Separator having low pore closure temperature and preparation method therefor

Abstract

Provided is a separator having a low pore closure temperature, comprising: a base membrane (1), which includes unbranched polyolefins and long-chain branched polyolefins; and a coating (2), which is formed on at least one surface of the base membrane (1) and includes: a heat-sensitive polymer material. By means of the above solution, the pore closure response time and the pore closure temperature of the separator can be greatly reduced, and consequently the safety of lithium ion batteries can be improved.

Description

Low closing temperature diaphragm and preparation method thereof Technical Field

[0001] The present invention relates to the technical field related to lithium battery separators, and further relates to a low-shutdown temperature separator and a preparation method thereof, thereby improving the safety performance of lithium batteries. Background Art

[0002] During the charge and discharge process of lithium batteries, especially high-energy-density lithium batteries, the internal temperature of the battery continues to rise as the redox reactions at the positive and negative electrodes proceed. This can lead to explosions due to thermal runaway, posing safety concerns. The separator, one of the four essential components within a battery, prevents short circuits and facilitates lithium ion transport. When the internal temperature of the battery rises rapidly, the separator quickly melts and closes the pores, blocking the passage of lithium ions, quickly ending the internal reactions and preventing explosions. Therefore, a separator with a low pore-closing temperature is crucial to the safety of lithium batteries.

[0003] Currently, low-closure-temperature diaphragms are prepared by introducing low-melting-point materials into polyolefin materials. Although this can lower the diaphragm's closure temperature, the closure response time is slow, and a large amount of heat accumulates inside the battery, causing the diaphragm to rupture after closure, leading to thermal runaway. There is also the preparation of PP / PE / PP composite diaphragms by three-layer co-extrusion. The resulting diaphragm's closure temperature is only equivalent to the melting point of PE, and the poor compatibility between PP and PE is a problem that must be considered. There is also the coating of a low-melting-point polymer on the surface of a polyolefin base film. However, when the battery temperature rises, the low-melting-point polymer expands and blocks the pores on the surface of the base film, thereby achieving the effect of lowering the diaphragm's closure temperature. However, when the battery temperature of the diaphragm prepared in this way further increases, the low-melting-point polymer on the surface of the base film will vaporize, generating bubbles and rupturing, causing the blocked pores to reappear and leading to closure failure. Summary of the Invention

[0004] The purpose of the present invention is to reduce the pore closing temperature and pore closing response time of the existing diaphragm, thereby improving the self-power-off function of the battery and thus improving the battery safety performance.

[0005] To achieve the above objectives, the present invention prepares a diaphragm substrate by wet film forming technology by mixing a certain proportion of linear unbranched polyethylene and polyethylene with a long-chain branched structure, and then coats a layer of heat-sensitive material on the surface of the diaphragm substrate to achieve the effect of reducing the closed-cell temperature and closed-cell response time.

[0006] Therefore, a first aspect of the present invention provides a low shut-down temperature diaphragm, comprising: a base film comprising: unbranched polyolefin and long-chain branched polyolefin; and a coating formed on at least one surface of the base film, comprising: a thermosensitive polymer material.

[0007] For example, the coating further comprises: ceramic particles and a binder.

[0008] For example, the unbranched polyolefin is unbranched polyethylene, and the long-chain branched polyolefin is long-chain branched polyethylene.

[0009] For example, the thermosensitive polymer material is one or more of N,N'-methylenebisacrylamide cross-linked polyacrylamide, polyolefin wax grafted maleic anhydride copolymer emulsion, polyvinyl chloride, polyacrylamide, and poly-N-isopropylacrylamide.

[0010] For example, the mass ratio of the unbranched polyolefin to the long-chain branched polyolefin is (5-9):(1-5).

[0011] For example, the mass ratio of the thermosensitive polymer material to the ceramic particles is (1-5):(5-9).

[0012] For example, the branching degree of the long-chain branched polyethylene is ≥10 / 1000C.

[0013] For example, the pore size of the base film is 0.01 μm to 1 μm; and / or the porosity of the base film is ≥30%; and / or the pore size concentration of the base film is ≥80%.

[0014] For example, the low closure temperature membrane closes at least 30% of the pores at 100° C.; and / or the low closure temperature membrane has a complete closure time of less than 1 minute at 130° C.

