阅读说明：本技术 一种燃料电池用复合双极板的制备方法 (Preparation method of composite bipolar plate for fuel cell ) 是由 胡宗辉 刘晨 于 2021-10-28 设计创作，主要内容包括：本发明提供了一种燃料电池用双极板的制备方法,包括如下步骤：将鳞片石墨粉体和树脂颗粒混合后,采用冷等静压进行成型后保压,经线切割和模压成型,得到预设的形状,然后固化,即得到所述复合双极板。本发明的提供的方法提高了生产效率,制备出的板材成型后密度均匀,气密性好和导电性高。(The invention provides a preparation method of a bipolar plate for a fuel cell, which comprises the following steps: and mixing the scale graphite powder and the resin particles, molding by adopting isostatic cool pressing, maintaining pressure, performing warp cutting and compression molding to obtain a preset shape, and then curing to obtain the composite bipolar plate. The method provided by the invention improves the production efficiency, and the prepared plate has uniform density, good air tightness and high conductivity after being formed.)

1. A preparation method of a composite bipolar plate for a fuel cell is characterized by comprising the following steps:

mixing the flake graphite powder and the resin particles, molding by adopting isostatic cool pressing, maintaining pressure, performing warp cutting and compression molding to obtain a preset shape, and then curing to obtain the composite bipolar plate;

the forming pressure of the cold isostatic pressing, the pressure maintaining pressure of the cold isostatic pressing, the average particle size of the crystalline flake graphite powder and the average particle size of the resin particles satisfy the following relations:

wherein r is₁Represents the average particle diameter r of the flake graphite powder₂Represents the average particle diameter of the resin particles, P₁Representing the forming pressure, P, of said cold isostatic pressing₂Representing the holding pressure, P, of the cold isostatic pressing₁: P₂K is greater than 1.1 and less than 1.3 for 10: 8-9.

2. The method of manufacturing a composite bipolar plate for a fuel cell according to claim 1, wherein:

the forming pressure of the cold isostatic pressing is 50-150 MPa;

the pressure maintaining pressure of the cold isostatic pressing is 40-135 MPa;

the particle size of the crystalline flake graphite powder is 30-120 mu m;

the average particle diameter of the resin particles is 10-40 μm.

3. The method of manufacturing a composite bipolar plate for a fuel cell according to claim 1, wherein:

the purity of the crystalline flake graphite powder is more than 99.9%;

the wire saw comprises a multi-wire saw.

4. The method of manufacturing a composite bipolar plate for a fuel cell according to claim 1, wherein:

the ratio of graphite in the crystalline flake graphite powder is 50-80 wt%.

5. The method of manufacturing a composite bipolar plate for a fuel cell according to claim 1, wherein:

the resin comprises a thermosetting resin;

the thermosetting resin comprises phenolic resin, epoxy resin, vinyl resin or polyimide.

6. The method of manufacturing a composite bipolar plate for a fuel cell according to claim 1, wherein:

the weight ratio of the crystalline flake graphite powder to the resin is 4: 1-0.25.

7. The method of manufacturing a composite bipolar plate for a fuel cell according to claim 1, wherein:

the curing temperature is 80-200 ℃.

8. The method of manufacturing a composite bipolar plate for a fuel cell according to claim 6, wherein:

the curing process also comprises the step of keeping the temperature for 1h when the temperature is raised by 20 ℃.

9. The method of manufacturing a composite bipolar plate for a fuel cell according to claim 1, wherein:

the thickness of the composite bipolar plate is 0.5-0.6 mm.

10. The method of manufacturing a composite bipolar plate for a fuel cell according to claim 1, wherein:

the uniformity of the density of the composite bipolar plate is less than +/-1%.

Technical Field

The invention relates to the technical field of fuel cell composite bipolar plates, in particular to a preparation method of a fuel cell composite bipolar plate.

Background

The fuel cell is a power generation device capable of converting chemical energy into electric energy, and the theoretical energy utilization rate of the fuel cell is as high as 85% -90%, which is far higher than the energy utilization rate of 21% of a traditional fuel oil automobile; the fuel cell only consumes hydrogen and oxygen, and the product is water, so that the fuel cell has the advantages of high efficiency, greenness, no pollution and the like compared with the traditional power generation mode. The cost of the fuel cell is high, wherein the cost of the bipolar plate accounts for 30-40% of the cost of the fuel cell.

