Positive electrode active material and method for producing same

Abstract

The present invention relates to a lithium transition metal oxide having a single particle form, a coating portion containing cobalt formed on the lithium transition metal oxide having a single particle form, and island-like LiCoO2 formed discontinuously on the surface, and the surface has a Raman spectrum showing a peak (500 cm) corresponding to the A1g vibration mode of LiNiO2. -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1 ~620cm -1 The present invention relates to a positive electrode active material in a single particle form in which the intensity ratio of the positive electrode active material to the positive electrode active material is greater than 1, and a method for producing the same.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0062286 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 in a single particle form and a method for producing the same. [Background technology]

[0003] Recently, with technological development and increased demand for mobile devices and electric vehicles, the demand for secondary batteries as an energy source has increased dramatically.

[0004] A lithium secondary battery generally comprises a positive electrode, a negative electrode, a separator and an electrolyte, and the positive electrode and the negative electrode contain active materials capable of intercalating and deintercalating lithium ions.

[0005] On the other hand, the positive electrode active material used in a lithium secondary battery generally has the form of spherical secondary particles formed by agglomeration of several hundred fine primary particles of submicron size. However, the positive electrode active material in the form of secondary particles has a problem that the secondary particles break as the aggregated primary particles separate during repeated charging and discharging, resulting in a deterioration of battery characteristics.

[0006] To solve these problems, development of single particle positive electrode active materials has been actively conducted, but when manufacturing a single particle positive electrode active material, it is necessary to sinter at a higher temperature than when manufacturing a secondary particle positive electrode active material, and there is a problem that the ratio of the NiO reduced layer on the particle surface increases. On the other hand, when the ratio of the NiO reduced layer on the surface of the positive electrode active material increases, problems such as an increase in battery resistance, a decrease in capacity, and a decrease in output occur, and therefore a surface treatment technology that can control the NiO reduced layer is required. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a positive electrode active material capable of realizing a battery having improved cycle characteristics such as capacity retention rate and resistance increase rate, and a method for producing the same. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a positive electrode active material and a method for producing the same.

[0009] (1) The present invention relates to a method for producing a lithium transition metal oxide having a single particle form, a coating portion containing cobalt formed on the lithium transition metal oxide having a single particle form, and island-like LiCoO2 formed discontinuously on the surface, and the method further relates to a method for producing a lithium transition metal oxide having a single particle form. -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1 ~620cm -1 The present invention provides a positive electrode active material in a single particle form, in which the ratio of the intensities of the particles is greater than 1.

[0010] (2) In the present invention, in the above (1), the positive electrode active material in the form of a single particle has an average particle diameter (D 50 ) is 0.1 μm to 10 μm.

[0011] (3) The present invention provides a positive electrode active material in the form of (1) or (2) above, wherein the positive electrode active material in the form of single particle is in the form of an aggregation of 50 or less primary particles each consisting of 10 or less single crystal grains.

[0012] (4) The present invention provides a positive electrode active material in a single particle form in any one of the above (1) to (3), wherein the lithium transition metal oxide in the single particle form is a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn).

[0013] (5) The present invention provides a positive electrode active material in the form of a single particle in any one of the above (1) to (4), wherein the lithium transition metal oxide in the form of a single particle has a composition represented by the following chemical formula 1: [Chemical formula 1] Li a Ni b Co c Mn d M 1 e O2 In the above Chemical Formula 1, M 1 is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S; 0.9≦a≦1.1, 0.8≦b<1.0, 0 <c<0.2、0<d<0.2、0≦e≦0.1、b+c+d+e=1である。

[0014] (6) In any one of (1) to (5) above, the present invention provides a positive electrode active material in a single particle form, wherein the coating portion is a region of 5 nm to 100 nm from the surface of the positive electrode active material toward the center.

[0015] (7) The present invention provides the positive electrode active material in the form of a single particle in any one of the above (1) to (6), wherein the molar ratio of cobalt to nickel present on the surface is 0.45 to 0.9.

[0016] (8) The present invention provides a method for producing a positive electrode active material in a single particle form, the method comprising the steps of: (A) mixing a lithium transition metal oxide in a single particle form and a cobalt source material to prepare a mixture; and (B) heat-treating the mixture at a temperature of 500° C. or higher and lower than 680° C.

[0017] (9) The present invention provides a method for producing a positive electrode active material in the form of a single particle according to the above (8), wherein in the step (A), the lithium transition metal oxide in the form of a single particle has a cation mixing of 5% or less.

[0018] (10) The present invention provides a method for producing a positive electrode active material in the form of a single particle according to the above (8) or (9), wherein in step (A), the single particle lithium transition metal oxide contains 20,000 ppm or less of lithium by-products.

