Patent Application
20230062739
The present description relates generally to systems and methods for storing electrolytes for use in a redox flow battery system and for flowing and rebalancing the electrolytes during operation of the redox flow battery system.
Redox flow batteries are suitable for grid-scale storage applications due to their capability for scaling power and capacity independently, as well as for charging and discharging over thousands of cycles with reduced performance losses in comparison to conventional battery technologies. An all-iron hybrid redox flow battery is particularly attractive due to incorporation of low-cost, earth-abundant materials. In general, iron redox flow batteries (IFBs) rely on iron, salt, and water for electrolyte, thus including simple, earth-abundant, and inexpensive materials, and eliminating incorporation of harsh chemicals and reducing an environmental footprint thereof.
The IFB may include a positive (redox) electrode where a redox reaction occurs and a negative (plating) electrode where ferrous iron (Fe2+) in the electrolyte may be reduced and plated. Various side reactions may compete with the Fe2+ reduction, including proton reduction, iron corrosion, and iron plating oxidation:
H++e−↔½H2 (proton reduction) (1)
Fe0+2H+↔Fe2++H2 (iron corrosion) (2)
2Fe3++Fe0↔3Fe2+ (iron plating oxidation) (3)
As most side reactions occur at the plating electrode, IFB cycling capabilities may be limited by available iron plating on the plating electrode. Exemplary attempts to ameliorate iron plating loss have focused on catalytic electrolyte rebalancing to address hydrogen (H2) gas generation from equations (1) and (2) and electrolyte charge imbalances (e.g., excess Fe3+) from equation (3) and ion crossover via equation (4):
Fe3++½H2→Fe2++H+ (electrolyte rebalancing) (4)
In some examples, the electrolyte rebalancing of equation (4) may be realized via a fuel cell setup, wherein the H2 gas and the electrolyte may be contacted at catalyst surfaces while applying a direct current (DC) across positive and negative electrode pairs. However, reliability issues may arise in fuel cells as a result of inadvertent reverse current spikes interrupting DC flow. In other examples, a trickle bed or jelly roll reactor setup may similarly contact the H2 gas and the electrolyte at catalyst surfaces. However, lower Fe3+ reduction rates of such setups may result in insufficiently rebalanced electrolyte during higher performance IFB operation, and a source of H2 gas may be provided to supply excess (H2 gas) reductant of equation (4). The source of H2 gas may include a standalone H2 gas storage tank and/or a head space storing H2 gas directly above or physically partitioned from the electrolyte in an electrolyte storage tank. In either case, to supply the H2 gas reductant in sufficient excess to overcome the lower Fe3+ reduction rates, the H2 gas and/or electrolyte storage tank may be rated for relatively high pressures, e.g., up to an upper threshold gauge pressure, such as 20 psi. As such, the H2 gas and/or electrolyte storage tank may be relatively expensive to manufacture in order to meet such pressure specifications. Further, such high pressures may limit an overall shape and configuration of the H2 gas and/or electrolyte storage tank. For example, high-pressure storage tanks are typically configured as cylindrical storage tanks, which may have relatively low packing densities and may therefore be less space effective for IFBs having rectangular prismatic or cuboidal components (e.g., outer casings, cell assembly stacks, etc.). Specifically, sides and ends of the (cylindrical) H2 gas and/or electrolyte storage tanks may include rounded corners and/or edges (e.g., in order to withstand hydrostatically induced pressure of contained gases), which may physically limit the packing densities of such H2 gas and/or electrolyte storage tanks.
In one example, the issues described above may be addressed by a redox flow battery system, including a plurality of redox flow battery cells, and a plurality of prismatic electrolyte storage tanks respectively fluidically coupled to the plurality of redox flow battery cells, wherein a gauge pressure in each of the plurality of prismatic electrolyte storage tanks may be maintained below 2 psi. In some examples, each of the plurality of prismatic electrolyte storage tanks may further be respectively fluidically coupled to a plurality of rebalancing cells configured to perform electrolyte rebalancing at relatively high Fe3+ reduction rates under relatively low partial pressures of H2 gas (e.g., as low as 25%). In this way, an amount of H2 gas supplied to each of the plurality of rebalancing cells may be significantly less than for typical rebalancing cell setups and each of the plurality of prismatic electrolyte storage tanks may therefore continually operate below 2 psi. Accordingly, costs in manufacturing the plurality of prismatic electrolyte storage tanks may be less than for electrolyte storage tanks rated for higher pressure ranges (as the plurality of prismatic electrolyte storage tanks may be constructed with materials and shapes limited to relatively low upper threshold gauge pressures, such as 2 psi or less, in some examples). Further, each of the plurality of prismatic electrolyte storage tanks may be configured with increased packing density compared to typical (e.g., relatively large non-prismatic/curvilinear) electrolyte and/or hydrogen gas storage tank configurations.
In some examples, to achieve relatively high rebalancing performance with relatively low amounts of H2 gas, a rebalancing cell (e.g., one of the plurality of rebalancing cells described above) may include a stack of electrode assemblies, each electrode assembly including positive and negative electrodes in face-sharing contact with one another such that the positive and negative electrodes may be continuously electrically conductive (e.g., at surfaces of the positive and negative electrodes in face-sharing contact). In additional or alternative examples, no electric current may be directed away from the rebalancing cell. In this way, electrolyte rebalancing in the rebalancing cell may be driven via internal electrical shorting of interfacing pairs of the positive and negative electrodes therein. Further, in some examples, the rebalancing cell may be configured to draw each of the liquid electrolyte and H2 gas (e.g., via forced convection, gravity feeding, capillary action, etc.) therethrough. By managing electrolyte and H2 gas flows in this way, in combination with the internal electrical shorting, the Fe3+ reduction rate of the rebalancing cell may be significantly improved over typical rebalancing cell setups (e.g., by a factor of 20 or more).
Further, in some examples, by internally shorting the interfacing pairs of the positive and negative electrodes in the rebalancing cell, each electrode assembly of the stack of electrode assemblies may be electrically decoupled from one another, such that no reverse electric current may be driven from one electrode assembly through the stack of electrode assemblies and degrade other electrode assemblies. In additional or alternative examples, internal electrical shorting of the interfacing pairs of the positive and negative electrodes may reduce electrical resistance relative to non-internally shorted electrode pairs and thereby increase respective redox reaction rates at the positive and negative electrodes. A cell potential of each electrode assembly may be concomitantly reduced, decreasing side reaction rates (e.g., rates of the reactions of equations (1)-(3)) therewith. In this way, both useful life and electrochemical performance may be improved in the rebalancing cell relative to a non-internally shorted cell.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
The following description relates to systems and methods for electrolyte distribution, rebalancing, and storage, for example, in a redox flow battery system including a rebalancing cell driven via internal electrical shorting of electrode assemblies included therein. In an exemplary embodiment, the rebalancing cell may be fluidically coupled to an electrolyte subsystem of the redox flow battery system. The redox flow battery system is depicted schematically in
In some examples, the redox flow battery system may include a hybrid redox flow battery. Hybrid redox flow batteries are redox flow batteries which may be characterized by deposition of one or more electroactive materials as a solid layer on an electrode (e.g., the negative electrode). Hybrid redox flow batteries may, for instance, include a chemical species which may plate via an electrochemical reaction as a solid on a substrate throughout a battery charge process. During battery discharge, the plated species may ionize via a further electrochemical reaction, becoming soluble in the electrolyte. In hybrid redox flow battery systems, a charge capacity (e.g., a maximum amount of energy stored) of the redox flow battery may be limited by an amount of metal plated during battery charge and may accordingly depend on an efficiency of the plating system as well as volume and surface area available for plating.
In some examples, electrolytic imbalances in the redox flow battery system may result from numerous side reactions competing with desired redox chemistry, including hydrogen (H2) gas generating reactions such as proton reduction and iron corrosion:
H++e−↔½H2 (proton reduction) (1)
Fe0+2H+↔Fe2++H2 (iron corrosion) (2)
and charge imbalances from excess ferric iron (Fe3+) generated during oxidation of iron plating:
2Fe3++Fe0↔3Fe2+ (iron plating oxidation) (3)
The reactions of equations (1) to (3) may limit iron plating and thereby decrease overall battery capacity. To address such imbalances, electrolyte rebalancing may be leveraged to both reduce Fe3+ and eliminate excess H2 gas via a single redox reaction:
Fe3++½H2→Fe2++H+ (electrolyte rebalancing) (4)
As described by embodiments herein, Fe3+ reduction rates sufficient for higher performance applications may be reliably achieved at lower H2 gas partial pressures via a rebalancing cell, such as the exemplary rebalancing cell of
As one example,
Exemplary methods of operating the redox flow battery system are depicted at
As shown in
“Anode” refers to an electrode where electroactive material loses electrons and “cathode” refers to an electrode where electroactive material gains electrons. During battery charge, the negative electrolyte gains electrons at the negative electrode 26, and the negative electrode 26 is the cathode of the electrochemical reaction. During battery discharge, the negative electrolyte loses electrons, and the negative electrode 26 is the anode of the electrochemical reaction. Alternatively, during battery discharge, the negative electrolyte and the negative electrode 26 may be respectively referred to as an anolyte and the anode of the electrochemical reaction, while the positive electrolyte and the positive electrode 28 may be respectively referred to as a catholyte and the cathode of the electrochemical reaction. During battery charge, the negative electrolyte and the negative electrode 26 may be respectively referred to as the catholyte and the cathode of the electrochemical reaction, while the positive electrolyte and the positive electrode 28 may be respectively referred to as the anolyte and the anode of the electrochemical reaction. For simplicity, the terms “positive” and “negative” are used herein to refer to the electrodes, electrolytes, and electrode compartments in redox flow battery systems.
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, and the like), wherein the negative electrode 26 includes metal iron. For example, at the negative electrode 26, ferrous iron (Fe2+) gains two electrons and plates as iron metal (Fe0) onto the negative electrode 26 during battery charge, and Fe0 loses two electrons and re-dissolves as Fe2+ during battery discharge. At the positive electrode 28, Fe2+ loses an electron to form ferric iron (Fe3+) during battery charge, and Fe3+ gains an electron to form Fe2+ during battery discharge. The electrochemical reaction is summarized in equations (5) and (6), wherein the forward reactions (left to right) indicate electrochemical reactions during battery charge, while the reverse reactions (right to left) indicate electrochemical reactions during battery discharge:
Fe2++2e−↔Fe0 −0.44 V (negative electrode) (5)
Fe2+↔2Fe3++2e− +0.77 V (positive electrode) (6)
As discussed above, the negative electrolyte used in the IFB may provide a sufficient amount of Fe2+ so that, during battery charge, Fe2+ may accept two electrons from the negative electrode 26 to form Fe0 and plate onto a substrate. During battery discharge, the plated Fe0 may lose two electrons, ionizing into Fe2+ and dissolving back into the electrolyte. An equilibrium potential of the above reaction is −0.44 V and this reaction therefore provides a negative terminal for the desired system. On the positive side of the IFB, the electrolyte may provide Fe2+ during battery charge which loses an electron and oxidizes to Fe3+. During battery discharge, Fe3+ provided by the electrolyte becomes Fe2+ by absorbing an electron provided by the positive electrode 28. An equilibrium potential of this reaction is +0.77 V, creating a positive terminal for the desired system.
The IFB may provide the ability to charge and recharge electrolytes therein in contrast to other battery types utilizing non-regenerating electrolytes. Charge may be achieved by respectively applying an electric current across the electrodes 26 and 28 via terminals 40 and 42. The negative electrode 26 may be electrically coupled via the terminal 40 to a negative side of a voltage source so that electrons may be delivered to the negative electrolyte via the positive electrode 28 (e.g., as Fe2+ is oxidized to Fe3+ in the positive electrolyte in the positive electrode compartment 22). The electrons provided to the negative electrode 26 may reduce the Fe2+ in the negative electrolyte to form Fe0 at the (plating) substrate, causing the Fe2+ to plate onto the negative electrode 26.
Discharge may be sustained while Fe0 remains available to the negative electrolyte for oxidation and while Fe3+ remains available in the positive electrolyte for reduction. As an example, Fe3+ availability may be maintained by increasing a concentration or a volume of the positive electrolyte in the positive electrode compartment 22 side of the redox flow battery cell 18 to provide additional Fe3+ ions via an external source, such as an external positive electrolyte chamber 52. More commonly, availability of Fe0 during discharge may be an issue in IFB systems, wherein the Fe0 available for discharge may be proportional to a surface area and a volume of the negative electrode substrate, as well as to a plating efficiency. Charge capacity may be dependent on the availability of Fe2+ in the negative electrode compartment 20. As an example, Fe2+ availability may be maintained by providing additional Fe2+ ions via an external source, such as an external negative electrolyte chamber 50 to increase a concentration or a volume of the negative electrolyte to the negative electrode compartment 20 side of the redox flow battery cell 18.
In an IFB, the positive electrolyte may include ferrous iron, ferric iron, ferric complexes, or any combination thereof, while the negative electrolyte may include ferrous iron or ferrous complexes, depending on a state of charge (SOC) of the IFB system. As previously mentioned, utilization of iron ions in both the negative electrolyte and the positive electrolyte may allow for utilization of the same electrolytic species on both sides of the redox flow battery cell 18, which may reduce electrolyte cross-contamination and may increase the efficiency of the IFB system, resulting in less electrolyte replacement as compared to other redox flow battery systems.
Efficiency losses in an IFB may result from electrolyte crossover through a separator 24 (e.g., ion-exchange membrane barrier, microporous membrane, and the like). For example, Fe3+ ions in the positive electrolyte may be driven toward the negative electrolyte by a Fe3+ ion concentration gradient and an electrophoretic force across the separator 24. Subsequently, Fe3+ ions penetrating the separator 24 and crossing over to the negative electrode compartment 20 may result in coulombic efficiency losses. Fe3+ ions crossing over from the low pH redox side (e.g., more acidic positive electrode compartment 22) to the high pH plating side (e.g., less acidic negative electrode compartment 20) may result in precipitation of Fe(OH)3. Precipitation of Fe(OH)3 may degrade the separator 24 and cause permanent battery performance and efficiency losses. For example, Fe(OH)3 precipitate may chemically foul an organic functional group of an ion-exchange membrane or physically clog micropores of the ion-exchange membrane. In either case, due to the Fe(OH)3 precipitate, membrane ohmic resistance may rise over time and battery performance may degrade. Precipitate may be removed by washing the IFB with acid, but constant maintenance and downtime may be disadvantageous for commercial battery applications. Furthermore, washing may be dependent on regular preparation of electrolyte, contributing to additional processing costs and complexity. Alternatively, adding specific organic acids to the positive electrolyte and the negative electrolyte in response to electrolyte pH changes may mitigate precipitate formation during battery charge and discharge cycling without driving up overall costs. Additionally, implementing a membrane barrier that inhibits Fe3+ ion crossover may also mitigate fouling.
Additional coulombic efficiency losses may be caused by reduction of H+ (e.g., protons) and subsequent formation of H2 gas, and a reaction of protons in the negative electrode compartment 20 with electrons supplied at the plated iron metal of the negative electrode 26 to form H2 gas.
