Online sensor for electrolyte precipitation detection in redox flow battery system

Abstract

A redox flow battery (RFB) system having a low cost online turbidity sensor to detect the early stage of electrolyte precipitate formation is described. The online turbidity sensor can be used in either an absorption mode or a scattering mode. The RFB system may optionally include an RGB color sensor to monitor charge-discharge cycles by detecting color changes in the electrolyte.

Description

[0001] Priority declaration

[0002] This application claims priority to U.S. patent application No. 17 / 932,458, filed on September 15, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0003] Energy storage systems play a key role in collecting and storing energy from a variety of sources for use in a variety of applications and industries, including buildings, transportation, utilities, and industry. A variety of energy storage systems are already in commercial use with new systems currently being developed to meet future storage needs. The development of cost-effective and eco-friendly energy storage systems is essential to solving the energy crisis and overcoming the mismatch between power generation and end use. Energy storage solutions currently being explored include electrochemical and battery storage, thermal storage, thermochemical storage, flywheel storage, compressed air storage, pumped hydro, magnetic storage, bio-storage, chemical storage, and hydrogen storage.

[0004] Renewable energy sources such as wind and solar are transient in nature in that they rely on environmental conditions and would benefit from associated energy storage to provide power when the wind is not blowing and the sun is not shining. Battery energy storage systems (BESS) such as redox flow batteries (RFBs) have attracted significant attention in large-scale stationary applications such as grid-scale energy storage. Some of the earliest published work detailing the use of redox flow batteries for storing electrical energy dates back to the 1950s, when German chemist Dr. Carl Walther Nicolai Kangro investigated the use of Fe 3+ / Fe 2 + Cr 6+ / Cr 3+ 、Ti 4+ / Ti 3+ and Cl - / Cl2 redox pairs in liquids to store electrical energy. In the 1970s, NASA continued to work in this field, producing the first iron-chromium redox flow battery in 1973 to store energy in future lunar bases. Although the interest in building a base on the moon has gradually faded, flow battery research has continued in other chemical fields, including zinc-bromine and all-iron flow batteries. In 1981, Hruska et al. demonstrated the ability of circulating all-iron redox flow batteries (IFBs), which is a battery energy storage device that is attractive for large-scale energy storage applications (such as load balancing and solar energy storage) due to the use of low-cost and large-scale available iron, salt and water as electrolytes and the chemical safety properties of the system. (Investigation of Factors Affecting Performance of theIron-Redox Battery (Research on the Factors Affecting the Performance of the Iron-Redox Battery), J.Electrochem.Soc., Vol. 28, No. 1, pp. 18-25, January 1981). In the late 1980s, Skyllas-Kazacos et al. from the University of New South Wales, Australia, used V 2+ / V 3+ and V 4+ / V 5+ Over the past 40 years, considerable effort has been put into developing all aspects of flow batteries.

[0005] Among the various energy storage technologies that have been considered and explored, redox flow batteries (RFBs) are unique because they can convert electrical energy into chemical potential energy by means of a reversible electrochemical reaction between two aqueous electrolyte solutions. In their simplest form, RFBs are electrochemical energy storage systems that directly and reversibly convert chemical energy into electrical energy. RFBs are typically composed of two external storage tanks, two circulation pumps, and a flow battery with a porous diaphragm, the external storage tanks are filled with active materials containing ions that can be in different valence states, and the porous diaphragm is located between the anode and the cathode and is used to separate the anolyte and the cathode electrolyte, and to utilize the current loop by allowing the transfer of balanced ions. Anolyte, cathode electrolyte, anode and cathode are usually referred to as negative electrolyte, positive electrolyte, negative electrode and positive electrode, respectively. Therefore, power and energy capacity can be independent, indicating that the storage capacity is determined by the amount of electrolyte used, and the rated power is determined by the effective area and number of battery stacks.

[0006] All-vanadium redox flow batteries (VRFBs) have been the most widely studied system because they use the same active material in both half-cells, which prevents electrolyte contamination from one half-cell to the other through crossover at the membrane. However, VRFBs are inherently expensive due to the use of high-cost vanadium.

[0007] Similar to VRFB, all-iron redox flow battery utilizes the same active material (Fe) in different valence states in both the positive and negative electrolytes for the positive and negative electrodes, respectively. The iron-based electrolyte solution is stored in an external storage tank and flows through the battery stack. The positive electrode side half-cell reaction involves Fe 2+ Loses electrons to form Fe 3+ And during discharge, Fe 3+ Gain electrons to form Fe 2+ ; This reaction is given by Equation 1. The negative electrode side half-cell reaction involves the deposition and dissolution of iron in the form of a solid plate; This reaction is given by Equation 2. The overall reaction is shown in Equation 3.

[0008] Redox Electrode:

[0009] Electrode plating:

[0010] total:

[0011] During normal operation of the RFB, small inefficiencies can create big problems over the life of the battery pack. These problems can stem from many reasons, such as: active material crossover across the membrane, parasitic side reactions, or incomplete discharge of the battery pack. Even small inefficiencies can ultimately result in a poorly performing battery pack in a product designed to last more than 20,000 cycles. Engineering design is often required to suppress or correct these inefficiencies.

