WO2016105130A1

WO2016105130A1 - Method and apparatus for controlling operation of redox flow battery

Info

Publication number: WO2016105130A1
Application number: PCT/KR2015/014194
Authority: WO
Inventors: 이지영; 홍민기; 예희창; 김수환
Original assignee: 오씨아이 주식회사
Priority date: 2014-12-23
Filing date: 2015-12-23
Publication date: 2016-06-30
Also published as: KR20160077530A

Abstract

The present invention relates to a method and an apparatus for controlling operation of a redox flow battery. The method for controlling operation of a redox flow battery according to one embodiment of the present invention comprises the steps of: measuring the initial internal resistance value of a cell module of a redox flow battery; determining whether or not the amount of change in the internal resistance value of the cell module relative to the initial internal resistance value exceeds a first reference value; and if the change amount exceeds the first reference value, controlling flow of an electric current applied to the cell module so that the potential difference between a (+) electrode and a (-) electrode of the cell module becomes smaller than a predetermined reference potential difference. The present invention has an advantage in that the efficiency of a redox flow battery can be enhanced by properly removing solid-state precipitates generated in the course of operation of the redox flow battery.

Description

Operation control method and apparatus of redox flow battery

The present invention relates to a method and apparatus for controlling operation of a redox flow battery.

The redox flow battery is a kind of secondary battery, and converts chemical energy into electrical energy or converts electrical energy into chemical energy through a charging or discharging process. However, in the conventional secondary battery, the material constituting the electrode itself participates in the oxidation / reduction reaction, whereas in the redox flow battery, the electrolyte contained in the electrolyte flowing on the electrode surface causes the oxidation / reduction reaction to perform charging and discharging. There is a difference. Accordingly, the redox flow battery may set the charge or discharge capacity by adjusting the electrode area and the volume of the electrolyte.

Such a redox flow battery is gradually reduced in efficiency as charging or discharging is repeatedly performed. The most important cause of the deterioration of the redox flow cell is the increase in the internal resistance of the cell. The increase in the internal resistance of the battery includes deterioration of the battery material, an increase in contact resistance, inflow of foreign substances, and a decrease in the reactivity of the electrode.

In particular, at the end of the charging or discharging process of the redox flow battery, the ion concentration of the electrolyte contained in the electrolyte rapidly increases locally, thus depositing the oxide of the electrolyte in the solid form on the surface of the electrode. As such, when a solid precipitate is formed on the surface of the electrode, the surface area of the electrode involved in the oxidation / reduction reaction is reduced, which leads to a decrease in the reactivity of the electrode.

According to the related art, in order to remove precipitates generated during operation of the redox flow battery, the electrolyte concentration and operating temperature are limitedly set, or the state of charge (SOC) of the battery is limited to a predetermined level or less. In addition, in order to remove such precipitates, an alkaline solution may be incorporated into a battery, or a method may be used in which an electrode is decomposed and washed with a cleaning solution or the like. However, the conventional method of limiting the operation conditions of the redox flow battery or stopping the operation has a problem of causing another efficiency degradation of the redox flow battery.

An object of the present invention is to provide a method and apparatus for controlling the operation of a redox flow battery which can increase the efficiency of the redox flow battery by appropriately removing the solid form precipitates generated during the operation of the redox flow battery.

Another object of the present invention is to provide a method and apparatus for controlling the operation of a redox flow battery which can increase the efficiency of the redox flow battery by removing precipitates without limiting the operation conditions of the redox flow battery or stopping the operation.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention, which are not mentioned above, can be understood by the following description, and more clearly by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

In order to achieve the above object, the present invention provides a method for controlling an operation of a redox flow battery, the method comprising: measuring an initial internal resistance value of a cell module of the redox flow battery; Determining whether the change amount of the resistance value exceeds the first reference value, and when the change amount exceeds the first reference value, the potential difference between the positive electrode and the negative electrode of the cell module is smaller than a predetermined reference potential difference. And controlling the flow of current applied to the cell module.

