Piercing needle, septum piercing strength testing device and testing method

Abstract

The application discloses a puncture needle, a diaphragm puncture strength test device and a test method. The puncture needle comprises a needle body and a puncture part. The cross section of the needle body is rectangular. The puncture part comprises a first taper surface group, a second taper surface group and a working end surface. One end of the first taper surface group and the second taper surface group is connected with a corresponding group of side surfaces of the needle body respectively. At least one of the first taper surface group and the second taper surface group is inwardly inclined to the axis direction of the needle body. The other end of the first taper surface group and the second taper surface group jointly connects to the edge of the working end surface. The cross section of the working end surface is rectangular. The structural design of the puncture part can generate a directional tearing force in the membrane surface, which can certainly cause a tearing hole to the existing dry method unidirectional stretching lithium battery diaphragm. The puncture needle overcomes the defect that the traditional half-spherical needle head can only generate a circular puncture hole and cannot cause tearing. The puncture needle realizes accurate testing on the tearing resistance of the diaphragm and can effectively guide the optimization of the diaphragm production process.

Description

Technical Field

[0001] This application relates to the field of diaphragm performance testing technology, specifically to a puncture needle, a diaphragm puncture strength testing device, and a testing method. Background Technology

[0002] Dry-stretched uniaxial lithium-ion battery separators are fabricated using a uniaxial stretching pore-forming process, resulting in lower transverse (TD) strength. During the cell stacking process, the separator is subjected to mechanical stress, making it prone to tearing and rupture, which affects the cell manufacturing yield.

[0003] The puncture strength test method in related technologies uses a hemispherical needle, which usually produces a circular through hole rather than a tear hole. This method can only simulate and characterize the ability of the diaphragm to resist foreign body puncture after stacking, but cannot cause diaphragm tearing. Therefore, it cannot characterize the tear resistance of the diaphragm during the stacking process.

[0004] Therefore, there is an urgent need for a testing device and method that can simulate the actual stress conditions of the cell stacking process, effectively induce diaphragm tearing, and thus objectively characterize the tear resistance of the dry lithium battery diaphragm stacking process. Summary of the Invention

[0005] The purpose of this application is to provide a puncture needle, a diaphragm puncture strength testing device and testing method to solve the technical problem that traditional hemispherical needles can only produce circular puncture holes and cannot cause tearing, thus failing to accurately test the tear resistance performance of the diaphragm.

[0006] Embodiments of this application provide a puncture needle for a diaphragm puncture strength testing device, comprising:

[0007] The needle body has a rectangular cross-section; and

[0008] The puncture section is disposed at one end of the needle body; the puncture section includes a first conical surface group, a second conical surface group, and a working end face; one end of the first conical surface group and the second conical surface group are respectively connected to a corresponding set of side faces of the needle body; at least one of the first conical surface group and the second conical surface group is inclined inward relative to the axial direction of the needle body; the other end of the first conical surface group and the second conical surface group are connected to the edge of the working end face; the cross-section of the working end face is rectangular.

[0009] In some optional embodiments, the first tapered surface group is inclined inward relative to the axial direction of the needle body, and the second tapered surface group extends along the axial direction of the needle body.

[0010] In some optional embodiments, the working end face is a cylindrical arc surface, and the cylindrical arc surface extends along the direction of the line connecting the centers of the second conical surface group.

[0011] In some optional embodiments, the radius of the cylindrical arc surface ranges from 0.1 mm to 0.3 mm.

[0012] In some optional embodiments, the working end face is a rectangular plane, and the long side of the rectangular plane extends along the direction of the line connecting the centers of the second conical surface group.

[0013] In some alternative embodiments, the first conical surface group includes two opposing side surfaces, the included angle between the two opposing side surfaces being 30°-120°.

[0014] In some alternative embodiments, the cross-section of the needle body is square.

[0015] In some optional embodiments, the ratio of the long side to the short side of the working end face ranges from 2 to 10.

