An electrode for a vanadium redox flow battery and a vanadium redox flow battery comprising the same

Abstract

An electrode for a vanadium redox flow battery and a vanadium redox flow battery including the same are disclosed. The disclosed electrode for a vanadium redox flow battery includes first carbon fibers having a diameter of 9 μm to 11 μm and second carbon fibers having a diameter of 6 μm to 8 μm.

Description

Technical Field

[0001] An electrode for a vanadium redox flow battery and a vanadium redox flow battery including the same are disclosed. More specifically, an electrode for a vanadium redox flow battery with low resistance and large surface area and a vanadium redox flow battery including the same are disclosed. Background Technology

[0002] Vanadium redox flow battery (VRFB) can be designed independently for output power and energy capacity, and has the advantages of long life and high safety, thus attracting much attention as a next-generation energy storage device.

[0003] The basic structure of a vanadium redox flow battery includes: an electrolyte tank for storing vanadium active materials in different oxidation states; a pump responsible for flow regulation and circulation; electrodes providing a reaction site for the active materials; and a separator for the positive and negative electrodes and a hydrogen ion exchange system (H₂O). + ) Migrating ion exchange membranes.

[0004] Unlike existing secondary batteries, the electrolyte in a vanadium redox flow battery is not contained within the battery cell, but rather stored in liquid form in a tank serving as an external storage device. It is supplied to the battery cell via a pump during charging and discharging. Since the energy capacity of the battery is determined by the amount of electrolyte contained in the storage container, and the output power is determined by the size and number of the single cell including the electrodes, both the energy capacity and output power can be easily adjusted. During charging, tetravalent vanadium ions (VO₄²⁻) in the positive electrode... 2+ ) is oxidized to the pentavalent form of vanadium ions (VO2). + ), vanadium ions in trivalent form in the negative electrode (V 3+ Vanadium ions are reduced to their divalent form (V2). 2+ The charging and discharging process utilizes the resulting oxidation / reduction potential difference between ions in the electrolyte to generate electrical energy. Conversely, during discharge, the oxidation number of vanadium ions changes. The chemical reactions involved in charging and discharging are shown below. In these chemical reactions, "SHE" is an abbreviation for "standard hydrogen electrode".

[0005] - Positive electrode: VO 2+ +H2O↔VO 2+ +2H + +e - (1.00 V vs. SHE)

[0006] - Negative electrode: V 3+ +e - ↔V 2+ (-0.26 V vs. SHE)

[0007] In this type of vanadium redox flow battery, the electrodes are extremely important, among which carbon felt (CF) is the most widely used.

[0008] Existing carbon felt electrodes suffer from high resistance and small surface area, resulting in low voltage and energy efficiency. Summary of the Invention

[0009] Technical issues

[0010] One embodiment of the present invention provides an electrode for a vanadium redox flow battery that has low resistance and large surface area.

[0011] Another embodiment of the present invention provides a vanadium redox flow battery including the electrodes for the vanadium redox flow battery.

[0012] Technical solution

[0013] One aspect of the present invention provides an electrode for a vanadium redox flow battery, comprising:

[0014] First carbon fibers with a diameter of 9 mm to 11 mm; and

[0015] The second carbon fiber has a diameter of 6 mm to 8 mm.

[0016] The weight ratio of the first carbon fiber to the second carbon fiber can be 50 to 80: 20 to 50.

[0017] The first carbon fiber and the second carbon fiber may each independently include PAN (polyacrylonitrile) based carbon fiber, Rayon (rayon) based carbon fiber, Pitch (pitch) based carbon fiber, or a combination thereof.

[0018] The thickness of the electrode used in the vanadium redox flow battery can be from 1 mm to 5 mm.

[0019] The total number of the first and second carbon fibers per unit weight of the electrode for the vanadium redox flow battery can be 120,000 ea / g or more.

[0020] The total surface area of ​​the first and second carbon fibers per unit weight of the electrode for the vanadium redox flow battery can be 1,500 cm². 2 / g or larger.

[0021] The density of the electrode used in the vanadium redox flow battery can be 0.08 g / cm³. 3 Up to 0.12 g / cm 3 .

