CN112086653B - Graphite felt structure for flow battery and flow battery using same - Google Patents
Graphite felt structure for flow battery and flow battery using same Download PDFInfo
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- CN112086653B CN112086653B CN201910517172.9A CN201910517172A CN112086653B CN 112086653 B CN112086653 B CN 112086653B CN 201910517172 A CN201910517172 A CN 201910517172A CN 112086653 B CN112086653 B CN 112086653B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/96—Carbon-based electrodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
- H01M8/184—Regeneration by electrochemical means
- H01M8/188—Regeneration by electrochemical means by recharging of redox couples containing fluids; Redox flow type batteries
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The utility model provides a graphite felt structure and use its redox flow battery for redox flow battery, it can reduce contact resistance, improves battery conversion efficiency, simultaneously, reduces pile internal pressure, ensures the leakproofness, guarantees the electrolyte velocity of flow, avoids the battery to scrap because of local overcharge to prolong the pile life-span. The planar direction includes: a first portion composed of a graphite felt material, and a second portion composed of a graphite felt and/or a material other than a graphite felt, the second portion having two or more axes of symmetry in the plane direction, the axes of symmetry passing through a center of the graphite felt structure in the plane direction, the graphite felt structure satisfying at least one of the following conditions (1) and (2): condition (1): the compression modulus of the second portion is greater than the compression modulus of the first portion; condition (2): the second portion has a thickness greater than a thickness of the first portion.
Description
Technical Field
The invention belongs to the field of flow battery equipment, and particularly relates to a graphite felt structure for a flow battery and the flow battery using the same.
Background
The flow battery technology has natural advantages of large-scale energy storage: the size of the electric storage quantity is linearly proportional to the volume of the electrolyte, and the charging and discharging power is determined by the size and the quantity of the galvanic pile, so that the flow battery with different charging and discharging powers from kW to MW level and different energy storage quantities from 1 hour to several days of sustainable discharging can be designed according to the requirements.
An important component inside the flow cell stack is the graphite felt. The general flow battery graphite felt assembly is that the whole graphite felt, a diaphragm and a graphite bipolar plate are sequentially overlapped, and the whole graphite felt is pressurized during assembly. The graphite felt is compressed while sealing is guaranteed, so that the contact resistance between the graphite felt and the graphite bipolar plate is reduced, and the energy conversion efficiency is improved.
The main drawbacks of this technique are as follows: 1. in order to ensure sealability and reduce contact resistance, the graphite felt may be excessively compressed. Therefore, the flow rate of the liquid electrolyte in the electric pile is reduced, the possibility of overcharge of the electrolyte in the electric pile is greatly increased, and the electric pile is blocked due to overcharge and finally scrapped. 2. Because the components in the stack are all made of flexible materials, it is difficult to ensure that the compression rate of each electric felt of dozens or even hundreds of single cells in the stack is the same. If there are a few felts that are too compressed, the corresponding cells will necessarily be overcharged, with the end result being that the stack will necessarily fail. 3. On the other hand, the graphite felt is compressed excessively, so that the pressure inside the pile is too high for a long time. Under the condition of internal high pressure, the sealing part is gradually invalid, and the electrolyte leakage condition occurs in the galvanic pile. And the resistance of the electrolyte is too high, so that the electrolyte pump runs in an overload mode, and the service life is greatly reduced. On the contrary, if the graphite felt is not compressed enough, the contact resistance is increased and the energy conversion efficiency of the battery is reduced.
Therefore, how to keep the lower resistance of the electrolyte and reduce the internal pressure of the pile while ensuring the reduction of the contact resistance is a key problem which is difficult to simultaneously consider under the existing graphite felt compression method.
Cited document 1CN206758557U
Cited document 2CN206516703U
Disclosure of Invention
Problems to be solved by the invention
In view of the above-mentioned shortcomings in the prior art, an object of the present invention is to provide a graphite felt structure for a flow cell and a flow cell using the same, which can reduce contact resistance and improve cell conversion efficiency, and at the same time, can reduce the internal pressure of a stack during assembly to ensure sealing performance, and at the same time, can ensure the flow rate of an electrolyte, and avoid the rejection of the cell due to overcharge, thereby prolonging the life of the stack.
Means for solving the problems
The technical scheme adopted by the invention to achieve the purpose is as follows.
