High-conductivity graphite bipolar plate and preparation method thereof

Abstract

The invention belongs to the technical field of battery energy storage, and discloses a high-conductivity graphite bipolar plate and a preparation method thereof, high-purity crystalline flake graphite is subjected to non-vulcanization intercalation, high-temperature expansion and purification to obtain expanded graphite; applying heterogeneous charges to the expanded graphite, the graphene and the resin powder, and uniformly mixing by using a convection type gas mixer; a low-density blank is formed through extrusion of a differential belt combined roller; carrying out cold double-roller calendering to obtain a medium-density blank; a high-density blank is obtained in a hot channel heating and hot double-roller calendering mode; a hot steel belt roller is used for completing primary shaping on a high-density blank, and after edge cutting and length slitting are conducted, a water-cooling pressurization platform is adopted for achieving final shaping of a product. The bipolar plate prepared by the invention has good mechanical properties and conductivity, can effectively improve the structural strength of a redox flow battery stack, reduces the ohmic polarization loss of the stack, and meets the requirements of high-current-density operation conditions. The product has the outstanding advantages of good quality uniformity, high production efficiency, low manufacturing energy consumption and the like, and the cost advantage is obvious.

Description

Technical Field

[0001] The present invention relates to the technical field of battery energy storage, and in particular to a high-conductivity graphite bipolar plate and a preparation method thereof. Background Art

[0002] As one of the core components of liquid flow batteries, bipolar plates support the overall frame structure of liquid flow batteries, block electrolytes, and provide a good propagation path for electrons. Therefore, bipolar plates need to have good mechanical properties, and should also have excellent gas barrier properties, electrical conductivity, and corrosion resistance.

[0003] Nowadays, flexible graphite bipolar plates made of expanded graphite as the core conductive material have a high share in market applications. In the process of forming flexible graphite bipolar plates, in addition to the compression and interlocking of the expanded graphite particles themselves, resin binders need to be introduced to achieve a stable combination of the expanded graphite particles, so as to obtain the good mechanical strength and corrosion resistance of the monopolar plate itself. At present, the preparation methods of flexible graphite bipolar plates mainly include infiltration method, wet mixing method, multilayer composite method and dry mixing method. The first two methods have the disadvantages of serious pollution and low efficiency. The conductivity of the products prepared by the multilayer composite method is biased. The dry mixing method can effectively avoid the above disadvantages.

[0004] Patent CN 111261893 A proposes a method for manufacturing highly conductive flexible graphite bipolar plates for flow batteries, which uses a high loading coefficient mixer to evenly mix expanded graphite powder and PVDF powder, and then vacuum hot presses or rolls them into high-density bipolar plate products. This method does not involve solvents and is easy to implement, but during the implementation of this method, the mixing uniformity of expanded graphite particles and PVDF is limited, and the expanded graphite itself is highly destructive, which affects the structural strength and conductivity of the bipolar plate.

[0005] Patent CN 117254053 A proposes a method for manufacturing highly conductive graphite bipolar plates, which uses high-pressure airflow to mix expanded graphite and fluoroplastic micropowder particles in a mixing pipe, and then obtains graphite bipolar plates through extrusion, calendering, and hot pressing processes. This high-pressure airflow mixing strategy is severely limited by the mixing container. For large-capacity and high-loading equipment, it is impossible to achieve highly uniform mixing in a short time, and it is difficult to ensure the uniformity of product quality in continuous operations. At the same time, the hot pressing process is inefficient, which restricts the efficiency of mass production.

[0006] In addition, with the substantial advancement of marketization and the increasing demand for the volume-to-power density of flow battery stacks at the application end, higher requirements are placed on the quality control uniformity and conductivity of flexible graphite bipolar plates. Therefore, the development of a high-conductivity, low-cost, high-uniformity flexible graphite bipolar plate molding solution has important commercial value. Summary of the invention

[0007] To solve the above problems, the present invention provides a highly conductive graphite bipolar plate and a preparation method thereof, which solve the problems of poor conductivity, unstable product uniformity and low production efficiency of existing graphite bipolar plates for liquid flow batteries.