[0016] Embodiments of this application provide a diaphragm puncture strength testing device, comprising:

[0017] The puncture needle as described in any of the above embodiments; and

[0018] A tensile testing machine includes a fixed base, a clamping component, and a driving mechanism. The fixed base is used to fix the puncture needle; the clamping component is used to clamp and fix the diaphragm sample to be tested; the driving mechanism is connected to the fixed base and is used to drive the puncture needle to puncture the diaphragm sample to be tested.

[0019] In some optional embodiments, the mounting base has a mounting cavity adapted to the needle body of the puncture needle, the mounting cavity having a first positioning structure, and the needle body having a second positioning structure, the first positioning structure cooperating with the second positioning structure to make the long side of the working end face perpendicular to the longitudinal direction of the diaphragm sample to be tested.

[0020] Embodiments of this application provide a method for testing diaphragm puncture strength, the steps of which include:

[0021] The diaphragm sample to be tested is fixed on the clamp, and the puncture needle is installed on the fixed base, so that the long side of the working end face of the puncture needle is perpendicular to the longitudinal direction of the diaphragm sample to be tested.

[0022] The puncture device is driven at a set speed using a drive mechanism to puncture the diaphragm sample to be tested. The force and displacement parameters during the puncture process are recorded to obtain the tear strength of the diaphragm sample to be tested.

[0023] In some optional embodiments, recording force and displacement parameters during the puncture process to obtain the tear strength of the diaphragm sample to be tested includes generating a force-displacement curve based on the force and displacement parameters, and taking the first peak value in the force-displacement curve as the tear strength of the diaphragm sample to be tested.

[0024] In some alternative embodiments, the puncture needle is the puncture needle described in any of the above embodiments.

[0025] In some optional embodiments, the membrane sample to be tested is a dry-stretched uniaxial lithium-ion battery membrane.

[0026] The puncture needle according to the above embodiment includes a needle body with a rectangular cross-section and a puncture portion disposed at one end of the needle body. At least one of the two sets of conical surfaces of the puncture portion is inclined to contract into a wedge-shaped structure. This allows the long side of the working end face to be aligned laterally with the separator and the short side to be aligned longitudinally with the separator when the puncture needle is placed in the correct direction. This generates a directional tearing force within the membrane surface, which inevitably induces tear holes in existing dry-stretched unidirectional lithium-ion battery separators. This overcomes the defect of traditional hemispherical needles, which can only produce circular puncture holes and cannot induce tearing, thus achieving accurate testing of the separator's tear resistance. Furthermore, the test results directly correspond to the actual application scenario where the separator is judged to be ineffective once an initial tear occurs during the stacking process. This accurately reflects the separator's tear resistance in the stacking process, providing practical guidance for separator preparation and effectively guiding the optimization of separator production processes to specifically solve the separator tearing problem during the stacking process.

[0027] According to the diaphragm puncture strength test method of the above embodiment, during the test, the long side of the working end face of the puncture needle is perpendicular to the longitudinal direction of the diaphragm sample to be tested, the long strip contact boundary of the working end face of the puncture needle is aligned with the transverse direction of the diaphragm, and the short side is aligned with the longitudinal direction of the diaphragm. During the puncture loading process, cracks can be induced to propagate longitudinally along the diaphragm, which can truly reproduce the failure mode of diaphragm tearing and rupture during the dry lithium battery diaphragm stacking process. This can improve the matching degree between the test results and the actual process failure, thereby improving the accuracy of the test evaluation. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the puncture needle in one embodiment of this application;

[0029] Figure 2 This is a schematic diagram of the puncture site in one embodiment of this application;

[0030] Figure 3 This is a schematic diagram of the cross-sectional structure of the puncture needle in one embodiment of this application;

[0031] Figure 4 This is a schematic diagram of the cross-sectional structure of the puncture needle in another embodiment of this application;

[0032] Figure 5 This is a schematic diagram of the diaphragm puncture strength testing device in one embodiment of this application;

[0033] Figure 6 This is a schematic diagram of the structure of the puncture needle and the fixation seat in one embodiment of this application;

[0034] Figure 7 This is a schematic diagram of the diaphragm puncture strength test process in one embodiment of this application;

[0035] Figure 8 This is a schematic diagram of the structure of the tear hole formed by the puncture needle in one embodiment of this application;

[0036] Figure 9 A schematic diagram of the puncture hole formed by a traditional hemispherical round-tipped puncture needle;

[0037] Figure 10 A schematic diagram of the force-displacement curve formed by a traditional hemispherical puncture needle;

[0038] Figure 11 This is a schematic diagram of the force-displacement curve formed by the puncture needle in one embodiment of this application.

