Redox flow battery system and cell stack thereof

Abstract

We describe a redox battery cell comprising a first electrode, a second electrode spaced apart from the first electrode, and a membrane disposed between the first and second electrodes, where the first electrode comprises a first flow field.

Description

Technical Field

[0001] The present disclosure generally relates to redox battery cells and redox battery stacks. Background Art

[0002] The use of renewable energy sources such as solar and wind power requires energy management that includes energy storage capabilities. Redox flow batteries (RFBs) are an option for both decentralized and centralized systems. RFBs are the only type of battery whose energy content and power output can be independently scaled, providing a high degree of flexibility for applications such as load balancing and frequency stabilization.

[0003] The current technology, all-vanadium RFBs, has significant advantages but presents unique challenges—low energy density (approximately 20 times lower than lithium-ion batteries) and low specific power density, which requires high-surface-area felt electrodes to mitigate this problem. Complex ions with multiple redox centers (for higher energy density) and high electron transfer rates (for high power density) could offer an alternative approach to this established system. However, these complex ions require in-depth structural and chemical analysis and redesign of the redox systems and the assembled stacks they comprise.

[0004] Redox flow batteries (RFBs) are one of the few options for storing energy from intermittent renewable energy sources such as wind and solar. While the concept of RFBs itself is very ingenious, as it allows for independent scaling of energy and power content, society has yet to decide on a universal battery chemistry. Currently, there are two schools of thought in principle: the first group advocates the use of dissolved transition metal ions (e.g., Fe 2+ / Fe 3+ 、V 2+ / V 3+ ), transition metal oxyanions (e.g., VO 2+ / VO 2+ ) or transition metal complexes (such as [Fe(CN)6] 4- / [Fe(CN)6] 3- ) as electron carriers (for simplicity, all three are referred to as metal ions), while the second group proposed the use of organic redox-active materials. Both approaches have their own unique advantages and disadvantages. The dominant redox couple of dissolved metal chemicals is the all-vanadium redox flow battery (VRFB). Utilizing the four oxidation states of vanadium (V 2+ 、V 3+ , VO 2+ , VO2 +), the advantage of this battery chemistry is that cross-over of species from one half-cell to the other across the separator does not result in chemical contamination, and the battery can be electrochemically rebalanced.

[0005] The main disadvantage of VRFB is that V 2+ / V 3+ and VO 2+ / VO2 + The kinetics of the redox reaction are slow, which limits the current density and thus the power density. Although there is debate in the literature about the correct electronic rate constant, k0, for the vanadium reaction and which half-cell is faster, it is approximately k0 = 10 -6 cm s -1 order of magnitude.

[0006] Organic redox couples can be low-cost and made from abundant elements, and due to their tunable structures, they offer greater variability than metal-ion redox couples. In recent years, a large number of organic redox couples have emerged. However, because most studies have been limited to laboratory cell operations, there is currently no insight into scaling up to larger cell areas, larger electrolyte volumes, and long-term cycling.

[0007] Another redox electrochemistry that can be used for RFBs uses polyanions, such as polyoxometalates (POMs). POMs form a class of discrete transition metal oxide nanoclusters. They are made from metals but have a high degree of structural diversity and, therefore, diverse electrochemistry.

[0008] POM as electrolyte in RFBs offers significant chemical and / or electrochemical advantages compared to known vanadium systems, such as:

[0009] 1. The electrons added to POM by reduction are usually delocalized on several metal atoms, which will promote fast electron transfer and thus achieve high current density;

[0010] 2. POM is anionic and larger than the solvated transition metal. Therefore, POM should not permeate through the ion exchange membranes commonly used in RFBs.

[0011] 3. Electron transfer in POMs is often coupled with cation or proton transfer. Therefore, the net charge of the polyoxyanion does not change upon oxidation or reduction. This concept is often found in biological systems, avoiding highly charged species and resulting in increased stability.

[0012] 4. Some POMs are highly soluble, with the maximum concentration depending on the type of POM, the electrolyte, and the presence of counterions. Combined with the multiple electron transfers per molecule, this can lead to high energy density.

[0013] Furthermore, since each POM, as the electrolyte's reduced-oxidation species ion, can transfer multiple electrons when used in redox cycles (such as redox flow batteries), it can achieve more efficient charging and discharging and greater stored charge density compared to conventional vanadium-based flow batteries. Furthermore, the lower charge transfer resistance of polyoxometalate (POM) electrolytes compared to vanadium electrolytes increases voltage efficiency and power density.

[0014] The POM electrolyte includes large reduced-oxidation species ions that permeate through the membrane more slowly than vanadium ions, which reduces the self-discharge of the flow battery.

[0015] However, specific reduction-oxidation properties, such as increased charge transfer rate or charge density, hinder the energy-efficient implementation of these new electrolyte types (including reduction-oxidation species ions with comparable charge transfer properties) into state-of-the-art redox flow batteries. Summary of the Invention

[0016] The inventors have recognized the need for improved redox battery cells in which, inter alia, the energy storage potential of reduced-oxidation species such as POM and comparable charge transfer properties can be fully utilized.

[0017] In one aspect of the present disclosure, a redox battery cell is provided. The redox battery cell according to the present disclosure comprises:

[0018] the first electrode,

[0019] a second electrode spaced apart from the first electrode, and

[0020] a membrane disposed between the first electrode and the second electrode,

[0021] The first electrode includes a first flow field.

[0022] For example, redox batteries can be used to convert electrical energy generated in renewable energy systems into chemical energy that can be stored until the electrical energy is needed at a later time. The redox batteries can then convert the chemical energy into electrical energy to supply the power grid, electric vehicles, etc.

[0023] In this aspect, a redox battery cell comprises a first electrode, a second electrode spaced apart from the first electrode, and a membrane disposed between the first and second electrodes. As used herein, the term "electrode" generally refers to a physical object (such as a solid or fluid) capable of delivering or drawing current to or from a power source. That is, as used herein, the term "electrode" can refer to a substance that provides or removes electrons, i.e., a conductive solid, as well as a conductive fluid. Thus, the redox battery cell as defined in claim 1 is characterized in that both the first electrode and the second electrode comprise solid structures. Thus, optionally, the redox battery cell as defined in claim 1 is characterized in that the first electrode comprises a solid structure, and wherein the second electrode comprises a fluid, such as a gas (preferably comprising air and / or oxygen), in contact with the second solid (e.g., metal) electrode. That is, if the second electrode comprises, for example, oxygen, the oxygen can participate in an electrochemical reaction with protons provided via the membrane and electrons provided to the second solid electrode via the charge collector in a two-electron process to produce water. Optionally, the second electrode comprises a fluid (such as a gas, preferably air), and a second solid electrode in contact with the fluid. That is, electrons provided from the first electrode during discharge may react with the fluid or gas at the second electrode.

[0024] The second electrode is spaced apart from the first electrode to avoid short circuit failure and tunneling current. That is, the second electrode is not in direct contact with the first electrode, but is spatially separated from the first electrode. The first and second electrodes can be spatially separated, for example, by a distance greater than 1 mm (internal electrode distance). For example, the internal electrode distance can range from 1 mm to 1 cm, or from 2 mm to 100 mm, or from 4 mm to 50 mm. Preferably, the internal electrode distance is 10 to 25 mm.

[0025] The first and second electrodes are separated, thus preventing short-circuit failures and tunneling currents. In addition to the spatial separation, the first and second electrodes are separated by a membrane arranged between the first and second electrodes. This membrane acts as an (electronic) separator for the first and second electrodes. This membrane allows for the transport of ionic charge carriers necessary to close the circuit during battery charge and discharge.

[0026] The first electrode includes a first flow field to efficiently operate the redox battery cell. As used herein, the term "flow field" may refer to a space or region in which a fluid (e.g., a liquid electrolyte) is distributed by introducing the fluid into a physical structure so as to adequately deliver the fluid to the desired location of the electrode. The flow field of the first electrode generally provides multiple functions of fundamental importance, including providing electrical continuity in the redox battery cell electrode as a current collector, and, for example, a charge collector coupled thereto.

[0027] In addition, the flow field can also serve as mechanical support for the membrane electrode assembly (MEA), which includes a first electrode, a second electrode, and a membrane disposed between the first and second electrodes, and can also be used to distribute the electrolyte. For example, it is known that the performance of a fuel cell depends largely on the efficient transport and uniform distribution of reactants to the electrode catalyst, as well as on proper water management of the fuel cell, that is, the supply and removal of water generated during fuel cell operation. Similarly, flow field design significantly affects the performance of redox battery cells by controlling electrolyte gradients, flow rates, pressure drops, water distribution and current density profiles, as well as the efficiency of utilization of redox species at the electrodes. Therefore, by providing a redox battery cell comprising a first electrode, wherein the first electrode includes a first flow field, the redox battery cell according to the present disclosure provides a cell that can accommodate a variety of redox species used in the redox electrolyte. By including a flow field in the first electrode, higher current density and, therefore, higher power density can be achieved compared to conventional electrodes without a flow field in the electrode, while also simplifying the battery device structurally, thereby improving its reliability and durability.

