electrodes for electrochemical devices

Abstract

According to one aspect of the present invention, there is provided a method for manufacturing a dry electrode, which can improve wrinkle characteristics of a non-coated portion of a current collector where an electrode active material layer is not formed.

Description

[Technical Field]

[0001] This application relates to electrodes for electrochemical elements, particularly dry electrodes, and methods for manufacturing the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0049198, filed on April 20, 2022, and all contents disclosed in the specification and drawings of said application are incorporated herein by reference. [Background technology]

[0003] The rapid increase in the use of fossil fuels has led to a growing demand for alternative and clean energy sources, and one of the most actively researched areas in this field is electrochemical power generation and energy storage.

[0004] Currently, a typical example of an electrochemical device that uses this type of electrochemical energy is the secondary battery, and its fields of application are gradually expanding.

[0005] Lithium-ion batteries, a prime 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, which can replace vehicles that use fossil fuels such as gasoline and diesel cars, which are one of the main causes of air pollution. Their applications are also expanding to include auxiliary power sources for grid-based power systems.

[0006] The manufacturing process for such lithium secondary batteries can be broadly divided into three stages: the electrode process, the assembly process, and the chemical conversion process. The electrode process can be further divided into the active material mixing process, the electrode coating process, the drying process, the rolling process, the slitting process, the winding process, and so on.

[0007] Of these steps, the active material mixing step is a process of mixing coating materials to form an electrode active layer in which an electrochemical reaction actually takes place at the electrode. More 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 powder bonding and adhesion to the current collector, and a solvent for viscosity imparting and powder dispersion, to produce a fluid slurry.

[0008] In a broad sense, the composition mixed to form the electrode active layer is also called an electrode mixture.

[0009] Subsequently, an electrode coating process is carried out in which the electrode mixture is applied onto an electrically conductive current collector, and a drying process is performed to remove the solvent contained in the electrode mixture. Finally, the electrodes are rolled to a predetermined thickness.

[0010] On the other hand, during the drying process, the solvent contained in the electrode mixture evaporates, which can cause defects such as pinholes and cracks in the already formed electrode active layer. Furthermore, because the inside and outside of the active layer are not dried uniformly, powder suspension may occur due to differences in the evaporation rate of the solvent; that is, powder from areas that dried earlier floats to the surface, forming gaps with areas that dried later, which can degrade the electrode quality.

[0011] Unlike conventional electrodes manufactured using solvents (also known as wet electrodes), recent research has focused on manufacturing electrodes without solvents (also known as dry electrodes).

[0012] The aforementioned dry electrodes are generally manufactured by laminating an electrode film, which contains an active material and a binder, onto a current collector. During the process, a high-shear mixing process such as jet milling is performed to fibrousize the binder. However, when such a high-shear mixing process is applied to a fragile active material, a large amount of fine powder with small particle sizes is generated, which tends to reduce the mechanical and electrochemical properties. If the high-shear mixing is excessive, it can cut the generated binder fibers and reduce the flexibility of the electrode film. In addition, during the jet milling process, components adhere to the inside of the equipment, obstructing the flow of high-pressure air and blocking the flow path, which is a problem that makes mass production difficult.

[0013] Furthermore, the electrode film manufactured in this way is made denser for lamination with the current collector, and high pressure is used during the process to bond it to the current collector. In this process, expansion occurs in the area of ​​the current collector where the electrode film is installed (the textured area), while no expansion occurs in the area of ​​the current collector where the electrode film is not installed (the plain area). This results in wrinkles forming mainly at the boundary between the textured and plain areas.

[0014] Therefore, there is an urgent need to develop new manufacturing technologies for dry electrodes that can solve these problems. [Overview of the Initiative] [Problems that the invention aims to solve]

[0015] Therefore, the problem that the present invention aims to solve is to provide an electrode and a method for manufacturing the same in which the degree of wrinkle formation at the boundary between a region on the current collector provided with an electrode active material layer (surfaced portion) and a region not provided with an electrode active material layer (plain portion) is improved.

[0016] Furthermore, the present invention provides a method for manufacturing an electrode, which minimizes the pulverization of the active material and maximally enhances the fibrillation of the binder, thereby providing a method for manufacturing an electrode with improved flexibility and mechanical properties.

Means for Solving the Problems

[0017] In order to solve the above problems, according to one aspect of the present invention, a method for manufacturing an electrode of the following embodiment is provided.

[0018] The method for manufacturing an electrode according to the first embodiment of the present invention includes: (S10) mixing an electrode material containing an electrode active material and a binder polymer to obtain a mixture; (S20) kneading the mixture at a high temperature and a low shear rate to obtain a mixture mass; (S30) pulverizing the mixture mass at a high shear rate to obtain a mixed powder for an electrode; (S40) subjecting the mixed powder for an electrode to calendering to obtain an electrode film; and (S50) laminating the electrode film on at least one surface of a current collector to form an electrode active material layer, wherein the compression ratio of the electrode film is 15% or less, and the compression ratio of the electrode film is defined by the following formula 1. [Formula 1] Compression ratio (%) = [(T B - T A ) / T B × 100 In Formula 1, T A is the thickness of the electrode film (electrode active material layer) after lamination, and T B is the thickness of the electrode film before lamination.

[0019] According to the second embodiment of the present invention, in the first embodiment, the length expansion ratio of the electrode film can be 4% or less. The length expansion ratio can be defined by the following formula 2. [Formula 2] Length expansion ratio (%) = [(L A - L B ) / L B × 100 In Formula 2, L A is the length of the electrode film (electrode active material layer) after lamination, and LB This is the length of the electrode film before lamination.

[0020] According to a third embodiment of the present invention, in the first or second embodiment, the porosity ratio of the electrode film is 100% to 140%, and the porosity ratio of the electrode film can be defined by the following formula 3. [Formula 3] Porosity ratio (%)=(P B / P A ) × 100 In the above formula 3, P A This is the porosity of the electrode film (electrode active material layer) after lamination, and P B This is the porosity of the electrode film before lamination.

[0021] According to the fourth embodiment of the present invention, in any of the first to third embodiments, the porosity of the electrode film before lamination in step (S50) may be 35% or less, and the porosity of the electrode film after lamination may be 30% or less.

[0022] According to the fifth embodiment of the present invention, in any of the first to fourth embodiments, the calendering process in step (S40) is performed once or two or more times, and the number of times it is performed under a pressure of 100 kg / cm or more is included at least once.

[0023] According to the sixth embodiment of the present invention, in any of the first to fifth embodiments, the kneading in step (S20) may be carried out for 1 to 30 minutes at a shear rate in the range of 10 / s to 500 / s.

[0024] According to the seventh embodiment of the present invention, in any of the first to sixth embodiments, the kneading in step (S20) may be carried out at a temperature in the range of 70°C to 200°C and at a pressure equal to or greater than atmospheric pressure.

[0025] According to the eighth embodiment of the present invention, a method for manufacturing an electrode, characterized in that, in any of the first to seventh embodiments, the method further includes the step of forming a primer layer on at least one surface of the current collector before the lamination in step (S50).

[0026] According to another aspect of the present invention, electrodes of the following embodiments are provided.

[0027] An electrode according to the ninth embodiment of the present invention is an electrode comprising a current collector and an electrode active material layer located on at least one surface of the current collector, the electrode active material layer comprising an electrode active material and a binder polymer, wherein the binder polymer is fibrous and binds the electrode active material, the electrode comprises a surfaced portion having the electrode active material layer and a current collector region facing the electrode active material layer, and a plain portion extending from both sides of the current collector region of the surfaced portion and including a current collector region not facing the electrode active material layer, the porosity of the electrode active material layer is 30% or less, and the surface of the plain portion is flat.

