JP2012204347A - Redox flow battery, and operation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a redox flow battery which can generate a high electromotive force, and to provide an operation method thereof.SOLUTION: The redox flow battery 1 performs charge/discharge by supplying a positive electrode electrolyte stored in a tank 106 for positive electrode, and a negative electrode electrolyte stored in a tank 107 for negative electrode to a battery element 100. The positive electrode electrolyte in the redox flow battery 1 contains Mn ions as a positive electrode active material, and the negative electrode electrolyte contains at least one kind of Ti ions, V ions, and Cr ions as a negative electrode active material. The redox flow battery 1 includes negative electrode side introduction piping 10 communicating with the inside of the tank 107 for negative electrode from the outside and introducing an oxidizing gas into the tank 107 for negative electrode, and a supply mechanism 11 for supplying the oxidizing gas into the tank 107 for negative electrode via the negative electrode side introduction piping 10.

Description

  The present invention relates to a redox flow battery and an operation method thereof. In particular, the present invention relates to a redox flow battery capable of obtaining a high electromotive force.

  In recent years, introduction of new energy such as solar power generation and wind power generation has been promoted worldwide as a countermeasure against global warming. Since these power generation outputs are affected by the weather, it is predicted that there will be a problem in the operation of the electric power system such that it becomes difficult to maintain the frequency and voltage when the mass introduction is advanced. As one of the countermeasures against this problem, it is expected to install a large-capacity storage battery to smooth the output fluctuation, save surplus power, and level the load.

  One of the large-capacity storage batteries is a redox flow battery. In a redox flow battery, charge and discharge are performed by supplying a positive electrode electrolyte and a negative electrode electrolyte respectively to a battery element in which a diaphragm is interposed between a positive electrode and a negative electrode. As the electrolytic solution, typically, an aqueous solution containing metal ions whose valence changes by oxidation-reduction is used. Typical examples include an iron-chromium redox flow battery using iron ions for the positive electrode and Cr ions for the negative electrode, and a vanadium redox flow battery using V ions for both the positive electrode and the negative electrode (for example, Patent Document 1).

JP 2006-147374 A

  Vanadium redox flow batteries have been put to practical use and are expected to be used in the future. However, the conventional iron-chromium redox flow battery and vanadium redox flow battery cannot be said to have a sufficiently high electromotive force. To meet future global demand, a new redox that has a higher electromotive force and can stably supply metal ions used in active materials, preferably stably and inexpensively. Development of a flow battery is desired.

  Then, one of the objectives of this invention is providing the redox flow battery from which a high electromotive force is obtained. Another object of the present invention is to provide a redox flow battery operating method capable of maintaining a state having excellent battery characteristics.

In order to improve the electromotive force, it is conceivable to use a metal ion having a high standard redox potential as the active material. The standard redox potential of the metal ion of the positive electrode active material used in the conventional redox flow battery is 0.77 V for Fe ²⁺ / Fe ^{3+ and} 1.0 V for V ⁴⁺ / V ⁵⁺ . The present inventors are water-soluble metal ions as the metal ions of the positive electrode active material, have a higher standard redox potential than conventional metal ions, are relatively cheaper than vanadium, and are excellent in terms of resource supply. The redox flow battery using manganese, which is considered to be The standard oxidation-reduction potential of Mn ²⁺ / Mn ³⁺ is 1.51 V, and Mn ions have preferable characteristics for constituting a redox pair having a larger electromotive force.

  Here, the redox flow battery is a battery using an aqueous solution as an electrolytic solution. Therefore, in this redox flow battery, hydrogen gas may be generated at the negative electrode and oxygen gas may be generated at the positive electrode due to water decomposition as a side reaction accompanying the charge / discharge reaction. As a result of investigations by the present inventors, in a redox flow battery using a positive electrode electrolyte containing Mn ions as a positive electrode active material, the oxidation-reduction potential of Mn as the positive electrode active material has been conventionally used as the positive electrode active material. It has been found that the side reaction at the positive electrode is dominant because it has a more noble potential than Fe and V. In this case, the state of charge of the negative electrode electrolyte (SOC: State of Charge, sometimes referred to as charge depth) gradually becomes higher than that of the positive electrode electrolyte. As described above, when a difference in the state of charge occurs between the two electrolyte solutions, the battery capacity of the redox flow battery is greatly reduced as compared with the initial state, and thus a countermeasure is required.

