Non-woven fabric composite membrane material, and preparation method therefor and use thereof

Abstract

A non-woven fabric composite membrane material, and a preparation method therefor and a use thereof. The non-woven fabric composite membrane material has a three-dimensional network structure, and the membrane material is composed of ultra-long carbon nanotubes and a high polymer membrane, wherein the ultra-long carbon nanotubes are loaded on the fiber surface of the high polymer membrane, and / or a self-supporting network formed by the ultra-long carbon nanotubes is deposited in pores of the high polymer membrane. The ultra-long carbon nanotubes and polyolefin are prepared into a composite membrane material by means of an in-situ composite non-woven fabric processing technology as a lithium battery separator, and by means of excellent conductivity, mechanical properties and thermal stability of the carbon nanotubes, the composite membrane material effectively inhibits the heat shrinkage of polyolefin separators and increases the separator breaking temperature while improving the ion transport properties, thereby improving the mechanical properties of polyolefin fiber membranes and the holding capacity of polyolefin fiber membranes in an electrolyte, and improving the safety and the power density of electric vehicles.

Description

Non-woven composite membrane material, preparation method and application thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese patent application number 202410046894.1, filed with the Patent Office of China on January 11, 2024, entitled “A non-woven composite membrane material, preparation method and application thereof,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of carbon material processing and preparation, and in particular to a non-woven composite membrane material, a preparation method and applications thereof. Background Art

[0004] In recent years, the development of green energy technologies has promoted the widespread application of lithium-ion batteries in electric vehicles, hybrid vehicles, green grid energy storage, and other fields. This has also prompted the development of lithium batteries towards high-capacity, high-rate, fast-charging and high-safety power batteries.

[0005] According to the different electrolytes, lithium batteries can be divided into liquid lithium batteries and solid lithium batteries. Liquid lithium batteries are structurally divided into positive electrodes, negative electrodes, separators, electrolytes, etc. Among them, the separator is known as the third "electrode material" in the battery. It is a microporous membrane processed and formed from non-good electronic conductor materials. When participating in the assembly of lithium-ion batteries, it is sandwiched between the positive and negative electrodes and is completely immersed in the electrolyte. The separator can prevent negatively charged electrons from freely passing through the inside of the battery, but allows positively charged lithium ions to pass freely. Compared with some new lithium battery separators under development, polyolefin separators such as polypropylene and polyethylene separators have become the most widely used separator products with the highest market share in the lithium battery market due to their excellent mechanical and chemical stability, high production efficiency and low production cost.

[0006] A qualified polyolefin separator must provide pores for the rapid migration of ions. Within a certain range, the higher the porosity of the separator, the more conducive it is to the penetration of lithium ions 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 and cause an internal short circuit in the battery. At the same time, polyolefin separators have poor retention of electrolyte solutions. Excessive porosity often leads to a decrease in the mechanical properties of the separator, and shrinkage or melting deformation will occur at high temperatures, which can easily lead to internal short circuits in the battery, and then cause the battery to catch fire or explode. Coating ceramic powder on the surface of polyolefin separators is the most commonly used method in industry to solve the thermal stability of separators, but ceramic powders usually have weak bonding with the separator, and usually require the additional use of polymer binders. The use of binders will significantly increase the thickness of the separator, which is not conducive to the efficient transmission of ions in the separator.

[0007] As lithium-ion battery manufacturing technology continues to improve, the requirements for separator performance will also become increasingly stringent. Maximizing separator porosity and increasing pore size without compromising the separation between the positive and negative electrodes or sacrificing mechanical properties is a key technical challenge in developing a new generation of high-power charge-discharge batteries.

[0008] Overview

[0009] In response to the above-mentioned problems existing in the prior art, the present invention provides a non-woven composite membrane material, a preparation method and its application. The present invention uses non-woven fabric processing technology to in-situ composite high aspect ratio ultra-long carbon nanotubes with polyolefin fibers to develop a new generation of high-safety, high charge and discharge power non-woven composite membrane materials that can be used as diaphragms.

[0010] The specific content of the invention is as follows:

[0011] In a first aspect, the present invention provides a non-woven composite membrane material, wherein the membrane material has a three-dimensional network structure and 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

[0012] A self-supporting network formed by the ultra-long carbon nanotubes is deposited in the pores of the polymer film;

[0013] The polymer film is composed of one or more of polypropylene, polypropylene derivatives, polyethylene and polyethylene derivatives;

[0014] The diameter of the bundle of the ultra-long carbon nanotubes is less than 100 mm, and the length of the ultra-long carbon nanotubes is greater than 1 mm.

