Flawless redox battery

Abstract

To provide a flowless redox battery which is lightweight, improved in shape freedom, especially capable of being thinned like paper and capable of dealing with thousands of times of charge / discharge.SOLUTION: A flowless redox battery includes electrodes formed from carbon fiber fabrics, electrolyte layers and a separator. The electrolyte layers are provided on both surfaces of the separator, and the electrolyte layers provided on both the surfaces are held by two electrodes. The electrolyte layer is an electrolyte paste layer containing a vanadium ion redox solution with diluted sulfuric acid as an electrolyte and carbon fillers. Regarding the carbon fiber fabric forming the electrode, a specific surface area ranges from 0.1 m2 / g to 100 m2 / g, a thickness ranges from 50 μm / Mpa to 200 μm / Mpa, a basis weight ranges from 20 g / m2 to 120 g / m2, a thickness resistance value ranges from 2.1 mΩ / Mpa / cm2 to 8.0 mΩ / Mpa / cm2, and a distance between the two electrodes is 0.05 mm or more and 0.5 mm or less.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This invention relates to a flawless redox battery using carbon fiber fabric (carbon cloth) as electrodes. [Background technology]

[0002] Secondary batteries, which can be repeatedly charged and discharged, are attracting attention as an energy storage source with a low environmental impact. Industrial secondary batteries include lead-acid batteries, sodium-sulfur batteries, and redox flow batteries. Among these, redox flow batteries using vanadium electrolyte operate at room temperature, and because the active material is stored in a liquid state in an external tank, they have advantages such as easier regeneration and a longer lifespan compared to the electrolytes of other secondary batteries. However, obtaining sufficient electrical capacity requires a large tank, making it difficult to obtain a lightweight, compact, and high-output redox battery. Therefore, to obtain a lightweight, compact, and high-output redox battery, a flowless redox battery that does not circulate the electrolyte has been proposed. Furthermore, studies are being conducted on flowless vanadium redox batteries, which use electrodes with an electrolyte containing vanadium as the active material supported on a current collector, to reduce the internal resistance of the battery, efficiently achieve high energy density, high capacity, and enable lightweight and compact design (see, for example, Patent Document 1).

[0003] However, a battery that is lightweight, flexible, highly shaped, and capable of thousands of charge-discharge cycles has yet to be realized. If such a battery were to be realized, it would be extremely attractive as a power source for environmental and biological monitoring. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2014-130778 [Overview of the project] [Problems that the invention aims to solve]

[0005] Therefore, the objective of the present invention is to provide a flowless redox battery that is lightweight, offers a high degree of freedom in shape, can be made particularly thin like paper, and can withstand thousands of charge-discharge cycles. [Means for solving the problem]

[0006] The flowless redox battery of the present invention comprises an electrode formed from a carbon fiber fabric, an electrolyte layer, and a separator. The electrolyte layer is provided on both sides of the separator, and the electrolyte layer provided on both sides is sandwiched between the two electrodes. The electrolyte layer is an electrolyte paste layer containing a vanadium ion redox solution with dilute sulfuric acid as the electrolyte and a carbon filler. The carbon fiber fabric forming the electrode is Specific surface area is 0.1 m² 2 / g~100m 2 It is within the range of / g. The thickness is within the range of 50 μm / Mpa to 200 μm / Mpa. Weight: 20g / m 2 ~120g / m 2 It is within the range, The thickness resistance is 2.1 mΩ / Mpa / cm 2 ~8.0 mΩ / Mpa / cm 2 It is within the range, The contact angle is within the range of 0° to 10°. The device is characterized in that the distance between the two electrodes is 0.05 mm or more and 0.5 mm or less.

[0007] In the flawless redox battery of the present invention, the carbon fiber fabric preferably has an opening ratio in the range of 15% to 75%.

[0009] In the flowless redox battery of the present invention, it is preferable that the electrode leads are sealed with a sealing material.

