Highly gas-tight high-strength graphite bipolar plate material, method for producing same, and graphite bipolar plate

Abstract

The present application relates to a kind of high air-tightness high-strength graphite bipolar plate material and its preparation method and graphite bipolar plate, belong to fuel cell technical field.The graphite bipolar plate material of the present application includes aluminum magnesium alloy phase and graphite matrix, aluminum magnesium alloy phase is embedded in the air hole of the graphite matrix by the way of high-pressure injection.Because the aluminum magnesium alloy filled in the air hole of graphite is metal, the organization density is very high, and plasticity is good, not only can the porosity of graphite bipolar plate material be reduced to 0~0.5%, but also can increase the strength and toughness of graphite bipolar plate material, facilitate processing ultra-thin bipolar plate and mass production, help to reduce the weight, volume and production cost of hydrogen fuel cell stack, improve the power density of fuel cell, meet the urgent needs of current market for high-power hydrogen fuel cell.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fuel cell, and particularly relates to a graphite bipolar plate material with high air tightness and high strength, a preparation method thereof and a graphite bipolar plate. BACKGROUND

[0002] The bipolar plate is one of the key components in the fuel cell. Generally, the bipolar plate accounts for more than 80% of the total mass of the stack and accounts for about 30% of the total cost, and the volume of the fuel cell stack is basically occupied by the bipolar plate. The bipolar plate plays a role of separating fuel and oxidant, collecting and outputting current, and guiding raw gas. The performance of the bipolar plate depends on the material properties of the bipolar plate. Among the three types of bipolar plates of graphite, metal and composite material, the graphite bipolar plate becomes the current domestic fuel cell application mainstream due to its good electrical conductivity, thermal conductivity, stability and corrosion resistance. The graphite bipolar plate requires good air tightness to avoid gas leakage during the operation of the battery, which leads to internal air hydrogen mutual connection and causes safety accidents. Graphite is a porous and brittle material with low strength and high brittleness, which cannot meet the air tightness requirement of the bipolar plate. Generally, the porosity is reduced by the process of impregnating resin to meet the performance requirements of the bipolar plate.

[0003] The preparation process of the graphite bipolar plate mainly includes mechanical processing, mold pressing and injection molding. The mechanical processing is the mainstream process for preparing the graphite bipolar plate in China. The graphite bipolar plate is generally prepared by impregnating resin on the graphite plate raw material to reduce the porosity and improve the air tightness and strength, and then mechanically processing to obtain the bipolar plate. Patent CN101483240B provides a processing method for ultra-thin graphite bipolar plate of fuel cell. The method is to put the graphite bipolar plate blank into a solution of thermosetting resin for vacuum impregnation, then perform heat curing treatment, and process the flow channel by mechanical processing to prepare the graphite bipolar plate. This method does not solve the problem that the free formaldehyde in the resin itself is easy to escape during resin curing, forming pores. Moreover, as a high molecular material, the thermosetting resin can only improve the compressive strength of graphite by about 30%, and has an adverse effect on the electrical conductivity of the graphite bipolar plate. At the same time, the mechanical processing method has high cost and is not conducive to mass production, which affects the commercial application of hydrogen fuel cell.

[0004] The information disclosed in this section of background art is only intended to increase the understanding of the overall background of the present application, and should not be considered as admitting or implying in any form that the information constitutes prior art known to those skilled in the art. SUMMARY

[0005] In order to solve the technical problems of poor air tightness and compressive strength of the graphite bipolar plate in the prior art, the present application provides a graphite bipolar plate material with high air tightness and high strength, a preparation method thereof and a graphite bipolar plate.

[0006] The first aspect of the present application provides a graphite bipolar plate material, which comprises an aluminum-magnesium alloy phase and a graphite matrix, and the aluminum-magnesium alloy phase is embedded in the air hole of the graphite matrix. In some embodiments, the chemical formula of the aluminum-magnesium alloy phase is: Al (100-x) Mg x , wherein 2≤x≤7; the aluminum-magnesium alloy in this ratio range has good corrosion resistance and high strength. Preferably, x can be, but is not limited to, 2.5, 3, 4, 5, 6.5; more preferably, the aluminum-magnesium alloy is Al 96 Mg4, Al 97 Mg3, and Al 94 Mg6.

