Redox flow battery

Abstract

To provide a redox flow battery capable of bringing out a large current density.SOLUTION: Provided is a redox flow battery 100 that is charged and discharged by supplying a positive electrode electrolyte and a negative electrode electrolyte to a battery cell which comprises a positive electrode 104, a negative electrode 105, and a barrier membrane 101 interposed between the positive electrode 104 and the negative electrode 105. The positive electrode electrolyte and the negative electrode electrolyte are molten salt. The positive electrode electrolyte contains a trivalent titanium ion and a tetravalent titanium ion. The negative electrode electrolyte contains a bivalent titanium ion and a trivalent titanium ion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a redox flow battery. [Background technology]

[0002] Currently, the introduction of renewable energy is accelerating rapidly. However, how to store and release electricity generated by renewable energy has become an issue. One known technology for storing and releasing electricity is the vanadium ion redox flow battery, which utilizes the electrode reaction of vanadium ions (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2011 / 111717 Summary of the Invention [Problem to be solved by the invention]

[0004] However, because vanadium ion redox flow batteries use an aqueous electrolyte, the solubility of the active material in the electrolyte is low, which poses the problem of low current density that can be extracted.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a redox flow battery that can extract a large current density. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention has the following aspects. [1] A redox flow battery that is charged and discharged by supplying a positive electrode electrolyte and a negative electrode electrolyte to a battery cell that includes a positive electrode, a negative electrode, and a diaphragm interposed between the positive electrode and the negative electrode, the positive electrode electrolyte and the negative electrode electrolyte are molten salts, the positive electrode electrolyte contains trivalent titanium ions and tetravalent titanium ions, The redox flow battery, wherein the negative electrode electrolyte contains divalent titanium ions and trivalent titanium ions. [2] The redox flow battery according to [1], wherein the molten salt is a molten salt of lithium chloride and potassium chloride, a molten salt of sodium chloride and potassium chloride, a molten salt of magnesium chloride, sodium chloride and potassium chloride, or a molten salt of lithium fluoride, sodium fluoride and potassium fluoride. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a redox flow battery that can extract a large current density. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a redox flow battery according to one embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing a cyclic voltammogram in Example 1. [Figure 3] FIG. 1 is a diagram showing a square wave voltammogram in Example 1. [Figure 4] FIG. 10 is a diagram showing a cyclic voltammogram in Example 2. [Figure 5] FIG. 10 is a diagram showing a square wave voltammogram in Example 2. [Figure 6] FIG. 10 is a diagram showing charge / discharge curves in Example 3. [Figure 7] FIG. 10 is a diagram showing charge / discharge curves in Example 4. [Figure 8] FIG. 10 is a diagram showing charge / discharge curves in Example 5. [Figure 9] FIG. 10 is a diagram showing charge / discharge curves in a comparative example. [Figure 10] FIG. 10 is a diagram showing charge / discharge curves in Example 6. [Figure 11]FIG. 10 is a diagram showing charge / discharge curves in Example 7. [Figure 12] FIG. 10 is a diagram showing charge / discharge curves in Example 8. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a redox flow battery according to the present invention will be described by showing an embodiment with reference to Fig. 1. However, the present invention is not limited to the following embodiment.

[0010] [Redox flow battery] FIG. 1 is a schematic diagram showing a redox flow battery according to one embodiment of the present invention. 1, a redox flow battery 100 is typically connected to a power generation unit (e.g., a solar power generator, a wind power generator, or other general power plant) and a load such as a power grid or a consumer via an AC / DC converter, and is charged using the power generation unit as a power supply source and discharged using the load as a power supply destination. To perform the above charging and discharging, the following battery system is constructed, which includes the redox flow battery 100 and a circulation mechanism (tank, piping, pump) that circulates an electrolyte through the redox flow battery 100.