[0012] Current processes and systems for rebalancing all-iron RFB cells involve reducing Fe3+ to Fe2+ to control the state of charge of the positive electrolyte. Different engineering approaches (electrochemical or catalytic) have demonstrated electrolyte rebalancing within all-iron redox flow batteries; however, the basic principles of iron ion reduction remain largely the same as those taught by Thaller and Noah, where H2(g) is oxidized to produce protons (2H+) and electrons (2e-), which enable the catalytic reduction of Fe3+ in the positive electrolyte to Fe2+. Reduction of Fe3+ to Fe2+ enables the state of charge of the positive electrolyte to be changed; however, protons (H+) migrate into the positive electrolyte. This process results in the removal of protons (H+) from the negative electrolyte (during hydrogen evolution) and their release into the positive electrolyte (during rebalancing). The result of removing protons from the negative electrolyte (H2 precipitation) and inserting them into the positive electrolyte (H2 recombination) is a deviation of the electrolyte pH from the optimal operating value (positive electrolyte acidity increases, while negative electrolyte acidity decreases). Increasing the pH of the negative electrolyte can result in the inability to completely oxidize the plated iron to ferrous cations, or the oxidation or loss of Fe0 from the battery in the form of iron hydroxide, iron oxide, or iron flakes. This results in a reduction in the capacity of the negative electrolyte and causes precipitates / sediments to circulate in the electrolyte loop, which over time can lead to the formation of blockages. Direct introduction of Fe3+ cations into a higher pH negative electrolyte can result in the precipitation of iron hydroxide or iron oxide byproducts, which can lead to electrolyte flow blockage and battery failure.

[0013] One of the biggest challenges to long-term operation of RFBs is the precipitation of electrolytes. For example, in an iron flow battery (IFB), the hydrogen evolution reaction increases the pH of the negative electrolyte, leading to the precipitation of iron hydroxide. The formed precipitate can adhere to the diaphragm and electrodes, reducing membrane conductivity and interfering with the adsorption of iron ions at the electrode surface. Almost all RFB systems (including but not limited to V, Fe and Zn) suffer from this problem.

[0014] Ideally, an IFB is operated with a negative electrolyte solution in a very narrow pH window, such that it is as high as possible to limit the possibility of H2 generation at the negative electrode and as low as possible to suppress the formation of unwanted iron oxides and hydroxides. However, the pH profile throughout a large IFB device is not uniform, and it is conceivable that the pH measured immediately after leaving the stack may be higher than the bulk electrolyte, resulting in localized areas in the system that are prone to precipitate formation.

[0015] The precipitate formed and staying in the battery stack is usually dissolved back into the electrolyte by continuous charge and discharge cycles. However, any material separated from the stack or system manifold can settle in the electrolyte storage tank and become difficult to dissolve back into the solution, and it is difficult to pump back into the solution via the electrolyte loop, thereby potentially causing damage to process equipment and instruments, or causing blockage in the electrolyte pipeline or battery stack. In addition, the formation of iron-based precipitates will reduce the concentration of active redox species in the RFB, thereby reducing the total capacity of the electrolyte. If the precipitate settles to the bottom of the tank and does not dissolve in the solution, this effect will worsen over time. In this way, the precipitate suspended in the electrolyte and any other undesirable particles may be harmful to the system mechanical reliability, electrochemical performance and subsequent system efficiency.

[0016] Therefore, a simple and effective method is needed to identify the formation of precipitates during RFB operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 One embodiment of an RFB system with a turbidity sensor is shown.

[0018] Figure 2 Another embodiment of an RFB system with a rebalance cell and a turbidity sensor is shown.

[0019] Figure 3 Another embodiment of an RFB system having a rebalance cell, a diffusion cell, and a turbidity sensor is shown.

[0020] Figure 4 is a graph showing turbidity and pH as a function of time. DETAILED DESCRIPTION

[0021] A low-cost online turbidity sensor can detect the formation of electrolyte precipitates at an early stage. The online turbidity sensor can be used in absorption mode or scattering mode to capture pH changes of the negative electrolyte and detect the formation of precipitates. As the pH increases, the sensor signal begins to drift downward due to the formation and accumulation of precipitates. For example, in a hybrid redox flow battery pack (such as an IFB), it is desirable to monitor the formation of electrolyte precipitates at an early stage. This may allow the operator to take action to prevent battery pack performance degradation. By monitoring the formation of precipitates in real time, the turbidity sensor may also allow the operator to operate the RFB at a higher efficiency (DoD) without reducing the life of the battery pack.

[0022] In addition, turbidity sensors can also be used to detect the amount of bubbles generated in the hydrogen evolution reaction (HER). It can be used together with a pressure sensor to monitor the HER condition in the RFB system.

