KR101367035B1 - Manufacturing method of composite bipolar plate - Google Patents

Abstract

Disclosed is a method for manufacturing a composite bipolar plate having a low-priced high-quality film structure to fit a redox flow battery. The method for manufacturing a composite bipolar plate for a redox flow battery comprises the steps of: providing a conductive filler; providing a binder resin having a polymeric binder dissolved in a solvent; forming slurry by mixing and stirring the binder resin including 30 to 40 wt% of the conductive filler, 25 to 35 wt% of the solvent and 20 to 30 wt% of the polymeric binder, and 0.5 to 1.5 wt% of a dispersant; producing a film via a tape casting method using the slurry; and stacking and laminating the film. [Reference numerals] (AA) Raw material; (BB) Prototype; (S1) Mix and stir a conductive filler (carbon, graphite, etc) and a binder resin (thermoplastic, thermosetting) (filler : resin = 8: 2); (S2) Produce a film via a tape casting method using produced slurry (ink) (thickness of the film : 5 to 200μm, drying temperature: 80°C, transfer speed: 23.6 m/min); (S3) Laminate the final composite film manufactured by stacking the produced film (lamination condition: 60MPa, 80°C)

Description

MANUFACTURING METHOD OF COMPOSITE BIPOLAR PLATE}

The present invention relates to a method for producing a separator or bipolar plate for a redox flow battery or a fuel cell, and to a method for producing a low cost, high quality thin structure composite bipolar plate suitable for a cell for a redox flow battery.

The redox flow battery is composed of porous electrodes (anode and cathode), bipolar plates, and frames on both sides of the ion exchange membrane (diaphragm). In this case, the bipolar plate is a plate that separates each cell of the stack, and the conductivity is required to minimize the internal resistance of the battery, and the electrolyte is not leaked to the adjacent cells, and thus the characteristic is surely blocked. In addition, since bipolar plates may also generate heat shrinkage due to pressure and temperature change due to electrolyte, drawing characteristics are also required to prevent breakage due to high mechanical strength (tensile strength) and deformation.

Conventional bipolar plates consist of conductive fillers (carbon materials) or structures (carbon ingots), binder resins (thermoplastic or thermosetting resins), and functional additives. Conventionally, in manufacturing a separator plate or a bipolar plate (hereinafter referred to as a 'bipolar plate') of a redox flow battery, the graphite ingot is cut to a dimension required by cutting and roughing, followed by planar polishing. After the resin impregnation process is performed at least three times, there is a process of precise cutting to the required product standard. However, the conventional bipolar plate manufacturing method, it is difficult to apply mass production because the manufacturing cost is very high by performing the cutting process and resin impregnation, there is a problem that the uniformity of the product quality and dimensions change according to the wear rate of the tool. .

On the other hand, in order to solve this problem, the graphite powder and the powder of the thermoplastic or thermosetting binder resin by dry heat mixing to produce a graphite composite and compression molding the graphite composite into a press mold, or injection molding to produce a composite bipolar plate. The composite bipolar plate manufacturing process, which compresses or injects into a mold, is a technique of dissolving and stirring at an appropriate high temperature in order to bind and compound a conductive filler (graphite or carbon) and a binder resin (thermosetting or thermoplastic) before inserting raw materials into the molding process. There is a need for optimal control of the temperature and pressure of the mold during compression and injection molding. In addition, during injection molding, at least 30% or more of the conductive filler (graphite or carbon) is filled to secure conductivity, and thus the flowability (fluidity) of the composite in the mold is very low, and as a result, the quality of the product to be injected and molded is reduced. There is a problem of being uneven. In particular, the bipolar plate according to the prior art has a problem in that the cost of the material increases because there is a limit to the thickness control of the product.

According to embodiments of the present invention to provide a bipolar plate manufacturing method that can be manufactured without using expensive cutting and resin impregnation, and can reduce the manufacturing cost.

It is also an object of the present invention to provide a method for producing a bipolar plate which prevents the uniformity of the quality and dimensions of the product from changing with the wear rate of the tool.

In addition, according to embodiments of the present invention, there is provided a method of manufacturing a bipolar plate that is thin and can reduce the manufacturing cost.