[0011] The redox flow battery 100 includes a cathode cell 102 incorporating a cathode 104, an anode cell 103 incorporating an anode 105, and a diaphragm 101 that separates the cathode cell 102 and the anode cell 103 and allows ions to pass through as needed. A cathode electrolyte tank 106 is connected to the cathode cell 102 via pipes 108 and 110. A anode electrolyte tank 107 is connected to the anode cell 103 via pipes 109 and 111. The pipe 108 includes a pump 112 for circulating the cathode electrolyte. The pipe 109 includes a pump 113 for circulating the anode electrolyte.

[0012] The redox flow battery 100 circulates and supplies the positive electrode electrolyte in the positive electrode electrolyte tank 106 to the positive electrode cell 102 (positive electrode 104) using pipes 108, 110 and a pump 112, and also circulates and supplies the negative electrode electrolyte in the negative electrode electrolyte tank 107 to the negative electrode cell 103 (negative electrode 105) using pipes 109, 111 and a pump 113. Charging and discharging are performed in accordance with a valence change reaction of metal ions that serve as active materials in the positive electrode electrolyte in the positive electrode cell 102 and a valence change reaction of metal ions that serve as active materials in the negative electrode electrolyte in the negative electrode cell 103.

[0013] The diaphragm 101 may be made of a porous material such as magnesium oxide (MgO). Alternatively, glass fiber with a high porosity may be used as the diaphragm 101. As will be described later, the redox flow battery 100 uses a positive electrode electrolyte containing trivalent titanium ions (Ti 3+ ) and tetravalent titanium ions (Ti 4+ ) and the negative electrode electrolyte contains divalent titanium ions (Ti 2+ ) and trivalent titanium ions (Ti 3+ ), the redox flow battery 100 functions normally even when a partition wall with a large surface roughness through which substances can easily move physically is used. Furthermore, the redox flow battery 100 can function as a battery even if the positive electrode electrolyte and the negative electrode electrolyte are mixed to some extent through the partition wall 101, and therefore can be said to be resistant to cross-contamination. In other words, the redox flow battery 100 has excellent resilience against cross-contamination. It is believed that this characteristic of excellent resilience becomes even more advantageous as the scale of power storage becomes larger. Examples of the positive electrode 104 and the negative electrode 105 include electrodes made of carbon materials such as graphite, fullerene, and carbon nanotubes.

[0014] The positive electrode electrolyte and the negative electrode electrolyte are molten salts. The molten salt is not particularly limited as long as it has a low melting point, but is preferably a molten salt of lithium chloride and potassium chloride (LiCl-KCl) (melting point: 350°C to 500°C), a molten salt of sodium chloride and potassium chloride (NaCl-KCl) (melting point: 700°C to 750°C), a molten salt of magnesium chloride, sodium chloride and potassium chloride (MgCl-NaCl-KCl) (melting point: 400°C to 500°C), a molten salt of lithium fluoride, sodium fluoride and potassium fluoride (LiF-NaF-KF) (melting point: 460°C to 600°C), or a molten salt of lithium chloride, potassium chloride and cesium chloride (LiCl-KCl-CsCl) (melting point: 270°C to 400°C).

