Patent ID: 8236449

Claim:
A lithium ion secondary battery comprising: a positive electrode capable of charging and discharging; a negative electrode capable of charging and discharging; and a non-aqueous electrolyte, wherein said positive electrode includes active material particles, said active material particles include secondary particles of a lithium composite oxide, having a surface layer portion, said lithium composite oxide is represented by Li x M 1-y L y O 2 , where 0.85≦x≦1.25; 0.005≦y≦0.35; element M includes Ni and Co; element L is at least one selected from the group consisting of an alkaline earth element, a transition metal element other than Ni and Co, a rare-earth element, a IIIb group element, and a IVb group element, wherein, an atomic ratio a of Co relative to the total of said element M and said element L is 0.05≦a≦0.25, wherein, said secondary particles include a secondary particle with a crack which reaches an inner portion of the secondary particle from the surface layer portion and a secondary particle without a crack, wherein, a ratio R of the number of said secondary particles with a crack to the number of said secondary particles without a crack is 2% or more and 5% or less, wherein, said secondary particles being an aggregated plurality of primary particles, the average particle size of said primary particles is 0.1 to 3.0 μm, the average particle size of said active material particles is 10 to 30 μm, at least said surface layer portion of said 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, said element Me is distributed more in said surface layer portion of said active material particles compared with an inner portion of said secondary particle, and said element me is distributed more in said surface layer portion compared with a second formed by said crack.