JPS6070672A - Method of operating redox-flow secondary battery - Google Patents

Abstract

PURPOSE:To stabilize charge-and-discharge cycles of a redox-flow secondary battery by equalizing the charged states of anolyte and catholyte by detecting the concentrations of a ferrous and a ferric compound in the anolyte in order to detect the overcharged state of the anolyte and reducing an excess of ferric ion contained in the anolyte into ferrous ion according to the result of the detection. CONSTITUTION:A detection means such as a voltammetry cell 1 is installed in a stream located in the back of a chamber 12 (for reducing the active material of anolyte) which is a component of a balance cell 11 installed in an anolyte line 2. The cell 1 is used to observe oxidoreductive waves of anolyte to measure the concentrations of a ferrous compound and a ferric compound in order to detect the overcharged state of the anolyte. On the basis of the result of the detection, reduction of the ferric compound is performed in the rebalance cell 11 according to the required amount of anolyte rebalance calculated from the value determined by a detector 1 and the measured open circuit voltage. By the means mentioned above, it is possible to repeat charge-and-discharge cycles of a redox-flow secondary battery over a prolonged period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a redox flow type secondary battery, and particularly to a method of operating a redox flow type secondary battery suitable for matching the state of charge of both electrolytes.

In line with the demand for flattening the power load, the development of secondary batteries has recently been attracting attention, and one example of such batteries is known as a secondary battery manufactured using electrolyte. In this battery, charging or discharging reactions occur while the electrolyte flows into or out of the electrolytic cell. It can be divided into negative electrode liquid, which causes battery reactions. The positive and negative electrode fluids contain substances that have oxidizing and reducing properties, that is, substances that can cause oxidation and reduction reactions reversibly, such as iron chloride (ferrous or ferric iron) under acidic hydrochloric acid, and negative electrode fluids. A so-called redox flow type secondary battery uses chromium chloride or titanium chloride under hydrochloric acid acidity.

Conventional redox flow type secondary batteries of this type
As shown in the figure (excluding the detector 1 for detecting active material concentration, etc., which is characteristically provided according to the present invention), the cell (electrolytic cell) 7 forming the main body is equipped with a diaphragm 10 that selectively allows protons to pass therethrough. It is divided into a positive electrode chamber 8 and a negative electrode chamber 9.

In such a configuration, if an iron chloride solution under hydrochloric acid acidity of the positive electrode m81c and a chromium chloride solution under hydrochloric acid acidity are introduced into and out of the negative electrode chamber 9, a charge/discharge reaction proceeds independently in each chamber. That is, during charging, ferrous iron is electrolyzed to ferric iron in the positive electrode chamber 8, and nichrome is electrolyzed to first PM in the negative electrode chamber 9. At this time, protons are transferred from the positive electrode chamber 8 to the negative electrode through the diaphragm IO. Transmits to chamber 9. Through this charging, a solution containing a large amount of ferric compounds is obtained from the positive electrode chamber 8, and a solution containing a large amount of chromium compounds is obtained from the negative electrode chamber 9, but these are temporarily stored in their respective tanks (not shown). The liquid is then sent to each chamber of the cell again during discharge. During this discharging, a reaction opposite to that during charging occurs, and an output is taken out to the outside of the battery.

