Positive electrode active material

Abstract

The present invention relates to a positive electrode active material including lithium composite transition metal oxide particles in the form of single particles or secondary particles including two or more grains, the positive electrode active material comprising: a first coating portion which is present on the surface of the particles and in the grain boundaries, and contains cobalt (Co); and a second coating portion which is present only on the surface of the particles and in the grain boundaries directly connected to the surface, and contains at least one selected from the group consisting of aluminum (Al), zirconium (Zr), tungsten (W), niobium (Nb), boron (B), titanium (Ti), yttrium (Y), and magnesium (Mg).

Description

positive electrode active material

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0067996, filed May 24, 2024, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a positive electrode active material.

[0005]

[0006] As technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used.

[0007] Lithium-composite transition metal oxides are used as cathode active materials in lithium secondary batteries. Among these, lithium-cobalt-composite metal oxides such as LiCoO2, which exhibit high operating voltage and excellent capacity characteristics, are primarily used. However, LiCoO2 suffers from poor thermal properties due to crystal structure instability following delithiation. Furthermore, its high cost limits its mass use as a power source in fields such as electric vehicles.

[0008] As materials to replace the above LiCoO2, lithium manganese composite metal oxides (such as LiMnO2 or LiMn2O4), lithium iron phosphate compounds (such as LiFePO4), or lithium nickel composite metal oxides (such as LiNiO2) have been developed. Among these, research and development on lithium nickel composite metal oxides, which have a high reversible capacity of about 200 mAh / g and thus facilitate the implementation of large-capacity batteries, is being more actively conducted. However, LiNiO2 has inferior thermal stability compared to LiCoO2, and there is a problem that when an internal short circuit occurs due to external pressure in a charged state, the positive electrode active material itself decomposes, causing the battery to burst and catch fire.

[0009] Accordingly, as a method to improve the low thermal stability while maintaining the excellent reversible capacity of LiNiO2, lithium composite transition metal oxides in which some of the Ni is replaced with Co, Mn, or Al have been developed. Among these, development of high-Ni cathode active materials with a high Ni content and cathode active materials in the form of single particles is actively underway to improve the characteristics of lithium secondary batteries.

[0010] However, high-Ni cathode active materials and single-particle cathode active materials have the problem of a high proportion of NiO reduction layers on the particle surface. Meanwhile, when the proportion of NiO reduction layers on the surface of the cathode active material increases, problems such as increased battery resistance, decreased capacity development, and decreased output occur. Accordingly, a surface treatment technology capable of controlling the NiO reduction layer is required.

[0011]

[0012] The object of the present invention is to provide a cathode active material capable of implementing a battery with improved capacity characteristics and lifespan characteristics.

[0013]

[0014] To solve the above problem, the present invention provides a positive electrode active material.

[0015]

[0016] (1) The present invention provides a cathode active material comprising a lithium composite transition metal oxide particle in the form of a single particle or a secondary particle including two or more grains, a first coating portion that exists on the surface and grain boundary of the particle and includes cobalt (Co); and a second coating portion that exists only on the surface and grain boundary directly connected to the surface of the particle and includes at least one selected from the group consisting of aluminum (Al), zirconium (Zr), tungsten (W), niobium (Nb), boron (B), titanium (Ti), yttrium (Y), and magnesium (Mg).

[0017] (2) The present invention provides a positive electrode active material in the above (1), wherein the lithium composite transition metal oxide includes nickel (Ni), cobalt (Co), and manganese (Mn).

[0018] (3) The present invention provides a positive electrode active material in (1) or (2) above, wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 1.

[0019] [Chemical Formula 1]

[0020] Li a Ni b Co c Mn d M 1 e O2

[0021] In the above chemical formula 1,

[0022] M 1 is at least one selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P and S,

[0023] 0.9≤a≤1.1, 0.5≤b<1.0, 0 <c<0.5, 0<d<0.5, 0≤e≤0.1이다.

[0024] (4) The present invention provides a positive electrode active material in any one of the above (1) to (3), wherein the first coating portion exists in the form of a coating layer, a discontinuously formed island form, or a combination thereof.

[0025] (5) The present invention provides a positive electrode active material in any one of the above (1) to (4), wherein the first coating portion includes at least one selected from the group consisting of lithium cobalt oxide, cobalt oxide, and cobalt hydroxide.

[0026] (6) The present invention provides a positive electrode active material in any one of the above (1) to (5), wherein the second coating portion exists in the form of a coating layer, a discontinuously formed island form, or a combination thereof.

[0027] (7) The present invention provides a positive electrode active material in any one of the above (1) to (6), wherein the second coating part includes an oxide including at least one selected from the group consisting of Al, Zr, W, Nb, B, Ti, Y, and Mg.

[0028] (8) In any one of the above (1) to (7), the positive electrode active material has an average particle diameter (D 50 ) provides a positive electrode active material having a diameter of 1.0㎛ to 30.0㎛.

[0029]

[0030] The positive electrode active material of the present invention comprises a first coating portion that exists on the surface and grain boundaries of lithium composite transition metal oxide particles and includes cobalt (Co); and a second coating portion that exists only on the surface and grain boundaries directly connected to the surface of lithium composite transition metal oxide particles and includes at least one selected from the group consisting of aluminum (Al), zirconium (Zr), tungsten (W), niobium (Nb), boron (B), titanium (Ti), yttrium (Y), and magnesium (Mg), thereby improving the capacity characteristics and life characteristics of a battery including the same. Specifically, the positive electrode active material of the present invention can control the NiO reduction layer, which is a defect at the interface, through the first coating portion and the second coating portion, thereby improving the capacity characteristics and life characteristics of a battery including the same.

[0031] That is, according to the present invention, the electrochemical performance of the positive electrode active material can be improved through selective coating on the surface and grain boundary of the positive electrode active material.

