Composite cathode active material for lithium secondary battery, preparing method thereof, and lithium secondary battery cathode including the same

Abstract

A composite cathode active material for a lithium secondary battery comprising a lithium cobalt-based oxide, wherein a particle coating portion is arranged in an island shape on one surface of the lithium cobalt-based oxide, and the particle coating portion comprises a first coating layer containing a lithium titanium-based oxide, wherein a lithium-deficient cobalt oxide phase is included in an internal region of the lithium cobalt-based oxide arranged corresponding to the particle coating portion, such that the molar ratio of lithium to cobalt is 0.9 or less, and a first lithium zirconium-based oxide existing in a spaced-away state from the surface of the lithium cobalt-based oxide is provided. A method for manufacturing the composite cathode active material and a lithium secondary battery containing the cathode comprising the same are also provided.

Description

Technology Field

[0001] The invention relates to a composite cathode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery containing a cathode including the same. Background Technology

[0002] With the recent development of the advanced electronics industry, the miniaturization and lightweighting of electronic equipment have become possible, leading to an increase in the use of portable electronic devices. As a power source for these portable electronic devices, lithium-ion batteries, which have high energy density and can be used for a long time, are widely used.

[0003] Lithium cobalt oxide (LiCoO2) is widely used as a positive electrode active material for high-density lithium secondary batteries. However, when lithium cobalt oxide is used as a positive electrode active material, the material comes into contact with the electrolyte in the battery environment, and the interfacial structure is destroyed due to corrosion by HF, especially at high temperatures, leading to the leaching of cobalt (Co) and a reduction in capacity.

[0004] Lithium cobalt oxide is doped with aluminum to prevent structural collapse of the layered cathode active material in high-voltage environments. However, when aluminum is doped in this way, the high-voltage characteristics do not reach a satisfactory level, so improvement is required. The problem to be solved

[0005] One aspect is to provide a novel composite cathode active material for a lithium secondary battery with improved stability and a method for manufacturing the same.

[0006] Another aspect is to provide a lithium secondary battery containing a cathode comprising the aforementioned composite cathode active material for lithium secondary batteries, which has improved stability at high voltage and enhanced high-temperature characteristics. means of solving the problem

[0007] According to one side

[0008] A composite cathode active material for lithium secondary batteries containing lithium cobalt-based oxide, and

[0009] A particle coating portion is arranged in an island shape on one surface of the above-mentioned lithium cobalt-based oxide, and the particle coating portion includes a first coating layer containing a lithium titanium-based oxide.

[0010] The internal region of the lithium cobalt-based oxide disposed corresponding to the particle coating portion comprises a lithium-deficient cobalt oxide phase having a molar ratio of lithium to cobalt of 0.9 or less, and

[0011] A composite cathode active material for a lithium secondary battery is provided, comprising a first lithium zirconium-based oxide existing spaced apart from the surface of a lithium cobalt-based oxide.

[0012] A step of obtaining a first precursor mixture by mixing the lithium cobalt-based oxide, titanium precursor, and cobalt hydroxide described above according to another aspect, and heat-treating the first precursor mixture;

[0013] A method for manufacturing a composite cathode active material for a lithium secondary battery described above is provided, comprising the step of mixing the first heat-treated product and a zirconium precursor to obtain a second precursor mixture, and performing a second heat treatment on the second precursor mixture.

[0014] The content of the zirconium precursor is 0.6 to 1.4 parts by weight based on 100 parts by weight of the lithium cobalt-based oxide. And the content of the cobalt hydroxide is 3.5 to 7 parts by weight based on 100 parts by weight of the lithium cobalt-based oxide.

[0015] The heat treatment of the first precursor mixture is carried out at 850°C to 980°C, and the heat treatment of the second precursor mixture is carried out at 950°C to 1000°C.

[0016] According to another aspect, a lithium secondary battery containing a positive electrode including the positive electrode active material described above is provided. Effects of the invention

[0017] The composite cathode active material according to one embodiment not only improves conductivity but also has a surface phase transition suppression effect and can suppress surface side reactions with the electrolyte. By providing a cathode containing such a composite cathode active material, a lithium secondary battery with improved high voltage characteristics can be manufactured. Brief explanation of the drawing

[0018] Figure 1a schematically shows the structure of a composite cathode active material according to one embodiment. Figure 1b is an enlarged view of the particle coating portion of Figure 1a. FIG. 1c shows the structure of a composite cathode active material according to another embodiment. Figure 1d is an enlarged view of a portion of Figure 1c. Figure 1e shows an enlarged view of a portion of Figure 1a. Figures 2a and 2b show high-resolution transmission electron microscopy (HR-TEM) analysis images of a composite cathode active material prepared according to Example 1. Figures 3a to 3h show the results of scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS) analysis of the composite cathode active material prepared according to Example 1. Figure 4 schematically shows the structure of a lithium secondary battery according to one embodiment. Figures 5, 6a to 6f show the results of SEM-EDS (energy dispersive X-ray spectroscopy) analysis for the composite cathode active material prepared according to Example 1. Figures 7a and 7b are the TEM analysis results for the composite cathode active material of Example 1. Figure 7c is the SEM analysis result of the composite cathode active material of Example 1. Figure 8a shows the TEM analysis results for the composite cathode active material of Example 1. Figure 8b is a TEM image of the lithium-deficient cobalt oxide phase A1 region of Figure 8a. Figure 8c is a TEM image of the surface coating area A2 of Figure 8a. FIGS. 9a to 9e are analysis results for evaluating conductivity in the bulk region, particle coating region, and surface coating region of the composite cathode active material obtained according to Example 1. Figures 10a to 10e show the results of energy filtering transmission electron microscope and electron beam energy loss (EF-TEM & EELS) analysis of the composite cathode active material of Example 1. Figures 11a to 11d show the results of HR-TEM analysis. Figures 12a to 12c show the HR-TEM analysis results for the composite cathode active material of Example 1. Figure 13a shows the TEM-EDS analysis results for the composite cathode active material of Example 1. Figures 13b and 13c show the TEM-EDS analysis results in region 1 and region 2 of the composite cathode active material of Example 1. Specific details for implementing the invention

[0019] A composite cathode active material according to exemplary embodiments, a method for manufacturing the same, and a lithium secondary battery having a cathode including the same will be described in more detail below.

[0020] A composite cathode active material for a lithium secondary battery is provided, comprising a lithium cobalt-based oxide, wherein a particle coating portion is arranged in an island shape on the surface of the lithium cobalt-based oxide, the particle coating portion comprises a first coating layer containing a lithium titanium-based oxide, and the internal region of the lithium cobalt-based oxide arranged corresponding to the particle coating portion comprises a lithium-deficient cobalt oxide phase having a molar ratio of lithium to cobalt of 0.9 or less, and a first lithium zirconium-based oxide existing in a spaced-away state from the surface of the lithium cobalt-based oxide.

[0021] In the internal region of the lithium cobalt-based oxide arranged corresponding to the particle coating portion, the meaning of "arranged corresponding to the particle coating portion" indicates that the internal region is located at the periphery of the particle coating portion, and the internal region may be arranged in contact with the particle coating portion or spaced apart from it.

[0022] The internal region disposed in contact with the particle coating portion of the lithium cobalt-based oxide is hereinafter referred to as the "first internal region." Furthermore, the first lithium zirconium-based oxide is included in a particle state at a location spaced apart from the internal region.

[0023] A surface coating portion is disposed in the internal region of the other surface of the lithium cobalt-based oxide, and the surface coating portion contains a third coating layer having a spinel crystal structure. The internal region of the other surface of the lithium cobalt-based oxide represents the remaining region of the lithium cobalt-based oxide excluding the first internal region, and is indicated as the "second internal region." Furthermore, the other surface of the lithium cobalt-based oxide represents the remaining surface (i.e., the second surface) excluding the surface of the lithium cobalt-based oxide where the particle coating portion is formed (i.e., the first surface).

[0024] Lithium cobalt oxide (LiCoO2) is a high-capacity cathode active material that has a structure in which lithium, cobalt, and oxygen are regularly arranged along the

[0111] crystal plane of a rock salt structure, i.e., an O3-type layered structure. When a lithium secondary battery equipped with a cathode containing such lithium cobalt oxide is charged, lithium ions are deintercalated out of the crystal lattice of the lithium cobalt oxide.

[0025] When the charging voltage of a lithium secondary battery increases, the amount of lithium ions deintercalated in the crystal lattice of lithium cobalt oxide increases, and at least a portion of the O3-type layered structure may undergo a phase transition to an O1-type layered structure (O1 phase) in which Li is not present in the crystal lattice. Accordingly, in the range where the charging voltage is 4.52V or higher (based on a full cell), a phase transition may occur to an H1-3-type layered structure (H1-3 phase) in which both the O3-type and O1-type layered structures exist within the crystal lattice of lithium cobalt oxide. Thus, the phase transition from the O3-type layered structure to the H1-3-type layered structure and the O1-type layered structure is at least partially irreversible. Furthermore, in the H1-3-type layered structure and the O1-type layered structure, the amount of lithium ions capable of intercalation / deintercalation decreases. When such a phase transition occurs, the storage and lifespan characteristics of the lithium secondary battery are inevitably subject to rapid degradation. In addition, when lithium cobalt oxide comes into contact with the electrolyte, the interfacial structure is destroyed due to corrosion by HF, especially at high temperatures, leading to Co leaching and capacity reduction, and structural collapse of the layered cathode active material may occur in a high-voltage environment.

[0026] To solve the aforementioned problems, it has been proposed to use aluminum and magnesium-doped lithium cobalt oxide as a positive electrode active material. However, lithium secondary batteries employing a positive electrode using such a positive electrode active material do not achieve satisfactory high-voltage characteristics, so improvement is required.