In order for such a battery to withstand long-term use as a secondary battery, the charge/discharge cycle described above must be continued well, and for this purpose, the current efficiency during charge/discharge reactions in the positive electrode chamber and negative electrode chamber must be improved. must match each other. Generally, when a solution of an iron compound is used as the catholyte,
The charge/discharge reaction in the positive electrode chamber proceeds at a rate of t'z i o o%. However, if the solution of the chromium compound exemplified above is used as the negative electrode liquid, the reaction in the negative electrode chamber will be approximately 10% during discharge.
Although the process proceeds under a flow efficiency of 0, during charging, a reaction occurs in which the nichrome compound is reduced to the monochrome compound, and a side reaction in which protons are reduced to generate hydrogen also occurs. Therefore, at the end of charging, the amount of ferrous compounds generated in the negative electrode chamber is relatively small compared to the ferric compound generated in the positive wS chamber (the positive electrode liquid is overcharged with respect to the negative electrode liquid). If the charging/discharging cycle is repeated in this state, the charging state (charge 11. depth ratio) of the bipolar liquid will be greatly disrupted, and it will eventually become difficult to repeat the charging/discharging reaction. Due to these circumstances, in redox flow type secondary batteries, it is usually necessary to perform a reversing operation to match the charging states of both electrolytes, and it is actually In some cases, a glue balance method is used in which hydrogen gas generated from the negative electrode chamber during charging rises to reduce the ferric compound. This method assumes that the difference in the state of charge of the bipolar liquid is caused only by the hydrogen gas generated from the negative electrode chamber during charging, and collects the generated hydrogen gas and consumes it all for the reduction of the ferric compound. This makes it possible to prevent overcharging of the catholyte and to allow charging and discharging cycles to be carried out over a fairly long period of time. However, such conventional methods have the following (1) and 0)
There are drawbacks as shown below.

(1) Variations in the state of charge between the two electrodes are not only caused by the generation of hydrogen gas mentioned above, but can also occur due to, for example, the battery active material leaking unilaterally into the other electrode group, although the deviation is small. Therefore, it is unreasonable in the long term to reduce the delta diiron compound by trapping only the generated hydrogen gas.

(2) The state of charge of bipolar fluids is mainly determined by measuring the open circuit voltage, charge release, and sleep pressure in cells (electrolytic cells), etc. It is also difficult to apply this method to cases where charging and discharging cycles are repeated.

The purpose of the present invention is to solve the above-mentioned drawbacks of the prior art,
An object of the present invention is to provide a method of operating a redox flow type secondary battery that can match the state of charge between both electrodes even when charging/discharging and recycling is repeated over a long period of time.

In order to achieve the above object, the present invention provides a method for operating a redox flow type secondary battery using a solution containing an iron compound selected from mutually convertible ferrous and ferric compounds as a positive electrode liquid. In this step, the overcharged state of the positive electrode solution is detected by measuring the @ degree of the ferrous compound and the ferric compound, and based on the detection result, the excess ferric compound in the positive electrode solution is converted to the ferrous compound. It is characterized by reducing the catholyte and bringing the catholyte into a normal charging state.

Regarding the battery active material in the electrode solution used in the present invention, an iron compound selected from ferrous compounds and ferric compounds is used for the positive electrode solution, as described above, but for the negative electrode solution, which is the counter electrode solution, an iron compound selected from ferrous compounds and ferric compounds is used. There is no particular restriction as long as it has a function, and conventionally used compounds such as chromium or titanium are generally applicable.

In addition, as for the means (hereinafter simply referred to as a detector) for detecting the overcharge state of the catholyte, any known means can be applied as long as this purpose is achieved, but in particular, it is possible to apply current or voltage to the working electrode. In portammetry, the current or voltage waveform based on ferrous and/or ferric compounds is observed by applying a current or voltage to the working electrode, and the concentration of both is determined from this. Iron compounds and/
Alternatively, coulometry is used to obtain the tonicity based on a ferric compound and calculate the concentration of both, and a configuration that uses optical absorption of ferrous or ferric compounds to calculate the concentration of both. Absorption photometry is suitable. If we take into account the degree and charging time of the battery active material (total iron compound) that falls into the positive electrode liquid in this way, and the depth (ratio of ferric compound wind to total iron compound amount), this Since it is possible to determine the ratio of the charge depth of the bipolar liquid from the state of charge of the anode liquid determined from the open-circuit voltage value, it is possible to set up the balance required to reduce the ferric compound based on this. Become.

Hereinafter, the present invention will be explained in more detail with reference to Examples. In addition, in the apparatus (illustrated) used in the examples, the display of the electrical system including the power supply, electronic load device, etc. is omitted.