[0039] Explanation of reference numerals in the attached figures:

[0040] 10-Puncture needle; 11-Needle body; 111-Second positioning structure; 12-Puncture part; 121-First conical surface group; 1211-First conical surface; 1212-Second conical surface; 122-Second conical surface group; 1221-Third conical surface; 1222-Fourth conical surface; 123-Working end face; 1231-Long side; 20-Tension testing machine; 21-Fixed seat; 211-Mounting cavity; 2111-First positioning structure; 22-Clamping component; 23-Drive mechanism; Y-Axis direction; α-Included angle; A1-First direction; A2-Second direction. Detailed Implementation

[0041] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments. Similar elements in different embodiments are referred to by related similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the present application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to the present application are not shown or described in the specification. This is to avoid obscuring the core parts of the present application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0042] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification and drawings are only for the clear description of a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[0043] The serial numbers assigned to components in this document, such as "first" and "second," are used only to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages).

[0044] This application provides a puncture needle (hereinafter referred to as "puncture needle") for a membrane puncture strength testing device. This needle can puncture a dry-stretched uniaxial lithium battery membrane sample in the transverse (TD direction) direction to form an approximately rectangular strip-shaped hole extending in the longitudinal (MD direction), thereby testing the transverse (TD direction) puncture strength of the dry-stretched uniaxial lithium battery membrane. This solves the technical problem in related technologies where hemispherical needle puncture tests can only form circular through holes and cannot induce tearing of the dry-stretched lithium battery membrane, thus only obtaining puncture strength and not tear strength to characterize tearing ability. This application designs the needle body cross-section as rectangular and provides a working end face at one end of the puncture section, ensuring that the puncture needle, when placed in the correct direction, will inevitably induce membrane tearing and create a tear hole, thereby achieving quantitative testing of the membrane tear strength.

[0045] It should be noted that in this application, the longitudinal direction (MD direction) refers to the material feeding direction of the machine during diaphragm preparation; the transverse direction (TD direction) refers to the direction perpendicular to the longitudinal direction (MD direction) within the diaphragm plane. Transverse (TD direction) tearing failure mainly occurs during the dry diaphragm stacking process.

[0046] Please see Figure 1 and Figure 2 The puncture needle 10 includes a needle body 11 and a puncture portion 12. The needle body 11 has a rectangular cross-section, and the puncture portion 12 is disposed at one end of the needle body 11. The puncture portion 12 includes a first conical surface group 121, a second conical surface group 122, and a working end face 123. One end of the first conical surface group 121 and the second conical surface group 122 are respectively connected to a set of side surfaces corresponding to the needle body 11. At least one of the first conical surface group 121 and the second conical surface group 122 is inclined inward relative to the axial direction Y of the needle body 11. The other ends of the first conical surface group 121 and the second conical surface group 122 are connected to the edge of the working end face 123. The cross-section of the working end face 123 is rectangular, that is, the puncture portion 12 forms a wedge structure. When the puncture needle 10 is inserted into the dry uniaxial stretching lithium battery separator sample to be tested in the correct direction, the in-plane tearing force generated by the rectangular cross-section working end face 123 can cause the separator sample to be tested to tear to form a tear hole. For example, the tear hole is a strip-shaped hole rather than a traditional circular puncture hole. Based on the characteristics of the diaphragm itself (molecular chain orientation in the MD direction), the strip-shaped hole extends longitudinally (MD direction).

[0047] It should be noted that the cross-section of the needle body 11 refers to the cross-section perpendicular to its axis. In this application, the cross-section of the needle body 11 is the cross-section in the direction Y, which is perpendicular to the axis of the needle body 11. The cross-section of the working end face 123 also refers to the cross-section in the direction Y, which is perpendicular to the axis of the needle body 11.

