A conductive flash evaporation sheet, its preparation method and application

Abstract

This application belongs to the field of flash spinning, specifically disclosing a conductive flash-spun sheet, its preparation method, and its application. The conductive flash-spun sheet of this application comprises the following components in parts by weight: 100 parts high-density polyethylene, 4-20 parts carbon-based conductive agent, 3-10 parts conductive whiskers, 5-15 parts porous silica, 1-5 parts polyvinyl alcohol, 1-5 parts compatibilizer, and 0-2 parts additives. The conductive whiskers include zinc oxide whiskers and conductive potassium titanate whiskers. This application provides the main conductivity of the flash-spun nonwoven fabric by adding a carbon-based conductive agent, while simultaneously compounding conductive whiskers and porous silica to form a stable and effective conductive network structure, significantly reducing the resistance of the flash-spun nonwoven fabric. Furthermore, the polyvinyl alcohol and compatibilizer improve the dispersibility of the carbon-based conductive agent and conductive whiskers, comprehensively achieving improved conductivity of the flash-spun nonwoven fabric while maintaining its good mechanical properties and high air permeability.

Description

Technical Field

[0001] This application belongs to the field of flash spinning, specifically relating to a conductive flash sheet, its preparation method, and its application. Background Technology

[0002] Membrane electrode electrolyzers (MEEs) electrocatalytically reduce carbon dioxide to carbon monoxide, formic acid, ethanol, ethylene, acetic acid, and other carbon-based fuel chemicals at a certain current density, making them one of the most promising electrolysis systems. Key components of a MEE electrolyzer include a gas diffusion electrode consisting of a gas diffusion layer (GDE) and a catalyst layer. During electrolysis, flowing CO2 gas comes into contact with the electrolyte and catalyst layer through the GDE, forming a three-phase interface that provides the reaction site. Therefore, the GDE needs to simultaneously ensure adequate contact between the reactant gas, the catalytically active sites, and water. This requires the GDE to maintain effective transport of reactant gases and water within the gas diffusion layer, necessitating certain hydrophobicity, permeability, conductivity, and structural strength.

[0003] Currently, carbon paper is widely used as a gas diffusion layer. Carbon paper is a composite material made from carbon fiber. Its lightweight, smooth surface, corrosion resistance, uniform porosity, and high conductivity make it widely used in fuel cells, lithium batteries, and electrocatalysis. A catalyst solution or slurry is coated onto the surface of the carbon paper to form a catalytic layer. The coated carbon paper is then used as part of the membrane electrode assembly (MEA) and assembled with other components to form a complete electrochemical reaction system. Carbon paper is typically made from chopped carbon fibers and has a porous fibrous structure, exhibiting significant hydrophilicity. Before use, it needs to be hydrophobically modified, such as by modifying it with polytetrafluoroethylene (PTFE). The modified carbon paper can establish effective channels for gas and water conduction. However, even after working in an electric field environment for a period of time, the hydrophobic layer of the hydrophobic modified carbon paper will still be damaged, rendering it unable to perform its specific functions, leading to battery failure and reduced battery life. Furthermore, the hydrophobic modification process is complex and requires stringent conditions, resulting in a significant increase in the price of the modified carbon paper, which is detrimental to cost reduction and large-scale production.

[0004] Polyolefin fiber materials, such as high-density polyethylene (HDPE), are not only inexpensive and easy to produce, but also possess good hydrophobicity and a certain degree of air permeability. If they could replace carbon paper as a gas diffusion layer, their production difficulty and cost could be significantly reduced. However, polyolefin fiber materials are insulating materials and require prior conductive modification to reduce their resistance. The conventional approach is to add conductive agents to the polyolefin material, creating a conductive network within the material to impart conductivity and lower resistance. However, current polyolefin composites incorporating conductive materials such as carbon black, graphene, carbon fiber, and metals often fail to form an effective conductive network with the polymer due to various factors including the dispersion, compatibility, size, structure, oxidative degradation, and stability of these conductive materials. This not only significantly reduces the air permeability and mechanical properties of the polyolefin fiber materials but also provides only a slight improvement in conductivity, failing to meet the requirements of practical gas diffusion layers. Summary of the Invention

[0005] In view of the problem of poor conductivity of existing conductive polyolefin fiber materials, the purpose of this application is to provide a conductive flash sheet, its preparation method and application.

