Diaphragm and preparation method and application thereof

Abstract

The invention belongs to the technical field of diaphragm preparation, and particularly relates to a diaphragm as well as a preparation method and application thereof. The diaphragm comprises a base membrane and a composite coating arranged on the surface of at least one side of the base membrane, the composite coating comprises aramid fibers and a solid electrolyte; a first position and a second position are taken along the same TD direction of the diaphragm, the first position is adjacent to the tab leading-out side, and the second position is far away from the tab leading-out side; the mass ratio of the aramid fibers to the solid electrolyte in the composite coating at the first position is recorded as Wa, the mass ratio of the aramid fibers to the solid electrolyte in the composite coating at the second position is recorded as Wb, and Wa is larger than Wb; and the distance between the first position and the second position along the TD direction of the diaphragm is marked as D which is not less than 3cm. The diaphragm can relieve diaphragm shrinkage and internal thermal stress of a battery cell caused by local overheating, and improve the problems that the expansion of an electrode material is aggravated due to local overheating and uneven stress is caused by local expansion of the battery cell, so that the battery cell performance of the battery is improved, and the service life of the battery is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of diaphragm preparation, and particularly relates to a diaphragm and a preparation method and application thereof. BACKGROUND

[0002] As one of key components of lithium batteries, the diaphragm mainly functions to block the physical contact between the positive and negative electrodes and has a certain pore structure to transmit lithium ions. Common diaphragm substrates mainly include polyethylene and polypropylene substrates, which have the characteristics of low cost and high mechanical strength. In order to improve the overall heat resistance of the diaphragm, different types of heat-resistant coatings, such as boehmite coatings and aluminum oxide coatings, are usually coated on the surface of the polyolefin substrate.

[0003] The heat-resistant coating of the existing diaphragm coating is mainly an isotropic coating uniformly distributed. Since the tabs are arranged at different positions of the lithium battery, the current density distribution is not uniform at different positions, the current density near the tab is higher than that at other positions, more Joule heat is generated in the area with high current density, the local temperature rises, the local overheating causes the diaphragm to shrink, which leads to internal short circuit of the battery, further increases the risk of thermal runaway of the battery cell, and reduces the service life of the battery cell. SUMMARY

[0004] To solve the above technical problems, the application provides a diaphragm and a preparation method and application thereof.

[0005] To this end, the application provides the following technical solutions.

[0006] The first aspect of the application provides a diaphragm, comprising a base film and a composite coating arranged on at least one side surface of the base film; the composite coating comprises aramid fiber and solid-state electrolyte; a first position and a second position are taken along the same TD direction of the diaphragm, the first position is adjacent to the tab leading-out side, and the second position is away from the tab leading-out side; the mass ratio of the aramid fiber to the solid-state electrolyte in the composite coating at the first position is denoted as W a , the mass ratio of the aramid fiber to the solid-state electrolyte in the composite coating at the second position is denoted as W b , and W a , W b satisfy W a > W b ; the distance between the first position and the second position along the TD direction of the diaphragm is denoted as D, and the D is greater than or equal to 3 cm.

[0007] The application adjusts the proportion of aramid fiber in the composite coating near the lead-out side of the polar ear to be higher than that far from the lead-out side of the polar ear, and the proportion of the solid-state electrolyte to be lower than that far from the lead-out side of the polar ear, so as to compensate for the problem of low current density far from the lead-out side of the polar ear, improve ion transmission distribution, realize uniform distribution of electric field, relieve membrane shrinkage and internal thermal stress of the battery caused by local overheating, improve the performance and service life of the battery.

[0008] The TD direction refers to the transverse direction, and the MD direction refers to the longitudinal direction.

[0009] As an optional implementation, the W a , W b , D satisfy the following relationship 1:

[0010] Relationship 1.

[0011] The application satisfies the above relationship, which is beneficial to further relieve local overheating and improve the service life of the battery. For example, the above (W a -W b ) / D is 0.2, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, etc. It should be noted that the upper limit of the value of D is related to the width of the separator in the TD direction, and the value of D is less than or equal to the width of the separator in the TD direction.

[0012] As an optional implementation, the mass ratio of aramid fiber and solid-state electrolyte in the composite coating is 1:9-9:1; it should be noted that the mass ratio of aramid fiber and solid-state electrolyte in the composite coating at the first position and the second position satisfies the above range, and W a > W b . For example, the mass ratio of aramid fiber and solid-state electrolyte is 1:9, 4:9, 8:9, 12:9, 20:9, 25:9, 30:9, 40:9, 45:9, 50:9, 55:9, 60:9, 70:9, 80:9, etc.

