Method for testing peel strength of battery cell pole piece

Abstract

The invention discloses a method for testing the peel strength of a battery cell pole piece, which comprises the following steps of: attaching a pole piece sample on a substrate adhered with a double-sided adhesive tape, wherein the area of a sample testing area is less than or equal to 100mm, an active layer is adhered towards the substrate, and a clamp connecting area is a single-layer foil; and performing a surface peeling test through a tensile machine, and calculating the peeling strength P (N / cm) according to the ratio of the maximum tensile force value to the area of the test area. According to the method, a test unit is reduced from a traditional strip sample to a small-area sample, and the method can be used for evaluating the bonding strength of small-scale test samples, leftover materials and micro-areas; and a surface stripping mode is adopted, so that the bonding force is intensively reflected, and the measurement precision and sensitivity are improved. And meanwhile, multi-point sampling is supported, and the coating uniformity of the pole piece can be counted and analyzed.

Description

Technical Field

[0001] This invention relates to the field of peel strength testing technology, and in particular to a method for testing the peel strength of battery cell electrodes. Background Technology

[0002] In the field of lithium-ion battery manufacturing, the interfacial bonding performance of electrodes has a crucial impact on the electrochemical performance and process stability of the battery. Peel strength, as an important indicator for evaluating bonding performance, is defined as the maximum force required to peel materials bonded to the same contact surface along a unit width. Specifically, in battery electrodes, it characterizes the bonding strength between the active material layer and the current collector foil.

[0003] Currently, the industry commonly uses 90° or 180° peel tests to evaluate electrode peel strength. Taking the 180° method as an example (see reference). Figure 1 The standard procedure includes: 1) Die-cutting the electrode to be tested into strips with a length of 200mm and a width of 10-50mm; 2) Pasting double-sided tape of the same width as the electrode onto a stainless steel plate, then aligning and bonding the electrode material layer with the double-sided tape, and pressing it with a rubber roller; 3) On a tensile testing machine, fixing the steel plate in the lower clamp position, pulling the foil with the upper clamp to separate it from the active layer, and recording the average tensile force; the ratio of the average tensile force to the width of the electrode strip being tested is the peel strength of the electrode.

[0004] However, while this method is effective in most applications, it still has many limitations: 1) Small-area electrode samples cannot be prepared: For this type of electrode sample, the area is too small to be die-cut into the minimum size required for traditional peel strength testing, making testing impossible; 2) Measurement results for low-bond-strength electrodes are inaccurate: In some electrode systems, such as all-solid-state lithium battery systems, due to the addition of electrolytes and the limitation of lithium-ion conduction, there are stringent requirements for the selection of solvent binders and the amount of binders used. The electrode bond strength is usually not high. Even if the tensile testing machine range is changed and the sensitivity is improved, high consistency cannot be achieved due to the limitations of the peel test method; 3) The difference in peel strength at different locations of the electrode cannot be represented: The bond strength at different locations of the electrode is not always consistent. The above test method calculates the peel strength by the average force value of the sample strip, which cannot reflect the difference in peel strength at different locations of the electrode. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for testing the peel strength of battery cell electrodes.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for testing the peel strength of battery cell electrodes is provided, comprising the following steps: Step 1: Prepare the substrate, the surface of which is covered with double-sided tape; Step 2: Cut the electrode sheet to be tested to obtain an electrode sample. The electrode sample includes a test area and a fixture connection area. The test area includes an active layer and a foil, and the active layer of the test area is bonded to the double-sided adhesive tape. The fixture connection area is a single layer of foil. Step 3: Fix the substrate to the lower clamp of the tensile testing machine and fix the clamp connection area to the upper clamp of the tensile testing machine; start the tensile testing machine and lift the upper clamp upward at a constant rate until the active layer of the electrode sample is completely peeled off from the foil. Step 4: Record the tensile strength curve, take the maximum tensile strength value in the curve, calculate the ratio of the maximum tensile strength value to the test area of ​​the electrode sample, and obtain the peel strength P, in N / cm².

[0007] Furthermore, the area of ​​the test area is 10~1000mm², preferably 10~100mm².

[0008] Furthermore, the electrode sample is square, rectangular, or circular.

[0009] Furthermore, the area of ​​the double-sided tape is the same as the area of ​​the test area, and the test area completely covers the double-sided tape area.

[0010] Furthermore, the substrate is a stainless steel sheet with a smooth, level surface.

[0011] Furthermore, the method includes testing multiple samples of the same electrode sheet to obtain the peel strength at different locations on the electrode sheet.

[0012] Furthermore, the upper clamping lifting rate of the tensile testing machine is 10 mm / min to 100 mm / min, preferably 30 mm / min to 70 mm / min.

