A composite bipolar plate for all-vanadium redox flow battery and its preparation method

Abstract

The present invention relates to a composite bipolar plate for all-vanadium redox flow batteries and a method for its preparation. The method comprises the following steps: mixing a conductive carbon material with a phosphate solution or a phosphate ester solution to obtain a conductive filler; mechanically mixing the conductive filler with an acrylic resin solution to obtain a mixture; and compression molding the mixture. This invention addresses the problems of high porosity and poor corrosion resistance associated with conventional bipolar plates, while also providing high-performance composite bipolar plates produced using this method.

Description

Technical Field

[0001] The present invention relates to the technical field of all-vanadium redox flow battery energy storage, and in particular to a composite bipolar plate for an all-vanadium redox flow battery and a preparation method thereof. Background Art

[0002] As a highly efficient electrochemical energy storage technology, vanadium redox flow batteries (VRFBs) offer significant advantages, including high power output, long cycle life, scalability, and environmental friendliness. They have been applied in areas such as grid peak regulation and renewable energy integration. As the core component of VRFBs, bipolar plates perform multiple functions, including current collection and conduction, electrolyte isolation, and supporting the battery structure. Currently, carbon-plastic composite bipolar plates have become the mainstream choice due to their excellent corrosion resistance, superior mechanical properties, and manageable costs. They are typically manufactured by extrusion or compression molding of a conductive carbon material (such as graphite, carbon fiber, etc.) and a resin matrix (such as a thermoplastic or thermosetting resin).

[0003] However, conventional carbon-plastic composite bipolar plates (CBPs) exhibit significant defects during their fabrication. Firstly, the interfacial compatibility between the resin matrix and the carbon material is insufficient. Furthermore, the high-viscosity resin has poor fluidity, making it difficult to completely fill the pores of the carbon material. In particular, the nanocarbon material easily agglomerates, resulting in high porosity in the CBPs. This leads to cross-contamination between the positive and negative electrolytes and a decrease in the battery's Coulombic efficiency. Secondly, under high-voltage conditions, the carbon material is susceptible to corrosion from contact with the electrolyte, leading to stack failure. Therefore, reducing the porosity of the CBPs and improving their corrosion resistance have become key issues hindering the long-term stable operation of VRFBs. Summary of the Invention

[0004] In response to the above-mentioned problems in the prior art, the present invention proposes a composite bipolar plate for all-vanadium liquid flow batteries and a preparation method thereof, which solves the problems of high porosity and poor corrosion resistance of traditional bipolar plates, and provides a high-performance composite bipolar plate prepared by this method.

[0005] Specifically, the present invention proposes a method for preparing a composite bipolar plate for an all-vanadium redox flow battery, comprising the following steps:

[0006] mixing a conductive carbon material with a phosphate solution or a phosphate ester solution to obtain a conductive filler;

[0007] Mechanically mixing the conductive filler with an acrylic resin solution to obtain a mixture;

[0008] The mixture is compression molded.

[0009] According to one embodiment of the present invention, the conductive carbon material is selected from conductive carbon black, Ketjen black, carbon fiber, carbon nanotube, carbon nanofiber, natural graphite, expanded graphite or graphene.

[0010] According to one embodiment of the present invention, the weight percentage of the phosphate solution or the phosphate ester solution to the weight percentage of the conductive carbon material is 1.0-20.0%.

[0011] According to one embodiment of the present invention, if the conductive carbon material is selected from conductive carbon black, Ketjen black, carbon fiber, carbon nanotube or carbon nanofiber, the conductive carbon material and the phosphate or phosphate ester solution are mixed by ball milling for 10 to 60 minutes;

[0012] If the conductive carbon material is selected from natural graphite, expanded graphite or graphene, the conductive carbon material and the phosphate or phosphate ester solution are mixed by pressure impregnation, the pressure used in the pressure impregnation is 0.8-1.5 MPa, and the duration is 2-5 hours.

