Dry electrode containing mixed powder for electrode

Abstract

To provide a dry electrode having high dispersibility of a conductive material.SOLUTION: The dry electrode obtained by the manufacturing method according to the present disclosure has high dispersibility of the conductive material in the electrode active material layer. Accordingly, when the content of the conductive agent in the electrode is constant, the internal resistance of the electrode active material layer and the interfacial resistance with the current collector are reduced as the dispersibility is higher. Also, in a case in which the dry electrode having high dispersibility is applied to a battery, since ohmic resistance is reduced during the operation of the battery, a voltage drop may be improved, and high output efficiency may be improved. In a case in which the dispersibility of the conductive agent is extremely poor, the deterioration of the electrode active material may be non-uniform depending on the position in the electrode, which is disadvantageous for the life characteristics of the battery. In addition, the evaluation tool according to the present invention can confirm the dispersibility of the conductive material in the electrode as a quantitative value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims priority to Korean Patent Application No. 10-2022-0049196, filed on April 20, 2022. The present invention relates to a dry electrode containing a mixed powder for manufacturing a dry electrode, and having a high degree of dispersion of a conductive material. [Background technology]

[0002] As interest in energy storage technology grows and its application fields expand to include mobile phones, tablet computers, laptop computers, and camcorders, as well as the energy sources of electric vehicles (EVs) and hybrid electric vehicles (HEVs), research and development of electrochemical devices is increasing. In this context, electrochemical devices are attracting the most attention, with the development of rechargeable lithium-ion secondary batteries attracting particular attention. In recent years, research and development into new electrode and battery designs has been actively conducted to improve the capacity density and specific energy of such batteries.

[0003] Recently, dry electrode manufacturing methods that do not use solvents have been proposed to reduce the deterioration of electrode materials due to solvents used in electrode manufacturing and to reduce side reactions caused by residual organic solvents after electrode manufacturing.

[0004] A dry electrode can be manufactured by mixing electrode materials, such as an electrode active material, a conductive material, and a binder resin, in powder form without using a solvent to prepare a mixed powder for an electrode, calendering the mixed powder to prepare a free-standing dry electrode film, and laminating the film with a current collector. For example, prior art documents such as U.S. Patent Publication No. US2005-0266298A1 have proposed a method of fiberizing a binder through a high-shear mixing process such as jet milling during the manufacture of an electrode mixture, and then compressing the mixture into a film.

[0005] In order to improve the energy density during electrode manufacturing, methods have been considered to increase the content of active material in the electrode, but in this case, the content of conductive material is relatively reduced, which may increase resistance and reduce the output characteristics of the battery. For electrodes manufactured using conventional wet processes, methods have been applied that maximize the content of electrode active material by increasing dispersibility even when using a relatively small amount of conductive material, such as using a linear conductive material or adding a dispersant during slurry manufacturing.

[0006] However, when electrodes are manufactured using a dry process without using a solvent, it is difficult to improve dispersibility by adding a dispersant. Furthermore, because strong shear forces are applied during the production of electrode powder mixtures, adding linear conductive materials can cause them to break due to the shear forces, preventing them from maintaining their original length and resulting in insufficient formation of conductive paths. Therefore, research is needed to develop a manufacturing method for dry electrodes that can improve the dispersibility of conductive materials during dry electrode production. Furthermore, there is a need for an evaluation tool that can confirm the dispersibility of conductive materials in dry electrodes. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Application Publication No. 2005 / 0266298 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a dry electrode in which a conductive material is highly dispersible. Another object of the present invention is to provide a method for confirming the degree of dispersion of a conductive material in a dry electrode.

[0009] It will be readily apparent that other objects and advantages of the present invention can be achieved by the means or methods and combinations thereof recited in the claims. [Means for solving the problem]

[0010] A first aspect of the present invention is a dry electrode for an electrochemical device, the dry electrode including an electrode active material layer derived from a dry electrode film, the electrode active material layer including an electrode mixed powder, the electrode mixed powder being thermocompressed to form a sheet having a predetermined thickness, the electrode mixed powder including an electrode active material and a binder polymer, The electrode active material layer has a conductive material dispersion index 1 (Index 1) of 3.5 μm as determined by the following equation 1 for one or more arbitrary cross sections inside the layer. -1 and / or the dispersion index 2 of the conductive material according to the following formula 2 is 10 or more. [Formula 1] Index 1 (μm -1 )=Boundary measured / A [Formula 2] Index 2=Boundary measured / L circle In Equation 1, Boundary measured is the periphery of the conductive material region measured at a predetermined cross section of the electrode active material layer, A is the area of ​​the portion defined as the conductive material region measured at a predetermined cross section of the electrode active material layer, and in Equation 2, L circle is the circumference of a circle with the same area as the area of ​​the measured conductive material region.

[0011] According to a second aspect of the present invention, in the first aspect, the electrode active material layer has a conductive material dispersion index 1 (Index 1) of 3.5 μm or less for one or more arbitrary cross sections inside the electrode active material layer according to Equation 1. -1 The dispersion index 2 of the conductive material according to the formula 2 is 10 or more.

[0012] According to a third aspect of the present invention, in the first or second aspect, the dispersibility index 1 and the dispersibility index 2 are (Step 1) preparing a cross-sectional sample in which an arbitrary cross section inside an electrode active material layer is exposed; (Step 2) obtaining a 2D scale map of the resistance distribution of the electrode cross-section sample; (Step 3) masking the conductive material area; (Step 4) calculating the perimeter and area of ​​the masked region and substituting the calculated perimeter and area into Equation 1 and / or Equation 2 to confirm the dispersion degree of the conductive material in the electrode active material layer.

[0013] According to a fourth aspect of the present invention, in any one of the first to third aspects, the electrode active material layer is formed on one surface of an electrode current collector, and the cross section is a plane parallel to or perpendicular to the part of the electrode active material layer facing the current collector.

[0014] According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the binder polymer is fibrous, and the fibrous state is the result of kneading due to shear stress.

[0015] According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the binder polymer contains polytetrafluoroethylene (PTFE), polyolefin, or a mixture thereof.

[0016] A seventh aspect of the present invention is a method for manufacturing a dry electrode according to any one of the first to fifth aspects, the method including: a step (S10) of mixing electrode materials including an electrode active material and a binder polymer; a step (S20) of kneading the mixed electrode materials; a step (S30) of grinding the resultant of the step (S20) to obtain an electrode mixture powder; and a step (S40) of compressing and molding the electrode mixture powder to manufacture a self-standing dry electrode film, wherein the step (S20) is performed at a temperature of 60°C or higher.

[0017] According to an eighth aspect of the present invention, in the seventh aspect, the step (S20) is carried out at a temperature range of 60°C to 250°C.

[0018] According to a ninth aspect of the present invention, in the seventh or eighth aspect, the method further comprises bonding the dry electrode film and a current collector by a lamination process.

[0019] A tenth aspect of the present invention is an electrochemical element comprising a positive electrode, a negative electrode, and a separator or solid electrolyte membrane interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is a dry electrode according to any one of the first to sixth aspects. [Effects of the Invention]

[0020] A dry electrode obtained by a manufacturing method according to one embodiment of the present invention has high dispersibility of the conductive material in the electrode active material layer. Therefore, when the content of the conductive material in the electrode is constant, higher dispersibility reduces the internal resistance of the electrode active material layer and the interfacial resistance with the current collector. Furthermore, when a dry electrode with high dispersibility is applied to a battery, the ohmic resistance during battery operation can be reduced, improving voltage drop and improving power efficiency. If the dispersibility of the conductive material is extremely poor, the deterioration of the electrode active material may vary depending on the position within the electrode, which is detrimental to the battery's lifespan. Furthermore, the evaluation tool according to the present invention can quantitatively evaluate the dispersibility of the conductive material in the electrode.

