Filter determination system and determination method for evaluating dissolution quality of binder solution for secondary battery electrodes

Abstract

The present invention relates to a filter determination system and a determination method for evaluating the dissolution quality of a binder solution for secondary battery electrodes. The filter determination system for evaluating the dissolution quality of a binder solution for secondary battery electrodes according to the present invention comprises: a pressure vessel for accommodating a binder solution; a pressure medium supply source for supplying a pressure medium of a predetermined pressure to the pressure vessel; a filter connected to the pressure vessel by a tube; a flow rate measuring unit for measuring the flow rate of the binder solution filtered by the filter; and a determination unit for determining the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate by repeatedly measuring the flow rate using filters with different pore sizes, and determining a filter having a filter size within an optimal pore size range based on the time point. In addition, the present invention relates to a filter determination method for evaluating the dissolution quality of a binder solution for secondary batteries.

Description

Technical Field

[0001] The present invention relates to a filter determination system and method for evaluating the dissolution quality of a secondary battery electrode binder solution. More specifically, the present invention relates to a system and method for determining an optimal filter capable of shortening the evaluation time when evaluating the quality of a secondary battery electrode binder solution. Background Art

[0002] As the technology of mobile devices, automobiles, and energy storage devices develops and their demand increases, the demand for batteries as energy sources is also rapidly increasing. Therefore, many studies have been conducted on lithium secondary batteries with high energy density and high discharge voltage, and such lithium secondary batteries have been widely used.

[0003] The electrode for lithium secondary battery is formed by applying a mixture layer containing active materials on an electrode substrate made of metal foil, and the mixture layer is formed as a positive electrode or negative electrode slurry is applied to the electrode substrate and then dried. The electrode slurry is manufactured by mixing a solid (such as a positive electrode / negative electrode active material) and a conductive material with a binder solution and then drying the mixture.

[0004] The binder allows the active material to adhere to the active material, or allows the active material to adhere to the electrode substrate, thereby improving the adhesion of the electrode and adjusting the viscosity of the slurry. Since the binder is mixed with the active material, the conductive material, etc. in the form of a binder solution dissolved in a predetermined solvent, the dissolution quality of the binder affects the quality characteristics of the electrode slurry or the electrode. For example, when the dissolution quality of the binder (such as CMC or PVDF) is poor, various problems may occur, such as increased slurry viscosity, surface defects of the electrode coating, etc. The dissolution quality of the binder depends on the minimization level of insolubles in the binder solution.

[0005] Conventionally, in order to evaluate the dissolution quality of an adhesive solution, the adhesive that has not completely dissolved in the solution is simply observed with the naked eye, or after applying the adhesive solution to an OHP film with a blade of a specific thickness, the number of foreign matters on the film is counted with the naked eye. Alternatively, in the case of a PVDF solution, a method of counting the number of foreign matters remaining in a nylon mesh filter by filtering the solution using a filter is adopted.

[0006] However, according to the former method, it is difficult to identify the overall quality of the solution due to the small amount of sample, and since foreign matter may flow in and they cannot be distinguished from undissolved matter, the measurement accuracy is not high. In addition, since the evaluation is performed by the naked eye, there may be a large error depending on the evaluator.

[0007] In the method of measuring the amount of foreign matter using a mesh filter, foreign matter from the filter itself may flow into the filter, or bubbles may be generated during the filtration process, and foreign matter may be trapped in these bubbles. In some cases, water is mixed during filtration, and PVDF precipitates in the solution, thereby phase-separating from NMP as a solvent. Therefore, the reproducibility and accuracy of the dissolution quality evaluation are very low.

[0008] In order to solve these problems, the inventors of the present invention devised a method for quantitatively evaluating the dissolution quality of an adhesive solution using an in-line filter, in which the evaluation is performed without errors caused by an evaluator while reducing the influence of the external environment.

[0009] However, in the case of such a dissolution quality evaluation method, it sometimes takes too long to evaluate the dissolution quality depending on the type or pore size of the filter used. If the evaluation time is too long, the productivity of manufacturing the electrode slurry using the binder solution will decrease.

[0010] Therefore, there is a need for a technology for improving productivity by reducing the dissolution quality evaluation time of a binder solution used for manufacturing a secondary battery electrode.

