Redox flow battery system and stack

Abstract

A single redox battery cell is described that includes 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 includes a first flow field.

Description

Detailed Description of the Invention

[0001] [Technical Field] The present disclosure relates generally to single redox battery cells and redox battery cell stacks. 〔background〕

[0002] The use of renewable energy sources such as solar and wind requires energy management, including energy storage capabilities. Redox flow batteries (RFBs) are an option that can be used in centralized as well as decentralized systems. RFBs are the only type of battery whose energy content and power output can be scaled independently, offering great flexibility for applications such as load leveling and frequency stabilization.

[0003] Current technology, all-vanadium RFBs, offer clear advantages but suffer from distinct problems: low energy density (approximately 20 times lower than that of lithium-ion batteries) and low specific power density, which require large surface area felt electrodes to mitigate. Complex ions with multiple redox centers (higher energy density) and high electron transfer rates (higher power density) may offer an alternative approach to this established system. However, these complex ions require substantial structural and chemical analysis and redesign of the redox system and the assembly stacks that comprise it.

[0004] Redox flow batteries (RFBs) are one of the few options for storing energy from intermittent renewable sources such as wind and solar. The RFB concept itself is quite elegant as it can scale energy and power independently, but the community has not yet decided on a universal battery chemistry. Currently, there are essentially two schools of thought: the first group uses 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 (e.g., [Fe(CN)6] 4- / [Fe(CN)6] 3- ) as the electron carrier (hereafter, for simplicity, all three will be referred to as metal ions), while the second group proposes the use of organic redox-active materials. Both approaches have their advantages and disadvantages. A prominent example of a redox couple with dissolved metal chemistry is the all-vanadium redox flow battery (VRFB). There are four oxidation states of vanadium (V 2+ , V 3+ ,VO 2+ ,VO 2+ This battery chemistry, utilizing a .S.I.T. ), has the advantage that species crossover from one half-cell through the separator to the other half-cell does not lead to chemical contamination, and the battery can be electrochemically rebalanced.

[0005] The main disadvantage of VRFB is that 2+ / V 3+ and VO 2+ / VO 2+ The slow rate of the redox reaction of vanadium, which limits the current density and therefore the power density, is a major issue. The exact electronic rate constant k0 for the vanadium reaction and which half-cell is faster is debated in the literature, but k0 = 10 -6 cm·s -1 The order is:

[0006] Organic redox couples can be fabricated from low-cost, abundant elements, and their tunable structures offer greater versatility than metal-ion redox couples. Numerous organic redox couples have been published in recent years. However, most research has been limited to laboratory cell operation, and scale-up to larger cell areas, larger electrolyte volumes, and extended cycling is currently lacking.

[0007] Another type of redox electrochemistry that can be employed in RFBs uses polyanions, such as polyoxometalates (POMs), which form discrete transition metal oxide nanoclusters. Although prepared from metals, polyoxometalates offer a high degree of structural diversity, making them a versatile electrochemistry.

[0008] POM as an electrolyte in RFBs offers significant chemical and / or electrochemical advantages over known vanadium systems, including: 1. Electrons added to POM by reduction are often delocalized across multiple metal atoms, facilitating fast electron transfer that enables high current densities.

[0009] 2. POMs are anions and larger than solvated transition metals. Therefore, POMs should not permeate the ion-exchange membranes typically used in RFBs;

[0010] 3. Electron transfer by POMs is often coupled with cation or proton transfer. Therefore, the net charge of the polyoxoanion does not change upon oxidation or reduction. This concept, often found in biological systems, avoids highly charged species and leads to improved stability;

[0011] 4. Some POMs are highly soluble, with the maximum concentration determined by the type of POM, the electrolyte, and the counterions present. This, combined with the transfer of multiple electrons per molecule, can result in high energy densities.

[0012] Furthermore, each POM as a redox species ion in the electrolyte can transfer multiple electrons when used in a redox cycle, such as in a redox flow battery, allowing for more efficient charging and discharging and higher storage charge density compared to conventional vanadium-ion flow batteries. Furthermore, the lower charge transfer resistance of polyoxometalate (POM) electrolytes compared to vanadium electrolytes increases voltage efficiency and power density.

[0013] The POM electrolyte contains large redox species ions that permeate the membrane slower than vanadium ions, reducing the self-discharge of the flow battery.

[0014] However, certain redox properties, such as increased charge transfer rate or charge density, prevent the energy-efficient implementation of these novel electrolyte types containing redox species ions with comparable charge transfer properties into state-of-the-art redox flow batteries. 〔summary〕

[0015] The present inventors have recognized a need for improved single redox battery cells that can fully utilize the energy storage capabilities of redox species such as POM and redox species with comparable charge transfer properties.

[0016] In one embodiment according to the present disclosure, there is provided a single redox battery cell comprising: a first electrode; a second electrode spaced apart from the first electrode; and a membrane disposed between the first electrode and the second electrode, wherein the first electrode comprises a first flow field.

[0017] As an example, a redox battery cell can be used to convert electrical energy generated in a renewable energy system into chemical energy that can be stored until a demand for electrical energy arises, after which the redox battery cell can convert the chemical energy into electrical energy for supplying a power grid, an electric vehicle, or the like.

[0018] In this embodiment, the 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. The term "electrode" as used herein generally refers to a physical object (e.g., solid or fluid) capable of receiving an electric current from or to a power source. That is, the term "electrode" as used herein refers not only to an electron donor or electron remover, i.e., an electronically conductive solid, but also to an electronically conductive fluid. Thus, the redox battery cell defined in claim 1 can be characterized in that both the first and second electrodes comprise solid structures. Alternatively, the redox battery cell defined in claim 1 can be characterized in that the first electrode comprises a solid structure and the second electrode comprises a fluid, such as a gas (preferably containing air and / or oxygen), in contact with a second solid (e.g., metal) electrode. That is, if the second electrode contains oxygen, for example, the oxygen can participate in an electrochemical reaction between protons supplied to the second solid electrode through the membrane and electrons supplied to the second solid electrode through the charge collector in a two-electron process to produce water. Alternatively, the second electrode may comprise a fluid such as a gas, preferably air, and a second solid electrode in contact with the fluid, i.e., electrons supplied from the first electrode during discharge can react with the fluid or gas at the second electrode.

