Method and system for operating a redox flow battery

Abstract

A system and method for a redox flow battery is provided. In one embodiment, a method of operating a redox flow battery includes providing a pulsed power signal to the redox flow battery in response to a state of charge (SOC) of the redox flow battery decreasing below a lower threshold redox flow battery SOC, charging the redox flow battery, where providing the pulsed power signal includes providing a pulse width modulated (PWM) charging voltage signal to the redox flow battery, the PWM charging voltage signal varying between an upper threshold charging voltage and an open circuit voltage (OCV).

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63 / 363,612, entitled "METHODS AND SYSTEMS FOR OPERATING REDOX FLOW BATTERY," filed April 26, 2022. The entire contents of the above-identified application are hereby incorporated by reference for all purposes.

[0002] This description relates generally to methods and systems for operating redox flow batteries. [Background technology]

[0003] Redox flow batteries, such as all-iron redox flow batteries (IFBs), are advantageous compared to lithium-ion type batteries due to their low cost, long run times, low fire risk, and the potential for long life with unlimited cycling. However, because the electrolyte is aqueous, redox flow batteries may have lower power and energy densities compared to lithium-ion batteries. Reducing the performance loss of IFBs can help close the power and energy density gap versus traditional batteries. The performance loss of IFBs can be primarily attributed to losses at the plating electrodes, as well as losses at the redox electrodes and ohmic resistance losses. Operating redox flow batteries at higher temperatures can help reduce ohmic resistance losses, but material costs may be higher to ensure robustness of the system piping when operating at higher temperatures. Reducing the plating gap at the plating electrodes can also help improve the efficiency of redox flow batteries. However, retrofitting existing systems to accommodate reduced plating gaps can be complex and costly. Summary of the Invention

[0004] One approach that at least partially addresses the above-mentioned problem includes a method of operating a redox flow battery, including charging the redox flow battery, where charging the redox flow battery includes providing a pulsed power signal to the redox flow battery in response to a state of charge (SOC) of the redox flow battery decreasing below a lower threshold redox flow battery SOC. Providing the pulsed power signal includes providing a pulse width modulated (PWM) charging voltage signal to the redox flow battery, where the PWM charging voltage signal varies between an upper threshold charging voltage and an open circuit voltage (OCV). In this manner, a technical effect of improving the voltaic efficiency and energy efficiency of the redox flow battery system while maintaining the coulombic efficiency of the redox flow battery system may be achieved. Furthermore, the improved voltaic efficiency and energy efficiency are achieved while maintaining the operating temperature of the redox flow system, thereby reducing material costs and maintaining the reliability and durability of the system piping. Furthermore, since improved voltaic and energy efficiency are achieved while maintaining the plating gap in the plating electrode, it becomes easier to retrofit existing redox flow battery systems to achieve improved voltaic and energy efficiency without increasing manufacturing costs and complexity.

[0005] It should be understood that the foregoing summary is provided to introduce in a simplified form a selection of concepts that are further described in the Detailed Description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims that follow the Detailed Description. Moreover, the claimed subject matter is not limited to implementations that solve shortcomings noted above or in any part of this disclosure. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 shows a schematic diagram of an exemplary redox flow battery system including a power module and an electrolyte subsystem. [Diagram 2]FIG. 2 shows a schematic diagram of an electrical energy storage system of the power module of FIG. 1, including multiple stacks of redox flow battery cells. [Figure 3A] 1 shows an example plot of a pulse width modulated (PWM) charge and discharge voltage signal. [Figure 3B] 1 shows an example plot of a pulse width modulated (PWM) charge and discharge voltage signal. [Figure 4] 1 shows an example of a graph comparing the positive electrode potential in continuous charging and pulse charging. [Diagram 5] 1 shows an example of a graph comparing the negative electrode potential in continuous charging and pulse charging. [Figure 6A] 1 shows a graph of Voltaic efficiency as a function of duty cycle. [Figure 6B] 1 shows a graph of coulombic efficiency as a function of duty cycle. [Figure 6C] 1 shows a graph of energy efficiency as a function of duty cycle. [Figure 7A] 1 shows a graph relating plating efficiency to the pH of the electrolyte. [Figure 7B] 1 shows a graph relating state of charge (SOC) to open circuit voltage (OCV). [Figure 8] 1 and 2, including charging and discharging the redox flow battery. [Figure 9] 1 and 2, including charging and discharging the redox flow battery. [Figure 10] 1 and 2, including charging and discharging the redox flow battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] A redox flow battery system including a power module and an electrolyte subsystem is shown in FIG. 1. As shown in FIG. 2, a power module of the redox flow battery system may include one or more cell stacks, each including a plurality of redox flow battery cells. Each of the redox flow battery cells may be continuously charged and / or continuously discharged, or may be pulse charged and / or pulse discharged. Continuous charging involves providing a continuous charging voltage signal from a power source to the redox flow battery, while continuous discharging involves providing a continuous discharging voltage signal from the redox flow battery cell to a load. Pulse charging involves providing a pulse width modulated (PWM) voltage signal from a power source to the redox flow battery cell, while pulse discharging involves providing a PWM voltage signal from the redox flow battery cell to a load. Examples of PWM voltage signals are shown in FIG. 3A and FIG. 3B, while FIG. 4 and FIG. 5 compare electrode potentials of continuous charge / discharge and pulse charge / discharge of the redox flow battery system. Performance data obtained from continuous charge / discharge versus pulse charge / discharge are shown in Figures 6A, 6B, and 6C. Figures 7A and 7B show the relationship between plating efficiency and the pH of the plating electrolyte, and between the open circuit voltage (OCV) and state of charge (SOC) of the redox flow battery system. These relationships can affect the performance of the redox flow battery during charge and discharge cycles. A method of operating a redox flow battery, including charging and discharging one or more redox flow battery cells, is shown in Figures 8-10.

[0008] 1, in the redox flow battery system 10, the negative electrode 26 may be referred to as the plating electrode and the positive electrode 28 may be referred to as the redox electrode. The negative electrolyte in the plating side (e.g., negative electrode compartment 20) of the redox flow battery cell 18 may be referred to as the plating electrolyte and the positive electrolyte on the redox side (e.g., positive electrode compartment 22) of the redox flow battery cell 18 may be referred to as the redox electrolyte.

[0009] "Anode" refers to an electrode at which an electroactive material loses electrons, and "cathode" refers to an electrode at which an electroactive material gains electrons. During battery charging, the negative electrolyte gains electrons at the negative electrode 26, which is the cathode of the electrochemical reaction. During battery discharging, the negative electrolyte loses electrons, and the negative electrode 26 is the anode of the electrochemical reaction. Alternatively, during battery discharging, the negative electrolyte and the negative electrode 26 may be referred to as the anolyte and anode, respectively, of the electrochemical reaction, while the positive electrolyte and the positive electrode 28 may be referred to as the catholyte and cathode, respectively, of the electrochemical reaction. During battery charging, the negative electrolyte and the negative electrode 26 may be referred to as the catholyte and cathode, respectively, of the electrochemical reaction, while the positive electrolyte and the positive electrode 28 may be referred to as the anolyte and anode, respectively, of the electrochemical reaction. For simplicity, the terms "positive" and "negative" are used herein to refer to the electrodes, electrolytes, and electrode compartments in a redox flow battery system.

[0010] One example of a hybrid redox flow battery is an all-iron redox flow battery (IFB), in which the electrolyte includes iron ions in the form of iron salts (e.g., FeCl2, FeCl3, etc.) and the negative electrode 26 includes metallic iron. For example, ferrous iron (Fe 2+ ) gains two electrons during battery charging and becomes iron metal (Fe 0 ) on the negative electrode 26, and Fe 0 During battery discharge, it loses two electrons to become Fe 2+ At the positive electrode 28, Fe 2+ During battery charging, ferric iron (Fe 3+ ) and Fe 3+ During battery discharge, it gains electrons to form Fe 2+ The electrochemical reactions are summarized in equations (1) and (2), where the forward reaction (left to right) represents the electrochemical reaction during battery charging, while the reverse reaction (right to left) represents the electrochemical reaction during battery discharging. Fe 2+ +2e - ←→Fe 0 -0.44V (negative electrode) (1) 2Fe 2+←→2Fe 3+ +2e - +0.77V (positive electrode) (2)

[0011] As mentioned above, the negative electrolyte used in the IFB is Fe 2- accepts two electrons from the negative electrode 26 to form Fe 0 and plated onto the substrate. 2+ During battery discharge, the plated Fe 0 loses two electrons to become Fe 2+ and can dissolve back into the electrolyte. The equilibrium potential of the above reaction is -0.44 V, so this reaction provides the negative terminal for the desired system. On the positive side of the IFB, the electrolyte loses electrons and becomes Fe 3- During battery charging, Fe is oxidized to 2+ During battery discharge, Fe provided by the electrolyte 3+ by absorbing electrons provided by the positive electrode 28. 2+ The equilibrium potential for this reaction is +0.77V, creating a positive terminal in the desired system.

[0012] The IFB may provide the ability to charge and recharge the electrolyte therein, in contrast to other battery types that utilize non-regenerative electrolytes. Charging may be accomplished by applying a current across electrodes 26 and 28 via terminals 40 and 42, respectively. The negative electrode 26 contains (e.g., Fe 2+ But Fe 3+ The negative side of a voltage source may be electrically coupled via terminal 40 such that electrons may be delivered to the negative electrolyte via positive electrode 28 (as Fe is oxidized to Fe 2+ is reduced to form Fe on the (plating) substrate. 0 Formation of Fe 2+ is plated onto the negative electrode 26.

[0013] Discharge is Fe 0 remains available in the negative electrolyte for oxidation, and Fe 3+remains available in the positive electrolyte for reduction. 3+ The availability of Fe can be increased by adding additional Fe via an external source, such as the external positive electrolyte chamber 52. 3+ This can be maintained by increasing the concentration or volume of positive electrolyte in the positive electrode compartment 22 of the redox flow battery cell 18 to provide ions. More generally, during discharge, 0 The availability of Fe is an issue in IFB systems, where the amount of Fe available for discharge is 0 can be proportional to the surface area and volume of the negative electrode substrate and the plating efficiency. The charging capacity is 2+ As an example, Fe 2+ The availability of Fe can be increased by adding additional Fe via an external source, such as the external negative electrolyte chamber 50. 2+ This can be maintained by providing ions to increase the concentration or volume of negative electrolyte to the negative electrode compartment 20 side of the redox flow battery cell 18.

[0014] In an IFB, the positive electrolyte includes ferrous, ferric, ferric complexes, or any combination thereof, while the negative electrolyte may include ferrous or ferrous complexes depending on the state of charge (SOC) of the IFB system. As previously mentioned, the utilization of iron ions in both the negative and positive electrolytes allows for the utilization of the same electrolyte species on both sides of the redox flow battery cell 18, which may reduce electrolyte cross-contamination and increase the efficiency of the IFB system, resulting in less electrolyte exchange compared to other redox flow battery systems.

[0015] SOC may be described as the ratio of the amount of charge stored in an electrical energy storage device (e.g., a redox flow battery) to the full or total theoretical amount of charge that can be stored in the electrical energy storage device. In one example, initiating charging of the redox flow battery may be in response to the SOC decreasing below a lower threshold redox flow battery SOC, and stopping charging of the redox flow battery may be in response to the SOC increasing above an upper threshold redox flow battery SOC. In another example, the rate of charging and discharging power of the redox flow battery system may depend on the SOC. Measuring the oxidation / reduction potential (ORP) of the positive electrolyte may provide a measure of SOC by determining the amount of Fe in the positive electrolyte. 3+ The ORP provides an indication of ions. However, side reactions at the negative electrode can reduce the accuracy of the ORP as a measure of SOC by offsetting the overall battery capacity from a positive state of charge. In another example, the SOC can be determined by calculating the plating efficiency at the negative electrode. The plating efficiency indicates the rate of coulombic charge entering and leaving the redox flow battery, and can be useful in assessing the SOC of the redox flow battery, as further described herein.

