Microporous membrane, preparation method therefor, and use thereof

Abstract

The present application relates to a microporous membrane, a preparation method therefor and the use thereof. The microporous membrane contains an ionic liquid, the ionic liquid comprising a first ionic liquid, and the mass percentage of the ionic liquid in the microporous membrane being 0.01%-6%. The microporous membrane has an appropriate ionic liquid content, so that the microporous membrane, when being applied to the field of batteries, can reduce the capacity fading of batteries while keeping good air permeability, tensile strength and heat shrinkage, when being applied to the field of clothing fabrics, can endow fabrics with both good air and moisture permeability and appropriate oil absorption performance, and when being applied to the field of composite current collectors, can improve the electroplating effect during processes for manufacturing current collectors, thereby effectively controlling the moisture and resistance of surfaces of the current collectors.

Description

Microporous membranes, their preparation methods and applications Technical Field

[0001] This application relates to the field of microporous membranes, and in particular to a microporous membrane, its preparation method, and its application. Background Technology

[0002] Currently, microporous membranes struggle to meet the increasingly demanding market requirements for membrane products. For example, in the lithium-ion battery field, separators are required to be ultra-thin, possess high mechanical strength, and exhibit excellent pore size uniformity to achieve high conductivity and high energy density, among other electrochemical properties. In the apparel fabric field, microporous membranes are required to have good pore structure, mechanical strength, and thickness to meet the fabric's requirements for comfort, waterproofing, and high moisture permeability. Furthermore, in the composite current collector field, high mechanical strength, uniform pore size, and high temperature resistance are essential to achieve low resistance and good electrochemical consistency. Clearly, whether in the lithium battery, apparel fabric, or composite current collector fields, there are various performance requirements for membranes, necessitating the development of a microporous membrane with comprehensive performance that meets the market demands of these fields. Summary of the Invention

[0003] Based on this, some embodiments of this application provide a microporous membrane with good overall performance, so as to meet the requirements of membrane application in different fields.

[0004] In addition, some other embodiments of this application also provide a method for preparing a microporous membrane and its application.

[0005] A microporous membrane containing an ionic liquid, the ionic liquid comprising a first ionic liquid, wherein the mass percentage of the ionic liquid in the microporous membrane is 0.01% to 6%.

[0006] In some embodiments, the hydrophilic-lipophilic balance value of the first ionic liquid is <10.

[0007] In some embodiments, the hydrophilic-lipophilic balance value of the first ionic liquid is 3 to 7.

[0008] In some embodiments, the weight-average molecular weight of the first ionic liquid is 200 to 1000.

[0009] In some embodiments, the boiling point of the first ionic liquid is 200°C to 500°C.

[0010] In some embodiments, the viscosity of the first ionic liquid at 25°C is 20cp to 100cp.

[0011] In some embodiments, the mass percentage of the first ionic liquid in the microporous membrane is 0.01% to 6%.

[0012] In some embodiments, the mass percentage of the first ionic liquid in the microporous membrane is 0.1% to 5%.

[0013] In some embodiments, the microporous membrane further contains a second ionic liquid, the second ionic liquid having a hydrophilic-lipophilic balance value greater than that of the first ionic liquid.

[0014] In some embodiments, the weight-average molecular weight of the second ionic liquid is less than that of the first ionic liquid.

[0015] In some embodiments, the difference between the hydrophilic-lipophilic balance value of the second ionic liquid and the hydrophilic-lipophilic balance value of the first ionic liquid is <10.

[0016] In some embodiments, the hydrophilic-lipophilic balance value of the second ionic liquid is 10 to 20.

[0017] In some embodiments, the weight-average molecular weight of the second ionic liquid is 100 to 250.

[0018] In some embodiments, the boiling point of the second ionic liquid is 100°C to 500°C.

[0019] In some embodiments, the viscosity of the second ionic liquid at 25°C is 10 cp to 50 cp.

[0020] In some embodiments, the viscosity of the second ionic liquid at 25°C is 5 cp to 20 cp lower than that of the first ionic liquid at 25°C.

[0021] In some embodiments, the mass percentage of the second ionic liquid in the microporous membrane is 0.01% to 3%.

[0022] In some embodiments, the mass percentage of the second ionic liquid is 0.1% to 0.5%.

[0023] In some embodiments, the first ionic liquid and the second ionic liquid are each independently selected from one or more of imidazole salts, pyridine salts, quaternary ammonium salts, quaternary phosphonium salts, and pyrrolidines.

[0024] In some embodiments, the first ionic liquid and the second ionic liquid are each independently selected from 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium methyl sulfate, 1,3-dimethylimidazolium dimethyl phosphate, 1,3-dimethylimidazolium tetrafluoroborate, 3-dimethylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluoroantimonate, 1,3-dimethylimidazolium trifluoromethanesulfonate, 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium perchlorate, 1,3-dimethylimidazolium One or more of the following: nitrates, 1,3-dimethylimidazolium methanesulfonate, 1,3-dimethylimidazolium p-toluenesulfonate, 1,3-dimethylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, ethyl 1-ethyl-3-methylimidazolium sulfate, methyl 1-ethyl-3-methylimidazolium sulfate, diethyl 1-ethyl-3-methylimidazolium phosphate, dimethyl 1-ethyl-3-methylimidazolium phosphate, tetrafluoroborate, hexafluorophosphate, and antimonylate.

[0025] In some embodiments, the microporous membrane includes homopolymers or copolymers of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and norbornene, thermoplastic polyurethane elastomers, polyolefin elastomers, polyethylene terephthalate, polyurethane, or a mixture of polymers thereof.

[0026] In some embodiments, the microporous membrane comprises one or more of polyethylene, polypropylene, and ethylene-propylene copolymer.

[0027] In some embodiments, the viscosity-average molecular weight of the microporous membrane is 100,000 to 15,000,000.

[0028] In some embodiments, the microporous membrane further contains additives, including one or more of antioxidants, metal soaps, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments.

[0029] In some embodiments, the additive accounts for 0.01% to 5% of the total mass of the microporous membrane.

[0030] In some embodiments, the additive accounts for 0.1% to 1% of the total mass of the microporous membrane.

[0031] In some embodiments, the microporous membrane comprises multiple layers of sub-membranes stacked together, with different polymers in adjacent sub-membranes, and both containing the first ionic liquid.

[0032] In some embodiments, the average pore size of the microporous membrane is 20 nm to 200 nm.

[0033] In some embodiments, the average pore size of the microporous membrane is 60 nm to 200 nm.

[0034] In some embodiments, the transverse tensile strength of the microporous membrane is 500 kgf / cm². 2 ~5000 kgf / cm 2 .

[0035] In some embodiments, the longitudinal tensile strength of the microporous membrane is 1000 kgf / cm². 2 ~5000 kgf / cm 2 .

[0036] In some embodiments, the puncture strength of the microporous membrane is 150 gf to 1000 gf.

[0037] In some embodiments, the porosity of the microporous membrane is 10% to 90%.

[0038] In some embodiments, the porosity of the microporous membrane is 60% to 90%.

[0039] In some embodiments, the air permeability of the microporous membrane is 10 sec / 100cc to 1000 sec / 100cc.

[0040] In some embodiments, the air permeability of the microporous membrane is 10 sec / 100 cc to 100 sec / 100 cc.

[0041] In some embodiments, the thickness of the microporous membrane is 2 μm to 120 μm.

[0042] In some embodiments, the thickness of the microporous membrane is ≤5 μm.

[0043] In some embodiments, the wettability of the microporous membrane is increased by 20% to 50% compared to a microporous membrane of the same material and the same pore structure that does not contain the ionic liquid.

[0044] A method for preparing a microporous membrane includes the following steps:

[0045] A mixture comprising polymer and ionic liquid is mixed, extruded, and cooled to form an intermediate film.

[0046] The intermediate membrane is stretched, extracted, and heat-set to obtain the microporous membrane.

[0047] The ionic liquid includes a first ionic liquid, and the mass percentage of the ionic liquid in the microporous membrane is 0.01% to 6%.

[0048] In some embodiments, the hydrophilic-lipophilic balance value of the first ionic liquid is <10.

[0049] In some embodiments, the hydrophilic-lipophilic balance value of the first ionic liquid is 3 to 7.

[0050] In some embodiments, the weight-average molecular weight of the first ionic liquid is 200 to 1000.

[0051] In some embodiments, the boiling point of the first ionic liquid is 200°C to 500°C.

[0052] In some embodiments, the mass ratio of the polymer to the ionic liquid is (5-60):(40-95).

[0053] In some embodiments, the extractant in the extraction step includes dichloromethane; or...

[0054] In the extraction step, the extractant includes a mixed solvent of a second ionic liquid and water, wherein the hydrophilic-lipophilic balance value of the second ionic liquid is greater than that of the first ionic liquid.

[0055] In some embodiments, the difference between the hydrophilic-lipophilic balance value of the second ionic liquid and the hydrophilic-lipophilic balance value of the first ionic liquid is <10.

[0056] In some embodiments, the hydrophilic-lipophilic balance value of the second ionic liquid is 10 to 20.

[0057] In some embodiments, the weight-average molecular weight of the second ionic liquid is less than that of the first ionic liquid.

[0058] In some embodiments, the weight-average molecular weight of the second ionic liquid is 100 to 250.

[0059] In some embodiments, the boiling point of the second ionic liquid is 100°C to 500°C.

[0060] In some embodiments, the viscosity of the second ionic liquid at 25°C is 10 cp to 50 cp.

[0061] In some embodiments, the viscosity of the second ionic liquid at 25°C is 5 cp to 20 cp lower than that of the first ionic liquid at 25°C.

[0062] In some embodiments, the extractant comprises a mixed solvent of a second ionic liquid and water, wherein the mass percentage concentration of the second ionic liquid in the extractant is 5% to 10%.

[0063] In some embodiments, after the extraction step, the process further includes washing the extracted microporous membrane intermediate with water, separating it with a reverse osmosis membrane, and drying it.

[0064] In some embodiments, the temperature T of the mixed extrusion 挤 For T 挤 =Polymer melting point T m +(15℃~60℃).

[0065] In some of these embodiments, T 挤 =Polymer melting point T m +(15℃~45℃).

[0066] In some embodiments, in the step of mixing and extruding a mixture comprising a polymer and an ionic liquid, the melt index of the polymer is 0.6 g / 10 min to 10 g / 10 min.

[0067] In some embodiments, the melt index of the polymer is 0.6 g / 10 min to 6 g / 10 min.

[0068] Applications of the microporous membranes described above, or microporous membranes prepared by the methods described above, in lithium batteries, gas separation, heat exchange, composite current collectors, clothing fabrics, or water treatment.

[0069] A secondary battery, wherein the separator of the secondary battery comprises the microporous membrane described above or a microporous membrane prepared by the preparation method described above.

[0070] Some embodiments of this application use microporous membranes with appropriate ionic liquid content, enabling them to maintain good air permeability, tensile strength, and thermal shrinkage while reducing battery capacity decay when applied in the battery field. However, excessive ionic liquid content can lead to excessive chelation between the cations and anions in the ionic liquid and components in the battery electrolyte, affecting the electrolyte viscosity in liquid lithium-ion batteries and reducing ionic conductivity, air permeability, strength, and heat resistance. Conversely, insufficient ionic liquid content fails to effectively improve electrochemical performance. Other microporous membranes used in the field of apparel fabrics in this application, with appropriate ionic liquid content, allow the fabric to possess both good air and moisture permeability and suitable oil absorption properties, improving the fabric's performance. Still other microporous membranes used in the field of composite current collectors in this application, with appropriate ionic liquid content, help improve the electroplating effect during current collector preparation, thereby effectively controlling the moisture and resistance on the current collector surface.