[0021] The drawings attached to this specification illustrate preferred embodiments of the present invention and serve to facilitate a better understanding of the technical concepts of the present invention as well as the contents of the invention, and therefore the present invention should not be interpreted as being limited to only the matters depicted in the drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings attached to this specification may be exaggerated to emphasize a clearer description. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a scanning spreading resistance microscopy (SSRM) image of Example 1. [Figure 2] This is an image obtained by masking the conductive material area in Figure 1. [Figure 3]1 is an SSRM image of Comparative Example 1. [Figure 4] This is an image obtained by masking the conductive material area in Figure 3. [Figure 5] 1 is a histogram of Example 1. [Figure 6] 1 is a histogram of Comparative Example 1. [Figure 7] 1 is a schematic diagram of an electrode according to an embodiment of the present invention. [Figure 8] FIG. 1 is a schematic diagram for calculating the QBR value of an electrode active material layer. [Figure 9] 1 is a schematic diagram illustrating a process for manufacturing a unit film for an electrode according to an embodiment of the present invention. [Figure 10] 1 is a schematic diagram of an electrode lamination process according to an embodiment of the present invention; [Figure 11a] FIG. 1 is a schematic diagram of a method for preparing an electrode cross-section sample. [Figure 11b] FIG. 1 is a schematic diagram of a method for preparing an electrode cross-section sample. [Figure 12a] 10 is a histogram of Example 7. [Figure 12b] FIG. 10 is a diagram showing a pattern in which an active material region and a conductive material region are overlapped. [Figure 13] 10 shows an SSRM image of Example 5 and an image confirmed by masking the conductive material region. [Figure 14] 1 shows an SSRM image of Example 6 and an image obtained by masking the conductive material region. [Figure 15] 1 is an SSRM image of the electrode of Example 7. [Figure 16] This is an image obtained by masking the conductive material area in Figure 15. [Figure 17] This is an image obtained by masking the conductive material region from the obtained histogram without correction for the electrode of Example 7. [Figure 18] 10 is an image of the electrode of Example 7 after masking the conductive material area after correction. [Figure 19]1 is a display screen showing the area and perimeter of a conductive material region calculated using Gwyddion software. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will now be described in more detail to aid in understanding the invention.

[0024] The terms and words used in this specification and claims should not be interpreted limited to their ordinary and dictionary meanings, but should be interpreted in a meaning and concept that corresponds to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of the term in order to explain the invention in the best way.

[0025] The terms used in this specification are used to describe exemplary embodiments and are not intended to limit the present invention. Unless otherwise specified, the singular includes the plural.

[0026] Furthermore, throughout the specification, when a part "comprises" another component, it does not mean that the other component is excluded, but that the part may further include the other component, unless otherwise specified.

[0027] Furthermore, the terms "about," "substantially," and the like used throughout this specification, when given manufacturing and material tolerances inherent in the stated meaning, are used to mean a numerical value or a value close to that numerical value, in order to prevent unscrupulous infringers from unfairly using disclosure content in which precise or absolute numerical values ​​are stated to aid in the understanding of this application.

[0028] Throughout this specification, the phrase "A and / or B" means "A, B, or all of these."

[0029] The present invention relates to a dry electrode manufactured by pressing a powder mixture for a dry electrode, and a method for manufacturing the dry electrode. The dry electrode of the present invention can be used as an electrode for an electrochemical device such as a lithium ion secondary battery.

[0030] <Dry electrodes> Dry electrodes will be described in more detail below. In the present invention, the dry electrode includes an electrode active material layer derived from a free-standing dry electrode film. For example, the dry electrode may include a current collector and an electrode active material layer derived from a dry electrode film disposed on at least one surface of the current collector, and the dry electrode film and the current collector may be bonded together by a lamination process or the like.

[0031] <Dry electrode film> The dry electrode film refers to a free-standing electrode film manufactured using an electrode material including an electrode active material and a binder without the use of a solvent. In this specification, the term "free-standing" refers to a film that can maintain its independent form without relying on other components and can be moved or handled by itself. In the present invention, the dry electrode film may be formed by compressing an electrode powder mixture, as described below. For example, the powder mixture may have a layered structure formed by accumulating the powder mixture through compression. The powder mixture is a powdered electrode material including an electrode active material and a binder polymer, and may be obtained by pulverizing a mixture block including the electrode active material and the binder polymer, as described below.

[0032] <Ingredient content> Meanwhile, in one embodiment of the present invention, the electrode active material layer may contain 80 wt% or more or 90 wt% or more of an electrode active material based on the total weight of the electrode active material layer. Also, in one embodiment of the present invention, the electrode active material layer may further contain a conductive material, if necessary. The conductive material may be contained in an amount of 20 wt% or less, 10 wt% or less, or 5 wt% or less, based on 100 wt% of the electrode active material layer, and, taking conductivity into consideration, may be contained in an amount of 0.1 wt% or more. For example, the conductive material in the electrode active material layer may be contained in a range of about 0.1 wt% to 5 wt%.

[0033] According to an embodiment of the present invention, the content of the electrode active material in the electrode active material layer may be 85 wt% to 98 wt%. Within the above range, the content of the binder polymer may be 0.5 wt% to 10 wt%, and the content of the conductive material may be 0.5 wt% to 5 wt%.

[0034] Meanwhile, in the present invention, the electrode active material layer is derived from a dry electrode film, and the content ratio of materials in the dry electrode film may be in the same range as that of the electrode active material layer.

[0035] <Electrode active material> Meanwhile, the electrode active material layer may include a positive electrode active material or a negative electrode active material depending on the polarity of the battery. Non-limiting examples of the positive electrode active material include lithium transition metal oxides or lithium metal iron phosphates, as long as they are in the form of metal oxides, for example, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; 1+x Mn 2-x Lithium manganese oxides such as O4 (x=0~0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); chemical formula: LiMn 2-x Mx Examples of the lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (M=Co, Ni, Fe, Cr, Zn, or Ta, x=0.01 to 0.1) or Li2Mn3MO8 (M=Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion; lithium metal phosphate LiMPO4 (M=Fe, Co, Ni, or Mn), disulfide compounds; and Fe2(MoO4)3.

[0036] Non-limiting examples of the negative electrode active material include carbon such as non-graphitizable carbon and graphite-based carbon; x Fe2O3(0 <x≦1)、Li x WO2(0≦x≦1), Sn x Me 1-x Me' y O z Examples of suitable conductive materials include metal composite oxides such as (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2, and Group 3 elements of the periodic table, and halogens; 0x≦1; 1≦y≦3; 1≦z≦8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; silicon-based oxides such as SiO, SiO / C, and SiO2; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; and Li-Co-Ni-based materials.

[0037] <Binder polymer> In the present invention, the binder polymer is not limited to any particular type as long as it can be fibrillated during the manufacturing method described below, particularly during the process of manufacturing the mixture mass. "Fibrillation" refers to a process in which a high molecular weight polymer is finely divided, and can be performed, for example, using mechanical shearing force. The surface of the polymer fibers fibrillated in this manner is unraveled to generate numerous fine fibers (fibrils). Non-limiting examples of such binder polymers include polytetrafluoroethylene (PTFE), polyolefin, or a mixture thereof, more specifically, polytetrafluoroethylene (PTFE). Specifically, the polytetrafluoroethylene (PTFE) may be present in an amount of 60 wt% or more based on the total weight of the entire binder polymer. Meanwhile, in this case, the binder material may further include one or more of polyethylene oxide (PEO), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), and polyolefin polymers.

[0038] <Conductive material> In the present invention, the electrode active material layer of the dry electrode may further include a conductive material. In a specific embodiment of the present invention, the conductive material may be incorporated into the electrode active material layer by being included in the electrode powder mixture. The conductive material may be any conductive material that does not induce chemical changes in the battery and has conductivity. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specifically, the conductive material may include at least one selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes to ensure uniform mixing of the conductive material and improve conductivity. More specifically, the conductive material may include activated carbon. Meanwhile, in one embodiment of the present invention, it is preferable to increase the amount of dot-shaped conductive material such as carbon black in order to improve dispersibility in the process of manufacturing the electrode powder mixture for the dry electrode.

[0039] <Filler> Meanwhile, depending on the case, a filler, which is a component that suppresses expansion of the electrode, may be further added to the mixture. The filler is not particularly limited as long as it does not induce chemical changes in the battery and is a fibrous material. For example, fibrous materials such as olefin polymers such as polyethylene and polypropylene; glass fiber, carbon fiber, etc. may be used.

[0040] <Current collector> Meanwhile, in one embodiment of the present invention, the current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity, and may be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the current collector may have fine irregularities on its surface to increase adhesion of the positive electrode active material, and may be used in various forms such as a film, sheet, foil, net, porous material, foam, nonwoven fabric, etc.

[0041] Meanwhile, in one embodiment of the present invention, the current collector may be entirely or partially coated with a conductive primer to reduce surface resistance and improve adhesion. Here, the conductive primer may include a conductive material and a binder. The conductive material may be any conductive material, for example, a carbon-based material. The binder may include a solvent-soluble fluorine-based binder (including PVdF and PVdF copolymers), an acrylic binder, or a water-based binder.

[0042] <Dispersion of conductive material> In the present invention, the electrode active material layer has a conductive material dispersion index 1 (Index 1) of 3.5 μm or less in one or more arbitrary cross sections within the electrode active material layer, as determined by the following equation 1: -1 or more and / or the dispersion index 2 of the conductive material according to the following formula 2 (Index 2) is 10 or more. Preferably, the electrode active material layer has a dispersion index 1 of 3.5 μm or more. -1 or more, and the dispersibility index 2 is 10 or more. On the other hand, the electrode active material layer has a dispersibility index 1 of 40 μm or more. -1 It is preferable that the dispersion index 2 of the electrode active material layer is 50 or less. The dispersion index 1 and the dispersion index 2 are determined by visually processing one or more arbitrary cross sections of the electrode active material layer on a two-dimensional scale (2D mapping image) to obtain a boundary of a portion defined as a conductive material region. measuredAfter deriving the diameter (A) and area (A), these values ​​can be substituted into the following formulas 1 and 2 to calculate the formula.

