Porous diaphragm, preparation method therefor, and use thereof

Abstract

A porous diaphragm, a preparation method therefor, and a use thereof. The porous diaphragm comprises a polyolefin porous substrate, an ionic liquid, and polyethylene oxide. The polyolefin porous substrate comprises a plurality of polyolefin fibrils and pores formed by mutual overlapping of the plurality of polyolefin fibrils. The ionic liquid and the polyethylene oxide are at least attached to surfaces of the plurality of polyolefin fibrils inside the polyolefin porous substrate. Compared with the polyolefin porous substrate, the porous diaphragm has an average volumetric pore size reduced by 40% to 86% and a thickness increased by 1.5% or less. The porous diaphragm has relatively high ionic conductivity, can effectively reduce internal resistance of a battery cell, also has relatively high puncture strength, thereby further improving battery safety performance. Furthermore, it can also avoid problems such as adhesion and delamination that are likely to occur during winding of the porous diaphragm.

Description

A porous membrane, its preparation method and application Technical Field

[0001] This application relates to the field of diaphragm technology, such as a porous diaphragm, its preparation method, and its application. Background Technology

[0002] The four key materials of a lithium-ion battery are the positive electrode material, the negative electrode material, the electrolyte, and the separator. The main function of the separator is to separate the positive and negative electrode materials. Lithium-ion battery separators have a large number of interconnected micropores, which allow electrolyte ions to pass freely to form a charging and discharging circuit. When the battery is overcharged or the temperature rises, the separator can separate the positive and negative electrodes through its pore-closing function to prevent them from directly contacting each other and short-circuiting. This achieves the function of blocking current conduction and preventing the battery from overheating or even exploding, thus preventing the two electrodes from contacting each other and short-circuiting.

[0003] With the rapid development of lithium-ion batteries, the market has placed higher demands on the energy density and safety of lithium-ion batteries, which in turn has placed higher requirements on the performance of separators.

[0004] Currently, most separators on the market achieve high battery safety by applying specific coatings to the surface of polyolefin-based membranes, such as ceramic coatings or fluorinated resin coatings. While these methods can improve battery safety to some extent, they still cannot meet the market's requirements for high energy density and high ion conductivity.

[0005] Therefore, to address the aforementioned technical issues, it is necessary to develop a porous membrane with high electrical conductivity and the ability to flexibly adjust microporosity and air permeability to meet the requirements of high energy density in batteries.

[0006] Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] This application provides a porous membrane, its preparation method, and its application. The porous membrane has high ionic conductivity, which can effectively reduce the internal resistance of the battery cell and improve the safety performance of the battery. At the same time, the preparation process is simple, and it is not easy to cause problems such as adhesion and delamination during the winding process. It can also flexibly adjust the microporosity and air permeability.

[0009] In a first aspect, this application provides a porous membrane, the porous membrane comprising a polyolefin porous substrate, an ionic liquid, and polyethylene oxide;

[0010] The polyolefin porous substrate comprises a plurality of polyolefin fibrils and pores formed by the overlapping of the plurality of polyolefin fibrils, wherein the ionic liquid and polyethylene oxide are attached to at least the surfaces of the plurality of polyolefin fibrils inside the polyolefin porous substrate.

[0011] Compared to the polyolefin porous substrate, the average volumetric pore size of the porous membrane is reduced by 40% to 86%, and the thickness is increased by less than 1.5%.

[0012] Secondly, this application provides a method for preparing a porous membrane, the method comprising the following steps:

[0013] A porous polyolefin substrate containing multiple polyolefin fibrils is immersed in a solution containing an ionic liquid, such that the ionic liquid adheres to at least the surface of multiple polyolefin fibrils inside the porous polyolefin substrate.

[0014] The porous polyolefin substrate with ionic liquid is then immersed in a solution containing polyethylene oxide, so that the polyethylene oxide and ionic liquid are physically bonded to at least the surface of multiple polyolefin fibrils inside the polyolefin substrate. After drying and shaping, the porous membrane is obtained.

[0015] Compared to the polyolefin porous substrate, the average volumetric pore size of the porous membrane is reduced by 40% to 86%, and the thickness is increased by less than 1.5%.

[0016] Thirdly, this application also provides a method for preparing a porous membrane, the method comprising the following steps:

[0017] Polyolefins and plasticizers are melt-mixed and extruded, then cooled to form a precursor film;

[0018] The precursor membrane is stretched to form multiple stretched membranes containing polyolefin fibrils;

[0019] The stretched film is immersed in an extraction solution containing an ionic liquid for extraction to remove the plasticizer. The ionic liquid adheres to the surface of multiple polyolefin fibrils to obtain an intermediate film.

[0020] The intermediate film is immersed in a solution containing polyethylene oxide, so that after removal, the polyethylene oxide and ionic liquid are physically bonded to at least the surface of multiple polyolefin fibrils inside the polyolefin substrate. After drying and shaping, the porous membrane is obtained.

[0021] Compared to the polyolefin porous substrate, the average volumetric pore size of the porous membrane is reduced by 40% to 86%, and the thickness is increased by less than 1.5%.

[0022] Fourthly, this application provides a battery comprising at least one of the porous membranes described in the first aspect, the porous membranes prepared by the preparation method described in the second aspect, or the porous membranes prepared by the preparation method described in the third aspect.

[0023] Compared with related technologies, this application has the following advantages:

[0024] (1) The porous membrane provided in this application includes a polyolefin porous substrate, an ionic liquid, and polyethylene oxide. The polyolefin porous substrate comprises a plurality of polyolefin fibrils and pores formed by the overlapping of the plurality of polyolefin fibrils. The ionic liquid and polyethylene oxide are at least attached to the surfaces of the plurality of polyolefin fibrils inside the polyolefin porous substrate. Compared with the polyolefin porous substrate, the average volume pore size of the porous membrane is reduced by 40% to 86%, and the thickness is increased by less than 1.5%. By attaching the ionic liquid and polyethylene oxide at least to the surfaces of the plurality of polyolefin fibrils inside the polyolefin porous substrate, the obtained porous membrane has a high ionic conductivity, which can effectively reduce the internal resistance of the battery cell and effectively improve the safety performance of the battery.

