Positive electrode active material, and positive electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode active material, and a positive electrode and a lithium secondary battery comprising same, the positive electrode active material comprising a lithium transition metal oxide and a coating portion including a metal oxide located on the surface of the lithium transition metal oxide, being in the form of a single particle, and capable of improving initial capacity and resistance performance by having an average particle diameter and an average particle diameter ratio satisfying specific ranges.

Description

Cathode active material, cathode and lithium secondary battery containing same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0019562, filed February 8, 2024, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery.

[0005]

[0006] As technological developments and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, with their high energy density and voltage, long cycle life, and low self-discharge rate, are becoming widely used.

[0007] Recently, with the advancement of technology such as electric vehicles, the demand for high-capacity secondary batteries is increasing, and accordingly, research on cathodes using high-nickel (High Ni) cathode active materials with excellent capacity characteristics is being actively conducted.

[0008] Since the high-nickel cathode active material uses a co-precipitation method to manufacture it, the manufactured high-nickel cathode active material has a secondary particle form in which primary particles are aggregated. However, the active material in the form of secondary particles has the disadvantage that microcracks occur in the secondary particles during long-term charge / discharge processes, causing side reactions. In addition, when the electrode density is increased to improve energy density, the secondary particles cause structural collapse, which reduces the active material and electrolyte, resulting in a decrease in energy density and a decrease in life characteristics.

[0009] To address the issues inherent in high-nickel cathode active materials in the form of secondary particles, single-particle nickel-based cathode active materials have recently been developed. Single-particle nickel-based cathode active materials exhibit minimal particle breakage even when increasing electrode density for high energy density. They also enable high electrode rolling densities, offering advantages in terms of volumetric capacity. Furthermore, their low gas generation rate enhances cell stability.

[0010] However, since the positive electrode active material in the form of a single particle has a small specific surface area, there is little interface that can react with the electrolyte, and since the path through which lithium ions must come out from inside becomes long, there is a problem of reduced initial discharge capacity and increased resistance.

[0011] Therefore, in order to improve these problems, there is a need to develop a single-particle cathode active material with excellent single-particle density and improved electrochemical performance.

[0012]

[0013] The problem to be solved in the present invention is to provide a cathode active material in the form of a single particle, which can improve electrochemical performance by controlling the average particle size ratio and / or the degree of single particle formation through coating.

[0014] In addition, the problem to be solved in the present invention is to provide a positive electrode with improved electrochemical performance by including the positive electrode active material as described above.

[0015] In addition, the problem to be solved in the present invention is to provide a lithium secondary battery having improved electrochemical performance, such as initial capacity and resistance performance, including the positive electrode.

[0016]

[0017] (1) The present invention comprises a lithium transition metal oxide; and a coating formed on the surface of the lithium transition metal oxide, and is in the form of a single particle and has an average particle diameter (D50 ) is 3 μm or more and 10 μm or less, and an average particle size ratio calculated from the following equation 1 is 0.75 or more.

[0018] [Formula 1]

[0019] Average particle size ratio = D SEM / D 50

[0020] In the above equation 1, D SEM The area of ​​each particle is calculated through the number of pixels corresponding to each of n particles (at least 10 or more) present in the SEM image, and the particle diameter and volume of each particle present in the SEM image are calculated using the radius value of a circle having the same area as the area of ​​each particle, and the particle diameter at the point where the cumulative volume distribution according to particle diameter becomes 50%, and D 50 is the particle diameter at the point where the volume cumulative distribution according to particle size measured through laser diffraction particle size analysis reaches 50%.

[0021] (2) The present invention provides a positive electrode active material in the above (1), wherein the lithium transition metal oxide contains nickel at 80 mol% or more based on the total moles of transition metals.

[0022] (3) The present invention provides a positive electrode active material in (1) or (2) above, wherein the lithium transition metal oxide has a composition represented by the following chemical formula 1.

[0023] [Chemical Formula 1]

[0024] Li a Ni b Co c M 1 d M 2 e O2

[0025] In the above chemical formula 1, M 1 is Mn, Al or a combination thereof,

[0026] M 2is at least one selected from the group consisting of Al, W, Co, B, Zr, Y, Ce, Hf, La, Ba, F, P, S, Nb, Ta, Sc, Cr, V, Cu, Sr, Ti, Mg, Mo, Sn, Fe, Zn and Si,

[0027] 0.9≤a≤1.3, 0.8≤b<1, 0 <c<0.3, 0<d<0.3, 0≤e≤0.2, b+c+d+e=1이다.

[0028] (4) The present invention provides a positive electrode active material in any one of the above (1) to (3), wherein the coating part includes at least one metal element selected from the group consisting of Ni, Co, Mn, Al, B, Ti, Ta, W, and Nb.

[0029] (5) The present invention is a positive electrode active material in any one of the above (1) to (4), wherein the single particle form is a single particle form or a pseudo-single particle form formed by agglomeration of two or more and 30 or less primary particles.

[0030] (6) In any one of (1) to (5), the positive electrode active material has a particle size of 7.5 μm as calculated from the following equation 2. 3 The following positive electrode active material is provided.

[0031] [Formula 2]

[0032] Single particle magnetization (μm) 3 ) =

[0033] In the above equation 2, radius(grain) is the individual radius (μm) of grains whose cross-sectional size of a single particle is 0.1 μm or more as measured from backscatter electron diffraction analysis (EBSD) of a cross-sectional SEM image of a positive electrode manufactured with a single particle positive active material, and n is the number of grains.

[0034] (7) In the present invention, in the above (6), the single particle size is 5.0 μm. 3 Above, 7.5 μm3 The following positive electrode active material is provided.

[0035] (8) The present invention provides a positive electrode active material having an average particle size ratio of 0.75 or more and 1.0 or less in any one of the above (1) to (7).

[0036] (9) The present invention provides a positive electrode comprising any one of the positive electrode active materials of (1) to (8).

[0037] (10) The present invention provides a lithium secondary battery comprising the positive electrode of the above (9); a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

[0038]

[0039] The positive electrode active material of the present invention is a positive electrode active material in the form of a single particle, and includes a coating portion containing a metal oxide, and has an average particle size ratio (D SEM / D 50 ) By satisfying this specific range, it can exhibit excellent capacity and output characteristics while having low initial resistance.

