Electrode drying quality evaluation device and electrode drying quality evaluation method

Abstract

The present invention relates to an electrode drying quality evaluation device, which includes an oven providing a space for drying an electrode, a measurement unit located at the exit of the oven for measuring color coordinate values ​​of an electrode active material layer of the dried electrode, and a determination unit for determining whether the electrode is poorly dried based on the color coordinate values. The determination unit sets a reference value and determines that the electrode is poorly dried if the measured color coordinate values ​​are small and the difference between the measured color coordinate values ​​and the reference value is equal to or greater than a predetermined value.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0109043 dated August 28, 2020, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an electrode drying quality evaluation device and an electrode drying quality evaluation method, and more particularly, to an electrode drying quality evaluation device and an electrode drying quality evaluation method through measurement of simple color coordinate values ​​of an electrode. [Background technology]

[0003] Recently, rechargeable secondary batteries have been widely used as energy sources for wireless mobile devices. Secondary batteries are also attracting attention as energy sources for electric vehicles and hybrid electric vehicles, which have been presented as a solution to address air pollution caused by existing gasoline and diesel vehicles that use fossil fuels. Therefore, the types of applications that use secondary batteries are becoming increasingly diverse due to the advantages of secondary batteries, and secondary batteries are expected to be applied to more fields and products in the future.

[0004] Such secondary batteries may be classified into lithium ion batteries, lithium ion polymer batteries, lithium polymer batteries, etc. according to the configuration of the electrodes and electrolyte, and among them, the use of lithium ion polymer batteries, which are less likely to leak electrolyte and are easy to manufacture, is increasing. In general, secondary batteries are classified into cylindrical batteries and prismatic batteries in which an electrode assembly is housed in a cylindrical or prismatic metal can, and pouch-type batteries in which an electrode assembly is housed in a pouch-type case of an aluminum laminate sheet, according to the shape of the battery case. The electrode assembly housed in the battery case is a chargeable and dischargeable power generating element having a positive electrode, a negative electrode, and a separator structure interposed between the positive electrode and the negative electrode, and is classified into a jelly roll type in which a separator is interposed between a long sheet-like positive electrode and a negative electrode coated with an active material and wound up, and a stack type in which a plurality of positive electrodes and negative electrodes of a predetermined size are stacked in sequence with a separator interposed between them.

[0005] Such electrodes can be manufactured by coating an electrode slurry containing an electrode active material and a solvent on a current collector to form an electrode active material layer, followed by drying and rolling. The quality of the electrode is determined by the drying conditions. If the amount of drying heat is excessive, a significant amount of binder in the electrode slurry migrates to the surface during the drying process, reducing the adhesive strength of the electrode. If the amount of drying heat is low, the solvent remains in the electrode, causing roll contamination during the coating and rolling processes. Such increased roll contamination causes defects on the electrode surface, and the residual solvent in the electrode is a major cause of safety issues such as gas generation and swelling in the battery, so it is necessary to develop an evaluation method that can determine whether the electrode is dry or not.

[0006] In relation to this, in the past, the degree of drying was evaluated by measuring the change in the weight of the electrode using a device such as a web gauge. Specifically, the weight per unit area of ​​the electrode slurry before drying is calculated by calculating the difference in the weight of the electrode before and after coating. The weight per unit area of ​​the electrode slurry after drying is calculated in the same manner. Next, the presence or absence of residual solvent is determined from the difference between the theoretical weight of the electrode, which is derived from the solid content in the electrode slurry and the weight per unit area of ​​the electrode slurry before drying, and the previously calculated weight per unit area of ​​the electrode slurry after drying.

[0007] However, this method requires that the weight of the electrode be measured three times in total: before coating, after coating, and after drying. In addition, in the case of an electrode in which electrode slurry is coated on both sides of the current collector, the weight of the electrode slurry coated on both sides must be measured before and after drying, so the weight must be measured a total of five times. This makes the evaluation time-consuming and costly. In addition, the web gauge used to measure the weight of the electrode is 85 Since radioactive isotopes such as Kr are used, the problem of radiation exposure can arise.

[0008] Therefore, there is a need to develop an apparatus and method for evaluating the drying quality of an electrode that can solve the above problems. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been devised to solve the above-mentioned problems, and aims to provide an electrode drying quality evaluation device and an electrode drying quality evaluation method that can determine the presence or absence of remaining solvent in an electrode during processing to quickly determine the degree of dryness of the electrode, thereby reducing the time and cost required for evaluation and ensuring safety during the evaluation process. [Means for solving the problem]

[0010] The device for evaluating the drying quality of an electrode according to the present invention includes an oven that provides a space in which the electrode is dried, a measurement unit located at an outlet of the oven that measures a color coordinate value of an electrode active material layer for the dried electrode, and a judgment unit that judges whether or not the electrode is poorly dried from the color coordinate value, wherein the judgment unit sets a reference value and judges that the drying state of the electrode is poor if the measured color coordinate value is smaller than the reference value and the difference between the measured color coordinate value and the reference value is equal to or greater than a predetermined value.

