Redox flow battery with Raman spectrometer

Abstract

The redox flow battery includes a cell having a first electrode and a second electrode and an ion exchange layer therebetween, a first circulation loop and a second circulation loop in fluid communication with the first electrode and the second electrode, respectively, a first electrolyte storage tank and a second electrolyte storage tank in the first circulation loop and the second circulation loop, respectively, a first electrolyte and a second electrolyte contained in the first circulation loop and the second circulation loop, respectively, and a Raman spectrometer on at least one of the first circulation loop or the second circulation loop to determine a state of charge of at least one of the first electrolyte or the second electrolyte. The Raman spectrometer includes a laser light source and is rated to emit a laser at a wavelength of 694 nanometers to 1444 nanometers.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This disclosure claims priority to U.S. Patent Application No. 17 / 721,509, filed April 22, 2022. [Background technology]

[0002] Flow batteries, also known as redox flow batteries or redox flow cells, are designed to convert electrical energy into storable chemical energy and then re-release it back into electrical energy when there is a later demand. For example, flow batteries may be used in conjunction with renewable energy systems, such as wind power systems, to store energy in excess of consumer demand and later release that energy when there is more demand.

[0003] A typical flow battery contains a redox flow cell with negative and positive electrodes separated by an electrolyte layer, which may include a separator such as an ion exchange membrane. A negative fluid electrolyte (sometimes called anolyte or negolyte) is delivered to the negative electrode, and a positive fluid electrolyte (sometimes called catholyte or posolite) is delivered to the positive electrode, promoting a reversible redox reaction between the redox couple. Upon charging, the supplied electrical energy causes a reduction reaction in one electrolyte and an oxidation reaction in the other electrolyte. The separator prevents the electrolytes from freely and rapidly mixing, allowing ions to selectively pass through to complete the redox reaction. Upon discharging, chemical energy contained in the liquid electrolyte is released in a reverse reaction, drawing electrical energy from the electrodes. Summary of the Invention [Means for solving the problem]

[0004] The redox flow battery includes a cell having a first electrode and a second electrode and an ion exchange layer disposed therebetween, a first circulation loop and a second circulation loop in fluid communication with the first electrode and the second electrode, respectively, a first electrolyte storage tank and a second electrolyte storage tank in the first circulation loop and the second circulation loop, respectively, and a first electrolyte and a second electrolyte contained in the first circulation loop and the second circulation loop, respectively. On at least one of the first circulation loop or the second circulation loop is a Raman spectrometer for determining the state of charge of at least one of the first electrolyte or the second electrolyte. The Raman spectrometer includes a laser light source and is rated to emit a laser at a wavelength between 694 nanometers and 1444 nanometers.

[0005] In a further embodiment of any of the preceding embodiments, the first electrolyte is a manganese electrolyte, the second electrolyte is a polysulfide electrolyte, and the Raman spectrometer is on the first circulation loop.

[0006] In a further embodiment of any of the preceding embodiments, the wavelength is 1064 nanometers + / - 1 nanometer.

[0007] In a further embodiment of any of the preceding embodiments, the Raman spectrometer includes a probe on at least one of the first circulation loop or the second circulation loop.

[0008] In a further embodiment of any of the preceding embodiments, the Raman spectrometer includes a control module, the control module configured to collect spectrometer data and determine a state of charge of at least one of the first electrolyte or the second electrolyte from the spectrometer data.

[0009] In a further embodiment of any of the preceding embodiments, the control module is configured with the spectrometer data and calibration data that provides a correlation between concentration and state of charge.

[0010] In a further embodiment of any of the preceding embodiments, the cell has an inlet side where the first and second circulation loops feed the first and second electrolytes, respectively, to the cell, and an outlet side where the first and second electrolytes discharge from the cell to the feed of the first and second circulation loops, respectively, and the Raman spectrometer is located above the outlet side of the cell.

[0011] In a further embodiment of any of the preceding embodiments, the first electrolyte is a manganese electrolyte and the second electrolyte is a polysulfide electrolyte, a Raman spectrometer is on the first circulation loop, the Raman spectrometer includes a probe on the first circulation loop, the Raman spectrometer includes a laser light source rated to emit a laser at a wavelength of 1064 nanometers + / - 1 nanometer, the cell has an inlet side where the first circulation loop and the second circulation loop respectively feed the first electrolyte and the second electrolyte into the cell, the cell has an outlet side where the first electrolyte and the second electrolyte discharge from the cell to feed the first circulation loop and the second circulation loop respectively, and the probe is located on the outlet side of the cell.

