WO2018207367A1 - Aqueous solution secondary battery, charge-discharge method for aqueous solution secondary battery, electrolytic solution for use in aqueous solution secondary battery, flow battery system and power-generation system - Google Patents

Aqueous solution secondary battery, charge-discharge method for aqueous solution secondary battery, electrolytic solution for use in aqueous solution secondary battery, flow battery system and power-generation system Download PDF

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WO2018207367A1
WO2018207367A1 PCT/JP2017/018110 JP2017018110W WO2018207367A1 WO 2018207367 A1 WO2018207367 A1 WO 2018207367A1 JP 2017018110 W JP2017018110 W JP 2017018110W WO 2018207367 A1 WO2018207367 A1 WO 2018207367A1
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electrolyte
positive electrode
secondary battery
negative electrode
potential
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PCT/JP2017/018110
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French (fr)
Japanese (ja)
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渉太 伊藤
杉政　昌俊
酒井　政則
北川　雅規
修一郎 足立
祐一 利光
明博 織田
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日立化成株式会社
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Priority to PCT/JP2017/018110 priority Critical patent/WO2018207367A1/en
Priority to JP2019516865A priority patent/JP6935816B2/en
Publication of WO2018207367A1 publication Critical patent/WO2018207367A1/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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/36—Accumulators not provided for in groups H01M10/05-H01M10/34
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the present invention relates to an aqueous secondary battery, an aqueous secondary battery charge / discharge method, an aqueous secondary battery electrolyte, a flow battery system, and a power generation system.
  • Examples of high-capacity storage devices for power storage include sodium sulfur (NAS) batteries, lead storage batteries, redox flow batteries, and the like. Since NAS batteries have a large capacity and a long life, they are proposed for use in peak shift applications, renewable energy power grid linkage applications, and the like. Lead-acid batteries are highly reliable, backed by more than 100 years of history, and have a low cost per unit storage capacity, which is advantageous for large-scale use. It has been proposed for a wide range of uses such as leveling of offices. A redox flow battery can be easily increased in capacity by increasing the capacity of a tank, and is therefore suitable for power storage applications.
  • NAS batteries sodium sulfur (NAS) batteries
  • lead storage batteries lead storage batteries
  • redox flow batteries and the like. Since NAS batteries have a large capacity and a long life, they are proposed for use in peak shift applications, renewable energy power grid linkage applications, and the like.
  • Lead-acid batteries are highly reliable, backed by more than 100 years of history, and have a low cost per unit
  • NAS battery Since the NAS battery has an operating temperature as high as 300 ° C., there is a risk of ignition, and there is a risk of generating toxic gases such as sulfurous acid gas when ignited. Since lead-acid batteries have a low volumetric energy density, they require a large installation area and lead is subject to regulation worldwide as represented by the RoHS directive. It is also possible to become.
  • a redox flow battery has a low risk of ignition if it is an aqueous electrolyte, and has a high safety.
  • a conventional metal ion such as vanadium is used as a positive and negative electrode active material, the volume energy density is low.
  • Patent Document 1 discloses a redox flow battery using chromium ions as a negative electrode active material and halogen ions as a positive electrode active material. The use of iodide ions as halogen ions is also disclosed.
  • Patent Document 2 discloses a redox flow battery using an aqueous solution of a halogen oxoacid compound as a negative electrode electrolyte.
  • Halogen oxo acid compounds include iodates, and mention is also made of using an oxidation-reduction reaction between iodate ions and iodide ions.
  • Patent Document 3 and Non-Patent Document 1 disclose redox flow batteries using metal ions and iodide ion polymers as components of an electrolytic solution. In particular, Non-Patent Document 1 discloses that ethanol or ethylene glycol is added to an aqueous electrolyte containing zinc iodide as an active material, thereby suppressing iodine precipitation.
  • Iodide ions have high solubility in water and are prone to oxidation-reduction reactions. Therefore, they can be expected as electrode active materials that can achieve high energy density and excellent battery characteristics for aqueous secondary batteries that use water as the electrolyte. .
  • iodide ions in the electrolytic solution may precipitate as iodine (I 2 ) on the electrode surface by an oxidation reaction to form a film, which may cause various problems. For example, when the iodine film formed on the electrode surface is increased in resistance, the oxidation current value corresponding to the charging current value as a battery may be reduced.
  • an aqueous secondary battery generally has a low concentration of a charge reaction product in an electrolyte solution in a state of a low charge rate, so that a sufficient discharge output may not be obtained.
  • the present invention relates to an aqueous secondary battery and an aqueous secondary battery charging method in which formation of an iodine film on the electrode surface is suppressed and excellent discharge characteristics at a low charging rate, and an aqueous secondary battery used in these. It aims at providing the electrolyte solution for batteries, and the flow battery system and electric power generation system using these.
  • An aqueous secondary battery comprising an organic compound capable of separating reaction products.
  • the content ratio of the organic compound is 1% by volume to 50% by volume of at least one of the positive electrode electrolyte and the negative electrode electrolyte containing the organic compound.
  • ⁇ 3> The aqueous secondary battery according to ⁇ 1> or ⁇ 2>, wherein the organic compound includes at least one selected from ketones, carboxylic acid esters, and carbonates.
  • the aqueous solution type secondary battery as described.
  • a positive electrode electrolyte solution pump; and the positive electrode electrolyte solution pump can circulate the positive electrode electrolyte solution between the positive electrode electrolyte storage tank and the positive electrode active material reaction tank.
  • the negative electrode electrolyte solution feeding pump is configured to circulate the negative electrode electrolyte solution between the negative electrode electrolyte storage tank and the negative electrode active material reaction tank.
  • ⁇ 6> The aqueous secondary solution according to any one of ⁇ 1> to ⁇ 5>, wherein the positive electrode electrolyte includes the iodide ion and the organic compound, and the negative electrode electrolyte includes a negative electrode active material.
  • the negative electrode active material contains at least one metal ion selected from the group consisting of zinc, chromium, titanium, iron, tin, vanadium, lead, manganese, cobalt, nickel, copper, and lithium, ⁇ 6>
  • ⁇ 8> The aqueous secondary battery according to ⁇ 6> or ⁇ 7>, wherein the negative electrode active material contains zinc ions.
  • aqueous solution comprising a positive electrode, a negative electrode, and an electrolytic solution, wherein the electrolytic solution includes iodide ions, a negative electrode active material, and an organic compound capable of separating an oxidation reaction product of the iodide ions.
  • Secondary battery ⁇ 10> The aqueous secondary battery according to ⁇ 9>, wherein the content of the organic compound is 1% by volume to 50% by volume of the electrolytic solution.
  • the organic compound includes at least one selected from ketones, carboxylic acid esters, and carbonates.
  • the organic compound includes any one of ⁇ 9> to ⁇ 11>, including at least one selected from the group consisting of methyl ethyl ketone, methyl acetate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.
  • the aqueous solution type secondary battery as described.
  • the negative electrode active material contains at least one metal ion selected from the group consisting of zinc, chromium, titanium, iron, tin, vanadium, lead, manganese, cobalt, nickel, copper, and lithium, ⁇ 9>
  • the aqueous solution type secondary battery according to any one of to ⁇ 12>.
  • ⁇ 14> The aqueous secondary battery according to any one of ⁇ 9> to ⁇ 13>, wherein the negative electrode active material contains zinc ions.
  • ⁇ 15> The aqueous secondary battery according to any one of ⁇ 9> to ⁇ 14>, wherein the positive electrode is positioned below the negative electrode in the vertical direction.
  • ⁇ 16> The aqueous solution according to any one of ⁇ 9> to ⁇ 15>, further comprising a diaphragm disposed between the positive electrode and the negative electrode and dividing the electrolyte into a positive electrode electrolyte and a negative electrode electrolyte. Secondary battery.
  • An active material reaction tank containing the electrolyte solution, an electrolyte storage tank, and an electrolyte solution feed pump, further comprising the electrolyte solution tank and the active material reaction tank.
  • the aqueous solution type secondary battery according to any one of ⁇ 9> to ⁇ 16>, wherein the electrolyte solution can be circulated between the first electrode and the second electrode.
  • ⁇ 21> Water, at least one selected from the group consisting of iodine (I 2 ), triiodide ion (I 3 ⁇ ), and pentaiodide ion (I 5 ⁇ ), methyl ethyl ketone, methyl acetate, and ethyl acetate And at least one organic compound selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.
  • ⁇ 22> The electrolyte solution for an aqueous secondary battery according to ⁇ 21>, wherein the content of the organic compound is 1% by volume to 50% by volume of the electrolytic solution for an aqueous secondary battery.
  • a charge / discharge method for an aqueous secondary battery using an electrolytic solution containing iodide ions as a positive electrode active material comprising a step of separating an oxidation reaction product of iodide ions generated in the electrolytic solution.
  • the electrolytic solution for an aqueous secondary battery according to ⁇ 21> or ⁇ 21> which is used as an electrolytic solution for a charging / discharging method of an aqueous secondary battery.
  • a power generation system comprising: a power generation device; and the flow battery system according to ⁇ 24>.
  • the formation of the iodine film on the electrode surface is suppressed, and the aqueous solution type secondary battery excellent in the discharge characteristics at a low charge rate, the method for charging the aqueous solution type secondary battery, and the aqueous solution system used in these An electrolyte for secondary batteries, and a flow battery system and a power generation system using the same are provided.
  • FIG. 1 It is a schematic sectional drawing which shows the structural example of the aqueous solution type secondary battery of 1st Embodiment. It is a schematic sectional drawing which shows the structural example in case the aqueous solution type secondary battery of 1st Embodiment is further provided with the apparatus for making electrolyte solution flow. It is a schematic sectional drawing which shows the structural example of the aqueous solution type secondary battery of 2nd Embodiment. It is a schematic sectional drawing which shows the structural example in case the aqueous solution type secondary battery of 2nd Embodiment is further equipped with the diaphragm 5 between the positive electrode 1 and the negative electrode 2.
  • FIG. 1 It is a schematic sectional drawing which shows the structural example of the aqueous solution type secondary battery of 1st Embodiment. It is a schematic sectional drawing which shows the structural example in case the aqueous solution type secondary battery of 1st Embodiment is further provided with the apparatus for making electrolyte solution flow. It is a schematic
  • FIG. 6 is a graph showing a reverse pulse voltammogram (initial potential 0.90 V to 1.10 V and pulse width 50 ms). It is a graph which shows a reverse pulse voltammogram (initial electric potential 1.40V, 1.50V, and pulse width 50ms). It is a graph which shows a reverse pulse voltammogram (initial electric potential 1.40V, 1.50V, and pulse width 50ms). It is a graph which shows a normal pulse voltammogram (pulse width 50, 500, and 5000 ms). It is a graph which shows a normal pulse voltammogram (pulse width 50, 500, and 5000 ms).
  • each component may contain a plurality of corresponding substances.
  • the content or content of each component is the total content or content of the multiple types of substances present in the composition unless otherwise specified. Means quantity.
  • the term “film” or “film” includes only a part of the region in addition to the case where the film or the film is formed over the entire region. The case where it is formed is also included.
  • the aqueous secondary battery of this embodiment is A positive electrode, a negative electrode, a positive electrode electrolyte, a negative electrode electrolyte, and a diaphragm, wherein at least one of the positive electrode electrolyte and the negative electrode electrolyte is an iodide ion and an oxidation reaction product of the iodide ion And a separable organic compound.
  • the aqueous secondary battery having the above-described configuration is excellent in discharge characteristics at a low charge rate while suppressing the formation of an iodine film on the electrode surface. More specifically, by containing an organic compound capable of separating the oxidation reaction product of iodide ions in the electrolytic solution, dissolution of the iodine film formed on the electrode surface is promoted and separated from the electrolytic solution. It was found that by using the oxidation reaction product for the reduction reaction of the positive electrode, a sufficient discharge output can be obtained even in a low charge rate state.
  • the electrolyte solution contains an organic compound capable of separating the oxidation reaction product of iodide ions, thereby promoting the dissolution of the iodine film formed on the electrode surface and the separated oxidation.
  • the technical idea of utilizing the reaction product for the reduction reaction of the positive electrode is not described.
  • the “aqueous solution type secondary battery” means a secondary battery using an aqueous solution in which a component necessary for water is dissolved as an electrolytic solution.
  • an electricity storage device such as a redox flow battery (flow battery) can be used.
  • positive electrode electrolyte means an electrolyte in contact with the positive electrode
  • negative electrode electrolyte means an electrolyte in contact with the negative electrode
  • an “oxidation reaction product of iodide ion” means a substance generated by an oxidation reaction of iodide ion. Examples thereof include iodine (I 2 ), triiodide ion (I 3 ⁇ ), pentaiodide ion (I 5 ⁇ ), and combinations thereof.
  • the electrolyte is divided into a positive electrode electrolyte and a negative electrode electrolyte.
  • An aqueous secondary battery having such a configuration is also referred to as a “two-component aqueous secondary battery”.
  • the positive electrode electrolyte is an organic compound that can separate an iodide ion and an oxidation reaction product of iodide ion (hereinafter simply referred to as “ It is preferable that the positive electrode electrolyte contains iodide ions and an organic compound, and the negative electrode electrolyte contains a negative electrode active material.
  • the aqueous secondary battery of this embodiment is excellent in energy density because iodide ions are used as the active material contained in the electrolytic solution. Furthermore, the organic compound contained in the electrolyte separates the oxidation reaction product of iodide ions, so that the dissolution of the iodine film formed on the electrode surface is promoted, and the oxidation current value is reduced due to the formation of the iodine film. In addition, the effect of suppressing the sublimation of the I 2 molecules diffused from the iodine film into the electrolyte can be expected. Furthermore, since the oxidation reaction product separated by the organic compound can be used for the reduction reaction at the positive electrode, a high output discharge can be obtained even in a low charge rate state where the concentration of the charge reaction product is lean.
  • an oxidation reaction product of iodide ions contained in the electrolytic solution is selectively separated using an organic compound.
  • the mode of separating the iodide ion oxidation reaction product using an organic compound is not particularly limited, but the electrolyte is separated into a hydrophobic substance containing an iodide ion oxidation reaction product and a bulk aqueous solution. Is preferred.
  • the hydrophobic substance may be obtained by forming a network structure with an organic compound, for example, an iodide ion and its oxidation reaction product, a cation, and a small amount of water. For example, it may be in a hydrophobic liquid state.
  • the solubility of iodine molecules in hydrophobic substances is higher than that in water, and it exists more stably in hydrophobic substances.
  • iodine molecules In addition to being sublimable, iodine molecules have a low solubility in water of about 1 mM. For this reason, iodine molecules present in water easily sublime from the gas-liquid interface, but sublimation of iodine molecules present in a hydrophobic substance is suppressed. Therefore, by separating the oxidation reaction product of iodide ions as a hydrophobic substance, sublimation of iodine molecules can be suppressed, and a decrease in iodide ions in the electrolytic solution can be suppressed.
  • the oxidation reaction product of iodide ion is separated as a hydrophobic substance
  • the oxidation reaction product of iodide ion is present in the separated hydrophobic substance at a higher concentration than in the bulk aqueous solution. Therefore, a high output discharge can be obtained even in a low charge rate state by contacting a hydrophobic substance with the positive electrode and using the oxidation reaction product contained therein for the reduction reaction of the positive electrode.
  • the positive electrode is configured to be positioned below the vertical direction, the oxidation reaction product contained in the hydrophobic substance that precipitates because the specific gravity is larger than that of the bulk aqueous solution is reduced at the positive electrode. Can be used.
  • the organic compound is not particularly limited as long as it can separate the oxidation reaction product of iodide ion. However, for the reason described above, the oxidation reaction product of iodide ion can be separated as a hydrophobic substance. And is more preferably an organic compound having a higher affinity for I 2 molecules than water. An organic compound having an affinity for I 2 molecules higher than that of water promotes dissolution of the iodine film by coordination of the organic compound with the iodine film. For this reason, formation of an iodine film can be suppressed more efficiently. When the organic compound does not form a hydrophobic substance, the organic compound is preferably dissolved in the electrolyte.
  • Examples of the organic compound include at least one selected from the group consisting of ketone, carboxylic acid ester, and carbonate ester.
  • Specific examples of the ketone include methyl ethyl ketone.
  • Specific examples of the carboxylic acid ester include methyl acetate and ethyl acetate.
  • Specific examples of the carbonate ester include dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.
  • ketones are preferable from the viewpoint of reducing the viscosity of an aqueous solution (electrolytic solution) containing the ketone and reducing battery resistance.
  • Carboxylic acid esters are more chemically stable than iodine than ketones, and are preferred from the viewpoint of increasing coulomb efficiency.
  • Carbonate ester is preferable in that it has a large specific gravity and has a high ability to separate an oxidation reaction product of iodide ion as a hydrophobic substance.
  • the organic compound contained in the electrolytic solution may be only one type or two or more types.
  • the content of the organic compound in the electrolytic solution is preferably 1% by volume to 50% by volume at room temperature (25 ° C.) and normal pressure, and more preferably 5% by volume to 40% by volume.
  • the content of the organic compound in the electrolytic solution is 1% by volume or more, the oxidation reaction product of iodide ions tends to be favorably separated even in a high charge rate state, and when it is 50% by volume or less, There exists a tendency for the fall of the electrical conductivity of electrolyte solution to be suppressed.
  • the content of the organic compound in the electrolyte can be identified, for example, by measuring the retention time corresponding to the concentration of the organic compound and the molecular weight of the monitor ion by gas chromatography.
  • the electrolytic solution may contain a supporting electrolyte salt.
  • the supporting electrolyte salt functions as an auxiliary agent for increasing the ionic conductivity of the electrolytic solution.
  • the electrolytic solution contains the supporting electrolyte salt, the ionic conductivity of the electrolytic solution is increased, and the internal resistance of the aqueous secondary battery tends to be reduced.
  • the supporting electrolyte salt is not particularly limited as long as it is a compound that dissociates in the electrolytic solution to form ions.
  • Examples thereof include a lithium salt, an alkyl piperidinium salt, and an alkyl pyrrolidinium salt.
  • the supporting electrolyte salt may be used alone or in combination of two or more. Further, the salt containing iodine can serve as both the positive electrode active material and the supporting electrolyte salt.
  • the electrolytic solution may contain a pH buffer.
  • the pH buffering agent include acetate buffer, phosphate buffer, citrate buffer, borate buffer, tartaric buffer, Tris buffer, and the like.
  • FIG. 1 is a schematic cross-sectional view showing an example of a configuration example of the aqueous solution type secondary battery of the present embodiment.
  • the solid arrows in FIG. 1 indicate the flow of electrons during charging, and the dotted arrows indicate the reaction of ions during charging.
  • the aqueous secondary battery shown in FIG. 1 includes a positive electrode 1, a negative electrode 2, a positive electrode active material reaction tank 3, a negative electrode active material reaction tank 4, and a diaphragm 5.
  • the positive electrode active material reaction tank 3 and the negative electrode active material reaction tank 4 contain a positive electrode electrolyte and a negative electrode electrolyte, respectively.
  • the positive electrode electrolyte contains an iodide ion as a positive electrode active material and an organic compound capable of separating the oxidation reaction product of iodide ions, and the negative electrode electrolyte contains the negative electrode active material.
  • the material of the positive electrode 1 is preferably selected from those having corrosion resistance to iodide ions contained in the positive electrode electrolyte. Specific examples include metals having high corrosion resistance such as titanium, carbon materials, and the like. From the viewpoint of cost, a carbon material is preferable.
  • the shape of the positive electrode 1 is not particularly limited. From the viewpoint of obtaining a larger output, a shape having a large specific surface area is preferable. Examples of the shape having a large specific surface area include porous bodies, felts, and papers.
  • the material of the negative electrode 2 is not particularly limited, and can be selected according to the type of the negative electrode active material to be used. For example, when zinc is used as the negative electrode active material, a carbon material, zinc, zinc-plated metal material or the like in which zinc is deposited on the surface is used as the negative electrode. Examples of the shape of the negative electrode 2 include a mesh, a porous body, a punching metal, and a flat plate, but are not particularly limited.
  • the positive electrode electrolyte contained in the positive electrode active material reaction vessel 3 contains iodide ions as the positive electrode active material.
  • the positive electrode electrolyte solution containing iodide ions can be prepared by dissolving an iodine compound in the electrolyte solution.
  • an iodine compound sodium iodide, potassium iodide, zinc iodide, hydrogen iodide, lithium iodide, ammonium iodide, barium iodide, calcium iodide, magnesium iodide, strontium iodide and the like can be used.
  • the concentration of iodide ion in the positive electrode electrolyte is not particularly limited, but is preferably 0.01M to 20M, and more preferably 0.1M to 10M.
  • concentration is 0.01 M or more, a sufficient energy density tends to be obtained, and when it is 20 M or less, the organic compound described later tends to be sufficiently dissolved in the positive electrode electrolyte.
  • the negative electrode electrolyte contained in the negative electrode active material reaction vessel 4 contains a negative electrode active material (X + ).
  • a reduction reaction product (X) is generated by the reduction reaction of the negative electrode active material.
  • the negative electrode active material is not particularly limited as long as the standard redox potential of the reaction system is lower than the standard redox potential of the positive electrode (0.536 V when the positive electrode active material is iodide ion).
  • ions such as zinc, chromium, titanium, iron, tin, vanadium, lead, manganese, cobalt, nickel, copper, lithium, quinone materials, viologen, and the like can be given.
  • metal ions are preferable, and zinc ions are more preferable.
  • Zinc ions are more soluble in water than other metal ions (for example, zinc chloride has a solubility of 30 M or more), have a low standard oxidation-reduction potential for dissolution and precipitation ( ⁇ 0.76 V), and are inexpensive.
  • the negative electrode electrolyte containing metal ions can be prepared by dissolving the metal compound in the electrolyte.
  • a negative electrode electrolyte containing zinc ions can be prepared by dissolving a zinc compound such as zinc chloride, zinc iodide, zinc bromide, zinc fluoride, zinc nitrate, zinc sulfate, and zinc acetate.
  • the diaphragm 5 serves to separate the positive electrode electrolyte and the negative electrode electrolyte.
  • the material of the diaphragm 5 is not particularly limited.
  • an ion exchange membrane having excellent acid resistance and high ion conductivity can be mentioned as a preferable example, but a porous membrane, a glass filter, and the like can also be suitably used.
  • FIG. 2 is a schematic cross-sectional view showing a configuration in the case where the aqueous secondary battery shown in FIG. 1 further includes a device for causing the electrolyte to flow. Descriptions of elements provided in the aqueous secondary battery shown in FIG. 2 that are the same as those provided in the aqueous secondary battery shown in FIG. 1 are omitted.
  • a positive electrode 1 includes a positive electrode 1, a negative electrode 2, a positive electrode active material reaction tank 3, a negative electrode active material reaction tank 4, and a diaphragm 5. Furthermore, a positive electrode electrolyte storage tank 6 and a positive electrode electrolyte feed pump 8 for supplying the positive electrode electrolyte to the positive electrode active material reaction tank 3, and a negative electrode electrolysis for supplying the negative electrode electrolyte to the negative electrode active material reaction tank 4.
  • a liquid storage tank 7 and a negative electrode electrolyte feed pump 9, and an external power source 10 that drives the positive electrode electrolyte feed pump 8 and the negative electrode electrolyte feed pump 9 are provided.
  • the arrow indicates the direction in which the electrolyte flows.
  • the positive electrode electrolyte is supplied from the positive electrode electrolyte storage tank 6 to the positive electrode active material reaction tank 3 by the positive electrode electrolyte feed pump 8, and the oxidation-reduction reaction of iodine proceeds.
  • the negative electrode electrolyte is supplied from the negative electrode electrolyte storage tank 7 to the negative electrode active material reaction tank 4 by the negative electrode electrolyte feed pump 9, and the redox reaction of the negative electrode active material proceeds.
  • the positive electrode electrolyte feed pump 8 and the negative electrode electrolyte feed pump 9 are driven by an external power source 10.
  • a battery that charges and discharges by flowing an electrolyte is called a redox flow battery.
  • the redox flow battery has an advantage that the capacity can be easily increased by increasing the capacity of the tank for storing the electrolyte because the battery capacity depends on the amount of the electrolyte.
  • circulation of the electrolyte promotes dissolution of the iodine film by the organic compounds contained in the electrolyte, effectively suppressing the formation of the iodine film and effectively preventing clogging of the flow path by the iodine film. Is done.
  • the flow of the electrolyte in the aqueous secondary battery is performed by driving the positive electrolyte feed pump 8 and the negative electrolyte feed pump 9 by the external power source 10. You may drive the positive electrode electrolyte liquid feed pump 8 and the negative electrode electrolyte liquid feed pump 9 using the electric power by the next battery itself.
  • the configuration is a self-supporting system with no external power supply.
  • the aqueous secondary battery of this embodiment includes a positive electrode, a negative electrode, and an electrolytic solution, and the electrolytic solution can separate iodide ions, a negative electrode active material, and an oxidation reaction product of the iodide ions.
  • An organic compound An organic compound.
  • the aqueous secondary battery of the present embodiment is not divided into a positive electrode electrolyte containing a positive electrode active material (iodide ion) and a negative electrode electrolyte containing a negative electrode active material, and the same electrolyte is a positive electrode active material. (Iodide ion) and a negative electrode active material are contained.
  • the aqueous secondary battery having such a configuration is also referred to as “one-component aqueous secondary battery”.
  • aqueous secondary battery of the present embodiment details and preferred aspects of the positive electrode, the negative electrode, the electrolytic solution, the active material (the positive electrode active material and the negative electrode active material), the organic compound and the like are the aqueous solution secondary battery of the first embodiment.
  • FIG. 3 is a schematic cross-sectional view showing an example of the configuration example of the aqueous solution type secondary battery of the present embodiment. Solid arrows indicate the flow of electrons during charging, and dotted arrows indicate the reaction of ions during charging.
  • the aqueous secondary battery shown in FIG. 3 includes a positive electrode 1, a negative electrode 2, and an active material reaction tank 11.
  • the active material reaction tank 11 contains an electrolytic solution.
  • the electrolyte contains an iodide ion as a positive electrode active material, a negative electrode active material, and an organic compound capable of separating an oxidation reaction product of iodide ions.
  • the positive electrode is preferably located below the negative electrode in the vertical direction. Since the positive electrode is positioned below the negative electrode, the oxidation reaction product of iodide ions separated by the organic compound is precipitated in the electrolytic solution and collected on the positive electrode side. Thereby, the oxidation reaction product of iodide ions can be effectively used for the reduction reaction at the positive electrode.
  • the aqueous secondary battery of the present embodiment it is preferable to use a material having a property that the reduction reaction product stays in the vicinity of the negative electrode as the negative electrode active material.
  • generated with the positive electrode and the negative electrode can respectively exist in the positive electrode side and the negative electrode side, respectively, and it becomes possible to isolate
  • an aqueous secondary battery as a one-pack type are: (1) The diaphragm disposed between the positive electrode and the negative electrode can be omitted. (2) Water molecules move between the positive electrode side and the negative electrode side during charging and discharging. (3) Because the oxidation reaction product of iodide ions separated by the organic compound is precipitated and collects on the positive electrode side, the electrolyte solution is made to flow. (4) When a device for flowing the electrolyte is provided, it is not necessary to distinguish between the positive electrode side and the negative electrode side, and the configuration can be simplified.
  • the aqueous secondary battery of this embodiment may include a diaphragm 5 between the positive electrode 1 and the negative electrode 2.
  • FIG. 4 is a schematic cross-sectional view showing a configuration when the aqueous secondary battery shown in FIG. 3 further includes a diaphragm 5 between the positive electrode 1 and the negative electrode 2. Descriptions of elements provided in the aqueous secondary battery shown in the figure that are common to those provided in the aqueous secondary battery shown in FIG. 1 are omitted.
  • the details and preferred aspects of the diaphragm 5 provided in the aqueous secondary battery shown in FIG. 4 are the same as the details and preferred aspects of the diaphragm 5 provided in the aqueous secondary battery of the first embodiment.
  • the aqueous solution type secondary battery of the present embodiment may further include a device for flowing the electrolytic solution.
  • FIG. 5 shows an electrolytic solution storage tank 12 for supplying the electrolytic solution to the active material reaction tank 11 and an electrolytic solution feed pump 13 as devices for allowing the aqueous secondary battery shown in FIG. 4 to flow the electrolytic solution.
  • FIG. 2 is a schematic cross-sectional view showing a configuration in a case where the apparatus further includes an external power source 10 that drives the electrolyte solution pump 13.
  • the aqueous solution type secondary battery shown in FIG. 5 includes both the diaphragm 5 and a device for causing the electrolyte to flow, an embodiment without the diaphragm 5 may be used.
  • the arrow indicates the direction in which the electrolyte flows.
  • the electrolytic solution is supplied from the electrolytic solution storage tank 12 to the active material reaction tank 11 by the electrolytic solution feeding pump 13.
  • An oxidation-reduction reaction of iodide ions proceeds at the positive electrode, and an oxidation reaction product is generated during the oxidation reaction.
  • the negative electrode the redox reaction of the negative electrode active material proceeds, and a reduction reaction product is generated during the reduction reaction.
  • the electrolyte solution feed pump 13 is driven by the external power supply 10.
  • the flow of the electrolyte in the aqueous secondary battery is performed by driving the electrolyte feed pump 13 by the external power source 10, but the electric power generated by the aqueous secondary battery itself is used.
  • the electrolyte solution pump 13 may be driven.
  • the configuration is a self-supporting system with no external power supply.
  • the charge / discharge method for an aqueous secondary battery of the present embodiment (hereinafter also simply referred to as charge / discharge method) is a charge / discharge method for an aqueous secondary battery using an electrolytic solution containing iodide ions as a positive electrode active material. And a step of separating an oxidation reaction product of iodide ions generated in the electrolytic solution.
  • the charging / discharging method When the charging / discharging method is applied as a charging / discharging method for an aqueous secondary battery, an oxidation reaction product of iodide ions generated by charging is selectively separated from the electrolytic solution. As a result, dissolution of the high-resistance iodine film formed on the electrode surface is promoted, and a decrease in the oxidation current value is suppressed. I 2 molecules diffused from the iodine film into the electrolyte solution sublimate outside the system. Suppressed and reduced concentration of iodide ion in the electrolyte solution, because the separated oxidation reaction product is used for the reduction reaction at the positive electrode, improving the output characteristics of the aqueous secondary battery at low charge rate Can be expected.
  • the method for separating the oxidation reaction product of iodide ions generated in the electrolytic solution is not particularly limited.
  • a method of separating an oxidation reaction product of iodide ions using an electrolytic solution used in the above-described aqueous secondary battery can be mentioned.
  • the electrolytic solution for an aqueous secondary battery of the present embodiment includes water, iodide ions, and an organic compound capable of separating an oxidation reaction product of iodide ions, It is used as an electrolytic solution for the above-described charge / discharge method of an aqueous secondary battery.
  • the electrolytic solution for an aqueous secondary battery of the present embodiment is at least one selected from the group consisting of water, iodide ions, methyl ethyl ketone, methyl acetate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.