[0007] In some embodiments, the air permeability coefficient of the graphite bipolar plate material is 0.5-1.0*10 -6 cm 3 .s -1 .cm -2 ;

[0008] And / or, the bending strength of the graphite bipolar plate material is 90-110Mpa;

[0009] And / or, the resistivity of the graphite bipolar plate material is 2-5μΩ·m;

[0010] And / or, the thickness of the graphite bipolar plate material is 0.4-1mm.

[0011] The second aspect of the present application provides a preparation method of a graphite bipolar plate material, which comprises: under vacuum conditions, injecting an aluminum-magnesium alloy melt into a graphite matrix to form a graphite bipolar plate material with an aluminum-magnesium alloy phase.

[0012] In some embodiments, the atomic mass percentage of magnesium in the magnesium-aluminum alloy is 2%-7%; and / or, the raw material of the magnesium-aluminum alloy melt is a magnesium-aluminum alloy, and / or industrial pure aluminum and magnesium ingot. Magnesium and aluminum are light in weight, the density of aluminum is only 2.7g / cm 3 , and the density of magnesium is only 1.74g / cm 3 , which is even lower than the density of the graphite matrix. The electrical conductivity, corrosion resistance and strength of the aluminum-magnesium alloy in this ratio range are the best among light alloys. Therefore, filling the graphite air hole with a magnesium-aluminum alloy can not only improve the electrical conductivity and corrosion resistance of the graphite product, but also improve the mechanical strength of the graphite product without significantly increasing the weight of the graphite product.

[0013] In some embodiments, the raw material of the graphite matrix is isostatic pressing graphite or die pressing graphite.

[0014] In some embodiments, the graphite matrix before high-pressure injection needs to be pretreated, and the pretreatment includes cleaning, drying and preheating under vacuum. By cleaning and drying, the powder, debris and moisture on the surface of the graphite matrix are washed away, so that the aluminum-magnesium alloy melt can well penetrate into the pores of the graphite matrix, preventing the formation of bubbles.

[0015] In some embodiments, the preheating temperature is 350-400℃; preferably, the preheating time is 6-12h. During preheating, the graphite matrix is kept in a vacuum state, and the gas in the pores of the graphite matrix is discharged under the action of negative pressure, preparing for the subsequent penetration of the aluminum-magnesium alloy melt. The graphite matrix is preheated in advance, and the aluminum-magnesium melt will not immediately solidify when it contacts the preheated graphite matrix, affecting the penetration of the graphite matrix pores.

[0016] In some embodiments, the pressure of the high-pressure injection is 50-100Mpa.

[0017] Specifically, the graphite bipolar plate material preparation method provided by the application is performed according to the following steps:

[0018] Preparation of aluminum-magnesium alloy melt: The industrial pure aluminum and magnesium ingots are heated to 720-750℃ in a vacuum induction furnace for smelting, and the atomic percentage of magnesium in the aluminum-magnesium alloy is between 2%-7%;

[0019] Preparation of graphite matrix blank: The graphite raw material block is cut into a certain number of graphite matrix blanks with consistent size, preferably, the thickness of the blank is between 3-7mm, and further preferably, the area of the blank is 50cm*50cm-100cm*100cm. The graphite raw material block can be isostatic pressing graphite or die pressing graphite.

[0020] Cleaning and drying: The powder and debris on the surface of the graphite matrix blank are cleaned with alcohol, and then placed in a drying oven and heated to 105-110℃ for drying;

[0021] Preheating of high-pressure compounding device and blank: The graphite matrix blank is placed in a high-pressure injection composite device, and each piece of graphite bipolar plate matrix blank is fixed at a certain distance in the shelf in the device. The shelf has uniform grids on each layer, and the shelf and the grids are coated with a release lubricant. The composite device and the graphite bipolar plate matrix blank are preheated to 350-400℃, and vacuumed to -0.1Mpa. The vacuum degree is maintained for 6-12h.