[0015] Optionally, the ultra-long carbon nanotubes and the polymer film are bonded to each other via van der Waals forces.

[0016] Optionally, the porosity of the three-dimensional network structure is 80-90%.

[0017] In a second aspect, the present invention provides a method for preparing the non-woven composite membrane material according to the first aspect, the preparation method comprising:

[0018] The carbon nanotube powder is put into a jet mill and sheared by a high-speed airflow to obtain flocculent carbon nanotubes with a bundle diameter of less than 100 mm and a length of more than 1 mm.

[0019] The polymer melt-blown material and the electret masterbatch are mixed in a mass ratio of (90-98): (2-10), and then fed into a twin-screw extruder; the flocculent carbon nanotubes are fed into a continuous feeding device;

[0020] After the twin-screw extruder shears and blends the feed materials, multiple die heads extrude polymer fibers toward the spinneret at a temperature of 120-250° C., while the continuous feeding device continuously feeds the flocculent carbon nanotubes perpendicularly to the extrusion direction of the polymer fibers, so that the polymer fibers and the flocculent carbon nanotubes come into contact with each other and are drawn by hot air and deposited together onto the spinneret to form a precursor of the composite membrane material.

[0021] The precursor collected and transported by the rotary screen is subjected to multiple rolling and slitting to be rolled up, so as to obtain the non-woven composite membrane material of the ultra-long carbon nanotubes and the polymer membrane.

[0022] Optionally, the flocculent carbon nanotubes are continuously added at a feeding rate of 2.0 to 4.5 g / min.

[0023] Optionally, the array carbon nanotube is a single carbon nanotube or a carbon nanotube bundle;

[0024] The diameter of a single carbon nanotube is 1.5 to 8.0 nm, and the aspect ratio is 10 5 ~10 6 ;

[0025] The diameter of the carbon nanotube bundle is 10 to 1000 mm.

[0026] Optionally, the high-speed airflow shearing operating frequency of the airflow pulverizer is 50 to 300 Hz, and the processing time is 20 to 300 s.

[0027] 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.

[0028] Optionally, the melt index of the polymer meltblown material is 1200 to 1700 g / 10 min.

[0029] In a third aspect, the present invention provides an application of the non-woven composite membrane material described in the first aspect, wherein the non-woven composite membrane material is used as a diaphragm material for the assembly and preparation of lithium batteries.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] The present invention provides a non-woven composite membrane material having 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 surfaces of the polymer membrane, and / or a self-supporting network formed by the ultra-long carbon nanotubes is deposited within the pores of the polymer membrane. The present invention utilizes an in-situ composite non-woven fabric processing technique to prepare the composite membrane material, combining the ultra-long carbon nanotubes with a polyolefin. This fully utilizes the performance advantages of the carbon nanotubes and the polyolefin. The self-supporting network formed by the high-aspect-ratio ultra-long carbon nanotubes creates strong van der Waals interactions with the polyolefin, enabling a tight bond without an adhesive.

[0032] More importantly, the non-woven composite membrane material provided by the present invention is used as a diaphragm material in lithium batteries. With the help of the excellent conductivity, mechanical properties and thermal stability of carbon nanotubes themselves, the composite membrane material can effectively suppress the thermal shrinkage of the polyolefin diaphragm while improving the ion transmission performance, increase the membrane rupture temperature, thereby greatly improving the mechanical properties of the polyolefin fiber membrane and its retention ability in the electrolyte. Furthermore, the double-layer composite membrane structure formed by ultra-long carbon nanotubes and polyolefins can realize the thermal closed-pore function of the composite membrane. After the polyolefin membrane melts, the melted polyolefin resin fills the three-dimensional pores in the ultra-long carbon nanotube fiber network, which plays a role in isolating the positive and negative electrodes and cutting off the current, preventing the thermal runaway of the lithium battery, thereby ensuring the safe operation of the battery. Therefore, the non-woven composite membrane material provided by the present invention can be used as a new generation of high-performance lithium battery diaphragms, greatly improving the safety and power density of electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or related technologies, the following is a brief introduction to the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0034] FIG1 shows a flow chart of a method for preparing a non-woven composite membrane material according to an embodiment of the present invention;

[0035] FIG2 shows a scanning electron microscope image of flocculent carbon nanotubes provided by an embodiment of the present invention;

[0036] FIG3 shows an optical microscope characterization image of a non-woven composite membrane material provided by an embodiment of the present invention;

[0037] FIG4 shows a set of optical microscope characterization images of the non-woven composite membrane material provided by an embodiment of the present invention. Specific embodiments

[0038] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0039] If no specific experimental steps or conditions are specified in the examples, the experiments can be carried out according to the conventional experimental steps or conditions described in the prior art. The reagents and other instruments used, if the manufacturers are not specified, are all commercially available conventional reagents.