[0032]

[0033] Figure 1 is a SEM image of a positive electrode active material to illustrate the surface and grain boundaries described herein.

[0034] Figure 2 is a HAADF-STEM image and EDS element (cobalt) mapping image of the surface of the positive electrode active material of Example 1.

[0035] Figure 3 is a HAADF-STEM image and EDS element (cobalt) mapping image inside the positive electrode active material of Example 1.

[0036] Figure 4 is a table showing the HAADF-STEM image and EDS element (cobalt, aluminum) mapping image of the surface of the positive electrode active material of Example 2 and quantitative data at a specific portion.

[0037] Figure 5 is a table showing the HAADF-STEM image and EDS element (cobalt and aluminum) mapping image of the positive electrode active material of Comparative Example 1, and quantitative data at specific portions.

[0038] Figure 6 is a TEM image of the surface of the positive electrode active material of Comparative Example 1.

[0039] Figure 7 is a TEM image of the surface of the positive electrode active material of Example 1.

[0040]

[0041] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best possible manner.

[0042] It should be understood that the terms “include,” “comprising,” or “having” used in this specification are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0043] The term "on" in this specification means not only when a configuration is formed directly on top of another configuration, but also when a third configuration is interposed between these configurations.

[0044] In this specification, the term "single particle form" is a concept that contrasts with the spherical secondary particle form formed by agglomeration of tens to hundreds of primary particles manufactured by a conventional method, and means a form in which 1 to 50 primary particles are aggregated. Specifically, in the present invention, the particle in the single particle form may be a single particle composed of 1 primary particle, or may be a form in which 2 to 50, 2 to 40, 2 to 30, 2 to 20, 2 to 15, 2 to 10, or 2 to 5 primary particles are aggregated. In this case, "primary particle" means the smallest unit of a particle recognized when observing a positive electrode active material through a scanning electron microscope (SEM).

[0045] In this specification, “secondary particle form” means a form in which more than 50 to several hundred primary particles are aggregated.

[0046] Meanwhile, the primary particle may be composed of 1 to 10 grains, and the grains can be analyzed using an electron backscatter diffraction (EBSD) analyzer. The grains are units that are indicated by the same color in the electron backscatter diffraction (EBSD) Euler map data of one positive electrode active material particle, and there is no grain boundary within the grain. In other words, the grains are single crystal grains with a regularly arranged crystal lattice structure.

[0047] In this specification, the average particle diameter (D 50 ) means the particle size based on 50% of the volume cumulative particle size distribution of the positive electrode active material or lithium transition metal oxide powder. The average particle diameter (D 50) can be measured using a laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then finding the particle size corresponding to 50% of the volume cumulative amount.

[0048]

[0049] Hereinafter, the present invention will be described in detail.

[0050]

[0051] positive electrode active material

[0052]

[0053] The present invention provides a cathode active material comprising a lithium composite transition metal oxide particle in the form of a single particle or a secondary particle including two or more grains, a first coating portion present on the surface and grain boundaries of the particle and including cobalt (Co); and a second coating portion present only on the surface and grain boundaries directly connected to the surface of the particle and including at least one selected from the group consisting of aluminum (Al), zirconium (Zr), tungsten (W), niobium (Nb), boron (B), titanium (Ti), yttrium (Y), and magnesium (Mg).

[0054] The cathode active material according to the present invention may include lithium composite transition metal oxide particles in the form of single particles or secondary particles, including two or more, specifically three or more, four or more, or five or more grains.

[0055] Fig. 1 is a SEM image of a positive electrode active material for explaining the surface and grain boundary of the particle described in the present specification. The red lines in Fig. 1(A) and Fig. 1(B) indicate the surface of the particle (the boundary between the positive electrode active material and the outside), the light green line in Fig. 1(B) indicates a grain boundary directly connected to the surface (the first grain boundary), and the light blue line in Fig. 1(C) indicates a grain boundary not directly connected to the surface (the second grain boundary). In Fig. 1(C), each boundary line has a vertex of the third degree or higher as its start and end points.

[0056] That is, according to the present invention, the first coating portion may be present on the surface of the particle and the first grain boundary and / or the second grain boundary, and the second coating portion may be present only on the surface of the particle and the first grain boundary.

[0057]

[0058] The present inventors have found that when a cathode active material includes lithium composite transition metal oxide particles in the form of single particles or secondary particles including two or more grains, and includes a first coating portion that is present on the surface and grain boundaries of the particles and includes cobalt (Co); and a second coating portion that is present only on the surface and grain boundaries directly connected to the surface of the particles and includes at least one selected from the group consisting of aluminum (Al), zirconium (Zr), tungsten (W), niobium (Nb), boron (B), titanium (Ti), yttrium (Y), and magnesium (Mg), the performance of a battery including the same, particularly capacity and lifespan characteristics, is improved, and have completed the present invention.

[0059] Meanwhile, if the first coating portion does not exist, there is a problem of initial capacity reduction, if the second coating portion does not exist, there is a problem of rapid degradation due to the occurrence of a NiO reduction layer during cycle evaluation, and if the second coating portion exists even on a grain boundary that is not directly connected to the surface, there is a problem of capacity reduction due to blocking of the Li Path.

[0060] According to the present invention, the second coating part may specifically include at least one selected from the group consisting of aluminum (Al), zirconium (Zr), tungsten (W), niobium (Nb), titanium (Ti), yttrium (Y), and magnesium (Mg), and more specifically, may include at least one selected from the group consisting of aluminum (Al) and zirconium (Zr).

[0061]

[0062] According to the present invention, the lithium composite transition metal oxide may be a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn). In this case, the lithium composite transition metal oxide may contain nickel (Ni) in an amount of 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, or 85 mol% or more among all metals excluding lithium.