The fuel cell mainly comprises an electric pile and system components, wherein the electric pile is the core of the whole fuel cell and comprises a cell unit consisting of a membrane electrode and a bipolar plate, a current collecting plate, an end plate, a sealing ring and the like; the membrane electrode directly influences the power density, durability and service life of the fuel cell; the bipolar plate has the functions of separating reaction gas, removing heat and discharging chemical reaction products (water); the air tightness, the electric and thermal conductivity, the mechanical properties and the corrosion resistance of the bipolar plate can affect the performance of the whole electric pile, thereby affecting the service performance of the battery, wherein the air tightness and the electric conductivity of the bipolar plate have the greatest influence on the performance of the battery.

The bipolar plates commonly used in the market at present can be divided into metal bipolar plates, graphite bipolar plates and composite bipolar plates; the service life of the fuel cell is greatly influenced by the defect of poor corrosion resistance of the metal bipolar plate, the metal bipolar plate needs to be subjected to surface treatment, and the process is complex, so that the cost is increased; the graphite bipolar plate has larger brittleness, a machining method is mainly adopted in the current market, the machining difficulty is high, a complex flow field is difficult to form, the cost is high, and the large-batch production is not facilitated; the composite bipolar plate can overcome the defects of difficult processing, poor strength, high cost and poor corrosion resistance of a metal plate of a graphite material, and the composite bipolar plate is produced in batches by mainly adopting a compression molding method, so that two problems can be encountered in the production process, namely, the production period of tabletting is longer, the flatness of the pressed plate hardly meets the use requirement, and the uniformity of density is poorer. And the gas tightness and the electrical conductivity of the bipolar plate are affected due to the flatness and the density uniformity of the plate. Therefore, based on these two problems, it is urgently needed to find a more efficient preparation method to improve the production efficiency and optimize the uniformity of the bipolar plate.

Disclosure of Invention

The invention aims to provide a preparation method of a composite bipolar plate for a fuel cell, which is efficient and uniform in density.

The invention is realized by adopting the following technical scheme.

A preparation method of a composite bipolar plate for a fuel cell comprises the following steps:

mixing the flake graphite powder and the resin particles, molding by adopting isostatic cool pressing, maintaining pressure, performing warp cutting and compression molding to obtain a preset shape, and then curing to obtain the composite bipolar plate;

the forming pressure of the cold isostatic pressing, the pressure maintaining pressure of the cold isostatic pressing, the average particle size of the crystalline flake graphite powder and the average particle size of the resin particles satisfy the following relations:

wherein r is₁Represents the average particle diameter r of the flake graphite powder₂Represents the average particle diameter of the resin particles, P₁Representing the forming pressure, P, of said cold isostatic pressing₂Representing the holding pressure, P, of the cold isostatic pressing₁ : P₂K is greater than 1.1 and less than 1.3 for 10: 8-9.

Preferably, the forming pressure of the cold isostatic pressing is 50-150 MPa;

preferably, the pressure maintaining pressure of the cold isostatic pressing is 40-135 MPa;

preferably, the particle size of the crystalline flake graphite powder is 30-120 μm;

preferably, the average particle diameter of the resin particles is 10 to 40 μm.

Preferably, the purity of the crystalline flake graphite powder is more than 99.9%;

preferably, the wire sawing comprises multi-wire sawing.

Preferably, the proportion of graphite in the crystalline flake graphite powder is 50-80 wt%.

Preferably, the resin comprises a thermosetting resin;

preferably, the thermosetting resin includes a phenol resin, an epoxy resin, a vinyl resin or a polyimide.

Preferably, the weight ratio of the crystalline flake graphite powder to the resin is 4: 1-0.25.

Preferably, the curing temperature is 80-200 ℃.

Preferably, the curing process further comprises the step of keeping the temperature for 1 hour when the temperature is increased by 20 ℃.

Preferably, the thickness of the composite bipolar plate is 0.5-0.6 mm.

Preferably, the uniformity of the density of the composite bipolar plate is less than ± 1%.

Compared with the prior art, the invention has the following technical effects:

the method provided by the invention improves the production efficiency, and the prepared composite bipolar plate has uniform density, good air tightness and high conductivity after being molded and cured.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference are exemplary only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

