Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material, which includes a lithium composite transition metal oxide in a single particle form containing two or more elements selected from nickel, cobalt, and manganese, and the lithium composite transition metal oxide has a particle size distribution that satisfies the following formula 1: JPEG2026500574000013.jpg71170 The mode is the particle size value when the y value is maximum on 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: %).

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0000404, filed January 2, 2023, and Korean Patent Application No. 10-2023-0192483, filed December 27, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

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

[0004] Previously, much research has been conducted into producing high-nickel cathode active materials in the form of secondary particles formed by agglomeration of spherical primary particles, and this research has focused on producing cathode active materials with uniform particle size (i.e., small particle size deviation). However, when the particle size of the cathode active material is uniform, the density of the cathode active material present in the cathode active material layer after pressure is applied to manufacture the cathode in the cathode manufacturing process is low, making it difficult to achieve high energy density.

[0005] Therefore, there is a need to develop a positive electrode active material that can achieve a high rolling density. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] KR2021-0070893 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the above problems, and aims to provide a positive electrode active material that is in a single particle form and is adjusted to have a specific particle size distribution, thereby achieving a high rolling density.

[0008] Another object of the present invention is to provide a positive electrode and a lithium secondary battery that contain the above positive electrode active material and thereby have a low porosity in the positive electrode active material layer. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a positive electrode active material, and a positive electrode and a lithium secondary battery containing the same.

[0010] (1) The present invention provides a positive electrode active material comprising a lithium composite transition metal oxide in the form of a single particle, which contains two or more elements selected from nickel, cobalt, and manganese, and the lithium composite transition metal oxide has a particle size distribution that satisfies the following formula 1:

number

number

[0011] (2) The present invention provides the positive electrode active material according to (1) above, wherein the skewness is 0.4 to 0.8.

[0012] (3) The present invention provides a positive electrode active material according to (1) or (2), wherein the mode is 3 to 10.

[0013] (4) The present invention provides a positive electrode active material according to any one of (1) to (3) above, wherein the lithium transition metal composite oxide is a single particle or a secondary particle formed by agglomerating 10 or less primary particles.

[0014] (5) The present invention provides a positive electrode active material according to any one of the above (1) to (4), wherein the lithium transition metal composite oxide contains nickel in an amount of 60 mol % or more of all metals other than lithium.

[0015] (6) The present invention provides a positive electrode active material according to any one of the above (1) to (5), 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 In the above Chemical Formula 1, M 1 is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, P, Y, Na, and Ca, 0.9≦x≦1.3, 0.6≦a<1.0, 0 <b<0.4、0<c<0.4、0≦d≦0.2、a+b+c+d=1である。

[0016] (7) In any one of the above (1) to (6), the present invention is characterized in that the lithium composite transition metal oxide is D 50 The positive electrode active material has a particle size of 4 μm to 10 μm.

[0017] (8) In any one of the above (1) to (7), the present invention is characterized in that the lithium composite transition metal oxide is D min The positive electrode active material has a particle size of 0.5 μm to 4 μm.

[0018] (9) In any one of the above (1) to (8), the present invention is characterized in that the lithium composite transition metal oxide is D 10 The positive electrode active material has a particle size of 1 μm to 7 μm.

[0019] (10) In any one of the above (1) to (9), the present invention is characterized in that the lithium composite transition metal oxide is D max The positive electrode active material has a particle size of 11 μm to 31 μm.

[0020] (11) The present invention provides a positive electrode active material according to any one of the above (1) to (10), wherein the lithium composite transition metal oxide has a standard deviation of particle size of 1 to 4.

[0021] (12) The present invention is directed to any one of the above (1) to (11), wherein the rolling density is 3.57 g / cm 3 The positive electrode active material described above is provided.

[0022] (13) The present invention is directed to any one of the above (1) to (12), wherein the tap density is 2.4 g / cm 3 ~2.7g / cm 3 The present invention provides a positive electrode active material in which

[0023] (14) The present invention provides a positive electrode comprising a current collector and a positive electrode active material layer formed on the current collector and containing the positive electrode active material according to any one of (1) to (13) above.

