WO2022209113A1 - Electrode, battery cell, and redox flow battery - Google Patents

Electrode, battery cell, and redox flow battery Download PDF

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Publication number
WO2022209113A1
WO2022209113A1 PCT/JP2022/000390 JP2022000390W WO2022209113A1 WO 2022209113 A1 WO2022209113 A1 WO 2022209113A1 JP 2022000390 W JP2022000390 W JP 2022000390W WO 2022209113 A1 WO2022209113 A1 WO 2022209113A1
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WIPO (PCT)
Prior art keywords
fibers
fiber assembly
binder
electrode
fiber
Prior art date
Application number
PCT/JP2022/000390
Other languages
French (fr)
Japanese (ja)
Inventor
雄大 池上
雍容 董
正幸 大矢
尚馬 伊田
貴 五十嵐
良平 岩原
Original Assignee
住友電気工業株式会社
東洋紡株式会社
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Application filed by 住友電気工業株式会社, 東洋紡株式会社 filed Critical 住友電気工業株式会社
Publication of WO2022209113A1 publication Critical patent/WO2022209113A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells

Definitions

  • the present disclosure relates to electrodes, battery cells, and redox flow batteries.
  • This application claims priority based on Japanese Patent Application No. 2021-063776 dated April 2, 2021, and incorporates all the descriptions described in the Japanese application.
  • Patent Document 1 discloses a redox flow battery electrode that is arranged to face a redox flow battery membrane.
  • This electrode includes a fiber aggregate having a plurality of carbon fibers.
  • This fiber assembly contains soft carbon fibers having a Young's modulus of 200 GPa or less.
  • the electrodes of the present disclosure are Equipped with a fiber assembly in which a plurality of fibers are combined,
  • the fiber assembly has a sheet shape,
  • the average degree of orientation of the plurality of fibers is 0.3 or less,
  • the average degree of orientation is the value obtained by dividing the angle of each of the plurality of fibers with respect to a horizontal line orthogonal to the thickness direction in the cross section of the fiber assembly along the thickness direction of the fiber assembly by 90°. Average value.
  • the battery cell of the present disclosure is A positive electrode, a negative electrode, and a diaphragm, At least one of the positive electrode and the negative electrode is the electrode of the present disclosure.
  • the redox flow battery of the present disclosure comprises A battery cell of the present disclosure is provided.
  • FIG. 1 is a schematic diagram showing the configuration of a redox flow battery according to an embodiment.
  • FIG. 2 is a schematic diagram showing the configuration of a cell stack provided in a redox flow battery.
  • FIG. 3A is a schematic diagram showing the configuration of electrodes according to the embodiment.
  • FIG. 3B is a schematic cross-sectional view showing an enlarged interior of a portion surrounded by a dashed line in FIG. 3A.
  • FIG. 4 is a schematic diagram showing an enlarged cross section of a fiber assembly provided in the electrode according to the embodiment, showing a case where the fiber assembly is a cloth.
  • FIG. 5 is a schematic diagram showing an enlarged surface of a fiber assembly provided in the electrode according to the embodiment, showing a case where the fiber assembly is a cloth.
  • FIG. 1 is a schematic diagram showing the configuration of a redox flow battery according to an embodiment.
  • FIG. 2 is a schematic diagram showing the configuration of a cell stack provided in a redox flow battery.
  • FIG. 6 is a schematic diagram showing an enlarged cross-section of a fiber assembly provided in the electrode according to the embodiment, showing a case where the fiber assembly is a non-woven fabric.
  • FIG. 7 is a schematic diagram showing an enlarged cross section of a fiber assembly provided in the electrode according to the embodiment, showing a case where the fiber assembly is paper.
  • FIG. 8A is a diagram explaining a method of measuring an average orientation degree of fibers in an electrode according to the embodiment;
  • FIG. 8B is an enlarged view of a region surrounded by a dashed line in FIG. 8A.
  • FIG. 9 is a schematic diagram showing an example of having carbon particles on the surface of the fiber in the electrode according to the embodiment.
  • FIG. 10 is a schematic diagram showing an example in which the electrode according to the embodiment has a catalyst on the surface of the fiber.
  • a redox flow battery is required to have high current efficiency as one of its battery performances.
  • the effect of the fibers contained in the electrode sticking into the diaphragm is considered to be one of the factors for the decrease in current efficiency.
  • the fibers constituting the positive electrode and the negative electrode stick into the diaphragm, holes are formed in the diaphragm and the positive electrode electrolyte and the negative electrode electrolyte are mixed.
  • a short circuit can occur between the positive and negative electrodes. If a short circuit occurs between the electrodes, it will lead to a decrease in current efficiency. Therefore, from the viewpoint of suppressing a decrease in the current efficiency of the redox flow battery, it is required to suppress short-circuiting caused by the fibers sticking into the diaphragm in the electrode provided with the fiber assembly.
  • One object of the present disclosure is to provide an electrode capable of suppressing sticking of fibers to a diaphragm. Another object of the present disclosure is to provide a battery cell and a redox flow battery with high current efficiency.
  • the electrode of the present disclosure can suppress sticking of fibers to the diaphragm.
  • the battery cell and redox flow battery of the present disclosure have high current efficiency.
  • An electrode according to an embodiment of the present disclosure Equipped with a fiber assembly in which a plurality of fibers are combined,
  • the fiber assembly has a sheet shape,
  • the average degree of orientation of the plurality of fibers is 0.3 or less,
  • the average degree of orientation is the value obtained by dividing the angle of each of the plurality of fibers with respect to a horizontal line orthogonal to the thickness direction in the cross section of the fiber assembly along the thickness direction of the fiber assembly by 90°. Average value.
  • the above electrodes undergo a battery reaction with the electrolyte in the redox flow battery.
  • the electrode described above can prevent the fibers from sticking into the diaphragm provided in the battery cell for the following reasons.
  • An electrode having an average degree of orientation of 0.3 or less has a small amount of fibers protruding in the thickness direction of the diaphragm on the first surface of the electrode facing the diaphragm. In other words, the amount of fibers that tend to stick into the diaphragm is small.
  • the smaller the average degree of orientation the smaller the amount of fibers that easily stick into the diaphragm.
  • the above fiber assembly is a porous body having voids between fibers.
  • An electrode comprising a fiber aggregate allows electrolyte to flow through the electrode.
  • the fiber assembly includes a first form in which a plurality of fibers are entangled to maintain their shape, and a second form in which a plurality of fibers are bound together to maintain their shape.
  • Specific examples of the fiber assembly of the first form are cloth and nonwoven fabric.
  • a specific example of the fiber assembly of the second form is paper.
  • a content rate of the plurality of fibers in the fiber assembly may be 20% by mass or more.
  • the fiber assembly may be cloth or non-woven fabric.
  • a cloth or non-woven fabric is composed of a plurality of intertwined fibers, so there are many voids between the fibers. Therefore, since the electrode including the fiber assembly has a relatively large porosity, the electrolytic solution can easily flow through the electrode.
  • An average length of the plurality of fibers may be 25 mm or more.
  • the fibers of the above electrodes tend to get entangled with each other. Therefore, the shape of the fiber assembly is easily maintained by mechanical bonding due to the entanglement of the fibers.
  • the fiber assembly may contain a binder attached to the surfaces of the plurality of fibers.
  • the above electrodes can bind fibers together with a binder.
  • the shape of the fiber assembly can be maintained by binding the fibers together with the binder.
  • the fiber assembly is paper, A binder attached to the surfaces of the plurality of fibers may be included.
  • the thickness of the electrodes can be made thinner. Paper maintains its shape by binding a plurality of fibers together with a binder. Paper is easier to make thinner than cloth or non-woven fabric. Therefore, the electrode provided with the fiber assembly can make the battery cell thinner.
  • the average degree of orientation may be 0.1 or less.
  • the above electrodes can further suppress the sticking of the fibers into the diaphragm.
  • An average length of the plurality of fibers may be 20 mm or less.
  • Paper is made up of a plurality of fibers bound together by a binder, so it can maintain its shape even if the fiber length is short.
  • a content of the binder in the fiber assembly may be 20% by mass or more and 80% by mass or less.
  • the above electrodes tend to secure voids between fibers while maintaining the shape of the fiber assembly.
  • the reason why the shape of the fiber assembly is easily maintained is that the content of the binder is 20% by mass or more, so that the binding of the fibers by the binder can be easily secured.
  • the reason why it is easy to secure voids between fibers is that when the content of the binder is 80% by mass or less, reduction in voids between fibers due to the binder can be suppressed.
  • the binder may include a carbon-based first binder.
  • the above electrodes can ensure electrical continuity between the fibers with the first binder.
  • the reason for this is that the first binder is made mainly of carbon and thus has electrical conductivity. Carbon is also resistant to electrolytes.
  • the binder may include a second binder mainly composed of a conductive metal oxide.
  • the above electrodes can ensure electrical continuity between the fibers with the second binder. Also, the conductive metal oxide has resistance to the electrolyte.
  • the electrodes are Carbon particles may be supported on the surfaces of the plurality of fibers.
  • the carbon particles function as reaction points with the electrolyte.
  • the above electrode can improve battery reactivity with the electrolyte.
  • the above electrodes are capable of firmly supporting carbon particles on the surface of the fiber.
  • the electrodes are A catalyst may be supported on the surfaces of the plurality of fibers.
  • the catalyst activates the battery reaction between the electrolyte and the electrodes.
  • the above electrode can improve battery reactivity between the electrolyte and the electrode.
  • the catalyst may be supported by the binder.
  • the above electrodes are capable of firmly supporting the catalyst on the surface of the fiber.
  • the catalyst contains at least one metal element selected from the group consisting of titanium, vanadium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tin, antimony, thallium, hafnium, tantalum, tungsten, rhenium, and iridium. It may be composed of a metal oxide that
  • the metal oxide containing the above metal element has a catalytic effect that activates the cell reaction.
  • the above metal oxides are suitable for catalysts.
  • the plurality of fibers may be composed of at least one selected from the group consisting of carbon, titanium, and tungsten.
  • the above electrodes are suitable for redox flow battery electrodes.
  • the fibers that make up the electrodes function as reaction fields for cell reactions with the electrolyte.
  • Carbon, titanium, and tungsten are electrically conductive and resistant to electrolytes.
  • Carbon, titanium, and tungsten are preferred fiber materials.
  • a battery cell according to an embodiment of the present disclosure is A positive electrode, a negative electrode, and a diaphragm, At least one of the positive electrode and the negative electrode is the electrode according to any one of (1) to (17) above.
  • the above battery cell has high current efficiency because at least one of the positive electrode and the negative electrode is the electrode of the present disclosure described above.
  • the reason for this is that, as described above, the electrodes of the present disclosure can suppress short circuits caused by fibers sticking into the diaphragm. In the battery cell described above, since a short circuit is unlikely to occur between the positive electrode and the negative electrode, a decrease in current efficiency can be suppressed.
  • a porosity of the fiber assembly in the electrode may be 30% by volume or more and 89% by volume or less.
  • the porosity of the fiber assembly is 30% by volume or more, so that the electrolytic solution can be easily circulated in the electrode.
  • the porosity of the fiber assembly is 89% by volume or less, it is possible to suppress a decrease in the contact area with the electrolytic solution in the electrode, that is, the reaction area. Further, if the porosity is 89% by volume or less, it is possible to suppress a decrease in the strength of the fiber assembly.
  • the above redox flow battery includes the battery cells of the present disclosure, it has high current efficiency.
  • the RF battery 1 is one of electrolyte circulation type storage batteries.
  • the positive electrode electrolyte and the negative electrode electrolyte are electrolyte solutions containing, as active materials, metal ions whose valences change due to oxidation-reduction.
  • the RF battery 1 charges and discharges using the difference between the oxidation-reduction potential of the metal ions contained in the positive electrode electrolyte and the oxidation-reduction potential of the metal ions contained in the negative electrode electrolyte.
  • the electrolytic solution is, for example, a vanadium-based electrolytic solution or a titanium-manganese-based electrolytic solution.
  • vanadium-based electrolytes both the positive electrode electrolyte and the negative electrode electrolyte contain vanadium (V) ions.
  • the positive electrolyte contains manganese (Mn) ions
  • the negative electrolyte contains titanium (Ti) ions.
  • the RF battery 1 is typically connected to the power generation section 8 and the load 9 via the AC/DC converter 7 and the substation equipment 71 .
  • the RF battery 1 can charge the power generated by the power generation unit 8 and discharge the charged power to the load 9 .
  • the power generation unit 8 is power generation equipment using natural energy such as solar power generation and wind power generation, and other general power plants.
  • the RF battery 1 is used, for example, for load leveling applications, momentary sag compensation, emergency power supply applications, and output smoothing applications for natural energy power generation.
  • the RF battery 1 includes a battery cell 100 that performs charging and discharging, a positive electrode electrolyte tank 106 and a negative electrode electrolyte tank 107 that respectively store a positive electrode electrolyte and a negative electrode electrolyte, and a positive electrode electrolyte tank 106 and a negative electrode electrolyte tank 107.
  • a circulation channel for circulating each electrolytic solution between each tank and the battery cell 100 is provided.
  • the basic configuration of the RF battery 1 a known configuration can be used as appropriate.
  • a battery cell 100 includes a positive electrode 104 , a negative electrode 105 and a diaphragm 101 .
  • the diaphragm 101 is arranged between the positive electrode 104 and the negative electrode 105 .
  • a battery cell 100 is separated into a positive electrode cell 102 and a negative electrode cell 103 by a diaphragm 101 .
  • a positive electrode 104 is placed in the positive cell 102 .
  • a negative electrode 105 is arranged in the negative cell 103 .
  • the diaphragm 101 is, for example, an ion exchange membrane permeable to hydrogen ions.
  • the positive electrode 104 and the negative electrode 105 undergo a battery reaction with the electrolyte.
  • Each electrode of the positive electrode 104 and the negative electrode 105 is composed of, for example, a sheet-like porous body.
  • the positive electrode 104 and the negative electrode 105 are the electrodes 10 having a fiber aggregate 30 including a plurality of fibers 20 as shown in FIGS. 3A and 3B described later.
  • a positive electrode electrolyte is supplied to the positive electrode cells 102 that constitute the battery cells 100 .
  • a negative electrode electrolyte is supplied to the negative electrode cell 103 .
  • the RF battery 1 of the present example includes, as shown in FIG. Further, the RF battery 1 includes an outbound pipe 109 and a return pipe 111 that connect between the battery cell 100 and the negative electrode electrolyte tank 107 .
  • a pump 112 is provided in the outbound pipe 108 .
  • a pump 113 is provided in the outbound pipe 109 .
  • the positive electrode electrolyte is supplied to the positive electrode cell 102 from the positive electrode electrolyte tank 106 by the pump 112 through the outgoing pipe 108 .
  • the positive electrode electrolyte discharged from the positive electrode cell 102 through the positive electrode cell 102 is returned to the positive electrode electrolyte tank 106 through the return pipe 110 .
  • the negative electrode electrolyte is supplied from the negative electrode electrolyte tank 107 to the negative electrode cell 103 by the pump 113 through the outgoing pipe 109 .
  • the negative electrode electrolyte discharged from the negative electrode cell 103 through the negative electrode cell 103 is returned to the negative electrode electrolyte tank 107 through the return pipe 111 .
  • the forward pipes 108 and 109 and the return pipes 110 and 111 constitute a circulation flow path for each electrolytic solution.
  • the RF battery 1 may be configured with a single battery cell 100 or may be configured with a plurality of battery cells 100 .
  • a cell stack 200 in which a plurality of battery cells 100 are stacked is provided.
  • the cell stack 200 is configured by sandwiching a sub-stack 200s between two end plates 210 from both sides and tightening them with a tightening mechanism 230.
  • FIG. 2 shows a cell stack 200 comprising multiple substacks 200s.
  • the substack 200s includes a laminate and supply/discharge plates 220 provided at both ends of the laminate.
  • the cell frame 120, the positive electrode 104, the diaphragm 101, and the negative electrode 105 are repeatedly laminated in this order.
  • the supply/discharge plate 220 is connected to the outgoing pipes 108 and 109 and the return pipes 110 and 111 shown in FIG.
  • the number of stacked battery cells 100 in the cell stack 200 can be selected as appropriate.
  • the cell frame 120 of this example includes a bipolar plate 121 arranged between the positive electrode 104 and the negative electrode 105, and a frame 122 provided around the bipolar plate 121. have. Inside the frame 122, the bipolar plate 121 and the frame 122 form a recess 122o. The recesses 122o are formed on both sides of the bipolar plate 121, respectively.
  • Bipolar plate 121 has a first surface facing positive electrode 104 and a second surface facing negative electrode 105 .
  • the positive electrode 104 is arranged in the concave portion 122 o on the first surface side of the bipolar plate 121 .
  • the negative electrode 105 is arranged in the concave portion 122 o on the second surface side of the bipolar plate 121 .
  • Each concave portion 122o forms each cell space of the positive electrode cell 102 and the negative electrode cell 103 shown in FIG. 1 described above.
  • one battery cell 100 is formed by arranging the positive electrode 104 and the negative electrode 105 with the diaphragm 101 interposed between the bipolar plates 121 of the adjacent cell frames 120 .
  • an annular sealing member 127 is arranged between the frames 122 of the cell frames 120 .
  • the sealing member 127 is an O-ring, flat packing, or the like.
  • the frame 122 of the cell frame 120 has liquid supply manifolds 123 and 124 and liquid discharge manifolds 125 and 126 .
  • the positive electrode electrolyte is supplied from the liquid supply manifold 123 to the positive electrode 104 through the liquid supply slit 123s.
  • the positive electrode electrolyte supplied to the positive electrode 104 is discharged to the drainage manifold 125 through the drainage slit 125s.
  • the negative electrode electrolyte is supplied from the liquid supply manifold 124 to the negative electrode 105 through the liquid supply slit 124s.
  • the negative electrode electrolyte supplied to the negative electrode 105 is discharged to the drainage manifold 126 through the drainage slit 126s.
  • the liquid supply manifolds 123 and 124 and the liquid discharge manifolds 125 and 126 are provided through the frame 122, and the cell frames 120 are laminated to constitute flow paths for the respective electrolytes. Each of these flow paths is connected to each of the outbound pipes 108 and 109 and the inbound pipes 110 and 111 shown in FIG.
  • the cell stack 200 can circulate the positive electrode electrolyte and the negative electrode electrolyte to each battery cell 100 through each of the channels.
  • the battery cell 100 of this example is configured such that the electrolytic solution is supplied from the lower side of the positive electrode 104 and the negative electrode 105, respectively, and the electrolytic solution is discharged from the upper side of the positive electrode 104 and the negative electrode 105. That is, the electrolytic solution flows from the lower edge portion toward the upper edge portion of each of the positive electrode 104 and the negative electrode 105 .
  • Electrode 10 An electrode 10 according to an embodiment will be described with reference to FIGS. 3A and 3B.
  • the electrode 10 is used as the positive electrode 104 and the negative electrode 105 of the battery cell 100 (see FIG. 1) described above.
  • the electrode 10 performs a battery reaction using an electrolytic solution.
  • the electrode 10 has a first surface 11 (see FIG. 3A) facing the diaphragm 101 when the battery cell 100 is constructed.
  • the electrode 10 of this embodiment has a sheet shape, as shown in FIG. 3A.
  • the electrode 10 includes a fiber assembly 30 in which a plurality of fibers 20 are combined, as shown in FIG. 3B.
  • One of the features of the electrode 10 is that the average degree of orientation of the plurality of fibers 20 is within a specific range.
  • the fiber assembly 30 has a sheet shape.
  • the fiber aggregate 30 is a porous body having voids between the fibers 20 . Therefore, when the battery cell 100 (see FIG. 1) is configured, the electrolyte flows inside the electrode 10 .
  • the fiber assembly 30 typically has a first form in which a plurality of fibers 20 are entangled to maintain their shape, and a second form in which a plurality of fibers 20 are bound to maintain their shape.
  • ⁇ First form> 4 and 6 show enlarged schematic cross-sectional views of the fiber assembly 31 in the first embodiment.
  • the above cross section is a cross section cut along the thickness direction of the fiber assembly 31 .
  • the thickness direction is a direction orthogonal to the first surface 11 shown in FIG. 3A.
  • the first surface 11 is either the surface facing each other or the back surface of the fiber assembly 30 .
  • Specific examples of the first form of the fiber assembly 31 are cloth and non-woven fabric.
  • the fiber assembly 31 shown in FIG. 4 is a cloth.
  • a fiber assembly 31 shown in FIG. 6 is a nonwoven fabric.
  • arrow V indicates the thickness direction
  • arrow H indicates the horizontal direction perpendicular to the thickness direction.
  • the fiber assembly 31 made of cloth is woven with threads 20s obtained by bundling and twisting a large number of fibers 20, as shown in FIG.
  • the cloth is formed by alternately weaving first yarns 21s and second yarns 22s crossing the first yarns 21s.
  • a specific example of the method for manufacturing the fiber assembly 31 made of cloth will be described later.
  • the fiber assembly 31 made of nonwoven fabric is obtained by intertwining independent individual fibers 20 .
  • a non-woven fabric is formed by entangling a web in which a plurality of fibers 20 are laminated, by entangling the fibers 20 in the lamination direction.
  • the stacking direction corresponds to the thickness direction of the fiber assembly 31 .
  • the entangling treatment can be performed by, for example, a needle punching method or a hydroentangling method.
  • Nonwoven fabrics include felt, spunlace, Malifleece, and the like. A specific example of the method for manufacturing the fiber assembly 31 made of nonwoven fabric will be described later.
  • FIG. 7 shows a schematic cross-sectional view enlarging the cross section of the fiber assembly 32 in the second embodiment.
  • the fiber assembly 32 includes a plurality of fibers 20 and binders 25 attached to the surfaces of the fibers 20 .
  • the binder 25 does not necessarily have to be adhered to the surface of all the fibers 20 among the plurality of fibers 20 , as long as it is adhered to most of the fibers 20 .
  • the binder 25 may be attached to all or part of the surface of each fiber 20 . It is preferable that the binder 25 is attached to almost the entire area of the plurality of fibers 20 without being unevenly attached locally.
  • the binder 25 has a function of binding the fibers 20 together.
  • the binder 25 has a function of supporting at least one of the carbon particles 40 and the catalyst 50 shown in FIGS. 9 and 10 on the surfaces of the fibers 20 .
  • the carbon particles 40 and catalyst 50 will be described later.
  • a specific example of the second form of the fiber assembly 32 is paper.
  • the binder 25 is made of a material resistant to electrolyte.
  • the binder 25 contains, for example, one selected from the group consisting of carbon, resin, and conductive metal oxide.
  • Conductive metal oxides are, for example, metal oxides such as tin oxide, indium tin oxide (ITO), and antimony tin oxide (ATO).
  • a fiber assembly 32 made of paper is obtained by binding a plurality of fibers 20 together with a binder 25 .
  • the paper is obtained by forming a slurry obtained by mixing a plurality of fibers 20 and raw materials of the binder 25, and then drying the slurry.
  • the slurry is obtained by dispersing the fibers 20 in a solvent.
  • the raw material of the binder 25 is mixed with the solvent.
  • the solvent may be either water or an organic solvent.
  • Organic solvents include methanol, ethanol, propyl alcohol, isopropanol, butanol, pentanol, hexanol, and the like.
  • heat treatment may be performed after the slurry is made into paper.
  • the raw material of the binder 25 is, for example, an organic binder such as thermosetting resin or thermoplastic resin.
  • Thermosetting resins are typically phenol resins, pitch resins, and epoxy resins.
  • Thermoplastic resins are typically polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polyvinylidene chloride (PVDC).
  • PTFE polytetrafluoroethylene
  • PVDF polyvinylidene fluoride
  • PVDC polyvinylidene chloride
  • the binder 25 includes resins such as PTFE, PVDF, PVDC.
  • a solution in which metal ions are dissolved is used as the raw material of the binder 25 .
  • the metal ions are tin ions, indium ions, antimony ions, and the like. By heat-treating this solution, the binder 25 containing the metal oxide can be formed.
  • a specific example of the method of manufacturing the fiber assembly 32 made of paper will be described later.
  • the binder 25 in the fiber assembly 32 preferably contains a first binder mainly composed of carbon. Carbon is electrically conductive. By including the first binder in the binder 25, even if there are portions where the fibers 20 are not in contact with each other, electrical continuity between the fibers 20 can be ensured via the first binder.
