KR20180036391A - Method for controlling operation of redox flow battery - Google Patents

Abstract

According to the invention, the present invention relates to a method for driving a first pump and a second pump for circulating an anode electrolyte and a cathode electrolyte respectively to the redox flow batteries. To this end, the method comprises the following steps: a first driving step of applying first voltage to a first pump and applying second voltage to a second pump; a second driving step of applying third voltage to the first pump and applying second voltage to the second pump; a third driving step of applying fourth voltage to the first pump and applying second voltage to the second pump; and a fourth driving step of applying first voltage to the first pump and applying second voltage to the second pump, wherein at least one of the third voltage and the fourth voltage is different from the first voltage.

Description

METHOD FOR CONTROLLING OPERATION OF REDOX FLOW BATTERY [0002]

The present invention relates to a redox flow cell, and more particularly, to a method for controlling redox flow cells.

The redox flow cell is an energy storage system that stores the generated power in a grid and supplies it at the required time to increase energy efficiency.

A redox flow cell is a stack comprising a bipolar electrode and a membrane which are repeatedly laminated, a laminate of a current collector plate and an end cap laminated on both sides of the outermost layer, and an electrolyte solution is supplied to the stack And an electrolyte tank for storing an electrolytic solution flowing out after the internal reaction in the stack.

The electrolyte contains an active material, which enables oxidation and reduction of the active material to enable charging and discharging, and is an important factor determining the capacity of the battery.

Among them, the electrolyte of the zinc / bromine flow cell is composed of zinc ions and bromide ions. In the case of bromide ions, bromine is converted to bromine at the time of charging. Since the solubility of bromine is low, it can easily be vaporized and lost. As a result, the amount of the reactant is reduced to deteriorate performance, or there is a safety risk.

In order to compensate for this, the bromine complex is formed by introducing a bromine complex to increase the solubility of bromine, thereby preventing loss of bromine and ensuring stability. However, by forming a bromine complex, the viscosity increases and changes the flowability and affects the internal pressure.

Also, in the case of zinc ions, the zinc ions are applied to the electrodes at the time of charging to narrow the gap between the channels, thereby changing the internal pressure, thereby causing a crossover phenomenon. Such a crossover phenomenon shortens the life of the battery.

Accordingly, it is an object of the present invention to provide a redox-flow battery in which the performance of a flow cell is not deteriorated by minimizing a crossover phenomenon even if charging and discharging proceed.

According to an aspect of the present invention, there is provided a method of driving a first pump and a second pump for circulating an anode electrolyte and a cathode electrolyte in a redox flow cell, A second driving step of applying a voltage of the second pump to a second voltage, a first driving step of applying a voltage of the second pump to a second voltage, a second driving step of applying a voltage of the first pump to a third voltage, A third driving step of applying a voltage of one pump to a fourth voltage and applying a voltage of the second pump to a second voltage and a third driving step of applying a voltage of the first pump to a first voltage, 2 voltage, and at least one of the third voltage and the fourth voltage is a voltage different from the first voltage.

Wherein the first driving step carries out charging from 30% to 80% of the completed charging amount from the start of charging the redox flow battery, the second driving step proceeds after the first driving step, The third driving step proceeds after the second driving step and proceeds from the discharge start of the redox flow battery to the first discharge voltage, and the fourth driving step is performed after the discharge start time of 30% to 80% 3 drive step, and may proceed from the first discharge voltage until the first drive step proceeds.

The redox flow cell includes a stack for generating current, a first pipe connected to the first pump for supplying the anode electrolyte to the stack, and a second pipe connected to the second pump for supplying the cathode electrolyte to the stack, In the first driving step, the pressure of the first pipe is higher than the pressure of the second pipe. In the second driving step and the third driving step, the pressure of the second pipe is higher than the pressure of the first pipe, The pressure of the first pipe may be higher than the pressure of the second pipe.

Wherein the second driving step is continued until the pressure difference between the first pipe and the second pipe becomes the first pressure difference and the third driving step is performed when the pressure difference between the first pipe and the second pipe becomes equal to the first pressure difference The pressure of the first pipe is higher than the pressure of the second pipe.