[0040]

[0041] Figure 1 is a SEM image of the positive electrode active material of Example 1 of the present invention.

[0042] Figure 2 is a SEM image of the positive electrode active material of Example 2 of the present invention.

[0043] Figure 3 is an SEM image of the positive electrode active material of Example 3 of the present invention.

[0044] Figure 4 is a SEM image of the positive electrode active material of Example 4 of the present invention.

[0045] Figure 5 is an SEM image of the positive electrode active material of Comparative Example 1 of the present invention.

[0046] Figure 6 is an electron backscatter diffraction (EBSD) Euler map of one positive electrode active material particle of Example 1 of the present invention.

[0047] Figure 7 is an electron backscatter diffraction (EBSD) Euler map of one positive electrode active material particle of Example 2 of the present invention.

[0048] Figure 8 is an electron backscatter diffraction (EBSD) Euler map of one positive electrode active material particle of Example 3 of the present invention.

[0049] Figure 9 is an electron backscatter diffraction (EBSD) Euler map of one positive electrode active material particle of Example 4 of the present invention.

[0050] Figure 10 is an electron backscatter diffraction (EBSD) Euler map of one positive electrode active material particle of Comparative Example 1 of the present invention.

[0051]

[0052] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best possible manner.

[0053]

[0054] In the present invention, the term 'single particle form' is a concept that contrasts with a spherical secondary particle form of a cathode active material formed by agglomeration of tens to hundreds of primary particles manufactured by a conventional method, and includes a form formed by agglomeration of 2 or more and 30 or less primary particles. Specifically, the single particle form of the cathode active material in the present invention may be a single particle form composed of 1 primary particle, or may be a pseudo-single particle form formed by agglomeration of 2 or more and 30 or less primary particles. In this case, 'primary particle' means the smallest particle unit recognized when observing the cathode active material through a scanning electron microscope.

[0055] In the present invention, the term 'average particle diameter (D 50)' means the particle size at the 50% point of the volume cumulative distribution according to particle size. The above average particle size is calculated 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 from Microtrac), and measuring the difference in diffraction pattern according to particle size when the particles pass through the laser beam to calculate the particle size distribution, and calculating the particle diameter at the point where it becomes 50% of the volume cumulative distribution according to particle size in the measuring device, thereby obtaining D 50 can be measured.

[0056] In the present invention, the term 'D SEM (Average particle diameter measured using SEM image)' can be measured by calculating the area of ​​each particle through the number of pixels corresponding to each of n particles (at least 10 or more) existing in a specific magnification (e.g., 2K) image among SEM images, calculating the particle diameter and volume of each particle existing in the SEM image using the radius value of a circle having the same area as the area of ​​each particle, and calculating the particle diameter corresponding to 50% of the accumulated volume.

[0057]

[0058] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0059]

[0060] positive electrode active material

[0061] The present invention comprises a lithium transition metal oxide; and a coating formed on the surface of the lithium transition metal oxide, and is in the form of a single particle and has an average particle diameter (D 50 ) is 3 μm or more and 10 μm or less, and an average particle size ratio calculated from the following equation 1 is 0.75 or more.

[0062] [Formula 1]

[0063] Average particle size ratio = D SEM / D 50

[0064] In the above equation 1, D SEM The area of ​​each particle is calculated through the number of pixels corresponding to each of n particles (at least 10 or more) present in the SEM image, and the particle diameter and volume of each particle present in the SEM image are calculated using the radius value of a circle having the same area as the area of ​​each particle, and the particle diameter at the point where the cumulative volume distribution according to particle diameter becomes 50%, and D 50 is the particle diameter at the point where the volume cumulative distribution according to particle size measured through laser diffraction particle size analysis reaches 50%.

[0065] The lithium transition metal oxide may contain nickel in an amount of 80 mol% or more, and specifically, may contain nickel in an amount of 85 mol% or more, based on the total moles of transition metals. That is, the lithium transition metal oxide may be a high-nickel (High Ni) lithium transition metal oxide. In this case, the energy density of a lithium secondary battery including the lithium transition metal oxide may be further improved.

[0066] The above lithium transition metal oxide may have a composition represented by the following chemical formula 1.

[0067] [Chemical Formula 1]

[0068] Li a Ni b Co c M 1 d M 2 e O2

[0069] In the above chemical formula 1, M 1 is Mn, Al or a combination thereof,

[0070] M 2 is at least one selected from the group consisting of Al, W, Co, B, Zr, Y, Ce, Hf, La, Ba, F, P, S, Nb, Ta, Sc, Cr, V, Cu, Sr, Ti, Mg, Mo, Sn, Fe, Zn and Si,

[0071] 0.9≤a≤1.3, 0.8≤b<1, 0 <c<0.3, 0<d<0.3, 0≤e≤0.2, b+c+d+e=1이다.

[0072] The above a refers to the molar ratio of lithium in the lithium transition metal oxide, and may be 0.9 or more, 1.0 or more, and may also be 1.3 or less, 1.2 or less, or 1.1 or less.

[0073] The above b refers to the molar ratio of nickel among the total transition metals, and may be 0.8 or more, 0.81 or more, 0.82 or more, 0.83 or more, 0.84 or more, 0.85 or more, and may also be 0.95 or less, 0.93 or less, 0.91 or less, or 0.89 or less.

[0074] The above c refers to the molar ratio of cobalt among the total transition metals, and may be greater than 0, 0.02 or more, 0.04 or more, 0.06 or more, 0.08 or more, or 0.1 or more, and may also be less than 0.3, 0.28 or less, 0.26 or less, 0.24 or less, 0.22 or less, 0.2 or less, 0.15 or less, or 0.13 or less.

[0075] The above d is a metallic element M among all transition metals. 1 It means the molar ratio, and can be more than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, and can also be less than 0.3, 0.25 or less, 0.2 or less, 0.15 or less, 0.1 or less, 0.05 or less.

[0076] M 2 may be a doping element, and the above e is M among the entire transition metals. 2 It means the molar ratio, and can be 0 or more, 0.02 or more, 0.04 or more, 0.06 or more, 0.08 or more, and can also be 0.2 or less, 0.18 or less, 0.16 or less, 0.14 or less, 0.12 or less.