[0011] In one example, the color coordinate values ​​are L * It is.

[0012] In another example, the color coordinate values ​​are gray values ​​according to a gray scale.

[0013] In one example, the measurement unit includes a spectrophotometer or a colorimeter.

[0014] In another example, the measurement unit includes an image sensor capable of taking an image of the surface of the electrode active material layer.

[0015] In one example, the determining unit derives the reference value from an average value of color coordinate values ​​for a plurality of electrodes.

[0016] In another example, the determining unit derives the reference value from a profile of color coordinate values ​​of the electrode according to the residual solvent content in the electrode.

[0017] In a specific example, the determining unit determines that the dryness of the electrode is poor when the difference between the measured color coordinate value and the reference value is 0.5 or more.

[0018] The present invention also provides a method for evaluating the drying quality of an electrode, comprising the steps of: manufacturing an electrode by forming an electrode active material layer containing an electrode active material on a current collector, and drying the electrode by placing the electrode active material layer in an oven of the above-mentioned electrode drying quality evaluation device; measuring color coordinate values ​​of the electrode active material layer for the dried electrode; and judging whether the electrode is poorly dried from the color coordinate values, in which the electrode drying state is judged to be poor if the measured color coordinate values ​​are smaller than a reference value and the difference between the measured color coordinate values ​​and the reference value is equal to or greater than a predetermined value.

[0019] In a specific example, the electrodes may not be rolled.

[0020] In one example, the color coordinate values ​​are L * It could be.

[0021] In another example, the color coordinate values ​​are gray values ​​according to a gray scale.

[0022] In one example, the step of measuring the color coordinate value of the electrode active material layer may be performed via a spectrophotometer or a colorimeter.

[0023] In another example, the step of measuring the color coordinate value of the electrode active material layer includes a process of photographing the surface of the electrode through illumination and an image sensor to obtain an image, and converting color information of the image into color coordinates.

[0024] In one example, the reference value is derived from an average of color coordinate values ​​for a plurality of electrodes after manufacturing the plurality of electrodes.

[0025] In another example, the reference value is derived from a profile of the color coordinates of the electrode as a function of the residual solvent content in the electrode.

[0026] In this case, the reference value can be derived from the color coordinate value of the electrode that satisfies the target content of the residual solvent in the electrode.

[0027] Also, if the difference between the measured color coordinate value and the reference value is 0.5 or more, it can be determined that the dryness of the electrode is poor.

[0028] In this case, the content of residual solvent in the electrode determined to be a non-defective product may be 1 wt % or less.

[0029] The present invention also provides a method for manufacturing an electrode, comprising the steps of evaluating the drying quality of an electrode according to the electrode drying quality evaluation method of claim 1, and rolling an electrode determined to be a non-defective product. Effect of the Invention

[0030] The present invention can reduce the time and cost required for measurement by simply measuring the color coordinates after manufacturing and drying the electrode, and can easily determine the degree of drying of the electrode and the presence or absence of drying defects. In addition, the measurement device uses lighting and sensors instead of a web gauge, ensuring safety during the evaluation process. [Brief description of the drawings]

[0031] [Figure 1] 1 is a block diagram showing a configuration of an electrode drying quality evaluation device according to the present invention. [Diagram 2] 1 is a schematic diagram showing an operation method of the electrode drying quality evaluation device according to the present invention. [Diagram 3] 1 is a flowchart showing the steps of a method for evaluating the drying quality of an electrode according to the present invention. [Figure 4] 4 shows color coordinates of an electrode according to an embodiment of the present invention, and the resulting measurement of the amount of residual moisture in the electrode. [Diagram 5] 4 shows color coordinates of an electrode according to an embodiment of the present invention, and the resulting measurement of the amount of residual moisture in the electrode. [Figure 6] 1 shows color coordinates of an electrode according to an embodiment of the present invention, and a measurement of the amount of residual moisture in the electrode based on the color coordinates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The present invention will be described in detail below. Before that, the terms or words used in the specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best describe his own invention.

[0033] In this application, the terms "comprise" and "have" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described herein, and should be understood as not precluding the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. In addition, when a layer, film, region, plate, or other part is described as being "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between. Conversely, when a layer, film, region, plate, or other part is described as being "under" another part, this includes not only the case where it is "directly under" the other part, but also the case where there is another part in between. In addition, in this application, being "on" may include not only the case where it is located on the top, but also the case where it is located on the bottom.

[0034] The present invention will be described in detail below.

[0035] FIG. 1 is a block diagram showing the configuration of an electrode drying quality evaluation device according to the present invention.

[0036] Referring to FIG. 1, an electrode drying quality evaluation device 10 according to the present invention includes an oven 11 providing a space in which an electrode is dried, a measurement unit 12 located at the exit of the oven 11 for measuring a color coordinate value of an electrode active material layer of the dried electrode, and a judgment unit 13 for judging whether or not the electrode is poorly dried from the color coordinate value, the judgment unit 13 setting a reference value, and judging that the drying state of the electrode is poor if the measured color coordinate value is smaller than the reference value and the difference between the measured color coordinate value and the reference value is equal to or greater than a preset value.