[0071] The above-mentioned method for preparing microporous membranes uses ionic liquids, which have good compatibility with various polymers and can be applied to more polymer systems. Furthermore, the microporous membranes prepared by this method have better performance. Attached Figure Description

[0072] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the disclosed drawings without creative effort.

[0073] Figure 1 is a scanning electron microscope image (magnification 20Kx) of a polypropylene microporous membrane prepared by the microporous membrane preparation method of some embodiments of this application.

[0074] Figure 2 is a scanning electron microscope image (magnification 20Kx) of polypropylene microporous membrane prepared by the traditional dry uniaxial stretching process.

[0075] Figure 3 is a scanning electron microscope image (20Kx magnification) of polyethylene microporous membrane prepared by the traditional wet biaxial stretching process. Detailed Implementation

[0076] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0077] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0078] Unless otherwise stated or in case of conflict, the terms or phrases used in this application shall have the following meanings:

[0079] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" and "second" may explicitly or implicitly include at least one of those features.

[0080] In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise expressly and specifically limited.

[0081] In this application, "one or more" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0082] Unless otherwise specified, all percentage concentrations mentioned in this application refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0083] In this application, terms such as "further," "even more," "particularly," "for example," "like," "example," and "exemplary" are used for descriptive purposes to indicate a connection in the coverage of different technical solutions presented earlier and later, but should not be construed as limiting the preceding technical solution or restricting the scope of protection herein. Unless otherwise specified herein, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0084] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "present" or "absent." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. In this application, descriptions such as "optionally contains" and "optionally includes" indicate "contains or does not contain." "Optional component X" indicates whether component X exists or does not exist, or whether component X is contained or not.

[0085] When a numerical range is disclosed in this application, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed in this application should be understood to include any and all subranges to which they are included.

[0086] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0087] The terms "comprising" and "having," and any variations thereof, used in the embodiments of this application, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or components inherent to such processes, methods, products, or devices.

[0088] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0089] In this application, a microporous membrane refers to a membrane formed having a large number of micropores on its surface and interior, with at least some of the micropores being interconnected, allowing gas or liquid to pass through from one surface of the membrane to the other. The “surface” of the membrane refers to the surface with the largest surface area.

[0090] Currently, microporous membranes are struggling to meet the increasingly demanding requirements of the market for membrane products. Whether in the lithium battery field, the apparel fabric field, or the composite current collector field, comprehensive performance requirements such as thickness, porosity, air permeability, and mechanical strength are being put forward for microporous membranes. Therefore, it is urgent to develop a microporous membrane that can meet the market requirements of the above fields.

[0091] Researchers have creatively discovered that the overall performance of microporous membranes obtained through industrialization is difficult to improve significantly. One reason is the limitation of existing preparation processes, which mainly include wet and dry processes. The wet process employs thermally induced phase separation, requiring good compatibility between the pore-forming agent and the film-forming substrate. Currently, paraffin oil is widely used as the pore-forming agent in industrial production, and its compatible substrate material is polyethylene (PE). However, it is difficult to adapt to other polymer materials and apply them to industrial production. This is because the current paraffin oil co-extrusion system cannot meet the requirements for uniform mixing with polymer melts from different systems to obtain high-quality intermediate films. For example, a melt mixture of PE and paraffin oil with a low melt index (below 0.6 g / 10 min, 190℃, 2.16 kg) (PE mass percentage of the melt is 30%, also known as melt solids content) has poor melt flowability and cannot meet the requirements for cooling and film formation, thus failing to produce qualified, high-quality membrane products. To increase fluidity, existing solutions often involve reducing the melt solids content to below 15%. This leads to a significant amount of paraffin oil seeping out during phase separation, affecting subsequent manufacturing processes such as unstable or ineffective stretching. The resulting membranes are of extremely poor quality and fail to meet application requirements. Another solution is to continuously increase the extrusion temperature to improve melt fluidity; however, this causes polymer molecule degradation and paraffin oil volatilization, resulting in products that do not meet requirements. Dry processes are applicable to a wider range of polymer systems compared to wet processes, but microporous membranes produced by dry processes generally exhibit inferior heat resistance, thickness, pore size uniformity, and permeability compared to those produced by wet processes. For example, microporous membranes produced by dry uniaxial stretching have poor transverse strength, poor consistency, difficulty in achieving thinner membranes, and higher permeability. The dry biaxial stretching process has very high requirements for the preparation environment. If environmental control and the control of dust and burrs on the electrode are insufficient, the resulting microporous membrane will have a high short-circuit rate. Moreover, because this process is difficult to control the pore size, it is prone to uneven pore size distribution. Therefore, the performance improvement of microporous membranes obtained in current industrial applications is very limited. Traditional processes face significant limitations in ensuring that microporous membranes have a thin thickness range while also maintaining various properties such as mechanical strength.

[0092] Based on this, this application provides a microporous membrane with good overall performance, and a preparation method for obtaining a microporous membrane with good overall performance that is suitable for industrialization.

[0093] In a first aspect, this application provides a microporous membrane containing an ionic liquid, the ionic liquid including a first ionic liquid, wherein the mass percentage of the ionic liquid in the microporous membrane is 0.01% to 6%.

[0094] Microporous membranes with appropriate ionic liquid content maintain good air permeability, tensile strength, and thermal shrinkage, while reducing capacity decay in battery applications. However, excessive ionic liquid content can lead to excessive chelation between the cations and anions in the ionic liquid and components in the battery electrolyte, affecting electrolyte viscosity in liquid lithium-ion batteries and reducing ionic conductivity, air permeability, strength, and heat resistance. Conversely, insufficient ionic liquid content fails to effectively improve electrochemical performance. Other microporous membranes used in apparel fabrics, with appropriate ionic liquid content, allow fabrics to possess both good air and moisture permeability and suitable oil absorption, improving fabric performance. Furthermore, other microporous membranes used in composite current collectors, with appropriate ionic liquid content, help improve electroplating effects during current collector preparation, thus effectively controlling surface moisture and resistance.

[0095] The first ionic liquid is an ionic salt that is liquid below 100°C. The first ionic liquid can form a homogeneous phase with the polymer under high temperature conditions. Below 100°C, it will separate into an ionic liquid and a polymer solid phase, which is beneficial for preparation methods applicable to different polymer systems and can obtain microporous membranes with good uniformity.

[0096] The microporous membrane contains several fibrils, which are interwoven to form pores. Ionic liquids adhere to the surface of the fibrils inside the microporous membrane through their oleophilic ends. The fibrils in the microporous membrane are obtained by stretching and oriented the polymer during film preparation. The extractant extracts the pore-forming agent from the film to form pores.

[0097] Heat resistance can be tested and evaluated using existing testing methods. For example, it can be tested as follows: cut the microporous membrane into a 297mm×210mm sample, draw a 100mm×100mm outline in the middle, place it between 22 sheets of A4 paper (11 sheets on the top and 11 on the bottom), and then place it on a stainless steel wire mesh rack in the middle of a 150℃ constant temperature oven for 1 hour. After baking, remove it and let it cool to room temperature (25℃), measure the side length of the outline, and take the average value L. The heat shrinkage rate is calculated as (100-L) / 100×100%.

[0098] Ionic conductivity can be tested and evaluated using existing methods, such as the following: Cut four microporous membrane samples with a diameter of 45 mm from a flat surface. Immerse the samples in an electrolyte (1.0 M LiPF6 in a 3:3:4 volume ratio of EC / EMC / DMC (ethylene carbonate / ethyl methyl carbonate / dimethyl carbonate) solvent) and seal for 30 min. Pour approximately 15 mL of 1 mol / L electrolyte (1.0 M LiPF6 in a 3:3:4 volume ratio of EC / EMC / DMC solvent) into a sheet resistance testing fixture. Place one, two, three, and four microporous membranes in the fixture for testing. Plot a linear fit with the number of microporous membrane layers as the x-axis and the microporous membrane resistance as the y-axis. Calculate the slope and goodness of fit of the line. When the goodness of fit is greater than 0.999, the slope is the sheet resistance Q of the microporous membrane. Calculate the ionic conductivity using the formula: σ = d / Q.

[0099] Where d is the thickness of the microporous membrane, in μm;

[0100] Q is the surface resistance, measured in ohms (Ω·cm). 2 ;

[0101] σ is the ionic conductivity, measured in S / cm.

[0102] In some embodiments, the wettability of the microporous membrane is ≤120 s. The microporous membrane possesses suitable wettability, which improves the battery's ionic conductivity and energy density while further reducing the battery's internal resistance. For example, the battery's energy density can be tested using the following steps:

[0103] 1) The positive electrode active material NCM811, conductive agent SP, conductive agent KS-6, and binder PVDF are mixed in solvent NMP at a mass ratio of 90:2:1:3 to prepare a positive electrode slurry. The slurry is then coated onto the aluminum foil surface of an 8μm current collector (aluminum foil thickness 1μm). The slurry is then dried in an oven at 95℃ and rolled on a roller press to obtain the positive electrode.

[0104] 2) The active material artificial graphite, the conductive agent acetylene black, and the binder CMC / SBR (sodium carboxymethyl cellulose / styrene-butadiene rubber, mass ratio 1:1) are added to water in a mass ratio of 90:5:5 and dispersed evenly to prepare a negative electrode slurry. The slurry is coated on the copper foil surface of a 5μm current collector (copper foil thickness 1μm), dried in an oven at 85℃, and then rolled in a roller press to obtain the negative electrode.

[0105] 3) In a dry room with a dew point <-40℃, after stacking and packaging the positive electrode, separator, and negative electrode sheets, follow the formula of 2.5g / m 2 The electrolyte (Xinzhoubang, LBC3008A) was injected in a certain proportion to obtain the battery.

[0106] Test method: The battery is tested within a voltage range of 3.0V to 4.5V. The discharge plateau voltage is determined by cyclic voltammetry at a rate of 0.5C. Then, the battery is discharged at a constant current of 1C from a fully charged state, and the discharge capacity is measured. The mass energy density is calculated using the following formula:

[0107] It is understood that in this application, not only the energy density of the battery can be tested by the above method, but also the energy density of the current collector, that is, the current collector used in the battery separator or the current collector used in the composite current collector. When used in the composite current collector, a conventional commercially available battery separator can be used as the separator in the test, such as the polyethylene microporous membrane (porosity 38%) with a thickness of 7μm from Shenzhen Xingyuan Material Technology Co., Ltd.

[0108] The wettability of the microporous membrane refers to the wettability of a 5 mm² area when wetted with 2 μL of electrolyte (analytical grade, propylene carbonate). 2 The time corresponding to the microporous membrane.

[0109] In some embodiments, the wettability of the microporous membrane is ≤100s. Further, in some embodiments, the wettability of the microporous membrane is 20–80s. Specifically, the wettability of the microporous membrane can be any value or a range of any two of the following: 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, 60s, 65s, 75s, 80s, 85s, 90s, 95s, and 100s.

[0110] In some embodiments, the wettability test method for microporous membranes is as follows: The microporous membrane is cut into a 10mm × 10mm square, placed on a glass slide, and stretched taut with tape to ensure a smooth membrane surface. 2μL of electrolyte (analytical grade, propylene carbonate) is taken using a syringe and dropped onto the microporous membrane sample. The wettability area of ​​the droplet is measured to be 5mm². 2 Time for microporous membranes.

[0111] In some embodiments, the wettability of the microporous membrane is increased by 20% to 50% compared to a microporous membrane of the same material and the same pore structure that does not contain the first ionic liquid.

