Composite particles containing electrode materials and electrodes for electrochemical elements containing them

Abstract

The present invention relates to an electrode and an electrochemical device including the same, the electrode including a current collector and an electrode active material layer formed on the current collector, the electrode active material layer including granules, the granules having a higher binder content in a surface portion than in a center portion.

Description

[Technical Field]

[0001] The present invention relates to composite particles for dry electrodes and electrodes for electrochemical elements containing the same. This application claims priority to Korean Patent Application No. 10-2022-0013754 filed on 28 January 2022 and Korean Patent Application No. 10-2022-0031703 filed on 14 March 2022, and all contents disclosed in the specifications and drawings of said applications are incorporated herein by reference. [Background technology]

[0002] With the rapid increase in fossil fuel use, the demand for alternative and clean energy sources is growing, and one of the most active research areas in this field is electrochemical power generation and energy storage. Currently, a typical example of an electrochemical element that uses such electrochemical energy is the secondary battery, and its range of applications is expanding rapidly. Lithium-ion secondary batteries, a representative example of such secondary batteries, are not only used as an energy source for mobile devices, but are also increasingly being used as a power source for electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution. Their range of applications is also expanding to include power supply auxiliary power sources in grid systems.

[0003] Such secondary batteries are manufactured through an electrode manufacturing process, an electrode assembly manufacturing process, and a chemical conversion process. The electrode manufacturing process typically involves manufacturing an electrode slurry, coating it onto an electrode current collector, and then drying it. Subsequent processes such as rolling, slitting, and winding are carried out after drying. Of these, the electrode slurry manufacturing process is a process of blending components to form an electrode active material layer in which an electrochemical reaction actually occurs at the electrode. Specifically, it involves mixing the electrode active material, which is an essential element of the electrode, with other additives such as conductive materials and fillers, a binder for binding powders together and adhering them to the current collector, and a solvent for providing viscosity and dispersing powders, to produce a fluid slurry.

[0004] In conventional electrodes where a slurry coating method is applied to form an electrode active material layer as described above, the binder material in the electrode cannot be uniformly distributed in the thickness direction of the electrode, and a larger amount is concentratedly distributed on the surface of the electrode active material layer, which causes the problem that sufficient binding force between the electrode active material layer and the current collector cannot be secured. This phenomenon is caused by the migration of the binder material moving to the surface layer due to evaporation of the solvent during drying of the slurry.

[0005] Therefore, in order to solve such problems, there is a demand for developing an electrode for electrochemical devices having a uniform distribution of the binder material. Summary of the Invention Problem to be Solved by the Invention

[0006] An object of the present invention is to provide an electrode having a uniform binder distribution in the thickness direction of the electrode active material layer. Another object of the present invention is to provide granular particles containing an electrode material exhibiting a specific binder distribution, and a dry electrode produced using the same. The objects and advantages of the present invention can be achieved by the means and combinations thereof set forth in the claims. Means for Solving the Problem

[0007] According to a first aspect of the present invention, there is provided a granule for an electrode of an electrochemical device, wherein the granule comprises an electrode active material and an electrode binder, the electrode active material is bound by the electrode binder, based on 100 wt% of the total weight of the electrode active material and the electrode binder, the content of the electrode binder in a surface portion is higher than the content of the electrode binder in a central portion, the surface portion is a region extending 30% of the radius from the surface of the granule toward the center of the granule, and the central portion is a portion other than the surface portion.

[0008] According to a second aspect of the present invention, in the first aspect, the surface portion is a region extending 20% of the radius from the surface of the granule toward the center of the granule.

[0009] According to a third aspect of the present invention, in the first or second aspect, the surface portion is a region extending from the surface of the granules toward the center of the granules by 10% of the radius.

[0010] According to the fourth aspect of the present invention, in any one of the first to third surfaces, the granules have an aspect ratio of 0.5 to 1.0.

[0011] According to the fifth aspect of the present invention, in any one of the first to fourth surfaces, the granules have an aspect ratio of 0.75 to 1.0.

[0012] According to the sixth aspect of the present invention, in any one of the first to fifth surfaces, the particle size D of the granules 50 The particle size ranges from 0.1 μm to 1,000 μm.

[0013] According to the seventh aspect of the present invention, in any one of the first to sixth aspects, the granules contain two or more electrode active material materials.

[0014] According to the eighth aspect of the present invention, the present invention relates to an electrode for an electrochemical element, wherein the electrode includes a current collector and an electrode active material layer located on the current collector, and the electrode active material layer includes an electrode active material and an electrode binder, and is formed by introducing granules on any one of the first to seventh surfaces to collect current in a layered structure.

[0015] According to the ninth aspect of the present invention, in the eighth aspect, the electrode active material layer has a multilayer structure in which two or more unit active material layers are stacked.

[0016] According to the tenth aspect of the present invention, in the eighth or ninth aspect, the electrode active material layer has a difference of 10 wt% or less between the binder content (wt%) in the upper 100 wt% and the binder content (wt%) in the lower 100 wt% with respect to the point where the thickness of the electrode active material layer is 50% from the current collector.

[0017] According to the eleventh aspect of the present invention, in any one of the eighth to tenth aspects, the electrode active material layer has a binder content difference of 10 wt% or less between the region from the current collector to the electrode surface layer, relative to the thickness of the electrode active material layer, and the region from the surface layer of the electrode active material layer to the current collector, up to 15%.

[0018] According to the twelfth aspect of the present invention, in any one of the eighth to eleventh surfaces, the current collector has a primer layer disposed on at least one surface, the primer layer covers all or at least part of the surface, and includes a second conductive material and a second binder.

[0019] According to the thirteenth aspect of the present invention, the electrochemical element includes a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein the negative electrode is described in any of the eighth to twelfth aspects. [Effects of the Invention]

[0020] The granules according to the present invention have a high binder content on the surface of the particles, which reduces the detachment of granules from the electrode active material layer when a planarization process such as calendering is performed after the granules have been scattered on a current collector to form the electrode active material layer. As a result, contamination of equipment used in the planarization process (e.g., calender rolls) is reduced. Furthermore, by manufacturing electrodes using the granules, electrodes can be obtained in which the binder distribution is uniform in the thickness direction of the electrode active material layer. As a result, the adhesion between the electrode active material layer and the current collector is excellent, and the morphological stability of the electrode active material layer is improved.

[0021] The following drawings accompanying this specification illustrate preferred embodiments of the invention and, together with the detailed description of the invention, serve to further illustrate the technical idea of ​​the invention. The invention should not be construed as being limited solely to what is shown in the drawings. [Brief explanation of the drawing]

[0022] [Figure 1]This is an SEM image of the granular particles observed in this example. [Figure 2] This shows a cross-section of an electrode manufactured by the manufacturing method according to Example 1 of the present invention. [Figure 3] This graph shows the binder content distribution in the thickness direction of the electrode active material layer in an electrode manufactured by the manufacturing method according to Example 1 of the present invention. [Figure 4] This shows a cross-section of an electrode manufactured by the manufacturing method according to Comparative Example 4 of the present invention. [Figure 5] This graph shows the binder content distribution in the thickness direction of the electrode active material layer in an electrode manufactured by the manufacturing method according to Comparative Example 4 of the present invention. [Figure 6] This is a schematic diagram of an electrode according to one embodiment of the present invention. [Figure 7] This is a schematic diagram for calculating the QBR value of the electrode layer. [Figure 8] This is a cross-sectional image of the granular particles produced in Example 1. [Figure 9] This is a cross-sectional image of the granular particles produced in Example 2. [Figure 10] This is a cross-sectional image of the granular particles produced in Example 3. [Figure 11] This is a cross-sectional image of the granular particles produced in Comparative Example 1. [Figure 12] This is a cross-sectional image of the granular particles produced in Comparative Example 2. [Figure 13a] This graph shows the binder resin content from the center to the surface of the granular particles obtained from Examples 1, 2, and 3, and Comparative Examples 1 and 2. [Figure 13b] This graph shows the binder resin content from the center to the surface of the granular particles obtained from Examples 1, 2, and 3, and Comparative Examples 1 and 2. [Figure 14] The distribution of the electrode load amount of the negative electrode according to Example 1 is shown. [Figure 15] The distribution of the electrode load amount for the negative electrode according to Comparative Example 1 is shown. [Figure 16]This is a photograph showing granules fixed within hardened epoxy resin. [Figure 17] This is a schematic diagram illustrating the distinction between the surface and central part of the granular particles of the present invention. [Modes for carrying out the invention]

[0023] The present invention will be described in detail below. However, the present invention is not limited to the following, and each component may be modified in various ways or selectively mixed as needed. Therefore, it should be understood that all variations, equivalents, or substitutes included in the spirit and technical scope of the present invention may be incorporated.

