Puncture needle for short circuit test in laminated battery and test method

Abstract

The invention provides a pricking needle for testing short circuit in a laminated battery and a testing method. The pricking needle comprises a conical part, a tearing part and a needle rod part which are connected in sequence. The maximum diameter of the tearing part is greater than the maximum diameter of the bottom of the conical part, so that a step for tearing the size magnitude of the battery cell unit in the battery cell is formed between the tearing part and the bottom of the conical part, and the maximum height of the step is greater than or equal to the thickness of one battery cell unit. The maximum diameter of the tearing part is less than or equal to the thickness of the ten battery cell units, and the length of the tearing part is 1-5mm. Preferably, at least the surface material of the needle rod part is plastic, so that the local internal short circuit condition in the battery cell can be controlled and simulated. In the test method, the pricking needles pierce into the battery cell in a manner of being approximately parallel to the lamination plane of the laminated battery, and simultaneous short circuit of a large number of battery cell units can be further prevented, so that the condition that the lithium dendrites of the energy storage lithium ion battery pierce the diaphragm to cause micro short circuit of local battery cell units is simulated.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to a puncture needle and a testing method for internal short circuit testing of laminated batteries. Background Art

[0002] With the rapid development of the energy industry in recent years, lithium-ion batteries have gradually become the primary energy storage medium due to their high energy density and long cycle life. However, lithium-ion batteries contain a large amount of active materials and easily decomposable combustible substances. Under abuse conditions, they are highly susceptible to thermal runaway, resulting in fire and explosion, which poses a serious threat to social security. Therefore, conducting appropriate abuse testing on large-capacity lithium-ion batteries is of great significance. Among them, the internal short-circuit test is more dangerous than other abuse tests and is most likely to cause thermal runaway. Current needle penetration testing methods are mainly used for automotive power batteries. The test standards focus on the possibility that sharp objects on the ground pierce the underbody of the vehicle and then penetrate the battery cells while the vehicle is in motion, causing internal short circuits. Therefore, a conductive steel needle is used to penetrate the battery plates perpendicularly, creating a large-scale internal short circuit within the battery cell. Energy storage lithium-ion batteries are placed in a static energy storage system, where the operating environment is limited and they are not exposed to foreign object intrusion. Internal short circuits in energy storage lithium-ion batteries primarily occur after prolonged charge-discharge cycles, when lithium precipitates form, puncturing the separator and causing localized short circuits within the battery cells. Therefore, testing for micro-short circuits within energy storage lithium-ion batteries requires a test device and method that differs significantly from traditional needle penetration testing. Summary of the Invention

[0003] In response to the above problems, the present invention provides a needle and a testing method for internal short circuit testing of laminated batteries, wherein the needle includes a conical portion, a tearing portion, and a needle shaft portion connected in sequence. The maximum diameter of the tearing portion is greater than the maximum diameter of the bottom of the conical portion, so that a step of the order of the size of a battery cell is formed between the tearing portion and the bottom of the conical portion for tearing the battery cell in the battery cell, and the maximum height of the step is greater than or equal to the thickness of one battery cell. The maximum diameter of the tearing portion is less than or equal to the thickness of ten battery cells, and the length of the tearing portion is 1 to 5 mm. Preferably, at least the surface material of the needle shaft portion is plastic or an insulating low thermal conductivity wrapping layer, thereby reducing the heat dissipation of the battery through the needle, and better controlling and simulating the local internal short circuit situation inside the battery cell. In the testing method, the needle penetrates the battery cell in a manner roughly parallel to the laminate plane of the laminated battery, which can more accurately simulate the internal short circuit condition of the energy storage battery.

[0004] The technical solutions provided by the present invention are as follows:

[0005] According to the present invention, a needle for short-circuit testing in stacked batteries is provided, the needle comprising a conical portion, a tearing portion, and a needle shaft portion. The tearing portion extends radially outward from the bottom of the conical portion to form a step of the tearing portion. The maximum height of the step, i.e., the maximum radial height, is greater than or equal to the thickness of one battery cell, and the maximum diameter of the tearing portion is less than or equal to the thickness of ten battery cells. The battery cell comprises a positive electrode sheet, an isolation layer, and a negative electrode sheet. The length of the tearing portion is approximately 1 to 5 mm, and the material of the conical portion and the tearing portion is a conductive material. The needle shaft portion is connected to the tearing portion, and the diameter of the needle shaft portion is approximately 1 to 8 mm. The diameter of the needle shaft portion may be less than or equal to the maximum diameter of the tearing portion.