[0025] (2) Unlike coated diaphragms that are directly coated with polyethylene oxide coating, the porous diaphragm provided in this application can effectively avoid the problem of excessive adhesion caused by coating with polyethylene oxide coating, which leads to severe adhesion and difficulty in delamination or delamination during the film winding and roll-up process.

[0026] (3) The preparation process of the porous membrane provided in this application is relatively simple, and the porosity and air permeability can be flexibly controlled.

[0027] After reading and understanding the detailed description, other aspects can be understood. Detailed Implementation

[0028] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0029] Unless otherwise specified, the raw materials and equipment involved in the following specific embodiments are all conventional materials and equipment in the art, and can be purchased commercially.

[0030] During the research process, the applicant of this application creatively discovered that the problem with polyolefin membranes with a separate coating on the surface provided in the related technology is that the coating is obviously formed on the surface of the polyolefin porous substrate and cannot penetrate into the internal pores of the polyolefin porous substrate. Therefore, compared with the polyolefin porous substrate before coating, the thickness of the coated membrane obtained after coating is significantly increased, and it may block some of the pores on the surface of the polyolefin porous substrate, but the improvement in conductivity is very limited.

[0031] In view of the above, the first specific embodiment of this application provides a porous membrane, the porous membrane comprising a polyolefin porous substrate, an ionic liquid and polyethylene oxide;

[0032] The polyolefin porous substrate comprises a plurality of polyolefin fibrils and pores formed by the overlapping of the plurality of polyolefin fibrils, wherein the ionic liquid and polyethylene oxide are attached to at least the surfaces of the plurality of polyolefin fibrils inside the polyolefin porous substrate.

[0033] The average volumetric pore size of the porous membrane, compared to the polyolefin porous substrate, is reduced by 40% to 86% (e.g., a range of 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 86%, or any two thereof), and the thickness is increased by less than 1.5% (e.g., a range of 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1%, 0.9%, 0.7%, 0.5%, 0.45%, 0.4%, 0.35%, 0.3%, 0.25%, 0.2%, 0.15%, 0.1%, 0.01%, 0%, or any two thereof).

[0034] Unlike coated membranes with separate coatings on their surfaces provided in related technologies, the polyolefin porous substrate provided in this application comprises multiple polyolefin fibrils and pores formed by the overlapping of these fibrils. The ionic liquid and polyethylene oxide are attached to at least the surfaces of the multiple polyolefin fibrils within the polyolefin porous substrate, meaning the polyethylene oxide is not a separate coating from the polyolefin porous substrate. Consequently, the surface of the porous membrane provided in this application does not have a noticeable coating. Although the thickness of the resulting porous membrane does not significantly increase compared to the original polyolefin porous substrate, the average volumetric pore size changes significantly. This indicates that the polyethylene oxide successfully enters the surfaces of the multiple polyolefin fibrils and the pores formed by the overlapping of these fibrils, successfully altering the original structure of the polyolefin porous substrate. Part of the polyethylene oxide is directly attached to the surface of the polyolefin fibrils, while some is adsorbed through the ionic liquid, forming a physical interaction with it and thus more firmly adhering to the polyolefin. The surface of the fibrils can effectively improve the ionic conductivity of the resulting porous membrane, reduce the internal resistance of the battery cell, and further reduce the amount of electrolyte used, thereby improving the safety of the battery cell. Moreover, compared with the polyolefin porous substrate before coating, when the increase in thickness of the porous membrane is less than 1.5% and the decrease in average volume pore size is 40% to 86%, not only can the pore structure of the resulting porous membrane have better capillary action to allow the electrolyte to quickly penetrate into the membrane, but it can also ensure that the electrochemical performance is improved without causing significant changes in the quality of the polyolefin porous substrate.

[0035] It should be noted that the polyolefin porous substrate contains multiple polyolefin fibrils that are different from the fibers in nonwoven fabrics. They are formed by polymer molecular chains during the preparation of the polyolefin porous substrate, which are oriented and entangled along the stretching direction during the stretching process.

[0036] Furthermore, unlike coated diaphragms that are directly coated (e.g., by roller coating, vapor deposition, etc.), the porous diaphragm provided in this application can effectively avoid the problem of excessive adhesion caused by the coating of polyethylene oxide, resulting in severe adhesion and difficulty in delamination or delamination during the winding and roll-up process of the film itself.

[0037] In this application, the reduction in the average volumetric pore size and the increase in the thickness of the porous membrane can be calculated using the following formula:

[0038] Average volumetric pore size reduction (%) = (Average volumetric pore size of porous membrane - Average volumetric pore size of polyolefin porous substrate) / Average volumetric pore size of porous membrane × 100%;

[0039] The average volumetric pore size of the polyolefin porous substrate and the average volumetric pore size of the porous membrane were both measured using a PMI instrument (Jia Yun Co., Ltd., CFP-1500AE model). The wetting solution used for the test was Galwick (surface tension of 15.9 dynes / cm at 25℃), and the test temperature was 25℃. The unit is nm.

[0040] Thickness increase (%) = (thickness of porous membrane - thickness of polyolefin porous substrate) / thickness of porous membrane × 100%;

[0041] The thickness of the porous membrane and the thickness of the polyolefin substrate can be tested according to the method provided in GB-T 36363-2018.

[0042] In some specific embodiments, the amount of ionic liquid attached to the porous membrane is 0.01wt% to 0.5wt%, for example, 0.011wt%, 0.0151wt%, 0.02wt%, 0.025wt%, 0.03wt%, 0.035wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.08wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, or any combination thereof. Limiting the proportion of ionic liquid adhering to the porous membrane within the above-mentioned range can further ensure that the quality of the obtained porous membrane does not change, and can enable polyethylene oxide to adhere more firmly to the surface of polyolefin fibrils through the physical interaction between it and the ionic liquid. In addition, the appropriate amount of ionic liquid adhering can also provide a good ion movement channel for the battery, thereby further improving the electrochemical performance and electrochemical safety of the porous membrane.