  • the first binder is typically an organic binder such as phenol resin, pitch resin, or epoxy resin that is carbonized by the above heat treatment. “Containing mainly carbon” means containing 60% by mass or more of carbon. The carbon content in the first binder may be 80% by mass or more, or may be 100% by mass.
  • the binder 25 is substantially composed only of the first binder. Specifically, the binder 25 is substantially composed only of carbon.
  • the content of carbon in the binder 25 is substantially 100% by mass.
  • the binder 25 is made of resin such as PTFE, PVDF, or PVDC, as described above, that is, when the binder 25 is not carbonized, electrical conduction between the fibers 20 is ensured by contact between the fibers 20 .
  • the binder 25 may contain a second binder mainly composed of a conductive metal oxide.
  • a second binder mainly composed of a conductive metal oxide By including the second binder in the binder 25, even if there are portions where the fibers 20 are not in contact with each other, electrical continuity between the fibers 20 can be ensured via the second binder.
  • the phrase "mainly composed of a conductive metal oxide” means containing 60% by mass or more of a conductive metal oxide.
  • the content of the conductive metal oxide in the second binder may be 80% by mass or more, or may be 100% by mass.
  • the content of fibers 20 in fiber assembly 30 is, for example, 20% by mass or more.
  • the content of the fibers 20 may be 30% by mass or more.
  • the content of the fibers 20 may be 100% by mass.
  • the content of the fibers 20 may differ depending on the form of the fiber assembly 30.
  • the fiber assembly 31 in the first form such as cloth or non-woven fabric, can be composed only of the fibers 20 .
  • the content of the fibers 20 in the fiber assembly 31 is, for example, 20% by mass or more and 100% by mass or less.
  • the content of the fibers 20 in the fiber assembly 31 may be 30% by mass or more, more than 50% by mass, more than 70% by mass, or more than 75% by mass.
  • the fiber assembly 31 is substantially composed only of the fibers 20 . That is, the content of the fibers 20 in the fiber assembly 31 is substantially 100% by mass.
  • the content of the fibers 20 in the fiber assembly 32 in the second form such as paper, is, for example, 25% by mass or more and 75% by mass or less, and further 30% by mass or more and 70% by mass or less.
  • the content rate of the fibers 20 in the fiber assembly 30 is obtained by " ⁇ (total mass of the fibers 20 contained in the fiber assembly 30)/(mass of the fiber assembly 30) ⁇ x 100".
  • the content of the fibers 20 is calculated by analyzing a secondary electron image and an X-ray CT (Computed Tomography) image of the fiber assembly 32 . Specifically, first, the secondary electron image and the X-ray CT image are compared to confirm that the fiber image of the X-ray CT image is correctly obtained.
  • the content of the fibers 20 is calculated by "DxAxTx(1/V)x(1/S)x100".
  • D Density of the fiber itself (g/cm 3 )
  • A Volume of fiber obtained from X-ray CT image (cm 3 )
  • T Thickness of fiber assembly (cm)
  • V Volume of measurement field of view of X-ray CT image (cm 3 )
  • S Mass per unit area obtained by actually measuring the mass of the fiber assembly (g/cm 2 )
  • the thickness T is the thickness when the fiber assembly 30 is not compressed.
  • the content of the binder 25 in the fiber assembly 32 is, for example, 20% by mass or more and 80% by mass or less.
  • the content of the binder 25 is 20% by mass or more, the fibers 20 are easily bound together by the binder 25 . Therefore, it is easy to maintain the shape of the fiber assembly 32 .
  • the content of the binder 25 is 80% by mass or less, it is easy to secure voids in the fiber assembly 32 . Therefore, it is easy to circulate the electrolytic solution in the electrode 10 .
  • the content of the binder 25 may be 30% by mass or more and 70% by mass or less, or 45% by mass or more and 65% by mass or less.
  • the content of the binder 25 is determined by subtracting the content of the fibers 20 from 100% by mass, assuming that the mass of the fiber assembly 32 is 100% by mass.
  • the first form of the fiber assembly 31 may not include the binder 25, but may include the binder 25.
  • the binder 25 binds the fibers 20 together, thereby making it easier to maintain the shape of the fiber assembly 31 .
  • the content of the binder 25 in the fiber assembly 31 is, for example, 80% by mass or less.
  • the content of the binder 25 in the fiber assembly 31 may be 50% by mass or less, 40% by mass or less, less than 30% by mass, or less than 20% by mass.
  • the thickness of the fiber assembly 30 (see FIG. 3A) is, for example, 0.1 mm or more and 5.0 mm or less, and further 0.2 mm or more and 3.0 mm or less.
  • the thickness of the fiber assembly 30 is 0.1 mm or more, even if the electrode 10 is compressed when assembled into the battery cell 100, it is easy to secure the reaction area with the electrolytic solution in the electrode 10 .
  • the thickness of the fiber assembly 30 is 5.0 mm or less, even if the electrode 10 is compressed when assembled into the battery cell 100, the electrolytic solution can easily flow through the electrode 10.
  • the thickness of the fiber assembly 30 is 5.0 mm or less, the thickness of the electrode 10 can be reduced.
  • the above-mentioned thickness refers to the thickness in a non-compressed state, i.e., in a natural state where no external force is applied, rather than in a compressed state assembled in the battery cell 100 (see FIG. 1).
  • the thickness of the fiber assembly 30 may differ depending on the form of the fiber assembly 30.
  • the thickness of the fiber assembly 31 in the first form such as cloth or non-woven fabric, is, for example, 0.2 mm or more and 5.0 mm or less, and further 0.3 mm or more and 2.0 mm or less.
  • the thickness of the fiber assembly 32 in the second form such as paper, is, for example, 0.1 mm or more and 1.0 mm or less, and further 0.3 mm or more and 0.6 mm or less. Since the fiber assembly 32 in the second embodiment can be made thinner than the fiber assembly 31 in the first embodiment, it is easier to make the battery cell 100 (see FIG. 1) thinner.
  • the compressibility of the fiber assembly 30 is, for example, 30% or more and 95% or less, and further 40% or more and 70% or less.
  • the reaction area with the electrolytic solution does not change before and after compression, but the volume of the fiber assembly 30 after compression decreases, so the reaction area with the electrolytic solution per unit volume increases.
  • the compressibility is 30% or more, the reaction area per unit volume of the electrode 10 increases, so the reaction efficiency with the electrolytic solution increases.
  • the compressibility is 95% or less, it is easy to ensure the voids in the electrode 10 and allow the electrolytic solution to flow.
  • the compressibility is 95% or less, damage to the fiber assembly 30 due to excessive compression can be suppressed.
  • the compressibility is obtained by " ⁇ (T 0 ⁇ T 1 )/T 0 ⁇ 100", where T 1 is the thickness in the compressed state and T 0 is the thickness in the uncompressed state.
  • the porosity of the fiber assembly 30 is, for example, 30% by volume or more and 89% by volume or less, and further 40% by volume or more and 80% by volume or less.
  • the above-mentioned porosity is the porosity in a state in which the battery cell 100 (see FIG. 1) is assembled and compressed.
  • the porosity is 30% by volume or more, the electrolytic solution can be easily circulated in the electrode 10 .
  • the porosity is 89% by volume or less, it is possible to suppress the decrease in the reaction area with the electrolytic solution in the electrode 10 .
  • the porosity can be obtained by " ⁇ (Va ⁇ Vt)/Va ⁇ 100" where Vt is the true volume and Va is the apparent volume.
  • the true volume Vt can be obtained, for example, by analyzing the X-ray CT image and calculating the volume excluding voids in the fiber assembly 30 .
  • the apparent volume Va is the volume of the fiber assembly 30 including fibers and voids.
  • the porosity of the fiber assembly 30 may vary depending on the form of the fiber assembly 30.
  • the fiber assembly 31 in the first form such as cloth or non-woven fabric, has a porosity of, for example, 30% to 89% by volume, and further 40% to 80% by volume.
  • the porosity of the fiber assembly 32 in the second form such as paper, is, for example, 40% by volume or more and 89% by volume or less, and further 60% by volume or more and 80% by volume or less.
  • the fiber assembly 32 in the second form contains a large amount of the binder 25, and therefore has a smaller porosity than the fiber assembly 31 in the first form. Since the fiber assembly 31 in the first embodiment has a relatively large porosity, it is easy for the electrolytic solution to flow.
  • the fibers 20 (see FIG. 3B) function as a reaction field where metal ions, which are active materials in the electrolyte, undergo battery reactions.
  • the average degree of orientation of the plurality of fibers 20 forming the fiber assembly 30 is 0.3 or less.
  • the “average degree of orientation” means the degree of inclination of the fibers 20 with respect to a horizontal line orthogonal to the thickness direction of the fiber assembly 30 in the cross section of the fiber assembly 30 .
  • the cross section is a cross section along the thickness direction of the fiber assembly.
  • the "average degree of orientation” is the average value obtained by dividing the angle of each of the plurality of fibers 20 with respect to the horizontal line by 90°, where the angle along the thickness direction of the fiber assembly 30 is 90°. The smaller the value of the average degree of orientation, the less fibers 20 are oriented in the thickness direction of the fiber assembly 30 . That is, it can be said that the fiber assembly 30 having a small average degree of orientation has few fibers 20 along the thickness direction and many fibers 20 along the horizontal direction.
  • the average degree of orientation is given in the range from 0 to 1.
  • FIG. 8A shows an enlarged example of a cross section of the fiber assembly 30.
  • FIG. 8A The fiber assembly 30 shown in FIG. 8A is a cloth.
  • the fiber assembly 30 (see FIG. 3A) is cut along the thickness direction. Specifically, the fiber assembly 30 is cut in the thickness direction with the first surface 11 horizontal so that the thickness direction of the fiber assembly 30 is vertical.
  • a cross section of the cut fiber assembly 30 is observed with a scanning electron microscope (SEM). Acquire 10 or more visual fields by changing the observation position.
  • the field of view is a rectangle with dimensions of 600 ⁇ m ⁇ 450 ⁇ m.
  • One diagonal line d is drawn for one field of view.
  • the magnification of the field of view is, for example, 200 times. The magnification may be changed as appropriate depending on the form of the fiber aggregate 30 .
  • 10 or more fibers 20 are selected among the fibers 20 crossing the diagonal d.
  • fitting is performed on the portion that intersects the diagonal line d. Specifically, a fitted straight line is obtained for a 10 ⁇ m-long portion of the fiber 20 centered on the intersection with the diagonal line d (see also FIG. 8B).
  • the least squares method can be used.
  • the least-squares method for example, for the 10 ⁇ m portion of the fiber 20, a line segment passing through the center of the fiber 20 is extracted, and the least-squares method is applied to the points dividing the line segment into 10 equal parts.
  • the straight line fitted to each selected fiber 20 is indicated by a thick dashed line.
  • the angle to be measured is the acute angle of 0° or more and 90° or less of the two angles formed by the fitted straight line and the horizontal line.
  • the degree of orientation with respect to the horizontal is determined. The degree of orientation is calculated by "(the angle of the straight line with respect to the horizontal line)/90°".
  • the average value of the orientation degrees of the fitted straight lines for all fields of view is taken as the average orientation degree. That is, by selecting 10 or more fibers 20 for each field of view in 10 or more fields of view, the average degree of orientation of a total of 100 or more fibers 20 is obtained.
  • the number of fibers 20 selected in one field of view may be 20 or more, or even 30 or more.
  • the average degree of orientation may be 0.25 or less.
  • the average degree of orientation may vary depending on the form of the fiber assembly 30.
  • the fiber assembly 31 in the first form such as cloth or non-woven fabric has an average degree of orientation of, for example, 0.05 or more and 0.3 or less.
  • the average degree of orientation is 0.05 or more, the shape of the fiber aggregate 31 can be easily maintained by mechanical bonding due to the entanglement of the fibers 20 .
  • the average degree of orientation is 0.3 or less, it is possible to suppress sticking of the fibers 20 into the diaphragm 101 as described above.
  • the average degree of orientation may be 0.1 or more and 0.25 or less, and further 0.15 or more and 0.25 or less.
  • the average degree of orientation is, for example, 0.1 or less. Since the fiber assembly 32 in the second embodiment maintains its shape by binding the fibers 20 together with the binder 25, the average degree of orientation can be made relatively small (see FIG. 7). In a second form, the average degree of orientation may be 0.05 or less.
  • a method for reducing the average degree of orientation is, for example, the following method.
  • the weaving pitch is the center-to-center distance p between the first yarns 21s adjacent to each other with the second yarn 22s interposed therebetween when the fiber assembly 31 is viewed from above as shown in FIG.
  • the greater the pitch of the weave the smaller the angle of the fibers 20 with respect to the above horizontal line. That is, since the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 is reduced, the average degree of orientation is reduced.
  • the weave pitch is, for example, 1.5 mm or more, or even 2.0 mm or more.
  • the thickness of the thread 20s should be changed according to the weaving pitch.
  • the fiber assembly 30 When the fiber assembly 30 is made of nonwoven fabric, for example, it is preferable to press the fiber assembly 30 in the thickness direction. Since the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 is reduced by pressing, the average degree of orientation is reduced.
  • the press pressure is, for example, 0.05 MPa or more and 0.5 MPa or less.
  • Another way is to reduce the number of entanglements per unit area, for example. In the case of hydroentanglement, for example, the number of nozzles for jetting water streams is reduced, or the pressure of water streams is lowered.
  • needle punching for example, the number of needle punches is reduced, or the number of times of punching is reduced. For example, the number of punching is less than 250 times/cm 2 . As the number of entanglements decreases, the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 decreases. Therefore, the average degree of orientation becomes small.
  • the fiber assembly 30 When the fiber assembly 30 is made of paper, for example, fibers 20 having a relatively long fiber length may be used. When the fiber length is relatively long, the fibers 20 tend to lie flat during papermaking, and the fibers 20 tend to align horizontally. Therefore, since the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 is reduced, the average degree of orientation is reduced. For example, the fiber length is 10 mm or more. Alternatively, as described above, the fiber assembly 30 may be pressed in the thickness direction.
  • the fiber 20 may be any material as long as it has electrical conductivity and resistance to the electrolytic solution.
  • the fibers 20 may be either carbon fibers or metal fibers.
  • the fibers 20 are composed of, for example, at least one selected from the group consisting of carbon, titanium, and tungsten.
  • Specific examples of carbon fibers include PAN-based carbon fibers made from polyacrylonitrile (PAN) fibers and pitch-based carbon fibers made from pitch fibers. Carbon fibers are obtained by burning and carbonizing organic fibers such as PAN fibers and pitch fibers.
  • the metal fibers may be composed of pure titanium or pure tungsten, or may be composed of an alloy of titanium or an alloy of tungsten.
  • the average diameter of the plurality of fibers 20, that is, the average fiber diameter is, for example, 1 ⁇ m or more and 20 ⁇ m or less.
  • the average fiber diameter is 1 ⁇ m or more, the strength of the fiber assembly 30 can be easily secured.
  • the average fiber diameter is 20 ⁇ m or less, the flexibility of the fibers 20 can be easily increased. Therefore, when the battery cell 100 (see FIG. 1) is constructed, the fibers 20 are less likely to pierce the diaphragm 101 . Further, if the average fiber diameter is 20 ⁇ m or less, the surface area per unit volume of the electrode 10 increases, so that it is easy to secure the reaction area with the electrolytic solution.
  • the average fiber diameter may be 5 ⁇ m or more.
  • the fiber diameter is obtained, for example, by observing the cross section of the fiber assembly 30 with an SEM and measuring the outer diameter of the fiber 20.
  • the fiber diameter is the diameter of a circle having an area equal to the cross-sectional area of the fiber 20 .
  • the “cross-sectional area of the fiber 20” refers to the cross-sectional area of the fiber 20 perpendicular to the longitudinal direction.
  • the average fiber diameter is, for example, the average value of 10 or more fiber diameters.
  • the number of fibers 20 whose fiber diameter is to be measured may be 20 or more, or even 30 or more.
  • the average length of the plurality of fibers 20 may differ depending on the form of the fiber assembly 30 .
  • the fiber assembly 31 in the first form such as cloth or non-woven fabric has an average fiber length of, for example, 25 mm or more, and further 30 mm or more. When the average fiber length is 25 mm or more, the fibers 20 are easily entangled with each other, and the shape of the fiber assembly 31 is easily maintained. In the case of cloth, the average fiber length is, for example, 80 mm or more. In the case of nonwoven fabric, the average fiber length is, for example, 25 mm or more and 100 mm or less.
  • the fiber assembly 32 see FIG.
  • the average fiber length is, for example, 20 mm or less. If the average fiber length is long, the fibers 20 are likely to be arranged along the horizontal direction. In general, the fiber assembly 32 in the second mode maintains its shape by binding the fibers 20 together with the binder 25, so the fiber length may be shorter than the fiber assembly 31 in the first mode.
  • the average fiber length may be 10 mm or less, 5 mm or less, or even 3 mm or less.
  • the lower limit of the length of the fibers 20 forming the paper is, for example, 0.1 mm or more, and further 0.3 mm or more, or 0.5 mm or more.
  • the fiber length can be obtained, for example, by measuring the length of the fiber 20 by analyzing the X-ray CT image.
  • the average fiber length is, for example, the average value of 10 or more fiber lengths.
  • the number of fibers 20 whose fiber length is measured may be 20 or more, or even 30 or more.
  • the fibers 20 may have carbon particles 40 on the surface of the fibers 20 as shown in FIG. 9 in order to improve battery reactivity with the electrolyte.
  • the fibers 20 may have a catalyst 50 on the surface of the fibers 20 as shown in FIG. 9 and 10 show cross sections along the longitudinal direction of the fiber 20.
  • Carbon particles 40 are carried on the surface of the fiber 20, as shown in FIG.
  • the carbon particles 40 do not necessarily have to be carried on the surfaces of all the fibers 20 among the plurality of fibers 20 as long as they are carried on most of the fibers 20 .
  • the carbon particles 40 need only be carried on at least part of the surface of each fiber 20 . It is preferable that the carbon particles 40 are carried almost all over the plurality of fibers 20 without being unevenly carried locally.
  • the term “carrying” as used herein means that the carbon particles 40 are attached to the fibers 20 in an electrically conductive state. At least part of the carbon particles 40 may be embedded in the fibers 20 .
  • the carbon particles 40 improve battery reactivity with the electrolyte by functioning as reaction points with the electrolyte.
  • the carbon particles 40 are composed of graphite, carbon black, or the like, for example.
  • the carbon particles 40 exist dispersedly on the surface of the fiber 20 .
  • the shape of the carbon particles 40 is typically spherical.
  • the shape of the carbon particles 40 can take various shapes such as a spherical shape, a needle shape, and a thin plate shape.
  • the particle size of the carbon particles 40 is, for example, 100 nm or more and 50 ⁇ m or less. "Particle size" here means average particle size.
  • the particle size of the carbon particles 40 can be measured, for example, as follows.
  • a cross section of the fiber assembly 30 is observed with an SEM or a transmission electron microscope (TEM).
  • the size of the field of view is, for example, 100 ⁇ m ⁇ 50 ⁇ m or more and 200 ⁇ m ⁇ 100 ⁇ m or less.
  • the magnification of the field of view is, for example, 3000 times.
  • a carbon particle 40 within the field of view is extracted.
  • the number of carbon particles 40 to be extracted is, for example, 10 or more.
  • the diameter of a circle having an area equal to the area of the carbon particle 40 is obtained, and the average value is taken as the particle size of the carbon particle 40 .
  • the number of carbon particles 40 whose particle diameters are measured may be 20 or more, or even 30 or more.
  • the carbon particles 40 are carried on the surface of the fiber 20 by the binder 25.
  • the binder 25 By having the binder 25 , the carbon particles 40 are firmly supported on the surface of the fiber 20 .
  • Binder 25 may be omitted. Carbon particles 40 may be attached directly to the surface of fiber 20 .
  • the binder 25 contains a first binder mainly composed of carbon or a second binder mainly composed of a conductive metal oxide, even if the binder 25 is interposed between the fibers 20 and the carbon particles 40, The carbon particles 40 can be carried in an electrically conductive state with the fibers 20 . In other words, electrical continuity between the carbon particles 40 and the fibers 20 can be ensured. Also, electrical continuity between the carbon particles 40 can be ensured via the binder 25 .
  • the binder 25 is composed of a resin such as PTFE, PVDF, or PVDC as described above, that is, when it is not carbonized, the contact between the carbon particles 40 and the fibers 20 causes electrical continuity is ensured. Also, electrical continuity between the carbon particles 40 is ensured by the contact between the carbon particles 40 .
  • the content of the carbon particles 40 is, for example, 10% by mass or more and 60% by mass or less.
  • the content of the carbon particles 40 is the ratio of the mass of the carbon particles 40 when the mass of the fiber assembly 30 (see FIG. 3A) is 100% by mass.
  • the mass of the fiber assembly 30 is the sum of the fibers 20, the binder 25 and the carbon particles 40.
  • the mass of the fiber assembly 30 includes the catalyst 50 as well.
  • the content of the carbon particles 40 is 10% by mass or more, the battery reactivity with the electrolytic solution can be easily increased.
  • the content of the carbon particles 40 is 60% by mass or less, the strength of the fiber assembly 30 can be easily secured.
  • the content of the carbon particles 40 may be 20% by mass or more and 50% by mass or less, and further 25% by mass or more and 45% by mass or less.
  • the content of the carbon particles 40 is determined by, for example, a thermogravimetric method (TG method).
  • the content of the binder 25 is, for example, 10% by mass or more and 70% by mass or less when the mass of the fiber assembly 30 is 100% by mass.
  • the content of the binder 25 is 10% by mass or more, the carbon particles 40 are easily supported on the surface of the fiber 20 by the binder 25 .
  • the content of the binder 25 may be appropriately set so that the carbon particles 40 can be supported on the surfaces of the fibers 20 .
  • the content of the binder 25 may be 10% by mass or more and 60% by mass or less, and further 20% by mass or more and 50% by mass or less.
  • the content of each binder is determined by, for example, a thermogravimetric method (TG method).
  • the fibers 20 supporting the carbon particles 40 are obtained by applying a coating liquid containing the carbon particles 40 to the fiber assembly 30 and then drying.
  • the coating liquid is, for example, carbon particles 40 dispersed in a solvent.
  • the coating liquid may contain a stabilizer and the like, if necessary.
  • the coating liquid further contains the raw material of the binder 25 .
  • the solvent may be either water or an organic solvent.
  • the solvent is preferably an organic solvent.
  • Organic solvents include methanol, ethanol, propyl alcohol, isopropanol, butanol, pentanol, hexanol, and the like.
  • the raw material of the binder 25 dissolves the above metal ions in a solvent.
  • the solvent is preferably contained in an amount of 70% by mass or more and 95% by mass or less based on 100% by mass of the coating liquid.
  • Stabilizers include acetylacetone.
  • the stabilizer is preferably contained in an amount of 1% by mass or more and 10% by mass or less based on 100% by mass of the coating liquid.
  • the heat treatment temperature may be 400° C. or higher and 600° C. or lower, and further 450° C. or higher and 550° C. or lower.
  • the heat treatment time may be 15 minutes or more and 2 hours or less, or 30 minutes or more and 1 hour or less.
  • the carbon particles 40 adhere to the surfaces of the fibers 20 by drying after applying the coating liquid to the fiber assembly 30 .
  • the carbon particles 40 can be supported on the surfaces of the fibers 20 by the binder 25 as described above.
  • Catalyst 50 is supported on the surface of fiber 20 as shown in FIG.
  • the catalyst 50 does not necessarily have to be carried on the surfaces of all the fibers 20 among the plurality of fibers 20 , as long as it is carried on most of the fibers 20 .
  • the catalyst 50 may be carried on at least a part of the surface of each fiber 20 . It is preferable that the catalyst 50 is carried almost all over the plurality of fibers 20 without being unevenly carried locally.
  • the catalyst 50 improves the battery reactivity with the electrolyte by activating the battery reaction between the electrolyte and the electrodes.
  • the catalyst 50 is composed of, for example, a metal oxide containing a metal element.
  • the metal element is, for example, at least one selected from the group consisting of titanium, vanadium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tin, antimony, thallium, hafnium, tantalum, tungsten, rhenium, and iridium.
  • the metal oxide may contain one type of metal element selected from the above group, or may be a composite oxide containing multiple types of metal elements.
  • the metal oxide that is the catalyst 50 preferably contains the same metal element as the metal element forming the fibers 20 .
