Positive electrode active material layer composition, positive electrode and secondary battery including same

Abstract

Provided is a positive electrode active material layer composition comprising a positive electrode active material and a conductive material, wherein the conductive material includes carbon nanotubes, and the ratio (D50 / d50) of the volume cumulative 50% particle diameter (D50) of the positive electrode active material to the volume cumulative 50% particle diameter (d50) of the carbon nanotubes satisfies expression 1 below. <Expression 1> 2.0≤D50 / d50≤2.5

Description

Cathode active material layer composition, cathode, and secondary battery including the same

[0001] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2024-0081414, dated June 21, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material layer composition, a positive electrode, and a secondary battery including the same.

[0003] Secondary battery electrodes are manufactured by coating an active material on the surface of a metal electrode current collector. The electrode current collector may be, for example, a metal foil made of aluminum or copper, and the active material is coated in slurry form on one or both sides of the electrode current collector. Carbon nanotubes, which have high electrical conductivity, are increasingly being used as conductive materials for batteries.

[0004] An object of the present invention is to provide a positive electrode active material layer composition to which specific conditions are applied according to the correlation between the particle size of the positive electrode active material and the particle size of the conductive material, which affect the improvement of electrode resistance and electronic performance.

[0005] The purpose of the present invention is to provide a positive electrode active material layer composition in which the content of a conductive material is applied based on the correlation between the particle size of the positive electrode active material and the particle size of the conductive material.

[0006] The objectives of the present invention are not limited to those mentioned above. Other objectives and advantages of the present invention not mentioned above can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the objectives and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0007] In one embodiment of the present invention, a positive electrode active material layer composition is provided, which includes a positive electrode active material and a conductive material, wherein the conductive material includes carbon nanotubes, and wherein a ratio of a volume cumulative 50% particle size (D50) of the positive electrode active material to a volume cumulative 50% particle size (d50) of the carbon nanotubes (D50 / d50) satisfies the following equation 1.

[0008] <Formula 1>

[0009] 2.0 ≤ D50 / d50 ≤ 2.5

[0010] The cumulative 50% volume particle diameter (D50) of the positive electrode active material may be 7 µm to 8 µm, and the cumulative 50% volume particle diameter (d50) of the carbon nanotube may be 2.5 µm to 4.0 µm.

[0011] The above-mentioned positive electrode active material may have a composition having a bimodal particle size distribution showing two peaks at particle sizes of 3 µm to 5 µm and 10 µm to 12 µm.

[0012] The mass ratio of the positive electrode active material and the carbon nanotube may be a value according to a formula for calculating the percolation threshold using the ratio (D50 / d50).

[0013] The mass of the carbon nanotube may be 0.70 to 0.75 wt% among 100 wt% of the sum of the mass of the positive electrode active material and the carbon nanotube.

[0014] The above positive electrode active material may be a lithium composite transition metal compound represented by the following chemical formula 1.

[0015] [Chemical Formula 1]

[0016] Li a Ni (1-x-y) Co x M1 y M2 w O2

[0017] In the above chemical formula 1,

[0018] 1.0≤a≤1.5, 0 <x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0<x+y≤0.2 이고,

[0019] M1 is at least one metal among Mn and Al,

[0020] M2 is at least one metallic element selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

[0021] The above carbon nanotube may include at least one selected from the group consisting of single-walled carbon nanotubes, multi-walled carbon nanotubes, bundled carbon nanotubes, and combinations thereof.

[0022] In one embodiment of the present invention, a positive electrode for a secondary battery is provided, including: a current collector; and a positive electrode active material layer provided on the current collector and including the positive electrode active material layer composition.

[0023] The positive electrode active material layer may include 80 to 99 wt% of the positive electrode active material based on the total weight of the positive electrode active material layer.

[0024] In one embodiment of the present invention, a secondary battery including the positive electrode, negative electrode, and separator is provided.

[0025] The positive electrode active material layer composition according to one embodiment of the present invention can reduce the electrode resistance of a secondary battery using the positive electrode active material layer manufactured therefrom.

[0026] A positive electrode active material layer composition according to one embodiment of the present invention improves the life characteristics of a secondary battery using a positive electrode active material layer manufactured therefrom.

[0027] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0028] Figure 1 is a graph showing the relationship between the particle size ratio of the positive active material and the conductive material and the electrochemical performance in battery cells manufactured in examples and comparative examples.

[0029] Figure 2 is a graph showing the relationship between the relative content of the conductive material and the electrochemical performance in battery cells manufactured in examples and comparative examples.

[0030] Figure 3 is a graph showing the relationship between the particle size ratio of the positive electrode active material and the conductive material and the relative content of the conductive material in battery cells manufactured in examples and comparative examples.

[0031] Figure 4 is a perspective view of a battery can that can be applied to the battery cell of the embodiment.

[0032] Figures 5 and 6 are perspective views showing the states before and after lamination of the first electrode, the second electrode, and the separator for manufacturing an electrode assembly to be accommodated in a battery can, respectively, and Figure 7 is a plan view of the lamination state of Figure 6.

[0033] FIG. 8 and FIG. 9 are perspective and side views of an electrode assembly manufactured by winding the laminate of FIG. 6 and FIG. 7 into a jelly-roll shape.