[0028] In some examples, multiple repetitions of electrodes having a flow field / membrane / electrode unit cell can be considered as battery cells and can be used in a stacked arrangement.

[0029] In some examples, the second electrode of the redox battery cell includes a (second) flow field.

[0030] Similar to the first electrode, the second electrode may also include a second flow field. The second flow field of the second electrode generally provides the technical effects discussed above for the first electrode. By also providing a flow field (i.e., a second flow field) for the second electrode, the versatility of the redox battery cell can be further increased by allowing for more energy-efficient combinations of different electrolytes and / or concentrations in contact with the first and second electrodes.

[0031] In some examples, the first and / or second electrodes include an all-solid structure.

[0032] As used herein, the term "all-solid structure" may refer to a solid structure having a three-dimensional geometry that generally maintains its size and shape at least under typical operating conditions of a redox battery (temperature range of -20°C to 90°C, humidity range of 0% relative humidity to aqueous environment, etc.). An "all-solid structure" may be a porous structure or a dense structure. By providing a redox battery cell having an electrode comprising an all-solid structure, various geometric features may be implemented in the electrode, thereby achieving stable, durable, and more versatile and generally available charge distribution and transfer, as well as electrolyte distribution. Both the first and / or second electrode may comprise an all-solid structure.

[0033] Alternatively, as described above, the first electrode may comprise an all-solid structure, and the second electrode may comprise a fluid (or vice versa).

[0034] In some examples, the first flow field forms an integral part of the first electrode.

[0035] As used herein, the term "integral part" may define a component or feature (e.g., a flow field) as being integrally attached to a different component or feature (e.g., an electrode). If the first flow field forms an integral part of the first electrode, these two features exist as a single component in the redox battery cell, providing electrical conductivity and electrolyte distribution. To provide the first flow field as an integral part of the first electrode, the flow field can be provided as a separate solid component attached to the electrode, or the electrode and flow field can be integrally fabricated as a single piece. In the latter case, charge transfer between the flow field and the electrode is optimized by eliminating charge transfer resistances such as Mott-Schottky contacts, grain boundaries, etc. In prior art redox batteries, carbon cloth is often used to provide electrolyte distribution. However, the use of carbon cloth, which has low conductivity and uncontrolled electrolyte distribution, significantly hinders efficient charge transfer and, consequently, significantly reduces the energy efficiency of the battery. By providing an electrode including the flow field as an integral part, the redox battery cell of the present disclosure can be structurally simplified compared to electrochemical devices known in the prior art.

[0036] In some examples, the first flow field is thus an integral part of the first electrode. Similarly, as described later, the second flow field can be an integral part of the second electrode. In some examples, the electrode is thus a monolithic component of the redox battery cell. That is, the flow field can be a monolithic component or can be formed as a monolithic component, thereby providing a monolithic assembly of the electrode and flow field. In some examples, the redox battery cell thus includes a first monolithic electrode (formed from a single workpiece) having a flow field integrated into the electrode.

[0037] In some examples, the first electrode is formed substantially from one piece (a monolithic electrode) and includes the flow field as a one-piece component. That is, the electrode can be in the form of a unitary or monolithic piece / component of a redox battery cell and include the flow field as a structure integral to the electrode (integrally formed). That is, the electrode (including the flow field) can be a single workpiece. As described above, this single workpiece serving as the electrode can be in the form of a monolithic workpiece. That is, the electrode can be seamless in the assembled redox battery cell.

[0038] Therefore, the term "monolithic" as used herein refers to an electrode that includes a flow field as an integral structure. In some examples, the electrode can be provided as a monolithic cuboid or plate, wherein the flow field structure is milled / molded / formed into the cuboid structure. The flow field can be incorporated into the monolithic electrode as a relief (reduction).

[0039] That is, the structure is characterized as an integral entity formed by a coherent assembly of single pieces or interconnected parts, highlighting the indivisibility of the two functions (electrode and flow field) provided by the monolithic structure in the entire system. Therefore, the structure can have a monolithic composition, indicating that it is composed of a single material or a uniform combination of materials, forming a cohesive and indivisible unit. Therefore, this one-piece design of electrode + flow field can highlight the need for the absence of separate components or combinations, thereby reinforcing the concept of a monolithic entity. In addition to the pre-formed electrode + flow field structure, the indivisibility of the structure emphasizes that it is configured in such a way that it cannot be easily divided into different parts without compromising its functionality. This coherent assembly can be characterized by seamlessly integrating the various components as a single cohesive entity. Therefore, in some instances, the electrode and flow field can be unified to provide excellent electrolyte distribution while having excellent electronic conductivity due to the boundaryless and therefore virtually resistance-free flow of current.

[0040] Specifically, as discussed further below, a monolithic (seamless) electrode including a flow field as a component can be prepared from a variety of conductive materials. In some examples, the monolithic electrode including a flow field as an integral feature is formed from a monolithic aluminum, a monolithic carbon-coated aluminum, a monolithic copper, a monolithic carbon-coated copper, a monolithic nickel, a monolithic carbon-coated nickel, a monolithic iron, a monolithic carbon-coated iron, a monolithic steel, a monolithic carbon-coated steel, a monolithic stainless steel, a monolithic carbon-coated stainless steel, a monolithic carbon, a monolithic glassy carbon, a monolithic graphite, a monolithic titanium, a monolithic tantalum, a monolithic carbon-coated titanium, a monolithic carbon-coated tantalum, a monolithic metal carbide-coated titanium, a monolithic metal carbide-coated tantalum, preferably selected from the group consisting of monolithic graphite, monolithic aluminum, monolithic carbon-coated aluminum, monolithic copper, and monolithic carbon-coated copper.

[0041] Various methods can be used to prepare the integral flow field and / or monolithic electrode including the flow field, including but not limited to the following. By incorporating the electrode including the flow field, the flow field structure can be implemented in the pre-assembly of the electrodes of the redox battery cell. Thus, there is no need to combine (e.g., by pressing, compacting, etc.) the components of the battery assembly to form the flow field. Specifically, because such a pressing or compacting step may result in structural weaknesses in the easily assembled battery, the pre-formed monolithic first electrode (and optionally the monolithic second electrode) provides the structural integrity and reliability of the complete system for the redox battery cell, and the system can also be implemented and tested during pre-assembly.

[0042] Creating a monolithic electrode structure involves forming a single integrated piece without the need for assembly (e.g., pressing, compacting, hot pressing) of multiple parts. Monolithic electrode structures (including the flow field as an integral part) for use in redox flow batteries or other electrochemical devices can be prepared using various methods.

[0043] In some examples, the first electrode including the first flow field can thus be manufactured by forming, molding, 3D printing, casting, foaming, deposition methods, electro-discharge machining, etc. Thus, the monolithic electrode can be a cast electrode, a molded electrode, a 3D printed electrode, a deposited (electrodeposition, chemical vapor deposition) electrode, etc. Methods for preparing such a monolithic structure that can be readily incorporated into a redox battery cell include:

[0044] Casting: In this method, the mixture of electrode materials is prepared in liquid form, typically as a slurry or suspension. The liquid mixture is then poured or cast into a mold of the desired shape. Once the material solidifies, it forms a monolithic structure. Post-casting steps such as drying and curing may be performed.

[0045] Molding: Molding involves forming a material into a desired shape using a mold. The material, which can be conductive or composite, is placed into a mold and subjected to pressure and / or heat to take the shape of the mold. This process can produce fine and complex structures, providing control over the final shape of a monolithic electrode.

[0046] 3D printing (additive manufacturing): Additive manufacturing techniques, such as 3D printing, are capable of building three-dimensional structures layer by layer. This approach allows for precise control over the design and architecture of electrodes. A variety of materials, including conductive or composite materials, can be used in 3D printing to create monolithic electrodes with specific geometries.

[0047] Foam formation: Foaming methods involve creating a foam structure of the electrode material. This can be achieved by introducing a foaming agent or gas into a liquid mixture of the electrode materials. The resulting foam can be molded into the desired form and subsequently cured, creating a monolithic structure with a porous and interconnected network.

[0048] Chemical Vapor Deposition (CVD): CVD is a method of depositing thin films of material onto a substrate through a chemical reaction in the gas phase. While this method is often used for coatings, it can also be adapted to form monolithic structures by depositing material layer by layer to build cohesive structures.

