JP2015122229A - Electrode, and redox flow cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode which can reduce cell resistivity of a fluid circulation type cell, and excellent in productivity.SOLUTION: An electrode 1 used for a fluid circulation type cell comprises: a conductive thick fiber layer 10 including as a main constituent a conductive thick fiber of which the diameter is 5 μm or more and 20 μm or less on average; and a thin fiber layer 11 including as a main constituent a conductive thin fiber of which the diameter is 0.005 μm or more and 4 μm or less on average, and which is arranged in one side of the thick fiber layer 10. Preferably, a porosity of the thin fiber layer is 80% or more and 99.9% or less, and a porosity of the thick fiber layer is 60% or more and 90% or less.

Description

  The present invention relates to an electrode used in a fluid flow type battery such as a fuel cell or a redox flow battery, and a redox flow battery using the electrode.

  A representative example of the fluid flow type battery is a redox flow battery (RF battery). An RF battery is a battery that charges and discharges using a difference in oxidation-reduction potential between ions contained in a positive electrode electrolyte and ions contained in a negative electrode electrolyte.

  FIG. 2 is an operation principle diagram of the RF battery 100 using vanadium ions as positive and negative active materials. As shown in FIG. 2, the RF battery 100 includes a battery cell 100 </ b> C separated into a positive electrode cell 102 and a negative electrode cell 103 by a diaphragm 101 that transmits hydrogen ions (protons). A positive electrode 104 is built in the positive electrode cell 102, and a positive electrode electrolyte tank 106 for storing a positive electrode electrolyte is connected via conduits 108 and 110. Similarly, the negative electrode cell 103 contains a negative electrode 105 and is connected to a negative electrolyte tank 107 for storing a negative electrolyte through conduits 109 and 111. The electrolyte stored in the tanks 106 and 107 is circulated in the cells 102 and 103 by the pumps 112 and 113 during charging and discharging.

  The battery cell 100C is normally formed inside a structure called a cell stack 200, as shown in the lower diagram of FIG. As shown in the upper diagram of FIG. 3, the cell stack 200 includes a cell frame 120 including a bipolar plate 121 integrated with a frame-shaped frame body 122, a positive electrode 104, a diaphragm 101, and a negative electrode 105 in this order. The structure laminated | stacked by is provided. In this configuration, the gap between the cell frames 120 is sealed with the seal structure 127, and one battery cell 100 </ b> C is formed between the bipolar plates 121 of the adjacent cell frames 120.

  Distribution of the electrolyte solution to the battery cell 100 </ b> C in the cell stack 200 is performed by the supply manifolds 123 and 124 formed in the frame body 122 and the drainage manifolds 125 and 126. The positive electrode electrolyte is supplied from the liquid supply manifold 123 to the positive electrode 104 disposed on the one surface side of the bipolar plate 121 through a groove formed on one surface side (the front surface side of the paper) of the frame body 122. The positive electrode electrolyte is discharged to the drainage manifold 125 through a groove formed in the upper portion of the frame body 122. Similarly, the negative electrode electrolyte is supplied from the liquid supply manifold 124 to the negative electrode 105 disposed on the other surface side of the bipolar plate 121 through a groove formed on the other surface side (the back surface of the paper) of the frame body 122. Is done. The negative electrode electrolyte is discharged to the drainage manifold 126 through a groove formed in the upper part of the frame body 122.

  The electrodes 104 and 105 constituting the cell 100C are often made of a porous conductive material so that the flow of the electrolyte, which is a fluid, does not hinder the flow of the electrolyte from the supply side to the drain side ( For example, see Patent Documents 1 to 3).

JP-A-8-287938 JP-A-8-46196 JP 2006-156029 A

  In recent years, construction of an energy system in consideration of the natural environment is expected, and improvement in battery performance of fluid flow type batteries such as fuel cells and RF batteries is expected. For example, fuel cells are expected to improve power generation efficiency, and storage batteries such as RF batteries are expected to improve charge / discharge efficiency. As means for meeting such expectations, development of an electrode capable of reducing the cell resistivity of a fluid flow type battery is required.

