JPS6316574A - Electrolyte flow type secondary battery - Google Patents

Abstract

PURPOSE:To improve the charging/discharging efficiency by providing monitoring cells on both sides of the electrolyte inlet and outlet of a reaction cell, and controlling the supply of the electrolyte to the reaction cell in responce to the starting voltage measured by the monitoring cell. CONSTITUTION:A monitoring cell 6 is provided on the electrolyte inlet side of a reaction cell 1, while a monitoring cell 7 is provided on the electrolyte outlet side. A judgment circuit 8 judges whether the difference of starting electric power between the monitoring cells 6, 7 is maintained at the predetermined value or not. The circuit 8 judges that an excessive electrode reaction has occurred in the reaction cell 1, if the difference is larger than the prescribed value, and gives control signals to a pump drive inverter 9 so as to increase the supply of electryte to the reaction cell 1. On the contrary the circuit 8 gives control signals for lowering the pump revolutions of supply pumps 4, 5 to the inverter 9 to reduce the aforesaid supply if the defference is smaller than the value. It is thus possible to improve the charging/discharging efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrolyte flow type secondary battery that performs charging and discharging by supplying an electrolyte to a reaction cell.

[Prior Art] As an electrolyte flow type secondary battery, for example, a redox flow m secondary battery is known. In this type of redox flow type secondary battery, an electrolytic solution containing an active material flows between an electrolytic solution tank and a reaction cell to perform charging and discharging operations. As the electrolyte, for example, hydrochloric acid is used, and as the active material, for example, FeCl2 and CrCfL are used.

During the charging operation, Fe2+ ions change to Fe"÷ions and Cr3+ ions change to Crz+ ions, while during the discharging operation, an electrochemical reaction occurs in the opposite direction.

In such a redox flow type secondary battery, a flow meter or the like is conventionally attached to the electrolyte piping, and a supply bomb is operated without control so as to always maintain a flow rate above a certain level during charging and discharging operations. Therefore, although the amount of electrolyte supplied to the reaction cell is always kept above a certain level, the flow rate fluctuates due to the change in viscosity due to changes in the active material due to charging and discharging operations.

[Problems to be Solved by the Invention] FIG. 4 shows the relationship between the depth of charge and the amount of effective active material in a Fe-Cr redox flow secondary battery. Here, the depth of charge is an index indicating the state of charge, and when the electrolyte is Fe-Cr-based, the p
eZ +, Fe! The ratio of the effective active material to the total ions of +, Cr", and Cr2+ is shown. Here, the effective active material is the reactant of the electrode reaction in the reaction cell, and the effective active material during charging is Fe at the positive electrode. ”, Cr'+ ions at the negative electrode, and F at the positive electrode are effective active materials during discharge.
e3+ and Cr2+ ions at the negative electrode.

As shown in FIG. 4, during charging, the effective active material decreases as the depth of charge increases and charging progresses, and during discharging, the effective active material decreases as the discharge progresses, that is, as the depth of charge decreases. As charging or discharging progresses and the effective active material that should contribute to the electrode reaction decreases, it becomes impossible to secure the effective active material necessary for the reaction, and the efficiency of the electrode reaction and charge/discharge efficiency decreases. Charging and discharging are performed within a range of depth of charge, for example, a depth of charge of 15% to 85%.

Figure 5 shows the relationship between the amount of effective active material supplied to the reaction cell per unit time and the depth of charge when the operating range of a normal pump without any control is set to a depth of charge of 15 to 85%. show. FIG. 5 shows only the case of charging. The amount of effective active material supplied to the reaction cell is lowest at a depth of charge of 85%. In conventional secondary batteries,
As mentioned above, since the amount of electrolyte supplied to the reaction cell is always kept almost constant, the state with the lowest amount of effective active material is used as the reference, and the amount of electrolyte is adjusted so that the charging reaction can be sufficiently carried out even in this state. supplying.

Therefore, when the depth of charge is less than 80%, only the amount of active material in the area shown in FIG. This means that the substance does not contribute to the electrode reaction.

