WO2019181982A1 - Electrolyte for redox flow battery and redox flow battery - Google Patents

Electrolyte for redox flow battery and redox flow battery Download PDF

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Publication number
WO2019181982A1
WO2019181982A1 PCT/JP2019/011591 JP2019011591W WO2019181982A1 WO 2019181982 A1 WO2019181982 A1 WO 2019181982A1 JP 2019011591 W JP2019011591 W JP 2019011591W WO 2019181982 A1 WO2019181982 A1 WO 2019181982A1
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metal element
ions
redox flow
concentration
flow battery
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PCT/JP2019/011591
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French (fr)
Japanese (ja)
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浩 安田
鈴木　雅博
みゆき 冨田
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昭和電工株式会社
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Priority to JP2020507858A priority Critical patent/JPWO2019181982A1/en
Publication of WO2019181982A1 publication Critical patent/WO2019181982A1/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
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • 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
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to an electrolyte for a redox flow battery, and a redox flow battery using the electrolyte for a redox flow battery.
  • a redox flow battery is a secondary battery that performs charging and discharging by supplying a positive electrode electrolyte and a negative electrode electrolyte to a battery cell in which a diaphragm is interposed between a positive electrode and a negative electrode.
  • An electrolyte solution for a redox flow battery used in such a redox flow battery normally uses a metal element whose valence is changed by oxidation and reduction as an active material.
  • a vanadium (V 2+ / V 3+ -V 4+ / V 5+ ) based redox flow battery electrolyte using vanadium ions as an active material of both electrodes can be mentioned.
  • Patent Document 1 discloses an electrolyte for a redox flow battery containing vanadium ions as an active material and having a total concentration of impurity element ions of 220 mass ppm or less, and an increase in cell resistance of the redox flow battery can be suppressed. However, there is no specific description of how much the increase in cell resistance was suppressed in correlation with the reduction in the concentration of impurity element ions.
  • the present invention has been made in view of the above situation, and the concentration of ions of metal elements other than vanadium is within a range where there is no practical problem. And it aims at providing a redox flow battery provided with the electrolyte solution for redox flow batteries.
  • the present invention has the following configuration.
  • the concentration of chromium ions is 40 to 120 mass ppm (2) Manganese ion concentration is 5-15 mass ppm (3) Cobalt ion concentration is 6-18 mass ppm (4) Nickel ion concentration of 12-100 mass ppm (5) Copper ion concentration is 7 to 21 mass ppm (6) Zinc ion concentration is 6-18 mass ppm [5]
  • Magnesium ion concentration is 43-300 ppm by mass (8)
  • the concentration of aluminum ions is 35 to 100 ppm by mass (9)
  • the concentration of calcium ions is 51 to 1000 ppm by mass [6]
  • Electrolyte. [7] The electrolyte solution for a redox flow battery according to [6], wherein the concentration of ions of each metal element in the metal element group M3 satisfies at least one of the following (10) to (11).
  • the concentration of sodium ions is 50 to 30000 mass ppm (11)
  • the concentration of potassium ions is 42-20000 mass ppm.
  • a redox flow battery comprising the redox flow battery electrolyte solution according to any one of [1] to [8].
  • a redox flow including a preparation step of preparing a total concentration of ions of metal elements of two metal element groups of the metal element group M1 and the metal element group M2 in a range of more than 220 ppm by mass and 1700 ppm by mass or less. Manufacturing method of battery electrolyte.
  • a redox flow battery can be provided.
  • the redox flow battery electrolyte of the present invention (hereinafter also referred to as RFB electrolyte) contains vanadium ions as an active material, a metal element group M1 composed of chromium, manganese, cobalt, nickel, copper, and zinc, magnesium, and aluminum. And the total concentration of ions of the metal element of the two metal element groups including the metal element group M2 made of calcium is more than 220 mass ppm and not more than 1700 mass ppm. It is considered that the performance of the redox flow battery is better when the metal element group M1 and the metal element group M2 contained in the electrolyte solution for redox flow battery are smaller.
  • the present invention does not strictly exclude the presence of impurity elements other than the aforementioned metal elements in the RFB electrolyte solution of the present invention, but deteriorates the characteristics of the redox flow battery due to inevitable impurities caused by raw materials and / or manufacturing processes.
  • the total concentration of ions of the metal elements of the two metal element groups described above is preferably more than 220 ppm by mass and 1690 ppm by mass, more preferably more than 220 ppm by mass and 1600 ppm by mass, and even more preferably 240 ppm. It is mass ppm or more and 1500 mass ppm or less.
  • the RFB electrolyte When the total concentration of metal element ions contained in the RFB electrolyte is within the above range, the RFB electrolyte can be prepared at a reduced cost, and when the RFB electrolyte of the present invention is used in a redox flow battery, The discharge capacity reduction rate described later can be suppressed without substantially impairing the performance of the redox flow battery.
  • the total concentration of ions of the metal element group M1 contained in the RFB electrolyte of the present invention is, for example, more than 90 ppm by mass and 500 ppm by mass or less, preferably more than 90 ppm by mass and less than 300 ppm by mass, more Preferably it is more than 90 mass ppm and 290 mass ppm or less, More preferably, it is more than 90 mass ppm and 280 mass ppm or less, Most preferably, it is more than 90 mass ppm and 260 mass ppm or less.
  • concentration of the metal element ion of two metal element groups of the metal element group M1 and the metal element group M2 is more than 220 mass ppm and 1700 mass ppm or less.
  • the total concentration of ions of the metal element of the metal element group M2 contained in the RFB electrolyte of the present invention is, for example, 130-1500 mass ppm, preferably 130-1400 mass ppm, more preferably 130-1300 mass. ppm, more preferably 130 to 1200 ppm by mass.
  • concentration of the metal element ion of two metal element groups of the metal element group M1 and the metal element group M2 is more than 220 mass ppm and 1700 mass ppm or less.
  • the discharge capacity reduction described later The rate is preferable because it is excellent in practical use.
  • the cell resistance ratio described later Is also preferable because it can be kept low.
  • the total concentration of ions of the metal elements of the metal element group M1 and the total concentration of ions of the metal elements of the metal element group M2 included in the RFB electrolyte solution are 90 mass ppm or less and less than 130 mass ppm, respectively, redox flow Although the characteristics of the battery are good, the preparation of the RFB electrolyte is expensive.
  • concentration of ions, such as each metal element is a value when it measures at 20 degreeC.
  • the ion concentration of each metal element of the metal element group M1 included in the RFB electrolyte of the present invention is 40 to 180 mass ppm of chromium ions, 5 to 35 mass ppm of manganese ions, and 6 concentrations of cobalt ions. It is preferable to satisfy at least one of ⁇ 35 mass ppm, nickel ion concentration of 12-180 mass ppm, copper ion concentration of 7-40 mass ppm, and zinc ion concentration of 6-35 mass ppm.
  • the concentration of ions of each metal element in the metal element group M1 satisfies at least one of the following (1) to (6).
  • the concentration of chromium ions is 40 to 120 mass ppm
  • Manganese ion concentration is 5-15 mass ppm
  • Cobalt ion concentration is 6-18 mass ppm
  • Nickel ion concentration of 12-100 mass ppm Copper ion concentration is 7 to 21 mass ppm
  • Zinc ion concentration is 6-18 mass ppm If the ion concentration of each metal element in the metal element group M1 satisfies at least one of the above requirements (1) to (6), the discharge capacity reduction rate to be described later is in a range where there is no practical problem. More preferred.
  • the ions of the metal elements in the metal element group M1 are likely to be involved in the generation of precipitates such as metal oxides deposited on the electrodes. It is preferable because it can be considered that the reduction in battery performance of a typical redox flow battery can be suppressed and contributes to the reduction of the discharge capacity reduction rate described later. It is more preferable to satisfy all of the above requirements (1) to (6)
  • the concentration of ions of each metal element of the metal element group M2 included in the RFB electrolyte of the present invention is as follows: magnesium ion concentration is 43 to 440 mass ppm, aluminum ion concentration is 35 to 250 mass ppm, and calcium ion concentration. Preferably satisfies at least one of 51 to 1040 ppm by mass.
  • the ion concentration of each metal element in the metal element group M2 satisfies at least one of the following (7) to (9).
  • Magnesium ion concentration is 43-300 ppm by mass
  • the concentration of aluminum ions is 35 to 100 ppm by mass (9)
  • the concentration of calcium ions is 51 to 1000 ppm by mass If the concentration of ions of each metal element in the metal element group M2 satisfies at least one of the above requirements (7) to (9), the discharge capacity reduction rate described later is preferable because it is in an excellent range with no practical problems. . It is more preferable to satisfy all of the above requirements (7) to (9)
  • the concentration of ions of each metal element of the metal element group M1 and the concentration of ions of each metal element of the metal element group M2 are both in the concentration ranges of the above requirements (1) to (9), the discharge described later
  • the capacity reduction rate is preferable because it is excellent in practical use and has a low cell resistance ratio.
  • the RFB electrolytic solution of the present invention may further contain ions of metal elements of the metal element group M3 consisting of sodium and potassium in the range of 80 to 50000 mass ppm.
  • the total concentration of ions of the metal elements of the metal element group M3 is more preferably 90 to 45000 mass ppm, further preferably 100 to 33000 mass ppm, and further preferably 100 to 10,000 mass ppm.
  • the total concentration of ions of the metal element of the metal element group M3 is at most within the above-mentioned range compared to the total concentration of ions of the metal element of the two metal element groups of the metal element group M1 and the metal element group M2. If so, the discharge capacity reduction rate, which will be described later, is in a practically acceptable range, which is preferable.
  • the concentration of ions of each metal element in the metal element group M3 satisfies at least one of the following (10) to (11).
  • the concentration of sodium ions is 50 to 30000 mass ppm (11)
  • the concentration of potassium ions is 42-20000 mass ppm. If the concentration of ions of each metal element in the metal element group M3 satisfies at least one of the above requirements (10) to (11), the discharge capacity reduction rate to be described later is within a practically no problem range, which is preferable.
  • the vanadium ions present as an active material in the RFB electrolyte of the present invention are divalent vanadium ions (V 2+ ), trivalent vanadium ions (V 3+ ), tetravalent vanadium ions (VO 2+ ), and pentavalent vanadium ions. It is at least one kind of vanadium ion (VO 2 + ).
  • the total concentration of vanadium ions in the RFB electrolyte is preferably 0.5 to 4.0 mol / L. Within this range, the generation of precipitates containing vanadium is suppressed while ensuring the energy density.
  • the concentration of vanadium ions contained in the RFB electrolytic solution of the present invention is more preferably 0.5 to 3.0 mol / L, still more preferably 0.5 to 2.5 mol / L.