[0012] A method according to an example of the disclosure includes collecting spectrometer data from an electrolyte in a redox flow battery (RFB) using a Raman spectrometer during operation of the RFB to charge or discharge electrical energy. The Raman spectrometer includes a laser light source and is rated to emit a laser at wavelengths between 694 nanometers and 1444 nanometers. Comparing the spectrometer data to calibration data determines a state of charge of the electrolyte and, based on the state of charge, determines whether a rebalance needs to be performed on the RFB.

[0013] In a further embodiment of any of the preceding embodiments, the RFB includes a cell having a first electrode and a second electrode and an ion exchange layer disposed therebetween, a first circulation loop and a second circulation loop in fluid communication with the first electrode and the second electrode, respectively, and a first electrolyte storage tank and a second electrolyte storage tank in the first circulation loop and the second circulation loop, respectively, an electrolyte is contained in the first circulation loop, and a Raman spectrometer is on the first circulation loop.

[0014] In a further embodiment of any of the preceding embodiments, the Raman spectrometer includes a probe on at least one of the first circulation loop or the second circulation loop.

[0015] In a further embodiment of any of the preceding embodiments, the cell has an inlet side where the first and second circulation loops feed the first and second electrolytes, respectively, to the cell, and an outlet side where the first and second electrolytes discharge from the cell to the feed of the first and second circulation loops, respectively, and the Raman spectrometer is located above the outlet side of the cell.

[0016] In a further embodiment of any of the preceding embodiments, the electrolyte is a manganese electrolyte.

[0017] In a further embodiment of any of the preceding embodiments, the wavelength is 1064 nanometers + / - 1 nanometer.

[0018] The present disclosure may include any one or more of the individual features disclosed above and / or below, taken alone or in any combination thereof.

[0019] The present disclosure may include any one or more of the individual features disclosed above and / or below, taken alone or in any combination thereof.

[0020] The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 illustrates an exemplary redox flow battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] FIG. 1 illustrates a schematic of an example of a redox flow battery ("RFB") 20. The RFB 20 includes a cell 22 (or multiple cells). The cell 22 includes a first electrode 22a, a second electrode 22b, and an ion-selective separator layer 22c between the electrodes 22a and 22b. For example, the electrodes 22a, 22b may be porous carbon structures, such as carbon paper or felt. The separator layer may be an ion-selective separator layer 22c that electrically isolates the electrodes while allowing selected ions to pass through to complete the redox reaction.

[0023] The first circulation loop 26 is in fluid communication with the first electrode 22a of the cell 22, and the second circulation loop 28 is in fluid communication with the second electrode 22b of the cell 22. As used herein, "loop" refers to a continuous closed circuit flow path. The first circulation loop 26 and the second circulation loop 28 may include electrolyte storage tanks 30 and 32, respectively. A first (negative) electrolyte 34 is contained in the first circulation loop 26 (i.e., in fluid communication with the tank 30), and a second (positive) electrolyte 36 is contained in the second circulation loop 28 (i.e., in fluid communication with the tank 32). One or more pumps P may be provided within each of the loops 26 / 28 and function to circulate the electrolyte 34 / 36 through the loops 26 / 28. As will be understood, the terms "first" and "second" are intended to distinguish that there are two different electrolytes / electrodes / loops. Further, it should be understood that the terms "first" and "second" are interchangeable in that a first electrolyte / electrode / loop can alternatively be referred to as a second electrolyte / electrode, and vice versa.

[0024] A variety of different electrochemically active species may be used in the RFB 20. One example of a set of species used in the first and second electrolytes 34 / 36 is manganese and sulfur, respectively. For example, the first electrolyte 34 is a manganese electrolyte contained in the first circulation loop 26 (i.e., in fluid communication with the tank 30) and the second electrolyte 36 is a polysulfide electrolyte contained in the second circulation loop 28 (i.e., in fluid communication with the tank 32). The first electrolyte 34 circulates through the first electrode 22a and the second electrolyte 36 circulates through the second electrode 22b. Although examples herein may be described with reference to manganese and polysulfide electrolytes, it should be understood that the examples are not so limited and other chemistries may be beneficial.

[0025] Manganese in the first electrolyte 34 generally refers to permanganates or manganates in an alkaline or basic solution. For example, the first electrolyte 34 may be 1 M sodium permanganate (NaMnO4) in 7.5 M sodium hydroxide (NaOH), or, as another example, 2 M NaMnO4 in 3 M NaOH. Polysulfides in the second electrolyte 36 generally refer to salts of sulfur in a basic pH solution. For example, in sodium hydroxide, the polysulfides have the formula Na2S x (x is 1 to 8). In one example, the second electrolyte 36 is 1 M Na2S in 7.5 M sodium hydroxide. x may be also possible.