[0013] According to one embodiment of the present invention, the method for preparing the phosphate solution is to add a metal compound to a room-temperature phosphoric acid solution, wherein the phosphoric acid concentration of the room-temperature phosphoric acid solution is 60% to 80%, the metal compound includes a metal oxide, a metal hydroxide, or a mixture of the metal oxide and the metal hydroxide, the metal oxide is one or more of aluminum metal oxide, magnesium metal oxide, or calcium metal oxide, and the metal hydroxide is one or more of aluminum hydroxide, magnesium hydroxide, or calcium hydroxide;

[0014] The molar ratio of the metal compound to the room temperature phosphoric acid solution is 0.25 to 1:1;

[0015] The phosphate ester solution is industrial acrylic polyphosphate or polyester phosphate.

[0016] According to one embodiment of the present invention, the acrylic resin monomer and the initiator are mechanically stirred and mixed to obtain the acrylic resin solution;

[0017] The weight percentage of the initiator to the weight percentage of the acrylic resin monomer is 0.5-2.0%, and the mechanical mixing time is 5 min-30 min.

[0018] According to one embodiment of the present invention, the initiator is a peroxide, and the peroxide is selected from one or more of benzoyl peroxide, tert-amyl peroxide 2-ethylhexanoate, diisopropyl benzene peroxide, tert-butyl peroxide 2-ethylhexanoate, 3,3-bis(tert-butylperoxy)ethyl butyrate, tert-butyl peroxybenzoate, tert-amyl peroxybenzoate, tert-amyl peroxyacetate, 1,1,-bis(tert-amylperoxy)cyclohexane, tert-amyl hydroperoxide, and di-tert-butylbenzene peroxide.

[0019] According to one embodiment of the present invention, the ratio of the conductive filler to the acrylic resin solution is 10 to 25 parts of acrylic resin and 75 to 90 parts of the conductive filler, and the mechanical stirring mixing time is 10 to 30 minutes.

[0020] According to one embodiment of the present invention, the mixture is subjected to compression molding at a temperature of 100 to 170° C., a pressure of 5 to 20 MPa, and a time of 30 to 90 min.

[0021] The present invention also provides a composite bipolar plate for an all-vanadium liquid flow battery, which is prepared by any of the aforementioned preparation methods.

[0022] The present invention provides a composite bipolar plate for an all-vanadium redox flow battery and a preparation method thereof. By modifying a conductive carbon material with phosphate or phosphate ester and cross-linking and curing an acrylic resin, a dense structure is formed, so that the bipolar plate has the characteristics of low porosity and high corrosion resistance.

[0023] It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are included to provide further explanation of the present invention, are incorporated into and constitute a part of this application, illustrate embodiments of the present invention, and together with this specification serve to explain the principles of the present invention. In the drawings:

[0025] Figure 1 A flow chart showing a method for preparing a composite bipolar plate for an all-vanadium redox flow battery according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0026] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] Unless otherwise specified, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application. Meanwhile, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to actual proportional relationships. Technology, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments can have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, and therefore, once an item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0030] In the description of this application, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "horizontal, vertical, vertical, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of this application; the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0031] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is solely for the purpose of distinguishing the corresponding components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application. Furthermore, while the terms used in this application are selected from commonly known and commonly used terms, some terms mentioned in this specification may have been selected by the applicant at his or her discretion, and their detailed meanings are explained in the relevant sections of this description. Furthermore, this application should be understood not only by the actual terms used, but also by the meaning implied by each term.

[0032] Figure 1A flow chart of a method for preparing a composite bipolar plate for an all-vanadium redox flow battery according to an embodiment of the present invention is shown. As shown in the figure, a method for preparing a composite bipolar plate for an all-vanadium redox flow battery comprises the following steps:

[0033] S1: Mixing a conductive carbon material with a phosphate solution or a phosphate ester solution to obtain a conductive filler. By coating or penetrating the carbon material with the solution, the conductive filler is endowed with pore-filling and corrosion-resistant properties, laying the foundation for improved bipolar plate performance.

[0034] S2, mechanically mixing the conductive filler with the acrylic resin solution to obtain a mixture. The prepared conductive filler is mechanically mixed with the acrylic resin solution to uniformly disperse the conductive filler in the resin system to form a plastic mixture to ensure the quality of subsequent molding.