[0024] (15) The present invention provides a lithium secondary battery comprising the positive electrode according to (14) above, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0025] The positive electrode active material of the present invention is in the form of a single particle and satisfies the (skewness / (mode×3)) of 0.03 to 0.04 according to the above formula 1. When a positive electrode is produced using this material, the porosity of the positive electrode active material layer decreases when the same pressure is applied, and the contact area between the positive electrode active material and the conductive material increases. As a result, the charge capacity of the lithium secondary battery can be increased and the life characteristics can be improved. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a graph showing particle size distributions of positive electrode active materials prepared in Examples and Comparative Examples. [Figure 2] 1 is an SEM image of the positive electrode active material prepared in Example 1. [Figure 3] 1 is a SEM image of the positive electrode active material prepared in Example 2. [Figure 4] 1 is a SEM image of the positive electrode active material prepared in Example 3. [Figure 5] 1 is a SEM image of the positive electrode active material prepared in Comparative Example 1. [Figure 6] 1 is a SEM image of the positive electrode active material prepared in Comparative Example 2. [Figure 7] 1 is a SEM image of the positive electrode active material prepared in Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0028] The terms and words used in the description of the present invention and the claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best describe their inventions.

[0029] In the present invention, the term "primary particle" means the smallest particle unit that can be distinguished as a single mass when a cross section of a positive electrode active material is observed through a scanning electron microscope (SEM), and may consist of multiple crystal grains.

[0030] In the present invention, the term "secondary particles" refers to secondary structures formed by aggregation of more than 10 primary particles. The particle size of the secondary particles can be measured using a particle size analyzer.

[0031] In the present invention, the term "D 10"," "D 50 " and "D 90 " and " are the 10% points of the volume cumulative distribution by particle size (D 10 ), 50% point (D 50 ) and 90% point (D 90 ) means the particle size at 10 , D 50 and D 90 The powder to be measured is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer (e.g., S3500 manufactured by Microtrac). When the particles pass through a laser beam, the difference in the diffraction pattern due to particle size is measured, and the volume cumulative distribution by particle size is calculated. The particle diameters at the points of 10%, 50%, and 90% of the volume cumulative distribution by particle size in the measuring device are calculated, thereby obtaining the D 10 , D 50 and D 90 can be measured.

[0032] In the present invention, the term "single particle form" means that the positive electrode active material and / or lithium composite transition metal oxide particles are both single particles and particles in the form of an aggregation of 2 to 10 particles. That is, the positive electrode active material and / or lithium composite transition metal oxide in the form of a single particle of the present invention may include one or more types of positive electrode active material and / or lithium composite transition metal oxide particles selected from the group consisting of single particles and particles in the form of an aggregation of 2 to 10 particles.

[0033] positive electrode active material The present invention provides a positive electrode active material.

[0034] A positive electrode active material according to the present invention includes a lithium composite transition metal oxide in the form of a single particle, which includes two or more elements selected from nickel, cobalt, and manganese, and the lithium composite transition metal oxide has a particle size distribution that satisfies the following formula 1. The inventors of the present invention discovered that when the (skewness / (mode×3)) according to the following formula 1 is 0.03 to 0.04, the rolled density of the positive electrode active material is high, and thus an electrode with a high energy density can be realized, leading to the completion of the present invention. Specifically, the (skewness / (mode×3)) according to the following formula 1 may be 0.030 or more, 0.031 or more, 0.032 or more, or 0.033 or more, or may be 0.037 or less, 0.038 or less, 0.039 or less, or 0.040 or less.

[0035]

number

[0036] In the formula 1, The skewness is a value calculated by the following formula 2:

[0037]

number

[0038] The mode is the particle size value when the y value is maximum on 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: %).

[0039] On the other hand, when the skewness / (mode x 3) of the formula 1 is less than 0.03, the amount of small particles (fine powder) is small due to the uniform particle size, resulting in a low volume filling rate and a problem that a high rolling density cannot be achieved. On the other hand, when the skewness is more than 0.04, the proportion of small particles increases excessively, resulting in a problem that a high rolling density cannot be achieved.

[0040] For reference, when the (skewness / (mode×3)) in the above formula 1 is a negative number, the ratio of large particles (large powder) increases, which results in a problem that high rolling density cannot be achieved.

