Lithium composite oxide for lithium secondary battery and method for producing same

Abstract

To provide a lithium composite oxide having interface distance of an inside of a secondary particle and a crystal structure in a surface part being different from each other, decreased residual Li, and improved capacity characteristics, resistance characteristics, and life characteristics, and a manufacturing method of the lithium composite oxide.SOLUTION: A lithium composite oxide is a secondary particle formed by aggregation of a plurality of a primary particles, having a Co coating layer on a surface of the secondary particle, and showing Co ion concentration gradient to an inside of the particle. A manufacturing method of a lithium composite oxide secondary particle represented by the formula below includes reacting a precursor containing NiCoM1M2 with lithium, heating, and alkaline washing, followed by blending (coating) with a M2 solution, drying, and then doping with M3. LiNi1-(x1+y1+z1)Cox1M1y1M2z1M3r1Oa (M1 is Mn or Al; M2 and M3 are Al, Ba, B, Co, Ce, Cr, F,Li, Mg, Mn, Mo, etc.; 0.95≤≤1.05; 1.50≤a≤2.1; 0.02≤x1≤0.25; 0.01≤y1≤0.20; 0≤z1≤0.20; 0≤r1≤0.20)SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lithium composite oxide for lithium secondary batteries and a method for manufacturing the same. More specifically, in a conventional cathode active material in which lithium ion diffusion pathways are formed in the a-axis and c-axis directions of a crystal structure, water washing is performed during the manufacturing process to reduce residual lithium. However, as a result of water washing, although the residual lithium is reduced, a problem occurs in that performance is deteriorated. In response to this, the surface is coated with a different element, and the interplanar distance of the crystal structure between primary particles located inside the secondary particles and primary particles located on the surface of the secondary particles changes, thereby improving capacity characteristics, resistance characteristics, and life characteristics. The present invention relates to a lithium composite oxide for lithium secondary batteries and a method for manufacturing the same. [Background technology]

[0002] As technology and demand for mobile devices improve, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which exhibit high energy density and working potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used. The positive electrode active material for lithium secondary batteries is mainly lithium-containing cobalt oxide (LiCoO2), but other lithium-containing manganese oxides such as LiMnO2 with a layered crystal structure and LiMn2O4 with a spinel crystal structure, as well as lithium-containing nickel oxide LiNiO2, are also being considered. Among the cathode active materials, LiCoO2 is the most widely used due to its excellent lifespan characteristics and charge / discharge efficiency, but it has drawbacks such as low capacity and high cost due to limited cobalt resources used as a raw material, limiting its price competitiveness for mass use as a power source in medium- to large-sized batteries such as electric vehicles.Of the cathode active materials, lithium manganese oxides such as LiMnO2 and LiMn2O4 have advantages such as low cost, environmental friendliness, and excellent thermal safety due to the abundant manganese resources used as a raw material, but have drawbacks such as low capacity and poor high-temperature characteristics and cycle characteristics.

[0003] A method for preparing a lithium composite oxide generally involves preparing a transition metal precursor, mixing the transition metal precursor with a lithium compound, and then calcining the mixture. The lithium compound used in this process is LiOH and / or Li2CO3. Generally, when the Ni content of the positive electrode active material is 65% or less, Li2CO3 is used. When the Ni content is 65% or more, LiOH is preferably used due to its low-temperature reaction. However, nickel-rich systems with a Ni content of 65% or more have the problem of high residual lithium in the form of LiOH and Li2CO3 on the surface of the positive electrode active material due to their low-temperature reaction. This residual lithium, i.e., unreacted LiOH and Li2CO3, reacts with the electrolyte inside the battery, causing gas generation and swelling, which seriously reduces high-temperature safety. Furthermore, unreacted LiOH can cause gelation due to its high viscosity during slurry mixing before electrode plate production.

[0004] In order to remove such unreacted Li, a water washing process is generally performed after the preparation of the active material, which significantly reduces the amount of residual lithium. However, in this case, the water washing process causes surface damage to the positive electrode active material, which reduces capacity and efficiency characteristics, and also causes other problems such as increased resistance during high-temperature storage. Therefore, a method for reducing the residual lithium and improving capacity, efficiency, and life characteristics is needed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Republic of Korea Patent Publication No. 10-2011-0108566 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to solve the above problems, an object of the present invention is to provide a lithium composite oxide having a new structure that reduces residual lithium and improves capacity characteristics, resistance characteristics, and life characteristics. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides lithium composite oxide secondary particles formed by agglomeration of a plurality of primary particles, wherein the primary particles located at the surface of the secondary particles have a Co coating layer on the surface thereof, and within the primary particles located at the surface of the secondary particles, a Co ion concentration gradient is present from the surface coating layer toward the center of the particle. The lithium composite oxide secondary particles according to the present invention are secondary particles formed by aggregation of primary particles, and are characterized in that the primary particles located at the surface regions of the secondary particles among the primary particles have a Co coating layer on their surfaces. That is, the lithium composite oxide secondary particles according to the present invention are characterized in that the Co coating layer is not formed on the entire primary particles constituting the secondary particles, but is formed on the surfaces of the primary particles located at the surface regions of the secondary particles. In the lithium composite oxide secondary particles according to the present invention, when defining the primary particles located on the surface of the secondary particles, the thickness of the surface of the secondary particles is 0.3 to 1 um from the outermost periphery of the secondary particles.

[0008] The lithium composite oxide secondary particles according to the present invention are characterized in that the thickness of the Co coating layer formed on the surface of the primary particle located in the surface region of the secondary particle is 50 to 150 nm. The Co coating layer formed on the surface of the primary particle may be formed on the entire primary particle located in the surface region of the secondary particle, or may be formed only on the portion of the secondary particle in contact with the surface of the primary particle located in the surface region of the secondary particle. In the lithium composite oxide secondary particles according to the present invention, the primary particles located on the surface of the secondary particles are characterized in that the Co concentration decreases in a concentration gradient of 0.05 to 0.07 Co mol % per 1 nm in the particle center direction.

