A combined mold for one-step forming of a fuel cell bipolar plate and a method thereof

Abstract

The application discloses a kind of once forming preparation fuel cell bipolar plate mould and method thereof, belong to fuel cell bipolar plate preparation technical field;The application uses a set of combined mould, including lower mould 1, preforming cooling cavity 6 and upper mould 2, lower precast block 7 is placed in succession from lower to upper in the center of lower mould 1, preforming cooling cavity 6 and upper precast block 5, then upper mould 2 is combined with lower mould 1, and the forming of bipolar plate is completed once in press;The bipolar plate manufacturing process of the application does not need secondary glue bonding, and there is no risk of cooling cavity leakage, compared with prior art, the application reduces material, equipment and labor cost, and the product prepared is also more excellent in performance.

Description

Technical Field

[0001] This invention relates to the field of fuel cell bipolar plate fabrication technology, specifically to molds and methods for fabricating fuel cell bipolar plates. Background Technology

[0002] Bipolar plates, also known as current collectors, are a crucial component of fuel cells. Current bipolar plate assemblies are manufactured using a thermosetting molding method to separately prepare cathode and anode plates (also called monopolar plates) from composite materials. This involves cold-pressing the composite material into a mold cavity, heating the mold to a specific temperature, and then curing it under pressure. It's important to note that thermosetting molding can only press one type of plate at a time using a single mold; producing both cathode and anode plates requires two sets of molds. If both types of plates are to be produced on the same press, this can only be done by changing the molds. This is clearly disadvantageous for mass production of bipolar plates.

[0003] The second step in the existing process is to glue the cooling channel surfaces of the cathode plate and the anode plate together to form an electrode assembly. This bonding process needs to be carried out in a dust-free environment with stable temperature and humidity. The glue is applied to the bonding area of ​​the cooling channel surface of the cathode plate using dispensing or printing equipment, and then the cooling channel surface of the anode plate is attached to the cooling channel surface of the cathode plate. After that, the bonded bipolar plates are placed in a clamping fixture and fastened with bolts to form a small pile of bipolar plate semi-finished products. Finally, the glue is cured in a dryer to complete the preparation of the bipolar plate assembly semi-finished product, and a cooling cavity channel is formed between the cathode plate and the anode plate.

[0004] In summary, existing bipolar plate manufacturing processes have the following drawbacks: First, the production process itself is complex, with high costs for manpower, fixtures, and equipment, and requires significant factory space. Second, the cooling chamber formed by bonding bipolar plates is prone to leakage due to air bubbles, with leaks often occurring at the adhesive bonding surface. Without quality control, leaking plates will lead to fuel cell stack failure. To control the risk of substandard bipolar plates entering the next stacking process, 100% inspection of semi-finished bipolar plates is required to identify leak points. Due to the time and equipment required for plate process inspection, the bonding and leak detection processes have become bottlenecks in bipolar plate assembly capacity.

[0005] To address the shortcomings of existing technologies, patent document CN113437320A provides a method for preparing graphite bipolar plates through one-time molding. This method eliminates the need for welding two types of monopolar plates and bonding them with adhesive in existing production processes. Furthermore, the graphite bipolar plates prepared by this integrated molding process exhibit good integrity, low resistivity, and a relatively lower aging rate, thus improving service life. This method represents a significant improvement over existing technologies. However, the fabrication of the intermediate coolant channel mold in this method requires the use of FDM technology, which is inconvenient and costly, making it unsuitable for large-scale industrial production.

[0006] Therefore, providing a simpler and more applicable method for molding fuel cell bipolar plates is a technical problem that urgently needs to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a one-time molding process for preparing a fuel cell bipolar plate assembly mold and method thereof. Using a single mold, a pre-formed cooling channel model is positioned between two pre-pressed material blocks, and the bipolar plate is formed in one step in a press. The resulting bipolar plate assembly includes cathode and anode reaction surface channels, and also includes a pre-formed cooling cavity. The present invention is simpler and more stable than existing processes.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a combined mold for one-time molding of fuel cell bipolar plates, comprising, from bottom to top, a lower mold, a pre-formed cooling cavity, and an upper mold; wherein, the lower mold is provided with a cathode flow channel, the upper mold is provided with an anode flow channel, a baffle is provided around the cathode flow channel on the lower mold, a baffle is provided around the anode flow channel on the upper mold, inlet and outlet modules are provided at two short sides inside the baffle of the lower mold, inlet and outlet holes that cooperate with the inlet and outlet modules are provided at two short sides inside the baffle of the upper mold, guide posts are provided on the baffle of the lower mold, and positioning holes corresponding to the guide posts are provided on the baffle of the upper mold, with guide sleeves that cooperate with the guide posts fixed in the positioning holes.