[0015] In the molten salt of lithium chloride and potassium chloride (LiCl-KCl), the blending ratio of lithium chloride to potassium chloride is preferably 4:6 to 6:4 in molar ratio. When the blending ratio of lithium chloride to potassium chloride is within the above range, the positive electrode electrolyte and the negative electrode electrolyte can dissolve predetermined amounts of titanium ions, which will be described later. In the molten salt of sodium chloride and potassium chloride (NaCl-KCl), the molar ratio of sodium chloride to potassium chloride is preferably 4:6 to 6:4. When the molar ratio of sodium chloride to potassium chloride is within the above range, the positive electrode electrolyte and the negative electrode electrolyte can dissolve predetermined amounts of titanium ions, which will be described later. In the molten salt of magnesium chloride, sodium chloride, and potassium chloride (MgCl-NaCl-KCl), the molar ratio of magnesium chloride, sodium chloride, and potassium chloride is preferably 6:2:2 to 4:3:3. When the molar ratio of magnesium chloride, sodium chloride, and potassium chloride is within the above range, the positive electrode electrolyte and the negative electrode electrolyte can dissolve predetermined amounts of titanium ions, which will be described later. In the molten salt of lithium fluoride, sodium fluoride, and potassium fluoride (LiF-NaF-KF), the blending ratio of lithium fluoride, sodium fluoride, and potassium fluoride is preferably 5:1:4 to 4:1:5 in molar ratio. When the blending ratio of lithium fluoride, sodium fluoride, and potassium fluoride is within the above range, the positive electrode electrolyte and the negative electrode electrolyte can dissolve predetermined amounts of titanium ions, which will be described later. In the molten salt of lithium chloride, potassium chloride, and cesium chloride (LiCl-KCl-CsCl), the compounding ratio of lithium chloride, potassium chloride, and cesium chloride, in terms of molar ratio, is preferably 5:2:3 to 6:2:2. When the compounding ratio of lithium chloride, potassium chloride, and cesium chloride is within the above range, the positive electrode electrolyte and the negative electrode electrolyte can dissolve predetermined amounts of titanium ions, which will be described later.

[0016] The positive electrode electrolyte contains trivalent titanium ions (Ti 3+ ) and tetravalent titanium ions (Ti 4+ ) containing trivalent titanium ions (Ti 3+ ) and tetravalent titanium ions (Ti 4+ ) originates, for example, from titanium(III) chloride (TiCl3) dissolved in the positive electrode electrolyte. - ) may be introduced. The trivalent titanium ions (Ti 3+ The content of trivalent titanium ions (Ti) in the positive electrode electrolyte is preferably 0.5 mol / L to 8 mol / L, more preferably 1 mol / L to 6 mol / L, and even more preferably 2 mol / L to 5 mol / L. 3+ If the content of trivalent titanium ions (Ti) in the positive electrode electrolyte is less than the lower limit, charging cannot be performed sufficiently. 3+ If the content of titanium halide exceeds the upper limit, the titanium halide will not be able to dissolve in the molten salt and will precipitate. Tetravalent titanium ions (Ti 4+The content of tetravalent titanium ions (Ti 4+ If the content of tetravalent titanium ions (Ti) in the positive electrode electrolyte is less than the lower limit, the current density that can be extracted during discharge will be small. 4+ If the content of titanium halide exceeds the upper limit, the titanium halide cannot be dissolved in the molten salt and is lost by evaporation. The trivalent titanium ions (Ti 3+ ) content and tetravalent titanium ions (Ti 4+ ) may be equal or different.

[0017] The negative electrode electrolyte contains divalent titanium ions (Ti 2+ ) and trivalent titanium ions (Ti 3+ ) containing divalent titanium ions (Ti 2+ ) and trivalent titanium ions (Ti 3+ ) originates, for example, from titanium (III) chloride (TiCl3) dissolved in the negative electrode electrolyte. Also, fluoride ions (F - ) may be introduced. Divalent titanium ions (Ti 2+ The content of divalent titanium ions (Ti) in the negative electrode electrolyte is preferably 0.5 mol / L to 8 mol / L, more preferably 1 mol / L to 6 mol / L, and even more preferably 2 mol / L to 5 mol / L. 2+ If the content of divalent titanium ions (Ti) in the negative electrode electrolyte is less than the lower limit, the current density that can be extracted during discharge will be small. 2+ If the content of titanium halide exceeds the upper limit, the titanium halide will not be able to dissolve in the molten salt and will precipitate. The trivalent titanium ions (Ti 3+ The content of trivalent titanium ions (Ti) in the negative electrode electrolyte is preferably 0.5 mol / L to 8 mol / L, more preferably 1 mol / L to 6 mol / L, and even more preferably 2 mol / L to 5 mol / L. 3+If the content of trivalent titanium ions (Ti) in the negative electrode electrolyte is less than the lower limit, charging cannot be performed sufficiently. 3+ If the content of titanium halide exceeds the upper limit, the titanium halide will not be able to dissolve in the molten salt and will precipitate. Divalent titanium ions (Ti 2+ ) content and trivalent titanium ion (Ti 3+ ) may be equal or different.