[0019] (11) The present invention provides the method for producing a positive electrode active material in a single particle form according to any one of the above (8) to (10), wherein in the step (A), a molar ratio of the lithium transition metal oxide in a single particle form to a cobalt raw material is 1:0.0001 to 0.1.

[0020] (12) The present invention provides the method for producing a positive electrode active material in a single particle form according to any one of the above (8) to (11), wherein in the step (A), the mixing is a dry mixing.

[0021] (13) The present invention provides the method for producing a positive electrode active material in a single particle form according to any one of the above (8) to (12), wherein the heat treatment in the step (B) is carried out in an oxygen atmosphere. Effect of the Invention

[0022] The positive electrode active material according to the present invention has a peak (500 cm) corresponding to the A1g vibration mode of LiNiO2 in the Raman spectrum on the surface. -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1 ~620cm -1 ) satisfies a ratio of intensity exceeding 1, and the cycle characteristics of a battery containing the same can be improved. [Brief description of the drawings]

[0023] [Figure 1] 1 shows Raman spectra of the surfaces of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 3 to 5. [Diagram 2] 1 shows Raman spectra of the surfaces of the positive electrode active materials of Comparative Examples 1 and 2. [Diagram 3]FIG. 1A is an SEM image of the positive electrode active material of Example 1; FIG. 1B is an SEM image of the positive electrode active material of Example 2; FIG. 1C is an SEM image of the positive electrode active material of Example 1; and FIG. 1D is an SEM image of the positive electrode active material of Comparative Example 2. [Figure 4] 1A is a SEM image of one positive electrode active material particle of Example 1, and FIG. 1B is electron backscatter diffraction (EBSD) Eular map data of one positive electrode active material particle of Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The terms and words used in this specification 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.

[0025] In this specification, the terms "including," "comprising," or "having" are intended to specify the presence of embodied features, numerals, steps, components, or combinations thereof, but are not intended to preclude the presence or additional possibility of one or more other features, numerals, steps, components, or combinations thereof.

[0026] As used herein, the term "on" is meant to include not only when one structure is formed immediately on top of another structure, but also when a third structure is interposed between the structures.

[0027] In this specification, the term "single particle positive electrode active material" refers to a positive electrode active material consisting of 50 or less primary particles, which is a concept that is contrasted with a spherical secondary particle positive electrode active material formed by agglomeration of several hundred primary particles produced by a conventional method. Specifically, in the present invention, the single particle positive electrode active material may be a single particle consisting of one primary particle, or may be a secondary particle form in which 2 to 50, 2 to 40, 2 to 30, 2 to 20, 2 to 15, 2 to 10, or 2 to 5 primary particles are aggregated. Here, the "primary particle" refers to the smallest unit of a particle that can be recognized when observing the positive electrode active material through a scanning electron microscope.

[0028] Meanwhile, the primary particles may be composed of 10 or less single crystal grains, and the grains may be analyzed using an electron backscatter diffraction (EBSD) analyzer. The single crystal grains are units that are represented by the same color in the electron backscatter diffraction (EBSD) Eular map data of one positive electrode active material particle, and are grains that do not have grain boundaries within the grains.

[0029] In this specification, the average particle size (D 50 The average particle size (D) refers to the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material or lithium transition metal oxide powder. 50 ) can be measured using the laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W. Then, a volume cumulative particle size distribution graph is obtained, and the particle diameter corresponding to 50% of the volume cumulative amount is obtained.

[0030] In this specification, the average grain size (D EBSD) means the particle size at 50% of the volume cumulative particle size distribution of single crystal grains obtained by EBSD analysis using SEM. The EBSD analysis can be performed by acquiring images using a SEM-EBSD device (e.g., Quanta200 manufactured by FEI-Velocity super OIM 8 manufactured by EDAX), and analyzing the images using image analysis software (EDAX OIM Analysis).

[0031] The present invention will be described in detail below.

[0032] positive electrode active material The present invention relates to a lithium transition metal oxide having a single particle form, a coating portion containing cobalt formed on the lithium transition metal oxide having a single particle form, and island-like LiCoO2 formed discontinuously on the surface, and the surface has a Raman spectrum showing a peak (500 cm) corresponding to the A1g vibration mode of LiNiO2. -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1 ~620cm -1 The present invention provides a positive electrode active material in a single particle form, in which the ratio of the intensities of the particles is greater than 1.

[0033] The present inventors have found that the positive electrode active material is in the form of a single particle and contains islands of LiCoO2 discontinuously formed on the surface, and that the Raman spectrum of the surface shows a peak (500 cm2) corresponding to the A1g vibration mode of LiNiO2. -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1 ~620cm -1 The inventors have found that when the ratio of the intensities of the peaks (500 cm) and (600 cm) of the positive electrode active material is greater than 1, the performance of the battery containing the positive electrode active material, particularly the cycle characteristics, is improved. -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1~620cm -1 ) can be greater than 1, 1.5, 2 or greater.