[0028] According to the tenth embodiment of the present invention, in the ninth embodiment, a primer layer may be further included between the current collector and the electrode active material layer.

[0029] According to yet another aspect of the present invention, an electrochemical element of the following embodiment is provided.

[0030] An electrochemical element according to the 11th embodiment of the present invention includes a positive electrode, a negative electrode, and a separation layer interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode may be an electrode according to the 9th or 10th embodiment.

[0031] According to the twelfth embodiment of the present invention, in the eleventh embodiment, the separation layer may be a separation membrane or a solid electrolyte membrane. [Effects of the Invention]

[0032] According to one embodiment of the present invention, it is possible to provide an electrode and a method for manufacturing the same in which the wrinkle characteristics of the region on the current collector where the electrode active material layer is not formed (blank portion) are improved. In particular, by improving the wrinkle characteristics of the boundary between the region on the current collector where the electrode active material layer is formed and the blank portion where the electrode active material layer is not formed, it is possible to provide an electrode and a method for manufacturing the same in which the blank portion is flat.

[0033] According to one embodiment of the present invention, by introducing a grinding step after a high-temperature, low-shear kneading step instead of a high-shear mixing step, it is possible to provide a dry electrode in which the micronization of the active material is minimized, the fibrousization of the binder is maximized, and the cutting of the fibrous binder is minimized.

[0034] Furthermore, because it bypasses the high-shear jet milling process and instead goes through mixing and grinding steps using a kneader, there is no problem of the flow path becoming blocked due to the aggregation of constituent components, which is advantageous for mass production.

[0035] The following drawings accompanying this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further illustrate the technical idea of ​​the invention; therefore, the present invention shall not be construed as being limited solely to what is shown in the drawings. [Brief explanation of the drawing]

[0036] [Figure 1] This is a schematic diagram of the process for manufacturing a composite film using one embodiment of the present invention. [Figure 2] This is a schematic diagram of the process for manufacturing a composite film using one embodiment of the present invention. [Figure 3] This is a schematic diagram of an electrode lamination process according to one embodiment of the present invention. [Figure 4A] This is a top view photograph of an electrode where the surface of the plain area is not flat. [Figure 4B] This is a side view of an electrode where the surface of the plain area is not flat. [Figure 5]Figure 5 shows photographs of the appearance of electrodes manufactured according to Example 1 and Comparative Examples 1 to 3 in this specification. The plain and textured areas of the electrodes are indicated in Figure 5. [Modes for carrying out the invention]

[0037] The present invention will be described in detail below.

[0038] The present invention relates to a method for manufacturing a dry electrode and a dry electrode, which involves manufacturing an electrode film by pressurizing a mixed powder for electrodes and then laminating this film with a current collector to manufacture an electrode.

[0039] In this specification, the term "electrode film" means an electrode material containing an electrode active material and a binder, manufactured in the form of a free-standing, single sheet without the intervention of a solvent. In this specification, the term "free-standing" means that it can maintain its own form without relying on other components and can be moved and handled on its own. Furthermore, in this specification, the electrode film can be described as a "dry electrode film" in that it is manufactured without the intervention of a solvent.

[0040] In the present invention, the electrode film can be formed by pressing a mixed powder for electrodes, as described later. For example, the mixed powder can be accumulated by pressing to form a layered structure. The mixed powder for electrodes is a powdered electrode material containing an electrode active material and a binder polymer, and may be obtained by crushing a mixture mass containing the electrode active material and the binder polymer, as described later.

[0041] In the present invention, the single electrode film may constitute the electrode active material layer. Alternatively, the single electrode film may be used as a unit electrode film, and a laminate formed by stacking multiple such unit electrode films may constitute the electrode active material layer. The electrode active material layer of the present invention is not particularly limited as long as it has a sheet shape of a predetermined thickness formed by pressing together electrode mixed powder.

[0042] According to one aspect of the present invention, a method for manufacturing an electrode is provided, comprising the steps of: (S10) mixing electrode materials containing an electrode active material and a binder polymer to obtain a mixture; (S20) kneading the mixture at high temperature and low shear rate to obtain a mixture mass; (S30) crushing the mixture mass at high shear to obtain a mixed powder for electrodes; (S40) calendering the mixed powder for electrodes to obtain an electrode film; and (S50) laminating the electrode film onto at least one surface of a current collector to form an electrode active material layer.

[0043] In the electrode manufacturing method described above, the compression ratio of the electrode film according to the following formula 1 is 15% or less. [Formula 1] Compression rate (%)=[(T B -T A ) / T B ]×100 In the above formula 1, T A This is the thickness of the electrode film (electrode active material layer) after lamination, and T B This is the thickness of the electrode film before lamination.

[0044] In conventional dry electrode manufacturing processes, a problem has been observed where, during the lamination step, when pressure is applied to bond the current collector and the electrode film, the shape of the current collector changes due to partial expansion or non-expansion of the current collector.

[0045] Therefore, the inventors of the present invention have completed the present invention by finding that in the lamination process of the manufacturing process of dry electrodes, the problem of change in the shape of the current collector can be improved by the compression ratio of the electrode film due to lamination, thereby enabling the manufacture of electrodes with a flat plain portion on the current collector.

[0046] Furthermore, the inventors of the present invention have found that in the lamination process of the manufacturing process of dry electrodes, the flatness of the plain portion can be further improved not only by the compression ratio but also by the rate of change in the length of the electrode film before and after lamination.

[0047] Furthermore, we found that in the lamination process of the dry electrode manufacturing process, the problem of change in the shape of the current collector can be further improved by adjusting the ratio of voids before and after lamination.

[0048] Furthermore, we discovered that the flatness of the plain areas can be further improved by controlling the void ratio of the electrode film before and after lamination in the lamination process of the dry electrode manufacturing process.

[0049] In this specification, the terms "electrode film before lamination" and "electrode film after lamination" refer to the electrode film subject to physical property evaluation before and after the lamination process in (S50). Thus, the term "electrode film before lamination" can refer to the electrode film immediately before lamination, and according to one embodiment of the present invention, it can refer to the electrode film obtained in step (S40). Furthermore, the term "electrode film after lamination" can refer to the electrode film immediately after lamination, and according to one embodiment of the present invention, it can refer to the electrode active material layer obtained in step (S50).

[0050] In this specification, the term "surfaced area" means a region on at least one surface of the current collector on which an electrode active material layer (also referred to as an electrode film) is formed. In other words, the surfaced area means the electrode active material layer and the current collector region facing the electrode active material layer. The term "blank area" means a region that is not a surfaced area, that is, a region of the current collector on which an electrode active material layer is not formed. In other words, the blank area means a region of the current collector extending from both sides of the current collector region of the surfaced area and not facing the electrode active material layer.

[0051] In the present invention, as described above, the compression ratio according to the following formula 1 is 15% or less. [Formula 1] Compression rate (%)=[(T B -T A ) / T B ]×100 In the above formula 1, T A This is the thickness of the electrode film (electrode active material layer) after lamination, and T B This is the thickness of the electrode film before lamination.

[0052] In this specification, the compressibility of the electrode film can be defined as the ratio of the thickness reduction of the electrode film due to compression at the moment of lamination for installation with the current collector, and can be defined by the above formula 1.