The IFB electrolyte (e.g., FeCl2, FeCl3, FeSO4, Fe2(SO4)3, and the like) may be readily available and may be produced at low costs. 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 offer higher reclamation value because the same electrolyte may be used for the negative electrolyte and the positive electrolyte, consequently reducing cross-contamination issues as compared to other systems. Furthermore, because of iron's electron configuration, iron may solidify into a generally uniform solid structure during plating thereof on the negative electrode substrate. For zinc and other metals commonly used in hybrid redox batteries, solid dendritic structures may form during plating. A stable electrode morphology of the IFB system may increase the efficiency of the battery in comparison to other redox flow batteries. Further still, iron redox flow batteries may reduce the use of toxic raw materials and may operate at a relatively neutral pH as compared to other redox flow battery electrolytes. Accordingly, IFB systems may reduce environmental hazards as compared with all other current advanced redox flow battery systems in production.
Continuing with
The negative electrode compartment 20 may include the negative electrode 26, and the negative electrolyte may include electroactive materials. The positive electrode compartment 22 may include the positive electrode 28, and the positive electrolyte may include electroactive materials. In some examples, multiple redox flow battery cells 18 may be combined in series or in parallel to generate a higher voltage or electric current in the redox flow battery system 10.
Further illustrated in
The redox flow battery system 10 may also include a first bipolar plate 36 and a second bipolar plate 38, each positioned along a rear-facing side, e.g., opposite of a side facing the separator 24, of the negative electrode 26 and the positive electrode 28, respectively. 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. In other examples, however, the bipolar plates 36 and 38 may be arranged proximate but spaced away 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 the terminals 40 and 42, respectively, either via direct contact therewith or through the negative and positive electrodes 26 and 28, respectively. The IFB electrolytes may be transported to reaction sites at the negative and positive electrodes 26 and 28 by the first and second bipolar plates 36 and 38, resulting from conductive properties of a material of the bipolar plates 36 and 38. Electrolyte flow may also be assisted by the negative and positive electrolyte pumps 30 and 32, facilitating 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 a presence of the first and second bipolar plates 36 and 38.
As illustrated in
The redox flow battery system 10 may further include the integrated multi-chambered electrolyte storage tank 110. The multi-chambered electrolyte storage tank 110 may be divided by a bulkhead 98. The bulkhead 98 may create multiple chambers within the multi-chambered electrolyte storage tank 110 so that both the positive and negative electrolytes may be included within a single tank. The negative electrolyte chamber 50 holds negative electrolyte including the electroactive materials, and the positive electrolyte chamber 52 holds positive electrolyte including the electroactive materials. The bulkhead 98 may be positioned within the multi-chambered electrolyte storage tank 110 to yield a desired volume ratio between the negative electrolyte chamber 50 and the positive electrolyte chamber 52. In one example, the bulkhead 98 may be positioned to set a volume ratio of the negative and positive electrolyte chambers 50 and 52 according to a stoichiometric ratio between the negative and positive redox reactions.
As shown, the electrolyte flow path 124 may fluidically couple the integrated multi-chambered electrolyte storage tank 110 to the redox flow battery cell 18 and each of the rebalancing reactors 80 and 82. In some examples, the electrolyte flow path 124 may be a closed flow path in the sense that, during operation of the redox flow battery system 10, the negative and positive electrolytes may be circulated through only one redox flow battery cell 18 along the electrolyte flow path without entering any other redox flow battery cell or being otherwise expelled from the redox flow battery system 10. In such examples, when the redox flow battery system 10 includes a plurality of redox flow battery cells 18, a plurality of (closed) electrolyte flow paths 124 may be included in the redox flow battery system 10, a number of the plurality of electrolyte flow paths 124 being equivalent to a number of the plurality of redox flow battery cells 18. In this way, and as described in greater detail below with reference to
The electrolyte flow path 124 may include a negative electrolyte flow loop 120 and a positive electrolyte flow loop 122, where the negative and positive electrolytes may be cycled through the negative and positive electrolyte flow loops 120 and 122, respectively. The negative and positive electrolyte flow loops 120 and 122 may be fully or almost fully fluidically decoupled from one another (e.g., fluidic coupling may occur only via the spillover hole 96, when included in the bulkhead 98 of the integrated multi-chambered electrolyte storage tank 110). As shown, the negative electrolyte flow loop 120 may sequentially cycle through the negative electrolyte chamber 50 of the integrated multi-chambered electrolyte storage tank 110, the negative electrolyte pump 30, the negative electrode compartment 20 of the redox flow battery cell 18, and the (negative) rebalancing reactor 80, flowing therefrom back to the negative electrolyte chamber 50 of the integrated multi-chambered electrolyte storage tank 110. As further shown, the positive electrolyte flow loop 122 may sequentially pass through the positive electrolyte chamber 52 of the integrated multi-chambered electrolyte storage tank 110, the positive electrolyte pump 32, the positive electrode compartment 22 of the redox flow battery cell 18, and the (positive) rebalancing reactor 82, flowing therefrom back to the positive electrolyte chamber 52 of the integrated multi-chambered electrolyte storage tank 110. Accordingly, electrolyte solutions primarily stored in the multi-chambered electrolyte storage tank 110 may be pumped via the negative and positive electrolyte pumps 30 and 32 throughout the redox flow battery system 10: electrolyte stored in the negative electrolyte chamber 50 may be pumped via the negative electrolyte pump 30 through the negative electrode compartment 20 side of the redox flow battery cell 18, and electrolyte stored in the positive electrolyte chamber 52 may be pumped via the positive electrolyte pump 32 through the positive electrode compartment 22 side of the redox flow battery cell 18. In this way, during operation of the redox flow battery system 10, the negative and positive electrolytes may be cycled through the redox flow battery cell 18 largely independently of one another via the negative and positive electrolyte flow loops 120 and 122, respectively.
Although not shown in
Further still, 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 way, the field hydration system may facilitate commissioning of the redox flow battery system 10, including installing, filling, and hydrating the redox flow battery system 10, at an end-use location. Furthermore, prior to commissioning 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 filling and hydrating the redox flow battery system 10, before delivering the redox flow battery system 10 to the end-use location. In one example, the end-use location may correspond to a location where the redox flow battery system 10 is to be installed and utilized for on-site energy storage. Said another way, the redox flow battery system 10 may be designed such that, once installed and hydrated at the end-use location, a position of the redox flow battery system 10 may become fixed, and the redox flow battery system 10 may no longer be deemed a portable, dry system. Thus, from a perspective of an end-user, the dry, portable redox flow battery system 10 may be delivered on-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, the redox flow battery system 10 being free of or without water and wet electrolyte. Once hydrated, the redox flow battery system 10 may be referred to as a wet, non-portable system, the redox flow battery system 10 including wet electrolyte.
The electrolyte rebalancing reactors 80 and 82 may be connected in line or in parallel with the recirculating flow paths of the electrolyte at the negative and positive sides of the redox flow battery cell 18, respectively, in the redox flow battery system 10. One or more rebalancing reactors may be connected in-line with the recirculating flow paths of the electrolyte at the negative and positive sides of the battery, and other rebalancing reactors may be connected in parallel, for redundancy (e.g., a rebalancing reactor may be serviced without disrupting battery and rebalancing operations) and for increased rebalancing capacity. In one example, the electrolyte rebalancing reactors 80 and 82 may be placed in a return flow path from the negative and positive electrode compartments 20 and 22 to the negative and positive electrolyte chambers 50 and 52, respectively. The electrolyte rebalancing reactors 80 and 82 may serve to rebalance electrolyte charge imbalances in the redox flow battery system 10 occurring due to side reactions, ion crossover, and the like, as described herein.
In some examples, one or both of the rebalancing reactors 80 and 82 may include trickle bed reactors, where the H2 gas and the (liquid) electrolyte may be contacted at catalyst surfaces in a packed bed for carrying out the electrolyte rebalancing reaction. Additionally or alternatively, one or both of the rebalancing reactors 80 and 82 may have catalyst beds configured in a jelly roll. In additional or alternative examples, one or both of the rebalancing reactors 80 and 82 may include flow-through type reactors that are capable of contacting the H2 gas and the electrolyte and carrying out the electrolyte rebalancing reactions absent a packed catalyst bed. However, lower Fe3+ reduction rates (e.g., on the order of ˜1-3 mol/m2hr) during electrolyte rebalancing may preclude implementation of such rebalancing reactor configurations in higher performance applications.
In other examples, one or both of the rebalancing reactors 80 and 82 may include fuel cells, where the H2 gas and the electrolyte may be contacted at catalyst surfaces for carrying out the electrolyte rebalancing reaction and where a closed circuit may be formed by directing electric current from the fuel cells through an external load. However, reverse current spikes [e.g., transient increases in reverse electric current, where “reverse electric current” may be used herein to refer to any electric current traveling along an electrical pathway in a direction opposite from expected (that is, opposite from a “forward” direction)] in such fuel cells may be unavoidable in certain circumstances, undermining a reliability of such rebalancing reaction configurations.
To increase the Fe3+ reduction rate without sacrificing an overall reliability of the rebalancing reactors 80 and 82, embodiments of the present disclosure provide a rebalancing cell, such as the rebalancing cell of
To realize the internally shorted circuit, each electrode assembly of the stack of internally shorted electrode assemblies may include an interfacing pair of positive and negative electrodes (e.g., configured in face-sharing contact with one another so as to be continuously electrically conductive). As used herein, a pair of first and second components (e.g., positive and negative electrodes of an electrode assembly) may be described as “interfacing” with one another when the first component is arranged adjacent to the second component such that the first and second components are in face-sharing contact with one another (where “adjacent” is used herein to refer to any two components having no intervening components therebetween). Further, as used herein, “continuously” when describing electrical conductivity of multiple electrodes may refer to an electrical pathway therethrough having effectively or practically zero resistance at any face-sharing interfaces of the multiple electrodes.
In an exemplary embodiment, the (positive) rebalancing reactor 82 may be the rebalancing cell including the stack of internally shorted electrode assemblies. Higher Fe3+ reduction rates may be desirable to rebalance the positive electrolyte, as significant amounts of Fe3+ may be generated at the positive electrode 28 during battery charging (see equation (6)). In additional or alternative embodiments, the (negative) rebalancing reactor 80 may be of like configuration [Fe3+ may be generated at the negative electrode 26 during iron plating oxidation (see equation (3))].
In such rebalancing cell configurations, the higher Fe3+ reduction rates may be accomplished with relatively low H2 gas partial pressures with minimal impact on performance. As such, in some examples, the H2 gas may be flowed from the integrated multi-chambered electrolyte storage tank 110 to the rebalancing reactors 80 and 82 at a partial pressure of less than an upper partial pressure threshold, such as 80%. In one example, the upper partial pressure threshold may be 25%, and the rebalancing cell including the stack of internally shorted electrode assemblies as described herein may accordingly be operated at least down to 25% H2 gas partial pressure (see
By configuring the rebalancing reactors 80 and/or 82 in this way, less H2 gas may be included in the gas head spaces 90 and 92 for electrolyte rebalancing, and the integrated multi-chambered electrolyte storage tank 110 may be constructed with fewer considerations as to pressurized containment, such that a shape and/or an overall size of the integrated multi-chambered electrolyte storage tank 110 may be selected for overall space and packing density rather than for containing high storage pressures. As such, and as discussed in detail below with reference to
Moreover, by selecting a more space-effective, low-pressure configuration, a volume of the electrolyte solution utilized in the redox flow battery system 10 may be partitioned into multiple, smaller integrated multi-chambered electrolyte storage tanks 110 (e.g., one integrated multi-chambered electrolyte storage tank 110 respectively fluidically coupled to each redox flow battery cell 18), thereby further increasing the packing density, while providing a greater flexibility in component placement within the redox flow battery system 10. For example, by partitioning the volume of the electrolyte solution in this way, a plurality of fluidically isolated redox flow battery subsystems 150 may be formed (each with an integrated multi-chambered electrolyte storage tank 110 fluidically coupled to a redox flow battery cell 18) which may operate substantially independently of one another. Accordingly, the redox flow battery system 10 may be configured as a modular redox flow battery pack including a plurality of redox flow batteries (e.g., the plurality of fluidically isolated redox flow battery subsystems 150), wherein redox flow batteries may be added or removed with relative ease and simplicity. For example, and as described in detail below with reference to
During operation of the redox flow battery system 10, sensors and probes may monitor and control chemical properties of the electrolyte such as electrolyte pH, concentration, SOC, and the like. For example, as illustrated in
For example, a sensor may be positioned in an external acid tank (not shown) to monitor acid volume or pH of the external acid tank, wherein acid from the external acid tank may be supplied via an external pump (not shown) to the redox flow battery system 10 in order to reduce precipitate formation in the electrolytes. Additional external tanks and sensors may be installed for supplying other additives to the redox flow battery system 10. For example, various sensors including, temperature, conductivity, and level sensors of a field hydration system may transmit signals to the controller 88. Furthermore, 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. Sensor information may be transmitted to the controller 88 which may in turn actuate the pumps 30 and 32 to control electrolyte flow through the redox flow battery cell 18, or to perform other control functions, as an example. In this manner, the controller 88 may be responsive to one or a combination of sensors and probes.
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 example of
For example, an increase in pH of the negative electrolyte chamber 50, or the negative electrode compartment 20, may indicate that H2 gas is leaking from the redox flow battery system 10 and/or that the reaction rate is too slow with the available hydrogen partial pressure, and the controller 88, in response to the pH increase, may increase a supply of H2 gas from the integrated multi-chambered electrolyte storage tank 110 to the redox flow battery system 10. As a further example, the controller 88 may supply H2 gas from the integrated multi-chambered electrolyte storage tank 110 in response to a pH change, wherein the pH increases beyond a first threshold pH or decreases beyond a second threshold pH. In the case of an IFB, the controller 88 may supply additional H2 gas to increase a rate of reduction of Fe3+ ions and a rate of production of protons, thereby reducing the pH of the positive electrolyte. Furthermore, the pH of the negative electrolyte may be lowered by hydrogen reduction of Fe3+ ions crossing over from the positive electrolyte to the negative electrolyte or by protons, generated at the positive side, crossing over to the negative electrolyte due to a proton concentration gradient and electrophoretic forces. In this manner, the pH of the negative electrolyte may be maintained within a stable region, while reducing the risk of precipitation of Fe3+ ions (crossing over from the positive electrode compartment 22) as Fe(OH)3.
Other control schemes for controlling a supply rate of H2 gas from the integrated multi-chambered electrolyte storage tank 110 responsive to a change in an electrolyte pH or to a change in an electrolyte SOC, detected by other sensors such as an oxygen-reduction potential (ORP) meter or an optical sensor, may be implemented. Further still, the change in pH or SOC triggering action of the controller 88 may be based on a rate of change or a change measured over a time period. The time period for the rate of change may be predetermined or adjusted based on time constants for the redox flow battery system 10. For example, the time period may be reduced if a recirculation rate is high, and local changes in concentration (e.g., due to side reactions or gas leaks) may quickly be measured since the time constants may be small.
