A highly permeable carbon fiber composite paper and its preparation method

Abstract

This invention relates to a high-permeability carbon fiber composite paper and its preparation method. The high-permeability carbon fiber composite paper is obtained by casting a slurry onto a flat surface, drying it, and then heat-treating it. The slurry is prepared by mixing short-cut carbon fibers, water, binder, and dispersant as the main raw materials. The zero-shear viscosity of the slurry at 25°C is 2000–30000 mPa·s. The mass fraction of short-cut carbon fibers in the slurry is less than 5%. The length of the short-cut carbon fibers is 0.1–10 mm, and the proportion of short-cut carbon fibers with a length of 0.1–5 mm is more than 75%. The obtained high-permeability carbon fiber composite paper contains carbon fibers and resin carbon, which is formed by carbonization of the binder. In the high-permeability carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions, resulting in a looser overlap between the carbon fibers in the prepared product, increasing the porosity of the carbon fiber composite paper, and enhancing gas permeability. Furthermore, the method of this invention uses a casting process, which allows for continuous production, is environmentally friendly, and has low cost.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber composite paper technology, and relates to a highly breathable carbon fiber composite paper and its preparation method. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are among the most important hydrogen energy conversion devices, providing clean and efficient power in a variety of transportation, stationary, and portable electricity applications. Their high power density, low weight, and small size make them a preferred alternative to traditional fuel cell systems in transportation applications.

[0003] The gas diffusion layer is a crucial component of proton exchange membrane fuel cells (PEMFCs), playing a vital role in electron conduction, reactant gas transport, and hydrothermal management within the fuel cell stack. Short carbon fiber composite paper, due to its high porosity, permeability, electrical and thermal conductivity, excellent mechanical strength, and outstanding corrosion resistance, has become a primary material for the gas diffusion layer in PEMFCs, and a significant factor limiting the performance of these fuel cells.

[0004] The mainstream preparation method for short carbon fiber composite paper is wet papermaking. Reference 1 (Diffusion mediamaterials and characterisation[M]. John Wiley & Sons, Ltd., 2010.) describes the specific steps of wet papermaking as follows:

[0005] (1) A certain length of carbon fiber (usually 2-10 mm) is evenly dispersed in water with a dispersant, then formed into a precursor by a paper machine and dried.

[0006] (2) The dried precursor is immersed in a phenolic resin solution of a certain concentration to adsorb phenolic resin and improve the performance of the final product.

[0007] (3) The precursor adsorbed with phenolic resin is dried and then hot-pressed.

[0008] (4) Under a certain pressure in an inert environment, high temperature treatment is carried out to remove non-carbon elements, so that the carbon fibers can be interconnected through residual carbon to form a conductive network structure.

[0009] However, the wet papermaking technology for preparing short carbon fiber composite paper has many drawbacks, as follows:

[0010] (I) In wet papermaking technology, when carbon fiber slurry is filtered and formed through a screen, the carbon fibers are preferentially distributed within the plane of the screen due to the influence of fluid pressure. After resin impregnation, it is further hot-pressed under a pressure of about 20 MPa, which further improves the in-plane orientation distribution of the carbon fibers. This stacked structure of random planar pores means that when carbon paper is used as a gas diffusion layer, the planar stacked carbon fibers hinder the vertical passage of gas, resulting in relatively low air permeability. Furthermore, due to the limitation of the planar stacking method of carbon fibers, it is difficult to increase the porosity of carbon paper, which in turn affects the improvement of air permeability.

[0011] The reason for this problem is that in carbon fiber composite paper, the fibers are rigid, straight, and randomly oriented, resulting in an irregularly distributed stack of planar pores with high vertical tortuosity and a high overlap density between carbon fibers, thus leading to low air permeability. Existing technologies often increase air permeability by increasing the length of carbon fibers to improve pore size. However, as the length of carbon fibers increases, the paper's uniformity decreases, and due to limitations in the carbon fiber stacking method, increasing porosity is difficult, affecting air permeability. Furthermore, because the fibers preferentially orient in the plane, the microstructure exhibits high anisotropy, which in turn affects gas transport characteristics, thermal conductivity, and electrical conductivity.

[0012] (II) The base paper often needs to be impregnated with phenolic resin to enhance the performance of the final product. However, phenolic resin has poor wettability on carbon fibers and cannot achieve the ideal situation of only bonding the overlapping points of carbon fibers. Therefore, in practice, it often blocks many pores formed by the overlapping of carbon fibers, reducing the air permeability of carbon fiber paper.

[0013] Chinese patent CN111900418A uses a small amount of nanocellulose to replace PVA fibers in wet papermaking, giving the precursor a certain mechanical strength. This reduces char residue and improves the air permeability of the carbon paper. However, only a small portion of the char residue in the carbon paper comes from the binder used in the precursor molding process, thus the improvement in air permeability is very limited. Chinese patent CN113564749A uses a composite spinning process of phenolic resin and PVA in wet papermaking, improving the adhesion of phenolic resin to carbon fibers and thus increasing the air permeability of the carbon paper. However, due to the poor spinnability of phenolic resin and the low proportion of phenolic resin in the composite fiber, it is difficult to control the balance between the strength and air permeability of the carbon paper. Chinese patent CN 115775890A describes a method of obtaining highly permeable carbon paper by dripping carbon fiber slurry onto a microcrystalline cellulose template and then calcining to remove the microcrystalline cellulose template, but the prepared carbon paper has poor uniformity and strength.

[0014] Therefore, it is of great significance to study a highly permeable carbon fiber composite paper and its preparation method without sacrificing mechanical strength in order to solve the above problems. Summary of the Invention

[0015] The purpose of this invention is to solve the problems existing in the prior art and to provide a highly breathable carbon fiber composite paper and its preparation method.

[0016] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0017] A method for preparing a highly permeable carbon fiber composite paper involves casting a slurry onto a flat surface, drying it at room temperature (25°C), and then subjecting it to heat treatment to obtain the highly permeable carbon fiber composite paper.