[0053] In the present invention, the compressibility of the electrode film may be 15% or less, for example, 10% or less, 5% or less, or 2% or less. For example, the compressibility may be from 0.1% to 15%, from 1% to 12%, from 1% to 10%, from 1% to 5%, or from 1% to 2%. In the present invention, since the electrode film is compressed after the lamination process for manufacturing the electrode, its thickness decreases compared to the thickness before lamination. Therefore, a high compressibility may mean that the degree of compression of the electrode film is high, and as a result, the pressure applied to the electrode and the current collector is high. This may mean that the degree of expansion of the area of ​​the current collector on which the electrode film is installed, i.e., the textured area, is high, and as a result, deformation of the plain area of ​​the current collector may occur. Conversely, a low compressibility may mean that the degree of compression of the electrode film is low, and as a result, the pressure applied to the electrode and the current collector is low. In this case, it may mean that the adhesion between the electrode and the current collector is poor. The present invention offers the advantage of minimizing the degree of deformation of the current collector's shape and ensuring excellent adhesion between the electrode and the current collector by setting the compression ratio according to Formula 1 within the above range. However, the mechanism of the present invention is not limited to this.

[0054] In this specification, unless otherwise defined, the thickness of the electrode film can be measured using known means for measuring the thickness of each component in the art, such as a thickness measuring instrument or SEM imaging. In one embodiment of the present invention, the thickness of the electrode film can be measured using a thickness measuring instrument (Mitutoyo, VL-50S-B), but is not limited thereto.

[0055] In one embodiment of the present invention, the length expansion rate of the electrode film before and after lamination according to the following formula 2 may be 4% or less. [Formula 2] Length expansion coefficient (%) = [(L A -L B ) / L B ]×100 In the above formula 2, L A L is the length of the electrode film after lamination. BThis is the length of the electrode film before lamination.

[0056] In one embodiment of the present invention, if the compression ratio due to lamination exceeds the above range, the degree of length deformation of the electrode film before and after lamination increases, which can cause a change in the shape of the current collector. Accordingly, according to one embodiment of the present invention, the length expansion rate of the electrode film may be 4% or less, for example, 3% or less, 2% or less, 1.5% or less, 1% or less, 0.5% or less, or 0% (i.e., no length deformation is observed at all). For example, the length expansion rate of the electrode film may be 0.1% to 4%, 0.1% to 3%, 0.1% to 2%, 0.1% to 1%, or 0.1% to 0.5%.

[0057] In this specification, unless otherwise defined, the length of the electrode film may mean the length measured in the machine direction (MD) of the electrode film. The term "machine direction of the electrode film" means the production direction of the electrode film during the manufacturing process of the electrode film. Figure 1 shows a schematic diagram of a process for manufacturing an electrode film by calendering an electrode mixed powder according to one embodiment of the present invention. Referring to Figure 1, when the electrode mixed powder 120 is fed between a plurality of rolls 110, an electrode film 130 is formed along one direction. At this time, the direction in which the manufactured electrode film travels can be defined as the machine direction (MD) of the electrode film.

[0058] The mechanical orientation (MD) of the electrode film coincides with the orientation direction of the fibers within the electrode film, and can therefore be confirmed through the orientation direction of the fibers in the manufactured film. For example, the mechanical orientation of the electrode film can be confirmed through a scanning electron microscope (SEM) image of the electrode film. The orientation direction of the fibers confirmed through the SEM image can coincide with the mechanical orientation (MD) of each of the electrode unit films.

[0059] In the present invention, as described above, the electrode active material layer may have a sheet shape of a predetermined thickness formed by heat-pressing at least one electrode mixed powder containing an electrode active material and a binder polymer. As a result, the electrode active material layer may contain multiple pores in its structure depending on the properties and tap density of the electrode mixed powder, and thus the electrode active material layer has a porosity within a predetermined range.

[0060] In this specification, unless otherwise defined, the porosity can be determined by the following relational expression, using the actual density calculated based on the actual density and composition of each component, after measuring the apparent density of the electrode film alone by subtracting the volume and weight of the current collector from the volume and weight of the electrode. Porosity (%) = {1 - (Apparent density / Actual density)} × 100

[0061] In one embodiment of the present invention, the porosity ratio of the electrode film before and after lamination is 100% to 140%, and the porosity ratio of the electrode film can be defined by the following formula 3. [Formula 3] Porosity ratio (%)=(P B / P A ) × 100 In the above formula 3, P A This is the porosity of the electrode film (electrode active material layer) after lamination, and P B This is the porosity of the electrode film before lamination.

[0062] In one embodiment of the present invention, the void ratio of the electrode film before and after lamination according to formula 3 may be 100% to 140%, for example, 100% to 130%, 100% to 125%, 100% to 125%, 100% to 120%, 100% to 110%, or 100% to 105%. In one embodiment of the present invention, by adjusting the void ratio of the electrode film before and after lamination in step (S50) to satisfy a specific range, it is possible to suppress deformation of the shape of the current collector after lamination and to ensure adhesion between the electrode film and the current collector, but the present invention is not limited thereto.

[0063] In one embodiment of the present invention, the void ratio of the electrode film before lamination in step (S50) is 35% or less, within the range that satisfies the void ratio of the electrode film before and after lamination, for example, 15% to 35%, 20% to 35%, 20% to 33%, 30% to 35%, 20% to 30%, 20% to 25%, or 30% to 33%, but is not limited thereto.

[0064] In other embodiments of the present invention, the void ratio of the electrode film after lamination in step (S50) is 30% or less, for example, 20% to 30%, 22% to 28%, or 23% to 26%, within a range that satisfies the void ratio of the electrode film before and after lamination.

[0065] In yet another embodiment of the present invention, within the range that satisfies the void ratio of the electrode film before and after lamination, the void ratio of the electrode film before lamination in step (S50) may be 35% or less, and the void ratio of the electrode film after lamination may be 30% or less.

[0066] In one embodiment of the present invention, if the void ratios of the electrode films before and after lamination in step (S50) satisfy the above range, it may be preferable in terms of ensuring flatness in the plain portion of the electrode and ensuring adhesion between the electrode and the current collector, but the present invention is not limited thereto.

[0067] In one embodiment of the present invention, if the porosity of the electrode film before lamination is reduced to a target porosity level in the electrode film after lamination, a lower porosity ratio is formed between the pre- and post-lamination portions, which is an even more advantageous effect in ensuring the flatness of the plain portion. However, the present invention is not limited thereto.

[0068] In the following, a method for manufacturing an electrode in which the wrinkle phenomenon in the plain area is improved, while satisfying at least one of the conditions of compression ratio, length expansion ratio, and void ratio before and after lamination as described above during the lamination process of step (S50), will be described in detail for each step.

[0069] First, step (S10) is the step of obtaining a mixture of electrode materials by mixing electrode materials to obtain an electrode mixed powder used in the manufacture of an electrode film.

[0070] The electrode material comprises an electrode active material and a binder polymer.

[0071] The electrode active material may be a positive electrode active material or a negative electrode active material, depending on the polarity of the electrode being manufactured.