[0041] According to the present invention, the skewness is a measure statistically indicating the asymmetry of a specific distribution, and may be a value according to Pearson's second skewness coefficient (median skewness), and may be 0.4 to 0.8. Specifically, the skewness may be 0.40 or more, 0.43 or more, 0.46 or more, 0.49 or more, 0.52 or more, or 0.55 or more, or 0.59 or less, 0.62 or less, 0.65 or less, 0.68 or less, 0.71 or less, 0.74 or less, 0.77 or less, or 0.80 or less. In this case, a wide particle size distribution and high rolling density may be achieved.

[0042] According to the present invention, the mode is the particle size (unit: μm) value when the y value is maximum on the particle size distribution curve, and may be 3 to 10. Specifically, the mode may be 3.0 or more, 3.5 or more, 4.0 or more, 4.5 or more, or 5.0 or more, or 6.5 or less, 7.0 or less, 7.5 or less, 8.0 or less, 8.5 or less, 9.0 or less, 9.5 or less, or 10.0 or less. In this case, optimal particle size conditions are achieved that can increase the volume filling rate, and high rolling density can be achieved.

[0043] According to the present invention, the positive electrode active material may include a lithium composite transition metal oxide in a single particle form. Specifically, the lithium composite transition metal oxide in a single particle form may be a secondary particle formed by agglomeration of 10 or fewer primary particles. Conventional positive electrode active materials in the form of secondary particles formed by agglomeration of more than 10 primary particles require increased porosity to minimize cracks caused by pressure during rolling to manufacture an electrode, which ultimately reduces the energy density of the lithium secondary battery. However, the positive electrode active material of the present invention, which has the form of a single particle or secondary particles formed by agglomeration of 10 or fewer primary particles, can minimize cracks caused by volume changes within the unit cell during charge and discharge of the lithium secondary battery, and in particular, can minimize cracks caused by pressure during rolling to manufacture the electrode. Therefore, when using the positive electrode active material of the present invention, rolling to manufacture an electrode can be performed with a lower porosity, thereby improving the energy density of the lithium secondary battery.

[0044] According to the present invention, in order to improve capacity, the lithium composite transition metal oxide may contain nickel in an amount of 60 mol% or more, 70 mol% or more, 80 mol% or more, or 85 mol% or more of all metals other than lithium. That is, the lithium composite transition metal oxide may be a high-nickel lithium composite transition metal oxide that contains nickel and has a nickel (Ni) content of 60 mol% or more, 70 mol% or more, 80 mol% or more, or 85 mol% or more relative to all transition metals. In this case, a high nickel content can ensure high energy density.

[0045] According to the present invention, the lithium composite transition metal oxide may have a composition represented by the following Chemical Formula 1.

[0046] [Chemical formula 1] Li x Ni a Co b Mn c M 1 d O2

[0047] In the above Chemical Formula 1, M 1 is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, P, Y, Na, and Ca, 0.9≦x≦1.3, 0.6≦a<1.0, 0 <b<0.4、0<c<0.4、0≦d≦0.2、a+b+c+d=1である。

[0048] In the above Chemical Formula 1, M 1 may be a doping element that can be contained in the lithium composite transition metal oxide, and can be appropriately selected as necessary.

[0049] In Chemical Formula 1, x is the molar ratio of lithium to the transition metal in the lithium composite transition metal oxide, and may be 0.9 or more, 0.95 or more, or 1.0 or more, or may be 1.1 or less, 1.07 or less, 1.05 or less, or 1.03 or less.

[0050] In the formula 1, a, b, c, and d represent nickel (Ni), cobalt (Co), manganese (Mn), and a doping element (M 1)). As a specific example, a is the molar fraction of nickel (Ni) among the transition metals, and may 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 may be less than 1.0, 0.99 or less, 0.98 or less, 0.97 or less, or 0.96 or less. Furthermore, b is the molar fraction of cobalt (Co) among the transition metals, and may be greater than 0, 0.01 or more, 0.02 or more, or 0.03 or more, and may 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 c is the molar fraction of manganese (Mn) among the transition metals, and may be greater than 0, 0.01 or greater, or 0.05 or greater, or may 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 d is the molar fraction of manganese (Mn) among the transition metals. 1 ), and may 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. It may also 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.