[0037] As described above, in the past, the degree of drying was evaluated by measuring the change in the weight of the electrode using a device such as a web gauge, but in this case, it is necessary to perform individual measurements on the electrode slurry coated on the current collector. Therefore, the evaluation is time-consuming and expensive. Furthermore, the web gauge for measuring the weight of the electrode has a problem in that the operator may be exposed to radiation.

[0038] Therefore, the present invention can easily determine the degree of drying of the electrode and the presence or absence of drying defects by measuring simple color coordinate values ​​after manufacturing and drying the electrode, thereby reducing the time and cost required for measurement. Also, since lighting and a sensor are used as measuring devices instead of a web gauge, safety in the evaluation process can be ensured.

[0039] Hereinafter, each component of the device for evaluating drying quality of an electrode according to the present invention will be described in detail.

[0040] FIG. 2 is a schematic diagram showing an operation method of the electrode drying quality evaluation device according to the present invention.

[0041] 2 together with FIG. 1, oven 11 provides a space in which electrode 20 is inserted and dried. The oven 11 has a hot air nozzle (not shown) or an infrared heater (not shown) therein for drying electrode 20. The hot air nozzle and the infrared heater may be arranged at regular intervals along the direction in which electrode 20 is transported, and apply hot air or infrared rays from a direction perpendicular to electrode 20. Specific details regarding the hot air nozzle and the infrared heater are well known to those skilled in the art, and therefore will not be described in detail.

[0042] On the other hand, the electrode 20 is manufactured by forming an electrode active material layer 22 on a current collector 21 .

[0043] Here, the electrode active material layer 22 may be formed by applying an electrode slurry including an electrode active material, a conductive material, and a binder onto a current collector 21. The electrode 20 may be a negative electrode or a positive electrode, and the current collector may be a positive electrode current collector or a negative electrode current collector.

[0044] In the present invention, the positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may have fine irregularities on its surface to increase the adhesive force of the positive electrode active material, and may be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0045] In the case of a negative electrode current collector sheet, it is generally made to a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the positive electrode current collector, the surface can be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0046] In the present invention, the positive electrode active material contains two or more transition metals as a lithium transition metal oxide, which is a substance capable of causing an electrochemical reaction. For example, lithium cobalt oxide (LiCoO2) substituted with one or more transition metals, layered compounds such as lithium nickel oxide (LiNiO2), lithium manganese oxide substituted with one or more transition metals, and lithium manganese oxide having the chemical formula LiNi 1-y M y Lithium nickel oxide represented by the formula LiO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga, containing one or more elements among the above elements, and 0.01≦y≦0.7), 1+z Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Li 1+z Ni 0.4 Mn 0.4 Co 0.2 O2, etc., Li 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e) A e (wherein, -0.5≦z≦0.5, 0.1≦b≦0.8, 0.1≦c≦0.8, 0≦d≦0.2, 0≦e≦0.2, b+c+d<1, M=Al, Mg, Cr, Ti, Si or Y, and A=F, P or Cl), 1+x M 1-y M'y PO 4-z X z (Here, M = transition metal, preferably Fe, Mn, Co or Ni, M’ = Al, Mg or Ti, X = F, S or N, 0.5 ≦ x ≦ +0.5, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.1), and examples include olivine-type lithium metal phosphates represented by this formula, but it is not limited to these only.

[0047] The negative electrode active material is, for example, carbon such as graphitizable carbon and graphite-based carbon; 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), etc. metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc. can be used.

[0048] The above conductive material is usually added at 1 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc., conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, nickel powder, conductive whiskers such as zinc oxide, potassium titanate, conductive metal oxides such as titanium oxide, conductive materials such as polyphenylene derivatives, etc. can be used.

[0049] The binder is a component that assists in binding the active material and conductive material, etc., and binding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the weight of the entire mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butylene rubber, fluororubber, various copolymers, etc.

[0050] Meanwhile, such an electrode slurry may be prepared by dissolving an electrode active material, a conductive material, a binder, and the like in a solvent. The type of the solvent is not particularly limited as long as it can disperse the electrode active material, and either an aqueous solvent or a non-aqueous solvent may be used. For example, the solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, and the like, and one or a mixture of two or more of these may be used. The amount of the solvent used is not particularly limited as long as it can be adjusted to a degree that allows the slurry to have an appropriate viscosity in consideration of the coating thickness of the slurry, production yield, workability, and the like.

[0051] Meanwhile, the measurement unit 12 measures the color coordinate value of the dried electrode 20. In this case, the color coordinate value of the electrode may be a color coordinate value measured at a specific point on an electrode active material layer, or a number of measurement points on the electrode active material layer may be selected and then the average value of the color coordinate values ​​measured at the measurement points may be used as the color coordinate value.

[0052] 2, the measuring unit 12 may measure color coordinate values ​​after the electrode 20 is removed from the oven 11. To this end, the measuring unit 12 may be installed to be located at the exit of the oven 11. In addition, in the present invention, when the electrode active material layers 22 are formed on both sides of the current collector 21 as shown in FIG. 2, the measuring unit 12 may be located on both sides of the electrode 20 to measure the dryness state of each electrode active material layer 22.

