A process for fabricating flow battery channel plates with high surface forming quality

Abstract

This invention discloses a high-quality surface forming process for flow battery channel plates, belonging to the field of flow battery technology. The process includes: S1: oxidation intercalation treatment using natural flake graphite as raw material; S2: high-temperature expansion treatment to obtain graphite worm powder with an expansion ratio of 200 to 250 mL / g; S3: multi-stage rolling processing to form a pre-pressed plate; S4: molding treatment to obtain the flow plate. This invention, through systematic testing, selected an expansion ratio range of 200 to 250 mL / g. Within this range, the graphite worms exhibit suitable curling degree, moderate porosity, and uniform and dense packing, demonstrating excellent compressibility, flowability, and elastic recovery ability during molding. The resulting flow plate has a surface roughness Ra < 1 μm on the smooth area, a channel structure dimensional deviation < ±0.05 mm, and no cracks, bubbles, or defects at the channel edges, significantly improving surface forming quality, enhancing contact with the electrodes, and improving the distribution of stack clamping force, which is beneficial for improving the overall performance and long-term operational reliability of the flow battery.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, and more specifically to a process for preparing flow battery flow channel plates with high surface forming quality. Background Technology

[0002] Vanadium redox flow batteries are considered one of the most mature and suitable long-term energy storage technologies for large-scale commercial applications due to their significant advantages, including decoupled power and capacity design, long cycle life, high intrinsic safety, and environmental friendliness. The flow channel bipolar plate, as the core multifunctional component of the flow battery, plays a crucial role in current collection and conduction, mechanical support, electrolyte distribution and isolation, and multi-cell series connection. Its quality and performance directly determine the stack's energy efficiency, cycle life, and manufacturing cost.

[0003] In existing technologies, poor surface forming quality of the flow channel plate is a key defect restricting the performance and reliability of flow battery stacks. Its harm manifests on multiple levels: the small contact area between the flow channel plate and the electrode leads to the degradation of electrochemical performance; uneven surface results in uneven distribution of stack clamping force, greatly increasing the risk of mechanical reliability and sealing failure; in addition, surface defects can accelerate performance degradation during long-term operation, seriously affecting the long-term stability and service life of the battery.

[0004] Flexible expanded graphite is produced by high-temperature expansion of natural flake graphite after acidic oxidation intercalation, resulting in a loose, porous, worm-like structure. This worm-like structure endows the material with excellent compressibility, resilience, and flowability, as well as superior mechanical strength in bending and compression. Furthermore, the graphite worms can form a self-supporting, continuous conductive network, maintaining high conductivity even after compression and resin impregnation, making it a reliable material for flow battery channel plates.

[0005] However, when using flexible expanded graphite to prepare flow channel plates, the expansion ratio of the expanded graphite significantly affects the surface molding quality of the final product. If the expansion ratio is too low, the graphite worms exhibit low curling degree, thicker sheets, and poor flexibility, resulting in a larger surface roughness after compression molding, and cracks and defects easily appearing at the flow channel edges. If the expansion ratio is too high or the process parameters are mismatched, it may lead to high-temperature oxidation ablation and pulverization effects, causing a decrease in expansion volume and an increase in mass loss rate. Therefore, how to select a suitable expansion ratio range and corresponding preparation process to balance the compressibility, flowability, and density of the material, and to suppress incomplete flow channel filling and surface defect generation during compression molding, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] Vanadium redox flow batteries, as a mature long-term energy storage technology, rely on their bipolar flow channels for crucial functions such as current collection and conduction, mechanical support, electrolyte distribution and isolation, and multi-cell series connection. Poor surface molding quality of the flow channel plates is a key defect restricting the performance and reliability of the battery stack. Specifically, this manifests as: a small contact area between the flow channel plate and the electrodes, leading to deteriorated electrochemical performance; uneven surface distribution resulting in uneven stack clamping force, significantly increasing the risk of mechanical reliability and sealing failure; and surface defects accelerating performance degradation during long-term operation, affecting battery lifespan.