[0008] The present invention adopts the following technical means to achieve the purpose of the invention:

[0009] A method for preparing a highly conductive graphite bipolar plate comprises the following steps:

[0010] S1. Expanded graphite processing: high-purity flake graphite is intercalated with an intercalating agent to obtain expandable graphite, which is then expanded and purified at high temperature to obtain expanded graphite;

[0011] S2. Mixing: using a convection gas mixer to evenly mix expanded graphite, graphene and resin powder;

[0012] S3. Low-density billet rolling: The mixed material is placed on the lower roller surface of the belt combination roller of the material placing machine through the material box, and then the flat material roller and the upper belt roller work together to form a low-density billet;

[0013] S4. Medium-density billet rolling: cold roll rolling is used to complete the preliminary rolling of the low-density billet to obtain a medium-density billet;

[0014] S5. High-density billet rolling: The medium-density billet is heated through a hot channel and then rolled using hot rollers to obtain a high-density billet;

[0015] S6. Product shaping: The high-density billet obtained after hot double-roll rolling is initially shaped using hot steel belt rollers. After trimming and length slitting, the final shaping of the product is achieved using a water-cooled pressurized platform.

[0016] Preferably, the intercalation agent in step S1 includes an activator and an organic acid.

[0017] Furthermore, the activator comprises an acid solution and an oxidant, wherein the acid solution is one of nitric acid, phosphoric acid, and perchloric acid, and the oxidant is one of hydrogen peroxide and potassium permanganate; and the organic acid is one of formic acid, acetic acid, acetic anhydride, propionic acid, oxalic acid, citric acid, and itaconic acid or a mixture thereof.

[0018] Furthermore, during the processing of the expanded graphite, the mass ratio of flake graphite, activator and organic acid is 1:0.6-1.2:1.0-1.5, wherein the mass ratio of acid solution and oxidant in the activator is 1:0.4-1.0.

[0019] Preferably, the flake graphite in step S1 has a purity of 98-99.9%; the expansion temperature is 300-650° C., and the expansion ratio is 100-350 times.

[0020] Preferably, the purification equipment in step S1 is an airflow centrifugal separator for removing solid impurities in the expanded graphite.

[0021] Preferably, in step S2, the convection gas mixer is equipped with an electrostatic generator, which can apply different charges to the expanded graphite and the mixture of graphene and resin respectively; and the air flow pressure in the convection gas mixer is 0.1-1.2 MPa.

[0022] Preferably, in step S2, the expanded graphite is a mixture with an expansion multiple between 100 and 350 times and a size between 30 and 120 meshes, accounting for 75 to 90% by weight; the graphene particle size is 5 to 50 μm, accounting for 1 to 5% by weight; the resin is one of polyvinylidene fluoride, maleic anhydride modified polypropylene, ethylene-chlorotrifluoroethylene copolymer, polyphenylene sulfide, thermoplastic phenolic resin and polychlorotrifluoroethylene, with a particle size of 5 to 30 μm and a weight share of 8 to 20%.

[0023] Furthermore, in step S2, the melt index of the raw materials of polyvinylidene fluoride, maleic anhydride modified polypropylene, ethylene-chlorotrifluoroethylene copolymer, polyphenylene sulfide, thermoplastic phenolic resin and polychlorotrifluoroethylene should be higher than 10 g / 10 min.

[0024] Preferably, the height of the mixed material after passing through the flat roller in step S3 is controlled within the range of 50-100 mm, the upper and lower belt rollers of the material distributor have a roller speed of 1-3 m / min, and the low-density blank formed after extrusion by the upper and lower belt rollers has a height of 10-50 mm and a density of 0.08-0.15 g / cm 3 .

[0025] Furthermore, in step S3, the roller speed of the upper belt roller of the material placing machine is slightly higher than the roller speed of the lower belt roller, and the difference between the two is 0.1-0.3 m / min.

