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

Abstract

Disclosed are a composite positive electrode active material for a lithium secondary battery including a lithium cobalt-based oxide; a method for manufacturing the same; and a lithium secondary battery including a positive electrode including the composite positive electrode active material, wherein in the composite positive electrode active material for a lithium secondary battery, a particle coating portion is arranged in the form of an island on one surface of a lithium cobalt-based oxide, the particle coating portion includes a first coating layer including a lithium titanium-based oxide, and a surface coating portion is arranged in an inner region of another surface of the lithium cobalt-based oxide.

Description

[0001] Cross-references to related applications

[0002] This application is based on and claims priority to Korean Patent Application No. 10-2021-0152434, filed on November 8, 2021, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure relates to composite positive electrode active materials for lithium secondary batteries, methods for preparing the same, and lithium secondary batteries including a positive electrode containing the composite positive electrode active material. Background Technology

[0004] Recently, with the development of advanced electronics industry leading to miniaturization and weight reduction of electronic devices, the use of portable electronic devices is increasing. Lithium-ion batteries, with their high energy density and long lifespan, are widely used as the power source for these portable electronic devices.

[0005] Lithium cobalt oxide (LiCoO2) is widely used as the positive electrode active material in high-density lithium secondary batteries. However, when lithium cobalt oxide is used as the positive electrode active material, the active material comes into contact with the electrolyte in the battery environment, and especially at high temperatures, the interface structure is destroyed due to HF corrosion, resulting in the dissolution of cobalt (Co) and a reduction in the capacity of the lithium secondary battery.

[0006] To prevent the layered positive electrode active material structure from collapsing in a high-voltage environment, aluminum is doped into lithium cobalt oxide.

[0007] However, when aluminum is doped in this way, the high-voltage characteristics do not reach a satisfactory level, and therefore, improvements are needed. Summary of the Invention

[0008] On the one hand, it provides novel composite positive electrode active materials for lithium secondary batteries with improved stability and their manufacturing methods.

[0009] On the other hand, it provides lithium secondary batteries that have improved stability at high voltages and enhanced high-temperature characteristics by containing a positive electrode containing a composite positive electrode active material for lithium secondary batteries.

[0010] Other aspects will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the embodiments presented in this disclosure.

[0011] According to one aspect, a composite positive electrode active material for lithium secondary batteries, comprising lithium cobalt oxides, is provided, wherein...

[0012] The particle-coated portion is arranged in the form of an island on one surface of the lithium cobalt-based oxide, the particle-coated portion includes a first coating layer containing a lithium titanium-based oxide, and

[0013] The surface-coated portion is arranged in an inner region of the other surface of the lithium cobalt-based oxide.

[0014] According to another aspect, there is provided a method of manufacturing a composite positive electrode active material for a lithium secondary battery, the method including: obtaining a first precursor mixture by mixing a lithium cobalt-based oxide containing magnesium and aluminum, a titanium precursor, and a cobalt hydroxide, and performing a primary heat treatment on the first precursor mixture to prepare a primary heat-treated product; and

[0015] obtaining a second precursor mixture by mixing the primary heat-treated product and a zirconium precursor, and performing a secondary heat treatment on the second precursor mixture.

[0016] The amount of the cobalt hydroxide is 1 to 3 parts by weight with respect to 100 parts by weight of the lithium cobalt-based oxide. Also, the amount of the zirconium precursor is 0.2 to 0.54 parts by weight with respect to 100 parts by weight of the lithium cobalt-based oxide.

[0017] The zirconium precursor is zirconium oxide, and the titanium precursor is at least one selected from the group consisting of titanium hydroxide, titanium chloride, titanium sulfate, and titanium oxide.

[0018] The heat treatment of the first precursor mixture is performed at 850 to 980°C, and the heat treatment of the second precursor mixture is performed at 750 to 900°C.

[0019] According to another aspect, there is provided a lithium secondary battery including: a positive electrode including the above-described composite positive electrode active material;

[0020] a negative electrode; and

[0021] an electrolyte arranged between the positive electrode and the negative electrode. BRIEF DESCRIPTION OF DRAWINGS

[0022] The above and other aspects, features and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0023] Figure 1A schematically illustrating a structure of a composite positive electrode active material according to an embodiment;

[0024] Figure 1B schematically illustrating a structure of a composite positive electrode active material according to another embodiment;

[0025] Figures 2A to 2FResults of a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) analysis of the composite cathode active material prepared according to Example 1 are shown.

[0026] Figure 3 The structure of a lithium secondary battery according to the embodiment is schematically illustrated; and

[0027] Figure 4 Results of a high resolution transmission electron microscope (HR-TEM) analysis of the composite cathode active material of Example 1 are shown. DETAILED DESCRIPTION

[0028] Reference will now be made in detail embodiments, which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments can have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present description. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Expressions such as "at least one of," when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

[0029] Hereinafter, the composite cathode active material, a method of preparing the same, and a lithium secondary battery including a positive electrode comprising the composite cathode active material according to exemplary embodiments will be described in more detail.

[0030] Lithium cobalt oxide (LiCoO2) is a high-capacity cathode active material and has an O3-type layered structure in which lithium, cobalt, and oxygen are regularly arranged along the

[111] plane of a rock-salt structure as O-Li-O-Co-O-Li-O-Co-O. When a lithium secondary battery having a positive electrode including such lithium cobalt oxide is charged, lithium ions are deintercalated from the lithium cobalt oxide lattice to the outside of the lattice.

[0031] When the charging voltage of the lithium secondary battery increases, the amount of lithium ions deintercalated from the lattice of the lithium cobalt oxide increases, and at least a portion of the O3-type layered structure can undergo a phase transition to an O1-type layered structure (O1 phase) in which Li is not present in the lattice. Accordingly, when the (full-cell-based) charging voltage is 4.52 V or higher, the lithium cobalt oxide can undergo a phase transition to an H1-3-type layered structure (H1-3 phase) in which both the O3-type layered structure and the O1-type layered structure are present in the lattice of the lithium cobalt oxide. As such, 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. Also, in the H1-3-type layered structure and the O1-type layered structure, the lithium ions that can be intercalated / deintercalated decrease. When such a phase transition occurs, the storage and life characteristics of the lithium secondary battery inevitably rapidly deteriorate. In addition, when the lithium cobalt oxide contacts the electrolyte, especially at high temperatures, the interface structure can be destroyed due to corrosion by HF, leading to elution of Co and reduction of the battery capacity, and the structure of the positive active material having a layered structure can collapse under a high-voltage environment.

[0032] To solve this problem, it is proposed to use a lithium cobalt oxide doped with aluminum and magnesium as a positive active material. However, a lithium secondary battery employing a positive electrode using such a positive active material has high-voltage characteristics that do not reach a satisfactory level and needs improvement.

[0033] To solve the above problem, a composite positive active material according to an embodiment is produced.

[0034] The composite positive active material according to the embodiment has a structure in which, when a lithium cobalt-based oxide having a certain amount of aluminum and magnesium is reacted with a titanium precursor, a zirconium precursor, and a cobalt precursor, the magnesium of the lithium cobalt-based oxide moves to the surface, and a particle-coated portion having a first coating layer containing a lithium titanium-based oxide is formed in the form of islands on the surface of the lithium cobalt-based oxide by the Mg-Ti Kirkendall effect.

[0035] The composite positive active material according to the embodiment has a particle-coated portion and a surface-coated portion, and thus the reaction area between the composite positive active material and the electrolyte decreases, and side reactions are effectively suppressed.

[0036] The composite positive active material according to the embodiment is a lithium cobalt-based oxide, the particle-coated portion can be arranged in the form of islands on one surface (i.e., a first surface) of the lithium cobalt-based oxide, and the surface-coated portion can be arranged in a first internal region arranged in contact with or adjacent to the other surface (i.e., a second surface) of the lithium cobalt-based oxide.

