A method of characterizing binder distribution in a battery electrode sheet

Abstract

The application provides a method for characterizing the binder distribution in a battery pole piece, comprising the following steps: performing a layered peeling treatment on an active material layer to obtain a peeling thickness-peeling force relationship; and obtaining the binder distribution information in the battery pole piece according to the peeling thickness-peeling force relationship. The method obtains the peeling thickness-peeling force relationship through the layered peeling treatment, and according to the peeling thickness-peeling force relationship, the content of the binder in the battery pole piece can be directly reflected, and the spatial position distribution of the binder can also be directly reflected. The method has the advantages of low cost, easy operation and high safety, and is suitable for batch detection of the battery pole piece.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, and specifically relates to a method for characterizing the distribution of binder in battery electrodes. Background Technology

[0002] Lithium-ion battery slurry consists of active material, conductive agent, binder, and solvent. This slurry is coated onto a current collector (foil), and after drying, the battery electrode is obtained. The binder's role is to bond the active material, conductive agent, and current collector together. In related technologies, there is a risk that the binder may float to the surface during the drying process as the solvent evaporates. This floating binder reduces the adhesion between the current collector and the active material, leading to peeling during subsequent manufacturing processes and battery cycling. Therefore, effectively evaluating the distribution of the binder within the active material layer is crucial for setting battery manufacturing parameters during battery production.

[0003] Currently, most methods for determining the distribution of binders on battery electrodes involve thermogravimetric analysis (TGA) after layer-by-layer peeling or cross-sectional elemental analysis. For example, patent document CN114184513A discloses a method for detecting the binder distribution in a lithium-ion battery negative electrode sheet. This method involves artificially dividing the electrode material area into upper, middle, and lower powder layers, peeling them off, and using a thermogravimetric analyzer to measure the difference in binder content between the upper and lower powder layers. Similarly, patent document CN107831178A discloses a method for detecting the distribution of binders in a lithium-ion battery negative electrode sheet. This method involves cutting the negative electrode sheet and then using elemental analysis to test the cross-section to obtain the binder distribution on the battery electrode sheet.

[0004] However, the above methods cannot provide a detailed characterization of the binder distribution in the active material layer, and the testing cost is high, making them unsuitable for batch testing of battery electrodes. Summary of the Invention

[0005] This invention provides a method for characterizing the distribution of binders in battery electrodes. This method obtains the peeling thickness-peeling force relationship through a layered peeling process. The peeling thickness-peeling force relationship can not only intuitively reflect the binder content in the battery electrode, but also intuitively reflect the spatial distribution of the binder. This method has the advantages of low cost, easy operation, and high safety, and is suitable for batch testing of battery electrodes.

[0006] The method for characterizing the binder distribution in battery electrodes provided by this invention includes the following steps:

[0007] The active material layer is subjected to a layer-by-layer peeling process to obtain peeling thickness and peeling force data, and the peeling thickness-peeling force relationship is obtained.

[0008] Based on the peel thickness-peel force relationship, the adhesive distribution information in the battery electrode sheet is obtained;

[0009] The delamination process for the active material layer includes the following steps: attaching the first adhesive layer to one side of the active material layer, attaching one side of the second adhesive layer to the other side of the active material layer, and performing a delamination process on the active material layer.

[0010] The active material layer contains active material particles, and the thickness of the second adhesive layer is greater than or equal to the D50 particle size of the active material particles and less than the D90 particle size of the active material particles.

[0011] The method described above further includes the following steps before performing the delamination process on the active material layer:

[0012] The battery electrode is fixed to the substrate by the first adhesive layer, so that one side of the first adhesive layer is attached to the substrate and the other side of the first adhesive layer is attached to one side of the active material layer.

[0013] After the current collector on the battery electrode is peeled off from the active material layer, the other side of the active material layer is exposed.

[0014] In the method described above, the active material layer includes a first sub-active material layer, a second sub-active material layer, a third sub-active material layer, ... a (n-1)th sub-active material layer, along the direction from near to far from the current collector. The peeling force corresponding to the first sub-active material layer is A1, the peeling force corresponding to the second sub-active material layer is A2, the peeling force corresponding to the third sub-active material layer is A3, and so on, with the peeling force corresponding to the (n-1)th sub-active material layer being A... n-1 Where n≥3,

[0015] The overall peel force of the battery electrode is (A1+A2+A3+…+A…). n-1 ) / (n-1).

