Dry electrode for electrochemical device and method for manufacturing same

Abstract

The present invention relates to a dry electrode comprising a dry electrode film as an electrode active material layer, the electrode active material layer comprising an electrode active material and a binder resin, in which the binder resin is fibrillated, and the electrode active material layer has an average pore diameter of 5.0 [mu] m or more and a porosity of 15 vol% to 50 vol%, and the average aperture is calculated based on the longest aperture.

Description

TECHNICAL FIELD

[0001] This application claims priority to Korean Patent Application No. 10-2023-0105146, filed on August 10, 2023, in Korea, the disclosure of which is incorporated herein by reference. The present disclosure relates to a dry electrode for an electrochemical device including a dry electrode film. Further, the present disclosure relates to a method for manufacturing the same. BACKGROUND

[0002] As the use of fossil fuels is increasing, the demand for the use of alternative energy and clean energy is increasing, and in such circumstances, many studies are being conducted in the field of generating and storing energy using electrochemistry. At present, a typical example of an electrochemical device using electrical energy and chemical energy is a secondary battery, and the application range of the secondary battery is gradually expanding. A lithium secondary battery, which is one of typical secondary batteries, is not only used as an energy source for mobile devices, but also used as a power source for electric vehicles and hybrid electric vehicles that replace vehicles using fossil fuels, such as gasoline vehicles and diesel vehicles, which are considered to be one of the main causes of air pollution, and the application range of the lithium secondary battery is expanding to auxiliary power through a power grid. The method of manufacturing a lithium secondary battery is roughly divided into three steps: an electrode manufacturing process, an electrode assembly manufacturing process, and a formation / aging process. The electrode manufacturing process is subdivided into an electrode material mixing process, an electrode coating process, a drying process, a roll-pressing process, a cutting process, and a winding process. Among them, the electrode material mixing process is a process of mixing components for forming an electrode active layer in which an electrochemical reaction actually occurs in an electrode, specifically, mixing an electrode active material, which is an essential element of an electrode, with additives such as a conductive material, a filler, a binder for bonding and adhering a powder to a current collector, and a solvent for imparting viscosity and dispersion ability to prepare a flowable slurry.

[0003] The mixed composition for forming the electrode active material is broadly referred to as an electrode mixture. Subsequently, an electrode coating process of applying the electrode mixture to a conductive current collector, and a drying process for removing a solvent contained in the electrode mixture are performed, and additionally, the electrode is roll-pressed to a predetermined thickness.

[0004] Meanwhile, as the solvent contained in the electrode mixture evaporates in the drying process, defects such as pinholes or cracks can occur in the electrode active layer that has been formed. In addition, the active layer is not uniformly dried on all the entire internal / external regions, and due to the difference in the solvent evaporation rate, some regions are dried earlier and the powder floats at the corresponding region, while some other regions are dried later at a certain time interval, resulting in low quality of the electrode.

[0005] To solve this problem, dryers that uniformly dry the inner and outer regions of the active layer and adjust the solvent evaporation rate have been developed, but these dryers are very expensive and require a considerable amount of cost and time to operate them, thus being disadvantageous in terms of the manufacturing process. Therefore, many studies have recently been conducted to manufacture dry electrodes without solvents.

[0006] Manufacture of the dry electrode has the effects of environmental friendliness, process simplification, and cost savings. In addition, in the manufacture of a wet electrode, binder resin migration occurs during drying of the electrode slurry, but such binder resin migration does not occur in the manufacture of a dry electrode, and thus the manufactured electrode has a uniform binder resin distribution in the thickness direction. Through the uniform binder resin distribution, problems of battery capacity reduction, performance deterioration, and short lifespan can be prevented.

[0007] However, in the manufacture of a dry electrode, when the binder resin is fibrillated too fine or the pore size is small, the narrow pores hinder the migration of Li ions, resulting in electrode capacity reduction during high-rate charge / discharge. Therefore, in addition to the uniform binder / conductive material distribution in the vertical direction (thickness direction) of the electrode, an electrode structure design for fast ion transport is required to improve high-rate charge / discharge. The present disclosure requires research into structure control of a dry electrode film effective for high-rate charge / discharge through an optimal level of kneading process. SUMMARY

[0008] TECHNICAL PROBLEM

[0009] The present disclosure is designed to solve the above problems, and the present disclosure aims to provide a dry electrode having an advantageous structure for high-rate charge / discharge, in which an electrode active material layer has a uniform binder / conductive material distribution, and small deviation and uniform size pores to minimize the ratio of excessively large or small pores.

[0010] The present disclosure also aims to provide a method for manufacturing a dry electrode having the above structure.

[0011] It will be readily understood that these and other objects and advantages of the disclosure can be achieved by the means or methods as set forth in the appended claims and their combinations.

[0012] TECHNICAL SOLUTION

[0013] A first aspect of the present disclosure relates to a dry electrode for an electrochemical device, in which an electrode active material layer includes a dry electrode film, the electrode active material layer contains an electrode active material and a binder resin, the binder resin is fibrillated, the electrode active material layer has an average pore diameter of 5.0 μm or more and a porosity of 15% by volume to 50% by volume, and the average pore diameter is calculated based on the longest pore diameter. In the above aspect, the average pore diameter of the electrode active material layer can be 6.0 μm or more.

[0014] In any one of the above aspects, the average pore diameter of the electrode active material layer can be 6.5 μm or more.

[0015] In any one of the above aspects, in the electrode active material layer, the average diameter (μm) of pores having a diameter of 4 μm to 8 μm can be 6.5 μm or more.

[0016] In any one of the above aspects, in the electrode active material layer, the ratio of the number of pores having a diameter of 4 μm to 8 μm to the total number of pores can be 80% or more.

[0017] In any one of the above aspects, in the electrode active material layer, the ratio of the volume of pores having a diameter of 4 μm to 8 μm to the total pore volume can be 60% or more.

[0018] In any one of the above aspects, in the electrode active material layer, the geodesic tortuosity (τ geo ) according to the following Equation 1 can be 1.15 or less:

[0019] [Equation 1]

[0020]

[0021] In the above Equation 1, L represents the thickness of the electrode active material layer, and L eff represents the lithium ion movement path length in the electrode active material layer.

[0022] In any one of the above aspects, in the electrode active material layer, the physical tortuosity (τ phy ) according to the following Equation 2 can be 3 or less:

[0023] [Equation 2]

[0024]

[0025] In the above Equation 2, ε represents the porosity of the electrode active material layer, δ0represents the electrolyte conductivity, and δ effrepresents the effective electrolyte conductivity generated by the pore structure.

[0026] In any one of the above aspects, the binder resin can include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a polyolefin, or a mixture of two or more thereof.

[0027] In any one of the above aspects, the crystallinity of the dry electrode film can be greater than 0% and 10% or less.

[0028] In any one of the above aspects, the binder resin can include fibrillated fibrils, a portion of the fibrillated fibrils having a diameter of 1 μm or more.

[0029] In any one of the above aspects, the fibrillated binder resin can include fibrils, a portion of the fibrils having a diameter of 1 μm or more having a length of 5 μm or more.

[0030] The present disclosure can provide a method for manufacturing a dry electrode film according to any one of the above aspects, the method can include the steps of: (S10) preparing a powdery blend including an electrode active material, a conductive material, and a binder resin; (S20) kneading the powdery blend to prepare a blocky blend; (S30) grinding the blocky blend to obtain an electrode powder; and (S40) calendering the electrode powder.

[0031] In any one of the above aspects, the D50 of the electrode powder obtained in (S30) can be in the range of 100 μm to 700 μm.

[0032] Each embodiment can be independently implemented, or alternatively, two or more of the above-described embodiments can be combined.

[0033] Advantages

[0034] The dry electrode according to the present disclosure can have an electrode active material layer in which the ratio of pores having too small or too large diameters is low, and the pores have a small pore size deviation and uniform pore sizes, so that lithium (Li) migration is easy, thereby achieving low Li diffusion resistance and fast lithium transport, thereby reducing or inhibiting overvoltage, and improving high-rate charge / discharge characteristics. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings illustrate exemplary embodiments of the present disclosure and, together with the following detailed description, provide a better understanding of the technical aspects of the present disclosure, so the present disclosure is not to be construed as being limited to the accompanying drawings.

[0036] Figures 1a to 1c The pore shape and size distribution of Example 1, Comparative Example 1, and Comparative Example 2, respectively, are shown.

[0037] Figure 1d The pore size and relative probability (%) of each of Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0038] Figure 1e is a reference diagram showing the classified pore shape.

[0039] Figures 2a to 2d The charge curves of Comparative Example 1, Comparative Example 2, and Example 1 as a function of C-rate are shown.

[0040] Figures 3a to 3d The discharge curves of Comparative Example 1, Comparative Example 2, and Example 1 as a function of C-rate are shown.

[0041] Figure 4 A scanning electron microscope (SEM) image of the electrode active material layer in the electrode according to Example 1 is shown.

[0042] Figure 5 A SEM image of the electrode active material layer in the electrode according to Comparative Example 2 is shown.

[0043] Figures 6 to 11 Image processing results of the electrode active material region and the binder region in a random cross-section of the electrode according to each of Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0044] Figures 12a to 14b The SOC 3D mapping of the delithiated region at the end of charge of the electrode according to each of Example 1, Comparative Example 1, and Comparative Example 2 is shown.

[0045] Figure 15 is a graph showing the results of calculating the short-range line tortuosity and the physical tortuosity of the electrode active material layer in the electrode according to each of Example 1, Comparative Example 1, and Comparative Example 2.

[0046] Figure 16 is a schematic diagram of an electrode according to one embodiment of the present disclosure.

[0047] Figure 17 is a schematic diagram showing the calculation of the QBR value of the electrode active material layer.

[0048] Figure 18 is a graph exemplarily showing the grayscale values of each material of the electrode obtained using a focused ion beam (FIB) apparatus. Figure 19 is a graph showing each variable in Equation 3 and Equation 4.

[0049] Figure 20 and Figure 21 is an SEM image showing the mixture powder containing the electrode active material particles and the fibrillated binder resin prepared in Example 1. DETAILED DESCRIPTION

[0050] Hereinafter, the present disclosure will be described in greater detail to help the understanding of the present disclosure.

[0051] It is to be understood that the terms or words used in the present specification and the appended claims should not be interpreted as being limited to the commonly used meanings and dictionary definitions, but should be interpreted based on the meanings and concepts corresponding to the technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define the terms appropriately for the best explanation of the present disclosure.

