Fuel cell composite bipolar plate and preparation method thereof

Abstract

The present invention relates to a fuel cell composite bipolar plate and a preparation method thereof, comprising a graphite plate (1) and a frame (2) arranged outside the graphite plate (1), wherein a connection reinforcement portion is provided at the connection between the graphite plate (1) and the frame (2). Compared with the prior art, the bipolar plate of the present invention meets the requirements for thinning bipolar plates while having good mechanical strength and electrical conductivity.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a fuel cell composite bipolar plate and a preparation method thereof. Background Art

[0002] As fuel cell technology matures, as a zero-pollution, high-efficiency power generation device that can directly convert chemical energy into electrical energy, fuel cells have been increasingly used in communication base stations, vehicle power, distributed power sources and other fields. Bipolar plates are one of the core components of fuel cells, playing the role of distributing gas, conducting heat and electrical energy. As the requirements for volume power density of fuel cells gradually increase, the lightweighting of bipolar plates and membrane electrodes has become an inevitable trend. Currently, bipolar plates mainly include metal bipolar plates, graphite bipolar plates, and bipolar plates made of multilayer materials that use two materials at the same time. Among them, graphite bipolar plates formed by mixed material die-casting are considered to have the most accurate molding dimensions and can fully meet the requirements of sealing and conductivity.

[0003] In the currently available information on graphite bipolar plates, the plates are manufactured using a uniform material, such as a solidified mixture of graphite, resin, and additives. To ensure the material's electrical and thermal conductivity, the resin content in the mixture is relatively low, resulting in relatively weak strength and failing to meet the high strength requirements of certain non-conductive areas of the bipolar plate. However, as the demand for thinner and lighter bipolar plates becomes increasingly stringent, these areas with higher strength requirements have become a bottleneck limiting the development of graphite bipolar plates.

[0004] Existing technologies mainly focus on the formulation of composite plate materials or directly changing the bipolar plate base material to improve and balance the relationship between sealing, conductivity and strength. For example, invention patent CN108511764A keeps the carbon content in the composite conductive plate at a low level, and invention patent CN110581291A directly uses silicon plates made of doped conductive crystalline silicon material. However, the above methods still cannot take into account the relationship between strength, conductivity and thinness, and do not fundamentally solve the bottleneck problem of materials. Summary of the Invention

[0005] The object of the present invention is to provide a fuel cell composite bipolar plate and a preparation method thereof, which can meet the requirements of lightweight and thin bipolar plates while having good mechanical strength and electrical conductivity.

[0006] The objectives of the present invention can be achieved through the following technical solutions: A fuel cell composite bipolar plate comprises a graphite plate and a frame arranged on the outside of the graphite plate, wherein a connection reinforcement portion is provided at the connection between the graphite plate and the frame. The bipolar plate of the present invention is a further subdivision of regional functions, wherein the frame is a non-reactive zone and the graphite plate is a reactive zone. The frame portion can be made of a stronger material, such as a non-conductive material, without considering the conductivity factor, thereby reducing the thickness of this portion and thus reducing the thickness of the entire bipolar plate. The graphite plate, under the protection of the frame, serves as the reactive zone and can be made of a material with higher conductivity to improve the conductivity. The connection reinforcement portion further improves the connection strength and stability between the graphite plate and the frame, thereby ensuring that the fuel cell composite bipolar plate of the present invention has both good mechanical strength and conductivity while meeting the requirements of thin and lightweight bipolar plates.

[0007] Furthermore, the connection reinforcement portion includes a non-planar structure provided on the inner edge of the frame, and the outer edge shape of the graphite plate matches the non-planar structure. The provision of the non-planar structure can enhance the mechanical strength of the connection between the graphite plate and the frame.

[0008] Preferably, the non-planar structure is arranged at the bottom of the inner edge of the frame and extends toward the graphite plate. This design can improve the connection strength between the graphite plate and the frame while improving the stability of the graphite plate on the frame.