The invention firstly provides a graphite felt structure for a flow battery, which is characterized by comprising the following components in a plane direction: a first part consisting of graphite felt material, and a second part consisting of graphite felt and/or a material other than graphite felt,
the second portion has two or more symmetry axes in the plane direction, the symmetry axes passing through the center of the graphite felt structural body in the plane direction,
the graphite felt structure satisfies at least one of the following conditions (1) and (2):
condition (1): the compression modulus of the second portion is greater than the compression modulus of the first portion;
condition (2): the second portion has a thickness greater than a thickness of the first portion.
According to the graphite felt structure described above,
according to the graphite felt structure described above, in the case where a plurality of second portions are included, each of the plurality of second portions satisfies at least one of the conditions (1) and (2), respectively.
The graphite felt structure according to any one of the above, wherein in the condition (1), the compressive modulus has a continuous gradient change or a discontinuous gradient change between the second portion and the first portion,
in the condition (2), the thickness has a continuous gradient change or a discontinuous gradient change between the second portion and the first portion.
The graphite felt structure according to any one of the above, wherein the material other than graphite felt is a polymer, a carbon material, or a combination thereof.
The graphite felt structure according to any one of the above, wherein the second portion is composed of a graphite felt, and satisfies the following condition (3) or (4):
condition (3): the thickness of the second portion of graphite felt is the same as the thickness of the first portion of graphite felt, and the bulk density of the second portion of graphite felt is greater than the bulk density of the first portion of graphite felt;
condition (4): the second portion of graphite felt has a bulk density that is the same as the first portion of graphite felt, and the second portion of graphite felt has a thickness that is greater than the first portion of graphite felt.
The graphite felt structure according to any one of the preceding claims, wherein the graphite felt of the first portion has a bulk density of 0.08-0.3g/cm in a state in which the graphite felt structure is assembled into a flow battery by compression3The range of (1).
The graphite felt structure according to any one of the preceding claims, wherein the graphite felt of the first portion has a bulk density of 0.08-0.3g/cm in a state in which the graphite felt structure is assembled into a flow battery by compression3The range of (1).
The graphite felt structure according to any one of the above, wherein a compression amount of the graphite felt of the first portion is 0 to 40% in a state where the graphite felt structure is assembled into a flow battery by compression.
The graphite felt structure according to any one of the above, wherein the first partial area accounts for 60% or more of a total area of the graphite felt structure in a planar direction.
The graphite felt structure according to any one of the above, which is obtained by splicing or laminating a plurality of graphite felts, or by splicing or laminating at least one graphite felt and at least one material other than the graphite felt.
Further, the present invention also provides a flow battery that is manufactured using the graphite felt structure according to any one of the above.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the graphite felt structure body for the flow battery and the flow battery using the graphite felt structure body, the contact resistance can be reduced, the battery conversion efficiency is improved, meanwhile, the internal pressure of the galvanic pile is reduced, the sealing performance is ensured, the flow velocity of electrolyte is ensured, the rejection of the battery due to local overcharge is avoided, and therefore the service life of the galvanic pile is prolonged.
Drawings
Fig. 1 is a plan view showing an example of the structure of the graphite felt of the present invention.
Fig. 2 is a side view showing an example of the constitution of the graphite felt of the present invention.
Fig. 3 is a side view showing an example of the constitution of the graphite felt of the present invention.
Fig. 4 is a side view showing an example of the constitution of the graphite felt of the present invention.
Fig. 5 is a side view showing an example of the constitution of the graphite felt of the present invention.
Description of the reference numerals
1 first part
2 second part
Detailed Description
The following describes specific embodiments of the present invention. It should be noted that the following may be considered as a specific list or illustration of various embodiments of the invention and should not be considered as a limitation on the embodiments of the invention.
The invention first provides a graphite felt structure for a flow battery, which comprises a first part and a second part which are different from each other in compression modulus and/or thickness in a plane direction.