[0026] Furthermore, in step S3, the extrusion pressure of the upper and lower belt rollers of the material placing machine is 1 to 5 MPa.

[0027] Preferably, in step S4, the diameter of the cold roller is 400-600 mm, the roller speed is 1-3 m / min, the rolling pressure is 1-10 MPa, the height of the medium-density blank is 2-8 mm, and the density is 0.2-1.0 g / cm 3 .

[0028] Preferably, in step S5, the temperature of the hot channel is 100-260°C, the temperature of the hot roller is 120-300°C, the diameter of the hot roller is 500-700 mm, the roller speed is 1-3 m / min, the rolling pressure is 1-10 MPa, the thickness of the high density blank is 0.6-1.0 mm, and the density is 1.6-1.8 g / cm 3 .

[0029] Preferably, in step S6, the temperature of the hot steel strip roller is 150-350°C, the roller speed is 1-3 m / min, the rolling pressure is 8-15 MPa; the temperature of the water-cooled pressurizing platform is lower than 30°C, the pressurizing pressure is 10-25 MPa, and the pressurizing cooling time is 10-30 s. After shaping, the thickness is 0.6-1.0 mm and the density is 1.6-1.8 g / cm 3 Finished graphite bipolar plates.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. A highly conductive graphite bipolar plate and its preparation method. The use of non-sulfur intercalation agents to prepare expanded graphite can effectively reduce environmental pollution, the expanded graphite has better expansion uniformity, the solid impurity content is greatly reduced, and the quality control level is improved. At the same time, this expansion strategy has a low degree of damage to the crystal structure of the graphite itself, and the prepared bipolar plate has better conductivity and mechanical properties.

[0032] 2. The use of convection gas mixer can overcome the density and particle size differences between materials, without liquid pollution, and no physical structural damage to the raw materials. It can be started and stopped immediately, and the consistency of mixing uniformity is not limited by the mixing container, which is more conducive to large-scale continuous operation. The strategy of applying different charges to the expanded graphite and small-particle graphene and resin mixture in advance can prevent the raw materials from self-aggregating, induce graphene and resin to enter the expanded graphite interlayer structure, and further improve the uniformity of material mixing.

[0033] 3. Conventionally, the upper and lower belt rollers are at the same speed. The differential belt roller extrusion molding process in the present invention can improve the regularity of the spatial arrangement orientation of the expanded graphite particles, realize the long-range orderly arrangement of the graphite particles, and cooperate with the rear-stage hot channel and hot roller pressing exhaust treatment to effectively reduce the rebound phenomenon of the bipolar plate blank during the molding process, and improve the internal graphite continuity and surface flatness of the product. At the same time, the hot roller pressing process can improve the bonding effect between the expanded graphite itself and the resin and graphite components, and the product has better conductivity and mechanical strength.

[0034] 4. The use of hot steel belt rollers and pressurized rapid cooling shaping strategies can eliminate the changes in internal stress of the bipolar plate caused by changes in resin molecular orientation and partial crystallization during the cooling process, which in turn leads to reduced plate flatness and uneven thickness defects. The process time is short, energy consumption is low, and continuous operation can be performed, greatly improving production efficiency and product quality consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the process flow for preparing highly conductive graphite bipolar plates.

[0036] Among them: 1. expansion furnace; 2. air flow centrifugal separator; 3. convection gas mixer; 31. positive charge storage box; 32. negative charge storage box; 33. mixing tank; 4. material distribution machine; 41. unloading box; 42. lower belt roller; 43. flat material roller; 44. upper belt roller; 5. cold counter roller; 6. hot channel; 7. hot counter roller; 8. hot steel belt roller; 9. water-cooled pressurized platform. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be further clearly and completely described in combination with the embodiments of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0038] Intercalation treatment refers to spraying or soaking the intercalation agent (acid and oxidant) into the interior of the flake graphite structure, which is one of the processes in the preparation of expanded graphite.

