Method for producing graphite-based monopolar plates for bipolar plates, graphite-based monopolar plate and bipolar plate as well as an apparatus for producing graphite-based monopolar plates

Abstract

The invention relates to a method for producing graphite-based monopolar plates for graphite-based bipolar plates, in particular for use in fuel cells, the method comprising the following steps: a) providing (100) a graphite-based sheet material, b) roll-forming the sheet material provided, by means of calendering (200) and embossing (300), c) impregnating (400) the formed sheet material, d) washing (500) the impregnated sheet material, e) curing (700) the washed sheet material and f) separating (900) the cured sheet material into graphite-based monopolar plates. The invention also relates to a graphite-based monopolar plate produced by a method according to the invention, to a graphite-based bipolar plate comprising two graphite-based monopolar plates according to the invention as well as to an apparatus for producing graphite-based monopolar plates by a method according to the invention.

Description

[0001] Method for producing graphite-based monopolar plates for bipolar plates, graphite-based monopolar plate and bipolar plate and a device for producing graphite-based monopolar plates

[0002] The invention relates to a method for producing graphite-based monopolar plates, a monopolar plate produced by the method and a bipolar plate comprising two monopolar plates, as well as a device for producing graphite-based monopolar plates.

[0003] Bipolar plates are very flat components with structured surfaces that comprise two firmly connected monopolar plates. Each monopolar plate forms a pole, anode, and cathode. Bipolar plates are a central component of fuel cells, whose functions include the homogeneous supply of reaction gases, cooling, spatial separation of the half-cells, and mechanical stability. In addition to meeting performance requirements such as high electrical conductivity and a long service life, low manufacturing costs are essential.

[0004] To date, graphite-based monopolar plates for bipolar plates have been manufactured in batch processes, i.e., in discontinuous production, by performing the individual process steps for each monopolar plate individually. This requires numerous manual steps, resulting in higher manufacturing costs and only limited scalability to larger production volumes. EP4037040A1 and CN212113895U propose roll forming to increase the production of monopolar plates. The starting material for the monopolar plates, for example, expandable graphite, can be first calendered and then embossed.

[0005] However, even when using roller forming, it is still common practice to separate the monopolar plates after the embossing process or to use individual plates directly in the flatbed embossing process. After embossing, the separated monopolar plates or individual plates are impregnated with a resin to seal the media channels of the plate. This is usually done under vacuum, and excess resin is then washed or blown off the surface. Finally, the monopolar plates are dried, for example, with heat or compressed air, and cured. Optionally, an outgassing process by heating the monopolar plates can also be followed.

[0006] A disadvantage of the batch-based implementation of this process is that the production of monopolar plates is very time-consuming, as the monopolar plates have to be transported from one station to the next.

[0007] It is the object of the invention to further develop the method mentioned at the outset in such a way that manual work steps, in particular transport of the graphite-based monopolar plates from one station to the next, can be avoided or at least reduced.

[0008] This object is achieved by a method having the features of claim 1, a graphite-based monopolar plate according to claim 18, a graphite-based bipolar plate according to claim 20, and a device for producing graphite-based monopolar plates according to claim 21. Advantageous embodiments are the subject of the respective dependent claims.

[0009] The inventive method for producing graphite-based monopolar plates for graphite-based bipolar plates, in particular for use in fuel cells, comprises the following steps: a. Providing a graphite-based web material, b. Roll forming the provided web material by calendering and embossing, c. Impregnating the formed web material, d. Washing the impregnated web material, e. Curing the washed web material, and f. Singling the cured web material into graphite-based monopolar plates. Because the inventive method performs singulation as the last step after curing, the invention enables the production of monopolar plates in a web-based process. Instead of singulating the monopolar plates immediately after embossing and performing the subsequent steps in a batch process, the monopolar plates remain in a web.This can increase the level of automation, thereby reducing production costs and improving scalability.

[0010] Preferably, the method comprises winding the web material after the roll forming process and unwinding the web material after the impregnation process. The invention thus allows the impregnation process to take place in the wound state of the embossed web material.

[0011] Impregnation can involve saturating the wound web material with a resin to seal structures introduced into the monopolar plates during embossing, such as media channels. After impregnation, the impregnated web material is unwound and can be made available for subsequent process steps as a continuous strip.

