Flow battery purification

Abstract

The controller blocks the flow of the positive electrolyte through the positive electrode chamber of the flow battery to retain the positive electrolyte in the positive electrode chamber and hydraulically isolate the flow battery without stopping the flow of the negative electrolyte through the negative electrode chamber of the flow battery; when retaining the positive electrolyte in the positive electrode chamber, the flow battery discharges until hydrogen gas escapes at the reaction surface of the positive electrode chamber; and then stops discharging and restarts the flow of the positive electrolyte through the positive electrode chamber.

Description

Technical Field

[0001] The present invention relates to the control of a flow battery. Background Art

[0002] An electrochemical cell may include an anode side and a cathode side separated by a separator device. The anode side may include an anode current collector, an anode electroactive material (which oxidizes during discharge), and an electrolyte. The cathode side may include a cathode current collector, a cathode electroactive material (which reduces during discharge), and an electrolyte. The separator device separating the anode side and the cathode side allows ions to flow therebetween. The current collectors, electroactive materials, electrolyte, and separator device thus form an electrochemical reactor that converts chemical energy into electrical energy. The current collectors may be (externally) electrically connected together to form an electrical circuit. Summary of the Invention

[0003] A method for purifying a flow battery includes retaining a positive electrolyte solution in a positive electrode chamber of the flow battery to hydraulically isolate the flow battery without stopping the flow of a negative electrolyte solution through a negative electrode chamber of the flow battery; and discharging the flow battery while retaining the positive electrolyte solution in the positive electrode chamber such that successively charged species of the positive electrolyte solution in the positive electrode chamber are consumed, electrochemically obstructive transition metal contaminants on a reaction surface of the positive electrode chamber are electrochemically reduced and become electrochemically non-obstructive, and hydrogen gas escapes at the reaction surface over a predetermined period of time. The method further includes, after the predetermined period of time has ended, stopping the discharge and restarting the flow of the positive electrolyte solution through the positive electrode chamber.

[0004] A control system for a flow battery includes a controller that stops the flow of a positive electrolyte solution through a positive electrode chamber of the flow battery to retain the positive electrolyte solution in the positive electrode chamber and hydraulically isolate the flow battery without stopping the flow of a negative electrolyte solution through a negative electrode chamber of the flow battery. The controller also discharges the flow battery while retaining the positive electrolyte solution in the positive electrode chamber until hydrogen gas escapes at a reaction surface of the positive electrode chamber, and subsequently stops the discharge and restarts the flow of the positive electrolyte solution through the positive electrode chamber.

[0005] A control system for a flow battery includes a controller that stops the flow of a positive electrolyte solution through a positive electrode chamber of the flow battery without stopping the flow of a negative electrolyte solution through a negative electrode chamber of the flow battery. The controller also discharges the flow battery while the flow of the positive electrolyte solution through the positive electrode chamber is stopped, and after the voltage of the flow battery has remained at or below a threshold for at least a predetermined period of time, stops the discharge and restarts the flow of the positive electrolyte solution through the positive electrode chamber. Brief Description of the Drawings

[0006] Figure 1It is a schematic diagram of a flow battery system.

[0007] Figure 2 It is for purification Figure 1 flow chart of the control algorithm of the flow battery. Specific embodiments

[0008] Various embodiments are described herein. However, it should be understood that the disclosed embodiments are merely examples and other embodiments may employ various alternative forms. These figures are not necessarily to scale. Some features may be enlarged or reduced to show details of particular components. Accordingly, the specific structural and functional details disclosed herein should not be construed as limiting, but merely as a representative basis for those skilled in the art.

[0009] The various features illustrated and described in any one of the figures may be combined with the illustrated features in one or more other figures to produce embodiments that are not explicitly illustrated or described. Combinations of the illustrated features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desired for a particular application or embodiment.

[0010] A flow battery is a rechargeable battery in which an electrolyte containing one or more dissolved electroactive species flows (flows in and out) through an electrochemical reactor that converts chemical energy into electrical energy. An additional electrolyte containing one or more dissolved electroactive species is stored externally, typically in a tank, and is typically pumped through the electrochemical reactor (or reactors). Thus, a flow battery can have a capacity that varies according to the size of the external storage tank.

