A flexible graphite bipolar plate and its preparation method

Abstract

The present 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 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. The flexible graphite bipolar plate prepared by the present invention has good electrical conductivity, sealing performance, and flexural strength.

Description

Technical Field

[0001] 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. Background Art

[0002] A fuel cell can directly convert chemical energy into electrical energy. It is an efficient and clean electrochemical power generation device that has received attention and research at home and abroad in recent years and has been widely used in fields such as aerospace, submarines, automobiles, and portable power sources. The bipolar plate is an important component in a hydrogen fuel cell and has 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. The bipolar plate has a great influence on the performance of the fuel cell. Flexible graphite has a high specific surface area and good chemical stability. The bipolar plate made of flexible graphite has advantages such as convenient operation and corrosion resistance, and has become one of the research directions for fuel cell bipolar plates.

[0003] Patent CN114566669B discloses a flexible graphite bipolar plate and its preparation method and application. By using a special mold for two pressings and then using resin for vacuum impregnation, the problem of a large difference in the density between the flow channel shoulder and the bottom of the bipolar plate is solved. The preparation process is simple and the cost is low. However, the resin used in the invention is brittle after curing, resulting in poor anti-bending performance and uneven stress of the graphite bipolar plate, which affects the stability and overall performance of the battery.

[0004] Patent CN117410513B discloses a preparation method of a flexible composite graphite bipolar plate. By performing high-temperature treatment on graphite short fibers, then performing high-temperature expansion with graphene powder and graphite powder in proportion, and then homogenizing the expanded product and then performing calendering molding in a mold, a flexible composite graphite bipolar plate is obtained. The bipolar plate prepared by this invention has high bending performance and good electrical conductivity. However, this invention directly expands the graphite without intercalation treatment, which may result in poor sealing performance of the obtained bipolar plate and affect the performance of the battery.

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

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

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

[0008] The first aspect of the present invention provides a flexible graphite bipolar plate, which contains 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.

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

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

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

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

[0013] When preparing a flexible graphite bipolar plate, it is often necessary to add a phenolic resin with good bonding properties. However, the phenolic resin is brittle after curing and is easily cracked by external forces, affecting the flexibility of the flexible graphite bipolar plate. In the present invention, a polymer with a specific number average molecular weight is obtained by polymerizing 3-vinyloxypropylamine and acrolein, and then used to modify the phenolic resin. The obtained phenolic resin has good toughness, enhancing the anti-bending property of the flexible graphite bipolar plate. The possible reason is that a large number of alkane segments are added to increase the flexibility of the phenolic resin. In addition, amino groups are evenly distributed on the alkane segments, increasing the compatibility with the modified epoxy resin, further enhancing the anti-bending performance of the flexible graphite bipolar plate.

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

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

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

[0017] B1. Add epoxy resin, tetra-isopropyl titanate, and acrylic acid into reaction vessel 3, and react at 70 - 80 °C for 5 - 6 h to obtain an epoxy resin containing double bonds.

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

[0019] To improve the adhesiveness and mechanical strength of phenolic resin, phenolic resin and epoxy resin are usually used in combination. However, the compatibility between epoxy resin and flexible graphite is poor, resulting in easy detachment after bonding and poor sealing performance of the flexible graphite bipolar plate. In the present invention, epoxy resin is modified by grafting double bonds and then polymerized with 2-methyl-1,3-propanediol to obtain a modified epoxy resin containing multiple hydroxyl groups, which increases the compatibility with flexible graphite and has stronger adhesive force. At the same time, the bipolar plate has good electrical conductivity, sealing performance, and flexural resistance. The possible reason is that the presence of multiple hydroxyl groups can generate hydrogen bond interactions between flexible graphite and modified phenolic resin, increasing the compatibility of the three, increasing the adhesive force, and improving both the sealing performance and flexural resistance. In addition, the added ester groups and hydroxyl groups increase the coordination with iron ions in flexible graphite, increasing the electrical 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-methyl-1,3-propanediol in step B2 is 1:(0.4 - 0.7).

[0022] The present invention makes the modified epoxy resin more compatible with phenolic resin and enables flexible graphite to bond better together by limiting the viscosity of epoxy resin, increasing the sealing performance; and further increases the toughness of epoxy resin and the coordination ability with iron ions in flexible graphite by limiting the mass ratio of the epoxy resin containing double bonds to 2-methyl-1,3-propanediol, increasing the flexural resistance and electrical conductivity.