[0018] The slurry is prepared by mixing short-cut carbon fibers, water, binder and dispersant as the main raw materials;

[0019] The slurry has a zero-shear viscosity of 2000–30000 mPa·s at 25°C;

[0020] The mass fraction of short-cut carbon fibers in the slurry is less than 5%; the length of the short-cut carbon fibers is 0.1 to 10 mm, and the proportion of short-cut carbon fibers with a length of 0.1 to 5 mm is more than 75%.

[0021] The heat treatment includes carbonization and graphitization;

[0022] According to the concept of "crowding factor N" proposed by Kerekes et al., it is defined as the number of fibers in the spherical space formed by the rotation of a single fiber, as shown in the following formula, where Cv, L and d represent the volume fraction, length and diameter of carbon fiber (CF), respectively.

[0023]

[0024] It can be seen that as N increases, the possibility of collisions between fibers increases. When fibers overlap to form a coherent network, the flowability of fibers decreases, and the rotation of a single fiber is hindered, which will cause flocculation between fibers.

[0025] In traditional wet papermaking, 1g of carbon fiber dispersed in 5-10L of water results in low dispersion uniformity. In cast papermaking, 1g of carbon fiber dispersed in 50-200mL of water leads to a much higher mass fraction of carbon fiber compared to wet papermaking, making uniform dispersion difficult. In this invention, the majority of the chopped carbon fibers are 0.1-5mm in length. Experiments show that when the solid content and diameter of the chopped carbon fibers remain constant, shortening the length reduces the nitrogen (N) value of the carbon fiber aqueous dispersion. A lower N value indicates fewer chopped carbon fibers in the same space, less contact between fibers, and improved flowability, thus reducing flocculation and improving the macroscopic uniformity of the carbon fiber aqueous dispersion. Therefore, this invention uses a casting method to prepare a high-permeability carbon fiber composite paper with excellent performance.

[0026] As a preferred technical solution:

[0027] The method for preparing a highly permeable carbon fiber composite paper as described above further includes thermal crosslinking, which is performed before carbonization, and the thermal crosslinking and carbonization are performed sequentially.

[0028] The preparation method of the high-permeability carbon fiber composite paper described above includes other additives in the raw materials of the slurry. The other additives are one or more of glycerin, defoamer, crosslinking agent, pore-forming agent, reinforcing agent and conductive filler. Glycerin can provide flexibility to the composite paper, and the defoamer reduces the bubbles in the cast slurry, thereby avoiding the generation of bubbles during casting.

[0029] In the preparation method of the high-permeability carbon fiber composite paper described above, the mass fraction of the dispersant in the slurry is 0.01-1%, the mass fraction of the binder is 0.1-20%, and the mass fraction of other additives is less than 10%; the mass fraction of glycerol is 1-100% of the binder, the mass fraction of the defoamer is 1-50% of the binder, the mass fraction of the crosslinking agent is 0.1-100% of the binder, and the mass fractions of the pore-forming agent, reinforcing agent, and conductive filler in the slurry are all in the range of 0.01-5%.

[0030] The method for preparing a highly breathable carbon fiber composite paper as described above includes the following: the adhesive is one or more of sodium carboxymethyl cellulose, polyethylene oxide, polyvinyl alcohol, rosin, and their derivatives; the dispersant is one or more of sodium carboxymethyl cellulose, polyethylene oxide, polyacrylamide, and anionic polyacrylamide; the crosslinking agent is a reagent that enables the adhesive to crosslink, such as glyoxal; the pore-forming agent is one or more of polyvinyl butyral, polyvinyl butyral-modified phenolic resin, polyvinyl alcohol, polyvinyl alcohol-modified phenolic resin, ammonium bicarbonate, ammonium chloride, and starch; and the reinforcing agent is polyvinyl butyral-modified phenolic resin, polyvinyl alcohol-modified... The adhesive is formulated with one or more of the following: phenolic resin, water-soluble polyurethane, aramid, polyamide epichlorohydrin, boric acid and its derivatives, phosphoric acid and its derivatives, and bromide; the conductive filler is one or more of the following carbon-based conductive fillers: carbon powder, carbon black, graphene, and carbon nanotubes; the adhesive used has good adhesion, and after the base paper is carbonized, the carbon fibers can still be interconnected through the resin carbon to form a loose three-dimensional network structure; the adhesive used has a moderate residual carbon content, so that the carbon fibers cannot be bonded due to too low a residual carbon content, resulting in low strength of the finished product, and the pores are not blocked due to too high a residual carbon content, resulting in low air permeability, pore size, and porosity.

[0031] The preparation method of the high-permeability carbon fiber composite paper described above has the following process parameters for thermal cross-linking: temperature 20-300℃, pressure 0-10MPa, and time 5-180min.

[0032] The carbonization process parameters are: temperature 800~1200℃, pressure 0~20MPa, time 30~180min, and atmosphere is inert gas;

[0033] The graphitization process parameters are: temperature 2000~2800℃, pressure 0~10MPa, time 30~150min, and inert gas atmosphere.

[0034] In the preparation method of the high-permeability carbon fiber composite paper described above, the casting height (i.e. the coating height) is less than 10 mm.