[0112] It should be noted that "same material" means that the two microporous membranes being compared use the same film-forming main material and additives, and "same pore structure" means that the average pore size of the two microporous membranes differs by less than 10%, and the integral area of ​​their pore size distribution curves overlaps by more than 85%. The pore size and pore size distribution curve can be measured using a capillary porosity meter, for example, using a PMI instrument (Jia Yun Co., Ltd., CFP-1500AE model) with a Galwick immersion solution (surface tension of 15.9 dynes / cm at 25℃) at 25℃. The pore size is expressed in nm. Of course, other conventional testing methods in this industry can also be used.

[0113] In some embodiments, the hydrophilic-lipophilic balance (HLB) value of the first ionic liquid is <10. For example, the HLB value of the first ionic liquid can be, but is not limited to, any value or a range between any two values ​​from 0, 1, 2, 3, 3.2, 3.5, 3.6, 3.8, 4, 4.1, 4.3, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.3, 5.6, 5.9, 6, 6.2, 6.6, 6.8, 7, 7.3, 8, 8.2, 8.4, 8.9, 9, 9.5, and 10. When the HLB value of the first ionic liquid is within the above range, it exhibits good lipophilicity, enabling it to better bind with the polymer in the microporous membrane and further enhancing the wettability of the microporous membrane.

[0114] Optionally, the hydrophilic-lipophilic balance value of the first ionic liquid is 3 to 7. This is beneficial when microporous membranes are applied in lithium-ion batteries. An HLB value within this range helps improve the electrolyte wettability and liquid absorption / retention properties of the separator, thereby further enhancing battery cycle performance and energy density. For example, battery cycle performance can be characterized by battery capacity retention rate. The battery capacity retention rate can be obtained according to the method specified in the national standard GB / T31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles," which measures the battery's cycle performance, i.e., the capacity retention rate after 500 charge-discharge cycles at a 1C rate. The cycle temperature of the assembled battery is room temperature (25℃). Energy density testing has been discussed previously. As already provided, this will not be repeated here. When applied to the field of clothing fabrics, controlling the HLB value within a certain range can further reduce the oil absorption of the fabric and further improve its performance, thereby further reducing the cleaning frequency. The oil absorption can be evaluated, for example, by dropping 2 μL of paraffin oil (40℃, viscosity 45±5 cp) onto a 10cm*10cm film surface and observing the diffusion area for 5 minutes; a larger diffusion area indicates higher oil absorption. When applied to the field of battery current collectors, controlling the HLB value within a certain range helps to further control the moisture on the current collector surface, and can also further improve the electroplating effect and assembly efficiency of the current collector. The moisture content on the current collector surface can be tested using the Karl Fischer method (volume method), based on the volume of reagent consumed and the titration rate. The HLB value of the ionic liquid in this application can be determined and calculated using emulsification methods, critical micelle concentration, etc., but this application is not limited to these methods.

[0115] In some embodiments, the weight-average molecular weight of the first ionic liquid is 200 to 1000. For example, the weight-average molecular weight of the first ionic liquid can be, but is not limited to, any value or a range between any two of 200, 300, 400, 500, 600, 700, 800, 900, and 1000. The molecular weight of the ionic liquid can be determined directly by mass spectrometry. The molecular weight can also be obtained by measuring the molecular ion peak of the ionic liquid using techniques such as electrospray ionization (ESI) or matrix-assisted laser desorption / ionization (MALDI). Of course, nuclear magnetic resonance, light scattering, and other methods can also be used for testing; this application is not limited to these methods.

[0116] The weight-average molecular weight of the first ionic liquid meets the above-mentioned range, which is beneficial to further improve the pore size uniformity and mechanical strength of the microporous membrane. Simultaneously, it further enhances the battery cycle performance when the microporous membrane is applied in the lithium-ion battery field. For example, battery cycle performance can be characterized by the battery capacity retention rate. The battery capacity retention rate can be obtained according to the method specified in the national standard GB / T31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles," that is, the capacity retention rate after 500 charge-discharge cycles at a 1C rate, with the assembled battery cycling at room temperature (25℃). When applied to the field of clothing fabrics, the microporous membrane is beneficial to further improve the softness and processability of the fabric. Softness can be reflected by characterizing its stiffness, according to GB / T... Measurement 41567 is performed. Specifically, the slot width is 10.0 mm. The microporous membrane is placed on the sample stage and the slot is covered. One-third of the microporous membrane is in front of the slot and two-thirds is behind the slot. The microporous membrane is pressed into the slot with a test head to complete one test and then returned to the initial position. The maximum force required for this process is used to characterize the stiffness of the microporous membrane. When the microporous membrane is applied to the field of battery current collectors, it further improves the consistency of the electrochemical performance of the current collector. Specifically, it can be characterized by the standard deviation of the sheet resistance of the current collector surface. For example, a composite current collector is made by electroplating a 1 μm thick aluminum foil or copper foil on the surface of the microporous membrane. A four-probe resistance tester is used to test at five positions around and in the center of the composite current collector, and the standard deviation value is taken.

[0117] In some embodiments, the boiling point of the first ionic liquid is 200°C to 500°C. Specifically, the boiling point of the first ionic liquid may be, but is not limited to, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, 250°C, 255°C, 275°C, 280°C, 285°C, 290°C, 295°C, 300°C, 320°C, 340°C, 350°C, 360°C, 380°C, 400°C, 420°C, 440°C, 450°C, 460°C, 480°C, 500°C, or any range of two of these values. The boiling point can be determined by conventional testing methods, including but not limited to distillation.

[0118] The first ionic liquid has a suitable boiling point, which further enhances the mechanical strength of the microporous membrane while ensuring that the microporous membrane has a good pore structure.

[0119] In some embodiments, the viscosity of the first ionic liquid at 25°C is 20 cp to 100 cp. The viscosity can be determined using existing viscosity testing methods, such as placing a sample treated in a constant-temperature water bath at 25°C for 1 hour into a rotational viscometer and taking the viscosity reading. Specifically, the viscosity of the first ionic liquid can be any value or a range between any two values ​​from 20 cp, 30 cp, 40 cp, 50 cp, 60 cp, 70 cp, 80 cp, 90 cp, to 100 cp.

[0120] The aforementioned first ionic liquid exhibits suitable viscosity and good fluidity at room temperature, which helps to further improve the pore uniformity of the microporous membrane while maintaining good thickness consistency. Therefore, when applied to lithium-ion batteries, it is beneficial for further improving battery cycle performance and energy density. In the application of clothing fabrics, it can enhance the fabric's breathability, moisture permeability, and oil absorption properties, improving its usability. In the application of composite current collectors, it helps to further improve the electroplating effect during current collector preparation, thus having a certain effect on controlling the moisture content and resistance of the current collector surface. Specifically, the resistance of the current collector can be characterized by its surface sheet resistance. For example, a composite current collector is made by electroplating a 1μm thick copper or aluminum foil onto the surface of the microporous membrane. A four-probe resistance meter is used to measure the resistance at five locations around the perimeter and center of the composite current collector, and the average value is taken.

[0121] In some embodiments, the first ionic liquid is selected from one or more of ionic liquids such as imidazole salts, pyridine salts, quaternary ammonium salts, quaternary phosphonium salts, and pyrrolidines.

[0122] Specifically, the first ionic liquid is selected from 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium methyl sulfate, 1,3-dimethylimidazolium dimethyl phosphate, 1,3-dimethylimidazolium tetrafluoroborate, 3-dimethylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluoroantimonate, 1,3-dimethylimidazolium trifluoromethanesulfonate, 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium perchlorate, 1,3-dimethylimidazolium nitrate ... One or more of the following: imidazole methanesulfonate, 1,3-dimethylimidazolium p-toluenesulfonate, 1,3-dimethylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, ethyl 1-ethyl-3-methylimidazolium sulfate, methyl 1-ethyl-3-methylimidazolium sulfate, diethyl 1-ethyl-3-methylimidazolium phosphate, dimethyl 1-ethyl-3-methylimidazolium phosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, and 1-ethyl-3-methylimidazolium hexafluoroantimonate.

[0123] It is understood that the above only lists some commonly used types of ionic liquids, but it is not limited to these. Other ionic liquids can also be used, as long as they meet the above conditions. They will not be listed exhaustively here.

[0124] In some embodiments, the mass percentage of the first ionic liquid in the microporous membrane is 0.01% to 6%. For example, the mass percentage of the first ionic liquid may be, but is not limited to, 0.01%, 0.02%, 0.05%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, or any range of two of these values. In some embodiments, the mass percentage of the first ionic liquid in the microporous membrane is 0.1% to 5%. Furthermore, in some embodiments, the mass percentage of the first ionic liquid in the microporous membrane is 0.1% to 0.5%. By controlling the content of the first ionic liquid, the ionic conductivity of the microporous membrane can be improved, which is beneficial for improving battery cycle performance when the microporous membrane is applied in lithium-ion batteries.

[0125] In some embodiments, the microporous membrane comprises homopolymers or copolymers of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and norbornene, thermoplastic polyurethane elastomers (TPU), polyolefin elastomers (POE), polyethylene terephthalate (PET), polyurethane (PU), or mixtures of polymers thereof.

[0126] In some embodiments, the microporous membrane comprises a polyolefin. For example, the microporous membrane comprises a homopolymer or copolymer of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene.

[0127] In some embodiments, the microporous membrane comprises one or more of polyethylene, polypropylene, and ethylene-propylene copolymer.

[0128] In some embodiments, the viscosity-average molecular weight of the microporous membrane is 100,000 to 15,000,000. The viscosity-average molecular weight of the polymer can be determined using conventional methods, including but not limited to measuring the intrinsic viscosity at 135°C with decahydronaphthalene as a solvent according to GB1841-1980, thereby calculating the viscosity-average molecular weight.

[0129] When applied in the field of lithium batteries, in some embodiments, the viscosity-average molecular weight of the microporous membrane is 1 million to 15 million, which helps to further improve the mechanical strength of the microporous membrane and thus further improve electrochemical safety.

[0130] When applied to the field of apparel fabrics, in some embodiments, the viscosity-average molecular weight of the microporous membrane is 100,000 to 1,500,000, which is beneficial to further improve the softness and processability of the fabric. The softness can be reflected by characterizing its stiffness. According to GB / T 41567, the groove width is 10.0 mm. The microporous membrane is placed on the sample stage and the groove is covered. One-third of the microporous membrane is in front of the groove and two-thirds is behind the groove. The microporous membrane is pressed into the groove with the test head to complete one test and then returned to the initial position. The maximum force required for this process is used to characterize the stiffness of the microporous membrane.

[0131] When applied to the field of composite current collectors, in some embodiments, the viscosity-average molecular weight of the microporous membrane is 1 million to 6 million, which is beneficial to further improve the mechanical strength of the microporous membrane and thus improve the energy density of the composite current collector.

[0132] In some embodiments, the viscosity-average molecular weight of the microporous membrane can be between 1 million and 6 million. In some embodiments, the viscosity-average molecular weight of the microporous membrane can be between 3 million and 6 million. Specifically, the viscosity-average molecular weight of the microporous membrane can be 1 million, 1.1 million, 1.2 million, 1.3 million, 1.4 million, 1.5 million, 1.6 million, 1.7 million, 1.8 million, 1.9 million, 2 million, 2.1 million, 2.2 million, 2.3 million, 2.4 million, 2.5 million, 2.6 million, 2.7 million, 2.8 million, 2.9 million, 3 million, 3.1 million, 3.2 million, 3.3 million, 3.4 million, or 3 million. The range of any one of the following values ​​or any two values: 500,000, 3,600,000, 3,700,000, 3,800,000, 3,900,000, 4,000,000, 4,100,000, 4,200,000, 4,300,000, 4,400,000, 4,500,000, 4,600,000, 4,700,000, 4,800,000, 4,900,000, 5,000,000, 5,100,000, 5,200,000, 5,300,000, 5,400,000, 5,500,000, 5,600,000, 5,700,000, 5,800,000, 5,900,000, and 6,000,000.