[0016] In the method described above, the distribution of the binder in the first sub-active material layer is A1 / (A1+A2+A3+…+A…). n-1 The distribution of the binder in the second active material layer is A2 / (A1+A2+A3+…+A…). n-1 The distribution of the binder in the third active material layer is A3 / (A1+A2+A3+…+A…). n-1 ), and so on, the distribution of the binder in the (n-1)th sub-active material layer is A. n-1 / (A1+A2+A3+…+A n-1 ).

[0017] The method described above, wherein the degree of floating of the adhesive is (A) n-1-(A1+A2+A3+…+A n-1 ) / (n-1)) / ((A1+A2+A3+…+A n-1 ) / (n-1)) to obtain the degree of buoyancy of the adhesive.

[0018] In the method described above, the thickness of the first adhesive layer and the second adhesive layer is not greater than the thickness of the active material layer.

[0019] In the method described above, the orthographic projection of the second adhesive layer on the substrate covers the orthographic projection of the battery electrode on the substrate; and / or, the orthographic projection of the first adhesive layer on the substrate lies within the orthographic projection of the battery electrode on the substrate.

[0020] In the method described above, the width of the first adhesive layer is not greater than the width of the battery electrode sheet;

[0021] The length of the first adhesive layer is no greater than the length of the battery electrode.

[0022] In the method described above, the width of the battery electrode is 10-50 mm and the length is 20-50 cm;

[0023] The width of the first adhesive layer is 10-50 mm and the length is 5-15 cm.

[0024] In the method described above, the peeling speed during the layer peeling process is (10-200) mm / min.

[0025] The implementation of this invention has at least the following beneficial effects:

[0026] The method for characterizing the binder distribution in battery electrodes provided by this invention obtains the peeling thickness-peeling force relationship through layer-by-layer peeling treatment, which can intuitively reflect the binder content and spatial distribution of the binder in the battery electrodes, thereby realizing the evaluation of the binder distribution in the battery electrodes. In addition, this method has the advantages of low cost, easy operation and high safety, and is suitable for batch testing of battery electrodes. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a layer-by-layer peeling process for the active material layer in one embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of peeling off battery electrodes in one embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of peeling off battery electrodes in another embodiment of the present invention.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1-Current collector; 101-First active material layer / active material layer; 102-Second active material layer; 201-First adhesive layer; 202-Second adhesive layer; 3-Substrate. Detailed Implementation

[0032] The specific embodiments listed below are merely descriptions of the principles and features of the present invention. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The method for characterizing the binder distribution in a battery electrode provided by the present invention includes the following steps: performing a layer-by-layer peeling process on the active material layer to obtain the peeling thickness-peeling force relationship; and obtaining the binder distribution information in the battery electrode based on the peeling thickness-peeling force relationship.

[0034] The battery electrode includes a current collector and an active material layer located on at least one functional surface of the current collector. That is, the battery electrode can be a battery electrode with an active material layer coated on one side or on both sides. The delamination process in this invention only applies to the active material layer of the battery electrode.

[0035] In this invention, a single layer of active material is peeled off into multiple sub-layers along the thickness direction of the active material layer through a layer-by-layer peeling process. As each sub-layer is peeled off sequentially, the thickness of the peeled sub-layer and the peeling force are obtained, thus determining the peeling thickness-peeling force relationship. The thickness of each peeled sub-layer is essentially consistent, with fluctuations not exceeding 1 μm.

[0036] In this invention, the number of sub-active material layers is not limited and can be adjusted according to actual conditions. The thickness of each sub-active material layer can be equal or unequal.

[0037] This invention does not impose many limitations on the delamination process; for example, adhesive tape can be used for delamination. The thickness of the delamination of the sub-active material layer can be calculated by subtracting the thickness of the residual active material layer from the initial thickness of the active material layer. The peel force can be measured using the 180° peel force measurement method.