[0040] Ultra-long carbon nanotubes possess excellent mechanical properties, with strength up to 100 times that of steel and a theoretical Young's modulus of 5TPa. They are ideal fillers for preparing composite materials with excellent mechanical properties. Furthermore, ultra-long carbon nanotubes exhibit excellent electrical conductivity, reaching 1000 to 2000 S / cm, enabling the preparation of conductive composite materials with low percolation values ​​and high conductivity. Their aspect ratio is extremely high, ranging from 100 to 1,000,000. Adding a small amount of ultra-long carbon nanotubes can significantly improve a material's mechanical, electrical, and thermal properties. Importantly, they possess excellent flexibility, and their mechanical properties remain unaffected when mixed with other materials and subjected to external forces such as shear.

[0041] Therefore, the present invention proposes to manufacture a composite diaphragm by combining ultra-long carbon nanotubes and polyolefins through non-woven fabric processing technology, and to modify the polyolefin material with the performance advantages of carbon nanotubes to obtain a lithium battery diaphragm with high safety and power density. The self-supporting network spontaneously formed by ultra-long carbon nanotubes with high aspect ratio is deposited in the pores of polyolefin fibers. This all-carbon structure has a strong van der Waals interaction with polyolefins, which can achieve a tight fit without a binder. At the same time, relying on the excellent conductivity, mechanical properties and thermal stability of carbon nanotubes themselves, this composite structure can effectively inhibit the thermal shrinkage of the polyolefin diaphragm while improving the ion transmission performance, increase the membrane rupture temperature, thereby greatly improving the mechanical properties of the polyolefin fiber membrane and its retention ability in the electrolyte. Moreover, the double-layer diaphragm structure can realize the thermal closure function of the composite diaphragm. After the polyolefin membrane melts, the melted polyolefin resin fills the three-dimensional pores in the ultra-long carbon nanotube fiber network, which plays a role in isolating the positive and negative electrodes and cutting off the current, preventing the lithium battery from thermal runaway, thereby ensuring the safe operation of the battery. The specific implementation content is as follows:

[0042] In the first aspect, the present invention provides a non-woven composite membrane material, which has a three-dimensional network structure and 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 the ultra-long carbon nanotubes is negatively deposited in the pores of the polymer membrane.

[0043] During specific implementation, the polymer film selected in the embodiment of the present invention is specifically composed of one or more of polypropylene, polypropylene derivatives, polyethylene and polyethylene derivatives; in the embodiment of the present invention, the polymer film is prepared by a melt-blown process, that is, the polymer film is formed by stacking ultrafine fibers formed by melt-spinning a polymer, and a large number of pores are distributed on its surface. Since the bundle diameter of the ultra-long carbon nanotubes selected in the embodiment of the present invention is less than 100 mm, and the length of the ultra-long carbon nanotubes is greater than 1 mm. This type of ultra-long carbon nanotube can form a very strong van der Waals interaction force with polyolefins, and can achieve the situation where the ultra-long carbon nanotubes are loaded on the surface of the polyolefin ultra-fine fibers without a binder, and / or the self-supporting network formed by the ultra-long carbon nanotubes is deposited in the pores formed by the stack of polyolefin ultra-fine fibers without falling off.

[0044] In a second aspect, the present invention provides a method for preparing the non-woven composite membrane material according to the first aspect. FIG1 shows a flow chart of a method for preparing a non-woven composite membrane material according to an embodiment of the present invention. As shown in FIG1 , the preparation method comprises:

[0045] Step 1: Place carbon nanotube powder into a jet mill, and after shearing with high-speed airflow, collect flocculent carbon nanotubes with a bundle diameter of less than 100 mm and a length of more than 1 mm.

