Pressure relief device with ultralow pressure relief pressure and application thereof

Abstract

The invention relates to a pressure relief device with ultralow pressure relief pressure and application thereof, and belongs to the technical field of pressure relief devices. The pressure relief device with the ultralow pressure relief pressure comprises a hollow protective film and an ejector pin, and the ejector pin is arranged in the protective film; the ejector pin comprises a main pin and an auxiliary pin arranged on one side of the main pin in a bent mode. The tips of the main needles face the top of the protective film, and the tips of the auxiliary needles face the bottom of the protective film. The pressure relief device with the ultralow pressure relief pressure is applied to the sodium ion battery, the valve is opened early, and a defective battery cell can be recognized in time and replaced; the radiation range is small, and the stability of surrounding batteries is prevented from being affected by violent valve opening.

Description

Technical Field

[0001] The present invention belongs to the technical field of pressure relief devices, and in particular relates to an ultra-low pressure relief device and applications thereof. Background Art

[0002] Currently, lithium-ion battery explosion-proof valves primarily utilize metal scoring structures (such as aluminum foil scoring) or polymer films, with pressure relief thresholds typically ranging from 0.5 MPa to 2 MPa. The pressure relief thresholds for different battery types vary depending on the battery system and packaging method. For example, ternary lithium batteries produce high gas during thermal runaway and tend to have lower thresholds (such as 0.8 MPa to 1.2 MPa). Lithium iron phosphate batteries produce less gas and may have a slightly higher threshold (1.2 MPa to 1.8 MPa). Cylindrical batteries have high metal shell strength and require higher pressure to trigger (1.0 MPa to 2.0 MPa). Prismatic batteries often have aluminum shell explosion-proof valves located on the top cover, with lower thresholds (0.4 MPa to 1.0 MPa). However, this type of design suffers from excessively high trigger pressures, making it difficult to meet the ultra-low pressure relief requirements (<0.2 MPa) for solid-state batteries, flexible batteries, and sodium-ion batteries.

[0003] High-safety sodium-ion batteries feature thermal stability exceeding 900°C for the positive and negative electrode active materials, and no CEI and SEI side reactions between the electrolyte and the positive and negative electrode active materials. This completely avoids the stage where gas accumulation and a sharp rise in internal battery pressure due to reactions between the positive and negative electrodes and the electrolyte occur. Opening the battery valve only requires the release of the electrolyte, which has vaporized due to high temperatures. Conventional batteries have excessive pressure relief. To ensure battery safety, a pressure relief device with ultra-low pressure relief is required. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an ultra-low pressure relief device and its application.

[0005] The first object of the present invention is to provide an ultra-low pressure relief device, comprising a hollow protective film and a ejector pin, wherein the ejector pin is arranged in the protective film; the ejector pin comprises a main pin and a secondary pin bent on one side of the main pin; the tip of the main pin faces the top of the protective film, and the tip of the secondary pin faces the bottom of the protective film.

[0006] In one embodiment of the present invention, the material of the ejector pin is selected from aluminum, stainless steel, PVC or ABS hard plastic.

[0007] In one embodiment of the present invention, the distance h1 from the tip of the main needle to the top of the protective membrane and the distance h2 from the tip of the secondary needle to the bottom of the protective membrane are independently 0.5mm-2mm, for example, they can be 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2mm, etc., and the distance h1 from the tip of the main needle to the top of the protective membrane is smaller than the distance h2 from the tip of the secondary needle to the bottom of the protective membrane; because only in this way, in the actual triggering process, the upper membrane is punctured first and then the lower membrane is punctured; otherwise, when the lower membrane is punctured first, the upper membrane forms a convex state under the internal pressure and cannot be punctured to form pressure relief.

[0008] In one embodiment of the present invention, the radius of curvature of the secondary needle is 0.1 μm-200 μm, for example, it can be 0.1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm , 95μm, 100μm, 105μm, 110μm, 115μm, 120μm, 125μm, 130μm, 135μm, 140μm, 145μm, 150μm, 155μm, 160μm, 165μm, 170μm, 175μm, 180μm, 185μm, 190μm, 195μm, 200μm, etc.

