A nonwoven composite membrane material, its preparation method and its application

Abstract

The application provides a non-woven fabric composite film material, a preparation method and application thereof, and has a three-dimensional net structure, and the film material is composed of super-long carbon nanotubes and a polymer film; wherein the super-long carbon nanotubes are loaded on the fiber surface of the polymer film, and / or a self-supporting network formed by the super-long carbon nanotubes is deposited in the pores of the polymer film. The super-long carbon nanotubes and polyolefin are prepared into a composite film material through an in-situ composite non-woven fabric processing technology, and are used as a lithium battery diaphragm; with the excellent electric conductivity, mechanical property and thermal stability of the carbon nanotubes, the composite film material can improve the ion transmission performance, effectively inhibit the thermal shrinkage of the polyolefin diaphragm, improve the film breaking temperature, greatly improve the mechanical property of the polyolefin fiber film and the holding capacity of the polyolefin fiber film in the electrolyte, and can be used as a new generation of high-performance lithium battery diaphragm, and greatly improve the safety and power density of an electric vehicle.

Description

Technical Field

[0001] This invention relates to the field of carbon material processing and preparation technology, and in particular to a nonwoven composite membrane material, its preparation method, and its application. Background Technology

[0002] In recent years, the development of green energy technologies has promoted the widespread application of lithium-ion batteries in electric vehicles, hybrid vehicles, and green grid energy storage. This has also driven the development of lithium batteries towards high-capacity, high-rate, fast-charging and discharging, and high-safety power batteries.

[0003] Based on the electrolyte, lithium batteries can be divided into liquid lithium batteries and solid lithium batteries. Liquid lithium batteries structurally consist of a positive electrode, a negative electrode, a separator, and an electrolyte. Among these, the separator, often referred to as the third "electrode material," is a microporous membrane made from a non-conductive material. During lithium-ion battery assembly, it is sandwiched between the positive and negative electrodes and completely immersed in the electrolyte. The separator prevents negatively charged electrons from freely passing through the battery, but allows positively charged lithium ions to pass freely. Compared to some new lithium battery separators under development, polyolefin separators such as polypropylene and polyethylene separators have become the most widely used and highest-market-share separator products in the lithium battery market due to their excellent mechanical and chemical stability, high production efficiency, and low production cost.

[0004] A qualified polyolefin separator must provide pores that allow for rapid ion migration. Within a certain range, the higher the porosity of the separator, the more favorable it is for lithium ion penetration, and the greater its ionic conductivity. However, if the pore size of the separator is too large, it will lose its isolation effect on the positive and negative electrode materials. Tiny active particles in the electrode materials may pass through the separator to the other side, causing an internal short circuit in the battery. At the same time, polyolefin separators have poor retention of electrolyte solution. Excessive porosity often leads to a decrease in the mechanical properties of the separator, resulting in shrinkage or melting deformation at high temperatures, which can easily lead to an internal short circuit in the battery, and subsequently cause the battery to catch fire or explode. Coating the surface of the polyolefin separator with ceramic powder is the most common method used in industry to solve the thermal stability of the separator. However, the bonding force between ceramic powder and the separator is usually weak, and additional polymer binders are usually required. The use of binders significantly increases the thickness of the separator, which is not conducive to the efficient transport of ions within the separator.

[0005] As lithium battery manufacturing technology continues to improve, the requirements for separator performance will also become increasingly stringent. How to maximize separator porosity and increase pore size without compromising positive and negative electrode isolation or sacrificing mechanical properties is a key technical challenge that needs to be addressed in developing next-generation high-power charge / discharge batteries. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, this invention provides a nonwoven composite membrane material, its preparation method, and its application. This invention utilizes nonwoven fabric processing technology to in-situ composite high aspect ratio ultra-long carbon nanotubes with polyolefin fibers, developing a new generation of high-safety, high-charge-discharge power nonwoven composite membrane material that can be used as a separator.

[0007] The specific details of the invention are as follows:

[0008] In a first aspect, the present invention provides a nonwoven composite membrane material having a three-dimensional network structure, wherein the membrane material is composed of ultralong carbon nanotubes and a polymer membrane; wherein the ultralong carbon nanotubes are loaded on the fiber surface of the polymer membrane, and / or

[0009] A self-supporting network formed by the ultralong carbon nanotubes is deposited in the pores of the polymer film;

[0010] The polymer film is composed of one or more of polypropylene, polypropylene derivatives, polyethylene, and polyethylene derivatives.

[0011] The diameter of the ultra-long carbon nanotube bundle is less than 100 mm, and the length of the ultra-long carbon nanotube is greater than 1 mm.