[0038] When the peel thickness is basically uniform, the magnitude of the peel force can directly reflect the binder content in the battery electrode. The greater the peel force, the higher the binder content; the smaller the peel force, the lower the binder content. Combining the peel thickness-peel force relationship can directly reflect the binder content in each sub-active material layer, and thus obtain the spatial distribution of the binder in the active material layer in the thickness direction.

[0039] According to the research of this invention, the method provided by this invention can provide a refined characterization of the binder distribution in the active material layer, making it suitable for batch testing of battery electrodes. This is because, in battery electrodes, the active material, conductive agent, and solvent have no adhesion to the current collector; the role of the binder is to bond the active material, conductive agent, and current collector together. The peeling force is mainly contributed by the binder. This invention obtains the peeling thickness-peeling force relationship through layer-by-layer peeling treatment. The magnitude of the peeling force can directly reflect the binder content in the battery electrode, and the spatial distribution of the binder can be directly reflected by combining the peeling thickness-peeling force relationship. This invention can achieve detection through physical layer-by-layer peeling treatment. Compared with chemical methods, the method provided by this invention has the advantages of low cost, ease of operation, and high safety, making it suitable for batch testing of battery electrodes.

[0040] In one embodiment, along the direction from near the current collector to away from the current collector, the active material layer includes a first sub-active material layer, a second sub-active material layer, a third sub-active material layer, and so on, up to the (N-1)th sub-active material layer. The peeling force corresponding to the first sub-active material layer is A1, the peeling force corresponding to the second sub-active material layer is A2, the peeling force corresponding to the third sub-active material layer is A3, and so on, up to the (n-1)th sub-active material layer. n-1 The overall peeling force of the battery electrode is (A1+A2+A3+…+A…). n-1 ) / (n-1). Where n≥3, further n≥4, and even further n≥5.

[0041] The distribution of the binder in the first sub-active material layer is A1 / (A1+A2+A3+…+A…). n-1 The distribution of the binder in the second active material layer is A2 / (A1+A2+A3+…+A…). n-1 The distribution of the binder in the third active material layer is A3 / (A1+A2+A3+…+A…). n-1 ), and so on, the distribution of the binder in the (N-1)th sub-active material layer is A. n-1 / (A1+A2+A3+…+A n-1 This method allows for the quantification of the binder in the sub-active material layer, which is beneficial for further characterizing the binder content.

[0042] Besides visually reflecting the distribution of binder in battery electrodes, this invention is also noteworthy for its ability to evaluate the degree of binder buoyancy in battery electrodes. In one embodiment, the degree of binder buoyancy in the battery electrode is evaluated based on the peel thickness-peel force relationship. For example, along the direction from near the current collector to far away from the current collector, the degree of binder buoyancy is evaluated as (A... n-1-(A1+A2+A3+…+A n-1 ) / (n-1)) / ((A1+A2+A3+…+A n-1 ) / (n-1)) to obtain the degree of buoyancy of the adhesive.

[0043] Before performing the delamination process on the active material layer, the battery electrode sheet is pretreated to ensure that the active material layer is completely peeled off from the current collector. In one embodiment, the process before performing the delamination process on the active material layer includes the following steps: fixing the battery electrode sheet to the substrate with a first adhesive layer, such that one side of the first adhesive layer is adhered to the substrate and the other side of the first adhesive layer is adhered to one side of the active material layer; after peeling the current collector off the active material layer from the battery electrode sheet, the other side of the active material layer is exposed.

[0044] The substrate has a smooth and glossy surface, which is conducive to the adhesion of the first adhesive layer. In the specific implementation process, the largest surface of the substrate is wiped with ethanol and dried before use.

[0045] In the specific implementation process, 3M tape is used to carry out the above bonding steps. For example, the tape includes a first release paper, a first adhesive layer, and a second release paper. First, the first release paper of the tape is peeled off to expose one side of the first adhesive layer. Along one end of the substrate, one side of the first adhesive layer is adhered to the surface of the substrate. Then, the second release paper is peeled off to expose the other side of the first adhesive layer. Along one end of the substrate, the other side of the first adhesive layer is adhered to one side of the active material layer.