[0048] In some embodiments, the first conical surface group 121 is inclined inward relative to the axial direction Y of the needle body 11, and the second conical surface group 122 extends along the axial direction Y of the needle body 11. That is, after the puncture part 12 is inclined inward from two opposite sides, the four sides of the puncture part 12 are connected one-to-one by the four edges of the working end face 123 to form the puncture part 12. Figure 2 As shown, the first conical surface group 121 includes a first conical surface 1211 and a second conical surface 1212 arranged opposite to each other along the second direction A2. The second conical surface group 122 includes a third conical surface 1221 and a fourth conical surface 1222 arranged opposite to each other along the first direction A1. The first conical surface 1211 and the second conical surface 1212 are inclined inward (i.e., contracted) relative to the axial direction Y of the needle body 11. The third conical surface 1221 and the fourth conical surface 1222 extend along the axial direction Y of the needle body 11. The other end of the first conical surface 1211, the second conical surface 1212, the third conical surface 1221 and the fourth conical surface 1222 away from the needle body 11 is connected (or connected) to the working end face 123.

[0049] Of course, in other embodiments, the first conical surface group 121 and the second conical surface group 122 can both be inclined inward relative to the axial direction Y of the needle body 11, and then connected by a rectangular working end face 123. In this case, the inclination angle of the second conical surface group 122 is smaller than that of the first conical surface group 121, so that it can be connected one-to-one with the edge of the rectangular working end face 123.

[0050] Please see Figure 3 In some embodiments, the working end face 123 is a cylindrical arc surface, and the cylindrical arc surface extends along the direction of the center line of the second conical surface group 122. That is, the long side 1231 of the cross-section of the cylindrical arc surface extends along the direction of the center line of the second conical surface group 122 (i.e., the first direction A1), and the short side extends along the second direction A2. During puncture, the long side 1231 is set parallel to the transverse (TD direction) of the diaphragm and perpendicular to the longitudinal (MD direction) to test the transverse tear strength of the diaphragm.

[0051] It should be noted that a cylindrical arc surface is a curved surface formed by a straight line (generatrix) moving parallel to and sweeping along a circular arc trajectory; it can also be understood as a part of the outer surface of a cylinder.

[0052] The cylindrical arc surface is set at one end of the puncture part 12. That is, an arc transition structure with a certain radius of curvature is processed at the front end of the conical structure, so that one end of the puncture part 12 is a blunt arc surface rather than a sharp corner. During the puncture process, when the cylindrical arc surface comes into contact with the diaphragm sample to be tested, it will not scratch the diaphragm sample to be tested at the moment of contact due to the puncture part 12 being too sharp. This avoids the test error caused by scratches and ensures the accuracy and repeatability of the test results.

[0053] In some embodiments, the radius of the cylindrical arc surface ranges from 0.1 mm to 0.3 mm. For example, the radius of the cylindrical arc surface can be 0.1 mm, 0.2 mm, or 0.3 mm, or any value between any two of these values. Designing it within this radius range effectively prevents the puncture part 12 from being too sharp and scratching the diaphragm sample under test, while also ensuring that the puncture part 12's penetration capability is not weakened due to excessively large rounded corners, thus guaranteeing the stability of the testing process.

[0054] Please see Figure 4 In some other embodiments, the working end face 123 is a rectangular plane, with the long side 1231 of the rectangular plane extending along the direction of the line connecting the centers of the second conical surface group 122 (i.e., the first direction A1), and the short side extending along the second direction A2.

[0055] Please see Figure 3 and Figure 4In some embodiments, the first conical surface group 121 includes two opposing sides arranged along the second direction A2, with an included angle α between the two opposing sides being 30°-120°. That is, the included angle α between the first conical surface 1211 and the second conical surface 1212 is 30°-120°. This can also be understood as the tilt angle of each side (relative to the axial direction Y of the needle body 11) ranging from 15° to 60°, or the cone angle of the wedge-shaped structure being 30°-120°. When the cone angle is less than 30°, the tearing force induced by the oblique puncture force within the membrane surface is too low, making it difficult to induce tearing. When the cone angle is greater than 120°, the in-plane tearing force is too large, causing the diaphragm to tear rapidly, which easily leads to test errors. For example, a cone angle of 60° provides a moderate tearing force, resulting in stable and repeatable test results.