[0011] Prior art literature

[0012] Patent Literature

[0013] (Patent Document 1) Korean Patent Publication No. 10-2017-0111722 Summary of the invention

[0014] Technical issues

[0015] The present invention solves at least a part of the above problems. For example, one aspect of the present invention provides a filter determination system and method for evaluating the dissolution quality of a binder solution for a secondary battery electrode, wherein the evaluation time can be shortened by determining the best filter that can quantitatively evaluate the dissolution quality of the binder solution.

[0016] Technical Solution

[0017] The filter determination system for evaluating the dissolution quality of a binder solution for secondary battery electrodes of the present invention for solving the above-mentioned problems comprises: a pressure vessel, which contains a binder solution; a pressure medium supply source, which supplies a pressure medium of a predetermined pressure to the pressure vessel; a filter, which is connected to the pressure vessel by a tube; a flow rate measuring unit, which measures the flow rate of the binder solution filtered by the filter; and a determination unit, which measures the time point when the flow rate reaches a specific value predetermined in consideration of an initial flow rate by repeatedly measuring the flow rate using filters with different pore sizes, and determines a filter having a pore size within an optimal pore size range based on the time point.

[0018] As an example, the determination unit may determine the filter having the time point equal to or less than a predetermined time point as a filter having a pore size within an optimal pore size range.

[0019] As an example, the pressure medium may be nitrogen, and the nitrogen having a predetermined pressure may be supplied from a pressure medium supply source to the pressure vessel.

[0020] As a specific example, the tube may extend into the pressure vessel, and an end of the tube may be mounted adjacent to a bottom of the pressure vessel.

[0021] As an example, the filter may be an in-line filter installed in series in the tube.

[0022] Specifically, the in-line filter may include a filter member, an elastic member pressing the filter member, and a housing accommodating the filter member and the elastic member.

[0023] As one aspect of the present invention, a filter determination method for evaluating the dissolution quality of a binder solution for a secondary battery includes: injecting a predetermined amount of a binder solution into a pressure vessel; transferring the binder solution to a filter by supplying a pressure medium of a predetermined pressure to the pressure vessel; filtering the binder solution using the filter; measuring the flow rate of the binder solution passing through the filter; repeatedly measuring the flow rate by using each filter with a different pore size, and measuring the time point when the flow rate reaches a specific value predetermined in consideration of an initial flow rate; and determining a filter having the time point equal to or less than the predetermined time point as a filter having a pore size within an optimal pore size range.

[0024] As an example, a filter having a pore size that makes the time point the earliest time point may be determined as a filter having an optimal pore size.

[0025] As an example, the binder as the solute of the binder solution can be at least one selected from the group consisting of: a non-aqueous binder, such as polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM or polytetrafluoroethylene (PTFE); an aqueous binder, such as acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR) or acrylic rubber; and a polymer resin, such as hydroxyethyl cellulose or carboxymethyl cellulose.

[0026] As an example, the solvent of the binder solution may be at least one selected from the group consisting of an organic solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or dimethylacetamide, and water.

[0027] As a specific example, the binder solution may be a PVDF solution obtained by dissolving a predetermined content of PVDF in an NMP solvent.

[0028] As an example, a filter whose time point when the flow rate decreases to 50% of the initial flow rate is less than a predetermined time point can be determined as a filter having a pore size within an optimal pore size range.

[0029] As another example, a filter having a time point when the flow rate decreases to 80% of the initial flow rate that is less than a predetermined time point may be determined as a filter having a pore size within an optimal pore size range.

[0030] Beneficial Effects

[0031] According to the present invention, it is possible to determine an optimal filter for quantitatively evaluating the dissolution quality of a secondary battery electrode binder solution.

[0032] Furthermore, by using the optimal filter to evaluate the dissolution quality of the binder solution, the evaluation time can be significantly shortened, thereby improving the productivity of the binder solution and electrode slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of a filter determination system for evaluating the dissolution quality of a secondary battery electrode binder solution according to the present invention.

[0034] Figure 2 is shown as Figure 1 Photographs of the components of the filter that make up the system.

[0035] Figure 3 This is a flowchart showing the procedure of the filter determination method for evaluating the dissolution quality of the secondary battery binder solution according to the present invention.

[0036] Figure 4 : is a graph showing that the time point when the flow rate reaches a certain value predetermined in consideration of the initial flow rate varies with the pore size of the filter according to one embodiment of the present invention.