[0063] According to the present invention, the lithium composite transition metal oxide may have a composition specifically represented by the following chemical formula 1.

[0064] [Chemical Formula 1]

[0065] Li a Ni b Co c Mn d M 1 e O2

[0066] In the above chemical formula 1,

[0067] M 1is at least one selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P and S,

[0068] 0.9≤a≤1.1, 0.5≤b<1.0, 0 <c<0.5, 0<d<0.5, 0≤e≤0.1이다.

[0069] The above b refers to the atomic fraction of nickel among metal elements other than lithium in the lithium transition metal oxide, and may be 0.5 or more, or 0.6 or more, and may be 0.95 or less, 0.96 or less, 0.97 or less, 0.98 or less, 0.99 or less, or less than 1.0.

[0070] The above c refers to the atomic fraction of cobalt among metal elements other than lithium in the lithium transition metal oxide, and may be greater than 0, 0.01 or more, 0.02 or more, or 0.03 or more, and may be 0.1 or less, 0.2 or less, 0.3 or less, 0.4 or less, or less than 0.5.

[0071] The above d refers to the atomic fraction of manganese among metal elements excluding lithium in the lithium transition metal oxide, and may be greater than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, or 0.08 or more, and may be 0.35 or less, 0.4 or less, or less than 0.5.

[0072] The above e is M among the metal elements excluding lithium in the lithium transition metal oxide. 1 It refers to the elemental fraction of an element, which can be 0 or greater, 0.02 or less, 0.05 or less, or 0.1 or less.

[0073]

[0074] In the present invention, the first coating portion is a coating portion formed not only on the particle surface, which is the outermost part of the lithium composite transition metal oxide, the grain boundary directly connected to the surface, but also on the grain boundary inside the particle that is not directly connected to the surface, as the cobalt-containing raw material penetrates into the grain boundary of the lithium composite transition metal oxide when the lithium composite transition metal oxide and the cobalt-containing raw material are dry-mixed and then heat-treated.

[0075] According to the present invention, the first coating portion may exist in the form of a coating layer, a discontinuously formed island shape, or a combination thereof.

[0076] According to the present invention, the first coating portion may include at least one selected from the group consisting of lithium cobalt oxide, cobalt oxide, and cobalt hydroxide.

[0077]

[0078] In the present invention, the second coating portion is a coating portion formed only on the surface, which is the outermost part of the lithium composite transition metal oxide, and the grain boundary directly connected to the surface, when the raw material containing at least one selected from the group consisting of a lithium composite transition metal oxide or a sintered product of a lithium composite transition metal oxide and a cobalt-containing raw material (hereinafter, M-containing raw material) is dry-mixed and then heat-treated, so that the M-containing raw material penetrates only into the grain boundary directly connected to the surface of the lithium composite transition metal oxide. In other words, the second coating portion is a coating portion that is not formed on a boundary that is not directly connected to the surface.

[0079] According to the present invention, the second coating portion may exist in the form of a coating layer, a discontinuously formed island shape, or a combination thereof.

[0080] According to the present invention, the second coating part may include an oxide including at least one selected from the group consisting of Al, Zr, W, Nb, B, Ti, Y, and Mg. Specifically, the second coating part may include an oxide including at least one selected from the group consisting of Al and Zr. More specifically, the second coating part may include an oxide including Al, an oxide including Zr, or an oxide including Al and Zr. The oxide including at least one selected from the group consisting of Al, Zr, W, Nb, B, Ti, Y, and Mg (hereinafter, M) is lithium M oxide and / or M oxide. For example, when M is Al, it may be lithium aluminum oxide and / or aluminum oxide.

[0081]

[0082] In the present invention, the coating portion being present in the form of a coating layer means that it exists in the form of a thin layer on part or all of the surface or grain boundary of the lithium composite transition metal oxide particle. In addition, the coating portion being present in the form of a discontinuously formed island means that the coating portion does not entirely cover the surface or grain boundary of the lithium composite transition metal oxide particle, but is partially dispersed in the form of small particles.

[0083]

[0084] According to the present invention, the positive electrode active material has an average particle diameter (D 50 ) may be 1.0㎛ to 30.0㎛. Specifically, the average particle diameter (D) of the positive electrode active material in the form of a single particle 50 ) may be 1.0㎛, 2.0㎛, 3.0㎛ or more, 20.0㎛, 25.0㎛, or 30.0㎛ or less. In this case, the rolling rate of the battery including the positive electrode active material can be increased, thereby further improving the performance of the battery.

[0085]

[0086] The positive electrode active material according to the present invention can be manufactured by the following manufacturing method, but is not limited thereto.

[0087] The cathode active material according to the present invention can be manufactured according to a manufacturing method (first manufacturing method (hereinafter, manufacturing method 1)) including: (A) a step of mixing a lithium composite transition metal oxide and a cobalt (Co)-containing raw material, and then performing a first heat treatment at 650°C to 900°C to manufacture a sintered product; and (B) a step of dry mixing the sintered product and a raw material containing M (wherein M is at least one selected from the group consisting of Al, Zr, W, Nb, B, Ti, Y, and Mg), and then performing a second heat treatment at 200°C to 600°C.

[0088] The cathode active material according to the present invention can be manufactured according to a manufacturing method (second manufacturing method (hereinafter, manufacturing method 2)) including the steps of dry mixing a lithium composite transition metal oxide, a cobalt (Co)-containing raw material, and a M (wherein M is at least one selected from the group consisting of Al, Zr, W, Nb, B, Ti, Y, and Mg)-containing raw material, performing a first heat treatment at 650°C to 900°C, and a second heat treatment at 200°C to 600°C.