[0043] [Formula 1] Index 1(a -1 )=Boundary measured / A In Equation 1, Boundary measured means the perimeter of the portion defined as the conductive material region measured at a predetermined cross section of the electrode active material layer, and A means the area of ​​the portion defined as the conductive material region measured at a predetermined cross section of the electrode active material layer. In Equation 1, a is the unit used. If the unit of the perimeter is μm, the unit of the dispersity index 1 is μm. -1 It could be.

[0044] [Formula 2] Index 2=Boundary measured / L circle In Equation 2, Boundary measured is the same as Equation 1, and L circle is the circumference of a circle having the same area as the area of ​​the defined conductive material region. For any closed curve, the smallest circumference is when the pattern of the closed curve is a circle. Therefore, imagine a virtual circle having the same area as the entire area (A) of the conductive material region, calculate the length of the circumference of that circle, and divide the circumference of the actual conductive material region by the circumference of the virtual circle. The larger the value of Index 2, the higher the degree of dispersion can be interpreted as.

[0045] Said L circle can be calculated based on the following Equations 1 and 2:

number

number

[0046] Therefore, Equation 2 can be expressed as Equation 2A below.

number

[0047] In other words, the area of ​​a circle is {(radius of the circle (r))} 2 ×π}, from which the radius (r) of the virtual circle can be determined, and once the radius is determined, the outer periphery (circumference, 2π) of the virtual circle can be calculated.

[0048] The higher the dispersibility index 1 and dispersibility index 2, the more uniformly the conductive material is dispersed in the electrode active material layer without agglomerating and dispersing locally. That is, a high ratio of the periphery of a conductive material region to the area of ​​the conductive material region, or a high ratio of the periphery of a conductive material region to the circumference of a circle having the same area as the conductive material region, means that the conductive material is uniformly distributed in the electrode.

[0049] For example, the dispersibility index 1 and the dispersibility index 2 can be confirmed for two or more different cross sections of the electrode active material layer, and the dispersibility index 1 for all cross sections is 3.5 μm. -1 and the dispersity index2 for all cross sections is 10 or more.

[0050] In the present invention, the cross section may be formed parallel to the current collector-facing portion. Alternatively, the cross section may be formed parallel to the current collector-facing portion, perpendicular to the current collector-facing portion, or at a predetermined angle with the current collector-facing portion. Since the present invention is intended to confirm the dispersion degree of the conductive material inside the electrode active material layer, the angle between the exposed surface and the current collector-facing portion is not limited to a specific range as long as the inside is exposed to an extent that allows the dispersion index 1 and dispersion index 2 to be confirmed.

[0051] In one embodiment of the present invention, the dispersibility index 1 measured in a cross section of a predetermined portion within a range of 10% thickness from the top to the bottom in the thickness direction of the electrode active material layer and the dispersibility index 1 measured in a cross section of a predetermined portion within a range of 10% thickness from the bottom to the top are 3.5 μm. -1In addition, the dispersibility index 2 measured in a cross section of a predetermined portion within a range of 10% of the thickness from the top to the bottom in the thickness direction of the electrode active material layer, and the dispersibility index 2 measured in a cross section of a predetermined portion within a range of 10% of the thickness from the bottom to the top, may be 10 or more.

[0052] Meanwhile, the lower part of the electrode active material layer refers to the surface facing the current collector (current collector-facing portion), and the upper part may be the surface opposite to the current collector-facing portion (back side), which may be the portion facing the separator or solid electrolyte membrane.

[0053] The dispersion index 1 and dispersion index 2 can be determined by visualizing the distribution of the electrode material, particularly the conductive material, in any cross section of the electrode active material layer, and then calculating the perimeter and area of ​​the portion where the conductive material is distributed (the conductive material region) and substituting the calculated values. The distribution of the electrode material contained in the electrode active material layer is determined on a microscopic scale below the microscale. Therefore, the visualization of the conductive material distribution can be determined by analyzing the conductive network of the cross section of the electrode active material layer using electronic visualization methods such as atomic force microscopy (AFM) and scanning spreading resistance microscopy (SSRM), as described below.

[0054] Next, the method for calculating the dispersibility index 1 and the dispersibility index 2 will be described in detail.

[0055] The method includes a step (step 1) of exposing an arbitrary cross section of the inside of an electrode for an electrochemical device to prepare an electrode cross section sample; Step 2: Obtaining resistance data of the electrode active material and the conductive material of the electrode cross-section sample using a scanning spreading resistance microscope; Step 3: obtaining a logarithmic scale image and a histogram of the resistance data; and (Step 4) calculating the dispersibility index 1 and / or the dispersibility index 2. Each step will be described in detail below.

[0056] (Step 1) First, a dry electrode is prepared, and a cross-section of the electrode active material layer is exposed to prepare an electrode cross-section sample. The electrode may include an electrode active material layer formed on at least one surface of a current collector. The electrode active material layer includes an electrode active material, a conductive material, and a binder resin. Then, a predetermined thickness of the surface of the electrode active material layer is removed using an ion beam for ion milling to expose the cross-section of the electrode active material layer. Ion milling refers to a method of etching a material by accelerating ions of an inert gas from a wide beam ion source onto the surface of a sample in a vacuum. Ion milling is based on the sputtering phenomenon, in which ions or atoms of an inert gas (e.g., argon) are accelerated with an appropriate voltage to remove atoms from the sample surface. This allows for the preparation of an electrode cross-section sample with a clean cross-section free of physical damage, and allows for more clearly visible conductive material regions from the electrode. According to one embodiment of the present invention, the inert gas may be argon. Irradiating the electrode with an argon ion beam allows for more stable preparation of the electrode cross-section sample. In one embodiment of the present invention, the ion beam current of the ion milling device may be 100 μA to 250 μA. Specifically, the ion beam current of the ion milling device may be 110 μA to 150 μA, or 200 μA to 230 μA. By adjusting the ion beam current of the ion milling device within the above range, the time required to prepare the electrode cross-section sample can be shortened and redeposition of the electrode material on the cross-section of the sample can be prevented, thereby preparing an electrode cross-section sample with a cleaner cross-section.

[0057] Through such ion milling, surface information of the electrode with excellent roughness can be obtained, and desired information such as observation or visualization data can be obtained using an electron microscope.

[0058] 11a and 11b are schematic diagrams illustrating a method for preparing an electrode cross-section sample. The electrode cross-section sample is obtained by etching and removing a portion 11s from the surface to a predetermined depth in the thickness direction (height) of the electrode active material layer by ion milling, thereby exposing a predetermined plane within the electrode active material layer.

[0059] Meanwhile, in an embodiment of the present invention, the step of preparing the electrode cross-section sample may further include the step of impregnating the electrode with a polymer containing epoxy groups to fill internal pores of the electrode with the polymer containing epoxy groups before performing the ion milling. The method of impregnating the electrode with the polymer containing epoxy groups may be a method commonly used in the art. For example, the polymer containing epoxy groups may be applied to the electrode, or the electrode may be immersed in a solution of the polymer containing epoxy groups.

[0060] According to one embodiment of the present invention, the electrode analysis method may further include measuring the resistance of the polymer containing epoxy groups filled in the pores of the electrode cross-section sample. By filling the internal pores of the electrode with the polymer containing epoxy groups, the resistance of the pores in the electrode cross-section sample can be obtained using a scanning spreading resistance microscope. Specifically, the resistance of the polymer material filling the pores can be measured to obtain resistance data. This allows the regions where the pores are located to be identified, and the electrode active material region, conductive material region, and pore region of the electrode cross-section sample can be more accurately distinguished from the composite image.

[0061] According to one embodiment of the present invention, the epoxy group-containing polymer may be an epoxy resin polymer containing a cyclic structure within its molecular structure, specifically an epoxy resin polymer containing an aromatic group (e.g., a phenyl group). Specific examples of the epoxy group-containing polymer containing an aromatic group include, but are not limited to, biphenyl-type epoxy group-containing polymers, dicyclopentadiene-type epoxy group-containing polymers, naphthalene-type epoxy group-containing polymers, dicyclopentadiene-modified phenol-type epoxy group-containing polymers, cresol-type epoxy group-containing polymers, bisphenol-type epoxy group-containing polymers, xylene-based epoxy group-containing polymers, multifunctional epoxy group-containing polymers, phenol novolac epoxy group-containing polymers, triphenolmethane-type epoxy group-containing polymers, and alkyl-modified triphenolmethane epoxy group-containing polymers. Specific examples include, but are not limited to, any one of epoxyethane (ethylene oxide), 1,3-epoxypropane (trimethylene oxide), and bisphenol-A-epichlorohydrin.