[0018] In the redox flow battery 100, an electronic reaction represented by the following formula (1) occurs at the positive electrode. The potential of the positive electrode due to this electronic reaction is −0.3 V vs. Cl / Cl - is.

[0019] [ka]

[0020] In the redox flow battery 100, an electronic reaction represented by the following formula (2) occurs at the negative electrode. The potential of the negative electrode due to this electronic reaction is −2.1 V vs. Cl / Cl - is.

[0021] [ka]

[0022] The redox flow battery 100 generates an electromotive force due to the above-mentioned electronic reactions at the positive electrode and the negative electrode. The electromotive force of the redox flow battery 100 is determined by the potential of the positive electrode (-0.3 V vs. Cl / Cl - ) and the negative electrode potential (-2.1V vs. Cl2 / Cl - ) is the potential difference, which is 1.8 V. Since the electromotive force of a conventional vanadium ion redox flow battery is 1.4 V, the electromotive force of the redox flow battery 100 is approximately 29% higher than that of a vanadium ion redox flow battery.

[0023] In order for the redox flow battery 100 to generate electromotive force, the molten salt in the positive electrode cell 102 and the molten salt in the negative electrode cell 103 must be heated to a temperature above the melting point of the molten salt. After the electronic reactions at the positive electrode and the negative electrode start, the temperature of the molten salt can be maintained above the melting point by the heat of the reactions, making it unnecessary to heat the molten salt. In order to maintain the temperature of the molten salt above the melting point, it is preferable to provide a heat insulating material around the outer periphery of the positive electrode cell 102 and the negative electrode cell 103.

[0024] In the redox flow battery 100, the positive electrode electrolyte and the negative electrode electrolyte are molten salts, and therefore, the divalent titanium ions (Ti 2+ ), trivalent titanium ions (Ti 3+ ) and tetravalent titanium ions (Ti 4+ ) can be increased, resulting in a high current density. In other words, the redox flow battery 100 can achieve a high current density (rapid charging and high output) during charging and discharging. Furthermore, because the positive electrode electrolyte and the negative electrode electrolyte are molten salts, the redox flow battery 100 is not restricted by the decomposition of water and has a higher electromotive force than a vanadium ion redox flow battery.

[0025] In addition, since the redox flow battery 100 has a higher electromotive force than the vanadium ion redox flow battery, the number of stacked battery cells can be reduced. 2+ ), trivalent titanium ions (Ti 3+ ), tetravalent titanium ions (Ti 4+ )) can be significantly reduced in cost and the space utilization efficiency can be improved.

[0026] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications can be made. [Example]

[0027] The effects of the present invention will be made clearer by the following examples. Note that the present invention is not limited to the following examples, and can be practiced by making appropriate modifications within the scope of the present invention.

[0028] [Example 1] "Cyclic Voltammetry Measurement" A LiCl-KCl molten salt containing 0.3 mol / L of TiCl3 was placed in the electrode cell. The working electrode is made of graphite, and the reference electrode is Ag. + A / Ag electrode was used as the electrode, and a graphite electrode was used as the counter electrode. The working electrode, reference electrode, and counter electrode were connected to a potentiostat, and the working electrode, reference electrode, and counter electrode were immersed in a LiCl-KCl molten salt containing TiCl3. The potential was increased or decreased at a sweep rate of 200 mV / s or 400 mV / s, and the current value was measured. The temperature of the LiCl-KCl molten salt containing TiCl3 during the measurement was set to 450°C. In this measurement, the electronic reaction represented by the above formula (1) occurs. FIG. 2 shows the resulting cyclic voltammogram.