[0133] In some embodiments, the microporous membrane further contains a second ionic liquid, which is an ionic salt that is liquid below 50°C. The hydrophilic-lipophilic balance (HLP) value of the second ionic liquid is greater than that of the first ionic liquid. This indicates that the second ionic liquid is more hydrophilic than the first ionic liquid, and the first ionic liquid is more lipophilic than the second ionic liquid. When applied to lithium-ion batteries, this improves the electrolyte wettability and liquid absorption / retention properties of the separator, thereby further enhancing battery cycle performance and energy density. When applied to apparel fabrics, it further improves the fabric's breathability, moisture permeability, and suitable oil absorption properties, thus enhancing the fabric's performance. When applied to composite current collectors, it helps to further improve the electroplating effect during current collector preparation, thereby further controlling the moisture and resistance on the current collector surface.

[0134] In some embodiments, the difference between the hydrophilic-lipophilic balance value of the second ionic liquid and that of the first ionic liquid is <10. Specifically, the hydrophilic-lipophilic balance value of the second ionic liquid is 10 to 20. For example, the hydrophilic-lipophilic balance value of the second ionic liquid can be, but is not limited to, any value from 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range consisting of any two of these values. Controlling the hydrophilic-lipophilic balance value of the second ionic liquid within a certain range is beneficial for further improving the air permeability of the microporous membrane. When applied in lithium-ion batteries, it helps to further reduce battery capacity decay while maintaining good air permeability, tensile strength, and thermal shrinkage of the microporous membrane, thereby further improving battery cycle performance and energy density. When applied in the field of clothing fabrics, it helps to further improve the moisture permeability and comfort of the microporous membrane, wherein the moisture permeability can be tested according to GB / T 12704.1 positive cup method. When applied to the field of composite current collectors, the microporous membrane in the composite current collector field helps to further improve the electroplating effect in the current collector preparation process, thereby further controlling the moisture and resistance on the current collector surface to obtain better results.

[0135] In some embodiments, the weight-average molecular weight of the second ionic liquid is lower than that of the first ionic liquid. The second ionic liquid, being smaller than the first, exhibits better hydrophilicity. Therefore, controlling the molecular weight of the second ionic liquid to be smaller than that of the first ionic liquid is beneficial for synergistically improving the permeability of the microporous membrane. When applied in the lithium-ion battery field, this is beneficial for further improving battery cycle performance and energy density. When applied in the apparel fabric field, it is beneficial for further improving the moisture permeability and comfort of the microporous membrane, where moisture permeability can be tested using the positive cup method in GB / T 12704.1. When applied in the field of composite current collectors, the microporous membrane in this field helps to further improve the electroplating effect during the current collector preparation process, thereby better controlling the moisture and resistance on the current collector surface.

[0136] In some embodiments, the weight-average molecular weight of the second ionic liquid is 100–250. For example, the weight-average molecular weight of the second ionic liquid can be, but is not limited to, any value from 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, or a range of any two of these values. Controlling the weight-average molecular weight of the second ionic liquid within a certain range is beneficial for further improving the permeability of the microporous membrane. When applied to lithium-ion batteries, this is beneficial for further improving battery cycle performance and energy density. When applied to clothing fabrics, it is beneficial for further improving fabric moisture permeability and comfort, where moisture permeability can be tested using the positive cup method according to GB / T12704.1. When applied to composite current collectors, it is beneficial for further reducing the resistance of the composite current collector. Specifically, the resistance of the current collector can be characterized by its surface sheet resistance. For example, a composite current collector can be made by electroplating a 1μm thick copper or aluminum foil on the surface of a microporous membrane. A four-probe resistance tester can be used to test the resistance at five locations around the composite current collector and at its center, and the average value can be taken.

[0137] In some embodiments, the boiling point of the second ionic liquid is 100°C to 500°C. For example, the boiling point of the second ionic liquid may be, but is not limited to, any value of 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, 255℃, 260℃, 265℃, 270℃, 275℃, 280℃, 285℃, 290℃, 295℃, 300℃, 320℃, 340℃, 350℃, 360℃, 380℃, 400℃, 420℃, 440℃, 450℃, 460℃, 480℃, 500℃, or a range of any two of these values. The above configuration helps to further improve the air permeability of the microporous membrane, thereby further improving the battery cycle performance and energy density, further improving the moisture permeability of clothing fabrics, and when applied to the field of current collectors, it helps to further reduce the resistance of composite current collectors.

[0138] In some embodiments, the viscosity of the second ionic liquid at 25°C is 10 cp to 50 cp. For example, the viscosity of the second ionic liquid can be any value or a range between any two values ​​from 10 cp, 12 cp, 15 cp, 18 cp, 20 cp, 22 cp, 25 cp, 28 cp, 30 cp, 32 cp, 35 cp, 38 cp, 40 cp, 42 cp, 45 cp, 48 cp, to 50 cp. Adopting the above configuration is beneficial for further improving the air permeability of the microporous membrane, thereby further improving the battery cycle performance and energy density, further improving the moisture permeability of clothing fabrics, and, when applied in the field of composite current collectors, further reducing the resistance of the composite current collector.

[0139] In some embodiments, the viscosity of the second ionic liquid at 25°C is 5 to 20 cp lower than that of the first ionic liquid at 25°C. Specifically, the viscosity of the second ionic liquid at 25°C can be any value or a range between any two values ​​that are lower than the viscosity of the first ionic liquid at 25°C by 5, 7, 9, 11, 13, 15, 17, 19, or 20 cp. By controlling the viscosity difference between the second and first ionic liquids, it is beneficial to further improve the pore size uniformity of the microporous membrane and better control its porosity, thereby further improving battery cycle performance and energy density, further improving the moisture permeability of clothing fabrics, and, when applied in the field of composite current collectors, further reducing the resistance of the composite current collector.

[0140] In some embodiments, the mass percentage of the second ionic liquid in the microporous membrane is 0.01% to 3%. For example, the mass percentage of the second ionic liquid may be, but is not limited to, any value or a range of any two of the following: 0.01%, 0.02%, 0.05%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, and 3%.

[0141] In some embodiments, the mass percentage of the second ionic liquid in the microporous membrane is 0.1% to 0.5%. Controlling the mass percentage of the second ionic liquid within a certain range is beneficial for further improving the product's breathability, thus contributing to improved battery cycle performance and energy density when applied to lithium-ion batteries. When applied to apparel fabrics, it helps improve fabric moisture permeability and comfort, with moisture permeability tested using the positive cup method according to GB / T 12704.1. When applied to composite current collectors, it helps improve the electroplating effect during composite current collector preparation, allowing for better control of surface moisture and resistance.

[0142] It is understood that the mass percentage of the second ionic liquid in this application can be tested by the following method: Weigh a 10cm × 10cm microporous membrane sample (M1), place the microporous membrane sample in 100mL of DCM solvent, sonicate at 100Hz for 15min, dry at 80℃ for 5min, weigh the sample (M2), and calculate the mass percentage using the following formula:

[0143] In some embodiments, the second ionic liquid is selected from one or more of ionic liquids such as imidazole salts, pyridine salts, quaternary ammonium salts, quaternary phosphonium salts, and pyrrolidines.

[0144] Specifically, the second ionic liquid is selected from 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium methyl sulfate, 1,3-dimethylimidazolium dimethyl phosphate, 1,3-dimethylimidazolium tetrafluoroborate, 3-dimethylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluoroantimonate, 1,3-dimethylimidazolium trifluoromethanesulfonate, 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium perchlorate, 1,3-dimethylimidazolium nitrate ... One or more of the following: imidazole methanesulfonate, 1,3-dimethylimidazolium p-toluenesulfonate, 1,3-dimethylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, ethyl 1-ethyl-3-methylimidazolium sulfate, methyl 1-ethyl-3-methylimidazolium sulfate, diethyl 1-ethyl-3-methylimidazolium phosphate, dimethyl 1-ethyl-3-methylimidazolium phosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, and 1-ethyl-3-methylimidazolium hexafluoroantimonate.

[0145] It is understood that the above only lists some commonly used types of ionic liquids, but it is not limited to these. Other ionic liquids can also be used, as long as they meet the above conditions. They will not be listed exhaustively here.

[0146] It is understood that the second ionic liquid and the first ionic liquid can be of the same type, as long as they meet at least one of the above-defined ranges for HLB value, weight-average molecular weight, boiling point, and viscosity at 25°C. For example, the HLB value can be controlled by changing the structure of the anion and cation, such as by changing the alkyl chain length of the cation or introducing different functional groups, or by adding some high-boiling solvents, such as high-boiling ethers (ether solvents with a boiling point ≥300°C. Specifically, this may include one or more of ethylene glycol phenyl ether and propylene glycol phenyl ether).

[0147] In some embodiments, the microporous membrane further contains additives, including one or more of the following known additives: antioxidants, metal soaps, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments. Metal soaps refer to metal salts formed by the reaction of metals other than alkali metals, metal oxides, or salts with fatty acids, rosin acids, naphthenic acids, etc., such as, but not limited to, calcium stearate and zinc stearate.

[0148] In some embodiments, the additive mass accounts for 0.01% to 5% of the total mass of the microporous membrane.

[0149] In some embodiments, the mass percentage of the additive in the microporous membrane is 0.1% to 1% of the total mass of the microporous membrane. For example, the mass percentage of the additive in the total mass of the microporous membrane may be, but is not limited to, 0.01%, 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range of these values. By controlling the mass percentage of the additive, it is beneficial to ensure the film-forming properties and quality of the microporous membrane while achieving the desired effects from the additive.

[0150] It is understood that this application does not impose any particular limitation on the way the additive is added to the microporous membrane. For example, it can be added by mixing with the main film-forming material of the microporous membrane during the preparation of the microporous membrane, or by immersing the intermediate membrane in a solution containing the additive at a certain stage of the preparation of the microporous membrane, or by coating the microporous membrane, etc.

[0151] In some embodiments, the microporous membrane comprises multiple layers of sub-membranes stacked together, wherein adjacent sub-membranes contain different polymers and each contains a first ionic liquid. It is understood that the first ionic liquid in each sub-membrane may be the same or different.

[0152] This application does not specifically limit the average pore size of the microporous membrane. However, based on considerations of mechanical strength, ion permeability, electrochemical safety, and windproof properties of clothing fabrics, in some embodiments, the average pore size of the microporous membrane is 20 nm to 200 nm. For example, the average pore size of the microporous membrane can be any value or a range between any two values ​​between 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, and 200 nm.

[0153] In some embodiments, the average pore size of the microporous membrane is 60 nm to 200 nm. The average pore size of the microporous membrane can be measured using a capillary porosity meter, for example, using a PMI instrument (Chia Yun Co., Ltd., CFP-1500AE model) with Galwick immersion solution (surface tension of 15.9 dynes / cm at 25°C) at 25°C. The pore size is expressed in nm. Of course, other conventional testing methods in the industry can also be used for testing.

[0154] This application does not specifically limit the mechanical strength of the microporous membrane. However, considering factors such as heat resistance, processability, and electrochemical safety, in some embodiments, the transverse tensile strength (TD strength) of the microporous membrane is 500 kgf / cm². 2 ~5000 kgf / cm 2 For example, the TD strength of a microporous membrane can be, but is not limited to, 500 kgf / cm². 2 1000kgf / cm 2 1500kgf / cm 2 2000 kgf / cm 2 2500kgf / cm 2 3000 kgf / cm 2 3500kgf / cm 2 4000 kgf / cm 2 4500kgf / cm 2 5000 kgf / cm 2 Or the range formed by any two of these values.