[0019] 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 spaced apart from the first electrode. The first and second electrodes can be spatially spaced apart by a distance (inter-electrode distance) of, for example, more than 1 mm. For example, the inter-electrode distance can be in the range of 1 mm to 1 cm, or 2 mm to 100 mm, or 4 mm to 50 mm. Preferably, the inter-electrode distance is 10 mm to 25 mm.

[0020] The first and second electrodes are spaced apart to avoid short circuit failures and tunneling currents. In addition to the spatial separation, the first and second electrodes are further separated by a membrane disposed between the first and second electrodes. The membrane acts as an (electronic) separator between the first and second electrodes. The membrane allows for the movement of ionic charge carriers necessary to close the circuit during charging and discharging of the battery.

[0021] The first electrode comprises a first flow field for efficient operation of the redox battery single cell. As used herein, the term "flow field" may refer to a space or region into which a fluid, such as a liquid electrolyte, is introduced and distributed through a physical structure to appropriately deliver said fluid to a desired location on the electrode. The first electrode flow field generally serves several essential functions, including as a current collector and, for example, as a charge collector coupled thereto, to provide electrical continuity to the redox battery single cell electrode.

[0022] Furthermore, the flow field can function as a mechanical support for the membrane electrode assembly (MEA), which consists of a first electrode, a second electrode, and a membrane disposed between the first and second electrodes, as well as to distribute the electrolyte. For example, it is well known that the performance of a fuel cell is highly dependent on the efficient transport and uniform distribution of reactants to the electrode catalyst and proper water management in the fuel cell, i.e., the supply and removal of water generated during fuel cell operation. Similarly, flow field design significantly influences the performance of a redox battery unit cell by controlling the electrolyte gradient, flow rate, pressure drop, water distribution, current density profile, and the utilization efficiency of redox species at the electrodes. Therefore, by providing a redox battery unit cell including a first electrode, the first electrode is provided with a first flow field, and the redox battery unit cell according to the present disclosure provides a unit cell that is adaptable to a wide range of redox species used in redox electrolytes. By including a flow field in the first electrode, higher currents, and therefore power densities, can be achieved compared to conventional electrodes that do not include a flow field, while the battery device can be structurally simplified, thereby improving its reliability and durability.

[0023] In some examples, multiple repetitions of electrodes with flow field / membrane / electrode sub-cells may be considered a single cell and used in a stacked arrangement.

[0024] In some examples, the second electrode of the redox battery single cell comprises a (second) flow field.

[0025] Like the first electrode, the second electrode may also include a second flow field. The second electrode's second flow field is generally provided for technical purposes, as discussed above for the first electrode. By providing a flow field (i.e., a second flow field) in the second electrode, the versatility of the redox battery unit cell can be further enhanced by enabling the energy-efficient combination of more possible combinations of different electrolyte solutions and / or concentrations in contact with the first and second electrodes.

[0026] In some examples, the first electrode and / or the second electrode comprise an all-solid-state structure. As used herein, the term "all-solid-state structure" may refer to a solid structure that has three dimensions as its geometric body and generally maintains its dimensions and shape at least under normal operating conditions of a redox battery (temperatures ranging from -20°C to 90°C, humidity ranging from 0% relative humidity to an aqueous environment, etc.). An "all-solid-state structure" may be a porous structure or a dense structure. By providing a redox battery unit cell having electrodes with an all-solid-state structure, various geometric features can be implemented in the electrodes, resulting in stability and durability, greater versatility, and generally improved charge distribution and transport, as well as electrolyte distribution. Both the first electrode and / or the second electrode may comprise an all-solid-state structure.

[0027] Alternatively, as described above, the first electrode may comprise an all-solid structure and the second electrode may comprise a fluid, or the first electrode may comprise a fluid and the second electrode may comprise an all-solid structure, hi some examples, the first flow field forms an integral part of the first electrode.

[0028] As used herein, the term "integral component" can be defined as a component or technical feature (such as a flow field) being integrally attached to a different component or technical feature (such as an electrode). When a first flow field forms an integral part of a first electrode, these two technical features exist within a single redox battery cell as a single component that provides electrical conductivity and electrolyte distribution. To provide a first flow field as an integral part of a 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 fabricated as a single unit. In the latter case, charge transfer between the flow field and the electrode is optimized by neutralizing charge transfer resistance from Mott-Schottky contacts, grain boundaries, etc. Prior art redox batteries often use carbon cloth to provide electrolyte distribution. However, the use of carbon cloth, which has low electrical conductivity and uncontrolled electrolyte distribution, significantly hinders efficient charge transfer, thereby significantly reducing the energy efficiency of the battery. By providing electrodes with an integral part of the flow field, the redox battery unit cell of the present disclosure can be structurally simplified compared to known electrochemical devices in the prior art.

[0029] In some examples, the first flow field is thus an integral part of the first electrode. Similarly, the second flow field can be an integral part of the second electrode, as described below. In some examples, the electrode is thus a monolithic component of the redox battery unit 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 unit cell thus comprises a first monolithic electrode (formed from a single material) with the flow field integrated therewith.

[0030] In some embodiments, the first electrode is thus essentially formed of a single piece (monolithic electrode) and includes the flow field in a single piece. That is, the electrode can be in the form of a single or monolithic member / component of the redox battery unit cell, and includes the flow path as a structure that is integral with (unitarily formed with) the electrode. That is, the electrode (including the flow field) can be a single working piece. Such a single working piece as the electrode can be in the form of a monolithic piece, as described above. That is, the electrode can be seamless in the assembled redox battery unit cell.

