Preparation method of graphite bipolar plate material with ultralow resin content and high strength

Abstract

The invention relates to a fuel cell preparation technology, and aims to provide a preparation method of a high-strength graphite bipolar plate material with ultralow resin content. The method comprises the following steps: in the preparation process of a graphite powder material, realizing directional aggregation of graphite microchips by using ceric ammonium nitrate; the thermal expansion direction of graphite is regulated and controlled by utilizing lithium ions and magnesium ions, and nearly-spherical worm graphite is obtained by matching electrochemical and microwave heating processes; by doping metal elements, the surface energy of the graphite powder is improved; and polymethyl methacrylate-nylon acid methyl ester is used, so that the resin and the graphite phase are continuously distributed. According to the invention, an amplitude-modulated decomposition bicontinuous phase separation structure is formed on the basis that the interfacial energy between resin and graphite is reduced, so that the characteristics of high strength and high toughness can be achieved under the condition of low resin content, and the mechanical property of the composite bipolar plate is further improved; due to low resin content, the composite graphite bipolar plate obtained by the invention has good electrical conductivity and thermal conductivity.

Description

Technical Field

[0001] The present invention relates to a fuel cell preparation technology, and in particular to an ultra-low resin content graphite bipolar plate material and a preparation method thereof. Background Art

[0002] Fuel cell bipolar plates are one of the core components of a fuel cell stack. They connect the individual modules, separate the reacting fuel and oxidant gases, collect and transmit current, dissipate the heat generated by the reaction to maintain a uniform temperature field in the cell, remove reaction products, and support the fuel cell. Therefore, bipolar plates must possess high electrical conductivity, high mechanical strength, good thermal conductivity, and excellent corrosion resistance to meet and adapt to the application requirements of fuel cells.

[0003] At present, there are three main types of mainstream bipolar plate materials, including graphite materials, metal materials and composite materials. Among them, graphite bipolar plates are made by pressing natural graphite or expanded graphite, but they have problems such as high porosity, high brittleness, low bending strength, and easy cracking. At the same time, in order to achieve non-porous pure graphite bipolar plates and improve their gas barrier properties, extremely harsh processing conditions are required, which is not conducive to industrial production and the expansion of industrial scale. Metal bipolar plates are difficult to overcome the problem of corrosion resistance in acidic environments. In the existing technology, composite bipolar plates are often obtained by metal plating to improve performance, but there are also problems with complex metal plating processes and high costs.

[0004] Composite bipolar plates are a promising alternative to graphite and metal bipolar plates, combining the corrosion resistance and high conductivity of graphite bipolar plates with the high mechanical properties of metal bipolar plates. Composite bipolar plates are filled with resin to reduce the porosity of graphite bipolar plates and improve their mechanical properties, but this resin filling inevitably leads to a loss of electrical conductivity. While high graphite filling can improve electrical and thermal conductivity, excessive filling can degrade mechanical properties.

[0005] Therefore, how to obtain good electrical conductivity and thermal conductivity due to high filling while still maintaining excellent mechanical properties becomes a problem that needs to be solved for composite graphite bipolar plates. Summary of the Invention

[0006] The technical problem to be solved by the present invention is a method for preparing a high-strength graphite bipolar plate material with ultra-low resin content.

[0007] To solve the technical problem, the solution of the present invention is:

[0008] The present invention further provides a method for preparing an ultra-low resin content high-strength graphite bipolar plate material, comprising the following steps:

[0009] (1) adding natural flake graphite to a mixed acid of formic acid and concentrated nitric acid, stirring at room temperature to obtain a mixture 1;

[0010] (2) adding N,N-dimethylformamide, butanone, 1,3-propylene glycol and isobutyric acid to the first mixture, stirring at room temperature to obtain the second mixture;

[0011] (3) adding ammonium persulfate, hexadecyltrimethylammonium bromide, potassium permanganate, potassium ferrate and ceric ammonium nitrate to the second mixture, and stirring to obtain the third mixture;

[0012] (4) adding magnesium nitrate and lithium nitrate to the mixture three, and stirring to obtain a liquid mixture four;

[0013] (5) adding the mixture 4 into the electrolytic cell, applying a DC voltage of 45-55 V to both ends of the electrolytic cell, and performing electrolysis for 20-30 minutes under continuous stirring to obtain the mixture 5;

[0014] (6) The mixture 5 is washed with distilled water for multiple times, and vacuum dried to obtain powder 1; after microwave heating, the mixture is cooled to room temperature to obtain powder 2; the powder 2 is then sieved using a vibrating screen to obtain powders of different particle sizes of 1500 mesh, 350 mesh, 200 mesh, 20 mesh and 2 mesh, and the mixture is re-mixed to obtain a multi-particle size mixed powder;

[0015] (7) Adding the multi-size mixed powder and the polymethyl methacrylate-methyl nylonate mixture into a double planetary disperser, stirring under vacuum conditions to obtain a mixture VI;

[0016] (8) isostatically pressing the mixture 6 into a plate 1; then, heating the mixture in a nitrogen atmosphere by a stepwise heating method to obtain a plate 2;

[0017] (9) Phthalic anhydride, maleic anhydride, E-44 epoxy resin, hexafunctional polyurethane acrylate, and polydimethylsiloxane-modified acrylate are mixed and stirred to obtain a mixture 7; the plate 2 is immersed in the mixture 7 and subjected to a pressure treatment to obtain a plate 3;

[0018] (10) Heat-treating the plate 3 to obtain the plate 4; polishing the surface of the plate 4 to remove excess solidified resin, thereby obtaining an ultra-low resin content high-strength graphite bipolar plate material.