  On the other hand, in order to promote the spread of fluid flow type batteries, it is also expected to improve the productivity of fluid flow type batteries. As part of the improvement in productivity, there is a demand for improvement in electrode productivity.

  The present invention has been made in view of the above circumstances, and one of the objects of the present invention is to provide an electrode that can reduce the cell resistivity of a fluid flow battery and is excellent in productivity. . Another object of the present invention is to provide a redox flow battery using the electrode of the present invention.

  The electrode of the present invention is an electrode used in a fluid flow type battery, and has a thick fiber layer mainly composed of conductive thick fibers having an average diameter of 5 μm to 20 μm, and an average of 0.005 μm to 4 μm. And a fine fiber layer provided mainly on one surface side of the thick fiber layer.

  The electrode of the present invention can reduce the cell resistivity of a fluid flow type battery and is excellent in productivity.

It is the schematic of the electrode of embodiment used for a fluid flow type battery. It is an operation | movement principle figure of a redox flow battery. It is a schematic block diagram of the cell stack of a redox flow battery.

[Description of Embodiment of the Present Invention]
First, the contents of the embodiment of the present invention will be listed and described.

[1] The electrode according to the embodiment is an electrode used for a fluid flow type battery, and a thick fiber layer mainly composed of conductive thick fibers having a diameter of 5 μm or more and 20 μm or less on the average, and an average of 0.00. A fine fiber layer mainly composed of conductive fine fibers having a diameter of 005 μm or more and 4 μm or less and provided on one side of the thick fiber layer.

  By providing the electrode with a fine fiber layer containing fine fibers having the above-mentioned fiber diameter, the cell resistivity of a fluid flow type battery (hereinafter simply referred to as a battery) to which this electrode is applied can be reduced. This is considered to be because by reducing the fiber diameter, the surface area of the electrode increases and the active point of the battery reaction at the electrode increases. In addition, it is considered that reducing the fiber diameter increases the porosity of the electrode and facilitates the fluid to reach every corner of the electrode, thereby contributing to a reduction in the cell resistivity of the battery.

  The productivity of the electrode can be improved by providing the electrode with a thick fiber layer containing thick fibers having the above-mentioned fiber diameter. This is because the thick fiber layer is superior in strength and strong to the fine fiber layer, and thus can prevent the fine fiber layer from being damaged when the electrode is produced. In addition, since the electrode whose predetermined strength is guaranteed by the thick fiber layer is difficult to be damaged when transported to the production site of the battery or cut into a desired shape, it contributes to the improvement of battery productivity.

[2] Examples of the electrode according to the embodiment include an electrode in which the fine fiber layer has a porosity of 80% or more and 99.9% or less and the thick fiber layer has a porosity of 60% or more and 90% or less. .

  For example, in the case of a redox flow battery, if the porosity of the fine fiber layer is small, the three-dimensional ion conduction path in the electrolytic solution filled in the gap of the fine fiber layer is decreased, and the cell resistivity of the battery is increased. On the other hand, if the porosity of the fine fiber layer is 80% or more and 99.9% or less, the ion conduction path in the electrolyte filled in the void portion of the fine fiber layer increases, and the cell resistivity of the battery is increased. Can be reduced. On the other hand, if the porosity of the thick fiber layer is 60% or more and 90% or less, the flow of fluid is not extremely inhibited by the thick fiber layer, and the cell resistivity of the battery is increased by the thick fiber layer. Can be suppressed.

[3] Examples of the electrode according to the embodiment include an electrode in which the fine fiber layer has a higher porosity than the thick fiber layer.

  As already mentioned, it is the fine fiber layer that increases the active point of the battery reaction at the electrode. Therefore, by increasing the porosity of the fine fiber layer in the electrode, the fluid can easily spread to every corner of the fine fiber layer, and the cell resistivity of the entire electrode can be reduced.

[4] Examples of the electrode according to the embodiment include an electrode in which the fine fiber layer is formed by a solid phase method or a liquid phase method.

