Composite graphite bipolar plate under action of pulsed electric field and preparation method of composite graphite bipolar plate

Abstract

The invention relates to a composite graphite bipolar plate under the action of a pulsed electric field and a preparation method thereof. The preparation method comprises the following steps: uniformly mixing modified graphite, crystalline flake graphite and resin, and drying to obtain composite powder; putting the composite powder into a mold, applying a pulsed electric field along the normal direction of the horizontal plane of the mold, and applying reciprocating vibration of a mold cavity along the horizontal direction of the horizontal plane of the mold; and carrying out hot mold pressing on the mold subjected to reciprocating vibration of the pulsed electric field and the mold cavity, and molding to obtain the composite graphite bipolar plate. Compared with the prior art, the method has the advantages that the pulsed electric field is applied on the basis of the traditional thermosetting method so as to change the orientation of the graphite particles in the current uniform state, so that the excellent conductivity of the graphite is better represented on the conductivity of the bipolar plate. And in an alternating electric field generated by the pulse electric field, the polarized particles repel each other, so that the dispersity of the powder is improved. By changing the orientation of the graphite, the conductivity of the polar plate is greatly improved, the production efficiency is high, and the product performance is good.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a composite graphite bipolar plate under the action of a pulsed electric field and its preparation method. Background Technology

[0002] A fuel cell is a device that directly generates electricity by reacting fuel (such as hydrogen) with oxygen through a chemical reaction. Its working principle is similar to a battery, but unlike a traditional battery, a fuel cell is an energy conversion device that continuously converts chemical energy into electrical energy by constantly supplying fuel (such as hydrogen) and oxygen. With the increasing demand for clean energy, fuel cell technology is gradually becoming an important direction for replacing traditional internal combustion engines and batteries. With the growing awareness of environmental protection, hydrogen fuel cells are receiving particular attention.

[0003] In fuel cells, bipolar plates are a crucial component, serving multiple functions including electrical connection, gas distribution, cooling, and structural support. Different types of bipolar plate materials significantly impact the performance and lifespan of fuel cells. Common bipolar plate materials include metallic materials and composite materials. Metallic bipolar plate materials include titanium alloys, stainless steel, and copper, while composite graphite bipolar plates are made from carbon-based materials (such as graphite and composite graphite). Metallic bipolar plates typically possess good electrical conductivity and mechanical strength, but they are highly susceptible to corrosion, requiring anti-corrosion treatments such as coatings or application of precious metals, making the processing cost of metallic materials relatively high. Graphite materials offer good electrical conductivity and are corrosion-resistant and heat-resistant, but have limitations in structural strength and processability; therefore, reinforced composite materials are sometimes used.

[0004] Composite graphite bipolar plates are bipolar plates made by combining graphite with other materials (such as resin, carbon fiber, etc.). Compared with traditional single graphite bipolar plates, composite graphite bipolar plates combine the excellent conductivity of graphite with the advantages of composite materials, resulting in better mechanical properties, processing performance, and corrosion resistance. Common processing methods include thermosetting and thermoplastic methods. For existing thermosetting methods, graphite particles (mainly flake graphite and expanded graphite) are usually uniformly mixed with thermosetting resin, and then the mixture is placed in a mold for hot molding. However, the uniform state of graphite in the powder cannot fully reflect the excellent conductivity of its layered structure, resulting in poor performance.

[0005] To address the above issues, the orientation of graphite can be altered. In traditional processes, graphite particles are mostly layered, resulting in highly uniform orientation after mixing. However, during hot molding, the layered structure tends to tilt towards the bipolar plate plane, leading to a higher horizontal conductivity than the normal conductivity. This traditional process structure prevents graphite's superior electrical conductivity from being fully realized. The layered structure and uniform orientation of graphite particles also hinder the formation of good interfacial connections, resulting in typically high interfacial resistance. Therefore, changing the graphite orientation can improve conductivity without altering the material structure and with minimal impact on other properties, thus resolving the issue of not fully realizing graphite's excellent electrical conductivity.

[0006] Common methods for altering graphite orientation include filler pretreatment, molding process parameter optimization, and electromagnetic-assisted orientation. Among these, electromagnetic-assisted orientation is a highly efficient, non-contact method with extremely high orientation. However, this process faces the following challenges: the graphite particles in the resulting solid material have poor flowability; the graphite particles have weak polarity, making it difficult to change their orientation using electromagnetic means; and the high-intensity pulsed electric field has a strong thermal effect, which can cause the material to solidify prematurely, making it difficult to achieve the expected results of the process.

[0007] Patent publication number CN118977434A discloses a molding manufacturing method for composite graphite bipolar plates, including the following steps: S1, introducing a mixture containing composite graphite bipolar plate raw materials into a pre-made mold; S2, applying a field effect to the upper and lower molding plates. This technical solution improves the arrangement or flowability of the filler to a certain extent by introducing an external field. However, this method still has obvious limitations, making it difficult to fundamentally overcome the problem of anisotropic conductivity of composite graphite bipolar plates, and the conductivity of the prepared bipolar plates in the normal direction still needs to be improved. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of graphite's conductivity not being fully reflected in the performance of the bipolar plate. Based on the problems of poor graphite flowability, difficulty in changing orientation, and premature curing of materials in electromagnetically assisted orientation, this invention provides a composite graphite bipolar plate under the action of a pulsed electric field and its preparation method. On the basis of the traditional thermosetting method, a pulsed electric field is applied to change the orientation of graphite particles in the current uniform state, so that the excellent conductivity of graphite is better reflected in the conductivity of the bipolar plate.

[0009] Under the influence of a pulsed electric field, graphite particles undergo interfacial polarization (Maxwell-Wagner polarization) due to differences in conductivity, resulting in uneven charge distribution on or within the particles and the formation of dipole moments. The polarized particles experience dielectric force in the pulsed electric field, propelling them towards regions with higher electric field strength. During this process, the particles continuously adjust their positions to reduce energy. The anisotropic conductivity of graphite particles makes them more inclined to align with the direction of high conductivity along the electric field to minimize system resistance. Furthermore, the transient nature of the pulsed electric field prevents particle agglomeration or thermal damage caused by prolonged energization. Simultaneously, under the alternating electric field generated by the pulsed electric field, the polarized particles generate mutually repulsive Coulomb forces, breaking up agglomeration caused by van der Waals forces and improving the dispersibility of the powder in solvents or binders.

