Positive electrode active material and method for producing same

Abstract

The present invention relates to a positive electrode active material including a coating portion containing cobalt formed on the surface portion, and an island portion discontinuously formed on at least one selected from the group consisting of the surface portion and the coating portion, the island portion including at least one selected from the group consisting of aluminum (Al) and zirconium (Zr) in an amount of 0.08 mol % to 2.50 mol % relative to the total moles of metals contained in the lithium transition metal oxide, and a method for producing the positive electrode active material.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0062251, filed May 20, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material and a method for producing the same. [Background technology]

[0003] Recently, with the development of technologies such as electric vehicles, the demand for high-capacity secondary batteries is increasing. Accordingly, research on positive electrodes using high nickel (High Ni) positive electrode active materials with excellent capacity characteristics is being actively conducted.

[0004] The high-nickel positive electrode active material is manufactured by co-precipitation, and the manufactured high-nickel positive electrode active material has the form of secondary particles formed by aggregation of primary particles. However, the active material having the form of secondary particles has the disadvantage that fine cracks occur in the secondary particles during a long-term charge / discharge process, causing side reactions, and when the density of the electrode is increased to improve the energy density, the secondary particles cause the structure to collapse, resulting in a decrease in the active material and electrolyte, resulting in a decrease in energy density and a decrease in life characteristics.

[0005] In order to solve the problems of such secondary particle-type high nickel positive electrode active materials, single particle type nickel-based positive electrode active materials have been developed recently. Single particle type nickel-based positive electrode active materials have the advantage that the particles do not collapse even when the density of the electrode is increased for high energy density. However, single particle type nickel-based positive electrode active materials require a relatively high sintering temperature to manufacture them, and the layered structure of R-3m is not properly maintained, and lithium is released from the crystal structure, causing a phase change to an Fm-3m rock-salt structure such as NiO, which reduces the crystallinity of the positive electrode active material, and the ratio of NiO increases on the surface of the manufactured single particle, and the increase in NiO increases resistance, resulting in a decrease in energy density and output. In addition, when the sintering temperature is low, there is a problem that the material exists in the form of over-sintered secondary particles, and the improvement effect on life and gas generation does not reach the level expected from single particles.

[0006] Therefore, there is still a need to develop a positive electrode active material that has high electrode density and exhibits excellent life and output characteristics. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] KR 2019-0094529 A1 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a positive electrode active material that has high electrode density and exhibits excellent life characteristics and output characteristics.

[0009] Another object of the present invention is to provide a method for producing a positive electrode active material having high electrode density and exhibiting excellent life characteristics and output characteristics. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides a positive electrode active material.

[0011] (1) The present invention provides a positive electrode active material comprising a lithium transition metal oxide in the form of a single particle divided into a surface portion and a core, a coating portion containing cobalt formed on the surface portion, and island portions discontinuously formed on at least one selected from the group consisting of the surface portion and the coating portion, the island portions containing 0.08 mol % to 2.50 mol % of one or more selected from the group consisting of aluminum and zirconium with respect to the total number of moles of the positive electrode active material.

[0012] (2) The present invention provides a positive electrode active material according to (1) above, wherein the island portions are dispersed and distributed on at least one surface selected from the group consisting of the surface portion and the coating portion.

[0013] (3) The present invention provides a positive electrode active material according to the above (1) or (2), wherein the island portion contains 0.13 to 2.50 mol % of aluminum based on the total number of moles of the positive electrode active material.

[0014] (4) The present invention provides a positive electrode active material according to any one of the above (1) to (3), wherein the island portion contains 0.08 to 2.50 mol % of zirconium based on the total number of moles of the positive electrode active material.

[0015] (5) The present invention provides a positive electrode active material according to any one of (1) to (4), wherein a total area of ​​the coating portion is 10% to 100% of a total area of ​​an outer surface of the lithium transition metal oxide.

[0016] (6) The present invention provides a positive electrode active material according to any one of (1) to (5) above, wherein the surface portion is a region extending from an outermost surface of the lithium transition metal oxide in a single particle form to a depth of 1 nm to 50 nm toward the center.

[0017] (7) The present invention provides a positive electrode active material according to any one of the above (1) to (6), wherein the nickel contained in the surface portion has an average oxidation number of +2.36 to +3.00.

[0018] (8) The present invention provides a positive electrode active material according to any one of (1) to (7) above, wherein the cobalt and nickel satisfy a Co / Ni value (mol / mol) of 0.1 to 0.8 based on the entire surface portion and coating portion.

[0019] (9) The present invention provides the positive electrode active material according to any one of the above (1) to (8), wherein the coating portion is located in an island shape on the outer side of the surface portion.

[0020] (10) The present invention is directed to any one of the above (1) to (9), wherein the coating portion is LiCoO 2 The present invention provides a positive electrode active material having the composition:

[0021] (11) The present invention is directed to any one of the above (1) to (10), wherein the island portion is LiCoAlO 2 The present invention provides a positive electrode active material comprising:

[0022] (12) The present invention provides a positive electrode active material according to any one of the above (1) to (11), wherein the lithium transition metal oxide is a lithium composite transition metal oxide containing nickel, cobalt, and manganese.

[0023] (13) The present invention provides a positive electrode active material according to any one of the above (1) to (12), wherein the lithium transition metal oxide is a lithium composite transition metal oxide represented by the following chemical formula 1: [Chemical formula 1] Li a Ni x Co y M 1 z M 2 1-x-y-z O 2 In the above Chemical Formula 1, M 1is one or more selected from the group consisting of Mn and Al, 2 is one or more selected from the group consisting of B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf, and is 1.0≦a≦1.3, 0.6≦x<1.0, 0≦y≦0.4, and 0≦z≦0.4.

[0024] (14) The present invention provides a positive electrode active material according to any one of the above (1) to (13), wherein the lithium transition metal oxide is a lithium composite transition metal oxide represented by the following chemical formula 2: [Chemical formula 2] Li a Ni b Co c Mn d M 1 e O 2 In the above Chemical Formula 2, 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, and 0.9≦a≦1.1, 0.8≦b<1, 0 <c<0.2、0<d<0.2、0≦e<0.1、b+c+d+e=1である。

[0025] In order to achieve the above object, the present invention provides a method for producing a positive electrode active material.

[0026] (15) The present invention provides a method for producing a positive electrode active material, the method comprising: 1) mixing lithium transition metal oxide particles in a single particle form, a cobalt source, and one or more selected from the group consisting of an aluminum source and a zirconium source; and 2) heat-treating the mixture of step 1).

