Electrode for vanadium redox flow battery and vanadium redox flow battery comprising same

Abstract

Disclosed are an electrode for a vanadium redox flow battery and a vanadium redox flow battery comprising same. The disclosed electrode for a vanadium redox flow battery comprises: a first carbon fiber having a diameter of 9-11 ㎛; and a second carbon fiber having a diameter of 6-8 ㎛.

Description

Electrode for vanadium redox flow battery and vanadium redox flow battery including same

[0001] Disclosed are an electrode for a vanadium redox flow battery and a vanadium redox flow battery comprising the same. More specifically, disclosed are an electrode for a vanadium redox flow battery having low electrical resistance and a large surface area, and a vanadium redox flow battery comprising the same.

[0002] Vanadium redox flow batteries (VRFBs) are attracting attention as next-generation energy storage devices because they can independently design output and energy capacity, and have the advantages of long life and safety.

[0003] The basic structure of a vanadium redox flow battery consists of electrolyte tanks storing vanadium active materials with different oxidation states, a pump for flow control and circulation, electrodes that provide a place for the active materials to react, and a device for separation of the two electrodes and hydrogen ions (H). + ) is composed of an ion exchange membrane that is responsible for the movement of water.

[0004] Unlike conventional secondary batteries, the vanadium redox flow battery does not contain the electrolyte inside the cell, but rather stores it in a liquid state in an external storage tank, and is supplied to the inside of the cell using a pump during the charge and discharge process. The energy capacity developed from the battery is determined by the amount of electrolyte contained in the storage container, and the output is determined by the size and number of single cells containing electrodes, so the size of the energy capacity and output can be easily controlled. When charging, the vanadium ion (VO) in the tetravalent form at the positive electrode 2+ ) is a pentavalent form of vanadium ion (VO2 + ) is oxidized to vanadium ion (V) in trivalent form at the cathode. 3+ ) is a divalent form of vanadium ion (V 2+) generates electrical energy by utilizing the oxidation / reduction potential difference of ions in the electrolyte that occurs as the vanadium ion is reduced. During discharge, the oxidation number of vanadium ions changes in reverse, and the chemical reaction equation for charge and discharge is as follows. In the chemical reaction equation below, "SHE" is an abbreviation for "standard hydrogen electrode".

[0005] - Bipolar: VO 2+ + H2O ↔ VO2 + + 2H + + e - (1.00 V vs. SHE)

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

[0007] In these vanadium redox flow batteries, the electrodes are very important, and carbon felt (CF) is the most widely used.

[0008] Conventional carbon felt electrodes have problems such as high electrical resistance and small surface area, resulting in low voltage efficiency and energy efficiency.

[0009] One embodiment of the present invention provides an electrode for a vanadium redox flow battery having low electrical resistance and a large surface area.

[0010] Another embodiment of the present invention provides a vanadium redox flow battery comprising the electrode for the vanadium redox flow battery.

[0011] One aspect of the present invention is:

[0012] First carbon fiber having a diameter of 9 to 11 μm; and

[0013] An electrode for a vanadium redox flow battery is provided, comprising a second carbon fiber having a diameter of 6 to 8 μm.

[0014] The weight ratio of the first carbon fiber to the second carbon fiber may be 50 to 80:20 to 50.

[0015] The first carbon fiber and the second carbon fiber may each independently include PAN (polyacrylonitrile)-based carbon fiber, Rayon-based carbon fiber, Pitch-based carbon fiber, or a combination thereof.

[0016] The electrode for the above vanadium redox flow battery may have a thickness of 1 to 5 mm.

[0017] The total number of the first carbon fiber and the second carbon fiber per unit weight of the electrode for the vanadium redox flow battery may be 120,000 ea / g or more.

[0018] The total surface area of ​​the first carbon fiber and the second carbon fiber per unit weight of the electrode for the vanadium redox flow battery is 1,500 cm 2 / g can be more than that.

[0019] The density of the electrode for the above vanadium redox flow battery is 0.08 to 0.12 g / cm 3 It could be.

[0020] Another aspect of the present invention is:

[0021] A vanadium redox flow battery comprising the above electrode for a vanadium redox flow battery is provided.

[0022] An electrode for a vanadium redox flow battery according to one embodiment of the present invention has low electrical resistance and a large surface area, thereby improving voltage efficiency and energy efficiency and reducing electrical resistance.

