Safety system and method for flow batteries

Abstract

Safety of redox flow battery systems employing CN ligand electrolytes involves preventing the production of toxic HCN during operation. Disclosed herein are systems for detecting parameters that can lead to the production of HCN when a redox flow battery is operated in a fault condition, which perform corrective actions to ensure that HCN is not formed and further to restore the redox flow battery to a normal operating condition. Also disclosed herein are methods of using the systems.

Description

[0001] Statement on Federally Funded Research

[0002] This invention was made with government support from the Advanced Materials and Manufacturing Technologies Office—US Department of Energy, grant number DE-EE0009795. The government holds certain rights to this invention. Technical Field

[0003] This invention generally relates to energy storage. More specifically, this invention relates to systems for detecting, preventing, and mitigating safety consequences arising from the accidental mixing of reactants in redox flow batteries, and methods of using such systems. Background Technology

[0004] A redox flow battery (RFB) uses two liquid or solution-phase chemicals: a negative electrolyte (also called an anode electrolyte or negative electrode electrolyte) and a positive electrolyte (also called a cathode electrolyte or positive electrode electrolyte). These react at the negative and positive electrodes, respectively, in a device called a flow battery stack, which consists of one or more flow battery cells (sometimes called "batteries"). These flow battery cells are electrochemical cell units. The battery stack extracts electrical energy from the chemical reaction. Used chemicals are stored in their individual containers and can be recharged using electricity from sources such as solar panels, allowing the chemical reaction to proceed in reverse.

[0005] Compared to solid-state batteries such as lithium-ion batteries, flow batteries have an advantage in terms of longer-duration energy storage. Longer-duration batteries can be produced simply by using larger tanks for either the positive or negative electrode electrolyte, without the need to spend money on unnecessarily large flow battery stacks.

[0006] Key factors for the commercial success of flow batteries are cost and the avoidance of critical materials in either the negative or positive electrode electrolyte. These two factors are often interrelated. For example, the most commonly used flow battery chemistry uses vanadium as both the negative and positive electrode electrolyte; however, global vanadium production is limited, and most of the world's vanadium is produced in China and Russia, raising concerns about supply chains and geopolitics. Furthermore, the high and volatile price of vanadium makes the cost floor of vanadium-based flow battery systems higher than that of current lithium-ion batteries. As the cost of lithium-ion batteries continues to decline, this cost gap will likely persist or even widen.

[0007] For the reasons mentioned above, the use of organic redox active compounds as one of the negative or positive electrode electrolytes in RFBs has been a subject of in-depth research, as they can be produced from abundant and inexpensive materials without requiring any critical materials. In some cases, both the negative and positive electrode electrolytes of these organic RFBs are organic materials (e.g., viologen derivatives as the negative electrode electrolyte and TEMPO derivatives as the positive electrode electrolyte), and in other cases, only one of the negative and positive electrode electrolytes is an organic material, such as quinone derivatives as the negative electrode electrolyte and ferrocyanide as the positive electrode electrolyte. To date, a large number of organic negative electrode electrolytes have been studied and reported in the prior art, such as quinones, alloxazines, viologens, naphthalenediimides, phenazines, and so on.

[0008] In other cases, the negative or positive electrolyte, or both, may contain more than one organic compound. These mixtures can be different isomers of the relevant compounds, having the same type of redox core with different surrounding functional groups, or completely different molecules. Similarly, if one or more of the electrolytes contain redox-active inorganic substances, they can be salts composed of redox-active cations and redox-inert anions (e.g., in the case of methyl viologen dichloride or 1,1'-bis((3-trimethylammonium)propyl)ferrocene dichloride), or salts composed of redox-inert cations and redox-active anions (e.g., sodium ferrocyanide, potassium ferrocyanide, ammonium ferrocyanide, lithium ferrocyanide, and mixtures thereof), or both the cation and anion can be redox-active. Combinations of more than one redox-active ion and redox-inert counterion are also possible, such as sodium ferrocyanide and potassium ferrocyanide, methyl viologen dichloride and ethyl viologen dichloride, methyl viologen dichloride and ethyl viologen dibromide, etc. Finally, for convenience, a combination of the same redox-active compound (whether in neutral molecule or ionic form) in two or more different oxidation states should be considered the same compound, such as sodium ferrocyanide and potassium ferricyanide. This is reasonable because during the normal operation of the RFB, redox-active substances cycle between oxidized and reduced states and are expected to exist in any proportion of those states.

[0009] In flow batteries, the negative and positive electrolytes are typically separated from each other by a separator, which may include a cation exchange membrane, anion exchange membrane, bipolar membrane, microporous separator, or polymer with inherent microporosity. Other cases without separators have also been reported, and instead, RFBs utilize phase separation or laminar flow between two immiscible fluids to minimize the mixing or crossover of the negative and positive electrolyte materials. This can have adverse effects such as high self-discharge, chemical degradation, capacity loss due to the ineffective delivery of the negative or positive electrolyte to the negative and positive electrodes, respectively. Crossover or undesirable mixing can occur due to the diffusion of a chemical through the separator, physical damage to the separator (e.g., pores or tears), leakage paths around the separator, or, in the absence of a separator, non-laminar or other turbulent mixing of the negative and positive electrolyte fluids.

[0010] When the RFB is charged (i.e., has a state of charge (SOC) above zero), some of the negative electrolyte is in a reduced state, and some of the positive electrolyte is in an oxidized state. Generally, the higher the SOC of the RFB, the greater the proportion of the negative electrolyte in the reduced state and the greater the proportion of the positive electrolyte in the oxidized state. To maximize the battery potential and thus energy density of the RFB, the negative electrolyte typically has a high negative reduction potential, and the positive electrolyte typically has a high positive reduction potential; the battery potential is the difference between the reduction potentials of the negative and positive electrolytes. For this reason, the negative electrolyte in its reduced state is a strong reducing agent, and the positive electrolyte in its oxidized state is a strong oxidizing agent.

