Electrode slurry inspection method

Abstract

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

Description

Technical Field

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2022-0175750, filed on December 15, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a method for inspecting electrode slurry, and more particularly, to a method for inspecting electrode slurry for quantifying physical degradation (gelation, particle agglomeration, etc.) of positive electrode slurry using an electrochemical method. Background Art

[0003] For a secondary battery, an electrode may 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, it may be prepared by kneading the active material, a conductive material, a binder, and a solvent.

[0005] While rheological properties such as viscosity are regularly monitored in electrode slurry plants, electrode slurries with unexpected physical degradation (partial solidification, sedimentation, etc.) may be introduced into the electrode manufacturing process, which may ultimately have a negative impact on the performance and lifetime of the battery.

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

[0007] To solve this problem, the physical properties of the electrode slurry can be measured using a viscometer or the like, but this requires expensive measuring instruments and makes it difficult to detect uneven phenomena (gelation, agglomeration, etc.) such as precipitation and coagulation of fine slurry.

[0008] Therefore, there is a need for a method that can accurately and quickly detect the physical degradation state of electrode slurry in a simple manner. Summary of the invention

[0009] Technical issues

[0010] The present invention relates to a method for inspecting electrode slurry, and more particularly, to a method for inspecting electrode slurry for quantifying physical degradation (gelation, particle agglomeration, etc.) of positive electrode slurry using an electrochemical method.

[0011] The technical problems to be solved by the present invention are not limited to the above-mentioned technical problems, and ordinary technicians in the field to which the present invention belongs will clearly understand other unmentioned technical problems from the following description.

[0012] Technical Solution

[0013] The method for inspecting electrode slurry of the present invention may include:

[0014] a positive electrode slurry preparation step ( S10 ) of mixing a positive electrode active material, a conductive material, a binder, and a solvent to prepare a positive electrode slurry;

[0015] an electrode insertion step (S20) of inserting a working electrode, a counter electrode, and a reference electrode into the positive electrode slurry;

[0016] A first impedance acquisition step (S30), measuring impedance at a set frequency through the working electrode, the counter electrode and the reference electrode to obtain a first impedance value;

[0017] a second impedance acquisition step (S40) of measuring impedance at a set frequency to obtain a second impedance value after a set time has passed after the first impedance acquisition step (S30); and

[0018] The determining step ( S50 ) compares the magnitude of the first impedance with the magnitude of the second impedance to determine the state of the positive electrode slurry.

[0019] Effects of the Invention

[0020] The method for inspecting electrode slurry of the present invention enables accurate and rapid detection of the physical deterioration state of the electrode slurry in a simple manner.

[0021] The method for inspecting electrode slurry of the present invention is capable of quantifying physical degradation (gelation, particle agglomeration, etc.) of positive electrode slurry using an electrochemical method.

[0022] The method for inspecting electrode slurry of the present invention enables prediction of the curing level of the electrode slurry based only on the magnitude (absolute value) of impedance in the low-frequency region. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a block diagram illustrating a method for inspecting electrode paste according to the present invention.

[0024] Figure 2 is a graph showing an impedance spectrum.

[0025] Figure 3 is a graph showing results according to an experimental example. DETAILED DESCRIPTION

[0026] The method for inspecting electrode slurry of the present invention may include:

[0027] a positive electrode slurry preparation step ( S10 ) of mixing a positive electrode active material, a conductive material, a binder, and a solvent to prepare a positive electrode slurry;

[0028] an electrode insertion step (S20) of inserting a working electrode, a counter electrode, and a reference electrode into the positive electrode slurry;

[0029] A first impedance acquisition step (S30), which measures impedance at a set frequency through the working electrode, the counter electrode and the reference electrode to obtain a first impedance value;

[0030] a second impedance acquisition step (S40) of measuring impedance at a set frequency to obtain a second impedance value after a set time has passed after the first impedance acquisition step (S30); and

[0031] The determining step ( S50 ) compares the magnitude of the first impedance with the magnitude of the second impedance to determine the state of the positive electrode slurry.

[0032] In the positive electrode slurry preparation step ( S10 ) of the method for inspecting electrode slurry of the present invention, the positive electrode active material may include lithium metal oxide.