[0024] When a part of the specification is described as "including" a certain component, unless otherwise specified, it means that it may include other components, rather than excluding them.

[0025] Terms used throughout this specification, such as “approximately” and “substantially,” are used to mean, when specific manufacturing and material tolerances are presented, either numerical or near-numerical, and are used to prevent unscrupulous infringers from unfairly using disclosures that refer to precise or absolute numerical values ​​to aid in understanding this application.

[0026] Throughout this specification, the phrase "A and / or B" means "A or B, or both."

[0027] The specific terms used herein are for convenience only and are not limiting. Terms such as “up,” “down,” “left,” “right,” “front,” “back,” “inside,” and “outside” are used to describe the relative position or orientation between components rather than absolute positions, or to indicate position or orientation in referenced drawings. The aforementioned terms include other words containing these terms, their derivatives, and words with similar meanings.

[0028] As used herein, "glass transition temperature Tg" refers to a measurement taken by a method commonly known in the art, which may be, for example, differential scanning calorimetry (DSC).

[0029] In this specification, the term "porosity" refers to the ratio of the volume occupied by pores to the total volume in a given structure, with the unit % being the unit, and can be used interchangeably with terms such as void ratio and porosity. In the present invention, the measurement of porosity is not particularly limited, and in one embodiment of the present invention, it can be measured, for example, by the Brunauer-Emmett-Teller (BET) method using nitrogen gas, or by the mercury osmosis method (Hg porosimeter) and ASTM D-2873. Alternatively, the true density of the separation membrane can be calculated from the density of the separation membrane (apparent density), the composition ratio of the materials contained in the separation membrane, and the density of each component, and the porosity of the separation membrane can be calculated from the difference between the apparent density and the true density.

[0030] The term "average particle size D50" used in the above specification refers to the particle size at the 50% point of the cumulative particle number distribution by particle size, and this particle size may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size as the particles pass through the laser beam. The D50 particle size can be measured by calculating the particle diameter at the point where the cumulative particle number distribution by particle size in the measuring device reaches 50%.

[0031] In this specification, the "thickness" of each layer contained in the electrode may refer to a value measured by a known method for measuring thickness. The method for measuring thickness is not limited to this, but for example, it may be a value measured using a thickness measuring instrument (Mitutoyo, VL-50S-B).

[0032] As used herein, "specific surface area" may be a value measured by a known method for measuring specific surface area. The method for measuring specific surface area is not limited to, but may include, for example, a flow-type or fixed-type method.

[0033] The present invention relates to electrode granules and electrodes for electrochemical elements formed by the accumulation of the granules in a layered structure under pressure. The electrochemical elements of the present invention include all elements that perform electrochemical reactions, specifically including all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor elements. In the present invention, the electrochemical element is preferably a secondary battery, and more preferably a lithium-ion secondary battery.

[0034] <Granules> The electrode granules of the present invention will be described in detail below. In the present invention, the granules may take the form of composite particles containing an electrode active material, an electrode binder, and any optional components added as needed. In one embodiment of the present invention, the granules may be secondary particles formed by granulating two or more electrode active material particles bound together by the electrode binder. In the present invention, the electrode active material may mean an aggregate of particles. Here, the diameter of each particle of the electrode active material may be 0.05 μm to 2 μm. In one embodiment of the present invention, the electrode active material may be 80 wt% or more or 90 wt% or more of the total weight of the granules, and the electrode binder may be included in an amount of 20 wt% or less or 10 wt% or less. In one embodiment of the present invention, the granules may further contain an electrode conductive material as an optional component as needed. The electrode conductive material may be included in an amount of 0.1 wt% to 20 wt%, preferably 0.1 wt% to 10 wt%, per 100 wt% of the granules. For example, the conductive material may be contained in the granules in an amount ranging from approximately 0.1 wt% to 5 wt%.

[0035] According to an embodiment of the present invention, the content of the electrode active material in the granules may be 85 wt% to 98 wt%. Within the above range, the content of the electrode binder may be 0.5 wt% to 10 wt%, and the content of the electrode conductive material may be 0.5 wt% to 5 wt%. According to still another embodiment, the content of the electrode active material may be 90 wt% to 98 wt%, the content of the electrode binder may be 0.5 wt% to 5 wt%, and the content of the electrode conductive material may be 0.5 wt% to 5 wt%.

[0036] FIG. 17 is a schematic diagram illustrating the surface portion and the central portion of the granule of the present invention. Referring to this, in the present invention, the amount of the electrode binder contained in the surface portion 102 of the granule is larger than the amount of the electrode binder contained in the central portion 101 of the granule. The amount of the binder may refer to weight or volume.

[0037] Concurrently or independently, for the granules, based on 100 wt% of the total weight of the granules, the content (wt%) of the electrode binder contained in the central portion 101 of the granules is B c / G t the content (wt%) of the electrode binder contained in the surface portion 102 of the granules is higher than B s / G t Here, the B c is the weight of the binder contained in the central portion, B s is the weight of the binder contained in the surface portion, and G t refers to the total weight of the granular particles.

[0038] Concurrently or independently, for the granules, based on 100 vol% of the total volume of the granules, the content (vol%) of the electrode binder contained in the central portion 101 of the granules is B c / G t the content (vol%) of the electrode binder contained in the surface portion 102 of the granules is higher than B s / G t Here, the B c is the volume of the binder contained in the central portion, B s is the volume of the binder contained in the surface portion, and G tThis refers to the total volume of granular particles.

[0039] Here, the surface portion may mean the region near the surface of the granule from the surface of the granule toward a predetermined depth toward the center of the granule. The central portion means the portion other than the surface portion. In one embodiment of the present invention, the surface portion may mean, more specifically, the surface region from the surface of the granule toward the center of the granule toward 30% of the radius. In one embodiment of the present invention, the surface portion may mean the surface region from the surface of the granule toward 30% of the radius, the surface region toward 20%, the surface region toward 15%, the surface region toward 10%, or the surface region toward 5%. Preferably, the surface portion may mean the surface region from the surface of the granule toward 20% of the radius.

[0040] On the other hand, in one embodiment of the present invention, the surface portion may mean the region from the center of the granule outward toward the lanule surface at 70% or more of the radius. In one embodiment of the present invention, the surface portion may mean, for example, the region up to the granule surface at 80% or more, 85% or more, 90% or more, or 95% or more of the radius.

[0041] In one embodiment of the present invention, the center of the granule may mean the point at half the maximum diameter of the granule. In the present invention, the radius may mean the distance from the center of the granule to each point on the surface of the granule. In one embodiment of the present invention, the surface and the center can be divided along each radius based on points at the same distance from each surface of the granule, specifically, points up to 30%, 20%, 10%, 5%, or 1% of the radius from the surface.

[0042] In one embodiment of the present invention, in the region from the center of the granule to the surface of the granule with a radius of 90% or more, the content of the electrode binder relative to 100 wt% of the total weight of the granule in that region may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0043] In yet another embodiment of the present invention, in the region from the center of the granule to the granule surface with a radius of 95% or more, the content of the electrode binder relative to 100 wt% of the total weight of the granules in that region may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0044] In yet another embodiment of the present invention, in the region from the center of the granule to the granule surface with a radius of 99% or more, the content of the electrode binder relative to 100 wt% of the total weight of the granule in that region may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0045] In one embodiment of the present invention, in the region from the center of the granule to the granule surface with a radius of 90% or more, the content of the electrode binder relative to 100 vol% of the total volume of the granule in that region may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more.