[0009] Further preferably, the cross-sectional shape of the non-planar structure includes a dovetail groove, a cone, a concave shape, or a convex shape; and the thickness of the non-planar structure does not exceed the thickness of the graphite plate and the frame. The non-planar structure can also be a more complex raised structure to strengthen the connection between the frame and the graphite plate. To ensure the proper function of the graphite plate, the non-planar structure must not disrupt the continuity of the graphite plate, nor must it undermine its strength. Preferably, the thickness of the non-planar structure does not exceed 70% of the thickness of the graphite plate to prevent the connecting portion from being too thin, which could weaken the strength of the graphite plate.

[0010] The graphite plate is located at the center of the frame. The frame is provided with two channel areas, which are symmetrically arranged on both sides of the graphite plate.

[0011] The channel area is provided with a hydrogen channel, a cooling water channel, and an air channel; the hydrogen channel, cooling water channel, and air channel are all waist-shaped holes of the same size. The waist-shaped holes have a smooth contour, which can reduce damage to the frame structure and improve the frame strength.

[0012] The graphite plate is provided with multiple parallel linear flow channels; the area of ​​the graphite plate accounts for 55% to 75% of the total area of ​​the composite bipolar plate. The area of ​​the graphite plate cannot be too large or too small. If it is too small, the efficiency will be reduced, while if it is too large, the overall structural strength of the composite bipolar plate will be weakened.

[0013] A method for preparing the fuel cell composite bipolar plate comprises first injecting, extruding, or die-casting a resin powder to form a frame. The frame is then placed in a mold cavity, composite graphite powder is added to the mold, and the mold is further closed for die-casting. The mold is then heated and demolded to complete the preparation of the fuel cell composite bipolar plate. The resin powder is preferably a high-strength, non-conductive material.

[0014] Preferably, the resin powder comprises the following components in parts by weight: 8 to 12 parts of graphite powder, 8 to 12 parts of reinforcing material, and 75 to 85 parts of resin; the composite graphite powder comprises the following components in parts by weight: 65 to 75 parts of graphite powder or expanded graphite powder, 15 to 25 parts of resin, and 8 to 12 parts of conductive agent.

[0015] Further preferably, the reinforcing material comprises carbon fiber or glass fiber; the conductive agent comprises short carbon fiber or carbon black; and the resin comprises PPS, PVC, PP, or PVDF, with the resin powder being the same type as that in the composite graphite powder. Using the same resin for the frame and graphite plate improves the interfacial bonding strength at the junction between the frame and graphite plate, strengthening the connection between the two interfacial media.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The present invention divides the fuel cell composite bipolar plate into a frame and a graphite plate, which serve as the non-reactive zone and the reactive zone, respectively, thereby further subdividing the regional functions of the bipolar plate. Generally speaking, the bipolar plate ports and the bridge portion connected to the flow field have higher strength requirements. In the present invention, because the conductivity factor is not considered, the material strength of this portion is greatly improved, thereby reducing the thickness of this portion and, in turn, the thickness of the entire bipolar plate.

[0018] 2. The present invention uses non-conductive materials in the port area, which fundamentally solves the problem of short-distance bridging between adjacent bipolar plates in the port due to reaction water or coolant after the stack is assembled, thus avoiding and reducing external power generation losses.

[0019] 3. The present invention uses non-conductive materials in the frame. When the stack is assembled, the isolation between adjacent bipolar plates can be eliminated without causing short circuits, greatly improving the reliability of the stack. This makes the stack itself IP67 compliant without the need for additional external packaging.