The graphite felt material is obtained by processing a carbon felt at a high temperature of more than 2000 ℃ in vacuum or inert atmosphere, and the carbon content of the graphite felt material is higher than that of the carbon felt and reaches more than 99%. The graphite felt is divided into three types, namely asphalt-based graphite felt, polyacrylonitrile-based graphite felt and viscose-based graphite felt, due to the different raw felts. The graphite felt structure of the present invention comprises a first portion and a second portion having different compressive moduli and/or different thicknesses in the planar direction, relative to the uniform structure that conventional graphite felts generally have. It is obvious that the graphite felt has a uniform material structure in the plane direction unlike the conventional graphite felt. The inventors have found that the graphite felt of the uniform material structure described above is originally thought to have the performance of being able to be easily assembled and to avoid non-uniformity in the distribution of resistance within the graphite felt laminate during assembly, preventing a reduction in the efficiency of the flow battery. But the actual situation is not satisfactory. The inventors speculate that this is determined by the compression of the graphite felt itself in a homogeneous structure: the excessive compression can cause the excessive internal pressure of the whole electric pile, the flow rate of the electrolyte is reduced, and the local overcharge phenomenon is easy to generate locally, so that the electric pile is scrapped; too little compression can cause too much contact resistance between the graphite felt and the bipolar plate, reducing the energy conversion efficiency of the battery. The homogeneous structure of the graphite felt makes it difficult to satisfy both the purpose of ensuring a good flow rate of the electrolyte and the reduction of the contact resistance. According to the technical scheme of the invention, due to the existence of the second part with larger compression modulus and/or thickness, the overall pressure is reduced when the graphite felts in the stack are laminated, and lower contact resistance and good electrolyte flow rate can be still ensured, so that the efficiency of the flow battery is improved.
Specifically, the graphite felt structure of the present invention is characterized by comprising, in a planar direction: a first part consisting of graphite felt material, and a second part consisting of graphite felt and/or a material other than graphite felt,
the second portion has two or more symmetry axes in the plane direction, the symmetry axes passing through the center of the graphite felt structural body in the plane direction,
the graphite felt structure satisfies at least one of the following conditions (1) and (2):
condition (1): the compression modulus of the second portion is greater than the compression modulus of the first portion;
condition (2): the second portion has a thickness greater than a thickness of the first portion.
In the graphite felt structure of the present invention, the first portion and the second portion may each include one or more. In the case where a plurality of first portions and/or second portions are included, at least one first portion and at least one second portion may satisfy at least one of the above-described conditions (1) and (2).
In the present application, the phrase "the second portion has two or more symmetry axes in the plane direction, the symmetry axes passing through the center of the graphite felt structure in the plane direction", and when there is one second portion, means that the shape of the projection of the second portion in the plane direction is symmetrical with respect to at least two straight axes passing through the center of the graphite felt structure in the plane direction; when the second portion is a plurality of second portions, the distribution of projections of the plurality of second portions in the plane direction is axisymmetric with respect to at least two straight lines passing through the center of the graphite felt structure in the plane direction.
It should be noted that, in the case that the shape or distribution of the projection of the second portion in the plane direction is in an irregular structure, or an S-shaped or serpentine structure, etc., does not satisfy the structure of the present application, the resistance of the electrolyte flowing in the stack is locally or wholly increased, which has an unrealistic requirement for the liquid circulation pump, and when the flow battery operates, if even a small change occurs in the relative position of the first portion and the second portion, the resistance of the electrolyte is affected, which causes the flow rate difference between the single cells, directly causes the overcharge damage of some single cells, and finally the entire stack fails.
In some preferred embodiments of the present invention, a plurality of second portions are included, and it is further preferable that each of the plurality of second portions satisfies at least one of the above-described conditions (1) and (2), respectively.
In some embodiments of the invention, the plurality of second portions may not contact each other. In this case, it is preferable that the plurality of second portions are all located inside (i.e., in a region other than the peripheral edge portion) of the graphite felt structure, in other words, the peripheral edge portion of the graphite felt structure is constituted only by the first portion. In this case, from the viewpoint of the workability of production, it is more preferable that the plurality of second portions are spaced from the peripheral edge portion of the graphite felt structure by at least 0.5 cm.
In some preferred embodiments of the present invention, the second portion is present in plural and forms a regular pattern in a planar direction, more preferably, the second portions are formed in the same planar shape and/or material as each other, and most preferably, the second portions are formed in the same planar shape and material as each other. Here, the "planar shape" refers to a projected shape in a planar direction. By arranging the second portion as described above, the graphite felt has excellent uniformity in the planar direction in a state of being incorporated in the flow battery, and can more evenly achieve both maintenance of the flow rate of the electrolyte and reduction of the contact resistance. Further, such a structure can provide convenience in workability, and also can make the respective second portions more uniform in a compressed state when assembling the graphite felt laminate.
In the above condition (1), the compression modulus of the second portion is not particularly limited as long as it is larger than that of the first portion. The compression modulus may have a continuous gradient change or a discontinuous gradient change between the second portion and the first portion, and the magnitude of the gradient is not particularly limited and may be appropriately selected within a range that does not affect the effect of the present application.