[0023] Another potential benefit of an online turbidity sensor is the ability to monitor charge-discharge cycles by detecting slight color changes in the electrolyte during the charge-discharge cycle. For example, in some RFBs (such as IFBs), the color of the electrolyte changes during the charge-discharge process. As more precipitate forms, less Fe 2+ The ions can be reduced, and the sensor's response to the color change slowly decreases. The color change is related to the state of charge (SoC) of the electrolyte. The SoC of the electrolyte can be determined using an online RGB color sensor for measuring the color of the electrolyte. Alternatively, a combination of an LED or other light source with a wavelength in the range of 400nm to 900nm and a photodiode can be used to determine the color change of the electrolyte. In this case, the color change of the electrolyte will cause the peak wavelength of the light absorbed by the electrolyte to shift. By using a luminescent wavelength with a peak close to the peak wavelength of the light absorbed by the electrolyte, the color change can be detected by measuring the intensity of the light passing through the electrolyte using a photodiode.

[0024] By using turbidity sensors together with other online sensors such as RGB (red / green / blue) sensors, a model can be developed to monitor the health of redox flow battery stacks and identify potential failure modes such as precipitation due to pH changes, separation of plated metal from electrodes, etc.

[0025] Turbidity sensors can also be used to detect other failure modes, such as separation of iron-plated particles from the electrodes and decomposition of membranes or other battery components.

[0026] Data from turbidity sensors and other sensors can be used to develop a process model. The process model and sensor data obtained during operation can then be used to monitor and predict the condition of the RFB. This can allow the operator to optimize RFB performance and maximize cycle length.

[0027] In-line sensors with built-in flow cells can be connected directly in the flow loop. Turbidity probes without flow cells can be installed in a T-connector and then connected to the flow loop. The sensor can be installed in the main flow or in a bypass flow.

[0028] Careful placement of turbidity sensors and / or color sensors in an RFB system, particularly a hybrid system, helps maintain the health of the entire system. Turbidity sensors may be located before or after an individual stack or string of stacks, as well as before or after the electrolyte storage tanks, to detect the formation and accumulation of precipitates in the electrolyte and minimize the occurrence of blockages within the stack or the introduction of solids into the electrolyte tanks. Filters may also be positioned before or after system rebalancing components (if present), such as a system that implements hydrogen recombination or a system that implements electrolyte tank rebalancing (if present). In systems such as iron flow batteries, iron precipitates (such as Fe0 or Fe2O3, Fe(OH)3, Fe(OH)2, etc.) are less stable at lower pH values ​​and can redissolve back into the electrolyte during battery cycling. Alternatively, the formation of precipitates in an IFB system may require corrective action to ensure that the system continues to operate at optimal efficiency.

[0029] Various types of RFBs may be used. Suitable RFBs include, but are not limited to, Fe / Sn, Fe / Ti, Fe / Cr, Fe / Fe, Fe / Zn, V / V, Zn / Br, and Zn / Ce.

[0030] The redox active species of RFBs depend on the type of RFB. The redox active species of Fe / Sn RFBs include Fe 2+ / Fe 3+ and Sn 0 / Sn 2+ The redox active species of Fe / Ti RFB include Fe 2+ / Fe 3+ and Ti 3+ / Ti 4+ The redox active species of Fe / Cr RFB include Fe 2+ / Fe 3+ and Cr 2+ / Cr 3+ The redox active species of Fe / Fe RFB include Fe 2+ / Fe 3+ and Fe 2+ / Fe 0 The redox active species of Fe / Zn RFB include Fe 2+ / Fe 3+ and Zn 0 / Zn 2+ The redox active species of V / V RFB include VO2 + / VO 2+ and V 2+ / V 3+ The redox active species of Zn / Br RFB include Br2 / Br - and Zn 0 / Zn 2 + The redox active species of Zn / Ce RFB include Ce 3+ / Ce 4+ and Zn 2+ / Zn 0 .

[0031] One aspect of the present invention is a redox flow battery system. In one embodiment, the redox flow battery system includes: at least one rechargeable battery, the at least one rechargeable battery including a positive electrode, a negative electrode and a separator, the separator being positioned between the positive electrode and the negative electrode; a positive electrolyte tank including a positive electrolyte in fluid communication with the positive electrode, the positive electrolyte flowing from the positive fluid tank to the positive electrode and from the positive electrode to the positive electrolyte tank in a positive electrolyte flow loop; and a negative electrolyte tank including a negative electrolyte in fluid communication with the negative electrode, the negative electrolyte flowing from the negative fluid tank to the negative electrode and from the negative electrode to the negative electrolyte tank in a negative electrolyte flow loop; and a turbidity sensor in the negative electrolyte flow loop for monitoring precipitates or hydrogen bubbles or both in the negative electrolyte, or a turbidity sensor in the positive electrolyte flow loop for monitoring precipitates in the positive electrolyte, or both.

[0032] In some embodiments, the turbidity sensor in the negative electrolyte flow loop is positioned between the negative electrolyte tank and the negative electrode, or between the negative electrode and the negative electrolyte tank, or both; or wherein the turbidity sensor in the positive electrolyte flow loop is positioned between the positive electrolyte tank and the positive electrode, or between the positive electrode and the positive electrolyte tank, or both.

[0033] In some embodiments, the turbidity sensor is located in the negative flow loop or in the slipstream from the negative flow loop; or wherein the turbidity sensor is located in the positive flow loop or in the slipstream from the positive flow loop; or both.