  • the fiber 20 may consist of a single element and the catalyst 50 may consist of an oxide of that element.
  • the catalyst 50 is made of titanium oxide (TiO 2 ).
  • the catalyst 50 is made of tungsten oxide ( WO3).
  • the catalyst 50 exists dispersedly on the surface of the fiber 20 .
  • Catalyst 50 is typically particulate.
  • the particle shape includes various shapes such as a spherical shape, a needle shape, and a thin plate shape.
  • the particle size of the catalyst 50 is, for example, 1 nm or more and 100 nm or less. "Particle size” here means average particle size.
  • the particle size of the catalyst 50 can be measured by the same method as the particle size of the carbon particles 40 described above.
  • the catalyst 50 is supported on the surface of the fiber 20 by the binder 25.
  • the binder 25 By having the binder 25 , the catalyst 50 is strongly supported on the surface of the fiber 20 .
  • Binder 25 may be omitted. Catalyst 50 may adhere directly to the surface of fiber 20 .
  • the second binder 25 contains a carbon-based first binder or a conductive metal oxide-based second binder
  • the binder 25 is interposed between the fibers 20 and the catalyst 50.
  • the catalyst 50 can be supported in an electrically conductive state with the fibers 20 . In other words, electrical continuity between the catalyst 50 and the fibers 20 can be ensured. Also, electrical continuity between the catalysts 50 can be ensured through the binder 25 .
  • the binder 25 is composed of a resin such as PTFE, PVDF, or PVDC, as described above, that is, when it is not carbonized, the contact between the catalyst 50 and the fibers 20 causes electricity to flow between the catalyst 50 and the fibers 20 . Electrical continuity is ensured. In addition, electrical continuity between the catalysts 50 is ensured by the contact between the catalysts 50 .
  • the content of the catalyst 50 is, for example, 1% by mass or more and 30% by mass or less.
  • the content of the catalyst 50 is the ratio of the mass of the catalyst 50 when the mass of the fiber assembly 30 (see FIG. 3A) is 100% by mass.
  • the content of the catalyst 50 is 1% by mass or more, it is easy to increase the battery reactivity with the electrolytic solution.
  • the higher the content of the catalyst 50 the easier it is to increase the battery reactivity, but the proportion of the fibers 20 is relatively decreased, so that the strength of the fiber assembly 30 may be lowered.
  • the content of the catalyst 50 is 30% by mass or less, the strength of the fiber assembly 30 can be easily secured.
  • the content of the catalyst 50 may be 1% by mass or more and 20% by mass or less, and further 1% by mass or more and 10% by mass or less.
  • the content of the catalyst 50 is obtained by, for example, a thermogravimetry method (TG method).
  • the fibers 20 supporting the catalyst 50 can be obtained by applying a coating liquid containing the metal elements constituting the metal oxide to the fiber assembly 30 and then heat-treating it in an oxygen-containing atmosphere.
  • the coating liquid contains, for example, a raw material of the metal element constituting the metal oxide and a solvent.
  • the coating liquid may contain a stabilizer and the like, if necessary.
  • the coating liquid further contains the raw material of the binder 25 .
  • Metal alkoxides, chlorides, acetates, organometallic compounds, and the like are available as raw materials for the metal elements constituting the metal oxides.
  • Solvents include water, organic solvents, and the like. For the types and contents of the organic solvent and the stabilizer, and the conditions for the heat treatment, it is preferable to refer to the items described for the coating liquid of the carbon particles 40 described above.
  • the atmosphere containing oxygen may be, for example, air.
  • the metal elements forming the metal oxide are thermally diffused into the fiber assembly 30 and oxidized. Then, the catalyst 50 made of metal oxide adheres to the surface of the fiber 20 .
  • the catalyst 50 can be supported on the surface of the fibers 20 by the binder 25 as described above.
  • the electrode 10 of the embodiment described above can suppress the fibers 20 from sticking into the diaphragm 101 when the battery cell 100 is constructed.
  • the reason is that the average degree of orientation is 0.3 or less. If the average degree of orientation is 0.3 or less, the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 is small. Therefore, it is possible to prevent the fibers 20 from sticking into the diaphragm 101 .
  • the electrode 10 is used as the electrode of the RF battery 1 , it is possible to suppress short circuits caused by the fibers 20 sticking into the diaphragm 101 . As a result, a decrease in the current efficiency of the RF battery 1 can be suppressed.
  • the battery cell 100 of the embodiment and the RF battery 1 including the battery cell 100 have high current efficiency.
  • the reason for this is that the positive electrode 104 and the negative electrode 105 that constitute the battery cell 100 are the electrodes 10 of the embodiment, so that short circuits caused by the fibers 20 sticking into the diaphragm 101 can be suppressed. Since a short circuit is less likely to occur between the positive electrode and the negative electrode, a decrease in current efficiency can be suppressed.
  • Fiber aggregates with different average orientation degrees of fibers were prepared. The current efficiency was investigated when the prepared fiber assembly was used as an electrode of an RF battery.
  • each prepared fiber assembly was designated as sample No. 1. 1 to No. 3, and sample no. 11 to No. 13. Sample no. 1 and no. The fiber assembly in the 11 electrodes is a non-woven fabric. Sample no. 2 and No. In 12, the fiber assembly is cloth. Sample no. 3 and No. In 13, the fiber assembly is paper. All of the fibers forming each fiber assembly are carbon fibers.
  • Sample No. 1 in which the fiber assembly is a non-woven fabric. Electrode No. 1 had a structure in which carbon particles were supported on the surface of the fiber by a binder. That is, sample no. 1 has carbon particles and a binder in addition to carbon fibers. The particle size of the carbon particles is 15 ⁇ m. The content of carbon particles is 35% by mass. The binder content is 35% by mass. The material of the binder is carbon. Sample No. in which the fiber assembly is paper. 3 and No. The material of the binder for the electrode No. 13 is also carbon.
  • the electrodes of each sample were used to construct each RF battery with a single battery cell.
  • electrodes of the same sample were used for the positive electrode and the negative electrode constituting the battery cell.
  • Each area of the positive electrode and the negative electrode was 9 cm 2 .
  • the diaphragm is a 25 ⁇ m thick Nafion® membrane.
  • the positive electrode electrolyte and the negative electrode electrolyte are titanium-manganese based electrolytes.
  • the titanium-manganese-based electrolytic solution is obtained by dissolving titanium ions and manganese ions at concentrations of 1M (mol/L) in an aqueous solution of sulfuric acid at a concentration of 5M (mol/L).
  • a charge/discharge test was performed on each RF battery.
  • the charging/discharging test conditions were a constant current with a current density of 70 mA/cm 2 .
  • the charge end voltage was set to 1.5V, and the discharge end voltage was set to 1.0V.
  • the current efficiency was determined.
  • the current efficiency is obtained by "(amount of discharged electricity/amount of charged electricity) ⁇ 100".
  • the charge quantity of electricity is obtained by "(charging time) x (current density x electrode area)”.
  • the amount of discharged electricity is obtained by “(discharge time) ⁇ (current density ⁇ electrode area)”.
  • Table 1 shows the current efficiency (%) of each RF cell with electrodes of each sample.
  • the specifications of the fiber assembly and fibers in the electrode of each sample, and the compression ratio and porosity of the fiber assembly when composing the battery cell are as follows. Table 1 shows the average degree of orientation in percentage.
  • the average degree of orientation is 30% or less, that is, 0.3 or less.
  • the average degree of orientation is 10% or less, that is, 0.1 or less.
  • the current efficiency of sample no. The current efficiency is high compared to that of 13.
  • Sample no. The current efficiency of 3 satisfies 90% or more, further 95% or more, particularly 99% or more.
  • sample No. 1 to No. 3 is sample no. 11 to No. It can be seen that the decrease in current efficiency can be suppressed more than 13. Sample no. 1 to No. The reason why the decrease in the current efficiency could be suppressed in 3 is considered to be that the sticking of the fibers into the diaphragm could be suppressed. Sample no. 1 to No. In 3, since the average degree of orientation is small, the fibers are less likely to stick into the diaphragm. Therefore, sample no. 1 to No. In 3, a short circuit caused by sticking of the fiber into the diaphragm is suppressed, and thus a decrease in current efficiency is suppressed.
  • Redox flow battery 10 electrode, 11 first surface 20 fiber, 25 binder 20s yarn, 21s first yarn, 22s second yarn 30, 31, 32 fiber assembly 40 carbon particles 50 catalyst 7 AC/DC converter 71 substation equipment 8 power generation unit 9 load 100 battery cell 101 diaphragm 102 positive electrode cell 103 negative electrode cell 104 positive electrode 105 negative electrode 106 positive electrode electrolyte tank 107 negative electrode electrolyte tank 108, 109 forward pipe 110, 111 return pipe 112, 113 pump 120 cell frame 121 bipolar plate 122 frame 122o recess 123, 124 liquid supply manifold 125, 126 drainage manifold 123s, 124s liquid supply slit 125s, 126s drainage slit 127 sealing member 200 cell stack 200s substack 210 end plate, 220 feed/discharge plate, 230 tightening mechanism p center distance d diagonal

Abstract

This electrode comprises a fiber assembly formed by combining a plurality of fibers. The fiber assembly has a sheet-like shape, with an average orientation of the plurality of fibers being 0.3 or less. In a cross section of the fiber assembly along the thickness direction, the average degree of orientation is the average of values obtained by dividing, by 90 degrees, each angle of the plurality of fibers with respect to a horizontal line orthogonal to a thickness direction of the fiber assembly.

Description

電極、電池セル、及びレドックスフロー電池Electrodes, battery cells, and redox flow batteries
　本開示は、電極、電池セル、及びレドックスフロー電池に関する。
　本出願は、２０２１年４月２日付の日本国出願の特願２０２１－０６３７７６に基づく優先権を主張し、前記日本国出願に記載された全ての記載内容を援用するものである。 The present disclosure relates to electrodes, battery cells, and redox flow batteries.
This application claims priority based on Japanese Patent Application No. 2021-063776 dated April 2, 2021, and incorporates all the descriptions described in the Japanese application.
　特許文献１は、レドックスフロー電池の隔膜と向かい合って配置されるレドックスフロー電池用電極を開示する。この電極は、複数本の炭素繊維を有する繊維集合体を備える。この繊維集合体は、ヤング率が２００ＧＰａ以下の柔炭素繊維を含む。 Patent Document 1 discloses a redox flow battery electrode that is arranged to face a redox flow battery membrane. This electrode includes a fiber aggregate having a plurality of carbon fibers. This fiber assembly contains soft carbon fibers having a Young's modulus of 200 GPa or less.
国際公開第２０１７／０６８９４４号WO2017/068944
　本開示の電極は、
　複数の繊維が組み合わされた繊維集合体を備え、
　前記繊維集合体はシート形状を有し、
　前記複数の繊維の平均配向度は０．３以下であり、
　前記平均配向度は、前記繊維集合体の厚さ方向に沿った前記繊維集合体の断面において、前記厚さ方向と直交する水平線に対する前記複数の繊維の各々の角度を９０°で割った値の平均値である。 The electrodes of the present disclosure are
Equipped with a fiber assembly in which a plurality of fibers are combined,
The fiber assembly has a sheet shape,
The average degree of orientation of the plurality of fibers is 0.3 or less,
The average degree of orientation is the value obtained by dividing the angle of each of the plurality of fibers with respect to a horizontal line orthogonal to the thickness direction in the cross section of the fiber assembly along the thickness direction of the fiber assembly by 90°. Average value.
　本開示の電池セルは、
　正極電極と、負極電極と、隔膜とを備え、
　前記正極電極及び前記負極電極の少なくとも一方の電極は、本開示の電極である。 The battery cell of the present disclosure is
A positive electrode, a negative electrode, and a diaphragm,
At least one of the positive electrode and the negative electrode is the electrode of the present disclosure.
　本開示のレドックスフロー電池は、
　本開示の電池セルを備える。 The redox flow battery of the present disclosure comprises
A battery cell of the present disclosure is provided.
図１は、実施形態に係るレドックスフロー電池の構成を示す概略図である。FIG. 1 is a schematic diagram showing the configuration of a redox flow battery according to an embodiment. 図２は、レドックスフロー電池に備えるセルスタックの構成を示す概略図である。FIG. 2 is a schematic diagram showing the configuration of a cell stack provided in a redox flow battery. 図３Ａは、実施形態に係る電極の構成を示す概略図である。FIG. 3A is a schematic diagram showing the configuration of electrodes according to the embodiment. 図３Ｂは、図３Ａの一点鎖線で囲まれる部分の内部を拡大して示す概略断面図である。FIG. 3B is a schematic cross-sectional view showing an enlarged interior of a portion surrounded by a dashed line in FIG. 3A. 図４は、実施形態に係る電極に備える繊維集合体の断面を拡大して示す概略図であって、繊維集合体がクロスである場合を示す。FIG. 4 is a schematic diagram showing an enlarged cross section of a fiber assembly provided in the electrode according to the embodiment, showing a case where the fiber assembly is a cloth. 図５は、実施形態に係る電極に備える繊維集合体の表面を拡大して示す概略図であって、繊維集合体がクロスである場合を示す。FIG. 5 is a schematic diagram showing an enlarged surface of a fiber assembly provided in the electrode according to the embodiment, showing a case where the fiber assembly is a cloth. 図６は、実施形態に係る電極に備える繊維集合体の断面を拡大して示す概略図であって、繊維集合体が不織布である場合を示す。FIG. 6 is a schematic diagram showing an enlarged cross-section of a fiber assembly provided in the electrode according to the embodiment, showing a case where the fiber assembly is a non-woven fabric. 図７は、実施形態に係る電極に備える繊維集合体の断面を拡大して示す概略図であって、繊維集合体がペーパーである場合を示す。FIG. 7 is a schematic diagram showing an enlarged cross section of a fiber assembly provided in the electrode according to the embodiment, showing a case where the fiber assembly is paper. 図８Ａは、実施形態に係る電極における繊維の平均配向度の測定方法を説明する図である。FIG. 8A is a diagram explaining a method of measuring an average orientation degree of fibers in an electrode according to the embodiment; 図８Ｂは、図８Ａの一点鎖線で囲まれる領域を拡大した図である。FIG. 8B is an enlarged view of a region surrounded by a dashed line in FIG. 8A. 図９は、実施形態に係る電極において、繊維の表面に炭素粒子を有する例を示す概略図である。FIG. 9 is a schematic diagram showing an example of having carbon particles on the surface of the fiber in the electrode according to the embodiment. 図１０は、実施形態に係る電極において、繊維の表面に触媒を有する例を示す概略図である。FIG. 10 is a schematic diagram showing an example in which the electrode according to the embodiment has a catalyst on the surface of the fiber.
　［本開示が解決しようとする課題］
　レドックスフロー電池の更なる電池性能の向上が望まれている。レドックスフロー電池は、電池性能の一つとして、電流効率が高いことが要求される。 [Problems to be Solved by the Present Disclosure]
Further improvement of the battery performance of the redox flow battery is desired. A redox flow battery is required to have high current efficiency as one of its battery performances.
　繊維集合体を備える電極を備えるレドックスフロー電池では、電極に含まれる繊維の隔膜への突き刺さりによる影響が、電流効率の低下の要因の一つであると考えられる。正極電極及び負極電極を構成する繊維が隔膜に突き刺さると、隔膜に孔が空いて、正極電解液と負極電解液とが混ざる。その結果、正極と負極との間で短絡が生じ得る。電極間に短絡が発生すると、電流効率の低下を招く。したがって、繊維集合体を備える電極において、レドックスフロー電池の電流効率の低下を抑制する観点から、繊維が隔膜に突き刺さることに起因する短絡を抑制することが求められている。 In a redox flow battery equipped with an electrode comprising a fiber assembly, the effect of the fibers contained in the electrode sticking into the diaphragm is considered to be one of the factors for the decrease in current efficiency. When the fibers constituting the positive electrode and the negative electrode stick into the diaphragm, holes are formed in the diaphragm and the positive electrode electrolyte and the negative electrode electrolyte are mixed. As a result, a short circuit can occur between the positive and negative electrodes. If a short circuit occurs between the electrodes, it will lead to a decrease in current efficiency. Therefore, from the viewpoint of suppressing a decrease in the current efficiency of the redox flow battery, it is required to suppress short-circuiting caused by the fibers sticking into the diaphragm in the electrode provided with the fiber assembly.
　本開示は、繊維の隔膜への突き刺さりを抑制できる電極を提供することを目的の一つとする。また、本開示は、電流効率が高い電池セル、及びレドックスフロー電池を提供することを別の目的の一つとする。 One object of the present disclosure is to provide an electrode capable of suppressing sticking of fibers to a diaphragm. Another object of the present disclosure is to provide a battery cell and a redox flow battery with high current efficiency.
　［本開示の効果］
　本開示の電極は、繊維の隔膜への突き刺さりを抑制できる。本開示の電池セル、及びレドックスフロー電池は、電流効率が高い。 [Effect of the present disclosure]
The electrode of the present disclosure can suppress sticking of fibers to the diaphragm. The battery cell and redox flow battery of the present disclosure have high current efficiency.
　［本開示の実施形態の説明］
　最初に本開示の実施態様を列記して説明する。 [Description of Embodiments of the Present Disclosure]
First, the embodiments of the present disclosure are listed and described.
　（１）本開示の実施形態に係る電極は、
　複数の繊維が組み合わされた繊維集合体を備え、
　前記繊維集合体はシート形状を有し、
　前記複数の繊維の平均配向度は０．３以下であり、
　前記平均配向度は、前記繊維集合体の厚さ方向に沿った前記繊維集合体の断面において、前記厚さ方向と直交する水平線に対する前記複数の繊維の各々の角度を９０°で割った値の平均値である。 (1) An electrode according to an embodiment of the present disclosure,
Equipped with a fiber assembly in which a plurality of fibers are combined,
The fiber assembly has a sheet shape,
The average degree of orientation of the plurality of fibers is 0.3 or less,
The average degree of orientation is the value obtained by dividing the angle of each of the plurality of fibers with respect to a horizontal line orthogonal to the thickness direction in the cross section of the fiber assembly along the thickness direction of the fiber assembly by 90°. Average value.
　上記の電極は、レドックスフロー電池において、電解液との間で電池反応を行う。上記の電極は、レドックスフロー電池の電池セルを構成したとき、以下の理由により、電池セルに備える隔膜に繊維が突き刺さることを抑制できる。上記平均配向度が０．３以下である電極は、電極における隔膜と向かい合う第一の面において、隔膜の厚さ方向に突出する繊維の量が少ない。換言すれば、隔膜に刺さり易い繊維の量が少ない。上記平均配向度が小さいほど、隔膜に刺さり易い繊維の量が少ない。上記の電極は、レドックスフロー電池の電極に使用した場合、繊維が隔膜に突き刺さることに起因する短絡を抑制できる。上記の電極は、レドックスフロー電池の電流効率の低下を抑制できる。 The above electrodes undergo a battery reaction with the electrolyte in the redox flow battery. When the battery cell of the redox flow battery is constructed, the electrode described above can prevent the fibers from sticking into the diaphragm provided in the battery cell for the following reasons. An electrode having an average degree of orientation of 0.3 or less has a small amount of fibers protruding in the thickness direction of the diaphragm on the first surface of the electrode facing the diaphragm. In other words, the amount of fibers that tend to stick into the diaphragm is small. The smaller the average degree of orientation, the smaller the amount of fibers that easily stick into the diaphragm. When the electrode described above is used as an electrode of a redox flow battery, it can suppress short circuits caused by sticking of the fibers into the diaphragm. Said electrode can suppress the deterioration of the current efficiency of the redox flow battery.
　上記の繊維集合体は、繊維間に空隙を有する多孔質体である。繊維集合体を備える電極は、電極内に電解液を流通させることが可能である。繊維集合体は、複数の繊維同士が絡み合って形状が維持される第一の形態と、複数の繊維同士が結着されて形状が維持される第二の形態とを含む。上記第一の形態の繊維集合体の具体例は、クロス、不織布である。上記第二の形態の繊維集合体の具体例は、ペーパーである。 The above fiber assembly is a porous body having voids between fibers. An electrode comprising a fiber aggregate allows electrolyte to flow through the electrode. The fiber assembly includes a first form in which a plurality of fibers are entangled to maintain their shape, and a second form in which a plurality of fibers are bound together to maintain their shape. Specific examples of the fiber assembly of the first form are cloth and nonwoven fabric. A specific example of the fiber assembly of the second form is paper.
　（２）上記の電極において、
　前記繊維集合体における前記複数の繊維の含有率が２０質量％以上でもよい。 (2) In the above electrode,
A content rate of the plurality of fibers in the fiber assembly may be 20% by mass or more.
　上記の電極は、電極の機械的強度を確保し易い。その理由は、繊維集合体に含まれる繊維の割合が多いほど、繊維集合体の芯となる基材の割合が増えることになるからである。そのため、繊維集合体の強度を高め易い。 With the above electrodes, it is easy to ensure the mechanical strength of the electrodes. The reason for this is that the higher the ratio of the fibers contained in the fiber assembly, the higher the ratio of the base material serving as the core of the fiber assembly. Therefore, it is easy to increase the strength of the fiber assembly.
　（３）上記の電極において、
　前記繊維集合体は、クロス又は不織布でもよい。 (3) In the above electrode,
The fiber assembly may be cloth or non-woven fabric.
　クロス又は不織布は、複数の繊維同士が絡み合うことにより構成されることから、繊維間に多くの空隙が存在する。そのため、上記繊維集合体を備える電極は、空隙率が比較的大きいので、電極内に電解液が流通し易い。 A cloth or non-woven fabric is composed of a plurality of intertwined fibers, so there are many voids between the fibers. Therefore, since the electrode including the fiber assembly has a relatively large porosity, the electrolytic solution can easily flow through the electrode.
　（４）上記の電極において、
　前記複数の繊維の平均長さが２５ｍｍ以上でもよい。 (4) In the above electrode,
An average length of the plurality of fibers may be 25 mm or more.
　上記の電極は、繊維同士が絡み易い。そのため、繊維同士の絡み合いによる機械的な結合により上記繊維集合体の形状が維持され易い。 The fibers of the above electrodes tend to get entangled with each other. Therefore, the shape of the fiber assembly is easily maintained by mechanical bonding due to the entanglement of the fibers.
　（５）上記の電極において、
　前記繊維集合体は、前記複数の繊維の表面に付着されたバインダを含んでもよい。 (5) In the above electrode,
The fiber assembly may contain a binder attached to the surfaces of the plurality of fibers.
　上記の電極は、バインダにより繊維同士を結着することができる。バインダによる繊維同士の結着により上記繊維集合体の形状を維持できる。 The above electrodes can bind fibers together with a binder. The shape of the fiber assembly can be maintained by binding the fibers together with the binder.
　（６）上記の電極において、
　前記繊維集合体はペーパーであり、
　前記複数の繊維の表面に付着されたバインダを含んでもよい。 (6) In the above electrode,
The fiber assembly is paper,
A binder attached to the surfaces of the plurality of fibers may be included.
　上記の電極は、電極の厚さを薄くできる。ペーパーは、複数の繊維同士がバインダにより結着されることにより形状が維持される。ペーパーは、クロスや不織布よりも薄くし易い。そのため、上記繊維集合体を備える電極は、電池セルを薄型化できる。 The thickness of the electrodes can be made thinner. Paper maintains its shape by binding a plurality of fibers together with a binder. Paper is easier to make thinner than cloth or non-woven fabric. Therefore, the electrode provided with the fiber assembly can make the battery cell thinner.
　（７）上記（６）に記載の電極において、
　前記平均配向度が０．１以下でもよい。 (7) In the electrode according to (6) above,
The average degree of orientation may be 0.1 or less.
　上記の電極は、繊維の隔膜への突き刺さりをより抑制できる。 The above electrodes can further suppress the sticking of the fibers into the diaphragm.
　（８）上記（６）又は（７）に記載の電極において、
　前記複数の繊維の平均長さが２０ｍｍ以下でもよい。 (8) In the electrode according to (6) or (7) above,
An average length of the plurality of fibers may be 20 mm or less.
　ペーパーは、複数の繊維同士がバインダによって結着されることにより構成されることから、繊維長が短くても形状を維持できる。 Paper is made up of a plurality of fibers bound together by a binder, so it can maintain its shape even if the fiber length is short.