[0015] For example, the air permeability of the low closed-cell temperature membrane is higher than that of the base membrane, and the difference in air permeability between the low closed-cell temperature membrane and the base membrane is less than 10s / 100mL.

[0016] The second aspect of the present invention proposes a method for preparing the above-mentioned low closed-cell temperature diaphragm, which includes: mixing the unbranched polyolefin and the long-chain branched polyolefin, and then melt-extruding them into cast sheets through a twin-screw extruder to obtain the base film; coating a slurry containing the heat-sensitive polymer material on the surface of the base film; and drying the slurry to form the coating.

[0017] A third aspect of the present invention provides a battery comprising: a positive electrode, a negative electrode, and the low shut-down temperature separator, wherein the low shut-down temperature separator is located between the positive electrode and the negative electrode.

[0018] This invention uses linear unbranched polyethylene and nonlinear long-chain branched polyethylene as raw materials, prepares a base membrane using a wet-process separator technique, then coats the base membrane with a heat-sensitive material and dries it. The resulting separator can significantly reduce the separator's closure response time and closure temperature, thereby improving the safety of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1 is a schematic diagram showing a low-shutdown-temperature diaphragm according to the present invention;

[0020] FIG2 is a flow chart illustrating a method for preparing a low-shutdown-temperature diaphragm according to the present invention. DETAILED DESCRIPTION

[0021] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0022] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0023] The present invention utilizes thermosensitive materials to coat polyethylene to form a low-closure-temperature diaphragm. Specifically, the diaphragm base is composed of linear unbranched polyethylene and polyethylene with a long-chain branched structure. When the battery temperature rises, the polyethylene with a long-chain branched structure has the characteristic of a low melting point and can close the internal pores of the diaphragm. The thermosensitive material coated on the diaphragm base can close the pores on the surface of the diaphragm. This can effectively and quickly reduce the diaphragm closure response time and closure temperature, prevent the battery temperature from further rising and causing the diaphragm to rupture and cause thermal runaway, thereby greatly improving the safety performance of the lithium battery.

[0024] Please refer to Figure 1. The low closed-cell temperature diaphragm of the present invention includes: a base film (1) comprising: unbranched polyolefin and long-chain branched polyolefin; and a coating (2) formed on at least one surface of the base film (1) and comprising: a thermosensitive polymer material.

[0025] First, the base film (1) is discussed as follows. The base film (1) can be a wet-process membrane. The pore size of the base film (1) can be 0.01 μm to 1 μm, for example, 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1 μm. The porosity of the base film (1) can be ≥30%, for example, ≥30%, 35%, 40%, 45%, 50%, 55%, or 60%. The pore concentration of the base film (1) can be ≥80%, for example, ≥80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90%. Furthermore, the mass ratio of the unbranched polyolefin to the long-chain branched polyolefin may be (5-9):(1-5), for example, 5:1, 5:2, 5:3, 5:4, 5:5, 6:1, 6:2, 6:3, 6:4, 6:5, 7:1, 7:2, 7:3, 7:4, 7:5, 8:1, 8:2, 8:3, 8:4, 8:5, 9:1, 9:2, 9:3, 9:4, or 9:5. An example of the unbranched polyolefin may be unbranched polyethylene, and an example of the long-chain branched polyolefin may be long-chain branched polyethylene. The degree of branching of the long-chain branched polyethylene may be ≥10 / 1000C, for example ≥10 / 1000C, 11 / 1000C, 12 / 1000C, 13 / 1000C, 14 / 1000C, 15 / 1000C, 16 / 1000C, 17 / 1000C, 18 / 1000C, 19 / 1000C, or 20 / 1000C.

[0026] Next, the coating (2) is discussed as follows. Examples of thermosensitive polymer materials may be one or more of N,N'-methylenebisacrylamide cross-linked polyacrylamide, polyolefin wax grafted maleic anhydride graft copolymer emulsion, polyvinyl chloride, polyacrylic acid acrylamide, and poly-N-isopropyl acrylamide. The particle size of the thermosensitive polymer material may be 0.1 μm to 10 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. In order to further impart better performance to the diaphragm, the coating (2) may further include: ceramic particles and a binder. Examples of ceramic particles may be one or more of alumina and boehmite, and examples of binders may be polyacrylate binders. The mass ratio of the thermosensitive polymer material to the ceramic particles can be (1-5):(5-9), for example, 1:5, 1:6, 1:7, 1:8, 1:9, 2:5, 2:6, 2:7, 2:8, 2:9, 3:5, 3:6, 3:7, 3:8, 3:9, 4:5, 4:6, 4:7, 4:8, 4:9, 5:5, 5:6, 5:7, 5:8, or 5:9.