[0027] (16) The present invention provides the method for producing a positive electrode active material according to (15), further comprising mixing an additional metal source in the step 1).

[0028] (17) The present invention provides the method for producing a positive electrode active material according to (15) or (16), wherein the heat treatment in step 2) is carried out at 500 to 800°C. Effect of the Invention

[0029] The positive electrode active material of the present invention is a positive electrode active material containing a lithium transition metal oxide in the form of a single particle, and includes a coating portion containing cobalt and a surface portion with a reduced NiO layer. As a result, the positive electrode active material has high electrode density and can exhibit excellent life characteristics and output characteristics. [Brief description of the drawings]

[0030] [Figure 1] 4 shows TEM and TEM EDS (Al element map and Co element map) images of a thin film sample of the positive electrode active material of Example 1. [Diagram 2] 6A and 6B are TEM EDS images (Al element map, Co element map) of the thin film sample of the positive electrode active material of Example 1 at other positions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The present invention will now be described in further detail in order to facilitate understanding of the present invention.

[0032] The terms and words used in the description of the present invention and the claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0033] In the present invention, the term "primary particle" refers to the smallest particle unit that can be distinguished as a single mass when a cross section of a positive electrode active material is observed through a scanning electron microscope (SEM), and may be composed of a plurality of crystal grains.

[0034] In the present invention, the term "secondary particle" refers to a secondary structure formed by aggregation of a plurality of primary particles. The average particle size of the secondary particles can be measured using a particle size analyzer.

[0035] In the present invention, the term "single particle type" may be used instead of the term "single particle form", and refers to a form that is in contrast to the form of secondary particles formed by agglomeration of hundreds of primary particles produced by conventional methods. In addition, in the present invention, the term "single particle type positive electrode active material" or "lithium transition metal oxide in a single particle form" refers to a concept in contrast to a positive electrode active material in a form of secondary particles formed by agglomeration of hundreds of primary particles produced by conventional methods, and refers to a positive electrode active material or lithium transition metal active material consisting of 1 to 50 particles or less, 1 to 40 particles or less, 1 to 30 particles or less, 1 to 20 particles or less, 1 to 15 particles or less, 1 to 10 particles or less, or 1 to 5 particles or less.

[0036] In the present invention, the term "monocrystalline" may be used instead of the term "single crystal" and refers to a positive electrode active material or lithium transition metal oxide containing 50 or less crystal grains, specifically 1 to 30 crystal grains. Generally, a single crystal particle refers to a particle in which the entire sample is composed of only one grain or grain region. In the present invention, a positive electrode active material or a lithium transition metal oxide in the form of a single particle may exhibit properties similar to those of a single crystal grain since it contains a small number of crystal grains.

[0037] The term "single particle" refers to the smallest unit of a particle that can be recognized when observing a positive electrode active material through a scanning electron microscope, and the term "grain" or "grain region" refers to a region in which atoms in a sample are arranged continuously and periodically in one direction. The grains can be analyzed using an electron backscatter diffraction (ESBD) analyzer.

[0038] In the present invention, the term "average particle size (D 50The "average particle size" refers to the particle size at the 50% point of the volume cumulative distribution by particle size. The average particle size is determined by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., S3500 manufactured by Microtrac), measuring the difference in the diffraction pattern due to the particle size when the particles pass through a laser beam, calculating the particle size distribution, and calculating the particle diameter at the 50% point of the volume cumulative distribution by particle size in the measuring device. 50 can be measured.

[0039] The positive electrode active material of the present invention includes a lithium transition metal oxide in the form of a single particle divided into a surface portion and a core, a coating portion containing cobalt formed on the surface portion, and an island portion discontinuously formed on at least one selected from the group consisting of the surface portion and the coating portion, and the island portion includes at least one selected from the group consisting of aluminum (Al) and zirconium (Zr) in an amount of 0.08 mol % to 2.50 mol % with respect to the total number of moles of the positive electrode active material.

[0040] The surface portion of the lithium transition metal oxide in the form of a single particle has a layered (R-3m) structure and has a high NiO content before the coating portion containing cobalt is formed on the surface portion, and the formation of the NiO is induced by the high sintering temperature required during the preparation of the lithium transition metal oxide in the form of a single particle. The NiO contained in the surface portion of the lithium transition metal oxide in the form of a single particle may cause an increase in resistance and a decrease in energy density and output.

[0041] The positive electrode active material of the present invention includes a coating portion containing cobalt formed by a process of mixing the single-particle lithium transition metal oxide with a cobalt source (raw material) and then heat-treating the mixture, and the coating portion may be a layer formed by diffusing the cobalt from the surface of the single-particle lithium transition metal oxide toward the center during the heat-treatment process. In the positive electrode active material of the present invention, the NiO layer on the surface is converted into a layered structure of nickel cobalt manganese (NCM) oxide during the process of forming the coating portion, thereby reducing and eliminating causes of increased resistance, decreased energy density, and decreased output, and exhibiting excellent electrochemical properties.

[0042] The island portion is discontinuously formed on one or more selected from the group consisting of the surface portion and the coating portion, and specifically, may be distributed in a dispersed manner on one or more surfaces selected from the group consisting of the surface portion and the coating portion. That is, the island portion may be formed in an island shape on one or more surfaces of the outer side of the surface portion and the cobalt coating. The term "distributed in a dispersed manner" may indicate that the island portion is not formed entirely, but is formed partially, and in this case, is formed in a dispersed manner.

[0043] The island portion can be formed by mixing the aluminum with the cobalt of the coating portion or by forming the island portion separately from the cobalt, depending on the distribution position of the island portion. 2 O 3 Aluminum oxides such as LiAlO 2 , Li 5 AlO 4 , LiAl 5 O 8 Li, etc. h Al i O j Lithium aluminum oxide in the form of Co 2 AlO 4 Cobalt aluminum oxide, such as LiAlCoO 3 , Li x Aly Co 1-y O 2 (0.9≦x≦1.1, 0.01≦y≦0.1) k Al l Co (1-m) Specifically, the island portion may be LiCoAlO 2 The islands may include the zirconium as zirconium oxide, lithium zirconium oxide, cobalt zirconium oxide, or lithium cobalt zirconium oxide.

[0044] The surface portion refers to the outside of the lithium transition metal oxide in single particle form, and means a region having a predetermined thickness from the outermost portion toward the center of the lithium transition metal oxide in single particle form, specifically, a region having a depth of 1 nm to 50 nm, specifically 5 nm to 30 nm, from the outermost portion toward the center of the lithium transition metal oxide in single particle form.