[0062] (Step 2) Next, after the electrode cross-section sample is prepared in step 1, a 2D scale map of the resistance distribution of the electrode cross-section sample is obtained using a conductive network analysis method (scanning spreading resistance microscopy). Figure 1 shows a 2D scale map image of Example 1 obtained by this method.

[0063] Specifically, an atomic force microscopy (AFM) device can be used to scan the surface of the electrode cross-section sample to obtain a 2D-scaled image. This measurement produces a map in which the electrical resistance values ​​are represented by color shading, allowing the distribution of surface resistance to be visually confirmed by the differences in color tone (shading). First, a sample is prepared for measurement with the AFM device. The cross-section sample prepared by the above process is attached to an AFM metal disk with the cross-section facing upward, and a silver paste or the like is applied to the AFM metal disk so that a conductive path is formed between the portion of the cross-section other than the milled cross-section. The prepared AFM sample is loaded into the device, and after laser alignment, the cross-section is selected as the measurement area using an optical microscope. Then, an atomic force microscope probe is contacted with the electrode cross-section, and the current flowing through the sample between the AFM probe and the contact electrode is measured. The spreading resistance is obtained from the measured current. According to one embodiment of the present invention, the operating conditions of the scanning spreading resistance microscope for analyzing the electrode cross-section sample are, for example, as follows: The AFM device is not particularly limited as long as it can visually image the resistance distribution using scanning spreading resistance microscopy. For example, a cypher ES (Oxford Instruments) can be used. According to a specific example of the present invention, a Dual-gain ORCA can be used as the cantilever holder, and AR (Oxford Instruments) can be used as the driving software. Specific driving conditions include contact mode, image pixel size of 512 x 512 to 1024 x 1024, scan speed of 0.2 Hz to 1.0 Hz, bias of 2.0 V or less, and set point of 1.0 V or less. For example, the image pixel size can be 512 x 512, the scan speed can be 0.5 Hz, the bias can be 2.0 V or less, and the set point can be 0.2 V. A solid diamond AFM probe (AD-40-As, Adama) made of boron-doped single-crystal diamond can be used as the AFM probe.

[0064] Meanwhile, in one embodiment of the present invention, the obtained cross-sectional sample is preferably subjected to AFM measurement under an atmosphere-protected condition such as a glove box, and the cross-sectional sample can be loaded into a sealed cell body to maintain the atmosphere-protected condition.

[0065] (Step 3) Once the 2D-scale map is obtained through step 2, the conductive material region is defined. The term "definition" can also be expressed as "masking" because a visual display method is applied. For example, Figures 17 and 18 show the conductive material region identified from the histogram for the electrode of Example 7 in black.

[0066] A method for defining the conductive material region will be specifically described below. First, the resistance data obtained using a scanning spreading resistance microscope is processed and converted to a logarithmic scale to obtain a logarithmic scale image (log(resistance) image), and a log resistance distribution histogram, which represents the materials that make up the electrode cross-section sample, is extracted from the logarithmic scale image.

[0067] From the histogram, it can be determined whether the area corresponding to each pixel is an electrode active material area, a pore or binder area, or a conductive material area, and the conductive material area distribution in the 2D map image can be quantified using information about each pixel whose corresponding area has been determined.

[0068] Specifically, the log(R / Ω) value corresponding to the minimum value between the conductive material peak and the electrode active material peak in the histogram is set as the limit value, and the region having a value smaller than that value is masked as the conductive material region. At this time, the numerical value may be corrected by adding or subtracting 0.1 to 0.5 to the minimum value.

[0069] In one embodiment, the correction may be performed by adding a value of 0.1 to 0.5 to the log(R / Ω) value corresponding to the minimum value. This is to correct for areas in the histogram where the active material region and the conductive material region overlap and are not shown as conductive material regions. For example, the correction value may be determined by dividing the histogram into left and right sides based on the peak of the conductive material region, and correcting the bottom on the right side so that it has the same value as the horizontal distance from the peak to the bottom on the left side.

[0070] FIGS. 5, 6, and 12a are log resistance distribution histograms extracted from logarithmic scale images (log(resistance) images) for the electrodes of Example 1, Comparative Example 1, and Example 7, respectively. Referring to these, the conductive material peak and the electrode active material peak can be identified, and the minimum value between them can be identified. However, as described above, even in the section after the minimum, there is a conductive material section that is not shown overlapping with the active material region, so the values ​​are corrected as described above. FIG. 12b is an example of the predicted overlapping pattern of the active material region and the conductive material region in the uncorrected histogram for the electrode of Example 7.

[0071] When corrected in this way, the portion that overlaps with the active material region and is not visible on the histogram is shown as the conductive material region, allowing for more accurate evaluation of values.

[0072] Meanwhile, FIG. 17 shows the SSRM image with the conductive material regions masked based on the pre-correction values. The conductive material regions are masked with a hue not present in the original image, and in this embodiment, are masked in black. Looking at the dotted circle in FIG. 17, the conductive material remains unmasked. The unmasked portions retain their blue hue when their hue is confirmed. Meanwhile, FIG. 18 shows the conductive material regions masked based on the post-correction values. It can be seen that the unmasked portions (retained in blue) in FIG. 17 are masked in black in FIG. 18.

[0073] Meanwhile, among the masked regions as conductive material regions, regions located within the active material are removed to eliminate errors, which are errors that occur during the sample preparation process, such as conductive material adhering to the exposed cross-section of the active material, or errors that occur during the imaging process, and which clearly show that the conductive material is not distributed within the active material in an actual electrode, so they are preferably removed.

[0074] Meanwhile, after the conductive material area is masked, an image showing only the conductive material area is extracted (contrast masked) as shown in Figures 2, 4, 6, the bottom of Figure 13, the bottom of Figure 14, and Figure 16, and provided for calculation in step 4.

[0075] In one embodiment of the present invention, the masking of the conductive material region may be performed using a program that visualizes data obtained from scanning probe microscopy, such as AFM. In one embodiment of the present invention, the masking may be performed using Gwyddion software. However, if the image contains many images with too small a pixel size, it may be difficult to accurately identify the perimeter or area of ​​the conductive material region, which may act as noise when calculating the dispersion, resulting in errors. Therefore, during the masking process, images with excessively small pixels may be removed. For example, when using the Gwyddion program, grain filtering may be used to remove small regions of less than 3 pixels from being masked as conductive material regions. If fine regions of less than 3 pixels are included, the perimeter of the conductive material region may be calculated as an excessively high value, so they are removed before measurement. Meanwhile, Figure 5 shows a histogram obtained using the above method, which confirms the distinction between the active material region and the conductive material region.

[0076] (Step 4) Once the masking of the conductive material region is completed through step 3 (i.e., the definition of the conductive material region), the perimeter and area of ​​the masked region can be confirmed and the dispersion index 1 can be calculated according to the above Equation 1. In Equation 1, Boundary measuredThe perimeter value of the masking area is applied to , and the area value of the masking area is applied to A.

[0077] Alternatively, the radius of a circle having the same area as the masking area can be calculated, and the circumference of the circle can be calculated from the radius. By substituting the circumference of the circle into A, the dispersibility index 2 can be calculated using Equation 2.

[0078] Meanwhile, in the present invention, the area and perimeter of the masked conductive material region can be calculated using an image processing program such as Gwyddion software. Figure 19 is a display screen showing the area and perimeter calculated through the program.

[0079] <Dry electrode manufacturing method> In one embodiment of the present invention, the dry electrode satisfying the dispersibility index 1 and the dispersibility index 2 can be manufactured by the following manufacturing method.

[0080] For example, a method for manufacturing a dry electrode is as follows: (S10) preparing a powder mixture containing an electrode active material, a conductive material, and a binder resin; (S20) kneading the powder mixture at a temperature ranging from 70°C to 200°C to prepare a mixture mass; (S30) pulverizing the mixture mass to obtain a mixed powder containing mixed particles; (S40) calendering the electrode powder to obtain a free-standing dry electrode film.

[0081] In addition, the dry electrode film obtained in (S40) may be bonded to one or both sides of an electrode current collector to manufacture a dry electrode (S50).

[0082] <Manufacturing mixed powder> First, a mixed powder for electrodes is produced. The mixed powder for an electrode is a powdered electrode material containing an electrode active material and a binder polymer, and may be obtained by, for example, pulverizing a mixture block containing an electrode active material and a binder polymer, as described below. In this specification, the mixed powder refers to an aggregate of mixed particles containing two or more electrode materials. Each mixed particle constituting the mixed powder may contain one or more selected from an electrode active material, a binder, and a conductive material. In a specific embodiment, the mixed particle may contain an electrode active material and a binder. The particles may further contain a conductive material. Meanwhile, the electrode powder may contain one or more of the electrode active material, the binder, and the conductive material that remain without constituting the mixed particle. Meanwhile, the mixed powder for an electrode can be obtained by the following manufacturing method.