[0077] The above coating portion may include one or more metal elements selected from the group consisting of Ni, Co, Mn, Al, B, Ti, Ta, W, and Nb.

[0078] The metal element included in the above coating may be included in the form of a metal oxide, and specifically, M x O y , M x (OH) y It can be in the form of, more specifically, M x O y may be in the form (where M is a metal element). Here, M is a metal element, and the values ​​of x and y can be determined according to the oxidation number of the metal element.

[0079] The above coating portion is a portion formed when the coating raw material diffuses from the surface of the lithium transition metal oxide toward the center when mixing the lithium transition metal oxide and the coating raw material and then performing a heat treatment. Therefore, the composition of the coating portion may be similar to the composition of the lithium transition metal oxide included in the positive electrode active material of the present invention, but the proportion of the metal element included in the coating raw material in the total metal excluding lithium is higher than that of the lithium transition metal oxide.

[0080] When the coating portion is formed on the surface of the lithium transition metal oxide, it may be formed on a part or all of the outer surface, and may be formed at 10% or more and 100% or less (area %) based on the total area of ​​the surface. Specifically, the coating portion may be formed on a part of the surface of the lithium transition metal oxide, and may be formed at 20% or more, 30% or more, 40% or more, 50% or more, and further may be formed at 95% or less, 90% or less, 85% or less, or 80% or less based on the total area of ​​the surface.

[0081] The positive electrode active material of the present invention is in the form of a single particle, and the single particle form may be in the form of a single particle or in the form of a pseudo-single particle formed by agglomeration of two or more and 30 or less primary particles.

[0082] The average particle diameter of the positive electrode active material of the present invention may be specifically 3.1 μm or more, 3.2 μm or more, 3.3 μm or more, 3.4 μm or more, 3.5 μm or more, 3.6 μm or more, 3.7 μm or more, 3.8 μm or more, 3.9 μm or more, and may also be 9 μm or less, 8 μm or less, 7 μm or less, 6 μm or less, 5 μm or less, 4.5 μm or less, 4.4 μm or less, 4.3 μm or less, 4.2 μm or less.

[0083] When the average particle size satisfies the above range, it can have a large specific surface area, resulting in low initial resistance and high capacity. If the average particle size is smaller than the above range, gelation of the slurry may occur during electrode manufacturing due to particle agglomeration, and if the average particle size is larger than the above range, the migration path of lithium ions coming out of the particles becomes longer, resulting in problems such as increased initial resistance and decreased capacity.

[0084] The positive electrode active material of the present invention has an average particle size ratio calculated from the above formula 1 of 0.75 or more.

[0085] The above average particle size ratio is D, which is the average particle size of the positive electrode active material measured through laser diffraction particle size analysis. 50 The average particle diameter of the positive electrode active material analyzed through SEM images is D SEM is the ratio of the average particle diameter D measured by laser diffraction analysis when comparing particles composed of several small primary particles with single particles having the same or similar particle size range. 50 The values ​​have similar values, but D SEMSince the diameter of a single particle is calculated, in the case of a particle composed of multiple primary particles, the primary particles are recognized as individual particles and D SEM This is measured smaller, i.e. D SEM The value of D is the actual 50 In similar cases, it can be expected that the positive electrode active material particles have a form close to a single particle rather than a particle composed of multiple primary particles, and through this, D SEM / D 50 It can be confirmed that the closer the average particle size ratio value is to 1, the higher the degree of single particle formation in terms of shape. Therefore, the closer the average particle size ratio is to 1, the more the positive electrode active material has a shape close to a single particle.

[0086] The average particle size ratio of the positive electrode active material of the present invention may be specifically 0.75 or more, 0.76 or more, 0.77 or more, or 0.78 or more. In addition, the average particle size ratio may be 1.0 or less, and specifically 0.98 or less, 0.96 or less, 0.94 or less, 0.92 or less, 0.90 or less, 0.88 or less, 0.86 or less, 0.84 or less, or 0.82 or less. The positive electrode active material of the present invention may have a single particle form with a low initial resistance and excellent capacity characteristics and output characteristics when the average particle size ratio satisfies the above range, and when the average particle size ratio is smaller than the above range, the initial resistance may be high and the capacity and output characteristics may deteriorate.

[0087] In addition, the cathode active material of the present invention has a single particle size of 7.5 μm as calculated from the following equation 2. 3 It could be as follows:

[0088] [Formula 2]

[0089] Single particle magnetization (μm) 3 ) =

[0090] In the above equation 2, radius(grain) is the individual radius (μm) of grains whose cross-sectional size of single particles is 0.1 μm or more, as measured from backscatter electron diffraction analysis (EBSD) of a cross-sectional SEM image of a positive electrode manufactured with a single-particle positive electrode active material, and n is the number of grains (unitless number).

[0091] The radius of the above grain is calculated by calculating the diameter of a circle having the same area as the area formed by the hexagonal points with the same crystal orientation contained within the grain as confirmed by EBSD measurement. Therefore, the higher the degree of single particle size calculated by the above formula, the larger the grain radius obtained as above, meaning that the portion with the same crystal orientation recognized as a single grain is large.

[0092] The above single particle magnetization is specifically 7.4 μm 3 Below, 7.3 μm 3 Below, 7.2 μm 3 Below, 7.1 μm 3 It may be less than or equal to 5.0 μm. In addition, the single particle magnetization is 3 It may be more than 5.1 μm, specifically 3 Above, 5.2 μm 3 Above, 5.3 μm 3 Above, 5.4 μm 3 Above, 5.5 μm 3 Above, 5.6 μm 3 Above, 5.7 μm 3 Above, 5.8 μm 3 Above, 5.9 μm 3 Above, 6.0 μm 3 It may be ideal. The cathode active material of the present invention has a single particle size distribution that satisfies the above range, and thus has a low initial resistance and excellent capacity and output characteristics while being in the form of a single particle.

[0093]

[0094] Method for manufacturing positive electrode active material

[0095] The positive electrode active material of the present invention may be manufactured through the following manufacturing method.