[0022] High-pressure injection compounding:The high-temperature aluminum-magnesium alloy melt is injected into the inner chamber of the composite device until the whole cavity is filled, and then the pressure is increased to 50-100 MPa, and the pressure is maintained until the aluminum-magnesium alloy melt solidifies; under the action of high pressure, the aluminum-magnesium alloy melt enters the pores of the graphite bipolar plate base material, and after stripping treatment, a graphite bipolar plate material containing an aluminum-magnesium alloy phase is obtained.

[0023] The third aspect of the present application provides a graphite bipolar plate comprising the above-mentioned graphite bipolar plate or the graphite bipolar plate prepared by the above-mentioned preparation method.

[0024] Compared with the prior art, the present application achieves the following technical effects:

[0025] (1) The high-air-tightness high-strength graphite bipolar plate new material and the preparation method provided by the present application, since the aluminum-magnesium alloy filled in the pores of graphite is a metal with high density, the porosity of the graphite bipolar plate material can be reduced to 0-0.5%, the sealing effect is very good, the air permeability coefficient of the graphite bipolar plate material can be reduced to 0.5*10 -6 , which is much lower than the air permeability coefficient of the current graphite bipolar plate.

[0026] (2) The composite aluminum-magnesium alloy phase has good electrical conductivity and corrosion resistance. Compared with impregnated resin, filling the composite aluminum-magnesium alloy phase not only does not reduce the electrical conductivity of the graphite bipolar plate, but also improves the electrical conductivity of the graphite bipolar plate, while maintaining the corrosion resistance of the graphite bipolar plate.

[0027] (3) The composite aluminum-magnesium alloy phase has very low density, similar to the high-molecular-weight thermosetting resin, which not only maintains the advantage of light weight of the graphite bipolar plate, but also greatly improves the brittleness of the graphite material, greatly improves the strength and toughness of the bipolar plate, and has very good mechanical processing performance, which can reduce the thickness of the graphite bipolar plate and process 0.4mm ultra-thin graphite bipolar plate.

[0028] (4) The graphite bipolar plate material prepared by the process has high strength and good plasticity, the flow channel processing method of the bipolar plate can be diversified, which is very flexible and simple, can be stamped or molded, has high production efficiency, is convenient for processing ultra-thin bipolar plates and batch production, helps to reduce the weight, volume and production cost of the hydrogen fuel cell stack, improves the power density of the fuel cell, and meets the urgent needs of the market for high-power hydrogen fuel cells. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a schematic diagram of the high-pressure injection composite device in Example 1;

[0030] In the figure:

[0031] 1 - melt inlet; 2 - movable slide; 3 - pressurized medium; 4 - blank holder; 5 - outlet; 6 - pressurization system. DETAILED DESCRIPTION

[0032] The technical solutions of the present application are illustrated below by specific examples. It should be understood that one or more steps mentioned in the present application do not exclude other methods and steps before or after the combination steps, or other methods and steps can be inserted between these explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. Unless otherwise specified, the numbering of each method step is only for the purpose of identifying each method step, and is not intended to limit the arrangement order of each method or to limit the scope of the implementation of the present application. Changes or adjustments of the relative relationship can also be considered as the scope of the implementation of the present application without substantial technical content changes.

[0033] The raw materials and instruments used in the examples are not specifically limited in source and can be purchased in the market or prepared according to the conventional methods well known to those skilled in the art.

[0034] Example 1: Preparation method of a high-air-tightness high-strength graphite bipolar plate material

[0035] The preparation method of a high-air-tightness high-strength graphite bipolar plate material comprises the following steps:

[0036] (1) Preparation of aluminum-magnesium alloy melt: the raw materials are industrial pure aluminum and magnesium ingots, both with a purity of 99.9%, and a certain proportion of industrial pure aluminum and magnesium ingots are heated to 750°C in a vacuum induction furnace for smelting to obtain an aluminum-magnesium alloy melt, with a chemical composition formula of Al 98 Mg2;

[0037] (2) Preparation of graphite bipolar plate blank: graphite raw material blocks are cut into a certain number of graphite matrix blanks with consistent size, with a thickness of 3 mm and an area of 50 cm*50 cm, and the graphite raw material is isostatic pressing graphite;

[0038] (3) Cleaning and drying: the powder debris on the surface of the graphite bipolar plate blank is cleaned with alcohol, and then placed in a drying oven and heated to 105°C for drying.