[0035] S3, the mixture is molded into a shape, and under the action of heat and pressure, the resin is cross-linked and solidified, and at the same time, the phosphate or phosphate ester melts and fills the pores, finally forming a composite bipolar plate for all-vanadium liquid flow batteries with conductive, barrier and structural support functions.

[0036] In some examples, the conductive carbon material is selected from conductive carbon black, Ketjen black, carbon fiber, carbon nanotubes, carbon nanofibers, natural graphite, expanded graphite, or graphene. These materials, with their excellent electrical conductivity, are crucial for ensuring the bipolar plate's conductive properties, ensuring efficient current conduction in subsequent batteries. Furthermore, the varying morphologies and properties of these materials facilitate different subsequent mixing processes.

[0037] In some examples, the weight percentage of the phosphate solution or phosphate ester solution to the conductive carbon material is 1.0-20.0%. Controlling the amount of phosphate solution or phosphate ester solution is a key step in the preparation method. Setting the weight ratio of the phosphate solution or phosphate ester solution to the conductive carbon material to 1.0-20.0% ensures that the phosphate / ester solution, acting as a modifier, fully coats the conductive carbon material, effectively filling the internal pores of the bipolar plate and improving corrosion resistance, while also avoiding the impact of excessive dosage on material conductivity and molding quality, thereby achieving an optimal balance in bipolar plate performance.

[0038] In some examples, if the conductive carbon material is selected from conductive carbon black, Ketjen black, carbon fiber, carbon nanotube, or carbon nanofiber, the conductive carbon material and the phosphate or phosphate ester solution are mixed by ball milling. The mechanical grinding force allows the phosphate / ester solution, acting as a modifier, to uniformly coat the conductive carbon material, improving interfacial compatibility. Furthermore, the ball milling time is 10 to 60 minutes to ensure effective mixing.

[0039] If the conductive carbon material is selected from natural graphite, expanded graphite, or graphene, the conductive carbon material and the phosphate or phosphate ester solution are mixed using pressure impregnation, with a pressure of 0.8 to 1.5 MPa and a duration of 2 to 5 hours. Pressure impregnation utilizes pressure to drive the solution into the pores between graphite layers, achieving full filling of the modifier (phosphate solution or phosphate ester solution) while maintaining the integrity of the layer structure. As is easy to understand, the differentiated process design for different conductive carbon materials ensures that carbon materials of varying forms can all be efficiently combined with the modifier, laying a solid foundation for the subsequent densification and molding of the bipolar plates.

[0040] In some examples, the phosphate solution is prepared by adding a metal compound to a 60-80% concentration of a room temperature phosphoric acid solution at a molar ratio of 0.25 to 1:1. This ratio and concentration setting ensure that the solution has good fluidity and reactivity, facilitating the subsequent effective coating and pore filling of the conductive carbon material. The metal compound includes a metal oxide, a metal hydroxide, or a mixture of the metal oxide and the metal hydroxide. The metal oxide is one or more of aluminum metal oxide, magnesium metal oxide, or calcium metal oxide; the metal hydroxide is one or more of aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

[0041] The phosphate ester solution directly uses industrial-grade acrylic polyphosphate or polyester phosphate. Leveraging its mature synthesis process and stable chemical properties, it quickly bonds with carbon materials, contributing to improved bipolar plate density and corrosion resistance. The rational preparation and selection of both solutions (phosphate and phosphate ester) are crucial for ensuring the effectiveness of bipolar plate modification.

[0042] In some cases, the preparation of the acrylic resin solution is crucial for ensuring the quality of bipolar plate molding. The acrylic resin monomer is mechanically mixed with 0.5-2.0% initiator for 5-30 minutes, ensuring uniform dispersion of the initiator throughout the resin system. Precise control of this ratio and mixing time effectively triggers the resin's cross-linking polymerization reaction, allowing the acrylic resin to fully cure during subsequent compression molding. This enhances the mechanical strength and structural stability of the bipolar plate, ensuring its effective support and barrier properties during battery operation.