[0155] In some embodiments, the longitudinal tensile strength (MD strength) of the microporous membrane is 1000 kgf / cm². 2 ~5000 kgf / cm 2 For example, the molecular weight density (MD) of a microporous membrane can be, but is not limited to, 1000 kgf / cm². 2 1500kgf / cm 2 2000kgf / cm 2 2500kgf / cm 2 3000 kgf / cm 2 3500kgf / cm 2 4000 kgf / cm 2 4500kgf / cm 2 5000 kgf / cm 2 Or the range formed by any two of these values.

[0156] In some embodiments, the puncture strength of the microporous membrane is 150 gf to 1000 gf. For example, the puncture strength of the microporous membrane may be, but is not limited to, 150 gf, 200 gf, 250 gf, 300 gf, 350 gf, 400 gf, 450 gf, 500 gf, 550 gf, 600 gf, 650 gf, 700 gf, 750 gf, 800 gf, 850 gf, 900 gf, 950 gf, 1000 gf, or a range of any two of these values.

[0157] This invention does not particularly limit the porosity of the microporous membrane. However, based on considerations of mechanical strength, ion permeability, electrochemical safety, and the moisture permeability and breathability of clothing fabrics, in some embodiments, the porosity of the microporous membrane is 10% to 90%. For example, the porosity of the microporous membrane can be, but is not limited to, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any combination of these values. In some embodiments, the porosity of the microporous membrane is 60% to 90%. Further, in some embodiments, the porosity of the microporous membrane is 70% to 90%.

[0158] This application does not specifically limit the air permeability of the microporous membrane. However, based on considerations of mechanical strength, ion permeability and electrochemical safety, and the moisture permeability and breathability of clothing fabrics, in some embodiments, the air permeability of the microporous membrane is 10 sec / 100cc to 1000 sec / 100cc. For example, the air permeability of the microporous membrane may be, but is not limited to, 10 sec / 100cc, 20 sec / 100cc, 30 sec / 100cc, 40 sec / 100cc, 50 sec / 100cc, 60 sec / 100cc, 70 sec / 100cc, 80 sec / 100cc, 90 sec / 100cc, 100 sec / 100cc, 200 sec / 100cc, 400 sec / 100cc, 600 sec / 100cc, 800 sec / 100cc, 1000 sec / 100cc, or a range consisting of any two of these values. In some embodiments, the air permeability of the microporous membrane is 10 sec / 100 cc to 100 sec / 100 cc.

[0159] This application does not specifically limit the thickness of the microporous membrane. However, considering factors such as mechanical strength, internal resistance, and the need for thinner fabrics, in some embodiments, the thickness of the microporous membrane is between 2 μm and 120 μm. For example, the thickness of the microporous membrane can be, but is not limited to, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 8 μm, 10 μm, 20 μm, 50 μm, 80 μm, 100 μm, 120 μm, or any combination of these values. In some embodiments, the thickness of the microporous membrane is ≤5 μm.

[0160] It is understood that the tensile strength (including longitudinal and transverse tensile strength) in this application can refer to GB / T 36363-2018. When testing transverse tensile strength, a strip with a longitudinal width of 15 mm is cut and clamped at both ends of the fixture, and the tensile testing machine speed is set to 200 mm / min. When testing the longitudinal tensile strength of the microporous membrane, a strip with a transverse width of 15 mm is cut and tested, and other parameter settings are consistent with the conditions for the transverse tensile strength test. Puncture strength can be tested according to GB / T 36363-2018. After flattening and clamping the microporous membrane sample, puncture it at a rate of 300 mm / min, and determine the puncture strength data. Furthermore, porosity, air permeability, and thickness can be tested according to GB / T 36363-2018. Of course, other test methods can also be used for the aforementioned test items.

[0161] Secondly, this application provides a method for preparing a microporous membrane, comprising the following steps:

[0162] A mixture comprising polymer and ionic liquid is mixed, extruded, and cooled to form an intermediate film.

[0163] The intermediate membrane was stretched, extracted, and heat-set to obtain a microporous membrane;

[0164] The ionic liquid includes a first ionic liquid, and the mass percentage of the ionic liquid in the microporous membrane is 0.01% to 6%.

[0165] In some embodiments, the mass percentage of the ionic liquid in the microporous membrane is 0.1% to 5%. Specifically, the mass percentage of the ionic liquid in the microporous membrane can be any value or a range between any two values ​​from 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, to 5.0%. Controlling the mass percentage of ionic liquid in microporous membranes within a certain range helps improve the overall performance of microporous membranes in different application fields.

[0166] Extensive research has revealed that mixing ionic liquids with polymers, especially those containing a first ionic liquid, without the need for commonly used paraffin oils or white oils, achieves better compatibility with various polymers, making it applicable to a wider range of polymer systems, and resulting in microporous membranes with superior performance. Therefore, this application provides a novel method entirely different from traditional membrane fabrication systems, offering a new research direction and approach for wet processes and solving the limitation on the use of polymer systems in traditional processes.

[0167] In some embodiments, the wettability of the microporous membrane is ≤120s. The microporous membrane possesses suitable wettability, which can further reduce the battery's internal resistance while improving the battery's ionic conductivity and energy density. The ionic conductivity and energy density can be tested using the methods described above in this application.

[0168] The wettability of the microporous membrane refers to the wettability of a 5 mm² area when wetted with 2 μL of electrolyte (analytical grade, propylene carbonate). 2 The time corresponding to the microporous membrane.

[0169] In some embodiments, the wettability of the microporous membrane is ≤100s. Further, in some embodiments, the wettability of the microporous membrane is 20–80s. Specifically, the wettability of the microporous membrane can be any value or a range of any two of the following: 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, 60s, 65s, 75s, 80s, 85s, 90s, 95s, and 100s.

[0170] In some embodiments, the wettability test method for microporous membranes is as follows: The microporous membrane is cut into a 10mm × 10mm square, placed on a glass slide, and stretched taut with tape to ensure a smooth membrane surface. 2μL of electrolyte (analytical grade, propylene carbonate) is taken using a syringe and dropped onto the microporous membrane sample. The wettability area of ​​the droplet is measured to be 5mm². 2 Time for microporous membranes.

[0171] In some embodiments, the wettability of the microporous membrane is improved by 20% to 50% compared to a microporous membrane of the same material and pore structure without the ionic liquid. It should be noted that "same material" means that the two microporous membranes used in comparison employ the same film-forming host material and additives, and "same pore structure" means that the average pore size of the two microporous membranes differs by less than 10%, and the integral area overlap of their pore size distribution curves is greater than 85%. The pore size and pore size distribution curve can be measured using a capillary porosity meter, for example, using a PMI instrument (Jia Yun Co., Ltd., CFP-1500AE model) with a Galwick wettant (surface tension of 15.9 dynes / cm at 25°C) at 25°C. The pore size is expressed in nm. Of course, other conventional testing methods in the industry can also be used.

[0172] In some embodiments, the hydrophilic-lipophilic balance (HLB) value of the first ionic liquid is <10. For example, the HLB value of the first ionic liquid can be, but is not limited to, any value or a range between any two values ​​from 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9.5. In some embodiments, the HLB value of the first ionic liquid is 3 to 7. The HLB value is used to characterize the hydrophilicity and lipophilicity of a substance; the smaller the HLB value, the stronger the lipophilicity, and vice versa. Generally, the HLB value of paraffin is 0, and the HLB value of polyethylene glycol is 20, which are used as standards. When the HLB value of the first ionic liquid is within the above range, it has good lipophilicity and can have good high-temperature compatibility with polymers in microporous membranes, making the above preparation method applicable to more polymer systems. The HLB value of this application can be determined and calculated by emulsification, critical micelle concentration, etc., and this application is not limited thereto.

[0173] In some embodiments, the weight-average molecular weight of the first ionic liquid is 200 to 1000. For example, the weight-average molecular weight of the first ionic liquid can be, but is not limited to, any value or a range between any two of 200, 300, 400, 500, 600, 700, 800, 900, and 1000. A suitable weight-average molecular weight of the first ionic liquid allows for good high-temperature compatibility with polymers, thus making it suitable for high-temperature preparation processes of more polymer systems and resulting in higher-quality microporous membranes. The molecular weight of the ionic liquid can be directly determined by mass spectrometry. Alternatively, the molecular ion peak of the ionic liquid can be measured using techniques such as electrospray ionization (ESI) or matrix-assisted laser desorption / ionization (MALDI) to obtain the molecular weight. Nuclear magnetic resonance (NMR) and light scattering methods can also be used, but this application is not limited to these methods.

[0174] In some embodiments, the boiling point of the first ionic liquid is 200°C to 500°C. The high boiling point of the first ionic liquid allows it to better form a homogeneous phase with the polymer at high temperatures, which further facilitates the formation of intermediate films with uniform thickness and better film-forming properties through blending and extrusion. This helps to form microporous films with better overall performance, meeting the needs of different application scenarios. Specifically, the boiling point of the first ionic liquid may be, but is not limited to, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, 255℃, 260℃, 265℃, 270℃, 275℃, 280℃, 285℃, 290℃, 295℃, 300℃, 320℃, 340℃, 350℃, 360℃, 380℃, 400℃, 420℃, 440℃, 450℃, 460℃, 480℃, 500℃, or a range of any two of these values. The boiling point can be determined by conventional testing methods, including but not limited to distillation.

[0175] In some embodiments, the viscosity of the first ionic liquid at 25°C is 20 cp to 100 cp. Specifically, the viscosity of the first ionic liquid can be any value or a range between any two values ​​from 20 cp, 30 cp, 40 cp, 50 cp, 60 cp, 70 cp, 80 cp, 90 cp, and 100 cp. The aforementioned first ionic liquid has a suitable viscosity at room temperature, good fluidity, which is beneficial for mixing with polymers and for better control of thickness, porosity, and pore size during the preparation process. The viscosity can be determined using conventional testing methods, including but not limited to reading the viscosity after placing the sample treated in a constant-temperature water bath at 25°C for 1 hour into a rotational viscometer.

[0176] In some embodiments, the first ionic liquid is selected from one or more of imidazole salts, pyridine salts, quaternary ammonium salts, quaternary phosphonium salts, and pyrrolidines. It is understood that the ionic liquid may also have functionalized groups, such as hydroxyl, carboxyl-functionalized ionic liquids, ether groups, ester groups, amino groups, cyano groups, etc.

[0177] Specifically, the first ionic liquid is selected from 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium methyl sulfate, 1,3-dimethylimidazolium dimethyl phosphate, 1,3-dimethylimidazolium tetrafluoroborate, 3-dimethylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluoroantimonate, 1,3-dimethylimidazolium trifluoromethanesulfonate, 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium perchlorate, 1,3-dimethylimidazolium nitrate ... One or more of the following: imidazole methanesulfonate, 1,3-dimethylimidazolium p-toluenesulfonate, 1,3-dimethylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, ethyl 1-ethyl-3-methylimidazolium sulfate, methyl 1-ethyl-3-methylimidazolium sulfate, diethyl 1-ethyl-3-methylimidazolium phosphate, dimethyl 1-ethyl-3-methylimidazolium phosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, and 1-ethyl-3-methylimidazolium hexafluoroantimonate.

[0178] It is understood that the above only lists some commonly used types of ionic liquids, but it is not limited to these. Other ionic liquids can also be used, as long as they meet the above conditions. They will not be listed exhaustively here.

[0179] In some embodiments, the mixture comprising the polymer and the ionic liquid may further include a high-boiling-point ether solvent, for example, an ether solvent with a boiling point ≥300°C. Specifically, the ether solvent may be one or more of ethylene glycol phenyl ether and propylene glycol phenyl ether. Adding the aforementioned high-boiling-point ether solvent is beneficial for further improving the compatibility between the ionic liquid and the polymer.

