Fuel cell stack pressure homogenization fluid-solid coupling additional packaging structure and use method thereof

Abstract

The invention provides a fuel cell stack pressure homogenization fluid-solid coupling additional packaging structure and a use method thereof, and belongs to the technical field of large fuel cell stack packaging. Key function components of the packaging structure are a fluid pressurizing bag in the fuel cell stack and a controllable hydraulic pump outside the fuel cell stack, and the controllable hydraulic pump is communicated with the interior of the fluid pressurizing bag and used for adjusting hydraulic pressure in the fluid pressurizing bag; and under the action of concentrated packaging force, the non-uniform deformation of the upper end plate can be adapted, and the concave area is filled, so that the packaging force is uniformly transmitted to the internal components of the cell stack. Damage caused by too large hydraulic pressure or clamp loosening and packaging failure caused by too small hydraulic pressure can be avoided; the universality is high, the effect of uniformly transmitting packaging force can be achieved for different packaging clamps, and the stress uniformity of a battery assembly is remarkably improved; the end plate can replace an insulating plate in a fuel cell stack, the requirement for the rigidity of the end plate is low, the thickness of the end plate can be further reduced, and a certain contribution is made to the lightweight design of the fuel cell stack.

Description

Technical Field

[0001] The present invention belongs to the technical field of large fuel cell stack packaging, and relates to a device structure design and a use method thereof for improving uneven pressure of a large fuel cell stack assembly under concentrated packaging force. Background Art

[0003] Fuel cells are often used by stacking multiple single cells into a battery stack. Common fuel cell stack packaging methods are bolt packaging and steel strip packaging. Due to the large packaging force requirements in engineering, both common packaging methods will cause uneven deformation of the end plate and then transmit uneven packaging force to the internal battery components, affecting battery efficiency. Specifically, (1) In the case of bolt packaging, the end plate bends toward the outer edge to form a concave area in the center, which cannot transmit uniform packaging force to the inside of the battery stack, resulting in stress concentration in the outer circle of the battery component and excessive stress gradient between the inner and outer circles; (2) In the case of steel strip packaging, the end plate bends toward the steel strip binding point, and the arched area formed between adjacent steel strips cannot transmit uniform packaging force to the internal battery components. The problem of uneven force transmission is particularly prominent in the bolt packaging method.

[0004] Under the action of packaging force, the gas diffusion layer (Gas Diffusion Layer, referred to as GDL) deforms the most. Under the action of non-uniform packaging force, the GDL undergoes non-uniform compression deformation: excessive packaging force will cause the GDL porosity to decrease, the battery reaction efficiency to decrease, and may even cause the membrane electrode assembly (Membrane Electrode Assembly, referred to as MEA) related components to yield or even be damaged; while too small packaging force will increase the interface contact resistance and seriously affect the system efficiency, and may even cause the overall structure packaging of the battery stack to fail. Therefore, the design of the end plate structure, the number and distribution of bolts and steel belts, the bolt torque and the size of the steel belt tightening force, and the size of the steel belt have become very difficult.

[0005] In summary, there is an urgent need for a more universal method to homogenize the packaging force transmitted by the end plate to ensure that the battery stack can operate stably and efficiently during service. Summary of the invention

[0006] In view of the existing packaging technology problems, the present invention provides a fuel cell stack pressure equalization fluid-solid coupling additional packaging structure, which includes a controllable hydraulic pump and a pair of fluid pressurization bags. The advantage of the fluid pressurization bag is that it utilizes the continuity and fluidity of the fluid, and under the action of the uneven packaging force transmitted by the end plate, it undergoes adaptive deformation, effectively fills the recessed area of ​​the end plate, and then achieves the effect of uniformly transmitting the packaging force to the inside of the battery stack; the controllable hydraulic pump connects the fluid pressurization bag with the water storage device through a pipeline, monitors the hydraulic pressure difference between the fluid pressurization bag and the water storage device through an internal sensor, and then controls the liquid exchange between the fluid pressurization bag and the water storage device through an internal valve, so as to achieve the purpose of controlling the hydraulic pressure in the fluid pressurization bag. The controllable hydraulic pump can not only ensure that the fluid pressurization bag is well fitted with the end plate and the battery assembly respectively during assembly, but also can better monitor the working state of the fluid pressurization bag through the internal sensor when the battery stack is in service, and can effectively prevent the packaging fixture from loosening and causing packaging failure, so as to facilitate replacement or maintenance.

