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, wherein the binder resin is fiberized, and the electrode active material layer has an average pore diameter of 5.0 ㎛ or more and a porosity of 15 vol% to 50 vol%, and the average pore diameter is calculated on the basis of the longest diameter of pores.

Description

Dry electrode for electrochemical device and method for manufacturing same

[0001] This application claims priority to Korean Patent Application No. 10-2023-0105146, filed August 10, 2023. The present invention relates to a dry electrode for an electrochemical device comprising a dry electrode film. The present invention also relates to a method for manufacturing the same.

[0002]

[0003] The rapid increase in fossil fuel use has led to a growing demand for alternative and clean energy sources. As part of this, the most actively researched area is the field of electrochemical power generation and storage. Secondary batteries are a prime example of electrochemical devices that utilize electrochemical energy, and their applications are expanding. Lithium secondary batteries, a representative example of these secondary batteries, are not only used as an energy source for mobile devices, but are also increasingly being used as power sources for electric and hybrid electric vehicles, replacing gasoline and diesel vehicles, which are major sources of air pollution. Their applications are also expanding to include auxiliary power sources through grid integration. The manufacturing process for lithium secondary batteries is largely divided into three stages: electrode manufacturing, electrode assembly manufacturing, and formation. The electrode manufacturing process is further subdivided into electrode mixture mixing, electrode coating, drying, rolling, slitting, and winding. Among these, the electrode mixture mixing process is a process of mixing components for forming an electrode active layer in which an actual electrochemical reaction occurs in the electrode. Specifically, it mixes the electrode active material, which is an essential element of the electrode, and other additives such as conductive materials and fillers, a binder for inter-powder bonding and adhesion to a current collector, and a solvent for imparting viscosity and dispersing powder, to manufacture a slurry having fluidity.

[0004] The composition mixed in this way to form an electrode active layer is also referred to as an electrode mixture in a broad sense. Subsequently, an electrode coating process is performed to apply the electrode mixture onto an electrically conductive current collector, followed by a drying process to remove the solvent contained in the electrode mixture. Additionally, the electrode is rolled to produce a predetermined thickness.

[0005] Meanwhile, during the drying process, the solvent contained in the electrode mixture may evaporate, causing defects such as pinholes or cracks in the already formed electrode active layer. Furthermore, since the inside and outside of the active layer are not uniformly dried, the difference in solvent evaporation rates may cause powder floating, i.e., powders in areas that dry first may float to form gaps with areas that dry relatively later, which may deteriorate electrode quality.

[0006] To address the above issues, drying devices capable of controlling the solvent evaporation rate while ensuring uniform drying of the interior and exterior of the active layer are being considered. However, these devices are very expensive and require significant operating costs and time, which poses a disadvantage in terms of manufacturing process efficiency. Therefore, active research has recently been conducted into manufacturing dry electrodes that do not use solvents.

[0007] This dry electrode manufacturing method is environmentally friendly, streamlined, and offers cost savings. Furthermore, unlike wet electrode manufacturing, which typically involves binder resin migration as the electrode slurry dries, dry electrode manufacturing eliminates this phenomenon, resulting in a uniform thickness distribution of the binder resin in the manufactured electrode. This uniform binder resin distribution prevents degradation of battery capacity, performance, and lifespan.

[0008] However, when the binder resin is fiberized too finely or the pore size is small during the manufacture of a dry electrode, the migration of Li ions is hindered by the narrow internal pores, which causes a problem of a decrease in the capacity of the electrode during high-rate charge / discharge. Therefore, it is necessary to design an electrode structure that can exhibit high-rate charge / discharge effectiveness by smoothing the movement of ions along with a uniform binder / conductor distribution in the vertical direction (thickness direction) of the electrode. Accordingly, the present invention requires research on structural control of a dry electrode film that is effective in high-rate charge / discharge effectiveness through an appropriate level of kneading process.

[0009]

[0010] The present invention is intended to solve the above-mentioned problem, and aims to provide a dry electrode having a structure advantageous for high-rate charge / discharge by uniformly distributing a binder / conductive material within an electrode active material layer, forming uniform pores with little deviation, and minimizing the proportion of pores that are too large or too small.

[0011] In addition, another object of the present invention is to provide a manufacturing method for manufacturing a dry electrode having the above structure.

[0012] In addition, it will be readily apparent that the objects and advantages of the present invention can be realized by the means or methods described in the claims and combinations thereof.

[0013]

[0014] A first aspect of the present invention relates to a dry electrode for an electrochemical device, wherein the electrode active material layer includes a dry electrode film, the electrode active material layer includes an electrode active material and a binder resin, the binder resin is fiberized, the electrode active material layer has an average pore diameter of 5.0 µm or more, a porosity of 15 vol% to 50 vol%, and the average pore diameter is calculated based on the longest diameter of the pores. In the aforementioned aspect, the electrode active material layer may have an average pore diameter of 6.0 µm or more.

[0015] In at least one of the aforementioned aspects, the electrode active material layer may have an average pore diameter of 6.5 μm or more.

[0016] In at least one of the aforementioned aspects, the electrode active material layer may have pores with a diameter of 4 μm to 8 μm, and an average diameter (μm) of 6.5 μm or more.

[0017] In at least one of the aforementioned aspects, the electrode active material layer may have a ratio of the number of pores having a diameter of 4 μm to 8 μm to the total number of pores of 80% or more.

[0018] In at least one of the aforementioned aspects, the electrode active material layer may have a ratio of the volume of pores having a diameter of 4 μm to 8 μm to the volume of the entire pores of 60% or more.

[0019] In at least one of the aforementioned aspects, the electrode active material layer may have a geodesic tortuosity (τgeo) of 1.15 or less according to the following equation 1.

[0020]

[0021] [Formula 1]

[0022]

[0023] In the above equation 1, L is the thickness of the electrode active material layer, L effrefers to the length of the movement path of lithium ions within the electrode active material layer.

[0024] In at least one of the aforementioned aspects, the electrode active material layer may have a Physical tortuosity (τphy) of 3 or less according to Equation 2 below.

[0025]

[0026] [Formula 2]

[0027]

[0028]

[0029] In the above formula 2, ε is the porosity of the electrode active material layer, and δ0 is the electrolyte conductivity δ eff refers to the effective electrolyte conductivity due to the pore structure.

[0030] In at least one of the aforementioned aspects, the binder resin may include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyolefin, or a mixture of two or more thereof.

[0031] In at least one of the aforementioned aspects, the crystallinity of the dry electrode film may be greater than 0 and less than or equal to 10%.

[0032] In at least one of the aforementioned aspects, the binder resin may include a portion of the fiberized fibrils having a diameter of 1 μm or more.

[0033] In at least one of the aforementioned aspects, the fiberized binder resin may include fibrils having a length of 5 μm or more and a diameter of 1 μm or more.

[0034] The present invention can provide a method for manufacturing a dry electrode film according to any one of the aforementioned aspects, and the method can include: (S10) a step of manufacturing a powder blend including an electrode active material, a conductive material, and a binder resin; (S20) a step of manufacturing a mixture lump by kneading the powder blend; (S30) a step of obtaining an electrode powder by pulverizing the mixture lump; and (S40) a step of calendering the electrode powder.

[0035] In at least one of the aforementioned aspects, the electrode powder obtained in (S30) may have a D50 of 100 μm to 700 μm.

[0036] Each of the above embodiments may be implemented independently, or alternatively, two or more of the above embodiments may be implemented in combination.

[0037]

[0038] The dry electrode according to the present invention has a small proportion of pores with too small or too large diameters inside the electrode active material layer, a small deviation in pore size, and a uniform pore size, so that lithium (Li) migration is easy, and the Li diffusion resistance is low, so that lithium movement is smooth, and overvoltage can be lowered or the occurrence of overvoltage can be suppressed, and high-rate charge / discharge characteristics can be improved.

[0039]

[0040] The following drawings attached to this specification illustrate preferred embodiments of the present invention, and together with the detailed description of the invention described below, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be interpreted as being limited to matters described in such drawings.

[0041] Figures 1a to 1c show the distribution of pore shapes and sizes of Example 1, Comparative Example 1, and Comparative Example 2, respectively.

[0042] Figure 1d shows the pore diameter and frequency (relative probility, %) of each of Example 1, Comparative Example 1, and Comparative Example 2.

[0043] Figure 1e is a reference diagram showing the pore shapes.

[0044] Figures 2a to 2d show charging curves for each C-rate of Comparative Example 1, Comparative Example 2, and Example 1.

[0045] Figures 3a to 3d show discharge curves for each C-rate of Comparative Example 1, Comparative Example 2, and Example 1.

[0046] Figure 4 shows an SEM image of the electrode active material layer in the electrode according to Example 1.

[0047] Figure 5 shows an SEM image of the electrode active material layer in the electrode according to Comparative Example 2.

[0048] Figures 6 to 11 show the results of image processing of the electrode active material region and binder region for an arbitrary cross-section of the electrode according to Example 1, Comparative Example 1, and Comparative Example 2, respectively.

[0049] Figures 12a to 14b show SOC 3D mapping of the internal de-lithiated region at the moment of charge termination in the electrodes according to Example 1, Comparative Example 1, and Comparative Example 2, respectively.

[0050] Figure 15 is a graph showing the results of calculating the geodesic tortuosity and physical tortuosity of the electrode active material layer in the electrodes according to Example 1, Comparative Example 1, and Comparative Example 2, respectively.

[0051] Figure 16 is a schematic diagram of an electrode according to one embodiment of the present invention.

[0052] Figure 17 is a schematic diagram for calculating the QBR value of an electrode active material layer.

[0053] Figure 18 is an exemplary graph showing the material-specific brightness values ​​of electrodes obtained using a FIB device. Figure 19 is a graph explaining each variable of Equations 3 and 4.

[0054] Figures 20 and 21 are SEM images of the mixed powder manufactured in Example 1, showing the shape containing electrode active material particles and fiberized binder resin.