[0010] The objective of this invention can be achieved through the following technical solutions:

[0011] In one aspect, the present invention provides a method for preparing a composite graphite bipolar plate under the action of a pulsed electric field, comprising the following steps:

[0012] S1. Modified graphite, flake graphite, and resin are uniformly mixed and dried to obtain composite powder.

[0013] S2. Place the composite powder into a mold, apply a pulsed electric field along the normal direction of the horizontal plane of the mold, and simultaneously apply reciprocating vibration of the mold cavity along the horizontal direction of the horizontal plane of the mold.

[0014] S3. The mold subjected to pulsed electric field and reciprocating vibration of the mold cavity is hot-pressed to form a composite graphite bipolar plate.

[0015] Further, in step S1, the modified graphite is one or more of the following: oxide-modified graphite, amino-modified graphite, carboxyl-modified graphite, sulfonic acid-modified graphite, fluorinated graphite, heteroatom-doped graphite, and polymer-modified graphite. By changing the surface functional groups of the modified graphite, the modified graphite acquires stronger polarity, satisfying its ability to exhibit a certain degree of ordered arrangement under the action of a pulsed electric field. Furthermore, the interaction between functional groups can enable the graphite-resin to form a better bonding structure, satisfying the flowability of the composite material during the pressing process.

[0016] Furthermore, the modified graphite is in flake form.

[0017] Furthermore, the heteroatoms in the heteroatom-doped graphite include one or more of nitrogen, boron, phosphorus, sulfur, and fluorine. Heteroatom doping, as described in this invention, refers to the process of introducing non-carbon elements such as nitrogen, boron, phosphorus, sulfur, and fluorine into the crystal lattice of a graphite matrix to replace carbon atoms or form defect structures, thereby controlling its physicochemical properties.

[0018] Furthermore, the heteroatom-doped graphite includes single-unit doped graphite, binary doped graphite, and multi-unit doped graphite.

[0019] Furthermore, single-unit doped graphite includes nitrogen-doped graphite, boron-doped graphite, phosphorus-doped graphite, sulfur-doped graphite, and fluorine-doped graphite.

[0020] Bi-doped graphite includes nitrogen-boron co-doped graphite, nitrogen-phosphorus co-doped graphite, nitrogen-sulfur co-doped graphite, nitrogen-fluorine co-doped graphite, boron-phosphorus co-doped graphite, boron-sulfur co-doped graphite, boron-fluorine co-doped graphite, phosphorus-sulfur co-doped graphite, phosphorus-fluorine co-doped graphite, and sulfur-fluorine co-doped graphite.

[0021] Multi-doped graphite includes nitrogen-boron-phosphorus co-doped graphite, nitrogen-boron-sulfur co-doped graphite, nitrogen-boron-fluorine co-doped graphite, boron-phosphorus-sulfur co-doped graphite, boron-phosphorus-fluorine co-doped graphite, phosphorus-sulfur-fluorine co-doped graphite, nitrogen-boron-phosphorus-sulfur co-doped graphite, nitrogen-boron-phosphorus-fluorine co-doped graphite, boron-phosphorus-sulfur-fluorine co-doped graphite, and nitrogen-boron-phosphorus-sulfur-fluorine co-doped graphite.

[0022] Furthermore, the modified graphite is obtained by modifying graphite particles.

[0023] Furthermore, the modification process involves immersing graphite particles in a reagent capable of modifying or altering the functional groups on the graphite surface.

[0024] The reagent is one or more of the following: oxidizing modifier, amino modifier, carboxyl modifier, sulfonic acid modifier, fluorinating modifier, heteroatom dopant, or polymer modifier.

[0025] Further, in step S1, the resin is one or more of epoxy resin, phenolic resin, acrylic resin, vinyl ester resin, furan resin or urea-formaldehyde resin.

[0026] Furthermore, in step S1, the particle size of the flake graphite is 100-2000 mesh, preferably 300-1000 mesh.

[0027] Further, in step S1, based on a total mass of 100 parts for the modified graphite, flake graphite, and resin, the modified graphite comprises 1-20 parts, the flake graphite 60-80 parts, and the resin 10-30 parts. Preferably, the modified graphite comprises 10-15 parts, the flake graphite 65-75 parts, and the resin 15-25 parts.

[0028] Furthermore, in step S1, the drying temperature is 40–70°C, preferably 50–60°C.

[0029] Furthermore, in step S2, the horizontal plane of the mold is the upper and lower surfaces of the mold.

[0030] Further, in step S2, the total duration of the pulsed electric field ranges from 5 to 300 s, preferably from 30 to 120 s; the peak value of the electric field intensity of the pulsed electric field ranges from 1 to 50 KV / cm, preferably from 5 to 20 KV / cm; and the frequency ranges from 1 to 10000 Hz.

[0031] Further, in step S2, the application mode of the pulsed electric field is at least one of an intermittent pulse sequence or a continuous pulse mode.

[0032] Furthermore, the intermittent pulse sequence consists of periodically repeating pulse groups, each pulse group including a pulse duration and a pulse interval. The pulse duration is 1–500 ms, preferably 10–100 ms; the pulse interval is 2–1000 ms, preferably 20–200 ms, and the pulse interval and pulse duration are positively correlated, lasting a total of 10–120 s.

[0033] The duration of the continuous pulse mode is 0.1 to 10 seconds, preferably 0.5 to 3 seconds.

[0034] Further, in step S2, the waveform of the pulsed electric field is any one or more combinations of square wave, sine wave, or exponentially decaying wave. Different types of pulsed electric fields have different degrees of impact on the orientation of graphite. The strong dielectric force generated by the instantaneous high field strength of the square wave pulse can instantly polarize graphite particles, reduce charge relaxation time, promote particle orientation, and provide continuous torque during the flat-top phase, promoting stable alignment of particles along the electric field direction, making it suitable for highly conductive graphite systems. Under the action of the sinusoidal AC pulsed electric field, the particles rotate periodically with the electric field, eventually achieving net orientation due to fluid resistance, making it suitable for dynamically adjusting the particle orientation angle and reducing the risk of local overheating. The initial peak electric field of the exponentially decaying pulse can strongly polarize graphite, and the subsequent decay phase reduces energy consumption, making it suitable for rapid orientation triggering, and it can be generated using a simple RC circuit, resulting in low implementation cost.