  According to the solid phase method or the liquid phase method, a fine fiber layer containing fine fibers having a desired fiber diameter and having a large porosity can be easily formed on one side of the thick fiber layer.

[5] Examples of the electrode according to the embodiment include an electrode having a two-layer structure of a fine fiber layer and a thick fiber layer.

  A two-layer electrode can be manufactured with high productivity. For example, if a thick fiber layer having excellent strength is prepared and a fine fiber layer is formed on one side of the thick fiber layer, the fine fiber layer can be prevented from being damaged during the manufacturing process of the electrode.

[6] As an electrode according to the embodiment, an electrode having a three-layer structure mainly including fine fibers and including a conductive layer provided on the other surface side of the thick fiber layer can be exemplified.

  The electrode having the three-layer structure can improve the contact resistance between the thick fiber layer and the bipolar plate. In a redox flow battery, the electrode is sandwiched between stacked bipolar plates and compressed. By attaching a conductive layer mainly composed of fine fibers to the bipolar plate side of the thick fiber layer, the contact area between the thick fiber layer and the bipolar plate can be increased, and the contact resistance can be reduced.

[7] Examples of the electrode according to the embodiment include an electrode having an average thickness of the fine fiber layer of 10 μm to 500 μm and an average thickness of the thick fiber layer of 100 μm to 500 μm.

  An electrode comprising a fine fiber layer and a thick fiber layer having the above thickness is excellent in balance between strength and electrode performance.

[8] Examples of the electrode according to the embodiment include an electrode in which the average thickness of the fine fiber layer is larger than the average thickness of the thick fiber layer.

  According to the said structure, the battery which is excellent in battery performance can be produced rather than the electrode whose average thickness of a fine fiber layer is smaller than the average thickness of a thick fiber layer. As described above, since it is the fine fiber layer that increases the active point of the battery reaction in the electrode, if the proportion of the fine fiber layer in the electrode is increased, the active point of the battery reaction in the electrode can be greatly increased. Because.

[9] As an electrode according to the embodiment, an electrode in which the tensile strength of the thick fiber layer is 98 kPa or more can be exemplified.

A thick fiber layer having a tensile strength of 98 kPa (about 1 kgf / cm ² ) or more can sufficiently serve as a substrate for holding the fine fiber layer.

[10] Examples of the electrode according to the embodiment include an electrode in which the thick fiber layer is carbon paper or carbon cloth.

  Carbon paper and carbon cloth are suitable as a thick fiber layer because they have sufficient conductivity and tensile strength.

[11] A redox flow battery according to the embodiment includes the electrode of the above-described embodiment.

  The redox flow battery of the embodiment is excellent in battery performance. This is because the cell resistivity of the redox flow battery is reduced by including the electrode of the embodiment.

[Details of the embodiment of the present invention]
Hereinafter, specific examples of the electrode according to the present embodiment will be described with reference to the drawings. In addition, this invention is not necessarily limited to these illustrations, is shown by the claim, and intends that all the changes within the claim, the meaning equivalent, and the range are included.

<Embodiment 1>
Embodiment 1 demonstrates the electrode 1 used for the redox flow battery (henceforth RF battery) which is a typical example of a fluid flow type battery based on FIG. Since the configuration other than the electrode 1 can adopt the same configuration as the conventional RF battery 100 described with reference to FIGS. 2 and 3, detailed description thereof will be omitted.

≪Electrode≫
The electrode 1 of the present embodiment has a multilayer structure including at least a thick fiber layer 10 and a fine fiber layer 11. The thick fiber layer 10 is preferably disposed on the bipolar plate 121 side on the right side of the paper, and the fine fiber layer 11 is preferably disposed on the left side of the diaphragm 101 on the paper surface. Of these two layers, the main layer for the battery reaction is the fine fiber layer 11, and the thick fiber layer 10 serves as a base material for holding the fine fiber layer 11 so as not to be damaged. Hereinafter, a detailed configuration of each layer will be described.

