Flexible graphite bipolar plate and preparation method thereof

Abstract

The invention belongs to the technical field of bipolar plates for fuel cells, and particularly relates to a flexible graphite bipolar plate and a preparation method thereof, the flexible graphite bipolar plate comprises the following raw materials: 80-90 parts of flexible graphite, 65-75 parts of reinforced resin, 8-12 parts of a diluent, and 60-70 parts of a solvent; the reinforced resin is modified phenolic resin and modified epoxy resin, and the mass ratio of the modified phenolic resin to the modified epoxy resin is (1.9-2.2): 1. The flexible graphite bipolar plate prepared by the preparation method disclosed by the invention has good conductivity, sealing property and breaking strength.

Description

Technical Field

[0001] The present invention belongs to the technical field of bipolar plates for fuel cells, and in particular relates to a flexible graphite bipolar plate and a preparation method thereof. Background Art

[0002] Fuel cells can directly convert chemical energy into electrical energy. They are efficient and clean electrochemical power generation devices. In recent years, they have attracted domestic and foreign attention and research, and have been widely used in aerospace, submarines, automobiles, portable power sources and other fields. Bipolar plates are an important component in hydrogen fuel cells and have multiple functions, such as current collection, heat conduction, and sealing. In a fuel cell stack, the mass of the bipolar plate accounts for about 80% of the total mass of the entire fuel cell stack. Bipolar plates have a great influence on the performance of fuel cells. Flexible graphite has a high specific surface area and good chemical stability. Bipolar plates made of flexible graphite have the advantages of easy operation and corrosion resistance, and have become one of the research directions of fuel cell bipolar plates.

[0003] Patent CN114566669B discloses a flexible graphite bipolar plate and its preparation method and application. The plate is pressed twice using a special mold and then vacuum impregnated with resin to solve the problem of large density difference between the shoulder and the bottom of the bipolar plate. The preparation process is simple and the cost is low. However, the resin used in the present invention is very brittle after curing, resulting in poor bending resistance of the graphite bipolar plate and uneven force, which affects the stability and overall performance of the battery.

[0004] Patent CN117410513B discloses a method for preparing a flexible composite graphite bipolar plate, which comprises subjecting short graphite fibers to high-temperature treatment, and then subjecting them to high-temperature expansion with graphene powder and graphite powder in proportion, and then homogenizing the expanded product, and then placing it in a mold for calendering to obtain a flexible composite graphite bipolar plate. The bipolar plate prepared by the invention has high bending performance and good conductivity, but the invention does not subject the graphite to intercalation treatment and direct expansion, which may result in poor sealing of the obtained bipolar plate, affecting the performance of the battery.

[0005] Therefore, there is an urgent need in the market for a flexible graphite bipolar plate with good bending resistance and good sealing. Summary of the invention

[0006] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a flexible graphite bipolar plate with good electrical conductivity, good bending resistance and good sealing performance.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] The first aspect of the present invention provides a flexible graphite bipolar plate, which comprises the following raw materials, measured by weight: 80-90 parts of flexible graphite, 65-75 parts of reinforcing resin, 8-12 parts of diluent, and 60-70 parts of solvent; the reinforcing resin is a modified phenolic resin and a modified epoxy resin, and the mass ratio of the two is (1.9-2.2):1.

[0009] In some embodiments, the method for preparing the modified phenolic resin comprises the following steps:

[0010] A1, add 3-vinyloxypropylamine, acrolein, and azobisisobutyronitrile into reaction vessel 1, and stir and react at 70-80° C. for 1-2 hours to obtain a polymer with a number average molecular weight of 500-800;

[0011] A2. Add phenol to reaction container 2, adjust the pH to 2-3 with phosphoric acid, heat to 85-95° C., dropwise add a 35-40wt% formaldehyde aqueous solution and a mixed solution of the polymer obtained in step A1, stir and react for 1-2h after the dropwise addition is completed, and then dry at 120-140° C. and -0.1MPa to 0.1MPa to obtain a modified phenolic resin.

[0012] Preferably, in step A1, the mass ratio of 3-vinyloxypropylamine to acrolein is (1-1.5):1.

