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

Abstract

The present invention relates to a positive electrode active material comprising a lithium composite transition metal oxide in the form of a single particle and comprising two or more elements selected from the group consisting of nickel, cobalt and manganese, in which the lithium composite transition metal oxide has a particle size distribution satisfying the following mathematical formula 1: [mathematical formula 1] 1.1 < = R / Llt; 2.0 in the mathematical formula 1, R is an area formed by the right particle size distribution curve and the x-axis in a particle size distribution curve in which the x-axis is the particle size (unit: [mu] m) of the lithium composite transition metal oxide and the y-axis is the volume percentage (unit:%), with a peak point having the maximum y value as a reference, and L is an area formed by the right particle size distribution curve and the x-axis in the particle size distribution curve, with a peak point having the maximum y value as a reference, with a peak point having the maximum y value as a reference. And an area formed by the x-axis and the left particle size distribution curve.

Description

Technical Field

[0001] Cross - reference to related applications

[0002] This application claims the benefit of priority of Korean Patent Application No. 10-2023-0000403, filed on Jan. 2, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical field

[0003] The present invention relates to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery. Background Art

[0004] Recently, with the development of technologies such as electric vehicles, the demand for high-capacity batteries has been increasing continuously. Accordingly, research on high-Ni-based positive electrode active materials having excellent capacity characteristics has also been actively conducted.

[0005] Conventionally, as a high-Ni-based positive electrode active material, a great deal of research has been conducted to prepare a positive electrode active material in the form of secondary particles in which spherical primary particles are aggregated. In this case, the research aims to prepare a positive electrode active material having a uniform particle size (i.e., a small particle size deviation). However, when the particle size of the positive electrode active material is uniform, after pressure is applied in the process of manufacturing a positive electrode to manufacture the positive electrode, the density of the positive electrode active material present in the positive electrode active material layer is low, and thus it is difficult to achieve a high energy density.

[0006] Therefore, it is necessary to develop a positive electrode active material capable of achieving a high rolling density.

[0007] [Prior Art Documents]

[0008] [Patent Documents]

[0009] (Patent Document 1) KR 2021-0070893 A Summary of the Invention

[0010] Technical problem

[0011] To solve the above problems, an aspect of the present invention provides a positive electrode active material in the form of single particles and adjusted to have a specific particle size distribution shape to achieve a high rolling density.

[0012] In addition, another aspect of the present invention provides a positive electrode and a lithium secondary battery having a small porosity of a positive electrode active material layer by including the positive electrode active material.

[0013] Technical solution

[0014] In order to solve the above problems, according to one aspect of the present invention, a positive electrode active material, a positive electrode including the same, and a lithium secondary battery are provided.

[0015] (1) According to one aspect of the present invention, there is provided a positive electrode active material comprising a lithium composite transition metal oxide in the form of single particles comprising two or more selected from nickel, cobalt, and manganese, wherein the lithium composite transition metal oxide has a particle size distribution satisfying the following mathematical formula 1:

[0016] [Mathematical formula 1]

[0017] 1.1 ≤ R / L < 2.0

[0018] In the above mathematical formula 1,

[0019] R is an area formed by the particle size distribution curve on the right side and the x-axis with the peak point having the maximum y value as a reference in a particle size distribution curve in which the x-axis is the particle diameter of the lithium composite transition metal oxide (unit: μm) and the y-axis is the volume percentage (unit: %), and

[0020] L is the area formed by the x-axis and the particle size distribution curve on the left side with respect to the peak point having the maximum y value in the particle size distribution curve.

[0021] (2) In the above (1) of the present invention, there is provided a positive electrode active material in which the lithium composite transition metal oxide is a single particle or a secondary particle in which at most 10 primary particles are agglomerated.

[0022] (3) In the above (1) or (2) of the present invention, there is provided a positive electrode active material wherein the lithium composite transition metal oxide contains at least 60 mol % of nickel in all metals other than lithium.

[0023] (4) In any one of the above (1) to (3) of the present invention, there is provided a positive electrode active material, wherein the lithium composite transition metal oxide has a composition represented by the following Chemical Formula 1:

[0024] [Chemical formula 1]

[0025] Li x Ni a Co b Mn c M 1 d O2

[0026] In the above chemical formula 1,

[0027] M 1is at least one selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, P, Y, Na, and Ca, and

[0028] 0.9 ≤ x ≤ 1.3, 0.6 ≤ a < 1.0, 0 < b < 0.4, 0 < c < 0.4, 0 ≤ d ≤ 0.2 and a + b + c + d = 1.

[0029] (5) In any one of the above (1) to (4) of the present invention, a positive electrode active material is provided, wherein the D 50 of the lithium composite transition metal oxide is 5 μm to 15 μm.

[0030] (6) In any one of the above (1) to (5) of the present invention, a positive electrode active material is provided, and the calendering density of the positive electrode active material is at least 3.55 g / cm 3 .

[0031] (7) In any one of the above (1) to (6) of the present invention, a positive electrode active material is provided, and the tap density of the positive electrode active material is 2.40 g / cm 3 to 2.70 g / cm 3 .

