JP2003303611A - Operating method of redox flow battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operating method of a redox flow battery that can suppress reduction of battery capacity without adding a new electrolyte from the outside, even if the balance of the valence value is deviated from 3.5. <P>SOLUTION: This is an operating method of a redox flow battery in which an electrolyte of each electrode is supplied for circulation respectively from a positive electrode tank storing a positive electrode electrolyte and a negative electrode tank storing a negative electrode electrolyte to the positive electrode and the negative electrode that are divided by a diaphragm. In particular, when the balance of the valence value of the electrolyte of both electrodes is deviated from 3.5, the electrolyte of one tank is moved to the other tank through a piping. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for operating a redox flow battery. In particular, the present invention relates to a method for operating a redox flow battery that can suppress a decrease in battery capacity even if the valence balance deviates from 3.5.

[0002]

2. Description of the Related Art It has been proposed to use a redox flow battery for load leveling applications, voltage sag / blackout countermeasures, and the like.

Particularly, the vanadium redox flow battery has a high electromotive force, a large energy density, and since the electrolytic solution is a single element system, it can be regenerated by charging even if the positive electrode electrolytic solution and the negative electrode electrolytic solution are mixed. It has many advantages that it can.

However, even in such a redox flow battery, various ions and solvents in the electrolytic solution move through the diaphragm when charging and discharging are repeated, and the amount of the electrolytic solution in the positive electrode and the negative electrode increases or decreases. For example, when an anion diaphragm is used,
Liquid transfer occurs from the positive electrode side to the negative electrode side, and the amount of the electrolytic solution becomes unbalanced, so that one of the electric capacities significantly decreases.

In order to solve the problem associated with such liquid transfer, conventionally, the liquid amount is adjusted by connecting or mixing the positive electrode electrolytic solution and the negative electrode electrolytic solution every fixed number of charge / discharge cycles. As a conventional technique for adjusting the liquid amount, Japanese Utility Model Publication No. 4-11340, Japanese Utility Model Publication No. 4-124754, and Japanese Patent Application Laid-Open No. 11-
Those described in JP-A-204124 and JP-A-2001-167787 are known.

Further, as a technique for regenerating the above electrolytic solution,
For example, there is one described in Japanese Patent Laid-Open No. 2000-30721.

[0007]

However, in the redox flow battery, by repeating charging and discharging, the valence balance of the electrolytic solution deviates from 3.5, that is, the valence balance collapses,
There is a problem that the battery capacity decreases.

None of the conventional techniques for adjusting the liquid amount described above considers the valence balance of the electrolytic solution, and does not consider when the valence balance of the electrolytic solution is broken.

On the other hand, the above-mentioned Japanese Patent Laid-Open No. 2000-30721 describes a method for recovering the balance of the valence balance by newly adding an electrolytic solution from the outside when the balance of the valence balance is lost. However, with this technique, not only the liquid filling work for newly adding the electrolytic solution is necessary, but also the required amount of the electrolytic solution may not be added depending on the capacity of the tank.
Also, with this technology, the molar concentration of V ^{4+ in} the positive electrode and V ^{3+ in the} negative electrode
However, it does not specifically disclose the amount of electrolyte to be added. Furthermore, there is also a problem that the cost increases because an additional electrolytic solution is prepared separately.

Therefore, the main object of the present invention is to operate a redox flow battery capable of suppressing a decrease in battery capacity without adding an electrolytic solution from the outside even if the valence balance deviates from 3.5. To provide a method.

[0011]

The present invention achieves the above object by moving the electrolytic solution of one tank to the other tank and adjusting the amount of electrolytic solution when the valence balance deviates from 3.5. .

That is, the present invention relates to a redox flow battery in which the electrolytic solution of each electrode is circulated and supplied from the positive electrode tank storing the positive electrode electrolytic solution and the negative electrode tank storing the negative electrode electrolytic solution to the positive electrode and the negative electrode separated by the diaphragm. It is a driving method. Then, when the valence balance of the electrolytic solutions of both electrodes deviates from 3.5, the electrolytic solution of one tank is moved to the other tank via a pipe. The valence balance K is defined by Equation 1 below. An example is shown in which a vanadium solution is used as the electrolytic solution for both electrodes.