[0031] Thus, the term "monolithic" as used herein refers to an electrode that includes a flow field as a unitary structure. In some examples, the electrode may be provided as a monolithic cube or plate, with the flow field structure carved / molded / formed into the cube structure. The flow field may be incorporated as a relief (recess) into the monolithic electrode.

[0032] That is, the structure is characterized as an integrated entity formed from a single piece or a coherent assembly of interconnected components, emphasizing the inseparability of the two functions (electrode and flow field) provided by the monolithic structure in the overall system. Thus, the structure can have an integral component, which indicates that it is composed of a single material or a combination of homogeneous materials that form a coherent, inseparable unit. Thus, such a single-piece design of the electrode and flow field can emphasize the absence of the need for separate components or assemblies and reinforce the concept of a monolithic structure. In addition to preformed electrode and flow field structures, the inseparability of the structure emphasizes that it cannot be easily separated into separate parts without compromising its function. Such a coherent assembly can be characterized by the seamless integration of the various components and functioning as a single cohesive whole. Thus, in some examples, the electrode and flow field can be integrated to provide excellent electrolyte distribution while possessing excellent electronic conductivity for boundaryless, and therefore substantially resistance-free, current flow.

[0033] Specifically, forming a monolithic (seamless) electrode incorporating a flow field as an integral feature can be prepared from a variety of electronically conductive materials, as further described below. In some examples, the monolithic electrode incorporating a flow field as an integral feature is formed from the group consisting of monolithic aluminum, monolithic carbon-coated aluminum, monolithic copper, monolithic carbon-coated copper, monolithic nickel, monolithic carbon-coated nickel, monolithic iron, monolithic carbon-coated iron, monolithic steel, monolithic carbon-coated steel, monolithic stainless steel, monolithic carbon-coated stainless steel, monolithic carbon, monolithic glassy carbon, monolithic graphite, monolithic titanium, monolithic tantalum, monolithic carbon-coated titanium, monolithic carbon-coated tantalum, monolithic metal carbide-coated titanium, monolithic metal carbide-coated tantalum, preferably monolithic graphite, monolithic aluminum, monolithic carbon-coated aluminum, monolithic copper, and monolithic carbon-coated copper.

[0034] Various methods can be used to prepare an integrated flow field and / or a monolithic electrode with a flow field, including but not limited to the following. By incorporating an electrode with a flow field, the flow field structure can be implemented in the electrode pre-assembly of a redox battery unit cell. This eliminates the need to combine (e.g., via pressing, compression, etc.) the cell components to form the flow field. Specifically, because such pressing or compression steps can easily result in structural weaknesses in the assembled cell, pre-forming the monolithic first electrode (and optionally the monolithic second electrode) provides the redox battery unit cell with the structural integrity and reliability of a complete system that can be further pre-assembled and tested.

[0035] Fabrication of a monolithic electrode structure involves forming a single, integrated part from multiple components without the need for assembly (e.g., pressing, compacting, hot pressing). A variety of methods can be used to prepare monolithic electrode structures (including the flow field as an integral part) for use in redox flow batteries or other electrochemical devices.

[0036] In some examples, the first electrode comprising the first flow field can thus be manufactured by molding, casting, 3D printing, casting, foam forming, deposition, electro-discharge machining, etc. Thus, the monolithic electrode can be a cast electrode, a molded electrode, a 3D printed electrode, a vapor deposited (electrodeposited, chemical vapor deposited) electrode, etc. Methods for preparing such monolithic structures that can be readily incorporated into a redox battery single cell include:

[0037] Casting: In this method, a mixture of electrode materials is prepared in a liquid form, often as a slurry or suspension. The liquid mixture is then poured or cast into a mold of the desired shape. Once the material solidifies, a monolithic structure is formed. After the casting process, post-processing steps such as drying and curing may be applied.

[0038] Forming: The forming process involves using a mold to form a material into the desired shape. The material, which may be a conductive material or a composite, is placed in a mold and pressure and / or heat is applied to force it into the shape of the mold. This process provides control over the final shape of the monolithic electrode and allows for the production of sophisticated and complex structures.

[0039] 3D printing process (additive manufacturing): Additive manufacturing techniques such as 3D printing allow for the layer-by-layer construction of three-dimensional structures. This method allows for precise control over the design and structure of the electrode. The 3D printing process can create monolithic electrodes with specific geometries using a variety of materials, including conductive materials and composites.

[0040] Foaming: The foaming method involves forming a foamed structure of the electrode material. This can be achieved by introducing a foaming agent or gas into a liquid mixture of the electrode material. The resulting shape can be molded into the desired shape and then solidified to form a monolithic structure with a porous and interconnected network.

[0041] Chemical vapor deposition (CVD): CVD is a method for depositing thin films of materials onto a substrate by chemical reactions in the gas phase. This method is often used for coatings, but can also be adapted to form monolithic structures by depositing materials layer by layer to form a cohesive structure.

[0042] Electrodeposition: Electrodeposition involves the electrochemical reduction of metal ions onto a conductive substrate. By controlling the deposition parameters, it is possible to build a uniformly distributed monolithic structure on the electrode material. This method is commonly used for metal-based electrodes.

[0043] Providing the flow field as an integral (single / monolithic) component of the electrode can offer various technical advantages over single redox battery cells, which have an arrangement in which the flow field is formed when the single cell is assembled and pressed (e.g., pressed / hot-pressed). In particular, established assembly methods (e.g., by pressing / hot-pressing fiber mats or conductive components) introduce physical and electrical boundaries into the device, which creates resistivity, significantly impacts electrolyte and current flow, and reduces overall efficiency. Furthermore, providing a single redox battery cell with a monolithic structure that combines the electrode and flow field allows for the use of various material combinations within the cell, since assembly does not require detrimental pressing or compression steps (such as force or shear) to form the flow field structure adjacent to the electrode.