[0046] In the specific implementation, the carbon nanotube powder used in this step is a commercially available array carbon nanotube prepared in large quantities by a nano-agglomeration fluidization method. The array carbon nanotube has a diameter of 1.5 to 8.0 nm and an aspect ratio of 10. 5 ~10 6 Single carbon nanotubes or carbon nanotube bundles with a diameter of 10 to 1000 mm. This step uses airflow shear dispersion technology to crush carbon nanotube agglomerates or array carbon nanotubes (ultrafine particles). Its basic principle is that when the airflow mill is fed, several high-pressure airflows are ejected simultaneously. At the intersection of the jet airflows, the materials to be crushed are sheared, collided, squeezed, and rubbed against each other under the impetus of the powerful supersonic airflow, and are crushed in an instant. The high-speed airflow shearing working frequency is 50 to 300 Hz, and the processing time is 20 to 300 seconds. The crushed materials enter the classification chamber and are separated under the action of the centrifugal field. The products with qualified particle size are collected by the collector, and the large particles are still returned to the crushing chamber for further crushing. For carbon nanotube agglomerates or array carbon nanotubes, this method can effectively break the carbon nanotube macro-body into flocculent carbon nanotubes, while still maintaining the loose structure of the secondary agglomerates or bundles. In addition, the use of airflow shear can also remove most of the residual catalyst carriers in the carbon nanotube product, achieving the effect of purification.

[0047] Step 2: Mix the polymer melt-blown material and the electret masterbatch in a mass ratio of (90-98): (2-10), and then feed the mixture into a twin-screw extruder; and feed the flocculent carbon nanotubes into a continuous feeding device.

[0048] Step 3: After the twin-screw extruder shears and blends the feed, multiple groups of heads extrude polymer fibers toward the spinneret at 120-250°C. At the same time, the continuous feeding device continuously feeds flocculent carbon nanotubes perpendicular to the extrusion direction of the polymer fibers, so that the polymer fibers and flocculent carbon nanotubes come into contact with each other and are drawn by hot air and deposited together onto the spinneret to form a precursor of the composite membrane material.

[0049] Step 4: The precursor collected and transported by the rotary screen is rolled and slit multiple times to form a roll, thereby producing a non-woven composite membrane material composed of ultra-long carbon nanotubes and a polymer membrane.

[0050] In specific implementation, the diameter of the bundle of flocculent carbon nanotubes obtained after the treatment in step 1 is less than 100 mm and the length is greater than 1 mm. It is further used in the preparation process of non-woven membrane materials (steps 2 to 4). Specifically, a polymer melt-blown material in a specific ratio (mass ratio of (90 to 98): (2 to 10)) is mixed with an electret masterbatch, and then fed into a screw extruder through a feeding device. The melt after extrusion and melting is accurately measured by a metering pump and fed into a special melt distribution chamber. After rectification, it enters the spinning melt pool, is ejected into filaments through the spinning micropores, and then is sprayed and stretched into ultrafine fibers under the action of a high-speed, high-pressure hot air flow. At the same time, the flocculent carbon nanotubes are fed into a continuous feeding device, which continuously feeds the flocculent carbon nanotubes at a feeding rate of 2.0 to 4.5 g / min perpendicular to the extrusion direction of the ultrafine fibers (polymer fibers). During this process, the polymer fibers and the flocculent carbon nanotubes come into contact in the form of aerosols and are drawn by hot air and deposited together on the spinneret, forming a precursor of the composite membrane material. The precursor of the composite membrane material is further rolled, slit and rolled into a roll to produce a non-woven composite membrane material composed of ultra-long carbon nanotubes and polymer membranes.

[0051] In some embodiments, the composition of the polymer meltblown material includes: 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, and the melt index of the polymer meltblown material is 1200 to 1700 g / 10 min.

[0052] In a third aspect, the present invention provides an application of the non-woven composite membrane material according to the first aspect, wherein the non-woven composite membrane material is used as a diaphragm material for the assembly and preparation of lithium batteries.

[0053] In order to enable those skilled in the art to understand the present application more clearly, the non-woven composite membrane material, preparation method and application thereof described in the present application are now described in detail through the following examples.

[0054] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. The materials and reagents used in the examples are all commercially available unless otherwise specified.

[0055] Example 1:

[0056] (1) Large diameter ultra-long carbon nanotube bundles are sheared and dispersed into flocculent carbon nanotubes by airflow

[0057] Weigh 1.0 g of a large amount of carbon nanotube arrays with a length of more than 5 mm and place them into a jet mill;

[0058] After shearing with high-speed airflow at a rotational frequency of 230 Hz for 30 seconds, dispersed carbon nanotube samples were collected from the lower barrels of the cyclone separator and the pulse dust collector. The crude carbon nanotube sample collected from the cyclone separator barrel was then fed into a jet mill and sheared with high-speed airflow at a frequency of 230 Hz for 30 seconds to obtain the dispersed flocculent carbon nanotubes. Because the carbon nanotubes in the bundle have high strength along the c-axis, only weak van der Waals forces exist between the bundles. Therefore, when the carbon nanotube array is sheared, it is torn into smaller bundles along the c-axis. Thus, after shearing, flocculent carbon nanotubes are obtained.