[0013]

[Equation 2]

When the valence balance K calculated by the above mathematical formula 1 is 3.5, the battery capacity becomes maximum. This valence balance is broken when the positive electrode and the negative electrode differ in the amount of electricity consumed by side reactions such as gas reactions other than battery reactions and the intrusion of oxygen. For example, if the amount of electricity consumed in the side reaction is negative electrode side <positive electrode side, the valence balance shifts to 3.0 side, and if negative electrode side> positive electrode side, the valence balance shifts to 4.0 side. It also collapses when the electrolyte flows out due to an accident. Conventionally, even if the valence balance deviates from 3.5, the operation is continued as it is, and the decrease in battery capacity cannot be suppressed. In addition, as a method of suppressing such a decrease in battery capacity, as described in JP 2000-30721 A, there is no choice but to add a new electrolytic solution from the outside to recover the collapse of the valence balance. It was

[0016] Here, it is also conceivable to allow the battery capacity to decrease within a certain limit due to the loss of the valence balance, and to operate the battery. Specifically, when the valence balance is 3.5, it is best to determine the allowable range of the valence balance so that the decrease in battery capacity and side reactions are within the allowable limits. However, this operation method allows the decrease of the battery capacity to some extent, and does not positively suppress the decrease of the battery capacity. In addition, this operation method not only requires maintenance and management in order to maintain the valence balance within a prescribed allowable range, but also requires a cost for a remanufacturing plant, which may increase the cost.

Therefore, the present inventors define the present invention by obtaining the following knowledge as a result of various studies to solve the above problems. Even if liquid transfer occurs due to repeated charging and discharging, the valence balance does not change. There is a theoretical relationship between the breakage of the valence balance and the battery capacity, specifically, the relationship that the negative electrode electrolyte amount ratio at the time when the battery capacity reaches a peak varies depending on the valence balance. From the above relationship, the valence balance is 3.
Even if it deviates from 5, it is possible to maintain a battery capacity almost equal to the battery capacity when the valence balance is 3.5, or it is possible to sufficiently suppress the decrease in battery capacity.

Based on these findings, the present invention does not restore the valence balance to 3.5 as in the conventional case when the valence balance deviates from 3.5 due to the side reaction as described above. The valence balance remains deviated from 3.5 and is not changed, and the electrolytic solution in the tank is moved by piping to change the amount of electrolytic solution, thereby suppressing the decrease in battery capacity. The negative electrode electrolyte solution amount ratio is the ratio of the negative electrode electrolyte solution amount to the average of the electrolyte solution amounts of both electrodes, and is represented by the following mathematical formula 2.

[0018]

[Equation 3]

The present invention will be described in more detail below. In the present invention, the movement of the electrolytic solution is performed so that the decrease in the battery capacity can be suppressed with respect to the valence balance. In particular, when the valence balance of the electrolyte solution exceeds 3.5 (disrupted to the positive), the negative electrode electrolyte solution is moved to the positive electrode tank, and when the valence balance falls below 3.5 (disrupted to the negative), the positive electrode electrolyte solution Is preferably transferred to the negative electrode tank. When the valence balance exceeds 3.5, the ratio of the amount of the negative electrode electrolyte when the battery capacity reaches its peak tends to be smaller than 1 as described later. Therefore, in order to make the amount ratio of the negative electrode electrolyte solution smaller than 1, the negative electrode electrolyte solution is moved to the positive electrode tank and the positive electrode electrolyte solution is increased. On the contrary, when the valence balance is less than 3.5, the amount ratio of the negative electrode electrolyte at the time when the battery capacity reaches a peak also tends to be larger than 1. Therefore, in order to make the amount ratio of the negative electrode electrolyte solution larger than 1, the positive electrode electrolyte solution is moved to the negative electrode tank to increase the negative electrode electrolyte solution.

More preferably, the electrolytic solution is moved so that the battery capacity becomes maximum with respect to the valence balance, that is, the negative electrode electrolytic solution amount ratio takes a peak value. Specifically, it is advisable to move the electrolytic solution until the amount of the electrolytic solution in each tank becomes the amount that satisfies the following formulas 3 and 4.

