Flow battery state of health indicator

Abstract

A state-of-charge indicator device for a redox flow battery system, the state-of-charge indicator device having a reference cell device for measuring a potential difference between a positive electrolyte and a negative electrolyte and an auxiliary reference electrolyte device, the auxiliary reference electrolyte device comprising a separate auxiliary electrolyte reservoir, the invention relates to a reference cell device comprising an auxiliary reference electrolyte reservoir for accommodating a redox electrode associated with a reference electrolyte, means for measuring the potential difference between the auxiliary reference electrolyte and the electrolyte of the reference cell device, and an ion channel conduit connecting the auxiliary reference electrolyte reservoir and the electrolyte of the reference cell device, the ion channel conduit being configured to have a low fluid diffusivity, wherein the conduit comprises a wicking device for absorbing the electrolyte and maintaining an ionic connection between the respective electrolyte of the auxiliary reference electrolyte reservoir and the reference cell device.

Description

Technical Field

[0001] The present invention relates to the field of redox flow batteries. More specifically, the present invention relates to a health state or charge state of an electrolyte in a flow battery, a device or reference battery for detecting the health state or charge state of an electrolyte, a method for manufacturing the device, a method for detecting, monitoring or correcting the health state or charge state of an electrolyte in a flow battery, and a redox flow battery with a health state indicator. Background Art

[0002] An imbalance in the charge state of the positive and negative electrolytes of a redox flow battery (eg, a vanadium redox flow battery) may occur over time or use.

[0003] When the charge state of a vanadium redox flow battery is unbalanced, the energy storage capacity and performance of the flow battery will decrease.

[0004] In order to determine the imbalance of the charge state of a flow battery, a measurement or indication of the charge state of each positive and negative electrolyte is required. In the absence of reliable information about the charge balance between the two electrolytes, the flow battery may operate based on false information, which may lead to hazards due to overcharging or overdischarging of the electrolytes, or at least limit the available depth of discharge and battery efficiency. The lack of reliable information about the charge balance between the two electrolytes also means that remedial or corrective actions (whether manual or automatic) cannot be taken in a timely manner.

[0005] Several methods have been proposed to measure the state of charge of electrolytes in flow batteries.

[0006] WO-A-90 / 03666 describes a method for indirectly detecting the charge state of the electrolyte in the bipolar state by light absorption, density and viscosity measurements. However, optical measurements are susceptible to instrument drift (caused by changes in the light source and detector over time and temperature), while in-line density and viscosity measurements require expensive equipment (especially for relatively harsh chemical conditions and the high resolution required for VRFB).

[0007] An online potentiometric titration technique is proposed in JP 09-101286. However, this method has an extreme requirement for controlling the titration volume of the electrolyte, which limits the method and makes it difficult to apply it in commercial systems.

[0008] Methods for measuring electrolyte potential at inert redox electrodes have also been proposed before.

[0009] A conventional reference electrode is suggested in WO-A-90 / 03666. However, the reference electrode is susceptible to contamination and thus voltage drifts after prolonged immersion in the test electrolyte. Therefore, these methods are not practical for commercial systems where maintenance intervals are as long as months or years.

[0010] A dynamic hydrogen electrode is proposed in WO-A-2014 / 184617. The dynamic hydrogen electrode uses platinum group metals to catalyze the production of hydrogen. However, platinum group metals are easily dissolved or contaminated in the electrolyte, so unstable results are obtained after long-term use. In addition, the dissolved catalyst will be deposited on the negative electrode of the liquid flow battery and promote the unbalanced reaction (producing hydrogen).

[0011] US-A-2018 / 0375132 proposes a reference cell in which one half-cell has a reference electrolyte of similar composition and known charge state, and the other half-cell has a test electrolyte flowing through it. However, cells using membrane separation are prone to mass transfer through the membrane, resulting in relatively rapid changes in the composition of the reference electrolyte.

[0012] The inventors have designed a device and apparatus that can be used to detect or verify the charge state of an electrolyte in a redox flow battery. The device and apparatus are simple to use, low cost, stable and durable.

[0013] Problems to be solved by the present invention

[0014] What is needed is a robust and low-cost method and apparatus for independently measuring or detecting the state of charge of the electrolyte in each electrode of a redox flow battery.

[0015] The object of the present invention is to provide a method and a device or system that can measure or detect the charge state of one or both electrolytes and / or determine the health state of a flow battery.

[0016] Another object of the present invention is to provide a method and apparatus or system for determining when an operation should be performed to resolve a charge state imbalance problem between electrolytes in a flow battery. Summary of the invention

[0017] A first aspect of the present invention provides a state of charge or state of health indicator device for a redox flow battery system, the redox flow battery system comprising a battery pack of the redox flow battery, a positive electrolyte tank and a conduit for circulating the positive electrolyte through the battery pack, a negative electrolyte tank and a conduit for circulating the negative electrolyte through the battery pack of the flow battery, the indicator device comprising:

[0018] a reference cell device comprising a device for measuring a potential difference between a positive electrolyte of or from a positive electrolyte tank of a flow battery and a negative electrolyte of or from a negative electrolyte tank of a flow battery; and

[0019] At least one auxiliary reference electrolyte device comprising

[0020] a separate auxiliary electrolyte reservoir for containing a redox electrode associated with a reference electrolyte of known composition comparable to the desired or initial composition of the flow battery electrolyte and providing a reference for the flow battery electrolyte, and having a known state of charge;

[0021] means for measuring the potential difference between the auxiliary reference electrolyte and the corresponding electrolyte of the reference cell device; and

[0022] An ion channel conduit connecting an auxiliary reference electrolyte reservoir and a corresponding electrolyte of a reference cell device, the conduit being configured to have a low fluid diffusion capability or rate, preferably wherein the conduit comprises a wicking device, preferably wherein the wicking device is used to absorb the electrolyte and maintain an ionic connection between the auxiliary reference electrolyte reservoir and the corresponding electrolyte of the reference cell device.

[0023] A second aspect of the present invention provides a state of charge or state of health indicator device (or apparatus or system) for a redox flow battery system, the redox flow battery system comprising a battery pack of the redox flow battery, a positive electrolyte tank and a conduit for circulating the positive electrolyte through the battery pack, a negative electrolyte tank and a conduit for circulating the negative electrolyte through the battery pack of the flow battery, the indicator device comprising:

[0024] a reference cell comprising a positive half-cell having a positive electrolyte reservoir in fluid circulation communication with a positive electrolyte tank of a flow battery, a negative half-cell having a negative electrolyte reservoir in fluid circulation communication with a negative electrolyte tank, and a device for measuring a potential difference between the two electrodes of the reference cell; and

[0025] At least one auxiliary reference electrolyte device (or device or system or subsystem), comprising:

[0026] a separate auxiliary electrolyte reservoir for containing a redox electrode associated with a reference electrolyte of known composition comparable to the desired or initial composition of the flow battery electrolyte and providing a reference for the flow battery electrolyte, and having a known state of charge;

[0027] means for measuring the potential difference between the auxiliary reference electrolyte and the corresponding half-cell of the reference cell; and

[0028] An ion channel conduit connecting the auxiliary reference electrolyte reservoir and the electrolyte of the corresponding half-cell of the reference cell, the conduit being configured for low fluid diffusion capacity or rate, wherein the conduit preferably includes a wicking device, the wicking device preferably being used to absorb the electrolyte and maintain ionic connection between the auxiliary reference electrolyte reservoir and the electrolyte of the corresponding half-cell of the reference cell.

[0029] A third aspect of the present invention provides a state of charge or state of health indicator device for a redox flow battery system, the redox flow battery system comprising a redox flow battery battery pack, a positive electrolyte tank and a conduit for circulating the positive electrolyte through the battery pack, a negative electrolyte tank and a conduit for circulating the negative electrolyte through the battery pack of the flow battery, the indicator device comprising:

[0030] At least one auxiliary reference electrolyte device comprising

[0031] a separate auxiliary electrolyte reservoir for containing a redox electrode associated with a reference electrolyte of known composition comparable to the desired or initial composition of the flow battery electrolyte and providing a reference for the flow battery electrolyte, and having a known state of charge;

[0032] means for measuring the potential difference between the auxiliary reference electrolyte and the corresponding electrolyte of the flow cell (or reference cell device); and

[0033] an ion channel conduit connecting the auxiliary reference electrolyte reservoir and the corresponding electrolyte of the flow battery (or reference cell device), the conduit being configured for low fluid diffusion capacity or rate, wherein the conduit preferably includes a wicking device, the wicking device preferably being used to absorb the electrolyte and maintain ionic connection between the auxiliary reference electrolyte reservoir and the corresponding electrolyte of the flow battery (or reference cell device);

[0034] and a device for determining the charge state or charge state representation of the other electrolyte (usually the negative electrolyte) of the liquid flow battery, for example by providing a reference cell, the reference cell comprising a positive half-cell, a negative half-cell and a device for measuring the potential difference between the two electrodes of the reference cell, the positive half-cell having a positive electrolyte reservoir, the positive electrolyte reservoir being in fluid circulation communication with the positive electrolyte tank of the liquid flow battery, the negative half-cell having a negative electrolyte reservoir, the negative electrolyte reservoir being in fluid circulation communication with the negative electrolyte tank; and

[0035] A fourth aspect of the present invention provides an indicator system for the health status of a redox flow battery system, the indicator system comprising a charge state indicator device as described above, and configured to determine the health status of the redox flow battery system, preferably by measuring the charge state of at least one electrode electrolyte and another electrode electrolyte or a representation thereof of the flow battery (optionally, continuously, periodically or intermittently), preferably determining the relative oxidation state of the corresponding electrolytes, and preferably issuing an alarm, indicating or taking remedial measures when the determined relative oxidation state exceeds a predetermined limit.