[0010] In the flowless redox battery of the present invention, it is preferable that the sealing material has a conductive portion formed on a film substrate.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a flowless redox battery that is lightweight, has a high degree of freedom in shape, can be made particularly thin like paper, and can withstand charge and discharge thousands of times.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a schematic structural diagram of the flowless redox battery of the present invention. [Figure 2] FIG. 2 is a diagram for explaining the manufacturing method of the flowless redox battery of the present invention in an example. [Figure 3] FIG. 3 is a graph showing the results of the power generation performance test in Example 1. [Figure 4] FIG. 4 is a graph showing the results of the power generation performance test in Comparative Example 1. [Figure 5] FIG. 5 is a graph comparing the charge and discharge characteristics of Example 1 and Comparative Example 1. [Figure 6] FIG. 6 is a graph showing the results of the power generation performance test in Comparative Example 2.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the flowless redox battery of the present invention will be described with reference to the drawings. However, the present invention is not limited or restricted to the following examples. The drawings referred to below are schematically drawn, and the ratios of the dimensions of the objects drawn in the drawings may differ from the ratios of the dimensions of actual objects. The ratios of the dimensions of objects may also differ between the drawings.

[0014] In the present invention, a redox battery with a charge-discharge cycle number of thousands of times, an electrode made of a carbon fiber fabric (sheet-like carbon cloth) having sufficient conductivity and a high effective electrode area, and a combination of electrolyte compositions for optimally functioning these components are used to provide a novel flowless redox battery that is lightweight, flexible, has a free shape, and has a charge-discharge cycle number of thousands of times.

[0015] The flowless redox battery of the present invention uses a carbon fiber fabric as an electrode, and the carbon fiber fabric has a specific range of specific surface area, thickness, basis weight, and sheet resistance value.

[0016] FIG. 1 is an example of a schematic structural diagram of the flowless redox battery of the present invention. As shown in FIG. 1, in the flowless redox battery 10, electrolyte layers 3, 3 are provided on both sides of a separator 1. The electrolyte layers 3, 3 provided on both sides of the separator 1 are sandwiched between two electrodes 4, 4. FIG. 2 is a diagram for explaining a manufacturing method in an embodiment of the flowless redox battery of the present invention. The electrolyte layer 3 can be formed by attaching a frame 2 provided with a formation location of the electrolyte layer 3 to the separator 1 and applying it within the frame 2.

[0017] [Electrode] The specific surface area of the carbon fiber fabric is preferably within the range of 0.1 m 2 / g to 100 m 2 / g and large. The specific surface area is the N2 BET value. The specific surface area can be increased by, for example, one to two digits by subjecting the carbon fiber fabric to an activation treatment, and a desired suitable range of specific surface area values can be obtained by adjusting the activation treatment conditions and the like. In order to construct a thin charge-discharge system, it is necessary to increase the actual electrode area. Therefore, the specific surface area is set within a predetermined range.

[0018] The thickness of the carbon fiber fabric is within the range of 50 μm / Mpa to 200 μm / Mpa. The thickness is 1 cm 2This value (μm / MPa) was read using a Mitutoyo digital thickness gauge when pressed with a pressing plate at 1 MPa, and is an indicator of the thickness when used as a battery. Ideally, the thickness under normal conditions should be approximately 0 to a few percent above the thickness of the battery cell frame.

[0019] The basis weight of the carbon fiber fabric is 20 g / m². 2 ~120g / m 2 It is within the range, preferably 40m 2 / g~110m 2 It is within the range of / g. In this application, "basis weight" refers to "a unit representing the mass per unit area of ​​woolen fabrics, etc., as defined in Japanese Industrial Standard (JIS) L02028, where 1m 2 This is synonymous with "grams per serving".

[0020] Furthermore, the thickness resistance of the carbon fiber fabric is 2.1 mΩ / Mpa / cm 2 ~8.0 mΩ / Mpa / cm 2 Within the range and low, preferably 2.5 mΩ / Mpa / cm² 2 ~6.0 mΩ / Mpa / cm 2 It is within the range. The aforementioned thickness resistance value is 1 cm 2 Resistance in the thickness direction (mΩ / Mpa / cm) when sandwiched between silver plates and subjected to a 100N pressure. 2 )

[0021] The flowless redox battery of the present invention is characterized in that the distance between electrodes 4, 4 is 0.05 mm or more and 0.5 mm or less. Preferably, the distance between electrodes is in the range of 0.15 mm or more and 0.17 mm or less.