[0033] In the positive electrode slurry preparation step (S10) of the method for inspecting electrode slurry of the present invention,

[0034] The conductive material may be selected from the group consisting of carbon black, conductive fibers, metal powders, conductive whiskers, conductive metal oxides, conductive polymers, and a mixture of two or more thereof.

[0035] In the positive electrode slurry preparation step (S10) of the method for inspecting electrode slurry of the present invention, the binder can be selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber (SBR), and a mixture of two or more thereof.

[0036] In the electrode insertion step (S20) of the method for inspecting electrode slurry of the present invention, the working electrode, the counter electrode and the reference electrode are set in a rectangular plate shape, and the working electrode can have a width of 10 mm to 50 mm, a thickness of 0.1 mm to 2 mm, and a length of 10 mm to 50 mm, and the counter electrode can have a width of 10 mm to 50 mm, a thickness of 0.1 mm to 2 mm, and a length of 10 mm to 50 mm, and the reference electrode can have a width of 10 mm to 50 mm, a thickness of 0.1 mm to 2 mm, and a length of 10 mm to 50 mm.

[0037] In the first impedance acquisition step ( S30 ) and the second impedance acquisition step ( S40 ) of the method for inspecting electrode slurry of the present invention, the set frequency may be 10 Hz or less.

[0038] In the second impedance acquisition step ( S40 ) of the method for inspecting electrode slurry of the present invention, the set time may be 10 hours or more.

[0039] The positive electrode slurry measured by the method for inspecting electrode slurry of the present invention may have a value obtained by dividing the magnitude of the second impedance by the magnitude of the first impedance, which is 2 or less.

[0040] Method for inspecting electrode slurry of the present invention

[0041] Between the electrode inserting step (S20) and the first impedance acquiring step (S30), the following steps may also be included:

[0042] An impedance spectrum acquisition step, which acquires impedance spectrum data of multiple frequencies through a working electrode, a counter electrode and a reference electrode;

[0043] a function acquisition step, which obtains a function with a real part as an independent variable and an imaginary part as a dependent variable by fitting the impedance spectrum data; and

[0044] A set frequency selection step is performed to select a set frequency from frequencies corresponding to impedance values ​​whose real parts are larger than the real parts at the peaks of the functions.

[0045] Mode for carrying out the invention

[0046] Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. In this regard, the size or shape of the components shown in the accompanying drawings may be exaggerated for clarity and ease of description. In addition, terms specifically defined in consideration of the configuration and operation of the present invention may vary according to the intention or habit of the user or operator. The definitions of these terms should be made based on the content throughout this specification.

[0047] Figure 1 is a block diagram illustrating a method for inspecting electrode paste according to the present invention. Figure 2 is a graph showing an impedance spectrum. Figure 3 is a graph showing results according to an experimental example.

[0048] In the following, reference Figures 1 to 3 , the method for inspecting electrode slurry of the present invention will be described in detail.

[0049] The method for inspecting electrode slurry of the present invention can predict changes in rheological properties of electrode slurry by analyzing the impedance of the electrode slurry measured at a low frequency.

[0050] In the method for inspecting electrode slurry of the present invention, measurement is performed for about 10 seconds when the initial electrode slurry is manufactured to record the initial state, and then immediately before the electrode slurry is used, measurement is performed for about 10 seconds to record the current state, and the current state is compared with the initial state to determine the degree of degradation of the electrode slurry. In other words, the method for inspecting electrode slurry of the present invention can quickly determine whether the electrode slurry is usable by simply measuring the electrode slurry stored for a long time for about 10 seconds.

[0051] like Figure 1 As shown in , the method for inspecting electrode slurry of the present invention may include:

[0052] a positive electrode slurry preparation step ( S10 ) of mixing a positive electrode active material, a conductive material, a binder, and a solvent to prepare a positive electrode slurry;

[0053] an electrode insertion step (S20) of inserting a working electrode, a counter electrode, and a reference electrode into the positive electrode slurry;

[0054] A first impedance acquisition step (S30), which measures impedance at a set frequency through the working electrode, the counter electrode and the reference electrode to obtain a first impedance value;

[0055] a second impedance acquisition step (S40) of measuring impedance at a set frequency to obtain a second impedance value after a set time has passed after the first impedance acquisition step (S30); and

[0056] The determining step ( S50 ) compares the magnitude of the first impedance with the magnitude of the second impedance to determine the state of the positive electrode slurry.