[0012] To remove excess resin, washing can be performed by spraying the top and bottom surfaces of the web material with a washing medium, by pulling the web material through a bath of a washing medium, or by applying a film of a washing medium to the top and bottom surfaces of the web material. Washing can be performed at a temperature between 20 °C and 90 °C, for example, by adjusting the washing medium and / or the surrounding environment to the appropriate temperature.

[0013] Washing is preferably carried out using water as the washing medium. However, additives may be added to the water to, for example, improve the removal of excess resin.

[0014] Preferably, excess water can be blown off the web material after washing is complete. This is particularly preferably done after the relevant section of the web material has left a washing area.

[0015] Curing preferably involves heating the web material to or above the activation temperature of a resin used in impregnating the web material. This can be done, for example, in a curing oven. Curing preferably involves restricting the freedom of movement of the web material in the vertical direction. The vertical direction is understood here to be a direction perpendicular to the length and width of the web material. This can be achieved, for example, by curing the web material in a press, in particular in a flat press. This can prevent or at least reduce warping of the web material.

[0016] Separation may involve separating embossed monopolar plates from the web material. This can be done, for example, by cutting the web material into sections corresponding to the embossed pattern.

[0017] After washing, the process preferably includes drying the web material, for example, in a drying oven. This allows excess water to evaporate from the web material. Particularly preferably, the web material can be preheated for the subsequent process steps. The preheating temperature is, for example, between 50°C and 80°C.

[0018] The process further preferably comprises outgassing the web material after curing. This allows the web material to outgas the resin components that did not react during curing, as well as the reaction products formed during curing. Outgassing particularly preferably takes place at an outgassing temperature below the decomposition temperature of the resin used during impregnation, in particular below 160°C.

[0019] Pure graphite can be used as the graphite-based sheet material, but a graphite composite material, particularly expanded graphite, is preferred. The graphite-based sheet material can comprise a thermoset or thermoplastic as a matrix material. Carbon black, graphene, carbon fibers, or expanded graphite can also be used as fillers to improve the properties of the sheet material in terms of conductivity, strength, and / or stiffness.

[0020] A further aspect of the invention relates to a graphite-based monopolar plate produced by a method according to the invention. The invention thus makes it possible to provide a graphite-based monopolar plate cost-effectively. The monopolar plate preferably has a thickness of 0.05 to 1.5 mm. Furthermore, the invention is directed to a graphite-based bipolar plate comprising two graphite-based monopolar plates according to the invention. This makes it possible to provide a cost-effectively manufactured bipolar plate.

[0021] Finally, the invention relates to a device for producing graphite-based monopolar plates according to a method according to the invention. For this purpose, the device comprises a first unwinder, rolls for calendering and embossing, an impregnation station, and devices for washing, curing, and separating. The invention thus enables the web-based production of graphite-based monopolar plates, which can increase production speed compared to batch-based production.

[0022] For curing, the device may, for example, comprise a curing oven, and for separating, a cutting machine.

[0023] Preferably, the device comprises a winder and a second unwinder. The winder is configured to wind the graphite-based web material after embossing, so that the web material can be impregnated in the rolled-up state in the impregnation station, for example, by soaking it in resin. The second unwinder is configured to unwind the impregnated web material and feed it to the washing device.

[0024] The device preferably comprises at least one pair of rollers for calendering and one pair of rollers for embossing. The distance between two rollers of a roller pair can be adjustable. This allows the thickness of the web material and thus the resulting thickness of the graphite-based monopolar plates to be varied.

[0025] Furthermore, the device can preferably comprise at least two pairs of calendering rollers. The distance between the rollers of at least one pair of calendering rollers can differ from the distance between the rollers of at least one other pair of calendering rollers. Thus, the invention enables the thickness of the web material to be reduced stepwise, for example, by having a first pair of calendering rollers with a greater distance between the rollers than a second pair of calendering rollers. Further details of the invention are explained with reference to the following figures. In the figures:

[0026] Figure 1 shows a method for producing a monopolar plate according to the prior art; and

[0027] Figure 2 shows a method according to the invention for producing graphite-based monopolar plates for graphite-based bipolar plates.

