A method of assembling a flexible graphite plate stack for reuse

Abstract

The application provides a flexible graphite plate stack assembly method, which comprises the following steps: S1: stack disassembly: obtaining actual compression force N1 in the stack before disassembly; S2: stack assembly: re-stacking and assembling each component of the disassembled stack according to an assembly sequence, applying a press-fit force to the bare stack, and setting a target value of the press-fit force as N2, wherein the range of N2 is (1-1.5)*N1, and N2 satisfies the condition of being less than a design press-fit force F of the stack; and S3: stack fastening: when the press-fit force applied to the bare stack gradually increases to N2, the increase of the press-fit force is stopped, the bare stack after the press-fit force is applied is fastened by using a fastening component, and the re-assembly of the stack is completed. The re-assembled stack can ensure good stack sealing performance, prevent deformation of a flexible graphite plate flow channel structure in the stack, and avoid problems of reduced flow channel flux and increased flow resistance.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell stack assembly technology, and relates to a method for assembling a reusable flexible graphite plate stack. Background Technology

[0002] A fuel cell is a device that directly converts the chemical energy of fuel into electrical energy. It boasts high energy conversion efficiency and offers advantages such as environmental friendliness, zero pollution, and zero emissions. Fuel cell stacks using flexible graphite plates as bipolar plates leverage the excellent conductivity, corrosion resistance, and lightweight properties of graphite materials to further improve the performance, lifespan, and power density of fuel cell stacks. As research into flexible graphite plate fuel cells deepens, disassembly and reassembly of the cells inevitably occur. However, flexible graphite plates have low mechanical strength and deform under significant compressive forces. Furthermore, their poor compression resilience means that some compression cannot be recovered, resulting in irreversible deformation. Therefore, re-pressing reused flexible graphite plates with the original design compression force carries risks such as flow channel collapse, reduced flow flux, and significantly increased fluid resistance, all of which negatively impact stack performance. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a reusable flexible graphite plate fuel cell stack assembly method, which ensures that the reusable flexible graphite plate maintains the flow channel structure without collapsing after reassembly of the fuel cell stack, and guarantees good fuel cell stack sealing performance.

[0004] To achieve the above objectives, the present invention provides a reusable flexible graphite plate fuel cell assembly method using the following technical solution:

[0005] The present invention provides a method for assembling a reusable flexible graphite plate fuel cell, comprising the following steps:

[0006] S1: Battery stack disassembly: Before disassembling the battery stack, obtain the actual clamping force N1 inside the battery stack;

[0007] S2: Fuel Cell Stack Assembly: Reassemble the components of the disassembled fuel cell stack according to the assembly sequence, applying a pressing force to the bare stack. The target value of the pressing force is set as N2, where N2 ranges from (1 to 1.5) * N1, and N2 is less than the designed pressing force F of the fuel cell stack; and

[0008] S3: Stack fastening: When the pressing force applied to the bare stack gradually increases to N2, the pressing force is stopped, and the bare stack after the pressing force is applied is fastened with fastening components to complete the stack reassembly.

[0009] Preferably, in step S1, obtaining the actual clamping force N1 within the fuel cell stack further includes the following steps:

[0010] S11: Remove the external components of the fuel cell stack, including electrical connection components and fluid connection components, to obtain the bare stack;

[0011] S12: Place the bare stack on the press working platform along the stacking direction, and set the press preload N0, where N0 is much smaller than the stack design pressing force F;

[0012] S13: Loosen the fuel cell stack fastening components. The bare stack bounces back along the stacking direction. At this time, the pressure of the end plate of the bare stack on the press plate changes. That is, due to the height rebound, the pressure of the bare stack is transferred from the fastening components to the press plate. After all the fastening components are completely loosened and the pressure change stabilizes, read the pressure value N1 of the press at this time. This is the actual clamping force N1 in the fuel cell stack.

[0013] Preferably, in step S1, the actual clamping force N1 of the fuel cell stack is in the range of 60~85%*F.

[0014] Preferably, in step S12, F0 is 0.05F~0.2F.

[0015] Preferably, after step S1, the components inside the bare stack are inspected or repaired after the press pressure is completely removed.

[0016] Preferably, in step S2, the bare stack comprises a reusable flexible graphite plate.

[0017] Preferably, in step S2, a press is used to apply a pressing force to the bare stack.

[0018] Preferably, in S3, when the pressing force applied to the bare stack gradually increases to N2, the pressing force is stopped by stopping the stroke of the upper pressure plate of the press.