[0013] As an optional implementation, the solid-state electrolyte includes inorganic solid-state electrolyte and / or organic solid-state electrolyte.

[0014] As an optional implementation, the inorganic solid-state electrolyte includes at least one of LLTO, LLZO, LLZTO and LATP;

[0015] As an optional implementation, the organic solid-state electrolyte includes at least one of PEO, PVDF, PAN, PMMA and PPO.

[0016] As an optional implementation, the aramid fiber includes at least one of para-aramid fiber, meta-aramid fiber, ortho-aramid fiber, and heterocyclic aramid fiber.

[0017] As an optional implementation, the thickness of the single-side composite coating is 0.5-5 μm.

[0018] As an optional implementation, the air permeability increase value of the single-side composite coating is ≤80 s / 100 c; for example, the air permeability increase value is 40 s / 100 c, 45 s / 100 c, 50 s / 100 c, 55 s / 100 c, 60 s / 100 c, 65 s / 100 c, 70 s / 100 c, 75 s / 100 c, 80 s / 100 c, etc.

[0019] As an optional implementation, the base film includes a polyolefin separator; for example, the polyolefin separator includes a polyethylene film and a polypropylene film.

[0020] As an optional implementation, the thickness of the base film is 5-9 μm; for example, the thickness of the base film is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, etc.

[0021] The second aspect of the present application provides a preparation method of the above-mentioned separator, which comprises: preparing a plurality of slurries by mixing aramid fiber and solid electrolyte in different mass proportions, using segmented feeding, coating the base film on at least one side surface of the base film, and drying.

[0022] When coating, the coating can be performed by using a method known in the art, such as gravure roll coating, narrow-gap extrusion coating, and spraying.

[0023] When the composite coating is prepared by using the method, the slurries with different aramid fiber proportions are placed in the feeding groove in the TD direction of the separator from the side close to the tab leading-out side to the side away from the tab leading-out side, and the slurries are placed in the order of decreasing proportion. After coating and drying, the composite coating is formed. The number of portions of the slurries can be 2, 3, 4, 5, 7, 9, etc., and the proportions of aramid fiber in the plurality of portions of the slurries are different.

[0024] The third aspect of the present application provides a battery comprising the above-mentioned separator.

[0025] As an optional implementation, the battery comprises a plurality of tabs, and the plurality of tabs are arranged on the same side of the separator. It should be noted that the distance between adjacent tabs can be set according to the conventional setting.

[0026] As an optional implementation, the battery further comprises a positive electrode tab and a negative electrode tab, and the positive electrode tab and the negative electrode tab are prepared by using an electrode tab known in the art.

[0027] The technical scheme of the present application has the following advantages:

[0028] 1. The diaphragm provided by the present application comprises a base film and a composite coating arranged on at least one side surface of the base film; the composite coating comprises aramid and solid electrolyte; a first position and a second position are taken along the same TD direction of the diaphragm, the first position is adjacent to the tab leading-out side, and the second position is away from the tab leading-out side; the mass ratio of the aramid to the solid electrolyte in the composite coating at the first position is denoted as W a , the mass ratio of the aramid to the solid electrolyte in the composite coating at the second position is denoted as W b , W a , W b satisfy W a > W b ; the distance between the first position and the second position along the TD direction of the diaphragm is denoted as D, and the D is greater than or equal to 3 cm. Aramid belongs to aromatic polyamide, which is beneficial to improve the thermal dimensional stability and flame retardancy of the diaphragm, improve the high-temperature safety performance of the battery, and the solid electrolyte is an ion conductor with ion transmission function, which is beneficial to improve the ion transmission performance. In the present application, the composite coating containing aramid and solid electrolyte is formed on the surface of the base film, the mass ratio of aramid and solid electrolyte at different positions of the coating is regulated along the TD direction of the diaphragm, and when the coating is applied to the battery cell, the coating with high solid electrolyte proportion and low aramid proportion is located away from the tab leading-out side, which can compensate for the low current density away from the tab leading-out side, regulate the ion transmission distribution, realize uniform distribution of electric field, avoid local overheating, relieve the shrinkage of the diaphragm, improve the local overheating of the existing battery cell, and relieve the problem of uneven stress caused by local expansion of the battery cell, thereby improving the performance and service life of the battery cell. In addition, the composite coating also has the advantages of heat resistance, lightness and thinness.

[0029] 2. The preparation method of the diaphragm provided by the present application, when forming the coating on the surface of the diaphragm, the gravure roll coating process is preferably used, which has the advantages of high coating efficiency and low cost. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the specific embodiments of the present application or the technical scheme in the prior art, the drawings needed in the following specific embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creating any creative labor.