[0089]

[0090] The positive electrode active material according to the present invention can be manufactured by appropriately controlling the mixing method (dry mixing), heat treatment temperature, and types of cobalt-containing raw materials and M-containing raw materials.

[0091]

[0092] That is, the cathode active material according to the present invention can be manufactured by first mixing and first heat-treating a lithium composite transition metal oxide and a cobalt-containing raw material, and then additionally dry-mixing and second heat-treating an M-containing raw material, or by dry-mixing a lithium composite transition metal oxide, a cobalt-containing raw material, and an M-containing raw material at once, first heat-treating, and then second heat-treating.

[0093]

[0094] Hereinafter, the manufacturing method of the positive electrode active material will be described in more detail. Specifically, the common elements of the manufacturing methods 1 and 2 will be described first, followed by a description of each manufacturing method.

[0095]

[0096] According to the present invention, the lithium composite transition metal oxide may be a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn). In this case, the lithium composite transition metal oxide may contain nickel (Ni) in an amount of 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, or 85 mol% or more among all metals excluding lithium.

[0097] According to the present invention, the lithium composite transition metal oxide may have a composition specifically represented by the following chemical formula 1.

[0098] [Chemical Formula 1]

[0099] Li a Ni b Co c Mn d M 1 e O2

[0100] In the above chemical formula 1,

[0101] M 1is at least one selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P and S,

[0102] 0.9≤a≤1.1, 0.5≤b<1.0, 0 <c<0.5, 0<d<0.5, 0≤e≤0.1이다.

[0103] The above b refers to the atomic fraction of nickel among metal elements other than lithium in the lithium transition metal oxide, and may be 0.5 or more, or 0.6 or more, and may be 0.95 or less, 0.96 or less, 0.97 or less, 0.98 or less, 0.99 or less, or less than 1.0.

[0104] The above c refers to the atomic fraction of cobalt among metal elements other than lithium in the lithium transition metal oxide, and may be greater than 0, 0.01 or more, 0.02 or more, or 0.03 or more, and may be 0.1 or less, 0.2 or less, 0.3 or less, 0.4 or less, or less than 0.5.

[0105] The above d refers to the atomic fraction of manganese among metal elements excluding lithium in the lithium transition metal oxide, and may be greater than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, or 0.08 or more, and may be 0.35 or less, 0.4 or less, or less than 0.5.

[0106] The above e is M among the metal elements excluding lithium in the lithium transition metal oxide. 1 It refers to the elemental fraction of an element, which can be 0 or greater, 0.02 or less, 0.05 or less, or 0.1 or less.

[0107] The above lithium composite transition metal oxide can be manufactured by mixing a cathode active material precursor (e.g., transition metal hydroxide, transition metal oxyhydroxide, etc.), a lithium raw material (e.g., lithium carbonate (Li2CO3), lithium hydroxide (LiOH), LiNO3, CH3COOLi, Li2(COO)2, etc.), and optionally a doping element (e.g., Y, Zr, Al) raw material, and firing at high temperature. At this time, the firing may be a single-stage firing or a multi-stage firing. Meanwhile, when the firing is a two-stage firing, the lithium raw materials may be mixed all before the first firing, or may be mixed separately before the first firing and before the second firing. Meanwhile, the firing may be performed at a temperature of 700°C to 1000°C in an oxygen atmosphere. When the above firing is performed in two stages, the first firing can be performed at a temperature of 700°C to 1000°C in an oxygen atmosphere, and the second firing can be performed at a temperature of 500°C to 1000°C in an oxygen atmosphere.

[0108]

[0109] According to the present invention, the cobalt (Co)-containing raw material may be at least one selected from the group consisting of cobalt hydroxide, cobalt oxide, cobalt acetate, cobalt nitride, and cobalt acetylacetonate. For example, the cobalt (Co)-containing raw material may be Co(OH)2, Co2O3, etc., and preferably Co(OH)2. On the other hand, when a highly reactive material, such as Co(OH)3, cobalt acetate, etc., is used as the cobalt raw material, there may be a problem that too much Co penetrates inside, resulting in almost no coating portion including cobalt.

[0110] According to the present invention, the cobalt (Co)-containing raw material may be mixed in an amount of 0.1 mol% to 5.0 mol% relative to the lithium composite transition metal oxide. When the content of the cobalt-containing raw material is within the above range, the layered crystal structure of the positive electrode active material is well maintained, thereby suppressing the formation of a reduction layer on the surface, and further improving electrochemical performance.

[0111]

[0112] According to the present invention, the M-containing raw material may be at least one selected from the group consisting of M-containing hydroxide, M-containing oxide, M-containing acetate, M-containing nitrate, and M-containing acetylacetonate. For example, the M-containing raw material may be Al(OH)3, Al2O3, ZrO2, WO3, Y2O3, H3BO3, Ta2O5, Nb2O5, MgO, MoO3, etc., and preferably Al(OH)3, Al2O3, ZrO3, H3BO3.

[0113] According to the present invention, the M-containing raw material may be mixed in an amount such that the M element is 200 ppm to 20,000 ppm based on the total weight of the lithium composite transition metal oxide. When the content of the M-containing raw material is within the above range, the layered crystal structure of the positive electrode active material is well maintained, thereby suppressing the formation of a reduction layer on the surface, and the electrochemical performance can be further improved.

[0114]

[0115] (Manufacturing method 1)

[0116] The above manufacturing method 1 includes (A) a step of mixing a lithium composite transition metal oxide and a cobalt (Co)-containing raw material, and then performing a first heat treatment at 650°C to 900°C to manufacture a sintered product; and (B) a step of dry mixing the sintered product and a raw material containing M (wherein M is at least one selected from the group consisting of Al, Zr, W, Nb, B, Ti, Y, and Mg), and then performing a second heat treatment at 200°C to 600°C.