[0028] Fig. 1 shows a prior art method for producing a monopolar plate for a graphite-based bipolar plate. Production is predominantly carried out in a batch-based process. The starting material is provided via an unwinder 100, which is then calendered 200 with calendering rolls and subsequently embossed 300 with embossing rolls. After the embossing process, the plates are separated 310 by a cutting tool. In alternative methods, web material is not provided as the starting material via an unwinder 100, but rather individual plates are used in the flatbed embossing process.

[0029] What both processes have in common is that the subsequent process steps, such as impregnation, washing, and curing, are carried out in batches, which is time-consuming. Because all the panels must be transported from one station to the next, sometimes manually.

[0030] Fig. 2 shows a method for producing graphite-based monopolar plates for graphite-based bipolar plates, which enables a web-based process and thus reduces or avoids transport processes and increases the degree of automation, so that production costs can be reduced and / or production speed can be increased. The method comprises the following steps: a. providing 100 a graphite-based web material, b. roll forming the provided web material by calendering 200 and embossing 300, c. impregnating 400 the formed web material, d. washing 500 the impregnated web material, e. curing 700 the washed web material, and f. singulating 900 the cured web material into graphite-based monopolar plates.The method can be carried out with a device for producing graphite-based monopolar plates, which comprises a first unwinder, rolls for calendering and embossing, an impregnation station as well as a washing device, a drying oven, a curing oven, a degassing oven and a cutting tool for separating.

[0031] The supply takes place via the first unwinder. The graphite-based sheet material here is expandable graphite, but can alternatively be pure graphite or another graphite composite material. Furthermore, the graphite-based sheet material can comprise a thermoset or thermoplastic as a matrix material and / or carbon black, graphene, carbon fibers, or expandable graphite as a filler.

[0032] In the method shown in Figure 2, the device comprises a winder and a second unwinder. This allows the web material to be wound up 370 after the roller forming 200, 300, and unwound 450 after the impregnation 400, so that the embossed web material can be impregnated in the wound state. During the impregnation 400, the wound web material can thus be impregnated with a resin.

[0033] For calendering 200 and embossing 300, the device here comprises a pair of calendering rollers and a pair of embossing rollers, respectively. The distance between two rollers of a roller pair is adjustable. This allows the distance to be adjusted so that monopolar sheets of the desired thickness can be produced.

[0034] In alternative embodiments not shown, the device can comprise at least two pairs of calendering rollers. In addition, the distance between the rollers of at least one pair of calendering rollers can differ from the distance between the rollers of at least one other pair of calendering rollers. Thus, the device enables a desired thickness of the web material to be achieved in stages.

[0035] After impregnation 400, the resin-impregnated, wound web material is unwound 450 by the second unwinder and fed as a web to the washing device. The washing process serves to remove excess resin from the surface of the web material. Washing 500 is carried out here by spraying the top and bottom sides of the web material, with water at a temperature of 55°C being used as the washing medium. In alternative embodiments, washing 500 can be carried out by pulling the web material through a water bath or by providing a liquid film on the top and bottom sides of the web material. Additives can also be added to the water, and the temperature can vary between 20°C and 90°C. After leaving the washing device, excess water can be blown off.

[0036] After washing 500, the web material is dried 600 in a drying oven. Excess water evaporates from the web material. Furthermore, the web material is preheated to a temperature of 65°C for subsequent processes. In alternative embodiments, the drying temperature may vary, but is in a range of 50°C to 80°C.

[0037] After washing 500 and drying 600, the method comprises curing 700 in the curing oven, in which the web material is heated to or above the activation temperature of the resin used in impregnating 400 the web material. To prevent or at least reduce warping of the web material, the web material's freedom of movement is restricted during curing 700. For this purpose, the curing oven here comprises a flat press, so that the web material cannot expand freely in the vertical direction, relative to the length and width of the web material.

[0038] Following curing (700), the process involves outgassing (800) the web material in the outgassing oven. This process releases unreacted resin components and reaction products formed during curing (700). The outgassing temperature is below the decomposition temperature of the resin, in this case below 160°C.

[0039] Finally, the separation 900 occurs by separating embossed monopolar plates from the web material. This is done here by the cutting tool. The resulting graphite-based monopolar plates have a thickness of 0.05 to 1.5 mm, depending on the desired application. Graphite-based bipolar plates can comprise two graphite-based monopolar plates that are firmly bonded together.