[0039] Examples 1-10

[0040] The present invention provides a highly conductive graphite bipolar plate and a preparation method thereof, and the specific process steps are as follows:

[0041] S1. Expanded graphite processing: flake graphite with a purity of 98-99.9% is selected and mixed with an intercalation agent to prepare expandable graphite, which is then expanded in an expansion furnace 1 at high temperature and purified in an airflow centrifugal separator 2 to obtain expanded graphite raw material.

[0042] The intercalant comprises an activator and an organic acid, wherein the activator is a mixture of an acid solution and an oxidant, wherein the acid solution is one of nitric acid, phosphoric acid, and perchloric acid, and the oxidant is one of hydrogen peroxide and potassium permanganate; and the organic acid is one of formic acid, acetic acid, acetic anhydride, propionic acid, oxalic acid, citric acid, and itaconic acid, and a mixture thereof. In this embodiment, the acid solution is nitric acid, the oxidant is hydrogen peroxide, and the organic acid is oxalic acid.

[0043] During the processing of the expanded graphite, the mass ratio of flake graphite, activator and organic acid is 1:0.6-1.2:1.0-1.5, wherein the mass ratio of acid solution and oxidant in the activator is 1:0.4-1.0. In this embodiment, the mass ratio of various chemical components required for preparing expanded graphite is flake graphite: activator: oxalic acid = 1:0.8:1.2, wherein the mass ratio of nitric acid and hydrogen peroxide in the activator is 1:0.8.

[0044] The expansion temperature and expansion ratio depend on the type and amount of the intercalant, the expansion temperature is 300-650°C, and the expansion ratio is 100-350 times. In this embodiment, the expansion temperature is 550°C, and the expansion ratio is 180 times.

[0045] S2. Mixing: Select an expanded graphite mixture with an expansion ratio between 100 and 350 times and a mesh number between 30 and 120 as the main carbon material. In this embodiment, the three mesh numbers of 50, 80 and 100 are preferred, the expansion ratio is 180 times, and the overall weight accounts for 75-90%. A positive charge is applied to it by an electrostatic generator in the positive charge storage box 31 on one side of the convection gas mixer 3. Graphene with a particle size between 10 and 30 μm is preferred as the second conductive carbon material, accounting for 1-5% by weight. Resin powder with good fluidity and strong corrosion resistance is selected as a bipolar plate structure strengthener, including one of polyvinylidene fluoride, maleic anhydride modified polypropylene, ethylene-trifluorochloroethylene copolymer, polyphenylene sulfide, thermoplastic phenolic resin and polychlorotrifluoroethylene, the particle size is preferably 8-20 μm, and the weight accounts for 8-20%. At the same time, in order to ensure that the resin has a stronger bonding effect and processing feasibility on the graphite material, the resin melt index should be higher than 10g / 10min. After mixing graphene with resin powder, put it into the negative charge storage box 32 on the other side of the convection gas mixer 3, and use an electrostatic generator to apply a negative charge opposite to expanded graphite. High-pressure gas is used to counter-discharge the expanded graphite mixture and graphene and resin mixture raw materials with heterogeneous charges, and fully mixed in the mixing tank 33. In the present embodiment, the side airflow pressure of the expanded graphite mixture is 0.4MPa, and the side airflow pressure of the graphene and resin mixture is 0.7MPa. The charge pretreatment strategy adopted for the raw material can effectively prevent the raw material from self-aggregation, induce small-particle raw materials to better enter the inside of the expanded graphite intercalation gap, and the convection gas mixing method has no physical damage to the expanded graphite raw material, ensuring structural integrity in the subsequent molding process. This raw material mixing strategy also has the advantages of starting and stopping, the mixing effect is not limited by the container volume, the mixing uniformity is high, and there is no liquid post-processing, which is more conducive to batch continuous production operations.