[0052] The terms used herein are used to describe the exemplary embodiments and are not intended to limit the present disclosure. As used herein, the singular forms are intended to include the plural forms unless the context clearly indicates otherwise.

[0053] It is to be understood that the terms "include", "comprise", or "have" when used in the present specification and the appended claims, indicate the presence of the stated elements but do not preclude the presence or addition of one or more other elements.

[0054] The particle size D 10 , D 50 , and D 90 , as used herein, refer to the particle size at 10%, 50%, and 90% of the cumulative particle size distribution of the particles, respectively. The particle size can be measured using a laser diffraction method. Specifically, the particle size distribution is calculated by dispersing a target powder in a dispersion medium, feeding it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and measuring the difference in diffraction patterns according to the particle size when the particles pass through a laser beam. The particle size D 10 , D 50 , and D 90 may be measured by calculating the particle size at 10%, 50%, and 90% of the cumulative particle size distribution of the particles in the measuring device. For example, a sample and a surfactant (e.g., a non-ionic surfactant, Triton-X, etc.) can be added to a dispersion medium and ultrasonically dispersed to obtain a dispersion, the dispersion can be placed in a laser diffraction particle size distribution measuring device (Microtrac S3500), and a volume-based particle size distribution can be measured. The dispersion medium can include water. The amount of the sample is not limited to a specific range, but can be in the range of about 0.1 g to 20 g. However, the amount can be adjusted in experiments. At the same time, the amount of the surfactant and the amount of water can be appropriately adjusted according to the amount of the sample. Alternatively, the D 10 , D 50 , and D 90 of the particles can be determined by a 3-dimensional (3D) modeling method as described below.

[0055] The "thickness" of each layer included in the electrode as used herein can represent a value measured by a known thickness measurement method. The thickness can be, for example, a value measured using a thickness measuring device (Mitutoyo, VL-50S-B), but the thickness measurement method is not limited thereto.

[0056] In the present specification, the electrode includes a dry electrode film as an electrode active material layer. The dry electrode and the dry electrode film refer to those manufactured by a dry manufacturing process that does not use a solvent to disperse electrode components such as an electrode active material, a conductive material, and a binder.

[0057] In the present disclosure, the dry electrode is an electrode for an electrochemical device, which can be, for example, a secondary battery, and the secondary battery can more specifically be a lithium ion secondary battery.

[0058] [Dry electrode]

[0059] A first aspect of the present disclosure relates to a dry electrode. The dry electrode includes a current collector and a dry electrode film as an electrode active material layer on at least one surface of the current collector. As described below, the dry electrode can be obtained by combining the dry electrode film and the current collector together via a lamination process. The dry electrode film contains an electrode active material and a binder resin, and if necessary, can also contain a conductive material.

[0060] The dry electrode film can have a plate-like structure formed by compacting an electrode powder (powder) via a dry method. The electrode powder includes a combination of mixture particles containing an electrode active material and a binder resin. If necessary, the mixture particles can also contain a conductive material. The dry electrode film according to the present disclosure has a porous structure, and the porous structure is generated by pores caused by interstitial volumes between the mixture particles. Furthermore, in the dry electrode film, the binder resin can be treated by a fibrillation process as described below, so that it is split into smaller parts and the surface becomes loose to generate many fine fibers (fibrils). In addition, the electrode powder can also contain free electrode active materials or binder resins that are not included in the granular substance.

[0061] [Porosity]

[0062] In the present disclosure, the porosity of the dry electrode film can be 15 to 50 vol%, and preferably can be controlled to a value of 45 vol% or less, or 40 vol% or less, or 35 vol% or less, or 30 vol% or less within the foregoing range. The lower limit of the porosity can be controlled to 20 vol% or more, for example. When the porosity is within the foregoing range, it is preferable in terms of various effects. In contrast, outside the foregoing range, when the porosity is too small, the electrolyte is not sufficiently wetted, and is not preferable in terms of life characteristics or output characteristics, and when the porosity is too large, an increase in volume is required to achieve the same capacity, and thus is not preferable in terms of energy density per volume. In one embodiment of the present disclosure, after measuring the apparent density of the dry electrode film, the porosity can be calculated by the following [Equation 1a] using the actual density (net density) calculated based on the actual densities and compositions of the respective components.

[0063] [Equation 1a]

[0064] Porosity (vol%) = {1 - (apparent density / net density)} x 100

[0065] Meanwhile, in the above Equation 1a, the apparent density can be calculated by the following Equation 1b.

[0066] [Equation 1b]

[0067] Apparent density (g / cm3) = (weight of the object (g)) / {(thickness of the object (cm)) x (area of the object (cm2))} 3 2

[0068] The apparent density, or generally, the bulk density, is a measure of how much space each unit volume of material occupies, and includes holes or empty spaces contained in the material. That is, the apparent density includes the material in a solid state and the holes in its volume. The apparent density can be calculated by dividing the mass of the material by the total volume. All holes or empty spaces in the material are included in the apparent density. The formula for calculating the apparent density is given as the following Equation 1c.

[0069] [Equation 1c]

[0070] Apparent density = mass / total volume

[0071] ​​The mass can be measured using a weight. In the case of a material in a regular shape (e.g., a cube, a cylinder, etc.), the corresponding dimensions can be measured using a suitable tool, such as a tape measure or a caliper, and this is a well-known method widely used in the corresponding technical field. In the case of a material in an irregular shape, the volume can be measured by measuring the density of a liquid and then measuring the change in the volume of a known volume. The change in the volume can be equal to the volume of the material. Any other method known to one of ordinary skill in the art can be applied to measure the volume or the apparent density.

[0072] The net density (or true density) refers to the actual density of a material regardless of the voids or pores contained in the material. This is a value obtained by dividing the mass of a solid material by its actual volume, and the empty space is excluded from the volume. The net density can be calculated by dividing the mass of the material by the solid (non-empty) volume. The formula for calculating the net density is given as the following relation 1d.

[0073] [Relation 1d]

[0074] Net density = mass / solid volume (not considering pore volume)

[0075] Alternatively, the net density can be determined according to ISO 12154:2014 using a gas pycnometer method or any other measurement method known to an expert in the corresponding field.

[0076] Meanwhile, in one embodiment of the present disclosure, the porosity can be calculated from 3D data obtained by the 3D structure modeling method of the electrode as described below.

[0077] Meanwhile, in the present disclosure, the porosity can be better achieved by the pore size and the size of the fibrillated binder as described below.

[0078] [Pore size]

[0079] In the present disclosure, the dry electrode film can have a uniform pore size and a small deviation. Therefore, this can have a beneficial effect on easy movement and diffusion of lithium ions during charging / discharging and improved fast charging and high output characteristics.

[0080] In the dry electrode film according to the present disclosure, the total volume of pores having a diameter of 2 μm or more and 10 μm or less, based on 100% by volume of all the pores, can be 90% by volume or more. For example, it can be in the range of 90% by volume to 99.99% by volume. Preferably, the volume of pores having a diameter of 4 μm or more and 8 μm or less, based on the total pore volume of the electrode, can be 60% by volume or more, or 65% by volume or more, or 70% by volume or more. For example, it can be in the range of 60% by volume to 99.99% by volume, or 65% by volume to 99.99% by volume, or 70% by volume to 99.99% by volume.

[0081] In the electrode active material layer, the volume of pores (micropores) having a pore diameter of 0.5 μm or less, or less than 0.5 μm, based on the apparent volume, can be 10% by volume or less, or 5% by volume or less, or 3% by volume or less, or 1% by volume or less. Meanwhile, within the foregoing range, the volume of micropores can be 0.0001% by volume or more, or 0.001% by volume or more. Preferably, the volume of pores having a diameter of 1 μm or less, or 2 μm or less, or 3 μm or less, can be 10% by volume or less, or 5% by volume or less, or 3% by volume or less, or 1% by volume or less. Meanwhile, within the foregoing range, the volume of micropores can be 0.0001% by volume or more, or 0.001% by volume or more. Furthermore, in one exemplary embodiment, in the electrode active material layer, the volume of pores (macropores) having a pore diameter of 10 μm or more, based on the apparent volume, can be 10% by volume or less, 7% by volume or less, or 5% by volume or less, or 3% by volume or less, or 1% by volume or less. Meanwhile, within the foregoing range, the volume of macropores can be 0.0001% by volume or more, or 0.001% by volume or more.

[0082] In the dry electrode film, the number of pores having a diameter of 2 μm or more and 10 μm or less, or 4 μm or more and 8 μm or less, can be 80% or more of the total number of pores. Meanwhile, within the foregoing range, the number of pores can be 99.99% or less.

[0083] The average pore diameter of the pores contained in the dry electrode film can be 5.0 μm or more, or 6.0 μm or more, or 6.5 μm or more. Meanwhile, the average pore diameter can be 20.0 μm or less, 13.0 μm or less, 10.0 μm or less, or 9.0 μm or less. Within the foregoing range, the average pore diameter can be 6.0 μm or more and 10.0 μm or less. Alternatively, the average pore diameter can be 6.5 μm or more and 9.0 μm or less.

[0084] The average pore size of the pores having a diameter of 2 μm or more and 10 μm or less in the dry electrode film can be 5 μm or more, preferably 6.0 μm or more, and preferably 6.5 μm or more.

[0085] In one embodiment of the present disclosure, in the dry electrode film, the average pore diameter of the pores having a diameter of 4 μm or more and 8 μm or less can be 6.0 μm or more, and preferably 6.5 μm or more. Within the foregoing range, the average pore diameter of the pores having a diameter of 4 μm or more and 8 μm or less can be 20.0 μm or less, 13.0 μm or less, 10.0 μm or less, or 9.0 μm or less. Within the foregoing range, the average pore diameter can be 6.0 μm or more and 10.0 μm or less, or 6.5 μm or more and 9.0 μm or less.

[0086] Figure 1d is a graph showing the pore size and shape distribution of a dry electrode according to Example 1 of the present disclosure, which shows a smaller pore size deviation compared to a comparative example. The dry electrode film according to the present disclosure can have a large average pore diameter of 5.0 μm or more, a low ratio of micropores of less than 4 μm and macropores of more than 8 μm, and a small pore size deviation, achieving uniform lithium ion diffusion and fast movement of lithium ions in the electrode, thereby improving high-rate charge / discharge.