[0011] Referring to Figure 1 , the flow battery 10 may include a positive side 12 and a negative side 14 separated by a separator 16 (e.g., an ion exchange membrane). The positive side 12 includes a positive electrode chamber 18, a positive current collector 20, and a positive electrolyte reservoir 22. Similarly, the negative side 14 includes a negative electrode chamber 24, a negative current collector 26, and a negative electrolyte reservoir 28. The separator 16 allows ion flow between the electroactive materials in the positive electrode chamber 18 and the negative electrode chamber 24. Thus, the chambers 18, 24, the current collectors 20, 26, and the separator 16 form an electrochemical reactor 30 that converts chemical energy into electrical energy (and in some settings, electrical energy into chemical energy). Accordingly, the positive current collector 20 and the negative current collector 26 may be (externally) electrically connected (together or with other current collectors) to form an electrical circuit.

[0012] The positive electrolyte 32 and the negative electrolyte 34 are typically combined with electrolytes for transporting positive and negative reaction material ions, respectively, through soluble intermediates. The positive electrolyte 32 and the negative electrolyte 34 are circulated on the respective sides of the flow battery 10 to drive the reaction within the electrochemical reactor 30. Thus, the positive electrolyte 32 and the negative electrolyte 34 are movable. To this end, the positive side 12 further includes an inlet / outlet pipe 36 that is in fluid communication with the positive electrode chamber 18 and the positive electrolyte reservoir 22, and a circulation pump 38, a heat exchanger 40, and a valve 42 are each operably arranged with the inlet / outlet pipe 36. The circulation pump 38, as its name implies, circulates the positive electrolyte 32 through the positive electrode chamber 18, the positive electrolyte reservoir 22, and the inlet / outlet pipe 36. The heat exchanger 40 can be operated to control the temperature of the positive electrolyte 32. The valve 42 can be operated to control the inflow and / or outflow of the positive electrolyte 32 into and out of the positive electrode chamber 18.

[0013] The negative side 14 includes an inlet / outlet pipe 44, a circulation pump 46, a heat exchanger 48, and a valve 50. The inlet / outlet pipe 44 is in fluid communication with the negative electrode chamber 24 and the negative electrolyte reservoir 28, and the circulation pump 46, the heat exchanger 46, and the valve 50 are each operably arranged with the inlet / outlet pipe 44. The circulation pump 46 circulates the negative electrolyte 34 through the anode chamber 24, the anode electrolyte reservoir 28, and the inlet / outlet pipe 44. The heat exchanger 46 can be operated to control the temperature of the negative electrolyte 34. The valve 50 can be operated to control the inflow and / or outflow of the negative electrolyte 34 into and out of the negative electrode chamber 24.

[0014] The negative side 14 may include a slurry of zinc oxide and sodium hydroxide mixed in the negative electrolyte reservoir 28 to ensure maximum dissolution of the active material (zincate) in solution. This solution can be used as the negative electrolyte 34 of the flow battery 10. During charging, the soluble zincate reacts at the surface of the negative current collector 26, depositing zinc metal 52 on the surface of the negative current collector 26 (adjacent to the negative electrode chamber 24). During discharging, the load reverses the reaction, oxidizing the zinc metal 52 from the surface of the negative current collector 26. The discharge product is typically stored in the negative electrolyte reservoir 28, but it should be managed to ensure that it does not deposit elsewhere in the system.

[0015] One or more controllers 54 may operate circulation pumps 38, 46 and valves 42, 50 to flow positive electrolyte 32 and negative electrolyte 34 into and out of chambers 18, 24 and reservoirs 22, 28, respectively. Such flow typically requires control of the liquid flow and temperature. Accordingly, the flow battery 10 may include current, voltage, temperature, and / or other sensors arranged in a known manner with the electrochemical reactor 30, reservoirs 22, 28, etc., and they are in communication with one or more controllers 54 to facilitate control. For multiple cells (such as in a combined cell), a typical flow system can become more complex because multiple cells may use the same reservoir.

[0016] Normal operation of the flow battery 10 may result in charged species present in the positive electrolyte 32 and the formation of electrochemically obstructive transition metal decomposition products / contaminants (e.g., iron oxide contaminants) on the reactive surface of the positive current collector 20 (the surface partially defining the positive chamber 18). These contaminants limit the available reaction electrode surface area and impede the operation of the flow battery 10. Accordingly, an effective method for removing such contaminants is necessary to maintain the efficiency of the system.