[0056] In some embodiments, the needle body 11 has a square cross-section. For example, the cross-sectional dimensions of the needle body 11 are 1mm × 1mm or 2mm × 2mm.

[0057] Of course, in other embodiments, the cross-section of the needle body 11 is rectangular. For example, the cross-sectional dimensions of the needle body 11 are 1mm × 2mm.

[0058] The above-mentioned dimensional design gives the needle body 11 sufficient rigidity to complete the puncture action, and enables it to remain stable during the puncture process without bending or deformation.

[0059] In some embodiments, the ratio of the long side 1231 to the short side of the working end face 123 ranges from 2 to 10. If the ratio is less than 2, the working end face 123 is close to a square, the linear features disappear, and the stress is not easily concentrated and spread along the long side 1231 during puncture, which easily produces a near-circular puncture hole, degenerating into the effect of a traditional hemispherical needle. It is difficult to reproduce the long strip tear failure of the dry diaphragm TD, resulting in failure to achieve the testing purpose of this application. If the ratio is greater than 10, the working end face 123 is too narrow and the short side is extremely small, which will result in poor structural strength of the puncture needle 10. It is easy to break the edge and deform the blade when subjected to impact during puncture, resulting in a short needle life. At the same time, when puncturing the diaphragm, it is easy to directly cut the diaphragm, and the puncture process is no longer a slow tear, resulting in distorted test results. In addition, the narrow and long structure increases the processing difficulty of the structure, resulting in poor dimensional consistency of the puncture part 12, thereby increasing the test dispersion of different puncture needles 10. Setting it between a ratio of 2 and 10 facilitates the creation of strip-shaped tear holes with controllable morphology and regular boundaries.

[0060] Please see Figure 5This application provides a diaphragm puncture strength testing device, including a puncture needle 10 and a tensile testing machine 20. The tensile testing machine 20 includes a fixed base 21, a clamping member 22, and a driving mechanism 23. The puncture needle 10 is the puncture needle 10 in any of the above embodiments, and its structure has been described in detail above, so it will not be repeated here. The fixed base 21 is used to fix the puncture needle 10; the clamping member 22 is used to clamp and fix the diaphragm sample to be tested; the driving mechanism 23 is connected to the fixed base 21 and is used to drive the puncture needle 10 to puncture the diaphragm sample to be tested. The driving mechanism 23 can be a drive motor or a cylinder.

[0061] Please see Figure 6 In some embodiments, the mounting base 21 has a mounting cavity 211 adapted to the needle body 11 of the puncture needle 10. The mounting cavity 211 has a first positioning structure 2111, and the needle body 11 has a second positioning structure 111. The first positioning structure 2111 and the second positioning structure 111 cooperate to make the long side 1231 of the working end face 123 extend along the first direction A1, and during testing, it can be perpendicular to the longitudinal direction (MD) of the diaphragm sample to be tested and parallel to the transverse direction (TD) of the diaphragm sample to be tested.

[0062] The first positioning structure 2111 and the second positioning structure 111 can be constructed as protrusions or grooves. For example, when the first positioning structure 2111 is a protrusion, the corresponding second positioning structure 111 is a groove that fits it. Alternatively, when the first positioning structure 2111 is a groove, the corresponding second positioning structure 111 is a protrusion that fits it. The number of the first positioning structure 2111 and the second positioning structure 111 can be one, two, or more, as long as it enables the installation and positioning of the puncture needle 10; no further limitations are imposed here. For example, two of each of the first positioning structure 2111 and the second positioning structure 111 are provided. The two first positioning structures 2111 are arranged sequentially along the first direction A1, and the two second positioning structures 111 are arranged sequentially along the direction of the line connecting the centers of the second conical surface group 122 (i.e., the first direction A1), that is, respectively set on the third conical surface 1221 and the fourth conical surface 1222. After assembling them with the first positioning structure 2111, it can be effectively ensured that the long side 1231 of the working end face 123 is perpendicular to the longitudinal direction (MD direction) of the diaphragm sample to be tested during the test. Of course, in other examples, the two first positioning structures 2111 can be arranged sequentially along the second direction A2, and the two second positioning structures 111 can be arranged sequentially along the second direction A2, as long as it is ensured that they can be positioned and installed so that the long side 1231 of the working end face 123 is perpendicular to the longitudinal direction (MD direction) of the diaphragm sample to be tested during the test.