[0007] Compared with solid devices with the same function at present, the fluid in the bag and the continuous fluid-solid coupling response of the bag in the present invention can fill the deformation area of ​​the end plate more timely and effectively; compared with gas devices with the same function, the fluid in the present invention has a small compressible expansion amount, so it is safer in use.

[0008] Referring to the application of fuel cell stacks in automobiles, it is possible to consider connecting the controllable hydraulic pump in this invention to the automobile water tank to make the design more compact. The existence of the fluid pressurized bag makes it unnecessary to increase the thickness of the end plate to increase the rigidity and thus increase the dead weight. Its good insulation also makes it unnecessary to install an insulating plate in the battery stack, which is conducive to the lightweight design of the battery stack. The large specific heat capacity of the fluid in the bag also plays a certain role in the heat dissipation of the battery during operation.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A fuel cell stack pressure equalization fluid-solid coupling additional packaging structure is a device to improve the uneven packaging force on fuel cell stack components. The key components of the device are the fluid pressurizing bag 5 and the controllable hydraulic pump 12. Under the concentrated packaging force, the device can adapt to the uneven deformation of the upper end plate 4, fill the concave area and evenly transfer the packaging force to the internal components of the battery stack. Specifically:

[0011] The fluid pressurizing bag 5 is assembled between the upper end plate 4 and the collector plate 6. Its size should be between the size of the upper end plate 4 and the size of the collector plate 6. To prevent stress concentration, its cross section is designed as a rectangle with rounded corners. The center of the contact surface with the upper end plate 4 is provided with an interface for connecting the pipeline with the controllable hydraulic pump 12. The controllable hydraulic pump 12 is connected to the inside of the fluid pressurizing bag 5 through a pipeline running through the upper end plate 4. It monitors the hydraulic pressure in the fluid pressurizing bag 5 through an internal sensor and then adjusts the hydraulic pressure. The specific adjustment method is as described above.

[0012] Common packaging methods for the fuel cell stack are bolt packaging and steel strip packaging. For the bolt packaging, the torque of the bolt 1 is the packaging force; for the steel strip packaging, the tightening force of the steel strip 10 is the packaging force.

[0013] Furthermore, a positioning groove is opened at the bottom of the upper end plate 4 to limit the displacement of the fluid pressurization bag 5. The size of the positioning groove should be larger than the size of the fluid pressurization bag 5 and the rectangular positioning groove should be rounded. The depth of the positioning groove should be consistent with the thickness of the fluid pressurization bag 5.

[0014] Furthermore, in order to facilitate the assembly of the pipeline and the fluid pressurizing bag 5 , a hole is formed through the center of the upper end plate 4 , and the hole diameter should be larger than the pipeline diameter and coincide with the center interface of the fluid pressurizing bag 5 .

[0015] In the bolt packaging method, the upper end plate 4 includes an upper end plate and a lower end plate, and the upper and lower end plates are connected by bolts 1 and nuts 2, and a gasket 3 is arranged between the nut 2 and the upper end plate 4. The fluid pressurization bag 5, the collector plate 6, the bipolar plate 7, the sealing gasket 8, the membrane electrode 9 and a number of single cells 11 are placed on the inner side of the upper and lower end plates in sequence. The packaging torque is increased by rotating the nut 2, and during this process, the upper end plate 4 is deformed by bending toward the outer edge and being concave inside. The deformation of the upper end plate 4 squeezes the fluid pressurization bag 5 inward, forming a state in which the outer edge is thin and the center is thick, thereby compensating for the uneven deformation of the upper end plate 4 in time, while the lower surface of the fluid pressurization bag 5 remains in a planar state and fits tightly with the collector plate 6;

[0016] In the steel strip packaging method, the upper and lower end plates are connected by several steel strips 10, and the fluid pressurization bag 5, the collector plate 6, the bipolar plate 7, the sealing gasket 8, the membrane electrode 9 and several single cells 11 are placed in the upper end plate 4 in sequence. Similarly, the upper end plate 4 bends at the point where the steel strip 10 acts, and a concave area is generated between adjacent steel strips 10. The fluid pressurization bag 5 deforms adaptively and fills the concave area of ​​the upper end plate 4 in time, and its lower surface remains in a flat state and fits closely with the collector plate 6.