　（９）上記（５）から（８）のいずれか一つに記載の電極において、
　前記繊維集合体における前記バインダの含有率が２０質量％以上８０質量％以下でもよい。 (9) In the electrode according to any one of (5) to (8) above,
A content of the binder in the fiber assembly may be 20% by mass or more and 80% by mass or less.
　上記の電極は、繊維集合体の形状を維持しながら、繊維間の空隙を確保し易い。繊維集合体の形状を維持し易い理由は、バインダの含有率が２０質量％以上であることで、バインダによる繊維同士の結着を確保し易いからである。繊維間の空隙を確保し易い理由は、バインダの含有率が８０質量％以下であることで、バインダによって繊維間の空隙が減少することを抑制できるからである。 The above electrodes tend to secure voids between fibers while maintaining the shape of the fiber assembly. The reason why the shape of the fiber assembly is easily maintained is that the content of the binder is 20% by mass or more, so that the binding of the fibers by the binder can be easily secured. The reason why it is easy to secure voids between fibers is that when the content of the binder is 80% by mass or less, reduction in voids between fibers due to the binder can be suppressed.
　（１０）上記（５）から（９）のいずれか一つに記載の電極において、
　前記バインダは、炭素を主体とする第一のバインダを含んでもよい。 (10) In the electrode according to any one of (5) to (9) above,
The binder may include a carbon-based first binder.
　上記の電極は、第一のバインダによって繊維間の電気的導通を確保できる。その理由は、第一のバインダは、炭素を主体とすることで、導電性を有するからである。また、炭素は、電解液に対する耐性を有する。 The above electrodes can ensure electrical continuity between the fibers with the first binder. The reason for this is that the first binder is made mainly of carbon and thus has electrical conductivity. Carbon is also resistant to electrolytes.
　（１１）上記（５）から（１０）のいずれか一つに記載の電極において、
　前記バインダは、導電性金属酸化物を主体とする第二のバインダを含んでもよい。 (11) In the electrode according to any one of (5) to (10) above,
The binder may include a second binder mainly composed of a conductive metal oxide.
　上記の電極は、第二のバインダによって繊維間の電気的導通を確保できる。また、導電性金属酸化物は、電解液に対する耐性を有する。 The above electrodes can ensure electrical continuity between the fibers with the second binder. Also, the conductive metal oxide has resistance to the electrolyte.
　（１２）上記の電極は、
　前記複数の繊維の表面に担持された炭素粒子を有してもよい。 (12) The electrodes are
Carbon particles may be supported on the surfaces of the plurality of fibers.
　上記の電極では、炭素粒子が電解液との反応点として機能する。上記の電極は、電解液との電池反応性を向上させることが可能である。 In the above electrodes, the carbon particles function as reaction points with the electrolyte. The above electrode can improve battery reactivity with the electrolyte.
　（１３）上記（５）から（１１）のいずれか一つに記載の電極は、
　前記複数の繊維の表面に担持された炭素粒子を有し、
　前記炭素粒子は、前記バインダによって担持されていてもよい。 (13) The electrode according to any one of (5) to (11) above,
Having carbon particles supported on the surfaces of the plurality of fibers,
The carbon particles may be supported by the binder.
　上記の電極は、繊維の表面に炭素粒子を強固に担持させることが可能である。 The above electrodes are capable of firmly supporting carbon particles on the surface of the fiber.
　（１４）上記の電極は、
　前記複数の繊維の表面に担持された触媒を有してもよい。 (14) The electrodes are
A catalyst may be supported on the surfaces of the plurality of fibers.
　触媒は電解液と電極との電池反応を活性化させる。上記の電極は、電解液と電極との電池反応性を向上させることが可能である。 The catalyst activates the battery reaction between the electrolyte and the electrodes. The above electrode can improve battery reactivity between the electrolyte and the electrode.
　（１５）上記（５）から（１１）、及び（１３）のいずれか一つに記載の電極は、
　前記複数の繊維の表面に担持された触媒を有し、
　前記触媒は、前記バインダによって担持されていてもよい。 (15) The electrode according to any one of (5) to (11) and (13) above,
Having a catalyst supported on the surfaces of the plurality of fibers,
The catalyst may be supported by the binder.
　上記の電極は、繊維の表面に触媒を強固に担持させることが可能である。 The above electrodes are capable of firmly supporting the catalyst on the surface of the fiber.
　（１６）上記（１４）又は（１５）に記載の電極において、
　前記触媒は、チタン、バナジウム、ジルコニウム、ニオブ、モリブデン、ルテニウム、ロジウム、パラジウム、スズ、アンチモン、タリウム、ハフニウム、タンタル、タングステン、レニウム、及びイリジウムからなる群より選択される少なくとも一種の金属元素を含有する金属酸化物で構成されてもよい。 (16) In the electrode according to (14) or (15) above,
The catalyst contains at least one metal element selected from the group consisting of titanium, vanadium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tin, antimony, thallium, hafnium, tantalum, tungsten, rhenium, and iridium. It may be composed of a metal oxide that
　上記金属元素を含有する金属酸化物は、電池反応を活性化させる触媒効果を有する。上記金属酸化物は、触媒に好適である。 The metal oxide containing the above metal element has a catalytic effect that activates the cell reaction. The above metal oxides are suitable for catalysts.
　（１７）上記の電極において、
　前記複数の繊維は、炭素、チタン、及びタングステンからなる群より選択される少なくとも一種で構成されてもよい。 (17) In the above electrode,
The plurality of fibers may be composed of at least one selected from the group consisting of carbon, titanium, and tungsten.
　上記の電極は、レドックスフロー電池の電極に好適である。電極を構成する繊維は、電解液との間で電池反応を行う反応場として機能する。炭素、チタン、及びタングステンは、導電性を有すると共に、電解液に対する耐性を有する。炭素、チタン、及びタングステンは、繊維の材質に好適である。 The above electrodes are suitable for redox flow battery electrodes. The fibers that make up the electrodes function as reaction fields for cell reactions with the electrolyte. Carbon, titanium, and tungsten are electrically conductive and resistant to electrolytes. Carbon, titanium, and tungsten are preferred fiber materials.
　（１８）本開示の実施形態に係る電池セルは、
　正極電極と、負極電極と、隔膜とを備え、
　前記正極電極及び前記負極電極の少なくとも一方の電極は、上記（１）から（１７）のいずれか一つに記載の電極である。 (18) A battery cell according to an embodiment of the present disclosure is
A positive electrode, a negative electrode, and a diaphragm,
At least one of the positive electrode and the negative electrode is the electrode according to any one of (1) to (17) above.
　上記の電池セルは、正極電極及び負極電極の少なくとも一方の電極が上述した本開示の電極であることから、電流効率が高い。その理由は、上述したように、本開示の電極は、繊維が隔膜に突き刺さることに起因する短絡を抑制できるからである。上記の電池セルは、正極と負極との間で短絡が発生し難いため、電流効率の低下を抑制できる。 The above battery cell has high current efficiency because at least one of the positive electrode and the negative electrode is the electrode of the present disclosure described above. The reason for this is that, as described above, the electrodes of the present disclosure can suppress short circuits caused by fibers sticking into the diaphragm. In the battery cell described above, since a short circuit is unlikely to occur between the positive electrode and the negative electrode, a decrease in current efficiency can be suppressed.
　（１９）上記の電池セルにおいて、
　前記電極における前記繊維集合体の空隙率が３０体積％以上８９体積％以下でもよい。 (19) In the above battery cell,
A porosity of the fiber assembly in the electrode may be 30% by volume or more and 89% by volume or less.
　上記の電池セルは、繊維集合体の空隙率が３０体積％以上であることで、電極内に電解液を流通させ易い。繊維集合体の空隙率が８９体積％以下であることで、電極における電解液との接触面積、即ち反応面積の減少を抑制できる。また、空隙率が８９体積％以下であれば、繊維集合体の強度の低下を抑制できる。 In the battery cell described above, the porosity of the fiber assembly is 30% by volume or more, so that the electrolytic solution can be easily circulated in the electrode. When the porosity of the fiber assembly is 89% by volume or less, it is possible to suppress a decrease in the contact area with the electrolytic solution in the electrode, that is, the reaction area. Further, if the porosity is 89% by volume or less, it is possible to suppress a decrease in the strength of the fiber assembly.
　（２０）本開示の実施形態に係るレドックスフロー電池は、
　上記（１８）又は（１９）に記載の本開示の電池セルを備える。 (20) A redox flow battery according to an embodiment of the present disclosure,
The battery cell of the present disclosure according to (18) or (19) above is provided.
　上記のレドックスフロー電池は、本開示の電池セルを備えることから、電流効率が高い。 Since the above redox flow battery includes the battery cells of the present disclosure, it has high current efficiency.
　［本開示の実施形態の詳細］
　本開示の実施形態に係る電極、電池セル、及びレドックスフロー電池の具体例を、以下に図面を参照して説明する。図中の同一符号は同一又は相当部分を示す。以下、レドックスフロー電池を「ＲＦ電池」と呼ぶ場合がある。
　なお、本発明はこれらの例示に限定されるものではなく、請求の範囲によって示され、請求の範囲と均等の意味および範囲内でのすべての変更が含まれることが意図される。
　以下、先に、電池セル及びＲＦ電池について説明し、その後、電極について詳しく説明する。 [Details of the embodiment of the present disclosure]
Specific examples of electrodes, battery cells, and redox flow batteries according to embodiments of the present disclosure will be described below with reference to the drawings. The same reference numerals in the drawings indicate the same or corresponding parts. Hereinafter, the redox flow battery may be referred to as "RF battery".
The present invention is not limited to these exemplifications, but is indicated by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.
Hereinafter, the battery cell and the RF battery will be described first, and then the electrodes will be described in detail.
　＜ＲＦ電池＞
　初めに、図１を参照して、実施形態に係るＲＦ電池１、及びＲＦ電池１に備える電池セル１００を説明する。ＲＦ電池１は、電解液循環型の蓄電池の一つである。ＲＦ電池１において、正極電解液及び負極電解液は、酸化還元により価数が変化する金属イオンを活物質として含有する電解液である。ＲＦ電池１は、正極電解液に含まれる金属イオンの酸化還元電位と、負極電解液に含まれる金属イオンの酸化還元電位との差を利用して充放電を行う。電解液は、例えば、バナジウム系電解液、チタン－マンガン系電解液である。バナジウム系電解液では、正極電解液及び負極電解液の双方がバナジウム（Ｖ）イオンを含有する。チタン－マンガン系電解液では、正極電解液がマンガン（Ｍｎ）イオンを含有し、負極電解液がチタン（Ｔｉ）イオンを含有する。 <RF battery>
First, an RF battery 1 according to an embodiment and a battery cell 100 included in the RF battery 1 will be described with reference to FIG. The RF battery 1 is one of electrolyte circulation type storage batteries. In the RF battery 1, the positive electrode electrolyte and the negative electrode electrolyte are electrolyte solutions containing, as active materials, metal ions whose valences change due to oxidation-reduction. The RF battery 1 charges and discharges using the difference between the oxidation-reduction potential of the metal ions contained in the positive electrode electrolyte and the oxidation-reduction potential of the metal ions contained in the negative electrode electrolyte. The electrolytic solution is, for example, a vanadium-based electrolytic solution or a titanium-manganese-based electrolytic solution. In vanadium-based electrolytes, both the positive electrode electrolyte and the negative electrode electrolyte contain vanadium (V) ions. In the titanium-manganese-based electrolyte, the positive electrolyte contains manganese (Mn) ions, and the negative electrolyte contains titanium (Ti) ions.
　ＲＦ電池１は、代表的には、交流／直流変換器７や変電設備７１を介して発電部８及び負荷９に接続される。ＲＦ電池１は、発電部８で発電された電力を充電したり、充電した電力を負荷９に放電したりすることが可能である。発電部８は、太陽光発電や風力発電などの自然エネルギーを利用した発電設備やその他一般の発電所である。ＲＦ電池１は、例えば、負荷平準化用途、瞬低補償、非常用電源などの用途、自然エネルギー発電の出力平滑化用途に利用される。 The RF battery 1 is typically connected to the power generation section 8 and the load 9 via the AC/DC converter 7 and the substation equipment 71 . The RF battery 1 can charge the power generated by the power generation unit 8 and discharge the charged power to the load 9 . The power generation unit 8 is power generation equipment using natural energy such as solar power generation and wind power generation, and other general power plants. The RF battery 1 is used, for example, for load leveling applications, momentary sag compensation, emergency power supply applications, and output smoothing applications for natural energy power generation.
　ＲＦ電池１は、充放電を行う電池セル１００と、正極電解液及び負極電解液をそれぞれ貯留する正極電解液タンク１０６及び負極電解液タンク１０７と、正極電解液タンク１０６及び負極電解液タンク１０７の各タンクと電池セル１００との間で各電解液をそれぞれ循環させる循環流路とを備える。ＲＦ電池１の基本構成は、公知の構成を適宜利用できる。 The RF battery 1 includes a battery cell 100 that performs charging and discharging, a positive electrode electrolyte tank 106 and a negative electrode electrolyte tank 107 that respectively store a positive electrode electrolyte and a negative electrode electrolyte, and a positive electrode electrolyte tank 106 and a negative electrode electrolyte tank 107. A circulation channel for circulating each electrolytic solution between each tank and the battery cell 100 is provided. As for the basic configuration of the RF battery 1, a known configuration can be used as appropriate.
　＜電池セル＞
　電池セル１００は、正極電極１０４と、負極電極１０５と、隔膜１０１とを備える。隔膜１０１は正極電極１０４と負極電極１０５との間に配置される。電池セル１００は、隔膜１０１によって正極セル１０２と負極セル１０３とに分離されている。正極電極１０４は正極セル１０２に配置されている。負極電極１０５は負極セル１０３に配置されている。隔膜１０１は、例えば、水素イオンを透過するイオン交換膜である。正極電極１０４及び負極電極１０５は、電解液との間で電池反応を行う。正極電極１０４及び負極電極１０５の各電極は、例えば、シート状の多孔質体で構成されている。本実施形態では、正極電極１０４及び負極電極１０５は、後述する図３Ａ、図３Ｂに示すように、複数の繊維２０を含む繊維集合体３０を備える電極１０である。 <Battery cell>
A battery cell 100 includes a positive electrode 104 , a negative electrode 105 and a diaphragm 101 . The diaphragm 101 is arranged between the positive electrode 104 and the negative electrode 105 . A battery cell 100 is separated into a positive electrode cell 102 and a negative electrode cell 103 by a diaphragm 101 . A positive electrode 104 is placed in the positive cell 102 . A negative electrode 105 is arranged in the negative cell 103 . The diaphragm 101 is, for example, an ion exchange membrane permeable to hydrogen ions. The positive electrode 104 and the negative electrode 105 undergo a battery reaction with the electrolyte. Each electrode of the positive electrode 104 and the negative electrode 105 is composed of, for example, a sheet-like porous body. In this embodiment, the positive electrode 104 and the negative electrode 105 are the electrodes 10 having a fiber aggregate 30 including a plurality of fibers 20 as shown in FIGS. 3A and 3B described later.
　電池セル１００を構成する正極セル１０２には、正極電解液が供給される。負極セル１０３には、負極電解液が供給される。本例のＲＦ電池１は、図１に示すように、電池セル１００と正極電解液タンク１０６との間を接続する往路配管１０８及び復路配管１１０を備える。さらにＲＦ電池１は、電池セル１００と負極電解液タンク１０７との間を接続する往路配管１０９及び復路配管１１１を備える。往路配管１０８には、ポンプ１１２が設けられている。往路配管１０９には、ポンプ１１３が設けられている。正極電解液は、正極電解液タンク１０６からポンプ１１２によって往路配管１０８を通って正極セル１０２に供給される。正極セル１０２を通り正極セル１０２から排出された正極電解液は、復路配管１１０を通って正極電解液タンク１０６に戻される。負極電解液は、負極電解液タンク１０７からポンプ１１３によって往路配管１０９を通って負極セル１０３に供給される。負極セル１０３を通り負極セル１０３から排出された負極電解液は、復路配管１１１を通って負極電解液タンク１０７に戻される。つまり、各往路配管１０８，１０９及び各復路配管１１０，１１１によって、各電解液の循環流路が構成されている。 A positive electrode electrolyte is supplied to the positive electrode cells 102 that constitute the battery cells 100 . A negative electrode electrolyte is supplied to the negative electrode cell 103 . The RF battery 1 of the present example includes, as shown in FIG. Further, the RF battery 1 includes an outbound pipe 109 and a return pipe 111 that connect between the battery cell 100 and the negative electrode electrolyte tank 107 . A pump 112 is provided in the outbound pipe 108 . A pump 113 is provided in the outbound pipe 109 . The positive electrode electrolyte is supplied to the positive electrode cell 102 from the positive electrode electrolyte tank 106 by the pump 112 through the outgoing pipe 108 . The positive electrode electrolyte discharged from the positive electrode cell 102 through the positive electrode cell 102 is returned to the positive electrode electrolyte tank 106 through the return pipe 110 . The negative electrode electrolyte is supplied from the negative electrode electrolyte tank 107 to the negative electrode cell 103 by the pump 113 through the outgoing pipe 109 . The negative electrode electrolyte discharged from the negative electrode cell 103 through the negative electrode cell 103 is returned to the negative electrode electrolyte tank 107 through the return pipe 111 . In other words, the forward pipes 108 and 109 and the return pipes 110 and 111 constitute a circulation flow path for each electrolytic solution.
　ＲＦ電池１は、単数の電池セル１００を備える構成でもよいし、複数の電池セル１００を備える構成でもよい。本例では、図１に示すように、複数の電池セル１００が積層されたセルスタック２００を備える。セルスタック２００は、図２に示すように、サブスタック２００ｓをその両側から２枚のエンドプレート２１０で挟み込み、締付機構２３０によって締め付けることで構成されている。図２は、複数のサブスタック２００ｓを備えるセルスタック２００を示している。サブスタック２００ｓは、積層体と、積層体の両端に設けられる給排板２２０を備える。積層体は、セルフレーム１２０、正極電極１０４、隔膜１０１、負極電極１０５が順に繰り返し積層される。給排板２２０には、上述した図１に示す往路配管１０８、１０９及び復路配管１１０、１１１が接続される。セルスタック２００における電池セル１００の積層数は適宜選択できる。 The RF battery 1 may be configured with a single battery cell 100 or may be configured with a plurality of battery cells 100 . In this example, as shown in FIG. 1, a cell stack 200 in which a plurality of battery cells 100 are stacked is provided. As shown in FIG. 2, the cell stack 200 is configured by sandwiching a sub-stack 200s between two end plates 210 from both sides and tightening them with a tightening mechanism 230. As shown in FIG. FIG. 2 shows a cell stack 200 comprising multiple substacks 200s. The substack 200s includes a laminate and supply/discharge plates 220 provided at both ends of the laminate. In the laminate, the cell frame 120, the positive electrode 104, the diaphragm 101, and the negative electrode 105 are repeatedly laminated in this order. The supply/discharge plate 220 is connected to the outgoing pipes 108 and 109 and the return pipes 110 and 111 shown in FIG. The number of stacked battery cells 100 in the cell stack 200 can be selected as appropriate.
　本例のセルフレーム１２０は、図１、図２に示すように、正極電極１０４と負極電極１０５との間に配置される双極板１２１と、双極板１２１の周囲に設けられる枠体１２２とを有する。枠体１２２の内側には、双極板１２１と枠体１２２により凹部１２２ｏが形成される。凹部１２２ｏは、双極板１２１の両側にそれぞれ形成されている。双極板１２１は、正極電極１０４と向かい合う第一の面と、負極電極１０５と向かい合う第二の面とを有する。双極板１２１の第一の面側の凹部１２２ｏには正極電極１０４が配置される。双極板１２１の第二の面側の凹部１２２ｏには負極電極１０５が配置される。各凹部１２２ｏは、上述した図１に示す正極セル１０２及び負極セル１０３の各セル空間を形成する。 As shown in FIGS. 1 and 2, the cell frame 120 of this example includes a bipolar plate 121 arranged between the positive electrode 104 and the negative electrode 105, and a frame 122 provided around the bipolar plate 121. have. Inside the frame 122, the bipolar plate 121 and the frame 122 form a recess 122o. The recesses 122o are formed on both sides of the bipolar plate 121, respectively. Bipolar plate 121 has a first surface facing positive electrode 104 and a second surface facing negative electrode 105 . The positive electrode 104 is arranged in the concave portion 122 o on the first surface side of the bipolar plate 121 . The negative electrode 105 is arranged in the concave portion 122 o on the second surface side of the bipolar plate 121 . Each concave portion 122o forms each cell space of the positive electrode cell 102 and the negative electrode cell 103 shown in FIG. 1 described above.
　このように、隣り合う各セルフレーム１２０の双極板１２１の間に、隔膜１０１を挟んで正極電極１０４及び負極電極１０５が配置されることにより、１つの電池セル１００が形成される。各セルフレーム１２０の枠体１２２の間には、例えば環状のシール部材１２７が配置される。シール部材１２７はＯリング、平パッキンなどである。電池セル１００を構成したとき、正極電極１０４及び負極電極１０５は、隔膜１０１と向かい合うように配置される。正極電極１０４及び負極電極１０５は、厚さ方向に圧縮された状態で収納される。つまり、正極電極１０４及び負極電極１０５の各電極における隔膜１０１と向かい合う面は、隔膜１０１に押し付けられた状態となる。圧縮状態での正極電極１０４及び負極電極１０５の各厚さは、上記各凹部１２２ｏの深さによって決まる。 In this way, one battery cell 100 is formed by arranging the positive electrode 104 and the negative electrode 105 with the diaphragm 101 interposed between the bipolar plates 121 of the adjacent cell frames 120 . For example, an annular sealing member 127 is arranged between the frames 122 of the cell frames 120 . The sealing member 127 is an O-ring, flat packing, or the like. When the battery cell 100 is constructed, the positive electrode 104 and the negative electrode 105 are arranged to face the diaphragm 101 . The positive electrode 104 and the negative electrode 105 are stored while being compressed in the thickness direction. That is, the surfaces of the positive electrode 104 and the negative electrode 105 facing the diaphragm 101 are pressed against the diaphragm 101 . Each thickness of the positive electrode 104 and the negative electrode 105 in the compressed state is determined by the depth of each recess 122o.
　図２に示すように、セルフレーム１２０の枠体１２２は、給液マニホールド１２３，１２４及び排液マニホールド１２５，１２６を有する。本例では、正極電解液は、給液マニホールド１２３から給液スリット１２３ｓを介して正極電極１０４に供給される。正極電極１０４に供給された正極電解液は、排液スリット１２５ｓを介して排液マニホールド１２５に排出される。同様に、負極電解液は、給液マニホールド１２４から給液スリット１２４ｓを介して負極電極１０５に供給される。負極電極１０５に供給された負極電解液は、排液スリット１２６ｓを介して排液マニホールド１２６に排出される。給液マニホールド１２３，１２４及び排液マニホールド１２５，１２６は、枠体１２２に貫通して設けられており、セルフレーム１２０が積層されることによって各電解液の流路を構成する。これら各流路は、給排板２２０を介して図１に示す往路配管１０８，１０９及び復路配管１１０，１１１の各配管にそれぞれつながっている。セルスタック２００は、上記各流路によって、各電池セル１００に正極電解液及び負極電解液を流通させることが可能である。 As shown in FIG. 2, the frame 122 of the cell frame 120 has liquid supply manifolds 123 and 124 and liquid discharge manifolds 125 and 126 . In this example, the positive electrode electrolyte is supplied from the liquid supply manifold 123 to the positive electrode 104 through the liquid supply slit 123s. The positive electrode electrolyte supplied to the positive electrode 104 is discharged to the drainage manifold 125 through the drainage slit 125s. Similarly, the negative electrode electrolyte is supplied from the liquid supply manifold 124 to the negative electrode 105 through the liquid supply slit 124s. The negative electrode electrolyte supplied to the negative electrode 105 is discharged to the drainage manifold 126 through the drainage slit 126s. The liquid supply manifolds 123 and 124 and the liquid discharge manifolds 125 and 126 are provided through the frame 122, and the cell frames 120 are laminated to constitute flow paths for the respective electrolytes. Each of these flow paths is connected to each of the outbound pipes 108 and 109 and the inbound pipes 110 and 111 shown in FIG. The cell stack 200 can circulate the positive electrode electrolyte and the negative electrode electrolyte to each battery cell 100 through each of the channels.