[0034] In some embodiments, the turbidity sensor comprises a flow cell, an absorption turbidity sensor, or a light scattering turbidity sensor.

[0035] In some embodiments, the turbidity sensor is positioned directly in the negative electrolyte flow loop or the positive electrolyte flow loop, or both.

[0036] In some embodiments, the turbidity sensor is positioned in a connector that is in fluid communication with the negative electrolyte flow circuit or the positive flow circuit or both.

[0037] In some embodiments, the redox flow battery system further comprises: a color sensor in the positive electrolyte flow loop for determining the state of charge of the positive electrolyte, or a color sensor in the negative electrolyte flow loop for determining the state of charge of the negative electrolyte, or both, wherein the color sensor comprises a red / green / blue (RGB) sensor or a light source and a photodiode.

[0038] In some embodiments, the redox flow battery system further comprises: a rebalance cell, a diffusion cell, or both.

[0039] In some embodiments, the redox flow battery system further comprises: a color sensor for determining the state of charge of the positive electrolyte located between the positive electrode and the positive electrolyte tank in the positive electrolyte flow loop, or a color sensor for determining the state of charge of the negative electrolyte located between the negative electrode and the negative electrolyte tank in the negative electrolyte flow loop, or both, wherein the color sensor comprises a red / green / blue (RGB) sensor or a light source and a photodiode.

[0040] In some embodiments, the redox flow battery comprises a hybrid flow battery system.

[0041] In some embodiments, the redox flow battery system comprises an iron flow battery system.

[0042] Another aspect of the present invention is a redox flow battery system. In one embodiment, the redox flow battery system includes: at least one rechargeable battery, the at least one rechargeable battery including a positive electrode, a negative electrode and a separator, the separator being positioned between the positive electrode and the negative electrode; a positive electrolyte tank, the positive electrolyte tank including a positive electrolyte in fluid communication with the positive electrode, the positive electrolyte flowing from the positive fluid tank to the positive electrode and from the positive electrode to the positive electrolyte tank in a positive electrolyte flow loop; and a negative electrolyte tank, the negative electrolyte tank including a negative electrolyte in fluid communication with the negative electrode, the negative electrolyte flowing from the negative fluid tank to the negative electrode and from the negative electrode to the negative electrolyte in a negative electrolyte flow loop. A liquid tank; a turbidity sensor in the negative electrolyte flow loop for monitoring precipitates or hydrogen bubbles or both in the negative electrolyte, or a turbidity sensor in the positive electrolyte flow loop for monitoring precipitates in the positive electrolyte, or both; wherein the turbidity sensor comprises a flow battery, an absorption turbidity sensor or a light scattering turbidity sensor; wherein the turbidity sensor is positioned between the negative electrolyte tank and the negative electrode, or between the negative electrode and the negative electrolyte tank, or both; or wherein the turbidity sensor is positioned between the positive electrolyte tank and the positive electrode, or between the positive electrode and the positive electrolyte tank, or both; or both.

[0043] In some embodiments, the turbidity sensor is located in the negative flow loop or in the slipstream from the negative flow loop; or wherein the turbidity sensor is located in the positive flow loop or in the slipstream from the positive flow loop; or both.

[0044] In some embodiments, the turbidity sensor is positioned directly in the negative electrolyte flow loop or the positive electrolyte flow loop, or both.

[0045] In some embodiments, the turbidity sensor is positioned in a connector that is in fluid communication with the negative electrolyte flow circuit or the positive flow circuit or both.

[0046] In some embodiments, the redox flow battery system further comprises: a color sensor in the positive electrolyte flow loop for determining the state of charge of the positive electrolyte, or a color sensor in the negative electrolyte flow loop for determining the state of charge of the negative electrolyte, or both, wherein the color sensor comprises a red / green / blue (RGB) sensor or a light source and a photodiode.

[0047] In some embodiments, the redox flow battery system further includes a rebalancing cell in fluid communication with the negative electrolyte tank or the positive electrolyte tank or both, and in fluid communication with the positive electrode and the positive electrolyte tank.

[0048] In some embodiments, the redox flow battery system further comprises: a color sensor for determining the state of charge of the positive electrolyte located between the positive electrode and the positive electrolyte tank in the positive electrolyte flow loop, or a color sensor for determining the state of charge of the negative electrolyte located between the negative electrode and the negative electrolyte tank in the negative electrolyte flow loop, or both, wherein the color sensor comprises a red / green / blue (RGB) sensor or a light source and a photodiode.

[0049] In some embodiments, the redox flow battery comprises a hybrid flow battery system.

[0050] In some embodiments, the redox flow battery system comprises an iron flow battery system.

[0051] Figure 1 One embodiment of an RFB system 100 is shown. It should be noted that although the RFB system is described as an IFB, the RFB system is not limited to an IFB system. Other RFB systems may also be used.

[0052] The RFB system 100 includes a rechargeable battery 105, which includes a negative electrode 110, a positive electrode 115, and a separator 120. There are a negative electrolyte tank 125 and a positive electrolyte tank 130.