[0009] In the lithium composite oxide secondary particles according to the present invention, the primary particles located on the surface of the secondary particles are characterized in that the Co concentration at the boundary of the primary particles is higher than the Co concentration inside the primary particles. In the lithium composite oxide secondary particles according to the present invention, the primary particles located on the surface of the secondary particles have a dc / dh ratio of 2 to 10, where dc is the length of the secondary particle in the direction toward the center and dh is the length perpendicular to the center. That is, the primary particles located on the surface of the lithium composite oxide secondary particles according to the present invention are formed in an elliptical or rod shape with an aspect ratio of 2 to 10.

[0010] In the lithium composite oxide secondary particles according to the present invention, when the inter-plane distance of the crystal structure in the primary particles located inside the secondary particles among the primary particles is d1 and the inter-plane distance of the crystal structure in the primary particles located on the surface of the secondary particles is d2, the d1 and d2 satisfy the following <Relationship 1>: <Relationship 1> d1>d2

[0011] That is, the lithium composite oxide secondary particles according to the present invention are characterized in that the inter-plane distance within the primary particles located inside the secondary particles is different from the inter-plane distance within the primary particles located on the surface of the secondary particles, and the inter-plane distance of the primary particles located inside the secondary particles is larger than the inter-plane distance of the primary particles located on the surface of the secondary particles. In the lithium composite oxide secondary particles according to the present invention, when the interplanar distance of the crystal structure at the boundary surface of the Co coating layer of the primary particle located at the surface portion of the secondary particle is d3, the d1, d2, and d3 satisfy the following <Relationship 2>. <Relationship 2> d1>d3≧d2

[0012] The lithium composite oxide secondary particles according to the present invention are characterized in that the interplanar distance of the crystal structure changes as a Co coating layer is included on the surface of the primary particle located on the surface of the secondary particle. The lithium composite oxide secondary particles according to the present invention are characterized in that the interplanar distance d1 of the crystal structure in the primary particles located inside the secondary particles is 4.8 nm or more. The lithium composite oxide secondary particles according to the present invention are characterized in that the interplanar distance d2 of the crystal structure within the primary particles located on the surface of the secondary particles is 4.7 nm or less. In the secondary particles of the lithium composite oxide according to the present invention, the interplanar distances d1 and d2 refer to the average of 10 adjacent interplanar distances centered on the interplanar distance of a portion measured from the results of a crystal structure analysis such as a TEM analysis of the positive electrode active material.

[0013] The lithium composite oxide secondary particles according to the present invention are characterized in that at least one peak appears at the positions of (104), (110), (113), (101), (102), and (003) in XDR analysis. The secondary particles of lithium composite oxide according to the present invention are characterized in that, in the Co 2p core-level spectrum analysis obtained through XPS measurement, the binding energy (P1) of the spin-orbit-spit 2p3 / 2 peak and the binding energy (P2) of the 2p1 / 2 peak are as follows: 779 eV≦(P1)≦780 eV 794 eV ≦ (P2) ≦ 795 eV

[0014] The lithium composite oxide secondary particles according to the present invention are characterized in that the ratio of the peak intensity (I531) around 531 eV to the peak intensity (I528) around 528.5 eV in the O 1s core-level spectrum analysis obtained through XPS measurement is as follows: (I 531 ) / (I 528 )≦2

[0015] The lithium composite oxide secondary particles according to the present invention are characterized in that the ratio of the peak intensity (I289) around 289 eV to the peak intensity (I284) around 284.5 eV in the C 1s core-level spectrum analysis obtained through XPS measurement is as follows: (I 289) / (I 284 )≦0.9

[0016] The lithium composite oxide secondary particles according to the present invention are characterized by being represented by the following <Chemical Formula 1>. [ka] (In the <Chemical Formula 1>, M1 is Mn or Al, M2 and M3 are metals selected from the group consisting of Al, Ba, B, Co, Ce, Cr, F, Li, Mg, Mn, Mo, P, Sr, Ti, and Zr, and 0.95≦x1≦1.05, 1.50≦a≦2.1, 0.02≦x1≦0.25, 0.01≦y1≦0.20, 0≦z1≦0.20, and 0≦r1≦0.20)

[0017] The present invention also provides A first step of preparing a positive electrode active material precursor for a lithium secondary battery, represented by the following <Chemical Formula 2>: [ka] (In the <Chemical Formula 2>, M1 is Mn or Al, and M2 is a metal selected from the group consisting of Al, Ba, B, Co, Ce, Cr, F, Li, Mg, Mn, Mo, P, Sr, Ti, and Zr, where 0≦x2≦0.25, 0≦y2≦0.20, and 0≦z2≦0.20.)

[0018] a second step of reacting the precursor of the positive electrode active material for a lithium secondary battery with a lithium compound and subjecting the resulting mixture to a first heat treatment to prepare a positive electrode active material; a third step of washing the positive electrode active material with distilled water or an alkaline aqueous solution; a fourth step of coating the washed positive electrode active material with a solution containing a metal M2 selected from the group consisting of Al, Ba, B, Co, Ce, Cr, F, Li, Mg, Mn, Mo, P, Sr, Ti, and Zr; a fifth step of drying the positive electrode active material particles; a sixth step of mixing the dried cathode active material with a metal M3 selected from the group consisting of Al, Ba, B, Co, Ce, Cr, F, Li, Mg, Mn, Mo, P, Sr, Ti, and Zr, and performing a second heat treatment to dope the metal M3 into the interior of the particles.