[0039] (4) Preheating of high-pressure injection device and blank: the graphite bipolar plate blank is placed in the high-pressure injection device, such as Figure 1As shown, the high-pressure injection device is provided with blank fixing frame 4, and the blank fixing frames are spaced apart at a certain distance. Each layer of blank fixing frame 4 is provided with a grid of uniform size, and each layer of blank fixing frame 4 and the grid on the blank fixing frame are coated with a demolding lubricant. The graphite bipolar plate blank is fixed on the blank fixing frame 4. The high-pressure injection device and the graphite bipolar plate blank are preheated to 350°C, and vacuumized to -0.1 Mpa. The vacuum degree is maintained for 6 hours.

[0040] (5) High-pressure injection compounding: the high-temperature aluminum-magnesium alloy melt is injected into the high-pressure injection device from the melt inlet 1 until the entire cavity is filled, and then the pressurizing system 6 is pressurized by the pressurizing medium 3, with a pressure of 50 Mpa. The pressure is maintained until the aluminum-magnesium alloy melt solidifies. Under the action of high pressure, the aluminum-magnesium alloy melt will enter the pores of the graphite bipolar plate blank. After the high-pressure injection is completed, a graphite bipolar plate composite new material blank containing an aluminum-magnesium alloy phase is obtained.

[0041] (6) Peeling: the graphite bipolar plate blank on the blank fixing frame 4 and the aluminum-magnesium alloy solidified together are pushed out of the high-pressure injection inner chamber from the outlet 5 by using the movable slide bar 2. Then, the excess aluminum-magnesium alloy is peeled off from the graphite bipolar plate blank by using the grid of the blank fixing frame 4. Then, the graphite bipolar plate substrate is milled to a certain thickness to polish and clean the aluminum-magnesium alloy scraps on the surface of the blank, thereby obtaining a 0.6 mm thick graphite bipolar plate material with a smooth surface containing an aluminum-magnesium alloy.

[0042] The graphite bipolar plate prepared by the above method has high air tightness, and the air permeation coefficient is less than 0.5*10 -6 cm 3 .s - 1 .cm -2 , the bending strength is 90 MPa, the electrical resistivity is low, only 2 μΩ·m, that is, it has high electrical conductivity; the above-mentioned graphite bipolar plate material is placed in a NaCl solution with a mass concentration of 35% and a pH of 6.5-7.2 at 35°C, soaked for 24 hours, and then taken out. It is found that there is no obvious corrosion phenomenon on the surface of the material.

[0043] Example 2: A method for preparing a graphite bipolar plate material with high air tightness and high strength

[0044] (1) Preparation of aluminum-magnesium alloy melt: the raw materials are industrial pure aluminum and magnesium ingots, both with a purity of 99.9%. A certain proportion of industrial pure aluminum and magnesium ingots are melted in a vacuum induction furnace heated to 730°C to obtain an aluminum-magnesium alloy melt, and the chemical composition formula is Al 95 Mg5.

[0045] (2) Preparation of graphite bipolar plate blank: cut the graphite raw material block into a certain number of graphite bipolar plate blanks with consistent size, thickness of 5 mm, area of 70 cm*70 cm, and the graphite raw material is a molded graphite;

[0046] (3) Cleaning and drying: clean the powder debris on the surface of the graphite bipolar plate blank with alcohol, and then place it in a drying oven and heat it to 110°C for drying;

[0047] (4) Preheat the high-pressure composite device and the blank: place the graphite bipolar plate blank in the high-pressure injection device, which is provided with a blank fixing frame, and the blank fixing frames are spaced apart at a certain distance. Each layer of blank fixing frame is provided with a grid of consistent size, and each layer of blank fixing frame and the grid on the blank fixing frame is coated with a release lubricant. The graphite bipolar plate blank is fixed on the blank fixing frame. The high-pressure injection device and the graphite matrix bipolar plate blank are preheated to 380°C, and vacuumized to -0.1 Mpa. Maintain the vacuum degree for 9h;

[0048] (5) High-pressure injection composite: inject the high-temperature aluminum-magnesium alloy melt into the high-pressure injection device from the melt inlet until the entire cavity is filled, then pressurize the system 6 through the pressurizing medium 3, the pressure is 70 Mpa, and the pressure is maintained until the aluminum-magnesium alloy melt solidifies. Under the action of high pressure, the aluminum-magnesium alloy melt will enter the pores of the graphite bipolar plate blank, and a graphite bipolar plate composite new material blank containing aluminum-magnesium alloy phase is obtained.