[0022] The carbon fiber fabric preferably has an aperture ratio in the range of 15% to 75%, and more preferably in the range of 50% to 75%. Here, the aperture ratio can be defined as the ratio of the transmitted light area to the measurement area. By having an aperture ratio within the above range, it is possible to maintain the function as an electrode by ensuring conductive carbon fibers that allow electrons to be easily transmitted by increasing the specific surface area, while also allowing for the filling of a large amount of electrolyte. If the aperture ratio is less than 15%, the amount of electrolyte that can be filled is small, which tends to shorten the lifespan, and if the aperture ratio exceeds 75%, the strength may be insufficient.

[0023] The carbon fiber fabric preferably has a contact angle in the range of 0° to 10°, and more preferably in the range of 0° to 5°. Since electrodes in a flawless redox battery are required to be made of a material that easily adheres to the electrolyte inside the battery cell and facilitates electron exchange, it is preferable that the contact angle, which is an indicator of hydrophilicity, is within the aforementioned range. The carbon fiber fabric preferably has enough hydrophilicity that, for example, a 1 μL drop of water placed in contact with its surface instantly diffuses into the fabric fibers.

[0024] While plain weave, satin weave, double weave, matte weave, etc., can be used for the woven fabric, a plain double weave that can form a groove structure due to its weave structure is particularly preferred.

[0025] [Separator] The flowless redox battery of the present invention has a separator (porous membrane) between the electrolyte paste layers. Examples of separators include ion exchange membranes that allow specific ions to pass through. Examples of ion exchange membranes include SelemionAPS® (manufactured by Asahi Glass Co., Ltd.), Nafion® (manufactured by DuPont), and Neosepta®. In particular, the ions that the ion membrane can selectively pass through include at least one ion selected from the group consisting of protons, sulfate ions, and sulfite ions. As the separator used in the present invention, it is preferable to use a membrane that is cationic and has high ion exchange capacity, high permanent selectivity, and high resistivity, and ion exchange membranes commercially available under the trade names Nafion® and Neosepta® (manufactured by Astom Co., Ltd.) can be suitably used.

[0026] [Electrolytes] The flawless redox battery of the present invention uses an electrolyte paste containing a vanadium ion redox solution with dilute sulfuric acid as the electrolyte and a carbon filler as the electrolyte. By using a vanadium ion redox solution system with dilute sulfuric acid as the electrolyte, it is possible to achieve several thousand charge-discharge cycles. Furthermore, since carbon fiber fabric is used as the electrode, the electrolyte is used as an electrolyte paste containing a carbon filler in the solution to prevent the electrolyte from seeping into the electrode. The electrolyte contains an amount that is sufficient to allow the battery to reach a charge state from 0 to 100%. As the carbon filler, carbon black, carbon nanotubes, graphene, fullerene, etc. can be used. The electrolyte paste can be prepared, for example, by mixing and dispersing carbon black in a volume ratio of 1 / 3 into an electrolyte solution prepared by dissolving 2M vanadium ions in a 2M aqueous sulfuric acid solution and forming a paste.

[0027] By combining these elements to form a sealed battery structure, it is possible to prevent water loss and ion leakage from the electrolyte, enabling thousands of charge-discharge cycles. To form the sealed battery structure, it is preferable to seal the electrode 4 with a sealing material 5, except for the lead-out portion 4A. In Figure 1, the lead-out portion 4A of the electrode 4 is reinforced by being sandwiched between copper plates 6.

[0028] As the sealing material, it is preferable to use a thin, flexible material that is resistant to electrolytes, and a film substrate such as Kapton® tape can be used. If the sealing material is a film substrate with a conductive portion formed thereon, it is preferable because the electrodes can be used as is simply by attaching the sealing material, without sandwiching them between copper plates. As a film substrate with a conductive portion formed thereon, it is possible to use Kapton tape that has been copper-plated or printed with conductive paint so that it can conduct electricity with the electrodes.

[0029] While voltage stabilization circuits such as DC-DC converters are practically essential for using capacitors as power sources, which are energy storage devices capable of thousands of charge-discharge cycles, the flowless redox battery of the present invention, as an energy storage device, eliminates or simplifies these requirements in principle.