The first pressure difference may be greater than 0 and less than or equal to 1 Psi, and the third and fourth voltages may range from 17V to 24V.

The difference between the first voltage and the second voltage, the difference between the third voltage and the second voltage, and the difference between the fourth voltage and the second voltage may be less than 5V.

The third voltage may have a voltage value lower than the first voltage, and the fourth voltage may have a voltage value higher than the first voltage.

The stack of redox flow cells may comprise eight cells.

As in the present invention, when the voltage of the pump is varied according to the intervals during the course of charging / discharging, the crossover phenomenon can be reduced.

Therefore, it is possible to prevent the lifetime of the battery from being reduced due to the crossover phenomenon, thereby providing a long-life redox-flow battery.

1 is a schematic block diagram of a redox flow cell according to an embodiment of the present invention.
Figure 2 is an exploded perspective view of the stack applied to Figure 1;
3 is a cross-sectional view taken along line III-III in FIG.
4 is a cross-sectional view taken along the line IV-IV in Fig.
5 is a graph showing energy efficiency according to Comparative Examples and Examples.
6 is a graph showing the charge amount efficiency according to Comparative Examples and Examples.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. In the following detailed description, the names of components are categorized into the first, second, and so on in order to distinguish them from each other in the same relationship, and are not necessarily limited to the order in the following description. Throughout the specification, when an element is referred to as "comprising ", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise. It should be noted that terms such as " ... unit ", "unit of means "," part of item ", "absence of member ", and the like denote a unit of a comprehensive constitution having at least one function or operation it means.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram of a redox flow cell according to an embodiment of the present invention, FIG. 2 is an exploded perspective view of the stack applied to FIG. 1, and FIG. 3 is a cross- And Fig. 4 is a cross-sectional view cut along the line IV-IV in Fig.

1 and 2, a redox flow battery according to an embodiment of the present invention includes a stack 100, an electrolytic solution supplying unit 110 for supplying an electrolyte solution to the stack 100, And a circulation unit for connecting the electrolytic baths 200, 300, 400 and the electrolytic baths 200, 300, 400 to the stack 100.

The stack 100 may be connected to external charges through the bus bars B1 and B2 to discharge the current generated inside the stack 100. [

For example, the stack 100 can be formed by stacking a plurality of unit cells C1 and C2. For convenience of explanation, in the embodiment of the present invention, the first unit cell C1 and the second unit cell C2 located on both the left and right sides will be described as an example.

3 and 4, the stack 100 includes a membrane 10, a spacer 20, an electrode plate 30, a membrane flow frame 40, an electrode flow frame 50, a first current collector plate 61 A second current collecting plate 62, a first end cap 71, and a second end cap 72. The first end cap 62 and the second end cap 62 are electrically connected to each other.

Since the stack 100 has a plurality of unit cells C1 and C2, the two membrane flow frames 50, which are disposed at the center of the electrode flow frame 50 and are arranged in a symmetrical structure on both sides of the electrode flow frame 50, And a pair of first end caps 71 and second end caps 72, which are disposed on the outer periphery of the membrane flow frame 40, respectively.

The membrane 10 is configured to pass ions and is coupled to the center of the membrane flow frame 40 in the thickness direction, and the electrode plate 30 is coupled to the center in the thickness direction of the electrode flow frame.

The first end cap 71, the membrane flow frame 40, the electrode flow frame 50, the membrane flow frame 40 and the second end cap 72 are disposed and the membrane 10 and the electrode plate 30 The plurality of unit cells C1 to C2 are formed by bonding the membrane flow frame 40, the electrode flow frame 50 and the first and second end caps 71 and 72 to each other with the spacers 20 interposed therebetween. The stack 100 is formed.

The electrode plates 61 and 62 are formed such that the anode electrode 32 is formed on one side and the cathode electrode 31 is formed on the other side in the portion where the plurality of unit cells C1 and C2 are connected to form a plurality of unit cells C1 And C2 are connected in series to form a bipolar electrode. A carbon coating layer may be formed on the cathode electrode 31.