[0023] In some embodiments, the diluent is 3-hydroxy-2-butanone 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 preparation method of the flexible graphite includes the following steps:

[0026] S1. At room temperature, add graphite and potassium permanganate into the reaction vessel 5. While ultrasonicating, dropwise add a mixed solution of phosphoric acid aqueous solution with a concentration of 74 - 90 wt% and 2 - methylacetanilide - citric acid ionic liquid. The ultrasonic power is 130 - 140 W, the ultrasonic temperature is 30 - 40 °C. After the dropping is completed, continue ultrasonicating for 2 - 3 h, wash until neutral, and dry to obtain expandable graphite;

[0027] S2. Add the expandable graphite obtained in step S1 into the impregnating solution and soak for 15 - 20 min, filter, and dry to obtain modified expandable graphite;

[0028] S3. Expand the modified expandable graphite obtained in step S2 at 920 - 960 °C to obtain graphite worms. After cooling the graphite worms, press them 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 rate is 1 - 2 ml / s; the expansion volume of the expandable graphite is 425 - 440 ml / g; the length of the graphite worms is 30 - 35 mm.

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

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

[0032] In some embodiments, the preparation method of the ionic liquid comprises the following steps: Dissolve 2 - methylacetanilide and citric acid in ethanol, stir at 40 - 50 °C for 11 - 13 h, and dry 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 impregnating solution, calculated as 100% by mass percentage, comprises the following raw materials: phosphoric acid 2 - 4%, modified polyethylene glycol - phenylboronic acid catechol ester - polyglutamic acid 2 - 3%, boric acid 0.5 - 1%, metal ionic liquid 6 - 8%, and the balance is water.

[0035] In some embodiments, the preparation method of the modified polyethylene glycol - phenylboronic acid catechol ester - polyglutamic acid comprises the following steps: Add polyethylene glycol - phenylboronic acid catechol ester - polyglutamic acid, 3 - amino - 3 - methylbutyric acid, and tetra - isopropyl titanate into dichloromethane, react at 70 - 80 °C for 5 - 6 h, and perform rotary evaporation to obtain the compound, thus obtaining it.

[0036] Preferably, the mass ratio of polyethylene glycol-phenylboronic acid catechol 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 diethylphosphonoacetic acid to dichloromethane, add concentrated sulfuric acid while stirring, react at 70-80 °C for 5-6 h, 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 h, and extract to obtain the metal ionic liquid.

[0040] Preferably, the mass ratio of 1-hydroxyethyl-3-methylimidazolium chloride to diethylphosphonoacetic 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] The second aspect of the present invention provides a method for preparing a flexible graphite bipolar plate, comprising the following steps:

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

[0044] Ⅱ. Immerse the flexible graphite in the resin diluent obtained in step Ⅰ for impregnation for 15-20 min, dry at 85-95 °C for 1-2 h, then under vacuum conditions, use a mold to press, the pressure is 70-80 Mpa, the vacuum degree is -0.1 MPa to 0.1 MPa, and then cure 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 from flexible graphite, a reinforcing resin and other additives has good sealing performance, flexural resistance and electrical conductivity.

[0047] 2. The present invention polymerizes 3-vinyloxypropylamine and acrolein to obtain a polymer with a specific number-average molecular weight, and then uses it to modify phenolic resin, and the obtained phenolic resin has good toughness, enhancing the anti-bending property 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] Preparation method of phenolic resin, comprising the following steps: Add 11.3 g of phenol to reaction vessel 6, adjust the pH to 2.5 with 75 wt% phosphoric acid aqueous solution, heat up to 90 °C and dropwise add 25 g of 37 wt% formaldehyde aqueous solution at a dropping rate of 2 ml / s. After the dropping is completed, stir and react for 1.5 h, and then dry under the conditions of 130 °C and 0 MPa to obtain phenolic resin.

[0060] Preparation Example 4

[0061] Preparation method of modified epoxy resin-1, comprising the following steps:

[0062] B1. Add 2 g of epoxy resin, 0.01 g of tetra-isobutyl titanate, and 4 g of acrylic acid to reaction vessel 3, and react at 75 °C for 5.5 h to obtain an epoxy resin containing double bonds;

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

[0064] Among them, the viscosity of the epoxy resin is 3000 mPa·s.

