Lithium Transition Metal Oxide, Positive Electrode Additive for Lithium Secondary Battery, and Lithium Secondary Battery Comprising the Same

Abstract

A lithium transition metal oxide capable of minimizing a side reaction with an electrolyte, thereby suppressing the generation of gas during charging and discharging of a lithium secondary battery is provided. A lithium transition metal oxide is represented by Chemical Formula 1, wherein a lattice parameter of a unit lattice satisfies Equations 1 and 2. A positive electrode additive for a lithium secondary battery, and a lithium secondary battery are also provided.

Claims

1. A lithium transition metal oxide represented by the following Chemical Formula 1, wherein a lattice parameter of a unit lattice satisfies the following Equations 1 and 2:
Li.sub.6Co.sub.1-xM.sub.xO.sub.4  [Chemical Formula 1] wherein, M is at least one element selected from the group consisting of a group 2 element, a group 13 element, a group 14 element, a 4th period transition metal, a 5th period transition metal, and a 6th period transition metal, and x is 0.05 to 0.80;
6.53200 Å≤a=b≤6.54400 Å  [Equation 1]
4.64930 Å≤c≤4.65330 Å  [Equation 2] in Equations 1 and 2, a, b and c are lattice parameters of the lithium transition metal oxide obtained by an XRD Rietveld refinement method using CuKα rays.

2. The lithium transition metal oxide of claim 1, wherein the lithium transition metal oxide has a unit lattice volume (V) of 198.350 Å.sup.3 to 199.170 Å.sup.3.

3. The lithium transition metal oxide of claim 1, wherein the group 2 element is at least one selected from the group consisting of Mg, Ca, Sr and Ba, the group 13 element is at least one selected from the group consisting of Al, Ga and In, the group 14 element is at least one selected from the group consisting of Si, Ge and Sn, the 4th period transition metal is at least one selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, the 5th period transition metal is at least one selected from the group consisting of Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag and Cd, and the 6th period transition metal is at least one selected from the group consisting of Lu, Hf, Ta, W, Re, Os, Ir, Pt and Au.

4. The lithium transition metal oxide of claim 1, wherein the M is at least one element selected from the group consisting of Zn, Al, Mg, Ti, Zr, Nb and W.

5. The lithium transition metal oxide of claim 1, wherein the lithium transition metal oxide is at least one compound selected from the group consisting of Li.sub.6Co.sub.0.95Zn.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Zn.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Zn.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Zn.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Zn.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Zn.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Zn.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Zn.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Zn.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Zn.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Zn.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Zn.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Zn.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Zn.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Zn.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95Al.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Al.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Al.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Al.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Al.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Al.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Al.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Al.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Al.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Al.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Al.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Al.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Al.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Al.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Al.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Al.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95Mg.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Mg.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Mg.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Mg.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Mg.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Mg.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Mg.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Mg.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Mg.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Mg.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Mg.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Mg.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Mg.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Mg.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Mg.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Mg.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95Ti.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Ti.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Ti.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Ti.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Ti.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Ti.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Ti.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Ti.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Ti.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Ti.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Ti.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Ti.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Ti.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Ti.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Ti.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Ti.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95Zr.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Zr.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Zr.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Zr.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Zr.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Zr.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Zr.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Zr.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Zr.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Zr.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Zr.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Zr.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Zr.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Zr.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Zr.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Zr.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95Nb.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Nb.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Nb.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Nb.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Nb.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Nb.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Nb.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Nb.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Nb.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Nb.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Nb.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Nb.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Nb.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Nb.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Nb.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Nb.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95W.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9W.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85W.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8W.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75W.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7W.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65W.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6W.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55W.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5W.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45W.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4W.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35W.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3W.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25W.sub.0.75O.sub.4, and Li.sub.6Co.sub.0.2W.sub.0.8O.sub.4.

6. A method for preparing the lithium transition metal oxide of claim 1, comprising: a first step of obtaining a raw material mixture by solid-state mixing of lithium oxide, cobalt oxide and hetero-element (M) oxide to form a mixture; and a second step of obtaining a compound represented by the following Chemical Formula 1 by calcining the mixture obtained in the first step under an inert atmosphere and at a temperature of 550° C. to 750° C.:
Li.sub.6Co.sub.1-xM.sub.xO.sub.4  [Chemical Formula 1] wherein, M is at least one element selected from the group consisting of a group 2 element, a group 13 element, a group 14 element, a 4th period transition metal, a 5th period transition metal, and a 6th period transition metal, and x is 0.05 to 0.80.

7. The method for preparing the lithium transition metal oxide of claim 6, wherein in the second step, the mixture obtained in the first step is heated at a heating rate of 1.4° C./min to 2.0° C./min under an inert atmosphere to perform calcination at a temperature of 550° C. to 750° C. for 2 to 20 hours.