[0035] This invention also provides a highly permeable carbon fiber composite paper prepared by the method described in any of the preceding claims, comprising carbon fibers and resin carbon, wherein the resin carbon is formed by carbonization of an adhesive. In the highly permeable carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions, resulting in a three-dimensional pore structure. Carbon fibers longer than the casting height tend to have a planar orientation, and more than 75% of them have an angle of less than 30° with an infinite number of mutually parallel XY planes. Carbon fibers shorter than the casting height tend to have a planar or vertical orientation, and more than 50% of them have an angle of greater than 10° with an infinite number of mutually parallel XY planes. This invention uses a casting method to prepare carbon fiber composite paper. In the casting slurry, the carbon fibers are freely oriented. During casting, carbon fibers longer than the casting height are more likely to preferentially oriented along the casting plane due to hydrodynamic forces and the limitation of the casting height, exhibiting a planar orientation tendency. Carbon fibers shorter than the casting height are less affected and maintain their original free orientation distribution. In the final high-permeability carbon fiber composite paper, over 75% of the carbon fibers longer than the casting height have an angle of less than 30° with an infinite number of parallel XY planes; over 50% of the carbon fibers shorter than the casting height have an angle of greater than 10° with an infinite number of parallel XY planes. In contrast, in existing technologies, carbon fiber composite paper obtained through wet papermaking has carbon fibers distributed in a planar orientation within each layer. In this invention, the connection methods between carbon fibers include the following four types: carbon fibers with a planar orientation tend to overlap each other, and the overlap points are wrapped with resin carbon; carbon fibers with a planar orientation tend to overlap with carbon fibers with a vertical orientation tend to overlap each other, and the overlap points are wrapped with resin carbon; carbon fibers are connected by resin carbon, and the connected carbon fibers have no direct contact points with each other; and carbon fibers with a vertical orientation tend to overlap each other, and the overlap points are wrapped with resin carbon.

[0036] In traditional wet papermaking technology, carbon fiber slurry is first filtered to remove moisture. The carbon fibers overlap within the plane of the filter screen, and this planar layered stacking forms carbon fiber base paper. After impregnation with phenolic resin, it undergoes hot pressing at 5–30 MPa pressure for shaping, further improving the orientation distribution of the carbon fibers in the plane, resulting in a denser planar stacked structure. Therefore, the final structure of wet-process carbon fiber composite paper is: carbon fibers overlap in the plane through resin carbon, and a planar layered structure is stacked in the vertical plane. This porous structure makes the path for gas passage complex and tortuous, resulting in very limited improvement in air permeability.

[0037] This invention employs a casting process, dispersing carbon fibers of varying lengths in an aqueous binder solution. During casting, high shear rate stirring allows the carbon fibers to freely disperse and orient. During casting, the slurry operates at a low shear rate; due to its high viscosity, the carbon fibers are less prone to movement, thus maintaining their orientation. During casting, carbon fibers with high aspect ratios tend towards planar orientation, while those with low aspect ratios largely maintain their original orientation. Longer fibers with planar orientation can overlap with a significant portion of shorter, vertically oriented fibers. During drying, solvent evaporation causes asymmetrical movement of the carbon fibers, with some shorter fibers orienting vertically under the influence of water molecules. After drying, the resulting base paper contains carbon fibers that are freely oriented and distributed within the resin matrix (binder) as reinforcement, representing a typical fiber-reinforced composite material. Furthermore, within the base paper, carbon fibers do not necessarily overlap; one fiber can be connected to another through the resin matrix. After the base paper is heat-treated and then carbonized and shrunk with resin, the main ways in which carbon fibers overlap are: ① Carbon fibers with a planar orientation overlap each other, and the overlap point is wrapped by resin carbon; ② Carbon fibers with a planar orientation overlap each other with carbon fibers with a vertical orientation, and the overlap point is wrapped by resin carbon; ③ Carbon fibers are connected by resin carbon, and there is no direct contact point between the connected carbon fibers; ④ Carbon fibers with a vertical orientation overlap each other, and the overlap point is wrapped by resin carbon. Unlike the overlapping method in wet papermaking (the overlapping of planar-oriented long carbon fibers and the fixation by resin residue at the overlapping points), in the overlapping types of this invention: the angle between the long fibers and an infinite number of parallel XY planes in method ① is greater than the angle between the long fibers and an infinite number of parallel XY planes in wet papermaking, so the vertical height of the hole is relatively large and the hole structure is looser; method ② is the main overlapping form of this invention that increases the hole size, which can significantly widen the vertical dimension of the hole and increase the size of the hole; the overlapping method in method ③ plays an auxiliary role in increasing the size of the hole; method ④ is an overlapping method with a smaller proportion, but the overlapping between fibers with a vertical orientation can maximize the size of the hole.

[0038] This invention employs a casting process, achieving usable strength solely through adhesives and reinforcing agents, eliminating the need for additional phenolic impregnation and thus preventing the reduction of air permeability in the carbon fiber composite paper due to phenolic resin. Existing technologies suffer from decreased air permeability due to the addition of adhesives. While the amount of adhesive used in this invention is similar to that of existing technologies, its unique pore structure results in significantly larger pore sizes in the carbon fiber composite paper prepared by this invention compared to existing technologies, leading to greater air permeability while maintaining the same amount of residual carbon through the added adhesive.

[0039] As a preferred technical solution:

[0040] The high-permeability carbon fiber composite paper described above has a thickness of 30–400 μm.

[0041] The high-permeability carbon fiber composite paper described above has a porosity of 80-95%, a pore size of 20-100 μm, and an air permeability of 2000-4000 ml·mm / (cm). 2 ·hr·mmAq), with a tensile strength of 10~50MPa.

[0042] Beneficial effects:

[0043] (1) The method for preparing a high-permeability carbon fiber composite paper of the present invention is that the proportion of short-cut carbon fibers with a length of 0.1 to 5 mm in the short-cut carbon fibers is more than 75%, which reduces the occurrence of flocculation and improves the macroscopic uniformity of the carbon fiber aqueous dispersion; the casting process can be used for continuous production and does not require impregnation with phenolic resin, thus avoiding the reduction of air permeability and pore size due to the pore blockage caused by the residual carbon of phenolic resin; the obtained high-permeability carbon fiber composite paper can be rolled up, which greatly improves the flexibility of production and reduces the production cost.

[0044] (2) The method for preparing a high-permeability carbon fiber composite paper of the present invention involves only the evaporation and removal of a small amount of water as solvent in the entire production process, which greatly reduces environmental pollution and pollution treatment costs.