[0022] Another aspect of the present invention provides a vanadium redox flow battery.

[0023] It includes the electrode for the vanadium redox flow battery.

[0024] Beneficial effects

[0025] According to an embodiment of the present invention, the electrode for a vanadium redox flow battery has low resistance and large surface area, thereby improving voltage efficiency and energy efficiency and reducing resistance. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a method for measuring the resistance of an electrode for a vanadium redox flow battery according to an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of an apparatus for evaluating the performance of an electrode for a vanadium redox flow battery according to an embodiment of the present invention by cyclic voltammetry.

[0028] Figure 3 To utilize Figure 2 The cyclic voltammetry curve obtained from the device.

[0029] Figure 4 A schematic diagram of an apparatus for evaluating the performance of a unit cell including an electrode for a vanadium redox flow battery according to an embodiment of the present invention. Detailed Implementation

[0030] Hereinafter, an electrode for a vanadium redox flow battery and a vanadium redox flow battery including the electrode according to an embodiment of the present invention will be described in detail.

[0031] In this specification, "carbon fiber" refers to a fiber obtained by carbonizing PAN (polyacrylonitrile)-based oxidized fiber, Rayon (rayon)-based oxidized fiber, Pitch (asphalt)-based oxidized fiber, or a combination thereof at a carbonization process of 600°C to 1,000°C, followed by graphitization at a graphitization process of 1,300°C to 2,400°C. When the temperatures of the carbonization process and the graphitization process are respectively within the aforementioned ranges, the carbon fiber can have the same size, structure, and properties.

[0032] An electrode for a vanadium redox flow battery according to an embodiment of the present invention includes a first carbon fiber with a diameter of 9 μm to 11 μm and a second carbon fiber with a diameter of 6 μm to 8 μm. When the diameters of the first carbon fiber and the second carbon fiber are respectively within the ranges described, an electrode for a vanadium redox flow battery with reduced resistance and increased total number and total surface area per unit weight of the first and second carbon fibers can be obtained.

[0033] The weight ratio of the first carbon fiber to the second carbon fiber can be 50 to 80: 20 to 50. When the weight ratio of the first carbon fiber to the second carbon fiber is within the range described above, an electrode for a vanadium redox flow battery can be obtained that exhibits reduced resistance and increases in both the total number and total surface area of ​​the first and second carbon fibers per unit weight.

[0034] The first carbon fiber and the second carbon fiber may each independently include PAN (polyacrylonitrile) based carbon fiber, Rayon (rayon) based carbon fiber, Pitch (pitch) based carbon fiber, or a combination thereof.

[0035] In addition, the thickness of the electrode used in vanadium redox flow batteries can be from 1 mm to 5 mm, for example, from 1 mm to 3 mm.

[0036] The total number of the first and second carbon fibers per unit weight of the electrode for the vanadium redox flow battery can be 120,000 ea / g or more. Thus, if the total number of the first and second carbon fibers per unit weight of the electrode for the vanadium redox flow battery increases, the connectivity between the fibers increases, which leads to a decrease in the electrode's resistance. This, in turn, increases the electron mobility of the vanadium redox flow battery including the electrode during charging and discharging, thereby improving the battery's efficiency during operation.

[0037] Furthermore, the total surface area of ​​the first and second carbon fibers per unit weight of the electrode for the vanadium redox flow battery can be 1,500 cm². 2 / g or greater. Thus, if the total surface area of ​​the first and second carbon fibers per unit weight of the electrode for the vanadium redox flow battery increases, the electrode surface area capable of generating active species (vanadium ions with various oxidation states) increases, thereby promoting the rapid reaction of active species under high current, and thus improving the efficiency of the vanadium redox flow battery including the electrode.

[0038] The density of the electrode used in the vanadium redox flow battery can be 0.08 g / cm³. 3 Up to 0.12 g / cm 3 When the density of the electrode for the vanadium redox flow battery is within the specified range, compared to a density higher than this range, the fluidity of the electrolyte in the vanadium redox battery including the electrode is improved, thereby enabling the voltage efficiency, energy efficiency, and charge / discharge capacity to be maintained at a higher level.