[0016] Voltage losses in redox flow batteries are caused by kinetic, ohmic, and mass transport losses at the electrodes. Ohmic losses arise from the voltage drop due to the movement of electrons in the electrical circuit and the movement of ions through the electrolyte and between the electrolyte and the electrodes. The kinetic losses of the plating and redox electrodes depend on the electrode area, the reaction exchange current, the equilibrium potential, the number of electrons in the reaction, and the reaction temperature. The ohmic losses depend on the ionic conductivity of the electrolyte and the contact resistance of the conductive parts. As the temperature increases, the mobility of ions through the electrolyte and from the electrolyte to the electrodes, and the conductivity through the electrodes increases, so both the ohmic losses and the kinetic losses of the plating and redox electrodes are lower.

[0017] The efficiency of electrical energy storage devices, including redox flow batteries, can be indicated by Coulombic (or charge) efficiency (CE), Voltaic efficiency (VE), and energy efficiency (EE). These are measures of how efficiently a battery can convert chemical energy into electrical energy and vice versa, respectively. CE represents the charge efficiency of electrons moving in a redox flow battery, and is the ratio of the total charge extracted from the battery over a charge / discharge cycle of a particular redox flow battery to the total charge put into the battery. VE represents the ratio of the average charge voltage to the average discharge voltage. Losses occur because the charge voltage is higher than the rated voltage and activates the chemical reactions in the battery. EE is the product of CE and VE (EE=CE*VE), similar to how energy is the product of charge and voltage.

[0018] The performance loss can be formulated according to equations (3) and (4). E 充電 =E pos +E neg +IR=(E eq pos +η + )+(E eq neg +η - )+IR (3) E 放電 =E pos +E neg -IR=(E eq pos +η + )-(E eq neg +η - )-IR (4) E eq pos =E 0 pos -RT / nF*ln([Fe 3+ ] / [Fe 2+ ]) (5) E eq neg =E 0 neg -RT / nF*ln([Fe 2+ ] / [Fe 0 ]) (6) Here, E 充電 is the charging potential, Epos is the positive electrode potential, E neg is the negative electrode potential, and IR (ohmic loss) is equal to the product of the ohmic resistance R and the current I to drive the redox reaction at the positive electrode. E pos is the equilibrium positive electrode potential E eq pos and the additional positive electrode loss voltage η due to efficiency losses at the positive electrode + Similarly, E neg is the equilibrium negative electrode potential E eq neg and the additional negative electrode loss voltage η due to efficiency losses at the negative (plating) electrode - The balanced positive electrode potential and the balanced negative electrode potential are given by equations (5) and (6), as described for the example IFB system.

[0019] Efficiency losses in the IFB can result from electrolyte crossover through the separator 24 (e.g., ion exchange membrane barrier, microporous membrane, etc.). For example, Fe in a positive electrolyte 3+ The ion is Fe 3+ The negative electrolyte can then be driven toward the negative electrolyte by the ion concentration gradient and the electrophoretic force across the separator 24. The Fe ions then penetrate the separator 24 and cross over into the negative electrode compartment 20. 3+ Fe ions crossing over from the low pH redox side (e.g., the more acidic positive electrode compartment 22) to the high pH plating side (e.g., the less acidic negative electrode compartment 20) can result in coulombic efficiency losses. 3+The ions may result in the precipitation of Fe(OH)3, which may degrade the separator 24 and cause permanent battery performance and efficiency loss. For example, Fe(OH)3 precipitates may chemically foul the organic functional groups of the ion exchange membrane or physically clog the micropores of the ion exchange membrane. In either case, the Fe(OH)3 precipitates may cause the membrane's ohmic resistance to increase over time, resulting in reduced battery performance. The precipitates may be removed by washing the IFB with acid, but the constant maintenance and downtime may be disadvantageous for commercial battery applications. Furthermore, washing may depend on periodic preparation of the electrolyte, contributing to additional processing costs and complexity. Alternatively, the addition of certain organic acids to the positive and negative electrolytes in response to electrolyte pH changes may mitigate precipitate formation during battery charge and discharge cycles without driving up the overall cost. Additionally, Fe 3+ Implementing a membrane barrier that inhibits ionic crossover may also mitigate fouling.

[0020] The additional coulombic efficiency loss is H + (e.g., protons) and subsequent formation of H2 gas, as well as the reaction of protons in the negative electrode compartment 20 with electrons supplied to the plated iron metal of the negative electrode 26 to form H2 gas.

[0021] IFB electrolytes (e.g., FeCl2, FeCl3, FeSO4, Fe2(SO4)3, etc.) may be readily available and may be produced at low cost. In one example, the IFB electrolyte may be formed from ferrous chloride (FeCl2), potassium chloride (KCl), manganese(II) chloride (MnCl2), and boric acid (H3BO3). The IFB electrolyte may provide a higher recycle value since the same electrolyte may be used for the negative and positive electrolytes, resulting in reduced cross-contamination issues compared to other systems. Furthermore, due to the electron configuration of iron, it may solidify into a generally uniform solid structure during plating onto the negative electrode substrate. In the case of zinc and other metals commonly used in hybrid redox batteries, solid dendritic structures may form during plating. The stable electrode morphology of the IFB system may increase the efficiency of the battery compared to other redox flow batteries. Furthermore, the iron redox flow battery may reduce the use of toxic raw materials and operate at a relatively neutral pH compared to other redox flow battery electrolytes. Therefore, the IFB system may pose less environmental hazard than all other current advanced redox flow battery systems in production.

[0022] Continuing with FIG. 1, a schematic diagram of a redox flow battery system 10 is shown. The redox flow battery system 10 may include a redox flow battery cell 18 fluidly coupled to an integrated multi-chamber electrolyte storage tank 110. The redox flow battery cell 18 may include a negative electrode compartment 20, a separator 24, and a positive electrode compartment 22. The separator 24 includes an electrically insulating ionically conductive barrier that prevents bulk mixing of the positive and negative electrolytes while allowing conduction of certain ions. For example, as discussed above, the separator 24 may include an ion exchange membrane and / or a microporous membrane.

[0023] The negative electrode compartment 20 may include a negative electrode 26 and the negative electrolyte may include an electroactive material. The positive electrode compartment 22 may include a positive electrode 28 and the positive electrolyte may include an electroactive material. In some embodiments, multiple redox flow battery cells 18 may be combined in series or parallel to generate higher voltages or currents in the redox flow battery system 10.

[0024] 1 are negative and positive electrolyte pumps 30 and 32, both of which are used to pump electrolyte solution through the redox flow battery system 10. Electrolyte is stored in one or more tanks external to the cell and is pumped through the negative electrode compartment 20 and positive electrode compartment 22 of the redox flow battery cell 18 via the negative electrolyte pump 30 and positive electrolyte pump 32, respectively.

[0025] The redox flow battery system 10 may also include a first bipolar plate 36 and a second bipolar plate 38, each positioned along a back side of the negative electrode 26 and the positive electrode 28, respectively, e.g., opposite the side facing the separator 24. The first bipolar plate 36 may be in contact with the negative electrode 26 and the second bipolar plate 38 may be in contact with the positive electrode 28. However, in other embodiments, the bipolar plates 36 and 38 may be arranged in close proximity to the electrodes 26 and 28, but spaced apart from the electrodes 26 and 28 and housed within the respective electrode compartments 20 and 22. In either case, the bipolar plates 36 and 38 may be electrically coupled to terminals 40 and 42, respectively, via direct contact with the negative and positive electrodes 26 and 28, or via the negative and positive electrodes 26 and 28, respectively. The IFB electrolyte may be transported to the reaction sites of the negative and positive electrodes 26 and 28 by the first and second bipolar plates 36 and 38 due to the conductive properties of the materials of the bipolar plates 36 and 38. The flow of electrolyte may also be assisted by the negative and positive electrolyte pumps 30 and 32 to facilitate forced convection through the redox flow battery cell 18. Reacted electrochemical species may also be directed away from the reaction sites by a combination of forced convection and the presence of the first and second bipolar plates 36 and 38.

[0026] As illustrated in FIG. 1 , the redox flow battery cell 18 may further include a negative battery terminal 40 and a positive battery terminal 42. When a charging current is applied to the battery terminals 40 and 42, the positive electrolyte may be oxidized (lose one or more electrons) at the positive electrode 28 and the negative electrolyte may be reduced (gain one or more electrons) at the negative electrode 26. During battery discharge, reverse redox reactions may occur on the electrodes 26 and 28. In other words, the positive electrolyte may be reduced (gain one or more electrons) at the positive electrode 28 and the negative electrolyte may be oxidized (lose one or more electrons) at the negative electrode 26. A potential difference across the battery may be maintained by electrochemical redox reactions in the positive electrode compartment 22 and the negative electrode compartment 20, which may induce a current through the current collectors while the reactions persist. The amount of energy stored by a redox battery may be limited by the amount of electroactive material available in the electrolyte for discharge, depending on the total amount of electrolyte and the solubility of the electroactive material.

[0027] The redox flow battery system 10 may further include an integrated multi-chamber electrolyte storage tank 110. The multi-chamber electrolyte storage tank 110 may be divided by a bulkhead 98. The bulkhead 98 may create multiple chambers within the multi-chamber electrolyte storage tank 110 such that both positive and negative electrolytes may be contained within a single tank. The negative electrolyte chamber 50 holds a negative electrolyte containing an electroactive material, and the positive electrolyte chamber 52 holds a positive electrolyte containing an electroactive material. The bulkhead 98 may be positioned within the multi-chamber electrolyte storage tank 110 to provide a desired volume ratio between the negative electrolyte chamber 50 and the positive electrolyte chamber 52. In one embodiment, the bulkhead 98 may be positioned to set the volume ratio of the negative electrolyte chamber 50 and the positive electrolyte chamber 52 according to a stoichiometric ratio between the negative redox reaction and the positive redox reaction. FIG. 1 further illustrates a fill height 112 of the multi-chamber electrolyte storage tank 110, which may indicate the liquid level within each tank compartment. 1 also shows a gas headspace 90 located above the fill height 112 of the negative electrolyte chamber 50, and a gas headspace 92 located above the fill height 112 of the positive electrolyte chamber 52. The gas headspace 92 may be utilized to store H2 gas that is generated during the operation of the redox flow battery (e.g., by the side reactions of proton reduction and iron corrosion) and is carried to the multi-chamber electrolyte storage tank 110 with electrolyte returning from the redox flow battery cell 18. The H2 gas may naturally separate at the gas-liquid interface (e.g., the fill height 112) in the multi-chamber electrolyte storage tank 110, thereby eliminating the need to have an additional gas-liquid separator as part of the redox flow battery system 10. Once separated from the electrolyte, the H2 gas may fill the gas headspaces 90 and 92. Thus, the stored H2 gas can help to purge other gases from the multi-chamber electrolyte storage tank 110, thereby acting as an inert gas blanket to reduce oxidation of electrolyte species, which can help reduce redox flow battery capacity loss.In this manner, utilizing an integrated multi-chamber electrolyte storage tank 110 may eliminate the need to have separate negative and positive electrolyte storage tanks, hydrogen storage tanks, and gas-liquid separators common to conventional redox flow battery systems, thereby simplifying the system design, reducing the physical footprint of the redox flow battery system 10, and reducing system costs.

[0028] FIG. 1 also shows a spillover hole 96, which may create an opening in a bulkhead 98 between the gas headspaces 90 and 92 and provide a means of equalizing gas pressure between the chambers 50 and 52. The spillover hole 96 may be located at a threshold height above the fill height 112. The spillover hole 96 may further enable the ability to self-balance the electrolyte in each of the negative and positive electrolyte chambers 50 and 52 in the event of a cell crossover. In the case of an all-iron redox flow battery system, the same electrolyte (Fe 2+ ) are used in both the negative and positive electrode compartments 20 and 22, so that electrolyte spillover between the negative electrolyte chamber 50 and the positive electrolyte chamber 52 may reduce overall system efficiency, but overall electrolyte composition, battery module performance, and battery module capacity may be maintained. Flange joints may be utilized for all plumbing connections between the inlet and outlet multi-chamber electrolyte storage tank 110 to maintain a leak-free, continuously pressurized condition. The multi-chamber electrolyte storage tank 110 may include at least one outlet from each of the negative and positive electrolyte chambers 50 and 52, and at least one inlet to each of the negative and positive electrolyte chambers 50 and 52. Additionally, one or more outlet connections may be provided from the gas headspaces 90 and 92 to direct H2 gas to the rebalancing reactors 80 and 82.

