Positive electrode active material comprising lithium-rich lithium manganese-based oxide and further comprising lithium tungsten compound, or additionally tungsten compound on the lithium-rich lithium manganese-based oxide, and positive electrode for lithium secondary battery comprising the same

Abstract

A positive electrode active material includes a lithium-rich lithium manganese-based oxide, wherein the lithium-rich lithium manganese-based oxide is represented by the following chemical formula (1),
Li.sub.1+aNi.sub.xCo.sub.yMn.sub.zM.sub.vO.sub.2-bA.sub.b  (1) wherein, 0<a≤0.2, 0<x≤0.4, 0<y≤0.4, 0.5≤z≤0.9, 0≤v≤0.2, a+x+y+z+v=1, and 0≤b≤0.5; M is one or more elements selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga, In, Ru, Nb, and Sn; and A is one or more elements selected from the group consisting of P, N, F, S and Cl; wherein (i) lithium tungsten (W) compound, or the (i) lithium tungsten (W) compound and (ii) tungsten (W) compound
are contained on the lithium-rich lithium manganese-based oxide; in an amount of 0.1% to 7% by weight based on the total weight of the positive electrode active material, wherein the (i) lithium tungsten (W) compound includes a composite of the (ii) tungsten (W) compound and a lithium.

Claims

1. A positive electrode active material comprising a lithium-rich lithium manganese-based oxide, wherein the lithium-rich lithium manganese-based oxide is represented by the following chemical formula (1),
Li.sub.1+aNi.sub.xCo.sub.yMn.sub.zM.sub.vO.sub.2-bA.sub.b  (1) wherein, 0<a≤0.2, 0<x≤0.4, 0<y≤0.4, 0.5≤z≤0.9, 0≤v≤0.2, a+x+y+z+v=1, and 0≤b≤0.5; M is one or more elements selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga, In, Ru, Nb, and Sn; and A is one or more elements selected from the group consisting of P, N, F, S and Cl; wherein (i) lithium tungsten (W) compound, or the (i) lithium tungsten (W) compound and (ii) tungsten (W) compound are present as a coating on a surface of a lithium-rich lithium manganese-based oxide, wherein the (i) lithium tungsten (W) compound including a composite of the (ii) tungsten (W) compound and a lithium, and wherein the (i) lithium tungsten (W) compound, or the (i) lithium tungsten (W) compound and the (ii) tungsten (W) compound are contained in an amount of 0.1% to 7% by weight based on the total weight of the positive electrode active material.

2. The positive electrode active material according to claim 1, wherein the tungsten (W) compound is at least one selected from the group consisting of tungsten oxide, tungsten carbide, and tungsten nitride.

3. The positive electrode active material according to claim 1, wherein the lithium tungsten compound is Li.sub.2WO.sub.4, Li.sub.4WO.sub.5 or Li.sub.6W.sub.2O.sub.9.

4. A positive electrode comprising a positive electrode mixture comprising the positive electrode active material according to claim 1 formed on a current collector.

5. A secondary battery comprising the positive electrode according to claim 4.

6. A method for producing the positive electrode active material of claim 1, comprising: (i) mixing a lithium-rich manganese-based oxide and a tungsten (W)-containing raw material to form a mixture; (ii) heat treating the mixture; wherein the tungsten (W)-containing raw material is mixed so as to contained in an amount of 0.1% to 5% by weight based on a total weight of the lithium-rich lithium manganese-based oxide and the tungsten-containing raw material.

7. The method for producing the positive electrode active material according to claim 6, wherein the tungsten (W)-containing raw material is at least one selected from the group consisting of tungsten oxide, tungsten carbide, and tungsten nitride.

8. The method for producing the positive electrode active material according to claim 6, wherein the tungsten (W)-containing raw material reacts with lithium (Li) of a lithium-rich manganese-based oxide.

9. The method for producing the positive electrode active material according to claim 6, wherein the mixing is a dry mixing.

10. The method for producing the positive electrode active material according to claim 6, wherein the heat treating is performed at 300 to 800 degrees Celsius.

11. The method of claim 6, wherein the tungsten (W)-containing raw material has an average diameter (D50) of 0.05 μm to 1 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an SEM photograph of a positive electrode active material according to Example 1.

(2) FIG. 2 is an SEM photograph of the positive electrode active material according to Comparative Example 1.

(3) FIG. 3 is a comparative graph showing the press density according to Experimental Example 1.

(4) FIGS. 4 and 5 are graphs comparing press densities according to Reference Example 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) Hereinafter, the present invention will be described in further detail with reference to the following examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Preparation Example 1

(6) A precursor was synthesized so that the molar ratio of Ni, Co and Mn was 18:18:64, and then mixed with Li.sub.2CO.sub.3 so that the molar ratio of Li:(Ni+Mn+Co) became 1.35:1. The mixture was then calcinated in a furnace at 940° C. for 10 hours to prepare Li.sub.1.18Ni.sub.0.15Co.sub.0.15Mn.sub.0.52O.sub.2.