The invention provides a preparation method of a high-efficiency composite bipolar plate with uniform density for a fuel cell. Specifically, after the crystalline flake graphite powder and the resin particles are mixed, preliminary press forming is performed at normal temperature by using a cold isostatic pressing device. The primary molding can be formed into different shapes according to different molds. In some embodiments of the present invention, a mixed powder obtained by mixing the crystalline flake graphite powder and the resin particles is formed into a plate-shaped preform by cold isostatic pressing. Since the forces applied to the scale graphite powder and the resin particles in all directions during the cold isostatic pressing are the same, the uniformity of the preform obtained by the cold isostatic pressing is very high. However, in order to obtain a preform having very high uniformity, it is necessary to classify the scale graphite powder and the resin particles so that the resin particles can be uniformly filled in tetrahedral voids formed between the scale graphite powder particles. Because the scale graphite powder has higher hardness and the resin particles have lower hardness, when cold isostatic pressing is carried out, a higher pressure is firstly applied to fill the resin particles into the tetrahedral gaps, and then a lower pressure is applied to deform the resin particles, so that the scale graphite powder particles are better attached. Meanwhile, after the resin particles deform, gaps among the scale graphite powder particles can be further reduced, so that the prefabricated body is more compact and higher in uniformity. Because the scale graphite powder is rigid particles and the resin particles are deformable flexible particles, when the scale distribution is carried out on the scale graphite powder and the resin particles, the uniformity of the density of the finally prepared composite double-electrode plate is required to be less than +/-1%, and when the scale distribution is carried out on the scale distribution by adopting the scale graphite powder and the resin particles with different average particle diameters, the ratio of the average particle diameters of the scale graphite powder and the resin particles is not consistent but is deviated. This is because when the resin particles are small, they can also fill the octahedral gaps, and when the resin particles are large, the resin particles can be pressed by the crystalline flake graphite powder into the tetrahedral gaps formed by them using a large pressure holding pressure. Therefore, the molding pressure of the cold isostatic press, the holding pressure of the cold isostatic press, the average particle size of the flake graphite powder, and the average particle size of the resin particles satisfy the following relationship:

wherein r is₁Represents the average particle diameter r of the flake graphite powder₂Represents the average particle diameter of the resin particles, P₁Representing the forming pressure, P, of said cold isostatic pressing₂Representing the holding pressure, P, of the cold isostatic pressing₁ : P₂K is greater than 1.1 and less than 1.3 for 10: 8-9.

Compared with the conventional forming technology, the cold isostatic pressing forming technology has the advantages that the density of a finished product is high, the density of each position is uniform, the performance of the pressed finished product is excellent, a lubricant does not need to be added into powder generally, the pollution to the powder is reduced, and the forming time is short. The cold isostatic pressing can also reduce the space between powder particles and increase the density, the higher the true density of the composite bipolar plate is, the more compact the composite bipolar plate is, the smaller the longitudinal voltage drop is, the better the conductivity is, the higher the breaking strength is, and the better the flatness of the composite bipolar plate and the uniformity of the performance at each position are. And then cutting the prefabricated body into a plurality of thin plates by adopting a wire cutting mode. Because of the high uniformity of the preform, the preform can be cut into a plurality of uniform thin plates by means of wire cutting. And then, the thin plate is formed again by adopting a die pressing method, so that the thin plate is formed into other preset shapes. In some embodiments of the present invention, the sheet is compression molded in a mold with a complex flow field to provide a slotted bipolar plate. And finally, heating and curing to obtain the composite bipolar plate.

Specifically, the forming pressure of the cold isostatic pressing is 50-150 MPa; the pressure is too high, the prefabricated body can not bear and cracks appear; the pressure intensity is too low, the mechanical strength of the formed prefabricated body is not enough, and the use is influenced. The pressure maintaining pressure of the cold isostatic pressing is 40-135 MPa; the pressure is too high, the resin particles can be excessively extruded, and the uniformity of the prefabricated body is influenced; at too low a pressure, the resin particles do not set, resulting in too many voids in the preform and reduced uniformity.

Specifically, the particle size of the crystalline flake graphite powder is 30-120 microns; the particle size is too large, the bonding between the crystalline flake graphite and the resin is not tight enough, gaps exist in a system, and the strength is low; the particle size is too small, and the crystalline flake graphite cannot play a role in three-dimensional network conduction in a system, so that the electrical property is influenced. The average particle diameter of the resin particles is 10-40 μm. If the particle size is too large, the resin particles cannot fill all tetrahedral voids, if the particle size is too small, the tetrahedral voids will fill a plurality of resin particles, and at the same time, the resin particles will also fill part of the octahedral voids, thereby deteriorating the uniformity of the preform.

Specifically, the wire cutting includes multi-wire cutting. By adopting multi-line cutting, the preparation efficiency of the method is higher.

Specifically, the proportion of graphite in the crystalline flake graphite is 50-80 wt%. The proportion of the scale graphite is too high, and the strength is not enough; the ratio is too small and the resistance is too high. Specifically, the resin is a thermosetting resin. The thermosetting resin is cured after being heated, so that the flake graphite powder mixed in the resin is cured into the composite bipolar plate. Preferably, the thermosetting resin is one selected from phenolic resin, epoxy resin, vinyl resin or polyimide.