[0096] A method for manufacturing a cathode active material according to one embodiment of the present invention comprises the steps of: mixing a transition metal precursor with a lithium raw material, and then performing a first firing to obtain a first fired product (S10); crushing the first fired product, and then performing a second firing to obtain a second fired product (S20); and crushing the second fired product, mixing it with a coating raw material, and then performing a heat treatment to form a coating portion (S30).

[0097] (S10) Step

[0098] The above transition metal precursor may be purchased and used as a commercially available precursor such as nickel-cobalt-manganese hydroxide, or may be manufactured according to a precursor manufacturing method known in the art.

[0099] The above transition metal precursor can be manufactured, for example, by introducing a transition metal aqueous solution and an ammonium cation complex forming and basic compound into a reactor and performing a co-precipitation reaction while stirring.

[0100] The above transition metal aqueous solution can be prepared by dissolving a transition metal-containing raw material in a solvent such as water, and for example, it can be prepared by dissolving a nickel-containing raw material or a cobalt-containing raw material in water. In addition, if necessary, the above transition metal aqueous solution can be prepared by dissolving M 1 Metal-containing raw materials and / or M 2 It may further include metal-containing raw materials.

[0101] Meanwhile, the above transition metal-containing raw material may be an acetate, carbonate, nitrate, halide, sulfide or oxide of the transition metal.

[0102] Specifically, the nickel-containing raw material may be, for example, NiO, NiCO3ㆍ2Ni(OH)2ㆍ4H2O, NiC2O2ㆍ2H2O, Ni(NO3)2ㆍ6H2O, NiSO4, NiSO4ㆍ6H2O, nickel halide, or a combination thereof.

[0103] The above cobalt-containing raw material may be, for example, CoSO4, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O, CoSO4ㆍ7H2O or a combination thereof.

[0104] Above M 1 The metal-containing raw material may be a manganese-containing raw material and / or an aluminum-containing raw material. The manganese-containing raw material may be, for example, Mn2O3, MnO2, Mn3O. 4, It may be MnCO3, Mn(NO3)2, MnSO4ㆍH2O, manganese acetate, manganese halide, or a combination thereof, and the aluminum-containing raw material may be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3, aluminum halide, or a combination thereof. However, in the case of Al, it may be added together with the lithium raw material in the calcination step described later, instead of being added to the transition metal aqueous solution.

[0105] M 2 Contains raw materials M 2 It may be an acetate, carbonate, nitrate, sulfate, halide, sulfide or oxide of the metal.

[0106] The input amount of each of the above transition metal-containing raw materials can be determined by considering the molar ratio of the transition metal in the positive electrode active material to be ultimately produced.

[0107] Meanwhile, the ammonium cation complex forming agent may include at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. At this time, the solvent may be water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water.

[0108] The basic compound may be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. At this time, the solvent may be water, or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water.

[0109] As described above, the transition metal aqueous solution, ammonium cation complex forming agent, and basic compound are added in amounts such that the pH of the reaction solution becomes within the desired range.

[0110] Once precursor particles are formed as described above, the particles are separated from the reaction solution to obtain a transition metal precursor. For example, the reaction solution can be filtered to separate the transition metal precursor, and then the separated transition metal precursor can be washed and dried to obtain the transition metal precursor. Processes such as grinding and / or classification may also be performed as needed.

[0111] The transition metal precursor obtained as described above may have a composition represented by the following chemical formula 2.

[0112] [Chemical Formula 2]

[0113] Ni b Co c M 1 d M 2 e (OH)2

[0114] In the above chemical formula 2, b, c, d, e and M 1 , M 2 The description regarding may be within the range described above with respect to chemical formula 1.

[0115]

[0116] Next, the transition metal precursor and lithium raw material are mixed and then subjected to a first firing to form a first fired product. At this time, aluminum-containing raw material and / or M may be added as needed. 2 Raw materials containing metal elements can be mixed and fired together.

[0117] The above lithium raw material may be, for example, a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide, and more specific examples may include Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, Li3C6H5O7 or a mixture thereof.

[0118] Meanwhile, the lithium raw material may be mixed so that the molar ratio of lithium to the total molar ratio of transition metals included in the transition metal precursor is 0.9 or more and 1.1 or less, preferably 0.95 or more and 1.07 or less, and more preferably 1 or more and 1.05 or less. When the molar ratio of the transition metal precursor and the lithium raw material satisfies the above range, the layered crystal structure of the positive electrode active material is well developed, so that a positive electrode material with excellent electrochemical performance can be manufactured.

[0119] The above first firing temperature can be performed at a temperature of 700°C or higher and 1000°C or lower. Specifically, it can be 750°C or higher, 770°C or higher, 790°C or higher, 800°C or higher, 820°C or higher, 850°C or higher, 880°C or higher, and 990°C or lower, 980°C or lower, 970°C or lower, 960°C or lower, 950°C or lower, 940°C or lower, 930°C or lower, 920°C or lower.

[0120] In addition, the first firing time may be 5 hours or more and 35 hours or less, specifically, 7 hours or more, 9 hours or more, 11 hours or more, 13 hours or more, 15 hours or more, and also 30 hours or less, 28 hours or less, 25 hours or less, 22 hours or less, 20 hours or less.

[0121] Additionally, the above-mentioned primary firing can be performed in an air atmosphere or an oxygen atmosphere. In the present invention, the term "oxygen atmosphere" refers to an atmosphere containing oxygen sufficient for firing, including an air atmosphere. In particular, it refers to an atmosphere in which the oxygen partial pressure is higher than that of an air atmosphere.

[0122] When the first sintering is performed under the above conditions, a lithium transition metal oxide having excellent electrochemical properties can be formed in the form of a single particle. If the first sintering temperature is too low, the primary particles may not grow sufficiently, resulting in the production of a cathode active material in the form of a secondary particle rather than a single particle. In addition, if the temperature is too high, an excessive amount of electrically inactive rock-salt phase may be formed during the sintering process, resulting in a structurally unstable sintered product with low crystallinity, which may result in deterioration of the electrochemical properties.

[0123]

[0124] (S20) Step

[0125] When a primary fired product is formed through the primary firing as described above, a first crushing step of crushing the primary fired product is performed.

