A carbon fiber-based electrode for flow batteries and its preparation method

Abstract

This invention discloses a carbon fiber-based electrode for a flow battery and its preparation method. The method includes the following steps: selecting an electrode substrate material; inserting a pore-forming filler into the surface of the electrode substrate material; carbonizing the electrode substrate material with the inserted pore-forming filler to form a porous structure at the portion of the electrode substrate material with the inserted pore-forming filler; and graphitizing the electrode substrate material containing the porous structure to obtain the carbon fiber-based electrode for the flow battery. By designing uniformly dense manifolds on the electrode side of the carbon fiber-based electrode for the flow battery, the electrolyte mass transfer capability of the carbon fiber-based electrode for the flow battery in the direction perpendicular to the separator is improved, the rapid transport of active materials in the near-separator region is accelerated, the thickness of the ion transport layer on the electrode surface on the separator side is reduced, the electrochemical reaction rate is increased, and the polarization caused by mass transfer is reduced. This solves the problem of electrolyte flow obstruction inside the electrode in the prior art and improves the overall performance of the flow battery.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, specifically to a carbon fiber-based electrode for flow batteries and its preparation method. Background Technology

[0002] Flow batteries, as a type of green secondary battery, are widely used in large-scale energy storage systems due to their high energy density, long cycle life, and good safety. Electrodes, as a key component of flow batteries, directly affect the overall performance of the battery. Carbon fiber-based electrodes have become the primary choice for flow battery electrodes due to their excellent conductivity and stability. Existing methods for preparing carbon fiber-based electrodes mainly include a pre-oxidation stage and a carbonization / graphitization stage. In the pre-oxidation stage, carbon fibers undergo cyclization, dehydrogenation, and oxidation processes to form carbon fibers with high molecular weight properties. In the carbonization / graphitization stage, carbon fibers undergo shrinkage and structural transformation to form carbon fibers with high rigidity. However, in the above-mentioned methods, existing electrodes lack effective flow channels, which obstructs the flow of electrolyte within the electrode, affecting the convective mass transfer of electrolyte to the separator side, and consequently impacting the reaction rate and voltage efficiency of the flow battery. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a carbon fiber-based electrode for flow batteries and a method for preparing the same, so as to solve the technical problems mentioned in the prior art.

[0004] A carbon fiber-based electrode for a flow battery includes an electrode substrate. The surface of the electrode substrate has a plurality of confluence holes to form an electrolyte transport channel on the electrode side of the electrode substrate, for the electrolyte to flow from the electrode side to the separator side.

[0005] The manifold is formed by carbonizing the surface of the electrode substrate using a pore-forming filler.

[0006] Optionally, the density of the manifold holes is 1-15 per cm. 2 ;

[0007] Preferably, the diameter of the manifold is 0.2-3 mm.

[0008] Optionally, the thickness of the electrode substrate is 0.5-5 mm;

[0009] Preferably, the depth of the manifold is at least half the thickness of the electrode substrate.

[0010] A method for preparing a carbon fiber-based electrode for a flow battery, the method comprising the following steps:

[0011] Select an electrode substrate material and insert a pore-forming filler into the surface of the electrode substrate material;

[0012] The electrode substrate material with the pore-forming filler inserted is carbonized to form a pore structure in the part of the electrode substrate material with the pore-forming filler inserted.

[0013] The electrode substrate material containing the porous structure is graphitized to obtain the carbon fiber-based electrode for the flow battery.

[0014] Optionally, the electrode substrate material is selected from carbon-based precursor materials;

[0015] The carbon-based precursor material is polyacrylonitrile-based carbon felt, polyacrylonitrile-based graphite felt, polyacrylonitrile-based carbon cloth, or polyacrylonitrile-based carbon paper.

[0016] Preferably, the thickness of the carbon-based precursor material is 0.8-10 mm.

[0017] Optionally, the method further includes: pre-oxidizing the electrode substrate material before inserting the pore-forming filler on the surface of the electrode substrate material;

[0018] The pre-oxidation treatment conditions are: oxidation treatment at 270-290℃ for 85-95 minutes in an air atmosphere.

[0019] Optionally, the pore-forming filler is made of a material that does not deform during high-temperature sintering and does not undergo a carbonization reaction;

[0020] Preferably, the pore-forming filler is made of carbon-based material;

[0021] More preferably, the pore-forming filler is made of carbon fiber bundles or high-carbon needles.

[0022] Optionally, the diameter of the pore-forming filler is 1-3 mm;

[0023] Preferably, the penetration depth of the pore-forming filler is at least half the thickness of the electrode substrate material.

[0024] Optionally, the conditions for the carbonization treatment are:

[0025] The carbonization temperature is 950-1050℃, and the carbonization time is 1.8-2.2h;

[0026] Preferably, the carbonization process is carried out under a protective atmosphere.