The method of manufacturing a composite bipolar plate for a redox flow battery according to the embodiments of the present invention includes the steps of providing a conductive filler, providing a binder resin in which a polymer binder is dissolved in a solvent, the conductive filler 30 to 40 wt%, Forming a slurry by mixing and stirring the binder resin and 0.5 to 1.5 wt% of the binder resin and the dispersant containing 25 to 35wt% of the solvent and the polymer binder 20 to 30wt% to prepare a film by a tape casting process using the slurry And laminating and laminating the film.

According to one side, the conductive filler, graphite, carbon (Carbon), carbon nanotubes (Carbon Nano Tube, CNT), vapor grown carbon fiber (Vapor Grown Carbon Fiber, VGCF), KB (Ketjen Black), Any one or more of carbon fibers may be used. The conductive filler includes graphite, and the graphite may use particles having a specific surface area of 3.0 m 2 / g or less. Preferably, the graphite may use particles having a specific surface area of 2.0 m 2 / g or less.

According to one side, the content of the conductive filler may have a range of 40wt% to 95wt% in the composite bipolar plate after the lamination is completed. Preferably, the content of the conductive filler may be in the range of 60wt% to 95wt% in the composite bipolar plate. More preferably, the content of the conductive filler may have a range of 80wt% to 90wt% in the composite bipolar plate.

According to one side, the binder resin may comprise a thermoplastic or thermosetting resin. For example, the polymer binder may include polyvinyl butyral (PVB). In addition, the binder resin may include 10 wt% or more of polyvinyl butyral (PVB). In addition, the solvent for dissolving the binder resin may include toluene or ethanol.

According to one side, the thickness of the film may be formed to 10㎛ to 200㎛. Preferably, the thickness of the film may be formed to 50㎛ to 200㎛.

According to one side, the lamination step may be performed by applying a load of 60 MPa at a temperature of 80 ℃ to the laminated film.

As described above, according to the embodiments of the present invention, the conventional high temperature thermal melt compounding process of the conductive filler and the binder resin is changed to a melt compounding process in a solvent at room temperature, and the conventional compression and injection process is a solution film forming tape By changing to the process of manufacturing and laminating by casting method, it overcomes the limitations of the change of physical properties of resin and the mixing ratio of conductive filler by high temperature heat melting, and solves the fluidity (flow) of materials in compression and injection molding. It allows bipolar plate production.

In addition, the composite bipolar plate manufacturing process according to the embodiments of the present invention is easy to control the thickness is not necessary to manufacture a separate compression or injection mold, thereby greatly reducing the manufacturing process cost of the product. In particular, the thickness of the bipolar plate of the redox flow battery tends to be thinned from less than 8 cm to 10 cm in recent years. Therefore, in the case of conventional compression and injection molding, the thinner the thickness, the quality problem and the cost increase problem occur. The present invention has a very advantageous aspect in this respect.

1 is a flowchart illustrating a method of manufacturing a composite bipolar plate according to an embodiment of the present invention.
Figure 2 is a schematic diagram of a tape casting process for explaining a method of manufacturing a composite bipolar plate according to an embodiment of the present invention.
3 is a photograph of a prototype of a composite bipolar plate manufactured according to an embodiment of the present invention.
Figure 4 is a SEM & EDX (Energy Dispersive X-ray Spectroscopy) and EPMA (Electro-Probe Micro Analyzer) analysis results showing the characteristics of the prototype of the composite bipolar plate prepared according to an embodiment of the present invention.
5 is a SEM surface of the slurry composite for each kind of conductive filler in the bipolar plate sheet applied according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments will be described in detail with reference to the accompanying drawings, but the present invention is not limited to or limited by the embodiments. In describing the embodiments, a detailed description of well-known functions or constructions may be omitted so as to clarify the gist of the present invention.

Hereinafter, a method of manufacturing a composite bipolar plate according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. For reference, FIG. 1 is a flowchart illustrating a method of manufacturing a composite bipolar plate according to an embodiment of the present invention, and FIG. 2 is a tape illustrating a method of manufacturing a composite bipolar plate according to an embodiment of the present invention. Schematic diagram of the casting process.

Referring to the drawings, first, a binder slurry and a dispersant dissolved in a conductive filler and a solvent are appropriately stirred at room temperature to prepare a composite slurry (ink) (S1).

Specifically, the conductive filler and the binder resin are mixed at a ratio of 8: 2. Here, the composite slurry is formed by mixing a conductive filler, a binder resin and a dispersant. For example, looking at the composition of the composite slurry, the conductive filler may include 30 ~ 40wt%, 25 ~ 35wt% solvent, 20 ~ 30wt% polymer binder, 0.5 ~ 1.5wt% dispersant.