[0065] Preparation Example 5

[0066] Preparation method of modified epoxy resin-2, the specific steps are the same as those in Preparation Example 3, the difference is that the addition amount of 2-methylidene-1,3-propanediol is 1 g.

[0067] Preparation Example 6

[0068] Preparation method of modified epoxy resin-3, the specific steps are the same as those in Preparation Example 3, the difference is that the viscosity of the epoxy resin is 7000 mPa·s.

[0069] Preparation Example 7

[0070] Preparation method of ionic liquid, comprising the following steps: Dissolve 10 g of 2-methylacetanilide and 14 g of citric acid in 100 ml of absolute ethanol, stir at 45 °C for 12 h, and dry to obtain the ionic liquid.

[0071] Preparation Example 8

[0072] Preparation method of modified polyethylene glycol-phenylboronic acid catechol-polyglutamic acid, comprising the following steps: Add 10 g of polyethylene glycol-phenylboronic acid catechol-polyglutamic acid, 2.4 g of 3-amino-3-methylbutyric acid, and 0.01 g of tetra-isopropyl titanate to 500 ml of dichloromethane, react at 75 °C for 5.5 h, and perform rotary evaporation to obtain the product.

[0073] Preparation Example 9

[0074] Preparation method of metal ionic liquid, comprising the following steps:

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

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

[0077] Preparation Example 10

[0078] Preparation method of flexible graphite, comprising the following steps:

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

[0080] S2. Add 10 g of the expandable graphite obtained in step S1 into 8 L of impregnating solution, soak for 18 min, filter, and dry to obtain modified expandable graphite;

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

[0082] Wherein the impregnating solution, calculated on a mass percentage of 100%, comprises the following raw materials: 75 wt% phosphoric acid 3%, modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid 2.5%, boric acid 0.8%, metal ionic liquid 7%, water 86.7%.

[0083] Example 1

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

[0085] Wherein, 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 absolute ethanol, and the mass ratio of the two is 1:5.

[0086] The preparation method of the flexible graphite bipolar plate in this embodiment includes the following steps:

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

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

[0089] Example 2

[0090] A flexible graphite bipolar plate, in parts by weight, includes the following raw materials: 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 - hydroxy - 2 - butanone and n - butanol, and the mass ratio of the two is 1:3; the solvent is water and absolute ethanol, and the mass ratio of the two is 1:3.

[0092] The preparation method of the flexible graphite bipolar plate in this embodiment includes the following steps:

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

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

[0095] Example 3

[0096] A flexible graphite bipolar plate, in parts by weight, includes the following raw materials: 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 - hydroxy - 2 - butanone and n - butanol, and the mass ratio of the two is 1:5; the solvent is water and absolute ethanol, and the mass ratio of the two is 1:6.

[0098] The preparation method of the flexible graphite bipolar plate in this embodiment includes the following steps:

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

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

[0101] Example 4

[0102] A flexible graphite bipolar plate and its preparation method. The specific implementation method is the same as that of Example 1, except that the modified phenolic resin - 1 is replaced with the modified phenolic resin - 2 in equal amounts.

[0103] Example 5

[0104] A flexible graphite bipolar plate and its preparation method. The specific implementation method is the same as that of Example 1, except that the modified epoxy resin - 1 is replaced with the modified epoxy resin - 2 in equal amounts.

[0105] Example 6

[0106] A flexible graphite bipolar plate and its preparation method. The specific implementation method is the same as that of Example 1, except that the modified epoxy resin - 1 is replaced with the modified epoxy resin - 3 in equal amounts.

[0107] Comparative Example 1

[0108] A flexible graphite bipolar plate and its preparation method. The specific implementation method is the same as that of Example 1, except that the modified phenolic resin - 1 is replaced with phenolic resin in equal amounts.

[0109] Comparative Example 2

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

[0111] Performance Test

[0112] 1. Conductivity Measurement

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

[0114] 2. Anti - bending Performance Measurement

[0115] The flexural properties of the flexible graphite bipolar plates prepared in the above examples and comparative examples were determined according to "GB / T 3074.1-2008 Determination Method for Flexural Strength of Graphite Electrodes".