[0006] To achieve the above objectives, the following technical solutions are specifically included:

[0007] A conductive flash evaporation sheet comprises the following components in parts by weight: 100 parts high-density polyethylene, 4-20 parts carbon-based conductive agent, 3-10 parts conductive whiskers, 5-15 parts porous silica, 1-5 parts polyvinyl alcohol, 1-5 parts compatibilizer, and 0-2 parts additives. The conductive whiskers include zinc oxide whiskers and conductive potassium titanate whiskers. The resistivity of the conductive flash evaporation sheet is less than or equal to 200 mΩ·cm, and the density of the conductive flash evaporation sheet is greater than or equal to 0.4 g / cm. 3 And less than or equal to 0.5 g / cm 3 .

[0008] This application describes a flash-spun nonwoven fabric produced through a flash spinning process. This process involves extruding a high-density polyethylene matrix spinning solution at a pressure above the solvent's boiling point into an atmospheric pressure environment. Due to the rapid pressure drop, the solvent evaporates rapidly, transforming into extremely fine fiber filaments. These filaments are then separated, collected, processed, and reinforced to obtain the flash-spun nonwoven fabric product. Compared to traditional nonwoven materials, flash-spun nonwoven fabrics not only have finer and more uniform fiber filaments but also offer higher forming efficiency and a shorter production cycle, which is beneficial for subsequent fabrication of thin diffusion layers.

[0009] In the conductive flash-evaporated sheet of this application, the carbon-based conductive agent provides the main conductive function, reducing the resistance of the flash-evaporated nonwoven fabric. Conductive whiskers and porous silica assist the conductive agent in building a conductive network. Among them, zinc oxide whiskers with a special four-needle-shaped spatial three-dimensional structure and fibrous conductive potassium titanate whiskers constitute the main skeleton structure. Porous silica and conductive agent are interspersed in the skeleton structure, which not only significantly improves the conductivity of the system, but also does not significantly reduce the mechanical properties of the system. At the same time, the presence of porous silica provides more pore structure, improving the air permeability of the system. Polyvinyl alcohol can increase the surface wettability of porous silica, zinc oxide whiskers and conductive potassium titanate whiskers, which not only improves the blending of porous silica, zinc oxide whiskers and conductive potassium titanate whiskers with the polymer matrix, improves the uniformity of the system, improves the dispersibility of conductive agent, conductive whiskers and porous silica, but also improves hydrophobicity to a certain extent. Furthermore, compatibilizers can significantly improve the compatibility between components, preventing a decrease in the mechanical properties of the system caused by the addition of porous silica, zinc oxide whiskers, and conductive potassium titanate whiskers. Therefore, the conductive flash sheet of this application, based on carbon-based conductive agents, conductive whiskers, porous silica, polyvinyl alcohol, and compatibilizers, can balance good conductivity, air permeability, and mechanical properties, making it more suitable for use in battery diffusion layers.

[0010] Preferably, the average particle size of the porous silica is greater than or equal to 0.01 μm and less than or equal to 3 μm. More preferably, the average particle size of the porous silica is greater than or equal to 1 μm and less than or equal to 2 μm. Specifically, the average particle size of the porous silica can be one or any two of the following: 0.01 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, and 3 μm.

[0011] The average particle size of porous silica affects its contact distance and area with conductive agents and conductive whiskers. In the nanoscale range, porous silica has a longer contact distance and a smaller contact area with conductive agents and conductive whiskers. In the range where the average particle size of porous silica is greater than or equal to 1 μm and less than or equal to 2 μm, the contact distance between porous silica and conductive agents and conductive whiskers is shorter and the contact area is larger.

[0012] Preferably, the specific surface area of ​​porous silica is greater than or equal to 100 m². 2 / g and less than or equal to 1500m 2 / g. Porous silica contains mesopores and micropores, which can significantly improve the gas permeability of the system. It also has a high specific surface area, which is more conducive to the adsorption of reactive gases, reduces the resistance to the transport of gases and other substances, and promotes the transport of substances.

[0013] The average particle size of porous silica can be measured by laser method, and the specific surface area of ​​porous silica can be obtained by BET test.