[0180] In some embodiments, the mass ratio of polymer to ionic liquid is (5–60):(40–95). Specifically, the mass ratio of polymer to ionic liquid can be any value or a range between any two values ​​from 5:95, 7:93, 9:91, 11:89, 13:87, 15:85, 17:83, 19:81, 21:79, 23:77, 25:75, 27:73, 29:71, 31:69, 33:67, 35:65, 37:63, 39:61, 41:59, 43:57, 45:55, 47:53, 49:51, 51:49, 53:47, 55:45, 57:43, 59:41, to 60:40. Controlling the mass ratio of polymer to ionic liquid within a certain range helps to control melt flow during processing, improve the quality of intermediate films, and make the prepared microporous films have better overall performance such as pore formation consistency and mechanical strength.

[0181] In some embodiments, the polymer is selected from homopolymers or copolymers of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene, thermoplastic polyurethane elastomers (TPU), polyolefin elastomers (POE), polyethylene terephthalate (PET), polyurethane (PU), or mixtures of polymers thereof. In some embodiments, the polymer is selected from polyolefins, for example, homopolymers or copolymers of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene. In some embodiments, the polymer is selected from one or more of polyethylene, polypropylene, and ethylene-propylene copolymers. The application of the first ionic liquid to microporous membranes expands the types of microporous membranes applicable not only to polyethylene (PE) systems but also to other polymer systems such as polypropylene (PP).

[0182] Researchers have creatively discovered that traditional wet-process microporous membrane preparation methods use liquid paraffin oil as a pore-forming agent. However, due to the poor compatibility of paraffin oil with different polymer melt systems, it can only effectively use polyethylene (PE) as the main raw material for microporous membranes. This limits the production of membranes using other polymer raw material systems and restricts further improvements in the performance of microporous membranes, hindering their application in various fields. Currently, some raw materials with melting points above 170℃ (such as PP) cannot be processed into a suitable melt in existing paraffin oil melt systems, making it difficult to produce microporous membranes. Alternatively, dry processes can only produce microporous membranes with poor performance consistency (e.g., porosity, strength). This application, through extensive research, has found that using a first ionic liquid eliminates the need for traditional pore-forming agents such as liquid or solid paraffin oil, achieving better compatibility with a wider range of polymers. This makes it applicable to more polymer systems, and the resulting microporous membranes exhibit superior performance.

[0183] In some embodiments, in the step of mixing and extruding a mixture comprising a polymer and an ionic liquid, the mixing of the polymer and the ionic liquid can be done in one step or in multiple steps.

[0184] It is understood that a single mixing involves mixing all the components, including the polymer and the ionic liquid, at once, where the polymer and the ionic liquid can be one or more types. Multiple mixing involves mixing the polymer and ionic liquid in two or more separate batches, where the polymer and ionic liquid content is the same or different in each batch, and the types of polymer and ionic liquid used in each batch can also be the same or different.

[0185] In some embodiments of this application, the multiple mixing steps can meet the needs of microporous membrane products for more diverse performance and more differentiated application scenarios.

[0186] In some embodiments, the polymer has a viscosity-average molecular weight of 100,000 to 15 million. When applied in the field of lithium batteries, in some embodiments, the polymer's viscosity-average molecular weight can be 1 million to 15 million, which is beneficial for further improving the mechanical strength of the microporous membrane and thus further improving electrochemical safety. When applied in the field of apparel fabrics, in some embodiments, the polymer's viscosity-average molecular weight is 100,000 to 1.5 million, which is beneficial for balancing the softness and processability of the fabric. When applied in the field of composite current collectors, in some embodiments, the polymer's viscosity-average molecular weight is 1 million to 6 million, which is beneficial for further improving the mechanical strength of the microporous membrane and thus improving the energy density of the composite current collector.

[0187] In some embodiments, the viscosity-average molecular weight of the polymer can be between 1 million and 6 million. Further, in some embodiments, the viscosity-average molecular weight of the polymer can be between 3 million and 6 million. Specifically, the viscosity-average molecular weight of the polymer can be 1 million, 1.1 million, 1.2 million, 1.3 million, 1.4 million, 1.5 million, 1.6 million, 1.7 million, 1.8 million, 1.9 million, 2 million, 2.1 million, 2.2 million, 2.3 million, 2.4 million, 2.5 million, 2.6 million, 2.7 million, 2.8 million, 2.9 million, 3 million, 3.1 million, 3.2 million, 3.3 million, 3.4 million, or 3.5 million. The viscosity-average molecular weight (MAM) of the polymer can be any value or a range between any two values ​​from 0,000, 3,600,000, 3,700,000, 3,800,000, 3,900,000, 4,000,000, 4,100,000, 4,200,000, 4,300,000, 4,400,000, 4,500,000, 4,600,000, 4,700,000, 4,800,000, 4,900,000, 5,000,000, 5,100,000, 5,200,000, 5,300,000, 5,400,000, 5,500,000, 5,600,000, 5,700,000, 5,800,000, 5,900,000, and 6,000,000. Controlling the MMA within the range specified in this application helps control melt flowability during processing and improves the quality of intermediate films. The MMA can be determined using conventional methods, including but not limited to measuring the intrinsic viscosity at 135°C using decahydronaphthalene as a solvent according to GB 1841-1980, thereby calculating the MMA.

[0188] It is understood that the methods for preparing microporous membranes in some embodiments of this application are also applicable to the preparation of microporous membranes with other molecular weights and other thicknesses.

[0189] Unlike traditional wet processes, this method uses ionic liquids mixed with polymers, which has less impact on polymer cooling and crystallization, results in more thorough phase separation, and allows for greater flexibility in adjusting the solid content during extrusion, leading to better melt quality. This makes it easier to adjust micropore size, porosity, and other parameters. For example, traditional wet and dry stretching techniques struggle to achieve porosities above 60% for PE and PP microporous membranes, typically remaining between 20% and 60%. In some embodiments of this application, the preparation method uses ionic liquids mixed with polymers without the addition of pore-forming agents such as paraffin oil, enabling the preparation of microporous membranes with higher porosities. For instance, the porosity of the microporous membrane can be adjusted between 10% and 90%, and further, between 60% and 90%. Traditional wet and dry stretching processes struggle to achieve average pore sizes exceeding 60 nanometers for PE and PP microporous membranes, typically ranging from 20 nm to 50 nm. Some embodiments of this application utilize preparation methods that can adjust the average pore size range of the microporous membrane between 20 nm and 200 nm to meet the performance requirements of different applications (e.g., mechanical strength, ion permeability, electrochemical safety, and windproof properties of clothing fabrics). Furthermore, the average pore size of the microporous membrane can reach above 60 nm, for example, between 60 nm and 200 nm. For example, the average aperture can be any value or a range between any two values ​​between 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, 105nm, 110nm, 115nm, 120nm, 125nm, 130nm, 135nm, 140nm, 145nm, 150nm, 155nm, 160nm, 165nm, 170nm, 175nm, 180nm, 185nm, 190nm, 195nm, and 200nm. Furthermore, in some embodiments of this application, using an ionic liquid containing a first ionic liquid as a pore-forming agent, it is possible to prepare microporous membranes with lower permeability, for example, permeability of 10 sec / 100 cc to 100 sec / 100 cc (the permeability of microporous membranes prepared by conventional wet and dry processes is 90 sec / 100 cc to 500 sec / 100 cc).

[0190] In some embodiments, during the step of mixing and extruding the polymer and ionic liquid, the mixing and extrusion temperature T 挤 For T 挤 =Polymer melting point T m +(15℃~60℃). In some embodiments, T 挤 =Polymer melting point T m+(15℃~45℃). Controlling the extrusion temperature within the polymer melting point Tm+(15℃~60℃) helps to reduce the risk of polymer degradation at excessively high temperatures while ensuring processability. Furthermore, a lower extrusion temperature means it is easier to reach the phase separation temperature, resulting in higher production efficiency. Under the same conditions, the production line can operate at a faster and more efficient speed, ultimately producing a microporous membrane with better overall performance, meeting the performance requirements of microporous membranes in different application scenarios.

[0191] Specifically, if the polymer is a polyolefin, its mixing and extrusion temperature can be from 145°C to 300°C. In some embodiments, the polymer is a polyolefin, and its mixing and extrusion temperature can be from 145°C to 200°C. For example, the mixing and extrusion temperature can be, but is not limited to, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, or any combination of these values. As mentioned earlier, traditional wet-process paraffin oil-polyethylene co-extrusion biaxial systems require extrusion temperatures set high above the polymer's melting point to increase fluidity. However, in some embodiments of this application, compared to traditional paraffin oil pore-forming agents, the extrusion temperature can be further reduced, resulting in higher fluidity at a relatively lower and suitable temperature, thus reducing the risk of polymer degradation due to increased temperature. For example, under the same conditions, the extrusion temperature can be reduced by 30–60°C, effectively reducing the risk of polymer oxidation or molecular weight degradation due to high temperatures. Furthermore, a lower extrusion temperature means it is easier to reach the phase separation temperature, resulting in higher production efficiency. Under the same conditions, the production line can achieve faster and more efficient production speeds.

[0192] In some embodiments, during the step of extruding the mixture comprising the polymer and the ionic liquid, the melt index of the polymer is 0.6 g / 10 min to 10 g / 10 min. In some embodiments, the melt index of the polymer is 0.6 g / 10 min to 6 g / 10 min. The test conditions for the melt index are as follows: polymers with a viscosity-average molecular weight below 1 million are tested at 190°C and 2.16 kg; polymers with a viscosity-average molecular weight above 1 million are tested at 190°C and 21.6 kg. The ionic liquid includes a first ionic liquid, which gives the blend system a suitable melt index, resulting in good high-temperature fluidity of the melt, thereby ensuring uniform mixing of the blend system, improving the quality of the intermediate film, and reducing processing difficulty. The polymer can also be selected from polymers with a melting point below 300°C, such as polyolefins, which can also form good synergies with the ionic liquid, further improving the processability of the microporous membrane.

[0193] In some embodiments, during the step of mixing and extruding the mixture comprising the polymer and the ionic liquid, additives may also be added. These additives include one or more known additives such as antioxidants, metal soaps like calcium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments. Adding additives can improve the properties of the microporous membrane, such as its antioxidant properties.

[0194] Specifically, the mass ratio of additive to polymer is 1:(20 to 10000). In some embodiments, the mass ratio of additive to polymer is 1:(100 to 1000). For example, the mass ratio of additive to polymer may be, but is not limited to, 1:20, 1:50, 1:80, 1:100, 1:150, 1:200, 1:250, 1:300, 1:350, 1:400, 1:450, 1:500, 1:550, 1:600, 1:650, 1:700, 1:750, 1:800, 1:850, 1:900, 1:950, 1:1000, 1:2000, 1:3000, 1:5000, 1:8000, 1:10000, or any range of two of these values. By controlling the mass ratio of additives to polymers, it is beneficial to ensure the film-forming properties and quality of microporous membranes while achieving the corresponding effects brought by additives.

[0195] It is understood that the additive is not limited to the step of mixing and extruding the mixture including the polymer and the ionic liquid. In other embodiments, the additive can also be added by immersing the intermediate membrane in a solution containing the additive at a certain stage of the preparation process of the microporous membrane, or by coating the microporous membrane. This application does not make any particular limitation.

[0196] Specifically, in some embodiments, the preparation method of some embodiments of this application may further include steps such as cooling and molding, stretching, extraction, and heat setting.