[Thick fiber layer]
The thick fiber layer 10 is a layer mainly composed of conductive thick fibers. The thick fiber layer 10 only needs to have high conductivity and strength as a base material.

  First, the configuration of the thick fibers that make up the thick fiber layer 10 will be described. The characteristics required for the material constituting the thick fibers are to have conductivity and not to be corroded by the electrolytic solution. A typical example of a material that satisfies such characteristics is carbon. In addition, metals such as Ti and stainless steel can be used as the material for the thick fibers. Here, as already described, since the layer that is the main component of the battery reaction is the fine fiber layer 11, the material of the thick fibers constituting the thick fiber layer 10 may be a material that causes the battery reaction. A material that does not cause a battery reaction may be used.

  The average diameter of the thick fibers is 5 μm or more and 20 μm or less. With such a thick fiber, the thick fiber layer 10 can have strength as a base material. A preferable average diameter of the thick fibers is 7 μm or more and 12 μm or less, and a more preferable average diameter of the thick fibers is 7 μm or more and 10 μm or less. An average diameter can be calculated | required by averaging the result measured 5 or more points | pieces per 1 visual field under a microscope. This measurement method is the same for the average diameter of fine fibers described later.

  The thick fiber layer 10 including the thick fibers having the above configuration preferably has a porosity of a certain level or more. This is because if the porosity of the thick fiber layer 10 is low, the flow of the electrolyte solution in the stacking direction of the bipolar plate 121 and the diaphragm 101 and the ionic conduction via protons in the electrolyte solution are hindered. Therefore, the porosity of the thick fiber layer 10 is preferably 60% or more and 90% or less. If the porosity is 60% or more, the flow of the electrolyte solution and the ionic conduction in the stacking direction become smooth. Moreover, if the porosity is 90% or less, the thick fiber layer 10 can have sufficient strength to exhibit the function as a base material. The porosity of the thick fiber layer 10 is more preferably 60% or more and 90% or less, and the porosity of the thick fiber layer 10 is more preferably 75% or more and 85% or less. The porosity can be obtained by calculation from the volume and mass of the thick fiber layer.

Moreover, it is preferable that the thick fiber layer 10 has a predetermined tensile strength as a base material for holding the fine fiber layer 11. For example, the tensile strength of the thick fiber layer 10 is preferably 1 kgf / cm ² (about 98 kPa) or more.

  The average thickness of the thick fiber layer 10 is preferably 100 μm or more and 500 μm or less. If it is such thickness, the fine fiber layer 11 mentioned later can be hold | maintained firmly and the damage of the fine fiber layer 11 can be prevented effectively. The average thickness can be obtained by averaging five or more different measurement results. As shown in FIG. 3, the electrodes 104 and 105 used in the form of the cell stack 200 are compressed between the two cell frames 120 and 120. Therefore, it can be considered that the thickness of the electrode 1 before compression shown in FIG. 1 is about 1 to 1.25 times the thickness of the electrodes 104 and 105 in the cell stack 200.

  Examples of the thick fiber layer 10 that satisfies the above-described characteristics include carbon paper and carbon cloth. Carbon paper which is a composite material of carbon fiber and carbon has sufficient conductivity and tensile strength. A carbon cloth which is a woven or non-woven fabric of carbon fibers also has sufficient conductivity and tensile strength.

For example, the carbon paper containing thick fibers having a fiber diameter of 7 μm and having a porosity of 80% and an average thickness of 0.1 mm has a tensile strength of 3 kgf / cm ² (about 294 kPa). When the average thickness of the carbon is 0.4 mm, the tensile strength is 8 kgf / cm ² (about 785 kPa). The tensile strength of carbon paper having a porosity of 90% and an average thickness of 0.4 mm is 4 kgf / cm ² (about 392 kPa).

[Fine fiber layer]
The fine fiber layer 11 is a layer mainly composed of conductive fine fibers. The fine fiber layer 11 only needs to have high conductivity and a function of causing a battery reaction. Hereinafter, the configuration of the fine fiber layer 11 will be described in detail. The method for obtaining the dimensions of each component of the fine fiber layer 11 is the same as that for the thick fiber layer 10.

