Positive electrode active material and method for producing same

Abstract

The present invention relates to a positive electrode active material including a lithium transition metal oxide in the form of a single particle that is divided into a surface portion and a core, and a coating portion containing cobalt formed on the surface portion, the positive electrode active material including cobalt and nickel in an amount that satisfies a value (mol / mol) of Co / Ni of 0.1 to 0.8 based on the entire surface portion and coating portion, 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. 10-2022-0062252 filed on 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 that is divided into a surface portion and a core, and a coating portion containing cobalt formed on the surface portion, the positive electrode active material containing cobalt and nickel in an amount that satisfies a value (mol / mol) of Co / Ni of 0.1 to 0.8 based on the entire surface portion and coating portion.

[0012] (2) The present invention provides a positive electrode active material according to the above (1), wherein the surface portion has a layered (R-3m) structure.

[0013] (3) The present invention provides a positive electrode active material according to (1) or (2) above, wherein the surface portion is a region having a depth of 1 nm to 50 nm from the outermost portion toward the center of the single-particle lithium transition metal oxide.

[0014] (4) The present invention provides a positive electrode active material according to any one of the above (1) to (3), wherein the nickel contained in the surface portion has an average oxidation number of +2.36 to +3.00.

[0015] (5) The present invention provides a positive electrode active material according to any one of (1) to (4) above, wherein the coating portion is formed on the outside of the surface portion, covering 10% to 100% of the total area of ​​the outside of the surface portion.

[0016] (6) The present invention provides the positive electrode active material according to any one of (1) to (5) above, wherein the coating portion is located in an island shape on the outer side of the surface portion.

[0017] (7) The present invention is directed to any one of the above (1) to (6), wherein the coating portion is LiCoO 2 The present invention provides a positive electrode active material having the composition:

[0018] (8) The present invention provides a positive electrode active material according to any one of the above (1) to (7), wherein the lithium transition metal oxide is a lithium composite transition metal oxide containing nickel, cobalt, and manganese.

[0019] (9) The present invention provides a positive electrode active material in any one of the above (1) to (8), 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 is 1.0≦a≦1.3, 0.6≦x<1.0, 0≦y≦0.4, and 0≦z≦0.4.

[0020] (10) The present invention provides a positive electrode active material according to any one of the above (1) to (9), 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。

[0021] In order to achieve the above-mentioned other object, the present invention provides a method for producing the above-mentioned positive electrode active material.

[0022] (11) The present invention provides a method for producing a positive electrode active material, comprising the steps of: 1) mixing lithium transition metal oxide particles in a single particle form and a cobalt source; and 2) heat-treating the mixture of step 1).

[0023] (12) The present invention provides the method for producing a positive electrode active material according to (11), further comprising mixing an additional metal source in the step 1).

[0024] (13) The present invention provides the method for producing a positive electrode active material according to (11) or (12), wherein the heat treatment in step 2) is carried out at 500 to 800°C. Effect of the Invention

[0025] 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The present invention will now be described in further detail in order to facilitate understanding of the present invention.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 by containing a small number of crystal grains.

[0032] 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.

[0033] In the present invention, the term "average particle size (D 50 The "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.

[0034] The positive electrode active material of the present invention includes a lithium transition metal oxide in the form of a single particle that is divided into a surface portion and a core, and cobalt formed on the surface portion, and includes cobalt and nickel in an amount that satisfies a value (mol / mol) of Co / Ni of 0.1 to 0.8 based on the entire surface portion and coating portion.

[0035] The surface portion of the lithium transition metal oxide in the form of a single particle may have a layered (R-3m) structure, and has a high NiO content before the cobalt-containing coating portion 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, a decrease in energy density and output, etc.

[0036] 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.

[0037] The lithium transition metal oxide in the form of a single particle is divided into a surface portion and a core. The surface portion refers to the outside of the lithium transition metal oxide in the form of a single particle, and means a region having a predetermined thickness from the outermost portion of the lithium transition metal oxide in the direction toward the center of the lithium transition metal oxide in the form of a single particle, specifically, a region having a depth of 1 nm to 50 nm, specifically, 5 to 30 nm, from the outermost portion of the lithium transition metal oxide in the direction toward the center of the lithium transition metal oxide in the form of a single particle.

[0038] The core refers to the inside of the single-particle lithium transition metal oxide excluding the surface portion.