[0045] (3) A method for preparing a high-permeability carbon fiber composite paper according to the present invention, wherein the permeability, resistivity, pore size and tensile strength of the high-permeability carbon fiber composite paper can be effectively controlled by adjusting the length distribution and solid content of carbon fibers in the slurry, and the type and content of adhesives and additives, so as to meet the performance requirements of gas diffusion layers for fuel cells under different environmental requirements.

[0046] (3) The high-permeability carbon fiber composite paper prepared by the method of the present invention has carbon fibers that are freely oriented in three dimensions, making its pore structure three-dimensional; the overlap between carbon fibers is more loose, which increases the pore size and porosity of the carbon fiber composite paper, enhances the gas permeability, and improves the gas transmission efficiency. Attached Figure Description

[0047] Figure 1 This is a flow chart of the casting process;

[0048] Figure 2 The images show the main overlapping structure of carbon fibers in carbon fiber composite paper obtained by wet papermaking and casting methods and their scanning electron microscope (SEM) images. (a) is the wet papermaking method, and the right image in (a) is the SEM image of Comparative Example 1; (b) is the casting method, and the right image in (b) is the SEM image of Example 1.

[0049] Wherein, 1-material barrel, 2-casting cutter head. Detailed Implementation

[0050] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0051] The test methods involved in the embodiments are as follows:

[0052] Porosity, pore size, tensile strength, resistivity, and air permeability: tested according to GB / T 20042.7-2014 standard;

[0053] Zero-shear viscosity: The rheological profile of the cast slurry was measured using a rotational rheometer (MCR302e, Anton Paar) with a 25mm parallel plate clamp and a clamp gap of 1mm. The shear rate range was 0.1–100 s⁻¹. -1 The temperature range is 25–50℃; the zero-shear viscosity is derived from the rheological curve, that is, the viscosity at a shear rate of 0.

[0054] Example 1

[0055] A method for preparing a highly breathable carbon fiber composite paper, comprising the following specific steps:

[0056] (1) Preparation of raw materials:

[0057] Short-cut carbon fiber: Grade: T700; composed of 20% carbon fiber with a length of 0.5mm, 20% carbon fiber with a length of 1mm, 20% carbon fiber with a length of 1.5mm, 20% carbon fiber with a length of 2mm, 10% carbon fiber with a length of 2.5mm and 10% carbon fiber with a length of 3mm.

[0058] Adhesive: Polyvinyl alcohol; Manufacturer: Shanghai Titan, Mw: 205000;

[0059] Dispersant: Sodium carboxymethyl cellulose; Manufacturer: Shanghai Aladdin, Mw: 250000;

[0060] Glycerin; Manufacturer: Shanghai Titan; Purity: AR;

[0061] Defoamer: Manufacturer is Shanghai Wenhua Chemical Pigment Co., Ltd., brand name is S-10;

[0062] water;

[0063] (2) Figure 1 As shown, at room temperature (25°C), short-cut carbon fibers, water, adhesive, dispersant, glycerin, and defoamer were added to feed cylinder 1 as raw materials, and the mixture was reacted in 200 seconds. -1 Mix at a shear rate until the binder is completely dissolved to obtain a slurry;

[0064] The slurry contains 1% chopped carbon fiber, 0.1% dispersant, 1% binder, 0.25% glycerol, and 0.5% defoamer; the slurry has a zero-shear viscosity of 5675 mPa·s at 25°C.

[0065] (3) Adjust the height of the casting cutter head 2 to a casting height of 2.5mm and a casting speed of 0.1s. -1 The slurry was cast onto the surface of a flat plate at a certain shear rate, dried at room temperature (25°C), and then carbonized to obtain a highly permeable carbon fiber composite paper.

[0066] The carbonization process parameters are: under N2 atmosphere, at a temperature of 1000℃ and a pressure of 40Pa for 90 minutes;

[0067] The graphitization process parameters are: under N2 atmosphere, at a temperature of 2200℃ and a pressure of 40Pa for 30 minutes;

[0068] The final high-permeability carbon fiber composite paper comprises carbon fibers and resin carbon. The resin carbon is formed by carbonization of an adhesive. In the high-permeability carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions. Carbon fibers longer than the casting height tend to be planar oriented, with 76% having an angle of less than 30° with an infinite number of parallel XY planes. Carbon fibers shorter than the casting height tend to be planar or vertically oriented, with 54% having an angle of greater than 10° with an infinite number of parallel XY planes. The carbon fibers are connected in four ways: carbon fibers with a planar orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers with a planar orientation tend to overlap with carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers are connected by resin carbon, and the connected carbon fibers have no direct contact points with each other; and carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon. The high-permeability carbon fiber composite paper has a thickness of 140 μm and a basis weight of 26 g / m². 2 The high-permeability carbon fiber composite paper has a porosity of 91%, a pore size of 64 μm, and an air permeability of 2652 ml·mm / (cm). 2 The resistivity is 5.6 mΩ·cm and the tensile strength is 26 MPa.

[0069] The process of producing carbon fiber composite paper by casting according to the present invention can be carried out continuously, and the resulting high-permeability carbon fiber composite paper can be processed from roll to roll, which greatly reduces the complexity of the process and the production cost.

[0070] Comparative Example 1

[0071] A method for preparing carbon fiber composite paper using a wet papermaking process, the specific steps of which are as follows:

[0072] (1) 2g of short carbon fiber with a length of 3mm, 0.2g of polyvinyl alcohol fiber with a length of 3mm (manufacturer: Shandong Changgu Engineering Materials), 2g of dispersant (polyethylene oxide, manufacturer: Zhengzhou Liheng Chemical, Mw: 8 million) and 0.5g of defoamer (manufacturer: Shanghai Wenhua Chemical Pigment Co., Ltd., brand name: S-10) were added to 10L of water at room temperature and mixed and stirred to obtain a slurry;

[0073] (2) The pulp is dried by conventional wet papermaking, i.e., a circular copper wire mesh with a diameter of 25cm. After drying, it is impregnated in a 10wt% phenolic resin / ethanol solution for 20min. After impregnation, it is dried at 100℃ to obtain the base paper. The dried base paper is hot-pressed at 180℃ and 30MPa for 15min to obtain carbon fiber composite paper.