[0087] In the present disclosure, the pore diameter is based on the longest pore diameter. In addition, the average pore diameter can be the average diameter, and can be calculated based on the following relation equation 2.

[0088] [Relation Equation 2]

[0089] Average diameter = (Σd / n)

[0090] In the above relation equation, Σd is the sum of all measured pore diameters, and n is the total number of target pores.

[0091] In one specific embodiment of the present disclosure, the pores can have an oblong shape, an elongated spherical shape, a flat spherical shape, and a spherical shape. Here, based on the total pore volume of the electrode 100 vol%, the oblong shape pores can be contained in 35 vol% or more, 40 vol% or more, 43 vol% or more, or 45 vol% or more. Meanwhile, based on the total pore volume of 100 vol%, the oblong shape pores can be 60 vol% or less, or 55 vol% or less. Meanwhile, based on the total pore volume of the electrode 100%, the dry electrode film can contain less than 5 vol% or less than 3 vol% of spherical pores. Meanwhile, based on the total pore volume of 100 vol%, the spherical pores can be 0.001 vol% or more, or 0.01 vol% or more.

[0092] Here, based on Krumbein Sphericity, oblate, prolate, and oblate spheroid shapes have values of 0.4 to less than 0.8, and based on Krumbein Sphericity, spherical shape has values of 0.8 to 1.0. Meanwhile, in the present disclosure, oblate, prolate, and oblate spheroid can be classified according to the ratios of a, b, and c below. Oblate is a shape in which b and c are similar but a is large. Meanwhile, when a and b are similar and c is large, it is classified as prolate, and when b and c are larger than a, it is classified as oblate spheroid. In one specific embodiment, oblate represents a being greater than 0.45 and less than 0.6, for example, greater than 0.45 and 0.55 or less, preferably 0.5, b being 0.1 to 0.15, and c being 1-a-b (c = 1-a-b). Meanwhile, prolate represents a being 0.6 to 0.65, b being 0.175 to 0.2, and c being 1-a-b (c = 1-a-b), and oblate spheroid represents a being 0.40 to 0.45, b being 0.4 to 0.45, and c being 1-a-b (c = 1-a-b). Figure 1e Each shape is schematically shown.

[0093] In the present disclosure, Krumbein Sphericity can be calculated by the following Equation 5.

[0094] [Equation 5]

[0095]

[0096] Here, a refers to the longest aperture (length of the longest axis), b refers to the length of the intermediate axis of the aperture (length of the intermediate axis), and c refers to the shortest aperture (length of the shortest axis). Here, oblate shape refers to a pore having a value of 0.4 to 0.8 based on Krumbein Sphericity, and spherical shape refers to a pore having a value of 0.8 to 1.0 based on Krumbein Sphericity.

[0097] In one specific embodiment of the present disclosure, the structure, shape, and size of the pores, for example, the aperture, the average aperture, and the volume, can be measured by a multi-layer image of a focused ion beam (FIB) scanning electron microscope (SEM) section and converted into 3 dimensions via 3D reconstruction. Alternatively, the pore size and distribution (pore size distribution) can be calculated using a capillary flow porometry method. The capillary flow porometry method is a method that wets an object using a wetting solution having a low surface tension, applies pressure with air to push the wetting solution filled in the pores, and measures the pore size and distribution by the pressure required to push the wetting solution filled in the pores.

[0098] [Fiber diameter of binder resin in dry electrode film]

[0099] In the dry electrode film, the binder resin comprises fibrillated fibrils. In the present disclosure, the fibrils can comprise portions having a diameter of 300 nm or greater, or 500 nm or greater, or 700 nm or greater, or 1 μm or greater. Preferably, the fibrillated binder resin can comprise fibrils having portions of 300 nm or greater in diameter with a length of 3 μm or greater, or 5 μm or greater, or 7 μm or greater, or 10 μm or greater, or 15 μm or greater, or 10 μm or greater, or 20 μm or greater. Alternatively, the fibrillated binder resin can comprise fibrils having portions of 500 nm or greater in diameter with a length of 3 μm or greater, or 5 μm or greater, or 7 μm or greater, or 10 μm or greater, or 15 μm or greater, or 10 μm or greater, or 20 μm or greater. Alternatively, the fibrillated binder can comprise fibrils having portions of 700 nm or greater in diameter with a length of 3 μm or greater, or 5 μm or greater, or 7 μm or greater, or 10 μm or greater, or 15 μm or greater, or 10 μm or greater, or 20 μm or greater. Alternatively, the fibrillated binder resin can comprise fibrils having portions of 1 μm or greater in diameter with a length of 3 μm or greater, or 5 μm or greater, or 7 μm or greater, or 10 μm or greater, or 15 μm or greater, or 20 μm or greater. In a more particular embodiment, the dry electrode film can comprise at least one fibril having portions of 1 μm or greater in diameter with a length of 50 μm or greater.

[0100] Meanwhile, in the dry electrode film, the diameter of the fibrillated binder resin can be 7 μm or less, or 5 μm or less, or 3 μm or less, or 2 μm or less. In one embodiment of the present disclosure, the diameter and length of the fibril can be determined through SEM images of the manufactured dry electrode film. In addition, an appropriate image processing program can also be applied to distinguishably display the binder resin from other components. The image processing program can include known programs such as Avizo, Image J. In the present disclosure, when the fibril diameter of the binder resin is within the aforementioned range, it is advantageous to achieve a dry electrode film having a large pore size and a small deviation. Meanwhile, in the dry electrode film, the fibrillation of the binder resin and the fibril diameter and length caused by the fibrillation can be controlled by the kneading process conditions and / or the calendering process as described below. For example, they can be adjusted by controlling the rotation speed (rpm) and / or the kneading time of the kneader. Alternatively, they can be adjusted by the speed and / or pressure of the calender. Meanwhile, as described below, the structural characteristics of the pores of the dry electrode film, such as porosity, pore size, and shape, can also be adjusted by the size of the electrode powder after the milling process. This will be described in the description of the milling process.

[0101] [QBR]

[0102] According to one embodiment of the present disclosure, the dry electrode film can have a Quantified Binder Ratio (QBR) of 0.9 to 1.1. In the present disclosure, the dry electrode film satisfying the QBR value is preferably a dry electrode film for a positive electrode.

[0103] The QBR is defined by the following [Equation 3].

[0104] [Equation 3]

[0105]

[0106] In the above equation, Bs represents the average fluorine content in the surface region of the electrode active material layer within 15% of the total thickness of the electrode active material layer from the outermost surface of the electrode active material layer, and Bf represents the average fluorine content in the bottom region of the electrode active material layer within 15% of the total thickness of the electrode active material layer from the interface of the electrode active material layer in contact with the current collector.

[0107] Figure 16 is a schematic view of an electrode according to one embodiment of the present disclosure. Referring to Figure 16 , the electrode 10 includes an electrode current collector 12; and an electrode active material layer 11 located on the electrode current collector 12 and containing an active material, a conductive material, a binder, and a fluoroelastomer.

[0108] Based on the total thickness (d), the electrode active material layer 11 has an electrode active material layer surface region 11s within 15% of the total thickness (d) of the electrode active material layer from the outermost surface of the electrode active material layer, and an electrode active material layer bottom region 11f within 15% of the total thickness (d) of the electrode active material layer from the electrode active material layer interface in contact with the current collector.

[0109] In the above equation QBR, Bs represents the average fluorine content in the electrode active material layer surface region 11s, and Bf represents the average fluorine content in the electrode active material layer bottom region 11f.

[0110] In this case, QBR can be calculated by the following method.

[0111] First, a target electrode for determining QBR is selected, and a cross section of the selected electrode is prepared using Ar ion milling. Subsequently, energy dispersive X-ray spectroscopy (EDS) mapping of constituent elements in the electrode active material layer of the electrode cross section is performed using an EDS detector of a SEM device.

[0112] From the EDS mapping results, a line profile in the thickness direction of the electrode active material layer is extracted, the average fluorine content Bs of the fluorine-containing binder in the electrode active material layer surface region and the average fluorine content Bf of the fluorine-containing binder in the electrode active material layer bottom region are extracted from the extracted line profile results, and QBR is calculated using the above [Equation 2].

[0113] In this case, the electrode active material layer surface region is a region within 15% of the total thickness of the electrode active material layer from the outermost surface in the thickness direction of the electrode active material layer, and the electrode active material layer bottom region is a region within 15% of the total thickness of the electrode active material layer from the electrode active material layer interface in contact with the current collector.

[0114] Figure 17 is a schematic diagram showing the calculation of the QBR value of the electrode active material layer. Referring to Figure 17 , the X-axis represents the thickness of the electrode active material layer, i.e., the distance from the surface to the current collector, and the Y-axis represents the fluorine intensity. The A line represents the fluorine intensity of the fluorine-containing binder extracted by EDS mapping of fluorine in the electrode active material layer of the electrode cross section, and the B line is a trend line showing the trend of the A line by locally weighted scatterplot smoothing (LOWESS).

[0115] The QBR value represents the uniformity of the distribution of the fluorine-containing binder in the thickness direction of the electrode active material layer by the ratio of the amount of the fluorine-containing binder contained in the surface region of the electrode active material layer to the amount of the fluorine-containing binder contained in the bottom region. In this case, the amount of the fluorine-containing binder can be inferred from the fluorine contained in the used fluorine-containing binder.

[0116] The QBR value can be 1.1 or less, and according to one embodiment of the present disclosure, the QBR value can be 0.95 or more, 0.97 or more, 1.03 or less, 1.05 or less, and can be in the range of 0.95 to 1.05.

[0117] When the QBR value is in the range of 1.1 or less, an increase in the ratio of the amount of the fluorine-containing binder contained in the surface region of the electrode active material layer to the amount of the fluorine-containing binder contained in the bottom region due to the migration of the fluorine-containing binder to the electrode surface can be prevented, achieving uniform binder distribution in the thickness direction of the electrode active material layer in which the binder content in the region close to the current collector is not low, thereby improving the adhesion strength between the current collector and the electrode active material layer and increasing the electrical conductivity on the surface of the electrode active material layer and the charge / discharge rate.

[0118] [Meandering degree]

[0119] In one embodiment of the present disclosure, the meandering degree τ of the short-range line of the dry electrode film as given by the following [Equation 1] geo is preferably 1.15 or less.