[0026] The following equations show example reactions in cell 22 as well as the resulting electrode potentials (E o ) versus the standard hydrogen electrode (SHE) and the open cell voltage (OCV), and are referred to herein as E o Vs. SHE and OCV are defined as the difference between the standard electrode potentials of the two electrode reactions.

[0027] Negative: 2Na2S2←→Na2S4+2Na + +2e - E o =-0.492 vs. SHE Correct: 2NaMnO4+2Na + +2e - ←→2Na2MnO4 E o =+0.564 vs. SHE Net cell: 2Na2S2 + 2NaMnO4 ←→ Na2S4 + 2Na2MnO4 OCV=1.06V RFBs are susceptible to capacity loss for a variety of reasons. Capacity loss is a decrease in the amount of electrical energy that can be stored in (or provided by) the electrolyte of an RFB compared to the maximum amount of electrical energy that the electrolyte can store (or provide) at its initial or theoretical maximum concentration. For example, as ions pass through the separator membrane, they may undesirably precipitate as solids that cannot participate in electrochemical reactions or that self-discharge. Over time, such mechanisms can result in concentration imbalance between the electrolytes. This concentration imbalance reduces the capacity of each electrolyte, and therefore the entire system, to store and discharge electrical energy. Measures to restore capacity are known. However, to employ these measures effectively and to do so only when necessary, the concentrations must first be determined.

[0028] Capacity loss in an RFB can be diagnosed by monitoring the state of charge ("SOC") of the electrochemically active species in the electrolyte. For example, the SOC of an electrolyte can be expressed in terms of the concentrations of the various oxidation states of the electrochemically active species, i.e., the concentration of the oxidized form of species 1 divided by the sum of the concentrations of the oxidized and reduced forms of species 1. Some active materials can have more than two oxidation states attained in a given electrolyte. In an RFB system starting with a known molar amount of each active species in each electrolyte, deviations in the measured SOC between the opposing electrolytes can indicate an imbalance and cause attainable capacity loss. Alternatively, the overall active species concentration in the electrolytes (both oxidized and reduced) can drift due to active species crossover, active species decomposition, or solvent migration between the electrolytes, affecting the attainable capacity. To combat capacity loss, measures can be taken to restore capacity when deviations in SOC or total concentration between electrolytes reach a preset threshold.

[0029] Various methods are known for monitoring concentration and / or SOC. For example, observation of the open circuit voltage ("OCV") can be used as an indirect indicator of SOC. However, OCV only serves as the SOC of the system and only observes the complete cell voltage, and therefore does not indicate the individual state of the two electrolytes. Optical UV-Vis absorbance spectroscopy can also be used, especially for all-vanadium chemistries. However, some chemistries make reliable use of UV-Vis absorbance spectroscopy difficult. For example, manganese electrolytes can decompose into solid oxide species (suspended in the electrolyte), and these species exhibit strong absorbance bands, masking the absorbance profile of interest for species identification and making accurate measurements difficult. For polysulfide electrolytes, the correlation between polysulfide species and wavelength is concentration dependent, making accurate measurements difficult.

[0030] In this regard, as described in further detail below, the RFB 20 includes a Raman spectrometer 38 to determine the SOC of at least one of the first or second electrolytes 34 / 36. Unlike UV-Visible absorption spectroscopy, Raman spectroscopy relies on the interaction of light with molecular bond vibrations in the species compounds to produce Raman scattering, i.e., re-emission of the excitation light. For species of interest in the RFB 20, e.g., manganese and sulfur species, coherent scattering from by-products does not overwhelm the signal from the active species as much as coherent absorption in UV-Vis spectroscopy, so Raman spectroscopy can more easily distinguish between different species.

[0031] In the illustrated example, the Raman spectrometer 38 includes a control module 40, a probe 42 on one or both of the circulation loops 26 / 28, and an optical cable 44 connecting the control module 40 and the probe 42. The control module 40 includes a laser source 40a and an analysis module 40b. The laser source 40a generates light over a very narrow wavelength range, or substantially a single wavelength (monochromatic) light.

