Electrode slurry inspection method

Abstract

The present invention relates to an electrode slurry inspection method, and more particularly, to an electrode slurry inspection method for quantifying physical deterioration (gelation, particle agglomeration, etc.) of a positive electrode slurry by an electrochemical method.

Description

Technical Field

[0006] , , ,

[0007] ,

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0175750 filed on December 15, 2022, and all the contents disclosed in the document of the Korean Patent Application are incorporated herein by reference.

[0002] The present invention relates to an electrode slurry inspection method, and more particularly, to an electrode slurry inspection method for quantifying physical degradation (such as gelation and particle agglomeration) of a positive electrode slurry by an electrochemical method.

Background Art

[0003] In a secondary battery, an electrode can be manufactured by applying an electrode slurry to a substrate such as a metal foil and then drying it.

[0004] The electrode slurry contains an active material, and specifically, an active material, a conductive material, a binder, and a solvent are kneaded and provided.

[0005] Although rheology characteristics such as viscosity are regularly monitored in an electrode slurry factory, an electrode slurry with unforeseen physical degradation (such as partial coagulation and precipitation) is introduced into the electrode process. In such a case, it may ultimately have an adverse effect on the performance and lifespan of the battery.

[0006] Specifically, if a slurry with changed rheology characteristics is applied to a current collector under existing coating conditions, it may cause defects in the uniformity of the electrode interface state, etc., which may lead to battery defects.

[0007] To solve this problem, the physical properties of the electrode slurry can be measured through a viscometer, etc., but expensive measuring instruments are required, and there are difficulties in detecting non-uniform phenomena (such as gelation and agglomeration) such as fine slurry precipitation and coagulation.

[0008] Therefore, there is a need for a technology that can accurately and quickly detect the physical degradation state of electrode slurry using a simple method. [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention relates to an electrode slurry inspection method, and more specifically, to an electrode slurry inspection method that quantifies the physical degradation (gelation, particle agglomeration, etc.) of a positive electrode slurry using an electrochemical method.

[0010] The technical problems that this invention aims to solve are not limited to those described above, and any other technical problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0011] The electrode slurry inspection method of the present invention includes: a positive electrode slurry preparation step (step S10) in which a positive electrode slurry is prepared by mixing a positive electrode active material, a conductive material, a binder and a solvent; an electrode insertion step (step S20) in which a working electrode, a counter electrode and a reference electrode are inserted into the positive electrode slurry; a first impedance acquisition step (step S30) in which the impedance is measured from a set frequency through the working electrode, the counter electrode and the reference electrode to obtain a first impedance value; a second impedance acquisition step (step S40) in which the impedance is measured from the set frequency to obtain a second impedance value after a set time has elapsed since the first impedance acquisition step (step S30); and a determination step (step S50) in which the state of the positive electrode slurry is determined by comparing the absolute value of the first impedance and the absolute value of the second impedance. [Effects of the Invention]

[0012] The electrode slurry inspection method of the present invention can accurately and quickly detect the physical deterioration state of an electrode slurry in a simple manner.

[0013] The electrode slurry inspection method of the present invention can quantify the physical degradation of the positive electrode slurry (such as gelation and particle agglomeration) using an electrochemical method.

[0014] The electrode slurry inspection method of the present invention makes it possible to predict the solidification level of the electrode slurry using only the absolute value of the impedance in the low-frequency region. [Brief explanation of the drawing]

[0015] [Figure 1] This is a block diagram showing the electrode slurry inspection method of the present invention. [Figure 2] This is a graph showing the impedance spectrum. [Figure 3] This graph shows the results from experimental examples. [Modes for carrying out the invention]

[0016] The electrode slurry inspection method of the present invention includes: a positive electrode slurry preparation step (step S10) in which a positive electrode slurry is prepared by mixing a positive electrode active material, a conductive material, a binder and a solvent; an electrode insertion step (step S20) in which a working electrode, a counter electrode and a reference electrode are inserted into the positive electrode slurry; a first impedance acquisition step (step S30) in which an impedance is measured from a set frequency through the working electrode, the counter electrode and the reference electrode to obtain a first impedance value; a second impedance acquisition step (step S40) in which an impedance is measured from the set frequency to obtain a second impedance value after a set time has elapsed since the first impedance acquisition step (step S30); and a determination step (step S50) in which the state of the positive electrode slurry is determined by comparing the absolute value of the first impedance and the absolute value of the second impedance.