[0045] The core means the inside of the lithium transition metal oxide in the form of a single particle other than the surface portion.

[0046] Based on the entire surface portion and coating portion, the cobalt and nickel may satisfy a Co / Ni value (mol / mol) of 0.10 to 0.80, specifically 0.15 to 0.80, 0.20 to 0.80, 0.10 to 0.75, 0.15 to 0.75, and more specifically 0.20 to 0.75. If the Co / Ni value is too small compared to the above range, cobalt diffuses excessively into the interior of the lithium transition metal oxide particles in the form of a single particle, the cobalt concentration in the surface layer decreases, and the effect of the cobalt coating is not easily achieved. In the process of excessive diffusion of cobalt into the interior of the particles, a NiO deteriorated layer may also be formed on the surface of the particles. Also, if the Co / Ni value is too large compared to the above range, the coated cobalt may be too low, and the NiO deteriorated layer may also be formed on the surface of the particles. 3 O 4 or lithium cobalt oxide (Li x COy O z In this case, the NiO degradation layer of the lithium transition metal oxide in the form of a single particle cannot be sufficiently converted into a nickel cobalt manganese (NCM) oxide layer structure, and an unnecessary amount of cobalt coating layer formed on the surface of the lithium transition metal oxide may act as a resistor or cause a decrease in capacity.

[0047] The coating portion may be formed on the outside of the surface portion, i.e., on the outermost surface of the lithium transition metal oxide in the form of single particles, or may be formed on a part or the whole of the outside of the surface portion, and may be formed on 10% to 100% (area %) based on the total area of ​​the outside of the surface portion. Specifically, the cobalt coating may be formed on a part of the outside of the surface portion, and may be formed on 30% to 90% of the total area of ​​the outside of the surface portion.

[0048] The coating portion may be formed in an island shape on the outer side of the surface portion. The island shape refers to a shape in which the coating portion is discontinuously formed on the outer side of the surface portion, that is, the coating portion may be partially dispersed and distributed on the outermost surface of the single-particle lithium transition metal oxide.

[0049] The coating portion is LiCoO 2 Specifically, the coating portion may include an island-shaped LiCoO 2 It can be included as:

[0050] The surface portion has a layered (R-3m) structure, and the nickel (Ni) contained in the surface portion may have an average oxidation number of +2.36 to +3.00, and the average oxidation number of the nickel contained in the surface portion may be specifically +2.36 to +2.95, +2.36 to +2.91, +2.37 to +2.95, and more specifically +2.37 to +2.91. The average oxidation number of the nickel contained in the surface portion may vary depending on the coating amount of cobalt forming the coating portion, and when the range is satisfied, an appropriate amount of the coating portion is formed on the surface, and the NiO deterioration layer of the lithium transition metal oxide is sufficiently converted into a nickel cobalt manganese (NCM) oxide layer structure, so that problems such as cation mixing and structural instability due to the collapse of the layer structure of the NiO deterioration layer can be prevented. Thus, the surface portion can include a nickel cobalt manganese oxide layer structure converted from the NiO layer.

[0051] In addition, in the positive electrode active material according to one embodiment of the present invention, the average oxidation number of nickel (Ni) from the outermost part to a depth of 10 nm toward the center of the single particle lithium transition metal oxide may be +2.50 to +3.00, specifically, +2.50 to +2.95, +2.50 to +2.90, +2.50 to +2.88, +2.52 to +2.95, +2.52 to +2.90, +2.52 to +2.88, and more specifically, +2.54 to +2.86. When the average oxidation number of nickel satisfies the range of the average oxidation number up to 10 nm, the nickel may show an oxidation number gradient at the surface portion, and an appropriate reduction effect on the NiO deterioration layer of the single particle lithium transition metal oxide may be obtained.

[0052] The island portion contains one or more selected from the group consisting of aluminum (Al) and zirconium (Zr) in an amount of 0.08 mol % to 2.50 mol % relative to the total number of moles of the positive electrode active material, specifically, 0.09 mol % to 2.50 mol %, 0.09 to 2.30 mol %, 0.09 to 2.00 mol %, 0.09 to 1.80 mol %, 0.09 to 1.70 mol %, 0.09 to 1.60 mol %, 0.09 to 1.50 mol %, 0.10 to 2.30 mol %, 0.10 to 2.00 mol %, 0.10 to 1.80 mol %, 0.10 to 1.70 mol %, 0.10 to 1.60 mol %, 0.10 to 1.50 mol %, 0.13 The amount of the aryl group may be from 0.15 to 2.30 mol%, 0.13 to 2.00 mol%, 0.13 to 1.80 mol%, 0.13 to 1.70 mol%, 0.13 to 1.60 mol%, 0.13 to 1.50 mol%, 0.14 to 2.30 mol%, 0.14 to 2.00 mol%, 0.14 to 1.80 mol%, 0.14 to 1.70 mol%, 0.14 to 1.60 mol%, 0.14 to 1.50 mol%, 0.15 to 2.30 mol%, 0.15 to 2.00 mol%, 0.15 to 1.80 mol%, 0.15 to 1.70 mol%, 0.15 to 1.60 mol%, or 0.15 to 1.50 mol%, and more specifically, the amount may be from 0.18 to 1.00 mol%.

[0053] More specifically, when the island portion contains aluminum, the content of aluminum is 0.13 mol % to 2.50 mol %, specifically, 0.13 to 2.30 mol %, 0.13 to 2.00 mol %, 0.13 to 1.80 mol %, 0.13 to 1.70 mol %, 0.13 to 1.60 mol %, 0.13 to 1.50 mol %, 0.14 to 2.30 mol %, or 0.14 to 2.00 mol %, based on the total number of moles of the positive electrode active material. , 0.14 to 1.80 mol%, 0.14 to 1.70 mol%, 0.14 to 1.60 mol%, 0.14 to 1.50 mol%, 0.15 to 2.30 mol%, 0.15 to 2.00 mol%, 0.15 to 1.80 mol%, 0.15 to 1.70 mol%, 0.15 to 1.60 mol%, or 0.15 to 1.50 mol%, and more specifically, it may contain 0.18 to 1.00 mol%. When the island portion contains zirconium, the zirconium content is 0.08 mol % to 2.50 mol %, specifically, 0.09 mol % to 2.50 mol %, 0.09 to 2.30 mol %, 0.09 to 2.00 mol %, 0.09 to 1.80 mol %, 0.09 to 1.70 mol %, 0.09 to 1.60 mol %, 0.09 to 1.50 mol %, 0.10 to 2.30 mol %, 0.10 to 2.00 mol %, 0.10 to 1.80 mol %, 0.10 to 1.70 mol%, 0.10-1.60 mol%, 0.10-1.50 mol%, 0.13-2.30 mol%, 0.13-2.00 mol%, 0.13-1.80 mol%, 0.13-1.70 mol%, 0.13-1.60 mol%, 0.13-1.50 mol%, 0.14-2.30 mol%, 0.14-2.00 mol%, 0.14-1.80 mol%, 0.14-1.70 mol%, 0.14-1.60 mol%, or 0.14-1.50 mol%. In this case, the total amount of aluminum and zirconium can satisfy the above-mentioned range of the content of one or more selected from the group consisting of aluminum and zirconium.