[0126] The above first crushing step is intended to crush the agglomerated positive electrode active materials and to appropriately control the particle size and shape of the particles in the positive electrode material, and can be performed using a crushing device well known in the art, such as a jet-mill crusher or a ball-mill crusher.

[0127] By appropriately controlling the grinding conditions such as grinding pressure, input speed, etc. in the first grinding step, the particle size distribution and primary particle shape of the lithium transition metal oxide particles can be controlled.

[0128] For example, the first crushing step may be performed under crushing pressure conditions of 1.5 bar or more and 2.5 bar or less, specifically, 1.6 bar or more and 1.7 bar or more, and also 2.4 bar or less, 2.3 bar or less, 2.2 bar or less, 2.1 bar or less, and 2.0 bar or less. When the crushing pressure of the first crushing step satisfies the above range, it is easy to manufacture a cathode material having the desired average particle size ratio of primary particles.

[0129] In addition, the first crushing step can be performed at an input speed of 600 rpm or more and 1200 rpm or less, and specifically, can be performed at an input speed of 650 rpm or more, 700 rpm or more, 750 rpm or more, 800 rpm or more, and 950 rpm or more, and can also be performed at an input speed of 1150 rpm or less, 1100 rpm or less, 1050 rpm or less, 1000 rpm or less, and 950 rpm or less. When the input speed of the first crushing step satisfies the above range, the D of the positive electrode active material 50 And / or it is easy to control the average particle diameter of the primary particles within a desired range.

[0130]

[0131] Next, the primary fired product crushed through the first crushing step is subjected to a secondary firing.

[0132] The above secondary firing temperature can be performed at a temperature of 600°C or higher and 1000°C or lower. Specifically, it can be 650°C or higher, 700°C or higher, 750°C or higher, 770°C or higher, 790°C or higher, 800°C or higher, and 990°C or lower, 980°C or lower, 970°C or lower, 960°C or lower, 950°C or lower, or 900°C or lower.

[0133] In addition, the secondary firing time may be 5 hours or more and 35 hours or less, specifically, 7 hours or more, 9 hours or more, 11 hours or more, 13 hours or more, 15 hours or more, 17 hours or more, 19 hours or more, and also 33 hours or less, 30 hours or less, 27 hours or less, 25 hours or less, 23 hours or less.

[0134] Additionally, the secondary firing can be performed in an air atmosphere or an oxygen atmosphere.

[0135] When secondary firing is performed under the above conditions, a positive electrode active material having excellent electrochemical properties and the desired primary particle size distribution can be easily formed.

[0136]

[0137] (S30) Step

[0138] Next, a second crushing step is performed to crush the secondary fired product obtained through the above secondary firing.

[0139] The second crushing step may be performed under crushing pressure conditions of, for example, 1.5 bar or more, 2.5 bar or less, specifically, 1.6 bar or more, 1.7 bar or more, and also 2.4 bar or less, 2.3 bar or less, 2.2 bar or less, 2.1 bar or less, or 2.0 bar or less.

[0140] In addition, the second crushing step can be performed at an input speed of 600 rpm or more and 1200 rpm or less, and specifically, can be performed at an input speed of 650 rpm or more, 700 rpm or more, 750 rpm or more, 800 rpm or more, and 950 rpm or more, and can also be performed at an input speed of 1150 rpm or less, 1100 rpm or less, 1050 rpm or less, 1000 rpm or less, and 950 rpm or less. When the input speed of the second crushing step satisfies the above range, the D of the positive electrode active material 50 And / or it is easy to control the average particle diameter of the primary particles within a desired range.

[0141]

[0142] Next, the secondary sintered product pulverized through the second pulverization step is mixed with the coating raw material and then heat-treated to form a coating portion.

[0143] The above coating raw material may be an acetate, carbonate, nitrate, sulfate, halide, sulfide or oxide containing a coating element.

[0144] The above coating element may be one or more metal elements selected from the group consisting of Ni, Co, Mn, Al, B, Ti, Ta, W, and Nb.

[0145] Meanwhile, the above mixing may be performed as a solid mixing or a liquid mixing, and the heat treatment may be performed at an appropriate temperature depending on the type of element to be coated. For example, the heat treatment may be performed at a temperature of 400°C or higher and 1000°C or lower. Specifically, the heat treatment temperature may be 450°C or higher, 500°C or higher, 550°C or higher, 600°C or higher, 620°C or higher, 640°C or higher, or 660°C or higher, and further, 950°C or lower, 900°C or lower, 880°C or lower, 860°C or lower, 840°C or lower, or 820°C or lower.

[0146] The above heat treatment may be performed for 5 hours or more and 25 hours or less in order to increase the crystallinity of the coating portion, and more specifically, may be performed for 7 hours or more, 9 hours or more, 11 hours or more, or 13 hours or more, and may also be performed for 23 hours or less, 21 hours or less, 19 hours or less, or 17 hours or less.

[0147]

[0148] anode

[0149] The present invention provides a positive electrode comprising the positive electrode active material.

[0150] According to one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material.

[0151] According to one embodiment of the present invention, the positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to by the positive electrode active material layer and does not react within the voltage range of the battery. The positive electrode current collector may be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0152] According to one embodiment of the present invention, the positive electrode active material layer may optionally include a conductive material and a binder, together with the positive electrode active material, as needed. In this case, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics may be exhibited within this range.

[0153] According to one embodiment of the present invention, the conductive material is used to provide conductivity to the electrode, and in the battery to be formed, any conductive material that does not cause a chemical change and has electronic conductivity can be used without particular limitation. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0154] According to one embodiment of the present invention, the binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylalcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and polymers in which hydrogens of these are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above binder may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0155] According to one embodiment of the present invention, the positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the positive electrode can be manufactured by 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, a conductive material, and a dispersant in a solvent as needed, onto a positive electrode current collector, followed by drying and rolling, or by casting the composition for forming a positive electrode active material layer onto a separate support, and then laminating the film obtained by peeling it from the support onto a positive electrode current collector.

[0156] According to one embodiment of the present invention, the solvent may be a solvent generally used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one of these may be used alone or as a mixture of two or more. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0157]

[0158] lithium secondary battery

[0159] The present invention provides a lithium secondary battery including the positive electrode.