[0043] In some examples, the choice of initiator plays a key role in the cross-linking polymerization of acrylic resin. Peroxides are selected as initiators, such as one or more of benzoyl peroxide, tert-amyl peroxy-2-ethylhexanoate, diisopropylbenzene peroxide, tert-butyl peroxy-2-ethylhexanoate, ethyl 3,3-bis(tert-butylperoxy)butyrate, tert-butyl peroxybenzoate, tert-amyl peroxybenzoate, tert-amyl peroxyacetate, 1,1-bis(tert-amylperoxy)cyclohexane, tert-amyl hydroperoxide, and di-tert-butylbenzene peroxide. These peroxides can decompose to produce free radicals during the mixing and molding process, effectively initiating cross-linking reactions in the acrylic resin monomers. The initiator ensures that the acrylic resin is fully cured, thereby improving the overall strength and structural stability of the bipolar plate and ensuring its reliable performance in all-vanadium redox flow batteries.

[0044] In some examples, the ratio of conductive filler to acrylic resin solution is 10-25 parts acrylic resin to 75-90 parts conductive filler. This ratio ensures that the conductive carbon material forms a continuous conductive network, giving the bipolar plate excellent current conductivity, while also bonding and coating the carbon material through the appropriate amount of resin matrix, ensuring the mechanical strength of the bipolar plate. The corresponding mechanical stirring mixing time is 10-30 minutes to evenly disperse the conductive filler in the resin solution, avoid agglomeration, and provide a uniform and stable material foundation for subsequent molding.

[0045] In some examples, the mixture is compression molded at a temperature of 100-170°C, a pressure of 5-20 MPa, and a duration of 30-90 minutes. At temperatures of 100-170°C and pressures of 5-20 MPa, the phosphate / ester modifier melts and fills the pores of the carbon material, while the acrylic resin crosslinks and solidifies under the action of an initiator. The two interact to form a dense structure, effectively reducing the porosity of the bipolar plate and improving corrosion resistance. Furthermore, a 30-90 minute hold time ensures a full reaction between the modifier and the resin, ensuring uniformity and stability within the bipolar plate's internal structure, ultimately achieving an optimal balance of conductive, barrier, and mechanical properties.

[0046] Example 1

[0047] According to the preparation method of the present invention, an aluminum dihydrogen phosphate solution is first prepared. Aluminum hydroxide is added to a 70% phosphoric acid solution at a molar ratio of 1:3. Subsequently, expanded graphite, carbon fiber, and carbon black are selected as conductive carbon materials in a mass ratio of 80:10:10. A 10% (relative to the mass of the carbon material) aluminum dihydrogen phosphate solution is added to the carbon fiber and carbon black mixture and ball milled for 30 minutes to prepare a preformed filler. The expanded graphite is then pressure-impregnated with the same proportion of aluminum dihydrogen phosphate solution at 1.0 MPa for 2 hours to prepare a preformed filler. The two preformed fillers are then mixed to form a conductive filler. Next, acrylic resin monomer and 1.0% benzoyl peroxide are mechanically stirred to prepare an acrylic resin solution. Afterwards, the mixture was mechanically stirred for 30 minutes in a ratio of 15 parts acrylic resin to 85 parts conductive filler to be thoroughly mixed. Finally, the mixture was poured into a 10 cm × 10 cm mold and molded at 150°C for 60 minutes to obtain a polyacrylic acid composite bipolar plate modified with aluminum dihydrogen phosphate. It should be noted that the aluminum hydroxide in Example 1 is only for example and not for limitation. The aluminum hydroxide can be replaced by other metal compounds, and the molar ratio can be adjusted and added to a phosphoric acid solution of a set concentration. The metal compound can be one or more of aluminum metal oxide, magnesium metal oxide or calcium metal oxide, or one or more of aluminum hydroxide, magnesium hydroxide or calcium hydroxide, or a mixture of the aforementioned metal oxides and metal hydroxides.