[0197] In some embodiments, during the cooling and forming step, the cooling method may be rapid roller contact cooling, or other cooling methods such as water cooling and air cooling, or a combination of two or more cooling methods, to cool and form the sheet. The cooling and forming temperature is 10℃ to 60℃. In some embodiments, the cooling and forming temperature is 10℃ to 30℃. For example, the cooling and forming temperature may be, but is not limited to, any value or a range of any two of the following: 10℃, 12℃, 14℃, 15℃, 16℃, 18℃, 20℃, 22℃, 24℃, 25℃, 26℃, 28℃, 30℃, 32℃, 34℃, 35℃, 36℃, 38℃, 40℃, 42℃, 44℃, 45℃, 46℃, 48℃, 50℃, 52℃, 54℃, 55℃, 56℃, 58℃, and 60℃. Controlling the cooling and molding temperature within the range specified in this application helps to achieve more thorough phase separation, improves the quality of the intermediate membrane, and can control the comprehensive properties of the final microporous membrane, such as pore size uniformity and mechanical strength, while also taking into account the economic efficiency of the process.

[0198] In some embodiments, the biaxial stretching process may involve first performing a longitudinal stretch with a stretching ratio of 3 to 19 times, followed by a transverse stretch with a stretching ratio of 5 to 19 times. In some embodiments, the longitudinal stretching ratio is 10 to 19 times. For example, the longitudinal stretching ratio may be, but is not limited to, any value from 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, and 19 times, or a range of any two of these values. In some embodiments, the transverse stretching ratio is 10 to 19 times. For example, the transverse stretching ratio may be, but is not limited to, any value from 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, and 19 times, or a range of any two of these values.

[0199] In other embodiments, the biaxial stretching process may also involve simultaneous transverse and longitudinal stretching, with a total stretching ratio, for example, ranging from 15 to 361 times. In some embodiments, the total stretching ratio is 100 to 361 times. For example, the total stretching ratio may be, but is not limited to, any value from 15, 30, 50, 80, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, and 361 times, or a range consisting of any two of these values. It is understood that controlling the biaxial stretching ratio within the range of this application allows the intermediate film after cooling and molding to be oriented in each stretching direction, thereby facilitating the control of the microporous film to obtain suitable mechanical strength or stiffness, and thus meeting the usage requirements of different application scenarios.

[0200] In some embodiments, the extraction temperature is 15°C to 50°C. For example, the extraction temperature can be, but is not limited to, any value among 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C, or a range of any two of these values. Using the above settings is beneficial for improving extraction efficiency, controlling the content of ionic liquid and extractant on the final microporous membrane, controlling the pore uniformity of the microporous membrane, and exhibiting suitable wettability, water permeability, oil absorption, and electrochemical safety, thereby meeting the usage requirements of different application scenarios.

[0201] In some embodiments, the stretching ratio for transverse heat setting is 1 to 2 times, and the heat setting temperature is 90 to 300°C. In some embodiments, the heat setting temperature is 90 to 180°C, and further, the heat setting temperature can be 90 to 145°C. For example, the stretching ratio for transverse heat setting can be, but is not limited to, any value from 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 times, or a range of any two of these values. The heat-setting temperature can be, but is not limited to, any value or a range of any two of the following: 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, and 300℃. By controlling the stretching ratio and temperature of the transverse heat-setting within the range of this application, the crystallinity of the microporous membrane is further improved through the dual effects of heating and molecular orientation, thus solidifying the microporous structure of the membrane and helping to enhance its overall performance, thereby meeting the needs of different application scenarios.

[0202] In some embodiments, the extractant in the extraction step includes dichloromethane. Traditional paraffin oil / polyethylene co-extrusion biaxial stretching processes primarily use low-boiling-point solvents such as dichloromethane as extractants to remove pore-forming agents causing phase separation in the film. In some embodiments of this application, the pore-forming agent includes a first ionic liquid, and conventionally used dichloromethane extractants can also be used for extraction, following conventional extraction processes. The extracted extractant is then directly separated by distillation. During the drying process, the gaseous dichloromethane is adsorbed or compressed, and finally condensed and recovered for reuse.

[0203] In other embodiments, the extraction step uses a mixed solvent of a second ionic liquid and water as the extractant. The second ionic liquid has a higher hydrophilic-lipophilic balance (HLP) value than the first ionic liquid. This indicates that the second ionic liquid is more hydrophilic than the first, and the first ionic liquid is more lipophilic than the second, thus enabling the extraction of the first ionic liquid. The extracted film intermediate is then dried to remove water, yielding a microporous film.

[0204] In some embodiments, the difference between the hydrophilic-lipophilic balance value of the second ionic liquid and that of the first ionic liquid is <10. In some embodiments, the hydrophilic-lipophilic balance value of the second ionic liquid is 10-20. This configuration improves the air permeability of the microporous membrane when applied to lithium batteries, the moisture permeability when applied to clothing fabrics, and reduces the resistance of the composite current collector when applied to composite current collectors. Specifically, the resistance of the composite current collector can be characterized by its surface sheet resistance. For example, a composite current collector can be made by electroplating a 1μm thick copper or aluminum foil onto the surface of the microporous membrane, and the resistance can be measured at five locations (around the periphery and center) using a four-probe resistance meter, and the average value is taken.

[0205] In some embodiments, the weight-average molecular weight of the second ionic liquid is lower than that of the first ionic liquid. The lower weight-average molecular weight of the second ionic liquid results in better hydrophilicity. This lower weight-average molecular weight of the second ionic liquid is beneficial for the air permeability of the microporous membrane when applied to lithium batteries, for the moisture permeability in clothing fabrics, and for reducing the resistance of composite current collectors when used in composite current collectors.

[0206] In some embodiments, the weight-average molecular weight of the second ionic liquid is 100–250. For example, the weight-average molecular weight of the second ionic liquid can be, but is not limited to, any value or a range between any two of 100, 115, 130, 145, 160, 175, 190, 205, 220, 235, and 250. Controlling the molecular weight of the second ionic liquid within a certain range is beneficial for improving the air permeability of the microporous membrane when applied to lithium batteries, the moisture permeability when applied to clothing fabrics, and for reducing the resistance of the composite current collector when applied to composite current collectors.

[0207] In some embodiments, the boiling point of the second ionic liquid is 100°C to 500°C. Specifically, the boiling point of the second ionic liquid can be 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, etc. The temperature range is defined as any value or any two values ​​within the range of ℃, 235℃, 240℃, 245℃, 250℃, 255℃, 275℃, 280℃, 285℃, 290℃, 295℃, 300℃, 320℃, 340℃, 350℃, 360℃, 380℃, 400℃, 420℃, 440℃, 450℃, 460℃, 480℃, and 500℃. This configuration improves the air permeability of the microporous membrane when applied to lithium batteries, the moisture permeability when applied to clothing fabrics, and reduces the resistance of composite current collectors when applied to current collectors.

[0208] In some embodiments, the viscosity of the second ionic liquid at 25°C is 10 cp to 50 cp. Specifically, the viscosity of the second ionic liquid at 25°C can be any value or a range between any two of the following: 10 cp, 12 cp, 14 cp, 16 cp, 18 cp, 20 cp, 22 cp, 24 cp, 26 cp, 28 cp, 30 cp, 32 cp, 34 cp, 36 cp, 38 cp, 40 cp, 42 cp, 44 cp, 46 cp, 48 cp, and 50 cp. This configuration improves the air permeability of the microporous membrane when applied to lithium batteries, the moisture permeability when applied to clothing fabrics, and reduces the resistance of the composite current collector when applied to composite current collectors.

[0209] In some embodiments, the viscosity of the second ionic liquid at 25°C is 5 to 20 cp lower than that of the first ionic liquid at 25°C. Specifically, the viscosity of the second ionic liquid at 25°C can be any value or a range between any two values ​​that are lower than the viscosity of the first ionic liquid at 25°C by 5, 7, 9, 11, 13, 15, 17, 19, or 20 cp. This configuration improves extraction efficiency and helps control the ionic liquid content on the surface of the microporous membrane. Furthermore, the interaction between the two ionic liquids and the polymer results in a microporous membrane with excellent overall performance, meeting the needs of various application scenarios.

[0210] In some embodiments, the second ionic liquid is selected from one or more of imidazole salts, pyridine salts, quaternary ammonium salts, quaternary phosphonium salts, pyrrolidines, and functionalized ionic liquids.

[0211] Specifically, the second ionic liquid is selected from 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium methyl sulfate, 1,3-dimethylimidazolium dimethyl phosphate, 1,3-dimethylimidazolium tetrafluoroborate, 3-dimethylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluoroantimonate, 1,3-dimethylimidazolium trifluoromethanesulfonate, 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium perchlorate, 1,3-dimethylimidazolium nitrate ... One or more of the following: imidazole methanesulfonate, 1,3-dimethylimidazolium p-toluenesulfonate, 1,3-dimethylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, ethyl 1-ethyl-3-methylimidazolium sulfate, methyl 1-ethyl-3-methylimidazolium sulfate, diethyl 1-ethyl-3-methylimidazolium phosphate, dimethyl 1-ethyl-3-methylimidazolium phosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, and 1-ethyl-3-methylimidazolium hexafluoroantimonate.

[0212] It is understood that the above only lists some commonly used types of ionic liquids, but it is not limited to these. Other ionic liquids can also be used, as long as they meet the above conditions. They will not be listed exhaustively here.

[0213] In some embodiments, the mass percentage concentration of the second ionic liquid in the extractant is 5% to 10%. For example, the mass percentage concentration of the second ionic liquid in the extractant can be, but is not limited to, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any combination of these values. Adopting the above configuration helps to improve the demulsification efficiency during the extraction process, resulting in higher extraction efficiency. Simultaneously, it reduces the use of low-boiling-point organic extractants, lowers the organic waste gas generated during production, making the production process more environmentally friendly. Furthermore, it allows for control of the ionic liquid content on the final microporous membrane, enabling the microporous membrane to possess superior overall performance.

[0214] In some embodiments, after the extraction step, the method further includes: washing the extracted microporous membrane intermediate with water, separating it with a reverse osmosis membrane, and drying it.

[0215] The ionic liquid in the microporous membrane intermediate is removed by washing with water, and the first ionic liquid, the second ionic liquid and water can be separated by reverse osmosis membrane separation, which facilitates subsequent recycling and reuse.

[0216] It should be noted that after extraction and before drying, other steps can be added as needed, such as washing, wetting, and cross-linking.

[0217] In some embodiments, a washing step is further included after extraction. The washing solution includes an ionic liquid and a washing agent, the washing agent including water, and the ionic liquid being the ionic liquid described in this application. The mass percentage concentration of the second ionic liquid in the washing solution is not higher than 10%. A concentration of no more than 10% of the ionic liquid in the washing solution can effectively control the diffusion rate of the ionic liquid extractant from the film into the washing solution, ensuring washing efficiency and washing quality.

[0218] In some embodiments, a multi-stage washing method can be used during the washing process, wherein the concentration of the ionic liquid in the washing solution of each subsequent wash is no higher than 30 wt% of the concentration of the ionic liquid in the washing solution of the previous wash. Controlling the concentration of the ionic liquid in the washing solution to decrease sequentially can better control the washing efficiency. Furthermore, controlling the concentration of the ionic liquid in the washing solution of each subsequent wash to be no higher than 30 wt% of the concentration of the ionic liquid in the washing solution of the previous wash can better control the residual content of the ionic liquid in the membrane while maintaining high washing efficiency. Secondly, it can also better prevent the ionic liquid extractant in the membrane from being washed too quickly, which could cause the microporous structure to collapse and affect the quality of the microporous membrane.

[0219] In some embodiments, the washing process further includes a step of performing a second spraying with a second spray liquid, the second spray liquid comprising water.