[0030] Furthermore, lithium-ion batteries, as energy storage devices that can withstand thousands of charge-discharge cycles, require electronic circuits that enable precise charging and discharging in order to achieve their performance and ensure safety. However, the flowless redox battery of the present invention, in principle, does not require or simplifies these circuits. Compared to capacitors and lithium-ion batteries, the flowless redox battery of the present invention is fundamentally superior in terms of weight reduction, flexibility, and the degree of freedom in shape.

[0031] The flowless redox battery of the present invention has a maximum voltage of approximately 0.8V per cell, and its voltage can be easily fine-tuned by series connection. Therefore, it can easily accommodate desired voltages, such as 3V or 5V. Furthermore, it can take on a flexible shape in principle. The ability to charge and discharge in such a shape is highly desirable from the standpoint of application development. [Examples]

[0032] The present invention will be described in detail below with reference to examples.

[0033] [Example 1] A flawless redox battery 10 was constructed using carbon fiber fabric (carbon cloth) as electrodes, as shown in Figure 1. The flawless redox battery was assembled using the following procedure shown in Figure 2.

[0034] [Attaching frame 2 to separator 1] For separator 1, a piece of Nafion® NRE-212 (thickness 51 μm) was cut to 17 mm x 17 mm and immersed in a VOSO4 aqueous solution. A 10 mm x 10 mm frame 2 for preventing electrolyte leakage was attached to separator 1. Frame 2 was made by layering three 0.055 mm thick Kapton® tapes to a thickness of 0.165 mm, cutting it to 20 mm x 20 mm, and cutting out a 10 mm x 10 mm hole in the center. Frames were attached to both sides of separator 1.

[0035] [Formation of electrolyte layer 3] 1.41 g of VOSO4·nH2O (n=3~4) was dissolved in 3 ml of 2 M sulfuric acid aqueous solution. 2 g of carbon black (Yoneyama 01761, density and / or relative density 1.8~2.1 (water=1)) was added to this solution and mixed well until it became a paste, which was used as the electrolyte. The prepared electrolyte was applied to both sides of the separator in the aforementioned frame and pressed tightly to form electrolyte layer 3. The volume of the applied electrolyte was 16.5 μL (10 mm × 10 mm × 0.165 mm) on one side.

[0036] [4 electrodes attached] Electrode 4 was made from a carbon fiber fabric, cut to 10 mm x 20 mm, produced from untwisted spun yarn in which 65 or more single filaments with a single filament diameter of 8 μm or less are bundled together in an untwisted state. The electrodes were placed on both sides of the coated electrolyte layer 3 so as to cover it. At that time, the carbon fiber fabric was made to adhere closely to the paste of the electrolyte layer 3. This carbon fiber fabric had a thickness of 200 μm / MPa and a basis weight of 110 g / m². 2 It is a double-woven plain fabric with grooves. Its specific surface area (N2BET value) is 0.2 m². 2 The resistance value at a thickness of 6.0 mΩ / Mpa / cm² is 6.0 mΩ / Mpa / cm². 2 That was the case.

[0037] [Sealed] A 0.055mm thick Kapton® tape was cut into 20mm x 20mm pieces and used as the sealing material 5. The sealing material 5 was applied over the frame 2 on which the electrolyte layer 3 and electrodes 4 were placed, sealing the battery except for the electrode lead-out portion 4A.

[0038] [Electrode Reinforcement] The electrode lead-out portion 4A of the obtained battery was sandwiched between copper plates 6 for clip reinforcement during charge-discharge testing, and this configuration (Figure 1) was used for charge-discharge testing and other purposes.

[0039] The distance between electrodes 4,4 (distance between carbon cloths) was 0.381 mm or less.

[0040] The charge-discharge characteristics and cycle capacity changes of the obtained battery were evaluated. The results are shown in Figure 3. It was found that the battery exhibited charge-discharge voltages of 0.6-0.8V and continued to function as a rechargeable battery even after more than 6000 charge-discharge cycles.

[0041] [Comparative Example 1] A flawless redox battery was fabricated in the same manner as in Example 1, except that carbon paper was used as the electrode instead of carbon fiber fabric. Toray Industries, Inc.'s "TGP-H-060" carbon paper was used. The charge-discharge characteristics and cycle capacity changes of the obtained battery were evaluated. The results are shown in Figure 4. The battery showed a charge-discharge voltage of 0.6 to 0.8 V, and the number of charge-discharge cycles was 975, indicating that the capacity degradation was faster than that of the battery in Example 1.