[0012] Optionally, the ultralong carbon nanotubes and the polymer film are bonded together by van der Waals forces.

[0013] Optionally, the porosity of the three-dimensional mesh structure is 80-90%.

[0014] In a second aspect, the present invention provides a method for preparing the nonwoven composite film material described in the first aspect above, the method comprising:

[0015] Carbon nanotube powder is placed in an air jet mill and subjected to high-speed air jet shearing to obtain flocculent carbon nanotubes with a tube bundle diameter of less than 100 mm and a length of more than 1 mm.

[0016] After mixing polymer meltblown material with a mass ratio of (90-98):(2-10) with electret masterbatch, the mixture is fed into a twin-screw extruder; the flocculent carbon nanotubes are then fed into a continuous feeding device.

[0017] After the twin-screw extruder shears and blends the feed material, multiple die heads extrude polymer fibers onto the spinneret at 120–250°C. Simultaneously, the continuous feeding device continuously feeds the flocculent carbon nanotubes perpendicular to the extrusion direction of the polymer fibers, so that the polymer fibers and the flocculent carbon nanotubes come into contact and are jointly deposited onto the spinneret by hot air traction to form the precursor of the composite membrane material.

[0018] The precursor, collected and conveyed by the circular mesh, is subjected to multiple rolling, slitting, and winding processes to obtain a nonwoven composite membrane material composed of ultra-long carbon nanotubes and polymer membrane.

[0019] Optionally, the feeding rate of the flocculent carbon nanotubes is maintained at 2.0-4.5 g / min.

[0020] Optionally, the arrayed carbon nanotubes are single carbon nanotubes or bundles of carbon nanotubes;

[0021] The individual carbon nanotubes have a diameter of 1.5–8.0 nm and an aspect ratio of 10. 5 ~10 6 ;

[0022] The diameter of the carbon nanotube bundles is 10–1000 mm.

[0023] Optionally, the high-speed airflow shearing operating frequency of the airflow pulverizer is 50-300Hz, and the processing time is 20-300s.

[0024] Optionally, the polymer meltblown material comprises: a polymer, a nucleating agent, a molecular weight regulator, and an antioxidant; wherein the polymer is one or more of polypropylene, polypropylene derivatives, polyethylene, and polyethylene derivatives.

[0025] Optionally, the melt flow index of the polymer meltblown material is 1200-1700 g / 10 min.

[0026] Thirdly, the present invention provides an application of the nonwoven composite membrane material described in the first aspect above, wherein the nonwoven composite membrane material is used as a separator material in the assembly and preparation of lithium batteries.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] This invention provides a nonwoven composite membrane material with a three-dimensional network structure, composed of ultra-long carbon nanotubes and a polymer membrane. The ultra-long carbon nanotubes are loaded onto the fiber surface of the polymer membrane, and / or a self-supporting network formed by the ultra-long carbon nanotubes is deposited in the pores of the polymer membrane. This invention prepares the composite membrane material by in-situ composite nonwoven fabric processing of ultra-long carbon nanotubes and polyolefins, fully utilizing the performance advantages of both carbon nanotubes and polyolefins. The self-supporting network spontaneously formed by the high aspect ratio ultra-long carbon nanotubes exhibits strong van der Waals interactions with the polyolefin, enabling tight bonding without adhesives.

[0029] More importantly, the nonwoven composite membrane material provided by this invention, when used as a separator material in lithium batteries, leverages the excellent conductivity, mechanical properties, and thermal stability of carbon nanotubes to effectively suppress the thermal shrinkage of the polyolefin separator while improving ion transport performance and increasing the membrane rupture temperature. This significantly enhances the mechanical properties of the polyolefin fiber membrane and its retention capacity in the electrolyte. Furthermore, the bilayer composite membrane structure formed by ultra-long carbon nanotubes and polyolefin enables the composite separator to achieve thermal pore-closing. After the polyolefin membrane melts, the melted polyolefin resin fills the three-dimensional pores in the ultra-long carbon nanotube fiber network, effectively isolating the positive and negative electrodes and cutting off the current, preventing thermal runaway of the lithium battery and ensuring safe battery operation. Therefore, the nonwoven composite membrane material provided by this invention can serve as a new generation of high-performance lithium battery separators, significantly improving the safety and power density of electric vehicles. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 A flowchart illustrating the preparation method of the nonwoven composite membrane material provided in an embodiment of the present invention is shown.

[0032] Figure 2 The image shows a scanning electron microscope (SEM) characterization of the flocculent carbon nanotubes provided in an embodiment of the present invention.