[0017] In the electrode slurry inspection method of the present invention, in the positive electrode slurry preparation step (step S10), the positive electrode active material contains a lithium metal oxide.

[0018] In the positive electrode slurry preparation step (step S10) of the electrode slurry inspection method of the present invention, the conductive material is selected from the group comprising carbon black, conductive fibers, metal powder, conductive whiskers, conductive metal oxides, conductive polymers, and mixtures of two or more of these.

[0019] In the positive electrode slurry preparation step (step S10) of the electrode slurry inspection method of the present invention, the binder is selected from the group comprising polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber (SBR), and mixtures of two or more of these.

[0020] In the electrode insertion step (step S20) of the electrode slurry inspection method of the present invention, the working electrode, the counter electrode, and the reference electrode are provided in the shape of a rectangular plate, the working electrode is formed to have a width of 10 to 50 mm, a thickness of 0.1 to 2 mm, and a length of 10 to 50 mm, the counter electrode is formed to have a width of 10 to 50 mm, a thickness of 0.1 to 2 mm, and a length of 10 to 50 mm, and the reference electrode is formed to have a width of 10 to 50 mm, a thickness of 0.1 to 2 mm, and a length of 10 to 50 mm.

[0021] In the first impedance acquisition step (step S30) and the second impedance acquisition step (step S40) of the electrode slurry inspection method of the present invention, the set frequency may be 10 Hz or less.

[0022] In the second impedance acquisition step (step S40) of the electrode slurry inspection method of the present invention, the set time may be 10 hours or more.

[0023] For the positive electrode slurry measured by the electrode slurry inspection method of the present invention, the value obtained by dividing the absolute value of the second impedance by the absolute value of the first impedance may be 2 or less.

[0024] The electrode slurry inspection method of the present invention further includes an impedance spectrum acquisition step of acquiring impedance spectrum data for a plurality of frequencies through the working electrode, the counter electrode, and the reference electrode between the electrode insertion step (step S20) and the first impedance acquisition step (step S30); a function acquisition step of acquiring, through fitting, a function having the real part as an independent variable and the imaginary part as a dependent variable with the impedance spectrum data; a set frequency selection step of selecting the set frequency from among the frequencies corresponding to impedance values having a real part larger than the real part at the maximum point in the function.

[0025] Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. In this process, the sizes, shapes, etc. of the components shown in the drawings may be exaggerated for clarity and convenience of explanation. Also, terms specifically defined in consideration of the configuration and operation of the present invention may vary depending on the intention or convention of the user and operator. Definitions for such terms must be made based on the content throughout this specification.

[0026] FIG. 1 is a block diagram showing the electrode slurry inspection method of the present invention. FIG. 2 is a graph showing an impedance spectrum. FIG. 3 is a graph showing the results of an experimental example.

[0027] Hereinafter, the electrode slurry inspection method of the present invention will be described in detail with reference to FIGS. 1 to 3.

[0028] The electrode slurry inspection method of the present invention predicts changes in the rheological properties of the electrode slurry by analyzing the impedance of the electrode slurry measured from a low frequency.

[0029] The electrode slurry inspection method of the present invention allows for the determination of the degree of deterioration of the electrode slurry by measuring the initial state of the electrode slurry for approximately 10 seconds in its newly manufactured state, recording the initial state, and then measuring the current state for approximately 10 seconds immediately before use, comparing it to the initial state. In other words, the electrode slurry inspection method of the present invention allows for the rapid determination of whether an electrode slurry that has been stored for a long time is in a usable state by simply measuring it for approximately 10 seconds.

[0030] As shown in Figure 1, the electrode slurry inspection method of the present invention includes: a positive electrode slurry preparation step (step S10) in which a positive electrode slurry is prepared by mixing a positive electrode active material, a conductive material, a binder and a solvent; an electrode insertion step (step S20) in which a working electrode, a counter electrode and a reference electrode are inserted into the positive electrode slurry; a first impedance acquisition step (step S30) in which an impedance is measured from a set frequency through the working electrode, the counter electrode and the reference electrode to obtain a first impedance value; a second impedance acquisition step (step S40) in which an impedance is measured from the set frequency to obtain a second impedance value after a set time has elapsed since the first impedance acquisition step (step S30); and a determination step (step S50) in which the state of the positive electrode slurry is determined by comparing the absolute value of the first impedance and the absolute value of the second impedance.

