JP2009016216A - Operation method of redox flow battery composed of plurality of modules - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operation method of a redox flow battery composed of a plurality of modules, which can always maintain no difference of potential among a plurality of modules during operation, without adding separately a device and without deteriorating cycle efficiency. <P>SOLUTION: In the operation method of a redox flow battery composed of a plurality of modules having a plurality of electrolyte circulation systems, the flow-rate of the electrolytic liquid of the module with a small self-discharge amount is established larger than the flow-rate of the electrolytic liquid of the module with a large self-discharge amount in order to equalize the potential difference between the modules A, B. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for operating a redox flow battery having a plurality of modules having a plurality of electrolyte circulation systems.

  The electrolyte solution of the redox flow battery system is generally configured to be supplied in parallel to all cells from the electrolyte storage tank, but in order to increase the cell voltage, when increasing the number of cells in series, In order to suppress current loss due to “shunt current” (leakage current) generated through the electrolyte in the pipe, a “multiple module configuration” is often used for the purpose of electrically separating the electrolyte circulation system.

  In this case, if charging / discharging is continued, the amount of self-discharge of the battery cells in each module is not necessarily the same, and therefore a difference gradually appears in the charging depth between the modules. If charging / discharging is continued as it is, the charging state (charging depth) of a module with a smaller amount of self-discharge becomes higher, and there is a concern that an overvoltage is applied to the cells in the module, resulting in cell loss. Further, if the operation is continued in such a state, there is a concern that the required battery capacity cannot be secured from the viewpoint of the battery capacity of the entire multi-module configuration. Note that the cause of the difference in self-discharge amount between modules is due to the difference in the characteristics of the diaphragm (ion exchange membrane) and the degree of deterioration over time.

  Therefore, various proposals have been made in order to solve the problem of the potential difference generated between the modules. For example, by mixing the positive and negative electrolytes of a module with a high charge state, the charge state is matched to a lower charge module, or the positive and negative electrolytes of multiple modules are mixed together Thus, a method of averaging the state of charge between modules has been proposed (see, for example, Patent Document 1).

JP 2005-340029 JP

The conventional method for eliminating the potential difference as described above is an intermittent adjustment method in which the potential difference is adjusted when the potential difference between the modules becomes large enough to be detected by the voltage measuring means. Therefore, it is impossible to make an adjustment so that there is always no potential difference between the plurality of modules during operation.

In addition, when adjusting the potential difference, special pipes, valves, etc. for performing operations that are not necessary for normal operation such as mixing positive and negative electrolytes or electrolytes of the same polarity are mixed. There is also a drawback that additional equipment is required, and that equipment costs are required.

Further, when the positive and negative electrode electrolytes are mixed, there is a problem that the efficiency of the cycle is temporarily lowered due to a temporary rise in the temperature of the electrolyte solution at that location. That is, when positive and negative electrolytes are mixed, heat is generated due to a change in the amount of self-discharge. Moreover, since the charged electrolyte solution will be discharged at a time, current loss will occur at that time, resulting in a temporary reduction in efficiency.

  The present invention has been made in view of such circumstances, and a plurality of components that can be maintained in a state in which there is no potential difference between a plurality of modules at all times during operation without adding a separate device and without reducing cycle efficiency. An object of the present invention is to provide a method for operating a redox flow battery having a module configuration.

The method for operating a redox flow battery having a plurality of modules according to the present invention is a method for operating a redox flow battery having a plurality of modules having a plurality of electrolyte circulation systems.
In order to equalize the potential difference between the modules, the operation is performed by setting the electrolyte flow rate of the module having a small self-discharge amount to be larger than the electrolyte flow rate of the module having a large self-discharge amount.

By the way, the inventors have found characteristics in which the self-discharge amount changes depending on conditions such as the electrolyte flow rate, the state of charge, the electrolyte temperature, etc., while variously examining the self-discharge characteristics of the redox flow battery. In particular, we focused on the electrolyte flow rate as a readily controllable factor and investigated its characteristics. An example of the result is shown in FIG. In this test, a redox flow battery with two modules 1 and 2 is charged, the electrolyte is circulated under various flow conditions, and the characteristics that the cell voltage of each module decreases over time can be clearly understood. It was. In other words, a slight difference in self-discharge amount was observed between modules 1 and 2, but it was found that the self-discharge amount increased as the flow rate increased, and conversely, the self-discharge amount decreased as the flow rate decreased. . That is, the self-discharge amount changes in proportion to the flow rate. In this test, the flow rate is changed in a considerably wider range than the actual rated flow rate. However, in actuality, the rated flow rate is secured and the self-discharge amount between modules is sufficiently adjusted by adjusting the flow rate between 10% and 20%. We were able to confirm that it can be adjusted. That is, it has been found that variation in the characteristics of the redox flow battery can be adjusted by adjusting the flow rate to this extent. Based on the above knowledge, the inventors have operated in the case where there is no problem in the characteristics of the electrodes between the modules, there is a difference in the characteristics of the diaphragm, and there is a difference in the self-discharge amount between the modules. In order to maintain a state in which there is no potential difference among a plurality of modules at all times, it has been found that the method of operating by adjusting the flow rate of the electrolyte as described above is appropriate.