  Based on the examination and knowledge described above, the present invention is defined below.

  The redox flow battery of the present invention is stored in a positive electrode electrolyte stored in a positive electrode tank and in a negative electrode tank in a battery element including a positive electrode, a negative electrode, and a diaphragm interposed between the two electrodes. It is a redox flow battery that charges and discharges by supplying a negative electrode electrolyte. The positive electrode electrolyte in the redox flow battery of the present invention contains Mn ions as the positive electrode active material, and the negative electrode electrolyte contains at least one of Ti ions, V ions, and Cr ions as the negative electrode active material. The redox flow battery of the present invention communicates from the outside to the inside of the negative electrode tank, and the negative electrode side introduction pipe for introducing the oxidizing gas into the negative electrode tank, and the negative electrode tank through the negative electrode side introduction pipe And a negative electrode side supply mechanism for supplying an oxidizing gas therein.

  Further, the operating method of the redox flow battery of the present invention is an operating method of the redox flow battery using the above redox flow battery of the present invention, in order to oxidize the negative electrode active material contained in the negative electrode electrolyte, the negative electrode tank The oxidizing gas is introduced inside.

  According to the above-described redox flow battery of the present invention and its operation method, when the charge state between the positive electrode electrolyte and the negative electrode electrolyte is different while charging and discharging are repeated, an oxidizing gas is introduced into the negative electrode electrolyte. The difference can be reduced by oxidizing the negative electrode electrolyte. If the difference between the charged states of both electrolytes is reduced, the battery capacity of the redox flow battery can be restored to a state close to the initial battery capacity.

  Hereinafter, preferred embodiments of the redox flow battery of the present invention and the operation method thereof will be described.

  As one embodiment of the redox flow battery of the present invention, the oxidizing gas is preferably a gas containing oxygen.

  The oxidizing gas is not particularly limited as long as the negative electrode electrolyte can be oxidized. For example, chlorine may be used. However, in consideration of safety when handling the oxidizing gas, it is preferable to use a gas containing oxygen, for example, pure oxygen, ozone, or air.

  The redox flow battery of the present invention preferably includes a gas phase communication pipe that communicates the gas phase of the positive electrode tank and the gas phase of the negative electrode tank.

  As already described, oxygen gas is generated as a side reaction on the positive electrode side. Therefore, if the gas-phase communication pipe is provided, the oxygen gas generated on the positive electrode side can be used for oxidation of the negative electrode electrolyte. By always opening the gas phase communication pipe, oxygen gas can be introduced from the positive electrode tank to the negative electrode tank. Of course, the gas phase communication pipe may be normally closed and may be opened when the oxidizing gas is introduced from the negative electrode side introduction pipe into the negative electrode tank.

  The redox flow battery of the present invention preferably includes a monitor mechanism for monitoring the state of charge of the redox flow battery.

Examples of the monitoring mechanism include using a monitor cell having the same configuration as the battery element. The monitor cell may be configured to supply positive and negative electrolytic solutions actually used from the positive electrode tank and the negative electrode tank. In addition, a monitor mechanism (for example, a transparent window provided in a pipe connecting the tank and the tank and the battery element) that makes it possible to visually check the transparency of the electrolytic solution can be exemplified. As will be described later, when Ti ions are used as the negative electrode active material, the solution of trivalent Ti ions (Ti ³⁺ ) is black, and the solution of tetravalent Ti ions (Ti ⁴⁺ ) is almost transparent. That is, when the redox flow battery is completely discharged and Ti ⁴⁺ becomes dominant in the negative electrode electrolyte, if the transparency of the negative electrode electrolyte is low, the charged state of the negative electrode electrolyte is higher than the charged state of the positive electrode electrolyte. If the transparency of the negative electrode electrolyte is high, the state of charge of both electrolytes can be determined to be comparable.

  It is preferable that the negative electrode side introduction pipe provided in the redox flow battery of the present invention is opened in the liquid phase of the negative electrode tank.

  The negative electrode side introduction pipe may be opened in the gas phase, but opening in the liquid phase can oxidize the negative electrode electrolyte more efficiently.

  The redox flow battery of the present invention preferably includes a stirring mechanism that is provided inside the negative electrode tank and stirs the negative electrode electrolyte.