[0007] Flexible expanded graphite possesses excellent compressibility, resilience, and conductivity, making it a reliable material for fabricating flow battery channel plates. However, the expansion ratio of expanded graphite significantly impacts the surface molding quality of the final product. If the expansion ratio is too low, the graphite worm curling is minimal, the sheets are thick, and the flexibility is poor, resulting in a large surface roughness after molding and a tendency for cracks and defects to appear at the flow channel edges. Conversely, if the expansion ratio is too high or the process parameters are mismatched, it may lead to high-temperature oxidation and ablation, as well as pulverization, resulting in a decrease in expansion volume and an increased mass loss rate.

[0008] Therefore, how to select a suitable expansion ratio range and corresponding preparation process to balance the compressibility, flowability and density of the material, suppress incomplete channel filling and surface defect generation during the molding process, and prepare flow battery channel plates with high surface molding quality is a technical problem that urgently needs to be solved in this field.

[0009] To address the aforementioned technical problems, this invention provides a process for fabricating a high-surface-forming quality flow battery channel plate, comprising the following steps: S1: Using natural flake graphite as raw material, an oxidation intercalation process is carried out; S2: The graphite after the oxidation intercalation treatment is subjected to high-temperature expansion treatment to obtain graphite worm powder with an expansion ratio of 200 to 250 mL / g. S3: The graphite worm powder is subjected to multi-stage roller pressing to form a pre-pressed board; S4: The pre-pressed plate is subjected to molding to obtain the flow battery channel plate.

[0010] The core of this invention lies in the fact that, through systematic testing and screening, the expansion ratio range of 200-250 mL / g was determined to be the optimal range. Within this expansion ratio range, the worm graphite exhibits suitable curling, moderate interlamellar porosity, and a uniform and dense packing structure, demonstrating excellent compressibility, flowability, and elastic recovery during molding. This effectively suppresses defects such as surface roughness, flow channel defects, and edge cracks during the molding process.

[0011] Furthermore, in steps S1-S2, the fixed carbon content of the natural flake graphite is ≥99.8%, and the mesh size is 80 mesh. The selection of natural flake graphite with the above parameters is an optimized choice based on prioritizing the mesh size of the flake graphite through previous trial production experience. This is beneficial for obtaining graphite worm powder with uniform structure and stable performance during subsequent oxidation intercalation treatment and high-temperature expansion.

[0012] Further, in steps S1-S2, the oxidation intercalation treatment employs a sulfuric acid-nitric acid mixed acid oxidation intercalation method. By controlling the amount of intercalating agent, expandable graphite with different expansion ratios can be obtained. When the target expansion ratio is 200-250 mL / g, the preferred amount of intercalating agent is 1.2-1.5 times the mass of natural flake graphite. The amount of intercalating agent directly affects the expansion driving force of the expanded graphite. Within this range, it can provide a suitable expansion driving force for subsequent high-temperature expansion, ensuring that the worm graphite obtains the ideal curling degree and lamellar structure.

[0013] Furthermore, in steps S1-S2, the high-temperature expansion is carried out under stirring conditions at a stirring speed of 10 rpm. Using a stirring expansion furnace for expansion ensures that the expandable graphite is heated evenly, avoiding local overheating or insufficient expansion, and is beneficial for obtaining graphite worm powder with a uniform expansion ratio.

[0014] Further, in steps S1-S2, the high-temperature expansion temperature is 1000℃, and the expansion time is 15-20s. The expansion temperature is positively correlated with the expansion ratio, but there is an optimal range, and a temperature-time synergistic effect is required. If the temperature is too low, the intercalating agent will not decompose completely, resulting in insufficient expansion; if the time is too long, high-temperature oxidation and ablation will occur, and the pulverization effect will lead to a decrease in the expanded volume. Through systematic testing, this invention has demonstrated that under the conditions of 1000℃ and 15-20s, it can obtain graphite worm powder with an expansion ratio of 200-250 mL / g and a uniform and dense structure, effectively balancing expansion efficiency and product quality.

[0015] Furthermore, in steps S3-S4, the molding process is cold molding. Under the premise that the molding equipment, process parameters (pressure, temperature, vacuum), and preparation environment are consistent, the same weight of graphite worm powder is weighed for molding to ensure that the density of the prepared flow battery channel plate products is consistent.