[0014] Preferably, the mass ratio of zinc oxide whiskers to conductive potassium titanate whiskers is (1-12):1, and more preferably, the mass ratio is (3-11):1. Zinc oxide whiskers and conductive potassium titanate whiskers, as the framework of the conductive network, possess unique morphological structures that enhance the toughness and strength of the system, and they also exhibit good conductivity, providing more favorable conductive channels for the conductive agent. Furthermore, it has been found that a higher amount of zinc oxide whiskers than conductive potassium titanate whiskers is more beneficial for improving the conductivity of the system.

[0015] Preferably, the zinc oxide whiskers have an average diameter greater than or equal to 0.5 μm and less than or equal to 5 μm, and an average length greater than or equal to 10 μm and less than or equal to 50 μm. Specifically, the average diameter can be any one or a combination of 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, and 5 μm. Similarly, the average length can be any one or a combination of 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, and 50 μm. The dimensions of commercially available zinc oxide whiskers are sufficient to meet the requirements of the conductive flash evaporation sheet of this application.

[0016] Preferably, the conductive potassium titanate whiskers have an average diameter greater than or equal to 0.05 μm and less than or equal to 5 μm, and an average length greater than or equal to 0.8 μm and less than or equal to 30 μm. More preferably, the conductive potassium titanate whiskers have an average diameter greater than or equal to 0.1 μm and less than or equal to 0.5 μm, and an average length greater than or equal to 3 μm and less than or equal to 15 μm. Specifically, the average diameter can be any one or any two of the following: 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, and 5 μm. Specifically, the average length can be any one or any two of the following: 0.8 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm.

[0017] Potassium titanate whiskers are inherently non-conductive, but they can be made conductive through simple conductive modification, such as coating or loading conductive materials. This not only imparts conductivity but also maintains their unique fibrous morphology and good dispersibility, preventing agglomeration in the polymer matrix and allowing for better dispersion within the system. This, in turn, synergistically enhances the conductivity of the system with zinc oxide whiskers. However, excessively small diameters and lengths of potassium titanate whiskers hinder contact with conductive agents and zinc oxide whiskers, while excessively large diameters and lengths lead to breakage, compromise morphological stability, and poor compatibility with zinc oxide whiskers. Therefore, conductive potassium titanate whiskers with an average diameter greater than or equal to 0.1 μm and less than or equal to 0.5 μm, and an average length greater than or equal to 3 μm and less than or equal to 15 μm, are preferred for improving the conductivity and mechanical properties of the system.

[0018] The diameter and length of zinc oxide whiskers and conductive potassium titanate whiskers can be obtained by scanning electron microscopy.

[0019] More preferably, the conductive potassium titanate whiskers are antimony tin oxide modified potassium titanate whiskers.

[0020] The conductivity of potassium titanate whiskers can be modified using conventional methods, such as antimony tin oxide doping. The preparation method of antimony tin oxide modified potassium titanate whiskers includes the following steps:

[0021] (1) Stirring tin chloride, antimony chloride, ethanol, and acetylacetone together to react and obtain a precursor solution.

[0022] (2) Disperse potassium titanate whiskers in water with stirring to obtain a suspension. Add the precursor solution to the suspension and react at 80–95°C for 1.5–6 h. Then raise the temperature to 100–120°C and stir until the solvent is completely evaporated to obtain the precursor product.

[0023] (3) The precursor product is calcined at 450-600℃ for 0.5-4h to obtain conductive potassium titanate whiskers.

[0024] Preferably, in steps (1)-(2), the mass ratio of tin chloride, antimony chloride, acetylacetone, anhydrous ethanol, potassium titanate whiskers and water is 0.5-1:0.5-1:0.1-0.3:20-50:3-5:40-60.

[0025] Preferably, in step (1), the reaction time is greater than or equal to 1 hour and less than or equal to 3 hours.

[0026] Preferably, in step (2), the temperature of stirring and dispersing is greater than or equal to 50°C and less than or equal to 65°C.