For example, the conductive filler may be graphite, carbon, carbon nanotube (CNT), vapor grown carbon fiber (VGCF), KB (Ketjen Black), carbon fiber. One or more materials of (Carbon Fiber) may be used. In addition, the binder resin may be a thermoplastic or thermosetting resin. In addition, the binder resin may include a polymer binder, and polyvinyl butyral (PVB) may be used. Toluene or ethanol may be used as the solvent for dissolving the binder resin.

Here, the filling rate of the conductive filler in the bipolar plate finally prepared using the slurry prepared as described above may be increased from at least 40wt% to 95wt%. Preferably, the content of the conductive filler in the bipolar plate can be maintained at least 60wt% or more, it is possible to maintain up to 95wt%. More preferably, it is possible to maintain the content of the conductive filler in the bipolar plate at 80wt% to 90wt%. That is, the content of the conductive filler in the composite slurry is 30 ~ 40wt% of the conductive filler, it is possible to maintain the filling rate of the conductive filler in 40 ~ 95wt% in the bipolar plate is dried and manufactured.

Specifically, the conductive filler uses graphite, and the graphite may be a powder having a specific surface area of 3.0 m 2 / g or less. Preferably, graphite may be a powder having a specific surface area of 2.0 m 2 / g or less. Here, the smaller the specific surface area of graphite, the higher the electrical conductivity for the same binder resin content. A description of the specific surface area and electrical conductivity of the graphite will be described later with reference to FIG. 5.

At this time, the viscosity of the slurry is adjusted by using a solvent to be suitable for the tape casting process, preferably adjusted to about 500 ~ 1000cp level is used.

Next, using the prepared slurry is continuously produced in the form of a film of a constant thickness by a solution film forming method, that is, a tape casting process, and dried at a predetermined temperature to produce a film in the form of a green sheet (S2).

 For reference, the tape casting device 100 according to the present embodiment, as shown in Figure 2, large storage unit 110, transfer unit 120, blade 130, height adjusting unit 140 and It is configured to include a heating unit 150. However, since the tape casting apparatus 100 is not a gist of the present invention, the tape casting apparatus 100 will be briefly described, and detailed configuration and explanation will be omitted.

Storage unit 110 stores the slurry (S), the lower portion is opened to serve to discharge the slurry (S) to the outside. The transfer unit 120 transfers the transfer film T in one direction and applies the slurry S on the transfer unit 120. For example, the transfer unit 120 includes a transfer motor that rotates in one direction, and a gnomer roll, which is connected to them and rotates together and which is conveyed with the conveying film T coated with the slurry S. In addition, the transfer film T may be made of a PET material or the like. The blade 130 is provided on a path through which the slurry S is discharged, and serves to control the thickness of the slurry S applied to the transfer film T by adjusting the discharge amount of the slurry S. In this embodiment, the blade 130 is a configuration consisting of the first blade 132 and the second blade 134 disposed on the discharge path of the slurry (S). However, the present invention is not limited thereto, and the configuration and shape of the blade 130 may be changed in various ways. The height adjusting unit 140 adjusts the height of the blade 130 in the vertical direction so that the thickness of the slurry S applied to the transfer film T can be changed. The heating unit 150 is provided on a path through which the transfer film T is transferred, and supplies heat to the transfer film T.

According to the present invention, by using the tape casting apparatus 100, it is possible to manufacture a bipolar plate using only one process, and to manufacture a thin bipolar plate of less than 1 mm.

The manufacturing process of the bipolar plate by the tape casting device 100 according to the present embodiment is as follows.

First, the composite slurry (S) is put and the height of the blade 130 is adjusted using the height adjusting unit 140.

For example, the thickness of the film P of the green sheet form manufactured by the tape casting process has a thickness of 10-200 micrometers. Preferably, the thickness of the film P is manufactured in 50-200 micrometer thickness. Here, the thickness of the film to be produced is molded to an appropriate thickness according to the height of the blade 130 of the tape casting device 100.

Next, when the transfer motor is rotated so that the moving speed of the transfer film T is maintained at a constant speed, the transfer film T moves on the heating unit 150 in the direction of the arrow, and the slurry S is transferred onto the transfer film T. ) Is coated to a certain thickness. Here, the tape casting device 100 to provide a slurry (S) at a constant speed during the manufacture of the film (P) to produce a film (P), for example, can be produced by transporting at a speed of 23.6 cm / min. .

