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]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0175750 dated December 15, 2022, and all contents disclosed in the documents 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 deterioration (gelation, particle agglomeration, etc.) of a positive electrode slurry by an electrochemical method. [Background technology]

[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 the electrode slurry.

[0004] The electrode slurry contains an active material, and specifically, is prepared by kneading the active material, a conductive material, a binder, and a solvent.

[0005] Although rheological properties such as viscosity are regularly monitored at electrode slurry factories, electrode slurries that have undergone unexpected physical deterioration (partial coagulation, precipitation, etc.) may be introduced into the electrode process, which may ultimately have a negative impact on the performance and lifespan of the battery.

[0006] Specifically, if a slurry with altered rheological properties is applied to a current collector under existing coating conditions, it may cause defects in the uniformity of the electrode interface, which may lead to battery failure.

[0007] To solve this problem, the physical properties of the electrode slurry can be measured using a viscometer, but this requires expensive equipment and has the drawback of being difficult to detect inhomogeneous phenomena such as precipitation and coagulation of fine slurry (gelation, agglomeration, etc.).

[0008] Therefore, there is a need for a technology that can accurately and quickly detect the physical deterioration state of an electrode slurry in a simple manner. Summary of the Invention [Problem to be solved by the invention]

[0009] 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.

[0010] The technical problems that the present invention aims to solve are not limited to the above-mentioned technical problems, and 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) of preparing a positive electrode slurry by mixing a positive electrode active material, a conductive material, a binder, and a solvent; an electrode insertion step (step S20) of inserting a working electrode, a counter electrode, and a reference electrode into the positive electrode slurry; a first impedance acquisition step (step S30) of measuring impedance at 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) of measuring impedance at the set frequency after a set time has elapsed after the first impedance acquisition step (step S30) to obtain a second impedance value; and a determination step (step S50) of determining a state of the positive electrode slurry by comparing an absolute value of the first impedance with an absolute value of the second impedance. Effect of the Invention

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

[0013] The electrode slurry inspection method of the present invention can quantify physical deterioration (gelation, particle agglomeration, etc.) of the positive electrode slurry by an electrochemical method.

[0014] The electrode slurry inspection method of the present invention makes it possible to predict the coagulation level of the electrode slurry only from the absolute impedance value in the low frequency range. [Brief description of the drawings]

[0015] [Figure 1] 1 is a block diagram showing an electrode slurry inspection method of the present invention; [Diagram 2] 1 is a graph showing an impedance spectrum. [Diagram 3] 13 is a graph showing results of an experimental example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The electrode slurry inspection method of the present invention includes a positive electrode slurry preparation step (step S10) of preparing a positive electrode slurry by mixing a positive electrode active material, a conductive material, a binder, and a solvent; an electrode insertion step (step S20) of inserting a working electrode, a counter electrode, and a reference electrode into the positive electrode slurry; a first impedance acquisition step (step S30) of measuring impedance 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) of measuring impedance from the set frequency after a set time has elapsed after the first impedance acquisition step (step S30) to obtain a second impedance value; and a determination step (step S50) of determining a state of the positive electrode slurry by comparing an absolute value of the first impedance with an absolute value of the second impedance.

[0017] In the positive electrode slurry preparation step (step S10) of the electrode slurry inspection method of the present invention, the positive electrode active material contains 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 including 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 including polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber (SBR), and a mixture 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 acquiring step (step S30) and the second impedance acquiring step (step S40) of the electrode slurry inspecting method of the present invention, the set frequency may be 10 Hz or less.

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

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

[0024] 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 of acquiring impedance spectrum data for a plurality of frequencies through the working electrode, the counter electrode, and the reference electrode; a function acquisition step of acquiring, through fitting, a function having a real part as an independent variable and an imaginary part as a dependent variable in the impedance spectrum data; and a set frequency selection step of selecting the set frequency from among frequencies corresponding to impedance values ​​having a real part larger than the real part at a maximum point in the function.

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this process, the size and shape of components shown in the drawings may be exaggerated for clarity and convenience of explanation. In addition, terms specifically defined in consideration of the configuration and operation of the present invention may vary depending on the intention or practice of a user or operator. The definition of such terms should be based on the overall content of 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, and Fig. 3 is a graph showing the results of an experimental example.

[0027] The electrode slurry inspection method of the present invention will be described in detail below with reference to FIGS.

[0028] The electrode slurry inspection method of the present invention predicts changes in the rheological properties of an electrode slurry by analyzing the impedance of the electrode slurry measured at low frequencies.

[0029] The electrode slurry inspection method of the present invention measures the initial state of the electrode slurry after it is produced for about 10 seconds, records the initial state, and then measures the electrode slurry for about 10 seconds immediately before it is used, comparing the current state with the initial state to grasp the degree of deterioration of the electrode slurry. That is, the electrode slurry inspection method of the present invention can quickly grasp whether the electrode slurry is in a usable state by simply measuring the electrode slurry that has been stored for a long time for about 10 seconds.

[0030] As shown in FIG. 1, the electrode slurry inspection method of the present invention includes a positive electrode slurry preparation step (step S10) of preparing a positive electrode slurry by mixing a positive electrode active material, a conductive material, a binder, and a solvent; an electrode insertion step (step S20) of inserting a working electrode, a counter electrode, and a reference electrode into the positive electrode slurry; a first impedance acquisition step (step S30) of measuring impedance at 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) of measuring impedance at the set frequency after a set time has elapsed after the first impedance acquisition step (step S30) to obtain a second impedance value; and a determination step (step S50) of determining a state of the positive electrode slurry by comparing an absolute value of the first impedance with an absolute value of the second impedance.

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

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

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

[0034] In the positive electrode slurry preparation step (step S10), the binder is selected from the group including polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber (SBR), and a mixture of two or more thereof.