[0035] Furthermore, in step S2, the reciprocating vibration frequency of the mold cavity ranges from 1 to 100 Hz, preferably from 20 to 50 Hz, and the vibration amplitude ranges from 0.01 to 0.5 mm, preferably from 0.05 to 0.2 mm.

[0036] Furthermore, in step S2, when a pulsed electric field is applied along the normal direction of the horizontal plane of the mold, the composite powder is at room temperature.

[0037] Furthermore, in step S2, the mold includes an upper mold and a lower mold, and the upper and lower molds are insulated from each other.

[0038] Further, in step S3, the hot molding conditions are: 15-60 MPa, 150-200°C, preferably 50-60 MPa, 160-180°C.

[0039] In another aspect, the present invention also provides a composite graphite bipolar plate under the action of a pulsed electric field, which is prepared by the aforementioned preparation method.

[0040] Furthermore, the thickness of the composite graphite bipolar plate is 0.3–2 mm.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] (1) This invention alters the orientation of graphite particles in a homogeneous state after mixing by applying a pulsed electric field. This not only causes the layered structure of graphite to be oriented towards the normal of the bipolar plate, thus better reflecting the excellent conductivity of graphite in the conductivity of the bipolar plate, but also enables the graphite particles to form a better connection structure, reducing the interfacial resistance. In addition, this process only changes the orientation of the graphite without altering the network structure in the mixed material, so it has little impact on other properties of the bipolar plate, greatly improving the conductivity of the plate.

[0043] (2) By applying cavity movement to the mold, the present invention breaks the aggregated state of graphite and reduces flow resistance through dynamic action, thereby improving the flowability of graphite.

[0044] (3) The present invention modifies the graphite surface by grafting or modifying surface functional groups, so that the graphite matrix has electromagnetic response characteristics and adjustable interface effects, enabling it to overcome the viscous resistance of the dispersed system and achieve directional alignment under the action of a pulsed electric field.

[0045] (4) The present invention generates a Coulomb force that repels each other under the action of an alternating electric field generated by a pulsed electric field, thereby breaking the soft agglomeration caused by van der Waals forces and improving the dispersibility of powder in solvents or binders. Attached Figure Description

[0046] Figure 1 The following are schematic diagrams of the composite graphite bipolar plate of the present invention: (A) Comparative Example 1, (B) Example 1. Detailed Implementation

[0047] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the given embodiments without creative effort are within the scope of protection of this application.

[0048] Unless otherwise specified, the reagents, methods, instruments and equipment used in this invention are conventional reagents, methods, instruments and equipment in the art.

[0049] The modified graphite described in the following examples is oxide-modified graphite prepared using the conventional Hummers method. The specific process of the Hummers method used to prepare oxide graphite is as follows:

[0050] (1) Low-temperature intercalation stage

[0051] Under ice-water bath conditions (0°C), concentrated H2SO4 (98%) was added to the reaction vessel and stirred. Natural graphite powder was then slowly added and mixed thoroughly. KMnO4 (oxidant) was then added in batches. During this stage, the temperature must be controlled to not exceed 20°C to avoid a violent reaction between KMnO4 and concentrated H2SO4. SO42- ions were inserted between the graphite layers, initially forming an intercalation complex. The reaction lasted for 1 hour.

[0052] (2) Mesotemperature oxidation stage

[0053] Remove the ice-water bath and heat the reaction system to 40℃ (controlled by a warm water bath), then stir the reaction at this temperature for 2 hours. During this stage, the intercalation complex is further oxidized by KMnO4, the C-C bonds in the graphite layer are broken, and oxygen-containing functional groups such as hydroxyl (-OH) and epoxy (-O-) are introduced. The graphite gradually transforms into graphite oxide precursor, and the system becomes viscous and brown in color.

[0054] (3) High-temperature hydrolysis and termination reaction stage

[0055] Slowly add deionized water dropwise to the reaction system (the dropping rate needs to be controlled to avoid a sudden temperature rise due to exothermic reactions), while simultaneously heating the system to 98°C and stirring at this temperature for 30 minutes. During this stage, excess KMnO4 is diluted by water and further oxidizes the graphite. Finally, a small amount of H2O2 (30%) is added to terminate the reaction (reducing the remaining KMnO4, changing the system color from brownish-black to bright yellow), and introducing carboxyl groups (-COOH, mainly located at the edges of the graphite oxide).

[0056] (4) Post-processing stage

[0057] After the reaction was complete, the system was allowed to stand and cool, and the product was repeatedly washed with 5% dilute HCl solution (to remove residual SO42- and Mn). 2+ The washing solution was washed with deionized water until no white precipitate was found after testing with BaCl2 (proving that there was no SO42- residue); then it was washed with deionized water until neutral (pH≈7), and finally separated by centrifugation, filtration and freeze drying to obtain layered oxide-modified graphite.

[0058] The amino-modified graphite described in the following examples was prepared using graphite oxide prepared by the Hummers method as raw material, and was grafted with ethylenediamine molecules via an amidation reaction. The specific process is as follows:

[0059] (1) Pretreatment stage of graphite oxide dispersion

[0060] The graphene oxide powder prepared by the Hummers method was dispersed in deionized water to prepare a suspension with a concentration of 2 mg / mL. The suspension was then sonicated (300 W) for 2 hours to ensure uniform dispersion, resulting in a brownish-yellow graphene oxide dispersion. Under stirring, a 0.1 mol / L NaOH solution was added dropwise to the dispersion to adjust the pH to 9, causing the carboxyl groups (-COOH) at the edges and defects of the graphene oxide to deprotonate and form activated carboxylate groups (-COO₂). - ), used for subsequent amidation reactions.