In this way, in conventional redox flow type secondary batteries,
Since an excessive amount of electrolyte that cannot contribute to the electrode reaction is supplied, energy loss due to the supply pump increases, and the charging/discharging efficiency of the battery as a whole is forced to decline.

The purpose of the present invention is to provide an electrolyte flow type secondary battery that solves these problems, improves charging and discharging efficiency, and can increase battery capacity by widening the operating depth of charge range. be.

[Means for Solving the Problems] The electrolyte flow type secondary battery of the present invention is provided with a monitor cell on both the electrolyte inlet side and the outlet side of the reaction cell, and the monitor cell performs measurement. The reaction cell is equipped with a control means for adjusting the amount of electrolyte supplied to the reaction cell in accordance with the generated electromotive voltage.

[Function] In the electrolyte flow type secondary battery of the present invention, a monitor cell is provided on both the electrolyte inlet side and the outlet side of the reaction cell, and the electromotive force generated in the monitor cell is calculated according to the Nernst equation. Therefore, it corresponds to the amount of effective active material in the electrolyte flowing through the monitoring cell. therefore,
The amount of effective active material on the inlet and outlet sides of the reaction cell can be detected from this electromotive force, and the control means can be used to supply electrolyte to the reaction cell in response to changes in the amount of effective active material in the reaction cell. Can be adjusted.

[Embodiment] FIG. 1 is a schematic diagram showing an embodiment of the present invention. A monitor cell 6 is provided on the electrolyte inlet side of the reaction cell 1, and a monitoring self is provided on the electrolyte outlet side of the reaction cell 1. Electrolyte tanks 2 and 3 are connected to the reaction cell 1 via the monitoring cell 6.7 and piping, respectively. Supply pumps 4 and 5 are respectively attached to the pipes on the electrolyte inlet side. The reaction cell 1 is usually of a multi-stage connection type in which a plurality of unit cells are stacked and connected in series in order to increase the generated voltage.

A connection line for transmitting the electromotive voltage to the discrimination circuit 8 is attached to the monitor cell 6.7. A connection line for transmitting a control signal from the discrimination circuit 8 is installed between the discrimination circuit 8 and the pump driving inverter 9. Further, a connection line for transmitting electric power for driving the pumps is installed between the pump driving inverter 9 and the supply pumps 4 and 5.

During charging and discharging, the supply pump 4.5 is driven to supply the electrolyte in the electrolyte tanks 2 and 3 to the reaction cell 1. At this time, the electrolytic solution supplied to the reaction cell 1 is supplied through the inside of the monitoring cell 6. In the monitoring cell 6, an electromotive voltage is generated depending on the concentration of effective active material in the electrolytic solution supplied to the reaction cell 1.

After the electrode reaction, the electrolyte discharged from the reaction cell 1 passes through the monitoring cell and returns to the electrolyte tank 2# from the piping.
It will be returned within 3. In the monitoring self, an electromotive voltage is generated depending on the concentration of effective active material in the electrolytic solution discharged from the reaction cell 1. The electromotive voltages of the monitor cell 6 and the monitor self are transmitted through connection lines and sent to the discrimination circuit 8, respectively.

The determination circuit 8 determines whether the difference between the electromotive force of the monitor cell 6 and the electromotive force of the monitor self is maintained at a set value. If the difference in electromotive voltage is larger than the set value,
Because the amount of electrolyte supplied to reaction cell 1 is small, reaction cell 1
Excessive electrode reaction is occurring inside. Therefore, in this case, a control signal is given to the pump drive inverter 9 to increase the amount of electrolyte supplied to the reaction cell 1, thereby increasing the pump rotational speed of the supply pumps 4 and 5 and increasing the amount of electrolyte supplied to the reaction cell 1. The amount of electrolyte supplied to No. 1 is increased.