[0029] Although not shown in FIG. 1 , the integrated multi-chamber electrolyte storage tank 110 may further include one or more heaters thermally coupled to each of the negative electrolyte chamber 50 and the positive electrolyte chamber 52. In an alternative example, only one of the negative electrolyte chamber 50 and the positive electrolyte chamber 52 may include one or more heaters. If only the positive electrolyte chamber 52 includes one or more heaters, the negative electrolyte may be heated by transferring heat generated in the redox flow battery cell 18 to the negative electrolyte. In this manner, the redox flow battery cell 18 may heat the negative electrolyte and facilitate temperature regulation of the negative electrolyte. The one or more heaters may be operated by the controller 88 to regulate the temperature of the negative electrolyte chamber 50 and the positive electrolyte chamber 52 independently or together. For example, in response to the electrolyte temperature falling below a threshold temperature, the controller 88 may increase the power supplied to the one or more heaters such that the heat flux to the electrolyte may be increased. The electrolyte temperature may be indicated by one or more temperature sensors attached to the multi-chamber electrolyte storage tank 110, such as sensors 60 and 62. By way of example, the one or more heaters may include coil-type heaters or other immersion heaters immersed in the electrolyte fluid, or surface mantle-type heaters that conductively transfer heat through the walls of the negative and positive electrolyte chambers 50 and 52 to heat the fluid therein. Other known types of tank heaters may be used without departing from the scope of this disclosure. Additionally, the controller 88 may deactivate one or more heaters in the negative and positive electrolyte chambers 50 and 52 in response to a liquid level below a solids fill threshold level. Stated differently, in some embodiments, the controller 88 may activate one or more heaters in the negative and positive electrolyte chambers 50 and 52 only in response to a liquid level above a solids fill threshold level. In this manner, activation of one or more heaters without sufficient liquid in the negative and / or positive electrolyte chambers 50, 52 may be avoided, thereby reducing the risk of overheating or burning out of the heater(s).

[0030] Still further, one or more inlet connections may be provided to each of the negative and positive electrolyte chambers 50 and 52 from a field hydration system (not shown). In this manner, the field hydration system may facilitate the start-up of the redox flow battery system 10, including installation, charging, and hydration of the redox flow battery system 10, at the end-use location. Furthermore, prior to the start-up of the redox flow battery system 10 at the end-use location, the redox flow battery system 10 may be dry assembled at a battery manufacturing facility different from the end-use location, without the need to charge and hydrate the redox flow battery system 10 before shipping it to the end-use location. In one embodiment, the end-use location may correspond to a location where the redox flow battery system 10 is installed and utilized for on-site energy storage. In other words, the redox flow battery system 10 may be designed such that once installed and hydrated at the end-use location, the location of the redox flow battery system 10 is fixed and the redox flow battery system 10 may no longer be considered a portable dry system. Thus, from an end user's perspective, the dry portable redox flow battery system 10 may be delivered to a site, after which the redox flow battery system 10 may be installed, hydrated, and commissioned. Prior to hydration, the redox flow battery system 10 may be referred to as a dry portable system, in which the redox flow battery system 10 does not include or is free of water and wet electrolyte. Once hydrated, the redox flow battery system 10 may be referred to as a wet non-portable system, in which the redox flow battery system 10 includes wet electrolyte.

[0031] 1, the electrolyte solution initially stored in the multi-chamber electrolyte storage tank 110 can be pumped throughout the redox flow battery system 10 via negative and positive electrolyte pumps 30 and 32. The electrolyte stored in the negative electrolyte chamber 50 can be pumped through the negative electrode compartment 20 side of the redox flow battery cell 18 via the negative electrolyte pump 30, and the electrolyte stored in the positive electrolyte chamber 52 can be pumped through the positive electrode compartment 22 side of the redox flow battery cell 18 via the positive electrolyte pump 32.

[0032] The electrolyte rebalancing reactors 80 and 82 may be connected in-line or in parallel with the electrolyte recirculation flow paths at the negative and positive sides of the redox flow battery cells 18 in the redox flow battery system 10, respectively. One or more rebalancing reactors may be connected in-line with the electrolyte recirculation flow paths at the negative and positive sides of the battery, and other rebalancing reactors may be connected in parallel for redundancy (e.g., the rebalancing reactors may be maintained without interrupting the battery and rebalancing operation) and for increased rebalancing capacity. In one embodiment, the electrolyte rebalancing reactors 80 and 82 may be disposed in the return flow paths from the negative and positive electrode compartments 20 and 22, respectively, to the negative and positive electrolyte chambers 50 and 52.

[0033] The electrolyte rebalancing reactors 80 and 82 can be useful for rebalancing electrolyte charge imbalances in the redox flow battery system 10 that occur due to side reactions, ionic crossover, etc., as described herein. In one example, the electrolyte rebalancing reactors 80 and 82 can include trickle bed reactors in which H2 gas and electrolyte can contact at a catalyst surface in a packed bed to perform the electrolyte rebalancing reaction. In another example, the rebalancing reactors 80 and 82 can include flow-through reactors in which H2 gas and electrolyte can contact and perform the electrolyte rebalancing reaction without a packed catalyst bed.

[0034] During operation of the redox flow battery system 10, the sensors and probes may monitor and control electrolyte chemical properties, such as electrolyte pH, concentration, SOC, ORP, etc. For example, as illustrated in FIG. 1, sensors 62 and 60 may be positioned to monitor the state of the positive and negative electrolytes in the positive and negative electrolyte chambers 52 and 50, respectively. In another example, each of the sensors 62 and 60 may include one or more electrolyte level sensors to indicate the level of electrolyte in the positive and negative electrolyte chambers 52 and 50, respectively. As another example, sensors 72 and 70, also illustrated in FIG. 1, may monitor the state of the positive and negative electrolytes in the positive and negative electrode compartments 22 and 20, respectively. The sensors 72 and 70 may be pH probes, optical probes, pressure sensors, voltage sensors, etc. It will be understood that sensors may be positioned elsewhere throughout the redox flow battery system 10 to monitor electrolyte chemical properties and other properties.

[0035] For example, sensors may be placed in an external acid tank (not shown) to monitor the amount of acid or pH in the external acid tank, and acid from the external acid tank may be supplied to the redox flow battery system 10 via an external pump (not shown) to reduce precipitate formation in the electrolyte. Additional external tanks and sensors may be installed to supply other additives to the redox flow battery system 10. For example, various sensors including temperature, conductivity, and level sensors of the field hydration system may send signals to the controller 88. Additionally, the controller 88 may send signals to actuators such as valves and pumps of the field hydration system during hydration of the redox flow battery system 10. The sensor information is sent to the controller 88, which may then, by way of example, operate the pumps 30 and 32 to control electrolyte flow through the redox flow battery cell 18, or perform other control functions. In this manner, the controller 88 may respond to one or a combination of sensors and probes.

[0036] The redox flow battery system 10 may further include a source of H2 gas. In one example, the source of H2 gas may include a separate dedicated hydrogen gas storage tank. In the embodiment of FIG. 1, H2 gas may be stored in and supplied from the integrated multi-chamber electrolyte storage tank 110. The integrated multi-chamber electrolyte storage tank 110 may supply additional H2 gas to the positive electrolyte chamber 52 and the negative electrolyte chamber 50. The integrated multi-chamber electrolyte storage tank 110 may alternately supply additional H2 gas to the inlets of the electrolyte rebalancing reactors 80 and 82. As an example, a mass flow meter or other flow control device (which may be controlled by the controller 88) may regulate the flow rate of H2 gas from the integrated multi-chamber electrolyte storage tank 110. The integrated multi-chamber electrolyte storage tank 110 may replenish H2 gas generated within the redox flow battery system 10. For example, if a gas leak is detected in the redox flow battery system 10 or if the reduction reaction rate is too slow at low hydrogen partial pressure, H2 gas can be provided from the integrated multi-chamber electrolyte storage tank 110 to rebalance the SOC of the electroactive materials in the positive and negative electrolytes. As an example, the controller 88 can provide H2 gas from the integrated multi-chamber electrolyte storage tank 110 in response to a measured change in pH or in response to a measured change in the SOC of the electrolyte or electroactive materials.

[0037] For example, an increase in pH in the negative electrolyte chamber 50 or the negative electrode compartment 20 may indicate that H2 is leaking from the redox flow battery system 10 and / or that the reaction rate is too slow at the available hydrogen partial pressure, and the controller 88 may increase the supply of H2 gas from the integrated multi-chamber electrolyte storage tank 110 to the redox flow battery system 10 in response to the increase in pH. As a further example, the controller 88 may supply H2 gas from the integrated multi-chamber electrolyte storage tank 110 in response to a pH change where the pH increases above a first threshold pH or decreases above a second threshold pH. In the case of an IFB, the controller 88 may supply additional H2 gas to increase the pH of the redox flow battery system 10.3+ This can increase the rate of reduction of ions and the rate of production of protons, thereby decreasing the pH of the positive electrolyte. Furthermore, the pH of the negative electrolyte can be increased by increasing the rate of Fe crossover from the positive electrolyte to the negative electrolyte. 3+ The pH of the negative electrolyte can be lowered by hydrogen reduction of the ion or by protons generated on the positive side crossing over to the negative electrolyte due to the proton concentration gradient and electrophoretic forces. In this way, the pH of the negative electrolyte is reduced by Fe(OH)3. 3+ The risk of precipitation of ions (crossing over from the positive electrode compartment 22) can be kept within a stable region.

[0038] Other control schemes may be implemented to control the rate of H2 gas supply from the integrated multi-chamber electrolyte storage tank 110 in response to changes in electrolyte pH or changes in electrolyte SOC detected by other sensors, such as an oxygen reduction potential (ORP) meter or optical sensor. Still further, the change in pH or SOC trigger action of the controller 88 may be based on a rate of change or a change measured over a period of time. The period of the rate of change may be predetermined or adjusted based on the time constant of the redox flow battery system 10. For example, if the recirculation rate is high, the period may be shortened and the time constant may be small so that local changes in concentration (e.g., due to side reactions or gas leaks) may be measured quickly.

[0039] The controller 88 may further execute a control scheme based on the operating mode of the redox flow battery system 10. For example, during a charging mode, the controller 88 may provide current from a power source (such as an external electrical energy source 279) conductively coupled to the terminals 40 and 42 to charge the redox flow battery 18. As described in further detail below with reference to Figures 2-8, charging the redox flow battery 18 may include pulse charging the redox flow battery 18, whereby a pulsed current and / or voltage signal is provided from the power source to the redox flow battery 18. In another example, during a discharging mode, the controller 88 may regulate the discharge of the redox flow battery 18 to power an electrical load (such as an external electrical energy consuming device 278) conductively coupled to the terminals 40 and 42. As described in further detail below with reference to Figures 2-8, discharging the redox flow battery 18 may include pulse discharging the redox flow battery 18, whereby a pulsed current and / or voltage signal is provided from the redox flow battery 18 to an electrical load.

[0040] As another example, the controller 88 may control the charging and discharging of the redox flow battery cell 18 to cause pre-formation of iron at the negative electrode 26 during system conditioning (system conditioning may include an operating mode used to optimize the electrochemical performance of the redox flow battery system 10 outside of battery cycling). That is, during system conditioning, the controller 88 may adjust one or more operating conditions of the redox flow battery system 10 to plate iron metal on the negative electrode 26 to increase the charge capacity of the battery during a subsequent battery cycle (thus iron metal may be pre-formed for the battery cycle). The controller 88 may further perform electrolyte rebalancing, as discussed above, to remove excess hydrogen gas from the redox flow battery system 10 and to plate iron metal on the negative electrode 26 to increase the charge capacity of the battery during a subsequent battery cycle (thus iron metal may be pre-formed for the battery cycle). 3+In this manner, preforming iron at the negative electrode 26 and performing electrolyte rebalancing during system conditioning may increase the overall capacity of the redox flow battery cell 18 during battery cycling by mitigating iron plating losses. As used herein, battery cycling (also referred to as "charge cycling") may include alternating between charge and discharge modes of the redox flow battery system 10.