  The negative electrode electrolyte can be efficiently oxidized by stirring the negative electrode electrolyte. The effect is improved by combining with opening the negative electrode side introduction pipe into the liquid phase.

  The positive electrode electrolyte used in the redox flow battery of the present invention preferably contains Ti ions.

When Mn ions are used as the positive electrode active material, there is a problem that MnO ₂ is deposited with charge and discharge. On the other hand, as a result of the study by the present inventors, although the detailed mechanism is unknown, it becomes clear that the above precipitation can be effectively suppressed by making the positive electrode electrolyte contain Ti ions together with Mn ions. Yes.

  As described above, when the positive electrode electrolyte contains Mn ions and Ti ions, the negative electrode electrolyte preferably contains Ti ions as the negative electrode active material, and further contains Mn ions.

  The said structure is a structure which makes the metal ion seed | species in a positive electrode electrolyte solution, and the metal ion seed | species in a negative electrode electrolyte equal. By doing so, (1) the metal ions move to the counter electrode through the diaphragm of the battery element, effectively avoiding the phenomenon of battery capacity reduction due to the relative reduction of the metal ions that originally react at each electrode Yes, (2) Liquid transfer with charge / discharge over time (a phenomenon in which the electrolyte solution of one electrode moves to the other electrode through the diaphragm) causes variations in the electrolyte volume and ion concentration of both electrodes Even if this occurs, effects such as (3) excellent electrolyte solution manufacturability can be obtained by mixing the electrolyte solutions of both electrodes and the like.

  When the metal ion species contained in both electrolytes are the same, the redox flow battery of the present invention preferably includes a liquid phase communication pipe that communicates the liquid phase of the positive electrode tank and the liquid phase of the negative electrode tank. .

  The fact that the metal ion species contained in both electrolytes is common means that both electrolytes may be mixed. When both electrolytes are mixed, the redox flow battery is completely discharged. Further, as will be described later, when a Ti / Mn electrolyte is used for both electrolytes, it is preferable to oxidize the mixed electrolyte after mixing both electrolytes and complete discharge state. Can be easily identified. This is because the Ti / Mn electrolyte solution becomes transparent when discharged.

  When the liquid phase communication pipe is provided, the redox flow battery of the present invention communicates from the outside of the positive electrode tank to the inside, and introduces a positive electrode side introduction pipe for introducing an oxidizing gas into the positive electrode tank, and a positive electrode side introduction And a positive electrode side supply mechanism that supplies the oxidizing gas into the positive electrode side tank through a pipe.

  If it is set as the said structure, when opening a liquid phase communicating pipe | tube and mixing both electrolyte solution, a mixed electrolyte solution can be oxidized rapidly.

  On the other hand, as an embodiment of the operation method of the redox flow battery of the present invention, the introduction of the oxidizing gas is preferably performed when the charge states of the positive electrode electrolyte and the negative electrode electrolyte are different.

  By correcting the difference when the charged states of the two electrolytes are different, efficient redox flow battery operation can be performed. Unlike this configuration, the redox flow battery can be operated while introducing the oxidizing gas into the negative electrode tank.

  As one mode of the operation method of the redox flow battery of the present invention, it is preferable that the charged state of the positive electrode electrolyte and the negative electrode electrolyte are made substantially the same by controlling the amount of the oxidizing gas introduced.

  Adjustment of the introduction amount of the oxidizing gas is preferably performed based on the monitoring results of monitoring the charge states of both electrolytes with a monitor cell. In this way, by aligning the state of charge of both electrolytes, it is possible to lengthen the time until a difference occurs between the states of charge of both electrolytes.

  As an embodiment of the operation method of the redox flow battery of the present invention, the transparency of the negative electrode electrolyte may be used.

As described above, when Ti ions are used as the negative electrode active material, the transparency of the negative electrode electrolyte is observed when the redox flow battery is completely discharged and Ti ⁴⁺ in the negative electrode electrolyte becomes dominant. Thus, the difference between the charged states of both electrolytes can be confirmed. It can be seen that the more Ti ³⁺ is present in the discharged negative electrode electrolyte, the lower the transparency of the negative electrode electrolyte and there is a difference in the state of charge between the two electrolytes. Moreover, as shown in the embodiment described later, when Mn ions are used as the positive electrode active material, the state of charge of the positive electrode electrolyte can also be determined from the transparency of the positive electrode electrolyte. This point will be described in detail in the embodiment.