[0057] In the positive electrode slurry preparation step ( S10 ), the positive electrode slurry may be prepared by mixing a positive electrode active material, a conductive material, a binder, and a solvent.

[0058] In the positive electrode slurry preparation step ( S10 ), the positive electrode active material may include lithium metal oxide.

[0059] In the positive electrode slurry preparation step ( S10 ), the conductive material may be selected from the group consisting of carbon black, conductive fibers, metal powders, conductive whiskers, conductive metal oxides, conductive polymers, and a mixture of two or more thereof.

[0060] In the positive electrode slurry preparation step (S10), the binder may be selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber (SBR), and a mixture of two or more thereof.

[0061] In the electrode insertion step (S20), the working electrode, the counter electrode and the reference electrode are arranged in a rectangular plate shape, and the working electrode, the counter electrode and the reference electrode are arranged in a rectangular plate shape, and the working electrode can have a width of 10mm to 50mm, a thickness of 0.1mm to 2mm, and a length of 10mm to 50mm, and the counter electrode can have a width of 10mm to 50mm, a thickness of 0.1mm to 2mm, and a length of 10mm to 50mm, and the reference electrode can have a width of 10mm to 50mm, a thickness of 0.1mm to 2mm, and a length of 10mm to 50mm.

[0062] The plate-shaped working electrode, counter electrode, and reference electrode may be inserted into the positive electrode slurry at a predetermined distance from each other and electrically connected to a power device for applying alternating current and a measuring device for measuring impedance.

[0063] In the first impedance acquisition step (S30) and the second impedance acquisition step (S40), the set frequency may be 10 Hz or less. As described above, in the method for inspecting electrode slurry of the present invention, measurement is performed for about 10 seconds at the beginning of electrode slurry production, and then measurement is performed for about 10 seconds just before use to determine the degradation of the electrode slurry and determine whether the electrode slurry is available for use. This can be achieved by measuring impedance at a relatively low frequency of 10 Hz.

[0064] The first impedance acquisition step (S30) may include measuring an initial state of the electrode slurry. The second impedance acquisition step (S40) may include measuring a state of the electrode slurry immediately before use. Therefore, the set time may correspond to the time the electrode slurry is stored.

[0065] In the second impedance acquisition step ( S40 ), the set time may be 10 hours or more. In other words, the method for inspecting electrode slurry of the present invention can quickly determine the rheological degradation of electrode slurry stored for a long time (eg, up to 10 hours or more).

[0066] Specifically, when the magnitude of the second impedance measured by the method for inspecting the electrode slurry divided by the magnitude of the first impedance is 2 or less, it may be determined that the electrode slurry is in a normal state.

[0067] The method for inspecting electrode slurry of the present invention may further include between the electrode inserting step (S20) and the first impedance acquiring step (S30):

[0068] An impedance spectrum acquisition step, which acquires impedance spectrum data of multiple frequencies through a working electrode, a counter electrode and a reference electrode;

[0069] a function acquisition step, which obtains a function with a real part as an independent variable and an imaginary part as a dependent variable by fitting the impedance spectrum data; and

[0070] A set frequency selection step is performed to select a set frequency from frequencies corresponding to impedance values ​​whose real parts are larger than the real parts at the peaks of the functions.

[0071] When the impedance is measured by applying AC power of multiple frequencies to the electrode slurry, a different impedance value can be obtained for each frequency. The impedance value obtained in this way is displayed on the complex plane by applying a negative sign to the imaginary part of the impedance, thereby obtaining Figure 2 Here, the (0, 0) coordinate is the impedance at the highest frequency, and the impedance value decreases in the direction of the arrow. In addition, if the electrode slurry deteriorates, Figure 2 The diameter of the semicircular portion in the graph of may be enlarged. Therefore, when the electrode slurry deteriorates, Figure 2 The point P shown in becomes farther from the origin, and the absolute values ​​of the impedance in the normal state and the degraded state can show a significant difference. The method for inspecting electrode slurry of the present invention realizes accurate electrode slurry inspection by using the magnitude of the impedance at a frequency lower than point P as a determination value.