[0041] It will be understood that all components except the sensors 60 and 62 and the integrated multi-chamber electrolyte storage tank 110 (and components included therein) may be considered to be included in the power module 120. Thus, the redox flow battery system 10 may be described as including the power module 120 fluidly coupled to the integrated multi-chamber electrolyte storage tank 110 and communicatively coupled to the sensors 60 and 62. In some examples, each of the power module 120 and the multi-chamber electrolyte storage tank 110 may be included in a single housing (not shown) such that the redox flow battery system 10 may be included in a single location as a single unit. It will be further understood that the positive electrolyte, the negative electrolyte, the sensors 60 and 62, the electrolyte rebalancing reactors 80 and 82, and the integrated multi-chamber electrolyte storage tank 110 (and components included therein) may be considered to be included in the electrolyte subsystem 130. Thus, the electrolyte subsystem 130 may provide one or more electrolytes to the redox flow battery cells 18 (and components included therein).

[0042] 2, which is a schematic block diagram of an electric energy storage system 200 including a plurality of IFB cells 175a-175x and a controller 88. In one example, the power module 120 of the redox flow battery system 10 of FIG. 1 may include the electric energy storage system 200. In this manner, the redox flow battery system 10 may include one or more stacks of IFB cells (e.g., electric energy storage cell stacks 201, 202, 203, and 204, also referred to as cell stacks 201-204). The controller 88 may read the voltage levels of the electric energy storage cell stacks 201-204 and the currents flowing through the electric energy storage cell stacks 201-204 via the sensor 210. The controller 88 may also selectively operate the contactors 220-223, the main contactor 301, and the charger 277. The controller 88 may receive input from and provide output to a human / machine interface 290, which may be a display panel, a remote device, a push button panel, or other known interface. The controller 88 may communicate data (e.g., SOC values) to the external controller 250 over a network (e.g., a local area network (LAN), a controller area network (CAN), or other known network) such that the external controller 250 may operate the external electric energy consuming device 278 and the external electric energy source 279 in conjunction with the operation of the electric energy storage system 200. The external controller 250 as well as the external electric energy consuming device 278 and the external electric energy source 279 may be external to the redox flow battery system 10. The controller 88 may receive data and instructions from the human / machine interface 290 (e.g., a display panel, a keyboard, push buttons, etc.). Additionally, the controller 88 may transmit data to the human / machine interface 290 and the external controller 250.

[0043] The IFB cells 175a-175x are the same as the redox flow battery cells 18 shown in FIG. 1. The letter designations are provided merely to identify the individual electrical energy storage cells. The IFB cells 175a-175f are disposed in a first cell stack 201. The IFB cells 175g-175l are disposed in a second cell stack 202. The IFB cells 175m-175r are disposed in a third cell stack 203. The IFB cells 175s-175x are disposed in a fourth cell stack 204. Although FIG. 2 shows four cell stacks in the electrical energy storage system 200, the electrical energy storage system 200 is not limited to four electrical energy storage cell stacks. Rather, the electrical energy storage system 200 may include 1 to N electrical energy storage cell stacks, where N is an integer. Further, each electrical energy storage cell stack shown in FIG. 2 includes six electrical energy storage cells (e.g., 175a-175f). However, electrical energy storage system 200 is not limited to six electrical energy storage cells in each electrical energy storage cell stack. Rather, electrical energy storage system 200 may include 1 to M electrical energy storage cells in an electrical energy storage cell stack, where M is an integer. Each of electrical energy storage cells 175a-175x includes a positive side 116 and a negative side 114. In some examples, M of each cell stack of cell stacks 201-204 may include a positive side 116 and a negative side 114. 番目 The negative side 114 of the energy storage cell of each of the cell stacks 201-204 may be grounded. 番目 The negative side 114 of the energy storage cell may be floating and bussed with the adjacent cell stack, as indicated by dashed line 182.

[0044] Each of the electric energy storage cell stacks 201-204 includes a contactor 220-223 for selectively and individually coupling and decoupling the electric energy storage cell stacks 201-204 to a power conductor or bus 260. The contactor 220 includes a first side 220a directly coupled to the power conductor 260 and a second side 220b directly coupled to the electric energy storage cell stack 201. Similarly, the contactors 221-223 include first sides 221a, 222a, and 223a directly coupled to the power conductor 260 and second sides 221b, 222b, and 223b directly coupled to the electric energy storage cell stacks 202-204. When the electric energy storage system 200 is inactive, the contactors 220-223 may be opened (e.g., such that no current flows through the contactors). Additionally, the contactors 220-223 may be individually opened and closed (e.g., so that current flows through the contactors) to selectively electrically isolate selected electrical energy storage cell stacks 201-204 from the power conductors 260 when one or more of the electrical energy storage cells 175a-175x are cleaned. The contactors 220-223 may be selectively opened and closed via the controller 88.

[0045] The charger 277 may provide charge to the power conductors 260 when commanded by the controller 88. The power conductors 260 may distribute charge to the electric energy storage cell stacks 201-204 when the contactors 220-223 are closed. Additionally, the charger 277 may provide charge to the individual electric energy storage cell stacks 201-204 individually. For example, the charger 277 may charge only the electric energy storage cell stack 201 when the contactor 220 is closed and the contactors 221-223 are open. In another example of individually charging the electric energy cell stacks, the charger 277 may charge only the electric energy storage cell stacks 201 and 204 when the contactors 220 and 223 are closed and the contactors 221 and 222 are open. The charger 277 may be selectively activated to provide charge and deactivated to stop providing charge via the controller 88. Charger 277 may also be commanded to supply charge until power conductors 260, and the electrical energy storage cell stack electrically coupled to power conductors 260, are at a charge level or voltage level requested by controller 88.

[0046] Electrical energy storage system 200 also includes a main contactor 301 that may be opened or closed via controller 88. Main contactor 301 may be closed to electrically couple power conductors 260 to an external electrical energy source (e.g., solar cell, wind turbine, hydroelectric generator, etc.) 279 and an external electrical energy consumer (e.g., household appliances, industrial motors, vehicle propulsion, etc.) 278. Main contactor 301 may be opened to electrically isolate IFB cell electrical energy conductors 260 from external electrical energy source 279 and external electrical energy consumer 278. External electrical energy source 279 and external electrical energy consumer 278 are external to electrical energy storage system 200.

[0047] 7A, a graph 800 is shown illustrating an example relationship between the pH of the plating (negative) electrolyte of the IFB and the plating efficiency of the negative electrode. The vertical axis represents the negative electrolyte plating efficiency, which increases in the direction of the vertical axis arrow. The horizontal axis represents the plating electrolyte pH, which increases in the direction of the horizontal axis arrow. Curve 802 represents the relationship between the plating electrolyte pH and the negative electrode plating efficiency, which may be referred to as the Coulombic efficiency for the negative plating reaction. In one example, the relationship between plating efficiency and pH represented by curve 802 may be expressed as shown in Equation (7) below. Plate eff =0.138*ln(pH)+0.8514 (7) During the ceremony, Plate eff is the plating efficiency of the negative electrode, ln is the natural logarithm, and pH is the pH value of the plating electrolyte.

[0048] In one example, plating efficiency may be empirically determined by adjusting the pH of the plating electrolyte and determining the plating efficiency for each pH value during charging of the IFB. Plating efficiency may be determined by measuring the actual weight of metal deposited on the negative electrode during charging of the IFB and dividing by the theoretical weight of metal that may be deposited on the negative electrode during charging of the iron flow electric energy storage cell according to Faraday's law.

[0049] 7B, a graph 850 is shown illustrating an example relationship between the SOC and open circuit voltage (OCV) of a battery. In one example, OCV represents the battery voltage measured at the positive and negative busbars of electrical energy storage system 200. Graph 850 represents a function that outputs the SOC of a redox flow battery. This function may be referenced or indexed via the OCV (e.g., the voltage of the IFB cell or cell stack when the IFB cell or cell stack is disconnected from an external electrical load). The vertical axis represents plated OCV, where OCV increases in the direction of the vertical axis arrow. The horizontal axis represents SOC%, where SOC% increases in the direction of the horizontal axis arrow. Curve 852 represents the relationship between SOC% and OCV. In one example, the OCV and SOC represented by curve 852 may be expressed as: OCV The relationship between can be expressed as shown in equation (8). SOC OCV =-0.518*OCV 2 +67.098*OCV-2010.7(8) SOC OCV is the SOC of the redox flow battery determined as a function of the OCV of the redox flow battery.

[0050] In one embodiment, the relationship between SOC and OCV can be determined empirically by measuring the OCV and then fully discharging a battery while measuring the amount of charge leaving the battery during the discharge process. The amount of charge leaving the battery during the discharge process divided by the theoretical amount of charge the battery can store indicates the SOC for a particular OCV.

[0051] The SOC values ​​of the positive and negative electrolytes can be calculated from equations (9) and (10).

number

number

[0052] V pos,0 and V neg,0 can be determined by level sensors such as sensors 60 and 62. Alternatively, V pos,0 and V neg,0 may be a characteristic of the redox flow battery system and may be stored in the non-volatile memory of the on-board controller 88. tot may be measured by a current sensor that may be integrated with the controller 88 and / or the external controller 250. α refers to the effective electrode area of ​​the redox flow battery, and Δt i refers to the time interval between summation steps. [Fe 2+ ]0 is the initial concentration of ferrous ions in the positive and negative electrolytes, which can be measured by sensors 60 and 62. Fe2+ and N Fe3+ refers to the flux density (change in concentration per area per time) of ferrous and ferric ions from the positive electrolyte to the negative electrolyte, respectively, and is measured by sensors 60 and 62, Aα Determined in relation to Δt i In another example, the flux density can be determined by empirically evaluating the ion transport in the redox flow battery by ex situ ion chromatography measurements of the concentration of electrolyte ions. s,pos,i and I s,neg,i In one example, the shunt current in an electrical energy storage cell stack can be empirically determined by measuring the battery capacity loss over an idling condition while no external current is applied but all battery cells are connected via an electrolyte shunt path.

[0053] During charging, the SOC of a redox flow battery is given by equation (11). SOC = max(SOC pos ,SOC neg ) (11) Max is the argument SOC pos and SOC neg During discharge, the SOC of a redox flow battery is given by equation (12). SOC = min(SOC pos ,SOC neg ) (12) Min is the argument SOC pos and SOC neg These SOC values ​​are based on positive and negative electrolytes, respectively. The SOC values ​​determined from equations (9) and (10) based on positive and negative electrolytes are the smaller of the SOC from equation (8) (based on the measured OCV). OCV SOC / SOC can be compared. OCVIf the SOC ratio is less than the threshold SOC ratio, it may indicate electrolyte degradation due to, for example, side reactions or electrolyte crossover. As an example, the controller 88 may switch from charging the redox flow battery electric energy cell stack to discharging the redox flow battery electric energy cell stack when the SOC increases to above the upper threshold redox flow battery SOC during charging. Similarly, the controller 88 may switch from discharging the redox flow battery electric energy cell stack to charging the redox flow battery electric energy cell stack when the SOC decreases to below the lower threshold redox flow battery SOC during discharging. Alternatively, the external controller 250 may request that the redox flow battery electric energy storage system transition from discharging to charging or vice versa. The upper threshold redox flow battery SOC and the lower threshold redox flow battery SOC may be predetermined amounts and may correspond to when the electric energy cell stack is charged to capacity and fully discharged, respectively.