  • the total concentration of vanadium ions in the RFB electrolyte is a divalent vanadium ion (V 2+ ), a trivalent vanadium ion (V 3+ ), a tetravalent vanadium ion (VO 2+ ), and a pentavalent vanadium ion (VO). 2 + ).
  • the vanadium source of vanadium ions present as an active material in the RFB electrolytic solution of the present invention is preferably heavy oil fuel combustion ash.
  • the heavy oil fuel combustion ash is combustion ash generated when the heavy oil fuel is burned.
  • the RFB electrolytic solution of the present invention preferably contains sulfate ions (SO 4 2 ⁇ ). When sulfate ions are present, the various vanadium ions described above tend to dissolve more stably.
  • the concentration of sulfate ions contained in the RFB electrolyte is preferably 1.0 to 10.0 mol / L, more preferably 1.0 to 8.0 mol / L, and still more preferably 2.0 to 6.0 mol. / L.
  • the RFB electrolyte of the present invention is at least one selected from the group consisting of fluoride ions (F ⁇ ), chloride ions (Cl ⁇ ), bromide ions (Br ⁇ ), and phosphate ions (PO 4 3 ⁇ ).
  • An anion may be further contained. Among these, it is more preferable that chlorine ion (Cl ⁇ ) is contained. It is considered that the resistance of the electrolytic solution is reduced by further containing these anions. Furthermore, it is expected that the solubility of vanadium ions in the RFB electrolyte solution is improved.
  • the total concentration of the aforementioned anions contained in the RFB electrolyte is preferably 0.01 to 2.00 mol / L, more preferably 0.10 to 1.50 mol / L, and still more preferably 0.10 to 1.00 mol. / L.
  • the total concentration of anions is the total concentration of fluoride ions (F ⁇ ), chloride ions (Cl ⁇ ), bromide ions (Br ⁇ ), and phosphate ions (PO 4 3 ⁇ ).
  • the redox flow battery of the present invention includes the RFB electrolyte described above. As other configurations of the redox flow battery, known configurations can be employed.
  • the redox flow battery of the present invention is used in a form called a battery cell stack in which a battery cell is a minimum unit, which is a single unit or a plurality of stacked units, and an electrolytic solution (positive electrode electrolyte, The negative electrode electrolyte solution) is circulated to charge and discharge.
  • a redox flow battery is interposed between a positive electrode and a negative electrode, a positive electrode cell incorporating a positive electrode, a negative electrode cell incorporating a negative electrode, and separates both cells and transmits predetermined ions.
  • a battery cell having a diaphragm (for example, an ion exchange membrane) is a main component.
  • a charge / discharge reaction is performed in the battery cell (positive electrode cell, negative electrode cell), and power can be taken out or stored.
  • the charge / discharge reaction in the battery cell is, for example, as follows.
  • the method for obtaining the RFB electrolyte solution of the present invention is not particularly limited as long as the total concentration of ions of the metal elements of the two metal element groups of the metal element group M1 and the metal element group M2 can be obtained as the concentration in the above range.
  • Waste containing vanadium element can be used as a raw material.
  • combustion ash containing vanadium element is used as a raw material
  • the redox flow battery electrolyte contains two metal element groups M1 and M2
  • the RFB electrolyte solution of the present invention is obtained by a method for producing an electrolyte solution for a redox flow battery including a preparation step of preparing a total concentration of ions of metal elements in a metal element group in a range of more than 220 mass ppm and 1700 mass ppm or less. be able to.
  • the combustion ash containing vanadium element is, for example, combustion ash such as heavy oil fuel containing vanadium element.
  • a method for obtaining an RFB electrolyte solution using combustion ash such as heavy oil fuel containing vanadium element as a raw material can be carried out, for example, as described in Japanese Patent No. 381805. In this case, it is not necessary to carry out all the steps described in Japanese Patent No. 381805 and prepare it with high purity.
  • the vanadium-containing compound is obtained in which the total concentration of the metal element ions of the two metal element groups of the metal element group M1 and the metal element group M2 is in the above-described range when the electrolyte is used. May be terminated, or the time of each process may be shortened.
  • the obtained vanadium-containing compound and sulfuric acid can be mixed and adjusted to an appropriate vanadium ion concentration to obtain a redox flow battery electrolyte.
  • An electrolyte solution for redox flow battery that is more than ppm and 1700 mass ppm or less, preferably from an electrolyte solution for redox flow battery that satisfies at least one of the above requirements (1) to (6), or from the above requirement (7)
  • An electrolyte solution for redox flow battery that satisfies at least one of (9) is obtained.
  • the concentration of the metal element ions in Table 1 was measured by appropriately diluting 100 ml of the RFB electrolyte solution prepared in each example as necessary to obtain an inductively coupled plasma emission spectrometer (ICP-OES) (device name: VISTA- Quantification was performed using PRO, manufactured by SII Nanotechnology.
  • ICP-OES inductively coupled plasma emission spectrometer
  • Example 1 (1) Preparation of RFB Electrolytic Solution An RFB electrolytic solution simulating an electrolytic solution for vanadium redox flow battery using heavy oil fuel combustion ash containing vanadium element as a raw material was prepared by the following procedure. Note that the RFB electrolytes obtained in Example 1 and Examples 2 to 13 and Comparative Examples 2 to 4 described later are RFB electrolytes obtained by assuming the procedure described in Japanese Patent No. 3831805, which will be described later. The RFB electrolytic solution obtained in Comparative Example 1 is an RFB electrolytic solution obtained by assuming the procedure described in Japanese Patent No. 3831805, and has a longer processing time than Examples 1 to 13 and Comparative Examples 2 to 4. In addition, it is assumed that impurities are removed by repeating crystallization.
  • V 2 (SO 4 ) 3 0.9 mol of vanadium sulfate (V 2 (SO 4 ) 3 ) and 1.8 mol of vanadium oxide sulfate (VOSO 4 ) were added to 1000 ml of sulfuric acid aqueous solution having a sulfuric acid (H 2 SO 4 ) concentration of 4.0 mol / L.
  • the mixture was stirred and mixed with pure water so that the volume of the solution was 2000 mL, and stirred to prepare 2000 mL of a vanadium-containing sulfuric acid aqueous solution.
  • An RFB electrolyte solution containing ions of metal elements other than vanadium at concentrations as shown in Table 1 by adding a sulfate compound of the following metal elements (aluminum only is a hydroxide) to the obtained vanadium-containing sulfuric acid aqueous solution ( 1) was obtained.
  • a sulfate compound of the following metal elements aluminum only is a hydroxide
  • a product manufactured by Nacalai Tesque was used as the compound of each metal element added. Chromium; chromium (III) sulfate hydrate (Cr 2 (SO 4) 3 ⁇ xH 2 O). Since it contains multiple types of hydrates, it was heated at 80 ° C. for 24 hours and dehydrated.
  • Manganese Manganese (II) sulfate pentahydrate (MnSO 4 .5H 2 O) (purity 99.0% or more). Cobalt; cobalt (II) sulfate heptahydrate (CoSO 4 .7H 2 O) (purity 99.0% or more). Nickel: nickel sulfate (II) hexahydrate (NiSO 4 .6H 2 O) (purity 99.0% or more). Copper: Copper (II) sulfate pentahydrate (CuSO 4 .5H 2 O) (purity 99.5% or more). Zinc: Zinc sulfate heptahydrate (ZnSO 4 .7H 2 O) (purity 99.5% or more).
  • Aluminum Aluminum hydroxide (Al (OH) 3 ) (purity 97.0% or more).
  • Calcium Calcium sulfate dihydrate (CaSO 4 .2H 2 O) (purity 98.0% or more).
  • Sodium; sodium sulfate (Na 2 SO 4) (purity 98.5% or higher). Potassium; potassium sulfate (K 2 SO 4) (99.0% purity).
  • the redox flow battery is a carbon felt (model number: AAF304ZS, manufactured by Toyobo Co., Ltd.) having an area of 50 cm 2 (5 cm ⁇ 10 cm) as a pair of positive electrode and negative electrode, and Nafion (registered trademark) (product name: product name).
  • NRE-212 manufactured by Sigma-Aldrich was used to obtain a single cell redox flow battery.
  • Cell resistance ratio The cell resistance of the redox flow battery using the RFB electrolyte (1) was determined from the following formula.
  • Cell resistance ( ⁇ ⁇ cm 2 ) ⁇ V 1 (V) ⁇ V 2 (V) ⁇ / ⁇ 2 ⁇ current density (A / cm 2 ) ⁇
  • the cell resistance ratio (cell resistance ratio) after the end of 10 cycles of discharge was determined with the cell resistance of the redox flow battery in the case of using the RFB electrolyte solution (c1) of Comparative Example 1 described later as 1.00.
  • the cell resistance ratio of the RFB electrolyte (1) is also shown in Table 1.
  • the reduction rate (discharge capacity reduction rate) (%) of the discharge capacity at the 20th cycle relative to the discharge capacity at the 10th cycle of the redox flow battery using the RFB electrolyte solution (1) was determined from the following formula.
  • Charging capacity (Ah) Charging current (A) ⁇ Charging time (h)
  • Discharge capacity (Ah) discharge current (A) ⁇ discharge time (h)
  • Discharge capacity reduction rate (%) ⁇ 1 ⁇ (discharge capacity at 20th cycle (Ah) / 10th discharge capacity (Ah)) ⁇ ⁇ 100
  • Examples 2 to 13 and Comparative Examples 1 to 4 (1) Preparation of RFB electrolyte solution RFB electrolysis of each example was carried out in the same manner as in Example 1 except that the concentrations of ions of each metal element other than vanadium contained in the RFB electrolyte solution were changed to the concentrations shown in Table 1, respectively. Liquids (2) to (13) and (c1) to (c4) were prepared. (2) Electrochemical evaluation The electrochemical evaluation was performed in the same manner as in Example 1. The cell resistance ratio and the discharge capacity reduction rate are shown together in Table 1.
  • the RFB electrolyte solution in which the total concentration of ions of the metal element groups of the metal element group M1 and the metal element group M2 is greater than 220 mass ppm and less than or equal to 1700 mass ppm is It can be seen that the performance of the redox flow battery is not substantially impaired even when compared with the case where the RFB electrolyte solution of Comparative Example 1 having a small reduction rate and high cost is used.
  • the total concentration of vanadium ions measured using a UV-vis spectrophotometer (UV-1700 manufactured by SHIMADZU) was 1 in each of the RFB electrolytes (1) to (13) and (c1) to (c4). 0.8 mol / L.
  • the electrolyte solution for a redox flow battery of the present invention can be prepared at a reduced cost and can be suitably used for a redox flow battery.