[0055]

[0056] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0057] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0058] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0059] When a part in this specification is said to “comprise” or “have” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0060] Particle size D used in this specification 10 , D 50 and D 90D means the particle diameter at the 10%, 50% and 90% points of the cumulative distribution of the number of particles according to the particle diameter, respectively. The particle diameter may be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the particle size distribution is calculated by measuring the difference in the diffraction pattern according to the particle size when the particles pass through the laser beam. By calculating the particle diameter at the points where it becomes 10%, 50% and 90% of the cumulative distribution of the number of particles according to the particle diameter in the measuring device, D 10 , D 50 and D 90 The particle size can be measured. For example, a sample and a surfactant (e.g., nonionic surfactant, Triton-X, etc.) are added to a dispersion medium, and the dispersion obtained by ultrasonic dispersion is set on a laser diffraction particle size distribution measuring device (Microtrac S3500), and the particle size distribution on a volume basis can be measured. The dispersion medium may include water. The amount of the sample is not specified, but may be about 0.1 g to 20 g. However, the amount can be adjusted accordingly in the experiment. Meanwhile, the amounts of surfactant and water can be appropriately adjusted according to the amount of the sample. Alternatively, the D1 of the particles can be measured using the 3D modeling method described below. 0, You can check D50 and D90.

[0061] The "thickness" of each layer included in the electrode in this specification may refer to a value measured by a known method for measuring thickness. The method for measuring thickness is not limited thereto, but may be, for example, a value measured using a thickness gauge (Mitutoyo, VL-50S-B).

[0062] In this specification, the electrode includes a dry electrode film as an electrode active material layer. The dry electrode and dry electrode film refer to those manufactured by a dry manufacturing process that does not use a solvent for dispersing electrode components such as an electrode active material, a conductive material, and a binder.

[0063] In the present invention, the dry electrode is an electrode for an electrochemical device, and the electrochemical device may be, for example, a secondary battery, and more specifically, the secondary battery may be a lithium ion secondary battery.

[0064]

[0065] [Dry electrode]

[0066] A first aspect of the present invention relates to a dry electrode. The dry electrode comprises a current collector and a dry electrode film disposed on at least one side of the current collector as an electrode active material layer. As described below, the dry electrode can be obtained by bonding the dry electrode film and the current collector through a lamination process. The dry electrode film comprises an electrode active material and a binder resin, and may further comprise a conductive material as needed.

[0067]

[0068] The above dry electrode film may have a plate-like structure formed by dry pressing of electrode powder. The electrode powder comprises an aggregate of mixed particles including an electrode active material and a binder resin. If necessary, the mixed particles may further include a conductive material. The dry electrode film according to the present invention has a porous structure, and this porous structure is derived from pores formed by the interstitial volume between the mixed particles. In addition, in the dry electrode film, the binder resin is subjected to a finely divided treatment by a fiberization process described below, so that the binder resin is released on the surface, thereby having a plurality of fine fibers (fibrils). In addition, the electrode powder may further include some free electrode active material or binder resin, etc., without being granulated.

[0069]

[0070] [Gongdo]

[0071] In the present invention, the dry electrode film may have a porosity of 15 vol% to 50 vol%, and preferably within the above range, it may 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. The lower limit of the porosity may be controlled to, for example, 20 vol% or more. When the porosity satisfies the above range, it is preferable in terms of various effects. On the other hand, when the porosity is too small outside the above range, it is difficult to impregnate the electrolyte, which is not preferable in terms of life characteristics, output characteristics, etc., and when the porosity is too large, the volume increases to express the same capacity, which is not preferable in terms of energy density per volume. In one embodiment of the present invention, the porosity can be obtained by measuring the apparent density of the dry electrode film and using the actual density (net density) calculated based on the actual density and composition of each component by the following [Relational Formula 1a].

[0072]

[0073] [Relationship 1a]

[0074] Porosity (vol%) = {1 - (apparent density / actual density)} x 100

[0075]

[0076] Meanwhile, the apparent density in the above relational expression 1a can be calculated from the following relational expression 1b.

[0077]

[0078] [Relationship 1b]

[0079] Apparent density (g / cm) 3 ) = (Weight of the measured object (g)) / {(Thickness of the measured object (cm))x(Area of ​​the measured object (cm) 2 ))}

[0080]

[0081] Apparent density, or more commonly known as bulk density, is a measure of how much space a substance occupies per unit volume, including the voids or empty space contained within it. In other words, apparent density includes both the solid material and the voids within its volume. Apparent density can be calculated by dividing the mass of a material by its total volume, including all pores or empty space within the material. The formula for calculating apparent density is shown in Equation 1c below.

[0082]

[0083] [Relationship 1c]

[0084] Apparent density = mass / total volume

[0085]

[0086] The mass can be measured using a scale. For materials of regular shape (e.g., a cube, a cylinder, etc.), the dimensions can be measured using appropriate tools such as a tape measure or calipers, which are well known in the art. For irregularly shaped samples, the volume can be measured by measuring the displacement of a liquid to determine the change in a known volume. The change in volume can be equal to the volume of the material. Those skilled in the art can apply other known methods for measuring the volume or apparent density.

[0087] The above net density (true density) refers to the intrinsic density of a material, excluding any voids or pores contained within it. It is the mass of a solid material divided by its actual volume, excluding empty space. True density can be calculated by dividing the mass of a material by its solid, non-empty volume. The formula for calculating true density is shown in Equation 1d below.

[0088]

[0089] [Relationship 1d]

[0090] True density = mass / solid volume (not considering pore volume)

[0091]

[0092] Alternatively, it can be determined using the gas volcanometry method according to ISO 12154:2014 or any other measurement method known to experts in the field.

[0093]

[0094] Meanwhile, in one embodiment of the present invention, the porosity can be calculated from 3D data obtained through a 3D structure modeling method of the electrode as described below.

[0095] Meanwhile, in the present invention, the porosity can be better implemented by the size of the pores and the size of the fiberized binder described later.

[0096]

[0097] [Pore size]

[0098] In the present invention, the dry electrode film has uniform pore sizes with little variation. This facilitates the movement and diffusion of lithium ions during charging and discharging, and is advantageous for improving fast charging and high-output characteristics.

[0099] The dry electrode film according to the present invention has a total volume of pores having a diameter of 2 ㎛ or more and 10 ㎛ or less among 100 vol% of the total pores, which is 90 vol% or more. For example, it may be 90 vol% to 99.99 vol%. Preferably, the volume of pores having a diameter of 4 ㎛ or more and 8 ㎛ or less may be 60 vol% or more, or 65 vol% or more, or 70 vol% or more, based on the total volume of pores in the electrode. For example, it may be 60 vol% to 99.99 vol%, or 65 vol% to 99.99 vol%, or 70 vol% to 99.99 vol%.

[0100] The electrode active material layer may have a volume of pores (micropores) having a pore diameter of 0.5 μm or less, or less than 0.5 μm, relative to the apparent volume, of 10 vol% or less, or 5 vol% or less, or 3 vol% or less, or 1 vol% or less. Meanwhile, the volume of the micropores may be 0.000 l vol% or more, or 0.001 vol% or more within the aforementioned range. Preferably, the volume of pores having a diameter of 1 μm or less, or 2 μm or less, or 3 μm or less may be 10 vol% or less, or 5 vol% or less, or 3 vol% or less, or 1 vol% or less. Meanwhile, the volume of the micropores may be 0.0001 vol% or more, or 0.001 vol% or more within the aforementioned range. In addition, in a preferred embodiment, the electrode active material layer may have a volume of pores having a diameter of 10 μm or more (macro pores) relative to the apparent volume of 10 vol% or less, 7 vol% or less, or 5 vol% or less, or 3 vol% or less, or 1 vol% or less. Meanwhile, the volume of the macro pores may be 0.0001 vol% or more, or 0.001 vol% or more, within the aforementioned range.

[0101] The above dry electrode film may have pores having a diameter of 2 µm or more and 10 µm or less, or 4 µm or more and 8 µm or less, in an amount of 80% or more relative to the total number of pores. Meanwhile, the number of pores may be 99.99% or less within the aforementioned range.

[0102] The pores included in the above dry electrode film have an average pore diameter of 5.0 μm or more, or 6.0 μm or more, or 6.5 μm or more. Meanwhile, the average pore diameter may be 20.0 μm or less, 13.0 μm or less, 10.0 μm or less, or 9.0 μm or less. Within the above range, the average pore diameter may be 6.0 μm or more and 10.0 μm or less, or 6.5 μm or more and 9.0 μm or less.

[0103] The average pore size of the pores having a pore diameter of 2 ㎛ or more and 10 ㎛ or less included in the above dry electrode film may be 5 ㎛ or more, preferably 6.0 ㎛ or more, and preferably 6.5 ㎛ or more.

[0104] In one embodiment of the present invention, the average pore diameter of the pores having a diameter of 4 ㎛ to 8 ㎛ in the dry electrode film may be 6.0 ㎛ to 8 ㎛, preferably 6.5 ㎛ to 8 ㎛. Within the above range, the average pore diameter of the pores having a diameter of 4 ㎛ to 8 ㎛ may be 20.0 ㎛ to 8 ㎛, 13.0 ㎛ to 8 ㎛, 10.0 ㎛ to 8 ㎛, or 9.0 ㎛ to 8 ㎛. Within the above range, the average pore diameter may be 6.0 ㎛ to 10.0 ㎛, or 6.5 ㎛ to 9.0 ㎛.

[0105]

[0106] FIG. 1d is a graph showing the distribution of pore size and shape for a dry electrode according to Example 1 of the present invention, and it can be confirmed that the deviation in pore size is smaller than that of the comparative example. As such, the dry electrode film according to the present invention has a large average pore diameter of 5.0 ㎛ or more, a small ratio of fine pores less than 4 ㎛ and macro pores exceeding 8 ㎛, and a small deviation in pore size, which is advantageous in securing uniform lithium ion diffusion, and the movement of lithium ions within the electrode is smooth, which is advantageous in high-rate charge / discharge.

[0107] In the present invention, the diameter of the pores is based on the longest diameter of the pores. In addition, the average diameter of the pores is the mean diameter, and can be calculated based on the following relational expression 2.

[0108]

[0109] [Relationship 2]

[0110] Mean diameter = (Σd / n)

[0111]

[0112] In the above relationship, Σd is the sum of the diameters of all measured pores, and n is the total sum of the number of target pores.

[0113]

[0114] In a specific embodiment of the present invention, the pores may have a flat bar, a prolate spheroid, an oblate spheroid, and a sphere. Here, the flat bar-shaped pores may be included in an amount of 35 vol% or more, 40 vol% or more, 43 vol% or more, or 45 vol% or more, based on 100 vol% of the total pore volume of the electrode. Meanwhile, the flat bar-shaped pores may be 60 vol% or less, or 55 vol% or less, based on 100 vol% of the total pore volume of the electrode. Meanwhile, the dry electrode film may include spherical pores in an amount of less than 5 vol% or less than 3 vol%, based on 100% of the total pore volume of the electrode. Meanwhile, the spherical pores may be 0.001 vol% or more, or 0.01 vol% or more, based on 100 vol% of the total pore volume of the electrode.