[0032] (8) According to another aspect of the present invention, a positive electrode is provided, which includes:

[0033] a current collector; and

[0034] a positive electrode active material layer formed on the current collector and including the positive electrode active material according to any one of the above (1) to (7).

[0035] (9) In the above (8) of the present invention, a positive electrode is provided, wherein the porosity of the positive electrode active material layer is 16% by volume to 24% by volume.

[0036] (10) According to still another aspect of the present invention, a lithium secondary battery is provided, which includes:

[0037] a positive electrode according to the above (8) or (9);

[0038] a negative electrode;

[0039] a separator interposed between the positive electrode and the negative electrode; and

[0040] an electrolyte.

[0041] Advantageous effects

[0042] The positive electrode active material of the present invention is in the form of single particles, and the R / L value according to Mathematical Formula 1 satisfies 1.1 to 2.0. When the positive electrode is prepared using the positive electrode active material, the porosity of the positive electrode active material layer decreases when the same pressure is applied, whereby the contact area between the positive electrode active material and the conductive material increases. As a result, the charging capacity of the lithium secondary battery can be increased and the life characteristics can be improved. Description of the Drawings

[0043] Figure 1 It is a particle size distribution diagram of each positive electrode active material prepared in the examples and comparative examples.

[0044] Figure 2 It is an SEM image of the positive electrode active material prepared in Example 1.

[0045] Figure 3 It is an SEM image of the positive electrode active material prepared in Example 2.

[0046] Figure 4 It is an SEM image of the positive electrode active material prepared in Example 3.

[0047] Figure 5 It is an SEM image of the positive electrode active material prepared in Comparative Example 1.

[0048] Figure 6 It is an SEM image of the positive electrode active material prepared in Comparative Example 2.

[0049] Figure 7 It is an SEM image of the positive electrode active material prepared in Comparative Example 3. Detailed Description of the Invention

[0050] Hereinafter, the present invention will be described in more detail so as to be more clearly understood.

[0051] It should be understood that the words or terms used in the specification and claims of the present invention should not be construed as being limited to the meanings defined in a common dictionary. It should be further understood that the words or terms should be construed as having meanings consistent with their meanings in the context of the relevant field of the present invention and the technical gist, based on the principle that the inventor may appropriately define the meanings of the words or terms to best explain the present invention.

[0052] As used herein, the term "primary particle" refers to the smallest particle unit that is distinguishable as a single block when observing a cross section of the positive electrode active material through a scanning electron microscope (SEM), and may be composed of a plurality of crystal grains.

[0053] As used herein, the term "secondary particle" refers to a secondary structure formed by the aggregation of more than 10 primary particles. The particle size of the secondary particle can be measured by a particle size analyzer.

[0054] As used herein, the term "D 10 ", "D 50 ", and "D 90 " respectively refer to the particle sizes at the 10% point (D 10 ), 50% point (D 50 ), and 90% point (D 90 ) of the volume cumulative distribution according to particle size. D 10 , D 50 , and D 90 can be measured by the following steps: Dispersing the powder to be measured in a dispersion medium, introducing the powder into a commercially available laser diffraction particle size measuring instrument (e.g., S3500 manufactured by Microtrac, Inc.), measuring the difference in the diffraction pattern with particle size as the particles pass through the laser beam to calculate the volume cumulative distribution according to particle size, and calculating the particle sizes at the 10%, 50%, and 90% points of the volume cumulative distribution according to particle size in the measuring instrument.

[0055] As used herein, the term "single particle form" means including both single particles of the positive electrode active material and / or lithium composite transition metal oxide, and forms in which two to ten particles are agglomerated therein. That is, the positive electrode active material in the single particle form of the present invention and / or the lithium composite transition metal oxide in the single particle form may include one or more selected from single particles and particles in which two to ten positive electrode active material and / or lithium composite transition metal oxide particles are agglomerated.

[0056] Positive electrode active material

[0057] The present invention provides a positive electrode active material.

[0058] The positive electrode active material according to the present invention contains a lithium composite transition metal oxide, the lithium composite transition metal oxide is in the form of single particles and contains two or more selected from nickel, cobalt, and manganese, and the lithium composite transition metal oxide has a particle size distribution satisfying the following Mathematical Formula 1. That is, when obtaining a particle size distribution curve in which the x-axis is the particle size (unit: μm) of the lithium composite transition metal oxide and the y-axis is the volume percentage (unit: %) of the lithium composite transition metal oxide having a particle size corresponding to the x-axis in all the lithium composite transition metal oxides, the lithium composite transition metal oxide satisfies the following Mathematical Formula 1. When the R / L value according to the following Mathematical Formula 1 is 1.1 or more and less than 2.0, since the positive electrode active material has a wide particle size distribution, the calendering density is high, and thus, an electrode with a high energy density can be achieved. Specifically, the R / L value according to the following Mathematical Formula 1 can be 1.100, 1.200, 1.300, or 1.400 to 1.800, 1.850, 1.900, 1.950, or less than 2.000.

[0059] [Mathematical formula 1]

[0060] 1.1 ≤ R / L < 2.0

[0061] In the above Mathematical formula 1,

[0062] R is the area formed by the particle size distribution curve on the right side and the x-axis, with the peak point having the maximum y value as the reference in the particle size distribution curve where the x-axis is the particle size (unit: μm) of the lithium composite transition metal oxide and the y-axis is the volume percentage (unit: %), and

[0063] L is the area formed by the x-axis and the particle size distribution curve on the left side, with the peak point having the maximum y value as the reference in the particle size distribution curve.

