A preparation method and application of flexible graphite

Abstract

The invention belongs to the technical field of graphite materials and particularly relates to a preparation method and application of flexible graphite. The preparation method of the flexible graphite comprises the following steps: S1, adding graphite and potassium permanganate into a reaction container at room temperature, dropwise adding a mixed solution of phosphoric acid and an ionic liquid while ultrasonicating, the ultrasonic power being 130-140 W and the ultrasonic temperature being 30-40° C., continuing ultrasonicating for 2-3 hours after the dropwise addition is completed, washing until neutral, and drying to obtain expandable graphite; S2, adding the expandable graphite obtained in step S1 into an impregnation solution and soaking for 15-20 minutes, filtering, and drying to obtain modified expandable graphite; and S3, expanding the modified expandable graphite obtained in step S2 at 920-960° C. to obtain graphite worms, cooling the graphite worms and pressing them at 85-95° C. and 19-21 MPa for 130-170 seconds to obtain flexible graphite. The flexible graphite prepared by the preparation method of the present invention has good expansion property, excellent compressibility, resilience and high temperature resistance, and good tensile strength.

Description

Technical Field

[0001] The invention belongs to the technical field of graphite materials, and particularly relates to a preparation method and application of flexible graphite. Background Art

[0002] Carbon is the skeleton element of biological organisms, primarily present in the atmosphere, Earth's crust, and living organisms as a single substance or compound. Traditional carbon materials include charcoal, activated carbon, and natural graphite. With the advancement of technology, new carbon materials such as diamond, porous carbon, and flexible graphite have gradually become the focus of research and development in the field of carbon materials. Flexible graphite is made from natural graphite. By utilizing the graphite's layered structure through chemical treatment and high-temperature expansion, it exhibits excellent compressibility, resilience, sealing, softness, and plasticity. It can be used to prepare sealing materials, battery materials, flame retardants, and other materials, and has broad application prospects.

[0003] Patent CN102963884A discloses a method for preparing enhanced flexible graphite. This method utilizes a composite oxidation process using a combination of oxidants KMnO4, H2O2, and KClO3 and a sulfur-free intercalant HNO3 to produce a sulfur-free expandable graphite with an expansion ratio exceeding 250 ml / g. By rationally proportioning the expandable graphite particle size and employing a staged pressing process, air is more thoroughly expelled from the material, resulting in a denser pressing. This method eliminates air from the material and allows for a tighter pressing. The sulfur-free flexible graphite exhibits a tensile strength exceeding 5.3 MPa, excellent corrosion resistance, and a long service life, making it suitable for use as a high-grade sealing material. However, this invention utilizes nitric acid as an intercalant, which produces a large amount of acidic wastewater, polluting the environment.

[0004] Patent CN108545737A discloses a method for preparing flexible graphite without high-temperature expansion, comprising the following steps: (1) uniformly mixing flaky graphite with appropriate amounts of concentrated sulfuric acid and hydrogen peroxide at ≤10°C; (2) allowing the resulting mixture to stand at room temperature to obtain expanded graphite; (3) desulfurizing the obtained expanded graphite by high-temperature baking, while simultaneously condensing the post-baking gas to recover the sulfuric acid; and (4) pressing the desulfurized expanded graphite to obtain flexible graphite. This method eliminates the high-temperature expansion step in the preparation of expanded graphite, recovers sulfuric acid, avoids environmental pollution caused by the treatment of acid-containing wastewater, and reduces costs. However, this invention still requires a large amount of concentrated sulfuric acid, which poses a safety hazard during the production process and can harm operators.

[0005] Therefore, there is an urgent need to develop a method for preparing flexible graphite that is environmentally friendly and can reduce safety hazards. Summary of the Invention

[0006] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for preparing flexible graphite, and the obtained flexible graphite has good tensile strength, excellent high temperature resistance, compressibility and resilience.

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

[0008] A first aspect of the present invention provides a method for preparing flexible graphite, comprising the following steps:

[0009] S1. Add graphite and potassium permanganate to a reaction vessel at room temperature, and dropwise add a mixed solution of 74-90 wt% aqueous phosphoric acid solution and ionic liquid while ultrasonicating at an ultrasonic power of 130-140 W and an ultrasonic temperature of 30-40° C. After the addition is complete, continue ultrasonicating for 2-3 hours, wash until neutral, and dry to obtain expandable graphite;

[0010] S2, adding the expandable graphite obtained in step S1 to the impregnation solution and soaking it for 15-20 minutes, filtering it, and drying it to obtain modified expandable graphite;

[0011] S3. Expanding the modified expandable graphite obtained in step S2 at 920-960° C. to obtain graphite worms. After cooling the graphite worms, pressing at 85-95° C. and 19-21 MPa for 130-170 seconds to obtain flexible graphite.