[0027] Preferably, the molecular weight of polyvinyl alcohol (PVA) is greater than or equal to 25,000 and less than or equal to 300,000; more preferably, the molecular weight of polyvinyl alcohol (PVA) is greater than or equal to 80,000 and less than or equal to 130,000. Commercially available polyvinyl alcohol can meet the requirements of the flash-evaporated nonwoven fabric of this application. Preferably, low molecular weight polyvinyl alcohol is more conducive to wetting and dispersing conductive whiskers and silica, thus improving the uniformity of the system.

[0028] Preferably, the compatibilizer includes at least one of POE-g-MAH (ethylene-octene copolymer grafted with maleic anhydride), PE-g-MAH (polyethylene grafted with maleic anhydride), and LLDPE-g-MAH (linear low-density polyethylene grafted with maleic acid).

[0029] Maleic anhydride-grafted compatibilizers have higher polarity, which not only facilitates gas adsorption but also improves the compatibility between the polymer matrix and conductive whiskers and porous silica, enhancing the blending effect and increasing the system homogeneity, thereby improving conductivity and mechanical properties. Compared to other types of compatibilizers, LLDPE-g-MAH is more compatible with LDPE; therefore, LLDPE-g-MAH is a superior compatibilizer, providing a greater improvement in conductivity and mechanical strength. Furthermore, there are no special requirements regarding the source or grade of the compatibilizer; it can be prepared in-house or purchased commercially.

[0030] Preferably, the high-density polyethylene (HDPE) has a melt index greater than or equal to 5 g / 10 min and less than or equal to 15 g / 10 min at 190°C and 2.16 kg load, according to ASTM D1238.

[0031] More preferably, the high-density polyethylene has a melt index of 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, 9 g / 10 min, 10 g / 10 min, 11 g / 10 min, 12 g / 10 min, 13 g / 10 min, 14 g / 10 min, or 15 g / 10 min, according to ASTM D1238 at 190°C and 2.16 kg load, or any two of these values.

[0032] There are no special requirements for the source and grade of high-density polyethylene raw materials. They can be made in-house or purchased from the market. For example, commercially available MH602 type HDPE can be used, or other types of raw materials can be used.

[0033] Preferably, the carbon-based conductive agent includes at least one of graphene, conductive carbon black, and carbon fiber.

[0034] More preferably, the average thickness of the graphene sheets is greater than or equal to 0.2 mm and less than or equal to 0.5 mm, specifically it can be one or any two of 0.2 mm, 0.3 mm, 0.4 mm, and 0.5 mm.

[0035] More preferably, the average length of the carbon fiber is greater than or equal to 0.1 mm and less than or equal to 1 mm, specifically it can be one or any two of the following: 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, and 1 mm.

[0036] Carbon-based conductive agents are lightweight, have good conductivity, and easily form conductive networks with other conductive components. In particular, fibrous carbon fibers can significantly shorten the contact distance between conductive components, thereby improving conductivity and its stability.

[0037] Preferably, the additives include at least one of antioxidants, lubricants, and flame retardants.

[0038] More preferably, the antioxidant includes at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), tris[2,4-di-tert-butylphenyl] phosphite (antioxidant 168), and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076).

[0039] Adding other additives can further improve the overall performance of the flash nonwoven fabric. Other additives may include oxygenating agents, lubricants, flame retardants, etc.

[0040] Preferably, the thickness of the conductive flash sheet is greater than or equal to 0.1 mm and less than or equal to 0.2 mm. More preferably, the thickness of the conductive flash sheet is greater than or equal to 0.11 mm and less than or equal to 0.13 mm. Thinner conductive flash sheets are more conducive to reducing the transport resistance of their reactants. Moreover, since the conductive flash sheet of this application can maintain good flexibility and sufficient mechanical properties at a smaller thickness, it can meet the actual application requirements of battery diffusion layers.

[0041] Preferably, the conductive flash sheet, tested according to GB / T 24218.3-2010, has a longitudinal breaking strength greater than or equal to 240 N / 5 cm and less than or equal to 253 N / 5 cm, and a transverse breaking strength greater than or equal to 250 N / 5 cm and less than or equal to 266 N / 5 cm.

[0042] Preferably, the air permeability of the conductive flash sheet, tested according to GB / T 5453-1997, is greater than or equal to 30 mm / s and less than or equal to 38 mm / s.