[0023] FIG. 1 is a drawing for explaining a method for measuring the electrical resistance of an electrode for a vanadium redox flow battery according to one embodiment of the present invention.

[0024] FIG. 2 is a drawing showing a device for evaluating the performance of an electrode for a vanadium redox flow battery according to one embodiment of the present invention by cyclic voltammetry.

[0025] Fig. 3 is a graph showing a cyclic voltammetry obtained using the device of Fig. 2.

[0026] FIG. 4 is a drawing showing a device for evaluating the performance of a unit cell including an electrode for a vanadium redox flow battery according to one embodiment of the present invention.

[0027] Hereinafter, an electrode for a vanadium redox flow battery according to one embodiment of the present invention and a vanadium redox flow battery including the same will be described in detail.

[0028] In this specification, "carbon fiber" means a fiber manufactured by carbonizing PAN (polyacrylonitrile)-based oxide fiber, Rayon-based oxide fiber, Pitch-based oxide fiber, or a combination thereof through a carbonization process at 600 to 1,000°C and then graphitizing through a graphitization process at 1,300 to 2,400°C. When the temperature of the carbonization process and the temperature of the graphitization process are each within the above ranges, the carbon fiber can have the same size, structure, and characteristics.

[0029] An electrode for a vanadium redox flow battery according to one embodiment of the present invention includes a first carbon fiber having a diameter of 9 to 11 μm and a second carbon fiber having a diameter of 6 to 8 μm. When the diameter of the first carbon fiber and the diameter of the second carbon fiber are each within the above range, an electrode for a vanadium redox flow battery having reduced electrical resistance and improved total number and total surface area of ​​the first carbon fiber and the second carbon fiber per unit weight can be obtained.

[0030] The weight ratio of the first carbon fiber to the second carbon fiber may be 50 to 80:20 to 50. When the weight ratio of the first carbon fiber to the second carbon fiber is within the above range, an electrode for a vanadium redox flow battery can be obtained in which the electrical resistance is reduced and the total number and total surface area of ​​the first carbon fiber and the second carbon fiber per unit weight are both improved.

[0031] The first carbon fiber and the second carbon fiber may each independently include PAN (polyacrylonitrile)-based carbon fiber, Rayon-based carbon fiber, Pitch-based carbon fiber, or a combination thereof.

[0032] Additionally, the electrode for the vanadium redox flow battery may have a thickness of 1 to 5 mm, for example, 1 to 3 mm.

[0033] The total number of the first carbon fibers and the second carbon fibers per unit weight of the electrode for the vanadium redox flow battery may be 120,000 ea / g or more. As such, when the total number of the first carbon fibers and the second carbon fibers per unit weight of the electrode for the vanadium redox flow battery increases, the degree of connectivity between the fibers increases, which results in a decrease in the electrical resistance of the electrode, and this in turn increases the mobility of electrons during charge and discharge in a vanadium redox flow battery including the electrode, resulting in an improvement in efficiency during battery operation.

[0034] In addition, the total surface area of ​​the first carbon fiber and the second carbon fiber per unit weight of the electrode for the vanadium redox flow battery is 1,500 cm 2 / g or more. In this way, when the total surface area of ​​the first carbon fiber and the second carbon fiber per unit weight of the electrode for the vanadium redox flow battery increases, the surface area of ​​the electrode where active species (vanadium ions having various oxidation states) can be generated increases, thereby promoting a rapid reaction of the active species at high current, thereby improving the efficiency of the vanadium redox flow battery including the electrode.

[0035] The density of the electrode for the above vanadium redox flow battery is 0.08 to 0.12 g / cm 3It may be. When the density of the electrode for the vanadium redox flow battery is within the above range, the flowability of the electrolyte in the vanadium redox battery including the electrode is improved compared to when the density is higher than the above range, so that the voltage efficiency, energy efficiency, and charge / discharge capacity can be maintained at high levels.

[0036] Another aspect of the present invention provides a vanadium redox flow battery comprising the electrode for the vanadium redox flow battery described above.

[0037] Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited to the following examples.