[0019] As a preferred embodiment of the present invention, in step (1), the mass fraction of concentrated nitric acid is 65%, the volume ratio of formic acid to concentrated nitric acid is 2.5-3.5:1; the particle size of natural flake graphite is 4-24 μm, and the mass ratio of natural flake graphite to mixed acid is 12-24%; and the stirring treatment time is 10-30 minutes.

[0020] As a preferred embodiment of the present invention, in step (2), the mass ratio of N,N-dimethylformamide, butanone, 1,3-propylene glycol and isobutyric acid is 1-2.5:1:1:1.5, and the total mass accounts for 15-25% of the mass of the mixture; the stirring time is 10-30 minutes.

[0021] As a preferred embodiment of the present invention, in step (3), the mass ratio of ammonium persulfate, hexadecyltrimethylammonium bromide, potassium permanganate, potassium ferrate and ceric ammonium nitrate is 3-5:0.2:1:1:2, and the total mass accounts for 3.5-5.5% of the mass of the mixture; the stirring time is 1-2 hours.

[0022] As a preferred embodiment of the present invention, in step (4), the mass ratio of magnesium nitrate to lithium nitrate is 1-3:1, and the total mass accounts for 0.1-0.3% of the mass of the mixture; the stirring time is 1-2 hours.

[0023] As a preferred embodiment of the present invention, in step (6), the washing refers to adding the mixture five to 5 to 7 times the mass of distilled water, stirring and mixing for 10 to 20 minutes and then filtering; repeating this operation 3 to 5 times; the vacuum drying refers to placing the washed mixture five in a vacuum oven at 60 to 80°C for 3 to 7 hours; the microwave heating treatment refers to placing the dried mixture five in a microwave heating furnace and treating it at a power of 1200 to 2000 W for 20 to 30 seconds; in the multi-particle size mixed powder, the mass ratio of 1500 mesh, 350 mesh, 200 mesh, 20 mesh and 2 mesh powders is 0.8:1.3~1.7:2.5:4.1:6.3.

[0024] As a preferred embodiment of the present invention, in step (7), the mass fraction of polymethyl methacrylate in the polymethyl methacrylate-methyl nylonate mixture is 3 wt %; the mixture accounts for 3-5% of the total mass of the multi-particle mixed powder; the stirring speed of the double planetary disperser is 100-300 rpm, the vacuum is sealed to 5-7 Pa, and the stirring time is 1-3 hours.

[0025] As a preferred embodiment of the present invention, in step (8), the pressure of the isostatic pressing method is controlled to be 100-120 MPa, and the thickness of the plate 1 is 1-3 mm; the step-by-step heating method for heating treatment means first heating the temperature to 210-230°C and keeping the temperature for 2-4 hours, then heating the temperature to 420-440°C and keeping the temperature for 1-3 hours, and then cooling to room temperature.

[0026] As a preferred embodiment of the present invention, in step (9), phthalic anhydride, maleic anhydride, E-44 epoxy resin, hexafunctional polyurethane acrylate, and polydimethylsiloxane-modified acrylate are mixed in a mass ratio of 0.005:0.003:1:3:8 and stirred for 30 to 40 minutes to obtain a mixture seven; the pressure treatment refers to pressurizing to 30 to 50 MPa and maintaining the pressure for 12 to 36 hours, and after depressurizing, taking out the plate and scraping off excess mixture seven on the surface of the plate.

[0027] As a preferred embodiment of the present invention, in step (10), the heating treatment refers to heating the plate to 170-190° C. and keeping the temperature for 24-48 hours.

[0028] Description of the invention principle:

[0029] The present invention adds ammonium cerium nitrate and lithium nitrate to the graphite powder material during preparation, and uses electrochemical (electrolysis) and microwave heating processes and corresponding parameters to produce nearly spherical vermicular graphite. This process utilizes the high-valent cerium ions in the ammonium cerium nitrate to occupy defect sites in the graphite, achieving directional aggregation of graphite flakes. The small size of lithium and magnesium ions penetrates the interlayers of the graphite, regulating the direction of thermal expansion. This microstructural adjustment results in nearly spherical vermicular graphite, which improves the graphite's compaction density, reduces porosity, and enhances mechanical strength.

[0030] In the subsequent process, the present invention combines the optimized gradation obtained from a large number of experiments, and by adding iron elements during the preparation process, regulates the surface electronic structure of the worm graphite to increase the Fermi level, thereby reducing the interfacial energy between the resin and the graphite, which is more conducive to the formation of a special spinodal decomposition bicontinuous phase separation structure, so that the resin material forms a continuous filling inside the graphite bipolar plate, greatly enhancing the mechanical properties of the material. The mixed powder can be regulated by doping with metal elements to obtain a graphite powder with high surface energy. Combined with a specific concentration of polymethyl methacrylate-methyl nylonate mixture, the spinodal decomposition occurs inside the plate during isostatic pressing and subsequent step-by-step heating, so that the resin and graphite phases in the composite graphite bipolar plate are continuously distributed, forming a bicontinuous structure. This structural feature can achieve high strength and high toughness characteristics under low resin content conditions.