[0042] Figure 5 shows a graph comparing the charge-discharge characteristics of Example 1 (C-cloth) and Comparative Example 1 (C-paper). It can be seen that the flowless redox battery of the present invention in Example 1 has approximately three times the cycle life compared to the battery of Comparative Example 1 made of carbon paper.

[0043] [Comparative Example 2] A flawless redox battery was fabricated in the same manner as in Example 1, except that a carbon plate (2 mm thick) was used as the electrode instead of carbon fiber fabric. This carbon plate is made by sintering carbon with phenolic resin, and is dense and non-porous. In this example, under the same conditions as when using carbon fiber fabric in Example 1 (CC-CV, 10 mA, upper limit voltage 0.8 V), the maximum voltage was reached in less than 1 second and charging stopped, making charging impossible. Therefore, Figure 6 shows a graph observing the voltage rise when constant current charging was performed, ignoring the maximum voltage. It is thought that charging at 0.8 V was difficult because the carbon plate used had insufficient bonding between carbon particles, was hydrophobic, and had high internal resistance due to the effects of adhesion to the electrolyte and specific surface area. Furthermore, it was confirmed that the electrodes deteriorated (became brittle) due to sulfuric acid over time.

[0044] [Contact angle evaluation] To evaluate the hydrophilicity of the electrode materials, the contact angle was measured. The contact angle was measured using a measuring instrument called "VCA Optima" (Product Inc., USA). In Example 1, when a 1 μL (1.24 mm in diameter) spherical droplet of pure water was brought into contact with the carbon fiber fabric used in Example 1, it was immediately absorbed and diffused between the weave and fibers (the contact angle was evaluated as 0°). In Comparative Example 1, the carbon paper used in Example 1 had a contact angle of 136°, and the spherical droplet of pure water remained on the surface without being absorbed or diffused. Even when the droplet was 5 μL, it did not spread.

[0045] When the carbon fiber fabric of Example 1 is used as an electrode, the absence of phenolic resin and the like is considered to be one of the reasons for the extended cycle. In the case of conventional electrodes made of carbon paper containing a binder resin (Comparative Example 1) or electrodes made by sintering carbon with phenolic resin (Comparative Example 2), the resin components tend to deteriorate over time due to the sulfuric acid contained in the electrolyte. The electrode used in this example is less susceptible to deterioration by sulfuric acid.

[0046] The flowless redox battery of the present invention can be incorporated into small sensors. Because it is lightweight and flexible, it is suitable for applications such as sensors for monitoring the environment and living organisms. [Explanation of symbols]

[0047] 1 Separator 2 slots 3. Electrolyte layer (electrolyte paste) 4 electrodes 4A Electrode extraction section 5. Sealing material 6 copper plate 10. Flawless Redox Battery

Claims

1. It comprises an electrode formed from a carbon fiber fabric, an electrolyte layer, and a separator. The electrolyte layer is provided on both sides of the separator, and the electrolyte layer provided on both sides is sandwiched between the two electrodes. The electrolyte layer is an electrolyte paste layer containing a vanadium ion redox solution with dilute sulfuric acid as the electrolyte and a carbon filler. The carbon fiber fabric forming the electrode is Specific surface area is 0.1 m² ２ / g to 100m ２ It is within the range of / g, The thickness is within the range of 50 μm / MPa to 200 μm / MPa. Weight: 20 g / m ２ ~120g / m ２ It is within the range, The thickness resistance is 2.1 mΩ / MPa / cm ２ ~8.0mΩ / Mpa / cm ２ It is within the range, The contact angle is within the range of 0° to 10°. A flowless redox battery characterized in that the distance between the two electrodes is 0.05 mm or more and 0.5 mm or less.

2. The aforementioned carbon fiber fabric has an opening ratio in the range of 15% to 75%, wherein the flawless redox battery is as described in claim 1.

3. A flowless redox battery according to claim 1 or 2, wherein the electrode leads are sealed with a sealing material.

4. The flowless redox battery according to claim 3, wherein the sealing material is a film substrate with a conductive portion formed thereon.

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