[0074] (3) Carbonize the hot-pressed carbon fiber composite paper to obtain high-permeability carbon fiber composite paper.

[0075] The carbonization process parameters are: under N2 atmosphere, at a temperature of 1000℃ and a pressure of 40Pa for 90 minutes;

[0076] The graphitization process parameters are: under N2 atmosphere, at a temperature of 2200℃ and a pressure of 40Pa for 30 minutes;

[0077] The final carbon fiber composite paper has a thickness of 220 μm and a basis weight of 84 g / m². 2 The carbon fiber composite paper has a porosity of 76%, a pore size of 26 μm, and an air permeability of 800 ml·mm / (cm). 2 The resistivity is 5.4 mΩ·cm and the tensile strength is 31 MPa.

[0078] Comparison will be made between Example 1 and Example 1, such as... Figure 2 As shown, Figure 2 (a) In the carbon fiber composite paper obtained by wet papermaking shown in the right figure, the carbon fibers are arranged in a planar stacked manner, and a considerable portion of the resin carbon will block the pore structure of the carbon fiber overlap, resulting in a reduction in air permeability and pore size. Generally speaking, the shorter the carbon fiber, the worse the air permeability. However, the short-cut carbon fibers used in this invention are even shorter, but the air permeability is very good, which demonstrates the advantages of the carbon fiber overlap structure of this invention. In addition, if step (2) is not performed in Comparative Example 1, the paper obtained by wet papermaking will have no strength after carbonization and will disintegrate.

[0079] Figure 2 (a) The left figure shows the main overlapping structure of carbon fibers in carbon fiber composite paper obtained by wet papermaking. The planar stacked structure is very dense. When used as a gas diffusion layer, the gas often needs to pass through many tortuous channels, resulting in low air permeability of carbon fiber composite paper. Figure 2 (b) The left figure shows the main overlapping structure of carbon fibers in the carbon fiber composite paper of the present invention. The overlapping methods between carbon fibers are mainly: ① Carbon fibers with a planar orientation tend to overlap each other, and the overlapping points are wrapped by resin carbon (i.e., the overlapping type of wet papermaking); ② Carbon fibers with a planar orientation tend to overlap each other with carbon fibers with a vertical orientation tend to overlap each other, and the overlapping points are wrapped by resin carbon; ③ Carbon fibers are connected by resin carbon, and there are no direct contact points between the connected carbon fibers; ④ Carbon fibers with a vertical orientation tend to overlap each other, and the overlapping points are wrapped by resin carbon. Among them, the overlapping methods of ②, ③, and ④ are additional structures of the present invention, which can form a three-dimensional hole, increase the size and vertical height of the hole, make the overlapping between carbon fibers more fluffy, increase the porosity of the carbon fiber composite paper, enhance the vertical permeability of gas, and improve the gas transmission efficiency. Figure 2(b) In the carbon fiber composite paper obtained in the right figure, a considerable portion of the carbon fibers have an angle greater than 30° with the XY plane, which increases the size of the pores and reduces the curvature of the gas passage.

[0080] Example 2

[0081] A method for preparing a highly permeable carbon fiber composite paper is basically the same as in Example 1, except that: a pore-forming agent (i.e., ammonium bicarbonate) with a mass fraction of 0.9% is added to the slurry, and correspondingly, the mass fraction of water is reduced by 0.9%; the zero-shear viscosity of the slurry at 25°C is 6013 mPa·s.

[0082] The final high-permeability carbon fiber composite paper comprises carbon fibers and resin carbon. The resin carbon is formed by carbonization of an adhesive. In the high-permeability carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions. Carbon fibers longer than the casting height tend to be planar oriented, with 77% having an angle of less than 30° with an infinite number of parallel XY planes. Carbon fibers shorter than the casting height tend to be planar or vertically oriented, with 56% having an angle of greater than 10° with an infinite number of parallel XY planes. The carbon fibers are connected in four ways: carbon fibers with a planar orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers with a planar orientation tend to overlap with carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers are connected by resin carbon, and the connected carbon fibers have no direct contact points with each other; and carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon. The high-permeability carbon fiber composite paper has a thickness of 140 μm and a basis weight of 25 g / m². 2 The high-permeability carbon fiber composite paper has a porosity of 95%, a pore size of 98 μm, and an air permeability of 3941 ml·mm / (cm). 2 The resistivity is 5.9 mΩ·cm and the tensile strength is 23 MPa.

[0083] Example 3

[0084] A method for preparing a highly permeable carbon fiber composite paper is basically the same as in Example 1, except that (1) a reinforcing agent (ammonium dihydrogen phosphate) with a mass fraction of 0.5% is added to the slurry, and correspondingly, the mass fraction of water is reduced by 0.5%; the zero-shear viscosity of the slurry at 25°C is 7042 mPa·s.

[0085] The final high-permeability carbon fiber composite paper comprises carbon fibers and resin carbon. The resin carbon is formed by carbonization of an adhesive. In the high-permeability carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions. Carbon fibers longer than the casting height tend to be planar oriented, with 79% having an angle of less than 30° with an infinite number of parallel XY planes. Carbon fibers shorter than the casting height tend to be planar or vertically oriented, with 60% having an angle of greater than 10° with an infinite number of parallel XY planes. The carbon fibers are connected in four ways: carbon fibers with a planar orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers with a planar orientation tend to overlap with carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers are connected by resin carbon, and the connected carbon fibers have no direct contact points with each other; and carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon. The high-permeability carbon fiber composite paper has a thickness of 140 μm and a basis weight of 30 g / m². 2 The high-permeability carbon fiber composite paper has a porosity of 89%, a pore size of 48 μm, and an air permeability of 2318 ml·mm / (cm). 2 The resistivity is 4.7 mΩ·cm and the tensile strength is 45 MPa.

