JP2006012425A - Operation method of redox flow battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operation method of a redox flow battery minimizing reduction in circuit voltage thereof even for long-term use. <P>SOLUTION: In this operation method of the redox flow battery including a cell circulating electrolyte in a tank by a pump, a cell storing the electrolyte as the cell even in stopping the pump is used. During standby where instantaneous drop resistance operation of discharging electricity to a load in case of instantaneous drop or short-time service interruption is not performed, auxiliary charge is performed while circulating the electrolyte by intermittently starting the pump, without performing float charging, to keep a predetermined circuit voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an operation method of a redox flow battery suitable for measures against instantaneous voltage drop and short-time power failure. In particular, the present invention relates to a method for operating a redox flow battery in which the efficiency of a pump that circulates an electrolytic solution is high and the decrease in circuit voltage can be reduced over a long period of use.

FIG. 1 is an explanatory diagram showing the operating principle of a 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 incorporates a positive electrode 104 and a negative electrode 105. A positive electrode tank 101 for supplying / discharging the positive electrode electrolyte is connected to the positive electrode cell 100A via conduits 106 and 107. Similarly, a negative electrode tank 102 for introducing / discharging the negative electrode electrolyte is also connected to the negative electrode cell 100B via conduits 109 and 110. Each electrolyte solution uses an aqueous solution of ions such as vanadium ions that change in valence, and is circulated to the cell 100 with pumps 108 and 111, and charged and discharged along with the valence change reaction of the ions at the positive and negative electrodes 104 and 105. Do. For example, when an electrolytic solution containing vanadium ions is used, the reaction that occurs during charging and discharging in the cell is 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)

  FIG. 2 is a schematic configuration diagram of a cell stack used in the above battery. Usually, the above-described battery uses a configuration called a cell stack 200 in which a plurality of sub-stacks 201 in which a plurality of cells are stacked are further stacked. The cell stack 200 is connected to a system such as a power generation facility or a consumer (load) via a DC / AC converter (inverter), and performs charging / discharging (see FIG. 1).

  Each cell includes the positive electrode 104 and the negative electrode 105 made of carbon felt on both sides of the diaphragm 103 as described above. A cell frame 210 including a plastic carbon bipolar plate 211 and a frame frame 212 formed on the outer periphery thereof is disposed outside each of the positive electrode 104 and the negative electrode 105. The frame 212 includes a plurality of manifolds (holes) that serve as electrolyte flow paths by stacking a large number of cells. The flow paths of the electrolyte solutions are the conduits 106, 107, 109, 110 in FIG. Is connected to In FIG. 2, the vertical arrows shown in the electrodes 104 and 105 indicate the direction in which the electrolyte flows, and the horizontal arrows in the diaphragm 103 and the bipolar plate 211 indicate the direction in which the current flows.

  The cell stack is configured to supply an electrolyte from a manifold on the lower side of the cell frame and to discharge from the manifold on the upper side of the cell frame by a pump operation. For this reason, when the pump is stopped, the electrolyte in the cell frame is lowered by its own weight, and the electrode cannot be maintained in an impregnated state. Therefore, when the above-mentioned redox flow battery is used for float charging in order to use for instantaneous voltage drop or short-time power failure, it is necessary to start the pump at all times so that the electrode is impregnated with the electrolyte and to distribute the electrolyte to the cell. . For this reason, the power loss of the pump becomes large, or the shunt current flows through the electrolytic solution in the manifold to cause the loss, so that the battery efficiency is lowered overall. Float charging means that a redox flow battery and a load are connected in parallel to the power supply, and a constant voltage is always applied to the battery so that it is in a charged state. In this method, power is supplied from a battery to a load.

  Therefore, as described in Patent Documents 1 and 2, the standby state in which the operation corresponding to the voltage drop that discharges to the load at the time of voltage drop is not performed, and the electrode (cell) is impregnated with the electrolyte even when the pump is stopped The redox flow battery which can hold | maintain is proposed. Since this redox flow battery includes an electrolyte supply manifold and a discharge manifold on the upper side of the cell frame, the electrolyte solution in the cell does not escape even when the pump is stopped. Therefore, it is possible to perform float charging while the pump is stopped during the above-described standby period, and it is possible to reduce the pump loss and to prevent the electrolyte from remaining in the manifold while the pump is stopped and to suppress the loss due to the shunt current. Realize. Further, in the technique described in Patent Document 2, float charging is efficiently performed by intermittently starting the pump and circulating the electrolyte during the standby.