[0046] In yet another embodiment of the present invention, in the region from the center of the granule to the granule surface with a radius of 95% or more, the content of the electrode binder relative to 100 vol% of the total volume of the granule in that region may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more.

[0047] In yet another embodiment of the present invention, in the region from the granule center to the granule surface with a radius of 99% or more, the content of the electrode binder relative to 100 vol% of the total volume of the granules in that region may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more.

[0048] In one embodiment of the present invention, in the granule surface region up to a radius of 10% from the granule surface, the content of the electrode binder relative to 100 wt% of the total weight of the granules in that region may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0049] In yet another embodiment of the present invention, in the region from the granule surface to a radius of 5% of the granule surface, the content of the electrode binder relative to 100 wt% of the total weight of the granules in that region may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0050] In yet another embodiment of the present invention, in a region from the granule surface to the granule surface at a radius of 1% or more, the content of the electrode binder relative to 100 wt% of the total weight of the granules in that region may be 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0051] In one embodiment of the present invention, in the granule surface region up to a radius of 10% from the granule surface, the content of the electrode binder relative to 100 vol% of the total volume of granules in that region may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more.

[0052] In yet another embodiment of the present invention, in the granule surface region up to 5% of the radius from the granule surface, the content of the electrode binder relative to 100 vol% of the total volume of granules in that region may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 wt% or more, or 90 vol% or more.

[0053] In yet another embodiment of the present invention, in a region from the granule surface to a granule surface with a radius of 1% or more, the content of the electrode binder relative to 100 vol% of the total volume of granules in that region may be 50 vol% or more, 60 vol% or more, 70 vol% or more, 80 vol% or more, or 90 vol% or more.

[0054] Figure 1 is a schematic SEM image of granular particles according to an embodiment of the present invention. Referring to Figure 1, a region with a high binder content is observed on the surface of the granules, extending from the surface towards the particle center to a predetermined depth. The binder distribution in the area other than the surface, i.e., the central part (core) surrounded by the surface, is less than that of the surface.

[0055] More specifically, the granules may comprise a central part containing multiple electrode active materials and a surface part located on all or part of the outside of the central part and containing an electrode binder that binds the electrode active materials together. That is, in the central part of the granules, the multiple electrode active materials form aggregates through surface contact, line contact, point contact, or two or more of these contacts, and in the surface part of the granules, the electrode binder is located on part or all of the outside of such aggregates, fixing and binding the multiple electrode active materials in the central part of the granules together.

[0056] According to one embodiment of the present invention, the central part also contains a small amount of electrode binder, which can serve to connect and fix the multiple electrode active materials in the central part to each other. However, as mentioned above, it is desirable that the proportion of electrode binder is higher in the surface area than in the central part.

[0057] On the other hand, in one embodiment of the present invention, the granules may have an aspect ratio of 0.5 to 1.0, preferably 0.75 to 1.0. The aspect ratio may represent the ratio of the length of the short axis to the length of the long axis of the granules. In yet another embodiment of the present invention, the average aspect ratio of the granules may have a value of 0.5 to 1.0, preferably 0.75 to 1.0, in which case the average aspect ratio may represent the ratio of the average length of the long axis to the average length of the short axis of the granular particles. In this case, the average length of the short axis may represent the average length in the axial direction having the shortest length of the granules, and the average length of the long axis may represent the average length in the axial direction having the longest length of the granules. When the aspect ratio of the granules satisfies such a range, it is advantageous in that it has sufficient fluidity suitable for the process.

[0058] On the other hand, in one embodiment of the present invention, the particle size of the granules may be in the range of 0.1 μm to 1,000 μm based on the longest diameter of the particles. In yet another embodiment of the present invention, the average particle size D50 of the granules may be in the range of 0.1 to 1,000 μm.

[0059] <Dry electrodes> One aspect of the present invention is an electrode for an electrochemical element comprising a current collector and an electrode active material layer located on the current collector. The electrode active material layer comprises an electrode active material and an electrode binder, and is formed by the accumulation of granules having the aforementioned constituent characteristics in a layered structure under pressure. The electrode active material layer and the current collector will be described in more detail below.

[0060] <Electrode active material layer> The electrode active material layer comprises an electrode active material and an electrode binder. In the present invention, the electrode active material layer may have a form in which the granules are pressurized and accumulated in a layered structure. When the granules are introduced into an electrode, the aspect ratio and particle size range do not need to be maintained in their initial state by a calendering process or the like described below. The electrode active material layer may contain 80 wt% or more, 90 wt% or more, 95 wt% or more, or 99 wt% or more of the granules per 100 wt% of the electrode active material layer. On the other hand, in one embodiment, the electrode active material layer may further include an electrode active material, an electrode binder, an electrode conductive material, etc., that are granulated and exist in a state of being separated from the granules. Alternatively, it may further include granular particles whose aspect ratio and / or particle size range are not within the ranges described above.

[0061] The electrode active material layer has pores due to interstitial volumes, which are spaces between the granules, and exhibits porous properties derived from this structure. In one embodiment of the present invention, it is desirable that the electrode active material layer has a porosity of 20 vol% to 40 vol% when considering aspects such as electrolyte impregnation, morphological stability, and ionic conductivity.

[0062] On the other hand, according to one embodiment of the present invention, the thickness of the electrode active material layer may be, for example, 30 μm to 300 μm, but is not limited thereto.

[0063] According to yet another embodiment of the present invention, the electrode active material layer may consist of a single layer comprising one unit active material layer.

[0064] According to another embodiment of the present invention, the electrode active material layer may have a multilayer structure in which two or more unit active material layers are stacked. In this case, the electrode materials contained in each unit active material layer, such as the electrode active material and the electrode binder, may be the same or different for each layer, but are not limited thereto. Furthermore, if necessary, each layer may contain an electrode conductive material, in which case the electrode conductive materials of each layer may also be the same or different from each other.

[0065] <Electrode active material layer> Furthermore, in one embodiment of the present invention, the electrode active material layer has a uniform binder distribution with respect to its thickness. In a specific embodiment, the electrode active material layer may show a difference of 10 wt% or less between the binder content (wt%) in the upper 100 wt% and the binder content (wt%) in the lower 100 wt% with respect to the point where the electrode active material layer is 50% from the current collector. Also, with respect to the thickness of the electrode active material layer, the difference in binder content between the region from the current collector to the surface of the electrode up to 15% thickness and the region from the surface of the electrode active material layer to the current collector up to 15% thickness may show a value of 10 wt% or less.

[0066] Such a binder distribution may be due to the fact that the electrode active material layer according to the present invention is manufactured by the compression of the granules. As will be described later, the electrode manufacturing method of the present invention is characterized in that, after manufacturing granular particles containing electrode material, the granular particles are scattered on a current collector or the like and pressurized so that the granules accumulate in a layered structure. In the case of electrode manufacturing methods that involve slurry production, when the slurry dries, the evaporation of the solvent induces binder migration, and the binder becomes concentrated on the surface of the electrode. However, in the present invention, since a method of accumulating dry granules by compression is applied without using a solvent, the binder migration phenomenon does not occur. Therefore, the binder shows a uniform distribution in the thickness direction in each unit layer.

[0067] <Electrode material> According to one embodiment of the present invention, the electrode active material layer may include an electrode active material and an electrode binder, and may further include an electrode conductive material if necessary. For example, in the electrode active material layer, the mixing ratio of the electrode active material, electrode conductive material, and electrode binder is such that the electrode active material:electrode conductive material:electrode binder is 80-99 parts by weight:0.5-10 parts by weight:0.5-10 parts by weight, and more specifically, it may be 90-99 parts by weight:0.5-5 parts by weight:0.5-10 parts by weight.