[0006] Specifically, the needle includes a conical portion, a tearing portion and a needle shaft portion connected in sequence. The cone angle of the conical portion can be, for example, 30 to 60 degrees, preferably 45 degrees. The maximum diameter of the tearing portion is greater than the diameter of the bottom of the conical portion. The tearing portion can be a cylinder, or a strip, an upright sheet, a spike, etc. arranged on a base. Since there is a diameter difference between the outer diameter of the tearing portion and the bottom diameter of the conical portion, a step with a drop value is formed between the tearing portion and the bottom of the conical portion. In the process of the needle piercing the laminated battery, the axis of the needle is roughly parallel to the laminate plane of the laminated battery. When the conical portion first pierces the battery cell and enters the interior of the battery cell, the tearing portion enters the battery cell together with the conical portion. According to different selections of piercing speed, piercing time and piercing force, the needle can penetrate the battery cell to different depths. After the conical portion penetrates the laminated battery with its axis approximately parallel to the laminate plane, the stepped portion of the tearing portion first cuts or slashes through the cell, such as the separator layer, before the rear portion of the tearing portion continues to partially tear the laminate. Therefore, rather than penetrating the cell perpendicularly to the laminate, creating a large-scale short circuit within the cell, the needle's tip enters the laminate horizontally, then the tearing portion of the needle locally tears the laminate. The height of the step of the tearing portion is greater than or equal to the thickness of one cell, the maximum diameter of the tearing portion is less than or equal to the thickness of ten cells, and the length of the tearing portion along the needle's axis is approximately 1 to 5 mm. This allows the size of the tearing portion within the laminated battery to be controlled. For example, the tearing portion can be limited to a thickness greater than one cell and less than ten cells in the thickness direction of the laminate. The conductive portion of the tearing portion electrically connects the positive and negative electrodes of one or a few cells whose separator layer has been punctured, thereby creating a localized micro-short circuit within the cell. Different from the needles used in traditional puncture tests, the needles of the present invention will only trigger internal short circuits of a single or a small number of battery cells inside the battery, i.e., micro short circuits of the cells, thereby simulating the actual internal short circuit conditions of a lithium-ion energy storage battery.

[0007] The tearing portion can be a cylindrical body with a maximum diameter greater than the maximum diameter of the bottom of the conical portion, and a step between the cylindrical body and the bottom of the conical portion is used to tear the interior of the laminate. The tearing portion can also include a plurality of elongated serrations, evenly spaced along the circumference of the conical portion, with the serrations protruding outward from the bottom of the conical portion in the radial direction of the conical portion (i.e., the radial direction of the needle). For example, the tearing portion can be a plurality of elongated serrations disposed on a base cylindrical body. The diameter of the cylindrical body can be approximately equal to the diameter of the bottom of the conical portion. The elongated serrations protrude outward from the cylindrical body, and the cross-section of the serrations can be rectangular, trapezoidal, triangular, or the like. The angle of inclination between the longitudinal extension of the elongated serrations and the axis of the needle shaft can be between 0° and 5°. In other words, the elongated serrations can extend along the axis of the needle shaft, or they can extend at an inclination relative to the axis of the needle shaft. When the longitudinal extension of the saw teeth forms a certain angle with the axis of the needle shaft, the saw teeth can more easily cut and tear the laminated cells when the needle penetrates the interior of the laminated battery. Furthermore, the depth of the long saw teeth can be uniform or gradually decrease in depth from the conical portion toward the needle shaft. When the saw teeth gradually decrease in depth toward the needle shaft, a smaller tearing area can be defined at the front end of the tearing portion, thereby limiting the tearing range within the battery cell.

[0008] The needle shaft portion can be made of an insulating low thermal conductivity material or the outer surface of the needle shaft portion can be covered with an insulating low thermal conductivity material. Preferably, the insulating material of the needle shaft portion is a plastic material with low thermal conductivity (≤0.5W / (m·K)) and high temperature resistance (≥180°C), such as reinforced nylon, aromatic nylon, polyphenylene sulfide, polyaryletherketone or tetrafluoroethylene. Further preferably, the needle shaft portion can be an insulating material with an elastic foam layer structure, thereby more effectively sealing the holes pierced by the cone portion and the tearing portion. The needle shaft portion can be an integral cylinder, or the needle shaft portion can include a rod core and a sleeve. The sleeve can be sleeved on the rod core by hot melting, bonding, etc. According to another embodiment, the outer layer of the needle shaft portion can be an insulating coating, and the material of the insulating coating can be an oxide ceramic material or a nitride ceramic material, such as an aluminum oxide, zirconium oxide or silicon nitride ceramic layer.