[0064] On the other hand, there are limitations. When the R / L value according to the above Mathematical formula 1 is less than 1.1, the positive electrode active material does not have a wide particle size distribution, and because there are many particles with small particle sizes, it cannot have a high calendaring density. And when the R / L value is 2.0 or more, there are large powders, so the positive electrode active material cannot have a high calendaring density.

[0065] According to the present invention, the positive electrode active material may include a lithium composite transition metal oxide in the form of single particles. As a specific example, the lithium composite transition metal oxide in the form of single particles is single particles or secondary particles in which at most 10 primary particles are agglomerated. For a conventional positive electrode active material in the form of secondary particles in which more than 10 primary particles are agglomerated, in order to minimize the cracks generated by pressure during the calendaring of the electrode manufacturing, it has to increase the porosity, which in turn leads to deterioration of the energy density of the lithium secondary battery. However, when the positive electrode active material has the form of single particles or secondary particles in which at most 10 primary particles are agglomerated, such as the positive electrode active material of the present invention, during the charging and discharging of the lithium secondary battery, the cracks caused by the volume change in the unit lattice can be minimized, especially the cracks generated by pressure during the calendaring of the electrode manufacturing can be minimized. Therefore, when using the positive electrode active material of the present invention, during the calendaring for manufacturing the electrode, calendaring can be performed at a lower porosity, thereby improving the energy density of the lithium secondary battery.

[0066] According to the present invention, in terms of capacity improvement, the content of nickel among all metals other than lithium in the lithium composite transition metal oxide can be at least 60 mol%, at least 70 mol%, at least 80 mol% or at least 85 mol%. That is, the lithium composite transition metal oxide can contain nickel and can be a high-Ni type lithium composite transition metal oxide, in which the content of nickel (Ni) relative to all transition metals is at least 60 mol%, at least 70 mol%, at least 80 mol% or at least 85 mol%. In this case, a high energy density can be ensured by the high nickel content.

[0067] According to the present invention, the lithium composite transition metal oxide can have a composition represented by the following Chemical Formula 1:

[0068] [Chemical Formula 1]

[0069] Li x Ni a Co b Mn c M 1 d O2

[0070] Wherein, in the above Chemical Formula 1,

[0071] M 1 is at least one selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, P, Y, Na, and Ca, and

[0072] 0.9 ≤ x ≤ 1.3, 0.6 ≤ a < 1.0, 0 < b < 0.4, 0 < c < 0.4, 0 ≤ d ≤ 0.2 and a + b + c + d = 1.

[0073] In the above Chemical Formula 1, M 1 can be a doping element that can be contained in the lithium composite transition metal oxide and can be appropriately selected as needed.

[0074] In the above Chemical Formula 1, x is the molar ratio of lithium to transition metals in the lithium composite transition metal oxide and can be 0.9 or more, 0.95 or more, or 1.0 or more, and can also be 1.1 or less, 1.07 or less, 1.05 or less, or 1.03 or less.

[0075] In the above Chemical Formula 1, a, b, c, and d can be the contents of nickel (Ni), cobalt (Co), manganese (Mn), and doping element (M 1) mole fraction. As a specific example, the above a represents the mole fraction of nickel (Ni) in the transition metal, which can be 0.6 or more, 0.7 or more, 0.8 or more, 0.85 or more, 0.88 or more, 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, 0.94 or more, 0.95 or more or 0.96 or more, and can also be less than 1.0, 0.99 or less, 0.98 or less, 0.97 or less or 0.96 or less. In addition, the above b represents the mole fraction of cobalt (Co) in the transition metal, which can be greater than 0, 0.01 or more, 0.02 or more or 0.03 or more, and can be less than 0.4, 0.3 or less, 0.2 or less, 0.1 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less or 0.05 or less. The above c represents the mole fraction of manganese (Mn) in the transition metal, which can be greater than 0, 0.01 or more or 0.05 or more, and can be less than 0.4, 0.3 or less, 0.2 or less, 0.1 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less or 0.05 or less. The above d is the mole fraction of the doping element (M 1 ) in the transition metal, which can be 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, 0.16 or more, 0.17 or more, 0.18 or more or 0.19 or more, and can be less than 0.20, 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, 0.10 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less or 0.01 or less.

[0076] According to the present invention, the D of the lithium composite transition metal oxide 50 can be 5 μm to 15 μm. Specifically, the D of the lithium composite transition metal oxide 50 can be 5 μm or 6 μm to 7 μm, 10 μm, 12 μm or 15 μm. In this case, since the positive electrode active material can have the highest calendering density, the electrode porosity can be reduced.

[0077] According to the present invention, the D of the lithium composite transition metal oxide min can be 0.5 μm to 4 μm. Specifically, the D of the lithium composite transition metal oxide minIt can be 0.50 μm, 1.00 μm or 1.50 μm to 2.50 μm, 3.00 μm, 3.50 μm or 4.00 μm. In this case, there are some fine powders, so that the volume filling rate can be improved.