[0053] The negative electrolyte circulates in a negative electrolyte loop from the negative electrolyte tank 125 to the negative electrode 110 in the rechargeable battery 105 and back to the negative electrolyte tank 125. There is an online turbidity sensor 135 on the line 140 from the negative electrolyte tank 125 to the negative electrode 110 in the rechargeable battery 105, and there is another online turbidity sensor 145 on the line 150 from the negative electrode 110 in the rechargeable battery 105 to the negative electrolyte tank 125.

[0054] The positive electrolyte circulates in a positive electrolyte loop from the positive electrolyte tank 130 to the positive electrode 115 in the rechargeable battery 105 and back to the positive electrolyte tank 130. On the line 160 from the positive electrode 115 in the rechargeable battery 105 to the positive electrolyte tank 130 there is an RGB sensor 155.

[0055] Figure 2 Another embodiment of an RFB system 200 is shown with a rebalanced cell 275. The RFB system 200 includes a rechargeable battery 205 including a negative electrode 210, a positive electrode 215, and a separator 220. There is a negative electrolyte tank 225 and a positive electrolyte tank 230. The RFB system includes a rebalanced cell 275 including a negative electrode 280, a positive electrode 285, and a separator 290.

[0056] The negative electrolyte circulates in a negative electrolyte loop from the negative electrolyte tank 225 to the negative electrode 210 in the rechargeable battery 205 and back to the negative electrolyte tank 225. There is an online turbidity sensor 235 on the line 240 from the negative electrolyte tank 225 to the negative electrode 210 in the rechargeable battery 205, and there is another online turbidity sensor 245 on the line 250 from the negative electrode 210 in the rechargeable battery 205 to the negative electrolyte tank 225.

[0057] The positive electrolyte circulates from the positive electrolyte tank 230 to the positive electrode 215 in the rechargeable battery 205. The positive electrolyte flows from the positive electrode 215 in the rechargeable battery 205 to the positive electrode 285 of the rebalanced battery 275. Hydrogen gas from the negative electrolyte tank 225 flows through the pipeline 295 to the negative electrode 280 of the rebalanced battery 275, wherein Fe +3 By H + ions are converted to Fe +2 .Fe +2 The increased level of positive electrolyte flows from the positive electrode 285 of the rebalance cell 275 to the positive electrolyte tank 230. On the line 297 from the rebalance cell 275 to the positive electrolyte tank 230 there is an RGB sensor 255.

[0058] Figure 3 Another embodiment of the RFB system 200 is shown with a rebalance cell 275 and a diffusion cell 400. The RFB system 300 includes a rechargeable battery 305 including a negative electrode 310, a positive electrode 315, and a separator 320. There is a negative electrolyte tank 325 and a positive electrolyte tank 330. The rebalance cell 375 includes a negative electrode 380, a positive electrode 385, and a separator 390. The diffusion cell 400 includes a negative electrode 405, a positive electrode 410, and a separator 415.

[0059] The negative electrolyte may be circulated directly from the negative electrolyte tank 325 to the negative electrode 310 in the rechargeable battery 305 through lines 342 and 343. Alternatively, the negative electrolyte may flow from the negative electrolyte tank 325 to the negative electrode 405 of the diffusion cell 400 through line 344, and then to the negative electrode 310 in the rechargeable battery 305 through line 343. The flow path is controlled by valve 341. The negative electrolyte flows back from the negative electrode 310 of the rechargeable battery 305 to the negative electrolyte tank 325 through line 316. There is an online turbidity sensor 335 on line 340 from the negative electrolyte tank 325 to valve 341, and there is another online turbidity sensor 345 on line 343.

[0060] The positive electrolyte circulates from the positive electrolyte tank 330 to the positive electrode 410 in the diffusion cell 400 through the pipeline 401. On the pipeline 401 from the positive electrolyte tank 330 to the diffusion cell 400 there is an RGB sensor 403.

[0061] The positive electrolyte flows from the positive electrode 410 in the diffusion cell 400 to the positive electrode 315 of the rechargeable battery 305 through the pipeline 416. Then, the positive electrolyte flows from the positive electrode 315 of the rechargeable battery 305 to the positive electrode 385 of the rebalancing battery 375 through the pipeline 317. The hydrogen gas from the negative electrolyte tank 325 flows to the negative electrode 380 of the rebalancing battery 375 through the pipeline 395. Part of the hydrogen gas is oxidized to H + ions, pass through the membrane 390, and convert Fe +3 Converted to Fe +2 .Fe +2 The increased level of positive electrolyte flows from the positive electrode 385 of the rebalance cell 375 to the positive electrolyte tank 330 via line 397 .

[0062] Unreacted hydrogen flows from the negative electrode 380 of the rebalance cell 375 to the positive electrolyte tank 330 via line 399 .

[0063] Hydrogen gas flows between the positive electrolyte tank 330 and the negative electrolyte tank 325 via line 420 to balance the headspace pressure in these tanks.

