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

Abstract

A lithium transition metal oxide, which is a lithium cobalt oxide containing a hetero-element, is 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. The hetero-element includes a 4th period transition metal; and at least one selected from the group consisting of a group 2 element, a group 13 element, a group 14 element, a 5th period transition metal, and a 6th period transition metal. A positive electrode additive for a lithium secondary battery, and a lithium secondary battery are also provided.

Claims

1. A lithium transition metal oxide, which is a lithium cobalt oxide containing a hetero-element, wherein the hetero-element comprises a 4th period transition metal; and at least one selected from the group consisting of a group 2 element, a group 13 element, a group 14 element, a 5th period transition metal, and a 6th period transition metal.

2. The lithium transition metal oxide of claim 1, wherein 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 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 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.

3. The lithium transition metal oxide of claim 1, wherein the hetero-element comprises Zn; and at least one selected from the group consisting of Al, Mg, Ti, Zr, Nb and W.

4. The lithium transition metal oxide of claim 1, wherein the hetero-element is included in an amount of 5 mol% to 80 mol% based on the total metal elements excluding lithium in the lithium transition metal oxide.

5. The lithium transition metal oxide of claim 1, wherein the 4th period transition metal of the hetero-element is included in an amount of 10 mol% to 70 mol% based on the total metal elements excluding lithium in the lithium transition metal oxide; and the at least one element selected from the group consisting of a group 2 element, a group 13 element, a group 14 element, a 5th period transition metal, and a 6th period transition metal of the hetero-element is included in an amount of 1 mol% to 20 mol% based on the total metal elements excluding lithium in the lithium transition metal oxide.

6. The lithium transition metal oxide of claim 1, wherein the lithium transition metal oxide is represented by the following Chemical Formula 1: ##STR00003## wherein, M is a group 2 element, a group 13 element, a group 14 element, a 5th period transition metal, or a 6th period transition metal, x is 0.1 to 0.7, and y is 0.01 to 0.2.

7. The lithium transition metal oxide of claim 6, wherein the M is at least one selected from the group consisting of Al, Mg, Ti, Zr, Nb, and W.