[0051] According to the present invention, the lithium composite transition metal oxide is D 50 The D of the lithium composite transition metal oxide may be 4 μm to 10 μm. 50Specifically, the particle size may be 4.00 μm or more, 4.50 μm or more, or 5.00 μm or more, or 6.00 μm or less, 6.50 μm or less, 7.00 μm or less, 7.50 μm or less, 8.00 μm or less, 8.50 μm or less, 9.00 μm or less, 9.50 μm or less, or 10.00 μm or less. In this case, the particle size distribution can increase the volume filling rate, and the tap density can be high.

[0052] According to the present invention, the lithium composite transition metal oxide is D min The D of the lithium composite transition metal oxide may be 0.5 μm to 4 μm. min Specifically, the particle size may be 0.500 μm or more, 1.000 μm or more, or 1.500 μm or more, or 2.500 μm or less, 3.000 μm or less, 3.500 μm or less, or 4.000 μm or less. In this case, a certain amount of fine powder is present, which can increase the volume filling rate.

[0053] According to the present invention, the lithium composite transition metal oxide is D 10 The D of the lithium composite transition metal oxide may be 1 μm to 7 μm. 10 Specifically, the particle size may be 1.00 μm or more, 1.50 μm or more, 2.00 μm or more, 2.50 μm or more, or 3.00 μm or more, or 4.00 μm or less, 5.00 μm or less, 6.00 μm or less, or 7.00 μm or less. In this case, the small particles provide a good volume filling rate and a high rolling density.

[0054] According to the present invention, the lithium composite transition metal oxide is D max The D of the lithium composite transition metal oxide may be 11 μm to 31 μm. maxSpecifically, the diameter may be 11.00 μm or more, 12.00 μm or more, 13.00 μm or more, 14.00 μm or more, or 15.00 μm or more, or 19.00 μm or less, 20.00 μm or less, 21.00 μm or less, 24.00 μm or less, 27.00 μm or less, or 31.00 μm or less. In this case, there is no large powder, and high rolling density can be achieved.

[0055] According to the present invention, the lithium composite transition metal oxide may have a standard deviation of particle size of 1 to 4. Specifically, the standard deviation may be 1.000 or more, 1.100 or more, 1.200 or more, 1.300 or more, or 1.550 or more, or may be 2.000 or less, 3.000 or less, 3.300 or less, 3.600 or less, or 4.000 or less. In this case, a wide particle size distribution can be achieved, and the volume filling rate can be increased.

[0056] According to the present invention, the positive electrode active material has a rolling density of 3.570 g / cm 3 Specifically, the rolling density of the positive electrode active material may be 3.570 g / cm or more. 3 , 3.575g / cm 3 , 3.580g / cm 3 More than 3.585g / cm 3 More than 3.590g / cm 3 More than 3.595g / cm 3 or more than 3.600 g / cm 3 or more, 3.720 g / cm 3 Below, 3.730g / cm 3 Below, 3.740g / cm 3 or less, or 3.750 g / cm 3 In this case, even if the same force is applied in the rolling process of the electrode, the electrode has a low porosity, so that the energy density can be increased, and when rolling with a roll press in the electrode manufacturing process, the linear pressure applied to the electrode is lowered to show the same porosity, which has the advantage of improving processability.

[0057] The rolling density is calculated by the following formula 3 when a force corresponding to 9,000 kgf is applied to form pellets using an automatic pellet press.

[0058] Specifically, the rolling density is a value determined by the following (1) to (3).

[0059] (1) Using an automatic pellet press (Carver, 3887.4), a cylindrical mold was used to adjust the zero point for thickness against a circular pellet holder.

[0060] (2) Place the positive electrode active material in the circular pellet holder, apply a force equivalent to 9,000 kgf, and measure the thickness of the pellet.

[0061] (3) Calculate the pellet volume using the following formula 2, and calculate the rolling density using the following formula 3.