　本例の電池セル１００では、正極電極１０４及び負極電極１０５の下側からそれぞれ電解液が供給され、正極電極１０４及び負極電極１０５の上側から電解液が排出されるように構成されている。つまり、正極電極１０４及び負極電極１０５の各電極の下縁部から上縁部に向かって電解液が流れる。 The battery cell 100 of this example is configured such that the electrolytic solution is supplied from the lower side of the positive electrode 104 and the negative electrode 105, respectively, and the electrolytic solution is discharged from the upper side of the positive electrode 104 and the negative electrode 105. That is, the electrolytic solution flows from the lower edge portion toward the upper edge portion of each of the positive electrode 104 and the negative electrode 105 .
　＜電極＞
　図３Ａ、図３Ｂを参照して、実施形態に係る電極１０を説明する。電極１０は、上述した電池セル１００（図１参照）の正極電極１０４及び負極電極１０５に利用される。電極１０は、電解液を利用して電池反応を行う。電極１０は、電池セル１００を構成したとき、隔膜１０１と向かい合う第一の面１１（図３Ａ参照）を有する。 <Electrode>
An electrode 10 according to an embodiment will be described with reference to FIGS. 3A and 3B. The electrode 10 is used as the positive electrode 104 and the negative electrode 105 of the battery cell 100 (see FIG. 1) described above. The electrode 10 performs a battery reaction using an electrolytic solution. The electrode 10 has a first surface 11 (see FIG. 3A) facing the diaphragm 101 when the battery cell 100 is constructed.
　本実施形態の電極１０は、図３Ａに示すように、シート形状を有する。電極１０は、図３Ｂに示すように、複数の繊維２０が組み合わされた繊維集合体３０を備える。電極１０の特徴の一つは、複数の繊維２０の平均配向度が特定の範囲である点である。 The electrode 10 of this embodiment has a sheet shape, as shown in FIG. 3A. The electrode 10 includes a fiber assembly 30 in which a plurality of fibers 20 are combined, as shown in FIG. 3B. One of the features of the electrode 10 is that the average degree of orientation of the plurality of fibers 20 is within a specific range.
　（繊維集合体）
　繊維集合体３０はシート形状を有する。繊維集合体３０は繊維２０間に空隙を有する多孔質体である。そのため、電池セル１００（図１参照）を構成したとき、電極１０の内部に電解液が流通する。繊維集合体３０は、代表的には、複数の繊維２０同士が絡み合って形状が維持される第一の形態と、複数の繊維２０同士が結着されて形状が維持される第二の形態とがある。 (Fiber assembly)
The fiber assembly 30 has a sheet shape. The fiber aggregate 30 is a porous body having voids between the fibers 20 . Therefore, when the battery cell 100 (see FIG. 1) is configured, the electrolyte flows inside the electrode 10 . The fiber assembly 30 typically has a first form in which a plurality of fibers 20 are entangled to maintain their shape, and a second form in which a plurality of fibers 20 are bound to maintain their shape. There is
　　〈第一の形態〉
　図４、図６は、第一の形態における繊維集合体３１の断面を拡大した概略断面図を示す。上記断面は、繊維集合体３１の厚さ方向に沿って切断した断面である。上記厚さ方向は、図３Ａに示す第一の面１１に直交する方向である。第一の面１１は、繊維集合体３０の互いに向き合う表面と裏面のいずれかの面である。第一の形態の繊維集合体３１の具体例は、クロス、不織布である。図４に示す繊維集合体３１はクロスである。図６に示す繊維集合体３１は不織布である。図中、矢印Ｖは厚さ方向、矢印Ｈは厚さ方向と直交する水平方向を示す。 <First form>
4 and 6 show enlarged schematic cross-sectional views of the fiber assembly 31 in the first embodiment. The above cross section is a cross section cut along the thickness direction of the fiber assembly 31 . The thickness direction is a direction orthogonal to the first surface 11 shown in FIG. 3A. The first surface 11 is either the surface facing each other or the back surface of the fiber assembly 30 . Specific examples of the first form of the fiber assembly 31 are cloth and non-woven fabric. The fiber assembly 31 shown in FIG. 4 is a cloth. A fiber assembly 31 shown in FIG. 6 is a nonwoven fabric. In the figure, arrow V indicates the thickness direction, and arrow H indicates the horizontal direction perpendicular to the thickness direction.
　クロスからなる繊維集合体３１は、平面視したとき、図５に示すように、多数の繊維２０を束ねて撚り合わせた糸２０ｓが織られたものである。クロスは、第一の糸２１ｓと、第一の糸２１ｓと交差する第二の糸２２ｓとを交互に織り合わせて形成される。クロスからなる繊維集合体３１の製造方法の具体例については後述する。 As shown in FIG. 5, the fiber assembly 31 made of cloth is woven with threads 20s obtained by bundling and twisting a large number of fibers 20, as shown in FIG. The cloth is formed by alternately weaving first yarns 21s and second yarns 22s crossing the first yarns 21s. A specific example of the method for manufacturing the fiber assembly 31 made of cloth will be described later.
　不織布からなる繊維集合体３１は、独立した個々の繊維２０が交絡されたものである。不織布は、複数の繊維２０を積層したウェブを積層方向に交絡処理することにより、繊維２０同士を絡み合わせて形成される。積層方向は、繊維集合体３１の厚さ方向に相当する。交絡処理は、例えば、ニードルパンチ法、水流交絡法により行うことができる。不織布には、フェルト、スパンレース、マリフリースなどが含まれる。不織布からなる繊維集合体３１の製造方法の具体例については後述する。 The fiber assembly 31 made of nonwoven fabric is obtained by intertwining independent individual fibers 20 . A non-woven fabric is formed by entangling a web in which a plurality of fibers 20 are laminated, by entangling the fibers 20 in the lamination direction. The stacking direction corresponds to the thickness direction of the fiber assembly 31 . The entangling treatment can be performed by, for example, a needle punching method or a hydroentangling method. Nonwoven fabrics include felt, spunlace, Malifleece, and the like. A specific example of the method for manufacturing the fiber assembly 31 made of nonwoven fabric will be described later.
　　〈第二の形態〉
　図７は、第二の形態における繊維集合体３２の断面を拡大した概略断面図を示す。繊維集合体３２は、複数の繊維２０と、繊維２０の表面に付着されたバインダ２５とを含む。バインダ２５は、複数の繊維２０のうち、必ずしも全ての繊維２０の表面に付着されていなくてもよく、大部分の繊維２０に付着されていればよい。また、バインダ２５は、各繊維２０の表面の全部又は一部に付着されていればよい。バインダ２５は、複数の繊維２０の局所に偏って付着されることなく、ほぼ全域に付着されていることが好ましい。バインダ２５は、繊維２０同士を結着する機能を有する。その他、バインダ２５は、図９、図１０に示す炭素粒子４０及び触媒５０の少なくとも一方を繊維２０の表面に担持させる機能を有する。炭素粒子４０及び触媒５０については後述する。第二の形態の繊維集合体３２の具体例は、ペーパーである。バインダ２５は電解液に対する耐性を有する材料により構成される。バインダ２５は、例えば、炭素、樹脂、及び導電性金属酸化物からなる群より選択される一種を含む。導電性金属酸化物は、例えば、酸化スズ、酸化インジウムスズ（ＩＴＯ）、酸化アンチモンスズ（ＡＴＯ）などの金属酸化物である。 <Second form>
FIG. 7 shows a schematic cross-sectional view enlarging the cross section of the fiber assembly 32 in the second embodiment. The fiber assembly 32 includes a plurality of fibers 20 and binders 25 attached to the surfaces of the fibers 20 . The binder 25 does not necessarily have to be adhered to the surface of all the fibers 20 among the plurality of fibers 20 , as long as it is adhered to most of the fibers 20 . Also, the binder 25 may be attached to all or part of the surface of each fiber 20 . It is preferable that the binder 25 is attached to almost the entire area of the plurality of fibers 20 without being unevenly attached locally. The binder 25 has a function of binding the fibers 20 together. In addition, the binder 25 has a function of supporting at least one of the carbon particles 40 and the catalyst 50 shown in FIGS. 9 and 10 on the surfaces of the fibers 20 . The carbon particles 40 and catalyst 50 will be described later. A specific example of the second form of the fiber assembly 32 is paper. The binder 25 is made of a material resistant to electrolyte. The binder 25 contains, for example, one selected from the group consisting of carbon, resin, and conductive metal oxide. Conductive metal oxides are, for example, metal oxides such as tin oxide, indium tin oxide (ITO), and antimony tin oxide (ATO).
　ペーパーからなる繊維集合体３２は、複数の繊維２０同士がバインダ２５によって結着されたものである。ペーパは、複数の繊維２０とバインダ２５の原料とを混合したスラリーを抄造した後、乾燥することにより得られる。上記スラリーは、繊維２０を溶媒に分散させたものである。バインダ２５を含む形態では、溶媒にバインダ２５の原料を混ぜる。溶媒は、水、有機溶媒のいずれであってもよい。有機溶媒は、メタノール、エタノール、プロピルアルコール、イソプロパノール、ブタノール、ペンタノール、ヘキサノールなどである。バインダ２５の原料によっては、上記スラリーの抄造後に熱処理してもよい。バインダ２５が炭素又は樹脂を含む形態では、バインダ２５の原料は、例えば、熱硬化性樹脂、熱可塑性樹脂などの有機バインダである。熱硬化性樹脂は、代表的には、フェノール樹脂、ピッチ樹脂、エポキシ樹脂である。熱可塑性樹脂は、代表的には、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリ塩化ビニリデン（ＰＶＤＣ）である。バインダ２５の原料が上述の熱硬化性樹脂からなる有機バインダである場合、上記熱処理によって、有機バインダを炭素化する。その結果、バインダ２５は炭素を含む。バインダ２５の原料が上述の熱可塑性樹脂からなる有機バインダである場合、上記熱処理は不要である。つまり、有機バインダを炭素化しない。その結果、バインダ２５はＰＴＦＥ、ＰＶＤＦ、ＰＶＤＣなどの樹脂を含む。バインダ２５が導電性金属酸化物を含む形態では、バインダ２５の原料には、金属イオンが溶解した溶液を使用する。この金属イオンは、スズイオン、インジウムイオン、アンチモンイオンなどである。この溶液を熱処理することによって、上記金属酸化物を含むバインダ２５を形成することができる。ペーパーからなる繊維集合体３２の製造方法の具体例については後述する。 A fiber assembly 32 made of paper is obtained by binding a plurality of fibers 20 together with a binder 25 . The paper is obtained by forming a slurry obtained by mixing a plurality of fibers 20 and raw materials of the binder 25, and then drying the slurry. The slurry is obtained by dispersing the fibers 20 in a solvent. In the form containing the binder 25, the raw material of the binder 25 is mixed with the solvent. The solvent may be either water or an organic solvent. Organic solvents include methanol, ethanol, propyl alcohol, isopropanol, butanol, pentanol, hexanol, and the like. Depending on the raw material of the binder 25, heat treatment may be performed after the slurry is made into paper. In the form in which the binder 25 contains carbon or resin, the raw material of the binder 25 is, for example, an organic binder such as thermosetting resin or thermoplastic resin. Thermosetting resins are typically phenol resins, pitch resins, and epoxy resins. Thermoplastic resins are typically polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polyvinylidene chloride (PVDC). When the raw material of the binder 25 is the above-described organic binder made of the thermosetting resin, the above-described heat treatment carbonizes the organic binder. As a result, binder 25 contains carbon. When the raw material of the binder 25 is the organic binder made of the above-described thermoplastic resin, the above heat treatment is unnecessary. That is, the organic binder is not carbonized. As a result, the binder 25 includes resins such as PTFE, PVDF, PVDC. In the form in which the binder 25 contains a conductive metal oxide, a solution in which metal ions are dissolved is used as the raw material of the binder 25 . The metal ions are tin ions, indium ions, antimony ions, and the like. By heat-treating this solution, the binder 25 containing the metal oxide can be formed. A specific example of the method of manufacturing the fiber assembly 32 made of paper will be described later.
　繊維集合体３２におけるバインダ２５は、炭素を主体とする第一のバインダを含むことが好ましい。炭素は導電性を有する。バインダ２５が第一のバインダを含むことで、繊維２０同士が接触していない箇所があっても、第一のバインダを介して繊維２０間の電気的導通を確保できる。第一のバインダは、典型的には、上述のように、フェノール樹脂、ピッチ樹脂、エポキシ樹脂などの有機バインダが上記熱処理によって炭素化したものである。「炭素を主体とする」とは、炭素を６０質量％以上含むことを意味する。第一のバインダにおける炭素の含有率は、８０質量％以上でもよく、１００質量％でもよい。本例では、バインダ２５が実質的に第一のバインダのみで構成されている。具体的には、バインダ２５が実質的に炭素のみで構成されている。つまり、バインダ２５における炭素の含有率が実質的に１００質量％である。バインダ２５が、上述のように、ＰＴＦＥ、ＰＶＤＦ、ＰＶＤＣなどの樹脂により構成されている場合、即ち炭素化していない場合、繊維２０同士の接触によって繊維２０間の電気的導通が確保される。 The binder 25 in the fiber assembly 32 preferably contains a first binder mainly composed of carbon. Carbon is electrically conductive. By including the first binder in the binder 25, even if there are portions where the fibers 20 are not in contact with each other, electrical continuity between the fibers 20 can be ensured via the first binder. As described above, the first binder is typically an organic binder such as phenol resin, pitch resin, or epoxy resin that is carbonized by the above heat treatment. “Containing mainly carbon” means containing 60% by mass or more of carbon. The carbon content in the first binder may be 80% by mass or more, or may be 100% by mass. In this example, the binder 25 is substantially composed only of the first binder. Specifically, the binder 25 is substantially composed only of carbon. That is, the content of carbon in the binder 25 is substantially 100% by mass. When the binder 25 is made of resin such as PTFE, PVDF, or PVDC, as described above, that is, when the binder 25 is not carbonized, electrical conduction between the fibers 20 is ensured by contact between the fibers 20 .
　バインダ２５は、導電性金属酸化物を主体とする第二のバインダを含んでもよい。バインダ２５が第二のバインダを含むことで、繊維２０同士が接触していない箇所があっても、第二のバインダを介して繊維２０間の電気的導通を確保できる。「導電性金属酸化物を主体とする」とは、導電性金属酸化物を６０質量％以上含むことを意味する。第二のバインダにおける導電性金属酸化物の含有率は、８０質量％以上でもよく、１００質量％でもよい。 The binder 25 may contain a second binder mainly composed of a conductive metal oxide. By including the second binder in the binder 25, even if there are portions where the fibers 20 are not in contact with each other, electrical continuity between the fibers 20 can be ensured via the second binder. The phrase "mainly composed of a conductive metal oxide" means containing 60% by mass or more of a conductive metal oxide. The content of the conductive metal oxide in the second binder may be 80% by mass or more, or may be 100% by mass.
　　〈繊維の含有率〉
　上記第一の形態及び第二の形態の両方において、繊維集合体３０（図３Ｂ参照）における繊維２０の含有率は、例えば２０質量％以上である。繊維集合体３０に含まれる繊維２０の割合が多いほど、繊維集合体３０の強度を高め易い。よって、電極１０の機械的強度が確保され易い。繊維２０の含有率は、３０質量％以上でもよい。繊維集合体３０の形態が第一の形態では、繊維２０の含有率は１００質量％でもよい。 <Fiber content>
In both the first embodiment and the second embodiment, the content of fibers 20 in fiber assembly 30 (see FIG. 3B) is, for example, 20% by mass or more. The greater the ratio of the fibers 20 contained in the fiber assembly 30, the easier it is to increase the strength of the fiber assembly 30. Therefore, the mechanical strength of the electrode 10 is easily ensured. The content of the fibers 20 may be 30% by mass or more. When the form of the fiber assembly 30 is the first form, the content of the fibers 20 may be 100% by mass.
　繊維２０の含有率は、繊維集合体３０の形態によって異なることがある。クロス、不織布といった第一の形態では、繊維集合体３１（図４、図６参照）は繊維２０のみで構成することが可能である。繊維集合体３１における繊維２０の含有率は、例えば２０質量％以上１００質量％以下である。繊維集合体３１における繊維２０の含有率は、更に、３０質量％以上、５０質量％超、７０質量％超、７５質量％超でもよい。本例では、繊維集合体３１が実質的に繊維２０のみで構成されている。つまり、繊維集合体３１における繊維２０の含有率が実質的に１００質量％である。ペーパーといった第二の形態では、繊維集合体３２（図７参照）における繊維２０の含有率は、例えば２５質量％以上７５質量％以下、更に３０質量％以上７０質量％以下である。 The content of the fibers 20 may differ depending on the form of the fiber assembly 30. In the first form such as cloth or non-woven fabric, the fiber assembly 31 (see FIGS. 4 and 6) can be composed only of the fibers 20 . The content of the fibers 20 in the fiber assembly 31 is, for example, 20% by mass or more and 100% by mass or less. The content of the fibers 20 in the fiber assembly 31 may be 30% by mass or more, more than 50% by mass, more than 70% by mass, or more than 75% by mass. In this example, the fiber assembly 31 is substantially composed only of the fibers 20 . That is, the content of the fibers 20 in the fiber assembly 31 is substantially 100% by mass. In the second form such as paper, the content of the fibers 20 in the fiber assembly 32 (see FIG. 7) is, for example, 25% by mass or more and 75% by mass or less, and further 30% by mass or more and 70% by mass or less.
　繊維集合体３０における繊維２０の含有率は、「｛（繊維集合体３０に含まれる繊維２０の合計質量）／（繊維集合体３０の質量）｝×１００」により求められる。ペーパーといった第二の形態の場合、繊維２０の含有率は、繊維集合体３２の二次電子像とＸ線ＣＴ（Ｃｏｍｐｕｔｅｄ　Ｔｏｍｏｇｒａｐｈｙ）像とを解析することにより計算で求められる。具体的には、まず二次電子像とＸ線ＣＴ像とを比較し、Ｘ線ＣＴ像の繊維像が正しく得られていることを確認する。そして、繊維２０の含有率は、「Ｄ×Ａ×Ｔ×（１／Ｖ）×（１／Ｓ）×１００」により計算する。
　　Ｄ：繊維自体の密度（ｇ／ｃｍ３）
　　Ａ：Ｘ線ＣＴ像から求めた繊維の体積（ｃｍ３）
　　Ｔ：繊維集合体の厚さ（ｃｍ）
　　Ｖ：Ｘ線ＣＴ像の測定視野の体積（ｃｍ３）
　　Ｓ：繊維集合体の質量を実際に測定して求めた単位面積あたりの質量（ｇ／ｃｍ２）
　上記厚さＴは、繊維集合体３０が圧縮されていない状態での厚さである。 The content rate of the fibers 20 in the fiber assembly 30 is obtained by "{(total mass of the fibers 20 contained in the fiber assembly 30)/(mass of the fiber assembly 30)} x 100". In the case of the second form such as paper, the content of the fibers 20 is calculated by analyzing a secondary electron image and an X-ray CT (Computed Tomography) image of the fiber assembly 32 . Specifically, first, the secondary electron image and the X-ray CT image are compared to confirm that the fiber image of the X-ray CT image is correctly obtained. The content of the fibers 20 is calculated by "DxAxTx(1/V)x(1/S)x100".
D: Density of the fiber itself (g/cm 3 )
A: Volume of fiber obtained from X-ray CT image (cm 3 )
T: Thickness of fiber assembly (cm)
V: Volume of measurement field of view of X-ray CT image (cm 3 )
S: Mass per unit area obtained by actually measuring the mass of the fiber assembly (g/cm 2 )
The thickness T is the thickness when the fiber assembly 30 is not compressed.
　　〈バインダの含有率〉
　繊維集合体３２（図７参照）におけるバインダ２５の含有率は、例えば２０質量％以上８０質量％以下である。バインダ２５の含有率が２０質量％以上であることで、バインダ２５によって繊維２０同士を結着させ易い。よって、繊維集合体３２の形状を維持し易い。バインダ２５の含有率が８０質量％以下であることで、繊維集合体３２内の空隙を確保し易い。よって、電極１０内に電解液を流通させ易い。バインダ２５の含有率は、３０質量％以上７０質量％以下、４５質量％以上６５質量％以下でもよい。 <Binder content>
The content of the binder 25 in the fiber assembly 32 (see FIG. 7) is, for example, 20% by mass or more and 80% by mass or less. When the content of the binder 25 is 20% by mass or more, the fibers 20 are easily bound together by the binder 25 . Therefore, it is easy to maintain the shape of the fiber assembly 32 . When the content of the binder 25 is 80% by mass or less, it is easy to secure voids in the fiber assembly 32 . Therefore, it is easy to circulate the electrolytic solution in the electrode 10 . The content of the binder 25 may be 30% by mass or more and 70% by mass or less, or 45% by mass or more and 65% by mass or less.
　バインダ２５の含有率は、繊維集合体３２の質量を１００質量％として、１００質量％から繊維２０の含有率を引くことにより求められる。 The content of the binder 25 is determined by subtracting the content of the fibers 20 from 100% by mass, assuming that the mass of the fiber assembly 32 is 100% by mass.
　第一の形態の繊維集合体３１（図４、図６参照）において、上記バインダ２５を含まなくてもよいが、バインダ２５を含むことを許容する。繊維集合体３１がバインダ２５を含む場合、バインダ２５が繊維２０同士を結着することにより繊維集合体３１の形状がより維持され易くなる。繊維集合体３１におけるバインダ２５の含有率は、例えば８０質量％以下である。繊維集合体３１におけるバインダ２５の含有率は、更に、５０質量％以下、４０質量％以下、３０質量％未満、２０質量％未満でもよい。 The first form of the fiber assembly 31 (see FIGS. 4 and 6) may not include the binder 25, but may include the binder 25. When the fiber assembly 31 contains the binder 25 , the binder 25 binds the fibers 20 together, thereby making it easier to maintain the shape of the fiber assembly 31 . The content of the binder 25 in the fiber assembly 31 is, for example, 80% by mass or less. The content of the binder 25 in the fiber assembly 31 may be 50% by mass or less, 40% by mass or less, less than 30% by mass, or less than 20% by mass.
　　〈厚さ〉
　繊維集合体３０（図３Ａ参照）の厚さは、例えば０．１ｍｍ以上５．０ｍｍ以下、更に０．２ｍｍ以上３．０ｍｍ以下である。繊維集合体３０の厚さが０．１ｍｍ以上であることで、電池セル１００に電極１０が組み込まれた際に圧縮されても、電極１０における電解液との反応面積を確保し易い。繊維集合体３０の厚さが５．０ｍｍ以下であることで、電池セル１００に電極１０が組み込まれた際に圧縮されても、電極１０内に電解液を流通させ易い。また、繊維集合体３０の厚さが５．０ｍｍ以下であれば、電極１０を薄型化できる。上記厚さは、電池セル１００（図１参照）に組み込まれて圧縮された状態での厚さではなく、圧縮されていない状態、即ち外力が作用していない自然状態での厚さをいう。 <thickness>
The thickness of the fiber assembly 30 (see FIG. 3A) is, for example, 0.1 mm or more and 5.0 mm or less, and further 0.2 mm or more and 3.0 mm or less. When the thickness of the fiber assembly 30 is 0.1 mm or more, even if the electrode 10 is compressed when assembled into the battery cell 100, it is easy to secure the reaction area with the electrolytic solution in the electrode 10 . Since the thickness of the fiber assembly 30 is 5.0 mm or less, even if the electrode 10 is compressed when assembled into the battery cell 100, the electrolytic solution can easily flow through the electrode 10. FIG. Moreover, if the thickness of the fiber assembly 30 is 5.0 mm or less, the thickness of the electrode 10 can be reduced. The above-mentioned thickness refers to the thickness in a non-compressed state, i.e., in a natural state where no external force is applied, rather than in a compressed state assembled in the battery cell 100 (see FIG. 1).