[0031] For these reasons, the resin content of the bipolar plate products of the present invention can be reduced to less than 8.5wt%, significantly lower than products produced using conventional technologies (typically 15wt%). Furthermore, due to the bicontinuous network structure within the plate, the products of the present invention maintain high strength (flexural strength >45 MPa), while products produced using conventional technologies typically have a maximum strength of around 30 MPa. While maintaining these two excellent properties, the products of the present invention have electrical conductivity >185 S / cm and thermal conductivity >28 W / m·K, resulting in excellent electrical and thermal conductivity.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention adjusts the electronic structure and interface state of graphite by introducing specific elements, thereby forming a special spinodal decomposition bicontinuous phase separation structure, so that the resin material forms a continuous filling inside the graphite bipolar plate, greatly enhancing the mechanical properties of the material.

[0034] 2. The present invention further improves the mechanical properties of the composite bipolar plate by optimizing the resin component. The resulting composite bipolar plate achieves a flexural strength of >45 MPa with a resin content of <8.5 wt%.

[0035] 3. Due to the low resin content, the composite graphite bipolar plate obtained by the present invention has good electrical conductivity and thermal conductivity; the product has an electrical conductivity of >185S / cm and a thermal conductivity coefficient of >28W / m·K. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a microstructure photo of the composite bipolar plate product of the present invention.

[0037] Figure 2 This is a microstructure photo of the composite bipolar plate product of the present invention (partial magnification).

[0038] Figure 3 This is a microstructure photo of the composite bipolar plate product in Comparative Example 1.

[0039] Figure 4 This is a microstructure photo of the composite bipolar plate product in Comparative Example 2.

[0040] Figure 5 This is a microstructure photo of the composite bipolar plate product in Comparative Example 3.

[0041] Figure 6 This is a microstructure photo of the composite bipolar plate product in Comparative Example 4. DETAILED DESCRIPTION

[0042] The present invention is described in detail below with reference to specific embodiments.

[0043] 1. Overview of the implementation scheme of the present invention

[0044] The method for preparing the ultra-low resin content high-strength graphite bipolar plate material provided by the present invention comprises the following steps:

[0045] (1) Add natural flake graphite with a particle size of 4 to 24 microns to a mixed acid of formic acid and concentrated nitric acid, and stir at room temperature for 10 to 30 minutes to obtain a mixture. As an optional example, the mass fraction of concentrated nitric acid is 65%, the volume ratio of formic acid to concentrated nitric acid is 2.5 to 3.5:1, and the mass ratio of natural flake graphite to the mixed acid is 12 to 24%. This step achieves the purpose of preliminary intercalation of flake graphite.

[0046] (2) Add N,N-dimethylformamide, butanone, 1,3-propylene glycol, and isobutyric acid to mixture one and stir at room temperature for 10 to 30 minutes to obtain mixture two. As an optional example, the mass ratio of N,N-dimethylformamide, butanone, 1,3-propylene glycol, and isobutyric acid is 1 to 2.5:1:1:1.5, and the total mass accounts for 15 to 25% of the mass of mixture one. This step achieves the second intercalation of flake graphite, further inserting N,N-dimethylformamide and isobutyric acid between the graphite layers on the basis of the initial intercalation.

[0047] (3) Add ammonium persulfate, hexadecyltrimethylammonium bromide, potassium permanganate, potassium ferrate, and ceric ammonium nitrate to mixture 2, and stir for 1 to 2 hours to obtain mixture 3; as an optional example, the mass ratio of ammonium persulfate, hexadecyltrimethylammonium bromide, potassium permanganate, potassium ferrate, and ceric ammonium nitrate is 3 to 5:0.2:1:1:2, and the total mass accounts for 3.5 to 5.5% of the mass of mixture 2. After the second intercalation step, the treatment in this step solidifies the intercalation structure of the second step, making it difficult to deintercalate in subsequent steps, thereby avoiding the consequence of being unable to expand.

[0048] (4) Adding magnesium nitrate and lithium nitrate to mixture three and stirring for 1 to 2 hours to obtain a liquid mixture four; as an optional example, the mass ratio of magnesium nitrate to lithium nitrate is 1 to 3:1, and the total mass accounts for 0.1 to 0.3% of the mass of mixture three. This step is used to adjust the surface energy of graphite, that is, by doping with magnesium and lithium, the electrons in the graphite are partially localized, thereby achieving the purpose of increasing its surface energy.

[0049] (5) Adding mixture 4 into an electrolytic cell, applying a DC voltage of 45 to 55 V to both ends of the electrolytic cell, and electrolyzing for 20 to 30 minutes under continuous stirring conditions to obtain mixture 5; continuous stirring during the electrolysis process can ensure the uniformity of the reaction system during the treatment process, thereby achieving the purpose of generating spherical structure graphite in one step.