[0019] Compared with the prior art, the beneficial effects of this invention are as follows:

[0020] The present invention discloses a method for assembling a reusable flexible graphite plate fuel cell stack. Before disassembling the fuel cell stack, a press is used to apply a pressure much smaller than the clamping force to the stack. After loosening the fuel cell stack fastening device, the actual clamping force of the fuel cell stack is obtained. After the fuel cell stack is re-stacked, a pressure similar to the obtained actual clamping force is applied to it. This ensures that the reassembled fuel cell stack has good sealing performance and prevents deformation of the flexible graphite plate flow channel structure inside the stack, thus avoiding the problems of reduced flow channel throughput and increased flow resistance. Attached Figure Description

[0021] Figure 1 A flowchart illustrating a preferred embodiment of the present invention for assembling a reusable flexible graphite plate fuel cell stack. Detailed Implementation

[0022] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The terms used in this specification, such as "front," "back," "left," "right," "inner," and "outer," are merely for clarity of description and are not intended to limit the scope of the invention. Any changes or adjustments to their relative relationships, without substantially altering the technical content, shall also be considered within the scope of the invention.

[0024] In the description of the following embodiments, unless otherwise expressly specified and limited, the term "connection" and other such terms should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an indirect connection through an intermediate medium; it can be the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0025] The preferred embodiment of this application provides a method for assembling a reusable flexible graphite plate fuel cell stack. First, the actual compaction force inside the stack before reassembly is obtained. After re-stacking the reusable flexible graphite plates inside the stack, a pressure similar to the actual compaction force inside the original stack is applied to the stack. Under this compaction force, the fuel cell stack has good sealing performance and can ensure that the flow channel structure of the flexible graphite plate does not deform, and will not cause a reduction in flow channel throughput or an increase in flow resistance.

[0026] To better understand this invention, the fuel cell stack structure is described in detail below. In this art, a fuel cell stack generally includes an inlet end plate, a core composed of multiple individual cells, disc spring supports, disc springs, and a distal end plate. Besides the individual cells in the center, the core also includes current collectors and insulating plates at both ends. These components are stacked sequentially and secured in a compressed state using fastening components. Additionally, the fuel cell stack components include external components such as electrical connection components and fluid connection components, for example, power terminals, inspection devices, and manifolds. Here, the portion of the fuel cell stack without external components is also referred to as a bare stack. Each individual cell consists of a bipolar plate and a membrane electrode assembly (MEA). The MEA contacts a hydrogen flow field plate and an air flow field plate on both sides, respectively. A sealing ring is present between the MEA frame and the bipolar plate to ensure the core's airtightness under compression. The bipolar plate is formed by bonding a hydrogen flow field plate and an air flow field plate together, creating a coolant cavity with a coolant flow field between the two plates.

[0027] The following is combined Figure 1A method for assembling a reusable flexible graphite plate stack of a preferred embodiment of the present invention will be described in detail. As Figure 1 shown, the stack assembly method of the present invention includes the following steps S1 to S3.

[0028] Step S1 is the stack disassembly step, and the actual pressing force N1 inside the stack is obtained before the stack is completely disassembled (during the disassembly process). Preferably, the stack disassembly in step S1 further includes the following steps S11 to S13. Specifically, in step S11, external components such as power terminals, inspection circuits, and manifolds of the stack are removed to obtain a bare stack. In step S12, the bare stack is placed on the working platform of the press with the intake end plate facing down along the stacking direction. A pre-pressure N0 of the press is set, and N0 is much smaller than the designed pressing force F of the stack. The press is started, and the upper platen of the press descends until it touches the distal end plate of the bare stack or alternatively a pressing block placed on the distal end plate of the bare stack, and the pre-pressure on the bare stack gradually increases to reach N0.

[0029] Here, the pre-pressure N0 is much smaller than the designed pressing force F of the stack. Preferably, N0 can be 0.05F to 0.2F, which not only ensures that the platen completely touches the distal end plate of the bare stack or the pressing block on the distal end plate, but also does not cause too much pressure on the single cells in the stack core to further compress.

[0030] Next is step S13. Keep the position of the upper platen of the press unchanged, that is, keep the pre-pressure unchanged, and gradually loosen the fastening components of the stack until they are completely loose. At this time, the upper platen ensures that the bare stack is still in a compressed state to transfer the pressing force exerted by the fastening device to the bare stack. During this process, the numerical value displayed by the pressure sensor on the press continuously increases. After the value is stable, read the pressure value N1 of the press at this time and record it. The N1 is the actual pressing force received by the single cells in the stack before disassembly. The actual pressing force N1 of this stack < F. Since the stack is stacked and compressed according to the designed pressing force F during the first assembly, internal components undergo certain deformations, including elastic deformation and permanent deformation. In addition, the inside of the stack is often in high-temperature and high-humidity conditions during operation, and the flexible graphite plate will creep. Therefore, the occurrence of these deformations makes the actual pressing force inside the stack less than the designed pressing force.