[0027] Finally, the following discussion focuses on low-shutdown temperature membranes. Low-shutdown temperature membranes can close at least 30% of the pores at 100°C, for example, at least 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the pores. Low-shutdown temperature membranes can close at least 60% of the pores at 110°C, for example, at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the pores. Low-shutdown temperature membranes can close at least 80% of the pores at 120°C, for example, at least 80%, 85%, 90%, 95%, or 100% of the pores. The low-closure temperature membrane can close at least 90% of the pores at 130°C, for example, at least 90%, 95%, or 100% of the pores. It should be added that the "pore closure percentage" mentioned above refers to the percentage of the porosity at a specific temperature relative to the porosity at room temperature (25°C). In addition, the complete closure time of the low-closure temperature membrane at 130°C can be less than 1 minute. It should be added that the "complete closure time" refers to the time required for the porosity to decrease to 0% after moving from room temperature (25°C) to a specific temperature. In addition, the air permeability of the low-closure temperature membrane is higher than that of the base film (1), and the difference in air permeability between the low-closure temperature membrane and the base film (1) is less than 10s / 100mL. It can be seen that under this condition, the coating (2) formed on the base film (1) will cause the air permeability of the membrane to increase slightly.

[0028] Please refer to FIG. 2 , which shows a method for preparing a low-shutdown-temperature diaphragm according to the present invention, comprising: melting a casting sheet ( S1 ), coating ( S2 ), and drying ( S3 ).

[0029] During melt casting (S1), the unbranched polyolefin and the long-chain branched polyolefin are mixed and then melt-extruded into a cast sheet through a twin-screw extruder to obtain a base film. During the mixing of the unbranched polyolefin and the long-chain branched polyolefin, pore-forming white oil and an antioxidant may be added. The pore-forming white oil can create pores in the base film, providing breathability, while the antioxidant can prevent yellowing caused by oxidation of the base film. Furthermore, after melt extrusion into a cast sheet, cooling, stretching, and extraction can be performed. Cooling solidifies the base film, stretching can form pores in the base film or reduce internal stress, and extraction can remove the pore-forming white oil and antioxidant from the base film.

[0030] During coating (S2), a slurry containing a heat-sensitive polymer material is applied to the surface of the base film. The slurry may further include ceramic particles and a binder. The binder content may be 0.1 wt% to 1 wt% based on the mass of the slurry, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or 1 wt%. Coating may be performed by roller coating, blade coating, spray coating, or spin coating.

[0031] When drying (S3), the slurry is dried to form a coating.

[0032] It should be noted that the materials mentioned here can refer to the relevant descriptions of the separator mentioned above. Moreover, the technical core of the preparation method of the present invention lies in the materials, not the parameters. Therefore, without disclosing the specific steps in detail, those skilled in the art can understand and implement it.

[0033] In summary, the separator of the present invention has a low closure temperature and a low closure response time, making it suitable for use as a barrier between positive and negative electrodes in batteries. Based on this, the battery of the present invention comprises: a positive electrode, a negative electrode, and the separator of the present invention, with the separator positioned between the positive and negative electrodes.

[0034] The present invention is further illustrated by the following examples:

[0035] Example 1

[0036] The branching degree of the selected long-chain branched polyethylene is 10 / 1000C, and the particle size of the thermosensitive polymer material is 0.5 μm.

[0037] The diaphragm is prepared as follows: unbranched polyethylene powder and long-chain branched polyethylene powder are mixed in a mass ratio of 7:3. The mixture is then melt-mixed with a pore-forming agent, white oil, and an antioxidant through a twin-screw extruder to form a cast sheet. After cooling, stretching, and extraction, the base membrane is formed. A mixed slurry consisting of a thermosensitive polymer material, ceramic particles, and a binder is applied to either surface of the prepared base membrane. The mass ratio of the thermosensitive polymer material to the ceramic particles is 2:8, and the binder accounts for 0.1 wt% of the total mixed slurry. The diaphragm is then dried to obtain the membrane.