[0039] Another aspect of the present invention provides a vanadium redox flow battery including the electrodes for the vanadium redox flow battery described above.

[0040] The present invention will be described below through the following embodiments, but the present invention is not limited to the following embodiments.

[0041] Example 1: Preparation of electrodes for vanadium redox flow batteries

[0042] 300 kg of PAN (polyacrylonitrile)-based oxidized fibers (Zoltek, OX staple fiber) are fed into the raw material inlet of the felt production line. Specifically, a first PAN-based oxidized fiber with a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxidized fiber with a length of 60 mm and a diameter of 10.5 μm are mixed at a weight ratio of 65:35 before being fed in. The fed PAN-based oxidized fibers are then conveyed to a mixing tank and mixed for 30 minutes while air is introduced. Subsequently, to prevent the mixed PAN-based oxidized fibers from tangling, they are mechanically dispersed through a can containing steel wire, and then formed into sheets of a certain thickness. The resulting sheets are cut into a certain size and stacked into eighteen layers. The stacked sheets are then pierced using a grooved tool to interweave them, thereby producing PAN-based oxidized fiber felt. Subsequently, the prepared PAN-based oxidized fiber felt is carbonized at 800°C and then graphitized at 1,700°C to obtain PAN-based carbon fiber felt. The prepared PAN-based carbon fiber felt is then activated by a thermal oxidation process at 700°C in an oxygen atmosphere to obtain an electrode for a vanadium redox flow battery.

[0043] Example 2: Preparation of electrodes for vanadium redox flow batteries

[0044] The first PAN-based oxide fiber with a length of 60 mm and a diameter of 13 μm was used instead of the first PAN-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm. Otherwise, the electrode for the vanadium redox flow battery was prepared using the same method as in Example 1.

[0045] Example 3: Preparation of electrodes for vanadium redox flow batteries

[0046] The first PAN-based oxide fiber with a length of 60 mm and a diameter of 16 μm was used instead of the first PAN-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm. Otherwise, the electrode for the vanadium redox flow battery was prepared using the same method as in Example 1.

[0047] Example 4: Preparation of electrodes for vanadium redox flow batteries

[0048] The second PAN-based oxide fiber with a length of 60 mm and a diameter of 9 μm was used instead of the second PAN-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm. Otherwise, the electrode for the vanadium redox flow battery was prepared using the same method as in Example 1.

[0049] Example 5: Preparation of electrodes for vanadium redox flow batteries

[0050] The second PAN-based oxide fiber with a length of 60 mm and a diameter of 12 μm was used instead of the second PAN-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm. Otherwise, the electrode for the vanadium redox flow battery was prepared using the same method as in Example 1.

[0051] Example 6: Preparation of electrodes for vanadium redox flow batteries

[0052] The electrodes for vanadium redox flow batteries were prepared using a first PAN-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm, with their weight ratio adjusted to 50:50. Otherwise, the electrodes were prepared using the same method as described in Example 1.

[0053] Example 7: Preparation of electrodes for vanadium redox flow batteries

[0054] The electrodes for vanadium redox flow batteries were prepared using a first PAN-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm, with the weight ratio of the two fibers adjusted to 80:20. Otherwise, the electrodes were prepared using the same method as described in Example 1.

[0055] Example 8: Preparation of electrodes for vanadium redox flow batteries

[0056] Rayon-based oxide fiber (Rontek, polyeter staple fiber) was used instead of PAN-based oxide fiber (Zoltek, OX staple fiber), and the electrode for the vanadium redox flow battery was prepared using the same method as in Example 1. Specifically, a first Rayon-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm and a second Rayon-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm were used in a weight ratio of 65:35.

[0057] Example 9: Preparation of electrodes for vanadium redox flow batteries

[0058] The electrode for the vanadium redox flow battery was prepared using the same method as in Example 1, except that Pitch-based oxide fiber (Osaka Gas, OG) was used instead of PAN (polyacrylonitrile)-based oxide fiber (Zoltek, OX staple fiber). Specifically, a first Pitch-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm and a second Pitch-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm were used in a weight ratio of 65:35.