[0120] The meandering degree of the short-range line can indicate the length of the lithium ion movement path through the pores in the electrode. Therefore, in order to reduce the lithium ion movement path, τ geo is preferably 1.15 or less.

[0121] [Equation 1]

[0122]

[0123] In the above [Equation 1], L denotes the thickness of the electrode active material layer, L eff denotes the length of the lithium ion movement path in the electrode active material layer.

[0124] In the present disclosure, the meandering degree τ of the short-range line geo may be determined by modeling the electrode active material layer in 3 dimensions using a 3D structure modeling tool and calculating the movement path based thereon.

[0125] 3D modeling can include, for example, obtaining multiple cross-sections of the composite electrode using FIB and SEM, and converting into a 3D structure to analyze the contact area between particles, pore structure, etc. Alternatively, analysis can be performed by extracting the internal structure of the composite electrode in 3D form using micro / nano computed tomography (CT). Alternatively, a 3D electrode structure formation, analysis modeling, and simulation tool, such as GeoDict, AVIZO, MATBOX, can be used.

[0126] In one embodiment of the present disclosure, the method using FIB and SEM can be described in detail below.

[0127] First, the electrode sample can be processed by a light source selected from Ga+, plasma, or laser according to the sample volume of the electrode. For example, to obtain an image at a nanoscale resolution, the sample can be processed by cutting the electrode using a Ga+ light source, and to obtain an image at a microscale resolution, the sample can be processed by cutting the electrode using a plasma or laser light source. In this case, the cutting speed and interval of the electrode sample can be adjusted by setting the voltage and current of the FIB device.

[0128] As described above, the sample image of the electrode obtained using the FIB device can be a SEM image showing a cross-section of the electrode sample. For each electrode element contained in the electrode, such as the electrode active material, the conductive material, the binder, the pores in the electrode, and the aluminum current collector, the SEM image can be represented in different brightness. Figure 18 is an exemplary graph showing the gray value of each material of the electrode obtained using the FIB device. Referring to Figure 18 , it is determined that the pores in the electrode and each electrode material show different gray values.

[0129] Subsequently, the obtained electrode cross-section SEM image can undergo processing, such as contrast adjustment using a Fast Fourier Transform (FFT) filter or a non-Local Means (NLM) filter, and as a result of the image data processing, digital data of the reconstructed 3D structure can be obtained.

[0130] The digital data can be visualized as a 2D or 3D graphical image, and provide a wide variety of numerical information related to the electrode structure. After reconstructing the 3D structure of the electrode, L eff .

[0131] In one embodiment of the present disclosure, the tau geo can be calculated using a neurite tracing program based on FiJi / Image J, and the calculation is based on Equation 3 below.

[0132] [Equation 3]

[0133]

[0134] [Equation 4]

[0135]

[0136] In the above [Equation 3], L refers to a predetermined straight line length in a random direction, and in the above length L, dl i refers to a length component corresponding to each deflection angle. Each deflection angle can be calculated by the angle between two vectors in the 3D space of each path, and each path can be defined by the tracking program used. In addition, the deflection angle can be defined by the above [Equation 4]. For each variable in the above [Equation 3] and [Equation 4], refer to Figure 19 , and in the above Equation 4, v denotes a vector, specifically, a vector v i at a specific position and a vector v i at a relative position with respect to v i+1 , and x, y, and z denote each component of the vector.

[0137] For the method for calculating τ geo , refer to IOP Conf. Series: Earth and Environmental Science 311 (2019) 012041”, doi:10.1088 / 1755-1315 / 311 / 1 / 012041.

[0138] Meanwhile, the above [Equation 1] and [Equation 2] can be analyzed as follows. The 3D electrode structure reconstructed by the above method is composed of voxels, a set of voxels connecting the surfaces in the thickness direction of the electrode is found by a calculation algorithm, and the value of L eff is calculated based on a set of the shortest pore voxels (the smallest number of voxels). In this case, it can be calculated by multiplying the edge value of the voxel by the number of voxels connecting between the surfaces.

[0139] In addition, the physical tortuosity τ phy of the dry electrode film as given by the above [Equation 2] is preferably 3 or less. In a battery including the dry electrode film according to the present disclosure, the tortuosity is affected by the ionic conductivity of the electrolyte solution injected into the battery. Therefore, when considering the physical tortuosity value, it is preferable to consider the congestion phenomenon inside the electrode due to the electrolyte solution.

[0140] [Equation 2]

[0141]

[0142] In the above [Equation 2], ε denotes the porosity of the electrode active material layer, δ0 denotes the electrolyte conductivity, and δ eff denotes the effective electrolyte conductivity generated by the pore structure.

[0143] In the present disclosure, the porosity ε can be calculated from the pore volume calculated by 3D reconstruction.

[0144] The electrolyte conductivity δ0 can be calculated by calculating the interaction between electrolyte molecules and lithium ions. In one embodiment of the present disclosure, the electrolyte conductivity δ0 can be set based on an Advanced Electrolyte Model (AEM) which is based on a statistical mechanics model of NPNRAMSA (mean spherical approximation) developed by Kevin Gering at Idaho National Laboratory (Journal of The Electrochemical Society, 165 (14) A3350-A3359 (2018)). The AEM can calculate a variety of properties (viscosity, ionic conductivity, diffusivity, transport number, and activity coefficient, etc.) of electrolytes through interactions (solvent-solvent, solvent-ion, ion) by modeling at the molecular scale.

[0145] Meanwhile, the effective ion conductivity δ eff of the electrode of the present disclosure can be calculated by applying the following equations (a) to (c) (Laplace equation and Ohm's law equation) to the calculated 3D reconstructed structure.

[0146]

[0147]

[0148]

[0149] In the above equations (a) to (c), is the local conductivity (S·m -1 ), is the local current density (A·m -1 ), is the local potential V, is the effective conductivity (S·m -1 ), and V is the pore volume (m 3 ).

[0150] [Load amount]

[0151] In the present disclosure, the loading amount of the electrode active material in the dry electrode film can be in the range of 3 mAh / cm 2 to 15 mAh / cm 2 , and specifically 4 mAh / cm 2 to 10 mAh / cm 2 . Here, the loading amount of the active material can be calculated by the following [Equation 4].

[0152] [Equation 4]

[0153] Loading amount (mAh / cm 2 ) = Capacity of active material (mAh / g) x Weight content ratio of active material in dry electrode film (wt%) x Weight of dry electrode film per unit area (g / cm 2 )

[0154] [Binder resin]

[0155] In the present disclosure, the binder resin is not limited to a specific type, and can include any type of binder resin that can be fibrillated by the steps (S10) and / or (S20) described below. Fibrillation refers to a process of splitting a polymer into smaller parts, for example, which can be performed using mechanical shearing force. The fibrillated polymer fibers can become loose in the surface and / or the bulk, thereby generating a large amount of fine fibers (fibrils). Non-limiting examples of the binder resin can include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyolefin, or a mixture of two or more thereof, specifically, the binder resin can include polytetrafluoroethylene (PTFE), and more specifically, the binder resin can be polytetrafluoroethylene (PTFE). Specifically, polytetrafluoroethylene (PTFE) can be included in an amount of 30 wt% or more, based on the total weight of the binder resin. Meanwhile, in this case, the binder resin can include polyethylene oxide (PEO) and / or polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) in addition to the above-described substances.

[0156] [Electrode active material]

[0157] In the present disclosure, the dry electrode can be a cathode, and the electrode active material can be a cathode active material.

[0158] The cathode active material is not limited to a specific material, and can include any type of lithium transition metal oxide, lithium metal iron phosphate, or metal oxide. The cathode active material can include at least one of: a layered compound, such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound having one or more transition metal substitutions; a formula Li 1+x Mn 2-xLiMnO3, LiMn2O3, LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7; lithium nickel oxides represented by the formula LiNi 1-x M x O2(M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, x is in the range of 0.01 to 0.5) represent a Ni-site lithium nickel oxide such as Li(Ni,Co,Mn,Al)O2 in which the Ni content in the metal portion other than Li is 50% or more; lithium manganese composite oxides represented by the formula LiMn 2-x M x O2(M = Co, Ni, Fe, Cr, Zn, or Ta, x is in the range of 0.01 to 0.1) or Li2Mn3MO8(M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which Li is partially substituted by alkaline earth metal ions in the formula; lithium metal phosphates LiMPO4(M = Fe, CO, Ni, or Mn); disulfide compounds; Fe2(MoO4)3. However, the positive electrode active material is not limited thereto.

[0159] Alternatively, the dry electrode can be a negative electrode, and in this case, the electrode active material can be a negative electrode active material. The negative electrode active material can include: carbon such as non-graphitized carbon or graphite-based carbon; metal composite oxides such as Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2, and Group 3 elements of the periodic table, halogen; 0≤x≤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, 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; Li-Co-Ni-based materials. In the present disclosure, the electrode can preferably be a positive electrode.

[0160] [conductive material]

[0161] The conductive material is not limited to a specific type, and can include any material having an electrically conductive property without causing any chemical change in the corresponding battery. For example, the conductive material can include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; fluorocarbons; metal powders such as aluminum or nickel powders; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, and specifically, for uniform mixing of the conductive material and improved electrical conductivity, the conductive material can include at least one selected from activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, activated carbon.

[0162] [Current collector]

[0163] The current collector is not limited to a specific type, and can include those having a high electrical conductivity without causing any chemical change in the battery. For example, the current collector can include, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, copper, or aluminum or stainless steel treated on the surface with carbon, nickel, titanium, or silver. The current collector can have a microtexture on the surface to increase the adhesion strength of the positive active material, and can be in a variety of types such as a film, a sheet, a foil, a mesh, a porous body, a foam, or a nonwoven.

[0164] Further, all or a part of the current collector can be coated with a conductive primer to reduce the electrical resistance and improve the adhesion strength on the surface. Here, the conductive primer can include a conductive material and a binder, and the conductive material can include any material having an electrically conductive property without limitation. The conductive material can include, for example, a carbon-based material. The binder can include a fluorine-based binder (including PVDF and a PVDF copolymer) soluble in a solute, an acrylic binder, and a water-based binder.