[0034] On the other hand, in the Raman spectrum of the surface of the positive electrode active material, a peak corresponding to the A1g vibration mode of LiNiO2 (500 cm -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (500 cm -1 ~600cm -1 If the ratio of the intensities of the positive electrode active material and the positive electrode active material is less than 1, the Co ions partially penetrate too deeply into the positive electrode active material, resulting in a high ratio of the NiO reduced layer on the surface of the positive electrode active material.

[0035] According to the present invention, the positive electrode active material in the form of a single particle has an average particle size (D 50 Specifically, the average particle diameter (D 50 ) may be 0.1 μm, 1.0 μm, 2.0 μm or more and 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm or less. In this case, the rolling ratio of the battery including the positive electrode active material in the form of single particles can be increased, and the battery performance can be further improved.

[0036] According to the present invention, the positive electrode active material in the form of single particles may be in the form of primary particles consisting of 10 or less single crystal grains, which are aggregated to 50 or less, specifically 30, 20, 10, 5 or less. In this case, the capacity and resistance performance of the battery can be improved, and the occurrence of cracks in the particles during repeated charging and discharging can be reduced. Here, the single crystal grains have an average particle size (D EBSD Specifically, the average grain size (D EBSD ) can be 0.1 μm, 1.0 μm, 2.0 μm or more, and 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm or less.

[0037] According to the present invention, the lithium transition metal oxide in the form of a single particle may be a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co) and manganese (Mn). Here, the lithium transition metal oxide in the form of a single particle may contain 80 mol % or more, 85 mol % or more of nickel (Ni) among all metals other than lithium.

[0038] According to the present invention, the lithium transition metal oxide in the form of single particles may specifically have a composition represented by the following Chemical Formula 1.

[0039] [Chemical formula 1] Li a Ni b Co c Mn d M 1 e O2

[0040] In the above Chemical Formula 1, M 1 is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S; 0.9≦a≦1.1, 0.8≦b<1.0, 0 <c<0.2、0<d<0.2、0≦e≦0.1、b+c+d+e=1である。

[0041] The b represents the atomic fraction of nickel among metal elements other than lithium in the lithium transition metal oxide, and may be 0.8 or 0.85 or more and 0.95 or 0.98 or less.

[0042] The c represents the atomic fraction of cobalt among metal elements other than lithium in the lithium transition metal oxide, and may be 0.01 or more, 0.1 or less, and 0.2 or less.

[0043] The d indicates the atomic fraction of manganese among metal elements other than lithium in the lithium transition metal oxide, and may be 0.01 or more, 0.1, or 0.2 or less.

[0044] The e is M among the metal elements other than lithium in the lithium transition metal oxide. 1 It means the element fraction of an element, which can be 0 or more and 0.02, 0.05, 0.1 or less.

[0045] In the present invention, the coating portion is a layer formed by diffusing cobalt from the surface to the center of the lithium transition metal oxide in the form of a single particle when the lithium transition metal oxide in the form of a single particle and the cobalt raw material are mixed and then heat-treated. Therefore, the composition of the coating portion is the same as that of the lithium transition metal oxide in the form of a single particle contained in the positive electrode active material of the present invention, but the ratio of cobalt to the total metal other than lithium is higher than that of the lithium transition metal oxide in the form of a single particle. Meanwhile, as cobalt diffuses from the surface of the lithium transition metal oxide in the form of a single particle toward the center, Ni present in the lithium transition metal oxide in the form of a single particle may be replaced with Co, and the coating portion may have the same structure as the lithium transition metal oxide in the form of a single particle, i.e., a layered structure.

[0046] According to the present invention, the coating portion may be a region of 5 nm to 100 nm from the surface of the positive electrode active material toward the center, specifically, the coating portion may be a region of 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm from the surface of the positive electrode active material toward the center.

[0047] In the present specification, the coating portion is a region from the surface of the positive electrode active material to a point where the Co content measured by a TEM-EDX experiment is more than 1.1 times the overall average Co content (mol%) of the positive electrode active material. Here, in the TEM-EDX experiment, a thin film sample having a thickness of 100 nm to 200 nm is prepared from the positive electrode active material powder using a Helios G4 UX FIB device manufactured by FEI, and then the x-ray spectrum of elements at each position of the sample is measured using a Titan G2 80-200 ChemiSTEM device and an EDX (in-column super-X Energy Dispersive X-ray spectroscopy) unit (ChemiSTEM technology) manufactured by FEI, and the molar ratio (mol%) value of each element can be obtained by comparing the intensities.