[0017] A single cell 11 is composed of a pair of bipolar plates 7, a sealing gasket 8 and a membrane electrode 9. Under the action of packaging force, each single cell forms a tight overall structure by relying on the friction between the components.

[0018] The fluid pressurizing bag 5 is made of non-metallic insulating material with good sealing performance, and is provided with fluid inside. The specific material and thickness of the pressurizing bag need to be determined according to the pressure condition and impedance and airtightness characteristics of the battery components in the battery stack, such as the Mises stress and contact stress of each component, the output voltage and current of the battery stack, etc. The selection of the fluid in the fluid pressurizing bag 5 needs to be determined according to its viscosity, and the specific parameters include viscosity, shear stress, and shear rate.

[0019] A method for using a fuel cell stack pressure equalization fluid-solid coupling additional packaging structure comprises the following steps:

[0020] Step 1, assembling fuel cell components;

[0021] Step 2, adjust the controllable hydraulic pump 12, give the fluid pressurizing bag 5 a pre-pressure and check its air tightness. If the fluid pressurizing bag 5 leaks, it should be repaired or replaced in time;

[0022] Step 3, if the fluid pressurization bag 5 has good air tightness, the upper end plate 4, the clamp (bolt 1, nut 2 or steel belt 10) and the fluid pressurization bag 5 can be assembled. First, fit the non-interface end of the fluid pressurization bag 5 to the collector plate 6, and then pass the pipeline through the opening of the upper end plate 4 to connect with the controllable hydraulic pump 12, to ensure that the upper and lower surfaces of the fluid pressurization bag 5 are in good contact with the upper end plate 4 and the collector plate 6 respectively, and adjust the controllable hydraulic pump 12 so that the pressure in the fluid pressurization bag 5 is sufficient to support the upper end plate 4. For the bolt packaging method, align the bolt holes on the edges of the upper and lower upper end plates 4, pass the bolt 1 through the bolt hole of the end plate, insert the gasket 3 into the bolt 1, and then use the electronic torque wrench to screw in the nut 2. The pre-tightening force should not be too large to ensure that the gasket 3 is always in good contact with the upper end plate 4 and the nut 2 during the process, and there is no thread slippage. For the steel belt packaging method, there is a certain pre-pressure in the fluid pressurization bag 5, and the steel belt 10 can be inserted in sequence without the action of a press after positioning;

[0023] Step 4, after completing the pre-assembly of the fixture, check the fit between the fixture and the upper end plate 4, the fluid pressurization bag 5 and the upper end plate 4, and each single cell in the battery stack. If the fit is good, for the bolt packaging method, add the torque of the bolt 1 and the nut 2 to the design value through the electronic torque wrench. During this process, the controllable hydraulic pump 12 should be continuously adjusted to increase the hydraulic pressure in the fluid pressurization bag 5 to the design value. For the steel strip packaging method, adjust the controllable hydraulic pump 12 to adjust the hydraulic pressure in the fluid pressurization bag 5 to the design value;

[0024] Step 5, test the pressure condition of the internal single battery components and the impedance, airtightness or other characteristics of the battery. If the battery is detected to be abnormal, change the structural design material and size of the fluid pressurization bag 5, and repeat the process of steps 2, 3 and 4. If the test is qualified, the packaging process of the battery stack is completed.

[0025] The beneficial effects of the present invention are:

[0026] (1) The main functioning device of the present invention is a fluid pressurizing bag, which is in the shape of a rectangular bag with rounded corners. The controllable hydraulic pump connected to it can adjust the pressure inside the bag in real time. While ensuring good contact between the bag and the end plate and the collector plate, it can also monitor the hydraulic pressure inside the bag to avoid damage caused by excessive hydraulic pressure or loosening of the clamp and packaging failure caused by insufficient hydraulic pressure;