The controller 88 may further execute control schemes based on an operating mode of the redox flow battery system 10. For example, and as discussed in detail below with reference to
In examples wherein the rebalancing reactors 80 and 82 are configured as rebalancing cells including stacks of internally shorted electrode assemblies, the controller 88 may control operation of the redox flow battery system 10 at relatively low H2 gas partial pressures, such that multiple, space-effective, low-pressure storage tanks (e.g., integrated multi-chambered electrolyte storage tanks 110) may be included for electrolyte storage and distribution. Accordingly, the redox flow battery cells 18 included in the redox flow battery system 10 may be fluidically decoupled from one another such that a modularity of the redox flow battery system 10 may be increased (e.g., fewer coupling elements and less complex configurations may be employed to add on further redox flow battery cells 18). Moreover, by fluidically isolating the redox flow battery cells 18 from one another, the redox flow battery cells 18 may be electrically coupled in series such that a potential difference thereacross may be ramped up and relatively high voltage external loads may be powered by the redox flow battery system 10 absent any DC-to-DC boost converter(s). For example, and as discussed in detail with reference to
As yet another example, the controller 88 may further control charging and discharging of the redox flow battery cell 18 so as to cause iron preformation at the negative electrode 26 during system conditioning (where system conditioning may include an operating mode employed to optimize 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 improve a battery charge capacity during subsequent battery cycling (thus, the iron metal may be preformed for battery cycling). In this way, preforming iron at the negative electrode 26 and running electrolyte rebalancing during the system conditioning may increase an overall capacity of the redox flow battery cell 18 during battery cycling by mitigating iron plating loss. As used herein, battery cycling (also referred to as “charge cycling”) may include alternating between a charging mode and a discharging mode of the redox flow battery system 10.
It will be appreciated that all components apart from the sensors 60 and 62 and the integrated multi-chambered electrolyte storage tank 110 (and components included therein) may be considered as being included in a power module 130. As such, the redox flow battery system 10 may be described as including the power module 130 fluidly coupled to the integrated multi-chambered electrolyte storage tank 110 and communicably coupled to the sensors 60 and 62. In some examples, each of the power module 130 and the multi-chambered electrolyte storage tank 110 may be included in a single housing or packaging (not shown), such that the redox flow battery system 10 may be contained as a single unit in a single location. It will further be appreciated the positive electrolyte, the negative electrolyte, the sensors 60 and 62, the electrolyte rebalancing reactors 80 and 82, and the integrated multi-chambered electrolyte storage tank 110 (and components included therein) may be considered as being included in an electrolyte subsystem 140. As such, the electrolyte subsystem 140 may supply one or more electrolytes to the redox flow battery cell 18 (and components included therein).
In some examples, and as discussed above, the redox flow battery system 10 may be configured as a redox flow battery pack including a plurality of fluidically isolated redox flow battery subsystems 150. In such examples, each of the plurality of fluidically isolated redox flow battery subsystems 150 may include all components of the redox flow battery system 10 apart from the controller 88. More specifically, each of the plurality of fluidically isolated redox flow battery subsystems 150 may include a separate integrated multi-chambered electrolyte storage tank 110, separate electrolyte pumps 30 and 32, a separate redox flow battery cell 18, separate rebalancing reactors 80 and 82, etc. Accordingly, each of the plurality of fluidically isolated redox flow battery subsystems 150 may be referred to herein as a redox flow battery, where each redox flow battery may be independently configured to output electrical power during discharge. In such configurations, the controller 88 may be communicably coupled to each of the redox flow batteries and may therefore control operating states of each of the redox flow batteries in tandem or individually, as determined based on a given application.
Referring now to
A number of rebalancing cells 202 included in the redox flow battery system and a number of electrode assemblies included in the stack of internally shorted electrode assemblies are not particularly limited and may increase to accommodate correspondingly higher performance applications. For example, a 75 kW redox flow battery system may include two rebalancing cells 202 including a stack of 20 electrode assemblies (e.g., a stack of 19 bipolar assemblies with 2 end plates positioned at opposite ends of the stack).
As shown, the stack of internally shorted electrode assemblies may be removably enclosed within an external cell enclosure or housing 204. Accordingly, in some examples, the cell enclosure 204 may include a top cover removably affixed to an enclosure base, such that the top cover may be temporarily removed to replace or diagnose one or more electrode assemblies of the stack of internally shorted electrode assemblies. In additional or alternative examples, the cell enclosure 204, depicted in
The cell enclosure 204 may further be configured to include openings or cavities for interfacial components of the rebalancing cell 202. For example, the cell enclosure 204 may include a plurality of inlet and outlet ports configured to fluidically couple to other components of the redox flow battery system. In one example, and as shown, the plurality of inlet and outlet ports may include polypropylene (PP) flange fittings fusion welded to PP plumbing.
In an exemplary embodiment, the plurality of inlet and outlet ports may include an electrolyte inlet port 206 for flowing the electrolyte into the cell enclosure 204 and an electrolyte outlet port 208 for expelling the electrolyte from the cell enclosure 204. In one example, the electrolyte inlet port 206 may be positioned on an upper half of the cell enclosure 204 and the electrolyte outlet port 208 may be positioned on a lower half of the cell enclosure 204 (where the upper half and the lower half of the cell enclosure 204 are separated along the z-axis by a plane parallel with each of the x- and y-axes). Accordingly, the electrolyte outlet port 208 may be positioned lower than the electrolyte inlet port 206 with respect to the direction of gravity (e.g., along the axis g).
Specifically, upon the electrolyte entering the cell enclosure 204 via the electrolyte inlet port 206, the electrolyte may be distributed across the stack of internally shorted electrode assemblies, gravity fed through the stack of electrode assemblies, wicked up (e.g., against the direction of gravity) through positive electrodes of the stack of internally shorted electrode assemblies to react at the catalytic surfaces of the negative electrodes in a cathodic half reaction, and expelled out of the cell enclosure 204 via the electrolyte outlet port 208. To assist in the gravity feeding of the electrolyte and decrease a pressure drop thereof, the rebalancing cell 202 may further be tilted or inclined with respect to the direction of gravity via a sloped support coupled to the cell enclosure 204. In some examples, tilting of the cell enclosure 204 in this way may further assist in electrolyte draining of the rebalancing cell 202 (e.g., during an idle mode of the redox flow battery system) and keep the catalytic surfaces relatively dry (as the catalytic surfaces may corrode after being soaked in the electrolyte for a sufficient duration, in some examples).
As shown, the sloped support 220 may tilt the cell enclosure 204 at an angle 222 such that planes of electrode sheets of the stack of internally shorted electrode assemblies are inclined with respect to a lower surface (not shown) on which the sloped support 220 rests at the angle 222. In some examples, the angle 222 (e.g., of the cell enclosure 204 with respect to the lower surface) may be between 0° and 30° (in embodiments wherein the angle 222 is substantially 0°, the rebalancing cell 202 may still function, though the pressure drop may be greater and electrolyte crossover to the negative electrodes may be reduced when the cell enclosure 204 is tilted). In some examples, the angle 222 may be between 2° and 30°. In some examples, the angle 222 may be between 2° and 20°. In one example, the angle 222 may be about 8°. Accordingly, the pressure drop of the electrolyte may be increased by increasing the angle 222 and decreased by decreasing the angle 222. Further aspects of the sloped support 220 are described in greater detail below with reference to
As further shown, the electrolyte outlet port 208 may include a plurality of openings in the cell enclosure 204 configured to expel at least a portion of the electrolyte (each of the plurality of openings including the PP flange fitting fusion welded to PP plumbing). For instance, in
The electrolyte inlet port 206 and the electrolyte outlet port 208 may be positioned on the cell enclosure 204 based on a flow path of the electrolyte through the stack of internally shorted electrode assemblies (e.g., from the electrolyte inlet port 206 to the electrolyte outlet port 208 and inclusive of channels, passages, plenums, wells, etc. within the cell enclosure 204 fluidically coupled to the electrolyte inlet port 206 and the electrolyte outlet port 208). In some examples, and as shown, the electrolyte inlet port 206 and the electrolyte outlet port 208 may be positioned on adjacent sides of the cell enclosure 204 (e.g., faces of the cell enclosure 204 sharing a common edge). In other examples, the electrolyte inlet port 206 and the electrolyte outlet port 208 may be positioned on opposite sides of the cell enclosure 204. In other examples, the electrolyte inlet port 206 and the electrolyte outlet port 208 may be positioned on the same side of the cell enclosure 204.
In some examples, the electrolyte inlet port 206 may be positioned on a face of the cell enclosure 204 facing a negative direction of the x-axis. In additional or alternative examples, the electrolyte inlet port 206 may be positioned on a face of the cell enclosure 204 facing a positive direction of the x-axis. In one example, and as shown, one opening of the electrolyte inlet port 206 may be positioned on the face of the cell enclosure 204 facing the negative direction of the x-axis and another opening of the electrolyte inlet port 206 may be positioned on the face of the cell enclosure 204 facing the positive direction of the x-axis.
In some examples, the plurality of inlet and outlet ports may further include a hydrogen gas inlet port 210 for flowing the H2 gas into the cell enclosure 204 and a hydrogen gas outlet port 212 for expelling the H2 gas from the cell enclosure 204. In one example, and as shown, each of the hydrogen gas inlet port 210 and the hydrogen gas outlet port 212 may be positioned on the lower half of the cell enclosure 204 (e.g., at a lowermost electrode assembly of the stack of internally shorted electrode assemblies along the z-axis). In another example, each of the hydrogen gas inlet port 210 and the hydrogen gas outlet port 212 may be positioned on the upper half of the cell enclosure 204 (e.g., at an uppermost electrode assembly of the stack of internally shorted electrode assemblies along the z-axis). In yet another example, the hydrogen gas inlet port 210 may be positioned on the lower half of the cell enclosure 204 and the hydrogen gas outlet port 212 may be positioned on the upper half of the cell enclosure 204. In such an example, the hydrogen gas inlet port 210 may be positioned lower than the hydrogen gas outlet port 212 with respect to the direction of gravity (e.g., along the axis g).
Specifically, upon the H2 gas entering the cell enclosure 204 via the hydrogen gas inlet port 210, the H2 gas may be distributed across and through the stack of internally shorted electrode assemblies via forced convection (e.g., induced by flow field configurations of respective flow field plates, as discussed in greater detail below with reference to
The hydrogen gas inlet port 210 and the hydrogen gas outlet port 212 may be positioned on the cell enclosure 204 based on a flow path of the H2 gas through the stack of internally shorted electrode assemblies [e.g., from the hydrogen gas inlet port 210 to the hydrogen gas outlet port 212 (when included) and inclusive of channels, passages, plenums, etc. within the cell enclosure 204 fluidically coupled to the hydrogen gas inlet port 210 and the hydrogen gas outlet port 212 (when included)]. In some examples, and as shown, the hydrogen gas inlet port 210 and the hydrogen gas outlet port 212 may be positioned on opposite sides of the cell enclosure 204. In other examples, the hydrogen gas inlet port 210 and the hydrogen gas outlet port 212 may be positioned on adjacent sides of the cell enclosure 204. In other examples, the hydrogen gas inlet port 210 and the hydrogen gas outlet port 212 may be positioned on the same side of the cell enclosure 204. Further, though the hydrogen gas inlet port 210 is shown in
In one example, the hydrogen gas inlet port 210, the hydrogen gas outlet port 212, the electrolyte inlet port 206, and the electrolyte outlet port 208 may be positioned on the cell enclosure 204 in a crosswise configuration. Specifically, the crosswise configuration may include the hydrogen gas outlet port 212 and the electrolyte inlet port 206 being positioned on different sides (e.g., faces) of the upper half of the cell enclosure 204 and the hydrogen gas inlet port 210 and the electrolyte outlet port 208 being positioned on different sides of the lower half of the cell enclosure 204.
In other examples, no hydrogen gas outlet port 212 may be present for expelling H2 gas which has not reacted at the catalytic surfaces of the negative electrodes and which has not flowed through the negative electrodes into the electrolyte. In such examples, however, the pressure release outlet port 214 for expelling unreacted H2 gas from the electrolyte may still be present, and the unreacted H2 gas may only be expelled from the cell enclosure 204 after flowing through the negative electrodes into the electrolyte and through the pressure release outlet port 214. Exemplary rebalancing cell configurations lacking the hydrogen gas outlet port 212, whether or not including the pressure release outlet port 214, may be referred to as “dead ended configurations.” In dead ended configurations, substantially all of the H2 gas may be forced into contact with the catalytic surfaces of the negative electrodes, whereat the H2 gas may either decompose via the anodic half reaction and/or the H2 gas may enter the electrolyte after passing through the negative electrodes (e.g., without reacting at catalytic surfaces thereof).
Referring now to
In some examples, the plate 304 may be composed of a material having a low electrical conductivity, such as a plastic or other polymer, so as to reduce undesirable shorting events. Accordingly, in one example, the plate 304 may be formed from the same material as the cell enclosure 204 of
As shown, the plate 304 may include a plurality of inlets and outlets therethrough. For example, the plurality of inlets and outlets may include an electrolyte outlet channel section 316, a hydrogen gas inlet channel section 318a, and a hydrogen gas outlet channel section 318b. Specifically, the plate 304 may include the electrolyte outlet channel section 316 for directing the electrolyte out of the rebalancing cell, the hydrogen gas inlet channel section 318a for directing the H2 gas into the rebalancing cell and across the negative electrode 310, and the hydrogen gas outlet channel section 318b for directing the H2 gas out of the rebalancing cell. The plate 304 may further include an electrolyte inlet well 312 for receiving the electrolyte at the electrode assembly 302, the electrolyte inlet well 312 fluidically coupled to a plurality of electrolyte inlet passages 314a set into a berm 314b positioned adjacent to the carbon foam 306 for distributing the received electrolyte across the carbon foam 306. In some examples, the electrolyte inlet well 312 may receive the electrolyte from an electrolyte inlet port (e.g., the electrolyte inlet port 206 of
It will be appreciated that, though the hydrogen gas inlet channel section 318a is described herein as a section of a hydrogen gas inlet channel and the hydrogen gas outlet channel section 318b is described herein as a section of a hydrogen gas outlet channel, in other examples, the channel section 318b may be a section of a hydrogen gas inlet channel (e.g., for directing the H2 gas into the rebalancing cell and across the negative electrode 310 after receiving the H2 gas from the hydrogen gas inlet port) and the channel section 318a may be a section of a hydrogen gas outlet channel (e.g., for directing the H2 gas out of the rebalancing cell by expelling the H2 gas through the hydrogen gas outlet port). In other examples, the rebalancing cell may have a dead ended configuration and no hydrogen gas outlet port may be fluidically coupled to the hydrogen gas outlet channel section 318b. In such examples, the hydrogen gas outlet channel section 318b may direct the H2 gas back across the negative electrode 310 or the hydrogen gas outlet channel section 318b may instead be configured as another hydrogen gas inlet channel section (e.g., for directing a portion of the H2 gas into the rebalancing cell and across the negative electrode 310 after receiving the portion of the H2 gas from the hydrogen gas inlet port).