The "compressive modulus" refers to a compressive modulus of the graphite felt structure in the thickness direction thereof, and is a value obtained by dividing a compressive stress when the graphite felt structure is subjected to the compressive stress in the thickness direction thereof by an amount of elastic deformation occurring in the thickness direction. The determination method comprises the following steps: the original thickness H of the graphite felt is firstly measured under the condition of 0 stress by using an Instron device under the condition of room temperature0(ii) a Under the application of stress p1In the case of (2), the actual thickness H of the graphite felt was measured1(ii) a Using the formula E ═ p1*H0/(H0-H1) The compressive modulus of the graphite felt is obtained.
Preferably, the ratio of the compression modulus of the second part to the compression modulus of the first part is (1-10): 1, more preferably (2-7): 1. in general, the compression modulus of the first part, in other words the compression modulus of the graphite felt material constituting the first part, is 10 to 1000Pa, preferably 10 to 500 Pa.
In addition, in the condition (2), the thickness of the second portion is not particularly limited as long as it is larger than that of the first portion. The thickness may have a continuous gradient change or a discontinuous gradient change between the second portion and the first portion, and the magnitude of the gradient is not particularly limited and may be appropriately selected within a range that does not affect the effect of the present application. The ratio of the thickness of the second portion to the thickness of the first portion is preferably 4:3 to 2: 1.
According to the invention, the graphite felt structure body adopts the composition of the condition (1), so that the first part cannot be excessively compressed by using the second part with large compression modulus to resist the compression force in the later electric pile assembling process, the internal integral pressure of the electric pile is ensured to be small, and the flow rate of electrolyte is ensured; meanwhile, the second part with a large compression modulus has relatively more excellent conductivity, so that the contact resistance can be effectively reduced, and the energy conversion efficiency of the battery can be improved.
According to the invention, the graphite felt structure body is formed under the condition (2), so that in the later electric pile assembling process, the upper part of the thick second part is compressed, the compression ratio of the first part is smaller, the integral pressure in the electric pile is ensured to be smaller, and the flow rate of electrolyte is ensured; meanwhile, the second part with thick thickness is compressed in a larger proportion, and the density is increased after compression, so that the contact resistance can be effectively reduced, and the energy conversion efficiency of the battery is improved.
In some embodiments of the invention, the second portion is comprised of graphite felt and/or a material other than graphite felt. Here, the material other than the graphite felt (also referred to as another material in the present specification) may be a polymer, a carbon material, or a combination thereof, and is not particularly limited as long as it is a conductive porous corrosion-resistant material, and a material having compatibility with other constituent elements of the flow battery may be selected as necessary. Examples of the polymer include: conductive polymer materials such as polypyrrole, polyphenylene sulfide, polyphthalocyanine, polyaniline, and polythiophene, and conductive rubbers such as silver-filled silicone rubber and graphite-filled silicone rubber. Examples of the carbon material include graphite other than graphite felt forms such as graphite powder, flake graphite, and expanded graphite, core-shell structure nanocarbon, three-dimensionally ordered macroporous carbon, activated carbon fiber, graphene, carbon nanotube, carbon nanohorn, and combinations thereof, and molded bodies mainly composed of these, such as carbon fiber cloth and carbon brick.
In some preferred embodiments of the present invention, it is preferable that the second part is composed of a graphite felt, and the following condition (3) or (4) is satisfied:
condition (3): the thickness of the second portion of graphite felt is the same as the thickness of the first portion of graphite felt, and the bulk density of the second portion of graphite felt is greater than the bulk density of the first portion of graphite felt;
condition (4): the second portion of graphite felt has a bulk density that is the same as the first portion of graphite felt, and the second portion of graphite felt has a thickness that is greater than the first portion of graphite felt.
In the condition (3), when the thickness of the graphite felt of the second portion is equal to the thickness of the graphite felt of the first portion, the volume density of the graphite felt of the second portion is set to be higher than the volume density of the graphite felt of the first portion, so that a high flow rate of the electrolyte is achieved by the first portion having a low volume density and a low resistance is achieved by the second portion having a high volume density in the subsequent stack assembly process, thereby improving the energy conversion efficiency of the battery.