[0029] "Square-wave voltammetry measurements" The potential was swept in a rectangular wave pattern across the working electrode, and the response current was measured. The type of electrode reaction occurring was analyzed based on the potential and current. The temperature of the LiCl-KCl molten salt containing TiCl3 during the measurement was set to 450°C. In this measurement, the electronic reaction represented by the above formula (1) occurs. The square wave voltammogram obtained is shown in FIG. From the results shown in Figures 2 and 3, the potential of the LiCl-KCl molten salt containing TiCl3 is -0.3 V vs. Cl2 / Cl - It was found that...

[0030] [Example 2] "Cyclic Voltammetry Measurement" A LiCl-KCl molten salt containing 0.3 mol / L of TiCl3 was placed in the electrode cell. The working electrode is made of graphite, and the reference electrode is Ag. + The values ​​were converted to chlorine evolution standards using a / Ag electrode, and a graphite electrode was used as the counter electrode. The working electrode, reference electrode, and counter electrode were connected to a potentiostat, and the working electrode, reference electrode, and counter electrode were immersed in a LiCl-KCl molten salt containing TiCl3. The potential was increased and decreased at a sweep rate from 200 mV / s to 400 mV / s, and the current value was measured. The temperature of the LiCl-KCl molten salt containing TiCl3 during the measurement was set to 450°C. In this measurement, the electronic reaction represented by the above formula (2) and the electronic reaction represented by the following formula (3) occur. FIG. 4 shows the resulting cyclic voltammogram.

[0031] [ka]

[0032] "Square-wave voltammetry measurements" The potential was swept in a rectangular wave pattern across the working electrode, and the response current was measured. The type of electrode reaction occurring was analyzed based on the potential and current. The temperature of the LiCl-KCl molten salt containing TiCl3 during the measurement was set to 450°C. In this measurement, the electronic reaction represented by the above formula (2) and the electronic reaction represented by the above formula (3) occur. The square wave voltammogram obtained is shown in FIG. From the results shown in Figures 4 and 5, it was found that the potential of the LiCl-KCl molten salt containing TiCl3 was -2.1 V in the electronic reaction represented by the above formula (2) and -2.4 V in the electronic reaction represented by the above formula (3). Therefore, it was found that the redox flow battery having the electrode cell of Experimental Example 1 as the positive electrode cell and the electrode cell of Experimental Example 2 as the negative electrode cell had an electromotive force of 1.8V.

[0033] [Example 3] "Charge / discharge capacity measurement" A LiCl-KCl molten salt containing 0.3 mol / L of TiCl3 was placed in the electrode cell. An electrode made of carbon fiber cloth was used as the positive electrode current collector, and a crucible-type graphite electrode was used as the negative electrode current collector. The negative electrode was immersed in a LiCl-KCl molten salt containing TiCl3, and the current density was set to 10 mA / cm 2 The charge and discharge capacities were measured by increasing and decreasing the voltage. The battery was charged to 2V and discharged to 1.1V. The temperature of the LiCl-KCl molten salt containing TiCl3 during the measurement was set to 450°C. In this measurement, the electronic reaction represented by the above formula (1) occurs. FIG. 6 shows the resulting charge-discharge curves. The results shown in Figure 6 show that the charge and discharge curves almost fold back.

[0034] [Example 4] "Charge / discharge capacity measurement" A LiCl-KCl molten salt containing 0.3 mol / L of TiCl3 was placed in the electrode cell. The working electrode was a carbon fiber cloth electrode, and the negative electrode current collector was a crucible-type graphite electrode. The positive and negative electrodes were immersed in a LiCl-KCl molten salt containing TiCl3, and the current density was set to 10 mA / cm. 2 The charge and discharge capacities were measured by increasing and decreasing the voltage. The battery was charged to 1.8V and discharged to 1.2V. The temperature of the LiCl-KCl molten salt containing TiCl3 during the measurement was set to 450°C. In this measurement, the electronic reaction represented by the above formula (2) occurs. FIG. 7 shows the resulting charge-discharge curves. The results shown in Figure 7 show that the charge curve and discharge curve almost fold back.

