Method for evaluating adhesive force of glued diaphragm

Abstract

The invention relates to a method for evaluating the adhesive force of a glued diaphragm. The method comprises the following steps: (1) stacking a pole piece and the glued diaphragm, winding the pole piece and the glued diaphragm to form a roll core, and performing hot pressing; (2) cutting the opened middle roll core from the second circle to the fifth circle; (3) stripping the glued diaphragm in the cut roll core from the attached pole piece for a certain distance, clamping the glued diaphragm with an opening by a clamp of a tension meter A, and clamping the pole piece with the opening on the same side by a clamp of a tension meter B; (4) the tension meter A and the tension meter B clamp the glued diaphragm and the pole piece and then move in opposite directions at the same speed at the same time; and (5) imaging and testing an included angle between the pole piece and the glued diaphragm by using CCD imaging detection equipment in the moving process until the included angle does not change any more, recording the numerical value of the included angle at the moment, and evaluating the adhesive force between the glued diaphragm and the pole piece according to the size of the included angle. According to the method for evaluating the adhesive force of the glued diaphragm, the adhesive force between diaphragms with different gluing types and diaphragms with different gluing amounts can be compared, and the accuracy of the method is high.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a method for evaluating the adhesion of a glue-coated diaphragm. Background Art

[0002] In recent years, the market demand for lithium battery separators has continued to increase, and the proportion of coated films has continued to increase. The entire industry involves a large number of coated separators for lithium-ion batteries. The coating layer in the coated separator is mainly made of polymer materials such as PVDF and PMMA. The coated separator can not only provide the bonding force between the separator and the electrode, making it easier to shape the battery cell and more convenient to put it into the aluminum shell; it can also be well bonded to the electrode, and is not easily washed away by gas production during the battery formation process. In extreme cases, it is not easy to cause a short circuit. At the same time, it can make the entire battery cell have a relatively low internal resistance, and the battery cell also has a relatively good cycle life. In addition, the copolymer of PVDF in the coating layer has good wettability with the electrolyte, which can quickly improve the wettability of the separator and improve battery productivity.

[0003] The adhesive force of the glue-coated diaphragm is a crucial performance, and the size of the adhesive force of the glue-coated diaphragm affects the comprehensive performance of the lithium-ion battery. If the adhesive force is too small, the glue layer cannot play a role, there will be a gap between the diaphragm and the pole piece, it is easy to have residual gas, and the diaphragm will be wrinkled. Such macro defects on the interface between the diaphragm and the pole piece will lead to uneven distribution of internal resistance, and the battery will be partially overcharged or over-discharged during the cycle, which will affect the consistency and cycle stability of the battery; if the adhesive force is too large, it will increase the internal resistance of the battery cell and reduce the cycle performance of the battery. By evaluating the adhesive force of the glue layer of the glue-coated diaphragm, the appropriate process can be selected to ensure battery performance.

[0004] Currently, there is no standard method or related research in the industry to evaluate the adhesion of glue-coated diaphragms. Therefore, there is an urgent need for a method to evaluate the adhesion of glue-coated diaphragm electrodes. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the adhesion of glue-coated membranes, which can compare the adhesion between membranes of different glue-coating types and membranes with different glue-coating amounts, and the method has high accuracy.

[0006] The technical solution adopted by the present invention to solve the above problem is: a method for evaluating the adhesion of a glue-coated diaphragm, comprising the following steps: (1) stacking the electrode and the glue-coated diaphragm so that the glue-coated layer of the glue-coated diaphragm faces the electrode, and winding them into a winding core using a winding machine, and hot pressing the wound winding core to obtain a hot-pressed winding core; (2) Gradually open the hot-pressed core to ensure that the adhesive layer in the adhesive-coated diaphragm is well attached to the electrode and is not subjected to pulling force, and cut the core between the second and fifth circles to obtain a rectangular core; (3) Peel off the glue-coated diaphragm and the corresponding electrode in the cut core for a certain distance, then clamp the open glue-coated diaphragm with the clamp of tensile gauge A, and clamp the open electrode on the same side with the clamp of tensile gauge B; (4) After the force gauge A and the force gauge B clamp the glue-coated diaphragm and the electrode, they move in opposite directions at the same time, and the moving speed remains consistent; (5) When the glue-coated diaphragm and the electrode are moved by the pulling force, the CCD imaging detection equipment is used to image and test the angle between the electrode and the glue-coated diaphragm until the angle no longer changes. The value of the angle at this time is recorded, and the size of the angle is used to evaluate the size of the adhesion between the glue-coated diaphragm and the electrode. The larger the angle, the greater the adhesion, and the smaller the angle, the smaller the adhesion.

[0007] Preferably, in step (1), the hot pressing temperature is 90-95° C., the hot pressing time is 30-60 seconds, and the hot pressing pressure is 2500-4500 kgf.