[0053] The measurement unit 12 may include a light capable of irradiating light onto the surface of the electrode 20. In this case, the type of the light is not particularly limited as long as it can irradiate light onto the surface of the electrode active material layer 22, and for example, an LED light may be used.

[0054] The present invention quantifies the dryness of the electrodes through color coordinate measurement by installing only a simple device capable of measuring color coordinates at the outlet of the oven, and can reduce the time and cost required for evaluation while simplifying the configuration of the measuring device. Also, since LEDs are used as the lighting, the safety of the operator can be ensured compared to a web gauge.

[0055] In one example, the color coordinate value is L * It can be. * is the L defined by CIE * a * b * It is one of the variables that represent the color difference meter. * a * b * In the color difference meter, the color coordinate L * is a value related to the lightness measured from the object, and is displayed from 0 to 100. The a and b values ​​are values ​​related to chromaticity, which indicates color and saturation, with the horizontal axis being a and the vertical axis being b, with the +a side indicating red, the -a side indicating green, the +b side indicating yellow, and the -b side indicating blue. In other words, the present invention uses L, which is related to lightness and darkness among color coordinates. *In particular, if the electrode 20 is not dried, the average refractive index at the surface of the electrode active material layer 22 decreases due to the solvent remaining in the electrode active material layer 22, and the reflectance decreases accordingly. * The values ​​are measured to be lower than normal.

[0056] In another example, the color coordinate value may be a gray value according to a gray scale. That is, an image of the dry state of the surface of the electrode 20 may be converted into a gray scale in which only light and dark can be confirmed, and the gray value may be measured from the gray scale to determine whether the electrode 20 is dry or not. If the electrode 20 is not dried, it will show a darker color than the dried electrode 20, and the gray value will be measured as smaller than in a normal case.

[0057] In this manner, in the present invention, the above color coordinates are used which can uniformly measure the brightness of the surface of the electrode active material layer 22, and by quantitatively measuring the brightness of the surface of the electrode active material layer 22, it is possible to intuitively judge whether the electrode is dry or not.

[0058] In this case, in one example, the measurement unit 12 may use a color difference meter as a sensor for measuring the color coordinate value of the electrode active material layer 22. Specifically, the measurement unit 12 may include a spectrophotometer or a colorimeter. In this case, the color coordinate value of the surface of the electrode active material layer 22 may be measured directly.

[0059] Such a color difference meter may be, for example, a CM2600d manufactured by Konica Minolta, Inc. Specifically, the color difference meter may be used as a color difference meter, and the measurement mode may be set to SCI (Specular Component Included) or SCE (Specular Component Excluded), standard light source D65 (color temperature: 6500K), and CIE 1964 10° standard observer, and then the color difference meter may be brought into contact with the position to be measured after white correction.

[0060] In this manner, the color coordinate values ​​can be measured directly using a color difference meter on the electrode 20, but the color coordinate values ​​can also be measured indirectly using an image taken of the surface of the electrode active material layer 22.

[0061] In another example, the measurement unit 12 includes an image sensor capable of capturing an image of the surface of the electrode active material layer 22. In this case, the electrode 20, specifically, the surface of the electrode active material layer 22 is captured through the image sensor to obtain an image of the surface of the electrode active material layer 22. In this case, the image sensor may use a camera. Once the image is obtained, it is converted into a color coordinate system to be measured, and color coordinate values ​​are measured. For example, the image captured through the camera is converted into a grayscale, and then the grayness or L of the image is measured. * The value may be measured.

[0062] When the color coordinate values ​​are measured, the determination unit 13 determines whether or not the electrodes are dry from the color coordinate values. To this end, the determination unit 13 sets a reference value for determining whether or not the electrodes are dry. Also, the determination unit 13 determines that the electrodes are good if the measured color coordinate values ​​meet a preset electrode dryness quality evaluation standard, and determines that the electrodes are not dry if the measured color coordinate values ​​do not meet the preset electrode dryness quality evaluation standard. The determination unit 13 is connected to the measurement unit 12 through a network, and the color coordinate values ​​stored in the measurement unit 12 can be transmitted to and analyzed by the determination unit 13.

[0063] Specifically, the determining unit 13 determines that the dryness of the electrodes is poor when the measured color coordinate values ​​are smaller than the reference values ​​and the difference between the measured color coordinate values ​​and the reference values ​​is equal to or greater than a predetermined value.

[0064] In one example, the determination unit 13 may derive a reference value from an average value of color coordinate values ​​for a plurality of electrodes. In this case, a plurality of electrodes may be manufactured in advance and then color coordinate values ​​for the electrodes may be measured in order to derive the reference value. Alternatively, the determination unit may obtain an average value of color coordinate values ​​measured for a plurality of electrodes to be measured. If the color coordinate value of any one of the plurality of electrodes is smaller than the average value by a preset value or more, the determination unit determines the electrode as defective.