[0036] A fifth aspect of the present invention provides an auxiliary reference electrolyte device for the above-mentioned charge state or health state indicator, the auxiliary reference electrolyte device comprising:

[0037] a separate auxiliary electrolyte reservoir for containing a redox electrode associated with a reference electrolyte of known composition comparable to the desired or initial composition of the flow battery electrolyte and providing a reference for the flow battery electrolyte, and having a known state of charge;

[0038] means for measuring the potential difference between the auxiliary reference electrolyte and the associated electrolyte of the reference cell arrangement or the associated half-cell of the reference cell; and

[0039] An ion channel conduit for connecting an auxiliary reference electrolyte reservoir and an electrolyte in a corresponding electrolyte of a reference cell device or a corresponding half-cell of a reference cell, wherein the conduit is configured for low fluid diffusion capacity or rate, wherein the conduit preferably includes a wicking device, and the wicking device is preferably used to absorb the electrolyte and maintain ionic connection between the auxiliary reference electrolyte reservoir and the corresponding electrolyte of the reference cell device or the corresponding half-cell of the reference cell.

[0040] A sixth aspect of the present invention provides a redox flow battery comprising a redox flow battery pack, a positive electrolyte tank and a conduit for circulating the positive electrolyte through the battery pack, a negative electrolyte tank and a conduit for circulating the negative electrolyte through the flow battery pack, and a charge state or health state indicator as described above.

[0041] The seventh aspect of the present invention provides a method for monitoring the charge state or health state of a redox flow battery, the method comprising providing a charge state or health state indicator as described above, and causing the charge state or health state indicator to periodically measure the charge between a reference cell and an auxiliary reference electrolyte and the corresponding half-cells of the reference cell, thereby determining the charge state of the system, and optionally, issuing an alarm for charge imbalance of the flow battery electrolyte based on the difference between the charge state of the two poles of the reference cell of the flow battery and a predetermined threshold.

[0042] An eighth aspect of the present invention provides a method for maintaining a charge balance state in a redox flow battery, the method comprising:

[0043] Monitoring the state of charge in the flow battery by providing a state of charge or health indicator as described above, and causing the state of charge or health indicator to measure the charge at the two electrodes of the reference cell and the charge between the auxiliary reference electrolyte and the corresponding half-cell of the reference cell periodically or in response to an action or in response to an event, and thereby determining the state of charge and / or health of the system; and

[0044] When the difference in state of charge between the positive electrolyte and the negative electrolyte exceeds one or more predetermined thresholds or satisfies one or more predetermined criteria, one or more maintenance actions are taken on the flow battery.

[0045] Advantages of the Invention

[0046] The charge state or health state indicator of the present invention has the stability advantage of a standard reference battery, but also optimizes the problem of voltage drift in the reference battery caused by battery electrolyte contamination. It can maintain measurement consistency throughout the service life of the flow battery, thereby more accurately measuring the battery's health state and using the battery capacity more fully and safely throughout the battery's service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 shows a perspective view of a charge status indicator device according to an embodiment of the present invention;

[0048] Figure 2a to Figure 2c is a perspective view of an ion channel conduit used in a charge state indicator device according to an embodiment of the present invention; and

[0049] Figure 3 is a schematic diagram of a charge state or health state indicator according to an embodiment of the present invention;

[0050] Figure 4 is a simplified piping and instrumentation diagram of a flow battery of an embodiment of one aspect of the present invention, including a state of charge or state of health indicator of an embodiment of another aspect of the present invention;

[0051] Figure 5a and Figure 5b : is a graph showing the relationship between the voltage and the absolute current of a flow battery reference battery in a flow battery including a charge state indicator according to an embodiment of the present invention ( Figure 5a ) and the positive electrolyte and auxiliary electrolyte of the reference cell in the flow battery ( Figure 5b ) between the voltage and the absolute current; and

[0052] Figure 6 An image showing an experimental setup for determining the diffusion rate through an ion channel conduit in a secondary reference electrolyte apparatus, used in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0053] The charge state or health state indicator for a redox flow battery system of the present invention is applicable to a redox flow battery having a redox flow battery stack, a positive electrolyte tank, a negative electrolyte tank, and conduits for circulating the electrolyte from the tanks through various parts of the battery stack.

[0054] The battery pack referred to here refers to the liquid flow battery cell excluding the separator, electrode or current collector and battery frame. The battery pack may include one or more battery cells (usually arranged in parallel and provided with a single combined electrolyte supply or multiple parallel electrolyte supplies by each electrolyte tank).

[0055] A flow battery cell generally includes two half-cells for carrying electrolyte, the electrolyte is provided by corresponding electrolyte tanks, and the two half-cells are separated by an ion selective membrane. Each half-cell has an electrode or current collector, which is connected to a circuit that provides a power source or load for charging or discharging the battery.

[0056] The electrolyte is typically circulated from each electrolyte tank through the cell or batteries by means of a pump.

[0057] The state of charge or health indicator device includes at least one auxiliary reference electrolyte (interchangeably referred to herein as auxiliary electrolyte) device configured to determine the state of charge of an electrolyte of one electrode of the flow battery (usually the positive electrolyte). Optionally, a second auxiliary electrolyte device is provided to determine the state of charge of a second electrolyte of the flow battery (usually the negative electrode).

[0058] The charge state or health state indicator includes a reference cell, a reference cell device or a device for determining the charge state of a second / other electrolyte of a liquid flow battery (the first electrolyte is the electrolyte determined by an auxiliary electrolyte device), wherein the second / other electrolyte is typically a negative electrode electrolyte, or includes a characterization device (proxy means) for determining information characterizing the charge state of a second electrolyte (typically a negative electrode electrolyte).

[0059] The charge state of the second / other electrolyte of the flow battery can be determined by any suitable means, for example, a second auxiliary electrolyte device can be provided to determine the charge state of the second electrolyte (usually the negative electrode) of the flow battery. The characterization device for determining information characterizing the charge state of the second electrolyte (usually the negative electrode electrolyte) can be any suitable device, and the charge state of the second electrolyte is similar to the measurement results of the characterization device or can be estimated by the measurement results of the characterization device. In a particularly preferred embodiment, the characterization device is a reference cell device or reference cell of the flow battery.

[0060] The reference cell device comprises a device for measuring the potential difference between a positive electrolyte and a negative electrolyte, the positive electrolyte being the electrolyte of the positive electrolyte tank of the flow battery or the electrolyte from the positive electrolyte tank, and the negative electrolyte being the electrolyte of the negative electrolyte tank of the flow battery or the electrolyte from the negative electrolyte tank. Preferably, the state of charge or health indicator device comprises (and the reference cell device is) at least one reference cell of the flow battery.

[0061] In a reference cell apparatus, a device for measuring the potential difference between a positive electrolyte in or from a positive electrolyte tank of a liquid flow battery and a negative electrolyte in or from a negative electrolyte tank of a liquid flow battery may include electrodes arranged in association with each electrolyte (e.g., with each electrolyte tank), and a voltmeter or similar instrument (for measuring the potential difference) connected to the two electrodes.

[0062] At least one reference cell (included in certain aspects and preferred embodiments of the present invention) includes a positive half-cell and a negative half-cell, the positive half-cell having a positive electrolyte reservoir, the positive electrolyte reservoir being in fluid circulation communication with the positive electrolyte tank of the flow battery, and the negative half-cell having a negative electrolyte reservoir, the negative electrolyte reservoir being in fluid circulation communication with the negative electrolyte tank. At least one reference cell includes a device for measuring the potential difference between the two poles of the reference cell. For example, the device may include electrodes arranged in association with each half-cell and a voltmeter or similar instrument connected to each electrode. The device is preferably configured to determine the open circuit voltage on the reference cell, i.e., the voltage between the positive and negative electrolytes of the flow battery.

[0063] The positive and negative half-cells of the reference cell may be in fluid communication with the respective electrolyte tanks of the flow battery by any suitable means, such as conduits connecting the positive and negative half-cells of the reference cell to the respective electrolyte tanks, more preferably means for circulating electrolyte from the electrolyte tanks to the flow battery pack and / or from the flow battery pack to the electrolyte tanks via conduits. Optionally, the half-cells of the reference cell are connected to the electrolyte tanks by conduits so as to lead to and from the return arms of the conduit system so as to circulate electrolyte from the tanks through the flow battery pack, but preferably the electrolyte is delivered from the tanks to the battery pack (e.g., at a location just before the electrolyte enters the battery pack) via the conduits.

[0064] Preferably, the electrolyte flows to the battery in a direction parallel to its flow to the reference cell. The positive and negative electrolytes flow out near the battery inlet (through branching of the conduit) and can then be anywhere downstream in the battery (between the battery outlet and the tank) or directly back to the tank.