[0061] (2) Amide grafting reaction stage

[0062] Excess ethylenediamine (EDA) was added to the pretreated graphene oxide dispersion, with a mass ratio of EDA to GO of 10:1. Subsequently, condensing agents N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide (NHS) were added, with a molar ratio of EDC·HCl to GO of 2:1 and a molar ratio of NHS to EDC·HCl of 1:1. Under nitrogen protection, the reaction system was heated to 80°C and stirred under reflux for 24 hours. During this process, EDC·HCl first reacts with the carboxyl groups on the GO surface to generate an active intermediate. This intermediate, under the action of NHS, forms a more stable active ester, which then undergoes a nucleophilic substitution reaction with the amino group (-NH2) of ethylenediamine to form a stable amide bond (-CONH-). This covalently grafts the ethylenediamine molecule onto the GO backbone, exposing the terminal primary amino group (-NH2), thus achieving amino modification.

[0063] (3) Product purification stage

[0064] After the reaction is complete, the reaction system is cooled to room temperature. The black product is collected by vacuum filtration. Subsequently, the precipitate is washed at least five times alternately with anhydrous ethanol and deionized water until the washings show no color change when tested with ninhydrin reagent (indicating the absence of free ethylenediamine residue). This step completely removes unreacted ethylenediamine, condensing agents, and their byproducts.

[0065] (4) Drying and collecting stage

[0066] The purified product after washing was redispersed in deionized water and vacuum dried (60℃, 24 hours) to obtain a fluffy black solid powder, which is amino-modified graphite.

[0067] A method for preparing a composite graphite bipolar plate under pulsed electric field includes the following steps:

[0068] S1. Modified graphite, flake graphite, and resin are uniformly mixed and dried to obtain composite powder.

[0069] S2. Place the composite powder into a mold, apply a pulsed electric field along the normal direction of the horizontal plane of the mold, and simultaneously apply reciprocating vibration of the mold cavity along the horizontal direction of the horizontal plane of the mold.

[0070] S3. The mold subjected to pulsed electric field and reciprocating vibration of the mold cavity is hot-pressed to form a composite graphite bipolar plate.

[0071] In some specific embodiments, in step S1, the modified graphite is one or more of the following: oxide-modified graphite, amino-modified graphite, carboxyl-modified graphite, sulfonic acid-modified graphite, fluorinated graphite, heteroatom-doped graphite, and polymer-modified graphite. By changing the surface functional groups of the modified graphite, the modified graphite acquires stronger polarity, satisfying its ability to exhibit a certain degree of ordered arrangement under the action of a pulsed electric field. Furthermore, the interaction between functional groups can enable the graphite-resin to form a better bonding structure, satisfying the flowability of the composite material during the pressing process.

[0072] In some specific embodiments, the modified graphite is in flake form.

[0073] In some specific embodiments, the heteroatoms in the heteroatom-doped graphite include one or more of nitrogen, boron, phosphorus, sulfur, and fluorine. Heteroatom doping, as described in this invention, refers to the process of introducing non-carbon elements such as nitrogen, boron, phosphorus, sulfur, and fluorine into the crystal lattice of a graphite matrix to replace carbon atoms or form defect structures, thereby controlling its physicochemical properties.

[0074] In some specific embodiments, the heteroatom-doped graphite includes single-unit doped graphite, binary doped graphite, and multi-unit doped graphite.

[0075] In some specific embodiments, the unit doped graphite includes nitrogen-doped graphite, boron-doped graphite, phosphorus-doped graphite, sulfur-doped graphite, and fluorine-doped graphite.

[0076] Bi-doped graphite includes nitrogen-boron co-doped graphite, nitrogen-phosphorus co-doped graphite, nitrogen-sulfur co-doped graphite, nitrogen-fluorine co-doped graphite, boron-phosphorus co-doped graphite, boron-sulfur co-doped graphite, boron-fluorine co-doped graphite, phosphorus-sulfur co-doped graphite, phosphorus-fluorine co-doped graphite, and sulfur-fluorine co-doped graphite.

[0077] Multi-doped graphite includes nitrogen-boron-phosphorus co-doped graphite, nitrogen-boron-sulfur co-doped graphite, nitrogen-boron-fluorine co-doped graphite, boron-phosphorus-sulfur co-doped graphite, boron-phosphorus-fluorine co-doped graphite, phosphorus-sulfur-fluorine co-doped graphite, nitrogen-boron-phosphorus-sulfur co-doped graphite, nitrogen-boron-phosphorus-fluorine co-doped graphite, boron-phosphorus-sulfur-fluorine co-doped graphite, and nitrogen-boron-phosphorus-sulfur-fluorine co-doped graphite.

[0078] In some specific embodiments, the modified graphite is obtained by modifying graphite particles.

[0079] In some specific embodiments, the modification process is as follows: the graphite particles are soaked in a reagent that can modify or alter the functional groups on the graphite surface.

[0080] The reagent is one or more of the following: oxidizing modifier, amino modifier, carboxyl modifier, sulfonic acid modifier, fluorinating modifier, heteroatom dopant, or polymer modifier.

[0081] In some specific embodiments, in step S1, the resin is one or more of epoxy resin, phenolic resin, acrylic resin, vinyl ester resin, furan resin, or urea-formaldehyde resin.

[0082] In some specific embodiments, in step S1, the particle size of the flake graphite is 100-2000 mesh, preferably 300-1000 mesh.

[0083] In some specific embodiments, in step S1, based on a total mass of 100 parts for the modified graphite, flake graphite, and resin, the modified graphite comprises 1-20 parts, the flake graphite 60-80 parts, and the resin 10-30 parts. Preferably, the modified graphite comprises 10-15 parts, the flake graphite 65-75 parts, and the resin 15-25 parts.

[0084] In some specific embodiments, in step S1, the drying temperature is 40-70°C, preferably 50-60°C.

[0085] In some specific embodiments, in step S2, the horizontal plane of the mold is the upper and lower surfaces of the mold.

[0086] In some specific embodiments, in step S2, the total duration of the pulsed electric field ranges from 5 to 300 s, preferably from 30 to 120 s; the peak value of the electric field intensity of the pulsed electric field ranges from 1 to 50 KV / cm, preferably from 5 to 20 KV / cm; and the frequency ranges from 1 to 10000 Hz.