[0008] Preferably, the length of the rectangular roll core in step (2) is 30-50 cm.

[0009] Preferably, in step (3), the glue-coated diaphragm in the cut winding core and the corresponding electrode are peeled off by 10 mm.

[0010] Preferably, the moving rate in step (4) is 200-250 mm / min.

[0011] Preferably, in step (4), the dynamometer A and the dynamometer B clamp the glue-coated diaphragm and the pole piece and then move simultaneously in opposite directions via rollers to ensure that the traction forces acting on the glue-coated diaphragm and the pole piece are in the horizontal direction.

[0012] Preferably, in the test for evaluating the adhesion of the glue-coated diaphragm, the glue-coated diaphragm is on the upper layer and the electrode is on the lower layer.

[0013] Compared with the prior art, the advantages of the present invention are: The method for evaluating the adhesive force of the glue-coated diaphragm of the present invention can compare the adhesive force between films of different glue-coated types and diaphragms with different glue-coated amounts, and the method has high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the adhesive strength evaluation equipment for the glue-coated diaphragm and the electrode of the present invention.

[0015] Among them, 1 is the glue-coated diaphragm, 2 is the test electrode, 3 is the clip of tensile gauge A, and 4 is the clip of tensile gauge B. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below with reference to the accompanying drawings.

[0017] like Figure 1 As shown, it is a schematic diagram of the adhesive strength evaluation of the glue-coated diaphragm and the electrode in this embodiment. Example 1

[0018] Tested with 48173170-120Ah lithium iron phosphate positive plate A method for evaluating the adhesion of a glue-coated diaphragm comprises the following steps: (1) Stack the positive electrode sheet and the glue-coated diaphragm in the order of positive electrode sheet and glue-coated diaphragm (Xingyuan diaphragm, with 14+3um specification, 3um glue layer, PVDF coating component, PP base film) from top to bottom, and use a winding machine to wind it into a core, and hot press the wound core to obtain a hot-pressed core. The hot pressing temperature is 90°C, the hot pressing time is 60s, and the hot pressing pressure is 3500Kgf. The glue layer of the glue-coated diaphragm faces the positive electrode sheet.

[0019] (2) Gradually open the hot-pressed core to ensure that the adhesive layer in the adhesive-coated separator is well attached to the positive electrode sheet and the negative electrode sheet without being pulled, and cut the core between the second and fifth circles to obtain a rectangular core; the cut core length is 30 cm; (3) Peel off the glue-coated separator and the corresponding positive electrode sheet in the cut core by 10 mm, then clamp the opened glue-coated separator with the clamp of tensile gauge A, and clamp the opened positive electrode sheet on the same side with the clamp of tensile gauge B, with the glue-coated separator on the top and the positive electrode sheet on the bottom; (4) After the tensile gauge A and the tensile gauge B clamp the glue-coated diaphragm and the positive electrode, they move in opposite directions at the same time, and the moving speed remains consistent, which is 200 mm / min; (5) When the coated diaphragm and the positive electrode are subjected to traction, the CCD imaging detection equipment is used to image and test the angle between the electrode and the coated diaphragm until the angle no longer changes (at this time, the coated diaphragm and the positive electrode are peeled off to half the length of the cut core), and the value of the angle at this time is recorded as 153°. Example 2

[0020] The only difference from Example 1 is that the glue-coated diaphragm is a ZTE glue-coated diaphragm with a specification of 14+1um, a glue coating layer of 1um, a coating component of PVDF, and a base film of PP.

[0021] The test angle is 96° Example 3

[0022] Take the 48173170-120Ah lithium iron phosphate positive electrode test as an example A method for evaluating the adhesion of a glue-coated diaphragm comprises the following steps: (1) The positive electrode sheet, the glue-coated separator, and the negative electrode sheet are stacked in the order of positive electrode sheet, glue-coated separator (thick double-sided glue-coated separator, with a specification of 9+2+2um, a glue layer of 2um, a coating component of PVDF, and a base film of PE base film), and negative electrode sheet from top to bottom, and are wound using a winding machine to form a core. The wound core is hot-pressed to obtain a hot-pressed core. The hot-pressing temperature is 90°C, the hot-pressing time is 30s, and the hot-pressing pressure is 2500Kgf. The glue layers on both sides of the glue-coated separator are facing the positive electrode sheet and the negative electrode sheet, respectively.

[0023] (2) Gradually open the hot-pressed core to ensure that the adhesive layer in the adhesive-coated separator is well attached to the positive electrode sheet and the negative electrode sheet without being subjected to pulling force. Cut the core between the second and fifth circles to obtain a rectangular core; the length of the cut core is 30 cm.