[0160] According to one embodiment of the present invention, the lithium secondary battery may include the positive electrode; the negative electrode; a separator interposed between the positive electrode and the negative electrode, and an electrolyte. In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0161] According to one embodiment of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0162] According to one embodiment of the present invention, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0163] According to one embodiment of the present invention, the negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material.

[0164] According to one embodiment of the present invention, a compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β(0<β<2), SnO2, 바나듐 산화물, 리튬 바나듐 산화물과 같이 리튬을 도프 및 탈도프할 수 있는 금속산화물; 또는 Si-C 복합체 또는 Sn-C 복합체과 같이 상기 금속질 화합물과 탄소질 재료를 포함하는 복합물 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다. 또한, 상기 음극활물질로서 금속 리튬 박막이 사용될 수도 있다. 또한, 탄소재료는 저결정성 탄소 및 고결정성 탄소 등이 모두 사용될 수 있다. 저결정성 탄소로는 연화탄소 (soft carbon) 및 경화탄소 (hard carbon)가 대표적이며, 고결정성 탄소로는 무정형, 판상, 인편상, 구형 또는 섬유형의 천연 흑연 또는 인조 흑연, 키시 흑연 (Kish graphite), 열분해 탄소 (pyrolytic carbon), 액정 피치계 탄소섬유 (mesophase pitch based carbonfiber), 탄소 미소구체 (meso-carbon microbeads), 액정피치 (Mesophase pitches) 및 석유와 석탄계 코크스 (petroleum or coal tar pitch derived cokes) 등의 고온 소성탄소가 대표적이다. 상기 음극 활물질은 음극 활물질층의 전체 중량을 기준으로 80 중량% 내지 99 중량%로 포함될 수 있다.

[0165] According to one embodiment of the present invention, the binder of the negative electrode active material layer is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0166] According to one embodiment of the present invention, the conductive material of the negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0167] According to one embodiment of the present invention, the negative electrode can be manufactured by applying and drying 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, on a negative electrode current collector, or by casting the composition for forming a negative electrode active material layer on a separate support, and then laminating the film obtained by peeling it off from the support on a negative electrode current collector.

[0168] According to one embodiment of the present invention, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used as a separator in a lithium secondary battery can be used without particular limitation, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0169] According to one embodiment of the present invention, the electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery. As a specific example, the electrolyte may include an organic solvent and a lithium salt.

[0170] According to one embodiment of the present invention, the organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylenecarbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0171] According to one embodiment of the present invention, the lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the anion of the lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - At least one selected from the group consisting of may be used, and the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the concentration of the lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0172] According to one embodiment of the present invention, in addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0173] A lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent capacity characteristics, output characteristics, and life characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0174] There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0175] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0176] Accordingly, according to one embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0177] According to one embodiment of the present invention, the battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0178]

[0179] Example

[0180] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention solely to these examples.

[0181]

[0182] Example 1

[0183] Transition metal precursor Ni 0.85 Co 0.105 Mn 0.045 (OH)2 and LiOH were mixed so that the molar ratio of transition metal:Li was 1:1.04, and the first calcination was performed in an oxygen atmosphere at a temperature of 900℃ for 17 hours to obtain the first calcined product.

[0184] Then, the above primary sintered product was pulverized using a jet-mill pulverizer at room temperature under the conditions of a pulverizing pressure of 1.8 bar and an input speed of 900 rpm.

[0185] Next, the crushed primary fired product was subjected to secondary firing at a temperature of 820℃ for 21 hours to obtain a secondary fired product.

[0186] Then, the above secondary sintered product was pulverized using a jet-mill pulverizer at room temperature under the conditions of pulverizing pressure of 1.8 bar and input speed of 900 rpm, and Li[Ni 0.85 Co 0.105 Mn 0.045 ]A lithium transition metal composite oxide having a composition of O2 was obtained.

[0187] Next, the lithium transition metal composite oxide obtained above was finely ground at room temperature using a jet-mill fine grinder under the conditions of a grinding pressure of 1.8 bar and an input speed of 900 rpm, and then the ground lithium transition metal composite oxide was mixed with Co(OH)2 as a coating raw material and heat-treated at 680°C for 15 hours to manufacture a cathode active material having a coating layer formed thereon.

[0188]

[0189] Example 2

[0190] A positive electrode active material was manufactured in the same manner as in Example 1, except that the heat treatment temperature was 710°C after mixing the coating material.

[0191]

[0192] Example 3

[0193] A positive electrode active material was manufactured in the same manner as in Example 1, except that the heat treatment temperature was 770°C after mixing the coating material.

[0194]

[0195] Example 4

[0196] A positive electrode active material was manufactured in the same manner as in Example 1, except that the heat treatment temperature was set to 800°C after mixing the coating material.

[0197]

[0198] Comparative Example 1

[0199] Li[Ni obtained by crushing after secondary calcination in Example 1 0.85 Co 0.105 Mn 0.045 ] Lithium nickel oxide having a composition of O2 was used as the positive electrode active material.

[0200]

[0201] Comparative Example 2

[0202] A positive electrode active material was manufactured in the same manner as in Example 1, except that the secondary firing temperature was changed to 800°C and coating was not performed.

[0203]

[0204] Comparative Example 3

[0205] After the secondary firing, a positive electrode active material was manufactured in the same manner as in Example 1, except that heat treatment was performed without adding coating raw materials in the coating process.

[0206]

[0207] Comparative Example 4

[0208] A cathode active material was manufactured in the same manner as in Example 1, except that the first firing temperature was changed to 890°C and TiO2 was added as a doping raw material in an amount of 5000 ppm relative to the total weight of the pulverized first fired product during the second firing and then fired.

[0209]

[0210] Comparative Example 5

[0211] A cathode active material was manufactured in the same manner as in Example 1, except that the first firing temperature was changed to 890°C and TiO2 was added as a doping raw material in an amount of 4000 ppm relative to the total weight of the pulverized first fired product during the second firing and then fired.