8. 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.0.77Zn.sub.0.2Al.sub.0.03O.sub.4, Li.sub.6Co.sub.0.76Zn.sub.0.2Al.sub.0.04O.sub.4, Li.sub.6Co.sub.0.75Zn.sub.0.2Al.sub.0.05O.sub.4, Li.sub.6Co.sub.0.7Zn.sub.0.25Al.sub.0.05O.sub.4, Li.sub.6Co.sub.0.65Zn.sub.0.25Al.sub.0.1O.sub.4, Li.sub.6Co.sub.0.67Zn.sub.0.3Al.sub.0.03O.sub.4, Li.sub.6Co.sub.0.66Zn.sub.0.3Al.sub.0.04O.sub.4, Li.sub.6Co.sub.0.65Zn.sub.0.3Al.sub.0.05O.sub.4, Li.sub.6Co.sub.0.6Zn.sub.0.3Al.sub.0.1O.sub.4, Li.sub.6Co.sub.0.77Zn.sub.0.2Mg.sub.0.03O.sub.4, Li.sub.6Co.sub.0.76Zn.sub.0.2Mg.sub.0.04O.sub.4, Li.sub.6Co.sub.0.75Zn.sub.0.2Mg.sub.0.05O.sub.4, Li.sub.6Co.sub.0.7Zn.sub.0.25Mg.sub.0.05O.sub.4, Li.sub.6Co.sub.0.67Zn.sub.0.3Mg.sub.0.03O.sub.4, Li.sub.6Co.sub.0.66Zn.sub.0.3Mg.sub.0.04O.sub.4, Li.sub.6Co.sub.0.65Zn.sub.0.3Mg.sub.0.05O.sub.4, Li.sub.6Co.sub.0.77Zn.sub.0.2Ti.sub.0.03O.sub.4, Li.sub.6Co.sub.0.76Zn.sub.0.2Ti.sub.0.04O.sub.4, Li.sub.6Co.sub.0.75Zn.sub.0.2Ti.sub.0.05O.sub.4, Li.sub.6Co.sub.0.72Zn.sub.0.25Ti.sub.0.03O.sub.4, Li.sub.6Co.sub.0.67Zn.sub.0.3Ti.sub.0.03O.sub.4, Li.sub.6Co.sub.0.66Zn.sub.0.3Ti.sub.0.04O.sub.4, Li.sub.6Co.sub.0.65Zn.sub.0.3Ti.sub.0.05O.sub.4, Li.sub.6Co.sub.0.77Zn.sub.0.2Zr.sub.0.03O.sub.4, Li.sub.6Co.sub.0.76Zn.sub.0.2Zr.sub.0.04O.sub.4, Li.sub.6Co.sub.0.75Zn.sub.0.2Zr.sub.0.05O.sub.4, Li.sub.6Co.sub.0.72Zn.sub.0.25Zr.sub.0.03O.sub.4, Li.sub.6Co.sub.0.67Zn.sub.0.3Zr.sub.0.03O.sub.4, Li.sub.6Co.sub.0.66Zn.sub.0.3Zr.sub.0.04O.sub.4, Li.sub.6Co.sub.0.65Zn.sub.0.3Zr.sub.0.05O.sub.4, Li.sub.6Co.sub.0.77Zn.sub.0.2Nb.sub.0.03O.sub.4, Li.sub.6Co.sub.0.76Zn.sub.0.2Nb.sub.0.04O.sub.4, Li.sub.6Co.sub.0.75Zn.sub.0.2Nb.sub.0.05O.sub.4, Li.sub.6Co.sub.0.67Zn.sub.0.3Nb.sub.0.03O.sub.4, Li.sub.6Co.sub.0.66Zn.sub.0.3Nb.sub.0.04O.sub.4, Li.sub.6Co.sub.0.65Zn.sub.0.3Nb.sub.0.05O.sub.4, Li.sub.6Co.sub.0.77Zn.sub.0.2W.sub.0.03O.sub.4, Li.sub.6Co.sub.0.76Zn.sub.0.2W.sub.0.04O.sub.4, Li.sub.6Co.sub.0.75Zn.sub.0.2W.sub.0.05O.sub.4, Li.sub.6Co.sub.0.67Zn.sub.0.3W.sub.0.03O.sub.4, Li.sub.6Co.sub.0.66Zn.sub.0.3W.sub.0.04O.sub.4, and Li.sub.6Co.sub.0.65Zn.sub.0.3W.sub.0.05O.sub.4.

9. A method for preparing the lithium transition metal oxide of claim 1, comprising: a first step of solid-state mixing lithium oxide, cobalt oxide and hetero-element oxide to form a mixture; and a second step of obtaining the lithium transition metal oxide of claim 1 by calcining the mixture obtained in the first step under an inert atmosphere and at a temperature of 550° C. to 750° C.

10. The method for preparing the lithium transition metal oxide of claim 9, 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.

11. A positive electrode additive for a lithium secondary battery, comprising the lithium transition metal oxide of claim 1.

12. 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.

13. 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 11.

14. A lithium secondary battery, comprising the positive electrode for the lithium secondary battery of claim 12; a negative electrode; a separator; and an electrolyte.

15. The lithium secondary battery of claim 14, 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.

16. A lithium secondary battery, comprising the positive electrode for the lithium secondary battery of claim 13; 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 5 and Comparative Examples 1 to 2.

[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 6 to 12.

[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 13 and Comparative Examples 3 to 6.

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

Synthesis of lithium transition metal oxide

[0197] A raw material mixture was prepared by solid-state mixing of Li.sub.2O, CoO, ZnO and MgO at a molar ratio of Li: Co: Zn: Mg = 6: 0.77: 0.2: 0.03.