[0037] Explanation of symbols

[0038] 1: Adhesive solution

[0039] 10: Pressure Vessel

[0040] 11: Pressure gauge

[0041] 12: Solution discharge pipe

[0042] 12a: Part of a tube

[0043] 13: On / off valve

[0044] 20: Pressure medium supply source

[0045] 21: Pressure medium on / off valve

[0046] 22: Pressure medium supply pipeline

[0047] 30: Inline filter

[0048] 31: Filter component

[0049] 32: Elastic component

[0050] 33: Shell

[0051] 34: Gasket

[0052] 40: Flow rate measurement unit

[0053] 50: Determine the unit DETAILED DESCRIPTION

[0054] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The terms and words used in this specification and claims should not be interpreted as limited to common terms or dictionary terms, and the inventors can appropriately define the concepts of the terms in order to best describe their inventions. The terms and words should be interpreted as meanings and concepts consistent with the technical concept of the present invention.

[0055] In the present application, it should be understood that terms such as "comprising" or "having" are intended to indicate features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and they do not preclude the possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts or combinations thereof. In addition, when a part such as a layer, a film, a region, a plate, etc. is referred to as being "on" another part, this includes not only the case where the part is "directly" on the other part, but also the case where other parts are inserted therebetween. On the other hand, when a part such as a layer, a film, a region, a plate, etc. is referred to as being "under" another part, this includes not only the case where the part is "directly" under the other part, but also the case where other parts are inserted therebetween. In addition, being arranged "on..." in the present application may include being arranged on the lower part as well as the upper part.

[0056] The object of the present invention is to determine the best filter for a method for evaluating dissolution quality by an online filter, which can quantitatively evaluate the quality of an adhesive solution without errors caused by an evaluator while reducing the influence of the external environment. That is, in the present invention, the adhesive solution flows in a pressure vessel, a pipe, and an online filter connected to the pressure vessel and the pipe. Therefore, the present invention is based on a dissolution quality evaluation system or method, wherein the adhesive solution is not exposed to the outside during the dissolution quality evaluation process.

[0057] Figure 1 Schematic diagram of a filter determination system for evaluating the dissolution quality of a secondary battery electrode binder solution according to the present invention.

[0058] The filter determination system 100 includes: a pressure vessel 10, which contains a binder solution; a pressure medium supply source 20, which supplies a pressure medium of a predetermined pressure to the pressure vessel 10; a filter 30, which is connected to the pressure vessel 10 through a tube 12; a flow rate measuring unit 40, which measures the flow rate of the binder solution 1 filtered by the filter 30; and a determination unit 50, which determines a filter having a pore size within an optimal pore size range.

[0059] The filter determination system 100 of the present invention contains the adhesive solution 1 in the pressure vessel 10 so that the adhesive solution used for dissolution quality evaluation is not exposed to the external environment. The pressure vessel 10 is a container that is sealed and pressure-applied, and is a container that can withstand a predetermined pressure. For example, a container that can withstand the pressure when a pressure medium having a predetermined pressure is supplied can be used as the pressure vessel 10. That is, the pressure vessel 10 of the system 100 is a container having sealing properties and pressure resistance, and is a container that can hold the adhesive solution 1 for secondary batteries. The capacity of the pressure vessel can be appropriately selected within the range of being able to hold an amount of adhesive solution suitable for filtering. For example, a pressure vessel with a capacity of 20 kg can be used. The amount of adhesive solution contained in the pressure vessel can be appropriately selected within the capacity range of the pressure vessel. For example, 1 kg to 5 kg of solution can be filled in the pressure vessel 10.

[0060] In order to transfer the binder solution to the filter 30, a pressure medium supply source 20 is necessary. For example, in the case where the binder solution is contained in the pressure vessel 10, if a pressure medium having a greater pressure than that in the pressure vessel is supplied to the pressure vessel 10, the binder solution 1 in the container can be transferred to the filter 30 by the pressure. Dry air or an inert gas (which does not affect the physical and chemical properties of the binder solution) can be used as the pressure medium. In particular, nitrogen can be used as the pressure medium in terms of management and manufacturing costs. The pressure medium supply source 20, such as a nitrogen supply source, can be a nitrogen tank containing high-pressure compressed nitrogen. Nitrogen at a predetermined pressure is supplied from the pressure medium supply source to the pressure vessel 10 through a supply line 22. An on / off valve or a control valve 21 for controlling the flow of the pressure medium can be installed at the supply line 22.