[0043] In this application, the content of ionic liquid in the porous membrane can be tested using existing methods, such as by weighing: a 10cm × 10cm porous membrane sample is weighed and recorded as M1. The porous membrane sample is then placed in 100mL of DCM solvent, sonicated at 100Hz for 15min, dried at 80℃ for 5min, and weighed again and recorded as M2. The content of ionic liquid in the porous membrane sample is then calculated using the following formula:

[0044] For the porous membrane provided in this application, there are no special requirements for the specific average volumetric pore size of the polyolefin porous substrate and the porous membrane, as long as they meet the conventional applications in the art and the limitations of this solution. However, based on considerations of improving electrochemical performance, in some specific embodiments, the average volumetric pore size of the polyolefin porous substrate can be 30 nm to 100 nm, for example, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any combination thereof. Furthermore, considering the comprehensive strength and electrochemical performance of the obtained porous membrane, in some specific embodiments, the average volumetric pore size of the polyolefin porous substrate can be 45 nm to 65 nm.

[0045] To better ensure that the porous membrane has a better capillary effect so that the electrolyte can penetrate into the membrane more quickly to improve electrochemical performance, and at the same time further improve the puncture resistance of the porous membrane, in some specific embodiments, the average volumetric pore size of the porous membrane can be 5nm to 60nm, for example, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm or any combination thereof.

[0046] Similarly, this application does not have special requirements for the thickness of the polyolefin porous substrate and the porous membrane, as long as they meet the conventional applications in the art and the limitations of this solution. However, in some specific embodiments, considering the energy density of the battery, the thickness of the porous membrane can be 1μm to 25μm, for example, 1μm, 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 22μm, 24μm, 25μm or any combination thereof.

[0047] During the research process, the applicant of this application also creatively discovered that: the traditional wet process for preparing membranes usually uses dichloromethane as an extractant. Since dichloromethane can dissolve well with plasticizers (including paraffin oil, etc.), separation and purification require a large amount of energy. Ionic liquids, on the other hand, have water solubility and a certain degree of lipophilicity. When ionic liquids are added to the extract, they can produce microemulsions with plasticizers, thus cleaning the plasticizers and forming pores. At the same time, they can also serve as an intermediate medium to overcome the surface tension of the membrane micropores and introduce water molecules into the nanoscale micropores. Subsequently, the property that water and polyethylene oxide can dissolve in a certain proportion can be used to introduce polyethylene oxide into the membrane micropores, thereby realizing the preparation of porous membranes containing polyethylene oxide.

[0048] In view of the above, a second specific embodiment of this application provides a method for preparing a porous membrane, the method comprising the following steps:

[0049] A porous polyolefin substrate containing multiple polyolefin fibrils is immersed in a solution containing an ionic liquid, such that the ionic liquid adheres to at least the surface of multiple polyolefin fibrils inside the porous polyolefin substrate.

[0050] A porous polyolefin substrate coated with ionic liquid is immersed in a solution containing polyethylene oxide, so that polyethylene oxide and ionic liquid are physically bonded to the surface of at least a number of polyolefin fibrils inside the polyolefin substrate. After drying and shaping, the porous membrane is obtained.

[0051] The average volumetric pore size of the porous membrane, compared to the polyolefin porous substrate, is reduced by 40% to 86% (e.g., a range of 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 86%, or any two thereof), and the thickness is increased by less than 1.5% (e.g., a range of 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1%, 0.9%, 0.7%, 0.5%, 0.45%, 0.4%, 0.35%, 0.3%, 0.25%, 0.2%, 0.15%, 0.1%, 0.01%, 0%, or any two thereof).

[0052] A third embodiment of this application provides a method for preparing a porous membrane, the method comprising the following steps:

[0053] Polyolefins and plasticizers are melt-mixed and extruded, and then cooled to form a precursor film.

[0054] The precursor membrane is stretched to form a stretched membrane containing multiple polyolefin fibrils;

[0055] The stretched film is immersed in an extraction solution containing ionic liquid for extraction to remove the plasticizer and to allow the ionic liquid to adhere to the surface of the plurality of polyolefin fibrils, thereby obtaining an intermediate film.

[0056] The intermediate film is immersed in a solution of polyethylene oxide, so that after removal, the polyethylene oxide and ionic liquid are physically bonded to the surface of at least a number of polyolefin fibrils inside the polyolefin substrate. After drying and shaping, the porous membrane is obtained.

[0057] The average volumetric pore size of the porous membrane, compared to the polyolefin porous substrate, is reduced by 40% to 86% (e.g., a range of 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 86%, or any two thereof), and the thickness is increased by less than 1.5% (e.g., a range of 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1%, 0.9%, 0.7%, 0.5%, 0.45%, 0.4%, 0.35%, 0.3%, 0.25%, 0.2%, 0.15%, 0.1%, 0.01%, 0%, or any two thereof).

[0058] In this application, there are no special requirements for the specific type of ionic liquid, as long as it has water solubility and a certain degree of lipophilic effect; in some specific embodiments, the ionic liquid includes any one or a combination of at least two of imidazole ionic liquids, pyridine ionic liquids, alkyl sulfonic acid ionic liquids, quaternary ammonium ionic liquids, quaternary phosphorus ionic liquids, pyrrolidine ionic liquids, or piperidine ionic liquids, and may further be selected as 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl ... The salt is any one or a combination of at least two of the following: 1-butyl-3-methylimidazolium acetate, 1-octadecyl sulfonate sodium salt, 1-pentadecanyl sulfonate sodium salt, 1-ethyl-3-methylimidazolium difluorosulfonylimide salt, 1-butyl-3-methyl difluorosulfonylimide salt, 1-ethyl-3-methyl ditrifluorosulfonylimide salt, 1-butyl-3-methyl ditrifluorosulfonylimide salt, dodecyl quaternary ammonium salt, octadecyl quaternary ammonium salt, 1-ethyl-3-methyl ditrifluorosulfonylimide salt, or N-alkylpyridine.