[0212]

[0213] Experimental Example 1 - Measurement of average particle size ratio

[0214] 1) Average particle diameter (D) using laser diffraction method 50 ) measurement

[0215] After dispersing the particles of each of the positive electrode active materials of Examples 1 to 4 and Comparative Example 1 in a dispersion medium, they were introduced into a laser diffraction measuring device (Microtrac MT 3000), irradiated with ultrasonic waves of 28 kHz at an output of 60 W, and then the particle size corresponding to 50% of the volume accumulation amount in the measuring device was calculated and measured.

[0216] 2) Average particle diameter (D) through SEM image SEM ) measurement

[0217] SEM images (magnification: 3000x) were obtained for each of the positive electrode active materials of Examples 1 to 4 and Comparative Example 1 (Figs. 1 to 5), and five images among these images were analyzed and an average value was calculated. The analysis of each image was performed by calculating the area of ​​each particle through the number of pixels corresponding to each particle present in the image, calculating the particle diameter and volume of each particle present in the SEM image using the radius value of a circle having the same area as the area of ​​each particle, and calculating the particle diameter corresponding to 50% of the accumulated volume and measuring it.

[0218]

[0219] The results of the above two average particle size measurements are shown in Table 1 below.

[0220]

[0221] Category D 50 (μm)D SEM (μm) Average particle size ratio (D) SEM / D 50 ) Example 14.04 3.24 0.80 Example 24.12 3.24 0.79 Example 34.07 3.20 0.79 Example 44.07 3.19 0.78 Comparative Example 14.41 3.24 0.73 Comparative Example 24.28 3.01 0.70 Comparative Example 34.24 3.31 0.78 Comparative Example 44.44 2.82 0.64 Comparative Example 54.67 2.9 10.62

[0222]

[0223] As can be seen from the results in Table 1 above, the average particle size ratio of Examples 1 to 4 is higher than that of Comparative Examples 1 and 2, which did not undergo coating and heat treatment. This indicates that the additional heat treatment after the secondary firing allowed the primary particles to agglomerate into a single particle, and thus, it was confirmed that the degree of single particle formation was further increased.

[0224] In the case of Comparative Example 3, a coating portion was not formed because heat treatment was performed without a coating material after the secondary firing, but it was confirmed that single particles were formed due to additional heat treatment, and the average particle size ratio increased compared to Comparative Examples 1 and 2.

[0225] In the case of Comparative Examples 4 and 5, coating was performed in the same manner as in Example 1, but it was confirmed that particle growth occurred relatively less due to the lower primary firing temperature compared to the Example, and thus the average particle size ratio was lower than that of the Example.

[0226]

[0227] Experimental Example 2 - Measurement of single particle magnetization

[0228] The particle size distribution of the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 and 3 was measured through SEM EBSD (electron backscatter diffraction) analysis. The electron backscatter diffraction (EBSD) Euler map data of one particle of the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 and 3 are shown in FIGS. 6 to 10, respectively.

[0229] EBSD analysis was performed using HITACHI's IM5000 (acceleration voltage: 6 kV), irradiating the anode with an argon (Ar) ion beam and cutting it using ion milling to obtain a cross-section of the anode. Using FEI's Quanta200-EDAX's Velocity super OIM 8 (acceleration voltage: 20 kV), the cross-section of the anode was measured and analyzed. EDAX OIM Analysis was used as the image processing-EBSD quantification analysis software.

[0230] In the EBSD analysis, the positive electrode was prepared by adding a positive electrode active material, a carbon black (Denka, DenkaBlack) conductive agent, and a PVdF (Kureha, KF1300) binder in a weight ratio of 94.5:3.5:2 to a N-methylpyrrolidone (NMP) (Daejung Chemicals & Metals) solvent to prepare a composition for forming a positive electrode active material layer, and then applying the composition for forming a positive electrode active material layer to one surface of an aluminum foil current collector having a thickness of 20 ㎛, and drying at a temperature of 130°C for 3 hours.

[0231] As described above, the individual radius (μm) (radius(grain)) of grains whose cross-sectional size is 0.1 μm or larger was obtained through SEM EBSD analysis, and this value was substituted into the following equation to calculate the degree of single-particle magnetization (n is the number of grains).

[0232] [Formula 2]

[0233] Single particle magnetization (μm) 3 ) =

[0234] The single particle magnetization degree calculated using the above equation 2 is shown in Table 2 below.

[0235]

[0236] Separation Single Particle Magnetization Example 16.65 Example 27.01 Example 36.79 Example 46.35 Comparative Example 18.30 Comparative Example 36.29

[0237]

[0238] When measuring the degree of single particle size using Equation 2 above through EBSD analysis, the portion with the same crystal orientation is recognized as a single particle. When heat treatment is performed after secondary calcination, phenomena such as crystal agglomeration occur in some parts of the particle interior, so the portion recognized as a single particle is smaller than when heat treatment is not performed, and the degree of single particle size tends to be measured lower.

[0239] This can also be confirmed through Table 2, where, unlike Examples 1 to 4 in which a coating process (additional heat treatment) was performed after secondary firing, Comparative Example 1 in which such a coating process was not performed showed a relatively high value for the degree of single particle size.

[0240] Meanwhile, when comparing Examples 1 to 4, which performed additional heat treatment, with Comparative Example 3, Examples 1 to 4, which performed heat treatment by adding coating raw materials together, had higher single particle size values ​​than Comparative Example 3, which performed heat treatment without adding coating raw materials, confirming that the addition of coating raw materials affected the increase in single particle size.

[0241]

[0242] Experimental Example 3 - Electrochemical Characteristics Evaluation

[0243] 1) Manufacturing of positive and coin half-cells

[0244] Using the positive electrode active material manufactured in Example 1, a composition for forming a positive electrode active material layer (positive electrode slurry) was manufactured by adding carbon black (Denka, DenkaBlack) as a conductive material and PVdF (Kureha, KF1300) as a binder to a solvent (Daejung Chemicals, N-methylpyrrolidone (NMP)) at a weight ratio of 96.5:1.5:2 (positive electrode active material: conductive material: binder).

[0245] The above-mentioned manufactured positive electrode slurry was applied to one side of an aluminum foil current collector having a thickness of 12 μm, and then dried at 130°C for 3 hours to form a positive electrode active material layer. Subsequently, the positive electrode active material layer was rolled using a roll pressing method to manufacture a positive electrode.