[0038] Example 2

[0039] The branching degree of the selected long-chain branched polyethylene is 10 / 1000C, and the particle size of the thermosensitive polymer material is 0.5 μm.

[0040] The diaphragm is prepared as follows: unbranched polyethylene powder and long-chain branched polyethylene powder are mixed in a 5:5 mass ratio, then melt-mixed with white oil and an antioxidant using a twin-screw extruder to form a cast sheet. After cooling, stretching, and extraction, a base membrane is formed. A mixed slurry consisting of a thermosensitive polymer material, ceramic particles, and a binder is applied to either surface of the prepared base membrane. The ratio of the thermosensitive polymer material to the ceramic particles is 2:8, with the binder comprising 0.1 wt% of the mixed slurry. The diaphragm is then dried to obtain the membrane.

[0041] Example 3

[0042] The branching degree of the selected long-chain branched polyethylene is 10 / 1000C, and the particle size of the thermosensitive polymer material is 0.5 μm.

[0043] The diaphragm is prepared as follows: unbranched polyethylene powder and long-chain branched polyethylene powder are mixed in a mass ratio of 3:7, then melt-mixed with white oil and an antioxidant using a twin-screw extruder to form a cast sheet. After cooling, stretching, and extraction, a base membrane is formed. A mixed slurry consisting of a thermosensitive polymer material, ceramic particles, and a binder is applied to either surface of the prepared base membrane. The mass ratio of the thermosensitive polymer material to the ceramic particles is 2:8, and the binder accounts for 0.1 wt% of the total mixed slurry. The diaphragm is then dried to obtain the membrane.

[0044] Example 4

[0045] The branching degree of the selected long-chain branched polyethylene is 15 / 1000C, and the particle size of the thermosensitive polymer material is 0.5 μm.

[0046] The diaphragm is prepared as follows: unbranched polyethylene powder and long-chain branched polyethylene powder are mixed in a mass ratio of 7:3. The mixture is then melt-mixed with a pore-forming agent, white oil, and an antioxidant through a twin-screw extruder to form a cast sheet. After cooling, stretching, and extraction, the base membrane is formed. A mixed slurry consisting of a thermosensitive polymer material, ceramic particles, and a binder is applied to either surface of the prepared base membrane. The mass ratio of the thermosensitive polymer material to the ceramic particles is 2:8, and the binder accounts for 0.1 wt% of the total mixed slurry. The diaphragm is then dried to obtain the membrane.

[0047] Example 5

[0048] The branching degree of the selected long-chain branched polyethylene is 20 / 1000C, and the particle size of the thermosensitive polymer material is 0.5 μm.

[0049] The diaphragm is prepared as follows: unbranched polyethylene powder and long-chain branched polyethylene powder are mixed in a mass ratio of 7:3. The mixture is then melt-mixed with a pore-forming agent, white oil, and an antioxidant through a twin-screw extruder to form a cast sheet. After cooling, stretching, and extraction, the base membrane is formed. A mixed slurry consisting of a thermosensitive polymer material, ceramic particles, and a binder is applied to either surface of the prepared base membrane. The mass ratio of the thermosensitive polymer material to the ceramic particles is 2:8, and the binder accounts for 0.1 wt% of the total mixed slurry. The diaphragm is then dried to obtain the membrane.

[0050] Example 6

[0051] The branching degree of the selected long-chain branched polyethylene is 10 / 1000C, and the particle size of the thermosensitive polymer material is 0.5 μm.

[0052] The diaphragm is prepared as follows: unbranched polyethylene powder and long-chain branched polyethylene powder are mixed in a mass ratio of 7:3. The mixture is then melt-mixed with a pore-forming agent, white oil, and an antioxidant through a twin-screw extruder to form a cast sheet. After cooling, stretching, and extraction, the base membrane is formed. A mixed slurry consisting of a thermosensitive polymer material, ceramic particles, and a binder is applied to either surface of the prepared base membrane. The mass ratio of the thermosensitive polymer material to the ceramic particles is 5:5, and the binder accounts for 0.1 wt% of the total mixed slurry. The diaphragm is then dried to obtain the membrane.