[0054] When the total mole number of one or more selected from the group consisting of aluminum and zirconium contained in the island portion satisfies the above range, the positive electrode active material is prevented from causing a side reaction with the electrolyte, thereby improving cycle characteristics such as an increase in capacity retention rate and a decrease in resistance increase rate. When the content of the aluminum, zirconium or a mixture thereof is insufficient, the effect of containing the appropriate amount of the aluminum, zirconium or aluminum and zirconium as described above is insufficient, and when the content is too large, the effect of including the island portion is difficult to be achieved.

[0055] The lithium transition metal oxide in the form of single particles may be a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co) and manganese (Mn).

[0056] Specifically, the lithium transition metal oxide in the form of a single particle may be a lithium composite transition metal oxide represented by the following Chemical Formula 1.

[0057] [Chemical formula 1] Li a Ni x Co y M 1 z M 2 1-x-y-z O 2

[0058] In the above Chemical Formula 1, M 1 is one or more selected from the group consisting of Mn and Al, 2 is one or more selected from the group consisting of B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf, and is 1.0≦a≦1.3, 0.6≦x<1.0, 0≦y≦0.4, and 0≦z≦0.4.

[0059] Specifically, the lithium transition metal oxide may be a lithium composite transition metal oxide represented by the following Chemical Formula 2.

[0060] [Chemical formula 2] Li a Ni b Co c Mn d M 1 e O 2

[0061] In the above Chemical Formula 2, 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, and 0.9≦a≦1.1, 0.8≦b<1, 0 <c<0.2、0<d<0.2、0≦e<0.1、b+C+d+e=1である。

[0062] Specifically, the lithium transition metal oxide may be a lithium composite transition metal oxide represented by the following Chemical Formula 3.

[0063] [Chemical formula 3] Li g Ni h Co i Mn j O 2

[0064] In the above formula 3, 0.9≦g≦1.1, 0.8≦h<1, 0 <i<0.2、0<j<0.2、h+i+j=1である。

[0065] The positive electrode active material has an average particle size (D 50 Specifically, the average particle size (D 50 The positive electrode active material according to one embodiment of the present invention may have an average particle size (D 50When the average particle size of the particles is within the above range, it can have advantages in terms of rolling ratio, electrode voids, etc., and when the average particle size is too small or too large compared to the above range, it can degrade performance in terms of electrode capacity, life characteristics, resistance, etc.

[0066] The present invention also provides a method for producing the positive electrode active material.

[0067] The positive electrode active material may be prepared by a method including: 1) mixing one or more selected from the group consisting of a lithium transition metal oxide particle in a single particle form, a cobalt source, and an aluminum source and a zirconium source; and 2) heat-treating the mixture of step 1).

[0068] In step 1), the cobalt source may be used in an amount of 0.1 mol % to 10 mol %, specifically 0.5 mol % to 5 mol %, and more specifically 1 mol % to 3 mol %, based on the positive electrode active material. If the cobalt source is used in an amount less than this range, a sufficient cobalt coating may not be formed on the outside of the surface portion of the lithium transition metal oxide particles, and if the cobalt source is used in an excessive amount, an excessive cobalt coating may be formed or unreacted cobalt compound may remain on the surface of the particles, resulting in defects such as increased resistance and decreased capacity.

[0069] At least one selected from the group consisting of the aluminum source and the zirconium source may be mixed with the cobalt coating and coated together, or may be formed as a separate coating, and may be formed in an island shape on at least one selected from the group consisting of the surface portion and the coating portion of the single-crystalline lithium transition metal oxide particle.

[0070] In the step 1), the one or more selected from the group consisting of the aluminum source and the zirconium source is 0.13 mol % to 2.50 mol %, specifically, 0.13 to 2.30 mol %, 0.13 to 2.00 mol %, 0.13 to 1.80 mol %, 0.13 to 1.70 mol %, 0.13 to 1.60 mol %, 0.13 to 1.50 mol %, or 0.14 to 2.30 mol %, based on the total number of moles of the positive electrode active material. , 0.14-2.00 mol%, 0.14-1.80 mol%, 0.14-1.70 mol%, 0.14-1.60 mol%, 0.14-1.50 mol%, 0.15-2.30 mol%, 0.15-2.00 mol%, 0.15-1.80 mol%, 0.15-1.70 mol%, 0.15-1.60 mol%, or 0.15-1.50 mol%, or more specifically, 0.18-1.00 mol%.

[0071] When one or more selected from the group consisting of the aluminum source and the zirconium source are used in the above-mentioned range, island portions can be formed to an appropriate extent, and the produced positive electrode active material can be prevented from causing a side reaction with the electrolyte, thereby improving cycle characteristics such as an increase in capacity retention rate and a decrease in resistance increase rate.

[0072] When one or more selected from the group consisting of the aluminum source and the zirconium source are used in an amount that is less than the above range, aluminum-containing islands may not be formed to an appropriate degree outside the surface of the lithium transition metal oxide particles. When the aluminum source is used in an excessive amount, the effect of reducing the deteriorated NiO layer that is intended to be achieved by the cobalt coating may be reduced, and the excessively generated islands may act as a resistance layer, causing a decrease in performance.

[0073] Also, in step 1), a process of further mixing an additional metal source in addition to the cobalt and aluminum may be performed. The additional metal source may be used together with the cobalt source and the aluminum source, and may be coated on the surface of the single particle lithium transition metal oxide through the subsequent steps. The coating formed by the additional metal source may be included in the coating portion formed by the cobalt source, the island portion formed by one or more selected from the group consisting of the aluminum source and the zirconium source, or may be formed by a separate metal coating.

[0074] The mixing in step 1) may be a dry mixing, for example, a powdered cobalt source material may be mixed with a lithium transition metal oxide in a single particle form without a solvent. Such dry mixing may be a simple mixing process, and may exhibit advantages of cost reduction and quality stabilization due to the simplification of the process. In the method for producing a positive electrode active material according to an embodiment of the present invention, the lithium transition metal oxide particles in a single particle form, a cobalt (Co) source, an aluminum source, and a zirconium source are dry mixed and then heat-treated, so that the coating portion may be formed in an island shape.