  As one form of the operation method of the redox flow battery of the present invention, it is preferable to operate while monitoring the charge state of the redox flow battery.

  For the monitoring method, the transparency of the electrolytic solution may be used, and if it is a redox flow battery including a monitor cell, the monitor cell may be used.

  The redox flow battery of the present invention is a redox flow battery having a high electromotive force and capable of recovering a decrease in battery capacity caused by charging and discharging. Moreover, the operating method of the redox flow battery of the present invention can recover the reduced battery capacity when the battery capacity of the redox flow battery of the present invention decreases due to charging / discharging.

1 is a schematic diagram of a redox flow battery shown in Embodiment 1. FIG. It is a schematic explanatory drawing which shows the formation state of the negative electrode side introduction piping in the negative electrode tank of the redox flow battery shown in FIG. 1, (A) is the state which the negative electrode side introduction piping opened to the gaseous phase of the negative electrode tank, (B ) Is a state where the negative electrode side introduction pipe is open to the liquid phase of the negative electrode tank, (C) is a state where a stirring mechanism is present in the liquid phase in addition to the state of (A), and (D) is a state of (B). It is a figure which shows the state which has a stirring mechanism in a liquid phase in addition to. 3 is a schematic diagram of a redox flow battery shown in Embodiment 2. FIG. 6 is a graph showing the relationship between the number of operating days of the redox flow battery shown in Test Example 1 and the battery capacity (Ah).

<Embodiment 1>
≪Overall structure≫
Hereinafter, an outline of a redox flow battery (hereinafter referred to as RF battery) 1 using Mn ions as a positive electrode active material and Ti ions as a negative electrode active material will be described with reference to FIGS. A solid line arrow in FIG. 1 means charging, and a broken line arrow means discharging. In addition, the metal ion shown in FIG. 1 has shown the typical form, and forms other than illustration may be included. For example, FIG. 1 shows Ti ⁴⁺ as the tetravalent Ti ions, but other forms such as TiO ²⁺ may also be included.

  As shown in FIG. 1, the RF battery 1 typically includes a power generation unit (for example, a solar power generator, a wind power generator, other general power plants, etc.) and power via an AC / DC converter. It is connected to a load such as a grid or a customer, is charged using the power generation unit as a power supply source, and is discharged using the load as a power supply target. Similar to the conventional RF battery, the RF battery 1 includes a battery element 100 and a circulation mechanism (tank, piping, pump) that circulates the electrolyte in the battery element 100. The RF battery 1 is different from the conventional one in that Mn ions are used as the positive electrode active material of the positive electrode electrolyte solution, and a configuration for suppressing a decrease in battery capacity due to charge / discharge (a negative electrode side introduction pipe 10 and The negative electrode side supply mechanism 11) is provided. Hereinafter, each configuration of the RF battery 1 will be described in detail, and then an operation method of the RF battery 1 will be described.

[Battery elements and circulation mechanism]
The battery element 100 provided in the RF battery 1 includes a positive electrode cell 102 incorporating a positive electrode 104, a negative electrode cell 103 incorporating a negative electrode 105, and a diaphragm 101 that separates the cells 102 and 103 and transmits ions. Prepare. A positive electrode tank 106 that stores a positive electrode electrolyte is connected to the positive electrode cell 102 via pipes 108 and 110. A negative electrode tank 107 for storing a negative electrode electrolyte solution is connected to the negative electrode cell 103 via pipes 109 and 111. The pipes 108 and 109 are provided with pumps 112 and 113 for circulating the electrolyte solution of each electrode. The battery element 100 uses the pipes 108 to 111 and the pumps 112 and 113 to the positive electrode cell 102 (positive electrode 104) and the negative electrode cell 103 (negative electrode 105), respectively. The negative electrode electrolyte solution 107 is circulated and charged in accordance with the valence change reaction of metal ions (Mn ions for the positive electrode and Ti ions for the negative electrode) that become the active material in the electrolyte solution of each electrode. Discharge.

