JP2004207177A - Redox flow battery and operation method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a redox flow battery capable of preventing lowering of battery characteristics. <P>SOLUTION: A setting part 2 is arranged to a gas-phase part 10 of a tank 101 supplying and exhausting electrolyte liquid to and from a cell of the redox flow battery, and an oxygen removing substance 1 is filled in a box 3 of the setting part 2. Such deterioration of battery characteristics that the valence number of the electrolyte liquid is changed by reaction with oxygen gas, or that the battery capacity is reduced, or that charging/discharging efficiency is reduced by increase of internal resistance is prevented by removing the oxygen gas, intruded from outside or generated by a side reaction, by the oxygen removing substance 1. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a redox flow battery and a method for operating the same. In particular, the present invention relates to a redox flow battery capable of suppressing a decrease in battery characteristics, and an operation method thereof.
[0002]
[Prior art]
Redox flow batteries have conventionally been used for load leveling and countermeasures against momentary power failures. FIG. 2 is an explanatory diagram showing the operation principle of the redox flow battery. This battery includes a cell 100 separated into a positive electrode cell 100A and a negative electrode cell 100B by a diaphragm 103 made of an ion exchange membrane. Each of the positive electrode cell 100A and the negative electrode cell 100B has a built-in positive electrode 104 and a negative electrode 105. A positive electrode tank 101 for supplying and discharging a positive electrode electrolyte is connected to the positive electrode cell 100A via conduits 106 and 107. A negative electrode tank 102 for introducing and discharging a negative electrode electrolyte is also connected to the negative electrode cell 100B via conduits 109 and 110 in the same manner. An aqueous solution of ions whose valence changes, such as vanadium ion, is used as each electrolytic solution, and is circulated by pumps 108, 111 to perform charge / discharge along with the valence change reaction of ions at the positive and negative electrodes 104, 105. For example, when an electrolyte containing vanadium ions is used, the reactions that occur during charging and discharging in the cell are as follows.
The positive ^{electrode: V 4+ → V 5+ + e} - ( ^{charging) V 4+ ← V 5+ + e} - ( discharge)
The negative ^{electrode: V 3+ + e - → V} 2+ ( ^{charging) V 3+ + e - ← V} 2+ ( discharge)
[0003]
As shown in Fig. 2, in a redox flow battery that utilizes the oxidation-reduction reaction of vanadium ions, when oxygen gas enters from the outside, it reacts with the active substance in the electrolyte to reduce the amount of the active substance, and the battery efficiency decreases. There is. Also, when oxygen gas entering from the outside oxidizes the divalent vanadium ion (V ²⁺ ) of the negative electrode, the valence balance of the electrolytic solution is disrupted, and the redox pair (V ²⁺ / V ⁵⁺ or V ³⁺ / V ⁴⁺ ) decreases in absolute amount. In such a state, if the charge / discharge operation is repeated, the battery capacity (battery stored power amount) may be reduced, or the internal resistance may increase to lower the charge / discharge efficiency.
[0004]
Therefore, in order to keep the oxygen gas concentration constant, in the conventional redox flow battery, the air in the gas phase created in the tank for each electrode is replaced with an inert gas such as nitrogen gas and sealed, An inert gas is constantly flowed through the section.
[0005]
Further, in order to prevent oxygen gas from entering, Patent Document 1 proposes that a tubular member connecting a cell and a tank be made of a plastic material having an oxygen permeability coefficient of a certain value or less. Patent Literature 2 proposes manufacturing a tank with a sheet obtained by laminating an oxygen-impermeable metal on plastic.
[0006]
On the other hand, Patent Literature 3 discloses a method of regenerating an electrolyte having a valence balance that has been lost by adding vanadium ions to the electrolyte and causing a chemical reaction. Patent Document 4 discloses a method in which a redox flow battery is connected to a regenerating device for an electrolytic solution, and the electrolytic solution is regenerated by oxidizing or reducing the electrolytic solution.