[0020] 4. The present invention uses a splicing method, which allows the frame to be formed in advance, effectively improving work efficiency;

[0021] 5. The present invention improves the connection strength between the frame and the graphite plate by setting a non-planar structure on the frame and selecting and designing the resin materials used for the frame and the graphite plate;

[0022] 6. The present invention can reduce the overall development difficulty of the electrode plate. Compared with the reaction zone, the structure and shape of the frame are more complex. The present invention can separate the frame and the reaction zone through the design of the frame and graphite plate, thereby effectively reducing the overall development difficulty of the electrode plate;

[0023] 7. The present invention can reduce the consumption of graphite materials in the reaction zone and the difficulty of development. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic structural diagram of the composite bipolar plate for a fuel cell according to the present invention;

[0025] Figure 2 This is a cross-sectional view of the intersection of the frame and the graphite plate of Example 1;

[0026] Figure 3 This is a cross-sectional view of the intersection of the frame and the graphite plate of Example 2;

[0027] Figure 4 This is a cross-sectional view of the intersection of the frame and the graphite plate of Example 3;

[0028] Figure 5 This is a cross-sectional view of the intersection of the frame and the graphite plate of Example 4;

[0029] In the figure: 1-graphite plate, 11-straight flow channel, 2-frame, 21-non-planar structure, 22-channel area. DETAILED DESCRIPTION

[0030] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following embodiments.

[0031] Example 1

[0032] A fuel cell composite bipolar plate, such as Figures 1-2 As shown, the device comprises a graphite plate 1 and a frame 2. The inner edge of the frame 2 is provided with a non-planar structure 21 with a convex cross-section. The graphite plate 1 is positioned inside the frame 2, and the outer edge of the graphite plate 1 matches the non-planar structure 21, ensuring a stable connection between the graphite plate 1 and the frame 2. The graphite plate 1 has multiple parallel linear flow channels 11, and the frame 2 has channel regions 22, which are symmetrically arranged on the left and right sides of the graphite plate 1. The channel regions 22 contain hydrogen channels, cooling water channels, and air channels.

[0033] The method for preparing the fuel cell composite bipolar plate comprises the following steps:

[0034] (1) Weighing 10 parts of graphite powder, 10 parts of carbon fiber, and 80 parts of PPS resin by weight, and mixing them uniformly to obtain resin powder; weighing 70 parts of graphite powder, 20 parts of PPS resin, 5 parts of short carbon fiber, and 5 parts of carbon black by weight, and mixing them uniformly to obtain composite graphite powder;

[0035] (2) The resin powder is injection molded to form a frame 2, and then the frame 2 is placed in a mold cavity. Composite graphite powder is added to the mold, and the mold is further closed and die-casted. Hot pressing, heating, and demolding are used to complete the preparation of the fuel cell composite bipolar plate.

[0036] Example 2

[0037] A fuel cell composite bipolar plate, such as Figure 3 As shown, it includes a graphite plate 1 and a frame 2. The inner edge of the frame 2 is provided with a non-planar structure 21 with a dovetail groove cross-section. The rest of the structure is the same as that of Example 1.

[0038] The method for preparing the fuel cell composite bipolar plate comprises the following steps:

[0039] (1) Weighing 8 parts of graphite powder, 12 parts of carbon fiber, and 75 parts of PVC resin by weight, and mixing them uniformly to obtain resin powder; weighing 65 parts of graphite powder, 25 parts of PVC resin, and 8 parts of carbon black by weight, and mixing them uniformly to obtain composite graphite powder;

[0040] (2) The resin powder is injection molded to form a frame 2, and then the frame 2 is placed in a mold cavity. Composite graphite powder is added to the mold, and the mold is further closed and die-casted. Hot pressing, heating, and demolding are used to complete the preparation of the fuel cell composite bipolar plate.

[0041] Example 3

[0042] A fuel cell composite bipolar plate, such as Figure 4 As shown, it includes a graphite plate 1 and a frame 2. The inner edge of the frame 2 is provided with a non-planar structure 21 with a conical cross-section. The rest of the structure is the same as that of Example 1.

[0043] The method for preparing the fuel cell composite bipolar plate comprises the following steps:

[0044] (1) Weighing 12 parts of graphite powder, 8 parts of glass fiber, and 85 parts of PP resin by weight, and mixing them uniformly to obtain resin powder; weighing 75 parts of expanded graphite powder, 15 parts of PP resin, and 12 parts of short carbon fiber by weight, and mixing them uniformly to obtain composite graphite powder;

[0045] (2) The resin powder is injection molded into a frame 2, and then the frame 2 is placed in a mold cavity. Composite graphite powder is added to the mold, and the mold is further closed and die-casted. Vacuum hot pressing is used for die casting, and heating and demolding are performed to complete the preparation of the fuel cell composite bipolar plate.