Preparation Example 2

(7) A precursor was synthesized so that the molar ratio of Ni, Co and Mn was 12:12:76, and then mixed with Li.sub.2CO.sub.3 so that the molar ratio of Li:(Ni+Mn+Co) became 1.4:1. The mixture was then calcinated in a furnace at 940° C. for 10 hours to prepare Li.sub.1.2Ni.sub.0.1CO.sub.0.1Mn.sub.0.6O.sub.2.

Preparation Example 3

(8) A precursor was synthesized so that the molar ratio of Ni, Co and Mn was 22:22:56, and then mixed with Li.sub.2CO.sub.3 so that the molar ratio of Li:(Ni+Mn+Co) became 1.2:1. The mixture was then calcinated in a furnace at 940° C. for 10 hours to prepare Li.sub.1.1Ni.sub.0.2CO.sub.0.2Mn.sub.0.5O.sub.2.

Example 1

(9) Li.sub.1.18Ni.sub.0.15Co.sub.0.15Mn.sub.0.52O.sub.2 and WO.sub.3 were mixed in a weight ratio of 98:2 by using a ball mill, and the mixture was calcinated in a furnace at 600° C. for 10 hours to produce a positive electrode active material.

(10) The SEM photograph of the synthesized positive electrode active material is shown in FIG. 1.

(11) Referring to FIG. 1, it can be confirmed that in the case of the positive electrode active material according to Example 1, powders such as fine powders having a size of several hundred of nanometers presented on the surface of the active material in Comparative Example 1 were clearly reduced in Example 1 as compared with the positive electrode active material according to Comparative Example 1 shown in FIG. 2, and thus the surface of the active material of Example 1 became smoother than the surface of the active material of Comparative Example 1.

(12) As a result of analyzing the positive electrode active material as described above, it was confirmed that it contains the composition of the lithium tungsten oxide. At this time, the content thereof was confirmed to be about 2.1 to 2.5% by weight based on the total weight of the positive electrode active material.

Example 2

(13) A positive electrode active material was produced in the same manner as in Example 1, except that Li.sub.1.18Ni.sub.0.15Co.sub.0.15Mn.sub.0.52O.sub.2 prepared in Preparation Example 1 and WO.sub.3 were mixed in a weight ratio of 96:4 by using a ball mill.

(14) As a result of analyzing the positive electrode active material as described above, it was confirmed that it contains the composition of the lithium tungsten oxide. At this time, the content thereof was confirmed to be about 4.1 to 5% by weight based on the total weight of the positive electrode active material.

Example 3

(15) A positive electrode active material was produced in the same manner as in Example 1, except that Li.sub.1.2Ni.sub.0.1CO.sub.0.1Mn.sub.0.6O.sub.2 prepared in Preparation Example 2 and WO.sub.3 were mixed in a weight ratio of 96:4 by using a ball mill.

(16) As a result of analyzing the positive electrode active material as described above, it was confirmed that it contains the composition of the lithium tungsten oxide. At this time, the content thereof was confirmed to be about 2.1 to 2.5% by weight based on the total weight of the positive electrode active material.

Example 4

(17) A positive electrode active material was produced in the same manner as in Example 1, except that Li.sub.1.1Ni.sub.0.2CO.sub.0.2Mn.sub.0.5O.sub.2 prepared in Preparation Example 3 and WO.sub.3 were mixed in a weight ratio of 98:2 by using a ball mill.

(18) As a result of analyzing the positive electrode active material as described above, it was confirmed that it contains the composition of the lithium tungsten oxide. At this time, the content thereof was confirmed to be about 2.1 to 2.5% by weight based on the total weight of the positive electrode active material.

Comparative Example 1

(19) Li.sub.1.18Ni.sub.0.15Co.sub.0.15Mn.sub.0.52O.sub.2 prepared in Preparation Example 1 was prepared as a positive electrode active material.

(20) The SEM photograph of the synthesized positive electrode active material is shown in FIG. 2.

Comparative Example 2

(21) A positive electrode active material was produced in the same manner as in Example 1, except that Li.sub.1.18Ni.sub.0.15Co.sub.0.15Mn.sub.0.52O.sub.2 prepared in Preparation Example 1 and WO.sub.3 were mixed in a weight ratio of 93:7 by using a ball mill.

(22) As a result of analyzing the positive electrode active material as described above, it was confirmed that it contains the composition of the lithium tungsten oxide. At this time, the content thereof was confirmed to be about 7.1 to 8.8% by weight based on the total weight of the positive electrode active material.

Experimental Example 1

(23) The powder press density was measured for each of the positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 and 2, and the results are shown in FIG. 3 below.