[0011] It is generally believed that organic molecules can be degraded and decomposed by exposure to sufficiently strong oxidizing or reducing agents. Sometimes, the reaction is associated with the release or absorption of protons (or conversely, the absorption or release of hydroxide ions), and in other cases, there is no associated release or absorption of protons (or the opposite regarding hydroxide ions). In those cases where the release or absorption of protons or hydroxide ions is present, this is accomplished through a change in the pH of the solution, and pH changes can have additional adverse effects on the RFB, such as causing dissolved negative or positive electrolytes to precipitate from the solution, decompose, or accelerate decomposition reactions that would otherwise be at a sufficiently low rate under normal operating conditions. pH changes can also have undesirable effects, such as corrosion, etching, or weakening of wetting materials in the RFB, including separators, piping systems, pumps, tanks, and associated sensors and control systems. In other cases, pH changes may cause previously or normally dissolved chemicals to volatilize and escape as vapors or gases from the positive or negative electrolyte solution. The chemical substances may be present normally in the negative or positive electrode electrolyte, or they may be produced as a result of additional decomposition reactions listed above. Possible substances include carbon dioxide, hydrogen cyanide, hydrogen chloride, hydrogen bromide, etc.

[0012] In one specific scenario, an RFB (Reactive Fusion Battery) containing an organic redox-active compound as the negative electrode electrolyte and a positive electrode electrolyte containing ferrocyanide / ferricyanide may undergo a cross-permeation event, where a small amount of the organic negative electrode electrolyte mixes with an excess of the ferricyanide positive electrode electrolyte. Ferricyanide, acting as an oxidant, can oxidize the organic negative electrode electrolyte during the reaction, causing proton release or uptake, thereby lowering the pH of the positive electrode electrolyte fluid. Furthermore, ferrocyanide and ferricyanide are unstable at low pH, causing some cyanide ligands to dissociate and enter the positive electrode electrolyte solution as free cyanide ions. At a sufficiently low pH (pK of hydrogen cyanide or HCN), the cross-permeation event can occur. aAt 9.2), cyanide ions are protonated and may escape from the solution as free hydrogen cyanide vapor or gas.

[0013] Organic RFB has been on the market for a shorter time than vanadium RFB, and not all possible side reactions are yet understood. Detailed systems and methods for detecting, stopping, preventing, mitigating, or reversing the adverse effects of cross-diffusion in organic RFB have not been reported, but they are necessary for safe and reliable operation, market acceptance, and therefore overall commercial success. Summary of the Invention

[0014] This overview is provided to present, in a simplified form, a selection of concepts further described herein. This overview is not intended to identify necessary or essential features of the claimed subject matter. Nor is it intended to limit the scope of the claimed subject matter.

[0015] The redox flow battery system disclosed herein may include a redox flow battery device and a hydrogen cyanide or cyanide ion (hereinafter referred to as CN) detection sensor. The redox flow battery device may include: a first tank containing a negative electrode electrolyte solution, a second tank containing a positive electrode electrolyte solution, and a flow battery stack capable of extracting electrical energy from the chemical reaction between the negative and positive electrode electrolyte solutions and supplying electrical energy to induce a reverse reaction in the negative and positive electrode electrolyte solutions. The flow battery stack may be configured to receive the negative electrode electrolyte solution from the first tank and return the negative electrode electrolyte solution to the first tank, and is configured to receive the positive electrode electrolyte solution from the second tank and return the positive electrode electrolyte solution to the second tank.

[0016] This document also discloses methods for maintaining a safe operating state of a redox flow battery system. In some aspects, the method may include: providing the redox flow battery system, processing output data from a CN detection sensor to determine a fault state of the redox flow battery device, and performing corrective actions to resolve the fault state to a normal operating state. Attached Figure Description

[0017] The accompanying drawings, which form part of this specification, are included to further illustrate certain aspects of the invention. A better understanding of the invention can be achieved by referring to the detailed description and the accompanying drawings.

[0018] Figure 1 A schematic diagram of a redox flow battery system is shown.

[0019] While the invention disclosed herein is susceptible to various modifications and alternatives, only a few specific aspects are illustrated by way of example in the accompanying drawings, which are described in detail below. The accompanying drawings and detailed description of the specific aspects are not intended to limit the breadth or scope of the inventive concept or the appended claims in any way. Rather, the drawings and detailed description are provided to illustrate the inventive concept to those skilled in the art and to enable such persons to make and use the inventive concept.

[0020] definition

[0021] To more clearly define the terminology used herein, the following definitions are provided. Unless otherwise specified, the following definitions apply to this invention. If a term is used in this disclosure but is not specifically defined herein, it may be derived from the IUPAC Compendium of Chemical Terminology, 2nd Edition (1997). nd The definition provided in Ed (1997) shall be used as long as it does not conflict with any other disclosure or definition applied herein or render any claim to which the definition applies uncertain or unenforceable. In the event of any conflict between any definition or usage provided in any document incorporated herein by reference and the definition or usage provided herein, the definition or usage provided herein shall prevail.

[0022] In this document, features of the subject matter are described so that combinations of different features may be conceived in particular aspects. For each aspect and feature disclosed herein, all combinations are considered that will not adversely affect the compounds, compositions, processes, or methods described herein, with or without explicit description of particular combinations. Furthermore, unless expressly stated otherwise, any aspect or feature disclosed herein may be combined to describe inventive compounds, compositions, processes, or methods consistent with this disclosure.

[0023] Although compositions, processes, and methods are described in a way that "comprises" various components or steps, unless otherwise specified, compositions, processes, and methods may also be "consistent primarily of" various components or steps or "composed of" various components or steps. Unless otherwise stated, the terms "a," "an," and "the" are intended to include a plurality of alternatives, such as at least one alternative. For example, as used herein, "CN detector," "CN sensor," and "CN detection sensor" may be used to refer to a single CN detection sensor or multiple sensors for detecting CN. In this way, references to "CN detector," "CN sensor," and "CN detection sensor" are not limited to a single sensor configured to directly detect CN, but may also refer to multiple sensors operating together to detect states that may result in or be present in a CN within the RFB system.

[0024] It should be understood that "CN detection sensor" can generally be used to refer to any sensor used to indicate the presence or potential generation of CN. Therefore, a pH sensor located within an electrolyte tank can be considered a CN detection sensor, where it is configured to detect pH changes that may lead to CN generation, even in the absence of CN. It should also be understood that mentioning CN is generally intended to encompass both HCN gas and its anionic form when dissolved in the electrolyte solution. - CN).