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Abstract

An electrolyte for a redox flow battery is provided in which preparation costs are reduced by setting the concentration of ions of metal elements other than vanadium within a range that does not result in any practical problems. In this electrolyte for a redox flow battery, which contains vanadium ions as the active substance, the total concentration of ions of metal elements in two metal element groups — the metal element group M1 consisting of chromium, manganese, cobalt, nickel, copper and zinc, and the metal element group M2 consisting of magnesium, aluminum and calcium — is higher than 220 ppm by mass and less than or equal to 1700 ppm by mass.

Description

レドックスフロー電池用電解液およびレドックスフロー電池Redox flow battery electrolyte and redox flow battery
　本発明は、レドックスフロー電池用電解液、およびこのレドックスフロー電池用電解液を用いたレドックスフロー電池に関する。 The present invention relates to an electrolyte for a redox flow battery, and a redox flow battery using the electrolyte for a redox flow battery.
　地球温暖化への対策として、太陽光発電、風力発電といった自然エネルギー（いわゆる、再生可能エネルギー）を利用した発電が世界的に活発に行なわれている。これらの発電出力は、天候などの自然条件に大きく左右されるため、全ての発電電力に占める自然エネルギー由来の電力の割合が増えると、電力系統の運用に際しての問題、例えば周波数や電圧の維持が困難になるといった問題がある。この問題の対策の一つとして、大容量の蓄電池を併置して、発電電力変動の平滑化、負荷の平準化などを図ることが挙げられる。
　大容量の蓄電池の一つにレドックスフロー電池がある。レドックスフロー電池は、正極電極と負極電極との間に隔膜を介在させた電池セルに正極電解液及び負極電解液をそれぞれ供給して充放電を行う二次電池である。このようなレドックスフロー電池に用いられるレドックスフロー電池用電解液は通常、酸化還元により価数が変化する金属元素を活物質として利用している。例えば、両極の活物質としてバナジウムイオンを用いたバナジウム（Ｖ２＋／Ｖ３＋－Ｖ４＋／Ｖ５＋）系レドックスフロー電池用電解液を挙げることができる。 As countermeasures against global warming, power generation using natural energy (so-called renewable energy) such as solar power generation and wind power generation is actively performed worldwide. These power generation outputs are greatly influenced by natural conditions such as the weather, so if the proportion of power derived from natural energy in all generated power increases, problems in the operation of the power system, for example, maintenance of frequency and voltage, etc. There is a problem that it becomes difficult. One of the countermeasures against this problem is to smooth the fluctuation of the generated power and level the load by arranging a large-capacity storage battery.
One of the large-capacity storage batteries is a redox flow battery. A redox flow battery is a secondary battery that performs charging and discharging by supplying a positive electrode electrolyte and a negative electrode electrolyte to a battery cell in which a diaphragm is interposed between a positive electrode and a negative electrode. An electrolyte solution for a redox flow battery used in such a redox flow battery normally uses a metal element whose valence is changed by oxidation and reduction as an active material. For example, a vanadium (V 2+ / V 3+ -V 4+ / V 5+ ) based redox flow battery electrolyte using vanadium ions as an active material of both electrodes can be mentioned.
特許第５５９０５１３号公報Japanese Patent No. 5590513
　ここで、純度の高い金属バナジウムは価格が高いことから、バナジウム源としてバナジウムを含む廃棄物を再利用する検討がなされている。バナジウムを含む再利用可能な廃棄物としては、磁鉄鉱スラグ、重質油燃焼灰、石油精製残渣、廃触媒等が挙げられる。これらの中で、重質油燃料を燃焼した際に発生する燃焼灰は、埋め立てに際して含有重金属の除去が求められ、重質油燃焼灰に含有されるバナジウム化合物を精製処理して、バナジウムイオンを含むレドックスフロー電池用電解液を調製することができる。 Here, since high-purity metal vanadium is expensive, studies have been made to reuse waste containing vanadium as a vanadium source. Examples of reusable waste containing vanadium include magnetite slag, heavy oil combustion ash, petroleum refining residue, waste catalyst, and the like. Among these, the combustion ash generated when burning heavy oil fuel is required to remove heavy metals contained in the landfill, and the vanadium compound contained in the heavy oil combustion ash is refined to produce vanadium ions. The electrolyte solution for redox flow batteries containing can be prepared.
　特許文献１においては、活物質としてバナジウムイオンを含み、不純物元素イオンの合計濃度が２２０質量ｐｐｍ以下であるレドックスフロー電池用電解液が開示されており、レドックスフロー電池のセル抵抗の増加が抑えられることが記載されているが、不純物元素イオンの濃度を低減させたことと相関してどの程度までセル抵抗の増加を抑えられたのか具体的な記載はない。 Patent Document 1 discloses an electrolyte for a redox flow battery containing vanadium ions as an active material and having a total concentration of impurity element ions of 220 mass ppm or less, and an increase in cell resistance of the redox flow battery can be suppressed. However, there is no specific description of how much the increase in cell resistance was suppressed in correlation with the reduction in the concentration of impurity element ions.
　前述した燃焼灰を処理してバナジウム化合物を精製する工程は複雑であり、また高純度まで純度を上げていくことは至難であるため、含有する不純物元素の濃度を低減させた高純度バナジウム系レドックスフロー電池用電解液の調製コストは高いものとなる。従って、特許文献１に開示のレドックスフロー電池用電解液を調製することは、レドックスフロー電池のコスト高の要因となってしまう。このため、バナジウム源として、例えば燃焼灰等の廃棄物を利用する場合には、廃棄物中に含有する、バナジウム以外の不純物元素である金属元素のイオンを、過度に低減させる必要がなく、実用上問題がない範囲の濃度までの低減で済めば、電解液の調製コストを安くできる点で望ましい。
　本発明は、上記の状況に鑑みてなされたものであり、バナジウム以外の金属元素のイオンの濃度を実用上の問題がない範囲として、調製コストを抑えたレドックスフロー電池用電解液、その製造方法及びレドックスフロー電池用電解液を備えるレドックスフロー電池を提供することを目的とする。 The process of purifying the vanadium compound by treating the combustion ash as described above is complicated, and it is difficult to increase the purity to a high purity. Therefore, a high-purity vanadium redox in which the concentration of the impurity element contained is reduced. The preparation cost of the electrolytic solution for the flow battery is high. Therefore, the preparation of the redox flow battery electrolyte disclosed in Patent Document 1 causes a high cost of the redox flow battery. For this reason, when using waste such as combustion ash as a vanadium source, it is not necessary to excessively reduce metal element ions, which are impurity elements other than vanadium, contained in the waste. If it is sufficient to reduce the concentration to a range where there is no problem, it is desirable in that the preparation cost of the electrolytic solution can be reduced.
The present invention has been made in view of the above situation, and the concentration of ions of metal elements other than vanadium is within a range where there is no practical problem. And it aims at providing a redox flow battery provided with the electrolyte solution for redox flow batteries.
　本発明は以下に示す構成を備える。 The present invention has the following configuration.
［１］活物質としてバナジウムイオンを含むレドックスフロー電池用電解液であって、クロム、マンガン、コバルト、ニッケル、銅および亜鉛からなる金属元素群Ｍ１と、マグネシウム、アルミニウムおよびカルシウムからなる金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度が、２２０質量ｐｐｍより多く１７００質量ｐｐｍ以下であるレドックスフロー電池用電解液。
［２］前記金属元素群Ｍ１の金属元素のイオンの合計濃度が、９０質量ｐｐｍより多く３００質量ｐｐｍ以下である前項［１］に記載のレドックスフロー電池用電解液。
［３］前記金属元素群Ｍ２の金属元素のイオンの合計濃度が、１３０～１４００質量ｐｐｍである前項［１］または［２］に記載のレドックスフロー電池用電解液。
［４］前記金属元素群Ｍ１の各金属元素のイオンの濃度が、下記（１）から（６）の少なくとも一つを満たす前項［１］～［３］のいずれか一項に記載のレドックスフロー電池用電解液。
（１）クロムイオンの濃度が４０～１２０質量ｐｐｍ
（２）マンガンイオンの濃度が５～１５質量ｐｐｍ
（３）コバルトイオンの濃度が６～１８質量ｐｐｍ
（４）ニッケルイオンの濃度が１２～１００質量ｐｐｍ
（５）銅イオンの濃度が７～２１質量ｐｐｍ
（６）亜鉛イオンの濃度が６～１８質量ｐｐｍ
［５］前記金属元素群Ｍ２の各金属元素のイオンの濃度が、下記（７）から（９）の少なくとも一つを満たす前項［１］～［４］のいずれか一項に記載のレドックスフロー電池用電解液。
（７）マグネシウムイオンの濃度が４３～３００質量ｐｐｍ
（８）アルミニウムイオンの濃度が３５～１００質量ｐｐｍ
（９）カルシウムイオンの濃度が５１～１０００質量ｐｐｍ
［６］ナトリウムおよびカリウムからなる金属元素群Ｍ３の金属元素のイオンを合計濃度８０～５００００質量ｐｐｍの範囲で、さらに含む前項［１］～［５］のいずれか一項に記載のレドックスフロー電池用電解液。
［７］前記金属元素群Ｍ３の各金属元素のイオンの濃度が、下記（１０）から（１１）の少なくとも一つを満たす前項［６］に記載のレドックスフロー電池用電解液。
（１０）ナトリウムイオンの濃度が５０～３００００質量ｐｐｍ
（１１）カリウムイオンの濃度が４２～２００００質量ｐｐｍ
［８］バナジウム源が重質油燃料の燃焼灰である前項［１］～［７］のいずれか一項に記載のレドックスフロー電池用電解液。
［９］前項［１］～［８］のいずれか一項に記載のレドックスフロー電池用電解液を備えるレドックスフロー電池。
［１０］バナジウム元素を含む燃焼灰を原料として用いる請求項［１］～［８］のいずれか一項に記載のレドックスフロー電池用電解液の製造方法であって、レドックスフロー電池用電解液が含む、前記金属元素群Ｍ１と前記金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度を２２０質量ｐｐｍより多く１７００質量ｐｐｍ以下となる範囲に調製する調製工程を含むレドックスフロー電池用電解液の製造方法。 [1] A redox flow battery electrolyte containing vanadium ions as an active material, a metal element group M1 composed of chromium, manganese, cobalt, nickel, copper and zinc, and a metal element group M2 composed of magnesium, aluminum and calcium And the total concentration of ions of the metal elements of the two metal element groups is more than 220 ppm by mass and not more than 1700 ppm by mass.
[2] The redox flow battery electrolytic solution according to [1], wherein the total concentration of metal element ions of the metal element group M1 is greater than 90 mass ppm and less than or equal to 300 mass ppm.
[3] The electrolyte solution for a redox flow battery according to [1] or [2] above, wherein the total concentration of ions of the metal elements in the metal element group M2 is 130 to 1400 mass ppm.