[0033] Figure 3 An optical microscope characterization image of the nonwoven composite film material provided in an embodiment of the present invention is shown;

[0034] Figure 4 A set of optical microscope characterization images of the nonwoven composite film material provided in the embodiments of the present invention are shown. Detailed Implementation

[0035] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0036] Specific experimental steps or conditions are not specified in the examples; however, they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products.

[0037] Ultralong carbon nanotubes possess excellent mechanical properties, with a strength up to 100 times that of steel and a theoretical Young's modulus of up to 5 TPa, making them ideal fillers for preparing composite materials with superior mechanical properties. Furthermore, ultralong carbon nanotubes exhibit good electrical conductivity, ranging from 1000 to 2000 S / cm, enabling the preparation of conductive composite materials with low percolation values ​​and high conductivity. Their extremely high aspect ratios, ranging from 100 to 1,000,000, mean that adding even small amounts of ultralong carbon nanotubes can significantly improve the mechanical, electrical, and thermal properties of materials. Importantly, they possess excellent flexibility, and their mechanical properties are not compromised when mixed with other materials and subjected to shear or other external forces.

[0038] Therefore, this invention proposes to manufacture a composite separator by processing ultra-long carbon nanotubes and polyolefins using non-woven fabric technology. The performance advantages of carbon nanotubes are leveraged to modify the polyolefin material, resulting in a lithium battery separator with high safety and power density. A self-supporting network spontaneously formed by high aspect ratio ultra-long carbon nanotubes is deposited within the pores of the polyolefin fibers. This all-carbon structure exhibits strong van der Waals interactions with the polyolefin, enabling tight bonding without binders. Simultaneously, relying on the excellent conductivity, mechanical properties, and thermal stability of carbon nanotubes, this composite structure can effectively suppress the thermal shrinkage of the polyolefin separator while improving ion transport performance, increasing the membrane rupture temperature, thereby significantly enhancing the mechanical properties of the polyolefin fiber membrane and its retention capacity in the electrolyte. Furthermore, the double-layer separator structure enables the composite separator to achieve thermal pore-closing. After the polyolefin membrane melts, the melted polyolefin resin fills the three-dimensional pores in the ultra-long carbon nanotube fiber network, effectively isolating the positive and negative electrodes, cutting off the current, preventing thermal runaway of the lithium battery, and thus ensuring safe battery operation. Specific implementation details are as follows:

[0039] In a first aspect, the present invention provides a nonwoven composite membrane material having a three-dimensional network structure, wherein the membrane material is composed of ultra-long carbon nanotubes and a polymer membrane; wherein the ultra-long carbon nanotubes are loaded on the fiber surface of the polymer membrane, and / or a self-supporting network formed by ultra-long carbon nanotubes is negatively deposited in the pores of the polymer membrane.

[0040] In specific implementation, the polymer membrane selected in this embodiment of the invention is composed of one or more of polypropylene, polypropylene derivatives, polyethylene, and polyethylene derivatives. In this embodiment, the polymer membrane is prepared by melt-blowing, that is, the polymer membrane is formed by stacking ultrafine fibers formed by melt spinning of polymer, and its surface has a large number of pores. Since the diameter of the ultralong carbon nanotubes selected in this embodiment of the invention is less than 100 mm and the length of the ultralong carbon nanotubes is greater than 1 mm, these ultralong carbon nanotubes can form strong van der Waals interactions with polyolefins. This allows ultralong carbon nanotubes to be loaded on the surface of polyolefin ultrafine fibers without a binder, and / or the self-supporting network spontaneously formed by ultralong carbon nanotubes to be deposited in the pores formed by the stacking of polyolefin hydrocarbon ultrafine fibers without falling off.

[0041] Secondly, the present invention provides a method for preparing the nonwoven composite film material described in the first aspect above. Figure 1 A flowchart illustrating the preparation method of the nonwoven composite film material provided in an embodiment of the present invention is shown, as follows: Figure 1 As shown, the preparation method includes:

[0042] Step 1: Place the carbon nanotube powder into an air jet mill, and after high-speed air jet shearing, collect flocculent carbon nanotubes with a tube bundle diameter of less than 100 mm and a length of more than 1 mm.