[0017] See Figure 1 and Figure 2, during operation 56, the positive electrolyte is retained within the positive electrode chamber of the flow battery while maintaining the flow of the negative electrolyte through the negative electrode chamber of the flow battery. One or more controllers 54 may shut off pump 38 and close valve 42 to retain the positive electrolyte 32 within the positive electrode chamber 18, while valve 50 is opened to maintain the operation of pump 46 such that the negative electrolyte 34 continues to flow through the negative electrode chamber 24. During operation 58, the flow battery discharges while retaining the positive electrolyte within the positive electrode chamber. One or more controllers 54 may connect a load across the current collectors 20, 26 to discharge the flow battery 10. During operation 60, for at least a predetermined period of time (e.g., 20 seconds, etc.), it is determined whether hydrogen gas has escaped from the surface of the positive current collector. One or more controllers 54 may require that each cell voltage be at or below a predetermined voltage threshold (e.g., 300 millivolts), at which threshold it is known that hydrogen gas generation occurs at the positive current collector 20 for at least a predetermined period of time. The predetermined voltage threshold may be determined by simulation or testing and is different for different flow battery setups. If no, operation 60 is repeated. If yes, during operation 62, the flow battery discharge is stopped. One or more controllers 54 may disconnect the load from the current collectors 20, 26. During operation 64, then the flow of the positive electrolyte through the positive electrode chamber is restarted. One or more controllers 54 may open valve 42 and turn on pump 38. These operations may be performed periodically or as needed. Additionally, if the state of charge of the flow battery is less than a certain value (which may be determined by simulation or testing), these operations may be excluded: if the state of charge is too low, such retention and discharge may cause other problems.

[0018] Several processes occur during the discharge of the flow battery 10 while retaining the positive electrolyte 32 within the positive electrode chamber 18. First, the electroactive charged species (e.g., trivalent iron) dissolved in the positive electrolyte 32 within the positive electrode chamber 18 is consumed along with a corresponding amount of reactant in the negative electrolyte 34. This is the normal battery reaction. Once the electroactive charged species dissolved in the positive electrolyte 32 is consumed, there is still sufficient voltage potential between the positive electrolyte and negative electrolyte systems to allow other reactions to occur at the reaction surface of the positive current collector 20. The next such (available) reaction is the reduction of any electrochemically obstructive transition metal contaminants (oxides / hydroxides) on the reaction surface of the positive current collector 20 to produce electrochemically non-obstructive or conductive deposits. Once such obstructive deposits have been reduced, the third and final reaction involves the electrolysis of the electrolyte water, accompanied by the escape of hydrogen gas from the reaction surface of the positive current collector 20.

[0019] Each of these reactions can be identified by its unique total cell voltage potential. During this process, the reaction that occurs at the highest voltage always occurs first, and the voltage remains at the voltage required for that reaction until all reactants are consumed. Reduction of any electrochemically obstructive transition metal contaminants does not occur until the dissolved electroactive charged material in the positive electrolyte 32 within the positive electrode chamber 18 is consumed. Similarly, hydrogen gas does not begin to escape until the electrochemically obstructive transition metal contaminants are consumed. Thus, the escape of hydrogen gas and its associated cell voltage signature demonstrate that the charged material has been consumed and the contaminants have become non-obstructive.

[0020] The algorithms, methods, or processes disclosed herein can be delivered to or implemented by a computer, controller, or processing device, which can include any dedicated electronic control unit or programmable electronic control unit. Similarly, the algorithms, methods, or processes can be stored in various forms as computer- or controller-executable data and instructions, including but not limited to information permanently stored on a non-writable storage medium (such as a read-only storage device), and information stored on a writable storage medium (such as an optical disc, random access storage device, or other magnetic and optical media) that can be written. The algorithms, methods, or processes can also be implemented in software-executable objects. Alternatively, the algorithms, methods, or processes can be embodied in whole or in part using suitable hardware components, such as application-specific integrated circuits, field-programmable gate arrays, state machines, or other hardware components or devices, or a combination of firmware, hardware, and software components.

[0021] Although the exemplary embodiments are described above, it does not mean that these embodiments describe all possible forms encompassed by the claims. The flow battery 10 can be, for example, a cobalt cyanide flow battery, a ferrocyanide flow battery, or a manganese cyanide flow battery. Other configurations are also possible.