[4] The redox flow according to any one of [1] to [3], wherein the concentration of ions of each metal element in the metal element group M1 satisfies at least one of the following (1) to (6): Battery electrolyte.
(1) The concentration of chromium ions is 40 to 120 mass ppm
(2) Manganese ion concentration is 5-15 mass ppm
(3) Cobalt ion concentration is 6-18 mass ppm
(4) Nickel ion concentration of 12-100 mass ppm
(5) Copper ion concentration is 7 to 21 mass ppm
(6) Zinc ion concentration is 6-18 mass ppm
[5] The redox flow according to any one of [1] to [4], wherein the concentration of ions of each metal element in the metal element group M2 satisfies at least one of the following (7) to (9): Battery electrolyte.
(7) Magnesium ion concentration is 43-300 ppm by mass
(8) The concentration of aluminum ions is 35 to 100 ppm by mass
(9) The concentration of calcium ions is 51 to 1000 ppm by mass
[6] The redox flow battery according to any one of items [1] to [5], further including metal element ions of metal element group M3 composed of sodium and potassium in a total concentration range of 80 to 50000 mass ppm. Electrolyte.
[7] The electrolyte solution for a redox flow battery according to [6], wherein the concentration of ions of each metal element in the metal element group M3 satisfies at least one of the following (10) to (11).
(10) The concentration of sodium ions is 50 to 30000 mass ppm
(11) The concentration of potassium ions is 42-20000 mass ppm.
[8] The redox flow battery electrolyte according to any one of [1] to [7] above, wherein the vanadium source is combustion ash of heavy oil fuel.
[9] A redox flow battery comprising the redox flow battery electrolyte solution according to any one of [1] to [8].
[10] The method for producing an electrolyte solution for a redox flow battery according to any one of [1] to [8], wherein combustion ash containing vanadium element is used as a raw material. A redox flow including a preparation step of preparing a total concentration of ions of metal elements of two metal element groups of the metal element group M1 and the metal element group M2 in a range of more than 220 ppm by mass and 1700 ppm by mass or less. Manufacturing method of battery electrolyte.
　本発明によれば、調製におけるコストを抑え、実用に問題がない範囲の濃度でバナジウム以外の金属元素のイオンを含むバナジウム系レドックスフロー電池用電解液、およびこのレドックスフロー電池用電解液を用いたレドックスフロー電池を提供することができる。 According to the present invention, a vanadium-based redox flow battery electrolyte containing ions of metal elements other than vanadium at a concentration within a range where there is no problem in practical use while suppressing cost in preparation, and this redox flow battery electrolyte were used. A redox flow battery can be provided.
　以下、本発明のレドックスフロー電池用電解液について詳細に説明する。 Hereinafter, the electrolyte solution for redox flow batteries of the present invention will be described in detail.
（レドックスフロー電池用電解液）
　本発明のレドックスフロー電池用電解液（以下、ＲＦＢ電解液とも記す）は、活物質としてバナジウムイオンを含み、クロム、マンガン、コバルト、ニッケル、銅および亜鉛からなる金属元素群Ｍ１と、マグネシウム、アルミニウムおよびカルシウムからなる金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度が、２２０質量ｐｐｍより多く１７００質量ｐｐｍ以下である。レドックスフロー電池用電解液に含まれる金属元素群Ｍ１や金属元素群Ｍ２は少ないほうがレドックスフロー電池の性能が良いと考えられるが、金属元素群Ｍ１や金属元素群Ｍ２の高レベルな除去にはコストがかかる。しかし、金属元素群Ｍ１と金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度を上記範囲とすることで、レドックスフロー電池の性能が実用上の問題なく、且つ、除去にかかるコストが抑えられるレドックスフロー電池用電解液となる。
　なお、本発明のＲＦＢ電解液における前述した金属元素以外の不純物元素の存在を厳密に排除するものでなく、原料および／または製造過程などに起因する不可避不純物、その他、レドックスフロー電池の特性を劣化させない範囲内の他の不純物が本発明のＲＦＢ電解液に含まれることは差し支えない。
　前述した２つの金属元素群の金属元素のイオンの合計濃度は、好ましくは２２０質量ｐｐｍより多く１６９０質量ｐｐｍ以下であり、より好ましくは２２０質量ｐｐｍより多く１６００質量ｐｐｍ以下であり、さらに好ましくは２４０質量ｐｐｍ以上１５００質量ｐｐｍ以下である。ＲＦＢ電解液が含む金属元素のイオンの合計濃度が前述の範囲であると、コストを抑えてＲＦＢ電解液を調製することができるとともに、本発明のＲＦＢ電解液をレドックスフロー電池に用いたとき、レドックスフロー電池の性能を実質的に損なうことなく、後述する放電容量低減率を抑制することができる。 (Electrolytic solution for redox flow battery)
The redox flow battery electrolyte of the present invention (hereinafter also referred to as RFB electrolyte) contains vanadium ions as an active material, a metal element group M1 composed of chromium, manganese, cobalt, nickel, copper, and zinc, magnesium, and aluminum. And the total concentration of ions of the metal element of the two metal element groups including the metal element group M2 made of calcium is more than 220 mass ppm and not more than 1700 mass ppm. It is considered that the performance of the redox flow battery is better when the metal element group M1 and the metal element group M2 contained in the electrolyte solution for redox flow battery are smaller. However, it is costly to remove the metal element group M1 and the metal element group M2 at a high level. It takes. However, by setting the total concentration of the metal element ions of the two metal element groups of the metal element group M1 and the metal element group M2 within the above range, the performance of the redox flow battery can be removed without any practical problems. It becomes the electrolyte solution for redox flow batteries which can suppress this cost.
The present invention does not strictly exclude the presence of impurity elements other than the aforementioned metal elements in the RFB electrolyte solution of the present invention, but deteriorates the characteristics of the redox flow battery due to inevitable impurities caused by raw materials and / or manufacturing processes. Other impurities within the range that are not allowed to be contained may be contained in the RFB electrolyte of the present invention.
The total concentration of ions of the metal elements of the two metal element groups described above is preferably more than 220 ppm by mass and 1690 ppm by mass, more preferably more than 220 ppm by mass and 1600 ppm by mass, and even more preferably 240 ppm. It is mass ppm or more and 1500 mass ppm or less. When the total concentration of metal element ions contained in the RFB electrolyte is within the above range, the RFB electrolyte can be prepared at a reduced cost, and when the RFB electrolyte of the present invention is used in a redox flow battery, The discharge capacity reduction rate described later can be suppressed without substantially impairing the performance of the redox flow battery.
　本発明のＲＦＢ電解液が含む金属元素群Ｍ１の金属元素のイオンの合計濃度は、例えば９０質量ｐｐｍより多く５００質量ｐｐｍ以下であり、好ましくは９０質量ｐｐｍより多く３００質量ｐｐｍ以下であり、より好ましくは９０質量ｐｐｍより多く２９０質量ｐｐｍ以下であり、さらに好ましくは９０質量ｐｐｍより多く２８０質量ｐｐｍ以下であり、特に好ましくは９０質量ｐｐｍより多く２６０質量ｐｐｍ以下である。なお、上述のとおり、金属元素群Ｍ１と金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度が２２０質量ｐｐｍより多く１７００質量ｐｐｍ以下であることも満たす必要がある。
　また、本発明のＲＦＢ電解液が含む金属元素群Ｍ２の金属元素のイオンの合計濃度は、例えば１３０～１５００質量ｐｐｍであり、好ましくは１３０～１４００質量ｐｐｍであり、より好ましくは１３０～１３００質量ｐｐｍであり、さらに好ましくは１３０～１２００質量ｐｐｍである。なお、上述のとおり、金属元素群Ｍ１と金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度が２２０質量ｐｐｍより多く１７００質量ｐｐｍ以下であることも満たす必要がある。
　本発明のＲＦＢ電解液が含む、金属元素群Ｍ１の金属元素のイオンの合計濃度または金属元素群Ｍ２の金属元素のイオンの合計濃度が、それぞれ前述した範囲内であると、後述する放電容量低減率は実用上問題なく優れているので好ましい。本発明のＲＦＢ電解液が含む、金属元素群Ｍ１の金属元素のイオンの合計濃度および金属元素群Ｍ２の金属元素のイオンの合計濃度が、それぞれ前述した範囲内であると、後述するセル抵抗比も低く抑えられるので好ましい。ＲＦＢ電解液が含む、金属元素群Ｍ１の金属元素のイオンの合計濃度および金属元素群Ｍ２の金属元素のイオンの合計濃度を、それぞれ９０質量ｐｐｍ以下、１３０質量ｐｐｍ未満とすることは、レドックスフロー電池の特性は良好であるものの、ＲＦＢ電解液の調製がコスト高となる。
　なお、本明細書において、各金属元素等のイオンの濃度は、２０℃で測定したときの値である。 The total concentration of ions of the metal element group M1 contained in the RFB electrolyte of the present invention is, for example, more than 90 ppm by mass and 500 ppm by mass or less, preferably more than 90 ppm by mass and less than 300 ppm by mass, more Preferably it is more than 90 mass ppm and 290 mass ppm or less, More preferably, it is more than 90 mass ppm and 280 mass ppm or less, Most preferably, it is more than 90 mass ppm and 260 mass ppm or less. In addition, as above-mentioned, it is also necessary to satisfy | fill that the sum total density | concentration of the metal element ion of two metal element groups of the metal element group M1 and the metal element group M2 is more than 220 mass ppm and 1700 mass ppm or less.
The total concentration of ions of the metal element of the metal element group M2 contained in the RFB electrolyte of the present invention is, for example, 130-1500 mass ppm, preferably 130-1400 mass ppm, more preferably 130-1300 mass. ppm, more preferably 130 to 1200 ppm by mass. In addition, as above-mentioned, it is also necessary to satisfy | fill that the sum total density | concentration of the metal element ion of two metal element groups of the metal element group M1 and the metal element group M2 is more than 220 mass ppm and 1700 mass ppm or less.
When the total concentration of ions of the metal element of the metal element group M1 or the total concentration of ions of the metal element of the metal element group M2 included in the RFB electrolyte of the present invention is within the above-described range, the discharge capacity reduction described later The rate is preferable because it is excellent in practical use. When the total concentration of ions of the metal element of the metal element group M1 and the total concentration of ions of the metal element of the metal element group M2 included in the RFB electrolyte solution of the present invention are within the ranges described above, the cell resistance ratio described later Is also preferable because it can be kept low. When the total concentration of ions of the metal elements of the metal element group M1 and the total concentration of ions of the metal elements of the metal element group M2 included in the RFB electrolyte solution are 90 mass ppm or less and less than 130 mass ppm, respectively, redox flow Although the characteristics of the battery are good, the preparation of the RFB electrolyte is expensive.