[0078] According to the present invention, the D of the lithium composite transition metal oxide 10 can be from 1 μm to 7 μm. Specifically, the D of the lithium composite transition metal oxide 10 can be 1.00 μm, 1.50 μm, 2.00 μm, 2.50 μm or 3.00 μm to 4.00 μm, 5.00 μm, 6.00 μm or 7.00 μm. In this case, due to the small particle size, the volume filling rate is improved, and a high calendering density can be obtained.

[0079] According to the present invention, the D of the lithium composite transition metal oxide 90 can be from 7 μm to 15 μm. Specifically, the D of the lithium composite transition metal oxide 90 can be 7.00 μm or 7.50 μm to 11.00 μm, 12.00 μm, 13.00 μm, 14.00 μm or 15.00 μm. In this case, since there are no large powders, a high calendering density can be obtained.

[0080] According to the present invention, the D of the lithium composite transition metal oxide max can be from 11 μm to 31 μm. Specifically, the D of the lithium composite transition metal oxide max can be 11.00 μm, 12.00 μm, 13.00 μm, 14.00 μm or 15.00 μm to 27.00μm or 31.00 μm. In this case, since there are no large powders, a high calendering density can be obtained.

[0081] According to the present invention, the calendering density of the positive electrode active material can be at least 3.55 g / cm 3 . Specifically, the calendering density of the positive electrode active material can be 3.55 g / cm 3 , 3.56 g / cm 3 or 3.57 g / cm 3 to 3.73 g / cm 3 , 3.74 g / cm 3 or 3.75 g / cm 3In this case, even when the same force is applied during the electrode rolling process, the electrode porosity is low, so the energy density can be increased, and during rolling using a rolling mill in the process of manufacturing the electrode, the linear pressure applied to the electrode to exhibit the same porosity is reduced, thereby improving the processability.

[0082] The rolling density is the rolling density calculated by the following Mathematical Formula 3 when forming pellets by applying a force using an automatic granulator until a force equivalent to 9,000 kgf is reached.

[0083] Specifically, the rolling density is a value obtained according to the following (1) to (3):

[0084] (1) Using an automatic granulator (Carver, Inc., 3887.4), adjust the thickness reference point using a cylindrical mold of a circular pellet retainer;

[0085] (2) Put the positive electrode active material into the circular pellet retainer and measure the thickness of the pellet formed by applying a force until a force equivalent to 9,000 kgf is reached; and

[0086] (3) Calculate the pellet volume using the following Mathematical Formula 2 and calculate the rolling density using the following Mathematical Formula 3.

[0087] [Mathematical Formula 2]

[0088] Pellet volume (cm 3 ) = π (radius of the circular pellet retainer) 2 × thickness of the pellet

[0089] [Mathematical Formula 3]

[0090] Rolling density (g / cm 3 ) = weight (g) of the positive electrode active material / pellet volume (cm 3 )

[0091] According to the present invention, the tapped density of the positive electrode active material can be 2.40 g / cm 3 to 2.70 g / cm 3 . Specifically, the tapped density of the positive electrode active material can be 2.40 g / cm 3 , 2.45 g / cm 3 or 2.50 g / cm 3 to 2.70 g / cm 3 , 2.75 g / cm 3 or 2.80 g / cm 3。In this case, even when the same force is applied during the electrode rolling process, the electrode porosity is low, so the energy density can be increased, and during the rolling using a rolling mill in the process of manufacturing the electrode, the linear pressure applied to the electrode to exhibit the same porosity is reduced, thereby improving the processability.

[0092] The tapped density is an index indicating how much positive electrode active material can be filled into a volume only by tapping without applying a separate pressure, and is a value calculated according to the following Mathematical Formula 4 after measuring the volume obtained by putting the positive electrode active material into a cylinder using a tapped density meter (manufactured by J.Engelsmann AG, Jolting Volumeter Type STAV II) and then tapping 1,800 times.

[0093] [Mathematical Formula 4]

[0094] Tapped density (g / cm 3 ) = weight (g) of positive electrode active material / volume (cm 3 )

[0095] Positive electrode

[0096] The present invention provides a positive electrode comprising the above positive electrode active material.

[0097] According to the present invention, the positive electrode comprises: 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 comprises the positive electrode active material according to the present invention.

[0098] According to the present invention, in order to prevent the overload of the rollers and not affect the thickness of the current collector during rolling using a rolling mill in the process of manufacturing the electrode, the porosity of the positive electrode active material layer can be 16% by volume to 24% by volume. Specifically, the porosity of the positive electrode active material layer according to the present invention can be 16% by volume, 17% by volume or 18% by volume to 20% by volume, 21% by volume, 22% by volume or 24% by volume. In this case, since the positive electrode has a high electrode density, the thickness of the electrode can be reduced and the energy density per unit volume can be increased.

[0099] The positive electrode current collector may include a metal having high conductivity and is not particularly limited as long as the positive electrode active material layer can easily adhere thereto and is not reactive within the voltage range of the battery. As the positive electrode current collector, for example, stainless steel, aluminum, nickel, titanium, fired carbon; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used. In addition, the thickness of the positive electrode current collector is generally 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0100] The positive electrode active material layer may contain, as needed, a positive electrode active material and optionally a conductive material and a binder. In this case, the content of the positive electrode active material can be 80 to 99% by weight, more specifically 85 to 98.5% by weight, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited within this range.