[0083] <Dry mixing> First, an electrode material mixture containing an electrode active material and a binder polymer is prepared. The electrode material mixture may further contain the aforementioned conductive material and / or additives, as necessary, in the above-described content ratios. The mixing for preparing the mixture is performed so that the electrode materials, such as the electrode active material and the binder polymer, have a uniform dispersed phase within the mixture. Because the present invention is a dry electrode that does not use a solvent, the mixture is performed in powder form without adding a solvent. Therefore, the electrode materials may be mixed by various methods, without any limitation, as long as they can be simply mixed. For example, the electrode materials may be mixed by adding them to a known device such as a mixer or blender and stirring them.

[0084] In one specific embodiment, the electrode material may be mixed in powder form in a device such as a mixer or blender.

[0085] In one embodiment of the present invention, the mixing time is not particularly limited, but may be 1 second to 10 minutes. Meanwhile, the mixing speed is not particularly limited, but may be appropriately controlled within a range of about 3,000 rpm to 30,000 rpm. Specifically, to ensure high uniformity, the mixing may be performed in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, or more specifically, at 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute.

[0086] As will be described later, the binder resin is mainly fiberized in step (S20), although some thick fiberization may occur in step (S10).

[0087] <Binder fiberization process> Next, the obtained electrode material mixture is subjected to a fiberization process to fiberize the binder polymer. In the present invention, the fiberization process may be preferably performed using a low-shear kneading method, for example, a kneader such as a kneader. As the binder polymer is fiberized by this kneading, the electrode materials, such as the electrode active material added in powder form, are bonded or connected to form a mixture mass. Since no solvent is added during the kneading, the mixture mass may have a solid content of 100%. As the binder resin is fiberized by this kneading, the electrode active material and the conductive material are bonded or connected to form a mixture mass.

[0088] In one embodiment of the present invention, the kneading may be controlled to a speed of 10 rpm to 100 rpm. For example, the kneading may be controlled to 20 rpm or more or 40 rpm or more within the above range, with the upper limit being, for example, 70 rpm or less. The kneading may be carried out for 1 minute to 10 minutes. For example, the kneading may be carried out for 3 minutes to 7 minutes at a speed of 40 rpm to 70 rpm within the above range.

[0089] More preferably, the kneading can be performed for 5 minutes or less, or 3 minutes or less. The lower the tap compression ratio of the obtained electrode powder mixture, the more effective the manufacturing process of an electrode film using the powder. However, the tap compression ratio decreases in the early stages of kneading and remains almost constant after a certain point. Since excessive kneading time can result in excessive fiberization and breakage of the fiberized binder resin filaments, it is sufficient to control the kneading time within the above range to ensure an appropriate tap compression ratio.

[0090] Meanwhile, the shear rate of the kneading may be controlled within a range of 10 / s to 500 / s. In one specific embodiment of the present invention, the kneading may be performed for 1 minute to 30 minutes, and the shear rate may be controlled within a range of 30 / s to 100 / s.

[0091] The kneading step may be carried out at a high temperature and a pressure equal to or higher than atmospheric pressure, more specifically, under a pressure higher than atmospheric pressure. More specifically, the kneading may be carried out at a temperature in the range of 20°C to 230°C, and may be controlled to a temperature of 20°C or higher, 50°C or higher, or to a temperature of 230°C or lower, or 200°C or lower.

[0092] If the kneading is performed at a temperature outside the above range, the binder polymer may not be sufficiently fibrous and the added materials may not be sufficiently agglomerated, making it difficult to form a film in the subsequent calendering process for forming the electrode film into a sheet. On the other hand, if the kneading is performed at an excessively high temperature, the binder polymer may be rapidly fibrous and the already formed fibers may be cut by the shear force continuously applied during the kneading process, which is undesirable.

[0093] Furthermore, the mixing may be carried out at atmospheric pressure or higher, specifically at a pressure of 1 atm to 3 atm, and more specifically at 1.1 atm to 3 atm. Mixing at a pressure outside the above range is not preferable because excessive shear force and pressure may be applied, resulting in problems such as cutting of the formed fibers or excessively high density of the mixture mass. That is, according to the present invention, the intended effects of the present invention can be achieved by performing a low shear mixing process at high temperature and pressure conditions above atmospheric pressure, instead of high shear mixing.

[0094] <Grinding> Then, the mixture mass produced through the kneading step is pulverized to obtain a powdered electrode mixture.

[0095] The mixture mass obtained through the kneading process may be directly pressed and formed into a sheet (calendering process), but in this case, strong pressure and high temperature must be applied to form it into a target thickness, which may result in an excessively high density of the dry electrode film or an inconsistent film. Therefore, the obtained mixture mass is pulverized as described above to produce a mixed powder for an electrode.

[0096] The pulverization may be performed using equipment such as, but not limited to, a blender or a grinder. In one embodiment of the present invention, the pulverization may be performed in a grinder at a speed of 5,000 rpm to 20,000 rpm or 10,000 rpm to 18,000 rpm. The pulverization process may be performed for 30 seconds to 10 minutes, more specifically, 30 seconds to 1 minute. If the pulverization is performed at a too low rpm or for too short a time outside the above range, the material may not be pulverized sufficiently, resulting in powder of a size unsuitable for film formation. If the pulverization is performed at a too high rpm or for too long a time, a large amount of fine powder may be generated, which is undesirable.

[0097] In one embodiment of the present invention, the particle size (D50) of the mixed particles obtained through the pulverization process may be appropriately adjusted to within a range of 10 μm to 800 μm. In a specific embodiment, the particle size (D50) of the mixed particles may be adjusted to within a range of 100 μm to 800 μm.

[0098] Meanwhile, in the present invention, the obtained mixed powder for an electrode contains PTFE and / or polyolefin as a binder resin, and the crystallinity (Xc) of the binder resin may be 20% or less.

[0099] In the present invention, the crystallinity (Xc) can be measured using a differential scanning calorimeter (DSC) and is based on the temperature (peak temperature) at which the highest enthalpy is observed during crystallization. Specifically, the crystallinity can be calculated by multiplying the melting enthalpy (ΔHm) actually measured by DSC by the melting enthalpy (ΔHm) of a theoretically perfect crystal (100% crystallinity). 0 ) (equilibrium heat of fusion) value and expressed as a percentage, and can be calculated by the following formula 3. Here, the theoretical enthalpy of fusion of a perfect crystal (ΔHm 0 For the enthalpy of melting, refer to academic papers such as "Polymer Handbook" (J. Brandrup et al., 2003) and "Polymer." For example, the theoretical enthalpy of melting of perfectly crystalline PTFE is 85.4 J / g (Polymer, Vol. 46 (2005), 8872-8882). Meanwhile, thermal analysis of polymers, such as DSC, can usually be measured and calculated according to ASTM D3418-21. [Formula 3] Xc(%)=(ΔHm÷ΔHm0)×100

[0100] Meanwhile, in one embodiment of the present invention, the mixed powder for an electrode has a low resistivity, which is advantageous in minimizing the generation of fine powder and improving the processability of forming the powder into a film. In one embodiment of the present invention, the mixed powder preferably has a resistivity of 700 Ω·cm or less when pressed under a pressure of 50 MPa. A high resistivity outside this range is not preferred because it may increase the resistance of the subsequently manufactured composite film and dry electrode, thereby reducing battery performance.

[0101] The resistivity can be calculated by placing 2 g of electrode powder in a 22 mm diameter ceramic container with a built-in four-point probe at the bottom, pressing the container with a force of 2,000 kgf, i.e., a pressure of about 50 MPa, measuring the resistance, and multiplying the result by the thickness of the pressed electrode powder.

[0102] <Dry electrode film and dry electrode> The present invention also relates to a dry electrode film including the mixed powder, and a dry electrode including the dry electrode film. The dry electrode film refers to a free-standing single sheet manufactured using an electrode material including an electrode active material and a binder without the use of a solvent. As used herein, the term "free-standing" refers to a film that can maintain its independent form without relying on other components and can be moved and handled by itself. In the present invention, the dry electrode film may be formed by compressing the electrode mixed powder, as described below. For example, the electrode mixed powder may have a layered structure formed by accumulating through compression. In the present invention, the dry electrode includes an electrode active material layer derived from the free-standing dry electrode film. For example, the dry electrode may include a current collector and an electrode active material layer derived from the dry electrode film disposed on at least one surface of the current collector, and the dry electrode film and the current collector may be bonded together by a lamination process or the like.