[0027] The composite cathode active material according to one embodiment was devised to solve the above-mentioned problems, and has a structure in which a lithium cobalt-based oxide having a predetermined amount of aluminum and magnesium is reacted with titanium (Ti), zirconium (Zr), and cobalt (Co) precursors, and the magnesium of the lithium cobalt-based oxide moves to the surface, and through the Mg-Ti Kirkendall effect, a particle coating part having a first coating layer containing a lithium titanium-based oxide is formed in an island shape on the surface of the lithium cobalt-based oxide.

[0028] The above lithium cobalt-based oxide has a layered structure of the R-3m rhombohedral system. A surface coating having a spinel crystal structure is formed on the lithium cobalt-based oxide. Here, the surface coating may contain, for example, lithium cobalt-based oxide A. Lithium cobalt-based oxide A is, for example, LiCo2O4. Here, lithium cobalt-based oxide A is distinguished from the lithium cobalt-based oxide that is the core active material.

[0029] In the composite cathode active material according to one embodiment, the reaction area between the composite cathode active material and the electrolyte is reduced due to the presence of the particle coating portion and the surface coating portion described above, thereby efficiently suppressing side reactions.

[0030] Additionally, a first lithium zirconium-based oxide is located spaced apart from the surface where the particle coating portion is formed in the lithium cobalt-based oxide. To explain this more specifically, the first lithium zirconium-based oxide may exist spaced apart from the first surface and / or the second surface of the lithium cobalt-based oxide in a second internal region that is in contact with the first internal region and / or the second surface of the lithium cobalt-based oxide.

[0031] In the composite cathode active material according to one embodiment, the first lithium zirconium-based oxide may contain a greater amount of particles at a location spaced apart from the first internal region than at a location spaced apart from the second internal region. The presence of the above-described first lithium zirconium-based oxide provides excellent surface stabilization and surface phase transition suppression effects at high voltage, and further improves conductivity.

[0032] A lithium-deficient cobalt oxide phase is included in the region in contact with the particle coating portion within the above lithium cobalt-based oxide, wherein the molar ratio of lithium to cobalt is 0.9 or less. Here, the lithium-deficient cobalt oxide phase has p-semiconductor characteristics, which improves the electrical conductivity of the composite cathode active material and exhibits excellent capacity, lifespan, and output characteristics, particularly under high voltage conditions.

[0033] A composite cathode active material according to one embodiment is a lithium cobalt-based oxide, and a particle coating portion is disposed in an island shape on one surface (i.e., a first surface) of the lithium cobalt-based oxide, and a surface coating portion is disposed in a first internal region that is in contact with or adjacent to another surface (i.e., a second surface) of the lithium cobalt-based oxide.

[0034] The above particle coating part includes a first coating layer containing lithium titanium-based oxide.

[0035] A second coating layer containing a second lithium zirconium-based oxide may be further included on the upper portion of the first coating layer. The surface coating portion includes a third coating layer having a spinel crystal structure and is present in a first internal region of the lithium cobalt-based oxide in contact with the particle coating portion, and includes a lithium-deficient cobalt oxide phase in which the molar ratio of lithium to cobalt is 0.9 or less and lithium is deficient.

[0036] The above lithium cobalt-based oxide contains magnesium and aluminum. The content of aluminum (Al) in the lithium cobalt-based oxide is 4,000 ppm or more, for example, 4,000 to 6,000 ppm. In this specification, the aluminum ppm content refers to the mass of aluminum per million of the total mass of the cathode active material.

[0037] The aluminum content is 1.5 mol% to 3.0 mol%, or 2.0 mol% to 2.5 mol%, based on the total metals excluding lithium in the core active material. When the aluminum content is within the above range, the structural stability of the composite cathode active material is improved, thereby enabling the production of a composite cathode active material with minimized high-voltage characteristics, capacity reduction, and resistance increase. Additionally, the magnesium (Mg) content in the lithium cobalt-based oxide is 1,000 ppm or more, for example, 1,000 to 1,500 ppm. In this specification, the magnesium ppm content refers to the mass of magnesium per million of the total cathode active material mass.

[0038] The magnesium content is 0.25 mol% to 0.7 mol% based on the total metal content of the core active material. In addition, in the composite cathode active material according to one embodiment, the titanium content is 500 to 800 ppm and the zirconium content is 2,100 to 4,000 ppm. In this specification, the ppm content of titanium refers to the mass of titanium per million total mass of the cathode active material, and the ppm content of zirconium refers to the mass of zirconium per million total mass of the cathode active material.

[0039] Even if the aluminum content in the composite cathode active material is 4000 ppm or more as described above, the phenomenon of aluminum diffusing into the coating layer as the Al content increases hardly occurs, and some Al can be doped into Li sites, thereby performing a structural stabilization effect. Therefore, it has excellent high-temperature characteristics and improved surface resistance, resulting in excellent conductivity. Consequently, this composite cathode active material improves the structural stability of the crystal structure of the lithium cobalt-based oxide even under high temperature and high voltage environments, and thus enables the realization of a cathode active material with excellent lifespan and storage characteristics and improved resistance characteristics.

[0040] In this specification, the high voltage is in the range of 4.3V to 4.8V.

[0041] In a composite cathode active material according to one embodiment, the ratio of the magnesium content to the cobalt content contained in the lithium-deficient cobalt oxide (moles of magnesium / moles of cobalt) is greater than the ratio of the magnesium content to the cobalt content of the lithium cobalt-based oxide (moles of magnesium / moles of cobalt). This magnesium content distribution is formed by the movement of magnesium in the lithium cobalt-based oxide through the Mg-Ti Kirkendall effect.

[0042] Figure 1a schematically shows the structure of a composite cathode active material according to one embodiment.

[0043] Referring to FIG. 1a, the composite cathode active material (10) comprises a particle coating portion (12) and a surface coating portion (13) on at least one surface, i.e., a first surface (17a), of a lithium cobalt-based oxide (11), and the particle coating portion (12) and the surface coating portion (13) may have a layered form.

[0044] As shown in FIG. 1b, the particle coating portion (12) contains a first coating layer (12a) containing a lithium titanium oxide that is placed in contact with a lithium cobalt oxide, and a second coating layer (12b) containing a second lithium zirconium oxide that is placed on top of the first coating layer (12).

[0045] A first lithium zirconium-based oxide (15) may exist spaced apart from the first surface (17a) in contact with the particle coating portion (12). As shown in FIG. 1d, the first lithium zirconium-based oxide (15) is positioned spaced apart from the first surface (17a) by a predetermined distance h. Here, the spaced distance h is 150 nm or less, or 140 nm or less, for example, 90 nm to 140 nm.

[0046] The first lithium zirconium-based oxide is in a particulate state and may exist in an island form. The particle size is 0.5 to 3 μm. As shown in FIG. 1a, the first lithium zirconium oxide is distributed spaced apart from each other in the x-axis direction.

[0047] FIG. 1e is an enlarged view of a portion of FIG. 1a, wherein a particle coating portion (12) is disposed on top of a lithium cobalt-based oxide, a lithium-deficient cobalt oxide phase (14) exists below the particle coating portion (12), and a first lithium zirconium-based oxide (15) exists below it. FIG. 1e is illustrated as having the lithium-deficient cobalt oxide phase (14) and the first lithium zirconium-based oxide (15) existing in separate layers. Alternatively, the structure may have a lithium-deficient cobalt oxide phase (14) and the first lithium zirconium-based oxide (15) formed in a single layer.

[0048] In this specification, particle size refers to the average particle diameter when the particles are spherical, and the major axis length when the particles are non-spherical, such as plate-shaped or needle-shaped. Particle size can be verified using a particle size measuring instrument, a scanning electron microscope, or a transmission electron microscope. The average particle diameter may be expressed as, for example, D50.

[0049] Unless otherwise specifically defined in this specification, D50 refers to the average diameter of a particle corresponding to 50% of the cumulative volume in a particle size distribution, and in a distribution curve accumulated from the smallest particle to the largest particle, it refers to the value of the particle diameter corresponding to 50% of the smallest particle when the total number of particles is set to 100%. The average particle diameter (D50) can be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer (e.g., HORIBA, LA-950 laser particle size analyzer) or by measuring from TEM or SEM images. Alternatively, the average particle diameter (D50) can be easily obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this.

[0050] The first lithium zirconium-based oxide (15) described above may exist in a first internal region or outside the first internal region where the lithium-deficient cobalt oxide phase (14) described later exists.

[0051] The first lithium zirconium-based oxide (15) may also exist in a second internal region in contact with the second surface (17b) of the lithium cobalt-based oxide, although this is not shown in the drawing.

[0052] According to one embodiment, the first lithium zirconium-based oxide (15) is located below the particle coating portion (12). Here, the first lithium zirconium-based oxide (15) has a layered structure. The presence and crystal structure of the first lithium zirconium-based oxide can be confirmed from HR-TEM. The layered structure of the first lithium zirconium-based oxide described above is maintained even after repeatedly performing charge-discharge cycles for the lithium secondary battery. Here, the number of charge-discharge cycles is, for example, 100 times or more.

[0053] In FIG. 1a, the particle coating portion (12) has a semicircular shape, but this does not mean that it is limited to this shape. When the particle coating portion exists in an island shape, the surface resistance of the composite cathode active material is improved compared to when it has a continuous shape. The size of the particle coating portion is 3.0 µm or less, for example, 0.5 to 3 µm. Here, the size of the particle coating portion represents the major axis length and can be measured using a scanning electron microscope or a transmission electron microscope.

[0054] A surface coating portion (13) exists in the second internal region in contact with the second surface (17b) of the lithium cobalt-based oxide (11). The surface coating portion (13) contains a third coating layer having a spinel crystal structure. The presence of such a surface coating portion improves the high-temperature life characteristics of the composite cathode active material.