[0050] (6) The mixture 5 is washed with distilled water for several times, and vacuum dried to obtain powder 1; after microwave heating, it is cooled to room temperature to obtain powder 2; the powder 2 is sieved with a vibrating screen to obtain powders of different particle sizes of 1500 mesh, 350 mesh, 200 mesh, 20 mesh and 2 mesh respectively, and re-mixed to obtain a multi-particle size mixed powder; as an optional example, the washing refers to adding the mixture 5 to 7 times the mass of distilled water, stirring and mixing for 10 to 20 minutes, and then Filtering; repeating this operation 3-5 times; the vacuum drying refers to placing the washed mixture 5 in a vacuum oven at 60-80°C for 3-7 hours; the microwave heating refers to placing the dried mixture 5 in a microwave oven and heating it at a power of 1200-2000W for 20-30 seconds; in the multi-size mixed powder, the mass ratio of 1500 mesh, 350 mesh, 200 mesh, 20 mesh, and 2 mesh powders is 0.8:1.3-1.7:2.5:4.1:6.3. In this step, the spherical graphite is expanded by microwave heating, and a high filling rate of the graphite powder is achieved through screening and subsequent grading. Based on this treatment, when the mixture is subsequently mixed with a polymethyl methacrylate-methyl nylonate mixture, the resulting mixture still has a certain degree of flexibility and wettability, rather than drying into a hard lump.

[0051] (7) The multi-size mixed powder and the polymethyl methacrylate-methyl nylonate mixed solution are added to a double planetary disperser and stirred under vacuum conditions for 1 to 3 hours to obtain a mixture VI; as an optional example, the mass fraction of polymethyl methacrylate in the polymethyl methacrylate-methyl nylonate mixed solution is 3 wt %; the mixed solution accounts for 3 to 5% of the total mass of the multi-size mixed powder; the stirring speed of the double planetary disperser is 100 to 300 rpm, and the vacuum is sealed to 5 to 7 Pa. Through the treatment of this step, the powder and the polymethyl methacrylate-methyl nylonate mixed solution are uniformly mixed.

[0052] (8) Mixture 6 is pressed into plate 1 by isostatic pressing; then, in a nitrogen atmosphere, the mixture is heated by a step-by-step heating method to obtain plate 2. As an optional example, the pressure of the isostatic pressing method is controlled to be 100-120 MPa, and the thickness of plate 1 is 1-3 mm. The step-by-step heating method includes first heating the mixture to 210-230°C and holding the temperature for 2-4 hours, then heating the mixture to 420-440°C and holding the temperature for 1-3 hours, and then cooling the mixture to room temperature. Through this step, the purpose of preparing a plate with a continuous pore structure is achieved.

[0053] (9) Phthalic anhydride, maleic anhydride, E-44 epoxy resin, hexafunctional polyurethane acrylate, and polydimethylsiloxane-modified acrylate are mixed and stirred for 30 to 40 minutes to obtain a mixture 7; the plate 2 is immersed in the mixture 7 and subjected to a pressure treatment to obtain a plate 3; as an optional example, the mass ratio of phthalic anhydride, maleic anhydride, E-44 epoxy resin, hexafunctional polyurethane acrylate, and polydimethylsiloxane-modified acrylate is 0.005:0.003:1:3:8. The pressure treatment refers to applying pressure to 30 to 50 MPa and maintaining the pressure for 12 to 36 hours. After the pressure is released, the plate is removed and the excess mixture 7 on the surface of the plate is scraped off. Through this step, the purpose of filling the resin into the continuous pore structure of the graphite is achieved.

[0054] (10) Heating the plate 3 to 170-190°C and maintaining the temperature for 24-48 hours to obtain the plate 4; this step achieves the purpose of resin curing. The surface of the plate 4 is further polished to remove excess cured resin, thereby obtaining a high-strength graphite bipolar plate material with an ultra-low resin content.

[0055] II. Examples and Comparative Examples

[0056] Example 1:

[0057] A method for preparing an ultra-low resin content high-strength graphite bipolar plate material comprises the following steps:

[0058] (1) Formic acid and concentrated nitric acid (65%) were mixed in a volume ratio of 2.5:1 to obtain mixed acid 1;

[0059] (2) adding natural flake graphite with a particle size of 4 to 12 μm to the mixed acid obtained in step (1), stirring at room temperature for 10 minutes to obtain a mixture (1); the mass ratio of the natural flake graphite to the mixed acid obtained in step (1) is 12%;

[0060] (3) Add N,N-dimethylformamide, butanone, 1,3-propylene glycol and isobutyric acid in a mass ratio of 1:1:1:1.5 to the mixture 1 obtained in step 2, and stir at room temperature for 10 minutes to obtain a mixture 2; the total mass of N,N-dimethylformamide, butanone, 1,3-propylene glycol and isobutyric acid accounts for 15% of the mass of the mixture 1 obtained in step (2);

[0061] (4) adding ammonium persulfate, hexadecyltrimethylammonium bromide, potassium permanganate, potassium ferrate and cerium ammonium nitrate in a mass ratio of 3:0.2:1:1:2 to the mixture 2 obtained in step (3), and the total mass accounts for 3.5% of the mass of the mixture 2; stirring for 1 hour to obtain a mixture 3;