[0065] In the reference cell, the positive electrolyte generally has one inlet and one outlet (through one half-cell of the reference cell), and the negative electrolyte generally has one inlet and one outlet (through the opposite half-cell of the reference cell). The electrolytes are preferably electronically isolated but ionically connected by an ion exchange membrane (or microporous membrane) within the reference cell.

[0066] The height of the reference cell relative to the tank and battery pack is not critical. In practical operation, the reference cell is preferably substantially at the same height as the battery pack (to prevent the battery pack from being positioned too low and electrolyte from being siphoned out of the tank in the event of a leak).

[0067] Preferably, the reference cell is provided with a temperature sensor or thermometer to adjust the potential difference measurement associated with the reference cell according to the temperature. Optionally, the temperature sensor can be configured to measure or determine the temperature of the reference cell in the electrolyte in one or both half-cells of the reference cell and / or on other components of the reference cell, such as the housing.

[0068] The auxiliary reference electrolyte device is a feature of the charge state or health state indicator and is also another aspect of the present invention. The auxiliary reference electrolyte device includes a separate auxiliary electrolyte reservoir, a device for measuring the potential difference between the auxiliary reference electrolyte or each auxiliary reference electrolyte and the corresponding half-cell of the reference cell (or the corresponding electrolyte of the reference cell device or liquid flow battery), and an ion channel conduit connecting the auxiliary reference electrolyte reservoir or each auxiliary reference electrolyte reservoir and the corresponding half-cell of the reference cell (or the corresponding electrolyte of the reference cell device or liquid flow battery). The ion channel conduit preferably includes a wicking device (wicking means), which is preferably used to absorb the electrolyte and maintain the ionic connection between the auxiliary reference electrolyte reservoir and the corresponding half-cell of the reference cell (or the corresponding electrolyte of the reference cell device or liquid flow battery).

[0069] In some applications, temperature gradients may occur, which may cause outgassing of gases dissolved in the electrolyte in the ion channel conduit. The outgassing may cause bubbles to form in the ion channel conduit, which may destroy the ionic connections in the ion channel conduit. The advantage of a wicking device is that the electrolyte absorbed by the wicking device will maintain the ionic connections in the ion channel conduit when bubbles form.

[0070] Alternatively, the wicking device may extend through only a portion of the ion channel conduit, such as by positioning the wicking device at a single high point in the ion channel conduit, or positioning the wicking device at or extending through two or more high points where there is a risk of bubble formation or entrapment.

[0071] The wicking means preferably extends continuously along the entire length of the ion channel conduit.

[0072] Preferably, the wicking means extends from the ion channel conduit to the auxiliary reference electrolyte reservoir and / or the corresponding half-cell of the reference cell (or the corresponding electrolyte of the reference cell device or the flow battery). Preferably, the wicking means extends at most 10 mm, more preferably at most 8 mm, more preferably at most 6 mm, such as to 5 mm from the ion channel conduit. Preferably, the wicking means extends at least 0.5 mm, more preferably at least 1 mm, more preferably at least 2 mm, such as at least 3 mm from the ion channel conduit.

[0073] The wicking means is preferably hydrophilic and / or non-conductive (usually σ < 10 -3 S / cm). The wicking means preferably comprises (or consists of) silica, ceramic and / or a hydrophilic polymer, such as silica, ceramic and / or hydrophilic polymer fibers.

[0074] The wicking means is preferably a core or thread, preferably composed of bundled (such as woven, wound or braided) fibers. The wicking means is a core or thread with a diameter preferably of 0.4 mm to 8 mm, preferably 1 mm to 6 mm, more preferably 2 mm to 4 mm, for example about 3 mm.

[0075] In one embodiment, the ion channel conduit is defined by a wicking means that optionally extends through a flexible sleeve or tubing.

[0076] The separated auxiliary electrolyte reservoir is used to accommodate the redox electrode and the reference electrolyte. The reference electrolyte is selected from a known composition, which is preferably the same as the required composition of the corresponding electrolyte of the flow battery and is in a predetermined known charge state. The required composition of the corresponding electrolyte of the flow battery is usually the initial composition (before any degradation or contamination occurs). The size of the separated auxiliary electrolyte reservoir can be selected arbitrarily. For example, the electrolyte volume of the separated auxiliary electrolyte reservoir is preferably at least 10 ml, preferably not more than 10 liters. More preferably, the electrolyte volume is between 30 ml and 1000 ml, more preferably between 50 ml and 750 ml, and more preferably at least 100 ml. In one embodiment, the electrolyte volume is at least 400 ml, such as 400 ml to 600 ml. In another embodiment, particularly when the ion channel conduit is relatively narrow, long or curved / circular (as described below), the volume of the separate auxiliary electrolyte reservoir is at most 500 ml, for example 100 ml to 350 ml, more preferably at most 250 ml, and even more preferably at most 200 ml.

[0077] The separate auxiliary electrolyte reservoir is preferably a housing containing a space or volume for receiving a certain amount of the above electrolyte and receiving or accommodating a redox electrode for measuring or detecting the potential difference between the auxiliary electrolyte and other electrolytes in the reservoir.

[0078] The redox electrode can take almost any form. The redox electrode can be a simple flat plate, a rod, or a porous three-dimensional shape that fills a space (felt, foam, etc.). It must be positioned to be (at least partially) immersed in the electrolyte in the auxiliary reservoir. The redox electrode should be chemically stable to the electrolyte in the reservoir. Therefore, carbon or carbon composites (such as carbon and polypropylene) are more preferred.

[0079] Preferably, the auxiliary reference electrolyte device also includes a temperature sensor, which is preferably associated with a separate auxiliary electrolyte reservoir or housing or a fixture that is thermally connected to the above-mentioned components, so as to perform temperature correction on any potential difference measurement. The temperature sensor can take any suitable form. Since the temperature sensor is used to measure the temperature of the electrolyte in the separated auxiliary electrolyte reservoir, it must maintain good thermal contact with the electrolyte. For example, the temperature sensor can be immersed in the electrolyte (possibly in a hot well, or with a suitable protective layer), or in close contact with the electrode (carbon generally has a higher thermal conductivity, so it can be used to transfer heat to the thermal sensor). In this second solution, it is usually necessary to perform thermal insulation around the air side of the thermal sensor to obtain accurate measurements.

[0080] The means for measuring the potential difference between the auxiliary reference electrolyte or each auxiliary reference electrolyte and the corresponding half-cell of the reference cell (or the corresponding electrolyte of the reference cell device or liquid flow battery) can be any suitable device or instrument, such as a voltmeter connected to the redox electrode in a separate auxiliary electrolyte reservoir and a suitable electrode in the corresponding half-cell of the reference cell (or the electrolyte in the reference cell device or liquid flow battery or an electrolyte associated therewith, such as an electrolyte tank).

[0081] The ion channel conduit connecting the auxiliary reference electrolyte reservoir and the corresponding half-cell of the reference cell is configured to have a low fluid diffusion capacity or rate. The ion channel conduit can be provided as any suitable device, but generally includes a tubular member that provides a fluid connection between the auxiliary reference electrolyte reservoir and the half-cell of the reference cell (or the electrolyte therein). If the ion channel conduit includes a tubular member, a wicking device (e.g., a core or wire as defined above) is preferably arranged inside the tubular member. The resistivity of the ion channel conduit along its length (e.g., between the auxiliary reference electrolyte reservoir and the half-cell of the reference cell) is preferably less than or equal to 1 MOhm. The ion channel conduit preferably does not have any film or barrier that may prevent (or inhibit) the ions and fluids between the auxiliary reference electrolyte and the corresponding half-cell of the reference cell, and the auxiliary reference electrolyte and the corresponding half-cell of the reference cell are preferably connected to an open fluid through the ion channel conduit.

[0082] The ion channel conduit can be any suitable length, and the suitable length (depending on the geometry, such as aperture, curvature and number of turns) preferably suppresses the rapid fluid mixing of the auxiliary electrolyte and the flow battery electrolyte that are fluidly connected through the ion channel conduit. Preferably, the length of the ion channel conduit is at least 5 cm, more preferably, at most 10 meters. More preferably, the length of the ion channel conduit does not exceed 5 meters, preferably does not exceed about 2 to 2.5 meters. The length of the ion channel conduit is preferably between 10 cm and 1.5 meters, more preferably between 15 cm and 1.2 meters, for example, between 20 cm and 1 meter, or optionally at most 75 cm, preferably between about 30 cm and about 50 cm. In one embodiment, for example, if a pipe with a larger aperture is used as the ion channel conduit, the length can be longer, for example, from 50 cm to 5 meters, such as from 1.5 meters to 2.5 meters.

[0083] The ion channel conduit can have any suitable pore size, and a suitable pore size can be selected according to the length of the conduit and other geometric features to inhibit the auxiliary electrolyte and the flow battery electrolyte from mixing through the conduit. The pore size of the ion channel conduit is preferably at least 0.5 mm. The pore size is at most 10 mm, preferably not more than 7.5 mm. The ion channel conduit is preferably a small-aperture conduit, and its pore size is preferably small enough to inhibit the laminar flow of the electrolyte through the conduit. More preferably, the inner pore diameter of the ion channel conduit is between 1 and 5 mm, preferably between 2.5 and 4 mm, such as between 3 and 3.5 mm.