[0043] Preferably, the resistivity of the conductive flash sheet, tested according to GB / T20042.7 proton exchange membrane fuel cell, is greater than or equal to 60 mΩ·cm and less than or equal to 199 mΩ·cm.

[0044] Preferably, the density of the conductive flash sheet is greater than or equal to 0.45 g / cm³. 3 And less than or equal to 0.48 g / cm³ 3 .

[0045] A method for preparing a conductive flash evaporation sheet includes the following steps:

[0046] (1) The raw materials are blended, extruded, and granulated to obtain masterbatch.

[0047] (2) Mix the masterbatch and solvent, then heat and purge with nitrogen to make the temperature inside the mixing device greater than or equal to 200°C and less than or equal to 230°C, and the pressure greater than or equal to 10 MPa and less than or equal to 12 MPa, to obtain the spinning solution.

[0048] (3) The spinning solution is subjected to flash spinning, cold pressing and hot rolling to obtain conductive flash sheet.

[0049] Preferably, the solvent has a boiling point of less than or equal to 100°C.

[0050] More preferably, the solvent includes at least one of benzene, toluene, butane, pentene, n-hexane, heptane, octane, cyclohexane, dichloromethane, carbon tetrachloride, chloroform, chloromethane, chlorofluoromethane, and chloroethane.

[0051] More preferably, the mass ratio of the solid phase to the liquid phase in the spinning solution is (10:90) to (30:70).

[0052] This application also provides the application of a conductive flash evaporation sheet in the preparation of a gas diffusion layer for a battery. The gas diffusion layer of the battery includes the gas diffusion layer of an electrolytic cell for the electrocatalytic reduction of carbon dioxide. The conductive flash evaporation sheet of this application has a small thickness, low resistance, low diffusion resistance, high permeability, excellent hydrophobicity, and high tear strength. It can provide sufficient support strength for the bonding of the catalyst layer and other battery components, is not easily torn, and has a long lifespan. This provides a scientifically feasible solution for promoting the replacement of carbon paper as the battery diffusion layer.

[0053] Compared with the prior art, this application has the following beneficial effects: This application provides the main conductivity of flash nonwoven fabric by adding carbon-based conductive agent, and at the same time, it combines conductive whiskers and porous silica to form a stable and effective conductive network structure, which significantly reduces the resistance of flash nonwoven fabric. Furthermore, it improves the dispersibility of carbon-based conductive agent and conductive whiskers by polyvinyl alcohol and compatibilizer, thus comprehensively improving the conductivity of flash nonwoven fabric while maintaining its good mechanical properties and high air permeability. Detailed Implementation

[0054] To better illustrate the purpose, technical solution, and advantages of this application, the following description, in conjunction with specific embodiments and comparative examples, aims to provide a detailed understanding of the content of this application, rather than limiting it. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this application are all commonly used reagents and instruments, all of which can be purchased commercially. For example, corresponding raw materials purchased from companies such as Qilu Petrochemical, Hangzhou Jikang New Materials Co., Ltd., Nantong Aoxin Electronic Technology Co., Ltd., Merck, Sigma-Aldrich, and Dongguan Shengli New Materials Co., Ltd. can be used, or raw materials with corresponding characteristics from other companies can be used, and there are no special requirements regarding the grade of the corresponding raw materials.

[0055] The following description of some of the raw materials used in the examples and comparative examples:

[0056] HDPE: Melt index of 6 g / 10 min at 190℃ and 2.16 kg load.

[0057] Tetraneous zinc oxide whiskers: diameter 0.5–5 μm, length 10–50 μm.

[0058] Potassium titanate whiskers 1: average diameter 50-100nm, average length 1μm.

[0059] Potassium titanate whiskers 2: average diameter 0.1-0.3 μm, average length 3-5 μm.

[0060] Potassium titanate whiskers 3: average diameter 0.2-0.5 μm, average length 5-15 μm.

[0061] Potassium titanate whiskers 4: average diameter 3-5 μm, average length 10-30 μm.

[0062] Conductive potassium titanate whiskers 1-4 are homemade, including the following steps:

[0063] (1) Mix 0.8 parts by weight of tin chloride, 0.8 parts by weight of antimony chloride, 40 parts by weight of ethanol and 0.2 parts by weight of acetylacetone, and stir for 1.5 h to obtain a precursor solution.