[0061] The pressure medium has a pressure greater than the internal pressure of the pressure vessel 10 and has a predetermined pressure such that the binder solution 1 in the pressure vessel 10 is delivered to the filter. When the pressure medium is nitrogen, nitrogen at a pressure of about 1 bar to 7 bar may be delivered to the pressure vessel 10.

[0062] If the solution is filled in the pressure container 10, the solution in the pressure container 10 can be transferred to the outside by applying a certain pressure to the space f above the solution. To this end, the pressure container 10 is connected to the solution discharge pipe 12, and the solution discharge pipe 12 is connected to the filter 30. Figure 1As shown, the solution discharge pipe 12 extends to the inside of the pressure vessel 10, and the end of the solution discharge pipe 12 is placed adjacent to the bottom of the pressure vessel 10. Therefore, a portion 12a of the solution discharge pipe 12 is immersed in the adhesive solution 1. In this way, when the solution discharge pipe 12 is installed adjacent to the bottom of the pressure vessel 10, if a constant pressure is applied to the space above the solution to push the solution to the filter side, most of the solution can be delivered to the filter 30. An on / off valve 13 is installed on the solution discharge pipe 12 between the pressure vessel 10 and the filter 30. In addition, a pressure gauge 11 may be connected to the pressure vessel 10 to measure the pressure inside the pressure vessel 10.

[0063] The binder solution 1 pushed up from the pressure vessel 10 is transported to the filter through the pipe 12. At this time, the filter 30 is an online filter installed in series in the pipe. The online filter is a filter that is installed in the pipeline in sequence so that the solution flow through the pipeline passes through the filter and continuously enters the subsequent pipe. Therefore, when the online filter is used, the binder solution passing through the pipe and the filter is not exposed to the outside during the filtering process. Therefore, it can be prevented from being contaminated by the external environment during the filtering process for dissolution quality evaluation.

[0064] Figure 2 is shown as Figure 1 Photograph of the components of the inline filter that make up the system. Figure 2 The filter 30 includes a filter member 31, an elastic member 32 pressing the filter member 31, and a housing 33 accommodating the filter member 31 and the elastic member 32. The elastic member 32 fixes the filter member 31 and makes the filter member 31 closely connected to the housing, thereby preventing the solution from leaking. In addition, the in-line filter 30 includes a gasket 34 for preventing the solution from leaking. The front end and the rear end of the filter are connected to the pipe.

[0065] The pore size of the filter member 31 can be variously selected in consideration of the type of binder used, the flow rate of the solution, and foreign matter characteristics (e.g., the size of undissolved matter, etc.) As described above, a filter member having a suitable pore size in the range of 0.5 μm to 100 μm can be selected.

[0066] The flow rate of the binder solution filtered in the filter is measured in the flow rate measuring unit 40. For example, the flow rate measuring unit 40 may be an electronic scale. A container (e.g., a beaker) is mounted on the electronic scale, and the flow rate of the filtered binder solution falling into the beaker can be measured. The flow rate measuring unit can measure the cumulative amount of the solution that has been filtered for a predetermined time.

[0067] In addition, the flow rate determination unit 40 can measure the time point when the flow velocity of the adhesive solution reaches a predetermined specific value in consideration of the initial flow rate. For example, the flow velocity of the solution falling in the container can be measured at fixed time intervals, and the flow velocity per second in a specific time period can be obtained by calculating the mean value of the flow velocity. If the flow velocity per second is obtained, the flow velocity and the initial flow velocity (g / minute) per minute can be obtained. In addition, since the flow velocity per second decreases along with the filtration time, the time point when the flow velocity reaches a specific value can be calculated by calculating the change of the flow velocity per second and the flow velocity reduction time. Therefore, in this manual, the time point when the flow velocity reaches a predetermined specific value in consideration of the initial flow velocity means until the initial flow velocity is reduced to the time spent by the specific flow velocity.

[0068] The flow rate measuring unit 40 is connected to the determination unit 50, and the flow rate data measured in the flow rate measuring unit 40 is communicated to the determination unit 50. The determination unit 50 can calculate the accumulated amount of filtration and the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate through a predetermined program.

