Method for testing stripping force of pole piece of lithium ion battery and application

Abstract

The invention provides a lithium ion battery pole piece stripping force test method and application, and relates to the technical field of batteries. According to the testing mode, the adhesive tape is adhered to the surface of the untested coating of the pole piece before stripping, so that the toughness of the pole piece can be remarkably enhanced, the bending radian between the pole piece and the fixed substrate in the subsequent 180-degree stripping process is supported, meanwhile, the pole piece is not excessively bent in combination with a pre-stripping treatment mode, and the service life of the pole piece is prolonged. According to the test method, the current collector and the to-be-tested coating can be obviously separated, the coating which is not tested is well adhered to the current collector and is not broken and powder does not fall off, under the condition, a stripping force curve is smooth and stable, the problem of stripping force value jump does not occur, and the test method has the advantages that the test method is simple and convenient, and the test efficiency is high. And the test result is reliable. The test does not need to add other equipment, is easy to implement, and can also enable the pole piece which can generate creases to obtain the average peel strength result which is closer to the average peel strength of the pole piece.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a test method and application for the peel force of lithium-ion battery electrodes. Background Art

[0002] The peel strength refers to the force required to completely remove the material from the substrate. In a lithium battery, the peel strength between the foil and the coating on the electrode determines the adhesion between the two, which is of great significance for battery performance evaluation and improvement. The industry generally uses the 180° peel method to quantitatively measure the peel strength of battery electrodes. The specific process is as follows: The side of the coating of the lithium-ion battery electrode to be tested is pasted on a steel plate through double-sided tape, and then the free end of the electrode is folded 180°. The free end of the electrode is clamped on the upper fixture of a tensile testing machine, while one end of the steel plate is clamped on the lower fixture. The coating is directly peeled off using the tensile testing machine, and the peeled strength value is recorded and read.

[0003] The normal electrode after peeling is as Figure 5 (a) or Figure 6 (a) shows: The foil and the coating are clearly separated, and the coating on the unpeeled side adheres well to the foil without breaking or powdering. In this case, the peel force curve is smooth and stable, and the test result is reliable. However, in the actual peel test process, it is often encountered that the electrode is folded excessively, resulting in continuous or discontinuous, regular or irregular creases on the electrode, causing the coating dressing on the unpeeled side to break and fall off. In this case, the suddenly increased tensile force after the foil of the electrode is folded and the internal extrusion force caused by the falling off of the coating dressing will cause the peel curve to rise abnormally. Each crease is a sudden peak reflected on the peel force curve. For example Figure 2 (a) and (b) show that very dense creases are also smooth on the peel force curve, but that is not the true peel force value. For example Figure 3 (a) and (b) show that ultimately the average peel strength value obtained by the test also loses its reference value.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] Aiming at the deficiencies and defects existing in the prior art, the present invention aims to provide a test method and application for the peel force of lithium-ion battery electrodes. This test method is particularly suitable for the peel test of electrodes that generate creases, powder shedding and other phenomena during the peeling process, so as to improve the problem that the average peel strength test value measured by the conventional test method for such electrodes is completely distorted and loses its reference value.

[0006] In order to achieve the above object, the following technical solutions are adopted:

[0007] The first object of the present invention is to provide a test method for the peel force of lithium-ion battery electrodes, including the following steps:

[0008] (a) Stick the side of the electrode sheet with the coating to be tested onto the fixed substrate through double-sided tape;

[0009] Wherein, a free end X is reserved for the electrode sheet and a free end Y is reserved for the fixed substrate for peeling use;

[0010] (b) Stick the tape on the side of the electrode sheet with the untested coating, and then roll the electrode sheet with the tape stuck on it;

[0011] (c) Pre-peel the electrode sheet with the tape stuck on it after rolling, so that the initial peeling end of the coating to be tested on the electrode sheet is peeled off from the current collector;

[0012] (d) After the pre-peeling treatment, clamp the free end Y of the fixed substrate on the lower fixture of the tensile testing machine, clamp the free end X of the electrode sheet on the upper fixture of the tensile testing machine, perform 180° peeling on the electrode sheet, and test its peeling force.

[0013] Further, on the basis of the above technical solution of the present invention, in step (a), the length of the double-sided tape is respectively less than the lengths of the fixed substrate and the electrode sheet.

[0014] Further, on the basis of the above technical solution of the present invention, in step (a), the fixed substrate includes a stainless steel substrate or a hard plastic substrate.