[0037] The particle-coated portion includes a first coating layer containing a lithium titanium-based oxide.

[0038] The second coating layer containing a lithium-zirconium-based oxide can be further included on the first coating layer. In addition, the surface-coated portion can include a third coating layer having a spinel crystal structure.

[0039] The lithium-cobalt-based oxide according to the embodiments includes magnesium and aluminum. In the lithium-cobalt-based oxide, the amount of aluminum (Al) is 4,000 ppm or more (e.g., 4,000 ppm to 6,000 ppm). The content of aluminum is 1.5 mol% to 3.0 mol%, or 2.0 mol% to 2.5 mol% with respect to the total metal excluding lithium in the core active material. As used herein, the ppm content of aluminum refers to the mass of one millionth of the mass of aluminum with respect to the total positive electrode active material.

[0040] When the aluminum content is within the range, the structural stability of the composite positive electrode active material is improved, and thus, a composite positive electrode active material in which the high-voltage characteristics are improved, the reduction in battery capacity is minimized, and the increase in resistance is minimized can be obtained. In addition, in the lithium-cobalt-based oxide, the amount of magnesium (Mg) is 1,000 ppm or more (e.g., 1,000 ppm to 1,500 ppm). The content of magnesium is 0.25 mol% to 0.7 mol% with respect to the total metal excluding lithium in the core active material. As used herein, the ppm content of magnesium refers to the mass of one millionth of the mass of magnesium with respect to the total positive electrode active material.

[0041] Even when the aluminum content in the composite positive electrode active material is 4,000 ppm or more as described above, although the Al content increases, aluminum is rarely diffused to the coating layer, and the effect of the structural stability of the composite positive electrode active material can also be achieved since a part of Al is doped to the Li site. Therefore, the composite positive electrode active material has excellent electrical conductivity due to excellent high-temperature characteristics and improved surface resistance. Accordingly, even in a high-temperature and high-voltage environment, such a composite positive electrode active material has enhanced structural stability of the crystal structure of the lithium-cobalt-based oxide, and thus, a positive electrode active material having excellent lifespan and storage characteristics and improved resistance characteristics can be implemented.

[0042] In the present specification, "high voltage" refers to a voltage in the range of 4.3 V to 4.8 V.

[0043] In the composite positive electrode active material according to the embodiments, the amount of titanium can be 500 ppm to 800 ppm, and the amount of zirconium can be 2,100 ppm to 4,000 ppm. As used herein, the ppm content of titanium refers to the mass of one millionth of the mass of titanium with respect to the total positive electrode active material, and the ppm content of zirconium refers to the mass of one millionth of the mass of zirconium with respect to the total positive electrode active material.

[0044] Figure 1AThe structure of the composite positive electrode active material according to the embodiment is schematically explained.

[0045] Referring to Figure 1A , the composite positive electrode active material 10 can include the particle-coated portion 12 on at least one surface (i.e., the first surface 14 of the lithium cobalt-based oxide 11) and the surface-coated portion 13 on at least one surface (i.e., the second surface 15 of the lithium cobalt-based oxide 11), as well as the particle-coated portion 12. The surface-coated portion 13 can have a layer form.

[0046] As Figure 1B shown in the above, the particle-coated portion 12 contains a first coating layer 12a disposed in contact with the lithium cobalt-based oxide and a second coating layer 12b disposed on the first coating layer 12a. The first coating layer contains a lithium titanium-based oxide, and the second coating layer contains a lithium zirconium-based oxide.

[0047] In Figure 1A , the particle-coated portion 12 has a semicircular shape, but is not limited thereto. When the particle-coated portion 12 exists in the form of an island, the surface resistance of the composite positive electrode active material is further improved, as compared to the case when the particle-coated portion has a continuous form. The size of the particle-coated portion can be 3.0 µm or less (e.g., 0.5 µm to 3 µm). Here, the size of the particle-coated portion refers to the thickness, which can be measured by using a scanning electron microscope or a transmission electron microscope.

[0048] In the present specification, the "thickness" of the particle-coated portion refers to the distance in the direction from the outer surface of the lithium cobalt oxide particle to the outer surface of the particle-coated portion.

[0049] The surface-coated portion 13 is present in the inner region in contact with the second surface 15 of the lithium cobalt-based oxide 11. The surface-coated portion 13 includes a third coating layer having a spinel crystal structure. When the surface-coated portion 13 is present, the high-temperature life characteristics of the composite positive electrode active material can be improved.

[0050] As used herein, as Figure 1A shown in the above, the first surface 14 refers to one surface of the lithium cobalt-based oxide 11 on which the particle-coated portion 12 is formed. Also, the second surface 15 refers to the other surface of the lithium cobalt-based oxide 11 on which the surface-coated portion 13 is formed.

[0051] In the composite positive electrode active material according to the embodiment, the lithium-deficient cobalt oxide has a spinel crystal structure (Co3O4 spinel phase (Fd-3m)).

[0052] Specific examples of the lithium-deficient cobalt oxide are a compound represented by Formula 5, a compound represented by Formula 5-1, a compound represented by Formula 5-2, or any combination thereof:

[0053] Formula 5

[0054] Li 1-α Mg a Co 1-x M x O2,

[0055] wherein in Formula 5, M is W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, Nb, or any combination thereof, 0.01≤α≤0.5, 0≤a≤0.05, and 0≤x≤0.05,

[0056] Formula 5-1

[0057] Li 1-α Mg a Co 2-x M x O 4，

[0058] wherein in Formula 5-1, M is W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, Nb, or any combination thereof, 0.01≤α≤0.5, 0≤a≤0.05, and 0≤x≤0.05,

[0059] Formula 5-2

[0060] Co 3-x M x O4

[0061] wherein in Formula 5-2, M is W, Mo, Zr, Ti, Mg, Ta, Al, Fe, V, Cr, Ba, Ca, Nb, or any combination thereof, 0≤x≤0.05.

[0062] The lithium-deficient cobalt oxide can include, for example, Li 0.95 CoO2, Li 0.95 Co2O4, Li 0.8 Mg 0.007 CoO2, or any combination thereof.

[0063] The thickness of the particle-coated portion 12 can be, for example, 100 nm to 500 nm.

[0064] According to an embodiment, the particle-coated portion 12 includes a first coating layer 12a.

[0065] According to another embodiment, as Figure 1B shown in FIG. 1, the particle-coated portion 12 has a structure in which the second coating layer 12b is disposed on the first coating layer 12a, and a boundary of the first coating layer 12a and the second coating layer 12b can be formed non-uniformly. Referring to Figure 1BThe boundary of the first coating layer 12a and the second coating layer 12b is not uniform, but can be formed uniformly in some cases.

[0066] 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 thicker 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 in this range, a composite positive electrode active material having improved surface resistance can be obtained.

[0067] The surface coating portion 13 includes a third coating layer having a spinel crystal structure. Here, the thickness of the third coating layer can be not more than 100 nm (for example, 10 nm to 100 nm). The third coating layer can contain, for example, lithium cobalt-based oxide A.

[0068] In the present specification, the "thickness" of the particle coating portion refers to the distance in the direction from the outer surface of the lithium cobalt oxide particle to the outer surface of the particle coating portion. The thickness of the first coating layer refers to the distance in the direction from the outer surface of the lithium cobalt oxide particle to the outer surface of the first coating layer. The thickness of the second coating layer refers to the distance from the outer surface of the first coating layer to the outer surface of the particle coating portion. The thickness of the third coating layer refers to the distance from the outer surface of the first coating layer to the inner surface of the third coating layer. The thickness can be determined by SEM or TEM analysis of the cross section of the particle. If the coating layer has a non-uniform thickness, the thickness can be determined by the average distance. In the embodiment, the thickness is determined by SEM or TEM analysis.

