Non-aqueous electrolyte secondary battery

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, said positive electrode active material comprising a lithium-containing composite oxide represented by the formula 1: Li x Ni 1-y-z-v-w Co y Al z M 1 v M 2 w O 2 ,

wherein the element M 1 in said formula 1 is at least one selected from the group consisting of Mn, Ti, Y, Nb, Mo, and W,

the element M 2 in said formula 1 includes at least two selected from the group consisting of Mg, Ca, Sr, and Ba, the element M 2 including at least Mg with an atom number of w1 and Ca with an atom number of w2, the ratio of the total of Mg and Ca to the element M 2 being 50 atomic percent or more,

said formula 1 satisfies 0.97≦x≦1.1, 0.05≦y≦0.35, 0.005≦z≦0.1, 0.0001≦v≦0.05, 0.0001≦w≦0.05, 0.1≦v/w≦10 and 2≦w1/w2≦20,

said composite oxide comprises primary particles, said primary particles forming secondary particles,

said primary particles have a mean particle size of 0.1 μm or more and 3 μm or less, and

said secondary particles have a mean particle size of 8 μm or more and 20 μm or less.

2. The positive electrode active material in accordance with claim 1 , wherein the BET specific surface area of said composite oxide as measured by nitrogen gas adsorption is 0.2 m 2 /g or more and 1.5 m 2 /g or less.

3. The positive electrode active material in accordance with claim 1 , wherein said composite oxide has a tap density of 2.2 g/cm 3 or more and 2.8 g/cm 3 or less.

4. The positive electrode active material in accordance with claim 1 , wherein said composite oxide is crystalline such that the Li occupancy in a Li site as determined by Rietveld analysis is 97% or more.

5. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator interposed between said positive electrode and said negative electrode, and an electrolyte,

wherein said positive electrode includes a positive electrode active material comprising a lithium-containing composite oxide,

said composite oxide is represented by the formula 1: Li x Ni 1-y-z-v-w Co y Al z M 1 v M 2 w O 2 ,

the element M 1 in said formula 1 is at least one selected from the group consisting of Mn, Ti, Y, Nb, Mo, and W,

the element M 2 in said formula 1 includes at least two selected from the group consisting of Mg, Ca, Sr, and Ba, the element M 2 including at least Mg with an atom number of w1 and Ca with an atom number of w2, the ratio of the total of Mg and Ca to the element M 2 being 50 atomic percent or more,

said formula 1 satisfies 0.97≦x≦1.1, 0.05≦y≦0.35, 0.005≦z≦0.1, 0.0001≦v≦0.005, 0.0001≦w≦0.05, 0.1≦v/w≦10 and 2≦w1/w2≦20,

said composite oxide comprises primary particles, said primary particles forming secondary particles,

said primary particles have a mean particle size of 0.1 μm or more and 3 μm or less, and

said secondary particles have a mean particle size of 8 μm or more and 20 μm or less.

6. The non-aqueous electrolyte secondary battery in accordance with claim 5 , wherein the BET specific surface area of said composite oxide as measured by nitrogen gas adsorption is 0.2 m 2 /g or more and 1.5 m 2 /g or less.

7. The non-aqueous electrolyte secondary battery in accordance with claim 5 , wherein said composite oxide has a tap density of 2.2 g/cm 3 or more and 2.8 g/cm 3 or less.

8. The non-aqueous electrolyte secondary battery in accordance with claim 5 , wherein said composite oxide is crystalline such that the Li occupancy in a Li site as determined by Rietveld analysis is 97% or more.

9. A method for producing a positive electrode active material that comprises a lithium-containing composite oxide represented by the formula 1: Li x Ni 1-y-z-v-w Co y Al z M 1 v M 2 w O 2 , said method comprising the steps of:

(a) preparing a hydroxide represented by the formula 2: Ni 1-y-v-w Co y M 1 v M 2 w (OH) 2 ;

(b) adding an Al-containing compound to said hydroxide to obtain a first composition;

(c) baking said first composition in an oxidizing atmosphere to obtain a first oxide;

(d) adding a Li-containing compound to said first oxide to obtain a second composition; and

(e) baking said second composition in an oxidizing atmosphere to obtain the lithium-containing composite oxide represented by the formula 1 as a second oxide,

wherein the element M 1 in said formulae 1 and 2 is at least one selected from the group consisting of Mn, Ti, Y, Nb, Mo, and W,

the element M 2 in said formulae 1 and 2 includes at least two selected from the group consisting of Mg, Ca, Sr, and Ba, the element M 2 including at least Mg and Ca,

said formulae 1 and 2 satisfy 0.05≦y≦0.35, 0.0001≦v≦0.05, and 0.0001≦w≦0.05, and

said formula 1 satisfies 0.97≦x≦1.1 and 0.005≦z≦0.1.

10. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery in accordance with claim 9 , wherein said step (b) comprises a step of adding NaAlO 2 to said hydroxide that is stirred in water and then adjusting the pH of the water to 10 to 8 by using an acid.

11. The method for producing a positive electrode active material in accordance with claim 9 , wherein in said step (c), said first composition is baked at 500° C. or more and 1100° C. or less in an oxidizing atmosphere.

12. The method for producing a positive electrode active material in accordance with claim 9 , wherein in said step (e), said second composition is baked at 600° C. or more and 850° C. or less in an oxidizing atmosphere.