  The battery element 100 is normally used in a form called a cell stack in which a plurality of battery elements are stacked. The cells 102 and 103 constituting the battery element 100 discharge a bipolar plate (not shown) in which a positive electrode 104 is disposed on one surface and a negative electrode 105 on the other surface, a liquid supply hole for supplying an electrolytic solution, and an electrolytic solution. A configuration using a cell frame having a drain hole to be formed and having a frame (not shown) formed on the outer periphery of the bipolar plate is representative. By laminating a plurality of cell frames, the liquid supply hole and the drainage hole constitute an electrolyte flow path, and the flow path is connected to the pipes 108 to 111. The cell stack is configured by repeatedly stacking a cell frame, a positive electrode 104, a diaphragm 101, a negative electrode 105, a cell frame,. As the basic configuration of the RF battery, a known configuration can be used as appropriate.

[Electrolyte]
As the positive and negative electrolytes used in the RF battery 1 of the present embodiment, a common one containing Mn ions and Ti ions is used. On the positive electrode side, Mn ions work as a positive electrode active material, and on the negative electrode side, Ti ions work as a negative electrode active material. Further, the Ti ions on the positive electrode side suppress the precipitation of MnO ₂ for unknown reasons. Each concentration of Mn ions and Ti ions is preferably 0.3M or more and 5M or less.

Solvents for the electrolyte include H ₂ SO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , H ₃ PO ₄ , H ₄ P ₂ O ₇ , K ₂ PO ₄ , Na ₃ PO ₄ , K ₃ PO ₄ , HNO ₃ , at least one aqueous solution selected from KNO ₃ and NaNO ₃ can be used.

[Negative electrode side piping]
The negative electrode side introduction pipe 10 is a pipe for introducing an oxidizing gas into the negative electrode tank 107. As the oxidizing gas, pure oxygen, air, ozone and the like can be used. The negative electrode side introduction pipe 10 only needs to communicate with the negative electrode tank 107. For example, as shown in FIG. 2A, the anode tank 107 is opened in the gas phase, and as shown in FIG. 2B, the anode tank 107 is opened in the liquid phase. Is mentioned. In addition, as shown to FIG.2 (C) and (D), it can also be set as the form which added the stirring mechanism 12, such as a screw, to the structure of FIG. 2 (A) or (B). The negative electrode tank 107 is provided with an open valve (not shown) so that the pressure in the negative electrode tank 107 does not become unnecessarily high even if the oxidizing gas is introduced from the negative electrode side introduction pipe 10. .

  The negative electrode side introduction pipe 10 is preferably provided with an opening / closing mechanism such as a valve, so that communication / non-communication of the negative electrode side introduction pipe 10 can be controlled. It is preferable that the negative electrode side introduction pipe 10 is closed at all times to suppress evaporation of the negative electrode electrolyte.

[Negative electrode supply mechanism]
The negative electrode side supply mechanism 11 is configured to introduce an oxidizing gas into the negative electrode tank 107 through the negative electrode side introduction pipe 10. For example, a blower (when the negative electrode side introduction pipe 10 is in gas phase communication), a pressure feed pump, or the like can be used.

[Others]
Although not shown, the RF battery 1 may include a monitor cell for monitoring the battery capacity. The monitor cell is basically a single cell smaller than the battery element 100 having the same configuration as that of the battery element 100. The monitor cell receives positive and negative electrolytes from the positive electrode tank 106 and the negative electrode tank 107, and Similarly, an electromotive force is generated. The battery capacity of the RF battery 1 can be known from the electromotive force.

≪Operation method of RF battery≫
When the RF battery 1 having the above configuration is operated (charging / discharging is repeated), the battery capacity gradually decreases. In that case, the RF battery 1 is completely discharged, the negative electrode side introduction pipe 10 described above is opened, and the negative electrode side supply mechanism 11 is operated to introduce an oxidizing gas into the negative electrode tank 107. The determination of the timing for introducing the oxidizing gas and the determination of the introduction amount of the oxidizing gas may be performed based on the electromotive force detected by the monitor cell when the RF battery 1 has a monitor cell. In addition, the above determination can be made based on the transparency of the negative electrode electrolyte. Trivalent Ti (Ti ³⁺ ) is brown, and tetravalent Ti (Ti ⁴⁺ ) is almost colorless and transparent. Therefore, if the decrease in transparency of the negative electrode electrolyte is confirmed visually or by spectroscopic analysis or light transmittance, oxidizing gas It is preferable that the introduction of the oxidizing gas is started and the introduction of the oxidizing gas is ended with an increase in transparency.