In that operation method, for example, before starting operation (by trial operation etc.), first, in order to grasp the amount of self-discharge between modules (battery characteristics), the electrolyte is circulated at the rated flow rate in each module. (Under the same flow conditions) and measure the potential difference between the modules. Next, if there is a potential difference between the modules, in order to equalize the voltage balance between the modules, the electrolyte flow rate of the module with a small self-discharge amount is set larger than the electrolyte flow rate of the module with a large self-discharge amount. . The degree of adjustment can be obtained in advance as data such as a formula or a table by experiments or the like.

Thus, the operation is started by setting the electrolyte flow rate in each module according to the potential difference. Then, during operation, a state where no potential difference is generated can be maintained at all times. That is, when the electromotive force is E, the current is I, and the resistance is R, the terminal voltage at the time of discharge represented by V = E-IR is represented by V. By increasing the electrolyte flow rate, the amount of self-discharge can be increased to lower the electromotive force, and the balance of the terminal voltage V between the modules can be equalized. By performing the operation in which the voltage balance between the modules is equalized, the degree to which each battery is damaged due to overcharging or the like during operation is reduced, and long-term reliability as a battery having a plurality of modules is improved. . Further, in this method, since only the adjustment of the electrolyte flow rate is required as described above, it is not necessary to separately add devices such as pipes and valves, and the equipment cost can be reduced. And since special operation, such as the operation which mixes electrolyte solution like the past, becomes unnecessary, the temperature of electrolyte solution does not rise or efficiency fluctuates, and an operating state is stabilized.

  According to the method for operating a redox flow battery having a multi-module configuration according to the present invention, the electrolyte flow rate of a module with a smaller self-discharge amount is set higher than the electrolyte flow rate of a module with a higher self-discharge amount. Since the operation is performed by equalizing the voltage balance between the modules, it is possible to maintain a state in which no potential difference is always generated during the operation. Thereby, damage due to overcharging or the like is reduced, and long-term reliability as a battery having a plurality of modules is improved. Further, there is no need to add a separate device such as a pipe or a valve, and the equipment cost can be reduced. And the temperature of electrolyte solution does not rise or the efficiency fluctuates, and the operating state is stabilized.

Hereinafter, a method for operating a redox flow battery having a multi-module configuration according to an embodiment of the present invention will be described.
FIG. 1 shows a configuration of a redox flow battery having a plurality of modules. This redox flow battery is composed of two modules A and B each having a pair of cell stacks 100A and 100B. Each of the cell stacks 100A and 100B has a common positive electrode electrolyte tank 2A and 2B and a negative electrode electrolyte. Liquid tanks 3A and 3B are connected. The forward path of the electrolyte solution connecting the tanks 2A, 2B, 3A, 3B and the cell stacks 100A, 100B is indicated by a solid line, and the return path is indicated by a broken line.

  Although not shown, each cell stack 100A, 100B has a stacked configuration in which, for example, 6 substacks are connected in series, and each substack has a stacked configuration in which, for example, 18 cells are connected in series. It has become. In each cell constituting these cell stacks 100A and 100B, pumps 9A, 9B, 12A, and so on are respectively provided in the outward path so that the electrolyte can be supplied from the electrolyte tanks 2A and 2B for the positive electrode and the electrolyte tanks 3A and 3B for the negative electrode. 12B is provided. These pumps 9A, 9B, 12A and 12B are connected to the output side of the computer 200, respectively, while the input side of the computer 200 has voltmeters V21A and 21B for measuring the potential difference between the modules A and B. It is connected. The computer 200 also performs control related to charging / discharging with an external power system (see FIG. 2).

  As shown in FIG. 2, the basic configuration of each cell 1 that is the minimum unit of a battery is that a positive electrode cell having a positive electrode 5 and a negative electrode cell having a negative electrode 6 are arranged on both sides of a diaphragm 4, and the electrodes Each of 5 and 6 is connected to a positive electrode electrolyte tank 2 (2A, 2B) and a negative electrode electrolyte tank 3 (3A, 3B) through a circulation path consisting of forward paths 7, 10 and return paths 8, 11. Each of the positive electrode electrolyte and the negative electrode electrolyte is circulated and supplied. Adjacent cells, that is, the positive electrode and the negative electrode are separated by a bipolar plate (not shown).

In the method of operating a redox flow battery having a multi-module configuration composed of such a stacked assembly of cells, first, before operation (by trial operation, etc.), the amount of self-discharge between modules A and B (battery characteristics) In each module A and B, the positive and negative electrolytes are circulated at the rated flow rate (same flow rate condition), and several charge / discharge cycles are repeated, and the potential difference between modules A and B is repeated. Measure. The difference in the amount of self-discharge can be determined from the degree of potential difference between the modules at that time.