[0043] In practice, the carbon nanotube powder used in this step is a commercially available arrayed carbon nanotube prepared in large quantities using a nano-aggregation fluidization method. Specifically, the arrayed carbon nanotubes have a diameter of 1.5–8.0 nm and an aspect ratio of 10. 5 ~10 6 This process involves pulverizing single carbon nanotubes or carbon nanotube bundles with diameters ranging from 10 to 1000 mm. The process utilizes airflow shear dispersion technology to break down carbon nanotube aggregates or arrayed carbon nanotubes (ultrafine particles). The basic principle is that during feeding, several high-pressure airflows are simultaneously injected into the airflow mill. At the confluence of these airflows, the material to be pulverized is subjected to shearing, collision, compression, and friction under the powerful supersonic airflow, resulting in instantaneous pulverization. The high-speed airflow shearing operates at a frequency of 50–300 Hz, with a processing time of 20–300 s. The pulverized material enters a classification chamber, where it is separated under centrifugal force. Products with acceptable particle sizes are collected, while larger particles return to the pulverizing chamber for further pulverization. For carbon nanotube aggregates or arrayed carbon nanotubes, this method effectively breaks down macroscopic carbon nanotubes into flocculent carbon nanotubes while maintaining the loose structure of secondary aggregates or bundles. Furthermore, airflow shearing can remove most of the residual catalyst support from the carbon nanotube product, achieving a purification effect.

[0044] Step 2: Mix the polymer meltblown material with electret masterbatch at a mass ratio of (90-98):(2-10) and feed it into a twin-screw extruder; feed the flocculent carbon nanotubes into a continuous feeding device.

[0045] Step 3: After the twin-screw extruder shears and blends the feed material, multiple die heads extrude polymer fibers onto the spinneret at 120-250°C. At the same time, a continuous feeding device continuously feeds flocculent carbon nanotubes perpendicular to the polymer fiber extrusion direction, so that the polymer fibers and flocculent carbon nanotubes come into contact and are jointly deposited onto the spinneret by hot air traction, forming the precursor of the composite membrane material.

[0046] Step 4: The precursor collected and conveyed by the circular mesh is rolled, slit and wound into rolls multiple times to obtain a nonwoven composite membrane material composed of ultra-long carbon nanotubes and polymer membrane.

[0047] In specific implementation, the flocculent carbon nanotubes obtained after step 1 have a tube bundle diameter of less than 100 mm and a length of more than 1 mm. They are then further used in the preparation process of nonwoven membrane materials (steps 2-4). Specifically, a specific ratio (mass ratio of (90-98):(2-10)) of polymer meltblown material is mixed with electret masterbatch, and then fed into a screw extruder via a feeding device. The extruded and plasticized melt is precisely metered by a metering pump and sent into a special melt distribution chamber. After rectification, it enters the spinning melt pool, is sprayed into filaments through spinning micropores, and then stretched into ultrafine fibers under the action of a high-speed, high-pressure hot air stream. Simultaneously, flocculent carbon nanotubes are fed into a continuous feeding device, which continuously feeds the flocculent carbon nanotubes at a feeding rate of 2.0-4.5 g / min, perpendicular to the extrusion direction of the ultrafine fibers (polymer fibers). During this process, the polymer fibers and flocculent carbon nanotubes come into contact in the form of an aerosol and are jointly deposited onto the spinneret by hot air traction, forming the precursor of the composite membrane material. The precursor of the composite membrane material is further rolled, slit, and wound into rolls to obtain a nonwoven composite membrane material composed of ultralong carbon nanotubes and polymer membranes.

[0048] In some embodiments, the polymer meltblown material comprises: a polymer (selected from one or more of polypropylene, polypropylene derivatives, polyethylene, and polyethylene derivatives), a nucleating agent, a molecular weight regulator, and an antioxidant, wherein the melt flow index of the polymer meltblown material is 1200–1700 g / 10 min.

[0049] Thirdly, the present invention provides an application of the nonwoven composite membrane material of the first aspect above, wherein the nonwoven composite membrane material is used as a separator material in the assembly and preparation of lithium batteries.

[0050] To enable those skilled in the art to better understand this application, the following embodiments are provided to illustrate in detail a nonwoven composite membrane material, its preparation method, and its application.

[0051] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the examples are commercially available.

[0052] Example 1:

[0053] (1) Large-diameter ultra-long carbon nanotube bundles are dispersed into flocculent carbon nanotubes by airflow shearing.

[0054] Weigh 1.0g of the carbon nanotube array prepared in large quantities with a length of more than 5mm and place it into an air jet mill;

[0055] Dispersed carbon nanotube samples were collected from the lower drums of a cyclone separator and a pulse dust collector after being sheared by high-speed airflow for 30 seconds at a rotational frequency of 230 Hz. The coarse carbon nanotube samples collected in the cyclone separator drum were then fed into an air jet mill and sheared by high-speed airflow for 30 seconds at a working frequency of 230 Hz, after which the dispersed flocculent carbon nanotubes were collected. Because the carbon nanotubes in the bundle have high strength along the c-axis, and only weak van der Waals forces exist between the bundles, when the carbon nanotube array is sheared, it is torn into smaller bundles along the c-axis. Thus, flocculent carbon nanotubes are obtained through shearing.