[0034] Figures 10 and 11 are perspective views showing a state in which a current collector plate is attached to the upper portion of the electrode assembly and no current collector plate is attached to the lower portion.

[0035] Fig. 12 is a cross-sectional view showing the process of accommodating the electrode assembly of Figs. 10 and 11 into a battery can.

[0036] Figure 13 is a cross-sectional view showing the process of welding the first electrode terminal and the current collector plate.

[0037] Figure 14 is a drawing showing the process of pressing a cap into a battery can.

[0038] Figure 15 is a cross-sectional view showing a state in which the electrode connection part of the cap is joined to the tab of the second electrode of the electrode assembly and the mating surface of the cap is joined to the mating wall surface of the battery can.

[0039] The above-described objects, features, and advantages will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily practice the technical idea of ​​the present invention. In describing the present invention, if it is determined that a detailed description of known technologies related to the present invention may unnecessarily obscure the gist of the present invention, a detailed description thereof will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0040] Hereinafter, the phrase "any configuration is placed on (or below)" a component or "on (or below)" a component may mean that any configuration is placed in contact with the upper surface (or lower surface) of said component, and that other configurations may be interposed between said component and any configuration placed on (or below) said component.

[0041] Additionally, when it is described that a component is "connected," "coupled," or "connected" to another component, it should be understood that the components may be directly connected or connected to one another, but that other components may also be "interposed" between the components, or that each component may be "connected," "coupled," or "connected" through another component.

[0042]

[0043] In one embodiment of the present invention, a positive electrode active material layer composition is provided, which includes a positive electrode active material and a conductive material, wherein the conductive material includes carbon nanotubes, and wherein a ratio of a volume cumulative 50% particle size (D50) of the positive electrode active material to a volume cumulative 50% particle size (d50) of the carbon nanotubes (D50 / d50) satisfies the following equation 1.

[0044] <Formula 1>

[0045] 2.0 ≤ D50 / d50 ≤ 2.5

[0046] Dispersing carbon nanotubes using ultrasound, a mill, or a high-pressure homogenizer changes the particle size of the carbon nanotubes, which in turn changes the electrode properties. Therefore, since the particle size of carbon nanotubes is related to electrode properties, it is necessary to control the particle size of the carbon nanotubes to an appropriate level in order to ensure good adhesion to the surface of the electrode active material and improve resistance and battery performance.

[0047] A secondary battery including a positive electrode that applies a positive electrode active material layer composition having particle size conditions satisfying the above formula 1 has improved electrode resistance and electronic performance.

[0048] In this specification, "D50" and "d50" are particle size values ​​defined in the volume cumulative distribution of powder measured using the laser diffraction method. Specifically, D50 is the particle diameter when the volume cumulative amount of the positive electrode active material is 50%, and d50 is the particle diameter when the volume cumulative amount of the carbon nanotube is 50%. For example, the particle size value of the volume cumulative distribution can be measured by dispersing the positive electrode active material powder or the carbon nanotube powder in a dispersion medium such as ethanol, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, and then obtaining a volume cumulative particle size distribution graph.

[0049] The above positive electrode active material may include a single-crystal lithium composite metal oxide, a polycrystalline lithium composite metal oxide, or a combination of at least one thereof.

[0050] In this specification, a single cystal particle refers to a particle in which the crystal lattice structure is regularly maintained throughout the particle, and includes a single particle, i.e., a primary particle in which the particles are separated and / or dispersed in an independent phase without being mutually aggregated in morphology, or a secondary particle in which 2 to 10 such primary particles are aggregated.

[0051] In this specification, polycrystal means a secondary particle formed by agglomeration of multiple primary particles.

[0052] In this specification, 'particle' may mean both primary and secondary particles, unless otherwise defined, without distinction.

[0053] In one embodiment, the positive electrode active material may have a composition having a bimodal particle size distribution (or bimodal particle size distribution) that exhibits two peaks at particle sizes of 3 μm to 5 μm and 10 μm to 12 μm. For example, when the positive electrode active material is a mixture of a single-crystal lithium composite metal oxide and a polycrystalline lithium composite metal oxide, a bimodal distribution is exhibited as the peak appearing in the particle size distribution of only the single-crystal lithium composite metal oxide and the peak appearing in the particle size distribution of only the polycrystalline lithium composite metal oxide are combined. By using a positive electrode active material having a bimodal particle size distribution in the above numerical range to satisfy Equation 1, the electrode resistance and electronic performance of a secondary battery to which the same is applied can be improved.

[0054] In one embodiment, the positive electrode active material may have a volume cumulative 50% particle size (D50) of 7 μm to 8 μm. The volume cumulative 50% particle size (D50) of the positive electrode active material is a value measured for the entire mixture when the positive electrode active material is a mixture of a single-crystal lithium composite metal oxide and a polycrystalline lithium composite metal oxide. By satisfying Equation 1 with a positive electrode active material having a volume cumulative 50% particle size (D50) within the above numerical range, the electrode resistance and electronic performance of a secondary battery to which the positive electrode active material is applied can be improved.