The plurality of inlets and outlets may be configured to improve electrolyte and H2 gas flow throughout the rebalancing cell. As an example, a size of each of the hydrogen gas inlet channel section 318a and the hydrogen gas outlet channel section 318b may be selected to minimize a pressure drop therethrough, thereby aiding in flow distribution into each electrode assembly 302 of the stack of internally shorted electrode assemblies. As another example, a size of each electrolyte inlet passage 314a and a total number of the plurality of electrolyte inlet passages 314a relative to the berm 314b may be selected to induce a relatively small pressure drop to substantially evenly distribute electrolyte flow. In such an example, the selection of the size of each electrolyte passage 314a and the total number of the plurality of electrolyte inlet passages 314a may be dependent on a number of factors specific to a given configuration of the rebalancing cell, such as a size of an electrolyte flow field and a desired electrolyte flow rate.
In additional or alternative examples, the electrolyte outlet channel section 316 may further be configured for distributing the electrolyte through multiple openings included in the electrolyte outlet port. For instance, in the exploded view 300 of
Further, when the electrode assembly 302 is included in a stack of electrode assemblies, electrolyte outlet channel sections 316, hydrogen gas inlet channel sections 318a, and hydrogen gas outlet channel sections 318b may align to form a continuous electrolyte outlet channel, a continuous hydrogen gas inlet channel, and a continuous hydrogen gas outlet channel, respectively (as variously shown in
As further shown, a plurality of sealing inserts may be affixed (as used herein, “affix,” “affixed,” or “affixing” includes, but is not limited to, gluing, attaching, connecting, fastening, joining, linking, or securing one component to another component through a direct or indirect relationship) or otherwise coupled to the plate 304. As an example, the plurality of sealing inserts may include a hydrogen gas inlet channel seal insert 320a and a hydrogen gas outlet channel seal insert 320b for inducing flow of the H2 gas across the negative electrode 310 by mitigating H2 gas bypass. Specifically, the hydrogen gas inlet channel seal insert 320a and the hydrogen gas outlet channel seal insert 320b may be affixed or otherwise coupled adjacent to the hydrogen gas inlet channel section 318a and the hydrogen gas outlet channel section 318b, respectively, on a side of the plate 304 including the carbon foam 306, the positive electrode 308, and the negative electrode 310. In some examples, and as discussed in greater detail with reference to
As another example, the plurality of sealing inserts may further include each of a hydrogen gas inlet channel O-ring 322a and a hydrogen gas outlet channel O-ring 322b for respectively sealing an interface of the hydrogen gas inlet channel section 318a with a hydrogen gas inlet channel section of another electrode assembly and an interface of the hydrogen gas outlet channel section 318b with a hydrogen gas outlet channel section of another electrode assembly. Specifically, the hydrogen gas inlet channel O-ring 322a and the hydrogen gas outlet channel O-ring 322b may be affixed or otherwise coupled to the plate 304 so as to respectively circumscribe the hydrogen gas inlet channel section 318a and the hydrogen gas outlet channel section 318b.
As another example, the plurality of sealing inserts may further include an overboard O-ring 324 for sealing an interface of the electrode assembly 302 with another electrode assembly at outer edges thereof. Specifically, the overboard O-ring 324 may be affixed or otherwise coupled to the plate 304 so as to circumscribe each of the electrolyte inlet well 312, the plurality of electrolyte inlet passages 314a, the berm 314b, the electrolyte outlet channel section 316, the hydrogen gas inlet channel section 318a, and the hydrogen gas outlet channel section 318b.
The carbon foam 306 may be positioned in a cavity 326 of the plate 304 between the berm 314b and the electrolyte outlet channel section 316 along the y-axis and between the hydrogen gas inlet channel section 318a and the hydrogen gas outlet channel section 318b along the x-axis. Specifically, the carbon foam 306 may be positioned in face-sharing contact with a side of the plate 304 forming a base of the cavity 326. In some examples, the carbon foam 306 may be formed as a continuous monolithic piece, while in other examples, the carbon foam 306 may be formed as two or more carbon foam sections. In an exemplary embodiment, the carbon foam 306 may be conductive, permeable, and porous, providing a distribution field for the electrolyte being gravity fed therethrough from the plurality of electrolyte inlet passages 314a. In some examples, a pore distribution of the carbon foam 306 may be between 10 and 100 PPI. In one example, the pore distribution may be 30 PPI. In additional or alternative examples, a permeability of the carbon foam 306 may be between 0.02 and 0.5 mm2. As such, each of the pore distribution and the permeability, in addition to an overall size, of the carbon foam 306 may be selected to target a relatively small pressure drop and thereby induce convection of the electrolyte from the carbon foam 306 into the positive electrode 308. For example, the pressure drop may be targeted to between 2 to 3 mm of electrolyte head rise.
In some examples, the carbon foam 306 may be replaced with a flow field plate configured to transport the electrolyte into the positive electrode 308 via convection induced by a flow field configuration of the flow field plate. Specifically, the flow field plate may be fluidically coupled to each of the plurality of electrolyte inlet passages 314a and the electrolyte outlet channel section 316. In one example, the flow field plate may be integrally formed in the plate 304 of the electrode assembly 302, positioned beneath the positive electrode 308 with respect to the z-axis. In other examples, the flow field plate may be a separate, removable component.
In some examples, and as described in detail below with reference to
In certain examples, and as discussed in greater detail below with reference to
The positive electrode 308 may be positioned in the cavity 326 in face-sharing contact with a side of the carbon foam 306 opposite from the plate 304 along the z-axis. In an exemplary embodiment, the positive electrode 308 may be a wicking conductive carbon felt, sponge, or mesh which may bring the electrolyte flowing through the carbon foam 306 into contact with the negative electrode 310 via capillary action. Accordingly, in some examples, the positive electrode 308 may be conductive and porous (though less porous than the carbon foam 306 in such examples). In one example, the electrolyte may be wicked into the positive electrode 308 when the porosity of the carbon foam 306 is within a predefined range (e.g., below an upper threshold porosity so as to retain enough solid material to promote wicking up and into the positive electrode 308 and above a lower threshold porosity so as to not impede electrolyte flow through the carbon foam 306). In an additional or alternative example, each of a sorptivity of the positive electrode 308 may decrease and a permeability of the positive electrode 308 may increase with an increasing porosity of the positive electrode 308 (e.g., at least until too little solid material of the positive electrode 308 remains to promote wicking of the electrolyte, such as when a critical porosity of the positive electrode 308 is reached). In some examples, surfaces of the positive electrode 308 may be sufficiently hydrophilic for desirable rebalancing cell operation (e.g., by facilitating thorough electrolyte wetting and thereby forming an ionically conductive medium). In such examples, an overall hydrophilicity of the positive electrode 308 may be increased by coating or treating the surfaces thereof. Further, though at least some of the H2 gas may pass into the positive electrode 308 in addition to a portion of the electrolyte wicked into the positive electrode 308, the positive electrode 308 may be considered a separator between a bulk of the H2 gas thereabove and a bulk of the electrolyte therebelow.
In some examples, each of the positive electrode 308 and the negative electrode 310 may be formed as a continuous monolithic piece (e.g., as opposed to discrete particles or a plurality of pieces), such that interphase mass-transport losses across boundary layer films may be reduced when bringing the electrolyte into contact with the H2 gas at the catalytic surfaces of the negative electrode 310, thereby promoting ionic and proton movement. In contrast, a packed bed configuration including discretely packed catalyst particles may include mass-transport limiting boundary layer films surrounding each individual particle, thereby reducing a rate of mass-transport of the electrolyte from a bulk thereof to surfaces of the particles.
The negative electrode 310 may be positioned in the cavity 326 in face-sharing contact with a side of the positive electrode 308 opposite from the carbon foam 306 along the z-axis, such that a three-phase contact interface between the (wicked) electrolyte, the catalytic surfaces of the negative electrode 310, and the H2 gas may be formed for proton (e.g., H+) and ionic movement (H3O+) therethrough. In tandem, the positive electrode 308 may reduce an overall electronic resistance by providing a conductive path for electrons to move into the electrolyte front and reduce Fe3+ ions thereat.
In an exemplary embodiment, the negative electrode 310 may be a porous non-conductive material or a conductive carbon substrate with a metal catalyst coated thereon. In some examples, the porous non-conductive material may include polytetrafluoroethylene (PTFE), polypropylene, or the like. In some examples, the conductive carbon substrate may include carbon cloth or carbon paper. In some examples, the metal catalyst may include a precious metal catalyst. In some examples, the precious metal catalyst may include Pt. In additional or alternative examples, the precious metal catalyst may include Pd, Rh, Ru, Ir, Ta, or alloys thereof. In some examples, a relatively small amount (e.g., 0.2 to 0.5 wt %) of the precious metal catalyst supported on the conductive carbon substrate may be employed for cost considerations. In practice, however, the amount of the precious metal catalyst is not particularly limited and may be selected based on one or more of a desired rate of reaction for the rebalancing cell and an expected lifetime of the rebalancing cell. Furthermore, alloys included in the precious metal catalyst may be utilized to reduce cost and increase a corrosion stability of the precious metal catalyst. For example, 10% addition of Rh to Pt may reduce corrosion of Pt by Fe3+ by over 98%. In other examples, the metal catalyst may include a non-precious metal catalyst selected for stability in ferric solution and other such acidic environments (e.g., molybdenum sulfide). In one example, the negative electrode 310 may include carbon cloth coated with 1.0 mg/cm2 Pt and may include a microporous layer bound with a polytetrafluoroethylene (PTFE) binder (e.g., for hydrophobicity). Indeed, inclusion of the PTFE binder may increase a durability of rebalancing cell performance over extended durations relative to electrode assemblies formed using other binders.
In some examples, such as when the precious metal catalyst includes Pt, soaking of the negative electrode 310 may eventually result in corrosion of the precious metal catalyst. In other examples, and as discussed in greater detail above with reference to
In an exemplary embodiment, the electrode assembly 304, including each of the carbon foam 306, the positive electrode 308, and the negative electrode 310, may be under compression along the z-axis, with the positive electrode 308 having a greater deflection than the carbon foam 306 and the negative electrode 310 under a given compressive pressure. Accordingly, a depth of the cavity 326 may be selected based on a thickness of the carbon foam 306, a thickness of the positive electrode 308, a desired compression of the positive electrode 308, and a thickness of the negative electrode 310. Specifically, the depth of the cavity 326 may be selected to be greater than a lower threshold depth of a sum of the thickness of the carbon foam 306 after substantially complete compression thereof and the thickness of the positive electrode 308 after substantially complete compression thereof (to avoid overstressing and crushing of the carbon foam 306, which may impede electrolyte flow) and less than an upper threshold depth of a sum of the thickness of the carbon foam 306 and the thickness of the positive electrode 308 (to avoid zero compression of the positive electrode 308 and possibly a gap, which may result in insufficient contact of the H2 gas and the electrolyte). For instance, in an example wherein the thickness of the carbon foam 306 is 6 mm, the thickness of the positive electrode 308 is 3.4 mm, the desired compression of the positive electrode 308 is 0.4 mm (so as to achieve a desired compressive pressure of 0.01 MPa), and the thickness of the negative electrode 310 is 0.2 mm, the depth of the cavity 326 may be 9.2 mm (=3.4 mm+6 mm+0.2 mm−0.4 mm). As another example, the thickness of the carbon foam 306 may be between 2 and 10 mm, the thickness of the positive electrode 308 may be between 1 and 10 mm, the desired compression of the positive electrode 308 may be between 0 and 2.34 mm (so as to achieve the desired compressive pressure of 0 to 0.09 MPa), and the thickness of the negative electrode 310 may be between 0.2 and 1 mm, such that the depth of the cavity 326 may be between 0.86 and 21 mm. In additional or alternative examples, the thickness of the positive electrode 308 may be 20% to 120% of the thickness of the carbon foam 306. In one example, the thickness of the positive electrode 308 may be 100% to 110% of the thickness of the carbon foam 306. In one example, the depth of the cavity 326 may further depend upon a crush strength of the carbon foam 306 (e.g., the depth of the cavity 326 may be increased with decreasing crush strength). For instance, a foam crush factor of safety (FOS) may be 5.78 when the depth of the cavity 326 is 9.2 mm (e.g., when the desired compression of the positive electrode is 0.4 mm). The foam crush FOS may have a minimum value of 0.34 in some examples, where foam crush FOS values less than 1 may indicate that at least some crushing is expected. In some examples, the crush strength of the carbon foam 306 may be reduced by heat treatment of the carbon foam 306 during manufacturing thereof (from 0.08 MPa to 0.03 MPa, in one example). It will be appreciated that the electrode assembly 302 may be configured such that the depth of the cavity 326 is as low as possible (e.g., within the above constraints), as generally thinner electrode assemblies 302 may result in a reduced overall size of the rebalancing cell and a reduced electrical resistance across the electrode assembly 302 (e.g., as the electrolyte flow may be closer to the negative electrode 310).
In this way, the electrode assembly 302 may include a sequential stacking of the carbon foam 306 and an interfacing pair of the positive electrode 308 and the negative electrode 310 being in face-sharing contact with one another and being continuously electrically conductive. Specifically, a first interface may be formed between the positive electrode 308 and the carbon foam 306 and a second interface may be formed between the positive electrode 308 and the negative electrode 310, the second interface being opposite to the first interface across the positive electrode 308, and each of the carbon foam 306, the positive electrode 308, and the negative electrode 310 may be electrically conductive. Accordingly, the electrode assembly 302 may be internally shorted, such that electric current flowing through the electrode assembly 302 may not be channeled through an external load.
In an exemplary embodiment, and as discussed above, forced convection may induce flow of the H2 gas into the electrode assembly 302 and across the negative electrode 310 (e.g., via a flow field plate interfacing with the negative electrode 310; not shown at
½H2→H++e− (anodic half reaction) (4a)
The proton (H+) and the electron (e−) may be conducted across the negative electrode 310 and into the positive electrode 308. The electrolyte, directed through the electrode assembly 302 via the carbon foam 306, may be wicked into the positive electrode 308. At and near the second interface between the positive electrode 308 and the negative electrode 310, Fe3+ in the electrolyte may be reduced via equation (4b):
Fe3++e−→Fe2+ (cathodic half reaction) (4b)
Summing equations (4a) and (4b), the electrolyte rebalancing reaction may be obtained as equation (4):
Fe3++½H2→Fe2++H+ (electrolyte rebalancing) (4)
Since the electrode assembly 302 is internally shorted, a cell potential of the electrode assembly 302 may be driven to zero as:
0=(Epos−Eneg)−(ηact+ηmt+ηohm) (7)
where Epos is a potential of the positive electrode 308, Eneg is a potential of the negative electrode 310, ηact is an activation overpotential, ηmt is a mass transport overpotential, and ηohm is an ohmic overpotential. For the electrode assembly 302 as configured in
ηohm=ηelectrolyte+ηfelt (8)
Accordingly, performance of the electrode assembly 302 may be limited at least by an electrical resistivity σelectrolyte of a the electrolyte and an electrical resistivity σfelt of the carbon felt. The electrical conductivity of the electrolyte and the electrical conductivity of the carbon felt may further depend on a resistance Relectrolyte of the electrolyte and a resistance Rfelt of the carbon felt, respectively, which may be given as:
R
electrolyte=σelectrolyte×telectrolyte/Aelectrolyte (9)
R
felt=σfelt×tfelt/Afelt (10)
where telectrolyte is a thickness of the electrolyte (e.g., a height of the electrolyte front), tfelt is a thickness of the carbon felt (e.g., the thickness of the positive electrode 308), Aelectrolyte is an active area of the electrolyte (front), and Afelt is an active area of the carbon felt. Accordingly, the performance of the electrode assembly 302 may further be limited based on a front location of the electrolyte within the carbon felt and therefore the distribution of the electrolyte across the carbon foam 306 and an amount of the electrolyte wicked into the carbon felt forming the positive electrode 308.