  Here, the introduction of the oxidizing gas may be performed simultaneously with the operation of the RF battery 1. By doing so, the RF battery 1 can be operated while suppressing a decrease in the battery capacity of the RF battery 1. At this time, in consideration of evaporation of the negative electrode electrolyte, it is preferable that the negative electrode side introduction pipe 10 is not opened constantly but is opened intermittently. In addition, it is preferable to monitor the amount of the negative electrode electrolyte and add a solvent as needed.

<Embodiment 2>
In the second embodiment, an RF battery 2 having an additional configuration to the configuration of the first embodiment will be described based on FIG. FIG. 3 is a simple drawing showing only the connection state of each pipe.

≪Overall structure≫
In addition to the configuration of the RF battery of the first embodiment, the RF battery 2 of the second embodiment includes a gas phase communication pipe 13, a liquid phase communication pipe 14, a positive electrode side introduction pipe 15, and a positive electrode side supply mechanism 16. Prepare.

[Gas-phase communication pipe]
The gas phase communication pipe 13 is a pipe that communicates the gas phase of the positive electrode tank 106 and the gas phase of the negative electrode tank 107. By providing the gas-phase communication pipe 13, oxygen generated by a side reaction on the positive electrode side with charge / discharge can be introduced into the negative electrode tank 107. It is preferable to provide a valve or the like in the gas-phase communication pipe 13 so that communication / non-communication between the tanks 106 and 107 can be adjusted.

[Liquid phase communication pipe]
The liquid phase communication pipe 14 is a pipe that communicates the liquid phase of the positive electrode tank 106 and the liquid phase of the negative electrode tank 107. By providing the liquid phase communication pipe 14, the electrolyte solution in both tanks 106 and 107 can be mixed. The liquid phase communication pipe 14 is provided with a valve or the like so that the electrolytes stored in the tanks 106 and 107 are not mixed during charging and discharging.

  Here, in the case of the configuration having the liquid phase communication pipe 14 that can mix the positive electrode electrolyte and the negative electrode electrolyte, the metal ion species contained in both electrolytes must be shared. For example, both electrolytic solutions may be electrolytic solutions containing Mn ions and Ti ions. In the positive electrode electrolyte, Mn ions function as a positive electrode active material, and in the negative electrode electrolyte, Ti ions function as a negative electrode active material.

[Positive electrode inlet piping and positive electrode supply mechanism]
The positive electrode side introduction pipe 15 and the positive electrode side supply mechanism 16 can adopt the same configurations as the negative electrode introduction pipe 10 and the negative electrode side supply mechanism 11, respectively.

[Others]
A stirring mechanism is preferably provided in the liquid phase of the positive electrode tank 106 as in the first embodiment.

≪Operation method of RF battery≫
When charging / discharging with the RF battery 2, the gas phase communication pipe 13 is basically opened, and the liquid phase communication pipe 14 is closed. On the other hand, when the battery capacity of the RF battery 2 is recovered, the gas phase communication pipe 13 is opened and the liquid phase communication pipe 14 is also opened. By opening the liquid phase communication tube 14, the positive and negative electrolytes are mixed together, and the RF battery 2 is quickly discharged. Then, an oxidizing gas is introduced from the negative electrode side introduction pipe 10 into the negative electrode tank 107, and an oxidizing gas is also introduced from the positive electrode side introduction pipe 15 into the positive electrode tank 106. At that time, if the tanks 106 and 107 are provided with a stirring mechanism, the stirring mechanism may be operated.

As in the first embodiment, the timing for recovering the battery capacity of the RF battery 2, the introduction amount of the oxidizing gas, and the timing of the end of the introduction are the same as those in the first embodiment. Transparency can be used. Here, the Mn ³⁺ solution is colored, and the Mn ²⁺ solution is almost colorless and transparent. When the RF battery 2 is discharged, if Mn ²⁺ becomes dominant in the electrolyte, the transparency of the electrolyte becomes high. . Similarly, when the RF battery 2 is discharged, the Ti ⁴⁺ solution that becomes dominant in the electrolyte is almost colorless and transparent. Therefore, the transparency of the mixed electrolyte obtained in a state where the battery capacity is reduced is low, and the transparency of the mixed electrolyte in a state where the battery capacity is restored by the oxidizing gas is increased.