[0054] Charging and discharging the electric energy cell stack of a redox flow battery may include pulse charging and pulse discharging the electric energy cell stack of a redox flow battery. Referring now to FIG. 3A, an example 300 of an oscillating voltage signal provided to a redox flow battery during charging is shown. The oscillating voltage signal includes a pulse width modulated (PWM) signal that varies between a lower pulse limit 308 and an upper pulse limit 304, with a pulse amplitude 320 given by the difference between the upper pulse limit 304 and the lower pulse limit 308. Each pulse maintains the voltage at the upper pulse limit 304 for a pulse duration 322, followed by an idle time 324 during which the charging voltage drops to the lower pulse limit 308. In this way, the oscillating voltage signal during charging has a characteristic pulse period 326 defined by the sum of the pulse duration 322 and the idle time 324, as given by equation (13). Additionally, the duty cycle of the PWM signal is represented by the ratio of the pulse duration 322 to the pulse period 326, as given by equation (14), and the % idle time is given by equation (15). Pulse period = pulse duration + idle time (13) Duty cycle (%) = 100% * pulse duration / pulse period (14) %Idle Time = 100% * Idle Time / Pulse Period = 100 - Duty Cycle (15)

[0055] In one example, pulse charging a redox flow battery may include providing a PWM voltage signal that varies between a lower threshold charging voltage (pulse lower limit 308) and an upper threshold charging voltage (pulse upper limit 304), the lower threshold charging voltage being less positive than the upper threshold charging voltage. For a redox flow battery, the upper threshold charging voltage may correspond to a threshold charging power. As an example, the threshold charging power may include 50 kW or 60 kW. In some examples, the charging power and / or charging power density may be predetermined by an operator according to the power demands of a particular application. The threshold charging power may be achieved by providing a charging current to the redox flow battery at a threshold charging current density. In one example, the charging current density, expressed in units of current per electrode effective area, is 45 mA / cm. 2 Further, the lower threshold charging voltage may correspond to the OCV of the redox flow battery. Still further, during the idle time 324 between charging pulses, the controller 88 may set the current to 0 A so that no power is supplied to the redox flow battery. Furthermore, since the OCV of the redox flow battery varies with the SOC (as shown in FIG. 9), the pulse lower limit may vary during charging of the redox flow battery. In one example, the pulse amplitude 320 of the PWM voltage signal during charging may be maintained at a predetermined value during charging. Thus, both the pulse lower limit 308 and the pulse upper limit 304 may vary during charging of the redox flow battery to maintain the pulse charging at the threshold charging power, as shown in FIGS. 4 and 5. Thus, the charging current may be provided to achieve a desired charging current density and pulse amplitude 320 of the PWM voltage signal. In another example, as further described with reference to FIGS. 6A-6C, the duty cycle of the PWM voltage signal may vary during charging and / or discharging to improve the performance characteristics (e.g., VE, CE and / or EE) of the redox flow battery system.

[0056] 3B, an example oscillating voltage signal 350 provided to a redox flow battery during discharge is shown. The oscillating voltage signal includes a PWM signal that swings between a lower pulse limit 354 and an upper pulse limit 358, with a pulse amplitude 360 ​​given by the difference between the upper pulse limit 358 and the lower pulse limit 354. Each individual pulse maintains the voltage at the upper pulse limit 358 for a pulse duration 362, followed by an idle time 364 during which the discharge voltage drops to the lower pulse limit 354. In this manner, the oscillating voltage signal during discharge has a characteristic pulse period 366 defined by the sum of the pulse duration 362 and the idle time 364, as given by equation (13). Furthermore, the duty cycle of the PWM signal is represented by the ratio of the pulse duration 362 to the pulse period 366, as given by equation (14).

[0057] In one example, pulsing discharging the redox flow battery may include providing a PWM voltage signal that varies between a lower threshold discharge voltage (pulse lower limit 354) and an upper threshold discharge voltage (pulse upper limit 358), the lower threshold discharge voltage being less negative than the upper threshold discharge voltage. For a redox flow battery, the upper threshold discharge voltage may correspond to a threshold discharge power. As an example, the threshold discharge power may include -10 kW, with the negative sign indicating the power (e.g., current and voltage) provided from the redox flow battery. In some examples, the discharge power and / or discharge power density may be pre-determined by an operator according to the power demands of a particular application. The threshold discharge power may be achieved by providing a discharge current from the redox flow battery at a threshold discharge current density. In one example, the discharge current density is 45 mA / cm 2Further, the lower threshold discharge voltage may correspond to the OCV of the redox flow battery. Further, during the idle time 364 between the charge pulses, the controller 88 may set the current to 0 A so that no power is provided from the redox flow battery. Further, the pulse lower limit 354 may vary during the discharge of the redox flow battery because the OCV of the redox flow battery varies with the SOC. In one example, the pulse amplitude 360 ​​of the PWM voltage signal during the discharge may be maintained at a predetermined value. Thus, both the pulse lower limit 354 and the pulse upper limit 358 may vary during the discharge of the redox flow battery to maintain the pulse discharge at the threshold discharge power as shown in FIG. 4 and FIG. 5. Thus, the discharge current may be provided to achieve a desired discharge current density and pulse amplitude 360 ​​of the PWM voltage signal.

[0058] 4, a graph 400 is shown comparing the positive electrode potential for continuous charge and continuous discharge cycles of a redox flow battery with the positive electrode potential for pulse charge and pulse discharge cycles of a redox flow battery. In the example of FIG. 4, the redox flow battery can be an IFB, although other types of redox flow batteries can be utilized. Furthermore, other than differences in the nature of the charge / discharge voltage signals provided to / from the redox flow battery, the operating parameters and characteristics of the redox flow battery (e.g., electrode material structure and configuration, flow configuration, electrolyte flow rate and composition, electrolyte volume, temperature, membrane type, charge / discharge current density, electrode plating preformation, electrolyte rebalancing rate, etc.) remain the same.

[0059] During charging (continuous and pulsed), the redox flow battery system is charged from the SOC of the lower threshold redox flow battery to the SOC of the upper threshold redox flow battery, while during discharging (continuous and pulsed), the redox flow battery system is discharged from the SOC of the upper threshold redox flow battery to the SOC of the lower threshold redox flow battery. In one example, the SOC of the lower threshold redox flow battery comprises 20% of the maximum SOC of the redox flow battery, and the SOC of the upper threshold redox flow battery comprises 80% of the maximum SOC of the redox flow battery. In another example, the SOC of the lower threshold redox flow battery comprises 35% of the maximum SOC of the redox flow battery, and the SOC of the upper threshold redox flow battery comprises 65% of the maximum SOC of the redox flow battery. The increase in performance (e.g., VE and / or EE) of a redox flow battery system upon pulse charging (and / or pulse discharging) compared to continuous charging (and / or continuous discharging) may depend on the lower threshold SOC and / or the upper threshold SOC.

[0060] Furthermore, in one example, during charging, if the SOC increases to above an upper threshold SOC, the redox flow battery system can be switched from pulse charging to continuous charging to increase plating efficiency and shorten the charging time (e.g., faster charging). Similarly, during discharging, if the SOC decreases to below a lower threshold SOC, the redox flow battery system can be switched from pulse discharging to continuous discharging to shorten the discharging time (e.g., faster discharging).

[0061] 4, in a first example, the IFB is continuously charged from the SOC of the lower threshold redox flow battery to the SOC of the upper threshold redox flow battery during a continuous charging period 410, and then continuously discharged from the SOC of the upper threshold redox flow battery to the SOC of the lower threshold redox flow battery during a continuous discharging period 414. The IFB is then pulse charged from the SOC of the lower threshold redox flow battery during a pulse charging period 420, and then pulse discharged from the SOC of the upper threshold redox flow battery to the SOC of the lower threshold redox flow battery during a pulse discharging period 424. In a second example, the IFB is continuously charged from the SOC of the lower threshold redox flow battery to the SOC of the upper threshold redox flow battery during a continuous charging period 430, and then continuously discharged from the SOC of the upper threshold redox flow battery to the SOC of the lower threshold redox flow battery during a continuous discharging period 434. The IFB is then pulse charged from the SOC of the lower threshold redox flow battery during the pulse charge period 440, and then pulse discharged from the SOC of the upper threshold redox flow battery to the SOC of the lower threshold redox flow battery during the pulse discharge period 444. By continuously operating the IFB to perform continuous charge / discharge cycles followed by pulse charge / discharge cycles, cycle efficiencies can be continuously compared, thereby mitigating the effects of electrolyte crossover and other forms of system degradation that may occur over the life of the redox flow battery system. In FIG. 4, the peaks and dips in the positive electrode potential immediately prior to the continuous charge periods 410 and 430 are artifacts of the electronic switching device under test and are not indicative of the performance of the continuous charge or continuous discharge. Additionally, the abnormal spikes in the positive electrode potential during the pulse charge period 420 and at the end of the pulse charge period 440 are also artifacts of the electronic switching device under test and are not indicative of the performance of the pulse charge or pulse discharge.

[0062] During the continuous charge periods (410, 430) and pulse charge periods (420, 440), the redox flow battery is charged and the positive electrode potential increases as the SOC increases. Conversely, during the continuous discharge periods (414, 434) and pulse discharge periods (424, 444), the redox flow battery is discharged and the positive electrode potential decreases as the SOC decreases. During continuous charge, the charging voltage signal (e.g., positive electrode potential) provided to the IFB is adjusted to a desired current density (e.g., 45 mA / cm 2 During pulse charging, the pulse lower limit is set to the OCV, and the pulse amplitude and pulse upper limit are selected to maintain the desired current density (e.g., 45 mA / cm) for a given duty cycle. 2 ) and charging power (e.g., 50 or 60 kW). During continuous discharge, the discharge voltage signal (e.g., positive electrode potential) supplied to the IFB is selected to maintain a desired current density (e.g., 45 mA / cm 2 During pulse discharge, the pulse lower limit is set to the OCV, and the pulse amplitude and pulse upper limit are selected to maintain the desired current density (e.g., 45 mA / cm) for a given duty cycle. 2 ) and discharge power (e.g., -10 kW). In one example, the discharge current is maintained at -0.5 A during the discharge pulse. Compared to the continuous charge cycle, the pulse charge / discharge cycle increased VE by 4-5%, but the change in CE was negligible. This result is based on electronic control, and the CE is assumed to be close to 100% CE. Therefore, the increase in VE is also reflected in the change in EE between the continuous charge / discharge cycle and the pulse charge / discharge cycle. In other words, the EE increased by 4-5% for the pulse charge / discharge cycle compared to the continuous charge cycle. As the charge power and discharge power increase, the performance improvement in terms of VE and EE of the pulse charge / discharge compared to the continuous charge / discharge may increase.

[0063] Referring now to FIG. 5, a graph 500 of negative electrode potential versus time for the IFB system utilized in FIG. 4 and described above is shown. Graph 500 compares the negative electrode performance between pulsed and non-pulsed tests by overlaying plots corresponding to pulsed charge and discharge cycles 510 with plots corresponding to continuous charge and discharge cycles 520. Graph 500 shows that the increase in VE results primarily from a decrease in the negative overpotential. In battery systems, overpotential refers to the potential difference (or voltage difference) between a theoretically or thermodynamically determined voltage and the actual voltage under operating conditions. In redox flow batteries, overpotential indicates that more energy is consumed to drive the redox reaction than is thermodynamically determined. In other words, as applied to graph 500, during continuous charging, the magnitude of the negative electrode potential is greater (e.g., more negative) than during pulse charging, indicating a lower VE because a higher voltage (more energy) is provided to the redox flow battery during continuous charging. Similarly, during pulse discharge, the magnitude of the pulsed negative electrode potential is greater (more negative) than during continuous discharge, indicating that a higher voltage (more energy) is delivered by the redox flow battery during pulse discharge than during continuous discharge, resulting in a higher VE during pulse discharge. Note that any abnormal spikes in the negative electrode potential during pulse charge and at the end of the pulse charge period are artifacts of the electronic switching device being tested and are not indicative of the pulse charge or pulse discharge performance.

[0064] In contrast to the higher VE for pulsed charging compared to continuous charging, the plating efficiency test for pulsed charging is slightly lower than for continuous charging. The measured plating efficiency is 91%, slightly lower than 93% for the same system conditions without pulsing. The decrease in plating efficiency during pulsed charging is most likely caused by the idle time between pulses. The longer the idle time (e.g., the lower the duty cycle), the longer the charge and discharge cycle. Thus, the time it takes to plate a given amount of material onto the plating electrode increases with the idle time. The longer charge and discharge cycle for pulsed charging compared to continuous charging is shown in Figure 5. The continuous charging of the redox flow battery is completed after about 13,000 seconds, while the pulse charging of the redox flow battery is completed after 15,000 seconds. Furthermore, the continuous discharging of the redox flow battery is completed after about 10,000 seconds, while the pulse charging of the redox flow battery is completed after about 15,000 seconds.