[0087] In some specific embodiments, in step S2, the pulsed electric field is applied in at least one of an intermittent pulse sequence or a continuous pulse mode.

[0088] In some specific embodiments, the intermittent pulse sequence consists of periodically repeating pulse groups, each pulse group including a pulse duration and a pulse interval. The pulse duration is 1 to 500 ms, preferably 10 to 100 ms; the pulse interval is 2 to 1000 ms, preferably 20 to 200 ms, and the pulse interval and pulse duration are positively correlated, lasting a total of 10 to 120 s.

[0089] The duration of the continuous pulse mode is 0.1 to 10 seconds, preferably 0.5 to 3 seconds.

[0090] In some specific embodiments, in step S2, the waveform of the pulsed electric field is any one or more combinations of square wave, sine wave, or exponentially decaying wave. Different types of pulsed electric fields have different degrees of effect on the change in graphite orientation. The strong dielectric force generated by the instantaneous high field strength of the square wave pulse can instantly polarize graphite particles, reduce charge relaxation time, promote particle orientation, and provide continuous torque in the flat-top phase, promoting stable alignment of particles along the electric field direction, which is suitable for highly conductive graphite systems; under the action of the sinusoidal AC pulsed electric field, the particles rotate periodically with the electric field, and eventually achieve net orientation due to fluid resistance, which is suitable for dynamically adjusting the particle orientation angle and can reduce the risk of local overheating; the initial peak electric field of the exponentially decaying pulse can strongly polarize graphite, and the subsequent decay phase reduces energy consumption, which is suitable for rapid orientation triggering, and can be generated using a simple RC circuit, resulting in low implementation cost.

[0091] In some specific embodiments, the vibration frequency of the reciprocating vibration of the mold cavity in step S2 is in the range of 1 to 100 Hz, preferably 20 to 50 Hz, and the vibration amplitude is in the range of 0.01 to 0.5 mm, preferably 0.05 to 0.2 mm.

[0092] In some specific embodiments, in step S2, when a pulsed electric field is applied along the normal direction of the horizontal plane of the mold, the composite powder is at room temperature.

[0093] In some specific embodiments, in step S2, the mold includes an upper mold and a lower mold, and the upper and lower molds are insulated from each other.

[0094] In some specific embodiments, in step S3, the hot molding conditions are: 15-60 MPa, 150-200°C, preferably 50-60 MPa, 160-180°C.

[0095] A composite graphite bipolar plate under pulsed electric field is prepared by the aforementioned preparation method.

[0096] In some specific embodiments, the thickness of the composite graphite bipolar plate is 0.3–2 mm.

[0097] Each of the above embodiments can be implemented individually or in any combination of two or more.

[0098] The following description uses specific examples to illustrate the point.

[0099] Example 1

[0100] A method for preparing a composite graphite bipolar plate under pulsed electric field includes the following steps:

[0101] (1) Preparation of composite powder

[0102] Based on a total mass of 100 parts for the modified graphite, flake graphite, and resin, 10 parts of the modified graphite, 70 parts of the flake graphite, and 20 parts of the resin were weighed, uniformly mixed, and dried at 60°C for 2 hours to obtain a composite powder. The flake graphite was purchased from Shenzhen Hanhui Graphite Co., Ltd., with a particle size of 320 mesh. The resin was a mixture of epoxy resin and phenolic resin at a mass ratio of 4:6. The phenolic resin was produced by Sinopharm Chemical Reagent Co., Ltd., and was a low molecular weight phenolic resin liquid, catalog number 80032861. The epoxy resin was produced by Maclean, model 6002-bisphenol A epoxy resin (EP), with an epoxy value of 0.46-0.5 mol / 100g.

[0103] (2) Apply a pulsed electric field

[0104] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak value of the electric field intensity is 10KV / cm, the frequency is 200Hz, and it lasts for 1s.

[0105] (3) Apply reciprocating motion to the mold cavity

[0106] While applying a pulsed electric field along the normal direction of the mold's horizontal plane, a reciprocating vibration of the mold cavity along the horizontal direction of the mold's horizontal plane is also applied, with an amplitude of 0.2 mm, a frequency of 30 Hz, and a duration of 1 s.

[0107] (4) The mold, after being treated with a pulsed electric field and reciprocating motion of the mold cavity, is placed in a hot press for hot molding. The hot molding conditions are 50 MPa and 170°C. After final molding and demolding, a 0.79 m thick composite graphite bipolar plate is obtained, as shown in the schematic diagram. Figure 1 As shown.

[0108] Example 2

[0109] Compared with Example 1, most of them are the same, except for step (1) in the preparation of the composite powder:

[0110] Based on a total mass of 100 parts for the modified graphite, flake graphite, and resin, weigh 1 part of the modified graphite, 79 parts of the flake graphite, and 20 parts of the resin, mix them evenly, and dry them at 60°C for 2 hours to obtain a composite powder.

[0111] Example 3

[0112] Compared with Example 1, most of them are the same, except for step (1) in the preparation of the composite powder:

[0113] Based on a total mass of 100 parts for the modified graphite, flake graphite, and resin, weigh 5 parts of the modified graphite, 75 parts of the flake graphite, and 20 parts of the resin, mix them evenly, and dry them at 60°C for 2 hours to obtain a composite powder.

[0114] Example 4

[0115] Compared with Example 1, most of them are the same, except for step (1) in the preparation of the composite powder:

[0116] Based on a total mass of 100 parts for the modified graphite, flake graphite, and resin, weigh 15 parts of the modified graphite, 65 parts of the flake graphite, and 20 parts of the resin, mix them evenly, and dry them at 60°C for 2 hours to obtain a composite powder.

[0117] Example 5

[0118] Compared with Example 1, most of them are the same, except for step (1) in the preparation of the composite powder:

[0119] Based on a total mass of 100 parts for the modified graphite, flake graphite, and resin, weigh 20 parts of the modified graphite, 60 parts of the flake graphite, and 20 parts of the resin, mix them uniformly, and dry them at 60°C for 2 hours to obtain a composite powder.