[0021]

[Equation 4]

As will be described later, even when the valence balance K exceeds 3.5, the actual negative electrode electrolyte solution amount ratio (R) is smaller than the negative electrode electrolyte solution amount ratio (Rmax) when the battery capacity reaches a peak, Conversely, R may be larger than Rmax even when K is less than 3.5. In the former case, it is preferable to move the positive electrode electrolytic solution to the negative electrode tank, and in the latter case, it is preferable to move the negative electrode electrolytic solution to the positive electrode tank. Therefore, in order to suppress the decrease in the battery capacity more reliably, it is preferable to move the electrolytic solution so that the amount of the electrolytic solution is defined by the above mathematical expressions 3 and 4.

In the present invention, the movement of the electrolytic solution in the tank is carried out not by taking the electrolytic solution out of the battery system, but by using the piping provided in the battery. As such a pipe, for example, a pipe for supplying and discharging an electrolytic solution can be cited. When the supply / discharge pipe is used, an anion exchange membrane or a cation exchange membrane is used, and the electrolytic solution can be moved by operating the battery. Alternatively, it can also be moved by changing the liquid supply pressure of the electrolyte such as increasing the liquid supply pressure on one side and decreasing the liquid supply pressure on the other side. Further, the pipe may be separately provided for moving the electrolytic solution. For example, it is preferable to connect both tanks by a communication pipe and use this communication pipe. And the movement of the electrolyte is
This is done via this communication pipe. A valve is preferably provided in the communication pipe. In addition, a pump or the like may be provided in the communication pipe so that the electrolytic solution can be easily moved. As a method of moving the electrolytic solution through the communication pipe without using a pump, for example, there is a method of moving the electrolytic solution by gravity by providing a height difference on the liquid level of the electrolytic solution in each tank. In order to provide a height difference in the liquid level of the electrolytic solution, the bottom area of one tank may be smaller than the bottom area of the other tank. Further, the weight member may be stored in one of the tanks. The weight material is preferably a resin tank or rubber tank containing water, a weight, or the like, which can be submerged at the bottom of the tank, such as a plastic-lined concrete block. In addition, it is possible to use a rubber tank or the like that can change the volume of the tank.

The operation method of the present invention is not limited to the vanadium redox flow battery using a vanadium solution as an electrolytic solution.
Fe ³⁺ / Fe ²⁺ solution for positive electrode electrolyte, Cr ²⁺ / Cr ³⁺ solution for negative electrode electrolyte, Br ₂ / Br ^- solution for positive electrode electrolyte, Cr ²⁺ / for negative electrode electrolyte It is most suitable for redox flow batteries using Cr ³⁺ solution.

In the case of a redox flow battery using a Fe ³⁺ / Fe ²⁺ solution as the positive electrode electrolyte and a Cr ²⁺ / Cr ³⁺ solution as the negative electrode electrolyte, the valence balance K may be calculated from the following values. . N _P5 : Molar concentration (mol ³ ) of trivalent iron ion (Fe ³⁺ ) in the positive electrode tank
/ l) N _n5 : molar concentration of ferric ion (Fe ³⁺ ) in the anode tank (mol
/ l) N _P4 : Molar concentration of ferrous iron (Fe ²⁺ ) in the positive electrode tank (mol
/ l) N _n4 : Molar concentration of ferrous ion (Fe ²⁺ ) in the negative electrode tank (mol
/ l) N _P3 : Molar concentration of trivalent chromium ion (Cr ³⁺ ) in the positive electrode tank
(mol / l) N _n3 : molar concentration of trivalent chromium ion (Cr ³⁺ ) in the negative electrode tank
(mol / l) N _P2 : Molar concentration of divalent chromium ion (Cr ²⁺ ) in the positive electrode tank
(mol / l) N _n2 : Molar concentration of divalent chromium ion (Cr ²⁺ ) in the negative electrode tank
(mol / l)

On the other hand, in the case of a redox flow battery using a Br ₂ / Br ⁻ solution as the positive electrode electrolyte and a Cr ²⁺ / Cr ³⁺ solution as the negative electrode electrolyte, the valence balance K may be obtained from the following value. . N _P5 : Molar concentration of bromine (Br ₂ ) in the positive electrode tank × 2 (mol / l) N _n5 : Molar concentration of bromine (Br ₂ ) in the negative electrode tank × 2 (mol / l) N _P4 : In the positive electrode tank bromine ion (Br ^-) molar (mol /
l) N _n4: bromide ions in the negative electrode in the tank (Br ^- molar) (mol /
l) N _P3 : molar concentration of trivalent chromium ion (Cr ³⁺ ) in the positive electrode tank
(mol / l) N _n3 : molar concentration of trivalent chromium ion (Cr ³⁺ ) in the negative electrode tank
(mol / l) N _P2 : Molar concentration of divalent chromium ion (Cr ²⁺ ) in the positive electrode tank
(mol / l) N _n2 : Molar concentration of divalent chromium ion (Cr ²⁺ ) in the negative electrode tank
(mol / l)

