: a pair of electrodes comprising a positive electrode and a negative electrode; a separator comprising a microporous film; and a non-aqueous electrolyte, wherein said positive electrode and said negative electrode are wound with said separator interposed therebetween, said positive electrode comprises: a positive electrode core material; and a positive electrode material mixture layer carried on said positive electrode core material, said positive electrode material mixture layer comprising a composite lithium oxide, said negative electrode comprises: a negative electrode core material; and a negative electrode material mixture layer carried on said negative electrode core material, said negative electrode material mixture layer comprising a negative electrode material capable of absorbing and desorbing lithium, in the case where the winding direction is in a longitudinal direction, said positive electrode is provided with a positive electrode current collector portion on one end thereof in said longitudinal direction, said positive electrode current collector portion being a protrusion of said positive electrode core material on which said positive electrode material mixture layer is not carried, a part of a positive electrode lead is welded to said positive electrode current collector portion, an entire surface of said positive electrode material mixture layer and a part of said positive electrode current collector portion are covered with a porous electron-insulating layer, and said porous electron-insulating layer contains 50 wt % or more of an inorganic oxide filler and below 50 wt % of a binder.