[0063] In some embodiments, the tensile testing machine 20 is an electronic universal testing machine. It can also be understood that the diaphragm puncture strength testing device provided in the embodiments of this application includes an electronic universal testing machine and the puncture needle 10 in any of the aforementioned embodiments. That is, the puncture needle 10 of the electronic universal testing machine is improved and can be directly assembled into an existing electronic universal testing machine without modifying the machine body. The fixed base 21 of the electronic universal testing machine is used to install and fix the puncture needle 10; the clamping component 22 of the testing machine is used to clamp and fix the diaphragm sample to be tested; the driving mechanism 23 of the testing machine drives the puncture needle 10 to move towards the diaphragm sample to complete the puncture test. During the test, the electronic universal testing machine can collect and record force-displacement parameters in real time, generate a force-displacement curve, and take the first peak force of the force-displacement curve as the tear resistance strength of the diaphragm sample to be tested.

[0064] Please see Figure 7 The embodiments of this application provide a method for testing diaphragm puncture strength, the steps of which include:

[0065] S101: Fix the diaphragm sample to be tested onto the clamp and install the puncture needle onto the fixed base, so that the long side of the working end face of the puncture needle is perpendicular to the longitudinal direction of the diaphragm sample to be tested.

[0066] The placement of the puncture needle is essential for initiating diaphragm tearing. When the long side of its working end face is perpendicular to the longitudinal direction (MD direction) or parallel to the transverse direction (TD direction), the short side of the working end face is along the longitudinal direction (MD direction) of the diaphragm. During puncture, stress concentration mainly occurs at both ends of the short side distributed along the MD direction, where initial cracks preferentially initiate. Since the diaphragm molecular chains are oriented along the MD direction, the fracture energy required for crack propagation along the MD direction is lower. The initial crack continues to extend along the MD direction due to material anisotropy, while transverse (TD direction) propagation is suppressed, ultimately forming a tear-like pore extending along the longitudinal (MD) direction. If the directions are opposite or not completely perpendicular, tearing will not occur, or the test values ​​will be unrepresentative.

[0067] S102: The puncture is performed on the diaphragm sample to be tested by using a drive mechanism at a set speed, and the force and displacement parameters during the puncture process are recorded to obtain the tear strength of the diaphragm sample to be tested.

[0068] In some embodiments, recording force and displacement parameters during the puncture process to obtain the tear strength of the diaphragm sample to be tested includes generating a force-displacement curve based on the force and displacement parameters, and taking the first peak value in the force-displacement curve as the tear strength of the diaphragm sample to be tested.

[0069] Unlike traditional hemispherical round-tipped puncture needles that form a round hole, such as Figure 9 As shown, the test curve will form a force peak, such as Figure 10As shown, when this application uses a puncture needle for puncture, a strip-shaped hole is formed, such as... Figure 8 As shown, the force-displacement curve will exhibit three peaks, corresponding to the first tear point, the second tear point, and the final puncture point of the diaphragm sample under test, respectively. Figure 11 As shown, the first peak value corresponds to the force value when the diaphragm sample under test undergoes initial tearing. This corresponds to the actual application scenario where the diaphragm sample under test fails once it tears during the stacking process. Therefore, the first peak value is used as the tear strength.

[0070] In some embodiments, the speed set above is 100 mm / min-140 mm / min. For example, the speed set is 120 mm / min, which is determined with reference to the puncture test method in GB / T1041-1992. At this speed, the puncture process is smooth, the peak characteristics of the force-displacement curve are obvious, and the test results are stable, thereby ensuring the standardization of test conditions and the comparability of test results.

