Electrode for lithium secondary battery, method for preparing same, and lithium secondary battery comprising same

Abstract

Provided is an electrode for a lithium secondary battery including an active layer including an electrode active material, a conductive material and a binder, wherein the binder is fibrillated in multiple directions.SOLUTION: The active layer has an average particle size (D50) of 200 μm to 500 μm when ground in a 000rpm for 30 seconds using a blender with four blades. In the electrode for a lithium secondary battery, since the binder included in the active layer is fibrillated in multiple directions, the binding force between the electrode active material, the conductive material and the binder in the active layer is improved, and furthermore, the durability of the electrode is improved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same. More specifically, the present invention relates to an electrode for a lithium secondary battery including a multidirectionally fiberized binder in an active layer, a manufacturing method thereof, and a lithium secondary battery including the same.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0123848, filed September 16, 2021, Korean Patent Application No. 10-2021-0123856, filed September 16, 2021, and Korean Patent Application No. 10-2022-0116025, filed September 15, 2022, and all contents disclosed in the documents of the relevant Korean patent applications are incorporated herein by reference. [Background technology]

[0003] The demand for secondary batteries as an energy source is rapidly increasing due to technological development and increasing demand for mobile devices. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] When fabricating electrodes for lithium secondary batteries, an electrode active material, a conductive material, and a binder are mixed to form a mixture containing the electrode active material. The resulting mixture is then applied to an electrode current collector and pressed using a device such as a roll to manufacture the electrode. When pressed by the roll, binders, such as polytetrafluoroethylene (PTFE), undergo fiberization, primarily on the surface that comes into contact with the roll. This fiberization occurs in the machine direction (MD) of the roll, primarily forming the binder located on the surface of the electrode. Even with binder fiberization, the electrode active material, conductive material, and binder inside the electrode remain dispersed in the form of small particles, which can result in poor electrode durability. Electrode durability, which is related to the electrode's lifespan, directly affects battery performance. In particular, when electrodes are fabricated using a dry process, the adhesive strength between the electrode active material, conductive material, and binder particles can be relatively weak. Therefore, binder fiberization plays an even more important role in improving electrode durability.

[0005] In the relevant technical field, research into improving the durability of electrodes used in lithium secondary batteries has been ongoing, and the present inventors have completed the present invention through such research. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Korean Patent Publication No. 10-2014-0136952 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides an electrode for a lithium secondary battery that can improve the binding strength between an electrode active material, a conductive material, and a binder, a method for manufacturing the same, and a lithium secondary battery including the same. [Means for solving the problem]

[0008] According to a first aspect of the present invention, there is provided an electrode for a lithium secondary battery, which includes an active layer including an electrode active material, a conductive material, and a binder, wherein the binder is multidirectionally fiberized.

[0009] In one embodiment of the present invention, the active layer has an average particle size (D) of 10,000 rpm when ground for 30 seconds using a blender with four blades. 50 ) is 200 μm to 500 μm.

[0010] In one embodiment of the present invention, the active layer has a tensile strength in the MD direction of 7.5 kgf / cm 2 That's all.

[0011] In one embodiment of the present invention, the active layer has a tensile strength ratio in the MD / TD of 1 to 1.3.

[0012] In one embodiment of the present invention, the electrode active material has an average particle size (D 50 ) is a lithium transition metal oxide having a particle size of 7 μm to 30 μm.

[0013] In one embodiment of the present invention, the conductive material is a carbon-based material or a metal material.

[0014] In one embodiment of the present invention, the binder comprises polytetrafluoroethylene.

[0015] In one embodiment of the present invention, the binder is contained in the active layer in an amount of 0.5 wt % to 5 wt % based on the total weight of the electrode active material.

[0016] According to a second aspect of the present invention, there is provided a method for manufacturing an electrode for a lithium secondary battery, the method comprising the steps of (1) mixing an electrode active material, a conductive material, and a binder stored at a low temperature, (2) primarily fiberizing the mixed material at a high temperature, (3) pulverizing the fiberized material at room temperature, and (4) secondarily fiberizing the pulverized material to manufacture an active layer.

[0017] In one embodiment of the present invention, in step (1), the electrode active material, conductive material, and binder stored at -20°C to -1°C are mixed in a blender rotating at 5,000 rpm to 20,000 rpm.

[0018] In one embodiment of the present invention, a kneader that applies a shear force of 20 N·m to 200 N·m to the mixed materials in step (2) is used.

[0019] In one embodiment of the present invention, the mixed materials in step (2) are first fiberized in a twin screw kneader rotating at 10 rpm to 50 rpm at 50° C. to 70° C.

[0020] In one embodiment of the present invention, in step (3), the fiberized material is pulverized in a blender rotating at 5,000 rpm to 20,000 rpm at room temperature.

[0021] In one embodiment of the present invention, the ground material in step (4) is secondarily fiberized in a three-roll mill rotating at 5 rpm to 20 rpm at 40° C. to 60° C.