[0025] Because the stack within the RFB can operate as a galvanic cell during flow battery discharge and as an electrolytic cell during flow battery charging, for clarity, the terms anode, cathode, cathode electrolyte, or anode electrolyte will not be used in the remainder of this document. This is because the same electrode can be referred to as either anode or cathode depending on whether the battery is charging or discharging. Instead, the terms negative electrode, positive electrode, negative electrolyte, or positive electrolyte will be used. Electrolyte will refer to both negative and positive electrolytes collectively.

[0026] Various numerical values ​​are disclosed herein. Unless otherwise stated, when a series of values ​​is disclosed, the purpose is to individually disclose or claim protection each possible range that can be reasonably defined as the endpoint of a particular range, and any subranges and combinations thereof encompassed therein. For example, disclosing that a CN detection threshold can be >5 ppm, >6 ppm, >8 ppm, >10 ppm, >4 ppm, >3 ppm, >2 ppm, >1 ppm, etc., would be understood as disclosing that a CN detection threshold can be in the range of 1 ppm to 10 ppm, 2 ppm to 8 ppm, etc. As another example, disclosing that a CN detection threshold can be a positive or negative electrode electrolyte pH below pH <9.2, pH <9.5, pH <10.0, pH <10.5, pH <11.0, pH <11.5, pH <12.0 would also be understood as disclosing that a CN detection threshold can be in the pH range of a positive or negative electrode electrolyte of 9.2 to 12.0, 10.5 to 12.0, etc.

[0027] Generally, whether explicitly stated or not, quantities, sizes, formulations, parameters, ranges, or other quantities or characteristics are referred to as “about” or “approximately”. Claims, regardless of whether modified by the terms “about” or “approximately”, include equivalents of the quantity or characteristic.

[0028] Although any methods, apparatus, and materials similar to or equivalent to those described herein may be used in the implementation or testing of the invention, typical methods, apparatus, and materials are described herein.

[0029] All publications and patents mentioned herein are incorporated herein by reference in their entirety for the purpose of describing and disclosing, for example, the constructs and methods described in publications and patents, and may be used in conjunction with the invention currently described. Detailed Implementation

[0030] This document discloses a redox flow battery system comprising a redox flow battery and components for detecting CN to ensure the safe operation of the redox flow battery (even in a damaged state). This document also discloses methods for operating the redox flow battery system and maintaining it in a safe state.

[0031] system

[0032] This invention provides a redox flow battery system including a redox flow battery. The redox flow battery is not limited to a specific chemistry and can generally employ various chemistry for both the negative and positive electrode electrolytes, provided that at least one of the negative and positive electrode electrolytes contains an organic redox active material. Suitable combinations include: quinones paired with another quinone, quinones paired with ferrocyanide / ferricyanide (Fe(CN)), pyrazines paired with Fe(CN), phenazines paired with Fe(CN), ionoline derivatives paired with ferrocene derivatives, ionoline derivatives paired with TEMPO derivatives, naphthalimide derivatives paired with ferrocene derivatives, naphthalimide derivatives paired with TEMPO derivatives, and many other examples in the prior art.

[0033] One or both of the negative and positive electrode electrolyte solutions may also contain one or more supporting electrolytes, which are typically added to ensure the solution is at an appropriate pH and to improve the conductivity of the negative and positive electrode electrolyte solutions. Examples of supporting electrolytes may include: strong acids, such as sulfuric acid or hydrochloric acid; strong bases, such as sodium hydroxide or potassium hydroxide; neutral salts, such as sodium sulfate or potassium chloride; or pH buffers, such as potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium bicarbonate, etc. The negative and positive electrode electrolyte solutions may also contain additives to improve the solubility of the active material in the solution. The solvent for the negative and positive electrode electrolyte solutions may be water.

[0034] The amounts, volumes, or charge capacities of the negative and positive electrode electrolyte solutions need not be equal or substantially equal. They can be any amounts. In some embodiments, it is advantageous to supply an excess of either the negative or positive electrode electrolyte in the redox flow battery.

[0035] In some respects, redox flow batteries may also comprise a single electrochemical cell, or alternatively, more than one cell. Regarding multiple electrochemical cells, the cells may be of the same or different sizes. In other respects, the cells may be arranged in series or parallel to form an electrochemical stack; such a stack itself may be arranged in an array, thereby being electrically or hydraulically connected in series or parallel, wherein the electrical and hydraulic connections are independent of each other. In the following text, when referring to such or any other electrochemical system, the use of the terms "cell" or "stack" should also be understood to be interchangeable, referring to one or more cells that themselves comprise one or more stacks.

[0036] In addition to the battery cells or stack and the negative and positive electrolyte solutions, redox flow batteries also include additional components required for the normal operation of the redox flow battery system, including tanks (separate or compartmentalized) for the negative and positive electrolyte solutions, pumps for circulating the negative and positive electrolytes, pipe and piping systems for connecting the tanks to the battery cells and stack and back, and any number of associated control systems, sensors, and power electronics required for normal operation.

[0037] Figure 1 An example of a redox flow battery system 100, including a redox flow battery as described herein, is shown. Typically, the redox flow battery system 100 includes a redox flow battery and its associated components for safe operation. The redox flow battery system may include a housing 102 surrounding each or any of the system components. As shown, the housing 102 surrounds the redox flow battery, a control unit 104, an electrochemical processing unit 106 in fluid communication with a chemical additive storage tank 108, and various sensors, pipes, piping systems, and wiring for interconnecting the respective components. The control unit 104 is shown mounted to the housing 102; however, in other respects, the control unit may be located on any component portion of the redox flow battery system 100, for example, on the outside of the user-accessible housing 102, or in a remote location such as a control room. Similarly, in other respects, the electrochemical processing unit 106 may be separated from the housing and placed in a more distant location suitable for a given embodiment of the redox flow battery system.