  First, the configuration of the fine fibers constituting the fine fiber layer 11 will be described. The characteristics required for the fine fiber material are to have conductivity and to cause a battery reaction. A typical example of a material that satisfies such characteristics is carbon. In addition, a metal fiber or the like on which a catalyst is supported can be used as a fine fiber material.

  The average diameter of the fine fibers is 0.005 μm (5 nm) or more and 4 μm or less. With such a thin fiber, the surface area of the electrode can be increased and the number of places where a battery reaction occurs with the electrolyte can be increased. Moreover, if it is a fine fiber of such thickness, a sufficient quantity of space | gap will be formed in the fine fiber layer 11, and electrolyte solution can be spread in the fine fiber layer 11 thoroughly. As a result, the cell resistivity of the RF battery can be significantly reduced as compared with the conventional case. A preferable average diameter of the fine fibers is 0.05 μm or more and 1.0 μm or less, and a more preferable average diameter of the fine fibers is 0.05 μm or more and 0.3 μm or less.

  The fine fiber layer 11 including fine fibers having the above-described configuration preferably has a certain porosity or more. This is because if the porosity of the fine fiber layer 11 is low, the flow of the electrolyte solution in the stacking direction of the bipolar plate 121 and the diaphragm 101 and the ionic conduction via protons in the electrolyte solution are hindered. Further, in the fine fiber layer 11 where the battery reaction occurs, since the electrolyte solution and ion conduction are required to be better than the thick fiber layer 10, the porosity of the fine fiber layer 11 is the thick fiber layer. It is preferable that the porosity is higher than 10. Therefore, the porosity of the fine fiber layer 11 is preferably 80% or more and 99.9% or less. The porosity of the fine fiber layer 11 is more preferably 90% or more and 99.9% or less, and the porosity of the fine fiber layer 11 is more preferably 92% or more and 99.9% or less.

  Moreover, it is preferable that the average thickness of the fine fiber layer 11 is 10 micrometers or more and 500 micrometers or less. If the fine fiber layer 11 containing many fine fibers has many active points for battery reaction and has an average thickness of 10 μm or more, the fine fiber layer 11 exhibits the effect of sufficiently reducing the cell resistivity of the RF battery. The average thickness of the fine fiber layer 11 is more preferably 50 μm or more and 300 μm or less.

(Formation method of fine fiber layer)
The fine fiber layer 11 is formed on one side of the thick fiber layer 10. For forming the fine fiber layer 11 on one side of the thick fiber layer 10, it is preferable to use a solid phase method or a liquid phase method. For example, a template carbonization method, an electrospinning method, a melt-blow method, or the like can be used. These techniques are suitable for forming the fine fiber layer 11 composed of the fine fibers satisfying the above-mentioned fiber diameter and satisfying the above-mentioned porosity, and are tightly adhered to the thick fiber layer 10. 11 can be formed. After the fine fiber layer 11 is formed, the fine fiber layer 11 is preferably subjected to flameproofing treatment and carbonization treatment.

  Moreover, if it is the said solid phase method or a liquid phase method, the electrode 1 can be manufactured with high productivity by the roll to roll (roll-to-roll) system. Specifically, the fine fiber layer 11 is formed on the surface of the thick fiber layer 10 by a solid phase method or a liquid phase method while the thick fiber layer 10 wound around the first roll is fed out to the second roll. The electrode 1 on which the fine fiber layer 11 is formed on the layer 10 is wound around a second roll. Here, the electrode 1 can be produced while winding the electrode 1 around the second roll because the thick fiber layer 10 mechanically protects the fine fiber layer 11 and suppresses damage to the fine fiber layer 11. is there.