[0049] Electrodeposition: Electrodeposition involves the electrochemical reduction of metal ions onto a conductive substrate. By controlling the deposition parameters, a monolithic structure with a uniform distribution of electrode material can be constructed. This method is commonly used for metal-based electrodes.

[0050] Providing the flow field as an integral (one-piece / monolithic) part of the electrode can provide various technical advantages over redox battery cells comprising arrangements in which the flow field is formed during assembly and pressing (e.g., pressing / hot pressing) of the cell. In particular, because established assembly methods (e.g., by pressing / hot pressing a fiber mat and a conductive component) introduce physical and electrical boundaries into the device, thereby introducing resistivity into the device, electrolyte flow and current flow can be significantly affected, and overall efficiency can be reduced. Furthermore, by providing a redox battery cell having a monolithic structure as a combination of electrode and flow field, a variety of material combinations can be used in the battery, as no damaging pressing or compacting step (force or shear) is required in the assembly to form the flow field structure adjacent to the electrode.

[0051] Further advantages of using a one-piece flow field / electrode assembly are discussed below.

[0052] Simplified Design and Manufacturing: Integrating the flow field into the electrodes simplifies the overall design of the redox flow battery. This integration typically results in a more compact and streamlined system, reducing the number of separate components. This simplified design can simplify the manufacturing process, reduce assembly costs, and improve the overall reliability of the system.

[0053] Enhanced Structural Integrity: Monolithic integration of the flow field into the electrode structure enhances the structural integrity of the redox flow battery. This integration provides improved support for the flow field, reducing the risk of mechanical failure or deformation. Improved structural integrity is crucial for maintaining the long-term reliability of the battery, especially in applications with dynamic environmental conditions.

[0054] Improved conductivity: Monolithic integration of the flow field with the electrodes allows for better control of the system's conductivity. This is particularly important for ensuring efficient electron transfer during electrochemical reactions. Enhanced conductivity contributes to lower internal resistance, which is beneficial for achieving higher energy conversion efficiency and faster charge / discharge rates.

[0055] Optimized Flow Paths: Monolithic integration allows for optimized flow paths within the electrode itself. This means the design can be tuned to ensure that the electrolyte flows evenly across the entire electrode surface, maximizing utilization of the active material. Well-optimized flow paths help prevent dead zones or areas of poor flow, promoting uniform electrochemical reactions.

[0056] Reduced System Complexity: Monolithic integration of the flow field into the electrodes reduces the number of separate components and connections within the redox flow battery. This reduction in complexity simplifies system maintenance, improves reliability, and makes the battery system more user-friendly. It also reduces the likelihood of potential failure points, contributing to the long-term stability of the system.

[0057] Improved Sealing and Leakage Prevention: Monolithic integration can facilitate better sealing between the flow field and electrodes. Effective sealing is crucial to preventing electrolyte leakage, which can pose safety risks and compromise the overall performance of redox flow batteries. Integrated designs generally provide better control over the sealing mechanism, enhancing the overall robustness of the system.

[0058] Optimal electrolyte management: Monolithic integration allows for better management of the electrolyte within the electrode structure. This includes controlling the distribution, flow rate, and uniformity of the electrolyte. Optimal electrolyte management is critical to maintaining the electrochemical performance of redox flow batteries and preventing issues such as uneven wear or degradation of electrode materials.

[0059] In summary, making the flow field an integral part of a monolithic component of a redox flow battery electrode offers advantages related to simplified design, enhanced structural integrity, improved conductivity, optimized flow paths, reduced system complexity, better sealing, and optimal electrolyte management. These advantages collectively contribute to a more efficient, reliable, and cost-effective energy storage system. Similarly, the second flow field of the second electrode can also be formed from a monolithic structure comprising the electrode and flow field.

[0060] In some examples, the second flow field forms an integral part of the second electrode. As discussed with respect to the first flow field of the first electrode, the second electrode can also be in the form of a monolithic component, i.e., a monolithic second electrode, which includes the second flow field as an integral part. By providing a redox battery cell having a first electrode and a second electrode—the first electrode including the first flow field as a monolithic structure and the second electrode including the second flow field as a monolithic structure—a synergistic effect can be achieved in terms of adjusting the monolithic electrode + flow field structure on both sides of the redox battery cell.

[0061] Similar to the first electrode, the second electrode may also include a second flow field, wherein the second flow field forms an integral part of the second electrode. The second flow field of the second electrode is typically provided as an integral part thereof to achieve the technical effects discussed above for the first electrode.

[0062] In some examples, the first flow field and the second flow field are substantially symmetrical with respect to a membrane disposed between the first electrode and the second electrode.

[0063] As used herein with respect to a flow field, the term "substantially symmetrical" may refer to a flow field that is substantially symmetrical about a line corresponding to or parallel to a membrane disposed between first and second electrodes. That is, the first and second flow fields may have the same shape and size, with the first flow field being disposed closer to the membrane than the second flow field. Alternatively, the second flow field is disposed closer to the membrane than the first flow field. Alternatively, the first flow field and the second flow field are disposed at substantially the same distance from the membrane.

[0064] By providing a redox battery cell in which the first and second flow fields are substantially symmetrical relative to a membrane disposed between the first and second electrodes, the structural stability and charge transfer of the redox battery cell can be improved. That is, by providing substantially symmetrical flow fields on both sides of the membrane relative to the membrane, structural deformation caused by differential electrolyte flow or pressure can be prevented. Furthermore, by providing substantially symmetrical flow fields on both sides of the membrane, charge transfer can be optimized. That is, by providing a flow field in which a fully charged first electrolyte flows symmetrically to a fully discharged second electrolyte, charge transfer between the two species through the membrane can be optimized.

[0065] In some examples, the first and / or second electrode comprises one or more components selected from aluminum, carbon-coated aluminum, copper, carbon-coated copper, nickel, carbon-coated nickel, iron, carbon-coated iron, steel, carbon-coated steel, stainless steel, carbon-coated stainless steel, carbon, glassy carbon, and graphite, preferably one or more components selected from graphite, aluminum, carbon-coated aluminum, copper, and carbon-coated copper.

[0066] In general, the first and / or second electrodes can be any electron-conducting material as described above. If the electrodes include one or more of the above-described compounds, the electrical conductivity of the electrodes is improved while providing structural stability to the redox battery cell. Furthermore, graphite, aluminum, carbon-coated aluminum, copper, and carbon-coated copper offer surprisingly good electrical conductivity combined with structural stability while avoiding cost-intensive materials. Carbon coatings can be provided on metals using plasma spraying, thermal spraying, sputter coating, pulsed laser deposition, sol-gel dip coating, electrophoretic deposition, hot isostatic pressing, ion beam assisted deposition, or other known methods.

[0067] In some examples, the first electrode comprising the first flow field is composed of graphite, aluminum, carbon-coated aluminum, copper, or carbon-coated copper. In some examples, the second electrode comprising the second flow field is composed of graphite, aluminum, carbon-coated aluminum, copper, or carbon-coated copper.

[0068] Electrodes composed of graphite, aluminum, carbon-coated aluminum, copper, or carbon-coated copper provide excellent electrical conductivity, charge transfer performance, and lifespan by reducing or preventing possible decomposition of the electrode by reaction with the electrolyte or other functional groups or adsorbed species caused by possible contamination. As a result, the coulombic efficiency of charge and discharge during cycling is also improved.

[0069] In some examples, the membrane comprises one or more inorganic membranes, optionally ceramic or zeolite membranes, or one or more organic membranes, optionally synthetic or natural polymer membranes.

[0070] The membrane may comprise one or more organic membranes, for example, synthetic or natural polymer membranes.

[0071] Most industrial membranes are composed of either synthetic or natural polymers; membranes containing either type of polymer are called organic membranes. Examples of synthetic polymers include polytetrafluoroethylene (PTFE), polyamide-imide (PAI), and polyvinylidene fluoride (PVDF), while natural polymers include rubber, wool, and cellulose used in dialysis.

[0072] Artificial polymers can be synthesized by polymerizing a monomer or copolymerizing two or more monomers. Polymers can have three common configurations: linear (such as polyethylene), branched (such as polysulfone), and cross-linked (such as phenolic resin). Linear polymers are more soluble in organic solvents. They become soft or moldable with increasing temperature and are called thermoplastic polymers. Cross-linked polymers, on the other hand, are virtually insoluble in organic solvents. They do not soften with increasing temperature and are called thermosetting polymers.