[0007]
[Patent Document 1]
JP-A-60-225366 (refer to claims)
[Patent Document 2]
JP 2001-043885 Gazette (see claims)
[Patent Document 3]
JP 2000-030721 A (see claims)
[Patent Document 4]
JP-A-62-90875 (claims, see FIG. 1)
[0008]
[Problems to be solved by the invention]
However, commercially available nitrogen gas usually contains oxygen gas, albeit in a trace amount. Conventionally, it has been considered that such an extremely small amount of oxygen does not affect the battery performance. However, as a result of the study by the present inventor, even in the case of a very small amount of oxygen gas, especially in a long-term operation, the oxidative deterioration of the exchange membrane and the cells, the decrease of the battery capacity, the increase of the internal resistance, the increase of the battery efficiency, etc. It has been found that the battery performance may be affected such as deterioration. Therefore, it is desired to eliminate a trace amount of oxygen gas. In addition, there is also a problem that the cost is high in the method of always flowing the inert gas.
[0009]
On the other hand, oxygen gas may be generated by decomposition of water as a side reaction although it is extremely small in addition to entering from outside. The techniques of Patent Documents 1 and 2 can effectively prevent invasion of oxygen gas from the outside, and have achieved sufficient results. However, as described above, even a very small amount of oxygen gas may affect battery performance. In addition to preventing oxygen gas from entering from outside, it is also desirable to remove oxygen gas generated by this side reaction. It is.
[0010]
On the other hand, when the valence balance is lost due to the reaction with oxygen gas, it is conceivable to cope by regenerating the electrolyte as in the techniques of Patent Documents 3 and 4. These techniques have a sufficient effect to improve the battery performance even if oxygen gas is generated by the side reaction as described above. However, the technique of Patent Document 4 requires the use of a complicated playback device. According to the technique of Patent Document 3, a large amount of electrolyte is not added, and a complicated regenerator is not required. However, in an installation place such as a remote island, it may be difficult to perform additional work of the electrolyte. In addition, since a small amount of a separate electrolytic solution is required, the cost tends to be high.
[0011]
Accordingly, a main object of the present invention is to provide a redox flow battery capable of suppressing a problem due to oxygen gas with a simple configuration and preventing a decrease in battery performance, and a method of operating the same.
[0012]
[Means for Solving the Problems]
The present invention achieves the above object by providing an electrical component through which an electrolyte flows with an oxygen removing substance.
[0013]
That is, the redox flow battery of the present invention is characterized in that a battery component for supplying and discharging an electrolytic solution to and from a cell includes an oxygen removing substance. In addition, the method for operating a redox flow battery of the present invention includes providing an oxygen removing substance in a battery component that supplies and discharges an electrolytic solution to a cell, and controlling the oxygen concentration in the gas phase of the battery component to 200 ppm or less. Features.
[0014]
In a battery component constituting a redox flow battery, for example, a tank, a conduit, and the like are required to have insulation and acid resistance, and thus are usually formed of a resin such as polyethylene, polyvinyl chloride, or rubber. These resins are not completely impervious to oxygen gas, but are permeable to oxygen gas in a trace amount. For example, for a 14 mm thick polyethylene tank, the rate is about 14 ml / m ² · day. Therefore, an oxygen gas that has entered from the outside exists in a gas phase portion such as a tank formed of the resin. In addition, there is a trace amount of oxygen gas generated not only by external intrusion but also by side reaction. Conventionally, these trace amounts of oxygen gas have been considered to have no problem in practical use.However, as a result of investigations by the present inventors, it has been found that they may cause a valence balance of the electrolyte to be lost in the long term. Obtained. Therefore, the present invention provides for the use of an oxygen-removing substance in order to further extend the life until the valence balance is lost. Further, conventionally, the amount of oxygen gas at which the battery performance is reduced has not been defined quantitatively. Therefore, the present invention defines the control amount of the oxygen gas. Hereinafter, the present invention will be described in more detail.
[0015]
In the present invention, the oxygen removing substance may be any substance that can remove oxygen gas, and examples thereof include an iron powder-based oxygen removing substance whose main component is iron. Other examples include metal powders such as Co and Ni, and zeolites having oxygen adsorption ability. A commercially available product may be used. Further, it is preferable to use an oxygen-removing substance having a display function of visually confirming the state of removal of oxygen, such as a change in color when a certain amount of oxygen is removed, because it is easy to grasp the replacement time and the like.