[0009] According to the present invention, a test method for short circuit testing in a laminated battery is also provided. The test method uses the needle described above, which penetrates the laminated battery in a direction generally parallel to the laminated battery. During the process of the needle penetrating the laminated battery, first, the conical portion of the needle penetrates the battery cell. The needle can pierce the electrode sheets and the separator, or the needle is used only to penetrate between the laminated sheets. Subsequently, the tearing portion of the needle tears the positive electrode sheet, the negative electrode sheet, and the separator. In a direction perpendicular to the laminated battery, the tearing portion tears between one and ten battery cells within the battery cell, thereby achieving a micro short circuit within the battery.

[0010] In addition, in order to enable the puncture needle to better tear the laminate, the puncture needle can also penetrate the laminated battery at an angle of 0° to 5° between the axis of the puncture needle and the plane of the laminate; or, the puncture needle can penetrate the laminated battery in a rotating manner; or, the puncture needle is partially withdrawn after penetrating the laminated battery, and then penetrates the laminated battery again, and this is repeated N times, 2≤N≤5.

[0011] In the description of the present invention, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right" and "top, bottom" are usually based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention.

[0012] The advantages of the present invention are:

[0013] 1) The present invention only triggers a short circuit in a single or a small number of battery cells in the battery during the battery puncture test, which can more realistically simulate the internal short circuit condition of the energy storage lithium-ion battery;

[0014] 2) The design of the insulating heat tunnel of the needle shaft can ensure that during the battery needle penetration test, the overall current of the needle is small. Only the cone and the tearing part generate a weak current due to the connection with the positive and negative poles of the battery cell unit. The remaining insulating part of the needle shaft does not generate current. Therefore, the needle itself does not act as a heat source to generate a large amount of heat, which can avoid non-battery heat generation and reduce the heat dissipation of the battery through the needle. Therefore, the needle penetration test using the present invention can better control and simulate the local internal short circuit situation inside the battery cell;

[0015] 3) By limiting the step height and maximum diameter of the tearing portion of the needle and controlling the angle of the needle's penetration, the range of the micro-short circuit area inside the battery can be more accurately controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1(a) and 1(b) is a schematic diagram of a needle piercing a battery cell according to the present invention;

[0017] Figure 2 is a schematic diagram of a needle according to the present invention;

[0018] Figure 3 is a partial schematic diagram of a needle according to a first embodiment of the present invention;

[0019] Figure 4 is a partial schematic diagram of a needle according to a second embodiment of the present invention;

[0020] Figure 5 is a partial schematic diagram of a needle according to a third embodiment of the present invention;

[0021] Figure 6 FIG. 4 is a partial schematic diagram of a needle according to a fourth embodiment of the present invention.

[0022] Reference Signs List

[0023] 1——Battery cell unit

[0024] 101——Positive electrode

[0025] 102——Isolation layer

[0026] 103——Negative electrode

[0027] 2--Piercing needle

[0028] 201——cone

[0029] 202——Tear Department

[0030] 202a——Plinth

[0031] 202b——Sawtooth

[0032] 202c——Groove

[0033] 203——Needle shaft DETAILED DESCRIPTION

[0034] The present invention will be further described below through examples with reference to the accompanying drawings. It will be understood that the specific embodiments described herein are intended only to explain the relevant inventions and are not intended to limit the inventions. It should also be noted that, for ease of description, only portions relevant to the relevant inventions are shown in the accompanying drawings. It should be noted that the embodiments and features of the embodiments in this application may be combined with each other unless there is a conflict.