[0044] Further advantages arising from the use of integrated flow field / electrode components are discussed below.

[0045] Simplified design and manufacturing: Integrating the flow field into the electrodes simplifies the overall design of a redox flow battery. This integration often leads to a smaller, more efficient system and reduces the number of separate parts. The simplified design can simplify the manufacturing process, reduce assembly costs, and improve the overall reliability of the system.

[0046] Improved structural integrity: Monolithic integration of the flow field into the electrode structure can improve the structural integrity of redox flow batteries. This integration provides improved support for the flow field and reduces the risk of mechanical failure or deformation. Improved structural integrity is crucial for maintaining the long-term reliability of the battery, especially in applications involving dynamic environmental conditions.

[0047] Improved electrical conductivity: The monolithic integration of electrodes and flow fields allows for better control of the electrical conductivity of the system, which is particularly important for ensuring efficient electron transfer during electrochemical reactions. Improved electrical conductivity contributes to lower internal resistance, which is beneficial for achieving higher energy conversion efficiency and faster charge / discharge rates.

[0048] Optimized Flow Path: Monolithic integration allows for optimized flow paths within the electrode itself, meaning the design can be tailored to ensure that the electrolyte flows evenly across the entire electrode surface, maximizing utilization of the active material. A well-optimized flow path prevents dead zones or areas of poor flow, promoting a uniform electrochemical reaction.

[0049] 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 easier to use. It also reduces the possibility of potential points of failure, contributing to the long-term stability of the system.

[0050] Improved sealing and leakage prevention: Monolithic integration allows for improved sealing between the flow field and electrodes. Effective sealing is crucial to prevent electrolyte leakage, which can lead to safety hazards and compromise the overall performance of the redox flow battery. Integrated designs often provide better control over the sealing mechanism and improve the overall robustness of the system.

[0051] Optimal electrolyte management: Monolithic integration enables superior management of the electrolyte within the electrode structure. This includes control of electrolyte distribution, flow rate, and uniformity. Optimal electrolyte management is crucial to maintaining the electrochemical performance of redox flow batteries and preventing issues such as uneven wear and degradation of electrode materials.

[0052] In summary, integrating a flow field into the monolithic component of a redox flow battery electrode provides benefits related to simplified design, improved structural integrity, improved electrical conductivity, optimized flow paths, reduced system complexity, improved sealing, and optimized electrolyte management. These benefits collectively contribute to a more efficient, reliable, and cost-effective energy storage system. Similarly, the second flow field for the second electrode can also be formed from a monolithic structure comprising the electrode and flow field.

[0053] In some examples, the second flow field forms an integral part of the second electrode. As described for 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 with the second flow field as an integral part. By providing a single redox battery cell having a first electrode with a monolithic first flow field and a second electrode with a monolithic second flow field, synergistic effects can be achieved in coordinating the monolithic electrode and flow field structures on either side of the single redox battery cell.

[0054] Like the first electrode, the second electrode may also include a second flow field, which forms an integral part of the second electrode, and the second flow field of the second electrode is generally provided as an integral part thereof for the technical effects as described above for the first electrode.

[0055] 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.

[0056] The term "substantially symmetrical" as used herein with respect to a flow field can refer to a flow field that corresponds to a membrane disposed between a first electrode and a second electrode, or that is substantially symmetrical with respect to a line parallel to the membrane. That is, the first and second flow fields can have the same shape and dimensions, but the first flow field is positioned closer to the membrane than the second flow field. Alternatively, the second flow field can be positioned closer to the membrane than the first flow field. Alternatively, the first flow field is positioned substantially the same distance from the membrane as the second flow field.

[0057] By providing a single redox battery cell, the first and second flow fields are substantially symmetrical with respect to a membrane disposed between the first and second electrodes, thereby increasing the structural stability and charge transfer of the single redox battery cell. That is, by providing flow fields on both sides of the membrane that are substantially symmetrical with respect to the membrane, structural deformation due to different electrolyte flows or pressures 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 with a fully discharged second electrolyte, charge transfer between the two species across the membrane can be optimized.

[0058] In some examples, the first and / or 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, graphite, preferably graphite, aluminum, carbon-coated aluminum, copper, and carbon-coated copper.

[0059] In general, the first and / or second electrodes can be any electronically conductive material, as described above. When the electrodes comprise one or more of the above compounds, the electrode's electrical conductivity is improved while simultaneously providing structural stability to the redox battery cell. Furthermore, graphite, aluminum, carbon-coated aluminum, copper, and carbon-coated copper provide surprisingly good electrical conductivity combined with structural stability while avoiding costly materials. Carbon coatings can be applied to 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.

[0060] In some examples, the first electrode comprising the first flow field comprises graphite, aluminum, carbon-coated aluminum, copper, or carbon-coated copper, hi some examples, the second electrode comprising the second flow field may comprise graphite, aluminum, carbon-coated aluminum, copper, or carbon-coated copper.

[0061] Electrodes made of graphite, aluminum, carbon-coated aluminum, copper, or carbon-coated copper offer superior conductivity, charge transfer characteristics, and lifespan by reducing or preventing electrode degradation due to potential reactions between the electrode and the electrolyte or other functional groups or absorbed species caused by potential contamination, resulting in improved charge / discharge coulombic efficiency during cycling.

[0062] In some examples, the membrane may comprise one or more inorganic membranes, optionally ceramic or zeolite membranes, or one or more organic membranes, optionally synthetic or natural polymer membranes.

[0063] The membrane may comprise one or more organic membranes, such as synthetic or natural polymer membranes.

[0064] The majority of industrial membranes are made from synthetic or natural polymers, and membranes containing both types of polymers are known as 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.