[0086] Example 4

[0087] A method for preparing a highly permeable carbon fiber composite paper is basically the same as in Example 1, except that a conductive filler (carbon powder) with a mass fraction of 0.25% is added to the slurry, and correspondingly, the mass fraction of water is reduced by 0.25%; the zero-shear viscosity of the slurry at 25°C is 6731 mPa·s.

[0088] The final high-permeability carbon fiber composite paper comprises carbon fibers and resin carbon. The resin carbon is formed by carbonization of an adhesive. In the high-permeability carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions. Carbon fibers longer than the casting height tend to be planar oriented, with 77% having an angle of less than 30° with an infinite number of parallel XY planes. Carbon fibers shorter than the casting height tend to be planar or vertically oriented, with 54% having an angle of greater than 10° with an infinite number of parallel XY planes. The carbon fibers are connected in four ways: carbon fibers with a planar orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers with a planar orientation tend to overlap with carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers are connected by resin carbon, and the connected carbon fibers have no direct contact points with each other; and carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon. The high-permeability carbon fiber composite paper has a thickness of 180 μm and a basis weight of 38 g / m².2 The high-permeability carbon fiber composite paper has a porosity of 85%, a pore size of 26μm, and an air permeability of 2078 ml·mm / (cm). 2 The resistivity is 3.1 mΩ·cm and the tensile strength is 32 MPa.

[0089] Example 5

[0090] A method for preparing a highly permeable carbon fiber composite paper is basically the same as in Example 1, except that the mass fraction of short-cut carbon fibers in the slurry is increased from 1% to 1.5%, and the mass fraction of water is reduced by 0.5% accordingly; the zero-shear viscosity of the slurry at 25°C is 8872 mPa·s.

[0091] The final high-permeability carbon fiber composite paper comprises carbon fibers and resin carbon. The resin carbon is formed by carbonization of an adhesive. In the high-permeability carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions. Carbon fibers longer than the casting height tend to be planar oriented, with 78% having an angle of less than 30° with an infinite number of parallel XY planes. Carbon fibers shorter than the casting height tend to be planar or vertically oriented, with 58% having an angle of greater than 10° with an infinite number of parallel XY planes. The carbon fibers are connected in four ways: carbon fibers with a planar orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers with a planar orientation tend to overlap with carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers are connected by resin carbon, and the connected carbon fibers have no direct contact points with each other; and carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon. The high-permeability carbon fiber composite paper has a thickness of 200 μm and a basis weight of 37 g / m². 2 The high-permeability carbon fiber composite paper has a porosity of 92%, a pore size of 56 μm, and an air permeability of 2374 ml·mm / (cm). 2 The resistivity is 4.2 mΩ·cm and the tensile strength is 39 MPa.

[0092] Example 6

[0093] A method for preparing a highly breathable carbon fiber composite paper, comprising the following specific steps:

[0094] (1) Preparation of raw materials:

[0095] Short-cut carbon fiber: composed of 20% carbon fiber with a length of 0.5 mm, 20% carbon fiber with a length of 1 mm, 20% carbon fiber with a length of 1.5 mm, 20% carbon fiber with a length of 2 mm, 10% carbon fiber with a length of 2.5 mm and 10% carbon fiber with a length of 3 mm.

[0096] Adhesive: Polyvinyl alcohol; Manufacturer: Shanghai Titan, Mw: 205000;

[0097] Dispersant: Sodium carboxymethyl cellulose; Manufacturer: Shanghai Aladdin, Mw: 250000;

[0098] Glycerin; Manufacturer: Shanghai Titan; Purity: AR;

[0099] Defoamer: Manufacturer is Shanghai Wenhua Chemical Pigment Co., Ltd., brand name is S-10;

[0100] Crosslinking agent: glyoxal;

[0101] water;

[0102] (2) At room temperature (25°C), short-cut carbon fibers, water, adhesive, dispersant, glycerin, defoamer, and crosslinking agent are added to the feed cylinder as raw materials, and the mixture is stirred for 200 seconds. -1 Mix at a shear rate until the binder is completely dissolved to obtain a slurry;

[0103] The slurry contains 1% chopped carbon fiber, 0.1% dispersant, 1% binder, 0.25% glycerol, 0.5% defoamer, and 0.3% crosslinking agent by mass; the slurry has a zero-shear viscosity of 5914 mPa·s at 25°C.

[0104] (3) Adjust the height of the casting cutter head to a casting height of 2.5mm and a casting speed of 0.1s. -1 The slurry was cast onto the surface of a flat plate at a shear rate of 25°C and dried at room temperature. Then, thermal crosslinking and carbonization were carried out sequentially to obtain a highly permeable carbon fiber composite paper.

[0105] The thermal crosslinking process parameters are: under N2 atmosphere, at a temperature of 60℃ and a pressure of 40Pa for 180 minutes;

[0106] The carbonization process parameters are: under N2 atmosphere, at a temperature of 1000℃ and a pressure of 40Pa for 90 minutes;

[0107] The graphitization process parameters are: under N2 atmosphere, at a temperature of 2200℃ and a pressure of 40Pa for 30 minutes;

[0108] The final high-permeability carbon fiber composite paper comprises carbon fibers and resin carbon. The resin carbon is formed by carbonization of an adhesive. In the high-permeability carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions. Carbon fibers longer than the casting height tend to be planar oriented, with 77% having an angle of less than 30° with an infinite number of parallel XY planes. Carbon fibers shorter than the casting height tend to be planar or vertically oriented, with 56% having an angle of greater than 10° with an infinite number of parallel XY planes. The carbon fibers are connected in four ways: carbon fibers with a planar orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers with a planar orientation tend to overlap with carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers are connected by resin carbon, and the connected carbon fibers have no direct contact points with each other; and carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon. The high-permeability carbon fiber composite paper has a thickness of 140 μm and a basis weight of 31 g / m². 2 The high-permeability carbon fiber composite paper has a porosity of 88%, a pore size of 57 μm, and an air permeability of 2321 ml·mm / (cm). 2 The resistivity is 4.7 mΩ·cm and the tensile strength is 42 MPa.