[0031] Figure 1 is a schematic diagram of the TD direction of the diaphragm and the tab position in Example 1 of the present application. DETAILED DESCRIPTION

[0032] The following examples are provided to better further understand the present application and are not limited to the best mode contemplated, do not limit the scope of the application, and are not intended to suggest that the application must be practiced in the manner of the examples provided, nor does it imply that the application will not work as defined in any of the following examples. Any product, or any method or process, that is equivalent in function or structure to any of the examples described herein is within the scope of the present application.

[0033] Unless otherwise indicated, conventional methods of chemistry, molecular biology, recombinant technology, and biochemistry, including the generation of recombinant DNA molecules, the insertion of DNA molecules into plasmids, the transformation of host cells, the growth and culture of host cells, and the purification of DNA molecules and proteins, were used in accordance with standard protocols that are well known in the art. Unless otherwise indicated, the reagents and instruments used were conventional reagents and instruments that are commercially available.

[0034] Example 1

[0035] The present example provides a separator, comprising a PE base film and a composite coating layer arranged on one surface of the PE base film, the composite coating layer comprising meta-aramid and lithium aluminum titanium phosphate (LATP), the thickness of the composite coating layer being 3 μm, the air permeability increase being 80 s / 100 c, the thickness of the PE base film being 7 μm, and the proportion of aramid in the composite coating layer adjacent to the tab leading side being higher than the proportion of aramid in the composite coating layer away from the tab leading side along the TD direction of the separator. The schematic diagram of the TD direction of the separator and the tab position is shown in Figure 1 .

[0036] The preparation method of the above-mentioned separator comprises:

[0037] The solid-state electrolyte and the meta-aramid are prepared into five different slurries in a mass ratio of 9:1, 7:3, 5:5, 3:7, and 1:9. The slurries are sorted in descending order of the mass ratio, the slurry with a high proportion of aramid is arranged close to the tab leading side, and the slurry is injected into the segmented feeding groove separated from each other along the TD direction of the separator. The length of each feeding groove along the TD direction of the separator is 3 cm. After the segmented feeding, the single-sided gravure roller is coated on the surface of the PE base film, dried, and a separator containing a composite coating layer is obtained. Along the same TD direction of the separator, the proportion of aramid in the composite coating layer adjacent to the tab leading side is high, and the proportion of solid-state electrolyte in the composite coating layer away from the tab leading side is high.

[0038] The separator prepared in the present example satisfies the relationship formula 1, and the value of D is 3 cm.

[0039] Example 2

[0040] The embodiment provides a diaphragm, which comprises a PE base film and a composite coating layer arranged on one surface of the PE base film, the composite coating layer comprises meta-aramid and lithium aluminum titanium phosphate (LATP), the thickness of the composite coating layer is 3 mu m, the air permeability increase is 76 s / 100 c, the thickness of the PE base film is 7 mu m, along the TD direction of the diaphragm, the proportion of aramid in the composite coating layer near the tab leading-out side is higher than the proportion of aramid in the composite coating layer away from the tab leading-out side, and the value of D is 3 cm.

[0041] The preparation method of the diaphragm comprises the following steps:

[0042] The solid electrolyte and the meta-aramid are prepared into five slurries with different compositions in a mass ratio of 9:1, 8:2, 7:3, 6:4 and 5:5, the slurries are sorted in a descending order of the mass ratio, the slurry with a high proportion of aramid is arranged near the tab leading-out side, and the slurries are injected into separate segmented feeding grooves along the TD direction of the diaphragm, the length of each feeding groove along the TD direction of the diaphragm is 3 cm, the feeding grooves are segmented, and then the single-sided roller is used to coat the PE base film, and drying is performed to obtain the diaphragm with the composite coating layer.

[0043] The diaphragm prepared in the embodiment satisfies the relationship formula 1.

[0044] Embodiment 3

[0045] The embodiment provides a diaphragm, which comprises a PE base film and a composite coating layer arranged on one surface of the PE base film, the composite coating layer comprises meta-aramid and lithium aluminum titanium phosphate (LATP), the thickness of the composite coating layer is 3 mu m, the air permeability increase is 80 s / 100 c, the thickness of the PE base film is 7 mu m, along the TD direction of the diaphragm, the proportion of aramid in the composite coating layer near the tab leading-out side is higher than the proportion of aramid in the composite coating layer away from the tab leading-out side, and the value of D is 3 cm.