[0031] After step S1, lift the upper platen of the press to remove the pressure, and then the single cells of the stack can be disassembled for inspection or repair. Next is step S2, the stack is reassembled. When reassembling, use a positioning tooling to re-stack each component of the bare stack in the assembly order, including the single cells reused in the original stack. The press performs a pressing operation on the stacked body, that is, the bare stack. Set the target value of the pressing force of the press to N2, and the range of N2 is set to (1 to 1.5) * N1, and N2 still satisfies being less than the designed pressing force F.

[0032] It should be noted that the flexible graphite bipolar plates, after compression and high-temperature operation, have already undergone significant permanent deformation and creep. If they are compressed and tightened again with the designed pressing force, the flow channel structure will deform or even collapse. The present invention uses N2 as the clamping force for repeated assembly of the fuel cell stack, which can ensure both good fuel cell stack sealing and prevent deformation of the graphite plate flow field structure.

[0033] In step S3, the press is started to press the bare stack. After the upper pressure plate of the press applies pressure to the far end plate of the bare stack to N2, the upper pressure plate stops its stroke. Fastening components are used to fasten the bare stack after the pressing force is applied according to the design requirements, thereby completing the reassembly of the stack.

[0034] In some preferred embodiments, the actual clamping force N1 measured after the fastening components of the fuel cell stack are loosened in step S1 is related to the designed clamping force F and the length of the fuel cell stack operation time. The larger the designed clamping force F, the larger the actual clamping force N1; the longer the fuel cell stack operation time, the smaller the actual clamping force N1.

[0035] In some preferred embodiments, the actual clamping force N1 of the fuel cell stack ranges from 60% to 85% of F. If the measured actual clamping force N1 is less than 60% of F, it is not suitable for reassembly using the method of this invention. In one preferred embodiment, the screw-type fuel cell stack composed of 15 single cells is designed with a clamping force F of 25 kN, a pre-pressure N0 of 2 kN, and an actual clamping force N1 of 18 kN measured after loosening the screw. Then, when clamping again, a clamping force N2 of 22 kN is used. This ensures that the internal flexible graphite plate is not over-pressurized, preventing deformation of the flow field structure, while also ensuring good sealing and electrical contact performance of the assembled fuel cell stack. The fuel cell stack assembled in this way will not show a significant increase in the flow resistance of the reactant gas and coolant during performance testing. The flow resistance is calculated by measuring the pressure of the fluid at the inlet and outlet of the fuel cell stack on the fuel cell test bench and performing a difference calculation. For example, the coolant flow resistance is the coolant pressure before entering the stack minus the coolant pressure after exiting the stack. Flow resistance is a very important parameter in the operation of fuel cell stacks, which directly affects the performance of the cells. Excessive gas flow resistance affects the uniform distribution of reactant gas in the flow channel, and excessive coolant flow resistance affects the heat dissipation of fuel cell stacks.

[0036] As a comparative example, the flexible graphite plate stack that was repeatedly assembled was pressed again using the designed pressing force F. During the performance test, such a stack showed a significant increase in flow resistance, with the flow resistance of the reaction gas or coolant doubling or even increasing several times, resulting in a decrease in battery performance.

[0037] Table 1 below shows examples and comparative examples of reassembling 15 single-cell stacks using the method of the present invention. The coolant cavity flow resistance and airtightness test data are values ​​obtained by testing each stack under the same test conditions.

[0038]

[0039] As can be seen from Examples 1-3 in the table above, when the relationship between the reassembly clamping force N2 and the actual clamping force N1 is controlled between 1 and 1.5, the coolant cavity flow resistance of the reassembled fuel cell stack is very close to that of the newly assembled fuel cell stack, indicating that the flow channel structure is not deformed. This shows that the assembly method of the present invention can essentially maintain the performance of the newly assembled fuel cell stack. Preferably, when N1 is small (closer to 60%*F), approximately 1.5 times N2 can be used; when N1 is large (closer to 85%*F), approximately 1 times N2 can be used, while N2 must be less than the fuel cell stack design clamping force F. However, when N2 in Comparative Example 2 exceeds 1.5 times N1, reaching 1.6666 times N1, the coolant cavity flow resistance of the reassembled fuel cell stack reaches 60.2 kPa, far exceeding the coolant cavity flow resistance of 25.1 kPa of the newly assembled fuel cell stack, more than double the coolant cavity flow resistance of the newly assembled fuel cell stack, leading to a sharp decline in the performance of the reassembled fuel cell stack. As can be seen from Comparative Example 3, when N1 is large, although N2 is controlled to be 1.1792*N1 (close to 1 time), the coolant cavity flow resistance measured in Comparative Example 3 reaches 38.5 kPa because N2 fails to meet the condition of being less than F. This is a significant improvement compared to the coolant cavity flow resistance of the newly installed fuel cell stack.