[0116] 3. Measurement of gas leakage rate

[0117] The gas leakage rates of the flexible graphite bipolar plates prepared in the above examples and comparative examples were measured using an airtightness 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] From the comparison of the experimental data of Examples 1-3 in Table 1, it can be seen that the flexible graphite bipolar plate has good electrical conductivity, flexural strength and sealing performance; by comparing Example 4 with Example 1, it can be seen that the change in the ratio of aqueous formaldehyde solution to polymer in 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 epoxy resin containing double bonds to 2-methylenepropane-1,3-diol in modified epoxy resin-2 may lead to a weakening of the interaction with the flexible graphite, and all properties decline; by comparing Example 6 with Example 1, it can be seen that the increase in the viscosity of the epoxy resin in the modified epoxy resin may cause uneven mixing with the flexible graphite, resulting in a decrease in both the sealing performance 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 both the flexural strength and sealing performance 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 results in a decline in all properties.

[0122] The above are only preferred embodiments of the present invention and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes, but as long as it does not depart from the technical content of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence 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, By weight, it contains the following raw materials: 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; The preparation method of the modified phenolic resin includes the following steps: A1. Add 3 - vinyloxypropylamine, acrolein, and azobisisobutyronitrile to reaction vessel 1, stir and react at 70 - 80 °C for 1 - 2 h to obtain a polymer with a number average molecular weight of 500 - 800; A2. Add phenol to reaction vessel 2, adjust the pH to 2 - 3 with phosphoric acid, heat up to 85 - 95 °C and dropwise add a mixed solution of 35 - 40 wt% formaldehyde aqueous solution and the polymer obtained in step A1. After the dropping is completed, stir and react for 1 - 2 h, and then dry under the conditions of 120 - 140 °C and -0.1 MPa to 0.1 MPa to obtain the modified phenolic resin; The preparation method of the modified epoxy resin includes the following steps: B1. Add epoxy resin, tetra - isobutyl titanate, and acrylic acid to reaction vessel 3, react at 70 - 80 °C for 5 - 6 h to obtain an epoxy resin containing double bonds; B2. Add the epoxy resin containing double bonds obtained in step (1), 2 - methylene - 1,3 - propanediol, and azobisisobutyronitrile to reaction vessel 4, react at 70 - 80 °C for 1 - 2 h to obtain the modified epoxy resin.

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

3. The flexible graphite bipolar plate according to claim 1, characterized in that, In step B1, the viscosity of the epoxy resin is 2500 - 5000 mPa·s.

4. The flexible graphite bipolar plate according to claim 1, wherein, In step B2, the mass ratio of the epoxy resin containing double bonds to 2 - methylene - 1,3 - propanediol is 1:(0.4 - 0.7).

5. The flexible graphite bipolar plate according to claim 1, wherein, The diluent is 3 - hydroxy - 2 - butanone and n - butanol, and the mass ratio of the two is 1:(3 - 5).

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

7. The flexible graphite bipolar plate according to claim 1, wherein The preparation method of the flexible graphite includes the following steps: S1. Add graphite and potassium permanganate to reaction vessel 5 at room temperature, dropwise add a mixed solution of phosphoric acid aqueous solution with a concentration of 74 - 90 wt% and ionic liquid while ultrasonicating. The ultrasonic power is 130 - 140 W, the ultrasonic temperature is 30 - 40 °C. After the dropping is completed, continue ultrasonicating for 2 - 3 h, wash until neutral, and dry to obtain expandable graphite; S2. Add the expandable graphite obtained in step S1 to the impregnating solution, soak for 15 - 20 min, filter, and dry to obtain modified expandable graphite; S3. Expand the modified expandable graphite obtained in step S2 at 920 - 960 °C to obtain graphite worms. After cooling the graphite worms, press at 85 - 95 °C and 19 - 21 MPa for 130 - 170 s to obtain flexible graphite.

8. A method for preparing a flexible graphite bipolar plate according to any one of claims 1-7, characterized in that, It includes the following steps: Ⅰ. Add the reinforcing resin to the diluent, stir at room temperature for 30 - 40 min, and then add the solvent and stir for 20 - 30 min to obtain a resin diluent; Ⅱ. Immerse the flexible graphite in the resin diluent obtained in Step I for 15 - 20 minutes, dry it at 85 - 95 °C for 1 - 2 hours, then under vacuum conditions, press it using a mold, with a pressure of 70 - 80 Mpa and a vacuum degree of -0.1 MPa to 0.1 MPa, and then cure it at 160 - 170 °C to obtain the product.

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