[0019] In the method for producing a positive electrode active material according to the present invention, the fourth step is characterized by carrying out a coating reaction with a solution containing Co. In the method for producing a positive electrode active material according to the present invention, the concentration of the Co-containing solution in the fourth step is 1 to 10 mol %. The present invention also provides secondary particles of a lithium composite oxide produced by the production method of the present invention. The present invention also provides a lithium secondary battery containing the lithium composite oxide secondary particles according to the present invention. The lithium secondary battery according to the present invention is characterized in that the residual lithium is 6000 ppm or less. [Effects of the Invention]

[0020] The lithium composite oxide according to the present invention exhibits improved capacitance, resistance, and life characteristics as the interplanar distance of the crystal structure between the primary particles located inside the secondary particles and the primary particles located on the surface of the secondary particles is changed by coating with a different element and washing with water in the precursor step and / or active material preparation step. [Brief explanation of the drawings]

[0021] [Figure 1] 1 shows the results of measuring the diffraction pattern and interplanar distance of the LiCoO2 positive electrode active material of Comparative Example 1 of the present invention. [Figure 2] 3 shows the results of measuring a TEM photograph and an EDX photograph of a positive electrode active material prepared in one embodiment of the present invention. [Figure 3] 1 shows the results of measuring the diffraction pattern and interplanar distance of a positive electrode active material prepared in an example of the present invention. [Figure 4]3 shows the results of measuring a TEM photograph and an EDX photograph of a positive electrode active material prepared in one embodiment of the present invention. [Figure 5] 1 shows the results of measuring the diffraction pattern and interplanar distance of a positive electrode active material prepared in an example of the present invention. [Figure 6] 1 shows the results of measuring the change in concentration of Ni, Co, and Al from the surface toward the center of a positive electrode active material prepared in an example of the present invention. [Figure 7] 1 shows the results of measuring an EDX photograph of a positive electrode active material prepared in one embodiment of the present invention. [Figure 8] 1 shows the results of measuring the diffraction pattern and interplanar distance of a positive electrode active material prepared in an example of the present invention. [Figure 9] 3 shows the results of measuring a TEM photograph and an EDX photograph of a positive electrode active material prepared in one embodiment of the present invention. [Figure 10] 1 shows the results of measuring the change in concentration of Ni, Co, and Al from the surface toward the center of a positive electrode active material prepared in an example of the present invention. [Figure 11] 1 shows the results of measuring the change in concentration of Ni, Co, and Al from three points on the surface of a positive electrode active material toward the center thereof, which was fabricated in accordance with an embodiment of the present invention. [Figure 12] 1 shows the results of measuring the diffraction patterns and interplanar distances of the positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 13] 1 shows the results of measuring the diffraction patterns and interplanar distances of the positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 14] 1 shows the results of measuring the diffraction patterns and interplanar distances of the positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 15] 1 shows the results of measuring an EDX photograph of an active material produced in a comparative example of the present invention. [Figure 16] 1 shows the results of measuring an EDX photograph of an active material produced in a comparative example of the present invention. [Figure 17] 1 shows the results of measuring the diffraction patterns and interplanar distances of the positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 18] 1 shows the results of measuring the diffraction patterns and interplanar distances of the positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 19] 1 shows the results of measuring the diffraction patterns and interplanar distances of the positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 20] 1 shows the results of measuring the change in concentration of Ni, Co, and Al from the surface toward the center of a positive electrode active material prepared in an example of the present invention. [Figure 21] 1 shows the results of measuring the diffraction patterns and interplanar distances of the positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 22] 1 shows the results of XRD measurement of positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 23] 1 shows the results of XRD measurement of positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 24] 1 shows the results of XRD measurement of positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 25] 1 shows the results of XRD measurement of positive electrode active materials prepared in an example of the present invention and a comparative example. [Figure 26] 1 shows the results of XPS measurements of positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 27a] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 27b] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 27c] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 27d] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 27e] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 28a]1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 28b] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 28c] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 28d] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 28e] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 29a] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 29b] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 29c] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 29d] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 29e] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 30a] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 30b] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 30c] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 30d] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 30e]1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 31a] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 31b] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 31c] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 31d] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. [Figure 31e] 1 shows the results of measuring the characteristics of batteries including the positive electrode active materials prepared in an example and a comparative example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. <Comparative Example 1> In Comparative Example 1, commercially available LiCoO2 positive electrode active material was used.

[0023] <Experimental Example> Measurement of distance between crystal structures The diffraction patterns and interplanar distances of the primary particles located on the surface of the secondary particles of the LiCoO2 positive active material of Comparative Example 1 and the primary particles located inside the particles were measured, and the results are shown in FIG. LiCoO2 positive electrode active material particles were placed on a carbon grid, carbon coated, PT coated, and sliced ​​with an ion beam through a TEM pretreatment process. The sample was then magnified 20 to 25 million times, and the inter-plane distance of the area to be measured was measured as the average distance of 10 inter-plane distances on either side of the inter-plane distance to be measured. As shown in FIG. 1, the diffraction patterns of the primary particles located inside and on the surface of the secondary particles of the LiCoO2 cathode active material all had a hexagonal structure, and the interplanar distance of the primary particles located inside and on the surface of the secondary particles was measured to be 4.70 nm.

[0024] <Example 1> Preparation of positive electrode active material First, a NiCo(OH) precursor was prepared by coprecipitation. Li2CO3 and LiOH were added as lithium compounds to the prepared precursor, and Al and Mg were added as M1. The resulting precursor was then subjected to a first heat treatment to prepare a cathode active material for a lithium secondary battery. Distilled water was prepared, and the prepared positive electrode active material for a lithium secondary battery was placed in the distilled water, and the temperature was maintained while the prepared positive electrode active material for a lithium secondary battery was washed with water. Thereafter, 0.03 mol of cobalt sulfate aqueous solution was added to the washing solution of the positive active material at a constant rate for 1 hour, and the positive active material was stirred to coat the surface of the positive active material with Co in M2, followed by washing with water and drying at 120°C under vacuum conditions. The coated positive electrode active material was added with Ti as M3, and subjected to a second heat treatment at 450° C. to prepare a positive electrode active material for a lithium secondary battery.