[0022] In one embodiment of the present invention, the particles pulverized in step (3) are selected to contain only particles having a particle size of 1 mm or less before being subjected to secondary fiberization in step (4).

[0023] In one embodiment of the present invention, the particles milled in step (3) are selected to have a Hausner ratio of 1.6 or less before being secondarily fiberized in step (4). [Effects of the Invention]

[0024] In the electrode for a lithium secondary battery according to the present invention, the binder contained in the active layer is fiberized in multiple directions, thereby improving the binding strength between the electrode active material, the conductive material, and the binder in the active layer, thereby improving the durability of the electrode. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic view showing an active layer manufactured by pressing rolls from above and below according to the prior art; [Figure 2] 1 is a schematic diagram illustrating an active layer manufactured according to an embodiment of the present invention. [Figure 3a] 1 is a SEM image (magnification: ×3,000) of the inside of an active layer manufactured according to Comparative Example 1. [Figure 3b] 1 is a SEM image (magnification: ×3,000) of the exterior of the active layer manufactured according to Comparative Example 1. [Figure 4a] 1 is a SEM image (magnification: ×3,000) of the inside of an active layer manufactured according to Example 1. [Figure 4b] 1 is a SEM image (magnification: ×3,000) of the exterior of the active layer manufactured according to Example 1. [Figure 5] 1 is a graph showing the size distribution of pulverized particles obtained by pulverizing the active layers prepared in Example 1 and Comparative Example 1. [Figure 6] 10 is a graph showing the results of bulk density and tap density measured in Experimental Example 5. [Figure 7] 1 is a graph showing a measure of fluidity by the Hausner ratio. DETAILED DESCRIPTION OF THE INVENTION

[0026] The embodiments provided by the present invention can all be achieved by the following description. The following description should be understood as describing preferred embodiments of the present invention, and it should be understood that the present invention is not necessarily limited thereto.

[0027] Unless the measurement conditions and methods for the physical properties described herein are specifically described, the physical properties are measured according to the measurement conditions and methods commonly used by those skilled in the art.

[0028] According to one embodiment of the present invention, there is provided an electrode for a lithium secondary battery, which includes an active layer including an electrode active material, a conductive material, and a binder, and in which the binder is multidirectionally fiberized. Here, "multidirectionally fiberized" does not mean that the linear structures formed by fiberization are aligned in a specific direction, but rather that they are irregularly positioned, so that the overall linear structure does not have a specific direction. According to one embodiment of the present invention, the multidirectionally fiberized binder is not densely packed in a direction parallel to the surface near the surface of the active layer, but is uniformly distributed without a specific direction even in the center of the active layer.

[0029] Typically, when manufacturing an electrode for a lithium secondary battery, an electrode active material, a conductive material, and a binder are mixed to form a mixture containing the electrode active material. Considering the processability of the mixture, the mixture can be used in the form of a slurry by adding it to a solvent such as water or an organic solvent. The mixture is then coated on an electrode current collector and pressed using a device such as a roll to manufacture the electrode. When the mixture is prepared using a dry method without a solvent, the functionality of the binder may be reduced, resulting in a decrease in the bonding strength between the electrode active material, conductive material, and binder. This problem can be resolved by fiberizing the binder using pressure. However, when the surface of the mixture is pressed using a roll, fiberization often occurs mainly around the surface that contacts the roll, as shown in Figure 1, or only in a specific direction along the direction of the roll, resulting in insufficient bonding strength between the components. The present invention provides an electrode for a lithium secondary battery in which the bonding strength between the components of the active layer within the electrode is improved through multidirectional fiberization of the binder. Unlike Figure 1, the active layer in which the binder is fiberized in multiple directions can have a structure as shown in Figure 2.

[0030] The active layer refers to a layer including an electrode active material, a conductive material, and a binder. When a current collector is present in an electrode, the active layer refers to a material layer coated on the current collector, and thus refers to a layer that is distinct from the current collector of the electrode. Since the active layer includes an electrode active material, it is active in an electrochemical reaction within the electrode. In terms of including the electrode active material, the active layer can be referred to as an electrode active material layer, and in terms of being formed by mixing the electrode active material, a conductive material, and a binder, the active layer can be referred to as a mixed layer.

[0031] According to one embodiment of the present invention, the active layer is ground using a blender with four blades (manufacturer: Waring, equipment: LB10S, grinding container: SS110) at 10,000 rpm for 30 seconds to obtain an average particle size (D 50 The average particle size (D 50) is the diameter (median diameter) of particles at 50% cumulative volume of particle size distribution, and refers to the particle size at the point where the cumulative value reaches 50% on the cumulative curve obtained by calculating the particle size distribution on a volume basis and setting the total volume to 100%. 50 ) can be measured by laser diffraction. Specifically, the average particle size (D 50 ) is 200 μm or more, 210 μm or more, 220 μm or more, 230 μm or more, 240 μm or more, 250 μm or more, and 500 μm or less, 490 μm or less, 480 μm or less, 470 μm or less, 460 μm or less, 450 μm or less, and is 200 μm to 500 μm, 230 μm to 470 μm, 250 μm to 450 μm. 50 ) is significantly larger than the size of individual particles of the electrode active material, conductive material, and binder that make up the active layer, and is a value indicated by the binding of the above components due to the fiberization of the binder.