[0059] In this application, there are no special requirements for the selection of the polyolefin substrate; in some specific embodiments, the polyolefin substrate includes a polyolefin porous membrane.

[0060] Similarly, in this application, there are no special requirements for the type of polyolefin porous membrane; in some specific embodiments, the material of the polyolefin porous membrane includes polyethylene, polypropylene, polybutene, polypentene, polyhexene, polyoctene, polymethylpentene or mixtures thereof, or any one or a combination of at least two of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, heptene or octene.

[0061] In this application, there are no special requirements for the molecular weight of the polyolefin substrate. However, in order to ensure that the obtained porous membrane has better film-forming processability, and at the same time ensure that the obtained porous membrane has better strength and heat resistance, in some specific embodiments, the viscosity-average molecular weight of the polyolefin substrate can be selected as 400,000 to 2,500,000, for example, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,200,000, 1,400,000, 1,600,000, 1,800,000, 2,000,000, 2,200,000, 2,400,000, 2,500,000 or any combination thereof.

[0062] In this application, the viscosity-average molecular weight of the polyolefin substrate can be measured using relevant technical methods, such as gel permeation chromatography (GPC).

[0063] The preparation methods of the second and third specific embodiments will be explained in more detail below. In this application, polyolefin and plasticizer are melt-mixed and extruded, and then cooled to form a precursor film.

[0064] In some embodiments, the plasticizer may be selected from organic compounds that can form a homogeneous solution with polyolefins below their boiling point, such as any one or a combination of at least two of decahydronaphthalene, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decanol, nonanol, diphenyl ether, n-decane, n-dodecane, or paraffin oil, and may further be selected from paraffin oil and / or dioctyl phthalate.

[0065] In some specific embodiments, the plasticizer content in the precursor membrane is 50wt% to 85wt%, for example, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, or any combination thereof, and further optionally 60wt% to 80wt%. When the total plasticizer content in the precursor membrane meets the above range, good compatibility between the polyolefin and the plasticizer can be ensured, which is beneficial for forming a porous membrane with good pore structure and air permeability.

[0066] In some specific embodiments, the melt mixing temperature can be between 160°C and 260°C, for example, a range of 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, or any combination thereof, and more preferably between 180°C and 250°C. When the melt mixing temperature meets the above range, it is beneficial for the polyolefin and plasticizer to have good thermodynamic blending and be extruded in gel form, avoiding breakage during stretching and uneven thickness of the porous membrane during the preparation process.

[0067] In some specific embodiments, the melt mixing can be performed using a single-spindle extruder or a twin-spindle extruder.

[0068] In some specific embodiments, a cooled precursor film can be formed by extruding a composition comprising polyolefin and plasticizer using an extruder equipped with a T-die, and then using a conventional casting or calendering process with water or air cooling.

[0069] In this application, the precursor membrane is stretched to form a stretched membrane containing polyolefin fibrils.

[0070] In some specific implementations, stretching can be performed by using rollers or a tenter frame for successive or simultaneous stretching.

[0071] The stretching temperature can be 60℃ to 200℃, for example, 60℃, 70℃, 80℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃ or any combination thereof, and can be further selected as 80℃ to 140℃.

[0072] In some specific embodiments, the stretching includes transverse stretching and / or longitudinal stretching, and may further be asynchronous stretching in both the transverse and longitudinal directions.

[0073] Here, "longitudinal" refers to the direction parallel to the direction of movement of the polyolefin substrate when preparing the plasticizer-containing polyolefin substrate, and "transverse" refers to the direction perpendicular to the direction of movement of the polyolefin substrate.

[0074] In some specific embodiments, the stretching ratio of the transverse stretching is 8 to 12 times, for example, 8 times, 8.5 times, 9 times, 9.5 times, 10 times, 10.5 times, 11 times, 11.5 times, 12 times or any combination thereof.

[0075] In some specific embodiments, the longitudinal stretching ratio is 5 to 10 times, for example, 5 times, 5.5 times, 6 times, 6.5 times, 7 times, 7.5 times, 8 times, 8.5 times, 9 times, 9.5 times, 10 times or any combination thereof.

[0076] In a second specific embodiment provided in this application, the stretch film is immersed in an extraction solution containing an ionic liquid for extraction to remove the plasticizer and to allow the ionic liquid to adhere to the surface of a plurality of polyolefin fibrils, thereby obtaining an intermediate film.

[0077] In some specific embodiments, the method for extracting the stretch membrane can be single-tank extraction or multi-stage overflow extraction; wherein, multi-stage overflow extraction refers to the process in which the overflow direction of the extractant is opposite to the movement direction of the polyolefin substrate during extraction.

[0078] In some specific embodiments, during the multi-stage overflow extraction process, along the direction of movement of the stretched membrane, the temperature of the subsequent extraction is less than or equal to the temperature of the previous extraction; the temperature of the subsequent extraction in the stepwise extraction is controlled not to be higher than the temperature of the previous extraction. As the plasticizer is extracted, the plasticizer inside the film gradually decreases, causing the overall structure of the film to lose support. Therefore, the extraction temperature is adjusted accordingly as the plasticizer inside the film decreases, which better controls the thermal shrinkage of the film and thus better maintains the microporous structure of the film. At the same time, a suitable extraction temperature can ensure better extraction effect and extraction efficiency, and can better and faster extract the plasticizer inside the film.

[0079] In some specific embodiments, the extraction temperature is 30°C to 55°C, for example, 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 55°C or any combination thereof.

[0080] In some specific embodiments, the extraction can be selected as multi-stage overflow extraction, and at least three extraction tanks are provided along the movement direction of the stretched membrane. The extract in each extraction tank overflows and flows in the opposite direction of the stretch membrane movement, so that the mass percentage of plasticizer extracted in the extract decreases sequentially along the movement direction of the stretch membrane. By setting three or more gradient concentrations of extract, the circulation flow rate of the extract can be reduced, thereby avoiding excessive impact tension on the membrane surface caused by the flow of extract, which could lead to membrane deformation and adverse effects on the pore structure and thermal shrinkage of the final product. In addition, it can also effectively save energy consumption costs in the extraction stage.