[0046] The preparation method of the diaphragm comprises the following steps:

[0047] The solid electrolyte and the meta-aramid are prepared into seven slurries with different compositions in a mass ratio of 8:2, 7:3, 6:4, 5:5, 4:6, 3:7 and 2:8, the slurries are sorted in a descending order of the mass ratio, the slurry with a high proportion of aramid is arranged near the tab leading-out side, and the slurries are injected into separate segmented feeding grooves along the TD direction of the diaphragm, the length of each feeding groove along the TD direction of the diaphragm is 3 cm, the feeding grooves are segmented, and then the single-sided roller is used to coat the PE base film, and drying is performed to obtain the diaphragm.

[0048] Embodiment 4

[0049] The embodiment provides a diaphragm, which comprises a PE base film and a composite coating arranged on one surface of the PE base film, the composite coating comprises para-aramid and lithium lanthanum zirconium oxide (LLZO), the thickness of the composite coating is 3 mu m, the air permeability increase is 72 s / 100 c, the thickness of the PE base film is 7 mu m, and the proportion of aramid in the composite coating adjacent to the tab leading-out side is higher than the proportion of aramid in the composite coating away from the tab leading-out side along the TD direction of the diaphragm.

[0050] The preparation method of the diaphragm comprises the following steps:

[0051] Five slurries with different compositions are prepared by mixing solid electrolytes and para-aramid at mass ratios of 9:1, 7:3, 5:5, 3:7 and 1:9, the slurries are sorted according to the mass ratio from large to small, the slurry with a high proportion of aramid is arranged close to the tab leading-out side, and the slurries are injected into separate segmented feeding grooves along the TD direction of the diaphragm, the length of each feeding groove along the TD direction of the diaphragm is 3 cm, and then the slurries are coated on the surface of the PE base film by single-sided roller coating, and dried to obtain the diaphragm.

[0052] Embodiment 5

[0053] The embodiment provides a diaphragm, which comprises a PE base film and a composite coating arranged on one surface of the PE base film, the composite coating comprises para-aramid and lithium lanthanum zirconium oxide (LLZO), the thickness of the composite coating is 3 mu m, the air permeability increase is 72 s / 100 c, the thickness of the PE base film is 7 mu m, and the proportion of aramid in the composite coating adjacent to the tab leading-out side is higher than the proportion of aramid in the composite coating away from the tab leading-out side along the TD direction of the diaphragm.

[0054] The preparation method of the diaphragm comprises the following steps:

[0055] Five slurries with different compositions are prepared by mixing solid electrolytes and para-aramid at mass ratios of 9:1, 7:3, 5:5, 3:7 and 1:9, the slurries are sorted according to the mass ratio from large to small, the slurry with a high proportion of aramid is arranged close to the tab leading-out side, and the slurries are injected into separate segmented feeding grooves along the TD direction of the diaphragm, the length of each feeding groove along the TD direction of the diaphragm is 3 cm, and then the slurries are coated on the surface of the PE base film by single-sided roller coating, and dried to obtain the diaphragm.

[0056] Embodiment 6

[0057] The embodiment provides a diaphragm, which comprises a PE base film and a composite coating arranged on one surface of the PE base film, the composite coating comprises para-aramid and lithium lanthanum zirconium oxide (LLZO), the thickness of the composite coating is 3 mu m, the air permeability increase is 72 s / 100 c, the thickness of the PE base film is 7 mu m, and the proportion of aramid in the composite coating adjacent to the tab leading-out side is higher than the proportion of aramid in the composite coating away from the tab leading-out side along the TD direction of the diaphragm.

[0058] The preparation method of the diaphragm comprises the following steps:

[0059] PAN and heterocyclic aramid were prepared into 5 different slurry with mass ratio of 9:1, 7:3, 5:5, 3:7, 1:9, and the above slurry was injected into the separate segmented feeding groove along the TD direction of the separator according to the mass ratio from large to small, and the length of each feeding groove along the TD direction of the separator was 8 cm. After the segmented feeding, the single-sided roller was coated on the surface of the PE base film, dried, and the separator was obtained.

[0060] Comparative Example 1

[0061] The present comparative example provides a separator, which comprises a PE base film and a composite coating layer arranged on one surface of the PE base film, the composite coating layer comprises meta-aramid and lithium aluminum titanium phosphate (LATP) with a mass ratio of 1:1, the thickness of the composite coating layer is 3 μm, the air permeability increase is 78 s / 100c, the thickness of the PE base film is 7 μm, and the composite coating layer is a uniform coating layer.

[0062] The preparation method of the above separator comprises:

[0063] The solid-state electrolyte and the meta-aramid are prepared into a slurry according to the mass ratio, and the above slurry is uniformly single-sided roller coated on the surface of the PE base film, dried, and the separator is obtained.