[0013] Preparation of flexible graphite bipolar plates often requires the addition of phenolic resins with good bonding effects. However, the phenolic resins are relatively brittle after curing and are easily cracked by external forces, which affects the flexibility of the flexible graphite bipolar plates. The present invention obtains a polymer with a specific number average molecular weight by polymerizing 3-vinyloxypropylamine and acrolein, and then uses the polymer to modify the phenolic resin to obtain a phenolic resin with good toughness, thereby enhancing the bending resistance of the flexible graphite bipolar plates. The possible reason is that the addition of a large number of alkane segments increases the flexibility of the phenolic resin. In addition, the uniform distribution of amino groups on the alkane segments increases the compatibility with the modified epoxy resin, thereby further enhancing the bending resistance of the flexible graphite bipolar plates.

[0014] In some embodiments, the mass ratio of the 35-40 wt % formaldehyde aqueous solution in step A2 to the polymer obtained in step A1 is 1:(1-2).

[0015] The present invention reduces the brittleness of the phenolic resin by limiting the mass ratio of the 35-40wt% formaldehyde aqueous solution to the polymer obtained in step A1, while not affecting the adhesiveness of the phenolic resin.

[0016] In some embodiments, the method for preparing the modified epoxy resin comprises the following steps:

[0017] B1, adding epoxy resin, tetraisotitanate and acrylic acid into reaction vessel 3, reacting at 70-80° C. for 5-6 hours to obtain epoxy resin containing double bonds;

[0018] B2. Add the double bond-containing epoxy resin obtained in step (1), 2-methylene-1,3-propanediol and azobisisobutyronitrile into reaction vessel 4, and react at 70-80° C. for 1-2 hours to obtain a modified epoxy resin.

[0019] In order to improve the adhesion and mechanical strength of phenolic resin, phenolic resin is usually used in combination with epoxy resin, but the compatibility of epoxy resin with flexible graphite is poor, which leads to easy falling off after bonding, resulting in poor sealing of flexible graphite bipolar plates. The present invention obtains a modified epoxy resin containing multiple hydroxyl groups by modifying the epoxy resin by grafting double bonds and then polymerizing it with 2-methylene-1,3-propanediol. The compatibility with flexible graphite is increased, the adhesion is stronger, and the bipolar plate has good conductivity, sealing and flexural resistance. The possible reason is that the presence of multiple hydroxyl groups can produce hydrogen bonds between flexible graphite and modified phenolic resin, which increases the compatibility of the three, increases the adhesion, and improves the sealing and flexural resistance. In addition, the added ester group and hydroxyl group increase the coordination effect with the iron ions in the flexible graphite, thereby increasing the conductivity.

[0020] In some embodiments, the viscosity of the epoxy resin in step B1 is 2500-5000 mPa·s.

[0021] In some embodiments, the mass ratio of the epoxy resin containing double bonds to 2-methylene-1,3-propanediol in step B2 is 1:(0.4-0.7).

[0022] The present invention limits the viscosity of the epoxy resin so that the modified epoxy resin is more compatible with the phenolic resin and the flexible graphite is more easily bonded together, thereby improving the sealing performance; and limits the mass ratio of the epoxy resin containing double bonds and 2-methylene-1,3-propylene glycol so as to further increase the toughness of the epoxy resin and the coordination ability with iron ions in the flexible graphite, thereby improving the bending resistance and the electrical conductivity.

[0023] In some embodiments, the diluent is 3-hydroxybutanone and n-butanol, and the mass ratio of the two is 1:(3-5).

[0024] In some embodiments, the solvent is water and ethanol, and the mass ratio of the two is 1:(3-6).

[0025] In some embodiments, the method for preparing the flexible graphite comprises the following steps:

[0026] S1. Add graphite and potassium permanganate into a reaction vessel 5 at room temperature, and dropwise add a mixed solution of a 74-90wt% aqueous phosphoric acid solution and a 2-methylacetanilide-citric acid ionic liquid while ultrasonically adding the mixed solution at a power of 130-140W and a temperature of 30-40°C. After the addition is complete, continue ultrasonication for 2-3h, wash until neutral, and dry to obtain expandable graphite;

[0027] S2, adding the expandable graphite obtained in step S1 into the impregnation solution and soaking for 15-20 min, filtering, and drying to obtain modified expandable graphite;

[0028] S3, expanding the modified expandable graphite obtained in step S2 at 920-960° C. to obtain graphite worms, and after cooling the graphite worms, pressing at 85-95° C. and 19-21 MPa for 130-170 s to obtain flexible graphite.