[0075] The heat treatment in step 2) may be performed at 500° C. to 800° C., specifically, 600° C. to 800° C., and more specifically, 650° C. to 750° C. When the heat treatment temperature is within the above range, a cobalt coating mixed on the surface of the lithium transition metal oxide in the form of a single particle, specifically, formed in the form of islands on the surface of the lithium transition metal oxide, is formed as LiCoO 2Cobalt, which existed as a phase, penetrates into the interior of the lithium transition metal oxide in the form of a single particle to an appropriate depth, and the NiO layer, which is a deteriorated layer, can be appropriately changed into a nickel cobalt manganese (NCM) oxide layer structure, so that the surface portion of the lithium transition metal oxide in the form of a single particle has a layered type (R-3m) structure, and the surface portion includes an oxidation number gradient layer in which the oxidation number of nickel increases toward the outermost side, thereby exhibiting excellent effects in cell performance such as charge / discharge capacity, initial efficiency, and initial resistance. If the heat treatment temperature in the step 2) is low, the thickness of the coating portion becomes large and an excessive amount of the coating portion is formed, making it difficult to exhibit the advantages of the formation of the coating portion as described above. If the heat treatment temperature in the step 2) is high, cobalt is doped deeply into the interior of the lithium transition metal oxide in the form of a single particle, and there is a possibility that the coating portion is not appropriately formed on the surface portion.

[0076] The heat treatment in step 2) can be performed for 2 hours to 12 hours, specifically, for 2 hours to 9 hours, and more specifically, for 2 hours to 6 hours. When the heat treatment is performed within the above time range, excellent productivity can be exhibited and uniform firing can be performed.

[0077] The cobalt source may be a cobalt-containing oxide, hydroxide, oxyhydroxide, carbonate, sulfate, halide, sulfide, acetate, nitrate, carboxylate, or a combination thereof, for example, Co(OH). 2 , CoOOH, Co(OCOCH 3 ) 2 4H 2 O, Co(NO 3 ) 2 6H 2 O or Co(SO 4 ) 2 7H 2 O, and any one or a mixture of two or more of these can be used. Specifically, Co(OH) 2 can be used.

[0078] The aluminum source may be an aluminum-containing oxide, hydroxide, oxyhydroxide, carbonate, sulfate, halide, sulfide, acetate, nitrate, carboxylate, or a combination thereof, for example, Al 2 O 3 , Al(OH) 3 ,AlSO 4 , AlCl 3 , Al-isopropoxide, AlNO 3 , AlF, etc., but are not limited thereto.

[0079] The zirconium source may be, but is not limited to, an oxide, hydroxide, oxyhydroxide, carbonate, sulfate, halide, sulfide, acetate, nitrate, carboxylate, or a combination thereof containing zirconium.

[0080] The additional metal source may be, for example, an oxide, hydroxide, oxyhydroxide, carbonate, sulfate, halide, sulfide, acetate, nitrate, carboxylate, or a combination thereof, containing one or more elements selected from the group consisting of Ti, W, B, F, P, Mg, Fe, Cr, V, Cu, Ca, Zn, Nb, Mo, Sr, Sb, Bi, Si, Cr, Hf, Ta, La, Ba, Ce, Sn, Y, and S. Specifically, ZnO, TiO 2 , WO 3 , H 2 BO 3 , HBO 2 , H 3 BO 3 , H 2 B 4 O 7 , B 2 O 3 , C 6 H 5 B(OH) 2 , (C 6 H 5 O) 3 B, (CH 3 (CH 2 ) 3 O) 3 B, C 3 H9 B 3 O 6 , (C 3 H 7 O 3 ) B, Li 3 WO 4 , (NH 4 ) 10 W 12 O 41 5H 2 O, NH 4 H 2 PO 4 These include, but are not limited to, the following:

[0081] The additional metal source may be used in an amount such that the total amount of the additional metal and the aluminum is 100 ppm to 50,000 ppm, specifically 200 ppm to 10,000 ppm, based on the total number of moles of metal in the positive electrode active material. When the additional metal is included in the above range together with the aluminum, it is expected that the side reaction with the electrolyte may be effectively suppressed, and the electrochemical properties may be further improved.

[0082] In one embodiment of the present invention, the lithium transition metal oxide particles in the form of single particles may be prepared by mixing a transition metal oxide precursor and a lithium source material, performing primary firing, crushing the pre-fired product prepared by the primary firing, and then performing secondary firing.

[0083] According to yet another embodiment of the present invention, there is provided a positive electrode comprising the above positive electrode active material.

[0084] Specifically, the positive electrode includes a positive electrode current collector, and a positive electrode active material layer formed on the positive electrode current collector and including the above-mentioned positive electrode active material.

[0085] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0086] The positive electrode active material layer may contain a conductive material and a binder in addition to the positive electrode active material described above.

[0087] In this case, the conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause a chemical change in the battery to be constructed and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and one or more of these can be used alone or in combination. The conductive material can usually be contained in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

[0088] The binder serves to improve the adhesion between the 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, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and one or more of these may be used alone or in combination. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

[0089] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, which is manufactured by mixing or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling. Here, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0090] The solvent may be a solvent commonly used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc., and one or more of these may be used alone or in combination. The amount of the solvent used may be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for the manufacture of a positive electrode, taking into consideration the coating thickness of the slurry and the manufacturing yield.

[0091] As another method, the positive electrode can also be produced by casting the composition for forming a positive electrode active material layer on another support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0092] According to yet another embodiment of the present invention, there is provided an electrochemical device including the positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0093] The lithium secondary battery specifically includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is as described above. The lithium secondary battery may further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0094] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0095] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity, and may be, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy. The negative electrode current collector may have a thickness of usually 3 to 500 μm, and like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0096] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0097] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of the negative electrode active material 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 alloys, Sn alloys, and Al alloys; SiO x (0 <x<2)、SnO 2 , vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a thin film of metallic lithium may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Representative examples of low crystalline carbon include soft carbon and hard carbon, and representative examples of high crystalline carbon include amorphous, plate-like, flake-like, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, carbon microbeads, mesophase pitches, and high-temperature fired carbon such as petroleum or coal tar pitch derived cokes.

[0098] The binder and the conductive material are as described above in the positive electrode.