[0081] In some specific embodiments, before immersing the intermediate film in a solution containing polyethylene oxide, i.e. after the final extraction, the content of the ionic liquid in the extract is ≤0.5wt%, for example, 0.5wt%, 0.4wt%, 0.3wt%, 0.2wt%, 0.1wt%, or any combination thereof.

[0082] Furthermore, in some specific embodiments, before immersing the intermediate film in a solution containing polyethylene oxide, i.e. after the final extraction, the residual content of plasticizer in the extract is ≤0.3wt%, for example, 0.3wt%, 0.25wt%, 0.2wt%, 0.15wt%, 0.1wt%, 0.5wt%, or any combination thereof.

[0083] In some specific embodiments, before immersing the polyolefin porous substrate with ionic liquid into a solution containing polyethylene oxide, i.e., after immersing the polyolefin porous substrate in a solution containing ionic liquid, the content of ionic liquid in the obtained polyolefin porous substrate with ionic liquid is ≤1 wt%, for example, 1 wt%, 0.9 wt%, 0.8 wt%, 0.7 wt%, 0.6 wt%, 0.5 wt%, 0.4 wt%, 0.3 wt%, 0.2 wt%, 0.1 wt%, or any combination thereof. When the above range is met, on the one hand, it can be ensured that the film has a certain amount of ionic liquid when immersed in the polyethylene oxide aqueous solution, which can help the polyethylene oxide aqueous solution better penetrate into the pores of the intermediate film to better coat the surface of the polyolefin fibrils attached to the film; on the other hand, it can also ensure that the obtained intermediate film has sufficient porous structure for polyethylene oxide to enter, and that the intermediate film has a certain amount of ionic liquid when immersed in the polyethylene oxide aqueous solution, which can help the polyethylene oxide aqueous solution better penetrate into the pores of the intermediate film to better attach to the surface of the polyolefin fibrils attached to the film.

[0084] In this application, an intermediate film or a polyolefin porous substrate coated with ionic liquid is immersed in a solution containing polyethylene oxide. After removal, the polyethylene oxide and ionic liquid are physically bonded to at least the surfaces of multiple polyolefin fibrils inside the polyolefin substrate. After drying and shaping, the porous membrane is obtained.

[0085] In this application, there are no special requirements for the polyethylene oxide. However, in order to ensure the uniformity of the polyethylene oxide loading on the surface of the polyolefin fiber, in some specific embodiments, the kinematic viscosity of the polyethylene oxide can be 120 mPa·s to 1000 mPa·s, for example, 120 mPa·s, 150 mPa·s, 200 mPa·s, 250 mPa·s, 300 mPa·s, 400 mPa·s, 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, 1000 mPa·s, or any combination thereof.

[0086] In this application, the kinematic viscosity of the polyethylene oxide can be tested by the following method: the polyethylene oxide is prepared into a 1% aqueous solution and then measured using a rotational viscometer at a test temperature of 25±2℃ and a pressure of 101kPa.

[0087] In some embodiments, the content of polyethylene oxide in the polyethylene oxide-containing solution can be from 10 wt% to 30 wt%, for example, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 25 wt%, 28 wt%, 30 wt%, or any combination thereof. When the content of the polyethylene oxide solution meets the above range, it is beneficial for the polyethylene oxide to penetrate more fully into the micropores inside the film and to be uniformly dispersed on the surface of the fibrils of the film, while ensuring a certain coating amount, so that the dried film has a suitable pore structure for electrolyte filling.

[0088] In some specific embodiments, the temperature at which the polyethylene oxide-containing solution is immersed is between 20°C and 40°C, for example, 20°C, 22°C, 24°C, 26°C, 28°C, 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, or any combination thereof. Selecting such a suitable immersion temperature facilitates the thermal motion of the polyethylene oxide molecular chains, promotes penetration into the micropores of the film, and ensures that the pore structure of the film is not damaged.

[0089] In some specific embodiments, the immersion time in the polyethylene oxide-containing solution is 30s to 180s, for example, 30s, 40s, 50s, 60s, 70s, 80s, 100s, 120s, 140s, 160s, 180s, or any combination thereof. Selecting the above-mentioned suitable immersion time facilitates the full adhesion of polyethylene oxide to the surface of the polyolefin porous membrane and its physical bonding with the ionic liquid, and controls the formation of a suitable pore structure.

[0090] In some specific embodiments, the proportion of polyethylene oxide adhering in the porous membrane obtained by the preparation method can be 10wt% to 25wt%, for example, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, or any combination thereof. Limiting the proportion of polyethylene oxide adhering in the porous membrane to the above range can ensure that the polyethylene oxide and electrolyte in the micropores of the membrane in the battery cell system are in an ideal ratio, enabling the battery cell to maintain a good balance in terms of safety, ionic conductivity, and interface stability.

[0091] In some specific embodiments, the drying temperature is 20°C to 60°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C or any combination thereof.

[0092] In some specific implementation methods, the drying time is 10s to 30s, for example, 10s, 12s, 14s, 16s, 18s, 20s, 22s, 24s, 26s, 28s, 30s or any combination thereof.

[0093] When the drying temperature and drying time are within the ranges described above, it can be ensured that the solvent in the obtained porous membrane is fully evaporated without affecting the quality of the porous membrane.

[0094] In some specific embodiments, the shaping temperature is 100°C to 135°C, for example, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C or any combination thereof.

[0095] In some specific embodiments, the shrinkage rate of the film after the shaping is completed is ≤0.9%, for example, a range of 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, or any two of these, further ≤0.8%.

[0096] Furthermore, in order to more flexibly adjust the microporosity and air permeability of the final porous membrane, a secondary transverse stretching step can be performed before the shaping process.