[0010] As a further preferred embodiment of the technical solution of the present invention, the combined mold further includes one or more precast block molds.

[0011] As a further preferred embodiment of the technical solution of the present invention, the material of the preformed cooling cavity is a thermally conductive hollow metal or non-metal frame, foam net, metal or non-metal fins, or cast metal or non-metal cavity.

[0012] As a further preferred embodiment of the technical solution of the present invention, the inlet / outlet module is detachable and is installed by means of an installation port on the lower mold that mates with the inlet / outlet module.

[0013] In a second aspect, the present invention provides a method for preparing a fuel cell bipolar plate using the above-mentioned combined mold in a single molding process, comprising the following steps:

[0014] S1. Place the material in the precast block mold and press it into shape to obtain the lower precast block and the upper precast block;

[0015] S2. Place the lower preform, preformed cooling cavity and upper preform from bottom to top in the center of the lower mold. Then, close the upper mold and lower mold and form it in the press. Remove the inlet and outlet modules to facilitate the forming of the bipolar plate, and obtain the fuel cell bipolar plate formed in one step.

[0016] As a further preferred embodiment of the technical solution of the present invention, the material in step S1 is composed of graphite powder, resin and curing agent.

[0017] As a further preferred embodiment of the technical solution of the present invention, the lower precast block and the upper precast block have the same weight and thickness in step S1.

[0018] As a further preferred embodiment of the technical solution of the present invention, in step S2, the material is pressed for 0.5 to 5 minutes at 100 to 200°C and 100 to 500 tons of pressure.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. This invention eliminates the two production steps of bonding the cathode plate cooling channel surface and the anode plate cooling channel surface to form the cooling channel and leak testing of the cooling channel in the existing process, which greatly shortens the production cycle and improves the reliability of the bipolar plate assembly; at the same time, it reduces the risk of leakage caused by incomplete bonding of the cathode plate and anode plate during use.

[0021] 2. The production mold of this invention is reduced from two sets to one set (upper mold and lower mold), thereby reducing the initial investment in molds and eliminating the need to stop production during the press to replace the molds. The mold of this invention consists of two parts: an upper mold and a lower mold. The pre-formed cold-pressed material block and the pre-forming cooling cavity are placed between the upper and lower molds. The material is formed under the pressure and high temperature of the press. When the press is opened, the workpiece determined by the shape of the mold is obtained. The upper and lower molds require high precision in their assembly, and the high-hardness high-quality alloy steel material used is often imported. Therefore, reducing the investment in molds is of great importance.

[0022] 3. The one-time molding process of this invention requires less equipment investment, is easy to operate, and has low cost, and can be widely applied to the production process of bipolar plates. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the combined mold for fabricating fuel cell bipolar plates in a single molding process according to the present invention.

[0024] Figure 2 This is a schematic diagram of the lower mold for the one-step molding of fuel cell bipolar plates according to the present invention;

[0025] Figure 3 This is a schematic diagram of the installation of the upper mold, guide pillars, and inlet / outlet module for the one-time molding of fuel cell bipolar plates according to the present invention.

[0026] Figure 4 This is a schematic diagram of the upper mold for one-step fabrication of fuel cell bipolar plates according to the present invention.

[0027] The components are as follows: 1. Lower mold; 1-1. Guide post mounting hole; 1-2. Inlet / outlet module mounting port; 1-3. Cathode flow channel; 1-4. Baffle; 2. Upper mold; 2-1. Positioning hole; 2-2. Guide sleeve; 2-3. Inlet / outlet hole; 2-4. Anode flow channel; 3. Guide post; 4. Inlet / outlet module; 5. Upper preformed block; 6. Preformed cooling cavity; 7. Lower preformed block. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0031] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention in light of the specific circumstances.

[0032] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0033] Please see Figure 1 , Figure 2 , Figure 3 and Figure 4 A composite mold for one-step fabrication of fuel cell bipolar plates includes, from bottom to top, a lower mold 1, guide pillars 3, inlet / outlet modules 4, a lower preform block 7, a preformed cooling cavity 6, an upper preform block 5, and an upper mold 2. The lower mold 1 has guide pillar mounting holes 1-1, inlet / outlet module mounting ports 1-2, a cathode flow channel 1-3, and a baffle 1-4. The upper mold 2 has positioning holes 2-1, guide sleeves 2-2, inlet / outlet holes 2-3, an anode flow channel 2-4, and a baffle 1-4.