[0015] Further, on the basis of the above technical solution of the present invention, in step (b), the tape includes at least one of double-sided tape, paper tape, electrical tape or transparent tape.

[0016] Further, on the basis of the above technical solution of the present invention, in step (b), the tape is transparent tape.

[0017] Further, on the basis of the above technical solution of the present invention, in step (b), the sticking area of the tape on the side of the electrode sheet with the untested coating corresponds to the sticking area of the double-sided tape on the side of the electrode sheet with the coating to be tested.

[0018] Further, on the basis of the above technical solution of the present invention, in step (b), use a roller to roll the electrode sheet with the tape stuck on it, and the number of times the roller rolls back and forth is not less than 3 times.

[0019] Further, on the basis of the above technical solution of the present invention, in step (c), the distance at which the initial peeling end of the coating to be tested on the electrode sheet is peeled off from the current collector is 1-2 cm.

[0020] Further, on the basis of the above technical solution of the present invention, in step (d), after the pre-stripping treatment, the tensile testing machine is first zeroed and calibrated, and then the free end Y of the fixed substrate is clamped on the lower fixture of the tensile testing machine, and the free end X of the pole piece is clamped on the upper fixture of the tensile testing machine.

[0021] Further, on the basis of the above technical solution of the present invention, the method for testing the stripping force of the lithium-ion battery pole piece is mainly applicable to the pole pieces that will have abnormal stripping during the stripping test.

[0022] The second object of the present invention is to provide an application of the above method for testing the stripping force of the lithium-ion battery pole piece in the battery field.

[0023] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0024] (1) The present invention provides a method for testing the stripping force of a lithium-ion battery pole piece. Specifically, the surface of the coating to be tested of the pole piece is pasted on a fixed substrate, then the tape is pasted on the surface of the untested coating of the pole piece, and then the pole piece with the tape pasted is roll-pressed. The pole piece with the tape pasted after roll-pressing is first pre-stripped and then 180° stripped to test the stripping force of the pole piece. This testing method can significantly enhance the toughness of the pole piece by only pasting the tape on the surface of the untested coating of the pole piece before stripping, so as to support the bending arc between the pole piece and the fixed substrate during the subsequent 180° stripping process. At the same time, combined with the pre-stripping treatment method, the pole piece will not be overly folded, avoiding continuous or discontinuous, regular or irregular creases caused by excessive folding of the pole piece. This testing method can make the current collector and the coating to be tested be significantly separated, and the untested coating adheres well to the current collector without breaking or falling powder. In this case, the stripping force curve is flat and stable, and there will be no problem of sudden jump in the stripping force value, making the test result reliable. This testing method does not require additional equipment and is easy to implement. At the same time, it can also make the pole pieces that will produce creases and powder falling obtain the "average stripping strength" result closer to the pole piece itself.

[0025] (2) The present invention also provides an application of the above method for testing the stripping force of the lithium-ion battery pole piece in the battery field. Due to the advantages of the above method for testing the stripping force of the lithium-ion battery pole piece, this testing method can be widely applied to fields such as battery performance testing and evaluation. Description of the Drawings

[0026] Figure 1 (a) is a photo of the bending state between a normal pole piece and a steel plate after 180° stripping test;

[0027] Figure 1 (b) is a photo of the bending state between an abnormal pole piece and a steel plate after 180° stripping test;

[0028] Figure 2 (a) is a state diagram of the pole piece after peeling obtained by using the existing test method for peeling force;

[0029] Figure 2 (b) is Figure 2 the peeling force curve diagram corresponding to the two pole pieces in (a);

[0030] Figure 3 (a) is another state diagram of the pole piece after peeling obtained by using the existing test method for peeling force;

[0031] Figure 3 (b) is Figure 3 the peeling force curve diagram corresponding to the two pole pieces in (a);

[0032] Figure 4 This is a schematic process flow diagram of the test method for the peeling force of the pole piece provided by the present invention;

[0033] Figure 5 This is a state diagram of the pole piece after peeling obtained by using the test methods for the peeling force of Comparative Example 2 and Example 2 of the present invention, where (a) corresponds to Comparative Example 2 and (b) corresponds to Example 2;

[0034] Figure 6 This is a state diagram of the pole piece after peeling obtained by using the test methods for the peeling force of Comparative Example 3 and Example 3 of the present invention, where (a) corresponds to Comparative Example 3 and (b) corresponds to Example 3;