[0109] Example 7

[0110] A method for preparing a highly breathable carbon fiber composite paper, comprising the following specific steps:

[0111] (1) Preparation of raw materials:

[0112] Short-cut carbon fiber: composed of 20% carbon fiber with a length of 0.5 mm, 20% carbon fiber with a length of 1 mm, 20% carbon fiber with a length of 1.5 mm, 20% carbon fiber with a length of 2 mm, 10% carbon fiber with a length of 2.5 mm and 10% carbon fiber with a length of 3 mm.

[0113] Adhesive: Sodium carboxymethyl cellulose; Manufacturer: Shanghai Aladdin, Mw: 250000;

[0114] Dispersant: Polyethylene oxide, manufactured by Zhengzhou Liheng Chemical, brand name Mw: 8 million;

[0115] Glycerin; manufacturer: Shanghai Titan; purity: AR.

[0116] Defoamer: Manufacturer is Shanghai Wenhua Chemical Pigment Co., Ltd., brand name is S-10;

[0117] water;

[0118] (2) At room temperature (25°C), chopped carbon fibers, water, adhesive, dispersant, glycerin, and defoamer are added to the feed cylinder as raw materials, and the mixture is stirred for 200 seconds. -1 Mix at a shear rate until the binder is completely dissolved to obtain a slurry;

[0119] The slurry contains 1% chopped carbon fiber, 0.1% dispersant, 1.5% binder, 0.25% glycerol, and 0.5% defoamer; the slurry has a zero-shear viscosity of 7142 mPa·s at 25°C.

[0120] (3) Adjust the height of the casting cutter head to a casting height of 2.5mm and a casting speed of 0.1s. -1 The slurry was cast onto the surface of a flat plate at a shear rate of 25°C and dried at room temperature. Then, thermal crosslinking and carbonization were carried out sequentially to obtain a highly permeable carbon fiber composite paper.

[0121] The thermal crosslinking process parameters are: under N2 atmosphere, at a temperature of 150℃ and a pressure of 40Pa for 180 minutes;

[0122] The carbonization process parameters are: under N2 atmosphere, at a temperature of 1000℃ and a pressure of 40Pa for 90 minutes;

[0123] The graphitization process parameters are: under N2 atmosphere, at a temperature of 2200℃ and a pressure of 40Pa for 30 minutes;

[0124] The final high-permeability carbon fiber composite paper comprises carbon fibers and resin carbon. The resin carbon is formed by carbonization of an adhesive. In the high-permeability carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions. Carbon fibers longer than the casting height tend to be planar oriented, with over 75% having an angle less than 30° with an infinite number of parallel XY planes. Carbon fibers shorter than the casting height tend to be planar or vertically oriented, with 52% having an angle greater than 10° with an infinite number of parallel XY planes. The carbon fibers are connected in four ways: carbon fibers with a planar orientation overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers with a planar orientation overlap each other with carbon fibers with a vertical orientation, and the overlap point is wrapped with resin carbon; carbon fibers are connected by resin carbon, and the connected carbon fibers have no direct contact points; and carbon fibers with a vertical orientation overlap each other, and the overlap point is wrapped with resin carbon. The high-permeability carbon fiber composite paper has a thickness of 150 μm and a basis weight of 31 g / m². 2 The high-permeability carbon fiber composite paper has a porosity of 90%, a pore size of 62μm, and an air permeability of 2528 ml·mm / (cm). 2The resistivity is 5.2 mΩ·cm and the tensile strength is 31 MPa.

[0125] Example 8

[0126] A method for preparing a highly breathable carbon fiber composite paper, comprising the following specific steps:

[0127] (1) Preparation of raw materials:

[0128] Short-cut carbon fiber: composed of 20% carbon fiber with a length of 0.5 mm, 20% carbon fiber with a length of 1 mm, 20% carbon fiber with a length of 1.5 mm, 20% carbon fiber with a length of 2 mm, 10% carbon fiber with a length of 2.5 mm and 10% carbon fiber with a length of 3 mm.

[0129] Adhesive: Polyethylene oxide, manufactured by Zhengzhou Liheng Chemical, Mw: 8 million;

[0130] Dispersant: Anionic polyacrylamide, manufactured by Shanghai Titan, Mw: 8 million;

[0131] Glycerin; Manufacturer: Shanghai Titan; Purity: AR;

[0132] Defoamer: Manufacturer is Shanghai Wenhua Chemical Pigment Co., Ltd., brand name is S-10;

[0133] water;

[0134] (2) At room temperature (25°C), chopped carbon fibers, water, adhesive, dispersant, glycerin, and defoamer are added to the feed cylinder as raw materials, and the mixture is stirred for 200 seconds. -1 Mix at a shear rate until the binder is completely dissolved to obtain a slurry;

[0135] The slurry contains 1% chopped carbon fiber, 0.1% dispersant, 1.5% binder, 0.25% glycerol, and 0.5% defoamer; the slurry has a zero-shear viscosity of 6778 mPa·s at 25°C.

[0136] (3) Adjust the height of the casting cutter head to a casting height of 2.5mm and a casting speed of 0.1s. -1 The slurry was cast onto the surface of a flat plate at a certain shear rate, dried at room temperature (25°C), and then carbonized to obtain a highly permeable carbon fiber composite paper.