[0062] (5) Adding magnesium nitrate and lithium nitrate in a mass ratio of 1:1 to the mixture obtained in step (4), and stirring for 1 to 2 hours to obtain a liquid mixture fourth; the total mass of the magnesium nitrate and lithium nitrate accounts for 0.1% of the mixture third obtained in step (4);

[0063] (6) Add the mixture 4 obtained in step (5) to an electrolytic cell for electrolysis, apply a 45V DC voltage to both ends of the electrolytic cell, and electrolyze for 20 minutes to obtain a mixture 5; stir continuously during the electrolysis process to ensure the uniformity of the reaction system during the treatment process.

[0064] (7) Add 5 times the mass of distilled water to the mixture obtained in step (6), stir and mix for 10 minutes, and then filter; repeat the above steps 3 times, and then vacuum dry in a 60°C oven for 3 hours to obtain powder 1;

[0065] (8) Powder 1 was placed in a microwave heating furnace with a heating power of 1200 W for 20 seconds, and then cooled to room temperature to obtain powder 2;

[0066] (9) The powder 2 obtained in step (8) was sieved through a vibrating screen to obtain 1500-mesh powder 3, 350-mesh powder 4, 200-mesh powder 5, 20-mesh powder 6, and 2-mesh powder 7;

[0067] (10) Powder 3, Powder 4, Powder 5, Powder 6 and Powder 7 were mixed in a mass ratio of 0.8:1.3:2.5:4.1:6.3, and 3% of the total mass of polymethyl methacrylate 3wt% nylon acid methyl ester / solution was added, and the mixture was stirred at 100 rpm using a double planetary disperser, sealed and evacuated to 5 Pa, and stirred for 1 hour to obtain mixture 6;

[0068] (11) isostatically pressing the mixture obtained in step (10) into a plate having a thickness of 1 mm at a pressure of 100 MPa;

[0069] (12) The plate 1 obtained in step (11) was heated to 210°C in a nitrogen atmosphere and kept at this temperature for 2 hours, and then heated to 420°C and kept at this temperature for 1 hour to obtain plate 2;

[0070] (13) Phthalic anhydride, maleic anhydride, E-44 epoxy resin, hexafunctional polyurethane acrylate, and polydimethylsiloxane-modified acrylate were mixed in a mass ratio of 0.005:0.003:1:3:8, and stirred for 30 minutes to obtain a mixture 7. The plate 2 obtained in step (12) was immersed in the mixture 7, pressurized to 30 MPa, maintained at the pressure for 12 hours, and the plate was released to remove the plate, and the excess mixture 7 on the surface of the plate was scraped off to obtain a plate 3.

[0071] (14) Heating the plate 3 to 170°C and keeping the temperature for 24 hours to obtain the plate 4;

[0072] (15) After polishing the four surfaces of the plate obtained in step (14) to remove excess cured resin, an ultra-low resin content and high-strength graphite bipolar plate material is obtained.

[0073] The obtained graphite bipolar plate material has a resin content of 8.3wt%, an electrical conductivity of >189S / cm, a bending strength of 64Mpa, and a thermal conductivity of 28.5W / m·K.

[0074] Example 2:

[0075] A method for preparing an ultra-low resin content high-strength graphite bipolar plate material comprises the following steps:

[0076] (1) Formic acid and concentrated nitric acid (65%) were mixed in a volume ratio of 3.5:1 to obtain mixed acid 1;

[0077] (2) adding natural flake graphite having a particle size of 12 to 24 μm to the mixed acid obtained in step (1), stirring at room temperature for 30 minutes to obtain a mixture; the mass ratio of the natural flake graphite to the mixed acid obtained in step (1) is 24%;

[0078] (3) Add N,N-dimethylformamide, butanone, 1,3-propylene glycol and isobutyric acid in a mass ratio of 2:1:1:1.5 to the mixture 1 obtained in step 2, and stir at room temperature for 30 minutes to obtain a mixture 2; the total mass of N,N-dimethylformamide, butanone, 1,3-propylene glycol and isobutyric acid accounts for 25% of the mass of the mixture 1 obtained in step (2);

[0079] (4) adding ammonium persulfate, hexadecyltrimethylammonium bromide, potassium permanganate, potassium ferrate and cerium ammonium nitrate in a mass ratio of 5:0.2:1:1:2 to the mixture II obtained in step (3), and the total mass accounts for 5.5% of the mass of the mixture II; stirring for 2 hours to obtain a mixture III;

[0080] (5) Adding magnesium nitrate and lithium nitrate in a mass ratio of 3:1 to the mixture obtained in step (4), and stirring for 2 hours to obtain a liquid mixture fourth; the total mass of the magnesium nitrate and lithium nitrate accounts for 0.3% of the mixture third obtained in step (4);

[0081] (6) Add the mixture 4 obtained in step (5) to an electrolytic cell for electrolysis, apply a 55V DC voltage to both ends of the electrolytic cell, and electrolyze for 30 minutes to obtain a mixture 5; stir continuously during the electrolysis process to ensure the uniformity of the reaction system during the treatment process.