In another aspect of the present invention, the operation control device of the redox flow battery, the measuring unit for measuring the initial internal resistance value of the cell module of the redox flow battery and the amount of change of the internal resistance value of the cell module relative to the initial internal resistance value It is determined whether the first reference value is exceeded, and if the change amount exceeds the first reference value, the potential difference between the positive electrode and the negative electrode of the cell module is smaller than a predetermined reference potential difference. It is another feature that the control unit for controlling the flow of the current applied to the cell module.

According to the present invention as described above, there is an advantage that the efficiency of the redox flow battery can be improved by appropriately removing the solid form precipitates generated during the operation of the redox flow battery.

In addition, according to the present invention there is an advantage that the efficiency of the redox flow battery can be improved by removing the precipitate without limiting the operation conditions or stop operation of the redox flow battery.

1 is a block diagram of an operation control apparatus of a redox flow battery and a redox flow battery according to an embodiment of the present invention.

2 is a flowchart illustrating an operation control method of a redox flow battery according to an exemplary embodiment of the present invention.

3 is a graph showing a general charge and discharge curve of the redox flow battery.

4 is a graph showing a charge and discharge curve of the redox flow battery appearing according to the operation control of the redox flow battery according to an embodiment of the present invention.

5 is a graph showing a charging curve of a redox flow battery according to the prior art and the redox flow battery according to the operation control of the redox flow battery according to an embodiment of the present invention.

6 is a graph showing a discharge curve of the redox flow battery according to the prior art and the redox flow battery according to the operation control of the redox flow battery according to an embodiment of the present invention.

7 is a graph illustrating voltage efficiency before and after performing the operation control of the redox flow battery according to an embodiment of the present invention.

The above objects, features, and advantages will be described in detail with reference to the accompanying drawings, whereby those skilled in the art to which the present invention pertains may easily implement the technical idea of the present invention. In describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

Referring to FIG. 1, a redox flow battery includes a positive electrode tank 102, a negative electrode tank 104, a cell module 106, a positive electrode pump 114, and a negative electrode pump ( 116). A positive electrode electrolyte containing a positive electrode electrolyte is stored in the positive electrode tank 102, and a negative electrode electrolyte containing a negative electrode electrolyte is stored in the negative electrode tank 104. do. In addition, the positive electrode pump 114 moves the positive electrode electrolyte stored in the positive electrode tank 102 into the cell module 106, and the positive electrode electrolyte passing through the cell module 106 is again returned. Return to the positive electrode tank 102. Similarly, the negative electrode pump 116 moves the negative electrode electrolyte stored in the negative electrode tank 104 into the cell module 106, and the negative electrode electrolyte passing through the cell module 106 is again returned. Return to the negative electrode tank 104.

In one embodiment of the present invention, the redox flow battery uses vanadium ions as the electrolyte, and V ⁵⁺ and V ⁴⁺ are used as the (+) electrode electrolyte stored in the (+) electrode tank 102 (- ) V ³⁺ and V ²⁺ are used as the ^negative electrode electrolyte stored in the electrode tank 104. When the same element is used as the positive electrode electrolyte and the negative electrode electrolyte, respectively, the same element is relatively free of contamination of the electrolyte, no side reaction occurs, and the electrode can be electrochemically regenerated.

Referring back to FIG. 1, the cell module 106 includes a positive electrode 110, a negative electrode 112, and an ion exchange membrane 108. The positive electrode 110 and the negative electrode 112 are connected to the power supply 118, respectively, and the power supply 118 is connected to the second direction 12, that is, to charge the cell module 106. -) Supply current so that current flows from the electrode to the (+) electrode. The ion exchange membrane 108 prevents mixing between the positive electrode electrolyte and the electrolyte ions contained in the negative electrode electrolyte in the cell module 106, and allows only the transfer of charge carrier ions of each electrolyte. In addition, when the redox flow battery is discharged, a load (not shown) may be connected to the cell module 106. In this case, a current may flow in the first direction 11, that is, in the positive electrode. Flow toward the negative electrode.