8. A positive electrode additive for a lithium secondary battery, comprising a lithium transition metal oxide represented by the following Chemical Formula 1, wherein a lattice parameter of a unit lattice satisfies the following Equations 1 and 2:
Li.sub.6Co.sub.1-xM.sub.xO.sub.4  [Chemical Formula 1] wherein, M is at least one element selected from the group consisting of a group 2 element, a group 13 element, a group 14 element, a 4th period transition metal, a 5th period transition metal, and a 6th period transition metal, and x is 0.05 to 0.80;
6.53200 Å≤a=b≤6.54400 Å  [Equation 1]
4.64930 Å≤c≤4.65330 Å  [Equation 2] in Equations 1 and 2, a, b and c are lattice parameters of the lithium transition metal oxide obtained by an XRD Rietveld refinement method using CuKα rays.

9. The positive electrode additive for the lithium secondary battery of claim 8, wherein the lithium transition metal oxide has a unit lattice volume (V) of 198.350 Å.sup.3 to 199.170 Å.sup.3.

10. The positive electrode additive for the lithium secondary battery of claim 8, wherein: the group 2 element is at least one selected from the group consisting of Mg, Ca, Sr and Ba, the group 13 element is at least one selected from the group consisting of Al, Ga and In, the group 14 element is at least one selected from the group consisting of Si, Ge and Sn, the 4th period transition metal is at least one selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, the 5th period transition metal is at least one selected from the group consisting of Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag and Cd, and the 6th period transition metal is at least one selected from the group consisting of Lu, Hf, Ta, W, Re, Os, Ir, Pt and Au.

11. The positive electrode additive for the lithium secondary battery of claim 8, wherein the M is Zn, Al, Mg, Ti, Zr, Nb, or W.

12. The positive electrode additive for the lithium secondary battery of claim 8, wherein the lithium transition metal oxide is at least one compound selected from the group consisting of Li.sub.6Co.sub.0.95Zn.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Zn.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Zn.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Zn.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Zn.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Zn.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Zn.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Zn.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Zn.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Zn.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Zn.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Zn.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Zn.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Zn.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Zn.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95Al.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Al.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Al.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Al.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Al.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Al.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Al.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Al.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Al.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Al.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Al.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Al.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Al.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Al.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Al.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Al.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95Mg.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Mg.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Mg.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Mg.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Mg.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Mg.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Mg.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Mg.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Mg.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Mg.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Mg.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Mg.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Mg.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Mg.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Mg.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Mg.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95Ti.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Ti.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Ti.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Ti.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Ti.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Ti.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Ti.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Ti.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Ti.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Ti.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Ti.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Ti.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Ti.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Ti.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Ti.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Ti.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95Zr.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Zr.sub.0.1O.sub.4, Li.sub.6Co.sub.0.855Zr.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Zr.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Zr.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Zr.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Zr.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Zr.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Zr.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Zr.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Zr.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Zr.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Zr.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Zr.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Zr.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Zr.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95Nb.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9Nb.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85Nb.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8Nb.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75Nb.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7Nb.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65Nb.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6Nb.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55Nb.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5Nb.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45Nb.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4Nb.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35Nb.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3Nb.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25Nb.sub.0.75O.sub.4, Li.sub.6Co.sub.0.2Nb.sub.0.8O.sub.4; Li.sub.6Co.sub.0.95W.sub.0.05O.sub.4, Li.sub.6Co.sub.0.9W.sub.0.1O.sub.4, Li.sub.6Co.sub.0.85W.sub.0.15O.sub.4, Li.sub.6Co.sub.0.8W.sub.0.2O.sub.4, Li.sub.6Co.sub.0.75W.sub.0.25O.sub.4, Li.sub.6Co.sub.0.7W.sub.0.3O.sub.4, Li.sub.6Co.sub.0.65W.sub.0.35O.sub.4, Li.sub.6Co.sub.0.6W.sub.0.4O.sub.4, Li.sub.6Co.sub.0.55W.sub.0.45O.sub.4, Li.sub.6Co.sub.0.5W.sub.0.5O.sub.4, Li.sub.6Co.sub.0.45W.sub.0.55O.sub.4, Li.sub.6Co.sub.0.4W.sub.0.6O.sub.4, Li.sub.6Co.sub.0.35W.sub.0.65O.sub.4, Li.sub.6Co.sub.0.3W.sub.0.7O.sub.4, Li.sub.6Co.sub.0.25W.sub.0.75O.sub.4, and Li.sub.6Co.sub.0.2W.sub.0.8O.sub.4.

13. A positive electrode for a lithium secondary battery, comprising a positive electrode active material, a binder, a conductive material, and the lithium transition metal oxide of claim 1.

14. A positive electrode for a lithium secondary battery, comprising a positive electrode active material, a binder, a conductive material, and the positive electrode additive for the lithium secondary battery of claim 8.

15. A lithium secondary battery, comprising the positive electrode for the lithium secondary battery of claim 13; a negative electrode; a separator; and an electrolyte.

16. The lithium secondary battery of claim 15, wherein the negative electrode comprises at least one negative electrode active material selected from the group consisting of a carbonaceous material and a silicon compound.