[0165] [Amount]

[0166] In one embodiment of the present disclosure, the electrode active material, the binder resin, and the conductive material can each be included in the electrode active material layer at a weight ratio of 80 to 98 weight%, 0.5 to 10 weight%, and 0.5 to 10 weight%, respectively. To this end, the powdered blend can include the electrode active material, the binder resin, and the conductive material at a weight ratio of 80 to 98 weight%, 0.5 to 10 weight%, and 0.5 to 10 weight%, respectively. In one specific embodiment, the binder resin can be included in a range of 0.5 to 5 weight% or 0.5 to 3 weight% based on 100 weight% of the electrode active material layer. In the present disclosure, the amount of the electrode components is not limited to a specific range, and can be appropriately adjusted to achieve a desired level of electrochemical performance of the battery.

[0167] When the amount of the binder resin is too large, the average pore diameter in the electrode active material layer obtained can be small. In addition, when the amount of the binder resin increases, the amount of the electrode active material decreases, resulting in a low energy density, and the binder resin can act as a resistance component, resulting in poor resistance characteristics. In contrast, when the amount of the binder resin is too small, sufficient fibrillation can not be achieved, and agglomeration can be insufficient to form a bulk blend, making it difficult to manufacture a dry electrode film or the characteristics of the dry electrode film can be deteriorated. When the fibrillation of the binder is not sufficient, the features in terms of porosity and pore structure described above can not be easily achieved.

[0168] When the amount of the conductive material is too large, the capacity can decrease due to the small amount of the active material, and when the amount of the conductive material is too small, sufficient conductivity can not be achieved or the characteristics of the dry electrode film can be deteriorated.

[0169] If necessary, the electrode active material layer can include a filler to suppress swelling of the electrode. The filler is not limited to a specific type, and includes any fibrous material that does not cause any chemical change in the corresponding battery, for example, an olefin-based polymer such as polyethylene or polypropylene, and a fibrous material such as glass fiber or carbon fiber. The filler is preferably included in an amount of 5% by weight or less, or 3% by weight or less, or 1% by weight or less, based on 100% by weight of the electrode active material layer.

[0170] Meanwhile, the present disclosure provides a secondary battery including a dry electrode as a unit cell, and an energy storage system including the secondary battery as a unit cell, the secondary battery including the dry electrode as a positive electrode, and an electrode assembly including a positive electrode, a negative electrode, and a separator, together with a non-aqueous electrolyte containing lithium, is accommodated in a battery case. In this case, the detailed structure of the secondary battery and the energy storage system is well known in the art, and the description thereof is omitted.

[0171] [Electrode manufacturing method]

[0172] A second aspect of the present disclosure relates to a method for manufacturing an electrode according to the present disclosure.

[0173] In one specific embodiment, the method for manufacturing an electrode includes:

[0174] (S10) a step of preparing a powdery blend including an electrode active material, a conductive material, and a binder resin;

[0175] (S20) a step of kneading the powdery blend to prepare a bulk blend;

[0176] (S30) a step of grinding the bulk blend to obtain an electrode powder including mixture particles; and

[0177] (S40) a step of calendering the electrode powder to obtain a self-supporting dry electrode film.

[0178] Step (S20) can be performed at a temperature range of 70 to 200 °C.

[0179] As described below, the dry electrode film can be attached to one or both surfaces of the electrode current collector to manufacture an electrode (S50).

[0180] In one embodiment of the present disclosure, a lamination step of placing the dry electrode film obtained through the calendering step on at least one surface of the current collector and applying pressure can be performed. Through lamination, the dry electrode film can be placed on the current collector, and pressure can be applied to bind the current collector and the dry electrode film together, and thereby manufacture an electrode. A pressing member such as a lamination jig or a roller can be used. The pressing can be performed by a hot melt pressing method, for example, when a lamination roller is used, the temperature of the roller can be controlled in the range of 20 to 200 °C.

[0181] Hereinafter, the method for manufacturing a dry electrode according to the present disclosure will be described in more detail.

[0182] First, a blend containing an electrode active material, a conductive material, and a binder resin is prepared (S10). In this step, the electrode materials are mixed in a powder phase without using a solvent by a dry method. The method used is not limited to a specific one, but various methods for uniform mixing can be applied. In one specific embodiment, the electrode materials can be fed into a mixer or a blender and mixed together in a powder phase.

[0183] In one embodiment of the present disclosure, the mixing time is not limited to a specific range, but the mixing can be performed for 1 second to 10 minutes. At the same time, the mixing speed is not limited to a specific range, but can be appropriately controlled in the range of about 3,000 rpm to 30,000 rpm. In one specific example, the mixing can be performed in a mixer at 5,000 rpm to 20,000 rpm for 30 seconds to 2 minutes, specifically at 10,000 rpm to 15,000 rpm for 30 seconds to 1 minute, to ensure high uniformity.

[0184] As described below, the binder resin is primarily fibrillated through step (S20). However, partial coarse fibrillation of the binder resin can be performed in step (S10).

[0185] Subsequently, a kneading process is performed on the obtained powder blend (S20).

[0186] In one embodiment of the present disclosure, the kneading can be performed, for example, by a kneader. Since the binder resin is fibrillated by the kneading, the electrode active material and the conductive material can be combined or connected to obtain a bulk blend.

[0187] In the present disclosure, the kneading of step (S20) can be controlled in the range of 10 rpm to 100 rpm. For example, within the foregoing range, the kneading can be controlled at a speed of 20 rpm or more or 70 rpm or less. The kneading can be performed for 1 minute to 30 minutes. For example, within the foregoing range, the kneading can be performed at 20 rpm to 70 rpm for 3 minutes to 10 minutes.

[0188] The kneading can be controlled in the range of a shear rate of 5 / second to 1000 / second. In one embodiment of the present disclosure, the kneading can be performed for 1 minute to 30 minutes, and the shear rate can be controlled in the range of 10 / second to 500 / second. Meanwhile, the kneading process can be performed at a pressure of atmospheric pressure or more, specifically, 1 atm to 3 atm, more specifically, 1.1 atm to 3 atm.

[0189] In the present disclosure, the kneading step can be performed at a high temperature and at atmospheric pressure or more, more specifically, at a pressure condition higher than atmospheric pressure. More specifically, the kneading can be performed in the range of 70°C to 200°C, specifically, 90°C to 150°C.

[0190] In the present disclosure, the kneading process can be adjusted to achieve the above-mentioned pore characteristics of the dry electrode film, such as porosity, pore size, and pore distribution.

[0191] For example, outside the aforementioned range, when the kneading step is performed at a low temperature, the mixture powder and / or the dry electrode film can have a low fibrillation level of the binder resin or can not form a large diameter fiber. For example, the mixture powder can not form a fiber having a diameter of 700 nm or more, or 1 μm or more, or 1.2 μm or more, or 1.5 μm or more. For example, the dry electrode film can not form a fiber of the binder resin having a diameter of 300 nm or more, or 500 nm or more, or 700 nm or more, or 1 μm or more. Alternatively, the dry electrode film can not form a fiber having a length of 5 μm or more in a diameter range of 300 μm or more, or 500 nm or more, or 700 nm or more, or 1 μm or more. Alternatively, the electrode mixture powder can not form a fiber having a length of 5 μm in a diameter range of 700 nm or more, or 1.0 μm or more, or 1.2 μm or more, or 1.5 μm or more. When the diameter and / or length of the fibrillated binder resin is small, the diameter deviation can increase, or the ratio of excessively small and / or large pores can increase. In addition, the binder fibrillation and agglomeration by kneading are insufficient, and it is not easy to form a film during calendering. Meanwhile, when the kneading is performed at too high a temperature, the binder fibrillation occurs rapidly, and subsequently formed fibers can be damaged by too high a shear force.

[0192] In one embodiment of the present disclosure, outside the aforementioned range, when the kneading is performed at too high a pressure, the formed fibers can be damaged due to the application of excessive shear force and pressure, or the density of the bulk blend can be too high.

[0193] According to one exemplary embodiment of the present disclosure, when the high temperature and low shear mixing process is performed as described above, it is advantageous to achieve the intended effects of the present disclosure. Meanwhile, if necessary, the kneading can be performed in a pressure condition higher than the atmospheric pressure.

[0194] Subsequently, the bulk blend prepared by the kneading step is ground to obtain an electrode powder (S30).

[0195] Specifically, the bulk blend prepared by the kneading can be directly calendered, but in this case, the bulk blend can be pressed into a thin film shape at a strong pressure and a high temperature, and thus, the density of the film increases too high or a uniform film cannot be obtained. According to the present disclosure, the prepared bulk blend undergoes a grinding step.

[0196] In this case, the milling can be performed using a known grinding / milling machine such as a blender or a mill, but is not limited thereto. In one specific embodiment of the present disclosure, the milling can be controlled in a speed range of 3,000 rpm to 30,000 rpm. For example, the milling speed can be 20,000 rpm or less, or 15,000 rpm or less, or 12,000 rpm or less. Meanwhile, the milling time can be appropriately controlled in a range of 1 second to 10 minutes. For example, the milling time can be 7 minutes or less, or 5 minutes or less, or 3 minutes or less, or 1 minute or less. However, the milling speed and time are not necessarily limited to the aforementioned ranges. As one specific example, the milling can be performed at 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, or at 10,000 rpm to 18,000 rpm for 30 seconds to 1 minute.

[0197] Outside the aforementioned ranges, when the milling is performed at too low rpm or for a short milling time, the milling can be performed insufficiently, thereby producing a mixture particle of a size unsuitable for forming a film. In contrast, when the milling is performed at too high rpm or for a long milling time, a fine powder of a large amount of small mixture particles can be produced.

[0198] [The mixture particle]

[0199] In one embodiment of the present disclosure, the electrode powder obtained through the milling process can be a combination of mixture particles, and the particle size D50 of the mixture particles can be 100 μm to 700 μm, and the particle size D50 can be appropriately adjusted within the aforementioned range in view of the electrical and chemical properties of the battery to which the dry electrode according to the present disclosure is applied. In one specific embodiment, the particle size D50 of the mixture particles can be about 150 μm or more, or 200 μm or more, or 250 μm or more, or 350 μm or more. Meanwhile, the particle size D50 of the mixture particles can be 650 μm or less, or 600 μm or less, or 550 μm or less, or 500 μm or less. The particle size D50 of the mixture particles can be adjusted by the rpm and / or time of the milling process. The mixture particle is a result of agglomeration of the electrode active material particles and the fibrillated binder resin. The electrode powder including the mixture particles is formed into a dry electrode film having a predetermined thickness by calendering in a subsequent process.