[0097] In some specific embodiments, the temperature of the secondary transverse stretching is 120℃ to 140℃, for example, 120℃, 122℃, 124℃, 126℃, 128℃, 130℃, 132℃, 134℃, 136℃, 138℃, 140℃ or any combination thereof.

[0098] In some specific embodiments, the stretching ratio of the secondary stretching is 1.3 to 1.8 times, for example, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times, or any combination thereof.

[0099] The fourth embodiment of this application provides a battery, the battery comprising at least one of the porous membranes described in the first embodiment, the porous membranes prepared by the preparation method described in the second embodiment, or the porous membranes prepared by the preparation method described in the third embodiment.

[0100] In one embodiment, the battery is a liquid battery or a semi-solid battery. To more intuitively demonstrate the technical effects of the porous separator provided in this application, specific implementation examples and data are described below.

[0101] Example 1

[0102] This embodiment provides a porous membrane with an average volumetric pore size of 10 nm and a thickness of 10.12 μm, comprising a porous polyethylene substrate, polyethylene oxide (kinematic viscosity of 500 mPa·s), and 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0103] The polyethylene porous substrate has an average volumetric pore size of 55 nm and a thickness of 10 μm. It contains multiple polyolefin fibers and pores formed by the overlapping of the multiple polyolefin fibers. The 1-ethyl-3-methylimidazolium tetrafluoroborate and polyethylene oxide are attached to at least the surface of the multiple polyolefin fibers inside the polyolefin porous substrate, such that the amount of 1-ethyl-3-methylimidazolium tetrafluoroborate attached in the porous membrane is 0.1 wt% and the amount of polyethylene oxide attached is 20 wt%.

[0104] Furthermore, compared to the porous polyethylene substrate, the average volumetric pore size of the porous membrane is reduced by 82%, and the thickness is increased by 1.2%.

[0105] The method for preparing the porous membrane provided in this embodiment includes the following steps:

[0106] (1) Mix polyethylene resin (viscosity average molecular weight of 1 million) and paraffin oil in a mass ratio of 30:70, add them to a twin-screw extruder, melt and knead at 200℃~220℃ to form a melt, and then cast and cool at 20℃ to form a precursor film.

[0107] (2) The obtained precursor film is subjected to asynchronous stretching in the transverse and longitudinal directions to form a stretched film containing multiple polyolefin fibrils; wherein the transverse stretching temperature is 125℃ and the stretching ratio is 12 times, and the longitudinal stretching temperature is 110℃ and the stretching ratio is 8 times.

[0108] (3) The obtained stretched membrane is passed into an extraction tank for multi-stage overflow extraction. A total of six extraction tanks are set along the direction of membrane movement: extraction tank 1, extraction tank 2, extraction tank 3, extraction tank 4, extraction tank 5, and extraction tank 6. The temperatures of extraction tanks 1-6 are 55℃, 50℃, 45℃, 40℃, 40℃, and 35℃, respectively. Each tank contains an extract solution composed of deionized water and 1-ethyl-3-methylimidazolium tetrafluoroborate. The concentration of 1-ethyl-3-methylimidazolium tetrafluoroborate in the extract solution of each tank is controlled by independent spray overflow flow rates. The mass percentage of acid salts resulted in the following: the content of 1-ethyl-3-methylimidazolium tetrafluoroborate in the extracts of extraction tanks 1-6 was 7.4 wt%, 4.6 wt%, 2.5 wt%, 1.4 wt%, 0.8 wt%, and 0.05 wt%, respectively. The extracts could displace the paraffin oil in the stretched film, allowing the paraffin oil to enter the extraction tanks. The paraffin oil content in the extracts of extraction tanks 1-6 was 6 wt%, 3.5 wt%, 2 wt%, 1.2 wt%, 0.7 wt%, and 0.2 wt%, respectively. After extraction, an intermediate film was obtained.

[0109] (4) The obtained intermediate film is immersed in a 25wt% aqueous solution of polyethylene oxide for wetting. The wetting temperature is 30℃ and the time is 100s. After removal, it is dried at 50℃ for 20s. Then, it is stretched laterally at 130℃ with a stretching ratio of 1.5 times. Finally, it is shaped at 130℃ to ensure that the shrinkage rate of the film after shaping is <0.9%, thus obtaining the porous membrane.

[0110] Example 2

[0111] This embodiment provides a porous membrane, which differs from Embodiment 1 as follows:

[0112] In step (4) of the preparation method, the content of the polyethylene oxide aqueous solution is 10wt%, so that the amount of polyethylene oxide adhering in the obtained porous membrane is 8wt%, the average volume pore size of the obtained porous membrane is 12nm, and the thickness is 10.1μm; and compared with the polyethylene porous substrate, the average volume pore size of the porous membrane is reduced by 78%, and the thickness is increased by 1%.

[0113] All other materials, conditions, and parameters are the same as in Example 1.

[0114] Example 3

[0115] This embodiment provides a porous membrane, which differs from Embodiment 1 as follows:

[0116] In step (4) of the preparation method, the content of the polyethylene oxide aqueous solution is 20wt%, so that the amount of polyethylene oxide adhering in the obtained porous membrane is 15wt%, the average volumetric pore size of the obtained porous membrane is 15nm, and the thickness is 10.1μm; and compared with the polyethylene porous substrate, the average volumetric pore size of the porous membrane is reduced by 73%, and the thickness is increased by 1%.

[0117] All other materials, conditions, and parameters are the same as in Example 1.

[0118] Example 4

[0119] This embodiment provides a porous membrane, which differs from Embodiment 1 as follows:

[0120] In step (4) of the preparation method, the content of the polyethylene oxide aqueous solution is 28wt%, so that the amount of polyethylene oxide adhering in the obtained porous membrane is 24wt%, the average volumetric pore size of the obtained porous membrane is 8nm, and the thickness is 10.14μm; and compared with the polyethylene porous substrate, the average volumetric pore size of the porous membrane is reduced by 85%, and the thickness is increased by 1.4%.