[0068] The electrode may be a positive or negative electrode. When the electrode is the positive electrode, the positive electrode active material is not limited to lithium transition metal oxides or lithium metallic iron phosphorus oxides, or metal oxides. For example, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; 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, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M xO₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3) a Ni-site type lithium nickel oxide represented by; the chemical formula LiMn 2-x M x O₂ (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li₂Mn₃MO₈ (where M = Fe, Co, Ni, Cu or Zn) a lithium manganese composite oxide represented by; Li in which part of lithium in the chemical formula is substituted with aluminum ions 1+x (Ni a Co b MncAld d ) 1-x O₂ (x = 0~0.03, a = 0.3~0.95, b = 0.01~0.35, c = 0.01~0.5, d = 0.001~0.03, a+b+c+d=1); lithium metal phosphate LiMPO₄ (where M is Fe, Co, Ni or Mn), disulfide compounds; and Fe₂(MoO₄)₃ are mentioned, but the negative electrode active material is not limited only to these.

[0069] In another embodiment of the present invention, when said electrode is used as a negative electrode, said electrode active material may be a negative electrode active material. Examples of said negative electrode active material include: carbon such as non-graphitizable carbon, graphite-based carbon such as natural graphite and artificial graphite; Li x ₓFe₂O₃ (0 ≦ x ≦ 1), Li x ₓWO₂ (0 ≦ x ≦ 1), Sn x yMe 1-x zMe' y On z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, group 1, group 2, and group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) 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; and Li-Co-Ni-based materials, but may be used without being limited only to these.

[0070] In one embodiment of the present invention, the granular particles may contain two or more different electrode active material materials within a single particle. The electrode active material is not particularly limited as long as it contains the components described above. For example, the granules may contain artificial graphite and natural graphite as electrode active materials, or the artificial graphite and natural graphite may be mixed in a predetermined ratio.

[0071] The electrode conductive material is not particularly limited as long as it is conductive without inducing a chemical change in the battery. 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, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used. More specifically, to ensure uniform mixing of the electrode conductive material and improve conductivity, it may include one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes. More specifically, it may include activated carbon. On the other hand, in one embodiment of the present invention, the granular particles may contain two or more different conductive materials within a single particle. For example, the granules may be a mixture of carbon black and carbon nanotubes as conductive materials in a predetermined ratio.

[0072] In the present invention, the electrode binder is not particularly limited as long as it is used as a material for an electrochemical element binder, but may include, for example, a diene polymer, an acrylate polymer, a fluorine polymer, a styrene polymer, or two or more of these.

[0073] Examples of the diene polymers include polymers containing monomer units derived from conjugated dienes such as butadiene and isoprene, and their hydrogenated products. The proportion of monomer units derived from conjugated dienes in the diene polymer is usually 40 wt% or more, preferably 50 wt% or more, and more preferably 60 wt% or more.

[0074] Specifically, examples include conjugated diene homopolymers such as polybutadiene or polyisoprene; aromatic vinyl-conjugated diene copolymers such as styrene-butadiene copolymer (SBR), which may be carboxylated; vinyl cyanide conjugated diene copolymers such as acrylonitrile-butadiene copolymer (NBR); and hydrogenated SBR and hydrogenated NBR.

[0075] The styrene-based polymer is a polymer having repeating units derived from styrene monomers, and examples include styrene homopolymers (polystyrene) and styrene copolymers. Examples of styrene copolymers include styrene-ethylene-butadiene copolymer, styrene-butadiene-propylene copolymer, styrene-isoprene copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-butadiene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-isoprene block copolymer, and styrene-ethylene-propylene-styrene block copolymer, among other block copolymers.

[0076] Examples of the acrylate polymers include polymers containing monomer units derived from acrylic acid esters and / or methacrylic acid esters. The proportion of monomer units derived from acrylic acid esters and / or methacrylic acid esters in the acrylate polymer is usually 40 wt% or more, preferably 50 wt% or more, and more preferably 60 wt% or more. Specific examples of acrylate polymers include crosslinked acrylate polymers such as 2-ethylhexyl acrylate-methacrylic acid-acrylonitrile-ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate-methacrylic acid-methacrylonitrile-ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate-styrene-methacrylic acid-ethylene glycol dimethacrylate copolymer, butyl acrylate-acrylonitrile-diethylene glycol dimethacrylate copolymer, and butyl acrylate-acrylic acid-trimethylolpropane trimethacrylate copolymer; copolymers of ethylene and (meth)acrylic acid esters such as ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl acrylate copolymer, and ethylene-ethyl methacrylate copolymer; and polymers obtained by grafting radical polymerizable monomers onto the ethylene and (meth)acrylic acid ester copolymers. Examples of radical polymerizable monomers used in the graft polymers include methyl methacrylate, acrylonitrile, and methacrylic acid. In addition, copolymers of ethylene and (meth)acrylic acid, such as ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers, can be used as dispersible binders.

[0077] The fluorine-based polymer may include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride copolymers such as PVdF-HFP. More specifically, it may include polytetrafluoroethylene (PTFE), and more specifically, it may be polytetrafluoroethylene (PTFE).

[0078] On the other hand, in one embodiment of the present invention, the granular particles may contain two or more different binder materials within a single particle. For example, the granules may be a mixture of styrene-butadiene rubber (SBR) and an acrylate polymer in a predetermined ratio as the binder material.

[0079] In one embodiment of the present invention, when the electrode is a positive electrode, the positive electrode binder may contain a fluorine-based copolymer. In one specific embodiment, the positive electrode fluorine-based copolymer may contain PTFE, and more preferably, PTFE may be present in an amount of 60 wt% or more based on the total weight of the binder. Of course, the positive electrode binder may further contain fluorine-based copolymers other than PTFE, styrene-based copolymers, polyolefin-based copolymers, PEO (polyethylene oxide), acrylate-based copolymers, and the like.

[0080] On the other hand, in one embodiment of the present invention, when the electrode is a negative electrode, the negative electrode binder may contain one or more of diene copolymers and styrene polymers, and may contain 60 wt% or more of the total weight of the binder. In one specific embodiment, the negative electrode styrene-butadiene block copolymer may contain 60 wt% or more of the total weight of the binder. On the other hand, it goes without saying that the negative electrode binder may also contain fluorine copolymers, polyolefin copolymers, PEO (polyethylene oxide), acrylate copolymers, and the like.

[0081] On the other hand, according to one embodiment of the present invention, when the electrode binder includes an electrode binder having a double bond, for example, when the electrode is a negative electrode, the negative electrode active material layer may have a first QBR (Quantified Binder Ratio) of 2.0 or less.

[0082] The first QBR is defined by the following mathematical formula. The first QBR = ABS / ABf

[0083] In the above mathematical formula, ABs represents the average value of the double bond content in the surface region of the negative electrode active material layer from the outermost surface to within 15% of the total thickness of the negative electrode active material layer, and ABf represents the average value of the double bond content in the bottom region of the negative electrode active material layer from the interface of the negative electrode active material layer facing the current collector to within 15% of the total thickness of the negative electrode active material layer.

[0084] Figure 6 is a schematic diagram of an electrode according to one embodiment of the present invention. Referring to Figure 6, the electrode 10 comprises an electrode current collector 12 and an electrode active material layer 11 located on the electrode current collector 12 and containing an electrode active material and a fluorine-containing electrode binder.

[0085] The electrode active material layer 11 has a surface region 11s of the electrode active material layer 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 a bottom region 11f of the electrode active material layer from the interface of the electrode active material layer facing the electrode current collector to within 15% of the total thickness d of the electrode active material layer.

[0086] In the first mathematical formula QBR, ABs represents the average value of the double bond content of the binder in the surface region 11s of the electrode active material layer, and ABf represents the average value of the double bond content of the binder in the bottom region 11f of the electrode active material layer.

[0087] In this case, the first QBR can be calculated using the following method. First, an electrode to be used to confirm the first QBR is selected, and a cross-section of the selected negative electrode is fabricated using argon ion milling. Subsequently, the components in the negative electrode active material layer of the fabricated electrode cross-section are mapped using an Energy Dispersive X-ray Spectroscopy (EDS) detector on a Scanning Electron Microscope (SEM).