[0009] In one embodiment of the present invention, the protective film includes an upper film and a lower film; the upper film is convex, that is, it bulges upward; the lower film is concave, that is, it is concave downward; and the ejector pin is arranged at the bottom of the lower film.

[0010] In one embodiment of the present invention, the thickness of the upper film is 5μm-100μm, for example, it can be 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, etc.; the puncture strength P1 is 5N / cm-20N / cm, for example, it can be 5N / cm, 6N / cm, 7N / cm, 8N / cm, 9N / cm, 10N / cm, 11N / cm, 12N / cm, 13N / cm, 14N / cm, 15N / cm, 16N / cm, 17N / cm, 18N / cm, 19N / cm, 20N / cm, etc.

[0011] In one embodiment of the present invention, the upper film is selected from a metal film or an organic film; the material of the metal film is selected from aluminum and / or nickel; the material of the organic film is selected from one or more of polyethylene (PE), polytetrafluoroethylene (PTFE), polypropylene (PC) and polyethylene terephthalate (PET).

[0012] In one embodiment of the present invention, the lower film includes a gas barrier film on the side close to the ejector pin and a breathable support film on the side away from the ejector pin; the thickness of the gas barrier film is 5 μm-20 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc.; the Gurley value is greater than 5000s / 100mL, for example, 5000s / 100mL, 5100s / 100mL, 5200s / 100mL, 5300s / 10 0mL, 5400s / 100mL, 5500s / 100mL, 5600s / 100mL, 5700s / 100mL, 5800s / 100mL, 5900s / 100mL, 6000s / 100mL, 6100s / 100mL, 6200s / 100mL, 6300s / 100mL, 6400s / 100mL, 6500s / 100mL, 6600s / 100mL, 6700s / 100mL, 6800s / 100mL, 6900s / 100mL, 7000s / 100mL, etc.; the breathable support membrane The thickness is 20μm-100μm, for example, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, etc.; the Gurley value does not exceed 50s / 100mL, for example, 5s / 100mL, 10s / 100mL, 15s / 100mL, 20s / 100mL, 25s / 100mL, 30s / 100mL, 35s / 100mL, 40s / 100mL, 45s / 100mL, 50s / 100mL, etc.; the puncture strength P2 is 10N / cm-30N / cm, for example, it can be 10N / cm, 11N / cm, 12N / cm, 13N / cm, 14N / cm, 15N / cm, 16N / cm, 17N / cm, 18N / cm, 19N / cm, 20N / cm, 21N / cm, 22N / cm, 23N / cm, 24N / cm, 25N / cm, 26N / cm, 27N / cm, 28N / cm, 29N / cm, 30N / cm, etc., and the puncture strength P2 of the breathable support membrane is greater than the puncture strength P1 of the upper membrane.

[0013] In one embodiment of the present invention, the gas barrier membrane has low permeability, and the material is selected from aluminum foil, aluminized polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyvinylidene chloride (PVDC), etc.; the material of the breathable support membrane is selected from PTFE stretched porous membrane, PET non-woven fabric, polyethylene (PE) uniaxially stretched microporous membrane, polypropylene (PP) uniaxially stretched microporous membrane, aramid paper, etc.

[0014] In one embodiment of the present invention, the lower membrane has extremely low air permeability (close to sealing) in a normal state, and after being triggered, the air permeability increases sharply due to deformation or damage.

[0015] In one embodiment of the present invention, the curvature of the upper membrane and the lower membrane is independently 1: (1-20), for example, it can be (1:1), (1:1.5), (1:2), (1:2.5), (1:3), (1:3.5), (1:4), (1:4.5), (1:5), (1:5.5), (1:6), (1:6.5), (1:7), (1:7.5), (1:8), (1:8.5), (1:9), (1:9.5), (1:10), (1:10.5), (1:11.5), (1:12.5), (1:13.5), (1:14.5), (1:15.5), (1:16), (1:17.5), (1:18.5), (1:19.5), (1:10.5), (1:11.5), (1:12.5), (1:13.5), (1:14.5), (1:15.5), (1:16.5), (1:17.5), (1:18.5), (1:19.5), (1:1 :11), (1:11.5), (1:12), (1:12.5), (1:13), (1:13.5), (1:14), (1:14.5), (1:15), (1:15.5), (1:16), (1:16.5), (1:17), (1:17.5), (1:18), (1:18.5), (1:19), (1:19.5), (1:20), etc.; Among them, the curvature refers to the ratio of the highest point of the curve (arc height) to the straight-line distance between the two end points (chord length).