[0027] Optionally, the conditions for the graphitization treatment are:

[0028] The graphitization temperature is 1900-2300℃, and the graphitization time is 1-3 hours.

[0029] Preferably, the graphitization process is carried out under a protective atmosphere.

[0030] The beneficial effects that this invention can produce include:

[0031] This invention provides a carbon fiber-based electrode for a flow battery and its preparation method. By designing uniformly dense manifolds on the electrode side of the carbon fiber-based electrode, the mass transfer capability of the electrode in the direction perpendicular to the separator is improved. This accelerates the rapid transport of active materials in the near-separator region, reduces the thickness of the ion transport layer on the electrode surface on the separator side, increases the electrochemical reaction rate, reduces polarization caused by mass transfer, and improves voltage efficiency and electrolyte utilization during charge and discharge. This solves the problem of obstructed electrolyte flow inside the electrode in existing technologies, thereby improving the overall performance of the flow battery. The manifolds in this preparation method are thermoformed, which avoids fiber breakage, felt structure damage, and pore springback problems during post-processing of the carbon fiber electrode, resulting in stability comparable to that of electrodes without manifolds. Furthermore, this preparation method is simple, easy to operate, suitable for large-scale production, and can reduce production costs and improve production efficiency. Attached Figure Description

[0032] Figure 1 This is a schematic flowchart of a method for preparing a carbon fiber-based electrode for a flow battery according to the present invention.

[0033] Figure 2 This is a schematic diagram of the structure of a carbon fiber-based electrode for a flow battery according to the present invention;

[0034] In the figure: 1. Electrode substrate, 2. Manifold. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Please see Figure 1As shown, this invention provides a method for preparing a carbon fiber-based electrode for a flow battery. The preparation method includes the following steps: Step 1, pre-oxidation stage: Selecting a carbon-based precursor material of a predetermined thickness as the electrode substrate raw material, and subjecting the electrode substrate raw material to pre-oxidation treatment. The treatment conditions are: oxidation treatment at 270-290℃ for 85-95 minutes in an air atmosphere to form a pre-oxidized fiber felt with high molecular properties; Step 2, manufacturing manifold 2: Uniformly inserting multiple high-carbon needles or carbon fiber bundles into the surface of the pre-oxidized fiber felt in a vertical direction as pore-forming filler to ensure that the manifold 2 formed on the surface of the carbon fiber-based electrode of the flow battery has the shortest electrolyte transport path and the minimum pressure loss; Step 3, carbonization stage: Carbonizing the pre-oxidized fiber felt with pore-forming filler... The pre-oxidized fiber felt is placed in a carbonization furnace and carbonized at 950-1050℃ for 1.8-2.2 hours under a protective atmosphere to form an inherent and non-rebounding pore structure on its surface. During the heat treatment, the pore-forming filler generates internal stress within the pre-oxidized fiber felt, causing the fibers to naturally twist during shrinkage and structural transformation, forming an inherent and non-rebounding pore structure that serves as a channel for electrolyte transfer to the separator in the flow battery. Step four, graphitization stage: The pore-forming filler is removed from the pre-oxidized fiber felt, and the pre-oxidized fiber felt is placed in a graphitization furnace and graphitized at 1900-2300℃ for 1-3 hours under a protective atmosphere to obtain a carbon fiber-based electrode for the flow battery with manifold 2. In the above, the carbon-based precursor material is polyacrylonitrile-based carbon felt, polyacrylonitrile-based graphite felt, polyacrylonitrile-based carbon cloth, or polyacrylonitrile-based carbon paper. The thickness of the carbon-based precursor material is 0.8-10 mm, the diameter of the pore-forming filler is 1-3 mm, and the density of the pore-forming filler is 1-2 pores / cm³. 2 The penetration depth of the pore-forming filler is at least half the thickness of the electrode substrate material. The protective atmosphere of the carbonization furnace and graphitization furnace is nitrogen, helium, or argon.

[0037] It should be noted that in this embodiment, the carbon-based precursor material will shrink during the carbonization process, with a thickness shrinkage of 40% to 50%. After the pore-forming filler is removed, the pre-oxidized fiber felt will shrink slightly under inherent stress during the graphitization stage, so that the pore diameter of the manifold 2 is slightly smaller than the diameter of the pore-forming filler.

[0038] Please see Figure 2As shown, the present invention also provides a carbon fiber-based electrode for a flow battery. This carbon fiber-based electrode is fabricated using the method described above. The electrode includes an electrode substrate 1, on the surface of which a plurality of manifolds 2 are uniformly formed to create electrolyte transport channels on the electrode side of the electrode substrate 1, allowing the electrolyte to flow from the electrode side to the separator side. The manifolds 2 are formed by carbonizing the surface of the electrode substrate 1 using pore-forming filler. Specifically, the thickness of the electrode substrate 1 is 0.5-5 mm, and the density of the manifolds 2 is 1-15 per cm³. 2 The diameter of the manifold 2 is 0.2-3 mm, and the depth of the manifold 2 is at least half the thickness of the electrode substrate 1.