[0048] Example 2

[0049] The process of this example is essentially the same as that of Example 1. However, during the preparation of the conductive filler, the addition of aluminum dihydrogen phosphate solution was increased to 20% (relative to the mass of the carbon material). The effect of varying the modifier dosage on bipolar plate performance was further investigated. The remaining steps, including solution preparation, mechanical mixing, and compression molding, followed the same process parameters as in Example 1, ultimately producing aluminum dihydrogen phosphate-modified polyacrylic acid composite bipolar plates.

[0050] Example 3

[0051] The preparation process of Example 3 remained unchanged, with only the addition ratio of aluminum dihydrogen phosphate solution adjusted to 1.0% (relative to the mass of the carbon material). By reducing the amount of modifier, the performance of the bipolar plates at different addition levels was compared. The process parameters of Example 1 were used for conductive filler preparation, resin solution mixing, and compression molding, ultimately resulting in aluminum dihydrogen phosphate-modified polyacrylic acid composite bipolar plates.

[0052] Example 4

[0053] In this example, a ready-made acrylic polyphosphate solution (Solvay, SIPOMER© PAM-100) was used in place of the aluminum dihydrogen phosphate solution. To prepare the conductive filler, expanded graphite, carbon fiber, and carbon black were prepared in a mass ratio of 80:10:10. 10.0% (relative to the mass of the carbon material) of the acrylic polyphosphate solution was added to each. The carbon fiber and carbon black mixture was ball-milled for 30 minutes, and the expanded graphite was pressure-impregnated at 1.0 MPa for 2 hours. In subsequent steps, the process parameters for preparing the acrylic resin solution, mechanical mixing, and compression molding were the same as in Example 1, ultimately yielding a polyacrylic acid composite bipolar plate modified with acrylic acid-terminated polyphosphate.

[0054] Example 5

[0055] The preparation process and component addition ratios of Example 5 remained unchanged from those of Example 1, with the aluminum dihydrogen phosphate solution being replaced with a magnesium dihydrogen phosphate solution. The magnesium dihydrogen phosphate solution was prepared by adding magnesium oxide to a 70% phosphoric acid solution at a molar ratio of 1:2. The performance of composite bipolar plates modified with different phosphates was compared by varying the type of modifier. The process parameters of Example 1 were used for conductive filler preparation, resin solution mixing, and compression molding, resulting in magnesium dihydrogen phosphate-modified polyacrylic acid composite bipolar plates.

[0056] Example 6

[0057] The preparation process and component ratios of Example 6 remained unchanged from Example 1, with the only difference being that the aluminum dihydrogen phosphate solution was replaced with a calcium dihydrogen phosphate solution. The calcium dihydrogen phosphate solution was prepared by adding calcium hydroxide to a 70% phosphoric acid solution at a molar ratio of 1:2. The performance of composite bipolar plates modified with different phosphates was compared by varying the type of modifier. The process parameters of Example 1 were used for conductive filler preparation, resin solution mixing, and compression molding, resulting in polyacrylic acid composite bipolar plates modified with calcium dihydrogen phosphate.

[0058] Example 7

[0059] The preparation process and component ratios of Example 7 remained unchanged from those of Example 1, with the only difference being that the raw materials for the aluminum dihydrogen phosphate solution were replaced with two aluminum metal compounds. The aluminum dihydrogen phosphate solution was prepared by adding aluminum oxide and aluminum hydroxide to a 70% phosphoric acid solution at a molar ratio of 1:3:12. The performance of composite bipolar plates modified with aluminum dihydrogen phosphate was compared by adding more aluminum metal compounds. The process parameters of Example 1 were used for conductive filler preparation, resin solution mixing, and compression molding, resulting in aluminum dihydrogen phosphate-modified polyacrylic acid composite bipolar plates.