[0046] Example 4

[0047] A fuel cell composite bipolar plate, such as Figure 5 As shown, it includes a graphite plate 1 and a frame 2. The inner edge of the frame 2 is provided with a non-planar structure 21 with a concave cross-section shape. The rest of the structure is the same as that of Example 1.

[0048] The method for preparing the fuel cell composite bipolar plate comprises the following steps:

[0049] (1) Weighing 10 parts of graphite powder, 10 parts of glass fiber, and 80 parts of PVDF resin by weight, and mixing them uniformly to obtain resin powder; weighing 70 parts of graphite powder, 20 parts of PVDF resin, and 10 parts of carbon black by weight, and mixing them uniformly to obtain composite graphite powder;

[0050] (2) The resin powder is injection molded into a frame 2, and then the frame 2 is placed in a mold cavity. Composite graphite powder is added to the mold, and the mold is further closed and die-casted. Vacuum hot pressing is used for die casting, and heating and demolding are performed to complete the preparation of the fuel cell composite bipolar plate.

[0051] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A fuel cell composite bipolar plate, characterized in that: It comprises a graphite plate (1) and a frame (2) arranged outside the graphite plate (1), and a connection reinforcement portion is provided at the connection between the graphite plate (1) and the frame (2); The connection reinforcement portion includes a non-planar structure (21) arranged on the inner edge of the frame (2), and the outer edge shape of the graphite plate (1) matches the non-planar structure (21); The non-planar structure (21) is arranged at the bottom of the inner edge of the frame (2) and extends toward the graphite plate (1); The cross-sectional shape of the non-planar structure (21) includes a dovetail groove shape, a cone shape, a concave shape, or a convex shape; the thickness of the non-planar structure (21) does not exceed the thickness of the graphite plate (1) and the frame (2); The preparation method of the fuel cell composite bipolar plate comprises the following steps: firstly, resin powder is injection molded, extruded or die-casted to prepare a frame (2); then the frame (2) is placed in a mold cavity; composite graphite powder is added to the mold; the mold is further closed and die-casted; heating and demolding are performed to complete the preparation of the fuel cell composite bipolar plate.

2. The fuel cell composite bipolar plate according to claim 1, characterized in that: The graphite plate (1) is located at the center of the frame (2). The frame (2) is provided with two channel areas (22), and the two channel areas (22) are symmetrically arranged on both sides of the graphite plate (1).

3. The fuel cell composite bipolar plate according to claim 2, characterized in that: The channel area (22) is provided with a hydrogen channel, a cooling water channel and an air channel; the hydrogen channel, the cooling water channel and the air channel are all waist-shaped holes with the same size.

4. The fuel cell composite bipolar plate according to claim 1, characterized in that: A plurality of linear flow channels (11) are arranged in parallel on the graphite plate (1); the area of ​​the graphite plate (1) accounts for 55% to 75% of the total area of ​​the composite bipolar plate.

5. The fuel cell composite bipolar plate according to claim 1, characterized in that: The resin powder comprises the following components by weight: 8 to 12 parts of graphite powder, 8 to 12 parts of reinforcing material, and 75 to 85 parts of resin; the composite graphite powder comprises the following components by weight: 65 to 75 parts of graphite powder or expanded graphite powder, 15 to 25 parts of resin, and 8 to 12 parts of conductive agent.

6. The fuel cell composite bipolar plate according to claim 5, characterized in that: The reinforcing material includes carbon fiber and glass fiber; the conductive agent includes short carbon fiber and carbon black; the resin includes PPS, PVC, PP and PVDF, and the resin powder is of the same type as the resin in the composite graphite powder.

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