Conversely, if the difference in electromotive voltage is smaller than the set value, the amount of electrolyte supplied to the reaction cell 1 is excessive. Therefore, a control signal for lowering the pump rotation speed of the supply pump 4.5 is given to the pump drive inverter 9 from the discrimination circuit 8, thereby reducing the pump rotation speed of the supply pump 4.5 and increasing the rotation speed to the reaction cell 1. Electrolyte supply amount decreases.

Especially when the amount of electrolyte supplied to reaction cell 1 is small,
Side reactions other than charge/discharge reactions occur within the reaction cell 1. Therefore, adjusting the amount of electrolyte supplied is also effective in suppressing such side reactions.

In the embodiment shown in Fig. 1, the electrolyte supply amount is controlled by adjusting the rotation speed of the supply pump in order to adjust the g, but the electrolyte supply amount may also be adjusted by other means such as valve operation. good. Further, the control means using the monitor cell described above can be provided in combination with other electrolyte supply amount control means.

Note that the depth of charge of the secondary battery can be detected from the electromotive voltage values of the monitoring cells provided on both the electrolyte inlet side and the outlet side.

FIG. 2 is an exploded perspective view showing an example of a monitoring cell used in the present invention. The monitor cell shown in Figure 2 is
It has a structure similar to a unit cell in a reaction cell,
Carbon cloth 12.13 is provided on both sides of the diaphragm 11. Further, a graphite plate 14.15 is provided on the outside of the carbon cloth 12.13, and the graphite plate 14.15 connects the diaphragm 11 and the carbon cloth 12.
゜13 is being held.

The carbon cloths 12 and 13 have a horizontally elongated shape in order to minimize the fluid resistance of the electrolytic solution flowing inside the carbon cloths. The carbon cloths 12 and 13 are supported by a frame 16 and a frame 17, respectively. A slit 16C116d and slits 17c and 17d are formed between the frame body 16.17 and the carbon cloth 12.13. Cutouts 16a and 16b for supplying and discharging electrolyte are formed in the slits 16c and 16d. Similarly, cutouts 17a and 17b for supplying and discharging the electrolyte are formed in the slits 17c and 17d.

The graphite plates 14.15 are each supported by a frame 18.19. A notch 16a in the frame 18,
An inlet 18a and an outlet 18b for inflowing and outflowing the electrolytic solution are formed at positions corresponding to 16b. An inlet 17a and an outlet 19b are also formed in the frame 19 at positions corresponding to the notches 17a and 17b, through which the electrolytic solution flows in and out. Inflow ports 18a, 19
Electrolyte piping is connected to a and the outflow ports 18b and 19b, respectively.

As shown by the arrow in FIG. 2, one of the electrolytes is supplied from the inlet 18a to the carbon cloth 12 through the notch 16a, and is discharged through the notch 16b and the outlet 18b.

The other electrolyte also passes through the inlet 19as notch 17a, is supplied to the carbon cloth 13, and is supplied to the carbon cloth 13 through the notch 17b1 and the outlet 19.
It is discharged through b.

The electromotive force generated in the monitor cell is transferred to the graphite plate 14.
．． 15 can be taken out as terminals. As a monitoring cell, it is preferable to minimize the fluid resistance. Therefore, the shape of the carbon cloth is preferably short in the direction of flow of the electrolyte solution and long in the direction perpendicular to the direction of flow of the electrolyte solution. It is also recommended to use coarsely woven carbon cloth to allow the electrolyte to pass through easily.

FIG. 3 is a sectional view showing another example of the monitoring cell used in the present invention. Inside the monitor cell 20, there is a diaphragm 2.
1 is provided, and the diaphragm 21 is provided with a diaphragm support member 22 .
Supported by 23.

On both sides of the diaphragm 21, end faces of graphite rods 24 and 25 are arranged to face each other. A gap is formed between the diaphragm 21 and the end faces of the graphite rods 24, 25, through which the electrolyte can flow.