[0120] Example 6

[0121] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0122] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak value of the electric field intensity is 10KV / cm, the frequency is 200Hz, and the duration is 0.1s.

[0123] Example 7

[0124] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0125] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak value of the electric field intensity is 10KV / cm, the frequency is 200Hz, and it lasts for 0.5s.

[0126] Example 8

[0127] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0128] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, and it lasts for 2s.

[0129] Example 9

[0130] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0131] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, and it lasts for 3s.

[0132] Example 10

[0133] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0134] The composite powder is placed in a mold, and the pulse mode is selected as an intermittent pulse sequence. Under room temperature conditions, an intermittent sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, the pulse duration is 10ms, the pulse interval is 50ms, and the total duration is 60s.

[0135] Example 11

[0136] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0137] The composite powder is placed in a mold, and the pulse mode is selected as intermittent pulse sequence. Under room temperature conditions, an intermittent sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, the pulse duration is 30ms, the pulse interval is 150ms, and the total duration is 60s.

[0138] Example 12

[0139] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0140] The composite powder is placed in a mold, and the pulse mode is selected as an intermittent pulse sequence. Under room temperature conditions, an intermittent sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, the pulse duration is 60ms, the pulse interval is 300ms, and the total duration is 60s.

[0141] Example 13

[0142] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0143] The composite powder is placed in a mold, and the pulse mode is selected as intermittent pulse sequence. Under room temperature conditions, an intermittent sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, the pulse duration is 90ms, the pulse interval is 450ms, and the total duration is 60s.

[0144] Example 14

[0145] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0146] The composite powder is placed in a mold, and the pulse mode is selected as an intermittent pulse sequence. Under room temperature conditions, an intermittent sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, the pulse duration is 120ms, the pulse interval is 600ms, and the total duration is 60s.

[0147] Example 15

[0148] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0149] The composite powder is placed in a mold, and the pulse mode is selected as intermittent pulse sequence. Under room temperature conditions, an intermittent sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, the pulse duration is 60ms, the pulse interval is 300ms, and the total duration is 10s.

[0150] Example 16

[0151] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0152] The composite powder is placed in a mold, and the pulse mode is selected as an intermittent pulse sequence. Under room temperature conditions, an intermittent sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, the pulse duration is 60ms, the pulse interval is 300ms, and the total duration is 30s.

[0153] Example 17

[0154] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0155] The composite powder is placed in a mold, and the pulse mode is selected as intermittent pulse sequence. Under room temperature conditions, an intermittent sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, the pulse duration is 60ms, the pulse interval is 300ms, and the total duration is 90s.

[0156] Example 18

[0157] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0158] The composite powder is placed in a mold, and the pulse mode is selected as intermittent pulse sequence. Under room temperature conditions, an intermittent sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, the pulse duration is 60ms, the pulse interval is 300ms, and the total duration is 120s.

[0159] Example 19

[0160] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0161] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak value of the electric field intensity is 1KV / cm, the frequency is 200Hz, and it lasts for 1s.

[0162] Example 20

[0163] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0164] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak value of the electric field intensity is 5KV / cm, the frequency is 200Hz, and it lasts for 1s.

[0165] Example 21

[0166] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0167] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak value of the electric field intensity is 15KV / cm, the frequency is 200Hz, and it lasts for 1s.

[0168] Example 22

[0169] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0170] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 20KV / cm, the frequency is 200Hz, and it lasts for 1s.

[0171] Example 23

[0172] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0173] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak value of the electric field intensity is 10KV / cm, the frequency is 50Hz, and it lasts for 1s.

[0174] Example 24

[0175] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0176] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak value of the electric field intensity is 10KV / cm, the frequency is 100Hz, and it lasts for 1s.

[0177] Example 25

[0178] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0179] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 300Hz, and it lasts for 1s.

[0180] Example 26

[0181] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0182] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 400Hz, and it lasts for 1s.

[0183] Example 27

[0184] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0185] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous square wave pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak value of the electric field intensity is 10KV / cm, the frequency is 200Hz, and it lasts for 1s.

[0186] Example 28

[0187] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0188] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous exponentially decaying wave pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 200Hz, and it lasts for 1s.

[0189] Example 29

[0190] Compared to Example 1, most aspects are the same, except for step (3) in which the mold cavity vibration is applied:

[0191] While applying a pulsed electric field along the normal direction of the mold's horizontal plane, a reciprocating vibration of the mold cavity along the horizontal direction of the mold's horizontal plane is also applied, with an amplitude of 0.01 mm, a frequency of 30 Hz, and a duration of 1 s.

[0192] Example 30

[0193] Compared to Example 1, most aspects are the same, except for step (3) in which the mold cavity vibration is applied:

[0194] While applying a pulsed electric field along the normal direction of the mold's horizontal plane, a reciprocating vibration of the mold cavity along the horizontal direction of the mold's horizontal plane is also applied, with an amplitude of 0.1 mm, a frequency of 30 Hz, and a duration of 1 s.

[0195] Example 31

[0196] Compared to Example 1, most aspects are the same, except for step (3) in which the mold cavity vibration is applied:

[0197] While applying a pulsed electric field along the normal direction of the mold's horizontal plane, a reciprocating vibration of the mold cavity along the horizontal direction of the mold's horizontal plane is also applied, with an amplitude of 0.3 mm, a frequency of 30 Hz, and a duration of 1 s.

[0198] Example 32

[0199] Compared to Example 1, most aspects are the same, except for step (3) in which the mold cavity vibration is applied:

[0200] While applying a pulsed electric field along the normal direction of the mold's horizontal plane, a reciprocating vibration of the mold cavity along the horizontal direction of the mold's horizontal plane is also applied, with an amplitude of 0.4 mm, a frequency of 30 Hz, and a duration of 1 s.

[0201] Example 33

[0202] Compared to Example 1, most aspects are the same, except for step (3) in which the mold cavity vibration is applied:

[0203] While applying a pulsed electric field along the normal direction of the mold's horizontal plane, a reciprocating vibration of the mold cavity along the horizontal direction of the mold's horizontal plane is also applied, with an amplitude of 0.2 mm, a frequency of 10 Hz, and a duration of 1 s.