17. A lithium secondary battery, comprising the positive electrode for the lithium secondary battery of claim 14; a negative electrode; a separator; and an electrolyte.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0193] FIG. 1 is a graph showing a correlation between the irreversible capacity and the amount of gas generation of the lithium secondary batteries of Examples 1 to 3 and Comparative Example 1.

[0194] FIG. 2 is a graph showing a correlation between the irreversible capacity and the amount of gas generation of the lithium secondary batteries of Examples 1 and 4 to 7.

[0195] FIG. 3 is a graph showing capacity cycle retention according to the accumulation of charge/discharge cycles of the lithium secondary batteries of Example 8 and Comparative Examples 2 to 4.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0196] Hereinafter, the function and effect of the present invention will be described in more detail through specific examples. However, these examples are provided for illustrative purposes only. The scope of the invention is not intended to be limited by these examples, and it is apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention.

Example 1

[0197] (1) Synthesis of Lithium Transition Metal Oxide A raw material mixture was prepared by solid-state mixing of Li.sub.2O, CoO and ZnO at a molar ratio of Li:Co:Zn=6:0.7:0.3.

[0198] The raw material mixture was heated at a heating rate of 1.6° C./min under an Ar atmosphere for 6 hours, and then calcined at 600° C. for 12 hours so as to obtain a lithium transition metal oxide of Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4.

[0199] The lithium transition metal oxide was pulverized by using a jaw crusher, and then classified by using a sieve shaker.

[0200] (2) Preparation of Lithium Secondary Battery

[0201] A positive electrode material slurry was prepared by mixing the lithium transition metal oxide (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) as a positive electrode additive, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder at a weight ratio of 95:3:2 in an organic solvent (N-methylpyrrolidone). The positive electrode material slurry was applied to one surface of a current collector, which was an aluminum foil having a thickness of 15 μm, and was rolled and dried to prepare a positive electrode. For reference, in this experiment, a positive electrode active material was not added to the positive electrode material. The addition of the positive active material is shown in Example 8 below.

[0202] A negative electrode material slurry was prepared by mixing natural graphite as a negative electrode active material, carbon black as a conductive material, and carboxymethylcellulose (CMC) as a binder at a weight ratio of 95:3:2 in an organic solvent (N-methylpyrrolidone). The negative electrode material slurry was applied to one surface of a current collector, which was a copper foil having a thickness of 15 μm, and was rolled and dried to prepare a negative electrode.

[0203] A non-aqueous organic solvent was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) at a volume ratio of 3:4:3. An electrolyte was prepared by dissolving lithium salts of LiPF.sub.6 at a concentration of 0.7 M and LiFSI at a concentration of 0.5 M in the non-aqueous organic solvent.

[0204] An electrode assembly was prepared by interposing porous polyethylene as a separator between the positive electrode and the negative electrode, and the electrode assembly was placed inside the case. A lithium secondary battery in the form of a pouch cell was manufactured by injecting the electrolyte into the case.

Example 2

[0205] Except for using MgO instead of ZnO, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.7Mg.sub.0.3O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Example 3

[0206] Except for using Al.sub.2O.sub.3 instead of ZnO, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.7Al.sub.0.3O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Example 4

[0207] Except for using a raw material mixture obtained by solid-state mixing of Li.sub.2O, CoO and ZnO at a molar ratio of Li:Co:Zn=6:0.9:0.1, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.9Zn.sub.0.1O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Example 5

[0208] Except for using a raw material mixture obtained by solid-state mixing of Li.sub.2O, CoO and ZnO at a molar ratio of Li:Co:Zn=6:0.8:0.2, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.8Zn.sub.0.2O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Example 6

[0209] Except for using a raw material mixture obtained by solid-state mixing of Li.sub.2O, CoO and ZnO at a molar ratio of Li:Co:Zn=6:0.6:0.4, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.6Zn.sub.0.4O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Example 7

[0210] Except for using a raw material mixture obtained by solid-state mixing of Li.sub.2O, CoO and ZnO at a molar ratio of Li:Co:Zn=6:0.5:0.5, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.5Zn.sub.0.5O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Example 8

[0211] Except for further adding the positive electrode active material in the preparation of the positive electrode and changing the composition of the negative electrode active material in the preparation of the negative electrode, a lithium secondary battery was manufactured by the same method as in above Example 1.

[0212] Specifically, a positive electrode material slurry was prepared by mixing a NCMA(Li[Ni,Co,Mn,Al]O.sub.2)-based compound (NTA-X12M, L&F) as a positive electrode active material, the lithium transition metal oxide (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) as a positive electrode additive, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder at a weight ratio of 93.8:1.2:3:2 in an organic solvent (N-methylpyrrolidone). The positive electrode material slurry was applied to one surface of a current collector, which was an aluminum foil having a thickness of 15 μm, and was rolled and dried to prepare a positive electrode.

[0213] A negative electrode material slurry was prepared by mixing a mixture of natural graphite and SiO (weight ratio=9:1) as a negative electrode active material, carbon black as a conductive material, and carboxymethylcellulose (CMC) as a binder at a weight ratio of 95:3:2 in an organic solvent (N-methylpyrrolidone). The negative electrode material slurry was applied to one surface of a current collector, which was a copper foil having a thickness of 15 μm, and was rolled and dried to prepare a negative electrode.