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The valence balance was changed and the relationship between the battery capacity and the negative electrode electrolyte amount ratio with respect to the valence balance was examined. First, an outline of the vanadium redox flow battery used in this example will be described. FIG. 1 is an explanatory diagram showing an outline of a redox flow battery, and FIG. 2 is a schematic diagram showing a state in which a positive electrode tank and a negative electrode tank are connected by a communication pipe. In FIG. 1, the communication pipe that connects both tanks is omitted, and in FIG. 2, the cells are omitted and only the connected state of both tanks is shown. This battery consists of a positive electrode cell 1A and a negative electrode cell 1 with a diaphragm 4 that allows the passage of ions.
It comprises a cell 1 separated into B and. Positive cell 1A and negative cell
Each of 1B has a positive electrode 5 and a negative electrode 6 built therein.
A positive electrode tank 2 for supplying and discharging a positive electrode electrolytic solution is connected to the positive electrode cell 1A via conduits (pipes) 7 and 8. Similarly, a negative electrode tank 3 for supplying and discharging a negative electrode electrolytic solution is connected to the negative electrode cell 1B via conduits (pipes) 10 and 11.
As each electrolytic solution, an aqueous solution of vanadium ions whose valence changes is circulated by pumps 9 and 12, and charging / discharging is performed along with the valence change reaction of the ions in the positive electrode 5 and the negative electrode 6. In this example, the positive electrode tank 2 and the negative electrode tank 3 are connected by communication pipes 20 and 21 (see FIG. 2) for moving the electrolytic solution from one tank to the other tank.

Next, a method of measuring the valence balance will be described. The valence balance K was calculated by the above-mentioned mathematical formula 1. Formula
Positive electrode electrolyte amount A _P (l), negative electrode electrolyte amount A which is the specified value of 1
_n (l) is measured by a liquid level meter 27 such as a liquid level gauge or a liquid level meter provided in each tank 2, 3. Similarly, the molar concentration of each valence vanadium ion (V ⁵⁺ , V ⁴⁺ , V ³⁺ , V ²⁺ ) at both electrodes N _{P5 to} N _P2 (m
ol / l) and N _{n5 to} N _n2 (mol / l) are measured by analyzing the electrolytic solution off-line or by measuring the self-potential.

In the electrolytic solution used in this example, the positive electrode electrolytic solution was V (4
Value) / V (5 values) sulfuric acid aqueous solution, the negative electrode negative electrode liquid is V (3 values)
/ V (divalent) sulfuric acid aqueous solution. The molar concentration of each valent vanadium ion and the amount of each electrolyte solution at the start of the experiment are shown below.

(Positive Electrolyte) (Negative Electrolyte) A _P : 3 (l) A _n : 3 (l) N _P5 : 0 (mol / l) N _n5 : 0 (mol / l) N _P4 : 2 ( mol / l) N _n4 : 0 (mol / l) N _P3 : 0 (mol / l) N _n3 : 2 (mol / l) N _P2 : 0 (mol / l) N _n2 : 0 (mol / l)

The valence balance was changed by adjusting the amount of the electrolyte solution, and the battery capacity and the ratio R of the negative electrode electrolyte solution to the valence balance were examined. Figure 3 shows the results. The graph of FIG. 3 shows the battery capacities when the negative electrode electrolyte volume ratio R is changed from 0.88 to 1.12. For the valence balances 3.45, 3.50 and 3.55. The negative electrode electrolyte volume ratio R is
It was calculated from the above-mentioned formula 2. The battery capacity in FIG. 3 shows a relative ratio with the valence balance of 3.5 and the negative electrode electrolyte amount ratio R of 1 as 100%.