[0065] Artificial polymers can be synthesized by the polymerization of a monomer or the copolymerization of two or more monomers. There are three general configurations of polymerization: linear chain, such as polyethylene; branched chain, such as polysulfone; and cross-linked, such as phenol-formaldehyde. Linear polymers are easily soluble in organic solvents. They become more flexible or moldable with increasing temperature and are known as thermoplastic polymers. Cross-linked polymers, on the other hand, are poorly soluble in organic solvents. They do not soften with increasing temperature and are known as thermosetting polymers. The choice of polymer must be based on its compatibility with the membrane fabrication technology and the intended application. For example, the polymer must have low affinity for the permeate while being able to withstand harsh cleaning conditions that could otherwise cause membrane fouling. Chain-chain interactions, chain rigidity, functional group polarity, and stereoisomerism must also be considered when selecting the polymer and fabricating the organic membrane.

[0066] The membrane may comprise one or more inorganic membranes, such as ceramic or zeolite membranes.

[0067] Ceramic membranes consist of a metal (e.g., aluminum or titanium) and a non-metal (e.g., oxide, nitride, or carbide). Because ceramic membranes are generally inert, they are used in strongly acidic or basic environments, but are equally suitable for weakly acidic, weakly basic, or neutral pHs. A disadvantage of ceramic membranes is their sensitivity to temperature gradients, which can lead to cracking of the membrane.

[0068] Zeolite membranes are commonly used for highly selective gas separations because of their highly uniform pore size, but they can also be used as membranes for liquid systems such as the disclosed redox battery single cells. Disadvantages of zeolite membranes include their relatively low fluid flux and the requirement for thick membrane layers to prevent cracks and pinholes.

[0069] In some examples, the membrane comprises one or more composite membranes, such as polyphosphate membranes. Polyphosphate membranes comprise an organic polymer and an inorganic phosphate compound, making them polymer-phosphate composite membranes. Polyphosphate composites for membrane fabrication can be synthesized, for example, by reacting ammonium phosphate with silicon oxide in the presence of ammonia. An exemplary composite material has the formula NH4PO3 / (NH4)PO3SiPO 13 The composite may comprise a compound having the formula: NH4PO3. Additional phosphate components, such as NH4PO3, may also be present in the composite. Polyphosphate films are characterized by very high ionic conductivity in humid atmospheres and liquids, and exhibit thermal and chemical stability (e.g., for pH values ​​in the range of 2-10) up to at least 300°C. This makes them suitable for redox battery applications. The conductivity value of polyphosphate films is at least 1.0 x 10 at 50°C in dry hydrogen during heating cycles. -5 S cm -1 to at least 1.0 × 10 at 300 °C -2 S cm -1 The conductivity value is at least 5.0 × 10 at 100 °C in a humid hydrogen atmosphere. -2 S cm -1 to at least 5.0 × 10 at 300 °C -1 S cm -1 It can vary up to.

[0070] In some examples, the membrane is an ionic or nonionic size-selective membrane with a pore size in the range of 5 Å to 100 Å, preferably 10 Å to 50 Å. Pore size (or pore diameter) can be measured using gas porosimetry (gas adsorption) or mercury (intrusion) porosimetry. The selected pore size can be tailored to a specific application / electrolyte. For example, membranes can be selected to retain particles, molecules, or ions with dimensions of 1 nm, 2 nm, 5 nm, or 10 nm. Pore size can also be defined by molecular weight cutoff (MWCO). That is, membranes can 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 of greater than approximately 4.1 nm).

[0071] In some examples, the first flow field comprises one or more first inlets coupled to the first storage tank and / or one or more first outlets coupled to said first storage tank, preferably wherein the one or more first inlets of the first flow field are positioned substantially opposite corresponding respective first inlets of the one or more first outlets of the first flow field.

[0072] A fluid, such as an electrolyte, can be supplied to the first flow field through one or more first inlets. Additionally or alternatively, the fluid can exit the first flow field through one or more first outlets. The first flow field is coupled to a first storage tank through one or more first inlets and one or more first outlets. The first storage tank can be supplied with the first electrolyte. Providing one or more first inlets can create inlet turbulence in the first flow field. Such 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. Such increased flow rate is particularly beneficial for redox species that exhibit fast charge transfer (e.g., due to charge delocalization). Such turbulence can also be created by providing only one inlet and multiple outlets.

[0073] The one or more inlets and one or more outlets are preferably arranged in substantially opposite positions. By providing the one or more inlets and one or more outlets on substantially opposite sides of the flow field, a common macroscopic and controllable flow direction is created.

[0074] In some examples, the second flow field comprises one or more second inlets coupled to the second storage tank and / or one or more second outlets coupled to the second storage tank, preferably the one or more second inlets of the second flow field being positioned substantially opposite a corresponding one of the one or more second outlets of the second flow field.

[0075] As with the first flow field, with respect to the second flow field, a fluid, such as an electrolyte, can be supplied to the second flow field through one or more second inlets. Additionally or alternatively, the fluid can exit 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 generally provided for the technical effect described above for the first flow field. By providing the second flow field with one or more inlets and / or outlets, preferably arranged substantially opposite each other, the second electrolyte in the second flow field can also be provided with turbulence, as described above for the first flow field.

[0076] In some examples, the first flow field includes a plurality of first inlets coupled to the first storage tank, and by providing a plurality of first inlets, inlet turbulence in the first flow field can be created as described above to provide a characteristic flow velocity and turbulence intensity for the first flow field.

[0077] In some examples, the second flow field includes a plurality of second inlets coupled to the second storage tank, which can create inlet turbulence in the second flow field, as described above, to provide characteristic flow velocities and turbulence intensities in the second flow field.

[0078] In some examples, the inlet diameter of a first one of the first inlets is different from the inlet diameter of a second one of the first inlets and / or the inlet shape of a first one of the first inlets is different from the inlet shape of a second one of the first inlets. In some examples, the inlet diameter of a first one of the second inlets is different from the inlet diameter of a second one of the second inlets and / or the inlet shape of a first one of the second inlets is different from the inlet shape of a second one of the second inlets.