　繊維集合体３０の厚さは、繊維集合体３０の形態によって異なることがある。クロス、不織布といった第一の形態では、繊維集合体３１（図４、図６参照）の厚さは、例えば０．２ｍｍ以上５．０ｍｍ以下、更に０．３ｍｍ以上２．０ｍｍ以下である。ペーパーといった第二の形態では、繊維集合体３２（図７参照）の厚さは、例えば０．１ｍｍ以上１．０ｍｍ以下、更に０．３ｍｍ以上０．６ｍｍ以下である。第二の形態における繊維集合体３２は、第一の形態における繊維集合体３１よりも薄くできるので、電池セル１００（図１参照）をより薄型化し易い。 The thickness of the fiber assembly 30 may differ depending on the form of the fiber assembly 30. In the first form such as cloth or non-woven fabric, the thickness of the fiber assembly 31 (see FIGS. 4 and 6) is, for example, 0.2 mm or more and 5.0 mm or less, and further 0.3 mm or more and 2.0 mm or less. In the second form such as paper, the thickness of the fiber assembly 32 (see FIG. 7) is, for example, 0.1 mm or more and 1.0 mm or less, and further 0.3 mm or more and 0.6 mm or less. Since the fiber assembly 32 in the second embodiment can be made thinner than the fiber assembly 31 in the first embodiment, it is easier to make the battery cell 100 (see FIG. 1) thinner.
　　〈圧縮率〉
　電池セル１００（図１参照）を構成したとき、繊維集合体３０（図３Ａ参照）の圧縮率は、例えば３０％以上９５％以下、更に４０％以上７０％以下である。繊維集合体３０において、電解液との反応面積は圧縮前後で変わらないが、圧縮後の繊維集合体３０の体積は減るので、単位体積あたりにおける電解液との反応面積は増えることになる。圧縮率が３０％以上であることで、電極１０の単位体積あたりの上記反応面積が増えるので、電解液との反応効率が高くなる。圧縮率が９５％以下であることで、電極１０内の空隙を確保して、電解液を流通させ易い。また、圧縮率が９５％以下であれば、過度の圧縮による繊維集合体３０の損傷を抑制できる。圧縮率は、圧縮状態での厚さをＴ１、非圧縮状態での厚さをＴ０とすると、「｛（Ｔ０－Ｔ１）／Ｔ０｝×１００」により求められる。 <Compression rate>
When the battery cell 100 (see FIG. 1) is constructed, the compressibility of the fiber assembly 30 (see FIG. 3A) is, for example, 30% or more and 95% or less, and further 40% or more and 70% or less. In the fiber assembly 30, the reaction area with the electrolytic solution does not change before and after compression, but the volume of the fiber assembly 30 after compression decreases, so the reaction area with the electrolytic solution per unit volume increases. When the compressibility is 30% or more, the reaction area per unit volume of the electrode 10 increases, so the reaction efficiency with the electrolytic solution increases. When the compressibility is 95% or less, it is easy to ensure the voids in the electrode 10 and allow the electrolytic solution to flow. Moreover, if the compressibility is 95% or less, damage to the fiber assembly 30 due to excessive compression can be suppressed. The compressibility is obtained by "{(T 0 −T 1 )/T 0 }×100", where T 1 is the thickness in the compressed state and T 0 is the thickness in the uncompressed state.
　　〈空隙率〉
　電池セル１００（図１参照）を構成したとき、繊維集合体３０（図３Ａ参照）の空隙率は、例えば３０体積％以上８９体積％以下、更に４０体積％以上８０体積％以下である。上記空隙率は、電池セル１００（図１参照）に組み込まれて圧縮された状態での空隙率である。空隙率が３０体積％以上であることで、電極１０内に電解液を流通させ易い。空隙率が８９体積％以下であることで、電極１０における電解液との反応面積の減少を抑制できる。また、空隙率が８９体積％以下であれば、繊維集合体３０の強度の低下を抑制できる。空隙率は、真の体積をＶｔ、見かけの体積をＶａとすると、「｛（Ｖａ－Ｖｔ）／Ｖａ｝×１００」により求められる。真の体積Ｖｔは、例えば、Ｘ線ＣＴ像を解析することにより、繊維集合体３０中の空隙を除いた体積を計算することで求められる。見かけの体積Ｖａは、繊維と空隙とを含む繊維集合体３０の体積である。 <Porosity>
When the battery cell 100 (see FIG. 1) is configured, the porosity of the fiber assembly 30 (see FIG. 3A) is, for example, 30% by volume or more and 89% by volume or less, and further 40% by volume or more and 80% by volume or less. The above-mentioned porosity is the porosity in a state in which the battery cell 100 (see FIG. 1) is assembled and compressed. When the porosity is 30% by volume or more, the electrolytic solution can be easily circulated in the electrode 10 . When the porosity is 89% by volume or less, it is possible to suppress the decrease in the reaction area with the electrolytic solution in the electrode 10 . Further, if the porosity is 89% by volume or less, a decrease in the strength of the fiber assembly 30 can be suppressed. The porosity can be obtained by "{(Va−Vt)/Va}×100" where Vt is the true volume and Va is the apparent volume. The true volume Vt can be obtained, for example, by analyzing the X-ray CT image and calculating the volume excluding voids in the fiber assembly 30 . The apparent volume Va is the volume of the fiber assembly 30 including fibers and voids.
　繊維集合体３０の空隙率は、繊維集合体３０の形態によって異なることがある。クロス、不織布といった第一の形態では、繊維集合体３１（図４、図６参照）の空隙率は、例えば３０体積％以上８９体積％以下、更に４０体積％以上８０体積％以下である。ペーパーといった第二の形態では、繊維集合体３２（図７参照）の空隙率は、例えば４０体積％以上８９体積％以下、更に６０体積％以上８０体積％以下である。一般に、第二の形態における繊維集合体３２は、バインダ２５を多く含むため、第一の形態における繊維集合体３１に比べて空隙率が小さくなる。第一の形態における繊維集合体３１は、空隙率が比較的大きいので、電解液を流通させ易い。 The porosity of the fiber assembly 30 may vary depending on the form of the fiber assembly 30. In the first form such as cloth or non-woven fabric, the fiber assembly 31 (see FIGS. 4 and 6) has a porosity of, for example, 30% to 89% by volume, and further 40% to 80% by volume. In the second form such as paper, the porosity of the fiber assembly 32 (see FIG. 7) is, for example, 40% by volume or more and 89% by volume or less, and further 60% by volume or more and 80% by volume or less. In general, the fiber assembly 32 in the second form contains a large amount of the binder 25, and therefore has a smaller porosity than the fiber assembly 31 in the first form. Since the fiber assembly 31 in the first embodiment has a relatively large porosity, it is easy for the electrolytic solution to flow.
　（繊維）
　繊維２０（図３Ｂ参照）は、電解液中の活物質である金属イオンが電池反応を行う反応場として機能する。 (fiber)
The fibers 20 (see FIG. 3B) function as a reaction field where metal ions, which are active materials in the electrolyte, undergo battery reactions.
　　〈平均配向度〉
　繊維集合体３０を構成する複数の繊維２０の平均配向度は０．３以下である。「平均配向度」とは、繊維集合体３０の断面において、繊維集合体３０の厚さ方向と直交する水平線に対する繊維２０の傾き度合いを意味する。上記断面は、繊維集合体の厚さ方向に沿った断面である。「平均配向度」は、繊維集合体３０の厚さ方向に沿う角度を９０°とし、上記水平線に対する複数の繊維２０の各々の角度を９０°で割った値の平均値である。平均配向度の値が小さいほど、繊維集合体３０の厚さ方向に配向する繊維２０が少ないことを示す。つまり、平均配向度の値が小さい繊維集合体３０は、厚さ方向に沿う繊維２０が少なく、水平方向に沿う繊維２０が多いといえる。平均配向度は０から１の範囲で与えられる。 <Average degree of orientation>
The average degree of orientation of the plurality of fibers 20 forming the fiber assembly 30 is 0.3 or less. The “average degree of orientation” means the degree of inclination of the fibers 20 with respect to a horizontal line orthogonal to the thickness direction of the fiber assembly 30 in the cross section of the fiber assembly 30 . The cross section is a cross section along the thickness direction of the fiber assembly. The "average degree of orientation" is the average value obtained by dividing the angle of each of the plurality of fibers 20 with respect to the horizontal line by 90°, where the angle along the thickness direction of the fiber assembly 30 is 90°. The smaller the value of the average degree of orientation, the less fibers 20 are oriented in the thickness direction of the fiber assembly 30 . That is, it can be said that the fiber assembly 30 having a small average degree of orientation has few fibers 20 along the thickness direction and many fibers 20 along the horizontal direction. The average degree of orientation is given in the range from 0 to 1.
　繊維２０の平均配向度の測定方法について、図８Ａ、図８Ｂを参照して説明する。図８Ａは、繊維集合体３０の断面の一例を拡大して示したものである。図８Ａに示す繊維集合体３０はクロスである。まず、繊維集合体３０（図３Ａ参照）を厚さ方向に沿って切断する。具体的には、繊維集合体３０の厚さ方向が垂直方向となるように、第一の面１１を水平にして繊維集合体３０を厚さ方向に切断する。そして、図８Ａに示すように、切断した繊維集合体３０の断面を走査型電子顕微鏡（ＳＥＭ）で観察する。観察位置を変えて１０箇所以上の視野を取得する。視野は、６００μｍ×４５０μｍの大きさを有する長方形とする。１つの視野につき、１本の対角線ｄを引く。視野の倍率は、例えば２００倍とする。倍率は、繊維集合体３０の形態によって適宜変更してもよい。各視野において、対角線ｄに交差する繊維２０のうち、１０本以上の繊維２０を選択する。選択した各繊維２０について、対角線ｄと交差する部分に対してフィッティングする。具体的には、繊維２０における対角線ｄとの交差点を中心とする長さ１０μｍ部分について、フィッティングした直線を求める（図８Ｂも参照）。上記フィッティングは、例えば、最小二乗法を用いることができる。最小二乗法を用いる場合、例えば、繊維２０の上記１０μｍの部分について、繊維２０の中心を通る線分を抽出し、その線分を１０等分する点に対して最小二乗法を適用するとよい。図８Ａ、図８Ｂでは、選択した各繊維２０において、フィッティングした直線を太い破線で示す。フィッティングした直線の水平線に対する角度を測定する。測定する角度は、フィッティングした直線と水平線とがなす２つの角度のうち、０°以上９０°以下の鋭角側の角度とする。フィッティングした各直線について、水平線に対する配向度を求める。上記配向度は、「（水平線に対する上記直線の角度）／９０°」により計算する。全ての視野について、フィッティングした各直線の上記配向度の平均値を平均配向度とする。つまり、１０箇所以上の視野において、１つの視野につき１０本以上の繊維２０を選択することにより、合計で１００本以上の繊維２０の上記平均配向度を求める。１つの視野において選択する繊維２０の数は、２０本以上、更に３０本以上でもよい。 A method for measuring the average degree of orientation of the fibers 20 will be described with reference to FIGS. 8A and 8B. FIG. 8A shows an enlarged example of a cross section of the fiber assembly 30. FIG. The fiber assembly 30 shown in FIG. 8A is a cloth. First, the fiber assembly 30 (see FIG. 3A) is cut along the thickness direction. Specifically, the fiber assembly 30 is cut in the thickness direction with the first surface 11 horizontal so that the thickness direction of the fiber assembly 30 is vertical. Then, as shown in FIG. 8A, a cross section of the cut fiber assembly 30 is observed with a scanning electron microscope (SEM). Acquire 10 or more visual fields by changing the observation position. The field of view is a rectangle with dimensions of 600 μm×450 μm. One diagonal line d is drawn for one field of view. The magnification of the field of view is, for example, 200 times. The magnification may be changed as appropriate depending on the form of the fiber aggregate 30 . In each field of view, 10 or more fibers 20 are selected among the fibers 20 crossing the diagonal d. For each selected fiber 20, fitting is performed on the portion that intersects the diagonal line d. Specifically, a fitted straight line is obtained for a 10 μm-long portion of the fiber 20 centered on the intersection with the diagonal line d (see also FIG. 8B). For the above fitting, for example, the least squares method can be used. When using the least-squares method, for example, for the 10 μm portion of the fiber 20, a line segment passing through the center of the fiber 20 is extracted, and the least-squares method is applied to the points dividing the line segment into 10 equal parts. In FIGS. 8A and 8B, the straight line fitted to each selected fiber 20 is indicated by a thick dashed line. Measure the angle of the fitted straight line with respect to the horizontal. The angle to be measured is the acute angle of 0° or more and 90° or less of the two angles formed by the fitted straight line and the horizontal line. For each straight line fitted, the degree of orientation with respect to the horizontal is determined. The degree of orientation is calculated by "(the angle of the straight line with respect to the horizontal line)/90°". The average value of the orientation degrees of the fitted straight lines for all fields of view is taken as the average orientation degree. That is, by selecting 10 or more fibers 20 for each field of view in 10 or more fields of view, the average degree of orientation of a total of 100 or more fibers 20 is obtained. The number of fibers 20 selected in one field of view may be 20 or more, or even 30 or more.
　平均配向度が小さいほど、繊維集合体３０の厚さ方向に配向する繊維２０の数が少ない。そのため、電池セル１００（図１参照）を構成したとき、隔膜１０１の表面と直交するように配置される繊維２０の数が少ない。このような繊維集合体３０は、繊維２０が隔膜１０１に突き刺さることを抑制できる。平均配向度は、０．２５以下でもよい。 The smaller the average degree of orientation, the smaller the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 . Therefore, when the battery cell 100 (see FIG. 1) is constructed, the number of fibers 20 arranged perpendicular to the surface of the diaphragm 101 is small. Such a fiber assembly 30 can prevent the fibers 20 from sticking into the diaphragm 101 . The average degree of orientation may be 0.25 or less.
　平均配向度は、繊維集合体３０の形態によって異なることがある。クロス、不織布といった第一の形態における繊維集合体３１（図４、図６参照）では、平均配向度は、例えば０．０５以上０．３以下である。平均配向度が０．０５以上であることで、繊維２０同士の絡み合いによる機械的な結合により繊維集合体３１の形状を維持し易い。平均配向度が０．３以下であることで、上述したように、繊維２０の隔膜１０１への突き刺さりを抑制できる。第一の形態では、平均配向度は、０．１以上０．２５以下、更に０．１５以上０．２５以下でもよい。ペーパーといった第二の形態における繊維集合体３２では、平均配向度は、例えば０．１以下である。第二の形態における繊維集合体３２は、バインダ２５による繊維２０同士の結着により形状を維持するため、平均配向度を比較的小さくできる（図７参照）。第二の形態では、平均配向度は、０．０５以下でもよい。 The average degree of orientation may vary depending on the form of the fiber assembly 30. The fiber assembly 31 (see FIGS. 4 and 6) in the first form such as cloth or non-woven fabric has an average degree of orientation of, for example, 0.05 or more and 0.3 or less. When the average degree of orientation is 0.05 or more, the shape of the fiber aggregate 31 can be easily maintained by mechanical bonding due to the entanglement of the fibers 20 . When the average degree of orientation is 0.3 or less, it is possible to suppress sticking of the fibers 20 into the diaphragm 101 as described above. In the first form, the average degree of orientation may be 0.1 or more and 0.25 or less, and further 0.15 or more and 0.25 or less. In the fiber assembly 32 in the second form such as paper, the average degree of orientation is, for example, 0.1 or less. Since the fiber assembly 32 in the second embodiment maintains its shape by binding the fibers 20 together with the binder 25, the average degree of orientation can be made relatively small (see FIG. 7). In a second form, the average degree of orientation may be 0.05 or less.
　平均配向度を小さくする方法は、例えば、以下のような方法である。 A method for reducing the average degree of orientation is, for example, the following method.
　　　（クロス）
　繊維集合体３０がクロスからなる場合、例えば、織りのピッチを大きくするとよい。織りのピッチとは、図５に示すように繊維集合体３１を平面視したとき、第二の糸２２ｓを挟んで隣り合う第一の糸２１ｓ間の中心間距離ｐである。織りのピッチが大きいほど、上述の水平線に対する繊維２０の角度が小さくなる。つまり、繊維集合体３０の厚さ方向に配向する繊維２０の数が減ることから、平均配向度が小さくなる。織りのピッチは、例えば１．５ｍｍ以上、更に２．０ｍｍ以上である。織りのピッチに合わせて糸２０ｓの太さは変更するとよい。 (cross)
When the fiber assembly 30 is made of cloth, for example, it is preferable to increase the weaving pitch. The weaving pitch is the center-to-center distance p between the first yarns 21s adjacent to each other with the second yarn 22s interposed therebetween when the fiber assembly 31 is viewed from above as shown in FIG. The greater the pitch of the weave, the smaller the angle of the fibers 20 with respect to the above horizontal line. That is, since the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 is reduced, the average degree of orientation is reduced. The weave pitch is, for example, 1.5 mm or more, or even 2.0 mm or more. The thickness of the thread 20s should be changed according to the weaving pitch.
　　　（不織布）
　繊維集合体３０が不織布からなる場合、例えば、繊維集合体３０を厚さ方向にプレスするとよい。プレスすることによって繊維集合体３０の厚さ方向に配向する繊維２０の数が減るため、平均配向度が小さくなる。プレス圧は、例えば０．０５ＭＰａ以上０．５ＭＰａ以下とする。別の方法は、例えば、単位面積あたりの交絡数を少なくする。水流交絡の場合、例えば、水流を噴射するノズルの数を減らしたり、水流の圧力を低くしたりする。ニードルパンチの場合、例えば、ニードルパンチの本数を減らしたり、パンチング回数を減らしたりする。例えば、パンチング回数を２５０回／ｃｍ２未満とする。交絡数が少ないほど、繊維集合体３０の厚さ方向に配向する繊維２０の数が減る。そのため、平均配向度が小さくなる。 (non-woven fabric)
When the fiber assembly 30 is made of nonwoven fabric, for example, it is preferable to press the fiber assembly 30 in the thickness direction. Since the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 is reduced by pressing, the average degree of orientation is reduced. The press pressure is, for example, 0.05 MPa or more and 0.5 MPa or less. Another way is to reduce the number of entanglements per unit area, for example. In the case of hydroentanglement, for example, the number of nozzles for jetting water streams is reduced, or the pressure of water streams is lowered. In the case of needle punching, for example, the number of needle punches is reduced, or the number of times of punching is reduced. For example, the number of punching is less than 250 times/cm 2 . As the number of entanglements decreases, the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 decreases. Therefore, the average degree of orientation becomes small.
　　　（ペーパー）
　繊維集合体３０がペーパーからなる場合、例えば、繊維長が比較的長い繊維２０を用いるとよい。繊維長が比較的長いと、抄造する際に繊維２０が寝易く、繊維２０が水平方向に揃い易い。そのため、繊維集合体３０の厚さ方向に配向する繊維２０の数が減ることから、平均配向度が小さくなる。例えば、繊維長は１０ｍｍ以上である。その他、上述したように、繊維集合体３０を厚さ方向にプレスしてもよい。 (paper)
When the fiber assembly 30 is made of paper, for example, fibers 20 having a relatively long fiber length may be used. When the fiber length is relatively long, the fibers 20 tend to lie flat during papermaking, and the fibers 20 tend to align horizontally. Therefore, since the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 is reduced, the average degree of orientation is reduced. For example, the fiber length is 10 mm or more. Alternatively, as described above, the fiber assembly 30 may be pressed in the thickness direction.
　　〈材質〉
　繊維２０は、導電性を有すると共に、電解液に対する耐性を有するものであればよい。繊維２０は、炭素繊維、金属繊維のいずれであってもよい。繊維２０は、例えば、炭素、チタン、及びタングステンからなる群より選択される少なくとも一種で構成される。炭素繊維の具体例は、ポリアクリロニトリル（ＰＡＮ）繊維を原料とするＰＡＮ系炭素繊維、ピッチ繊維を原料とするピッチ系炭素繊維などである。炭素繊維は、ＰＡＮ繊維、ピッチ繊維などの有機繊維を焼成して炭素化することによって得られる。金属繊維は、純チタン又は純タングステンで構成されてもよいし、チタンの合金又はタングステンの合金で構成されていてもよい。 <Material>
The fiber 20 may be any material as long as it has electrical conductivity and resistance to the electrolytic solution. The fibers 20 may be either carbon fibers or metal fibers. The fibers 20 are composed of, for example, at least one selected from the group consisting of carbon, titanium, and tungsten. Specific examples of carbon fibers include PAN-based carbon fibers made from polyacrylonitrile (PAN) fibers and pitch-based carbon fibers made from pitch fibers. Carbon fibers are obtained by burning and carbonizing organic fibers such as PAN fibers and pitch fibers. The metal fibers may be composed of pure titanium or pure tungsten, or may be composed of an alloy of titanium or an alloy of tungsten.
　　〈繊維径〉
　複数の繊維２０の平均径、即ち平均繊維径は、例えば１μｍ以上２０μｍ以下である。平均繊維径が１μｍ以上であることで、繊維集合体３０の強度を確保し易い。平均繊維径が２０μｍ以下であることで、繊維２０の可撓性を高め易い。そのため、電池セル１００（図１参照）を構成したとき、繊維２０が隔膜１０１に突き刺さり難くなる。また、平均繊維径が２０μｍ以下であれば、電極１０の単位体積あたりの表面積が増えるので、電解液との反応面積を確保し易い。平均繊維径は、５μｍ以上でもよい。 <Fiber diameter>
The average diameter of the plurality of fibers 20, that is, the average fiber diameter is, for example, 1 μm or more and 20 μm or less. When the average fiber diameter is 1 μm or more, the strength of the fiber assembly 30 can be easily secured. When the average fiber diameter is 20 μm or less, the flexibility of the fibers 20 can be easily increased. Therefore, when the battery cell 100 (see FIG. 1) is constructed, the fibers 20 are less likely to pierce the diaphragm 101 . Further, if the average fiber diameter is 20 μm or less, the surface area per unit volume of the electrode 10 increases, so that it is easy to secure the reaction area with the electrolytic solution. The average fiber diameter may be 5 μm or more.
　繊維径は、例えば、繊維集合体３０の断面をＳＥＭで観察し、繊維２０の外径を計測することにより求められる。繊維径は、繊維２０の断面積と等しい面積を持つ円の直径とする。「繊維２０の断面積」とは、繊維２０の長手方向に直交する断面の面積をいう。平均繊維径は、例えば１０本以上の繊維径の平均値とする。繊維径を測定する繊維２０の数は、２０本以上、更に３０本以上でもよい。 The fiber diameter is obtained, for example, by observing the cross section of the fiber assembly 30 with an SEM and measuring the outer diameter of the fiber 20. The fiber diameter is the diameter of a circle having an area equal to the cross-sectional area of the fiber 20 . The “cross-sectional area of the fiber 20” refers to the cross-sectional area of the fiber 20 perpendicular to the longitudinal direction. The average fiber diameter is, for example, the average value of 10 or more fiber diameters. The number of fibers 20 whose fiber diameter is to be measured may be 20 or more, or even 30 or more.
　　〈繊維長〉
　複数の繊維２０の平均長さ、即ち平均繊維長は、繊維集合体３０の形態によって異なることがある。クロス、不織布といった第一の形態における繊維集合体３１（図４、図６参照）では、平均繊維長は、例えば２５ｍｍ以上、更に３０ｍｍ以上である。平均繊維長が２５ｍｍ以上であることで、繊維２０同士が絡み易く、繊維集合体３１の形状を維持し易い。クロスの場合、平均繊維長は、例えば８０ｍｍ以上である。不織布の場合、平均繊維長は、例えば２５ｍｍ以上１００ｍｍ以下である。ペーパーといった第二の形態における繊維集合体３２（図７参照）では、平均繊維長は、例えば２０ｍｍ以下である。平均繊維長が長いと、繊維２０が水平方向に沿うように配置され易い。一般に、第二の形態における繊維集合体３２は、バインダ２５による繊維２０同士の結着により形状を維持するため、第一の形態における繊維集合体３１に比べて繊維長が短くてもよい。ペーパーの場合、平均繊維長は、１０ｍｍ以下、５ｍｍ以下、更に３ｍｍ以下でもよい。ペーパーを構成する繊維２０の長さの下限は、例えば０．１ｍｍ以上、更に０．３ｍｍ以上、０．５ｍｍ以上である。 <Fiber length>
The average length of the plurality of fibers 20 , that is, the average fiber length may differ depending on the form of the fiber assembly 30 . The fiber assembly 31 (see FIGS. 4 and 6) in the first form such as cloth or non-woven fabric has an average fiber length of, for example, 25 mm or more, and further 30 mm or more. When the average fiber length is 25 mm or more, the fibers 20 are easily entangled with each other, and the shape of the fiber assembly 31 is easily maintained. In the case of cloth, the average fiber length is, for example, 80 mm or more. In the case of nonwoven fabric, the average fiber length is, for example, 25 mm or more and 100 mm or less. In the fiber assembly 32 (see FIG. 7) in the second form such as paper, the average fiber length is, for example, 20 mm or less. If the average fiber length is long, the fibers 20 are likely to be arranged along the horizontal direction. In general, the fiber assembly 32 in the second mode maintains its shape by binding the fibers 20 together with the binder 25, so the fiber length may be shorter than the fiber assembly 31 in the first mode. For paper, the average fiber length may be 10 mm or less, 5 mm or less, or even 3 mm or less. The lower limit of the length of the fibers 20 forming the paper is, for example, 0.1 mm or more, and further 0.3 mm or more, or 0.5 mm or more.