[0029] Preferably, in step S1, the mass ratio of graphite to potassium permanganate is 1:(0.1-0.2), the dropping speed is 1-2 ml / s; the expansion volume of the expandable graphite is 425-440 ml / g; and the length of the graphite worms is 30-35 mm.

[0030] In some embodiments, the mass ratio of the 74-90 wt % phosphoric acid aqueous solution to the 2-methylacetanilide-citric acid ionic liquid in step S1 is (1.8-2):1.

[0031] In some embodiments, the ratio of expandable graphite to impregnation liquid in step S2 is 1 g: (0.8-1) L.

[0032] In some embodiments, the method for preparing the ionic liquid comprises the following steps: dissolving 2-methylacetanilide and citric acid in ethanol, stirring at 40-50° C. for 11-13 hours, and drying to obtain the ionic liquid.

[0033] In some embodiments, the mass ratio of 2-methylacetanilide to citric acid is 1:(1.3-1.5).

[0034] In some embodiments, the impregnation solution, calculated as 100% by mass, comprises the following raw materials: 2-4% phosphoric acid, 2-3% modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid, 0.5-1% boric acid, 6-8% metal ion liquid, and the remainder is water.

[0035] In some embodiments, the preparation method of the modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid comprises the following steps: adding polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid, 3-amino-3-methylbutyric acid, and tetraisotitanate to dichloromethane, reacting at 70-80°C for 5-6h, and rotary evaporating to obtain a compound.

[0036] Preferably, the mass ratio of polyethylene glycol-catechol phenylboronic acid ester-polyglutamic acid to 3-amino-3-methylbutyric acid is 1:(0.2-0.3).

[0037] In some embodiments, the method for preparing the metal ionic liquid comprises the following steps:

[0038] (1) Add 1-hydroxyethyl-3-methylimidazolium chloride and diethylphosphoacetic acid to dichloromethane, add concentrated sulfuric acid while stirring, react at 70-80° C. for 5-6 hours, and rotary evaporate to obtain a compound;

[0039] (2) Add ferric chloride to the compound obtained in step (1), stir at 75-85° C. for 36-38 hours, and extract to obtain a metal ion liquid.

[0040] Preferably, the mass ratio of 1-hydroxyethyl-3-methylimidazolium chloride to diethylphosphoacetic acid is 1:(1.2-1.4).

[0041] In some embodiments, the mass ratio of the compound to ferric chloride in step (2) is 1:(0.5-0.6).

[0042] A second aspect of the present invention provides a method for preparing a flexible graphite bipolar plate, comprising the following steps:

[0043] Ⅰ. Add the reinforcing resin to the diluent, stir at room temperature for 30-40 minutes, then add the solvent and stir for 20-30 minutes to obtain a resin dilution;

[0044] Ⅱ. Immerse the flexible graphite in the resin dilution obtained in step Ⅰ for 15-20 minutes, dry it at 85-95°C for 1-2 hours, and then press it with a mold under vacuum conditions at a pressure of 70-80Mpa and a vacuum degree of -0.1MPa~0.1MPa, and then cure it at 160-170°C to obtain.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The flexible graphite bipolar plate prepared by the present invention through flexible graphite, reinforcing resin and other additives has good sealing, bending resistance and conductivity.

[0047] 2. The present invention obtains a polymer with a specific number average molecular weight by polymerizing 3-vinyloxypropylamine and acrolein, and then uses the polymer to modify the phenolic resin, so that the phenolic resin has good toughness, thereby enhancing the bending resistance of the flexible graphite bipolar plate.