<Test Example 1>
Next, an RF battery 2 having the same configuration as that of Embodiment 2 described with reference to FIG. 3 was produced. As the positive electrode electrolyte and the negative electrode electrolyte, an electrolyte mixed with sulfuric acid having a concentration of 2M, 1M MnSO ₄ (Mn ²⁺ ), and 1M TiOSO ₄ (Ti ⁴⁺ ) was used. The positive and negative electrolytes were 3 L each, and sealed in the respective tanks 106 and 107 in an airtight state with external air. Nitrogen gas was sealed in the gas phase portion to suppress oxidation. The battery element 100 used was a single cell having an electrode area of 500 cm ² to which a carbon felt electrode and a cation exchange membrane were applied. The liquid phase communication pipe 14 and the gas phase communication pipe 13 were both closed.

A charge / discharge test was conducted using the Ti / Mn RF battery 2 thus fabricated. The initial performance was a current efficiency of 99%, a cell resistivity of 1.5 Ωcm ² , and a battery capacity of 45 Ah. When the RF battery 2 was operated (charged / discharged) for about one month, the battery capacity gradually decreased to about 75% of the initial level. Further, the operation of the RF battery 2 was continued. When the battery capacity of the RF battery 2 reached about 65% of the initial value about 65 days after the start of the operation, the operation of the RF battery 2 was once stopped. Note that both the liquid-phase communication pipe 14 and the gas-phase communication pipe 13 were closed during the operation period of the RF battery 2.

When the operation of the RF battery 2 was stopped, the components of the gas staying in the gas phase of the positive electrode tank 106 were analyzed. Oxygen gas was detected at several volume percent, and very little CO ₂ was detected. Hydrogen gas was below the detection limit. On the other hand, the gas component in the gas phase in the negative electrode tank 107 was almost nitrogen gas.

  Next, the liquid phase communication tube 14 was opened, and the positive electrode electrolyte and the negative electrode electrolyte were sufficiently mixed, whereby the RF battery 2 was completely discharged. The electrolyte solution mixed at this time was black (colored and opaque).

  Next, air (oxidizing gas) was introduced into the tanks 106 and 107 from the positive electrode side introduction pipe 15 and the negative electrode side introduction pipe 10 provided in the positive electrode tank 106 and the negative electrode tank 107. At that time, when the mixed electrolyte in each of the tanks 106 and 107 was visually observed, it was confirmed that the mixed electrolyte gradually changed to transparency. Finally, when it was visually confirmed that the mixed electrolyte was almost transparent, the introduction of air was stopped (approximately 7 days from the start to the end). And after completion | finish of introduction | transduction of air, charging / discharging was repeated again. The graph of FIG. 4 shows changes in the battery capacity of the RF battery 2 from the start to the end of the test.

  As is clear from the results of the graph shown in FIG. 4, it was confirmed that the battery capacity of the RF battery 2 was significantly recovered by introducing air into the mixed electrolyte.

<Test Example 2>
Using the RF battery 2 having the same configuration as in Test Example 1, this time, the charge / discharge test was started in a state where the gas phase communication tube 13 was opened (the liquid phase communication tube 14 was closed). By doing so, it was about 90 days after the start of the test until the battery capacity dropped to about 65% of the initial stage, and it was confirmed that the rate of decrease of the battery capacity of the RF battery 2 was moderate. This result was not enough to say that the decrease in the battery capacity of the RF battery 2 could be effectively suppressed.

  Then, next, charging / discharging (the gas phase communication pipe 13 was opened and the liquid phase communication pipe 14 was closed) was repeated while air was introduced from the negative electrode side introduction pipe 10 into the negative electrode tank 107. As a result, a phenomenon in which the battery capacity gradually recovered was observed. At this time, the amount of air introduced into the negative electrode tank 107 is adjusted by opening / closing the negative electrode side introduction pipe 10, blowing pressure control of the negative electrode side supply mechanism 11, blowing time control, etc. I was able to control it. Furthermore, when the amount of air introduced was controlled according to the state of charge of the positive and negative electrolytes measured by the monitor cell, it was possible to control the battery capacity constantly. By applying this result, for example, when the battery capacity is reduced by 10% compared to the initial capacity from the measurement result in the monitor cell, a predetermined amount of air is introduced into the negative electrode tank 107 for a predetermined time. Thus, stable operation of the RF battery 2 can be realized.

  The present invention is not limited to the above-described embodiment, and can be implemented with appropriate modifications without departing from the gist of the present invention. For example, V ions or Cr ions can be used as the negative electrode active material of the negative electrode electrolyte used. In that case, the structure of Embodiment 1 on the assumption that positive and negative electrolytes are not mixed is employed.