[0024] (3) Peel off the glue-coated separator and the corresponding positive electrode sheet in the cut roll core by 10 mm, then clamp the opened glue-coated separator with the clamp of tensile gauge A, and clamp the opened positive electrode sheet on the same side with the clamp of tensile gauge B, with the glue-coated separator on the top and the positive electrode sheet on the bottom.

[0025] (4) After the force gauge A and the force gauge B clamp the glue-coated diaphragm and the positive electrode, they move in opposite directions at the same time, and the moving speed remains consistent at 200 mm / min.

[0026] (5) During the movement of the glue-coated separator and the positive electrode sheet under the pulling force, the CCD imaging detection equipment is used to image and test the angle between the electrode sheet and the glue-coated separator until the angle no longer changes (at this time, the glue-coated separator and the positive electrode sheet are peeled to half the length of the cut core), and the value of the angle at this time is recorded as 158°.

[0027] (6) Peel off 10 mm of the adhesive-coated separator and the corresponding negative electrode sheet in the cut roll core in steps (3), (4) and (5), and then clamp the open adhesive-coated separator with the clamp of tensile gauge A and clamp the open negative electrode sheet on the same side with the clamp of tensile gauge B, with the adhesive-coated separator on the top and the positive electrode sheet on the bottom.

[0028] (7) After the tensile gauge A and the tensile gauge B clamp the glue-coated diaphragm and the negative electrode sheet, they move in opposite directions at the same time, and the moving speed remains consistent at 200 mm / min.

[0029] (8) When the coated diaphragm and the negative electrode are subjected to traction, the CCD imaging detection equipment is used to image and test the angle between the electrode and the coated diaphragm until the angle no longer changes. The value of the angle at this time is recorded as 108°. Example 4

[0030] Steps (1), (2), (3), (4) and (5) of Example 3 are carried out, and the "cutting of the core between the 2nd and 5th turns" in step (2) is replaced by cutting the core of the innermost 5 turns, and the value of the angle is 136°.

[0031] In addition to the above embodiments, the present invention also includes other implementation modes. Any technical solutions formed by equivalent transformation or equivalent replacement should fall within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating the adhesion of a glue-coated diaphragm, characterized in that: The following steps are involved: (1) stacking the electrode and the glue-coated diaphragm so that the glue-coated layer of the glue-coated diaphragm faces the electrode, and winding them into a winding core using a winding machine, and hot pressing the wound winding core to obtain a hot-pressed winding core; (2) Gradually open the hot-pressed core to ensure that the adhesive layer in the adhesive-coated diaphragm is well attached to the electrode and is not subjected to pulling force, and cut the core between the second and fifth circles to obtain a rectangular core; (3) Peel off the glue-coated diaphragm and the corresponding electrode in the cut core for a certain distance, then clamp the open glue-coated diaphragm with the clamp of tensile gauge A, and clamp the open electrode on the same side with the clamp of tensile gauge B; (4) After the force gauge A and the force gauge B clamp the glue-coated diaphragm and the electrode, they move in opposite directions at the same time, and the moving speed remains consistent; (5) When the glue-coated diaphragm and the electrode are moved by the pulling force, the CCD imaging detection equipment is used to image and test the angle between the electrode and the glue-coated diaphragm until the angle no longer changes. The value of the angle at this time is recorded, and the size of the angle is used to evaluate the size of the adhesion between the glue-coated diaphragm and the electrode. The larger the angle, the greater the adhesion, and the smaller the angle, the smaller the adhesion.

2. The method for evaluating the adhesion of a glue-coated diaphragm according to claim 1, characterized in that: In step (1), the hot pressing temperature is 90-95°C, the hot pressing time is 30-60s, and the hot pressing pressure is 2500-4500Kgf.

3. The method for evaluating the adhesion of a glue-coated diaphragm according to claim 1, characterized in that: The length of the rectangular roll core in step (2) is 30-50 cm.

4. The method for evaluating the adhesion of a glue-coated diaphragm according to claim 1, characterized in that: In step (3), the glue-coated diaphragm in the cut core and the corresponding electrode are peeled off by 10 mm.

5. The method for evaluating the adhesion of a glue-coated diaphragm according to claim 1, characterized in that: The moving speed in step (4) is 200-250 mm / min.

6. The method for evaluating the adhesion of a glue-coated diaphragm according to claim 1, characterized in that: In step (4), the dynamometer A and the dynamometer B clamp the glue-coated diaphragm and the pole piece and move in opposite directions simultaneously via rollers to ensure that the traction forces acting on the glue-coated diaphragm and the pole piece are in the horizontal direction.

7. The method for evaluating the adhesion of a glue-coated diaphragm according to claim 1, characterized in that: In the test of evaluating the adhesion of the glue-coated diaphragm, the glue-coated diaphragm is on the upper layer and the electrode is on the lower layer.

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