[0016] In one embodiment of the present invention, the distance h between the top of the upper membrane and the bottom of the lower membrane is 2 mm-10 mm, for example, it can be 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm, etc.

[0017] The second object of the present invention is to provide an explosion-proof valve, comprising the ultra-low pressure relief device and a protective cover; the ultra-low pressure relief device is arranged in the protective cover to play a protective role and avoid rupture of the upper membrane caused by external force.

[0018] In one embodiment of the present invention, the pressure relief threshold of the explosion-proof valve is 0.1 MPa-0.2 MPa, and the time difference δT between the ejector needle piercing the upper membrane and the internal pressure of the battery dropping to atmospheric pressure is less than 10 ms.

[0019] The third object of the present invention is to provide a sodium ion battery, comprising a positive electrode, a negative electrode and the explosion-proof valve; the active material of the positive electrode is selected from Na4Fe3(PO4)2(P2O7), Na4Fe 3-x Mn x (PO4)2(P2O7), Na4Mn3(PO4)2(P2O7) and Na3MnTi(PO4)3, wherein 0<x<3; the active material of the negative electrode is selected from one or more of NaTi2(PO4)3, Na3Fe2(PO4)3 and Na3MnTi(PO4)3.

[0020] The technical solution of the present invention has the following advantages over the prior art:

[0021] (1) The explosion-proof valve of the present invention is applied to sodium ion batteries. When the internal pressure of the battery increases, the lower membrane moves upward, driving the ejector pin to first pierce the upper membrane and then the gas barrier membrane of the lower membrane. At this time, the breathable support membrane of the lower membrane can achieve timely pressure relief.

[0022] (2) The explosion-proof valve of the present invention is applied to sodium ion batteries. The valve is opened early, and problematic cells can be identified and replaced in time.

[0023] (3) The explosion-proof valve of the present invention has a small radiation range, which prevents the valve from opening and drastically affecting the stability of surrounding batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0025] Figure 1-Figure 3 Schematic diagram of the explosion-proof valve of the present invention;

[0026] Figure 4 is a schematic diagram of the ejector pin of the present invention;

[0027] Figure 5 A schematic diagram of a test battery of the present invention;

[0028] Explanation of the reference numerals: 1-thrust needle, 11-main needle, 12-auxiliary needle, 2-upper membrane, 3-lower membrane, 4-connecting portion with the aluminum shell cover, 5-aluminum shell cover, 6-connecting portion between the upper membrane and the lower membrane, 7-protective cover, 8-battery shell, 9-vent. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0030] In the present invention, unless otherwise specified, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like used in the present invention to indicate directions or positional relationships are only for the purpose of facilitating the description of the present invention and simplifying the description, and are not intended to indicate or imply that the devices or components referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes and should not be understood as indicating or implying relative importance; in addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediate medium, or it can be internal communication between two components. For those of ordinary skill in the art, the specific meanings of the above terms in this patent can be understood according to specific circumstances.

[0031] In the present invention, unless otherwise specified, the Gurley value involved in the present invention is the value of 100 mL of air passing through 6.45 cm under standard pressure difference. 2 The time (in seconds) required for a sample with an area of 1 square inch to pass through the sample is tested using a Gurley air permeability tester according to standard ASTM D726. The higher the Gurley value, the worse the air permeability of the material.

[0032] In the present invention, unless otherwise specified, the puncture strength test involved in the present invention is to test the puncture strength of the selected membrane using a universal material testing machine according to the standard GB / T 10004-2008, and the puncture device is a steel needle with a diameter of 1 mm.