[0101] The conductive material is used to provide conductivity to the electrode, and any conductive material can be used without particular limitation as long as it has appropriate electron conductivity and does not cause adverse chemical changes in the battery. Specific examples of the conductive material can be the following substances: graphite such as natural graphite or artificial graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, and carbon fiber; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one of them or a mixture of two or more of them can be used. The content of the conductive material can be 0.1% by weight to 15% by weight based on the total weight of the positive electrode active material layer.

[0102] The binder is used to improve the binding between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of the binder can be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers or various copolymers in which hydrogen is replaced by Li, Na, or Ca, and any one of them or a mixture of two or more of them can be used. The content of the binder can be 0.1% by weight to 15% by weight based on the total weight of the positive electrode active material layer.

[0103] In addition to using the above-mentioned positive electrode active material, the positive electrode can be prepared according to typical methods for preparing positive electrodes. Specifically, the positive electrode can be prepared by the following operations: coating a composition for forming a positive electrode active material layer on a positive electrode current collector, the composition being prepared by dissolving or dispersing the above-mentioned positive electrode active material and, optionally, a binder, a conductive material, and a dispersant in a solvent as needed; then drying and calendering the coated positive electrode current collector; or, the positive electrode can be prepared by casting a composition for forming a positive electrode active material layer on a separate carrier and then laminating the film separated from the carrier on the positive electrode current collector.

[0104] The solvent can be a solvent commonly used in the art. The solvent can include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and any one of them or a mixture of two or more of them can be used. Considering the coating thickness of the slurry and the manufacturing yield, the solvent can dissolve or disperse the positive electrode active material, the conductive material, the binder, and the dispersant, and can have a viscosity that can provide excellent thickness uniformity during the subsequent coating for preparing the positive electrode, and then the amount of the solvent used may be sufficient.

[0105] Lithium secondary battery

[0106] The present invention provides a lithium secondary battery including a positive electrode.

[0107] According to the present invention, the lithium secondary battery includes: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte. The lithium secondary battery may also optionally include a battery container for accommodating the electrode assembly including the positive electrode, the negative electrode, and the separator; and a sealing member for sealing the battery container.

[0108] The negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0109] There is no particular limitation on the negative electrode current collector as long as it has high conductivity and does not cause adverse chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon; copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.; and aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector usually has a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, fine concavities and convexities can be formed on the surface of the current collector to improve the binding force of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as a film, a sheet, a foil, a net, a porous body, a foam body, and a non-woven fabric body.

[0110] The negative electrode active material layer contains a negative electrode active material and, optionally, a binder and a conductive material.

[0111] A compound capable of reversibly embedding and de-embedding lithium can be used as a negative electrode active material. Specific examples of the negative electrode active material can be the following substances: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; (semi) metallic materials capable of forming an alloy with lithium such as silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloy, Sn alloy, or Al alloy; (semi) metal oxides which may or may not be doped with lithium such as SiO β (0 < β < 2), SnO2, vanadium oxides, and lithium vanadium oxides; or composite materials containing (semi) metallic materials and carbonaceous materials such as Si-C composite materials or Sn-C composite materials, and any one of them or a mixture of two or more of them can be used. In addition, a thin film of metallic lithium can be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Typical examples of low-crystalline carbon can include soft carbon and hard carbon, and typical examples of high-crystalline carbon can include irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbeads, mesophase pitch, and high-temperature sintered carbon such as coke derived from petroleum or coal tar pitch. Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 80% by weight to 99% by weight.

[0112] The binder of the negative electrode active material layer is a component that helps the binding between the conductive material, the active material, and the current collector, and based on the total weight of the negative electrode active material layer, the binder is usually added in an amount of 0.1% by weight to 10% by weight. Examples of the binder can include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, various copolymers thereof, etc.

[0113] According to an 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 based on the total weight of the negative electrode active material layer, the conductive material can be added in an amount of 10% by weight or less, preferably 5% by weight or less. There is no particular limitation on the conductive material as long as it has conductivity and does not cause an adverse chemical change in the battery, and for example, the following conductive materials can be used: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers such as carbon fiber or metal fiber; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0114] The negative electrode active material layer can be prepared by coating a negative electrode current collector with a composition for forming a negative electrode active material layer and drying the coated negative electrode current collector, the composition being prepared by dissolving or dispersing a negative electrode active material and optionally a binder and a conductive material in a solvent, or the negative electrode active material layer can be prepared by casting a composition for forming a negative electrode active material layer on a separate carrier and then laminating a film separated from the carrier on the negative electrode current collector.

[0115] The separator separates the negative electrode and the positive electrode and provides a path for the movement of lithium ions. Any separator can be used as the separator without particular limitation as long as it is commonly used in lithium secondary batteries. In particular, a separator having a high moisture retention capacity for the electrolyte and a low resistance to the transfer of electrolyte ions is preferred. Specifically, a porous polymer film, such as a porous polymer film prepared from a polyolefin polymer such as a homopolymer of ethylene, a homopolymer of propylene, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, can be used; or a laminated structure having two or more layers thereof. In addition, a typical porous nonwoven fabric, such as a nonwoven fabric formed from high melting point glass fibers or polyethylene terephthalate fibers, can be used. In addition, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure can be optionally used.