[0016]
The amount of the oxygen-removing substance may be an amount that can sufficiently remove the oxygen gas that enters or is generated, and may be appropriately changed according to the state of removing oxygen. Further, it may be appropriately changed according to the constituent material of the tank, the storage amount of the electrolytic solution in the tank, the operation cycle, and the like. Then, it is preferable to adjust the amount of the oxygen removing substance so that the oxygen concentration in the gas phase becomes 200 ppm or less. As is clear from the test described later, when the oxygen concentration in the gas phase is 200 ppm or less, the valence balance hardly changes over a long period of time. When the operation of the battery is stopped for a periodic inspection or the like, the oxygen removing substance may be replaced so that the oxygen concentration can be maintained. Further, the replacement frequency may be appropriately changed depending on the state of the oxygen removing substance to be arranged.
[0017]
Examples of the battery component in which the oxygen-removing substance is arranged include a tank for storing an electrolytic solution, and a conduit arranged between the tank and the cell for flowing the electrolytic solution. When it is arranged in a tank, an installation part may be provided in the gas phase part of the tank. The installation section may be provided inside the tank, or may be provided detachably separately from the tank.
In the former case, for example, a configuration in which a shelf on which an oxygen-removing substance can be placed inside a tank and an opening / closing port on an outer wall of the tank so that the oxygen-removing substance can be installed on the shelf can be given. It is preferable to provide a transparent window at the opening / closing port, in the case of an oxygen removing substance having a display function as described above, since the state of removing oxygen can be confirmed. In the latter case, for example, a box-shaped body in which an oxygen-removing substance can be arranged and which can be hermetically sealed, and a pipe for connecting to a gas phase portion inside the tank can be used. It is preferable that a transparent window be provided in the box-like body so that the state of oxygen removal can be confirmed in the case of an oxygen removing substance having a display function as described above. It is preferable to provide a valve in the piping. This is because, when the box-shaped body is removed by exchanging the oxygen removing substance or the like, by closing the valve, the gas-tight state of the gas phase inside the tank can be maintained. On the other hand, in the case of disposing it in a conduit, a configuration including an installation portion including a box-like body and a pipe similar to the above is exemplified. Note that the oxygen-removing substance is arranged so as not to come into contact with the electrolytic solution.
[0018]
In the present invention, the measurement of the oxygen concentration in the gas phase may be performed, for example, by collecting a part of the gas in the gas phase and using a gas chromatograph. In addition, it is also possible to analyze by combining a gas chromatograph and a mass spectrum.
[0019]
In the present invention, the electrolyte preferably has a high electromotive force, a high energy density, and contains vanadium ions which are a single element system that can be regenerated by charging even when the cathode electrolyte and the anode electrolyte are mixed. It is. For example, a vanadium sulfate solution and the like can be mentioned. In the present invention, the tank for storing the electrolytic solution and the conduit for flowing the electrolytic solution may be made of a resin such as polyethylene, polyvinyl chloride, or rubber. These resins may permeate external oxygen in the long term, but the present invention removes the permeated oxygen with an oxygen-removing substance, thereby suppressing problems such as a loss of valence balance of the electrolytic solution. can do. Further, a tank or a conduit formed of a resin laminated with an oxygen-impermeable metal may be used. At this time, invasion of oxygen from the outside can be effectively prevented.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
A redox flow battery of AC2kW x 2 hours was fabricated and operated, and the change in valence balance was examined. In this test, a redox flow battery shown in FIG. 2 was assembled using a vanadium sulfate solution containing vanadium ions as an electrolyte. For each sample, two tanks each having a capacity of 230 l (liter) were prepared, and a positive electrode electrolyte (V ⁴⁺ : 1.8 mol / l) and a negative electrode electrolyte (V ³⁺ : 1.8 mol / l) were provided in each tank. 200 l (liter) was added, and the volume of the gas phase portion of the tank was adjusted to 30 l (liter). In addition, in this test, a battery including a cell stack in which two sets of subcell stacks each including 22 cells (electrode size: 20 cm × 25 cm) were stacked in series was used.