[0055] In one embodiment, the positive electrode active material may be a lithium composite transition metal compound represented by the following chemical formula 1.

[0056] [Chemical Formula 1]

[0057] Li a Ni (1-x-y) Co x M1 y M2 w O2

[0058] In the above chemical formula 1,

[0059] 1.0≤a≤1.5, 0 <x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0<x+y≤0.2 이고,

[0060] M1 is at least one metal among Mn and Al,

[0061] M2 is at least one metallic element selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

[0062] The carbon nanotube included as the above-mentioned conductive material may include, for example, at least one selected from the group consisting of single-walled carbon nanotubes, multi-walled carbon nanotubes, bundled carbon nanotubes, and combinations thereof.

[0063] In one embodiment, the cumulative 50% volume diameter (d50) of the carbon nanotubes may be 2.5 μm to 4.0 μm. By satisfying Equation 1 with carbon nanotubes having a cumulative 50% volume diameter (d50) within the above numerical range, the electrode resistance and electronic performance of a secondary battery to which the carbon nanotubes are applied can be improved.

[0064] In one embodiment, the mass ratio of the positive electrode active material and the carbon nanotube, which is the conductive material, may be a value obtained by applying the ratio (D50 / d50) to a formula for calculating a percolation threshold (X). That is, the mass ratio of the positive electrode active material and the carbon nanotube may be a value obtained by applying the ratio (D50 / d50) to a formula for calculating a percolation threshold.

[0065] The content of the above conductive material can be implemented at an optimal ratio with respect to the positive electrode active material within a limited space of a secondary battery to optimize battery performance. By obtaining the content of the above conductive material by applying the content according to the percolation threshold (X) calculation of the particle size range of the positive electrode active material and carbon nanotube according to Equation 1, a secondary battery applying the content ratio of the positive electrode active material and conductive material at the corresponding ratio can exhibit excellent battery performance.

[0066] When the conductive material surrounds the active material, and a critical point is reached where a conductive path through which electricity can flow is formed, electricity begins to flow. In other words, the volume required for the conductive material to completely percolate between the active materials is calculated as the percolation threshold (X). For example, when the conductive material particle size is constant, the volume of the conductive material required for percolation increases as the particle size of the active material increases. In this way, the percolation threshold (X) is calculated using the particle sizes of the active material and the conductive material as variables, and the relative content of the conductive material to the active material is derived from the calculated X value.

[0067]

[0068] Specifically, the percolation threshold (X) is calculated by the following calculation formula 1, and the mass a of the carbon nanotube and the mass b of the positive electrode active material are obtained.

[0069]

[0070] <Calculation Formula 1>

[0071] Y = -0.0981 × D50 / d50 + 1.0509

[0072] X = 0.02077 × Y

[0073] a = X × (the true density of the above carbon nanotube)

[0074] b = (1-X) × (density of the positive electrode active material)

[0075] a is the mass of the carbon nanotube, and b is the mass of the positive electrode active material.

[0076]

[0077] If the D50 / d50 value in the above calculation formula 1 is adjusted to satisfy formula 1, the Y value is determined, and from this, the percolation threshold value X is calculated, and a and b can be determined. From the calculated values ​​of a and b, a / (a+b) can be obtained to calculate the mass ratio of the carbon nanotube to the positive electrode active material.

[0078] When the numerical range of the above equation 1 is within the above equation 1, the mass ratio of the above carbon nanotube to the above cathode active material satisfies the range of the following equation 2.

[0079] <Formula 2>

[0080] 0.007 ≤ a / (a+b) ≤ 0.0075

[0081]

[0082] In one embodiment, the mass of the carbon nanotubes may be 0.70 to 0.75 wt% among the sum of 100 wt% of the mass of the positive electrode active material and the carbon nanotubes. When the conductive material contains only the carbon nanotubes, the content ratio of the carbon nanotubes ultimately corresponds to the content of the conductive material.

[0083] In one embodiment, the conductive material may include only the carbon nanotubes without further including any other conductive material other than the carbon nanotubes.

[0084] In one embodiment, the conductive material may further include a conductive material other than the carbon nanotubes. The conductive material other than the carbon nanotubes may be a known material that does not cause a chemical change within the battery and has electronic conductivity, and may include, for example, 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives.

[0085]

[0086] The above-mentioned positive electrode active material layer composition may further include known components in addition to the positive electrode active material and the conductive material.

[0087] For example, the positive electrode active material layer composition may further include a binder. The binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof, but is not limited thereto.

[0088] The above-mentioned positive electrode active material layer composition may further include known additives depending on the function to be imparted.

[0089] In one embodiment, the positive electrode active material layer formed of the positive electrode active material layer composition may include 80 to 99 wt% of the positive electrode active material, for example, 85 to 99 wt%, or for another example, 90 to 99 wt%, based on the total weight of the positive electrode active material layer.

[0090] The positive electrode active material layer formed with the above positive electrode active material layer composition may include the carbon nanotubes as a conductive material in a content ratio that satisfies the above formula 2 with respect to the content of the positive electrode active material included.

[0091]

[0092] In one embodiment of the present invention, a positive electrode for a secondary battery is provided, including: a current collector; and a positive electrode active material layer provided on the current collector and including the positive electrode active material layer composition.