The heating unit 150 is used to dry and manufacture the bipolar plate while maintaining the temperature of the transport film T at an appropriate temperature. For example, the drying temperature of the film P in the tape casting apparatus 100 is 80 占 폚. Here, the temperature is maintained at about 80 캜 so that heat treatment or drying is performed at once, and shrinkage can prevent peeling and cracking.

As described above, the tape casting method according to the present invention can change the height of the blade, the feed rate, and the heat supplied to the transfer film in response to the viscosity of the slurry, and thus can be used to prepare thin films of various kinds of bipolar plates.

According to this embodiment, the tape casting process can achieve good thickness control and desired surface condition with a low-cost process for producing high quality laminating parts. In addition, by using a tape casting process, good thickness control and desired surface condition can be obtained at low cost. In addition, a bipolar plate sheet for a redox flow battery manufactured by a tape casting process using a composite slurry dissolved in a solvent can be manufactured into a thin film having a level of about 1 mm.

Next, dozens of sheets of the produced film are laminated as needed, and a composite bipolar plate is manufactured by compressing and laminating the laminated film by applying a predetermined force (S3).

For example, lamination may be performed at a temperature of 80 ° C. under a load of 60 MPa. And lamination of the above conditions can be carried out four times each 5 minutes to produce a bipolar plate.

3 to 5 are diagrams for explaining the prototype and surface state of the bipolar plate manufactured according to an embodiment of the present invention.

First, Figure 3 is a photograph of the prototype of the bipolar plate produced by the bipolar plate manufacturing method described above. Referring to FIG. 3, a bipolar plate sheet for a redox flow battery, which is a thin film having a level of about 1 mm, may be manufactured by using a tape casting process.

4 are photographs showing the results of SEM & EDX (Energy Dispersive X-ray Spectroscopy or XEDS) and EPMA (Electro-Probe Micro Analyzer) analysis on the prototype surface of FIG. 3. Referring to the drawings, in FIG. 4, in the left figure, green shows a distribution diagram of the conductive filler (graphite), and in the right figure, red shows the strength of the conductive filler. Referring to FIG. 4, it can be seen that the distribution of the conductive filler (graphite) increases due to a phenomenon almost identical to that of the left EDX result.

5 is an SEM surface observation result of the slurry composites of each kind of conductive filler in the bipolar plate sheet prepared according to the embodiments of the present invention, the SEM surface of the slurry composites of each type of the conductive filler in the applied bipolar plate sheet. In Figure 5, Samples 1 to 4 are samples of bipolar plates, each made using different kinds of graphite as conductive fillers. For reference, Samples 1 to 4 were prepared by mixing four kinds of graphite and a resin binder in the same ratio (the ratio of graphite is 80 wt% or more) to prepare a film by a tape casting method. In this case, the ratio of graphite was described with respect to the composition ratio of the graphite filler and resin only in the state in which the weight of the solvent was removed from the slurry composition, that is, in a dried state after bipolar casting. That is, the films prepared by mixing different kinds of graphite in the same resin binder and using a tape casting method are referred to as Samples 1 to 4, respectively. In addition, the specific surface area and particle size of graphite used in Samples 1 to 4 are as described in FIG. 5.

And in order to confirm the surface state of the film manufactured by the samples 1-4, the relationship of the shape and electrical resistance characteristic of the film surface was shown in the state which did not compress the manufactured film. Referring to FIG. 5, as can be seen from the drawings, SEM surface observation results of Samples 1 to 4 show that the surfaces of Samples 1 and 2 and Samples 3 and 4 are different from each other. Specifically, when the characteristics of the graphite as a variable at the same resin content, it can be seen that the smaller the specific surface area than the particle size and shape of the graphite, the more uniform the dispersion and the impregnation of the resin. In the case of Samples 1 and 2, the shape of the graphite is so clear that the resin binder is hardly visible, but Samples 3 and 4 show that the resin binder is aggregated on the graphite surface. Therefore, it can be seen that graphite having a small specific surface area may exhibit a relatively low electrical resistance (743 mΩ.cm) despite the same resin content.