[0117]

[0118] The above step (A) is a step of manufacturing a sintered product by mixing a lithium composite transition metal oxide and a cobalt (Co)-containing raw material and then performing a first heat treatment at 650°C to 900°C. As in step (A), when the lithium composite transition metal oxide and the cobalt-containing raw material are dry-mixed and then heat-treated at a specific temperature, the cobalt-containing raw material penetrates into the grain boundary of the lithium composite transition metal oxide, thereby forming a first coating portion containing cobalt not only on the surface, which is the outermost part of the lithium composite transition metal oxide, and the grain boundary directly connected to the surface, but also on the boundary not directly connected to the surface.

[0119] According to the present invention, the mixing in step (A) may be a dry mixing process, simply mixing a powdered cobalt-containing raw material with a lithium composite transition metal oxide without a solvent. This simplifies the process, reducing costs and producing a positive electrode active material of uniform quality.

[0120] According to the present invention, the first heat treatment of step (A) may be performed at 650°C to 900°C. Specifically, the first heat treatment may be performed at 650°C or higher, 660°C or higher, 670°C or higher, 680°C or higher, 690°C or higher, or 700°C or higher, and may be performed at 800°C or lower, 810°C or lower, 820°C or lower, 830°C or lower, 840°C or lower, 850°C or lower, 860°C or lower, 870°C or lower, 880°C or lower, 890°C or lower, or 900°C or lower. When the first heat treatment temperature of step (A) is within the above range, the cobalt (Co)-containing raw material is decomposed and uniformly spread, so that a coating layer is advantageously formed uniformly on the surface and grain boundary of the lithium transition metal oxide particles.

[0121] Meanwhile, if the first heat treatment temperature of step (A) is less than 650°C, the cobalt-containing raw material may not be decomposed, so the coating layer may not be formed or may grow locally in agglomeration on the surface of the positive electrode active material. If it exceeds 900°C, the thermal energy may be too high, so the coating layer may not grow uniformly and the cobalt-containing raw materials may grow in agglomeration. In addition, lithium composite transition metal oxide particles may also clump together due to the high thermal energy.

[0122] According to the present invention, the first heat treatment of step (A) can be performed under an oxygen atmosphere or an air atmosphere. Here, an oxygen atmosphere means an atmosphere in which the oxygen partial pressure is higher than that of an air atmosphere.

[0123] According to the present invention, the first heat treatment of step (A) can be performed for 1 to 25 hours to increase the crystallinity of the coating portion.

[0124]

[0125] The step (B) above is a step of dry-mixing the sintered product manufactured in the step (A) and the raw material containing M (wherein M is at least one selected from the group consisting of Al, Zr, W, Nb, B, Ti, Y, and Mg), and then performing a second heat treatment at 200°C to 600°C. When the sintered product and the raw material containing M are dry-mixed as in step (B) and then heat-treated at a specific temperature, the M-containing raw material penetrates only into the grain boundary directly connected to the surface of the lithium composite transition metal oxide, and a second coating is formed only on the surface, which is the outermost part of the lithium composite transition metal oxide, and the grain boundary directly connected to the surface.

[0126] According to the present invention, the mixing in step (B) may be a dry mixing process, simply mixing the powder-type M-containing raw material into the sintered product without a solvent. In this case, the process can be simplified, thereby reducing costs, and a positive electrode active material with uniform quality can be produced.

[0127] Meanwhile, when wet mixing is performed instead of dry mixing, there are problems such as wastewater being generated during the process of filtering the precipitated material after using the solvent and discarding the remaining solvent, and the problem of additional process steps.

[0128] According to the present invention, the secondary heat treatment of step (B) may be performed at 200°C to 600°C. Specifically, the secondary heat treatment may be performed at 200°C or higher, 250°C or higher, 300°C or higher, 350°C or higher, or 400°C or higher, and may be performed at 450°C or lower, 500°C or lower, 550°C or lower, or 600°C or lower. When the secondary heat treatment temperature is within the above range, the second coating portion is coated only on the surface and the grain boundary directly connected to the surface, so that the Li ion path of the internal primary particles is not disturbed, and the formation of a NiO reduction layer is suppressed during the life evaluation, thereby having the advantage of improving the lifespan.

[0129] Meanwhile, if the secondary heat treatment temperature of step (B) is less than 200°C, the M-containing raw material may not be decomposed, so the coating layer may not be formed. If it exceeds 600°C, the heat energy is too high, so the coating layer may not grow uniformly and the M-containing raw materials may grow together in agglomeration. In addition, the lithium composite transition metal oxide may also cause particles to clump together due to the high heat energy.

[0130] According to the present invention, the secondary heat treatment of step (B) can be performed under an oxygen atmosphere or an air atmosphere. Here, an oxygen atmosphere means an atmosphere in which the oxygen partial pressure is higher than that of an air atmosphere.

[0131] According to the present invention, the secondary heat treatment in step (B) can be performed for 1 to 25 hours to increase the crystallinity of the coating portion.

[0132]

[0133] (Manufacturing method 2)

[0134] The above manufacturing method 2 includes a step of dry mixing a lithium composite transition metal oxide, a cobalt (Co)-containing raw material, and a M (wherein M is at least one selected from the group consisting of Al, Zr, W, Nb, B, Ti, Y, and Mg)-containing raw material, and then performing a first heat treatment at 650°C to 900°C and a second heat treatment at 200°C to 600°C.

[0135] The above manufacturing method 2 is a method of dry mixing a lithium composite transition metal oxide, a cobalt-containing raw material, and an M-containing raw material at once and performing a first heat treatment and a second heat treatment at once. In this case, since the decomposition temperature is different for each coating raw material, the cobalt-containing raw material penetrates into all grain boundaries of the lithium composite transition metal oxide, and the M-containing raw material penetrates only into grain boundaries directly connected to the surface of the lithium composite transition metal oxide. As a result, both the first coating portion and the second coating portion are formed on the surface, which is the outermost part of the lithium composite transition metal oxide, and the grain boundaries directly connected to the surface, whereas only the first coating portion is formed on boundaries not directly connected to the surface.