[0012] 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.

[0013] The present invention first oxidizes graphite using potassium permanganate as an oxidant, and then adds a mixed solution of phosphoric acid and an ionic liquid as an intercalant, thereby solving the problem of traditionally using only a large amount of acidic reagents such as sulfuric acid and nitric acid as intercalants, which produces a large amount of acidic wastewater and pollutes the environment. In addition, by soaking the obtained expandable graphite in an impregnation solution, the obtained flexible graphite has excellent tensile strength and oxidation resistance.

[0014] In some embodiments, the mass ratio of the 74-90 wt % phosphoric acid aqueous solution to the ionic liquid in step S1 is (1.8-2):1.

[0015] The present invention limits the mass ratio of phosphoric acid and ionic liquid so that the two can more easily enter the interlayer of graphite. In addition, the molecular structure of the 2-methylacetanilide-citric acid ionic liquid is relatively large, which can enhance the intercalation effect.

[0016] In some embodiments, the ratio of expandable graphite to impregnation liquid in step S2 is 1 g: (0.8-1) L.

[0017] The present invention limits the ratio of expandable graphite to impregnating liquid so that the impregnating liquid can enter the interlayers of the expandable graphite, while preventing the impregnating liquid from accumulating excessively between the layers to reduce the compressibility and resilience of the flexible graphite.

[0018] 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.

[0019] In some embodiments, the mass ratio of 2-methylacetanilide to citric acid is 1:(1.3-1.5).

[0020] The present invention limits the mass ratio of 2-methylacetanilide and citric acid by sour and 2-Methylacetanilide-citric acid ionic liquid is prepared by a neutralization reaction between alkalis. The obtained ionic liquid contains amino and carboxyl groups with similar polarity to the oxidized graphite. Under the action of ultrasound, the interlayer force of the graphite is weakened, making it easier for the intercalant to enter the interlayer. The prepared expandable graphite has a larger expansion volume and increases the tensile strength of the flexible graphite.

[0021] In some embodiments, the impregnation solution comprises the following raw materials, calculated as 100% by mass: 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 balance is water.

[0022] 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 5-6 hours, and rotary evaporating to obtain the modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid.

[0023] Preferably, the mass ratio of the polyethylene glycol-catechol phenylboronic acid ester-polyglutamic acid to 3-amino-3-methylbutyric acid is 1:(0.2-0.3).

[0024] The present invention utilizes 3-amino-3-methylbutyric acid to modify polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid, so that it can react with an intercalant and evenly form an oxygen-isolating protective film on the surface and inside of the flexible graphite, thereby further improving its antioxidant properties.

[0025] In some embodiments, the method for preparing the metal ionic liquid comprises the following steps:

[0026] (1) Add 1-hydroxyethyl-3-methylimidazolium chloride and diethylphosphinoacetic acid to dichloromethane, add concentrated sulfuric acid while stirring, react at 70-80°C for 5-6 hours, and rotary evaporate to obtain the compound;

[0027] (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.

[0028] Preferably, the mass ratio of the 1-hydroxyethyl-3-methylimidazolium chloride to diethylphosphinoacetic acid is 1:(1.2-1.4).

[0029] The invention grafts 1-hydroxyethyl-3-methylimidazolium chloride onto diethylphosphoacetic acid, and then reacts with ferric chloride to obtain an iron-containing metal ion liquid. The iron-containing metal ion liquid is added to an impregnation solution so that the impregnation solution can be evenly distributed on the graphite surface, and the impregnated graphite still has good high-temperature resistance after calcination. This is probably because the cationic graft of the metal ion liquid contains multiple phosphorus groups, and the nitrogen atoms of the imidazole groups and the iron ions can interact with the intercalant, so that the phosphorus atoms can effectively remain inside the expandable graphite. Under the action of high temperature, phosphorus and oxygen are cross-linked, which can increase the high-temperature resistance of the flexible graphite. In addition, the presence of the iron atoms further increases the conductivity of the flexible graphite.