[0099] For example, the negative electrode active material layer may be produced by applying a negative electrode forming composition prepared by dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent onto a negative electrode current collector, followed by drying; alternatively, the negative electrode forming composition may be cast onto another support, and then peeled off from the support to obtain a film, which may be laminated onto the negative electrode current collector.

[0100] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator that is generally used as a separator in a lithium secondary battery can be used without any particular limitation. In particular, a separator that has low resistance to ion movement of the electrolyte and has excellent humidification ability of the electrolyte solution is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high-melting point glass fiber, a polyethylene terephthalate fiber, etc., can be used. In addition, a coated separator containing a ceramic component or a polymeric material can be used to ensure heat resistance or mechanical strength, and can be selectively used as a single layer or a multilayer structure.

[0101] In addition, examples of the electrolyte used in the present invention include 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 production of lithium secondary batteries, but are not limited to these.

[0102] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0103] The organic solvent can be used without any particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent can be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene carbonate). Examples of the solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethanol and isopropyl alcohol, nitriles such as R-CN (R is a C2-C20 straight-chain, branched or cyclic hydrocarbon group that can contain a double bond aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can enhance the charge / discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, so that the electrolyte can exhibit excellent performance.

[0104] The lithium salt can be used without any particular limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAl0 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiCl, LiI, or LiB(C 2 O 4 ) 2 The lithium salt may be used at a concentration within the range of 0.1 to 2.0 M. When the lithium salt concentration is within the above range, the electrolyte has appropriate conductivity and viscosity, and therefore can exhibit excellent electrolyte performance, allowing lithium ions to migrate effectively.

[0105] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress the decrease in the capacity of the battery, and improve the discharge capacity of the battery. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0106] As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, and is therefore useful in portable devices such as mobile phones, notebook computers and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0107] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0108] The battery module or battery pack may 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.

[0109] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0110] 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 also preferably as a unit battery in a medium- to large-sized battery module including a large number of battery cells. EXAMPLES

[0111] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0112] Manufacturing Example 1 Positive electrode active material precursor [composition: Ni 0.95 Co 0.03 Mn 0.02 (OH) 2 , average particle size (D 50 The mixture was mixed with LiOH as a lithium source material in a molar ratio of 1:1.05, and subjected to primary firing at a temperature of 850°C for 9 hours in an oxygen atmosphere to produce a pre-fired product. The pre-calcined product was crushed and then subjected to secondary calcination at a temperature of 750° C. for 9 hours in an oxygen atmosphere to produce a lithium transition metal oxide in the form of single particles.

[0113] Example 1 The lithium transition metal oxide in the form of a single particle produced in Production Example 1 and the powder-like cobalt source Co(OH) 2 (manufactured by HUAYOU COBALT) and aluminum source Al(OH) 3 were mixed in amounts of 97.82 mol %, 2 mol % and 0.18 mol %, respectively.

[0114] The mixture was heat-treated at a temperature of 700° C. for 5 hours to obtain a cake-like positive electrode active material, which was then pulverized to produce a powder-like single-particle type positive electrode active material.

[0115] Example 2 In Example 1, the aluminum source Al(OH) 3 A powdered single-particle type positive electrode active material was produced in the same manner as in Example 1, except that the amount of lithium transition metal oxide was adjusted accordingly to use 0.5 mol % of lithium transition metal oxide.

[0116] Example 3 In Example 1, the aluminum source Al(OH) 3 A powdered single-particle type positive electrode active material was produced in the same manner as in Example 1, except that the amount of lithium transition metal oxide was adjusted accordingly.

[0117] Example 4 The lithium transition metal oxide in the form of a single particle produced in Production Example 1, and the powder-like cobalt source Co(OH) 2 (manufactured by HUAYOU COBALT) and zirconium source ZrO 2 were mixed in amounts of 97.92 mol %, 2 mol % and 0.08 mol %, respectively.

[0118] The mixture was heat-treated at a temperature of 700° C. for 5 hours to obtain a cake-like positive electrode active material, which was then pulverized to produce a powder-like single-particle type positive electrode active material.

[0119] Example 5 In Example 4, the zirconium source ZrO 2 A powdered single-particle type positive electrode active material was produced in the same manner as in Example 4, except that the amount of lithium transition metal oxide was adjusted accordingly to use 0.5 mol % of lithium transition metal oxide.

[0120] Example 6 In Example 4, the zirconium source ZrO 2 A powdered single-particle type positive electrode active material was produced in the same manner as in Example 4, except that the amount of lithium transition metal oxide was adjusted accordingly.

[0121] Comparative Example 1 The single particle type lithium transition metal oxide prepared in Preparation Example 1 was used as a single particle type positive electrode active material.

[0122] Comparative Example 2 The lithium transition metal oxide in the form of a single particle produced in Production Example 1 and the powder-like cobalt source Co(OH) 2 (manufactured by HUAYOU COBALT) was mixed in amounts of 98 mol % and 2 mol %.

[0123] The mixture was heat-treated at a temperature of 700° C. for 5 hours to obtain a cake-like positive electrode active material, which was then pulverized to produce a powder-like single-particle type positive electrode active material.

[0124] Comparative Example 3 In Example 1, the aluminum source Al(OH) 3 A powdered single-particle type positive electrode active material was produced in the same manner as in Example 1, except that the amount of lithium transition metal oxide was adjusted accordingly to use 0.1 mol % of lithium transition metal oxide.

[0125] Comparative Example 4 In Example 1, the aluminum source Al(OH) 3 A powdered single-particle type positive electrode active material was produced in the same manner as in Example 1, except that the amount of lithium transition metal oxide was adjusted accordingly.

[0126] Comparative Example 5 The lithium transition metal oxide in the form of a single particle produced in Production Example 1, and the powder-like cobalt source Co(OH) 2 (manufactured by HUAYOU COBALT) and aluminum source Al(OH) 3 were mixed in amounts of 99.48 mol %, 0.02 mol % and 0.5 mol %, respectively.

[0127] The mixture was heat-treated at a temperature of 700° C. for 5 hours to obtain a cake-like positive electrode active material, which was then pulverized to produce a powder-like single-particle type positive electrode active material.

[0128] Comparative Example 6 The lithium transition metal oxide in the form of a single particle produced in Production Example 1, and the powder-like cobalt source Co(OH) 2 (manufactured by HUAYOU COBALT) and zirconium source ZrO 2 were mixed in amounts of 99.48 mol %, 0.02 mol % and 0.5 mol %, respectively.

[0129] The mixture was heat-treated at a temperature of 700° C. for 5 hours to obtain a cake-like positive electrode active material, which was then pulverized to produce a powder-like single-particle type positive electrode active material.