[0027] (2) The device of the present invention has strong versatility and can evenly transmit packaging force to different packaging fixtures. For the listed fuel cell products, after installing the device of the present invention, the center pressure of the membrane electrode is significantly increased, the edge pressure is relatively reduced, the center and outer circle pressure gradient is correspondingly reduced, and the force uniformity of the battery assembly is significantly improved;

[0028] (3) The present invention can replace the role of the insulating plate in the fuel cell stack, and has lower requirements on the rigidity of the end plate. The thickness of the end plate can be further reduced, which makes a certain contribution to the lightweight design of the fuel cell stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the structure of the 1 / 8 bolt packaging method of the fuel cell stack;

[0030] Figure 2 This is a schematic diagram of the structure of 1 / 4 of the steel strip packaging method of the fuel cell stack;

[0031] Figure 3 It is a schematic diagram of the additional packaging structure of pressure equalization fluid-solid coupling;

[0032] Figure 4 (a) is a cross-sectional schematic diagram of the unassembled pressure equalization fluid-solid coupling additional packaging structure under the bolt packaging method; Figure 4 (b) is a cross-sectional schematic diagram of the additional packaging structure of the assembly pressure equalization fluid-solid coupling under the bolt packaging method;

[0033] Figure 5 (a) is a cross-sectional schematic diagram of the unassembled pressure equalization fluid-solid coupling additional packaging structure under the steel strip packaging method; Figure 5 (b) is a schematic cross-sectional view of the additional packaging structure of the assembly pressure homogenization fluid-solid coupling under the steel strip packaging method;

[0034] In the figure: 1 bolt; 2 nut; 3 gasket; 4 upper end plate; 5 fluid pressurizing bag; 6 collector plate; 7 bipolar plate; 8 sealing gasket; 9 membrane electrode (MEA); 10 steel belt; 11 single cell; 12 controllable hydraulic pump.

[0035] Specific facilities

[0036] The present invention is described below in conjunction with specific implementation cases.

[0037] Taking a certain type of proton exchange membrane fuel cell product in two different packaging modes as an example, the specific implementation mode of the present invention is as follows:

[0038] (1) The implementation method of the invention in a certain type of fuel cell stack bolt packaging method is as follows:

[0039] 1) According to Figure 1 The fuel cell components are assembled in the positional relationship shown, and the fluid pressurizing bag 5 device is located between the upper end plate 4 and the collector plate 6. Before installing the bolts 1, nuts 2 and gaskets 3, it should be ensured that the pipeline of the fluid pressurizing bag 5 is connected to the controllable hydraulic pump 12 through the center hole of the upper end plate 4, and there is a certain pre-pressure in the fluid pressurizing bag 5 to ensure that the fluid pressurizing bag 5 is in good contact with the upper end plate 4 and the collector plate 6, and that each single cell 11 inside the battery stack is in good contact. Each single cell 11 is composed of a bipolar plate 7, a sealing gasket 8 and a membrane electrode (MEA) 9.

[0040] 2) If Figure 4 As shown in (b), the upper and lower end plates are connected by bolts 1, nuts 2 and gaskets 3. When increasing the pre-tightening force on the nut 2, it should be ensured that the gasket 3 always fits well with the upper end plate 4 and the nut 2 to avoid thread slippage, and the bolt pre-tightening force should not be too large.

[0041] 3) According to Figure 4 As shown in (b), the bolt torque is gradually increased. During this process, the controllable hydraulic pump 12 is adjusted so that the hydraulic pressure of the fluid pressurization bag 5 cooperates with the increased packaging torque. During this process, the upper end plate 4 bends toward the edge, and a recessed area appears in the center. The deformation of the upper end plate 4 causes the fluid pressurization bag 5 to adaptively deform. The surface in contact with the upper end plate 4 becomes thick in the middle and thin at the edges. The recessed area is filled in time, but it still maintains planar contact with the collector plate 6.

[0042] 4) After the bolt torque and the fluid pressure bag are increased to the design value, the pressure condition of the internal single battery assembly and the impedance and airtightness of the battery are tested. If the battery is detected to be abnormal and the assembly operation is confirmed to be correct, the structural design material and size of the fluid pressure bag 5 should be changed, and the processes 1), 2) and 3) should be repeated. If the test is qualified, the packaging process of the battery stack is completed.