[0073] Polymer selection must be based on compatibility with the membrane manufacturing technology and the intended application. For example, a polymer may need to have a low affinity for the permeate, while in other cases, it may need to withstand harsh cleaning conditions due to membrane fouling. Chain interactions, chain rigidity, functional group polarity, and stereoisomerism also need to be considered when selecting polymers and manufacturing organic membranes.

[0074] The membrane may comprise one or more inorganic membranes, for example, ceramic or zeolite membranes.

[0075] Ceramic membranes are composed of metals (e.g., aluminum or titanium) and nonmetals (e.g., oxides, nitrides, or carbides). Due to their inertness, they are typically used in highly acidic or alkaline environments, but are also suitable for weakly acidic and alkaline or neutral pH values. One disadvantage of ceramic membranes can be their sensitivity to temperature gradients, which can lead to membrane rupture.

[0076] Zeolite membranes are commonly used for highly selective gas separations due to their highly uniform pore size, but can also be used as membranes in liquid systems, such as the redox battery cells of the present disclosure. Zeolite membranes have few disadvantages, including relatively low fluid flux and the requirement for thicker membrane layers to prevent cracks and pinholes.

[0077] In some examples, the membrane comprises one or more composite membranes, for example, a polyphosphate membrane. The polyphosphate membrane comprises an organic polymer and an inorganic phosphate compound, i.e., a polymer phosphate composite membrane. Polyphosphate composite materials for membrane fabrication can be synthesized, for example, by reacting ammonium phosphate with silicon oxide in the presence of ammonia. An exemplary composite material can include a polymer having the general formula NH4PO3 / (NH4)2SiP4O 13Compounds. Additional phosphate components, such as NH4PO3, may also be present in the composite material. Polyphosphate membranes are characterized by very high ionic conductivity in humid atmospheres and liquids and exhibit thermal and chemical stability up to at least 300°C (e.g., pH values ​​ranging from 2 to 10). This makes them suitable for redox battery applications. During the heating cycle, the conductivity of the polyphosphate membrane in dry hydrogen can be increased from at least 1.0×10 at 50°C to - 5 S cm -1 changes to 1.0×10 at 300°C -2 S cm -1 , and in a humid hydrogen atmosphere, the conductivity value is at least 5.0×10 -2 S cm -1 changes to 5.0×10 at 300°C -1 S cm -1 .

[0078] In some embodiments, the membrane is an ionic or nonionic size selective membrane having a pore size range of to The preferred range is to The term "pore size" as used herein may refer to the effective pore size of one or more holes in a membrane. The pore size (or pore diameter) may be measured using gas porosimetry (gas adsorption) or mercury (intrusion) porosimetry. The selected pore size may be adjusted to suit a specific application / electrolyte. For example, a membrane may be selected to retain particles, molecules, or ions having a size of 1 nm, 2 nm, 5 nm, or 10 nm. The pore size may also be defined by a molecular weight cut-off (MWCO). In other words, the membrane may also be selected to have a MWCO of 200 daltons (corresponding to a pore size of approximately 1.3 nm), 400 daltons (corresponding to a pore size of approximately 1.8 nm), 600 daltons (corresponding to a pore size of approximately 2.1 nm), 1000 daltons (corresponding to a pore size of approximately 2.7 nm), or greater than 2000 daltons (corresponding to a pore size greater than approximately 4.1 nm).

[0079] In some instances, the first flow field includes one or more first inlets coupled to the first storage tank and / or one or more first outlets coupled to the first storage tank, wherein, preferably, the one or more first inlets of the first flow field are arranged substantially opposite to a corresponding one of the one or more first outlets of the first flow field.

[0080] A fluid, such as an electrolyte, can be provided to the first flow field through one or more first inlets. The fluid can additionally or alternatively leave the first flow field through one or more first outlets. The first flow field is connected to the first storage tank via one or more first inlets and one or more first outlets. In the first storage tank, a first electrolyte can be provided. By providing one or more first inlets, inlet turbulence can be created in the first flow field. This turbulence increases the flow rate of the electrolyte within the flow field. The increased flow rate allows more charge carriers to be removed from or introduced into the electrolyte. This increased flow rate is particularly beneficial for reducing and oxidizing species that exhibit rapid charge transfer (e.g., by delocalization of charge). This turbulence can also be created by providing only one inlet but providing multiple outlets.

[0081] The one or more inlets and the one or more outlets are preferably arranged substantially opposite each other.By providing the one or more inlets and the one or more outlets on substantially opposite sides of the flow field, an overall macroscopic and controllable flow direction is created.

[0082] In some instances, the second flow field includes one or more second inlets coupled to the second storage tank and / or one or more second outlets coupled to the second storage tank, wherein, preferably, the one or more second inlets of the second flow field are arranged substantially opposite to a corresponding one of the one or more second outlets of the second flow field.

[0083] Similar to the first flow field, for the second flow field, a fluid, such as an electrolyte, may also be provided to the second flow field through one or more second inlets. The fluid may additionally or alternatively leave the second flow field through one or more second outlets. The one or more second inlets and / or one or more second outlets of the second flow field are typically provided to achieve the technical effects discussed above for the first flow field. By also providing one or more inlets and / or outlets for the second flow field, preferably arranged substantially opposite to each other, the second electrolyte in the second flow field may also have turbulence as discussed above for the first flow field.

[0084] In some examples, the first flow field includes a plurality of first inlets coupled to the first storage tank. By providing a plurality of first inlets, inlet turbulence can be created in the first flow field as described above to provide a characteristic flow velocity and turbulence intensity within the first flow field.

[0085] In some examples, the second flow field includes a plurality of second inlets coupled to the second storage tank. By providing a plurality of second inlets, inlet turbulence can be created in the second flow field as described above, so as to also provide characteristic flow velocity and turbulence intensity in the second flow field.

[0086] In some examples, a first inlet diameter of the first inlet is different from a second inlet diameter of the first inlet, and / or a first inlet shape of the first inlet is different from a second inlet shape of the first inlet. In some examples, a first inlet diameter of the second inlet is different from a second inlet diameter of the second inlet, and / or a first inlet shape of the second inlet is different from a second inlet shape of the second inlet.

[0087] By providing inlets of different diameters and / or inlets of different shapes, the turbulence and / or flow rate created in the flow fields may be further modulated for the reduced-oxidation species used in the first and second flow fields.

[0088] In some examples, the first flow field includes a plurality of first outlets coupled to the first storage tank. By providing a plurality of first outlets, inlet turbulence can be created in the first flow field as described above to provide a characteristic flow velocity and turbulence intensity within the first flow field.

[0089] In some examples, the second flow field includes a plurality of second outlets coupled to the second storage tank. By providing a plurality of second outlets, inlet turbulence can be created in the second flow field as described above, so as to also provide characteristic flow velocity and turbulence intensity in the second flow field.

[0090] In some examples, the first outlet has a different outlet diameter than the second outlet of the first outlet, and / or the first outlet has a different outlet shape than the second outlet of the first outlet. In some examples, the first outlet has a different outlet diameter than the second outlet of the second outlet, and / or the first outlet has a different outlet shape than the second outlet of the second outlet.

[0091] By providing outlets of different diameters and / or outlets of different shapes, the turbulence and / or flow rate created in the flow field can be further modulated for the reduced-oxidation species used in the first and / or second flow field.

[0092] In some examples, the inlet diameter of the first one of the first inlets is different from the outlet diameter of the first one of the first outlets. In addition, in some examples, the inlet shape of the first one of the first inlets is different from the outlet shape of the first one of the first outlets.

[0093] By providing a combination of first inlets and first outlets of different diameters and / or shapes, the flow rate of a fluid (e.g., an electrolyte) can be controlled, thereby regulating and controlling the turbulence intensity in the first flow field without the need to integrate additional battery infrastructure (e.g., multiple pumps) into the redox battery cell.

[0094] In some examples, the inlet diameter of the first of the second inlets is different from the outlet diameter of the first of the second outlets. In addition, in some examples, the inlet shape of the first of the second inlets is different from the outlet shape of the first of the second outlets.

[0095] By making the inlet diameter and / or shape of the first of the second inlets different from the outlet diameter of the first of the second outlets, the technical effects discussed above for the first flow field can also be achieved for the second flow field.

[0096] In some instances, the first flow field includes one or more channels separated by ribs for delivering a first electrolyte to the first electrode. In some instances, the second flow field includes one or more channels separated by ribs for delivering a second electrolyte to the second electrode. By providing a first and / or second flow field including channels, a fluid (such as an electrolyte) can be directed from an inlet toward an outlet through a fixed path in the flow field. Thus, a second flow direction can be provided within the overall flow direction from the inlet to the outlet within the flow field. By providing a second flow direction through channels separated by ribs, the fluid follows a fixed path within the flow field, and the complete geometry of the flow field can be fully utilized for charge transfer from a fluid (such as an electrolyte) or charge transfer to a fluid (such as an electrolyte). In addition, the ribs that form the channels provide additional structural stability to the membrane electrode assembly (MEA).