[0016] The present invention also provides a flow battery channel plate, which is prepared by any of the above-described manufacturing processes. The surface roughness Ra of the smooth area of ​​the channel plate is <1μm, the dimensional deviation of the channel structure is <±0.05 mm, and there are no cracks, bubbles or defects at the edge of the channel.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Excellent surface forming quality: This invention utilizes graphite worm powder with an expansion ratio range of 200-250 mL / g, determined through systematic screening. The worms exhibit suitable curling, moderate interlayer porosity, and a uniform and dense packing structure. After compression molding, the smooth surface of the flow channel plate is flawless, the flow channel structure is highly accurate, and the flow channel edges are neat and free of defects such as cracks, bubbles, and flaws. This fundamentally solves the technical problem of poor surface forming quality in flexible expanded graphite flow channel plates.

[0018] 2. Excellent molding performance: The worm graphite raw material in this ratio range exhibits excellent compressibility, fluidity and elastic recovery during the molding process, which can effectively suppress defects such as surface roughness, flow channel defects and edge cracks during the molding process, and achieve high-quality molded graphite flow channel plates without internal delamination and pore defects.

[0019] 3. Improved overall performance of the battery stack: The high-quality flow channel plate prepared by the present invention can effectively increase the contact area with the electrode and improve the interfacial conductivity; the uniform surface is conducive to the uniform distribution of the battery stack clamping force, improving mechanical reliability and sealing performance; reducing surface defects helps to improve the airtightness and long-term operational reliability of the flow battery bipolar plate and extend the battery life.

[0020] 4. Strong process controllability and suitable for large-scale production: By controlling parameters such as the amount of intercalating agent, expansion temperature and time, this invention can stably obtain graphite worm powder with the target expansion ratio. The process parameters are clear and highly controllable, making it suitable for the large-scale production of flow battery flow channel plates. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a first-state diagram of the product molded by the present invention; Figure 3 This is a second state diagram of the product molded by the present invention; Figure 4 This is a third-state diagram of the product molded by the present invention. Detailed Implementation

[0022] To more clearly illustrate the overall concept of this application, a detailed explanation is provided below with reference to the accompanying drawings.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0024] Furthermore, it should be understood in the description of this application that the terms "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0025] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0026] In this application, unless otherwise expressly specified and limited, the "above" or "below" of the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In the description of this specification, references to terms such as "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0027] Example 1: Reference Figure 1 This embodiment details the fabrication process of the high surface forming quality flow battery channel plate, which is divided into four stages: S1-S4.

[0028] S1: Oxidation Intercalation Treatment Natural flake graphite with a fixed carbon content ≥99.8% and a mesh size of 80 was selected as the starting material. A sulfuric acid-nitric acid mixed acid oxidation intercalation method was used for treatment. Specifically, 100g of natural flake graphite was added to a reaction vessel, and 120-150g of a mixed acid intercalating agent (sulfuric acid to nitric acid volume ratio of 3:1) was slowly added under ice-water bath cooling conditions. The reaction temperature was controlled within the range of 0-5℃, and the reaction was stirred for 2 hours. After the reaction, the graphite was repeatedly washed with deionized water until neutral, and then dried in a vacuum drying oven at 80℃ for 12 hours to obtain expandable graphite.

[0029] S2: High-temperature puffing treatment The expandable graphite obtained from step S1 was added to a stirred expansion furnace and expanded at a constant stirring speed of 10 rpm at high temperature. The expansion temperature was controlled at 1000℃, and the expansion time was 15-20 seconds. Under these conditions, the expandable graphite expanded instantaneously to form a worm-like structure, with an expansion ratio of 200-250 mL / g. During the expansion process, stirring ensured uniform heating of the graphite, avoiding local overheating or insufficient expansion, ultimately yielding graphite worm powder with a uniform structure and appropriate curling degree.

[0030] S3: Multi-stage rolling process The graphite worm powder obtained in step S2 is subjected to multi-stage rolling processing. Specifically, a three-roll press is used, with roller gaps set successively to 3.0 mm, 2.0 mm, and 1.5 mm, and a rolling speed of 0.5 m / min. The graphite worm powder is evenly spread on a conveyor belt and passed through each stage of the rolling process, gradually compacting the loose graphite worm powder to form a pre-pressed sheet with uniform thickness and density. This multi-stage rolling process ensures appropriate porosity between the graphite worms and a uniform and dense packing structure, providing a good foundation for subsequent molding.