[0069] The dissolution quality of the target binder solution can be evaluated by the cumulative amount filtered and the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate. For example, when the same filter is used, it can be said that a solution with a large cumulative amount filtered has better dissolution quality than a solution with a small cumulative amount filtered. Since the insoluble matter in the solution adheres to the filter and the solution from which the insoluble matter has been removed passes through the filter, it can be said that the solution with a large cumulative amount filtered has good dissolution quality.

[0070] Furthermore, a solution in which the flow rate reaches a specific value predetermined in consideration of the initial flow rate at a later time point, for example, a solution in which the flow rate reaches a value corresponding to 80% of the initial flow rate at a later time point, has a better dissolution quality than a solution in which the flow rate reaches a value corresponding to 80% of the initial flow rate at an earlier time point. The fact that the time required to reduce to a flow rate corresponding to 80% of the initial flow rate is long means that the filter is less clogged. Therefore, in general, a solution in which the flow rate reaches a specific value predetermined in consideration of the initial flow rate at a later time point is excellent in dissolution quality.

[0071] However, the present invention focuses on which filter should be used to reduce the time required for dissolution quality evaluation, rather than on evaluating the dissolution quality of the binder solution itself through the filter determination system 100 .

[0072] To this end, the determination unit 50 does not only determine the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate. Instead, the determination unit 50 repeats the flow rate determination for each filter having different pore sizes, and determines the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate for each filter, thereby determining a filter having a pore size within the optimal pore size range based on the information of the time point. Specifically, the determination unit can determine a filter having a time point equal to or less than a predetermined time point as a filter having a pore size within the optimal pore size range. That is, the dissolution quality of the solution with a later time point at which the flow rate reaches a specific value predetermined in consideration of the initial flow rate is excellent, but if too much time is spent in evaluating the time point, the practicality of the evaluation of the dissolution quality of the binder solution is greatly reduced. These time points are different depending on the pore size of the filter used. Therefore, when the flow rate is determined by filtering the binder solution, the filter pore size that can quickly evaluate the defects of the binder solution affects the manufacturing productivity of the binder solution and the electrode slurry using the binder solution. The determination unit is capable of determining, for each filter, the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate, and determining the filter having a pore size within the optimal pore size range by comparing the time points. To this end, the determination unit has a predetermined program for determining, for filters of different pore sizes, the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate.

[0073] The process of determining the filter by the determination unit 50 will be described in detail with reference to the following method and embodiment of determining the filter.

[0074] Figure 3 This is a flowchart showing the procedure of the filter determination method for evaluating the dissolution quality of the secondary battery binder solution according to the present invention.

[0075] As shown in the figure, the filter determination method of the present invention comprises: injecting a predetermined amount of adhesive solution into a pressure vessel ( Figure 3 step (a)); transferring the binder solution to the filter by supplying a pressure medium of a predetermined pressure to the pressure vessel ( Figure 3 step (b)); filtering the binder solution using the filter ( Figure 3 step (c)); determining the flow rate of the binder solution through the filter ( Figure 3 step (d)); repeatedly measuring the flow rate by using each filter with different pore sizes, measuring the time point when the flow rate reaches a specific value predetermined taking into account the initial flow rate ( Figure 3 step (e)); and determining the filter having the time point equal to or less than the predetermined time point as a filter having a pore size within the optimal pore size range ( Figure 3 step (f)).

[0076] The process of placing the binder solution in the pressure vessel, providing a pressure medium to the pressure vessel to transfer the binder solution to the filter (e.g., an in-line filter), filtering the binder solution in the filter, and measuring the flow rate of the binder solution that has passed through the filter using a flow rate measuring unit (e.g., an electronic scale) has been described above with reference to Figure 1 , 2 describe.

[0077] In the method for determining the filter of the present invention, in order to determine a filter having a pore size within the optimal pore size range, the flow rate is repeatedly measured for filters with different pore sizes, thereby determining the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate for the filter. As described above, a solution having a late time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate has good dissolution quality, but if it is too late, too much time is spent in evaluating the solution, thereby reducing the productivity of the dissolution quality evaluation. Therefore, the present invention not only uses the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate to evaluate the dissolution quality, but also determines the filter with the optimal pore size by comparing the time points by pore size.

[0078] Specifically, a filter having the time point equal to or less than the predetermined time point is determined as a filter having a pore size within the optimal pore size range. The predetermined time point may be a time point when the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate is the earliest. In this case, a filter having a pore size when the time point when the flow rate reaches the specific value predetermined in consideration of the initial flow rate becomes the minimum value may become the optimal filter.