[0035] Figure 1(a) and 1(b)A schematic diagram of a needle inserted into a battery cell according to the present invention is shown. As shown in Figure 1, a laminated battery cell comprises multiple battery cells 1—i.e., battery reaction units. Each cell 1 includes a positive electrode sheet 101, a separator 102, and a negative electrode sheet 103. After prolonged battery use, lithium dendrites may form within the battery. These dendrites pierce the separator, causing localized micro-short circuits within the battery cells. To simulate this situation, and to avoid large-scale internal short circuits within the battery, the needle of the present invention is inserted into the battery cell approximately parallel to the battery cells. A step is formed between the tearing portion 202 of the needle and the bottom of the conical portion 201 due to the radial dimension difference. The height H of this step is greater than or equal to the thickness of one battery cell 1, and the maximum diameter D of the tearing portion 202 is less than or equal to the thickness of ten battery cells. First, the conical portion 201 of the needle is inserted into the battery cell. Subsequently, the tearing portion 202 tears the laminated sheets, including the separator, within several battery cells, causing internal short circuits within the cells located at the conductive tearing portion of the needle.

[0036] In the test method for short-circuit testing in laminated batteries, the needle's axis can be roughly parallel to the plane of the laminate—that is, the positive electrode sheet, negative electrode sheet, and separator—and the angle α between the needle's axis and the plane of the laminate can be 0° to 5°. The needle can penetrate the battery cell in a straight line, or it can rotate about its axis while penetrating in a straight line. Furthermore, the needle can penetrate once, or it can be inserted, partially withdrawn, and re-inserted in a reciprocating manner. The needle's penetration speed can be 3 mm / s, and the penetration depth of the battery cell can be 10 cm.

[0037] Figure 2 Schematic diagram of the needle according to the present invention. Figure 2 As shown, the needle 2 comprises a conical portion 201, a tearing portion 202, and a shaft portion 203, which are connected in sequence along the axis of the needle 2. The maximum diameter of the tearing portion 202 is greater than the diameter of the base of the conical portion 201, while the maximum diameter of the main body of the shaft portion 203 is less than or equal to the maximum diameter of the tearing portion 202. The tail end of the shaft portion 203 can be provided with a connection portion for connecting to a puncture device. The length of the conical portion 201 is approximately 3 to 10 mm, the length of the tearing portion 202 is approximately 1 to 5 mm, and the length of the shaft portion 203 is approximately 80 to 120 mm. The conical portion 201 and the tearing portion 202 are made of conductive material. The needle rod portion 203 can be a conductive needle rod integrally formed with the conical portion 201 and the tearing portion 202, or the needle rod portion 203 can be a conductive rod core with an insulating sleeve, or the needle rod portion 203 can be a conductor rod core sprayed with an insulating coating, or the needle rod portion 203 can be made of a whole insulating material and fixedly connected to the tearing portion 202.

[0038] Figure 3This is a partial schematic diagram of a needle according to a first embodiment of the present invention. In this embodiment, the tearing portion 202 is cylindrical, with an annular step formed between the tearing portion 202 and the conical portion 201. This step is used to tear the separator of a battery cell. The diameter of the needle shaft 203 is smaller than that of the tearing portion 202. The conical portion 201, tearing portion 202, and needle shaft 203 of this needle are integrally formed and made of low-carbon steel.

[0039] Figure 4 The figure is a partial schematic diagram of a needle according to a second embodiment of the present invention. In this embodiment, the tearing portion 202 comprises a base column 202a and a plurality of elongated serrations 202b. The diameter of the base column 202a is approximately the same as the diameter of the bottom of the conical portion 201. The plurality of elongated serrations 202b are evenly distributed around the circumference of the needle, with a predetermined distance between each pair of serrations 202b. The serrations 202b extend along the axis of the needle and have a triangular cross-section. The vertices of the plurality of serrations 202b lie approximately on the same circle, the diameter of which is the maximum diameter of the tearing portion 202. A step is formed between the serrations 202b and the bottom of the conical portion 201, which is used to tear the separator of the battery cell. The diameter of the needle shaft 203 is approximately equal to the diameter of the base column 202a of the tearing portion. The conical portion 201 and the tearing portion 202 of the needle are made of tungsten steel, and the needle shaft 203 is a rod core made of tungsten steel sprayed with an aluminum oxide coating.

[0040] Figure 5 The figure is a partial schematic diagram of a needle according to a third embodiment of the present invention. In this embodiment, the tearing portion 202 includes a base column 202a and a plurality of elongated serrations 202b. The diameter of the base column 202a is approximately the same as the diameter of the bottom of the conical portion 201. The plurality of elongated serrations 202b are evenly distributed around the circumference of the needle, with each pair of serrations 202b closely adjacent to each other. The serrations 202b extend along the axis of the needle and have a triangular cross-section. The vertices of the plurality of serrations 202b are approximately located on the same circle, the diameter of which is the maximum diameter of the tearing portion 202. A step is formed between the serrations 202b and the bottom of the conical portion 201, which is used to tear the separator of the battery cell. The diameter of the needle shaft 203 is approximately equal to the diameter of the base column 202a of the tearing portion. The conical portion 201 and the tearing portion 202 of the needle are made of low-carbon steel, and the needle shaft 203 is a low-carbon steel core covered with a high-temperature resistant polypropylene sleeve.