[0062] [Formula 2] Pellet volume (cm 3 ) = π (radius of circular pellet holder) 2 × Pellet thickness

[0063] [Formula 3] Rolling density (g / cm 3 ) = Weight of positive electrode active material (g) / Volume of pellet (cm 3 )

[0064] According to the present invention, the positive electrode active material has a tap density of 2.4 g / cm 3 ~2.7g / cm 3 The tap density of the positive electrode active material may be specifically 2.40 g / cm 3 More than 2.45g / cm 3 or more, or 2.50 g / cm 3 It may be 2.55 g / cm or more. 3 Below, 2.60g / cm 3 Below 2.65g / cm 3 or less, or 2.70 g / cm 3In this case, even if the same force is applied in the rolling process of the electrode, the electrode has a low porosity, so that the energy density can be increased, and when rolling with a roll press in the electrode manufacturing process, the linear pressure applied to the electrode is lowered to show the same porosity, which has the advantage of improving processability.

[0065] The tap density is an index that indicates how much of a positive electrode active material can be packed into one volume by tapping alone without applying any additional pressure. The tap density is calculated according to the following equation 4, in which a positive electrode active material is placed in a cylinder and tapped 1,800 times using a tap density meter (J. Engelsmann AG, Jolting Volumeter Type STAV II).

[0066] [Formula 4] Tap density (g / cm 3 ) = Weight (g) of positive electrode active material / Volume (cm 3 )

[0067] positive electrode The present invention provides a positive electrode containing the positive electrode active material.

[0068] According to the present invention, the positive electrode includes 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 includes the positive electrode active material according to the present invention.

[0069] According to the present invention, the positive electrode active material layer may have a porosity of 16 to 24% by volume to prevent excessive load from being applied to the roll during rolling with a roll press in the electrode manufacturing process and to prevent an effect on the thickness of the current collector. Specifically, the porosity of the positive electrode active material layer according to the present invention may be 16, 17, or 18% by volume or more, or 20, 21, 22, or 24% by volume or less. In this case, since the electrode has a high electrode density, the thickness of the electrode can be reduced, and the energy density per volume can be increased.

[0070] The positive electrode current collector may contain a highly conductive metal, and is not particularly limited as long as it is easily adhered to the positive electrode active material layer and is non-reactive within the battery voltage range. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel whose surfaces are surface-treated with carbon, nickel, titanium, silver, or the like. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0071] The positive electrode active material layer may optionally contain a conductive material and a binder in addition to the positive electrode active material. The positive electrode active material may be contained in an amount of 80 to 99 wt %, more specifically 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited within this range.

[0072] The conductive material is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations, as long as it does not cause chemical changes in the resulting battery and has electronic conductivity. 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 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; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material can be present in an amount of 0.1 wt % to 15 wt % based on the total weight of the positive electrode active material layer.

[0073] The binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples of the binder include 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 polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof. These may be used alone or in combination. The binder may be contained in an amount of 0.1% by weight to 15% by weight based on the total weight of the positive electrode active material layer.

[0074] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, which is prepared by dissolving or dispersing the positive electrode active material and, optionally, a binder, a conductive material, and a dispersant in a solvent, 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, peeling it off from the support, and laminating the resulting film onto a positive electrode current collector.

[0075] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and may be used alone or in combination. The amount of solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for manufacturing a positive electrode.

[0076] Lithium secondary battery The present invention provides a lithium secondary battery including the positive electrode.

[0077] According to the present invention, the lithium secondary battery includes the positive electrode, the negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. 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.

[0078] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0079] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector can be formed with fine irregularities to enhance the binding strength of the negative electrode active material. Various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics, can be used.

[0080] The negative electrode active material layer may optionally contain a binder and a conductive material in addition to the negative electrode active material.

[0081] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. 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 alloys, Sn alloys, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); and composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. These may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Representative examples of low-crystalline carbon include soft carbon and hard carbon, while representative examples of high-crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-sintered carbon such as petroleum or coal tar pitch-derived cokes. The negative electrode active material may be included in an amount of 80 wt% to 99 wt% of the total weight of the negative electrode active material layer.