[0069] The amount of lithium titanium-based oxide in the particle coating portion can be 0.05 parts by weight to 1.0 parts by weight with respect to 100 parts by weight of the lithium cobalt-based oxide, and the amount of lithium zirconium-based oxide in the particle coating portion can be 0.05 parts by weight to 0.2 parts by weight with respect to 100 parts by weight of the lithium cobalt-based oxide. When the content of the lithium titanium-based oxide and the lithium zirconium-based oxide is in this range, the diffusion coefficient of lithium ions increases and the electrical conductivity increases, so that a composite positive electrode active material having a stable structure in which the side reaction with the electrolyte is suppressed and the elution of cobalt is suppressed can be obtained.

[0070] The amount of lithium cobalt-based oxide A in the third coating layer of the surface coating portion can be 0.01 parts by weight to 1 parts by weight with respect to 100 parts by weight of the lithium cobalt-based oxide. The lithium cobalt-based oxide A can be, for example, LiCo2O4, and when the amount of the lithium cobalt-based oxide A is in this range, a composite positive electrode active material having improved electrical conductivity can be obtained.

[0071] When the content of the lithium titanium-based oxide in the first coating in the particle-coated portion, the amount of the lithium zirconium-based oxide in the second coating in the particle-coated portion, and the amount of the lithium cobalt-based oxide A in the surface-coated portion are within the ranges, the diffusion coefficient of lithium ions increases and the electrical conductivity increases, and thus a composite positive electrode active material having a stable structure in which a side reaction with an electrolyte is inhibited can be prepared.

[0072] Examples of the lithium titanium-based oxide in the first coating are compounds represented by Formula 1:

[0073] Formula 1

[0074] Li 2+a Ti (1-x-y) Co x Mg y O3,

[0075] wherein in Formula 1, -0.1 ≤ a ≤ 0.1, 0 < x ≤ 0.5, and 0 < y ≤ 0.1.

[0076] In Formula 1, x can be, 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 can be, for example, 0.01 to 0.08, 0.01 to 0.05, or 0.01 to 0.03.

[0077] The lithium titanium-based oxide can be, for example, Li2Ti 0.97 Co 0.02 Mg 0.01 O3, and the like.

[0078] Examples of the lithium zirconium-based oxide in the second coating are compounds represented by Formula 2:

[0079] Formula 2

[0080] Li 2+a Zr (1-x-z) Co z M2 x O3,

[0081] wherein in Formula 2, M2 is at least one element 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),

[0082] -0.1 ≤ a ≤ 0.1, 0 ≤ x < 1, and 0 ≤ z ≤ 0.1.

[0083] In Formula 2, z is 0.01 to 0.1, 0.01 to 0.08, or 0.01 to 0.05.

[0084] Examples of the lithium zirconium-based oxide can be Li2Zr0.99 Co 0.01 O3, etc.

[0085] The lithium cobalt-based oxide has a rhombohedral layered structure of R-3m. Also, the lithium cobalt-based oxide can be, for example, a compound represented by Formula 3.

[0086] Formula 3

[0087] Li a-b Mg b Co (1-x-y-b) Al x M3 y O2,

[0088] wherein in Formula 3, 0.9 ≤ a ≤ 1.1, 0 ≤ b ≤ 0.02, 0 ≤ x ≤ 0.04, and 0 ≤ y ≤ 0.01, and

[0089] M3 is one selected from the group consisting of Ni, K, Na, Ca, Mg, Si, Fe, Cu, Zn, Ti, Sn, V, Ge, Ga, B, P, Se, Bi, As, Zr, Mn, Cr, Ge, Sr, V, Sc, Y, and any combination thereof.

[0090] An example of the lithium cobalt-based oxide can be a compound represented by Formula 4:

[0091] Formula 4

[0092] Li a-b Mg b Co (1-x-b) Al x O2,

[0093] wherein in Formula 4, 0.9 ≤ a ≤ 1.1, 0.001 ≤ b ≤ 0.01, and 0.01 < x ≤ 0.03.

[0094] In Formula 4, a can be, for example, 0.9 to 1.05.

[0095] In Formula 3 and Formula 4, 0.015 < x ≤ 0.03 and 0.005 ≤ b ≤ 0.01.

[0096] The total thickness of the first coating layer and the second coating layer in the composite positive electrode active material according to the embodiment can be 500 nm to 800 nm, and the thickness of the third coating layer can be not greater than 100 nm (for example, 10 nm to 50 nm).

[0097] The second coating layer is disposed on the first coating layer, and the boundary between the first coating layer and the second coating layer can be uniform or non-uniform.

[0098] In the composite positive electrode active material according to the embodiment, the ratio of the thickness of the first coating layer to the thickness of the second coating layer can be 1.1:1 to 1.5:1. Here, the ratio of the thicknesses can be obtained by analysis using a scanning electron microscope or a transmission electron microscope. As used herein, the thickness of the first coating layer refers to the distance in the direction from the outer surface of the lithium cobalt oxide particle to the outer surface of the first coating layer. The thickness of the second coating layer refers to the distance from the outer surface of the first coating layer to the outer surface of the particle-coated portion.

[0099] The lithium cobalt-based oxide can be, for example, small particles, large particles, or a mixture thereof.

[0100] The size of the large particles can be 10 to 20 µm, and the size of the small particles can be 3 to 6 µm. In addition, in the mixture of the large particles and the small particles, the mixed weight ratio of the large particles to the small particles can be 7:3 to 9:1, 8:2 to 9:1, or 5:1 to 7:1. When the mixed weight ratio of the large particles to the small particles is in this range, the high-temperature life and the high-temperature storage characteristics are improved.

[0101] The size of the large particles can be 10 to 20 µm, 17 to 20 µm, or 18 to 20 µm. And, the size of the small particles can be 3 to 6 µm (for example, 3 to 5 µm or 3 to 4 µm).

[0102] In the present specification, when the particle is spherical, the size of the particle is the particle diameter, and when the particle is non-spherical (such as rod-shaped or needle-shaped), the size of the particle is the length of the long axis. In the present specification, when the particle is spherical, the size of the particle is the particle diameter, and when the particle is non-spherical, the size of the particle is the length of the long axis.

[0103] The particle diameter is, for example, the average particle diameter, and the length of the long axis is, for example, the average length of the long axis. The average particle diameter and the average length of the long axis indicate the average of the measured particle diameters and the measured lengths of the long axes, respectively.

[0104] The particle size can be determined by using a particle size analyzer, a scanning electron microscope, or a transmission electron microscope. For example, the average particle diameter can be the average particle diameter observed by using a scanning electron microscope (SEM). By using the SEM image, the average particle diameter can be calculated as the average particle diameter of about 10 to 30 particles.

[0105] For example, the average particle size can be a median particle size or a D50 particle size. Unless otherwise defined herein, the term "D50" as used herein refers to an average diameter corresponding to 50% by volume of the particles in a cumulative particle size distribution. When the total number of particles in a cumulative particle size distribution curve, in which the particles are sequentially accumulated in order from the particles having the smallest size to the particles having the largest size, is 100%, the term "D50" as used herein refers to a diameter corresponding to 50% in the cumulative particle size distribution curve. The average particle size D50 can be measured by using one or more appropriate methods available in the art, such as, for example, a method using a particle size analyzer (e.g., HORIBA, LA-950 laser particle size analyzer), a transmission electron microscope (TEM), or a scanning electron microscope (SEM). Alternatively, for example, after using a measuring device utilizing dynamic light scattering, data analysis can be performed to calculate the number of particles for each particle size range, which will provide the average particle size D50 value. In an embodiment, the average particle size is measured by using a transmission electron microscope (TEM) or a scanning electron microscope (SEM).

[0106] The composite cathode active material according to the embodiment can have a layered crystal structure, and the specific surface area can be 0.1 m 2 / g to 3 m 2 / g.

[0107] According to another aspect, there is provided a lithium secondary battery including: a positive electrode including the composite cathode active material; a negative electrode; and an electrolyte disposed between the positive electrode and the negative electrode.