[0059] Reference Example 1: Preparation of electrodes for vanadium redox flow batteries

[0060] The first PAN-based oxide fiber with a length of 60 mm and a diameter of 12 μm was used instead of the first PAN-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm. Otherwise, the electrode for the vanadium redox flow battery was prepared using the same method as in Example 1.

[0061] Reference Example 2: Preparation of electrodes for vanadium redox flow batteries

[0062] The first PAN-based oxide fiber with a length of 60 mm and a diameter of 17 μm was used instead of the first PAN-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm. Otherwise, the electrode for the vanadium redox flow battery was prepared using the same method as in Example 1.

[0063] Reference Example 3: Preparation of electrodes for vanadium redox flow batteries

[0064] The second PAN-based oxide fiber with a length of 60 mm and a diameter of 8 μm was used instead of the second PAN-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm. Otherwise, the electrode for the vanadium redox flow battery was prepared using the same method as in Example 1.

[0065] Reference Example 4: Preparation of electrodes for vanadium redox flow batteries

[0066] The second PAN-based oxide fiber with a length of 60 mm and a diameter of 13 μm was used instead of the second PAN-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm. Otherwise, the electrode for the vanadium redox flow battery was prepared using the same method as in Example 1.

[0067] Reference Example 5: Preparation of electrodes for vanadium redox flow batteries

[0068] The electrodes for vanadium redox flow batteries were prepared using a first PAN-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm, with their weight ratio adjusted to 40:60. Otherwise, the electrodes were prepared using the same method as in Example 1.

[0069] Reference Example 6: Preparation of electrodes for vanadium redox flow batteries

[0070] The electrodes for vanadium redox flow batteries were prepared using a first PAN-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm, with their weight ratio adjusted to 90:10. Otherwise, the electrodes were prepared using the same method as described in Example 1.

[0071] Comparative Example 1: Preparation of Electrodes for Vanadium Redox Flow Batteries

[0072] The electrodes for vanadium redox flow batteries were prepared using a first PAN-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm, with their weight ratio adjusted to 100:0. Otherwise, the electrodes were prepared using the same method as described in Example 1.

[0073] Comparative Example 2: Preparation of Electrodes for Vanadium Redox Flow Batteries

[0074] The electrodes for vanadium redox flow batteries were prepared using a first PAN-based oxide fiber with a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber with a length of 60 mm and a diameter of 10.5 μm, with the weight ratio of the two fibers adjusted to 0:100. Otherwise, the electrodes were prepared using the same method as described in Example 1.

[0075] The preparation conditions of the vanadium redox flow battery electrodes (VRFB electrodes) prepared in Examples 1 to 9, Reference Examples 1 to 6, and Comparative Examples 1 to 2 are summarized in Table 1 below.

[0076] Table 1

[0077]

[0078] Evaluation Example 1: Characteristic Evaluation of Electrodes for Vanadium Redox Flow Batteries

[0079] The characteristics of each vanadium redox flow battery electrode prepared in Examples 1 to 9, Reference Examples 1 to 6, and Comparative Examples 1 to 2 were evaluated according to the following method, and the results are shown in Table 2 below.

[0080] (1) Electrode thickness (mm): The thickness of the electrodes for vanadium redox flow batteries was measured using a dial thickness gauge from Mitsutoyo.

[0081] (2) Diameter of carbon fiber monofilament (μm): The carbon fiber felt was photographed using a scanning electron microscope (SEM) to obtain SEM images. The SEM images were then analyzed to measure the average diameter of the first carbon fiber and the average diameter of the second carbon fiber, and the average diameters were recorded as the diameter of the first carbon fiber and the diameter of the second carbon fiber, respectively. At this time, since the diameter of the first carbon fiber monofilament differs from that of the second carbon fiber monofilament by 1 μm or more, the first carbon fiber and the second carbon fiber can be easily distinguished from each other.