[0046] S3. Low-density billet rolling: The mixed material is placed on the surface of the belt roller 42 under the belt combination roller of the material placing machine 4 through the material box 41. The material is conveyed by the belt at a speed of 1.2m / min. The material is first flattened by the flat material roller 43, and the stacking height is 50-100mm. After being squeezed by the upper and lower belt rollers, the extrusion pressure is 4MPa, and the height is 10-50mm, and the density is 0.08-0.15g / cm 3 In order to improve the regularity of the spatial arrangement orientation of the expanded graphite particles and realize the long-range orderly arrangement of the graphite particles, the rear-stage hot channel 6 and the hot roller 7 are used for roller pressing and exhaust treatment to reduce the rebound phenomenon of the bipolar plate blank during the forming process, and to improve the internal graphite continuity and surface flatness of the product, the upper and lower belt rollers in the material distributor 4 adopt differential speed control means, and the speed of the upper belt roller 44 is slightly higher than that of the lower belt roller 42, and the difference between the two is 0.12m / min.

[0047] S4. Rolling of medium-density billet: The expanded graphite in the low-density billet formed after belt roller extrusion has the initial directional arrangement characteristics and has a certain degree of cross-linking. At this time, the billet density can be further increased by cold roller calendering to promote the spatial shaping of expanded graphite, graphene and resin particles to prevent local agglomeration defects in the subsequent heating process. In the cold roller calendering process, the calendering roller will provide a horizontal shear force and a vertical downward pressure to the billet. Too small a roller diameter, too high a roller speed and too large a rolling force will cause the expanded graphite to bear too high a shear force, which will then cause the continuous structure of the expanded graphite to be destroyed, and even produce cracking defects. In this embodiment, the roller diameter of the cold roller 5 is 400-600 mm, the roller speed is 1-3 m / min, and the rolling pressure is 1-10 MPa. Preferably, the roller diameter is 450 mm, the roller speed is 2 m / min, and the rolling pressure is 7 MPa. The height of the obtained medium-density blank is 2-8 mm, and the density is 0.2-1.0 g / cm 3 .

[0048] S5. High-density billet rolling: The medium-density billet obtained by the cold roller 5 rolling process is first heated by the hot channel 6 to increase the volatilization rate of the gas inside the billet and soften the internal resin particles to facilitate the subsequent hot roller 7 rolling molding. In order to prevent the resin particles from agglomerating due to heat, the heating temperature of the hot channel 6 should be slightly lower than the glass transition temperature of the resin. Combined with the resin category used in the present invention, the temperature of the hot channel 6 is set to 100-260°C in this embodiment. The processability of the billet after heating is greatly improved. At this time, the hot roller calendering method can obtain a billet with better surface morphology, higher density and more uniform texture. In the hot roller calendering process, there are multiple core process nodes such as plastic deformation of expanded graphite, resin melting, and extrusion of air. In this embodiment, combined with the resin melting parameters and the molding process requirements, the roller temperature of the hot roller 7 is set to 120-300°C, the roller diameter is 500-700mm, the roller speed is 1-3m / min, and the rolling pressure is 5-18MPa. Preferably, the roller diameter is 600mm, the roller speed is 2m / min, and the rolling pressure is 10MPa. The obtained high-density billet has a height of 0.6-1.0mm and a density of 1.6-1.8g / cm 3 .

[0049] S6. Product shaping: The high-density billet obtained by rolling with hot rollers 7 will cause changes in the internal stress of the bipolar plate during the cooling process due to changes in the orientation of the resin molecules and partial crystallization, which will then lead to reduced flatness of the plate and uneven thickness defects. In this embodiment, the product is firstly initially shaped by rolling with hot steel belt rollers 8. The roller temperature of the hot steel belt rollers 8 is 150-350°C, the roller speed is 1-3m / min, the rolling pressure is 8-20MPa, preferably, the roller speed is 2m / min, and the rolling pressure is 12MPa; after trimming and length slitting on the assembly line, the target size product is obtained. At this time, the product is pressurized and quickly cooled, which will induce the resin to be fixed in a very short time, effectively preventing the product from secondary defects caused by the resin during the cooling and hardening process. Among them, the temperature of the water-cooled pressurizing platform 9 should be kept below 30°C, the pressurizing pressure is 10-25MPa, and the pressurizing cooling time is controlled to be 10-30s, preferably, the pressurizing pressure is 18MPa, and the time is 15s. After secondary shaping, the thickness can be 0.6-1.0mm and the density can be 1.6-1.8g / cm 3 Finished graphite bipolar plates.