[0082] (7) Add 7 times the mass of distilled water to the mixture obtained in step (6), stir and mix for 20 minutes, and then filter; repeat the above steps 5 times, and then vacuum dry in an oven at 80°C for 7 hours to obtain powder 1;

[0083] (8) Powder 1 was placed in a microwave heating furnace with a heating power of 2000W for 30 seconds, and then cooled to room temperature to obtain powder 2;

[0084] (9) The powder 2 obtained in step (8) was sieved through a vibrating screen to obtain 1500-mesh powder 3, 350-mesh powder 4, 200-mesh powder 5, 20-mesh powder 6, and 2-mesh powder 7;

[0085] (10) Powder 3, Powder 4, Powder 5, Powder 6 and Powder 7 were mixed in a mass ratio of 0.8:1.7:2.5:4.1:6.3, and 3 wt% nylon acid methyl ester / solution of polymethyl methacrylate accounting for 5% of the total mass was added, and stirred at 300 rpm using a double planetary disperser, sealed and evacuated to 7 Pa, and stirred for 3 hours to obtain mixture 6;

[0086] (11) isostatically pressing the mixture obtained in step (10) into a plate having a thickness of 3 mm at a pressure of 120 MPa;

[0087] (12) The plate 1 obtained in step (11) was heated to 230°C in a nitrogen atmosphere and kept at this temperature for 4 hours, and then heated to 440°C and kept at this temperature for 3 hours to obtain plate 2;

[0088] (13) Phthalic anhydride, maleic anhydride, E-44 epoxy resin, hexafunctional polyurethane acrylate, and polydimethylsiloxane-modified acrylate were mixed in a mass ratio of 0.005:0.003:1:3:8, and stirred for 40 minutes to obtain a mixture 7. The plate 2 obtained in step (12) was immersed in the mixture 7, pressurized to 50 MPa, maintained at the pressure for 36 hours, and the plate was released to remove the plate, and the excess mixture 7 on the surface of the plate was scraped off to obtain a plate 3.

[0089] (14) Heating the plate 3 to 190°C and keeping the temperature for 48 hours to obtain the plate 4;

[0090] (15) After polishing the four surfaces of the plate obtained in step (14) to remove excess cured resin, an ultra-low resin content and high-strength graphite bipolar plate material is obtained.

[0091] The obtained graphite bipolar plate material has a resin content of 4.3wt%, an electrical conductivity of 201S / cm, a bending strength of 48Mpa, and a thermal conductivity of 35W / m·K.

[0092] Example 3:

[0093] A method for preparing an ultra-low resin content high-strength graphite bipolar plate material comprises the following steps:

[0094] (1) Formic acid and concentrated nitric acid (65%) were mixed in a volume ratio of 3:1 to obtain mixed acid 1;

[0095] (2) adding natural flake graphite with a particle size of 8 to 18 μm to the mixed acid obtained in step (1), stirring at room temperature for 20 minutes to obtain a mixture; the mass ratio of the natural flake graphite to the mixed acid obtained in step (1) is 18%;

[0096] (3) Add N,N-dimethylformamide, butanone, 1,3-propylene glycol and isobutyric acid in a mass ratio of 2.5:1:1:1.5 to the mixture 1 obtained in step 2, and stir at room temperature for 20 minutes to obtain a mixture 2; the total mass of N,N-dimethylformamide, butanone, 1,3-propylene glycol and isobutyric acid accounts for 20% of the mass of the mixture 1 obtained in step (2);

[0097] (4) adding ammonium persulfate, hexadecyltrimethylammonium bromide, potassium permanganate, potassium ferrate and cerium ammonium nitrate in a mass ratio of 4:0.2:1:1:2 to the mixture II obtained in step (3), with the total mass accounting for 4.5% of the mass of the mixture II; stirring for 1.5 hours to obtain a mixture III;

[0098] (5) Adding magnesium nitrate and lithium nitrate in a mass ratio of 2:1 to the mixture obtained in step (4), and stirring for 1.5 hours to obtain a liquid mixture four; the total mass of the magnesium nitrate and lithium nitrate accounts for 0.2% of the mixture three obtained in step (4);

[0099] (6) Add the mixture 4 obtained in step (5) to an electrolytic cell for electrolysis, apply a 50 V DC voltage to both ends of the electrolytic cell, and electrolyze for 25 minutes to obtain a mixture 5; stir continuously during the electrolysis process to ensure the uniformity of the reaction system during the treatment process.