[0082] The binder in the negative electrode active material layer is a component that helps bind the conductive material, active material, and current collector together, and is typically added in an amount of 0.1 to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0083] According to one embodiment of the present invention, the conductive material in 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 does not cause chemical changes in the battery and is conductive. Examples of such conductive materials include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0084] The negative electrode can be manufactured by applying a composition for forming a negative electrode active material layer, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, onto a negative electrode current collector and drying the applied composition. Alternatively, the negative electrode can be manufactured by casting the composition for forming a negative electrode active material layer onto a separate support, peeling it off from the support, and laminating the resulting film onto the negative electrode current collector.

[0085] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in lithium secondary batteries can be used without particular limitations. In particular, a separator with low resistance to electrolyte ion movement and excellent electrolyte impregnation capacity is preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and it can be selectively used in a single-layer or multi-layer structure.

[0086] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. Specific examples of the electrolyte include an organic solvent and a lithium salt.

[0087] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0088] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the anion of the lithium salt can be 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 - The lithium salt may be at least one selected from the group consisting of: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1M to 2.0M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0089] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcohol amine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. Here, the additives may be contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0090] A lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent capacity characteristics and life characteristics, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0091] The shape of the lithium secondary battery is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0092] The lithium secondary battery can be used as a battery cell used as a power source for small devices, and can also be preferably used as a unit battery in a medium- to large-sized battery module containing a large number of battery cells.

[0093] As a result, a battery module including the lithium secondary battery according to the present invention as a unit cell and a battery pack including the same can be provided.

[0094] 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.

[0095] While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms without departing from the spirit or scope of the present invention.

[0096] Examples and Comparative Examples Example 1 Ni 0.96 Co 0.03 Mn 0.01 Complex transition metal hydroxide (D 50 The mixture was mixed with LiOH so that the molar ratio of Li / Metal (Ni+Co+Mn) was 1.02, and the mixture was fired in an oxygen atmosphere at 830°C for 12 hours. The mixture was then pulverized using a jet mill to have the particle size distribution shown in Figure 1, and fired in an oxygen atmosphere at 770°C for 12 hours to produce LiNi 0.96 Co 0.03 Mn 0.01 A lithium transition metal composite oxide (positive electrode active material) in the form of a single particle having a composition represented by O2 was prepared.

[0097] Example 2 Ni 0.89 Co 0.03 Mn 0.08 Complex transition metal hydroxide (D 50The mixture was mixed with LiOH so that the molar ratio of Li / Metal (Ni+Co+Mn) was 1.05, and the mixture was fired in an oxygen atmosphere at 900°C for 9 hours. The mixture was then pulverized using a jet mill to have the particle size distribution shown in Figure 1, and fired in an oxygen atmosphere at 800°C for 12 hours to produce LiNi 0.89 Co 0.03 Mn 0.08 A lithium transition metal composite oxide (positive electrode active material) in the form of a single particle having a composition represented by O2 was prepared.

[0098] Example 3 Ni 0.96 Co 0.03 Mn 0.01 Complex transition metal hydroxide (D 50 The LiNi alloy was mixed with LiOH to a molar ratio of 1.02 (Li / Metal (Ni+Co+Mn): 6.3 μm). The mixture was subjected to primary firing at 830°C for 12 hours in an oxygen atmosphere, and then crushed using a jet mill to obtain the particle size distribution shown in Figure 1. The mixture was then subjected to secondary firing at 770°C for 12 hours in an oxygen atmosphere to obtain LiNi 0.96 Co 0.03 Mn 0.01 A lithium transition metal composite oxide (positive electrode active material) in the form of a single particle having a composition represented by O2 was prepared.

[0099] Comparative Example 1 In Example 1, Ni 0.96 Co 0.03 Mn 0.01 Complex transition metal hydroxide (D 50 :7μm) instead of Ni 0.96 Co 0.03 Mn 0.01 Complex transition metal hydroxide (D 50 The same procedure as in Example 1 was carried out except that LiNi 0.96 Co 0.03 Mn 0.01 A lithium transition metal composite oxide (positive electrode active material) having a composition represented by O2 was produced.

[0100] Comparative Example 2 The same procedure as in Example 2 was carried out, except that the primary firing was carried out in an oxygen atmosphere at 865°C for 12 hours. 0.89 Co 0.03 Mn 0.08 A lithium transition metal composite oxide (positive electrode active material) having a composition represented by O2 was produced.