[0030] In some embodiments, the mass ratio of the compound to ferric chloride in step (2) is 1:(0.5-0.6).

[0031] The present invention limits the mass ratio of the compound to ferric chloride so that the Cl - Can fully react with ferric chloride to generate [FeCl4] - , increasing the conductivity and the coordination effect of iron ions increase the tensile strength of flexible graphite.

[0032] A second aspect of the present invention provides an application of flexible graphite in a flexible graphite bipolar plate.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The present invention first oxidizes graphite with potassium permanganate as an oxidant, and then adds a mixed solution of phosphoric acid and ionic liquid as an intercalant. This solves the problem of traditionally using only a large amount of acidic reagents such as sulfuric acid and nitric acid as intercalants, which produces a large amount of acidic wastewater that pollutes the environment. In addition, by soaking the obtained expandable graphite in an impregnation solution, the obtained flexible graphite has excellent tensile strength and oxidation resistance.

[0035] 2. The present invention prepares 2-methylacetanilide and citric acid in a specific mass ratio by sour and The ionic liquid 2-methylacetanilide-citric acid is prepared by a neutralization reaction between alkalis. The obtained ionic liquid contains amino and carboxyl groups with similar polarity to the oxidized graphite. Under the action of ultrasound, the interlayer force of the graphite is weakened, making it easier for the intercalant to enter the interlayer. The prepared expandable graphite has a larger expansion volume and increased tensile strength.

[0036] 3. The present invention grafts 1-hydroxyethyl-3-methylimidazolium chloride onto diethylphosphoacetic acid, which is then reacted with ferric chloride to obtain an iron-containing metal ion liquid. The iron-containing metal ion liquid can be evenly distributed on the graphite surface, so that the graphite after impregnation and calcination has good high-temperature resistance. This may be because the cation grafted into the metal ion liquid contains multiple phosphorus groups, and the nitrogen atoms of the imidazole groups and the iron ions in the anions can interact with the intercalant, so that the phosphorus atoms can effectively remain inside the expandable graphite. Under high temperature, phosphorus and oxygen cross-link with each other, which can increase the high-temperature resistance of the flexible graphite. In addition, the presence of iron ions further increases the conductivity of the flexible graphite. DETAILED DESCRIPTION

[0037] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following examples and comparative examples are intended only to illustrate the present invention and are not intended to limit the present invention. Other combinations and various modifications within the scope of the present invention may be made without departing from the spirit or scope of the present invention.

[0038] In order to facilitate those skilled in the art to implement the present invention, some of the raw materials and manufacturers of the embodiments and comparative examples are described as follows:

[0039] The compounds and related reagents used in the following examples and comparative examples can all be purchased from the market, among which polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid was purchased from Xi'an Qiyue Biotechnology Co., Ltd. with Mn=600; natural flake graphite was purchased from Qingdao Mingrun Chenyue Graphite Co., Ltd. with a particle size of 50 mesh.

[0040] Preparation Example 1

[0041] The preparation method of ionic liquid-1 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 ionic liquid-1.

[0042] Preparation Example 2

[0043] The preparation method of ionic liquid-2 is the same as that of Preparation Example 1, except that the amount of citric acid added is 11 g.

[0044] Preparation Example 3

[0045] 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 product.

[0046] Preparation Example 4

[0047] The preparation method of metal ionic liquid-1 comprises the following steps:

[0048] (1) Add 10 g of 1-hydroxyethyl-3-methylimidazolium chloride and 13 g of diethylphosphinoacetic 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 rotary evaporate to obtain the compound;

[0049] (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 metal ionic liquid-1.

[0050] Preparation Example 5

[0051] The preparation method of metal ionic liquid-2 is the same as that of Preparation Example 4, except that the amount of ferric chloride added is 4.5 g.

[0052] Example 1

[0053] A method for preparing flexible graphite comprises the following steps:

[0054] S1. Add 10 g of natural flake graphite and 1.5 g of potassium permanganate to a reaction vessel at room temperature, and add 40 ml of a mixed solution of 75 wt% aqueous phosphoric acid solution and ionic liquid-1 dropwise while ultrasonicating. The mass ratio of 75 wt% aqueous phosphoric acid solution to ionic liquid-1 is 1.9:1. The dropping speed is 1 ml / s, the ultrasonic power is 135 W, and the ultrasonic temperature is 35 ° C. After the dropwise addition is completed, continue ultrasonicating for 2.5 hours, wash until neutral, and dry to obtain expandable graphite;

[0055] S2. Add 10 g of the expandable graphite obtained in step S1 to 8 L of impregnation solution and soak for 18 min, filter, and dry to obtain modified expandable graphite;

[0056] 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;

[0057] The impregnation solution, calculated as 100% by mass, includes 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-1, 7%, and water, 86.7%.