As shown in FIG. 3, it can be seen that the negative electrode electrolyte amount ratio R at which the battery capacity is maximized differs depending on the valence balance K. For example, when the valence balance K is 3.55, when the negative electrode electrolyte volume ratio R is smaller than 1 (R = 0.94), the battery capacity peaks, while the valence balance K is 3.4.
In the case of 5, the battery capacity has a peak when the negative electrode electrolyte amount ratio R is larger than 1 (R = 1.06). From this result, it is expected that the battery capacity can be improved by moving the electrolytic solution and adjusting the amount of the electrolytic solution without recovering the valence balance to 3.5. For example, when the valence balance K is 3.55, it is possible to lower the charge state of the positive electrode and increase the charge state of the negative electrode at the same battery voltage by moving the negative electrode electrolyte solution to the positive electrode tank and increasing the amount of the positive electrode electrolyte solution. it can. If the amount of the electrolytic solution before the transfer of the electrolytic solution is equal, the battery capacity becomes smaller than that in the case where the valence balance is 3.5 because of the positive electrode neck after the battery charging and the negative electrode neck after the battery discharging. However, in the present invention, by moving the electrolytic solution and adjusting the amount of the electrolytic solution, almost the same battery capacity as in the case of the valence balance of 3.5 can be obtained.

From FIG. 3, the valence balance K of the electrolytic solution is
It can be seen that when the value exceeds 3.5, the battery capacity tends to be maximum when the negative electrode electrolyte solution is moved to the positive electrode tank and the negative electrode electrolyte solution amount ratio R is made smaller than 1. Further, it can be seen that when the valence balance K is less than 3.5, the battery capacity tends to be maximized when the positive electrode electrolyte solution is moved to the negative electrode tank and the negative electrode electrolyte solution amount ratio R is made larger than 1.

In addition to the above results, each valence balance (K)
In, the negative electrode electrolyte amount ratio Rmax that maximizes the battery capacity was obtained. The results are shown in Fig. 4. The graph in Fig. 4 shows the negative electrode electrolyte volume ratio Rmax when the battery capacity is maximized for each valence balance, and Case 1 (70%, approximately 16kWh / m ³ ) and low utilization rate 2 (40
%, About 10kWh / m ³ ).

As shown in FIG. 4, it can be seen that the larger the valence balance K, the smaller the negative electrode electrolyte volume ratio Rmax at which the battery capacity is maximized. Therefore, it is understood that the movement of the electrolytic solution can be suppressed more effectively by decreasing the battery capacity as follows.

(1) The valence balance K is calculated by measuring the amount of the electrolytic solution on both electrodes and the molar concentration of each valent vanadium ion. (2) With respect to the calculated valence balance K, the negative electrode electrolyte amount ratio Rmax that maximizes the battery capacity is obtained from the graph shown in FIG. (3) so that the negative electrode electrolyte solution amount ratio Rmax is satisfied, that is, the positive electrode electrolyte solution amount An ′ after moving the electrolyte solution is the above-mentioned formula 3, and the same negative electrode electrolyte solution amount Ap ′ is such that the same formula 4 is satisfied. Then, move the electrolyte.

Next, using a vanadium redox flow battery in which both tanks based on FIGS. 1 and 2 were connected by a communication tube, when the valence balance of the electrolyte solution deviated from 3.5, the electrolyte solution was moved to move the negative electrode electrolyte solution. The relationship between the valence balance and the battery capacity when the volume ratio R was adjusted was examined. For comparison, the negative electrode electrolytic solution amount ratio R was maintained at 1 (positive electrode electrolytic solution amount: negative electrode electrolytic solution amount = 1:
The relationship between the valence balance and the battery capacity when kept at 1) was examined (conventional technology). The results are shown in FIGS. Figure 5
The graph shows the case where the utilization rate of active materials is high (70%,
Approximately 16kWh / m ³ ): Case 1, and the graph in Fig. 6 shows the case with low utilization (40%, about 10kWh / m ³ ): Case 2. Figures 5 and 6
Has a valence balance of 3.5 and a negative electrode electrolyte volume ratio R of 1
The relative ratio was shown by setting the value to 100%.