[0101] Comparative Example 3 The same procedure as in Example 1 was carried out, except that the primary firing was carried out in an oxygen atmosphere at 800°C for 12 hours. 0.96 Co 0.03 Mn 0.01 A lithium transition metal composite oxide (positive electrode active material) having a composition represented by O2 was produced.

[0102] Experimental example Experimental example 1: SEM image capture The positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 3 were photographed using a scanning electron microscope (SEM, Inspect F, manufactured by FEI), and the photographs are shown in FIGS. 2 to 7, respectively.

[0103] Experimental Example 2: Analysis of particle size and particle size distribution curve The positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to a particle size analyzer (PSD, manufactured by Microtrac, S3500) to measure D min , D 10 , D 50 , and D max The values ​​were measured and shown in Table 1 below, and a particle size distribution curve, with the particle size (unit: μm) of the lithium composite transition metal oxide on the x-axis and the volume percentage (unit: %) on the y-axis, is shown in Figure 1. In addition, (skewness / (mode x 3)) was calculated using the following equation 1 and shown in Table 1 below.

[0104]

number

[0105] In the formula 1, The skewness is a value calculated by the following formula 2:

[0106]

number

[0107] The mode is the particle size value when the y value is maximum on 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: %).

[0108] [Table 1]

[0109] As shown in Table 1, it was confirmed that the positive electrode active materials prepared in Examples 1 to 3 had a (skewness / (mode×3)) value according to Equation 1 of 0.03 to 0.04.

[0110] Experimental Example 3: Evaluation of rolled density and tapped density - Rolling density Using an automatic pellet press (Carver, 3887.4), a cylindrical mold was placed on a circular pellet holder with a diameter of 13 mm to adjust the zero point for thickness. Then, 3 g of each of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was placed in the circular pellet holder, and a force equivalent to 9,000 kgf was applied to measure the thickness of the formed pellets. The pellet volume was then calculated using Equation 2 below, and the rolling density was calculated using Equation 3 below. The results are shown in Table 2 below.

[0111] [Formula 2] Pellet volume (cm 3 ) = π (radius of circular pellet holder) 2 × Pellet thickness

[0112] [Formula 3] Rolling density (g / cm 3 ) = Weight of positive electrode active material (g) / Volume of pellet (cm3 )

[0113] -Tap density Using a tap density meter (J. Engelsmann AG, Jolt Volumeter Type STAV II), 50 g of each of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was placed in a 100 ml cylinder and tapped 1,800 times to measure the output volume. The tap density was calculated using the following equation 4 and is shown in Table 2 below.

[0114] [Formula 4] Tap density (g / cm 3 ) = Weight (g) of positive electrode active material / Volume (cm 3 )

[0115] [Table 2]

[0116] As shown in Table 2, the positive electrode active materials prepared in Examples 1 to 3 had a rolling density of 3.57 g / cm according to Equation 3. 3 or more, and the tap density is 2.40 g / cm 3 I was able to confirm that this was the case.

[0117] Experimental Example 4: Evaluation of charge capacity and life characteristics Lithium secondary batteries were manufactured using the positive electrode active materials manufactured in the examples and comparative examples, and the charge capacity and life characteristics of each lithium secondary battery were evaluated.

[0118] Specifically, the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were mixed with FX35 conductive material, KF9709 binder, and BM740H binder in a weight ratio of 95:2:3:0.15 in NMP solvent to prepare positive electrode slurries. The positive electrode slurries were applied to one side of an aluminum current collector, dried at 130°C, and rolled to achieve a positive electrode active material layer porosity of 20% by volume. Meanwhile, Li metal disks were used as the negative electrode active material. An electrode assembly was fabricated by interposing a separator between the positive and negative electrodes, and then the assembly was placed inside a battery case. An electrolyte was then injected into the case to fabricate a lithium secondary battery. The electrolyte was prepared by dissolving 1M LiPF6 in an EC / EMC / DMC (3 / 3 / 4, vol%) organic solvent.

[0119] The lithium secondary battery prepared as described above was charged in CC / CV mode at 25°C at a constant current of 0.1 C up to 4.25 V (cut-off current 0.05 C) and then discharged in CC mode down to 3.0 V, and the charge capacity was measured and shown in Table 3 below. Here, 1 C was set to 200 mA / g.