[0084] If the ion channel conduit includes a pipe assembly, the diameter of the wicking device (core or rope as defined above) is preferably smaller than the inner diameter / pore size of the pipe assembly. Therefore, preferably, the wicking device is loosely mounted in the hole of the pipe assembly of the ion channel conduit. The advantage of this feature is that the wicking device can be easily inserted through the pipe assembly of the ion channel conduit during assembly. Another advantage of this feature is that the electrolyte can be arranged in the space between the wicking device and the inner surface / pore surface of the pipe assembly of the conduit along the length of the ion channel conduit.

[0085] The inner diameter of the ion channel conduit should be small enough to prevent laminar flow (which may promote mixing between the auxiliary electrolyte and the flow battery electrolyte, but the inner diameter should also be large enough to avoid clogging by small particles that may be present in the flow battery electrolyte).

[0086] In one embodiment, for example, the ion channel conduit does not include a wicking device, and it is advantageous for the conduit to have a slightly larger pore size. This is because bubbles generated by degassing of the electrolyte in the ion channel conduit are unlikely to block the entire inner diameter / pore size of the conduit. Therefore, in this embodiment, the pore size of the ion channel conduit is preferably at least 3 mm, more preferably at least 4 mm, and more preferably at least 5 mm. The pore size is at most 10 mm, preferably no more than 8 mm. The inner pore diameter of the ion channel conduit is preferably between 3.5 mm and 7.5 mm, more preferably 4 mm to 7 mm, such as 4.5 mm to 6 mm, for example, the inner pore diameter is 5 mm.

[0087] In one embodiment, the ion channel conduit has a length of 20 cm to 2 m and an inner diameter of 2.5 mm to 4 mm.

[0088] The ion channel conduit preferably has one or more bends or elbows along its length. The ion channel conduit preferably has one or more vertical sections associated with one or more bends or elbows. The bends or elbows vary tangentially along the length of the ion channel by at least 30°, preferably at least 60°, more preferably at least 90°, more preferably at least 120°, such as at least 180°, more preferably at least 270°, and even more preferably greater than 360°.

[0089] Preferably, at least one curved portion or bend in the ion channel conduit defines at least one U-bend or loop. The direction of the U-bend or loop preferably has a vertical portion. Preferably, the ion channel conduit forms at least one loop along its length, preferably two or more loops, such as three loops. The provision of at least two loops in the ion channel conduit between the auxiliary electrolyte reservoir and the reference cell is particularly advantageous for slowing down the mixing of the flow battery electrolyte with the auxiliary electrolyte (e.g., compared to one loop or no loop). Therefore, including a loop or preferably two loops (preferably vertical loops) in the ion channel conduit reduces the mixing rate of the auxiliary electrolyte with the flow battery (or reference cell) electrolyte, which means that, with the same effective service life of the charge state indicator, a smaller volume of auxiliary electrolyte can be used, or with the same volume of auxiliary electrolyte, the service life of the charge state indicator can be extended.

[0090] The charge state or health state indicator of the present invention can be configured as follows: the auxiliary electrolyte corresponds to the positive electrolyte of the liquid flow battery (for example, the auxiliary electrolyte has a composition corresponding to the desired or initial composition of the positive electrolyte of the liquid flow battery), or the auxiliary electrolyte corresponds to the negative electrolyte of the liquid flow battery (for example, the auxiliary electrolyte has a composition corresponding to the desired or initial composition of the positive electrolyte of the liquid flow battery).

[0091] Optionally, there are two auxiliary reference electrolyte devices. In one embodiment, one auxiliary reference electrolyte device corresponds to the positive electrolyte of the flow battery (preferably the first half-cell of the reference battery), and the other auxiliary reference electrolyte device corresponds to the negative electrolyte of the flow battery (preferably the second half-cell of the reference battery). In another embodiment, both auxiliary reference electrolyte devices are configured to contain electrolytes corresponding to the positive electrolyte of the flow battery, wherein one auxiliary reference electrolyte device is connected to the positive electrolyte (e.g., the positive half-cell of the reference battery) through an ion channel conduit, and the other auxiliary reference electrolyte device is connected to the negative electrolyte (e.g., the negative half-cell of the reference battery) through a channel conduit, and the charge state of each electrolyte of the flow battery is determined by measuring the potential difference between the corresponding electrolyte of the flow battery (or the half-cell of the reference battery) and the corresponding auxiliary reference device connected to the ion channel conduit.

[0092] Preferably, at least one auxiliary electrolyte corresponds to the positive electrolyte, and the auxiliary reference electrolyte device (or pseudo reference cell) is configured such that: the potential difference measuring device is located between the auxiliary reference electrolyte and the positive half-cell of the reference cell, and the ion channel conduit connects the auxiliary reference electrolyte reservoir to the positive half-cell of the reference cell. Optionally, the charge state or health state indicator also includes a second auxiliary reference electrolyte device, wherein the second auxiliary electrolyte corresponds to the negative electrolyte of the flow battery (or may also correspond to the positive electrolyte), and the second auxiliary reference electrolyte device (or pseudo reference cell) is configured such that: the potential difference measuring device is located between the second auxiliary reference electrolyte and the negative half-cell of the reference cell, and its ion channel conduit connects the auxiliary reference electrolyte reservoir to the negative half-cell of the reference cell.

[0093] The state of charge or state of health indicator preferably comprises a temperature sensor for measuring the temperature of the or each flow battery electrolyte.

[0094] The state of charge or health indicator may further comprise a processor for controlling the measurement and recording of the potential difference and temperature associated with the auxiliary reference electrode arrangement or each auxiliary reference electrode arrangement and the corresponding or each half-cell of the reference cell, and optionally the processor is configured to transmit the measurements to a controller or data logger of the flow battery. The processor is preferably used or partly used to control or manage the operation of the flow battery to which the state of charge or health indicator is connected.

[0095] The charge state indicator is preferably configured to measure the charge state at a predetermined time period or according to a predetermined system action. For example, the charge state indicator device may be configured to determine the charge state once every 24 hours or every 7 days, preferably once every 24 hours to every 3 months, more preferably once every two days to every 2 months, for example once every week to every month. Additionally or alternatively, the charge state indicator device may also be configured to determine the charge state after each charge and discharge cycle or every thousand charge and discharge cycles, for example every 10 to 500 charge and discharge cycles, for example every 50 to 250 charge and discharge cycles.

[0096] The state of charge indicator can be configured to make a measurement (e.g., potential difference / temperature) such that the state of charge can be determined at any time using the measurement result, whether the flow battery is cycling or at rest, during a charging cycle or a discharging cycle, but preferably during the cycling of the flow battery. In addition, such measurement can be made at any predetermined state of charge, but preferably at an intermediate predetermined state of charge, such as from 20% to 80% state of charge, such as from 40% to 60% state of charge, preferably at a predetermined state of charge around 50%.

[0097] The charge state indicators described herein are generally preferably included in or installed in a redox flow battery.

[0098] Therefore, another aspect of the present invention provides a redox flow battery, which includes a redox flow battery pack, a positive electrolyte tank and a pipe for circulating the positive electrolyte through the battery pack, a negative electrolyte tank and a pipe for circulating the negative electrolyte through the flow battery pack, and a charge state or health state indicator as described above.

[0099] The redox flow battery may be of any suitable type, in particular a redox flow battery in which an imbalance in state of charge may occur (eg due to hydrogen evolution), but is in any event preferably a vanadium redox flow battery.

[0100] Another aspect of the above invention is a method for monitoring the charge state or health state of a redox flow battery, the method comprising providing a charge state or health state indicator as described above, and enabling the charge state indicator to periodically or irregularly measure the charge at the two poles of a reference cell and the charge between an auxiliary reference electrolyte and the corresponding half-cell of the reference cell, thereby determining the charge state of the system, and optionally issuing an alarm for charge imbalance of the flow battery electrolyte based on the difference between the charge state at the two poles of the reference cell of the flow battery and a predetermined threshold.

[0101] For example, such an alert may be a siren, a warning light, a notification (such as sent via email or text message to an engineer or contact person who should be notified), or any other appropriate alert means.

[0102] The state of health (or SOH) includes the state of charge (or SOC). The term "state of health indicator" as used herein may also be "state of charge indicator" where the context permits, and vice versa. The state of charge of an electrolyte refers to the charge level of the electrolyte. The state of charge of a flow battery referred to herein is preferably the state of charge of each (or two) electrolytes. In a preferred embodiment of a vanadium redox flow battery, the state of charge (SoC) of the positive electrolyte refers to the ratio of the concentration of V (V) in the positive electrolyte to the total vanadium, while the state of charge of the negative electrolyte refers to the ratio of the concentration of V (II) in the negative electrolyte to the total vanadium. In a preferably balanced (healthy) system, the SoC of the positive and negative electrolytes will be equal.

[0103] The state of health (SoH) can be defined in a variety of different ways for different battery chemistries. Preferably, in a vanadium redox flow battery system, the state of health refers to the deviation of the average oxidation state in the entire system electrolyte (including the positive and negative electrolytes) from the original value (for a vanadium redox flow battery system, the original value is about 3.50).