As shown in FIGS. 5 and 6, in the conventional technique in which the electrolytic solution is not moved, in order to keep the battery capacity at 90% or more, the valence balance is in the range of 3.45 to 3.55 in each case. Must be kept at. On the other hand, in the present invention in which the electrolytic solution is moved to adjust the negative electrode electrolytic solution amount ratio R, in the case of Case 1, if the valence balance is maintained in the range of 3.35 to 3.7, the battery capacity is maintained at 90% or more. be able to. Especially in case 2, a wider range (range of about 3.3 to 3.8)
Can keep the battery capacity above 90%. Furthermore, if the battery capacity is 80%, which is judged as the life of lead batteries,
It should be maintained at about 3.2 to 3.8.

As described above, the present invention has a valence balance of 3.5.
The requirements for side reactions, oxygen invasion, accuracy of the components of the electrolyte solution, etc., which cause deviations, become much looser, and the reduction in battery capacity can be easily and inexpensively realized.

Next, a specific structure for moving the electrolytic solution from one tank to the other tank will be described in more detail. As shown in FIG. 2, the two tanks 2 and 3 are either the positive tank 2 to the negative tank 3 or the negative tank 3 to the positive tank 2.
Communication pipes 20, 21 so that the electrolyte can be moved to
Are directly connected by. In this example, even if the liquid surface of the positive electrode electrolyte and the liquid surface of the negative electrode electrolyte do not match, a pump is installed in the piping path so that the electrolyte can be moved against gravity.
22 are provided. In addition, a valve 23 is attached to each communication pipe 20, 21.
~ 26 are provided.

To move the positive electrode electrolytic solution from the positive electrode tank 2 to the negative electrode tank 3, it is preferable to open the valves 23 and 24, close the valves 25 and 26, and appropriately use the pump 22. On the other hand, in order to move the negative electrode electrolytic solution from the negative electrode tank 3 to the positive electrode tank 2, the valve 25 and the valve 26 may be opened, the valve 23 and the valve 24 may be closed, and the pump 22 may be appropriately used. With this configuration, the electrolytic solution of the other pole can be efficiently moved from the tank of the one pole.

Other methods for moving the electrolytic solution include the following methods. (1) Method using a pump and a cross pipe for circulating an electrolyte solution in each electrode cell

FIG. 7 is a schematic diagram showing a state in which a cross pipe is provided in the pipe for supplying and discharging the electrolytic solution to each electrode cell. In this method, both tanks 2 and 3 are not directly connected like the communication pipes of the above example, but are indirectly connected by cross pipes 70 and 71, and one of them is connected through the cross pipes 70 and 71. Move the electrolyte of the other pole from the tank. That is, the cross pipes 70 and 71 are communication pipes that indirectly connect both tanks. In this method, pumps 9 and 12 for circulating the electrolyte solution in the positive electrode cell 1A and the negative electrode cell 1B.
Is also used as a pump for moving the electrolytic solution of the other pole from the tank of one pole. With this configuration, it is not necessary to provide a pump exclusively for moving the electrolytic solution for changing the negative electrode electrolytic solution ratio R, and the productivity and economy of the battery are excellent. In addition, the cross pipe 70, so that the electrolyte is not mixed unnecessarily
71 is provided with valves 72 and 73.
2, 73 are normally closed during operation.

To move the positive electrode electrolytic solution from the positive electrode tank 2 to the negative electrode tank 3, it is preferable to open the valve 72 provided in the cross pipe 70, close the valves 75 and 77, and appropriately use the pump 9. On the other hand, in order to move the negative electrode electrolyte solution from the negative electrode tank 3 to the positive electrode tank 2, the valve 73 provided in the cross pipe 71 is opened, the valves 74 and 76 are closed, and the pump is appropriately pumped.
It is recommended to use 12.

(2) Method using a specific diaphragm (when moving the electrolytic solution by using a pipe for supplying and discharging the electrolytic solution) In the method shown in the above embodiment and the method (1), an example using a pump is used. As shown, an example of not using a pump is a method using a specific diaphragm.