[0032] According to one embodiment of the present invention, the active layer has a tensile strength of 7.5 kgf / cm 2 As a result, the tensile strength ratio in the MD direction / TD direction is 1 to 1.3. Here, the MD (Machine Direction) direction refers to the direction in which the roll moves before finally manufacturing the sheet-shaped active layer, and the TD (Transverse Direction) direction refers to the direction perpendicular to the MD direction based on the plane of the electrode. Specifically, the tensile strength in the MD direction of the active layer is 7.5 kgf / cm 2 Above, 7.6kgf / cm 2 Above, 7.7kgf / cm 2 Above, 7.8kgf / cm 2 Over 7.9kgf / cm 2 Over 8.0kgf / cm 2 The higher the upper limit of the tensile strength in the MD direction of the active layer, the more the durability of the electrode can be improved. 2 Below, 18kgf / cm 2 Below, 16kgf / cm 2 Below, 14kgf / cm2 Hereinafter, 12 kgf / cm 2 Hereinafter, 10 kgf / cm 2 It may be the following. Generally, by rolling during the production of the final electrode, the tensile strength in the MD direction is shown to be higher than the tensile strength in the TD direction. The active layer according to a specific example of the present invention shows a high tensile strength in the TD direction while having a high tensile strength in the MD direction by secondary fibrillation. Specifically, the tensile strength ratio of the MD direction / TD direction is 1 or more, and the tensile strength in the TD direction is high, and it may be 1.30 or less, 1.28 or less, 1.26 or less, 1.24 or less, 1.22 or less, 1.20 or less. The active layer according to a specific example of the present invention can maintain firm durability regardless of the special direction because the binder is fibrillated in multiple directions through primary and secondary fibrillation. Since force does not act only in a specific direction during battery driving, having durability in all directions can contribute to improving battery performance. The active layer according to a specific example of the present invention has a tensile strength ratio of the MD direction / TD direction close to 1 and has excellent durability in almost all directions.

[0033] When the electrode active material is applied to the positive electrode, it can be a positive electrode active material, and when applied to the negative electrode, it can be a negative electrode active material. The positive electrode active material or the negative electrode active material is not particularly limited as long as it is generally used in the relevant technical field.

[0034] According to a specific example of the present invention, the positive electrode active material is a lithium transition metal oxide. The lithium transition metal oxide is Li 1+x M y O 2+Z (0 ≦ x ≦ 5, 0 < y ≦ 2, 0 ≦ z ≦ 2), where M is selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, V, and combinations thereof, and is not particularly limited within the above range. More specifically, the lithium transition metal oxide is LiCoO2, LiNiO2, LiMnO2, Li2MnO3, LiMn2O4, Li(Ni a Co b Mn c )O2(0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), LiNi1-y Co y O2 (O < y < 1), LiCo 1-y Mn y O2, LiNi 1-y Mn y O2 (O < y < 1), Li(Ni a Co b Mn c )O4 (0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-z Ni z O4 (0 < z < 2), LiMn 2-z Co z O4 (0 < z < 2) and is selected from this combination.

[0035] According to one specific example of the present invention, the negative electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. In specific examples, carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy; SiO 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); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. One or a mixture of two or more of these may be used. 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. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons 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-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0036] According to one embodiment of the present invention, the electrode active material has an average particle size (D 50 Specifically, the average particle size (D) of the particles is 7 μm to 30 μm. 50 The average particle size (D) of such particles is 7 μm or more, 7.5 μm or more, 8 μm or more, 8.5 μm or more, 9 μm or more, 9.5 μm or more, 10 μm or more, and 30 μm or less, 28 μm or less, 26 μm or less, 24 μm or less, 22 μm or less, 20 μm or less, or may be 7 μm to 30 μm, 8.5 μm to 24 μm, or 10 μm to 20 μm. 50 ) is the average particle size (D 50 Within the above range, the binding force of the electrode active material can be increased by forming the binder into multidirectional fibers.

[0037] The conductive material is used to impart conductivity to the electrode and can be any material that has electronic conductivity without causing a chemical change in the battery. Specific examples include graphite such as natural graphite or artificial graphite; carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon fiber, graphene, activated carbon, activated carbon fiber, and other carbon-based materials; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination.