[0053] Example 7

[0054] The branching degree of the selected long-chain branched polyethylene is 10 / 1000C, and the particle size of the thermosensitive polymer material is 0.5 μm.

[0055] The diaphragm is prepared as follows: unbranched polyethylene powder and long-chain branched polyethylene powder are mixed in a mass ratio of 7:3. The mixture is then melt-mixed with a pore-forming agent, white oil, and an antioxidant through a twin-screw extruder to form a cast sheet. After cooling, stretching, and extraction, the base membrane is formed. A mixed slurry consisting of a thermosensitive polymer material, ceramic particles, and a binder is applied to either surface of the prepared base membrane. The mass ratio of the thermosensitive polymer material to the ceramic particles is 7:3, and the binder accounts for 0.1 wt% of the total mixed slurry. The diaphragm is then dried to obtain the membrane.

[0056] Comparative Example 1

[0057] The preparation of the diaphragm is as follows: unbranched polyethylene powder, pore-forming agent white oil, and antioxidant are melt-mixed and extruded into cast sheets through a twin-screw extruder, and then cooled, stretched, and extracted to form a base film as the diaphragm.

[0058] Comparative Example 2

[0059] The branching degree of the selected long-chain branched polyethylene is 10 / 1000C.

[0060] The preparation of the diaphragm is as follows: unbranched polyethylene powder and long-chain branched polyethylene powder are mixed in a mass ratio of 7:3, melt-mixed with pore-forming agent white oil and antioxidant through a twin-screw extruder to form a cast sheet, and after cooling, stretching and extraction, a base film is formed as the diaphragm.

[0061] Comparative Example 3

[0062] The diaphragm is prepared as follows: Unbranched polyethylene powder, a pore-forming white oil, and an antioxidant are melt-mixed and extruded through a twin-screw extruder to form a cast sheet. After cooling, stretching, and extraction, a base membrane is formed. A mixed slurry consisting of a thermosensitive polymer material, ceramic particles, and a binder is applied to either surface of the prepared base membrane. The mass ratio of the thermosensitive polymer material to the ceramic particles is 2:8, and the binder accounts for 0.1% by weight of the mixed slurry. The diaphragm is then dried to obtain the membrane.

[0063] Test Characterization

[0064] Closed-cell temperature: The test is conducted using the temperature-increasing internal resistance method. The sample is cut into a fixed size and placed between two fixtures. Electrolyte is passed on both sides of the sample, and then heated and energized. The resistance curve of the sample as the temperature increases is derived from the data processing system, and the temperature corresponding to the point where the interval mutation occurs is set as the closed-cell temperature of the sample.

[0065] Air permeability: tested using Wangyan air permeability instrument GB / T 36363-2018.

[0066] Porosity: After the diaphragm passes the closed-cell temperature test, take it out and measure the sample thickness and weight. The determination formula is ε=1-S / (T*0.957) according to GB / T 36363-201, S: sample weight, unit: g / m 2 , T is the sample thickness, unit: μm, ε: porosity, unit: %.

[0067] Table 1

[0068] The following explanation is based on the results in Table 1. Comparison of Examples 1, 2, and 3 with Comparative Example 1 shows that a higher proportion of long-chain branched polyethylene is associated with a lower membrane pore-closing temperature. Comparison of Examples 1, 4, and 5 with Comparative Example 3 shows that a higher degree of polyethylene branching is associated with a lower membrane pore-closing temperature. This is because increasing the degree of branching reduces membrane crystallinity, causing the molecular weight within the membrane to melt as the temperature rises, closing the internal pores.

[0069] Comparison of Examples 1, 6, and 7 with Comparative Example 2 shows that increasing the content of the thermosensitive polymer effectively lowers the membrane's pore-closing temperature, but increases the air permeability (poorer air permeability). This is because the thermosensitive polymer responds quickly to heat, effectively closing the membrane's surface pores. Furthermore, after high-temperature treatment at 130°C for 60 seconds, the membrane's internal pores rapidly close, reducing the porosity to 0% and rapidly increasing the air permeability.