[0093] The above positive electrode active material layer can be formed on one or both sides of the current collector.

[0094] The current collector included in the positive electrode is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 1 to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. In one embodiment, the current collector may be a metal foil.

[0095] The above-described positive electrode active material layer can be manufactured from the above-described positive electrode active material layer composition. Accordingly, the positive electrode active material and the carbon nanotubes as the conductive material included in the positive electrode active material layer satisfy the particle size conditions of the above-described Equation 1, and also satisfy the content ratio of Equation 2. A detailed description of the positive electrode active material and the carbon nanotubes as the conductive material is as described above.

[0096] In one embodiment, the positive electrode active material layer may include 80 to 99 wt% of the positive electrode active material, for example, 85 to 99 wt%, or for another example, 90 to 99 wt%, based on the total weight of the positive electrode active material layer.

[0097]

[0098] In one embodiment of the present invention, a secondary battery including the positive electrode, negative electrode, and separator is provided.

[0099] The above negative electrode may include a current collector and a negative electrode active material layer formed on one or both sides of the current collector. The negative electrode active material layer may include a negative electrode active material, a conductive material, and a binder.

[0100] The current collector included in the negative electrode is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. For example, a transition metal that adsorbs carbon well, such as copper or nickel, can be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but is not limited thereto.

[0101] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. The negative electrode active material may be, for example, a carbon-based negative electrode active material such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, etc.; Si, Si-Me alloy (Me includes at least one selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiO y (0 <y<2), Si-C 복합체 등과 같은 실리콘계 음극 활물질; 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다.

[0102] The above positive electrode and the negative electrode can be manufactured according to a conventional method for manufacturing positive electrodes and negative electrodes, except that the positive electrode is manufactured by including the positive electrode active material layer composition described above and the positive electrode active material layer formed using the same. Specifically, the positive electrode active material composition can be manufactured by applying the positive electrode active material composition onto a current collector, followed by drying and rolling. The negative electrode active material layer can also be manufactured by applying the negative electrode active material layer composition including the negative electrode active material, the conductive material, and the binder onto a current collector, followed by drying and rolling.

[0103] As the solvent used in the positive electrode active material layer composition and the negative electrode active material layer composition, a known solvent may be used, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water. One of these may be used alone or as a mixture of two or more. The amount of the solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the composition, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode and the negative electrode. Alternatively, the positive electrode and the negative electrode may be manufactured by casting the active material layer composition on a separate support, and then laminating the film obtained by peeling it from the support on a current collector.

[0104]

[0105] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any known separator material can be used. For example, a material having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity can be selected. For example, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof can be used. As another example, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can be used. As another example, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0106] Examples of the above electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes.

[0107] In one embodiment, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0108]

[0109] Referring to FIGS. 4 to 15 below, the structure of a cylindrical battery cell according to an embodiment of the present invention will be described.

[0110] The battery cell of the embodiment may be, for example, a cylindrical battery cell having a form factor ratio (defined as the ratio of the diameter (Φ) to the height (H) of the cylindrical battery cell) of greater than about 0.4.

[0111] Here, the form factor refers to a value indicating the diameter and height of a cylindrical battery cell. Cylindrical battery cells applicable to a pressure tester may be, for example, 46110 cells, 48750 cells, 48110 cells, 48800 cells, and 46800 cells. In the numerical value indicating the form factor, the first two numbers indicate the diameter of the cell, the next two numbers indicate the height of the cell, and the final number 0 indicates that the cross-section of the cell is circular.

[0112] The battery cell to be applied to the pressure tester may be a cylindrical battery cell having a roughly cylindrical shape, a diameter of approximately 46 mm, a height of approximately 110 mm, and a form factor ratio of 0.418.

[0113] According to another embodiment, a battery cell may be a cylindrical battery cell having a generally cylindrical shape, a diameter of approximately 48 mm, a height of approximately 75 mm, and a form factor ratio of 0.640.

[0114] According to another embodiment, a battery cell may be a cylindrical battery cell having a generally cylindrical shape, a diameter of approximately 48 mm, a height of approximately 110 mm, and a form factor ratio of 0.418.

[0115] According to another embodiment, a battery cell may be a cylindrical battery cell having a generally cylindrical shape, a diameter of approximately 48 mm, a height of approximately 80 mm, and a form factor ratio of 0.600.

[0116] According to another embodiment, a battery cell may be a cylindrical battery cell having a generally cylindrical shape, a diameter of approximately 46 mm, a height of approximately 80 mm, and a form factor ratio of 0.575.

[0117] The pressure tester of the present invention can of course be applied to battery cells having a form factor ratio of approximately 0.4 or less, such as 18650 cells, 21700 cells, etc. For 18650 cells, the diameter is approximately 18 mm, the height is approximately 65 mm, and the form factor ratio is 0.277. For 21700 cells, the diameter is approximately 21 mm, the height is approximately 70 mm, and the form factor ratio is 0.300.

[0118] Referring to FIG. 4 and FIG. 12, the battery can (10) includes a cylindrical side wall portion (11) and a bottom portion (12) connected to one axial end of the side wall portion (11).