In addition, in this specification, the density | concentration of ions, such as each metal element, is a value when it measures at 20 degreeC.
　本発明のＲＦＢ電解液が含む金属元素群Ｍ１の各金属元素のイオンの濃度は、クロムイオンの濃度が４０～１８０質量ｐｐｍ、マンガンイオンの濃度が５～３５質量ｐｐｍ、コバルトイオンの濃度が６～３５質量ｐｐｍ、ニッケルイオンの濃度が１２～１８０質量ｐｐｍ、銅イオンの濃度が７～４０質量ｐｐｍおよび亜鉛イオンの濃度が６～３５質量ｐｐｍの少なくとも一つを満たすことが好ましい。 The ion concentration of each metal element of the metal element group M1 included in the RFB electrolyte of the present invention is 40 to 180 mass ppm of chromium ions, 5 to 35 mass ppm of manganese ions, and 6 concentrations of cobalt ions. It is preferable to satisfy at least one of ˜35 mass ppm, nickel ion concentration of 12-180 mass ppm, copper ion concentration of 7-40 mass ppm, and zinc ion concentration of 6-35 mass ppm.
　金属元素群Ｍ１の各金属元素のイオンの濃度は、下記（１）から（６）の少なくとも一つを満たすことがより好ましい。
（１）クロムイオンの濃度が４０～１２０質量ｐｐｍ
（２）マンガンイオンの濃度が５～１５質量ｐｐｍ
（３）コバルトイオンの濃度が６～１８質量ｐｐｍ
（４）ニッケルイオンの濃度が１２～１００質量ｐｐｍ
（５）銅イオンの濃度が７～２１質量ｐｐｍ
（６）亜鉛イオンの濃度が６～１８質量ｐｐｍ
　金属元素群Ｍ１の金属元素の各金属元素のイオンの濃度が、前述の要件（１）から（６）の少なくとも一つを満たせば、後述する放電容量低減率は実用上問題ない範囲であるのでより好ましい。
　金属元素群Ｍ１の金属元素のイオンは、電極上に析出する金属酸化物等の析出物の発生に関与しやすいと考えられ、いずれもそれぞれ前述の濃度範囲であれば、析出物に起因する経時的なレドックスフロー電池の電池性能の低下を抑制でき、後述する放電容量低減率を抑える方向に寄与すると考えられるので好ましい。
　前述の要件（１）から（６）の全てを満たすことがより好ましい More preferably, the concentration of ions of each metal element in the metal element group M1 satisfies at least one of the following (1) to (6).
(1) The concentration of chromium ions is 40 to 120 mass ppm
(2) Manganese ion concentration is 5-15 mass ppm
(3) Cobalt ion concentration is 6-18 mass ppm
(4) Nickel ion concentration of 12-100 mass ppm
(5) Copper ion concentration is 7 to 21 mass ppm
(6) Zinc ion concentration is 6-18 mass ppm
If the ion concentration of each metal element in the metal element group M1 satisfies at least one of the above requirements (1) to (6), the discharge capacity reduction rate to be described later is in a range where there is no practical problem. More preferred.
It is considered that the ions of the metal elements in the metal element group M1 are likely to be involved in the generation of precipitates such as metal oxides deposited on the electrodes. It is preferable because it can be considered that the reduction in battery performance of a typical redox flow battery can be suppressed and contributes to the reduction of the discharge capacity reduction rate described later.
It is more preferable to satisfy all of the above requirements (1) to (6)
　また、本発明のＲＦＢ電解液が含む金属元素群Ｍ２の各金属元素のイオンの濃度は、マグネシウムイオンの濃度が４３～４４０質量ｐｐｍ、アルミニウムイオンの濃度が３５～２５０質量ｐｐｍおよびカルシウムイオンの濃度が５１～１０４０質量ｐｐｍの少なくとも一つを満たすことが好ましい。 The concentration of ions of each metal element of the metal element group M2 included in the RFB electrolyte of the present invention is as follows: magnesium ion concentration is 43 to 440 mass ppm, aluminum ion concentration is 35 to 250 mass ppm, and calcium ion concentration. Preferably satisfies at least one of 51 to 1040 ppm by mass.
　金属元素群Ｍ２の各金属元素のイオンの濃度が、下記（７）から（９）の少なくとも一つを満たすことがより好ましい。
（７）マグネシウムイオンの濃度が４３～３００質量ｐｐｍ
（８）アルミニウムイオンの濃度が３５～１００質量ｐｐｍ
（９）カルシウムイオンの濃度が５１～１０００質量ｐｐｍ
　金属元素群Ｍ２の各金属元素のイオンの濃度が、前述の要件（７）から（９）の少なくとも一つを満たせば、後述する放電容量低減率は実用上問題ない優れた範囲であるので好ましい。
　前述の要件（７）から（９）の全てを満たすことがより好ましい More preferably, the ion concentration of each metal element in the metal element group M2 satisfies at least one of the following (7) to (9).
(7) Magnesium ion concentration is 43-300 ppm by mass
(8) The concentration of aluminum ions is 35 to 100 ppm by mass
(9) The concentration of calcium ions is 51 to 1000 ppm by mass
If the concentration of ions of each metal element in the metal element group M2 satisfies at least one of the above requirements (7) to (9), the discharge capacity reduction rate described later is preferable because it is in an excellent range with no practical problems. .
It is more preferable to satisfy all of the above requirements (7) to (9)
　金属元素群Ｍ１の各金属元素のイオンの濃度および金属元素群Ｍ２の各金属元素のイオンの濃度が、いずれもそれぞれ前述の要件（１）から（９）の濃度範囲であれば、後述する放電容量低減率は実用上問題なく優れることに加え、セル抵抗比も低く抑えられるので好ましい。 If the concentration of ions of each metal element of the metal element group M1 and the concentration of ions of each metal element of the metal element group M2 are both in the concentration ranges of the above requirements (1) to (9), the discharge described later The capacity reduction rate is preferable because it is excellent in practical use and has a low cell resistance ratio.
（金属元素群Ｍ３）
　本発明のＲＦＢ電解液は、ナトリウムおよびカリウムからなる金属元素群Ｍ３の金属元素のイオンを８０～５００００質量ｐｐｍの範囲でさらに含んでもよい。金属元素群Ｍ３の金属元素のイオンの合計濃度は、より好ましくは９０～４５０００質量ｐｐｍであり、さらに好ましくは１００～３３０００質量ｐｐｍであり、さらに好ましくは１００～１００００質量ｐｐｍである。金属元素群Ｍ３の金属元素のイオンの合計濃度は、金属元素群Ｍ１と金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度に比して多くても、前述した範囲内であれば、後述する放電容量低減率は実用上問題ない範囲であるので好ましい。 (Metal element group M3)
The RFB electrolytic solution of the present invention may further contain ions of metal elements of the metal element group M3 consisting of sodium and potassium in the range of 80 to 50000 mass ppm. The total concentration of ions of the metal elements of the metal element group M3 is more preferably 90 to 45000 mass ppm, further preferably 100 to 33000 mass ppm, and further preferably 100 to 10,000 mass ppm. The total concentration of ions of the metal element of the metal element group M3 is at most within the above-mentioned range compared to the total concentration of ions of the metal element of the two metal element groups of the metal element group M1 and the metal element group M2. If so, the discharge capacity reduction rate, which will be described later, is in a practically acceptable range, which is preferable.
　また、金属元素群Ｍ３の各金属元素のイオンの濃度が、下記（１０）から（１１）の少なくとも一つを満たすことがより好ましい。
（１０）ナトリウムイオンの濃度が５０～３００００質量ｐｐｍ
（１１）カリウムイオンの濃度が４２～２００００質量ｐｐｍ
　金属元素群Ｍ３の各金属元素のイオンの濃度が、前述の要件（１０）から（１１）の少なくとも一つを満たせば、後述する放電容量低減率は実用上問題ない範囲であるので好ましい。 More preferably, the concentration of ions of each metal element in the metal element group M3 satisfies at least one of the following (10) to (11).
(10) The concentration of sodium ions is 50 to 30000 mass ppm
(11) The concentration of potassium ions is 42-20000 mass ppm.
If the concentration of ions of each metal element in the metal element group M3 satisfies at least one of the above requirements (10) to (11), the discharge capacity reduction rate to be described later is within a practically no problem range, which is preferable.
（バナジウムイオン）
　本発明のＲＦＢ電解液中に活物質として存在するバナジウムイオンは、２価のバナジウムイオン（Ｖ２＋）、３価のバナジウムイオン（Ｖ３＋）、４価のバナジウムイオン（ＶＯ２＋）および５価のバナジウムイオン（ＶＯ２ ＋）の少なくとも一種である。ＲＦＢ電解液中のバナジウムイオンの合計濃度は、好ましくは０．５～４．０ｍｏｌ／Ｌであり、この範囲内であれば、エネルギー密度を確保しつつ、バナジウムを含む析出物の発生が抑制される。本発明のＲＦＢ電解液が含むバナジウムのイオンの濃度は、より好ましくは０．５～３．０ｍｏｌ／Ｌであり、さらに好ましくは０．５～２．５ｍｏｌ／Ｌである。ＲＦＢ電解液中のバナジウムイオンの合計濃度とは、２価のバナジウムイオン（Ｖ２＋）、３価のバナジウムイオン（Ｖ３＋）、４価のバナジウムイオン（ＶＯ２＋）および５価のバナジウムイオン（ＶＯ２ ＋）の合計濃度である。
　本発明のＲＦＢ電解液中に活物質として存在するバナジウムイオンのバナジウム源は、重質油燃料の燃焼灰であることが好ましい。重質油燃料の燃焼灰とは、重質油燃料を燃焼した際に発生する燃焼灰である。 (Vanadium ion)
The vanadium ions present as an active material in the RFB electrolyte of the present invention are divalent vanadium ions (V 2+ ), trivalent vanadium ions (V 3+ ), tetravalent vanadium ions (VO 2+ ), and pentavalent vanadium ions. It is at least one kind of vanadium ion (VO 2 + ). The total concentration of vanadium ions in the RFB electrolyte is preferably 0.5 to 4.0 mol / L. Within this range, the generation of precipitates containing vanadium is suppressed while ensuring the energy density. The The concentration of vanadium ions contained in the RFB electrolytic solution of the present invention is more preferably 0.5 to 3.0 mol / L, still more preferably 0.5 to 2.5 mol / L. The total concentration of vanadium ions in the RFB electrolyte is a divalent vanadium ion (V 2+ ), a trivalent vanadium ion (V 3+ ), a tetravalent vanadium ion (VO 2+ ), and a pentavalent vanadium ion (VO). 2 + ).