JP 2002-175822 A JP2003-100337

  As described above, the conventional redox flow battery is capable of maintaining a sufficient capacity by performing the float charging and intermittently circulating the electrolyte solution during standby without performing the sag operation. It can cope with declines and short-time power outages. However, as a result of investigations by the present inventors, it has been found that the circuit voltage of the conventional redox flow battery may decrease over a long period of use.

  Therefore, a main object of the present invention is to provide a method for operating a redox flow battery in which a decrease in circuit voltage is small even in long-term use.

  The present invention achieves the above-mentioned object by performing supplementary charging to compensate for the reduced capacity while circulating the electrolyte, instead of performing float charging during standby without performing an operation for dealing with instantaneous voltage drop.

  That is, the present invention is a method for operating a redox flow battery including a cell capable of circulating an electrolyte in a tank by a pump, and the cell is configured to store an electrolyte even when the pump is stopped. Is used. Then, during the standby time when the operation for dealing with the voltage sag is not performed, the pump is intermittently started and supplementary charging is performed while circulating the electrolytic solution to maintain a predetermined circuit voltage.

  In the present invention, the pump power can be saved and the battery efficiency can be increased without using the pump, that is, by using a cell that can store the electrolyte even when the pump is stopped. And, the present invention is not a float charge that always applies a constant voltage to the battery during the standby without performing a voltage sag response operation that discharges the load at the time of a voltage sag or a short time power failure. By intermittently performing supplementary charging to compensate for the reduced capacity while circulating the liquid, it is possible to reduce a decrease in circuit voltage in long-term use.

  Redox flow batteries are usually charged sufficiently from the power generation facilities and other systems, but if they are stopped and left in their original state, over time, self-discharge occurs through the diaphragm. The depth of charge of the electrolytic solution, the battery capacity, and the like are lowered, and the circuit voltage is lowered. Conventionally, in order to compensate for this decrease, float charging has been performed during standby in which the operation corresponding to the instantaneous drop is not performed. However, the inventors have stated that when performing float charging during standby, circuit voltage (electrolyte charging depth, battery capacity, etc.) may decrease even when the electrolyte is intermittently circulated. Based on the knowledge, we examined not performing float charging during standby. Specifically, during the standby time when the operation corresponding to the instantaneous voltage drop is not performed, the supplementary charge for compensating for the decrease in the circuit voltage was intermittently performed. At this time, in order to further reduce the pump loss, supplementary charging was performed without circulating the electrolytic solution, that is, only the electrolytic solution in the cell. As a result, the battery capacity was greatly reduced, and it was found that sufficient capacity could not be obtained in response to instantaneous voltage drop or short-time power outage. Based on this knowledge, in the present invention, it is defined that supplementary charging is performed while circulating the electrolytic solution during standby in which the operation for dealing with an instantaneous drop is not performed.

  The cell used in the present invention may have any configuration as long as the electrolyte can be stored even when the pump is stopped. In general, the electrolyte solution can be stored in the cell by forming an electrolyte solution supply side and discharge side manifold on the upper side of the cell frame. The cell described in Patent Document 2 may be used. It is preferable to use a cell stack by stacking a plurality of such cells. In addition to storing the electrolytic solution by devising the configuration of the cell itself, the electrolytic solution can be stored in the cell stack by providing a drain trap in the middle of the electrolytic solution conduit connected to the cell stack.

  In the present invention, since the cell capable of storing the electrolytic solution even when the pump is stopped as described above is used, the pump is basically stopped during standby. However, if the pump is stopped and the electrolytic solution is not circulated and only the electrolytic solution stored in the cell is subjected to supplementary charging, the circuit voltage may gradually decrease. Therefore, in the present invention, when supplementary charging is performed, the pump is started and the electrolytic solution is circulated.