[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.0.77Zn.sub.0.2Mg.sub.0.03O.sub.4.

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

Preparation of lithium secondary battery

[0200] A positive electrode material slurry was prepared by mixing the lithium transition metal oxide (Li.sub.6Co.sub.0.77Zn.sub.0.2Mg.sub.0.03O.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-methylpyrrolyl). The positive electrode material slurry was applied to one surface of a current collector, which was an aluminum foil having a thickness of 15 .Math.m, 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 13 below.

[0201] 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 .Math.m, and was rolled and dried to prepare a negative electrode.

[0202] 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.

[0203] 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

[0204] Except for using Al.sub.2O.sub.3 instead of MgO, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.77Zn.sub.0.2Al.sub.0.03O.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

[0205] Except for using TiO.sub.2 instead of MgO, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.77Zn.sub.0.2Ti.sub.0.03O.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

[0206] Except for using ZrO.sub.2 instead of MgO, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.77Zn.sub.0.2Zr.sub.0.03O.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

[0207] Except for using Nb.sub.2O.sub.5 instead of MgO, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.77Zn.sub.0.2Nb.sub.0.03O.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

[0208] Except for using a raw material mixture obtained by solid-state mixing of Li.sub.2O, CoO, ZnO and Al.sub.2O.sub.3 at a molar ratio of Li: Co: Zn: Al = 6: 0.7: 0.25: 0.05, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.7Zn.sub.0.25Al.sub.0.05O.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

[0209] Except for using MgO instead of Al.sub.2O.sub.3, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.7Zn.sub.0.25Mg.sub.0.05O.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 6.

Example 8

[0210] Except for using a raw material mixture obtained by solid-state mixing of Li.sub.2O, CoO, ZnO and TiO.sub.2 at a molar ratio of Li: Co: Zn: Ti = 6: 0.72: 0.25: 0.03, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.72Zn.sub.0.25Ti.sub.0.03O.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 9

[0211] Except for using ZrO.sub.2 instead of TiO.sub.2, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.72Zn.sub.0.25Zr.sub.0.03O.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 8.

Example 10

[0212] Except for using a raw material mixture obtained by solid-state mixing of Li.sub.2O, CoO, ZnO and Al.sub.2O.sub.3 at a molar ratio of Li: Co: Zn: Al = 6: 0.65: 0.3: 0.05, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.65Zn.sub.0.3Al.sub.0.05O.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

[0213] Except for using a raw material mixture obtained by solid-state mixing of Li.sub.2O, CoO, ZnO and Al.sub.2O.sub.3 at a molar ratio of Li: Co: Zn: Al = 6: 0.65: 0.25: 0.1, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.65Zn.sub.0.25Al.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 12

[0214] Except for using a raw material mixture obtained by solid-state mixing of Li.sub.2O, CoO, ZnO and Al.sub.2O.sub.3 at a molar ratio of Li: Co: Zn: Al = 6: 0.6: 0.3: 0.1, (1) a lithium transition metal oxide of Li.sub.6Co.sub.0.6Zn.sub.0.3Al.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 13

[0215] 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 6.

[0216] 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.0.25Al.sub.0.05O.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 .Math.m, and was rolled and dried to prepare a positive electrode.

[0217] 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 .Math.m and was rolled and dried to prepare a negative electrode.

[0218] 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.

Comparative Example 1

[0219] Except for mixing Li.sub.2O and CoO at a molar ratio of Li: Co = 6: 1 without the addition of ZnO and MgO, (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

[0220] Except for mixing Li.sub.2O,CoO and ZnO at a molar ratio of Li: Co: Zn = 6: 0.7: 0.3 without the addition of MgO, (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 3

[0221] Except for using Li.sub.6CoO.sub.4 obtained in above Comparative Example 1 instead of Li.sub.6Co.sub.0.7Zn.sub.0.25Al.sub.0.05O.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 13.