[0038] The conductive material may be a carbonaceous material or a metal material, and the metal material may include the above-mentioned metal powder, metal fiber, conductive metal oxide, etc. The conductive material may be spherical or linear particles. When the conductive material is spherical particles, the average particle diameter (D 50 ) may be 1 nm to 100 nm, specifically 5 nm to 70 nm, more specifically 10 nm to 40 nm. When the conductive material is a linear particle, the length of the linear particle may be 1 μm to 10 μm, specifically 2 μm to 9 μm, more specifically 3 μm to 8 μm, and the diameter of the vertical cross section may be 10 nm to 500 nm, specifically 50 nm to 350 nm, more specifically 100 nm to 200 nm. The particle size of the conductive material is determined by the average particle size (D 50 ) is significantly smaller than

[0039] The binder serves to improve adhesion between electrode active material particles and between the electrode active material and the electrode current collector. To achieve the object of the present invention, the binder may be a material that can be fiberized by, for example, applying pressure. It is not particularly limited as long as it is a fiberizable material commonly used as a binder in the relevant technical field. According to one embodiment of the present invention, the binder includes polytetrafluoroethylene. Since the binder exists in a fiberized state in the active layer, particle size is less important than for other components.

[0040] According to one embodiment of the present invention, the binder is contained in the active layer in an amount of 0.5 wt % to 5 wt %, specifically 1 wt % to 4.5 wt %, more specifically 1.5 wt % to 4 wt %, based on the total weight of the electrode active material. The present invention is significant in that it can increase the cohesion of the entire active layer even with a small amount of binder.

[0041] The binder may basically include a fiberized binder such as polytetrafluoroethylene, but the fiberized binder may be modified or an additional binder may be mixed. The additional binder may be any binder commonly used in the relevant technical field, as long as it has the functionality to improve adhesion between electrode active material particles and the adhesion between the electrode active material and the electrode current collector. According to one embodiment of the present invention, the additional binder may be selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyimide, polyamide-imide, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butylene rubber, fluororubber, and combinations thereof, but is not limited thereto.

[0042] The active layer may be coated on an electrode current collector and included in the electrode. The electrode current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the battery. 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. The electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the electrode current collector to enhance the adhesion of the electrode active material. It may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0043] According to one embodiment of the present invention, there is provided a method for manufacturing an electrode for a lithium secondary battery as described above. The method includes (1) mixing an electrode active material, a conductive material, and a binder stored at low temperature, (2) primarily fiberizing the mixed material at high temperature, (3) pulverizing the fiberized material at room temperature, and (4) secondary fiberizing the pulverized material to manufacture an active layer. The thus-manufactured active layer can be applied to an electrode current collector as needed to manufacture a final electrode.

[0044] Step (1) involves uniformly mixing the electrode active material, conductive material, and binder. By storing the electrode active material, conductive material, and binder at a low temperature, the particles can be prevented from agglomerating. According to one embodiment of the present invention, the electrode active material, conductive material, and binder are stored at a temperature between −20°C and −1°C. Specifically, the storage temperature is −20°C or higher, −19°C or higher, −18°C or higher, −17°C or higher, −16°C or higher, −15°C or higher, and −1°C or lower, −2°C or lower, −3°C or lower, −4°C or lower, or −5°C or lower, and is −20°C to −1°C, −17°C to −3°C, or −15°C to −5°C. These storage temperatures minimize adhesion between the electrode active material, conductive material, and binder particles, allowing the particles to be uniformly distributed through subsequent mixing. While the low-temperature storage can be extended, a sufficient effect can be achieved by storing the materials for about 5 to 15 minutes.

[0045] The electrode active material, conductive material, and binder stored at low temperature are mixed in a blender at room temperature for a short time. According to one embodiment of the present invention, the electrode active material, conductive material, and binder are mixed in a blender rotating at 5,000 rpm to 20,000 rpm. Specifically, the rotation speed is 5,000 rpm or more, 5,500 rpm or more, 6,000 rpm or more, 6,500 rpm or more, 7,000 rpm or more, 7,500 rpm or more, and 20,000 rpm or less, 19,000 rpm or less, 18,000 rpm or less, 17,000 rpm or less, 16,000 rpm or less, or 15,000 rpm or less, and may be 5,000 rpm to 20,000 rpm, 6,000 rpm to 17,000 rpm, or 7,500 rpm to 15,000 rpm. Such a rotation speed allows for effective and uniform mixing within a short time. By carrying out the mixing for a short period of time, such as within one minute, the low-temperature storage effect can be enhanced.

[0046] Step (2) is a step of primarily fiberizing the mixed materials, in which the binder contained in the mixed materials is fiberized and bound to the electrode active material and conductive material. A kneader capable of applying a certain level of shear force to the mixture can be used for the primary fiberization step. As used herein, the term "kneader" refers to a device capable of applying a shear force of, for example, 20 N·m to 200 N·m to the mixture. A device referred to as a "mixer" can also be considered a "kneader" if it is capable of applying the above shear force. The shear force refers to the maximum shear force applied to the mixture by the device, and this value is measured using a torque rheometer. Specifically, the shear force may be 20 N·m or more, 25 N·m or more, 30 N·m or more, 35 N·m or more, 40 N·m or more, 45 N·m or more, or 50 N·m or more, and 200 N·m or less, 190 N·m or less, 180 N·m or less, 170 N·m or less, 160 N·m or less, or 150 N·m or less, and may be 20 N·m to 200 N·m, 35 N·m to 170 N·m, or 50 N·m to 150 N·m. The shear force generated by such an apparatus may be suitable for fiberizing the binder. According to one embodiment of the present invention, the kneader may be a twin screw kneader or a paradoxical mixer, and more specifically, a twin screw kneader.