The membrane flow frame 40, the electrode flow frame 50 and the first end cap 71 are adhered to each other to set the internal volume S between the membrane 10 and the electrode plate 30, A first flow channel CH1 and a second flow channel CH2 for supplying an electrolyte solution to the first flow channel CH1 and the second flow channel CH2 are formed. The first flow channel CH1 and the second flow channel CH2 are configured to supply the electrolytic solution to both sides of the membrane 10 at a uniform pressure and amount, respectively.

The first channel channel CH1 connects the anode electrolyte solution inlet H21 and the internal volume S and the anode electrolyte solution outlet H22 so that the membrane 10 and the anode electrode 32 ) To allow the electrolyte to flow out after reaction with the anode electrolyte.

The second flow channel CH 2 connects the cathode electrolyte inlet H 31, the internal volume S and the cathode electrolyte outlet H 32 so that the membrane 10 and the cathode electrode 31 to allow the cathode electrolytic solution to flow out after the reaction.

The membrane flow frame 40, the electrode flow frame 50, the first end cap 71, and the second end cap 72 are made of an electrically insulating material including a synthetic resin component, .

The flow cell according to the present invention may be a zinc-bromine flow battery. During charging, a reaction as shown in [Equation 1] occurs between the membrane 10 and the cathode electrode 31, (2) may occur between the first electrode 32 and the second electrode.

[Equation 1]

2Br ^- → Br ₂ + 2e ^-

[Formula 2]

Zn ^{2 +} + 2e ^- → Zn

Conversely, during the discharge, a reverse reaction of [Equation 1] occurs between the membrane 10 and the cathode electrode 31, and an adverse reaction of [Equation 2] occurs between the membrane 10 and the anode electrode 32.

The first current collecting plate 61 and the second current collecting plate 62 collect current generated in the cathode electrode 31 and the anode electrode 32 or collect the current generated in the cathode electrode 31 and the anode electrode 32 And may be electrically connected to the outermost electrode plate 30 by bonding.

The first bus bar B1 and the second bus bar B2 are electrically connected to the first current collecting plate 61 and the second current collecting plate 62, Lt; RTI ID = 0.0 > 100 < / RTI >

The first end cap 71 receives a first current collecting plate 61 connected to the first bus bar B1 and an electrode plate 30 connected to the first current collecting plate 61, . The first end cap 71 may be integrally formed with the first current collecting plate 61 and the electrode plate 30 of the bus bar B1 and may be integrally formed with the first current collecting plate 61, The plate 30 can be inserted and molded by insert injection.

The second end cap 72 includes a second current collecting plate 62 connected to the second bus bar B2 and an electrode plate 30 connected to the second current collecting plate 62, Can be formed. The second end cap 72 may be formed by insert injection by inserting the second bus bar B2, the second current collector plate 62, and the electrode plate 30. FIG.

The first end cap 71 has anode and cathode electrolyte inlets H21 and H31 on one side and is connected to the first and second flow channels CH1 and CH2 so as to introduce the anode electrolyte and the cathode electrolyte respectively. The second end cap 72 has anode and cathode electrolyte outlets H22 and H32 on one side and is connected to the first and second flow channels CH1 and CH2 to discharge the anode electrolyte and the cathode electrolyte.

1 and 2, the anode electrolytic bath 200 supplies an anode electrolytic solution between the membrane 10 and the anode electrode 32 of the stack 100, and the membrane 10 and the anode electrode 32, The anode electrolyte solution flowing out through the space between the anode and the cathode. The anode electrolyte may be an electrolytic solution containing zinc.

The cathode electrolyzer 300 supplies a cathode electrolytic solution between the membrane 10 and the cathode electrode 31 of the stack 100. The catholyte may be an electrolytic solution containing bromine.