[0035] Figure 7 This is a state diagram of the pole piece after peeling obtained by using the test methods for the peeling force of Comparative Example 5 and Example 5 of the present invention, where (a) corresponds to Comparative Example 5 and (b) corresponds to Example 5;

[0036] Figure 8 This is a state diagram of the pole piece after peeling obtained by using the test methods for the peeling force of Comparative Example 6 and Example 6 of the present invention, where (a) corresponds to Comparative Example 6 and (b) corresponds to Example 6. Detailed implementation manners

[0037] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually in accordance with conventional conditions.

[0038] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0039] Whether it is the positive electrode sheet or the negative electrode sheet, during the 180° peeling test, due to the certain toughness of the electrode sheet itself, there will be a bend with a certain arc between the electrode sheet moving upward for peeling and the steel plate (fixed substrate) (as shown in Figure 1 (a), specifically manifested as there is a certain gap between the electrode sheet and the steel plate). When the toughness of the electrode sheet cannot maintain this arc under the tensile force, the electrode sheet will be folded (as shown in Figure 1 (b), specifically manifested as the electrode sheet has adhered to the surface of the steel plate), resulting in continuous or discontinuous, regular or irregular creases on the electrode sheet. From the performance perspective, it is that the electrode sheet becomes "brittle". The generation of creases in the peeling test will affect the peeling force value, as shown in Figure 2 and Figure 3 where the abscissa is the peeling interval and the ordinate is the peeling force. Figure 2 For the two electrode sheets in Figure 2 (a), no creases are generated in a certain peeling interval, and the corresponding Figure 3 (b) shows a relatively gentle change in the force value. If only the peeling force in this non-crease section is taken to calculate the average peeling force, the influence factor of the crease can be excluded, and the result is more referenceable. Such electrode sheets can also be used to evaluate the average peeling force through later data processing, after all, there is one or more intervals without creases. However, for electrode sheets with too dense creases, such as the left electrode sheet 1 in Figure 3 (a), the measured peeling force test value is not the true peeling force value, that is, the continuous creases cause the peeling force test value to be completely distorted (such as curve 1 in

[0040] According to the first aspect of the present invention, a method for testing the peeling force of a lithium-ion battery electrode sheet is provided, including the following steps:

[0041] (a) Paste the surface of the coating to be tested of the electrode sheet on the fixed substrate through double-sided tape;

[0042] wherein, a free end X is reserved for the electrode sheet and a free end Y is reserved for the fixed substrate for peeling use;

[0043] (b) Paste the tape on the surface of the untested coating of the electrode sheet, and then roll-press the electrode sheet with the tape pasted on it;

[0044] (c) Pre-strip the pole piece with the tape after rolling so that the coating to be tested on the pole piece is stripped from the initial end of the current collector;

[0045] (d) After the pre-stripping treatment, clamp the free end Y of the fixed substrate on the lower fixture of the tensile testing machine, and clamp the free end X of the pole piece on the upper fixture of the tensile testing machine, strip the pole piece at 180°, and test its stripping force.

[0046] In the present invention, the pole piece includes a current collector and coatings (i.e., active material layers) respectively disposed on two opposite surfaces of the current collector in the thickness direction. According to whether the coating is subjected to a stripping test, the coatings on the two opposite surfaces of the current collector can be divided into a coating to be tested and an untested coating. Thus, the two surfaces of the pole piece in the thickness direction are respectively an untested coating surface and a coating surface to be tested.

[0047] In step (a), the free end X of the pole piece is reserved, which is mainly used to be mounted on the upper fixture of the tensile testing machine through the free end X during stripping. The free end Y of the fixed substrate is reserved, which is mainly used to be mounted on the lower fixture of the tensile testing machine through the free end Y during stripping.

[0048] In step (b), the tape is pasted on the untested coating surface of the pole piece, mainly to increase the toughness of the pole piece to support the bending arc between the pole piece and the fixed substrate during the subsequent 180° (upward) stripping process, so that the pole piece is not overly folded, avoiding continuous or discontinuous, regular or irregular creases caused by excessive folding of the pole piece, and preventing the coating dressing on the unpeeled side from breaking and falling off, thereby avoiding sudden jumps in the stripping force value. After the tape is pasted on the untested coating surface of the pole piece, the pole piece with the tape pasted is then rolled to make the tape and the untested coating of the pole piece adhere tightly, preventing bubbles or the tape from detaching from the pole piece first during the stripping process and thus affecting the test.