[0043] (2) The implementation method of the invention in a certain type of fuel cell stack bolt packaging method is as follows:

[0044] 1) According to Figure 1The fuel cell components are assembled in the positional relationship shown, and the fluid pressurizing bag 5 device is located between the upper end plate 4 and the collector plate 6. Before installing the bolts 1, nuts 2 and gaskets 3, it should be ensured that the pipeline of the fluid pressurizing bag 5 is connected to the controllable hydraulic pump 12 through the center hole of the upper end plate 4, and there is a certain pre-pressure in the fluid pressurizing bag 5 to ensure that the fluid pressurizing bag 5 is in good contact with the upper end plate 4 and the collector plate 6, and that the single cells 11 inside the battery stack are in good contact.

[0045] 2) If Figure 5 As shown in (b), when the fluid pressurized bag 5 is not pressurized to the designed pressure, the steel belt 10 can be directly inserted into the upper and lower end plates after positioning to achieve a pre-assembled state.

[0046] 3) According to Figure 5 As shown in (b), the controllable hydraulic pump 12 is adjusted to increase the hydraulic pressure of the fluid pressurizing bag 5, thereby lifting the upper end plate 4 to make the steel belt 10 in a straight state. In this process, the upper end plate 4 is bent and deformed toward the action area of ​​the steel belt 10, and the fluid pressurizing bag 5 is also adaptively deformed to fill the bent concave area in time, but still maintains planar contact with the collector plate 6. The fluid pressurizing bag 5 transmits the concentrated packaging force of the clamp to the internal battery assembly relatively evenly.

[0047] 4) After the bolt torque and the fluid pressure bag are increased to the design value, the pressure condition of the internal single battery assembly and the impedance and airtightness of the battery are tested. If the battery is detected to be abnormal and the assembly operation is confirmed to be correct, the structural design material and size of the fluid pressure bag 5 should be changed, and the processes 1), 2) and 3) should be repeated. If the test is qualified, the packaging process of the battery stack is completed.

[0048] The above-described embodiments merely express the implementation methods of the present invention, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A fuel cell stack pressure equalization fluid-solid coupling additional packaging structure, characterized in that: The key functional components of the packaging structure are the fluid pressurizing bag (5) inside the fuel cell stack and the controllable hydraulic pump (12) outside the fuel cell stack; under the action of the concentrated packaging force, the packaging structure can adapt to the uneven deformation of the upper end plate (4), fill the recessed area and evenly transfer the packaging force to the internal components of the fuel cell stack; specifically: The fluid pressurization bag (5) is installed between the upper end plate (4) and the collector plate (6), and an interface connected to the controllable hydraulic pump (12) is provided at the center of the contact surface with the upper end plate (4); the controllable hydraulic pump (12) is connected to the inside of the fluid pressurization bag (5) through a pipeline running through the upper end plate (4), and it monitors the hydraulic pressure in the fluid pressurization bag (5) through an internal sensor and adjusts the hydraulic pressure.

2. A fuel cell stack pressure equalization fluid-solid coupling additional packaging structure according to claim 1, characterized in that: The size of the fluid pressurizing bag (5) is smaller than that of the upper end plate (4) and larger than that of the current collecting plate (6), and its cross section is designed to be a rectangle with rounded corners.

3. A fuel cell stack pressure equalization fluid-solid coupling additional packaging structure according to claim 1, characterized in that: A positioning groove is formed at the bottom of the upper end plate (4) to limit the displacement of the fluid pressurizing bag (5), and the depth of the positioning groove is the same as the thickness of the fluid pressurizing bag (5).

4. A fuel cell stack pressure equalization fluid-solid coupling additional packaging structure according to claim 1, characterized in that: Common packaging methods for the fuel cell stack are bolt packaging and steel strip packaging. For the bolt packaging, the torque of the bolt (1) is the packaging force; for the steel strip packaging, the tightening force of the steel strip (10) is the packaging force.