[0033] Example 1

[0034] Reference Figures 1-4 As shown, the explosion-proof valve of this embodiment includes an ultra-low pressure relief device and a protective cover 7; the ultra-low pressure relief device is arranged in the protective cover 7;

[0035] The ultra-low pressure relief device includes a hollow protective film and an ejector pin 1 made of aluminum and disposed within the protective film. The ejector pin 1 includes a main pin 11 and a secondary pin 12 bent to one side of the main pin 11. The curvature radius of the secondary pin 12 is 100 μm. The tip of the main pin 11 faces the top of the protective film, while the tip of the secondary pin 12 faces the bottom of the protective film.

[0036] The distance h1 from the tip of the main needle 11 to the top of the protective film is 0.5 mm, and the distance h2 from the tip of the auxiliary needle 12 to the bottom of the protective film is 1 mm, and h1<h2;

[0037] The protective film includes an upper film 2 and a lower film 3; the upper film 2 is convex, i.e., it bulges upward; the lower film 3 is concave, i.e., it is concave downward; the ejector pin 1 is fixed to the bottom of the lower film 3 by an integral molding method;

[0038] Taking the installation of the explosion-proof valve on the battery as an example, there are three ways to connect the upper membrane 2, the lower membrane 3 and the aluminum shell cover 5 of the battery:

[0039] (1) Figure 1 As shown, the upper film 2 and the lower film 3 are simultaneously connected to the aluminum shell cover plate 5, that is, the connection portion 4 between the protective film and the aluminum shell cover plate and the connection portion 6 between the upper film and the lower film coincide with each other; it should be noted that Example 2, Comparative Examples 1-2 and the Test Examples all adopt this method;

[0040] (2) Figure 2 As shown, the upper film 2 is first connected to the lower film 3 to form a connection portion 6 between the upper and lower films; the lower film 3 is then connected to the aluminum shell cover plate 5 to form a connection portion 4 with the aluminum shell cover plate;

[0041] (3) Figure 3 As shown, the lower film 3 is first connected to the upper film 2 to form a connection portion 6 between the upper and lower films; the upper film 2 is then connected to the aluminum shell cover plate 5 to form a connection portion 4 with the aluminum shell cover plate;

[0042] The upper film 2 is an aluminum film with a thickness of 20 μm and a puncture strength P1 of 12 N / cm;

[0043] The curvature of the upper membrane 2 and the lower membrane 3 is independently 1:10;

[0044] The distance h between the top of the upper film 2 and the bottom of the lower film 3 is 5 mm;

[0045] The lower membrane 3 includes a gas barrier membrane on the side close to the ejector pin 1 and a breathable support membrane on the side away from the ejector pin 1; the gas barrier membrane is made of aluminum foil with a thickness of 8 μm and a Gurley value of 6000 s / 100 mL;

[0046] The material of the breathable support membrane is PET non-woven fabric with a thickness of 50 μm, a Gurley value of 30 s / 100 mL, a puncture strength P2 of 30 N / cm, and P2>P1.

[0047] Example 2

[0048] The explosion-proof valve of this embodiment includes an ultra-low pressure relief device and a protective cover 7; the ultra-low pressure relief device is arranged in the protective cover 7;

[0049] The ultra-low pressure relief device includes a hollow protective film and an ejector pin 1. The ejector pin 1 is made of ABS hard plastic and is located inside the protective film. The ejector pin 1 includes a main pin 11 and a secondary pin 12 bent to one side of the main pin 11. The curvature radius of the secondary pin 12 is 40 μm. The tip of the main pin 11 faces the top of the protective film, and the tip of the secondary pin 12 faces the bottom of the protective film.