[0039] Example 1: Pre-oxidation stage: A 5mm thick polyacrylonitrile-based carbon felt was selected as the electrode substrate material. The electrode substrate material was pre-oxidized at 285℃ for 90 minutes to form a pre-oxidized fiber felt with high molecular properties. Manipulation hole 2: Multiple high-carbon needles or carbon fiber bundles with a diameter of 2mm were inserted into the surface of the pre-oxidized fiber felt in a rectangular array along the vertical direction as pore-forming fillers. The density of the pore-forming filler was 1 needle / cm². 2 The insertion depth is 4 mm; carbonization stage: the pre-oxidized fiber felt with inserted pore-forming filler is placed in a carbonization furnace and heated to 1020℃ for 2 hours to form inherent and non-rebounding manifolds 2 on the surface of the pre-oxidized fiber felt; graphitization stage: the pore-forming filler in the pre-oxidized fiber felt is removed, and the pre-oxidized fiber felt is placed in a graphitization furnace and heated to 2150℃ for high-temperature graphitization treatment for 1 hour to obtain the carbon fiber-based electrode for the flow battery. Specifically, the thickness of the carbon fiber-based electrode for the flow battery is 2.5 mm, and the density of the manifolds 2 is 2.5.

[0040] / cm 2 The diameter of manifold 2 is 1.5mm, and the depth of manifold 2 is 2.0mm.

[0041] Example 2: Pre-oxidation stage: A 5mm thick polyacrylonitrile-based carbon felt was selected as the electrode substrate material. The electrode substrate material was pre-oxidized at 280℃ for 90 minutes to form a pre-oxidized fiber felt with high molecular properties. Manipulation hole 2: Multiple high-carbon needles or carbon fiber bundles with a diameter of 2mm were inserted into the surface of the pre-oxidized fiber felt in a rectangular array along the vertical direction as pore-forming fillers. The density of the pore-forming filler was 2.5 needles / cm². 2The insertion depth is 4 mm; carbonization stage: the pre-oxidized fiber felt with the inserted pore-forming filler is placed in a carbonization furnace and heated to 1000℃ for 2 hours to form inherent and non-rebounding manifolds 2 on the surface of the pre-oxidized fiber felt; graphitization stage: the pore-forming filler in the pre-oxidized fiber felt is removed, and the pre-oxidized fiber felt is placed in a graphitization furnace and heated to 2200℃ for 1 hour to obtain the carbon fiber-based electrode for the flow battery. Specifically, the thickness of the carbon fiber-based electrode for the flow battery is 2.5 mm, and the density of the manifolds 2 is 2.5 per cm³. 2 The diameter of manifold 2 is 1.5mm, and the depth of manifold 2 is 2.0mm.

[0042] Example 3: The difference from Example 1 is that the diameter of the pore-forming filler is 2 mm, and the penetration depth of the pore-forming filler is 3.6 mm. Specifically, the thickness of the carbon fiber-based electrode of the flow battery is 2.5 mm, and the density of the manifold 2 is 2 per cm³. 2 The diameter of manifold 2 is 1.5mm, and the depth of manifold 2 is 1.8mm.

[0043] Example 4: The difference from Example 1 is that the density of the pore-forming filler is 2 pores / cm². 2 The diameter of the pore-forming filler is 3 mm, and the penetration depth of the pore-forming filler is 3.2 mm. Specifically, the thickness of the carbon fiber-based electrode for the flow battery is 2.5 mm, and the density of the manifold 2 is 2 per cm³. 2 The diameter of manifold 2 is 2.3 mm, and the depth of manifold 2 is 1.6 mm.

[0044] Example 5: The difference from Example 1 is that the density of the pore-forming filler is 1.5 pores / cm². 2 The diameter of the pore-forming filler is 3 mm, and the penetration depth of the pore-forming filler is 3.2 mm. Specifically, the thickness of the carbon fiber-based electrode for the flow battery is 2.5 mm, and the density of the manifold 2 is 1.5 pores / cm². 2 The diameter of manifold 2 is 2.3 mm, and the depth of manifold 2 is 1.6 mm.

[0045] Comparative Example 1: Polyacrylonitrile fiber felt with a thickness of 5 mm was selected and subjected to the same pre-oxidation, carbonization and graphitization processes to form a carbon fiber-based electrode for flow batteries with polymer properties.

[0046] In the above, the carbon fiber-based electrodes for flow batteries prepared in Examples 1-5 and Comparative Example 1 were used as the positive or negative electrodes of the flow batteries to test the overall performance of the batteries. The test results are shown in Table 1.