[0056] Figure 2 The following is a scanning electron microscope (SEM) characterization image of the flocculent carbon nanotubes provided in an embodiment of the present invention, as shown in the figure. Figure 2 As shown, flocculent carbon nanotubes are composed of carbon nanotube bundles with a diameter of 80-100 mm and a length still on the order of millimeters. Their apparent density is 12-18 g / L, and the carbon nanotubes still have good orientation within the bundles.

[0057] (2) Preparation of ultra-long carbon nanotube / polypropylene nonwoven composite membrane material by nonwoven fabric process

[0058] Polypropylene meltblown material (melt index 1450 g / 10 min) and electret masterbatch are premixed in a high-speed mixer for 20 min at a ratio of 97:3. The uniformly mixed material is fed into a twin-screw extruder by a feeding system. The temperatures of the twin screws 1-7 are set to 170℃, 185℃, 210℃, 220℃, 230℃, 230℃, and 230℃. The pipe temperature is set to 230℃. The hot air temperature is set to 260℃. The hot air volume is set to 950 rpm, the floor exhaust fan volume is set to 850 rpm, and the cold air volume is set to 850 rpm. The electret equipment voltage is 50KV and the current is 6.5mA.

[0059] The fed material is sheared and blended by a twin-screw extruder and then extruded in parallel by multiple sets of die heads. At the same time, the flocculent carbon nanotubes obtained by dispersion in step (1) above are continuously fed through the top of a vertical conveying pipe at a feeding speed of 2.0 g / min. The ultra-long carbon nanotube powder is discharged from the bottom and mixed with the extruded material. It is then deposited onto the spinneret by hot air traction. After being collected and conveyed by a circular mesh, it is subjected to high voltage electrostatic discharge and then cut and rolled up to prepare an ultra-long carbon nanotube / polypropylene nonwoven composite membrane material.

[0060] Figure 3 An optical microscope characterization image of the nonwoven composite film material provided in an embodiment of the present invention is shown. Figure 4 A set of optical microscope characterization images of the nonwoven composite film material provided in the embodiments of the present invention are shown, wherein, Figure 4 (left) and Figure 4 (Right) These are optical microscope characterizations under different focal planes. For example... Figure 3 , Figure 4 As shown, combined with optical microscopy characterization, it can be found that the loading mode of ultralong carbon nanotube powder and polypropylene fiber can be adsorption on the surface of polypropylene fiber (…). Figure 3 Alternatively, it can form a self-supporting network that fills the pores of the polypropylene fiber network. Figure 4 ). And, from Figure 4 A comparison of a set of optical microscope images shows that polypropylene fibers and ultralong carbon nanotubes exhibit obvious orientation on a single-layer network in the same plane. The fiber networks in different planes have different orientations, and the fiber networks in different directions form a three-dimensional mesh membrane structure with rich pores (porosity of about 85%).

[0061] Example 2:

[0062] (1) Small-diameter ultra-long carbon nanotube bundles are dispersed into flocculent carbon nanotubes by airflow shearing.

[0063] 2.0 g of a large-scale carbon nanotube array with a length exceeding 3 mm was weighed and placed into an air jet mill. The array was sheared by high-speed airflow for 120 s at a rotation frequency of 280 Hz. The dispersed carbon nanotube samples were collected from the lower barrels of a cyclone separator and a pulse dust collector, respectively. The coarse carbon nanotube sample collected from the cyclone separator barrel was then fed back into the air jet mill and sheared by high-speed airflow for 120 s at a rotation frequency of 280 Hz. The dispersed carbon nanotube sample was then collected. Because the carbon nanotubes in the bundle have high strength along the c-axis, and only weak van der Waals forces exist between the bundles, the carbon nanotube array was torn into smaller bundles along the c-axis when sheared. Thus, flocculent carbon nanotubes were obtained through shearing.

[0064] The resulting flocculent carbon nanotubes consist of bundles of carbon nanotubes with a diameter of 10-20 mm and a length still on the order of millimeters. Their apparent density is 3-5 g / L, and the carbon nanotubes in the bundles still have good orientation.