[0072] In one embodiment of the present invention, when the electrode is used as a positive electrode, the electrode active material may be a positive electrode active material. The positive electrode active material may include, but is not limited to, lithium transition metal oxides, lithium metallic iron phosphates, lithium nickel-manganese-cobalt oxides, and oxides in which lithium nickel-manganese-cobalt oxide is partially substituted with other transition metals, or two or more of these. Specifically, the positive electrode active material may include, for example, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals, and a compound with the 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, and 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 0.3), and the chemical formula LiMn 2-x M x Lithium manganese composite oxide represented by 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), lithium metal phosphate LiMPO4 (where M is Fe, CO, Ni, or Mn), and lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x=0~0.03, a=0.3~0.95, b=0.01~0.35, c=0.01~0.5, a+b+c=1) and lithium nickel-manganese-cobalt oxide, in which a portion is replaced by aluminum. a [Ni b Co c Mn d Al e ]1-f M1 f O2 (M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1), and an oxide in which part of lithium nickel-manganese-cobalt oxide is substituted with other transition metals Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg, and Mo), disulfide compounds, and Fe2(MoO4)3, etc., but not limited thereto only.

[0073] In another embodiment of the present invention, when the electrode is used as a negative electrode, the electrode active material can be a negative electrode active material. The negative electrode active material includes, for example, carbon such as graphitizable carbon and graphite-based carbon, and Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, 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 alloy, silicon-based alloy, tin-based alloy, silicon-based oxides such as SiO, SiO / C, SiO2, metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5, conductive polymers such as polyacetylene, Li-Co-Ni-based materials, etc. can be used, but not limited thereto only.

[0074] In one embodiment of the present invention, the electrode active material is a positive electrode active material, and the positive electrode active material is an oxide Li in which part of lithium nickel-manganese-cobalt oxide is substituted with aluminum 1+a [Ni b Co c Mn d Al e 1-a O2 (0 ≦ a ≦ 0.03, 0.3 ≦ b ≦ 0.95, 0 < c < 0.5, 0 < d < 0.5, 0.001 ≦ e ≦ 0.05, b + c + d + e = 1) can be used.

[0075] In another embodiment of the present invention, the positive electrode active material can be lithium manganese oxide, lithium metal iron phosphate, lithium nickel-manganese-cobalt oxide, or a mixture of two or more of these.

[0076] In one embodiment of the present invention, the binder polymer is not particularly limited as long as it can be fibrillated in the manufacturing method described later, particularly in the step of manufacturing the mixture mass. The fibrillation refers to a process of subdividing a polymer, and can be performed using, for example, mechanical shear force. The polymer fibers fibrillated in this way have their surfaces unraveled, and a large number of fine fibers (fibrils) are generated.

[0077] ​Non-limiting examples of such binder polymers include polytetrafluoroethylene (PTFE), polyolefins, or mixtures thereof. More specifically, they may include polytetrafluoroethylene (PTFE), and more specifically, they may be polytetrafluoroethylene (PTFE). Specifically, the polytetrafluoroethylene (PTFE) may be present in an amount of 60% by weight or more based on the total weight of all binder polymers. On the other hand, it goes without saying that the binder material may further include one or more of the following: PEO (polyethylene oxide), PVdF (polyvinylidene fluoride), PVdF-HFP (polyvinylidene fluoride-cohexafluoropropylene), and polyolefin polymers.

[0078] In one embodiment of the present invention, the electrode active material layer may further contain a conductive material. In one embodiment of the present invention, the conductive material may be contained in the electrode mixed powder and introduced into the electrode active material layer.

[0079] The conductive material is not particularly limited as long as it is conductive without causing a chemical change in the battery. For example, it can be graphite such as natural graphite or artificial graphite, carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black, conductive fibers such as carbon fibers or metal fibers, metal powders such as carbon fluoride, aluminum, or nickel powder, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, or conductive materials such as polyphenylene derivatives. More specifically, it can include one or more selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes to ensure uniform mixing of the conductive material and improve conductivity, and more specifically, it can include carbon black.

[0080] In one embodiment of the present invention, the content of the electrode active material relative to the total weight of the electrode material mixture may be, for example, 80% by weight or more, 90% by weight or more, or 85% by weight to 98% by weight. More specifically, it may be 90% by weight to 98% by weight, or 95% by weight to 98% by weight.

[0081] In one embodiment of the present invention, the content of the binder polymer relative to the total weight of the electrode material mixture may be, for example, 0.5% to 20% by weight, 0.5% to 10% by weight, or 2% to 15% by weight. More specifically, it may be 2% to 10% by weight, or 2% to 5% by weight.

[0082] In one embodiment of the present invention, as described above, the electrode material mixture further contains a conductive material, in which case the content of the conductive material relative to the total weight of the electrode material mixture may be, for example, 0.1% to 20% by weight, 0.5% to 10% by weight, or 0.5% to 5% by weight. More specifically, it may be 0.5% to 3% by weight, or 1% to 3% by weight.

[0083] In the present invention, the electrode active material layer originates from an electrode film formed by pressing together an electrode mixed powder made from the above-mentioned mixture of electrode materials, and the content ratio of the electrode materials may be within a similar range to that of the electrode active material layer.

[0084] In step (S10), the mixing of the electrode materials is carried out so as to uniformly distribute the electrode active material, binder polymer, and conductive material as needed. Since these components are mixed in powder form, the method is not particularly limited as long as it allows for simple mixing, and the materials can be mixed by various methods. However, since the above method aims to manufacture a dry electrode without using a solvent, the mixing can be carried out by dry mixing, and can be done by putting the materials into a device such as a blender or supermixer.

[0085] In one embodiment of the present invention, when the mixing is performed in a blender, in order to ensure uniformity, the mixture can be manufactured by mixing in a blender at 5,000 rpm to 20,000 rpm for 30 seconds to 20 minutes, or more specifically, at 10,000 rpm to 15,000 rpm for 30 seconds to 5 minutes.

[0086] In another embodiment of the present invention, when the mixing is performed in a supermixer, the mixing can be performed in the supermixer at 500 rpm to 2,500 rpm, specifically 1,000 rpm to 2,000 rpm, in order to ensure uniformity, thereby allowing adjustment of the process time.

[0087] Next, the step of kneading the electrode material mixture (S20) at a high temperature and low shear rate to obtain a mixture mass is performed.

[0088] The aforementioned step (S20) is a step to fibrousize the binder with the mixture prepared as described above, and is also called the kneading step.

[0089] In one embodiment of the present invention, low-shear kneading can be performed to resolve the problem of the binder being fibrous, the active material being pulverized, and the formed fibers being cut, but the step (S20) is not limited to this.

[0090] In this case, the above-mentioned kneading can be carried out using a kneading machine, such as a kneader, although this is not limited to this method.

[0091] Such kneading is a step in which the binder becomes fibrous and binds or connects the active material or the active material with the conductive material powder to form a mixture mass with 100% solid content.

[0092] In one embodiment of the present invention, the kneading in step (S20) can be carried out at a speed of 10 rpm to 100 rpm for 1 to 30 minutes, and more specifically, at a speed of 20 rpm to 50 rpm for 3 to 10 minutes.

[0093] In one embodiment of the present invention, the kneading in step (S20) can be carried out for 1 to 30 minutes at a shear rate in the range of 10 / s to 500 / s. More specifically, the shear rate can be carried out in the range of 30 / s to 100 / s. Furthermore, such a kneading step can be carried out under high temperature and pressure conditions above atmospheric pressure, and more specifically, under pressure conditions higher than atmospheric pressure.

[0094] In one embodiment of the present invention, in step (S20), the kneading can be carried out in the range of 70°C to 200°C, more specifically, in the range of 90°C to 180°C or 90°C to 150°C. While carrying out the kneading in the above temperature range may be preferable in terms of the ease of fiberization and agglomeration of the binder by kneading, and subsequent film formation during calendering, as well as the mechanical properties of the fiberized binder, the present invention is not limited thereto.