[0082] (3) Weight of carbon fiber monofilament (g): The theoretical density of carbon fiber (1.8 g / cm³) is calculated. 3 Multiply the volume of the carbon fiber monofilament (length: 60 mm, diameter of each carbon fiber) by the volume of the monofilament to calculate the weight of the carbon fiber monofilament contained in the electrode of the vanadium redox flow battery.

[0083] (4) Number of carbon fibers (ea / g): Divide the weight of the electrode for vanadium redox flow battery by the weight of the carbon fiber monofilament (length: 60 mm) to find the number of carbon fibers contained in the electrode for vanadium redox flow battery.

[0084] (5) Surface area of ​​carbon fiber monofilament (cm²) 2 Since the carbon fiber monofilament is cylindrical, the surface area of ​​the carbon fiber monofilament (length: 60 mm) can be easily calculated based on the length of 60 mm and the carbon fiber diameter measured in (2).

[0085] (6) Total surface area of ​​carbon fiber (cm²) 2 / g): Multiply the number of carbon fibers obtained in (4) by the surface area of ​​the carbon fiber monofilament calculated in (5) to obtain the total surface area of ​​the carbon fibers contained in the electrode for vanadium redox flow battery.

[0086] (7) Electrode density (g / cm³) 3 ): The measured weight per unit area of ​​the electrode (g / cm²) 2 Divide the electrode density by the electrode thickness (cm) measured in (1) to calculate the electrode density.

[0087] (8) Resistance of the electrodes (mΩ·cm) 2 ):like Figure 1 As shown, after placing the vanadium redox flow battery electrode between a pair of electrode plates and applying a load, with the electrode compressed by 20% relative to its initial thickness under the applied load, a load of 1.0 A / cm is applied to the pair of electrode plates.2 The resistance is determined by measuring the current (A) and voltage (V), and then dividing the measured voltage by the applied current.

[0088] Table 2

[0089]

[0090] Evaluation Example 2: Performance Evaluation of Electrodes for Vanadium Redox Flow Batteries

[0091] The electrodes for vanadium redox flow batteries prepared in Examples 1 to 9, Reference Examples 1 to 6, and Comparative Examples 1 to 2 were evaluated by cyclic voltammetry as follows, and the results are shown in Table 4 below.

[0092] (1) Measurement of ΔEp (mV): The electrodes of each vanadium redox flow cell (electrode size: 5 cm) were used. 2 It is fixed by a platinum mesh contained in the working electrode, and as... Figure 2 Configure as shown. At this point, use 3 M sulfuric acid / 25 mM V... 4+ / V 5+ Vanadium electrolyte was used as the electrolyte. Subsequently, the electrodes were connected to a cyclic voltammetry apparatus (METEK, VERSASTAT3), and a voltage was applied. The applied voltage was repeatedly increased from 0.6 V to 1.3 V and then decreased from 1.3 V to 0.6 V, while simultaneously measuring the current between the working electrode and the reference electrode. After the current measurement was completed, the following results could be obtained: Figure 3 The curve shown is analyzed, and ΔEp is calculated according to the following mathematical formula 1. ΔEp is a value expressed as the difference between the oxidation and reduction voltages, and is an indicator that confirms the rate of the redox reaction at the electrode and the rate of electron transfer in the resulting products.

[0093]

Mathematical Formula 1

[0094] △Ep (mV) = Absolute value of anode voltage - Absolute value of cathode voltage

[0095] (2) Current density (mA / cm) 2 Measurement of ) Figure 3 In the curve graph, the maximum value of the anode-side peak is recorded as the anode peak current density, and the maximum value of the cathode-side peak is recorded as the cathode peak current density. Additionally, in... Figure 3 In the curve, the anode region (0.6 V to 1.3 V) is V. 4+ → V 5+The oxidized region, the cathode region (1.3 V to 0.6 V), is V. 5+ →V 4+ The region that is reduced. The values ​​of the current density (anode peak current density and cathode peak current density) represent... Figure 3 The values ​​of the peak currents in the curve are indicators of the amount or extent of the reaction between vanadium and the electrode.