[0214] An electrode assembly was prepared by interposing porous polyethylene as a separator between the positive electrode and the negative electrode, and the electrode assembly was placed inside the case. A lithium secondary battery in the form of a pouch cell was manufactured by injecting the electrolyte into the case.

Example 9

[0215] Except for heating the raw material mixture at a rate of 1.6° C./min under an Ar atmosphere and calcining the same at 600° C. for 6 hours, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Example 10

[0216] Except for heating the raw material mixture at a rate of 1.6° C./min under an Ar atmosphere and calcining the same at 600° C. for 18 hours, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Example 11

[0217] Except for heating the raw material mixture at a rate of 1.9° C./min under an Ar atmosphere and calcining the same at 700° C. for 12 hours, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Comparative Example 1

[0218] Except for mixing Li.sub.2O and CoO at a molar ratio of Li:Co=6:1 without the addition of ZnO, (1) a lithium transition metal oxide of Li.sub.6CoO.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Comparative Example 2

[0219] Except for using Li.sub.6CoO.sub.4 obtained in above Comparative Example 1 instead of Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4 as a positive electrode additive in the preparation of the positive electrode, a lithium secondary battery was manufactured by the same method as in above Example 8.

Comparative Example 3

[0220] Except for mixing a NCMA(Li[Ni,Co,Mn,Al]O.sub.2)-based compound (NTA-X12M, L&F) as a positive electrode active material, DN2O (Li.sub.2NiO.sub.2, POSCO Chemical) instead of the lithium transition metal oxide (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) as a positive electrode additive, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder at a weight ratio of 91.2:3.8:3:2 in the preparation of the positive electrode, a lithium secondary battery was manufactured by the same method as in above Example 8.

Comparative Example 4

[0221] Except for not adding the positive electrode additive in the preparation of the positive electrode, a lithium secondary battery was manufactured by the same method as in above Example 8.

Comparative Example 5

[0222] Except for heating the raw material mixture at a rate of 0.5° C./min under an Ar atmosphere and calcining the same at 600° C. for 6 hours, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Comparative Example 6

[0223] Except for heating the raw material mixture at a rate of 5.0° C./min under an Ar atmosphere and calcining the same at 600° C. for 6 hours, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Comparative Example 7

[0224] Except for heating the raw material mixture at a rate of 10.0° C./min under an Ar atmosphere and calcining the same at 600° C. for 6 hours, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4 and (2) a lithium secondary battery including the same as a positive electrode additive were manufactured by the same method as in above Example 1.

Test Example 1

[0225] The lithium transition metal oxides obtained in above Examples 1 to 7 and above Comparative Example 1 were subjected to X-ray diffraction analysis (model name: D8 ENDEAVOR, manufactured by: Bruker) using CuKα rays as a source. The profile obtained through the X-ray diffraction analysis was calculated by a Rietveld refinement method so as to obtain a lattice parameter value of a unit lattice and a volume value.

TABLE-US-00001 TABLE 1 Lattice parameter (Å) Volume a = b c (Å.sup.3) Example 1 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 6.54111 4.65200 199.041 Example 2 (Li.sub.6Co.sub.0.7Mg.sub.0.3O.sub.4) 6.53211 4.64948 198.386 Example 3 (Li.sub.6Co.sub.0.7Al.sub.0.3O.sub.4) 6.53732 4.65003 198.726 Example 4 (Li.sub.6Co.sub.0.9Zn.sub.0.1O.sub.4) 6.54325 4.65107 199.131 Example 5 (Li.sub.6Co.sub.0.8Zn.sub.0.2O.sub.4) 6.54209 4.65150 199.079 Example 6 (Li.sub.6Co.sub.0.6Zn.sub.0.4O.sub.4) 6.54031 4.65259 199.071 Example 7 (Li.sub.6Co.sub.0.5Zn.sub.0.5O.sub.4) 6.53968 4.65326 199.008 Example 9 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 6.54127 4.65213 199.056 Example 10 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 6.54045 4.65172 198.989 Example 11 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 6.54080 4.65187 199.016 Comparative Example 1 6.54460 4.65069 199.197 (Li.sub.6CoO.sub.4) Comparative Example 5 6.53131 4.65098 198.888 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) Comparative Example 6 6.54351 4.65335 199.245 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) Comparative Example 7 6.54413 4.65361 199.294 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4)

[0226] Referring to above table 1, it is confirmed that the lithium transition metal oxides of Examples 1 to 7 have the composition of above Chemical Formula 1 and satisfy the lattice parameter values of above Equations 1 and 2. In contrast, it is confirmed that the lithium transition metal oxide of Comparative Example 1 does not include a hetero-element and thus does not have the composition of above Chemical Formula 1, and the lattice parameter value does not satisfy above Equations 1 and 2.

[0227] And, referring to Examples 1 and 4 to 7, as the amount of the introduced hetero-element increases, an a-axis lattice parameter value tends to relatively decrease and a c-axis lattice parameter value tends to relatively increase.