[0119] The above-mentioned bottom portion (12) and side wall portion (11) can be manufactured by forming a metal sheet with a nickel plated surface using a deep drawing process, and trimming the front end of the side wall portion (11) with a punch while holding it with a blank holder. Of course, the material of the can (10) is not limited to this.

[0120] A hole is formed in the center of the bottom portion (12), and a first electrode terminal (13) can be fitted into the hole. The first electrode terminal (13) can be riveted and fixed to the bottom portion (12) while a terminal gasket (14) is interposed therebetween. The terminal gasket (14) is interposed between the first electrode terminal (13) and the bottom portion (12), thereby sealing the inside and outside of the battery can (10) to prevent leakage of the electrolyte, and electrically insulating the first electrode terminal (13) and the bottom portion (12).

[0121] However, the method of connecting the first electrode terminal (13) and the bottom part (12) is not limited to this. For example, if the structure can seal between the first electrode terminal (13) and the bottom part (12) and electrically insulate the first electrode terminal (13) and the bottom part (12), various other fixing methods, such as a bolt-nut joint method, a glass seal method, or a chrome coating & PP-MAH thermal bonding method, can also be applied.

[0122] The first electrode terminal (13) above may have a first polarity, and the battery can (10) may have a second polarity. Accordingly, both the bottom portion (12) of the battery can (10) and the side wall portion (11) connected thereto may have a second polarity.

[0123] Accordingly, the battery can (10) can have both the first electrode terminal (13) and the second electrode terminal (15) positioned at one axial end. Then, the battery can (10) can have both the bus bar connected to the first electrode terminal (13) and the bus bar connected to the second electrode terminal (15) positioned at one axial end of the battery can (10), i.e., the upper end.

[0124] In one example, the first electrode terminal (13) may be a positive terminal and the second electrode terminal (15) may be a negative terminal. Of course, the opposite may also be true.

[0125] An electrode assembly (20) is accommodated within the battery can (10). The electrode assembly (20) is prepared by preparing a first electrode (21), a second electrode (22), and a separator (28) having a predetermined width and extending in the longitudinal direction as illustrated in FIG. 5, and then forming a laminated body by sequentially stacking the first electrode (21), the separator (28), the second electrode (22), and the separator (28) as illustrated in FIGS. 6 and 7, and then winding this around a core shaft to form a jelly roll.

[0126] The above first electrode (21) may be an anode, and the above second electrode (22) may be a cathode. Of course, the opposite may also be the case.

[0127] The above first electrode (21) and second electrode (22) are manufactured in the form of sheets. The electrode sheet is manufactured in the form in which an active material layer (24) is applied to the surface of a current collector (23). The electrode sheet has a holding portion (25) region where the active material layer (24) is applied, and a non-coated portion (26) region where the active material layer (24) is not applied. The positive electrode sheet has a non-coated portion (26) region on one side in the width direction, and the negative electrode sheet has a non-coated portion (26) region on the other side in the width direction.

[0128] The non-conductive portion (26) is exposed or protrudes in the width direction of the laminate. The non-conductive portion (26) itself functions as an electrode tab.

[0129] In the above-mentioned blank portion (26), notches can be formed at a predetermined interval to form flag-shaped notching tabs (27).

[0130] In the embodiment, the above-described notching tabs (27) are exemplified as having an equilateral trapezoidal shape. However, their shapes may be various, such as a semicircle, a semi-ellipse, a triangle, a rectangle, a parallelogram, etc.

[0131] In addition, in the embodiment, a form in which the notching tabs (27) arranged along the longitudinal direction have the same width is exemplified. However, the width of the notching tabs may be gradually or stepwise widened from the core side to the outer periphery side.

[0132] In addition, in the embodiment, a form in which the height of the notching tabs (27) gradually increases from the core side to the outer circumference side is exemplified. However, the height of these notching tabs may be implemented in a form in which they are constant or gradually decrease.

[0133] In addition, in the embodiment, a structure is exemplified in which a notching tab (27) is deleted in a predetermined section of the centrifugal end of the non-conductive portion (26) and a predetermined section of the centrifugal end. However, it is of course possible that the notching tab may not be deleted in the centrifugal end of the non-conductive portion, and that the notching tab may not be deleted in the centrifugal end of the non-conductive portion.

[0134] In the jelly roll-shaped electrode assembly (20), the notched tab (27) may be bent radially and flattened. The notched tab (27) may be bent radially inward or outward. In the embodiment, a structure in which the notched tab (27) is bent radially inward as illustrated in FIGS. 8 and 9 is exemplified.

[0135] The above-mentioned notched tabs (27) can be bent one by one during the process of forming a jelly roll-shaped electrode assembly (20) by winding the laminate. Alternatively, the above-mentioned notched tabs (27) can be bent all at once after the laminate is wound to form a jelly roll-shaped electrode assembly.

[0136] The notching tabs (27) of the first electrode (21) and the notching tabs (27) of the second electrode (22), which are bent and overlapped in the radial direction in this way, can provide a plane substantially perpendicular to the axial direction at both axial ends of the electrode assembly (20), as illustrated in FIG. 9.

[0137] A current collector plate (31) can be joined to a substantially flat surface provided by bending the notched tabs (27) exposed at both axial ends of the electrode assembly (20), as shown in FIG. 10.