[0204] Example 34

[0205] Compared to Example 1, most aspects are the same, except for step (3) in which the mold cavity vibration is applied:

[0206] While applying a pulsed electric field along the normal direction of the mold's horizontal plane, a reciprocating vibration of the mold cavity along the horizontal direction of the mold's horizontal plane is also applied, with an amplitude of 0.2 mm, a frequency of 20 Hz, and a duration of 1 s.

[0207] Example 35

[0208] Compared to Example 1, most aspects are the same, except for step (3) in which the mold cavity vibration is applied:

[0209] While applying a pulsed electric field along the normal direction of the mold's horizontal plane, a reciprocating vibration of the mold cavity along the horizontal direction of the mold's horizontal plane is also applied, with an amplitude of 0.2 mm, a frequency of 40 Hz, and a duration of 1 s.

[0210] Example 36

[0211] Compared to Example 1, most aspects are the same, except for step (3) in which the mold cavity vibration is applied:

[0212] While applying a pulsed electric field along the normal direction of the mold's horizontal plane, a reciprocating vibration of the mold cavity along the horizontal direction of the mold's horizontal plane is also applied, with an amplitude of 0.2 mm, a frequency of 50 Hz, and a duration of 1 s.

[0213] Example 37

[0214] Compared with Example 1, most of them are the same, except for step (1) in the preparation of the composite powder:

[0215] Based on a total mass of 100 parts for the amino-modified graphite, flake graphite, and resin, 10 parts of the modified graphite, 70 parts of the flake graphite, and 20 parts of the resin are weighed, mixed uniformly, and dried at 60°C for 2 hours to obtain a composite powder.

[0216] Comparative Example 1

[0217] A method for preparing a composite graphite bipolar plate includes the following steps:

[0218] (1) Preparation of composite powder

[0219] Based on a total mass of 100 parts for the modified graphite, flake graphite, and resin, 10 parts of the modified graphite, 70 parts of the flake graphite, and 20 parts of the resin were weighed, uniformly mixed, and dried at 60°C for 2 hours to obtain a composite powder. The flake graphite had a particle size of 320 mesh; the resin was epoxy resin and phenolic resin in a mass ratio of 4:6.

[0220] (2) The mold is placed in a hot press for hot molding under the conditions of 50 MPa and 170°C. After molding and demolding, a 0.82 mm thick composite graphite bipolar plate is obtained. Figure 1 As shown.

[0221] Comparative Example 2

[0222] Compared with Example 1, most of them are the same, except that in the preparation of the composite powder in step (1), no modified graphite is added. Based on the sum of the mass of the flake graphite and the resin being 100 parts, 80 parts of the flake graphite and 20 parts of the resin are weighed, and after being mixed evenly, they are dried at 60°C for 2 hours to obtain the composite powder.

[0223] Comparative Example 3

[0224] The majority of the differences are the same as in Example 1, except that in step (3) when a pulsed electric field is applied:

[0225] The composite powder is placed in a mold, and the pulse mode is selected as continuous mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak value of the electric field intensity is 0KV / cm (i.e., no electric field is applied), the frequency is 200Hz, and it lasts for 1s.

[0226] Comparative Example 4

[0227] The majority of the differences are the same as in Example 1, except that in step (3) when a pulsed electric field is applied:

[0228] The composite powder is placed in a mold, and the pulse mode is selected as continuous mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the normal direction of the horizontal plane of the mold. The peak electric field strength is 10KV / cm, the frequency is 0Hz (i.e., constant electric field), and it lasts for 1s.

[0229] Comparative Example 5

[0230] It is almost identical to Example 1, except that step (3) is omitted.

[0231] Comparative Example 6

[0232] The majority of the results are the same as in Example 1, except for step (2) in which a pulsed electric field is applied:

[0233] The composite powder is placed in a mold, and the pulse mode is selected as continuous pulse mode. Under room temperature conditions, a continuous sinusoidal pulse electric field is applied along the horizontal direction of the mold plane. The peak electric field strength is 10KV / cm, the frequency is 200Hz, and it lasts for 1s.

[0234] Performance testing:

[0235] The performance test results of the embodiments and comparative examples of this invention are shown in Table 1. The density was measured using an electronic density balance (model Mettler Toledo-XS205DU); the conductivity was tested using the four-probe method (model 4Probes Tech RTS-9 dual-electrical four-probe tester); the contact resistance was tested using a gold-plated electrode pressing method at a pressure of 1.5 MPa (model MTS Systems 810 series servo hydraulic testing machine); and the bending strength was tested using the three-point bending method (model New Sansi GMT4204 universal testing machine).

[0236] Table 1. Performance test results of the examples and comparative examples.

[0237]

[0238]

[0239] By comparing Example 1 with Comparative Examples 1 and 3, it was found that the electrical conductivity of Example 1 was greatly improved, but the bending strength decreased. The conclusion is that under the action of a pulsed electric field, graphite particles will be polarized. The polarized particles are subjected to dielectric force in the pulsed electric field, which promotes the high orientation of the particles, thereby greatly improving the electrical conductivity of the composite graphite plate. In addition, the layers of graphite are stacked together only by weak van der Waals forces and π-π bonds. When subjected to bending stress, cracks are easy to propagate along the interlayer, resulting in a partial decrease in the bending resistance.

[0240] By comparing Example 1 with Comparative Examples 1 and 6, it was found that the conductivity of Example 1 was effectively improved compared to Comparative Example 1, but the performance of Comparative Example 6 decreased. Therefore, it can be concluded that under the action of a pulsed electric field, the conductivity anisotropy of graphite particles makes them more inclined to align the high conductivity direction along the electric field direction in order to minimize the system resistance. Therefore, the pulsed electric field needs to be along the normal direction of the mold.

[0241] As can be seen from Example 1 and Comparative Example 4, the conductivity of the electrode plate decreased in Comparative Example 4. This indicates that the electric field frequency can dynamically adjust the orientation of graphite particles, thereby improving particle flowability and enhancing the orientation effect of graphite.