  The auxiliary charging is performed so that the circuit voltage (cell stack voltage) of the electrolytic solution is measured and the circuit voltage satisfies at least the set lower limit value. More specifically, it is performed so as to compensate for a decrease caused by self-discharge or the like so that a predetermined circuit voltage is obtained. And in order to make the water decomposition by applied voltage as small as possible, it is preferable to perform supplementary charging with an applied voltage near the circuit voltage. The circuit voltage may be measured by separately providing a monitor cell that is not charged / discharged in the system, and charging / discharging is performed on the system during the standby time when the circuit voltage is measured in the present invention. Since the battery is not operated, the circuit voltage can always be measured. Therefore, it is not necessary to provide a monitor cell. In addition, although this invention aims at charging based on a circuit voltage as mentioned above, for example, when a charge depth becomes larger than a setting, you may discharge suitably.

  Further, the auxiliary charging may be performed when the circuit voltage is measured and the circuit voltage drops below the set lower limit value, or may be performed periodically at a predetermined interval. Then, at the same time as the auxiliary charging is started, the pump is operated to circulate the electrolytic solution. In other words, according to the present invention, both the auxiliary charging control and the pump operation control are controlled based on the circuit voltage. When stopping the pump, the DC / AC converter connected to the grid is also in the stop mode (or standby mode), and when charging and discharging the pump, the DC / AC converter is also in the charging mode or Set to discharge mode.

  When standby operation is not performed, the above-mentioned supplementary charging is performed, and if an instantaneous voltage drop or short-time power failure occurs on the power supply side of a power generation facility, etc., discharging from the cell and supplying power to the load side Good. In the present invention, since the cell is in a charged state by intermittent charging performed intermittently, it is possible to perform discharge that can sufficiently cope with an instantaneous voltage drop and a short-time power failure.

  The discharge from the cell to the system may or may not be performed by circulating the electrolyte solution. When discharging by circulating the electrolytic solution, the electrolytic solution in the tank can also be used, and the discharge time can be extended.

  The electrolyte solution used in the present invention is preferably one in which the active material is vanadium ions.

  As described above, according to the operation method of the present invention, by using the cell stack that can store the electrolyte, it is not necessary to always operate the pump, and pump power loss can be suppressed. In addition, it is possible to maintain a sufficiently charged state by supplementary charging for the decrease in circuit voltage during standby when the operation for dealing with instantaneous voltage drop is not performed. it can. In particular, since supplementary charging is performed while circulating the electrolytic solution, a decrease in circuit voltage can be reduced even over a long period of use.

Embodiments of the present invention will be described below.
(Test example)
While waiting for the operation to respond to the voltage sag, perform float charging and periodically start the pump to circulate the electrolyte (pattern 1) and periodically start the pump and circulate the electrolyte We examined changes in battery performance in two driving methods called supplementary charging (Pattern 2).

  In this test, a configuration described in Patent Document 2, that is, a redox flow battery capable of storing an electrolytic solution in a cell was used. Specifically, it has a cell structure in which electrodes are stacked on a cell frame, and an electrolyte tank and pump are connected to this cell structure, and the electrolyte is supplied to the electrodes by pumping the electrolyte in the tank. In addition, a configuration in which a circulation flow path is formed in which the electrolytic solution that has passed through the electrode is returned to the tank again.

  The cell frame includes a plastic frame frame and a conductive plastic bipolar plate fixed in the frame, and a positive electrode is disposed on one side of the bipolar plate and a negative electrode is disposed on the other side. A cell stack was constructed by laminating a large number of these cell frames and positive and negative electrodes overlapped through a diaphragm made of an ion exchange membrane.

  In the cell frame, manifolds for supplying and discharging liquid are formed above (on the upper side) of the electrode arrangement surface, and this manifold is an electrolyte that extends in the stacking direction by stacking the cell frames. The flow path is configured.

  Under each manifold, slits that serve as electrolyte guides communicating between the manifold and the electrodes extend, and these slits connect each manifold and the upper edge side of the electrode. Further, when the flow of the electrolytic solution is stopped by stopping the pump, the electrolytic solution surface is prevented from reaching the manifold within the slit. In what was used by this test, the slit was comprised by forming a groove | channel in the front and back of a cell frame.

  Further, in this test, an electrolytic solution pool was formed below each slit. The electrolyte supplied from the reservoir through the manifold and slit is temporarily stored in the cell frame before being supplied to the electrode, and the electrolyte is filled along the side edge of the electrode to supply / discharge the electrode. The electrolyte solution pressure can be kept uniform, and the electrolyte solution can flow uniformly in the electrode. The liquid reservoir was a recess formed on the front and back surfaces of the frame frame, and was formed along the side edge of the electrode. In this test, an electrolytic solution in which the active material is vanadium ion was used.

