Lithium ion secondary battery and manufacturing method therefor

1. 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;

said positive electrode including active material particles;

said active material particles including at least a first lithium-nickel composite oxide forming a core portion thereof;

said first lithium-nickel composite oxide being represented by Li x Ni 1-y-z Co y Me x O 2

where 0.85≦x≦1.25, 0<y≦0.5, 0≦z≦0.5, 0<y+z≦0.75, and element Me is at least one selected from the group consisting of Al, Mn, Ti, Mg, and Ca;

a surface layer portion of said active material particles including:

(i) at least one selected from the group consisting of a nickel oxide having a NaCl crystal structure and a second lithium-nickel composite oxide including a domain having the NaCl crystal structure; and

(ii) element M not incorporated in the crystal structure of said first lithium-nickel composite oxide, said element M being at least one selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn.

2. The lithium ion secondary battery in accordance with claim 1 ,

wherein said nickel oxide having the NaCl crystal structure is at least one selected from the group consisting of NiO and cation-deficient Ni 1-δ O, and

said domain having the NaCl crystal structure has a structure in which Li in Li site in said first lithium-nickel composite oxide is replaced with Ni, Co, or Me.

3. The lithium ion secondary battery in accordance with claim 1 , wherein element M is distributed more at the outer side of said surface layer portion compared with the inner side thereof, and said nickel oxide is distributed more at the inner side of said surface layer portion compared with the outer side.

4. The lithium ion secondary battery in accordance with claim 1 , wherein 0<z≦0.5, and the concentration of element Me is high in the proximity of said surface layer portion compared with the inner portion of said active material particles.

5. The lithium ion secondary battery in accordance with claim 1 , wherein the amount of element M is 2 mol % or less relative to said first lithium-nickel composite oxide.

6. A method for producing a lithium ion secondary battery, the method comprising the steps of:

obtaining a positive electrode capable of charging and discharging;

obtaining a negative electrode capable of charging and discharging; and

assembling a battery including said positive electrode, said negative electrode, and a non-aqueous electrolyte:

said step of obtaining said positive electrode including the steps of:

(i) allowing a first lithium-nickel composite oxide represented by Li x Ni 1-y-z Co y Me x O 2

where 0.85≦x≦1.25, 0<y≦0.5, 0≦z≦0.5, 0<y+z≦0.75, and element Me is at least one selected from the group consisting of Al, Mn, Ti, Mg, and Ca, to carry element M of at least one selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn;

(ii) producing NiOOH on a surface of said first lithium-nickel composite oxide by moisture in the atmosphere by allowing said first lithium-nickel composite oxide carrying element M to stand under an environment with a temperature of 60° C. or less and a humidity of 20% or more;

(iii) preliminary baking said first lithium-nickel composite oxide with NiOOH produced on the surface thereof in a dry air atmosphere, and then carrying out a main baking in an oxygen atmosphere, thereby converting said NiOOH into at least one selected from the group consisting of NiO having a NaCl crystal structure, cation-deficient Ni 1-δ O having the NaCl-type crystal structure, and a second lithium-nickel composite oxide including a domain having the NaCl crystal structure, to obtain active material particles; and

(iv) forming a positive electrode including said active material particles.