[0046] The present invention does not impose too many limitations on the above bonding process. For example, roller pressing can be used. Specifically, a rubber roller with a mass of 2 to 5 kg is used to naturally press the active material layer, the first adhesive layer and the substrate 2 to 3 times to remove air bubbles. After waiting for 10 to 50 minutes, the first adhesive layer can better bond the active material layer and the substrate before proceeding with the subsequent peeling process.

[0047] like Figure 2 As shown, when the battery electrode is a battery electrode with an active material layer coated on one side, one side of the active material layer 101 is attached to the first adhesive layer 201. The current collector 1 on the battery electrode is peeled off from the active material layer 101 by tape peeling treatment, thereby exposing the other side of the active material layer 101. Then, the active material layer 101 is subjected to subsequent layer peeling treatment.

[0048] like Figure 3As shown, when the battery electrode is a battery electrode with active material layers coated on both sides, the battery electrode includes a first active material layer 101, a current collector 1, and a second active material layer 102. The above-mentioned test method can peel off either the first active material layer 101 or the second active material layer 102. For example, one side of the first active material layer 101 is attached to the first adhesive layer 201, and the second active material layer 102 and the current collector 1 on the battery electrode are peeled off from the first active material layer 101 using adhesive tape peeling, exposing the other side of the first active material layer, and then the first active material layer is subjected to subsequent delamination peeling. The present invention does not limit the specific process of delamination peeling; specifically, adhesive tape can be used for delamination peeling, such as... Figure 1 As shown, for example, in one embodiment of the present invention, the delamination process of the active material layer 101 includes the following steps: attaching one side of the second adhesive layer 202 to the other side of the active material layer 101, and performing a delamination process on the active material layer 101.

[0049] In the above embodiments, the thickness of the second adhesive layer can be directly tested, but because the second adhesive layer is relatively soft, it is prone to curling during testing. In this invention, the thickness of the peeled sub-active material layer can be obtained by the following method: After measuring the total thickness of the active material layer, tape, and substrate using a Malvern thickness gauge, the total thickness of the active material layer, tape, and substrate remaining on the substrate is measured again after each peeling. The difference between the two is the thickness of the peeled sub-active material layer. Subsequently, the peeling thickness data can be obtained by subtracting the total thickness before peeling from the total thickness after peeling for each subsequent peeling.

[0050] The present invention does not impose too many restrictions on the specific type of the second adhesive layer. It can be a single-sided adhesive or a double-sided adhesive, as long as one side of the second adhesive layer is in contact with one side of the active material layer.

[0051] The present invention does not impose too many limitations on the above bonding process. For example, roller pressing can be used. Specifically, a rubber roller with a mass of 2 to 5 kg is used to naturally press the material 2 to 3 times to remove air bubbles between the active material layer and the second adhesive layer. After waiting for 10 to 50 minutes, the second adhesive layer can be better bonded to the active material layer before the layer is peeled off.

[0052] The present invention does not impose too much limitation on the number of times the above-mentioned layer peeling process is performed. The specific number can be adjusted according to the actual situation, as long as each sub-active material layer can be peeled off and the thickness of the peeled sub-active material layer and the peeling force during peeling can be measured.

[0053] For example, one side of the second adhesive layer is bonded to the other side of the active material layer, and the active material layer is subjected to a first layer peeling process. The peeling force and the thickness of the active material layer remaining on the substrate are recorded. The peeling thickness is calculated by subtracting the thickness of the active material layer remaining on the substrate from the initial thickness of the active material layer before the first layer peeling process. The above steps are repeated to obtain the peeling thickness-peeling force relationship, thereby allowing the inference of the adhesive content and spatial distribution of the adhesive in each sub-active material layer.

[0054] This invention does not impose excessive limitations on the dimensions of the first and second adhesive layers, as long as proper adhesion is ensured. In one embodiment, the thickness of both the first and second adhesive layers is no greater than the thickness of the active material layer, to avoid excessive peel thickness that could affect the delamination process.

[0055] When the battery electrode is a battery electrode with an active material layer coated on one side, the thickness of the active material layer refers to the thickness of the active material layer on one side; when the battery electrode is a battery electrode with an active material layer coated on both sides, the thickness of the active material layer refers to half the thickness of the battery electrode.