[0048] 3. The present invention obtains a modified epoxy resin containing multiple hydroxyl groups by modifying the epoxy resin by grafting double bonds and then polymerizing it with 2-methylene-1,3-propanediol. The modified epoxy resin has increased compatibility with flexible graphite and stronger bonding force, and at the same time, the bipolar plate has good conductivity, sealing and flexural resistance. DETAILED DESCRIPTION

[0049] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following examples and comparative examples are only used to illustrate the present invention and are not intended to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0050] In order to facilitate those skilled in the art to implement the present invention, some raw materials and manufacturers of the embodiments and comparative examples are described as follows:

[0051] The compounds and related reagents used in the following examples and comparative examples can all be purchased from the market, among which polyethylene glycol-catechol phenylboronic acid-polyglutamic acid was purchased from Xi'an Qiyue Biotechnology Co., Ltd. with Mn=600, and epoxy resins were purchased from Shanghai Yantai E-Commerce Co., Ltd. with a viscosity of 3000 mPa·s and Wanqing Chemical Technology Co., Ltd. with a viscosity of 7000 mPa·s.

[0052] Preparation Example 1

[0053] The preparation method of modified phenolic resin-1 comprises the following steps:

[0054] A1, add 12g 3-vinyloxypropylamine, 10g acrolein, and 0.1g azobisisobutyronitrile into reaction vessel 1, and stir at 75°C for 1.5h to obtain a polymer with a number average molecular weight of 682;

[0055] A2. Add 11.3 g of phenol into reaction vessel 2, adjust the pH to 2.5 with 75 wt % phosphoric acid aqueous solution, raise the temperature to 90° C., and dropwise add 10 g of 37 wt % formaldehyde aqueous solution and 15 g of a mixed solution of the polymer obtained in step A1 at a dropping speed of 2 ml / s. After the dropwise addition is completed, stir the reaction for 1.5 h, and then dry at 130° C., 0 MPa to obtain modified phenolic resin-1.

[0056] Preparation Example 2

[0057] The preparation method of modified phenolic resin-2 has the same specific steps as Preparation Example 1, except that the amount of polymer added in step A2 is 10 g.

[0058] Preparation Example 3

[0059] The preparation method of phenolic resin comprises the following steps: adding 11.3 g of phenol into a reaction container 6, adjusting the pH to 2.5 with a 75 wt % phosphoric acid aqueous solution, heating to 90° C., dripping 25 g of a 37 wt % formaldehyde aqueous solution at a dripping speed of 2 ml / s, stirring and reacting for 1.5 h after the dripping is completed, and then drying at 130° C. and 0 MPa to obtain a phenolic resin.

[0060] Preparation Example 4

[0061] The preparation method of modified epoxy resin-1 comprises the following steps:

[0062] B1, add 2g epoxy resin, 0.01g tetraisobutyl titanate and 4g acrylic acid into reaction vessel 3, react at 75°C for 5.5h to obtain epoxy resin containing double bonds;

[0063] B2, add 1g of the epoxy resin containing double bonds obtained in step (1), 0.6g of 2-methylene-1,3-propanediol, and 0.01g of azobisisobutyronitrile into reaction vessel 4, and react at 75°C for 1.5h to obtain modified epoxy resin-1;

[0064] The viscosity of the epoxy resin is 3000 mPa·s.

[0065] Preparation Example 5

[0066] The preparation method of modified epoxy resin-2 has the same specific steps as Preparation Example 3, except that the added amount of 2-methylene-1,3-propanediol is 1 g.

[0067] Preparation Example 6

[0068] The preparation method of modified epoxy resin-3 has the same specific steps as Preparation Example 3, except that the viscosity of the epoxy resin is 7000 mPa·s.

[0069] Preparation Example 7

[0070] The preparation method of the ionic liquid comprises the following steps: dissolving 10 g of 2-methylacetanilide and 14 g of citric acid in 100 ml of anhydrous ethanol, stirring at 45° C. for 12 h, and drying to obtain the ionic liquid.

[0071] Preparation Example 8

[0072] The preparation method of modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid comprises the following steps: adding 10g polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid, 2.4g 3-amino-3-methylbutyric acid, and 0.01g tetraisotitanate to 500ml dichloromethane, reacting at 75°C for 5.5h, and rotary evaporating to obtain the modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid.