[0079] By providing inlets of different diameters and / or different shapes, the turbulence and / or flow rate created in the flow field can be further tailored towards the redox species ions used in the first and second flow fields.

[0080] In some examples, the first flow field includes a plurality of first outlets coupled to the first storage tank, which may be configured to create inlet turbulence in the first flow field as described above to provide a characteristic flow velocity and turbulence intensity in the first flow field.

[0081] In some examples, the second flow field includes a plurality of second outlets coupled to the second storage tank, which can create inlet turbulence in the second flow field as described above to provide a characteristic flow velocity and turbulence intensity in the second flow field.

[0082] In some examples, the outlet diameter of a first one of the first outlets is different from the diameter of a second one of the first outlets and / or the outlet shape of a first one of the first outlets is different from the outlet shape of a second one of the first outlets. In some examples, 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.

[0083] By providing outlets of different diameters and / or different shapes, the turbulence and / or flow rate created in the flow field can be further tailored towards the redox species ions used in the first and / or second flow fields.

[0084] In some examples, the inlet diameter of the first of the first inlets is different from the outlet diameter of the first of the first outlets. Further, in some examples, the inlet shape of the first of the first inlets is different from the outlet shape of the first of the first outlets.

[0085] By providing a combination of first inlets and first outlets of different diameters and / or shapes, the flow rate of the fluid (e.g., electrolyte) can be controlled, thereby adjusting and controlling the turbulence intensity of the first flow field without requiring the incorporation of additional cell infrastructure, such as multiple pumps, into the redox battery single cell.

[0086] 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. Further, 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.

[0087] By providing an inlet diameter and / or shape of the first of the second inlets that differs from the outlet diameter of the first of the second outlets, the technical effects described above for the first flow field can also be achieved for the second flow field.

[0088] In some examples, the first flow field includes one or more channels separated by ribs for supplying a first electrolyte to a first electrode. In some examples, the second flow field includes one or more channels separated by ribs for supplying a second electrolyte to a second electrode. By providing the first and / or second flow fields with channels, a fluid (e.g., an electrolyte) can be directed from an inlet through a fixed flow path within the flow field toward an outlet. This allows for a secondary flow direction within the overall flow direction from the inlet to the outlet within the flow field. By providing a secondary flow direction through channels separated by ribs, the fluid follows a fixed flow path within the flow field, allowing the complete shape of the flow field to be fully utilized for charge transfer to or from the fluid (e.g., an electrolyte). Additionally, the ribs forming the channels provide additional structural stability to the membrane-electrode assembly (MEA).

[0089] In some examples, the one or more channels form one or more of a single serpentine structure, a multiple serpentine structure, a mixed serpentine structure, a parallel structure, a discontinuous structure, a pin-shaped structure, a cross-shaped structure, a fractal interdigitated structure, a structure with asymmetric channels, a mesh structure, or a combination of two or more thereof.

[0090] A single serpentine structure is characterized by a single channel extending from the flow field inlet to the flow field outlet, with fluid flowing in opposite directions from the first section of the serpentine to the second section of the serpentine. The single serpentine channel can be in the form of a rectangular pattern, a circular pattern, or a combination of both. Single serpentine structures offer good fluid removal due to their high flow rates and coverage of the entire active area of ​​the flow field. However, depending on the specific geometry, single serpentine structures can lead to reactant depletion along the channel length, uneven redox species distribution, high pressure loss, air oxidant issues, the risk of excess liquid accumulation at high current densities, or fluid accumulation at bends that cause localized current density reductions.

[0091] A multi-serpentine structure is characterized by the presence of multiple single channels extending from the inlet of the flow field to the outlet of the flow field. The multi-serpentine channels can be in the form of a rectangular pattern, a circular pattern, or a combination thereof. Multi-serpentine structures offer lower pressure drop than single-serpentine structures, allow for sufficient water / fluid removal, cover the entire active area of ​​the flow field, and outperform single-serpentine structures, making them considered optimal for large active areas. However, depending on the specific geometry, multi-serpentine structures can still result in relatively high pressure drop due to the channel length and depletion of redox species along the channel length, resulting in uneven distribution of redox species in the flow field.

[0092] A mixed serpentine structure is characterized by the presence of more than one single serpentine structure within a flow field. For example, two or three single serpentine structures can be positioned adjacent to one another within a flow field. A multiple serpentine structure provides less pressure loss than a single serpentine structure. Depending on the specific geometry, a multiple serpentine structure can combine the technical advantages provided by the single and multiple serpentine structures described above.

[0093] A parallel structure is characterized by two or more channels coupled to an inlet being arranged substantially parallel to one another. The two or more channels are coupled to a first main channel connected to the inlet such that fluid flows through the main channel and then through the parallel channels through a flow field. The two or more channels are coupled to a second main channel connected to the outlet such that fluid flows through the parallel channels and then through the second main channel through a flow field. In a preferred example, the parallel channels are arranged substantially perpendicular to the main channel. A parallel structure provides low pressure loss and uniform fluid distribution. However, depending on the specific geometry, a parallel structure can result in water blockage within the channels resulting in blocked 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 prolonged operation, or low channel velocity.

[0094] A pin-type structure is characterized in that a plurality of first channels within the flow field are arranged substantially parallel, and a plurality of second channels within the flow field are also arranged substantially parallel, with the plurality of second channels arranged substantially perpendicular to the plurality of first channels. In this manner, the remaining all-solid pins in the flow field form isolated pins. Pin structures provide low pressure loss and are suitable for high reactant flow rates with low utilization. However, depending on the specific geometry, pin-type structures may result in non-uniform reactant distribution, non-uniform water removal, or non-uniform current density distribution.