[0103] Hereinafter, methods for manufacturing the dry electrode film and the dry electrode will be described in detail.

[0104] <Manufacturing method for dry electrode film> In one embodiment of the present invention, the dry electrode film may be obtained by compressing the electrode powder mixture. In this specification, the process of compressing the electrode powder mixture to manufacture a sheet-shaped dry electrode film is referred to as a calendering process. Through the calendering process, the dry electrode film may be provided in the form of a sheet having a predetermined thickness. For example, the dry electrode film may be in the form of a strip having an aspect ratio exceeding 1. In one embodiment of the present invention, the thickness of the dry electrode film may be 50 μm to 300 μm.

[0105] For example, the calendering process may be performed by a calendering method in which the electrode powder mixture is supplied to a calendering device and thermally pressed using a roll press included in the calendering device, and may be performed by a roll-to-roll continuous process.

[0106] In one embodiment of the present invention, the calendering device may include a roll press unit having two rollers arranged opposite to each other, and the electrode powder mixture may be compressed into a sheet by passing through the roll press unit. A plurality of roll press units may be arranged in series, and the dry electrode film may be compressed multiple times. The number of roll press units may be appropriately adjusted taking into account the thickness and rolling ratio of the dry electrode film. FIG. 9 is a schematic diagram of the calendering process 100. Referring to this diagram, the dry electrode film 130 is manufactured by compressing the powder mixture 120 multiple times using a calendering device including multiple calendering rollers 110.

[0107] Meanwhile, in each roll press unit, the rotational speed ratio of the two rollers may be independently controlled within a range of 1:1 to 1:10. For example, the rotational speed ratio of the two rollers in one or more roll press units may be independently controlled within a range of 1:1 to 1:3. Furthermore, the temperature of the rollers in each roll press unit may be independently controlled within a range of 100°C to 250°C. A dry electrode film may be manufactured through this calendering process. In one embodiment of the present invention, the crystallinity (d) of the binder resin in the obtained dry electrode film may be controlled to 10% or less. If the crystallinity of the obtained dry electrode film exceeds 10%, the crystallinity may be adjusted by adjusting the gap between the two rollers of the roll press unit or by controlling the speed ratio. For example, the degree of binder fiberization may be increased by reducing the gap and / or increasing the speed ratio. When the crystallinity is controlled to 10% or less, the flexibility of the dry electrode film is increased, which has the advantage of preventing breakage or cracking when wound up for storage or when unwound. In addition, the increased flexibility can improve the mechanical strength, such as improving the tensile strength and tensile elongation.

[0108] Meanwhile, in the present invention, the porosity of the dry electrode film may be 20 vol% to 50 vol%, and may be controlled within the above range, preferably to a value of 40 vol% or less or 35 vol% or less. A porosity within the above range is preferable in terms of various effects. On the other hand, if the porosity is too small outside the above range, it is difficult for the electrolyte to be impregnated, which is undesirable in terms of life characteristics, output characteristics, etc., and if it is too large, it is undesirable in terms of volume-specific energy density, as the volume required to achieve the same capacity increases. In one embodiment of the present invention, the porosity can be calculated using the following Equation 4, where the apparent density of the dry electrode film is measured and the true density is calculated based on the true density of each component and the composition: [Formula 4] Porosity (vol%) = {1 - (apparent density / true density)} x 100

[0109] <Dry electrode manufacturing method> Next, a method for manufacturing a dry electrode according to an embodiment of the present invention will be described. In one embodiment of the present invention, the dry electrode may be manufactured by bonding a dry electrode film and a current collector through a lamination process. Specifically, the obtained dry electrode film is laminated on one or both sides of a current collector, and the current collector and the dry electrode film are bonded through a lamination process to manufacture an electrode. The lamination may be a step of rolling the dry electrode film onto the current collector. The lamination may be performed using a roll press method using a lamination roller, which may be adjusted to a temperature of 20°C to 200°C. FIG. 10 is a schematic diagram illustrating a lamination process according to an embodiment of the present invention. Referring to this diagram, a dry electrode film 230 is bonded to a current collector 220 to manufacture a dry electrode 240, and the lamination process is performed by pressing with a lamination roller 210. Meanwhile, in the present invention, the dry electrode film attached to the current collector as a result of lamination may be referred to as an electrode active material layer. In addition, in the present invention, the dry electrode film and the electrode active material layer are derived from the electrode mixed powder, and the content ratios of the materials in the dry electrode film and the electrode active material layer may be in the same range as those of the mixed powder.

[0110] <qbr> Meanwhile, in one embodiment of the present invention, the binder polymer may include a fluorine-containing binder, and the electrode active material layer may have a QBR (Quantified Binder Ratio) of 1.1 or less. The QBR is defined by the following Equation 5. [Formula 5] QBR=Bs / Bf

[0111] In Equation 5, Bs represents the average fluorine content in a surface region of the electrode active material layer from the outermost surface to within 15% of the total thickness of the electrode active material layer, and Bf represents the average fluorine content in a bottom region of the electrode active material layer from the interface of the electrode active material layer facing the current collector to within 15% of the total thickness of the electrode active material layer. FIG. 7 is a schematic diagram of an electrode according to an embodiment of the present invention. Referring to FIG. 7, an electrode 10 includes an electrode current collector 12 and an electrode active material layer 11 disposed on the electrode current collector 12 and including an electrode active material and a binder polymer. The electrode active material layer 11 has a surface region 11s extending from the outermost surface to within 15% of the total thickness d of the electrode active material layer, and a bottom region 11f extending from the interface of the electrode active material layer facing the current collector to within 15% of the total thickness d of the electrode active material layer, where d is the total thickness of the electrode active material layer. In the above formula 5, QBR is defined as Bs, the average fluorine content in the surface region 11s of the electrode active material layer, and Bf, the average fluorine content in the bottom region 11f of the electrode active material layer. QBR can be calculated as follows:

[0112] First, an electrode for which QBR is to be confirmed is selected, and a cross section of the selected electrode is prepared using argon ion milling. Then, an energy dispersive X-ray spectroscopy (EDS) detector in a scanning electron microscope (SEM) is used to perform EDS mapping of the components in the electrode active material layer of the prepared electrode cross section.

[0113] A line profile in the thickness direction of the electrode active material layer is extracted from the results of EDS mapping, and from the extracted line profile results, the average value (Bs) of the fluorine content of the fluorine-containing binder in the surface region of the electrode active material layer and the average value (Bf) of the fluorine content of the fluorine-containing binder in the bottom region of the electrode active material layer are extracted, and the QBR value is calculated using the above-mentioned Equation 5.

[0114] In this case, the surface region of the electrode active material layer is the region from the outermost surface in the thickness direction of the electrode active material layer to within 15% of the total thickness of the electrode active material layer, and the bottom region of the electrode active material layer is the region from the interface of the electrode active material layer facing the current collector to within 15% of the total thickness of the electrode active material layer.

[0115] Figure 8 is a schematic diagram for calculating the QBR value of an electrode active material layer. Referring to Figure 8, the X-axis represents the thickness of the electrode active material layer, i.e., the distance from the surface toward the current collector, and the Y-axis represents the intensity of the fluorine component. Line A represents the intensity of the fluorine component of the fluorine-containing binder extracted by EDS mapping of the fluorine component in the electrode active material layer of the electrode cross section, and Line B is a trend line showing the tendency of Line A, smoothed using the LOWESS smoothing method, i.e., locally weighted scatterplot smoothing.

[0116] The QBR value indicates the uniformity of the distribution of the fluorine-containing binder in the thickness direction of the electrode active material layer, based on the ratio of the content of the fluorine-containing binder contained in the surface region to the content of the fluorine-containing binder contained in the bottom region of the electrode active material layer. Here, the content of the fluorine-containing binder can be estimated based on the fluorine component contained in the fluorine-containing binder used.

[0117] The QBR value is 1.1 or less, and according to an embodiment of the present invention, the QBR value may be 0.95 or more, 0.97 or more, 1.03 or less, 1.05 or less, or may be 0.95 to 1.05. When the QBR value is 1.1 or less, the fluorine-containing binder does not migrate to the surface of the electrode, which prevents a problem in which the content of the fluorine-containing binder in the surface region is higher than the content of the fluorine-containing binder in the bottom region of the electrode active material layer. As a result, the binder is distributed uniformly in the thickness direction of the electrode active material layer, and the binder content in the portion close to the current collector is not reduced. This improves the adhesion between the current collector and the electrode active material layer, and the conductivity at the surface of the electrode active material layer and the resulting charge / discharge rate can also be improved. The fluorine-containing binder may specifically include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), a PVdF-based copolymer such as polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), or two or more of these. Also, the fluorine-containing binder may include polytetrafluoroethylene alone, or may further include one or more of a PVdF-based copolymer such as polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), or polytetrafluoroethylene.