[0047] According to one embodiment of the present invention, the mixed material is primarily fiberized in a twin-screw kneader rotating at 10 to 50 rpm. Specifically, the rotation speed is 10 rpm or more, 12 rpm or more, 14 rpm or more, 16 rpm or more, 18 rpm or more, 20 rpm or more, and 50 rpm or less, 48 ​​rpm or less, 46 rpm or less, 44 rpm or less, 42 rpm or less, or 40 rpm or less, and may be 10 to 50 rpm, 16 to 46 rpm, or 20 to 40 rpm. These rotation speeds are significantly slower than those used during mixing, ensuring sufficient time for fiberization to proceed. The use of a twin-screw kneader allows sufficient pressure to be transmitted to the interior of the mixed material, enabling overall fiberization. A sufficient effect can be achieved by performing the primary fiberization for approximately 5 to 10 minutes.

[0048] When the primary fiberization is performed in the twin screw kneader, the binder can be made more moldable by performing the primary fiberization at a temperature higher than room temperature. According to one embodiment of the present invention, the primary fiberization is performed at a temperature between 50°C and 70°C. Specifically, the high temperature is 50°C or higher, 51°C or higher, 52°C or higher, 53°C or higher, 54°C or higher, or 55°C or higher, and 70°C or lower, 69°C or lower, 68°C or lower, 67°C or lower, 66°C or lower, or 65°C or lower, and may be 50°C to 70°C, 53°C to 67°C, or 55°C to 65°C. Such temperatures are suitable for binder fiberization.

[0049] Step (3) is a step of pulverizing the primarily fiberized material, which rearranges the primary fiberization through pulverization to produce more complex and multidirectional fiberization than the secondary fiberization. According to one embodiment of the present invention, the fiberized material is pulverized in a blender rotating at 5,000 rpm to 20,000 rpm at room temperature. Specifically, the rotation speed may be 5,000 rpm or more, 5,500 rpm or more, 6,000 rpm or more, 6,500 rpm or more, 7,000 rpm or more, 7,500 rpm or more, and 20,000 rpm or less, 19,000 rpm or less, 18,000 rpm or less, 17,000 rpm or less, 16,000 rpm or less, 15,000 rpm or less, or 5,000 rpm to 20,000 rpm, 6,000 rpm to 17,000 rpm, or 7,500 rpm to 15,000 rpm. This rotation speed allows for effective grinding to an appropriate size within a short period of time. By carrying out the mixing for a short period of time, such as within one minute, it is possible to prevent the fiberized particles from being excessively ground.

[0050] Step (4) is a secondary fiberization step of the pulverized material, in which the primary fiberization, rearranged through pulverization, is reconnected and fiberization of the missing portions is carried out. According to one embodiment of the present invention, the pulverized material is secondary fiberized in a three-roll mill rotating at 5 to 20 rpm. Specifically, the rotation speed is 5 rpm or more, 6 rpm or more, 7 rpm or more, 8 rpm or more, 9 rpm or more, 10 rpm or more, and 20 rpm or less, 19 rpm or less, 18 rpm or less, 17 rpm or less, 16 rpm or less, or 15 rpm or less, and may be 5 to 20 rpm, 8 to 17 rpm, or 10 to 15 rpm. These rotation speeds are significantly slower than those used during mixing and pulverization, ensuring sufficient time for fiberization to proceed. Using a three-roll mill allows for gradual fiberization by gradually narrowing the gap between the rolls, ultimately allowing for processing into a sheet. The primary fiberization naturally ends when all of the material has passed through the rolls.

[0051] When the secondary fiberization is performed using the three-roll mill, the binder's moldability is improved by performing the secondary fiberization at a temperature higher than room temperature. According to one embodiment of the present invention, the secondary fiberization is performed at a temperature between 40°C and 60°C. Specifically, the high temperature may be 40°C or higher, 41°C or higher, 42°C or higher, 43°C or higher, 44°C or higher, or 45°C or higher, and 60°C or lower, 59°C or lower, 58°C or lower, 57°C or lower, 56°C or lower, or 55°C or lower, and may be 40°C to 60°C, 43°C to 57°C, or 45°C to 55°C. These temperatures may be suitable for binder fiberization and complement the primary fiberization, allowing processing at a slightly lower temperature than the primary fiberization.