[0032] The laser travels through the optical cable 44, emanates from the probe 42, and passes through a window in the tubing forming the loop 26 / 28, for example, and enters the electrolyte of interest 34 or 36 in the RFB 20. The laser interacts with the species molecules in the electrolyte 34 or 36, generating Raman scattering that is received by the analysis module 40b via the optical cable 42 and returned as spectrometer data. The analysis module 40b includes hardware (e.g., one or more microprocessors, memory, etc.), software, or both, configured to analyze the spectrometer data and determine the concentration and oxidation state of the active materials, thereby enabling calculation of the SOC of a single electrolyte. As is commonly known in Raman spectroscopy, one or more filters may be present in the optical cable 42 and / or analysis module to reduce noise and condition the spectrometer data.

[0033] In the illustrated example, the Raman spectrometer 38 is shown on the first circulation loop 26. For example, the cell 22 has an inlet side 22c where the electrolyte 34 / 36 in the first and second circulation loops 26 / 28 is fed into the cell 22, and an outlet side 22d where the electrolyte 34 / 36 is discharged from the cell into the first and second circulation loops 26 / 28. The Raman spectrometer 38 is located on the outlet side 22d of the cell 22, i.e., downstream from the cell 22 but upstream of the storage tank 30 / 32. It should be understood that an additional Raman spectrometer 38 may be used on the second circulation loop 28, or a Raman spectrometer 38 may be used on the second circulation loop 28 instead of the first circulation loop 26. Such a location allows for greater accuracy in the measurement of the electrolyte 34 / 36, since the concentration of species in the electrolyte 34 / 36 immediately after it leaves the cell 22 closely represents the concentration inside the cell 22. Further downstream, electrolyte 34 / 36 is delivered into storage tank 30 / 32 and mixed with previous "used" electrolyte, which may have a slightly different concentration.

[0034] Typically, the laser source 40a is rated to emit a laser with a wavelength in the range of 694 nanometers to 1444 nanometers. The wavelength selected for a particular implementation can be matched to the particular species being analyzed to minimize noise, especially fluorescence noise that may mask the Raman scattering wavelength band of interest. For example, lasers are typically available over a range of standard wavelengths. By testing the species of interest at several of these wavelengths, one of ordinary skill in the art having the benefit of this disclosure can determine the best wavelength or wavelength range for a particular species.

[0035] In a further example, the wavelength is 1064 nanometers + / - 1 nanometer. Such a wavelength can be provided, for example, by a Nd:YAG laser source with a nominal power of 430 mW. The wavelength of 1064 nanometers is particularly suitable for the manganese electrolyte described above. At other lower wavelengths, the manganese species fluoresce over a wide range of wavelengths, resulting in significant noise and making it more difficult to identify the wavelength band of interest. However, at 1064 nanometers, fluorescence is minimal, allowing for increased resolution of the wavelength of interest.

[0036] The analysis module 40b includes a detector that receives the Raman scattering and generates an electrical signal that represents the spectrometer data, proportional to wavelength and intensity. The analysis module 40b determines the concentration and SOC of the electrolyte 34 or 36 based on the spectrometer data. For example, the analysis module 40b is provided with calibration data that correlates the spectrometer data to the concentration and SOC. Such calibration data can be derived from a control sample of a species of known concentration, which when analyzed by Raman spectroscopy produces a spectral wavelength scan of the Raman scattering response and response intensity. The scan or individual wavelengths or wavelength bands correlate to the known concentration of the control sample because the wavelength peaks and / or wavelength intensities are unique. Thus, the spectrometer data of the electrolyte 34 or 36, once collected, is input into the correlation produced by the control sample and the concentration, and the SOC value is measured. As will be appreciated, the spectrometer data and calibration data may be used directly for these purposes, but may instead be used to derive them into other meaningful data. Thus, the spectrometer data and calibration data may refer to the data itself or to a derivation of the data.

[0037] The RFB 20 also illustrates example methods, such as a method for maintaining the health of the RFB 20. For example, during operation of the RFB 20 to charge or discharge electrical energy, the Raman spectrometer 38 is used to collect spectrometer data from one of the electrolytes 34 / 36, as described above. The spectrometer data is then compared to the calibration data to determine the SOC. Based on the SOC, a decision is made as to whether a rebalance of activity needs to be performed on the RFB 20. For example, a threshold SOC may be established above which a rebalance is performed. The method of rebalancing is not particularly limited. Known rebalancing techniques may be utilized, such as, but not limited to, chemical treatment with an oxidizing or reducing agent, electrochemical treatment in a rebalancing cell, or addition of supplemental chemicals.

[0038] The Raman spectrometer 38 offers the capability to determine the SOC of species that are otherwise not amenable to UV-Visible absorption spectroscopy. Furthermore, selecting the appropriate laser wavelength for a given set of species can facilitate reduction of background noise, thus enabling high resolution measurements. Furthermore, SOC analysis can be performed in situ and on demand almost instantly, without the need to shut down the RFB.