For example, in general, when an anion exchange membrane (anion membrane) is used as a diaphragm to operate a battery, the electrolyte is from the positive electrode to the negative electrode, and when a cation exchange membrane (cation membrane) is used, the electrolyte is negative electrode. To the positive electrode. Here, the reason why the valence balance deviates from 3.5 as described above is, for example, a side reaction or invasion of oxygen into the battery. Therefore, in practice, the valence balance K exceeds 3.5, that is, the direction in which the negative electrode electrolyte is moved to increase the amount of the positive electrolyte, or the valence balance K is less than 3.5, that is, the positive electrolyte. In some cases, it may be possible to determine in advance whether the direction is to move to increase the amount of the negative electrode electrolyte. Therefore, the electrolytic solution can be moved by the diaphragm used. At this time, the valence balance K
It is preferable to select the diaphragm so that the direction in which the electrolytic solution moves in accordance with the change of 1 and the direction in which the electrolytic solution moves through the diaphragm match. For example, if the valence balance K is more than 3.5, use a cation exchange membrane to
When K is less than 3.5, an anion exchange membrane may be used. When the battery is operated, the movement of the electrolytic solution is performed through a pipe for supplying and discharging the electrolytic solution. Both tanks are
As shown in FIG. 8, it is preferable to connect by a pipe 80 including a valve 81. FIG. 8 is a schematic diagram showing a state in which the positive electrode tank and the negative electrode tank are connected by a pipe, and the cell is omitted and only the connection state of both tanks is shown. It is advisable to close the valve 81 of the pipe 80 and operate the battery until the amount of movement of the electrolytic solution through the diaphragm reaches an appropriate amount. When the amount of movement becomes excessive, the valve 81 may be temporarily opened and the electrolytic solution may be moved through the pipe 80 to adjust the amount of the electrolytic solution. Further, if a vent pipe is provided above both tanks, the movement of the electrolytic solution will be smoother.

(When the electrolytic solution is moved by using the communication pipe that directly connects both tanks) Contrary to the above, the valence balance K
Change the direction of moving the electrolytic solution and the direction of moving the electrolytic solution through the diaphragm does not match, i.e., the moving method of the electrolytic solution when the former direction and the latter direction are opposite. explain.

When an anion exchange membrane is used in a direction in which the valence balance K exceeds 3.5, and when a cation exchange membrane is used in a direction in which the valence balance K is less than 3.5, the electrolyte solution is changed according to the change in the valence balance. The direction in which the electrolyte is moved is opposite to the direction in which the electrolytic solution moves through the diaphragm. In these cases,
It is advisable to install both tanks at locations where there is a difference in height, or to use tanks that have different cross-sectional areas so that there is a height difference in the level of the stored electrolyte and the electrolyte is moved by gravity. . At this time, both tanks may be connected by a communication pipe, and the electrolytic solution may be moved through this communication pipe.

FIG. 9 is a schematic view showing a state in which the negative electrode tank is installed higher than the positive electrode tank and both tanks are connected by a communication pipe. FIG. 10 is a cross sectional area of the positive electrode tank and the positive electrode tank. FIG. 3 is a schematic diagram showing a state in which a negative electrode tank having a small size is connected by a communication pipe. Further, FIG. 11 is a schematic diagram showing a state in which a positive electrode tank and a negative electrode tank having a weight member stored therein are connected by a communication pipe. In both cases, the cells are omitted and only the connected state of both tanks is shown. For example, when an anion exchange membrane is used in a direction where the valence balance K exceeds 3.5, the installation location of the negative electrode tank 3 may be set higher than that of the positive electrode tank 2 as shown in FIG. 9, or the negative electrode tank 3 as shown in FIG. It is preferable to use a thin one having a cross-sectional area (bottom area) smaller than that of the positive electrode tank 2. In addition, as shown in FIG.
The weight material 112 may be housed inside to adjust the liquid level of the negative electrode tank 3. With these configurations, since there is a difference in height between the liquid surface of the positive electrode electrolyte and the liquid surface of the negative electrode electrolyte, even if there is liquid transfer from the positive electrode to the negative electrode through the diaphragm, the communication tubes 90, 100, 1
When the valves 91, 101, 111 of 10 are opened, the electrolytic solution can be moved from the negative electrode to the positive electrode according to gravity. Further, if a vent pipe is provided above both tanks, the movement of the electrolytic solution can be performed more smoothly.

(3) In addition to the method of changing the solution sending pressure, a pipe and a pump for supplying and discharging the electrolyte solution are used, and the pump is adjusted to reduce the solution sending pressure of one electrolyte solution and the other electrolyte solution. Increasing the delivery pressure may be mentioned. In this method, the liquid supply pressure is changed to change the liquid amount of the electrolytic solution.