[0070] Comparing Comparative Examples 1 and 2, it can be seen that replacing only part of the unbranched polyethylene with long-branched polyethylene can reduce the closed-cell temperature by 3.7°C and the porosity by 2% after high-temperature treatment at 130°C for 60 seconds, but it does not affect the air permeability after high-temperature treatment at 130°C for 60 seconds. Comparing Comparative Examples 1 and 3, it can be seen that only forming a heat-sensitive material layer can reduce the closed-cell temperature by 3.3°C and the porosity by 1% after high-temperature treatment at 130°C for 60 seconds, but it does not affect the air permeability after high-temperature treatment at 130°C for 60 seconds. Comparing Example 1 with Comparative Example 1, it can be seen that simultaneously replacing part of the unbranched polyethylene with long-branched polyethylene and forming a heat-sensitive material layer can reduce the closed-cell temperature by 7.4°C and reduce the porosity by 18% after high-temperature treatment at 130°C for 60 seconds, and increase the air permeability after high-temperature treatment at 130°C for 60 seconds by 9.4x10 4 s / 100mL. This indicates that replacing a portion of the unbranched polyethylene with long-branched polyethylene and forming a heat-sensitive material layer unexpectedly lowers the closed-cell temperature and porosity after a 130°C high-temperature treatment for 60 seconds, while also increasing the air permeability after a 130°C high-temperature treatment for 60 seconds. In other words, replacing a portion of the unbranched polyethylene with long-branched polyethylene and forming a heat-sensitive material layer not only unexpectedly lowers the closed-cell temperature but also unexpectedly reduces the closed-cell response time.

[0071] The above contents involving common knowledge are not described in detail and can be understood by those skilled in the art.

[0072] The above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention. The technical scope of the present invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A low closing temperature diaphragm, characterized in that: include: A base film comprising: unbranched polyolefin and long-chain branched polyolefin; as well as A coating layer is formed on at least one surface of the base film and includes a thermosensitive polymer material.

2. The low closing temperature diaphragm according to claim 1, characterized in that: The coating further comprises: ceramic particles and a binder.

3. The low closing temperature diaphragm according to claim 1, characterized in that: The unbranched polyolefin is unbranched polyethylene, and the long-chain branched polyolefin is long-chain branched polyethylene.

4. The low closing temperature diaphragm according to claim 1, characterized in that: The thermosensitive polymer material is one or more of N,N'-methylenebisacrylamide cross-linked polyacrylamide, polyolefin wax grafted maleic anhydride graft copolymer emulsion, polyvinyl chloride, polyacrylic acid acrylamide, and poly-N-isopropyl acrylamide.

5. The low closing temperature diaphragm according to claim 1, characterized in that: The mass ratio of the unbranched polyolefin to the long-chain branched polyolefin is (5-9):(1-5).

6. The low closing temperature diaphragm according to claim 2, characterized in that: The mass ratio between the thermosensitive polymer material and the ceramic particles is (1-5):(5-9).

7. The low closing temperature diaphragm according to claim 1, characterized in that: The branching degree of the long-chain branched polyethylene is ≥10 / 1000C.

8. The low closing temperature diaphragm according to claim 1, characterized in that: The pore size of the base film is 0.01 μm to 1 μm; and / or the porosity of the base film is ≥30%; and / or the pore size concentration of the base film is ≥80%.

9. The low closing temperature diaphragm according to claim 1, characterized in that: The low closure temperature membrane closes at least 30% of the pores at 100° C.; and / or the low closure temperature membrane has a complete closure time of less than 1 minute at 130° C.

10. The low closing temperature diaphragm according to claim 1, characterized in that: The air permeability of the low closed-cell temperature membrane is higher than that of the base membrane, and the difference in air permeability between the low closed-cell temperature membrane and the base membrane is less than 10s / 100mL.

11. A method for preparing a low-shutdown-temperature diaphragm according to claim 1, characterized in that: include: The unbranched polyolefin and the long-chain branched polyolefin are mixed and then melt-extruded into a cast sheet through a twin-screw extruder to obtain the base film; Applying a slurry containing the heat-sensitive polymer material on the surface of the base film; as well as The slurry is dried to form the coating.

12. A battery comprising: A positive electrode, a negative electrode, and the low shut-down temperature separator according to claim 1, wherein the low shut-down temperature separator is located between the positive electrode and the negative electrode.

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