[0095] In one embodiment of the present invention, in step (S20), the kneading can be carried out at atmospheric pressure or higher, more specifically at a pressure of 1 atm to 60 atm, or 1 atm to 30 atm, or 1 atm to 10 atm, 1.1 atm to 10 atm, 1.1 atm to 6 atm, or 1.1 atm to 3 atm. While it may be preferable in terms of the fiberization of the binder and the mechanical properties of the fiberized binder when the kneading is carried out within the above-mentioned pressure range, the present invention is not limited thereto.

[0096] Thus, in one embodiment of the present invention, it may be preferable to perform a low-shear mixing process under high temperature and pressure conditions above atmospheric pressure, instead of high-shear mixing.

[0097] Step (S30) is a step in which the result of step (S20), specifically the mixture mass obtained by kneading, is crushed to obtain a mixed powder for electrodes. To immediately process the result of step (S20), specifically the mixture mass, into a film, a process with high pressure and high temperature is required. This may cause problems such as the film becoming excessively dense or not being able to obtain a uniform film. Therefore, after crushing the mixture mass to obtain the powder for electrodes, the obtained powder is calendered.

[0098] In one embodiment of the present invention, the grinding may be performed by a blender, or by a device such as a grinder, such as a cutter mill or a fine impact mill, although this is not limited to the present invention.

[0099] In one embodiment of the present invention, when the grinding is performed using a blender, the grinding can be performed specifically at a speed of 500 rpm to 20,000 rpm for 30 seconds to 10 minutes, or more specifically at a speed of 1,000 rpm to 10,000 rpm for 30 seconds to 1 minute.

[0100] In another embodiment of the present invention, when the grinding is performed using a cutter mill, the grinding can be performed at a speed of 500 rpm or less, for example, 400 rpm to 500 rpm, for 10 to 60 seconds.

[0101] In yet another embodiment of the present invention, when the grinding is performed using an impact mill, the grinding can be performed specifically at a speed of 3,000 rpm to 8,000 rpm, for example, 4,000 rpm to 7,000 rpm, for 10 to 60 seconds.

[0102] In one embodiment of the present invention, if the grinding is carried out under the above-described conditions, it may be preferable in terms of suppressing the size of the powder and the generation of fine particles, but the present invention is not limited thereto.

[0103] In one embodiment of the present invention, after step (S30) and before the calendering process in step (S40), the step of classifying the pulverized electrode mixed powder may be further included in (S31). In the classifying step, the pulverized electrode mixed powder can be obtained by filtering out electrode mixed powder of a certain size or larger using a mesh having voids of a certain size or less.

[0104] Next, in step (S40), an electrode film is obtained by a method of pressure-bonding and molding the mixed powder for electrodes. In this specification, the step of pressure-bonding the mixed powder for electrodes to produce a sheet-like electrode film is described as a calendaring process. By the calendaring process, the electrode film can be provided in the shape of a sheet having a predetermined thickness. For example, the electrode film obtained through step (S40) can have a shape of a strip whose aspect ratio exceeds 1. In one embodiment of the present invention, the electrode film obtained through step (S40) can have a thickness of 50 μm to 300 μm. More specifically, the electrode film can have a thickness of 50 μm to 200 μm, 50 μm to 150 μm, 50 μm to 100 μm, 60 μm to 90 μm, 70 μm to 85 μm, 70 μm to 80 μm, 70 μm to 75 μm, or 80 μm to 85 μm.

[0105] In one embodiment of the present invention, when the electrode active material contained in the electrode film is an oxide Li 1+a [Ni b Co c Mn d Al e 1-a O2 (0 ≦ a ≦ 0.03, 0.3 ≦ b ≦ 0.95, 0 < c < 0.5, 0 < d < 0.5, 0.001 ≦ e ≦ 0.05, b + c + d + e = 1) is included, the electrode film, for example, has a thickness of 70 μm to 85 μm, 70 μm to 80 μm, or 70 μm to 75 μm, but is not limited thereto.

[0106] In another embodiment of the present invention, when the electrode active material contained in the electrode film includes lithium iron phosphate (LFP) as a positive electrode active material, the electrode film, for example, has a thickness of 110 μm to 120 μm, but is not limited thereto.

[0107] ​For example, the calendering process can be carried out by a calendering method in which the electrode mixture powder is supplied to a calendering device and heat-pressed using (multiple) roll presses included in the calendering device. Alternatively, the calendering process can be carried out by a roll-to-roll continuous process.

[0108] In one embodiment of the present invention, the calendering device may include a roll press section in which two rollers are arranged opposite each other, and the electrode mixed powder can pass through the roll press section and be pressed into a sheet shape. In one embodiment of the present invention, a plurality of the roll press sections are arranged in a continuous manner, and the electrode film can be pressed multiple times. The number of roll press sections can be appropriately adjusted considering the thickness of the electrode film and the rolling ratio.

[0109] Figure 1 is a schematic diagram illustrating the calendering process 100 according to one embodiment of the present invention. Referring to this, the electrode film 130 is manufactured by pressurizing the electrode mixed powder 120 multiple times using a calendering apparatus in which roll press sections, each having two calendering rollers 110 positioned opposite each other, are arranged in a continuous manner. As described above, the electrode film is manufactured without the use of a solvent and can therefore be called a dry electrode film.

[0110] Figure 2 is a schematic diagram illustrating the calendering process 100 according to another embodiment of the present invention. Referring to this, the electrode mixture film 130 is manufactured by pressurizing the electrode mixture powder 120 multiple times using a calendering apparatus in which two calendering rollers 110 are arranged opposite each other in a roll press section spaced apart at a predetermined interval.

[0111] On the other hand, each roll press section can independently control the rotation speed ratio of its two rollers within a range of 1:1 to 1:10. For example, in one or more roll press sections, the rotation speed ratio of its two rollers can be controlled at a ratio of 1:1 to 1:3. In addition, the temperature of the rollers in each roll press section can be independently controlled within a range of 50°C to 250°C. Electrode films can be manufactured by such a calendering process.

[0112] In one embodiment of the present invention, the closer the distance between the two rollers of the roll press section, the higher the compression pressure becomes, which allows for a lower porosity of the electrode film produced by calendering. Therefore, the calendering pressure can be adjusted by adjusting the distance between the two rollers or by adjusting the size of the rollers, depending on the desired porosity and thickness of the electrode film.

[0113] In one embodiment of the present invention, the calendering process in step (S40) can be performed once by a single roll press unit or two or more times by multiple roll press units.

[0114] In one embodiment of the present invention, the calendering process in step (S40) may include at least one instance where the calendering is performed under a pressure of, for example, 100 kg / cm or more. Preferably, if the electrode mixture powder is pressurized multiple times during the calendering process in step (S40), the pressurization can be performed under gradually decreasing pressure as the number of pressurizations is repeated. In this case, it may be preferable for the production of the target electrode film if the pressure during the final pressurization, i.e., the lowest pressure during the calendering process, is 100 kg / cm or more, but the present invention is not limited thereto.

[0115] In one embodiment of the present invention, the electrode active material used in the manufacture of the electrode film may include, for example, lithium nickel-manganese-cobalt-aluminum. The lower limit of the calender pressure exemplified above may vary depending on the type of electrode active material used in the manufacture of the electrode film, but the present invention is not limited thereto.