  The redox flow battery of the present invention has a large capacity for the purpose of stabilizing fluctuations in power generation output, storing electricity when surplus of generated power, load leveling, etc., for power generation of new energy such as solar power generation and wind power generation. It can utilize suitably for a storage battery. In addition, the redox flow battery of the present invention can be suitably used as a large-capacity storage battery that is provided in a general power plant and is intended for measures against instantaneous voltage drop / power outage and load leveling. The operating method of the redox flow battery of the present invention can be suitably used when the redox flow battery of the present invention is used in the above various applications.

DESCRIPTION OF SYMBOLS 1, 2 Redox flow battery 100 Battery element 101 Diaphragm 102 Positive electrode cell 103 Negative electrode cell 104 Positive electrode 105 Negative electrode 106 Positive electrode tank 107 Negative electrode tank 108,109,110,111 Piping 112,113 Pump 10 Negative electrode side introduction piping DESCRIPTION OF SYMBOLS 11 Negative electrode side supply mechanism 12 Agitation mechanism 13 Gas-phase communication pipe 14 Liquid phase communication pipe 15 Positive electrode side introduction piping 16 Positive electrode side supply mechanism

Claims (15)

A battery element including a positive electrode, a negative electrode, and a diaphragm interposed between the two electrodes is supplied with a positive electrolyte stored in the positive tank and a negative electrolyte stored in the negative tank. A redox flow battery for charging and discharging,
The positive electrode electrolyte contains Mn ions as a positive electrode active material,
The negative electrode electrolyte contains at least one of Ti ions, V ions, and Cr ions as a negative electrode active material,
A negative electrode side introduction pipe communicated from the outside of the negative electrode tank to the inside, and for introducing an oxidizing gas into the negative electrode tank;
A negative electrode side supply mechanism for supplying the oxidizing gas into the negative electrode tank through the negative electrode side introduction pipe;
A redox flow battery comprising:   The redox flow battery according to claim 1, wherein the oxidizing gas is a gas containing oxygen.   3. The redox flow battery according to claim 1, further comprising a gas phase communication pipe that communicates the gas phase of the positive electrode tank and the gas phase of the negative electrode tank. 4.   The redox flow battery according to claim 1, further comprising a monitor mechanism that monitors a state of charge of the redox flow battery.   The redox flow battery according to any one of claims 1 to 4, wherein the negative electrode side introduction pipe is open in a liquid phase of the negative electrode tank.   The redox flow battery according to any one of claims 1 to 5, further comprising a stirring mechanism that is provided inside the negative electrode tank and stirs the negative electrode electrolyte.   The redox flow battery according to claim 1, wherein the positive electrode electrolyte contains Ti ions.   The redox flow battery according to claim 7, wherein the negative electrode electrolyte contains Ti ions as a negative electrode active material, and further contains Mn ions.   9. The redox flow battery according to claim 8, further comprising a liquid phase communication pipe that communicates the liquid phase of the positive electrode tank and the liquid phase of the negative electrode tank. The positive electrode side introduction pipe communicated from the outside to the inside of the positive electrode tank, and for introducing an oxidizing gas into the positive electrode tank;
A positive electrode side supply mechanism for supplying the oxidizing gas into the positive electrode side tank via the positive electrode side introduction pipe;
The redox flow battery according to claim 9, comprising: It is the operating method of the redox flow battery using the redox flow battery as described in any one of Claims 1-10,
A method for operating a redox flow battery, wherein the oxidizing gas is introduced into the negative electrode tank in order to oxidize a negative electrode active material contained in the negative electrode electrolyte.   The method of operating a redox flow battery according to claim 11, wherein the introduction of the oxidizing gas is performed when charge states of the positive electrode electrolyte and the negative electrode electrolyte are different.   The operating method of the redox flow battery according to claim 12, wherein the charged state of the positive electrode electrolyte and the negative electrode electrolyte is made substantially the same by controlling the amount of the oxidizing gas introduced.   The method of operating a redox flow battery according to claim 13, wherein the transparency of the negative electrode electrolyte is used as a reference for controlling the introduction amount.   The operation method of the redox flow battery according to any one of claims 11 to 14, wherein the operation is performed while monitoring a charging state of the redox flow battery.

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