[0058] Example 2

[0059] A method for preparing flexible graphite comprises the following steps:

[0060] S1. Add 10 g of natural flake graphite and 1.5 g of potassium permanganate to a reaction vessel at room temperature, and add 40 ml of a mixed solution of 75 wt% aqueous phosphoric acid solution and ionic liquid-1 dropwise while ultrasonicating. The mass ratio of 75 wt% aqueous phosphoric acid solution to ionic liquid-1 is 1.9:1. The dropping speed is 1 ml / s, the ultrasonic power is 130 W, and the ultrasonic temperature is 30°C. After the addition is completed, continue ultrasonicating for 2 h, wash until neutral, and dry to obtain expandable graphite;

[0061] S2. Add 10 g of the expandable graphite obtained in step S1 to 5 L of impregnation solution and soak for 15 min, filter, and dry to obtain modified expandable graphite;

[0062] S3. Expand 8 g of the modified expandable graphite obtained in step S2 at 920°C to obtain graphite worms. Cool the graphite worms and press them at 85°C and 21 MPa for 130 seconds to obtain flexible graphite.

[0063] The impregnation solution, calculated as 100% by mass, includes the following raw materials: 75wt% phosphoric acid 2%, modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid 2%, boric acid 0.5%, metal ion liquid-1 6%, and water 89.5%.

[0064] Example 3

[0065] A method for preparing flexible graphite comprises the following steps:

[0066] S1. Add 10 g of natural flake graphite and 1.5 g of potassium permanganate to a reaction vessel at room temperature, and add 40 ml of a mixed solution of 75 wt% aqueous phosphoric acid solution and ionic liquid-1 dropwise while ultrasonicating. The mass ratio of 75 wt% aqueous phosphoric acid solution to ionic liquid-1 is 1.9:1. The dropping speed is 1 ml / s, the ultrasonic power is 140 W, and the ultrasonic temperature is 40°C. After the addition is completed, continue ultrasonicating for 3 h, wash until neutral, and dry to obtain expandable graphite;

[0067] S2. Add 10 g of the expandable graphite obtained in step S1 to 10 L of the impregnation solution and soak for 20 min, filter, and dry to obtain modified expandable graphite;

[0068] S3, expanding 8 g of the modified expandable graphite obtained in step S2 at 960° C. to obtain graphite worms, and then cooling the graphite worms and pressing them at 95° C. and 19 MPa for 170 s to obtain flexible graphite;

[0069] The impregnation solution, calculated as 100% by mass, includes the following raw materials: 75wt% phosphoric acid, 4%, modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid, 3%, boric acid, 1%, metal ion liquid-1, 8%, and water, 84%.

[0070] Example 4

[0071] A method for preparing flexible graphite, the specific implementation method is the same as that of Example 1, except that an equal amount of ionic liquid-1 is replaced by ionic liquid-2.

[0072] Example 5

[0073] A flexible graphite and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that an equal amount of metal ion liquid-1 is replaced by metal ion liquid-2.

[0074] Example 6

[0075] A flexible graphite and a preparation method thereof, the specific implementation manner is the same as that of Example 1, except that the amount of impregnation liquid added is 7 L.

[0076] Example 7

[0077] A flexible graphite and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that an equal amount of modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid is replaced by polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid.

[0078] Comparative Example 1

[0079] A method for preparing flexible graphite comprises the following steps:

[0080] S1. Add 10 g of natural flake graphite and 1.5 g of potassium permanganate to a reaction vessel at room temperature, and add 40 ml of a 75 wt% aqueous phosphoric acid solution dropwise while ultrasonicating at a dropping rate of 1 ml / s, an ultrasonic power of 135 W, and an ultrasonic temperature of 35 ° C. After the addition is complete, continue ultrasonicating for 2.5 h, wash until neutral, and dry to obtain expandable graphite;

[0081] S2. Expand 8 g of the modified expandable graphite obtained in step S1 at 940° C. to obtain graphite worms. After cooling the graphite worms, press at 5.5 MPa for 7 min, then heat to 90° C. and press for 150 s to obtain flexible graphite.