The two-phase electrolytic bath 400 accommodates a cathode electrolytic solution (two-phase electrolytic solution) flowing out between the membrane 10 and the cathode electrode 31 of the stack 100. The electrolytic solution of the two-phase electrolytic bath 400 can be separated into two phases depending on the specific gravity by the cathode electrolytic solution flowing out between the membrane 10 and the cathode 31. Of these, the middle dibromin is located at the bottom of the two-phase electrolyzer and the aqueous bromine is located at the top of the two-phase electrolyzer.

The two-phase electrolytic bath 400 may be connected to the cathode electrolytic bath 200 via an orb flow pipe (not shown), and the aqueous bromine located above the two-phase electrolytic bath 400 may be connected to the cathode electrolytic bath 300 ). ≪ / RTI > At this time, one end of the overflow pipe located in the cathode electrolytic bath 300 may be disposed adjacent to the water surface of the cathode electrolyzer 300, or may be disposed so as to be submerged in the water surface to minimize the generation of air bubbles in the electrolytic solution due to the falling of the electrolytic solution .

The circulation unit may include a plurality of pipes L21, L22, L31, L32, L41 and pumps P1, P2. An anode outlet H22 of the anode electrolyzer 200 and the anode outlet H22 of the stack are connected to a second pipe L22, The electrolytic bath 300 is connected to the cathode inlet H31 of the stack by a third pipe L31 and the cathode outlet H32 and the two-phase electrolytic bath 400 are connected to each other through a fourth pipe L32. At this time, the first pump L21 and the third pipe L31 may be provided with a first pump P1 and a second pump P2, respectively, and may be supplied to the first and second pumps P1 and P2 The electrolytic solution can be controlled by the valves V1 and V2.

The third pipe L31 connecting the cathode electrolyzer 300 and the cathode inlet H31 may further include a branch pipe L41 branched from the branch pipe and connected to the two-phase electrolytic bath 400. [ A two-way valve 500 may be installed in branch pipe L41.

The first pipe L21 and the third pipe L31 may be provided with pressure sensors PP1 and PP2 respectively and the second pipe L22 and the fourth pipe L32 may be provided with pressure sensors Can be installed. The voltages of the first pump P1 and the second pump P2 can be adjusted according to the measured pressure.

Specifically, the pressure until the battery is discharged after being charged can be changed to the first pressure section, the second pressure section, the third pressure section, the fourth pressure section and the fifth pressure section.

The pressure of the first pipe L21 is higher than the pressure of the third pipe L31 and the pressure of the first pipe L21 is higher than the pressure of the third pipe by more than 0 psi and less than 1 psi, The fourth pressure section is a section in which the pressure of the third pipe L31 is higher than the pressure of the first pipe L21 and the pressure of the first pipe L21 is a pressure section of the third pipe L31, In a section above the pressure, the pressure of the first pipe is higher than 0 psi and less than 1 psi below the pressure of the third pipe.

In this case, the second pressure interval may be up to 0 psi and less than 1 psi until the pressure difference between the first pipe L21 and the third pipe L31 becomes the first pressure difference. The third pressure section may have a pressure difference between the first pipe L21 and the third pipe L31 having a second pressure difference and the second pressure difference may have a pressure difference greater than 1 psi, For example, greater than 1 psi and less than 2 psi. The fourth pressure section may be a section in which the pressure difference between the first pipe L21 and the third pipe L31 has a first pressure difference.

The first pump P1 and the second pump P2 may be a DC pump. The first pump P1 and the second pump P2 may be powered by a separate power source. . The power produced in the stack 100 may be converted to a power source for driving the pump through a DC-DC converter (not shown) and then supplied to the pump.

The amount of the anode electrolyte and the cathode electrolyte supplied to the stack 100 may be varied according to the pumping operation of the first pump P1 and the second pump P2. In the embodiment of the present invention, The first pump P1 and the second pump P2 can be driven at different voltages in four stages.