[0073] Preparation Example 9

[0074] The preparation method of the metal ion liquid comprises the following steps:

[0075] (1) Add 10 g of 1-hydroxyethyl-3-methylimidazolium chloride and 13 g of diethylphosphoacetic acid to 100 ml of dichloromethane, add 1 ml of 95 wt% concentrated sulfuric acid while stirring, react at 75° C. for 5.5 h, and evaporate by rotary evaporation to obtain a compound;

[0076] (2) Add 5.5 g of ferric chloride to 10 g of the compound obtained in step (1), stir at 80° C. for 37 h, and extract to obtain a metal ion liquid.

[0077] Preparation Example 10

[0078] The method for preparing flexible graphite comprises the following steps:

[0079] S1. Add 10g natural flake graphite and 1.5g potassium permanganate into a reaction container at room temperature, and drop 40ml of a mixed solution of 75wt% phosphoric acid aqueous solution and ionic liquid while ultrasonicating, the mass ratio of 75wt% phosphoric acid aqueous solution to ionic liquid is 1.9:1, the dropping speed is 1ml / s, the ultrasonic power is 135W, the ultrasonic temperature is 35°C, and after the dropwise addition is completed, continue ultrasonicating for 2.5h, wash until neutral, and dry to obtain expandable graphite;

[0080] S2, adding 10g of the expandable graphite obtained in step S1 into 8L of impregnation solution and soaking for 18min, filtering, and drying to obtain modified expandable graphite;

[0081] S3, expanding 8 g of the modified expandable graphite obtained in step S2 at 940° C. to obtain graphite worms, and then cooling the graphite worms and pressing them at 90° C. and 20 MPa for 150 s to obtain flexible graphite;

[0082] The impregnation solution, calculated as 100% by mass, comprises the following raw materials: 75wt% phosphoric acid, 3%, modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid, 2.5%, boric acid, 0.8%, metal ion liquid, 7%, and water, 86.7%.

[0083] Example 1

[0084] A flexible graphite bipolar plate, comprising the following raw materials, in parts by weight: 85 parts of flexible graphite, 70 parts of reinforcing resin, 10 parts of diluent, and 65 parts of solvent;

[0085] Among them, the reinforcing resin is modified phenolic resin-1 and modified epoxy resin-1, and the mass ratio of the two is 2:1; the diluent is 3-hydroxybutanone and n-butanol, and the mass ratio of the two is 1:4; the solvent is water and anhydrous ethanol, and the mass ratio of the two is 1:5.

[0086] The method for preparing the flexible graphite bipolar plate in this embodiment comprises the following steps:

[0087] Ⅰ. Add the reinforcing resin to the diluent, stir at room temperature for 35 minutes, then add the solvent and stir for 25 minutes to obtain a resin dilution;

[0088] Ⅱ. Immerse the flexible graphite in the resin dilution obtained in step Ⅰ for 18 minutes, then dry it at 90°C for 1.5 hours, and then press it with a mold under vacuum conditions at a pressure of 75Mpa and a vacuum degree of 0MPa, and then cure it at 165°C to obtain.

[0089] Example 2

[0090] A flexible graphite bipolar plate, comprising the following raw materials, in parts by weight: 80 parts of flexible graphite, 65 parts of reinforcing resin, 8 parts of diluent, and 60 parts of solvent;

[0091] Among them, the reinforcing resin is modified phenolic resin-1 and modified epoxy resin-1, and the mass ratio of the two is 1.9:1; the diluent is 3-hydroxybutanone and n-butanol, and the mass ratio of the two is 1:3; the solvent is water and anhydrous ethanol, and the mass ratio of the two is 1:3.

[0092] The method for preparing the flexible graphite bipolar plate in this embodiment comprises the following steps:

[0093] Ⅰ. Add the reinforcing resin to the diluent, stir at room temperature for 30 minutes, then add the solvent and stir for 20 minutes to obtain a resin dilution;

[0094] Ⅱ. Immerse the flexible graphite in the resin dilution obtained in step Ⅰ for 15 minutes, then dry it at 85°C for 1 hour, and then press it with a mold under vacuum conditions at a pressure of 70Mpa and a vacuum degree of -0.1MPaPa, and then cure it at 160°C to obtain.