[0065] Further extending the processing time revealed that the diameter of the carbon nanotube bundles within the resulting flocculent carbon nanotubes no longer decreased significantly. This is mainly due to limitations imposed by the rotational speed and rotor thickness, making it difficult to further tear the carbon nanotube bundles into smaller fragments. Furthermore, the excellent flexibility of the carbon nanotube bundles allows the impact force to be released through bending.

[0066] (2) Preparation of ultra-long carbon nanotube / polypropylene nonwoven composite membrane material by nonwoven fabric process

[0067] Polypropylene meltblown material (melt index 1650 g / 10 min) and electret masterbatch are premixed in a high-speed mixer for 20 min at a ratio of 97:3. The uniformly mixed material is fed into a twin-screw extruder by a feeding system. The temperatures of the twin screws 1-7 are set to 170℃, 185℃, 210℃, 220℃, 230℃, 230℃, and 230℃; the pipe temperature is set to 230℃; the hot air temperature is set to 260℃; the hot air volume is set to 950 rpm; the floor exhaust fan volume is set to 850 rpm; and the cold air volume is set to 850 rpm. The electret equipment voltage is 50KV and the current is 6.5mA.

[0068] The fed material is sheared and blended by a twin-screw extruder and then extruded in parallel by multiple sets of die heads. At the same time, the flocculent carbon nanotubes obtained by dispersion in step (1) above are continuously fed through the top of a vertical conveying pipe at a feeding speed of 2.0 g / min. The ultra-long carbon nanotube powder is discharged from the bottom and mixed with the extruded material. It is then deposited onto the spinneret by hot air traction. After being collected and conveyed by a circular mesh, it is subjected to high voltage electrostatic discharge and then cut and rolled up to prepare an ultra-long carbon nanotube / polypropylene nonwoven composite membrane material.

[0069] The scanning electron microscope (SEM) characterization images of the flocculent carbon nanotubes obtained in this embodiment, as well as the optical microscope characterization images of the nonwoven composite membrane material, are largely the same as those in Example 1 (porosity approximately 80%), and will not be repeated here.

[0070] Example 3:

[0071] (1) Large-diameter ultra-long carbon nanotube bundles are dispersed into flocculent carbon nanotubes by airflow shearing.

[0072] Weigh 2.5g of the carbon nanotube array prepared in large quantities with a length of more than 5mm and place it into an air jet mill;

[0073] Dispersed carbon nanotube samples were collected from the lower drums of a cyclone separator and a pulse dust collector after being sheared by high-speed airflow for 60 seconds at a rotational frequency of 230 Hz. The coarse carbon nanotube samples collected in the cyclone separator drum were then fed into an air jet mill and sheared by high-speed airflow for 60 seconds at a working frequency of 230 Hz, after which the dispersed flocculent carbon nanotubes were collected. Because the carbon nanotubes in the bundle have high strength along the c-axis, and only weak van der Waals forces exist between the bundles, when the carbon nanotube array is sheared, it is torn into smaller bundles along the c-axis. Thus, flocculent carbon nanotubes are obtained through shearing.

[0074] (2) Preparation of ultra-long carbon nanotube / polypropylene nonwoven composite membrane material by nonwoven fabric process

[0075] Polypropylene meltblown material (melt index 1550 g / 10 min) and electret masterbatch are premixed in a high-speed mixer for 25 min at a ratio of 97:3. The uniformly mixed material is fed into a twin-screw extruder by a feeding system. The temperatures of the twin screws 1-7 are set to 170℃, 185℃, 210℃, 220℃, 230℃, 230℃, and 230℃; the pipe temperature is set to 230℃; the hot air temperature is set to 260℃; the hot air volume is set to 950 rpm; the floor exhaust fan volume is set to 850 rpm; and the cold air volume is set to 850 rpm. The electret equipment voltage is 50KV and the current is 6.5mA.

[0076] The fed material is sheared and blended by a twin-screw extruder and then extruded in parallel by multiple sets of die heads. At the same time, the flocculent carbon nanotubes obtained by dispersion in step (1) above are continuously fed through the top of a vertical conveying pipe at a feeding speed of 3.5 g / min. The ultra-long carbon nanotube powder is discharged from the bottom and mixed with the extruded material. It is then deposited onto the spinneret by hot air traction. After being collected and conveyed by a circular mesh, it is subjected to high voltage electrostatic discharge and then cut and rolled up to prepare an ultra-long carbon nanotube / polypropylene nonwoven composite membrane material.

[0077] The scanning electron microscope (SEM) characterization images of the flocculent carbon nanotubes obtained in this embodiment, as well as the optical microscope characterization images of the nonwoven composite membrane material, are largely the same as those in Example 1 (porosity approximately 89%), and will not be repeated here.