[0121] All other materials, conditions, and parameters are the same as in Example 1.

[0122] Example 5

[0123] This embodiment provides a porous membrane, which differs from Embodiment 1 as follows:

[0124] The average volumetric pore size of the polyolefin substrate is 30 nm, the amount of polyethylene oxide attached to the resulting porous membrane is 17 wt%, the average volumetric pore size of the resulting porous membrane is 10 nm, and the thickness is 10.15 μm; compared with the polyethylene porous substrate, the average volumetric pore size of the porous membrane is reduced by 67%, and the thickness is increased by 1.5%.

[0125] All other materials, conditions, and parameters are the same as in Example 1.

[0126] Example 6

[0127] This embodiment provides a porous membrane, which differs from Embodiment 1 as follows;

[0128] The average volumetric pore size of the polyolefin substrate is 80 nm, the amount of polyethylene oxide attached to the resulting porous membrane is 11 wt%, the average volumetric pore size of the resulting porous membrane is 45 nm, and the thickness is 10.01 μm; compared with the polyethylene porous substrate, the average volumetric pore size of the porous membrane is reduced by 44%, and the thickness is increased by 0.1%.

[0129] All other materials, conditions, and parameters are the same as in Example 1.

[0130] Example 7

[0131] This embodiment provides a porous membrane, which differs from Embodiment 1 in that...

[0132] The content of 1-ethyl-3-methylimidazolium tetrafluoroborate in the extract of extraction tanks 1 to 6 was adjusted to 7.4 wt%, 4.6 wt%, 2.5 wt%, 1.2 wt%, 0.4 wt%, and 0.01 wt%, respectively, so that the proportion of 1-ethyl-3-methylimidazolium tetrafluoroborate adhering to the porous membrane was 0.01 wt%. Other materials, conditions, and parameters were the same as in Example 1.

[0133] Example 8

[0134] This embodiment provides a porous membrane, which differs from Embodiment 1 in that the content of 1-ethyl-3-methylimidazolium tetrafluoroborate in the extract of extraction tanks 1 to 6 is adjusted to 7.4 wt%, 4.6 wt%, 2.5 wt%, 1.2 wt%, 0.8 wt%, and 0.3 wt% respectively, so that the proportion of 1-ethyl-3-methylimidazolium tetrafluoroborate adhering to the porous membrane is 0.5 wt%. Other materials, conditions, and parameters are the same as in Embodiment 1.

[0135] Example 9

[0136] This embodiment provides a porous membrane, which differs from Embodiment 1 in that the content of 1-ethyl-3-methylimidazolium tetrafluoroborate in the extract of extraction tanks 1 to 6 is adjusted to 7.4 wt%, 4.6 wt%, 2.5 wt%, 1.2 wt%, 0.9 wt%, and 0.4 wt% respectively, so that the proportion of 1-ethyl-3-methylimidazolium tetrafluoroborate adhering to the porous membrane is 0.6 wt%. Other materials, conditions, and parameters are the same as in Embodiment 1.

[0137] Comparative Example 1

[0138] This comparative example provides a porous membrane, which differs from Example 6 as follows:

[0139] In step (4) of the preparation method, the content of polyethylene oxide in the aqueous solution of polyethylene oxide is 9wt%, so that the amount of polyethylene oxide adhering in the obtained porous membrane is 2wt%, the average volume pore size of the obtained porous membrane is 60nm, and the thickness is 10.1μm; and compared with the polyethylene porous substrate, the average volume pore size of the porous membrane is reduced by 25%, and the thickness is increased by 1%.

[0140] All other materials, conditions, and parameters are the same as in Example 6.

[0141] Comparative Example 2

[0142] This comparative example provides a porous membrane, which differs from Example 6 as follows:

[0143] In step (4) of the preparation method, the content of polyethylene oxide in the aqueous solution of polyethylene oxide is 35wt%, so that the amount of polyethylene oxide adhering in the obtained porous membrane is 31wt%, the average volumetric pore size of the obtained porous membrane is 10nm, and the thickness is 10.2μm; and compared with the polyethylene porous substrate, the average volumetric pore size of the porous membrane is reduced by 88%, and the thickness is increased by 2%.

[0144] All other materials, conditions, and parameters are the same as in Example 6.

[0145] Comparative Example 3

[0146] This comparative example provides a porous membrane, which differs from Example 1 in that:

[0147] Step (4) of the preparation method includes: directly coating a 25wt% aqueous solution of polyethylene oxide onto the surface of a polyethylene substrate to obtain a porous membrane;

[0148] Furthermore, the amount of polyethylene oxide attached to the obtained porous membrane is 2wt%, the average volumetric pore size of the porous membrane is 50nm, and the thickness is 14μm; compared with the polyethylene porous substrate, the average volumetric pore size of the porous membrane is reduced by 9%, and the thickness is increased by 40%.

[0149] All other materials, conditions, and parameters are the same as in Example 1.

[0150] Comparative Example 4

[0151] This comparative example provides a porous membrane, which differs from Example 1 in that the amount of 1-ethyl-3-methylimidazolium tetrafluoroborate attached to the porous membrane is 0 wt%, while the other materials, conditions and parameters are the same as in Example 1.

[0152] Performance testing:

[0153] (1) Ionic conductivity: Tested in accordance with standard GB-T 36363-2018.

[0154] (2) Puncture strength: Tested in accordance with standard GB-T 36363-2018.

[0155] The porous membranes provided in Examples 1-9 and Comparative Examples 1-4 were tested according to the above test methods, and the test results are shown in Table 1.

[0156] Table 1

[0157] According to the data in Table 1:

[0158] (2) The porous membranes provided in Examples 1-9 possess both high ionic conductivity and high puncture strength. In particular, the porous membranes provided in Examples 1-4 achieve optimal ionic conductivity and puncture strength, with the ionic conductivity reaching as high as 0.75 × 10⁻⁶. -3 S / cm 2 ~0.99×10 -3 S / cm 2 The puncture strength is as high as 543gf to 634gf.