[0050] The distance h1 from the tip of the main needle 11 to the top of the protective film is 0.8 mm, and the distance h2 from the tip of the auxiliary needle 12 to the bottom of the protective film is 1 mm, and h1<h2;

[0051] The protective film includes an upper film 2 and a lower film 3; the upper film 2 is convex, i.e., it bulges upward; the lower film 3 is concave, i.e., it is concave downward; the ejector pin 1 is fixed to the bottom of the lower film 3 by gluing;

[0052] The upper film 2 is a polyethylene (PE) film with a thickness of 20 μm and a puncture strength P1 of 8 N / cm;

[0053] The curvature of the upper membrane 2 and the lower membrane 3 is independently 1:15;

[0054] The distance h between the top of the upper membrane 2 and the bottom of the lower membrane 3 is 7 mm;

[0055] The lower film 3 includes a gas barrier film on the side close to the ejector pin 1 and a breathable support film on the side away from the ejector pin 1;

[0056] The gas barrier membrane is made of polytetrafluoroethylene (PTFE), with a thickness of 10 μm and a Gurley value of 6000 s / 100 mL;

[0057] The material of the breathable support membrane is a polyethylene (PE) uniaxially stretched microporous membrane with a thickness of 50 μm, a Gurley value of 15 s / 100 mL, a puncture strength P2 of 30 N / cm, and P2>P1.

[0058] Comparative Example 1

[0059] The embodiment is basically the same as the embodiment 1, except that: the distance h1 from the tip of the main needle 11 to the top of the protective film is mm, and the distance h2 from the tip of the auxiliary needle 12 to the bottom of the protective film is 0.5 mm, that is, h1>h2.

[0060] Comparative Example 2

[0061] It is basically the same as Example 1, except that the upper film 2 is an aluminum film with a thickness of 100 μm and a puncture strength P1 of 50 N / cm, that is, P1 < P2.

[0062] Comparative Example 3

[0063] The aluminum-plastic film notched pressure relief valve in patent CN108428836A.

[0064] Test Case

[0065] Reference Figure 5 As shown, the explosion-proof valve processed according to the above embodiments and comparative examples is connected to the aluminum shell cover plate, which is welded to the battery shell 8 by laser welding, and a vent 9 is left on the battery shell 8. The gas production process of the battery is simulated by injecting helium into the battery shell 8, and a pressure sensor is used to record the internal pressure of the battery and the valve opening pressure. A high-speed camera is used to record the time difference δT between the time when the pressure relief valve pin pierces the membrane and the time when the internal pressure of the battery drops to the atmospheric pressure value.

[0066] Taking Example 1 as an example, the specific phenomena that occurred during the test are as follows:

[0067] Initial state: the upper membrane is intact, the gas barrier layer of the lower membrane is intact, and the battery shell is sealed;

[0068] Pressure triggering: With the injection of helium, the internal pressure of the battery shell gradually increases, and the lower membrane is pushed upward. When the pressure inside the shell increases to 0.15MPa (exceeding the trigger threshold of the upper membrane and ejector pin assembly), the lower membrane arches upward due to the pressure difference, pushing the main needle fixed to the lower membrane to move vertically. The tip of the main needle first pierces the upper membrane, forming a circular rupture with a diameter of about 1.2mm, breaking through the top sealing layer of the shell; then the tip continues to move, scratching the gas barrier membrane of the lower membrane, exposing the breathable support membrane underneath;

[0069] Pressure relief stage: The gas is quickly discharged through the rupture of the upper membrane and the exposed breathable support membrane of the lower membrane, and the pressure inside the battery shell is reduced to normal atmospheric pressure within 6ms.

[0070] The specific test results are shown in Table 1:

[0071] Table 1

[0072]

[0073]

[0074] As can be seen from Table 1, the pressure relief threshold of the explosion-proof valve in the embodiment is 0.1MPa-0.2MPa. The time difference δT between the time the ejector needle pierces the upper membrane and the time the internal pressure of the battery drops to atmospheric pressure is less than 10ms. Once the upper membrane is punctured, the pressure in the battery is released. This time difference δT is also the pressure relief response time of the battery pressure relief valve. Although the double membrane needs to be punctured to achieve pressure relief, due to the ingenuity of the design, if the lower membrane is punctured first, the gas will accumulate around the pressure relief valve. Therefore, puncturing the upper membrane first can quickly release the gas in a concentrated manner without prolonging the pressure relief response time. Through the synergistic effect of the ejector needle and the upper and lower membranes, a directional rupture channel can be quickly formed when the pressure reaches the critical value, significantly reducing the pressure relief pressure and shortening the pressure decay time.