[0038] Example 1: Preparation of electrodes for vanadium redox flow batteries

[0039] A total of 300 kg of PAN (polyacrylonitrile)-based oxide fiber (Zoltek, OX staple fiber) was fed into the fuel inlet of the felt manufacturing line. Specifically, a first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm were mixed and fed in a weight ratio of 65:35. Thereafter, the fed PAN-based oxide fiber was transferred to a mixing tank and mixed for 30 minutes while adding air. Thereafter, the mixed PAN-based oxide fiber was mechanically dispersed by passing it through a can equipped with a wire to prevent it from becoming entangled with each other, and then manufactured into sheets of a constant thickness. The manufactured sheets were cut into a constant size, laminated into 18 sheets, and punched with a grooved needle to weave the laminated sheets together, thereby manufacturing a PAN-based oxide fiber felt. Thereafter, the PAN-based oxide fiber felt manufactured above was carbonized through a carbonization process at 800°C and graphitized through a graphitization process at 1,700°C to manufacture a PAN-based carbon fiber felt. Thereafter, the PAN-based oxide fiber felt manufactured above was activated through a thermal oxidation process at 700°C in an oxygen atmosphere to obtain an electrode for a vanadium redox flow battery.

[0040] Example 2: Preparation of electrodes for vanadium redox flow batteries

[0041] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a first PAN-based oxide fiber having a length of 60 mm and a diameter of 13 μm was used instead of the first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm.

[0042] Example 3: Preparation of electrodes for vanadium redox flow batteries

[0043] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a first PAN-based oxide fiber having a length of 60 mm and a diameter of 16 μm was used instead of the first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm.

[0044] Example 4: Preparation of electrodes for vanadium redox flow batteries

[0045] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a second PAN-based oxide fiber having a length of 60 mm and a diameter of 9 μm was used instead of a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm.

[0046] Example 5: Preparation of electrodes for vanadium redox flow batteries

[0047] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a second PAN-based oxide fiber having a length of 60 mm and a diameter of 12 μm was used instead of a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm.

[0048] Example 6: Preparation of electrodes for vanadium redox flow batteries

[0049] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm were used in a weight ratio of 50:50.

[0050] Example 7: Preparation of electrodes for vanadium redox flow batteries

[0051] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm were used in a weight ratio of 80:20.

[0052] Example 8: Preparation of electrodes for vanadium redox flow batteries

[0053] A vanadium redox flow battery electrode was manufactured in the same manner as in Example 1, except that a Rayon-based oxide fiber (Rontek, polyether staple fiber) was used instead of a PAN (polyacrylonitrile)-based oxide fiber (Zoltek, OX staple fiber). Specifically, a first Rayon-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm and a second Rayon-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm were used in a weight ratio of 65:35.

[0054] Example 9: Preparation of electrodes for vanadium redox flow batteries

[0055] A vanadium redox flow battery electrode was manufactured in the same manner as in Example 1, except that a pitch-based oxide fiber (Osaka gas, OG) was used instead of a PAN (polyacrylonitrile)-based oxide fiber (Zoltek, OX staple fiber). Specifically, a first pitch-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm and a second pitch-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm were used in a weight ratio of 65:35.

[0056] Reference Example 1: Preparation of electrode for vanadium redox flow battery

[0057] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a first PAN-based oxide fiber having a length of 60 mm and a diameter of 12 μm was used instead of the first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm.

[0058] Reference Example 2: Preparation of electrodes for vanadium redox flow batteries

[0059] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a first PAN-based oxide fiber having a length of 60 mm and a diameter of 17 μm was used instead of the first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm.

[0060] Reference Example 3: Preparation of electrodes for vanadium redox flow batteries

[0061] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a second PAN-based oxide fiber having a length of 60 mm and a diameter of 8 μm was used instead of a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm.

[0062] Reference Example 4: Preparation of electrode for vanadium redox flow battery

[0063] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a second PAN-based oxide fiber having a length of 60 mm and a diameter of 13 μm was used instead of a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm.

[0064] Reference Example 5: Preparation of electrode for vanadium redox flow battery

[0065] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm were used in a weight ratio of 40:60.

[0066] Reference Example 6: Preparation of electrode for vanadium redox flow battery

[0067] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm were used in a weight ratio of 90:10.

[0068] Comparative Example 1: Preparation of electrode for vanadium redox flow battery

[0069] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm were used in a weight ratio of 100:0.

[0070] Comparative Example 2: Preparation of electrodes for vanadium redox flow batteries

[0071] An electrode for a vanadium redox flow battery was manufactured in the same manner as in Example 1, except that a first PAN-based oxide fiber having a length of 60 mm and a diameter of 14.5 μm and a second PAN-based oxide fiber having a length of 60 mm and a diameter of 10.5 μm were used in a weight ratio of 0:100.