[0049] In step (c), a pre-stripping treatment is performed on the initial stripping end of the coating to be tested on the pole piece and the current collector to avoid breakage of the pole piece due to folding at the initial stage of stripping.

[0050] Step (d) is mainly to perform a 180° stripping treatment on the pole piece using a tensile testing machine.

[0051] The present invention provides a method for testing the peel strength of a lithium-ion battery electrode sheet. Specifically, the surface of the coating to be tested on the electrode sheet is adhered to a fixed substrate, then a tape is adhered to the surface of the untested coating of the electrode sheet, and then the electrode sheet with the tape adhered is roll-pressed. The roll-pressed electrode sheet with the tape adhered is first pre-peeled and then peeled by 180° folding to test the peel strength of the electrode sheet; this testing method can significantly enhance the toughness of the electrode sheet by only adhering the tape to the surface of the untested coating of the electrode sheet before peeling, so as to support the bending arc between the electrode sheet and the fixed substrate during the subsequent 180° (upward) peeling process. At the same time, combined with the pre-peeling treatment method, the electrode sheet will not be overly folded, avoiding continuous or discontinuous, regular or irregular creases caused by excessive folding of the electrode sheet. This testing method can significantly separate the current collector from the coating to be tested, and the untested coating adheres well to the current collector without breaking or powdering. In this case, the peel force curve is smooth and stable, and there will be no problem of sudden jump in the peel force value, making the test result reliable. This testing method does not require additional equipment and is easy to implement. At the same time, it can also enable such electrode sheets that will generate creases to obtain a result closer to the "average peel strength" of the electrode sheet itself.

[0052] As an optional implementation manner of the technical solution of the present invention, in step (a), the lengths of the double-sided tapes are respectively smaller than the lengths of the fixed substrate and the electrode sheet, so as to reserve free ends on the fixed substrate and the electrode sheet for convenient peeling.

[0053] As an optional implementation manner of the technical solution of the present invention, in step (a), the fixed substrate usually only needs to be a hard substrate with a smooth and flat surface, such as a stainless steel substrate, a hard plastic plate, etc.

[0054] As an optional implementation manner of the technical solution of the present invention, in step (b), the tape includes at least one of a double-sided tape, a paper tape, an electrical tape, or a transparent tape. The above tapes can provide a certain adhesion force and increase the toughness of the electrode sheet.

[0055] As a preferred implementation manner of the technical solution of the present invention, the tape is a transparent tape. The inventor found through multiple comparative experiments that when the tape is a transparent tape, the achieved effect reaches a relatively optimal level.

[0056] As an alternative embodiment of the technical solution of the present invention, in step (b), the pasting area of the tape on the side of the pole piece with the untested coating corresponds to the pasting area of the double-sided tape on the side of the pole piece with the to-be-tested coating. Generally speaking, the pasting area of the tape on the side of the pole piece with the untested coating preferably completely covers the pasting area of the double-sided tape on the side of the pole piece with the to-be-tested coating. If the pasting area of the tape on the side of the pole piece with the untested coating is smaller than the pasting area of the double-sided tape on the side of the pole piece with the to-be-tested coating, on the one hand, it is not easy to operate and it is difficult to determine the middle position of the tape pasted on the side of the pole piece with the untested coating. On the other hand, it may result in insufficient toughness, and there may still be creases on the pole piece during the peeling process.

[0057] As an alternative embodiment of the technical solution of the present invention, in step (b), a roller is used to roll the pole piece pasted with the tape, and the number of times the roller rolls back and forth is at least 3 times, such as 3 times, 4 times or 5 times, etc. And through experimental verification, after the roller rolls back and forth 3 times, increasing the number of roller rolling times by 1 - 2 times has little effect on the result.

[0058] As an alternative embodiment of the technical solution of the present invention, in step (d), the distance at which the to-be-tested coating of the pole piece starts to peel from the initial end of the current collector is 1 - 2 cm.

[0059] As an alternative embodiment of the technical solution of the present invention, in step (c), the pre-peeling treatment includes the following steps: Place the fixed substrate pasted with the pole piece on a horizontal tabletop, with the side of the fixed substrate pasted with the pole piece facing up. Lift the free end X of the pole piece with one hand, and press the free end Y of the fixed substrate with the other hand. Lift the pole piece upward to make the pole piece adhered by the double-sided tape peel off a distance of 1 - 2 cm first.