[0078] Example 4:

[0079] (1) Large-diameter ultra-long carbon nanotube bundles are dispersed into flocculent carbon nanotubes by airflow shearing.

[0080] Weigh 2.5g of the carbon nanotube array prepared in large quantities with a length of more than 8mm and place it into an air jet mill;

[0081] Dispersed carbon nanotube samples were collected from the lower drums of a cyclone separator and a pulse dust collector after being sheared by high-speed airflow for 100 seconds at a rotational frequency of 300 Hz. The coarse carbon nanotube samples collected in the cyclone separator drum were then fed into an air jet mill and sheared by high-speed airflow for 100 seconds at a working frequency of 300 Hz, resulting in the collection of dispersed flocculent carbon nanotubes. Because the carbon nanotubes in the bundle have high strength along the c-axis, and only weak van der Waals forces exist between the bundles, when the carbon nanotube array is sheared, it is torn into smaller bundles along the c-axis. Thus, flocculent carbon nanotubes are obtained through shearing.

[0082] (2) Preparation of ultra-long carbon nanotube / polyethylene composite membrane by non-woven fabric process

[0083] Polyethylene meltblown material (melt index 1250-1500 g / 10 min) and electret masterbatch are premixed in a high-speed mixer for 15 min at a ratio of 96:4. The uniformly mixed material is fed into a twin-screw extruder by a feeding system. The temperatures of the twin screws 1-7 are set to 136℃, 150℃, 175℃, 186℃, 195℃, 195℃, and 195℃; the pipe temperature is set to 195℃; the hot air temperature is set to 225℃; the hot air volume is set to 800 rpm; the floor exhaust fan volume is set to 650 rpm; and the cold air volume is set to 650 rpm. The electret equipment voltage is 50KV and the current is 5.0mA.

[0084] The fed material is sheared and blended by a twin-screw extruder and then extruded in parallel by multiple sets of die heads. At the same time, the flocculent carbon nanotubes obtained in step (1) above are continuously fed from the top of the vertical conveying pipe at a feeding speed of 4.5 g / min. The ultra-long carbon nanotube powder is discharged from the bottom and mixed with the extruded material. It is then deposited onto the spinneret by hot air traction. After being collected and conveyed by the circular mesh, it is subjected to high voltage energization and then cut and wound into rolls to prepare an ultra-long carbon nanotube / polyethylene composite nonwoven membrane.

[0085] The scanning electron microscope (SEM) characterization images of the flocculent carbon nanotubes obtained in this embodiment, as well as the optical microscope characterization images of the nonwoven composite membrane material, are largely the same as those in Example 1 (porosity approximately 82%), and will not be repeated here.

[0086] Example 5:

[0087] (1) Small-diameter ultra-long carbon nanotube bundles are dispersed into flocculent carbon nanotubes by airflow shearing.

[0088] 2.5g of a large-scale carbon nanotube array with a length exceeding 3mm was weighed and placed in an air jet mill. The array was sheared by a high-speed airflow for 120s at a rotation frequency of 280Hz. The dispersed carbon nanotube samples were collected from the lower barrels of a cyclone separator and a pulse dust collector, respectively. The coarse carbon nanotube sample collected from the cyclone separator barrel was then fed back into the air jet mill and sheared by a high-speed airflow for 120s at a rotation frequency of 280Hz. The dispersed carbon nanotube sample was then collected. Because the carbon nanotubes in the bundle have high strength along the c-axis, and only weak van der Waals forces exist between the bundles, the carbon nanotube array is torn into smaller bundles along the c-axis when sheared. Thus, flocculent carbon nanotubes were obtained through shearing.

[0089] The resulting flocculent carbon nanotubes consist of bundles of carbon nanotubes with a diameter of 10-20 mm and a length still on the order of millimeters. Their apparent density is 3-5 g / L, and the carbon nanotubes in the bundles still have good orientation.

[0090] Further extending the processing time revealed that the diameter of the carbon nanotube bundles within the resulting flocculent carbon nanotubes no longer decreased significantly. This is mainly due to limitations imposed by the rotational speed and rotor thickness, making it difficult to further tear the carbon nanotube bundles into smaller fragments. Furthermore, the excellent flexibility of the carbon nanotube bundles allows the impact force to be released through bending.