[0050] Comparative Example A

[0051] Expanded graphite (i.e., sulfur-containing expanded graphite) prepared by using commercially available H2SO4 as an intercalation agent is used as one of the main materials of the graphite bipolar plate, and the graphite bipolar plate sample is prepared by applying the process route of the present invention.

[0052] Comparative Example B

[0053] This is a graphite bipolar plate product produced by a domestic manufacturer. The raw materials are flake graphite and polyvinylidene fluoride, and the molding process is hot compression molding.

[0054] The molding process parameters of the high conductive graphite bipolar plates prepared in Examples 1-10 and Comparative Example A are shown in Table 1.

[0055] Table 1 Forming process parameters of high conductive graphite bipolar plates prepared in Examples 1-10 and Comparative Example A

[0056]

[0057]

[0058] The performance test results of the high conductive graphite bipolar plates prepared in Examples 1-10 and Comparative Examples AB and the comparative example samples are shown in Table 2.

[0059] Table 2 Comparison of performance parameters of Examples 1-10 and Comparative Examples AB

[0060]

[0061] From the comparative data in Table 2, it can be found that the graphite bipolar plates prepared in Examples 1 to 10 exhibit excellent electrical conductivity and mechanical properties, and their electrical conductivity can reach 300S / cm and above. At the same time, they can also take into account good bending strength, tensile strength and compressive strength. In terms of performance, compared with sample A obtained by sulfur-containing intercalation agent, the expanded graphite prepared by the non-sulfur-containing intercalation agent used in the present invention has better crystalline phase structural integrity, giving the prepared graphite bipolar plate better electrical conductivity and mechanical properties. Compared with comparative example B, the graphite bipolar plate prepared by the present invention can not only improve the structural strength of the flow battery stack and extend its service life, but also reduce the ohmic polarization loss inside the stack and meet the requirements of high-density operating conditions. In terms of process, the graphite bipolar plate preparation strategy proposed in the present invention has outstanding advantages such as good product quality uniformity, high production efficiency and low energy consumption. While ensuring that the product has a high yield rate in the continuous production process, the manufacturing cost can be greatly reduced.

[0062] The above embodiments are only some of the embodiments of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and all other embodiments obtained without creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing a highly conductive graphite bipolar plate, characterized in that: The following steps are included: S1. Expanded graphite processing: high-purity flake graphite is intercalated with an intercalating agent to obtain expandable graphite, which is then expanded and purified at high temperature to obtain expanded graphite; S2. Mixing: using a convection gas mixer to evenly mix expanded graphite, graphene and resin powder; S3. Low-density billet rolling: The mixed material is placed on the lower roller surface of the belt combination roller of the material placing machine through the material box, and then the flat material roller and the upper belt roller work together to form a low-density billet; S4. Medium-density billet rolling: cold roll rolling is used to complete the preliminary rolling of the low-density billet to obtain a medium-density billet; S5. High-density billet rolling: The medium-density billet is heated through a hot channel and then rolled using hot rollers to obtain a high-density billet; S6. Product shaping: The high-density billet obtained after hot double-roll rolling is initially shaped using hot steel belt rollers. After trimming and length slitting, the final shaping of the product is achieved using a water-cooled pressurized platform.

2. The method for preparing a highly conductive graphite bipolar plate according to claim 1, characterized in that: In step S1, the intercalation agent includes an activator and an organic acid; the activator includes an acid solution and an oxidant, wherein the acid solution is one of nitric acid, phosphoric acid, and perchloric acid, and the oxidant is one of hydrogen peroxide and potassium permanganate; the organic acid is one of formic acid, acetic acid, acetic anhydride, propionic acid, oxalic acid, citric acid, and itaconic acid or a mixture thereof; the mass ratio of flake graphite, activator, and organic acid is 1:0.6-1.2:1.0-1.5, wherein the mass ratio of acid solution and oxidant in the activator is 1:0.4-1.