[0048] In the present invention, the LiCoO2 islands are discontinuously formed on the surface of the positive electrode active material. That is, the LiCoO2 islands do not entirely cover the surface of the positive electrode active material, but are partially dispersed and distributed. The LiCoO2 islands may be discontinuously formed in an area of ​​20% to 50% of the total area of ​​the surface of the positive electrode active material.

[0049] According to the present invention, the molar ratio of cobalt to nickel present on the surface of the positive electrode active material can be 0.45 to 0.9, specifically, 0.45 or more and 0.6, 0.7, 0.8, or 0.9 or less. In this case, the island-shaped LiCoO2 is appropriately present on the surface, and the cycle characteristics of the battery can be further improved. Meanwhile, the molar ratio of cobalt to nickel present on the surface of the positive electrode active material can be obtained by electron spectrochemical analysis (ESCA) using a K-alpha XPS device manufactured by Thermo Fisher. Here, the surface analyzed by the ESCA analysis can be a region from the outermost part of the positive electrode active material to 10 nm.

[0050] Method for producing positive electrode active material The present invention provides a method for producing a positive electrode active material in a single particle form, the method including the steps of: (A) mixing a lithium transition metal oxide in a single particle form and a cobalt raw material to prepare a mixture; and (B) heat-treating the mixture at a temperature of 500° C. or higher and lower than 680° C.

[0051] The method for producing a positive electrode active material according to the present invention includes a lithium transition metal oxide in the form of a single particle, a coating portion containing cobalt formed on the lithium transition metal oxide in the form of a single particle, and island-like LiCoO2 discontinuously formed on the surface, and the Raman spectrum of the surface shows a peak (500 cm) corresponding to the A1g vibration mode of LiNiO2. -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1 ~620cm -1 ) is greater than 1. That is, the method for producing the positive electrode active material is the method for producing the positive electrode active material according to the present invention. The positive electrode active material according to the present invention can be produced by appropriately adjusting the type of cobalt raw material as well as the temperature at which the mixture is heat-treated.

[0052] The method for producing the positive electrode active material will be described in more detail below.

[0053] (A) Step The step (A) is a step of preparing a mixture by mixing a lithium transition metal oxide in a single particle form and a cobalt source material.

[0054] In the step (A), the lithium transition metal oxide in the form of a single particle has an average particle size (D 50 Here, the positive electrode active material in the form of a single particle may be in the form of an aggregation of 50 or less primary particles each consisting of 10 or less single crystal grains.

[0055] According to the present invention, in step (A), the lithium transition metal oxide in the form of a single particle may have a cation mixing of 5% or less. In this case, the amount of impurities present in the resulting positive electrode active material is small, and the performance of the battery can be improved. The cation mixing value is a value measured by the ratio (%) of the substitution of lithium and other metal ion sites in the structure.

[0056] According to the present invention, in step (A), the single particle lithium transition metal oxide may contain lithium by-products in an amount of 20,000 ppm or less, which results in a small amount of impurities in the positive electrode active material produced, and reduces the entanglement phenomenon of the slurry (composition for forming the positive electrode active material) during the production of the positive electrode, improving the process.

[0057] The lithium transition metal oxide in the form of a single particle in step (A) may be prepared by mixing a positive electrode active material precursor (e.g., transition metal hydroxide, transition metal oxyhydroxide, etc.), a lithium source material (e.g., lithium carbonate (Li2CO3), lithium hydroxide (LiOH), LiNO3, CH3COOLi, Li2(COO)2, etc.), and optionally a doping element (e.g., Y, Zr, Al) source material, and firing the mixture at a high temperature. Here, the firing may be a one-step firing or a multi-step firing. Meanwhile, when the firing is a two-step firing, the lithium source material may be mixed all together before the primary firing, or may be mixed separately before the primary firing and the secondary firing. Meanwhile, the firing may be performed at a temperature of 700°C to 950°C in an oxygen atmosphere.

[0058] According to the present invention, in step (A), the molar ratio of the lithium transition metal oxide in a single particle form to the cobalt source material may be 1:0.0001-0.1, 1:0.001-0.05, or 1:0.01-0.05. That is, the content of the cobalt source material may be 0.01 mol%, 0.10 mol%, 1 mol% or more, 5 mol%, or 10 mol% or less with respect to the lithium transition metal oxide in a single particle form. When the content of the cobalt source material is within the above range, a coating portion containing cobalt is appropriately formed, and the performance of the battery can be further improved.

[0059] The cobalt source material may be acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide containing cobalt. For example, it may be Co(OH)2, Co2O3, etc., and preferably Co(OH)2. Meanwhile, when a highly reactive material such as Co(OH)3 or cobalt acetate is used as the cobalt source material, there may be a problem that Co penetrates excessively into the interior, resulting in almost no coating portion containing cobalt.