[0065] In one example, the controller 88 may transition from pulse charging to continuous charging (and vice versa) and from pulse discharging to continuous discharging (and vice versa) depending on the operating conditions of the redox flow battery system and the external power demand. As an example, the external power demand may be transmitted from the external controller 250 to the redox flow battery system 10. As previously mentioned, pulse charging and pulse discharging may improve the efficiency of the redox flow battery system, particularly the voltaic efficiency and the energy efficiency. However, the pulse charging and discharging cycles may be longer due to idle time, and the plating efficiency may be slightly reduced compared to continuous charging and discharging. Under certain operating conditions and / or external power demand conditions, it may also be desirable to shorten the charge and discharge cycle times. Thus, as shown in Table 1, the controller 88 may determine whether the SOC of the redox flow battery is greater than the continuous charging threshold SOC of the redox flow battery (SOC cont,充電,TH ) until it exceeds the SOC of the lower threshold redox flow battery (SOC 下側,TH ) and SOC上側,TH Therefore, in response to the SOC of the redox flow battery decreasing to below the lower threshold redox flow battery SOC, the controller 88 may start pulse charging the redox flow battery. Then, in response to the SOC of the redox flow battery increasing to above the continuous charge threshold redox flow battery SOC, the controller 88 may switch from pulse charging to continuous charging of the redox flow battery. Pulse charging the redox flow battery from the lower threshold redox flow battery SOC to the continuous charge threshold SOC and continuously charging the redox flow battery until it exceeds the continuous charge threshold SOC allows the redox flow battery system to maintain higher efficiencies (VE, CE, EE) while increasing plating efficiency and reducing charging cycle time. [Table 1] Table 1. Threshold SOC for pulse and continuous charge / discharge cycles

[0066] As another example, the controller 88 may be configured to detect whether the SOC of the redox flow battery is greater than the continuous discharge threshold SOC of the redox flow battery (SOC cont,放電,TH ) to below the SOC of the upper threshold redox flow battery (SOC 上側,TH ) and SOC 下側,THThus, in response to the SOC of the redox flow battery increasing to above the upper threshold redox flow battery SOC, the controller 88 may initiate a pulse discharge of the redox flow battery. Thereafter, in response to the SOC of the redox flow battery decreasing to below the continuous discharge threshold redox flow battery SOC, the controller 88 may switch from pulse discharge to continuous discharge of the redox flow battery. Pulse discharging the redox flow battery from the upper threshold redox flow battery SOC to the continuous discharge threshold SOC and continuously discharging the redox flow battery to below the continuous discharge threshold SOC allows the redox flow battery system to maintain higher efficiencies (VE, CE, EE) while increasing plating efficiency and decreasing discharge cycle time.

[0067] Furthermore, SOC cont,放電,TH and SOC cont,充電,TH The value of SOC can be adjusted depending on the desired charge / discharge cycle time, plating efficiency and / or system efficiency (VE, EE, CE). cont,充電,TH The value of SOC 上側,TH When the SOC is close to , the charging of the redox flow battery is essentially all pulse charging. cont,充電,TH The value of SOC 下側,TH When the SOC is close to 100%, the charging of the redox flow battery is essentially continuous charging. cont,充電,TH SOC 下側,TH and SOC 上側,TH When the SOC is at the midpoint between 0 and 1, charging the redox flow battery will bring the redox flow battery to 0 SOC. 下側,TH Pulse charge from the midpoint SOC to the midpoint SOC, then pulse charge the redox flow battery from the midpoint SOC to SOC 上側,TH In other words, the charging of the redox flow battery includes half pulse charging and half semi-continuous charging on an SOC basis. cont,充電,TH By increasing the SOC 下側,TH From SOC 上側,TH When charging to SOC, the pulse charge amount is increased compared to continuous charging. cont,充電,TH By lowering the SOC of the redox flow battery, 下側,THFrom SOC 上側,TH When charging to 100%, the pulse charging amount is reduced compared to continuous charging.

[0068] SOC cont,放電,TH The value of SOC 下側,TH When the SOC is close to 0.001, the discharge of the redox flow battery can be substantially all pulse discharge. cont,放電,TH The value of SOC 上側,TH When the SOC is close to 100%, the discharge of the redox flow battery can be substantially all continuous charging. cont,放電,TH SOC 下側,TH and SOC 上側,TH When the SOC is at the midpoint between 0.01 and 0.1, the discharge of the redox flow battery is half pulse discharge and half continuous discharge on an SOC basis. cont,放電,TH By lowering the SOC of the redox flow battery, 上側,TH From SOC 下側,TH When discharging to SOC, increase the pulse discharge amount compared to continuous discharge and cont,放電,TH By increasing the SOC 上側,TH From SOC 下側,TH When discharging to 100%, the pulse discharge amount is reduced compared to continuous discharge.

[0069] In one example, the SOC is increased to reduce charge cycle time and increase plating efficiency despite the reduced system efficiency. cont,充電,TH Thus, in response to the charge cycle increasing beyond a threshold charge cycle duration and / or the plating efficiency decreasing below a threshold charge plating efficiency, the SOC cont,充電,TH On the other hand, the SOC may be increased to increase the VE, EE and / or CE of the system, despite the increased charging cycle time and decreased plating efficiency. cont,充電,TH Thus, in response to the system efficiency (VE and / or EE) decreasing below a threshold charging efficiency, the SOC cont,充電,TH In another example, the SOC may be increased to shorten the discharge cycle time and increase plating efficiency despite reduced system efficiency. cont,放電,THThus, in response to the discharge cycle time increasing beyond the threshold discharge period and / or the plating efficiency decreasing below the threshold charge plating efficiency, the SOC cont,放電,TH On the other hand, it is possible to increase the SOC to increase the VE, EE and / or CE of the system, despite the increased charge cycle time and decreased plating efficiency. cont,放電,TH Thus, in response to the system efficiency (VE and / or EE) decreasing below the threshold discharge efficiency, the SOC cont,放電,TH can be reduced.

[0070] In a further example, the controller 88 may coordinate pulse charging / discharging and continuous charging / discharging across multiple redox flow batteries in an electric energy storage cell stack and / or across multiple electric energy storage cell stacks (e.g., one or more electric energy storage cell stacks 201, 202, 203, 204). Thus, during operation of the redox flow battery system 10, one or more redox flow batteries may be pulse charged while one or more other redox flow batteries may be continuously charged. Similarly, during operation of the redox flow battery system 10, one or more redox flow batteries may be pulse discharged while one or more other redox flow batteries may be continuously discharged. Furthermore, during operation of the redox flow battery system 10, the controller 88 may pulse charge and / or pulse discharge redox flow batteries in one or more electric energy storage cell stacks while continuously charging and / or continuously discharging redox flow batteries in one or more other electric energy storage cell stacks. Furthermore, each redox flow battery in the redox flow battery system 10 is capable of both pulse charging and continuous charging at any time, depending on the operating conditions and external power demands.

[0071] In another example, the controller 88 may perform only pulse charging / discharging for the redox flow batteries of one or more electric energy storage cell stacks in the redox flow battery system, while performing only continuous charging / discharging for the redox flow batteries of one or more other electric energy storage cell stacks in the redox flow battery system. In this way, one or more redox flow batteries may be dedicated to pulse charging / discharging, while other redox flow batteries may be dedicated to continuous charging / discharging. By pulse charging / discharging one or more redox flow batteries in the redox flow battery system while continuously charging / discharging one or more other redox flow batteries, the redox flow battery system may advantageously maintain a faster charge / discharge cycle time for supplying power on demand in the continuously charged / discharged redox flow batteries while maintaining a high system efficiency (VE, CE, EE) in the pulse charged / discharged redox flow batteries. In one example, in response to the redox flow battery efficiency (VE, CE and / or EE) decreasing below a threshold efficiency, the controller 88 may switch the redox flow battery to only continuous charge / discharge until the efficiency of the redox flow battery increases above the threshold efficiency. In another example, the controller 88 may adjust the SOC ratio (SOC / SOC OCV ) to fall below the threshold SOC ratio, the redox flow battery may be switched from pulse charge / discharge to only continuous charge / discharge. Furthermore, in response to switching one or more redox flow batteries from pulse charge / discharge to continuous charge / discharge, the controller 88 may switch one or more redox flow batteries from continuous charge / discharge operation to pulse charge / discharge operation. In particular, the controller 88 may select only one or more redox flow batteries that provide a battery efficiency (VE, CE, and / or EE) greater than the threshold efficiency for switching from continuous charge / discharge operation to pulse charge / discharge operation. In this manner, the efficiency and faster charge / discharge cycle time of the redox flow battery system may be maintained.

[0072] 6A-6C, graphs 600, 610, and 620 are shown depicting VE, CE, and EE data versus duty cycle, respectively, collected from a series of pulse and continuous charge / discharge tests performed using an IFB system. As shown in graph 600, VE is higher for pulse charge / discharge operation compared to continuous charge / discharge operation (e.g., duty cycle=0). In contrast, as shown in graph 610, CE is higher during pulse charge / discharge operation corresponding to a duty cycle of 10-15%. CE is lower for continuous charge / discharge (duty cycle=0) and pulse charge / discharge operation corresponding to a duty cycle greater than 25%. As a result, as shown in graph 620, EE is also highest for pulse charge / discharge operation corresponding to a duty cycle of 10-15%, and decreases at lower duty cycles (e.g., continuous charge / discharge, duty cycle=0) and higher duty cycles (greater than 25%).

[0073] Additional IFB performance data for pulse charge / discharge versus baseline (continuous charge / discharge) operation are summarized in Tables 2 and 3. Two sets of experiments were performed, the first set of charge and discharge at 60 kW (Table 2) and the second set of charge and discharge at 50 kW (Table 3). The IFB was cycled between 35% SOC and 80% SOC. In other words, charging of the redox flow battery system was initiated in response to the SOC decreasing below the lower threshold redox flow battery's 35% SOC, and discharging of the redox flow battery system was initiated in response to the SOC increasing above the upper threshold redox flow battery's 80% SOC. For cycling at 60 kW, pulse charging was performed with a charging power of 60 kW and a pulse duration of 1 minute. During pulse charging, a pulse voltage signal oscillating between a pulse upper voltage limit (e.g., equivalent to 60 kW) and a pulse lower voltage limit (OCV) was supplied to the redox flow battery system. During pulse charging, the idle time was 9 minutes and the charge duty cycle was 10%. Pulse discharge was performed with a discharge power of -10 kW and a pulse duration of 1 minute. During pulse discharge, a pulse voltage signal oscillating between a pulse upper voltage limit (e.g., equivalent to -10 kW) and a pulse lower voltage limit (OCV) was provided by the redox flow battery system. During pulse discharge, the idle time was 9 minutes and the discharge duty cycle was 10%. Under these pulse charge / discharge conditions, VE increased by 4% and EE increased by 3% compared to the baseline (continuous, 60 kW) charge and discharge conditions, as shown in Table 2, while CE was nearly maintained (-1% change). Due to the increase in VE, the capacity of the redox flow battery at 60 kW increased by 18% (e.g., 118% of the baseline capacity) with pulse charge / discharge compared to the baseline operation (continuous charge / discharge). [Table 2] Table 2. Comparison of 60kW pulse charge / discharge and baseline performance *Percentage of baseline capacity [Table 3] Table 3. Comparison of 50kW pulse charge / discharge and baseline performance *Percentage of baseline capacity

[0074] For the cycle at 50 kW, pulse charging was performed with a charging power of 50 kW and a pulse duration of 1 minute or 10 seconds. During pulse charging, a pulse voltage signal oscillating between a pulse upper limit voltage (e.g., equivalent to 60 kW) and a pulse lower limit voltage (OCV) was provided to the redox flow battery system. During pulse charging with a pulse duration of 1 minute, if the idle time was 9 minutes, the charging duty cycle was 10%. However, for pulse charging with a pulse duration of 10 seconds, the idle time between pulses was 1 second, and the charging duty cycle was 1.8%. Pulse discharging was performed with a discharge power of -10 kW and a pulse duration of 9 minutes. During pulse discharging, a pulse voltage signal oscillating between a pulse upper limit voltage (e.g., equivalent to -10 kW) and a pulse lower limit voltage (OCV) was provided from the redox flow battery system. During pulse discharging, the idle time was 1 minute, and the discharging duty cycle was 10%. Pulse charge / discharge with a pulse duration of 10 seconds increased VE by 3% and EE by 3%, while CE was nearly maintained (1% increase) compared to baseline (continuous, 50 kW) charge and discharge conditions, as shown in Table 3. Similarly, pulse charge / discharge with a pulse duration of 1 minute increased VE by 3%, EE by 6%, and CE by 5% compared to baseline (continuous, 50 kW) charge and discharge conditions. Furthermore, due to the increase in CE and VE, the overall capacity of the redox flow battery at 50 kW increased by 27% (e.g., 127% of baseline capacity) at 1 minute of idle and 57% (e.g., 157% of baseline capacity) at 10 seconds of idle compared to baseline operation, as shown in Table 3.