After determining Relectrolyte and Rfelt, an electric current Iassembly of the electrode assembly 302 may be determined as:
I
assembly=(Epos−Eneg)/(Relectrolyte+Rfelt) (11)
and a rate vrebalancing of the electrolyte rebalancing reaction (e.g., the rate of reduction of Fe3+) may further be determined as:
v
rebalancing
=I
assembly/(nFArebalancing) (12)
where n is a number of electrons flowing through the negative electrode 310, F is Faraday's constant, and Arebalancing is an active area of the electrolyte rebalancing reaction (e.g., an area of an interface between the electrolyte front and the negative electrode 310). As an example, for an uncompressed carbon felt having tfelt=3 mm, vrebalancing may have a maximum value of 113 mol/m2 hr.
Referring now to
As shown, and as indicated by arrows 408a, the H2 gas may enter the hydrogen gas inlet channel 404 via the hydrogen gas inlet port 210, flowing first into the hydrogen gas inlet plenum 406 and then sequentially through the hydrogen gas channel inlet sections 318a in a positive direction along the z-axis. A size and a shape of the hydrogen gas inlet plenum 406 is not particularly limited, though a minimum size (e.g., a minimum volume, a minimum flow path width) of the hydrogen gas inlet plenum 406 may be selected to avoid relatively high flow velocity and pressure drop resulting in poor H2 gas distribution. Further, the sloped support 220 may tilt the rebalancing cell 202 such that the hydrogen gas inlet channel 404 extends along the positive direction of the z-axis away from a direction of gravity (though not directly opposite to the direction of gravity, as discussed in detail above with reference to
As further shown, and as indicated by arrows 408b, at least some of the H2 gas may flow from the hydrogen gas inlet channel 404 across the hydrogen gas inlet channel seal insert 320a of each respective electrode assembly 302 and into one or more hydrogen gas inlet passages 452 fluidically coupled to the hydrogen gas inlet channel 404 and interfacing with each respective electrode assembly 302. In this way, each electrode assembly 302 included in the electrode assembly stack 402 may be fluidically coupled to each other electrode assembly stack 302 included in the electrode assembly stack 402 via the hydrogen gas inlet channel 404. In one example, a surface of the hydrogen gas inlet channel seal insert 320a of a given electrode assembly 302 opposite to the one or more hydrogen gas inlet passages 452 of the given electrode assembly 302 may be coincident with the same x-y plane as a surface of the negative electrode 310 of the given electrode assembly 302 opposite to the one or more hydrogen gas inlet passages 452 of the given electrode assembly. Further, in some examples, the hydrogen gas inlet channel seal insert 320a of the given electrode assembly 302 may extend from a locus of affixation or coupling with the plate 304 of the given electrode assembly 302 and partially overlap the positive electrode 308 of the given electrode assembly 302 along the z-axis, thereby assisting in sealing the positive electrode 308 at an edge thereof.
In an exemplary embodiment, the one or more hydrogen gas inlet passages 452 may not be wholly included in any given electrode assembly 302 and instead may be formed as one or more gaps between adjacent pairs of electrode assemblies 302 in the electrode assembly stack 402. In some examples, the one or more hydrogen gas inlet passages 452 interfacing with a given electrode assembly 302 may be configured in a flow field configuration, such that the H2 gas may be forcibly convected into the one or more hydrogen gas inlet passages 452 interfacing with the given electrode assembly 302. Specifically, and as described in detail below with reference to
In some examples, and as described in detail below with reference to
As further shown, and as indicated by arrows 408c, the H2 gas may be convected across the negative electrodes 310 of the electrode assembly stack 402 (e.g., at a flow rate of 10 to 50 l/min per m2 of the catalytic surfaces of the negative electrode 310). In some examples, the flow field plates interfacing with the respective electrode assemblies 302 may assist in the convection and distribute the H2 gas across the respective negative electrodes 310. The H2 gas may react with the catalytic surfaces of the negative electrodes 310 of the electrode assembly stack 402 in an anodic half reaction (see equation (4a)) to generate protons and electrons, which may then flow towards respective positive electrodes 308 and carbon foams 306. In some examples, at least some of the H2 gas may remain unreacted and may flow across the negative electrodes 310 of the electrode assembly stack 402 along the arrows 408c as well.
Referring now to
As shown in the schematic view 500 of
As shown in the schematic view 520 of
As shown in the schematic view 540 of
As shown in the schematic view 560 of
Referring now to
The electrolyte may enter the electrolyte inlet plenum 606a via the electrolyte inlet port, wherefrom the electrolyte may be directed into the one or more electrolyte inlet channels 614 via the one or more orifices 612, respectively. In some examples, a cross-sectional shape of the electrolyte inlet plenum 606a may be selected for ease of machining. As an example, the cross-sectional shape of the electrolyte inlet plenum 606a may be rectangular. As another example, the cross-sectional shape of the electrolyte inlet plenum 606a may be circular. A size of the electrolyte inlet plenum 606a may be selected to realize a relatively low pressure drop upon entry of the electrolyte into the rebalancing cell 202.
In some examples, a size of each of the one or more orifices 612 may be between 3 and 10 mm, as dependent on a total number of electrode assemblies 302 in the electrode assembly stack 402, an overall size of the rebalancing cell 202, and an electrolyte flow path design. The size and overall configuration of each of the one or more orifices 612 may be selected to maintain substantially even electrolyte flow throughout each electrode assembly 302 of the electrode assembly stack 402.
In some examples, each of the one or more electrolyte inlet channels 614 may be a continuous and unbroken channel configured adjacent to the electrode assembly stack 402. In other examples, each electrode assembly 302 of the electrode assembly stack 402 may include one or more electrolyte inlet channel sections corresponding to the one or more electrolyte inlet channels 614, respectively. In such examples, the electrode assemblies 302 of the electrode assembly stack 402 may be aligned such that the one or more electrolyte inlet channel sections of each electrode assembly 302 respectively form the one or more electrolyte inlet channels 614 with the one or more electrolyte inlet channel sections of each other electrode assembly 302.
In some examples, the one or more electrolyte inlet channels 614 may include a plurality of electrolyte inlet channels 614 and the one or more orifices 612 may include a plurality of orifices 612 respectively fluidically coupled to the plurality of electrolyte inlet channels 614, such that an electrolyte inlet manifold may be formed. In the cross-sectional view 600 of
In some examples, the electrolyte entering the electrolyte inlet plenum 606a may have an adjustable flow rate (e.g., by a controller of the redox flow battery system, such as the controller 88 of
In other examples, each of the plurality of electrolyte inlet channels 614 may be fluidically coupled to each and every electrode assembly 302 of the electrode assembly stack 402 so as to evenly distribute the electrolyte across the electrode assembly stack 402 with respect to both the x- and y-axes. In alternative examples, the one or more electrolyte inlet channels 614 may include only one electrolyte inlet channel 614 which may be fluidically coupled to each and every electrode assembly 302 of the electrode assembly stack 402.
In some examples, a cross-sectional shape of each of the one or more electrolyte inlet channels 614 may be a circle. However, the cross-sectional shape of each of the one or more electrolyte inlet channels 614 is not particularly limited and other geometric shapes may be employed. A size of each of the one or more electrolyte inlet channels 614 may be selected to realize a relatively low pressure drop for the electrolyte flow rate of ˜10-40 L/min per m2 of the catalytic surfaces of the negative electrode 310 (e.g., relatively small sizes may result in poor distribution of the electrolyte) while maintaining practical size considerations of the rebalancing cell 202 as a whole (e.g., relatively large sizes may result in an undesirably large rebalancing cell 202). In one example, the cross-sectional shape of each of the one or more electrolyte inlet channels 614 may be a circle having a diameter of between 10 and 30 mm.
Upon entering the one or more electrolyte inlet channels 614, a pressure therein may be substantially similar to a pressure of an electrolyte source (e.g., the negative and positive electrode compartments 22 and 20 and/or the integrated multi-chambered electrolyte storage tank 110 of
As further shown, and as indicated by arrows 608c, while flowing through the carbon foams 306 of the electrode assembly stack 402, at least some of the electrolyte may be induced into the positive electrodes 308 of the electrode assembly stack 402 towards the negative electrodes 310 of the electrode assembly stack 402 via capillary action. Fe3+ ions in the electrolyte may be reduced by electrons flowing through the negative electrodes 310 of the electrode assembly stack 402 in a cathodic half reaction (see equation (4b)) to generate Fe2+ ions. For each electrode assembly 302 of the electrode assembly stack 402, to ensure that no gap is present between the positive electrode 308 and the negative electrode 310 (which may result in a decreased Fe3+ reduction rate), a depth 652 of the cavity (e.g., the cavity 326 of
As further shown, and as indicated by arrows 608d, after flowing through the carbon foams 306 of the electrode assembly stack 402, the electrolyte may be directed through electrolyte outlet passages 658 of the electrode assembly stack 402, into the electrolyte outlet channel 604, and out through the electrolyte outlet port 208 therefrom. Specifically, for each given electrode assembly 302 of the electrode assembly stack 402, the electrolyte may flow from the carbon foam 306 through the electrolyte outlet passage 658 and into the electrolyte outlet channel section 316, wherefrom the electrolyte may flow with the direction of gravity (e.g., along the positive direction of the axis g) into the electrolyte outlet plenum 606b (after passing through any further electrolyte outlet channel sections 316 interposed between the given electrode assembly 302 and the electrolyte outlet plenum 606b). The electrolyte may then pass through the electrolyte outlet plenum 606b and into the electrolyte outlet port 208, wherefrom the electrolyte may be expelled from the rebalancing cell 202. In this way, the electrolyte may be directed from the electrolyte inlet port (e.g., the electrolyte inlet port 206 of
In some examples, an overall size of each of the electrolyte outlet passages 658 may be selected so as to be sufficiently large to generate a suitable pressure drop and to not overfill the electrolyte outlet plenum 606b (which may flood the electrode assemblies 302 at a bottom of the electrode assembly stack 402 with respect to the z-axis). Accordingly, in such examples, the overall size of each of the electrolyte outlet passages 658 may depend on an overall size of the electrolyte outlet plenum 606b and an overall number of openings corresponding to the electrolyte outlet port 208. In other examples, dimensions of the electrolyte outlet plenum 606b may be larger to accommodate an electrolyte outlet port 208 having fewer, larger openings. In examples wherein the electrolyte outlet port 208 is positioned on the face of the cell enclosure 204 facing the negative direction of the z-axis, larger openings may be accommodated while maintaining a thickness of a lowest electrode assembly 302 along the z-axis and the pressure drop may be further reduced (e.g., as the electrolyte would not flow at a ˜90° angle from the electrolyte outlet plenum 606b to the electrolyte outlet port 208).
As further shown, flow field plates 626 may respectively interface with the electrode assemblies 302 of the electrode assembly stack 402. In some examples, the flow field plate 626 may interface (e.g., be in face-sharing contact) with the negative electrode 310 of a given electrode assembly 302 and may be integrally formed in the plate 304 of an adjacent electrode assembly 302, positioned beneath the carbon foam 306 of the adjacent electrode assembly 302 with respect to the z-axis. In other examples, the flow field plate 626 interfacing with the negative electrode 310 of the given electrode assembly 302 may be a separate, removable component. Additionally, and as further shown, a topmost flow field plate 626 with respect to the z-axis may not be integrally formed with any electrode assembly 302 and may instead be included in the rebalancing cell 202 as either a separate, removable component or an integral feature of another component (e.g., the cell enclosure 204 of
In an exemplary embodiment, the one or more hydrogen gas inlet passages 452, configured to flow the H2 gas across a given electrode assembly 302, may be formed from the flow field plate 626 interfacing with the negative electrode 310 of the given electrode assembly 302. For instance, the one or more hydrogen gas inlet passages 452 may be configured as either a plurality of hydrogen gas inlet passages 452 parallel to one another and the x-axis (e.g., in the interdigitated flow field configuration or the partially interdigitated flow field configuration) or a single, coiled hydrogen gas inlet passage 452 into which the H2 gas may enter parallel to the x-axis (e.g., in the serpentine flow field configuration). In some examples, the one or more hydrogen gas inlet passages 452 may extend parallel to the x-axis while the electrolyte may flow through the carbon foam 306 of the given electrode assembly 302 parallel to the y-axis (as indicated by the arrows 608b). Accordingly, in such examples, the H2 gas may be directed into the electrode assembly stack 402 at a 90° angle from which the electrolyte may be directed into the electrode assembly stack 402.
In additional or alternative examples, the carbon foam 306 of a given electrode assembly 302 may be replaced with a flow field plate of substantially similar flow field configuration to the flow field plate 626. In one such example, the flow field configuration of the flow field plate replacing the carbon foam 306 of the given electrode assembly 302 may be oriented in the same direction as the flow field configuration of the flow field plate 626 with respect to the x- and y-axes. In another such example, the flow field configuration of the flow field plate replacing the carbon foam 306 of the given electrode assembly 302 may be oriented in a different direction as the flow field configuration of the flow field plate 626 (e.g., at a 90° angle, a 180° angle, or a 270° angle) with respect to the x- and y-axes.
Referring now to
As shown, the electrode assembly 702 may include a sequential stacking of a carbon foam 706, a positive electrode 708, and a negative electrode 710 on a plate 704, where the plate 704 may be in face-sharing contact with the carbon foam 706, the carbon foam 706 may be in face-sharing contact with the positive electrode 708, and the positive electrode 708 may be in face-sharing contact with the negative electrode 710. As further shown in the perspective view 750 of
In addition to an electrolyte inlet well 712 for receiving the electrolyte (e.g., from an electrolyte inlet port of the rebalancing cell), the plate 704 may include a plurality of inlets and outlets therethrough for directing flows of the H2 gas and the electrolyte. For example, the plurality of inlets and outlets may include a hydrogen gas inlet channel section 718a for receiving the H2 gas (e.g., from a hydrogen gas inlet port of the rebalancing cell), a hydrogen gas outlet channel section 718b for expelling the H2 gas (e.g., through a hydrogen gas outlet port of the rebalancing cell), and one or more electrolyte outlet passages 716 for expelling the electrolyte (e.g., through one or more electrolyte outlet ports of the rebalancing cell respectively accepted by and fitted to the one or more electrolyte outlet passages 716, the one or more electrolyte outlet ports configured as one or more fusion-welded plumbing flanges in an exemplary embodiment).