[0056] In this invention, the active material layer comprises active material particles. The thickness of the second adhesive layer can be limited according to the size of the active material particles, which is beneficial for maximizing the delamination of the active material layer and achieving precise characterization. In one embodiment, the thickness of the second adhesive layer is greater than or equal to the D50 particle size of the active material particles and less than the D90 particle size, ensuring a relatively consistent delamination thickness and facilitating more refined characterization of the binder distribution in the active material layer. If the thickness of the second adhesive layer is less than the D50 particle size of the active material particles, some sub-active material layers may not be delaminated; if the thickness of the second adhesive layer is greater than the D90 particle size of the active material particles, the delaminated sub-active material layers may be relatively thick.

[0057] This invention does not impose excessive limitations on the size of the second adhesive layer, as long as the first adhesive layer secures the active material layer and the substrate. In one embodiment, the orthographic projection of the second adhesive layer onto the substrate overlaps with the orthographic projection of the battery electrode onto the substrate; that is, the size of the second adhesive layer is greater than or equal to the size of the battery electrode in the extension direction. Further, the size of the second adhesive layer is greater than or equal to the size of the active material layer in the extension direction. In a preferred embodiment, the orthographic projections of the second adhesive layer and the active material layer onto the substrate overlap, which facilitates delamination.

[0058] This invention does not impose excessive limitations on the size of the first adhesive layer, as long as it enables delamination. In one embodiment of this invention, the orthographic projection of the first adhesive layer on the substrate lies within the orthographic projection of the battery electrode on the substrate. That is, the size of the first adhesive layer is less than or equal to the size of the battery electrode in the extension direction. Further, the size of the first adhesive layer is less than or equal to the size of the active material layer in the extension direction. In a preferred embodiment, the orthographic projections of the first adhesive layer and the active material layer on the substrate overlap, which facilitates delamination.

[0059] In this invention, the size of the first adhesive layer is adjusted according to the size of the battery electrode, as long as the above-mentioned relationship is satisfied. In one embodiment, the width of the first adhesive layer is not greater than the width of the battery electrode, and the length of the first adhesive layer is not greater than the length of the battery electrode.

[0060] The present invention does not impose excessive limitations on the dimensions of the battery electrode and the first adhesive layer. The battery electrode can be a conventional strip-shaped battery electrode in the art. For example, the width of the battery electrode is 10-50 mm and the length is 20-50 cm. Correspondingly, the width of the first adhesive layer is 10-50 mm and the length is 5-15 cm.

[0061] This invention does not impose excessive limitations on the delamination process and can employ conventional delamination equipment in the art. For example, the bottom of the substrate (the other side surface of the substrate) is fixed to the base of a universal tensile testing machine. A portion of the second adhesive layer that is not adhered to the active material layer is bent 180° in the reverse direction and then fixed to the upper part of the universal tensile testing machine. The delamination speed is set, and the test begins. The test is stopped once the delamination force stabilizes and remains stable for a period of time. The delamination speed during the delamination process is (10-200) mm / min.

[0062] This invention does not impose excessive limitations on the specific composition of the active material layer, which can be any conventional active material layer in the art. For example, the active material can be at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, Prussian white, lithium titanate, graphite, and silicon carbide; the binder includes at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR) emulsion, polyacrylic acid (PAA), and nitrile compounds; the thickener is sodium carboxymethyl cellulose (CMC); and the conductive agent is at least one of carbon black (SP), carbon nanotubes (CNT), graphite, vapor-grown carbon fiber (VGCF), and graphene.

[0063] The present invention does not impose too many restrictions on the specific type of substrate, for example, the substrate may be selected from steel plate.

[0064] In this invention, during the layered peeling process, since the nth active material layer is bonded to both the first adhesive layer and the second adhesive layer, the two opposite surfaces of the nth active material layer are bonded to both the first adhesive layer and the second adhesive layer, resulting in increased peeling force. At the same time, since the two opposite surfaces of the nth active material layer are bonded to both the first adhesive layer and the second adhesive layer, the active material layer peeled off by the second adhesive layer is not complete, thus resulting in a reduction in peeling thickness.