　繊維長は、例えば、Ｘ線ＣＴ像を解析することにより、繊維２０の長さを計測することにより求められる。平均繊維長は、例えば１０本以上の繊維長の平均値とする。繊維長を測定する繊維２０の数は、２０本以上、更に３０本以上でもよい。 The fiber length can be obtained, for example, by measuring the length of the fiber 20 by analyzing the X-ray CT image. The average fiber length is, for example, the average value of 10 or more fiber lengths. The number of fibers 20 whose fiber length is measured may be 20 or more, or even 30 or more.
　　〈その他〉
　繊維２０は、電解液との電池反応性を向上させるため、図９に示すように、繊維２０の表面に炭素粒子４０を有してもよい。繊維２０は、図１０に示すように、繊維２０の表面に触媒５０を有してもよい。図９、図１０では、繊維２０の長手方向に沿った断面を示している。 <others>
The fibers 20 may have carbon particles 40 on the surface of the fibers 20 as shown in FIG. 9 in order to improve battery reactivity with the electrolyte. The fibers 20 may have a catalyst 50 on the surface of the fibers 20 as shown in FIG. 9 and 10 show cross sections along the longitudinal direction of the fiber 20. FIG.
　　〈炭素粒子〉
　炭素粒子４０は、図９に示すように、繊維２０の表面に担持される。炭素粒子４０は、複数の繊維２０のうち、必ずしも全ての繊維２０の表面に担持されていなくてもよく、大部分の繊維２０に担持されていればよい。また、炭素粒子４０は、各繊維２０の表面の少なくとも一部に担持されていればよい。炭素粒子４０は、複数の繊維２０の局所に偏って担持されることなく、ほぼ全域に担持されていることが好ましい。ここでいう「担持」とは、繊維２０と電気的に導通した状態で炭素粒子４０が付着していることを意味する。炭素粒子４０の少なくとも一部が繊維２０に埋まっていてもよい。炭素粒子４０は、電解液との反応点として機能することで、電解液との電池反応性を向上させる。炭素粒子４０は、例えば、黒鉛、カーボンブラックなどで構成されている。 <Carbon particles>
Carbon particles 40 are carried on the surface of the fiber 20, as shown in FIG. The carbon particles 40 do not necessarily have to be carried on the surfaces of all the fibers 20 among the plurality of fibers 20 as long as they are carried on most of the fibers 20 . Moreover, the carbon particles 40 need only be carried on at least part of the surface of each fiber 20 . It is preferable that the carbon particles 40 are carried almost all over the plurality of fibers 20 without being unevenly carried locally. The term “carrying” as used herein means that the carbon particles 40 are attached to the fibers 20 in an electrically conductive state. At least part of the carbon particles 40 may be embedded in the fibers 20 . The carbon particles 40 improve battery reactivity with the electrolyte by functioning as reaction points with the electrolyte. The carbon particles 40 are composed of graphite, carbon black, or the like, for example.
　炭素粒子４０は、繊維２０の表面に分散して存在する。炭素粒子４０の形状は、代表的には、球状である。炭素粒子４０の形状は、球状の他、針状、薄板状など種々の形状をとり得る。炭素粒子４０の粒径は、例えば１００ｎｍ以上５０μｍ以下である。ここでの「粒径」は、平均粒径を意味する。 The carbon particles 40 exist dispersedly on the surface of the fiber 20 . The shape of the carbon particles 40 is typically spherical. The shape of the carbon particles 40 can take various shapes such as a spherical shape, a needle shape, and a thin plate shape. The particle size of the carbon particles 40 is, for example, 100 nm or more and 50 μm or less. "Particle size" here means average particle size.
　炭素粒子４０の粒径は、例えば次のようにして測定することができる。繊維集合体３０の断面をＳＥＭ又は透過型電子顕微鏡（ＴＥＭ）で観察する。視野の大きさは、例えば１００μｍ×５０μｍ以上２００μｍ×１００μｍ以下とする。視野の倍率は、例えば３０００倍とする。視野内における炭素粒子４０を抽出する。抽出する炭素粒子４０の数は、例えば１０個以上とする。各炭素粒子４０について、炭素粒子４０の面積と等しい面積を持つ円の直径を求め、その平均値を炭素粒子４０の粒径とする。粒径を測定する炭素粒子４０の数は、２０個以上、更に３０個以上でもよい。 The particle size of the carbon particles 40 can be measured, for example, as follows. A cross section of the fiber assembly 30 is observed with an SEM or a transmission electron microscope (TEM). The size of the field of view is, for example, 100 μm×50 μm or more and 200 μm×100 μm or less. The magnification of the field of view is, for example, 3000 times. A carbon particle 40 within the field of view is extracted. The number of carbon particles 40 to be extracted is, for example, 10 or more. For each carbon particle 40 , the diameter of a circle having an area equal to the area of the carbon particle 40 is obtained, and the average value is taken as the particle size of the carbon particle 40 . The number of carbon particles 40 whose particle diameters are measured may be 20 or more, or even 30 or more.
　本例では、炭素粒子４０がバインダ２５によって繊維２０の表面に担持されている。バインダ２５を有することで、炭素粒子４０が繊維２０の表面に強固に担持される。バインダ２５はなくてもよい。炭素粒子４０が繊維２０の表面に直接付着してもよい。 In this example, the carbon particles 40 are carried on the surface of the fiber 20 by the binder 25. By having the binder 25 , the carbon particles 40 are firmly supported on the surface of the fiber 20 . Binder 25 may be omitted. Carbon particles 40 may be attached directly to the surface of fiber 20 .
　バインダ２５が、炭素を主体とする第一のバインダ、又は導電性金属酸化物を主体とする第二のバインダを含む場合、繊維２０と炭素粒子４０との間にバインダ２５が介在しても、炭素粒子４０を繊維２０と電気的に導通した状態で担持させることができる。つまり、炭素粒子４０と繊維２０との間の電気的導通を確保できる。また、バインダ２５を介して炭素粒子４０間の電気的導通も確保できる。バインダ２５が、上述のように、ＰＴＦＥ、ＰＶＤＦ、ＰＶＤＣなどの樹脂により構成されている場合、即ち炭素化していない場合、炭素粒子４０と繊維２０との接触によって炭素粒子４０と繊維２０との間の電気的導通が確保される。また、炭素粒子４０同士の接触によって炭素粒子４０間の電気的導通が確保される。 When the binder 25 contains a first binder mainly composed of carbon or a second binder mainly composed of a conductive metal oxide, even if the binder 25 is interposed between the fibers 20 and the carbon particles 40, The carbon particles 40 can be carried in an electrically conductive state with the fibers 20 . In other words, electrical continuity between the carbon particles 40 and the fibers 20 can be ensured. Also, electrical continuity between the carbon particles 40 can be ensured via the binder 25 . When the binder 25 is composed of a resin such as PTFE, PVDF, or PVDC as described above, that is, when it is not carbonized, the contact between the carbon particles 40 and the fibers 20 causes electrical continuity is ensured. Also, electrical continuity between the carbon particles 40 is ensured by the contact between the carbon particles 40 .
　炭素粒子４０の含有率は、例えば１０質量％以上６０質量％以下である。炭素粒子４０の含有率は、繊維集合体３０（図３Ａ参照）の質量を１００質量％としたときの炭素粒子４０の質量の割合である。繊維集合体３０の質量は、繊維２０、バインダ２５、炭素粒子４０の合計とする。後述する触媒５０を有する場合は、繊維集合体３０の質量は、触媒５０も含めた質量とする。炭素粒子４０の含有率が１０質量％以上であることで、電解液との電池反応性を高め易い。炭素粒子４０の含有率が高いほど、電池反応性を高め易いが、相対的に繊維２０の割合が減少するため、繊維集合体３０の強度の低下を招くおそれがある。炭素粒子４０の含有率が６０質量％以下であることで、繊維集合体３０の強度を確保し易い。炭素粒子４０の含有率は、２０質量％以上５０質量％以下、更に２５質量％以上４５質量％以下でもよい。炭素粒子４０の含有率は、例えば、熱重量測定法（ＴＧ法）により求められる。 The content of the carbon particles 40 is, for example, 10% by mass or more and 60% by mass or less. The content of the carbon particles 40 is the ratio of the mass of the carbon particles 40 when the mass of the fiber assembly 30 (see FIG. 3A) is 100% by mass. The mass of the fiber assembly 30 is the sum of the fibers 20, the binder 25 and the carbon particles 40. When a catalyst 50 to be described later is included, the mass of the fiber assembly 30 includes the catalyst 50 as well. When the content of the carbon particles 40 is 10% by mass or more, the battery reactivity with the electrolytic solution can be easily increased. The higher the content of the carbon particles 40, the easier it is to increase the battery reactivity, but the proportion of the fibers 20 is relatively decreased, which may lead to a reduction in the strength of the fiber assembly 30. When the content of the carbon particles 40 is 60% by mass or less, the strength of the fiber assembly 30 can be easily secured. The content of the carbon particles 40 may be 20% by mass or more and 50% by mass or less, and further 25% by mass or more and 45% by mass or less. The content of the carbon particles 40 is determined by, for example, a thermogravimetric method (TG method).
　炭素粒子４０を有する形態では、バインダ２５の含有率は、繊維集合体３０の質量を１００質量％として、例えば１０質量％以上７０質量％以下である。バインダ２５の含有率が１０質量％以上であることで、バインダ２５によって、炭素粒子４０を繊維２０の表面に強固に担持し易い。バインダ２５の含有率が７０質量％以下であることで、相対的に繊維２０の割合が減少することによる繊維集合体３０の強度低下を抑制できる。バインダ２５の含有率は、炭素粒子４０を繊維２０の表面に担持できるように適宜設定すればよい。バインダ２５の含有率は、１０質量％以上６０質量％以下、更に２０質量％以上５０質量％以下でもよい。バインダ２５が上述した第一のバインダ、又は第二バインダを含む場合、それぞれのバインダの含有率は、例えば、熱重量測定法（ＴＧ法）により求められる。 In the form having the carbon particles 40, the content of the binder 25 is, for example, 10% by mass or more and 70% by mass or less when the mass of the fiber assembly 30 is 100% by mass. When the content of the binder 25 is 10% by mass or more, the carbon particles 40 are easily supported on the surface of the fiber 20 by the binder 25 . By setting the content of the binder 25 to 70% by mass or less, it is possible to suppress a reduction in the strength of the fiber assembly 30 due to a relative decrease in the ratio of the fibers 20 . The content of the binder 25 may be appropriately set so that the carbon particles 40 can be supported on the surfaces of the fibers 20 . The content of the binder 25 may be 10% by mass or more and 60% by mass or less, and further 20% by mass or more and 50% by mass or less. When the binder 25 contains the above-described first binder or second binder, the content of each binder is determined by, for example, a thermogravimetric method (TG method).
　炭素粒子４０を担持させた繊維２０は、炭素粒子４０を含有する塗布液を繊維集合体３０に塗布した後、乾燥することで得られる。塗布液は、例えば、炭素粒子４０を溶媒に分散させたものである。塗布液には、必要に応じて安定化剤などを含んでもよい。本例のように、バインダ２５を有する場合、塗布液は、更にバインダ２５の原料を含有する。溶媒は、水、有機溶媒のいずれであってもよい。バインダ２５の原料が上述の有機バインダである場合、溶媒は有機溶媒であるとよい。有機溶媒は、メタノール、エタノール、プロピルアルコール、イソプロパノール、ブタノール、ペンタノール、ヘキサノールなどである。バインダ２５を導電性金属酸化物で構成する場合は、バインダ２５の原料は上述の金属イオンを溶媒に溶解させる。溶媒は、塗布液を１００質量％として、７０質量％以上９５質量％以下含有するとよい。安定化剤は、アセチルアセトンなどである。安定化剤は、塗布液を１００質量％として、１質量％以上１０質量％以下含有するとよい。バインダ２５の原料が上述の熱硬化性樹脂からなる有機バインダである場合、或いは、溶媒に上述の金属イオンを溶解させた場合は、塗布液を塗布した後に熱処理するとよい。熱処理の条件は、例えば、熱処理温度を３００℃以上７００℃以下、熱処理時間を１０分以上５時間以下とする。熱処理温度は、４００℃以上６００℃以下、更に４５０℃以上５５０℃以下でもよい。熱処理時間は、１５分以上２時間以下、更に３０分以上１時間以下でもよい。 The fibers 20 supporting the carbon particles 40 are obtained by applying a coating liquid containing the carbon particles 40 to the fiber assembly 30 and then drying. The coating liquid is, for example, carbon particles 40 dispersed in a solvent. The coating liquid may contain a stabilizer and the like, if necessary. When the coating liquid has the binder 25 as in this example, the coating liquid further contains the raw material of the binder 25 . The solvent may be either water or an organic solvent. When the raw material of the binder 25 is the above-described organic binder, the solvent is preferably an organic solvent. Organic solvents include methanol, ethanol, propyl alcohol, isopropanol, butanol, pentanol, hexanol, and the like. When the binder 25 is composed of a conductive metal oxide, the raw material of the binder 25 dissolves the above metal ions in a solvent. The solvent is preferably contained in an amount of 70% by mass or more and 95% by mass or less based on 100% by mass of the coating liquid. Stabilizers include acetylacetone. The stabilizer is preferably contained in an amount of 1% by mass or more and 10% by mass or less based on 100% by mass of the coating liquid. When the raw material of the binder 25 is an organic binder made of the above-described thermosetting resin, or when the above-described metal ions are dissolved in a solvent, heat treatment may be performed after applying the coating liquid. The heat treatment conditions are, for example, a heat treatment temperature of 300° C. to 700° C. and a heat treatment time of 10 minutes to 5 hours. The heat treatment temperature may be 400° C. or higher and 600° C. or lower, and further 450° C. or higher and 550° C. or lower. The heat treatment time may be 15 minutes or more and 2 hours or less, or 30 minutes or more and 1 hour or less.
　上記塗布液を繊維集合体３０に塗布した後に乾燥することで、炭素粒子４０が繊維２０の表面に付着した状態となる。上記塗布液にバインダ２５の原料を含有する場合は、上述のように、バインダ２５によって繊維２０の表面に炭素粒子４０を担持させることができる。 The carbon particles 40 adhere to the surfaces of the fibers 20 by drying after applying the coating liquid to the fiber assembly 30 . When the raw material of the binder 25 is contained in the coating liquid, the carbon particles 40 can be supported on the surfaces of the fibers 20 by the binder 25 as described above.
　　〈触媒〉
　触媒５０は、図１０に示すように、繊維２０の表面に担持される。触媒５０は、複数の繊維２０のうち、必ずしも全ての繊維２０の表面に担持されていなくてもよく、大部分の繊維２０に担持されていればよい。また、触媒５０は、各繊維２０の表面の少なくとも一部に担持されていればよい。触媒５０は、複数の繊維２０の局所に偏って担持されることなく、ほぼ全域に担持されていることが好ましい。触媒５０は、電解液と電極との電池反応を活性化させることで、電解液との電池反応性を向上させる。 <catalyst>
Catalyst 50 is supported on the surface of fiber 20 as shown in FIG. The catalyst 50 does not necessarily have to be carried on the surfaces of all the fibers 20 among the plurality of fibers 20 , as long as it is carried on most of the fibers 20 . Moreover, the catalyst 50 may be carried on at least a part of the surface of each fiber 20 . It is preferable that the catalyst 50 is carried almost all over the plurality of fibers 20 without being unevenly carried locally. The catalyst 50 improves the battery reactivity with the electrolyte by activating the battery reaction between the electrolyte and the electrodes.
　触媒５０は、例えば、金属元素を含有する金属酸化物で構成されている。上記金属元素は、例えば、チタン、バナジウム、ジルコニウム、ニオブ、モリブデン、ルテニウム、ロジウム、パラジウム、スズ、アンチモン、タリウム、ハフニウム、タンタル、タングステン、レニウム、及びイリジウムからなる群より選択される少なくとも一種である。上記金属酸化物は、上記の群から選択される一種の金属元素を含むものでもよいし、複数種の金属元素を含む複合酸化物でもよい。 The catalyst 50 is composed of, for example, a metal oxide containing a metal element. The metal element is, for example, at least one selected from the group consisting of titanium, vanadium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tin, antimony, thallium, hafnium, tantalum, tungsten, rhenium, and iridium. . The metal oxide may contain one type of metal element selected from the above group, or may be a composite oxide containing multiple types of metal elements.
　繊維２０が上述した金属繊維である場合、触媒５０である金属酸化物は、繊維２０を構成する金属元素と同じ金属元素を含むことが好ましい。この場合、繊維２０は元素単体からなり、触媒５０はその元素の酸化物からなることでもよい。例えば、繊維２０がチタンで構成されている場合、触媒５０がチタン酸化物（ＴｉＯ２）で構成されている。例えば、繊維２０がタングステンで構成されている場合、触媒５０がタングステン酸化物（ＷＯ３）で構成されている。 When the fibers 20 are the metal fibers described above, the metal oxide that is the catalyst 50 preferably contains the same metal element as the metal element forming the fibers 20 . In this case, the fiber 20 may consist of a single element and the catalyst 50 may consist of an oxide of that element. For example, if the fibers 20 are made of titanium, the catalyst 50 is made of titanium oxide (TiO 2 ). For example, if the fibers 20 are made of tungsten, the catalyst 50 is made of tungsten oxide ( WO3).
　触媒５０は、繊維２０の表面に分散して存在する。触媒５０は、代表的には、粒子状である。粒子状には、球状、針状、薄板状など種々の形状が含まれる。触媒５０の粒径は、例えば１ｎｍ以上１００ｎｍ以下である。ここでの「粒径」は、平均粒径を意味する。触媒５０の粒径は、上述した炭素粒子４０の粒径と同様の方法により測定することができる。 The catalyst 50 exists dispersedly on the surface of the fiber 20 . Catalyst 50 is typically particulate. The particle shape includes various shapes such as a spherical shape, a needle shape, and a thin plate shape. The particle size of the catalyst 50 is, for example, 1 nm or more and 100 nm or less. "Particle size" here means average particle size. The particle size of the catalyst 50 can be measured by the same method as the particle size of the carbon particles 40 described above.
　本例では、触媒５０がバインダ２５によって繊維２０の表面に担持されている。バインダ２５を有することで、触媒５０が繊維２０の表面に強固に担持される。バインダ２５はなくてもよい。触媒５０が繊維２０の表面に直接付着してもよい。第二のバインダ２５が、炭素を主体とする第一のバインダ、又は導電性金属酸化物を主体とする第二のバインダを含む場合、繊維２０と触媒５０との間にバインダ２５が介在しても、触媒５０を繊維２０と電気的に導通した状態で担持させることができる。つまり、触媒５０と繊維２０との間の電気的導通を確保できる。また、バインダ２５を介して触媒５０間の電気的導通も確保できる。バインダ２５が、上述のように、ＰＴＦＥ、ＰＶＤＦ、ＰＶＤＣなどの樹脂により構成されている場合、即ち炭素化していない場合、触媒５０と繊維２０との接触によって触媒５０と繊維２０との間の電気的導通が確保される。また、触媒５０同士の接触によって触媒５０間の電気的導通が確保される。 In this example, the catalyst 50 is supported on the surface of the fiber 20 by the binder 25. By having the binder 25 , the catalyst 50 is strongly supported on the surface of the fiber 20 . Binder 25 may be omitted. Catalyst 50 may adhere directly to the surface of fiber 20 . When the second binder 25 contains a carbon-based first binder or a conductive metal oxide-based second binder, the binder 25 is interposed between the fibers 20 and the catalyst 50. Also, the catalyst 50 can be supported in an electrically conductive state with the fibers 20 . In other words, electrical continuity between the catalyst 50 and the fibers 20 can be ensured. Also, electrical continuity between the catalysts 50 can be ensured through the binder 25 . When the binder 25 is composed of a resin such as PTFE, PVDF, or PVDC, as described above, that is, when it is not carbonized, the contact between the catalyst 50 and the fibers 20 causes electricity to flow between the catalyst 50 and the fibers 20 . electrical continuity is ensured. In addition, electrical continuity between the catalysts 50 is ensured by the contact between the catalysts 50 .
　触媒５０の含有率は、例えば１質量％以上３０質量％以下である。触媒５０の含有率は、繊維集合体３０（図３Ａ参照）の質量を１００質量％としたときの触媒５０の質量の割合である。触媒５０の含有率が１質量％以上であることで、電解液との電池反応性を高め易い。触媒５０の含有率が高いほど、電池反応性を高め易いが、相対的に繊維２０の割合が減少するため、繊維集合体３０の強度の低下を招くおそれがある。触媒５０の含有率が３０質量％以下であることで、繊維集合体３０の強度を確保し易い。触媒５０の含有率は、１質量％以上２０質量％以下、更に１質量％以上１０質量％以下でもよい。触媒５０の含有率は、例えば、熱重量測定法（ＴＧ法）により求められる。 The content of the catalyst 50 is, for example, 1% by mass or more and 30% by mass or less. The content of the catalyst 50 is the ratio of the mass of the catalyst 50 when the mass of the fiber assembly 30 (see FIG. 3A) is 100% by mass. When the content of the catalyst 50 is 1% by mass or more, it is easy to increase the battery reactivity with the electrolytic solution. The higher the content of the catalyst 50, the easier it is to increase the battery reactivity, but the proportion of the fibers 20 is relatively decreased, so that the strength of the fiber assembly 30 may be lowered. When the content of the catalyst 50 is 30% by mass or less, the strength of the fiber assembly 30 can be easily secured. The content of the catalyst 50 may be 1% by mass or more and 20% by mass or less, and further 1% by mass or more and 10% by mass or less. The content of the catalyst 50 is obtained by, for example, a thermogravimetry method (TG method).
　触媒５０を担持させた繊維２０は、上記金属酸化物を構成する金属元素を含有する塗布液を繊維集合体３０に塗布した後、酸素を含む雰囲気中で熱処理することで得られる。塗布液は、例えば、上記金属酸化物を構成する金属元素の原料と溶媒とを含有する。塗布液には、必要に応じて安定化剤などを含んでもよい。本例のように、バインダ２５を有する場合、塗布液には、更にバインダ２５の原料を含有する。上記金属酸化物を構成する金属元素の原料は、金属アルコキシド、塩化物、酢酸塩、有機金属化合物などがある。溶媒は、水、有機溶媒などである。有機溶媒及び安定化剤のそれぞれの種類や含有量、熱処理の条件は、上述した炭素粒子４０の塗布液について説明した事項を参照するとよい。酸素を含む雰囲気は、例えば、空気でもよい。 The fibers 20 supporting the catalyst 50 can be obtained by applying a coating liquid containing the metal elements constituting the metal oxide to the fiber assembly 30 and then heat-treating it in an oxygen-containing atmosphere. The coating liquid contains, for example, a raw material of the metal element constituting the metal oxide and a solvent. The coating liquid may contain a stabilizer and the like, if necessary. When the binder 25 is included as in this example, the coating liquid further contains the raw material of the binder 25 . Metal alkoxides, chlorides, acetates, organometallic compounds, and the like are available as raw materials for the metal elements constituting the metal oxides. Solvents include water, organic solvents, and the like. For the types and contents of the organic solvent and the stabilizer, and the conditions for the heat treatment, it is preferable to refer to the items described for the coating liquid of the carbon particles 40 described above. The atmosphere containing oxygen may be, for example, air.
　上記塗布液を繊維集合体３０に塗布した後に熱処理することで、金属酸化物を構成する金属元素が繊維集合体３０内に熱拡散すると共に酸化する。そして、金属酸化物からなる触媒５０が繊維２０の表面に付着した状態となる。上記塗布液にバインダ２５の原料を含有する場合は、上述のように、バインダ２５によって繊維２０の表面に触媒５０を担持させることができる。 By heat-treating the fiber assembly 30 after applying the coating liquid, the metal elements forming the metal oxide are thermally diffused into the fiber assembly 30 and oxidized. Then, the catalyst 50 made of metal oxide adheres to the surface of the fiber 20 . When the raw material of the binder 25 is contained in the coating liquid, the catalyst 50 can be supported on the surface of the fibers 20 by the binder 25 as described above.