[0200] Meanwhile, in one embodiment of the present disclosure, the diameter of the binder fibers in the mixture particles can be 700 nm or more, or 1.0 μm or more, or 1.2 μm or more, or 1.5 μm or more. Meanwhile, the diameter of the binder fibers in the mixture particles is not limited to a specific range, but can be 10 μm or less, or 7 μm or less, or 5 μm or less, or 3 μm or less, or 2 μm or less. Meanwhile, in one embodiment of the present disclosure, the fibrillated binder resin in the mixture particles can include fibrils, and the length of the portion of the fibrils having a diameter of 700 nm or more can be 3 μm or more, or 5 μm or more, or 7 μm or more, or 10 μm or more, or 15 μm or more, or 10 μm or more, or 20 μm or more. Alternatively, the fibrillated binder resin can include fibrils, and the length of the portion of the fibrils having a diameter of 1.0 μm or more can be 3 μm or more, or 5 μm or more, or 7 μm or more, or 10 μm or more, or 15 μm or more, or 10 μm or more, or 20 μm or more. Alternatively, the fibrillated binder resin can include fibrils, and the length of the portion of the fibrils having a diameter of 1.2 μm or more can be 3 μm or more, or 5 μm or more, or 7 μm or more, or 10 μm or more, or 15 μm or more, or 10 μm or more, or 20 μm or more. Alternatively, the fibrillated binder resin can include fibrils, and the length of the portion of the fibrils having a diameter of 1.5 μm or more can be 3 μm or more, or 5 μm or more, or 7 μm or more, or 10 μm or more, or 15 μm or more, or 10 μm or more, or 20 μm or more. The diameter and length of the binder resin can be controlled in the kneading process and / or the grinding process described above.

[0201] Figure 20 and Figure 21 SEM images of the mixture powder prepared by Example 1 of the present disclosure are shown. Referring to FIG. 1, the electrode active material particles and the binder resin included in the mixture powder were observed, and fibrils having a diameter of 1 μm or more and a length of 5 μm or more were found in the binder resin. Figure 20 and Figure 21 , the electrode active material particles and the binder resin included in the mixture powder were observed, and fibrils having a diameter of 1 μm or more and a length of 5 μm or more were found in the binder resin.

[0202] In this disclosure, the electrode powder may comprise a mixture of particles, and the amount of the mixture particles may be 95% by weight or more, or 99% by weight or more. The mixture particles preferably comprise electrode active material and binder resin, and may also comprise conductive material when a conductive material is included during the preparation of the blend. Simultaneously, the electrode powder may contain small amounts of free electrode active material, binder resin, and conductive material not included in the mixture particles.

[0203] When electrode powder is obtained by the above method, a dry electrode is manufactured using the powder electrode. Specifically, after the grinding step is completed, the electrode powder can be calendered to manufacture a dry electrode film (S40).

[0204] In this disclosure, calendering is the process of compacting electrode powder into a film shape by rolling. The thickness of the resulting dry electrode film can be, for example, from 40 μm to 300 μm. In one embodiment of this disclosure, calendering can be performed using a calendering mill, which includes a roll press section having two rolls arranged facing each other. The calendering mill may include at least one roll press section. For example, a plurality of roll press sections can be arranged sequentially to perform multi-stage powder compaction. As described above, multiple calendering processes can be performed to produce a dry electrode film of the desired thickness by calendering the mixed particles. Meanwhile, the temperature of the rolls can be in the range of 50°C to 200°C. Simultaneously or independently, the rotational speed ratio of the two rolls in the roll press section can be controlled to be a ratio of 1:1 to 1:3.

[0205] Furthermore, in one specific embodiment of this disclosure, the crystallinity of the binder resin in the dry electrode film can be greater than 0% and 10% or less, and can be, for example, in the range of 5% or less. Crystallinity can be measured by differential scanning calorimetry (DSC) and is based on the temperature at which the highest enthalpy is achieved during crystallization (peak temperature). Specifically, crystallinity is determined by the melting enthalpy (ΔH) actually measured by DSC. m The value divided by the theoretical enthalpy of fusion (ΔH) of a perfect crystal (100% crystallinity) m 0 The percentage obtained from the enthalpy of fusion (ΔH) of the equilibrium enthalpy of fusion can be calculated using the following equation 5. Here, for the theoretically perfect crystal's enthalpy of fusion (ΔH)... m 0), reference can be made to the polymer handbook (J. Brandrup et al., 2003) or the Polymer Journal. For example, the melting enthalpy value of a theoretically perfect crystal of PTFE is 85.4 J / g (Polymer Journal Vol. 46 (2005) 8872~8882). At the same time, thermal analysis of a polymer by DSC can be generally measured and calculated according to ASTM D3418-21.

[0206] [Relationship 5]

[0207] Crystallinity (%) = (△H m ÷△H m 0 ) × 100

[0208] After the calendering step is performed, a self-supporting dry electrode film can be obtained, and it can be used as an electrode active material layer.

[0209] Since it does not contain a solvent, the dry electrode film manufactured as described above has no or little fluidity, and thus is easy to handle and can be formed into a desired shape for the manufacture of various types of electrodes. In addition, when an electrode is manufactured using the dry electrode film of the present disclosure, a drying process for solvent removal can be omitted, thereby greatly improving the electrode manufacturing process efficiency and solving problems encountered in the manufacture of dry electrodes, such as the breakage of fine powder or fibrillated binder of the active material.

[0210] At the same time, in one specific embodiment of the present disclosure, a system for manufacturing a dry electrode is provided. The system includes a blender for mixing raw materials including an active material, a conductive material, and a binder resin; a kneader for kneading the mixture to form a block-shaped blend; a grinder for grinding the block-shaped blend to form an electrode powder; a calender for forming the electrode powder into a dry electrode film; and a laminator for laminating the dry electrode film onto a current collector.

[0211] At the same time, the blender is used to mix raw materials, and as described above, the raw materials of the mixture can be mixed at a speed of 3,000 rpm to 30,000 rpm.

[0212] The kneader produces a block-shaped blend by kneading and fibrillates the binder. For this purpose, the kneader can be set to a range of 70°C to 200°C, and a pressure condition higher than atmospheric pressure. Specifically, the kneader can be set to a range of 90°C to 150°C, and a pressure condition of 1 atm to 3 atm, and more specifically a pressure condition of 1.1 atm to 3 atm.

[0213] A grinder is used to grind the block-shaped blend obtained by the kneader to form an electrode powder, and can include, for example, a blender or a grinder.

[0214] A calender is a forming machine for compacting the electrode powder into a film shape. In one specific embodiment of the present disclosure, the calender can include a roll press section having two rolls arranged facing each other, and a plurality of roll press sections can be arranged in series to perform multi-stage powder compaction.

[0215] A laminator is used to attach the dry electrode film formed by the calender to at least one surface of the current collector and roll-press it, and can include, for example, a roll press.

[0216] The porosity of the dry electrode and the dry electrode film according to the present disclosure can be determined by the calender and the laminator. The detailed structures of the blender, the kneader, the calender, and the laminator are well known in the art, and the description thereof is omitted.

[0217] Hereinafter, the present disclosure will be described in detail based on examples, comparative examples, and experimental examples according to the present disclosure to help those skilled in the art easily understand the present disclosure.

[0218] Preparation Example 1 : Pre-mixing of materials

[0219] As the positive active material, Li(Ni 0.85 Mn 0.05 Co 0.05 Al 0.05 )O2, carbon black, and polytetrafluoroethylene (PTFE) were fed into a mixer at a weight ratio of 96:1:3 and mixed at 15,000 rpm for 1 minute to prepare a powder blend.

[0220] Preparation Example 2: Preparation of electrode powder A

[0221] The temperature of the kneader was stabilized at 150°C, the obtained pre-mixed powder blend was fed into the kneader, which was then operated at 25 rpm for 3 minutes under a pressure of 1.1 atm to obtain a block-shaped blend. The block-shaped blend was fed into a grinder, which was operated at 10,000 rpm for 30 seconds to obtain an electrode powder. The obtained mixture particles had a diameter of about 300 μm to 700 μm, and a D50 of about 500 μm. Figure 20 and Figure 21 is an SEM image of the electrode powder prepared by Example 1 of the present disclosure. Referring to Figure 20 and Figure 21 , fibrils having a diameter of 1 μm or more and a length of 5 μm or more were found.

[0222] Preparation Example 3: Preparation of electrode powder B

[0223] A dry electrode was manufactured by the same method as powder A, except that the bulk blend was obtained by running the kneader for 2.5 minutes at 25 rpm.

[0224] Preparation Example 4: Preparation of electrode powder C

[0225] A dry electrode was manufactured by the same method as powder A, except that the bulk blend was obtained by running the kneader for 2.5 minutes at 25 rpm.

[0226] Preparation Example 5: Preparation of electrode powder D

[0227] A dry electrode was manufactured by the same method as powder A, except that the bulk blend was obtained by running the kneader for 20 minutes at 50 rpm.

[0228] Preparation Example 6: Preparation of electrode powder E

[0229] The temperature of the kneader was stabilized at 150°C, and the obtained pre-mixed powder blend was fed into the kneader, which was then run at 25 rpm for 3 minutes under a pressure of 1.1 atmospheres to obtain a bulk blend. The bulk blend was fed into a grinder, which was ground at 10,000 rpm for 2 minutes to obtain an electrode powder. The D50 of the obtained mixture particles was determined to be about 150 µm.

[0230] [Table 1]

[0231]

[0232] For each powder obtained in the preparation examples, the tap density and the bulk density were measured, and the measurement results are shown in Table 1 above. The same powder blend was used, but it was determined that there were significant property differences between the electrode powders depending on the applied powder preparation conditions, such as the kneading process or the grinding process.

[0233] The bulk density is the density based on the volume including the pores between the particles when the container is filled with the electrode powder, and refers to the apparent density under non-tapped or non-pressed conditions. In the present disclosure, the bulk density was measured using a powder tester (Powerpro Al, Better size instrument) according to ISO 3953:1993. Specifically, the powder was poured into a 250 ml mass cylinder by free fall and dispersed, and then the excess powder accumulated on the top of the mass cylinder was removed by a doctor blade, and the weight of the internal powder was measured, and the bulk density was calculated according to the following equation.