[0116] The electrolyte can 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, or a molten-type inorganic electrolyte that can be used to prepare a lithium secondary battery. Specifically, the electrolyte can contain an organic solvent and a lithium salt.

[0117] Any organic solvent can be used without particular limitation as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the following substances can be used as organic solvents: 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 solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic C2-C20 hydrocarbon group and may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate 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, which can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0118] A lithium salt can be used without 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 can be at least one selected from the following substances: 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 -, and as the lithium salt, the following substances can be used: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. It is preferred to use the lithium salt in the concentration range of 0.1 M to 2.0 M. When the concentration of the lithium salt is included in the above range, the electrolyte can have appropriate conductivity and viscosity, thereby exhibiting excellent performance, and lithium ions can move effectively.

[0119] In order to improve the life characteristics of the battery, suppress the reduction of the battery capacity and improve the discharge capacity of the battery, in addition to the electrolyte components, at least one additive can be included in the electrolyte, such as haloalkyl carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (poly)glycol dimethyl ethers, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride. In this case, the content of the additive can be 0.1 wt% to 5 wt% relative to the total weight of the electrolyte.

[0120] The lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent capacity characteristics and life characteristics, and can thus be used in: portable devices such as mobile phones, laptop computers and digital cameras; and the field of electric vehicles such as hybrid electric vehicles (HEV) and electric vehicles (EV).

[0121] There is no particular limitation on the shape of the lithium secondary battery, but a cylindrical type, a prismatic type, a pouch type or a coin type using a can can be used.

[0122] The lithium secondary battery can be used not only in a battery cell used as a power source for a small device, but also as a unit cell in a medium and large-sized battery module including a plurality of battery cells.

[0123] Therefore, the present invention can provide a battery module including a lithium secondary battery as a unit cell and a battery pack including the battery module.

[0124] The battery module or the battery pack can be used as a power source for at least one of the following medium and large-sized devices: power tools; electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (PHEV); or a power storage system.

[0125] Preferred Embodiment

[0126] Hereinafter, examples of the present invention will be described in detail in a manner that can be easily implemented by those of ordinary skill in the art to which the present invention pertains. However, the present invention can be implemented in many different forms and should not be construed as limited to the examples set forth herein.

[0127] Examples and comparative examples

[0128] Example 1

[0129] By mixing a composite transition metal hydroxide (D 0.96 Co 0.03 Mn 0.01 represented by (OH)2 with a composition of 7 μm) with LiOH such that the molar ratio of Li / metal (Ni + Co + Mn) becomes 1.02, firing once at 830 °C for 12 hours in an oxygen atmosphere, and pulverizing the fired mixture using a jet mill to have a particle size distribution curve as shown in 50 , and firing twice at 770 °C for 12 hours in an oxygen atmosphere, a lithium composite transition metal oxide (positive electrode active material) in the form of single particles and having a composition represented by LiNi Figure 1 Co 0.96 Co 0.03 Mn 0.01 O2 was prepared.

[0130] Example 2

[0131] By mixing a composite transition metal hydroxide (D 0.89 Co 0.03 Mn 0.08 represented by (OH)2 with a composition of 4.2 μm) with LiOH such that the molar ratio of Li / metal (Ni + Co + Mn) becomes 1.05, firing once at 880 °C for 12 hours in an oxygen atmosphere, and pulverizing the fired mixture using a jet mill to have a particle size distribution curve as shown in 50 , and firing twice at 800 °C for 12 hours in an oxygen atmosphere, a lithium composite transition metal oxide (positive electrode active material) in the form of single particles and having a composition represented by LiNi Figure 1 Co 0.89 Co 0.03 Mn 0.08 O2 was prepared.

[0132] Example 3

[0133] Prepared in the same manner as in Example 1 and having a single particle form and composed of LiNi 0.96 Co 0.03 Mn 0.01A lithium composite transition metal oxide (positive electrode active material) represented by O2, except that a composite transition metal oxide (D 0.96 Co 0.03 Mn 0.01 O) having a composition represented by is used instead of the composite transition metal hydroxide (D 50 : 7 μm) having a composition represented by Ni 0.96 Co 0.03 Mn 0.01 (OH)2 in Example 1. 50 : 7 μm).

[0134] Comparative Example 1

[0135] A lithium composite transition metal oxide (positive electrode active material) represented by LiNi 0.96 Co 0.03 Mn 0.01 O2 was prepared in the same manner as in Example 1, except that firing was carried out once at 800 °C instead of 830 °C in Example 1.

[0136] Comparative Example 2

[0137] A lithium composite transition metal oxide (positive electrode active material) represented by LiNi 0.89 Co 0.03 Mn 0.08 O2 was prepared in the same manner as in Example 2, except that firing was carried out once at 850 °C instead of 880 °C in Example 2.