[0138] The above-mentioned collector plate (31) can be manufactured by punching, trimming, piercing, and bending a metal sheet.

[0139] Referring to Fig. 10, the current collector plate (31) has a terminal connection portion (32) extending radially from the center, a ring portion (33) connecting the centrifugal edge of the terminal connection portion (32) in a circumferential direction, and an electrode connection portion (34) extending centripetally from the ring portion (33) but not connected to the terminal connection portion (32). The center of the terminal connection portion (32) covers at least a portion of the core hollow portion of the electrode assembly (20).

[0140] The above electrode connection part (34) is joined to the notched tab (27) of the first electrode (21) of the electrode assembly (20) by laser welding or the like before the electrode assembly (20) is placed in the battery can (10).

[0141] Referring to Fig. 11, a collector plate may not be connected to the notched tab (27) of the second electrode (22) of the electrode assembly (20). Of course, the present invention is not limited to a structure in which a collector plate is not connected to the notched tab (27) of the second electrode (22).

[0142] As illustrated in FIGS. 12 and 13, the electrode assembly (20) is accommodated in the battery can (10) in a state where the current collector plate (31) is aligned so as to face the bottom portion (12) of the battery can (10). At this time, an insulator (19) is interposed between the current collector plate (31) and the bottom portion (12) of the battery can (10) so as to electrically insulate the current collector plate (31) from the bottom portion (12).

[0143] And, the terminal connection part (32) of the current collector plate (31) is joined to the first electrode terminal (13) fixed to the battery can (10) by a method such as resistance welding, ultrasonic welding or laser welding. The welding device for forming the welding part (W) of the current collector plate (31) and the first electrode terminal (13) can approach the back surface of the center of the terminal connection part (32) of the current collector plate (31) through the core hollow part of the electrode assembly (20) from the other axial end of the electrode assembly (20) and perform welding. Of course, in addition to this, the current collector plate (31) and the first electrode terminal (13) can also be joined by a brazing or soldering method. In other words, various methods can be applied to the current collector plate (31) and the first electrode terminal (13) as long as they are a joining method that can electrically connect them and fix them to each other.

[0144] Referring to FIGS. 14 and 15, when the electrode assembly (20) is accommodated in the battery can (10) and the first electrode (21) is connected to the first electrode terminal (13), the notched tab (27) of the second electrode (22) can be directly connected to the cap (40) that is press-fitted through the open end of the battery can (10). Accordingly, the second electrode (22) is electrically connected through the welding portion (W) of the notched tab (27) and the cap (40). Of course, other joining methods such as brazing or soldering can be applied to the notched tab (27) and the cap (40) in addition to the welding method.

[0145] The edge of the cap (40) is electrically connected to the side wall (11) of the battery can (10) and sealed and fixed. Accordingly, the second electrode (22) can be electrically connected to the cap (40) and the battery can (10). Various methods, such as welding, brazing, and soldering, that can electrically connect and seal the joint between the cap (40) and the battery can (10) can be applied to the processing of the joint (M).

[0146]

[0147] Hereinafter, examples and comparative examples of the present invention will be described. The following examples are merely exemplary of the present invention, and the present invention is not limited to the examples described below.

[0148]

[0149] (Example)

[0150] Comparative Example 1

[0151] Lithium composite transition metal LiNi with single crystal particles having a D50 of 3.9 μm measured by laser diffraction as a cathode active material 94.5 Co 2.9 Mn 2.7O2 was prepared.

[0152] Carbon nanotube powders with d50 values ​​measured by laser diffraction as described in Table 1 were prepared as a conductive material and prepared as a 4.3 wt% pre-dispersant.

[0153] The calculation of the percolation threshold (X) according to the D50 of the positive electrode active material and the d50 of the carbon nanotube is shown in Table 1, and the content of carbon nanotubes calculated accordingly (the content of carbon nanotubes out of the total content of the positive electrode active material and carbon nanotubes of 100 wt%) is also shown in Table 1.

[0154] A composition for a positive electrode active material was prepared by mixing the prepared positive electrode active material and the carbon nanotube conductive agent in the content ratio calculated in Table 1, and PVDF binder and N-methylpyrrolidone.

[0155] After applying the composition for the above positive electrode active material to one side of an aluminum current collector sheet, drying at 120°C, and rolling, a positive electrode plate was manufactured.

[0156] To manufacture a negative electrode, a negative electrode slurry was prepared by mixing negative electrode active material (graphite): conductive agent (SW-CNT): binder (AX-B096): additive (BH230) in a weight ratio of 98.05:0.05:0.7:0.9 in water. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150°C, and then rolled to manufacture a negative electrode plate.

[0157] A separator was interposed between the positive and negative plates manufactured as described above, and the separator / positive plate / separator / negative plate were stacked in that order, and then wound to manufacture a jelly-roll type electrode assembly. The electrode assembly manufactured as described above was inserted into a cylindrical battery can, and an electrolyte was injected to manufacture a 4680 cell.