0.

3. The method for preparing a highly conductive graphite bipolar plate according to claim 1, wherein: The purity of the flake graphite in step S1 is 98-99.9%; the expansion temperature is 300-650° C., and the expansion ratio is 100-350 times; the purification equipment is an airflow centrifugal separator to remove solid impurities in the expanded graphite.

4. The method for preparing a highly conductive graphite bipolar plate according to claim 1, characterized in that: In step S2, the convection gas mixer is equipped with an electrostatic generator, which can apply different charges to the expanded graphite and the mixture of graphene and resin respectively; the air flow pressure in the convection gas mixer is 0.1-1.2 MPa.

5. The method for preparing a highly conductive graphite bipolar plate according to claim 1, characterized in that: In step S2, the expanded graphite is a mixture with an expansion multiple between 100 and 350 times and a size between 30 and 120 meshes, accounting for 75 to 90% by weight; the graphene particle size is 5 to 50 μm, accounting for 1 to 5% by weight; the resin is one of polyvinylidene fluoride, maleic anhydride modified polypropylene, ethylene-chlorotrifluoroethylene copolymer, polyphenylene sulfide, thermoplastic phenolic resin and polychlorotrifluoroethylene, with a particle size of 5 to 30 μm and a weight proportion of 8 to 20%; the melt index of polyvinylidene fluoride, maleic anhydride modified polypropylene, ethylene-chlorotrifluoroethylene copolymer, polyphenylene sulfide, thermoplastic phenolic resin and polychlorotrifluoroethylene raw materials should be higher than 10 g / 10 min.

6. The method for preparing a highly conductive graphite bipolar plate according to claim 1, wherein: In step S3, the height of the mixed material after passing through the flat material roller is controlled within the range of 50-100 mm, the upper and lower belt rollers of the material placing machine have a roller speed of 1-3 m / min, and the low-density blank formed after extrusion by the upper and lower belt rollers has a height of 10-50 mm and a density of 0.08-0.15 g / cm 3 ; The speed of the upper belt roller of the fabric machine is higher than that of the lower belt roller, and the difference between the two is 0.1~0.3m / min; the extrusion pressure of the upper and lower belt rollers of the fabric machine is 1~5MPa.

7. The method for preparing a highly conductive graphite bipolar plate according to claim 1, characterized in that: In step S4, the diameter of the cold roller is 400-600 mm, the roller speed is 1-3 m / min, the rolling pressure is 1-10 MPa, the height of the medium-density blank is 2-8 mm, and the density is 0.2-1.0 g / cm 3 .

8. The method for preparing a highly conductive graphite bipolar plate according to claim 1, wherein: In step S5, the temperature of the hot channel is 100-260°C, the temperature of the hot roller is 120-300°C, the diameter of the hot roller is 500-700mm, the roller speed is 1-3m / min, the rolling pressure is 1-10MPa, the thickness of the high density blank is 0.6-1.0mm, and the density is 1.6-1.8g / cm 3 .

9. The method for preparing a highly conductive graphite bipolar plate according to claim 1, wherein: In step S6, the roller temperature of the hot steel strip roller is 150-350°C, the roller speed is 1-3 m / min, and the rolling pressure is 8-15 MPa; the temperature of the water-cooled pressurizing platform is lower than 30°C, the pressurizing pressure is 10-25 MPa, and the pressurizing cooling time is 10-30 s; after shaping, the thickness is 0.6-1.0 mm and the density is 1.6-1.8 g / cm 3 Finished graphite bipolar plates.

10. A highly conductive graphite bipolar plate, characterized in that: It is prepared according to the preparation method according to any one of claims 1 to 9.

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