A direct cause of lowering the efficiency of the redox flow battery as shown in FIG. 1 is an increase in the internal resistance of the battery. Increasing the internal resistance of the battery is caused by deterioration of the battery material, an increase in contact resistance, inflow of foreign matter and a decrease in reactivity of the electrode. In particular, in the operation of the redox flow battery as shown in FIG. 1, the concentration of each vanadium ion is locally increased at the end of the charging and discharging process, and the vanadium oxide is solid on the

electrodes

110 and 112 surface. Precipitates. As such, when solid precipitates are formed on the surfaces of the

electrodes

110 and 112, the surface area to which the electrodes can react is reduced, which causes a decrease in reactivity of the

electrodes

110 and 112.

When charging occurs due to supply of current through the power supply unit 118 to the redox flow battery illustrated in FIG. 1 or discharge occurs due to connection of a load, the reactions occurring in the cell module 106 are as follows.

- (+) electrode: V → V ⁵⁺ ⁴⁺ + e ^-

- (-) ^{^{electrodes: V 3+ + e - → V}} 2+

- (+) ^{^{electrode: V 5+ + e - → V}} 4+

- (-) ^{^{electrodes: V 2+ → V 3+ + e}} -

That is, V ⁵⁺ and V ⁴⁺ ions are present at the (+) electrode of the redox flow battery, and V ³⁺ and V ²⁺ ions are present at the (−) electrode, and the electromotive force of the redox flow battery is About 1.4V. However, V ⁵⁺ ions present in the (+) electrode tend to be precipitated because they have low solubility compared to V ⁴⁺ ions. Therefore, when charging reaction occurs in the redox flow battery according to the current supply by the power supply 118, when there are more V ⁵⁺ ions than V ⁴⁺ ions in the (+) electrode, V ⁵⁺ ions are positive (+) It may precipitate in a solid form on the surface of the electrode 110.

When such a solid precipitate is formed on the surface of the positive electrode 110, the reactivity of the electrode 110 decreases, which leads to an increase in internal resistance of the redox flow battery. The operation control apparatus 120 of the redox flow battery according to the exemplary embodiment of the present invention removes the precipitates thus generated through an electrochemical method.

Referring back to FIG. 1, an operation control apparatus 120 of a redox flow battery according to an embodiment of the present invention includes a measuring unit 122 and a control unit 124. The measuring unit 122 measures an initial internal resistance value of the cell module 106. In one embodiment of the present invention, the measurement unit 122 measures the voltage, the open circuit voltage (OCV) and the current of the cell module 106 in real time, and the internal resistance value of the cell module 106 according to the following equation. Can be calculated.

[Equation 1]

R = (V _AVR -OCV _AVR ) / I

In Equation 1, R is the internal resistance value of the cell module 106, V _AVR is the average voltage value of the cell module 106, OCV _AVR is the average OCV value of the cell module 106, I is the cell module 106 Indicates the current flowing through The reason for using the average voltage value and the average OCV value of the cell module 106 in [Equation 1] is that the number of cells included in the cell module 106 may vary according to the configuration of the redox flow battery, This is because the voltage value of each cell included in the cell module 106 is calculated differently depending on whether the connection is serial or parallel.

The controller 124 uses the initial internal resistance value of the cell module 106 and the internal resistance value of the cell module 106 measured by the measuring unit 122 to determine the internal value of the cell module 106. The amount of change in the resistance value can be calculated. The controller 124 determines whether the change amount of the internal resistance value calculated as described above exceeds the first reference value, and when the change amount of the internal resistance value exceeds the first reference value, (+) of the cell module 106. The flow of current applied to the cell module is controlled such that the potential difference between the electrode 110 and the negative electrode 112 is smaller than a predetermined reference potential difference. In one embodiment of the present invention, the reference potential difference may be defined as the potential difference between the positive electrode 110 and the negative electrode 112 when the discharge of the redox flow battery is completed. At this time, in one embodiment of the present invention, the control unit 124 is the power supply unit 118 so that the potential difference between the (+) electrode 110 and the (-) electrode 112 of the cell module 106 is smaller than the reference potential difference. ) May supply current in the second direction 12.

In an embodiment of the present invention, the first reference value R1 may be defined as follows.