[0025] <Experimental example> TEM, EDX measurement TEM and EDX images of the positive electrode active material prepared in Example 1 were taken, and the results are shown in FIG. As shown in FIG. 2, in the case of the cathode active material prepared in Example 1 of the present invention, the Co concentration is high on the surface of the secondary particles and decreases as one moves from the surface to the interior of the secondary particles, indicating that the Co concentration within the secondary particles is not constant but exhibits a gradient.

[0026] <Experimental Example> Measurement of distance between crystal structures The diffraction patterns and interplanar distances of the primary particles located inside the secondary particles of the cathode active material prepared in Example 1 and the primary particles located on the surface coated with Co and Ti were measured, and the results are shown in FIG. 3. As shown in Figure 3, the thickness of the Co coating layer is approximately 80 nm, and the diffraction pattern of the primary particles located inside the secondary particles has a hexagonal structure. In the case of the primary particles located inside the secondary particles, the average interplanar distance of 10 adjacent planes in the TEM image was measured to be 4.88 nm. In contrast, in the case of the primary particles located on the surface where the Co coating layer is present, the diffraction pattern has a hexagonal structure, but the interplanar distance was measured to be 4.73 nm. This shows that the interplanar distance of the primary particles located on the surface is reduced compared to the primary particles located inside the secondary particles that are not coated with cobalt, and the interplanar distance of the primary particles located on the surface is changed to be similar to the interplanar distance of LiCoO2 in the comparative example.

[0027] <Example 2> Preparation of positive electrode active material A positive electrode active material of Example 2 was prepared by the same washing and coating processes as in Example 1, except that the concentration of the cobalt aqueous solution added to the washing solution for the positive electrode active material was 4 mol %.

[0028] <Experimental example> TEM, EDX measurement TEM and EDX images of the positive electrode active material prepared in Example 2 were taken, and the results are shown in FIG. As shown in FIG. 4, in the case of the cathode active material prepared in Example 2 of the present invention, the Co concentration is high on the surface of the secondary particles and decreases toward the interior of the secondary particles, indicating that the Co concentration is not constant but exhibits a gradient.

[0029] <Experimental Example> Measurement of distance between crystal structures The diffraction patterns and interplanar distances of the primary particles located inside the secondary particles of the positive active material prepared in Example 1 and the primary particles located on the surface coated with Co and Ti were measured, and the results are shown in FIG. 5. In Figure 5, the thickness of the surface Co coating layer is approximately 90 nm, and the diffraction pattern of the primary particles located inside the secondary particles has a hexagonal structure. In the case of the primary particles located inside the secondary particles, the average interplanar distance of 10 adjacent planes in the TEM image was measured to be 4.85 nm. In contrast, in the case of the primary particles located on the surface where the Co coating layer is present, the diffraction pattern has a hexagonal structure, but the interplanar distance was measured to be 4.73 nm. It can be seen that the interplanar distance of the primary particles located on the surface is reduced compared to the primary particles located inside the secondary particles that are not coated with cobalt, and the interplanar distance of the primary particles located on the surface is changed to be similar to the interplanar distance of LiCoO2 in the comparative example.

[0030] <Example 3> Preparation of NCM-based positive electrode active material The same procedure as in Example 1 was carried out, and the concentration of the cobalt aqueous solution added to the washing solution for the positive active material was set to 5 mol %, to prepare a positive active material of Example 3.

[0031] <Experimental Example> Concentration scanning The changes in the concentrations of Ni, Co, and Al were measured from the surface of the secondary particles of the positive electrode active material prepared in Example 3 toward the center of the particles, and the results are shown in FIG. As shown in FIG. 6, in the case of the cathode active material prepared in Example 3 of the present invention, the Co concentration in the Co coating layer increases from the surface toward the center, and then decreases toward the center, and the thickness of the Co coating layer is 0.1 μm.

[0032] <Experimental example> TEM, EDX EDX photographs of Ni, Co, and Al were taken from the surface of the secondary particles of the positive active material prepared in Example 3 toward the center of the particles, and the results are shown in FIG. As can be seen from FIG. 7, in the case of the cathode active material prepared in Example 3 of the present invention, the Co concentration increases from the surface toward the center of the Co-coated layer, but then decreases toward the center, with the Co concentration becoming higher along the boundaries of the primary particles.

[0033] <Experimental Example> Measurement of distance between crystal structures The diffraction patterns and interplanar distances of the primary particles located inside the secondary particles of the cathode active material prepared in Example 3 and the primary particles located on the surface coated with Co and Ti were measured, and the results are shown in FIG. 8. As shown in Figure 8, the thickness of the Co coating layer is approximately 100 nm, and the diffraction pattern of the primary particles located inside the secondary particles has a hexagonal structure. In the case of the primary particles located inside the secondary particles, the average interplanar distance of 10 adjacent planes in the TEM image was measured to be 4.84 nm. In contrast, in the case of the primary particles located on the surface where the Co coating layer is present, the diffraction pattern has a hexagonal structure, but the interplanar distance was measured to be 4.67 nm. It can be seen that the interplanar distance of the primary particles located on the Co-coated surface is reduced compared to the primary particles located inside the secondary particles that are not Co-coated, and the interplanar distance of the primary particles located on the surface is changed to be similar to the interplanar distance of LiCoO2 in the comparative example.

[0034] <Example 4> Preparation of NCM-based positive electrode active material The same procedure as in Example 1 was carried out, except that the concentration of the cobalt aqueous solution added to the washing solution for the positive active material was 10 mol %, and washing and coating were performed to prepare a positive active material of Example 4.