[0138] Comparative Example 3

[0139] A lithium composite transition metal oxide (positive electrode active material) represented by LiNi 0.96 Co 0.03 Mn 0.01 O2 was prepared in the same manner as in Example 1, except that a composite transition metal oxide (D 0.96 Co 0.03 Mn 0.01 O) having a composition represented by is used instead of the composite transition metal hydroxide having a composition represented by Ni 50 : 9 μm) in Example 1 and firing was carried out once at 910 °C instead of 830 °C. 0.96 Co 0.03 Mn 0.01 (OH)2 and firing was carried out once at 910 °C instead of 830 °C.

[0140] Experimental Example 1: Taking SEM images

[0141] The positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were respectively photographed using a scanning electron microscope (SEM, Inspect F manufactured by FEI), and are respectively shown in Figures 2 to 7 below.

[0142] Experimental Example 2: Analysis of particle size and particle size distribution curve

[0143] For the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3, the D min , D 10 , D 50 , D 90 and D max values were measured using a particle size analyzer (PSD, S3500 manufactured by Microtrac). The results are shown in Table 1 below, and the particle size distribution curve where the x-axis is the particle size of the lithium composite transition metal oxide (unit: μm) and the y-axis is the volume percentage (unit: %) of the lithium composite transition metal oxide having the particle size corresponding to the x-axis in all the lithium composite transition metal oxides is shown in Figure 1 below. In addition, the R / L value according to the following Mathematical Formula 1 was calculated, and the results are also shown in Table 1 below.

[0144] [Mathematical Formula 1]

[0145] 1.1 ≤ R / L < 2.0

[0146] In the above Mathematical Formula 1,

[0147] L is the area formed by the x-axis and the particle size distribution curve on the left, based on the peak point with the maximum y value in the particle size distribution curve, and

[0148] R is the area formed by the x-axis and the particle size distribution curve on the right, based on the peak point with the maximum y value in the particle size distribution curve.

[0149]

[0150] As shown in Table 1, it can be confirmed that the R / L values of the positive electrode active materials prepared in Examples 1 to 3 according to the above Mathematical Formula 1 are 1.1 to 2.0.

[0151] Experimental Example 3: Evaluation of calendered density and tapped density

[0152] - Calendered density

[0153] The thickness reference point was adjusted using a cylindrical die with a circular pellet retainer (Carver, Inc., 3887.4) having a diameter of 13 mm. Then, 3 g of the positive electrode active material prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was placed in the circular pellet retainer, and the thickness of the formed pellets was measured by applying a force until a force equivalent to 9,000 kgf was reached. Subsequently, the pellet volume was calculated using Mathematical Formula 2 below, and the calendering density was calculated using Mathematical Formula 3 below, and the results are shown in Table 2 below.

[0154] [Mathematical Formula 2]

[0155] Pellet volume (cm 3 ) = π (radius of the circular pellet retainer) 2 × thickness of the pellet

[0156] [Mathematical Formula 3]

[0157] Calendering density (g / cm 3 ) = weight of the positive electrode active material (g) / pellet volume (cm 3 )

[0158] - tapped density

[0159] The volume obtained after adding 50 g of the positive electrode active material prepared in Examples 1 to 3 and Comparative Examples 1 to 3 to a 100 mL cylinder using a tapped density meter (Jolting Volumeter Type STAV II manufactured by J.Engelsmann AG Co.) and tapping 1,800 times was measured. The tapped density was calculated using Mathematical Formula 4 below, and the results are shown in Table 2 below.

[0160] [Mathematical Formula 4]

[0161] Tapped density (g / cm 3 ) = weight of the positive electrode active material (g) / volume (cm 3 )

[0162]

[0163] As shown in Table 2 above, it was confirmed that the calendering density of the positive electrode active material prepared in Examples 1 to 3 according to Mathematical Formula 3 was 3.55 g / cm 3 or more and the tapped density was 2.40 g / cm 3 or more.

[0164] Experimental Example 4: Evaluation of Charge Capacity and Life Characteristics

[0165] Lithium secondary batteries were fabricated using the positive electrode active materials prepared in the use examples and comparative examples, and the charge capacity and life characteristics of each lithium secondary battery were evaluated.

[0166] Specifically, each of the positive electrode active materials prepared in Use Examples 1 to 3 and Comparative Examples 1 to 3, FX35 as a conductive material, KF9709 as a binder, and BM740H as a binder were mixed in an NMP solvent at a weight ratio of 95:2:3:0.15 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector, dried at 130 °C, and then rolled so that the porosity of the positive electrode active material layer became 20% by volume, thereby preparing a positive electrode. On the other hand, a Li metal disk was used as the negative electrode active material. After preparing an electrode assembly by inserting a separator between the positive electrode and the negative electrode prepared as described above, the electrode assembly was placed in a battery case, and then an electrolytic solution was injected into the case to prepare a lithium secondary battery. In this case, as the electrolytic solution, an electrolytic solution in which 1 M of LiPF6 was dissolved in an organic solvent of EC / EMC / DMC (3 / 3 / 4, % by volume) was injected to prepare a lithium secondary battery.

[0167] The lithium secondary battery prepared as described above was charged at 25 °C in a CC / CV mode at a constant current of 0.1C up to 4.25 V (the termination current was 0.05C), and then the charge capacity was measured while discharging in the CC mode until the voltage reached 3.0 V, and the results are shown in Table 3 below. In this case, 1C was set to 200 mA / g.