[0159] (2) Compared with Example 6, the average volume pore size reduction rate of the porous membrane provided in Comparative Example 1 is too low, resulting in extremely poor puncture strength; the average volume pore size reduction rate of the porous membrane provided in Comparative Example 2 is too high, resulting in extremely low ionic conductivity.

[0160] (3) Compared with Example 1, Comparative Example 3 directly coated the surface of the substrate with polyethylene oxide solution, resulting in a lower average volume pore size reduction rate and a higher thickness increase rate of the obtained porous membrane, which in turn resulted in poorer ionic conductivity and puncture strength.

[0161] (4) Compared with Example 1, the porous membrane provided in Comparative Example 4 has no ionic liquid residue, which also results in extremely low ionic conductivity.

[0162] The applicant declares that this application illustrates a porous membrane, its preparation method, and its application through the above embodiments; however, this application is not limited to the above process steps, meaning that this application does not necessarily rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the raw materials used, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this application.

Claims

1. A porous membrane comprising a polyolefin porous substrate, an ionic liquid, and polyethylene oxide; The polyolefin porous substrate comprises a plurality of polyolefin fibrils and pores formed by the overlapping of the plurality of polyolefin fibrils, wherein the ionic liquid and polyethylene oxide are attached to at least the surfaces of the plurality of polyolefin fibrils inside the polyolefin porous substrate. wherein Compared to the polyolefin porous substrate, the average volumetric pore size of the porous membrane is reduced by 40% to 86%, and the thickness is increased by less than 1.5%.

2. The porous separator of claim 1, wherein, The amount of ionic liquid attached to the porous membrane is 0.01wt% to 0.5wt%.

3. The porous separator according to claim 1 or 2, wherein, The average volumetric pore size of the porous membrane is 5 nm to 60 nm.

4. The porous separator according to any one of claims 1 to 3, wherein, The thickness of the porous membrane is 1 μm to 25 μm.

5. A method for preparing a porous membrane, comprising the following steps: A porous polyolefin substrate containing multiple polyolefin fibrils is immersed in a solution containing an ionic liquid, such that the ionic liquid adheres to at least the surface of multiple polyolefin fibrils inside the porous polyolefin substrate. The porous polyolefin substrate with ionic liquid is then immersed in a solution containing polyethylene oxide, so that the polyethylene oxide and ionic liquid are physically bonded to at least the surface of multiple polyolefin fibrils inside the polyolefin substrate. After drying and shaping, the porous membrane is obtained. wherein Compared to the polyolefin porous substrate, the average volumetric pore size of the porous membrane is reduced by 40% to 86%, and the thickness is increased by less than 1.5%.

6. A method for preparing a porous membrane, comprising the following steps: Polyolefins and plasticizers are melt-mixed and extruded, and then cooled to form a precursor film. The precursor membrane is stretched to form a stretched membrane containing multiple polyolefin fibrils; The stretched film is immersed in an extraction solution containing an ionic liquid for extraction to remove the plasticizer and to allow the ionic liquid to adhere to the surface of multiple polyolefin fibrils, thereby obtaining an intermediate film. The intermediate film is immersed in a solution containing polyethylene oxide, so that after removal, the polyethylene oxide and ionic liquid are physically bonded to at least the surface of multiple polyolefin fibrils inside the polyolefin substrate. After drying and shaping, the porous membrane is obtained. wherein Compared to the polyolefin porous substrate, the average volumetric pore size of the porous membrane is reduced by 40% to 86%, and the thickness is increased by less than 1.5%.

7. The production method according to claim 5 or 6, wherein The kinematic viscosity of the polyoxyethylene is 120–1000 mPa·s.

8. The production method according to claim 5 or 6, wherein The ionic liquid includes any one or a combination of at least two of the following: imidazole ionic liquids, pyridine ionic liquids, alkyl sulfonic acid ionic liquids, quaternary ammonium ionic liquids, quaternary phosphorus ionic liquids, pyrrolidine ionic liquids, or piperidine ionic liquids. Further, it may be selected as any one or a combination of at least two of the following: 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, sodium 1-octadecyl sulfonate, sodium 1-pentadecanyl sulfonate, 1-ethyl-3-methylimidazolium difluorosulfonylimide, 1-butyl-3-methyldifluorosulfonylimide, 1-ethyl-3-methylditrifluorosulfonylimide, 1-butyl-3-methylditrifluorosulfonylimide, dodecyl quaternary ammonium salt, octadecyl quaternary ammonium salt, 1-ethyl-3-methylditrifluorosulfonylimide imidazolium dinitrile salt, or N-alkylpyridine.

9. The process according to any one of claims 6 to 8, wherein, The extraction is a multi-stage overflow extraction.

10. The production method according to claim 9, wherein In the multi-stage overflow extraction process, at least three extraction tanks are provided along the movement direction of the stretch membrane, and the extract in each extraction tank overflows and flows in the opposite direction of the stretch membrane, so that the mass percentage of the extracted plasticizer in the extract decreases sequentially along the movement direction of the stretch membrane. Optionally, in the multi-stage overflow extraction process, along the direction of movement of the stretched membrane, the temperature of the later extraction is less than or equal to the temperature of the previous extraction.

11. The process according to any one of claims 6 to 10, wherein, The extraction temperature is 30℃~55℃; Optionally, the content of ionic liquid in the extract is ≤0.5 wt% before the intermediate film is immersed in a solution containing polyethylene oxide; Optionally, the residual plasticizer content in the extract is ≤0.3wt% before the intermediate film is immersed in a solution containing polyethylene oxide.

12. The process of any one of claims 6 to 11, wherein, The polyethylene oxide content in the solution is 10 wt% to 30 wt%.

13. A battery, wherein, The battery includes a porous membrane as described in any one of claims 1 to 4 or a porous membrane prepared by the preparation method described in any one of claims 5 to 12.

14. The battery of claim 13, wherein, The battery is a liquid battery or a semi-solid battery.

Images