[0035] <Experimental example> TEM, EDX measurement TEM and EDX images were taken of the surface of the secondary particles of the positive active material prepared in Example 4, and the results are shown in FIG. As shown in FIG. 9, in the case of the cathode active material prepared in Example 4 of the present invention, the Co concentration is high on the surface of the secondary particles and decreases toward the interior of the secondary particles, indicating that the Co concentration is not constant but exhibits a gradient. In addition, the EDX measurement results show that Co is distributed in rod-shaped primary particles, resulting in a high Co concentration measured around the rod-shaped primary particles.

[0036] <Experimental Example> Concentration scanning The changes in the concentrations of Ni, Co, and Al from the surface to the center of the secondary particles of the positive electrode active material prepared in Example 4 were measured, and the results are shown in FIG. As shown in FIG. 10, in the case of the cathode active material prepared in Example 4 of the present invention, the Co concentration increases from the surface toward the center in the coating layer portion where the Co is coated on the secondary particles, and then the Co concentration decreases toward the center, and the thickness of the Co coating layer where the Co is coated is 0.14 μm.

[0037] <Experimental Example> Concentration scanning The changes in the concentrations of Ni, Co, and Al were measured at three points on the surface of the secondary particles of the positive active material prepared in Example 4 from the surface toward the center of the particle, and the results are shown in FIG. As shown in FIG. 11, it can be seen that a concentration gradient layer is uniformly formed at three independent portions on the surface of the secondary particles of the positive active material prepared in Example 4, with a coating layer thickness of 0.14 μm.

[0038] <Experimental Example> Measurement of distance between crystal structures The diffraction patterns and interplanar distances of the primary particles located inside the secondary particles of the cathode active material prepared in Example 4 and the primary particles located on the surface coated with Co and Ti were measured, and the results are shown in FIG. 12 . As shown in FIG. 12, the thickness of the Co coating layer was 140 nm, and the diffraction pattern of the primary particles located inside the secondary particles was a hexagonal structure with an interplanar distance of 4.85 nm. In contrast, the diffraction pattern of the primary particles located on the surface coated with Co and Ti was a hexagonal structure with an interplanar distance of 4.69 nm. It can be seen that the interplanar distance of the primary particles located on the Co-coated surface is reduced compared to the primary particles located inside the secondary particles that are not Co-coated, and the interplanar distance of the primary particles located on the surface is changed to be similar to the interplanar distance of LiCoO2 in the comparative example.

[0039] <Experimental Example> Measurement of the distance between crystal structures at the coating boundary The diffraction patterns and interplanar distances were measured at the interior of the primary particles located on the surfaces of the secondary particles of the cathode active material prepared in Example 4 and at the interface of the coating layer within the primary particles located on the surfaces of the secondary particles. The results are shown in FIG. 13. As shown in FIG. 13, the diffraction pattern at the boundary between the primary particles located on the surface of the secondary particles of the positive electrode active material and the Co and Ti coated layer within the primary particles located on the surface of the secondary particles was a hexagonal structure, and the interplanar distance was measured to be 4.71 nm. In the case of primary particles located inside the secondary particles, the inter-plane distance was measured to be 4.85 nm, and in the case of primary particles located on the surface of the cobalt and Ti coated secondary particles, the inter-plane distance was measured to be 4.69 nm. In comparison, the inter-plane distance of 4.71 nm at the coating boundary surface within the primary particles located on the surface of the cobalt and Ti coated secondary particles is found to be the median value measured between the inter-plane distance of primary particles located inside the secondary particles and the inter-plane distance of primary particles located on the surface of the cobalt and Ti coated secondary particles. It can also be seen that the interplanar distance at the coating interface was changed to be similar to the interplanar distance of LiCoO2 in the comparative example.

[0040] <Experimental Example> Measurement of distance between crystal structures at the boundary surface of primary particles The diffraction pattern and interplanar distance at the boundary surface of the primary particle located on the surface of the Co and Ti coated secondary particle of the cathode active material prepared in Example 4 were measured and the results are shown in FIG. 14. As shown in FIG. 14, the diffraction pattern of the primary particles at the boundary between the primary particles located on the surface of the secondary particles of the positive electrode active material has a hexagonal structure, and the interplanar distances are measured to be 4.69 and 4.71 nm, which are intermediate values ​​between the interplanar distances of the core portion and the coating layer portion. It can also be seen that the interplanar distance at the boundary of the primary particles was changed to be similar to the interplanar distance of LiCoO2 of the comparative example.

[0041] <Example 5> Preparation of positive electrode active material The same procedure as in Example 1 was carried out, and the composition of the positive electrode active material for the lithium secondary battery that had undergone the first heat treatment was Li 1.02 Ni 0.816 Co 0.15 Al 0.034 The positive electrode active material of Example 5 was produced using O2 without adding Ti.

[0042] <Example 6> Preparation of positive electrode active material The same procedure as in Example 1 was carried out, and the composition of the positive electrode active material for the lithium secondary battery that had undergone the first heat treatment was Li 1.02 Ni 0.903 Co 0.08 Al 0.014 Mg 0.003 The positive electrode active material of Example 6 was prepared by using O2.

[0043] <Example 7> Preparation of positive electrode active material The same procedure as in Example 1 was carried out, and the composition of the positive electrode active material for the lithium secondary battery that had undergone the first heat treatment was Li 1.00 Ni 0.965 Co 0.02 Al 0.014 Mg 0.001 O2 to prepare the positive electrode active material of Example 7.

[0044] <Example 8> Preparation of positive electrode active material The same procedure as in Example 7 was carried out, except that the concentration of the cobalt aqueous solution added to the washing solution for the positive active material was 4 mol %, to prepare a positive active material of Example 8.