[0013] Furthermore, the electrode is a lithium battery electrode, including a negative electrode or a positive electrode.

[0014] The present invention adopts the above technical solution and has the following technical effects compared with the prior art: Traditional methods require cutting electrode strips up to 200mm long and 20mm wide, which cannot effectively assess the bonding strength of small-scale samples, electrode scraps, or specific tiny areas during the R&D stage. This invention reduces the test unit from "strips" to "samples with extremely small areas" (as low as 200mm² or even smaller), greatly reducing the requirements for electrode area and making peel strength testing possible in the above scenarios, thus expanding the applicability of the method.

[0015] Traditional testing methods rely on linear peeling, while this invention uses surface peeling, which concentrates the adhesive force of the entire test area into a peak tensile force, amplifying the peel strength in performance and thus achieving more accurate measurement.

[0016] Because of the small sampling area of ​​this invention, multiple samples can be easily and non-destructively cut from the same electrode sheet for testing. By analyzing the average and standard deviation of these multi-point data, not only can the overall bonding strength level be obtained, but also the consistency and uniformity of the electrode coating can be quantitatively evaluated, providing key data that traditional methods cannot provide for optimizing coating, drying and other preparation processes. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the "180° method" for testing the peel strength of battery cell electrodes in the prior art; Figure 2 This is a schematic diagram of the test method for the peel strength of the battery cell electrode of the present invention; Figure 3 This is a schematic diagram of an electrode sample in one embodiment of the present invention; The reference numerals in the attached figures are: 1-Stainless steel sheet; 2-Double-sided adhesive tape; 3-Active layer; 4-Foil; 5-Lower clamp; 6-Upper clamp; 7-Test area; 8-Clamp connection area. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0019] This invention provides a method for testing the peel strength of battery cell electrodes (see attached). Figure 2 and Figure 3 ), including the following steps: Step 1: Prepare a substrate (stainless steel sheet 1 with a smooth, level surface), with double-sided tape 2 attached to the surface of the substrate; Step 2: Cut the electrode sheet to be tested to obtain an electrode sample. The electrode sample includes a test area 7 and a clamp connection area 8. The test area 7 includes an active layer 3 and a foil 4. The area of ​​the test area 7 is 10~1000mm², preferably 10~100mm², and the active layer of the test area 7 is bonded to the double-sided tape (the area of ​​the double-sided tape is the same as the area of ​​the test area, and the test area completely covers the double-sided tape area); the clamp connection area is a single layer of foil 4. Step 3: Fix the substrate to the lower clamp 5 of the tensile testing machine and fix the clamp connection area 8 to the upper clamp 6 of the tensile testing machine; start the tensile testing machine and lift the upper clamp upward at a constant speed (10mm / min to 100mm / min, preferably 30mm / min to 70mm / min) until the active layer of the electrode sample is completely peeled off from the foil. Step 4: Record the tensile strength curve, take the maximum tensile strength value in the curve, calculate the ratio of the maximum tensile strength value to the test area of ​​the electrode sample, and obtain the peel strength P, in N / cm².

[0020] The peel strength is calculated using the following formula: P=F max / A Where P is the peel strength (N / cm²), Fmax is the maximum tensile force (N), and A is the area of ​​the test area of ​​the sample (cm²).

[0021] Preferably, the electrode sample is square, rectangular, or circular.

[0022] Preferably, the above method includes testing multiple samples of the same electrode sheet to obtain the peel strength at different locations of the electrode sheet.

[0023] Example 1 Take one sample electrode and cut it into three strips, each 10 mm wide and 200 mm long, transversely. For each sample strip, select five points at equal intervals from one end to the other. At each point, prepare... Figure 3 The individual sample unit shown has a test area of ​​10mm × 10mm (area 100mm²) square, with a 10mm long foil section reserved as a clamping connection area. A total of 15 effective individual sample units were prepared. Subsequently, the peel strength of each sample unit was tested using the method of this invention.

[0024] The preparation process of Sample 1 is as follows: During the slurry preparation process, artificial graphite (D50 of 15μm) was used as the negative electrode material, Li6PS5Cl (D50 of 3μm) as the electrolyte, sp as the conductive agent, and PVDF-HFP as the binder. The ratio of negative electrode material, electrolyte, conductive agent, and binder was 65:30:2:3, the solvent was isobutyl isobutyrate, and the slurry solid content was 55%. SEBS was dissolved in isobutyl isobutyrate and stirred in a double planetary stirrer to prepare a 3.667% concentration adhesive solution. The corresponding proportions of artificial graphite, Li6PS5Cl, and sp were taken, thoroughly mixed as dry powder, added to the binder adhesive solution, and stirred for 8 hours. After stirring, the slurry was degassed, sieved, and then evenly coated onto the copper foil surface using a doctor blade coater. After coating, the electrode was naturally dried at 25℃ for 3 hours, and then transferred to a 90℃ forced-air drying oven for 12 hours.