[0096] Evaluation Example 3: Vanadium redox flow battery performance evaluate

[0097] This constitutes a unit cell comprising the electrodes for each vanadium redox flow battery prepared in Examples 1 to 9, Reference Examples 1 to 6, and Comparative Examples 1 to 2. Specifically, after constructing the working cell and the reference cell, as follows... Figure 4 The settings are shown below. Furthermore, the evaluation conditions and methods for each unit cell are shown in Table 3 below. However, current was applied to the working cell, but not to the reference cell. While performing the charge-discharge cycles shown in Table 3 below, voltage efficiency, energy efficiency, and R50 were evaluated as follows, and the results are shown in Table 4 below.

[0098] Table 3

[0099]

[0100] (1) Evaluation of Coulomb efficiency (%): Evaluate Coulomb efficiency according to the following mathematical formula 2.

[0101]

Mathematical Formula 2

[0102] Coulombic efficiency (%) = Discharge capacity / Charge capacity × 100

[0103] (2) Evaluation of energy efficiency (%): Evaluate energy efficiency according to the following mathematical formula 3.

[0104]

Mathematical Expression 3

[0105] Energy efficiency (%) = Discharge energy / Charge energy × 100

[0106] (3) Evaluation of voltage efficiency (%): The voltage efficiency is evaluated according to the following mathematical formula 4.

[0107]

Mathematical Expression 4

[0108] Voltage efficiency (%) = Energy efficiency / Coulombic efficiency × 100

[0109] (4) R50 (Ω·cm) 2 Evaluation of R50: Evaluate R50 according to the following mathematical formula 5.

[0110]

Mathematical Expression 5

[0111] R50 (Ω·cm) 2 = (Absolute value of resistance at 50% charge + Absolute value of resistance at 50% discharge) / 2

[0112] Table 4

[0113]

[0114] Referring to Table 4 above, when using the vanadium redox flow battery electrodes prepared in Examples 1 to 9, compared with the vanadium redox flow battery electrodes prepared in Reference Examples 1 to 6 and Comparative Examples 1 to 2, ΔEp is lower, the cathode peak current density and anode peak current density are higher, the energy efficiency and voltage efficiency are both higher, and R50 is lower.

[0115] However, when using the vanadium redox flow battery electrodes prepared in Reference Examples 1 to 6 and Comparative Examples 1 to 2, compared with the case of using the vanadium redox flow battery electrodes prepared in Examples 1 to 9, ΔEp is higher, or at least one of the cathode peak current density and the anode peak current density is lower, or at least one of the energy efficiency and the voltage efficiency is lower, or R50 is higher.

[0116] The preferred embodiments of the present invention have been described above with reference to the accompanying drawings and examples. However, these are merely exemplary, and those skilled in the art should understand that various modifications and equivalent alternative embodiments can be made therein. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. An electrode for a vanadium redox flow battery, comprising: First carbon fiber with a diameter of 9 μm to 11 μm; as well as Second carbon fiber with a diameter of 6 μm to 8 μm.

2. The electrode for a vanadium redox flow battery according to claim 1, wherein, The weight ratio of the first carbon fiber to the second carbon fiber is 50 to 80: 20 to 50.

3. The electrode for a vanadium redox flow battery according to claim 1, wherein, The first carbon fiber and the second carbon fiber each independently comprise PAN (polyacrylonitrile) based carbon fiber, Rayon (rayon) based carbon fiber, Pitch (pitch) based carbon fiber, or a combination thereof.

4. The electrode for a vanadium redox flow battery according to claim 1, wherein, The thickness ranges from 1 mm to 5 mm.

5. The electrode for a vanadium redox flow battery according to claim 1, wherein, The total number of the first and second carbon fibers per unit weight is 120,000 ea / g or more.

6. The electrode for a vanadium redox flow battery according to claim 1, wherein, The total surface area of ​​the first and second carbon fibers per unit weight is 1,500 cm². 2 / g or larger.

7. The electrode for a vanadium redox flow battery according to claim 1, wherein, The density is 0.08 g / cm³. 3 Up to 0.12 g / cm 3 .

8. A vanadium redox flow battery comprising an electrode for a vanadium redox flow battery according to any one of claims 1 to 7.

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