[0071] In some embodiments, the membrane sample to be tested is a dry-stretched uniaxial lithium-ion battery membrane. Due to the anisotropy of its stretching and pore-forming process, the transverse (TD direction) strength of the dry-stretched uniaxial lithium-ion battery membrane is significantly lower than that in the longitudinal (MD direction), making it the membrane type most prone to tearing during the stacking process. The test method of this invention is particularly suitable for characterizing the tear resistance of such membranes.

[0072] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below with reference to specific embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0073] It should be noted that experimental methods in the following examples that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer; all reagents and raw materials involved are commercially available products.

[0074] Example 1

[0075] The long side of the working end face of the puncture needle was placed at different angles to the longitudinal direction (MD direction) of the diaphragm sample to be tested, and puncture tests were performed. The placement angles were 0° (perpendicular to the longitudinal direction (MD direction), 30° (30° angle with the longitudinal direction (MD direction), and 90° (parallel to the longitudinal direction (MD direction)). The test results are shown in Table 1 below.

[0076] Table 1. Puncture test results at different placement angles.

[0077]

[0078] As shown in Table 1, the test data are higher and fluctuate more when the angle is 30°, while the morphology of the diaphragm after puncture at 90° is not a tear-like pore but closer to the puncture morphology. This indicates that the tear strength test method requires the long side of the working end face of the puncture needle to be placed perpendicular to the longitudinal direction (MD direction) of the sample. If the direction is opposite or not completely perpendicular, the diaphragm tear cannot be induced or the values ​​are not representative.

[0079] Example 2

[0080] Three membrane samples with different porosities but the same thickness were selected for testing: Product 1, Product 2, and Product 3. All samples had a thickness of 12 μm and porosities of 33% for Product 1, 37% for Product 2, and 40% for Product 3. The puncture strength was measured using the puncture needle described in this application, and the samples were numbered 1-1, 2-1, and 3-1. The conventional puncture strength was measured using a traditional hemispherical puncture needle, and the samples were numbered 1-2, 2-2, and 3-2. The specific test results are shown in Table 2 below.

[0081] Table 2. Puncture test results of diaphragm samples with different porosities

[0082]

[0083] As shown in Table 2 above, the puncture strength of a traditional round-tipped needle does not represent the tear strength of the diaphragm. Product 3 has a high puncture strength and strong resistance to foreign object puncture, but its tear strength is low, resulting in a higher risk of tearing during the lamination process. Therefore, this tear strength testing method can guide the diaphragm manufacturing process and more effectively address the tearing problem of the diaphragm during lamination.

[0084] Example 3

[0085] Two products of the same model were selected, namely Product 4 and Product 5. The raw material of Product 4 is polypropylene resin, with 60% melt index of 0.9 g / 10 min and 40% melt index of 2.0 g / 10 min. The raw material of Product 5 is polypropylene resin, with 60% melt index of 0.8 g / 10 min and 40% melt index of 1.9 g / 10 min. The preparation process of both products is a dry uniaxial stretching process, with casting processing temperatures of 235℃ and 220℃, a total stretching speed ratio of 2.2, a heat treatment temperature of 145℃, a hot stretching temperature of 140℃, and a setting temperature of 150℃. The puncture strength was tested using the puncture needle of this application, and the samples were numbered 4-1 and 5-1. The conventional puncture strength was tested using a traditional hemispherical round-headed puncture needle, and the samples were numbered 4-2 and 5-2. The results are shown in Table 3 below.

[0086] Table 3. Puncture test results of diaphragm samples with different formulations.

[0087]

[0088] As shown in Table 3 above, the two products have different raw material formulations but undergo the same process, resulting in essentially the same puncture strength. However, tear strength tests revealed a significant difference in tear strength. This demonstrates that traditional puncture strength testing cannot characterize the tear resistance of the diaphragm or reveal differences in tear resistance. The puncture needle and established testing method of this application can effectively and accurately test the tear strength indicator and achieve effective differentiation.

[0089] This document describes various exemplary embodiments with reference to them. However, those skilled in the art will recognize that changes and modifications can be made to the exemplary embodiments without departing from the scope of this document. For example, various operational steps and components for performing operational steps can be implemented in different ways depending on the specific application or considering any number of cost functions associated with the operation of the system (e.g., one or more steps can be deleted, modified, or combined with other steps).