[0035] [Example 5] A redox flow battery was fabricated in which the electrode cell of Example 3 was used as a positive electrode cell, the electrode cell of Example 4 was used as a negative electrode cell, and a diaphragm made of magnesium oxide was interposed between the positive electrode cell and the negative electrode cell. The electrodes of the positive and negative cells were connected to an electrochemical measurement device, and the electrodes of the positive and negative cells were immersed in a LiCl-KCl molten salt containing TiCl3, and the current density was set to 10 mA / cm. 2 The charge and discharge capacities were measured by increasing and decreasing the voltage. The battery was charged to 2V and discharged to 1.1V. The temperature of the LiCl-KCl molten salt containing TiCl3 during the measurement was set to 450°C. FIG. 8 shows the resulting charge-discharge curves. The results shown in Figure 8 show that the charge curve and discharge curve almost fold back.

[0036] [Comparative Example] "Charge / discharge capacity measurement" A battery cell was fabricated, which included a positive electrode cell having a positive electrode, a negative electrode cell having a negative electrode, and a diaphragm interposed between the positive electrode cell and the negative electrode cell. A 2 mol / L aqueous sulfuric acid solution containing 1 mol / L vanadyl sulfate (VOSO4) was placed in the positive electrode cell and the negative electrode cell. The positive electrode was an electrode made of a graphite rod with a diameter of 10 mm, and the negative electrode was an electrode made of a graphite crucible with a diameter of 50 mm. The positive and negative electrodes were connected to an electrochemical measurement device, and the positive and negative electrodes were immersed in the above sulfuric acid aqueous solution, and the current density was set to 10 mA / cm. 2 The charge and discharge capacities were measured by increasing and decreasing the voltage. The battery was charged to 1.7V and discharged to 0.7V. The temperature of the sulfuric acid aqueous solution during measurement was set to 20°C. FIG. 9 shows the resulting charge-discharge curves. The results shown in Figure 9 reveal that the charge and discharge curves do not fold back.

[0037] [Example 6] "Charge / discharge capacity measurement" A battery cell was fabricated, which included a positive electrode cell having a positive electrode, a negative electrode cell having a negative electrode, and a diaphragm interposed between the positive electrode cell and the negative electrode cell. A LiCl-KCl molten salt containing 0.5 mol / L of TiCl3 was placed in the negative electrode cell, and a LiCl-KCl molten salt containing 0.5 mol / L of TiCl2 was placed in the positive electrode cell. The positive electrode was an electrode made of a graphite net having a diameter of 10 mm and a graphite rod having a diameter of 10 mm, and the negative electrode was an electrode made of a graphite crucible having a diameter of 50 mm. The positive and negative electrodes were connected to an electrochemical measurement device, and the positive electrode was immersed in the LiCl-KCl molten salt containing 1.5 mol / L of TiCl2, and the negative electrode was immersed in the LiCl-KCl molten salt containing 1.5 mol / L of TiCl3, and the current density was set to 40 mA / cm. 3 The charge and discharge capacities were measured by increasing and decreasing the voltage. The battery was charged to 1.7 V and discharged to 0.5 V. The temperature of the molten salt during the measurement was set to 450°C. FIG. 10 shows the resulting charge-discharge curves. The results shown in Figure 10 show that the charge and discharge curves almost fold back. Furthermore, even after repeated charge and discharge, there was little decay in charge and discharge capacity, demonstrating excellent cycle characteristics.