In the above condition (4), in the case where the bulk density of the graphite felt of the second portion is the same as the bulk density of the graphite felt of the first portion, the thickness of the graphite felt of the second portion is defined to be larger than the thickness of the graphite felt of the first portion, so that the second portion is compressed to a greater extent than the first portion in the subsequent stack assembly process, so that the bulk density of the graphite felt of the second portion becomes larger than the bulk density of the graphite felt of the first portion. Thus, a high flow rate of the electrolyte is achieved by the first portion having a small volume density, and a low resistance is achieved by the second portion having a large volume density, thereby improving the energy conversion efficiency of the battery.
In some preferred embodiments of the present invention, the bulk density of the graphite felt of the first portion is preferably in the range of 0.06-0.08g/cm in the state where the graphite felt structure of the present invention is assembled into a flow battery by compression3Further, in the case where the second part is composed of a graphite felt, the bulk density thereof is preferably 0.06 to 0.11g/cm3The range of (1).
In other preferred embodiments of the present invention, the porosity of the graphite felt of the first portion is in the range of 10-50% in the state of the graphite felt structure of the present invention assembled into a flow battery by compression, and further, the porosity is preferably in the range of 5-25% in the case where the second portion is comprised of graphite felt.
In other preferred embodiments of the present invention, the compression of the graphite felt of the first portion is preferably 0-40% in the state of the graphite felt structure of the present invention assembled into a flow battery by compression. In the above condition (4), it is preferable that the compressed amount of the graphite felt in the first part is 2 to 30% and the compressed amount of the graphite felt in the second part is 5 to 50%.
In another preferred embodiment of the present invention, in the graphite felt structure according to the present invention, the first partial area is preferably 60% or more, more preferably 70% or more, and still more preferably 80% or more of the total area of the graphite felt structure in the planar direction, and the upper limit may be 95%, preferably 90%. By thus defining the ratio of the first partial area to the total area of the graphite felt structure, it is possible to achieve both maintenance of the flow rate of the electrolyte solution and reduction of the contact resistance in a more balanced manner.
The graphite felt structure of the present invention is not particularly limited as long as it satisfies the above-described configuration, and can be designed by means of specific processing, experiments, and calculation model simulation results according to the required performance of the flow battery to be used.
In some preferred embodiments of the present invention, from the viewpoint of workability and workability, at least one surface of the first part and/or the second part is preferably a flat surface, and more preferably, the surfaces of the first part and/or the second part are both flat surfaces. The "plane" referred to herein is particularly preferably a plane perpendicular to the thickness direction of the graphite felt structure, that is, a plane in the plane direction, and the same applies to the "plane" mentioned later.
The graphite felt structure of the present invention can be processed in a conventional manner in the art. In one embodiment, a graphite felt sheet or block may be first prepared and processed on one major surface. For example, a mechanical device can be used to cut away portions of an optional depth and optional shape to obtain any desired protrusions on the major surface, and such process can be repeated to produce additional protrusions. Thus, the graphite felt structure of the present invention can be obtained. The method can obtain the bulges with required shape, size and distribution mode at will according to the requirement. The thus-obtained convex portion corresponds to the second portion of the graphite felt structure, and the non-convex portion corresponds to the first portion of the graphite felt structure. The same applies to the "projection" mentioned later.
In other embodiments, for example, when preparing graphite felt plates or blocks, the graphite felt structures can be obtained by directly forming the protrusions in the desired shape, size and distribution by selecting an appropriate mold in the forming stage.
In other embodiments, a graphite felt is coated at a selected location or locations with a solution of a polymer as a precursor so as to cover at least the surface of the selected location, and then heat treated at an elevated temperature to carbonize and graphitize the polymer to form projections integral with the graphite felt and protruding from the surface of the graphite felt, thereby providing a graphite felt structure.
In other embodiments, for a graphite felt, a solution of a polymer as a precursor is applied to selected locations, the solution is impregnated into the interior of the selected locations of the graphite felt, the polymer is carbonized and graphitized by heat treatment at elevated temperatures, and the coated locations are coplanar with the uncoated locations on the surface of the resulting graphite felt structure. The coated locations thus obtained (including the polymer solution impregnated epitaxial portions) correspond to the second portion of the graphite felt structure, and the uncoated locations correspond to the first portion of the graphite felt structure.