[0100] (7) Add 6 times the mass of distilled water to the mixture obtained in step (6), stir and mix for 15 minutes, and then filter; repeat the above steps 4 times, and then vacuum dry in a 70°C oven for 5 hours to obtain powder 1;

[0101] (8) Powder 1 was placed in a microwave heating furnace with a heating power of 1600 W for 25 seconds, and then cooled to room temperature to obtain powder 2;

[0102] (9) The powder 2 obtained in step (8) was sieved through a vibrating screen to obtain 1500-mesh powder 3, 350-mesh powder 4, 200-mesh powder 5, 20-mesh powder 6, and 2-mesh powder 7;

[0103] (10) Powder 3, Powder 4, Powder 5, Powder 6 and Powder 7 were mixed in a mass ratio of 0.8:1.5:2.5:4.1:6.3, and 3 wt% nylon acid methyl ester / solution of polymethyl methacrylate accounting for 4% of the total mass was added, and stirred at 200 rpm using a double planetary disperser, sealed and evacuated to 6 Pa, and stirred for 2 hours to obtain mixture 6;

[0104] (11) isostatically pressing the mixture obtained in step (10) into a plate having a thickness of 2 mm at a pressure of 110 MPa;

[0105] (12) The plate 1 obtained in step (11) was heated to 220°C in a nitrogen atmosphere and kept at this temperature for 3 hours, and then heated to 430°C and kept at this temperature for 2 hours to obtain plate 2;

[0106] (13) Phthalic anhydride, maleic anhydride, E-44 epoxy resin, hexafunctional polyurethane acrylate, and polydimethylsiloxane-modified acrylate were mixed in a mass ratio of 0.005:0.003:1:3:8, and stirred for 35 minutes to obtain a mixture 7. The plate 2 obtained in step (12) was immersed in the mixture 7, pressurized to 40 MPa, maintained at the pressure for 24 hours, and the plate was released to remove the plate, and the excess mixture 7 on the surface of the plate was scraped off to obtain a plate 3.

[0107] (14) Heating the plate 3 to 180°C and keeping the temperature for 36 hours to obtain the plate 4;

[0108] (15) After polishing the four surfaces of the plate obtained in step (14) to remove excess cured resin, an ultra-low resin content and high-strength graphite bipolar plate material is obtained.

[0109] The obtained graphite bipolar plate material has a resin content of 6.3wt%, an electrical conductivity of >194S / cm, a bending strength of 50Mpa, and a thermal conductivity of 31W / m·K.

[0110] Comparative Example 1

[0111] The composite graphite bipolar plate was prepared according to the scheme described in patent document CN119036899.

[0112] According to the raw material ratio recorded in the scheme, the resin content is 14wt%, which is much greater than the resin content in the products prepared in various embodiments of the present invention.

[0113] After testing, the composite graphite bipolar plate in Comparative Example 1 has an electrical conductivity of 105 S / cm, a bending strength of 28 MPa, and a thermal conductivity of 13 W / m·K.

[0114] Comparative Example 2

[0115] The composite graphite bipolar plate was prepared according to the scheme described in patent document CN118522908 A.

[0116] According to the raw material ratio recorded in the scheme, the resin content is 16wt%, which is much larger than the resin content in the products prepared in various embodiments of the present invention.

[0117] After testing, the composite graphite bipolar plate in Comparative Example 1 has an electrical conductivity of 101 S / cm, a bending strength of 24 MPa, and a thermal conductivity of 11 W / m·K.

[0118] Comparative Example 3

[0119] Composite graphite bipolar plates were prepared according to the scheme described in the journal article “Preparation and Performance of Graphite / Phenolic Resin Composite Bipolar Plates”, Journal of Composite Materials, 2015, 32 (3), 744.

[0120] According to the raw material ratio recorded in the scheme, the resin content is 20wt%, which is much greater than the resin content in the products prepared in various embodiments of the present invention.

[0121] After testing, the composite graphite bipolar plate in Comparative Example 1 had an electrical conductivity of 63 S / cm, a bending strength of 42 MPa, and a thermal conductivity of 11 W / m·K.

[0122] Comparative Example 4

[0123] Commercially available composite graphite bipolar plates were used, and the resin raw materials were used according to the instructions in the product manual.

[0124] Testing revealed that the commercially available product contained a resin content of 16 wt%, significantly greater than the resin content of the products produced in various embodiments of the present invention. The commercially available product also exhibited electrical conductivity of 124 S / cm, flexural strength of 33 MPa, and thermal conductivity of 18 W / m·K.

[0125] 3. Analysis and Conclusion

[0126] The products in Example 1 and Comparative Examples 1-4 were photographed using a scanning electron microscope. Figure 1-6 As shown. As can be seen from the picture, the resin and graphite phases in the product of Example 1 of the present invention are continuously distributed to form a bicontinuous structure. Therefore, even under lower resin filling conditions, it can still bring high strength and high toughness characteristics. In the products of Comparative Examples 1-4, the resin and graphite phases do not form a bicontinuous structure, so it is impossible to obtain higher strength and toughness under lower filling. Combined with the comparison of the resin content, electrical conductivity, flexural strength, and thermal conductivity test data of the products of each embodiment of the present invention and the comparative example products, the technical performance of the products of the present invention described above is further verified.