[0168] In addition, the lithium secondary battery prepared as described above was charged at 45 °C in a CC / CV mode at a constant current of 0.5C up to 4.25 V (the termination current 0.05C), and then discharged in the CC mode until the voltage reached 2.5 V, which was defined as one cycle. The cycle was repeated 50 times, and the percentage of the discharge capacity of the 50th cycle relative to the discharge capacity of the first cycle was determined as the capacity retention rate, and the results are shown in Table 3 below.

[0169]

[0170] Referring to Tables 1 to 3 and Figures 2 to 7 , it can be confirmed that by adjusting the firing temperature and particle size distribution, the positive electrode active materials prepared in Use Examples 1 to 3 are in the form of single particles, the R / L value according to the above Mathematical Formula 1 is adjusted to 1.1 to 2.0, and the rolling density according to Mathematical Formula 3 is 3.55 g / cm 3The above. In addition, from these results, it can be confirmed that when the positive electrode is prepared using the positive electrode active material according to the present invention, the porosity of the positive electrode active material layer decreases, so the contact area between the positive electrode active material and the conductive material increases, thereby increasing the charging capacity of the lithium secondary battery and improving the life characteristics.

[0171] On the other hand, it can be confirmed that in the positive electrode active material prepared in Comparative Example 1, single particles and secondary particles in which less than 10 uncrushed primary particles are aggregated are mixed, the R / L value according to Mathematical Formula 1 is greater than 2.0, and the calendering density and tap density of the positive electrode active material prepared in Comparative Example 1 are lower than those of the positive electrode active materials with the same composition prepared in Examples 1 and 3. In addition, it can be confirmed that the battery containing the positive electrode active material prepared in Comparative Example 1 has both a lower charging capacity and a lower capacity retention rate than the batteries containing the positive electrode active materials prepared in Examples 1 and 3.

[0172] In addition, it can be confirmed that in the positive electrode active material prepared in Comparative Example 2, single particles and secondary particles in which less than 10 uncrushed primary particles are aggregated are mixed, the R / L value according to Mathematical Formula 1 is greater than 2.0, and the calendering density and tap density of the positive electrode active material prepared in Comparative Example 2 are lower than those of the positive electrode active material with the same composition prepared in Example 2. In addition, it can be confirmed that the battery containing the positive electrode active material prepared in Comparative Example 2 has both a lower charging capacity and a lower capacity retention rate than the battery containing the positive electrode active material prepared in Example 2.

[0173] In addition, it can be confirmed that the positive electrode active material prepared in Comparative Example 3 has a large particle size, that is, there are many large powders, so the R / L value according to Mathematical Formula 1 is large, and the calendering density and tap density of the positive electrode active material prepared in Comparative Example 3 are lower than those of the positive electrode active materials with the same composition prepared in Examples 1 and 3. In addition, it can be confirmed that the battery containing the positive electrode active material prepared in Comparative Example 3 has a lower charging capacity and a lower capacity retention rate than the batteries containing the positive electrode active materials prepared in Examples 1 and 3.

Claims

1. A positive electrode active material, the positive electrode active material comprising a lithium composite transition metal oxide, the lithium composite transition metal oxide being in the form of single particles and comprising two or more selected from nickel, cobalt, and manganese, wherein the lithium composite transition metal oxide has a particle size distribution satisfying the following Mathematical Formula 1: [Mathematical Formula 1] 1.1 ≤ R / L < 2.0 Among them, In the above Mathematical Formula 1, R is the area formed by the particle size distribution curve on the right side and the x-axis, with the peak point having the maximum y value as a reference, in a particle size distribution curve where the x-axis is the particle diameter of the lithium composite transition metal oxide (unit: μm) and the y-axis is the volume percentage (unit: %), and L is the area formed by the x-axis and the particle size distribution curve on the left side, with the peak point having the maximum y value as a reference, in the particle size distribution curve.

2. The positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide is single particles or secondary particles in which at most 10 primary particles are aggregated.

3. The positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide contains 60 mol% or more of nickel among all metals other than lithium.

4. The positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide has a composition represented by the following Chemical Formula 1: [Chemical Formula 1] Li x Ni a Co b Mn c M 1 d O2 Among them, In the above Chemical Formula 1, M 1 is at least one selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, P, Y, Na, and Ca, and 0.9 ≤ x ≤ 1.3, 0.6 ≤ a < 1.0, 0 < b < 0.4, 0 < c < 0.4, 0 ≤ d ≤ 0.2 and a + b + c + d = 1.

5. The positive electrode active material according to claim 1, wherein the D of the lithium composite transition metal oxide 50 is from 5 μm to 15 μm.

6. The positive electrode active material according to claim 1, wherein the calendering density of the positive electrode active material is at least 3.55 g / cm 3 .

7. The positive electrode active material according to claim 1, wherein the tap density of the positive electrode active material is 2.40 g / cm 3 to 2.70 g / cm 3 .

8. A positive electrode, the positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material according to claim 1.

9. The positive electrode according to claim 8, wherein the porosity of the positive electrode active material layer is 16% by volume to 24% by volume.

10. A lithium secondary battery, the lithium secondary battery comprising: the positive electrode according to claim 8; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

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