[0052] After pulverization in step (3) and before secondary fiberization in step (4), the pulverized material can be screened. By selecting materials that can easily mix with each other from the pulverized material, defects in the active layer can be minimized and a uniform sheet shape can be produced when the active layer is subsequently fabricated through fiberization. The pulverized material can be screened based on particle size. A sieve can be used for this purpose. According to one embodiment of the present invention, particles with a particle size of 1 mm or less are selected from the pulverized material in step (3). Particles with a particle size of 1 mm or less have above-average fluidity and can be used to form a uniform sheet without any problems. However, particles with a particle size greater than 1 mm have very poor fluidity, which can result in defects such as pore formation in the resulting sheet. Essentially, the particle size distribution determined through pulverization results in a greater number of particles centered around the average diameter of the particles. Therefore, small particles are not only fewer in number but also occupy a smaller volume, so they do not have a significant adverse effect on sheet formation.

[0053] According to one embodiment of the present invention, the bulk density of the particles selected by the above-described method is 0.8 g / ml to 1.5 g / ml. Here, bulk density refers to the density when the particles are quietly charged without any special handling. Specifically, the bulk density is 0.8 g / ml or more, 0.9 g / ml or more, 1.0 g / ml or more, and 1.5 g / ml or less, 1.4 g / ml or less, or 1.3 g / ml or less, and may be 0.8 g / ml to 1.5 g / ml, 0.9 g / ml to 1.4 g / ml, or 1.0 g / ml to 1.3 g / ml. When particles are selected within this range, the degree of fluidity is at a level that does not adversely affect sheet production.

[0054] According to one embodiment of the present invention, the particles selected by the above method have a Hausner ratio of 1.6 or less. Here, the Hausner ratio refers to the tap density divided by the bulk density, and the tap density refers to the density after gently compressing the particles by beating them, as in measuring bulk density. When compressed by beating, the volume of the charged particles decreases, so the tap density is generally greater than the bulk density, and therefore the Hausner ratio is also 1.0 or greater. Specifically, the Hausner ratio is 1.6 or less, 1.5 or less, or 1.4 or less. When particles are selected within this range, the fluidity can be maintained at a level that does not adversely affect sheet production.

[0055] The electrode manufactured by the above method can be used in a lithium secondary battery, which is generally manufactured by inserting a separator between a positive electrode and a negative electrode and then injecting an electrolyte, but can be modified into various forms as needed.

[0056] The separator separates the anode and cathode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent humidification of the electrolyte is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure 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 can be used in either a single-layer or multi-layer structure.

[0057] The electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, or the like that can be used in manufacturing a lithium secondary battery, but is not limited thereto.

[0058] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0059] 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. Specific 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), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC); alcohol-based solvents such as ethanol and isopropyl alcohol; nitriles such as R-CN (where R is a C2 to C20 linear, branched, or cyclic hydrocarbon group that 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 low viscosity linear carbonates (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred, as they have high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries. In this case, mixing the cyclic carbonate and the chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent electrolyte performance. The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, and LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2 may also be used. The lithium salt concentration is preferably in the range of 0.1 to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0060] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0061] As described above, the lithium secondary battery including the electrode according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0062] According to another aspect of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0063] The battery module or battery pack may be used as a power source for one or more medium- to large-sized devices in a power tool; an electric vehicle (EV), a hybrid electric vehicle, and an electric vehicle (PHEV), including a plug-in hybrid electric vehicle; or a power storage system.

[0064] Preferred examples are presented below to aid in understanding the present invention. However, the following examples are provided merely to facilitate understanding of the present invention, and the present invention is not limited thereto.

[0065] Example Example 1 LiNi as electrode active material 0.5 Co 0.3 Mn 0.2 O2 (average particle size (D 50 ): 10 μm, Manufacturer: LG Chem, Product: HN803S) 96 wt%, VGCF (Vapor Grown Carbon Fiber, average particle size: 150 nm, average length: 6 μm, Manufacturer: Showa Denko, Product: VGCF-H) 2 wt%, polytetrafluoroethylene (average particle size (D 50A 2% by weight mixture of 601x (500 μm, manufacturer: Chemours) was stored in a -10°C freezer for 10 minutes. The prepared electrode active material, conductive material, and binder were removed from the freezer and mixed in a blender (manufacturer: Waring, equipment: LB10S, container: SS110) at room temperature and 10,000 rpm for 30 seconds. The mixed material was first fiberized in a twin-screw kneader (manufacturer: Brabender, product: Torque rheometer) at 60°C and 30 rpm for 5 minutes. The fiberized material was then pulverized in a blender (manufacturer: Waring, equipment: LB10S, container: SS110) at room temperature and 10,000 rpm for 30 seconds.

[0066] From the crushed particles, only particles with a particle size of 1 mm or less were selected separately, and the selected particles were then rolled in a three-roll mill (roll spacing: 150 μm / 100 μm, manufacturer: Kmtech, product: KRM-80B) at a temperature of 50°C and a rotation speed of 10 rpm to finally produce a sheet-shaped active layer.