  • An organic compound is at least one selected from the group consisting of water, iodide ions, methyl ethyl ketone, methyl acetate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.
  • the electrolytic solution of each of the above embodiments is used in an aqueous secondary battery
  • the oxidation reaction product of iodide ions generated by charging is selectively separated from the electrolytic solution.
  • dissolution of the high-resistance iodine film formed on the electrode surface is promoted, and a decrease in the oxidation current value is suppressed.
  • I 2 molecules diffused from the iodine film into the electrolyte solution sublimate outside the system. Suppressed and reduced concentration of iodide ion in the electrolyte solution, because the separated oxidation reaction product is used for the reduction reaction at the positive electrode, improving the output characteristics of the aqueous secondary battery at low charge rate We can expect effects such as being able to.
  • iodide ions and organic compounds contained in the electrolytic solution are the same as the details and preferred embodiments of iodide ions and organic compounds contained in the electrolytic solution used in the above-described aqueous secondary battery.
  • ⁇ Flow battery system Flow battery system of this embodiment, the aqueous secondary battery described above, by controlling the charging and discharging, a charging potential of the positive electrode, Ag / AgCl reference electrode - 1.5V or less relative to the potential of (Cl concentration saturation) And a control unit to be set.
  • the details and preferred embodiments of the aqueous secondary battery used in the flow battery system are the same as the details and preferred embodiments of the aqueous secondary battery described above.
  • the controller in the flow battery system may be in a state of being integrated with the aqueous secondary battery or not.
  • the charging potential of the positive electrode is preferably set to 1.3 V or less, and preferably set to 1.05 V or less, based on the potential of the Ag / AgCl reference electrode (Cl ⁇ concentration saturation). More preferred.
  • the charge potential of the positive electrode, Ag / AgCl reference electrode - describes the benefits of controlling so as not to exceed the reference value as a reference to the potential of (Cl concentration saturation).
  • the positive electrode electrolyte contains iodide ions as the positive electrode active material.
  • iodide ions (I ⁇ ) are oxidized at the positive electrode by the charging reaction shown in the following formulas (1) and (2) to normally generate I 3 ⁇ and I 2 , and the generated I 3 ⁇ And I 2 are reduced to I ⁇ by the discharge reaction shown in the formulas (1) and (2) at the positive electrode.
  • the reaction represented by the above formula (3) is reported to be an irreversible reaction, and the reaction rate of the reverse reaction is extremely small.
  • I 2 is generated from IO 3 ⁇ generated by the above formula (3) by the Dushman reaction represented by the following formula (4).
  • the chemical reaction rate of the above formula (4) is faster than the electrochemical reaction of the above formula (3), and the formula (5) in which the formula (3) and the formula (4) are constituent reactions.
  • the rate limiting process is the electrochemical reaction of formula (3). Therefore, the charge potential of the positive electrode, Ag / AgCl reference electrode - becomes particularly noticeable if it exceeds 1.05V relative to the potential of (Cl concentration saturation), 1.3V taking a safety margin, the 1.5V It may be set so as not to exceed, and it is estimated that the reactions of the above formulas (3) to (5) occur.
  • IO 3 ⁇ is generated based on the equation (3) by the positive electrode charging reaction.
  • IO 3 ⁇ has a slow reaction rate of the discharge reaction, which is the reverse reaction of the formula (3), and hardly returns to I ⁇ .
  • Equation (5) is the total reaction of the formula (3) and (4), IO 3 by the reaction I 2 - but is produced, in the same manner as in the reaction shown in equation (3)
  • the reaction shown in Formula (5) is also an irreversible reaction. For this reason, the generated IO 3 ⁇ has a slow reaction rate of the discharge reaction, which is the reverse reaction of the formula (5), and hardly returns to I 2 .
  • the proportion of IO 3 ⁇ that does not contribute to the discharge reaction increases, and the total concentration of I ⁇ and I 2 decreases, so that the flow gradually increases.
  • the battery system has a problem that the positive electrode discharge capacity and the positive electrode charge capacity decrease.
  • the flow cell system of the present embodiment controls the charging and discharging, a charging potential of the positive electrode, Ag / AgCl reference electrode - a control unit that sets below 1.05V relative to the potential of (Cl concentration saturation) ing.
  • Ag / AgCl reference electrode - can set the potential of the (Cl concentration saturation) below 1.5V as a reference
  • IO 3 during charging of the flow cell system - can inhibit the production reaction of.
  • the positive electrode discharge capacity and the positive electrode charge capacity can be maintained by maintaining the total concentration of iodine ions and iodine molecules when reversibly charging and discharging. Therefore, in this embodiment, a flow battery system that satisfies a practical charge condition can be provided.
  • the charge potential of the positive electrode in the flow battery system is not the charge voltage.
  • the charging potential is a voltage indicated with respect to an electrode having a certain reference potential.
  • the charging voltage is the difference in potential between the negative electrode and the positive electrode. Since the charging potential is based on a constant potential as a reference, if the potential is constant, it can be regarded as a constant value with respect to the reference electrode. However, in the case of a charging voltage between the negative electrode and the positive electrode, when the potential fluctuates in the same way between the negative electrode and the positive electrode, the voltage is apparently constant. Therefore, the potential of the positive electrode is not determined by the charging voltage, and needs to be measured with respect to the potential of the reference electrode for positive electrode serving as a reference.
  • Flow battery system controls the charging and discharging, a charging potential of the positive electrode, Ag / AgCl reference electrode - a control unit for setting a potential of (Cl concentration saturation) to 1.5V below as a reference.
  • Ag / AgCl reference electrode - can set the potential of the (Cl concentration saturation) below 1.5V as a reference
  • IO 3 during charging of the flow cell system - can inhibit the production reaction of.
  • the total concentration of iodine ions and iodine molecules (I ⁇ , I 3 ⁇ and I 2 ) during reversible charge / discharge is maintained, and the positive electrode discharge capacity and the positive electrode charge capacity are increased. Reduction is suppressed and cycle durability can be improved.
  • the positive electrode charging potential is set to 1.5 V or less with respect to the potential of the Ag / AgCl reference electrode (Cl ⁇ concentration saturation)” in principle means that the positive electrode charging potential is 1.5 V or less. It means that the flow battery is charged, and it is allowed that the charging potential of the positive electrode exceeds 1.5V. For example, when it is unavoidable that the charging potential of the positive electrode exceeds 1.5 V due to the influence of ripple noise or the like described later, the charging potential of the positive electrode may exceed 1.5 V.
  • control unit performs constant current charging until reaching the set voltage under the condition that the charging potential of the positive electrode does not exceed 1.5 V (vs. Ag / AgCl), and performs constant voltage charging after reaching the set voltage. Control the flow battery.
  • the control unit, the charging potential of the positive electrode, Ag / AgCl reference electrode - it is preferable to control the potential of the (Cl concentration saturation) to 1.5V below as a reference.
  • the charging potential of the positive electrode By controlling the charging potential of the positive electrode to 1.5 V (vs. Ag / AgCl) or less, deterioration of the positive electrode (particularly, carbon electrode) tends to be suppressed.
  • the positive electrode electrolyte contains ethanol as a good solvent for iodine molecules, the decomposition of ethanol is further suppressed by controlling the positive electrode charging potential to 1.5 V (vs. Ag / AgCl) or lower. There is a tendency.
  • the charging potential of the positive electrode is controlled to 1.5 V or less with respect to the potential of the Ag / AgCl reference electrode (Cl ⁇ concentration saturation)” means that the charging potential of the positive electrode is 1.5 V or less and the flow battery is charged. And the charge potential of the positive electrode is not allowed to exceed 1.5V.
  • the control unit sets the flow battery so as to cut the excess by a high frequency filter or the like. Control. If the charge potential of the positive electrode falls within the range of 1.05 V to 1.5 V (vs. Ag / AgCl) even if ripple noise described later is superimposed, the control unit does not have to perform special control. This is because the generation reaction of IO 3 ⁇ represented by the above-described equation (3) is considered difficult to follow a high-frequency signal such as ripple noise.
  • the charging potential of the positive electrode, Ag / AgCl reference electrode - is preferably set to less than 1.5V relative to the potential of (Cl concentration saturation), more be set below 1.3V Preferably, it is more preferably set to 1.05 V or less.
  • the positive electrode electrolyte may be periodically sampled during the operation period using a sampling unit described later. It is also possible to adjust the concentration of the component contained in the positive electrode electrolyte by adding the electrolyte or the component contained therein to the positive electrode.
  • the flow battery system may include a positive electrode reference electrode for measuring the positive electrode potential.
  • the reference electrode for a positive electrode may be any one that can be converted into a potential with respect to a standard hydrogen electrode potential and can exhibit a stable electrochemical potential.
  • a reference electrode serving as an electrochemical potential standard is shown in many textbooks as basics of electrochemistry (for example, Allen J. Bard and Larry R. Faulkner, “ELECTROCHEMICAL METHODS” p. 3, (1980), John. Wiley & Sons, Inc.). Examples of the reference electrode include an Ag / AgCl reference electrode, a saturated calomel electrode, and the like, and an Ag / AgCl reference electrode is preferable.
  • the positive electrode for the reference electrode the potential of the measured cathode Ag / AgCl reference electrode - as long as it can be converted to the potential of (Cl concentration sat) is not limited to Ag / AgCl reference electrode, the other reference electrode It may be used.
  • the flow battery system may further include a negative electrode reference electrode for measuring the negative electrode potential.
  • the reference electrode may be provided at one location on the positive electrode, preferably at one location on each of the positive and negative electrodes, and more preferably at a plurality of locations on each of the positive and negative electrodes.
  • the flow battery system may include a sampling unit that samples the positive electrode electrolyte.
  • a sampling unit that samples the positive electrode electrolyte.
  • concentration of the component contained in the positive electrode electrolyte is adjusted to a specified amount, a required amount, etc. It is possible to analyze whether there is a shortage.
  • the sampling unit may be disposed, for example, in the positive electrode electrolyte storage tank, or may be disposed in the circulation path. Moreover, the structure which samples a positive electrode electrolyte solution for every predetermined time may be sufficient as a sampling part.
  • the flow battery system analyzes the positive electrode electrolyte sampled by the sampling unit, and adjusts the concentration of components contained in the positive electrode electrolyte circulating between the positive electrode and the positive electrode electrolyte storage tank based on the analysis result.
  • a density adjusting unit may be provided. Since the flow battery system includes a concentration adjusting unit, when the concentration of the component contained in the positive electrode electrolyte sampled by the sampling unit is insufficient compared to the specified amount, the required amount, etc., the insufficient component is positive electrode electrolysis. The concentration of components added to the liquid and contained in the positive electrode electrolyte can be adjusted.
  • the concentration adjusting unit may be configured to add each component to the positive electrode electrolyte stored in the positive electrode electrolyte storage tank, or may be configured to add each component to the positive electrode electrolyte flowing through the circulation path. May be.
  • the addition of the iodine compound, additive, etc. to the positive electrode electrolyte may be during operation of the flow battery or may be stopped.
  • the flow battery system may include a potential measurement unit that measures a potential based on the concentrations of iodine ions and iodine molecules in the positive electrode electrolyte.
  • the potential measuring unit has, for example, a collecting electrode for measuring a potential based on the concentrations of iodine ions and iodine molecules, and a reference electrode serving as a reference for the electrochemical potential, and measures the electrochemical potential based on the reference electrode To do.
  • the concentration of iodine ions and iodine molecules can be determined from the measured electrochemical potential of the reference electrode standard.
  • the collecting electrode include a platinum electrode and a graphite electrode
  • examples of the reference electrode include an Ag / AgCl electrode.
  • the control unit can estimate a state of charge (SOC) based on the potential measured by the potential measurement unit.
  • SOC state of charge
  • the SOC of 0% basically means that I 3 ⁇ and I 2 are not included in the positive electrode electrolyte, and only I ⁇ . It shows the state.
  • An SOC of 100% basically indicates a state in which I ⁇ is not contained in the positive electrode electrolyte, but only I 3 ⁇ and I 2 .
  • the potential measuring unit may be disposed, for example, in a positive electrode electrolyte storage tank or may be disposed in a circulation path through which the positive electrode electrolyte circulates.
  • the flow battery system 100 includes a positive electrode 111, a negative electrode 112, a diaphragm 115, a positive electrode reference electrode 113, a positive electrode electrolyte 116, a positive electrode electrolyte storage tank 118, and a negative electrode electrolyte 117.
  • a negative electrolyte storage tank 119 When a negative electrolyte storage tank 119, a circulation path 120, 121 and pumps 122, 123 as a liquid feed unit, to control the charging and discharging, a charging potential of the positive electrode, Ag / AgCl reference electrode - of (Cl concentration saturation) A control unit (not shown) that sets the potential to 1.05 V or less with reference to the potential is provided.
  • each component which comprises the flow battery system 100 is as above-mentioned.
  • the flow battery system 100 shown in FIG. 6 includes a cell stack 130 including a plurality of single cells each including a positive electrode 111, a negative electrode 112, and a diaphragm 115.
  • FIG. 6 shows the cell stack 130 having five single cells, the number of single cells is not particularly limited.
  • the positive electrode reference electrode 113 and the negative electrode reference electrode 114 are arranged on the positive electrode 111 and the negative electrode 112 constituting the cell stack, and potential measurement using the reference electrode is possible. It has become.
  • a sampling unit 124 that samples the positive electrode electrolyte 116 and a potential measurement unit 125 that measures a potential based on the concentrations of iodine ions and iodine molecules in the positive electrode electrolyte 116 include a positive electrode electrolyte.
  • the positive electrode electrolyte 116 is circulated between the positive electrode chamber in which the positive electrode 111 is arranged and the positive electrode electrolyte storage tank 118, and the negative electrode chamber and the negative electrode electrolyte in which the negative electrode 112 is arranged.
  • Circulation paths 120 and 121 for circulating the negative electrode electrolyte 117 between the storage tank 119 and the liquid feed pumps 122 and 123 are arranged as a liquid feed section.
  • Charging / discharging of the flow battery system 100 is controlled by a control unit (not shown).
  • the control unit can set the charging potential of the positive electrode to 1.5 V (vs. Ag / AgCl) or less.
  • the power generation system of the present embodiment includes a power generation device and the above-described flow battery system.
  • the power generation system of this embodiment can level and stabilize power fluctuations or stabilize power supply and demand by combining a flow battery system and a power generation device.
  • the power generation system includes a power generation device.
  • the type of the power generation device is not particularly limited, and examples thereof include a power generation device that generates power using renewable energy, a hydroelectric power generation device, a thermal power generation device, and a nuclear power generation device. Among these, a power generation device that generates power using renewable energy is preferable.
  • the amount of power generated by power generators using renewable energy varies greatly depending on weather conditions, etc., but when combined with a flow battery system, the generated power can be leveled and supplied to the power system. .
  • Renewable energy includes wind power, sunlight, wave power, tidal power, running water, tide, geothermal heat, etc., preferably wind power or sunlight.
  • the generated power generated using renewable energy such as wind power and sunlight may be supplied to a high-voltage power system.
  • wind power generation and solar power generation are affected by weather such as wind direction, wind power, and weather, and thus generated power is not constant and tends to fluctuate greatly.
  • the generated power that is not constant is supplied to the high-voltage power system as it is, it is not preferable because it promotes instability of the power system.
  • the power generation system of the present embodiment can level the generated power waveform to the target power fluctuation level by superimposing the charge / discharge waveform of the flow battery system on the generated power waveform.
  • a charging potential exceeding 1.5 V (vs. Ag / AgCl) per unit cell of the flow battery system is used to supply power to the high voltage system.
  • the charging potential of the positive electrode of the single cell is 1.5 V (vs. Ag / AgCl)
  • the entire charging voltage of the single cell that is, the potential difference between the positive electrode and the negative electrode exceeds 3 V.
  • the charging voltage of each cell stack is 60V.
  • the charging voltage is 600V.
  • the flow battery system is charged by converting AC power generated by wind power generation or the like into DC power using an inverter. For this reason, the voltage range of the charge control voltage is determined in the relationship between the cell stack of the flow battery system and the output of the inverter.
  • the charging voltage applied to each single cell increases. Conversely, when the number of single cell series in the cell stack is large, the charging voltage applied to each single cell becomes small. Therefore, when a flow battery system is installed in a power generation system using renewable energy, the charging voltage applied per single cell of the flow battery system is determined based on the inverter output and the number of single cells in series in the cell stack as basic parameters. .
  • FIG. 7 is a configuration diagram when the power generation system is applied to the wind power generation field.
  • FB Flow Battery
  • PCS Power Conditioning System
  • 7 corresponds to the flow battery system of the present embodiment described above.
  • the generated power waveform shown in FIG. 7 is an example of a power waveform generated by the wind power generator.
  • the generated power varies greatly depending on the strength of the wind and the wind direction.
  • a power system such as a transmission line, it affects the stabilization of the power system. Therefore, when supplying electric power from wind power generation to the power system, it is necessary to suppress fluctuations in the power of the power system.
  • a charge / discharge waveform that reduces fluctuations in the generated power waveform is output from the flow battery system and superimposed on the generated power waveform.
  • the flow battery system plays a role of leveling generated power obtained by wind power generation and supplying it as stabilized power.
  • the power waveform when the power waveform of wind power generation is viewed on a shorter time scale is shown in FIG. While the power waveform in the relatively long time region shown in the region (a) and the region (b) in FIG. 8 is seen, the power waveform is shorter than the region (a), the region (a) and the region (b) In the meantime, in the three time regions on the longer side than the region (b), a pulse-like power generation waveform in the order of microseconds to milliseconds is seen.
  • the flow battery system uses the target output of the wind power generated for a certain time width as the central value, and if the generated power is lower than that, the power is supplemented by discharging, and if it exceeds the target output, the generated power is charged. However, charging / discharging may be controlled so as to approach the target output.
  • the inverter is a converter for exchanging power between the charge / discharge signal of the flow battery, which is DC information, and the generated power. Charging the flow battery is performed by converting AC power from the wind power generator into DC power. Inverters tend to generate pulsed high-frequency signals called ripple noise. Generally, these high-frequency signals can be removed by installing a capacitor that can support each frequency band in the PCS. However, in PCS in which these measures are not taken, a high-frequency ripple signal is applied to the flow battery.
  • the power signal supplied to the flow battery including ripple noise generated from the inverter, includes a high-frequency power signal that exceeds the following capability of the flow battery.
  • the power is basically converted into heat. This heat tends to concentrate on the electrode terminals of the flow battery, and tends to adversely affect the constituent materials of the flow battery.
  • the charging voltage applied per single cell of the flow battery system is determined based on the inverter output and the number of single cells in series in the cell stack as basic parameters. There is also a relationship. Therefore, it is preferable to design the flow battery system so that the charging potential of the positive electrode is 1.5 V (vs. Ag / AgCl) or less in consideration of the number of single cells in series, the number of cell stacks, and the charging voltage. Even if the design must accept that the voltage exceeds 1.5 V, the charge potential of the positive electrode can be controlled to 1.5 V (vs. Ag / AgCl) or less in order to ensure the life of the flow battery system. preferable.
  • the positive electrode electrolyte and the negative electrode electrolyte are included during the operation period. It is preferred to carry out the addition of the components. However, when a volatile component is included, it is preferable to analyze periodically even in an operating environment where the charge potential of the positive electrode does not exceed 1.5 V, and add the component if necessary.
  • the power generation system may be a system that controls charging / discharging of the flow battery system in accordance with the supply and demand of the generated power generated by the power generation device. For example, when the supply amount of the generated power generated by the power generation device exceeds the demand amount in the power system, the flow battery system performs charging, and the supply amount of the generated power generated by the power generation device is the demand in the power system. When the amount is lower, the power generation system may be controlled so that the flow battery system discharges.
  • the power generation system combines a power generation device using renewable energy and a flow battery system, so that the flow battery system functions as a low-cost, high-energy density power storage system, and further reduces CO2 emissions. It helps to solve the global problem of suppressing global warming.
  • the iodine film chemically reacts with iodide ions in the bulk aqueous solution and dissolves as triiodide ions (I 3 ⁇ ) (I ⁇ + I 2 ⁇ I 3 ⁇ ).
  • the iodine film grows on the electrode surface and the electrical resistance increases. Therefore, the oxidation current value is limited by the iodine film, and a steady state is obtained at a current value at which formation and dissolution of the iodine film antagonize.
  • the current value (mA) in a steady state where the current value is constant is about 30% higher than when the electrolytic solution without adding methyl ethyl ketone is used. It was. From the above results, it was found that by adding an organic compound to the electrolytic solution, dissolution of the iodine film was promoted, and the oxidation current value was improved.
  • FIG. 10 is a photograph of the hydrophobic substance generated when the measurement of FIG. 9 is performed.
  • This hydrophobic substance was in a liquid state, had a higher methyl ethyl ketone concentration than the bulk aqueous solution, and contained iodide ions and their oxidation reaction products, cations and water. Moreover, the produced
  • FIG. 11 is a graph showing an oxidation current value at an oxidation potential and a reduction current value at a reduction potential observed in a hydrophobic substance containing methyl ethyl ketone and an oxidation reaction product of iodide ions. is there.
  • the vertical axis in the graph represents current value (mA)
  • the horizontal axis represents time (s)
  • a positive current value represents an oxidation current value
  • a negative current value represents a reduction current value.
  • both an oxidation current and a reduction current were observed. From the above results, it was confirmed that both the oxidation reaction and the reduction reaction proceed in the hydrophobic substance.
  • FIG. 12 is a graph showing a potential waveform of normal pulse voltammetry performed in Example 2.
  • Ei represents an initial potential
  • ⁇ Es represents a pulse increment
  • tp represents a pulse width
  • ⁇ represents a pulse period.
  • the potential waveform shown in FIG. 12 was input to an electrochemical cell using a potentiostat as an electrochemical measuring device, and current values corresponding to each pulse potential and pulse time were measured.
  • the potentiostat is a general device in electrochemical measurement, and is controlled based on the electrochemical reaction that proceeds at the working electrode by controlling the pulse potential shown in FIG. 12 with respect to the reference electrode potential serving as a potential reference. It is a device that detects current.
  • a counter electrode is provided so that a current flows through the counter electrode.
  • the input resistance of the reference electrode is very large and is a direct current resistance, usually at a level of 10 14 ohms, and the current of the electrochemical reaction proceeding at the working electrode is in a circuit configuration that flows to the counter electrode.
  • the potentiostat includes a reference electrode serving as a potential reference, a working electrode subject to potential control, and a counter electrode. Recently, with the development of microcomputers, the normal pulse voltammetry waveform shown in FIG. 12 is generally integrated with the potentiostat function and can be programmed.
  • FIG. 13A and 13B are graphs showing normal pulse voltammograms obtained in Example 2 (pulse width 50 ms).
  • a voltammogram is a current-potential curve in which the current observed based on an electrochemical reaction is plotted against the potential.
  • 13A and 13B the horizontal axis represents potential (V vs. Ag / AgCl), and the vertical axis represents current density (mA / cm 2 ).
  • the current density is a value obtained by dividing the current value 50 ms after the step to the oxidation potential by the electrode area (the same applies hereinafter). The measurement was performed in an environment with a liquid temperature of 25 ° C.
  • FIG. 14 is a graph showing a potential waveform of reverse pulse voltammetry performed in Example 2.
  • Reverse pulse voltammetry can be performed using a programmed potentiostat similar to normal pulse voltammetry.
  • Ei is an initial potential
  • Ec is a potential at which a reaction of interest does not proceed (conditioning potential)
  • ⁇ Es is a reverse pulse potential increment
  • tc is a time for holding in Ec
  • td is a time for holding in Ei
  • tp is a reverse pulse width.
  • Ec was an immersion potential
  • ⁇ Es 0.05 V
  • tc 10 s
  • td 2 s.
  • Reverse pulse voltammetry has a function that allows more detailed examination of the behavior of the oxidation reaction of I ⁇ obtained by normal pulse voltammetry. That is, it can be verified what electrochemical behavior the product generated at the initial potential shows. When what is generated at the initial potential is an oxidation reaction product, when the reverse pulse potential reaches a certain potential region, the behavior of the reduction reaction of the oxidation reaction product can be captured.
  • the pulse potential of the reverse pulse is repeatedly incremented by the reverse pulse potential, and is stepped in the base direction with the initial potential Ei as the starting potential.
  • the oxidation potential reduction reaction is held at the conditioning potential Ec that is least likely to proceed.
  • the time (tc) during which the boundary condition of the working electrode recovers to the same level as before the reaction is held at the conditioning potential Ec.
  • the potential is stepped to the initial potential Ei, and an oxidation reaction (generally an oxidation or reduction reaction) proceeds on the working electrode during td.
  • a reverse pulse is applied. By repeating this, reverse pulse voltammetry is performed, and based on the relationship between the obtained reverse pulse current and potential, the reaction itself, the reaction mechanism, and the like can be examined closely.
  • FIGS. 15A and 15B are reverse pulse voltammograms performed in Example 2 (initial potentials 0.50 V, 0.55 V, and pulse width 50 ms).
  • FIGS. 15A and 15B are graphs showing the relationship between the step potential and the current value after being held at the initial potential (0.50 V, 0.55 V for 2 seconds).
  • FIG. 15A shows a solution containing 95 vol% of 20 mM sodium iodide aqueous solution containing 1 M sodium perchlorate and 5 vol% methyl ethyl ketone as the supporting electrolyte, and glassy carbon (diameter: 1.6 mm) for the electrode. And the result when the pulse width of the reverse pulse is 50 ms is shown.
  • 15B shows a solution containing 95 vol% of 20 mM sodium iodide aqueous solution containing 1 M sodium perchlorate as a supporting electrolyte and 5 vol% of propylene carbonate as an electrolyte, and glassy carbon (1.6 mm diameter) as an electrode. ) And the pulse width of the reverse pulse is 50 ms.
  • FIG. 16A and FIG. 16B are reverse pulse voltammograms carried out in Example 2, which show the effect of methyl ethyl ketone or propylene carbonate contained in the electrolyte (initial potential 0.60 V and pulse width 50 ms).
  • FIG. 16A shows a 95 mM 20 mM aqueous solution of sodium iodide containing 1 M sodium perchlorate as the supporting electrolyte and an aqueous solution containing 5 vol% of methyl ethyl ketone, and a 20 mM iodide containing 1 M sodium perchlorate as the supporting electrolyte. The results when using an aqueous sodium solution as the electrolytic solution are shown.
  • 16B shows a 95 mM 20 mM aqueous solution of sodium iodide containing 1 M sodium perchlorate as the supporting electrolyte, an aqueous solution containing 5 vol% of propylene carbonate, and a 20 mM iodine containing 1 M sodium perchlorate as the supporting electrolyte. The result when using each sodium hydroxide aqueous solution as an electrolytic solution is shown.
  • the reduction current was the same as in the case of no addition in the region of 0.3V to 0.6V, but the reduction current decreased in the region of 0.25V or less. This behavior is considered to be because the reduction of the iodine film and the dissolution of the iodine film are promoted by the inclusion of methyl ethyl ketone or propylene carbonate in the solution.
  • FIGS. 17A and 17B are reverse pulse voltammograms performed in Example 2 (initial potential 0.9 V to 1.1 V and pulse width 50 ms).
  • the initial potential is higher than the initial potential in FIGS. 16A and 16B.
  • the potential is set (similarly held for 2 seconds).
  • FIG. 17A shows the results when the conditions other than the initial potential are the same as those in FIG. 16A
  • FIG. 17B shows the results when the conditions other than the initial potential are the same as those in FIG. 16B.
  • the reduction current values observed in FIGS. 17A and 17B are roughly divided into two groups.
  • One group is the case where the initial potential is 0.9 V and 1.0 V, and it was observed that the reduction current value greatly increased as the reverse pulse potential was stepped to the base.
  • the other group is the case where the initial potential is set to 1.05V and 1.1V, and the reduction current value of the reverse pulse is lower than the case where the initial potential is set to 0.9V and 1.0V. It was. Since reverse pulse voltammetry looks at the difference in the reduction kinetics of chemical species generated at the initial potential, the difference in the reverse pulse voltammogram between these groups is considered to be the product difference due to the difference in the initial potential. Is the simplest.
  • the standard oxidation-reduction potentials of Formula (1) and Formula (2) are approximately equal at 0.536 V (standard hydrogen electrode potential), respectively. Accordingly, the oxidation reaction products of I ⁇ produced at the initial potential of reverse pulse voltammetry are I 2 and I 3 ⁇ .
  • the change of the standard electrode potential of the formula (7) with respect to the temperature is ⁇ 0.148 mV per 1 ° C. (Yuta Tamamushi, “Electrochemistry (2nd edition)” p.300, (1991), Tokyo Chemical Dojin). That is, in the environment of ⁇ 25 ° C. in which the temperature is decreased from 25 ° C. to 50 ° C., the standard electrode potential of the formula (2) is only changed by 7.4 mV from 0.536 (standard hydrogen electrode potential).
  • the electrochemical potential basically depends on the temperature, it is considered that the relationship between the battery reaction and the potential does not have a large fluctuation of the 100 mV level at the practical living environment temperature as described above.
  • Equation (3) is reported to be an irreversible reaction. Since Equation (3) is a irreversible reaction, even if the reverse pulse voltage reaches the reduction reaction area, resulting IO 3 - very small rate of reaction, the resulting IO 3 - is I by reduction - easily return to Guess that there is not.
  • I 2 is generated from IO 3 ⁇ generated by the above formula (4) by the Dushman reaction represented by the following formula (4).
  • the chemical reaction rate of the above formula (4) is faster than the electrochemical reaction of the above formula (3), and the rate limiting rate of the formula (5) using the formula (3) and the formula (4) as a constituent reaction.
  • the process is an electrochemical reaction of formula (3). Therefore, the charge potential of the positive electrode, Ag / AgCl reference electrode - presumably exceed the 1.05V reference to the potential of (Cl concentration saturation), the above reaction formula (3) to (5) has occurred Is done.
  • the reaction shown in Equation (5) is the total reaction of the formula (3) and (4), by the reaction I 2 IO 3 - but is generated in the same manner as in the reaction shown in equation (3), wherein The reaction shown in (5) is also an irreversible reaction. For this reason, it is presumed that the generated IO 3 ⁇ has a slow discharge reaction rate and is difficult to return to I 2 .
  • FIGS. 16A and 16B are reverse pulse voltammograms performed in Example 2 (initial potentials of 1.4 V, 1.5 V and a pulse width of 50 ms).
  • the initial potential is higher than the initial potential in FIGS. 16A and 16B.
  • the potential is set (similarly held for 2 seconds).
  • FIG. 18A shows the result when the same conditions as in FIG. 16A are used except for the initial potential
  • FIG. 18B shows the result when the same conditions as in FIG. 16B are used except for the initial potential.
  • the reduction current value observed by the reverse pulse is found to be lower when the initial potential is 1.5 V or more than when the initial potential is 1.4 V. It was. Further, it was found that the reduction current value tends to decrease as the initial potential is increased. From this, it was estimated that the electrode was inactivated by maintaining the initial potential at a noble potential of 1.5 V or higher.