[0038] A redox flow battery includes a first tank 110 containing a negative electrode electrolyte solution 112, e.g., a "negative electrode electrolyte tank," and a second tank 120 containing a positive electrode electrolyte solution 122, e.g., a "positive electrode electrolyte tank." The electrolyte tanks 110 and 120 may have the same capacity, or they may hold different capacities. They may be of any shape, such as cylindrical, rectangular, spherical, conical-bottomed, etc. The respective electrolyte solutions may flow through corresponding battery inlet lines 113 and 123 (from the negative electrode electrolyte tank and the positive electrode electrolyte tank, respectively, to the electrochemical cell) to the electrochemical cell unit 130 and contact the membrane 132 within the electrochemical cell unit 130. For clarity, further details of the internal components of the electrochemical cell unit 130 are omitted. Various configurations of the electrochemical cell unit suitable for redox flow batteries are considered herein, and these configurations will be apparent to those skilled in the art based on the content of this disclosure. Once the electrolyte solution passes through the electrochemical cell unit 130, the electrolyte solutions 112 and 122 return to the corresponding electrolyte tanks 110 and 120 via the battery output lines 114 and 124.

[0039] In the illustrated example, each input line also includes inline pumps 116, 126 to move the electrolyte solution into the electrochemical cell. A bypass 140 connects the positive electrolyte cell input 123 and the positive electrolyte cell output 124 via valves 140a, b. When the bypass 140 is in use, the flow of the positive electrolyte solution 122 is directed to bypass the electrochemical cell unit 130 and return to the positive electrolyte tank 120, thus bypassing the electrochemical cell unit 130. The negative electrolyte tank 110 also includes a bypass 142 configured to receive the flow of the negative electrolyte solution 112 from the cell input 113 to the cell output 114, thus bypassing the electrochemical cell unit 130.

[0040] like Figure 1 The electrolyte tanks 110 and 120 shown also include sampling circuits 118 and 128, configured to allow corresponding electrolyte solutions 112 and 122 to flow from the electrolyte tanks through detectors 197 and 198. While not required components of the RFB system disclosed herein, Figure 1The negative electrolyte tank 110 and positive electrolyte tank 120 of the illustrated embodiment include a hydraulic connection 170 located between the tanks. The hydraulic connection 170 includes a valve 172 and a pump 174 for controlling the flow of electrolyte solutions 112, 122 between the respective tanks. In some aspects, the RFB system may include multiple hydraulic connections between the negative electrolyte tank 110 and the positive electrolyte tank 120, each optionally including a pump and a valve to manage the flow between them. Alternatively, the hydraulic connections may be positioned to connect to points in tanks 110, 120 above the normal liquid level of electrolyte solutions 112, 122, such that it is not necessary to use valves or pumps to transfer excess volume from one tank to another.

[0041] The positive electrolyte tank 120 also includes an evaporation barrier 162 floating on the positive electrolyte solution 122. In some aspects, the floating evaporation barrier 162 may be connected to a level sensor to obtain a measurement of the liquid level in the tank. Although shown only in the positive electrolyte tank 120, it should be understood that any or both of the electrolyte tanks 110 and 120 may include an evaporation barrier. Similarly, a barrier liner 152 is shown present within the negative electrolyte tank 110 to prevent the negative electrolyte solution 112 from reacting with the material of the negative electrolyte tank 110. Although not shown, the positive electrolyte tank 120 may include a similar barrier liner.

[0042] The electrochemical processing unit 106 is shown to have a fluid connection with a storage tank 108 (which may store chemical additives for processing electrolyte solutions 112, 122) and corrects fault conditions occurring within the redox flow battery system by adding chemical additives to the respective electrolyte solutions via processing feed lines 154, 164. Each of the processing feed lines 154, 164 may intersect at a valve connection with a battery output line 114, 124 that returns the electrolyte solution to its respective electrolyte tank. In other respects, the processing feed lines 154 / 164 may operate in a loop with the electrochemical processing unit, wherein the electrolyte solution may be extracted from the redox flow battery (e.g., via battery output lines 114, 124) for processing at the electrochemical processing unit 106 and then returned to the same or different locations within the redox flow battery.

[0043] In some embodiments of the present invention, when the positive electrode electrolyte contains Fe(CN), the redox flow battery system includes specific sensors for detecting free cyanide ions, hydrogen cyanide, conditions favorable to the formation of free cyanide ions or hydrogen cyanide, or conditions related to the formation of free cyanide ions or hydrogen cyanide; for ease of communication, these will hereafter be referred to as “detecting CN,” “detection of CN,” “CN detection,” and other similar expressions. Expressions containing the abbreviation “CN” are intended to be interpreted in this manner.

[0044] The sensor can be configured to sample the following: negative electrode electrolyte fluid (e.g., sensor 180), positive electrode electrolyte fluid (e.g., sensor 181), top space in the tank above the negative electrode electrolyte fluid (e.g., sensor 182), top space in the tank above the negative electrode electrolyte fluid (e.g., sensor 183), the exterior adjacent to the redox flow battery system (e.g., sensor 184), or a combination thereof. In another embodiment of the invention, the sensor for CN detection is configured to sample the following: positive or negative electrolyte fluid, fluid about to enter the flow battery stack (e.g., sensors 185, 186), fluid just leaving the flow battery stack (e.g., sensors 187, 188), fluid about to leave the pump (e.g., sensors 189, 190), fluid about to enter the pump (e.g., sensors 191, 192), fluid about to circulate back to the electrolyte tank (e.g., sensors 193, 194), fluid just leaving the electrolyte tank (e.g., sensors 195, 196), or the sensor can sample the bulk fluid in the electrolyte tank (e.g., sensors 197, 198).

[0045] In some embodiments of the invention, for example when the sensors for CN detection are configured to sample the fluid electrolyte, they may include sensors configured to directly detect free cyanide or hydrogen cyanide, pH sensors, temperature sensors, colorimetric sensors, spectral sensors (infrared, visible, and ultraviolet / visible), electrochemical sensors, open-circuit voltage battery cells or sensors, conductivity sensors, hydraulic sensors, liquid level sensors, liquid density sensors, liquid viscosity sensors, and combinations thereof.

[0046] In other embodiments of the invention, for example when the sensors for CN detection are configured to sample the gaseous headspace above the fluid electrolyte or outside the immediate vicinity of the redox flow battery system, they may include: sensors configured to directly detect hydrogen cyanide, sensors configured to directly detect other gases (such as carbon dioxide or sulfur dioxide) associated with the headspace of the acidic fluid, temperature sensors, colorimetric sensors, spectral sensors (infrared, visible, and ultraviolet / visible), and electrochemical sensors.