[0059] Figure 2 shows a scanning electron microscope characterization of the flocculent carbon nanotubes provided by an embodiment of the present invention. As shown in Figure 2, the flocculent carbon nanotubes are composed of carbon nanotube bundles with a diameter of 80 to 100 mm, and the length is still on the order of millimeters. The apparent density is 12 to 18 g / L, and the carbon nanotubes still have good orientation in the bundles.

[0060] (2) Preparation of ultra-long carbon nanotube / polypropylene non-woven composite membrane materials by non-woven fabric process

[0061] The polypropylene meltblown material (melt index of 1450g / 10min) and the electret masterbatch are premixed in proportion in a high-speed mixer for 20min, and the mass ratio of the polypropylene meltblown material to the electret masterbatch is 97:3; the evenly mixed material is fed into the twin-screw extruder by the extraction system, and the temperatures of twin screws 1 to 7 are set to 170°C, 185°C, 210°C, 220°C, 230°C, 230°C, and 230°C; the pipeline temperature is set to 230°C; the hot air temperature is set to 260°C; the hot air volume is set to 950rpm, the ground exhaust fan air volume is 850rpm, and the cold air is set to 850rpm; the electret equipment voltage is 50KV and the current is 6.5mA.

[0062] The fed materials are 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 dispersed in step (1) are continuously fed through the top of a vertical conveying pipe at a feeding rate of 2.0 g / min; the ultra-long carbon nanotube powder is discharged from the bottom and mixed with the extruded material, and is jointly deposited on the spinneret by hot air traction, collected and transported by a rotary screen, and then subjected to high-voltage electrification, and then cut and rolled to prepare an ultra-long carbon nanotube / polypropylene non-woven composite membrane material.

[0063] Figure 3 shows an optical microscope characterization of the non-woven composite membrane material provided by an embodiment of the present invention, and Figure 4 shows a group of optical microscope characterizations of the non-woven composite membrane material provided by an embodiment of the present invention, wherein Figure 4 (left) and Figure 4 (right) are optical microscope characterizations under different focusing planes, respectively. As shown in Figures 3 and 4, combined with the optical microscope characterization, it can be found that the loading mode of the ultra-long carbon nanotube powder and the polypropylene fiber can be adsorbed on the surface of the polypropylene fiber (Figure 3), or it can be formed into a self-supporting network and filled in the pores of the polypropylene fiber network (Figure 4). Moreover, from the comparison of a group of optical microscope images shown in Figure 4, it can be seen that the polypropylene fibers and the ultra-long carbon nanotubes show obvious orientation on the single-layer network in the same plane, and the fiber networks in different planes have different orientations. The fiber networks in different directions form a three-dimensional mesh membrane structure with a rich pore structure (porosity of about 85%).

[0064] Example 2:

[0065] (1) Small diameter ultra-long carbon nanotube bundles are dispersed into flocculent carbon nanotubes by air flow shearing

[0066] 2.0g of a large-scale carbon nanotube array longer than 3mm was weighed and placed in a jet mill. The array was sheared with high-speed airflow at a rotational frequency of 280Hz for 120s, and the dispersed carbon nanotube samples were collected from the lower barrels of a cyclone separator and a pulse dust collector. The crude carbon nanotube sample collected in the cyclone separator barrel was then placed in a jet mill and sheared with high-speed airflow at a rotational frequency of 280Hz for 120s before the dispersed carbon nanotube sample was collected. Because the carbon nanotubes in the bundle have high strength along the c-axis, there are only weak van der Waals forces between the bundles. Therefore, when the carbon nanotube array is sheared, it is torn into smaller bundles along the c-axis. Thus, after shearing, flocculent carbon nanotubes are obtained.

[0067] The obtained flocculent carbon nanotubes consist of carbon nanotube bundles with a diameter of 10 to 20 mm and a length still in the order of millimeters. The apparent density is 3 to 5 g / L, and the carbon nanotubes still have good orientation in the bundles.

[0068] Further extending the processing time revealed that the diameter of the resulting flocculent carbon nanotube bundles no longer decreased significantly. This was primarily due to the limitations of the rotational speed and rotor thickness, which made it difficult for the carbon nanotube bundles within the flocculent carbon nanotubes to be further torn into smaller pieces. Furthermore, due to the excellent flexibility of the carbon nanotube bundles, the impact force was released by the bending of the bundles.