[0064] (2) Four parts by weight of potassium titanate whiskers 1 to 4 were each stirred and dispersed in 50 parts by weight of water at 60°C to obtain four suspensions. The precursor solution was added to each of the four suspensions and reacted at 90°C for 2 hours. Then the temperature was raised to 110°C and stirred until the solvent was completely evaporated to obtain the precursor product.

[0065] (3) The precursor products were calcined at 500°C for 3 hours to obtain conductive potassium titanate whiskers 1 to 4.

[0066] Porous silica 1: Surface area 590-690m² 2 / g, average particle size 20nm.

[0067] Porous silica 2: Surface area 900-1100m² 2 / g, average particle size 1μm.

[0068] Porous silica 3: Surface area 300-400m² 2 / g, average particle size 2μm.

[0069] Porous silica 4: Surface area 300-400m² 2 / g, average particle size 3μm.

[0070] Polyvinyl alcohol (PVA): Mw89000-98000.

[0071] Compatibilizer 1: Ethylene-octene copolymer grafted with maleic anhydride (POE-g-MAH).

[0072] Compatibilizer 2: Linear low-density polyethylene grafted with maleic anhydride (LLDPE-g-MAH).

[0073] Graphene: Sheet thickness 0.2-0.5mm, commercially available.

[0074] Carbon fiber: 0.5-1mm in length, commercially available.

[0075] The compound antioxidant is obtained by combining antioxidant 1010 and antioxidant 168 in a 1:1 ratio. Both antioxidant 1010 and antioxidant 168 are commercially available.

[0076] Example 1

[0077] A conductive flash-evaporated sheet, the composition of which is shown in Table 1, and the specific preparation method includes the following steps:

[0078] (1) High-density polyethylene, carbon-based conductive agent, conductive whiskers, porous silica, polyvinyl alcohol, compatibilizer and optional additives are mixed evenly in a mixer, and then transferred to a twin-screw extruder for melt extrusion granulation at 90-180℃ to obtain masterbatch. The temperature settings of the twin-screw extruder are: Zone 1 90-110℃, Zone 2 120-130℃, Zone 3 150-160℃, Zone 4 170-180℃, Zone 5 170-185℃, Zone 6 170-185℃, Zone 7 160-165℃, Zone 8 160-165℃, Zone 9 160-165℃, Zone 10 160-165℃. The screw speed of the twin-screw extruder is 180-220 rpm.

[0079] (3) The masterbatch is transferred to a reaction vessel containing a mixed solvent of difluorochloromethane and tetrafluorodichloroethane (the volume ratio of difluorochloromethane to tetrafluorodichloroethane is 15:85). The mixture is preheated to 180°C, then nitrogen gas is introduced to pressurize it to 12 MPa, and finally the temperature is raised to 225°C and stirred in a sealed container for 2 hours. After the temperature stabilizes, a spinning solution is obtained. The mass ratio of the solid phase to the liquid phase in the spinning solution is 15:85.

[0080] (4) Refer to CN115323628B and use flash spinning equipment 300 or other conventional spinning equipment to transfer the spinning solution to the nozzle for spinning. Then, the spinning solution is refracted and reflected by the rotating filament splitter to form a mesh and is laid on the moving screen. The speed of the sprayed air is 12000m / min, the frequency of the rotating filament splitter is 35Hz, and the forward speed of the moving screen is 45m / min. The collected mesh is cold-pressed at 0.5-1MPa and hot-rolled at 140℃ and 3-3.5MPa (hot rolling roll surface speed is 45-50m / min) to obtain conductive flash sheet material.

[0081] Examples 2-12

[0082] The conductive flash evaporation sheet of Examples 2-12 differs from that of Example 1 in that the raw material composition is as shown in Table 1, and the specific preparation method is the same as that of Example 1.

[0083] Comparative Examples 1-6

[0084] The conductive flash sheet of Comparative Examples 1 to 6 differs from Example 1 in that the raw material composition is as shown in Table 2, and the specific preparation method is the same as that of Example 1.