[0047] A redox flow battery system may include one or more CN detection sensors, and in the case of multiple CN detection sensors, the sensors may be of the same type or different types. Multiple CN detection sensors may be configured to all sample the same part of the redox flow battery system, the exterior of the redox flow battery system, or different parts of the redox flow battery system. In some embodiments of the invention, there may be multiple identical CN detection sensors, all sampling the same part of the redox flow battery system.

[0048] CN detection sensors are not necessarily physically located close to the redox flow battery system; other embodiments of the invention include sensors or other instruments for detecting CN in a non-in-situ manner, wherein they are configured to receive: samples taken from the electrolyte fluid, gas in the top space above the electrolyte fluid, or gas in the exterior adjacent to the redox flow battery system.

[0049] In other embodiments of the invention, the formation rate of free cyanide ions is reduced by strictly blocking light from the negative and positive electrode electrolyte solutions. In these embodiments of the invention, the redox flow battery system includes a housing to protect the tank, stack, and piping system from direct sunlight. In further embodiments of the invention, the flow battery system includes a tank, stack, or piping system made of a sufficiently thick opaque material to block all light from reaching the negative and positive electrode electrolyte solutions. In further embodiments of the invention, the flow battery system includes a tank, stack, or piping system with an additional light-absorbing coating.

[0050] In other embodiments of the invention, the redox flow battery system includes a barrier liner or coating on the interior of at least one of the negative electrode electrolyte tank, positive electrode electrolyte tank, or piping system, which reduces or eliminates side reactions between the fluid solution and the tank or piping system materials. The barrier liner or coating may contain polymers commonly used to impart chemical resistance to tanks and piping systems, such as vinyl esters, polypropylene, poly(tetrafluoroethylene), poly(vinylidene fluoride), poly(vinyl chloride), epoxy resins, phenolic resins, etc. The barrier liner or coating may also contain fillers commonly used to impart chemical resistance to the barrier or coating, such as glass fibers, glass sheets, carbon fibers, graphite, silica, alumina, titanium dioxide, zirconium oxide, etc.

[0051] In other embodiments of the invention, the redox flow battery system includes an evaporation barrier on the liquid surface in either the negative or positive electrolyte tank, which reduces the rate at which hydrogen cyanide evaporates into the top space of the tank, but can still move with changes in the bulk liquid level. Examples include membranes, floating covers, and other objects commonly used to reduce evaporation from tanks, ponds, or reservoirs that are typically exposed to air.

[0052] method

[0053] The methods involving the above include: (a) providing a redox flow battery system including one or more CN detection sensors, (b) operating the flow battery and the one or more CN detection sensors, (c) reading data from the one or more CN detection sensors and determining whether there are positive CN detection results above one or more specific thresholds, and then (d) performing one or more corrective actions to mitigate, control, reverse, or prevent the generation of free cyanide ions or hydrogen cyanide. The one or more corrective actions may be implemented automatically by a control system or manually with human intervention.

[0054] Examples of CN detection thresholds include 4.7 ppm (parts per million) (the NIOSH recommended limit for airborne exposure), or thresholds higher or lower than this number, such as >5 ppm, >6 ppm, >8 ppm, >10 ppm, >4 ppm, >3 ppm, >2 ppm, >1 ppm, >0.5 ppm, >0.2 ppm, >0.1 ppm, >0.05 ppm, 0.02 ppm, and 0.01 ppm. Other examples of CN detection thresholds include positive or negative electrode electrolyte pH values ​​below a set value, such as pH <9.2, pH <9.5, pH <10.0, pH <10.5, pH <11.0, pH <11.5, pH <12.0, pH <9.0, pH <8.5, pH <8.0, pH <7.5, pH <7.0, pH <6.5, pH <6.0, pH <5.5, pH <5.0, etc.

[0055] In some embodiments of the invention, multiple CN detection thresholds exist, and the correction actions associated with each individual CN detection threshold may be the same, or more generally differ in degree or nature. The CN detection sensor may operate intermittently on a fixed schedule or continuously, regardless of whether the redox flow battery itself is being cycled.

[0056] In some embodiments of the invention, one or more corrective actions include adjusting the hydraulic pressure difference of each electrolyte fluid by changing the pump speed or flow rate of each electrolyte, thereby reducing the bulk flow rate of the negative electrode electrolyte to the positive electrode electrolyte or the positive electrode electrolyte to the negative electrode electrolyte to a level below the bulk transfer threshold. The bulk transfer threshold level can be defined as a function of absolute flow rate, such as <10 mL / min, <5 mL / min, <2 mL / min, <1 mL / min, <0.5 mL / min, <0.2 mL / min, <0.1 mL / min, <0.05 mL / min, <0.02 mL / min, <0.01 mL / min, <0.005 mL / min, <0.002 mL / min, <0.001 mL / min, etc., or it can be defined as a percentage of the total initial negative or positive electrode electrolyte volume, such as 0.01% / day, 0.005% / day, 0.002% / day, 0.001% / day, 0.0005% / day, 0.0002% / day, 0.0001% / day, 0.00005% / day, 0.00002% / day, 0.00001% / day, etc.

[0057] In some embodiments of the invention, one or more corrective actions can be performed in advance without waiting for positive CN test results above one or more specific thresholds. In other embodiments of the invention, one or more corrective actions can be performed from the start of operation of the redox flow battery system.

[0058] In other embodiments of the invention, one or more corrective actions include adjusting the pH of the positive electrode electrolyte fluid, the negative electrode electrolyte fluid, or both. pH adjustment can be achieved by adding an external solution of an acid, base, or buffer solution from an external source to the positive electrode electrolyte fluid, the negative electrode electrolyte fluid, or both. The external solution may contain one or more solutes for achieving pH adjustment, such as sodium hydroxide, potassium hydroxide, mixtures of sodium hydroxide and potassium hydroxide, mixtures of potassium hydroxide and trisodium phosphate, and many other similar combinations that will be apparent to those skilled in the art.

[0059] In other embodiments of the invention, one or more corrective actions include adjusting and maintaining the temperature of the positive electrode electrolyte fluid, the negative electrode electrolyte fluid, or both, below or above a threshold level. Temperature adjustment can be achieved in a variety of ways that will be apparent to those skilled in the art, including contacting either electrolyte fluid with a heat exchanger, immersion heater, jacketed heater, or cooler supplied with steam or coolant. If heating is required, the redox flow battery can supply additional heat by charging or discharging the battery at a power higher than its rated power, thereby increasing the heat dissipated from the battery cells and stack of the redox flow battery.