[0060] As an alternative embodiment of the technical solution of the present invention, in step (d), after the pre-peeling treatment, first zero and calibrate the tensile testing machine, then clamp the free end Y of the fixed substrate on the lower fixture of the tensile testing machine, and clamp the free end X of the pole piece on the upper fixture of the tensile testing machine.

[0061] The method for testing the peeling force of the lithium-ion battery pole piece provided by the present invention is more suitable for pole pieces with abnormal peeling such as creases and material detachment after the peeling test. The test results after pasting the tape can be used to eliminate the interference of crease or material detachment factors on the test results, so as to improve the abnormal 180° peeling force test of the pole piece.

[0062] According to the second aspect of the present invention, there is also provided an application of the method for testing the peeling force of the lithium-ion battery pole piece provided in the first aspect of the present invention in the battery field.

[0063] Due to the advantages of the above-mentioned method for testing the peeling force of the lithium-ion battery pole piece, it can be widely used in fields such as battery performance testing and evaluation.

[0064] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0065] Example 1

[0066] The present embodiment provides a method for testing the peeling force of a lithium-ion battery (before negative electrode rolling). The thickness of the pole piece is 0.1710 mm, and the specific composition includes a current collector (copper foil, thickness 6 μm) and a negative electrode active material layer (i.e., a coating to be tested and a coating surface not to be tested) arranged on two opposite surfaces of the current collector. The negative electrode active material layer includes the following components in mass fractions: graphite 92%, conductive carbon black SP 2%, CMC 2% and SBR 4%.

[0067] The process flow of this test method is as follows Figure 4 (a)- Figure 4 (j), specifically comprising the following steps:

[0068] (a) The coating surface to be tested of the electrode is adhered to the steel plate by double-sided tape; wherein the electrode is reserved with a free end X and the steel plate is reserved with a free end Y for easy peeling;

[0069] Specifically, take a fixed substrate with a smooth surface of 15CM in length and 2.5CM in width, cut a piece of double-sided tape with a length of 10CM and a width of not less than 2.5CM, align the long end of the double-sided tape with the long end of the fixed substrate, and then stick the double-sided tape on the fixed substrate, ensuring that the width of the double-sided tape can completely cover one side of the width of the fixed substrate, cut off the excess double-sided tape along the width contour of the fixed substrate, use a 2.5KG roller to roll back and forth 3 times to make it stick closely to the fixed substrate, at this time, one end of the fixed substrate is not pasted with double-sided tape, which is the free end X;

[0070] Remove the double-sided adhesive protective layer, take a 22CM long electrode to be tested, align the double-sided adhesive end of the fixed substrate with the coated side of the electrode to be tested, press down and stick it, cut off the excess electrode along the width contour of the substrate, the width of the cut electrode is consistent with the width of the fixed substrate, which is 2.5CM, and the length is 22CM. At this time, there is an extra electrode at the free end of the fixed substrate, and the length of the electrode exceeds the free end of the fixed substrate by 7CM, which is the free end Y of the electrode.

[0071] (b) sticking the tape on the untested coating surface of the electrode, and then rolling the electrode with the tape, specifically:

[0072] Take a 15CM long transparent tape and stick it on the untested coating surface of the electrode along the long end of the fixed substrate. Cut off the excess transparent tape along the width outline of the fixed substrate, and then use a 2.5KG roller to roll back and forth 3-4 times to make it stick tightly.

[0073] (c) Pre-strip the initial end of the coating to be tested on the electrode sheet from the current collector, specifically: Place the fixed substrate with the electrode sheet pasted on a horizontal tabletop, with the side of the fixed substrate with the electrode sheet facing up. Lift the free end X of the electrode sheet with one hand and press the free end Y of the fixed substrate with the other hand. Pull up the electrode sheet to peel off the electrode sheet adhered by double-sided adhesive for a distance of 1-2 cm first.

[0074] (d) After the pre-stripping treatment, cut an additional 12 cm in length and 2.5 cm in width of the electrode sheet to be tested, clamp it on the upper fixture of the tensile testing machine, and zero the force value at this time; Remove the electrode sheet to be tested used for zeroing, clamp the free end X of the fixed substrate with the electrode sheet pasted on the lower fixture of the tensile testing machine, clamp the free end Y of the electrode sheet on the upper fixture of the tensile testing machine. After adjusting the tightness of the electrode sheet with the up and down keys, zero the displacement value at this time. Then start to strip the electrode sheet at 180° and test its stripping force.