[0039] Based on the entire surface portion and coating portion, the cobalt and nickel may satisfy the Co / Ni value (mol / mol) of, specifically, 0.15 to 0.80, 0.20 to 0.80, 0.10 to 0.75, 0.15 to 0.80, 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 is reduced, and the effect of forming the coating portion containing cobalt 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 O4 or lithium cobalt oxide (Li x CO y 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 coating formed on the surface of the lithium transition metal oxide may act as a resistor or cause a decrease in capacity.

[0040] 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 amount of cobalt coating that forms the coating portion, and when the range is satisfied, an appropriate amount of 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.

[0041] The average oxidation number of nickel (Ni) from the outermost part to the center of the single particle lithium transition metal oxide to a depth of 10 nm 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 single particle lithium transition metal oxide can have an appropriate reduction effect on the NiO deterioration layer.

[0042] 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 in an area of ​​10% to 100% (area %) of the total area of ​​the outside of the surface portion. Specifically, the coating portion may be formed on a part of the outside of the surface portion, and may be formed in an area of ​​30% to 90% of the total area of ​​the outside of the surface portion.

[0043] The coating portion may be formed in an island shape on the outer side of the surface portion. The island shape means a shape formed discontinuously 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 lithium transition metal oxide in the form of single particles.

[0044] The coating portion is LiCoO 2 Specifically, the coating portion may include an island-shaped LiCoO 2 It can be included as:

[0045] In the positive electrode active material according to one embodiment of the present invention, the single particles have an average particle size (D 50 ) may be 0.1 μm to 10 μm. When the average particle size of the single particles satisfies the above range, when they are aggregated to form a positive electrode active material or a lithium transition metal oxide in the form of a single particle, advantages may be obtained 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, performance may be reduced in terms of electrode capacity, life characteristics, resistance, etc.

[0046] 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).

[0047] 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.

[0048] [Chemical formula 1] Li a Ni x Co y M 1 z M 2 1-x-y-z O 2

[0049] 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 0.9≦a≦1.3, 0.6≦x<1.0, 0≦y≦0.4, and 0≦z≦0.4.

[0050] The a represents the molar ratio of lithium in the lithium transition metal oxide and may be 1.0≦a≦1.3, specifically 1.0≦a≦1.25, and more specifically 1.0≦a≦1.20.

[0051] The x represents the molar ratio of nickel to the total transition metals, and may be 0.6≦x<1.0, specifically 0.6≦x≦0.99 or 0.70≦x≦0.99, and more specifically 0.8≦x≦0.95. When the nickel content satisfies the above range, excellent capacity characteristics can be achieved.

[0052] The y indicates the molar ratio of cobalt to all transition metals, and may be 0≦y≦0.40, specifically 0≦y≦0.35, and more specifically 0.01≦y≦0.30.

[0053] The z is the element M among all transition metals. 1and can be 0≦z≦0.40, specifically 0≦z<0.35, and more specifically 0.01≦z≦0.30.

[0054] The 1-xyz is M among all transition metals. 2 and can be 0≦1−xyz≦0.4, specifically 0≦1−xyz≦0.35, and more specifically 0≦1−xyz≦0.30.

[0055] Specifically, the lithium transition metal oxide may be a positive electrode active material that is a lithium composite transition metal oxide represented by the following Chemical Formula 2.

[0056] [Chemical formula 2] Li a Ni b Co c Mn d M 1 e O 2

[0057] 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。

[0058] Specifically, the lithium transition metal oxide may be a lithium composite transition metal oxide represented by the following Chemical Formula 3.

[0059] [Chemical formula 3] Li g Ni h Co i Mn j O 2

[0060] 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。

[0061] 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 50 When 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.

[0062] The present invention also provides a method for producing the positive electrode active material.

[0063] The positive electrode active material may be prepared by a method including the steps of: 1) mixing lithium transition metal oxide particles in a single particle form and a cobalt source; and 2) heat-treating the mixture of step 1).

[0064] 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 that is too small compared to the above range, a sufficient coating portion cannot 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 amount that is too large, an excessive coating portion 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.

[0065] In step 1), a process of further mixing an additional metal source may be performed. The additional metal source may be used together with the cobalt source and may be coated on the surface of the single particle lithium transition metal oxide through the following steps. The coating formed by the additional metal source may be mixed with the coating formed on the outside of the surface of the single particle lithium transition metal oxide particles by the cobalt source and coated together, or may be formed as a separate coating. The additional metal source may be coated on the surface of the single particle lithium transition metal oxide and formed in the form of metal oxide, lithium metal oxide, cobalt metal oxide, or lithium cobalt metal oxide.