[0045] <Example 9> Preparation of positive electrode active material The same procedure as in Example 7 was carried out, except that the concentration of the cobalt aqueous solution added to the washing solution for the positive active material was 5 mol %, to prepare a positive active material of Example 9.

[0046] <Example 10> Preparation of positive electrode active material The same procedure as in Example 7 was carried out, and the composition of the positive electrode active material for the lithium secondary battery that had undergone the first heat treatment was changed to Li 1.00 Ni 0.985 Al 0.014 Mg0.001 O2 to prepare the positive electrode active material of Example 10. The final composition formulas in Examples 1 to 10 are summarized in Table 1 below. [Table 1]

[0047] <Comparative Example 2> The same procedure as in Example 4 was carried out, except that active material particles were added to a 0.1 mol cobalt aqueous solution, stirred, coated, and then dried to prepare a positive active material of Comparative Example 2.

[0048] <Comparative Example 3> A positive electrode active material of Comparative Example 3 was prepared in the same manner as in Example 4, except that Co was not added during washing with water, and the Ti addition process and the second heat treatment were not performed.

[0049] <Experimental example> TEM, EDX measurement TEM and EDX images were taken of the surface of the secondary particles of the positive active material prepared in Comparative Example 2, and the results are shown in FIG. As shown in FIG. 15, in the case of the cathode active material prepared in Comparative Example 2, Co is concentrated and distributed on the particle surface due to the process of adding active material particles to a cobalt aqueous solution and stirring it. However, since no subsequent heat treatment process is performed, the surface is not flat and Co is not doped into the interior.

[0050] <Comparative Example 4> The same procedure as in Comparative Example 3 was carried out, except that Ti was added at a concentration of 0.001 mol, and a second heat treatment was performed to prepare a positive electrode active material of Comparative Example 4.

[0051] <Comparative Example 5> The cathode active material for a lithium secondary battery was prepared in the same manner as in Comparative Example 3, and the first heat treatment was performed thereon, but without performing the water washing process, to prepare a cathode active material for Comparative Example 5.

[0052] <Comparative Example 6> The same procedure as in Comparative Example 3 was carried out, and the composition of the positive electrode active material for a lithium secondary battery that had been subjected to the first heat treatment was Li 1.00 Ni 0.815 Co 0.15 Al 0.014 The positive electrode active material of Comparative Example 6 was prepared by using O2.

[0053] <Comparative Example 7> The same procedure as in Comparative Example 4 was carried out, and the composition of the positive electrode active material for a lithium secondary battery that had been subjected to the first heat treatment was Li 1.02 Ni 0.903 Co 0.08 Al 0.014 Mg 0.003 The cathode active material of Comparative Example 7 was prepared by using O2.

[0054] <Comparative Example 8> The same procedure as in Comparative Example 4 was carried out, and the composition of the positive electrode active material for a lithium secondary battery that had been subjected to the first heat treatment was Li 1.00 Ni 0.965 Co 0.02 Al 0.014 Mg 0.001 O2 to prepare a positive electrode active material of Comparative Example 8.

[0055] <Comparative Example 9> The same procedure as in Comparative Example 4 was carried out, and the composition of the positive electrode active material for a lithium secondary battery that had been subjected to the first heat treatment was Li 1.00 Ni 0.985 Al 0.014 Mg 0.001 O2 to prepare a positive electrode active material of Comparative Example 9. The final composition formulas obtained by the primary firing in the above-mentioned Comparative Examples 1 to 9 are summarized in the following . [Table 2]

[0056] <Experimental example> TEM, EDX measurement TEM and EDX images were taken of the surface of the secondary particles of the positive active material prepared in Comparative Example 4, and the results are shown in FIG. As can be seen from FIG. 16, in the case of the cathode active material prepared in Comparative Example 4, a Co coating process was not performed after the preparation of the active material, and therefore the Co concentration was uniformly distributed within the particles, and no Co concentration gradient was observed from the surface to the interior of the particles.

[0057] <Experimental Example> Measurement of distance between crystal structures The diffraction pattern and interplanar distance were measured for the surface portions of the secondary particles of the positive active material prepared in Comparative Example 4, and the results are shown in FIG. As shown in FIG. 17, the diffraction pattern of the surface portion had a hexagonal structure, and the interplanar distance was measured to be 4.85 nm. The diffraction pattern and interplanar distance of the primary particles located inside the secondary particles of the positive active material prepared in Comparative Example 4 were measured, and the results are shown in FIG. As shown in FIG. 18, the diffraction pattern of the primary particles located inside the secondary particles of the positive electrode active material has a hexagonal structure, and the interplanar distance is measured to be 4.83 nm. This indicates that when no Co coating is performed, the interplanar distance between the primary particles located inside the secondary particles of the positive electrode active material and the primary particles located on the surface is almost similar even after the second heat treatment.

[0058] <Experimental Example> Measurement of distance between crystal structures at the boundary surface of primary particles The diffraction pattern and interplanar distance at the boundary surface of the primary particle located on the surface of the secondary particle of the positive active material prepared in Comparative Example 4 were measured and the results are shown in FIG. As shown in FIG. 19, the diffraction pattern at the boundary of the primary particles located on the surface of the secondary particles was a hexagonal structure, and the interplanar distances were measured to be 4.81 nm and 4.88 nm. 18 and 19, when no Co coating is performed, the diffraction patterns and interplanar distances inside and on the boundary surfaces of the primary particles are similar.

[0059] <Experimental Example> Concentration scanning The concentrations of Ni, Co, and Al were measured from the surface to the core of the secondary particles of the positive electrode active material prepared in Comparative Example 4, and the results are shown in FIG. It can be seen from FIG. 20 that in the case of the cathode active material prepared in Comparative Example 4 of the present invention, the concentrations of Ni, Co, and Al are constant within the particles.