[0075] Example 2

[0076] This example provides a method for testing the stripping force of an electrode sheet of a lithium-ion battery (after negative electrode rolling). Except that the thickness of the electrode sheet used is 0.1330 mm, the specific composition includes a current collector (copper foil, thickness 6 μm) and negative electrode active material layers provided on opposite two surfaces of the current collector (i.e., the surfaces of the coating to be tested and the coating not to be tested). The negative electrode active material layer includes the following components by mass fraction: graphite 92%, SP 2%, CMC 2%, and SBR 4%. The rest of the testing methods and steps are the same as those in Example 1.

[0077] Example 3

[0078] This example provides a method for testing the stripping force of an electrode sheet of a lithium-ion battery (before positive electrode rolling). Except that the thickness of the electrode sheet used is 0.2155 mm, the specific composition includes a current collector (aluminum foil, thickness 12 μm) and positive electrode active material layers provided on opposite two surfaces of the current collector (i.e., the surfaces of the coating to be tested and the coating not to be tested). The positive electrode active material layer includes the following components by mass fraction: LiFePO 4 92%, SP 3%, and PVDF 5%. The rest of the testing methods and steps are the same as those in Example 1.

[0079] Example 4

[0080] This example provides a method for testing the stripping force of an electrode sheet of a lithium-ion battery (after positive electrode rolling). Except that the thickness of the electrode sheet used is 0.1648 mm, the specific composition includes a current collector (aluminum foil, thickness 12 μm) and positive electrode active material layers provided on opposite two surfaces of the current collector (i.e., the surfaces of the coating to be tested and the coating not to be tested). The positive electrode active material layer includes the following components by mass fraction: LiFePO 492%, SP 3%, and PVDF 5%, and the remaining test methods and steps are the same as those in Example 1.

[0081] Example 5

[0082] This example provides a method for testing the peel strength of the electrode sheet of a lithium-ion battery (before negative electrode rolling). Except that the thickness of the electrode sheet (before negative electrode rolling) used is 0.1650 mm, the specific composition includes a current collector (copper foil, thickness 6 μm) and negative electrode active material layers provided on opposite surfaces of the current collector (i.e., the surfaces of the coating to be tested and the untested coating). The negative electrode active material layer includes the following components in mass fractions: graphite 95.8%, SP 1%, CMC 1.2%, and SBR 2%, and the remaining test methods and steps are the same as those in Example 1.

[0083] Example 6

[0084] This example provides a method for testing the peel strength of the electrode sheet of a lithium-ion battery (after positive electrode rolling). Except that the thickness of the electrode sheet (after positive electrode rolling) used is 0.1700 mm, the specific composition includes a current collector (aluminum foil, thickness 12 μm) and positive electrode active material layers provided on opposite surfaces of the current collector (i.e., the surfaces of the coating to be tested and the untested coating). The positive electrode active material layer includes the following components in mass fractions: LiFePO 4 97%, SP 1%, PVDF 1.9%, and dispersant polyvinylpyrrolidone 0.1%, and the remaining test methods and steps are the same as those in Example 4.

[0085] Comparative Example 1

[0086] This comparative example is a comparative experiment of Example 1. Except that step (b) is not carried out in the test method, that is, no tape is pasted on the untested coating surface of the electrode sheet, and the remaining steps are the same as those in Example 1.

[0087] Comparative Example 2

[0088] This comparative example is a comparative experiment of Example 2. Except that step (b) is not carried out in the test method, that is, no tape is pasted on the untested coating surface of the electrode sheet, and the remaining steps are the same as those in Example 2.

[0089] Comparative Example 3

[0090] This comparative example is a comparative experiment of Example 3. Except that step (b) is not carried out in the test method, that is, no tape is pasted on the untested coating surface of the electrode sheet, and the remaining steps are the same as those in Example 3.

[0091] Comparative Example 4

[0092] This comparative example is a comparative experiment of Example 4. Except that step (b) is not carried out in the test method, that is, no tape is pasted on the untested coating surface of the electrode sheet, the remaining steps are the same as those of Example 4.