  • Example 3 19A and 19B are normal pulse voltammograms (pulse widths 50, 500, and 5000 ms) performed in Example 3.
  • FIG. 19A shows a result when a solution containing 95% by volume of 3M sodium iodide aqueous solution and 5% by volume of methyl ethyl ketone is used as the electrolytic solution.
  • FIG. 19B shows the results when a solution containing 5 vol% of propylene carbonate in 95 vol% of 3M sodium iodide aqueous solution was used as the electrolytic solution.
  • the aqueous solution concentration on the order of 3M corresponds to the reaction active material concentration level in the actual flow battery.
  • the horizontal axis represents potential (V vs. Ag / AgCl), and the vertical axis represents current density.
  • FIG. 20A shows the results when a solution containing 95% by volume of 3M sodium iodide aqueous solution and 5% by volume of methyl ethyl ketone and a 3M sodium iodide aqueous solution were used as the electrolytes, respectively.
  • FIG. 20B shows the results when a solution containing 95% by volume of 3M sodium iodide aqueous solution and 5% by volume of methyl ethyl ketone and a 3M sodium iodide aqueous solution were used as the electrolytes, respectively.
  • Electrochemical measurement in which the concentration of the supporting electrolyte (sodium perchlorate in Example 2) is 50 times equivalent to the concentration of the reactive species of interest (I ⁇ in Example 2) is the influence of electrophoresis on mass transfer.
  • the electrochemical reaction can be observed while keeping the electric double layer structure that is an electrochemical reaction field constant. For this reason, there is an advantage that the existing electrochemical theory can be used simply in the study of the electrochemical reaction mechanism based on the absolute reaction kinetics. Therefore, in Example 2, the study on the electrochemical reaction was performed in a system containing a reactive species in the order of mM and a supporting electrolyte.
  • the electrochemical reaction was examined under the conditions of sodium iodide electrolyte solution in the actual flow battery concentration range, which does not include the supporting electrolyte, but basically it corresponds to the examination result in Example 2.
  • the charge potential control in the potential region exceeding 1.05 V is performed by the above formula (3) (I ⁇ + 3H 2 O ⁇ IO 3 ⁇ + 6H + + 6e ⁇ ) and formula (5) (I 2 + 6H 2 O ⁇ 2IO 3 ⁇ + 12H + + 10e ⁇ ), which is undesirable because IO 3 ⁇ is generated.
  • the charge potential of the flow battery containing methyl ethyl ketone or propylene carbonate in the positive electrode electrolyte does not exceed the positive electrode potential of 1.05 V (V vs. Ag / AgCl) that IO 3 ⁇ does not generate by charging. Recognize.
  • the flow path of the flow battery is narrowed by covering the positive electrode with a thick iodine film and the flow of the electrolytic solution itself is obstructed. In this respect, it is desirable that the charging potential does not exceed 1.4V.
  • the flow battery is a kind of secondary battery, and in order to stably manage the reaction active material involved in the charge / discharge reaction, the charge potential shown in Examples 2 and 3 is 1.05 V (V vs. Ag / AgCl). ) Charge control at the following potential is preferred. .
  • Example 4 Next, regarding the flow battery system shown in FIG. 6, the current potentials of the positive electrode and the negative electrode when the charge / discharge reaction was performed were examined.
  • a 1M sodium iodide (NaI) aqueous solution added with 5 vol% methyl ethyl ketone or propylene carbonate was used as the positive electrode electrolyte, and 1M chloride containing 0.5M zinc chloride (ZnCl 2 ) as the negative electrode electrolyte.
  • An ammonium (NH 4 Cl) aqueous solution was used, a carbon electrode was used as the positive electrode, and a zinc electrode (zinc coated mesh electrode) was used as the negative electrode.
  • FIG. 21 shows a schematic diagram of the electrode reaction of the flow battery system in Example 4.
  • FIG. 21 is a current-potential curve of the positive electrode and the negative electrode of the flow battery implemented in Example 4.
  • the current-potential curve is obtained under the condition of the flow battery system shown in FIG. 6 under the condition that the flow flow rate is 100 cm 3 / min and the battery is charged and discharged at a constant current.
  • the corresponding potential under various constant current controlled conditions is a value obtained by measuring the steady potential of each of the positive electrode and the negative electrode.
  • the potential of each of the positive electrode and the negative electrode is a potential with respect to the Ag / AgCl reference electrode.
  • the current density at which the potential of the positive electrode becomes 1.05 V is about 400 mA / cm 2 .
  • the charge control condition of the flow battery is such that the charge current density does not exceed 400 mA / cm 2 . This suppresses the positive electrode potential from reaching a potential region nobler than 1.05 V, and the flow battery can be operated while suppressing the generation of IO 3 ⁇ .
  • the negative electrode is basically a reaction between Zn and Zn 2+ , the potential may be controlled under the condition that the electrolytic solution does not decompose.

Abstract

This aqueous solution secondary battery comprises a positive electrode, a negative electrode, a positive electrode electrolytic solution, a negative electrode electrolytic solution, and a separation membrane. The positive electrode electrolytic solution and/or the negative electrode electrolytic solution contain iodide ions and an organic compound capable of separating oxidation reaction products of the iodide ions.

Description

水溶液系二次電池、水溶液系二次電池の充放電方法、水溶液系二次電池用電解液、フロー電池システム及び発電システムAqueous secondary battery, charging / discharging method for aqueous secondary battery, electrolytic solution for aqueous secondary battery, flow battery system and power generation system
　本発明は、水溶液系二次電池、水溶液系二次電池の充放電方法、水溶液系二次電池用電解液、フロー電池システム及び発電システムに関する。 The present invention relates to an aqueous secondary battery, an aqueous secondary battery charge / discharge method, an aqueous secondary battery electrolyte, a flow battery system, and a power generation system.
　近年、地球環境問題は深刻さを増しており、化石燃料に依存しない持続可能な社会の実現が強く求められている。特に大気中の二酸化炭素増加による地球温暖化は、地球規模での大きな課題となっている。そのため、発電時に二酸化炭素を排出しない風力や太陽光などの再生可能エネルギーの普及が、今後も世界的に促進されることが予想される。しかし、再生可能エネルギーは天候によって大きく出力が変動するので、そのままでは安定的な利用が困難である。そこでこの変動を平準化するため、安全・安価で大型化に適する電力貯蔵用蓄電デバイスの需要が高まっている。 In recent years, global environmental problems are becoming more serious, and there is a strong demand for a sustainable society that does not rely on fossil fuels. In particular, global warming due to an increase in carbon dioxide in the atmosphere has become a major issue on a global scale. Therefore, it is expected that the spread of renewable energy such as wind power and solar light that does not emit carbon dioxide during power generation will be promoted worldwide. However, since the output of renewable energy greatly varies depending on the weather, it is difficult to use it as it is. Therefore, in order to level the fluctuation, there is an increasing demand for a power storage device for power storage that is safe and inexpensive and suitable for upsizing.
　電力貯蔵用の大容量蓄電デバイスとしては、ナトリウム硫黄（ＮＡＳ）電池、鉛蓄電池、レドックスフロー電池等がある。ＮＡＳ電池は大容量で長寿命であるため、ピークシフト用途、再生可能エネルギー電力の系統連携用途等への利用が提案されている。鉛蓄電池は、１００年以上の歴史に裏打ちされた高い信頼性があり、単位蓄電容量当たりのコストが低く大型化に有利であるため、家庭用、事業所用等の夜間電力利用、再生可能エネルギー発電所の平準化などの幅広い用途に提案されている。レドックスフロー電池は、タンクの容量を増やすことで大容量化も容易に行えるため、電力貯蔵用途に適している。 Examples of high-capacity storage devices for power storage include sodium sulfur (NAS) batteries, lead storage batteries, redox flow batteries, and the like. Since NAS batteries have a large capacity and a long life, they are proposed for use in peak shift applications, renewable energy power grid linkage applications, and the like. Lead-acid batteries are highly reliable, backed by more than 100 years of history, and have a low cost per unit storage capacity, which is advantageous for large-scale use. It has been proposed for a wide range of uses such as leveling of offices. A redox flow battery can be easily increased in capacity by increasing the capacity of a tank, and is therefore suitable for power storage applications.
　一方で、各種蓄電デバイスには短所も存在する。ＮＡＳ電池は動作温度が３００℃と高温であるため、発火の危険があるうえに、発火すると亜硫酸ガス等の有毒ガスを発生する危険がある。鉛蓄電池は、体積エネルギー密度が低いため、広大な設置面積を必要とする上に、ＲｏＨＳ指令に代表されるように鉛が世界的に規制の対象となっていることから、将来的に規制対象となることも考えられる。レドックスフロー電池は、水溶液系電解質であれば発火の危険は低く安全性が高いものの、従来のバナジウムなどの金属イオンを正負極活物質とした場合は体積エネルギー密度が低いことが課題である。 On the other hand, various power storage devices have disadvantages. Since the NAS battery has an operating temperature as high as 300 ° C., there is a risk of ignition, and there is a risk of generating toxic gases such as sulfurous acid gas when ignited. Since lead-acid batteries have a low volumetric energy density, they require a large installation area and lead is subject to regulation worldwide as represented by the RoHS directive. It is also possible to become. A redox flow battery has a low risk of ignition if it is an aqueous electrolyte, and has a high safety. However, when a conventional metal ion such as vanadium is used as a positive and negative electrode active material, the volume energy density is low.
　そこで、安全性が高いことと、重量及び体積エネルギー密度が高いことを両立した大容量蓄電デバイスの開発が待たれている。中でも、ヨウ化物イオン（Ｉ－）を電極活物質として用いた大容量蓄電デバイスは、安全性と高エネルギー密度化を達成しうる大容量蓄電デバイスとして種々の検討がなされている。 Therefore, development of a large-capacity electricity storage device that is both compatible with high safety and high weight and volume energy density is awaited. Among these, various studies have been made on a large-capacity storage device using iodide ions (I − ) as an electrode active material as a large-capacity storage device that can achieve safety and high energy density.
　例えば、特許文献１には、負極活物質にクロムイオン、正極活物質にハロゲンイオンを用いるレドックスフロー電池が開示されている。ハロゲンイオンとしてヨウ化物イオンを用いることも開示されている。
　特許文献２には、ハロゲンオキソ酸化合物の水溶液を負極電解液として用いたレドックスフロー電池が開示されている。ハロゲンオキソ酸化合物にはヨウ素酸塩も含まれており、ヨウ素酸イオンとヨウ化物イオンとの酸化還元反応を用いることについても言及されている。
　特許文献３及び非特許文献１には、金属イオンとヨウ化物イオンポリマーを電解液の成分とするレドックスフロー電池が開示されている。特に非特許文献１には、ヨウ化亜鉛を活物質とする水溶液系電解液にエタノール又はエチレングリコールを添加し、これによりヨウ素の析出を抑制することが開示されている。 For example, Patent Document 1 discloses a redox flow battery using chromium ions as a negative electrode active material and halogen ions as a positive electrode active material. The use of iodide ions as halogen ions is also disclosed.
Patent Document 2 discloses a redox flow battery using an aqueous solution of a halogen oxoacid compound as a negative electrode electrolyte. Halogen oxo acid compounds include iodates, and mention is also made of using an oxidation-reduction reaction between iodate ions and iodide ions.
Patent Document 3 and Non-Patent Document 1 disclose redox flow batteries using metal ions and iodide ion polymers as components of an electrolytic solution. In particular, Non-Patent Document 1 discloses that ethanol or ethylene glycol is added to an aqueous electrolyte containing zinc iodide as an active material, thereby suppressing iodine precipitation.
特開昭６１－２４１７２号公報Japanese Patent Laid-Open No. 61-24172 特表２０１６－５２０９８２号公報Special table 2016-520982 gazette 米国特許出願公開第２０１５／０１４７６７３号US Patent Application Publication No. 2015/0147673
　ヨウ化物イオンは水への溶解度が高く、酸化還元反応が生じやすいため、水を電解液として用いる水溶液系二次電池の高エネルギー密度化と優れた電池特性を達成しうる電極活物質として期待できる。しかしながら、電解液中のヨウ化物イオンは酸化反応によって電極表面へヨウ素（Ｉ２）として析出して皮膜を形成し、様々な問題を生じる場合がある。例えば、電極表面に形成されたヨウ素皮膜が高抵抗化することで、電池としての充電電流値に対応する酸化電流値が低下するおそれがある。また、ヨウ素皮膜から水溶液中に拡散したヨウ素の分子が系外に昇華することで電解液中の活物質量が減少し、電池容量が低下するおそれがある。さらに、電解液を流動させて充放電を行うレドックスフロー電池の場合は、ヨウ素皮膜により電解液の流路が塞がれてしまうおそれがある。
　一方、水溶液系二次電池は一般に、低充電率の状態では充電反応生成物の電解液中の濃度が希薄なため、充分な放電出力が得られない場合がある。 Iodide ions have high solubility in water and are prone to oxidation-reduction reactions. Therefore, they can be expected as electrode active materials that can achieve high energy density and excellent battery characteristics for aqueous secondary batteries that use water as the electrolyte. . However, iodide ions in the electrolytic solution may precipitate as iodine (I 2 ) on the electrode surface by an oxidation reaction to form a film, which may cause various problems. For example, when the iodine film formed on the electrode surface is increased in resistance, the oxidation current value corresponding to the charging current value as a battery may be reduced. In addition, iodine molecules diffused from the iodine film into the aqueous solution sublimate out of the system, so that the amount of the active material in the electrolytic solution is reduced, and the battery capacity may be reduced. Furthermore, in the case of a redox flow battery in which charging / discharging is performed by flowing an electrolytic solution, the flow path of the electrolytic solution may be blocked by the iodine film.
On the other hand, an aqueous secondary battery generally has a low concentration of a charge reaction product in an electrolyte solution in a state of a low charge rate, so that a sufficient discharge output may not be obtained.
　本発明は、電極表面へのヨウ素皮膜の形成が抑制され、かつ低充電率での放電特性に優れる水溶液系二次電池及び水溶液系二次電池の充電方法、これらに使用される水溶液系二次電池用電解液、及びこれらを用いたフロー電池システム及び発電システムを提供することを目的とする。 The present invention relates to an aqueous secondary battery and an aqueous secondary battery charging method in which formation of an iodine film on the electrode surface is suppressed and excellent discharge characteristics at a low charging rate, and an aqueous secondary battery used in these. It aims at providing the electrolyte solution for batteries, and the flow battery system and electric power generation system using these.
＜１＞正極と、負極と、正極電解液と、負極電解液と、隔膜とを備え、前記正極電解液及び前記負極電解液の少なくともいずれか一方はヨウ化物イオンと、前記ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物とを含む、水溶液系二次電池。
＜２＞前記有機化合物の含有率は、前記有機化合物を含む前記正極電解液及び前記負極電解液の少なくともいずれか一方の１体積％～５０体積％である、＜１＞に記載の水溶液系二次電池。
＜３＞前記有機化合物はケトン、カルボン酸エステル及び炭酸エステルから選択される少なくとも１種を含む、＜１＞又は＜２＞に記載の水溶液系二次電池。
＜４＞前記有機化合物はメチルエチルケトン、酢酸メチル、酢酸エチル、炭酸ジメチル、炭酸エチルメチル及び炭酸プロピレンからなる群より選択される少なくとも１種を含む、＜１＞～＜３＞のいずれか１項に記載の水溶液系二次電池。
＜５＞前記正極電解液を収容する正極活物質反応槽と、前記負極電解液を収容する負極活物質反応槽と、正極電解液貯蔵タンクと、負極電解液貯蔵タンクと、正極電解液送液ポンプと、負極電解液送液ポンプと、をさらに備え、前記正極電解液送液ポンプは前記正極電解液貯蔵タンクと前記正極活物質反応槽との間で前記正極電解液を循環することができるように構成されており、前記負極電解液送液ポンプは前記負極電解液貯蔵タンクと前記負極活物質反応槽との間で前記負極電解液を循環することができるように構成されている、＜１＞～＜６＞のいずれか１項に記載の水溶液系二次電池。
＜６＞前記正極電解液が前記ヨウ化物イオンと前記有機化合物とを含み、前記負極電解液が負極活物質を含む、＜１＞～＜５＞のいずれか１項に記載の水溶液系二次電池。
＜７＞前記負極活物質は亜鉛、クロム、チタン、鉄、スズ、バナジウム、鉛、マンガン、コバルト、ニッケル、銅及びリチウムからなる群より選択される少なくとも１種の金属イオンを含む、＜６＞に記載の水溶液系二次電池。
＜８＞前記負極活物質は亜鉛イオンを含む、＜６＞又は＜７＞に記載の水溶液系二次電池。
＜９＞正極と、負極と、電解液とを備え、前記電解液はヨウ化物イオンと、負極活物質と、前記ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物と、を含む、水溶液系二次電池。
＜１０＞前記有機化合物の含有率は前記電解液の１体積％～５０体積％である、＜９＞に記載の水溶液系二次電池。
＜１１＞前記有機化合物はケトン、カルボン酸エステル及び炭酸エステルから選択される少なくとも１種を含む、＜９＞又は＜１０＞に記載の水溶液系二次電池。
＜１２＞前記有機化合物はメチルエチルケトン、酢酸メチル、酢酸エチル、炭酸ジメチル、炭酸エチルメチル及び炭酸プロピレンからなる群より選択される少なくとも１種を含む、＜９＞～＜１１＞のいずれか１項に記載の水溶液系二次電池。
＜１３＞前記負極活物質は亜鉛、クロム、チタン、鉄、スズ、バナジウム、鉛、マンガン、コバルト、ニッケル、銅及びリチウムからなる群より選択される少なくとも１種の金属イオンを含む、＜９＞～＜１２＞のいずれか１項に記載の水溶液系二次電池。
＜１４＞前記負極活物質は亜鉛イオンを含む、＜９＞～＜１３＞のいずれか１項に記載の水溶液系二次電池。
＜１５＞前記正極が鉛直方向において前記負極よりも下側に位置する、＜９＞～＜１４＞のいずれか１項に記載の水溶液系二次電池。
＜１６＞前記正極と前記負極との間に配置されて前記電解液を正極電解液と負極電解液とに分ける隔膜をさらに備える、＜９＞～＜１５＞のいずれか１項に記載の水溶液系二次電池。
＜１７＞前記電解液を収容する活物質反応槽と、電解液貯蔵タンクと、電解液送液ポンプと、をさらに備え、前記電解液送液ポンプは前記電解液貯蔵タンクと前記活物質反応槽との間で前記電解液を循環することができるように構成されている、＜９＞～＜１６＞のいずれか１項に記載の水溶液系二次電池。
＜１８＞正極活物質としてヨウ化物イオンを含む電解液を用いる水溶液系二次電池の充放電方法であって、前記電解液中に生成するヨウ化物イオンの酸化反応生成物を分離する工程を含む、水溶液系二次電池の充放電方法。
＜１９＞水と、ヨウ化物イオンと、ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物と、を含み、＜１８＞に記載の水溶液系二次電池の充放電方法の電解液として使用される、水溶液系二次電池用電解液。
＜２０＞前記有機化合物の含有率は前記水溶液系二次電池用電解液の１体積％～５０体積％である、＜１９＞に記載の水溶液系二次電池用電解液。
＜２１＞水と、ヨウ素（Ｉ２）、三ヨウ化物イオン（Ｉ３ －）及び五ヨウ化物イオン（Ｉ５ －）からなる群より選択される少なくとも１種と、メチルエチルケトン、酢酸メチル、酢酸エチル、炭酸ジメチル、炭酸エチルメチル及び炭酸プロピレンからなる群より選択される少なくとも１種の有機化合物と、を含む、水溶液系二次電池用電解液。
＜２２＞前記有機化合物の含有率は前記水溶液系二次電池用電解液の１体積％～５０体積％である、＜２１＞に記載の水溶液系二次電池用電解液。
＜２３＞正極活物質としてヨウ化物イオンを含む電解液を用いる水溶液系二次電池の充放電方法であって、前記電解液中に生成するヨウ化物イオンの酸化反応生成物を分離する工程を含む、水溶液系二次電池の充放電方法の電解液として使用される、＜２１＞又は＜２１＞に記載の水溶液系二次電池用電解液。
＜２４＞＜１＞～＜１７＞のいずれか１項に記載の水溶液系二次電池と、充放電を制御し、正極の充電電位を、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．５Ｖ以下に設定する制御部と、を備える、フロー電池システム。
＜２５＞発電装置と、＜２４＞に記載のフロー電池システムと、を備える発電システム。 <1> A positive electrode, a negative electrode, a positive electrode electrolyte, a negative electrode electrolyte, and a diaphragm, wherein at least one of the positive electrode electrolyte and the negative electrode electrolyte is iodide ion and oxidation of the iodide ion An aqueous secondary battery comprising an organic compound capable of separating reaction products.
<2> The content ratio of the organic compound is 1% by volume to 50% by volume of at least one of the positive electrode electrolyte and the negative electrode electrolyte containing the organic compound. Next battery.
<3> The aqueous secondary battery according to <1> or <2>, wherein the organic compound includes at least one selected from ketones, carboxylic acid esters, and carbonates.
<4> The organic compound according to any one of <1> to <3>, including at least one selected from the group consisting of methyl ethyl ketone, methyl acetate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate. The aqueous solution type secondary battery as described.
<5> A positive electrode active material reaction vessel containing the positive electrode electrolyte solution, a negative electrode active material reaction vessel containing the negative electrode electrolyte solution, a positive electrode electrolyte storage tank, a negative electrode electrolyte storage tank, and a positive electrode electrolyte supply solution A positive electrode electrolyte solution pump; and the positive electrode electrolyte solution pump can circulate the positive electrode electrolyte solution between the positive electrode electrolyte storage tank and the positive electrode active material reaction tank. The negative electrode electrolyte solution feeding pump is configured to circulate the negative electrode electrolyte solution between the negative electrode electrolyte storage tank and the negative electrode active material reaction tank. 1. The aqueous solution type secondary battery according to any one of 1> to <6>.
<6> The aqueous secondary solution according to any one of <1> to <5>, wherein the positive electrode electrolyte includes the iodide ion and the organic compound, and the negative electrode electrolyte includes a negative electrode active material. battery.
<7> The negative electrode active material contains at least one metal ion selected from the group consisting of zinc, chromium, titanium, iron, tin, vanadium, lead, manganese, cobalt, nickel, copper, and lithium, <6> The aqueous solution type secondary battery described in 1.
<8> The aqueous secondary battery according to <6> or <7>, wherein the negative electrode active material contains zinc ions.
<9> An aqueous solution comprising a positive electrode, a negative electrode, and an electrolytic solution, wherein the electrolytic solution includes iodide ions, a negative electrode active material, and an organic compound capable of separating an oxidation reaction product of the iodide ions. Secondary battery.
<10> The aqueous secondary battery according to <9>, wherein the content of the organic compound is 1% by volume to 50% by volume of the electrolytic solution.
<11> The aqueous secondary battery according to <9> or <10>, wherein the organic compound includes at least one selected from ketones, carboxylic acid esters, and carbonates.
<12> The organic compound includes any one of <9> to <11>, including at least one selected from the group consisting of methyl ethyl ketone, methyl acetate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate. The aqueous solution type secondary battery as described.
<13> The negative electrode active material contains at least one metal ion selected from the group consisting of zinc, chromium, titanium, iron, tin, vanadium, lead, manganese, cobalt, nickel, copper, and lithium, <9> The aqueous solution type secondary battery according to any one of to <12>.
<14> The aqueous secondary battery according to any one of <9> to <13>, wherein the negative electrode active material contains zinc ions.
<15> The aqueous secondary battery according to any one of <9> to <14>, wherein the positive electrode is positioned below the negative electrode in the vertical direction.
<16> The aqueous solution according to any one of <9> to <15>, further comprising a diaphragm disposed between the positive electrode and the negative electrode and dividing the electrolyte into a positive electrode electrolyte and a negative electrode electrolyte. Secondary battery.
<17> An active material reaction tank containing the electrolyte solution, an electrolyte storage tank, and an electrolyte solution feed pump, further comprising the electrolyte solution tank and the active material reaction tank. The aqueous solution type secondary battery according to any one of <9> to <16>, wherein the electrolyte solution can be circulated between the first electrode and the second electrode.
<18> A charge / discharge method for an aqueous secondary battery using an electrolytic solution containing iodide ions as a positive electrode active material, comprising a step of separating an oxidation reaction product of iodide ions generated in the electrolytic solution. And charging / discharging method for aqueous secondary battery.
<19> water, iodide ion, and an organic compound capable of separating an oxidation reaction product of iodide ion, and used as an electrolytic solution for a charge / discharge method of an aqueous secondary battery according to <18> An electrolytic solution for an aqueous secondary battery.
<20> The electrolyte solution for an aqueous secondary battery according to <19>, wherein the content of the organic compound is 1% by volume to 50% by volume of the electrolytic solution for an aqueous secondary battery.
<21> Water, at least one selected from the group consisting of iodine (I 2 ), triiodide ion (I 3 − ), and pentaiodide ion (I 5 − ), methyl ethyl ketone, methyl acetate, and ethyl acetate And at least one organic compound selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.
<22> The electrolyte solution for an aqueous secondary battery according to <21>, wherein the content of the organic compound is 1% by volume to 50% by volume of the electrolytic solution for an aqueous secondary battery.
<23> A charge / discharge method for an aqueous secondary battery using an electrolytic solution containing iodide ions as a positive electrode active material, comprising a step of separating an oxidation reaction product of iodide ions generated in the electrolytic solution. The electrolytic solution for an aqueous secondary battery according to <21> or <21>, which is used as an electrolytic solution for a charging / discharging method of an aqueous secondary battery.
<24> The aqueous secondary battery according to any one of <1> to <17>, the charge potential of the positive electrode, the charge potential of the positive electrode being controlled by the potential of the Ag / AgCl reference electrode (Cl − concentration saturation). And a control unit that sets the voltage to 1.5 V or less with reference to the flow battery system.
<25> A power generation system comprising: a power generation device; and the flow battery system according to <24>.
　本発明によれば、電極表面へのヨウ素皮膜の形成が抑制され、かつ低充電率での放電特性に優れる水溶液系二次電池及び水溶液系二次電池の充電方法、これらに使用される水溶液系二次電池用電解液、及びこれらを用いたフロー電池システム及び発電システムが提供される。 ADVANTAGE OF THE INVENTION According to this invention, the formation of the iodine film on the electrode surface is suppressed, and the aqueous solution type secondary battery excellent in the discharge characteristics at a low charge rate, the method for charging the aqueous solution type secondary battery, and the aqueous solution system used in these An electrolyte for secondary batteries, and a flow battery system and a power generation system using the same are provided.
第１実施形態の水溶液系二次電池の構成例を示す概略断面図である。It is a schematic sectional drawing which shows the structural example of the aqueous solution type secondary battery of 1st Embodiment. 第１実施形態の水溶液系二次電池が電解液を流動させるための装置をさらに備える場合の構成例を示す概略断面図である。It is a schematic sectional drawing which shows the structural example in case the aqueous solution type secondary battery of 1st Embodiment is further provided with the apparatus for making electrolyte solution flow. 第２実施形態の水溶液系二次電池の構成例を示す概略断面図である。It is a schematic sectional drawing which shows the structural example of the aqueous solution type secondary battery of 2nd Embodiment. 第２実施形態の水溶液系二次電池が正極１と負極２の間に隔膜５をさらに備える場合の構成例を示す概略断面図である。It is a schematic sectional drawing which shows the structural example in case the aqueous solution type secondary battery of 2nd Embodiment is further equipped with the diaphragm 5 between the positive electrode 1 and the negative electrode 2. FIG. 第２実施形態の水溶液系二次電池が電解液を流動させるための装置をさらに備える場合の構成例を示す概略断面図である。It is a schematic sectional drawing which shows the structural example in case the aqueous solution type secondary battery of 2nd Embodiment is further equipped with the apparatus for flowing an electrolyte solution. フロー電池システムの構成例を示す概略断面図である。It is a schematic sectional drawing which shows the structural example of a flow battery system. 発電システムの構成例を示す概略図である。It is the schematic which shows the structural example of an electric power generation system. 風力発電の発電電力短時間波形の一例を示す図である。It is a figure which shows an example of the power generation electric power short time waveform of wind power generation. メチルエチルケトンを添加した電解液と添加していない電解液について行った酸化電流値の測定結果を示すグラフである。It is a graph which shows the measurement result of the oxidation current value performed about the electrolyte solution which added methyl ethyl ketone, and the electrolyte solution which is not added. ヨウ化物イオンの酸化反応生成物を含む疎水性の物質の写真である。It is a photograph of the hydrophobic substance containing the oxidation reaction product of iodide ion. 疎水性の物質中で観測された酸化電位での酸化電流値と還元電位での還元電流値を示すグラフである。It is a graph which shows the oxidation current value in the oxidation potential observed in the hydrophobic substance, and the reduction current value in the reduction potential. ノーマルパルスボルタンメトリーの電位波形を示すグラフである。It is a graph which shows the electric potential waveform of normal pulse voltammetry. ノーマルパルスボルタモグラムを示すグラフである（パルス幅５０ｍｓ）。It is a graph which shows a normal pulse voltammogram (pulse width 50ms). ノーマルパルスボルタモグラムを示すグラフである（パルス幅５０ｍｓ）。It is a graph which shows a normal pulse voltammogram (pulse width 50ms). リバースパルスボルタンメトリーの電位波形を示すグラフである。It is a graph which shows the electric potential waveform of reverse pulse voltammetry. リバースパルスボルタモグラムを示すグラフである（初期電位０．５０Ｖ、０．５５Ｖ及びパルス幅５０ｍｓ）。It is a graph which shows a reverse pulse voltammogram (initial electric potential 0.50V, 0.55V and pulse width 50ms). リバースパルスボルタモグラムを示すグラフである（初期電位０．５０Ｖ、０．５５Ｖ及びパルス幅５０ｍｓ）。It is a graph which shows a reverse pulse voltammogram (initial electric potential 0.50V, 0.55V and pulse width 50ms). リバースパルスボルタモグラムであり、電解液中に含有するメチルエチルケトンの効果を示すグラフである（初期電位０．６０Ｖ及びパルス幅５０ｍｓ）。It is a reverse pulse voltammogram and is a graph showing the effect of methyl ethyl ketone contained in the electrolyte (initial potential 0.60 V and pulse width 50 ms). リバースパルスボルタモグラムであり、電解液中に含有するプロピレンカーボネートの効果を示すグラフである（初期電位０．６０Ｖ及びパルス幅５０ｍｓ）。It is a reverse pulse voltammogram, which is a graph showing the effect of propylene carbonate contained in the electrolyte (initial potential 0.60 V and pulse width 50 ms). リバースパルスボルタモグラムを示すグラフである（初期電位０．９０Ｖ～１．１０Ｖ及びパルス幅５０ｍｓ）。6 is a graph showing a reverse pulse voltammogram (initial potential 0.90 V to 1.10 V and pulse width 50 ms). リバースパルスボルタモグラムを示すグラフである（初期電位０．９０Ｖ～１．１０Ｖ及びパルス幅５０ｍｓ）。6 is a graph showing a reverse pulse voltammogram (initial potential 0.90 V to 1.10 V and pulse width 50 ms). リバースパルスボルタモグラムを示すグラフである（初期電位１．４０Ｖ、１．５０Ｖ及びパルス幅５０ｍｓ）。It is a graph which shows a reverse pulse voltammogram (initial electric potential 1.40V, 1.50V, and pulse width 50ms). リバースパルスボルタモグラムを示すグラフである（初期電位１．４０Ｖ、１．５０Ｖ及びパルス幅５０ｍｓ）。It is a graph which shows a reverse pulse voltammogram (initial electric potential 1.40V, 1.50V, and pulse width 50ms). ノーマルパルスボルタモグラムを示すグラフである（パルス幅５０、５００及び５０００ｍｓ）。It is a graph which shows a normal pulse voltammogram ( pulse width 50, 500, and 5000 ms). ノーマルパルスボルタモグラムを示すグラフである（パルス幅５０、５００及び５０００ｍｓ）。It is a graph which shows a normal pulse voltammogram ( pulse width 50, 500, and 5000 ms). ノーマルパルスボルタモグラムを示すグラフであり、電解液中に含有するメチルエチルケトンの効果を示したグラフである（パルス幅５０００ｍｓ）。It is a graph which shows a normal pulse voltammogram, and is a graph which showed the effect of the methyl ethyl ketone contained in electrolyte solution (pulse width 5000ms). ノーマルパルスボルタモグラムを示すグラフであり、電解液中に含有するプロピレンカーボネートの効果を示したグラフである（パルス幅５０００ｍｓ）。It is a graph which shows a normal pulse voltammogram, and is a graph which showed the effect of the propylene carbonate contained in electrolyte solution (pulse width 5000ms). フロー電池システムの電極反応を示す模式図である。It is a schematic diagram which shows the electrode reaction of a flow battery system. フロー電池の正極及び負極の電流電位曲線である。It is a current-potential curve of the positive electrode and negative electrode of a flow battery.