[0060] According to the present invention, the mixing in step (A) may be a dry mixing. That is, the powdered cobalt raw material may be simply mixed with the lithium transition metal oxide in the form of a single particle without using a solvent. In this case, the process may be simplified, the cost may be reduced, and a cathode active material having uniform quality may be produced.

[0061] Meanwhile, in the step (A), besides the lithium transition metal oxide and the cobalt source material in the form of single particles, a coating element-containing source material may be further mixed, and the metal element contained in the coating element-containing source material may be Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Sn, Y, Zn, Ce, F, P, and S. The coating element-containing source material may be acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide containing the metal element. For example, when the metal element is B, boric acid (H3BO3) may be used.

[0062] (B) Step Step (B) is a step of heat-treating the mixture at a temperature of 500°C or more and less than 680°C. As a result, 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, and island-like LiCoO2 is discontinuously formed on the surface of the positive electrode active material. In particular, when the heat treatment temperature is within the above range, Co present on the outside as the LiCoO2 phase does not penetrate much into the positive electrode active material during the temperature rise process, and the Raman spectrum of the surface of the produced positive electrode active material shows a peak (500 cm) corresponding to the A1g vibration mode of LiNiO2. -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1 ~620cm -1 ) can be greater than 1.

[0063] The heat treatment in step (B) can be performed at a temperature of 500° C. or more and less than 680° C. Specifically, the heat treatment temperature can be 500° C., 550° C., 600° C. or more and 660° C. or less and less than 680° C. When the heat treatment temperature is within the above range, a coating portion containing cobalt is appropriately formed, and the cycle characteristics of the battery can be further improved.

[0064] On the other hand, if the heat treatment temperature is less than 500°C, there is a problem that the coating portion containing cobalt is almost absent, and if it is 680°C or higher, there is a problem that during the heating process, a large amount of Co that exists on the outside as the LiCoO2 phase penetrates into the positive electrode active material, resulting in a decrease in the cycle characteristics of the battery.

[0065] The heat treatment in step (B) can be carried out for 2 to 12 hours in terms of productivity and firing uniformity. Specifically, the heat treatment in step (B) can be carried out for 2 hours or more, 6 hours, 9 hours, or 12 hours or less.

[0066] positive electrode The present invention can also provide a positive electrode containing the positive electrode active material.

[0067] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector and including the positive electrode active material.

[0068] 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 μm 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.

[0069] The positive electrode active material layer may contain a conductive material and a binder in addition to the positive electrode active material.

[0070] Here, the positive electrode active material may be included in an amount of 80% by weight to 99% by weight, more specifically, 85% by weight to 98% by weight, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics may be exhibited when included in the above content range.

[0071] Here, the conductive material is used to give 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 that is 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 among these, one type alone or a mixture of two or more types can be used. The conductive material can be contained in an amount of 1% by weight to 30% by weight based on the total weight of the positive electrode active material layer.

[0072] 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 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0073] The positive electrode can be manufactured by a normal 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 dissolving 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. In addition, as another method, the positive electrode can also be manufactured by casting the composition for forming a positive electrode active material layer onto another support, and then peeling it off from the support to obtain a film, which is then laminated onto a positive electrode current collector.

[0074] 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 is 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 production of a positive electrode, taking into consideration the coating thickness of the slurry and the manufacturing yield.

[0075] Lithium secondary battery In addition, the present invention can provide an electrochemical device including the positive electrode. The electrochemical device can be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0076] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is as described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0077] Also, the lithium secondary battery may optionally 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.

[0078] 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.

[0079] 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 μm 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.

[0080] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0081] 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 β(0<β<2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; 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.

[0082] The negative electrode active material may be included in an amount of 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0083] The binder is a component that facilitates bonding between the conductive material, the active material, and the current collector, and can usually be added in an amount of 0.1% by weight to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0084] The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and examples of such conductive materials include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0085] The negative electrode active material layer can be produced by applying a composition for forming a negative electrode active material layer, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, onto a negative electrode current collector and drying the composition. Alternatively, the negative electrode active material layer can be produced by casting the composition for forming a negative electrode active material layer onto a separate support, peeling it off from the support, and laminating the resulting film onto the negative electrode current collector.

[0086] 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 electrolyte humidification ability 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 in a single layer or multilayer structure.

[0087] In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel 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.

[0088] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0089] 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), 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 ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may 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 a 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.

[0090] The lithium salt can be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt is preferably used in a concentration range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, and therefore can exhibit excellent electrolyte performance, and lithium ions can move effectively.

[0091] 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% by weight to 5% by weight based on the total weight of the electrolyte.

[0092] 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 life characteristics, 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).

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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 as a unit battery for a medium- to large-sized battery module including a large number of battery cells.