[Equation 2]

R1 = R _I × a

In Equation 2, R _I represents an initial resistance value of the cell module 106 and a is a predetermined constant (eg, 1.05). As shown in Equation 2, since the first reference value R1 is a value determined by the initial resistance value R _I , it may vary depending on the configuration of the redox flow battery.

In one embodiment of the present invention, the control unit 124 is a cell module such that the potential difference between the (+) electrode 110 and the (-) electrode 112 of the cell module 106 is smaller than the reference potential difference only during a predetermined control time. The flow of current applied to 106 may be controlled.

In one embodiment of the present invention, the controller 124 is applied to the cell module 106 such that the potential difference between the positive electrode 110 and the negative electrode 112 of the cell module 106 is smaller than the reference potential difference. When the change in the internal resistance value of the cell module 106 measured after controlling the flow of current is less than the second reference value, the potential difference between the positive electrode 110 and the negative electrode 112 of the cell module 106 is determined. May control the flow of current applied to the cell module 106 to be greater than the reference potential difference. For example, the control unit 124 continuously measures the change amount of the internal resistance value of the cell module 106 after causing the power supply unit 118 to supply current in the second direction 12, and the measured change amount is the second reference value. If it is determined to fall down, the power supply unit 118 supplies the current in the first direction 11 again, so that the potential difference between the positive electrode 110 and the negative electrode 112 of the cell module 106 is reduced. It can be made larger than the reference potential difference.

In one embodiment of the present invention, the second reference value R2 may be defined as follows.

[Equation 3]

R2 = R _I × b

In Equation 3, R _I represents an initial resistance value of the cell module 106 and b is a predetermined constant (eg, 1.005). As shown in Equation 3, since the second reference value R2 is a value determined by the initial resistance value R _I , it may vary depending on the configuration of the redox flow battery.

First, the measurement unit 122 measures an initial internal resistance value of the cell module 106 (202). Then, the control unit 124 measures the amount of change in the internal resistance value of the cell module 106 with respect to the initial internal resistance value (204). To this end, the measurement unit 122 may measure the internal resistance of the cell module 106 in real time, and the controller 124 may calculate the difference between the measured internal resistance and the initial internal resistance as a change amount of the internal resistance. Can be.

Next, the controller 124 determines whether the calculated amount of change in internal resistance exceeds a preset first reference value (206). If the determination 206 results in that the internal resistance change amount does not exceed the first reference value, step 204 is performed again. However, as a result of the determination 206, when the internal resistance change amount exceeds the first reference value, the controller 124 determines that the potential difference between the positive electrode 110 and the negative electrode 112 of the cell module 106 is smaller than the reference potential difference. Control the flow of current applied to the cell module 106 (208).

When the redox flow battery of FIG. 1 operates normally, the power supply unit 118 flows current to the positive electrode 110 and the negative electrode 112 in the first direction 11. 3 is a graph showing a general charge and discharge curve of the redox flow battery. In Figure 3, point 302 represents the point where the discharge begins. As described above, when the current is supplied in the second direction 12 by the power supply unit 118, the charging of the redox flow battery proceeds, and the potential difference between the positive electrode and the negative electrode is 1.6V to 1.6V. To increase. Thereafter, when the load is connected to the cell module 106 at the point 302 and the discharge starts, the potential difference decreases to 1V again. In the present invention, the potential difference (for example, 1 V) when the discharge of the redox flow battery is completed as described above can be set as the reference potential difference.

4 is a graph showing a charge and discharge curve of the redox flow battery appearing according to the operation control of the redox flow battery according to an embodiment of the present invention. The curves before point 1 and after point 7 in FIG. 4 represent the general charge and discharge curves as in FIG. 3.

When the internal resistance change amount exceeds the first reference value as a result of determining whether the internal resistance change amount calculated in FIG. 2 exceeds a preset first reference value (206), the controller 124 may determine the intervals 1 to 4 of FIG. 2. Likewise, the flow of current flowing in the cell module 106 is controlled so that the potential difference between the positive electrode 110 and the negative electrode 112 is smaller than the reference potential difference, that is, the potential difference (for example, 1 V) at the time when discharge is completed. . As a result, the potential difference of the cell module 106 gradually decreases below zero from the reference potential difference.