[0060] In other embodiments of the invention, one or more corrective actions include stopping, slowing down, or bypassing the flow of the negative electrolyte solution, the positive electrolyte solution, or both to the cell and stack of the redox flow battery. This flow alteration can be applied to all cell and stack in the redox flow battery, or to a subgroup of all cell and stack in the redox flow battery.

[0061] In other embodiments of the invention, one or more corrective actions include: removing or replacing all battery cells and stacks in the flow battery, or subgroups of all battery cells and stacks in the flow battery, and, as appropriate, reconfiguring the piping system to connect new battery cells and stacks, or disconnecting previously existing battery cells and stacks.

[0062] In other embodiments of the invention, one or more corrective actions include intentionally creating a sufficiently large hydraulic pressure difference between the negative and positive electrolyte solutions by changing the pump speed or flow rate of each electrolyte, so as to cause widespread membrane failure and rapid mixing of the negative and positive electrolyte solutions with each other.

[0063] In other embodiments of the invention, the redox flow battery system further includes a hydraulic connection between a negative electrolyte tank and a positive electrolyte tank, which is typically kept closed by a valve, and one or more corrective actions include opening the valve and circulating fluid from the negative electrolyte tank to the positive electrolyte tank and back again to rapidly mix the contents of the negative electrolyte solution and the positive electrolyte solution with each other.

[0064] In other embodiments of the invention, one or more corrective actions include oxidative destruction of free cyanide ions or hydrogen cyanide, causing the concentration of those substances to drop below a threshold level. Oxidative destruction can be achieved chemically by adding an external strong oxidant to the negative or positive electrode electrolyte solution, such as chlorine, ozone, sodium or potassium hypochlorite solution, sodium or potassium chlorite solution, sodium or potassium chlorate solution, sodium or potassium perchlorate solution, potassium permanganate solution, and other external strong oxidants readily apparent to those skilled in the art. The external strong oxidant can be provided in a separate tank or generated electrochemically via an external electrochemical system. Alternatively, oxidative destruction can be achieved electrochemically by oxidizing the negative or positive electrode electrolyte solution at a suitably high potential using the cell and stack of a redox flow battery, or by providing an external electrochemical system (such as an electrolyzer typically used to remove cyanide by electrooxidation) to electrooxidize the negative or positive electrode electrolyte. The external electrochemical system may also be capable of any optional rebalancing that may be required later.

[0065] Example

[0066] Example 1

[0067] Redox flow battery systems containing quinone-based negative electrode electrolytes and Fe(CN) positive electrode electrolytes encounter a problem of slow but steady bulk transfer of the negative electrode electrolyte into the positive electrode electrolyte solution due to pores formed in the membrane of one of the cell units. This manifests as a decrease in the volume of the negative electrode electrolyte (or can fill level) over time and an increase in the volume of the positive electrode electrolyte. The quinone negative electrode electrolyte entering the Fe(CN) positive electrode electrolyte is oxidized by excess ferricyanide in the positive electrode electrolyte, and this process releases protons, which lower the pH of the positive electrode electrolyte. If not mitigated in time, the decreased pH causes the Fe(CN) positive electrode electrolyte to decompose and release free cyanide ions, and a further decrease in pH causes some of these free cyanide ions to be protonated and enter the top space above the positive electrode electrolyte as hydrogen cyanide gas. Conversely, the bulk transfer of the positive electrode electrolyte to the negative electrode electrolyte solution (in which a small amount of Fe(CN) mixes with an excess of the negative electrode electrolyte) is unrelated to any pH decrease, negative electrode electrolyte decomposition, or free cyanide formation, because the ferrocyanide is rapidly reduced to ferrous cyanide by the excess quinone negative electrode electrolyte in its reduced state and is no longer available to cause further decomposition. Further decomposition is associated with the oxidized form of ferrocyanide acting on the quinone negative electrode electrolyte.

[0068] The pH sensor in the positive electrolyte tank detected a drop in the pH of the positive electrolyte from an initial value of 12.5 to 10.5, and the level sensor in the positive electrolyte tank confirmed that the average volume of the positive electrolyte had increased over time. Although no free cyanide ions or hydrogen cyanide were detected, the pH drop triggered the control system to reduce the flow rate of the negative electrolyte fluid, resulting in a larger or less negative pressure differential between the positive and negative electrolyte fluids within the redox flow battery cell compared to before. The net result was to prevent or even reverse the bulk transfer of negative electrolyte to the positive electrolyte solution, thereby preventing further decrease in solution pH and preventing the formation of free cyanide ions or hydrogen cyanide. This was confirmed by the level and pH sensors. The UV / Vis sensor sampling the positive electrolyte fluid did not detect a further increase in the quinone concentration in the positive electrolyte fluid. For all future operations of the redox flow battery, the new pump rates for both the negative and positive electrolytes will be maintained.

[0069] Example 2

[0070] A redox flow battery system comprising a quinone-based negative electrode electrolyte and an Fe(CN) positive electrode electrolyte operates using negative and positive electrode electrolyte solutions flowing at a rate such that the hydraulic pressure of the positive electrode electrolyte in the cell remains at a slightly higher level compared to the negative electrode electrolyte, with a pressure differential of 0.5 psi. A pore is subsequently formed in the membrane of one of the cell units, but due to the hydraulic differential, bulk transfer of liquid occurs from the positive electrode electrolyte to the negative electrode electrolyte. Although no pH change in either the negative or positive electrode electrolyte was detected, a tank level sensor confirmed that the average volume of the negative electrode electrolyte began to increase over time, while the average volume of the positive electrode electrolyte began to decrease over time. In response, an internal leak was suspected, and the sampling frequency of the pH of both the negative and positive electrode electrolytes was increased.

[0071] Changes in average volume prompt redox flow battery operators to manually adjust the flow rates of the negative and positive electrode electrolyte solutions to minimize the bulk solution transfer rate while still ensuring that the overall net transfer is in the direction from the positive to the negative electrode electrolyte.