[0097] 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.

[0098] Manufacturing Example Manufacturing example 1: LiNi 0.88 Co 0.03 Mn 0.09 Preparation of lithium transition metal oxide in single particle form having a composition represented by O2 Ni 0.88 Co 0.03 Mn 0.09 It has a composition represented by (OH)2 and an average particle size (D 50The positive electrode active material precursor having a particle size of 3.5 μm was mixed with LiOH in a molar ratio of 1:1.05, and the mixture was subjected to primary firing at a temperature of 880° C. for 9 hours in an oxygen atmosphere to produce a pre-fired product. The pre-fired product was crushed and then subjected to secondary firing at a temperature of 780° C. for 9 hours in an oxygen atmosphere to produce LiNi 0.88 Co 0.03 Mn 0.09 A lithium transition metal oxide in the form of a single particle was prepared having the composition represented by O2.

[0099] Production example 2: LiNi 0.95 Co 0.03 Mn 0.02 Preparation of lithium transition metal oxide in single particle form having a composition represented by O2 Ni 0.95 Co 0.03 Mn 0.02 It has a composition represented by (OH)2 and an average particle size (D 50 The positive electrode active material precursor having a particle size of 3.5 μm was mixed with LiOH in a molar ratio of 1:1.05, and the mixture was 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-fired product was crushed and then subjected to secondary firing at a temperature of 750° C. for 9 hours in an oxygen atmosphere to produce LiNi 0.95 Co 0.03 Mn 0.02 A lithium transition metal oxide in the form of a single particle was prepared having the composition represented by O2.

[0100] Examples and Comparative Examples Example 1 A mixture was prepared by mixing the single particle lithium transition metal oxide prepared in Preparation Example 1 with powdered Co(OH)2 (manufactured by HUAYOU COBALT) in a molar ratio of 1:0.02. The mixture was heat-treated at 660°C for 5 hours in an oxygen atmosphere to prepare a single particle positive electrode active material.

[0101] Example 2 A positive electrode active material in the form of single particles was prepared in the same manner as in Example 1, except that the mixture was heat-treated at a temperature of 680°C.

[0102] Example 3 A mixture was prepared by mixing the single particle lithium transition metal oxide prepared in Preparation Example 2 with powdered Co(OH)2 (manufactured by HUAYOU COBALT) in a molar ratio of 1:0.02. The mixture was heat-treated at 660°C for 5 hours in an oxygen atmosphere to prepare a single particle positive electrode active material.

[0103] Comparative Example 1 The single particle lithium transition metal oxide produced in Production Example 1 was used as the positive electrode active material of Comparative Example 1.

[0104] Comparative Example 2 The single particle lithium transition metal oxide produced in Production Example 2 was used as the positive electrode active material of Comparative Example 2.

[0105] Comparative Example 3 A positive electrode active material was produced in the same manner as in Example 1, except that the mixture was heat-treated at a temperature of 700°C.

[0106] Comparative Example 4 A positive electrode active material was produced in the same manner as in Example 1, except that the mixture was heat-treated at a temperature of 720°C.

[0107] Comparative Example 5 A positive electrode active material was produced in the same manner as in Example 3, except that the mixture was heat-treated at a temperature of 700°C.

[0108] Experimental Example Experimental example 1: Positive electrode active material analysis -Raman spectroscopic analysis of the surface of the positive electrode active material Using a Raman spectrometer (manufactured by Nanophoton) (excitation laser wavelength: 532 nm), the surface Raman spectrum of each of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 5 was obtained and analyzed.

[0109] The Raman spectrum of the surface of each positive electrode active material is shown in FIG. 1 and FIG. 2. In the Raman spectrum, a peak corresponding to the A1g vibration mode of LiNiO2 (520 cm -1 ~580cm -1) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1 ~620cm -1 The intensity ratios of these are shown in Table 1 below.

[0110] For reference, no peak corresponding to LiCoO2 was observed in the Raman spectra of the surfaces of the positive electrode active materials of Comparative Examples 1 and 2 (see FIG. 2), and thus they are not shown in Table 1 below.

[0111] [Table 1]

[0112] Referring to Table 1, in the Raman spectra of the surfaces of the positive electrode active materials of Examples 1 to 3, the peak (500 cm) corresponding to the A1g vibration mode of LiNiO2 -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1 ~620cm -1 ) exceeds 1, whereas in Comparative Examples 3 to 5, it can be confirmed that the ratio is 1 or less.