[0072] The manufacturing conditions of the vanadium redox flow battery electrodes (VRFB electrodes) manufactured in Examples 1 to 9, Reference Examples 1 to 6, and Comparative Examples 1 to 2 are summarized and shown in Table 1 below.

[0073] Type of Oxidized Fiber Diameter of First Oxidized Fiber (㎛) Diameter of Second Oxidized Fiber (㎛) Weight Ratio of First Oxidized Fiber to Second Oxidized Fiber Example 1 PAN System 14.5 10.56 5:35 Example 2 PAN System 13.0 10.56 5:35 Example 3 PAN System 16.0 10.56 5:35 Example 4 PAN System 14.5 9.06 5:35 Example 5 PAN System 14.5 12.06 5:35 Example 6 PAN System 14.5 10.55 0:50 Example 7 PAN System 14.5 10.58 0:20 Example 8 Rayon System 14.5 10.56 5:35 Example 9 Pitch System 14.5 10.56 5:35 Reference Example 1 PAN System 12.0 10.56 5:35 Reference Example 2PAN Total 17.010.565:35Reference Example 3PAN Total 14.58.065:35Reference Example 4PAN Total 14.513.065:35Reference Example 5PAN Total 14.510.540:60Reference Example 6PAN Total 14.510.590:10Comparative Example 1PAN Total 14.510.5100:0Comparative Example 2PAN Total 14.510.50:100

[0074]

[0075] Evaluation Example 1: Characteristics Evaluation of Electrodes for Vanadium Redox Flow Battery

[0076] The characteristics of each of the vanadium redox flow battery electrodes manufactured in Examples 1 to 9, Reference Examples 1 to 6, and Comparative Examples 1 to 2 were evaluated using the following method, and the results are shown in Table 2 below.

[0077] (1) Electrode thickness (㎛): The thickness of the electrode for the vanadium redox flow battery was measured using a dial thickness gauge from Mitsutoyo.

[0078] (2) Diameter of 1 carbon fiber strand (㎛): After taking an SEM image by photographing the carbon fiber felt with a scanning electron microscope (SEM), the SEM image was analyzed to measure the average diameter of the first carbon fiber and the average diameter of the second carbon fiber, respectively, and each average diameter was recorded as the diameter of the first carbon fiber and the diameter of the second carbon fiber. At this time, since the diameter of 1 first carbon fiber strand and the diameter of 1 second carbon fiber strand differ by 1 ㎛ or more, the first carbon fiber and the second carbon fiber can be easily distinguished from each other.

[0079] (3) Weight of 1 strand of carbon fiber (g): Theoretical density of carbon fiber (1.8g / cm 3 ) and the volume of one carbon fiber strand (length: 60 mm, diameter of each carbon fiber) were multiplied to obtain the weight of one carbon fiber strand included in the electrode for a vanadium redox flow battery.

[0080] (4) Number of carbon fibers (ea / g): The number of carbon fibers included in the electrode for a vanadium redox flow battery was calculated by dividing the weight of the electrode for a vanadium redox flow battery by the weight of one strand of carbon fiber (length: 60 mm).

[0081] (5) Surface area of ​​one carbon fiber strand (cm) 2 ): Since the shape of one carbon fiber strand is a cylindrical shape, the surface area of ​​one carbon fiber strand (length: 60 mm) can be easily calculated from the length of 60 mm and the diameter of the carbon fiber measured in (2) above.

[0082] (6) Total surface area of ​​carbon fiber (cm) 2 / g): The surface area of ​​the entire carbon fibers included in the electrode for the vanadium redox flow battery was calculated by multiplying the number of carbon fibers obtained in (4) above and the surface area of ​​one carbon fiber strand calculated in (5) above.

[0083] (7) Density of electrode (g / cm) 3 ): Basis weight of measured electrode (g / cm 2 ) was divided by the electrode thickness (cm) measured in (1) above to calculate the electrode density.

[0084] (8) Electrical resistance of the electrode (mΩ·cm) 2 ): As shown in Fig. 1, an electrode for a vanadium redox flow battery is positioned between a pair of electrode plates, and then a load is applied to the pair of electrode plates so that the electrode is compressed by 20% of its initial thickness, and a pressure of 1.0 A / cm is applied to the electrode. 2 The voltage (V) was measured by applying a current (A), and the electrical resistance was obtained by dividing the measured voltage by the applied current.

