Lithium secondary battery

1. A lithium secondary battery comprising:

a positive electrode;

a negative electrode; and

a non-aqueous electrolyte including a lithium salt, an organic solvent and a multinitrile compound, wherein the multinitrile compound consists of one or more non-fluorinated multinitrile compounds,

wherein the positive electrode includes a positive active material including a lithium-metal oxide represented by the following Chemical Formula 1,

Li x M1 a M2 b M3 c O y   Chemical Formula 1

wherein M1, M2, and M3 are selected from the group consisting of Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, and B,

and 0<x≤1.1, 2≤y≤2.02, 0<a1, 0<b<1, 0<c<1, and 0a+b+c≤1,

wherein M3 has a concentration gradient range in which a concentration increases continuously from a center of the positive active material to a surface of the positive active material, M1 has a concentration gradient range in which a concentration decreases continuously from the center of the positive active material to the surface of the positive active material, and M2 has a constant concentration from the center of the positive active material to the surface of the positive active material, and

wherein M1 is nickel, and a of Formula 1 is 0.7797 or more throughout an entire region of the positive active material.

2. The lithium secondary battery of claim 1 , wherein the M2, and M3 are Co, and Mn, respectively.

3. The lithium secondary battery of claim 2 , wherein the a, b, and c of Formula 1 satisfy the relationships 0.7797≤a≤0.95 and 0.05≤b+c≤0.4.

4. The lithium secondary battery of claim 1 , wherein a shape of primary particles of the lithium-metal oxide is a rod type.

5. The lithium secondary battery of claim 1 , wherein the non-fluorinated multinitrile compound includes a dinitrile compound, a trinitrile compound or a blending thereof.

6. The lithium secondary battery of claim 1 , wherein the non-fluorinated multinitrile compound is composed of at least one selected from the group consisting of succinonitrile, sebarconitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1 ,7-dicyanoheptane, 1,8-dicyanooctane, 1,9-dicyanononane, 1,10-dicyanodecane, 1,12-dicyanododecane, tetramethylsuecinonitrile, 2methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4 ,-tetramethylglutaronitrile, 1,4-dicyanopentane, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,6-dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,3,5-hexanetricarbonitrile, and 1,3,6-hexanetricarbonitrile.

7. The lithium secondary battery of claim 1 , wherein the non-fluorinated multinitrile compound is composed of at least one selected from the group consisting of succinonitrile, glutaronitrile, adiponitrile, 1,3,5-hexanetricarbonitrile, and 1,3,6-hexanetricarbonitrile.

8. The lithium secondary battery of claim 1 , wherein the multinitrile compound is included in the non-aqueous electrolyte in a range of 0.1 to 10 wt % based on a total amount of the non-aqueous electrolyte.

9. The lithium secondary battery of claim 1 , wherein the multinitrile compound is included in the non-aqueous electrolyte in a range of 0.5 to 7 wt % based on a total amount of the non-aqueous electrolyte.

10. The lithium secondary battery of claim 1 , wherein the multinitrile compound is included in the non-aqueous electrolyte by a concentration at 1 to 7 wt % based on a total amount of the non-aqueous electrolyte.

11. The lithium secondary battery of claim 1 , wherein a charge voltage is in a range of 4.3 to 4.5 V.