[0104] If oxidation of the electrolyte occurs (e.g., through parasitic side reactions, such as hydrogen evolution; or oxygen entering the tank), the average oxidation state increases. The SoC of the positive and negative electrolytes will also be significantly different. If the average oxidation state reaches at least 3.65, the vanadium flow battery can be considered to be in a "critical" state of health, and the positive half-cell may be accidentally overcharged, causing irreversible damage to the battery pack. The increase in the average oxidation state becomes apparent as the discharge energy decreases.

[0105] In a preferred embodiment of the present invention, if the average oxidation state deviates from the equilibrium or healthy state (i.e., the normal original state) by 0.10, the health of the system is poor (for example, if the average oxidation state of the system is 3.6 or higher), and when the average oxidation state is 3.55 or higher, the health of the system can be considered to have decreased.

[0106] The average oxidation state can be determined by a single measurement of the charge state (such as the positive electrolyte and the entire reference cell) using the present system / device, but it is preferably calculated over an extended period of time (such as an hour or several days, or even a week or longer), preferably relying on the results of multiple measurements.

[0107] In one embodiment, the apparatus is configured to determine the state of charge of the positive electrolyte by determining the voltage difference between the positive half-cell of the reference cell and an auxiliary reference electrolyte device, wherein the auxiliary reference electrolyte is connected to the positive half-cell of the reference cell by an ion channel conduit as described above. The state of charge of the negative electrolyte can be determined by determining the voltage difference between the negative half-cell of the reference cell and a second auxiliary reference cell, which is connected to the negative half-cell of the reference cell by an ion channel conduit as described above, or (or additionally) by determining the difference between the open circuit voltage measured across the reference cell and the determined state of charge of the positive electrolyte (determined using the auxiliary reference electrolyte device as described above), preferably compensating for temperature changes. The state of charge of the negative electrolyte can be estimated as an "average" state of charge, i.e., a value obtained from the reference cell, which is generally considered to be between the states of charge of the positive and negative electrolytes.

[0108] When making these measurements, the potential produced at the positive electrode depends on the state of charge of the positive electrolyte. The potential produced at the negative electrode depends on the state of charge of the negative electrolyte. The reference cell measures the difference in potential between the positive and negative electrodes. Therefore, if both electrolytes are assumed to be in good balance, the value you get for "state of charge of the entire cell" is actually somewhere in between the positive and negative state of charge values. This relationship is quite complex and not a simple average.

[0109] In this preferred embodiment, the auxiliary reference electrode (after temperature compensation) provides a fixed voltage for comparison with the positive electrode. In this way, the charge state of the positive electrode electrolyte can be determined. This value is then compared to the "charge state of the entire battery" value (determined by measuring the voltage at the two poles of the reference battery). If the two are close, the charge state values ​​of the negative and positive electrodes must be similar, and the battery is considered "healthy". If the values ​​are different, it means that the charge state values ​​of the positive and negative electrolytes are different, and the battery is "unhealthy".

[0110] The device of the present invention can determine the charge state by measuring the potential difference between the corresponding electrolyte and the above-mentioned auxiliary electrolyte device, and then measuring and / or determining the charge state of another electrolyte (for example, by measuring the potential difference between the electrolyte of the flow battery or the electrolyte of the more preferred reference battery). The charge state (or a representative value of the charge state) of each electrolyte can then be determined by any suitable method, such as by a predetermined query table for a specific system or using a suitable empirical formula.

[0111] According to a preferred embodiment, the device or system comprises a device for determining the potential difference between the two electrodes of the reference cell (which can be expressed as E ref [V]) sensor, used to determine the potential difference (expressed as E) between the positive half-cell of the reference cell and the auxiliary reference cell (or pseudo-reference cell) ref-aux[V]), a sensor for determining the temperature of the reference cell (expressed as T1 [°C]), and a sensor for determining the temperature of the auxiliary reference cell (expressed as T2 [°C]). The charge state α of the reference cell and the charge α of the positive electrolyte pos It can be determined using an appropriate lookup table or empirical formula.

[0112] In one embodiment, α is determined by iterating an empirical equation until convergence, such as the form shown in Equation 1 below, which is applicable to an electrolyte containing 1.6M total vanadium and 4.0M total sulfate. The form of this equation is similar to the Nernst equation, but the Nernst equation cannot be directly used because the activity of the electroactive material is unknown.

[0113]

[0114] Where: F = 96500C mol -1

[0115] R=8.314JK -1 mol -1

[0116] Charge state of positive electrolyte α pos It can be determined by iterating an empirical equation, such as the form shown in Equation 2 below (where both the reference electrolyte and the active electrolyte contain 1.6 M total vanadium and 4.0 M total sulfate):

[0117]

[0118] In a preferred embodiment, the measurement is made at about 50% charge, but the measurement can be made at any suitable charge, but preferably when the charge is relatively stable. An intermediate charge portion of the charge state of the flow battery (e.g., from 20% to 80% charge, more preferably from 25% to 75% charge, more preferably from 30% to 70% charge, more preferably from 40% to 60% charge, or even from 45% to 55% charge) is preferred, not only because the flow battery is in the intermediate charge portion more frequently than other portions, but also because measurements and determinations made in the intermediate charge portion have smaller errors.

[0119] By comparing α and α pos The value of, for example, the value determined according to the above empirical formula (or by a lookup table or similar method), can determine the charge balance state of the positive and negative electrode electrolytes.

[0120] therefore,

[0121] If α pos >α, the electrolyte is oxidized and needs to be rebalanced

[0122] If α pos =α, then the electrolyte is balanced - no need to rebalance

[0123] If α pos <α, then the electrolyte is reduced - no need to rebalance

[0124] In a preferred embodiment, α and α pos The values ​​of can be integrated over an extended period of time (or more charge and discharge cycles). For example, α and α pos The value of can be integrated over a period of up to 30 days, more preferably over a period of 1 to 10 days. Such a period is effective because the oxidation rate of the system under normal operating conditions is quite slow (generally speaking, the average oxidation state may change by about 0.001-0.02 per month).

[0125] Preferably the measurements are made during a discharge or charge cycle or while the electrolyte is flowing (and through the reference cell) (measuring the potential difference across the reference cell and between the reference cell and the auxiliary reference cell, as well as the temperature).

[0126] Additionally, for cells using membranes, due to the large differences in concentration of electroactive materials, it is preferred to make important measurements immediately after the electrolytes are fully mixed. For membranes that do not cause significant changes in electroactive materials, concentration measurements can be made at any time.

[0127] Another aspect of the present invention is a method for maintaining a balanced charge state or health state (such as a balanced oxidation state of a redox flow battery), the method comprising monitoring the charge state in the flow battery by providing a charge state or health state indicator as described above, and causing the charge state or health state indicator (or a controller configured in association therewith) to periodically or in response to actions or in response to events measure the charges at the two poles of a reference battery and the charges between an auxiliary reference electrolyte and the corresponding half-cells of the reference battery, thereby determining the charge state and / or health state of the system; and taking one or more maintenance measures for the flow battery when the difference in charge state or oxidation state between the positive electrode electrolyte and the negative electrode electrolyte exceeds one or more predetermined thresholds or meets one or more predetermined criteria.

[0128] In one embodiment, the method includes monitoring the charge state in the flow battery by providing a charge state or health state indicator as described above, and causing the charge state or health state indicator to measure the charges at the two poles of a reference cell and the charges between an auxiliary reference electrolyte and corresponding half-cells of the reference cell periodically or in response to an action or in response to an event, thereby determining the charge state of the system; and when the determined charge state difference between the positive electrode electrolyte and the negative electrode electrolyte exceeds one or more predetermined thresholds or meets one or more predetermined criteria, taking one or more maintenance measures for the flow battery.

[0129] If the health of the flow battery degrades, e.g., reaches at least a critical state (as defined above), the system may optionally be configured to introduce performance limitations on the flow battery, such as limiting the maximum state of charge of the battery (e.g., determined based on a reference battery—the reference battery gives a value between the positive electrolyte and the negative electrolyte). This reduces the risk of system damage, but reduces the discharge energy of the battery.

[0130] In one embodiment, the method and system (e.g., its control system) are configured to cause (or suggest) remedial measures. Preferably, the system is configured to automatically take remedial measures when the health state is determined to be an oxidation state greater than a preset value (e.g., greater than 0.05 of the original level). The remedial measure may be to add a reducing agent to the electrolyte tank, for example, automatically adding a reducing agent to the electrolyte tank according to a predetermined charge state difference, thereby converting part of the V(V) into V(IV) (e.g., as described in WO-A-2018047079), and the remedial measure may also be to use an electrochemical rebalancing cell to generate oxygen, introduce oxygen into the positive electrolyte tank, and then electrochemically reduce the average oxidation state of vanadium in the electrolyte (e.g., as described in JP-A-3315508).

[0131] For example, the rebalancing action (such as the rate of adding reductant or the rebalancing cell current) may be proportional to the difference between the average oxidation state and the target oxidation state, or it may have a switching action if the difference exceeds a preset value.

[0132] In each case, any measured or determined state of charge value is preferably temperature corrected in order to generate state of charge or state of health data.

[0133] The invention will now be described in more detail with reference to the accompanying drawings without however limiting the invention.