[0031] S4: Compression molding process The pre-compressed sheet obtained in step S3 was placed in a molding machine and cold-molded under vacuum conditions (vacuum degree ≤ -0.095MPa). The mold temperature was controlled at room temperature (25±2℃), the molding pressure was 50MPa, and the holding time was 10 minutes. To ensure consistent product density, the same weight of graphite worm powder was accurately weighed before each molding. After molding, the pressure was slowly released, and the mixture was cooled to room temperature under vacuum. The resulting flow battery channel plate was then demolded.

[0032] In S1, expandable graphite was prepared using a sulfuric acid-nitric acid mixed acid oxidation intercalation method. A certain amount of expandable graphite was then added to a stirred expansion furnace (maintaining a rotation speed of 10 rpm). By controlling the high-temperature expansion (600 ℃, 800 ℃, 1000 ℃) and expansion time (10-30 s), graphite worm powder with the target expansion ratio (100-150 mL / g, 150-200 mL / g, 200-250 mL / g) was obtained. Specific preparation conditions are shown in the table below.

[0033] Comparative Example 1: In Comparative Example 1, which focuses on low expansion ratios, the difference from Example 1 is as follows: in step S1, the amount of intercalating agent is adjusted to 0.8-1.0 times the mass of natural flake graphite; in step S2, the expansion temperature is controlled at 600℃ and the expansion time is extended to 20-30 seconds, resulting in a graphite worm powder expansion ratio of only 100-150 mL / g.

[0034] Within this rate range, due to insufficient intercalator dosage and low expansion temperature, the intercalator decomposes incompletely, resulting in a lack of expansion driving force between graphite flakes. The resulting graphite worms exhibit extremely low curling degree, displaying a thicker lamellar structure and poor overall material flexibility. This powder with incompletely developed "worm" morphology has extremely poor flowability during subsequent molding, making it difficult to fully fill the microchannel structure of the mold cavity under high pressure. Furthermore, thick lamellar graphite is not prone to elastic deformation under pressure, easily leading to brittle fracture. Test results show that the surface roughness Ra of the smooth area of ​​the flow channel plate prepared in this comparative example is >15μm, and obvious cracks, damage, and incomplete filling defects are visible to the naked eye at the flow channel edges, completely failing to meet the basic requirements of flow batteries for plate flatness and sealing.

[0035] Comparative Example 2: In Comparative Example 1, the expansion ratio is used as a comparison with Example 1. The difference is that in step S1, the amount of intercalating agent is adjusted to 1.0-1.2 times the mass of natural flake graphite; in step S2, the expansion temperature is controlled at 800℃ and the expansion time is 15-20 seconds. The expansion ratio of the obtained graphite worm powder is 150-200 mL / g.

[0036] Compared to Comparative Example 1, the graphite worms in this magnification range began to exhibit a moderately curled morphology, with reduced sheet thickness and improved flexibility. The compressibility of the powder was significantly improved during compression molding. However, limited by the expansion temperature of 800℃, the expansion degree of some graphite sheets remained inconsistent, resulting in locally thicker "hard cores" within the powder. During compression molding, these incompletely expanded particles were difficult to completely crush and fuse, leading to localized over-accumulation on the product surface. Although the surface roughness of the smooth area was significantly improved compared to the low-magnification sample (Ra approximately 5-8 μm), unevenness due to density inconsistencies was still macroscopically observable. The insufficient smoothness of the smooth area could lead to uneven distribution of internal compressive force during prolonged operation, posing a risk of seal failure.

[0037] The flow battery flow channel plates prepared in the above three sets of examples / comparative examples were inspected using a roughness tester and an image measuring instrument. The results are shown in the table below:

[0038] As can be seen from the table above and the accompanying drawings, Comparative Example 1, due to its low expansion ratio, low degree of graphite worm curling, thick lamellars, and poor flexibility, resulted in extremely rough surfaces after molding, and obvious cracks and defects appeared at the flow channel edges. Comparative Example 2, although having a higher expansion ratio, still exhibited unevenness due to localized over-accumulation and uneven density on the molded surface. Example 1 of this invention, through systematic screening, determined an expansion ratio range of 200-250 mL / g. Within this range, the worm graphite exhibited suitable curling, moderate interlaminar porosity, and a uniform and dense packing structure. During molding, it demonstrated excellent compressibility, flowability, and elastic recovery, effectively suppressing defects such as surface roughness, flow channel defects, and edge cracks. The resulting flow channel plate had a surface roughness Ra < 1 μm in the smooth area, a flow channel structure dimensional deviation < ± 0.05 mm, and no cracks, bubbles, or defects at the flow channel edges, achieving high surface molding quality.