[0130] Experimental Example 1 1) EELS measurement and confirmation of Ni oxidation number The positive electrode active material powder was cut into a thin film sample with a thickness of 100 to 200 nm using FEI's Helios G4 UX FIB equipment, and the Ni L3 energy loss spectrum of the sample was measured using FEI's Titan G2 80-200 ChemiSTEM equipment and Gatan Continuum S EELS system. 2+ and Ni 3+ The average Ni oxidation number of the surface area of ​​the positive electrode active material was measured to a depth of 10 nm from the outermost portion toward the center by nonlinear least-square fitting using the reference spectrum.

[0131] 2) Surface Co / Ni measurement The Co / Ni content ratio of the surface of the positive electrode active material powder to a depth of 10 nm was measured by Electron Spectroscopy for Chemical Analysis (ESCA) using a Thermo Fisher K-alpha XPS device, and the results are shown in Table 1.

[0132] [Table 1]

[0133] Referring to Table 1, in Examples 1 to 3, the moles of aluminum contained in the island portion are 0.13 to 2.50 mol% relative to the total moles of the positive electrode active material, and the nickel contained in the surface portion has an oxidation number in the range of +2.4 to +3, and in Examples 4 to 6, the moles of zirconium contained in the island portion are 0.13 to 2.50 mol% relative to the total moles of the positive electrode active material, and the nickel contained in the surface portion has an oxidation number in the range of +2.4 to +3. As a result, it was confirmed that the positive electrode active materials of Examples 1 to 6 have an increased ratio of cobalt in the surface portion compared to the composition of the lithium transition metal oxide in the form of a single particle due to the influence of the cobalt coating formed on the outside of the surface portion of the lithium transition metal oxide in the form of a single particle, and the oxidation number of the contained Ni is increased, and the deterioration layer in the form of NiO, in which nickel has an oxidation state of +2, which was present in the surface portion of the positive electrode active material, was reduced.

[0134] On the other hand, it was confirmed that Comparative Examples 1 to 3 did not satisfy the condition that the moles of aluminum contained in the island portion should be 0.13 to 2.50 mol% relative to the total moles of the positive electrode active material. Also, Comparative Examples 1 and 4 to 6 showed Ni oxidation numbers less than +2.4, and it was confirmed that a considerable amount of a deteriorated layer in the form of NiO containing nickel having an oxidation state of +2 was present on the surface.

[0135] Meanwhile, images of the cross section of the single particle type positive electrode active material of Example 1 are shown in FIG. 1 and FIG. 2. The left side of FIG. 1 is a TEM image (index: HAADF) of the particle, the center is a TEM EDS image (index: Al-Ka) in which an Al coating can be seen, and the right side is a TEM EDS image (index: Co-Ka) in which a Co coating can be seen. Referring to FIG. 1, it can be seen that a cobalt coating is formed on the surface of the particle, and that an aluminum coating is formed on the surface of the cobalt coating or the particle. FIG. 2 is a TEM EDS image (index: Al-Ka) in which an Al coating obtained at another position can be seen, and a TEM EDS image (index: Co-Ka) in which a Co coating can be seen. Referring to FIG. 2, it can be seen that a cobalt coating and an aluminum coating are formed on the outside of the surface of the lithium transition metal oxide in the form of a single particle, and that they show an island shape.

[0136] Experimental Example 2 Cathode manufacturing Using the positive electrode active material prepared in Example 1, carbon black (DenkaBlack, manufactured by Denka Corporation) as a conductive material and PVdF (Kureha, KF1300) as a binder were added in a weight ratio of 95:3:2 (positive electrode active material:conductive material:binder) to a solvent (N-methylpyrrolidone (NMP), manufactured by Oi Chemical Industries, Ltd.) to prepare a composition for forming a positive electrode active material layer.

[0137] The prepared composition for forming a positive electrode active material layer was coated on one side of an aluminum foil current collector having a thickness of 20 μm and dried at 135° C. for 3 hours to form a positive electrode active material layer. Then, the positive electrode active material layer was rolled using a roll press method to prepare a positive electrode having a porosity of 20% in the positive electrode active material layer after rolling.

[0138] Instead of the positive electrode active material produced in Example 1, the positive electrode active materials of Examples 2 to 6 and Comparative Examples 1 to 6 were used to produce positive electrodes in the same manner as described above.

[0139] A coin half-cell was fabricated using the positive electrode and lithium metal as the negative electrode.

[0140] Electrochemical characterization The electrochemical characteristics of the half cell prepared as above were evaluated as follows.

[0141] The manufactured coin half-cells were charged at 25°C at a constant current (CC) of 0.2C to 4.25V, then charged at a constant voltage (CV) of 4.25V, and the first charge was performed until the charge current reached 0.05mAh, and the charge capacity was measured. Next, after leaving the cells for 20 minutes, they were discharged at a constant current of 0.2C to 2.5V, and the discharge capacity of the first cycle was measured. The charge / discharge efficiency of the first cycle was evaluated.

[0142] The battery was fully charged in the same manner, and a discharge current of 0.2 C was applied for 10 seconds. The initial resistance (DCIR) was measured by dividing the difference in voltage between immediately before and 10 seconds after the application of the current by the current. The results are shown in Table 2.

[0143] The cell that had completed the first cycle was transferred to a chamber at 45°C, and repeatedly charged and discharged at 0.33C until the 50th cycle. The discharge capacity at the 50th cycle was measured, and the discharge capacity at the 50th cycle was calculated relative to the discharge capacity at the first cycle to evaluate the capacity retention rate. In addition, at the 50th cycle, the cell was discharged at a constant current (CC) of 0.2C until the cell reached 2.5V, and the change in voltage from the fully charged state until 10 seconds after discharge was divided by the current to obtain the discharge resistance (50 th Measure the initial resistance (1 st The discharge resistance at the 50th cycle was calculated against the DCR to obtain the resistance increase rate (%). The results are shown in Table 2.

[0144] [Table 2]

[0145] Referring to Table 2, Examples 1 to 6, which satisfy the condition that the number of moles of aluminum or the number of moles of zirconium contained in the island portion is 0.13 to 2.50 mol % relative to the total number of moles of metal in the lithium transition metal oxide, exhibit high discharge capacity, excellent capacity retention, and low resistance increase rate, while Comparative Examples 1 to 4, which do not satisfy this condition, exhibit poor capacity retention and resistance increase rate compared to Examples 1 to 6, and Comparative Examples 1 and 4 also exhibit low discharge capacity values.