[0113] -Analysis of the morphology and Co element of the positive electrode active material Using an electron probe microanalyzer (JXA-iHP200F, manufactured by JEOL) (accelerating voltage: 15 kV, probe current: 20 nA, dwell time: 20 ms), SEM images of the positive electrode active materials of Examples 1 and 2 and EPMA Co element mapping data of the cross-sectional samples of the positive electrode active materials of Example 1 and Comparative Example 2 were obtained, which are shown in FIG. 3. Meanwhile, the cross-sectional samples of the positive electrode active materials of Example 1 and Comparative Example 2 were prepared by performing Ar ion milling for 2 hours using an argon ion milling system (IM-5000, manufactured by HITACHI) (accelerating voltage: 6 kV).

[0114] FIG. 3A is an SEM image of the positive electrode active material of Example 1, FIG. 3B is an SEM image of the positive electrode active material of Example 2, FIG. 3C is EPMA Co element mapping data of a cross-sectional sample of the positive electrode active material of Example 1, and FIG. 3D is EPMA Co element mapping data of a cross-sectional sample of the positive electrode active material of Comparative Example 2.

[0115] 3, it can be seen that the positive electrode active materials of Examples 1 and 2 are positive electrode active materials in the form of single particles, and that the positive electrode active material of Example 1 has many discontinuous islands of LiCoO2 formed on the surface (light red and yellow-green areas) as well as a coating formed by the cobalt that diffuses during the cobalt coating (sky blue areas).In contrast, it can be seen that the positive electrode active material of Comparative Example 2 has a coating in which Co is relatively uniformly distributed.

[0116] -Crystallization of positive electrode active material particles Fig. 4(A) is an SEM image of one particle of the positive electrode active material of Example 1, and Fig. 4(B) is electron backscatter diffraction (EBSD) Eular map data of one particle of the positive electrode active material of Example 1. Since single crystal grains are measured as the same color in the Eular map, it can be seen from Fig. 4 that the positive electrode active material of Example 1 is a particle composed of two single crystal grains.

[0117] The EBSD analysis was performed using HITACHI's IM5000 (accelerating voltage: 6 kV), irradiating the positive electrode with an argon (Ar) ion beam, cutting it by an ion milling method to obtain a cross section of the positive electrode, and measuring and analyzing the cross section of the positive electrode using JEOL's JSM-7900F (accelerating voltage: 20 kV). AztecCrystal manufactured by OXFORD Instruments was used as the image processing-EBSD quantification analysis software.

[0118] For the EBSD analysis, the positive electrode was prepared by adding a positive electrode active material, a conductive material made of carbon black (DenkaBlack, manufactured by Denka Corporation) and a binder made of PVdF (Kureha, KF1300) in a weight ratio of 95:3:2 to a solvent made of N-methylpyrrolidone (NMP) (manufactured by Oi Chemical Industries, Ltd.) to prepare a composition for forming a positive electrode active material layer, and then coating the composition for forming a positive electrode active material layer on one side of an aluminum foil current collector having a thickness of 20 μm and drying the composition at a temperature of 135° C. for 3 hours.

[0119] - Analysis of the molar ratio of cobalt to nickel present on the surface The molar ratio of cobalt to nickel (hereinafter, Co / Ni molar ratio) present on the surface of each of the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 5 was measured by electron spectrochemical analysis (ESCA) using a Thermo Fisher K-alpha XPS device (Al-Kα X-ray source: 1486.6 eV), and the results are shown in the following Table 2. The surface analyzed by the ESCA analysis is the region from the outermost surface to 10 nm deep of the positive electrode active material.

[0120] [Table 2]

[0121] Referring to Table 2, it can be seen that the positive electrode active materials of Examples 1 to 3 have a Co / Ni molar ratio of 0.45 to 0.55, whereas the positive electrode active materials of Comparative Examples 3 to 5 have a Co / Ni molar ratio of less than 0.45.

[0122] Experimental example 2: Battery characteristic evaluation (Half-cell manufacturing) The positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 5, a carbon black (DenkaBlack, manufactured by Denka Corporation) conductive material, and a PVdF (KF1300, manufactured by Kureha Corporation) binder were added in a weight ratio of 95:3:2 to an N-methylpyrrolidone (NMP) (manufactured by Oi Chemical Industries, Ltd.) solvent to produce a composition for forming a positive electrode active material layer.

[0123] The positive electrode active material layer-forming composition was applied to one side of an aluminum foil current collector having a thickness of 20 μm, and dried at a temperature of 135° C. for 3 hours to form a positive electrode active material layer. After rolling, the positive electrode active material layer was rolled using a roll press method so that the porosity of the positive electrode active material layer became 20% by volume, thereby manufacturing a positive electrode.

[0124] Along with the positive electrode, a half-cell was fabricated using lithium metal as the negative electrode.

[0125] (Evaluation of battery cycle characteristics) The half cells prepared above were charged at 25° C. at a constant current (CC) of 0.2 C up to 4.25 V, then charged at a constant voltage (CV) of 4.25 V until the charging current reached 0.05 mAh (cut-off current), and then left for 20 minutes, after which they were discharged at a constant current of 0.2 C down to 2.5 V.