[0055] The lithium-deficient cobalt oxide phase (14) is present in a first inner region in contact with the particle coating portion (12) of the lithium-cobalt-based oxide (11), and is in a lithium-deficient state with a molar ratio of lithium to cobalt of 0.9 or less. The lithium-deficient cobalt oxide phase (14) is present in a region of 1.3 µm or less, 1 µm or less, 900 nm or less, 800 nm or less, 500 nm or less, or 100 nm or less from the outermost surface of the lithium-cobalt-based oxide, or is present in a region corresponding to a distance of 90 to 100% from the center of the particle with respect to the radius of the lithium-cobalt-based oxide. The presence of the lithium-deficient cobalt oxide phase (14) can be confirmed through SEM and / or TEM analysis.

[0056] In the present specification, the first surface (17a) refers to one surface of the lithium cobalt-based oxide (11) on which a particle coating layer (12) is formed as shown in FIG. 1a. The second surface (17b) refers to another surface of the lithium cobalt-based oxide (11) on which a surface coating portion (13) is formed. The third surface (17c) refers to yet another surface of the lithium cobalt-based oxide (11) on which a lithium-deficient cobalt oxide phase (14) exists while being disposed in contact with the particle coating portion (12).

[0057] In FIG. 1a, the total surface of the composite cathode active material is shown as being composed of a first surface (17a), a second surface (17b), and a third surface (17c). Alternatively, as shown in FIG. 1c, the total surface of the composite cathode active material may be composed of a first surface (17a) and a second surface (17b), and a third surface may not exist. That is, the total surface of the lithium cobalt-based oxide may be composed of a first surface and a second surface, or may be composed of a first surface, a second surface, and a third surface. The first surface exists in the first internal region of the lithium cobalt-based oxide, and the second surface exists in the second internal region of the lithium cobalt-based oxide. And the third surface may exist in the first internal region as shown in FIG. 1a.

[0058] In the composite cathode active material according to one embodiment, the lithium-deficient cobalt oxide has a spinel crystal structure (Co3O4 Spinel phase (Fd-3m)). And the content of the lithium-deficient cobalt oxide phase is 0.1 to 1 weight part based on 100 weight parts of lithium cobalt-based oxide.

[0059] The above lithium-deficient cobalt oxide phase contains, for example, a compound represented by the following chemical formula 5, a compound represented by chemical formula 5-1, a compound represented by chemical formula 5-2, or a combination thereof.

[0060] [Chemical Formula 5]

[0061] Li 1-α Mg a Co 1-x M xO2

[0062] In the formula 5, M is W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, Nb or a combination thereof, and 0.1≤α≤0.5, 0 <a≤0.05, 0≤x≤0.05이고,

[0063] [Chemical Formula 5-1]

[0064] Li 1-α Mg a Co 2-x M x O4

[0065] In Chemical Formula 5-1, M is W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, Nb or a combination thereof, and 0.1≤α≤0.5, 0 <a≤0.05, 0≤x≤0.05이고,

[0066] [Chemical Formula 5-2]

[0067] Co 3-x M x O4

[0068] In chemical formula 5-2, M is W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, Nb or a combination thereof, and 0≤x≤0.05.

[0069] Lithium-deficient cobalt oxide phases are, for example, Co3O4, LiCo2O4, Li 0.8 Mg 0.007 CoO 2,

[0070] or includes that combination.

[0071] The composite positive active material (10) is provided with a particle coating portion (12) and is coated with a conductive material.

[0072] The resistance can be controlled to be low, and an excellent surface stabilization effect is obtained through the formation of the surface coating portion (13).

[0073] In the composite cathode active material, the first lithium zirconium-based oxide (15) can be, for example, a compound represented by the following chemical formula 6.

[0074] [Chemical Formula 6]

[0075] Li 2+a Zr (1-x-z) Co z M1 x O3

[0076] In Chemical Formula 6, M1 is one or more elements selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and aluminum (Al), and

[0077] -0.1≤a≤0.1, 0≤x<1, 0≤z≤0.5.

[0078] Compounds represented by chemical formula 6 are, for example, Li2Zr 0.95 Co 0.05 O3 can be cited.

[0079] The thickness of the particle coating portion (12) is, for example, 100 to 500 nm.

[0080] According to one embodiment, the particle coating portion (12) includes a first coating layer.

[0081] According to another embodiment, the particle coating portion (12) has a structure in which a second coating layer (12b) is disposed on top of a first coating layer (12a) as shown in FIG. 1b, and the boundary between the first coating layer (12a) and the second coating layer (12b) may be formed non-uniformly. According to FIG. 1b, the boundary between the first coating layer (12a) and the second coating layer (12b) is non-uniform, but in some cases, it may be formed uniformly.

[0082] The thickness of the first coating layer (12a) and the second coating layer (12b) is variable, but for example, the thickness of the first coating layer (12a) is greater than the thickness of the second coating layer (12b). The thickness of the first coating layer (12a) is 100 nm to 500 nm, and the thickness of the second coating layer (12b) is 100 nm to 300 nm. When the thickness of the first coating layer and the second coating layer is within the above range, a composite cathode active material with improved surface resistance can be obtained.

[0083] The surface coating portion (13) contains a third coating layer having a spinel crystal structure. Here, the thickness of the third coating layer is 100 nm or less, for example, 10 nm to 100 nm. The third coating layer contains, for example, lithium cobalt-based oxide A.

[0084] In this specification, the "thickness" of the particle coating portion, the first coating layer, the second coating layer, and the third coating layer refers to the major axis length if the thickness of each coating layer is non-uniform.

[0085] In the particle coating portion, the content of the lithium titanium-based oxide is 0.05 to 1.0 parts by weight based on 100 parts by weight of the lithium cobalt-based oxide, and the content of the second lithium zirconium-based oxide is 0.05 to 0.2 parts by weight based on 100 parts by weight of the lithium cobalt-based oxide. When the content of the second lithium zirconium-based oxide and the lithium zirconium cobalt oxide is within the above range, the lithium ion diffusion coefficient increases and the electrical conductivity increases, thereby allowing for the production of a composite cathode active material having a stabilized structure, suppressing side reactions with the electrolyte, and suppressing cobalt leaching.

[0086] The content of lithium cobalt-based oxide A in the third coating layer of the surface coating portion is 0.01 to 1 weight part based on 100 weight parts of lithium cobalt-based oxide. Lithium cobalt-based oxide A is, for example, LiCo2O4, and electrical conductivity is improved when the content of lithium cobalt-based compound A is within the above range.

[0087] When the content of the lithium titanium-based oxide of the first coating layer and the second lithium zirconium-based oxide of the second coating layer in the particle coating portion and the content of lithium cobalt oxide A in the surface coating portion are within the above range, a composite cathode active material can be manufactured having a structure stabilized by increasing the lithium ion diffusion coefficient and electrical conductivity, and suppressing side reactions with the electrolyte.

[0088] The lithium titanium-based oxide of the first coating layer above may be, for example, a compound represented by the following chemical formula 1.

[0089] [Chemical Formula 1]

[0090] Li 2+a Ti (1-x-y) Co x Mg y O3

[0091] In Chemical Formula 1, -0.1≤a≤0.1, 0 <x≤0.5, 0<y≤0.1이다.

[0092] In Chemical Formula 1, x is, for example, 0.01 to 0.3, 0.01 to 0.2, 0.01 to 0.1, or 0.01 to 0.05, and y is, for example, 0.01 to 0.08, 0.01 to 0.05, or 0.01 to 0.03.

[0093] Lithium titanium-based oxides are, for example, Li2Ti 0.97 Co 0.02 M 0.01 O3 can be cited.

[0094] The second lithium zirconium-based oxide of the second coating layer may be, for example, a compound represented by the following chemical formula 2.

[0095] [Chemical Formula 2]

[0096] Li 2+a Zr (1-x-z) Co z M2 x O3

[0097] In Chemical Formula 2, M2 is one or more elements selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and aluminum (Al), and

[0098] -0.1≤a≤0.1, 0≤x<1, 0≤z≤0.1.

[0099] In Chemical Formula 2, z is 0.01 to 0.1, 0.01 to 0.08, or 0.01 to 0.05.

[0100] Lithium-2 zirconium oxides are, for example, Li2Zr0.99 Co 0.01 O3, etc. can be cited.

[0101] The lithium cobalt-based oxide, which is the core active material, is a compound represented by, for example, Chemical Formula 3 below.

[0102] [Chemical Formula 3]

[0103] Li a-b Mg b Co (1-x-y-b) Al x M3 y O2

[0104] In Chemical Formula 3, 0.9≤a≤1.1, 0≤b≤0.02, 0≤x≤0.04, 0≤y≤0.01, and

[0105] M3 is Ni, K, Na, Ca, Mg, Si, Fe, Cu, Zn, Ti, Sn, V, Ge, Ga, B, P, Se, Bi, As, Zr, Mn, Cr, Ge, It is one selected from Sr, V, Sc, Y and combinations thereof.

[0106] The above lithium cobalt-based oxide is a compound represented by the following chemical formula 4.

[0107] [Chemical Formula 4]

[0108] Li a-b Mg b Co (1-x-b) Al x O2

[0109] Among the above chemical formula 4, 0.9≤a≤1.1, 0.001≤b≤0.01, 0.01 <x≤0.03이다.

[0110] In Chemical Formula 4, a is, for example, 0.9 to 1.05.

[0111] 0.015 in chemical formulas 3 and 4 <x≤0.03, 0.005≤b≤0.01이다.

[0112] In the composite cathode active material according to one embodiment, the total thickness of the first coating layer and the second coating layer is 200 nm to 800 nm, and the thickness of the third coating layer is 100 nm or less, for example, 10 nm to 50 nm.