[0085] Thickness of electrode (㎛) Diameter of 1 carbon fiber strand (㎛) Number of carbon fibers (ea / g) Surface area of ​​total carbon fibers (cm) 2 / g) Density of electrode (g / cm) 3 )Electrical resistance of the electrode (mΩ·cm) 2) First carbon fiber Second carbon fiber Example 12.52107160,9212,5560.095131 Example 22.5397178,9052,7160.096115 Example 32.55117147,6152,4240.096128 Example 42.56106191,3452,7410.094103 Example 52.51108141,1742,4170.097127 Example 62.48107179,3362,6990.098112 Example 72.56107142,5061,5420.090145 Example 82.51107175,5502,7880.095133 Example 92.46107137,9322,1910.093147 Reference Example 12.5387204,0472,9170.084149 Reference Example 22.55127137,4942,3150.094147 Reference Example 32.56105241,8023,0000.088163 Reference Example 42.55109127,6362,3090.084168 Reference Example 52.52107191,6122,7940.087151 Reference Example 62.50107130,2292,3180.094158Comparative example 12.5910-117,9522,2220.085178Comparative example 22.59-7240,7193,1750.074157

[0086]

[0087] Evaluation Example 2: Performance Evaluation of Electrodes for Vanadium Redox Flow Battery

[0088] Each of the vanadium redox flow battery electrodes manufactured in Examples 1 to 9, Reference Examples 1 to 6, and Comparative Examples 1 to 2 was evaluated as follows according to the cyclic voltammetry, and the results are shown in Table 4 below.

[0089] (1) Measurement of △Ep(mV): Each of the above vanadium redox flow battery electrodes (electrode size: 5 cm) 2 ) was fixed to the Pt mesh included in the working electrode and set as shown in Fig. 2. At this time, the electrolyte was 3M sulfuric acid / 25 mM V 4+ / V 5+A vanadium electrolyte was used. Afterwards, each electrode was connected to a cyclic voltammetry device (METEK, VERSASTAT3) and a voltage was applied. The current between the working electrode and the reference electrode was measured while repeating the process of increasing the applied voltage from 0.6 V to 1.3 V and then decreasing it from 1.3 V to 0.6 V. When the current measurement was completed, a graph like that shown in Fig. 3 was obtained, and the graph was analyzed to calculate △Ep according to the following mathematical equation 1. Here, △Ep is a value expressed using the difference in voltage values ​​of oxidation and reduction, and is an indicator that can be used to check how fast the redox reaction of the electrode occurs and the transfer speed of electrons, which are products after the reaction.

[0090] [Mathematical Formula 1]

[0091] △Ep(mV) = Absolute value of anodic voltage - Absolute value of cathodic voltage

[0092] (2) Current density (mA / cm) 2 ) Measurement: In the graph of Fig. 3, the maximum value of the anodic side peak was recorded as the anodic peak intensity, and the maximum value of the cathodic side peak was recorded as the cathodic peak intensity. In addition, in the graph of Fig. 3, the anodic region (0.6 V and 1.3 V) was recorded as V 4+ → V 5+ is the area where the oxide is oxidized, and the cathodic area (1.3 V - 0.6 V) is V 5+ → V 4+ This is the area where the current density (Anodic peak intensity and Cathodic peak intensity) is reduced. Here, the value of the current density (Anodic peak intensity and Cathodic peak intensity) is a numerical value representing the current size of each peak of the graph in Fig. 3, and is an indicator of the amount or degree of vanadium reacting with the electrode.

[0093] Evaluation Example 3: Performance Evaluation of a Vanadium Redox Flow Battery

[0094] A unit cell including each of the vanadium redox flow battery electrodes manufactured in Examples 1 to 9, Reference Examples 1 to 6, and Comparative Examples 1 to 2 was constructed. Specifically, a working cell and a reference cell were constructed and then set as shown in Fig. 4. In addition, the evaluation conditions and evaluation methods of each unit cell are shown in Table 3 below. However, current was applied to the working cell, but no current was applied to the reference cell. While performing the charge / discharge cycles in Table 3 below, voltage efficiency, energy efficiency, and R50 were evaluated as follows, and the results are shown in Table 4 below.