[0146] In Comparative Example 1, the lithium transition metal oxide in the form of a single particle prepared in Preparation Example 1 is used as it is as a positive electrode active material, and does not include a cobalt coating on the outside of the surface portion. Comparative Example 1 is inferior in discharge capacity, capacity retention rate, and resistance increase rate, which is determined to be due to the presence of NiO contained in the surface portion of the lithium transition metal oxide in the form of a single particle, as can be confirmed from the fact that the positive electrode active material of Comparative Example 1 shows a low oxidation number of +2.21 and a low Co / Ni ratio of 0.06. In addition, in Comparative Examples 5 and 6, as in Comparative Example 1, it can be confirmed that the coating portion containing cobalt is not properly formed on the outside of the surface portion of the lithium transition metal oxide in the form of a single particle, and thus the discharge capacity, capacity retention rate, and resistance increase rate are poor. Comparative Examples 5 and 6 are also determined to show inferior performance compared to Examples 1 to 6 due to the presence of NiO contained in the surface portion of the lithium transition metal oxide in the form of a single particle.

[0147] In addition, Comparative Example 4 also has poor discharge capacity, capacity retention rate, and resistance increase rate, but Comparative Example 4 has too much aluminum content, with the total number of aluminum moles contained being 3 mol% based on the total number of moles of the single particle type positive electrode active material. Referring to Table 1, Comparative Example 4, in which the total number of aluminum moles contained is 3 mol%, has a nickel oxidation number of +2.28 in the surface portion (up to 10 nm) and a Co / Ni ratio of 0.86 in the surface portion. Thus, when the amount of aluminum coating is increased, it can be confirmed that the NiO deterioration layer is not sufficiently converted to a nickel cobalt manganese (NCM) oxide layer structure despite the same amount of cobalt coating as in Examples 1 to 6, and therefore the appropriate NiO layer reduction effect cannot be obtained. In addition, it can be confirmed that the excessive Al composite compound coating layer acts as an additional resistor due to the decrease in charge capacity compared to Comparative Example 1.

[0148] On the other hand, Comparative Example 2 is a positive electrode active material that includes a cobalt coating but does not include an island portion containing aluminum, and Comparative Example 3 includes both a cobalt coating and an island portion containing aluminum, but the aluminum content is too low at a total of 0.1 mol%. Referring to Table 1, the positive electrode active materials of Comparative Examples 2 and 3 show similar levels to Examples 1 to 3 in terms of the oxidation number of nickel and the Co / Ni ratio of the surface portion, and it was confirmed that the NiO deterioration layer was similarly converted to a nickel-cobalt-manganese (NCM) oxide layer structure. However, it was confirmed that the positive electrode active materials of Comparative Examples 2 and 3, which do not include an island portion containing aluminum at the outermost portion or have a total aluminum content that is too low, have poor capacity retention rate at 50 cycles and resistance increase rate at 50 cycles compared to the positive electrode active materials of Examples 1 to 6, and thus have inferior life characteristics.

[0149] As a result, it was confirmed that when a coating portion containing cobalt is included on the surface portion and an appropriate amount of aluminum is included in the outermost island portion, side reactions with the electrolyte are effectively suppressed, thereby improving the life characteristics.

Claims

1. a lithium transition metal oxide in the form of a single particle, the single particle being divided into a surface portion and a core; a coating portion including cobalt formed on the surface portion; and an island portion discontinuously formed on at least one selected from the group consisting of the surface portion and the coating portion, The island portion contains 0.08 mol % to 2.50 mol % of one or more selected from the group consisting of aluminum and zirconium based on the total number of moles of the positive electrode active material.

2. The positive electrode active material according to claim 1 , wherein the island portions are distributed in a dispersed manner on at least one surface selected from the group consisting of the surface portion and the coating portion.

3. 2. The positive electrode active material according to claim 1, wherein the island portion contains 0.13 to 2.50 mol % of aluminum based on the total number of moles of the positive electrode active material.

4. 2. The positive electrode active material according to claim 1, wherein the island portion contains 0.08 to 2.50 mol % of zirconium based on the total number of moles of the positive electrode active material.

5. The positive electrode active material according to claim 1 , wherein a total area of ​​the coating portion is 10% to 100% of a total area of ​​an outer surface of the lithium transition metal oxide.

6. 2. The positive electrode active material according to claim 1, wherein the surface portion is a region having a depth of 1 nm to 50 nm from the outermost surface toward the center of the single-particle lithium transition metal oxide.

7. 2. The positive electrode active material according to claim 1, wherein the nickel contained in the surface portion has an average oxidation number of +2.36 to +3.

00.

8. 2. The positive electrode active material according to claim 1, wherein the cobalt and nickel satisfy a Co / Ni value (mol / mol) of 0.1 to 0.8 based on the entire surface portion and coating portion.

9. The positive electrode active material according to claim 1 , wherein the coating portion is located in an island shape on the outer side of the surface portion.

10. The coating portion is LiCoO ２ The positive electrode active material of claim 1 having a composition of:

11. The island portion is LiCoAlO ２ The positive electrode active material of claim 1 .

12. 2. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide is a lithium composite transition metal oxide containing nickel, cobalt, and manganese.

13. The positive electrode active material according to claim 1 , wherein the lithium transition metal oxide is a lithium composite transition metal oxide represented by the following Chemical Formula 1: [Chemical formula 1] Li ａ Ni ｘ Co ｙ M １ ｚ M ２ １－ｘ－ｙ－ｚ O ２ In the above Chemical Formula 1, M １ is one or more selected from the group consisting of Mn and Al, ２ is one or more selected from the group consisting of B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf, and 1.0≦a≦1.3, 0.6≦x<1.0, 0≦y≦0.4, and 0≦z≦0.

4.

14. The positive electrode active material according to claim 1 , wherein the lithium transition metal oxide is a lithium composite transition metal oxide represented by the following Chemical Formula 2: [Chemical formula 2] Li ａ Ni ｂ Co ｃ Mn ｄ M １ ｅ O ２ In the above Chemical Formula 2, M １ is one or more 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, and 0.9≦a≦1.1, 0.8≦b<1, 0<c<0.2, 0<d<0.2, 0≦e<0.1, and b+c+d+e=1.

15. 1) mixing lithium transition metal oxide particles in a single particle form, a cobalt source, and at least one selected from the group consisting of an aluminum source and a zirconium source; 2) heat-treating the mixture of step 1).

16. The method for producing a positive electrode active material according to claim 15, wherein in step 1), an additional metal source is further mixed.

17. The method for producing a positive electrode active material according to claim 15, wherein the heat treatment in step 2) is performed at 500 to 800° C.

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