[0040] The features of the invention disclosed in the above description, in the drawings and in the claims may be essential for the realization of the invention both individually and in any combination. List of reference symbols

[0041] 100 Ready en

[0042] 200 calendering

[0043] 300 coins

[0044] 310 cutting

[0045] 370 Winding

[0046] 400 Impregnation

[0047] 450 Unwinding

[0048] 500 washes

[0049] 600 Drying

[0050] 700 Curing

[0051] 800 outgassing

[0052] 900 Separation

Claims

Claims:

1. A method for producing graphite-based monopolar plates for graphite-based bipolar plates, in particular for use in fuel cells, comprising the steps of: a. providing (100) a graphite-based web material, b. roll forming the provided web material by calendering (200) and embossing (300), c. impregnating (400) the formed web material, d. washing (500) the impregnated web material, e. curing (700) the washed web material and f. singulating (900) the cured web material to form graphite-based monopolar plates.

2. Method according to claim 1, which comprises winding (370) of the web material after the roll forming (200, 300) and unwinding (450) of the web material after the impregnation (400), so that the impregnation (400) takes place in the wound state of the embossed web material.

3. The method according to claim 1 or 2, wherein the impregnation (400) comprises saturating the wound web material with a resin.

4. Method according to one of the preceding claims, wherein the washing (500) is carried out by spraying the top and bottom sides of the web material with a washing medium, by pulling the web material through a bath of a washing medium or by providing a film of a washing medium on the top and bottom sides of the web material.

5. Method according to one of the preceding claims, wherein the washing (500) takes place at a temperature between 20 °C and 90 °C.

6. Method according to one of the preceding claims, wherein the washing (500) is carried out with water as the washing medium.

7. A method according to any one of the preceding claims, wherein the curing (700) comprises heating the web material to or above the activation temperature of a resin used in impregnating (400) the web material.

8. Method according to one of the preceding claims, wherein the curing (700) comprises restricting the freedom of movement of the web material in the vertical direction, for example by curing (700) of the web material in a press, in particular in a flat press.

9. Method according to one of the preceding claims, wherein the singulating (900) comprises separating embossed monopolar plates from the web material.

10. Method according to one of the preceding claims, which comprises drying (600) the web material after washing (500).

11. The method of claim 10, wherein drying (600) comprises preheating the web material.

12. A method according to any one of claims 11 or 12, wherein the preheating is carried out to a temperature between 50 °C and 80 °C.

13. Method according to one of the preceding claims, which comprises outgassing (800) of the web material after curing (700).

14. The method according to claim 13, wherein the outgassing (800) takes place at an outgassing temperature below a decomposition temperature of a resin used in the impregnation (400), in particular below 160 °C.

15. Method according to one of the preceding claims, wherein the graphite-based web material comprises pure graphite or a graphite composite material, in particular expandable graphite.

16. Method according to one of the preceding claims, wherein the graphite-based web material comprises a thermosetting or thermoplastic as matrix material.

17. Method according to one of the preceding claims, wherein the graphite-based web material comprises carbon black, graphene, carbon fibers and / or expandable graphite as filler.

18. A graphite-based monopolar plate produced by a process according to any one of claims 1 to 17.

19. A graphite-based monopolar plate according to claim 18, which has a thickness of 0.05 to 1.5 mm.

20. A graphite-based bipolar plate comprising two graphite-based monopolar plates according to any one of claims 18 or 19.

21. Apparatus for producing graphite-based monopolar plates by a method according to any one of claims 1 to 17, comprising a first unwinder, rolls for calendering and embossing, an impregnation station and devices for washing, curing and separating.

22. Apparatus according to claim 21 comprising a winder and a second unwinder.

23. Apparatus according to claim 21 or 22, each comprising at least one pair of rollers for calendering and one pair of rollers for embossing.

24. Device according to claim 23, wherein a distance between two rollers of a roller pair is adjustable.

25. Device according to one of claims 21 to 24, which comprises at least two pairs of rollers for calendering.

26. Apparatus according to claim 25, wherein a distance between the rollers of at least one pair of rollers for calendering differs from a distance between the rollers of at least one other pair of rollers for calendering.

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