[0034] In the above technical solution, the fuel cell stack consists of multiple bipolar plates and membrane electrode assemblies. There are three sets of flow fields between the bipolar plates and membrane electrode assemblies in the stack: cathode (air or oxygen), anode (hydrogen), and cooling (coolant), corresponding to the three sets of inlet and outlet in the plates. The cathode and anode flow channels are composed of multiple sets of parallel concave flow channels and convex ridges. During the hot pressing process, the material flows and solidifies according to the structure of the mold to form the cathode plate and anode plate. The inlet and outlet modules on the lower mold, the inlet and outlet holes on the upper mold, and the baffles around the upper and lower molds are designed to ensure the synchronous forming of the inlet and outlet during the molding process. The inlet and outlet of the pre-formed cooling cavity coincide with the cooling end in the inlet and outlet module.

[0035] It is understandable that the design of the inlet / outlet and flow channel are important features of the bipolar plate of a fuel cell. In the dispersion area near the inlet / outlet, the flow channel and the backing are connected in a bifurcated form to the parallel flow channel and the backing in the middle of the plate. The design of the mold must be faithful to the design of the plate flow channel so that the composite material can be dispersed and flowed according to the mold design and finally solidified into a bipolar plate assembly. The structural design of the flow channel can refer to the existing technology and be designed as parallel, serpentine, parallel serpentine, interdigitated, etc. The specific design can be flexibly adjusted according to actual needs. This invention does not impose specific limitations on this.

[0036] In the above technical solution, the cooling chamber structure (pre-formed cooling chamber 6) of the fuel cell is similar to the cathode and anode flow fields, consisting of a series of coolant channels; the flowing coolant carries the waste heat generated during the fuel cell power generation process to the external radiator, and is discharged into the environment through heat exchange with the air; the design principle of the cooling flow field is to ensure that the cooling chamber has sufficient heat exchange area and maintain a uniform distribution of coolant pressure drop in the chamber, ensuring that the temperature of each point of the electrode assembly is within the optimal range during the fuel cell reaction process; in addition to following the above design principles of the cooling chamber, the material of the pre-formed cooling chamber needs to have a certain mechanical strength to withstand the mechanical pressure during the hot pressing process; as a preferred embodiment of the present invention, the materials that can be selected include thermally conductive hollow metal or non-metal frames, foam nets, metal or non-metal fins, or cast metal or non-metal chambers.

[0037] Preferably, the metal or non-metal cavity is formed by casting using a metallurgical process; the specific steps are: forming a mold with high-temperature resistant paraffin material, casting, increasing the temperature or burning with a flame, removing the mold and forming the cavity.

[0038] Preferably, the heat-conducting metal or non-metal fin material is processed into the required shape of the cooling cavity, and the fins are fixed between two thin metal sheets. The three are then welded together to form the cooling cavity.

[0039] Preferably, a heat-conducting hollow metal or non-metal frame, or a foam mesh, is processed into the shape of a cooling cavity, and the foam mesh or hollow frame is fixed between two thin metal sheets by welding, forming the three into a cooling cavity.

[0040] In the above technical solution, it can be understood that the preformed cooling cavity 6 is located in the center of the finished bipolar plate. To achieve this goal, the weight and thickness of the upper and lower preforms must be consistent so as to maintain the uniform distribution of material in the upper and lower parts of the cooling cavity during the material flow process. The molds of the upper and lower preforms are not required to do so and can be of various shapes. Through the cooperation of guide pillars and guide sleeves, the upper mold and the lower mold are fully matched.

[0041] Furthermore, the present invention provides a method for fabricating fuel cell bipolar plates using the above-mentioned combined mold in a single molding process, comprising the following steps:

[0042] S1. Place the material in the precast block mold and press it into shape to obtain the lower precast block and the upper precast block;

[0043] S2. Place the lower preform 7, the preformed cooling cavity 6 and the upper preform 5 from bottom to top in the center of the lower mold 1. Then, close the upper mold 2 and the lower mold 1 to form the material in the press, demold, and obtain the fuel cell bipolar plate formed in one step.