In other embodiments, the graphite felt may be formed by splicing graphite felt material used to form the first portion with graphite felt material or other material used to form the second portion. For example, a graphite felt sheet, both major surfaces of which are flat, is prepared as a graphite felt material for constituting the first part, and a plurality of graphite felt materials or other materials for constituting the second part, which have the same or different shapes from each other, are bonded to at least one major surface thereof to form projections. Alternatively, a graphite felt sheet having projections on one main surface and a flat surface on the other main surface is prepared as the graphite felt material for constituting the first part, and the graphite felt material or other material for constituting the second part is bonded to the portions of the aforementioned graphite felt on the main surface where the projections are not formed, and finally the graphite felt structure defined in the present invention is formed.
The graphite felt material or other material used to form the second portion described above may be bonded, if desired, with the aid of an adhesive when spliced as described above onto the graphite felt material used to form the first portion. The binder is electrically conductive, and for example, any of various commercially available conductive adhesives in the art can be used as long as it does not interfere with the electrode reaction in the flow battery. In a preferred embodiment, the conductive adhesive can be applied to the entire area of the splicing surface, or can form adhesive dots at one or more positions of the splicing surface in a dot bonding manner.
In a preferred embodiment, the splicing is performed in the presence of no chemical agents such as additional adhesives. An embodiment may be enumerated in which a first graphite felt sheet or graphite felt block is prepared, and a groove or through-hole is formed on one main surface of the first graphite felt sheet or graphite felt block. Thereafter, additional graphite felt blocks or other materials having a shape adapted to the grooves or through-holes are filled into the grooves or through-holes, so that the filled combined graphite felt can be stably present and used. In such a manner, additional graphite felt blocks or other material can form any shape or distribution of protrusions on one major surface of the first graphite felt block. Alternatively, in the case where the first graphite felt piece has a lower compression modulus than the additional graphite felt piece or other material, the groove or through-hole formed on the one main surface of the first graphite felt plate or graphite felt piece may be just filled with the additional graphite felt piece or other material in such a manner that the projection is not formed.
In other embodiments, the graphite felt structure of the present invention may be formed by stacking two or more graphite felt sheets or graphite felt blocks. For example, a graphite felt a having projections as described above on at least one main surface is prepared, another graphite felt B having the same or similar size as the graphite felt a and having through holes is prepared, and the graphite felt a and the graphite felt B are laminated, and at this time, the projections of the graphite felt a enter or pass through the through holes of the graphite felt B to form the graphite felt of the present invention. Similarly, the graphite felt A and the graphite felt B can be made of the same or different materials.
The same or different materials described above may refer to the same or different parameters or properties, including density, compressive modulus, porosity, etc.
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
For example, an example of the constitution of the graphite felt of the present invention is shown in fig. 1, in which the graphite felt has 1 first portion 1 and 4 second portions 2 in the plane direction.
Figure 2 shows an embodiment of the invention. Wherein, the compression modulus of the second part 2 is larger than that of the first part 1, and the thicknesses of the two parts are the same.
Figure 3 shows another embodiment of the present invention. Wherein the second portion 2 has a greater thickness than the first portion 1.
Figure 4 shows an embodiment of a spliced graphite felt structure wherein the second portion is formed by bonding carbon fiber cloth to a graphite felt sheet.
In fig. 5, another embodiment of a spliced graphite felt structure is shown wherein a higher compression modulus silver filled silicone rubber molded gasket as the second portion fills the through holes in the graphite felt sheet in a non-protruding manner.
Another embodiment of the invention is a flow battery made using the graphite felt of the invention as described above. The method for manufacturing the flow battery using the graphite felt may employ a conventional method, and is not particularly limited.
Examples
Example 1
Mixing commercially available graphite felt (activated graphite felt, thickness 3mm, volume density 0.08 g/cm)3) The graphite felt was cut into a size of 40cm in width and 35cm in length. Another commercially available graphite felt (activated graphite felt, thickness 4mm, bulk density 0.08 g/cm)3) Five circular graphite felt blocks were prepared by cutting into a circular shape having a diameter of 6 cm. Five circular cutouts having a diameter of 6cm in total were punched out at the center and four corners of the graphite felt sheet, respectively, and the five graphite felt pieces were embedded therein. The embedded graphite felt blocks fill the circular voids and protrude from the surface of the graphite felt sheet (forming cylindrical protrusions). The graphite felt structure of the present invention was thus prepared.
The graphite felt structure of the present invention prepared as described above was used as a carbon felt, a Nafion film was used as a separator, a graphite plate was used as a bipolar plate, a copper plate was used as a current collecting plate, and they were stacked, encapsulated, and then pressurized to produce a single cell. And (4) connecting 20 single batteries in series to manufacture the vanadium redox flow battery with the rated power of 1 KW.