[0066] The mixing in step 1) may be a dry mixing, for example, mixing a powdered cobalt source material with a lithium transition metal oxide in the form of a single particle without a solvent. Such dry mixing may be a simple mixing process, and the simplification of the process may provide advantages of cost reduction and quality stabilization.

[0067] 2) In the step of heat-treating the mixture in step 1), cobalt diffuses from the surface of the lithium transition metal oxide in the form of a single particle toward the center to form a coating portion. When the coating portion is formed, an island-shaped coating portion may be discontinuously formed on the surface of the lithium transition metal oxide. In a method for manufacturing a positive electrode active material according to an embodiment of the present invention, the lithium transition metal oxide particles in the form of a single particle and a cobalt (Co) source are dry-mixed and then heat-treated, so that the coating portion may be formed in an island shape.

[0068] The heat treatment in step 2) can be carried out at a temperature of 500°C to 800°C, specifically, 600°C to 800°C, and more specifically, 650°C to 750°C.

[0069] When the heat treatment temperature is within the above range, during the temperature rise process for the heat treatment, the cobalt present on the surface of the lithium transition metal oxide in the form of a single particle, specifically, the cobalt is formed in an island shape on the surface of the lithium transition metal oxide, and LiCoO 2 Cobalt, which existed as a phase, penetrates into the lithium transition metal oxide 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 part of the lithium transition metal oxide in the form of a single particle has a layered type (R-3m) structure, and the surface part 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 step 2) is low, the thickness of the coating part becomes thick and the coating part is formed in an excessive amount, making it difficult to exhibit the advantages of the formation of the coating part as described above, and if the heat treatment temperature in step 2) is high, cobalt is doped deeply into the lithium transition metal oxide in the form of a single particle, and the coating part may not be appropriately formed on the surface part.

[0070] 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.

[0071] 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 2O, and any one or a mixture of two or more of these can be used. Specifically, Co(OH) 2 can be used.

[0072] 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 Al, Ti, W, B, F, P, Mg, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, Cr, Hf, Ta, La, Ba, Ce, Sn, Y, and S. Specifically, ZnO, Al 2 O 3 , Al(OH) 3 ,AlSO 4 , AlCl 3 , Al-isopropoxide, AlNO 3 , TiO 2 , WO 3 , AlF, 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 H 9 B 3 O 6 , (C 3 H 7 O 3 ) B, Li 3 WO 4 , (NH 4 ) 10 W 12 O 41 5H 2O, NH 4 H 2 PO 4 These include, but are not limited to, the following:

[0073] The additional metal source may be used in an amount such that the additional metal 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 this range, it is expected that the side reaction with the electrolyte can be effectively suppressed, and the electrochemical properties can be further improved.

[0074] 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.

[0075] According to yet another embodiment of the present invention, there is provided a positive electrode comprising the above positive electrode active material.

[0076] 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.

[0077] 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.

[0078] The positive electrode active material layer may contain a conductive material and a binder in addition to the positive electrode active material described above.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] The negative electrode active material layer includes a negative electrode active material and, optionally, a binder and a conductive material.

[0089] 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.

[0090] The binder and the conductive material are as described above in the positive electrode.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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).

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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

[0103] 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.

[0104] 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.

[0105] 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) were mixed at a ratio of 98 mol % and 2 mol %.

[0106] 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.

[0107] Example 2 A powdered single particle type positive electrode active material was prepared in the same manner as in Example 1, except that the mixture was heat-treated at a temperature of 740°C.

[0108] Example 3 A powdered single particle type positive electrode active material was prepared in the same manner as in Example 1, except that the mixture was heat-treated at a temperature of 660°C.

[0109] 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.

[0110] Comparative Example 2 A powdered single particle type positive electrode active material was prepared in the same manner as in Example 1, except that the mixture was heat-treated at a temperature of 400°C.

[0111] Comparative Example 3 A powdered single particle type positive electrode active material was prepared in the same manner as in Example 1, except that the mixture was heat-treated at a temperature of 900° C.

[0112] Comparative 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) were mixed at a ratio of 99.98 mol % and 0.02 mol %.

[0113] The mixture was heat-treated at a temperature of 750° 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.