[0051]

As described above, according to the operating method of the redox flow battery of the present invention, even if the valence balance deviates from 3.5, the battery capacity can be reduced without separately preparing and adding an electrolytic solution. An excellent effect that it can be suppressed can be obtained. Further, the present invention is not to restore the valence balance, in order to suppress the decrease in battery capacity in the state where the valence balance is deviated from 3.5, side reactions that cause the valence balance to collapse, oxygen intrusion and It is possible to relax the requirement for the accuracy of the components of the electrolytic solution as compared with the conventional one. Further, the present invention is not only excellent in workability because there is no liquid filling work involved in the recovery of the valence balance, but also economical because it does not increase the cost due to the addition of an electrolytic solution.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of a redox flow battery.

FIG. 2 is a schematic diagram showing a state in which a positive electrode tank and a negative electrode tank are connected by a communication pipe.

FIG. 3 is a graph showing a relationship between a battery capacity and a negative electrode electrolyte solution amount ratio with respect to valence balance.

FIG. 4 is a graph showing the ratio of the amount of negative electrode electrolyte when the battery capacity is maximum with respect to valence balance.

[Fig. 5] Case (16kWh) where the utilization rate of active materials is high (70%)
/ m ³ ) shows the relationship between the valence balance and the battery capacity when the negative electrode electrolyte volume ratio R is adjusted, and the relationship between the valence balance and the battery capacity when the negative electrode electrolyte volume ratio R is maintained at 1. It is a graph.

[Figure 6] Case (10kWh) in which the utilization rate of active materials is low (40%)
/ m ³ ) shows the relationship between the valence balance and the battery capacity when the negative electrode electrolyte volume ratio R is adjusted, and the relationship between the valence balance and the battery capacity when the negative electrode electrolyte volume ratio R is maintained at 1. It is a graph.

FIG. 7 is a schematic diagram showing a state in which a cross pipe is provided in a pipe for supplying and discharging an electrolytic solution to each electrode cell.

FIG. 8 is a schematic view showing a state in which both tanks are connected by a pipe including a valve.

FIG. 9 is a schematic view showing a state in which a negative electrode tank is installed higher than a positive electrode tank and both tanks are connected by a communication pipe.

FIG. 10 is a schematic diagram showing a state in which a positive electrode tank and a negative electrode tank having a smaller cross-sectional area than the positive electrode tank are connected by a communication pipe.

FIG. 11 is a schematic diagram showing a state in which a positive electrode tank and a negative electrode tank having a weight member stored therein are connected by a communication pipe.

[Explanation of symbols]

1 cell 1A Positive cell 1B Negative cell 2 Positive tank
3 Negative tank 4 Diaphragm 5 Positive electrode 6 Negative electrode 7, 8, 10, 11
Conduit 9, 12 Pump 20, 21 Communication pipe 22 Pump 23 ~ 26 Valve 27 Liquid volume meter 70, 71 Cross piping 72 ~ 77 Valve 80 Piping 81 Valve 90, 100, 110 Communication pipe 91, 101, 111 Valve 112
Weight material

Continued front page    (72) Inventor Nobuyuki Tokuda             3-22 Nakanoshima 3-chome, Kita-ku, Osaka City, Osaka Prefecture             Kansai Electric Power Co., Inc. F term (reference) 5H026 AA10 CC06 CX05 HH00 RR01                 5H027 AA10 KK00

Claims (4)

[Claims] 1. A method of operating a redox flow battery in which an electrolytic solution of each electrode is circulated from a positive electrode tank storing a positive electrode electrolytic solution and a negative electrode tank storing a negative electrode electrolytic solution to a positive electrode and a negative electrode separated by a diaphragm, respectively. A method for operating a redox flow battery, which comprises moving the electrolyte solution of one tank to the other tank via a pipe when the valence balance of the electrolyte solutions of both electrodes deviates from 3.5. 2. The method for operating a redox flow battery according to claim 1, wherein the pipe is a communication pipe connecting both tanks, and the movement of the electrolytic solution is performed through the communication pipe. 3. When the valence balance of the electrolyte solution exceeds 3.5, the negative electrode electrolyte solution is moved to the positive electrode tank, and when the valence balance is less than 3.5, the positive electrode electrolyte solution is moved to the negative electrode tank. The method for operating the redox flow battery according to claim 1 or 2. 4. The electrolytic solution is moved until the amount of electrolytic solution in each tank reaches the following amount.
The method for operating the redox flow battery described in. [Equation 1]