[0116] Therefore, the porosity of the electrode film produced by the calendering process (i.e., the electrode film before lamination) may be 35% or less. Specifically, the porosity of the electrode film obtained through step (S40) may be 35% or less, 30% or less, and more specifically, 10% to 35%, 15% to 30%, 20% to 30%, 23% to 26%, or 22% to 24%.

[0117] In one embodiment of the present invention, the calendering process in step (S40) may include at least one instance where the calendering is performed under a pressure of, for example, 100 kg / cm or more. Preferably, as described above, if pressurization is performed multiple times during the calendering process, the pressure during the final pressurization may be 100 kg / cm or more, but the present invention is not limited thereto.

[0118] In one embodiment of the present invention, the calendering process in step (S40) can be carried out, for example, at a pressure of 500 kg / cm or less within the above-mentioned pressure range, but is not limited thereto.

[0119] In one embodiment of the present invention, the calendering in step (S40) can be performed in a range of, for example, 100 kg / cm to 500 kg / cm, or in a range of, for example, 200 kg / cm to 300 kg / cm. Alternatively, in order to reduce the porosity of the electrode film obtained by calendering and reduce the compression ratio in the lamination step, the calendering can be performed at a pressure of 300 kg / cm to 500 kg / cm, specifically 400 kg / cm to 500 kg / cm, 400 kg / cm to 450 kg / cm, or 415 kg / cm to 450 kg / cm.

[0120] In one embodiment of the present invention, as described above, the electrode film manufactured by the calendering process can have its binder polymer crystallinity controlled to 10% or less or less than 10%. More specifically, the crystallinity of the binder polymer in the electrode film manufactured by the calendering process can be 5% or less, specifically 1% or less, or 0%. Controlling the crystallinity of the binder polymer in the electrode film to 10% or less in this way increases the flexibility of the electrode film, which has the advantage of preventing breakage or cracking when it is wound up for storage or unwound. Furthermore, the increased flexibility can improve mechanical strength, such as tensile strength and tensile elongation, but the present invention is not limited to this.

[0121] In this specification, the degree of crystallinity (Xc) of the binder polymer can be measured by differential scanning calorimetry (DSC), with the temperature at the point in time when the highest enthalpy is observed during crystallization (peak temperature) as the reference. Specifically, the degree of crystallinity is expressed as a percentage by dividing the enthalpy of melt (ΔHm) measured by DSC by the enthalpy of melt (ΔHm°) (heat of fusion equilibrium) of a theoretical perfect crystal (100% crystallinity), and can be calculated by the following equation 4. Here, the enthalpy of melt of a theoretical perfect crystal can be found and used in a polymer handbook for known polymers, and for unknown substances or newly synthesized substances, it can be calculated by extrapolation, which involves extending the degree of crystallinity at two or more points. [Formula 4] Xc(%) = (ΔHm ÷ ΔHm°) × 100

[0122] According to one embodiment of the present invention, as described above, the porosity of the electrode film produced by the calendering process in this manner may be 35% or less.

[0123] Next, (S50) the electrode film manufactured as described above is laminated to one or both sides of the current collector to form an electrode active material layer. Then, the current collector and the electrode film are joined together to manufacture an electrode.

[0124] In one embodiment of the present invention, the current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., can be used. Furthermore, the current collector can improve the adhesion strength of the positive electrode active material by forming fine irregularities on its surface, and can take various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0125] In one embodiment of the present invention, the thickness of the current collector can be selected as needed and is not particularly limited, but may be, for example, 5 μm to 50 μm, specifically 10 μm to 30 μm, or 15 μm to 20 μm.

[0126] Furthermore, in one embodiment of the present invention, the current collector may be one which is entirely or partially coated with a conductive primer to reduce surface resistance and improve adhesion. Here, the conductive primer may include a conductive substance and a binder, and the conductive substance is not limited as long as it is a conductive substance, but may be a carbon-based substance, for example. The binder may include solvent-soluble fluorine-based (including PVDF and PVDF copolymers), acrylic-based binders, and aqueous-based binders.

[0127] For this purpose, in one embodiment of the present invention, the step of forming a primer layer on at least one surface of the current collector may be further included before the lamination in step (S50).

[0128] In one embodiment of the present invention, the lamination may be a step of rolling and adhering the electrode film to a predetermined thickness onto the current collector, or onto at least one surface of a current collector having a primer layer on at least one surface. The lamination may also be performed by a laminating roll, in which case the laminating roll can be maintained at a temperature from room temperature (25°C) to 200°C, but is not limited thereto.

[0129] Figure 3 is a schematic diagram illustrating the lamination process (200) according to one embodiment of the present invention. Referring to this, the electrode film 230 is joined to the current collector 220 to produce the electrode 240, and the lamination process is carried out by pressurization with a laminating roller 210. On the other hand, in the present invention, as described above, the electrode film attached to the current collector by lamination is also called the electrode active material layer.

[0130] According to the manufacturing method described above, electrodes are produced in which the electrode film has a compression ratio of 15% or less due to lamination.

[0131] In one embodiment of the present invention, the compression ratio of the electrode film by lamination may be 1% to 15%, 1% to 12%, 1% to 10%, or 1% to 5%.

[0132] In one embodiment of the present invention, an electrode that satisfies the above-described compression ratio of the electrode film can be manufactured with a flat surface in the plain portion.

[0133] According to another aspect of the present invention, an electrode is provided comprising a current collector and an electrode active material layer located on at least one surface of the current collector, the electrode active material layer comprising an electrode active material and a binder polymer, wherein the binder polymer is fibrous and binds the electrode active material, the electrode comprising a surfaced portion having the electrode active material layer and a current collector region facing the electrode active material layer, and a plain portion extending from both sides of the current collector region of the surfaced portion and including a current collector region not facing the electrode active material layer, the porosity of the electrode active material layer being 30% or less, and the surface of the plain portion being flat.

[0134] In one embodiment of the present invention, the porosity of the electrode active material layer may be 30% or less, 5% to 30%, 10% to 30%, 15% to 30%, 20% to 30%, 20% to 25%, 25% to 30%, or 23% to 26%.

[0135] In one embodiment of the present invention, a primer layer may be further included between the current collector and the electrode active material layer, but the present invention is not limited thereto.

[0136] The current collector, textured portion, textured portion, electrode active material layer, electrode mixed powder, primer layer, and void ratio are incorporated as described in the electrode manufacturing method.

[0137] In one embodiment of the present invention, the fact that the surface of the plain portion on at least one surface of the current collector that does not have the electrode active material layer is flat can be confirmed, for example, by visual observation of the electrode appearance and by measuring the maximum height of the uneven shape on the surface of the plain portion or the portion with an electrode.

[0138] For example, in one embodiment of the present invention, if the appearance of the electrode is observed visually, and no wrinkles are found in the plain area, then the surface of the plain area can be said to be flat.

[0139] In one embodiment of the present invention, the phrase "the surface of the plain portion is flat" can mean a shape in which no visible bends are formed on the surface of the region of the current collector where the electrode active material layer is not formed. Alternatively, it can mean a shape in which the height of the bends on the surface of the plain portion and / or the textured portion is 2 mm or less.

[0140] Figure 4A shows a photograph of an electrode where visible bending has formed on the surface of both the plain and textured areas. Referring to Figure 4A, it can be seen that if the plain area is not flat, wrinkles will also form on the textured area of ​​the electrode.

[0141] Figure 4B shows a photograph of the electrode bending shown in Figure 4A, viewed from the side. Referring to Figure 4B, an electrode with a non-flat surface in the plain area can be defined as an electrode with a maximum bending height exceeding 2 mm.