[0065] In another example, the determination unit 13 derives the reference value from a profile of color coordinate values ​​of the electrode according to the content of the residual solvent in the electrode. In this case, the reference value can be derived from the color coordinate values ​​of the electrode that satisfy a target content of the residual solvent in the electrode.

[0066] The profile is obtained by manufacturing a plurality of electrode samples under the same conditions and in the same process as the electrode to be measured, measuring the color coordinate values ​​after drying and the solvent content in the electrode, and then storing the color coordinate values ​​of the electrode samples according to the solvent content in the electrode in a database. For example, in order to determine the tendency of the color coordinate values ​​according to the solvent content in the electrode, the color coordinate values ​​may be graphed and stored in a database. The determination unit may set the color coordinate value of an electrode that satisfies a target solvent content in the electrode as a reference value in the database.

[0067] Meanwhile, in the present invention, the judgment unit 13 judges that the dryness state of the electrode is poor if the color coordinate value measured by the above-mentioned process is smaller than the reference value and the difference between the measured color coordinate value and the reference value is equal to or greater than a preset value, and the preset value may also be derived, for example, from the profile.

[0068] In a specific example, the determination unit 13 may determine that the dryness of the electrode is poor when the difference between the measured color coordinate value and the reference value is 0.5 or more. That is, the determination unit 13 may determine that the dryness of the electrode is poor when the measured color coordinate value is smaller than the reference value by 0.5 or more. When the difference between the measured color coordinate value and the reference value is within the above range, the electrode that satisfies the target residual solvent content in the electrode may be determined to be a good product.

[0069] The present invention also provides a method for evaluating the drying quality of an electrode.

[0070] FIG. 3 is a flow chart showing the steps of the method for evaluating the drying quality of an electrode according to the present invention.

[0071] Referring to FIG. 3, the electrode drying quality evaluation method includes a step (S10) of manufacturing an electrode by forming an electrode active material layer including an electrode active material on a current collector, and drying the electrode by inserting the electrode active material layer into an oven of the electrode drying quality evaluation device as described above, a step (S20) of measuring color coordinate values ​​of the electrode active material layer for the dried electrode, and a step (S30) of determining whether the electrode is poorly dried from the color coordinate values. If the measured color coordinate values ​​are smaller than a reference value and the difference between the measured color coordinate values ​​and the reference value is equal to or greater than a predetermined value, the electrode drying state is determined to be poor.

[0072] The present invention can easily determine the degree of drying and the presence or absence of drying defects of an electrode by measuring simple color coordinate values ​​after manufacturing and drying the electrode, thereby reducing the time and cost required for measurement. In addition, since lighting and sensors are used as measuring devices instead of web gauges, safety in the evaluation process can be ensured.

[0073] Each step of the method for evaluating the drying quality of an electrode according to the present invention will now be described in detail.

[0074] <Electrode manufacturing and drying> 3 together with FIGs. 1 and 2, first, in order to measure color coordinate values, an electrode 20 is manufactured by forming an electrode active material layer 22 containing an electrode active material on a current collector 21. Specific details regarding the electrode are the same as those described above.

[0075] When the preparation of the electrode 20 is completed, the electrode 20 is dried in the oven 11. At this time, the drying time and the amount of drying heat may be determined according to the specifications of the electrode, for example, the loading amount of the electrode active material or the solvent content in the electrode slurry. The dried electrode 20 is discharged from the oven 11.

[0076] <Color coordinate measurement> When the drying of the electrode 20 is completed, the color coordinate value of the dried electrode 20 is measured. At this time, the color coordinate value of the electrode active material layer 22 is measured by the measuring unit 12 of the electrode drying quality evaluation device 10 as described above. Since the measuring unit 12 is located near the outlet of the oven 11, the color coordinate value of the electrode 20 discharged from the oven 11 can be measured immediately. As described above, the color coordinate value of the electrode 20 may be a color coordinate value measured at a specific point of a certain electrode active material layer 22, or a number of measurement points may be selected in the electrode active material layer 22, and the average value of the color coordinate values ​​measured at the measurement points may be used as the color coordinate value.

[0077] The present invention simplifies the measurement method by installing only a simple device capable of measuring color coordinates near the exit of the oven and quantifying the dryness state of the electrode through color coordinate measurement, thereby reducing the time and cost required for evaluation.

[0078] Meanwhile, in a specific example of the present invention, the electrode may not be rolled. That is, the present invention does not evaluate an electrode that has been subjected to a rolling process, but evaluates an electrode that has not been subjected to a rolling process, thereby removing defective electrodes before the rolling process and significantly reducing the defective rate after the rolling process. This can prevent contamination of the rolling rolls and the like caused by residual solvent in the electrode during the rolling process. However, the present invention is not limited thereto, and color coordinates can be measured at any step after the electrode is dried.

[0079] In one example, the color coordinate value is L * As mentioned above, L * is a value related to the lightness measured from the object, and can be expressed from 0 to 100. If the electrode is not dried, the average refractive index at the surface of the electrode active material layer decreases due to the solvent remaining in the electrode active material layer. Therefore, it shows a dark color compared to a dried electrode, and L * The values ​​are measured to be lower than normal.