When the control unit 124 controls the potential difference between the (+) electrode 110 and the (−) electrode 112 to be smaller than the reference potential difference as shown in the sections 1 to 4 of FIG. 2, the (+) electrode 110 In Reaction:

^{^{- V 4+ + e - → V}} 3+

^{^{- V 3+ + e - → V}} 2+

In addition, in the sections 1 to 4, the following reaction occurs in the negative electrode 112.

^{^{- V 3+ → V 4+ + e}} -

^{^{- V 4+ → V 5+ + e}} -

By this reaction, the electrolyte present in the (+) electrode and the electrolyte present in the (-) electrode are completely changed from each other, so that V ⁵⁺ and V ⁴⁺ ions are present in the (-) electrode, and V in the (+) electrode. ³⁺ and V ²⁺ ions are present. Accordingly, the generation of solid precipitates generated from the (+) electrode 110 during charging of the redox flow battery may be prevented, so that the reactivity of the (+) electrode 110 may be restored.

Meanwhile, in one embodiment of the present invention, the controller 124 is applied to the cell module 106 such that the potential difference between the positive electrode 110 and the negative electrode 112 of the cell module 106 is smaller than the reference potential difference. If the amount of change in the internal resistance value of the cell module 106 measured after controlling the flow of the current to be less than the second reference value, the (+) electrode 110 and (-) electrode 112 of the cell module 106 The flow of current applied to the cell module 106 may be controlled such that the potential difference is greater than the reference potential difference. For example, the controller 124 continuously measures the amount of change in the internal resistance of the cell module 106, and if it is determined that the measured amount of change in the internal resistance falls below the second reference value, the sections 1 to 4 in the cell module 106. The current flows in the opposite direction to () so that the potential difference between the positive electrode 110 and the negative electrode 112 of the cell module 106 becomes larger than the reference potential difference as shown in the section 4 to 7 of FIG. 4. Can be. In the periods 4 to 7, the following reactions occur in the positive electrode 110.

^{^{- V 2+ → V 3+ + e}} -

^{^{- V 3+ → V 4+ + e}} -

In addition, the following reactions occur in the negative electrode 112 in the intervals 4 to 7.

^{^{- V 5+ + e - → V}} 4+

^{^{- V 4+ + e - → V}} 3+

As a result, the potential difference of the redox flow battery after the point 7 may be restored to the reference potential difference or more, and the normal charging and discharging process may be performed again.

5 is a graph showing a charging curve of a redox flow battery according to the prior art and the redox flow battery according to the operation control of the redox flow battery according to an embodiment of the present invention, Figure 6 is a prior art Is a graph showing a discharge curve of a redox flow battery according to the present invention and a redox flow battery according to an operation control of the redox flow battery according to an embodiment of the present invention.

Curve 502 in FIG. 5 shows the charging curve in the second cycle after the start of the operation of the redox flow battery, and curve 602 in FIG. 6 shows the discharge curve in the second cycle after the start of the operation of the redox flow battery. Indicates.

In addition, curve 504 in FIG. 5 shows a charging curve at the 103rd cycle after the start of operation of the redox flow battery, and curve 604 in FIG. 6 shows a discharge curve at the 103rd cycle after the start of operation of the redox flow battery. Indicates. As can be seen from FIG. 5 and FIG. 6, when the operating cycle of the redox flow battery increases, a larger voltage appears even though the same current flows during charging due to an increase in the internal resistance of the battery. Even if you pass, smaller voltage appears.

Meanwhile, the curve 506 of FIG. 5 and the curve 606 of FIG. 6 respectively correspond to the positive electrode 110 and the negative electrode 112 according to the operation control method of the redox flow battery according to the exemplary embodiment of the present invention. The charge and discharge curves at the 105 th cycle are respectively shown after controlling the potential difference of) to be smaller than the reference potential difference. As shown in FIGS. 5 and 6, when the operation control method of the redox flow battery according to the present invention is applied, the charge and discharge curves similar to those of the charge and discharge

curves

502 and 602 at the second cycle are reduced due to the decrease in the internal resistance of the battery. Discharge curves 506 and 606 reappear.