[0142] Accordingly, according to one embodiment of the present invention, an electrode whose maximum bending height is 2 mm or less can be defined as an electrode with a flat surface on the plain portion.

[0143] In one embodiment of the present invention, if the compression ratio of the electrode film according to the above formula 1 is 15% or less, the surface of the plain portion can be said to be flat.

[0144] In one embodiment of the present invention, if the length expansion rate of the electrode film according to the above formula 2 is 4% or less, the surface of the plain portion can be said to be flat.

[0145] In one embodiment of the present invention, if the porosity ratio of the electrode film according to formula 3 is between 100% and 140%, the surface of the plain portion can be said to be flat.

[0146] As described above, electrodes according to other embodiments of the present invention have flat wrinkles in the plain area, thus improving problems such as meandering phenomena where the electrode is biased to one side during the electrode assembly process, and winding defects. Therefore, since electrodes can be manufactured without a separate process to flatten the wrinkles in the plain area, the rate of electrode defects is greatly reduced, and the manufacturing process of electrodes and batteries is simplified.

[0147] According to yet another aspect of the present invention, an electrochemical element is provided which includes a positive electrode, a negative electrode, and a separation layer interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is used as the electrode described above.

[0148] In one embodiment of the present invention, the separation layer may be a separation membrane or a solid electrolyte membrane.

[0149] The aforementioned electrochemical elements include any elements that perform electrochemical reactions, and specific examples include all types of primary and secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor elements. In particular, among the secondary batteries, lithium secondary batteries, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries, are preferred.

[0150] Since the specific structure of the aforementioned electrochemical element is well known, a detailed explanation is omitted in this specification.

[0151] The electrochemical element according to the present invention may be included as a unit battery in an energy storage device, but the applications of the present invention are not limited thereto.

[0152] Since the specific structure of the aforementioned energy storage device is well known, a detailed explanation is omitted in this specification.

[0153] The present invention will be described in more detail below with reference to examples, but the following examples are for illustrative purposes only and the scope of the present invention is not limited to these examples.

[0154] [Electrode Manufacturing] Example 1 Lithium nickel cobalt manganese aluminum oxide (NCMA, Li[Ni) is used as the positive electrode active material. 0.87 Co 0.05 Mn 0.07 Al 0.01 A mixture was prepared by adding 96 wt% of 2O2, 1 wt% of carbon black as a conductive material, and 3 wt% of polytetrafluoroethylene (PTFE) as a binder polymer to a blender and mixing at 10,000 rpm for 1 minute. The temperature of the kneader was stabilized at 150°C, and after adding the mixture to the kneader, it was operated at a speed of 50 rpm for 5 minutes under a pressure of 1.1 atm to obtain a mixture mass. The mixture mass was added to the blender and pulverized at 10,000 rpm for 40 seconds, and then classified using a sieve with a mesh size of 1 mm to obtain a mixed powder for electrodes.

[0155] Subsequently, the electrode mixture powder was fed into a wrap calender (roll diameter: 200 mm, roll temperature: 100°C, 20 rpm) and the calendering process was repeated until the porosity was 35% or less. During this process, the pressure between the rolls during the final calendering was set to 221 kg / cm to produce the electrode film. The resulting electrode film had a thickness of 82 μm, a porosity (%) of 31%, and a load capacity of 5.11 mAh / cm². 2 That was the case.

[0156] A primer layer was formed on the current collector by applying a slurry for primer layer formation to aluminum foil and drying it. The primer layer contained carbon black and PVDF binder in a weight ratio of 1:2. The two electrode films produced above were then laminated to both sides of the aluminum foil (average thickness: 19 μm) on which the primer layer had formed, using a roll press maintained at room temperature to perform a lamination process so that the porosity of the electrode active material layer was 30% or less. The electrode films were then placed on the current collector to produce an electrode with electrode active material layers formed on both sides of the current collector. At this time, the thickness of the electrode film, i.e., the electrode active material layer, placed on the current collector was 75 μm, the porosity (%) was 25.9%, and the load capacity was 5.05 mAh / cm². 2 That was the case.

[0157] Example 2 The electrode film was manufactured in the same manner as in Example 1, except that the pressure between the rolls during the final calendering process was set to 264 kg / cm. In this case, the electrode film manufactured after calendering had a thickness of 81 μm, a porosity (%) of 30.1%, and a load of 5.11 mAh / cm². 2 That was the case.

[0158] Next, electrodes were manufactured by lamination using the same method as in Example 1. At this time, the thickness of the electrode film, i.e., the electrode active material layer, installed on the current collector was 72 μm, the porosity (%) was 23.1%, and the load was 5.0 mAh / cm². 2 That was the case.

[0159] Example 3 The electrode film was manufactured in the same manner as in Example 1, except that the pressure between the rolls during the final calendering process was set to 415 kg / cm. In this case, the electrode film produced after calendering had a thickness of 74 μm, a porosity (%) of 23.5%, and a load of 5.11 mAh / cm². 2 That was the case.

[0160] Next, electrodes were manufactured by lamination using the same method as in Example 1. At this time, the thickness of the electrode film, i.e., the electrode active material layer, installed on the current collector was 72 μm, the porosity (%) was 23.0%, and the load was 5.07 mAh / cm². 2 That was the case.

[0161] Comparative Example 1 The same method as in Example 1 was used, but the calendering process was carried out with a pressure of 115 kg / cm between the rolls during the final calendering step, so that the porosity during the calendering process exceeded 35%. At this time, the thickness of the electrode film immediately after calendering and before lamination was 92 μm, the porosity (%) was 37.2%, and the load was 5.21 mAh / cm. 2 That was the case.

[0162] Subsequently, using the same method as in Example 1, the electrode was laminated to have the same thickness and porosity as the electrode manufactured in Example 1, thereby producing an electrode with electrode active material layers formed on both sides of the current collector. At this time, the thickness of the electrode film (electrode active material layer) installed on the current collector was 74 μm, the porosity (%) was 26.0%, and the load capacity was 4.96 mAh / cm². 2 That was the case.

[0163] Comparative Example 2 By setting the pressure between the rolls to 210 kg / cm during the final calendering process using the same method as in Example 1, the electrode film thickness was 83 μm, the porosity (%) was 31.2%, and the load was 5.15 mAh / cm².2 An electrode film as described above was manufactured.

[0164] Thereafter, lamination was carried out in the same manner as in Example 1 to manufacture an electrode. At this time, by adjusting the lamination pressure, the thickness of the electrode film (electrode active material layer) installed on the current collector was 68 μm, the porosity (%) was 19.2%, and the load amount was 4.93 mAh / cm 2 An electrode as described above was manufactured.

[0165] Comparative Example 3 The same method as in Example 1 was used, but the pressure between the rolls during the final calendaring process was set to 85 kg / cm so that the porosity during the calendaring process exceeded 35% to manufacture an electrode film. At this time, the thickness of the electrode film immediately after calendaring and before lamination was 95 μm, the porosity (%) was 39.8%, and the load amount was 5.16 mAh / cm 2 It was as follows.

[0166] Thereafter, lamination was carried out in the same manner as in Example 1 so that the thickness and porosity were the same as those of the electrode manufactured in Example 1 to manufacture an electrode by lamination. At this time, the thickness of the electrode film (electrode active material layer) installed on the current collector was 76 μm, the porosity (%) was 29.0%, and the load amount was 4.87 mAh / cm 2 It was as follows.