[0108] Hereinafter, a method of preparing the composite cathode active material according to the embodiment will be described in detail.

[0109] To prepare the large-particle lithium cobalt-based oxide, a first mixture is obtained by mixing a cobalt precursor, a lithium precursor, and a metal precursor having a particle size of 4 μm to 7 μm.

[0110] Specifically, the first mixture of the precursors can be obtained by mixing while stoichiometrically controlling the mixing ratio of the lithium precursor, the cobalt precursor, and the metal precursor to obtain a lithium cobalt-based oxide represented by the following Formula 3:

[0111] Formula 3

[0112] Li a-b Mg b Co (1-x-y-b) Al x M3 y O2,

[0113] wherein in formula 3, 0.9≤a≤1.1, 0≤b≤0.02, 0≤x≤0.04, and 0≤y≤0.01, and

[0114] M3 is one selected from the group consisting of Ni, K, Na, Ca, Mg, Si, Fe, Cu, Zn, Ti, Sn, V, Ge, Ga, B, P, Se, Bi, As, Zr, Mn, Cr, Ge, Sr, V, Sc, Y, and any combination thereof.

[0115] The metal precursor can be at least one selected from, for example, a magnesium precursor, an aluminum precursor, and an M3 precursor.

[0116] As the lithium precursor, at least one selected from lithium hydroxide (LiOH), lithium carbonate (LiCO3), lithium chloride, lithium sulfate (Li2SO4), and lithium nitrate can be used. As the cobalt precursor, at least one selected from cobalt carbonate, cobalt hydroxide, cobalt chloride, cobalt sulfate, and cobalt nitrate can be used.

[0117] As the aluminum precursor, at least one selected from aluminum sulfate, aluminum chloride, and aluminum hydroxide can be used, and as the magnesium precursor, at least one selected from magnesium sulfate, magnesium chloride, and magnesium hydroxide can be used.

[0118] For the mixing, dry mixing (such as mechanical mixing) can be performed by using a ball mill, a Banbury mixer, a homogenizer, or a Hensel mixer. The dry mixing can reduce manufacturing costs compared to wet mixing.

[0119] The particle size of the cobalt precursor for preparing the first mixture can be 4 μm to 7 μm or 4 μm to 6.0 μm. When the particle size of the cobalt precursor is less than 4 μm or more than 7 μm, it is difficult to obtain a large-particle lithium cobalt-based oxide having a desired size.

[0120] Subsequently, by performing a preliminary heat treatment on the first mixture in air or under an oxygen atmosphere, a large-particle lithium cobalt-based oxide can be obtained. The preliminary heat treatment is performed at 800℃ to 1,100℃.

[0121] The particle size of the large-particle lithium cobalt-based oxide can be 10 μm to 20 μm or 17 μm to 20 μm (for example, 18 μm to 20 μm, for example, 19 μm).

[0122] Respectively, to prepare a small-particle lithium cobalt-based oxide, a second mixture is obtained by mixing a cobalt precursor having a particle size of 2 μm to 3 μm, a lithium precursor, and a metal precursor. Here, the metal precursor is the same as the metal precursor described when manufacturing the first mixture.

[0123] By performing a preliminary heat treatment on the second mixture, a small-particle lithium cobalt-based oxide is prepared. The preliminary heat treatment is performed at 800℃ to 1,000℃.

[0124] The particle size of the small particle lithium cobalt-based oxide can be 3 to 6 μm or 3 to 5 μm (e.g., 3 to 4 μm).

[0125] When the particle size of the cobalt precursor used to prepare the small particle lithium cobalt-based oxide is less than 2 μm or more than 3 μm, it is difficult to obtain a small particle lithium cobalt-based oxide having a desired size.

[0126] When the large particle lithium cobalt-based oxide and the small particle lithium cobalt-based oxide are prepared, the mixing ratio (Li / Me) of lithium and a metal (Me) other than lithium can be 0.9 to 1.1, 1.01 to 1.05, 1.02 to 1.04, 1.02 to 1.03, 1.022 to 1.028, or 1.023 to 1.026.

[0127] When the large particle lithium cobalt-based oxide and the small particle lithium cobalt-based oxide are prepared, the heating rate is 4 to 6 °C / min. When the heating rate is within this range, positive ion mixing can be prevented. When the heating rate is less than 4 °C / min, the phase stability at a high voltage is minimally improved. Also, the molar ratio of lithium and a metal other than lithium can be 1.01 to 1.05, 1.01 to 1.04, 1.02 to 1.03, or 1.04.

[0128] The above-described large particle lithium cobalt-based oxide and the small particle lithium cobalt-based oxide are mixed in a weight ratio of 7:3 to 1:9, and a first precursor mixture is obtained by mixing a titanium precursor and a cobalt hydroxide, and is heat-treated.

[0129] The amount of the cobalt hydroxide is 1 to 3 parts by weight with respect to 100 parts by weight of the lithium cobalt-based oxide. When the amount of the cobalt hydroxide is within this range, a desired composite cathode active material can be obtained.

[0130] The heat treatment is performed at 850 to 980 °C, and the heating rate is 2 to 10 °C / min, or 4 to 6 °C / min. When the heating rate is within this range, a spinel structure can be formed on the surface coating portion.

[0131] The heat treatment can be performed in air or under an oxygen atmosphere. Here, the oxygen atmosphere can be formed by using oxygen alone, or the oxygen atmosphere is formed by using oxygen and an inert gas (such as nitrogen).

[0132] A second precursor mixture is obtained by mixing the product heat-treated 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 performed at 750 to 900℃. The heating rate is 2 to 10℃ / min, for example, 4 to 6℃ / min. When the heating rate is in this range, the surface properties of the composite cathode active material can be controlled as needed.

[0133] Examples of the titanium precursor can be titanium oxide, titanium hydroxide, titanium chloride, or any combination thereof. Cobalt hydroxide has excellent chemical reactivity compared to cobalt oxide. When cobalt oxide is used as the cobalt precursor, because the particle size of cobalt oxide is large, a coating layer in the form of islands can be formed, and a coating layer according to the embodiments can not be formed.

[0134] Cobalt hydroxide having an average particle size of 50 to 300nm or 100 to 200nm is used. By using only cobalt hydroxide having such a size, a composite cathode active material having a coating layer according to the embodiments can be obtained.

[0135] The amount of cobalt hydroxide can be 1 to 3 parts by weight or 1.5 to 2.5 parts by weight with respect to 100 parts by weight of the lithium cobalt-based oxide. Also, the amount of the zirconium precursor can be 0.2 to 0.54 parts by weight with respect to 100 parts by weight of the lithium cobalt-based oxide.

[0136] The zirconium precursor can be zirconium oxide, zirconium hydroxide, zirconium chloride, zirconium sulfate, or any combination thereof.

[0137] The molar ratio of lithium to metals other than lithium in the precursor mixture is controlled to be 0.99 to 1 before heat treatment is performed. When the molar ratio of lithium to metals other than lithium is in the above range, a lithium cobalt composite oxide having improved high-voltage phase stability can be prepared.

[0138] The composite cathode active material according to the embodiments can be prepared according to a general manufacturing method other than a solid processing method, such as a spray pyrolysis method.

[0139] According to another aspect, a positive electrode including a lithium cobalt composite oxide is provided.

[0140] According to still another aspect, a lithium secondary battery including the positive electrode is provided. The manufacturing method of the lithium secondary battery is as follows.

[0141] The positive electrode is prepared according to the following method.