[0039] like Figure 2-4 As shown, the surface roughness of the flow channel plate prepared in Comparative Example 1 is extremely high, and obvious cracks and material defects caused by incomplete filling can be clearly observed at the flow channel edges. This is attributed to the low curling degree, thick lamellars, and poor flexibility of graphite worms in the expansion ratio range of 100-150 mL / g, which cannot effectively flow and fill the mold cavity during molding, and the thick lamellars are difficult to form a tight bond.

[0040] The surface roughness of the flow channel plate prepared in Comparative Example 2 was reduced, but local unevenness was still visible in the smooth area. This is because although the graphite worms in the 150-200 mL / g ratio range were moderately curled, the degree of expansion was uneven. The unexpanded "hard core" remaining in the powder formed local accumulation during molding, resulting in uneven overall product density and insufficient density and smoothness in the smooth area.

[0041] The surface of the flow channel plate prepared in Example 1 is extremely smooth and flat, with neat and sharp flow channel edges, free from any defects such as cracks, bubbles, or flaws. This directly verifies that the graphite worms in the expansion ratio range of 200-250 mL / g exhibit suitable curling degree, moderate interlayer porosity, and uniform and dense packing structure. During molding, they demonstrate excellent compressibility, flowability, and elastic recovery, enabling high-precision replication of the mold flow channel structure and fundamentally solving the technical problem of poor surface molding quality of flexible expanded graphite flow channel plates.

[0042] For any parts not mentioned in this application, existing technologies may be used or referenced.

[0043] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0044] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A process for fabricating a flow battery channel plate with high surface forming quality, characterized in that, Includes the following steps: S1: Using natural flake graphite as raw material, an oxidation intercalation process is carried out; S2: The graphite after the oxidation intercalation treatment is subjected to high-temperature expansion treatment to obtain graphite worm powder with an expansion ratio of 200 to 250 mL / g. S3: The graphite worm powder is subjected to multi-stage roller pressing to form a pre-pressed board; S4: The pre-pressed plate is subjected to molding to obtain the flow battery channel plate.

2. The preparation process according to claim 1, characterized in that, In steps S1-S2, the fixed carbon content of the natural flake graphite is ≥99.8%, and the mesh size is 80 mesh.

3. The preparation process according to claim 1, characterized in that, In steps S1-S2, the oxidation intercalation treatment adopts the sulfuric acid-nitric acid mixed acid oxidation intercalation method.

4. The preparation process according to claim 3, characterized in that, In steps S1-S2, the amount of intercalating agent used in the oxidation intercalation treatment is 1.2-1.5 times the mass of the natural flake graphite.

5. The preparation process according to claim 1, characterized in that, In steps S1-S2, the high-temperature puffing is carried out under stirring conditions, with a stirring speed of 10 rpm.

6. The preparation process according to claim 1 or 5, characterized in that, In steps S1-S2, the high-temperature puffing temperature is 1000℃ and the puffing time is 15-20s.

7. The preparation process according to claim 1, characterized in that, In steps S3-S4, the compression molding is performed under vacuum conditions.

8. The preparation process according to claim 1, characterized in that, In steps S3-S4, the same weight of the graphite worm powder is weighed and molded to ensure that the density of the prepared flow battery channel plate products is consistent.

9. The preparation process according to claim 1, characterized in that, The flow battery channel plate obtained in steps S3-S4 has a surface roughness Ra<1μm in the smooth area, a channel structure size deviation<±0.05 mm, and no cracks, bubbles or defects at the channel edge.

10. A flow channel plate for a flow battery, characterized in that, It is prepared by the preparation process described in any one of claims 1 to 9.

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