[0158]

[0159] Comparative Example 2

[0160] Lithium composite transition metal LiNi with polycrystalline particles having a D50 of 11.3 μm as measured by laser diffraction as a cathode active material 97.2 Co 0.3 Mn 2.5O2 was prepared.

[0161] Carbon nanotube powders with d50 values ​​measured by laser diffraction as described in Table 1 were prepared as conductive materials.

[0162] The calculation of the percolation threshold (X) according to the D50 of the positive electrode active material and the d50 of the carbon nanotube is shown in Table 1, and the content of carbon nanotubes calculated accordingly (the content of carbon nanotubes out of the total content of the positive electrode active material and carbon nanotubes of 100 wt%) is also shown in Table 1.

[0163] The prepared positive electrode active material and the carbon nanotube conductive agent were mixed in the content ratios calculated in Table 1, and a PVDF binder and N-methylpyrrolidone were mixed to prepare a composition for a positive electrode active material. A positive electrode plate was prepared in the same manner as in Example 1, except that the prepared composition for a positive electrode active material was used, and a 4680 cell was prepared using the same manner as in Example 1.

[0164]

[0165] Example 1-3 and Comparative Example 3-5

[0166] As a cathode active material, (i) a lithium composite transition metal LiNi having single crystal particles with a D50 of 3.9 μm measured by laser diffraction; 94.5 Co2.9 Mn 2.7O2 and (ii) Lithium composite transition metal LiNi of polycrystalline particles having a D50 of 11.3 μm as measured by laser diffraction. 97.2 Co 0.3 Mn 2.5O2 The D50 of the cathode active material prepared by mixing single crystal particles and polycrystalline particles was 7.6㎛ as measured by laser diffraction.

[0167] Carbon nanotube powders with d50 values ​​measured by laser diffraction as described in Table 1 were prepared as conductive materials.

[0168] The calculation of the percolation threshold (X) according to the D50 of the positive electrode active material and the d50 of the carbon nanotube is shown in Table 1, and the content of carbon nanotubes calculated accordingly (the content of carbon nanotubes out of the total content of the positive electrode active material and carbon nanotubes of 100 wt%) is also shown in Table 1.

[0169] The prepared positive electrode active material and the carbon nanotube conductive agent were mixed in the content ratios calculated in Table 1, and a PVDF binder and N-methylpyrrolidone were mixed to prepare a composition for a positive electrode active material. A positive electrode plate was manufactured in the same manner as in Example 1, except that the manufactured positive electrode active material composition was used, and a 4680 cell was manufactured using the same manner as in Example 1.

[0170]

[0171] Positive active material D50 [㎛] Conductive material d50 [㎛] D50 / d50 <Calculation formula 1> Calculated value Conductive material relative content [wt%] Y Percolation threshold, X [cm 3]a[g]b[g]Example 17.63.242.350.81890.01701040.03404.67900.72Example 27.63.222.360.81740.016980.03404.67920.72Example 37.63.502.170.83650.01737780.03484.67730.74Comparative Example 13.93.241.200.93560.01943640.03894.66750 .83Comparative Example 211.33.243.490.71300.01481240.02964.68950.63Comparative Example 37.62.912.610.79250.01646360.03294.68160.70Comparative Example 47.62.533.000.75550.01569420.03144.68530.67Comparative Example 57.64.231.800.87530.01818380.03644.67340.77

[0172] (Experimental example)

[0173] Electrode layer resistance evaluation

[0174] For the cells manufactured in Examples 1 to 3 and Comparative Examples 1 to 5, the electrode layer resistance was measured using an MP tester under the following conditions.

[0175] MP Tester: Equipment that measures electrode resistance by dividing it into ‘electrode layer resistance’ and ‘interfacial contact resistance between current collector and electrode layer.’

[0176] For the positive electrode, a 50 mm x 50 mm sample was taken at a point 5 mm from the base.

[0177] Using the measurement program (XF0517ERMv135e), the Measure Configuration value was set to current 100 Ua, the Voltage range was set to 0.5 V, the cross-sectional electrode layer thickness was input (total thickness 160 um, cross-sectional thickness = [total thickness / 2 - collector thickness] = 65 um), the collector thickness was input, and the collector resistivity value was input (Al foil: 2.82e-06). After positioning the electrode at the center of the Probe unit pin, the measurement was performed when the contact between the pin and the electrode was completed.

[0178]

[0179] Life assessment

[0180] For the 4680 cells manufactured in Examples 1 to 3 and Comparative Examples 1 to 5, each was charged to 4.2 V at 0.25 C constant current-constant voltage at 55°C, and discharged to 2.5 V at 0.33 C constant current, which was considered one cycle, and after repeating charge and discharge, the capacity retention rate after 100 cycles and the number of cycles at which the capacity retention rate reached 90% were measured.

[0181]

[0182] The results of the above evaluation are shown in Table 2 below.

[0183] D50 / d50Relative content of conductive material [wt%]Electrode layer resistance [mΩ]LifetimeExample 12.350.724.9292.7Example 22.360.724.9891.6Example 32.170.745.1091.7Comparative Example 11.200.837.1281.0Comparative Example 23.490.634.9878.0Comparative Example 32.610.705.9189.5Comparative Example 43.000.676.0184.2Comparative Example 51.800.775.2387.2

[0184] Figure 1 is a graph showing the results of a life evaluation for the particle size ratio D50 / d50 of the positive electrode active material and carbon nanotube (conductive material) for Examples 1 to 3 and Comparative Examples 1 to 5.