[0040] Furthermore, the above embodiments and comparative examples were subjected to airtightness tests to detect the fuel cell stack sealing performance. In this invention, the airtightness test was conducted by evaluating the external gas leakage flow rate of the three chambers of the fuel cell stack: the hydrogen chamber, the air chamber, and the coolant chamber. The test conditions were: air, room temperature, 200 kPa(a); the acceptance standard was ≤20 sccm. The unit kPa(a) represents kilopascals of absolute pressure, and sccm represents standard cubic centimeters per minute (a unit of gas volumetric flow rate). As shown in Table 1, the gas volumetric flow rates of Examples 1-3 were 8.2 sccm, 10.3 sccm, and 8.5 sccm, respectively, all meeting the acceptance standard. This indicates that even with a smaller clamping force compared to Comparative Examples 1-3, the embodiments of this invention still achieve excellent fuel cell stack sealing performance. Therefore, the embodiments of this invention can maintain excellent fuel cell stack sealing performance while achieving a lower coolant chamber flow resistance.

[0041] This invention is not limited to the above-described embodiments. Any changes in shape or structure are within the scope of protection of this invention. The scope of protection of this invention is defined by the appended claims. Those skilled in the art can make various changes, modifications, substitutions, combinations, and simplifications to these embodiments without departing from the principles and essence of this invention. All such changes and simplifications should be considered equivalent substitutions and fall within the scope of protection of this invention.

Claims

1. A method for assembling a reusable flexible graphite plate fuel cell stack, characterized in that, Includes the following steps: S1: Battery stack disassembly: Before disassembling the battery stack, obtain the actual clamping force N1 inside the battery stack; S2: Stack assembly: The components of the disassembled stack are reassembled according to the assembly sequence. A pressing force is applied to the bare stack. The target value of the pressing force is set as N2, and the range of N2 is (1~1.5)*N1. N2 is less than the stack design pressing force F. as well as S3: Stack fastening: When the pressing force applied to the bare stack gradually increases to N2, the pressing force is stopped, and the bare stack after the pressing force is applied is fastened using fastening components, completing the stack reassembly. In step S1, obtaining the actual clamping force N1 within the fuel cell stack also includes the following steps: S11: Remove the external components of the fuel cell stack, including electrical connection components and fluid connection components, to obtain the bare stack; S12: Place the bare stack on the press working platform along the stacking direction, and set the press preload N0, where N0 is much smaller than the stack design pressing force F; S13: Loosen the fuel cell stack fastening components. The bare stack bounces back along the stacking direction. At this time, the pressure of the end plate of the bare stack on the press plate changes. That is, due to the height rebound, the pressure of the bare stack is transferred from the fastening components to the press plate. After all the fastening components are completely loosened and the pressure change stabilizes, read the pressure value N1 of the press at this time. This is the actual clamping force N1 in the fuel cell stack.

2. The method for assembling a reusable flexible graphite plate fuel cell stack according to claim 1, characterized in that, In step S1, the actual clamping force N1 of the fuel cell stack is in the range of 60~85%*F.

3. The method for assembling a reusable flexible graphite plate fuel cell stack according to claim 1, characterized in that, In step S12, F0 is 0.05F~0.2F.

4. The reusable flexible graphite plate fuel cell assembly method according to claim 1, characterized in that, After step S1, the components inside the bare stack are inspected or repaired after the press pressure is completely removed.

5. The method for assembling a reusable flexible graphite plate fuel cell stack according to claim 1, characterized in that, In step S2, the bare stack includes reusable flexible graphite plates.

6. The method for assembling a reusable flexible graphite plate fuel cell stack according to claim 5, characterized in that, In step S2, a press is used to apply a pressing force to the bare stack.

7. The method for assembling a reusable flexible graphite plate fuel cell stack according to claim 1, characterized in that, In S3, when the pressing force applied to the bare stack gradually increases to N2, the pressing force is stopped by stopping the stroke of the upper pressure plate of the press.

Images