[0220] Before drying the wet membrane, a wetting step may be included, where the type of wetting solution can be freely selected according to the desired purpose. For example, to better control the ionic liquid content of the microporous membrane, the wetting solution may include the ionic liquid described in this application and water, wherein the mass percentage concentration of the ionic liquid in the wetting solution is 0.05% to 5%. For example, to achieve modification or crosslinking of the porous membrane, the wetting solution may include commonly used modifying agents, initiators, and crosslinking agents in the art. In some embodiments, a crosslinking step is performed after this wetting step to better achieve modification or crosslinking of the porous membrane. The mass percentage concentration of the ionic liquid in the wetting solution may be any value or a range between any two values ​​from 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, to 0.5%.

[0221] It is understood that the steps of cooling, forming, stretching, and heat setting can also be performed using existing methods in the art. For example, biaxial stretching can be performed separately in the transverse and longitudinal directions, or simultaneously in the transverse and longitudinal directions, which will not be elaborated here. In addition, the steps of cooling, forming, biaxial stretching, and heat setting can be performed using methods commonly used in the art, and can be carried out on the basis of existing wet process production lines, with high compatibility.

[0222] It is understood that after the heat setting step, there are also steps of winding and slitting, which can be done using existing methods in the field and will not be described in detail here.

[0223] In some embodiments of this application, since the pore-forming agent contains a first ionic liquid, an organic low-boiling-point solvent such as dichloromethane (DCM) can be selected for extraction and drying to remove the pore-forming agent. Alternatively, a suitable mixed solvent of a second ionic liquid and water can be selected, and a polar ionic liquid with demulsification efficiency can be added to the extraction environment. The pore-forming agent is then removed by washing with purified water. Because the drying portion of this extraction process contains only water, no organic waste gas is generated, making the production process more environmentally friendly. Furthermore, when adding additives such as antioxidants to the polymer and pore-forming agent blend system, using a mixed solvent of the second ionic liquid and water as the extractant is beneficial because the extractant has good hydrophilicity and is less likely to extract oil-soluble additives, allowing the additives to remain in the microporous membrane, which improves the performance of the microporous membrane.

[0224] Please refer to Figures 1 to 3. Figure 1 is a scanning electron microscope (SEM) image (magnification 20Kx) of a polypropylene microporous membrane prepared by the preparation method of some embodiments of this application; Figure 2 is a scanning electron microscope (SEM) image (magnification 20Kx) of a polypropylene microporous membrane prepared by a conventional dry uniaxial stretching process; Figure 3 is a scanning electron microscope (SEM) image (magnification 20Kx) of a polyethylene microporous membrane prepared by a conventional wet biaxial stretching process.

[0225] As can be seen from the above figures, the microporous membrane preparation method of this application can prepare polypropylene microporous membranes with good pore structure.

[0226] Thirdly, this application provides an application of a microporous membrane as described in the first aspect above, or a microporous membrane prepared by the preparation method described in the second aspect above, in lithium batteries, gas separation, heat exchange, composite current collectors, clothing fabrics, or water treatment.

[0227] It is understood that the above only provides some common applications of the aforementioned microporous membranes, but are not limited to these.

[0228] Fourthly, this application provides a secondary battery, wherein the separator comprises the microporous membrane described in the first aspect or the microporous membrane prepared by the preparation method described in the second aspect.

[0229] It is understood that the positive electrode, negative electrode, electrolyte, etc. in a secondary battery can be those commonly used in this field, and no special limitation is made here.

[0230] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0231] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A microporous membrane, characterized in that, The microporous membrane contains an ionic liquid, which includes a first ionic liquid, and the mass percentage of the ionic liquid in the microporous membrane is 0.01% to 6%.

2. The microporous membrane according to claim 1, characterized in that, The first ionic liquid satisfies one or more of the following conditions: (1) The hydrophilic-lipophilic balance value of the first ionic liquid is <10, and optionally, the hydrophilic-lipophilic balance value of the first ionic liquid is 3 to 7. (2) The weight-average molecular weight of the first ionic liquid is 200 to 1000; (3) The boiling point of the first ionic liquid is 200℃~500℃; (4) The viscosity of the first ionic liquid at 25°C is 20cp~100cp; (5) In the microporous membrane, the mass percentage of the first ionic liquid is 0.01% to 6%, and optionally, the mass percentage of the first ionic liquid is 0.1% to 5%.

3. The microporous membrane according to claim 2, characterized in that, The ionic liquid further includes a second ionic liquid, wherein the hydrophilic-lipophilic balance value of the second ionic liquid is greater than that of the first ionic liquid. And / or, the weight-average molecular weight of the second ionic liquid is less than that of the first ionic liquid.

4. The microporous membrane according to claim 3, characterized in that, The difference between the hydrophilic-lipophilic balance value of the second ionic liquid and the hydrophilic-lipophilic balance value of the first ionic liquid is <10; Optionally, the hydrophilic-lipophilic balance value of the second ionic liquid is 10 to 20; And / or, the weight-average molecular weight of the second ionic liquid is 100 to 250; And / or, the boiling point of the second ionic liquid is 100℃~500℃; And / or, the viscosity of the second ionic liquid at 25°C is 10cp to 50cp; Optionally, the viscosity of the second ionic liquid at 25°C is 5 cp to 20 cp lower than that of the first ionic liquid at 25°C. And / or, in the microporous membrane, the mass percentage of the second ionic liquid is 0.01% to 3%, optionally, the mass percentage of the second ionic liquid is 0.1% to 0.5%.

5. The microporous membrane according to claim 4, characterized in that, The first ionic liquid and the second ionic liquid are each independently selected from one or more of imidazole salts, pyridine salts, quaternary ammonium salts, quaternary phosphonium salts and pyrrolidines; Optionally, the first ionic liquid and the second ionic liquid are each independently selected from 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium methyl sulfate, 1,3-dimethylimidazolium dimethyl phosphate, 1,3-dimethylimidazolium tetrafluoroborate, 3-dimethylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluoroantimonate, 1,3-dimethylimidazolium trifluoromethanesulfonate, 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-dimethylimidazolium perchlorate, and 1,3-dimethylimidazolium nitrate. One or more of the following: 1,3-dimethylimidazolium methanesulfonate, 1,3-dimethylimidazolium p-toluenesulfonate, 1,3-dimethylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, 1-ethyl-3-methylimidazolium ethyl sulfate, 1-ethyl-3-methylimidazolium methyl sulfate, 1-ethyl-3-methylimidazolium diethyl phosphate, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, and 1-ethyl-3-methylimidazolium hexafluoroantimonate.

6. The microporous membrane according to any one of claims 1 to 5, characterized in that, The microporous membrane includes homopolymers or copolymers of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and norbornene, thermoplastic polyurethane elastomers, polyolefin elastomers, polyethylene terephthalate, polyurethane or a mixture of their polymers. Optionally, the microporous membrane comprises one or more of polyethylene, polypropylene, and ethylene-propylene copolymer; Optionally, the viscosity-average molecular weight of the microporous membrane is 100,000 to 15,000,000.

7. The microporous membrane according to any one of claims 1 to 5, characterized in that, The microporous membrane also contains additives, including one or more of antioxidants, metal soaps, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments. Optionally, in the microporous membrane, the additive accounts for 0.01% to 5% of the total mass of the microporous membrane; alternatively, the additive accounts for 0.1% to 1% of the total mass of the microporous membrane. And / or, the microporous membrane comprises multiple layers of sub-membranes stacked together, with different polymers in adjacent sub-membranes, and both containing the first ionic liquid.

8. The microporous membrane according to any one of claims 1 to 5, characterized in that, The microporous membrane satisfies one or more of the following conditions: (1) The average pore size of the microporous membrane is 20nm to 200nm, and optionally, the average pore size of the microporous membrane is 60nm to 200nm; (2) The transverse tensile strength of the microporous membrane is 500 kgf / cm. 2 ~5000 kgf / cm 2 ; (3) The longitudinal tensile strength of the microporous membrane is 1000 kgf / cm. 2 ~5000 kgf / cm 2 ; (4) The puncture strength of the microporous membrane is 150 gf to 1000 gf; (5) The porosity of the microporous membrane is 10% to 90%, and optionally, the porosity of the microporous membrane is 60% to 90%. (6) The air permeability of the microporous membrane is 10sec / 100cc to 1000sec / 100cc. Optionally, the air permeability of the microporous membrane is 10sec / 100cc to 100sec / 100cc. (7) The thickness of the microporous membrane is 2μm to 120μm, and optionally, the thickness of the microporous membrane is ≤5μm; (8) The wettability of the microporous membrane is increased by 20% to 50% compared with that of a microporous membrane of the same material and the same pore structure that does not contain the first ionic liquid.

9. A method for preparing a microporous membrane, characterized in that, Includes the following steps: A mixture comprising polymer and ionic liquid is mixed, extruded, and cooled to form an intermediate film. The intermediate membrane is stretched, extracted, and heat-set to obtain the microporous membrane. The ionic liquid includes a first ionic liquid, and the mass percentage of the ionic liquid in the microporous membrane is 0.01% to 6%.

10. The method for preparing a microporous membrane according to claim 9, characterized in that, One or more of the following conditions must be met: (1) The hydrophilic-lipophilic balance value of the first ionic liquid is <10; optionally, the hydrophilic-lipophilic balance value of the first ionic liquid is 3 to 7. (2) The weight-average molecular weight of the first ionic liquid is 200 to 1000; (3) The boiling point of the first ionic liquid is 200℃~500℃; (4) The mass ratio of the polymer to the ionic liquid is (5-60):(40-95).

11. The method for preparing a microporous membrane according to claim 9 or 10, characterized in that, In the extraction step, the extractant includes dichloromethane; or, In the extraction step, the extractant comprises a mixed solvent of a second ionic liquid and water, wherein the second ionic liquid satisfies one or more of the following conditions: (1) The hydrophilic-lipophilic balance value of the second ionic liquid is greater than that of the first ionic liquid. Optionally, the difference between the hydrophilic-lipophilic balance value of the second ionic liquid and that of the first ionic liquid is <10. Optionally, the hydrophilic-lipophilic balance value of the second ionic liquid is 10 to 20. (2) The weight-average molecular weight of the second ionic liquid is less than that of the first ionic liquid. Optionally, the weight-average molecular weight of the second ionic liquid is 100 to 250. (3) The boiling point of the second ionic liquid is 100℃~500℃; (4) The viscosity of the second ionic liquid at 25°C is 10cp~50cp; Optionally, the viscosity of the second ionic liquid at 25°C is 5 to 20 cp lower than that of the first ionic liquid at 25°C.

12. The method for preparing a microporous membrane according to claim 11, characterized in that, The extractant comprises a mixed solvent of a second ionic liquid and water, wherein the mass percentage concentration of the second ionic liquid in the extractant is 5% to 10%. And / or, after the extraction step, the process further includes: washing the extracted microporous membrane intermediate with water, separating it with a reverse osmosis membrane, and drying it.

13. The method for preparing a microporous membrane according to claim 9, characterized in that, The temperature T of the mixed extrusion 挤 For T 挤 =Polymer melting point T m +(15℃~60℃), optional, T 挤 =Polymer melting point T m +(15℃~45℃); And / or, in the step of mixing and extruding a mixture comprising a polymer and an ionic liquid, the polymer has a melt index of 0.6 g / 10 min to 10 g / 10 min; optionally, the polymer has a melt index of 0.6 g / 10 min to 6 g / 10 min.

14. The application of the microporous membrane according to any one of claims 1 to 8 or the microporous membrane prepared by the preparation method according to any one of claims 9 to 13 in lithium batteries, gas separation, heat exchange, composite current collectors, clothing fabrics or water treatment.

15. A secondary battery, characterized in that, The separator of the secondary battery includes the microporous membrane according to any one of claims 1 to 8 or the microporous membrane prepared by the preparation method according to any one of claims 9 to 13.

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