[0049] (6) Peeling: at the discharge port, use a movable slide rod to push the graphite bipolar plate blank on the blank fixing frame and the aluminum-magnesium alloy solidified together out of the high-pressure injection inner chamber, then use the grid on the blank fixing frame to separate the excess aluminum-magnesium alloy from the graphite bipolar plate blank matrix, then mill a certain thickness of the graphite bipolar plate matrix to polish and clean the aluminum-magnesium alloy debris on the surface of the blank, and obtain a 0.8 mm thick graphite bipolar plate material with smooth surface.

[0050] The graphite bipolar plate prepared by the above method has high air tightness, and the air permeation coefficient is less than 0.8*10 - 6 cm 3 .s -1 .cm -2 , the bending strength is 100 MPa, the resistivity is low, only 4 μΩ·m, indicating that the electrical conductivity is high; the above graphite bipolar plate material is placed in a NaCl solution with a mass concentration of 35% and a pH of 6.5-7.2 at 35°C, soaked for 24h, and then taken out. It is found that there is no obvious corrosion phenomenon on the surface of the material.

[0051] Example 3: A method for preparing a graphite bipolar plate material with high air tightness and high strength

[0052] (1) Preparation of aluminum magnesium alloy melt: the raw materials are industrial pure aluminum and magnesium ingot, both of which have a purity of 99.9%, a certain proportion of industrial pure aluminum and magnesium ingot is heated to 720℃ in a vacuum induction furnace for smelting to obtain an aluminum magnesium alloy melt, the chemical composition formula of which is Al 93 Mg7;

[0053] (2) Preparation of graphite bipolar plate blank: graphite raw material blocks are cut into a certain number of graphite bipolar plate blanks with consistent size, the thickness is 70mm, and the area is 70cm*70cm, the graphite raw material is molded graphite;

[0054] (3) Cleaning and drying: the powder debris on the surface of the graphite bipolar plate blank is cleaned with alcohol, and then placed in a drying oven heated to 105℃ for drying;

[0055] (4) Preheating of high-pressure composite device and blank: the graphite bipolar plate blank is placed in a specially designed high-pressure injection device, the high-pressure injection device is provided with a blank fixing frame, the blank fixing frames are spaced apart, each layer of blank fixing frame is provided with a grid of consistent size, and each layer of blank fixing frame and the grid on the blank fixing frame is coated with a release lubricant, the graphite bipolar plate blank is fixed on the blank fixing frame, the high-pressure injection device and the graphite bipolar plate blank are preheated to 380℃, and vacuumized to-0.1Mpa, and maintained at the vacuum degree for 9h;

[0056] (5) High-pressure injection composite: the high-temperature aluminum magnesium alloy melt is injected into the high-pressure injection device from the melt inlet until the entire cavity is filled, then the pressurizing system is pressurized through the pressurizing medium, the pressure is 70Mpa, and the pressure is maintained until the aluminum magnesium alloy melt solidifies, under the action of high pressure, the aluminum magnesium alloy melt enters the pores of the graphite bipolar plate blank, and a graphite bipolar plate composite new material blank containing an aluminum magnesium alloy phase is obtained;

[0057] (6) Peeling: at the discharge port, the graphite bipolar plate blank on the blank fixing frame and the aluminum magnesium alloy solidified together are pushed out of the high-pressure injection inner chamber through the movable slide rod, then the excess aluminum magnesium alloy and the graphite bipolar plate blank matrix are peeled off through the grid on the shelf, then the graphite bipolar plate matrix with a certain thickness is milled to polish and clean the aluminum magnesium alloy debris on the surface of the blank, and a 0.4mm-thick graphite bipolar plate with smooth surface is prepared.