[0064] The diffusion cell 400 is used to help balance the pH of the electrolyte. No voltage is applied to the diffusion cell 400, and no redox reaction occurs therein. Valve 341 controls when the diffusion cell is connected to the negative electrolyte flow path. In normal operation, the negative electrolyte flows directly from the negative electrolyte tank 325 to the negative electrode 310 of the rechargeable battery 305 through pipelines 340, 342 and 343. When the output of the turbidity sensor 335 drops below a first predetermined limit, indicating that the pH is higher than the desired operating level, valve 341 diverts the negative electrolyte flow to the diffusion cell 400 through pipeline 344. The diffusion cell 400 allows protons to diffuse from the positive electrolyte to the negative electrolyte through the diaphragm 415 to reduce the pH of the negative electrolyte. When the output of the turbidity sensor 335 reaches a second predetermined limit, indicating that the pH of the negative electrolyte is lower than the desired operating level, valve 341 disconnects the diffusion cell 400, and the negative electrolyte flows to the rechargeable battery 305 through pipelines 342 and 343.

[0065] Example

[0066] The turbidity sensor was installed between the negative tank and the negative electrode and tested with an IFB system containing an H2 rebalancing cell. Figure 2 A schematic diagram of the test setup is shown in . The turbidity sensor shows a repeating up-and-down pattern corresponding to the color change of the negative electrolyte during the charge-discharge cycle. During the battery charging process, as the Fe 2+ Reduced to Fe 0 and plated on the negative electrode, the color of the negative electrolyte changed to a very light green, and the output of the turbidity sensor increased. During discharge, Fe is converted back to Fe 2+ , and the output of the turbidity sensor decreases as the color of the negative electrolyte becomes darker.

[0067] like Figure 4 As shown in Figure 3, the response of the turbidity sensor correlates well with the pH change of the negative electrolyte. As the pH increases above 4.3, the sensor signal begins to drift downward due to the formation and accumulation of precipitates. The sensor response to the charge-discharge cycle of the battery pack also varies with the amount of Fe in the negative electrolyte. 2+ The concentration of ions decreases gradually.

[0068] Specific implementation plan

[0069] While the following is described in conjunction with specific embodiments, it should be understood that this description is intended to illustrate and not to limit the scope of the foregoing description and the appended claims.

[0070] A first embodiment of the present invention is a redox flow battery system, the redox flow battery system comprising: at least one rechargeable battery, the at least one rechargeable battery comprising a positive electrode, a negative electrode and a separator, the separator being positioned between the positive electrode and the negative electrode; a positive electrolyte tank, the positive electrolyte tank comprising a positive electrolyte in fluid communication with the positive electrode, the positive electrolyte flowing from the positive fluid tank to the positive electrode and from the positive electrode to the positive electrolyte tank in a positive electrolyte flow loop; and a negative electrolyte tank, the negative electrolyte tank comprising a negative electrolyte in fluid communication with the negative electrode, the negative electrolyte flowing from the negative fluid tank to the negative electrode and from the negative electrode to the negative electrolyte tank in a negative electrolyte flow loop; and a turbidity sensor in the negative electrolyte flow loop for monitoring precipitates or hydrogen bubbles or both in the negative electrolyte, or a turbidity sensor in the positive electrolyte flow loop for monitoring precipitates in the positive electrolyte, or both. An embodiment of the present invention is one, any or all of the preceding embodiments in this paragraph up to the first embodiment in this paragraph, wherein the turbidity sensor in the negative electrolyte flow loop is positioned between the negative electrolyte tank and the negative electrode, or between the negative electrode and the negative electrolyte tank, or both; or wherein the turbidity sensor in the positive electrolyte flow loop is positioned between the positive electrolyte tank and the positive electrode, or between the positive electrode and the positive electrolyte tank; or both. An embodiment of the present invention is one, any or all of the preceding embodiments in this paragraph up to the first embodiment in this paragraph, wherein the turbidity sensor is located in the negative flow loop or in the slipstream from the negative flow loop; or wherein the turbidity sensor is located in the positive flow loop or in the slipstream from the positive flow loop; or both. An embodiment of the present invention is one, any or all of the preceding embodiments in this paragraph up to the first embodiment in this paragraph, wherein the turbidity sensor comprises a flow battery, an absorption turbidity sensor, or a light scattering turbidity sensor. An embodiment of the present invention is one, any or all of the preceding embodiments in this paragraph up to the first embodiment in this paragraph, wherein the turbidity sensor is positioned directly in the negative electrolyte flow circuit or the positive electrolyte flow circuit or both. An embodiment of the present invention is one, any or all of the preceding embodiments in this paragraph up to the first embodiment in this paragraph, wherein the turbidity sensor is positioned in a connector in fluid communication with the negative electrolyte flow circuit or the positive flow circuit or both.An embodiment of the present invention is one, any one or all of the aforementioned embodiments in this paragraph up to the first embodiment in this paragraph, and the redox flow battery system further includes: a color sensor in the positive electrolyte flow loop for determining the state of charge of the positive electrolyte, or a color sensor in the negative electrolyte flow loop for determining the state of charge of the negative electrolyte, or both, wherein the color sensor includes a red / green / blue (RGB) sensor or a light source and a photodiode. An embodiment of the present invention is one, any one or all of the aforementioned embodiments in this paragraph up to the first embodiment in this paragraph, and the redox flow battery system further includes a rebalancing cell, a diffusion cell, or both. The embodiment of the present invention is one, any or all of the aforementioned embodiments in this paragraph up to the first embodiment in this paragraph, the redox flow battery system further includes: a color sensor for determining the state of charge of the positive electrolyte located between the positive electrode and the positive electrolyte tank in the positive electrolyte flow loop, or a color sensor for determining the state of charge of the negative electrolyte located between the negative electrode and the negative electrolyte tank in the negative electrolyte flow loop, or both, wherein the color sensor includes a red / green / blue (RGB) sensor or a light source and a photodiode. The embodiment of the present invention is one, any or all of the aforementioned embodiments in this paragraph up to the first embodiment in this paragraph, the redox flow battery system further includes: a diffusion cell, the diffusion cell including a positive electrode, a negative electrode and a diaphragm, the diaphragm is positioned between the positive electrode and the negative electrode, the diffusion cell is fluidly connected to the outlet of the positive electrolyte tank and the inlet of the positive electrode side of the rechargeable battery, and the diffusion cell is selectively connected to the outlet of the negative electrolyte tank and the inlet of the negative side of the rechargeable battery. An embodiment of the invention is one, any or all of the preceding embodiments in this paragraph up to the first embodiment in this paragraph, wherein the redox flow battery comprises a hybrid flow battery system. An embodiment of the invention is one, any or all of the preceding embodiments in this paragraph up to the first embodiment in this paragraph, wherein the redox flow battery system comprises an iron flow battery system.