[0067] Comparative Example 1 LiNi as electrode active material 0.5 Co 0.3 Mn 0.2 O2 (average particle size (D 50 ): 10 μm, Manufacturer: LG Chem, Product: HN803S) 96 wt%, VGCF (Vapor Grown Carbon Fiber, average particle size: 150 nm, average length: 6 μm, Manufacturer: Showa Denko, Product: VGCF-H) 2 wt%, polytetrafluoroethylene (average particle size (D 50A 2% by weight mixture of 601x (100 nm, manufacturer: Chemours, product: 601x) was stored in a -10°C freezer for 10 minutes. The prepared electrode active material, conductive material, and binder were removed from the freezer and mixed in a blender (manufacturer: Waring, equipment: LB10S, container: SS110) at room temperature and 10,000 rpm for 30 seconds. The mixed material was rolled in a three-roll mill (roll spacing: 150 μm / 100 μm, manufacturer: Kmtech, product: KRM-80B) at 50°C and 10 rpm to finally produce a sheet-shaped active layer.

[0068] Comparative Example 2 The active layer prepared in Comparative Example 1 was pulverized in a blender (manufacturer: Waring, equipment: LB10S, container: SS110) at room temperature and 10,000 rpm for 30 seconds. Particles with a size of 1 mm or less were selected from the pulverized particles, and the selected particles were rolled in a three-roll mill (roll spacing: 150 μm / 100 μm, manufacturer: Kmtech, product: KRM-80B) at 50°C and 10 rpm to finally prepare a sheet-shaped active layer.

[0069] Comparative Example 3 The average particle size (D 50 ) is 5μm LiNi 0.5 Co 0.3 Mn 0.2 A sheet-shaped active layer was prepared in the same manner as in Example 1, except that O2 was used.

[0070] Experimental example Experimental Example 1 The internal and external structures of the active layers manufactured in Example 1 and Comparative Example 1 were confirmed using a scanning electron microscope (SEM, magnification: ×3,000, manufacturer: JEOL, product: JSM-7200F), and are shown in Figure 3a (inside the active layer of Comparative Example 1), Figure 3b (outside the active layer of Comparative Example 1), Figure 4a (inside the active layer of Example 1), and Figure 4b (outside the active layer of Example 1).

[0071] Comparing Figures 3a and 4a showing the inside of the active layer, it was confirmed that the polytetrafluoroethylene was aggregated without being fibrillated inside the active layer of Comparative Example 1 (Figure 3a), whereas it was confirmed that the polytetrafluoroethylene was fibrillated inside the active layer of Example 1 (Figure 4a), and the electrode active material and conductive material were bound together by the fibrillated polytetrafluoroethylene.

[0072] Comparing Figures 3b and 4b for the outside of the active layer, the polytetrafluoroethylene was fibrillated in the outside of the active layer of Comparative Example 1 (Figure 3b), but the fibrillated area was not clearly visible, while the polytetrafluoroethylene was fibrillated again by roll pressure in the outside of the active layer of Example 1 (Figure 4b), so the fibrillated area was more clearly visible.

[0073] Experimental Example 2 The active layers prepared in Example 1 and Comparative Examples 1 and 2 were each milled at 10,000 rpm for 30 seconds using a milling device (manufacturer: Waring, equipment: LB10S, milling container: SS110), and the size of the milled particles was analyzed using an Optical PSD (Malvern Morphology). The results are shown in Figure 5.

[0074] In the active layer of Comparative Example 1, the degree of bonding between the materials constituting the active layer was not high, and the materials were pulverized into individual or small agglomerated particles. In the active layer of Comparative Example 2, the degree of bonding between the materials constituting the active layer was improved compared to Comparative Example 1 through two rollings, and the materials were pulverized into larger agglomerated particles than in Comparative Example 1. In the active layer of Example 1, the degree of bonding between the materials constituting the active layer was the highest by using a twin screw kneader during the primary fiberization, and the materials were pulverized into relatively much larger agglomerated particles compared to Comparative Examples 1 and 2. FIG. 5 shows the particle size distributions of Comparative Examples 1 and 2 and Example 1, each of which is shown separately. In fact, the average particle size (D 50 ) appears at 50 μm, and the average particle size (D 50 ) appears at 150 μm, and the average particle size (D 50 ) appeared at 400 μm.

[0075] Experimental Example 3 The tensile strength in the MD and TD directions of each active layer prepared in Example 1 and Comparative Examples 1 and 2 was analyzed using a tensile strength measuring device (manufacturer: LLOYD, product: LS1). The results are shown in Table 1 below.

[0076] [Table 1]

[0077] According to Table 1, Example 1 and Comparative Examples 1 and 2 all exhibited high tensile strength in the MD, but in the cases of Example 1 and Comparative Example 2, which were rolled after crushing, the tensile strength ratio in the MD / TD was 1.2 or less, indicating that the difference in tensile strength between the MD and TD was not significant. When a twin screw kneader was used in the primary fiberization as in Example 1, the tensile strengths in the MD and TD were each improved by 35% or more compared to Comparative Example 2, which used a roll mill in the primary fiberization.

[0078] Experimental Example 4 The tensile strength in the MD direction of each of the active layers prepared in Example 1 and Comparative Example 3 was analyzed using a tensile strength measuring device, and the results are shown in Table 2 below.