[0095] Conditions: Test type: SOC (state of cell) test Membrane: Commercial membrane (Dupont, N117) Electrolyte: 1.6M Vanadium, 4.2M H2SO4, Electrode surface area: 24.5cm 2 cut-off range1.0~1.65V(@ charge) / 1.65~1.0V(@ discharge)current densityConstant Current mode, 110mA / cm 2

[0096]

[0097] (1) Evaluation of Coulomb efficiency (%): Coulomb efficiency was evaluated according to the following mathematical formula 2.

[0098] [Equation 2]

[0099] Coulomb efficiency (%) = discharge capacity / charge capacity × 100

[0100]

[0101] (2) Evaluation of energy efficiency (%): Energy efficiency was evaluated according to the following mathematical formula 3.

[0102] [Equation 3]

[0103] Energy efficiency (%) = Discharge energy / Charge energy × 100

[0104]

[0105] (3) Evaluation of voltage efficiency (%): Voltage efficiency was evaluated according to the following mathematical formula 4.

[0106] [Equation 4]

[0107] Voltage efficiency (%) = Energy efficiency / Coulomb efficiency × 100

[0108]

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

[0110] [Equation 5]

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

[0112] Cyclic voltammetry unit cell performance evaluation△Ep(mV)Cathodic peak intensity (mA / cm 2 )Anodic peak intensity (mA / cm 2 )Coulombic efficiency(%)Energy efficiency(%)Voltage efficiency(%)R50(Ω·cm 2) Example 1 225 20.3 20.0 93.6 285.0 179.5 90.90 Example 2 20 222.1 21.4 93.8 185.7 7 80.4 6 0.86 Example 3 219 20.4 19.8 93.8 184.9 279.6 6 0.93 Example 4 19 223.9 23.2 93.8 5 86.4 5 81.1 3 0.82 Example 5 234 19.8 19.2 94.0 984.6 5 79.6 5 0.94 Example 6 19 023.8 23.4 93.8 286.1 280.8 0.83 Example 723219.318.894.0084.5379.460.95 Example 821121.921.093.8585.5380.270.88 Example 922219.318.794.0984.5679.570.96 Reference Example 124119.018.493.9684.4579.350.97 Reference Example 224019.218.694.0884.3179.320.97 Reference Example 324519.018.693.8584.2179.030.98 Reference Example 426317.916.893.7783.3478.151.09 Reference Example 525019.218.793.8284.3379.120.97Reference Example 626918.117.393.7383.5678.321.08Comparative Example 127117.216.494.0882.1277.261.13Comparative Example 226218.918.893.7083.9478.651.01

[0113]

[0114] Referring to Table 4 above, when the electrodes for vanadium redox flow batteries manufactured in Examples 1 to 9 were used, △Ep was lower, cathodic peak intensity and anodic peak intensity were higher, energy efficiency and voltage efficiency were both higher, and R50 was lower compared to when the electrodes for vanadium redox flow batteries manufactured in Reference Examples 1 to 6 and Comparative Examples 1 to 2 were used.

[0115] However, when the electrodes for vanadium redox flow batteries manufactured in Reference Examples 1 to 6 and Comparative Examples 1 to 2 were used, △Ep was higher, at least one of the cathodic peak intensity and the anodic peak intensity was lower, at least one of the energy efficiency and the voltage efficiency was lower, or R50 was higher compared to when the electrodes for vanadium redox flow batteries manufactured in Examples 1 to 9 were used.

[0116] While preferred embodiments of the present invention have been described above with reference to the drawings and examples, these are merely exemplary, and those skilled in the art will appreciate that various modifications and equivalent other embodiments are possible. Accordingly, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. First carbon fiber having a diameter of 9 to 11 μm; and An electrode for a vanadium redox flow battery comprising a second carbon fiber having a diameter of 6 to 8 μm.

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

3. In paragraph 1, An electrode for a vanadium redox flow battery, wherein the first carbon fiber and the second carbon fiber each independently include PAN (polyacrylonitrile)-based carbon fiber, Rayon-based carbon fiber, Pitch-based carbon fiber, or a combination thereof.

4. In paragraph 1, An electrode for a vanadium redox flow battery with a thickness of 1 to 5 mm.

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

6. In paragraph 1, The total surface area of ​​the first carbon fiber and the second carbon fiber per unit weight is 1,500 cm 2 / g or more vanadium redox flow battery electrode.

7. In paragraph 1, Density 0.08~0.12g / cm 3 Electrode for vanadium redox flow battery.

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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