[0090] While the principles herein have been illustrated in various embodiments, numerous modifications to the structures, arrangements, proportions, elements, materials, and components, particularly suited to specific environments and operational requirements, may be used without departing from the principles and scope of this disclosure. These modifications and other alterations or alterations will be included within the scope of this document. Those skilled in the art will recognize that many changes can be made to the details of the above embodiments without departing from the fundamental principles of this application.

Claims

1. A puncture needle for a diaphragm puncture strength testing device, characterized in that, include: The needle body has a rectangular cross-section; and The puncture section is disposed at one end of the needle body; the puncture section includes a first conical surface group, a second conical surface group, and a working end face; one end of the first conical surface group and the second conical surface group are respectively connected to a corresponding set of side faces of the needle body; at least one of the first conical surface group and the second conical surface group is inclined inward relative to the axial direction of the needle body; the other end of the first conical surface group and the second conical surface group are connected to the edge of the working end face; the cross-section of the working end face is rectangular.

2. The puncture needle according to claim 1, characterized in that, The first conical surface group is inclined inward relative to the axial direction of the needle body, and the second conical surface group extends along the axial direction of the needle body.

3. The puncture needle according to claim 2, characterized in that, The working end face is a cylindrical arc surface, and the cylindrical arc surface extends along the direction of the line connecting the centers of the second conical surface group.

4. The puncture needle according to claim 3, characterized in that, The radius of the cylindrical arc surface ranges from 0.1mm to 0.3mm.

5. The puncture needle according to claim 2, characterized in that, The working end face is a rectangular plane, and the long side of the rectangular plane extends along the direction of the line connecting the centers of the second conical surface group.

6. The puncture needle according to claim 2, characterized in that, The first conical surface group includes two oppositely arranged side surfaces, and the included angle between the two oppositely arranged side surfaces is 30°-120°.

7. The puncture needle according to any one of claims 1-6, characterized in that, The cross-section of the needle is square.

8. The puncture needle according to any one of claims 1-6, characterized in that, The ratio of the long side to the short side of the working end face ranges from 2 to 10.

9. A diaphragm puncture strength testing device, characterized in that, include: The puncture needle as described in any one of claims 1-8; as well as A tensile testing machine includes a fixed base, a clamping component, and a driving mechanism. The fixed base is used to fix the puncture needle; the clamping component is used to clamp and fix the diaphragm sample to be tested; the driving mechanism is connected to the fixed base and is used to drive the puncture needle to puncture the diaphragm sample to be tested.

10. The diaphragm puncture strength testing device according to claim 9, characterized in that, The fixing base has a mounting cavity adapted to the needle body of the puncture needle. The mounting cavity has a first positioning structure, and the needle body has a second positioning structure. The first positioning structure cooperates with the second positioning structure to make the long side of the working end face perpendicular to the longitudinal direction of the diaphragm sample to be tested.

11. A method for testing diaphragm puncture strength, characterized in that, The steps include: The diaphragm sample to be tested is fixed on the clamp, and the puncture needle is installed on the fixed base, so that the long side of the working end face of the puncture needle is perpendicular to the longitudinal direction of the diaphragm sample to be tested. The puncture device is driven at a set speed using a drive mechanism to puncture the diaphragm sample to be tested. The force and displacement parameters during the puncture process are recorded to obtain the tear strength of the diaphragm sample to be tested.

12. The method for testing diaphragm puncture strength according to claim 11, characterized in that, Recording the force and displacement parameters during the puncture process to obtain the tear strength of the diaphragm sample to be tested includes generating a force-displacement curve based on the force and displacement parameters, and taking the first peak value in the force-displacement curve as the tear strength of the diaphragm sample to be tested.

13. The method for testing diaphragm puncture strength according to claim 11, characterized in that, The puncture needle is the puncture needle according to any one of claims 1-8.

14. The method for testing diaphragm puncture strength according to claim 11, characterized in that, The membrane sample to be tested is a dry-stretched uniaxial lithium battery membrane.

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