(Other)
Furthermore, the electrode 1 may have a three-layer structure including a conductive layer 13 provided on the other surface side of the thick fiber layer 10 (see a portion indicated by an imaginary line). The conductive layer 13 can employ the same configuration as the fine fiber layer 11. In the cell stack 200 shown in FIG. 3, the electrode 1 (104 and 105 in FIG. 3) is sandwiched between the bipolar plates 121 and 121 to be stacked and compressed. By providing the conductive layer 13 mainly composed of fine fibers on the bipolar plate 121 side of the thick fiber layer 10, the contact area between the thick fiber layer 10 and the bipolar plate 121 can be increased and the contact resistance can be reduced.

[Configuration of RF battery other than electrodes]
In the description of the electrode 1, it was stated that the configuration of the RF battery 100 (see FIG. 2) other than the electrode 1 can be the same as the conventional one. However, when the RF battery 100 is configured using the electrode 1, it is preferable to form a flow channel through which the electrolytic solution flows on the surface of the bipolar plate 121 (see the upper diagram in FIG. 3). By forming the flow grooves in the bipolar plate 121, the electrolytic solution can be supplied from the entire surface of the bipolar plate 121 toward the electrode 1 (104.105 in FIG. 3), and the battery between the electrode 1 and the electrolytic solution can be supplied. The reaction is performed smoothly.

  The formation state of the flow grooves in the bipolar plate 121 is not particularly limited. For example, it may be provided with a series of flow grooves connected from the electrolyte supply side to the discharge side, a supply-side flow groove connected to the electrolyte supply side, a discharge-side flow groove connected to the electrolyte discharge side, May be provided. Any of the flow grooves is preferably configured to cover almost the entire surface of the bipolar plate.

<Example of analysis>
In the analysis example, a simulation is performed assuming an RF battery 100 using a two-layer electrode (condition I below) and an RF battery 100 using a single-layer electrode (condition II below). The resistivity (Ω · cm ² ) was determined. Specifically, the voltage distribution and the current distribution inside the battery were obtained by the calculation method described in the following document 1, and the cell resistivity was obtained from the difference between the cell voltage when the current was applied and when the current was not supplied. Further, the reaction area density A used in the simulation was obtained by using a general relationship that A is inversely proportional to d when the electrode fiber diameter is d. Furthermore, in a two-layer electrode, when the porosity of the electrode fiber is ε, the liquid permeability K of each electrode is proportional to d ² ε ³ / (1-ε) ² (called the Carman-Kozeny rule). It was assumed that the liquid permeability was the same for both layers. That is, the electrode fiber porosity on the membrane side of the two-layer structure electrode was set so that the liquid flow velocity distribution was the same as that of the single-layer structure electrode. In this analysis example, a single-cell RF battery including one positive electrode cell and one negative electrode cell is set as a simulation condition. However, for the sake of simplicity, it is assumed that the positive electrode and the negative electrode have the same structure. The simulation conditions are shown below.
Reference 1 ... A. A. Shah et al. "A dynamic performance model for redox-flow butteries involving solving specifications", Electrochimica Acta 53 (2008), p. 8087-8100

[Condition I]
-Electrode 1 ... Two-layer structure of thick fiber layer 10 and thin fiber layer 11-Thick fiber layer 10 ... Average diameter of thick fibers = 10 µm Porosity of thick fiber layer 10 = 60% Thickness of thick fiber layer 10 = 0.5 mm Electrode reaction area density A = 5000 [cm ² / cm ² ]
Fine fiber layer 11: average diameter of fine fibers = 0.5 μm Porosity of fine fiber layer = 99.3% Thickness of fine fiber layer 11 = 0.5 mm Electrode reaction area density A = 100000 [cm ² / cm ² ]
Electrolyte: State of charge (sometimes referred to as charge depth) 50% vanadium sulfate electrolyte. Electrolyte flow rate: 0.3 cc / min. / Cm ²
・ Charge density: 70 mA / cm ²

[Condition II]
-Electrode: One layer of porous layer-Porous layer: Average fiber diameter = 10 µm Porosity of porous layer = 60% Thickness of porous layer = 1.0 mm
・ Electrolyte, its flow rate, charge density: Same as condition I

When the cell resistivity was obtained by calculation under the above conditions, the cell resistivity in Condition I was 0.52 Ω · cm ² and the cell resistivity in Condition II was 1.1 Ω · cm ² . From this simulation result, it was found that when the fine fiber layer 11 including fine fibers having an average fiber diameter of 0.005 μm or more and 4 μm or less is provided on the electrode 1, the cell resistivity can be greatly reduced.