[0126] Next, the cell was transferred to a chamber at 45°C, charged to 4.25V at a constant current of 0.33C, then charged at a constant voltage (CV) of 4.25V, charged until the charge current reached 0.05mAh (cut-off current), and then discharged to 2.5V at a constant current of 0.33C, with 30 cycles of charge and discharge being performed. Here, the percentage of the discharge capacity of the 30th cycle relative to the discharge capacity of the first cycle was taken as the capacity retention rate, and is shown in Table 3 below. In addition, the percentage of the DCIR value of the 30th cycle relative to the DCIR value of the first cycle was taken as the resistance increase rate, and is shown in Table 3 below. For reference, the DCIR value of the nth cycle was calculated by dividing the voltage difference between the fully charged state and the voltage 10 seconds after the start of discharge, obtained by discharging to 2.5V at a constant current of 0.33C in the nth cycle, by the current.

[0127] [Table 3]

[0128] Referring to Table 3, it can be seen that the batteries including the positive electrode active materials of Examples 1 to 3 have superior cycle characteristics compared to the batteries including the positive electrode active materials of Comparative Examples. As a result, the batteries include LiCoO2 in the form of single particles and discontinuously formed islands on the surface, and the peak (500 cm) corresponding to the A1g vibration mode of LiNiO2 is observed in the Raman spectrum of the surface. -1 ~600cm -1 ) for the intensity of the peak corresponding to the A1g vibration mode of LiCoO2 (550 cm -1 ~620cm -1 In the case of a battery including the positive electrode active material according to the present invention, in which the intensity ratio of the positive electrode active material particles is greater than 1, the ratio of the NiO reduced layer present on the surface of the positive electrode active material particles is low, and it can be confirmed that the battery has excellent cycle characteristics.

Claims

1. a lithium transition metal oxide in single particle form; a coating portion including cobalt formed on the lithium transition metal oxide in the form of a single particle; Island-like LiCoO formed discontinuously on the surface ２ and In the Raman spectrum of the surface, LiNiO ２ The peak corresponding to the A1g vibration mode (500 cm －１ ~600cm －１ ) versus LiCoO ２ The peak corresponding to the A1g vibration mode (550 cm －１ ~620cm －１ ) is greater than 1.

2. The positive electrode active material in the form of a single particle has an average particle size (D ５０ 2. The positive electrode active material in a single particle form according to claim 1, wherein the particle diameter is 0.1 μm to 10 μm.

3. The positive electrode active material according to claim 1 , wherein the positive electrode active material in the form of a single particle is in the form of an aggregation of 50 or less primary particles each having 10 or less single crystal grains.

4. The positive electrode active material according to claim 1 , wherein the lithium transition metal oxide in the form of single particles is a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co) and manganese (Mn).

5. The positive electrode active material according to claim 1 , wherein the lithium transition metal oxide in the form of single particles has a composition represented by the following Chemical Formula 1: [Chemical formula 1] Li ａ Ni ｂ Co ｃ Mn ｄ M １ ｅ O ２ In the above Chemical Formula 1, M １ is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S; 0.9≦a≦1.1, 0.8≦b<1.0, 0<c<0.2, 0<d<0.2, 0≦e≦0.1, and b+c+d+e=1.

6. The positive electrode active material according to claim 1 , wherein the coating portion is a region from a surface of the positive electrode active material to a center of the positive electrode active material, the region being 5 nm to 100 nm in thickness.

7. 2. The positive electrode active material in the form of a single particle according to claim 1, wherein a molar ratio of cobalt to nickel present on the surface is 0.45 to 0.

9.

8. (A) mixing a lithium transition metal oxide in single particle form and a cobalt source material to prepare a mixture; (B) heat-treating the mixture at a temperature of 500° C. or higher and lower than 680° C.

9. 9. The method of claim 8, wherein in step (A), the lithium transition metal oxide in the form of single particles has a cation mixing of 5% or less.

10. 9. The method for producing a positive electrode active material in a single particle form according to claim 8, wherein in step (A), the single particle lithium transition metal oxide contains lithium by-products in an amount of 20,000 ppm or less.

11. 9. The method of claim 8, wherein in step (A), a molar ratio of the lithium transition metal oxide in the form of single particles to the cobalt raw material is 1:0.0001 to 0.

1.

12. The method for producing a positive electrode active material in a single particle form according to claim 8 , wherein in the step (A), the mixing is a dry mixing.

13. The method for producing a positive electrode active material in a single particle form according to claim 8 , wherein the heat treatment in step (B) is performed in an oxygen atmosphere.

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