[0137] The carbonization process parameters are: under N2 atmosphere, at a temperature of 1000℃ and a pressure of 40Pa for 90 minutes;

[0138] The graphitization process parameters are: under N2 atmosphere, at a temperature of 2200℃ and a pressure of 40Pa for 30 minutes;

[0139] The final high-permeability carbon fiber composite paper comprises carbon fibers and resin carbon. The resin carbon is formed by carbonization of an adhesive. In the high-permeability carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions. Carbon fibers longer than the casting height tend to be planar oriented, with 78% having an angle of less than 30° with an infinite number of parallel XY planes. Carbon fibers shorter than the casting height tend to be planar or vertically oriented, with 53% having an angle of greater than 10° with an infinite number of parallel XY planes. The carbon fibers are connected in four ways: carbon fibers with a planar orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers with a planar orientation tend to overlap with carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon; carbon fibers are connected by resin carbon, and the connected carbon fibers have no direct contact points with each other; and carbon fibers with a vertical orientation tend to overlap each other, and the overlap point is wrapped with resin carbon. The high-permeability carbon fiber composite paper has a thickness of 150 μm and a basis weight of 30 g / m². 2 The high-permeability carbon fiber composite paper has a porosity of 90%, a pore size of 56 μm, and an air permeability of 2431 ml·mm / (cm). 2 The resistivity is 4.8 mΩ·cm and the tensile strength is 28 MPa.

Claims

1. A method for preparing a highly permeable carbon fiber composite paper, characterized in that: Highly breathable carbon fiber composite paper is prepared by casting the slurry onto the surface of a flat plate, drying it at 25°C, and then heat-treating it. The slurry is prepared by mixing short-cut carbon fibers, water, binder and dispersant as the main raw materials; The raw materials of the slurry also include other additives, which are one or more of glycerin, defoamer, crosslinking agent, pore-forming agent, reinforcing agent and conductive filler; The slurry has a zero-shear viscosity of 2000–30000 mPa·s at 25°C; The mass fraction of chopped carbon fibers in the slurry is less than 5%; the chopped carbon fibers consist of 20% carbon fibers with a length of 0.5 mm, 20% carbon fibers with a length of 1 mm, 20% carbon fibers with a length of 1.5 mm, 20% carbon fibers with a length of 2 mm, 10% carbon fibers with a length of 2.5 mm and 10% carbon fibers with a length of 3 mm. The casting height is 2.5mm; The heat treatment includes carbonization and graphitization.

2. The method for preparing a highly permeable carbon fiber composite paper according to claim 1, characterized in that, The heat treatment also includes thermal crosslinking, which is performed before carbonization, and the thermal crosslinking, carbonization and graphitization are performed sequentially.

3. The method for preparing a highly permeable carbon fiber composite paper according to claim 1, characterized in that, The mass fraction of the dispersant in the slurry is 0.01-1%, the mass fraction of the binder is 0.1-20%, and the mass fraction of other additives is less than 10%. The mass fraction of glycerol is 1-100% of the binder, the mass fraction of the defoamer is 1-50% of the binder, the mass fraction of the crosslinking agent is 0.1-100% of the binder, and the mass fraction of the pore-forming agent, reinforcing agent, and conductive filler in the slurry is all in the range of 0.01-5%.

4. The method for preparing a highly permeable carbon fiber composite paper according to claim 3, characterized in that, The adhesive is one or more of sodium carboxymethyl cellulose, polyethylene oxide, polyvinyl alcohol, rosin and their derivatives; the dispersant is one or more of sodium carboxymethyl cellulose, polyethylene oxide, polyacrylamide and anionic polyacrylamide; the crosslinking agent is glyoxal; the pore-forming agent is one or more of polyvinyl butyral, polyvinyl butyral-modified phenolic resin, polyvinyl alcohol, polyvinyl alcohol-modified phenolic resin, ammonium bicarbonate, ammonium chloride and starch; the reinforcing agent is one or more of polyvinyl butyral-modified phenolic resin, polyvinyl alcohol-modified phenolic resin, water-soluble polyurethane, aramid, polyamide epichlorohydrin, boric acid and its derivatives, phosphoric acid and its derivatives and bromides; and the conductive filler is one or more of carbon powder, carbon black, graphene and carbon nanotubes.

5. The method for preparing a highly permeable carbon fiber composite paper according to claim 1, characterized in that, The process parameters for thermal crosslinking are: temperature 20–300℃, pressure 0–10MPa, and time 5–180min; The carbonization process parameters are: temperature 800~1200℃, pressure 0~20MPa, time 30~180min, and atmosphere is inert gas; The graphitization process parameters are: temperature 2000~2800℃, pressure 0~10MPa, time 30~150min, and inert gas atmosphere.

6. A highly breathable carbon fiber composite paper prepared by the method according to any one of claims 1 to 5, comprising carbon fibers and resin carbon, wherein the resin carbon is formed by carbonization of an adhesive, characterized in that: In high-permeability carbon fiber composite paper, the carbon fibers are freely oriented in three dimensions; carbon fibers longer than the casting height tend to be planar oriented, with over 75% having an angle of less than 30° with an infinite number of parallel XY planes; carbon fibers shorter than the casting height tend to be planar or vertically oriented, with over 50% having an angle of greater than 10° with an infinite number of parallel XY planes; the connection methods between carbon fibers include the following four: Carbon fibers with a planar orientation tend to overlap each other, and the overlap points are wrapped with resin carbon; carbon fibers with a planar orientation tend to overlap each other and the overlap points are wrapped with resin carbon; carbon fibers are connected by resin carbon, and there are no direct contact points between the connected carbon fibers. And the carbon fibers with a vertical orientation overlap each other, and the overlap points are wrapped by resin carbon.

7. The high-permeability carbon fiber composite paper according to claim 6, characterized in that, The thickness of the highly breathable carbon fiber composite paper is 30–400 μm.

8. The high-permeability carbon fiber composite paper according to claim 6, characterized in that, The porosity of the highly permeable carbon fiber composite paper is 80-95%, the pore size is 20-100 μm, and the air permeability is 2000-4000 ml·mm / (cm). 2 ·hr·mmAq), with a tensile strength of 10~50MPa.

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