[0065] The present invention will be further described below through specific embodiments and comparative examples.

[0066] Example 1

[0067] Battery electrodes with double-sided active material coatings were prepared using high-nickel ternary materials as the active material. The ratio of ternary material: SP:PVDF = 94.5%: 3%: 2.5%, and the coating surface density was 15 mg / cm³. 3 The battery electrode is cut into strips 20mm wide and 20cm long; the thickness of the battery electrode is about 116μm, the thickness of the aluminum foil is 16μm, the thickness of the single active material layer in the battery electrode is about 50μm; the D50 particle size of the active material particles is 8.5μm, and the D90 particle size of the active material particles is 16.3μm.

[0068] (1) Wipe the steel plate clean with anhydrous ethanol and let it dry. Use 3M tape with a first adhesive layer that is 20mm wide, 10cm long and 10μm thick to stick it on the battery electrode, so that one side of the first adhesive layer is attached to the steel plate and the other side of the first adhesive layer is attached to the other side of the active material layer. The battery electrode covers the first adhesive layer and the deviation on the left and right sides does not exceed 0.5mm. At the same time, ensure that the length direction of the battery electrode is parallel to that of the steel plate. Use a 2kg roller to roll back and forth on the battery electrode three times to remove air bubbles. Let it stand for 20 minutes before use.

[0069] The bottom of the steel plate is fixed to the bottom of the universal tensile tester. The battery electrode and 3M adhesive are gently peeled apart by hand. The electrode is folded 180° and fixed to the upper sensor of the tensile tester. After the universal tensile tester is zeroed, the peeling speed is set to 100 mm / min. The tensile tester is started to perform a peeling test. After peeling the current collector and active material layer on the battery electrode, one side of the active material layer is exposed. The test is stopped when the peeling force is stable and maintained for more than 5 seconds. A set of peeling forces (i.e. the peeling force between the active material layer and the aluminum foil) is obtained. The peeling thickness at this time is 0 μm.

[0070] (2) After measuring the total thickness of the active material layer, the first adhesive layer and the steel plate using a Malvern thickness gauge, take a 3M adhesive with a second adhesive layer of 20mm width and 20cm length and stick it on the electrode powder on the steel plate. Use a 2Kg roller to roll back and forth on the electrode 3 times to remove air bubbles. After standing for 20 minutes, peel it off. Adhere one side of the second adhesive layer to one side of the active material layer and perform a layered peeling process on the active material layer. The peeling test ends under the same conditions as above. Record the peeling force and test the thickness of the peeled sub-active layer, which is recorded as H1.

[0071] Repeat step (2) until the thickness of the peeled active layer is significantly reduced compared to the previous one, and then end the test to obtain the peel thickness-peel force relationship.

[0072] Example 2

[0073] Battery electrodes were prepared using high-nickel ternary materials as active materials, with the following ratio: ternary material: SP:PVDF = 94.5%: 2%: 3.5%, and the coating surface density was 15 mg / cm³. 3 The battery electrode is cut into strips 20mm wide and 20cm long. The thickness of the battery electrode is about 116μm, the thickness of the aluminum foil is 16μm, and the thickness of the single active material layer in the battery electrode is about 50μm. The D50 particle size of the active material particles is 8.5μm, and the D90 particle size of the active material particles is 16.3μm.

[0074] (1) Wipe the steel plate clean with anhydrous ethanol and let it dry. Use 3M tape with a width of 20mm, a length of 10cm and a thickness of 10μm to stick it on the battery electrode. Make one side of the first adhesive layer adhere to the steel plate and the other side of the first adhesive layer adhere to the other side of the active material layer. Ensure that the battery electrode is parallel to the length of the steel plate. Use a 2Kg roller to roll back and forth on the battery electrode 3 times to remove air bubbles. Let it stand for 20 minutes before use.

[0075] The bottom of the steel plate is fixed to the bottom of the universal tensile tester. The battery electrode and 3M adhesive are gently peeled apart by hand. The electrode is folded 180° and fixed to the upper sensor of the tensile tester. After the universal tensile tester is zeroed, the peeling speed is set to 100 mm / min. The tensile tester is started to perform a peeling test. After peeling the current collector and active material layer on the battery electrode, one side of the active material layer is exposed. The test is stopped when the peeling force is stable and maintained for more than 5 seconds. A set of peeling forces (i.e. the peeling force between the active material layer and the aluminum foil) is obtained. The peeling thickness at this time is 0 μm.