As further shown, the electrolyte inlet well 712 may be fluidically coupled to the sequential stacking of the carbon foam 706, the positive electrode 708, and the negative electrode 710 via a plurality of electrolyte inlet passages 714a set in a berm 714b extending parallel to the x-axis. Specifically, the plurality of electrolyte inlet passages 714a may be distributed across the berm 714b, a length of each of the plurality of electrolyte inlet passages 714a extending parallel to the y-axis. In some examples, and as shown in the perspective view 750 of
In some examples, an overall number of the plurality of electrolyte inlet passages 714a may be selected based on a target pressure drop of between 0.5 to 3 mm of electrolyte head rise (which may in turn be a function of an electrolyte flow rate and an overall size of the electrode assembly 702). In some examples, a shape of each of the plurality of electrolyte inlet passages 714a may be rectangular (e.g., for ease of manufacturing). However, the shape of each of the plurality of electrolyte inlet passages 714a is not particularly limited and other geometries may be employed.
In an exemplary embodiment, and as indicated by arrows 708a, the electrolyte inlet well 712 may receive the electrolyte from the electrolyte inlet port (e.g., the electrolyte inlet port 206 of
As further shown in
Referring now to
As shown, the flow field plate 826 may be formed in the plate 804 adjacent to an electrolyte outlet channel section 816 of the plate 804 and in fluidic communication with each of a hydrogen gas inlet channel section 818a and a hydrogen gas outlet channel section 818b of the plate 804. Specifically, the flow field plate 826 may include a plurality of inlet passages 852a, each of the plurality of inlet passages 852a being fluidically coupled to the hydrogen gas inlet channel section 818a. The flow field plate 826 may further include a plurality of outlet passages 852b, each of the plurality of outlet passages 852b being fluidically coupled to a hydrogen gas outlet channel section 818b of the plate 804. As further shown, the plurality of inlet passages 852a may be interdigitated with the plurality of outlet passages 852b, each passage of the plurality of inlet passages 852a and the plurality of outlet passages 852b being separated from each of at least one adjacent passage by a passage wall 856. In this way, the flow field plate 826 may be considered to be configured as an interdigitated flow field configuration (however, it will be appreciated that the flow field plate 826 may be configured as an alternative flow field configuration, such as a partially interdigitated flow field configuration or a serpentine flow field configuration). Specifically, the plurality of inlet passages 852a may extend along a positive direction of the x-axis, while the plurality of outlet passages 852b may extend along a negative direction of the x-axis, each passage of the plurality of inlet passages 852a and the plurality of outlet passages 852b terminating at an end wall 854.
As shown in the cross-sectional view 875 of
In an exemplary embodiment, the flow field plate 826 may be integrally formed in the electrode assembly 802 opposite to a surface 868 of the plate 804 with respect to the z-axis, the surface 868 including a sequential stacking of a carbon foam, a positive electrode, and a negative electrode (not shown at
As further shown in the cross-sectional view 875 of
In additional or alternative examples, the carbon foam 306 of
Referring now to
In some examples, the sloped support 220 may be formed from a relatively lightweight material. For instance, the sloped support 220 may be formed from a non-corrosive material with relatively high strength-to-weight ratio and impact strength and relatively low friction. In one example, the sloped support 220 may be formed from high-density polyethylene (HDPE).
In some examples, the sloped support 220 may be adjustable in that the angle 222 may be adjusted to level the cell enclosure of the rebalancing cell (not shown at
Referring now to
As further shown in plot 1000, curves 1002, 1004, and 1006 represent the Fe3+ reduction rates for the various rebalancing cells. Specifically, curve 1002 represents an average Fe3+ reduction rate for a typical jelly roll rebalancing reactor, curve 1004 represents an average Fe3+ reduction rate for a first exemplary rebalancing cell, and curve 1006 represents an average Fe3+ reduction rate for a second exemplary rebalancing cell. Each of the first and second exemplary rebalancing cells include a stack of internally shorted electrode assemblies through which H2 gas flows via convection and electrolyte flows via gravity feeding and capillary action. Each of the internally shorted electrode assemblies of the first and second exemplary rebalancing cells may include a sequential stacking of a carbon foam, a positive electrode, and a negative electrode. However, the negative electrodes of the first exemplary rebalancing cell include a Nafion™ binder, whereas the negative electrodes of the second exemplary rebalancing cell include a PTFE binder.
Regardless of which binder is included in the negative electrodes of the first and second exemplary rebalancing cells, both exhibit significantly improved Fe3+ reduction rates as compared to the typical jelly roll rebalancing reactor [which exhibits the average Fe3+ reduction rate of less than 5 mol/m2 hr (as indicated by curve 1002)]. For the first exemplary rebalancing cell, the average Fe3+ reduction rate may initially be ˜60 mol/m2 hr (as indicated by curve 1004) and for the second exemplary rebalancing cell, the Fe3+ reduction rate may be consistently at or above 50 mol/m2 hr (as indicated by curve 1006). However, the average Fe3+ reduction rate for the first exemplary rebalancing cell may deteriorate during extended use (as measured by the total amount of Fe3+ reduced). For example, the average Fe3+ reduction rate of the first exemplary rebalancing cell may deteriorate to less than 20 mol/m2 hr after about 3000 mol/m2 total Fe3+ is reduced (as indicated by curve 1004). However, the second exemplary rebalancing cell is shown to maintain Fe3+ reduction performance beyond 16000 mol/m2 total Fe3+ reduced. In this way, when the PTFE binder is employed in manufacturing the negative electrodes for rebalancing cells instead of the Nafion™ binder, a higher cell durability may be achieved, such that higher Fe3+ reduction rates may be consistently realized over extended operation of the rebalancing cells. Without wishing to be bound by theory, such differences in durability may be ascribed to lower salt buildup (which may prevent H2 gas from reaching catalytic surfaces of negative electrodes in the exemplary rebalancing cells), chloride poisoning of the catalytic surfaces of the negative electrodes, and/or water buildup in pores of the negative electrodes.
Referring now to
In an exemplary embodiment, the redox flow battery system may be the redox flow battery system of any of
At 1102, method 1100 may include receiving a power ON request. In one example, an operator of the redox flow battery pack may manually request active operation (e.g., initiation of electrolyte flow, initiation of H2 gas flow, and/or activation of auxiliary systems, such as heaters, pumps, etc., may be requested) of the redox flow battery pack. In another example, an external controller (e.g., associated with an external electrical system or load, such as the electrical grid) may request active operation of the redox flow battery pack. In some examples, active operation of the redox flow battery pack may include operating the redox flow battery pack in a charge mode, a discharge mode, or an idle mode. For example, when a desired power output is requested for the electrical grid (e.g., by the external controller), the redox flow battery pack may be operated in the discharge mode. Accordingly, in additional or alternative examples, at 1102, method 1100 may at least include receiving a request to switch to the discharge mode (e.g., from an inactive state or from the charge or idle modes).
At 1104, method 1100 may include circulating or cycling the electrolyte and the H2 gas through each of the plurality of redox flow batteries of the redox flow battery pack at the low internal pressure. Specifically, the low internal pressure may include the maximum pressure of the electrolyte and H2 gas within each of the plurality of redox flow batteries being maintained less than the threshold pressure (accordingly, the threshold pressure may correspond to a similarly low pressure). In one example, the threshold pressure may be 5 psi. In another example, the threshold pressure may be 2 psi. In another example, the threshold pressure may be 1 psi. Such low pressures may be achieved by fluidically coupling, within each of the plurality of redox flow batteries, a redox flow battery cell to a rebalancing cell configured to rebalance the electrolyte at a correspondingly low H2 gas partial pressure. As discussed above, in some examples, each of the plurality of redox flow batteries may be fluidically isolated from each other of the plurality of redox flow battery batteries. Accordingly, components within a given redox flow battery of the plurality of redox flow batteries (e.g., an electrolyte storage tank, a redox flow battery cell, a rebalancing cell, etc.) may be fluidically coupled to one another, but may be fluidically isolated from analogous components in each other of the plurality of redox flow batteries. For example, and as discussed in detail below with reference to
In an exemplary embodiment, each of the rebalancing cells respectively included in the plurality of redox flow batteries may be the rebalancing cell of
By fluidically isolating the plurality of redox flow batteries from one another and by internally electrically shorting the electrode assemblies of the rebalancing cells respectively included in the plurality of redox flow batteries in this way, excess coupling elements (e.g., piping flange fittings, electrical couplings, etc.) between the plurality of redox flow batteries may be minimized and series electrically coupling of the redox flow battery cells respectively included in the plurality of redox flow batteries may be facilitated. In an exemplary embodiment, the redox flow battery cells may be electrically coupled in series to one another and to the power inverter.
Accordingly, at 1106, method 1100 may include circulating or cycling an electric current across the redox flow battery cells respectively included in the plurality of redox flow batteries and the power inverter. Specifically, as each of the redox flow battery cells may be operated at a potential difference of 40 to 75 V and the power inverter may be operated at a potential difference of 600 to 1000 V. Accordingly, by electrically coupling the redox flow battery cells in series, the potential difference thereacross may be ramped up such that first and last redox flow battery cells of the series electrical coupling may be directly electrically coupled to the power inverter without any intervening voltage boosting components (e.g., without any DC-to-DC boost converter). In this way, the redox flow battery pack may be configured with less components, lower cost, and less complexity as compared to a redox flow battery pack including redox flow battery cells fluidically and electrically coupled in parallel.
At 1108, method 1100 may include reversible flowing the electric current between the power inverter and the electrical grid. As such, the (series coupled) redox flow battery cells respectively included in the plurality of redox flow batteries may be configured to provide power to a high-voltage system, such as the electrical grid, via the power inverter.
At 1110, method 1100 may include determining whether a power OFF request has been received. In one example, the operator of the redox flow battery pack may manually request inactive operation (e.g., ceasing of electrolyte flow, ceasing of H2 gas flow, and/or deactivation of auxiliary systems, such as heaters, pumps, etc., may be requested) of the redox flow battery pack. In another example, the external controller (e.g., associated with the external electrical system or load, such as the electrical grid) may request inactive operation of the redox flow battery pack. In some examples, inactive operation of the redox flow battery pack may include not operating the redox flow battery pack or operating the redox flow battery pack outside of the charge mode, the discharge mode, and the idle mode. For example, when the desired power output has been received by the electrical grid, the redox flow battery pack may be requested (e.g., by the external controller) to cease operating in the discharge mode. Accordingly, in additional or alternative examples, at 1110, method 1100 may at least include determining whether a request to switch from the discharge mode (e.g., to the inactive state or to the charge or idle modes) has been received. If the power OFF request is not received, method 1100 may return to 1104, where the electrolyte and the H2 gas may continue to be circulated across each of the plurality of redox flow batteries (e.g., such that the electric current may continue to circulate across the redox flow battery cells respectively included in the plurality of redox flow batteries and the power inverter and thereby provide power to the electrical grid). If the power OFF request is received, method 1100 may proceed to 1112, where method 1100 may include ceasing circulating the electrolyte and the H2 gas, and thereby the electric current (e.g., responsive to the power OFF request being received).
Referring now to
In an exemplary embodiment, the redox flow battery pack may be the redox flow battery system of any of
At 1132, method 1130 may include initiating pumping of the electrolyte from the electrolyte storage tank via the at least one electrolyte pump (e.g., the positive and negative electrolyte pumps). In one example, initiating pumping of the electrolyte may be responsive to receipt of a power ON request and/or a request to switch to a discharge mode (e.g., at 1102 of method 1100, as described in detail above with reference to
At 1134, method 1130 may include circulating the electrolyte and the H2 gas through the redox flow battery at the low internal pressure. Specifically, at 1136, method 1130 may include flowing the electrolyte through the electrolyte storage tank (e.g., from the at least one rebalancing cell and to the at least one electrolyte pump). For example, the positive electrolyte may be flowed through a positive electrolyte chamber of the electrolyte storage tank and the negative electrolyte may be flowed through a negative electrolyte chamber of the electrolyte storage tank. In some examples, the electrolyte storage tank may be rated up to an upper threshold gauge pressure of, for example, approximately 2 psi, as the at least one rebalancing cell may include a stack of internally shorted electrode assemblies and may accordingly utilize less H2 gas to reduce greater amounts of Fe3+ as compared to rebalancing cell setups absent internally electrically shorted pairs of electrodes (see below). In certain examples, the upper threshold gauge pressure may be a maximum pressure capable of being handled by the electrode storage tank due to a shape and/or a composition thereof. Accordingly, in one example, a gauge pressure in the electrolyte storage tank may be maintained below 2 psi (e.g., the upper threshold gauge pressure may be 2 psi). In another example, the gauge pressure in the electrolyte storage tank may be maintained below 1 psi (e.g., the upper threshold gauge pressure may be 1 psi). In other examples, the gauge pressure in the electrolyte storage tank may be maintained below 5 psi (e.g., the upper threshold gauge pressure may be 5 psi). At such low internal pressures, the electrolyte storage tank may be configured in a range of shapes (e.g., non-cylindrical) and sizes, such that a packing density of the electrolyte storage tank may be optimized for inclusion in the redox flow battery pack (e.g., relative to larger, high-pressure, cylindrical electrolyte storage tanks.
At 1138, method 1130 may include pumping the electrolyte via the at least one electrolyte pump (e.g., from the electrolyte storage tank and to the redox flow battery cell). For example, the positive electrolyte may be pumped via the positive electrolyte pump and the negative electrolyte may be pumped via the negative electrolyte pump.
At 1140, method 1130 may include flowing the electrolyte through the redox flow battery cell (e.g., from the at least one electrolyte pump to the at least one rebalancing cell). For example, the positive electrolyte may be flowed through a positive electrode compartment of the redox flow battery cell, wherein Fe3+ in the positive electrolyte may be reduced during the discharge mode (see equation (6)), and the negative electrolyte may be flowed through a negative electrode compartment of the redox flow battery cell, wherein Fe0 may be oxidized and dissolve as Fe2+ in the negative electrolyte during the discharge mode (see equation (5)).
At 1142, method 1130 may include each of flowing the electrolyte through the at least one rebalancing cell (e.g., from the redox flow battery cell and to the electrolyte storage tank) and flowing the H2 gas through the at least one rebalancing cell (e.g., from the electrolyte storage tank or another H2 gas source). For example, the positive electrolyte may be flowed through a positive rebalancing cell and the negative electrolyte may be flowed through a negative rebalancing cell. In an exemplary embodiment, and as discussed in detail below with reference to
In some examples, such as when each rebalancing cell of the at least one rebalancing cell includes a hydrogen gas outlet port, any unreacted H2 gas may flow from the at least one rebalancing cell back to a source of the H2 gas (e.g., the electrolyte storage tank or another H2 gas source). In additional or alternative examples, such as when each rebalancing cell of the at least one rebalancing cell is configured in a dead ended configuration (e.g., including no hydrogen gas outlet port), any unreacted H2 gas may flow across negative electrodes of the at least one rebalancing cell into the electrolyte and may respectively be expelled from the at least one rebalancing cell via at least one pressure release outlet port (e.g., to atmosphere).