[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 may be 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 may be 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 may be 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 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 10 Hz or less. As described above, the electrode slurry inspection method of the present invention measures the electrode slurry for about 10 seconds at the beginning of its preparation and measures it for about 10 seconds immediately before use, thereby grasping the deterioration of the electrode slurry and grasping 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) refers to measuring the initial state of the electrode slurry. The second impedance acquisition step (step S40) refers to measuring 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 acquiring step (step S40), the set time is 10 hours or more. That is, the electrode slurry inspection method of the present invention can quickly grasp the rheological deterioration of the electrode slurry stored for a long period of time of 10 hours or more.

[0040] Specifically, when the second impedance absolute value measured by the electrode slurry inspection method is divided by the first impedance absolute value and the value is equal to or less than 2, the electrode slurry is determined 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 of acquiring impedance spectrum data for a plurality of frequencies through the working electrode, the counter electrode, and the reference electrode; a function acquisition step of acquiring, through fitting, a function having a real part as an independent variable and an imaginary part as a dependent variable in the impedance spectrum data; and a set frequency selection step of selecting the set frequency from among frequencies corresponding to impedance values ​​having a real part larger than the real part at a maximum point in the function.

[0042] If an AC power source having a plurality of frequencies is applied to the electrode slurry and the impedance is measured, a different impedance value can be obtained for each frequency. If the impedance values ​​thus obtained are displayed on a complex plane by applying a negative value to the imaginary part of the impedance, a graph as shown in FIG. 2 can be obtained. In this case, the (0,0) coordinate is the largest high-frequency impedance value, and the lower the frequency impedance value, the lower the frequency impedance value. Furthermore, if the electrode slurry is altered, the diameter of the semicircle part in the graph of FIG. 2 is enlarged. Therefore, if the electrode slurry is altered, the point P shown in FIG. 2 becomes further away from the origin, and the absolute impedance values ​​in the normal state and the altered state show a clear difference. The electrode slurry inspection method of the present invention is capable of precise electrode slurry inspection by using the absolute value of the impedance at a frequency lower than the point P as a discrimination 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 measurement intervals, the positive electrode slurry was stored in an environment in which the positive electrode slurry could be altered and the solvent in the positive electrode slurry could be evaporated. The measurement of the positive electrode slurry was performed 11 times.

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

[0045] In Fig. 3, the parts connected by dotted lines are impedance values ​​at a low frequency of 1mHz. As shown in Fig. 3, at low frequencies, the absolute impedance value shows a clear difference depending on the degree of degradation (time exposed to the space where degradation can occur).

[0046] It can be seen that the difference between the absolute impedance value at the initial measurement (length A in FIG. 3) and the absolute impedance value 16 hours after the initial measurement (length B in FIG. 3) is more than twice as large.

[0047] Although the embodiment of the present invention has been described above, it is merely an example, and a person skilled in the art will understand that various modifications and equivalent embodiments are possible. Therefore, the true technical scope of the present invention should 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 the electrode slurry in a simple manner.

[0049] The electrode slurry inspection method of the present invention can quantify physical deterioration (gelation, particle agglomeration, etc.) of the positive electrode slurry by an electrochemical method.

[0050] The electrode slurry inspection method of the present invention makes it possible to predict the coagulation level of the electrode slurry only from the absolute impedance value in the low frequency range.

Claims

1. A positive electrode slurry preparation step (step S10) of preparing a positive electrode slurry by mixing a positive electrode active material, a conductive material, a binder, and a solvent; an electrode insertion step (step S20) of inserting a working electrode, a counter electrode, and a reference electrode into the positive electrode slurry; A first impedance acquisition step (step S30) of measuring impedance at a set frequency through the working electrode, the counter electrode, and the reference electrode to acquire a first impedance value; a second impedance acquisition step (S40) of measuring impedance from the set frequency to acquire a second impedance value after a set time has elapsed since the first impedance acquisition step (S30); a determination step (S50) of determining a state of the positive electrode slurry by comparing the absolute value of the first impedance with the absolute value of the second impedance; The electrode slurry inspection method includes:

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

3. In the positive electrode slurry preparation step (step S10), 2. The electrode slurry inspection method of claim 1, wherein the conductive material is selected from the group including carbon black, conductive fibers, metal powders, conductive whiskers, conductive metal oxides, conductive polymers, and mixtures of two or more thereof.

4. In the positive electrode slurry preparation step (step S10), 2. The electrode slurry inspection method of claim 1, wherein the binder is selected from the group including polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber (SBR), and mixtures of two or more thereof.

5. In the electrode insertion step (step S20), The working electrode, the counter electrode, and the reference electrode are provided in a rectangular plate shape, 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; 2. The electrode slurry inspection method according to claim 1, 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. In the first impedance acquisition step (step S30) and the second impedance acquisition step (step S40), The electrode slurry inspection method according to claim 1 , wherein the set frequency is 10 Hz or less.

7. In the second impedance acquisition step (step S40), The electrode slurry inspection method according to claim 6 , wherein the set time is 10 hours or more.

8. A positive electrode slurry, wherein a value obtained by dividing an absolute value of the second impedance measured by the electrode slurry inspection method according to claim 7 by an absolute value of the first impedance is 2 or less.

9. Between the electrode insertion step (step S20) and the first impedance acquisition step (step S30), acquiring impedance spectrum data for a plurality of frequencies through the working electrode, the counter electrode, and the reference electrode; A function acquisition step of acquiring a function having a real part as an independent variable and an imaginary part as a dependent variable through fitting the impedance spectrum data; a set frequency selecting step of selecting the set frequency from among frequencies corresponding to impedance values ​​having a real part larger than the real part at a maximum point in the function; The electrode slurry inspection method of claim 1 , further comprising:

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