[0031] In the positive electrode slurry preparation stage (step S10), the positive electrode slurry is prepared by mixing and kneading the positive electrode active material, conductive material, binder, and solvent.

[0032] In the positive electrode slurry preparation step (step S10), the positive electrode active material contains a lithium metal oxide.

[0033] In the positive electrode slurry preparation step (step S10), the conductive material is selected from the group comprising carbon black, conductive fibers, metal powder, conductive whiskers, conductive metal oxides, conductive polymers, and mixtures of two or more of these.

[0034] In the cathode slurry preparation step (step S10), the binder is selected from the group comprising polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber (SBR), and mixtures of two or more of these.

[0035] In the electrode insertion step (step S20), the working electrode, the counter electrode, and the reference electrode are provided in the shape of a rectangular plate, the working electrode is formed to have a width of 10 to 50 mm, a thickness of 0.1 to 2 mm, and a length of 10 to 50 mm, the counter electrode is formed to have a width of 10 to 50 mm, a thickness of 0.1 to 2 mm, and a length of 10 to 50 mm, and the reference electrode is formed to have a width of 10 to 50 mm, a thickness of 0.1 to 2 mm, and a length of 10 to 50 mm.

[0036] The plate-shaped working electrode, counter electrode, and reference electrode are inserted into the positive electrode slurry at a certain distance apart from each other and are electrically connected to a power supply device that applies AC power and a measuring device for impedance measurement.

[0037] In the first impedance acquisition step (step S30) and the second impedance acquisition step (step S40), the set frequency is also 10 Hz or less. As mentioned above, the electrode slurry inspection method of the present invention allows for measurement for a little over 10 seconds in the initial stages of electrode slurry production and measurement for a little over 10 seconds immediately before use to grasp the deterioration of the electrode slurry and to determine whether the electrode slurry is in a usable state. This is achieved by measuring the impedance at a relatively low frequency of 10 Hz.

[0038] The first impedance acquisition step (step S30) represents the measurement of the initial state of the electrode slurry. The second impedance acquisition step (step S40) represents the measurement of the state of the electrode slurry immediately before use. Therefore, the set time corresponds to the time the electrode slurry has been stored.

[0039] In the second impedance acquisition step (step S40), the set time is 10 hours or more. In other words, the electrode slurry inspection method of the present invention can quickly grasp the rheological changes of an electrode slurry that has been stored for a long period of time of 10 hours or more.

[0040] Specifically, when the value obtained by dividing the absolute value of the second impedance measured by the electrode slurry inspection method by the absolute value of the first impedance is 2 or less, the electrode slurry is judged to be in a normal state.

[0041] The electrode slurry inspection method of the present invention further includes, between the electrode insertion step (step S20) and the first impedance acquisition step (step S30), an impedance spectrum acquisition step in which impedance spectrum data is acquired for multiple frequencies through the working electrode, the counter electrode and the reference electrode; a function acquisition step in which a function is acquired by fitting the impedance spectrum data, with the real part being the independent variable and the imaginary part being the dependent variable; and a set frequency selection step in which the set frequency is selected from among frequencies corresponding to impedance values ​​having a real part even larger than the real part at the maximum point of the function.

[0042] By applying AC power supplies of multiple frequencies to an electrode slurry and measuring its impedance, different impedance values ​​can be obtained for each frequency. If these obtained impedance values ​​are plotted on the complex plane with a negative sign applied to the imaginary part of the impedance, a graph like that shown in Figure 2 can be obtained. In this case, the (0,0) coordinate represents the highest high-frequency impedance value, and the impedance values ​​decrease as you move in the direction of the arrow. Furthermore, if the electrode slurry is altered, the diameter of the semicircle in the graph of Figure 2 expands. Therefore, if the electrode slurry is altered, point P shown in Figure 2 moves further away from the origin, and there is a clear difference between the absolute impedance values ​​in the normal state and the altered state. The electrode slurry inspection method of the present invention enables precise electrode slurry inspection by using the absolute value of the low-frequency impedance, even lower than point P, as the discriminant value.

[0043] Experimental example The impedance of the positive electrode slurry was measured at 8-hour intervals from a frequency band of 1 MHz to 1 mHz. During the 8-hour interval, the slurry was stored in an environment where the solvent could vaporize and the slurry could undergo deterioration. The positive electrode slurry was measured 11 times.