Specifically, a first driving step of applying a voltage of the first pump to a first voltage and a voltage of the second pump to a second voltage, applying a voltage of the first pump to a third voltage, A third driving step of applying the voltage of the first pump to the fourth voltage and the voltage of the second pump to the second voltage, a second driving step of applying the voltage of the first pump to the second voltage, And a fourth driving step of applying the voltage of the second pump to the first voltage and the voltage of the second pump to the second voltage. At this time, at least one of the third voltage and the fourth voltage may be different from the first voltage. That is, the third voltage may be lower than the first voltage, and the fourth voltage may be higher than the first voltage. At this time, the third voltage and the fourth voltage may range from 17V to 24V.

The first driving step carries out charging from 30% to 80% of the completed charging amount from the beginning of charging the redox flow battery, the second driving step proceeds after the first driving step, % To 80%, and proceeds until the discharge starts. The third driving step proceeds after the second driving step, proceeds from the discharge start of the redox flow battery to the first discharge voltage, May be performed after the third driving step, and may proceed from the first discharge voltage until the first driving step proceeds again.

At this time, the first driving step proceeds in the first pressure section, the second driving step proceeds in the second pressure section, the third driving step proceeds in the third pressure section and the fourth pressure section, Lt; RTI ID = 0.0 > 5 < / RTI > Therefore, the first discharge voltage is the discharge voltage when the fourth pressure interval is changed to the fifth pressure interval.

For example, in the case of a stack having eight unit cells, the first driving step starts to charge and proceeds to 40Ahr / cell which is 50% of the full charge amount, and the pressure of the first pipe is higher than the pressure of the third pipe to be. The second driving step proceeds from 40 Ahr / cell after the start of charging to 80 Ahr / cell until the discharge is completed, and the pressure of the third pipe is higher than the pressure of the first pipe. The third driving step is started until the discharge voltage reaches the first discharge voltage of 0.75 V / cell, and the pressure of the third pipe is higher than the pressure of the first pipe. The fourth section may proceed below the first discharge voltage of 0.75 V / cell, and the pressure of the first pipe is higher than the pressure of the third pipe.

At this time, the first voltage may be 19V, the second voltage may be 17V to 24V, the third voltage may be 20V, and the first voltage and the second voltage may be less than 5V in voltage difference from the third voltage. If the second voltage is less than 17V, the flow of the electrolytic solution is not smooth and the electrolyte may not be delivered to the inside of the stack. When the voltage difference between the first voltage, the third voltage, the fourth voltage and the second voltage is 5V or more, the pressure difference between the first pump and the second pump causes a pressure difference inside the stack, thereby increasing the crossover phenomenon The electrolyte may not flow into the electrode, thereby causing a side reaction in the electrode, thereby damaging the battery.

Comparison of energy efficiency and charge efficiency

2.25 M zinc / bromine electrolytes were used in a zinc / bromododox flow cell having stacks of eight unit cells shown in FIG. At this time, the charge completion charge amount was 80 Ah / cell and the first discharge voltage was set to 0.75 V / cell to perform charge and discharge.

The first section starts charging and extends to 40Ahr / cell. The second section is a section from 40Ahr / cell after the start of charging to 80Ahr / cell before completion of charging. The third section starts discharge and the first discharge Cell is a period until the voltage reaches 0.75 V / cell, and the fourth period is a period that is less than the first discharge voltage.

Energy efficiency, voltage efficiency, and charge efficiency can be obtained from Equation 3, Equation 4, and Equation 5, respectively.

[Formula 3]

Energy Efficiency (EE) = (discharge energy (Wh) / charge energy (Wh)) * 100

[Formula 4]

Voltage Efficiency (VE) = (energy efficiency / charge efficiency) * 100

[Formula 5]

Current Efficiency (CE) = (Discharging Capacity (Ah) / Charging Capacity (Ah)) * 100

[Comparative Example]

The first pump in the first section, the second section, the third section and the fourth section was 19V while the second pump was maintained constant at 20V.

[Example 1]

The first pump is driven at 19V in the first section, 18.8V in the second section, 19V in the third section, and 19V in the fourth section, and the second pump is maintained constant at 20V in the first section to the fourth section Charging and discharging were carried out.