[0072] Example 3

[0073] Due to the pores formed in the membrane of one of the battery cells, redox flow battery systems containing quinone-based negative electrode electrolytes and Fe(CN) positive electrode electrolytes, including an external supply of concentrated sodium hydroxide solution, encounter the problem of slow but stable bulk transfer of the negative electrode electrolyte to the positive electrode electrolyte solution.

[0074] The pH sensor in the positive electrolyte tank detected that the pH of the positive electrolyte had dropped from the initial value of 12.0 to 11.5, and the liquid level sensor in the positive electrolyte tank confirmed that the average volume of the positive electrolyte had increased over time. Although no free cyanide ions or hydrogen cyanide were detected, the pH drop triggered the control system to add concentrated sodium hydroxide solution to the positive electrolyte solution to raise the pH back to the initial value of 12.0.

[0075] Example 4

[0076] Due to the pores formed in the membrane of one of the battery cells, redox flow battery systems containing quinone-based negative electrode electrolytes and Fe(CN) positive electrode electrolytes encounter the problem of slow but stable bulk transfer of the negative electrode electrolyte to the positive electrode electrolyte solution.

[0077] The pH sensor in the positive electrolyte tank detected that the pH of the positive electrolyte had dropped from an initial value of 12.5 to 12.0, and the level sensor in the positive electrolyte tank confirmed that the average volume of the positive electrolyte had increased over time. Although no free cyanide ions or hydrogen cyanide were detected, in response, the control system issued an alarm to the flow battery operator indicating a suspected internal leak.

[0078] The alert prompted operators of the redox flow battery to manually replace the individual stack in the larger array suspected of having an internal leak, after which the redox flow battery was restored to normal operation.

[0079] Example 5

[0080] Due to the pores formed in the membrane of one of the battery cells, redox flow battery systems containing quinone-based negative electrode electrolytes and Fe(CN) positive electrode electrolytes, including an external supply of a mixture of sodium hydroxide and potassium hydroxide solution, encounter the problem of slow but stable bulk transfer of the negative electrode electrolyte to the positive electrode electrolyte solution.

[0081] The pH sensor in the positive electrolyte tank detected that the pH of the positive electrolyte had dropped from an initial value of 12.5 to 11.5, and the level sensor in the positive electrolyte tank confirmed that the average volume of the positive electrolyte had increased over time. Although no free cyanide ions or hydrogen cyanide were detected, in response, the control system stopped the flow battery circulation, stopped the negative electrolyte pump and the positive electrolyte pump, and issued a suspected internal leak alarm to the flow battery operator.

[0082] The alarm prompted the redox flow battery operators to manually replace the individual stack in the larger array suspected of having an internal leak. The operators then initiated the addition of a mixture of sodium hydroxide and potassium hydroxide solution from an external supply to the positive electrode electrolyte solution to raise the pH back to the initial value of 12.5, and finally restored the redox flow battery to normal operation.

[0083] Unless otherwise specified, all figures used in this specification and claims to represent characteristic dimensions, quantities, volumes, charge capacities, states of charge, and other chemical and physical properties should be understood to be modified in all cases by the term "about". Therefore, unless indicated to the contrary, the numerical parameters listed in the foregoing specification and appended claims are approximations that can be varied according to the desired performance sought by a person skilled in the art using the teachings disclosed herein. The use of numerical ranges by endpoints includes all figures within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5; <10% includes 10%, 9.8%, 5.5%, 2%, 0.01%, and 0%; >90% includes 90%, 90.2%, 94.5%, 98%, 99.99%, and 100%) and any range within that range.

[0084] The foregoing description is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Various modifications and variations are possible in accordance with the foregoing teachings. Any or all features of the disclosed embodiments may be applied individually or in any combination and are not limiting, but merely illustrative. The scope of the invention is not limited by this detailed description, but is determined by the appended claims.

Claims

1. A redox flow battery system, the redox flow battery system comprising: Redox flow battery device, the redox flow battery device comprising: The first tank containing the negative electrode electrolyte solution; A second container containing the positive electrode electrolyte solution; A flow battery stack capable of extracting electrical energy from the chemical reaction between the negative and positive electrode electrolyte solutions, and capable of supplying electrical energy to induce a reverse reaction in the negative and positive electrode electrolyte solutions. The flow battery stack is configured to receive the negative electrode electrolyte solution from the first tank and return the negative electrode electrolyte solution to the first tank, and is configured to receive the positive electrode electrolyte solution from the second tank and return the positive electrode electrolyte solution to the second tank; and CN detection sensor.

2. The system according to claim 1, wherein the negative electrode electrolyte solution comprises an organic redox active material.

3. The system according to claim 2, wherein the positive electrode electrolyte solution comprises Fe(CN).

4. The system according to claim 1, further comprising a control system configured to: Accepts input from the CN detection sensor; and The operating parameters of the redox flow battery device are changed based on the input from the CN detection sensor.

5. The system according to claim 4, wherein the operating parameters include the flow rate of the negative electrode electrolyte solution.

6. The system according to claim 5, wherein the operating parameters further include the flow rate of the positive electrode electrolyte solution.

7. The system of claim 1, further comprising an electrolyte processing system configured to deliver a chemical additive to either or both of the negative electrode electrolyte solution and the positive electrode electrolyte solution, or to both the negative electrode electrolyte solution and the positive electrode electrolyte solution.

8. The system according to claim 7, wherein the chemical additive comprises an alkaline solution, an acidic solution, a buffer salt, a buffer solution, or an oxidizing agent.

9. The system of claim 8, wherein the oxidant comprises chlorine, ozone, permanganate, hypochlorite, chlorite, chlorate, or perchlorate.

10. The system of claim 7, wherein the electrolyte treatment system comprises a storage tank containing the chemical additive.

11. The system of claim 7, wherein the chemical additive is generated or produced by the electrolyte treatment system.

12. The system of claim 7, wherein the electrolyte processing unit is configured to: receive the negative electrode electrolyte solution from the first tank or the positive electrode electrolyte solution from the second tank, perform an electrochemical oxidation-reduction reaction on the negative electrode electrolyte solution or the positive electrode electrolyte solution, and return the processed negative electrode electrolyte solution or positive electrode electrolyte solution to the tank from which it originally came out.