[0071] A second embodiment of the present invention is a redox flow battery system, the redox flow battery system comprising: at least one rechargeable battery, the at least one rechargeable battery comprising a positive electrode, a negative electrode and a separator, the separator being positioned between the positive electrode and the negative electrode; a positive electrolyte tank, the positive electrolyte tank comprising a positive electrolyte in fluid communication with the positive electrode, the positive electrolyte flowing from the positive fluid tank to the positive electrode and from the positive electrode to the positive electrolyte tank in a positive electrolyte flow loop; and a negative electrolyte tank, the negative electrolyte tank comprising a negative electrolyte in fluid communication with the negative electrode, the negative electrolyte flowing from the negative fluid tank to the negative electrode and from the negative electrode in a negative electrolyte flow loop. Flowing to the negative electrolyte tank; a turbidity sensor in the negative electrolyte flow loop for monitoring precipitates or hydrogen bubbles or both in the negative electrolyte, or a turbidity sensor including a flow battery in the positive electrolyte flow loop for monitoring precipitates in the positive electrolyte, or both; wherein the turbidity sensor comprises a flow battery, an absorption turbidity sensor, or a light scattering turbidity sensor; wherein the turbidity sensor is positioned between the negative electrolyte tank and the negative electrode, or between the negative electrode and the negative electrolyte tank, or both; or wherein the turbidity sensor is positioned between the positive electrolyte tank and the positive electrode, or between the positive electrode and the positive electrolyte tank, or both; or both. An embodiment of the present invention is one, any one, or all of the preceding embodiments in this paragraph up to the second embodiment in this paragraph, wherein the turbidity sensor is located in the negative flow loop or in a slipstream from the negative flow loop; or wherein the turbidity sensor is located in the positive flow loop or in a slipstream from the positive flow loop; or both. An embodiment of the present invention is one, any one or all of the aforementioned embodiments in this paragraph up to the second embodiment in this paragraph, wherein the turbidity sensor is directly positioned in the negative electrolyte flow circuit or the positive electrolyte flow circuit or both. An embodiment of the present invention is one, any one or all of the aforementioned embodiments in this paragraph up to the second embodiment in this paragraph, wherein the turbidity sensor is positioned in a connector that is fluidly connected to the negative electrolyte flow circuit or the positive flow circuit or both. An embodiment of the present invention is one, any one or all of the aforementioned embodiments in this paragraph up to the second embodiment in this paragraph, wherein the redox flow battery system further includes: a color sensor in the positive electrolyte flow circuit for determining the state of charge of the positive electrolyte, or a color sensor in the negative electrolyte flow circuit for determining the state of charge of the negative electrolyte, or both, wherein the color sensor includes a red / green / blue (RGB) sensor or a light source and a photodiode.An embodiment of the present invention is one, any or all of the aforementioned embodiments in this paragraph up to the second embodiment in this paragraph, and the redox flow battery system also includes a rebalancing cell, and the rebalancing cell is fluidically connected to the negative electrolyte tank or the positive electrolyte tank or both, and is fluidically connected to the positive electrode and the positive electrolyte tank. An embodiment of the present invention is one, any or all of the aforementioned embodiments in this paragraph up to the second embodiment in this paragraph, and the redox flow battery system also includes: a color sensor for determining the state of charge of the positive electrolyte located between the positive electrode and the positive electrolyte tank in the positive electrolyte flow loop, or a color sensor for determining the state of charge of the negative electrolyte located between the negative electrode and the negative electrolyte tank in the negative electrolyte flow loop, or both, wherein the color sensor includes a red / green / blue (RGB) sensor or a light source and a photodiode. An embodiment of the present invention is one, any or all of the aforementioned embodiments in this paragraph up to the second embodiment in this paragraph, and the redox flow battery system also includes: a diffusion cell, the diffusion cell includes a positive electrode, a negative electrode and a diaphragm, the diaphragm is positioned between the positive electrode and the negative electrode, the diffusion cell is fluidly connected to the outlet of the positive electrolyte tank and the inlet of the positive electrode side of the rechargeable battery, and the diffusion cell is selectively connected to the outlet of the negative electrolyte tank and the inlet of the negative side of the rechargeable battery. An embodiment of the present invention is one, any or all of the aforementioned embodiments in this paragraph up to the second embodiment in this paragraph, wherein the redox flow battery includes a hybrid flow battery system. An embodiment of the present invention is one, any or all of the aforementioned embodiments in this paragraph up to the second embodiment in this paragraph, wherein the redox flow battery system includes an iron flow battery system.