[0185] Figure 2 is a graph showing the life evaluation results for the wt% content of conductive material obtained by percolation calculation for Examples 1 to 3 and Comparative Examples 1 to 5.

[0186] Figure 3 shows the relationship between the wt% content of the conductive material obtained by percolation calculation for the particle size ratio D50 / d50 of the positive electrode active material and the carbon nanotube (conductive material) for Examples 1 to 3 and Comparative Examples 1 to 5.

[0187]

[0188] From the results in Table 2 and FIGS. 1 to 3, it was confirmed that Examples 1 to 3 using positive electrodes manufactured with a particle size ratio D50 / d50 of the positive electrode active material and carbon nanotube (conductive material) satisfying Equation 1, and also manufactured with a relative content wt% of the conductive material calculated accordingly, excellently implemented both electrode layer resistance and life characteristics. Comparative Examples 1 to 5, which did not satisfy the conditions of Equation 1, used positive electrodes manufactured with a relative content wt% of the conductive material according to percolation calculation, but it was confirmed that, compared to Examples 1 to 3, both electrode layer resistance and life characteristics were not excellently implemented.

[0189]

[0190] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the exemplary embodiments disclosed herein, and that various modifications may be made by those skilled in the art within the scope of the technical spirit of the invention. Furthermore, even if the operational effects of the configurations of the invention have not been explicitly described and explained while describing the exemplary embodiments of the invention, it is also to be understood that the effects predictable by the configurations should be acknowledged.

[0191]

[0192] [Explanation of symbols]

[0193] 10: Battery can

[0194] 11: Side wall

[0195] 12: Bottom

[0196] 13: Positive terminal (first electrode terminal)

[0197] 14: Terminal gasket

[0198] 15: Negative terminal (second electrode terminal)

[0199] 19: Insulator

[0200] 20: Electrode assembly

[0201] 21: First electrode

[0202] 22: Second electrode

[0203] 23: Whole house

[0204] 24: Active material layer

[0205] 25: Maintenance Department

[0206] 26: Ministry of Immigration

[0207] 27: Notching tab

[0208] 28: Membrane

[0209] 31: Current collector board

[0210] 32: Terminal connection

[0211] 33: Ringbu

[0212] 34: Electrode connection

[0213] 40: Cap

Claims

1. A positive electrode active material layer composition comprising a positive electrode active material and a conductive material, wherein the conductive material comprises carbon nanotubes, and a ratio (D50 / d50) of a volume cumulative 50% particle size (D50) of the positive electrode active material to a volume cumulative 50% particle size (d50) of the carbon nanotubes satisfies the following equation 1. <Formula 1> 2.0 ≤ D50 / d50 ≤ 2.5 2. In paragraph 1, The cumulative 50% volume particle diameter (D50) of the positive electrode active material is 7 ㎛ to 8 ㎛, and the cumulative 50% volume particle diameter (d50) of the carbon nanotube is 2.5 ㎛ to 4.0 ㎛. A composition of a positive electrode active material layer.

3. In paragraph 1, The above-mentioned positive electrode active material has a composition having a bimodal distribution in which two peaks are shown at particle sizes of 3 ㎛ to 5 ㎛ and 10 ㎛ to 12 ㎛. A composition of a positive electrode active material layer.

4. In paragraph 1, The mass ratio of the above positive electrode active material and the above carbon nanotube is a value according to the formula for calculating the percolation threshold (D50 / d50). A composition of a positive electrode active material layer.

5. In paragraph 1, The mass of the carbon nanotube is 0.70 to 0.75 wt% among 100 wt% of the sum of the mass of the positive electrode active material and the carbon nanotube. A composition of a positive electrode active material layer.

6. In paragraph 1, The above positive electrode active material is a lithium composite transition metal compound represented by the following chemical formula 1. A composition of a positive electrode active material layer. [Chemical Formula 1] The a Nor (1-x-y) Co x M1 y M2 w O2 In the above chemical formula 1, 1.0≤a≤1.5, 0 <x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0<x+y≤0.2 이고, M1 is at least one metal among Mn and Al, M2 is at least one metallic element selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

7. In paragraph 6, The above carbon nanotube comprises at least one selected from the group consisting of single-walled carbon nanotubes, multi-walled carbon nanotubes, bundled carbon nanotubes, and combinations thereof. A composition of a positive electrode active material layer.

8. A positive electrode for a secondary battery, comprising: a current collector; and a positive electrode active material layer provided on the current collector and including a positive electrode active material layer composition according to any one of claims 1 to 7.

9. In paragraph 8, The positive electrode active material layer contains 80 to 99 wt% of the positive electrode active material based on the total weight of the positive electrode active material layer. anode.

10. A secondary battery comprising a positive electrode, a negative electrode, and a separator according to Article 9.

11. In paragraph 10, The above negative electrode comprises at least one selected from the group consisting of carbon-based negative electrode active materials, silicon-based negative electrode active materials, and combinations thereof. Secondary battery.

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