[0228] In addition, referring to Examples 1, 9 and 10, the a-axis and c-axis lattice parameter values tended to gradually decrease as the calcination time of the raw material mixture increased. Even in the case of Example 11 in which the calcination temperature was increased to 700° C., the lattice parameter value did not significantly decrease compared to Example 1.

[0229] In contrast, in the case of Comparative Example 5 in which the heating rate was low, crystal growth of the lithium transition metal oxide excessively occurred, and thus the a-axis and c-axis lattice parameter values were significantly reduced compared to Example 1. And, in the case of Comparative Examples 6 and 7 in which the heating rate was high, the crystal growth time of the lithium transition metal oxide was relatively insufficient compared to Example 1, thereby lowering the crystallinity. Thus, it is confirmed that the a-axis and c-axis lattice parameter values increase compared to Example 1.

Test Example 2

[0230] An experiment was conducted to confirm the amount of cumulative gas generation according to the initial charge capacity and the cumulative charge/discharge capacity of the lithium secondary battery, which varied depending on whether or not a hetero-element was introduced into Li.sub.6CoO.sub.4 and the type of the hetero-element.

[0231] Herein, the irreversible capacity may be defined as “charge capacity−discharge capacity=irreversible capacity,” and the cumulative irreversible capacity may be defined as the sum of irreversible capacities at every charge/discharge cycle.

[0232] For the lithium secondary batteries of Examples 1 to 3 and Comparative Example 1, the amount of cumulative gas generation according to the accumulation of charge/discharge cycles was measured by the following method, and the measured amount of gas generation according to the cumulative charge capacity is shown in the graph of FIG. 1.

[0233] (1) Measurement of Formation (Initial Charge) Capacity and Charge/Discharge Capacity

[0234] A pouch cell-type lithium secondary battery was subjected to a cycle of constant current-constant voltage charge up to 4.25 V and constant current discharge to 2.5 V at 0.1 C at 45° C. with resting for 20 minutes between charge and discharge, and then the formation capacity and the charge/discharge capacity were measured.

[0235] (2) Measurement of the Amount of Cumulative Gas Generation According to the Accumulation of Charge/Discharge

[0236] After the lithium secondary battery was operated under the charge/discharge conditions of above (1), the pouch cell at the time of measuring the amount of gas generation was temporarily recovered in the discharged state. Using a hydrometer (MATSUHAKU, TWD-150DM), a difference between the original weight of the pouch cell and the weight thereof in water was measured to calculate a change in volume in the pouch cell, and the change in volume was divided by a weight of the electrode active material so as to calculate the amount of gas generation per weight.

[0237] The following table 2 shows the amount of cumulative gas generation after the 1.sup.st, 2.sup.nd, 10.sup.th, 30.sup.th and 50.sup.th cumulative cycles after formation (0.sup.th charge/discharge).

TABLE-US-00002 TABLE 2 Formation Amount of gas Amount of cumulative gas Capacity generation generation (mL/g) (mAh/g) (mL/g) 1st 2nd 10th 30th 50th Example 1 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 795.2 103.6 0.02 0.12 0.34 0.64 0.76 Example 2 (Li.sub.6Co.sub.0.7Mg.sub.0.3O.sub.4) 846.4 106.6 0.40 0.64 2.50 5.55 6.02 Example 3 (Li.sub.6Co.sub.0.7Al.sub.0.3O.sub.4) 837.8 109.3 0.68 1.20 3.25 5.23 6.13 Comparative Example 1 903.0 129.1 5.92 6.91 8.04 9.17 10.10 (Li.sub.6CoO.sub.4) Example 9 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 783.2 101.4 0.05 0.15 0.37 0.69 0.82 Example 10 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 800.1 104.1 0.03 0.14 0.35 0.62 0.74 Example 11 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 803.4 105.2 0.04 0.11 0.27 0.56 0.61 Comparative Example 5 756.2 98.2 0.03 0.13 0.31 0.59 0.67 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) Comparative Example 6 739.2 95.1 0.07 0.19 0.42 0.73 0.95 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) Comparative Example 7 731.4 93.0 0.05 0.23 0.45 0.78 1.02 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4)

[0238] As shown in above table 2 and FIG. 1, the formation capacity of Comparative Example 1 was the most excellent as 903.0 mAh/g, but continuous gas generation was observed, and the amount of cumulative gas generation after the 50.sup.th cycle was 10 mL/g or more, which was much more than Examples 1 to 3. Accordingly, it can be seen that, in Comparative Example 1, the actual expression of the charge capacity of Li.sub.6CoO.sub.4 is mixed with the charge capacity caused by a side reaction with the electrolyte during the continuous charge and discharge, and thus it can be understood that an electrolyte oxidation reaction occurs to generate electrolyte decomposition gas.