Comparative Example 4

[0222] Except for using Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4 obtained in above Comparative Example 2 instead of Li.sub.6Co.sub.0.7Zn.sub.0.25Al.sub.0.05O.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 13.

Comparative Example 5

[0223] 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.0.25Al.sub.0.05O.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 13.

Comparative Example 6

[0224] 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 13.

Test Example 1

[0225] With respect to the lithium secondary batteries obtained in above Examples 1 to 12 and above Comparative Examples 1 and 2, 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 Table 1, FIG. 1 and FIG. 2. The amount of cumulative gas generation according to high-temperature storage is shown in Table 2.

Measurement of formation (initial charge) capacity and charge/discharge capacity

[0226] 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.

Measurement of the amount of cumulative gas generation according to the accumulation of charge/discharge

[0227] 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.

Measurement of the amount of cumulative gas generation according to high-temperature storage

[0228] 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.

[0229] The following table 1 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-00001 Formation Amount of cumulative gas generation (mL/g) Capacity (mAh/g) Amount of gas generation (mL/g) 1st 2nd 10th 30th 50th Example 1 (Li.sub.6Co.sub.0.77Zn.sub.0.2Mg.sub.0.03O.sub.4) 805.5 95.8 -0.22 -0.28 0.07 0.39 0.56 Example 2 (Li.sub.6Co.sub.0.77Zn.sub.0.2Al.sub.0.03O.sub.4) 746.6 85.1 -0.04 -0.14 -0.06 0.11 0.16 Example 3 (Li.sub.6Co.sub.0.77Zn.sub.0.2Ti.sub.0.03O.sub.4) 770.3 102.5 -0.08 -0.13 0.16 0.47 0.85 Example 4 763.1 91.8 -0.23 -0.22 0.17 0.64 0.83 ( Li.sub.6Co.sub.0.77Zn.sub.0.2Zr.sub.0.03o.sub.4) Example 5 (Li.sub.6Co.sub.0.77Zn.sub.0.2Nb.sub.0.03O.sub.4) 771.3 92.1 -0.33 -0.16 0.11 0.58 0.89 Example 6 (Li.sub.6Co.sub.0.7Zn.sub.0.25Al.sub.0.05O.sub.4) 822.6 113.1 -0.10 -0.14 -0.07 0.05 0.25 Example 7 (Li.sub.6Co.sub.0.7Zn.sub.0.25Mg.sub.0.05O.sub.4) 808.6 105.6 -0.11 0.03 0.05 0.36 0.53 Example 8 (Li.sub.6Co.sub.0.72Zn.sub.0.25Ti.sub.0.03O.sub.4) 801.0 107.0 -0.08 -0.07 0.35 0.92 0.97 Example 9 (Li.sub.6Co.sub.0.72Zn.sub.0.25Zr.sub.0.03O.sub.4) 787.6 105.4 -0.03 -0.04 0.45 1.16 1.46 Example 10 (Li.sub.6Co.sub.0.65Zn.sub.0.3Al.sub.0.05O.sub.4) 813.7 98.4 -0.35 -0.49 -0.16 -0.41 -0.28 Example 11 (Li.sub.6Co.sub.0.65Zn.sub.0.25Al.sub.0.1O.sub.4) 818.3 96.5 -0.03 -0.23 0.02 -0.09 -0.06 Example 12 (Li.sub.6Co.sub.0.6Zn.sub.0.3Al.sub.0.1O.sub.4) 807.2 96.2 -0.25 -0.19 -0.01 0.02 0.04 Comparative Example 1 (Li.sub.6CoO.sub.4) 903.0 129.1 5.92 6.91 8.04 9.17 10.10 Comparative Example 2 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 827.9 105.0 -0.16 -0.19 0.44 1.68 2.11

[0230] As shown in Table 1 and FIG. 1, Examples 1 to 5 had a smaller initial charge capacity than Comparative Examples 1 and 2. However, the amount of cumulative gas generation after 50.sup.th cycle was 1 mL/g or less in Examples 1 to 5, indicating a remarkably excellent effect of reducing gas. In particular, Example 1 had the largest initial charge capacity among the Examples, and also had the relatively small amount of cumulative gas generation. In Example 2, although the initial charge capacity was somewhat low, the amount of cumulative gas generation was the lowest, thereby indicating an excellent effect of reducing gas.