[0047] Table 1

[0048]

[0049]

[0050] As shown in Table 1, this invention improves the electrolyte mass transfer capability of the carbon fiber-based electrode in the direction perpendicular to the separator by designing uniformly dense manifolds 2 on the electrode side of the flow battery. This accelerates the rapid transport of active materials in the near-separator region, reduces the thickness of the ion transport layer on the electrode surface on the separator side, increases the electrochemical reaction rate, reduces polarization caused by mass transfer, and improves voltage efficiency and electrolyte utilization during charge and discharge. This solves the problem of electrolyte flow obstruction inside the electrode in existing technologies and improves the overall performance of the flow battery. The manifolds 2 in this preparation method are thermoformed, which avoids fiber breakage, felt structure damage, and pore springback problems during post-processing of the carbon fiber electrode, resulting in stability comparable to that of un-perforated electrodes. Furthermore, this preparation method is simple, easy to operate, suitable for large-scale production, and can reduce production costs and improve production efficiency.

[0051] Specifically, a corresponding needle plate can be designed based on the design density of the manifold holes 2 on the surface of the electrode substrate 1, as well as their hole diameter and hole depth. By controlling the needle density and needle size of the needle plate, the piercing depth can be optimized, thereby regulating and meeting the different requirements of the flow battery electrode. For example, the arrangement of the manifold holes 2 can be uniformly arrayed in rectangular, rhomboid, triangular or other shapes, and the distribution density of the manifold holes 2 can be adjusted.

Claims

1. A carbon fiber-based electrode for a flow battery, characterized in that, The carbon fiber-based electrode of the flow battery includes an electrode substrate (1), and a plurality of confluence holes (2) are formed on the surface of the electrode substrate (1) to form an electrolyte transport channel on the electrode side of the electrode substrate (1) for the electrolyte to flow from the electrode side to the membrane side. The manifold (2) is formed by carbonizing the surface of the electrode substrate (1) using a pore-forming filler. The pore-forming filler is made of a material that does not deform during high-temperature sintering and does not undergo carbonization.

2. The carbon fiber-based electrode for a flow battery according to claim 1, characterized in that, The density of the manifold (2) is 1-15 per cm³. 2 ; The diameter of the manifold (2) is 0.2-3 mm.

3. The carbon fiber-based electrode for a flow battery according to claim 1, characterized in that, The thickness of the electrode substrate (1) is 0.5-5 mm; The depth of the manifold (2) is at least half the thickness of the electrode substrate (1).

4. A method for preparing a carbon fiber-based electrode for a flow battery, characterized in that, The method includes the following steps: Select an electrode substrate material and insert a pore-forming filler into the surface of the electrode substrate material; wherein the pore-forming filler is a material that does not deform during high-temperature sintering and does not undergo a carbonization reaction; The electrode substrate material with the pore-forming filler inserted is carbonized to form a pore structure in the part of the electrode substrate material with the pore-forming filler inserted. The electrode substrate material containing the porous structure is graphitized to obtain the carbon fiber-based electrode for the flow battery.

5. The method for preparing a carbon fiber-based electrode for a flow battery according to claim 4, characterized in that, The electrode substrate is made from a carbon-based precursor material. The carbon-based precursor material is polyacrylonitrile-based carbon felt, polyacrylonitrile-based graphite felt, polyacrylonitrile-based carbon cloth, or polyacrylonitrile-based carbon paper. The thickness of the carbon-based precursor material is 0.8-10 mm.

6. The method for preparing a carbon fiber-based electrode for a flow battery according to claim 4, characterized in that, The method further includes: pre-oxidizing the electrode substrate material before inserting the pore-forming filler on the surface of the electrode substrate material; The pre-oxidation treatment conditions are: oxidation treatment at 270-290℃ for 85-95 minutes in an air atmosphere.

7. The method for preparing a carbon fiber-based electrode for a flow battery according to claim 4, characterized in that, The pore-forming filler is made of carbon-based material.

8. The method for preparing a carbon fiber-based electrode for a flow battery according to claim 4, characterized in that, The diameter of the pore-forming filler is 1-3 mm; The penetration depth of the pore-forming filler is at least half the thickness of the electrode substrate material.

9. The method for preparing a carbon fiber-based electrode for a flow battery according to claim 4, characterized in that, The conditions for the carbonization treatment are as follows: The carbonization temperature is 950-1050℃, and the carbonization time is 1.8-2.2h; The carbonization process is carried out under a protective atmosphere.

10. The method for preparing a carbon fiber-based electrode for a flow battery according to claim 4, characterized in that, The conditions for the graphitization process are as follows: The graphitization temperature is 1900-2300℃, and the graphitization time is 1-3 hours. The graphitization process is carried out under a protective atmosphere.

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