[0239] In contrast, with respect to Examples 1 to 3, it was found that the formation capacity was smaller than that of Comparative Example 1, but the amount of cumulative gas generation in the 50.sup.th cycle was also smaller than that of Comparative Example 1. In particular, although Example 1 was a hetero-element having the same molar ratio as in Examples 2 and 3, the amount of cumulative gas generation was 0.76 mL/g, thus showing a much more excellent effect of reducing the amount of gas generation compared to the amount of gas generation in Examples 2 and 3, which was 6.02 mL/g and 6.13 mL/g, respectively. Accordingly, it can be understood that the lithium cobalt oxide alloyed with Zn among the lithium cobalt oxides alloyed with a hetero-element effectively stabilizes a crystal phase, thereby reducing gas generation caused by a side reaction with an electrolyte.

[0240] In the case of Example 9 in which the calcination time was reduced to 6 hours, the formation capacity was lower than that of Example 1 due to somewhat insufficient crystallinity compared to Example 1 in which the calcination time was 12 hours, and it seems that the amount of cumulative gas generation in the 50.sup.th cycle is relatively high.

[0241] In the case of Example 10 in which the calcination time was increased to 18 hours and Example 11 in which the calcination temperature was increased to 700° C., it was found that the formation capacity was larger than that of Example 1 and the amount of cumulative gas generation in the 50.sup.th cycle was low. This may be considered to be caused by the increase in crystallinity with an increase in the calcination time or calcination temperature.

[0242] In the case of Comparative Example 5, it was found that crystal growth excessively occurred and the size of grains increased as the heating time increased, and thus the formation capacity was somewhat lower than that of Example 1 due to a decrease in the specific surface area. In contrast, in the case of Comparative Examples 6 and 7 in which the heating time was shortened, it seems that the size of grains became small, but the formation capacity was lowered due to a decrease in crystallinity. In addition, in the case of Comparative Examples 6 and 7, it seems that the amount of cumulative gas generation after the 50.sup.th cycle slightly increased compared to Example 1 due to instability caused by the decrease in crystallinity.

Test Example 3

[0243] An experiment was conducted to confirm the amount of cumulative gas generation according to the initial charge capacity and the cumulative charge/discharge capacity of the lithium secondary battery, which varied depending on how much Zn, one of the hetero-elements, was introduced into Li.sub.6CoO.sub.4. In addition, an experiment was conducted to confirm the amount of cumulative gas generation according to high-temperature storage after formation.

[0244] With respect to the lithium secondary batteries of Examples 1 and 4 to 7 and Comparative Example 1, the amount of cumulative gas generation according to the accumulation of charge/discharge cycles was measured by the following method, and the amount of gas generation according to the measured cumulative charge capacity is shown in table 3 and the graph of FIG. 2. The amount of cumulative gas generation according to the high-temperature storage time is shown in table 4.

[0245] (1) Measurement of Formation (Initial Charge) Capacity and Charge/Discharge Capacity

[0246] A pouch cell-type lithium secondary battery was subjected to a cycle of constant current-constant voltage charge up to 4.25 V and constant current discharge to 2.5 V at 0.1 C at a temperature of 45° C. with resting for 20 minutes between charge and discharge, and then the formation capacity and charge/discharge capacity were measured.

[0247] (2) Measurement of the Amount of Cumulative Gas Generation According to the Accumulation of Charge/Discharge

[0248] After the lithium secondary battery was operated under the charge/discharge conditions of above (1), the pouch cell at the time of measuring the amount of gas generation was temporarily recovered in the discharged state. Using a hydrometer (MATSUHAKU, TWD-150DM), a difference between the original weight of the pouch cell and the weight thereof in water was measured to calculate a change in volume in the pouch cell, and the change in volume was divided by a weight of the electrode active material so as to calculate the amount of gas generation per weight.

[0249] (3) Measurement of the Amount of Cumulative Gas Generation According to High-Temperature Storage

[0250] A pouch cell-type lithium secondary battery was subjected to a constant current-constant voltage charge up to 4.25 V at 0.1 C at a temperature of 45° C., collected to measure the formation capacity, and then stored in a 60° C. chamber. The lithium secondary battery was taken out at an interval of one week to measure a difference between the original weight of the pouch cell and the weight thereof in water by using a hydrometer (MATSUHAKU, TWD-150DM) and to calculate a change in volume in the pouch cell, after which the change in volume was divided by a weight of the electrode active material to calculate the amount of gas generation per weight.

[0251] The following table 3 shows the amount of cumulative gas generation after the 1.sup.st, 2.sup.nd, 10.sup.th, 30.sup.th and 50.sup.th cumulative cycles after formation (0.sup.th charge/discharge).