[0044] Figure 3 is a graph showing the impedance spectra for 11 measurements.

[0045] In Figure 3, the portion connected by the dotted line represents the impedance value at a low frequency of 1 mHz. As shown in Figure 3, it can be seen that at low frequencies, the absolute value of the impedance shows a clear difference depending on the degree of alteration (the time exposed to a space where alteration is possible).

[0046] The absolute impedance value at the initial measurement (length A in Figure 3) and the absolute impedance value after 16 hours have elapsed since the initial measurement (length B in Figure 3) show a difference of more than twofold.

[0047] Although embodiments of the present invention have been described above, these are merely illustrative, and those skilled in the art will understand that a wide variety of modifications and equivalent embodiments are possible. Therefore, the true scope of technical protection of the present invention must be determined by the claims. [Industrial applicability]

[0048] The electrode slurry inspection method of the present invention can accurately and quickly detect the physical deterioration state of an electrode slurry in a simple manner.

[0049] The electrode slurry inspection method of the present invention can quantify the physical degradation of the positive electrode slurry (such as gelation and particle agglomeration) using an electrochemical method.

[0050] The electrode slurry inspection method of the present invention makes it possible to predict the solidification level of the electrode slurry using only the absolute value of the impedance in the low-frequency region.

Claims

1. A positive electrode slurry preparation step (step S10) is performed by mixing the positive electrode active material, conductive material, binder and solvent to prepare the positive electrode slurry. The electrode insertion step (step S20) involves inserting the working electrode, counter electrode, and reference electrode into the positive electrode slurry, After steps S10 and S20, a first impedance acquisition step (step S30) is performed in which, in the initial state of the positive electrode slurry, the impedance is measured through the working electrode, the counter electrode and the reference electrode at a set frequency of 10 Hz or less to obtain a first impedance value. After 10 hours or more have elapsed since the first impedance acquisition step (step S30), a second impedance acquisition step (step S40) is performed in which the impedance is measured at the set frequency and the value of the second impedance is obtained. If the value obtained by dividing the absolute value of the second impedance by the absolute value of the first impedance is 2 or less, a determination step (step S50) is made in which it is determined that no rheological alteration has occurred in the positive electrode slurry. An electrode slurry inspection method, including [specific component].

2. In the aforementioned positive electrode slurry preparation step (step S10), The electrode slurry inspection method according to claim 1, wherein the positive electrode active material includes a lithium metal oxide.

3. In the aforementioned positive electrode slurry preparation step (step S10), The electrode slurry inspection method according to claim 2, wherein the conductive material is selected from the group comprising carbon black, conductive fibers, metal powder, conductive whiskers, conductive metal oxides, conductive polymers, and mixtures of two or more of these.

4. In the aforementioned positive electrode slurry preparation step (step S10), The electrode slurry inspection method according to claim 3, wherein the binder is selected from the group comprising fluorinated polyvinylidene-hexafluoropropylene copolymer (PVDF-co-HEP), fluorinated polyvinylidene, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber (SBR), and mixtures of two or more of these.

5. In the electrode insertion step (step S20), The working electrode, the counter electrode, and the reference electrode are provided in the shape of a rectangular plate. The working electrode is formed to have a width of 10 to 50 mm, a thickness of 0.1 to 2 mm, and a length of 10 to 50 mm. The aforementioned counter electrode is formed to have a width of 10 to 50 mm, a thickness of 0.1 to 2 mm, and a length of 10 to 50 mm. The electrode slurry inspection method according to claim 4, wherein the reference electrode is formed to have a width of 10 to 50 mm, a thickness of 0.1 to 2 mm, and a length of 10 to 50 mm.

6. Between the electrode insertion step (step S20) and the first impedance acquisition step (step S30), An impedance spectrum acquisition step in which impedance spectrum data is acquired for multiple frequencies through the working electrode, the counter electrode and the reference electrode, The function acquisition stage involves obtaining a function from the impedance spectrum data, where the real part is the independent variable and the imaginary part is the dependent variable, through fitting. A setting frequency selection step in which the setting frequency is selected from among frequencies corresponding to impedance values ​​having a real part larger than the real part at the local maximum point of the function, The electrode slurry inspection method according to claim 1, further comprising:

Images