[0113] The second coating layer is disposed on top of the first coating layer, and the interface between the first coating layer and the second coating layer may be uniform or non-uniform. In the composite cathode active material according to one embodiment, the ratio of the long axis length of the first coating layer to the long axis length of the second coating layer is 1.1 to 1.5. Here, the ratio of the long axis lengths can be obtained through scanning electron microscopy or transmission electron microscopy analysis.

[0114] The lithium cobalt-based oxide according to one embodiment is a mixture of small particles, large particles, or small and large particles.

[0115] The size of the above-mentioned large particles is 10 to 20 μm, and the size of the small particles is 3 to 6 μm. In addition, the mixing weight ratio of the large particles to the small particles in the mixture of the above-mentioned large particles and small particles is 7:3 to 9:1, 8:2 to 9:1, for example, 5:1 to 7:1. When the mixing weight ratio of the large particles to the small particles is within the above range, high-temperature life and high-temperature storage characteristics are improved.

[0116] The size of the above-mentioned coarse particles is 10 to 20 μm, 17 to 20 μm, for example 18 to 20 μm. And the size of the small particles is 3 to 6 μm, for example 3 to 5 μm, or 3 to 4 μm.

[0117] The composite cathode active material according to one embodiment has a layered crystal structure and a specific surface area of ​​0.1 to 3 m² 2 / g is.

[0118] According to another aspect, a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte interposed between them, comprising the composite positive electrode active material described above is provided.

[0119] In a lithium secondary battery according to one embodiment, a first lithium zirconium-based oxide may exist at a position spaced apart from the surface where a particle coating portion is formed in a lithium cobalt-based oxide even after repeated charge-discharge cycles.

[0120] Hereinafter, we will examine a method for manufacturing a composite cathode active material according to one embodiment.

[0121] First, the manufacturing methods for the large-grained lithium cobalt-based oxide and small-grained lithium cobalt-based oxide used in the production of composite cathode active materials are as follows.

[0122] To manufacture a counter-lithium cobalt-based oxide, a cobalt precursor, a lithium precursor, and a metal precursor having a size of 4 μm to 7 μm are mixed to obtain a first mixture.

[0123] Specifically, a precursor mixture can be obtained by mixing the lithium precursor, cobalt precursor, and metal precursor while stoichiometrically controlling the mixing ratio so as to obtain a lithium cobalt-based oxide represented by the desired chemical formula 3.

[0124] [Chemical Formula 3]

[0125] Li a-b Mg b Co (1-x-y-b) Al x M3 y O2

[0126] In Chemical Formula 3, 0.9≤a≤1.1, 0≤b≤0.02, 0≤x≤0.04, 0≤y≤0.01, and

[0127] M3 is Ni, K, Na, Ca, Mg, Si, Fe, Cu, Zn, Ti, Sn, V, Ge, Ga, B, P, Se, Bi, As, Zr, Mn, Cr, Ge, It is one selected from Sr, V, Sc, Y and combinations thereof.

[0128] The metal precursor may be one or more selected from, for example, magnesium precursor, aluminum precursor, and M3 precursor.

[0129] One or more lithium precursors selected from lithium hydroxide (LiOH), lithium carbonate (Li2CO3), lithium chloride, lithium sulfate (Li2SO4), and lithium nitrate (LiNO3) may be used. One or more cobalt precursors selected from cobalt carbonate, cobalt hydroxide, cobalt chloride, cobalt sulfate, and cobalt nitrate may be used. One or more aluminum precursors selected from aluminum sulfate, aluminum chloride, and aluminum hydroxide may be used, and one or more magnesium precursors selected from magnesium sulfate, magnesium chloride, and magnesium hydroxide may be used.

[0130] The M3 precursor may be one or more selected from chlorides, sulfates, hydroxides, and oxides containing M3 of Chemical Formula 3.

[0131] The above mixing can be performed using dry mixing, such as mechanical mixing, with a ball mill, Bambari mixer, homogenizer, Hensel mixer, etc. Dry mixing can reduce manufacturing costs compared to wet mixing.

[0132] The size of the cobalt precursor used in the preparation of the first mixture is, for example, 4 to 6.0 μm. If the size of the cobalt precursor is less than 4 μm or greater than 7 μm, it becomes difficult to prepare a large lithium cobalt-based oxide.

[0133] Next, the first mixture can be heat-treated in an air or oxygen atmosphere to obtain a large lithium cobalt-based oxide.

[0134] The particle size of the counter-lithium cobalt-based oxide is 17 μm to 21 μm, for example 18 μm to 20 μm, for example 19 μm.

[0135] Separately, to produce a fine-grained lithium cobalt-based oxide, a cobalt precursor, a lithium precursor, and a metal precursor having a size of 2 μm to 3 μm are mixed to obtain a second mixture. The second mixture is subjected to a first heat treatment to produce a fine-grained lithium cobalt-based oxide. Here, the metal precursor is the same as the metal precursor mentioned when producing the first mixture.

[0136] The size of the small lithium cobalt-based oxide particles is 2 μm to 8 μm, for example, 3 μm to 4 μm.

[0137] If the size of the cobalt precursor used in the manufacture of fine-grained lithium cobalt-based oxide is less than 2㎛, it becomes difficult to obtain fine-grained lithium cobalt-based oxide with the desired size. Also, if the size of the cobalt precursor exceeds 4㎛, the density decreases when mixed with coarse-grained oxide.

[0138] When manufacturing the above-described opposing lithium cobalt-based oxide and fine-grained lithium cobalt-based oxide, the molar ratio (Li / Me) of lithium and non-lithium metal (Me) is 0.9 to 1.1, 1.01 to 1.05, for example 1.02 to 1.04.

[0139] In the step of manufacturing the above-mentioned coarse lithium cobalt-based oxide and small lithium cobalt-based oxide, the heating rate is 4 to 6°C / min. When the heating rate is carried out within the above range, cation mixing can be prevented. If the heating rate is less than 4°C, the improvement in phase stability at high voltage is negligible.

[0140] The aforementioned large lithium cobalt-based oxide and small lithium cobalt-based oxide are mixed in a weight ratio of 8:2 to 1:9, and a titanium precursor and cobalt hydroxide are mixed therein to obtain a first precursor mixture, and then heat treatment is performed.

[0141] The content of cobalt hydroxide is 3.5 to 7 parts by weight, 4 to 6 parts by weight, 4.5 to 5.5 parts by weight, or 5 parts by weight based on 100 parts by weight of lithium cobalt-based oxide. When the content of cobalt hydroxide is within the above range, the desired lithium-deficient cobalt oxide phase is formed.

[0142] The above heat treatment is performed at 850°C to 980°C, and the heating rate may be 2°C / min to 10°C / min, for example, 4°C / min to 6°C / min. When the heating rate is within the above range, the formation of a spinel structure in the surface coating portion can be developed.

[0143] Heat treatment can be performed under an air or oxygen atmosphere. Here, the oxygen atmosphere can be formed using oxygen alone or using oxygen, nitrogen, and an inert gas together.

[0144] A second precursor mixture is obtained by mixing the heat-treated product according to the above process and the zirconium precursor, and the second precursor mixture is heat-treated. The heat treatment of the second precursor mixture is carried out at 950°C to 1000°C.

[0145] A composite cathode active material can be obtained in which a first lithium zirconium-based oxide exists in an internal region of a lithium cobalt-based oxide, which can be heat-treated within the above temperature range. The heating rate can be 2 ℃ / min to 10 ℃ / min, and for example, 4 ℃ / min to 6 ℃ / min. When the heating rate is within the above range, the surface structural characteristics of the composite cathode active material can be controlled.

[0146] Titanium precursors may include, for example, titanium oxide, titanium hydroxide, titanium chloride, titanium sulfate, or combinations thereof. Cobalt hydroxide has superior chemical reactivity compared to cobalt oxide. If cobalt oxide is used as the cobalt precursor, the large particle size of cobalt oxide results in the formation of an island-shaped coating layer, and the coating layer according to one embodiment cannot be formed.

[0147] Cobalt hydroxide with an average particle size of 50 nm to 300 nm or 100 nm to 200 nm is used. By using cobalt hydroxide having such a size, a composite cathode active material according to one embodiment having a desired coating layer can be manufactured. The average particle size can be confirmed through SEM, TEM, etc., or evaluated through a particle size analyzer.

[0148] The content of the zirconium precursor is controlled so that the zirconium content in the composite cathode active material is in the range of 4,500 to 6,750 ppm, for example, 0.6 to 1.4 parts by weight based on 100 parts by weight of lithium cobalt-based oxide. And the content of the titanium precursor is controlled so that the zirconium content in the composite cathode active material is in the range of 500 to 800 ppm.

[0149] Zirconium precursors are zirconium oxide, zirconium hydroxide, zirconium chloride, zirconium sulfate, or combinations thereof.

[0150] The composite cathode active material according to one embodiment can also be manufactured by general manufacturing methods, such as spray pyrolysis, in addition to the solid-state method described above.

[0151] According to another aspect, a lithium secondary battery comprising a cathode containing the aforementioned composite cathode active material is provided. A method for manufacturing the lithium secondary battery is described as follows.

[0152] The anode is prepared according to the following method.