　以下、本発明を実施するための形態について詳細に説明する。但し、本発明は以下の実施形態に限定されるものではない。以下の実施形態において、その構成要素（要素ステップ等も含む）は、特に明示した場合を除き、必須ではない。数値及びその範囲についても同様であり、本発明を制限するものではない。 Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and ranges thereof, and the present invention is not limited thereto.
　本開示において「～」を用いて示された数値範囲には、「～」の前後に記載される数値がそれぞれ最小値及び最大値として含まれる。
　本開示中に段階的に記載されている数値範囲において、一つの数値範囲で記載された上限値又は下限値は、他の段階的な記載の数値範囲の上限値又は下限値に置き換えてもよい。また、本開示中に記載されている数値範囲において、その数値範囲の上限値又は下限値は、実施例に示されている値に置き換えてもよい。
　本開示において各成分は該当する物質を複数種含んでいてもよい。組成物中に各成分に該当する物質が複数種存在する場合、各成分の含有率又は含有量は、特に断らない限り、組成物中に存在する当該複数種の物質の合計の含有率又は含有量を意味する。
　本開示において「膜」又は「皮膜」との語には、当該膜又は皮膜が存在する領域を観察したときに、当該領域の全体に形成されている場合に加え、当該領域の一部にのみ形成されている場合も含まれる。 In the present disclosure, numerical ranges indicated using “to” include numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical description. . Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.
In the present disclosure, each component may contain a plurality of corresponding substances. When multiple types of substances corresponding to each component are present in the composition, the content or content of each component is the total content or content of the multiple types of substances present in the composition unless otherwise specified. Means quantity.
In the present disclosure, the term “film” or “film” includes only a part of the region in addition to the case where the film or the film is formed over the entire region. The case where it is formed is also included.
　本開示において実施形態を図面を参照して説明する場合、当該実施形態の構成は図面に示された構成に限定されない。また、各図における部材の大きさは概念的なものであり、部材間の大きさの相対的な関係はこれに限定されない。 In the present disclosure, when an embodiment is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Moreover, the magnitude | size of the member in each figure is notional, The relative relationship of the magnitude | size between members is not limited to this.
＜水溶液系二次電池（第１実施形態）＞
　本実施形態の水溶液系二次電池は、
　正極と、負極と、正極電解液と、負極電解液と、隔膜とを備え、前記正極電解液及び前記負極電解液の少なくともいずれか一方はヨウ化物イオンと、前記ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物とを含む。 <Aqueous solution type secondary battery (first embodiment)>
The aqueous secondary battery of this embodiment is
A positive electrode, a negative electrode, a positive electrode electrolyte, a negative electrode electrolyte, and a diaphragm, wherein at least one of the positive electrode electrolyte and the negative electrode electrolyte is an iodide ion and an oxidation reaction product of the iodide ion And a separable organic compound.
　本発明者らが検討を行った結果、上記構成を有する水溶液系二次電池は電極表面へのヨウ素皮膜の形成が抑制され、かつ低充電率での放電特性に優れることがわかった。より具体的には、電解液にヨウ化物イオンの酸化反応生成物を分離可能な有機化合物を含有させることで、電極表面に形成されるヨウ素皮膜の溶解が促進されるとともに、電解液から分離した酸化反応生成物を正極の還元反応に利用することで低充電率の状態でも充分な放電出力が得られることがわかった。 As a result of investigations by the present inventors, it was found that the aqueous secondary battery having the above-described configuration is excellent in discharge characteristics at a low charge rate while suppressing the formation of an iodine film on the electrode surface. More specifically, by containing an organic compound capable of separating the oxidation reaction product of iodide ions in the electrolytic solution, dissolution of the iodine film formed on the electrode surface is promoted and separated from the electrolytic solution. It was found that by using the oxidation reaction product for the reduction reaction of the positive electrode, a sufficient discharge output can be obtained even in a low charge rate state.
　上述した特許文献のいずれにも、電解液にヨウ化物イオンの酸化反応生成物を分離可能な有機化合物を含有させることで、電極表面に形成されるヨウ素皮膜の溶解を促進し、かつ分離した酸化反応生成物を正極の還元反応に利用するという技術思想は記載されていない。 In any of the above-mentioned patent documents, the electrolyte solution contains an organic compound capable of separating the oxidation reaction product of iodide ions, thereby promoting the dissolution of the iodine film formed on the electrode surface and the separated oxidation. The technical idea of utilizing the reaction product for the reduction reaction of the positive electrode is not described.
　本開示において「水溶液系二次電池」とは、水に必要な成分を溶解した水溶液を電解液として用いる二次電池を意味する。具体的には、レドックスフロー電池（フロー電池）等の蓄電デバイスなどが挙げられる。 In the present disclosure, the “aqueous solution type secondary battery” means a secondary battery using an aqueous solution in which a component necessary for water is dissolved as an electrolytic solution. Specifically, an electricity storage device such as a redox flow battery (flow battery) can be used.
　本開示において「正極電解液」とは、正極と接触している電解液を意味し、「負極電解液」とは、負極と接触している電解液を意味する。以下の説明において、正極電解液と負極電解液の両方またはいずれか一方を単に「電解液」とも称する。 In the present disclosure, “positive electrode electrolyte” means an electrolyte in contact with the positive electrode, and “negative electrode electrolyte” means an electrolyte in contact with the negative electrode. In the following description, both or one of the positive electrode electrolyte and the negative electrode electrolyte is also simply referred to as “electrolyte”.
　本開示において「ヨウ化物イオンの酸化反応生成物」とは、ヨウ化物イオンの酸化反応によって生成する物質を意味する。例えば、ヨウ素（Ｉ２）、三ヨウ化物イオン（Ｉ３ －）、五ヨウ化物イオン（Ｉ５ －）及びこれらの組み合わせが挙げられる。 In the present disclosure, an “oxidation reaction product of iodide ion” means a substance generated by an oxidation reaction of iodide ion. Examples thereof include iodine (I 2 ), triiodide ion (I 3 − ), pentaiodide ion (I 5 − ), and combinations thereof.
　本実施形態の水溶液系二次電池は、電解液が正極電解液と負極電解液とに分かれている。このような構成を有する水溶液系二次電池は「二液型水溶液二次電池」とも称される。 In the aqueous secondary battery of the present embodiment, the electrolyte is divided into a positive electrode electrolyte and a negative electrode electrolyte. An aqueous secondary battery having such a configuration is also referred to as a “two-component aqueous secondary battery”.
　本実施形態の水溶液系二次電池では、正極電解液と負極電解液のうち、少なくとも正極電解液がヨウ化物イオンと、ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物（以下、単に「有機化合物」とも称する）とを含むことが好ましく、正極電解液がヨウ化物イオンと、有機化合物とを含み、負極電解液が負極活物質を含むことがより好ましい。 In the aqueous secondary battery of this embodiment, of the positive electrode electrolyte and the negative electrode electrolyte, at least the positive electrode electrolyte is an organic compound that can separate an iodide ion and an oxidation reaction product of iodide ion (hereinafter simply referred to as “ It is preferable that the positive electrode electrolyte contains iodide ions and an organic compound, and the negative electrode electrolyte contains a negative electrode active material.
　本実施形態の水溶液系二次電池は、電解液に含まれる活物質としてヨウ化物イオンを用いるため、エネルギー密度に優れている。さらに、電解液に含まれる有機化合物がヨウ化物イオンの酸化反応生成物を分離することで、電極表面に形成されたヨウ素皮膜の溶解が促進され、ヨウ素皮膜の形成に起因する酸化電流値の低下が抑制されるとともに、ヨウ素皮膜から電解液中に拡散したＩ２分子が系外に昇華するのを抑制する効果も期待できる。さらに、有機化合物によって分離した酸化反応生成物を正極における還元反応に利用することができるため、充電反応生成物の濃度が希薄な低充電率の状態でも高出力な放電を得ることができる。 The aqueous secondary battery of this embodiment is excellent in energy density because iodide ions are used as the active material contained in the electrolytic solution. Furthermore, the organic compound contained in the electrolyte separates the oxidation reaction product of iodide ions, so that the dissolution of the iodine film formed on the electrode surface is promoted, and the oxidation current value is reduced due to the formation of the iodine film. In addition, the effect of suppressing the sublimation of the I 2 molecules diffused from the iodine film into the electrolyte can be expected. Furthermore, since the oxidation reaction product separated by the organic compound can be used for the reduction reaction at the positive electrode, a high output discharge can be obtained even in a low charge rate state where the concentration of the charge reaction product is lean.
　本実施形態の水溶液系二次電池では、有機化合物を用いて電解液に含まれるヨウ化物イオンの酸化反応生成物を選択的に分離する。有機化合物を用いてヨウ化物イオンの酸化反応生成物を分離する態様は特に制限されないが、電解液をヨウ化物イオンの酸化反応生成物が含まれる疎水性の物質と、バルク水溶液とに分離することが好ましい。
　疎水性の物質は、例えば、有機化合物がヨウ化物イオン及びその酸化反応生成物と、カチオンと、少量の水とともにネットワーク構造を形成して得られるものであってもよい、疎水性の物質は、例えば、疎水性の液体の状態であってもよい。 In the aqueous secondary battery of this embodiment, an oxidation reaction product of iodide ions contained in the electrolytic solution is selectively separated using an organic compound. The mode of separating the iodide ion oxidation reaction product using an organic compound is not particularly limited, but the electrolyte is separated into a hydrophobic substance containing an iodide ion oxidation reaction product and a bulk aqueous solution. Is preferred.
The hydrophobic substance may be obtained by forming a network structure with an organic compound, for example, an iodide ion and its oxidation reaction product, a cation, and a small amount of water. For example, it may be in a hydrophobic liquid state.
　疎水性の物質に対するヨウ素分子の溶解度は水に対する溶解度よりも高く、疎水性の物質中ではより安定に存在する。ヨウ素分子は昇華性を有することに加え、水に対する溶解度が１ｍＭ程度と小さい。このため、水中に存在するヨウ素分子は気液界面から容易に昇華するが、疎水性の物質中に存在するヨウ素分子は昇華が抑制される。従って、ヨウ化物イオンの酸化反応生成物を疎水性の物質として分離することで、ヨウ素分子の昇華が抑制され、電解液中のヨウ化物イオンの減少を抑制することができる。 The solubility of iodine molecules in hydrophobic substances is higher than that in water, and it exists more stably in hydrophobic substances. In addition to being sublimable, iodine molecules have a low solubility in water of about 1 mM. For this reason, iodine molecules present in water easily sublime from the gas-liquid interface, but sublimation of iodine molecules present in a hydrophobic substance is suppressed. Therefore, by separating the oxidation reaction product of iodide ions as a hydrophobic substance, sublimation of iodine molecules can be suppressed, and a decrease in iodide ions in the electrolytic solution can be suppressed.
　ヨウ化物イオンの酸化反応生成物を疎水性の物質として分離する場合、分離された疎水性の物質には、ヨウ化物イオンの酸化反応生成物がバルク水溶液中よりも高い濃度で存在する。そのため、疎水性の物質を正極に接触させてそこに含まれる酸化反応生成物を正極の還元反応に用いることで、低充電率の状態でも高出力な放電を得ることができる。また、後述するように正極が鉛直方向にみて下部に位置するように構成する場合、バルク水溶液よりも比重が大きいために沈殿する疎水性の物質に含まれる酸化反応生成物を正極での還元反応に利用することができる。 When the oxidation reaction product of iodide ion is separated as a hydrophobic substance, the oxidation reaction product of iodide ion is present in the separated hydrophobic substance at a higher concentration than in the bulk aqueous solution. Therefore, a high output discharge can be obtained even in a low charge rate state by contacting a hydrophobic substance with the positive electrode and using the oxidation reaction product contained therein for the reduction reaction of the positive electrode. In addition, as described later, when the positive electrode is configured to be positioned below the vertical direction, the oxidation reaction product contained in the hydrophobic substance that precipitates because the specific gravity is larger than that of the bulk aqueous solution is reduced at the positive electrode. Can be used.
　有機化合物は、ヨウ化物イオンの酸化反応生成物を分離可能なものであれば特に制限されないが、上述した理由からヨウ化物イオンの酸化反応生成物を疎水性の物質として分離可能なものであることが好ましく、Ｉ２分子に対する親和力が水よりも高い有機化合物であることがより好ましい。Ｉ２分子に対する親和力が水よりも高い有機化合物は、ヨウ素皮膜に有機化合物が配位してヨウ素皮膜の溶解を促進する。このため、ヨウ素皮膜の形成をより効率よく抑制することができる。有機化合物は、疎水性の物質を形成していないときは電解液に溶解した状態であることが好ましい。 The organic compound is not particularly limited as long as it can separate the oxidation reaction product of iodide ion. However, for the reason described above, the oxidation reaction product of iodide ion can be separated as a hydrophobic substance. And is more preferably an organic compound having a higher affinity for I 2 molecules than water. An organic compound having an affinity for I 2 molecules higher than that of water promotes dissolution of the iodine film by coordination of the organic compound with the iodine film. For this reason, formation of an iodine film can be suppressed more efficiently. When the organic compound does not form a hydrophobic substance, the organic compound is preferably dissolved in the electrolyte.
　有機化合物としては、ケトン、カルボン酸エステル及び炭酸エステルからなる群より選択される少なくとも１種が挙げられる。ケトンとして具体的には、メチルエチルケトン等が挙げられる。カルボン酸エステルとして具体的には、酢酸メチル、酢酸エチル等が挙げられる。炭酸エステルとして具体的には、炭酸ジメチル、炭酸エチルメチル、炭酸プロピレン等が挙げられる。 Examples of the organic compound include at least one selected from the group consisting of ketone, carboxylic acid ester, and carbonate ester. Specific examples of the ketone include methyl ethyl ketone. Specific examples of the carboxylic acid ester include methyl acetate and ethyl acetate. Specific examples of the carbonate ester include dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate.
　上記化合物の中でも、ケトンはこれが含まれる水溶液（電解液）の粘度を低下させ、電池抵抗を低減させる観点から好ましい。カルボン酸エステルはケトンよりもヨウ素に対して化学的に安定であり、クーロン効率を高める観点から好ましい。炭酸エステルは比重が大きく、疎水性の物質としてヨウ化物イオンの酸化反応生成物を分離する能力が高い点で好ましい。 Among the above compounds, ketones are preferable from the viewpoint of reducing the viscosity of an aqueous solution (electrolytic solution) containing the ketone and reducing battery resistance. Carboxylic acid esters are more chemically stable than iodine than ketones, and are preferred from the viewpoint of increasing coulomb efficiency. Carbonate ester is preferable in that it has a large specific gravity and has a high ability to separate an oxidation reaction product of iodide ion as a hydrophobic substance.
　電解液に含まれる有機化合物は１種のみでもよく、２種以上であってもよい。また、有機化合物の電解液中の含有率は、常温（２５℃）常圧で１体積％～５０体積％であることが好ましく、５体積％～４０体積％であることがより好ましい。有機化合物の電解液中の含有率が１体積％以上であると、高充電率の状態でもヨウ化物イオンの酸化反応生成物が良好に分離される傾向にあり、５０体積％以下であると、電解液の導電率の低下が抑制される傾向にある。 The organic compound contained in the electrolytic solution may be only one type or two or more types. The content of the organic compound in the electrolytic solution is preferably 1% by volume to 50% by volume at room temperature (25 ° C.) and normal pressure, and more preferably 5% by volume to 40% by volume. When the content of the organic compound in the electrolytic solution is 1% by volume or more, the oxidation reaction product of iodide ions tends to be favorably separated even in a high charge rate state, and when it is 50% by volume or less, There exists a tendency for the fall of the electrical conductivity of electrolyte solution to be suppressed.
　有機化合物の電解液中の含有量は、例えば、ガスクロマトグラフィーにより、有機化合物の濃度に対応する保持時間と、モニターイオンの分子量を測定することで同定可能である。 The content of the organic compound in the electrolyte can be identified, for example, by measuring the retention time corresponding to the concentration of the organic compound and the molecular weight of the monitor ion by gas chromatography.
　電解液は、支持電解質塩を含有していてもよい。支持電解質塩は、電解液のイオン伝導率を高めるための助剤として機能する。電解液が支持電解質塩を含有することで、電解液のイオン伝導率が高まり、水溶液系二次電池の内部抵抗が低減する傾向にある。 The electrolytic solution may contain a supporting electrolyte salt. The supporting electrolyte salt functions as an auxiliary agent for increasing the ionic conductivity of the electrolytic solution. When the electrolytic solution contains the supporting electrolyte salt, the ionic conductivity of the electrolytic solution is increased, and the internal resistance of the aqueous secondary battery tends to be reduced.
　支持電解質塩は、電解液中で解離してイオンを形成する化合物であれば特に制限されない。具体的には、ＨＣｌ、ＨＮＯ３、Ｈ２ＳＯ４、ＨＣｌＯ４、ＮａＣｌ、Ｎａ２ＳＯ４、ＮａＣｌＯ４、ＫＣｌ、Ｋ２ＳＯ４、ＫＣｌＯ４、ＮａＯＨ、ＬｉＯＨ、ＫＯＨ、アルキルアンモニウム塩、アルキルイミダゾリウム塩、アルキルピペリジニウム塩、アルキルピロリジニウム塩等が挙げられる。支持電解質塩は１種を単独で用いてもよく、２種以上を併用してもよい。また、ヨウ素を含む塩は、正極活物質と支持電解質塩とを兼ねることができる。 The supporting electrolyte salt is not particularly limited as long as it is a compound that dissociates in the electrolytic solution to form ions. Specifically, HCl, HNO 3 , H 2 SO 4 , HClO 4 , NaCl, Na 2 SO 4 , NaClO 4 , KCl, K 2 SO 4 , KClO 4 , NaOH, LiOH, KOH, alkylammonium salt, alkylimidazo Examples thereof include a lithium salt, an alkyl piperidinium salt, and an alkyl pyrrolidinium salt. The supporting electrolyte salt may be used alone or in combination of two or more. Further, the salt containing iodine can serve as both the positive electrode active material and the supporting electrolyte salt.
　電解液は、ｐＨ緩衝剤を含有していてもよい。ｐＨ緩衝剤としては、酢酸緩衝液、リン酸緩衝液、クエン酸緩衝液、ホウ酸緩衝液、酒石緩衝液、トリス緩衝液等が挙げられる。 The electrolytic solution may contain a pH buffer. Examples of the pH buffering agent include acetate buffer, phosphate buffer, citrate buffer, borate buffer, tartaric buffer, Tris buffer, and the like.
　図１は、本実施形態の水溶液系二次電池の構成例の一例を示す概略断面図である。図１に示す実線の矢印は充電時における電子の流れを、点線の矢印は充電時におけるイオンの反応を示している。 FIG. 1 is a schematic cross-sectional view showing an example of a configuration example of the aqueous solution type secondary battery of the present embodiment. The solid arrows in FIG. 1 indicate the flow of electrons during charging, and the dotted arrows indicate the reaction of ions during charging.
　図１に示す水溶液系二次電池は、正極１と、負極２と、正極活物質反応槽３と、負極活物質反応槽４と、隔膜５と、を備えている。正極活物質反応槽３と負極活物質反応槽４は、それぞれ正極電解液と負極電解液を収容している。 The aqueous secondary battery shown in FIG. 1 includes a positive electrode 1, a negative electrode 2, a positive electrode active material reaction tank 3, a negative electrode active material reaction tank 4, and a diaphragm 5. The positive electrode active material reaction tank 3 and the negative electrode active material reaction tank 4 contain a positive electrode electrolyte and a negative electrode electrolyte, respectively.
　図１に示す水溶液系二次電池では、正極電解液が正極活物質としてのヨウ化物イオンと、ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物を含み、負極電解液が負極活物質を含んでいる。 In the aqueous secondary battery shown in FIG. 1, the positive electrode electrolyte contains an iodide ion as a positive electrode active material and an organic compound capable of separating the oxidation reaction product of iodide ions, and the negative electrode electrolyte contains the negative electrode active material. Contains.
　正極１の材質は、正極電解液に含まれるヨウ化物イオンに対する耐食性を有するものから選択されることが好ましい。具体的には、チタン等の耐食性の高い金属、炭素材料などが挙げられる。コストの観点からは、炭素材料が好ましい。正極１の形状は、特に制限されない。より大きな出力を得る観点からは、比表面積が大きい形状であることが好ましい。比表面積が大きい形状としては、多孔体、フェルト、ペーパー等が挙げられる。 The material of the positive electrode 1 is preferably selected from those having corrosion resistance to iodide ions contained in the positive electrode electrolyte. Specific examples include metals having high corrosion resistance such as titanium, carbon materials, and the like. From the viewpoint of cost, a carbon material is preferable. The shape of the positive electrode 1 is not particularly limited. From the viewpoint of obtaining a larger output, a shape having a large specific surface area is preferable. Examples of the shape having a large specific surface area include porous bodies, felts, and papers.
　負極２の材質は特に制限されず、使用する負極活物質の種類等に応じて選択できる。例えば、亜鉛を負極活物質として用いる場合は、炭素材料、亜鉛、亜鉛メッキした金属材料等の亜鉛が表面に析出するものを負極として使用する。負極２の形状としてはメッシュ、多孔体、パンチングメタル、平板等が挙げられるが、特に制限されない。 The material of the negative electrode 2 is not particularly limited, and can be selected according to the type of the negative electrode active material to be used. For example, when zinc is used as the negative electrode active material, a carbon material, zinc, zinc-plated metal material or the like in which zinc is deposited on the surface is used as the negative electrode. Examples of the shape of the negative electrode 2 include a mesh, a porous body, a punching metal, and a flat plate, but are not particularly limited.
　正極活物質反応槽３に含まれる正極電解液は、正極活物質としてのヨウ化物イオンを含んでいる。ヨウ化物イオンを含む正極電解液は、電解液にヨウ素化合物を溶解することで調製することができる。ヨウ素化合物としては、ヨウ化ナトリウム、ヨウ化カリウム、ヨウ化亜鉛、ヨウ化水素、ヨウ化リチウム、ヨウ化アンモニウム、ヨウ化バリウム、ヨウ化カルシウム、ヨウ化マグネシウム、ヨウ化ストロンチウム等を使用できる。ヨウ化物イオンの正極電解液中の濃度は特に限定されないが、０．０１Ｍ～２０Ｍであることが好ましく、０．１Ｍ～１０Ｍであることがより好ましい。ヨウ化物イオンの濃度が０．０１Ｍ以上であると充分なエネルギー密度が得られる傾向にあり、２０Ｍ以下であると正極電解液中に後述する有機化合物を充分に溶解できる傾向にある。 The positive electrode electrolyte contained in the positive electrode active material reaction vessel 3 contains iodide ions as the positive electrode active material. The positive electrode electrolyte solution containing iodide ions can be prepared by dissolving an iodine compound in the electrolyte solution. As the iodine compound, sodium iodide, potassium iodide, zinc iodide, hydrogen iodide, lithium iodide, ammonium iodide, barium iodide, calcium iodide, magnesium iodide, strontium iodide and the like can be used. The concentration of iodide ion in the positive electrode electrolyte is not particularly limited, but is preferably 0.01M to 20M, and more preferably 0.1M to 10M. When the iodide ion concentration is 0.01 M or more, a sufficient energy density tends to be obtained, and when it is 20 M or less, the organic compound described later tends to be sufficiently dissolved in the positive electrode electrolyte.
　正極電解液に含まれる有機化合物等の成分の詳細及び好ましい態様は、上述した電解液に含まれる有機化合物等の成分の詳細及び好ましい態様と同様である。 Details and preferred embodiments of components such as organic compounds contained in the positive electrode electrolyte are the same as details and preferred embodiments of components such as organic compounds contained in the above-described electrolyte.
　負極活物質反応槽４に含まれる負極電解液は、負極活物質（Ｘ＋）を含む。負極活物質の還元反応により、還元反応生成物（Ｘ）が生成する。負極活物質は、反応系の標準酸化還元電位が、正極の標準酸化還元電位（正極活物質がヨウ化物イオンである場合は０．５３６Ｖ）よりも低い物質であれば特に制限されない。例えば、亜鉛、クロム、チタン、鉄、スズ、バナジウム、鉛、マンガン、コバルト、ニッケル、銅、リチウム、キノン系材料、ビオロゲン等のイオンが挙げられる。これらの負極活物質の中でも金属イオンが好ましく、亜鉛イオンがより好ましい。亜鉛イオンは他の金属イオンに比べて水への溶解度が高く（例えば、塩化亜鉛の溶解度は３０Ｍ以上）、溶解析出反応の標準酸化還元電位が低く（－０．７６Ｖ）、かつ安価である。金属イオンを含む負極電解液は、電解液に当該金属の化合物を溶解することで調製することができる。例えば、亜鉛イオンを含む負極電解液は、塩化亜鉛、ヨウ化亜鉛、臭化亜鉛、フッ化亜鉛、硝酸亜鉛、硫酸亜鉛、酢酸亜鉛等の亜鉛化合物を溶解することで調製することができる。 The negative electrode electrolyte contained in the negative electrode active material reaction vessel 4 contains a negative electrode active material (X + ). A reduction reaction product (X) is generated by the reduction reaction of the negative electrode active material. The negative electrode active material is not particularly limited as long as the standard redox potential of the reaction system is lower than the standard redox potential of the positive electrode (0.536 V when the positive electrode active material is iodide ion). For example, ions such as zinc, chromium, titanium, iron, tin, vanadium, lead, manganese, cobalt, nickel, copper, lithium, quinone materials, viologen, and the like can be given. Among these negative electrode active materials, metal ions are preferable, and zinc ions are more preferable. Zinc ions are more soluble in water than other metal ions (for example, zinc chloride has a solubility of 30 M or more), have a low standard oxidation-reduction potential for dissolution and precipitation (−0.76 V), and are inexpensive. The negative electrode electrolyte containing metal ions can be prepared by dissolving the metal compound in the electrolyte. For example, a negative electrode electrolyte containing zinc ions can be prepared by dissolving a zinc compound such as zinc chloride, zinc iodide, zinc bromide, zinc fluoride, zinc nitrate, zinc sulfate, and zinc acetate.
　隔膜５は、正極電解液と負極電解液とを分ける役割を果たす。隔膜５の材質は特に制限されない。例えば、耐酸性に優れ、高いイオン伝導率を有するイオン交換膜が好ましい例として挙げられるが、多孔膜、ガラスフィルター等も好適に用いることができる。 The diaphragm 5 serves to separate the positive electrode electrolyte and the negative electrode electrolyte. The material of the diaphragm 5 is not particularly limited. For example, an ion exchange membrane having excellent acid resistance and high ion conductivity can be mentioned as a preferable example, but a porous membrane, a glass filter, and the like can also be suitably used.
　図２は、図１に示す水溶液系二次電池が電解液を流動させるための装置をさらに備える場合の構成を示す概略断面図である。図２に示す水溶液系二次電池が備える要素のうち図１に示す水溶液系二次電池が備える要素と共通するものについては、説明を省略する。 FIG. 2 is a schematic cross-sectional view showing a configuration in the case where the aqueous secondary battery shown in FIG. 1 further includes a device for causing the electrolyte to flow. Descriptions of elements provided in the aqueous secondary battery shown in FIG. 2 that are the same as those provided in the aqueous secondary battery shown in FIG. 1 are omitted.
　図２に示す水溶液系二次電池は、正極１と、負極２と、正極活物質反応槽３と、負極活物質反応槽４と、隔膜５と、を備えている。さらに、正極電解液を正極活物質反応槽３に供給するための正極電解液貯蔵タンク６及び正極電解液送液ポンプ８と、負極電解液を負極活物質反応槽４に供給するための負極電解液貯蔵タンク７及び負極電解液送液ポンプ９と、正極電解液送液ポンプ８及び負極電解液送液ポンプ９を駆動する外部電源１０とを備えている。 2 includes a positive electrode 1, a negative electrode 2, a positive electrode active material reaction tank 3, a negative electrode active material reaction tank 4, and a diaphragm 5. Furthermore, a positive electrode electrolyte storage tank 6 and a positive electrode electrolyte feed pump 8 for supplying the positive electrode electrolyte to the positive electrode active material reaction tank 3, and a negative electrode electrolysis for supplying the negative electrode electrolyte to the negative electrode active material reaction tank 4. A liquid storage tank 7 and a negative electrode electrolyte feed pump 9, and an external power source 10 that drives the positive electrode electrolyte feed pump 8 and the negative electrode electrolyte feed pump 9 are provided.