[0076] (2) After measuring the total thickness of the battery electrode, the first adhesive layer and the steel plate using a Malvern thickness gauge, take a 20mm wide and 20cm long 3M adhesive and stick it on the electrode powder on the steel plate. Use a 2Kg roller to roll back and forth on the electrode 3 times to remove air bubbles. After standing for 20 minutes, peel it off and attach one side of the second adhesive layer to one side of the active material layer. Perform layer peeling treatment on the active material layer. The peeling test ends under the same conditions as above. Record the peeling force and test the thickness of the peeled sub-active layer, which is recorded as H1.

[0077] Repeat step (2) until the thickness of the peeled active layer is significantly reduced compared to the previous one, and then end the test to obtain the peel thickness-peel force relationship.

[0078] Example 3

[0079] Battery electrodes were prepared using high-nickel ternary materials as active materials, with the following ratio: ternary material: SP: PVDF = 94.5%: 3%: 2.5%, and the coating surface density was 15 mg / cm³. 3 The battery electrode is cut into strips 15mm wide and 20cm long. The thickness of the active material layer is 50μm, the D50 particle size of the active material particles is 9.4μm, and the D90 particle size of the active material particles is 17.7μm.

[0080] (1) Wipe the steel plate clean with anhydrous ethanol and let it dry. Use 3M tape with a width of 15mm, a length of 10cm and a thickness of 10μm to stick it on the battery electrode, so that one side of the first adhesive layer is attached to the steel plate and the other side of the first adhesive layer is attached to the other side of the active material layer. Ensure that the battery electrode is parallel to the length direction of the steel plate. Use a 2Kg roller to roll back and forth on the battery electrode 3 times to remove the air bubbles. Let it stand for 20 minutes before use.

[0081] The bottom of the steel plate is fixed to the bottom of the universal tensile tester. The battery electrode and 3M adhesive are gently peeled apart by hand. The electrode is folded 180° and fixed to the upper sensor of the tensile tester. After the universal tensile tester is zeroed, the peeling speed is set to 100 mm / min. The tensile tester is started to perform a peeling test. After peeling the current collector and active material layer on the battery electrode, one side of the active material layer is exposed. The test is stopped when the peeling force is stable and maintained for more than 5 seconds. A set of peeling forces (i.e. the peeling force between the active material layer and the aluminum foil) is obtained. The peeling thickness at this time is 0 μm.

[0082] (2) After measuring the total thickness of the battery electrode, the first adhesive layer and the steel plate using a Malvern thickness gauge, take a 20mm wide and 20cm long 3M adhesive and stick it on the electrode powder on the steel plate. Use a 2Kg roller to roll back and forth on the electrode 3 times to remove air bubbles. After standing for 20 minutes, peel it off and attach one side of the second adhesive layer to one side of the active material layer. Perform layer peeling treatment on the active material layer. The peeling test ends under the same conditions as above. Record the peeling force and test the thickness of the peeled sub-active layer, which is recorded as H1.

[0083] Repeat step (2) until the thickness of the peeled active layer is significantly reduced compared to the previous one, and then end the test to obtain the peel thickness-peel force relationship.

[0084] Comparative Example

[0085] Using the electrode from Example 1, powder from the upper and lower layers was scraped off separately with a scraper. The upper layer was 25 μm thick material, and the lower layer was a 25 μm thick electrode. Thermogravimetric analysis (TG) was used to test the weight loss of PVDF and calculate the degree of buoyancy. The results are shown in Table 2.

[0086] Table 1 shows the peel thickness-peel force relationship in the examples.

[0087]

[0088]

[0089] In Table 1, the degree of buoyancy refers to the degree of buoyancy of the adhesive distribution of the sub-active material layer that is peeled off from the active material layer for the fourth time relative to the adhesive in the overall active material layer.