[0167] [Physical Property Evaluation] Thickness Measurement The thickness of the electrode film was measured using a thickness measuring machine (Mitutoyo Corporation, VL-50S-B).

[0168] Evaluation of Compression Ratio For the manufactured electrode, the compression ratio of the electrode film was evaluated according to the following formula (1). [Formula (1)] Compression ratio (%) = [(T B - T A ) / T B × 100 In the above formula (1), T Ais the thickness of the electrode film (electrode active material layer) after lamination, T B is the thickness of the electrode film before lamination.

[0169] Evaluation of length expansion ratio For the fabricated electrode, the length expansion ratio of the electrode film was evaluated by the following formula (2). [Formula (2)] Length expansion ratio (%) = [(L A - L B ) / L B × 100 In the above formula (2), L A is the length of the electrode film (electrode active material layer) after lamination, and L B is the length of the electrode film before lamination.

[0170] Measurement of porosity The apparent density of only the electrode film was measured by subtracting the volume and weight of the current collector from the volume and weight of the fabricated electrode, and the porosity of the electrode film before and after lamination was measured by the following formula using the actual density calculated based on the actual density and composition of each constituent component.

[0171] Evaluation of porosity ratio For the fabricated electrode, the porosity ratio was evaluated by the following formula (3). [Formula (3)] Porosity ratio (%) = P B / P A × 100 In the above formula (3), P A is the porosity of the electrode film (electrode active material layer) after lamination, and P B is the porosity of the electrode film before lamination.

[0172] Evaluation of wrinkle in plain part For the fabricated electrode, the appearance was visually observed to evaluate the wrinkle in the plain part, that is, the flatness of the plain part.

[0173] In this study, if wrinkles were clearly observed on the plain areas, the wrinkle characteristics of the plain areas were evaluated as "poor," and if no wrinkles were observed by visual inspection, the wrinkle characteristics of the plain areas were evaluated as "good."

[0174] Figure 5 shows photographs of the appearance of the electrodes of Example 1 and Comparative Example 1 manufactured as described above.

[0175] The physical properties of the electrodes manufactured according to Example 1, Example 2, and Comparative Examples 1 to 3 are summarized in Table 1 below.

[0176] [Table 1]

[0177] According to Table 1 and Figure 5, the electrodes of Examples 1 to 3, with a compression ratio of 15% or less, showed good wrinkles in the plain areas, while the electrodes of Comparative Examples 1 to 3, with a compression ratio exceeding 15%, showed poor wrinkles in the plain areas. In particular, referring to Figure 5, the electrode of Comparative Example 2 had a void ratio of 35% or less before lamination, but due to the high void ratio ratio, it was confirmed that wrinkles occurred not only strongly at the boundary between the plain and textured areas, but also in the textured areas. The electrode of Comparative Example 3 had a void ratio of 30% or less after lamination, and a void ratio ratio of 140% or less, but the void ratio before lamination was 35% or more, and the compression ratio and length expansion ratio were high, exceeding 15% and 4% respectively. As a result, the phenomenon of the electrode film being pressed during lamination was strongly observed, and it was confirmed that this caused particularly strong wrinkles in the lateral direction of the electrode and at the boundary between the plain and textured areas.

[0178] Furthermore, in Example 3, where the electrode film was obtained under high pressure during the calendering step in the manufacturing of the electrode film, it was confirmed that the wrinkle characteristics were significantly improved by reducing the compression ratio in the lamination step to 1% or less, thereby reducing the length expansion ratio and void ratio.

[0179] As described above with reference to embodiments and drawings of the present invention, any person with ordinary skill in the art to which the present invention belongs can make various applications and modifications within the scope of the present invention based on the above description. [Explanation of Symbols]

[0180] 100: Calendar process 110: Roller for calendar 120: Mixed powder for electrodes 130: Electrode film 200: Lamination process 210: Laminating roller 220: Current collector 230: Electrode film 240: Electrode

Claims

1. (S10) A step of mixing electrode materials containing an electrode active material and a binder polymer to obtain a mixture, (S20) The step of kneading the mixture at a temperature in the range of 70°C to 200°C and a shear rate in the range of 10 / s to 500 / s to obtain a mixture mass, (S30) The step of crushing the mixture mass by shearing at a speed in the range of 400 rpm to 20,000 rpm to obtain a mixed powder for electrodes, (S40) A step of obtaining an electrode film by calendering the electrode mixed powder, (S50) The step of laminating the electrode film onto at least one surface of the current collector to form an electrode active material layer, The compressibility of the electrode film is 1% or more and 15% or less, and the compressibility of the electrode film is defined by the following formula 1, [Formula 1] Compression rate (%) = [(T)] Ｂ -T Ａ ) / T Ｂ ]×100 In the above formula 1, T Ａ This is the thickness of the electrode film (electrode active material layer) after lamination. T Ｂ This is a method for manufacturing dry electrodes, where the thickness of the electrode film before lamination is specified.

2. The length expansion coefficient of the electrode film is 4% or less, and the length expansion coefficient is defined by the following formula 2: [Formula 2] Length expansion rate (%) = [(L Ａ -L Ｂ ) / L Ｂ ] × 100 In the above formula 2, L Ａ is the length of the electrode film (electrode active material layer) after lamination, L Ｂ The method for manufacturing a dry electrode according to claim 1, wherein is the length of the electrode film before lamination.

3. The porosity ratio of the electrode film is between 100% and 140%, and the porosity ratio of the electrode film is defined by the following formula 3: [Formula 3] Porosity ratio (%) = (P) Ｂ / P Ａ )×100 In the above formula 3, P Ａ This is the porosity of the electrode film (electrode active material layer) after lamination. P Ｂ The method for manufacturing a dry electrode according to claim 1, wherein is the porosity of the electrode film before lamination.

4. The method for manufacturing a dry electrode according to claim 1, wherein the porosity of the electrode film before lamination in step (S50) is 35% or less, and the porosity of the electrode film after lamination is 30% or less.

5. The method for manufacturing a dry electrode according to claim 1, characterized in that the calendering in step (S40) is performed once or two or more times, and at least one of those times is performed under a pressure of 100 kg / cm or more.

6. The method for manufacturing a dry electrode according to claim 1, characterized in that the kneading in step (S20) is carried out for 1 to 30 minutes.

7. The method for manufacturing a dry electrode according to claim 1, characterized in that the kneading in step (S20) is carried out under a pressure of normal pressure or higher.

8. The method for manufacturing a dry electrode according to claim 1, further comprising the step of forming a primer layer on at least one surface of the current collector before the lamination in step (S50).

9. A dry electrode comprising a current collector and an electrode active material layer located on at least one surface of the current collector and containing an electrode active material and a binder polymer, The binder polymer is fibrous and binds the electrode active material, The dry electrode comprises a surfaced portion having the electrode active material layer and a current collector region facing the electrode active material layer, and a surfaced portion extending from both sides of the current collector region of the surfaced portion and including a current collector region not facing the electrode active material layer. The porosity of the electrode active material layer is 30% or less. A dry electrode in which the surface of the plain portion is flat.

10. The dry electrode according to claim 9, further comprising a primer layer between the current collector and the electrode active material layer.

11. An electrochemical element comprising a positive electrode, a negative electrode, and a separation layer interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is a dry electrode according to claim 9 or 10.

12. The electrochemical element according to claim 11, wherein the separation layer is a separation membrane or a solid electrolyte membrane.

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