[0136] According to the present invention, the mixing of the above manufacturing method 2 may be a dry mixing method, simply mixing the lithium composite transition metal oxide, the powdered cobalt-containing raw material, and the powdered M-containing raw material without a solvent. In this case, the process can be simplified, thereby reducing costs, and a positive electrode active material having uniform quality can be produced.

[0137] Meanwhile, when wet mixing is performed instead of dry mixing, there are problems such as wastewater being generated during the process of filtering the precipitated material after using the solvent and discarding the remaining solvent, and the problem of additional process steps.

[0138] According to the present invention, the first heat treatment of the manufacturing method 2 may be performed at 650°C to 900°C. Specifically, the first heat treatment may be performed at 650°C or higher, 660°C or higher, 670°C or higher, 680°C or higher, 690°C or higher, or 700°C or higher, and may be performed at 800°C or lower, 810°C or lower, 820°C or lower, 830°C or lower, 840°C or lower, 850°C or lower, 860°C or lower, 870°C or lower, 880°C or lower, 890°C or lower, or 900°C or lower. When the temperature of the first heat treatment of the manufacturing method 2 is within the above range, there is an advantage in that the cobalt (Co)-containing raw material is uniformly spread while being decomposed, thereby uniformly forming a coating layer on the surface and grain boundary of the lithium transition metal oxide particles.

[0139] Meanwhile, if the temperature of the first heat treatment of Manufacturing Method 2 is less than 650℃, the cobalt-containing raw material may not be decomposed, so the coating layer may not be formed or may grow in agglomerates locally on the surface of the positive electrode active material. In addition, if the temperature of the first heat treatment exceeds 900℃, the thermal energy is too high, so the coating layer may not grow uniformly and the cobalt-containing raw materials may grow in agglomerates together, and the lithium composite transition metal oxide may also cause particles to agglomerate together due to the high thermal energy, or the structural instability of the active material may cause the advantages such as capacity and lifespan to be lost.

[0140] According to the present invention, the first heat treatment of the manufacturing method 2 can be performed under an oxygen atmosphere or an air atmosphere. Here, an oxygen atmosphere means an atmosphere in which the oxygen partial pressure is higher than that of an air atmosphere.

[0141] According to the present invention, the first heat treatment of the manufacturing method 2 can be performed for 1 to 25 hours to increase the crystallinity of the coating portion.

[0142]

[0143] According to the present invention, the secondary heat treatment of the manufacturing method 2 may be performed at 200°C to 600°C. Specifically, the secondary heat treatment may be performed at 200°C or higher, 250°C or higher, 300°C or higher, 350°C or higher, or 400°C or higher, and may be performed at 450°C or lower, 500°C or lower, 550°C or lower, or 600°C or lower.

[0144] Meanwhile, if the secondary heat treatment temperature of manufacturing method 2 is less than 200℃, the M-containing raw material may not be decomposed, so the coating layer may not be formed. If it exceeds 600℃, the heat energy is too high, so the coating layer may not grow uniformly and the M-containing raw materials may grow together in agglomeration. In addition, the lithium composite transition metal oxide may also cause particles to clump together due to the high heat energy.

[0145] According to the present invention, the secondary heat treatment of the above manufacturing method 2 can be performed under an oxygen atmosphere or an air atmosphere. Here, an oxygen atmosphere means an atmosphere in which the oxygen partial pressure is higher than that of an air atmosphere.

[0146] According to the present invention, the secondary heat treatment of the manufacturing method 2 may be performed for 1 to 25 hours to increase the crystallinity of the coating portion.

[0147]

[0148] anode

[0149] In addition, the present invention can provide a positive electrode including the positive electrode active material.

[0150] Specifically, the positive electrode includes a positive electrode current collector, and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector and including the positive electrode active material described above.

[0151] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 µm to 500 µm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0152]

[0153] The above positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material.

[0154] At this time, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 98 wt%, based on the total weight of the positive electrode active material layer. When included in the above content range, excellent capacity characteristics can be exhibited.

[0155] At this time, the conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one type alone or a mixture of two or more types thereof may be used. The conductive material may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0156]

[0157] The above binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0158]

[0159] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the positive electrode can be manufactured by coating a composition for forming a positive electrode active material layer, which is manufactured by dissolving or dispersing the positive electrode active material and optionally a binder and a conductive material in a solvent, on a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive material are as described above. Alternatively, the positive electrode can be manufactured by casting the composition for forming a positive electrode active material layer on a separate support, and then laminating the film obtained by peeling it from the support on a positive electrode current collector.

[0160] The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0161]

[0162] lithium secondary battery

[0163] In addition, the present invention can manufacture an electrochemical device including the positive electrode. The electrochemical device may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0164] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0165] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0166]

[0167] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0168] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0169]

[0170] The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0171] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β(0<β<2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0172] The above negative electrode active material may be included in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer.

[0173]

[0174] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0175] The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0176]

[0177] The negative electrode active material layer may be manufactured by applying and drying a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, or by casting the composition for forming a negative electrode active material layer on a separate support, and then laminating the film obtained by peeling it off from the support on a negative electrode current collector.