(24) Referring to FIG. 3, it can be confirmed that when the lithium tungsten compound is contained on the lithium-rich lithium manganese-based oxide according to the present invention, the press density is improved. It can also be confirmed that the press density improves as the content of these materials increases to a certain level. However, in Comparative Example 2 in which the content exceeds a certain level, the press density is lower than that of Comparative Example 1 in which the surface treatment is not performed, and it is confirmed that there is a limit to the appropriate amount of the tungsten (W) coating content. The positive electrode active material used in Examples and Comparative Examples according to the present invention exhibits low rate characteristics due to the problem in the composition of the material, and in order to overcome this problem, it has a structure of high BET unlike Reference Examples 1 and 2 below. Thus, a material with a high BET has the effect of smoothing the surface and increasing the powder press density during the surface treatment of WO.sub.3 at an appropriate level. However, the amount has an optimum point, and when this amount is exceeded, the press density is rather low, but the surface characteristics (BET) at the time of application of the optimum content are the same level as those of Reference Examples 1 and 2 below. The introduction of additional tungsten (W) raw materials is expected to play a role in preventing pressing.

Reference Example 1

(25) A positive electrode active material was produced in the same manner as in Example 1, except that LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2 and WO.sub.3 were mixed in a weight ratio of 98:2 by using a ball mill.

Reference Example 2

(26) A positive electrode active material was produced in the same manner as in Example 1, except that LiNi.sub.0.5Co.sub.0.2Mn.sub.0.3O.sub.2 and WO.sub.3 were mixed in a weight ratio of 98:2 by using a ball mill.

Reference Experimental Example

(27) In order to confirm the change in press densities when using only LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2 of Reference Example 1 as a positive electrode active material, and when using the positive electrode active material of Reference Example 1, and the change in press densities when using only LiNi.sub.0.5Co.sub.0.2Mn.sub.0.3O.sub.2 of Reference Example 2 as a positive electrode active material, and when using the positive electrode active material of Reference Example 2, the powder press densities were confirmed in the same manner as in Experimental Example 1 by using the positive electrode active materials, and the results are shown in FIGS. 4 and 5 below.

(28) Referring to FIGS. 4 and 5, it can be confirmed that in the case of using the lithium transition metal oxide having the compositions of Reference Examples 1 and 2, the press densities are rather reduced by the formation of the lithium tungsten compound. This is because, originally, the lithium transition metal oxide having the above composition has a high press density, whereas when the BET is low and thus a lithium tungsten compound is additionally formed, the homogeneity of the surface is rather lowered to impede pressing.

Experimental Example 2

(29) Each of the positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 and was used, and PVdF as a binder and Super-P as a conductive material were used. The positive electrode active material, the binder and the conductive material were mixed well in a weight ratio of 96:2:2 in NMP, and the mixture was coated onto an Al foil having a thickness of 20 μm, dried at 130° C. and pressed so that the porosity was 30%, thereby producing positive electrodes.

(30) An artificial graphite was as a negative electrode active material, and an artificial graphite:a conductive material (Super-P) and a binder (PVdF) were mixed in a weight ratio of 95:2.5:2.5, and the mixture was added to NMP as a solvent to prepare a negative electrode mixture slurry. The slurry was then coated on a copper foil in a thickness of 70 μm, dried and pressed at 130 degrees Celsius to produce a negative electrode.

(31) Secondary batteries were manufactured by using the positive electrode and the negative electrode, a polyethylene membrane (Celgard, thickness: 20 μm) as a separator, and a liquid electrolyte in which LiPF.sub.6 was dissolved at 1 M in a mixed solvent of ethylene carbonate, dimethylene carbonate, and diethyl carbonate in a ratio of 1:2:1.

(32) The above secondary batteries were tested for rate characteristics in a voltage range of 2.5 V to 4.6 V, and the results are shown in Table 1 below.

(33) TABLE-US-00001 TABLE 1 0.1 C/0.1 C 0.2 C/0.2 C 0.5 C/0.5 C vs. vs. vs. 0.1 C/0.1 C 0.1 C/0.1 C 0.1 C/0.1 C Example 1 100% 95%   81% Example 2 100% 94.7%   83.1% Example 3 100% 96.1%     82% Example 4 100% 94% 78.3% Comparative 100% 94% 70.3% Example 1 Comparative 100% 94% 80.8% Example 2

(34) Referring to Table 1, it can be confirmed that when the lithium tungsten compound is formed with the content according to the present invention, a better rate characteristic is exhibited as compared with the case where no lithium tungsten compound is formed (Examples 1 to 4 and Comparative Example 1). However, referring to Examples 1 and 2 and Comparative Example 2, it can be confirmed that when too much content of the lithium tungsten compound is mixed, the rate characteristic of Comparative Example 2 is rather decreased compared to Examples 1 and 2. This is expected to be because the reactant increases the resistance.

(35) While the present invention has been shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various applications and modifications can be made within the scope of the present invention based on the contents described above.

INDUSTRIAL APPLICABILITY

(36) As described above, the positive electrode active material according to the present invention includes the lithium-rich lithium manganese-based oxide (having a composition of Mn of 0.5 or more) in which a lithium tungsten compound, or both the lithium tungsten compound and a tungsten (W) compound is contained on a lithium-rich lithium manganese-based oxide, whereby not only it has the surface stability, and further, the tungsten-containing raw material reacts with Li existing in the lithium manganese-based oxide to form a lithium tungsten compound, and therefore, the surface roughness is reduced to improve the press density, but also the diffusion characteristics of lithium ions are improved, and the charge/reversal rate characteristics of the secondary battery including the same can be improved.