[0142] A positive electrode active material composition in which the composite positive electrode active material according to the embodiment, a binder, and a solvent are mixed is prepared. A conductive agent can be further included in the positive electrode active material composition. A positive electrode plate is prepared by directly coating the positive electrode active material composition on a metal current collector and drying. Alternatively, the positive electrode active material composition can be cast on a separate support, and then a film peeled from the support can be laminated on a positive electrode current collector to prepare a positive electrode plate. In the process of preparing the positive electrode, a first positive electrode active material that is a positive electrode active material commonly used for a lithium secondary battery can be further included. At least one 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 can be further included as the first positive electrode active material, but the first positive electrode active material is not limited thereto, and all substances usable as a positive electrode active material in the art can be used. For example, a compound represented by any one of the following formulas can be used: a A 1-b B 1 b D2(wherein, 0.90≤a≤1.8, and 0≤b≤0.5); Li a E 1-b B 1 b O 2-c D c (wherein, 0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); LiE 2-b B 1 b O 4-c D c (wherein, 0≤b≤0.5, and 0≤c≤0.05); Li a Ni 1-b-c Co b B 1 c D α (wherein, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α≤2); Li a Ni 1-b-c Co b B 1 c O 2-α F 1 α (wherein, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2); Li a Ni 1-b-c Mn b B 1 c D α(wherein, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α≤2); Li a Ni 1-b- c Mn b B 1 c O 2-α F 1 α (wherein, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2); Li a Ni b E c G d O2(wherein, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, and 0.001≤d≤0.1); Li a Ni b Co c Mn d GeO2(wherein, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0.001≤e≤0.1); Li a NiG b O2(wherein, 0.90≤a≤1.8, and 0.001≤b≤0.1); Li a CoG b O2(wherein, 0.90≤a≤1.8, 0.001≤b≤0.1); Li a MnG b O2(wherein, 0.90≤a≤1.8, and 0.001≤b≤0.1); Li a Mn2G b O4(wherein, 0.90≤a≤1.8, 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiI 1 O2; LiNiVO4; Li (3-f) J2(PO4)3(0≤f≤2); Li (3-f) Fe2(PO4)3(0≤f≤2); and LiFePO4. In the above formulas, A is Ni, Co, Mn, or any combination thereof; B 1 is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or any combination thereof; D is O, F, S, P, or any combination thereof; E is Co, Mn, or any combination thereof; F 1 is F, S, P, or any combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or any combination thereof; Q is Ti, Mo, Mn, or any combination thereof; I 1Cr, V, Fe, Sc, Y, or any combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or any combination thereof.

[0143] In the positive electrode active material composition, the binder can be polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyamide-imide, polyacrylic acid (PAA), and other various copolymers.

[0144] The conductive agent is not particularly limited in a range in which the conductive agent does not cause a chemical change in the battery and has electrical conductivity, and is, 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 summer black; conductive fibers, such as carbon nanotubes, carbon fibers, and metal fibers; fluorocarbon; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives.

[0145] The conductive agent can be used in an amount of 1 part by weight to 10 parts by weight, or 1 part by weight to 5 parts by weight. When the amount of the conductive agent is in this range, the electrode finally obtained has excellent electrical conductivity characteristics.

[0146] As non-limiting examples of the solvent, N-methylpyrrolidone or the like can be used, and the amount of the solvent used can be 20 parts by weight to 200 parts by weight with respect to 100 parts by weight of the positive electrode active material. When the amount of the solvent is in this range, the process of forming the positive electrode active material layer is easily performed.

[0147] The thickness of the positive electrode current collector is 3 μm to 500 μm, and the positive electrode current collector is not particularly limited in a range in which the positive electrode current collector does not cause a chemical change in the battery and has electrical conductivity, and is, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. The positive electrode current collector can increase the adhesion of the positive electrode active material by forming fine irregularities on the surface thereof, and various forms, such as a film, a sheet, a foil, a mesh, a porous body, a foam, and a nonwoven fabric, are possible.

[0148] On the other hand, it is also possible to form pores inside the electrode by further adding a plasticizer to the positive electrode active material composition and / or the negative electrode active material composition.

[0149] The contents of the positive active material, the conductive agent, the binder, and the solvent are at levels commonly used in lithium secondary batteries. One or more of the conductive material, the binder, and the solvent can be omitted depending on the purpose and configuration of the lithium secondary battery.

[0150] The negative electrode can be obtained by using almost the same method except that the negative active material is used instead of the positive active material in the process of manufacturing the positive electrode.

[0151] As the negative active material, a carbon-based material, silicon, silicon oxide, a silicon-based alloy, a silicon-carbon-based material composite, tin, a tin-based alloy, a metal oxide, or any combination thereof can be used.

[0152] The carbon-based material can be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon can be graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and the amorphous carbon can be soft carbon (carbon calcined at low temperature) or hard carbon, mesophase pitch carbonizate, calcined coke, graphene, carbon black, carbon nanotube, and carbon fiber, but is not necessarily limited thereto, and all carbon-based materials usable in the art can be used.

[0153] For the negative active material, one selected from the group consisting of Si, SiO x (0 < x < 2, for example, x can be 0.5 to 1.5), Sn, SnO2, a silicon-containing metal alloy, and a mixture thereof can be used. For the metal capable of forming a silicon alloy, at least one selected from the group consisting of Al, Sn, Ag, Fe, Bi, Mg, Zn, In, Ge, Pb, and Ti can be used.

[0154] The negative active material can include a metal / metalloid that can be alloyed with lithium, an alloy thereof, or an oxide thereof. For example, the metal / metalloid that can be alloyed with lithium can be Si, Sn, Al, Ge, Pb, Bi, Sb, a Si-Y alloy (where Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (except Si), a transition metal, a rare earth element, or any combination thereof), a Sn-Y alloy (where Y is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (except Sn), a transition metal, a rare earth element, or any combination thereof), or MnO x (0 < x ≤ 2), etc. The element Y can be 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, or any combination thereof. For example, the oxide of the metal / metalloid that can be alloyed with lithium can be a lithium titanium oxide, a vanadium oxide, a lithium vanadium oxide, SnO2, SiOx (0 < x < 2), etc.

[0155] The negative active material can include, for example, at least one selected from the group consisting of Group 13 elements, Group 14 elements, and Group 15 elements of the periodic table, specifically, at least one selected from the group consisting of Si, Ge, and Sn.

[0156] In the negative active material composition, a non-water-soluble binder, a water-soluble binder, or any combination thereof can be used as a binder.

[0157] As the non-water-soluble binder, ethylene propylene copolymer, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or any combination thereof can be used.

[0158] As the water-soluble binder, styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber (ABR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, oxirane-containing polymer, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, or any combination thereof can be used.

[0159] When the water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included as a thickening agent. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used. The amount of the thickening agent can be 0.1 parts by weight to 3 parts by weight with respect to 100 parts by weight of the negative active material.

[0160] As the conductive agent, a carbon material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; a metal-based material such as a metal powder or metal fiber of copper, nickel, aluminum, silver; a conductive polymer such as a polyphenylene derivative; or a mixture thereof can be used.

[0161] In the negative active material composition, the solvent can be the same as the solvent used in the positive active material composition. Also, the amount of the solvent is at a level commonly used in lithium secondary batteries.

[0162] A separator is interposed between the positive electrode and the negative electrode, and an insulating thin film having high ion permeability and mechanical strength is used.

[0163] The diameter of the pores of the separator is usually 0.01 to 10 μm, and the thickness of the separator is usually 5 to 20 μm. As such a separator, for example, an olefin polymer such as polypropylene is used; a sheet and a non-woven fabric made of glass fiber or polyethylene are used. When a solid polymer electrolyte is used as the electrolyte, the solid polymer electrolyte can also be the separator.

[0164] In a specific example of the olefin polymer in the separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and a mixed multilayer film such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, and the like can be used.

[0165] The non-aqueous electrolyte containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt.

[0166] As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, or an inorganic solid electrolyte is used.

[0167] The non-aqueous electrolyte includes an organic solvent. As the organic solvent, all solvents available in the art as organic solvents can be used. The organic solvent can be, for example, 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 a mixture thereof.

