US Patent 8236449 Lithium ion secondary battery with improved electrode stability and safety

A lithium ion secondary battery is provided including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes active material particles. The active material particles include secondary particles of a lithium composite oxide, and some of the secondary particles have a crack. At least a surface layer portion of the active material particles includes element Me of at least one selected from the group consisting of Mn, Al, Mg, Ca, Zr, B, W, Nb, Ta, In, Mo, and Sn. Element Me is distributed more in the surface layer portion compared with an inner portion of the active material particles.