[0115] Here, the shape of the flat bar, prolate spheroid and oblate spheroid refers to a shape having a value of 0.4 to less than 0.8 based on the Krumbein Sphericity, and the sphere shape refers to a shape having a value of 0.8 to 1.0 based on the Krumbein Sphericity. Meanwhile, in the present invention, Flat bar, Prolate and Oblate can be distinguished according to the ratio of a, b and c below. Flat bar refers to a shape in which b and c are similar but a is relatively large. Meanwhile, when a and b are similar and c is relatively large, it is distinguished as Prolate, and when b and c are relatively large compared to a, it is distinguished as Oblate. In a specific embodiment, Flat bar means that a is greater than 0.45 and less than 0.6, for example, greater than 0.45 and less than 0.55, preferably 0.5, b is from 0.1 to 0.15, and c is 1-ab (c=1-ab). Meanwhile, Prolate means that a is from 0.6 to 0.65, b is from 0.175 to 0.2, and c is 1-ab (c=1-ab), and Oblate means that a is from 0.40 to 0.45, b is from 0.4 to 0.45, and c is 1-ab (c=1-ab). Figure 1e schematically illustrates each form.

[0116]

[0117] In the present invention, the Krumbein Sphericity can be calculated through the following equation 5.

[0118]

[0119] [Formula 5]

[0120]

[0121]

[0122] Here, a represents the longest diameter (length of the longest axis) of the pore, b represents the length of the intermediate axis of the pore diameter, and c represents the shortest diameter (length of the shortest axis) of the pore. Here, the flat bar shape refers to a pore having a value of 0.4 to 0.8 based on the Krumbein Sphericity, and the sphere shape refers to a pore having a value of 0.8 to 1.0 based on the Krumbein Sphericity.

[0123] In a specific embodiment of the present invention, the structure, shape and size of the pores, such as the pore diameter, average pore diameter and volume, can be confirmed by a method of three-dimensionalizing through 3D reconstruction after measuring a multi-layer image of a FIB SEM cross-section. Alternatively, the pore size and distribution can be calculated using a capillary flow porosimetry method. The capillary flow porosimetry method is a method of measuring the pore size and distribution through the pressure required to push out the wetting solution filling the pores by wetting the measurement target using a wetting solution having low surface tension and then pressurizing the target using a gas.

[0124]

[0125] [Fiber diameter of binder resin in dry electrode film]

[0126] In the above dry electrode film, the binder resin includes fiberized fibrils. In the present invention, the fibrils may include a portion having a diameter of 300 nm or more, or 500 nm or more, or 700 nm or more, or 1 μm or more. Preferably, the fiberized binder resin may include fibrils having a section having a length of 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 in a portion having a diameter of 300 nm or more. Alternatively, the fiberized binder may include fibrils having a section having a length of 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 in a portion having a diameter of 500 nm or more. Alternatively, the fiberized binder resin may include fibrils having a section in which the length of a portion having a diameter of 700 nm or more is 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 fiberized binder resin may include fibrils having a section in which the length of a portion having a diameter of 1 μm or more is 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 20 μm or more. In a more specific embodiment, the dry electrode film may include at least one fibril in which the length of a portion having a diameter of 1 μm or more is 50 μm or more.

[0127] Meanwhile, the diameter of the fiberized binder resin in the dry electrode film may 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 invention, the diameter and length of the fibrils can be confirmed through an SEM image of the manufactured dry electrode film. In addition, an appropriate image processing program that can display the binder resin separately from other components may be further applied. The image processing program may use a known program such as Avizo or Image J. In the present invention, when the fibril diameter of the binder resin satisfies the above-described range, it is advantageous for implementing a dry electrode film with a large pore size and a small deviation. Meanwhile, the fiberization of the binder resin in the dry electrode film, and the diameter and length of the fibrils resulting from the fiberization, can be controlled through the kneading process conditions and / or the calendaring process described below. For example, it can be adjusted by controlling the rotation speed (rpm) of the kneading device and / or the kneading time. Alternatively, it can be controlled by the speed and / or pressure of the calendaring device. 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 controlled by the size of the electrode powder according to the grinding process. This will be described in detail in the grinding process section.

[0128]

[0129] [QBR]

[0130] According to one embodiment of the present invention, the dry electrode film may have a QBR (Quantified Binder Ratio) of 0.9 to 1.1. In the present invention, it is preferable that the dry electrode film satisfying the QBR value is a dry electrode film for a positive electrode.

[0131]

[0132] The above QBR is defined by the following [Relationship 3].

[0133]

[0134] [Relationship 3]

[0135] QBR = Bs / Bf

[0136]

[0137] In the above mathematical formula, Bs represents the average value of the fluorine content in the surface area of ​​the electrode active material layer from the outermost surface of the electrode active material layer to within 15% of the total thickness of the electrode active material layer, and Bf represents the average value of the fluorine content in the bottom area of ​​the electrode active material layer from the interface of the electrode active material layer facing the current collector to within 15% of the total thickness of the electrode active material layer.

[0138] Fig. 16 is a schematic diagram of an electrode according to one embodiment of the present invention. Referring to Fig. 16, the electrode (10) includes an electrode current collector (12); and an electrode active material layer (11) positioned on the electrode current collector (12) and including an active material, a conductive material, a binder, and a fluorinated elastomer.

[0139] The above electrode active material layer (11) has an electrode active material layer surface area (11s) from the outermost surface of the electrode active material layer to within 15% of the total thickness (d) of the electrode active material layer, and an electrode active material layer bottom area (11f) from the electrode active material layer interface facing the current collector to within 15% of the total thickness (d) of the electrode active material layer, based on the total thickness (d).

[0140] In the above mathematical formula QBR, Bs means the average value of the fluorine content in the surface area (11s) of the electrode active material layer, and Bf means the average value of the fluorine content in the bottom area (11f) of the electrode active material layer.

[0141] At this time, QBR can be calculated using the following method.

[0142] First, the electrode for which the QBR is to be confirmed is selected, and a cross-section of the selected electrode is manufactured using argon ion milling. Then, the components within the electrode active material layer of the manufactured electrode cross-section are mapped using the energy dispersive X-ray spectroscopy (EDS) detector of a scanning electron microscope (SEM).

[0143] From the EDS mapping results, a line profile is extracted in the direction of the thickness of the electrode active material layer, and among the extracted line profile results, the average value (Bs) of the fluorine content of the fluorine-containing binder in the surface area of ​​the electrode active material layer and the average value (Bf) of the fluorine content of the fluorine-containing binder in the bottom area of ​​the electrode active material layer are extracted, and the QBR value is calculated using the above [Relational Expression 2].

[0144]

[0145] At this time, the surface area of ​​the electrode active material layer is an area from the outermost surface in the thickness direction of the electrode active material layer to within 15% of the total thickness of the electrode active material layer, and the bottom area of ​​the electrode active material layer is an area from the interface of the electrode active material layer facing the current collector to within 15% of the total thickness of the electrode active material layer.

[0146]

[0147] Fig. 17 is a schematic diagram for calculating the QBR value of the electrode active material layer. Referring to Fig. 17, the X-axis represents the thickness of the electrode active material layer, i.e., the distance from the surface toward the current collector, and the Y-axis represents the intensity of the fluorine component. Line A represents the intensity of the fluorine component of the fluorine-containing binder extracted by EDS mapping the fluorine component in the electrode active material layer of the electrode cross-section, and line B is a trend line representing the tendency of line A, which is a line smoothed using the LOWESS smoothing method, i.e., the Locally-Weighted Scatterplot Smoother method.

[0148] The above QBR value is a numerical value indicating the uniformity of the distribution of the fluorine-containing binder in the thickness direction within the electrode active material layer through the ratio of the content of the fluorine-containing binder contained in the surface region to the content of the fluorine-containing binder contained in the bottom region of the electrode active material layer. At this time, the content of the fluorine-containing binder can be inferred through the fluorine component contained in the fluorine-containing binder used.

[0149] The above QBR value is 1.1 or less, and according to one embodiment of the present invention, the QBR value may be 0.95 or more, 0.97 or more, 1.03 or less, 1.05 or less, and may also be 0.95 to 1.05.

[0150] When the above QBR value satisfies the range of 1.1 or less, the problem of the fluorine-containing binder migrating to the electrode surface and the content of the fluorine-containing binder contained in the surface area increasing compared to the content of the fluorine-containing binder contained in the bottom area of ​​the electrode active material layer does not occur, and as a result, the binder is evenly distributed in the thickness direction of the electrode active material layer, so that the binder content in the area close to the current collector does not decrease, and thus the adhesive strength between the current collector and the electrode active material layer is improved, and the conductivity on the surface of the electrode active material layer and the charge / discharge speed accordingly can also be improved.

[0151]

[0152] [Tortuosity]

[0153] In one embodiment of the present invention, the dry electrode film preferably has a geodesic tortuosity (τ) according to the following [Formula 1] geo ) is less than or equal to 1.15.

[0154] The above geodesic tortuosity can indicate the length of the lithium ion migration path through the pores in the electrode. Therefore, τ is used to shorten the lithium ion migration path. geo It is desirable that the value be less than 1.15.

[0155]

[0156] [Formula 1]

[0157]

[0158]

[0159] In the above [Formula 1], L is the thickness of the electrode active material layer, L eff refers to the length of the movement path of lithium ions within the electrode active material layer.

[0160] In the present invention, the geodesic tortuosity (τ geo ) can be modeled in three dimensions using a three-dimensional structure modeling tool and the movement path can be calculated and confirmed based on this.

[0161] The above 3D modeling can be performed by, for example, obtaining cross-sections of multiple composite electrodes using FIB (Focused Ion Beam) and SEM, and then creating a 3D structure from these to analyze the interparticle contact area, pore structure, etc. Alternatively, analysis can be performed by extracting the interior of the composite electrode as a 3D structure using Micro / Nano CT (Computed Tomography). Alternatively, 3D electrode structure formation, analysis modeling, and simulation tools such as GeoDict, AVIZO, and MATBOX can be used.

[0162]

[0163] In one embodiment of the present invention, a method of using the FIB (Focused Ion Beam) and SEM can be specifically described as follows.

[0164] First, the electrode sample can be processed using a light source selected from Ga+, plasma, or laser depending on the sample volume of the electrode. For example, if an image is to be obtained at a resolution of nanometers, the sample can be processed by cutting the electrode using a Ga+ light source. If an image is to be obtained at a resolution of micrometers, the sample can be processed by cutting the electrode using a plasma light source or a laser light source. At this time, the cutting speed and gap of the electrode sample can be controlled by setting the voltage and current of the FIB device.