[0079] The term "less than a predetermined time" means that the time taken to determine the time point becomes less than a specific time, such as 10 minutes, 20 minutes, or 30 minutes. A filter having a pore size within the following pore size range in which the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate is equal to or less than a predetermined value can be determined as a filter having a pore size within the optimal pore size range.

[0080] The predetermined value may be changed according to the type of binder solution, the pore size of the filter, the type and size of the insoluble matter in the solution, the mixing time of the binder solution, the mixing temperature, and the type of mixing blades used. Importantly, regardless of the specifications of the binder solution, when the binder solution is filtered for each pore size according to the filter determination method of the present invention, the filter at the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate becomes the minimum value can be determined as a filter within the optimal range.

[0081] In addition, any adhesive commonly used in the relevant field can be used as a solute for a secondary battery electrode adhesive solution. For example, the adhesive as the solute of the adhesive solution can be selected from at least one of the following groups: non-aqueous adhesives, such as polyvinylidene fluoride-to-hexafluoropropylene (PVDF-to-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM or polytetrafluoroethylene (PTFE); aqueous adhesives, such as acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR) or acrylic rubber; and polymer resins, such as hydroxyethyl cellulose or carboxymethyl cellulose.

[0082] In addition, the solvent of the secondary battery electrode binder solution may be one selected from the group consisting of: an organic solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or dimethylacetamide, and water. As long as the electrode active material, the binder and the conductive material are dissolved and dispersed in consideration of the coating thickness and manufacturing yield of the electrode active material slurry, the amount of solvent used is sufficient.

[0083] In the binder solution for secondary batteries, a PVDF solution or a CMC solution suitable for evaluating the dissolution quality by a filtration method using an online filter can be used in the present invention. As a PVDF solution, a binder solution obtained by dissolving a predetermined content of PVDF as a solute in NMP as a solvent can be used. As a CMC solution, a binder solution obtained by dissolving a predetermined content of CMC in water can be used. As long as the binder solution can dissolve solids by mixing with electrode slurry and conductive material, the concentration of the binder solution is sufficient. Typically, a PVDF solution with a concentration of 1% to 15% and a CMC solution with a concentration of 0.1% to 10% can be used.

[0084] Example

[0085] Hereinafter, the present invention will be described in detail, but the present invention is not limited to these embodiments.

[0086] Example 1

[0087] PVDF powder was poured into NMP and stirred at 50° C. for 50 minutes to prepare a PVDF solution A having a concentration of 9%.

[0088] Place 1 gallon (3.7854 liters) of solution A into Figure 1A pressure vessel is placed in a pressure vessel, and 3.5 bar of nitrogen from a nitrogen source is added to the pressure vessel, thereby transferring the solution A in the pressure vessel to the filter to be filtered. The filter is an F1 series online filter of Hy-Lok Korean Company, and the filter member used is a stainless steel depth filter. The flow rate of the filtered solution is measured by using an electronic scale (GP30K electronic scale of AND Company), thereby measuring the cumulative amount of filtration and the time point when the flow rate reaches a specific value predetermined considering the initial flow rate. The initial flow rate measured by using each pore size of 0.5μm, 2μm, 7μm and 15μm and the time point when the flow rate reaches a specific value predetermined considering the initial flow rate are shown in Table 1 below.

[0089] In addition, based on the following Table 1, the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate in Example 1 is shown as a function of the filter pore size. Figure 4 .

[0090] Table 1

[0091]

[0092] As shown in Table 1 above and Figure 4 As shown, the filter with a pore size of 7 μm shows the minimum value at all time points when the flow rate reaches a specific value predetermined in consideration of the initial flow rate. That is, it can be seen that the filter with a pore size of 7 μm is the optimal pore size filter that can minimize the time required for the evaluation of the dissolution quality of Solution A.

[0093] In the filter with large pore size (i.e., the pore size of 15 μm of Example 1-4), the speed of insoluble matter filtering in the filter is excellent, but because the small insoluble matter passes through the filter, it takes a long time to reduce to a specific flow rate. This is because the size of most insoluble matter in PVDF is between 7 μm and 15 μm. In addition, in the case of a filter with a small pore size, since the filter is blocked by insoluble matter faster, the time point when the expected flow rate reaches a specific value predetermined in consideration of the initial flow rate will be accelerated. However, since the initial flow rate is small due to the small pore size, the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate is not accelerated in proportion to the pore size. Therefore, according to the dissolution quality or the size of the insoluble matter in the solution, the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate changes with the pore size of the filter. Therefore, it can be seen that the filter with the best pore size can be determined according to the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate.