[0021]
For sample No. 1, a polyethylene tank (8 mm thick) was used, and an installation part 2 was provided in the gas phase part of each tank as shown in FIG. 310 g (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name: Ageless ZPT (registered trademark), oxygen removal capacity: 11.6 l (liter)) was disposed in each case.
[0022]
Sample No. 2 was a polyethylene tank (polyethylene 8 mm thick) in which polyethylene terephthalate (PET, 12 μm thick) on which aluminum was deposited (7 μm thick) was coated with a polyethylene film (PE film, 40 μm thick). Using. An installation section 2 as shown in FIG. 1 is provided in the gas phase section of each tank, and an iron-based oxygen removing substance 1 (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name Ageless ZPT (registered trademark) ) And an oxygen removal capacity of 3 l (liter) were arranged in an amount of 80 g each.
[0023]
In Sample Nos. 1 and 2, the oxygen removing substance 1 was arranged as follows. In this example, as shown in FIG. 1, the tank 101 (102) was provided with a detachable installation section 2. The installation part 2 has a box-shaped body 3 made of polyethylene (coated in the same manner as the tank of the above sample No. 2) in which the oxygen removing substance 1 can be placed, and a gas phase inside the tank 101 (102). It is provided with a pipe 4 (made of polyethylene) connecting the part 10 and the box-shaped body 3, the box-shaped body 3 is provided with a transparent window 3 a (made of polypropylene), and the pipe 4 is provided with a valve 5. .
[0024]
Such a box 3 is attached to the tank 101 (102). Then, after disposing a required amount of the oxygen removing substance 1 in the box-shaped body 3, it is sufficiently filled with nitrogen gas and sealed. At this time, the valve 5 is closed. On the other hand, after flowing a predetermined amount of the electrolytic solution into the tank 101 (102), the gas phase part 10 is sufficiently filled with nitrogen gas. Then, the valve 5 is opened so that the gas in the gas phase portion 10 inside the tank 101 (102) can flow through the inside of the box-shaped body 3. As described above, the oxygen removing substance 1 is disposed in the gas phase portion 10 of the tank 101 (102). Note that the tank 101 (102) and the installation section 2 are kept airtight. The oxygen-removing substance 1 used in this test changes the color of the packaging container when a predetermined amount of oxygen is removed, and the window 3a provided in the box 3 should be used to confirm the oxygen-removing state of the oxygen-removing substance 1. Can be.
[0025]
For sample No. 3, a polyethylene tank (8 mm thick) was used, and no iron-based oxygen removing substance was disposed in the gas phase of the tank, and only nitrogen gas was sealed in the gas phase.
[0026]
For these sample Nos. 1 to 3, a continuous constant power charge / discharge of 2 hours charge / 2 hours discharge was performed for 4000 cycles (the number of cycles equivalent to about 15 years of operation). The charge / discharge conditions are shown below.
(Charging and discharging conditions)
Charge / discharge method: constant current Current density: 70 (mA / cm ² )
Charge end voltage: 1.55 (V)
Discharge end voltage: 1.00 (V)
Temperature: 25 ℃
[0027]
As a result, sample No. 1 had a battery capacity of 3.9 kW, and the ratio (V ³⁺ / V ⁴⁺ ) of trivalent vanadium ions (V ³⁺ ) and tetravalent vanadium ions (V ⁴⁺ ) after mixing the positive and negative electrolytes. ) Was 0.95, assuming that before driving was 1. Sample No. 2 had a battery capacity of 3.9 kW, and V ³⁺ / V ⁴⁺ was 0.96, assuming that 1 before operation. This shows that the provision of the oxygen-removing substance hardly changes the valence balance even if oxygen enters from the outside or oxygen is generated by a side reaction. From the above results, it is understood that it is more effective to use a battery component (a tank in this example) formed of a resin laminated with a metal impermeable to oxygen gas. In long-term operation, it is presumed that oxygen generated by a side reaction can be a factor that lowers battery performance. Specifically, oxygen gas reacts with pentavalent vanadium ions (V ⁵⁺ ) to form compounds such as peroxyvanadyl ions, which are oxidized and deteriorated by battery components such as ion exchange membranes and electrodes. Is presumed to promote. Therefore, it is presumed that the provision of the oxygen removing substance in the gas phase of the tank can further improve the battery performance.