[0118] <Compression ratio> Meanwhile, according to an embodiment of the present invention, the dry electrode film may have a compression ratio of 30% to 50%, 35% to 50%, or 40% to 50%. The compression ratio may be defined as the ratio of the thickness to which the dry electrode film is compressed at the moment of lamination to combine the dry electrode film with a current collector, and may be calculated using the following Equation 6: [Formula 6] Compression ratio (%) = Tp / T1 x 100

[0119] In Equation 6, Tp represents the thickness of the dry electrode film pressed and compressed in the lamination step, and T1 represents the thickness of the dry electrode film before the lamination step.

[0120] In the present invention, by adjusting the compression ratio in the lamination step to satisfy a specific range, it is possible to provide a dry electrode film with appropriate density and porosity, and excellent bonding strength between the dry electrode film and the current collector.

[0121] When the compression ratio is within the range of 30% to 50%, the pressure applied to the dry electrode film is sufficient, improving the adhesive strength between the dry electrode film and the current collector, thereby preventing the electrode active material layer from peeling off from the current collector in an electrode manufactured by a lamination process, and eliminating the problem of the electrode active material layer exhibiting a lower porosity than the target porosity or damage to the current collector due to an excessive increase in the density of the dry electrode film.

[0122] In an embodiment of the present invention, when dry electrode films are laminated on both sides of the current collector, the compression ratio (%) in Equation 6 above may be expressed as Equation 7 below. [Formula 7] 30≦(T1+0.5Tc-0.5Tgap) / T1×100≦50

[0123] In Equation 7, T1 represents the thickness of the dry electrode film before the lamination step, Tc represents the thickness of the current collector, and Tgap represents the gap between the first and second rolling rolls. The rolling ratio of the dry electrode film after the lamination step may be 20% or less, 18% or less, 15% or less, 5% to 15%, 6% to 15%, 7% to 15%, or 9% to 13%. The dry electrode film after the lamination step can be considered an electrode active material layer. The rolling ratio is defined as the ratio of the thickness of the dry electrode film after the lamination step to the thickness of the dry electrode film before the lamination step, and can be calculated using Equation 8 below. [Formula 8] Rolling ratio (%) = (T1-T2) / T1 x 100

[0124] In Equation 8, T1 represents the thickness of the dry electrode film before the lamination step, and T2 represents the thickness of the dry electrode film after the lamination step. When the rolling ratio satisfies the above range, the electrode active material layer in the manufactured dry electrode has appropriate density and porosity, and the adhesion strength with the current collector is improved.

[0125] In the dry electrode film, the increase rate of apparent density before and after lamination with the current collector can be calculated using the following Equation 9. [Formula 9] Apparent density increase rate (%) = (D2 - D1) / D1 x 100

[0126] In Equation 9, D1 is the apparent density of the dry electrode film before the lamination step (g / cm 3 ), and D2 is the apparent density (g / cm ) of the dry electrode film (i.e., the electrode active material layer) after the lamination step. 3 ) is shown.

[0127] The increase rate of the apparent density of the dry electrode film before and after lamination with the current collector may be 5% to 30%, 7% to 25%, or 10% to 20%, where D1 and D2 are 2.75 g / cm 3 ~3.5g / cm 3 Meanwhile, when the increase rate of the apparent density of the dry electrode film satisfies the above range, the adhesion between the dry electrode film and the current collector is improved, and problems such as the porosity falling outside the target range or damage to the positive electrode active material or the current collector can be prevented.

[0128] The apparent density of the dry electrode film before and after lamination with the current collector can be calculated by measuring the weight and thickness of the dry electrode film before lamination, measuring the weight and thickness of the electrode after lamination, and then subtracting the weight and thickness of the current collector to determine the weight and thickness of the film.

[0129] In one embodiment of the present invention, the active material loading of the dry electrode is 2.5 mAh / cm 2 ~15mAh / cm 2 Specifically, 4mAh / cm 2 ~10mAh / cm 2 Here, the active material loading amount is a value calculated by the following Equation 10. [Formula 10] Active material loading (mAh / cm 2 ) = Capacity of active material (mAh / g) × Weight ratio of active material in dry electrode (wt%) × Weight per unit area of ​​dry electrode (g / cm 2 )

[0130] In addition, in the dry electrode, the interface resistance between the electrode active material layer and the current collector is 5 Ω cm 2 For details, see below: 2Ω·cm 2 The interfacial resistance may be calculated by applying a current of 100 μA to the electrode using a multi-probe resistance measurement method, and measuring the resistance between the electrode active material layer and the current collector based on the potential difference measured between multiple probes. If the interfacial resistance satisfies the above range, the battery performance of a subsequently manufactured secondary battery can be improved.

[0131] The present invention also relates to an electrode assembly including the dry electrode obtained as described above, and an electrochemical device including the electrode assembly. The electrode assembly may include a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. In other embodiments, the electrode assembly may include a positive electrode, a negative electrode, and a solid electrolyte membrane interposed between the positive electrode and the negative electrode. In each embodiment, the positive electrode and / or the negative electrode may be a dry electrode having the characteristics described above.

[0132] The electrochemical device of the present invention includes any device in which an electrochemical reaction occurs, and specifically includes all types of primary batteries, secondary batteries, fuel cells, solar cells, capacitors such as supercapacitors, etc. Among the secondary batteries, lithium secondary batteries, including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, and lithium ion polymer secondary batteries, are particularly preferred.

[0133] Hereinafter, the present invention will be described in detail based on examples, comparative examples, and experimental examples so that those skilled in the art can easily understand the present invention.

[0134] Example <Manufacturing mixed powders for electrodes and dry electrode films> (Examples 1 to 4 and Example 7) Nickel-cobalt-manganese-aluminum composite oxide (Li(Ni,Co,Mn,Al)O2), carbon black, and polytetrafluoroethylene (PTFE) were added to a blender and mixed at approximately 10,000 rpm for approximately 1 minute to produce a mixture. The kneader temperature was then stabilized at approximately 150°C, and the mixture was added to the kneader and mixed under a pressure of approximately 1.1 atm to obtain a mixture mass. The kneading process was carried out at a speed of approximately 50 rpm for approximately 5 minutes. The mixture mass was added to the blender and pulverized at approximately 10,000 rpm for approximately 40 seconds, and then sieved through a 1 mm mesh sieve to obtain a mixed powder for an electrode. The mixed powder for an electrode was then added to a first laboratory calender (roll diameter: 88 mm, roll temperature: approximately 100°C, approximately 20 rpm) and compressed to produce a dry electrode film. The obtained dry electrode film was then placed on both sides of an aluminum thin film (19 μm thick) and bonded by a lamination process maintained at approximately 150°C to obtain an electrode. The thickness of the electrode active material layer on one side of the obtained electrode was approximately 80 μm. Meanwhile, the nickel-cobalt-manganese-aluminum composite oxide had a bimodal distribution, containing large particles (secondary particles) with a diameter of approximately 10 μm and single particles with a diameter of approximately 5 μm. Figure 1 is an SSRM image of the electrode of Example 1, and Figure 15 is an SSRM image of the electrode of Example 7. Meanwhile, Figure 2 is an SSRM image of the electrode of Example 1, and Figure 17 is an SSRM image of the electrode of Example 7, where the conductive material area was masked.

[0135] (Examples 5 and 6) An electrode was obtained in the same manner as in Example 1, except that a monomodal distribution nickel-cobalt-manganese-aluminum composite oxide containing single particles with a diameter of approximately 5 μm was used. The upper part of Figure 13 is an SSRM image of Example 5, and the lower part of Figure 13 is an image observed after the conductive material region was masked. The upper part of Figure 14 is an SSRM image of Example 6, and the lower part of Figure 14 is an image observed after the conductive material region was masked.

[0136] The content ratios of the components used in Examples 1 to 6, the types of conductive materials, and the specific surface areas of the conductive materials are shown in Table 1 below.

[0137] [Table 1]

[0138] [Table 2]

[0139] (Comparative Examples 1 to 4) Nickel-cobalt-manganese-aluminum composite oxide (Li(Ni,Co,Mn,Al)O2), carbon black, and polytetrafluoroethylene (PTFE) were placed in a blender and mixed at room temperature for approximately 1 minute at approximately 10,000 rpm to prepare a mixture. The mixture was then pulverized using a jet milling process (feeding pressure: 50 psi, grinding pressure: 45 psi) to obtain a mixed powder for electrodes. The kneading process used in the Examples was not performed in Comparative Examples 1 to 4. The mixed powder for electrodes was placed in a first laboratory calender (roll diameter: 88 mm, roll temperature: approximately 100°C, approximately 20 rpm) and pressed to prepare a dry electrode film. The obtained dry electrode film was then placed on both sides of an aluminum thin film (approximately 19 μm thick) and bonded through a lamination process maintained at approximately 150°C to obtain an electrode. The thickness of the electrode active material layer on one side of the obtained electrode was approximately 80 μm. Figure 3 is an SSRM image of Comparative Example 1, and Figure 4 is an image obtained by masking the conductive material area. On the other hand, the nickel-cobalt-manganese-aluminum composite oxide has a bimodal distribution, and contains large particles (secondary particles) with a diameter of about 10 μm and single particles with a diameter of about 5 μm.