[0064] Test Example

[0065] The present test example provides the performance of the separator prepared by each embodiment and comparative example, which is as follows:

[0066] The test method of air permeability value: under a constant pressure difference (usually 1.21 kPa), the time required for a certain volume (such as 100 mL) of gas to pass through the separator is measured. The specific operation steps are as follows: cut the separator sample from the film roll at a certain distance along the longitudinal direction, and the size of the sample is determined according to the width of the separator. Place the separator sample in the test head of the air permeability tester, and test the time required for 100 mL of air to pass through the separator under a pressure of 1.21 kPa. Take the average value of three test results as the air permeability of the separator. The air permeability of the separator and the base film is tested by this method, and the difference between the air permeability of the separator and the base film is the air permeability increase of the composite coating layer.

[0067] The test method of heat shrinkage rate: according to GB / T 36363-2018, draw a line of 10.0 cm x 10.0 cm on the separator along the MD x TD direction. After the separator is clamped in the middle with two pieces of sulfuric acid paper, it is placed in an oven. Measure three samples at the same temperature, and take the average value as the test result to obtain the heat shrinkage rate in the TD and MD directions.

[0068] Test method of ion conductivity: stainless steel is used as positive and negative electrode sheet, a symmetric battery is assembled, a linear curve is fitted according to the measured impedance, and ion conductivity σ = 0.1d / (Rs x A) is calculated according to the formula, wherein d is thickness (μm), Rs is resistance (Ω), and A is cross-sectional area (m 2 ).

[0069] Test method of local temperature rise: a thermistor is arranged on the blue light system, temperature change of the battery during normal operation is tested, and a value of local temperature rise is obtained.

[0070] Test results are shown in Table 1.

[0071] Table 1 test results of each example and comparative example

[0072]

[0073] It can be seen from the above handover that the heat shrinkage rate of the separator containing the composite coating of the application is small, and when it is applied to the battery, it has the advantages of low local temperature rise and high ion conductivity, etc., can alleviate the problems of local expansion and uneven stress caused by heating of the battery cell, and thus improve the service life of the battery and the performance of the battery cell.

[0074] Obviously, the above examples are only examples for clearly illustrating, and do not limit the embodiments. For ordinary skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, all the embodiments need not and cannot be exhausted. The obvious changes or variations derived therefrom are still within the protection scope of the application.

Claims

1. A diaphragm, characterized in that: The invention comprises a base film and a composite coating provided on at least one side of the base film; the composite coating comprises aramid and a solid electrolyte; a first position and a second position are taken along the same TD direction of the diaphragm, the first position being adjacent to the tab lead-out side, and the second position being away from the tab lead-out side; the mass ratio of the aramid to the solid electrolyte in the composite coating at the first position is recorded as W a The mass ratio of the aramid to the solid electrolyte in the composite coating at the second position is recorded as W b , the W a 、W b Meet W a >W b ; The distance between the first position and the second position along the TD direction of the diaphragm is recorded as D, and the D is ≥ 3 cm.

2. The diaphragm according to claim 1, characterized in that The W a 、W b , D satisfies the following relationship 1:

3. The diaphragm according to claim 1, characterized in that The mass ratio of aramid to solid electrolyte in the composite coating is 1:9-9:1; And / or, the solid electrolyte includes an inorganic solid electrolyte and / or an organic solid electrolyte.

4. The diaphragm according to claim 3, characterized in that The inorganic solid electrolyte includes at least one of LLTO, LLZO, LLZTO and LATP; And / or, the organic solid electrolyte includes at least one of PEO, PVDF, PAN, PMMA, and PPO.

5. The diaphragm according to claim 1, characterized in that The aramid fiber includes at least one of para-aramid fiber, meta-aramid fiber, ortho-aramid fiber and heterocyclic aramid fiber.

6. The diaphragm according to any one of claims 1 to 5, characterized in that: The thickness of the composite coating on one side is 0.5-5 μm; And / or, the increased air permeability value of the composite coating on one side is ≤80s / 100c.

7. The diaphragm according to any one of claims 1 to 5, characterized in that: The base film includes a polyolefin separator; Preferably, the base film has a thickness of 5-9 μm.

8. The method for preparing the diaphragm according to any one of claims 1 to 7, characterized in that: include: Aramid fiber and solid electrolyte are prepared into several slurries according to different mass ratios, and the slurries are coated on at least one side of the base film by adopting segmented feeding, and then dried.

9. A battery, characterized in that: The invention comprises the diaphragm according to any one of claims 1 to 7.

10. The battery according to claim 9, characterized in that The battery includes a plurality of tabs, and the plurality of tabs are arranged on the same side of the diaphragm.

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