[0168] As the organic solid electrolyte, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate polymer, a polyvinyl alcohol, or the like can be used.

[0169] As the inorganic solid electrolyte, for example, Li3N, Lil, Li5NI2, Li3N-Lil-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-Lil-LiOH, Li3PO4-Li2S-SiS2, or the like can be used.

[0170] The lithium salt is a substance that dissolves well in the non-aqueous electrolyte, and is, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, Li(FSO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F2x+ 1SO2)(C y F 2y+1 SO2)(wherein x, y are natural numbers), LiCl, LiI, or a mixture thereof. In addition, in order to improve charge / discharge characteristics, flame retardancy, and the like, for example, pyridine, triethyl phosphite, triethanolamine, a cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoramide, a nitrobenzene derivative, sulfur, a quinonimine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, a pyrrole, 2-methoxyethanol, aluminum trichloride, and the like can be added. In some cases, a halogen-containing solvent such as carbon tetrachloride, ethylene trifluoride, or the like can be further included to provide non-flammability. The preferred concentration of the lithium salt is in the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is included in this range, the electrolyte has proper conductivity and viscosity, and can exhibit excellent electrolyte performance, and lithium ions can move effectively.

[0171] The lithium secondary battery includes a positive electrode, a negative electrode, and a separator.

[0172] The positive electrode, the negative electrode, and the separator are wound or folded to be packaged in a battery case. Next, an organic electrolyte is injected into the battery case, and then the battery case is sealed with a cap assembly, and a lithium battery is completed. The battery case can have a cylindrical shape, a rectangular shape, or a thin film shape.

[0173] The separator can be disposed between the positive electrode and the negative electrode to form a battery structure. When the battery structure is impregnated with an organic electrolyte, and accommodated in a pouch and sealed, a lithium ion polymer battery is completed.

[0174] In addition, a plurality of battery structures can be laminated to form a battery pack, and such a battery pack can be used for all devices requiring high capacity and high power. For example, the battery pack can be used for a laptop computer, a smart phone, an electric vehicle, and the like.

[0175] The lithium secondary battery according to the embodiment is given as an example in a rectangular shape, but the present disclosure is not limited thereto, and can be used for batteries of various shapes such as a cylindrical shape, a pouch shape, or a coin shape.

[0176] Figure 3 A cross-sectional view schematically illustrating a representative structure of a lithium secondary battery according to an embodiment.

[0177] Reference Figure 3The lithium secondary battery 31 includes a positive electrode 33, a negative electrode 32, and a separator 34. The above-described positive electrode 33, negative electrode 32, and separator 34 are wound or folded to be packed in a battery case 35. The separator 34 is interposed between the positive electrode 33 and the negative electrode 32 according to the shape of the battery, and can form an alternately laminated battery structure. Next, an organic electrolyte is injected into the battery case 35, and then the battery case 35 is sealed with a cover fitting 36, and the lithium secondary battery 31 is completed. The battery case 35 can have a cylindrical shape, a rectangular shape, or a thin film shape. For example, the lithium secondary battery 31 can be a large thin film battery. The lithium secondary battery 31 can be a lithium ion battery. When a battery structure is packed in a pouch, impregnated with an organic electrolyte, and sealed, a lithium ion polymer battery is completed. In addition, a plurality of battery structures can be laminated to form a battery pack, and such a battery pack can be used for all devices requiring high capacity and high power. For example, the battery pack can be used for a laptop computer, a smart phone, an electric vehicle, etc.

[0178] The present disclosure will be described in greater detail by the following examples and comparative examples. However, the examples are intended to illustrate the present disclosure, and the scope of the present disclosure is not limited thereto.

[0179] (Preparation of composite positive electrode active material)

[0180] Example 1 : LCO + with Ti doped with 1,000 ppm Mg and 4,000 ppm (1.45 mol%) Al Surface coating of 700 ppm / Zr 2,250 ppm

[0181] A first mixture was obtained by mixing lithium carbonate, Co3O4 (D50: 4.5 μm), aluminum hydroxide Al(OH)3, and magnesium carbonate as a magnesium precursor. After heating the first mixture to 1088°C at a heating rate of 4.5°C / min, the first mixture was subjected to a preliminary heat treatment at the temperature for 15 hours in an air atmosphere, and Li 1.025 Mg 0.001 Co 0.985 Al 0.015 O2 large particles. Here, the molar ratio of lithium to metals other than lithium (Li / Me) was 1.025. The metals refer to cobalt and aluminum. The metal Me represents the sum of metal elements other than lithium.

[0182] Separately, a second mixture was obtained by mixing Co3O4 (D50: 2.5 μm) as a cobalt precursor, aluminum hydroxide Al(OH)3, lithium carbonate, and magnesium carbonate as a magnesium precursor, and the second mixture was heated to 940°C at a heating rate of 4.5°C / min, and subjected to a heat treatment at the temperature for 5 hours, and Li 1.025 Mg 0.001 Co 0.985 Al 0.015O2(D50: 3.5 μm) small particles. Here, the molar ratio of lithium to metal (Li / Me) is 1.025. The metal Me represents the sum of metal elements other than lithium.

[0183] After mixing the large particles and the small particles obtained in the process in a weight ratio of 8:2, titanium oxide and cobalt hydroxide (Co(OH)2) (average particle diameter: about 100 nm) were added, and a third mixture was obtained.

[0184] The third mixture was heat-treated at about 950°C. Here, the amount of cobalt hydroxide was 2 parts by weight with respect to 100 parts by weight of the large particles or the small particles, and the amount of titanium oxide was stoichiometrically controlled so that the amount of titanium in the composite positive electrode active material was about 700 ppm.

[0185] Subsequently, zirconium oxide was added to the heat-treated product to obtain a fourth mixture, and the fourth mixture was heat-treated at about 850°C. Here, the amount of zirconium oxide was stoichiometrically controlled so that the amount of zirconium in the composite positive electrode active material was about 2250 ppm.

[0186] By the heat treatment, a composite positive electrode active material containing Li 1.025 Mg 0.001 Co 0.985 Al 0.015 O2large particles (D50: 17 μm) and Li 1.025 Mg 0.001 Co 0.985 Al 0.015 O2small particles (D50: 3.5 μm) was obtained, in which the first coating layer and the third coating layer were arranged on the surface, and the second coating layer was arranged on the first coating layer. In addition, the first coating layer contained Li2Ti 0.97 Co 0.02 Mg 0.01 O3, the second coating layer contained Li2Zr 0.98 Co 0.02 O3, and the third coating layer contained LiCo2O 4。

[0187] Example 2: LCO + with Ti doped with 1,000 ppm Mg and 6,000 ppm (2.17 mol%) Al Surface coating of 700 ppm / Zr 2,250 ppm

[0188] A composite positive electrode active material was prepared in the same manner as in Example 1, except that Li 1.025 Mg 0.001 Co 0.978 Al 0.022 O2(D50: 17 μm) and Li 1.025 Mg 0.001 Co 0.978 Al 0.022O2(D50: 3.5 pm) as large particles and small particles.

[0189] Example 3

[0190] A composite cathode active material was prepared in the same manner as in Example 1, except that the amount of zirconium oxide in the fourth mixture was changed so that the amount of zirconium in the composite cathode active material could be about 4,000 ppm.

[0191] Comparative Example 1 : LCO doped with 1,000 ppm Mg [nanoparticle Co(OH)2coating]

[0192] Large particle and small particle composite cathode active materials were prepared in the same manner as in Example 2, except that aluminum hydroxide was not added when preparing the first mixture and the second mixture.

[0193] After mixing the large particles and the small particles obtained in this process in a weight ratio of 8:2, cobalt hydroxide (Co(OH)2) was added, and a third mixture was obtained. The third mixture was subjected to secondary heat treatment at about 900°C, and a bimodal composite cathode active material was obtained.