  In a redox flow battery having the above-described configuration, if the pump is not started, the electrolyte does not circulate, so that the electrolyte remains in the cell. The return of the electrolyte to the tank was adjusted so that the electrolyte level was just in the middle of the slit and did not reach the manifold. Thereby, electrolyte does not remain in the manifold, and loss due to shunt current can be suppressed.

  To adjust the return of the electrolyte, the manifold in the cell is positioned above the tank electrolyte surface, and the return channel that branches from the tank to the cell in the middle of the electrolyte supply channel and leads to the air in the tank It was done by providing. A valve was provided in the return channel. When the electrolyte is flowing, the valve is closed and the electrolyte is supplied into the cell. When the pump is stopped, the valve is opened, and the excess electrolyte in the manifold is returned to the tank via the return channel.

(pattern 1)
Prepare multiple redox flow batteries with the above-mentioned configuration, and charge each battery until it reaches a certain charging depth (for example, 90%) while starting the pump and circulating the electrolyte through the cell stack. After the completion, the pump was stopped and the float charging was performed in a state where the electrolyte was stored in the cell. During the float charging, the pump was intermittently started to circulate the electrolyte solution, and the electrolyte solution in the cell stack was replaced. Specifically, after stopping the pump for 20 minutes, the pump was started for 5 minutes. Under these conditions, the performance change of each battery was evaluated. As a result, there was a battery whose battery capacity decreased by about 10% after about 6 months.

(Pattern 2)
Prepare multiple redox flow batteries with the above-mentioned configuration, and charge each battery until it reaches a certain charging depth (for example, 90%) while starting the pump and circulating the electrolyte through the cell stack. After completion, the pump was stopped and the electrolyte was stored in the cell. Then, supplementary charging was performed so that the circuit voltage satisfied at least the set lower limit value while intermittently starting the pump and circulating the electrolyte. Specifically, the pump is started once every two hours for 10 minutes to circulate the electrolyte, and the circuit voltage of the cell stack is measured before the pump is started, and the circuit voltage is lower than the set lower limit value. A supplementary charge was made to compensate. When the pump was stopped, the DC / AC converter was also stopped at the same time, and when performing supplementary charging, the DC / AC converter was set to the charging mode. Under these conditions, the performance change of each battery was evaluated. As a result, in all the batteries, the decrease in battery capacity after about 6 months was very small, about 3%.

  From the above test results, during standby that does not perform the instantaneous voltage drop operation, by performing supplementary charging while circulating the electrolyte so that the circuit voltage satisfies the set lower limit value, the circuit voltage can be maintained over a long period of use. It can be seen that the decrease can be reduced. That is, it can be seen that the battery efficiency can be further improved by intermittently performing the auxiliary charging while circulating the electrolytic solution, rather than performing the float charging so that a constant voltage is constantly applied to the cell during standby. . In addition, by performing the above-mentioned supplementary charging, the cell can be maintained in a sufficiently charged state, as in the case of a redox flow battery that has been performing conventional float charging. It is possible to appropriately cope with the discharge from the cell.

  In addition, in the case of the said discharge, it may be started even if it does not start a pump. If the pump is not started, the power loss can be reduced. If the pump is started, long-time discharge is possible using the electrolyte in the tank.

  The present invention is suitable to be used for instantaneous voltage drop and short-time power failure response.

It is a basic principle figure of a redox flow battery. It is a block diagram of a cell stack.

Explanation of symbols

100 cell 100A positive electrode cell 100B negative electrode cell 101 positive electrode tank
102 Tank for negative electrode 103 Diaphragm 104 Positive electrode
105 Negative electrode 106,107 Conduit 108,111 Pump 109,110 Conduit
200 cell stack 201 sub stack
210 Cell frame 211 Bipolar plate 212 Frame frame

Claims (2)

A method of operating a redox flow battery comprising a cell capable of circulating an electrolyte in a tank by a pump,
As the cell, a cell having a configuration capable of storing the electrolyte even when the pump is stopped,
A redox flow battery operating method characterized by maintaining a predetermined circuit voltage by intermittently starting a pump and performing supplementary charging while circulating an electrolytic solution during standby without performing an operation corresponding to a voltage drop.   2. The operating method of the redox flow battery according to claim 1, wherein the active material of the electrolytic solution is vanadium ion.

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