Example 1 4N hydrochloric acid acidic 1 mol/l iron chloride water fn solution as positive electrode liquid,
A 1 mol/l chromium chloride aqueous solution acidified with 4N hydrochloric acid was used as the negative electrode liquid, and charging and discharging operations were carried out using the small cell device shown in FIG. The apparatus shown in FIG. 1 consists of a cation exchange MIO system with a diaphragm as an example, a redox flow type self-contained system having a positive electrode chamber 8 and a negative electrode chamber 9, which are divided into a positive electrode chamber 8 and a negative electrode chamber 9, and a negative electrode liquid 2-in-3 attached to the negative electrode chamber 9. Installed gas-liquid separator 15
and is provided in the positive electrode liquid line 2 attached to the positive electrode chamber 8,
In addition, the cation exchange membrane 10A, which is an example of a diaphragm, is divided from the hydrogen gas reaction chamber 13, and the positive electrode liquid active material reduction chamber 12, which is one component chamber of the balance cell 11 (same as the self-contained positive and negative electrode chambers) , a portametry cell l, which is an example of a detector shown in FIG.
! It mainly consists of a circulation pump 14 for feeding rabbit liquid.

In the figure, 14A and 15A are respectively a circulation pump and a gas-liquid separator installed in the electrolyte (4N hydrochloric acid aqueous solution in this example) line 4 attached to the hydrogen gas reaction chamber 13, and 5 is a hydrogen gas cylinder 6. This is a hydrogen line for guiding hydrogen gas sent from the circulation pump 14A to the discharge side electrolyte line of the circulation pump 14A.

The portammetry cell shown in FIG. 2, which is applied as an example of the detector 1, has a positive electrolyte population 18 and an outlet 19 at both ends.
It mainly consists of a working electrode 16 consisting of a stationary gold α9 pole in the center, and a counter electrode 17 consisting of a platinum wire wound in a coil. When the DC voltage is swept in such a configuration, the positive and temporary liquids are The oxidation-reduction waves shown in FIG. 3 can be observed for these waves, and from these wave heights one degree of the corresponding chemical species can be calculated. In addition, the above DC 1a pressure 11
Similar results can be obtained when a pulse voltage is applied by applying a pulse voltage. Each chamber 13 is filled with carbon cloth as an electrode.The self cell not only performs charging and discharging, but also has the function of occasionally cutting off charging and discharging and measuring the open circuit voltage.Rebalance cell 11 Then, the ferric compound is reduced according to the required amount of positive electrode fluid rebalance calculated from the measured value by the detector 1 and the measured value of the open circuit voltage.

In a small cell device with such a configuration, first, without operating the rebalance cell 11, and without operating the redox
Flow type self charging/discharging current density is 40mA/c++!
The bipolar liquids were repeatedly charged and discharged 10 times. As a result, it was found from the open circuit evening pressure and each measurement value of the detector 1 that the overcharge ratio of the positive electrode liquid to the negative electrode liquid was about 20 degrees. Therefore, this time, the bipolar liquids are circulated only by operating the pump 14 without charging and discharging, and at the same time, the rebalance cell 11 is operated to make the charge depth ratio of the bipolar liquids almost equal, and then the redox flow type A continuous charging/discharging experiment was conducted by operating the self-balancing cell 11 at the same time. At this point, the open circuit voltage and the detector 1 were measured from time to time, and the operating amount of the rebalance cell was adjusted based on the results. As a result, the results of continuous charging and discharging tests over 40 times were good, and the difference in the charging depth of both electrolytes at the end was 3%.
It was weak.

Example 2 As shown in Fig. 4, a KW class cell was manufactured using 96 redox flow cells each having an electrode area of 432 d in place of the unit cell (one redox flow cell) 7 shown in Fig. 1. A battery stack 21 is used, and a negative electrode liquid tank 23 and a positive electrode liquid tank 22 are provided in the negative electrode liquid line 3 and a positive electrode liquid line 2, respectively, an open circuit voltage measuring cell 20 is placed between the two tanks, and a positive electrode liquid tank 22 is provided. A line is provided to guide a portion of the positive electrode liquid sent from the rebalance cell 11 through the positive electrode active material reduction chamber 12 to the positive electrode liquid line, and a hydrogen gas reaction chamber 13 is provided. Instead of introducing hydrogen gas into the electrolytic solution, a reducing organic substance such as hairscorbic acid, a reducing agent such as metallic iron or ferrous chloride is added to the electrolytic solution, and an electrolytic tank 24 for storing the electrolytic solution is added. Using a kW class battery device having the same configuration as shown in Fig. 1 except for the above, continuous charging and discharging was carried out 40 times while determining the required rebalancing member and performing balancing based on this in the same manner as in Example 1. I drove.