　図２において、矢印は電解液の流動する方向を示している。図２に示す場合では、正極電解液は、正極電解液貯蔵タンク６から正極電解液送液ポンプ８により正極活物質反応槽３へ供給され、ヨウ素の酸化還元反応が進行する。負極電解液は、負極電解液貯蔵タンク７から負極電解液送液ポンプ９により負極活物質反応槽４へ供給され、負極活物質の酸化還元反応が進行する。正極電解液送液ポンプ８と負極電解液送液ポンプ９は、外部電源１０により駆動される。 In FIG. 2, the arrow indicates the direction in which the electrolyte flows. In the case shown in FIG. 2, the positive electrode electrolyte is supplied from the positive electrode electrolyte storage tank 6 to the positive electrode active material reaction tank 3 by the positive electrode electrolyte feed pump 8, and the oxidation-reduction reaction of iodine proceeds. The negative electrode electrolyte is supplied from the negative electrode electrolyte storage tank 7 to the negative electrode active material reaction tank 4 by the negative electrode electrolyte feed pump 9, and the redox reaction of the negative electrode active material proceeds. The positive electrode electrolyte feed pump 8 and the negative electrode electrolyte feed pump 9 are driven by an external power source 10.
　図２に示すように、電解液を流動させることで充放電を行う電池をレドックスフロー電池という。レドックスフロー電池は電池容量が電解液の量に依存するため、電解液を貯蔵するタンクの容量を増やすことで大容量化が容易に行えるという利点がある。また、電解液を循環させることで、電解液に含まれる有機化合物によるヨウ素皮膜の溶解が促進されるため、ヨウ素皮膜の形成が有効に抑制され、ヨウ素皮膜による流路の目詰まりが有効に防止される。 As shown in FIG. 2, a battery that charges and discharges by flowing an electrolyte is called a redox flow battery. The redox flow battery has an advantage that the capacity can be easily increased by increasing the capacity of the tank for storing the electrolyte because the battery capacity depends on the amount of the electrolyte. In addition, circulation of the electrolyte promotes dissolution of the iodine film by the organic compounds contained in the electrolyte, effectively suppressing the formation of the iodine film and effectively preventing clogging of the flow path by the iodine film. Is done.
　図２に示す構成では、水溶液系二次電池における電解液の流動は外部電源１０によって正極電解液送液ポンプ８及び負極電解液送液ポンプ９を駆動することで行っているが、水溶液系二次電池自体の発電による電力を用いて正極電解液送液ポンプ８及び負極電解液送液ポンプ９を駆動してもよい。この場合は、外部からの電力供給がない自立系の構成となる。 In the configuration shown in FIG. 2, the flow of the electrolyte in the aqueous secondary battery is performed by driving the positive electrolyte feed pump 8 and the negative electrolyte feed pump 9 by the external power source 10. You may drive the positive electrode electrolyte liquid feed pump 8 and the negative electrode electrolyte liquid feed pump 9 using the electric power by the next battery itself. In this case, the configuration is a self-supporting system with no external power supply.
＜水溶液系二次電池（第２実施形態）＞
　本実施形態の水溶液系二次電池は、正極と、負極と、電解液とを備え、前記電解液はヨウ化物イオンと、負極活物質と、前記ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物と、を含む。 <Aqueous Secondary Battery (Second Embodiment)>
The aqueous secondary battery of this embodiment includes a positive electrode, a negative electrode, and an electrolytic solution, and the electrolytic solution can separate iodide ions, a negative electrode active material, and an oxidation reaction product of the iodide ions. An organic compound.
　本実施形態の水溶液系二次電池は、電解液が正極活物質（ヨウ化物イオン）を含む正極電解液と負極活物質を含む負極電解液とに分かれておらず、同じ電解液が正極活物質（ヨウ化物イオン）と負極活物質を含んでいる。以下、このような構成を有する水溶液系二次電池を「一液型水溶液系二次電池」とも称する。 The aqueous secondary battery of the present embodiment is not divided into a positive electrode electrolyte containing a positive electrode active material (iodide ion) and a negative electrode electrolyte containing a negative electrode active material, and the same electrolyte is a positive electrode active material. (Iodide ion) and a negative electrode active material are contained. Hereinafter, the aqueous secondary battery having such a configuration is also referred to as “one-component aqueous secondary battery”.
　本実施形態の水溶液系二次電池において、正極、負極、電解液、活物質（正極活物質及び負極活物質）、有機化合物等の詳細及び好ましい態様は、第一実施形態の水溶液系二次電池における正極、負極、電解液、活物質、有機化合物等の詳細及び好ましい態様と同様である。 In the aqueous secondary battery of the present embodiment, details and preferred aspects of the positive electrode, the negative electrode, the electrolytic solution, the active material (the positive electrode active material and the negative electrode active material), the organic compound and the like are the aqueous solution secondary battery of the first embodiment. The details and preferred embodiments of the positive electrode, the negative electrode, the electrolytic solution, the active material, the organic compound, and the like in FIG.
　図３は、本実施形態の水溶液系二次電池の構成例の一例を示す概略断面図である。実線の矢印は充電時における電子の流れを、点線の矢印は充電時におけるイオンの反応を示している。 FIG. 3 is a schematic cross-sectional view showing an example of the configuration example of the aqueous solution type secondary battery of the present embodiment. Solid arrows indicate the flow of electrons during charging, and dotted arrows indicate the reaction of ions during charging.
　図３に示す水溶液系二次電池は、正極１と、負極２と、活物質反応槽１１とを備えている。活物質反応槽１１は、電解液を収容している。また、電解液は正極活物質としてのヨウ化物イオンと、負極活物質と、ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物を含んでいる。 The aqueous secondary battery shown in FIG. 3 includes a positive electrode 1, a negative electrode 2, and an active material reaction tank 11. The active material reaction tank 11 contains an electrolytic solution. Further, the electrolyte contains an iodide ion as a positive electrode active material, a negative electrode active material, and an organic compound capable of separating an oxidation reaction product of iodide ions.
　本実施形態の水溶液系二次電池は、正極が鉛直方向において負極よりも下側に位置することが好ましい。正極が負極よりも下側に位置することで、有機化合物によって分離されたヨウ化物イオンの酸化反応生成物が電解液中に沈殿し、正極側に集まる。これにより、ヨウ化物イオンの酸化反応生成物を正極での還元反応に有効に利用することができる。 In the aqueous solution type secondary battery of the present embodiment, the positive electrode is preferably located below the negative electrode in the vertical direction. Since the positive electrode is positioned below the negative electrode, the oxidation reaction product of iodide ions separated by the organic compound is precipitated in the electrolytic solution and collected on the positive electrode side. Thereby, the oxidation reaction product of iodide ions can be effectively used for the reduction reaction at the positive electrode.
　本実施形態の水溶液系二次電池では、負極活物質としては、その還元反応生成物が負極近傍に留まる性質を有する物質を用いることが好ましい。これにより、正極と負極でそれぞれ生成した充電反応生成物をそれぞれ正極側と負極側に存在させることができ、両者を空間的により分離することが可能となる。その結果、正極と負極でそれぞれ生成した充電反応生成物同士が接触して自己放電が生じるのを抑制することができる。 In the aqueous secondary battery of the present embodiment, it is preferable to use a material having a property that the reduction reaction product stays in the vicinity of the negative electrode as the negative electrode active material. Thereby, the charge reaction product produced | generated with the positive electrode and the negative electrode can respectively exist in the positive electrode side and the negative electrode side, respectively, and it becomes possible to isolate | separate both more spatially. As a result, it can suppress that the charge reaction product produced | generated with the positive electrode and the negative electrode respectively contacts and self-discharge arises.
　水溶液系二次電池を一液型にすることの利点としては（１）正極と負極の間に配置される隔膜を省略できる、（２）充放電に伴い正極側と負極側で水分子が移動して電解液量が不均一化するのを防ぐことができる、（３）有機化合物によって分離されたヨウ化物イオンの酸化反応生成物が沈澱して正極側に集まるため、電解液を流動させるための装置を省略できる、（４）電解液を流動させるための装置を設ける場合、正極側と負極側を区別する必要がなく構成を簡略化できる、等が挙げられる。 Advantages of using an aqueous secondary battery as a one-pack type are: (1) The diaphragm disposed between the positive electrode and the negative electrode can be omitted. (2) Water molecules move between the positive electrode side and the negative electrode side during charging and discharging. (3) Because the oxidation reaction product of iodide ions separated by the organic compound is precipitated and collects on the positive electrode side, the electrolyte solution is made to flow. (4) When a device for flowing the electrolyte is provided, it is not necessary to distinguish between the positive electrode side and the negative electrode side, and the configuration can be simplified.
　必要に応じ、本実施形態の水溶液系二次電池は、正極１と負極２の間に隔膜５を備えていてもよい。図４は、図３に示す水溶液系二次電池が正極１と負極２の間に隔膜５をさらに備える場合の構成を示す概略断面図である。図中に示す水溶液系二次電池が備える要素のうち図１に示す水溶液系二次電池が備える要素と共通するものについては、説明を省略する。 If necessary, the aqueous secondary battery of this embodiment may include a diaphragm 5 between the positive electrode 1 and the negative electrode 2. FIG. 4 is a schematic cross-sectional view showing a configuration when the aqueous secondary battery shown in FIG. 3 further includes a diaphragm 5 between the positive electrode 1 and the negative electrode 2. Descriptions of elements provided in the aqueous secondary battery shown in the figure that are common to those provided in the aqueous secondary battery shown in FIG. 1 are omitted.
　図４に示す水溶液系二次電池が備える隔膜５の詳細及び好ましい態様は、第一実施形態の水溶液系二次電池が備える隔膜５の詳細及び好ましい態様と同様である。一液型の水溶液系二次電池に隔膜を設けることにより、正極と負極でそれぞれ生成した充電反応生成物同士が接触することを更に抑制でき、一液型水溶液系二次電池のクーロン効率をさらに向上させることができる。 The details and preferred aspects of the diaphragm 5 provided in the aqueous secondary battery shown in FIG. 4 are the same as the details and preferred aspects of the diaphragm 5 provided in the aqueous secondary battery of the first embodiment. By providing a diaphragm in the one-pack type aqueous secondary battery, it is possible to further suppress the contact between the charge reaction products generated at the positive electrode and the negative electrode, respectively, and further improve the coulomb efficiency of the one-pack type aqueous secondary battery. Can be improved.
　必要に応じ、本実施形態の水溶液系二次電池は、電解液を流動させるための装置をさらに備えていてもよい。図５は、図４に示す水溶液系二次電池が電解液を流動させるための装置として、電解液を活物質反応槽１１に供給するための電解液貯蔵タンク１２と、電解液送液ポンプ１３と、電解液送液ポンプ１３を駆動する外部電源１０とをさらに備える場合の構成を示す概略断面図である。 If necessary, the aqueous solution type secondary battery of the present embodiment may further include a device for flowing the electrolytic solution. FIG. 5 shows an electrolytic solution storage tank 12 for supplying the electrolytic solution to the active material reaction tank 11 and an electrolytic solution feed pump 13 as devices for allowing the aqueous secondary battery shown in FIG. 4 to flow the electrolytic solution. FIG. 2 is a schematic cross-sectional view showing a configuration in a case where the apparatus further includes an external power source 10 that drives the electrolyte solution pump 13.
　図５に示す水溶液系二次電池は隔膜５と電解液を流動させるための装置をともに備えているが、隔膜５を備えない態様であってもよい。 Although the aqueous solution type secondary battery shown in FIG. 5 includes both the diaphragm 5 and a device for causing the electrolyte to flow, an embodiment without the diaphragm 5 may be used.
　図５において、矢印は電解液の流動する方向を示している。電解液は、電解液貯蔵タンク１２から電解液送液ポンプ１３により活物質反応槽１１へ供給される。正極ではヨウ化物イオンの酸化還元反応が進行し、酸化反応時には酸化反応生成物が生成する。一方、負極では負極活物質の酸化還元反応が進行し、還元反応時には還元反応生成物が生成する。電解液送液ポンプ１３は、外部電源１０により駆動される。 In FIG. 5, the arrow indicates the direction in which the electrolyte flows. The electrolytic solution is supplied from the electrolytic solution storage tank 12 to the active material reaction tank 11 by the electrolytic solution feeding pump 13. An oxidation-reduction reaction of iodide ions proceeds at the positive electrode, and an oxidation reaction product is generated during the oxidation reaction. On the other hand, in the negative electrode, the redox reaction of the negative electrode active material proceeds, and a reduction reaction product is generated during the reduction reaction. The electrolyte solution feed pump 13 is driven by the external power supply 10.
　図５に示す構成では、水溶液系二次電池における電解液の流動は外部電源１０によって電解液送液ポンプ１３を駆動することで行っているが、水溶液系二次電池自体の発電による電力を用いて電解液送液ポンプ１３を駆動してもよい。この場合は、外部からの電力供給がない自立系の構成となる。 In the configuration shown in FIG. 5, the flow of the electrolyte in the aqueous secondary battery is performed by driving the electrolyte feed pump 13 by the external power source 10, but the electric power generated by the aqueous secondary battery itself is used. The electrolyte solution pump 13 may be driven. In this case, the configuration is a self-supporting system with no external power supply.
＜水溶液系二次電池の充放電方法＞
　本実施形態の水溶液系二次電池の充放電方法（以下、単に充放電方法とも称する）は、正極活物質としてヨウ化物イオンを含む電解液を用いる水溶液系二次電池の充放電方法であって、前記電解液中に生成するヨウ化物イオンの酸化反応生成物を分離する工程を含む。 <Charging / discharging method of aqueous secondary battery>
The charge / discharge method for an aqueous secondary battery of the present embodiment (hereinafter also simply referred to as charge / discharge method) is a charge / discharge method for an aqueous secondary battery using an electrolytic solution containing iodide ions as a positive electrode active material. And a step of separating an oxidation reaction product of iodide ions generated in the electrolytic solution.
　上記充放電方法を水溶液系二次電池の充放電方法として適用すると、充電により生成したヨウ化物イオンの酸化反応生成物が選択的に電解液から分離される。これにより、電極表面に形成された高抵抗のヨウ素皮膜の溶解が促進されて酸化電流値の低下が抑制される、ヨウ素皮膜から電解液中に拡散したＩ２分子が系外に昇華するのが抑制されてヨウ化物イオンの電解液中の濃度低下が抑制される、分離した酸化反応生成物が正極における還元反応に利用されるため、水溶液系二次電池の低充電率での出力特性を向上できる、等の効果が期待できる。 When the charging / discharging method is applied as a charging / discharging method for an aqueous secondary battery, an oxidation reaction product of iodide ions generated by charging is selectively separated from the electrolytic solution. As a result, dissolution of the high-resistance iodine film formed on the electrode surface is promoted, and a decrease in the oxidation current value is suppressed. I 2 molecules diffused from the iodine film into the electrolyte solution sublimate outside the system. Suppressed and reduced concentration of iodide ion in the electrolyte solution, because the separated oxidation reaction product is used for the reduction reaction at the positive electrode, improving the output characteristics of the aqueous secondary battery at low charge rate Can be expected.
　電解液中に生成するヨウ化物イオンの酸化反応生成物を分離する方法は、特に制限されない。例えば、上述した水溶液系二次電池に使用される電解液を用いてヨウ化物イオンの酸化反応生成物を分離する方法が挙げられる。 The method for separating the oxidation reaction product of iodide ions generated in the electrolytic solution is not particularly limited. For example, a method of separating an oxidation reaction product of iodide ions using an electrolytic solution used in the above-described aqueous secondary battery can be mentioned.
＜水溶液二次電池用電解液（第１実施形態）＞
　本実施形態の水溶液系二次電池用電解液（以下、単に電解液とも称する）は、水と、ヨウ化物イオンと、ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物と、を含み、上述した水溶液系二次電池の充放電方法の電解液として使用される。 <Electrolyte for Aqueous Solution Secondary Battery (First Embodiment)>
The electrolytic solution for an aqueous secondary battery of the present embodiment (hereinafter also simply referred to as an electrolytic solution) includes water, iodide ions, and an organic compound capable of separating an oxidation reaction product of iodide ions, It is used as an electrolytic solution for the above-described charge / discharge method of an aqueous secondary battery.
＜水溶液二次電池用電解液（第２実施形態）＞
　本実施形態の水溶液系二次電池用電解液は、水と、ヨウ化物イオンと、メチルエチルケトン、酢酸メチル、酢酸エチル、炭酸ジメチル、炭酸エチルメチル及び炭酸プロピレンからなる群より選択される少なくとも１種の有機化合物と、を含む。 <Electrolyte for Aqueous Solution Secondary Battery (Second Embodiment)>
The electrolytic solution for an aqueous secondary battery of the present embodiment is at least one selected from the group consisting of water, iodide ions, methyl ethyl ketone, methyl acetate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate. An organic compound.
　上記各実施形態の電解液を水溶液系二次電池に使用した場合、充電により生成したヨウ化物イオンの酸化反応生成物が選択的に電解液から分離される。これにより、電極表面に形成された高抵抗のヨウ素皮膜の溶解が促進されて酸化電流値の低下が抑制される、ヨウ素皮膜から電解液中に拡散したＩ２分子が系外に昇華するのが抑制されてヨウ化物イオンの電解液中の濃度低下が抑制される、分離した酸化反応生成物が正極における還元反応に利用されるため、水溶液系二次電池の低充電率での出力特性を向上できる等の効果が期待できる。 When the electrolytic solution of each of the above embodiments is used in an aqueous secondary battery, the oxidation reaction product of iodide ions generated by charging is selectively separated from the electrolytic solution. As a result, dissolution of the high-resistance iodine film formed on the electrode surface is promoted, and a decrease in the oxidation current value is suppressed. I 2 molecules diffused from the iodine film into the electrolyte solution sublimate outside the system. Suppressed and reduced concentration of iodide ion in the electrolyte solution, because the separated oxidation reaction product is used for the reduction reaction at the positive electrode, improving the output characteristics of the aqueous secondary battery at low charge rate We can expect effects such as being able to.
　電解液に含まれるヨウ化物イオン及び有機化合物の詳細及び好ましい態様は、上述した水溶液系二次電池に用いられる電解液に含まれるヨウ化物イオン及び有機化合物の詳細及び好ましい態様と同様である。 Details and preferred embodiments of iodide ions and organic compounds contained in the electrolytic solution are the same as the details and preferred embodiments of iodide ions and organic compounds contained in the electrolytic solution used in the above-described aqueous secondary battery.
＜フロー電池システム＞
　本実施形態のフロー電池システムは、上述した水溶液系二次電池と、充放電を制御し、正極の充電電位を、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．５Ｖ以下に設定する制御部と、を備える。 <Flow battery system>
Flow battery system of this embodiment, the aqueous secondary battery described above, by controlling the charging and discharging, a charging potential of the positive electrode, Ag / AgCl reference electrode - 1.5V or less relative to the potential of (Cl concentration saturation) And a control unit to be set.
　上記フロー電池システムに用いられる水溶液系二次電池の詳細及び好ましい態様は、上述した水溶液系二次電池の詳細及び好ましい態様と同様である。フロー電池システムにおける制御部は、水溶液系二次電池と一体化した状態であっても一体化していない状態であってもよい。 The details and preferred embodiments of the aqueous secondary battery used in the flow battery system are the same as the details and preferred embodiments of the aqueous secondary battery described above. The controller in the flow battery system may be in a state of being integrated with the aqueous secondary battery or not.
　上記フロー電池システムにおいて、正極の充電電位は、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．３Ｖ以下に設定されることが好ましく、１．０５Ｖ以下に設定されることがより好ましい。 In the above flow battery system, the charging potential of the positive electrode is preferably set to 1.3 V or less, and preferably set to 1.05 V or less, based on the potential of the Ag / AgCl reference electrode (Cl − concentration saturation). More preferred.
　以下、フロー電池システムにて、正極の充電電位が、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として基準値を超えないように制御することの利点について記載する。 Hereinafter, in flow battery system, the charge potential of the positive electrode, Ag / AgCl reference electrode - describes the benefits of controlling so as not to exceed the reference value as a reference to the potential of (Cl concentration saturation).
　フロー電池システムにて、正極電解液は正極活物質としてヨウ化物イオンを含有する。このため、以下の式（１）及び（２）に示す充電反応により、正極にてヨウ化物イオン（Ｉ－）が酸化されてＩ３ －及びＩ２が通常生成され、生成されたＩ３ －及びＩ２は式（１）及び（２）に示す放電反応により、正極にて還元されてＩ－となる。 In the flow battery system, the positive electrode electrolyte contains iodide ions as the positive electrode active material. For this reason, iodide ions (I − ) are oxidized at the positive electrode by the charging reaction shown in the following formulas (1) and (2) to normally generate I 3 − and I 2 , and the generated I 3 − And I 2 are reduced to I − by the discharge reaction shown in the formulas (1) and (2) at the positive electrode.
　３Ｉ－⇔Ｉ３ －＋２ｅ－　　　（１）
　２Ｉ－⇔Ｉ２＋２ｅ－　　　（２） 3I − ⇔I 3 − + 2e − (1)
2I − ⇔I 2 + 2e − (2)
　フロー電池システムでは、正極の充電電位が、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．０５Ｖを超える場合、上記式（１）及び（２）で示す充電反応とともに以下式（３）で示すＩＯ３ －の生成反応が生じる（文献１：Ｐ．Ｂｅｒａｎ　ａｎｄ　Ｓ．Ｂｒｕｃｈｅｎｓｔｅｉｎ，Ｖｏｌｔａｍｍｅｔｒｙ　ｏｆ　Ｉｏｄｉｎｅ（Ｉ）Ｃｈｏｌｒｉｄｅ，Ｉｏｄｉｎｅ　ａｎｄ　Ｉｏｄａｔｅ　ａｔ　Ｒｏｔａｔｅｄ　Ｐｌａｔｉｎｕｍ　Ｄｉｓｋ　ａｎｄ　Ｒｉｎｇ－Ｄｉｓｋ　Ｅｌｅｃｔｒｏｄｅｓ，　Ａｎａｌｙｔｉｃａｌ　Ｃｈｅｍｉｓｔｒｙ，４０，１０４４（１９６８））。 In the flow cell system, the charge potential of the positive electrode, Ag / AgCl reference electrode - if it exceeds 1.05V relative to the potential of (Cl concentration saturation), below formula with charging reaction shown by the formula (1) and (2) The production reaction of IO 3 − shown in (3) occurs (Reference 1: P. Beran and S. Bruchenstein, Voltammetry of Iodine (I) Chloride, Iodine and Iodated at Rotated Platinum Disc and Electrified Disc and Electric Distinguished and Ridged Platinum Disk and Ridged Platinum Disk and Ridged Platinum Disk and Ridged , 1044 (1968)).
　Ｉ－＋３Ｈ２Ｏ→ＩＯ３ －＋６Ｈ＋＋６ｅ－　　　（３） I − + 3H 2 O → IO 3 − + 6H + + 6e − (3)
　上記式（３）で示す反応は不可逆な反応であると報告されており、逆反応の反応速度は極めて小さい。 The reaction represented by the above formula (3) is reported to be an irreversible reaction, and the reaction rate of the reverse reaction is extremely small.
　また、以下の式（４）で表されるＤｕｓｈｍａｎ反応により、上記式（３）で生成されたＩＯ３ －からＩ２が生成される。 Further, I 2 is generated from IO 3 − generated by the above formula (3) by the Dushman reaction represented by the following formula (4).
　ＩＯ３ －＋５Ｉ－＋６Ｈ＋→３Ｉ２＋３Ｈ２Ｏ　　　（４） IO 3 − + 5I − + 6H + → 3I 2 + 3H 2 O (4)
　更に、以下の式（５）は、上記式（３）及び式（４）の全反応（式（３）＋式（４））として求められる。 Furthermore, the following formula (5) is obtained as the total reaction (formula (3) + formula (4)) of the above formula (3) and formula (4).
　Ｉ２＋６Ｈ２Ｏ→２ＩＯ３ －＋１２Ｈ＋＋１０ｅ－　　　（５） I 2 + 6H 2 O → 2IO 3 − + 12H + + 10e − (5)
　上記文献１によれば、上記式（４）の化学反応速度は上記式（３）の電気化学反応に比べて速く、式（３）及び式（４）を構成反応とする式（５）の律速過程は、式（３）の電気化学反応である。このため、正極の充電電位が、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．０５Ｖを超える場合特に顕著になるが、安全マージンをとって１．３Ｖ、１．５Ｖを超えないように設定してもよく、上記式（３）～式（５）の反応が生じていると推測される。 According to the literature 1, the chemical reaction rate of the above formula (4) is faster than the electrochemical reaction of the above formula (3), and the formula (5) in which the formula (3) and the formula (4) are constituent reactions. The rate limiting process is the electrochemical reaction of formula (3). Therefore, the charge potential of the positive electrode, Ag / AgCl reference electrode - becomes particularly noticeable if it exceeds 1.05V relative to the potential of (Cl concentration saturation), 1.3V taking a safety margin, the 1.5V It may be set so as not to exceed, and it is estimated that the reactions of the above formulas (3) to (5) occur.
　このため、Ａｇ／ＡｇＣｌ参照電極の電位を基準として１．０５Ｖを超える正極充電電位で充電が繰り返される場合、正極の充電反応により式（３）に基づいてＩＯ３ －が生成される。ＩＯ３ －は式（３）の逆反応である放電反応の反応速度が遅く、Ｉ－に非常に戻りにくい。 For this reason, when charging is repeated at a positive electrode charging potential exceeding 1.05 V with respect to the potential of the Ag / AgCl reference electrode, IO 3 − is generated based on the equation (3) by the positive electrode charging reaction. IO 3 − has a slow reaction rate of the discharge reaction, which is the reverse reaction of the formula (3), and hardly returns to I − .
　更に、式（３）に基づき生成されたＩＯ３ －は、式（４）の反応により、電解液中のＩ－と反応し、正極での電子の授受を伴わずに電解液中のＩ－が消費される。 Furthermore, IO 3 generated based on equation (3) - by reaction of formula (4), I in the electrolyte - reacted with, in the electrolytic solution without electron transfer at the positive electrode I - Is consumed.
　また、式（３）及び式（４）の全反応である式（５）に示す反応により、Ｉ２が反応してＩＯ３ －が生成されるが、式（３）に示す反応と同様に、式（５）に示す反応も不可逆反応である。このため、生成されるＩＯ３ －は式（５）の逆反応である放電反応の反応速度が遅く、Ｉ２に非常に戻りにくい。 Further, by the reaction shown in Equation (5) is the total reaction of the formula (3) and (4), IO 3 by the reaction I 2 - but is produced, in the same manner as in the reaction shown in equation (3) The reaction shown in Formula (5) is also an irreversible reaction. For this reason, the generated IO 3 − has a slow reaction rate of the discharge reaction, which is the reverse reaction of the formula (5), and hardly returns to I 2 .
　したがって、１．０５Ｖを超える正極充電電位で充電が繰り返される場合、放電反応に寄与しないＩＯ３ －の割合が増加し、かつＩ－及びＩ２の濃度の合計が低下することによって、しだいにフロー電池システムは正極放電容量及び正極充電容量が低下するという問題がある。 Accordingly, when charging is repeated at a positive electrode charging potential exceeding 1.05 V, the proportion of IO 3 − that does not contribute to the discharge reaction increases, and the total concentration of I − and I 2 decreases, so that the flow gradually increases. The battery system has a problem that the positive electrode discharge capacity and the positive electrode charge capacity decrease.
　一方、本実施形態のフロー電池システムは、充放電を制御し、正極の充電電位を、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．０５Ｖ以下に設定する制御部を備えている。これにより、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．５Ｖ以下に設定でき、フロー電池システムの充電時にＩＯ３ －の生成反応を抑制できる。ＩＯ３ －の生成を抑制することで、可逆的に充放電する際のヨウ素イオン及びヨウ素分子の合計濃度を維持して正極放電容量及び正極充電容量を維持することができる。したがって、本実施形態では、実用可能な充電条件を満たすフロー電池システムを提供することができる。 On the other hand, the flow cell system of the present embodiment controls the charging and discharging, a charging potential of the positive electrode, Ag / AgCl reference electrode - a control unit that sets below 1.05V relative to the potential of (Cl concentration saturation) ing. Thus, Ag / AgCl reference electrode - can set the potential of the (Cl concentration saturation) below 1.5V as a reference, IO 3 during charging of the flow cell system - can inhibit the production reaction of. By suppressing the production of IO 3 − , the positive electrode discharge capacity and the positive electrode charge capacity can be maintained by maintaining the total concentration of iodine ions and iodine molecules when reversibly charging and discharging. Therefore, in this embodiment, a flow battery system that satisfies a practical charge condition can be provided.
　なお、フロー電池システムにおける正極の充電電位は、充電電圧ではない。充電電位とはある基準となる電位を持つ電極に対して示す電圧である。充電電圧は負極と正極の電位の差である。充電電位は基準になる一定の電位をベースにしているため、電位一定と言えば基準電極に対して一定の値とみなせる。しかし、負極と正極間の充電電圧の場合は負極と正極が同じように電位変動した場合は、電圧は見かけ上一定となる。したがって、正極の電位は充電電圧によって決まるものではなく、基準となる正極用参照電極の電位に対して計測する必要がある。 Note that the charge potential of the positive electrode in the flow battery system is not the charge voltage. The charging potential is a voltage indicated with respect to an electrode having a certain reference potential. The charging voltage is the difference in potential between the negative electrode and the positive electrode. Since the charging potential is based on a constant potential as a reference, if the potential is constant, it can be regarded as a constant value with respect to the reference electrode. However, in the case of a charging voltage between the negative electrode and the positive electrode, when the potential fluctuates in the same way between the negative electrode and the positive electrode, the voltage is apparently constant. Therefore, the potential of the positive electrode is not determined by the charging voltage, and needs to be measured with respect to the potential of the reference electrode for positive electrode serving as a reference.
（制御部）
　フロー電池システムは、充放電を制御し、正極の充電電位を、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．５Ｖ以下に設定する制御部を備える。これにより、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．５Ｖ以下に設定でき、フロー電池システムの充電時にＩＯ３ －の生成反応を抑制できる。ＩＯ３ －の生成を抑制することで、可逆的に充放電する際のヨウ素イオン及びヨウ素分子（Ｉ－、Ｉ３ －及びＩ２）の合計濃度を維持して正極放電容量及び正極充電容量の低下が抑えられ、サイクル耐久性が向上できる。 (Control part)
Flow battery system controls the charging and discharging, a charging potential of the positive electrode, Ag / AgCl reference electrode - a control unit for setting a potential of (Cl concentration saturation) to 1.5V below as a reference. Thus, Ag / AgCl reference electrode - can set the potential of the (Cl concentration saturation) below 1.5V as a reference, IO 3 during charging of the flow cell system - can inhibit the production reaction of. By suppressing the production of IO 3 − , the total concentration of iodine ions and iodine molecules (I − , I 3 − and I 2 ) during reversible charge / discharge is maintained, and the positive electrode discharge capacity and the positive electrode charge capacity are increased. Reduction is suppressed and cycle durability can be improved.