[0153] A positive active material composition is prepared by mixing a composite positive active material according to one embodiment, a binder, and a solvent. A conductive material may be further added to the positive active material composition. The positive active material composition is directly coated and dried onto a metal current collector to manufacture a positive plate. Alternatively, the positive active material composition may be cast onto a separate support, and then a film peeled from the support may be laminated onto a metal current collector to manufacture a positive plate. When manufacturing the positive, a first positive active material, which is a positive active material commonly used in lithium secondary batteries, may be further included. The first positive active material may further include one or more selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide, but is not necessarily limited to these, and any positive active material available in the relevant technical field may be used. For example, Li a A 1-b B b D2 (wherein 0.90≤a≤1.8, and 0≤b≤0.5); Li a E 1-b B b O 2-c D c (In the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE 2-b B b O 4-c D c (In the above formula, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b B c D α (In the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Co b B c O 2-α F α (In the above equation, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Lia Ni 1-b-c Mn b B c D α (In the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Mn b B c O 2-α F α (In the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni b E c G d O2(in the above equation, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1); Li a Ni b Co c Mn d GeO2(wherein the above formula, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1); Li a NiG b O2(in the above equation, 0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(in the above equation, 0.90≤a≤1.8, 0.001≤b≤0.1); Li a MnG b O2(in the above equation, 0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4 (wherein the above equation, 0.90≤a≤1.8, 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0≤f≤2); Li (3-f)A compound represented by any one of the chemical formulas of Fe2(PO4)3(0≤f≤2); LiFePO4 may be used. In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0154] In the cathode active material composition, the binder is polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyamideimide, polyacrylic acid (PAA), polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, lithium polyacrylate, lithium Examples include polymethacrylate, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers.

[0155] The above conductive material is not particularly limited as long as it possesses conductivity without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon nanotubes, carbon fibers, or metal fibers; fluorinated carbon; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titaniumate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0156] The content of the conductive material is used in an amount of 1 to 10 parts by weight or 1 to 5 parts by weight based on 100 parts by weight of the positive electrode active material. When the content of the conductive material is within the above range, the conductivity characteristics of the finally obtained electrode are excellent.

[0157] As a non-limiting example of the above solvent, N-methylpyrrolidone, etc., is used, and the solvent content is used in an amount of 20 to 200 parts by weight based on 100 parts by weight of the positive electrode active material. When the solvent content is in the above range, the process of forming the positive electrode active material layer is easy.

[0158] The above positive current collector has a thickness of 3 to 500 μm and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may also form fine irregularities on its surface to increase the adhesion of the positive active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

[0159] Meanwhile, it is also possible to form pores inside the electrode by adding a plasticizer to the above positive active material composition and / or negative active material composition.

[0160] The content of the above-mentioned positive active material, conductive material, binder, and solvent is at a level typically used in lithium secondary batteries. Depending on the application and composition of the lithium secondary battery, one or more of the above-mentioned conductive material, binder, and solvent may be omitted.

[0161] The cathode can be obtained by carrying out the process in almost the same way as described above, except that a cathode active material is used instead of a positive active material in the positive manufacturing process.

[0162] As the negative electrode active material, carbon-based materials, silicon, silicon oxide, silicon-based alloys, silicon-carbon material composites, tin, tin-based alloys, tin-carbon composites, metal oxides, or combinations thereof are used.

[0163] The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as natural graphite or artificial graphite in amorphous, plate-like, flake-like, spherical, or fibrous forms, and the amorphous carbon may be soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, graphene, carbon black, carbon nanotubes, and carbon fibers, but is not necessarily limited to these, and any material that can be used in the relevant technical field is acceptable.

[0164] The above negative electrode active material is Si, SiOx(0 <x<2, 예를 들어 0.5 내지 1.5), Sn, SnO2, 또는 실리콘 함유 금속 합금 및 이들이 혼합물로 이루어진 군에서 선택되는 것을 사용할 수 있다. 상기 실리콘 합금을 형성할 수 있는 금속으로는 Al, Sn, Ag, Fe, Bi, Mg, Zn, in, Ge, Pb 및 Ti 중에서 하나 이상 선택하여 사용할 수 있다.

[0165] The above-described negative electrode active material may include metals / metalloids alloyable with lithium, alloys thereof, or oxides thereof. For example, the metals / metalloids alloyable with lithium include Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y alloys (wherein Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a combination thereof, and is not Si), Sn-Y alloys (wherein Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a combination thereof, and is not Sn), MnOx (0 <x≤2) 등일 수 있다. 상기 원소 Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, 또는 이들의 조합일 수 있다. 예를 들어, 상기 리튬과 합금가능한 금속 / 준금속의 산화물은 리튬 티타늄 산화물, 바나듐 산화물, 리튬 바나듐 산화물, SnO2, SiO x (0 <x<2) 등일 수 있다.

[0166] The above-mentioned cathode active material may include, for example, one or more elements selected from the group consisting of elements of Group 13, Group 14, and Group 15 of the periodic table, specifically one or more elements selected from the group consisting of Si, Ge, and Sn.

[0167] In the cathode active material composition, the binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0168] The above-mentioned water-insoluble binders include ethylene propylene copolymer, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, and polyvinylidene.

[0169] Examples include fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0170] The above water-soluble binder may be styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber (ABR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyepichorhydrin, polyphosphazene, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0171] When a water-soluble binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickening agent. Examples of this cellulose-based compound include carboxymethyl cellulose and hydroxypropylmethyl cellulose.

[0172] One or more types of methyl cellulose, or alkali metal salts thereof, may be mixed and used. Na, K, or Li may be used as the alkali metal. The content of such a thickener may be 0.1 to 3 parts by weight per 100 parts by weight of the negative electrode active material.

[0173] The above conductive material may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber; metal-based materials such as metal powder or metal fiber, such as copper, nickel, aluminum, silver; conductive polymers such as polyphenylene derivatives; or conductive materials comprising a mixture thereof.

[0174] In the negative electrode active material composition, the same solvent as that used in the positive electrode active material composition may be used. Furthermore, the solvent content is at a level typically used in lithium secondary batteries.

[0175] The separator is interposed between the anode and the cathode, and a thin insulating film with high ion permeability and mechanical strength is used.

[0176] The pore diameter of the separator is generally 0.01 μm to 10 μm, and the thickness is generally 5 μm to 20 μm. Examples of such separators include olefinic polymers such as polypropylene; sheets or nonwoven fabrics made of glass fibers or polyethylene. When a solid polymer electrolyte is used as the electrolyte, the solid polymer electrolyte may also serve as the separator.

[0177] Specific examples of olefin-based polymers among the above separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof, and mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators may be used.

[0178] The above lithium salt-containing non-aqueous electrolyte consists of a non-aqueous electrolyte and a lithium salt.

[0179] Non-aqueous electrolytes used include non-aqueous electrolytes, organic solid electrolytes, or inorganic solid electrolytes.

[0180] The above-mentioned non-aqueous electrolyte contains an organic solvent. Any organic solvent that can be used as an organic solvent in the relevant technical field may be used. Examples include propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, fluoroethylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

[0181] For example, the above organic solid electrolyte may be used as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a polyvinyl alcohol, etc.

[0182] Examples of the above inorganic solid electrolytes may be used, such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc.

[0183] The above lithium salt is a substance that is easily soluble in the above-mentioned non-aqueous electrolyte, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, Li(FSO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1Examples include SO2 (where x and y are natural numbers), LiCl, LiI, or mixtures thereof. Additionally, for the purpose of improving charge / discharge characteristics and flame retardancy, the non-aqueous electrolyte may be supplemented with, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, halogen-containing solvents such as carbon tetrachloride or trifluoroethylene may be further included to impart non-flammability. It is preferable to use a lithium salt concentration within the range of 0.1M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0184] The above lithium secondary battery includes a positive electrode, a negative electrode, and a separator. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and of course, a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0185] The aforementioned positive electrode, negative electrode, and separator are wound or folded and accommodated in a battery case. Subsequently, an organic electrolyte is injected into the battery case and sealed with a cap assembly to complete a lithium secondary battery. The battery case may be cylindrical, prismatic, thin-film, etc.

[0186] A separator may be placed between the anode and cathode to form a battery structure. The battery structure is then stacked in a bicell structure, impregnated with an organic electrolyte, and the resulting product is contained in a pouch and sealed to complete a lithium-ion polymer battery.

[0187] In addition, the above-mentioned battery structures are stacked in multiple units to form a battery pack, and such a battery pack can be used in any device requiring high capacity and high output. For example, it can be used in laptops, smartphones, electric vehicles, etc.

[0188] Although the lithium secondary battery according to one embodiment is described as being of the prismatic type, the present invention is not limited thereto and can be applied to various types of batteries such as cylindrical, pouch, and coin types.

[0189] FIG. 4 is a cross-sectional view schematically illustrating a representative structure of a lithium secondary battery according to one embodiment.

[0190] Referring to FIG. 4, the lithium secondary battery (31) includes a positive electrode (33), a negative electrode (33), and a separator (34) containing a composite positive active material according to one embodiment. An electrode assembly in which the above-described positive electrode (33), negative electrode (32), and separator (34) are wound or folded is received in a battery case (35). Depending on the battery shape, a separator may be placed between the positive electrode and the negative electrode to form an alternately stacked battery structure. Subsequently, an organic electrolyte is injected into the battery case (35) and sealed with a cap assembly (86) to complete the lithium secondary battery (31). The battery case (35) may be cylindrical, prismatic, thin film, etc. For example, the lithium secondary battery (31) may be a large thin film battery. The lithium secondary battery may be a lithium-ion battery. A lithium-ion polymer battery is completed when the above-described battery structure is housed in a pouch, impregnated with an organic electrolyte, and sealed. Additionally, multiple above-described battery structures are stacked to form a battery pack, and such a battery pack can be used in any device requiring high capacity and high output. For example, it can be used in laptops, smartphones, electric vehicles, etc.

[0191] The present invention is explained in more detail through the following examples and comparative examples. However, the examples are intended to illustrate the present invention and do not limit the scope of the present invention.