[0091] (2) Preparation of ultra-long carbon nanotube / polyethylene composite membrane by non-woven fabric process

[0092] Polyethylene meltblown material (melt index 1500g / 10min) and electret masterbatch are premixed in a high-speed mixer for 15min at a ratio of 96:4. The uniformly mixed material is fed into a twin-screw extruder by a feeding system. The temperatures of the twin screws 1-7 are set to 136℃, 150℃, 175℃, 186℃, 195℃, 195℃, and 195℃; the pipe temperature is set to 195℃; the hot air temperature is set to 225℃; the hot air volume is set to 800rpm; the floor exhaust fan volume is set to 650rpm; and the cold air volume is set to 650rpm. The electret equipment voltage is 50KV and the current is 5.0mA.

[0093] The fed material is sheared and blended by a twin-screw extruder and then extruded in parallel by multiple sets of die heads. At the same time, the flocculent carbon nanotubes obtained in step (1) above are continuously fed from the top of the vertical conveying pipe at a feeding speed of 3.0 g / min. The ultra-long carbon nanotube powder is discharged from the bottom and mixed with the extruded material. It is then deposited onto the spinneret by hot air traction. After being collected and conveyed by the circular mesh, it is subjected to high voltage energization and then cut and rolled up to prepare an ultra-long carbon nanotube / polyethylene composite nonwoven membrane.

[0094] The scanning electron microscope (SEM) characterization images of the flocculent carbon nanotubes obtained in this embodiment, as well as the optical microscope characterization images of the nonwoven composite membrane material, are largely the same as those in Example 1 (porosity approximately 90%), and will not be repeated here.

[0095] The above provides a detailed description of the nonwoven composite membrane material, its preparation method, and its application provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A nonwoven composite film material, characterized by, The film material has a three-dimensional net structure, and is composed of super-long carbon nanotubes and a polymer film; wherein the super-long carbon nanotubes are loaded on the fiber surface of the polymer film, and / or A self-supporting network formed by the super-long carbon nanotubes is deposited in the pores of the polymer film; The polymer film is composed of one or more of polypropylene, a derivative material of polypropylene, polyethylene and a derivative material of polyethylene; The bundle diameter of the super-long carbon nanotubes is less than 100 mm, and the length of the super-long carbon nanotubes is greater than 1 mm; The preparation method of the non-woven fabric composite film material comprises: The carbon nanotube powder is placed in an airflow pulverizer, and after high-speed airflow shearing treatment, flocculent carbon nanotubes with a bundle diameter less than 100 mm and a length greater than 1 mm are collected; The polymer meltblown material with a mass ratio of (90-98):(2-10) is mixed with the electret master batch and then fed into a double-screw extruder; the flocculent carbon nanotubes are fed into a continuous feeding device; After shearing and blending of the feeding material by the double-screw extruder, a plurality of groups of machine heads extrude polymer fibers at 120-250 ℃ to the spinneret plate, and the continuous feeding device continuously feeds the flocculent carbon nanotubes vertically to the extrusion direction of the polymer fibers, so that the polymer fibers and the flocculent carbon nanotubes are in contact and are jointly deposited on the spinneret plate by hot air traction to form a precursor of the composite film material; The precursor collected and transported by a rotary screen is rolled up after multiple rollings and slitting, thereby obtaining the non-woven fabric composite film material of the super-long carbon nanotubes and the polymer film.

2. The nonwoven composite film material of claim 1, wherein The super-long carbon nanotubes and the polymer film are combined with each other by van der Waals force.

3. The nonwoven composite film material of claim 1, wherein The porosity of the three-dimensional net structure is 80-90%.

4. The nonwoven composite film material of claim 1, wherein The feeding speed of the continuously fed flocculent carbon nanotubes is maintained at 2.0-4.5 g / min.

5. The nonwoven composite film material of claim 1, wherein The carbon nanotubes are single carbon nanotubes or carbon nanotube bundles. The single carbon nanotube has a diameter of 1.5-8.0 nm and an aspect ratio of 10 5 ~10 6 ; The bundle diameter of the carbon nanotube is 10-1000 mm.

6. The nonwoven composite film material of claim 1, wherein The high-speed airflow shearing working frequency of the airflow pulverizer is 50-300 Hz, and the processing time is 20-300 s.

7. The nonwoven composite film material of claim 1, wherein The composition of the polymer meltblown material comprises polymer, nucleating agent, molecular weight regulator and antioxidant; wherein the polymer is one or more of polypropylene, a derivative material of polypropylene, polyethylene and a derivative material of polyethylene.

8. The nonwoven composite film material of claim 7, wherein, The melt index of the polymer meltblown material is 1200-1700 g / 10min.

9. Use of the nonwoven composite film material according to any one of claims 1 to 8, characterized in that The non-woven fabric composite film material is used as a separator material for assembling and preparing a lithium battery.

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