[0165] As described above, the sample image of the electrode obtained using the FIB device may be a SEM image representing a cross-section of the electrode sample. The SEM image may be displayed to have different contrast differences for each electrode element included in the electrode, such as the electrode active material, conductive material, binder, pores included in the electrode, and aluminum current collector. Fig. 18 is an exemplary graph showing the contrast values ​​for each material of the electrode obtained using the FIB device. Referring to this, it can be confirmed that the pores within the electrode and each electrode material exhibit different contrast values.

[0166] Thereafter, the obtained electrode cross-section SEM image can be processed, such as by adjusting the contrast using an FFT (Fast Fourier Transform) filter or an NLM (non-Local Means) filter, and as a result of the image data processing, digital data of the remodeled 3D structure can be obtained.

[0167] The above digital data can be implemented as a two-dimensional or three-dimensional graphic image and can provide various numerical information about the electrode structure. After remodeling the three-dimensional structure of the electrode in this way, L eff It produces.

[0168] In one embodiment of the present invention, the τ geo It can be calculated using the neurite tracer program based on FiJi / Image J, and the basis for calculation is as shown in Equation 3 below.

[0169]

[0170] [Formula 3]

[0171]

[0172]

[0173] [Formula 4]

[0174]

[0175]

[0176] In the above [Formula 3], L means a given straight line length in an arbitrary direction, and dl within the length L i means the length component corresponding to each deflection angle. Each deflection angle can be calculated by the angle between two vectors in three-dimensional space for each path, and each path is defined through the tracer program used. In addition, the deflection angle can be defined by the above [Formula 4]. Refer to Fig. 19 for each variable of the above [Formula 3] and [Formula 4], and in the above Formula 4, v represents a vector, and the vector v at a specific point i Vector v at a relative point to vi i+1 , and x, y and z represent each component of the vector.

[0177] The above τ geoThe method of calculating can be found in IOP Conf. Series: Earth and Environmental Science 311 (2019) 012041,” doi:10.1088 / 1755-1315 / 311 / 1 / 012041.

[0178] Meanwhile, the above [Formula 1] and [Formula 2] can be interpreted as follows. The 3D electrode structure remodeled by the above method is composed of voxel units, and a set of void voxels connecting surfaces in the direction of the electrode thickness is found through a calculation algorithm, and among them, the set of the shortest void voxels (composed of the smallest amount of voxels) is used as the standard. eff The value is calculated. At this time, it can be calculated by multiplying the edge value of the voxel and the number of connected voxels between the surfaces.

[0179]

[0180] Furthermore, the above dry electrode film has a physical tortuosity (τ) according to [Formula 2] below. phy ) is preferably 3 or less. In a battery including a dry electrode film according to the present invention, tortuosity is affected by the ionic conductivity of the electrolyte injected into the battery. Therefore, it is preferable to consider the Physical tortuosity value in consideration of the bottleneck phenomenon inside the electrode due to the electrolyte.

[0181]

[0182] [Formula 2]

[0183]

[0184]

[0185] In the above [Formula 2], ε is the porosity of the electrode active material layer, δ0 is the electrolyte conductivity, and δ effrefers to the effective electrolyte conductivity due to the pore structure.

[0186] In the present invention, the porosity (ε) may be applied to the volume of pores calculated through three-dimensional remodeling.

[0187] The conductivity (δ0) of the electrolyte can be calculated by calculating the interaction between electrolyte molecules and lithium ions. In one embodiment of the present invention, the conductivity (δ0) of the electrolyte can be set based on the Advanced Electrolyte Model (AEM), a statistical mechanics model based on NPNRAMSA (Mean Spherical Approximation) developed by Kevin Gering of Idaho National Laboratory (Journal of The Electrochemical Society, 165 (14) A3350-A3359 (2018)). AEM models the molecular scale and can calculate various properties of the electrolyte (viscosity, ionic conductivity, diffusivity, transport number, activity coefficients, etc.) through interactions (solvent-solvent, solvent-ion, ion).

[0188] Meanwhile, the effective ionic conductivity δ of the electrode of the present invention eff can be calculated by applying the following equations (a) to (c) (Laplace's equation and Ohm's equation) to the produced 3D remodeling structure.

[0189]

[0190] (a)

[0191] (b)

[0192] (c)

[0193]

[0194] In the above formulas (a) to (c) Silver local conductivity (S m -1 ) and, is Local current density (A·m -1 ) and, is the local potential(V), is the effective conductivity (S·m -1 ), and V is the volume of the void (m 3 ) am.

[0195]

[0196] [Loading amount]

[0197] In the present invention, the loading amount of the electrode active material in the dry electrode film is 3 mAh / cm 2 Up to 15 mAh / cm 2 It can be 4 mAh / cm in detail. 2 10 mAh / cm 2 It can be. Here, the loading amount of the active material can be calculated by the following method [Relational Expression 4].

[0198]

[0199] [Relationship 4]

[0200] Loading capacity (mAh / cm) 2 ) = Capacity of active material (mAh / g) x Weight content ratio of active material in dry electrode film (wt%) x Weight per unit area of ​​dry electrode film (g / cm 2 )

[0201]

[0202] [Binder resin]

[0203] In the present invention, the binder resin is not limited to a specific one as long as it can be fiberized through the steps (S10) and / or (S20) described below. The fiberization refers to a process of dividing a polymer into fine particles, and can be performed using, for example, mechanical shear force. The polymer fibers fiberized in this way have their surfaces and / or bodies loosened to produce a large number of fine fibers (fibrils). Non-limiting examples of such binder resins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyolefin, or a mixture of two or more thereof, and specifically, polytetrafluoroethylene (PTFE), and more specifically, polytetrafluoroethylene (PTFE). Specifically, the polytetrafluoroethylene (PTFE) may be included in an amount of 30 wt% or more based on the total binder resin weight. Meanwhile, at this time, it goes without saying that the binder resin may additionally contain PEO (polyethylene oxide) and / or PVdF-HFP (polyvinylidene fluoride-cohexafluoropropylene) in addition to the aforementioned components.

[0204]

[0205] [Electrode active material]

[0206] In the present invention, the dry electrode may be a positive electrode, and the electrode active material may be a positive electrode active material.

[0207] The above positive electrode active material is not limited to a specific component as long as it is in the form of a lithium transition metal oxide or lithium metal iron phosphate, or a metal oxide. Such positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide, represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.5), e.g. Li(Ni,Co,Mn,Al)O2 A metal other than Li, in which the fraction of Ni is 50% or more; chemical formula LiMn 2-x M x Lithium manganese composite oxides represented by O2 (wherein, M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein, M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which a portion of the Li in the chemical formula is replaced by an alkaline earth metal ion; lithium metal phosphate LiMPO4 (wherein, M is M = Fe, CO, Ni, or Mn), disulfide compounds; Fe2(MoO4)3, etc., and may include one or more of these, but are not limited thereto.

[0208]

[0209] Alternatively, the dry electrode may be a cathode, and the electrode active material may be a cathode active material. The cathode active material may be carbon such as non-graphitizable carbon, graphite carbon, etc.; Li xFe2O3(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, elements of group 1, 2, and 3 of the periodic table, halogens; 0x≤1; 1≤y≤3; 1≤z≤8) and other metal composite oxides; lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; silicon-based oxides such as SiO, SiO / C, and SiO2; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc. can be used. In the present invention, the electrode may preferably be a positive electrode.

[0210]

[0211] [Challenge]

[0212] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black; conductive fiber such as carbon fiber or metal fiber; metal powder such as fluorocarbon, aluminum, nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used. However, specifically, in order to uniformly mix the conductive material and improve conductivity, the conductive material may include at least one selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, and more specifically, the conductive material may include activated carbon.

[0213]

[0214] [entire house]

[0215] The current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The current collector can also form fine unevenness on its surface to increase the adhesive strength of the positive electrode active material, and various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric are possible.

[0216]

[0217] Furthermore, the current collector may be used with a conductive primer coated entirely or partially on the surface to lower resistance and improve adhesion. Here, the conductive primer may include a conductive material and a binder, and the conductive material is not limited to any conductive material, but may be, for example, a carbon-based material. The binder may include a fluorine-based binder (including PVDF and PVDF copolymer), an acrylic-based binder, and an aqueous binder that can be dissolved in a solvent.

[0218]

[0219] [Content]

[0220] In one embodiment of the present invention, in the electrode active material layer, the electrode active material, the binder resin, and the conductive material may be included in weight ratios of 80 wt% to 98 wt%, 0.5 wt% to 10 wt%, and 0.5 wt% to 10 wt%, respectively. To this end, the powder blend may include the electrode active material, the binder resin, and the conductive material in weight ratios of 80 wt% to 98 wt%, 0.5 wt% to 10 wt%, and 0.5 wt% to 10 wt%, respectively. In a specific embodiment, the binder resin may be included in a range of 0.5 wt% to 5 wt% or 0.5 wt% to 3 wt% relative to 100 wt% of the electrode active material layer. In the present invention, the content of the electrode components is not particularly limited, and it goes without saying that the content of the components can be appropriately adjusted so that the battery can exhibit a desired level of electrochemical performance.

[0221] If the content of the binder resin is too high, the average pore diameter of the resulting electrode active material layer may decrease. In addition, if the content of the binder resin increases, the content of the electrode active material may decrease, which may lower the energy density. In addition, since the binder resin may act as a resistance component, the resistance characteristics may deteriorate. On the other hand, if the content of the binder resin is too low, sufficient fiberization may not occur, which may result in problems such as not being able to coagulate enough to form a mixture lump, making it difficult to manufacture a dry electrode film, or deteriorating the physical properties of the dry electrode film. If the fiberization of the binder is not sufficient as described above, it may not be easy to achieve the aforementioned structural characteristics in terms of porosity and pore structure.

[0222] If the content of the above-mentioned conductive agent is too high, the content of the active material is relatively reduced, which may cause a capacity reduction problem. If the content of the above-mentioned conductive agent is too low, sufficient conductivity may not be secured or the properties of the dry electrode film may deteriorate, which is not desirable.

[0223] If necessary, the electrode active material layer may include a filler that suppresses electrode expansion. The filler is not particularly limited as long as it is a fibrous material that does not cause a chemical change in the battery. For example, olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber are used. The filler is preferably present in an amount of 5 wt% or less, or 3 wt% or less, or 1 wt% or less, relative to 100 wt% of the electrode active material layer.