[0069] (2) Preparation of ultra-long carbon nanotube / polypropylene non-woven composite membrane materials by non-woven fabric process

[0070] The polypropylene meltblown material (melt index of 1650g / 10min) and the electret masterbatch are premixed in proportion in a high-speed mixer for 20min, and the mass ratio of the polypropylene meltblown material to the electret masterbatch is 97:3; the evenly mixed material is fed into the twin-screw extruder by the extraction system, and the temperatures of twin screws 1 to 7 are set to 170℃, 185℃, 210℃, 220℃, 230℃, 230℃, and 230℃; the pipeline temperature is set to 230℃; the hot air temperature is set to 260℃; the hot air volume is set to 950rpm, the ground exhaust fan air volume is 850rpm, and the cold air is set to 850rpm; the electret equipment voltage is 50KV and the current is 6.5mA.

[0071] The fed materials are 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 dispersed in step (1) are continuously fed through the top of a vertical conveying pipe at a feeding rate of 2.0 g / min; the ultra-long carbon nanotube powder is discharged from the bottom and mixed with the extruded material, and is deposited together on the spinneret by hot air traction, collected and transported by a rotary screen, and then subjected to high-voltage electrification, and then cut and rolled to prepare an ultra-long carbon nanotube / polypropylene non-woven composite membrane material.

[0072] The scanning electron microscope characterization image of the flocculent carbon nanotubes obtained in this example and the optical microscope characterization image of the non-woven composite membrane material are substantially the same as those in Example 1 (porosity of about 80%) and are not repeated here.

[0073] Example 3:

[0074] (1) Large diameter ultra-long carbon nanotube bundles are sheared and dispersed into flocculent carbon nanotubes by airflow

[0075] Weigh 2.5 g of a large amount of carbon nanotube arrays longer than 5 mm and place them into a jet mill;

[0076] After shearing with high-speed airflow at a rotational frequency of 230 Hz for 60 seconds, dispersed carbon nanotube samples were collected from the lower barrels of the cyclone separator and the pulse dust collector. The crude carbon nanotube sample collected from the cyclone separator barrel was then fed into a jet mill and sheared with high-speed airflow at a frequency of 230 Hz for 60 seconds to obtain the dispersed flocculent carbon nanotubes. Because the carbon nanotubes in the bundle have high strength along the c-axis, only weak van der Waals forces exist between the bundles. Therefore, when the carbon nanotube array is sheared, it is torn into smaller bundles along the c-axis. Thus, after shearing, flocculent carbon nanotubes are obtained.

[0077] (2) Preparation of ultra-long carbon nanotube / polypropylene non-woven composite membrane materials by non-woven fabric process

[0078] The polypropylene meltblown material (melt index of 1550g / 10min) and the electret masterbatch are premixed in proportion in a high-speed mixer for 25 minutes, and the mass ratio of the polypropylene meltblown material to the electret masterbatch is 97:3; the evenly mixed materials are fed into the twin-screw extruder by the extraction system, and the temperatures of twin screws 1 to 7 are set to 170℃, 185℃, 210℃, 220℃, 230℃, 230℃, and 230℃; the pipeline temperature is set to 230℃; the hot air temperature is set to 260℃; the hot air volume is set to 950rpm, the ground exhaust fan air volume is 850rpm, and the cold air is set to 850rpm; the electret equipment voltage is 50KV and the current is 6.5mA.

[0079] The fed materials are 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 dispersed in step (1) are continuously fed through the top of a vertical conveying pipe at a feeding rate of 3.5 g / min; the ultra-long carbon nanotube powder is discharged from the bottom and mixed with the extruded material, and is deposited on the spinneret together by hot air traction, collected and transported by a circular screen, and then subjected to high-voltage electrification, and then cut and rolled to prepare an ultra-long carbon nanotube / polypropylene non-woven composite membrane material.

[0080] The scanning electron microscope characterization image of the flocculent carbon nanotubes obtained in this example and the optical microscope characterization image of the non-woven composite membrane material are substantially the same as those in Example 1 (porosity of about 89%) and are not repeated here.