[0094] Furthermore, the pore size within the optimal range may be changed depending on the specific flow rate reduction time point selected as the determination standard. For example, if 50% of the initial flow rate is used as the standard, a filter within the pore size range for a time of less than 40 minutes may be used as a filter having a pore size within the optimal pore size range. That is, the optimal pore size is 7 μm, and the time is 38 minutes, which is the shortest time, but if 40 minutes is the standard time, then according to Figure 4 , filters having pore sizes in the range of 6.2 μm to 8 μm can also be determined as filters having pore sizes within the optimal pore size range.

[0095] Alternatively, if the time point at which the flow rate reaches 80% of the initial flow rate is used as a criterion, a pore size of 7 μm becomes the optimal pore size when the time point is 8 minutes, and if the reduction time point is set to 10 minutes or less, then according to Figure 4 , the pore size range of 5.5 μm to 9 μm can be determined as the optimal pore size.

[0096] Example 2

[0097] The PVDF solution having the same composition as in Example 1 was stirred at 50° C. for 50 minutes while changing the type of stirring blades, thereby preparing Solution B. Solution B was filtered using a filter determination system under the same conditions as in Example 1, and the measurement was repeated using filters having different pore sizes of 2 μm and 7 μm. In this experiment, the initial flow rate and the time point when the flow rate reached a specific value predetermined in consideration of the initial flow rate are shown in Table 2 below.

[0098] Table 2

[0099]

[0100] In the case of Example 2, the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate is slightly different from that in Example 1, but the fact that the pore size 7 μm shows the minimum time is the same in Examples 1 and 2. In addition, the time point when the flow rate reaches 50% of the initial flow rate is equal to or less than 40 minutes, and the time point when the flow rate reaches 80% of the initial flow rate is equal to or less than 10 minutes. Therefore, the filter having a pore size within the corresponding pore size range (about 7 μm) can be determined as a filter within the optimal pore size range.

[0101] In sample A of Example 1 and sample B of Example 2, the time point when the flow rate reaches 80% of the initial flow rate is less than 10 minutes. This means that the initial flow rate is reduced to 80% of the initial flow rate in a very short period of 10 minutes, and thus sample A and sample B cannot be regarded as adhesive solutions of good quality. In addition, in the adhesive solutions of sample A and sample B, the flow rate continues to decrease to 70% or 50% of the initial flow rate, and thus the adhesive solutions can be regarded as adhesive solutions of poor quality. However, as shown above, when the dissolution quality of the adhesive solution of poor quality is examined, it can be seen that when a filter with a pore size of 7 μm (optimal pore size) is used for testing, the inspection time can be reduced to a minimum.

[0102] Example 3

[0103] The PVDF solution having the same composition as in Example 1 was stirred at 70° C. for 4 hours while changing the type of stirring blades, thereby preparing Solution C. Since different stirring blades and different stirring times were used, it is expected that the dissolution quality and filtration characteristics of Solution C are different from those of Solution A and Solution B. Solution C was filtered by a filter determination system under the same conditions as in Example 1, and the measurement was repeated using filters with different pore sizes of 2 μm and 7 μm. In this experiment, the initial flow rate and the time point when the flow rate reached a specific value predetermined in consideration of the initial flow rate are shown in Table 3 below.

[0104] Table 3

[0105]

[0106] The flow rate of the adhesive solution of sample C remained unchanged after decreasing to 80% of the initial flow rate. In addition, since the time required to reach the time point when the flow rate reached 80% of the initial flow rate in sample C was much longer than that in samples A and B, it was determined to be a good quality adhesive solution.

[0107] In addition, in Example 3, the time required to reach the time point when the flow rate reaches 80% of the initial flow rate is 42 minutes in the case of using a pore size of 7 μm, and 795 minutes in the case of using a pore size of 2 μm. In the case of using a pore size of 2 μm, the time is too long, so it is difficult to evaluate the dissolution quality. In Example 3-1, the time required to reach the time point when the flow rate reaches 80% of the initial flow rate is 42 minutes. Therefore, it can be seen that the filter with a pore size of 7 μm (optimum pore size) is effective in determining the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate of a good product.