[0224]

[0225] Meanwhile, the present invention provides a secondary battery including the above dry electrode, wherein the dry electrode is a positive electrode, and an electrode assembly including the positive electrode, the negative electrode, and the separator is housed in a battery case together with a lithium-containing non-aqueous electrolyte, and an energy storage device including the secondary battery as a unit battery. In this case, since the specific structures of the secondary battery and the energy storage device are known in the art, their descriptions are omitted herein.

[0226]

[0227] [Electrode manufacturing method]

[0228] A second aspect of the present invention relates to a method for manufacturing an electrode according to the present invention.

[0229]

[0230] In a specific embodiment, the method for manufacturing the electrode comprises:

[0231] (S10) A step of manufacturing a powder blend including an electrode active material, a conductive material, and a binder resin;

[0232] (S20) A step of kneading the above powder blend to produce a mixture lump;

[0233] (S30) A step of crushing the above mixture lump to obtain an electrode powder containing mixed particles; and

[0234] (S40) A step of obtaining a free-standing type dry electrode film by calendaring the electrode powder;

[0235] The above step (S20) can be performed at a temperature range of 70°C to 200°C.

[0236] As will be described later, the above electrode dry electrode film can be manufactured into an electrode by bonding it to one or both sides of an electrode current collector (S50).

[0237]

[0238] In one embodiment of the present invention, a lamination step may be performed in which the dry electrode film obtained through the calendering step is placed on at least one surface of a current collector and pressed. Through the lamination, the dry electrode film is placed on the current collector and then pressed to bond the current collector and the dry electrode film, thereby manufacturing an electrode. This may be performed using a pressing member such as a lamination jig or roller. The pressing may be performed by a hot pressing method, and for example, when a lamination roller is used, the temperature of the roller may be controlled in the range of 20°C to 200°C.

[0239]

[0240] Hereinafter, a method for manufacturing a dry electrode according to the present invention will be described in more detail.

[0241]

[0242] First, a blend containing an electrode active material, a conductive agent, and a binder resin is prepared (S10). In this step, the electrode materials are dry-mixed in powder form without using a solvent. Any method that allows for uniform mixing of the electrode materials is not limited to a specific method, and various methods may be applied. In one specific embodiment, the electrode materials may be mixed in powder form by placing them in a device such as a mixer or blender.

[0243]

[0244] In one embodiment of the present invention, the mixing time is not particularly limited, but may be performed for 1 second to 10 minutes. Meanwhile, the mixing speed is not particularly limited, but may be appropriately controlled within a range of about 3,000 rpm to 30,000 rpm. As a specific example, the mixing may 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, in order to ensure high uniformity.

[0245] As will be described later, the binder resin is primarily fiberized through step (S20). However, some coarse fiberization may also occur during step (S10).

[0246]

[0247] Next, a kneading process is performed on the powder blend obtained above (S20).

[0248]

[0249] In a specific embodiment of the present invention, the kneading may be performed using a kneader, for example. Through this kneading, the binder resin is fiberized, thereby binding or connecting the electrode active material and conductive materials to form a lump-like mixture.

[0250] In the present invention, the kneading in step (S20) can be controlled at a speed of 10 rpm to 100 rpm. For example, the kneading can be controlled at a speed of 20 rpm or more or 70 rpm or less within the above range. The kneading can be performed for 1 to 30 minutes. For example, the kneading can be performed at a speed of 20 rpm to 70 rpm within the above range for 3 to 10 minutes.

[0251] The above kneading can be controlled at a shear rate ranging from 5 / s to 1000 / s. In a specific embodiment of the present invention, the kneading can be performed for 1 to 30 minutes, and the shear rate can be controlled at a shear rate ranging from 10 / s to 500 / s. Meanwhile, the kneading process can be performed at a pressure higher than atmospheric pressure, specifically at a pressure of 1 atm to 3 atm, and more specifically at a pressure of 1.1 atm to 3 atm.

[0252] In the present invention, the kneading step may be performed under conditions of high temperature and pressure higher than atmospheric pressure, and more specifically, may be performed under conditions of pressure higher than atmospheric pressure. More specifically, the kneading may be performed at a temperature ranging from 70°C to 200°C, and more specifically, at a temperature ranging from 90°C to 150°C.

[0253] In the present invention, the kneading process can be controlled so that the dry electrode film can implement the pore characteristics described above, such as porosity, pore size, and pore distribution.

[0254] For example, if the kneading step is performed at a low temperature outside the above range, the binder resin may have a low degree of fiberization in the mixed powder and / or dry electrode film, or fibers with a large diameter may not be formed well. For example, fibers with a diameter of 700 nm or more, or 1 μm or more, or 1.2 μm or more, or 1.5 μm or more may not be formed well in the mixed powder. For example, fibers with a diameter of 300 nm or more, or 500 nm or more, or 700 nm or more, or 1 μm or more of the binder resin may not be formed well in the dry electrode film. Or, it may be difficult to form fibers in the dry electrode film in which the length of the section having a diameter of 300 nm or more, or 500 nm or more, or 700 nm or more, or 1 μm or more is 5 μm or more. Or, in the mixed electrode powder, it may be difficult to form fibers with a length of 5㎛ or more in a section with a diameter of 700nm or more, or 1.0㎛ or more, or 1.2㎛ or more, or 1.5㎛ or more. In such cases where the fiberized binder resin has a thin diameter and / or a short length, the deviation in diameter size may become large, or the proportion of pores that are too small and / or too large may become high. In addition, since the fiberization and kneading of the binder may not be well formed, the film formation may not be easily achieved during calendaring. On the other hand, when the kneading is performed at too high a temperature, the fiberization of the binder may occur rapidly, and there is a problem that the already formed fibers may be cut by excessive shear force thereafter, which is not preferable.

[0255] In one embodiment of the present invention, if the process is performed at a pressure that is too high, beyond the aforementioned range, it is not preferable because excessive shear force and pressure may be applied, causing problems such as the fibers formed being cut or the density of the mixture mass becoming too high.

[0256] According to a preferred embodiment of the present invention, performing the high-temperature, low-shear mixing process described above is advantageous in achieving the intended effects of the present invention. If necessary, the mixing process can be performed under pressures exceeding atmospheric pressure.

[0257] Next, the lump-shaped blend manufactured through the above-mentioned kneading step is pulverized to obtain electrode powder (S30).

[0258]

[0259] Specifically, the lump-like blend produced through the above kneading can be directly calendered, but in this case, the lump-like blend may need to be pressed under strong pressure and high temperature to produce a thin film, which may result in a problem of the film density becoming too high or a uniform film not being obtained. Therefore, according to the present invention, the produced lump-like blend undergoes the above pulverizing step.

[0260]

[0261] At this time, the pulverization is not limited, but can be performed using a known pulverizing device such as a blender or grinder. In a specific embodiment of the present invention, the pulverization speed can be controlled within a range of 3,000 rpm to 30,000 rpm. For example, the pulverization can be 20,000 rpm or less, or 15,000 rpm or less, or 12,000 rpm or less. Meanwhile, the pulverization time can be appropriately controlled within a range of 1 second to 10 minutes. For example, the pulverization time can be 7 minutes or less, or 5 minutes or less, or 3 minutes or less, or 1 minute or less. However, the pulverization speed and time are not particularly limited to the above ranges. As a specific example, the pulverization can be performed at a speed of 5,000 rpm to 20,000 rpm for 30 seconds to 10 minutes, or at a speed of 10,000 rpm to 18,000 rpm for 30 seconds to 1 minute.

[0262]

[0263] Outside the above range, if grinding is performed at too low a rpm or for too short a grinding time, sufficient grinding may not be achieved, which may result in mixed particles of a size unsuitable for filming. On the other hand, if grinding is performed at too high a rpm or for too long a grinding time, a large amount of fine particles with small mixed particles may be generated, which is undesirable.

[0264]

[0265] [Mixed particles]

[0266] In one embodiment of the present invention, the electrode powder obtained through the grinding process is an aggregate of mixed particles, and the mixed particles may have a particle size (D50) of 100 µm to 700 µm, and the particle size (D50) may be appropriately adjusted within the above range in consideration of the electrochemical characteristics of the battery to which the dry electrode according to the present invention is applied. In a specific embodiment, the particle size (D50) of the mixed particles may 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 mixed particles may 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 mixed particles may be adjusted by the rpm and / or time of the grinding process. The mixed particles are a result of agglomeration including a plurality of electrode active material particles and a fiberized binder resin. The electrode powder containing the above mixed particles is subjected to a calendaring process in a subsequent process to form a dry electrode film having a predetermined thickness.

[0267] Meanwhile, in one embodiment of the present invention, the diameter of the binder fibers in the mixed particles may 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 mixed particles is not particularly limited, but may 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 invention, the fiberized binder resin in the mixed particles may include fibrils having a section in which the length of a portion having a diameter of 700 nm or more is 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 fiberized binder resin may include fibrils having a section in which the length of a portion having a diameter of 1.0 μm or more is 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 fiberized binder resin may include fibrils having a section in which the length of a portion having a diameter of 1.2 μm or more is 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 fiberized binder resin may include fibrils having a section in which the length of a portion having a diameter of 1.5 μm or more is 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 above binder resin can be controlled in the above-described kneading process and / or grinding process.

[0268] Figures 20 and 21 show SEM images of a mixed powder manufactured through Example 1 of the present invention. Referring to these, electrode active material particles and binder resin included in the mixed powder are observed, and fibrils having a diameter of 1 µm or more and a length of 5 µm or more are confirmed in the binder resin.

[0269]

[0270] In the present invention, the electrode powder comprises mixed particles, and the content thereof may be 95 wt% or more or 99 wt% or more. The mixed particles preferably comprise an electrode active material and a binder resin, and when a conductive material is included during the preparation of the blend, the mixed particles may further comprise the conductive material. Meanwhile, the electrode powder may comprise a trace amount of an electrode active material, a binder resin, and a conductive material that are free and not included in the mixed particles.

[0271]

[0272] In this manner, when the electrode powder is obtained, a dry electrode is then manufactured using this electrode powder. Specifically, the electrode powder manufactured by completing the grinding step as described above is calendered to manufacture a dry electrode film (S40).