<Appendix>
The following additional notes are disclosed in relation to the embodiment of the present invention described above.

[Appendix 1]
An electrode having a single layer structure comprising a fine fiber layer mainly composed of conductive fine fibers having a diameter of 0.005 μm or more and 4 μm or less on average.

  According to the electrode of Supplementary Note 1, battery reactivity in the electrode can be improved. As already described, the electrode 1 according to the embodiment includes the thick fiber layer 10 as a base material that holds the fine fiber layer 11, but the fine fiber layer 11 is the main component of the battery reaction. Therefore, if attention is paid to the improvement of the battery reaction in the electrode 1, by using an electrode having a single-layer structure including a fine fiber layer mainly composed of conductive fine fibers having a diameter of 0.005 μm to 4 μm on average, The battery performance of the RF battery 100 can be improved. If the electrode according to Supplementary Note 1 has handling performance comparable to that of the first embodiment, it is necessary to select a material for the fine fibers constituting the fine fiber layer so that the fine fiber layer 11 has sufficient strength.

  Also in the electrode of appendix 1, the same configuration (such as porosity) as that of the fine fiber layer 11 of the embodiment can be adopted.

  The electrode of the present invention can be suitably used as an electrode of a fluid flow type battery such as a redox flow battery or a fuel cell. In addition, the redox flow battery of the present invention can be suitably used as a battery for load leveling or for measures against instantaneous voltage drop and power failure.

100 Redox flow battery (RF battery)
100C Battery Cell 101 Diaphragm 102 Positive Electrode Cell 103 Negative Electrode Cell 104 Positive Electrode 105 Negative Electrode 106 Positive Electrode Tank 107 Negative Electrode Tank 108-111 Piping 112, 113 Pump 1 Electrode 10 Thick Fiber Layer 11 Fine Fiber Layer 13 Conductive Layer 200 Cell Stack 120 Cell frame 121 Bipolar plate 122 Frame body 123, 124 Manifold for liquid supply 125, 126 Manifold for drainage 127 Seal structure

Claims (11)

An electrode used in a fluid flow type battery,
A thick fiber layer mainly composed of conductive thick fibers having an average diameter of 5 μm to 20 μm;
A fine fiber layer mainly composed of conductive fine fibers having a diameter of 0.005 μm or more and 4 μm or less on average, provided on one side of the thick fiber layer;
Electrode.   The electrode according to claim 1, wherein the fine fiber layer has a porosity of 80% or more and 99.9% or less, and the thick fiber layer has a porosity of 60% or more and 90% or less.   The electrode according to claim 1 or 2, wherein a porosity of the fine fiber layer is higher than a porosity of the thick fiber layer.   The electrode according to any one of claims 1 to 3, wherein the fine fiber layer is formed by a solid phase method or a liquid phase method.   The electrode according to any one of claims 1 to 4, wherein the electrode has a two-layer structure of the fine fiber layer and the thick fiber layer.   5. The electrode according to claim 1, further comprising a conductive layer mainly composed of the fine fibers and having a conductive layer provided on the other surface side of the thick fiber layer. 2. The electrode according to item 1.   The average thickness of the said fine fiber layer is 10 micrometers or more and 500 micrometers or less, and the average thickness of the said thick fiber layer is 100 micrometers or more and 500 micrometers or less, The electrode of any one of Claims 1-6.   The electrode according to any one of claims 1 to 7, wherein an average thickness of the fine fiber layer is larger than an average thickness of the thick fiber layer.   The electrode according to any one of claims 1 to 8, wherein the thick fiber layer has a tensile strength of 98 kPa or more.   The electrode according to any one of claims 1 to 9, wherein the thick fiber layer is carbon paper or carbon cloth.   A redox flow battery comprising the electrode according to claim 1.

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