[0075] 8-10, flow charts are shown for methods 900, 1000 and 1100 of operating a redox flow battery system, such as the redox flow battery cell system 10 of FIG. 1, including pulse charging and pulse discharging one or more redox flow batteries. The one or more redox flow batteries may be in a single cell stack or may be arranged across multiple cell stacks. Instructions for carrying out the methods 900, 1000 and 1100 may be executed by a controller, such as the controller 88 of FIGS. 1 and 2, based on executable instructions stored in a non-transitory memory of the controller 88 in combination with signals received from sensors of the redox flow battery cell system 10, such as the sensors described above with reference to FIGS. 1 and 2. The controller 88 may coordinate the operation of the redox flow battery system 10, including the power module 120 and the electrical energy storage system 200, and the electrolyte subsystem 130, using actuators of the redox flow battery system 10 according to methods described below.

[0076] 8 includes determining the operating conditions of the redox flow battery system, including electrolyte pH, SOC (e.g., SOC of the redox flow battery), electrolyte concentration, plating efficiency, VE, CE, EE, etc. Then, at 920, the method 900 determines whether the SOC of the redox flow battery is below a lower threshold redox flow battery SOC, i.e., SOC 下側,TH The SOC includes determining whether the SOC is less than the SOC 下側,THIn response to being not less than, the method 900 continues at 924 with determining whether an external request to charge the battery has been received. Receiving an external request to charge the redox flow battery may include receiving a signal from an external device, such as the external controller 250 of FIG. 2 communicatively coupled to the controller 88 of the redox flow battery system 10. In one example, the external controller 250 may monitor the power provided to the plurality of external electric energy consumption devices 278 and / or the external electric energy source 279, and may transmit a signal to charge one or more redox flow batteries in response to predicting an increase in power demand from the external electric energy consumption devices 278 or in response to the stored energy level of the external electric energy source 279 decreasing below a threshold energy level. In another example, the external request to charge the redox flow battery 10 may include receiving a user input to charge the redox flow battery 10 via the human / machine interface 290 of FIG. 2.

[0077] SOC at 920 <SOC 下側,TH In response to, or in response to receiving an external request to charge the redox flow battery at 924, the method 900 continues at 928, including initiating charging of the redox flow battery.

[0078] 9, a method 1000 for charging one or more redox flow batteries is shown. Charging the redox flow battery may include one or more of pulse charging and continuous charging. In particular, the method 1000 may operate the redox flow battery in a pulse charging mode or a continuous charging mode depending on the battery operating conditions.

[0079] Method 1000 starts with 1020 and SOC <SOC 下側,TH SOC <SOC 下側,THIn response to, the method 1000 continues at 1024 and includes pulse charging the redox flow battery. Pulse charging the redox flow battery may include stopping continuous charging of the redox flow battery. Returning to 1020, the method 1000 determines whether the SOC is greater than or equal to SOC 下側,TH If not, method 1000 proceeds to 1040 to <SOC cont,充電,TH SOC <SOC cont,充電,TH In response to, the method 1000 continues at 1044 and includes pulse charging the redox flow battery. Pulse charging the redox flow battery may include stopping continuous charging of the redox flow battery. Returning to 1040, the method 1000 determines whether the SOC is greater than or equal to SOC cont,充電,TH If not, method 1000 proceeds to 1060 to <SOC 上側,TH SOC <SOC 上側,TH In response to the command, the method 1000 continues at 1064 and includes continuously charging the redox flow battery. Continuously charging the redox flow battery may include ceasing the pulse charging of the redox flow battery. In this manner, according to the method 1000, the controller 88 may operate the redox flow battery in a pulse charging mode or a continuous charging mode based on the SOC of the redox flow battery. cont,充電,TH <SOC<SOC 上側,TH In this case, the redox flow battery is continuously charged and the SOC <SOC cont,充電,TH In this case, or SOC <SOC 下側,TH In this case, the redox flow battery is pulse charged.

[0080] In this way, both the efficiency (VE, CE and EE), charge cycle time and plating efficiency of the redox flow battery can be maintained. Furthermore, the controller 88 adjusts the SOC according to the desired efficiency, charge cycle time and plating efficiency. cont,充電,TH The controller 88 may adjust the value of SOC cont,充電,TH, to increase the propensity for continuous charging versus pulse charging, thereby shortening the charge cycle time and increasing plating efficiency despite a decrease in VE, CE, and / or EE. As an example, in response to the plating efficiency of a redox flow battery decreasing below a threshold plating efficiency, SOC cont,充電,TH Conversely, the controller 88 may reduce the SOC cont,充電,TH to reduce the tendency for continuous charging versus pulse charging, thereby increasing efficiency (VE, CE, and EE) despite increased charging cycle times and decreased plating efficiency. As an example, in response to the voltaic efficiency of a redox flow battery decreasing below a threshold voltaic efficiency, SOC cont,充電,TH After 1024, 1044 and 1064, and when SOC is SOC 上側,TH If not, then method returns to method 1000 after 1060, which returns to method 900 after 928. After 928, method 900 ends.

[0081] If there is no external request to charge the battery, the method returns to 924 and continues to 930 where the SOC of the redox flow battery is equal to or exceeds the upper threshold SOC of the redox flow battery, i.e., SOC 上側,TH The SOC includes determining whether the SOC is greater than SOC 上側,THIn response to not being greater, the method 900 continues at 934 with determining whether an external request to discharge the battery has been received. Receiving an external request to discharge the redox flow battery may include receiving a signal from an external device, such as an external controller 250 communicatively coupled to the controller 88 of the redox flow battery system 10. In one example, the external controller 250 may monitor the power provided to the plurality of external electric energy consumers 278 and / or the external electric energy source 279, and may transmit a signal to discharge one or more redox flow batteries in response to an increase in the power demand from the external electric energy consumers 278 or in response to the stored energy level of the external electric energy source 279 decreasing below a threshold energy level. In another example, the external request to discharge the redox flow battery 10 may include receiving a user input via the human / machine interface 290 to discharge the redox flow battery 10.

[0082] SOC>SOC at 930 上側,TH In response to, or in response to receiving an external request to discharge the redox flow battery at 934, the method 900 continues at 938 with initiating the discharge of the redox flow battery. Referring now to FIG. 10, a method 1100 for discharging one or more redox flow batteries is shown. The discharging of the redox flow battery may include one or more of a pulsed discharge and a continuous discharge. In particular, the method 1100 may operate the redox flow battery in a pulsed discharge mode or a continuous discharge mode depending on the battery operating conditions.

[0083] Method 1100 starts with 1120, SOC>SOC 上側,TH SOC > SOC 上側,TH In response to, the method 1100 continues at 1124 with pulse discharging the redox flow battery. Pulse discharging the redox flow battery may include stopping continuous discharging of the redox flow battery. Returning to 1120, the method 1100 determines whether the SOC is equal to or lower than the SOC. 上側,TH If not, the method 1100 proceeds to 1140 and cont,放電,THSOC > SOC cont,放電,TH In response to, the method 1100 continues at 1144 and includes pulse-discharging the redox flow battery. Pulse-discharging the redox flow battery may include stopping continuous discharging of the redox flow battery. Returning to 1140, the method 1100 determines whether the SOC is greater than or equal to SOC cont,放電,TH If not, the method 1100 proceeds to 1160 and 下側,TH SOC > SOC 下側,TH In response, the method 1100 continues at 1164, including continuously discharging the redox flow battery. Continuously discharging the redox flow battery may include ceasing the pulsed discharge of the redox flow battery.

[0084] In this manner, according to the method 1100, the controller 88 may operate the redox flow battery in a pulsed discharge mode or a discontinuous charge mode based on the SOC of the redox flow battery. cont,放電,TH >SOC>SOC 下側,TH When the redox flow battery is continuously charged, SOC>SOC cont,放電,TH If SOC > SOC 上側,TH In the case of SOC, the redox flow battery is pulse-charged. cont,放電,TH may be adjusted in response to a performance characteristic of the redox flow battery, such as voltaic efficiency, coulombic efficiency, energy efficiency, plating efficiency, etc. In one example, SOC may be adjusted in response to the plating efficiency of the redox flow battery decreasing below a threshold plating efficiency. cont,放電,TH As a further example, in response to the voltaic efficiency decreasing below a threshold voltaic efficiency, SOC cont,放電,TH can be reduced.

[0085] The technical effect of the methods 900, 1000 and 1100 may be achieved to improve the voltaic and energy efficiency of a redox flow battery system while maintaining the coulombic efficiency of the redox flow battery system. In this manner, the efficiency of the redox flow battery may be increased without the need for additional hardware or modifications. Furthermore, the improved voltaic and energy efficiency is achieved while maintaining the operating temperature of the redox flow system, thereby reducing material costs and maintaining the reliability and durability of the system piping. Furthermore, the improved voltaic and energy efficiency is achieved while maintaining the plating gap at the plating electrodes, making it easier to modify existing redox flow battery systems and achieve the improved voltaic and energy efficiency without increasing manufacturing costs and complexity.

[0086] In this way, both the efficiency (VE, CE, EE) of the redox flow battery and the discharge cycle time and plating efficiency can be maintained. Furthermore, the controller 88 adjusts the SOC according to the desired efficiency, charge cycle time, and plating efficiency. cont,放電,TH For example, the controller 88 may adjust the value of SOC cont,放電,TH , to increase the propensity for continuous discharge versus pulsed discharge, thereby shortening the charge cycle time and increasing plating efficiency despite reduced VE, CE and / or EE. Conversely, the controller 88 may increase the SOC cont、放電、TH may be reduced to reduce the tendency for continuous discharge versus pulsed discharge, thereby increasing efficiency (VE, CE, and EE) despite increased charge cycle times and reduced plating efficiency.

[0087] After 1124, 1144 and 1164, and SOC is SOC 下側,THIf not, then method 1100 returns to method 1100 after 1160, which returns to method 900 after 938. After 928, method 900 ends. If there is no external request to discharge the battery, then method 900 returns to method 900 at 934, which continues to 980, including maintaining the current operating mode of the redox flow battery (e.g., pulse charge, pulse discharge, continuous charge, continuous discharge, etc.). After 980, method 900 ends.