[0081] Example 4:

[0082] (1) Large diameter ultra-long carbon nanotube bundles are sheared and dispersed into flocculent carbon nanotubes by airflow

[0083] Weigh 2.5 g of a large amount of carbon nanotube arrays with a length of more than 8 mm and place them into a jet mill;

[0084] After shearing with high-speed airflow at a rotational frequency of 300 Hz for 100 seconds, dispersed carbon nanotube samples were collected from the lower barrels of the cyclone separator and the pulse dust collector, respectively. The crude carbon nanotube sample collected from the cyclone separator barrel was then fed into a jet mill and sheared with high-speed airflow at a frequency of 300 Hz for 100 seconds to obtain the dispersed flocculent carbon nanotubes. Because the carbon nanotubes in the bundle have high strength along the c-axis, only weak van der Waals forces exist between the bundles. Therefore, when the carbon nanotube array is sheared, it is torn into smaller bundles along the c-axis. Thus, after shearing, flocculent carbon nanotubes are obtained.

[0085] (2) Preparation of ultra-long carbon nanotube / polyethylene composite membrane by non-woven fabric process

[0086] The polyethylene meltblown material (melt index of 1250-1500g / 10min) and the electret masterbatch were premixed in proportion in a high-speed mixer for 15min. The mass ratio of the polyethylene meltblown material to the electret masterbatch was 96:4. The evenly mixed materials were fed into a twin-screw extruder by a pumping system. The temperatures of twin screws 1-7 were set to 136°C, 150°C, 175°C, 186°C, 195°C, 195°C, and 195°C; the pipeline temperature was set to 195°C; the hot air temperature was set to 225°C; the hot air volume was set to 800rpm, the ground exhaust fan air volume was 650rpm, and the cold air was set to 650rpm; the electret equipment voltage was 50KV and the current was 5.0mA;

[0087] The fed materials are 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 dispersed in step (1) are continuously fed from the top of a vertical conveying pipe at a feeding rate of 4.5 g / min. The ultra-long carbon nanotube powder is discharged from the bottom and mixed with the extruded material, and is then drawn by hot air and deposited on a spinneret. The powder is collected and transported by a rotary screen and subjected to high-voltage electrification. It is then cut and rolled to prepare an ultra-long carbon nanotube / polyethylene composite non-woven fabric membrane.

[0088] The scanning electron microscope characterization image of the flocculent carbon nanotubes obtained in this example and the optical microscope characterization image of the non-woven composite membrane material are substantially the same as those in Example 1 (porosity of about 82%) and are not repeated here.

[0089] Example 5:

[0090] (1) Small diameter ultra-long carbon nanotube bundles are dispersed into flocculent carbon nanotubes by air flow shearing

[0091] 2.5g of a large-scale carbon nanotube array longer than 3mm was weighed and placed in a jet mill. The array was sheared with high-speed airflow at a rotational frequency of 280Hz for 120s, and the dispersed carbon nanotube samples were collected from the lower barrels of a cyclone separator and a pulse dust collector. The crude carbon nanotube sample collected in the cyclone separator barrel was then placed in a jet mill and sheared with high-speed airflow at a rotational frequency of 280Hz for 120s before the dispersed carbon nanotube sample was collected. Because the carbon nanotubes in the bundle have high strength along the c-axis, there are only weak van der Waals forces between the bundles. Therefore, when the carbon nanotube array is sheared, it is torn into smaller bundles along the c-axis. Thus, after shearing, flocculent carbon nanotubes are obtained.

[0092] The obtained flocculent carbon nanotubes consist of carbon nanotube bundles with a diameter of 10 to 20 mm and a length still in the order of millimeters. The apparent density is 3 to 5 g / L, and the carbon nanotubes still have good orientation in the bundles.

[0093] Further extending the processing time revealed that the diameter of the resulting flocculent carbon nanotube bundles no longer decreased significantly. This was primarily due to the limitations of the rotational speed and rotor thickness, which made it difficult for the carbon nanotube bundles within the flocculent carbon nanotubes to be further torn into smaller pieces. Furthermore, due to the excellent flexibility of the carbon nanotube bundles, the impact force was released by the bending of the bundles.

[0094] (2) Preparation of ultra-long carbon nanotube / polyethylene composite membrane by non-woven fabric process

[0095] The polyethylene meltblown material (melt index of 1500g / 10min) and the electret masterbatch were premixed in proportion in a high-speed mixer for 15min. The mass ratio of the polyethylene meltblown material to the electret masterbatch was 96:4. The evenly mixed materials were fed into a twin-screw extruder by a pumping system. The temperatures of twin screws 1 to 7 were set to 136°C, 150°C, 175°C, 186°C, 195°C, 195°C, and 195°C; the pipeline temperature was set to 195°C; the hot air temperature was set to 225°C; the hot air volume was set to 800rpm, the ground exhaust fan air volume was 650rpm, and the cold air was set to 650rpm; the electret equipment voltage was 50KV and the current was 5.0mA;

[0096] The fed materials are 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 dispersed in step (1) are continuously fed from the top of a vertical conveying pipe at a feeding rate of 3.0 g / min. The ultra-long carbon nanotube powder is discharged from the bottom and mixed with the extruded material, and is deposited on the spinneret together by hot air traction. The powder is collected and transported by a rotary screen and then subjected to high-voltage electrification. It is then cut and rolled to prepare an ultra-long carbon nanotube / polyethylene composite non-woven fabric membrane.