[0108] Above, the present invention has been described in more detail by the drawings and embodiments. Accordingly, the embodiments described in the specification and the configurations described in the drawings are only the most preferred embodiments of the present invention and do not represent all technical concepts of the present invention. It should be understood that when submitting this application, there may be various equivalents and variants that replace them.

Claims

1. A filter determination system for evaluating the dissolution quality of a binder solution for secondary battery electrodes, the system comprising: a pressure vessel containing a binder solution; a pressure medium supply source, the pressure medium supply source supplying a pressure medium of a predetermined pressure to the pressure vessel; a filter connected to the pressure vessel by a tube; a flow rate measuring unit for measuring a flow rate of the binder solution filtered by the filter; as well as A determination unit that determines a time point when the flow rate reaches a specific value predetermined in consideration of an initial flow rate by repeatedly measuring the flow rate using filters having different pore sizes, and determines a filter having a pore size within an optimal pore size range based on the time point, the specific value being a percentage compared to the initial flow rate.

2. The system according to claim 1, wherein the determination unit determines a filter having the time point equal to or less than a predetermined time point as a filter having a pore size within an optimal pore size range, the predetermined time point being the earliest time point when the flow rate reaches a specific value predetermined in consideration of an initial flow rate. 3 . The system according to claim 1 , wherein the pressure medium is nitrogen gas, and the nitrogen gas having a predetermined pressure is supplied from the pressure medium supply source to the pressure container.

4. The system of claim 1, wherein the tube extends into the pressure vessel and an end of the tube is mounted adjacent a bottom of the pressure vessel.

5. The system of claim 1, wherein the filter is an in-line filter installed in series in the tube. 6 . The system according to claim 5 , wherein the in-line filter comprises a filter member, an elastic member pressing the filter member, and a housing accommodating the filter member and the elastic member.

7. A filter determination method for evaluating the dissolution quality of a binder solution for a secondary battery, the method comprising: injecting a predetermined amount of adhesive solution into the pressure vessel; transferring the binder solution to the filter by supplying a pressure medium of a predetermined pressure to the pressure container; filtering the binder solution using the filter; measuring a flow rate of the binder solution through the filter; Repeating the measurement of the flow rate by using each filter having a different pore size, measuring the time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate, the specific value being a percentage compared to the initial flow rate; and The filter having the time point equal to or less than a predetermined time point is determined as a filter having a pore size within the optimal pore size range, wherein the predetermined time point is the earliest time point when the flow rate reaches a specific value predetermined in consideration of the initial flow rate. 8 . The method according to claim 7 , wherein a filter having a pore size that makes the time point the earliest time point is determined as a filter having an optimal pore size. 9 . The method according to claim 7 , wherein the binder as a solute of the binder solution is at least one selected from the group consisting of: a non-aqueous binder, an aqueous binder.

10. The method according to claim 7, wherein the binder as the solute of the binder solution is a polymer resin. 11 . The method according to claim 9 , wherein a solvent of the binder solution is at least one selected from the group consisting of an organic solvent and water. 12 . The method according to claim 7 , wherein the binder solution is a polyvinylidene fluoride solution obtained by dissolving a predetermined content of polyvinylidene fluoride in an N-methylpyrrolidone solvent.

13. The method according to claim 12, wherein: The filter whose time point when the flow rate decreases to 50% of the initial flow rate is less than the predetermined time point is determined to be a filter having a pore size within the optimal pore size range.

14. The method according to claim 12, wherein: The filter for which the time point at which the flow rate decreases to 80% of the initial flow rate is less than the predetermined time point is determined to be a filter having a pore size within the optimal pore size range.

15. The method according to claim 9, wherein the non-aqueous binder is at least one selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, and polytetrafluoroethylene.

16. The method according to claim 7, wherein the binder is at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polyacrylic acid. 17 . The method according to claim 7 , wherein the adhesive is at least one selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber, and acrylic rubber.

18. The method according to claim 7, wherein the binder is at least one selected from the group consisting of hydroxyethyl cellulose and carboxymethyl cellulose. 19 . The method according to claim 11 , wherein the organic solvent is at least one selected from the group consisting of N-methylpyrrolidone, dimethylformamide, acetone, and dimethylacetamide.

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