[0085] Table 1

[0086]

[0087] Table 2

[0088]

[0089]

[0090] To verify the performance of the conductive flash sheet of this application, the products prepared in the above embodiments and comparative examples were subjected to the following performance tests. The specific methods and acceptance criteria are as follows:

[0091] (1) Fracture strength: Tested in accordance with GB / T 24218.3. The qualified standard is: MD (longitudinal) greater than or equal to 240N / 5cm, CD (transverse) greater than or equal to 250N / 5cm.

[0092] (2) Breathability: The test shall be conducted in accordance with GB / T 5453. A breathability of 30 mm / s or more shall be considered as qualified.

[0093] (3) Resistivity: Refer to GB / T20042.7 Proton Exchange Membrane Fuel Cell Part 7: Test Method for Carbon Paper Characteristics (Vertical Resistivity), the resistivity is less than or equal to 200 mΩ·cm.

[0094] (4) Sheet density: Sheet density (g / cm) 3 = Sheet mass (g / m) 2 Sheet thickness (μm) acceptance standard: density greater than or equal to 0.4 and less than or equal to 0.5 g / m 3 .

[0095] The performance results are shown in Table 3 below.

[0096] Table 3

[0097]

[0098]

[0099] As shown in Table 3 above, the conductive flash-evaporated sheet prepared in the above embodiments exhibits a tensile strength of MD (longitudinal) greater than or equal to 240 N / 5 cm and CD (transverse) greater than or equal to 250 N / 5 cm. The air permeability of the conductive flash-evaporated sheet prepared in the above embodiments is greater than or equal to 30 mm / s. The resistivity of conventional carbon paper is related to its thickness, and the same applies to conductive flash-evaporated sheets. However, since its thickness is correlated with the basis weight of the flash-evaporated nonwoven fabric, the relationship between basis weight and thickness is also considered when preparing or selecting conductive flash-evaporated sheets. Therefore, this application uses density to consider the basis weight and thickness of the sheet, with a density of 0.4-0.5 g / cm. 3 Under these conditions, the resistivity is less than or equal to 200 mΩ·cm. The conductive flash sheet of this application maintains superior mechanical properties while exhibiting high air permeability and conductivity.

[0100] As shown in Example 1 and Comparative Examples 1-3, zinc oxide whiskers and conductive potassium titanate whiskers can synergistically improve the conductivity of flash-evaporated nonwoven fabrics. In Comparative Example 6, the non-conductive potassium titanate whiskers had little effect on improving the conductivity of the system. Furthermore, based on Comparative Example 4, it can be seen that porous silica can significantly improve the conductivity of the system by interacting with both zinc oxide whiskers and conductive potassium titanate whiskers.

[0101] As can be seen from Examples and Comparative Example 5, PVA can wet porous silica, zinc oxide whiskers, and conductive potassium titanate whiskers. When combined with compatibilizers, it can improve the compatibilizer properties of the system and enhance the hydrophobicity, air permeability, and mechanical properties of flash nonwoven fabrics.

[0102] As shown in Examples 1 and 2, compared with graphene, when carbon fiber is used as the conductive agent, the flash nonwoven fabric has better conductivity, mechanical properties and air permeability.

[0103] As can be seen from Examples 1 and 3-4, the mass ratio of zinc oxide whiskers to conductive potassium titanate whiskers can be selected as (1:11):1, and a higher amount of zinc oxide whiskers is selected. This results in better conductivity of the flash-evaporated nonwoven fabric and is more beneficial for improving mechanical properties.

[0104] As can be seen from Examples 1 and 5, when the amount of porous silica is within a suitable range, it not only does not significantly improve the mechanical properties of flash nonwoven fabric, but also significantly improves its conductivity. However, as the amount of porous silica gradually increases, the mechanical properties, air permeability, and conductivity of the system show a downward trend. The inventors found that when the amount of porous silica in the system is greater than or equal to 5 parts by weight and less than or equal to 15 parts by weight, the mechanical properties, air permeability, and conductivity of the flash nonwoven fabric are better.