Referring to FIG. 7, it can be seen that as the operation cycle of the redox flow battery increases from the second cycle to the 100th cycle, the voltage efficiency of the battery decreases from 89.7% to 85% due to the increase in internal resistance.

Meanwhile, in FIG. 7, the point Q is such that the potential difference between the positive electrode 110 and the negative electrode 112 is smaller than the reference potential difference according to the operation control method of the redox flow battery according to the exemplary embodiment of the present invention. It represents the time point at which control is performed. As shown in FIG. 7, the internal resistance of the redox flow battery is reduced based on the point Q, and the voltage efficiency is restored to 89.8%.

As shown in Figure 5 to 7, according to the operation control method of the redox flow battery according to an embodiment of the present invention by removing the precipitate when the reactivity of the electrode due to the precipitate of the electrolyte appearing in the charging process of the electrode By regenerating the reactivity, the efficiency of the battery can be easily recovered.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by.

Claims

In the operation control method of the redox flow battery,

Measuring an initial internal resistance of a cell module of the redox flow battery;

Determining whether a change amount of an internal resistance value of the cell module with respect to the initial internal resistance value exceeds a first reference value; And

Controlling the flow of current applied to the cell module such that the potential difference between the positive electrode and the negative electrode of the cell module becomes smaller than a predetermined reference potential difference when the amount of change exceeds the first reference value.

Operation control method of a redox flow battery comprising.
The method of claim 1,

Determining whether the change amount of the internal resistance value of the cell module with respect to the initial internal resistance value exceeds a first reference value

Measuring the internal resistance value using an average voltage, an average OCV, and a current of the cell module; And

Calculating a difference between the measured internal resistance value and the initial internal resistance value;

Operation control method of a redox flow battery comprising.
The method of claim 1,

Controlling the flow of the current

Controlling the flow of the current so that a current flows from the (+) electrode toward the (−) electrode after discharge of the redox flow battery is completed.

Operation control method of a redox flow battery comprising.
The method of claim 1,

Controlling the flow of the current

Controlling the flow of current applied to the cell module such that the potential difference is less than the reference potential difference only during a preset control time.

Operation control method of a redox flow battery comprising.
The method of claim 1,

The potential difference is greater than the reference potential difference when the amount of change in the internal resistance value of the cell module measured after controlling the flow of current applied to the cell module to be smaller than the reference potential difference is less than a second reference value. Controlling the flow of current applied to the cell module

Operation control method of the redox flow battery further comprising.
In the operation control apparatus of the redox flow battery,

A measuring unit measuring an initial internal resistance of the cell module of the redox flow battery; And

It is determined whether the change amount of the internal resistance value of the cell module with respect to the initial internal resistance value exceeds a first reference value, and when the change amount exceeds the first reference value, the positive electrode of the cell module is determined. The control unit for controlling the flow of current applied to the cell module so that the potential difference between the (-) electrode is smaller than the predetermined reference potential difference

Operation control device of a redox flow battery comprising.
The method of claim 6,

The measuring unit

The internal resistance value is measured using the average voltage, average OCV, and current of the cell module.

The control unit

Calculate the difference between the measured internal resistance and the initial internal resistance

Operation control unit of redox flow battery.
The method of claim 6,

The control unit

After the discharge of the redox flow battery is completed to control the flow of the current so that the current flows from the (+) electrode toward the (-) electrode

Operation control unit of redox flow battery.
The method of claim 6,

The control unit

Controlling the flow of current applied to the cell module such that the potential difference is smaller than the reference potential difference only during a preset control time.

Operation control unit of redox flow battery.
The method of claim 6,

The control unit

The potential difference is greater than the reference potential difference when the amount of change in the internal resistance value of the cell module measured after controlling the flow of current applied to the cell module to be smaller than the reference potential difference is less than a second reference value. Controlling the flow of current applied to the cell module

Operation control unit of redox flow battery.