[0025] Comparative Example 1 Take one sample electrode and cut it into three strips, each 20 mm wide and 200 mm long, along the transverse direction. (Refer to...) Figure 1 The 180° peel test method shown is used to test peel strength.

[0026] Example 2 Take a sample diode and cut it into three strips, each 10 mm wide and 200 mm long, transversely. For each sample strip, select five points at equal intervals from one end to the other. At each point, prepare... Figure 3 The individual sample unit shown has a test area of ​​10mm × 10mm (area 100mm²) square, with a 10mm long foil section reserved as a clamping connection area. A total of 15 effective individual sample units were prepared. Subsequently, the peel strength of each sample unit was tested using the method of this invention.

[0027] The preparation process of sample two is as follows: During the slurry preparation process, artificial graphite (D50 of 15μm) was used as the negative electrode material, Li6PS5Cl (D50 of 3μm) as the electrolyte, sp as the conductive agent, and PVDF-HFP as the binder. The ratio of negative electrode material, electrolyte, conductive agent, and binder was 67:30:2:1, the solvent was isobutyl isobutyrate, and the slurry solid content was 55%. SEBS was dissolved in isobutyl isobutyrate and stirred in a double planetary stirrer to prepare a 1.22% concentration adhesive solution. The corresponding proportions of artificial graphite, Li6PS5Cl, and sp were taken, thoroughly mixed as dry powder, added to the binder adhesive solution, and stirred for 8 hours. After stirring, the slurry was degassed, sieved, and then evenly coated onto the copper foil surface using a doctor blade coater. After coating, the electrode was naturally dried at 25℃ for 3 hours, and then transferred to a 90℃ forced-air drying oven for 12 hours.

[0028] Comparative Example 2 Take a sample diode and cut it into three strips, each 20 mm wide and 200 mm long, along the transverse direction. (Refer to...) Figure 1 The 180° peel test method shown is used to test peel strength.

[0029] The test results are shown in Table 1 below: Table 1

[0030] As can be seen from Comparative Example 1 and Example 1, the traditional peel strength test method can only measure the average value of a specific area, but cannot obtain the peel strength value of the local area of ​​the electrode. As can be seen from Comparative Example 2 and Example 2, when the peel strength of the electrode is small, the traditional 180° test method has a large measurement error, while the test method of the present invention has a more accurate measurement result.

[0031] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing the peel strength of battery cell electrodes, characterized in that, Includes the following steps: Step 1: Prepare the substrate, the surface of which is covered with double-sided tape; Step 2: Cut the electrode sheet to be tested to obtain an electrode sample. The electrode sample includes a test area and a fixture connection area. The test area includes an active layer and a foil, and the active layer of the test area is bonded to the double-sided adhesive tape. The fixture connection area is a single layer of foil. Step 3: Fix the substrate to the lower clamp of the tensile testing machine and fix the clamp connection area to the upper clamp of the tensile testing machine; start the tensile testing machine and lift the upper clamp upward at a constant rate until the active layer of the electrode sample is completely peeled off from the foil. Step 4: Record the tensile strength curve, take the maximum tensile strength value in the curve, calculate the ratio of the maximum tensile strength value to the test area of ​​the electrode sample, and obtain the peel strength P, in N / cm².

2. The method for testing the peel strength of battery cell electrodes according to claim 1, characterized in that, The area of ​​the test zone is 10~1000mm².

3. The method for testing the peel strength of battery cell electrodes according to claim 1, characterized in that, The electrode sample is square, rectangular, or circular.

4. The method for testing the peel strength of battery cell electrodes according to claim 1, characterized in that, The area of ​​the double-sided tape is the same as the area of ​​the test area, and the test area completely covers the area of ​​the double-sided tape.

5. The method for testing the peel strength of battery cell electrodes according to claim 1, characterized in that, The substrate is a stainless steel sheet with a smooth, horizontal surface.

6. The method for testing the peel strength of battery cell electrodes according to claim 1, characterized in that, The method involves testing multiple samples of the same electrode to obtain the peel strength at different locations on the electrode.

7. The method for testing the peel strength of battery cell electrodes according to claim 1, characterized in that, The upper clamp lifting rate of the tensile testing machine is 10 mm / min to 100 mm / min.

8. The method for testing the peel strength of battery cell electrodes according to claim 1, characterized in that, The electrode is a lithium battery electrode, including a negative electrode or a positive electrode.

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