[0088] A line profile is extracted from the EDS mapping results in the thickness direction of the negative electrode active material layer. From the extracted line profile results, the average value Bs of the double bond content of the binder in the surface region of the electrode layer and the average value Bf of the double bond content of the binder in the bottom region of the electrode layer are extracted, and the first QBR value is calculated using the following formula. The first QBR = ABS / ABf

[0089] In this case, the surface region of the electrode active material layer is the region from the outermost surface in the thickness direction of the electrode active material layer to within 15% of the total thickness of the electrode active material layer, and the bottom region of the electrode active material layer is the region from the interface of the electrode active material layer facing the current collector to within 15% of the total thickness of the electrode active material layer.

[0090] Figure 7 is a schematic diagram for calculating the first QBR value of the electrode active material layer. Referring to Figure 7, the X axis represents the thickness of the electrode active material layer, i.e., the distance from the surface towards the current collector, and the Y axis represents the intensity of the fluorine component. Line A shows the intensity of the double bond component of the binder having double bonds, extracted by EDS mapping of the double bond component in the electrode active material layer at the electrode cross-section, and line B is a trend line showing the trend of line A, and is shown by smoothing using the LOWESS smoothing method, i.e., the Locally-Weighted Scatterplot Smoother method. In Figure 7, Bs represents the intensity of the binder at the electrode surface, and Bf represents the intensity of the binder at the bottom of the electrode (opposite the current collector).

[0091] The first QBR value is a numerical value that indicates the uniformity of the distribution of electrode binder in the thickness direction within the electrode active material layer, based on the ratio of the content of electrode binder contained in the surface region to the content of electrode binder contained in the bottom region of the electrode active material layer. In this case, the content of electrode binder can be estimated from the double bond components contained in the electrode binder used.

[0092] The first QBR value may be 2.0 or less, or 0.6 to 2.0, or 0.9 to 2.0, or 0.6 to 1.4, or 0.6 to 1.4, or 0.9 to 1.4, or 0.9 to 1.1.

[0093] When the first QBR satisfies this range, the binder migrates to the electrode surface, and the amount of electrode binder contained in the surface region is not greater than the amount of electrode binder contained in the bottom region of the electrode active material layer. As a result, the distribution of the binder in the thickness direction of the electrode active material layer is uniform, which is advantageous because it improves the adhesion between the current collector and the electrode active material layer, and increases the conductivity on the surface of the electrode active material layer and the charge / discharge rate thereafter.

[0094] On the other hand, in one embodiment of the present invention, the negative electrode may include a negative electrode binder having a double bond as a binder material, for example, a styrene-butadiene copolymer, in which case the second QBR value may be 2.0 or less.

[0095] According to one embodiment of the present invention, when the electrode contains a fluorine-based binder as a binder material, for example, when the electrode is a positive electrode, the positive electrode active material layer has a second QBR (Quantified Binder Ratio) of 1.1 or less, and the second QBR can be defined by the following mathematical formula. The second QBR = CBs / CBf

[0096] In the above mathematical formula, CBs represents the average value of the fluorine content of the electrode binder in the surface region of the electrode layer from the outermost surface of the electrode active material layer to within 15% of the total thickness of the electrode layer, and CBf represents the average value of the fluorine content of the electrode binder in the bottom region of the electrode active material layer from the interface of the electrode active material layer facing the electrode current collector to within 15% of the total thickness of the electrode active material layer.

[0097] The first QBR value is 1.1 or less, and according to one embodiment of the present invention, the first QBR value is 0.95 or more, 0.97 or more, 1.03 or less, 1.05 or less, and can also be between 0.95 and 1.05.

[0098] When the above-mentioned first QBR value is within the range of 1.1 or less, the fluorine-containing electrode binder migrates to the electrode surface, and the amount of fluorine-containing electrode binder contained in the surface region is not greater than the amount of fluorine-containing electrode binder contained in the bottom region of the electrode active material layer. As a result, the distribution of the binder in the thickness direction of the electrode active material layer is uniform, which is advantageous because it improves the adhesion between the current collector and the electrode active material layer, and increases the conductivity on the surface of the electrode active material layer and the resulting charge / discharge rate.

[0099] In one embodiment of the present invention, the positive electrode may contain a fluorine-based binder resin, in which case the first QBR value may be 1.1 or less.

[0100] On the other hand, in the present invention, the electrode binder may include diene polymers and crosslinked acrylate polymers, as they provide an active material layer with excellent bonding properties and surface smoothness, and enable the manufacture of electrodes for electrochemical elements with high capacitance and low internal resistance.

[0101] The electrode binder is not particularly limited in shape, but it is preferable that it be granular in form because it has good binding properties and can suppress the decrease in capacitance of the prepared electrode and degradation due to repeated charging and discharging. Examples of granular electrode binders include those in which dispersed binder particles, such as latex, are dispersed in water, or powders obtained by drying such dispersions. Such granular binders may preferably be included in the negative electrode.

[0102] In some cases, a filler, which is a component that suppresses the expansion of the electrode active material layer, may be further added to the electrode active material layer. The filler is not particularly limited as long as it does not induce a chemical change in the battery and is a fibrous material. For example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber can be used.

[0103] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc. can be used. Furthermore, the current collector can have fine irregularities formed on its surface to enhance the adhesion of the electrode active material, and can take various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0104] On the other hand, in one embodiment of the present invention, a conductive primer may be coated on the current collector, either entirely or partially.

[0105] The primer layer comprises a binder for the primer layer (hereinafter referred to as the second binder) and a conductive material for the primer layer (hereinafter referred to as the second conductive material), and the sum of the content of the second binder and the second conductive material in the primer layer may be 90 wt% or more.

[0106] An electrode according to one embodiment of the present invention includes an electrode active material layer containing granules, and in this case, a primer layer containing a second binder and a second conductive material is included, in which the sum of the content of the second binder and the second conductive material is 90 wt% or more, thereby ensuring the time-dependent stability of the primer layer, and thereby enabling the electrode to exhibit excellent physical properties such as adhesive strength and life characteristics, but the present invention is not limited to this.

[0107] According to one embodiment of the present invention, the primer layer comprises a second binder and a second conductive material, and may further comprise a dispersant.

[0108] According to another embodiment of the present invention, the primer layer includes a second binder and a second conductive material, but may substantially omit a dispersant.

[0109] According to one embodiment of the present invention, the second binder can be any known binder used for a primer layer, without any particular limitations.

[0110] In another embodiment of the present invention, it is desirable that the second binder be a polymer capable of ensuring the temporal stability of the primer layer. Specifically, the second binder may have a glass transition temperature Tg of 45°C or lower.

[0111] According to yet another embodiment of the present invention, the second binder is, for example, styrene-butadiene rubber (SBR), butadiene rubber (BR), nitrile-butadiene rubber (NBR), styrene-butadiene-styrene block polymer (SBS), styrene-ethylene-butadiene block polymer (SEB), styrene-(styrene-butadiene)-styrene block polymer, natural rubber (NR), isoprene rubber (IR), ethylene-propylene-diene ternary copolymer (EPDM), poly(ethylene-co-propylene-co-5-methylene-2-norbornene), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinyl chloride, polyvinylidene fluoride-hexafluoropropylene It may contain fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyethylhexylacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene, polypropylene, ethylene vinyl acetate copolymer, polyethylene oxide, polypropylene oxide, polyarylate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, or two or more of these.Specifically, the binder may include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, or two or more of these.

[0112] According to yet another embodiment of the present invention, the second binder may be one or more types selected from the types described above, having the glass transition temperature values ​​described above.

[0113] According to yet another embodiment of the present invention, the second binder may be styrene-butadiene rubber (SBR) having a glass transition temperature Tg of -40°C to 45°C, nitrile-butadiene rubber (NBR) having a glass transition temperature Tg of -40°C to 45°C, or a mixture thereof.

[0114] According to one embodiment of the present invention, the specific surface area of ​​the second conductive material is 30 m². 2 / g~1,400m 2 The particle size is / g and can be spherical. In this case, the size of the primary particles of the spherical conductive material may be, for example, 10nm to 100nm, specifically 15nm to 70nm, but is not limited to this.

[0115] According to yet another embodiment of the present invention, the second conductive material has a specific surface area of ​​10 m². 2 / g~400m 2 The conductive material may be tubular (tube type) in size / g. In this case, the diameter of the cross-section in the direction perpendicular to the longitudinal direction of the tubular conductive material may be 0.1nm to 3nm, specifically 0.3nm to 1.5nm, but is not limited to this.