[0058] The graphite bipolar plate prepared by the above method has high air tightness, and the air permeation coefficient is less than 0.8*10 - 6 cm 3 .s -1 .cm -2, the bending strength is 100Mpa, and the resistivity is only 4μΩ·m, which indicates that the conductivity is high; the graphite bipolar plate material is placed in a NaCl solution with a mass concentration of 35% and a pH of 6.5-7.2 at 35°C, soaked for 24h, and then taken out, and no obvious corrosion phenomenon is found on the surface of the material.

[0059] Example 4: A graphite bipolar plate

[0060] A graphite bipolar plate is processed using the graphite bipolar plate material prepared in Example 1, and the processing is as follows:

[0061] Flow channel processing: the graphite bipolar plate material can be directly punched into a flow channel on a punch press according to the design requirements of the flow field of the bipolar plate, and an anode plate and a cathode plate with a groove depth of 0.2mm and a thickness of 0.4mm are punched according to the requirements.

[0062] Dispensing sealing: after the graphite bipolar plate material is cleaned and subjected to air tightness detection, the anode plate and the cathode plate are bonded using glue, and finally a graphite bipolar plate is obtained.

[0063] Example 5: A graphite bipolar plate

[0064] A graphite bipolar plate is processed using the graphite bipolar plate material prepared in Example 2, and the processing is as follows:

[0065] Flow channel processing: the graphite bipolar plate material can be directly punched into a flow channel on a punch press according to the design requirements of the flow field of the bipolar plate, and an anode plate and a cathode plate with a groove depth of 0.2mm and a thickness of 0.8mm are punched according to the requirements.

[0066] Dispensing sealing: after the graphite bipolar plate material is cleaned and subjected to air tightness detection, the anode plate and the cathode plate are bonded using glue, and finally a graphite bipolar plate is obtained.

[0067] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the application. The exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the application be defined by the claims and their equivalents.

Claims

1. A graphite bipolar plate material, characterized in that, The graphite bipolar plate material includes an aluminum-magnesium alloy phase and a graphite matrix, wherein the aluminum-magnesium alloy phase is embedded in the pores of the graphite matrix; The chemical formula of the aluminum-magnesium alloy phase is: Al (100-x) Mg x Where 2≤x≤7; The raw material for the graphite matrix is ​​isostatic graphite or molded graphite, and the graphite matrix needs to be pretreated. The graphite bipolar plate material can be processed into an ultra-thin graphite bipolar plate of 0.4 mm.

2. The graphite bipolar plate material according to claim 1, characterized in that, The air permeability coefficient of the graphite bipolar plate material is 0.5~1.0*10. -6 cm 3 .s -1 .cm -2 ; And / or, the flexural strength of the graphite bipolar plate material is 90-110 MPa; And / or, the resistivity of the graphite bipolar plate material is 2-5 μΩ·m; And / or, the thickness of the graphite bipolar plate material is 0.4-1 mm.

3. A method for preparing the graphite bipolar plate material as described in claim 1, characterized in that, include: High-pressure injection of aluminum-magnesium alloy melt into a graphite matrix forms a graphite bipolar plate material with an aluminum-magnesium alloy phase.

4. The preparation method according to claim 3, characterized in that, The raw materials for the aluminum-magnesium alloy melt are magnesium-aluminum alloy and / or industrial pure aluminum and magnesium ingots.

5. The preparation method according to claim 3, characterized in that, The graphite matrix needs to be pretreated before high-pressure injection. The pretreatment includes cleaning, drying and preheating under vacuum.

6. The preparation method according to claim 5, characterized in that, The preheating temperature is 350~400℃.

7. The preparation method according to claim 5, characterized in that, The preheating time is 6-12 hours.

8. The preparation method according to claim 3, characterized in that, The pressure of the high-pressure injection is 50~100 MPa.

9. A graphite bipolar plate, characterized in that, Includes the graphite bipolar plate material according to any one of claims 1-2 or the graphite bipolar plate material prepared by the preparation method according to any one of claims 3-8.

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