[0273]

[0274] In the present invention, the calendering is to process the electrode powder into a film form by pressing, such as by rolling. The obtained dry electrode film may have a thickness of, for example, 40 μm to 300 μm. In one embodiment of the present invention, the calendering may be performed using a calender device including a roll press section in which two rollers are arranged to face each other. The calender device may include at least one roll press section. For example, a plurality of roll press sections may be arranged continuously so that the powder can be pressed in multiple stages. As described above, the calendering process may be performed multiple times to manufacture a dry electrode film having a desired thickness by calendering the mixed particles. Meanwhile, the temperature of the roller may be 50°C to 200°C. In addition or independently of this, the rotational speed ratio of the two rollers in the roll press section may be controlled at a ratio of 1:1 to 1:3.

[0275]

[0276] Meanwhile, in a specific embodiment of the present invention, the crystallinity of the binder resin in the dry electrode film may be greater than 0 and less than or equal to 10%, and may have a range of, for example, less than or equal to 5%. The crystallinity may be measured through differential scanning calorimetry (DSC), and is based on the temperature (peak temperature) at which the highest enthalpy is exhibited during crystallization. Specifically, the crystallinity is measured by the melting enthalpy (△H) actually measured in DSC. m ) value is theoretically the melting enthalpy (△H) of a perfect crystal (crystallization degree 100%) m 0 )(equilibrium heat of fusion) and expressed as a %, which can be calculated by the following equation 5. Here, the melting enthalpy value (△Hm0) of the theoretical perfect crystal can be referred to the polymer handbook (J. Brandrup et al., 2003) or academic papers such as Polymer. For example, the melting enthalpy value of the theoretical perfect crystal of PTFE is 85.4 J / g (Polymer Journal Vol. 46 (2005) 8872-8882). Meanwhile, thermal analysis of polymers such as DSC can be measured and calculated by ASTM D3418-21.

[0277]

[0278] [Relationship 5]

[0279] Crystallinity (%) = (△H m ÷ △H m 0 ) x 100

[0280]

[0281] After the above calendaring step is performed, a free-standing type dry electrode film can be obtained, which can be utilized as an electrode active material layer.

[0282]

[0283] The dry electrode film manufactured in this manner does not contain a solvent and has almost no fluidity, making it easy to handle and can be processed into a desired shape to be used in the manufacture of electrodes of various shapes. Furthermore, if the dry electrode film of the present invention is used in the manufacture of electrodes, the drying process for solvent removal can be omitted, thereby significantly improving the electrode manufacturing processability and resolving problems such as fine powder of active material or breakage of fiberized binder, which have been problems in the manufacture of existing dry electrodes.

[0284] Meanwhile, in a specific embodiment of the present invention, a system for manufacturing a dry electrode is provided. The system includes a blender device for mixing raw materials including an active material, a conductive material, and a binder resin; a kneader device for kneading the mixture to form a mixture lump; a crushing device for crushing the mixture lump to form an electrode powder; a calender device for forming the electrode powder into a dry electrode film; and a lamination device for laminating the dry electrode film and a current collector.

[0285] Meanwhile, the blender device is a mixer that mixes raw materials, and can mix the composite raw materials at a speed of 3,000 rpm to 30,000 rpm as described above.

[0286] The above kneader device kneads the mixture into a mixture lump and fiberizes the binder. For this purpose, the kneader device can be set to a temperature range of 70°C to 200°C and a pressure condition higher than atmospheric pressure. Specifically, the kneader device can be set to a temperature 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.

[0287] The above-mentioned crushing device is a device that crushes the mixture mass obtained from the above-mentioned kneader device to form powder for electrodes, and can be used, for example, as a blender or grinder.

[0288] The above-mentioned calendering device is a device that presses the electrode powder and forms it into a film form. In a specific embodiment of the present invention, the calendering device includes a roll press unit in which two rollers are arranged facing each other, and a plurality of roll press units are arranged continuously so that the powder can be pressed in multiple stages.

[0289] The above lamination device serves to attach and roll a dry electrode film formed by the calendar device to at least one surface of a current collector, and for example, a roll press device can be used.

[0290] The porosity of the dry electrode film according to the present invention can be determined by the calendar device and lamination device. The specific structures of the blender device, kneader device, calendar device, and lamination device are known in the art, and thus a detailed description thereof is omitted herein.

[0291]

[0292] Hereinafter, the present invention will be described in detail based on examples, comparative examples, and experimental examples so that those of ordinary skill in the art to which the present invention pertains can easily understand.

[0293]

[0294] Manufacturing Example 1: Pre-mixing of materials

[0295] Li(Ni) as a cathode active material 0.85 Mn 0.05 Co 0.05 Al 0.05 )O2, carbon black and polytetrafluoroethylene (PTFE) were added to a mixer at a weight ratio of 96:1:3 and mixed at 15,000 rpm for 1 minute to prepare a powder blend.

[0296]

[0297] Manufacturing Example 2: Manufacturing of electrode powder A

[0298] The temperature of the kneader was stabilized at 150°C, and the premixed powder blend obtained above was placed into the kneader, which was then operated at a speed of 25 rpm under a pressure of 1.1 atm for 3 minutes to obtain a mixture lump. The mixture lump was placed into a grinder and ground at 10,000 rpm for 30 seconds to obtain an electrode powder. The obtained mixed particles had a diameter of about 300 μm to 700 μm and a D50 of about 500 μm. Figures 20 and 21 show SEM images of the electrode powder manufactured through Example 1 of the present invention. Referring to them, fibrils having a diameter of 1 μm or more and a length of 5 μm or more are confirmed.

[0299]

[0300] Manufacturing Example 3: Manufacturing of electrode powder B

[0301] A dry electrode was manufactured in the same manner as in the manufacture of powder A, except that the mixture was kneaded at a speed of 25 rpm for 4.5 minutes to obtain a lump of the mixture.

[0302]

[0303] Manufacturing Example 4: Manufacturing of electrode powder C

[0304] A dry electrode was manufactured in the same manner as in the manufacture of powder A, except that the mixture was kneaded at a speed of 25 rpm for 2.5 minutes to obtain a lump of the mixture.

[0305]

[0306] Manufacturing Example 5: Manufacturing of electrode powder D

[0307] A dry electrode was manufactured in the same manner as in the manufacture of powder A, except that the mixture was kneaded at 50 rpm for 20 minutes to obtain a lump of the mixture.

[0308]

[0309] Manufacturing Example 6: Manufacturing of electrode powder E

[0310] The temperature of the kneader was stabilized at 150°C, and the premixed powder blend obtained above was placed into the kneader, which was then operated at a speed of 25 rpm under a pressure of 1.1 atm for 3 minutes to obtain a mixture mass. The mixture mass was placed into a grinder and ground at 10,000 rpm for 2 minutes to obtain an electrode powder. The obtained mixed particles were confirmed to have a D50 of approximately 150 μm.

[0311]

[0312] Tap densityBulk densityD50(㎛)Value(g / cc)Compared to powder blend(%)Value(g / cc)Compared to powder blend(%)Powder blendPremixed1.6980.827Powder A5001.29476%0.840102%Powder b4881.39482%0.909110%Powder C4941.24974%0.826100%Powder D3651.978116%1.203145%Powder E1521.45886%0.75291%

[0313]

[0314] The tap density and bulk density of each powder obtained in the above manufacturing example were measured and are shown in Table 1. Although the same powder blend was used, it was confirmed that there was a significant difference in the characteristics of the electrode powder depending on the powder manufacturing conditions, such as the applied kneading process or grinding process.

[0315]

[0316] The above bulk density refers to the apparent density in a state where no tap or packing is applied, and is a density based on the volume including the voids where particles are created when the electrode powder is filled into a container. In the present invention, the bulk density was measured using a powder measuring device (Powerpro Al, Better size instrument) and was measured based on the ISO 3953:1993 standard. Specifically, the powder was dispersed in a 250 ml graduated cylinder and filled by free falling, and then the excess powder accumulated on the top of the graduated cylinder was scraped off with a spatula, the weight of the powder remaining inside was measured, and the calculation was made according to the following formula.

[0317]

[0318] Bulk density = (internal weight (g)) / (volume of graduated cylinder filled with electrode powder (cc))

[0319]

[0320] Tapped density refers to the density measured after densely filling a container filled with powder by repeatedly dropping it from a constant height at a constant speed until the volume of the powder in the container becomes almost constant. In the present invention, the tapped density was measured using a powder measuring device (Powerpro Al, Better size instrument) and followed the ISO 3953:1993 standard. Specifically, 10 g / ml electrode powder was filled into a 250 ml graduated cylinder and tapping was performed 1250 times with a stroke length of 10 mm. When the volume change was within 2%, the volume at this time was taken as the final apparent volume. Thereafter, the tapped density was calculated from the following equation 6.

[0321]

[0322] [Relationship 6]

[0323] Tap density = mass of electrode powder (g) / final apparent volume of electrode powder (cc)

[0324]

[0325] Example 1

[0326] The electrode powder A obtained above was fed into a calendar roller (roll diameter: 88 mm, roll temperature: 100°C, roll speed ratio 20 / 24 rpm) and pressed into a plate shape. The formed result was then subjected to a calendering process under the same conditions to manufacture a standalone dry electrode film. Thereafter, it was laminated with aluminum (thickness: 20 μm) to manufacture a dry electrode. In the manufactured electrode, the thickness (single side) of the electrode active material layer was approximately 60 μm, and the total thickness of the electrode, including the thickness of the current collector, was approximately 140 μm. Fig. 4 shows an SEM image of the surface of the electrode manufactured in Example 1. Referring to this, it was confirmed that large pores existed between the electrode active material particles and that the diameter of the fibrils was 1 μm or more. In Fig. 4, fibrils having a section with a diameter of 1 μm or more and a length of 10 μm or more are confirmed, and it is estimated that the fibrils extend inward and have a section much longer than 10 μm. Meanwhile, the crystallinity of the binder in the obtained dry electrode film was measured and confirmed to be approximately 2.5%.

[0327]

[0328] Example 2

[0329] The electrode powder B obtained above was fed into a calendar roller (roll diameter: 88 mm, roll temperature: 100°C, roll speed ratio 20 / 24 rpm) and pressed into a plate shape. The formed resultant was then subjected to a calendaring process under the same conditions to manufacture a standalone dry electrode film. Thereafter, the dry electrode was manufactured by laminating it with aluminum (thickness: 20 μm).

[0330]

[0331] Example 3

[0332] The electrode powder C obtained above was fed into a calendar roller (roll diameter: 88 mm, roll temperature: 100°C, roll speed ratio 20 / 24 rpm) and pressed into a plate shape. The formed resultant was then subjected to a calendaring process under the same conditions to manufacture a standalone dry electrode film. Thereafter, the dry electrode was manufactured by laminating it with aluminum (thickness: 20 μm).