[0097] In some examples, the one or more channels form one or more of the following: a single serpentine structure, a multiple serpentine structure, a hybrid serpentine structure, a parallel structure, a discontinuous structure, a needle-like structure, a crisscross structure, an interdigitated structure, a fractal interdigitated structure, a structure including asymmetric channels, a network structure, or a combination of two or more thereof.

[0098] The single serpentine structure is characterized in that a single channel is provided from the inlet of the flow field to the outlet of the flow field, wherein the fluid flows from the first part of the serpentine in the opposite direction to the second part of the serpentine. The single serpentine channel can be in the form of a rectangular pattern, a circular pattern or a combination thereof. Due to the high flow rate and coverage of the entire effective area of ​​the flow field, the single serpentine structure provides good fluid removal. However, depending on the specific geometry, the single serpentine structure may cause reactant loss along the length of the channel, which may lead to uneven distribution of reducing and oxidizing species, high pressure drop, air oxidant problems, flooding risks at high current density, or fluid accumulation at bends, which leads to local current density reduction.

[0099] A multi-serpentine structure is characterized in that more than one single channel is provided from the flow field inlet to the flow field outlet. The multiple serpentine channels can be in the form of a rectangular pattern, a circular pattern, or a combination thereof. The multi-serpentine structure provides a smaller pressure drop than a single serpentine structure, sufficient water / fluid removal, coverage of the entire active area of ​​the flow field, higher performance compared to a single serpentine structure, and is considered to be the optimal structure for large active areas. However, depending on the specific geometry, the multi-serpentine structure may still result in a relatively high pressure drop due to the uneven distribution of the reduced-oxidized species in the flow field due to the length of the channel and the loss of the reduced-oxidized species along the length of the channel.

[0100] A hybrid serpentine structure is characterized by providing more than one single serpentine structure within a flow field. For example, two or three single serpentine structures can be arranged adjacent to each other in the flow field. Multiple serpentine structures provide a lower pressure drop than single serpentine structures. Depending on the specific geometry, multiple serpentine structures can combine the technical benefits provided by the combination of single and multiple serpentine structures described above.

[0101] The parallel structure is characterized in that two or more channels connected to the inlet are arranged substantially parallel to each other. In addition, the two or more channels are connected to a first main channel connected to the inlet so that the fluid flows in the main channel and then flows through the flow field through the parallel channels. In addition, the two or more channels are connected to a second main channel connected to the outlet so that the fluid flows through the parallel channels and then flows through the flow field through the second main channel. In a preferred embodiment, the parallel channels are arranged substantially perpendicular to the main channels. The parallel structure provides low pressure drop and uniform fluid distribution. However, depending on the specific geometry, the parallel structure may cause water blockage in the channel, resulting in obstructed flow or dead zones, insufficient water / fluid removal, insufficient pressure drop in channels near the outlet (channels geometrically close to the outlet), resulting in uneven fluid flow, unstable voltage after long-term operation, or low channel velocity.

[0102] The needle-type structure is characterized by a first plurality of channels in the flow field being arranged substantially parallel, and a second plurality of channels in the flow field being arranged substantially parallel, with the second plurality of channels being arranged substantially perpendicular to the first plurality of channels. Thus, the remaining fully solid needles in the flow field form isolated needles. The needle structure provides low pressure drop and is suitable for high reactant flow rates at low utilization levels. However, depending on the specific geometry, the needle-type structure may result in uneven reactant distribution, uneven water removal, or uneven current density distribution.

[0103] The crisscross structure is characterized by being based on a parallel structure with additional transverse channels. The combination of parallel and transverse channels allows a fluid (e.g., gas) to merge with water droplets. The crisscross structure provides improved fluid removal and generally has similar advantages to the parallel structure. However, depending on the specific geometry, the crisscross structure may also have similar disadvantages to the parallel structure described above.

[0104] Interdigitated (or discontinuous) structures are characterized by a structure consisting of two or more interdigitated solid ribs in a comb-like pattern. By using forced convection through a fluid diffusion layer (FDL) rather than diffusion, the interdigitated structure provides good fluid / air removal, good mass transfer, and provides the highest performance and uniform fluid distribution. However, depending on the specific geometry, the interdigitated structure can result in a high pressure drop, depending on the porosity and thickness of the FDL, and can cause long-term damage to the FDL.

[0105] The fractal interdigital structure is characterized in that the structure includes an interdigital structure as described above, wherein the interdigital structure is divided into two or more fractal upper structures. For example, the two or more upper structures can be arranged so that the flow field is divided by an interdigitated mid-section from the flow field inlet to the outlet.

[0106] Structures comprising asymmetric channels are characterized in that the channels can be tapered, converging, and stepped. Structures comprising asymmetric channels can combine tapering, converging, and stepping. In structures comprising asymmetric channels, one complete channel can be tapered while another channel can be converging. Furthermore, even another channel can be stepped. In structures comprising asymmetric channels, the channel can be tapered in one portion, converging in another portion, and stepped in another portion. Structures comprising one or more asymmetric channels provide improved performance, improved mass transfer, and improved water / fluid removal at low voltages. However, depending on the specific geometry, structures comprising one or more asymmetric channels may result in higher pressure drops or may be difficult to manufacture.

[0107] A mesh structure is characterized by channels forming a network of uniformly distributed openings of similar size. The mesh structure offers good performance within a limited current range, low pressure drop, and controllable contact area. However, depending on the specific geometry, the mesh structure can exhibit poor water / fluid removal at high power output, with concentrated fluid distribution at the center and low distribution around the edges. Furthermore, equivalent porosity characteristics can be difficult to fabricate, and the mesh structure can experience corrosion issues, high pressure drop, and may only be suitable for small devices.

[0108] In some embodiments, the channels form a combination of parallel and serpentine structures. By combining the parallel and serpentine structures formed by the channels in the flow field, the structure provides low pressure drop and uniform fluid distribution, as well as good fluid removal due to high flow rates, and covers the entire active area of ​​the flow field.

[0109] In some examples, one or more channels included in the first flow field are rectangular, square, parallelogram, trapezoid, triangular, or semicircular along at least a portion of each channel. Additionally or alternatively, in some examples, one or more channels included in the second flow field are rectangular, square, parallelogram, trapezoid, triangular, or semicircular along at least a portion of each channel. Depending on the structure formed by the channels and the viscosity of the fluid, different channel shapes can be implemented to optimize charge transfer in the flow field.

[0110] In some instances, the one or more channels included in the first flow field include one or more first microchannels and / or one or more first vortex promoters. Additionally or alternatively, in some instances, the one or more channels included in the second flow field include one or more second microchannels and / or one or more second vortex promoters.

[0111] As used herein, the term "microchannel" may refer to a channel having a hydraulic diameter of less than 1 mm, preferably in the range of 1 μm to 99 μm. As used herein, the term "vortex promoter" (or vortex generator) may refer to a solid physical object that can be provided in a flow field to interact with the fluid to create turbulence. In addition to the geometric structures formed by the channel or inlet and outlet configurations, turbulence and vortices can also be created or intensified in the flow field by adding microchannels and / or vortex promoters in the first and / or second flow field.

[0112] In some examples, one or more first and / or second vortex promoters include one or more of: one or more drop-shaped obstacles, one or more circular obstacles, one or more twisted strips, one or more coiled wires, one or more baffle types, one or more twisted strip coil wires, and one or more twisted strips with one or more rods.

[0113] In some examples, the ratio of the average channel width of the channels included in the first flow field to the average rib width of the ribs included in the first flow field is in the range of 0.25 to 5.0, preferably 0.4 to 2.0, and more preferably 0.5 to 1.5. In some embodiments, the ratio of the average channel width of the channels included in the second flow field to the average rib width of the ribs included in the second flow field is in the range of 0.25 to 5.0, preferably 0.4 to 2.0, and more preferably 0.5 to 1.5.

[0114] As described above, one or more channels in the first and second flow fields are separated by ribs. The ribs are formed by a solid structure of the flow field that is part of the electrode. By adjusting the ratio of channels to ribs, the flow field can be optimized with respect to the amount of fluid in the flow field, the flow rate, and the structural stability of the redox battery cell. That is, if the ratio of the average channel width of the channels included in the first flow field to the average rib width of the ribs included in the first flow field is close to the lower limit of 0.25, the ribs surrounding the channels are wider (on average) than the channels surrounded by the ribs. In this case, the mechanical stability of the battery is maximized. On the other hand, if the ratio of the average channel width of the channels included in the first flow field to the average rib width of the ribs included in the first flow field is close to the upper limit of 5.0, the ribs surrounding the channels are narrower (on average) than the channels surrounded by the ribs. Therefore, the amount of fluid in the flow field and the possible maximum charge transferred are maximized.