The vanadium source of vanadium ions present as an active material in the RFB electrolytic solution of the present invention is preferably heavy oil fuel combustion ash. The heavy oil fuel combustion ash is combustion ash generated when the heavy oil fuel is burned.
（硫酸イオン）
　本発明のＲＦＢ電解液は、硫酸イオン（ＳＯ４ ２－）を含むことが好ましい。硫酸イオンが存在すると、前述した種々のバナジウムイオンはより安定に溶解する傾向がある。ＲＦＢ電解液が含む硫酸イオンの濃度は、好ましくは１．０～１０．０ｍｏｌ／Ｌであり、より好ましくは１．０～８．０ｍｏｌ／Ｌであり、さらに好ましくは２．０～６．０ｍｏｌ／Ｌである。 (Sulfate ion)
The RFB electrolytic solution of the present invention preferably contains sulfate ions (SO 4 2− ). When sulfate ions are present, the various vanadium ions described above tend to dissolve more stably. The concentration of sulfate ions contained in the RFB electrolyte is preferably 1.0 to 10.0 mol / L, more preferably 1.0 to 8.0 mol / L, and still more preferably 2.0 to 6.0 mol. / L.
（硫酸イオン以外のアニオン）
　本発明のＲＦＢ電解液は、フッ化物イオン（Ｆ－）、塩化物イオン（Ｃｌ－）、臭化物イオン（Ｂｒ－）、およびリン酸イオン（ＰＯ４ ３－）からなる群から選ばれる少なくとも一種のアニオンをさらに含有してもよい。これらの中でも、塩素イオン（Ｃｌ－）を含むことがより好ましい。これらのアニオンをさらに含むことにより、電解液の抵抗が小さくなると考えられる。さらに、ＲＦＢ電解液中のバナジウムイオンの溶解度が向上することが期待される。ＲＦＢ電解液が含む前述したアニオンの合計濃度は、好ましくは０．０１～２．００ｍｏｌ／Ｌ、より好ましくは０．１０～１．５０ｍｏｌ／Ｌであり、さらに好ましくは０．１０～１．００ｍｏｌ／Ｌである。アニオンの合計濃度とは、フッ化物イオン（Ｆ－）、塩化物イオン（Ｃｌ－）、臭化物イオン（Ｂｒ－）、およびリン酸イオン（ＰＯ４ ３－）の合計濃度である。 (Anions other than sulfate ions)
The RFB electrolyte of the present invention is at least one selected from the group consisting of fluoride ions (F − ), chloride ions (Cl − ), bromide ions (Br − ), and phosphate ions (PO 4 3− ). An anion may be further contained. Among these, it is more preferable that chlorine ion (Cl − ) is contained. It is considered that the resistance of the electrolytic solution is reduced by further containing these anions. Furthermore, it is expected that the solubility of vanadium ions in the RFB electrolyte solution is improved. The total concentration of the aforementioned anions contained in the RFB electrolyte is preferably 0.01 to 2.00 mol / L, more preferably 0.10 to 1.50 mol / L, and still more preferably 0.10 to 1.00 mol. / L. The total concentration of anions is the total concentration of fluoride ions (F − ), chloride ions (Cl − ), bromide ions (Br − ), and phosphate ions (PO 4 3− ).
（レドックスフロー電池）
　本発明のレドックスフロー電池は前述したＲＦＢ電解液を含む。レドックスフロー電池のその他の構成としては、公知の構成を採用することができる。
　本発明のレドックスフロー電池は、電池セルを最小単位として、これを単独、又は複数枚積層した電池セルスタックと称される形態で使用され、電池セルに活物質を含む電解液（正極電解液、負極電解液）を循環させて充放電を行う。このようなレドックスフロー電池は、正極電極を内蔵する正極セルと、負極電極を内蔵する負極セルと、正極電極および負極電極の間に介在されて両セルを分離すると共に、所定のイオンを透過する隔膜（例えばイオン交換膜）とを有する電池セルを主構成とする。
　電池セル（正極セル、負極セル）内で充放電反応が行われ、電力の取出し又は貯蔵が可能となる。電池セルにおける充放電反応は、例えば次の通りである。
　　正極セル
　　　充電：ＶＯ２＋（Ｖ４＋）＋Ｈ２Ｏ→ＶＯ２ ＋（Ｖ５＋）＋２Ｈ＋＋ｅ－
　　　放電：ＶＯ２ ＋（Ｖ５＋）＋２Ｈ＋＋ｅ－→ＶＯ２＋（Ｖ４＋）＋Ｈ２Ｏ
　　負極セル
　　　充電：Ｖ３＋＋ｅ－→Ｖ２＋
　　　放電：Ｖ２＋→Ｖ３＋＋ｅ－ (Redox flow battery)
The redox flow battery of the present invention includes the RFB electrolyte described above. As other configurations of the redox flow battery, known configurations can be employed.
The redox flow battery of the present invention is used in a form called a battery cell stack in which a battery cell is a minimum unit, which is a single unit or a plurality of stacked units, and an electrolytic solution (positive electrode electrolyte, The negative electrode electrolyte solution) is circulated to charge and discharge. Such a redox flow battery is interposed between a positive electrode and a negative electrode, a positive electrode cell incorporating a positive electrode, a negative electrode cell incorporating a negative electrode, and separates both cells and transmits predetermined ions. A battery cell having a diaphragm (for example, an ion exchange membrane) is a main component.
A charge / discharge reaction is performed in the battery cell (positive electrode cell, negative electrode cell), and power can be taken out or stored. The charge / discharge reaction in the battery cell is, for example, as follows.
Positive cell charging: VO 2+ (V 4+) + H 2 O → VO 2 + (V 5+) + 2H + + e -
Discharge: VO 2 + (V 5+) + 2H + + e - → VO 2+ (V 4+) + H 2 O
Negative electrode charging: V 3+ + e − → V 2+
Discharge: V 2+ → V 3+ + e −
（レドックスフロー電池用電解液の調製方法）
　本発明のＲＦＢ電解液を得る方法としては、金属元素群Ｍ１と金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度が前述の範囲の濃度として得られる限り特に制限されないが、バナジウム元素を含む廃棄物を原料として用いることができ、例えば、バナジウム元素を含む燃焼灰を原料として用い、レドックスフロー電池用電解液が含む、金属元素群Ｍ１と金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度を２２０質量ｐｐｍより多く１７００質量ｐｐｍ以下となる範囲に調製する調製工程を含むレドックスフロー電池用電解液の製造方法により、本発明のＲＦＢ電解液を得ることができる。
　バナジウム元素を含む燃焼灰を原料として用いる、すなわち、バナジウムを含む廃棄物を再利用することにより、コストを抑えることができる。
　バナジウム元素を含む燃焼灰は、例えばバナジウム元素を含む重質油燃料等の燃焼灰である。バナジウム元素を含む重質油燃料等の燃焼灰を原料として、ＲＦＢ電解液を得る方法としては、例えば特許第３８３１８０５号公報の記載に従って行うことができる。この場合、特許第３８３１８０５号公報に記載の工程をすべて実施して高純度に調製する必要はない。例えば、電解液としたときに金属元素群Ｍ１と金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度が前述の範囲の濃度となるバナジウム含有化合物が得られた時点で処理を終了してもよく、また、各工程の時間を短くする等、簡略化してもよい。したがって、前者の場合は以降の処理を行わなくてよく、後者の場合は処理時間の短縮等ができるため、該処理にかかるコストを抑えることができる。得られたバナジウム含有化合物と硫酸とを混合し、適切なバナジウムイオン濃度に調製してレドックスフロー電池用電解液を得ることができる。
　このような製造方法により、バナジウム元素を含む重質油燃料の燃焼灰を原料として、金属元素群Ｍ１と金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度が、２２０質量ｐｐｍより多く１７００質量ｐｐｍ以下であるレドックスフロー電池用電解液、好ましくは、前述の要件（１）から（６）の少なくとも一つを満たすレドックスフロー電池用電解液や、前述の要件（７）から（９）の少なくとも一つを満たすレドックスフロー電池用電解液等が得られる。 (Preparation method of redox flow battery electrolyte)
The method for obtaining the RFB electrolyte solution of the present invention is not particularly limited as long as the total concentration of ions of the metal elements of the two metal element groups of the metal element group M1 and the metal element group M2 can be obtained as the concentration in the above range. , Waste containing vanadium element can be used as a raw material. For example, combustion ash containing vanadium element is used as a raw material, and the redox flow battery electrolyte contains two metal element groups M1 and M2 The RFB electrolyte solution of the present invention is obtained by a method for producing an electrolyte solution for a redox flow battery including a preparation step of preparing a total concentration of ions of metal elements in a metal element group in a range of more than 220 mass ppm and 1700 mass ppm or less. be able to.
By using combustion ash containing vanadium element as a raw material, that is, by reusing waste containing vanadium, costs can be reduced.
The combustion ash containing vanadium element is, for example, combustion ash such as heavy oil fuel containing vanadium element. A method for obtaining an RFB electrolyte solution using combustion ash such as heavy oil fuel containing vanadium element as a raw material can be carried out, for example, as described in Japanese Patent No. 381805. In this case, it is not necessary to carry out all the steps described in Japanese Patent No. 381805 and prepare it with high purity. For example, when the vanadium-containing compound is obtained in which the total concentration of the metal element ions of the two metal element groups of the metal element group M1 and the metal element group M2 is in the above-described range when the electrolyte is used. May be terminated, or the time of each process may be shortened. Therefore, in the former case, it is not necessary to perform the subsequent processing, and in the latter case, the processing time can be shortened, so that the cost for the processing can be suppressed. The obtained vanadium-containing compound and sulfuric acid can be mixed and adjusted to an appropriate vanadium ion concentration to obtain a redox flow battery electrolyte.
By such a manufacturing method, using the combustion ash of heavy oil fuel containing vanadium as a raw material, the total concentration of ions of the metal elements of the two metal element groups of the metal element group M1 and the metal element group M2 is 220 mass. An electrolyte solution for redox flow battery that is more than ppm and 1700 mass ppm or less, preferably from an electrolyte solution for redox flow battery that satisfies at least one of the above requirements (1) to (6), or from the above requirement (7) An electrolyte solution for redox flow battery that satisfies at least one of (9) is obtained.
　以下、本発明を実施例に基づいて具体的に説明する。なお、本発明はこれらの実施例にのみ限定されるものではない。また、実施例および比較例における電気化学評価は、以下の方法により行った。 Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples. Moreover, the electrochemical evaluation in an Example and a comparative example was performed with the following method.