[0192] (Manufacturing of composite cathode active material)

[0193] Example 1: LCO doped with Mg 1000 ppm, Al 6000 ppm + Ti 700 ppm / Zr 4500 ppm surface coating

[0194] Lithium carbonate, CO3O4 (D50: 4.5 μm), aluminum hydroxide Al(OH)3, and magnesium carbonate (MgCO3), which is a magnesium precursor, are mixed, and the mixing molar ratio of the said precursors is Li 1.04 Mg 0.005 Co 0.978 Al 0.022A first mixture was obtained by stoichiometric control to obtain O2. The first mixture was heated to 1088°C at a heating rate of 4.5°C / min, and then subjected to a first heat treatment at this temperature for 15 hours in an air atmosphere, thereby Li 1.04 Mg 0.005 Co 0.978 Al 0.022 Large particles having an average particle size (D50) of about 17 μm and a layered structure of O2 were prepared.

[0195] Separately, a second mixture was obtained by mixing the cobalt precursor Co3O4 (D50: 2.5 μm), aluminum hydroxide Al(OH)3, lithium carbonate, and the magnesium precursor magnesium carbonate in a molar ratio of Li:Co:Mg:Al of 1.04:0.9733:0.0050:0.0217. The second mixture was heated to 940°C at a heating rate of 4.5°C / min, and then heat-treated at this temperature for 5 hours to obtain Li 1.04 Mg 0.005 Co 0.978 Al 0.022 Fine particles (D50: 3.5㎛) having a layered structure of O2 were obtained.

[0196] The large particles and small particles obtained from the above process were mixed in a weight ratio of 8:2, and then titanium oxide and cobalt hydroxide (Co(OH)2) (average particle size: about 100 nm) were added to obtain a third mixture. This third mixture was heat-treated at about 950°C. Here, the content of cobalt hydroxide was 5 parts by weight based on 100 parts by weight of large or small particles, and the content of titanium oxide was stoichiometrically controlled so that the titanium content in the composite cathode active material was about 700 ppm.

[0197] Next, zirconium oxide was added to the heat-treated product to obtain a fourth mixture, and this fourth mixture was heat-treated at about 1000°C to obtain a composite cathode active material. Here, the content of zirconium oxide was stoichiometrically controlled so that zirconium was doped into the composite cathode active material at about 4500 ppm.

[0198] The composite cathode active material is Li in an allogrape state 1.04 Mg 0.005 Co 0.978 Al 0.022 O2 (D50: 17㎛) and Li in the form of fine particles 1.04 Mg 0.005 Co 0.978 Al 0.022 It has a bimodal state containing O2 (D50: 3.5㎛). The above-mentioned large particles and small particles both have a first coating layer disposed on a first surface and a second coating layer disposed on top of the first coating layer, and a third coating layer disposed in the second internal region of the composite cathode active material and disposed in contact with the first coating layer, while a lithium-deficient cobalt phase (Li) in the first internal region 0.8 Mg 0.007 It had a structure including CoO2. And the first coating layer was Li2Ti 0.97 Co 0.02 Mg 0.01 It contains O3, and the second coating layer is Li2Zr 0.98 Co 0.02 It contains O3, and the third coating layer contains LiCo2O4. In addition, in the first internal region in contact with the first coating layer of the composite cathode active material, Li, which is a first lithium zirconium-based oxide, 2 Zr 0.95 Co 0.05 The structure where O3 is located was shown.

[0199] Example 2: LCO doped with Mg 1000 ppm, Al 6000 ppm + Ti 700 ppm / Zr 6750 ppm surface coating

[0200] The large particles and small particles obtained according to Example 1 were mixed in a weight ratio of 8:2, and then titanium oxide and cobalt hydroxide (Co(OH)2) (average particle size: about 100 nm) were added to obtain a third mixture. This third mixture was heat-treated at about 950°C. Here, the content of cobalt hydroxide was 5 parts by weight based on 100 parts by weight of large or small particles, and the content of titanium oxide was stoichiometrically controlled so that the titanium content in the composite cathode active material was about 700 ppm.

[0201] Next, zirconium oxide was added to the heat-treated product to obtain a fourth mixture, and this fourth mixture was heat-treated at about 1000°C to obtain a composite cathode active material. Here, the content of zirconium oxide was stoichiometrically controlled so that zirconium was doped into the composite cathode active material at about 6750 ppm.

[0202] Example 3

[0203] A composite cathode active material was obtained by carrying out the same method as in Example 1, except that the weight ratio of large particles and small particles was changed to 7:3 instead of 8:2.

[0204] Comparative Example 1: LCO doped with Mg 1000 ppm and Al 4000 ppm

[0205] When preparing the first mixture and the second mixture, LiMg 0.005 Co 0.985 Al 0.015 Large and small cathode active materials were obtained by carrying out the same procedure as in Example 1, except that the mixing molar ratio of lithium oxide, CO3O4, and magnesium precursor MgCO3 was stoichiometrically controlled to obtain the desired result.

[0206] The large and small particles obtained from the above process were mixed in a weight ratio of 8:2, and then cobalt hydroxide (Co(OH)2) was added to obtain a third mixture. This third mixture was subjected to a second heat treatment at approximately 900°C to obtain large LiMg 0.005 Co 0.985 Al 0.015 (D50: 17㎛) and fine-grained LiCo 0.9805 Al 0.0145 Mg 0.005 A bimodal composite cathode active material containing O2 (D50: 3.5㎛) was obtained.

[0207] Comparative Example 2: LCO + Ti 700 ppm surface coating doped with Mg 1000 ppm and Al 4000 ppm

[0208] The large particles and small particles obtained according to Example 1 were mixed in a weight ratio of 8:2, and then titanium oxide and cobalt hydroxide (Co(OH)2) were added to obtain a third mixture. This third mixture was heat-treated at approximately 950°C, and then a bimodal composite cathode active material was prepared by proceeding in the same manner as in Example 1, except that zirconium oxide was added to the heat-treated product and the heat treatment process was not performed.

[0209] (Manufacturing of lithium-ion batteries)

[0210] Production Example 1

[0211] A mixture of the positive active material obtained according to Example 1, polyvinylidene fluoride, and carbon black, a conductive material, was mixed using a mixer to remove bubbles and prepared a slurry for forming a uniformly dispersed positive active material layer. N-methyl 2-pyrrolidone, a solvent, was added to the mixture, and the mixing ratio of the composite positive active material, polyvinylidene fluoride, and carbon black was 98:1:1 by weight. The slurry prepared according to the above process was coated onto an aluminum foil using a doctor blade to form a thin electrode plate, which was then dried at 135°C for at least 3 hours, followed by rolling and vacuum drying processes to produce a positive electrode.

[0212] A cathode was prepared by mixing natural graphite, carboxymethylcellulose (CMC), and styrene butadiene rubber (SBR) to obtain a composition for forming a cathode active material, and then coating and drying this composition onto a copper current collector. The weight ratio of natural graphite, CMC, and SBR was 97.5:1:1.5, and the content of distilled water was about 50 parts by weight per 100 parts by weight of the total weight of natural graphite, CMC, and SBR.

[0213] A lithium secondary battery was fabricated by interposing a separator (thickness: about 10 μm) made of a porous polyethylene (PE) film between the anode and the cathode and injecting an electrolyte. The electrolyte used was a solution containing 1.1 M LiPF6 dissolved in a solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3.

[0214] Production Example 2

[0215] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the composite cathode active material of Example 2 was used instead of the composite cathode active material of Example 1 when manufacturing the cathode.

[0216] Comparative Production Example 1-2

[0217] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the composite cathode active material of Comparative Examples 1-2 was used instead of the composite cathode active material of Example 1 when manufacturing the cathode.

[0218] Evaluation Example 1: HR STEM HAADF (high-resolution scanning transmission electron microscopy equipped with a high angular annular dark field detector) analysis (I)

[0219] HR STEM HAADF analysis was performed on the composite cathode active material prepared according to Example 1, and the results of the analysis are shown in FIGS. 2a and 2b. FIGS. 2b is an enlarged view of a portion of FIGS. 2a.

[0220] As shown in FIG. 2a, the composite cathode active material of Example 1 showed that a lithium-deficient cobalt oxide phase having a spinel phase up to 1.246 μm was observed on the first surface of the first internal region of the lithium-deficient cobalt oxide, and that a first lithium zirconium oxide having a layered structure of R-3m rhombohedral was present beneath the lithium-deficient cobalt oxide phase.

[0221] Evaluation Example 2: Charge / Discharge Characteristics

[0222] The lithium secondary battery prepared according to Production Example 1-2 and Comparative Production Example 1-2 was charged to SOC 90% at 25°C with a constant current and aged for 48 hours, after which it was cut off at a current rate of 0.05C while maintaining 4.58V in a constant current / constant voltage mode. Subsequently, it was discharged at a constant current rate of 0.5C until the voltage reached 3.0V during discharge (formation stage).

[0223] The lithium secondary battery that had undergone the above formation step was charged with a constant current of 0.2C until it reached 4.55V. After the charging was complete, the cell was discharged with a constant current of 0.2C until the voltage reached 3V after a rest period of about 10 minutes.

[0224] The initial charge / discharge efficiency was evaluated according to Equation 1 below, and the evaluation results are shown in Table 1 below.

[0225] <Equation 1>

[0226] Initial charge / discharge efficiency (%) = (Discharge capacity per cycle (0.2C) / Charge capacity per cycle (0.2C)) x 100

[0227] Evaluation Example 3: HR STEM HAADF Analysis (II)

[0228] A lithium secondary battery manufactured according to Example 1 was charged to SOC 90% at 25°C with a constant current and aged for 48 hours, after which it was cut off at a current rate of 0.05C while maintaining 4.58V in a constant current / constant voltage mode. Subsequently, it was discharged at a constant current rate of 0.5C until the voltage reached 3.0V during discharge (formation stage).

[0229] 1 of the above Mars phase st The lithium secondary battery that had undergone the cycle was charged with a constant current at 0.2C at 25℃ until it reached 4.55 V. After the cell was fully charged, it was allowed to rest for about 10 minutes, and then discharged with a constant current at 0.2C until the voltage reached 3 V. This cycle was repeated a total of 50 times.