[0080] In another example, the color coordinate value may be a gray value according to a gray scale. That is, an image of the dry state of the electrode surface may be converted into a gray scale in which only light and dark can be confirmed, and the gray value may be measured from the gray scale to determine whether the electrode is dry or not. If the electrode is not dried, it will show a darker color than a dried electrode, and the gray value will be measured as smaller than in a normal case.

[0081] In this manner, in the present invention, the color coordinates can be used to uniformly measure the brightness of the electrode surface, and by quantitatively measuring the brightness of the surface of the electrode active material layer, it is possible to determine whether the electrode is dry or not.

[0082] In one example, a color difference meter can be used as a sensor for measuring the color coordinate value of the electrode active material layer. Specifically, the step of measuring the color coordinate value of the electrode active material layer can be performed using a spectrophotometer or a colorimeter. In this case, the color coordinate value can be measured directly on the surface of the electrode active material layer.

[0083] Such a color difference meter can be used, for example, with a CM2600d manufactured by Konica Minolta, Inc. Specifically, the color difference meter can be used with a CM2600d manufactured by Konica Minolta, and the measurement mode can be set to SCI (Specular Component Included) or SCE (Specular Component Excluded), standard light source D65 (color temperature: 6500K), and CIE1964 10° standard observer, and then the color difference meter can be brought into contact with the position to be measured after white correction.

[0084] In another example, the step of measuring the color coordinate value of the electrode active material layer includes a process of photographing the surface of the electrode through illumination and an image sensor to obtain an image, and converting the color information of the image into color coordinates. In this case, the electrode, specifically, the surface of the electrode active material layer, is photographed through an image sensor to obtain an image of the electrode surface. In this case, the image sensor may use a camera. Once the image is obtained, it is converted into a color coordinate system to be measured, and color coordinate values ​​are measured. For example, the image photographed through the camera is converted into grayscale, and the grayness or L of the image is converted into a color coordinate system to be measured. * The value may be measured.

[0085] In the present invention, an LED light source is used as the lighting, which can ensure the safety of the worker compared to a web gauge.

[0086] <Determining whether drying is insufficient or not> When the color coordinate values ​​are measured, the presence or absence of poor electrode drying is judged from the measured color coordinate values. The present invention includes a step of judging the electrode as a good product when the measured color coordinate values ​​satisfy the pre-set electrode dryness quality evaluation standard, and judging the electrode as a defective product when the measured color coordinate values ​​do not satisfy the pre-set electrode dryness quality evaluation standard. This is performed by the judgment unit 13 included in the electrode dryness quality evaluation device as described above.

[0087] Specifically, in the present invention, a reference value of color coordinate values ​​is set for determining whether or not the electrode is dry enough, and if the color coordinate values ​​measured by the above-mentioned process are smaller than the reference value and the difference between the measured color coordinate values ​​and the reference value is equal to or greater than a specified value, it is determined that the electrode is dry enough.

[0088] In one example, the reference value may be derived from an average value of color coordinate values ​​for a plurality of electrodes after manufacturing the plurality of electrodes. In this case, the plurality of electrodes may be manufactured in advance and color coordinate values ​​for the plurality of electrodes may be measured in advance to derive the reference value. Alternatively, the average value of the color coordinate values ​​measured for the plurality of electrodes to be measured may be calculated. In this case, if the color coordinate value of any one of the plurality of electrodes is smaller than the average value by a predetermined value or more, the electrode may be determined to be defective.

[0089] In another example, the reference value may be derived from a profile of electrode color coordinate values ​​according to the content of the residual solvent in the electrode. The reference value may be derived from color coordinate values ​​of an electrode that meets a target content of the residual solvent in the electrode.

[0090] Specifically, a plurality of electrode samples are manufactured under the same conditions and in the same process as the electrode to be measured, and the color coordinate values ​​and the solvent content in the electrode are measured after drying. Then, the color coordinate values ​​according to the solvent content in the electrode of the electrode samples can be stored in a database. For example, in order to determine the tendency of the color coordinate values ​​according to the solvent content in the electrode, the color coordinate values ​​can be graphed and stored in a database. Next, in the database, the color coordinate value of an electrode that satisfies a target solvent content in the electrode can be set as a reference value.

[0091] Meanwhile, in the present invention, if the color coordinate values ​​measured by the above-mentioned process are smaller than the reference values ​​and the difference between the measured color coordinate values ​​and the reference values ​​is equal to or greater than a preset value, it is determined that the dryness of the electrode is poor, and the preset value may also be derived, for example, from the profile.

[0092] In a specific example, if the difference between the measured color coordinate value and the reference value is 0.5 or more, the dryness of the electrode may be determined to be poor. That is, if the measured color coordinate value is smaller than the reference value by 0.5 or more, the dryness of the electrode may be determined to be poor. If the difference between the measured color coordinate value and the reference value is within the above range, the electrode that satisfies the target residual solvent content in the electrode may be determined to be a good product.