[0333]

[0334] Comparative Example 1

[0335] As a cathode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode mixture slurry was prepared by adding 96 wt% of O2; NCM, 1 wt% of carbon black as a conductive agent, and 3 wt% of PVDF as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode mixture slurry was applied to an aluminum (Al) thin film, which is a positive electrode current collector, with a thickness of about 20 μm, dried, and then roll pressed to prepare a positive electrode.

[0336]

[0337] Comparative Example 2

[0338] The electrode powder D obtained above was fed into a calendar roller (roll diameter: 88 mm, roll temperature: 100°C, roll speed ratio 20 / 24 rpm) and pressed into a plate shape. The formed result was then subjected to a calendering process under the same conditions to manufacture a standalone dry electrode film. Thereafter, the dry electrode was manufactured by laminating with aluminum (20 μm in thickness). Fig. 5 shows an SEM image of the surface of the electrode manufactured in Comparative Example 2. Referring to this, electrode active material particles and binder resin can be confirmed, and it was confirmed that the binder resin fibrils were much thinner than those in Example 1, with a diameter of less than 1 μm.

[0339]

[0340] Comparative Example 3

[0341] The electrode powder E obtained above was fed into a calendar roller (roll diameter: 88 mm, roll temperature: 100°C, roll speed ratio 20 / 24 rpm) and pressed into a plate shape. The formed resultant was then subjected to a calendaring process under the same conditions to manufacture a standalone dry electrode film. Thereafter, the dry electrode was manufactured by laminating it with aluminum (thickness: 20 μm).

[0342]

[0343] Experimental Example 1: Evaluation of Charge-Discharge Efficiency According to Rate

[0344] A coin-type battery was manufactured using the electrode obtained in Example 1 and lithium metal. A separator was interposed between the electrode and the lithium metal, and an electrolyte containing an organic solvent (ethylene carbonate: dimethyl carbonate 7:3 volume ratio) and LiPF61M concentration was injected. Batteries were manufactured using the same method for the electrodes obtained in Comparative Examples 1 and 2.

[0345] For each battery, the capacity was measured by charging and discharging at an ambient temperature of 25℃. For each battery, charging was performed in CC (constant current) / CV (constant voltage) mode at rates of 2C, 1.5C, 1C, and 0.2C to 4.4 V, with a cut-off current of 0.05C. Discharging was performed under 1C and CC (constant current) conditions to 3 V. Charge and discharge were repeated 40 times under the same conditions.

[0346] Figures 2a to 2d are charging graphs, and Figures 3a to 3d are discharging graphs. Referring to these, it was confirmed that Example 1 and Comparative Examples 1 and 2 exhibit similar trends as the rate is lowered, but in the case of high-rate charging and discharging of 1C or higher, the battery of Example 1 exhibits superior charging and discharging efficiency.

[0347]

[0348] Experimental Example 2: 3D Modeling of Electrodes

[0349] For each of the electrodes of Examples 1 to 3 and Comparative Examples 1 to 3, 3D modeling was performed in the following order.

[0350] First, a cross-sectional image of the electrode was obtained using a FIB-SEM (Focused Ion Beam Scanning Electron Microscope). Ga was used as the light source. + was used, and the cutting speed of the electrode was set to 2.1 μA and the gap was set to 300 nm. The SEM image of each electrode cross-section obtained was filtered using an FFT (Fast Fourier Transform) filter to remove noise, and the electrode active material, conductive material, pores, current collector, and binder resin were made to have differences in brightness. Afterwards, the threshold of brightness for each material was set, and labeling and masking were performed for each material. Afterwards, the 3D structure was modeled for each material based on the image brightness value, and the 3D structure with the boundary between materials was modeled by applying the Canny Edge Detection, an edge detection algorithm. Additionally, the image was corrected so that the material was filled up to the watershed line of each material. In the 3D modeling, the voxel size was set to 100 μm. 3 Watershed is an image processing method that calculates the height based on the brightness value of the pixels of the image, assumes the image as a two-dimensional terrain, and divides the image into segmented areas that include a basin surrounded by a single outline when filled with water.

[0351]

[0352] Experimental Example 3: Porosity Distribution

[0353] From the 3D modeling structure of the electrode obtained by the above method, the structural characteristics of the pores, such as the porosity, average diameter (㎛), porosity (vol%), and volume fraction of pores with a diameter of 2 to 4 ㎛ (vol%) of each electrode, were confirmed. The number of voxels was confirmed in the 3D structure obtained above, and the porosity, pore diameter, and pore structure were calculated and derived. For example, if the electrode active material layer is composed of 100 voxels and 30 of them correspond to pores, the pore volume was calculated as 30 vol% as “(30 / 100) x 100”. In the case of the pore diameter, the watershed algorithm was used to form pore voxels with spherical / elliptical particles, and the number of voxels in the a, b, and c directions (mutually perpendicular directions) was confirmed, and then the diameter was calculated by multiplying it by the unit length of one voxel.

[0354] The above pore diameter is based on the longest diameter of the pore, and the above average diameter is based on the number average. These are summarized and shown in Table 2 below. In addition, Fig. 1d shows the pore distribution of the electrodes (electrode active material layers) of Example 1, Comparative Example 1, and Comparative Example 2.

[0355] Referring to this, in the case of the electrode active material layers of Examples 1 to 3 according to the present invention, it was confirmed that the number and volume distribution of pores were large in the range of about 4 ㎛ to 8 ㎛ in diameter. In addition, in the case of Examples 1 to 3, it was confirmed that the average diameter of the pores was larger than that of Comparative Examples 1 and 3, and was confirmed to be about 6.5 ㎛ or more. Meanwhile, in Comparative Examples 1 to 3, it was confirmed that the number of pores with a diameter of 4 ㎛ or less was larger than that of Examples 1 to 3. That is, it was confirmed that the electrode according to the present invention had a relatively uniform diameter and small deviation compared to Comparative Examples 1 to 3. Meanwhile, the electrodes of the Examples and the Comparative Examples had similar porosity ranges. As such, it was confirmed that the electrodes of the Examples and the Comparative Examples had similar porosities, but the structural characteristics of the internal pores had significant differences. Meanwhile, the porosity below was calculated based on [Relational Formula 1a].

[0356]

[0357] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Average pore diameter (㎛) (entire section) 6.91 ㎛ 6.89 ㎛ 6.95 ㎛ 6.41 ㎛ 6.43 ㎛ 6.50 ㎛ Average pore diameter (㎛) (pore diameter 4 ㎛ to 8 ㎛ section) 6.61 ㎛ 6.58 ㎛ 6.59 ㎛ 6.27 ㎛ 6.25 ㎛ 6.28 ㎛ Ratio of the number of pores with a pore diameter of 4 ㎛ to 8 ㎛ among the total number of pores (%) 84% 85% 79% 73.20% 68.98% 70.2% Porosity of dry electrode film (vol%) 24.6 vol% 24.6 vol% 24.6 vol% 24.6 vol% 24.6 vol% Volume of pores with a pore diameter of less than 4 ㎛ among the total pore ratio Ratio (vol%) 4.1 vol% 4.4 vol% 3.8 vol% 6.2 vol% 13.8 vol% 10.6 vol% Pore volume (vol%) (4 ㎛ to 8 ㎛ range) 69.32 vol% 70.41 vol% 68.64 vol% 61.91 vol% 56.76 vol% 62.1 vol%

[0358]

[0359] In addition, the pore shape was confirmed based on Krumbein Sphericity from the 3D modeling structure, and the ratio of prolate spheroid shape, oblate spheroid shape, and sphere shape was confirmed, which is summarized and shown in Table 3 below.

[0360]

[0361] Classification of pore shapes based on Krumbein Sphericity Volume ratio of each pore shape compared to 100 vol% of total porosity (vol%) Krumbein sphericity 0.4 or more and less than 0.8 0.8 or more and 1 or less Pore shape flat barprolate spheroid oblate spheroid Sphere Total Example 147 vol% 28 vol% 23 vol% 2 vol% 100 vol% Example 244 vol% 28 vol% 24 vol% 4 vol% 100 vol% Example 347 vol% 29 vol% 22 vol% 2 vol% 100 vol% Comparative example 140 vol% 32 vol% 17 vol% 11 vol% 100 vol% Comparative example 239 vol% 29 vol% 25 vol% 7 vol% 100 vol% Comparative example 337vol%32vol%22vol%9vol%100vol%

[0362]

[0363] Referring to Table 3 above, it was confirmed that Examples 1 to 3 had a proportion of flat bar-shaped pores exceeding 40 vol% in terms of the total pore volume. In addition, it was confirmed that Examples 1 to 3 had a proportion of spherical pores less than 5 vol% in terms of the total pore volume. According to the above results, differences were confirmed between the Examples and the Comparative Examples not only in terms of pore size but also in terms of pore shape. Here, the flat bar shape refers to a pore having a value of 0.4 to 0.8 based on the Krumbein Sphericity, and the sphere shape refers to a pore having a value of 0.8 to 1.0 based on the Krumbein Sphericity. In the above analysis, a pore having a value of 0.5, b 0.1 to 0.15, and c 1-ab was defined as a flat bar.

[0364]

[0365] Figures 1a, 1b, and 1c illustrate the distribution of each pore shape and size in the dry electrode films of Example 1, Comparative Example 1, and Comparative Example 2. In each figure, red indicates a flatbar shape, blue indicates a prolate spheroid shape, brown indicates an oblate spheroid shape, and green indicates a sphere shape. In Figure 1c, the flatbar shape, blue indicates a prolate spheroid shape, brown indicates an oblate spheroid shape, and green indicates a sphere shape are schematically illustrated.

[0366]

[0367] The above Krumbein Sphericity is a value calculated using the following formula 5, where a represents the longest diameter of the pore, b represents the median diameter of the pore, and c represents the shortest diameter of the pore.

[0368]

[0369] [Formula 5]

[0370]

[0371]

[0372] Here, a represents the longest axis of the pore, b represents the median axis of the pore, and c represents the shortest axis of the pore. Meanwhile, the Krumbein Sphericity can be calculated using an image obtained using an optical or electron microscope. Alternatively, the average pore size can be confirmed by measuring a multi-layer image of a FIB SEM cross-section and then performing 3D reconstruction to create a three-dimensional image.

[0373]

[0374] Experimental Example 4 QBR Measurement

[0375] Cross sections of the electrodes of Examples 1 to 3 and Comparative Examples 1 to 3 were fabricated using Ar ion milling. The cross sections refer to cross sections perpendicular to the electrode plane.