[0060] Example 8

[0061] The preparation process and component addition ratios of Example 8 remained unchanged from those of Example 1, with the sole aluminum dihydrogen phosphate solution being replaced with an aluminum-magnesium phosphate solution. The aluminum-magnesium phosphate solution was prepared by adding aluminum hydroxide and magnesium oxide at a molar ratio of 2:1:8 to a 70% phosphoric acid solution. Aluminum-magnesium composite phosphates were obtained from two-component metal compound raw materials, and the performance of composite bipolar plates modified with these two-component composite phosphates was compared. The process parameters of Example 1 were used for conductive filler preparation, resin solution mixing, and compression molding, ultimately resulting in a two-component aluminum-magnesium phosphate-modified polyacrylic acid composite bipolar plate.

[0062] Comparative Example 1

[0063] As a blank control, Comparative Example 1 did not modify the conductive carbon material with a phosphate or phosphate ester solution. Instead, expanded graphite, carbon fiber, and carbon black (at a mass ratio of 80:10:10) were used as conductive fillers. Acrylic resin monomer and 1.0% benzoyl peroxide were mechanically stirred to prepare a resin solution. Subsequently, a ratio of 15 parts acrylic resin to 85 parts conductive filler was mixed for 30 minutes. Finally, the solution was press-molded in a 10 cm × 10 cm mold at 150°C for 60 minutes to produce a conventional polyacrylic acid composite bipolar plate.

[0064] Test Case

[0065] To verify the performance of the bipolar plates in each example, air permeability and corrosion current density tests were conducted on the bipolar plates of Examples 1-8 and Comparative Example 1, respectively, according to the NB / T 42007-2013 standard. In addition, durability tests were conducted by assembling single cells. Electrodes with an active area of ​​48 cm² (2.5 mm thickness, manufactured by Liaoyang Jingu) were used, with a compression ratio of 30-35%. The active material concentrations of the positive and negative electrolytes were both 1.7 mol / L (V4+ / V5+ and V2+ / V3+, respectively), and the supporting electrolyte was 4.3 mol / L sulfuric acid, with a volume of 70 mL each. A 50 μm perfluorosulfonic acid ion membrane (manufactured by Suzhou Kerun) was used as the separator. Testing was conducted in galvanostatic mode at a current density of 200 mA / cm², with a charge limit of 1.55 V and a discharge limit of 1.00 V, for 2000 cycles to evaluate the durability of the bipolar plates in practical applications.

[0066] Table 1: Comparison of bipolar plate permeability of Examples 1-8 and Comparative Example 1

[0067]

[0068] The air permeability of Examples 1-8 is significantly lower than that of Comparative Example 1, with Example 2 having the lowest air permeability, indicating that the phosphate / ester modification can effectively fill the pores and improve the density.

[0069] Table 2: Comparison of corrosion resistance current of bipolar plates of Examples 1-8 and Comparative Example 1

[0070]

[0071] The corrosion currents of Examples 1-8 are all lower than that of Comparative Example 1, and Example 2 has the best effect, indicating that the modifier forms a protective film on the surface of the carbon material to inhibit the oxidation reaction.

[0072] Table 3: Comparison of the three major efficiencies of the single cells assembled with bipolar plates of Examples 1-8 and Comparative Example 1 after 2000 cycles

[0073]

[0074] In the comparison of single cell cycle efficiency, the energy efficiency: Examples 1-8 are 79.1% to 80.7%, and Comparative Example 1 is 76.9%, indicating that the modified bipolar plates of Examples 1-8 have lower energy loss; the voltage efficiency: Examples 1-8 are 82.0% to 83.3%, and Comparative Example 1 is 79.9%, indicating that the battery polarization loss of Examples 1-8 is reduced after modification; Coulombic efficiency: Examples 1-8 and Comparative Example 1 both exceed 96%, but the modified bipolar plates (such as Example 8 is 96.9%) have better Coulombic efficiency stability due to reduced electrolyte crosstalk.

[0075] The above test data show that the bipolar plates modified with phosphate / ester are superior to traditional bipolar plates in terms of density, corrosion resistance and battery cycle stability. Among them, Example 2 with a modifier dosage of 20% has the best overall performance, verifying the effectiveness of the preparation method of the present invention.

[0076] The present invention also provides a composite bipolar plate for an all-vanadium liquid flow battery, which is prepared by any of the aforementioned preparation methods.