[0116] The second conductive material is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, graphite such as natural graphite or artificial graphite; carbon black-based carbon compounds such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used. More specifically, activated carbon, graphite, carbon black, carbon nanotubes, or mixtures of two or more of these may be included for uniform mixing of the conductive material and improvement of conductivity, and more specifically, activated carbon may be included.

[0117] According to one embodiment of the present invention, the primer layer contains the composition described above and has a thickness of 300 nm to 1.5 μm, specifically 700 nm to 1.3 μm, but is not limited thereto.

[0118] <Method for producing granules> According to one embodiment of the present invention, the granules contained in the active material layer can be produced by a method comprising the steps of mixing an electrode active material and an electrode binder with a dispersion medium to produce a slurry, and spray-drying the slurry.

[0119] First, the electrode active material and electrode binder, along with selectively additional conductive materials and additives, are dispersed or dissolved in a dispersion medium (solvent for the negative electrode binder) to obtain a slurry in which the electrode conductive material and / or other additives are dispersed or dissolved together with the electrode active material and electrode binder.

[0120] The dispersion medium used to obtain the slurry is most preferably water, but an organic solvent may also be used. Examples of organic solvents include alkyl alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane, and diglyme; amides such as diethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone (hereinafter also referred to as NMP), and dimethylimidazolidinone; and sulfur-based solvents such as dimethyl sulfoxide and sulfolane; however, alcohols are preferred. Using an organic solvent with a lower boiling point than water can accelerate the drying rate during fluid granulation. Furthermore, since the dispersibility or solubility of the negative electrode binder may change, the viscosity and fluidity of the slurry can be adjusted according to the amount or type of dispersion medium, thereby improving production efficiency.

[0121] The amount of dispersion medium used when preparing the slurry may be such that the solid content concentration of the slurry is typically in the range of 1 wt% to 50 wt%, 5 wt% to 50 wt%, or 10 wt% to 30 wt%.

[0122] The method or sequence of dispersing or dissolving the electrode active material and electrode binder in the dispersion medium is not particularly limited. Examples include adding the electrode active material and electrode binder to the dispersion medium and mixing them, or dissolving or dispersing the electrode binder in the dispersion medium first, and then adding the electrode active material at the end and mixing it. If the slurry contains conductive materials and / or additives, these components may be added at the same time as the electrode active material. Examples of mixing means include mixing equipment such as ball mills, sand mills, bead mills, pigment dispersers, stone mills, ultrasonic dispersers, homogenizers, and planetary mixers. Mixing may be carried out, for example, at room temperature to 80°C for 10 minutes to several hours.

[0123] Next, the slurry is spray-dried. Spray drying is a method of drying by spraying the slurry into hot air. Examples of spraying methods used in the spray drying apparatus include the rotating disc method and the nozzle pressurization method. In the rotating disc method, the slurry is introduced to approximately the center of a rapidly rotating disc, and the slurry is dried in a mist form as it is separated from the disc by the centrifugal force of the disc. The rotation speed of the disc depends on the size of the disc, but is usually 5,000 rpm to 35,000 rpm, preferably 15,000 rpm to 30,000 rpm. On the other hand, in the nozzle pressurization method, the slurry is passed through a thin nozzle, and at the same time, a high-pressure fluid such as air or another liquid is sprayed together with it to dry it in a mist form.

[0124] In one embodiment of the present invention, the temperature of the hot air can be controlled to 80°C to 250°C, based on the temperature at the reactor inlet (at the time of introduction), on surfaces where a granular structure with a high content of electrode binder is formed on the surface. In the present invention, considering the gradient of binder content and aspect ratio, it can be preferably controlled to 175°C to 220°C, and more preferably to 180°C to 220°C. In the spray drying method, the method of drawing in the hot air is not particularly limited, and examples include a method in which the hot air and spray direction are parallel in the lateral direction, a method in which the hot air is sprayed from the top of the drying tower and descends together with the hot air, a method in which the sprayed droplets and hot air are in countercurrent contact, and a method in which the sprayed droplets flow parallel with the initial hot air and then fall by gravity and come into countercurrent contact. On the other hand, in one embodiment of the present invention, during spray drying, the outlet temperature of the reactor (temperature of the hot air discharged from the reactor) can be controlled to 90°C to 130°C.

[0125] If the outlet temperature and / or the difference between the inlet and outlet temperatures (ΔT) is low, drying may not be sufficient, resulting in the formation of particles with a high residual solvent content. Uniform spherical particles may not be produced, and the granules may aggregate or become irregular in shape. On the other hand, if the inlet temperature is too high and ΔT is large, the particles may be over-dried and not granulated, resulting in particles with a very small D50 and a low aspect ratio. Therefore, in order to control the particle size to an appropriate level while maintaining a high aspect ratio and minimizing binder aggregation, it is necessary to control the inlet and outlet temperatures within an appropriate range.

[0126] Furthermore, the resulting product obtained by selective spray drying, i.e., the granules, may be heat-treated to harden their surface, and the heat treatment temperature is usually between 80°C and 300°C.

[0127] <Method of manufacturing electrodes> According to one embodiment of the present invention, the method for manufacturing the electrode includes the steps of scattering a plurality of granules onto a current collector and pressurizing the scattered granules to form an electrode active material layer.

[0128] The granules produced by the method described above are scattered onto the current collector. At this time, at least one surface of the current collector may be provided with a primer layer containing the second conductive material and the second binder, as described above.

[0129] According to one embodiment of the present invention, prepared granules can be supplied to a roll-type pressure molding device by a supply device such as a screw feeder to form an active material layer. In this case, the active material layer can be directly laminated on the current collector by sending the current collector to the roll of the pressure molding device at the same time as the supply of granules. Alternatively, the granules can be scattered on the current collector, the thickness can be adjusted uniformly with a blade or the like, and then molded with a pressure device to form an electrode active material layer.

[0130] In these methods, the temperature during roll pressure forming is typically 0°C to 200°C, preferably higher than the melting point or glass transition temperature of the electrode binder, and more preferably 20°C or more higher. The forming speed during roll pressure forming can typically be 0.1 m / min to 20 m / min, or 1 m / min to 10 m / min. The linear pressure of the press between the rolls can typically be 0.2 kN / cm to 30 kN / cm, or 0.5 kN / cm to 10 kN / cm.

[0131] To eliminate variations in the thickness of the molded electrodes and increase the density of the electrode active material layer to achieve higher capacity, further pressurization may be performed as needed. The most common post-pressurization method is a roll press process. In the roll press process, two cylindrical rolls are placed parallel to each other at a narrow distance apart, and each is rotated in opposite directions, with the electrode sandwiched between them and pressurized. The temperature of the rolls may be controlled by heating or cooling.

[0132] According to another embodiment of the present invention, a secondary battery is provided in which the electrode assembly, including the positive electrode, negative electrode, and separator membrane, is housed together with a lithium-containing non-aqueous electrolyte in a battery case (cylindrical case, rectangular case, pouch, etc.), and an energy storage device is provided that includes the same as a unit battery. In this case, at least one of the positive electrode and negative electrode may be the aforementioned electrode.

[0133] The separation membrane may be made from ordinary porous polymer films used in conventional separation membranes, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, either alone or in laminations thereof. Alternatively, a thin insulating film with high ion permeability and mechanical strength may be used. The separation membrane may also include a safety-reinforced separator (SRS) in which a thin ceramic material is coated on the surface of the separation membrane. Furthermore, ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used, but are not limited to these.

[0134] The electrolyte solution comprises a lithium salt as the electrolyte and an organic solvent for dissolving it. The lithium salt can be used without restriction as long as it is one that is commonly used in electrolytes for secondary batteries. For example, as the anion of the lithium salt, F - Cl - , I - NO3 - , N(CN)2 -BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - One type can be selected from the group consisting of the following:

[0135] The organic solvent contained in the electrolyte can be any commonly used one or more, and typically one or more selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfide, and tetrahydrofuran can be used.