[0194] Comparative Example 2: LCO doped with 4,000 ppm (1.45 mol%) Al [nanoparticle Co(OH)2coating]

[0195] Large particle and small particle composite cathode active materials were prepared in the same manner as in Example 1, except that magnesium carbonate was not added when preparing the first mixture and the second mixture.

[0196] After mixing the large particles and the small particles obtained in this process in a weight ratio of 8:2, cobalt hydroxide (Co(OH)2) was added, and a third mixture was obtained. The third mixture was subjected to secondary heat treatment at about 900°C, and a bimodal composite cathode active material was obtained.

[0197] Comparative Example 3: LCO doped with 1,000 ppm Mg and 4,000 ppm (1.45 mol%) Al

[0198] Large particle and small particle composite cathode active materials were prepared in the same manner as in Example 1 to obtain Li 1.025 Mg 0.005 Co 0.985 Al 0.015 O2, except that the amounts of lithium carbonate, Co3O4, aluminum hydroxide Al(OH)3, and MgCO3 as a magnesium precursor were stoichiometrically controlled in preparing the first mixture and the second mixture.

[0199] After mixing the large particles and the small particles obtained in this process in a weight ratio of 8:2, cobalt hydroxide (Co(OH)2) was added, and a third mixture was obtained. The third mixture was subjected to secondary heat treatment at about 900°C, and a bimodal composite cathode active material was obtained. 1.025 Mg 0.005Co 0.985 Al 0.015 O2 large particles (D50: 17 μm) and Li 1.025 Mg 0.005 Co 0.985 Al 0.015 A bimodal composite cathode active material of O2 small particles (D50: 3.5 μm).

[0200] Comparative Example 4: LCO doped with 1,000 ppm Mg and 4,000 ppm (1.45 mol%) Al + with Ti Surface coating of 700 ppm [nanoparticle Co(OH)2coating)

[0201] After mixing the large particles and the small particles obtained according to Example 1 in a weight ratio of 8:2, titanium oxide and cobalt hydroxide (Co(OH)2) were added, and a third mixture was obtained. A bimodal composite cathode active material was prepared in the same manner as in Example 1, except that the third mixture was heat-treated to about 950°C, zirconium oxide was not added, and the heat-treated product was not heat-treated.

[0202] (Preparation of lithium secondary battery)

[0203] Manufacturing Example 1

[0204] A mixture of the composite cathode active material obtained according to Example 1, polyvinylidene fluoride, and carbon black as a conductive agent was mixed by using a mixer to remove air bubbles, thereby preparing a uniformly dispersed slurry for forming a composite cathode active material layer. A solvent of N-methyl 2-pyrrolidone was added to the mixture, and the mixing ratio of the composite cathode active material, polyvinylidene fluoride, and carbon black was 98:1:1 in weight ratio. The slurry prepared according to this process was coated on a thin film of aluminum by using a medical blade to prepare a thin electrode plate, and the plate was dried at 135°C for 3 hours or more, and then a positive electrode was prepared through a rolling and vacuum drying process.

[0205] For the negative electrode, a composition for forming a negative active material was obtained by mixing natural graphite, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR), and the negative active material composition was coated on a copper current collector and dried to prepare a negative electrode. The weight ratio of the natural graphite, CMC, and SBR was 97.5:1:1.5 with respect to the total weight of 100 parts by weight of the natural graphite, CMC, and SBR, and the amount of distilled water was about 50 parts by weight.

[0206] A separator (thickness: about 10 μm) consisting of a porous polyethylene (PE) film was placed between the positive electrode and the negative electrode, and an electrolyte was injected to prepare a lithium secondary battery. The electrolyte was a solution of 1.1 M LiPF6dissolved in a mixed solvent of ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3.

[0207] Manufacturing Examples 2 to 6

[0208] A lithium secondary battery was prepared in the same manner as in Production Example 1, except that when the positive electrode was prepared, each of the composite positive electrode active materials of Examples 2 to 6 was prepared instead of the composite positive electrode active material of Example 1.

[0209] Comparative Manufacturing Examples 1 to 4

[0210] A lithium secondary battery was prepared in the same manner as in Production Example 1, except that when the positive electrode was prepared, each of the composite positive electrode active materials of Comparative Examples 1 to 4 was prepared instead of the composite positive electrode active material of Example 1.

[0211] Evaluation Example 1 : Charge / Discharge Characteristics

[0212] The lithium secondary battery was charged at a constant current at 25°C until reaching a state of charge (SOC) of 90%, aged for 48 hours, and the battery was cut off at a current of 0.05°C rate while maintaining a voltage of 4.58V in a constant current / constant voltage mode. Subsequently, the battery was discharged at a constant current of 0.5C rate until the voltage reached 3.0V (formation process).

[0213] The lithium secondary battery that had undergone the formation process was charged at a constant current of 0.2C until the voltage reached 4.55V. After the charging was completed in the battery, there was a rest period of about 10 minutes, and the battery was discharged at a constant current of 0.2C until the voltage reached 3V.

[0214] The initial charge / discharge efficiency was evaluated according to Equation 1 below, and the evaluation results are shown in Table 1.

[0215] < Equation 1 >

[0216] Initial charge / discharge efficiency (%) = (discharge capacity at 0.2C at the first cycle / charge capacity at 0.2C at the first cycle) x 100

[0217] Evaluation Example 2: High Temperature Characteristics

[0218] The lithium secondary battery was charged at a constant current at 45°C until reaching a state of charge (SOC) of 90%, aged for 48 hours, and the battery was cut off at a current of 0.05°C rate while maintaining a voltage of 4.58V in a constant current / constant voltage mode. Subsequently, the battery was discharged at a constant current of 0.5C rate until the voltage reached 3.0V (formation process, first cycle).

[0219] The lithium secondary battery subjected to the first cycle of the formation process was charged at 45°C at a constant current of 0.2 C until the voltage reached 4.55 V. After the completion of the charging in the battery, there was a rest period of about 10 minutes, and then the battery was discharged at a constant current of 0.2 C until the voltage reached 3 V; and this cycle was repeated 50 times for evaluation.

[0220] The high-temperature life was evaluated according to Equation 2 below and the evaluation results are shown in Table 1.

[0221] <Equation 2>

[0222] Life (%) = (discharge capacity at the 40th cycle / charge capacity at the 1st cycle) x 100

[0223] Evaluation Example 3: Direct Current Resistance (DC-IR) Test

[0224] The lithium secondary batteries prepared in Manufacturing Examples 1 to 3 and Comparative Manufacturing Examples 1 to 4 were charged at 25°C at a constant current until the state of charge (SOC) reached 90%, aged for 48 hours, and the battery was cut off while maintaining the voltage at 4.58 V at a current of 0.05 C rate in a constant current / constant voltage mode. Subsequently, the battery was discharged at a constant current of 0.5 C rate until the voltage reached 3.0 V (formation process).

[0225] The lithium secondary battery subjected to the formation process was charged at a constant current of 0.2 C until the voltage reached 4.55 V. After the completion of the charging in the battery, there was a rest period of about 10 minutes, and then the battery was discharged at a constant current of 0.2 C until the voltage reached 3 V.

[0226] The direct current resistance (DC-IR) of the lithium secondary battery subjected to these processes was measured, and the results are shown in Table 1 below:

[0227] [Table 1]

[0228]

[0229] Referring to Table 1, the lithium secondary batteries of Manufacturing Examples 1 to 3 had significantly improved high-temperature life and enhanced resistance characteristics compared to the lithium secondary batteries of Comparative Manufacturing Examples 1 to 4.

[0230] In addition, the charge efficiency / discharge efficiency, high-temperature life, and DC-IR characteristics of the lithium secondary batteries of Manufacturing Examples 4 to 6 were evaluated in the same manner as the charge efficiency / discharge efficiency, high-temperature life, and DC-IR characteristics of the lithium secondary battery of Manufacturing Example 1 evaluated as described above.