[0134] Figure 1A state of charge or state of health indicator device 1 is shown, which has a reference cell 3 and a single auxiliary reference electrolyte device 5 associated therewith. The device 1 is used with a vanadium redox flow battery. The reference cell 3 includes a negative half-cell 7 and a positive half-cell 13, each of which has a corresponding electrolyte reservoir (not shown). The negative half-cell 7 is connected to a negative electrolyte tank (not shown) or a loop of a flow battery (not shown), and the negative electrolyte circulates with the negative electrolyte tank or the loop of the flow battery through a negative electrolyte inlet 9 and an outlet 11. The positive half-cell 13 is connected to a positive electrolyte tank (not shown) or a loop of a flow battery (not shown), and the positive electrolyte circulates with the positive electrolyte tank or the loop of the flow battery through a positive electrolyte inlet (not shown) and an outlet 17.

[0135] Like the standard reference cell, the potential difference between the two poles of the reference cell 3, i.e., the positive and negative half-cells 7 and 13, can be measured. Since the positive and negative half-cells 7 and 13 and the positive and negative electrolyte tanks of the flow battery are in a fluid circulation state, the potential difference can reflect the measured charge of the flow battery.

[0136] The auxiliary reference electrolyte device 5 has a cylindrical auxiliary electrolyte reservoir 19, which is used to store a reference electrolyte. The reference electrolyte can be the original component of the positive electrolyte of the flow battery or the original component of the comparative electrolyte. The reference electrolyte is in a predetermined charge state, usually close to a charge state of 50%. The reference electrolyte in the auxiliary electrolyte reservoir 19 is ionically connected to the positive electrolyte reservoir of the positive half-cell 13 of the reference battery 3 through a tube 21. The tube 21 passes through a tube connector 23 at the bottom of the auxiliary electrolyte reservoir 19 and a reference cell connector (not shown) at the bottom of the positive half-cell 13, providing an ion channel conduit between the auxiliary electrolyte reservoir 19 and the positive half-cell 13.

[0137] The tube 21 of the conduit channel provides an open, continuous fluid connection between the auxiliary electrolyte reservoir 19 and the electrolyte in the positive half-cell 13, without any obstructions or obstructions such as membranes or valves. The tube 21 of the conduit channel provides an uninterrupted ionic connection between the auxiliary electrolyte reservoir 19 and the positive half-cell 13 of the reference cell 3, thereby allowing accurate voltage difference measurement between the reference electrolyte in the auxiliary electrolyte reservoir 19 and the positive electrolyte of the flow battery in the positive half-cell 13.

[0138] The length of tube 21 is 60 cm (but can be up to 1.5 m) and the inner diameter is 3.2 mm. Such a length and diameter can provide ionic connection between the reference electrolyte in the auxiliary electrolyte reservoir 19 and the positive electrolyte in the positive half-cell 13, while fully inhibiting the mixing of the reference electrolyte (volume is 500 ml, but preferably lower, such as 100 ml) with the positive electrolyte in the positive half-cell 13, thereby substantially maintaining the composition of the reference electrolyte for a long time, and achieving continuous reliable and consistent reference measurement.

[0139] In order to further suppress the liquid mixing between the reference electrolyte and the positive electrolyte in the positive half-cell 13, a plurality of bends 25 are provided on the tube 21, and the angle of each bend changes by 90°. The two vertical parts 29 and the horizontal part 31 of the tube and the separated bends 25 together constitute a U-shaped bend. The U-shaped bend arrangement thus formed has its lowest point (horizontal part 31) lower than the auxiliary electrolyte reservoir 19 and the positive electrode 13.

[0140] The tube 21 between the auxiliary reference reservoir 19 and the positive half-cell 13 is free of blockage or interruption, which helps maintain a low resistivity of the tube 21 (ideally less than 1 ohm), so that the voltage difference between the reference electrolyte in the positive half-cell 13 and the positive electrolyte of the flow battery can be accurately measured with little interference from electronic "noise".

[0141] When in use, the auxiliary electrolyte reservoir 19 should be filled with sufficient reference electrolyte to substantially fill the reservoir 19 and tube 21, and should be substantially free of gas.

[0142] The auxiliary reservoir device 5 is physically mounted to the reference cell 3 by means of a bracket 27 which is mounted on top of the auxiliary electrolyte reservoir 19 and on the front or side of the reference cell 3. Thus, the auxiliary electrolyte reservoir 19 is positioned lower than the reference cell in use, which further reduces the risk of the reference electrolyte mixing and flowing back into the positive half-cell 13.

[0143] Reference cell electrodes (not shown) are provided in each of the positive and negative half cells 7, 13 of the reference cell 3, and means (not shown) for measuring the half-cell potential difference and means for storing and / or transmitting the resulting data are provided. Auxiliary electrodes (not shown) are provided in the auxiliary electrolyte reservoir 19 for measuring the electrolyte content.

[0144] The positive half-cell 13 and the auxiliary electrolyte reservoir 19 are each provided with a thermal sensor (not shown) for measuring the respective electrolyte temperature.

[0145] Figure 2a , Figure 2b and Figure 2cThree styles of ion channel conduits or tubes 21 for use with the charge state indicator device 1 are shown. Figure 2a The tube 21 in the Figure 1 The tube used in the auxiliary reservoir device 1. Figure 2a The tube 21 has an auxiliary reservoir end 33 and a reference cell end, and the auxiliary reservoir end 33 is used to connect to the auxiliary electrolyte reservoir 19 ( Figure 1 ), the reference cell end is used to connect to the positive half-cell 13 (or any half-cell), and the length of the tube 21 between the two ends 33, 35 is about 60 cm. Figure 2a The tube has an inner bore diameter of 3.2 mm and is characterized by a plurality of bends 25 along its length, preferably forming U-bends.

[0146] The material of the tube can be any suitable material that is stable to the electrolyte. This generally includes a mixture of one or more polymers, such as polyethylene, polypropylene, polyvinyl chloride, polytetrafluoroethylene and polyvinylidene fluoride, as well as flexible polymers (such as The tube is preferably translucent or transparent (to facilitate observation of air embossment or particle blockage).

[0147] The tube is preferably provided with a wicking means (as described above) extending through the tube (wicking means not shown).

[0148] Figure 2b and Figure 2c Demonstrates alternatives to any particular system Figure 2a The tube 21 in the figure is a variant of the tube 21 used. Figure 2b and Figure 2c The tubes in FIG. 2 are different in that they have more bends 25 to form one or more loops 37. As shown, the loops 37 are composed of a series of straight tube sections and 90° bends, but the loops 37 can be of any geometric shape, such as elliptical or circular / spiral. Figure 2b As shown, the loop 37 provided can reduce the diffusion and exchange of electrolyte (especially vanadium) between the auxiliary electrolyte reservoir 19 and the reference cell 3, thereby extending the time to obtain a stable reading from the auxiliary electrolyte reservoir. Figure 2a U-bends and Figure 2b In the single loop form, Figure 2c The second loop 37 in the tube 21 can significantly reduce the diffusion of electrolyte between the auxiliary electrolyte reservoir 19 and the reference cell 3. Therefore, by providing one or more loops 37 (or more U-shaped bends) in the tube 21 for Figure 1 In the device 1, the tube 21 can delay the electrolyte from the reference cell 3 and the electrolyte in the auxiliary electrolyte reservoir 19 from mixing to an unacceptable degree, and can also be as Figure 2aIt is shown that the same performance (in terms of diffusion suppression) can be achieved by shortening the tube 21 or increasing its inner bore diameter.

[0149] Figure 3 1 is a schematic diagram of a charge state indicator device 1 according to one embodiment of the present invention, which includes a reference cell 3 having a positive electrode 7 and a negative electrode 13 and a voltmeter 5 across the cell for measuring a potential difference. The indicator device also includes an auxiliary reference electrolyte device 5, which includes a reservoir 19 and a narrow bore tube 21 (as an ion conduit channel) connected to the positive electrode 7 of the reference cell 3. The positive and negative sides 7, 13 have respective inlets 15, 9 for positive and negative electrolytes and outlets 17, 11, respectively, the inlets 15, 9 feeding the positive and negative electrolytes into the reference cell 3 through pipes that transport the positive and negative electrolytes from the electrolyte tank of the fuel cell to the battery stack (preferably just before the battery stack), and the outlets 17, 11 returning the positive and negative electrolytes from the reference cell 3 to the pipes returning from the battery stack to the electrolyte tank (or directly to the electrolyte tank).

[0150] The potential difference between the two electrodes of the reference cell 3 can be measured by a voltmeter 5 , while the potential difference between the positive side 7 of the reference cell 3 and the auxiliary reservoir 19 can be measured by a voltmeter 39 .

[0151] Figure 4 The position of the state of charge indicator of a vanadium redox flow battery 41 is shown, and the vanadium redox flow battery 41 includes a positive electrolyte tank 43 containing a positive electrolyte 45 and a negative electrolyte tank 47 containing a negative electrolyte 49. The positive electrolyte 45 and the negative electrolyte 49 are circulated by a pump 51 through a positive supply line 55 and a positive return line 57 of a battery stack 53 and a negative supply line 59 and a negative return line 61. Arranged in parallel with the battery stack 53 is a reference cell 3, which is fed by positive and negative inlets 15, 9 from positive and negative supply lines 55 and 59 and returns to positive and negative return lines 57 and 61 through positive and negative outlets 17, 11. The positive side 7 of the reference cell 3 is connected to an auxiliary electrolyte reservoir 19 through a curved narrow bore tube 21.