[0088] The present disclosure provides support for a method of operating a redox flow battery, including charging the redox flow battery, where charging the redox flow battery includes providing a pulsed charging signal to the redox flow battery in response to a state of charge (SOC) of the redox flow battery decreasing below a lower threshold redox flow battery SOC, where providing the pulsed charging signal includes providing a pulse width modulated (PWM) charging voltage signal to the redox flow battery, where the PWM charging voltage signal varies between an upper threshold charging voltage and an open circuit voltage (OCV). In a first example of the method, the method further includes discharging the redox flow battery, where discharging the redox flow battery includes providing a pulsed discharge signal from the redox flow battery, where providing the pulsed discharge signal includes providing a PWM discharge voltage signal from the redox flow battery, where the PWM discharge voltage signal varies between the upper threshold discharge voltage and the OCV. In a second example of the method, optionally including the first example, the upper threshold charging voltage threshold varies according to the SOC of the redox flow battery, and charging the redox flow battery further comprises adjusting the charging current to maintain the pulsed charging signal at the threshold charging power while the PWM charging voltage signal is at the upper threshold charging voltage. In a third example of the method, optionally including one or both of the first and second examples, the upper threshold discharging voltage varies according to the SOC of the redox flow battery, and discharging the redox flow battery further comprises adjusting the discharging current to maintain the pulsed discharging signal at the threshold discharging power while the PWM discharging voltage signal is at the upper threshold discharging voltage. In a fourth example of the method, optionally including one or more or each of the first to third examples, the PWM charging voltage signal and the PWM discharging each include a duty cycle between the lower threshold charging duty cycle and the upper threshold charging duty cycle.

[0089] The present disclosure also provides support for a redox flow battery system including a power module including a redox flow battery, an electrolyte subsystem fluidly coupled to the redox flow battery, and a controller including executable instructions stored in a non-transitory memory for charging the redox flow battery, and also provides support for a redox flow battery system, where charging the redox flow battery includes pulse charging the redox flow battery in response to a state of charge (SOC) of the redox flow battery decreasing below a lower threshold redox flow battery SOC, and pulse charging includes providing a pulse width modulated (PWM) charging voltage signal to the redox flow battery, the PWM charging voltage signal varying between an upper threshold charging voltage and an open circuit voltage (OCV). In a first example of the system, the executable instructions further include discharging the redox flow battery, where discharging the redox flow battery includes pulse discharging the redox flow battery in response to the SOC of the redox flow battery being greater than the upper threshold redox flow battery SOC while the electrical load is coupled to the redox flow battery, where the pulse discharging includes providing a PWM discharge voltage signal from the redox flow battery, where the PWM discharge voltage signal varies between the upper threshold discharge voltage and the OCV. In a second example of the system that optionally includes the first example, the instructions for charging the redox flow battery further include providing a continuous charge voltage signal to the redox flow battery in response to the SOC of the redox flow battery increasing until the SOC of the redox flow battery exceeds the continuous charge threshold redox flow battery SOC, where the continuous charge threshold redox flow battery SOC is greater than the lower threshold redox flow battery SOC.In a third example of a system optionally including one or both of the first and second examples, the power module includes a plurality of redox flow battery cell stacks, each redox flow battery cell stack includes one or more redox flow batteries, and the executable instructions further include providing a PWM charging voltage signal or a continuous charging voltage signal to charge a first cell stack of the plurality of redox flow battery cell stacks and simultaneously providing a PWM charging voltage signal or a continuous charging voltage signal to charge a second cell stack of the plurality of redox flow battery cell stacks. In a fourth example of a system optionally including one or more of the first to third examples, the instructions for discharging the redox flow battery further include providing a continuous discharge voltage signal from the redox flow battery in response to the SOC of the redox flow battery decreasing below a continuous discharge threshold redox flow battery SOC, and the continuous discharge threshold redox flow battery SOC is less than the upper threshold redox flow battery SOC. In a fifth example of a system optionally including one or more of the first to fourth examples, the executable instructions further include: increasing the SOC of the continuous discharge threshold redox flow battery in response to the plating efficiency of the redox flow battery decreasing below a threshold plating efficiency; and decreasing the SOC of the continuous discharge threshold redox flow battery in response to the voltaic efficiency of the redox flow battery decreasing below a threshold voltaic efficiency. In a sixth example of a system optionally including one or more of the first to fifth examples, the executable instructions further include: decreasing the SOC of the continuous charge threshold redox flow battery in response to the plating efficiency of the redox flow battery decreasing below a threshold plating efficiency; and increasing the SOC of the continuous charge threshold redox flow battery in response to the voltaic efficiency of the redox flow battery decreasing below a threshold voltaic efficiency.

[0090] The present disclosure also provides support for a method of operating a redox flow battery, including pulse charging the redox flow battery in response to the SOC of the redox flow battery decreasing below a lower threshold redox flow battery SOC, and pulse discharging the redox flow battery in response to the SOC of the redox flow battery increasing above an upper threshold redox flow battery SOC. In a first example of the method, pulse charging the redox flow battery includes providing a pulse charging power signal to charge the redox flow battery, and oscillating the pulse charging power signal between a lower threshold charging power and an upper threshold charging power. In a second example of the method, which optionally includes the first example, the lower threshold charging power is equal to the open circuit voltage of the redox flow battery. In a third example of the method, which optionally includes one or both of the first and second examples, the upper threshold charging power is 50 kW and the upper threshold discharging power is -10 kW. In a fourth example of the method, optionally including one or more of the first to third examples, pulse charging the redox flow battery includes pulse charging with a pulse width modulated (PWM) power signal having a duty cycle between a lower threshold duty cycle and an upper threshold duty cycle. In a fifth example of the method, optionally including one or more of the first to fourth examples, pulse discharging the redox flow battery includes providing a pulse discharge power signal to discharge the redox flow battery, and oscillating the pulse discharge power signal between a lower threshold discharge power and an upper threshold discharge power. In a sixth example of the method, optionally including one or more of the first to fifth examples, pulse charging the redox flow battery includes pulse charging the redox flow battery above a threshold charge current density. In a seventh example of the method, optionally including one or more of the first to sixth examples, pulse charging the redox flow battery includes pulse discharging the redox flow battery below a threshold discharge current density.

[0091] The following claims particularly point out certain combinations and subcombinations that are deemed novel and unobvious. These claims may refer to "an" element or "first" element or equivalents. Such claims should be understood to include the incorporation of one or more such elements, and do not require or exclude two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed through amendment of the claims or through the presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, are also deemed to be included within the subject matter of this disclosure.

Claims

1. 1. A method of operating a redox flow battery, comprising:

1. A method of operating a redox flow battery, comprising: in response to a state of charge (SOC) of a redox flow battery decreasing below a lower threshold redox flow battery SOC, providing a pulsed charging signal to the redox flow battery, charging the redox flow battery, wherein providing the pulsed charging signal comprises providing a pulse width modulated (PWM) charging voltage signal to the redox flow battery, the PWM charging voltage signal varying between an upper threshold charging voltage and an open circuit voltage (OCV).

2. 2. The method of operating a redox flow battery of claim 1, further comprising discharging the redox flow battery including supplying a pulsed discharge signal from the redox flow battery, wherein supplying the pulsed discharge signal includes supplying a PWM discharge voltage signal from the redox flow battery, the PWM discharge voltage signal varying between an upper threshold discharge voltage and the OCV.

3. 3. The method of operating a redox flow battery according to claim 2, wherein the upper threshold charging voltage varies according to an SOC of the redox flow battery, and charging the redox flow battery further comprises adjusting a charging current to maintain the pulsed charging signal at a threshold charging power while the PWM charging voltage signal is at the upper threshold charging voltage.

4. 4. The method of operating a redox flow battery according to claim 3, wherein the upper threshold discharge voltage varies according to an SOC of the redox flow battery, and discharging the redox flow battery further comprises adjusting a discharge current to maintain the pulsed discharge signal at a threshold discharge power while the PWM discharge voltage signal is at the upper threshold discharge voltage.

5. 3. The method of operating a redox flow battery of claim 2, wherein the PWM charging voltage signal and the PWM discharging each include a duty cycle between a lower threshold charging duty cycle and an upper threshold charging duty cycle.

6. A redox flow battery system, a power module including a redox flow battery; an electrolyte subsystem fluidly coupled to the redox flow battery; A controller, The controller:

1. A redox flow battery system comprising: in response to a state of charge (SOC) of a redox flow battery decreasing below a lower threshold redox flow battery SOC, pulse charging the redox flow battery, the pulse charging comprising providing a pulse width modulated (PWM) charging voltage signal to the redox flow battery, the PWM charging voltage signal varying between an upper threshold charging voltage and an open circuit voltage (OCV).

7. 7. The redox flow battery system of claim 6, wherein the executable instructions further include discharging the redox flow battery, comprising pulsing discharging the redox flow battery in response to a SOC of the redox flow battery being greater than an upper threshold redox flow battery SOC while an electrical load is coupled to the redox flow battery, the pulsing discharging comprising providing a PWM discharge voltage signal from the redox flow battery, the PWM discharge voltage signal varying between an upper threshold discharge voltage and the OCV.

8. 8. The redox flow battery system of claim 7, wherein the instructions to charge the redox flow battery further include providing a continuous charging voltage signal to the redox flow battery in response to an increase in an SOC of the redox flow battery above an SOC of a continuous charge threshold redox flow battery, the SOC of the continuous charge threshold redox flow battery being greater than the SOC of the lower threshold redox flow battery.

9. 9. The redox flow battery system of claim 8, wherein the power module includes a plurality of redox flow battery cell stacks, each redox flow battery cell stack including one or more redox flow batteries, and the executable instructions further include providing the PWM charging voltage signal or the continuous charging voltage signal to charge a first redox flow battery cell stack of the plurality of redox flow battery cell stacks, while providing the PWM charging voltage signal or the continuous charging voltage signal to charge a second redox flow battery cell stack of the plurality of redox flow battery cell stacks.

10. 9. The redox flow battery system of claim 8, wherein the instructions to discharge the redox flow battery further include providing a continuous discharge voltage signal from the redox flow battery in response to the SOC of the redox flow battery decreasing below a continuous discharge threshold redox flow battery SOC, and the SOC of the continuous discharge threshold redox flow battery is less than the SOC of the upper threshold redox flow battery.

11. 11. The redox flow battery system of claim 10, wherein the executable instructions further comprise: increasing an SOC of the continuous discharge threshold redox flow battery in response to a plating efficiency of the redox flow battery decreasing below a threshold plating efficiency; and decreasing an SOC of the continuous discharge threshold redox flow battery in response to a voltaic efficiency of the redox flow battery decreasing below a threshold voltaic efficiency.

12. 11. The redox flow battery system of claim 10, wherein the executable instructions further comprise: lowering an SOC of the continuous charge threshold redox flow battery in response to a plating efficiency of the redox flow battery decreasing below a threshold plating efficiency; and raising an SOC of the continuous charge threshold redox flow battery in response to a voltaic efficiency of the redox flow battery decreasing below a threshold voltaic efficiency.

13. 1. A method of operating a redox flow battery, comprising: in response to a SOC of the redox flow battery decreasing below a lower threshold redox flow battery SOC, pulse charging the redox flow battery; and responsive to an increase in a SOC of the redox flow battery above an upper threshold redox flow battery SOC, pulse discharging the redox flow battery.

14. 14. The method of operating a redox flow battery of claim 13, wherein pulse charging the redox flow battery comprises: providing a pulse charging power signal to charge the redox flow battery; and oscillating the pulse charging power signal between a lower threshold charging power and an upper threshold charging power.

15. 15. The method of operating a redox flow battery according to claim 14, wherein the lower threshold charging power is equal to an open circuit voltage of the redox flow battery.

16. 15. The method of operating a redox flow battery of claim 14, wherein the upper threshold charge power is 50 kW and the upper threshold discharge power is -10 kW.

17. 15. The method of operating a redox flow battery of claim 14, wherein pulse charging the redox flow battery comprises pulse charging with a pulse width modulated (PWM) power signal, the PWM power signal having a duty cycle between a lower threshold duty cycle and an upper threshold duty cycle.

18. 14. The method of operating a redox flow battery according to claim 13, wherein pulsing discharging the redox flow battery comprises: providing a pulsed discharge power signal to discharge the redox flow battery; and oscillating the pulsed discharge power signal between a lower threshold discharge power and an upper threshold discharge power.

19. 14. The method of operating a redox flow battery according to claim 13, wherein pulse charging the redox flow battery comprises pulse charging the redox flow battery above a threshold charging current density.

20. 14. The method of operating a redox flow battery according to claim 13, wherein pulse charging the redox flow battery comprises pulse discharging the redox flow battery below a threshold discharge current density.

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