[0115] In some examples, the average channel width of the channels included in the first flow field is in the range of 1.0 to 5.0 mm, preferably 2.0 to 4.0 mm, wherein the average channel height of the channels included in the first flow field is in the range of 0.1 to 2.0 mm, preferably 0.5 to 1.0 mm, and the average rib width of the ribs included in the first flow field is in the range of 0.5 to 1.5 mm, preferably 0.75 to 1.25 mm. Additionally or alternatively, in some examples, the average channel width of the channels included in the second flow field is in the range of 1.0 to 5.0 mm, preferably 2.0 to 4.0 mm, wherein the average channel height of the channels included in the second flow field is in the range of 0.1 to 2.0 mm, preferably 0.5 mm to 1.0 mm, and the average rib width of the ribs included in the second flow field is in the range of 0.5 to 1.5 mm, preferably 0.75 to 1.25 mm.

[0116] Similar to the ratio of ribs to channels in fuel cells, by adjusting the absolute width and height of the channels and ribs, the mechanical stability and fluid volume in the flow field can be tuned and optimized.

[0117] In some examples, a first flow path of the first electrolyte in the first flow field of the first electrode (defined by the first flow field) and a second flow path of the second electrolyte in the second flow field of the second electrode (defined by the second flow field) are substantially parallel to each other.

[0118] Charge transfer may be optimized by providing flow paths, as generally defined by the general flow direction of fluid in the flow field from the one or more inlets to the one or more outlets, that are substantially parallel in the first and second flow fields.

[0119] In some examples, the first storage tank contains at least a first electrolyte, and the pH value of the first electrolyte is pH = 2 to pH = 8, preferably pH = 2 to pH = 5, and further preferably pH = 3.5 to pH = 4.5. In some examples, the pH value of the first electrolyte is 4.0 ± 0.2. Additionally or alternatively, in some examples, the second storage tank contains at least a second electrolyte, and the pH value of the second electrolyte is pH = 2 to pH = 8, preferably pH = 2 to pH = 5, and further preferably pH = 3.5 to pH = 4.5. In some examples, the pH value of the first (and / or second) electrolyte is 4.0 ± 0.2.

[0120] The standard potential of many redox species is particularly dependent on pH, offering the possibility of increasing the cell potential through pH adjustment. That is, since the anolyte and catholyte in a redox battery can be pH-dependent in terms of the resulting voltage (as expressed by the Nernst equation), by providing a pH value within the aforementioned range, the cell voltage can be optimized while simultaneously preventing energy losses due to side reactions (such as hydrogen evolution at the negative electrode). Furthermore, by providing a pH value within the aforementioned range, corrosion and / or health issues are avoided, thereby enabling durable and harmless operation of the redox battery cells.

[0121] In some examples, the first electrolyte comprises a first buffer system. Additionally or alternatively, in some examples, the second electrolyte comprises a second buffer system.

[0122] Side reactions and / or charge transfer can affect the pH of the electrolyte. To prevent significant pH excursions and provide a stable redox system over multiple redox cycles, a buffer system can be provided in the first and / or second electrolyte. Exemplary buffer systems include acetic acid / acetate buffers, carbonic acid, bicarbonate buffers, and dihydrogen phosphate / hydrogen phosphate buffers, and combinations thereof.

[0123] In some examples, the first and / or second electrolyte includes polyatomic ions, preferably selected from vanadates, molybdates, tungstates, niobates, tantalates, manganates, ferrates, nickelates, and mixtures thereof, preferably in a concentration range of 0.1 M to 2.0 M.

[0124] The polyatomic ions according to the present disclosure are preferably polyoxymetallates. Polyoxymetallates (POMs) are polyatomic ions, typically anions, which consist of three or more transition metal oxyanions, linked together by shared oxygen atoms to form a closed three-dimensional framework. The metal atoms can be Group 6 (Mo, W), Group 5 (V, Nb, Ta), transition metals, and Tc in a high oxidation state. POMs can be isopolymetalates consisting of only one metal and an oxide, or heteropolymetalates consisting of one metal, an oxide, and a main group oxyanion. Compared to monatomic ions, polyatomic ions exhibit beneficial properties such as fast redox reactions, stable chemical properties, multi-electron reactions, good redox reversibility, and low permeability. In particular, due to the charge delocalization in the polyatomic ions, multiple charges can be quickly and easily transferred from and to the polyatomic ions. Then, integrating the flow field into at least the first electrode allows efficient charge transfer from the POM in the electrolyte to the current collector when the battery is charged / discharged.

[0125] In some examples, the battery provides a range of 0.1A / cm 2 Up to 10A / cm 2 The current density is preferably in the range of 0.1A / cm 2 Up to 5A / cm 2 The current density is preferably in the range of 0.5 A / cm 2 to 2A / cm 2 current density.

[0126] By using polyatomic ions at concentrations such as those mentioned above, high current densities in the battery can be achieved. Furthermore, while regular planar electrodes are limited by their geometry and therefore do not allow such high current densities, integrating a flow field into at least one electrode enables efficient charge transfer to the current collector during battery discharge.

[0127] In some examples, the second electrode includes a fluid.

[0128] It has been discussed in detail above that the first and second electrodes can comprise an all-solid structure. However, the second electrode can optionally comprise a fluid. As used herein, the term "electrode" generally refers to a physical object (such as a solid or fluid) capable of delivering current to or drawing current from a power source. That is, the term "electrode" as used herein can refer to an electrical solid, but can alternatively refer to an electrical fluid. In structures where the second electrode comprises a fluid, the first electrode can include the technical features described above. Furthermore, while charge transferred via the membrane disposed between the first and second electrodes can be transferred from the first electrode comprising the first flow field (and the electrolyte distributed therein) to the second electrolyte, charge can also be transferred from the first electrode to a fluid, such as a gas. That is, electrons provided from the first electrode during discharge can react with the gas at the second electrode. For example, by reacting oxygen (contained in the ambient air) with electrons provided by the discharge of the electrolyte from the first electrode, the oxygen can be reduced and hydroxyl anions produced. By providing a redox battery cell in which the second electrode comprises a fluid (optionally including air and / or oxygen), the overall volume of the battery can be reduced while maintaining the battery's energy density due to, for example, the omission of the second electrolyte.

[0129] In some examples, the gas includes air. In some examples, the gas includes oxygen. By operating the redox battery cell with (ambient) air, the infrastructure surrounding the redox battery cell can be further simplified because no manual gas transfer is required.

[0130] In a further aspect according to the present disclosure, a redox battery stack is provided. The redox battery stack according to the present disclosure comprises one or more redox battery cells as defined in any of the example embodiments outlined in the present disclosure, wherein the stack further comprises one or more current collectors coupled to the first and / or second electrodes of the one or more redox batteries.

[0131] In some examples, the stack further includes a first pump for pumping the first electrolyte from the first tank to the first flow field of the first electrode.

[0132] In some examples, the stack further includes a second pump for pumping the second electrolyte from the second tank to the second flow field of the second electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0133] Further aspects, details and advantages of the present disclosure will become apparent from the following detailed description of exemplary embodiments and the accompanying drawings, in which:

[0134] Figure 1An exemplary redox battery cell is shown coupled to first and second electrolyte reservoirs for providing first and second electrolytes.

[0135] Figure 2 An exemplary redox battery cell is shown coupled to a single electrolyte tank providing electrolyte for a single electrolyte.

[0136] Figure 3A An exemplary single serpentine structure is shown.

[0137] Figure 3B An exemplary multi-serpentine structure is shown.

[0138] Figure 3C An exemplary hybrid serpentine structure is shown.

[0139] Figure 4A An exemplary parallel structure is shown.

[0140] Figure 4B An exemplary discontinuous structure is shown.

[0141] Figure 5A An exemplary needle-type structure is shown.

[0142] Figure 5B An exemplary crisscross structure is shown.

[0143] Figure 6A An exemplary fractal interdigitated structure is shown.

[0144] Figure 6B An exemplary structure including asymmetric channels is shown.

[0145] Figure 6C An exemplary mesh structure is shown.

[0146] Figure 7 Exemplary channel shapes are shown.

[0147] Figure 8 Shown is the Nyquist plot of an RFB with carbon felt and electrodes including a flow field in 1 M NaCl over the frequency range of 1 mHz to 1 mHz.