The graphite felt structure and the vanadium flow battery using the same were evaluated for each performance as follows.
(1) Internal resistance of
The evaluation method comprises the following steps: the inner group of the electric pile is quickly measured by using a simple charging and discharging electric device. The method comprises the steps of applying currents with different magnitudes to a galvanic pile, dividing the difference between galvanic pile voltage after the current is applied and galvanic pile open-circuit voltage after the current is cancelled by corresponding current density to obtain corresponding galvanic pile internal resistance.
Evaluation criteria:
the evaluation was excellent when the internal resistance was less than 1.2 ohm/cm, good when the internal resistance was 1.2-2.0 ohm/cm, and poor when the internal resistance was more than 2.0 ohm/cm.
(2) Energy efficiency
The evaluation method comprises the following steps: the energy efficiency is the stack current efficiency multiplied by the stack voltage efficiency. The stack is cycled between a maximum and a minimum of the defined voltage, wherein current efficiency is the sum of the charges flowing out of the stack during discharge divided by the sum of the charges flowing into the stack during charge; the voltage efficiency is the average voltage of the stack during discharge divided by the average voltage of the stack during charge.
Evaluation criteria:
the evaluation was excellent when the energy efficiency was more than 70%, good when the energy efficiency was 65-70%, and poor when the energy efficiency was less than 65%.
(3) Conservation rate of energy efficiency after 5000 cycles of charge and discharge
The evaluation method comprises the following steps: the energy efficiency after 5000 cycles was divided by the energy efficiency at the time of the initial charge-discharge cycle.
Evaluation criteria:
the evaluation was excellent when the energy efficiency retention rate was more than 90%, good when the energy efficiency retention rate was 85% to 90%, and poor when the energy efficiency retention rate was less than 85%.
By the above-described production method, the graphite felt structures of examples 1 and 2 were produced in the manner shown in table 1, and a vanadium flow battery was produced. The internal resistance, energy efficiency, and energy efficiency retention after 5000 cycles of charge and discharge of the vanadium redox flow battery obtained in each example were evaluated and are shown in table 1.
Example 2
Mixing commercially available graphite felt (activated graphite felt, thickness 3mm, volume density 0.08 g/cm)3) The graphite felt was cut into a size of 50cm in width and 25cm in length. Another commercially available graphite felt (activated graphite felt, thickness 4mm, bulk density 0.08 g/cm)3) Five circular graphite felt blocks were prepared by cutting into a circular shape having a diameter of 8 cm. Five circular openings having a diameter of 8cm were punched out at the center and four corners of the graphite felt sheet, respectively, and the five graphite felt pieces were embedded therein. The embedded graphite felt blocks fill the circular voids and protrude from the surface of the graphite felt sheet (forming cylindrical protrusions). The graphite felt structure of the present invention was thus prepared.
Then, a vanadium redox flow battery was produced in the same manner as in example 1, and the internal resistance, energy efficiency, and energy efficiency retention rate after 5000 cycles of charge and discharge of the obtained vanadium redox flow battery were evaluated in the same manner as in example 1, and are shown in table 1.
Example 3
The other commercially available graphite felt (activated graphite felt, thickness 4mm, bulk density 0.08 g/cm) used in example 2 was used3) Replacing with commercially available graphite felt (activated graphite felt, thickness of 5mm, volume density of 0.08 g/cm)3) Except for this, a graphite felt structure and a vanadium redox flow battery were produced in the same manner as in example 2, and the internal resistance, energy efficiency, and energy efficiency retention rate after 5000 cycles of charge and discharge of the obtained vanadium redox flow battery were evaluated in the same manner as in example 2, and are shown in table 1.
Example 4
The other commercially available graphite felt (activated graphite felt, thickness 4mm, bulk density 0.08 g/cm) used in example 2 was used3) Replacing with commercially available graphite felt (activated graphite felt, thickness 3mm, volume density 0.09 g/cm)3) Except for this, a graphite felt structure and a vanadium redox flow battery were produced in the same manner as in example 2, and the obtained vanadium redox flow battery was evaluated for internal resistance, energy efficiency, and after 5000 cycles of charge and discharge cycles in the same manner as in example 2The energy efficiency retention of (2) is shown in Table 1.