[0114] 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) were mixed at a ratio of 99.98 mol % and 0.02 mol %.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] [Table 1]

[0119] Referring to Table 1, the EELS measurement results showed that in Examples 1 to 3, the Co / Ni ratio in the surface region from the outermost portion to a depth of 10 nm in the center direction was 0.1 to 0.80, and was greater than the Co / Ni ratio of the single particle lithium transition metal oxide used in the preparation, confirming that the cobalt content in the surface region was relatively increased. In addition, the oxidation numbers of Ni in the surface region to a depth of 10 nm in Examples 1 to 3 were +2.60, +2.65, and +2.57, respectively, which is higher than the oxidation number of Ni in the surface region of Comparative Example 1, in which the single particle lithium transition metal oxide of Preparation Example 1 was used as the positive active material. As a result, in Examples 1 to 3, it was confirmed that due to the influence of the coating portion containing cobalt, the ratio of cobalt in the surface portion increased compared to the composition of the lithium transition metal oxide in the form of a single particle, and the oxidation number of the contained Ni increased, and the deterioration layer in the form of NiO in which nickel has an oxidation state of +2 that was present in the surface portion of the positive electrode active material was reduced.

[0120] The positive electrode active material of Comparative Example 1 used the lithium transition metal oxide in the form of single particles of Preparation Example 1 as the positive electrode active material as it is, and the positive electrode active material of Comparative Example 3 was mixed with a cobalt source and then heat-treated at 900°C, and the Co / Ni value contained in the surface portion up to a depth of 10 nm was smaller than 0.1, and the Ni contained in the surface portion had an oxidation number of less than +2.4. Also, the positive electrode active materials of Comparative Examples 4 and 5 were mixed with a small amount of cobalt source and then heat-treated at 750°C and 700°C, respectively, and the Co / Ni value contained in the surface portion up to a depth of 10 nm was greater than 0.1, but the Ni contained in the surface portion had an oxidation number of +2.25 and +2.27, respectively, which was less than +2.4, so it was confirmed that the deteriorated layer in the form of NiO was not sufficiently converted to a nickel-cobalt-manganese (NCM) oxide layer structure, and therefore the appropriate reduction effect of the NiO layer was not obtained.

[0121] Meanwhile, in Comparative Example 2, the Co / Ni value was 0.68, and it was confirmed that a coating was formed as cobalt diffused to the outside of the positive electrode active material. However, despite the formation of a sufficient amount of coating, it was confirmed that the deterioration layer in the form of NiO was not sufficiently converted to a nickel-cobalt-manganese (NCM) oxide layer structure, and therefore an appropriate NiO layer reduction effect was not obtained.

[0122] This confirmed that the positive electrode active materials of Comparative Examples 1 to 5 had a considerable amount of deteriorated layer in the form of NiO, which contained nickel having a +2 valence oxidation state and was present on the surface.

[0123] 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.

[0124] 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.

[0125] Instead of the positive electrode active material produced in Example 1, the positive electrode active materials of Examples 2 and 3 and Comparative Examples 1 to 5 were used to produce positive electrodes in the same manner as described above.

[0126] A coin half-cell was fabricated using the positive electrode and lithium metal as the negative electrode.

[0127] Electrochemical characterization The electrochemical characteristics of the half cell prepared as above were evaluated as follows.

[0128] 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.

[0129] 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.

[0130] [Table 2]

[0131] Referring to Table 2, it can be seen that the positive electrode active materials of Examples 1 to 3 have higher discharge capacity and efficiency than the positive electrode active materials of Comparative Examples 1 to 5, and also have lower initial resistance.

[0132] As a result, the cobalt-containing coating formed on the outside of the surface layer turns the NiO degradation layer into an NCM structure with a relatively high cobalt concentration, improving cation mixing and structural instability caused by the collapse of the layered structure. As a result, it was confirmed that problems such as increased resistance, decreased capacity, and decreased output can be solved.

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, The positive electrode active material contains cobalt and nickel in amounts that satisfy a Co / Ni value (mol / mol) of 0.1 to 0.8 based on the entire surface portion and coating portion.

2. The positive electrode active material according to claim 1, wherein the surface portion has a layered (R-3m) structure.

3. 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 portion toward the center of the single-particle lithium transition metal oxide.

4. 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.

5. The positive electrode active material according to claim 1 , wherein the coating portion is formed on an outer side of the surface portion over 10% to 100% of a total area of ​​the outer side of the surface portion.

6. 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.

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

8. 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.

9. 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.

10. 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.

11. 1) mixing lithium transition metal oxide particles in single particle form and a cobalt source; 2) heat-treating the mixture of step 1).

12. The method for producing a positive electrode active material according to claim 11 , wherein in step 1), an additional metal source is further mixed.

13. The method for producing a positive electrode active material according to claim 11, wherein the heat treatment in step 2) is performed at 500 to 800° C.

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