[0152] When the pump 51 is operating, the electrolyte can circulate through the battery pack 53 and the reference cell 5. The potential difference measurement is preferably performed while the pump is operating.

[0153] When the charge state of the positive electrolyte 45 is measured to be different from the charge state of the negative electrolyte 47 (estimated by measuring the potential difference between the two electrodes of the reference cell 5), the liquid flow battery 41 can be configured to take remedial measures, such as adding a reducing agent to the electrolyte.

[0154] Example

[0155] Embodiment 1:

[0156] according to Figure 1 The apparatus shown provides a state of charge or health indicator for a vanadium oxide redox flow battery, in which a reference cell is connected in parallel with the battery pack in the redox flow battery (a 5 kW battery pack in a 40 kWh battery). The auxiliary reference electrolyte is the positive electrolyte and has a SOC of 50%.

[0157] The battery initially contains discharged electrolyte with a state of charge close to 0%. The battery is charged and the pump continues to operate.

[0158] Figure 5a and Figure 5b is the potential difference diagram between the two electrodes of the reference battery ( Figure 5a ) and the potential difference diagram between the positive electrode of the reference cell and the auxiliary electrolyte of the auxiliary reference device ( Figure 5b ), in each case the potential difference diagrams are plotted against the absolute amount of charge passing through the battery.

[0159] from Figure 5a As can be seen in the graph, continued charging (as expected) causes the reference cell voltage to increase, then as the cell discharges, the reference cell voltage drops (followed by a small final charging period where the reference cell voltage increases again). The measurable voltage range of the reference cell is 0 to 1.6 volts, with an effective range of 1.25 to 1.45 volts.

[0160] The voltmeter also measures the potential difference between the positive electrode of the reference cell and the auxiliary electrode (of the auxiliary reference device), e.g. Figure 5b As shown. This measurement is lower when the state of charge of the positive electrolyte is lower than that of the auxiliary electrolyte (state of charge is 50%), and higher when the state of charge of the positive electrolyte is higher than that of the auxiliary electrolyte. To obtain an accurate difference, the reference cell and the auxiliary reservoir need to be temperature compensated. (Assuming they are isothermal, the positive electrolyte will be at a 50% state of charge when the potential difference is zero). The effective voltage range between the positive electrode of the reference cell and the auxiliary electrolyte of the auxiliary reference device is -0.01 to 0.04V.

[0161] The potential difference measurement at any particular point during the battery charge and discharge (or part of a charge cycle, a charge cycle, or an average over multiple charge cycles) can be inserted into the above empirical formula (or used from a lookup table) to determine fα pos and α, thereby evaluating the health status of the flow battery.

[0162] Embodiment 2:

[0163] A series of diffusion experiments were conducted to compare conduit sizes and geometries for fluid diffusion / mixing conditions used in the auxiliary reference electrolyte apparatus of the present invention.

[0164] In the experiment, the electrolyte tank was connected to a sulfuric acid test tube (as a reference cell and a pseudo-reference cell, respectively), and the flow of the electrolyte in the test tube was monitored. Pipes of different geometries and lengths were used to connect the tank and the test tube to understand the effects of these factors on the diffusion of the electrolyte. Since sulfuric acid is colorless, the concentration of the electrolyte in the test tube (blue) can be measured using ultraviolet visible light. By comparing the concentration of the electrolyte and the time taken, the diffusion rate can be quantified.

[0165] Use an inner diameter of 4.8 mm Six comparison experiments were conducted with tubes of the following lengths and geometries:

[0166] A 30 cm long; double loop

[0167] B 30 cm long; straight (no loop)

[0168] C 30 cm long; single loop

[0169] D 30 cm long; straight (no loop)

[0170] E 50 cm long; single loop

[0171] F 50cm long; double loop

[0172] The experimental setup is as follows. Figure 6 As shown ( Figure 6 Experiments with tubes E and F described above are shown).

[0173] Two sealed side arm test tubes 73 are placed in a test tube rack 75. The side arm test tubes 73 are connected by a 50 cm long, 4.8 mm inner diameter Tubes 69 and 71 are connected to outlet 67. The tubes 69, 71 extend substantially horizontally. A section of the tube 71 (experiment E above) was formed into a vertically oriented loop 79 by winding the tube around a rod 81 (made of cork) having a diameter of about 150-200 mm. A second section of the tube 69 (experiment F above) was wound twice around the rod 81 to form two vertically oriented loops 77.

[0174] Before connecting to the outlet 67, the test tube 73 is filled with 4.2M sulfuric acid until the test tube 73 and the connected test tubes 69, 71 are filled (15.2 ml), and then the ends of the test tube are clamped close to the free end. The test tube 73 is then sealed with a cap. The tubes 69, 71 are then connected to the electrolyte storage container 65 through the two outlets 67, which are close to the bottom of the container, which is at a similar height to the side arms of the test tube 73.

[0175] Add a certain amount of 1.6M TMS into the electrolyte storage container 65 2The vanadium electrolyte 63 is added until it is at the same height as the two outlets 67. Then the clamp is removed.

[0176] To test diffusion, 1 ml samples were taken from the test tubes (at irregular intervals starting about 2 months after the start of the experiment) and 1 ml of sulfuric acid was added. The extracted samples were measured with UV / visible light against a sulfuric acid standard (4.2 M).

[0177] The average permeability of vanadium was calculated from the measured UV / vis data and the diffusion rate in mol / day is shown in Table 1 below:

[0178] Table 1

[0179] A B C D E F mole / day <![CDATA[<1x 10 -6 ]]> n / a <![CDATA[1.04x 10 -5 ]]> <![CDATA[6.24x 10 -5 ]]> <![CDATA[7.79x 10 -6 ]]> <![CDATA[1.30x 10 -6 ]]>

[0180] Note: Results for Sample B, which was fully mixed at the end of the experiment, were not recorded.

[0181] According to the above experiments, the auxiliary reservoir can be less than 100 ml in volume, with the charge state of the auxiliary reservoir not exceeding 2% of the initial value after 12 months as the standard, and two loops are set in the pipeline. This will help reduce costs and integrate the auxiliary reservoir into the system while maintaining high efficiency.

[0182] This was calculated using the following methodology / assumptions:

[0183] Initial state of charge of the auxiliary electrolyte reference device = 0.50, total vanadium concentration [V] = 1.8 mol dm -3

[0184] V(IV) concentration in the auxiliary electrolyte reference device = [V(IV)]

[0185] ·At , V(IV) is D V The diffusion rate of V(V) is constantly moving towards the reference cell (no V(V) diffuses into the reference cell - this is obviously a "worst case" approximation)

[0186] Equal replacement rate of vanadium (at the state of charge of the auxiliary electrolyte reference device)

[0187] ·Auxiliary electrolyte reference device volume = V

[0188] The concentration of V(IV) in the auxiliary electrolyte reference device [V(IV)] is given by the following formula:

[0189]

[0190]

[0191] When SOCt＝0 =0.50, [V] = 1.8

[0192]

[0193] The maximum acceptable deviation from the initial SOC is 0.02, and the minimum time for such deviation to occur is 1 year.

[0194]

[0195] The unit of DV is mol.d -1 , V unit is L.

[0196] For the above pipe connections, the auxiliary electrolyte reference device volumes shown in Table 2 below will meet the specified standards.

[0197] Table 2

[0198]

[0199] Embodiment 3:

[0200] Experiments were conducted to investigate the ability of a 3 mm amorphous silica core to maintain ionic connectivity when trapped in an ion channel conduit (3.18 mm inner diameter).

[0201] A test tube material was chosen that was known to react with the electrolyte and generate gas, thereby producing bubbles during testing. A 3 mm amorphous silica core was inserted along the entire length of the tube. The tube was located between two electrolyte reservoirs and was in fluid communication with them. Both the reservoirs and the tube were filled with electrolyte. During testing, large bubbles were produced along almost the entire length of the tube.

[0202] The test continued, monitoring the performance of the silicon core under these conditions. As large bubbles formed, the resistance between the carbon fiber rods placed in the electrolyte reservoir increased over time - from about 1.6 kΩ to a peak of about 40 kΩ at 21 days. Presumably, the peak occurred when the bubble formation was at its maximum. As the test continued, the resistance value steadily decreased, reaching about 15 kΩ at 43 days, and remained stable until the reporting time (i.e. 70 days). During the test period, the color of the core changed from dark blue to light green and seemed to be stable, with no signs of degradation.

[0203] It can be seen that despite the large bubbles completely blocking the tube, the resistance of the carbon fiber rod in the corresponding reservoir remains relatively low and stable over time. Therefore, the experiment of Example 3 shows that even if the large bubbles completely block the tube as an ion channel conduit between two electrolyte reservoirs, ion conduction can still continue between the length of the tube and between the electrolyte reservoirs by virtue of the wicking device within the tube.

[0204] The present invention has been described with reference to preferred embodiments. However, variations and modifications may be made by those skilled in the art without departing from the scope of the present invention.