[0095] Example 3

[0096] A flexible graphite bipolar plate, comprising the following raw materials, in parts by weight: 90 parts of flexible graphite, 75 parts of reinforcing resin, 12 parts of diluent, and 70 parts of solvent;

[0097] Among them, the reinforcing resin is modified phenolic resin-1 and modified epoxy resin-1, and the mass ratio of the two is 2.2:1; the diluent is 3-hydroxybutanone and n-butanol, and the mass ratio of the two is 1:5; the solvent is water and anhydrous ethanol, and the mass ratio of the two is 1:6.

[0098] The method for preparing the flexible graphite bipolar plate in this embodiment comprises the following steps:

[0099] Ⅰ. Add the reinforcing resin to the diluent, stir at room temperature for 40 minutes, then add the solvent and stir for 30 minutes to obtain a resin dilution;

[0100] Ⅱ. Immerse the flexible graphite in the resin dilution obtained in step Ⅰ for 20 minutes, then dry it at 95°C for 2 hours, and then press it with a mold under vacuum conditions at a pressure of 80Mpa and a vacuum degree of 0.1MPa, and then cure it at 170°C to obtain.

[0101] Example 4

[0102] A flexible graphite bipolar plate and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that an equal amount of modified phenolic resin-1 is replaced by modified phenolic resin-2.

[0103] Example 5

[0104] A flexible graphite bipolar plate and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that an equal amount of modified epoxy resin-1 is replaced by modified epoxy resin-2.

[0105] Example 6

[0106] A flexible graphite bipolar plate and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that an equal amount of modified epoxy resin-1 is replaced by modified epoxy resin-3.

[0107] Comparative Example 1

[0108] A flexible graphite bipolar plate and a preparation method thereof, wherein the specific implementation manner is the same as that of Example 1, except that an equal amount of modified phenolic resin-1 is replaced by phenolic resin.

[0109] Comparative Example 2

[0110] A flexible graphite bipolar plate and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that an equal amount of modified epoxy resin-1 is replaced by epoxy resin with a viscosity of 3000 mPa·s.

[0111] Performance Testing

[0112] 1. Conductivity measurement

[0113] According to "YB / T 120-1997 Method for Determining Resistivity of Carbon Materials", the resistivity of the flexible graphite bipolar plates prepared in the above embodiments and comparative examples was measured. The smaller the resistivity, the stronger the conductivity.

[0114] 2. Determination of bending resistance

[0115] The bending resistance of the flexible graphite bipolar plates prepared in the above embodiments and comparative examples was measured according to "GB / T 3074.1-2008 Method for Determining the Bending Strength of Graphite Electrodes".

[0116] 3. Gas leakage rate measurement

[0117] The gas leakage rate of the flexible graphite bipolar plates prepared in the above embodiments and comparative examples was measured using a gas-tightness tester, the test pressure was 1 bar, and the test gas was hydrogen.

[0118] The test results are shown in Table 1.

[0119] Table 1

[0120]

[0121] By comparing the experimental data of Examples 1-3 in Table 1, it can be seen that the flexible graphite bipolar plate has good conductivity, flexural strength and sealing; by comparing Example 4 with Example 1, it can be seen that the change in the ratio of the formaldehyde aqueous solution and the polymer in the modified phenolic resin-2 may reduce the toughness of the modified phenolic resin, resulting in a decrease in the flexural strength of the flexible graphite; by comparing Example 5 with Example 1, it can be seen that the change in the ratio of the epoxy resin containing double bonds and 2-methylene-1,3-propanediol in the modified epoxy resin-2 may lead to a weakening of the force with the flexible graphite, and all performances are reduced; by comparing Example 6 with Example 1, it can be seen that the viscosity of the epoxy resin in the modified epoxy resin increases, and it may not be evenly mixed with the flexible graphite, resulting in a decrease in the sealing and conductivity of the bipolar plate; by comparing Comparative Example 1 with Example 1, it can be seen that the use of phenolic resin leads to a decrease in the flexural strength and sealing of the flexible graphite bipolar plate; by comparing Comparative Example 2 with Example 1, it can be seen that the use of unmodified epoxy resin reduces all performances.