[0136] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are desirable to use because they are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts in the electrolyte. Furthermore, when such cyclic carbonates are mixed with low-viscosity, low-dielectric-constant chain carbonates such as dimethyl carbonate and diethyl carbonate in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making their use even more desirable.

[0137] Selectively, the electrolyte stored according to the present invention may further contain additives such as overcharge inhibitors found in conventional electrolytes.

[0138] A lithium secondary battery according to one embodiment of the present invention can be completed by forming an electrode assembly by placing a separation membrane between the positive electrode and the negative electrode, placing the electrode assembly in, for example, a pouch, a cylindrical battery case, or a rectangular battery case, and injecting an electrolyte. Alternatively, a lithium secondary battery can be completed by stacking the electrode assemblies, impregnating them with an electrolyte, and then sealing the resulting product in a battery case.

[0139] In this case, the specific structure of the secondary battery and energy storage device is the same as that of conventionally known devices, so a detailed explanation is omitted in this specification.

[0140] The present invention will be described below with reference to specific examples. However, the examples of the present invention can be modified into many other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the industry.

[0141] Examples [Example 1] 1.Negative electrode (1) Preparation of current collector with primer layer Second conductive carbon black (specific surface area: 30 m²) 2 / g, particle size: 70nm), 30 parts by weight, styrene-butadiene rubber (SBR) (T) as the second binder. g A slurry for the primer layer was prepared by mixing 69 parts by weight of (-15℃) with 1 part by weight of carboxymethylcellulose (CMC) as a dispersant in water. At this time, the content ratio of conductive material, binder, and dispersant in the slurry was the same as the content ratio of conductive material, binder, and dispersant in the primer layer that was later formed. The solid content of the slurry for the primer layer was 7 wt%.

[0142] The prepared primer layer slurry was applied to one surface of a copper current collector (thickness: 10 μm), and dried at 130°C to form a primer layer on the surface of the copper current collector.

[0143] (2) Preparation of granules for negative electrode active material A slurry with a viscosity of approximately 1,000 cPs was prepared by mixing 1.91 parts by weight of natural graphite with a sphericity of 0.95 and 76.5 parts by weight of artificial graphite with an average sphericity of 0.9 as negative electrode active materials, carbon black (SuperC65) as a negative electrode conductive material, carboxymethylcellulose (daicel2200, aqueous solution form, solid content concentration 1.5 wt%) as a negative electrode dispersant, and modified styrene-butadiene copolymer (Grade Name AX-B119) as a negative electrode binder with water as a dispersion medium in a weight ratio of 95.6:1.0:1.1:2.3 using a homogenizer. At this time, the solid content in the slurry was 30 wt%. In the above weight ratio, the carboxymethylcellulose was calculated based on the solid content.

[0144] The manufactured slurry was introduced into a spray dryer along with hot air under pressure range conditions of -40 mmH2O and dried. The spray dryer conditions were controlled to an inlet temperature of 180°C, an outlet temperature of 90°C, and a rotation speed of 18,000 rpm. The resulting granules were then sieved to remove coarse particles larger than 150 μm, and further separated to remove fine particles smaller than 40 μm. The separated fine particles were mixed with the granules from which only the coarse particles had been removed to prepare negative electrode granules containing a larger amount of fine particles than the previous granules. These granules comprised a central part containing multiple negative electrode active materials and negative electrode conductive materials, and a surface part located outside the central part, containing a negative electrode binder that binds the negative electrode active materials and negative electrode conductive materials together. The average particle size D50 of the obtained granules was 66.5 μm, and the aspect ratio was 0.96. Figure 8 shows a cross-sectional image of the granular particles produced in Example 1, processed using the EPMA (electron probe microanalyze) method described later. The closed curve shown in the image connects points that are at the same distance from the surface.

[0145] (3) Manufacturing of the negative electrode On one surface of the current collector equipped with the primer layer, a thickness adjustment bar is used to adjust the current collector 25 cm 2 The granules prepared as described above were uniformly applied in an amount of 400 mg per unit, and the negative electrode was manufactured by applying pressure at a speed of 2 m / min at a pressure of 0.7 ton / cm and a temperature of 60°C using a sheeting machine (roll-to-roll hot rolling molding machine) to form a negative electrode active material layer.

[0146] [Example 2] Granules were produced in the same manner as in Example 1, except that the inlet temperature of the spray dryer was controlled to 180°C and the outlet temperature to 130°C. The average particle size D50 of the obtained granules was 61.4 μm, and the aspect ratio was 0.99. Figure 9 is a cross-sectional image of the granular particles produced in Example 2, shown after processing by the EPMA method described later. The closed curve shown in the image connects points that are at the same distance from the surface.

[0147] [Example 3] Granules were produced in the same manner as in Example 1, except that the inlet temperature of the spray dryer was controlled to 200°C and the outlet temperature to 110°C. The average particle size D50 of the obtained granules was 35.8 μm, and the aspect ratio was 0.77. Figure 10 shows a cross-sectional image of the granular particles produced in Example 3, processed using the EPMA method described later. The closed curve shown in the image connects points that are the same distance from the surface to the center of the granule.

[0148] [Comparative Example 1] Granules were produced in the same manner as in Example 1, except that the inlet temperature of the spray dryer was controlled to 170°C and the outlet temperature to 70°C. The average particle size D50 of the obtained granules was 42.8 μm, and the aspect ratio was 0.75. The negative electrode was also produced in the same manner as in Example 1, except that the granules produced in Comparative Example 1 were used instead of the granules produced in Example 1. In Comparative Example 1, the granules were slightly over-dried, resulting in an aspect ratio of 0.75 or less, and the particles were not uniformly spherical, with large variations between particles. Figure 11 shows a cross-sectional image of the granular particles produced in Comparative Example 1, processed by the EPMA method described later. Referring to this, it was confirmed that the binder resin (light color) was distributed throughout the entire cross-section of the granules. The closed curve shown in the image connects points that are at the same distance from the surface.

[0149] [Comparative Example 2] Granules were produced in the same manner as in Example 1, except that the inlet temperature of the spray dryer was controlled to 170°C and the outlet temperature to 140°C. The average particle size D50 of the obtained granules was 78.0 μm, and the aspect ratio was 0.37. In Comparative Example 2, because the difference between the inlet and outlet temperatures was small, the solvent was not sufficiently removed, and particles with a high amount of residual solvent were formed. As a result, the particles did not become uniformly shaped spherical particles, and they had a high water content and aggregated between particles.

[0150] Figure 12 shows a cross-sectional image of the granular particles produced in Comparative Example 2, processed using the EPMA method described later. Referring to this, it was confirmed that the binder resin (light color) is distributed throughout the entire cross-section of the granules. The closed curve shown in the image connects points that are at the same distance from the surface.

[0151] [Comparative Example 3] Granules were produced in the same manner as in Example 1, except that the inlet temperature of the spray dryer was controlled to 230°C and the outlet temperature to 90°C. In Comparative Example 3, the large difference between the inlet and outlet temperatures resulted in over-drying, preventing granulation and making granule production impossible.

[0152] [Comparative Example 4] A slurry with a solid content of 47 wt% was prepared by mixing 19.1 parts by weight of natural graphite with an average sphericity of 0.95 and 76.5 parts by weight of artificial graphite with an average sphericity of 0.9 as negative electrode active materials, 1 part by weight of carbon black (Super-C 65) as a negative electrode conductive material, 2.3 parts by weight of styrene-butadiene rubber (SBR) as a negative electrode binder, 1.1 parts by weight of carboxymethylcellulose (CMC) as a binder and thickener, and water as a dispersion medium.

[0153] A copper (Cu) thin film, which is a negative electrode current collector with a thickness of 10 μm, is coated with the slurry on one surface. The upper and lower active material layers thus formed are then rolled simultaneously using a roll pressing method with a drying apparatus equipped with a hot air blower and an IR heater, resulting in a dry weight of 400 mg / 25 cm² per unit area. 2 A negative electrode was manufactured that had a negative electrode active material layer with a load capacity of [amount].