[0230] As described above, after repeating the charge-discharge cycle 50 times, HR STEM HAADF analysis was performed on the composite cathode active material prepared according to Example 1.

[0231] As a result of the above analysis, it was confirmed that the region where the first lithium zirconium-based oxide exists in the composite cathode active material of Example 1 maintains its layered structure (R-3m). From this, it was found that the structural stability of the composite cathode active material of Example 1 is excellent even after repeated charging and discharging.

[0232] Evaluation Example 4: High-temperature life

[0233] The lithium secondary batteries of Production Example 1-2 and Comparative Production Example 1-2 were charged to SOC 90% at 45°C with a constant current and aged for 48 hours, after which they were cut off at a current rate of 0.05C while maintaining 4.58V in constant current / constant voltage mode. Subsequently, they were discharged at a constant current rate of 0.5C until the voltage reached 3.0V during discharge (Formation step, 1 st Cycle).

[0234] 1 of the above Mars phase st The lithium secondary battery that had undergone cycling was charged with a constant current at 0.2C at 45℃ until it reached 4.55 V. After the charging was complete, the cell was evaluated by repeating a cycle of constant current discharge at 0.2C until the voltage reached 3 V a total of 50 times, following a rest period of about 10 minutes.

[0235] High temperature life was evaluated according to Equation 2 below, and the evaluation results are shown in Table 1 below.

[0236] <Equation 2>

[0237] Lifespan (%) = (Discharge capacity per 50 cycles / Charge capacity per cycle) x 100

[0238] Evaluation Example 5: DC Resistance (DC-IR) Test

[0239] The lithium secondary batteries produced in Production Example 1, Production Example 2, Comparative Production Example 1, and Comparative Production Example 2 were charged to SOC 90% at 25°C with a constant current and aged for 48 hours, after which they were cut off at a current rate of 0.05C while maintaining 4.58V in constant current / constant voltage mode. Subsequently, they were discharged at a constant current rate of 0.5C until the voltage reached 3.0V during discharge (formation stage).

[0240] The lithium secondary battery that had undergone the above formation step was charged with a constant current of 0.2C until it reached 4.55 V. After the charging was complete, the cell was discharged with a constant current of 0.2C until the voltage reached 3 V.

[0241] The DC resistance (DCIR) of the lithium secondary battery after the above process was measured, and the results are shown in Table 1 below.

[0242] Coincell Production Example 1 Production Example 2 Comparative Production Example 1 Comparative Production Example 2 0.2C charging capacity (mAh) 208.0 207.5 209.4 209.5 0.2C discharge capacity (mAh) 192.4 192.0 195.8 195.7 0.2C Charge / Discharge Efficiency (%) 92.5 92.5 93.5 93.4 DCIR (mΩ) 10.5 10.5 18.3 13.2 High temperature lifespan (%) (@50cycle) 71.2 71.2 52.6 47.5

[0243] From Table 1, it was found that the lithium secondary batteries of Production Examples 1 and 2 had significantly improved high-temperature life and enhanced resistance characteristics compared to the lithium secondary batteries of Comparative Production Examples 1 and 2.

[0244] Evaluation Example 6: TEM-EDS Analysis (I)

[0245] TEM-EDS (energy dispersive X-ray spectroscopy) analysis was performed on the composite cathode active material of Example 1, and the analysis results are shown in Figures 3a to 3i. Figure 3a shows the EDS MAP measurement area, where Area 1 represents the lithium-deficient cobalt phase region and Area 2 represents the surface coating portion. Figures 3b, 3c, 3d, 3e, 3f, and 3g respectively show mapping images of Ti, Mg, O, Co, Zr, and O. Figures 3g and 3h show the EDS analysis results of Area 1 and Area 2 of Figure 3a, respectively.

[0246] Referring to this, it indicates that the Co component is evenly distributed in the lithium cobalt-based oxide region (core region) and the particle coating region of the composite cathode active material (Fig. 3e), and the Mg component appears in the particle coating region (Fig. 3c). Additionally, the Zr component appears in the particle coating region (Fig. 3f), and from Fig. 3d, it was found that the oxygen (O) component is uniformly distributed in both the core region and the particle coating region. From this, it was observed that Mg, Ti, Zr, and Co are mixed within the lithium cobalt-based oxide, and that the distribution of each element differs slightly. Furthermore, from Figs. 3g and 3h, it was found that Area 1 is a Co and Mg rich region compared to Area 2, and is in a poor state with O and Al deficient.

[0247] Evaluation Example 7: SEM-EDS Analysis

[0248] Energy dispersive X-ray spectroscopy (SEM-EDS) analysis was performed on the composite cathode active material prepared according to Example 1. A Spectra 300 (Thermo Fisher) was used for SEM-EDS.

[0249] The results of the above SEM-EDS analysis are shown in Figs. 5, 6a to 6f.

[0250] Referring to Fig. 5, it was found that magnesium is evenly distributed throughout the surface of the composite cathode active material of Example 1, and zirconium is present in the particle coating region.

[0251] Referring to FIGS. 6a to 6f, Zr was observed in the particle coating portion of the composite cathode active material of Example 1. It was also found that the content of cobalt and magnesium was high and the oxygen content was low in the particle coating portion region of the composite cathode active material of Example 1.

[0252] Evaluation Example 8: SEM and TEM Analysis

[0253] SEM and TEM analyses were performed on the composite cathode active material of Example 1.

[0254] Figures 7a and 7b show the TEM analysis results, with Figure 7b showing an enlarged view of the lithium-deficient cobalt oxide phase region in Figure 7a. Figure 7c shows the SEM analysis results, with the arrow indicating the lithium-deficient cobalt oxide phase region, which is a cobalt / magnesium-rich region. Figure 7b also shows the doping depth, particle coating region, and surface coating region.

[0255] Referring to Fig. 7b, the lithium-deficient cobalt oxide phase region is a cobalt / magnesium-rich region. Also, in Fig. 7b, the doping depth h of the lithium-deficient cobalt oxide phase is 1 μm or less. And region A represents the particle coating region, and region B represents the surface coating region.

[0256] Figure 8a is a TEM image of the crystal structure of the composite cathode active material of Example 1. A TEM image of region A1 in Figure 8a is shown in Figure 8b, and a crystal structure image of region A1 in Figure 8a is shown in Figure 8c.

[0257] As shown in Fig. 8b, the lithium-deficient cobalt oxide present inside the composite cathode active material particles exhibits a spinel crystal structure of space group Fd-3m, and it can be confirmed that the lithium cobalt-based oxide present inside the composite cathode active material particles has a layered crystal structure of space group R3m.

[0258] Evaluation Example 9: Conductivity Evaluation

[0259] The conductivity in the bulk region, particle coating region, and surface coating region of the composite cathode active material obtained according to Example 1 was evaluated using AFM. The evaluation results are shown in Figures 9a to 10e. Figures 9a and 9b are SEM images, Figures 9c and 9d are particle surface current images, and Figure 9e shows the change in current according to distance.

[0260] With reference to this, it was confirmed that the composite cathode active material obtained according to Example 1 had higher electrical conductivity near the particles compared to other regions when comparing the electrical conductivity of the Zr particles, near the particles, and the bulk surface of the lithium cobalt-based oxide (LCO).

[0261] Evaluation Example 10: Energy Filtering Transmission Electron Microscope and Electron Beam Energy Loss Analysis (Energy Filtering Transmission Electron Microscope & Electron Beam Energy Loss (EF-TEM & EELS))

[0262] delete

[0263] EF-TEM and EELS analysis were performed on the composite cathode active material of Example 1, and the analysis results are shown in FIGS. 10a to 10e. FIG. 10a shows the EDS MAP measurement area, FIG. 10b is the EDS lithium mapping image for the left square area of ​​FIG. 10a, and FIG. 10c is the EDS lithium mapping image for the right square area of ​​FIG. 10a. FIGS. 10d and FIG. 10e show the EELS analysis results for the particle coating portion and LCO, respectively.

[0264] delete

[0265] Referring to FIGS. 10a to 10e, it was found that in the composite cathode active material of Example 1, lithium is uniformly present in the particle coating portion and the internal region.

[0266] delete

[0267] Evaluation Example 11: HR-TEM (high-resolution transmission electron microscopy)

[0268] HR-TEM analysis was performed on the composite cathode active material of Example 1, and inside the LCO

[0269] The crystal structure of the existing lithium-deficient cobalt oxide phase was investigated. The results of the HR-TEM analysis are shown in Figures 11a to 11d. Figure 11a shows the analysis area, Figure 11b is an HR-TEM image showing an enlarged view of the arrowed area in Figure 11a, and Figures 11c and 11d are TEM images of the crystal structure for areas A and B of Figure 11b, respectively.

[0270] When observing the brightly visible region on the surface of the core active material, lithium cobalt-based oxide (LCO), and the LCO interface, a spinel-like phase was observed in which regular ordering with a length twice that of the existing d-spacing was generated in the (0-14) and (012) plane directions of the LCO layered structure.

[0271] In addition, HR-TEM analysis was performed on the composite cathode active material of Example 1 to investigate the crystal structure of the lithium-deficient cobalt oxide phase present inside the LCO. The results of the analysis are shown in Figures 12a to 12c. Figure 12b is a photograph of the crystal structure analysis for the area indicated by the left arrow in Figure 12a, and Figure 12c is a photograph of the crystal structure analysis for the area indicated by the right arrow in Figure 12a.

[0272] Referring to this, the coated region consists of multiple crystal grains, but as shown in Fig. 12b, the interface with LCO (HR image 1) was observed as epitaxial growth, and as shown in Fig. 12c, it showed results similar to the Rock salt (Fm-3m) phase formed on the LCO surface of the uncoated region (HR image 2).