　なお、「正極の充電電位を、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．５Ｖ以下に設定する」とは、原則的に、正極の充電電位を１．５Ｖ以下としてフロー電池を充電することを意味し、正極の充電電位が１．５Ｖを超えることも許容される。例えば、後述するリップルノイズ等の影響により、正極の充電電位が１．５Ｖを超えることが避けられない場合等には、正極の充電電位が１．５Ｖを超えることもあり得る。 Note that “the positive electrode charging potential is set to 1.5 V or less with respect to the potential of the Ag / AgCl reference electrode (Cl − concentration saturation)” in principle means that the positive electrode charging potential is 1.5 V or less. It means that the flow battery is charged, and it is allowed that the charging potential of the positive electrode exceeds 1.5V. For example, when it is unavoidable that the charging potential of the positive electrode exceeds 1.5 V due to the influence of ripple noise or the like described later, the charging potential of the positive electrode may exceed 1.5 V.
　例えば、制御部は、正極の充電電位が１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）を超えない条件で、設定電圧に達するまで定電流充電を行い、設定電圧に達した後は定電圧充電を行うようにフロー電池を制御する。 For example, the control unit performs constant current charging until reaching the set voltage under the condition that the charging potential of the positive electrode does not exceed 1.5 V (vs. Ag / AgCl), and performs constant voltage charging after reaching the set voltage. Control the flow battery.
　また、制御部は、正極の充電電位を、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．５Ｖ以下に制御することが好ましい。正極の充電電位を１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）以下に制御することにより、正極（特に、炭素電極）の劣化が抑えられる傾向にある。また、正極電解液がヨウ素分子に対する良溶媒としてエタノールを含有する場合には、正極の充電電位を１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）以下に制御することにより、エタノールの分解がより抑制される傾向にある。 The control unit, the charging potential of the positive electrode, Ag / AgCl reference electrode - it is preferable to control the potential of the (Cl concentration saturation) to 1.5V below as a reference. By controlling the charging potential of the positive electrode to 1.5 V (vs. Ag / AgCl) or less, deterioration of the positive electrode (particularly, carbon electrode) tends to be suppressed. Further, when the positive electrode electrolyte contains ethanol as a good solvent for iodine molecules, the decomposition of ethanol is further suppressed by controlling the positive electrode charging potential to 1.5 V (vs. Ag / AgCl) or lower. There is a tendency.
　なお、「正極の充電電位を、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．５Ｖ以下に制御する」とは、正極の充電電位を１．５Ｖ以下としてフロー電池の充電を行うことを意味し、正極の充電電位が１．５Ｖを超えることは許容されない。 “The charging potential of the positive electrode is controlled to 1.5 V or less with respect to the potential of the Ag / AgCl reference electrode (Cl − concentration saturation)” means that the charging potential of the positive electrode is 1.5 V or less and the flow battery is charged. And the charge potential of the positive electrode is not allowed to exceed 1.5V.
　例えば、制御部は、後述するリップルノイズ等の影響により、正極の充電電位が１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）を超える場合には、高周波フィルタ等により超過分をカットするようにフロー電池を制御する。後述するリップルノイズが重畳しても正極の充電電位が１．０５Ｖ～１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）の範囲に収まる場合、制御部は、特段の制御を行わなくてもよい。これは、前述した式（３）で表されるＩＯ３ －の生成反応は、リップルノイズのような高周波信号に追随し難いと考えられるためである。 For example, when the charge potential of the positive electrode exceeds 1.5 V (vs. Ag / AgCl) due to the influence of ripple noise, which will be described later, the control unit sets the flow battery so as to cut the excess by a high frequency filter or the like. Control. If the charge potential of the positive electrode falls within the range of 1.05 V to 1.5 V (vs. Ag / AgCl) even if ripple noise described later is superimposed, the control unit does not have to perform special control. This is because the generation reaction of IO 3 − represented by the above-described equation (3) is considered difficult to follow a high-frequency signal such as ripple noise.
　また、フロー電池システムでは、正極の充電電位を、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．５Ｖ未満に設定することが好ましく、１．３Ｖ以下に設定することがより好ましく、１．０５Ｖ以下に設定することが更に好ましい。
　正極の充電電位が１．５Ｖを超える条件でフロー電池システムを運用する場合、運用期間中、後述するサンプリング部を用いて正極電解液を定期的にサンプリングしてもよく、後述する濃度調整部を用いて正極への電解液又はそこに含まれる成分の追加を行い、正極電解液に含有される成分の濃度を調整してもよい。 Further, in the flow cell system, the charging potential of the positive electrode, Ag / AgCl reference electrode - is preferably set to less than 1.5V relative to the potential of (Cl concentration saturation), more be set below 1.3V Preferably, it is more preferably set to 1.05 V or less.
When the flow battery system is operated under the condition that the charging potential of the positive electrode exceeds 1.5V, the positive electrode electrolyte may be periodically sampled during the operation period using a sampling unit described later. It is also possible to adjust the concentration of the component contained in the positive electrode electrolyte by adding the electrolyte or the component contained therein to the positive electrode.
（正極用参照電極）
　フロー電池システムは、正極の電位を計測するための正極用参照電極を備えていてもよい。
　正極用参照電極は、標準水素電極電位（ｓｔａｎｄａｒｄ　ｈｙｄｒｏｇｅｎ　ｅｌｅｃｔｒｏｄｅ　ｐｏｔｅｎｔｉａｌ）に対する電位に換算可能で、安定した電気化学電位を示せるものであればよい。電気化学電位基準となる参照電極は、電気化学の基本事項として多くの教科書に示されている（例えば、Ａｌｌｅｎ　Ｊ．Ｂａｒｄ　ａｎｄ　Ｌａｒｒｙ　Ｒ．Ｆａｕｌｋｎｅｒ、「ＥＬＥＣＴＲＯＣＨＥＭＩＣＡＬ　ＭＥＴＨＯＤＳ」ｐ．３、（１９８０）、Ｊｏｈｎ　Ｗｉｌｅｙ　＆　Ｓｏｎｓ，Ｉｎｃ．）。参照電極としては、Ａｇ／ＡｇＣｌ参照電極、飽和カロメル電極（ｓａｔｕｒａｔｅｄ　ｃａｌｏｍｅｌ　ｅｌｅｃｔｒｏｄｅ）等が挙げられ、Ａｇ／ＡｇＣｌ参照電極が好ましい。 (Reference electrode for positive electrode)
The flow battery system may include a positive electrode reference electrode for measuring the positive electrode potential.
The reference electrode for a positive electrode may be any one that can be converted into a potential with respect to a standard hydrogen electrode potential and can exhibit a stable electrochemical potential. A reference electrode serving as an electrochemical potential standard is shown in many textbooks as basics of electrochemistry (for example, Allen J. Bard and Larry R. Faulkner, “ELECTROCHEMICAL METHODS” p. 3, (1980), John. Wiley & Sons, Inc.). Examples of the reference electrode include an Ag / AgCl reference electrode, a saturated calomel electrode, and the like, and an Ag / AgCl reference electrode is preferable.
　正極用参照電極としては、測定された正極の電位をＡｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位に換算できるものであれば、Ａｇ／ＡｇＣｌ参照電極に限定されず、他の参照電極を用いてもよい。 The positive electrode for the reference electrode, the potential of the measured cathode Ag / AgCl reference electrode - as long as it can be converted to the potential of (Cl concentration sat) is not limited to Ag / AgCl reference electrode, the other reference electrode It may be used.
　また、フロー電池システムは負極の電位を測定するための負極用参照電極を更に備えていてもよい。参照電極の設置箇所は、正極に１箇所あればよく、正極及び負極にそれぞれ１箇所あることが好ましく、正極及び負極にそれぞれ複数箇所あることがより好ましい。 The flow battery system may further include a negative electrode reference electrode for measuring the negative electrode potential. The reference electrode may be provided at one location on the positive electrode, preferably at one location on each of the positive and negative electrodes, and more preferably at a plurality of locations on each of the positive and negative electrodes.
（サンプリング部）
　フロー電池システムは、正極電解液をサンプリングするサンプリング部を備えていてもよい。サンプリング部にて正極電解液をサンプリングすることで、正極電解液に含有される成分の濃度の分析が可能であり、例えば、正極電解液に含有される成分の濃度が規定量、必要量等に比べて不足していないか分析することができる。 (Sampling part)
The flow battery system may include a sampling unit that samples the positive electrode electrolyte. By sampling the positive electrode electrolyte in the sampling section, it is possible to analyze the concentration of the component contained in the positive electrode electrolyte. For example, the concentration of the component contained in the positive electrode electrolyte is adjusted to a specified amount, a required amount, etc. It is possible to analyze whether there is a shortage.
　サンプリング部は、例えば、正極電解液貯蔵タンクに配置されていてもよく、循環経路に配置されていてもよい。また、サンプリング部は、所定の時間毎に正極電解液をサンプリングする構成であってもよい。 The sampling unit may be disposed, for example, in the positive electrode electrolyte storage tank, or may be disposed in the circulation path. Moreover, the structure which samples a positive electrode electrolyte solution for every predetermined time may be sufficient as a sampling part.
（濃度調整部）
　フロー電池システムは、サンプリング部によりサンプリングされた正極電解液を分析し、分析結果に基づいて、正極と正極電解液貯蔵タンクとの間を循環する正極電解液に含有される成分の濃度を調整する濃度調整部を備えていてもよい。フロー電池システムが濃度調整部を備えることで、サンプリング部にてサンプリングした正極電解液に含有される成分の濃度が規定量、必要量等に比べて不足している場合、不足する成分が正極電解液に添加され、正極電解液に含有される成分の濃度を調整することができる。 (Density adjustment unit)
The flow battery system analyzes the positive electrode electrolyte sampled by the sampling unit, and adjusts the concentration of components contained in the positive electrode electrolyte circulating between the positive electrode and the positive electrode electrolyte storage tank based on the analysis result. A density adjusting unit may be provided. Since the flow battery system includes a concentration adjusting unit, when the concentration of the component contained in the positive electrode electrolyte sampled by the sampling unit is insufficient compared to the specified amount, the required amount, etc., the insufficient component is positive electrode electrolysis. The concentration of components added to the liquid and contained in the positive electrode electrolyte can be adjusted.
　濃度調整部は、例えば、正極電解液貯蔵タンクに貯蔵されている正極電解液に各成分を添加する構成であってもよく、循環経路を流通する正極電解液に各成分を添加する構成であってもよい。また、正極電解液へのヨウ素化合物、添加物等の追加は、フロー電池の運転中であってもよく、停止中であってもよい。 For example, the concentration adjusting unit may be configured to add each component to the positive electrode electrolyte stored in the positive electrode electrolyte storage tank, or may be configured to add each component to the positive electrode electrolyte flowing through the circulation path. May be. Moreover, the addition of the iodine compound, additive, etc. to the positive electrode electrolyte may be during operation of the flow battery or may be stopped.
（電位計測部）
　フロー電池システムは、正極電解液中のヨウ素イオン及びヨウ素分子の濃度に基づく電位を計測する電位計測部を備えていてもよい。電位計測部は、例えば、ヨウ素イオン及びヨウ素分子の濃度に基づく電位を計測するための集電電極と、電気化学電位の基準となる参照電極とを有し、参照電極基準の電気化学電位を計測する。電気化学電位に関するネルンストの式を用いることにより、計測された参照電極基準の電気化学電位からヨウ素イオン及びヨウ素分子の濃度を求めることができる。集電電極としては、白金電極、グラファイト電極等が挙げられ、参照電極としては、Ａｇ／ＡｇＣｌ電極等が挙げられる。 (Potential measurement unit)
The flow battery system may include a potential measurement unit that measures a potential based on the concentrations of iodine ions and iodine molecules in the positive electrode electrolyte. The potential measuring unit has, for example, a collecting electrode for measuring a potential based on the concentrations of iodine ions and iodine molecules, and a reference electrode serving as a reference for the electrochemical potential, and measures the electrochemical potential based on the reference electrode To do. By using the Nernst equation relating to the electrochemical potential, the concentration of iodine ions and iodine molecules can be determined from the measured electrochemical potential of the reference electrode standard. Examples of the collecting electrode include a platinum electrode and a graphite electrode, and examples of the reference electrode include an Ag / AgCl electrode.
　制御部は、電位計測部により計測された電位に基づいて充電状態（ＳＯＣ：Ｓｔａｔｅ　Ｏｆ　Ｃｈａｒｇｅ）を推定することができる。例えば、酸化還元物質としてＩ－、Ｉ３ －、及びＩ２のみを考慮した場合、ＳＯＣが０％とは、基本的に正極電解液中にＩ３ －及びＩ２が含まれず、Ｉ－のみとなっている状態を示す。また、ＳＯＣが１００％とは、基本的に正極電解液中にＩ－が含まれず、Ｉ３ －及びＩ２のみとなっている状態を示す。 The control unit can estimate a state of charge (SOC) based on the potential measured by the potential measurement unit. For example, when only I − , I 3 − , and I 2 are considered as redox substances, the SOC of 0% basically means that I 3 − and I 2 are not included in the positive electrode electrolyte, and only I −. It shows the state. An SOC of 100% basically indicates a state in which I − is not contained in the positive electrode electrolyte, but only I 3 − and I 2 .
　電位計測部は、例えば、正極電解液貯蔵タンクに配置されていてもよく、正極電解液が循環する循環経路に配置されていてもよい。 The potential measuring unit may be disposed, for example, in a positive electrode electrolyte storage tank or may be disposed in a circulation path through which the positive electrode electrolyte circulates.
（フロー電池システムの構成例）
　本実施形態のフロー電池システムの一例を図６に示す。フロー電池システム１００は、図６に示すように、正極１１１と、負極１１２と、隔膜１１５と、正極用参照電極１１３と、正極電解液１１６と、正極電解液貯蔵タンク１１８と、負極電解液１１７と、負極電解液貯蔵タンク１１９と、送液部として循環経路１２０、１２１及びポンプ１２２、１２３と、充放電を制御し、正極の充電電位を、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．０５Ｖ以下に設定する制御部（不図示）を備える。なお、フロー電池システム１００を構成する各構成要素は、上述の通りである。 (Configuration example of flow battery system)
An example of the flow battery system of this embodiment is shown in FIG. As shown in FIG. 6, the flow battery system 100 includes a positive electrode 111, a negative electrode 112, a diaphragm 115, a positive electrode reference electrode 113, a positive electrode electrolyte 116, a positive electrode electrolyte storage tank 118, and a negative electrode electrolyte 117. When a negative electrolyte storage tank 119, a circulation path 120, 121 and pumps 122, 123 as a liquid feed unit, to control the charging and discharging, a charging potential of the positive electrode, Ag / AgCl reference electrode - of (Cl concentration saturation) A control unit (not shown) that sets the potential to 1.05 V or less with reference to the potential is provided. In addition, each component which comprises the flow battery system 100 is as above-mentioned.
　図６に示すフロー電池システム１００は、正極１１１と、負極１１２と、隔膜１１５と、を一つずつ備える単セルを複数備えるセルスタック１３０を備える。図６では、単セル数が５つであるセルスタック１３０を示しているが、単セル数は特に限定されない。また、図６に示すフロー電池システム１００では、セルスタックを構成する正極１１１と負極１１２とに正極用参照電極１１３及び負極用参照電極１１４が配置されており、参照電極を用いた電位計測が可能となっている。 The flow battery system 100 shown in FIG. 6 includes a cell stack 130 including a plurality of single cells each including a positive electrode 111, a negative electrode 112, and a diaphragm 115. Although FIG. 6 shows the cell stack 130 having five single cells, the number of single cells is not particularly limited. In the flow battery system 100 shown in FIG. 6, the positive electrode reference electrode 113 and the negative electrode reference electrode 114 are arranged on the positive electrode 111 and the negative electrode 112 constituting the cell stack, and potential measurement using the reference electrode is possible. It has become.
　図６に示すフロー電池システム１００では、正極電解液１１６をサンプリングするサンプリング部１２４と、正極電解液１１６中のヨウ素イオン及びヨウ素分子の濃度に基づく電位を計測する電位計測部１２５とが正極電解液貯蔵タンク１１８に配置されている。 In the flow battery system 100 shown in FIG. 6, a sampling unit 124 that samples the positive electrode electrolyte 116 and a potential measurement unit 125 that measures a potential based on the concentrations of iodine ions and iodine molecules in the positive electrode electrolyte 116 include a positive electrode electrolyte. Located in storage tank 118.
　図６に示すフロー電池システム１００では、正極１１１が配置された正極室と正極電解液貯蔵タンク１１８との間で正極電解液１１６を循環させ、かつ負極１１２が配置された負極室と負極電解液貯蔵タンク１１９との間で負極電解液１１７を循環させる循環経路１２０、１２１と送液ポンプ１２２、１２３が送液部として配置されている。 In the flow battery system 100 shown in FIG. 6, the positive electrode electrolyte 116 is circulated between the positive electrode chamber in which the positive electrode 111 is arranged and the positive electrode electrolyte storage tank 118, and the negative electrode chamber and the negative electrode electrolyte in which the negative electrode 112 is arranged. Circulation paths 120 and 121 for circulating the negative electrode electrolyte 117 between the storage tank 119 and the liquid feed pumps 122 and 123 are arranged as a liquid feed section.
　フロー電池システム１００の充放電は、図示を省略する制御部によって制御される。前述したとおり、制御部は、正極の充電電位を１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）以下に設定することができる。 Charging / discharging of the flow battery system 100 is controlled by a control unit (not shown). As described above, the control unit can set the charging potential of the positive electrode to 1.5 V (vs. Ag / AgCl) or less.
＜発電システム＞
　本実施形態の発電システムは、発電装置と、上述のフロー電池システムと、を備える。本実施形態の発電システムは、フロー電池システムと発電装置とを組み合わせることで、電力変動を平準化及び安定化したり、電力の需給を安定化したりすることができる。 <Power generation system>
The power generation system of the present embodiment includes a power generation device and the above-described flow battery system. The power generation system of this embodiment can level and stabilize power fluctuations or stabilize power supply and demand by combining a flow battery system and a power generation device.
　発電システムは、発電装置を備える。発電装置の種類は特に限定されず、再生可能エネルギーを用いて発電する発電装置、水力発電装置、火力発電装置、原子力発電装置等が挙げられる。中でも再生可能エネルギーを用いて発電する発電装置が好ましい。 The power generation system includes a power generation device. The type of the power generation device is not particularly limited, and examples thereof include a power generation device that generates power using renewable energy, a hydroelectric power generation device, a thermal power generation device, and a nuclear power generation device. Among these, a power generation device that generates power using renewable energy is preferable.
　再生可能エネルギーを用いた発電装置は、気象条件等によって発電量が大きく変動するが、フロー電池システムと組み合わせることで変動する発電電力を平準化して電力系統に平準化した電力を供給することができる。 The amount of power generated by power generators using renewable energy varies greatly depending on weather conditions, etc., but when combined with a flow battery system, the generated power can be leveled and supplied to the power system. .
　再生可能エネルギーとしては、風力、太陽光、波力、潮力、流水、潮汐、地熱等が挙げられるが、風力又は太陽光が好ましい。 Renewable energy includes wind power, sunlight, wave power, tidal power, running water, tide, geothermal heat, etc., preferably wind power or sunlight.
　風力、太陽光等の再生可能エネルギーを用いて発電した発電電力は、高電圧の電力系統に供給する場合がある。通常、風力発電及び太陽光発電は、風向、風力、天気等の気象によって影響を受けるため、発電電力は一定とならず、大きく変動する傾向にある。一定ではない発電電力を高電圧の電力系統にそのまま供給すると、電力系統の不安定化を助長するため好ましくない。本実施形態の発電システムは、例えば、フロー電池システムの充放電波形を発電電力波形に重畳させることで、目標とする電力変動レベルまで発電電力波形を平準化させることができる。 The generated power generated using renewable energy such as wind power and sunlight may be supplied to a high-voltage power system. In general, wind power generation and solar power generation are affected by weather such as wind direction, wind power, and weather, and thus generated power is not constant and tends to fluctuate greatly. If the generated power that is not constant is supplied to the high-voltage power system as it is, it is not preferable because it promotes instability of the power system. For example, the power generation system of the present embodiment can level the generated power waveform to the target power fluctuation level by superimposing the charge / discharge waveform of the flow battery system on the generated power waveform.
　上述したフロー電池システムをこのような再生可能エネルギー分野に適用する場合、高圧系に電力を供給するため、フロー電池システムの単セルあたり、１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）を超える充電電位が要求される場合が生じ得る。単セルの正極の充電電位が１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）である場合、単セルの全体の充電電圧、すなわち正極と負極との間の電位差は３Ｖを超える値になる。フロー電池システムの各セルスタックが２０セル直列された構成である場合、各セルスタックの充電電圧は６０Ｖになる。更に、１０個のセルスタックが直列されていると、充電電圧は６００Ｖになる。フロー電池システムの充電は、風力発電等による交流発電電力をインバータで直流電力に変換して実施される。このため、フロー電池システムのセルスタックとインバータの出力との関係において、充電制御電圧の電圧範囲が決まる。 When the above-described flow battery system is applied to such a renewable energy field, a charging potential exceeding 1.5 V (vs. Ag / AgCl) per unit cell of the flow battery system is used to supply power to the high voltage system. There may be cases where it is required. When the charging potential of the positive electrode of the single cell is 1.5 V (vs. Ag / AgCl), the entire charging voltage of the single cell, that is, the potential difference between the positive electrode and the negative electrode exceeds 3 V. When each cell stack of the flow battery system has a configuration in which 20 cells are connected in series, the charging voltage of each cell stack is 60V. Furthermore, when 10 cell stacks are connected in series, the charging voltage is 600V. The flow battery system is charged by converting AC power generated by wind power generation or the like into DC power using an inverter. For this reason, the voltage range of the charge control voltage is determined in the relationship between the cell stack of the flow battery system and the output of the inverter.
　インバータの充電電圧が一定の場合、セルスタックの単セル直列数が少ないと、個々の単セルに印加される充電電圧は大きくなる。逆に、セルスタックの単セル直列数が多いと、個々の単セルに印加される充電電圧は小さくなる。したがって、再生可能エネルギーを用いた発電システムにフロー電池システムを設置する場合、フロー電池システムの単セルあたりに印加される充電電圧は、インバータ出力及びセルスタックの単セル直列数を基本的パラメータとして決まる。 When the charging voltage of the inverter is constant, if the number of single cells in the cell stack is small, the charging voltage applied to each single cell increases. Conversely, when the number of single cell series in the cell stack is large, the charging voltage applied to each single cell becomes small. Therefore, when a flow battery system is installed in a power generation system using renewable energy, the charging voltage applied per single cell of the flow battery system is determined based on the inverter output and the number of single cells in series in the cell stack as basic parameters. .
　本実施形態の発電システムの一例を図２に示す。図７は、風力発電分野に発電システムを適用した場合の構成図である。図７中、ＦＢ（Ｆｌｏｗ　Ｂａｔｔｅｒｙ）はフロー電池を示し、ＰＣＳ（Ｐｏｗｅｒ　Ｃｏｎｄｉｔｉｏｎｉｎｇ　Ｓｙｓｔｅｍ）は交流直流変換のインバータ制御系を示す。図７のＦＢ及びＰＣＳが前述した本実施形態のフロー電池システムに対応する。 An example of the power generation system of this embodiment is shown in FIG. FIG. 7 is a configuration diagram when the power generation system is applied to the wind power generation field. In FIG. 7, FB (Flow Battery) indicates a flow battery, and PCS (Power Conditioning System) indicates an inverter control system for AC / DC conversion. 7 corresponds to the flow battery system of the present embodiment described above.
　図７に示す発電電力波形は、風力発電装置によって発電された電力波形の一例である。風力発電の場合は、風の強弱、風向等によって発電電力は大きく変動する。このように変動する電力が送電線等の電力系統に重畳されると、電力系統の安定化に影響する。したがって、風力発電による電力を電力系統に供給する場合、電力系統の電力が変動することを抑制する必要がある。 The generated power waveform shown in FIG. 7 is an example of a power waveform generated by the wind power generator. In the case of wind power generation, the generated power varies greatly depending on the strength of the wind and the wind direction. When the power that fluctuates in this way is superimposed on a power system such as a transmission line, it affects the stabilization of the power system. Therefore, when supplying electric power from wind power generation to the power system, it is necessary to suppress fluctuations in the power of the power system.
　この変動を抑制するため、発電電力波形の変動を緩和する充放電波形をフロー電池システムから出力し、発電電力波形に重畳させることになる。フロー電池システムは、風力発電により得られた発電電力を平準化し、安定化された電力として供給する役割を担う。 In order to suppress this fluctuation, a charge / discharge waveform that reduces fluctuations in the generated power waveform is output from the flow battery system and superimposed on the generated power waveform. The flow battery system plays a role of leveling generated power obtained by wind power generation and supplying it as stabilized power.
　ここで、風力発電の電力波形をより短い時間スケールで見た場合の電力波形を図８に示す。図８の（ａ）領域及び（ｂ）領域で示される、比較的長い時間領域における電力波形が見られる一方、（ａ）領域よりも短時間側、（ａ）領域と（ｂ）領域との間、（ｂ）領域よりも長時間側の３つの時間領域に、マイクロ秒オーダーからミリ秒オーダーであるパルス状の発電波形が見られる。このとき、フロー電池システムは、風力発電電力のある時間幅の目標出力を中心値として、それより下の発電電力の場合は放電により電力を補い、目標出力を上回る場合は発電電力を用いて充電し、目標出力に近づけるように充放電を制御してもよい。 Here, the power waveform when the power waveform of wind power generation is viewed on a shorter time scale is shown in FIG. While the power waveform in the relatively long time region shown in the region (a) and the region (b) in FIG. 8 is seen, the power waveform is shorter than the region (a), the region (a) and the region (b) In the meantime, in the three time regions on the longer side than the region (b), a pulse-like power generation waveform in the order of microseconds to milliseconds is seen. At this time, the flow battery system uses the target output of the wind power generated for a certain time width as the central value, and if the generated power is lower than that, the power is supplemented by discharging, and if it exceeds the target output, the generated power is charged. However, charging / discharging may be controlled so as to approach the target output.
　インバータは、直流情報であるフロー電池の充放電信号と発電電力との間で電力のやり取りを実施するための変換器である。フロー電池への充電は、風力発電装置からの交流電力を直流電力に変換して行われる。インバータは、リップルノイズといわれるパルス状の高周波信号が発生しやすい。一般的にそれぞれの周波数帯域に対応できるコンデンサをＰＣＳに設置することで、これらの高周波信号を除去することができる。しかし、これらの対策がなされていないＰＣＳでは、高周波リップル信号がフロー電池に印加されることになる。 The inverter is a converter for exchanging power between the charge / discharge signal of the flow battery, which is DC information, and the generated power. Charging the flow battery is performed by converting AC power from the wind power generator into DC power. Inverters tend to generate pulsed high-frequency signals called ripple noise. Generally, these high-frequency signals can be removed by installing a capacitor that can support each frequency band in the PCS. However, in PCS in which these measures are not taken, a high-frequency ripple signal is applied to the flow battery.
　フロー電池の応答速度が、風力発電のＰＣＳの出力変動に全て追随できれば理想であるが、実際は困難である。フロー電池の電極界面の電気二重層容量とフロー電池の抵抗とによって定義される時定数（ＣＲ）の存在により、マイクロ秒オーダーから数十ミリ秒オーダー領域の電力変動の信号には、電池反応が追随できない。図８に示す場合では、マイクロ秒オーダーからミリ秒オーダー領域の信号が集まり、リップルノイズも重畳した高周波信号が集まる時間領域の電力変動を、フロー電池の充放電で完全に平準化することは難しい。特に、大型のフロー電池の場合、電極の表面積が大きくなることで電気二重層容量が大きくなり、時定数が大きくなることで、この挙動が顕在化してくる。 It is ideal if the response speed of the flow battery can follow all the output fluctuations of the wind power PCS, but it is actually difficult. Due to the presence of the time constant (CR) defined by the electric double layer capacity at the electrode interface of the flow battery and the resistance of the flow battery, the battery reaction is not observed in the signal of power fluctuations in the order of microseconds to tens of milliseconds I can't follow. In the case shown in FIG. 8, it is difficult to completely equalize the power fluctuation in the time domain where the signals in the microsecond order to the millisecond order gather and the high-frequency signal in which the ripple noise is superimposed is collected by charging and discharging the flow battery. . In particular, in the case of a large-sized flow battery, this behavior becomes apparent when the electric double layer capacity increases and the time constant increases as the surface area of the electrode increases.
　フロー電池システムを風力発電、太陽光発電等に適用した場合、発電中、発電電力を平準化するためにインバータを経由して頻繁な充放電が繰り返される。インバータから発生するリップルノイズを含め、フロー電池に供給される電力信号の中には、フロー電池の追随能力を超えた高周波電力信号が含まれることになる。フロー電池が追随し得ない高周波電力信号がフロー電池に印加されると、その電力は基本的に熱に変換される。この熱はフロー電池の電極端子に集中しやすく、フロー電池の構成材料に悪影響を及ぼしやすい。 When the flow battery system is applied to wind power generation, solar power generation, etc., frequent charge / discharge is repeated via the inverter to level the generated power during power generation. The power signal supplied to the flow battery, including ripple noise generated from the inverter, includes a high-frequency power signal that exceeds the following capability of the flow battery. When a high frequency power signal that cannot be followed by a flow battery is applied to the flow battery, the power is basically converted into heat. This heat tends to concentrate on the electrode terminals of the flow battery, and tends to adversely affect the constituent materials of the flow battery.
　前述したとおり、フロー電池システムの単セルあたりに印加される充電電圧は、インバータ出力及びセルスタックの単セル直列数を基本的パラメータとして決まるが、要求される蓄電容量とセルスタックの直列数との関係もある。そこで、単セル直列数、セルスタック数、及び充電電圧を考慮し、正極の充電電位が１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）以下となるようにフロー電池システムを設計することが好ましい。設計上、１．５Ｖを超えることを受け入れざるを得ない場合においても、フロー電池システムの寿命を確保するため、正極の充電電位を１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）以下に制御することが好ましい。 As described above, the charging voltage applied per single cell of the flow battery system is determined based on the inverter output and the number of single cells in series in the cell stack as basic parameters. There is also a relationship. Therefore, it is preferable to design the flow battery system so that the charging potential of the positive electrode is 1.5 V (vs. Ag / AgCl) or less in consideration of the number of single cells in series, the number of cell stacks, and the charging voltage. Even if the design must accept that the voltage exceeds 1.5 V, the charge potential of the positive electrode can be controlled to 1.5 V (vs. Ag / AgCl) or less in order to ensure the life of the flow battery system. preferable.
　フロー電池システムの設計上、正極の充電電位が１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）を超える条件でフロー電池システムを運用する場合、運用期間中、正極電解液及び負極電解液又はこれに含まれる成分の追加を実施することが好ましい。但し、揮発性の成分を含む場合は、正極の充電電位が１．５Ｖを超えない運用環境においても、定期的に分析し、必要な場合は当該成分を追加することが好ましい。 In the design of the flow battery system, when the flow battery system is operated under the condition that the charging potential of the positive electrode exceeds 1.5 V (vs. Ag / AgCl), the positive electrode electrolyte and the negative electrode electrolyte are included during the operation period. It is preferred to carry out the addition of the components. However, when a volatile component is included, it is preferable to analyze periodically even in an operating environment where the charge potential of the positive electrode does not exceed 1.5 V, and add the component if necessary.