Referring now to
At 1162, method 1160 may include receiving the H2 gas and the electrolyte at the rebalancing cell via respective inlet ports thereof. Specifically, the electrolyte may be received at the rebalancing cell via a first inlet port and the H2 gas may be received at the rebalancing cell via a second inlet port. In one example, the first inlet port being positioned above the second inlet port with respect to a direction of gravity.
At 1164, method 1160 may include distributing the H2 gas and the electrolyte throughout the stack of internally shorted electrode assemblies. Specifically, the electrolyte may be distributed via an inlet manifold including a plurality of first inlet channels respectively coupled to the electrode assemblies of the stack of internally shorted electrode assemblies and the H2 gas may be distributed via a second inlet channel formed by the stack of internally shorted electrode assemblies and fluidically coupled to each electrode assembly of the stack of internally shorted electrode assemblies. In some examples, after distribution via the inlet manifold, the electrolyte may be distributed through first flow field plates respectively interfacing with positive electrodes of the stack of internally shorted electrode assemblies. In other examples, after distribution via the inlet manifold, the electrolyte may be distributed through activated carbon foams respectively interfacing with the positive electrodes. In some examples, after distribution via the second inlet channel, the H2 gas may be distributed through second flow field plates respectively interfacing with negative electrodes of the stack of internally shorted electrode assemblies.
At 1166, method 1160 may include inducing flows (e.g., crosswise, parallel, or opposing flows) of the H2 gas and the electrolyte at the low internal pressure to perform an electrolyte rebalancing reaction at the negative and positive electrodes of the stack of internally shorted electrode assemblies. The negative and positive electrodes may be distributed among the stack of internally shorted electrode assemblies in interfacing pairs of negative and positive electrodes. As discussed above, each positive electrode of the interfacing pairs of negative and positive electrodes may further interface with a respective activated carbon foam or a respective first flow field plate. In one example, the negative electrode may be a conductive carbon substrate having a Pt catalyst coated thereon and the positive electrode may be a carbon felt. In some examples, inducing flows of the H2 gas and the electrolyte at the low internal pressure may include: (i) at 1168, inducing flow of the H2 gas across the negative electrodes of the stack of internally shorted electrode assemblies via convection (e.g., forced convection via the second flow field plates interfacing with the negative electrodes of the stack of internally shorted electrode assemblies); and (ii) at 1170, inducing flow of the electrolyte across the positive electrodes of the stack of internally shorted electrode assemblies via one or more of gravity feeding (e.g., by tilting the rebalancing cell relative to a direction of gravity), capillary action (e.g., wicking up the electrolyte into the positive electrodes of the stack of internally shorted electrode assemblies), and convection (e.g., forced convection via the first flow field plates interfacing with the positive electrodes of the stack of internally shorted electrode assemblies). In one example, the flow of H2 gas may be induced across the negative electrodes at the low internal pressure by convection and the flow of the electrolyte may be induced across the positive electrodes at the low internal pressure by each of gravity feeding and capillary action. Upon flowing the H2 gas and the electrolyte across the negative and positive electrodes of the stack of internally shorted electrode assemblies, the electrolyte rebalancing reaction may be performed, including, at 1172, reacting the H2 gas with positively charged ions in the electrolyte to reduce the positively charged ions (see equation (4)). When the rebalancing cell is configured as described herein, a partial pressure of the H2 gas may be maintained at a relatively low value (e.g., below a threshold partial pressure, such as 25%) while still achieving sufficiently high reduction of the positively charged ions, such that the low internal pressure may be maintained correspondingly low, e.g., below the threshold pressure. As an example, the threshold pressure may be 5 psi. As another example, the threshold pressure may be 2 psi. As another example, the threshold pressure may be 1 psi.
At 1174, method 1160 may include expelling the electrolyte (having the reduced positively charged ions, e.g., a lower concentration of Fe3+ than upon being received at the first inlet port at 1162) and any unreacted H2 gas from the rebalancing cell via outlet ports thereof. Specifically, at 1176, the electrolyte may be expelled from the rebalancing cell via a first outlet port and, in some examples, at 1178, the unreacted H2 gas may be expelled from the rebalancing cell via a second outlet port. However, in other examples, the rebalancing cell may include a dead ended configuration for flowing the H2 gas and no second outlet port may be included. In either case, at least some unreacted H2 gas may flow through the negative electrodes of the stack of internally shorted electrode assemblies and into the electrolyte. Accordingly, expelling the unreacted H2 gas from the rebalancing cell may include, at 1180, expelling the unreacted H2 gas in the electrolyte via a pressure release outlet port (e.g., to prevent pressure from building up in the electrolyte and flooding the negative electrodes of the stack of internally shorted electrode assemblies).
Referring now to
Curve 1202 indicates that up to the H2 gas partial pressure of 25% (e.g., dashed line 1204), the Fe3+ reduction rate rises relatively sharply with increasing H2 gas partial pressure. However, at H2 gas partial pressures above 25%, the Fe3+ reduction rate levels off (maxing out at ˜150% at an H2 gas partial pressure of 100%) with increasing H2 gas partial pressure (specifically, and as shown, at H2 gas partial pressures above 25%, the normalized Fe3+ rate may be maintained greater than 100%). As such, the exemplary rebalancing cell may be operated as low as the H2 gas partial pressure of 25% with relatively little impact on the normalized Fe3+ rate (that is, an electrolyte may be sufficiently rebalanced by the rebalancing cell at the H2 gas partial pressure of 25% to achieve expected electrochemical performance of the all-iron hybrid redox flow battery system).
Referring now to
As shown in the schematic perspective view 1300 of
However, in some examples, and as shown in the schematic perspective view 1300, at least one of the circular base and circular top faces of the external housing 1308 may be a flat surface configured to flushly and interchangeably receive another flat surface, such as on an electrode assembly stack of a redox flow battery cell of the exemplary redox flow battery system (not shown at
As shown in the schematic perspective view 1320 of
For example, at least one edge of the external housing 1328 may be respectively flushly aligned with and received by (e.g., in physical contact with) at least one interior edge of the outer housing 1302, such that at least two faces forming the at least one edge of the external housing 1328 may respectively flushly receive (e.g., be positioned in physical contact with) at least two of the internal surfaces 1304 forming the at least one interior edge of the outer housing 1302. In some examples, and as shown in the schematic perspective view 1320, each of the at least two faces of the external housing 1328 forming the at least one edge of the external housing 1328 may be a flat surface configured to flushly and interchangeably receive another flat surface, such as on an electrode assembly stack of a redox flow battery cell of the exemplary redox flow battery system (not shown at
As respectively shown in the schematic perspective view 1340 of
For example, at least one edge of the at least one external housing 1348 may be respectively flushly aligned with and received by (e.g., in physical contact with) at least one interior edge of the outer housing 1302, such that at least two faces forming the at least one edge of the at least one external housing 1348 may respectively flushly receive (e.g., be positioned in physical contact with) at least two of the internal surfaces 1304 forming the at least one interior edge of the outer housing 1302. In some examples, and as shown in each of the schematic perspective views 1340 and 1360, each of the at least two faces of the at least one external housing 1348 may be a flat surface configured to flushly and interchangeably receive another flat surface, such as on an electrode assembly stack 1362 of a redox flow battery cell of the exemplary redox flow battery system (e.g., one of flat surfaces 1364), a flat surface of another electrolyte storage tank 1346 of the exemplary redox flow battery system (e.g., a face of the external housing 1348 of another electrolyte storage tank 1346), and the internal surface 1304. Accordingly, in one example, at least one face of the external housing 1348 may be parallel to at least one face of the outer housing 1302 (and/or the at least one flat surface 1364 corresponding to the electrode assembly stack 1362 and/or at least one face of another electrolyte storage tank 1346). In this way, by configuring the external housing 1348 to be prismatic (e.g., rectangular prismatic, such as cuboidal) in shape, at least two faces of the external housing 1348 and at least one edge defined by the at least two faces of the external housing 1348 may extend to a periphery of the outer housing 1302 (e.g., to at least two faces of the internal surface 1304 and at least one interior edge defined by the at least two faces of the internal surface 1304, respectively) with substantially no gap or space therebetween. Further, faces of adjacent pairs of the plurality of electrolyte storage tanks 1346 may be flushly aligned with one another along any of the x-, y-, and z-axes, such that a stackability and an overall compactness of the plurality of electrolyte storage tanks 1346 may be improved.
In one example, and as further shown in the schematic perspective view 1340 of
Each of the external housings 1308, 1328, and 1348 may house a flowing liquid electrolyte and/or gas therein, the flowing liquid electrolyte and/or gas flowing through each of the external housings 1308, 1328, and 1348 via corresponding outlet and inlet ports. Specifically, the outlet ports 1312a, 1332a, and 1352a may be configured to expel the flowing liquid electrolyte and/or gas (as respectively indicated by arrows 1314a, 1334a, and 1354a) from respective interiors of the electrolyte storage tanks 1306, 1326, and 1346 respectively enclosed by the external housings 1308, 1328, and 1348. Similarly, the inlet ports 1312b, 1332b, and 1352b may be configured to respectively receive the flowing liquid electrolyte and/or gas (as respectively indicated by arrows 1314b, 1334b, and 1354b) into the respective interiors of the electrolyte storage tanks 1306, 1326, and 1346 respectively enclosed by the external housings 1308, 1328, and 1348. As such, excepting at the outlet ports 1312a, 1332a, and 1352a and the inlet ports 1312b, 1332b, and 1352b, the external housings 1308, 1328, and 1348 may be hermetically sealed. Further, each of the outlet ports 1312a, 1332a, and 1352a and each of the inlet ports 1312b, 1332b, and 1352b may be fitted with flange fittings such that the flowing liquid electrolyte and/or gas may only enter or exit the interior of each of the electrolyte storage tanks 1306, 1326, and 1346 via piping fluidically coupling the interior to other components of the exemplary redox flow battery system (e.g., electrolyte pumps, redox flow battery cells, rebalancing cells, etc.). As such, the electrolyte storage tanks 1306, 1326, and 1346 may be considered to maintain a continuously pressurized state (e.g., of an electrolyte and/or H2 gas flow path) without leaks.
The walls of each of the external housings 1308, 1328, and 1348 may be manufactured with a wide range of thicknesses and compositions, such that the respective electrolyte storage tanks 1306, 1326, and 1346 may be rated for a correspondingly wide range of pressures. In some examples, a thickness of each wall of each of the external housings 1308, 1328, and 1348 may be greater than a lower threshold thickness, such as 5 mm, and less than an upper threshold thickness, such as 50 mm. In one example, the thickness of each wall of each of the external housings 1308, 1328, and 1348 may be less than 10 mm. In some examples, a composition of each wall of each of the external housings 1308, 1328, and 1348 may be selected from materials ranging in structural strength, including coated metal (e.g., metal coated with PTFE), polyethylene (such as HDPE), polypropylene, reinforced polypropylene, or reinforced fiberglass. In one example, each of the external housings 1308, 1328, and 1348 may be formed from polypropylene. In another example, each of the external housings 1308, 1328, and 1348 may be formed from reinforced polypropylene.
As indicated above, each of the electrolyte storage tanks 1306, 1326, and 1346 may be rated for a wide range of pressures, as dependent on an overall configuration (e.g., shape, relative size, wall thickness, wall composition, etc.) of the external housings 1308, 1328, and 1348. In some examples, each of the electrolyte storage tanks 1306, 1326, and 1346 may be rated up to 20 psi. In one example, each of the electrolyte storage tanks 1306, 1326, and 1346 may be rated up to 2 psi. Accordingly, in such an example, a gauge pressure in each of the electrolyte storage tanks 1306, 1326, and 1346 may be maintained below 2 psi. In another example, the gauge pressure in each of the electrolyte storage tanks 1306, 1326, and 1346 may be maintained below 1 psi. (e.g., each of the electrolyte storage tanks 1306, 1326, and 1346 may be rated up to 1 psi). In another example, the gauge pressure in each of the electrolyte storage tanks 1306, 1326, and 1346 may be maintained below 5 psi (e.g., each of the electrolyte storage tanks 1306, 1326, and 1346 may be rated up to 5 psi).
As further indicated above, the integrated multi-chambered electrolyte storage tank 110 of
It will be appreciated that the various components and features of
Referring now to
As shown in the schematic diagram 1400, the first exemplary redox flow battery system 1402 may include an electrolyte storage tank 1404 (wherein the electrolyte storage tank 1404 may be prismatic in shape, in some examples) which expels and receives an electrolyte along respective electrolyte flow paths 1406a and 1406c. Specifically, the electrolyte may be expelled from the electrolyte storage tank 1404 along the electrolyte flow path 1406a, as pumped therealong via an electrolyte pump 1408. The electrolyte pump 1408 may distribute the electrolyte along an electrolyte flow path 1406b to each of a plurality of electrode assembly stacks 1410 in parallel. In some examples, each of the plurality of electrode assembly stacks 1410 may include one or more redox flow battery cells (each of the one or more redox flow battery cells including a redox electrode and a plating electrode) and a rebalancing cell [the rebalancing cell including a stack of internally shorted electrode assemblies, where no electrical path is present to direct electric current away from the stack of internally shorted electrode assemblies (accordingly, in an exemplary embodiment, the rebalancing cell may be the rebalancing cell 202 of
As the plurality of electrode assembly stacks 1410 may be arranged in a parallel flow configuration, the electrolyte flow paths 1406b and 1406c may include parallel piping lengths fluidically coupled via various piping joints (e.g., tee joints, lateral joints, cross joints, etc.). Accordingly, additional piping lengths and piping joints may be employed to add on further electrode assembly stacks 1410, while removing electrode assembly stacks 1410 may result in a reduction of piping lengths or piping joints, or a replacement of the piping altogether with shorter piping (e.g., where piping lengths cannot be reduced).
As further shown in the schematic diagram 1400, the plurality of electrode assembly stacks 1410 may be respectively electrically coupled (e.g., at positive and negative terminals of each of the one of more redox flow battery cells included therein) to the plurality of DC-to-DC boost converters 1414 in parallel via electrical paths 1412a. The plurality of DC-to-DC boost converters 1414 may further be electrically coupled to the power inverter 1416 via an electrical path 1412b. The power inverter 1416 may further be electrically coupled to the electrical grid 1418 via an electrical path 1412c. In this way, an electric current may reversibly flow between the plurality of electrode assembly stacks 1410 and the electrical grid 1418 via the plurality of DC-to-DC boost converters 1414 and the power inverter 1416.