[0178]

[0179] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0180]

[0181] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0182] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0183] As the organic solvent, any solvent that can serve as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); Alcohol solvents such as ethyl alcohol, isopropyl alcohol, etc.; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc. can be used. Among these, carbonate solvents are preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of a battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0184]

[0185] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0186]

[0187] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0188]

[0189] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0190] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0191] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0192] There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0193] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0194]

[0195] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0196]

[0197] Manufacturing example

[0198] Manufacturing Example 1: Manufacturing of lithium transition metal oxide in the form of single particles with a composition of Ni88

[0199] Ni 0.88 Co 0.035 Mn 0.085 It has a composition represented by (OH)2 and an average particle diameter (D 50 ) is mixed with a positive electrode active material precursor of 3.5㎛ and LiOH in a molar ratio of 1:1.01, and a plastic product is manufactured by first firing at a temperature of 850℃ for 12 hours in an oxygen atmosphere, and the plastic product is pulverized, and then a second firing is performed at a temperature of 800℃ for 10 hours in an oxygen atmosphere to manufacture LiNi 0.88 Co 0.035 Mn 0.085 A lithium transition metal oxide in the form of a single particle having a composition represented by O2 was prepared.

[0200]

[0201] Manufacturing Example 2: Manufacturing of lithium transition metal oxide in the form of single particles with a composition of Ni68

[0202] Ni 0.68 Co 0.09 Mn 0.23 It has a composition represented by (OH)2 and an average particle diameter (D 50 ) is mixed with a positive electrode active material precursor of 3.5㎛ and LiOH in a molar ratio of 1:1.05, and a plastic product is manufactured by first firing at a temperature of 900℃ for 12 hours in an oxygen atmosphere, and the plastic product is pulverized, and then a second firing is performed at a temperature of 850℃ for 12 hours in an oxygen atmosphere to manufacture LiNi 0.68 Co 0.09 Mn 0.23 A lithium transition metal oxide in the form of a single particle having a composition represented by O2 was prepared.

[0203]

[0204] Manufacturing Example 3: Manufacturing of lithium transition metal oxide in the form of single particles with a composition of Ni62

[0205] Ni 0.62 Co 0.06 Mn 0.32It has a composition represented by (OH)2 and an average particle diameter (D 50 ) is mixed with a positive electrode active material precursor of 3.5㎛ and LiOH in a molar ratio of 1:1.05, and a plastic product is manufactured by first firing at a temperature of 900℃ for 12 hours in an oxygen atmosphere, and the plastic product is pulverized, and then a second firing is performed at a temperature of 850℃ for 12 hours in an oxygen atmosphere to manufacture LiNi 0.62 Co 0.06 Mn 0.32 A lithium transition metal oxide in the form of a single particle having a composition represented by O2 was prepared.

[0206]

[0207] Examples and Comparative Examples

[0208] Example 1

[0209] A mixture was prepared by dry mixing the lithium transition metal oxide manufactured in Manufacturing Example 1 with 2 mol% of powdered Co(OH)2 (Huayou Cobalt Co.), Al(OH)3 such that Al was 500 ppm based on the total weight of the lithium transition metal oxide, and ZrO2 such that Zr was 1,500 ppm based on the total weight of the lithium transition metal oxide. The mixture was first heat-treated at 720°C for 5 hours in an oxygen atmosphere, and then second heat-treated at 500°C for 3 hours in an oxygen atmosphere to prepare a cathode active material.

[0210]

[0211] Example 2

[0212] In Manufacturing Example 2, 2 mol% of powdered Co(OH)2 (Huayou Cobalt Co.) was dry mixed into the lithium transition metal oxide, and then a primary heat treatment was performed at 800°C for 5 hours in an oxygen atmosphere to manufacture a sintered product. Al2O3 was dry mixed into the sintered product so that Al was 1,500 ppm based on the total weight of the lithium transition metal oxide, and then a secondary heat treatment was performed at 450°C for 3 hours in an air atmosphere to manufacture a cathode active material.

[0213]

[0214] Comparative Example 1

[0215] A mixture was prepared by dry mixing the lithium transition metal oxide prepared in Manufacturing Example 3 with 2 mol% of powdered Co(OH)2 (Huayou Cobalt Co.), Al2O3 such that Al was 1,000 ppm based on the total weight of the lithium transition metal oxide, and ZrO2 such that Zr was 1,500 ppm based on the total weight of the lithium transition metal oxide. The mixture was heat-treated at 780°C for 5 hours in an oxygen atmosphere to prepare a cathode active material.

[0216]

[0217] Experimental example

[0218] Experimental Example 1: Analysis of positive electrode active material

[0219] (TEM analysis)

[0220] The cathode active materials manufactured in Examples 1, 2 and Comparative Example 1 were made into thin film samples with a thickness of about 100 nm using FEI Helios G5 FIB equipment, and then shape and composition analysis (HAADF-STEM, EDS element mapping) of the thin film samples were performed using FEI Titan cubed G2 60-300 equipment.

[0221] Figure 2 is a HAADF-STEM image and EDS element (cobalt) mapping image of the surface of the positive electrode active material of Example 1.

[0222] Figure 3 is a HAADF-STEM image and EDS element (cobalt) mapping image inside the positive electrode active material of Example 1.

[0223] Figure 4 is a table showing the HAADF-STEM image and EDS element (cobalt, aluminum) mapping image of the surface of the positive electrode active material of Example 2 and quantitative data at a specific portion.

[0224] Figure 5 is a table showing the HAADF-STEM image and EDS element (cobalt and aluminum) mapping image of the positive electrode active material of Comparative Example 1, and quantitative data at specific portions.

[0225] Figure 6 is a TEM image of the surface of the positive electrode active material of Comparative Example 1.

[0226] Figure 7 is a TEM image of the surface of the positive electrode active material of Example 1.