　正極の充電電位が１．５Ｖ（ｖｓ．Ａｇ／ＡｇＣｌ）を超えない条件でフロー電池システムを運用する場合においても、インバータのリップルノイズに関しては、正極の充電電位が１．５Ｖを超えるようなシグナルが含まれていると考えるのが妥当と思われる。インバータのリップルノイズは、フロー電池システムの劣化を促進するため、ＰＣＳにリップルノイズを吸収できる帯域幅のコンデンサを設置することが好ましい。 Even when the flow battery system is operated under the condition that the charging potential of the positive electrode does not exceed 1.5 V (vs. Ag / AgCl), the signal that the charging potential of the positive electrode exceeds 1.5 V is associated with the ripple noise of the inverter. It seems reasonable to think that it is included. Since the ripple noise of the inverter promotes the deterioration of the flow battery system, it is preferable to install a capacitor having a bandwidth capable of absorbing the ripple noise in the PCS.
　また、発電システムは、発電装置で発電された発電電力の需給に応じて、フロー電池システムの充放電を制御するシステムであってもよい。例えば、発電装置にて発電された発電電力の供給量が電力系統における需要量を上回る場合、フロー電池システムが充電を行い、かつ発電装置にて発電された発電電力の供給量が電力系統における需要量を下回る場合、フロー電池システムが放電を行うように発電システムが制御されていてもよい。 Further, the power generation system may be a system that controls charging / discharging of the flow battery system in accordance with the supply and demand of the generated power generated by the power generation device. For example, when the supply amount of the generated power generated by the power generation device exceeds the demand amount in the power system, the flow battery system performs charging, and the supply amount of the generated power generated by the power generation device is the demand in the power system. When the amount is lower, the power generation system may be controlled so that the flow battery system discharges.
　発電システムは、再生可能エネルギーを用いた発電装置とフロー電池システムとを組み合わせることで、フロー電池システムが低コストで高エネルギー密度の蓄電システムとして機能し、さらに、炭酸ガスの排出量の低減を図り、地球温暖化を抑制するという地球規模の課題の解決に役立つものである。 The power generation system combines a power generation device using renewable energy and a flow battery system, so that the flow battery system functions as a low-cost, high-energy density power storage system, and further reduces CO2 emissions. It helps to solve the global problem of suppressing global warming.
　以下、実施例により本発明を具体的に説明するが、本発明の範囲はこれらの実施例に限定されるものではない。 Hereinafter, the present invention will be specifically described with reference to examples, but the scope of the present invention is not limited to these examples.
［実施例１］
　電解液に含まれる有機化合物を用いてヨウ化物イオンの酸化反応生成物を分離した場合の効果について検証するため、下記の実験を行った。 [Example 1]
In order to verify the effect when the oxidation reaction product of iodide ion was separated using the organic compound contained in the electrolytic solution, the following experiment was conducted.
（１）電解液が有機化合物を含有することによる酸化電流値の向上効果を実験により調べた。具体的には、３Ｍのヨウ化ナトリウム（ＮａＩ）の水溶液に、有機化合物として５体積％のメチルエチルケトンを添加した電解液と、メチルエチルケトンを添加しなかった電解液をそれぞれ調製し、電極としてグラッシーカーボン電極を使用し、特定電位における酸化電流値の大きさを測定した。図９に測定結果を示す。図中の縦軸は電流値（ｍＡ）、横軸は時間（ｓ）をそれぞれ表している。 (1) The effect of improving the oxidation current value due to the fact that the electrolytic solution contains an organic compound was examined by experiments. Specifically, an electrolytic solution in which 5% by volume of methyl ethyl ketone as an organic compound was added to an aqueous solution of 3M sodium iodide (NaI) and an electrolytic solution in which methyl ethyl ketone was not added were prepared, and a glassy carbon electrode was used as an electrode. Was used to measure the magnitude of the oxidation current value at a specific potential. FIG. 9 shows the measurement results. In the figure, the vertical axis represents current value (mA), and the horizontal axis represents time (s).
　ヨウ素皮膜はバルク水溶液中のヨウ化物イオンと化学反応し、三ヨウ化物イオン（Ｉ３ －）となって溶解する（Ｉ－＋Ｉ２　→Ｉ３ －）。しかし、ヨウ素皮膜の形成速度が溶解速度を上回ると、電極表面でヨウ素皮膜が成長して電気抵抗が増大する。そのため、ヨウ素皮膜により酸化電流値が制限され、ヨウ素皮膜の形成と溶解が拮抗する電流値において定常状態となる。実験の結果、メチルエチルケトンを添加した電解液を用いた場合は、電流値が一定となる定常状態における電流値（ｍＡ）がメチルエチルケトンを添加していない電解液を用いた場合と比べて約３０％高かった。以上の結果から、有機化合物を電解液に添加することでヨウ素皮膜の溶解が促進され、酸化電流値が向上することがわかった。 The iodine film chemically reacts with iodide ions in the bulk aqueous solution and dissolves as triiodide ions (I 3 − ) (I − + I 2 → I 3 − ). However, when the formation rate of the iodine film exceeds the dissolution rate, the iodine film grows on the electrode surface and the electrical resistance increases. Therefore, the oxidation current value is limited by the iodine film, and a steady state is obtained at a current value at which formation and dissolution of the iodine film antagonize. As a result of the experiment, when the electrolytic solution added with methyl ethyl ketone is used, the current value (mA) in a steady state where the current value is constant is about 30% higher than when the electrolytic solution without adding methyl ethyl ketone is used. It was. From the above results, it was found that by adding an organic compound to the electrolytic solution, dissolution of the iodine film was promoted, and the oxidation current value was improved.
（２）図１０は、図９の測定を行った際に生成した疎水性の物質の写真である。この疎水性の物質は液体の状態であり、バルク水溶液よりもメチルエチルケトン濃度が高く、ヨウ化物イオンとその酸化反応生成物、カチオン及び水を含有していた。また、生成した疎水性の物質は、容器の底部に沈澱した。 (2) FIG. 10 is a photograph of the hydrophobic substance generated when the measurement of FIG. 9 is performed. This hydrophobic substance was in a liquid state, had a higher methyl ethyl ketone concentration than the bulk aqueous solution, and contained iodide ions and their oxidation reaction products, cations and water. Moreover, the produced | generated hydrophobic substance precipitated in the bottom part of the container.
（３）図１１は、メチルエチルケトンとヨウ化物イオンの酸化反応生成物とを含有する疎水性の物質中で観測された、酸化電位での酸化電流値と還元電位での還元電流値を示すグラフである。グラフ中の縦軸は電流値（ｍＡ）、横軸は時間（ｓ）をそれぞれ表し、正の電流値が酸化電流値を、負の電流値が還元電流値をそれぞれ表す。図１１に示すように、酸化電流と還元電流がともに観測された。以上の結果から、疎水性の物質中において酸化反応と還元反応がともに進行することが確認できた。 (3) FIG. 11 is a graph showing an oxidation current value at an oxidation potential and a reduction current value at a reduction potential observed in a hydrophobic substance containing methyl ethyl ketone and an oxidation reaction product of iodide ions. is there. The vertical axis in the graph represents current value (mA), the horizontal axis represents time (s), a positive current value represents an oxidation current value, and a negative current value represents a reduction current value. As shown in FIG. 11, both an oxidation current and a reduction current were observed. From the above results, it was confirmed that both the oxidation reaction and the reduction reaction proceed in the hydrophobic substance.
［実施例２］
　有機化合物としてメチルエチルケトン又はプロピレンカーボネートを含む電解液を用いて、ノーマルパルスボルタンメトリーによって酸化反応を調査し、正極の電極反応を検証した。
　図１２は、実施例２において実施した、ノーマルパルスボルタンメトリーの電位波形を示すグラフである。図１２中、Ｅｉは初期電位、ΔＥｓはパルス増分、ｔｐはパルス幅、及びτはパルス周期を表す。図１２に示される電位波形を電気化学計測装置であるポテンショスタットを使い電気化学セルに入力し、各パルス電位及びパルス時間に対応する電流値を計測した。 [Example 2]
Using an electrolytic solution containing methyl ethyl ketone or propylene carbonate as an organic compound, the oxidation reaction was investigated by normal pulse voltammetry, and the electrode reaction of the positive electrode was verified.
FIG. 12 is a graph showing a potential waveform of normal pulse voltammetry performed in Example 2. In FIG. 12, Ei represents an initial potential, ΔEs represents a pulse increment, tp represents a pulse width, and τ represents a pulse period. The potential waveform shown in FIG. 12 was input to an electrochemical cell using a potentiostat as an electrochemical measuring device, and current values corresponding to each pulse potential and pulse time were measured.
　ポテンショスタットは電気化学計測においては一般的な装置であり、電位の基準となる参照電極電位に対して、図１２に示されるパルス電位を制御し、作用電極で進行する電気化学反応に基づき観測される電流を検出する装置である。また、対極を設け、対極に電流が流れるように設計されている。参照電極の入力抵抗は非常に大きく直流抵抗で通常１０１４オームレベルであり、作用電極で進行する電気化学反応の電流は全て対極に流れる回路構成になっている。 The potentiostat is a general device in electrochemical measurement, and is controlled based on the electrochemical reaction that proceeds at the working electrode by controlling the pulse potential shown in FIG. 12 with respect to the reference electrode potential serving as a potential reference. It is a device that detects current. In addition, a counter electrode is provided so that a current flows through the counter electrode. The input resistance of the reference electrode is very large and is a direct current resistance, usually at a level of 10 14 ohms, and the current of the electrochemical reaction proceeding at the working electrode is in a circuit configuration that flows to the counter electrode.
　ポテンショスタットは、これら電位基準となる参照電極、電位制御の対象となる作用電極、及び対極の３電極を備える。最近はマイクロコンピュータの発達に伴い、図１２に示されるノーマルパルスボルタンメトリーの波形はポテンショスタット機能と一体化してプログラミングできるようになっているものが一般的である。 The potentiostat includes a reference electrode serving as a potential reference, a working electrode subject to potential control, and a counter electrode. Recently, with the development of microcomputers, the normal pulse voltammetry waveform shown in FIG. 12 is generally integrated with the potentiostat function and can be programmed.
　図１３Ａ及び図１３Ｂは、実施例２において得られたノーマルパルスボルタモグラムを示すグラフである（パルス幅５０ｍｓ）。ボルタモグラムとは、電気化学反応に基づき観測される電流を電位に対してプロットした電流電位曲線のことである。
　図１３Ａは、支持電解質として１Ｍの過塩素酸ナトリウム（ＮａＣｌＯ４）を含有する２０ｍＭのヨウ化ナトリウム水溶液９５ｖｏｌ％とメチルエチルケトン１０ｖｏｌ％を含有する溶液を電解液として使用し、電極にはグラッシーカーボン（直径１．６ｍｍ）を使用し、ΔＥｓ＝０．０５Ｖ及びτ＝２０ｓとしたときの結果を示す。
　図１３Ｂは、支持電解質として１Ｍの過塩素酸ナトリウム（ＮａＣｌＯ４）を含有する２０ｍＭのヨウ化ナトリウム水溶液９５ｖｏｌ％とプロピレンカーボネート１０ｖｏｌ％を含有する溶液を電解液として使用し、電極にはグラッシーカーボン（直径１．６ｍｍ）を使用し、ΔＥｓ＝０．０５Ｖ及びτ＝２０ｓとしたときの結果を示す。
　図１３Ａ及び図１３Ｂ中、横軸は電位（Ｖ　ｖｓ．Ａｇ／ＡｇＣｌ）、及び縦軸は電流密度（ｍＡ／ｃｍ２）を表す。電流密度は、酸化電位にステップ後５０ｍｓ後の電流値を電極面積で除した値である（以下、同様である）。測定は液温２５℃の環境で行った。 13A and 13B are graphs showing normal pulse voltammograms obtained in Example 2 (pulse width 50 ms). A voltammogram is a current-potential curve in which the current observed based on an electrochemical reaction is plotted against the potential.
FIG. 13A shows a solution containing 95 vol% of 20 mM sodium iodide aqueous solution containing 1M sodium perchlorate (NaClO 4 ) as a supporting electrolyte and 10 vol% methyl ethyl ketone as an electrolyte, and glassy carbon (diameter) for the electrode. 1.6 mm) is used, and the results when ΔEs = 0.05 V and τ = 20 s are shown.
FIG. 13B shows a solution containing 95% by volume of 20 mM sodium iodide aqueous solution containing 1M sodium perchlorate (NaClO 4 ) and 10% by volume of propylene carbonate as the supporting electrolyte, and glassy carbon ( The results are shown when ΔEs = 0.05 V and τ = 20 s are used.
13A and 13B, the horizontal axis represents potential (V vs. Ag / AgCl), and the vertical axis represents current density (mA / cm 2 ). The current density is a value obtained by dividing the current value 50 ms after the step to the oxidation potential by the electrode area (the same applies hereinafter). The measurement was performed in an environment with a liquid temperature of 25 ° C.
　次に、リバースパルスボルタンメトリーによって、ノーマルパルスボルタンメトリーとは逆反応の還元反応を調査し、正極の電極反応を検証した。 Next, reverse electrode voltammetry was used to investigate the reduction reaction that was the reverse of normal pulse voltammetry, and the positive electrode reaction was verified.
　図１４は、実施例２において実施した、リバースパルスボルタンメトリーの電位波形を示すグラフである。リバースパルスボルタンメトリーはノーマルパルスボルタンメトリーと同様にプログラミング化されたポテンショスタットを用いて実施することができる。Ｅｉは初期電位、Ｅｃは着目する反応が進行しない電位（コンディショニング電位）、ΔＥｓはリバースパルス電位増分、ｔｃはＥｃに保持する時間、ｔｄはＥｉに保持する時間及びｔｐはリバースパルス幅を表す。Ｅｃは浸漬電位、ΔＥｓ＝０．０５Ｖ、ｔｃ＝１０ｓ、ｔｄ＝２ｓとした。 FIG. 14 is a graph showing a potential waveform of reverse pulse voltammetry performed in Example 2. Reverse pulse voltammetry can be performed using a programmed potentiostat similar to normal pulse voltammetry. Ei is an initial potential, Ec is a potential at which a reaction of interest does not proceed (conditioning potential), ΔEs is a reverse pulse potential increment, tc is a time for holding in Ec, td is a time for holding in Ei, and tp is a reverse pulse width. Ec was an immersion potential, ΔEs = 0.05 V, tc = 10 s, td = 2 s.
　リバースパルスボルタンメトリーはノーマルパルスボルタンメトリーで得られたＩ－の酸化反応の挙動をより精査できる機能を有する。すなわち初期電位において生成した生成物がどのような電気化学挙動を示すのかを検証できる。初期電位で生成するものが酸化反応生成物である場合、リバースパルス電位がある電位領域に到達すると、酸化反応生成物の還元反応の挙動を捕捉することができる。 Reverse pulse voltammetry has a function that allows more detailed examination of the behavior of the oxidation reaction of I − obtained by normal pulse voltammetry. That is, it can be verified what electrochemical behavior the product generated at the initial potential shows. When what is generated at the initial potential is an oxidation reaction product, when the reverse pulse potential reaches a certain potential region, the behavior of the reduction reaction of the oxidation reaction product can be captured.
　リバースパルスのパルス電位はリバースパルス電位増分が繰り返されて、初期電位Ｅｉを出発電位として、卑な方向にステップされる。一回の電位ステップが終了すると、酸化反応還元反応が最も進行しにくいコンディショニング電位Ｅｃに保持される。コンディショニング電位Ｅｃに作用電極の境界条件が反応前と同等レベルに回復する時間（ｔｃ）保持される。ｔｃ時間後、初期電位Ｅｉに電位がステップされ、ｔｄの間、作用電極上で酸化反応（一般的には酸化又は還元反応）を進行させる。初期電位にｔｄ時間制御後、リバースパルスを印加する。この繰り返しでリバースパルスボルタンメトリーは実施され、得られたリバースパルスの電流と電位との関係を基に反応そのもの、反応機構等が精査可能となる。 The pulse potential of the reverse pulse is repeatedly incremented by the reverse pulse potential, and is stepped in the base direction with the initial potential Ei as the starting potential. When one potential step is completed, the oxidation potential reduction reaction is held at the conditioning potential Ec that is least likely to proceed. The time (tc) during which the boundary condition of the working electrode recovers to the same level as before the reaction is held at the conditioning potential Ec. After the time tc, the potential is stepped to the initial potential Ei, and an oxidation reaction (generally an oxidation or reduction reaction) proceeds on the working electrode during td. After controlling the initial potential for td time, a reverse pulse is applied. By repeating this, reverse pulse voltammetry is performed, and based on the relationship between the obtained reverse pulse current and potential, the reaction itself, the reaction mechanism, and the like can be examined closely.
　ノーマルパルスボルタンメトリー及びリバースパルスボルタンメトリーともに、それぞれのパルス間において作用電極の境界条件が共通になるため、反応生成物と電位との関係において、初期電位で反応する反応物質の濃度を一定とみなすことができ、電流と電位との関係を検討する上において、単純化できる点が大きいメリットである。一回のパルス終了後コンディショニング電位に戻るため、任意のパルス電位の情報は、当該パルスの前のパルス電位で生成した反応物等の履歴を伴わない。ノーマルパルスボルタンメトリー、及びリバースパルスボルタンメトリーの強みは上記のように、観測したい電気化学情報をシンプルに抽出できる点にあるといえる。 In both normal pulse voltammetry and reverse pulse voltammetry, the boundary conditions of the working electrode are common between each pulse, so the concentration of the reactant reacting at the initial potential can be considered constant in the relationship between the reaction product and the potential. It is a great merit that it can be simplified in examining the relationship between current and potential. Since it returns to the conditioning potential after the end of one pulse, the information of any pulse potential does not accompany the history of reactants and the like generated at the pulse potential before the pulse. It can be said that the strength of normal pulse voltammetry and reverse pulse voltammetry is that the electrochemical information to be observed can be simply extracted as described above.
　図１５Ａ及び図１５Ｂは、実施例２において実施した、リバースパルスボルタモグラムである（初期電位０．５０Ｖ、０．５５Ｖ及びパルス幅５０ｍｓ）。図１５Ａ及び図１５Ｂでは、初期電位（０．５０Ｖ、０．５５Ｖで２秒間保持した後の、ステップ電位と電流値との関係をグラフで示している。
　図１５Ａは、支持電解質として１Ｍの過塩素酸ナトリウムを含有する２０ｍＭのヨウ化ナトリウム水溶液９５ｖｏｌ％とメチルエチルケトンを５ｖｏｌ％含有する溶液を電解液として使用し、電極にはグラッシーカーボン（直径１．６ｍｍ）を使用し、リバースパルスのパルス幅は５０ｍｓとしたときの結果を示す。
　図１５Ｂは、支持電解質として１Ｍの過塩素酸ナトリウムを含有する２０ｍＭのヨウ化ナトリウム水溶液９５ｖｏｌ％とプロピレンカーボネートを５ｖｏｌ％含有する溶液を電解液として使用し、電極にはグラッシーカーボン（直径１．６ｍｍ）を使用し、リバースパルスのパルス幅は５０ｍｓとしたときの結果を示す。 15A and 15B are reverse pulse voltammograms performed in Example 2 (initial potentials 0.50 V, 0.55 V, and pulse width 50 ms). FIGS. 15A and 15B are graphs showing the relationship between the step potential and the current value after being held at the initial potential (0.50 V, 0.55 V for 2 seconds).
FIG. 15A shows a solution containing 95 vol% of 20 mM sodium iodide aqueous solution containing 1 M sodium perchlorate and 5 vol% methyl ethyl ketone as the supporting electrolyte, and glassy carbon (diameter: 1.6 mm) for the electrode. And the result when the pulse width of the reverse pulse is 50 ms is shown.
FIG. 15B shows a solution containing 95 vol% of 20 mM sodium iodide aqueous solution containing 1 M sodium perchlorate as a supporting electrolyte and 5 vol% of propylene carbonate as an electrolyte, and glassy carbon (1.6 mm diameter) as an electrode. ) And the pulse width of the reverse pulse is 50 ms.
　図１５Ａ及び図１５Ｂに示すように、初期電位を０．５Ｖ、０．５５Ｖとした場合は、還元反応に関する明確な限界電流が観測された。したがって、初期電位０．５Ｖ、０．５５Ｖにおける生成物はイオンであり、本条件においてはＩ３ －である。すなわち、Ｉ－の酸化反応生成物であるＩ３ －が還元される挙動が確認できた。 As shown in FIGS. 15A and 15B, when the initial potential was set to 0.5 V and 0.55 V, a clear limit current related to the reduction reaction was observed. Therefore, the products at the initial potentials of 0.5 V and 0.55 V are ions, and in this condition, they are I 3 − . That, I - I 3 is an oxidation reaction product - was confirmed behavior is reduced.
　図１６Ａ及び図１６Ｂは、実施例２において実施したリバースパルスボルタモグラムであり、電解液中に含有するメチルエチルケトン又はプロピレンカーボネートの効果を示したものである（初期電位０．６０Ｖ及びパルス幅５０ｍｓ）。
　図１６Ａは、支持電解質として１Ｍの過塩素酸ナトリウムを含有する２０ｍＭのヨウ化ナトリウム水溶液９５ｖｏｌ％とメチルエチルケトンを５ｖｏｌ％含有する水溶液と、支持電解質として１Ｍの過塩素酸ナトリウムを含有する２０ｍＭのヨウ化ナトリウム水溶液をそれぞれ電解液として使用したときの結果を示す。
　図１６Ｂは、支持電解質として１Ｍの過塩素酸ナトリウムを含有する２０ｍＭのヨウ化ナトリウム水溶液９５ｖｏｌ％とプロピレンカーボネートを５ｖｏｌ％含有する水溶液と、支持電解質として１Ｍの過塩素酸ナトリウムを含有する２０ｍＭのヨウ化ナトリウム水溶液をそれぞれ電解液として使用したときの結果を示す。 FIG. 16A and FIG. 16B are reverse pulse voltammograms carried out in Example 2, which show the effect of methyl ethyl ketone or propylene carbonate contained in the electrolyte (initial potential 0.60 V and pulse width 50 ms).
FIG. 16A shows a 95 mM 20 mM aqueous solution of sodium iodide containing 1 M sodium perchlorate as the supporting electrolyte and an aqueous solution containing 5 vol% of methyl ethyl ketone, and a 20 mM iodide containing 1 M sodium perchlorate as the supporting electrolyte. The results when using an aqueous sodium solution as the electrolytic solution are shown.
FIG. 16B shows a 95 mM 20 mM aqueous solution of sodium iodide containing 1 M sodium perchlorate as the supporting electrolyte, an aqueous solution containing 5 vol% of propylene carbonate, and a 20 mM iodine containing 1 M sodium perchlorate as the supporting electrolyte. The result when using each sodium hydroxide aqueous solution as an electrolytic solution is shown.
　図１６Ａ及び図１６Ｂに示すように、メチルエチルケトン又はプロピレンカーボネートが電解液に含有されていない場合、還元電流値は電位を卑にステップするにしたがって増加することが観測された。この挙動は、固相電気化学反応（例えば金属めっき面からの溶解反応）において観測される挙動である。溶液中からの拡散にともなう拡散過電圧が不要であるため、リバースパルスのパルス電位が増大するにしたがって、限界電流を示すことなく還元反応の電流が増大することを確認した。電解液がメチルエチルケトン又はプロピレンカーボネートを含む場合、０．３Ｖ～０．６Ｖの領域で還元電流は無添加の場合と同様だが、０．２５Ｖ以下の領域で還元電流が減少した。この挙動は、溶液中にメチルエチルケトン又はプロピレンカーボネートが含まれることによってヨウ素皮膜の還元とヨウ素皮膜の溶解が促進されているためと考えられる。 As shown in FIGS. 16A and 16B, when methyl ethyl ketone or propylene carbonate was not contained in the electrolyte, it was observed that the reduction current value increased as the potential was stepped. This behavior is a behavior observed in a solid-phase electrochemical reaction (for example, a dissolution reaction from a metal plating surface). Since the diffusion overvoltage accompanying diffusion from the solution is unnecessary, it was confirmed that as the pulse potential of the reverse pulse increases, the current of the reduction reaction increases without showing a limiting current. When the electrolyte contained methyl ethyl ketone or propylene carbonate, the reduction current was the same as in the case of no addition in the region of 0.3V to 0.6V, but the reduction current decreased in the region of 0.25V or less. This behavior is considered to be because the reduction of the iodine film and the dissolution of the iodine film are promoted by the inclusion of methyl ethyl ketone or propylene carbonate in the solution.
　図１７Ａ及び図１７Ｂは、実施例２において実施した、リバースパルスボルタモグラムであり（初期電位０．９Ｖ～１．１Ｖ及びパルス幅５０ｍｓ）、図１６Ａ及び図１６Ｂにおける初期電位よりもさらに高電位で初期電位を設定（同様に２秒間保持）している。
　図１７Ａは、初期電位以外は図１６Ａと同様の条件としたときの結果を示し、図１７Ｂは、初期電位以外は図１６Ｂと同様の条件としたときの結果を示す。 FIGS. 17A and 17B are reverse pulse voltammograms performed in Example 2 (initial potential 0.9 V to 1.1 V and pulse width 50 ms). The initial potential is higher than the initial potential in FIGS. 16A and 16B. The potential is set (similarly held for 2 seconds).
FIG. 17A shows the results when the conditions other than the initial potential are the same as those in FIG. 16A, and FIG. 17B shows the results when the conditions other than the initial potential are the same as those in FIG. 16B.
　図１７Ａ及び図１７Ｂにて観測された還元電流値は大きく二つのグループに分けられる。一つのグループは、初期電位を０．９Ｖ、１．０Ｖとした場合であり、リバースパルス電位を卑にステップするにしたがって、還元電流値が大きく増加することが観測された。一方、もう一つのグループは、初期電位を１．０５Ｖ、１．１Ｖとした場合であり、０．９Ｖ、１．０Ｖとした場合と比較して、リバースパルスの還元電流値は低い値であった。リバースパルスボルタンメトリーは初期電位において生成した化学種の還元反応速度の違いを見ているため、これらのグループ間のリバースパルスボルタモグラムの違いは、初期電位の違いによる、生成物の違いであると考えるのがもっともシンプルである。 The reduction current values observed in FIGS. 17A and 17B are roughly divided into two groups. One group is the case where the initial potential is 0.9 V and 1.0 V, and it was observed that the reduction current value greatly increased as the reverse pulse potential was stepped to the base. On the other hand, the other group is the case where the initial potential is set to 1.05V and 1.1V, and the reduction current value of the reverse pulse is lower than the case where the initial potential is set to 0.9V and 1.0V. It was. Since reverse pulse voltammetry looks at the difference in the reduction kinetics of chemical species generated at the initial potential, the difference in the reverse pulse voltammogram between these groups is considered to be the product difference due to the difference in the initial potential. Is the simplest.
　Ｉ－は以下の式（１）及び式（２）に示す反応により、Ｉ３ －及びＩ２を生成することが知られている。 I - by the reaction shown in the following equation (1) and (2), I 3 - and to generate the I 2 are known.
　２Ｉ－→Ｉ２＋２ｅ－　　　（１）
　３Ｉ－→Ｉ３ －＋２ｅ－　　　（２） 2I − → I 2 + 2e − (1)
3I − → I 3 − + 2e − (2)
　式（１）及び式（２）の標準酸化還元電位は、それぞれ０．５３６Ｖ（標準水素電極電位）でほぼ等しい。したがって、リバースパルスボルタンメトリーの初期電位において生成するＩ－の酸化反応生成物はＩ２及びＩ３ －である。式（７）の標準電極電位の温度に対する変化は１℃あたり－０．１４８ｍＶ（玉虫玲太、「電気化学（第２版）」ｐ．３００、（１９９１）、東京化学同人）である。すなわち２５℃から５０℃が低下した－２５℃の環境において式（２）の標準電極電位（ｓｔａｎｄａｒｄ　ｅｌｅｃｔｒｏｄｅ　ｐｏｔｅｎｔｉａｌ）は０．５３６（標準水素電極電位）からわずか７．４ｍＶ変化するにとどまる。電気化学電位は基本的に温度に依存しているが、上記に示すように実用生活環境温度において、電池反応と電位との関係は１００ｍＶレベルの大きい変動は無いと考えられる。 The standard oxidation-reduction potentials of Formula (1) and Formula (2) are approximately equal at 0.536 V (standard hydrogen electrode potential), respectively. Accordingly, the oxidation reaction products of I − produced at the initial potential of reverse pulse voltammetry are I 2 and I 3 − . The change of the standard electrode potential of the formula (7) with respect to the temperature is −0.148 mV per 1 ° C. (Yuta Tamamushi, “Electrochemistry (2nd edition)” p.300, (1991), Tokyo Chemical Dojin). That is, in the environment of −25 ° C. in which the temperature is decreased from 25 ° C. to 50 ° C., the standard electrode potential of the formula (2) is only changed by 7.4 mV from 0.536 (standard hydrogen electrode potential). Although the electrochemical potential basically depends on the temperature, it is considered that the relationship between the battery reaction and the potential does not have a large fluctuation of the 100 mV level at the practical living environment temperature as described above.
　ここで、初期電位が１．０５Ｖを超える場合には以下式（３）で示す反応によりＩＯ３ －が生成される。 Here, when the initial potential exceeds 1.05 V, IO 3 − is generated by the reaction represented by the following formula (3).
　Ｉ－＋３Ｈ２Ｏ→ＩＯ３ －＋６Ｈ＋＋６ｅ－　　　（３） I − + 3H 2 O → IO 3 − + 6H + + 6e − (3)
　前述のように、式（３）は不可逆な反応であると報告されている。式（３）は不可逆反応であるため、リバースパルス電位が還元反応領域に達しても、生成したＩＯ３ －の反応速度が非常に小さく、生成したＩＯ３ －が還元反応によりＩ－になかなか戻らないことが推測される。 As mentioned above, Formula (3) is reported to be an irreversible reaction. Since Equation (3) is a irreversible reaction, even if the reverse pulse voltage reaches the reduction reaction area, resulting IO 3 - very small rate of reaction, the resulting IO 3 - is I by reduction - easily return to Guess that there is not.
　また、以下の式（４）で表されるＤｕｓｈｍａｎ反応により、上記式（４）で生成されたＩＯ３ －からＩ２が生成される。 Further, I 2 is generated from IO 3 − generated by the above formula (4) by the Dushman reaction represented by the following formula (4).
　ＩＯ３ －＋５Ｉ－＋６Ｈ＋→３Ｉ２＋３Ｈ２Ｏ　　　（４） IO 3 − + 5I − + 6H + → 3I 2 + 3H 2 O (4)
　更に、以下の式（５）は、上記式（３）及び式（４）の全反応（式（３）＋式（４））として求められる。 Furthermore, the following formula (5) is obtained as the total reaction (formula (3) + formula (4)) of the above formula (3) and formula (4).