[0079] [Table 2]

[0080] According to Table 2, the average particle size (D 50 In the case of Comparative Example 3, the average particle size (D 50 The tensile strength in the MD direction was significantly lower than that in Example 1, in which the thickness was 10 μm.

[0081] Experimental Example 5 The particles milled in Example 1 were classified into five size ranges (based on particle size, range 1: over 45 μm and up to 150 μm, range 2: over 150 μm and up to 450 μm, range 3: over 450 μm and up to 850 μm, range 4: over 850 μm and up to 1,000 μm, range 5: over 1,000 μm), and the bulk density and tap density were measured. The Hausner ratio was then calculated and is shown in Table 3 below and FIG. 6.

[0082] [Table 3]

[0083] * Bulk density (g / ml): Measure the mass when particles are gently packed into a 100 ml cylinder and calculate the mass per unit volume (average value of 5 repeated measurements) (Manufacturer: SEISHIN, Product: KYT-4000) * Tap density (g / ml): After gently filling a 100 ml cylinder with particles, the particle-filled cylinder is tapped 1,000 times with a constant force using a tap density volumeter to compress it arbitrarily, and then the mass is measured to calculate the mass per unit volume (average value of 5 repeated measurements). * Hausner ratio: Tap density divided by bulk density The fluidity scale based on the Hausner ratio can be evaluated as shown in Table 4 and FIG. 7 according to the following criteria named by Henry H. Hausner.

[0084] [Table 4]

[0085] According to the fluidity scale based on the Hausner ratio in Table 4, it can be seen that in Table 3, section 5 has very poor fluidity, sections 3 and 4 have normal fluidity, and sections 1 and 2 have somewhat good fluidity. If there is a difference in fluidity depending on the crushed particles, unnecessary damage may occur when manufacturing an electrode through the subsequent secondary fiberization step.

[0086] Any simple modifications or variations of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be defined by the appended claims.

Claims

1. an active layer including an electrode active material, a conductive material, and a binder; The electrode for a lithium secondary battery, wherein the binder is multidirectionally fiberized.

2. The active layer was ground using a blender with four blades at 10,000 rpm for 30 seconds, with the average particle size (D ５０ 2. The electrode for a lithium secondary battery according to claim 1, wherein the thickness of the first electrode is 200 μm to 500 μm.

3. The active layer has a tensile strength of 7.5 kgf / cm in the MD direction. ２ 2. The electrode for a lithium secondary battery according to claim 1, wherein the electrode is one of the above.

4. 2. The electrode for a lithium secondary battery according to claim 1, wherein the active layer has a tensile strength ratio in the machine direction / transverse direction of 1 to 1.

3.

5. The electrode active material has an average particle size (D ５０ 2. The electrode for a lithium secondary battery according to claim 1, wherein the oxide is a lithium transition metal oxide having a particle size of 7 μm to 30 μm.

6. 2. The electrode for a lithium secondary battery according to claim 1, wherein the conductive material is a carbon-based material or a metal material.

7. 2. The electrode for a lithium secondary battery according to claim 1, wherein the binder contains polytetrafluoroethylene.

8. 2. The electrode for a lithium secondary battery according to claim 1, wherein the binder is contained in the active layer in an amount of 0.5 to 5 wt % based on the total weight of the electrode active material.

9. 2. A method for producing an electrode for a lithium secondary battery according to claim 1, comprising: (1) mixing an electrode active material, a conductive material, and a binder stored at low temperature; (2) first fiberizing the mixed material at a high temperature; (3) grinding the fiberized material at room temperature; and (4) A method for manufacturing an electrode for a lithium secondary battery, comprising: manufacturing an active layer through a step of secondary fiberizing the pulverized material.

10. 10. The method of claim 9, wherein in step (1), the electrode active material, the conductive material, and the binder stored at −20° C. to −1° C. are mixed in a blender rotating at 5,000 rpm to 20,000 rpm.

11. 10. The method of claim 9, wherein in step (2), a kneader is used to apply a shear force of 20 to 200 N·m to the mixed materials.

12. 10. The method of claim 9, wherein in step (2), the mixed materials are primarily fiberized in a twin screw kneader rotating at 10 rpm to 50 rpm at 50° C. to 70° C.

13. 10. The method of claim 9, wherein in step (3), the fiberized material is pulverized in a blender rotating at 5,000 rpm to 20,000 rpm at room temperature.

14. 10. The method of claim 9, wherein in step (4), the pulverized material is secondarily fiberized in a three-roll mill rotating at 5 rpm to 20 rpm at 40° C. to 60° C.

15. 10. The method of claim 9, wherein the particles pulverized in step (3) are sorted to include only particles having a particle size of 1 mm or less before being secondarily fiberized in step (4).

16. 10. The method of claim 9, wherein the particles pulverized in step (3) are selected to have a Hausner ratio of 1.6 or less before being subjected to the secondary fiberization in step (4).

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