Specifically, the weight ratio of the crystalline flake graphite powder to the resin is 4: 1-0.25. When the weight ratio of the crystalline flake graphite powder to the resin is within the range, the electrical property and the physical property of the composite bipolar plate prepared by the crystalline flake graphite powder are optimal. When the ratio is too large, the strength of the composite bipolar plate is insufficient. When the ratio is too small, the resistance of the composite bipolar plate is too large.

Specifically, the curing process also comprises the step of keeping the temperature for 1h when the temperature is raised by 20 ℃. The temperature rise speed is too fast, and the small molecular gas released in the curing reaction process of the resin in the plate is too fast discharged, so that bubbles are formed in the composite bipolar plate, and the uniformity of the composite bipolar plate is reduced.

The present invention will be further illustrated below by reference to examples and comparative examples.

The flake graphite used in the following examples and comparative examples had a purity of greater than 99.9%.

Comparative example 1

Flake graphite powder with the particle size of 30 microns accounting for 50wt% of graphite and phenolic resin with the particle size of 10 microns are mixed according to the weight ratio of 4:1, placing the obtained powder into a mold with a complex flow field, performing compression molding in a molding press under 50MPa pressure, and pressing for 1min to obtain a composite bipolar plate with a 1mm groove; and (3) putting the formed composite bipolar plate with the groove into an oven for curing, wherein the curing temperature is 80-200 ℃, the temperature is kept for 1h from 80 ℃ to 20 ℃ per liter, and the composite bipolar plate with the thickness of 0.5mm is obtained by adopting multi-wire cutting after natural cooling.

Example 1

Taking crystalline flake graphite with the particle size of 30 microns accounting for 50wt% and phenolic resin with the particle size of 10 microns as raw materials according to the weight ratio of 4:1, placing the obtained powder in isostatic pressing equipment, setting the pressure of 50MPa at normal temperature, and then pressing at 40MPa for 1min to obtain a 10mm flat-plate-shaped preform; cutting and punching the preliminarily pressed flat plate-shaped prefabricated body by using a multi-wire cutting machine to obtain 10 thin flat plate-shaped thin plates with the thickness of 1 mm; placing the processed flat sheet into a mold with a complex flow field for compression molding to obtain a grooved composite bipolar plate; and (3) putting the formed grooved composite bipolar plate into an oven for curing at the curing temperature of 80-200 ℃, preserving heat for 1h every 20 ℃ from 80 ℃, and naturally cooling to obtain the composite bipolar plate with the thickness of 0.5 mm.

Example 2

60wt% of crystalline flake graphite with the particle size of 60 microns and 20 micron epoxy resin with the particle size of 20 microns are mixed according to the weight ratio of 4: 0.75, mixing, placing the obtained powder in an isostatic pressing device, setting the pressure of 80MPa at normal temperature, and then pressing at 70MPa for 1min to obtain a 10mm flat-plate-shaped preform; cutting and punching the preliminarily pressed flat plate-shaped prefabricated body by using a multi-wire cutting machine to obtain 10 thin flat plates with the thickness of 1 mm; placing the processed flat plate in a mould with a complex flow field for compression molding to obtain a grooved composite bipolar plate; and (3) putting the formed bipolar plate with the groove into an oven for curing at the curing temperature of 80-200 ℃, preserving heat for 1h every 20 ℃, and naturally cooling to obtain the composite bipolar plate with the thickness of 0.6 mm.

Example 3

Taking 70wt% of crystalline flake graphite with the grain diameter of 80 microns and vinyl resin with the grain diameter of 23 microns as raw materials according to the weight ratio of 4: 0.5, placing the powder obtained after mixing in isostatic pressing equipment, setting the pressure of 100MPa at normal temperature, and then pressing in 80MPa for 1min to obtain a 10mm flat-plate-shaped preform; cutting and punching the preliminarily pressed flat plate-shaped prefabricated body by using a multi-wire cutting machine to obtain 10 thin flat plates with the thickness of 1 mm; placing the processed flat plate in a mould with a complex flow field for compression molding to obtain a grooved composite bipolar plate; and (3) putting the formed bipolar plate with the groove into an oven for curing at the curing temperature of 80-200 ℃, preserving heat for 1h every 20 ℃, and naturally cooling to obtain the composite bipolar plate with the thickness of 0.6 mm.