[0376] The components within the electrode layer of the cross-section of the fabricated electrode were EDS mapped using the EDS detector of the SEM equipment. The measurement area included the entire electrode active material layer and part of the current collector area, and the image pixel size was 1024, with a horizontal / vertical aspect ratio of 4. The EDS mapping measurement was performed for at least 10 frames under the condition of an acceleration voltage of 5 kV of the SEM, and data were measured for the components of the active material, conductive agent, binder, and current collector, excluding Li and H.

[0377] The line profile of EDS peak deconvolution in the electrode thickness direction was extracted from the EDS mapping results using EDS operation software (Oxford Aztec). Among the extracted line profile results, the average value (Bs) of the fluorine content of the fluorine-containing binder in the surface area of ​​the electrode active material layer and the average value (Bf) of the fluorine content of the fluorine-containing binder in the bottom area of ​​the electrode active material layer (the current collector-facing area) were extracted from the graph showing the change in normalized intensity of the binder component of the electrode active material layer from the surface of the electrode toward the current collector, and the QBR value was calculated using the following equation 2.

[0378]

[0379] [Relationship 2]

[0380] QBR = Bs / Bf

[0381]

[0382] At this time, the electrode surface area is an area from the outermost surface in the thickness direction of the electrode active material layer to within 15% of the total thickness of the electrode active material layer, and the electrode active material layer bottom area is an area from the current collector facing portion facing the current collector to within 15% of the total thickness of the electrode active material layer. The QBR values ​​calculated in each example and comparative example are summarized and shown in Table 4 below.

[0383]

[0384] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 QBR1.020.981.073.001.011.05

[0385]

[0386] Meanwhile, FIGS. 6, 8, and 10 show a three-dimensional image (left) and a cross-section (right) of a dotted line (A) obtained using the 3D modeling structure of the electrode according to Example 1, Comparative Example 1, and Comparative Example 2, respectively. The bolded portion in the cross-section represents pores. In addition, FIGS. 7, 9, and 11 show the volume fractions of the electrode components of Example 1, Comparative Example 1, and Comparative Example 2, respectively. In FIGS. 7, 9, and 11, (1) represents the volume fraction of the electrode active material, (2) represents the volume fraction of the pore, and (3) represents the volume fraction of the binder.

[0387] Referring to this, in the case of Comparative Example 1, the binder content decreases as it goes toward the current collector, but in the case of the present invention, it was confirmed that the binder content of the electrode surface and the current collector portion was maintained uniformly.

[0388]

[0389] Experimental Example 5: Confirming the resistance characteristics of the electrodes

[0390] The interfacial resistance and electrode resistance of each dry electrode obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were measured using an MP resistor from Hioki. The electrode obtained in each Example and Comparative Example was cut into 100 mm x 100 mm, and 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 interfacial resistance between the electrode / current collector layer were measured by the potential difference measured between 46 probes.

[0391] The thickness of the electrode active material layer, the thickness of the current collector, and the resistance value of the current collector were entered. 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 average value was calculated by measuring 5 times in the same manner. This is compared and shown in Table 5. Although the same powder blend was used, there was a significant difference in the characteristics of the electrode powder depending on the conditions of the applied kneading process, and it was confirmed that the electrode of the example had superior resistance characteristics to the electrode of the comparative example in the applied electrode.

[0392]

[0393] Electrode resistance (ohm·cm)Interface resistance (ohm·cm) 2 )Example 1700.30Example 2650.29Example 3640.32Comparative Example 2810.29Comparative Example 3750.33

[0394]

[0395] Experimental Example 6: De-lithiation area confirmation

[0396] Using the 3D modeling structure of the electrode (positive electrode) according to Example 1, Comparative Example 1, and Comparative Example 2, respectively, the movement of lithium ions during charging and discharging was simulated, and the delithiated area inside the electrode at the moment of 2C charging completion was represented by 3D mapping. In each drawing, the current collector is placed on the right, and it gets closer to the electrode surface as it goes to the left. Figures 12 to 14 show the simulation results for Example 1, Comparative Example 1, and Comparative Example 2, respectively. Referring to these, the batteries of Comparative Example 1 and Comparative Example 2 are observed to have a larger amount of delithiated lithium in the electrode (positive electrode). Both Comparative Example 1 and Comparative Example 2 were found to have a larger amount of delithiated lithium inside the electrode compared to the electrode surface (left side of the image), which is because the lithium did not move smoothly toward the electrode surface. On the other hand, it was confirmed that the battery of Example 1 had a smaller amount of delithiated lithium inside the electrode than the Comparative Example. That is, it was confirmed that the dry electrode according to the present invention has an advantage in lithium movement during high-rate charge / discharge.

[0397]

[0398] Experimental Example 7 Tortuosity Measurement

[0399] Example 1 Comparative Example 1 Comparative Example 2 Geodesic 1.12 1.09 1.16 Physical 2.54 3.59 2.34

[0400]

[0401] Figure 15 is a graph showing the results of calculating the Geodesic Tortuosity and Physical Tortuosity of the electrode active material layer in the electrodes according to Example 1, Comparative Example 1, and Comparative Example 2, respectively. Referring to this, it was confirmed that the electrode of Example 1 had significantly superior Geodesic Tortuosity and Physical Tortuosity compared to the electrode of Comparative Example 1. Accordingly, the battery to which the electrode of Example 1 was applied had superior electrochemical characteristics during charge and discharge compared to the battery to which the electrode of Comparative Example 1 was applied. Meanwhile, although the electrodes of Example 1 and Comparative Example 2 have similar Tortuosity, their pore structures are substantially different, and it was confirmed that the battery to which the electrode of Example 1 was applied had superior electrochemical characteristics compared to the battery to which the electrode of Comparative Example 2 was applied.

[0402]

[0403] Experimental Example 8 Crystallinity Measurement

[0404] The crystallinity of the binder resin was measured for the dry electrode films of Examples 1 to 3 and Comparative Example 3.

[0405]

[0406] Example 1 Example 2 Example 3 Comparative Example 2 Comparative Example 3 Crystallinity (%) 2.5% Less than 1% 4.2% Less than 1% 2.4%

[0407]

[0408] As a result of crystallinity measurement, Examples 1 to 3 and Comparative Examples 2 and 3 all exhibited crystallinity of less than 5%. Thus, it was confirmed that even though the binder resins exhibited similar crystallinity, there were differences in the pore structure of the electrode and the electrochemical performance of the battery.

[0409]

[0410] The crystallinity (Xc) was measured by weighing about 5 mg to 12 mg of the sample and putting it into a TA differential scanning calorimeter (DSC), and measuring the heat of fusion (△heat of fusion) according to the temperature while increasing the temperature at a rate of 10 °C / min in a temperature range of 25 to 360 °C in a nitrogen atmosphere. The melting point (Tm) and melting enthalpy (△Hm) were analyzed based on the temperature at the point where the highest enthalpy was observed during melting (peak temperature) using the TA TROIS program. The crystallinity of each sample was calculated by dividing the melting enthalpy (△Hm) actually measured in DSC by the melting enthalpy (△Hm0) of a theoretical perfect crystal (crystallization degree 100%), and expressing it as a % using the above equation 1. The theoretical melting enthalpy value of PTFE's perfect crystal was 85.4 J / g, and reference was made to Polymer Journal, Vol. 46 (2005), pp. 8872-8882.

Claims

1. A dry electrode including a dry electrode film as an electrode active material layer, The above electrode active material layer includes an electrode active material and a binder resin, and the binder resin is fiberized. A dry electrode for an electrochemical device, wherein the electrode active material layer has an average pore diameter of 5.0 ㎛ or more, a porosity of 15 vol% to 50 vol%, and the average pore diameter is calculated based on the longest diameter of the pores.

2. In paragraph 1, A dry electrode for an electrochemical device, wherein the above electrode active material layer has an average pore diameter of 6.0㎛ or more.

3. In paragraph 1, A dry electrode for an electrochemical device, wherein the above electrode active material layer has an average pore diameter of 6.5㎛ or more.

4. In paragraph 1, A dry electrode for an electrochemical device, wherein the electrode active material layer has pores with a diameter of 4 µm to 8 µm and an average diameter (µm) of 6.5 µm or more.

5. In paragraph 1, A dry electrode for an electrochemical device, wherein the electrode active material layer has a ratio of the number of pores having a diameter of 4 ㎛ to 8 ㎛ to the total number of pores of 80% or more.

6. In paragraph 1, A dry electrode for an electrochemical device, wherein the electrode active material layer has a ratio of the volume of pores having a diameter of 4 ㎛ to 8 ㎛ to the volume of the entire pores of 60% or more.

7. In paragraph 1, The above electrode active material layer is a dry electrode for an electrochemical device having a geodesic tortuosity (τgeo) of 1.15 or less according to the following equation 1: [Formula 1] In the above equation 1, L represents the thickness of the electrode active material layer, and Leff represents the length of the movement path of lithium ions within the electrode active material layer.

8. In paragraph 7, The above electrode active material layer is a dry electrode for an electrochemical device having a physical tortuosity (τphy) of 3 or less according to the following equation 2: [Formula 2] In the above formula 2, ε represents the porosity of the electrode active material layer, δ0 represents the electrolyte conductivity, and δ eff represents the effective electrolyte conductivity due to the pore structure.

9. In paragraph 1, A dry electrode for an electrochemical device, wherein the binder resin comprises polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyolefin, or a mixture of two or more thereof.

10. In paragraph 1, A dry electrode for an electrochemical device, wherein the crystallinity of the above dry electrode film is greater than 0% and less than or equal to 10%.

11. In paragraph 1, A dry electrode for an electrochemical device, wherein the binder resin includes a portion having a diameter of 1 ㎛ or more in the fiberized fibrils.

12. In paragraph 11, A dry electrode for an electrochemical device, wherein the fiberized binder resin includes a fiber having a length of 5 ㎛ or more and a diameter of 1 ㎛ or more. 13.(S10) A process for manufacturing a powder blend including an electrode active material, a conductive material, and a binder resin; (S20) A process for producing a mixture lump by kneading the above powdered blend in a range of 70°C to 200°C; (S30) A process of crushing the above mixture lump to obtain electrode powder; and (S40) A step of calendaring the electrode powder; A method for manufacturing a dry electrode film according to claim 1.

14. In paragraph 13, A method for manufacturing a dry electrode film having a D50 of 100 ㎛ to 700 ㎛ using the electrode powder obtained in the above (S30).

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