[0044] In the above technical solution, the material in step S1 consists of graphite powder, resin, and curing agent; under high pressure and high temperature, the resin and curing agent interact to form a polymer network, curing the graphite powder into a whole with mechanical properties; at room temperature, the composite material exists in powder form, but can be molded into preforms under pressure; the purpose of preparing preforms is to facilitate the weighing and positioning of the composite material in the mold; because the curing time of the composite material is very short, Figure 1 There are two preformed blocks surrounding the preformed cooling cavity, which allows the composite material to flow rapidly to the position restricted by the mold. As mentioned above, the preformed cooling cavity 6 is located in the center of the finished product. To achieve this goal, the weight and thickness of the upper and lower preformed blocks must be consistent to maintain a uniform distribution of material in the cooling cavity during material flow. It is understood that the shape of the preformed blocks can be flexibly adjusted according to actual needs. In addition to being easy to operate, the shape and size of the preformed blocks are related to the shape of the electrode plate and the flowability of the composite material. Therefore, they can be determined through trial molding and simulation in specific implementation. The process of making preformed blocks is similar to brick making. First, the loose composite material is placed in the preformed block mold, and then pressure is applied to produce preformed blocks. The shape of the preformed blocks can be circular, elliptical, square, rectangular, or various irregular shapes.

[0045] In the above technical solution, the pressure and temperature of the press can be flexibly adjusted according to the site conditions. As a preferred embodiment of the present invention, the molding conditions in step S2 are: pressing for 0.5 to 5 minutes at a pressure of 100 to 200°C and 100 to 500 tons.

[0046] The following further combines Figure 1 The implementation principle and process of the method for preparing fuel cell bipolar plates in one step according to the present invention are described as follows:

[0047] The prepared material is pressed into shape using a precast block mold to obtain a lower precast block and an upper precast block of equal weight and thickness; then, in a press, a structure is formed from bottom to top: lower mold 1 - lower precast block 7 - pre-forming cooling cavity 6 - upper precast block 5 - upper mold 2, which is then pressed into shape.

[0048] It is understood that the molding process in the above technical solution can be carried out by placing the lower preform 7, the pre-forming cooling cavity 6, and the upper preform 5 on the lower mold 1 in sequence, and finally closing the upper mold 2 to press and form; or the pre-pressed assembly of the lower preform 7-pre-forming cooling cavity 6-upper preform 5 can be prepared first, and then the completed pre-pressed assembly can be transferred to the thermosetting mold and pressed and formed. The specific implementation can be flexibly adjusted according to the actual needs, and the present invention does not impose specific limitations on this.

[0049] Example 1

[0050] A method for fabricating a fuel cell bipolar plate assembly mold in a single molding process includes the following steps:

[0051] S1. Use a die to cut 1mm thick 85% SS316 fiber felt into a structure with four sides smaller than the finished cooling cavity; then stamp to prepare a 0.1mm thick metal sheet for wrapping the structure, and spot weld the two sheets and the structure to form a pre-formed cooling cavity 6; the outer edge of the pre-formed cooling cavity 6 is smaller than the electrode plate size, and the distance from the edge of the electrode plate is 1.6mm around the perimeter.

[0052] S1. Place a 40-gram rectangular composite material lower pre-compression block in the center of the lower mold 1 of the thermosetting mold, then place the pre-formed cooling cavity 6 in the center of the lower pre-compression block 7, and finally place a 40-gram upper pre-compression block 5 on top of the pre-formed cooling cavity 6; after stabilizing the temperature of the upper and lower molds at 150°C, close the mold at the fastest speed and maintain a pressure of 250 tons for 45 seconds, then open the upper mold, remove the inlet and outlet modules 4, and take out the formed bipolar plate to obtain a one-time formed fuel cell bipolar plate.

[0053] Example 2

[0054] A method for fabricating a fuel cell bipolar plate assembly mold in a single molding process includes the following steps:

[0055] S1. Cut a 1mm thick aluminum alloy mesh filter foam (90% porosity) into a structure suitable for the pre-formed cooling cavity 6 using wire cutting, and place the structure into a pre-welded thin sheet metal package; prepare a 40g composite material-pre-formed cooling cavity 6-40g composite material pre-pressed assembly by cold pressing.

[0056] S1. Transfer the completed pre-pressed assembly to the lower mold 1 of the thermosetting mold, close the mold, and hold it at 150°C and 250 tons of pressure for 45 seconds to print the cathode and anode flow channels on the outer surface of the electrode assembly. Take out the formed electrode assembly to obtain a one-time formed fuel cell bipolar plate.

[0057] Example 3

[0058] A method for fabricating a fuel cell bipolar plate assembly mold in a single molding process includes the following steps:

[0059] S1. Use 0.075mm aluminum foil as the carrier of the cooling cavity. Spray glue on the lower aluminum foil, evenly distribute 0.1mm diameter spherical graphite on the glued aluminum foil, spray glue evenly again, and finally cover with the upper aluminum foil to form a pre-formed cooling cavity 6.