[0093] Comparative Example 5

[0094] This comparative example is a comparative experiment of Example 5. Except that step (b) is not carried out in the test method, that is, no tape is pasted on the untested coating surface of the electrode sheet, the remaining steps are the same as those of Example 5.

[0095] Comparative Example 6

[0096] This comparative example is a comparative experiment of Example 6. Except that step (b) is not carried out in the test method, that is, no tape is pasted on the untested coating surface of the electrode sheet, the remaining steps are the same as those of Example 6.

[0097] In order to compare the technical effects of the above examples and comparative examples, the following experimental examples are specially set up.

[0098] In each example and comparative example, when performing 180° peeling and testing the peeling force of the electrode sheet, GB / T2792-2014 is followed, the test speed is 100 mm / min, and three parallel sample tests are carried out for each example and comparative example. The specific test results are shown in Table 1-6 below. It should be noted that the mean difference in the following table refers to the absolute value of the difference between the mean of the comparative example and the mean of the example.

[0099] Table 1 Comparison of the average peeling strength of the negative electrode sheet before roller pressing between Comparative Example 1 and Example 1

[0100]

[0101] Table 2 Comparison of the average peeling strength of the negative electrode sheet after roller pressing between Comparative Example 2 and Example 2

[0102]

[0103] Table 3 Comparison of the average peeling strength of the positive electrode sheet before roller pressing between Comparative Example 3 and Example 3

[0104]

[0105]

[0106] Note: The average peeling strength of Example 3 is denoted as A, and the average peeling strength of Comparative Example 3 is denoted as B.

[0107] Table 4 Comparison of the average peeling strength of the positive electrode sheet after roller pressing between Comparative Example 4 and Example 4

[0108]

[0109] Table 5 Comparison of Average Peel Strength of Anode Sheets before Roller Compaction between Comparative Example 5 and Example 5

[0110]

[0111] Table 6 Comparison of Average Peel Strength of Cathode Sheets after Roller Compaction between Comparative Example 6 and Example 6

[0112]

[0113] From the peel states of the electrode sheets obtained at the end of the tests of each example and comparative example of the present invention, after the 180° peel test using Comparative Examples 1 - 4, there were no creases or material detachment phenomena on the electrode sheets, while after the peel test using the test methods of Examples 1 - 4, a small number of creases would appear on the electrode sheets, specifically as shown in Figure 5 and Figure 6 shown. And after the 180° peel test using the test methods of the above Comparative Examples 5 - 6 and Examples 5 - 6, creases, material detachment and other phenomena would occur on the electrode sheets, for example as shown in Figure 7 and Figure 8 shown. Among them, Figure 7 (a) and Figure 7 (b) are respectively the state diagrams of the peeled electrode sheets obtained by using the test methods of Comparative Example 5 and Example 5, Figure 8 (a) and Figure 8 (b) are respectively the state diagrams of the peeled electrode sheets obtained by using the test methods of Comparative Example 6 and Example 6. It can be seen from the comparison between Comparative Example 5 and Example 5, and between Comparative Example 6 and Example 6 that creases will be generated after peeling for both the electrode sheets without pasting transparent tape and those with transparent tape pasted, but the creases generated by the electrode sheets with transparent tape pasted are fewer than those generated by the electrode sheets without transparent tape pasted, and the depth of the generated creases is also slightly shallower.

[0114] And it can be seen from the data in the above Tables 1 - 6 that:

[0115] For the anode sheets before roller compaction, anode sheets after roller compaction, and cathode sheets after roller compaction that have no creases or material detachment phenomena after the 180° peel force test, when these three types of electrode sheets are tested by the 180° peel force test of the original method (without pasting transparent tape, i.e., Comparative Examples 1, 2 and 4) and the improved (pasting transparent tape, i.e., Examples 1, 2 and 4) 180° peel force test schemes, the difference in their average peel strength results is about ±1 N / m, that is, the original peel strength of the electrode sheet ≈ the average peel strength of the electrode sheet with transparent tape pasted.

[0116] Similarly, for the anode pre-rolling electrode sheet without creases and material detachment after the 180° peel strength test, the average peel strength tested using the improved method (sticking transparent tape, i.e., Example 3) is about 1.5 times that of the original method (without sticking transparent tape, i.e., Comparative Example 3). The difference is about ±1 N / m, which is relatively small and close to the error between parallel samples in this comparative example. That is, the original peel strength of the electrode sheet ≈ the average peel strength of the electrode sheet with transparent tape stuck / 1.5.