[0072] Although there is no further detailed description, it is believed that those skilled in the art can utilize the present invention to the greatest extent by using the foregoing description and can easily determine the essential characteristics of the present invention without departing from the spirit and scope of the present invention to make various changes and modifications of the present invention and adapt it to various usages and conditions. Therefore, the aforementioned preferred specific embodiments should be understood as merely illustrative and not limiting the rest of the present disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0073] In the foregoing, all temperatures are set forth in degrees Celsius and all parts and percentages are by weight unless otherwise indicated.

Claims

1. A redox flow battery system, the redox flow battery system comprising: at least one rechargeable battery (105), the at least one rechargeable battery comprising a positive electrode (115), a negative electrode (110), and a separator (120), the separator being positioned between the positive electrode (115) and the negative electrode (110); a positive electrolyte tank (130), the positive electrolyte tank comprising a positive electrolyte in fluid communication with the positive electrode (115), the positive electrolyte flowing from the positive electrolyte tank to the positive electrode (115) and from the positive electrode (115) to the positive electrolyte tank (130) in a positive electrolyte flow loop; and a negative electrolyte tank (125) comprising a negative electrolyte in fluid communication with the negative electrode (110), the negative electrolyte flowing from the negative electrolyte tank (125) to the negative electrode (110) and from the negative electrode (110) to the negative electrolyte tank (125) in a negative electrolyte flow loop; and A turbidity sensor (135) in the negative electrolyte flow loop for monitoring precipitates or hydrogen bubbles or both in the negative electrolyte, or a turbidity sensor in the positive electrolyte flow loop for monitoring precipitates in the positive electrolyte, or both.

2. A redox flow battery system according to claim 1, wherein the turbidity sensor (135) in the negative electrolyte flow loop is positioned between the negative electrolyte tank (125) and the negative electrode (110), or between the negative electrode (110) and the negative electrolyte tank (125), or both; or wherein the turbidity sensor in the positive electrolyte flow loop is positioned between the positive electrolyte tank (130) and the positive electrode (115), or between the positive electrode (115) and the positive electrolyte tank (130), or both.

3. A redox flow battery system according to claim 1, wherein the turbidity sensor (135) is located in the negative flow loop or in a slipstream from the negative flow loop; or wherein the turbidity sensor is located in the positive flow loop or in a slipstream from the positive flow loop; or both.

4. The redox flow battery system of claim 1, wherein the turbidity sensor (135) comprises a flow battery, an absorption turbidity sensor, or a light scattering turbidity sensor.

5. The redox flow battery system of claim 4, wherein the turbidity sensor (135) is positioned directly in the negative electrolyte flow loop or the positive electrolyte flow loop or both.

6. The redox flow battery system of claim 1, wherein the turbidity sensor (135) is positioned in a connector in fluid communication with the negative electrolyte flow circuit or the positive flow circuit or both.

7. The redox flow battery system of claim 1, further comprising: A color sensor (155) in the positive electrolyte flow loop for determining the state of charge of the positive electrolyte, or a color sensor in the negative electrolyte flow loop for determining the state of charge of the negative electrolyte, or both, wherein the color sensor (155) includes a red / green / blue (RGB) sensor or a light source and a photodiode.

8. The redox flow battery system of claim 1 , further comprising: Rebalance cell (375), diffusion cell (400), or both.

9. The redox flow battery system of claim 1, further comprising: A diffusion cell (400), the diffusion cell comprising a positive electrode (410), a negative electrode (405) and a diaphragm (415), the diaphragm being positioned between the positive electrode (410) and the negative electrode (410), the diffusion cell (400) being fluidically connected to the outlet of the positive electrolyte tank (330) and the inlet of the positive electrode (315) side of the rechargeable battery (305), and the diffusion cell (400) being selectively connected to the outlet of the negative electrolyte tank (325) and the inlet of the negative electrode (310) side of the rechargeable battery (305).

10. The redox flow battery system of claim 1, further comprising: A color sensor (155) for determining the state of charge of the positive electrolyte located between the positive electrode (115) and the positive electrolyte tank (130) in the positive electrolyte flow loop, or a color sensor for determining the state of charge of the negative electrolyte located between the negative electrode (110) and the negative electrolyte tank (125) in the negative electrolyte flow loop, or both, wherein the color sensor (155) includes a red / green / blue (RGB) sensor or a light source and a photodiode.

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