Next, in order to equalize the voltage balance between modules A and B, start the operation by setting the electrolyte flow rate of the module with less self-discharge amount higher than the electrolyte flow rate of the module with more self-discharge amount. To do. Then, the terminal voltage of the module having the smaller self-discharge amount is adjusted to the module having the larger self-discharge amount and the lower terminal voltage, and the operation is continued in a state where the voltage balance between the modules is equalized. Therefore, the degree to which each battery is damaged by overcharging or the like during operation is reduced, and long-term reliability as a battery having a plurality of modules is improved. Further, in this method, since only the adjustment of the electrolyte flow rate is required as described above, it is not necessary to add a separate device such as a pipe or a valve, and the equipment cost can be reduced. And since special operation, such as the operation which mixes electrolyte solution like the past, becomes unnecessary, the temperature of electrolyte solution does not rise or efficiency fluctuates, and an operating state is stabilized.

In such an operation involving adjustment of the electrolyte flow rate between modules A and B, data for obtaining an appropriate adjustment amount (ratio between modules) corresponding to the potential difference between modules A and B in advance. By storing (formula, table, etc.) in the computer 200, the output (electrolyte flow rate) of each pump 9A, 9B, 12A, 12B can be set. The flow rate may be adjusted by a flow rate adjusting valve or a throttle, and the opening degree may be automatically adjusted or manually adjusted.

By comparing the operation method involving adjustment of the electrolyte flow rate between the modules A and B with the conventional method, the effect can be understood more clearly. A comparative example will be described below.

<Comparative example>
In a two-module redox flow battery, both the positive and negative electrodes were charged and discharged at the same rated flow rate.When about 10 cycles passed, the electromotive force after the end of discharge between modules was measured with a monitor cell. It was found that a potential difference of about 3 mV occurred per cell. When this potential difference occurrence state was investigated for each cycle, it was found that the potential difference occurred almost in proportion to the cycle. At this point, in order to mix the positive and negative electrolytes of the module with higher voltage, a mixing pipe with a valve was installed and the mixing operation was carried out for several tens of seconds. The potential difference was eliminated to almost 0 mV. I was able to confirm. However, such a method is not practical because it requires a cost for procuring a valve and a mixed pipe and a connection work thereof, which is troublesome and costly.

<Example 1>
Using the redox flow battery having a multi-module configuration shown in FIG. 1 and the like, in the trial operation stage, the positive and negative electrolytes are circulated at the rated flow rate (same flow rate condition) in each module A and B. The potential difference between B was measured with voltmeters 21A and 21B. As a result, it was found that a potential difference of about 3 mV occurred per cell. Therefore, by mixing the positive and negative electrolytes of the module with higher voltage, once this potential difference is resolved, the flow rate of the electrolyte of the module with the higher potential difference is increased by about 10%. Operation was carried out at the flow rate setting. As a result, even after 10 cycles, a potential difference did not occur and a good operating state could be continued.

As is clear from the above, according to the operation method of the redox flow battery having a multi-module configuration of the present invention, the potential difference between the two modules is measured in advance, and the flow rate of the electrolyte is adjusted based on the measurement result. By continuing the operation, the voltage balance between the modules can always be kept equalized during the operation. Therefore, damage due to overcharging or the like is reduced, and long-term reliability as a battery having a plurality of modules is improved. Further, the measurement of the potential difference between the modules for flow rate adjustment may be performed prior to the operation, and there is no need to interrupt or stop the operation, and a high operating rate can be maintained. It should be noted that the present invention is not limited to the embodiment, and can be freely improved, changed, etc. as necessary without departing from the gist of the invention. For example, it goes without saying that the present operation method can be applied to a redox flow battery having a configuration of three modules or more.

  According to the operation method of the redox flow battery having a multi-module configuration of the present invention, the potential balance between the modules is always kept normal during the operation by adjusting the flow rate of the electrolyte solution between the modules in advance. Therefore, it is suitable for operation for improving long-term reliability of a battery having a plurality of modules.

It is a block diagram which shows the basic composition of the redox flow battery of the multiple module structure which concerns on embodiment of this invention. It is explanatory drawing of the basic composition of each cell. It is a graph which shows the change state of the self-discharge amount with respect to a flow rate change.

Explanation of symbols

A, B module
1
Cell 2,2A, 2B Cathode electrolyte tank 3,3A, 3B
Anode electrolyte tank
Four
Diaphragm 5 Positive electrode 6 Negative electrode 7,10 Outward path 8,11 Return path
9,9A, 9B, 12,12A, 12B Pump 21A, 21B
voltmeter
100A, 100B cell stack
200 computers

Claims (2)

A method of operating a redox flow battery having a plurality of modules having a plurality of electrolyte circulation systems,
To equalize the potential difference between modules, the multi-module configuration is characterized by operating with the electrolyte flow rate of the module with a small amount of self-discharge set larger than the electrolyte flow rate of the module with a large amount of self-discharge To operate the redox flow battery.   2. A plurality of self-discharge amounts of each module according to claim 1, wherein the self-discharge amount of each module is grasped by measuring the potential difference between the modules by circulating the electrolyte at a rated flow rate in each module in advance before operation. Operation method of module configuration redox flow battery.

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