　（イオンの濃度）
　表１の金属元素のイオンの濃度の測定は、各例において調製したＲＦＢ電解液１００ｍｌを必要に応じて適宜希釈して、誘導結合プラズマ発光分光分析装置（ＩＣＰ－ＯＥＳ）（装置名：ＶＩＳＴＡ－ＰＲＯ、エスアイアイ・ ナノテクノロジー社製）を用いて定量を行った。 (Ion concentration)
The concentration of the metal element ions in Table 1 was measured by appropriately diluting 100 ml of the RFB electrolyte solution prepared in each example as necessary to obtain an inductively coupled plasma emission spectrometer (ICP-OES) (device name: VISTA- Quantification was performed using PRO, manufactured by SII Nanotechnology.
実施例１：
　（１）ＲＦＢ電解液の調製
　バナジウム元素を含む重質油燃料の燃焼灰を原料とするバナジウム系レドックスフロー電池用電解液を模擬したＲＦＢ電解液を、以下の手順で調整した。なお、実施例１および後述する実施例２～１３及び比較例２～４で得られるＲＦＢ電解液は、特許第３８３１８０５号公報に記載の手順を想定して得たＲＦＢ電解液であり、後述する比較例１で得られるＲＦＢ電解液は、特許第３８３１８０５号公報に記載の手順を想定して得たＲＦＢ電解液であって実施例１～１３及び比較例２～４よりも処理時間を長くし且つ晶析を繰り返して不純物を除去することを想定したものである。
　硫酸（Ｈ２ＳＯ４）濃度が４．０ｍｏｌ／Ｌの硫酸水溶液１０００ｍｌに、０．９ｍｏｌの硫酸バナジウム（Ｖ２（ＳＯ４）３）と１．８ｍｏｌの酸化硫酸バナジウム（ＶＯＳＯ４）とを添加して撹拌し、溶液の体積が２０００ｍＬになるように、純水と混合し、撹拌してバナジウム含有硫酸水溶液２０００ｍＬを調製した。得たバナジウム含有硫酸水溶液に下記の各金属元素の硫酸化合物（アルミニウムのみは水酸化物）を添加することにより、バナジウム以外の金属元素のイオンを表１に記すとおりの濃度で含むＲＦＢ電解液（１）を得た。添加した各金属元素の化合物は、いずれもナカライテスク社製のものを用いた。
・クロム；硫酸クロム（ＩＩＩ）水和物（Ｃｒ２（ＳＯ４）３・ｘＨ２Ｏ）。複数種の水和物を含むので、８０℃で２４時間加熱して、脱水して用いた。
・マンガン；硫酸マンガン（ＩＩ）五水和物（ＭｎＳＯ４・５Ｈ２Ｏ）（純度９９．０％以上）。
・コバルト；硫酸コバルト（ＩＩ）七水和物（ＣｏＳＯ４・７Ｈ２Ｏ）（純度９９．０％以上）。
・ニッケル；硫酸ニッケル（ＩＩ）六水和物（ＮｉＳＯ４・６Ｈ２Ｏ）（純度９９．０％以上）。
・銅；硫酸銅（ＩＩ）五水和物（ＣｕＳＯ４・５Ｈ２Ｏ）（純度９９．５％以上）。
・亜鉛；硫酸亜鉛七水和物（ＺｎＳＯ４・７Ｈ２Ｏ）（純度９９．５％以上）。
・マグネシウム；硫酸マグネシウム七水和物（ＭｇＳＯ４・７Ｈ２Ｏ）（純度９９．５％以上）。
・アルミニウム；水酸化アルミニウム（Ａｌ（ＯＨ）３）（純度９７．０％以上）。
・カルシウム；硫酸カルシウム二水和物（ＣａＳＯ４・２Ｈ２Ｏ）（純度９８．０％以上）。
・ナトリウム；硫酸ナトリウム（Ｎａ２ＳＯ４）（純度９８．５％以上）。
・カリウム；硫酸カリウム（Ｋ２ＳＯ４）（純度９９．０％以上）。 Example 1:
(1) Preparation of RFB Electrolytic Solution An RFB electrolytic solution simulating an electrolytic solution for vanadium redox flow battery using heavy oil fuel combustion ash containing vanadium element as a raw material was prepared by the following procedure. Note that the RFB electrolytes obtained in Example 1 and Examples 2 to 13 and Comparative Examples 2 to 4 described later are RFB electrolytes obtained by assuming the procedure described in Japanese Patent No. 3831805, which will be described later. The RFB electrolytic solution obtained in Comparative Example 1 is an RFB electrolytic solution obtained by assuming the procedure described in Japanese Patent No. 3831805, and has a longer processing time than Examples 1 to 13 and Comparative Examples 2 to 4. In addition, it is assumed that impurities are removed by repeating crystallization.
0.9 mol of vanadium sulfate (V 2 (SO 4 ) 3 ) and 1.8 mol of vanadium oxide sulfate (VOSO 4 ) were added to 1000 ml of sulfuric acid aqueous solution having a sulfuric acid (H 2 SO 4 ) concentration of 4.0 mol / L. The mixture was stirred and mixed with pure water so that the volume of the solution was 2000 mL, and stirred to prepare 2000 mL of a vanadium-containing sulfuric acid aqueous solution. An RFB electrolyte solution containing ions of metal elements other than vanadium at concentrations as shown in Table 1 by adding a sulfate compound of the following metal elements (aluminum only is a hydroxide) to the obtained vanadium-containing sulfuric acid aqueous solution ( 1) was obtained. As the compound of each metal element added, a product manufactured by Nacalai Tesque was used.
Chromium; chromium (III) sulfate hydrate (Cr 2 (SO 4) 3 · xH 2 O). Since it contains multiple types of hydrates, it was heated at 80 ° C. for 24 hours and dehydrated.
Manganese: Manganese (II) sulfate pentahydrate (MnSO 4 .5H 2 O) (purity 99.0% or more).
Cobalt; cobalt (II) sulfate heptahydrate (CoSO 4 .7H 2 O) (purity 99.0% or more).
Nickel: nickel sulfate (II) hexahydrate (NiSO 4 .6H 2 O) (purity 99.0% or more).
Copper: Copper (II) sulfate pentahydrate (CuSO 4 .5H 2 O) (purity 99.5% or more).
Zinc: Zinc sulfate heptahydrate (ZnSO 4 .7H 2 O) (purity 99.5% or more).
Magnesium; magnesium sulfate heptahydrate (MgSO 4 .7H 2 O) (purity 99.5% or more).
Aluminum: Aluminum hydroxide (Al (OH) 3 ) (purity 97.0% or more).
Calcium: Calcium sulfate dihydrate (CaSO 4 .2H 2 O) (purity 98.0% or more).
Sodium; sodium sulfate (Na 2 SO 4) (purity 98.5% or higher).
Potassium; potassium sulfate (K 2 SO 4) (99.0% purity).
　（２）電気化学評価
　（レドックスフロー電池の作製）
　レドックスフロー電池は、１対の正極電極および負極電極として面積５０ｃｍ２（５ｃｍ×１０ｃｍ）のカーボンフェルト（型番：ＡＡＦ３０４ＺＳ、東洋紡株式会社製）と、イオン交換膜としてＮａｆｉｏｎ（登録商標）（製品名：ＮＲＥ－２１２、Ｓｉｇｍａ－Ａｌｄｒｉｃｈ社製）を用いて作製し、単セルのレドックスフロー電池を得た。
　（充放電特性の測定）
　正極電解液および負極電解液として、ＲＦＢ電解液（１）をそれぞれ５０ｍＬずつ用意し、正極電極および負極電極にそれぞれＲＦＢ電解液を５０ｍＬ／分の流量で循環しながら、電流１０Ａ（電流密度０．２Ａ／ｃｍ２）で充放電を行った。最初に充電を行い、電圧が１．７５Ｖになったところで充電を停止し、次に放電を行い、電圧が１．００Ｖになったところで放電終了とした。この充放電を合計２０サイクル繰り返し、各サイクルの充電時間（ｈ）、放電時間（ｈ）、および充放電中のセル電圧（Ｖ）を測定した。充電時に充電にかかる時間の半分の時点でのセル電圧をＶ１、放電時に放電にかかる時間の半分の時点でのセル電圧をＶ２とした。 (2) Electrochemical evaluation (Preparation of redox flow battery)
The redox flow battery is a carbon felt (model number: AAF304ZS, manufactured by Toyobo Co., Ltd.) having an area of 50 cm 2 (5 cm × 10 cm) as a pair of positive electrode and negative electrode, and Nafion (registered trademark) (product name: product name). NRE-212 (manufactured by Sigma-Aldrich) was used to obtain a single cell redox flow battery.
(Measurement of charge / discharge characteristics)
As the positive electrode electrolyte and the negative electrode electrolyte, 50 mL each of the RFB electrolyte (1) was prepared, and while circulating the RFB electrolyte at a flow rate of 50 mL / min. 2 A / cm 2 ) was charged and discharged. Charging was performed first, charging was stopped when the voltage reached 1.75V, then discharging was performed, and discharging was terminated when the voltage reached 1.00V. This charge / discharge was repeated for a total of 20 cycles, and the charge time (h), discharge time (h), and cell voltage (V) during charge / discharge of each cycle were measured. The cell voltage at half the time required for charging during charging was V 1 , and the cell voltage at half the time required for discharging during discharging was V 2 .
　（セル抵抗比）
　ＲＦＢ電解液（１）を用いたレドックスフロー電池のセル抵抗は、下記式から求めた。
セル抵抗（Ω・ｃｍ２）＝｛Ｖ１（Ｖ）－Ｖ２（Ｖ）｝／｛２×電流密度（Ａ／ｃｍ２）｝
　後述する比較例１のＲＦＢ電解液（ｃ１）を用いた場合のレドックスフロー電池のセル抵抗を１．００として、１０サイクル放電終了後のセル抵抗の比（セル抵抗比）を求めた。ＲＦＢ電解液（１）のセル抵抗比を表１に併せて示す。 (Cell resistance ratio)
The cell resistance of the redox flow battery using the RFB electrolyte (1) was determined from the following formula.
Cell resistance (Ω · cm 2 ) = {V 1 (V) −V 2 (V)} / {2 × current density (A / cm 2 )}
The cell resistance ratio (cell resistance ratio) after the end of 10 cycles of discharge was determined with the cell resistance of the redox flow battery in the case of using the RFB electrolyte solution (c1) of Comparative Example 1 described later as 1.00. The cell resistance ratio of the RFB electrolyte (1) is also shown in Table 1.