[0082] Performance Testing

[0083] The flexible graphite obtained in each example and comparative example was pressed into a 0.5 mm flexible graphite plate and subjected to the following tests.

[0084] 1. Compression rate and rebound rate

[0085] The compression rate and the rebound rate of the flexible graphite sheets obtained in each embodiment and comparative example were tested according to JBT / 9141.4-2013.

[0086] 2. Tensile strength

[0087] The tensile strength of the flexible graphite sheets obtained in various examples and comparative examples was tested according to JBT / 9141.2-2013.

[0088] 3. High temperature resistance

[0089] The thermal weight loss rate of the flexible graphite obtained in each embodiment and comparative example at 670° C. was tested according to JBT / 9141.7-2013.

[0090] The test results are shown in Table 1.

[0091] Table 1

[0092]

[0093] Comparing the experimental data of Examples 1-3 in Table 1, it can be seen that the flexible graphite obtained by the preparation method of the flexible graphite has greater tensile strength, good high temperature resistance, compressibility and resilience; Compared with Example 1, Example 4 shows that the ratio of 2-methylacetanilide and citric acid in the ionic liquid is changed, which may lead to a decrease in the purity of the ionic liquid, a weakening of the intercalation effect, and a decrease in the rebound rate, compressibility and high temperature resistance; Compared with Example 1, Example 5 shows that the ratio of the compound to ferric chloride in the metal ionic liquid is changed, which may lead to a decrease in the coordination effect. The tensile strength of the flexible graphite is weak; compared with Example 1, Example 6 shows that the change in the ratio of expandable graphite to the impregnating liquid may result in a decrease in the amount of impregnating liquid entering the flexible graphite interlayer, resulting in a decrease in the high temperature resistance of the flexible graphite; compared with Example 1, Example 7 shows that the use of unmodified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid may result in uneven distribution of the impregnating liquid between the layers, resulting in a decrease in the high temperature resistance of the flexible graphite; compared with Example 1, it can be seen that various properties of the flexible graphite obtained using the conventional preparation method are reduced.

[0094] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present 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 modifications, equivalent changes and modifications 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 are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing flexible graphite, characterized in that: The following steps are involved: S1. Add graphite and potassium permanganate to a reaction vessel at room temperature, and dropwise add a mixed solution of 74-90 wt% aqueous phosphoric acid solution and ionic liquid while ultrasonicating. The ultrasonic power is 130-140 W and the ultrasonic temperature is 30-40 ° C. After the dropwise addition is completed, continue ultrasonicating for 2-3 hours, wash until neutral, and dry to obtain expandable graphite; S2, adding the expandable graphite obtained in step S1 to the impregnation solution and soaking it for 15-20 minutes, filtering it, and drying it to obtain modified expandable graphite; S3, expanding the modified expandable graphite obtained in step S2 at 920-960° C. to obtain graphite worms, and then cooling the graphite worms and pressing them at 85-95° C. and 19-21 MPa for 130-170 s to obtain flexible graphite; In step S2, the ratio of expandable graphite to impregnation liquid is 1 g: (0.8-1) L; The preparation method of 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; The impregnation solution comprises the following raw materials, calculated as 100% by mass: 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 balance water; 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 5-6 hours, and rotary evaporating to obtain the modified polyethylene glycol-phenylboronic acid catechol ester-polyglutamic acid; The preparation method of the metal ionic liquid comprises the following steps: (1) Add 1-hydroxyethyl-3-methylimidazolium chloride and diethylphosphinoacetic acid to dichloromethane, add concentrated sulfuric acid while stirring, react at 70-80°C for 5-6 hours, and rotary evaporate to obtain the compound; (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.

2. The method for preparing flexible graphite according to claim 1, wherein In step S1, the mass ratio of the 74-90 wt% phosphoric acid aqueous solution to the ionic liquid is (1.8-2):

1.

3. The method for preparing flexible graphite according to claim 1, wherein The mass ratio of the 2-methylacetanilide to citric acid is 1:(1.3-1.5).

4. The method for preparing flexible graphite according to claim 1, wherein The mass ratio of the compound to ferric chloride in step (2) is 1:(0.5-0.6).

5. Use of the flexible graphite obtained by the method for preparing the flexible graphite according to any one of claims 1 to 4 in a flexible graphite bipolar plate.

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