13. The system according to claim 12, wherein the electrochemical redox reaction is an oxidation reaction.

14. The system of claim 13, wherein the electrolyte processing unit is also capable of performing an electrochemical reduction reaction on the negative electrode electrolyte solution from the first tank or the positive electrode electrolyte solution from the second tank.

15. The system of claim 1, further comprising a barrier liner or coating on the interior of the second tank containing the positive electrode electrolyte solution.

16. The system of claim 1, further comprising an evaporation barrier on the surface of the positive electrode electrolyte solution in the second tank.

17. The system of claim 1, further comprising a hydraulic connection between the first tank and the second tank, wherein a valve is located on the hydraulic connection.

18. The system of claim 1, wherein the CN detection sensor comprises a pH sensor located in the second tank, a liquid level sensor located in the second tank, an ultraviolet / visible light sensor located in a sample circuit fluidly connected to the positive electrode electrolyte solution, or any combination thereof.

19. The system of claim 1, wherein the CN detection sensor further comprises an HCN sensor located in the top space above the positive electrode electrolyte solution in the second tank.

20. The system of claim 18, wherein the CN detection sensor comprises a pH sensor in the second tank and a liquid level sensor in the second tank.

21. The system according to claim 1, wherein the CN detection sensor comprises: Sensors configured for the direct detection of free cyanide or hydrogen cyanide, pH sensors, temperature sensors, colorimetric sensors, spectral sensors, electrochemical sensors, open-circuit voltage sensors, conductivity sensors, hydraulic sensors, liquid level sensors, liquid density sensors, liquid viscosity sensors, sensors configured for the direct detection of carbon dioxide, sensors configured for the direct detection of sulfur dioxide, or any combination thereof.

22. A method, the method comprising: A redox flow battery system is provided, the redox flow battery system comprising: Redox flow battery device, the redox flow battery device comprising: The first tank containing the negative electrode electrolyte solution; A second container containing the positive electrode electrolyte solution; A flow battery stack capable of extracting electrical energy from the chemical reaction between the negative and positive electrode electrolyte solutions, and capable of supplying electrical energy to induce a reverse reaction in the negative and positive electrode electrolyte solutions. The flow battery stack is configured to receive the negative electrode electrolyte solution from the first tank and return the negative electrode electrolyte solution to the first tank, and is configured to receive the positive electrode electrolyte solution from the second tank and return the positive electrode electrolyte solution to the second tank; and CN detection sensor; Processing the output data from the CN detection sensor to determine the fault state of the redox flow battery device; and Corrective actions are taken to resolve the fault condition and restore the system to normal operation.

23. The method of claim 22, wherein the fault state is a measurement result from the CN detection sensor that is above or below a threshold.

24. The method of claim 22, wherein the correction action is performed in advance regardless of the data from the CN detection sensor, and then the correction action is changed once the CN detection sensor reports a measurement result that is above or below a threshold.

25. The method of claim 22, wherein the corrective action is used to mitigate, control, reverse, or prevent the generation of free cyanide ions or hydrogen cyanide.

26. The method of claim 22, wherein the corrective action comprises: The chemical additives are delivered to the negative electrode electrolyte solution, the positive electrode electrolyte solution, or both the negative electrode electrolyte solution and the positive electrode electrolyte solution using an electrochemical processing unit.

27. The method of claim 22, wherein the redox flow battery device further comprises an electrochemical processing unit configured to deliver chemical additives to the negative electrode electrolyte solution, the positive electrode electrolyte solution, or both the negative electrode electrolyte solution and the positive electrode electrolyte solution.

28. The method of claim 27, wherein the electrochemical processing unit is further configured to generate or produce the chemical additive, and the corrective action includes using the chemical additive system to deliver the chemical additive to the negative electrode electrolyte solution, the positive electrode electrolyte solution, or both the negative electrode electrolyte solution and the positive electrode electrolyte solution.

29. The method of claim 27, wherein the electrochemical treatment unit comprises a chemical additive storage tank.

30. The method of claim 27, wherein the chemical additive is selected from the group consisting of: alkaline solutions, acidic solutions, buffer salts, buffer solutions, and oxidizing agents.

31. The method according to claim 30, wherein the chemical additive is an oxidant selected from chlorine, ozone, permanganate, hypochlorite, chlorite, chlorate and perchlorate.

32. The method of claim 27, wherein the electrochemical processing unit is configured to: receive the negative electrode electrolyte solution from the first tank or the positive electrode electrolyte solution from the second tank, perform an electrochemical oxidation-reduction reaction on the negative electrode electrolyte solution or the positive electrode electrolyte solution, and return the processed negative electrode electrolyte solution or positive electrode electrolyte solution to the tank from which it originally came out.

33. The method of claim 22, wherein the corrective action comprises: The negative electrode electrolyte solution from the first tank or the positive electrode electrolyte solution from the second tank is transferred to the electrochemical processing unit; as well as Electrochemical oxidation-reduction reaction is performed on the negative electrode electrolyte solution or the positive electrode electrolyte solution, and The treated negative or positive electrolyte solution is returned to the original container from which it originated.

34. The method according to claim 22, wherein the electrochemical redox reaction is an oxidation reaction.

35. The method according to claim 22, wherein: The CN detector includes a pH sensor and a liquid level sensor located inside the positive electrode electrolyte tank; and The fault conditions include a pH below a threshold pH and a volume of the positive electrode electrolyte solution above a threshold pH.

36. The method of claim 35, wherein the corrective action comprises generating a positive pressure differential in the flow battery stack in the direction from the positive electrolyte to the negative electrolyte.

37. The method of claim 35, wherein the corrective action comprises adjusting the flow rate of the negative electrode electrolyte solution, the positive electrode electrolyte solution, or both into the flow battery stack.

38. The method of claim 37, further comprising adjusting the flow rate to minimize the bulk solution transfer rate.

39. The method of claim 35, wherein the corrective action comprises adding a sodium hydroxide solution to the positive electrode electrolyte solution to bring the pH back to the initial pH value.

40. The method of claim 39, wherein the sodium hydroxide solution is added manually.

41. The method of claim 39, wherein the initial pH value is in the range of 11.5 to 12.

5.

42. The method of claim 35, wherein the corrective action comprises: Issue an alert to the flow battery operator regarding a suspected internal leak within the components of the flow battery stack; and Manually replace any components of the flow battery stack suspected of having internal leaks.

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