[0242] As can be seen from Example 1 and Comparative Example 5, the electrode plate in Example 1 has better conductivity, which can improve the fluidity of graphite particles in the solid phase by the planar cavity vibration, making it easier for graphite particles to change orientation under the action of pulsed electric field.

[0243] As can be seen from Examples 1-5 and Comparative Example 2, the conductivity of Example 4 is the best. That is, a moderate ratio of graphite oxide (15 parts of modified graphite) can better improve the performance of the bipolar plate. Too little will make the graphite orientation change not obvious, while too much will make the dielectric force of graphite too strong and affect the flowability of particles.

[0244] As can be seen from Examples 1, 6-18, Examples 8 and 12 exhibit the most outstanding conductivity. It can be concluded that a longer pulse duration can better change the orientation characteristics of graphite oxide. However, if the duration is too long, it will cause premature curing due to thermal effects, resulting in thermal damage, which is not conducive to improving the performance of the electrode plate. Therefore, in the production of electrode plates with high conductivity requirements, intermittent pulse mode can be used and an intermittent pulse interval can be added to allow for timely cooling and avoid thermal damage.

[0245] As can be seen from Examples 1 and 19-22, the conductivity improvement of Example 21 is the most significant. That is, within a certain range, increasing the electric field strength (15KV / cm is optimal) can better change the orientation characteristics of graphite oxide. Too low an electric field strength has little effect on the orientation of graphite, while too high an electric field strength will lead to an aggravation of the thermal effect and cause thermal damage.

[0246] As can be seen from Examples 1 and 23-26, Example 25 has the best conductivity. That is, within a certain range, increasing the electric field frequency (300Hz is optimal) can improve the graphite orientation effect. A higher electric field frequency can generate a Coulomb force between polarized particles, which can improve the material dispersion. If it is too high, the graphite sheet will not be able to follow the electric field alternation effectively due to inertia.

[0247] Examples 1, 27, and 28 show that Example 27 exhibits the highest electrical conductivity, while Example 1 demonstrates the best flexural strength. This indicates that different types of pulsed electric fields have varying degrees of impact on graphite orientation. Square wave pulses are suitable for highly conductive graphite systems, showing a significant improvement in conductivity. Sine wave AC pulses are suitable for dynamically adjusting particle orientation angles and can reduce the risk of localized overheating, while having a smaller impact on flexural strength. The initial peak electric field of exponentially decaying pulses can strongly polarize graphite, but it is prone to thermal damage, resulting in a less significant improvement in conductivity.

[0248] As can be seen from Examples 1 and 29-36, the electrode plates in Examples 1 and 35 have good conductivity. That is, the appropriate vibration amplitude and frequency (amplitude 0.2 mm, frequency 40 Hz is optimal) can improve the orientation alignment effect. Excessive amplitude and frequency will break up the graphite alignment, while too low amplitude and frequency will not effectively improve the graphite fluidity, resulting in unclear orientation.

[0249] As can be seen from Examples 1, 37 and Comparative Example 2, modified graphite can effectively improve the orientation effect by increasing its own polarity and increasing the dielectric force it receives in the pulsed electric field. Moreover, different types of modified graphite have different gains in orientation. In this example, the effects of oxidized modified graphite and amino modified graphite are similar.

[0250] This invention effectively alters the orientation characteristics of graphite by applying a pulsed electric field, significantly improving the conductivity of the electrode. Simultaneously, it enhances the alignment efficiency, reduces energy consumption, and shortens the production cycle and cost by modifying the graphite and applying horizontal cavity vibration.

[0251] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for producing a composite graphite bipolar plate under the action of a pulsed electric field, characterized in that, The method comprises the following steps: S1, uniformly mixing modified graphite, flake graphite and resin, and drying to obtain a composite powder; S2, placing the composite powder into a mold, applying a pulsed electric field along the normal direction of the horizontal plane of the mold, and simultaneously applying reciprocating vibration of the mold cavity along the horizontal direction of the horizontal plane of the mold; S3, hot-pressing the mold subjected to the pulsed electric field and the reciprocating vibration of the mold cavity to form a composite graphite bipolar plate.

2. The method of claim 1, wherein the method further comprises the step of: In step S1, the modified graphite is one or more of oxidized modified graphite, amino-modified graphite, carboxyl-modified graphite, sulfonic acid-modified graphite, fluorinated modified graphite, heteroatom-doped graphite, and polymer-modified graphite.

3. The method of claim 1, wherein the method further comprises the step of: In step S1, the resin is one or more of epoxy resin, phenolic resin, acrylic resin, vinyl ester resin, furan resin, or urea-formaldehyde resin. ​ 4. The method of claim 1, wherein the method further comprises the step of: In step S1, the modified graphite is 1-20 parts, the flake graphite is 60-80 parts, and the resin is 10-30 parts, based on the total mass of the modified graphite, the flake graphite and the resin being 100 parts.

5. The method of claim 1, wherein the method further comprises the step of: In step S2, the total duration of the pulsed electric field ranges from 5 to 300 s, the peak electric field strength of the pulsed electric field ranges from 1 to 50 KV / cm, and the frequency ranges from 1 to 10,000 Hz. ​ 6. The method of claim 1, wherein the method further comprises: In step S2, the pulsed electric field is applied in at least one of an intermittent pulse sequence or a continuous pulse mode.

7. The method of claim 6, wherein the method further comprises the step of: The intermittent pulse sequence is composed of periodically repeated pulse groups, each pulse group comprising a pulse duration and a pulse interval, the pulse duration being 1-500 ms, the pulse interval being 2-1000 ms, and the pulse interval being positively correlated with the pulse duration. The continuous pulse mode has a duration of 0.1-10 s.

8. The method of claim 1, wherein the method further comprises the step of: In step S2, the waveform of the pulsed electric field is any one or a combination of square wave, sine wave or exponential decay wave.

9. The method of claim 1, wherein the method further comprises the step of: In step S2, the reciprocating vibration frequency of the mold cavity ranges from 1 to 100 Hz, and the vibration amplitude ranges from 0.01 to 0.5 mm. ​ 10. A composite graphite bipolar plate under the action of a pulsed electric field, which is prepared by the method of any one of claims 1-9.

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