[0154] Confirmation of binder distribution within granules The binder distribution within the granules was confirmed by analyzing the radial profile of the granule cross-section using EPMA (JXA-8350F, -15kV, 20nA stage mapping conditions). First, the binder in each granule obtained in Examples 1-3 and Comparative Examples 1 and 2 was stained with OsO4. For the staining, the granules were placed in glass containers with OsO4 crystals or aqueous solution, and the reagent was evaporated to allow the reaction to occur. After that, the mixture was mixed with epoxy resin, fixed in a silicone mold, and cured to obtain a granule matrix (see Figure 16). Next, cross-sectional samples were prepared from the granule matrix using an ion milling apparatus (Hitachi IM5000, acceleration voltage: 6kV). The conditions for preparing the cross-sections were an acceleration voltage of 6kV and an emission current of 400uA, and the milling time was appropriately adjusted so that the mask was not completely etched. The prepared cross-sectional samples were fixed to an EPMA apparatus, and the granules were positioned in the center of the display. The cross-sections were then scanned using the stage mapping method. Once the scan was complete, an image was created in the form of a mass map, taking into account atomic number effects, absorption effects, and fluorescence excitation effects. From the obtained mass map, elements in the range of 0-4 wt% were specified with 0-255 contrast values, and an Os map was extracted. The conventional backscattered electron image obtained during the EPMA analysis process and the Os map were combined into a single layer using Photoshop®. Then, closed curves were drawn from the granule boundaries in 30-pixel increments, and the Os content at each closed curve was analyzed. The Os content was interpolated by introducing the surface area of ​​the closed curve at each position so that the relative amounts could be compared for each position. Figure 13a shows the distribution (content) of binder resin in each part along the radius of the granules of each example and comparative example. Figure 13b shows the cumulative distribution of binder resin along the radius of the granules of each example and comparative example. Referring to this, it can be confirmed that in Examples 1-3, the binder content in the surface portion up to 70% or more of the granule surface radius, and especially up to 80% or more, is higher than in the center.In contrast, the granules obtained from Comparative Example 1 and Comparative Example 2 were found to have a higher binder content in the center than in the surface.

[0155] Confirmation of binder distribution in the negative electrode active material layer The negative electrodes produced in Example 1 and Comparative Example 4 were placed together in a glass container with OsO4 crystals or an aqueous solution and allowed to undergo a sufficient chemical reaction (deposition) for at least 3 hours by evaporating the reagent. Subsequently, cross-sections of the negative electrodes from both the Example and Comparative Example were fabricated using argon ion milling.

[0156] Using the EDS detector of a SEM device, the constituent components in the negative electrode active material layer of the negative electrode in the thickness direction of Example 1 and Comparative Example 4 were mapped using EDS mapping.

[0157] Figure 2 shows the EDS mapping results for the electrode of Example 1, and Figure 4 shows the EDS mapping results for the electrode of Comparative Example 4. Referring to these, it was confirmed that in the electrode of Example 1, the binder resin was distributed more towards the surface of the granules than towards the center of the granules. Furthermore, it was confirmed that the electrode of Example 1 was manufactured by a method of compressing granules, and that the binder was uniformly distributed in the thickness direction of the electrode. On the other hand, it was confirmed that the electrode of Comparative Example 4 had a higher binder content ratio in the surface layer of the electrode. Unlike the manufacturing method of the electrode of Example 1, the electrode of Comparative Example 4 was manufactured by an electrode slurry coating and drying method, and this binder distribution was due to binder migration due to solvent evaporation.

[0158] On the other hand, Figures 3 and 5 are graphs showing the average values ​​of the Os content of the binder bound to Os in the surface region of the negative electrode active material layer (the region from the surface to 15% in the direction of the current collector) and the Os content of the binder bound to Os in the bottom region of the electrode layer (the region from the current collector to 15% in the direction of the surface), respectively, extracted from the EDS mapping results. Figure 3 is for the electrode of Example 1, and Figure 5 is for the electrode of Comparative Example 4. Referring to these figures, it was confirmed that the deviation of the binder distribution in the electrode of Example 1 was smaller than that of the electrode of Comparative Example 4, with respect to the thickness direction of the electrode.

[0159] Confirmation of electrode load distribution The electrode load was measured on the surface (surface of the negative electrode active material layer, 100 mm x 150 mm size) of the negative electrode manufactured in Example 1 and the negative electrode manufactured in Comparative Example 1. The surface of each negative electrode was scanned using an inductance measuring device (TSS20, Lasertec). An induced current was applied while the negative electrode was at a certain distance away, and information on only the negative electrode active material layer formed on the current collector could be confirmed. An image showing uniformity was obtained based on the uniformity of the negative electrode active material layer (material distribution, thickness, porosity, etc.). It was confirmed that the negative electrode of Example 1 showed a uniform load of negative electrode active material across the surface of the negative electrode, while the negative electrode of Comparative Example 1 showed a difference in load between the left and right sides of the negative electrode. Figure 14 shows the distribution of electrode load of the negative electrode according to Example 1, showing a uniform distribution across the surface, while Figure 15 shows the distribution of electrode load of the negative electrode according to Comparative Example 1, confirming that variations occurred in each region. [Explanation of Symbols]

[0160] 10 electrodes 11 Electrode active material layer 11s surface area 11f bottom area 12 Electrode current collector 101 Center 102 Surface part

Claims

1. Electrode granules comprising an electrode active material and an electrode binder, The electrode active material is bound by the electrode binder, With respect to 100 wt% of the total weight of the electrode active material and the electrode binder, the content of the electrode binder in the surface portion is greater than the content of the electrode binder in the center portion. The surface portion is the area from the surface of the granule to 30% of the radius toward the center of the granule, and the central portion is the portion other than the surface portion. The granules are electrode granules having an aspect ratio of 0.75 to 1.

0.

2. A granule for dry electrodes containing an electrode active material and an electrode binder, The electrode active material is bound by the electrode binder, With respect to 100 wt% of the total weight of the electrode active material and the electrode binder, the content of the electrode binder in the surface portion is greater than the content of the electrode binder in the center portion. The surface portion is the area from the surface of the granule to 20% of the radius toward the center of the granule, and the central portion is the portion other than the surface portion. The granules are electrode granules having an aspect ratio of 0.75 to 1.

0.

3. A granule for dry electrodes containing an electrode active material and an electrode binder, The electrode active material is bound by the electrode binder, With respect to 100 wt% of the total weight of the electrode active material and the electrode binder, the content of the electrode binder in the surface portion is greater than the content of the electrode binder in the center portion. The surface portion is the area from the surface of the granule to 10% of the radius toward the center of the granule, and the central portion is the portion other than the surface portion. The granules are electrode granules having an aspect ratio of 0.75 to 1.

0.

4. Particle size D of the granules ５０ The electrode granules according to claim 1, wherein the particle size is 0.1 μm to 1,000 μm.

5. The electrode granules according to claim 1, wherein the granules contain two or more electrode active material materials.

6. Current collector and, An electrode comprising an electrode active material layer located on the current collector, The electrode active material layer comprises an electrode active material and an electrode binder, and is formed by introducing and accumulating granules according to any one of claims 1 to 5. The electrode active material layer is an electrode for an electrochemical element, wherein, in terms of the thickness of the electrode active material layer, when divided into upper and lower sections based on a point 50% from the current collector, the difference between the binder content (wt%) in the upper 100 wt% and the binder content (wt%) in the lower 100 wt% is 10 wt% or less.

7. The electrode for an electrochemical element according to claim 6, wherein the electrode active material layer has a multilayer structure in which two or more unit active material layers are stacked.

8. The electrode for an electrochemical element according to claim 6, wherein the electrode active material layer has a binder content difference of 10 wt% or less between a region extending 15% of the electrode surface from the current collector, relative to the thickness of the electrode active material layer, and a region extending 15% from the surface of the electrode active material layer towards the current collector.

9. The electrode for an electrochemical element according to claim 6, wherein the current collector has a primer layer disposed on at least one surface, the primer layer covers all or at least part of the surface and includes a second conductive material and a second binder.

10. An electrochemical element comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein the negative electrode is the electrode described in claim 6.

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