[0097] The scanning electron microscope characterization image of the flocculent carbon nanotubes obtained in this example and the optical microscope characterization image of the non-woven composite membrane material are substantially the same as those in Example 1 (porosity of about 90%) and are not repeated here.

[0098] References herein to "one embodiment," "an embodiment," or "one or more embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Furthermore, please note that instances of the phrase "in one embodiment" do not necessarily all refer to the same embodiment.

[0099] In the description provided herein, numerous specific details are described. However, it is understood that embodiments of the present disclosure may be practiced without these specific details. In some instances, well-known methods, structures, and techniques are not shown in detail so as not to obscure the understanding of this description.

[0100] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in the claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The present disclosure may be implemented by means of hardware comprising several different elements and by means of a suitably programmed computer. In a unit claim enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third etc. does not indicate any order. These words may be interpreted as names.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present disclosure.

Claims

1. A non-woven composite film material, characterized in that, The membrane material has a three-dimensional network structure and is composed of ultra-long carbon nanotubes and a polymer membrane. Among them, the ultra-long carbon nanotubes are loaded on the surface of the fibers 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; the composition of the polymer membrane is one or more of polypropylene, a derivative material of polypropylene, polyethylene, and a derivative material of polyethylene; the tube diameter of the ultra-long carbon nanotubes is less than 100 mm, and the length of the ultra-long carbon nanotubes is greater than 1 mm.

2. The non-woven composite film material according to claim 1, wherein The ultra-long carbon nanotubes and the polymer membrane are combined with each other by van der Waals forces.

3. The non-woven composite film material according to claim 1, wherein The porosity of the three-dimensional network structure is 80-90%.

4. A method for preparing the non-woven composite film material according to any one of claims 1 to 3 above, characterized in that, The preparation method includes: Putting carbon nanotube powder into a jet mill, and after being treated by high-speed air flow shearing, collecting flocculent carbon nanotubes with a tube diameter less than 100 mm and a length greater than 1 mm; Mixing a polymer meltblown material and a electret masterbatch with a mass ratio of (90-98):(2-10), and putting them into a twin-screw extruder; feeding the flocculent carbon nanotubes into a continuous feeding device; After the twin-screw extruder shears and blends the feedstock, while multiple groups of machine heads extrude polymer fibers onto a spinneret at 120-250 °C, the continuous feeding device continuously drops the flocculent carbon nanotubes perpendicular to the extrusion direction of the polymer fibers, so that the polymer fibers come into contact with the flocculent carbon nanotubes, and they are co-deposited onto the spinneret by hot air traction to form a precursor of the composite membrane material; The precursor collected and conveyed by a circular screen is subjected to multiple roller pressings and slit into rolls to obtain the non-woven composite membrane material composed of ultra-long carbon nanotubes and a polymer membrane.

5. The preparation method according to claim 4, characterized in that, The feeding speed at which the flocculent carbon nanotubes are continuously dropped is maintained at 2.0-4.5 g / min.

6. The preparation method according to claim 4, characterized in that, The array carbon nanotubes are single carbon nanotubes or carbon nanotube bundles; The diameter of the single carbon nanotube is 1.5 to 8.0 nm, and the aspect ratio is 10 5 ~10 6 ; The diameter of the carbon nanotube bundle is 10-1000 mm.

7. The preparation method according to claim 4, characterized in that The high-speed air flow shearing working frequency of the jet mill is 50-300 Hz, and the treatment time is 20-300 s.

8. The preparation method according to claim 4, characterized in that, The composition of the polymer meltblown material includes: a polymer, a nucleating agent, a molecular weight regulator, and an antioxidant; among them, the polymer is one or more of polypropylene, a derivative material of polypropylene, polyethylene, and a derivative material of polyethylene.

9. The preparation method according to claim 8, wherein The melt index of the polymer meltblown material is 1200-1700 g / 10 min.

10. Use of the non-woven composite film material according to any one of claims 1 to 3 above, characterized in that, The non-woven composite membrane material is used as a separator material for the assembly and preparation of lithium batteries.

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