[0077] The present invention provides a composite bipolar plate for all-vanadium redox flow batteries and its preparation method. By modifying the conductive carbon material with phosphates or phosphate esters and then crosslinking and curing it with acrylic resin, the plate's porosity is effectively reduced, corrosion resistance is enhanced, and the coulombic efficiency and cycle life of the all-vanadium redox flow battery are increased. This preparation method is simple, compatible with a variety of conductive carbon materials, and has promising prospects for industrial application.

[0078] It will be apparent to those skilled in the art that various modifications and variations may be made to the above exemplary embodiments of the present invention without departing from the spirit and scope of the present invention. Therefore, it is intended that the present invention cover modifications and variations of the present invention that fall within the scope of the appended claims and their equivalent technical solutions.

Claims

1. A method for preparing a composite bipolar plate for an all-vanadium redox flow battery, comprising the following steps: A conductive carbon material is mixed with a phosphate solution or a phosphate ester solution to obtain a conductive filler, wherein the conductive carbon material is selected from conductive carbon black, carbon fiber, carbon nanotube, natural graphite, expanded graphite or graphene; wherein, If the conductive carbon material is selected from conductive carbon black, carbon fiber, and carbon nanotubes, the conductive carbon material and the phosphate or phosphate ester solution are mixed by ball milling for 10 to 60 minutes; if the conductive carbon material is selected from natural graphite, expanded graphite, or graphene, the conductive carbon material and the phosphate or phosphate ester solution are mixed by pressure impregnation, and the pressure used for the pressure impregnation is 0.8 to 1.5 MPa for 2 to 5 hours. Mechanically mixing the conductive filler with an acrylic resin solution to obtain a mixture; The mixture is compression molded, wherein the compression molding temperature of the mixture is 100 to 170° C., the pressure is 5 to 20 MPa, and the time is 30 to 90 minutes.

2. The preparation method according to claim 1, wherein The weight percentage of the phosphate solution or the phosphate ester solution to the weight percentage of the conductive carbon material is 1.0-20.0%.

3. The preparation method according to claim 1, wherein The phosphate solution is prepared by adding a metal compound to a room-temperature phosphoric acid solution, wherein the phosphoric acid concentration of the room-temperature phosphoric acid solution is 60-80%, the metal compound comprises a metal oxide, a metal hydroxide, or a mixture of the metal oxide and the metal hydroxide, the metal oxide is one or more of aluminum metal oxide, magnesium metal oxide, or calcium metal oxide, and the metal hydroxide is one or more of aluminum hydroxide, magnesium hydroxide, or calcium hydroxide; The molar ratio of the metal compound to the room temperature phosphoric acid solution is 0.25 to 1:1; The phosphate ester solution is industrial acrylic polyphosphate or polyester phosphate.

4. The preparation method according to claim 1, wherein Mechanically stirring and mixing the acrylic resin monomer and the initiator to obtain the acrylic resin solution; The weight percentage of the initiator to the weight percentage of the acrylic resin monomer is 0.5-2.0%, and the mechanical mixing time is 5 min-30 min.

5. The preparation method according to claim 4, wherein The initiator is a peroxide, and the peroxide is selected from one or more of benzoyl peroxide, tert-amyl peroxide 2-ethylhexanoate, diisopropyl benzene peroxide, tert-butyl peroxide 2-ethylhexanoate, 3,3-bis(tert-butylperoxy)ethyl butyrate, tert-butyl peroxybenzoate, tert-amyl peroxybenzoate, tert-amyl peroxyacetate, 1,1,-bis(tert-amylperoxy)cyclohexane, tert-amyl hydroperoxide, and di-tert-butylbenzene peroxide.

6. The preparation method according to claim 4, wherein The ratio of the conductive filler to the acrylic resin solution is 10 to 25 parts of acrylic resin and 75 to 90 parts of the conductive filler, and the mechanical stirring mixing time is 10 minutes to 30 minutes.

7. A bipolar plate for an all-vanadium redox flow battery, prepared by the preparation method according to any one of claims 1 to 6.

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