[0127] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing an ultra-low resin content high-strength graphite bipolar plate material, characterized in that: The steps include: (1) adding natural flake graphite to a mixed acid of formic acid and concentrated nitric acid, stirring at room temperature to obtain a mixture 1; (2) adding N,N-dimethylformamide, butanone, 1,3-propylene glycol and isobutyric acid to the first mixture, stirring at room temperature to obtain the second mixture; (3) adding ammonium persulfate, hexadecyltrimethylammonium bromide, potassium permanganate, potassium ferrate and ceric ammonium nitrate to the second mixture, and stirring to obtain the third mixture; (4) adding magnesium nitrate and lithium nitrate to the mixture three, and stirring to obtain a liquid mixture four; (5) adding the mixture 4 into the electrolytic cell, applying a DC voltage of 45-55 V to both ends of the electrolytic cell, and performing electrolysis for 20-30 minutes under continuous stirring to obtain the mixture 5; (6) The mixture 5 is washed with distilled water for multiple times, and vacuum dried to obtain powder 1; after microwave heating, the mixture is cooled to room temperature to obtain powder 2; the powder 2 is then sieved using a vibrating screen to obtain powders of different particle sizes of 1500 mesh, 350 mesh, 200 mesh, 20 mesh and 2 mesh, and the mixture is re-mixed to obtain a multi-particle size mixed powder; (7) Adding the multi-size mixed powder and the polymethyl methacrylate-methyl nylonate mixture into a double planetary disperser, stirring under vacuum conditions to obtain a mixture VI; (8) isostatically pressing the mixture 6 into a plate 1; then, heating the mixture in a nitrogen atmosphere by a stepwise heating method to obtain a plate 2; (9) Phthalic anhydride, maleic anhydride, E-44 epoxy resin, hexafunctional polyurethane acrylate, and polydimethylsiloxane-modified acrylate are mixed and stirred to obtain a mixture 7; the plate 2 is immersed in the mixture 7 and subjected to a pressure treatment to obtain a plate 3; (10) Heat-treating the plate 3 to obtain the plate 4; polishing the surface of the plate 4 to remove excess solidified resin, thereby obtaining an ultra-low resin content high-strength graphite bipolar plate material.

2. The method according to claim 1, characterized in that In the step (1), the mass fraction of concentrated nitric acid is 65%, the volume ratio of formic acid to concentrated nitric acid is 2.5-3.5:1; the particle size of natural flake graphite is 4-24 μm, and the mass ratio of natural flake graphite to mixed acid is 12-24%; and the stirring treatment time is 10-30 minutes.

3. The method according to claim 1, characterized in that In the step (2), the mass ratio of N,N-dimethylformamide, butanone, 1,3-propylene glycol and isobutyric acid is 1-2.5:1:1:1.5, and the total mass accounts for 15-25% of the mass of the mixture; the stirring time is 10-30 minutes.

4. The method according to claim 1, wherein In the step (3), the mass ratio of ammonium persulfate, hexadecyltrimethylammonium bromide, potassium permanganate, potassium ferrate and ceric ammonium nitrate is 3-5:0.2:1:1:2, and the total mass accounts for 3.5-5.5% of the mass of the mixture; the stirring time is 1-2 hours.

5. The method according to claim 1, wherein In the step (4), the mass ratio of magnesium nitrate to lithium nitrate is 1-3:1, and the total mass accounts for 0.1-0.3% of the mass of the mixture; the stirring time is 1-2 hours.

6. The method according to claim 1, characterized in that In the step (6), the washing refers to adding the mixture five to 5 to 7 times the mass of distilled water, stirring and mixing for 10 to 20 minutes and then filtering; repeating this operation 3 to 5 times; the vacuum drying refers to placing the washed mixture five in a vacuum oven at 60 to 80°C for 3 to 7 hours; the microwave heating treatment refers to placing the dried mixture five in a microwave heating furnace and treating it at a power of 1200 to 2000 W for 20 to 30 seconds; in the multi-particle size mixed powder, the mass ratio of 1500 mesh, 350 mesh, 200 mesh, 20 mesh and 2 mesh powders is 0.8:1.3~1.7:2.5:4.1:6.

3.

7. The method according to claim 1, characterized in that In the step (7), the mass fraction of polymethyl methacrylate in the polymethyl methacrylate-methyl nylonate mixture is 3 wt %; the mixture accounts for 3-5% of the total mass of the multi-particle size mixed powder; the stirring speed of the double planetary disperser is 100-300 rpm, the vacuum is sealed and evacuated to 5-7 Pa, and the stirring time is 1-3 hours.

8. The method according to claim 1, characterized in that In the step (8), the pressure of the isostatic pressing method is controlled to be 100-120 MPa, and the thickness of the plate 1 is 1-3 mm; the step-by-step heating method for heating treatment means first heating to 210-230°C and keeping the temperature for 2-4 hours, then heating to 420-440°C and keeping the temperature for 1-3 hours, and then cooling to room temperature.

9. The method according to claim 1, characterized in that In the step (9), phthalic anhydride, maleic anhydride, E-44 epoxy resin, hexafunctional polyurethane acrylate, and polydimethylsiloxane-modified acrylate are mixed in a mass ratio of 0.005:0.003:1:3:8 and stirred for 30 to 40 minutes to obtain a mixture seven; the pressure treatment refers to pressurizing to 30 to 50 MPa and maintaining the pressure for 12 to 36 hours, and after depressurizing, taking out the plate and scraping off excess mixture seven on the surface of the plate.

10. The method according to claim 1, characterized in that In the step (10), the heating treatment refers to heating the plate to 170-190°C and keeping the temperature for 24-48 hours.

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