[0095] The cross-shaped structure is based on the parallel structure and further features lateral channels. The combination of parallel flow fields and lateral channels allows fluids (e.g., gas) to merge with water droplets. The cross-shaped structure provides improved fluid removal and offers the same overall advantages as the parallel structure. However, depending on the specific geometry, the cross-shaped structure may also have the same disadvantages as the parallel structure described above.

[0096] Interdigitated (or discontinuous) structures are characterized by two or more interdigitated finger-like solid ribs. Interdigitated structures offer excellent fluid / air removal, good mass transfer, and optimal performance and uniform fluid distribution by using forced convection through a fluid diffusion layer (FDL) instead of diffusion. However, depending on the specific geometry, interdigitated structures can result in high pressure drop and long-term damage to the FDL, depending on the porosity and thickness of the FDL.

[0097] A fractal interdigitated structure comprises an interdigitated structure as described above, characterized in that the interdigitated structure is divided into two or more fractal superstructures, which can be arranged, for example, such that the flow field is divided by an intermediate section that intersects from the inlet to the outlet of the flow field.

[0098] Structures with asymmetric channels are characterized in that the channels can be tapered, constricted, and stepped. Structures with asymmetric channels can also be a combination of tapered, constricted, and stepped. In structures with asymmetric channels, one complete channel can be tapered, while additional channels can be constricted. Additionally, channels can be stepped. In structures with asymmetric channels, a channel can be tapered in one section, constricted in another section, and stepped in another section. Structures with one or more asymmetric flow fields offer improved performance at lower voltages, improved mass transfer, and improved water / fluid removal. However, depending on the specific geometry, structures with one or more asymmetric channels can have high pressure losses or be difficult to manufacture.

[0099] Mesh structures are characterized by channels that form a network of uniformly distributed openings of similar dimensions. Mesh structures offer good performance over a limited current range, low pressure drop, and controllable contact area. However, depending on the specific geometry, mesh structures can exhibit poor water / fluid removal, with fluid distribution concentrated in the center and less distributed at the periphery under high power. Furthermore, uniform porosity is difficult to fabricate properly, and mesh structures can suffer from corrosion issues, high pressure drop, and be limited to small devices.

[0100] In some examples, the channels form a combination of parallel and serpentine structures. Due to the combination of parallel and serpentine structures formed by the channels in the flow field, this structure provides not only low pressure drop and uniform fluid distribution, but also good fluid removal with high flow rates and coverage of the entire active area of ​​the flow field.

[0101] In some examples, one or more channels included in the first flow field exhibit a rectangular, square, parallelogram, trapezoid, triangular, or semicircular shape along at least a portion of each channel. Additionally or alternatively, in some examples, one or more channels included in the second flow field exhibit a rectangular, square, parallelogram, trapezoid, triangular, or semicircular shape along at least a portion of each channel. Depending on the structure formed by the channel and the viscosity of the fluid, different shapes of the channel can be implemented to optimize charge transfer in the flow field.

[0102] In some examples, 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 examples, 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.

[0103] 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 a fluid to generate turbulence. In addition to the geometric structure formed by the channel or inlet and outlet configuration, turbulence and swirl can also be created or enhanced in a flow field by adding microchannels and / or vortex promoters in the first and / or second flow fields.

[0104] In some examples, the one or more first and / or second vortex promoters comprise one or more of one or more droplet-shaped obstacles, one or more circular obstacles, one or more twisted tapes, one or more coil wires, one or more baffle shapes, one or more twisted tape coil wires, and one or more twisted tapes with one or more rods.

[0105] In some examples, the ratio of the average rib width of the ribs in the first flow field to the average channel width of the channels in the first flow field ranges from 0.25 to 5.0, preferably from 0.4 to 2.0, and more preferably from 0.5 to 1.5. In some examples, the ratio of the average channel width of the channels in the second flow field to the average rib width of the ribs in the second flow field ranges from 0.25 to 5.0, preferably from 0.4 to 2.0, and more preferably from 0.5 to 1.5.

[0106] The one or more channels of the first and second flow fields are separated by ribs, as described above. The ribs are formed by the solid structure of the flow field as part of the electrode. By adjusting the ratio of channels to ribs, the flow field can be optimized for fluid volume, flow rate, and structural stability of the redox battery single cell. That is, when the ratio of the average channel width of the channels in the first flow field to the average rib width of the ribs in the first flow field is close to the lower limit of 0.25, the width of the ribs surrounding the channels is wider (on average) than the channels surrounded by the ribs. In this case, the mechanical stability of the cell is maximized. On the other hand, when the ratio of the average channel width of the channels in the first flow field to the average rib width of the ribs in the first flow field is close to the upper limit of 5.0, the width of the ribs surrounding the channels is narrower (on average) than the channels surrounded by the ribs. This maximizes the volume of fluid in the flow field and, therefore, the maximum amount of charge that can be transferred.

[0107] In some examples, the channels included in the first flow field have an average channel width in the range of 1.0 to 5.0 mm, preferably 2.0 to 4.0 mm, the channels included in the first flow field have an average channel height in the range of 0.1 to 2.0 mm, preferably 0.5 to 1.0 mm, and the ribs included 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. Additionally or alternatively, in some examples, the channels included in the second flow field have an average channel width in the range of 1.0 to 5.0 mm, preferably 2.0 to 4.0 mm, the channels included in the second flow field have an average channel height in the range of 0.1 to 2.0 mm, preferably 0.5 to 1.0 mm, and the ribs included 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.

[0108] By adjusting the absolute width and height of the channels and ribs, as well as the ratio of ribs to channels in the fuel cell, the mechanical stability and the amount of fluid in the flow field can be tuned and optimized.

[0109] In some examples, a first flow path defined by the first flow field of the first electrolyte in the first flow field at the first electrode and a second flow path defined by the second flow field of the second electrolyte in the second flow field at the second electrode are substantially parallel to each other.

[0110] Charge transfer can be optimized by providing a flow path, as generally defined by the overall flow direction of the fluid in the flow fields that is substantially parallel in the first and second flow fields, from one or more inlets to one or more outlets.