[0117] For the cathode pre-rolling electrode sheet and the anode post-rolling electrode sheet with creases and material detachment after the 180° peel strength test, the average peel strength tested using the original method (without sticking transparent tape, i.e., Comparative Example 5 and Comparative Example 6) for the 180° peel strength test is abnormally increased due to excessive creases, far exceeding the production preset value (the production preset value is the range given by engineers based on previous experimental records and experience). However, the average peel strength tested using the improved method (sticking transparent tape, i.e., Example 5 and Example 6) is closer to the production preset value (the production preset value of Example 5 < 20 N / m, and the production preset value of Example 6 < 30 N / m). This also shows that the generation of creases or material detachment in the peel test will cause the tested value of the average peel strength to be completely distorted and lose its reference value. Therefore, for the electrode sheet with creases and material detachment after the 180° peel strength test, the average peel strength tested using the improved method (sticking transparent tape) is more valuable as a reference.

[0118] From the above experimental data, it can be clearly seen that the test results obtained using the test method of the present invention have reference value, and a data model can be established by collecting more data to make the results more accurate. Therefore, for abnormal electrode sheets (with creases or material detachment) in the future, the test results after sticking tape can be used to eliminate the interference of creases or material detachment factors on the test results, so as to improve the abnormality of the 180° peel strength test of the electrode sheet.

[0119] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are within the scope of the claims of the present invention pending approval.

Claims

1. A method for testing the peeling force of a lithium-ion battery electrode, characterized in that: The following steps are involved: (a) The coating side of the electrode to be tested is adhered to the fixed substrate by double-sided tape; The pole piece has a reserved free end X and the fixed substrate has a reserved free end Y for peeling and use; (b) sticking the tape to the untested coating side of the electrode, and then rolling the electrode with the tape; (c) pre-peeling the electrode sheet with the tape attached after rolling, so that the coating to be tested of the electrode sheet is peeled off from the initial end of the current collector peeling; (d) After the pre-peeling treatment, the free end Y of the fixed substrate is clamped on the lower fixture of the tensile testing machine, and the free end X of the electrode is clamped on the upper fixture of the tensile testing machine. The electrode is peeled 180° and its peeling force is tested.

2. The method for testing the peeling force of a lithium-ion battery pole piece according to claim 1, characterized in that: In step (a), the length of the double-sided tape is smaller than the length of the fixed substrate and the pole piece, respectively.

3. The method for testing the peeling force of a lithium-ion battery pole piece according to claim 1, characterized in that: In step (a), the fixed substrate includes a stainless steel substrate or a hard plastic substrate.

4. The method for testing the peeling force of a lithium-ion battery pole piece according to claim 1, characterized in that: In step (b), the tape includes at least one of double-sided tape, paper tape, electrical tape or transparent tape.

5. The method for testing the peeling force of a lithium-ion battery pole piece according to claim 4, characterized in that: In step (b), the adhesive tape is a transparent adhesive tape.

6. The method for testing the peeling force of a lithium-ion battery pole piece according to claim 1, characterized in that: In step (b), the sticking area of ​​the tape on the untested coating side of the electrode piece corresponds to the sticking area of ​​the double-sided tape on the to-be-tested coating side of the electrode piece.

7. The method for testing the peeling force of a lithium-ion battery pole piece according to claim 1, characterized in that: In step (b), a roller is used to roll the pole piece with the tape attached thereto, and the roller is rolled back and forth no less than 3 times.

8. The method for testing the peeling force of a lithium-ion battery pole piece according to claim 1, characterized in that: In step (c), the distance between the coating to be tested of the electrode and the initial end of the current collector peeling is 1-2 cm.

9. The method for testing the peeling force of a lithium-ion battery pole piece according to claim 1, characterized in that: In step (d), after the pre-peeling treatment, the tensile testing machine is firstly zeroed and calibrated, and then the free end Y of the fixed substrate is clamped on the lower fixture of the tensile testing machine, and the free end X of the pole piece is clamped on the upper fixture of the tensile testing machine; And / or, the test method for the peeling force of a lithium-ion battery pole piece is mainly applicable to pole pieces that may produce peeling abnormalities during the peeling test.

10. Application of the method for testing the peeling force of a lithium-ion battery pole piece according to any one of claims 1 to 9 in the battery field.

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