[0072] Experimental Example

[0073] The impedance of the positive electrode slurry was measured in a frequency band of 1 MHz to 1 mHz at intervals of 8 hours. During the 8-hour measurement interval, the positive electrode slurry was stored under conditions where the solvent in the positive electrode slurry could evaporate to allow degradation. The positive electrode slurry was measured 11 times.

[0074] Figure 3 There may be a graph showing impedance spectra of 11 measurements.

[0075] Figure 3 The part connected by the dotted line in can be the impedance value at a low frequency of 1mHz. Figure 3 As shown in , it can be seen that at low frequencies, the magnitude of the impedance shows a significant difference depending on the degree of degradation (the time of exposure to the condition where degradation occurs).

[0076] Find the magnitude of the impedance at the first measurement ( Figure 3The length of A in the figure) and the magnitude of the impedance 16 hours after the first measurement ( Figure 3 The length of B in ) differs by more than twice.

[0077] Although the above describes the embodiments according to the present invention, they are merely illustrative, and those skilled in the art will appreciate that various modifications and equivalent embodiments may be made thereto. Therefore, the true technical protection scope of the present invention should be determined by the attached patent claims.

[0078] Industrial Applicability

[0079] The method for inspecting electrode slurry of the present invention enables accurate and rapid detection of the physical deterioration state of the electrode slurry in a simple manner.

[0080] The method for inspecting an electrode slurry of the present invention enables quantification of physical degradation (gelation, particle agglomeration, etc.) of a positive electrode slurry using electrochemical methods.

[0081] The method for inspecting electrode slurry of the present invention enables prediction of the curing level of the electrode slurry based only on the magnitude of impedance in the low-frequency region.

Claims

1. A method for inspecting electrode slurry, comprising: a positive electrode slurry preparation step (S10), wherein the positive electrode slurry preparation step mixes a positive electrode active material, a conductive material, a binder and a solvent to prepare a positive electrode slurry; An electrode insertion step (S20), wherein the electrode insertion step inserts a working electrode, a counter electrode, and a reference electrode into the positive electrode slurry; A first impedance acquisition step (S30), wherein the first impedance acquisition step measures 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 (S40), wherein the second impedance acquisition step measures impedance at the set frequency to obtain a second impedance value after a set time has passed after the first impedance acquisition step (S30); as well as A determination step (S50) is performed to compare the magnitude of the first impedance with the magnitude of the second impedance to determine the state of the positive electrode slurry.

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

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

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

5. The method for inspecting electrode slurry according to claim 1, wherein: In the electrode inserting step (S20), the working electrode, the counter electrode and the reference electrode are provided in a rectangular plate shape, and The working electrode has a width of 10 mm to 50 mm, a thickness of 0.1 mm to 2 mm, and a length of 10 mm to 50 mm. The counter electrode has a width of 10 mm to 50 mm, a thickness of 0.1 mm to 2 mm, and a length of 10 mm to 50 mm, and The reference electrode has a width of 10 mm to 50 mm, a thickness of 0.1 mm to 2 mm, and a length of 10 mm to 50 mm.

6. The method for inspecting electrode slurry according to claim 1, wherein: In the first impedance acquisition step (S30) and the second impedance acquisition step (S40), the set frequency is 10 Hz or less.

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

8. A positive electrode slurry having a value obtained by dividing the magnitude of the second impedance measured by the method for inspecting electrode slurry according to claim 7 by the magnitude of the first impedance, the value being 2 or less.

9. The method for inspecting electrode slurry according to claim 1, further comprising between the electrode inserting step (S20) and the first impedance acquiring step (S30): An impedance spectrum acquisition step, wherein the impedance spectrum acquisition step acquires impedance spectrum data of multiple frequencies through the working electrode, the counter electrode and the reference electrode; a function acquisition step, wherein the function acquisition step obtains a function with a real part as an independent variable and an imaginary part as a dependent variable by fitting the impedance spectrum data; and A set frequency selecting step of selecting the set frequency from frequencies corresponding to impedance values ​​whose real parts are larger than the real parts at the peaks of the function.

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