[0041] Figure 6This is a partial schematic diagram of a needle according to a fourth embodiment of the present invention. In this embodiment, the tearing portion 202 comprises a plurality of elongated serrations 202b formed on a cylindrical base. The diameter of the cylindrical base is larger than the diameter of the base of the conical portion 201. These serrations 202b are evenly spaced around the circumference of the needle, extending along the needle's axis. A groove 202c is formed between each pair of serrations 202b. The grooves 202c gradually become shallower and narrower from the base of the conical portion toward the shank portion 203, creating a smooth transition between the tearing portion 202 and the shank portion 203. The cross-section of the serrations 202b gradually changes from a triangle to a trapezoid, with the upper base of the trapezoid gradually widening and its height decreasing from the base of the conical portion 201 toward the shank portion 203. A step is formed between the serrations 202b and the base of the conical portion 201, which is used to tear the separators of the battery cells. The diameter of the needle shaft portion 203 is approximately equal to the diameter of the cylinder of the tearing portion 202. The cone portion 201, the tearing portion 202 and the needle shaft portion 203 of the needle are made of tungsten steel.

[0042] The specific embodiments of the present invention are not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A needle for short circuit testing of laminated batteries, characterized in that: The needle includes a conical portion, a tearing portion and a needle rod portion. The tearing portion extends outward from the bottom of the conical portion along the radial direction of the cone to form a step of the tearing portion. The maximum height of the step is greater than or equal to the thickness of one battery cell unit, and the maximum diameter of the tearing portion is less than or equal to the thickness of ten battery cell units. The battery cell unit includes a positive electrode sheet, an isolation layer and a negative electrode sheet. The length of the tearing portion is 1 to 5 mm. The material of the conical portion and the tearing portion is conductive material. The needle rod portion is connected to the tearing portion, and the diameter of the needle rod portion is 1 to 8 mm.

2. The needle for internal short circuit testing of laminated batteries according to claim 1, characterized in that: The tearing portion is a cylinder, and the maximum diameter of the cylinder is greater than the maximum diameter of the bottom of the conical portion.

3. The needle for internal short circuit testing of laminated batteries according to claim 1, characterized in that: The tearing portion includes a plurality of long strip-shaped saw teeth, which are evenly arranged along the circumference of the conical portion. The saw teeth protrude outward from the bottom of the conical portion along the radial direction of the conical portion.

4. The needle for internal short circuit testing of laminated batteries according to claim 3, characterized in that: The inclination angle between the extension line of the long strip sawtooth in the length direction and the axis of the needle rod part is 0° to 5°.

5. The needle for internal short circuit testing of laminated batteries according to claim 3, characterized in that: The depth of the long strip-shaped saw teeth gradually becomes shallower from the conical portion toward the needle shaft portion.

6. The needle for internal short circuit testing of laminated batteries according to claim 1, characterized in that: The needle rod portion is made of plastic material or the outer surface of the needle rod portion is covered with plastic material, and the plastic material is reinforced nylon, aromatic nylon, polyphenylene sulfide, polyaryletherketone or tetrafluoroethylene; or, the outer layer of the needle rod portion is an insulating coating, and the material of the insulating coating is an oxide ceramic material or a nitride ceramic material.

7. A test method for internal short circuit testing of laminated batteries, characterized in that: The testing method uses the puncture needle for internal short-circuit testing of stacked batteries according to any one of claims 1 to 6.

8. The test method for internal short circuit testing of laminated batteries according to claim 7, characterized in that: The puncture needle penetrates the laminated battery at an angle of 0° to 5° between the axis of the puncture needle and the plane of the laminate.

9. The test method for internal short circuit testing of laminated batteries according to claim 7, characterized in that: The puncture needle punctures the laminated battery in a rotating manner.

10. The test method for internal short circuit testing of laminated batteries according to claim 7, characterized in that: After piercing the laminated battery, the puncture needle is partially withdrawn and then pierces the laminated battery again, and this process is repeated N times, where 2≤N≤5.

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