[0273] Evaluation Example 12: TEM-EDS Analysis (II)

[0274] TEM-EDS analysis was performed on the composite cathode active material prepared according to Example 1, and the results of the analysis are shown in Fig. 13a.

[0275] Referring to Fig. 13a, a Zr-containing region of several tens of nanometers in size was observed inside the composite cathode active material particle (indicated by the arrow).

[0276] In addition, TEM-EDS analysis was performed on regions 1 and 2 of the composite cathode active material of Example 1, and the results are shown in FIG. 13b, FIG. 13c and Table 2 below, indicating the content of each element. FIG. 13c shows the EDS analysis results for the square area of ​​FIG. 13b.

[0277] element Atomic % (Atomic %) Area 1(LCO) Area 2(Li-Zr-O) O 59.10 65.64 Mg 0.37 0.39 Ca 0.10 2.98 Ti 0.26 0.30 Co 39.73 12.98 Zr 0.43 17.71

[0278] From Figures 13b, 13c and Table 2, it was confirmed that the Zr content was relatively high when the region of the first lithium zirconium-based oxide observed to be several tens of nm in size inside the LCO was magnified and measured by EDS.

[0279] delete

[0280] Although the above description has been made with reference to preferred manufacturing examples, those skilled in the art will understand that various modifications and changes can be made without departing from the spirit and scope of the claims set forth below. Explanation of the symbols

[0281] 31: Lithium-ion battery 32: Negative electrode 33: Anode 34: Separator 35: Battery Case

Claims

Claim 1 A composite cathode active material for a lithium secondary battery comprising a lithium cobalt-based oxide, wherein a particle coating portion is disposed in an island shape on one surface of the lithium cobalt-based oxide, and the particle coating portion comprises a first coating layer containing a lithium titanium-based oxide, wherein an internal region of the lithium cobalt-based oxide disposed corresponding to the particle coating portion comprises a lithium-deficient cobalt oxide phase having a molar ratio of lithium to cobalt of 0.9 or less, and a first lithium zirconium-based oxide existing spaced apart from the surface of the lithium cobalt-based oxide, wherein the aluminum content in the lithium cobalt-based oxide is 4,000 ppm or more and the magnesium content is 1,000 ppm or more, and the lithium-deficient cobalt oxide phase comprises a compound represented by Chemical Formula 5, a compound represented by Chemical Formula 5-1, or a compound represented by Chemical Formula 5-2, wherein the particle coating portion further comprises a second coating layer, and the second coating layer is disposed on top of the first coating layer. Composite cathode active material for lithium secondary batteries containing lithium zirconium-based oxide: [Chemical Formula 5]Li 1-α Mg a Co 1-x M x O2 chemical formula 5, M is W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, Nb or a combination thereof, 0.1 ≤ α ≤ 0.5, 0 <a≤0.05, 0≤x≤0.05이고,[화학식 5-1]Li 1-α Mg a Co 2-x M x In chemical formula 5-1 of O4, M is W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, Nb, or a combination thereof, where 0.1 ≤ α ≤ 0.5, 0 <a≤0.05, 0≤x≤0.05이고,[화학식 5-2]Co 3-x M x In the chemical formula 5-2 of O4, M is W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, Nb or a combination thereof, and 0≤x≤0.

05. Claim 2 In claim 1, the lithium cobalt-based oxide is a composite cathode active material for a lithium secondary battery comprising magnesium and aluminum. Claim 3 A composite cathode active material for a lithium secondary battery according to claim 1, wherein the ratio of the magnesium content to the cobalt content contained in the lithium-deficient cobalt oxide (moles of magnesium / moles of cobalt) is greater than the ratio of the magnesium content to the cobalt content of the lithium cobalt-based oxide (moles of magnesium / moles of cobalt). Claim 4 delete Claim 5 A composite cathode active material for a lithium secondary battery according to claim 1, wherein a surface coating portion is disposed in an internal region of another surface of the lithium cobalt-based oxide, and the surface coating portion contains a third coating layer having a spinel crystal structure. Claim 6 delete Claim 7 A composite cathode active material for a lithium secondary battery according to claim 1, wherein the content of the second lithium zirconium-based oxide is 0.05 to 0.2 parts by weight based on 100 parts by weight of lithium cobalt-based oxide. Claim 8 In claim 1, the second lithium zirconium-based oxide is a composite cathode active material for a lithium secondary battery comprising a compound represented by the following chemical formula 2: [Chemical Formula 2]Li 2+a Zr (1-x-z) Co z M2 x In the chemical formula 2 of O3, M2 is one or more elements selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and aluminum (Al), and -0.1≤a≤0.1, 0≤x<1, 0≤z≤0.

1. Claim 9 A composite cathode active material for a lithium secondary battery according to claim 1, wherein the inner region is arranged to be in contact with a particle coating portion, and the first lithium zirconium-based oxide comprises particles at a position spaced apart from the inner region. Claim 10 A composite cathode active material for a lithium secondary battery according to claim 1, wherein the first lithium zirconium-based oxide is present within 150 nm from the surface of a lithium cobalt-based oxide. Claim 11 In claim 1, the first lithium zirconium-based oxide has a layered crystal structure and is a compound represented by the following chemical formula 6, a composite cathode active material for a lithium secondary battery: [Chemical Formula 6]Li 2+a Zr (1-x-z) Co z M1 x In the chemical formula 6 of O3, M1 is one or more elements selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and aluminum (Al), and -0.1≤a≤0.1, 0≤x<1, 0≤z≤0.

5. Claim 12 A composite cathode active material for a lithium secondary battery according to claim 1, wherein the lithium-deficient cobalt oxide phase has a spinel crystal structure and the lithium-deficient cobalt oxide phase exists in a region within 100 nm of the outermost surface (third surface) of the lithium cobalt-based oxide. Claim 13 delete Claim 14 A composite cathode active material for a lithium secondary battery according to claim 1, wherein the lithium titanium-based oxide is a compound represented by the following chemical formula 1: [Chemical Formula 1]Li 2+a Ti (1-x-y) Co x Mg y In chemical formula 1 of O3, -0.1≤a≤0.1, 0 <x≤0.5, 0<y≤0.1이다. Claim 15 A composite cathode active material for a lithium secondary battery according to claim 5, wherein the surface coating portion comprises a lithium cobalt-based oxide A, and the lithium cobalt-based oxide A is LiCo2O4. Claim 16 A composite cathode active material for a lithium secondary battery according to claim 15, wherein the content of the lithium cobalt-based oxide A is 0.01 to 1 weight part based on 100 weight parts of the lithium cobalt-based oxide. Claim 17 In claim 1, the lithium cobalt-based oxide is a compound represented by the following chemical formula 3, a composite cathode active material for a lithium secondary battery: [Chemical Formula 3]Li a-b Mg b Co (1-x-y-b) Al x M3 y In chemical formula 3 of O2, 0.9≤a≤1.1, 0≤b≤0.02, 0≤x≤0.04, 0≤y≤0.01, and M3 is Ni, K, Na, Ca, Mg, Si, Fe, Cu, Zn, Ti, Sn, V, Ge, Ga, B, P, Se, Bi, As, Zr, Mn, Cr, Ge, It is one selected from Sr, V, Sc, Y and combinations thereof. Claim 18 A composite cathode active material for a lithium secondary battery according to claim 1, wherein the content of lithium titanium-based oxide in the particle coating portion is 0.05 to 1.0 parts by weight based on 100 parts by weight of lithium cobalt-based oxide. Claim 19 A composite cathode active material for a lithium secondary battery according to claim 1, wherein the lithium cobalt-based oxide is a small particle, a large particle, or a mixture of small particles and large particles, the size of the large particle is 10 to 20 μm, and the size of the small particle is 3 to 6 μm. Claim 20 delete Claim 21 A composite cathode active material for a lithium secondary battery according to claim 19, wherein the mixing weight ratio of the large particles to the small particles in the mixture of the large particles and small particles is 7:3 to 9:

1. Claim 22 A method for manufacturing a composite cathode active material for a lithium secondary battery according to any one of claims 1 to 3, 5, 7 to 12, 14 to 19, and 21, comprising the steps of: mixing a lithium cobalt-based oxide, a titanium precursor, and cobalt hydroxide to obtain a first precursor mixture, and performing a first heat treatment on the first precursor mixture to obtain a first heat-treated product; mixing the first heat-treated product and a zirconium precursor to obtain a second precursor mixture, and performing a heat treatment on the second precursor mixture, wherein the content of the zirconium precursor is 0.6 to 1.4 parts by weight based on 100 parts by weight of the lithium cobalt-based oxide. Claim 23 delete Claim 24 A method for manufacturing a composite cathode active material for a lithium secondary battery according to claim 22, wherein the content of the cobalt hydroxide is 3.5 to 7 parts by weight based on 100 parts by weight of a lithium cobalt-based oxide. Claim 25 A method for manufacturing a composite cathode active material for a lithium secondary battery, wherein, in claim 22, the zirconium precursor is zirconium oxide and the titanium precursor is one or more selected from titanium hydroxide, titanium chloride, titanium sulfate, and titanium oxide. Claim 26 A method for manufacturing a composite cathode active material for a lithium secondary battery according to claim 22, wherein the heat treatment of the first precursor mixture is carried out at 850°C to 980°C. Claim 27 A method for manufacturing a composite cathode active material for a lithium secondary battery according to claim 22, wherein the heat treatment of the second precursor mixture is carried out at 950°C to 1000°C. Claim 28 A lithium secondary battery comprising a positive electrode comprising a composite positive active material according to any one of claims 1 to 3, 5, 7 to 12, 14 to 19, and 21; a negative electrode; and an electrolyte interposed between the two.

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