[0246] Instead of the positive electrode active material manufactured in Example 1, a positive electrode was manufactured in the same manner as described above using the positive electrode active materials of Examples 2 to 4 and Comparative Example 1, respectively.

[0247] An electrode assembly was manufactured using lithium metal as an anode together with the above-manufactured anode, a porous polyethylene separator was interposed between the anode and the cathode, and the electrode assembly was placed inside a case, and an electrolyte was injected into the case to manufacture a coin half-cell. At this time, the electrolyte was manufactured by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (EC:DMC:EMC mixing volume ratio = 3:4:3).

[0248] 2) Electrochemical properties evaluation method

[0249] The coin half-cells manufactured above were charged at 25℃ with a constant current (CC) of 0.1C until the voltage reached 4.3V, and then charged with a constant voltage (CV) until the charge current reached 0.05C (cut-off current), and the charge capacity was measured. After leaving the cells for 20 minutes, they were discharged with a constant current of 0.05C until the voltage reached 2.5V, and the discharge capacity of the first cycle was measured. The efficiency was also measured by dividing the discharge capacity by the charge capacity. The cells were fully charged using the same method, and a discharge current of 0.05C was applied for 60 seconds. The initial resistance (DCIR) was measured by dividing the difference in voltage immediately before and after the current application by the current.

[0250] The results of the electrochemical property evaluation are shown in Table 3 below.

[0251]

[0252] ClassificationCharging capacity (mAh)Discharging capacity (mAh)Efficiency (%)Initial resistance (Ω)Example 1230.7212.392.019.5Example 2230.2212.692.418.7Example 3229.4212.492.618.3Example 4228.9211.892.519.1Comparative example 1229.1208.691.121.6Comparative example 2230.4209.090.720.6Comparative example 3230.8210.691.220.5Comparative example 4228.2207.891.019.1Comparative example 5228.4208.491.218.2

[0253]

[0254] Referring to Table 3 above, Examples 1 to 4 show similar or slightly higher charge capacities compared to Comparative Examples 1 and 2, which did not undergo coating (additional heat treatment). However, due to the additional heat treatment, single particles were formed at a significantly higher level than Comparative Examples 1 and 2, and it was confirmed that the discharge capacity absolutely increased, and as a result, the efficiency also increased and the initial resistance decreased.

[0255] In addition, when comparing Comparative Example 3, which was performed without additional heat treatment but without addition of coating raw materials and thus no coating portion was formed, with Examples 1 to 4, the charge capacity was similar to that of Comparative Example 3, but the discharge capacity was significantly improved, increasing efficiency, and the initial resistance was also reduced, confirming that the electrochemical properties of the positive electrode active materials of Examples 1 to 4 were remarkably excellent.

[0256] When the coating was performed, the particle growth was relatively less than that of the example due to the lower first firing temperature compared to the example, and the average particle size ratio was lower than that of the example, and when the example was compared with Comparative Examples 4 and 5, it was confirmed that both the charge capacity and the discharge capacity of Examples 1 to 4 increased compared to Comparative Examples 4 and 5, and that the efficiency and initial resistance were at an equally superior level.

Claims

1. A lithium transition metal oxide; and a coating formed on the surface of the lithium transition metal oxide, It is in the form of a single particle, Average particle diameter (D 50 ) is 3 μm or more and 10 μm or less, A positive electrode active material having an average particle size ratio of 0.75 or more calculated from the following equation 1: [Formula 1] Average particle size ratio = D SEM / D 50 In the above equation 1, D SEM The area of each particle is calculated through the number of pixels corresponding to each of n particles (at least 10 or more) present in the SEM image, and the particle diameter and volume of each particle present in the SEM image are calculated using the radius value of a circle having the same area as the area of each particle, and the particle diameter at the point where the cumulative volume distribution according to particle diameter becomes 50%, D 50 is the particle diameter at the point where the volume cumulative distribution according to particle size measured through laser diffraction particle size analysis reaches 50%.

2. In claim 1, The above lithium transition metal oxide is a positive electrode active material containing nickel at 80 mol% or more based on the total moles of transition metals.

3. In claim 1, The above lithium transition metal oxide is a positive electrode active material having a composition represented by the following chemical formula 1: [Chemical Formula 1] Li a Ni b Co c M 1 d M 2 e O2 In the above chemical formula 1, M 1 is Mn, Al or a combination thereof, M 2 is at least one selected from the group consisting of Al, W, Co, B, Zr, Y, Ce, Hf, La, Ba, F, P, S, Nb, Ta, Sc, Cr, V, Cu, Sr, Ti, Mg, Mo, Sn, Fe, Zn and Si, 0.9≤a≤1.3, 0.8≤b<1, 0 <c<0.3, 0<d<0.3, 0≤e≤0.2, b+c+d+e=1이다.

4. In claim 1, The above coating portion is a positive electrode active material comprising at least one metal element selected from the group consisting of Ni, Co, Mn, Al, B, Ti, Ta, W, and Nb.

5. In claim 1, The above single particle form is a positive electrode active material in the form of a single particle or a pseudo-single particle form formed by agglomeration of two or more and 30 or less primary particles.

6. In claim 1, The above positive electrode active material has a single particle size of 7.5 μm as calculated from the following equation 2. 3 The following positive electrode active materials: [Formula 2] Single particle magnetization (μm) 3 ) = In the above equation 2, radius(grain) is the individual radius (μm) of grains whose cross-sectional size of a single particle is 0.1 μm or more as measured from backscatter electron diffraction analysis (EBSD) of a cross-sectional SEM image of a positive electrode manufactured with a single particle positive active material, and n is the number of grains.

7. In claim 6, The above single particle size is 5.0 μm 3 Above, 7.5 μm 3 Below is the positive electrode active material.

8. In claim 1, A positive electrode active material having an average particle size ratio of 0.75 or more and 1.0 or less.

9. A positive electrode comprising the positive electrode active material of any one of claims 1 to 8.

10. The positive electrode of claim 9; cathode; a separator interposed between the anode and the cathode; and A lithium secondary battery containing an electrolyte.

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