The plurality of DC-to-DC boost converters 1414 may be included in the first exemplary redox flow battery system 1402 to ramp up an output voltage of each of the plurality of electrode assembly stacks 1410 for compatibility with the power inverter 1416. For example, each of the plurality of electrode assembly stacks 1410 may be operated within a first potential difference range (e.g., 40 to 75 V), while the power inverter 1416 may be operated within a second potential difference range higher than the first potential difference range (e.g., 600 to 1000 V, 850 to 1000 V, etc.). As such, an additional DC-to-DC boost converter 1414 may be included for each electrode assembly stack 1410 which may be added to the first exemplary redox flow battery system 1402.
It will be appreciated that, in the first exemplary redox flow battery system 1402, and as shown in the schematic diagram 1400, n electrode assembly stacks 1410 electrically coupled to n DC-to-DC boost converters 1414 are included, each of the n electrode assembly stacks 1410 and each of the n DC-to-DC boost converters 1414 being labeled with an index running from 1 to n. Further, though four electrode assembly stacks 1410 and four DC-to-DC boost converters 1414 are shown in
Referring now to
As shown in the schematic diagram 1500, the second exemplary redox flow battery system 1502 may include a plurality of electrolyte storage tanks 1504 respectively fluidically coupled to a plurality of electrode assembly stacks 1510 via a plurality of electrolyte pumps 1508, respectively. Accordingly, the second exemplary redox flow battery system 1502 may be configured as a redox flow battery pack including a plurality of redox flow batteries 1552, where each of the plurality of redox flow batteries 1552 may respectively include one of the plurality of electrolyte storage tanks 1504, one of the plurality of electrolyte pumps 1508, and one of the plurality of electrode assembly stacks 1510.
Each of the plurality of electrolyte storage tanks 1504 may be prismatic in shape (e.g., so as to increase a packing density relative to other shapes, such as regular or modified cylinders) and may expel an electrolyte along a respective one of a plurality of electrolyte flow paths 1506a and may receive the electrolyte along a respective one of a plurality of electrolyte flow paths 1506c. The plurality of electrolyte storage tanks 1504 may be respectively fluidically coupled to the plurality of electrolyte pumps 1508 via the plurality of electrolyte flow paths 1506a, respectively. Accordingly, the electrolyte may be expelled from each of the plurality of electrolyte storage tanks 1504 via a respective one of the plurality of electrolyte flow paths 1506a, as pumped therealong by a respective one of the plurality of electrolyte pumps 1508. Each of the plurality of electrolyte pumps 1508 may deliver the electrolyte to a respective one of the plurality of electrode assembly stacks 1510 via a respective one of a plurality of electrolyte flow paths 1506b. In some examples, each of the plurality of electrode assembly stacks 1510 may include one or more redox flow battery cells (each of the one or more redox flow battery cells including a redox electrode and a plating electrode) and a rebalancing cell [the rebalancing cell including a stack of internally shorted electrode assemblies, where no electrical path is present to direct electric current away from the stack of internally shorted electrode assemblies (accordingly, in an exemplary embodiment, the rebalancing cell may be the rebalancing cell 202 of
As each of the plurality of redox flow batteries 1552 may include a separate electrolyte storage tank 1504, a separate electrolyte pump 1508, and a separate electrode assembly stack 1510 from each other of the plurality of redox flow batteries 1552, each of the plurality of redox flow batteries 1552 (and components included therein) may be fluidically isolated from each other of the plurality of redox flow batteries 1552 (and components included therein) in some examples. As such, a modularity of the second exemplary redox flow battery system 1502 may be improved relative to redox flow battery systems in which each electrode assembly stack is fluidically coupled in parallel (e.g., the first exemplary redox flow battery system 1402 of
As further shown in the schematic diagram 1500, the plurality of electrode assembly stacks 1510 may be electrically coupled in series, such that each of the plurality of electrode assembly stacks 1510 may be directly electrically coupled (e.g., at positive and negative terminals of each of the one of more redox flow battery cells included therein) to at least one adjacent electrode assembly stack 1510 (e.g., at positive and negative terminals each of the one of more redox flow battery cells included therein) via at least one of a plurality of electrical paths 1512b, respectively. The plurality of electrode assembly stacks 1510 may further be electrically coupled to the power inverter 1516 via electrical paths 1512a and 1512c. Specifically, the power inverter 1516 may be directly electrically coupled to each of a first electrode assembly stack 1510 (indexed in the schematic diagram 1500 with “1′”) and a last (e.g., nth) electrode assembly stack 1510 (indexed in the schematic diagram 1500 with “n′”). Accordingly, each of the plurality of electrode assembly stacks 1510 may be directly electrically coupled to two adjacent electrode assembly stacks 1510 or to one adjacent electrode assembly stack 1510 and the power inverter 1516. The power inverter 1516 may further be electrically coupled to the electrical grid 1518 via an electrical path 1512d. In this way, an electric current may be sequentially cycled across the plurality of electrode assembly stacks 1510 and the power inverter 1516, wherefrom the electric current may reversibly flow to the electrical grid 1518 (e.g., between the power inverter 1516 and the electrical grid 1518).
By electrically coupling the plurality of electrode assembly stacks 1510 in series, a potential difference thereacross may be ramped up. Accordingly, an output voltage of the second exemplary redox flow battery system 1502 may be compatible with the power inverter 1516 without any DC-to-DC boost converter being present in the second exemplary redox flow battery system 1502 (e.g., no electrical path may be present to electrically couple a DC-to-DC boost converter to any of the plurality of electrode assembly stacks 1510 or components included therein). For example, the output voltage of the plurality of (series coupled) electrode assembly stacks 1510 may be within a potential difference range at which the power inverter 1516 may be operated (e.g., 600 to 1000 V, 850 to 1000 V, etc.). As such, both a complexity and a cost of the second exemplary redox flow battery system 1502 may be reduced relative to redox flow battery systems in which one or more DC-to-DC boost converters is provided to ramp up an output voltage of electrode assembly stack(s) included therein (e.g., the first exemplary redox flow battery system 1402 of
It will be appreciated that, in the second exemplary redox flow battery system 1502, and as shown in the schematic diagram 1500, n′ electrode assembly stacks 1510 fluidically coupled to n′ electrode storage tanks 1504 are included, each of the n′ electrode assembly stacks 1510 and each of the n′ electrode storage tanks 1504 being labeled with an index running from 1 to n′. Further, though four electrode assembly stacks 1510 and four electrolyte storage tanks 1504 are shown in
In this way, an electrolyte may be rebalanced in a redox flow battery system with a relatively high Fe3+ reduction rate and a relatively low H2 gas partial pressure, such that a pressure at which the electrolyte and the H2 gas are stored and distributed in the redox flow battery system may be reduced. In one example, the redox flow battery system may include a plurality of electrolyte storage tanks, where a gauge pressure in each of the plurality of electrolyte storage tanks may be maintained below a relatively low value (e.g., 2 psi). Accordingly, each of the plurality of electrolyte storage tanks may be configured with a broader range of wall thicknesses, compositions, and shapes as compared to electrolyte storage tanks utilized in conventional redox flow battery systems (which may contain higher pressures during redox flow battery system operation). For instance, each of the plurality of electrolyte storage tanks may be prismatic in shape. A technical effect of each of the plurality of electrolyte storage tanks being prismatic in shape is that the plurality of electrolyte storage tanks may be arranged in a more space effective manner relative to other shapes (e.g., cylinders), such that a packing density of the plurality of electrolyte storage tanks may be increased. An additional technical effect of each of the plurality of electrolyte storage tanks being prismatic in shape is that multiple electrolyte storage tanks may be included in and distributed across the redox flow battery system (e.g., a prismatic electrolyte storage tank may be provided for each one of a plurality of redox flow battery cells in the redox flow battery system), further increasing an overall space efficiency of the redox flow battery system.
In one example, a redox flow battery system, comprising: a plurality of redox flow battery cells; and a plurality of prismatic electrolyte storage tanks respectively fluidically coupled to the plurality of redox flow battery cells, wherein a gauge pressure in each of the plurality of prismatic electrolyte storage tanks is maintained below 2 psi. A first example of the redox flow battery system further includes wherein each of the plurality of redox flow battery cells comprises positive and negative electrode compartments respectively housing redox and plating electrodes, and wherein each prismatic electrolyte storage tank of the plurality of prismatic electrolyte storage tanks is fluidically coupled to each redox flow battery cell of the plurality of redox flow battery cells, respectively, via the positive and negative electrode compartments of the redox flow battery cell. A second example of the redox flow battery system, optionally including the first example of the redox flow battery system, further includes wherein each of the plurality of prismatic electrolyte storage tanks is partitioned into positive and negative electrolyte chambers respectively containing positive and negative electrolytes, the positive and negative electrolyte chambers further including respective gas head spaces containing H2 gas, and wherein the positive electrolyte chamber of each prismatic electrolyte storage tank of the plurality of prismatic electrolyte storage tanks is fluidically coupled to the positive electrode compartment of the redox flow battery cell of the plurality of redox flow battery cells fluidically coupled to the prismatic electrolyte storage tank, and wherein the negative electrolyte chamber of each prismatic electrolyte storage tank of the plurality of prismatic electrolyte storage tanks is fluidically coupled to the negative electrode compartment of the redox flow battery cell of the plurality of redox flow battery cells fluidically coupled to the prismatic electrolyte storage tank. A third example of the redox flow battery system, optionally including one or more of the first and second examples of the redox flow battery system, further comprises a plurality of positive rebalancing cells for electrolyte rebalancing of the positive electrolyte, the plurality of positive rebalancing cells being respectively fluidically coupled to: the positive electrode compartments of the plurality of redox flow battery cells; and the positive electrolyte chambers of the plurality of prismatic electrolyte storage tanks, wherein each of the plurality of positive rebalancing cells comprises interfacing pairs of positive and negative electrodes configured to drive electrolyte rebalancing of the positive electrolyte with the H2 gas via internal electrical shorting. A fourth example of the redox flow battery system, optionally including one or more of the first through third examples of the redox flow battery system, further comprises a plurality of negative rebalancing cells for electrolyte rebalancing of the negative electrolyte, the plurality of negative rebalancing cells being respectively fluidically coupled to: the negative electrode compartments of the plurality of redox flow battery cells; and the negative electrolyte chambers of the plurality of prismatic electrolyte storage tanks, wherein each of the plurality of negative rebalancing cells comprises interfacing pairs of positive and negative electrodes configured to drive electrolyte rebalancing of the negative electrolyte with the H2 gas via internal electrical shorting. A fifth example of the redox flow battery system, optionally including one or more of the first through fourth examples of the redox flow battery system, further comprises an outer housing, where at least one edge of each of the plurality of prismatic electrolyte storage tanks is flushly aligned with and received by at least one interior edge of the outer housing. A sixth example of the redox flow battery system, optionally including one or more of the first through fifth examples of the redox flow battery system, further includes wherein the redox flow battery system is an all-iron hybrid redox flow battery system.
In another example, a method for a redox flow battery pack, the method comprising: for a first redox flow battery of the redox flow battery pack: sequentially cycling an electrolyte from a first electrolyte storage tank of the first redox flow battery through a first redox flow battery cell of the first redox flow battery and a first rebalancing cell of the first redox flow battery; and flowing H2 gas from the first electrolyte storage tank to the first rebalancing cell; and for a second redox flow battery of the redox flow battery pack: sequentially cycling an electrolyte from a second electrolyte storage tank of the second redox flow battery through a second redox flow battery cell of the second redox flow battery and a second rebalancing cell of the second redox flow battery; and flowing H2 gas from the second electrolyte storage tank to the second rebalancing cell, wherein the H2 gas from the first and second electrolyte storage tanks is respectively flowed to the first and second rebalancing cells at a partial pressure of less than 80%. A first example of the method further includes wherein each of the first and second electrolyte storage tanks is non-cylindrical in shape. A second example of the method, optionally including the first example of the method, further includes wherein the H2 gas from the first electrolyte storage tank is reacted with positively charged ions in the electrolyte from the first electrolyte storage tank at respective interfaces of cathodes of the first rebalancing cell with anodes of the first rebalancing cell to reduce the positively charged ions, and wherein the H2 gas from the second electrolyte storage tank is reacted with positively charged ions in the electrolyte from the second electrolyte storage tank at respective interfaces of cathodes of the second rebalancing cell with anodes of the second rebalancing cell to reduce the positively charged ions. A third example of the method, optionally including one or more of the first and second examples of the method, further comprises: for the first redox flow battery, flowing unreacted H2 gas from the first rebalancing cell to the first electrolyte storage tank; and for the second redox flow battery, flowing unreacted H2 gas from the second rebalancing cell to the second electrolyte storage tank. A fourth example of the method, optionally including one or more of the first through third examples of the method, further comprises: for the first redox flow battery, expelling unreacted H2 gas from the first rebalancing cell via a first pressure release outlet port; and for the second redox flow battery, expelling unreacted H2 gas from the second rebalancing cell via a second pressure release outlet port. A fifth example of the method, optionally including one or more of the first through fourth examples of the method, further includes wherein the redox flow battery pack is operated within a temperature range of room temperature to 60° C.
In yet another example, a storage tank for a redox flow battery system, the storage tank comprising: a prismatic external housing including a flat surface configured to flushly and interchangeably receive an electrode assembly stack of a redox flow battery cell of the redox flow battery system, a flat surface of another storage tank of the redox flow battery system, and an internal surface of an outer housing of the redox flow battery system, wherein the prismatic external housing houses flowing liquid electrolyte and flowing gas. A first example of the storage tank further includes wherein a shape of the prismatic external housing is a rectangular prism or a cube. A second example of the storage tank, optionally including the first example of the storage tank, further includes wherein a thickness of each wall of the prismatic external housing is less than 10 mm. A third example of the storage tank, optionally including one or more of the first and second examples of the storage tank, further includes wherein the prismatic external housing is formed from high-density polyethylene, reinforced polypropylene, or reinforced fiberglass. A fourth example of the storage tank, optionally including one or more of the first through third examples of the storage tank, further comprises: one or more inlet ports configured to receive the flowing liquid electrolyte and the flowing gas into an interior of the storage tank enclosed by the prismatic external housing; and one or more outlet ports configured to expel the flowing liquid electrolyte and the flowing gas from the interior of the storage tank. A fifth example of the storage tank, optionally including one or more of the first through fourth examples of the storage tank, further includes wherein the interior of the storage tank enclosed by the prismatic external housing is partitioned into positive and negative electrolyte chambers by a bulkhead. A sixth example of the storage tank, optionally including one or more of the first through fifth examples of the storage tank, further includes wherein a spillover hole is positioned in the bulkhead at a threshold height above a fill height of the flowing liquid electrolyte.
The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.
The present application claims priority to U.S. Provisional Application No. 63/260,793 entitled “SYSTEMS AND METHODS FOR FLOWING, STORING, AND REBALANCING ELECTROLYTE IN REDOX FLOW BATTERY SYSTEM” filed Aug. 31, 2021. The entire contents of the above identified application is hereby incorporated by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 63260793 | Aug 2021 | US |