5. A fuel cell stack pressure equalization fluid-solid coupling additional packaging structure according to claim 4, characterized in that: In the bolt packaging method, the upper and lower end plates are connected by bolts (1) and nuts (2); a fluid pressurizing bag (5), a current collector plate (6), a bipolar plate (7), a sealing gasket (8), a membrane electrode (9) and a plurality of single cells (11) are placed in sequence on the inner sides of the upper and lower end plates; by rotating the nut (2) to increase the packaging torque, the upper end plate (4) is internally sunken and deformed, and the fluid pressurizing bag (5) is squeezed inward to compensate for the uneven deformation of the upper end plate (4), and the lower surface of the fluid pressurizing bag (5) remains in a flat state and fits tightly with the current collector plate (6); In the steel strip packaging method, the upper and lower end plates are connected by several steel strips (10), and the fluid pressurization bag (5), the collector plate (6), the bipolar plate (7), the sealing gasket (8), the membrane electrode (9) and a plurality of single cells (11) are placed in sequence inside the upper end plate (4); the upper end plate (4) bends toward the point where the steel strip (10) acts, and a recessed area is generated between adjacent steel strips (10), and the fluid pressurization bag (5) is adaptively deformed to fill the recessed area of ​​the upper end plate (4), and its lower surface remains in a flat state and fits tightly with the collector plate (6).

6. A fuel cell stack pressure equalization fluid-solid coupling additional packaging structure according to claim 5, characterized in that: A gasket (3) is arranged between the nut (2) and the upper end plate (4).

7. A fuel cell stack pressure equalization fluid-solid coupling additional packaging structure according to claim 5, characterized in that: In the bolt packaging method and the steel strip packaging method, a single cell (11) is composed of a pair of bipolar plates (7), a sealing gasket (8) and a membrane electrode (9), and each single cell forms a tight overall structure by relying on the friction between the components under the action of the packaging force.

8. The fuel cell stack pressure equalization fluid-solid coupling additional packaging structure according to claim 1, characterized in that: The fluid pressurizing bag (5) is made of a non-metallic insulating material with good sealing performance, and contains fluid.

9. The fuel cell stack pressure equalization fluid-solid coupling additional packaging structure according to claim 1, characterized in that: The material and thickness of the pressurizing bag are determined according to the pressure conditions, impedance and airtightness characteristics of the battery components in the battery stack, and the fluid in the fluid pressurizing bag (5) is determined according to its viscosity parameters.

10. A method for using the pressure equalization fluid-solid coupling additional packaging structure for a fuel cell stack according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1, assembling fuel cell components; Step 2, adjusting the controllable hydraulic pump (12), giving the fluid pressurizing bag (5) a pre-pressure and checking its air tightness; if the fluid pressurizing bag (5) leaks, it should be repaired or replaced in time; Step 3, pre-assembly of the fixture; If the fluid pressurizing bag (5) has good air tightness, assemble the upper end plate (4), the clamp and the fluid pressurizing bag (5), wherein the clamp includes bolts (1), nuts (2) or steel strips (10), ensuring that the upper and lower surfaces of the fluid pressurizing bag (5) are in contact with the upper end plate (4) and the collector plate (6) respectively, and the fluid pressurizing bag (5) supports the upper end plate (4) through a controllable hydraulic pump (12); For the bolt packaging method, the bolt holes at the edges of the upper and lower end plates are aligned, the bolts (1) pass through the end plates and are inserted into the gaskets (3), and then screwed into the nuts (2). The pre-tightening force requires that the gaskets (3) are always in contact with the upper end plates (4) and the nuts (2) during the process. For the steel strip packaging method, there is a certain pre-pressure in the fluid pressurized bag (5), and the steel strips (10) can be inserted in sequence after being positioned. Step 4, after completing the pre-assembly of the fixture, check the fit of each component; if the fit is good, for the bolt packaging method, add the torque of the bolt (1) and the nut (2) to the design value through the electronic torque wrench. During this process, the controllable hydraulic pump (12) should be continuously adjusted to increase the hydraulic pressure in the fluid pressurization bag (5) to the design value; for the steel strip packaging method, adjust the controllable hydraulic pump (12) to adjust the hydraulic pressure in the fluid pressurization bag (5) to the design value; Step 5, testing the pressure condition of the internal single battery components and the impedance, airtightness or other characteristics of the battery; if an abnormality is detected in the battery, the structural design material and size of the fluid pressurization bag (5) are changed, and the process of steps 2, 3 and 4 is repeated; If the test is qualified, the battery stack packaging process is completed.

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