　《作用効果》
　上述した実施形態の電極１０は、電池セル１００を構成したとき、繊維２０が隔膜１０１に突き刺さることを抑制できる。その理由は、平均配向度が０．３以下であるからである。平均配向度が０．３以下であれば、繊維集合体３０の厚さ方向に配向する繊維２０の数が少ない。そのため、繊維２０が隔膜１０１に突き刺さることを抑制できる。上記電極１０は、ＲＦ電池１の電極に利用した場合、繊維２０が隔膜１０１に突き刺さることに起因する短絡を抑制できる。その結果、ＲＦ電池１の電流効率の低下を抑制できる。 《Effect》
The electrode 10 of the embodiment described above can suppress the fibers 20 from sticking into the diaphragm 101 when the battery cell 100 is constructed. The reason is that the average degree of orientation is 0.3 or less. If the average degree of orientation is 0.3 or less, the number of fibers 20 oriented in the thickness direction of the fiber assembly 30 is small. Therefore, it is possible to prevent the fibers 20 from sticking into the diaphragm 101 . When the electrode 10 is used as the electrode of the RF battery 1 , it is possible to suppress short circuits caused by the fibers 20 sticking into the diaphragm 101 . As a result, a decrease in the current efficiency of the RF battery 1 can be suppressed.
　実施形態の電池セル１００、及び電池セル１００を備えるＲＦ電池１は、電流効率が高い。その理由は、電池セル１００を構成する正極電極１０４及び負極電極１０５が実施形態の電極１０であることで、繊維２０が隔膜１０１に突き刺さることに起因する短絡を抑制できるからである。正極と負極との間で短絡が生じ難くなるので、電流効率の低下を抑制できる。 The battery cell 100 of the embodiment and the RF battery 1 including the battery cell 100 have high current efficiency. The reason for this is that the positive electrode 104 and the negative electrode 105 that constitute the battery cell 100 are the electrodes 10 of the embodiment, so that short circuits caused by the fibers 20 sticking into the diaphragm 101 can be suppressed. Since a short circuit is less likely to occur between the positive electrode and the negative electrode, a decrease in current efficiency can be suppressed.
　［試験例１］
　繊維の平均配向度が異なる繊維集合体を用意した。用意した繊維集合体をＲＦ電池の電極に使用したときの電流効率を調べた。 [Test Example 1]
Fiber aggregates with different average orientation degrees of fibers were prepared. The current efficiency was investigated when the prepared fiber assembly was used as an electrode of an RF battery.
　この試験例では、不織布、クロス、及びペーパーの３種類の形態の繊維集合体を用意した。また、各形態の繊維集合体について、繊維の配向度が異なるものを２つ用意した。用意した各繊維集合体からなる電極を試料Ｎｏ．１からＮｏ．３、及び試料Ｎｏ．１１からＮｏ．１３とした。
　試料Ｎｏ．１及びＮｏ．１１の電極における繊維集合体は不織布である。試料Ｎｏ．２及びＮｏ．１２では、繊維集合体がクロスである。試料Ｎｏ．３及びＮｏ．１３では、繊維集合体がペーパーである。各繊維集合体を構成する繊維はいずれも、炭素繊維である。 In this test example, three types of fiber aggregates were prepared: nonwoven fabric, cloth, and paper. In addition, two fiber aggregates with different fiber orientations were prepared for each form. An electrode made of each prepared fiber assembly was designated as sample No. 1. 1 to No. 3, and sample no. 11 to No. 13.
Sample no. 1 and no. The fiber assembly in the 11 electrodes is a non-woven fabric. Sample no. 2 and No. In 12, the fiber assembly is cloth. Sample no. 3 and No. In 13, the fiber assembly is paper. All of the fibers forming each fiber assembly are carbon fibers.
　繊維集合体が不織布である試料Ｎｏ．１の電極については、繊維の表面に炭素粒子をバインダによって担持させた構成とした。つまり、試料Ｎｏ．１では、炭素繊維の他に、炭素粒子とバインダとを有する。炭素粒子の粒径は１５μｍである。炭素粒子の含有率は３５質量％である。バインダの含有率は３５質量％である。バインダの材質は炭素である。繊維集合体がペーパーである試料Ｎｏ．３及びＮｏ．１３の電極についても、バインダの材質は炭素である。 　Sample No. 1, in which the fiber assembly is a non-woven fabric. Electrode No. 1 had a structure in which carbon particles were supported on the surface of the fiber by a binder. That is, sample no. 1 has carbon particles and a binder in addition to carbon fibers. The particle size of the carbon particles is 15 μm. The content of carbon particles is 35% by mass. The binder content is 35% by mass. The material of the binder is carbon. Sample No. in which the fiber assembly is paper. 3 and No. The material of the binder for the electrode No. 13 is also carbon.
　各試料の電極を用いて、単一の電池セルを備えるＲＦ電池をそれぞれ構成した。各々のＲＦ電池において、電池セルを構成する正極電極及び負極電極には、同じ試料の電極を用いた。正極電極及び負極電極の各面積は９ｃｍ２とした。隔膜は、厚さ２５μｍのナフィオン（登録商標）膜である。正極電解液及び負極電解液は、チタン－マンガン系電解液である。チタン－マンガン系電解液は、硫酸の濃度が５Ｍ（ｍｏｌ／Ｌ）の水溶液に、チタンイオン及びマンガンイオンがそれぞれ１Ｍ（ｍｏｌ／Ｌ）の濃度で溶解したものである。 The electrodes of each sample were used to construct each RF battery with a single battery cell. In each RF battery, electrodes of the same sample were used for the positive electrode and the negative electrode constituting the battery cell. Each area of the positive electrode and the negative electrode was 9 cm 2 . The diaphragm is a 25 μm thick Nafion® membrane. The positive electrode electrolyte and the negative electrode electrolyte are titanium-manganese based electrolytes. The titanium-manganese-based electrolytic solution is obtained by dissolving titanium ions and manganese ions at concentrations of 1M (mol/L) in an aqueous solution of sulfuric acid at a concentration of 5M (mol/L).
　各々のＲＦ電池について、充放電試験を行った。充放電試験の条件は、電流密度が７０ｍＡ／ｃｍ２の定電流とした。充電終了電圧は１．５Ｖとし、放電終了電圧は１．０Ｖとした。充放電後、電流効率を求めた。電流効率は、「（放電電気量／充電電気量）×１００」により求められる。充電電気量は、「（充電時間）×（電流密度×電極面積）」により求められる。放電電気量は、「（放電時間）×（電流密度×電極面積）」により求められる。各試料の電極を備える各ＲＦ電池の電流効率（％）を表１に示す。 A charge/discharge test was performed on each RF battery. The charging/discharging test conditions were a constant current with a current density of 70 mA/cm 2 . The charge end voltage was set to 1.5V, and the discharge end voltage was set to 1.0V. After charging and discharging, the current efficiency was determined. The current efficiency is obtained by "(amount of discharged electricity/amount of charged electricity)×100". The charge quantity of electricity is obtained by "(charging time) x (current density x electrode area)". The amount of discharged electricity is obtained by “(discharge time)×(current density×electrode area)”. Table 1 shows the current efficiency (%) of each RF cell with electrodes of each sample.
　各試料の電極における繊維集合体及び繊維の仕様、並びに電池セルを構成したときの繊維集合体の圧縮率及び空隙率は、次のとおりである。表１では、平均配向度を百分率で示している。 The specifications of the fiber assembly and fibers in the electrode of each sample, and the compression ratio and porosity of the fiber assembly when composing the battery cell are as follows. Table 1 shows the average degree of orientation in percentage.
　（試料Ｎｏ．１）
　〈繊維〉
　材質：炭素
　平均配向度：０．２０４
　平均繊維径：１０μｍ
　平均繊維長：５０ｍｍ
　〈繊維集合体〉
　形態：不織布
　繊維の含有率：３０質量％
　炭素粒子の含有率：３５質量％
　バインダの含有率：３５質量％
　厚さ：１．４ｍｍ
　圧縮率：５０％
　空隙率：６０体積％ (Sample No. 1)
<fiber>
Material: Carbon Average degree of orientation: 0.204
Average fiber diameter: 10 μm
Average fiber length: 50mm
<Fiber assembly>
Form: nonwoven fabric Fiber content: 30% by mass
Carbon particle content: 35% by mass
Binder content: 35% by mass
Thickness: 1.4mm
Compression rate: 50%
Porosity: 60% by volume
　（試料Ｎｏ．１１）
　〈繊維〉
　材質：炭素
　平均配向度：０．４１３
　平均繊維径：１０μｍ
　平均繊維長：５０ｍｍ
　〈繊維集合体〉
　形態：不織布
　繊維の含有率：１００質量％
　厚さ：２．０ｍｍ
　圧縮率：６０％
　空隙率：７０体積％ (Sample No. 11)
<fiber>
Material: Carbon Average degree of orientation: 0.413
Average fiber diameter: 10 μm
Average fiber length: 50mm
<Fiber assembly>
Form: nonwoven fabric Fiber content: 100% by mass
Thickness: 2.0mm
Compression rate: 60%
Porosity: 70% by volume
　（試料Ｎｏ．２）
　〈繊維〉
　材質：炭素
　平均配向度：０．２４４
　平均繊維径：９μｍ
　平均繊維長：１００ｍｍ
　〈繊維集合体〉
　形態：クロス
　繊維の含有率：１００質量％
　厚さ：０．５ｍｍ
　圧縮率：６０％
　空隙率：４０体積％ (Sample No. 2)
<fiber>
Material: Carbon Average degree of orientation: 0.244
Average fiber diameter: 9 μm
Average fiber length: 100mm
<Fiber assembly>
Form: cloth Fiber content: 100% by mass
Thickness: 0.5mm
Compression rate: 60%
Porosity: 40% by volume
　（試料Ｎｏ．１２）
　〈繊維〉
　材質：炭素
　平均配向度：０．４９３
　平均繊維径：９μｍ
　平均繊維長：１００ｍｍ
　〈繊維集合体〉
　形態：クロス
　繊維の含有率：１００質量％
　厚さ：０．６ｍｍ
　圧縮率：６０％
　空隙率：６０体積％ (Sample No. 12)
<fiber>
Material: Carbon Average degree of orientation: 0.493
Average fiber diameter: 9 μm
Average fiber length: 100mm
<Fiber assembly>
Form: cloth Fiber content: 100% by mass
Thickness: 0.6mm
Compression rate: 60%
Porosity: 60% by volume
　（試料Ｎｏ．３）
　〈繊維〉
　材質：炭素
　平均配向度：０．０４５
　平均繊維径：１０μｍ
　平均繊維長：１５ｍｍ
　〈繊維集合体〉
　形態：ペーパー
　繊維の含有率：４０質量％
　バインダの含有率：６０質量％
　厚さ：０．５ｍｍ
　圧縮率：４０％
　空隙率：６０体積％ (Sample No. 3)
<fiber>
Material: Carbon Average degree of orientation: 0.045
Average fiber diameter: 10 μm
Average fiber length: 15mm
<Fiber assembly>
Form: Paper Fiber content: 40% by mass
Binder content: 60% by mass
Thickness: 0.5mm
Compression rate: 40%
Porosity: 60% by volume
　（試料Ｎｏ．１３）
　〈繊維〉
　材質：炭素
　平均配向度：０．１３５
　平均繊維径：１０μｍ
　平均繊維長：１．５ｍｍ
　〈繊維集合体〉
　形態：ペーパー
　繊維の含有率：５０質量％
　バインダの含有率：５０質量％
　厚さ：０．５ｍｍ
　圧縮率：４０％
　空隙率：６０体積％ (Sample No. 13)
<fiber>
Material: Carbon Average degree of orientation: 0.135
Average fiber diameter: 10 μm
Average fiber length: 1.5mm
<Fiber assembly>
Form: Paper Fiber content: 50% by mass
Binder content: 50% by mass
Thickness: 0.5mm
Compression rate: 40%
Porosity: 60% by volume
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１に示すように、繊維集合体が不織布又はクロスである試料Ｎｏ．１、Ｎｏ．２、Ｎｏ．１１、及びＮｏ．１２において、平均配向度が３０％以下、即ち０．３以下である試料Ｎｏ．１、Ｎｏ．２の電流効率は、試料Ｎｏ．１１、Ｎｏ．１２の電流効率に比較して高い。試料Ｎｏ．１、Ｎｏ．２の電流効率は、９０％以上、更に９５％以上、特に９９％以上を満たす。また、繊維集合体がペーパーである試料Ｎｏ．３及びＮｏ．１３において、平均配向度が１０％以下、即ち０．１以下である試料Ｎｏ．３の電流効率は、試料Ｎｏ．１３の電流効率に比較して高い。試料Ｎｏ．３の電流効率は、９０％以上、更に９５％以上、特に９９％以上を満たす。 　As shown in Table 1, sample No. 1, in which the fiber assembly is a nonwoven fabric or a cloth. 1, No. 2, No. 11, and no. In Sample No. 12, the average degree of orientation is 30% or less, that is, 0.3 or less. 1, No. The current efficiency of sample no. 11, No. High compared to the current efficiency of 12. Sample no. 1, No. The current efficiency of 2 satisfies 90% or more, further 95% or more, particularly 99% or more. Moreover, sample No. 1 in which the fiber assembly is paper. 3 and No. In Sample No. 13, the average degree of orientation is 10% or less, that is, 0.1 or less. The current efficiency of sample no. The current efficiency is high compared to that of 13. Sample no. The current efficiency of 3 satisfies 90% or more, further 95% or more, particularly 99% or more.
　繊維集合体の形態が同じ試料同士で比較したとき、試料Ｎｏ．１からＮｏ．３は、試料Ｎｏ．１１からＮｏ．１３よりも電流効率の低下を抑制できることが分かる。試料Ｎｏ．１からＮｏ．３において電流効率の低下を抑制できた理由は、繊維の隔膜への突き刺さりを抑制できたことによるものと考えられる。試料Ｎｏ．１からＮｏ．３では、平均配向度が小さいので、繊維の隔膜への突き刺さりが発生し難い。そのため、試料Ｎｏ．１からＮｏ．３では、繊維が隔膜に突き刺さることに起因する短絡が抑制されることから、電流効率の低下が抑制される。 When comparing samples with the same fiber assembly morphology, sample No. 1 to No. 3 is sample no. 11 to No. It can be seen that the decrease in current efficiency can be suppressed more than 13. Sample no. 1 to No. The reason why the decrease in the current efficiency could be suppressed in 3 is considered to be that the sticking of the fibers into the diaphragm could be suppressed. Sample no. 1 to No. In 3, since the average degree of orientation is small, the fibers are less likely to stick into the diaphragm. Therefore, sample no. 1 to No. In 3, a short circuit caused by sticking of the fiber into the diaphragm is suppressed, and thus a decrease in current efficiency is suppressed.
　１　レドックスフロー電池（ＲＦ電池）
　１０　電極、１１　第一の面
　２０　繊維、２５　バインダ
　２０ｓ　糸、２１ｓ　第一の糸、２２ｓ　第二の糸
　３０，３１，３２　繊維集合体
　４０　炭素粒子
　５０　触媒
　７　交流／直流変換器、７１　変電設備
　８　発電部、９　負荷
　１００　電池セル
　１０１　隔膜、１０２　正極セル、１０３　負極セル
　１０４　正極電極、１０５　負極電極
　１０６　正極電解液タンク、１０７　負極電解液タンク
　１０８，１０９　往路配管
　１１０，１１１　復路配管
　１１２，１１３　ポンプ
　１２０　セルフレーム
　１２１　双極板、１２２　枠体
　１２２ｏ　凹部
　１２３，１２４　給液マニホールド、１２５，１２６　排液マニホールド
　１２３ｓ，１２４ｓ　給液スリット、１２５ｓ，１２６ｓ　排液スリット
　１２７　シール部材
　２００　セルスタック、２００ｓ　サブスタック
　２１０　エンドプレート、２２０　給排板、２３０　締付機構
　ｐ　中心間距離
　ｄ　対角線 1 Redox flow battery (RF battery)
10 electrode, 11 first surface 20 fiber, 25 binder 20s yarn, 21s first yarn, 22s second yarn 30, 31, 32 fiber assembly 40 carbon particles 50 catalyst 7 AC/DC converter 71 substation equipment 8 power generation unit 9 load 100 battery cell 101 diaphragm 102 positive electrode cell 103 negative electrode cell 104 positive electrode 105 negative electrode 106 positive electrode electrolyte tank 107 negative electrode electrolyte tank 108, 109 forward pipe 110, 111 return pipe 112, 113 pump 120 cell frame 121 bipolar plate 122 frame 122o recess 123, 124 liquid supply manifold 125, 126 drainage manifold 123s, 124s liquid supply slit 125s, 126s drainage slit 127 sealing member 200 cell stack 200s substack 210 end plate, 220 feed/discharge plate, 230 tightening mechanism p center distance d diagonal

Claims (20)

  1. 　複数の繊維が組み合わされた繊維集合体を備え、
    　前記繊維集合体はシート形状を有し、
    　前記複数の繊維の平均配向度は０．３以下であり、
    　前記平均配向度は、前記繊維集合体の厚さ方向に沿った前記繊維集合体の断面において、前記厚さ方向と直交する水平線に対する前記複数の繊維の各々の角度を９０°で割った値の平均値である、
    電極。     Equipped with a fiber assembly in which a plurality of fibers are combined,
    The fiber assembly has a sheet shape,
    The average degree of orientation of the plurality of fibers is 0.3 or less,
    The average degree of orientation is the value obtained by dividing the angle of each of the plurality of fibers with respect to a horizontal line orthogonal to the thickness direction in the cross section of the fiber assembly along the thickness direction of the fiber assembly by 90°. is the average value,
    electrode.
  2. 　前記繊維集合体における前記複数の繊維の含有率が２０質量％以上である、請求項１に記載の電極。 The electrode according to claim 1, wherein the content of the plurality of fibers in the fiber aggregate is 20% by mass or more.
  3. 　前記繊維集合体は、クロス又は不織布である、請求項１又は請求項２に記載の電極。 The electrode according to claim 1 or 2, wherein the fiber assembly is cloth or nonwoven fabric.
  4. 　前記複数の繊維の平均長さが２５ｍｍ以上である、請求項１から請求項３のいずれか一項に記載の電極。 The electrode according to any one of claims 1 to 3, wherein the plurality of fibers have an average length of 25 mm or more.
  5. 　前記繊維集合体は、前記複数の繊維の表面に付着されたバインダを含む、請求項１から請求項４のいずれか一項に記載の電極。 The electrode according to any one of claims 1 to 4, wherein the fiber assembly includes a binder adhered to the surfaces of the plurality of fibers.
  6. 　前記繊維集合体はペーパーであり、
    　前記複数の繊維の表面に付着されたバインダを含む、請求項１又は請求項２に記載の電極。     The fiber assembly is paper,
    3. The electrode of claim 1 or claim 2, comprising a binder attached to the surfaces of the plurality of fibers.
  7. 　前記平均配向度が０．１以下である、請求項６に記載の電極。 The electrode according to claim 6, wherein the average degree of orientation is 0.1 or less.
  8. 　前記複数の繊維の平均長さが２０ｍｍ以下である、請求項６又は請求項７に記載の電極。 The electrode according to claim 6 or 7, wherein the plurality of fibers have an average length of 20 mm or less.
  9. 　前記繊維集合体における前記バインダの含有率が２０質量％以上８０質量％以下である、請求項５から請求項８のいずれか一項に記載の電極。 The electrode according to any one of claims 5 to 8, wherein the content of the binder in the fiber aggregate is 20% by mass or more and 80% by mass or less.
  10. 　前記バインダは、炭素を主体とする第一のバインダを含む、請求項５から請求項９のいずれか一項に記載の電極。 The electrode according to any one of claims 5 to 9, wherein the binder includes a carbon-based first binder.
  11. 　前記バインダは、導電性金属酸化物を主体とする第二のバインダを含む、請求項５から請求項１０のいずれか一項に記載の電極。 The electrode according to any one of claims 5 to 10, wherein the binder includes a second binder mainly composed of a conductive metal oxide.
  12. 　前記複数の繊維の表面に担持された炭素粒子を有する、請求項１から請求項１１のいずれか一項に記載の電極。 The electrode according to any one of claims 1 to 11, having carbon particles supported on the surfaces of the plurality of fibers.
  13. 　前記複数の繊維の表面に担持された炭素粒子を有し、
    　前記炭素粒子は、前記バインダによって担持されている、請求項５から請求項１１のいずれか一項に記載の電極。     Having carbon particles supported on the surfaces of the plurality of fibers,
    12. The electrode according to any one of claims 5 to 11, wherein said carbon particles are supported by said binder.
  14. 　前記複数の繊維の表面に担持された触媒を有する、請求項１から請求項１３のいずれか一項に記載の電極。 The electrode according to any one of claims 1 to 13, having a catalyst supported on the surfaces of the plurality of fibers.
  15. 　前記複数の繊維の表面に担持された触媒を有し、
    　前記触媒は、前記バインダによって担持されている、請求項５から請求項１１、及び請求項１３のいずれか一項に記載の電極。     Having a catalyst supported on the surfaces of the plurality of fibers,
    14. The electrode according to any one of claims 5 to 11 and 13, wherein the catalyst is supported by the binder.
  16. 　前記触媒は、チタン、バナジウム、ジルコニウム、ニオブ、モリブデン、ルテニウム、ロジウム、パラジウム、スズ、アンチモン、タリウム、ハフニウム、タンタル、タングステン、レニウム、及びイリジウムからなる群より選択される少なくとも一種の金属元素を含有する金属酸化物で構成される、請求項１４又は請求項１５に記載の電極。 The catalyst contains at least one metal element selected from the group consisting of titanium, vanadium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, tin, antimony, thallium, hafnium, tantalum, tungsten, rhenium, and iridium. 16. Electrode according to claim 14 or 15, comprising a metal oxide which
  17. 　前記複数の繊維は、炭素、チタン、及びタングステンからなる群より選択される少なくとも一種で構成される、請求項１から請求項１６のいずれか一項に記載の電極。 The electrode according to any one of claims 1 to 16, wherein the plurality of fibers are composed of at least one selected from the group consisting of carbon, titanium, and tungsten.
  18. 　正極電極と、負極電極と、隔膜とを備え、
    　前記正極電極及び前記負極電極の少なくとも一方の電極は、請求項１から請求項１７のいずれか一項に記載の電極である、
    電池セル。     A positive electrode, a negative electrode, and a diaphragm,
    At least one of the positive electrode and the negative electrode is the electrode according to any one of claims 1 to 17,
    battery cell.
  19. 　前記電極における前記繊維集合体の空隙率が３０体積％以上８９体積％以下である、請求項１８に記載の電池セル。 The battery cell according to claim 18, wherein the fiber assembly in the electrode has a porosity of 30% by volume or more and 89% by volume or less.
  20. 　請求項１８又は請求項１９に記載の電池セルを備える、
    レドックスフロー電池。     A battery cell comprising the battery cell according to claim 18 or claim 19,
    redox flow battery.
PCT/JP2022/000390 2021-04-02 2022-01-07 Electrode, battery cell, and redox flow battery WO2022209113A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4439922B2 (en) * 2002-03-26 2010-03-24 パナソニック株式会社 Electrolyte membrane electrode assembly, fuel cell using the same, and manufacturing method thereof
JP2019175833A (en) * 2018-03-29 2019-10-10 東レ株式会社 Redox flow battery electrode and redox flow battery
WO2019239732A1 (en) * 2018-06-12 2019-12-19 住友電気工業株式会社 Electrode for redox flow battery, and redox flow battery

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4439922B2 (en) * 2002-03-26 2010-03-24 パナソニック株式会社 Electrolyte membrane electrode assembly, fuel cell using the same, and manufacturing method thereof
JP2019175833A (en) * 2018-03-29 2019-10-10 東レ株式会社 Redox flow battery electrode and redox flow battery
WO2019239732A1 (en) * 2018-06-12 2019-12-19 住友電気工業株式会社 Electrode for redox flow battery, and redox flow battery

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