[0231] As a result of the evaluation, the lithium secondary batteries of Production Examples 4 to 6 showed the same excellent levels of charge / discharge efficiency, high-temperature life, and DC-IR characteristics as the lithium secondary battery of Production Example 1.

[0232] Evaluation Example 4: SEM-EDS Analysis

[0233] A scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) analysis was performed on the composite cathode active material prepared according to Example 1. For the SEM-EDS, a Spectra 300 (Thermo Fisher) was used.

[0234] The SEM-EDS analysis results are shown in FIG. 6. Figures 2A to 2F Figure 2A The regions measured by EDS mapping are shown. Figure 2B The image mapped for Ti is Figure 2C The image mapped for Mg is Figure 2D The image mapped for O is Figure 2E The image mapped for Co is, and Figure 2F The image mapped for Zr is.

[00236] Referring to these, the core region of the composite cathode active material and the region forming the coated particles indicate that the Co component is uniformly present, the Mg component appears in the region forming the coated particles, and the Zr and Ti components appear in the particle-coated region. It can be seen that the O component is uniformly distributed in both the core region and the coated particle region.

[0235] Evaluation Example 5: High Resolution Transmission Electron Microscopy (HR-TEM)

[0236] A high-resolution transmission electron microscope (HR-TEM) analysis was performed on the composite cathode active material of Example 1, and the analysis results are shown in FIG. 7. Figure 4

[0237] As a result of the analysis, it can be seen that in the composite cathode active material of Example 1, LiCo2O4 having a spinel structure is formed on the surface of the core active material particle having a layered structure (R-3m).

[0238] The composite cathode active material according to the embodiments has an effect of suppressing phase transition on the surface, and can suppress side reactions with electrolytes on the surface.

[0239] A lithium secondary battery having improved high-voltage characteristics can be prepared by applying a positive electrode including such a composite cathode active material. It should be understood that the embodiments described herein should be considered in a descriptive sense only and not for limitation purposes.

[0240] ​​The description of features or aspects of each embodiment typically should be considered in the context of other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the attached figures, those of ordinary skill in the art will understand that various changes in form and detail can be made without departing from the spirit and scope of the disclosure as defined by the appended claims.

Claims

1. A composite positive electrode active material for a lithium secondary battery, comprising: A lithium cobalt-based oxide, wherein a particle-coated portion including a first coating layer containing a lithium titanium-based oxide is arranged in the form of an island on a first surface of the lithium cobalt-based oxide, a surface-coated portion is arranged on a second surface of the lithium cobalt-based oxide, and the particle-coated portion further includes a second coating layer, and the second coating layer is arranged on the first coating layer and contains a lithium zirconium-based oxide, wherein the first surface refers to a surface of the lithium cobalt-based oxide on which the particle-coated portion is formed, and the second surface refers to a surface of the lithium cobalt-based oxide on which the surface-coated portion is formed, the lithium titanium-based oxide is a compound represented by Formula 1: Formula 1 Li 2+a Ti (1-x-y) Co x Mg y O3, wherein in Formula 1, -0.1 ≤ a ≤ 0.1, 0 < x ≤ 0.5, and 0 < y ≤ 0.1, the lithium zirconium-based oxide is a compound represented by Formula 2: Formula 2 Li 2+a Zr (1-x-z) Co z M2 x O3, wherein in Formula 2, M2 is at least one element selected from the group consisting of boron, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, iron, copper, and aluminum, -0.1 ≤ a ≤ 0.1, 0 ≤ x < 1, and 0 ≤ z ≤ 0.1, and the surface-coated portion includes a third coating layer having a spinel crystal structure. 2.The composite cathode active material for a lithium secondary battery of claim 1, wherein an amount of aluminum in the lithium cobalt-based oxide is 4,000 ppm or more, and an amount of magnesium in the lithium cobalt-based oxide is 1,000 ppm or more. 3.The composite cathode active material for a lithium secondary battery of claim 1, wherein the surface-coated portion includes a lithium cobalt-based oxide A, and the lithium cobalt-based oxide A includes LiCo2O4. 4.The composite cathode active material for a lithium secondary battery of claim 3, wherein an amount of the lithium cobalt-based oxide A is 0.01 parts by weight to 1 part by weight with respect to 100 parts by weight of the lithium cobalt-based oxide. 5.The composite cathode active material for a lithium secondary battery of claim 1, wherein the lithium cobalt-based oxide is a compound represented by Formula 3: Formula 3 Li a-b Mg b Co (1-x-y-b) Al x M3 y O2, wherein in Formula 3, 0.9 ≤ a ≤ 1.1, 0 ≤ b ≤ 0.02, 0 ≤ x ≤ 0.04, and 0 ≤ y ≤ 0.01, and M3 is one selected from the group consisting of Ni, K, Na, Ca, Mg, Si, Fe, Cu, Zn, Ti, Sn, V, Ge, Ga, B, P, Se, Bi, As, Zr, Mn, Cr, Ge, Sr, V, Sc, Y, and any combination thereof. 6.The composite cathode active material for a lithium secondary battery of claim 1, wherein in the particle-coated portion, an amount of the lithium titanium-based oxide is 0.05 parts by weight to 1.0 part by weight with respect to 100 parts by weight of the lithium cobalt-based oxide. 7.The composite cathode active material for a lithium secondary battery of claim 1, wherein in the particle-coated portion, an amount of the lithium zirconium-based oxide is 0.05 parts by weight to 0.2 part by weight with respect to 100 parts by weight of the lithium cobalt-based oxide.

8. The composite cathode active material for a lithium secondary battery according to claim 1, wherein the lithium cobalt-based oxide is in the form of small particles, large particles, or a mixture of small particles and large particles, wherein each of the large particles has a size of 10 to 20 μm, and each of the small particles has a size of 3 to 6 μm.

9. The composite cathode active material for a lithium secondary battery according to claim 8, wherein in the mixture of large particles and small particles, the mixed weight ratio of the large particles to the small particles is 7:3 to 9:

1.

10. A method of preparing a composite cathode active material for a lithium secondary battery, the method comprising: mixing a lithium cobalt-based oxide, a titanium precursor, and a cobalt hydroxide to obtain a first precursor mixture, and subjecting the first precursor mixture to a preliminary heat treatment to produce a preliminary heat-treated product; and mixing the preliminary heat-treated product and a zirconium precursor to obtain a second precursor mixture, and subjecting the second precursor mixture to a heat treatment to produce the composite cathode active material according to any one of claims 1 to 9.

11. The method of producing a composite cathode active material for a lithium secondary battery according to claim 10, wherein the amount of the cobalt hydroxide is 1 to 3 parts by weight with respect to 100 parts by weight of the lithium cobalt-based oxide.

12. The method of producing a composite cathode active material for a lithium secondary battery according to claim 10, wherein the amount of the zirconium precursor is 0.2 to 0.54 parts by weight with respect to 100 parts by weight of the lithium cobalt-based oxide.

13. The method of producing a composite cathode active material for a lithium secondary battery according to claim 10, wherein the zirconium precursor is zirconium oxide, and the titanium precursor is at least one selected from the group consisting of titanium hydroxide, titanium chloride, titanium sulfate, and titanium oxide.

14. The method of producing a composite cathode active material for a lithium secondary battery according to claim 10, wherein the preliminary heat treatment of the first precursor mixture is performed at 850 to 980°C.

15. The method of producing a composite cathode active material for a lithium secondary battery according to claim 10, wherein the heat treatment of the second precursor mixture is performed at 750 to 900°C.

16. A lithium secondary battery comprising: a positive electrode including the composite cathode active material according to any one of claims 1 to 9 or produced by the method of producing a composite cathode active material for a lithium secondary battery according to any one of claims 10 to 15; a negative electrode; and an electrolyte disposed between the positive electrode and the negative electrode.

Images