As a result, the rebalance reaction progressed well no matter which of the above reducing agents was added, and the difference in the depth of charge that occurred between the two electrode liquids was so slight that it did not pose any particular problem during operation.

For comparison, it was found that when the device was operated without rebalancing (no detector was used), the catholyte was overcharged by approximately 3 times after 1 charge and discharge. In addition, in the case of heat, the rate of overcharging mentioned above generally becomes very rapid, or it may fluctuate by 1 to 2. This method is not preferred.

Example 3 Same as the device used in Example 1, except that instead of the detector, a portammetry cell, a Cou-α measurement cell, and an absorbance cell for monitoring the ferric compound concentration were connected in series. We measured the battery active material concentration in the catholyte and the depth of charge using a small cell device with a similar configuration, and at the same time examined the correlation of these measurement results with the portammetry cell. As a result, it was found that both the coulometry cell and the absorbance cell had a good correlation with the portammetry cell, and therefore, it became clear that they could be satisfactorily used as a detector in the present invention.

As described above, according to the present invention, the concentration of ferrous compounds and ferric compounds contained in the catholyte of a redox flow type secondary battery is measured to detect an overcharged state of the catholyte, and the overcharge state of the catholyte is also detected. Based on the structure, excess ferric compounds in the positive electrode solution are reduced to ferrous compounds, and FI
ii) It is possible to match the charging and discharging conditions between the polar liquids, which allows for long-term use.

It becomes possible to repeat charging and discharging cycles over a period of time.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a redox flow related secondary battery device according to an embodiment of the present invention, FIG. 2 is a side sectional view of a portammetry cell applied as an example of the detector shown in FIG. 3
The figure is a current-voltage curve diagram when the voltage sweep method is applied to the volumometric cell of Figure 2, and Figure 4 is a system diagram of a redox flow type secondary battery device according to another embodiment of the present invention. It is. Explanations of the symbols in the figure are as follows. 1... (Positive electrode overcharge) detector, 2... Positive electrode liquid line, 3... Negative electrode liquid line, electrolyte line, 6... Hydrogen gas cylinder, 7... Redox flow type cell, 8
... Positive electrode good, 9... Negative electrode chamber, 10.10 people... Cation exchange membrane, 11... Rebalance cell, 12...
Positive electrode liquid active material reduction chamber, 13... hydrogen gas reaction chamber, 14
．． 14A, 141.142.143.144...Circulation pump, 16...Working electrode, 17...Counter electrode, 18...
- Positive electrode liquid inlet, 19... Positive electrode liquid outlet, 20... Open circuit voltage measurement cell, 21... Battery stack, 22... Positive electrode liquid tank, 23... Negative electrode liquid tank, 24... Electrolysis liquid tank. Figure 3 0. 020 -0.2 -0.4 Voltage (V)

Claims (1)

[Scope of Claims] , (1) A method for operating a redox flow type secondary battery using a solution containing an iron compound selected from mutually convertible ferrous and ferric compounds as a positive electrode liquid, comprising: The overcharged state of the catholyte is detected by measuring the concentration of ferrous and ferric compounds, and based on the detected pressure, excess ferric compounds in the catholyte are reduced to ferrous compounds to form a positive electrode. A method of operating a redox 70-G secondary battery characterized by transferring the liquid to a normal charging state. (2. Claim 1 is characterized in that the overcharge state of the catholyte is detected by a method selected from portammetry, coulometry, and spectrophotometry that utilizes optical absorption of iron complex ions. How to operate a redox flow type secondary battery.