　Ｉ２＋６Ｈ２Ｏ→２ＩＯ３ －＋１２Ｈ＋＋１０ｅ－　　　（５） I 2 + 6H 2 O → 2IO 3 − + 12H + + 10e − (5)
　上記文献１によれば、上記式（４）の化学反応速度は上記式（３）の電気化学反応に比べ早く、式（３）及び式（４）を構成反応とする式（５）の律速過程は、式（３）の電気化学反応である。このため、正極の充電電位が、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．０５Ｖを超える場合、上記式（３）～式（５）の反応が生じていると推測される。 According to the literature 1, the chemical reaction rate of the above formula (4) is faster than the electrochemical reaction of the above formula (3), and the rate limiting rate of the formula (5) using the formula (3) and the formula (4) as a constituent reaction. The process is an electrochemical reaction of formula (3). Therefore, the charge potential of the positive electrode, Ag / AgCl reference electrode - presumably exceed the 1.05V reference to the potential of (Cl concentration saturation), the above reaction formula (3) to (5) has occurred Is done.
　式（３）及び式（４）の全反応である式（５）に示す反応により、Ｉ２が反応してＩＯ３ －が生成されるが、式（３）に示す反応と同様に、式（５）に示す反応も不可逆反応である。このため、生成されるＩＯ３ －は放電反応速度が遅く、Ｉ２に戻りにくいことが推測される。 The reaction shown in Equation (5) is the total reaction of the formula (3) and (4), by the reaction I 2 IO 3 - but is generated in the same manner as in the reaction shown in equation (3), wherein The reaction shown in (5) is also an irreversible reaction. For this reason, it is presumed that the generated IO 3 − has a slow discharge reaction rate and is difficult to return to I 2 .
　このため、初期電位が１．０５Ｖを超える場合にＩＯ３ －が生成され、還元反応速度が小さいリバースパルスボルタモグラムになったと考えられる。 For this reason, it is considered that when the initial potential exceeds 1.05 V, IO 3 − is generated, and the reverse pulse voltammogram has a low reduction reaction rate.
　したがって、正極電解液中にメチルエチルケトン又はプロピレンカーボネートを含有する場合、正極の充電電位を１．０５Ｖを超える充電電位条件では、不可逆反応によりＩＯ３ －が生成されると考えられる。このため、正極の充電電位が１．０５Ｖを超えない状態で運転することが好ましいことがわかる。 Accordingly, when methyl ethyl ketone or propylene carbonate is contained in the positive electrode electrolyte, it is considered that IO 3 − is generated by an irreversible reaction under a charge potential condition where the charge potential of the positive electrode exceeds 1.05V. For this reason, it turns out that it is preferable to drive | operate in the state in which the charge potential of a positive electrode does not exceed 1.05V.
　図１８Ａ及び図１８Ｂは、実施例２において実施した、リバースパルスボルタモグラムであり（初期電位１．４Ｖ、１．５Ｖ及びパルス幅５０ｍｓ）、図１６Ａ及び図１６Ｂにおける初期電位よりもさらに高電位で初期電位を設定（同様に２秒間保持）している。
　図１８Ａは、初期電位以外は図１６Ａと同様の条件としたときの結果を示し、図１８Ｂは、初期電位以外は図１６Ｂと同様の条件としたときの結果を示す。 18A and 18B are reverse pulse voltammograms performed in Example 2 (initial potentials of 1.4 V, 1.5 V and a pulse width of 50 ms). The initial potential is higher than the initial potential in FIGS. 16A and 16B. The potential is set (similarly held for 2 seconds).
FIG. 18A shows the result when the same conditions as in FIG. 16A are used except for the initial potential, and FIG. 18B shows the result when the same conditions as in FIG. 16B are used except for the initial potential.
　図１８Ａ及び図１８Ｂに示すように、リバースパルスで観測される還元電流値は、初期電位を１．５Ｖ以上とした場合、初期電位を１．４Ｖとした場合と比較して低下することが分かった。更に、初期電位を高くするにしたがって還元電流値が低下する傾向にあることが分かった。このことから、初期電位を１．５Ｖ以上の貴な電位に保持することによって電極が不活性化していると推定した。 As shown in FIG. 18A and FIG. 18B, the reduction current value observed by the reverse pulse is found to be lower when the initial potential is 1.5 V or more than when the initial potential is 1.4 V. It was. Further, it was found that the reduction current value tends to decrease as the initial potential is increased. From this, it was estimated that the electrode was inactivated by maintaining the initial potential at a noble potential of 1.5 V or higher.
［実施例３］
　図１９Ａ及び図１９Ｂは、実施例３において実施した、ノーマルパルスボルタモグラムである（パルス幅５０、５００及び５０００ｍｓ）。実施例３では、パルス幅を５０ｍｓ、５００ｍｓ及び５０００ｍｓとしたときの電流密度を測定している。その他の条件は実施例２と同様である。
　図１９Ａは、３Ｍのヨウ化ナトリウム水溶液９５ｖｏｌ％にメチルエチルケトンを５ｖｏｌ％含有する溶液を電解液として使用したときの結果を示す。
　図１９Ｂは、３Ｍのヨウ化ナトリウム水溶液９５ｖｏｌ％にプロピレンカーボネートを５ｖｏｌ％含有する溶液を電解液として使用したときの結果を示す。
　３Ｍオーダーの水溶液濃度は、実フロー電池における反応活物質濃度レベルに対応する。図１９Ａ及び図１９Ｂ中、横軸は電位（Ｖ　ｖｓ．Ａｇ／ＡｇＣｌ）、及び縦軸は電流密度を表す。 [Example 3]
19A and 19B are normal pulse voltammograms ( pulse widths 50, 500, and 5000 ms) performed in Example 3. FIG. In Example 3, the current density when the pulse width is 50 ms, 500 ms, and 5000 ms is measured. Other conditions are the same as in the second embodiment.
FIG. 19A shows a result when a solution containing 95% by volume of 3M sodium iodide aqueous solution and 5% by volume of methyl ethyl ketone is used as the electrolytic solution.
FIG. 19B shows the results when a solution containing 5 vol% of propylene carbonate in 95 vol% of 3M sodium iodide aqueous solution was used as the electrolytic solution.
The aqueous solution concentration on the order of 3M corresponds to the reaction active material concentration level in the actual flow battery. 19A and 19B, the horizontal axis represents potential (V vs. Ag / AgCl), and the vertical axis represents current density.
　ｔｐ＝５０ｍｓでは電位の増加に対して単調に電流密度が増加した。パルス幅が５０ｍｓのタイムスケールではＩ２皮膜生成量は小さく、Ｉ－の電極反応は皮膜によって大きく阻害されていないことが分かった。 At tp = 50 ms, the current density increased monotonously with increasing potential. It was found that on the time scale with a pulse width of 50 ms, the amount of I 2 film produced was small, and the electrode reaction of I − was not greatly inhibited by the film.
　ｔｐ＝５００ｍｓでは１．５Ｖ付近から電流密度が低下した。パルス幅が５００ｍｓのタイムスケールでは、１．５Ｖ付近からＩ２皮膜が厚膜化し、Ｉ－の電極反応を阻害することが分かった。 At tp = 500 ms, the current density decreased from around 1.5V. It was found that on the time scale with a pulse width of 500 ms, the I 2 film thickened from around 1.5 V, and the I − electrode reaction was inhibited.
　ｔｐ＝５０００ｍｓでは、１．０Ｖ付近～１．８Ｖ付近にかけて電流値がほぼ同等であった。パルス幅が５０００ｍｓのタイムスケールでは、１．０Ｖ付近～１．８Ｖ付近の電位領域内でヨウ素皮膜の厚みは均衡に達していることが確認できた。 At tp = 5000ms, the current values were almost the same from around 1.0V to around 1.8V. In the time scale with a pulse width of 5000 ms, it was confirmed that the thickness of the iodine film reached an equilibrium within a potential region near 1.0 V to 1.8 V.
　図２０Ａ及び図２０Ｂは、ｔｐ＝５０００ｍｓとしたときの電解液中に含有されるメチルエチルケトン又はプロピレンカーボネートの効果を示したものである。
　図２０Ａは、３Ｍのヨウ化ナトリウム水溶液９５ｖｏｌ％とメチルエチルケトンを５ｖｏｌ％含有する溶液と、３Ｍのヨウ化ナトリウム水溶液をそれぞれ電解液として使用したときの結果を示す。
　図２０Ｂは、３Ｍのヨウ化ナトリウム水溶液９５ｖｏｌ％とメチルエチルケトンを５ｖｏｌ％含有する溶液と、３Ｍのヨウ化ナトリウム水溶液をそれぞれ電解液として使用したときの結果を示す。 20A and 20B show the effects of methyl ethyl ketone or propylene carbonate contained in the electrolyte when tp = 5000 ms.
FIG. 20A shows the results when a solution containing 95% by volume of 3M sodium iodide aqueous solution and 5% by volume of methyl ethyl ketone and a 3M sodium iodide aqueous solution were used as the electrolytes, respectively.
FIG. 20B shows the results when a solution containing 95% by volume of 3M sodium iodide aqueous solution and 5% by volume of methyl ethyl ketone and a 3M sodium iodide aqueous solution were used as the electrolytes, respectively.
　図２０Ａ及び図２０Ｂに示すように、電解液がメチルエチルケトン又はプロピレンカーボネートを含有する場合、１．０Ｖ付近～１．８Ｖ付近の電流は、電解液がメチルエチルケトン又はプロピレンカーボネートを含有しない場合と比較して大きく観測された。これは、電解液中のメチルエチルケトン又はプロピレンカーボネートによってヨウ素皮膜が薄膜化し、電極上で反応するヨウ化物イオンの量が増加したためと考えられる。 As shown in FIGS. 20A and 20B, when the electrolytic solution contains methyl ethyl ketone or propylene carbonate, the current in the vicinity of 1.0 V to 1.8 V is compared with the case where the electrolytic solution does not contain methyl ethyl ketone or propylene carbonate. Observed greatly. This is presumably because the amount of iodide ions reacting on the electrode increased due to the thinning of the iodine film by methyl ethyl ketone or propylene carbonate in the electrolytic solution.
　着目する反応種（実施例２ではＩ－）の濃度に対して支持電解質濃度（実施例２では過塩素酸ナトリウム）を５０倍等量レベルで設ける電気化学計測は、物質移動に関する電気泳動の影響を除き、電気化学反応場である電気二重層構造を一定に保ちつつ電気化学反応を観察できる。このため、絶対反応速度論にベースをおく電気化学反応機構検討において、既存の電気化学理論をシンプルに使えるメリットがある。そこで、実施例２では、電気化学反応に関する検討を、ｍＭオーダーの反応種、及び支持電解質を含有する系で実施した。本実施例では、支持電解質を含まない、実フロー電池濃度域のヨウ化ナトリウム電解液条件で電気化学反応に関する検討を行ったが、基本的に実施例２における検討結果に対応していることが分かる。すなわち、１．０５Ｖを超える電位領域における充電電位制御は、上記式（３）（Ｉ－＋３Ｈ２Ｏ→ＩＯ３ －＋６Ｈ＋＋６ｅ－）及び式（５）（Ｉ２＋６Ｈ２Ｏ→２ＩＯ３ －＋１２Ｈ＋＋１０ｅ－）に示すように、ＩＯ３ －が生成されるため望ましくない。 Electrochemical measurement in which the concentration of the supporting electrolyte (sodium perchlorate in Example 2) is 50 times equivalent to the concentration of the reactive species of interest (I − in Example 2) is the influence of electrophoresis on mass transfer. The electrochemical reaction can be observed while keeping the electric double layer structure that is an electrochemical reaction field constant. For this reason, there is an advantage that the existing electrochemical theory can be used simply in the study of the electrochemical reaction mechanism based on the absolute reaction kinetics. Therefore, in Example 2, the study on the electrochemical reaction was performed in a system containing a reactive species in the order of mM and a supporting electrolyte. In this example, the electrochemical reaction was examined under the conditions of sodium iodide electrolyte solution in the actual flow battery concentration range, which does not include the supporting electrolyte, but basically it corresponds to the examination result in Example 2. I understand. That is, the charge potential control in the potential region exceeding 1.05 V is performed by the above formula (3) (I − + 3H 2 O → IO 3 − + 6H + + 6e − ) and formula (5) (I 2 + 6H 2 O → 2IO 3 − + 12H + + 10e − ), which is undesirable because IO 3 − is generated.
　以上の結果から、正極電解液にメチルエチルケトン又はプロピレンカーボネートを含むフロー電池の充電電位はＩＯ３ －が充電により生成しない正極電位１．０５Ｖ（Ｖ　ｖｓ．Ａｇ／ＡｇＣｌ）を超えないことが好ましいことがわかる。 From the above results, it is preferable that the charge potential of the flow battery containing methyl ethyl ketone or propylene carbonate in the positive electrode electrolyte does not exceed the positive electrode potential of 1.05 V (V vs. Ag / AgCl) that IO 3 − does not generate by charging. Recognize.
　フロー電池において、正極が厚いヨウ素皮膜で覆われることでフロー電池の流路が狭められ、電解液のフローそのものが阻害される状況は望ましくない。この点において、充電電位は１．４Ｖを超えないことが望ましい。フロー電池は二次電池の一種であり、充放電反応に関与する反応活物質を安定に管理する上においては、実施例２、３で示された充電電位１．０５Ｖ（Ｖ　ｖｓ．Ａｇ／ＡｇＣｌ）以下の電位での充電制御が好ましい。　　　　　 In a flow battery, it is not desirable that the flow path of the flow battery is narrowed by covering the positive electrode with a thick iodine film and the flow of the electrolytic solution itself is obstructed. In this respect, it is desirable that the charging potential does not exceed 1.4V. The flow battery is a kind of secondary battery, and in order to stably manage the reaction active material involved in the charge / discharge reaction, the charge potential shown in Examples 2 and 3 is 1.05 V (V vs. Ag / AgCl). ) Charge control at the following potential is preferred. .
　図１８Ａ及び図１８Ｂから、１．５Ｖよりも貴な電位とすることでグラッシーカーボンが酸化することが確認されているため、メチルエチルケトン又はプロピレンカーボネートの分解を抑制する点に加えて正極の劣化を抑制する点から、実フロー電池において１．５Ｖ以下の電位で充電制御することが好ましいことがわかる。 From FIG. 18A and FIG. 18B, it is confirmed that the glassy carbon is oxidized when the potential is higher than 1.5 V. Therefore, in addition to suppressing the decomposition of methyl ethyl ketone or propylene carbonate, the deterioration of the positive electrode is suppressed. From this point, it can be seen that it is preferable to control charging at a potential of 1.5 V or less in an actual flow battery.
［実施例４］
　次に、図６に示すフロー電池システムについて、充放電反応を実施した場合の正極及び負極の電流電位について検討した。本実施例では、正極電解液として１Ｍヨウ化ナトリウム（ＮａＩ）水溶液に５ｖｏｌ％のメチルエチルケトン又はプロピレンカーボネートを添加した溶液を用い、負極電解液として０．５Ｍ塩化亜鉛（ＺｎＣｌ２）を含有する１Ｍ塩化アンモニウム（ＮＨ４Ｃｌ）水溶液を用い、正極として炭素電極を用い、かつ負極として亜鉛電極（亜鉛コートメッシュ電極）を用いた。 [Example 4]
Next, regarding the flow battery system shown in FIG. 6, the current potentials of the positive electrode and the negative electrode when the charge / discharge reaction was performed were examined. In this example, a 1M sodium iodide (NaI) aqueous solution added with 5 vol% methyl ethyl ketone or propylene carbonate was used as the positive electrode electrolyte, and 1M chloride containing 0.5M zinc chloride (ZnCl 2 ) as the negative electrode electrolyte. An ammonium (NH 4 Cl) aqueous solution was used, a carbon electrode was used as the positive electrode, and a zinc electrode (zinc coated mesh electrode) was used as the negative electrode.
　本実施例では、正極負極の電気化学反応及びそれぞれの標準電極電位は以下の通りであり、フロー電池の開回路電圧は標準状態で約１．３Ｖである。また、図２１に実施例４におけるフロー電池システムの電極反応の模式図を示している。 In this example, the electrochemical reaction of the positive and negative electrodes and the standard electrode potentials are as follows, and the open circuit voltage of the flow battery is about 1.3 V in the standard state. FIG. 21 shows a schematic diagram of the electrode reaction of the flow battery system in Example 4.
　負極　Ｚｎ⇔Ｚｎ２＋＋２ｅ－　　－０．７６Ｖ Negative electrode Zn⇔Zn 2+ + 2e -- 0.76V
　正極　３Ｉ－⇔Ｉ３ －＋２ｅ－　　　０．５３Ｖ
　　　　２Ｉ－⇔Ｉ２＋２ｅ－　　　０．５３Ｖ The positive electrode 3I - ⇔I 3 - + 2e - 0.53V
2I − ⇔I 2 + 2e − 0.53V
　図２１は、実施例４において実施した、フロー電池の正極及び負極の電流電位曲線である。電流電位曲線は、図６に示すフロー電池システムの構成で、フロー流量を１００ｃｍ３／分とし、一定電流で充電放電させた条件で得られたものである。 FIG. 21 is a current-potential curve of the positive electrode and the negative electrode of the flow battery implemented in Example 4. The current-potential curve is obtained under the condition of the flow battery system shown in FIG. 6 under the condition that the flow flow rate is 100 cm 3 / min and the battery is charged and discharged at a constant current.
　種々の定電流制御した条件における対応する電位は、正極及び負極それぞれの定常電位を測定して得られた値である。正極及び負極それぞれの電位はＡｇ／ＡｇＣｌ参照電極に対する電位である。本実施例のフロー電池環境下において、正極の電位が１．０５Ｖ（Ｖｖｓ．Ａｇ／ＡｇＣｌ）になる電流密度は約４００ｍＡ／ｃｍ２である。 The corresponding potential under various constant current controlled conditions is a value obtained by measuring the steady potential of each of the positive electrode and the negative electrode. The potential of each of the positive electrode and the negative electrode is a potential with respect to the Ag / AgCl reference electrode. In the flow battery environment of this example, the current density at which the potential of the positive electrode becomes 1.05 V (Vvs. Ag / AgCl) is about 400 mA / cm 2 .
　したがって、本実施例のフロー電池システムにおいて、フロー電池の充電制御条件は充電電流密度が４００ｍＡ／ｃｍ２を超えないようにすることが好ましい。これにより正極の電位が１．０５Ｖより貴な電位領域に到達することが抑制され、ＩＯ３ －の生成を抑制してフロー電池を運用することができる。 Therefore, in the flow battery system of this embodiment, it is preferable that the charge control condition of the flow battery is such that the charge current density does not exceed 400 mA / cm 2 . This suppresses the positive electrode potential from reaching a potential region nobler than 1.05 V, and the flow battery can be operated while suppressing the generation of IO 3 − .
　なお、負極は基本的にＺｎとＺｎ２＋間の反応であるため、電解液が分解しない条件で電位を制御すればよい。 Note that since the negative electrode is basically a reaction between Zn and Zn 2+ , the potential may be controlled under the condition that the electrolytic solution does not decompose.

Claims (25)

  1. 　正極と、負極と、正極電解液と、負極電解液と、隔膜とを備え、前記正極電解液及び前記負極電解液の少なくともいずれか一方はヨウ化物イオンと、前記ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物とを含む、水溶液系二次電池。 A positive electrode, a negative electrode, a positive electrode electrolyte, a negative electrode electrolyte, and a diaphragm, wherein at least one of the positive electrode electrolyte and the negative electrode electrolyte is an iodide ion and an oxidation reaction product of the iodide ion An aqueous secondary battery comprising an organic compound that can be separated.
  2. 　前記有機化合物の含有率は、前記有機化合物を含む前記正極電解液及び前記負極電解液の少なくともいずれか一方の１体積％～５０体積％である、請求項１に記載の水溶液系二次電池。 2. The aqueous secondary battery according to claim 1, wherein the content of the organic compound is 1% by volume to 50% by volume of at least one of the positive electrode electrolyte and the negative electrode electrolyte containing the organic compound.
  3. 　前記有機化合物はケトン、カルボン酸エステル及び炭酸エステルから選択される少なくとも１種を含む、請求項１又は請求項２に記載の水溶液系二次電池。 The aqueous solution type secondary battery according to claim 1 or 2, wherein the organic compound includes at least one selected from a ketone, a carboxylic acid ester, and a carbonate ester.
  4. 　前記有機化合物はメチルエチルケトン、酢酸メチル、酢酸エチル、炭酸ジメチル、炭酸エチルメチル及び炭酸プロピレンからなる群より選択される少なくとも１種を含む、請求項１～請求項３のいずれか１項に記載の水溶液系二次電池。 The aqueous solution according to any one of claims 1 to 3, wherein the organic compound includes at least one selected from the group consisting of methyl ethyl ketone, methyl acetate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate. Secondary battery.
  5. 　前記正極電解液を収容する正極活物質反応槽と、前記負極電解液を収容する負極活物質反応槽と、正極電解液貯蔵タンクと、負極電解液貯蔵タンクと、正極電解液送液ポンプと、負極電解液送液ポンプと、をさらに備え、前記正極電解液送液ポンプは前記正極電解液貯蔵タンクと前記正極活物質反応槽との間で前記正極電解液を循環することができるように構成されており、前記負極電解液送液ポンプは前記負極電解液貯蔵タンクと前記負極活物質反応槽との間で前記負極電解液を循環することができるように構成されている、請求項１～請求項６のいずれか１項に記載の水溶液系二次電池。 A positive electrode active material reaction vessel containing the positive electrode electrolyte solution, a negative electrode active material reaction vessel containing the negative electrode electrolyte solution, a positive electrode electrolyte storage tank, a negative electrode electrolyte storage tank, a positive electrode electrolyte feed pump, A positive electrode electrolyte solution pump, and the positive electrode electrolyte solution pump is configured to circulate the positive electrode electrolyte solution between the positive electrode electrolyte storage tank and the positive electrode active material reaction tank. The negative electrode electrolyte feed pump is configured to circulate the negative electrode electrolyte between the negative electrode electrolyte storage tank and the negative electrode active material reaction tank. The aqueous solution type secondary battery of any one of Claim 6.
  6. 　前記正極電解液が前記ヨウ化物イオンと前記有機化合物とを含み、前記負極電解液が負極活物質を含む、請求項１～請求項５のいずれか１項に記載の水溶液系二次電池。 6. The aqueous secondary battery according to claim 1, wherein the positive electrode electrolyte includes the iodide ion and the organic compound, and the negative electrode electrolyte includes a negative electrode active material.
  7. 　前記負極活物質は亜鉛、クロム、チタン、鉄、スズ、バナジウム、鉛、マンガン、コバルト、ニッケル、銅及びリチウムからなる群より選択される少なくとも１種の金属イオンを含む、請求項６に記載の水溶液系二次電池。 The negative electrode active material according to claim 6, comprising at least one metal ion selected from the group consisting of zinc, chromium, titanium, iron, tin, vanadium, lead, manganese, cobalt, nickel, copper, and lithium. Aqueous secondary battery.
  8. 　前記負極活物質は亜鉛イオンを含む、請求項６又は請求項７に記載の水溶液系二次電池。 The aqueous solution type secondary battery according to claim 6 or 7, wherein the negative electrode active material contains zinc ions.
  9. 　正極と、負極と、電解液とを備え、前記電解液はヨウ化物イオンと、負極活物質と、前記ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物と、を含む、水溶液系二次電池。 A positive electrode, a negative electrode, and an electrolytic solution, wherein the electrolytic solution includes an iodide ion, a negative electrode active material, and an organic compound that can separate an oxidation reaction product of the iodide ion. battery.
  10. 　前記有機化合物の含有率は前記電解液の１体積％～５０体積％である、請求項９に記載の水溶液系二次電池。 10. The aqueous secondary battery according to claim 9, wherein the content of the organic compound is 1% by volume to 50% by volume of the electrolytic solution.
  11. 　前記有機化合物はケトン、カルボン酸エステル及び炭酸エステルから選択される少なくとも１種を含む、請求項９又は請求項１０に記載の水溶液系二次電池。 The aqueous solution type secondary battery according to claim 9 or 10, wherein the organic compound includes at least one selected from a ketone, a carboxylic acid ester, and a carbonate ester.
  12. 　前記有機化合物はメチルエチルケトン、酢酸メチル、酢酸エチル、炭酸ジメチル、炭酸エチルメチル及び炭酸プロピレンからなる群より選択される少なくとも１種を含む、請求項９～請求項１１のいずれか１項に記載の水溶液系二次電池。 The aqueous solution according to any one of claims 9 to 11, wherein the organic compound includes at least one selected from the group consisting of methyl ethyl ketone, methyl acetate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate. Secondary battery.
  13. 　前記負極活物質は亜鉛、クロム、チタン、鉄、スズ、バナジウム、鉛、マンガン、コバルト、ニッケル、銅及びリチウムからなる群より選択される少なくとも１種の金属イオンを含む、請求項９～請求項１２のいずれか１項に記載の水溶液系二次電池。 The negative electrode active material contains at least one metal ion selected from the group consisting of zinc, chromium, titanium, iron, tin, vanadium, lead, manganese, cobalt, nickel, copper, and lithium. 12. The aqueous solution type secondary battery according to any one of 12 above.
  14. 　前記負極活物質は亜鉛イオンを含む、請求項９～請求項１３のいずれか１項に記載の水溶液系二次電池。 The aqueous solution type secondary battery according to any one of claims 9 to 13, wherein the negative electrode active material contains zinc ions.
  15. 　前記正極が鉛直方向において前記負極よりも下側に位置する、請求項９～請求項１４のいずれか１項に記載の水溶液系二次電池。 15. The aqueous solution-based secondary battery according to claim 9, wherein the positive electrode is positioned below the negative electrode in the vertical direction.
  16. 　前記正極と前記負極との間に配置されて前記電解液を正極電解液と負極電解液とに分ける隔膜をさらに備える、請求項９～請求項１５のいずれか１項に記載の水溶液系二次電池。 The aqueous solution system secondary according to any one of claims 9 to 15, further comprising a diaphragm disposed between the positive electrode and the negative electrode and dividing the electrolyte into a positive electrode electrolyte and a negative electrode electrolyte. battery.
  17. 　前記電解液を収容する活物質反応槽と、電解液貯蔵タンクと、電解液送液ポンプと、をさらに備え、前記電解液送液ポンプは前記電解液貯蔵タンクと前記活物質反応槽との間で前記電解液を循環することができるように構成されている、請求項９～請求項１６のいずれか１項に記載の水溶液系二次電池。 An active material reaction tank containing the electrolyte solution, an electrolyte solution storage tank, and an electrolyte solution feed pump are further provided, and the electrolyte solution feed pump is disposed between the electrolyte solution storage tank and the active material reaction tank. The aqueous solution-based secondary battery according to any one of claims 9 to 16, wherein the electrolyte solution is configured to be able to circulate.
  18. 　正極活物質としてヨウ化物イオンを含む電解液を用いる水溶液系二次電池の充放電方法であって、前記電解液中に生成するヨウ化物イオンの酸化反応生成物を分離する工程を含む、水溶液系二次電池の充放電方法。 A charge / discharge method for an aqueous solution type secondary battery using an electrolyte solution containing iodide ions as a positive electrode active material, the method comprising an aqueous solution system comprising a step of separating an oxidation reaction product of iodide ions generated in the electrolyte solution Charge / discharge method of secondary battery.
  19. 　水と、ヨウ化物イオンと、ヨウ化物イオンの酸化反応生成物を分離可能な有機化合物と、を含み、請求項１８に記載の水溶液系二次電池の充放電方法の電解液として使用される、水溶液系二次電池用電解液。 Water, iodide ion, and an organic compound capable of separating the oxidation reaction product of iodide ion, and used as an electrolyte for the charge / discharge method of the aqueous secondary battery according to claim 18, Electrolyte for aqueous secondary battery.
  20. 　前記有機化合物の含有率は前記水溶液系二次電池用電解液の１体積％～５０体積％である、請求項１９に記載の水溶液系二次電池用電解液。 The aqueous solution secondary battery electrolyte according to claim 19, wherein the content of the organic compound is 1% by volume to 50% by volume of the aqueous solution secondary battery electrolyte.
  21. 　水と、ヨウ素（Ｉ２）、三ヨウ化物イオン（Ｉ３ －）及び五ヨウ化物イオン（Ｉ５ －）からなる群より選択される少なくとも１種と、メチルエチルケトン、酢酸メチル、酢酸エチル、炭酸ジメチル、炭酸エチルメチル及び炭酸プロピレンからなる群より選択される少なくとも１種の有機化合物と、を含む、水溶液系二次電池用電解液。 Water, at least one selected from the group consisting of iodine (I 2 ), triiodide ion (I 3 − ), and pentaiodide ion (I 5 − ), and methyl ethyl ketone, methyl acetate, ethyl acetate, dimethyl carbonate And at least one organic compound selected from the group consisting of ethyl methyl carbonate and propylene carbonate.
  22. 　前記有機化合物の含有率は前記水溶液系二次電池用電解液の１体積％～５０体積％である、請求項２１に記載の水溶液系二次電池用電解液。 The electrolyte solution for an aqueous secondary battery according to claim 21, wherein the content of the organic compound is 1% by volume to 50% by volume of the electrolytic solution for the aqueous secondary battery.
  23. 　正極活物質としてヨウ化物イオンを含む電解液を用いる水溶液系二次電池の充放電方法であって、前記電解液中に生成するヨウ化物イオンの酸化反応生成物を分離する工程を含む、水溶液系二次電池の充放電方法の電解液として使用される、請求項２１又は請求項２１に記載の水溶液系二次電池用電解液。 A charge / discharge method for an aqueous solution type secondary battery using an electrolyte solution containing iodide ions as a positive electrode active material, the method comprising an aqueous solution system comprising a step of separating an oxidation reaction product of iodide ions generated in the electrolyte solution The electrolytic solution for an aqueous secondary battery according to claim 21 or 21, which is used as an electrolytic solution for a charging / discharging method of a secondary battery.
  24. 　請求項１～請求項１７のいずれか１項に記載の水溶液系二次電池と、充放電を制御し、正極の充電電位を、Ａｇ／ＡｇＣｌ参照電極（Ｃｌ－濃度飽和）の電位を基準として１．５Ｖ以下に設定する制御部と、を備える、フロー電池システム。 And aqueous secondary battery according to any one of claims 1 to 17, to control the charging and discharging, a charging potential of the positive electrode, Ag / AgCl reference electrode - reference to the potential of (Cl concentration saturation) A flow battery system comprising: a controller configured to set the voltage to 1.5 V or less.
  25. 　発電装置と、請求項２４に記載のフロー電池システムと、を備える発電システム。 A power generation system comprising a power generation device and the flow battery system according to claim 24.
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