[0060] <Experimental Example> Concentration scanning The concentrations of Ni, Co, and Al were measured in the direction parallel to the surface of the primary particles located on the surfaces of the secondary particles of the positive active material prepared in Comparative Example 4, and the results are shown in FIG. As can be seen from FIG. 21, in the case of the cathode active material prepared in Comparative Example 4, the concentrations of Ni, Co, and Al are constant within the particles, and since no Co coating is performed, the Co concentration does not show a gradient, and the interplanar distance is similar between the surface and the interior.

[0061] <Experimental Example> XRD Measurement XRD measurements were performed on the LiCoO2 positive electrode active materials of Example 4 and Comparative Example 1, and the results are shown in FIGS. 22 and 23. As shown in FIGS. 22 and 23, in the case of the Co and Ti coated cathode active material prepared in Example 4 of the present invention, (104), (110), (113), (101), (102), and (003) peaks were detected, similar to the LiCoO2 of Comparative Example 1.

[0062] <Experimental Example> XRD Measurement The positive electrode active material of Comparative Example 2 was subjected to XRD measurement, and the results are shown in FIG. As shown in FIG. 24, in the case of the positive electrode active material produced in Comparative Example 2 of the present invention, only the peaks due to Co(OH)2 were detected, and the (104), (110), (113), (101), (102), and (003) peaks that are characteristically detected in LiCoO2 were not detected.

[0063] <Experimental Example> XRD Measurement XRD measurements were performed on the positive electrode active materials of Comparative Example 4, which was not Co-coated, and Example 4, which was Co-coated and then heat-treated. The results are shown in FIG. As shown in FIG. 25, in the case of the positive electrode active material of Comparative Example 4, which is not subjected to the Co coating of the present invention, the (104), (110), (113), (101), (102), and (003) peaks that are characteristically detected in LiCoO2 are not detected.

[0064] <Experimental Example> XPS Measurement XPS was measured for the positive electrode active materials of Comparative Example 4 in which no Co coating was performed and Example 3 in which coating was performed with a cobalt aqueous solution having a concentration of 5 mol %, and the results are shown in FIG. 26, when cobalt coating is performed during the water washing process according to the present invention, the intensity of the Co 2p peak is greater than that of Comparative Example 4, and it can be seen that most of this peak is due to Co+3. It can also be seen that the intensity of the peak due to LI2CO3 is reduced compared to Comparative Example 4.

[0065] <Experimental Example> Residual Lithium Measurement The residual lithium in the composite oxides prepared in Examples 1 to 10 and Comparative Examples 4 to 9 was measured, and the results are shown in Table 3 below. To measure the residual lithium, 1 g of the active material was immersed in 5 g of distilled water and stirred for 5 minutes. The filtrate was taken and dissolved in 0.1 M HCl. The volume of HCl added until the pH of the filtrate reached 5 was measured to analyze the residual lithium of the active material. As can be seen from Table 3 below, in the case of the active material prepared according to the embodiment of the present invention, the amount of residual lithium is significantly reduced compared to the case of Comparative Example 5 where no calcination process is performed. [Table 3]

[0066] <Manufacturing example> Battery manufacturing The positive electrode active materials prepared in Examples 1 to 10 and Comparative Examples 4, 6 to 9 were mixed with Super-P as a conductive agent and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 92:5:3 to prepare a slurry. The slurry was uniformly coated on a 15 μm thick aluminum foil and dried in a vacuum at 135°C to prepare a positive electrode for a lithium secondary battery. A coin battery was fabricated using the positive electrode and a lithium wheel as counter electrodes, a porous polyethylene film (Celgard LLC, Celgard 2300, thickness: 25 μm) as a separator, and a liquid electrolyte in which LiPF6 was dissolved at a concentration of 1.15 M in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, according to a commonly known manufacturing process.

[0067] <Experimental Example> Battery characteristic measurement - Initial capacity The initial capacities of the batteries manufactured using the active materials manufactured in Examples 1 to 10 and Comparative Examples 4, 6 to 9 were measured, and the results are shown in Figure 27a (Examples 1 to 4, Comparative Example 4), Figure 27b (Example 5, Comparative Example 6), Figure 27c (Example 6, Comparative Example 7), Figure 27d (Examples 7 to 9, Comparative Example 8), and Figure 27e (Example 10, Comparative Example 9). Referring to FIGS. 27a to 27e, it was found that the capacity and efficiency characteristics of the Co-coated battery according to the embodiment of the present invention were superior to those of the comparative example. The initial capacity measurement results of the batteries manufactured using the active materials manufactured in Examples 1 to 10 and Comparative Examples 4, 6 to 9 are summarized in Table 4 below. [Table 4]

[0068] <Experimental Example> Battery characteristic measurement - efficiency characteristics The efficiency characteristics of the batteries manufactured using the active materials prepared in Examples 1 to 10 and Comparative Examples 4, 6 to 9 were measured, and the results are shown in Figure 28a (Examples 1 to 4, Comparative Example 4), Figure 28b (Example 5, Comparative Example 6), Figure 28c (Example 6, Comparative Example 7), Figure 28d (Examples 7 to 9, Comparative Example 8), and Figure 28e (Example 10, Comparative Example 9). Referring to FIGS. 28a to 28e, it was found that the capacity and efficiency characteristics of the Co-coated battery according to the embodiment of the present invention were superior to those of the comparative example. The efficiency characteristics of the batteries manufactured using the active materials manufactured in Examples 1 to 10 and Comparative Examples 4, 6 to 9 are shown in Table 5 below. [Table 5]