[Example 2]

Charging and discharging were carried out under the same conditions as in Example 1 except that 19 V was driven in the second section of the first pump and 19.3 V in the third section in the first embodiment.

[Example 3]

Charging and discharging were carried out under the same conditions as in Example 1, except that the first pump was driven at 18.8 V in the second section and 19.3 V in the third section in the first embodiment.

FIG. 5 is a graph showing energy efficiency according to Comparative Examples and Examples, and FIG. 6 is a graph showing charge efficiency according to Comparative Examples and Examples.

Referring to FIG. 5, it can be seen that the energy efficiencies of Examples 1, 2, and 3 are higher than those of Comparative Example 1. Also, referring to FIG. 6, it can be seen that the charge amount efficiency of Examples 1, 2, and 3 is higher than the charge amount efficiency of Comparative Example 1.

As described above, the voltage of the first pump and the voltage of the second pump are changed step by step during the course of charge / discharge as in the present invention, thereby minimizing the occurrence of crossover. Therefore, the crossover phenomenon is reduced, so that the lifetime of the flow cell can be increased.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, And it goes without saying that the invention belongs to the scope of the invention.

10: membrane 20: spacer
30: electrode plate 31: cathode electrode
32: anode electrode 40: membrane flow frame
50: electrode flow frame 61, 62: first and second collectors
71, 72: first and second end caps 100: stack
200: anode electrolyzer 300: cathode electrolyzer
400: Two phase electrolyzer

Claims (9)

A method of driving a first pump and a second pump for circulating an anode electrolyte and a cathode electrolyte in a redox flow cell,
A first driving step of applying a voltage of the first pump to a first voltage and a voltage of the second pump to a second voltage,
A second driving step of applying a voltage of the first pump to a third voltage and applying a voltage of the second pump to a second voltage,
A third driving step of applying a voltage of the first pump to a fourth voltage and applying a voltage of the second pump to a second voltage,
A fourth drive step of applying a voltage of the first pump to a first voltage and applying a voltage of the second pump to a second voltage,
Lt; / RTI >
Wherein at least one of the third voltage and the fourth voltage is different from the first voltage. The method of claim 1,
Wherein the first driving step carries out charging from 30% to 80% of the completed charge amount from the start of charging the redox flow battery,
Wherein the second driving step is performed after the first driving step until the discharge starts from 30% to 80% of the completed charging amount of the redox flow battery,
Wherein the third driving step is performed after the second driving step and proceeds from a discharge start of the redox flow battery to a first discharge voltage,
Wherein the fourth driving step proceeds after the third driving step and proceeds from the first discharging voltage until the first driving step proceeds. 3. The method of claim 2,
The redox flow cell includes a stack for generating current, a first pipe connected to the first pump for supplying an anode electrolyte to the stack, a second pipe connected to the second pump for supplying a cathode electrolyte to the stack, Including,
In the first driving step, the pressure of the first pipe is higher than the pressure of the second pipe,
In the second driving step and the third driving step, the pressure of the second pipe is higher than the pressure of the first pipe,
Wherein in the fourth driving step, the pressure of the first pipe is higher than the pressure of the second pipe. 4. The method of claim 3,
The second driving step proceeds until the pressure difference between the first pipe and the second pipe becomes the first pressure difference,
Wherein the third driving step is performed after the pressure difference between the first pipe and the second pipe exceeds the first pressure difference until the pressure of the first pipe is higher than the pressure of the second pipe, A method of driving a battery. 5. The method of claim 4,
Wherein the first pressure difference is greater than 0 and less than or equal to 1 Psi. The method of claim 1,
Wherein the third voltage and the fourth voltage are in the range of 17V to 24V. The method of claim 6,
Wherein a difference between the first voltage and the second voltage, a difference between the third voltage and the second voltage, and a difference between the fourth voltage and the second voltage are less than 5V. The method of claim 6,
Wherein the third voltage has a voltage value lower than the first voltage and the fourth voltage has a voltage value higher than the first voltage. The method of claim 1,
Wherein the stack of redox flow cells comprises eight cells.

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