[0022] The words used in the specification are descriptive rather than restrictive, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously mentioned, the features of the various embodiments can be combined to form further embodiments not explicitly described or illustrated in the present invention. Although the various embodiments can be described as providing advantages over one or more desirable features or being more preferred than other embodiments or the prior art, those of ordinary skill in the art will recognize that one or more features or characteristics may be sacrificed to achieve desirable overall system properties, depending on the specific application and implementation. These properties can include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, performance in use, weight, manufacturability, ease of assembly, etc. Thus, embodiments described as less desirable than other embodiments or prior art embodiments with respect to one or more features are not outside the scope of the disclosure and may be desirable for a particular application.

Claims

1. A method for purifying a flow battery, comprising: The positive electrolyte is intercepted from the positive electrolyte reservoir in the positive electrode chamber of the flow battery so that the positive electrolyte stops flowing through the flow battery without stopping the flow of the negative electrolyte from a negative electrolyte reservoir separated from the positive electrolyte reservoir through the negative electrode chamber of the flow battery; When the positive electrolyte stagnates and does not flow in the positive electrode chamber, the flow battery discharges, such that successively charged substances of the positive electrolyte in the positive electrode chamber are consumed, electrochemical obstructive transition metal contaminants on the reaction surface in the positive electrode chamber are electrochemically reduced and become electrochemically non-obstructive, and hydrogen gas escapes at the reaction surface within a predetermined time period; After the end of the predetermined time period, the discharge is stopped; and the flow of the positive electrolyte through the positive electrode chamber is restarted.

2. The method according to claim 1, further comprising: When the state of charge of the flow battery is below a predetermined threshold, the interception is prevented.

3. The method according to claim 1, wherein The electrochemical obstructive transition metal contaminants include iron contaminants.

4. The method according to claim 1, wherein The interception, discharge, and restart are performed periodically.

5. A control system for the method of purifying a flow battery according to any one of claims 1-4, comprising: A controller, which is programmed to stop the flow of the positive electrolyte from the positive electrolyte reservoir through the positive electrode chamber of the flow battery to intercept the positive electrolyte in the positive electrode chamber without stopping the flow of the negative electrolyte from a negative electrolyte reservoir separated from the positive electrolyte reservoir through the negative electrode chamber of the flow battery; when the positive electrolyte is intercepted in the positive electrode chamber, discharge the flow battery until hydrogen gas escapes at the reaction surface in the positive electrode chamber; and then stop the discharge and restart the flow of the positive electrolyte through the positive electrode chamber.

6. The control system according to claim 5, wherein The controller is further programmed to prevent the stopping when the state of charge of the flow battery is less than a predetermined threshold.

7. The control system according to claim 5, wherein During discharge, charged substances of the positive electrolyte in the positive electrode chamber are consumed, and electrochemical obstructive transition metal contaminants on the reaction surface are electrochemically reduced and become electrochemically non-obstructive.

8. The control system according to claim 7, wherein The electrochemical obstructive transition metal contaminants include iron contaminants.

9. The control system according to claim 5, wherein The flow battery is a metal cyanide flow battery.

10. The control system according to claim 9, wherein The flow battery is a cobalt cyanide flow battery, a ferrocyanide flow battery, or a manganese cyanide flow battery.

11. A control system for the method of purifying a flow battery according to any one of claims 1-4, comprising: A controller, which is programmed to stop the flow of the positive electrolyte from the positive electrolyte reservoir through the positive electrode chamber of the flow battery without stopping the flow of the negative electrolyte from a negative electrolyte reservoir separated from the positive electrolyte reservoir through the negative electrode chamber of the flow battery; when the flow of the positive electrolyte through the positive electrode chamber is stopped, discharge the flow battery; and after the voltage of the flow battery remains at or below a threshold for at least a predetermined time period, stop the discharge and restart the flow of the positive electrolyte through the positive electrode chamber.

12. The control system according to claim 11, wherein The controller is further programmed to prevent the stopping when the state of charge of the flow battery is less than a predetermined threshold.

13. The control system according to claim 11, wherein The flow battery is a metal cyanide flow battery.

14. The control system according to claim 13, wherein The flow battery is a cobalt cyanide flow battery, a ferrocyanide flow battery, or a manganese cyanide flow battery.

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