　（放電容量低減率）
　下記式からＲＦＢ電解液（１）を用いたレドックスフロー電池の１０サイクル目の放電容量に対する２０サイクル目の放電容量の低減率（放電容量低減率）（％）を求めた。
充電容量（Ａｈ）＝充電電流（Ａ）×充電時間（ｈ）
放電容量（Ａｈ）＝放電電流（Ａ）×放電時間（ｈ）
放電容量低減率（％）＝｛１－（２０サイクル目の放電容量（Ａｈ）／１０サイクル目の放電容量（Ａｈ））｝×１００ (Discharge capacity reduction rate)
The reduction rate (discharge capacity reduction rate) (%) of the discharge capacity at the 20th cycle relative to the discharge capacity at the 10th cycle of the redox flow battery using the RFB electrolyte solution (1) was determined from the following formula.
Charging capacity (Ah) = Charging current (A) × Charging time (h)
Discharge capacity (Ah) = discharge current (A) × discharge time (h)
Discharge capacity reduction rate (%) = {1− (discharge capacity at 20th cycle (Ah) / 10th discharge capacity (Ah))} × 100
　実施例２～１３、比較例１～４：
（１）ＲＦＢ電解液の調製
　ＲＦＢ電解液が含有するバナジウム以外の各金属元素のイオンの濃度を表１に記載の濃度にそれぞれ変更した以外は、実施例１と同様にして各例のＲＦＢ電解液（２）～（１３）および（ｃ１）～（ｃ４）を調製した。
（２）電気化学評価
　電気化学評価は、実施例１と同様にして評価を行った。セル抵抗比および放電容量低減率を併せて表１に示す。 Examples 2 to 13 and Comparative Examples 1 to 4:
(1) Preparation of RFB electrolyte solution RFB electrolysis of each example was carried out in the same manner as in Example 1 except that the concentrations of ions of each metal element other than vanadium contained in the RFB electrolyte solution were changed to the concentrations shown in Table 1, respectively. Liquids (2) to (13) and (c1) to (c4) were prepared.
(2) Electrochemical evaluation The electrochemical evaluation was performed in the same manner as in Example 1. The cell resistance ratio and the discharge capacity reduction rate are shown together in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１の結果より、金属元素群Ｍ１と、金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度が２２０質量ｐｐｍより多く１７００質量ｐｐｍ以下であるＲＦＢ電解液は、放電容量低減率が小さく、コスト高の比較例１のＲＦＢ電解液を用いた場合と比較してもレドックスフロー電池の性能は実質的に損なわれないことが分かる。なお、ＵＶ－ｖｉｓ分光光度計（ＳＨＩＭＡＤＺＵ社製　ＵＶ－１７００）を用いて測定したバナジウムイオンの合計濃度は、ＲＦＢ電解液（１）～（１３）および（ｃ１）～（ｃ４）それぞれにおいて、１．８ｍｏｌ／Ｌであった。 From the results of Table 1, the RFB electrolyte solution in which the total concentration of ions of the metal element groups of the metal element group M1 and the metal element group M2 is greater than 220 mass ppm and less than or equal to 1700 mass ppm is It can be seen that the performance of the redox flow battery is not substantially impaired even when compared with the case where the RFB electrolyte solution of Comparative Example 1 having a small reduction rate and high cost is used. The total concentration of vanadium ions measured using a UV-vis spectrophotometer (UV-1700 manufactured by SHIMADZU) was 1 in each of the RFB electrolytes (1) to (13) and (c1) to (c4). 0.8 mol / L.
　本発明のレドックスフロー電池用電解液は、コストを抑えて調製することができ、レドックスフロー電池に好適に用いることができる。 The electrolyte solution for a redox flow battery of the present invention can be prepared at a reduced cost and can be suitably used for a redox flow battery.

Claims (10)

  1. 　活物質としてバナジウムイオンを含むレドックスフロー電池用電解液であって、
    　クロム、マンガン、コバルト、ニッケル、銅および亜鉛からなる金属元素群Ｍ１と、マグネシウム、アルミニウムおよびカルシウムからなる金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度が、２２０質量ｐｐｍより多く１７００質量ｐｐｍ以下であるレドックスフロー電池用電解液。     An electrolyte for a redox flow battery containing vanadium ions as an active material,
    The total concentration of ions of the metal elements of the two metal element groups of the metal element group M1 composed of chromium, manganese, cobalt, nickel, copper, and zinc and the metal element group M2 composed of magnesium, aluminum, and calcium is 220 mass ppm. The electrolyte solution for redox flow batteries which is more than 1700 mass ppm.
  2. 　前記金属元素群Ｍ１の金属元素のイオンの合計濃度が、９０質量ｐｐｍより多く３００質量ｐｐｍ以下である請求項１に記載のレドックスフロー電池用電解液。 The electrolyte solution for a redox flow battery according to claim 1, wherein the total concentration of ions of the metal elements in the metal element group M1 is more than 90 ppm and not more than 300 ppm by mass.
  3. 　前記金属元素群Ｍ２の金属元素のイオンの合計濃度が、１３０～１４００質量ｐｐｍである請求項１または２に記載のレドックスフロー電池用電解液。 The electrolyte solution for a redox flow battery according to claim 1 or 2, wherein the total concentration of ions of the metal elements of the metal element group M2 is 130 to 1400 mass ppm.
  4. 　前記金属元素群Ｍ１の各金属元素のイオンの濃度が、下記（１）から（６）の少なくとも一つを満たす請求項１～３のいずれか一項に記載のレドックスフロー電池用電解液。
    （１）クロムイオンの濃度が４０～１２０質量ｐｐｍ
    （２）マンガンイオンの濃度が５～１５質量ｐｐｍ
    （３）コバルトイオンの濃度が６～１８質量ｐｐｍ
    （４）ニッケルイオンの濃度が１２～１００質量ｐｐｍ
    （５）銅イオンの濃度が７～２１質量ｐｐｍ
    （６）亜鉛イオンの濃度が６～１８質量ｐｐｍ     The electrolyte solution for a redox flow battery according to any one of claims 1 to 3, wherein the concentration of ions of each metal element in the metal element group M1 satisfies at least one of the following (1) to (6).
    (1) The concentration of chromium ions is 40 to 120 mass ppm
    (2) Manganese ion concentration is 5-15 mass ppm
    (3) Cobalt ion concentration is 6-18 mass ppm
    (4) Nickel ion concentration of 12-100 mass ppm
    (5) Copper ion concentration is 7 to 21 mass ppm
    (6) Zinc ion concentration is 6-18 mass ppm
  5. 　前記金属元素群Ｍ２の各金属元素のイオンの濃度が、下記（７）から（９）の少なくとも一つを満たす請求項１～４のいずれか一項に記載のレドックスフロー電池用電解液。
    （７）マグネシウムイオンの濃度が４３～３００質量ｐｐｍ
    （８）アルミニウムイオンの濃度が３５～１００質量ｐｐｍ
    （９）カルシウムイオンの濃度が５１～１０００質量ｐｐｍ     The redox flow battery electrolyte according to any one of claims 1 to 4, wherein the concentration of ions of each metal element in the metal element group M2 satisfies at least one of the following (7) to (9).
    (7) Magnesium ion concentration is 43-300 ppm by mass
    (8) The concentration of aluminum ions is 35 to 100 ppm by mass
    (9) The concentration of calcium ions is 51 to 1000 ppm by mass
  6. 　ナトリウムおよびカリウムからなる金属元素群Ｍ３の金属元素のイオンを、合計濃度８０～５００００質量ｐｐｍの範囲で、さらに含む請求項１～５のいずれか一項に記載のレドックスフロー電池用電解液。 The electrolyte solution for redox flow batteries according to any one of claims 1 to 5, further comprising ions of metal elements of metal element group M3 composed of sodium and potassium in a total concentration range of 80 to 50000 mass ppm.
  7. 　前記金属元素群Ｍ３の各金属元素のイオンの濃度が、下記（１０）から（１１）の少なくとも一つを満たす請求項６に記載のレドックスフロー電池用電解液。
    （１０）ナトリウムイオンの濃度が５０～３００００質量ｐｐｍ
    （１１）カリウムイオンの濃度が４２～２００００質量ｐｐｍ     The electrolyte solution for redox flow batteries according to claim 6, wherein the concentration of ions of each metal element in the metal element group M3 satisfies at least one of the following (10) to (11).
    (10) The concentration of sodium ions is 50 to 30000 mass ppm
    (11) The concentration of potassium ions is 42-20000 mass ppm.
  8. 　バナジウム源が重質油燃料の燃焼灰である請求項１～７のいずれか一項に記載のレドックスフロー電池用電解液。 The redox flow battery electrolyte according to any one of claims 1 to 7, wherein the vanadium source is combustion ash of heavy oil fuel.
  9. 　請求項１～８のいずれか一項に記載のレドックスフロー電池用電解液を備えるレドックスフロー電池。 A redox flow battery comprising the redox flow battery electrolyte according to any one of claims 1 to 8.
  10. 　バナジウム元素を含む燃焼灰を原料として用いる請求項１～８のいずれか一項に記載のレドックスフロー電池用電解液の製造方法であって、
    　レドックスフロー電池用電解液が含む、前記金属元素群Ｍ１と前記金属元素群Ｍ２との２つの金属元素群の金属元素のイオンの合計濃度を２２０質量ｐｐｍより多く１７００質量ｐｐｍ以下となる範囲に調製する調製工程を含むレドックスフロー電池用電解液の製造方法。

          The method for producing an electrolyte solution for a redox flow battery according to any one of claims 1 to 8, wherein combustion ash containing vanadium element is used as a raw material.
    The total concentration of ions of the metal elements of the two metal element groups of the metal element group M1 and the metal element group M2 included in the redox flow battery electrolyte is adjusted to a range in which the total concentration is greater than 220 mass ppm and less than or equal to 1700 mass ppm. The manufacturing method of the electrolyte solution for redox flow batteries including the preparation process to perform.

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08148177A (en) * 1994-11-17 1996-06-07 Kashimakita Kyodo Hatsuden Kk Manufacture of vanadium electrolyte of high purity
WO2013054921A1 (en) * 2011-10-14 2013-04-18 株式会社ギャラキシー Vanadium electrolyte, production method therefor, and production device therefor
WO2014203409A1 (en) * 2013-06-21 2014-12-24 住友電気工業株式会社 Redox flow battery electrolyte and redox flow battery
WO2015019974A1 (en) * 2013-08-07 2015-02-12 住友電気工業株式会社 Redox flow battery

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08148177A (en) * 1994-11-17 1996-06-07 Kashimakita Kyodo Hatsuden Kk Manufacture of vanadium electrolyte of high purity
WO2013054921A1 (en) * 2011-10-14 2013-04-18 株式会社ギャラキシー Vanadium electrolyte, production method therefor, and production device therefor
WO2014203409A1 (en) * 2013-06-21 2014-12-24 住友電気工業株式会社 Redox flow battery electrolyte and redox flow battery
WO2015019974A1 (en) * 2013-08-07 2015-02-12 住友電気工業株式会社 Redox flow battery

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