[0231] As shown in Table 1 and FIG. 2, in the case of Ti and Zr, the additional effect of reducing gas by the addition of hetero-elements was relatively insignificant. Referring to Examples 6, 10, 11, and 12, it was confirmed that the higher the molar content of Al, the greater the effect of reducing gas.

[0232] The following table 2 shows the amount of cumulative gas generation after one, two, three and four weeks after formation (0.sup.th charge) and storage at 60° C.

TABLE-US-00002 Amount of cumulative gas generation (mL/g) Week 1 Week 2 Week 3 Week 4 Example 1 (Li.sub.6Co.sub.0.77Zn.sub.0.2Mg.sub.0.03O.sub.4) -0.46 -0.38 0.35 0.42 Example 2 (Li.sub.6Co.sub.0.77Zn.sub.0.2Al.sub.0.03O.sub.4) -0.04 -0.04 0.69 0.56 Example 3 (Li.sub.6Co.sub.0.77Zn.sub.0.2Ti.sub.0.03O.sub.4) -0.13 -0.01 0.44 0.42 Example 4 (Li.sub.6Co.sub.0.77Zn.sub.0.2Zr.sub.0.03O.sub.4) -0.27 0.31 0.67 0.72 Example 5 (Li.sub.6Co.sub.0.77Zn.sub.0.2Nb.sub.0.03O.sub.4) -0.29 0.02 0.20 0.35 Example 6 (Li.sub.6Co.sub.0.7Zn.sub.0.25Al.sub.0.05O.sub.4) -0.52 -0.28 -0.22 -0.23 Example 7 (Li.sub.6Co.sub.0.7Zn.sub.0.25Mg.sub.0.05O.sub.4) -0.35 -0.23 0.25 0.26 Example 8 (Li.sub.6Co.sub.0.72Zn.sub.0.25Ti.sub.0.03O.sub.4) -0.10 0.26 0.91 1.14 Example 9 (Li.sub.6Co.sub.0.72Zn.sub.0.25Zr.sub.0.03O.sub.4) -0.11 0.27 1.00 1.23 Example 10 (Li.sub.6Co.sub.0.65Zn.sub.0.3Al.sub.0.05O.sub.4) -0.80 0.10 0.11 0.21 Example 11 (Li.sub.6Co.sub.0.65Zn.sub.0.25Al.sub.0.1O.sub.4) -0.60 -0.45 -0.69 -0.08 Example 12 (Li.sub.6Co.sub.0.6Zn.sub.0.3Al.sub.0.1O.sub.4) -0.58 -0.23 -0.17 -0.21 Comparative Example 1 (Li.sub.6CoO.sub.4) 9.95 10.19 9.70 9.56 Comparative Example 2 (Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) -0.15 -0.12 0.50 1.04

[0233] As shown in Table 2, Examples 1 to 5 were confirmed to have a significantly superior effect of reducing gas compared to Comparative Examples 1 and 2 with the amount of cumulative gas generation of 1 mL/g or less in high-temperature storage at 60° C.

[0234] Referring to Examples 6 to 12, it was confirmed that the lithium transition metal oxide into which Al was introduced had an excellent effect of reducing gas in high-temperature storage.

Test Example 2

[0235] With respect to the lithium secondary batteries of Example 13 and Comparative Examples 3 to 6 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 3.

Measurement of Formation (Initial Charge) Capacity and Charge/Discharge Capacity

[0236] 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.