[0234] Bulk density = (internal weight (g)) / (volume (cc) of the mass cylinder filled with the electrode powder)

[0235] Tapped density refers to a density measured after a container filled with a powder is repeatedly dropped at a constant speed to a certain height so that the powder is tightly compacted in the container until the volume of the powder in the container is almost uniform. In the present disclosure, the tapped density is measured using a powder measuring machine (Powerpro Al, Better size instrument) according to ISO 3953:1993. Specifically, 10 g of electrode powder is filled in a 250 ml mass cylinder, tapped 1250 times with a stroke length of 10 mm, and when the change in volume is equal to or less than 2%, the volume at that time is determined as the final apparent volume. Subsequently, the tapped density is calculated according to the following relational expression 6.

[0236] [Relational expression 6]

[0237] Tapped density = mass of electrode powder (g) / final apparent volume of electrode powder (cc)

[0238] Example 1

[0239] The obtained electrode powder A was fed into a calender roll (roll diameter: 88 mm, roll temperature: 100°C, roll speed ratio 20 / 24 rpm) and pressed into a plate shape, and the resultant formed was subjected to a calendering process under the same conditions to manufacture a self-supporting type dry electrode film. Subsequently, it was laminated with aluminum (thickness 20 μm) to manufacture a dry electrode. In the manufactured electrode, the thickness of the electrode active material layer (one side) was about 60 μm, and the total thickness of the electrode including the current collector was about 140 μm. Figure 4 is an SEM image showing the surface of the electrode prepared in Example 1. Referring to Figure 4 , it was determined that there were macropores between the electrode active material particles, and the diameter of the fibrils was 1 μm or more. Figure 4 The portion of the fibrils having a diameter of 1 μm or more was 10 μm or more long, and it was presumed that the fibrils would extend inward and have a portion much longer than 10 μm. At the same time, as a result of measuring the crystallinity of the binder in the obtained dry electrode film, the crystallinity of the binder was about 2.5%.

[0240] Example 2

[0241] The obtained electrode powder B was fed into a calender roll (roll diameter: 88 mm, roll temperature: 100°C, roll speed ratio 20 / 24 rpm) and pressed into a plate shape, and the resultant formed was subjected to a calendering process under the same conditions to manufacture a self-supporting type dry electrode film. Subsequently, it was laminated with aluminum (thickness 20 μm) to manufacture a dry electrode.

[0242] Example 3

[0243] The obtained electrode powder C was fed into a calender roll (roll diameter: 88 mm, roll temperature: 100°C, roll speed ratio 20 / 24 rpm) and pressed into a plate shape, and the resultant formed was subjected to a calendering process under the same conditions to manufacture a self-supporting dry electrode film. Subsequently, it was laminated with aluminum (thickness 20 μm) to manufacture a dry electrode.

[0244] Comparative Example 1

[0245] (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2; NCM), 1 wt% of carbon black as a conductive material, and 3 wt% of PVDF as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a cathode mixture slurry. The cathode mixture slurry was applied to an aluminum (Al) foil having a thickness of about 20 μm as a positive current collector, and then dried and roll-pressed to manufacture a cathode.

[0246] Comparative Example 2

[0247] The obtained electrode powder D was fed into a calender roll (roll diameter: 88 mm, roll temperature: 100°C, roll speed ratio 20 / 24 rpm) and pressed into a plate shape, and the resultant formed was subjected to a calendering process under the same conditions to manufacture a self-supporting dry electrode film. Subsequently, it was laminated with aluminum (thickness 20 μm) to manufacture a dry electrode. Figure 5 is an SEM image showing the surface of the electrode prepared in Comparative Example 2. Referring to Figure 5 , the electrode active material particles and the binder resin were observed, and it was determined that the fibrils of the binder resin were much finer than in Example 1 and had a diameter of less than 1 μm.

[0248] Comparative Example 3

[0249] The obtained electrode powder E was fed into a calender roll (roll diameter: 88 mm, roll temperature: 100°C, roll speed ratio 20 / 24 rpm) and pressed into a plate shape, and the resultant formed was subjected to a calendering process under the same conditions to manufacture a self-supporting dry electrode film. Subsequently, it was laminated with aluminum (thickness 20 μm) to manufacture a dry electrode.

[0250] Experimental Example 1 : Evaluation of charge / discharge efficiency as a function of the rate

[0251] A coin-type battery was manufactured using the electrode obtained in Example 1 and lithium metal. A separator was placed between the electrode and the lithium metal, and an electrolyte solution containing an organic solvent (ethylene carbonate: dimethyl carbonate 7:3 by volume) and LiPF61M was injected. Batteries were manufactured by the same method using the electrode obtained in each of Comparative Examples 1 and 2.

[0252] Each battery was charged / discharged at an ambient temperature of 25°C, and the capacity was measured. For each battery, charging was performed at different rates of 2C, 1.5C, 1C, and 0.2C in constant current (CC) / constant voltage (CV) mode until 4.4 V, and the cutoff current was 0.05C. Discharging was performed at 1C until 3V under constant current (CC) conditions. The charging / discharging was repeated 40 times under the same conditions.

[0253] Figures 2a to 2d is a charge graph, and Figures 3a to 3d is a discharge graph. Referring to the drawings, it was determined that Example 1 and Comparative Examples 1 and 2 exhibited similar trends when the rate was low, but the battery of Example 1 had high charging / discharging efficiency in the case of high rate charging / discharging of 1C or more.

[0254] Experimental Example 2: 3D modeling of the electrode

[0255] The electrode of each of Examples 1 to 3 and Comparative Examples 1 to 3 was 3D modeled in the following order.

[0256] First, a cross-sectional image of the electrode was obtained using a focused ion beam scanning electron microscope (FIB-SEM). As a light source, Ga + was used, and the cutting speed of the electrode was 2.1 μA, and the interval was set to 300 nm. Each of the obtained electrode cross-sectional SEM images was filtered using a fast Fourier transform (FFT) filter to remove noise and distinguish the brightness of each of the electrode active material, the conductive material, the pore, the current collector, and the binder resin. Subsequently, a threshold value of the brightness was set for each material, and each material was labeled and masked. Subsequently, 3D structure modeling of each material was performed based on the image brightness value. The 3D structure modeling representing the boundary between the materials was performed by applying an edge detection algorithm, such as Canny Edge Detection. In addition, image correction was performed until the materials were filled to the watershed line of each material. In the 3D modeling, the voxel size was set to 100 μm 3 The watershed refers to an image processing technique that calculates a height based on the pixel brightness value of the image, and divides the image into segments including basins surrounded by contour lines when filled with water under the assumption of a corresponding image of 2D geometry.

[0257] Experimental Example 3: Pore size distribution

[0258] The structural features of the pores of each electrode, such as the porosity, the average diameter (pm), the porosity (vol%) of the pores having a pore diameter of 2 pm to 4 pm, and the volume ratio (vol%) were determined from the 3D modeled structure of the electrode obtained by the above-described method. The number of voxels in the obtained 3D structure was determined, and the porosity, the pore diameter, and the pore structure were calculated. For example, assuming that the electrode active material layer contains 100 voxels and thirty of them correspond to pores, the pore volume was calculated as “(30 / 100) x 100”, that is, 30 vol%. As for the pore diameter, the voxels were formed from spherical / elliptical (ovate) particles using a watershed algorithm, and the number of voxels in the a, b, c directions (perpendicular to each other) was determined, and multiplied by the unit length of the voxels to calculate the diameter.

[0259] The pore diameter was based on the longest pore diameter, and the average diameter was based on the number average. Table 2 below summarizes them. In addition, Figure 1d The porosity distribution of the electrodes (electrode active material layers) of Example 1, Comparative Example 1, and Comparative Example 2 was shown.

[0260] Referring to Figure 1d , it was determined that the electrode active material layers according to Examples 1 to 3 of the present disclosure had a larger number and volume distribution of pores having a diameter in the range of about 4 pm to 8 pm. In addition, it was determined that Examples 1 to 3 had a larger average pore diameter than Comparative Examples 1 and 3, and the average pore diameter was about 6.5 pm or more. On the other hand, Comparative Examples 1 to 3 had a larger number of pores having a diameter of 4 pm or less than Examples 1 to 3. That is, it was determined that the electrodes according to the present disclosure had a more uniform diameter and a smaller deviation than Comparative Examples 1 to 3. At the same time, the electrodes of the examples and the comparative examples had a similar porosity range. It was determined that the electrodes of the examples and the comparative examples had a similar porosity, but the structural features of the internal pores were significantly different. At the same time, the following porosity was calculated based on [Equation 1a].

[0261] [Table 2]

[0262]

[0263] In addition, the pore shape was determined based on the Kröner sphericity from the 3D modeled structure, the ratio of the prolate spheroid shape, the oblate spheroid shape, and the spherical shape was determined, and Table 3 below summarizes them.

[0264] [Table 3] Pore shape classification based on Kröner sphericity

[0265]

[0266] Referring to Table 3 above, it was determined that in Examples 1 to 3, the ratio of the slit-shaped pores was greater than 40% by volume of the total pore volume. In addition, it was determined that in Examples 1 to 3, the ratio of the spherical pores was less than 5% by volume of the total pore volume. From the above results, it was determined that there was a difference not only in the pore size but also in the pore shape between the examples and the comparative examples. Here, the slit-shaped shape refers to a shape having a value of 0.4 to 0.8 based on the Klenbin sphericity, and the spherical shape refers to a shape having a value of 0.8 to 1.0 based on the Klenbin sphericity. In the analysis, a was determined to be 0.5, b was determined to be 0.1 to 0.15, and c was determined to be 1-a-b as the slit shape.

[0267] Figure 1a 、 Figure 1b and Figure 1c FIGS. 1 to 3 respectively show the distribution of the pore shape and size in the dry electrode film of Example 1, Comparative Example 1, and Comparative Example 2. In each of the drawings, red indicates the pore size in a slit shape, blue indicates a long spherical shape, brown indicates a flat spherical shape, and green indicates a spherical shape. Figure 1c The slit shape, the blue long spherical shape, the brown flat spherical shape, and the green spherical shape are schematically shown.

[0268] The Klenbin sphericity is a value calculated by Equation 5 below, in which a indicates the longest pore diameter, b indicates the average value of the pore diameter, and c indicates the shortest pore diameter.