Example 4

Taking crystalline flake graphite with the particle size of 120 microns accounting for 80wt% and polyimide resin with the particle size of 23 microns according to the weight ratio of 4: placing the powder obtained after mixing according to the weight ratio of 0.25 in isostatic pressing equipment, setting the pressure of 120MPa at normal temperature, and then pressing within the time of keeping the pressure of 100MPa for 1min to obtain a flat plate-shaped preform of 10 mm; cutting and punching the preliminarily pressed flat plate-shaped prefabricated body by using a multi-wire cutting machine to obtain 10 thin flat plates with the thickness of 1 mm; placing the processed flat plate in a mould with a complex flow field for compression molding to obtain a grooved composite bipolar plate; and (3) putting the formed bipolar plate with the groove into an oven for curing at the curing temperature of 80-200 ℃, preserving heat for 1h every 20 ℃, and naturally cooling to obtain the composite bipolar plate with the thickness of 0.6 mm.

Comparative example 2

Flake graphite accounting for 80wt% of graphite with the particle size of 120 microns and polyimide resin with the particle size of 5 microns are mixed according to the weight ratio of 4: placing the powder obtained after mixing according to the weight ratio of 0.25 in isostatic pressing equipment, setting the pressure of 120MPa at normal temperature, and then pressing in the pressure maintaining time of 90MPa for 1min to obtain a flat plate-shaped preform of 10 mm; cutting and punching the preliminarily pressed flat plate-shaped prefabricated body by using a multi-wire cutting machine to obtain 10 thin flat plates with the thickness of 1 mm; placing the processed flat plate in a mould with a complex flow field for compression molding to obtain a grooved composite bipolar plate; and (3) putting the formed bipolar plate with the groove into an oven for curing at the curing temperature of 80-200 ℃, preserving heat for 1h every 20 ℃, and naturally cooling to obtain the composite bipolar plate with the thickness of 0.6 mm.

Comparative example 3

Taking crystalline flake graphite with the particle size of 120 microns accounting for 80wt% and polyimide resin with the particle size of 45 microns according to the weight ratio of 4: placing the powder obtained after mixing according to the weight ratio of 0.25 in isostatic pressing equipment, setting the pressure of 120MPa at normal temperature, and then pressing in the pressure maintaining time of 90MPa for 1min to obtain a flat plate-shaped preform of 10 mm; cutting and punching the preliminarily pressed flat plate-shaped prefabricated body by using a multi-wire cutting machine to obtain 10 thin flat plates with the thickness of 1 mm; placing the processed flat plate in a mould with a complex flow field for compression molding to obtain a grooved composite bipolar plate; and (3) putting the formed bipolar plate with the groove into an oven for curing at the curing temperature of 80-200 ℃, preserving heat for 1h every 20 ℃, and naturally cooling to obtain the composite bipolar plate with the thickness of 0.6 mm.

Comparative example 4

Taking crystalline flake graphite with the particle size of 120 microns accounting for 80wt% and polyimide resin with the particle size of 23 microns according to the weight ratio of 4: placing the powder obtained after mixing according to the weight ratio of 0.25 in isostatic pressing equipment, setting the pressure of 120MPa at normal temperature, and then pressing in the pressure maintaining time of 70MPa for 1min to obtain a flat plate-shaped preform of 10 mm; cutting and punching the preliminarily pressed flat plate-shaped prefabricated body by using a multi-wire cutting machine to obtain 10 thin flat plates with the thickness of 1 mm; placing the processed flat plate in a mould with a complex flow field for compression molding to obtain a grooved composite bipolar plate; and (3) putting the formed bipolar plate with the groove into an oven for curing at the curing temperature of 80-200 ℃, preserving heat for 1h every 20 ℃, and naturally cooling to obtain the composite bipolar plate with the thickness of 0.6 mm. The volume resistivity and the flexural strength of the obtained graphite composite bipolar plate were measured by a four-probe resistance measurement method and a universal electronic testing machine, as shown in the following table:

experiment number	Volume resistivity/m omega ∙ cm	Variance of resistance	Flexural strength/MPa
				Comparative example 1	20.2	55	37.9
Example 1	8.8	0.5	54.1
				Example 2	8.2	0.6	55
Example 3	7.9	0.3	56.9
				Example 4	6.6	0.3	58.1
Comparative example 2	11.3	0.9	50.6
				Comparative example 3	12.3	1.1	44.7
Comparative example 4	11.6	2.1	40.9

As can be seen from the above table, the composite bipolar plate prepared by using isostatic cool pressing has higher electrical and physical properties than the composite bipolar plate prepared without using isostatic cool pressing. Moreover, as the smaller the resistance variance, the better the uniformity of the composite bipolar plate, it can be seen from the above table that the composite bipolar plate prepared by using the cold isostatic pressing has better uniformity.