Example 5
The other commercially available graphite felt (activated graphite felt, thickness 4mm, bulk density 0.08 g/cm) used in example 2 was used3) A graphite felt structure and a vanadium redox flow battery were produced in the same manner as in example 2 except that a commercially available polypropylene hollow plate (thickness 3mm) was used instead, and the internal resistance, the energy efficiency, and the energy efficiency retention rate after 5000 cycles of charge and discharge of the obtained vanadium redox flow battery were evaluated in the same manner as in example 2, and are shown in table 1.
Comparative example 1
A vanadium flow battery was produced as comparative example 1 using the same compression force as in example 1 in the compression process, except that the entire graphite felt having the same volume density as that of the graphite felt (main body portion except for the projections) of example 1 was used. The internal resistance, the energy efficiency and the energy efficiency retention rate after 5000 times of charge and discharge cycles of the vanadium redox flow battery obtained in each example and each comparative example were evaluated and compared.
TABLE 1
Note 1: the first partial area ratio is a ratio of the first partial area to the total area of the graphite felt structure.
Note 2: the thickness ratio refers to the ratio of the thickness of the second portion to the thickness of the first portion.
Note 3: the bulk density ratio a is a ratio of the bulk density of the graphite felt constituting the second part to the bulk density of the graphite felt constituting the first part.
Note 4: b is the ratio of the bulk density of the second portion to the bulk density of the first portion in the assembled state of the flow battery. The bulk density is a value obtained by measuring a graphite felt detached from a single battery which has not been subjected to the first charge and discharge after the preparation.
As can be seen from comparison between the embodiment of the application and the comparative example, according to the graphite felt structure and the flow battery using the same, the contact resistance can be reduced, the battery conversion efficiency is improved, meanwhile, the internal pressure of the galvanic pile is reduced, the sealing performance is ensured, the flow velocity of the electrolyte is ensured, and the situation that the battery is scrapped due to overcharging is avoided, so that the service life of the galvanic pile is prolonged.
Industrial applicability
The graphite felt structure and the flow battery using the same according to the present application are industrially useful because they can provide a flow battery having excellent performance and a long life by achieving a reduction in contact resistance, an improvement in battery conversion efficiency, a reduction in stack internal pressure, and a securing of electrolyte flow rate at the same time.
Claims (9)
1. A graphite felt structure for a flow battery, comprising in a planar direction: a first portion composed of a graphite felt material, and a plurality of second portions composed of graphite felt,
the plurality of second portions have two or more symmetry axes in the plane direction, the symmetry axes passing through the center of the graphite felt structural body in the plane direction,
a peripheral edge portion of the graphite felt structure is constituted only by the first portion, the plurality of second portions are each located in a region of the graphite felt structure other than the peripheral edge portion,
each of the plurality of second portions satisfies the following condition (1), respectively:
condition (1): the second portion has a compressive modulus greater than the compressive modulus of the first portion, and the ratio of the compressive modulus of the second portion to the compressive modulus of the first portion is (1.1-10): 1.
2. the graphite felt structure according to claim 1, wherein in the condition (1), the compressive modulus has a continuous gradient change or a discontinuous gradient change between the second portion and the first portion.
3. The graphite felt structure according to claim 1 or 2, wherein each of the plurality of second portions satisfies the following condition (3), respectively:
condition (3): the thickness of the second portion of graphite felt is the same as the thickness of the first portion of graphite felt, and the bulk density of the second portion of graphite felt is greater than the bulk density of the first portion of graphite felt.
4. The graphite felt structure according to claim 1 or 2, wherein the volume density of the graphite felt of the first part is in the range of 0.08-0.3g/cm in a state where the graphite felt structure is assembled into a flow battery by compression3The range of (1).
5. The graphite felt structure according to claim 1 or 2, wherein the porosity of the graphite felt of the first portion is in the range of 10-50% in a state where the graphite felt structure is assembled into a flow battery by compression.
6. The graphite felt structure according to claim 1 or 2, wherein the compression of the graphite felt of the first portion is 0-40% in a state where the graphite felt structure is assembled into a flow battery by compression.
7. The graphite felt structure according to claim 1 or 2, wherein the first partial area accounts for 60% or more of the total area of the graphite felt structure in the planar direction.
8. The graphite felt structure according to claim 1 or 2, wherein the graphite felt structure is obtained by splicing or laminating a plurality of graphite felts.
9. A flow battery produced using the graphite felt structure according to any one of claims 1 to 8.
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