[0148] Figure 9 Shown is the Bode plot of the RFB with carbon felt in 1 M NaCl over the frequency range of 1 mHz to 1 mHz.

[0149] Figure 10 Bode plots of the RFB with electrodes including a flow field in 1 M NaCl over the frequency range of 1 mHz to 1 mHz are shown.

[0150] Figure 11 Shown is a rate test of the RFB of the cell at an open circuit voltage of 0.95 V. IR-corrected discharge voltage and IR-corrected power density for the cell with carbon felt and electrodes including a flow field.

[0151] Figure 12 A block diagram of an exemplary redox battery stack is shown. DETAILED DESCRIPTION

[0152] In the following description, for purposes of explanation rather than limitation, specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent to one skilled in the art that the present disclosure may be practiced in other embodiments that depart from these specific details.

[0153] The example embodiments of the redox battery cells described herein allow for the use of a wide range of redox species in the redox electrolyte. By providing a first electrode comprising a flow field, higher currents, current densities (e.g., up to 10 A / cm2) can be provided by the cell or a stack comprising the cell. 2 ), thereby achieving power density.

[0154] Furthermore, including the first flow field in the first electrode allows for omitting the additional carbon felt typically used in the prior art in order to distribute the electrolyte comprising redox active species.

[0155] Besides the structural simplification of the system (by avoiding additional carbon felt or equivalent components for electrolyte distribution), the inclusion of flow fields in the electrodes significantly reduces the pumping performance required for electrolyte circulation, thereby reducing the overall power consumption of the cell.

[0156] Figure 1 An exemplary redox battery (100) is shown having electrodes (101), wherein a first electrode (101a) includes a flow field and a membrane (102) disposed between the first electrode (101a) and a second electrode (101b). Figure 1 In the exemplary redox battery cell shown, the flow field of the first electrode (101a) is coupled to a first reservoir (103), such as a negative electrolyte (negolyte) tank, and the second electrode (101b) is coupled to a second reservoir (104), such as a positive electrolyte (posolyte) tank. The current collector (105) is coupled to the first electrode (101a), i.e., the first current collector (105a), and to the second electrode (101b), i.e., the second current collector (105b). The first pump (106a) and the second pump (106b) are configured to provide the negative electrolyte and the positive electrolyte to the electrodes coupled thereto.

[0157] Figure 2Another exemplary redox battery (200) is shown in which the second electrode (201b) is an air electrode. That is, although the portion of the redox battery cell that can be connected to the negative electrolyte tank (203) is the same as Figure 1 The redox battery cell (100) shown is identical (including the pump (206) and membrane (202)), but the second electrode is an air electrode (201b) which includes a second solid electrode (which is part of the second electrode (201b) and thus Figure 2 That is, the charge transferred from the first electrode side via ions to the second electrode (201b) can be further transferred via electrochemical reactions (such as with oxygen):

[0158]

[0159] Current collectors (205a, 205b) are coupled to the first electrode and the second solid electrode of the air electrode (201b).

[0160] 3 to 6 show the flow field structures described above according to some example embodiments described herein, including single serpentine, multi-serpentine, mixed serpentine ( Figures 3A-3C ), parallel, discontinuous ( Figure 4A 、 4B ), needle type, cross type ( Figure 5A 、 5B ), fractal cross-finger type, including asymmetric channel, mesh type ( Figures 6A-6C ). In the selected configuration, the flow direction of electrolyte or fluid into and out of the flow field is indicated by arrows.

[0161] Figure 7 Select channel shapes are shown according to some example embodiments described herein, including rectangular, triangular, and semicircular.

[0162] Figure 8 Nyquist plots for a redox battery cell according to the present disclosure (with a first electrode including a flow field) in 1 M NaCl over a frequency range of 1 mHz to 1 mHz are shown, compared to a redox battery cell including an electrode without a flow field but with carbon felt for electrolyte distribution. While the shapes of the two plots are generally similar, the redox battery cell according to the present disclosure (represented by triangular measurement points) exhibits an overall lower ohmic resistance compared to the redox battery cell including the carbon felt (represented by circular measurement points).

[0163] Figure 9The Bode plot of a redox battery cell including electrodes without a flow field but including carbon felt for distributing the electrolyte is shown in 1M NaCl over a frequency range of 1mHz to 1mHz. In the Bode plot, the frequency is plotted vertically and the absolute value of the electrical phase shift and impedance are plotted on the horizontal axis. Figure 9 In the figure, the circular measurement points of the carbon felt system represent log(│Z│) vs. log(freq) and the square measurement points represent phase(Z) vs. log(freq) data.

[0164] Figure 10 The Bode plot of a redox battery cell (first electrode including flow field) according to the present disclosure is shown in 1M NaCl in the frequency range of 1mHz to 1mHz. Figure 10 , the circular measurement points represent data of log(│Z│) versus log(freq), and the square measurement points of the flow field system according to the present disclosure represent data of phase (Z) versus log(freq).

[0165] The Bode plots of the two systems also show generally similar trends. However, similar to the Nyquist plots described above, the overall resistance of the carbon felt system is greater compared to the flow field system according to the present disclosure. In particular, at low frequencies, the logarithmic resistance in the flow field system is more than halved. Without wishing to be bound by theory, it is hypothesized that the differences in the Nyquist and Bode plots are caused by the additional resistance and / or capacitance in the redox battery cells that include the carbon felt. For example, the transmission characteristics of such carbon felts commonly used in the prior art are known to be an important parameter, as transmission resistance can result in significant parasitic power losses depending on the configuration of the redox battery cells.

[0166] Figure 11 Shown are the results of an RFB rate test on a cell at an open circuit voltage of 0.95 V. The IR-corrected voltage for the carbon felt system is represented by the circular data points. The IR-corrected voltage for the flow field system is represented by the diamond data points. The IR-corrected power density for the carbon felt system is represented by the square data points. The IR-corrected power density for the flow field system is represented by the triangle data points. Figure 11 It was shown that the flow field system provides surprisingly increased discharge voltage and surprisingly increased power density compared to the carbon felt system.

[0167] Figure 12 An exemplary redox battery stack 200 is shown. Figure 12 The exemplary stack shown includes one redox battery cell and current collectors 110 electrically coupled to opposite sides of the redox battery cell.

[0168] It should be understood that the present disclosure has been described with reference to exemplary embodiments that may be varied in many aspects. Accordingly, the present invention is not to be limited except as by the appended claims.

Claims

1. A redox battery cell comprising: the first electrode, a second electrode spaced apart from the first electrode, and a membrane arranged between the first electrode and the second electrode, The first electrode includes a first flow field.

2. The redox battery cell of claim 1, wherein the second electrode comprises a second flow field. 3 . The redox battery cell according to claim 1 , wherein the first electrode and / or the second electrode comprises an all-solid structure.

4. A redox battery cell according to any one of claims 1 to 3, wherein the first flow field forms an integral part of the first electrode.

5. A redox battery cell according to any one of claims 1 to 4 in combination with claim 2, wherein the second flow field forms an integral part of the second electrode.

6. A redox battery cell according to any one of claims 1 to 5 in combination with claim 2, wherein the first flow field and the second flow field are substantially symmetrical with respect to the membrane arranged between the first electrode and the second electrode.

7. The redox battery cell according to claim 1 , wherein the first electrode and / or the second electrode comprises one or more components selected from the group consisting of aluminum, carbon-coated aluminum, copper, carbon-coated copper, nickel, carbon-coated nickel, iron, carbon-coated iron, steel, carbon-coated steel, stainless steel, carbon-coated stainless steel, carbon, glassy carbon, and graphite, preferably one or more components selected from the group consisting of graphite, aluminum, carbon-coated aluminum, copper, and carbon-coated copper.

8. The redox battery cell of claim 7, wherein the first electrode comprising the first flow field is composed of graphite, aluminum, carbon-coated aluminum, copper, or carbon-coated copper.

9. The redox battery cell according to claim 7 or 8 in combination with claim 2, wherein the second electrode comprising the second flow field is composed of graphite, aluminum, carbon-coated aluminum, copper or carbon-coated copper.

10. The redox battery cell according to claim 1, wherein The film includes one or more inorganic membranes, optionally metal, ceramic or zeolite membranes, or One or more organic membranes, optionally synthetic or natural polymer membranes.

11. Redox battery cell according to any one of claims 1 to 9, wherein the membrane comprises one or more composite membranes, optionally a polyphosphate membrane.