[0060] S1. The bipolar plates are pressed in a press and mold according to the method of implementation scheme 1 to obtain a one-time formed fuel cell bipolar plate.

[0061] The contact resistance of the bipolar plates obtained in Examples 1-3 was tested, and compared with the contact resistance (mΩ·cm) of bipolar plates manufactured by existing adhesive bonding processes. 2 The results of the comparison are shown in Table 1 below:

[0062] Table 1. Contact resistance of bipolar plates manufactured in Examples 1-3 and using existing adhesive bonding processes.

[0063] Example 1 56 37 32 29 Example 2 19.9 15.7 14.7 13.9 Example 3 18.2 9.6 5.3 7.1 Adhesive molding 104 81 76 73

[0064] As shown in Table 1, the contact resistance of the integrally molded bipolar plate is lower than that of the bipolar plate bonded with glue under all pressures. The cooling cavity structure also affects the contact resistance. Using aluminum alloy mesh filter foam sheet as the cooling cavity structure can improve the contact resistance of the bipolar plate. The cooling cavity structure based on spherical graphite has the lowest contact resistance.

[0065] Eleven bipolar plates prepared according to the method in Example 3 were used to form a small stack for fuel cell feasibility testing. The results were compared with those of an eleven-piece small stack composed of bipolar plates formed using existing technology. The results are as follows: When the output power of both small stacks was 2kW, the voltage difference between each bipolar plate and the copper electrode showed a regular change. The voltage difference at the center of the bipolar plates in the two small stacks was higher than that on both sides. This may be because the sides are subjected to greater pressure due to the bolt tightening, while the pressure at the center is lower and the resistance is higher. Comparing the voltage difference at the center of the bonded small stack and the integrally formed small stack, it can be seen that the average voltage difference of the integrally formed small stack is 11mV smaller than that of the bonded small stack, which is consistent with the test results of the contact resistance.

[0066] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite mold for one-time molding of fuel cell bipolar plates, characterized in that, The structure, from bottom to top, includes a lower mold, a pre-forming cooling cavity, and an upper mold. The lower mold has a cathode flow channel, and the upper mold has an anode flow channel. A baffle is located around the cathode flow channel on the lower mold, and a baffle is located around the anode flow channel on the upper mold. Inlet and outlet modules are located at two short sides inside the baffle of the lower mold, and inlet and outlet holes that mate with the inlet and outlet modules are located at two short sides inside the baffle of the upper mold. A guide post is located on the baffle of the lower mold, and a positioning hole is located on the baffle of the upper mold, corresponding to the position of the guide post. A guide sleeve that mates with the guide post is fixed in the positioning hole. The preformed cooling cavity is made of thermally conductive hollow metal or non-metal frame, foam mesh, metal or non-metal fins, or cast metal or non-metal cavity. The preformed cooling cavity is located in the center of the finished bipolar plate. To achieve this, the weight and thickness of the upper and lower preforms must be consistent in order to maintain a uniform distribution of material above and below the cooling cavity during material flow.

2. The combined mold for one-time molding of fuel cell bipolar plates according to claim 1, characterized in that, The combined mold also includes one or more precast block molds.

3. The combined mold for one-time molding of fuel cell bipolar plates according to claim 1, characterized in that, The import / export module is detachable and can be installed by using an installation port on the lower mold that mates with the import / export module.

4. A method for fabricating fuel cell bipolar plates in a single molding process using a combination mold according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Place the material in the precast block mold and press it into shape to obtain the lower precast block and the upper precast block; S2. Place the lower preform, preformed cooling cavity and upper preform from bottom to top in the center of the lower mold. Then, close the upper mold and lower mold and form it in the press. Remove the inlet and outlet modules to facilitate the forming of the bipolar plate, and obtain the fuel cell bipolar plate formed in one step.

5. The method for fabricating fuel cell bipolar plates in a single molding process according to claim 4, characterized in that, The material in step S1 consists of graphite powder, resin and curing agent.

6. The method for preparing fuel cell bipolar plates in a single molding process according to claim 4, characterized in that, In step S1, the lower precast block and the upper precast block have the same weight and thickness.

7. The method for preparing fuel cell bipolar plates in a single molding process according to claim 4, characterized in that, The molding conditions in step S2 are: pressing at 100~200℃ and 100~500 tons of pressure for 0.5~5 minutes.

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