[0120] In addition, the lithium secondary battery prepared as described above was charged in CC / CV mode at 45°C with a constant current of 0.5C up to 4.25V, and then discharged in CC mode down to 2.5V (cut-off current: 0.05C). This was defined as one cycle, and 50 cycles were repeated. The capacity retention was calculated as the percentage of the discharge capacity at the 50th cycle relative to the discharge capacity at the first cycle, and is shown in Table 3 below.

[0121] [Table 3]

[0122] 2 to 7, it was confirmed that the positive electrode active materials prepared in Examples 1 to 3 were in the form of single particles by adjusting the firing temperature and particle size distribution, and that the (skewness / (mode×3)) according to Equation 1 was adjusted to 0.03 to 0.04. In addition, the positive electrode active materials prepared in Examples 1 to 3 had a rolling density according to Equation 3 of 3.57 g / cm. 3 or more, and the tap density is 2.40 g / cm 3 It was confirmed that the above results were obtained. From these results, it was confirmed that when a positive electrode is manufactured using the positive electrode active material according to the present invention, the porosity of the positive electrode active material layer is reduced, and the contact area between the positive electrode active material and the conductive material is increased, thereby increasing the charge capacity of the lithium secondary battery and improving its life characteristics. Specifically, it was confirmed that the batteries containing the positive electrode active materials of Examples 1 and 3 have a more improved charge capacity than the batteries containing the positive electrode active materials of Comparative Examples 1 and 3 having the same composition, and the batteries containing the positive electrode active material of Example 2 have a more improved charge capacity than the batteries containing the positive electrode active material of Comparative Example 2 having the same composition. It was also confirmed that the batteries containing the positive electrode active materials of Examples 1 to 3 have a significantly improved capacity retention rate than the batteries containing the positive electrode active materials of Comparative Examples 1 to 3.

[0123] For reference, the positive electrode active materials of Comparative Examples 1 and 2, in which the (skewness / (mode × 3)) according to the above formula 1 exceeds 0.04, do not have a high rolling density due to an excessive increase in the proportion of fine powder, and it is believed that the performance of batteries containing these materials is poor.

Claims

1. The lithium composite transition metal oxide includes a single particle form containing two or more selected from nickel, cobalt, and manganese, The lithium composite transition metal oxide has a particle size distribution that satisfies the following formula 1: [Equation 1] In the formula 1, The skewness is a value calculated by the following formula 2: [Equation 2] The mode is the particle size value when the y value is maximum on 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: %).

2. 2. The positive electrode active material according to claim 1, wherein the skewness is 0.4 to 0.

8.

3. 2. The positive electrode active material according to claim 1, wherein the mode is 3 to 10.

4. The positive electrode active material according to claim 1 , wherein the lithium composite transition metal oxide is a single particle or a secondary particle formed by agglomeration of 10 or less primary particles.

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

6. 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 O ２ In the above Chemical Formula 1, M １ is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, P, Y, Na, and Ca, 0.9≦x≦1.3, 0.6≦a<1.0, 0<b<0.4, 0<c<0.4, 0≦d≦0.2, a+b+c+d=1.

7. The lithium composite transition metal oxide is D ５０ The positive electrode active material according to claim 1, wherein the average particle size is 4 μm to 10 μm.

8. The lithium composite transition metal oxide is D ｍｉｎ The positive electrode active material according to claim 1, wherein the average particle size is 0.5 μm to 4 μm.

9. The lithium composite transition metal oxide is D １０ The positive electrode active material according to claim 1, wherein the average particle size is 1 μm to 7 μm.

10. The lithium composite transition metal oxide is D ｍａｘ The positive electrode active material according to claim 1, wherein the average particle size is 11 μm to 31 μm.

11. 2. The positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide has a particle size standard deviation of 1 to 4.

12. Rolled density is 3.57 g / cm ３ The positive electrode active material according to claim 1 .

13. Tap density is 2.4 g / cm ３ ~2.7g / cm ３ The positive electrode active material according to claim 1 ,

14. a positive electrode current collector; a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material according to claim 1 .

15. The positive electrode according to claim 14; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

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