[0105] As can be seen from Examples 1 and 6-8, the diameter and length of conductive potassium titanate whiskers have a certain influence on the conductivity of flash-evaporated nonwoven fabric. As the diameter and length of conductive potassium titanate whiskers increase, the conductivity of flash-evaporated nonwoven fabric first increases and then decreases. Therefore, it is preferred that the average diameter of conductive potassium titanate whiskers is greater than or equal to 50 nm and less than or equal to 5 μm, and the average length is greater than or equal to 0.8 μm and less than or equal to 30 μm. More preferably, the average diameter is greater than or equal to 0.1 μm and less than or equal to 0.5 μm, and the average length is greater than or equal to 3 μm and less than or equal to 15 μm.

[0106] As shown in Examples 1 and 9-11, the average particle size of porous silica has a certain influence on the conductivity of flash-evaporated nonwoven fabric. As the average particle size of porous silica increases, the conductivity of flash-evaporated nonwoven fabric first increases and then decreases. The average particle size of porous silica can be selected as 10 nm and less than or equal to 3 μm. However, the effect of porous silica with smaller particle size combined with conductive agent, zinc oxide whiskers and conductive potassium titanate whiskers is relatively poor. Flash-evaporated nonwoven fabric with porous silica of greater than or equal to 1 μm and less than or equal to 2 μm has better conductivity.

[0107] As can be seen from Examples 1 and 12, compared with POE-g-MAH compatibilizer, LLDPE-g-MAH has better compatibility with HDPE matrix and other inorganic materials, resulting in better mechanical and electrical properties of flash nonwoven fabric.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A conductive flash evaporation sheet, characterized in that, The product comprises the following components in parts by weight: 100 parts high-density polyethylene, 4-20 parts carbon-based conductive agent, 3-10 parts conductive whiskers, 5-15 parts porous silica, 1-5 parts polyvinyl alcohol, 1-5 parts compatibilizer, and 0-2 parts additives; wherein the conductive whiskers include zinc oxide whiskers and conductive potassium titanate whiskers. The resistivity of the conductive flash sheet is less than or equal to 200 mΩ·cm; The density of the conductive flash sheet is greater than or equal to 0.4 g / cm³. 3 And less than or equal to 0.5 g / cm 3 ; The porous silica has an average particle size greater than or equal to 0.01 μm and less than or equal to 3 μm. The conductive potassium titanate whiskers have an average diameter greater than or equal to 0.05 μm and less than or equal to 5 μm, and an average length greater than or equal to 0.8 μm and less than or equal to 30 μm. The compatibilizer includes at least one of POE-g-MAH, PE-g-MAH, and LLDPE-g-MAH; The zinc oxide whiskers have an average diameter greater than or equal to 0.5 μm and less than or equal to 5 μm, and an average length greater than or equal to 10 μm and less than or equal to 50 μm.

2. The conductive flash sheet as described in claim 1, characterized in that, The average particle size of the porous silica is greater than or equal to 1 μm and less than or equal to 2 μm.

3. The conductive flash sheet as described in claim 1, characterized in that, The mass ratio of the zinc oxide whiskers to the conductive potassium titanate whiskers is (1-12):

1.

4. The conductive flash sheet as described in claim 1, characterized in that, The conductive potassium titanate whiskers have an average diameter greater than or equal to 0.1 μm and less than or equal to 0.5 μm, and an average length greater than or equal to 3 μm and less than or equal to 15 μm.

5. The conductive flash sheet as described in claim 1, characterized in that, The conductive potassium titanate whiskers are antimony tin oxide modified potassium titanate whiskers.

6. The conductive flash sheet as described in claim 1, characterized in that, Includes at least one of the following: A. The carbon-based conductive agent includes at least one of graphene, conductive carbon black, and carbon fiber; B. The additives include at least one of antioxidants, lubricants, and flame retardants.

7. A method for preparing the conductive flash evaporation sheet according to any one of claims 1-6, characterized in that, Includes the following steps: (1) The raw materials are blended, extruded and granulated to obtain masterbatch; (2) The masterbatch and solvent are mixed, then heated and nitrogen is introduced so that the temperature in the mixing device is greater than or equal to 200°C and less than or equal to 230°C, and the pressure is greater than or equal to 10MPa and less than or equal to 12MPa, to obtain a spinning solution. (3) The spinning solution is subjected to flash spinning, cold pressing and hot rolling to obtain the conductive flash sheet.

8. The application of the conductive flash evaporation sheet according to any one of claims 1-6 in the preparation of a gas diffusion layer for a battery.

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