[0093] In this case, the residual solvent content in the electrode determined to be a good product may be 1 wt% or less, specifically 0.5 wt% or less. When the residual solvent content in the electrode is within the above range, the electrode has excellent drying quality, and roll contamination in the rolling process, gas generation in the battery, swelling phenomenon, etc. can be prevented. The residual solvent content in the electrode determined to be a good product may vary depending on the composition of the electrode and the solid content in the electrode. In this way, the present invention can detect moisture of up to 1.0 wt% through measurement of color coordinates.

[0094] The present invention also provides a method for manufacturing an electrode, comprising the steps of evaluating the drying quality of an electrode according to the electrode drying quality evaluation method as described above, and rolling an electrode determined to be a non-defective product.

[0095] The electrode manufactured according to the method for manufacturing an electrode according to the present invention can be used as a positive electrode or a negative electrode in manufacturing a lithium secondary battery, and since it has excellent drying quality, it can reduce the defective rate of the lithium secondary battery.

[0096] The lithium secondary battery can be used in mobile devices such as mobile phones, notebook computers, and digital cameras, and in electric vehicles such as hybrid electric vehicles (HEVs).

[0097] In the following, the present invention will be described in detail with reference to examples in order to facilitate understanding of the present invention. However, the examples of the present invention may be modified in many different forms. The scope of the present invention should not be construed as being limited to the following examples. The examples of the present invention are provided to more completely explain the present invention to those having average knowledge in the art.

[0098] Example 1 <Electrode manufacturing> An electrode slurry was prepared by mixing 55 parts by weight of water with 41 parts by weight of natural graphite, 0.5 parts by weight of conductive material, 2.5 parts by weight of SBR, and 1 part by weight of CMC.

[0099] The electrode slurry was applied to one surface of a copper current collector having a thickness of 8 μm at a rate of 0.014 g / cm. 2 The electrode was manufactured by forming an electrode active material layer having a thickness of 144 μm by applying the slurry at a loading amount of 150 μm and drying the slurry. Next, an active material layer was formed on the other side of the current collector under the same process conditions to manufacture an electrode having a total active material layer thickness of 288 μm formed on both sides of the copper current collector. At this time, the solid content of the electrode slurry was 45 wt %.

[0100] <Measurement of color coordinate values> After manufacturing a plurality of the electrodes, a Konica Minolta CM2600d colorimeter was used, and the measurement mode was set to SCI, standard light source D65 (color temperature: 6500K), and CIE1964 10° standard observer. After white correction, the colorimeter was brought into contact with the position to be measured to measure the color coordinate value (L * ) was measured.

[0101] <Setting the reference value> The average color coordinate value of the plurality of electrodes thus manufactured was calculated and used as the reference value, which was 35.50 as shown in FIG.

[0102] <Determining whether drying is insufficient or not> For the manufactured electrodes, the color coordinate values ​​were determined to be defective if they were smaller than the reference value and the difference between the reference value and the measured color coordinate value was 0.5 or more. The point where the difference between the reference value and the color coordinate value was 0.5 is shown by a dotted line in FIG.

[0103] Example 2 Except for the fact that the content of SBR as a binder during electrode preparation was 1.0 part by weight, the presence or absence of poor drying of the electrode was evaluated in the same manner as in Example 1. At this time, the reference value was 35.28 as shown in Figure 5. In addition, the point where the difference between the reference value and the color coordinate value was 0.5 is shown by a dotted line in Figure 5.

[0104] Example 3 When manufacturing the electrode, a 1:1 mixture of natural graphite and artificial graphite was used, and the solid content was 40 wt %, but the presence or absence of poor drying of the electrode was judged in the same manner as in Example 1. In this case, the reference value was 38.66, as shown in Figure 6. In addition, the point where the difference between the reference value and the color coordinate value is 0.5 is shown by a dotted line in Figure 6.

[0105] Experimental Example The residual solvent content of the electrodes measured in Examples 1 to 3 was measured.

[0106] The residual solvent content of the electrode can be measured in the following manner.

[0107] Specifically, the weight per unit area of ​​the copper current collector before coating is measured, and then the weight per unit area of ​​the electrode (weight of the electrode active material layer + weight of the copper current collector) is measured after coating the electrode with the slurry, and the weight per unit area of ​​the electrode active material layer before drying is calculated by subtracting the weight per unit area of ​​the copper current collector.

[0108] Thereafter, the electrode is dried, and the weight per unit area of ​​the electrode after drying is measured, excluding the weight per unit area of ​​the copper current collector, and the weight per unit area of ​​the electrode active material layer after drying is measured.

[0109] The content of the residual solvent can be calculated from the weight of the electrode active material layer before and after drying and the content of the solid content in the electrode slurry.

[0110] In this case, the weight per unit area can be measured using a web gauge. Any commercially available web gauge can be used, for example, a Thermo Scientific (registered trademark) web gauge manufactured by Thermo Fisher.

[0111] The residual solvent content of the electrode measured in this way was then calculated as a color coordinate value (L * ) are shown in Figs. 4 to 6, respectively.