[0039] Although a combination of features is shown in the illustrated examples, not all features need to be combined to realize the advantages of various embodiments of the present disclosure. In other words, a system designed in accordance with an embodiment of the present disclosure does not necessarily include all of the features shown in any one of the drawings, or all of the portions shown generally in the drawings. Furthermore, selected features of one exemplary embodiment may be combined with selected features of other exemplary embodiments.

[0040] The foregoing description is exemplary in nature, rather than limiting. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.

Claims

1. a cell having a first electrode and a second electrode and an ion exchange layer disposed therebetween; a first circulation loop and a second circulation loop in fluid communication with the first electrode and the second electrode, respectively; a first electrolyte storage tank and a second electrolyte storage tank in the first circulation loop and the second circulation loop, respectively; a first electrolytic solution and a second electrolytic solution contained in the first circulation loop and the second circulation loop, respectively; a Raman spectrometer on at least one of the first circulation loop or the second circulation loop for determining a state of charge of at least one of the first electrolyte or the second electrolyte, the Raman spectrometer including a laser source rated to emit a laser at a wavelength of 694 nanometers to 1444 nanometers; A redox flow battery comprising:

2. 2. The redox flow battery of claim 1, wherein the first electrolyte is a manganese electrolyte, the second electrolyte is a polysulfide electrolyte, and the Raman spectrometer is on the first circulation loop.

3. 3. The redox flow battery of claim 2, wherein the wavelength is 1064 nanometers + / - 1 nanometer.

4. 2. The redox flow battery of claim 1, wherein the Raman spectrometer includes a probe on at least one of the first circulation loop or the second circulation loop.

5. 10. The redox flow battery of claim 1, wherein the Raman spectrometer includes a control module configured to collect spectrometer data and determine a state of charge of at least one of the first electrolyte or the second electrolyte from the spectrometer data.

6. 6. The redox flow battery of claim 5, wherein the control module is configured with the spectrometer data and calibration data providing a correlation between concentration and state of charge.

7. 2. The redox flow battery of claim 1, wherein the cell has an inlet side where the first and second circulation loops feed the first and second electrolytes, respectively, to the cell and an outlet side where the first and second electrolytes leave the cell to feed the first and second circulation loops, respectively, and the Raman spectrometer is located above the outlet side of the cell.

8. 2. The redox flow battery of claim 1, wherein the first electrolyte is a manganese electrolyte and the second electrolyte is a polysulfide electrolyte, the Raman spectrometer is on the first circulation loop, the Raman spectrometer includes a probe on the first circulation loop, the Raman spectrometer includes a laser light source rated to emit a laser at a wavelength of 1064 nanometers + / - 1 nanometer, the cell has an inlet side where the first circulation loop and the second circulation loop each feed the first electrolyte and the second electrolyte into the cell, the cell has an outlet side where the first electrolyte and the second electrolyte exit the cell to feed the first circulation loop and the second circulation loop, respectively, and the probe is located on the outlet side of the cell.

9. collecting spectrometric data from an electrolyte in a redox flow battery (RFB) using a Raman spectrometer during operation of the RFB to charge or discharge electrical energy, the Raman spectrometer including a laser light source rated to emit a laser at wavelengths from 694 nanometers to 1444 nanometers; comparing the spectrometer data with calibration data to determine a state of charge of the electrolyte; determining whether a rebalance needs to be performed on the RFB based on the state of charge; A method comprising:

10. The RFB is a cell having a first electrode and a second electrode and an ion exchange layer disposed therebetween; a first circulation loop and a second circulation loop in fluid communication with the first electrode and the second electrode, respectively; a first electrolyte storage tank and a second electrolyte storage tank in the first circulation loop and the second circulation loop, respectively; Including, the electrolyte is contained in the first circulation loop; The method of claim 9 , wherein the Raman spectrometer is on the first circulation loop.

11. The method of claim 10 , wherein the Raman spectrometer includes a probe on at least one of the first circulation loop or the second circulation loop.

12. 12. The method of claim 11, wherein the cell has an inlet side where the first and second circulation loops feed the first and second electrolytes, respectively, to the cell, and an outlet side where the first and second electrolytes leave the cell to feed the first and second circulation loops, respectively, and the Raman spectrometer is located above the outlet side of the cell.

13. The method of claim 10, wherein the electrolyte is a manganese electrolyte.

14. The method of claim 10, wherein the wavelength is 1064 nanometers + / - 1 nanometer.

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