[0075] Comparing Example 1 and Comparative Example 1, it can be seen that since the ejector pin is close to the lower membrane, the gas barrier layer of the lower membrane is punctured first, and the upper membrane forms a convex state under the internal pressure and cannot be punctured to form pressure relief.

[0076] Comparing Example 1 and Comparative Example 2, it can be seen that since the lower film is weaker than the upper film, the lower film is punctured first, and the upper film forms a convex state under the internal pressure and cannot be punctured to form pressure relief.

[0077] Comparing Example 1 and Comparative Example 3, it can be seen that the design without ejector pins and upper and lower membranes, relying solely on notches to release pressure, results in a very high pressure release, reaching 1.35 MPa. The time difference δT for the internal pressure of the cell to drop to atmospheric pressure is 20 ms. The root cause of this phenomenon is that the crack size generated when the notched aluminum foil ruptures is small, resulting in a restricted gas discharge channel and a significant lag in the pressure release process. This indicates that passive pressure relief methods that rely solely on notches have structural limitations. The design of an integrated mechanical trigger structure (such as an ejector pin) and a flexible sealing layer (such as upper and lower membranes) can achieve more efficient pressure management by actively controlling the crack propagation path and scale, providing a key optimization direction for battery safety design.

[0078] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A pressure relief device with ultra-low pressure relief, characterized in that: It includes a hollow protective film and a thimble, wherein the thimble is arranged in the protective film; the thimble includes a main needle and a secondary needle bent on one side of the main needle; the tip of the main needle faces the top of the protective film, and the tip of the secondary needle faces the bottom of the protective film.

2. The ultra-low pressure relief device according to claim 1, characterized in that: The distance from the tip of the main needle to the top of the protective film and the distance from the tip of the secondary needle to the bottom of the protective film are independently 0.5mm-2mm, and the distance from the tip of the main needle to the top of the protective film is smaller than the distance from the tip of the secondary needle to the bottom of the protective film.

3. The ultra-low pressure relief device according to claim 1, characterized in that: The curvature radius of the secondary needle is 0.1 μm-200 μm.

4. The ultra-low pressure relief device according to claim 1, characterized in that: The protective film includes an upper film and a lower film; the ejector pin is arranged at the bottom of the lower film.

5. The ultra-low pressure relief device according to claim 4, characterized in that: The thickness of the upper film is 5 μm-100 μm, and the puncture strength is 5 N / cm-20 N / cm.

6. The ultra-low pressure relief device according to claim 4, characterized in that: The lower membrane includes a gas barrier membrane on the side close to the ejector pin and a breathable support membrane on the side away from the ejector pin; the thickness of the gas barrier membrane is 5μm-20μm, and the Gurley value is greater than 5000s / 100mL; the thickness of the breathable support membrane is 20μm-100μm, the Gurley value does not exceed 50s / 100mL, the puncture strength is 10N / cm-30N / cm, and the puncture strength of the breathable support membrane is greater than the puncture strength of the upper membrane.

7. The ultra-low pressure relief device according to claim 4, characterized in that: The curvature of the upper membrane and the lower membrane is independently 1:(1-20).

8. The ultra-low pressure relief device according to claim 4, characterized in that: The distance between the top of the upper film and the bottom of the lower film is 2 mm to 10 mm.

9. An explosion-proof valve, comprising the ultra-low pressure relief device according to any one of claims 1 to 8 and a protective cover; the ultra-low pressure relief device is arranged in the protective cover.

10. A sodium ion battery comprising a positive electrode, a negative electrode and the explosion-proof valve according to claim 9, wherein the active material of the positive electrode is selected from Na4Fe3(PO4)2(P2O7), Na4Fe 3-x Mn x (PO4)2(P2O7), Na4Mn3(PO4)2(P2O7) and Na3MnTi(PO4)3, wherein 0<x<3; the active material of the negative electrode is selected from one or more of NaTi2(PO4)3, Na3Fe2(PO4)3 and Na3MnTi(PO4)3.

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