[0112] 4 to 6, the color coordinate value tends to decrease as the residual solvent content in the electrode increases. Electrodes that were determined to be good (electrodes with a difference between the measured color coordinate value and the reference value of less than 0.5, corresponding to electrodes located above the dotted line) had a residual solvent content of 0.5 wt% or less (Examples 1 and 2) or 1.0 wt% or less (Example 3), fulfilling the standard for good products. In other words, the present invention is capable of detecting moisture of up to 1.0 wt% by measuring the color coordinate.

[0113] The above description is merely illustrative of the technical idea of ​​the present invention, and various modifications and variations are possible within the scope of the essential characteristics of the present invention if one has ordinary knowledge in the technical field to which the present invention belongs. Therefore, the drawings disclosed in the present invention are for the purpose of explaining the technical idea of ​​the present invention, rather than for the purpose of limiting the scope of the technical idea of ​​the present invention, and such drawings should not be construed as limiting the scope of the technical idea of ​​the present invention. The scope of protection of the present invention should be interpreted by the scope of the claims, and all technical ideas within the scope equivalent thereto should be interpreted as being included in the scope of the rights of the present invention.

[0114] Meanwhile, in this specification, terms indicating directions such as up, down, left, right, front, and back are used, but it is obvious that such terms are used merely for convenience of explanation and may change depending on the position of the target object, the position of the observer, etc. [Explanation of symbols]

[0115] 10: Electrode drying quality evaluation device 11: Oven 12: Measuring part 13: Judgment section 20: Electrode 21: Current collector 22: Electrode active material layer

Claims

1. an oven which provides a space in which the electrodes are dried; a measuring unit located at an outlet of the oven and measuring a color coordinate value of an electrode active material layer of the dried electrode; a determination unit that determines whether or not the electrode is dry from the color coordinate value, the determining unit sets a reference value, and determines that the dryness of the electrode is poor when the measured color coordinate value is smaller than the reference value and a difference between the measured color coordinate value and the reference value is equal to or greater than a preset value; The color coordinate value is L*, The determination unit determines that the dryness of the electrode is poor when a difference between the measured color coordinate value and a reference value is 0.5 or more.

2. The device for evaluating drying quality of an electrode according to claim 1 , wherein the measurement unit includes a spectrophotometer or a colorimeter.

3. The device for evaluating drying quality of an electrode according to claim 1 or 2, wherein the measurement unit includes an image sensor that captures an image of a surface of an electrode active material layer.

4. The device for evaluating drying quality of an electrode according to claim 1 , wherein the determining unit derives the reference value from an average value of color coordinate values ​​for a plurality of electrodes.

5. The device for evaluating the drying quality of an electrode according to claim 1 , wherein the determining unit derives the reference value from a profile of electrode color coordinate values ​​according to a content of a residual solvent in the electrode.

6. A step of manufacturing an electrode by forming an electrode active material layer containing an electrode active material on a current collector, and drying the electrode by placing the electrode in an oven of the drying quality evaluation device according to claim 1; measuring the color coordinate value of the electrode active material layer on the dried electrode; and determining whether or not the electrodes are dry from the color coordinate values. If the measured color coordinate value is smaller than the reference value and the difference between the measured color coordinate value and the reference value is equal to or larger than a predetermined value, it is determined that the dryness of the electrode is poor; The color coordinate value is L*, The method for evaluating the drying quality of an electrode, wherein if the difference between the measured color coordinate value and the reference value is 0.5 or more, the drying state of the electrode is determined to be poor.

7. The method for evaluating the drying quality of an electrode according to claim 6, wherein the electrode is not rolled.

8. The method for evaluating drying quality of an electrode according to claim 6 or 7, wherein the step of measuring the color coordinate value of the electrode active material layer is performed via a spectrophotometer or a colorimeter.

9. 8. The method for evaluating drying quality of an electrode according to claim 6 or 7, wherein the step of measuring the color coordinate value of the electrode active material layer includes a step of photographing a surface of the electrode through illumination and an image sensor to obtain an image, and converting color information of the image into color coordinates.

10. The method for evaluating drying quality of an electrode according to claim 6 , wherein the reference value is derived from an average value of color coordinate values ​​of a plurality of electrodes after manufacturing the plurality of electrodes.

11. The method for evaluating the drying quality of an electrode according to claim 6 , wherein the reference value is derived from a profile of electrode color coordinate values ​​according to a content of the residual solvent in the electrode.

12. The method for evaluating the drying quality of an electrode according to claim 6 , wherein the reference value is derived from a color coordinate value of an electrode that satisfies a target content of residual solvent in the electrode.

13. The method for evaluating drying quality of an electrode according to claim 6 , wherein an electrode determined to be a non-defective has a residual solvent content of 1% by weight or less.

14. Evaluating the drying quality of the electrode according to the method for evaluating the drying quality of an electrode according to any one of claims 6 to 13; and A method for manufacturing an electrode, comprising the step of rolling an electrode determined to be a non-defective product.

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