[0028]
On the other hand, the battery capacity of the sample No. 3 having no oxygen removing substance was 3.5 kW, and the V ³⁺ / V ⁴⁺ was 0.85, assuming that the value before operation was 1. Compared to Sample No.1 and 2, the V ³⁺ / V ⁴⁺ sample No.3 deviates from 1, and V ⁵⁺ that existed in the cathode electrolyte before mixing, was present in the negative electrode electrolyte This is because V ⁴⁺ reacts with V ³⁺ to form V ⁴⁺ and V ⁴⁺ increases. That is, it is considered that the valence balance of Sample No. 3 may change when the sample is operated for a long period of time.
[0029]
Before mixing the electrolyte, the oxygen concentration in the tank of each electrode was measured. The measurement is performed by opening the valve 7 of the measurement pipe 6 provided in the tank 101 (102) as shown in FIG. 1, collecting the gas inside the tank 101 (102), and subjecting the gas to a gas chromatograph. Was. As a result, Sample No. 1 was 200 ppm, and Sample No. 2 was 150 ppm, which was 200 ppm or less. Further, when the battery components of Sample Nos. 1 and 2 were examined, no particular change was observed.
[0030]
On the other hand, in Sample No. 3, the oxygen concentration was 360 ppm, and it is considered that the valence balance changed due to oxygen invading from the outside and oxygen generated by a side reaction. Further, when the battery components were examined, it was found that some parts were oxidized at the diaphragm, electrodes, and the like.
[0031]
From the results of the above test, it can be seen that the provision of the oxygen-removing substance in the gas phase of the battery component such as the tank can suppress the deterioration of the battery performance. Further, it is presumed that not only the battery performance but also the oxidative deterioration of the diaphragm, the electrodes, and the like can be suppressed, and the life of the battery constituent members can be prolonged.
[0032]
【The invention's effect】
As described above, according to the redox flow battery of the present invention, the battery constituent member is provided with an oxygen removing substance to remove not only oxygen entering from the outside but also oxygen generated by a side reaction, so that the An excellent effect can be achieved in that the reduction of the active substance and the collapse of the valence balance of the electrolytic solution can be suppressed. Therefore, the redox flow battery of the present invention can prevent a decrease in battery performance as compared with the related art. In addition, by effectively collecting oxygen gas using the oxygen removing substance, deterioration of the battery components due to oxidation can be suppressed, and the life of the battery components can be extended. Further, since the redox flow battery of the present invention has a simple configuration in which an oxygen removing substance is disposed, the redox flow battery is excellent in workability and economical.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration near a tank in a redox flow battery of the present invention.
FIG. 2 is an explanatory diagram of an operation principle of a redox flow battery.
[Explanation of symbols]
1 Oxygen removing substance 2 Arrangement part 3 Box 3a Window 4 Piping 5, 7 Valve
6 Measurement pipe 10 Gas phase
100 cells 100A Positive cell 100B Negative cell 101 Positive tank
102 Negative tank 103 Diaphragm 104 Positive electrode 104 Positive and negative electrodes
105 Negative electrode 106 Conduit 108 Pump 109 Conduit

Claims (3)

A redox flow battery comprising a battery component for supplying and discharging an electrolytic solution to and from a cell, comprising an oxygen removing substance. The redox flow battery according to claim 1, wherein the battery constituent member is a tank in which an electrolyte is stored, and wherein the oxygen-removing substance is disposed in an installation portion provided in a gas phase portion of the tank. . A method for operating a redox flow battery, comprising: providing a battery component for supplying and discharging an electrolytic solution to a cell with an oxygen removing substance; and controlling an oxygen concentration in a gas phase portion of the battery component to 200 ppm or less.

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