[0069] <Experimental Example> Battery characteristic measurement - life characteristics The life characteristics of the batteries manufactured using the active materials manufactured in Examples 1 to 10 and Comparative Examples 4, 6 to 9 were measured, and the results are shown in Figure 29a (Examples 1 to 4, Comparative Example 4), Figure 29b (Example 5, Comparative Example 6), Figure 29c (Example 6, Comparative Example 7), Figure 29d (Examples 7 to 9, Comparative Example 8), and Figure 29e (Example 10, Comparative Example 9). 28a to 28e, it can be seen that when Co coating is performed according to the embodiment of the present invention, the life characteristics are improved compared to the comparative example. The results of measuring the life characteristics of the batteries manufactured using the active materials manufactured in Examples 1 to 10 and Comparative Examples 4, 6 to 9 are summarized in Table 6 below. [Table 6]

[0070] <Experimental Example> Battery characteristic measurement - High temperature storage characteristics The high-temperature storage characteristics of the batteries manufactured using the active materials manufactured in Examples 1 to 3, 5 to 10 and Comparative Examples 4, 6 to 9 were measured, and the results before storage are shown in Figure 30a (Examples 1 to 3, Comparative Example 4), Figure 30b (Example 5, Comparative Example 6), Figure 30c (Example 6, Comparative Example 7), Figure 30d (Examples 7 to 9, Comparative Example 8), and Figure 30e (Example 10, Comparative Example 9), and the results after storage are shown in Figure 31a (Examples 1 to 3, Comparative Example 4), Figure 31b (Example 5, Comparative Example 6), Figure 31c (Example 6, Comparative Example 7), Figure 31d (Examples 7 to 9, Comparative Example 8), and Figure 31e (Example 10, Comparative Example 9). Referring to Figures 30a to 30e and Figures 31a to 31e, when Co coating is performed according to the embodiment of the present invention, the impedance does not increase significantly after high temperature storage compared to the comparative example, and therefore the high temperature storage characteristics are significantly improved. The results of measuring the high-temperature storage characteristics of the batteries manufactured using the active materials manufactured in Examples 1 to 3, 5 to 10 and Comparative Examples 4, 6 to 9 are summarized in Table 7 below. [Table 7]

Claims

1. Lithium composite oxide secondary particles formed by agglomeration of a plurality of primary particles, the primary particles located within the surface portions of the secondary particles include a Co coating layer in a portion in contact with the surface of the secondary particles, the secondary particles include lithium, nickel, and cobalt; The lithium composite oxide secondary particles have a hexagonal structure, the thickness of the surface portion of the secondary particles is 0.3 to 1 μm; The secondary particles of the lithium composite oxide have a residual lithium content of 6000 ppm or less, The secondary particles have the following peak intensity ratios of 289 eV (I289) and 284.5 eV (I284) in C 1s core-level spectrum analysis obtained through XPS measurement: 0<(I289) / (I284)≦0.9 a thickness of the Co coating layer formed in the portion of the primary particle located in the surface portion of the secondary particle in contact with the surface of the secondary particle is 50 to 150 nm; The secondary particles are represented by the following <Chemical Formula 1>: 【Chemistry 1】 (In the <Chemical Formula 1>, M1 is Mn or Al, M2 and M3 are metals selected from the group consisting of Ba, B, Co, Ce, Cr, F, Li, Mg, Mn, Mo, P, Sr, Ti, and Zr, and 0.95≦X1≦1.05, 1.50≦a≦2.1, 0.02≦x1≦0.25, 0.01≦y1≦0.20, 0≦z1≦0.20, and 0≦r1≦0.20) The lithium composite oxide secondary particles are characterized in that they satisfy the following <Relational Formula 1>. <Relationship 1> d1>d2 (wherein d1 is the average distance between a total of 10 adjacent crystal structures in the primary particles located inside the secondary particles among the plurality of primary particles, as measured from the diffraction pattern, and d2 is the average distance between a total of 10 adjacent crystal structures in the primary particles located within the surface portions of the secondary particles, as measured from the diffraction pattern).

2. The lithium composite oxide secondary particles according to claim 1, wherein the primary particles located within the surface regions of the secondary particles exhibit a Co concentration gradient of 0.05 to 0.07 Co mol % per 1 nm in the particle center direction.

3. 2. The lithium composite oxide secondary particles according to claim 1, wherein the primary particles located within the surface portion of the secondary particles have a dc / dh ratio of 2 to 10, where dc is the length in the central direction and dh is the length in the direction perpendicular to the center.

4. The secondary particles are characterized in that, in an O 1s core-level spectrum analysis obtained through XPS measurement, the ratio of a peak intensity (I531) around 531 eV to a peak intensity (I528) around 528.5 eV is as follows: 0<(I531) / (I528)≦2 The lithium composite oxide secondary particles according to claim 1 .

5. A first step of preparing a positive electrode active material precursor for a lithium secondary battery represented by the following <Chemical Formula 2>; 【Chemistry 2】 (In the <Chemical Formula 2>, M1 is Mn or Al, M2 is a metal selected from the group consisting of Al, Ba, B, Co, Ce, Cr, F, Li, Mg, Mn, Mo, P, Sr, Ti, and Zr, and 0≦x2≦0.20, 0≦y2≦0.20, and 0≦z2≦0.20) a second step of reacting the positive electrode active material precursor for a lithium secondary battery with a lithium compound and performing a first heat treatment to produce a positive electrode active material; a third step of washing the positive electrode active material with distilled water or an alkaline aqueous solution; a fourth step of coating the washed positive electrode active material with a solution containing Co; a fifth step of drying the particles of the positive electrode active material; a sixth step of mixing the dried cathode active material with an element selected from the group consisting of Al, Ba, B, Co, Ce, Cr, F, Mg, Mn, Mo, P, Sr, Ti, and Zr, and performing a second heat treatment to dope the element into the interior of the particles; The method for producing secondary particles of lithium composite oxide according to claim 1, characterized in that the method comprises:

6. The method for producing secondary particles of lithium composite oxide according to claim 1, wherein the concentration of the solution containing Co in the fourth step is 1 to 10 mol %.

7. A lithium secondary battery comprising the lithium composite oxide secondary particles according to claim 1.

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