[0140] [Table 3]

[0141] [Table 4]

[0142] <Cross-sectional sample preparation> Electrodes obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were prepared. A solution containing an epoxy-based polymer having a weight average molecular weight of about 700 g / mol or less as a polymer containing an epoxy group was prepared. Each electrode was impregnated with the prepared epoxy-based polymer solution to fill the pores with the polymer. Then, using an ion milling apparatus (IB19520CCP, manufactured by Jeol) that irradiates an argon ion beam, a focused argon (Ar) ion beam was irradiated onto the positive electrode for the secondary battery to scrape off the surface and produce a cross-sectional sample having a clean cross-section. When irradiating with the argon ion beam, the ion beam current was set to 170 μA, and the gas flow rate was set to 1.5 cm 3 / min, and this was carried out for 3 hours. The cross-sectional sample had a cross-section parallel to the surface of the current collector corresponding to a depth of about 10% from the surface of the electrode active material layer exposed downward.

[0143] <SSRM Analysis Conditions> Device used: cypher ES (manufactured by Oxford Instruments), Dual-gain ORCA cantilever holder [Parameters] Mode: Contact Samples / Lines: 512×512, Scan rate: 0.5 Hz Bias: ~2V, Deflection set point voltage: ~0.2 Scan angle: 90° [AFM Mode] Model: AD-40-As (manufacturer: Adama) Tip: High-concentration boron-doped single-crystal diamond, tip height 300 nm Cantilever & Bulk tip: Diamond-coated silicon, reflective coating (Au) F = 180 kHz, k = 40 N / m Representative contact resistance: ~10 kΩ

[0144] <SSRM Analysis Method> After ion milling, the sample was transferred to a glove box without exposure to the atmosphere and loaded onto an AFM puck. Silver (Ag) paste was then applied between the electrode portions other than the fabricated cross section and the AFM puck to form an additional conductive path. The sample with the additional conductive path was then loaded into a sealed cell body and attached to the AFM instrument while maintaining its atmosphere-protected state. After laser alignment, the milled portion was selected as the measurement area using an optical microscope and measured under Ar flow. SSRM images were obtained in this manner. Figures 1, 3, the top row of Figure 13, the top row of Figure 14, and Figure 15 are SSRM images of Example 1, Comparative Example 1, Example 5, Example 6, and Example 7, respectively. The observed image size was 30 μm × 30 μm.

[0145] <Masking conductive material areas> The conductive material regions were masked from the acquired SSRM images using Gwyddion software.

[0146] First, a log(resistance) image was obtained, and a histogram of the log(resistance) distribution within the image was obtained. This was obtained using the height distribution function in the Calculate 1D Statistical function provided by the software. The limit point was determined by adding 0.2 to the log(R / Ω) value corresponding to the lowest point between the peak corresponding to the conductive material and the peak corresponding to the electrode active material in the histogram. Figure 12a shows the histogram for Example 7, and log(R / Ω) = 7.2 was set as the limit point. Based on this, the conductive material region was masked. In this case, a grain filtering function was used to remove regions corresponding to pixels less than 3 pixels in size, and regions located within the electrode active material were removed. Meanwhile, referring to Figures 5, 6, and 12a, it was confirmed that pixels corresponding to the electrode active material and pixels corresponding to the conductive material could be distinguished in the histogram obtained from the logarithmic scale image. In other words, it was found that the distribution of the conductive material region could be easily quantified using information on each pixel whose corresponding region was determined.

[0147] 2 shows the electrode of Example 1, the lower part of FIG. 13 shows the electrode of Example 5, the lower part of FIG. 14 shows the electrode of FIG. 6, FIG. 16 shows the electrode of Example 7, and FIG. 4 shows the electrode of Comparative Example 1, with the conductive material areas masked and only the masked conductive material areas shown in shades of color.

[0148] The grain-summary function was then used to determine the perimeter and area for the masked region.

[0149] Next, the dispersibility index 1 and the dispersibility index 2 were calculated by substituting the respective values ​​into Equation 1 and Equation 2, and the results are shown in Tables 5 and 6 below. From Tables 5 and 6, it can be seen that the dry electrode of the example manufactured by the kneading process has a dispersibility index 1 of 3.5 μm -1 It can be seen that the dispersibility index 2 is 10 or more. However, the dry electrode manufactured in the comparative example has a dispersibility index 1 of 3.5 μm. -1 The dispersion index 2 was less than 10. As described above, there are differences in the dispersion of conductive materials in electrodes that are the result of an electrode manufacturing process, and it was confirmed that the electrode according to the present invention exhibited an excellent dispersion index.

[0150] [Table 5]

[0151] [Table 6] [Explanation of symbols]

[0152] 10 electrodes 11 Electrode active material layer 11f bottom area 11s surface area 12 Electrode current collector 100 Calendering process 110 Roller 120 Mixed powder 130 Dry electrode film 200 Lamination process 210 Lamination Roller 220 Current Collector 230 Dry electrode film 240 Dry Electrode< / qbr>

Claims

1. A dry electrode for an electrochemical element, The dry electrode includes an electrode active material layer derived from a dry electrode film, the electrode active material layer includes an electrode mixed powder, and the electrode mixed powder is thermocompressed to form a sheet having a predetermined thickness; The electrode powder mixture includes an electrode active material and a binder polymer, The electrode active material layer has a thickness of 1000 nm or more, and the thickness of the electrode active material layer is determined by the following formula 1: [Formula 1] Index 1(μm －１ )=Boundary ｍｅａｓｕｒｅｄ / A The dispersion index 1 (Index 1) of the conductive material is 3.5 μm －１ The above and / or the following Equation 2: [Formula 2] Index 2=Boundary ｍｅａｓｕｒｅｄ / L ｃｉｒｃｌｅ The dispersion index 2 (Index 2) of the conductive material according to In Equation 1, Boundary ｍｅａｓｕｒｅｄ is the periphery of the conductive material region measured at a predetermined cross section of the electrode active material layer, A is the area of ​​the portion defined as the conductive material region measured at a predetermined cross section of the electrode active material layer, and in Equation 2, L ｃｉｒｃｌｅ is the circumference of a circle with the same area as the area of ​​the measured conductive material region [Equation 1] That is, dry electrodes.

2. The electrode active material layer has a conductive material dispersion index 1 (Index 1) of 3.5 μm according to Equation 1 for one or more arbitrary cross sections inside the electrode active material layer. －１ 2. The dry electrode according to claim 1, wherein the conductive material has a dispersion index 2 (Index 2) of 10 or more according to Equation 2.

3. The dispersibility index 1 and the dispersibility index 2 are A step (step 1) of preparing a cross-sectional sample in which an arbitrary cross section inside an electrode active material layer is exposed; Step 2: Obtaining a 2D scale map of the resistance distribution of the electrode cross-section sample; masking the conductive material areas (step 3); and (ii) calculating the perimeter and area of ​​the masked region and substituting the calculated perimeter and area into Equation 1 and / or Equation 2 to confirm the dispersion degree of the conductive material in the electrode active material layer (Step 4).

4. The dry electrode according to claim 1 , wherein the electrode active material layer is formed on one surface of an electrode current collector, and the cross section is a plane parallel to or perpendicular to a portion of the electrode active material layer facing the current collector.

5. 2. The dry electrode of claim 1, wherein the binder polymer is fiberized, and the fiberization is the result of kneading under shear stress.

6. The dry electrode of claim 1 , wherein the binder polymer comprises polytetrafluoroethylene, polyolefin, or a mixture thereof.

7. A method for manufacturing the dry electrode according to claim 1, comprising the steps of: A step (S10) of mixing an electrode material including an electrode active material and a binder polymer; A step (S20) of kneading the mixed electrode materials; Step (S30) of grinding the resultant of step (S20) to obtain an electrode mixture powder; and (S40) compressing the electrode mixture powder to manufacture a self-standing dry electrode film, The method for manufacturing a dry electrode, wherein the step (S20) is performed at a temperature of 60° C. or higher.

8. The method of claim 7, wherein the step (S20) is performed at a temperature ranging from 60°C to 250°C.

9. The method for manufacturing a dry electrode according to claim 7 , further comprising bonding the dry electrode film and a current collector by a lamination process.

10. 7. An electrochemical element comprising: a positive electrode; a negative electrode; and a separator or a solid electrolyte membrane interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is the dry electrode according to claim 1.

Images