[0269] [Equation 5]

[0270]

[0271] Here, a indicates the longest pore diameter (length of the long axis), b indicates the average value of the pore diameter (length of the intermediate axis), and c indicates the shortest pore diameter (length of the short axis). At the same time, the Klenbin sphericity can be calculated by using an image obtained by an optical or electron microscope. Alternatively, the average pore size can be determined by a method of measuring a multi-layer image of an FIB SEM section and converting it into 3D through 3D reconstruction.

[0272] Experimental Example 4: QBR measurement

[0273] A cross section of the electrode of each of Examples 1 to 3 and Comparative Examples 1 to 3 was prepared using Ar ion milling. The cross section refers to a cross section perpendicular to the electrode plane.

[0274] EDS mapping was performed on each constituent component of the electrode layer in the prepared electrode cross-section using the EDS detector of the SEM device. The measurement was performed on a measurement area including the entire electrode active material layer and part of the current collector area in 1024 image pixels of a size aspect ratio of 4. The EDS mapping measurement was performed by measuring a minimum of 10 frames under the condition of 5 kV acceleration voltage of the SEM to measure data of the components of the active material, the conductive material except Li, H, the binder, and the current collector.

[0275] The EDS peak deconvolution line profile in the thickness direction of the electrode was extracted from the EDS mapping result by the EDS operation software (Oxford Aztec). In the extracted line profile result, in a graph showing the change in the normalized binder intensity of the electrode active material layer in the direction from the surface of the electrode toward the current collector, the average fluorine content Bs of the fluorine-containing binder in the electrode active material layer surface region and the average fluorine content Bf of the fluorine-containing binder in the electrode active material layer bottom region (contacting the current collector) were extracted, and QBR was calculated using the following relation 2.

[0276] [Relation 2]

[0277]

[0278] In this case, the electrode surface region is a region within 15% of the total thickness of the electrode active material layer from the outermost surface in the thickness direction of the electrode active material layer, and the electrode active material layer bottom region is a region within 15% of the total thickness of the electrode active material layer from the current collector contact region contacting the current collector. Table 4 below summarizes the QBR calculated in each of the examples and comparative examples.

[0279] [Table 4]

[0280]

[0281] Meanwhile, Figure 6 , Figure 8 and Figure 10 show 3D images (left) and cross-sections of the dotted line (A) region (right) obtained using the 3D modeled structure of the electrode according to Example 1, Comparative Example 1, and Comparative Example 2, respectively. The dark region in the cross-section indicates a pore. In addition, Figure 7 , Figure 9 and Figure 11 show the volume fraction of the electrode components of Example 1, Comparative Example 1, and Comparative Example 2, respectively. In Figure 7 , Figure 9 and Figure 11 , (1) indicates the volume fraction of the electrode active material, (2) indicates the volume fraction of the pore, and (3) indicates the volume fraction of the binder.

[0282] Referring to the drawings, it is determined that the binder content is reduced toward the current collector in the case of Comparative Example 1, while the binder content in the electrode surface and the current collector is uniformly maintained in the present disclosure.

[0283] Experimental Example 5: Determination of the electrical resistance properties of the electrode

[0284] For each dry electrode obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the interface resistance and the electrode resistance were measured using a Hioki MP resistometer. The electrode obtained in each of the examples and comparative examples was cut into a size of 100 mm x 100 mm, a current of 100 uA was applied to the electrode, and the electrode resistance of the dry electrode film (electrode active material layer) and the interface resistance between the electrode layer / current collector layer were measured from the potential difference between 46 probes.

[0285] The thickness of the electrode active material layer, the thickness of the current collector, and the resistance of the current collector were input. Here, the thickness of the dry electrode film and the current collector were measured using a thickness gauge, and the resistance of the current collector was set to 2.82E-06 ohm. The resistance was measured at room temperature, and the measurement was performed five times in the same manner, and the average value was calculated. Table 5 shows the comparison results. The same powder blend was used, but it was determined that there was a significant difference in characteristics between the electrode powders depending on the kneading process conditions applied, and the electrode of the example had a resistance characteristic superior to that of the electrode of the comparative example.

[0286] [Table 5]

[0287]

[0288] Experimental Example 6: Identification of the delithiated region

[0289] An experiment was performed using a 3D modeled structure of the electrode (positive electrode) according to each of Example 1, Comparative Example 1, and Comparative Example 2 to simulate lithium ion movement during charging and discharging, and 3D mapping showed a delithiation region in the electrode at the end of 2C charging. In each drawing, the current collector is positioned, and moves closer to the electrode surface as it moves to the left. FIGS. 12 to 14 show the simulation results of Example 1, Comparative Example 1, and Comparative Example 2, respectively. Referring to FIGS. 12 to 14, a greater amount of delithiation was observed at the electrode (positive electrode) in the batteries of Comparative Example 1 and Comparative Example 2. Comparative Example 1 and Comparative Example 2 had a greater amount of delithiation inside the electrode than at the electrode surface (left side of the image) because the movement of lithium to the electrode surface was not good. In contrast, it was determined that the battery of Example 1 had a smaller amount of delithiation inside the electrode than the comparative examples. That is, it was determined that the dry electrode according to the present disclosure is advantageous for lithium movement during high-rate charging / discharging.

[0290] Experimental Example 7: Measurement of tortuosity

[0291] [Table 6]

[0292]

[0293] Figure 15 is a graph showing results of calculating the short-range line tortuosity and the physical tortuosity of the electrode active material layer in the electrode of each of Embodiment 1, Comparative Example 1, and Comparative Example 2. Referring to Figure 15 , it was determined that the electrode of Embodiment 1 has a better short-range line tortuosity and a physical tortuosity than the electrode of Comparative Example 1. Accordingly, the battery including the electrode of Embodiment 1 has better electrical and chemical characteristics during charging / discharging than the battery including the electrode of Comparative Example 1. On the other hand, it was determined that the electrode of Embodiment 1 and the electrode of Comparative Example 2 have similar tortuosity but are significantly different in terms of pore structure, and the battery including the electrode of Embodiment 1 has better electrical and chemical characteristics than the battery including the electrode of Comparative Example 2.

[0294] Experimental Example 8: Measurement of crystallinity

[0295] In the dry electrode film of each of Embodiment 1 to Embodiment 3 and Comparative Example 3, the crystallinity of the binder resin was measured.

[0296] [Table 7]

[0297]

[0298] As a result of measuring the crystallinity, Embodiment 1 to Embodiment 3, and Comparative Example 2 and Comparative Example 3 all exhibited a crystallinity of less than 5%. It was determined that although the binder resin exhibited similar crystallinity, there were differences in terms of the pore structure of the electrode and the electrical and chemical performance of the battery.

[0299] The crystallinity Xc was measured by weighing about 5 mg to 12 mg of a sample and placing it in a TA differential scanning calorimeter (DSC), and measuring the heat of fusion (△Hfusion) varying with temperature in a temperature range of 25°C to 360°C while raising the temperature at 10°C / minute under a nitrogen atmosphere. The melting point Tm and the heat of fusion (△H m ) were analyzed using a TA Instruments TROIS program based on the temperature at which the enthalpy during melting is at a maximum (peak temperature). The crystallinity of each sample is a % ratio obtained by dividing the actually measured heat of fusion (△H m ) value by the heat of fusion (△H m 0 ) value of a theoretically perfect crystal (crystallinity 100%) and calculated by the above relation 1. The heat of fusion value of a theoretically perfect PTFE crystal is 85.4 J / g, and refer to Polymer Journal Vol. 46 (2005) pp. 8872 to 8882.

Claims

1. A dry electrode for an electrochemical device, comprising a dry electrode film as the electrode active material layer, The electrode active material layer comprises an electrode active material and a binder resin, and the binder resin is fibrillated. The electrode active material layer has an average pore size of 5.0 μm or greater and a porosity of 15% to 50% by volume, and the average pore size is calculated based on the longest pore size.

2. The dry electrode for the electrochemical device according to claim 1, The average pore size of the electrode active material layer is 6.0 μm or larger.

3. The dry electrode for the electrochemical device according to claim 1, The average pore size of the electrode active material layer is 6.5 μm or larger.

4. The dry electrode for the electrochemical device according to claim 1, In the electrode active material layer, the average diameter (μm) of the pores with a diameter of 4 μm to 8 μm is 6.5 μm or greater.

5. The dry electrode for the electrochemical device according to claim 1, In the electrode active material layer, the ratio of the number of pores with a diameter of 4 μm to 8 μm to the total number of pores is 80% or greater.

6. The dry electrode for the electrochemical device according to claim 1, In the electrode active material layer, the volume of pores with a diameter of 4 μm to 8 μm accounts for 60% or more of the total pore volume.

7. The dry electrode for the electrochemical device according to claim 1, In the electrode active material layer, the geodesic tortuosity (τ) is determined according to the following equation 1. geo ) is 1.15 or less: [Equation 1] In Equation 1 above, L represents the thickness of the electrode active material layer, and L eff This indicates the length of the lithium ion migration path in the electrode active material layer.

8. The dry electrode for the electrochemical device according to claim 7, In the electrode active material layer, the physical tortuosity (τ) is determined according to the following equation 2. phy ) is 3 or less: [Equation 2] In Equation 2 above, ε represents the porosity of the electrode active material layer, δ0 represents the electrolyte conductivity, and δ eff This indicates the effective electrolyte conductivity generated by the porous structure.

9. The dry electrode for the electrochemical device according to claim 1, The adhesive resin mentioned herein includes polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyolefin, or a mixture of two or more thereof.

10. The dry electrode for the electrochemical device according to claim 1, The crystallinity of the dry electrode film is greater than 0% and is 10% or less.

11. The dry electrode for the electrochemical device according to claim 1, The adhesive resin contains fibrillated fibrils, some of which have a diameter of 1 μm or greater.

12. The dry electrode for the electrochemical device according to claim 11, The fibrillated adhesive resin comprises fibrils, wherein a portion of the fibrils with a diameter of 1 μm or greater has a length of 5 μm or greater.

13. A method for manufacturing the dry electrode film according to claim 1, the method comprising the following steps: (S10) Prepare a powdered blend comprising electrode active material, conductive material and binder resin; (S20) The powdered blend is kneaded in the range of 70°C to 200°C to prepare a block blend; (S30) The bulk blend is ground to obtain electrode powder; and (S40) The electrode powder is calendered.

14. The method for manufacturing a dry electrode film according to claim 13, The electrode powder obtained in (S30) has a D50 in the range of 100 μm to 700 μm.

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