TABLE-US-00003 TABLE 3 Formation Amount of gas Amount of cumulative gas Capacity generation generation (mL/g) (mAh/g) (mL/g) 1st 2nd 10th 30th 50th Example 1 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 795.2 103.6 0.02 0.12 0.34 0.64 0.76 Example 4 (Li.sub.6Co.sub.0.9Zn.sub.0.1O.sub.4) 842.1 108.1 0.53 0.76 3.15 5.07 5.44 Example 5 (Li.sub.6Co.sub.0.8Zn.sub.0.2O.sub.4) 827.9 105.0 −0.16 −0.19 0.44 1.68 2.11 Example 6 (Li.sub.6Co.sub.0.6Zn.sub.0.4O.sub.4) 756.6 99.1 −0.14 −0.22 0.00 −0.07 −0.18 Example 7 (Li.sub.6Co.sub.0.5Zn.sub.0.5O.sub.4) 692.3 85.3 0.41 0.25 0.16 0.06 0.14 Comparative Example 1 903.0 129.1 5.92 6.91 8.04 9.17 10.10 (Li.sub.6CoO.sub.4)

[0252] As shown in above table 3 and FIG. 2, it can be seen that the formation capacity and the amount of gas generation decreased as the Zn content in Li.sub.6CoO.sub.4 increased. This may be because the oxidation number of Zn does not change in Zn.sup.2+, and thus Zn does not contribute to the charge capacity, unlike Co, which is oxidized from Co.sup.2+ to CO.sup.4+ during initial charge as Zn is substituted at Co sites in Li.sub.6CoO.sub.4.

[0253] In Example 1, the amount of cumulative gas generation after the 50.sup.th cycle was 0.76 mL/g, which is within 1 mL/g. In the case of Examples 6 and 7, the amount of gas generation was smaller than that of Example 1, but the initial charge capacity was decreased. Example 1 may be considered to be the most excellent when comprehensively considered in terms of initial charge capacity, amount of cumulative gas generation after 50.sup.th cycle, and electrical conductivity of grains.

[0254] In the case of Example 6, the amount of gas generation was a negative value of −0.18 mL/g, which may be an experimental error of the hydrometer, thus meaning that gas generation hardly occurred. In other words, it can be seen that Example 6 is more excellent than Example 1 in terms of reducing gas generation.

[0255] The following table 4 shows the amount of cumulative gas generation after 1, 2, 3 and 4 weeks after storage at 60° C. after formation (0.sup.th charge/discharge).

TABLE-US-00004 TABLE 4 Amount of cumulative gas generation (mL/g) Week 1 Week 2 Week 3 Week 4 Example 1 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) −0.16 0.13 0.17 0.37 Example 4 (Li.sub.6Co.sub.0.9Zn.sub.0.1O.sub.4) 1.44 1.75 2.02 2.04 Example 5 (Li.sub.6Co.sub.0.8Zn.sub.0.2O.sub.4) −0.15 −0.12 0.50 1.04 Example 6 (Li.sub.6Co.sub.0.6Zn.sub.0.4O.sub.4) −0.56 −0.36 −0.23 0.39 Example 7 (Li.sub.6Co.sub.0.5Zn.sub.0.5O.sub.4) −0.60 −0.16 −0.11 0.10 Comparative Example 1 9.95 10.19 9.70 9.56 (Li.sub.6CoO.sub.4)

[0256] As shown in above table 4, it can be seen that the amount of cumulative gas generation decreased during the high-temperature storage at 60° C. as the Zn content in Li.sub.6CoO.sub.4 increased.

[0257] In particular, it was confirmed that Example 4 showed the amount of cumulative gas generation of 2.04 mL/g at week 4, which is a 78.6% decrease against Comparative Example 1. In Example 1, the amount of cumulative gas generation after four weeks was 0.37 mL/g, which is within 1 mL/g. Examples 6 and 7 also exhibited an excellent effect of reducing gas.

Test Example 4

[0258] With respect to the lithium secondary batteries of Example 8 and Comparative Examples 2 to 4 in which the positive electrode active material and the positive electrode additive are mixed and applied, the capacity cycle retention and the amount of cumulative gas generation according to the accumulation of charge/discharge cycles were measured by the following method, and the measured capacity retention and the amount of cumulative gas generation are shown in the graph of FIG. 3 and table 5.

[0259] (1) Measurement of Formation (Initial Charge) Capacity and Charge/Discharge Capacity

[0260] A pouch cell-type lithium secondary battery was subjected to a cycle of constant current-constant voltage charge up to 4.25 V and constant current discharge to 2.5 V at 0.1 C at a temperature of 45° C. with resting for 20 minutes between charge and discharge, and then the formation capacity and charge/discharge capacity up to 100.sup.th cycle were measured.

[0261] (2) Measurement of the Amount of Cumulative Gas Generation According to the Accumulation of Charge/Discharge

[0262] After the lithium secondary battery was operated under the charge/discharge conditions of above (1), the pouch cell at the time of measuring the amount of gas generation was temporarily recovered in the discharged state. Using a hydrometer (MATSUHAKU, TWD-150DM), a difference between the original weight of the pouch cell and the weight thereof in water was measured to calculate a change in volume in the pouch cell, and the change in volume was divided by a weight of the electrode active material so as to calculate the amount of gas generation per weight.

[0263] (3) Measurement of the Amount of Cumulative Gas Generation According to High-Temperature Storage

[0264] A pouch cell-type lithium secondary battery was subjected to a constant current-constant voltage charge up to 4.25 V at 0.1 C at a temperature of 45° C., collected to measure the formation capacity, and then stored in a 60° C. chamber. The lithium secondary battery was taken out at an interval of one week to measure a difference between the original weight of the pouch cell and the weight thereof in water by using a hydrometer (MATSUHAKU, TWD-150DM) and to calculate a change in volume in the pouch cell, after which the change in volume was divided by a weight of the electrode active material to calculate the amount of gas generation per weight.