During charging and discharging operations, a portion of the electrolytic solution that has flowed into the monitoring cell 20 passes between the 1 m 1121 gap and the end face of the graphite rod 24.25 and exits from the monitoring cell 20, as shown by the arrow in FIG. be discharged. Therefore, an electromotive voltage is generated in the graphite rods 24 and 25 that corresponds to the concentration of effective active material in the electrolytic solution.

As in the embodiment shown in FIG. 3, the monitor cell used in the present invention does not necessarily need to be provided with carbon cloth. Note that when monitoring the electromotive voltage, the internal resistance of the monitoring cell can be increased as long as the value of the electromotive voltage does not change significantly due to the minute current flowing through the voltmeter.

Although the monitor cell has been explained by illustrating it in FIGS. 2 and 3, the monitor cell used in this invention is not limited to these cells, and a pair of conductive cells as electrodes are connected to each other via a diaphragm. Any device can be used as long as it is provided with a member.

[Effects of the Invention] In the electrolyte flow type secondary battery of the present invention, a monitoring cell is provided on both the electrolyte inlet side and the outlet side, and the depth of charge is determined by detecting the electromotive voltage of the monitoring cell. At the same time, it is possible to detect a change in the amount of effective active material within the reaction cell. Further, the electrolyte flow type secondary battery of the present invention is provided with a control means for adjusting the amount of electrolyte supplied to the reaction cell, and the charging depth and the amount of moving sliding material detected by the monitoring cell are adjusted. The amount of electrolyte supplied to the reaction cell can be adjusted in response to changes in the amount of electrolyte. This reduces energy loss in the ζ supply pump and improves the charging and discharging efficiency of the secondary battery system as a whole.

In addition, in the electrolyte flow type secondary battery of the present invention, the amount of electrolyte supplied to the reaction cell can be adjusted according to the amount of effective active material in the electrolyte.
Those operating at ~85% can now be operated at depths of charge of 10-90% without incurring an increase in battery system efficiency.

Being able to operate over a wide range of charge depths allows effective use of electrolyte, which means that when designing the same amount of charge and discharge as before, it is possible to use a smaller amount of electrolyte than before. can.

Therefore, the size of the electrolyte tank can be made smaller than before, and the size of the secondary battery as a whole can be made smaller.

In the examples, a redox flow type secondary battery was explained as an example of an electrolyte flow type secondary battery, but the electrolyte flow type secondary battery of the present invention is charged by supplying an electrolyte to a reaction cell. It can be widely used for other types of devices that generate electric discharge.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention. FIG. 2 is an exploded perspective view showing an example of a monitoring cell used in the present invention. FIG. 3 is a sectional view showing another example of the monitoring cell used in the present invention. FIG. 4 is a diagram showing the relationship between the amount of effective active material and the depth of charge in a Fe-Cr based redox flow type secondary battery. FIG. 5 is a diagram showing the relationship between the amount of effective active material supplied to the reaction cell per unit time and the depth of charge during charging of a Fe-Cr based redox flow J1 secondary battery. In the figure, 1 is a reaction cell, 2 and 3 are electrolyte tanks, and 4 is a reaction cell.
．． 5 is a supply pump, 6.7 is a monitoring cell, 8 is a discrimination circuit, and 9 is a pump driving inverter. Figure 1 Figure 2 Figure 3 Figure 22j Figure 4 Figure f

Claims (3)

[Claims] (1) In an electrolyte flow type secondary battery that performs charging and discharging by supplying an electrolyte to a reaction cell, a monitoring cell provided on both the electrolyte inlet side and the outlet side of the reaction cell, and the monitor cell An electrolyte flow type secondary battery, comprising: a control means for adjusting the amount of electrolyte supplied to the reaction cell according to the electromotive voltage measured in the electromotive force. (2) The electrolyte flow type secondary battery according to claim 1, wherein the control means adjusts the rotation speed of a supply pump that supplies electrolyte to the reaction cell. (3) Claim 1, wherein the electrolyte flow type secondary battery is a redox flow type secondary battery.
The electrolyte flow type secondary battery according to item 1 or 2.