Measurement of the Amount of Cumulative Gas Generation According to the Accumulation of Charge/Discharge

[0237] 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.

Measurement of the Amount of Cumulative Gas Generation According to High-Temperature Storage

[0238] 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.

[0239] The following table 3 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-00003 Formation capacity (mAh/g) Amount of gas generation (mL/g) Capacity retention @ 100th cycle Charge capacity Discharge capacity 50th 100th Example 13 (NCMA + Li.sub.6Co.sub.0.7Zn.sub.0.25Al.sub.0.05O.sub.4) 243.5 214.8 0.05 0.07 91.7 Comparative Example 3 (NCMA + Li.sub.6CoO.sub.4) 243.3 215.4 0.03 0.24 88.5 Comparative Example 4 (NCMA + Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 243.4 214.9 0.14 0.16 88.2 Comparative Example 5 (NCMA + DN20) 242.2 214.5 0.02 0.11 86.3 Comparative Example 6 (NCMA) 236.0 201.3 0.10 0.20 86.2

[0240] As shown in above table 3 and FIG. 3, the discharge capacities of Example 13 and Comparative Examples 3 to 5 were larger than Comparative Example 6 in which the positive electrode additive (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.

[0241] In contrast, in the case of Comparative Example 6, 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.

[0242] In the case of Example 13, the amount of cumulative gas generation at the 100.sup.th cycle was 0.07 mL/g, which was less than 0.24 mL/g of Comparative Example 3 and less than 0.16 mL/g of Comparative Example 4 in which the sacrificial positive electrode material was not applied. In Example 13, since Al was additionally introduced into Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4 of Comparative Example 4 into which Zn was introduced, CoO.sub.2 formed after initial charge was more effectively stabilized than the case where only Zn was introduced. Accordingly, the side reaction with the electrolyte was effectively prevented, thereby suppressing additional gas generation.

[0243] In the case of Comparative Example 5, the amount of cumulative gas generation at the 50.sup.th cycle was the smallest as 0.02 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 3. In contrast, in the case of Example 13, 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.

[0244] In the case of Example 13, Comparative Example 3 and Comparative Example 4 to which the Co-based sacrificial positive electrode material was applied, the capacity retention at 100.sup.th cycle was 88.2% or more. Comparative Example 5 to which the Ni-based sacrificial positive electrode material was applied and Comparative Example 6 to which the sacrificial positive electrode material was not applied showed the capacity retention of 86.3% and 86.2%, respectively, which were significantly lower than that of Example 13. In particular, in the case of Example 13 to which Al was additionally introduced, it was confirmed that the capacity retention was significantly improved to 91.7%. This may be because the addition of Al stabilizes the crystal phase after initial charge to prevent side reactions with the electrolyte, as seen in the amount of cumulative gas generation described above.

[0245] Accordingly, when a Co-based sacrificial positive electrode material, in particular, a sacrificial positive electrode material having the composition of Chemical Formula 1 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.

[0246] The following table 4 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-00004 Amount of cumulative gas generation (mL/g) Week 1 Week 2 Week 3 Week 4 Example 13 (NCMA + Li.sub.6Co.sub.0.7Zn.sub.0.25Al.sub.0.05O.sub.4) 0.09 0.12 0.12 0.15 Comparative Example 3 (NCMA + Li.sub.6CoO.sub.4) 1.07 1.38 1.78 2.01 Comparative Example 4 (NCMA + Li.sub.6Co.sub.0.7Zn.sub.0.3O.sub.4) 0.11 0.14 0.18 0.22 Comparative Example 5 (NCMA + DN20) 0.54 0.65 0.80 0.82 Comparative Example 6 (NCMA) 0.21 0.29 0.53 0.55

[0247] As shown in above table 4, Example 13 showed the lowest amount of cumulative gas generation of 0.15 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.

[0248] In addition, Example 13 generated gas less than Comparative Example 6 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.

[0249] 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.