12. A redox battery cell according to any one of claims 1 to 11, wherein the membrane is an ionic or non-ionic size selective membrane with a pore size range of to The preferred range is to 13. The redox battery cell according to any one of claims 1 to 12, wherein the first flow field comprises one or more first inlets coupled to a first tank and / or one or more first outlets coupled to the first tank, wherein Preferably, the one or more first inlets of the first flow field are arranged substantially opposite a corresponding respective one of the one or more first outlets of the first flow field.

14. The redox battery cell according to claim 1 , wherein the second flow field comprises one or more second inlets coupled to a second tank and / or one or more second outlets coupled to the second tank, wherein Preferably, the one or more second inlets of the second flow field are arranged substantially opposite a corresponding respective one of the one or more second outlets of the second flow field.

15. The redox battery cell of claim 13 or 14, wherein the first flow field comprises a plurality of first inlets coupled to the first tank.

16. The redox battery cell of claim 14, wherein the second flow field comprises a plurality of second inlets coupled to the second tank.

17. The redox battery cell according to claim 15, wherein a first one of the first inlets has an inlet diameter different from an inlet diameter of a second one of the first inlets, and / or a first one of the first inlets has an inlet shape different from an inlet shape of the second one of the first inlets.

18. The redox battery cell according to claim 16 or 17, wherein a first one of the second inlets has an inlet diameter different from a second one of the second inlets and / or a first one of the second inlets has an inlet shape different from a second one of the second inlets.

19. The redox battery cell of any one of claims 13 to 18, wherein the first flow field comprises a plurality of first outlets coupled to the first tank.

20. The redox battery cell of any one of claims 14 to 19, wherein the second flow field comprises a plurality of second outlets coupled to the second tank.

21. The redox battery cell according to claim 19 or 20, wherein a first outlet diameter is different from a second outlet diameter of the first outlet and / or a first outlet shape is different from a second outlet shape of the first outlet.

22. The redox battery cell according to claim 20 or 21, wherein the outlet diameter of a first one of the second outlets is different from the outlet diameter of a second one of the second outlets, and / or the outlet shape of a first one of the second outlets is different from the outlet shape of a second one of the second outlets.

23. The redox battery cell according to any one of claims 19 to 22, wherein an inlet diameter of a first one of the first inlets is different from an outlet diameter of a first one of the first outlets.

24. The redox battery cell according to any one of claims 19 to 23, wherein an inlet shape of a first one of the first inlets is different from an outlet shape of a first one of the first outlets.

25. The redox battery cell according to any one of claims 20 to 24, wherein an inlet diameter of a first of the second inlets is different from an outlet diameter of a first of the second outlets.

26. The redox battery cell according to any one of claims 20 to 25, wherein an inlet shape of a first of the second inlets is different from an outlet shape of a first of the second outlets.

27. The redox battery cell of any one of claims 1 to 26, wherein the first flow field comprises one or more channels separated by ribs for delivering a first electrolyte to the first electrode.

28. A redox battery cell according to claim 2 or any one of claims 3 to 27 in combination with claim 2, wherein the second flow field comprises one or more channels separated by ribs for delivering a second electrolyte to the second electrode.

29. A redox battery cell according to claim 27 or 28, wherein the one or more channels form one or more of the following: Single serpentine structure, Multi-snake structure, Hybrid serpentine structure, Parallel structure, discontinuous structure, Needle-shaped structure, Cross structure, Cross-finger structure, Fractal interdigitated structure, including the structure of asymmetric channels, reticular structure, or a combination of one or more thereof.

30. The redox battery cell of claim 29, wherein the channels form a combination of a parallel structure and a serpentine structure.

31. The redox battery cell according to any one of claims 27 to 30, wherein the one or more channels included in the first flow field are rectangular, square, parallelogram, trapezoidal, triangular or semicircular in shape at least along a portion of the respective channel.

32. The redox battery cell according to claim 28 or any one of claims 29 to 31 in combination with claim 28, wherein the one or more channels included in the second flow field are rectangular, square, parallelogram, trapezoidal, triangular or semicircular along at least a portion of the respective channel.

33. The redox battery cell according to any one of claims 27 to 32, wherein the one or more channels included in the first flow field include one or more first microchannels and / or one or more first vortex promoters.

34. A redox battery cell according to claim 28 or any one of claims 29 to 33 in combination with claim 28, wherein the one or more channels included in the second flow field include one or more second microchannels and / or one or more second vortex promoters.

35. The redox battery cell of claim 33 or 34, wherein the one or more first and / or second vortex promoters comprise one or more of: one or more drop-shaped obstacles, one or more circular obstacles, one or more twisted ribbons, one or more coiled wires, one or more baffle types, one or more twisted ribbon coil wires, and one or more twisted ribbons with one or more rods.

36. The redox battery cell according to any one of claims 27 to 35, wherein a ratio of an average channel width of the channels included in the first flow field to an average rib width of the ribs included in the first flow field is in the range of 0.25 to 5.0, preferably 0.4 to 2.0, further preferably 0.5 to 1.

5.

37. A redox battery cell according to claim 28 or any one of claims 29 to 36 in combination with claim 28, wherein the ratio of the average channel width of the channels included in the second flow field to the average rib width of the ribs included in the second flow field is in the range of 0.25 to 5.0, preferably 0.4 to 2.0, further preferably 0.5 to 1.

5.

38. A redox battery cell according to any one of claims 27 to 37, wherein The average channel width of the channels included in the first flow field ranges from 1.0 to 5.0 mm, preferably from 2.0 to 4.0 mm, wherein The average channel height of the channels included in the first flow field is in the range of 0.1 to 2.0 mm, preferably 0.5 to 1.0 mm, and wherein The ribs comprised in the first flow field have an average rib width in the range of 0.5 to 1.5 mm, preferably 0.75 to 1.25 mm.

39. A redox battery cell according to claim 28 or any one of claims 29 to 38 in combination with claim 28, wherein The average channel width of the channels included in the second flow field ranges from 1.0 to 5.0 mm, preferably from 2.0 to 4.0 mm, wherein The average channel height of the channels included in the second flow field ranges from 0.1 to 2.0 mm, preferably from 0.5 to 1.0 mm, and wherein The ribs comprised in the second flow field have an average rib width in the range of 0.5 to 1.5 mm, preferably 0.75 to 1.25 mm.

40. The redox battery cell of any one of claims 1 to 39 in combination with claim 2, wherein a first flow path of a first electrolyte in a first flow field of the first electrode defined by the first flow field and a second flow path of a second electrolyte in a second flow field of the second electrode defined by the second flow field are substantially parallel to each other.

41. The redox battery cell according to any one of claims 13 to 40, wherein the first tank contains at least a first electrolyte having a pH value of pH=2 to pH=8, preferably pH=2 to pH=5, further preferably pH=3.5 to pH=4.

5.

42. The redox battery cell according to claim 14 or any one of claims 15 to 41 in combination with claim 14, wherein the second tank contains at least a second electrolyte having a pH value of pH=2 to pH=8, preferably pH=2 to pH=5, further preferably pH=3.5 to pH=4.

5.

43. The redox battery cell of claim 41 or 42, wherein the first electrolyte comprises a first buffer system.

44. A redox battery cell according to claim 42 or claim 43 in combination with claim 42, wherein the second electrolyte comprises a second buffer system.

45. The redox battery cell according to any one of claims 41 to 44, wherein the first electrolyte and / or the second electrolyte comprises polyatomic ions, preferably polyatomic ions selected from vanadates, molybdates, tungstates, niobates, tantalates, manganates, ferrates, nickelates and mixtures thereof, preferably in a concentration range of 0.1 M to 2.0 M.

46. ​​A redox battery cell according to any one of claims 1 to 45, wherein the cell provides a current in the range of 0.1 A / cm 2 Up to 10A / cm 2 The current density is preferably in the range of 0.1A / cm 2 Up to 5A / cm 2 The current density is preferably in the range of 0.5 A / cm 2 to 2A / cm 2 current density.

47. The redox battery cell of any one of claims 1 to 46, wherein the second electrode comprises a fluid.

48. The redox battery cell of claim 47, wherein the fluid comprises a gas.

49. The redox battery cell of claim 48, wherein the gas comprises air.

50. The redox battery cell of claim 48 or 49, wherein the gas comprises oxygen.

51. A redox battery cell stack comprising one or more redox battery cells as claimed in any one of the preceding claims, wherein the stack further comprises one or more current collectors coupled to the first and / or second electrodes of the one or more redox batteries.

52. The redox battery cell stack of claim 51 , wherein the stack further comprises a first pump for pumping a first electrolyte from a first tank to the first flow field of the first electrode.

53. A redox battery cell stack according to claim 51 or 52 in combination with claim 2, wherein the stack further comprises a second pump for pumping a second electrolyte from a second tank to the second flow field of the second electrode.

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