Claims

1. A charge state indicator device for a redox flow battery system, the redox flow battery system comprising a redox flow battery pack, a positive electrolyte tank and a conduit for circulating the positive electrolyte through the battery pack, a negative electrolyte tank and a conduit for circulating the negative electrolyte through the flow battery pack, the indicator device comprising: a reference cell device comprising means for measuring a potential difference between a positive electrolyte of or from a positive electrolyte tank of a flow battery and a negative electrolyte of or from a negative electrolyte tank of a flow battery; as well as At least one auxiliary reference electrolyte device comprising: a separate auxiliary electrolyte reservoir for containing a redox electrode associated with a reference electrolyte of known composition comparable to the desired or initial composition of the flow battery electrolyte and providing a reference for the flow battery electrolyte, and having a known state of charge; means for measuring the potential difference between the auxiliary reference electrolyte and the corresponding electrolyte of the reference cell device; and An ion channel conduit connecting the auxiliary reference electrolyte reservoir and the corresponding electrolyte of the reference cell device, the conduit being configured for low fluid diffusion capacity or rate, wherein the conduit includes a wicking device for absorbing the electrolyte and maintaining ionic connection between the auxiliary reference electrolyte reservoir and the corresponding electrolyte of the reference cell device.

2. The charge status indicator of claim 1, wherein the wicking means extends continuously along the entire length of the ion channel conduit.

3. A charge state indicator according to claim 1 or 2, wherein the wicking device extends from the ion channel conduit into the auxiliary reference electrolyte reservoir and / or the corresponding electrolyte of the reference cell device.

4. A charge status indicator according to any one of the preceding claims, wherein the wicking means is hydrophilic and / or electrically non-conductive.

5. The charge status indicator of any preceding claim, wherein the wicking means comprises silica (eg silica fibers), ceramic (eg ceramic fibers) and / or a hydrophilic polymer (eg hydrophilic polymer fibers).

6. A charge status indicator according to any preceding claim, wherein the wicking means is a core or thread, preferably consisting of bundled (eg woven, wound or braided) fibres.

7. A charge status indicator according to any one of the preceding claims, wherein the ion channel conduit comprises a tubular member providing a fluid connection between the auxiliary reference electrolyte reservoir and the corresponding electrolyte of the reference cell device.

8. The charge status indicator of claim 7, wherein the wicking means is disposed within the tubular member, wherein the wicking means is preferably a wick or wire disposed within the tubular member.

9. The charge status indicator of any one of the preceding claims, wherein the resistivity of the ion channel conduit is less than or equal to 1 MOhm.

10. The charge status indicator according to any of the preceding claims, wherein the ion channel conduit is free of any membrane or barrier and is in open fluid communication between the auxiliary reference electrolyte and the corresponding electrolyte of the reference cell device.

11. A charge status indicator according to any one of the preceding claims, wherein the ion channel conduit and the separate auxiliary electrolyte reservoir are submerged and substantially free of gas.

12. The charge state indicator according to any one of the preceding claims, wherein the inner diameter of the ion channel conduit is 0.5 mm to 10 mm, preferably 1 mm to 5 mm, more preferably 2.5 mm to 4 mm, such as 3 mm to 3.5 mm.

13. The charge status indicator of any preceding claim, wherein the wicking means is a core or wire having a diameter smaller than the inner diameter of the ion channel conduit (eg, such that the core or wire fits loosely within the conduit).

14. A charge state indicator according to any of the preceding claims, wherein the length of the ion channel conduit is 5 cm to 10 m, preferably up to about 5 m, more preferably up to about 2 m, more preferably 10 cm to 1.5 m, more preferably 15 cm to 1.2 m, for example 20 cm to 1 m or up to 75 cm, and preferably up to about 30 cm to 50 cm.

15. The charge status indicator according to any one of claims 12 to 14, wherein the ion channel conduit is a tubular member having an inner diameter of 2.5 to 4 mm and a length of 20 cm to 2 m.

16. A charge status indicator according to any one of the preceding claims, wherein the ion channel conduit has one or more bends or elbows along its length, such as U-bends or circular bends, preferably the ion channel conduit has a vertical section.

17. The charge status indicator of claim 16, wherein the ion channel conduit comprises one or more loops along its length.

18. A charge state indicator according to any one of the preceding claims, wherein the auxiliary electrolyte reservoir is configured to contain at least 100 ml of reference electrolyte, preferably not more than 10 liters, for example 200 ml to 1000 ml, such as 400 ml to 600 ml.

19. A charge state indicator according to any one of the preceding claims, wherein the auxiliary electrolyte arrangement comprises a temperature sensor for measuring the temperature of the electrolyte in the auxiliary electrolyte reservoir.

20. The charge status indicator according to claim 19, wherein a temperature sensor is provided for measuring the temperature of the corresponding electrolyte in the reference cell device and / or the corresponding electrolyte tank of the flow battery or the related circulation system.

21. A charge state indicator according to any of the preceding claims, wherein the auxiliary electrolyte corresponds to the positive electrolyte of the flow battery, and the auxiliary electrolyte device is configured for ion channel conduit connection and for measuring the potential difference between the auxiliary electrolyte reservoir and the positive electrolyte of the reference battery device.

22. A charge state indicator according to any of the preceding claims, comprising an auxiliary reference electrolyte device, wherein the auxiliary electrolyte corresponds to the negative electrolyte of the flow battery, the auxiliary electrolyte device being configured for connection to an ion channel conduit and for measuring a potential difference between the auxiliary electrolyte reservoir and the negative electrolyte of the reference battery device.

23. A charge status indicator according to any of the preceding claims, wherein the reference cell device comprises a reference cell, the reference cell comprising a positive half-cell and a negative half-cell, the positive half-cell having a positive electrolyte reservoir, the positive electrolyte reservoir being configured to be fluidically connected to a positive electrolyte reservoir of a flow battery, the negative half-cell having a negative electrolyte reservoir, the negative electrolyte reservoir being configured to be fluidically connected to a negative electrolyte tank, wherein the device for measuring the potential difference between an auxiliary reference electrolyte and a corresponding electrolyte of the reference cell device is configured to measure the potential difference between the auxiliary reference electrolyte and the corresponding half-cell of the reference cell.

24. A charge status indicator according to any preceding claim, arranged to measure the charge status at predetermined time periods in response to predetermined system actions.

25. A charge state indicator according to any one of the preceding claims, further comprising a processor for controlling temperature and / or voltage measurements of the charge state indicator and / or configured to communicate said measurements to a controller or data logger of the flow battery.

26. A charge state indicator according to any preceding claim, wherein the redox flow battery is a vanadium redox flow battery.

27. An indicator system for the health status of a redox flow battery system, the indicator system comprising a charge state indicator device according to any one of claims 1 to 26, and configured to determine the health status of the redox flow battery system, preferably by measuring the charge state of at least one electrode electrolyte and another electrode electrolyte or a representation thereof of the flow battery (optionally, continuously, periodically or intermittently), preferably determining the relative oxidation state of the corresponding electrolytes, and preferably issuing an alarm, indicating or taking remedial measures when the determined relative oxidation state exceeds a predetermined limit.

28. An auxiliary reference electrolyte device, used in the health status indicator according to claim 1, the auxiliary reference electrolyte device comprising: a separate auxiliary electrolyte reservoir for containing a redox electrode associated with a reference electrolyte of known composition comparable to the desired or initial composition of the flow battery electrolyte and providing a reference for the flow battery electrolyte, and having a known state of charge; a device for measuring the potential difference between the auxiliary reference electrolyte and the associated electrolyte of the reference cell arrangement or the associated half-cell of the reference cell; as well as an ion-channel conduit for connecting an auxiliary reference electrolyte reservoir and an electrolyte in a corresponding electrolyte of a reference cell device or a corresponding half-cell of a reference cell, the conduit being configured for low fluid diffusion capability or rate, wherein the conduit includes a wicking device for absorbing the electrolyte and maintaining ionic connection between the auxiliary reference electrolyte reservoir and the corresponding electrolyte of the reference cell device or the corresponding half-cell of the reference cell, and Preferably, the auxiliary reference electrolyte device is further defined as described in any one of claims 2 to 26.

29. A redox flow battery comprising a redox flow battery stack, a positive electrolyte tank and a conduit for circulating the positive electrolyte through the battery stack, a negative electrolyte tank and a conduit for circulating the negative electrolyte through the flow battery stack, and a charge state indicator according to any one of claims 1 to 26.

30. A method for monitoring the charge state and / or health state of a redox flow battery, the method comprising providing a charge state indicator as described in any one of claims 1 to 26, and causing the charge state indicator to periodically measure the charge between a reference cell and an auxiliary reference electrolyte and the corresponding half-cells of the reference cell, thereby determining the charge state of the system, and optionally issuing an alarm for charge imbalance of the flow battery electrolyte based on the difference between the charge state of the two poles of the reference cell of the flow battery and a predetermined threshold.

31. A method of maintaining charge state balance or oxidation state balance in a redox flow battery, the method comprising Monitoring the state of charge in a flow battery by providing a state of charge indicator as described in any one of claims 1 to 26, and causing the state of charge indicator to measure the charge between the two poles of a reference cell and between an auxiliary reference electrolyte and the corresponding half-cell of the reference cell periodically or in response to an action or in response to an event, thereby determining the state of charge and / or health state of the system; and When the difference in charge state or oxidation state between the positive electrolyte and the negative electrolyte exceeds one or more predetermined thresholds or meets one or more predetermined criteria, one or more maintenance actions are taken on the flow battery.

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