Then, using the graphite of Sample 1, a slurry having a graphite content of about 80 wt% was prepared, and a composite bipolar plate was manufactured under the above-described tape casting method, lamination and lamination conditions, and electrical resistance was measured. The value of mΩ.cm level could be confirmed.

For reference, a redox flow battery includes a porous electrode (anode and cathode), a bipolar plate, and a frame on both sides of an ion exchange membrane (diaphragm). The bipolar plate manufactured according to the above-described manufacturing method is used as a plate separating each cell from the stack, minimizes the internal resistance of the battery, and blocks the leakage of the electrolyte to the adjacent cells. In addition, since the bipolar plate has high mechanical strength and stretching characteristics, it is possible to prevent breakage due to deformation and heat shrinkage due to pressure and temperature change by the electrolyte.

This invention can manufacture a composite (slurry) by the solvent dissolution method, and can manufacture the composite bipolar plate for redox flow batteries of low cost high quality by the solution film-forming method (tape casting).

According to the embodiments of the present invention, a process of changing the high temperature hot melt compounding process of the conductive filler and the binder resin into a solution complexing process in a normal temperature solvent, and manufacturing and laminating by a tape casting process, which is a solution film forming method, instead of a compression and injection process, is used. As a result, it is possible to manufacture high quality composite bipolar plates by overcoming the limitations of the physical properties of the resin due to high temperature heat melting and the blending ratio of the conductive filler, and solving the fluidity (flow) of the material in compression and injection molding.

In addition, according to the embodiments of the present invention, the composite bipolar plate manufacturing process not only facilitates the fluidity (flow) problem, but also easy to control the thickness of the production of a product because it is not necessary to manufacture a separate compression or injection mold The process cost is greatly reduced. In particular, the thickness of the bipolar plate of the redox flow battery tends to be thinned from less than 8 cm to 10 cm. Therefore, in the case of conventional compression and injection molding, the thinner the thickness, the quality problem and the cost increase problem occur. The present invention has a very advantageous aspect in this respect.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (14)

Providing a conductive filler;
Providing a binder resin in which a polymer binder is dissolved in a solvent;
Forming a slurry by mixing and stirring the binder resin and the dispersant 0.5 to 1.5 wt%, including the conductive filler 30 to 40 wt%, the solvent 25 to 35 wt%, and the polymer binder 20 to 30 wt%;
Preparing a film by a tape casting process using the slurry; And
Stacking and laminating the film;
Method for producing a composite bipolar plate comprising a.
The method of claim 1,
The conductive filler may be graphite, carbon, carbon nanotube (CNT), vapor grown carbon fiber (VGCF), KB (Ketjen Black), carbon fiber (Carbon Fiber). A method for producing a composite bipolar plate in which at least one of)) is used.
3. The method of claim 2,
The conductive filler comprises graphite,
The graphite has a specific surface area of 3.0 m 2 / g or less method for producing a composite bipolar plate.
The method of claim 3,
The graphite has a specific surface area of 2.0 m 2 / g or less method for producing a composite bipolar plate.
The method of claim 1,
The conductive filler content, the method of producing a composite bipolar plate having a range of 40wt% to 95wt% in the composite bipolar plate after the lamination is completed.
The method of claim 5,
The conductive filler content is a method for producing a composite bipolar plate having a range of 60wt% to 95wt% in the composite bipolar plate.
The method of claim 5,
The content of the conductive filler is a method for producing a composite bipolar plate having a range of 80wt% to 90wt% in the composite bipolar plate.
The method of claim 1,
The binder resin is a method for producing a composite bipolar plate comprising a thermoplastic or thermosetting resin.
The method of claim 1,
The polymer binder is a method for producing a composite bipolar plate containing polyvinyl butyral (PVB).
10. The method of claim 9,
The binder resin is a method for producing a composite bipolar plate containing 10 wt% or more of polyvinyl butyral (PVB).
The method of claim 1,
The solvent for dissolving the binder resin is a method for producing a composite bipolar plate containing toluene or ethanol.
The method of claim 1,
The thickness of the film is a method for producing a composite bipolar plate of 10㎛ to 200㎛.
The method of claim 12,
The thickness of the film is 50㎛ to 200㎛ manufacturing method of the composite bipolar plate.
The method of claim 1,
The lamination step is a method of manufacturing a composite bipolar plate is carried out by applying a load of 60 MPa at a temperature of 80 ℃ to the laminated film.

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