[0122] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A flexible graphite bipolar plate, characterized in that: The invention comprises the following raw materials in parts by weight: 80-90 parts of flexible graphite, 65-75 parts of reinforcing resin, 8-12 parts of diluent and 60-70 parts of solvent; the reinforcing resin is modified phenolic resin and modified epoxy resin, and the mass ratio of the two is (1.9-2.2):

1.

2. The flexible graphite bipolar plate according to claim 1, characterized in that: The preparation method of the modified phenolic resin comprises the following steps: A1, add 3-vinyloxypropylamine, acrolein, and azobisisobutyronitrile into reaction vessel 1, and stir and react at 70-80° C. for 1-2 hours to obtain a polymer with a number average molecular weight of 500-800; A2. Add phenol to reaction container 2, adjust the pH to 2-3 with phosphoric acid, heat to 85-95° C., dropwise add a 35-40wt% formaldehyde aqueous solution and a mixed solution of the polymer obtained in step A1, stir and react for 1-2h after the dropwise addition is completed, and then dry at 120-140° C. and -0.1MPa to 0.1MPa to obtain a modified phenolic resin.

3. The flexible graphite bipolar plate according to claim 2, characterized in that: The mass ratio of the 35-40 wt % formaldehyde aqueous solution in step A2 to the polymer obtained in step A1 is 1:(1-2).

4. The flexible graphite bipolar plate according to claim 1, characterized in that: The preparation method of the modified epoxy resin comprises the following steps: B1, adding epoxy resin, tetraisobutyl titanate and acrylic acid into reaction vessel 3, reacting at 70-80° C. for 5-6 hours to obtain epoxy resin containing double bonds; B2. Add the double bond-containing epoxy resin obtained in step (1), 2-methylene-1,3-propanediol and azobisisobutyronitrile into reaction vessel 4, and react at 70-80° C. for 1-2 hours to obtain a modified epoxy resin.

5. The flexible graphite bipolar plate according to claim 4, characterized in that: The viscosity of the epoxy resin in step B1 is 2500-5000 mPa·s.

6. The flexible graphite bipolar plate according to claim 4, characterized in that: The mass ratio of the epoxy resin containing double bonds to 2-methylene-1,3-propylene glycol in the step B2 is 1:(0.4-0.7).

7. The flexible graphite bipolar plate according to claim 1, characterized in that: The diluent is 3-hydroxybutanone and n-butanol, and the mass ratio of the two is 1:(3-5).

8. The flexible graphite bipolar plate according to claim 1, characterized in that: The solvent is water and ethanol, and the mass ratio of the two is 1:(3-6).

9. The flexible graphite bipolar plate according to claim 1, characterized in that: The method for preparing the flexible graphite comprises the following steps: S1. Add graphite and potassium permanganate into a reaction vessel 5 at room temperature, and dropwise add a mixed solution of 74-90wt% phosphoric acid aqueous solution and ionic liquid while ultrasonicating, with an ultrasonic power of 130-140W and an ultrasonic temperature of 30-40°C. After the dropwise addition is completed, continue ultrasonicating for 2-3h, wash until neutral, and dry to obtain expandable graphite; S2, adding the expandable graphite obtained in step S1 into the impregnation solution and soaking for 15-20 min, filtering, and drying to obtain modified expandable graphite; S3, expanding the modified expandable graphite obtained in step S2 at 920-960° C. to obtain graphite worms, and after cooling the graphite worms, pressing at 85-95° C. and 19-21 MPa for 130-170 s to obtain flexible graphite.

10. A method for preparing a flexible graphite bipolar plate according to any one of claims 1 to 9, characterized in that: The following steps are involved: Ⅰ. Add the reinforcing resin to the diluent, stir at room temperature for 30-40 minutes, then add the solvent and stir for 20-30 minutes to obtain a resin dilution; Ⅱ. Immerse the flexible graphite in the resin dilution obtained in step Ⅰ for 15-20 minutes, dry it at 85-95°C for 1-2 hours, and then press it with a mold under vacuum conditions at a pressure of 70-80Mpa and a vacuum degree of -0.1MPa~0.1MPa, and then cure it at 160-170°C to obtain.

Images