[0090] Table 2

[0091]

[0092] As shown in Table 1, during the layer-by-layer peeling process of the active material layer, the peeling force gradually increases along the direction from the current collector to the distance from the current collector, indicating that the adhesive content gradually increases. The inventors believe that because the two opposing surfaces of the fifth peeled-off sub-active material layer are bonded to both the first and second adhesive layers, the peeling force increases. Furthermore, the fifth sub-active material layer peeled off from the second adhesive layer is not complete, resulting in a decrease in peeling thickness.

[0093] Comparative Example 1 is difficult to achieve fine layering, and this method uses thermogravimetric analysis (TG) for testing, which has a large error and is costly. Comparative data shows that the calculated upward sizing in the comparative example is too large, which is due to the error caused by averaging multiple layers. In contrast, the example can achieve fine layering and can calculate the content of adhesive in each layer.

[0094] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for characterizing the distribution of binder in battery electrodes, characterized in that, Includes the following steps: The active material layer is subjected to a layered peeling process to obtain peeling thickness and peeling force data, thus obtaining the peeling thickness-peeling force relationship. Along the direction from near to far from the current collector, the active material layer includes a first sub-active material layer, a second sub-active material layer, a third sub-active material layer… and a (n-1)th sub-active material layer. The peeling force corresponding to the first sub-active material layer is A1, the peeling force corresponding to the second sub-active material layer is A2, the peeling force corresponding to the third sub-active material layer is A3, and so on, with the peeling force corresponding to the (n-1)th sub-active material layer being A… n-1 Where n≥3, The overall peeling force of the battery electrode is (A1 + A2 + A3 + ... + A n-1 ) / (n-1); Based on the peel thickness-peel force relationship, the adhesive distribution information in the battery electrode sheet is obtained; The delamination process for the active material layer includes the following steps: attaching the first adhesive layer to one side of the active material layer, attaching one side of the second adhesive layer to the other side of the active material layer, and performing a delamination process on the active material layer. The active material layer contains active material particles, and the thickness of the second adhesive layer is greater than or equal to the D50 particle size of the active material particles and less than the D90 particle size of the active material particles.

2. The method according to claim 1, characterized in that, The following steps are included before the active material layer is subjected to delamination: The battery electrode is fixed to the substrate by the first adhesive layer, so that one side of the first adhesive layer is attached to the substrate and the other side of the first adhesive layer is attached to one side of the active material layer. After the current collector on the battery electrode is peeled off from the active material layer, the other side of the active material layer is exposed.

3. The method according to claim 1, characterized in that, The distribution of the binder in the first active material layer is A1 / (A1+A2+A3+…+A…). n-1 The distribution of the binder in the second active material layer is A2 / (A1+A2+A3+…+A…). n-1 The distribution of the binder in the third active material layer is A3 / (A1+A2+A3+…+A…). n-1 ), and so on, the distribution of the binder in the (N-1)th sub-active material layer is A n-1 / (A1+ A2+A3+…+A n-1 ).

4. The method according to claim 1, characterized in that, Based on the degree of floating of the adhesive (A) n-1 -(A1+ A2+A3+…+A n-1 ) / (n-1)) / ((A1+ A2+A3+…+A n-1 (n-1)) to obtain the degree of buoyancy of the adhesive.

5. The method according to claim 2, characterized in that, The thickness of the first adhesive layer and the second adhesive layer is no greater than the thickness of the active material layer.

6. The method according to any one of claims 1-5, characterized in that, The orthographic projection of the second adhesive layer on the substrate covers the orthographic projection of the battery electrode on the substrate; and / or, the orthographic projection of the first adhesive layer on the substrate lies within the orthographic projection of the battery electrode on the substrate.

7. The method according to any one of claims 1-5, characterized in that, The width of the first adhesive layer is not greater than the width of the battery electrode sheet; The length of the first adhesive layer is no greater than the length of the battery electrode.

8. The method according to claim 7, characterized in that, The width of the battery electrode is 10~50mm and the length is 20~50cm; The width of the first adhesive layer is 10~50mm and the length is 5~15cm.

9. The method according to any one of claims 1-5, characterized in that, The peeling speed during the layer peeling process is (10-200) mm / min.

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