[0038] [Example 7] "Charge / discharge capacity measurement" A battery cell was fabricated, which included a positive electrode cell having a positive electrode, a negative electrode cell having a negative electrode, and a diaphragm interposed between the positive electrode cell and the negative electrode cell. A LiCl-KCl molten salt containing 1.5 mol / L of TiCl3 was placed in the negative electrode cell, and a LiCl-KCl molten salt containing 1.5 mol / L of TiCl2 was placed in the positive electrode cell. The positive electrode was an electrode made of a graphite net having a diameter of 10 mm and a graphite rod having a diameter of 10 mm, and the negative electrode was an electrode made of a graphite crucible having a diameter of 50 mm. The positive and negative electrodes were connected to an electrochemical measurement device, and the positive electrode was immersed in the LiCl-KCl molten salt containing 1.5 mol / L of TiCl2, and the negative electrode was immersed in the LiCl-KCl molten salt containing 1.5 mol / L of TiCl3, and the current density was set to 10 mA / cm. 3 The charge and discharge capacities were measured by increasing and decreasing the voltage. The battery was charged to 1.8 V and discharged to 0.5 V. The temperature of the molten salt during the measurement was set to 400°C. FIG. 11 shows the resulting charge-discharge curves. The results shown in Figure 11 show that the charge and discharge curves almost fold back. Furthermore, even after repeated charge and discharge, there was little decay in charge and discharge capacity, demonstrating excellent cycle characteristics.

[0039] [Example 8] "Charge / discharge capacity measurement" A battery cell was fabricated, which included a positive electrode cell having a positive electrode, a negative electrode cell having a negative electrode, and a diaphragm interposed between the positive electrode cell and the negative electrode cell. A NaCl-KCl-MgCl molten salt containing 1.5 mol / L of TiCl was placed in the negative electrode cell, and a NaCl-KCl-MgCl molten salt containing 1.5 mol / L of TiCl was placed in the positive electrode cell. The positive electrode was an electrode made of a graphite net having a diameter of 10 mm and a graphite rod having a diameter of 10 mm, and the negative electrode was an electrode made of a graphite crucible having a diameter of 50 mm. The positive and negative electrodes were connected to an electrochemical measurement device, and the positive electrode was immersed in the LiCl-KCl molten salt containing 1.5 mol / L of TiCl2, and the negative electrode was immersed in the LiCl-KCl molten salt containing 1.5 mol / L of TiCl3, and the current density was set to 15 mA / cm. 3 The charge capacity and discharge capacity were measured by increasing and decreasing the voltage. The battery was charged to 2.0 V and discharged to 0.5 V. The temperature of the molten salt during the measurement was set to 480°C. FIG. 12 shows the resulting charge-discharge curves. The results shown in Figure 12 show that the charge and discharge curves almost fold back. Furthermore, even after repeated charge and discharge, there was little decay in charge and discharge capacity, demonstrating excellent cycle characteristics. [Industrial Applicability]

[0040] The redox flow battery of the present invention can create a large-capacity storage battery system suitable for ultra-large-scale power generation as a storage battery system for power generation using renewable energy. [Explanation of symbols]

[0041] 100 Redox flow battery 101 Diaphragm 102 positive electrode cell 103 negative electrode cell 104 Positive electrode 105 Negative electrode 106 Positive electrode electrolyte tank 107 Anode electrolyte tank 108,109,110,111 Piping 112,113 Pump

Claims

1. A redox flow battery that is charged and discharged by supplying a positive electrode electrolyte and a negative electrode electrolyte to a battery cell that includes a positive electrode, a negative electrode, and a diaphragm interposed between the positive electrode and the negative electrode, the positive electrode electrolyte and the negative electrode electrolyte are molten salts, the positive electrode electrolyte contains trivalent titanium ions and tetravalent titanium ions, the negative electrode electrolyte contains divalent titanium ions and trivalent titanium ions.

2. 2. The redox flow battery according to claim 1, wherein the molten salt is a molten salt of lithium chloride and potassium chloride, a molten salt of sodium chloride and potassium chloride, a molten salt of magnesium chloride, sodium chloride and potassium chloride, or a molten salt of lithium fluoride, sodium fluoride and potassium fluoride.

Images