[0227]

[0228] Referring to the TEM analysis results, it can be confirmed that the positive electrode active materials of Examples 1 and 2 have Co-containing coatings on the surface and grain boundaries of the particles (not only grain boundaries directly connected to the surface, but also grain boundaries inside the particles that are not directly connected to the surface), and Al-containing coatings on the surface and grain boundaries directly connected to the surface of the particles (Area #1 and Area #3 in FIG. 4). On the other hand, it can be confirmed that the Al-containing coatings do not exist on grain boundaries inside the particles that are not directly connected to the surface (Area #2 in FIG. 4).

[0229] In comparison, it can be confirmed that the positive electrode active material of Comparative Example 1 has a Co coating layer of the first coating portion and an Al coating layer of the second coating portion only on the particle surface (the Co and Al contents are high only on the particle surface, such as in Area #1 and Area #3 in FIG. 5, and the content of elements in the grain boundary (Area #2 in FIG. 5) directly connected to the surface is similar to the content of elements in the parent material (lithium transition metal oxide manufactured in Manufacturing Example 3), so it can be confirmed that the coating material does not enter the grain boundary and internal grain boundary directly connected to the surface).

[0230] In addition, it can be confirmed that a NiO reduction layer with a thickness of about 10 nm exists on the surface of the positive electrode active material of Comparative Example 1, whereas no NiO reduction layer exists on the surface of the positive electrode active material of Example 1. In other words, it can be confirmed that the positive electrode active material of Example 1 maintains a layered structure.

[0231]

[0232] Experimental Example 2: Battery Characteristics Evaluation

[0233] (Half-cell manufacturing)

[0234] Each of the positive electrode active materials manufactured in the examples and comparative examples, the carbon black (Denka, DenkaBlack) conductive agent, and the PVdF (Kureha, KF1300) binder were added to an N-methylpyrrolidone (NMP) (Daejung Chemicals & Metals Co., Ltd.) solvent at a weight ratio of 95:3:2 to manufacture a composition for forming a positive electrode active material layer.

[0235] The composition for forming the positive electrode active material layer was applied to one surface of an aluminum foil current collector having a thickness of 20 ㎛, and dried at a temperature of 135°C for 3 hours to form a positive electrode active material layer. Subsequently, the positive electrode was manufactured by rolling using a roll pressing method so that the porosity of the positive electrode active material layer became 20% by volume after rolling.

[0236] A half-cell was manufactured using lithium metal as an anode together with the above anode.

[0237] (Battery capacity evaluation)

[0238] The half-cells manufactured above were each charged at 25°C with a constant current (CC) of 0.2C until the voltage reached 4.25V, and then charged at a constant voltage (CV) of 4.25V until the charge current reached 0.05mAh (cut-off current), left for 20 minutes, and then discharged at a constant current of 0.2C until the voltage reached 2.5V.

[0239] (Battery life evaluation)

[0240] According to the above battery capacity evaluation, the lithium secondary battery that had completed one charge / discharge cycle was transferred to a 45°C chamber, and charged to 4.25 V with a constant current of 0.5 C and discharged to 2.5 V, which was performed 30 times as one cycle, and the discharge capacity in the first and 30th cycles was measured. The percentage of the discharge capacity in the 30th cycle compared to the discharge capacity in the first cycle was calculated and presented as the capacity retention rate (%) in Table 1 below.

[0241]

[0242] Charge capacity (mAh / g)Discharge capacity (mAh / g)Capacity retention rate (%)Example 1233.7208.698.2Example 2214.5198.797.6Comparative example 1206.4189.294.9

[0243] Referring to Table 1, it can be confirmed that the batteries including the positive active materials of the examples have superior charge / discharge capacity and capacity retention rate compared to the batteries including the positive active materials of the comparative examples.

[0244] As a result, in the case of a battery including a positive electrode active material including the first coating portion and the second coating portion according to the present invention, it can be confirmed that the ratio of the NiO reduction layer present on the surface of the positive electrode active material particles is low, and thus the capacity characteristics and life characteristics are excellent.

Claims

1. Containing lithium composite transition metal oxide particles in the form of single particles or secondary particles containing 1.2 or more grains, A first coating portion that exists on the surface and grain boundary of the above particles and includes cobalt (Co); and A cathode active material comprising a second coating portion, which exists only on the surface of the particle and the grain boundary directly connected to the surface, and includes at least one selected from the group consisting of aluminum (Al), zirconium (Zr), tungsten (W), niobium (Nb), boron (B), titanium (Ti), yttrium (Y), and magnesium (Mg).

2. In claim 1, The above lithium composite transition metal oxide is a cathode active material containing nickel (Ni), cobalt (Co) and manganese (Mn).

3. In claim 1, The above lithium composite transition metal oxide is a positive electrode active material having a composition represented by the following chemical formula 1: [Chemical Formula 1] Li a Ni b Co c Mr d M 1 e O2 In the above chemical formula 1, M 1 is at least one selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P and S, 0.9≤a≤1.1, 0.5≤b<1.0, 0 <c<0.5, 0<d<0.5, 0≤e≤0.1이다.

4. In claim 1, The positive electrode active material wherein the first coating portion exists in the form of a coating layer, a discontinuously formed island form, or a combination thereof.

5. In claim 1, A cathode active material, wherein the first coating portion comprises at least one selected from the group consisting of lithium cobalt oxide, cobalt oxide, and cobalt hydroxide.

6. In claim 1, The above second coating portion is a positive electrode active material that exists in the form of a coating layer, a discontinuously formed island form, or a combination thereof.

7. In claim 1, A cathode active material comprising an oxide including at least one selected from the group consisting of Al, Zr, W, Nb, B, Ti, Y, and Mg, wherein the second coating portion is formed of Al, Zr, W, Nb, B, Ti, Y, and Mg.

8. In claim 1, The above positive electrode active material has an average particle diameter (D 50 ) is a positive electrode active material having a diameter of 1.0㎛ to 30.0㎛.

Images