[0265] The following table 5 shows the formation (0.sup.th charge/discharge) capacity, the amount of cumulative gas generation after the 50.sup.th and 100.sup.th cumulative cycles, and the discharge capacity retention after the 100.sup.th cycle.

TABLE-US-00005 TABLE 5 Formation Amount capacity of gas Capacity (mAh/g) generation retention Charge Discharge (mL/g) @ 100th capacity capacity 50th 100th cycle Example 8 (NCMA + 243.4 214.9 0.14 0.16 88.2 Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) Comparative Example 2 243.3 215.4 0.03 0.24 88.2 (NCMA + Li.sub.6CoO.sub.4) Comparative Example 3 242.2 214.5 0.02 0.11 86.3 (NCMA + DN20) Comparative Example 4 236.0 201.3 0.10 0.20 86.2 (NCMA)

[0266] As shown in above table 5 and FIG. 3, the discharge capacities of Example 8 and Comparative Examples 2 and 3 were 214.9 mAh/g, 215.4 mAh/g, and 214.5 mAh/g, respectively, which were larger than Comparative Example 4 in which the sacrificial positive electrode material was not applied. It can be seen that the sacrificial positive electrode material compensates for the irreversible lithium consumed in the formation of the SEI layer at the negative electrode.

[0267] In contrast, in the case of Comparative Example 4, there was no sacrificial positive electrode material to compensate for irreversible lithium, and thus lithium of the positive electrode material was consumed, resulting in a decrease in the discharge capacity and indicating a discharge capacity of 201.3 mAh/g.

[0268] In the case of Example 8, the amount of cumulative gas generation at the 100.sup.th cycle was 0.16 mL/g, which was less than 0.24 mL/g of Comparative Example 2 and less than 0.20 mL/g of Comparative Example 4 in which the sacrificial positive electrode material was not applied.

[0269] In the case of Comparative Example 3, the amount of cumulative gas generation at the 100.sup.th cycle was the smallest as 0.11 mL/g, but the amount of increased gas generation from the 50.sup.th cycle to the 100.sup.th cycle was 0.09 mL/g, thus having a chance that the gas generation will continue to increase thereafter. This is also the same as in Comparative Example 2. In contrast, in the case of Example 8, the amount of increased gas generation from the 50.sup.th cycle to the 100.sup.th cycle was 0.02 mL/g, and thus it can be seen that the gas generation is suppressed as the charge/discharge cycle continues.

[0270] In the case of the capacity retention at 100.sup.th cycle, both Example 8 and Comparative Example 2, to which the Co-based sacrificial positive electrode material was applied, were excellent as 88.2%. Comparative Example 3 to which the Ni-based sacrificial positive electrode material was applied and Comparative Example 4 to which the sacrificial positive electrode material was not applied showed the capacity retention of 86.3% and 86.2%, respectively, which were lower than those of Example 8 and Comparative Example 2.

[0271] Accordingly, when a Co-based sacrificial positive electrode material, in particular, a sacrificial positive electrode material alloyed with Zn is applied to a lithium secondary battery including an actual positive electrode material, it can be confirmed that the material preserves the initial discharge capacity and suppresses the amount of gas generation in the battery, and the capacity retention is also excellent after the 100.sup.th cycle.

[0272] The following table 6 shows the amount of cumulative gas generation after one, two, three and four weeks after formation (0.sup.th charge) and storage at 72° C.

TABLE-US-00006 TABLE 6 Amount of cumulative gas generation (mL/g) Week 1 Week 2 Week 3 Week 4 Example 8 (NCMA + 0.11 0.14 0.18 0.22 Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) Comparative Example 2 1.07 1.38 1.78 2.01 (NCMA + Li.sub.6CoO.sub.4) Comparative Example 3 0.54 0.65 0.80 0.82 (NCMA + DN20) Comparative Example 4 0.21 0.29 0.53 0.55 (NCMA)

[0273] As shown in above table 6, Example 8 showed the lowest amount of cumulative gas generation of 0.22 mL/g after four weeks. This may be because, like the result of the charge/discharge cycle, the hetero-element introduced into Li.sub.6CoO.sub.4 effectively stabilizes CoO.sub.2 formed after the initial charge so as to prevent a side reaction with an electrolyte, thereby suppressing additional gas generation.

[0274] In addition, Example 8 generated gas less than Comparative Example 4 in which the sacrificial positive electrode material was not applied, and this result may be an experimental error, or the positive electrode additive included in the lithium secondary battery is likely to not only suppress gas generation but also absorb the generated gas.

[0275] In the above, although the present invention has been described with reference to limited embodiments and drawings, the present invention is not limited thereto, and various modifications and variations are possible within the technical idea of the present invention and within the equivalent scope of the claims to be described below by those skilled in the art to which the present invention pertains.