[0111] In some examples, the first storage tank contains at least a first electrolyte having a pH value of pH=2 to pH=8, preferably pH=2 to pH=5, and more preferably pH=3.5 to pH=4.5. In some examples, the first electrolyte has a pH value of 4.0±0.2. Additionally or alternatively, in some examples, the second storage tank contains at least a second electrolyte having a pH value of pH=2 to pH=8, preferably pH=2 to pH=5, and more preferably pH=3.5 to pH=4.5. In some examples, the first (and / or second) electrolyte has a pH value of 4.0±0.2.

[0112] The standard potentials of many redox species are particularly dependent on pH, and adjusting the pH can increase the cell potential. Because the resulting voltage (expressed by the Nernst equation) of the negative and positive electrode electrolysis of a redox battery is pH-dependent, providing a pH value within the above range can optimize the cell voltage while preventing energy loss due to side reactions such as hydrogen evolution at the negative electrode. Furthermore, providing a pH within the above range avoids corrosion and / or health concerns, thereby enabling durable and safe operation of redox battery single cells.

[0113] 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.

[0114] Side reactions and / or charge transfer can affect the pH of the electrolyte. To prevent significant pH fluctuations 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 acetate / acetate buffers, carbonate, bicarbonate buffers, and dihydrogen phosphate / dihydrogen phosphate buffers, and combinations thereof.

[0115] In some examples, the first and / or second electrolyte comprises polyatomic ions, preferably selected from the group consisting of vanadate, molybdate, tungstate, niobate, tantalate, manganate, ferrate, nickelate, and mixtures thereof, preferably at a concentration ranging from 0.1 M to 2.0 M.

[0116] The polyatomic ions disclosed herein are preferably polyoxymetalates. Polyoxymetalates (POMs) are polyatomic ions, typically anions, in which three or more transition metal oxyanions are linked by shared oxygen atoms to form a closed three-dimensional structure. The metal atoms can be Group 6 (Mo, W), Group 5 (V, Nb, Ta), transition metals, and high oxidation states of Tc. POMs include isopolymetalates, which consist of only one metal and its oxide, and heteropolymetalates, which consist of one metal, its oxide, and a main group oxyanion. Compared to monoatomic 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, charge delocalization in polyatomic ions allows multiple charges to be transferred quickly and easily from or to polyatomic ions. Integrating a flow field into at least the first electrode enables efficient charge transfer from the POM to the current collector in the electrolyte during battery charging and discharging.

[0117] In some examples, the cell has a current of 0.1 A / cm 2 to 10A / cm 2 , preferably 0.1 A / cm 2 to 5A / cm 2, and more preferably 0.5 A / cm 2 to 2A / cm 2 provides a current density in the range of

[0118] For example, by using polyatomic ions at these concentrations, high current densities can be achieved in the cell. Furthermore, while conventional planar electrodes are limited by their geometry and cannot achieve such high current densities, incorporating a flow field into at least one electrode can efficiently transfer charge to the current collector when discharging the battery.

[0119] In some examples, the second electrode comprises a fluid. It has been described in detail above that the first and second electrodes can have an all-solid structure. However, the second electrode can alternatively comprise a fluid. As used herein, the term "electrode" generally refers to a physical object (e.g., a solid or a fluid) that can extract and supply current from a power source. That is, as used herein, the term "electrode" can refer to an electronically conductive solid or an electronically conductive fluid. In a structure in which the second electrode comprises a fluid, the first electrode can have the technical features described above. Furthermore, while charge transferred through a membrane disposed between the first and second electrodes can be transferred from the first electrode (and the electrolyte distributed therein) comprising the first flow field to the second electrolyte, charge can also be transferred from the first electrode to a fluid such as a gas. That is, electrons supplied from the first electrode during discharge can react with the gas at the second electrode. For example, the reaction of electrons supplied by the discharge of the electrolyte at the first electrode with oxygen (contained in the surrounding air) can reduce oxygen and generate hydroxy anions. By providing a single 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, for example, by omitting the second electrolyte, while maintaining the energy density of the battery.

[0120] In some examples, the fluid comprises a gas. In some examples, the gas comprises oxygen. By operating the redox battery unit cell on (ambient) air, the infrastructure surrounding the redox battery unit cell can be further simplified, as no artificial gas transfer is required.

[0121] In a further aspect according to the present disclosure, a redox battery cell stack is provided, comprising one or more redox battery cells as defined in any one of the exemplary embodiments outlined throughout the present disclosure, the stack further comprising one or more current collectors coupled to the first electrode and / or the second electrode of the one or more redox batteries.

[0122] In some examples, the stack further comprises a first pump for pumping a first electrolyte from a first storage tank to the first flow field of the first electrode.

[0123] In some examples, the stack further comprises a second pump for pumping a second electrolyte from a second storage tank to the second flow field of the second electrode.

[0124] BRIEF DESCRIPTION OF THE DRAWINGS Further aspects, details, and advantages of the present disclosure will become apparent from the following detailed description of exemplary embodiments and drawings:

[0125] FIG. 1 shows an exemplary single redox battery cell coupled to first and second electrolyte storage tanks for supplying first and second electrolytes. FIG. 2 shows an exemplary single redox battery cell coupled to a single electrolyte storage tank for supplying electrolyte for a single electrolyte. FIG. 3A shows an exemplary single serpentine structure. FIG. 3B shows an exemplary multi-serpentine structure. FIG. 3C shows an exemplary mixed serpentine structure. FIG. 4A shows an exemplary parallel configuration. FIG. 4B shows an exemplary discontinuous structure. FIG. 5A shows an exemplary pin-type structure. FIG. 5B shows an exemplary cross-shaped structure. FIG. 6A shows an exemplary interdigitated structure. FIG. 6B shows an exemplary structure with asymmetric channels. FIG. 6C shows an exemplary mesh structure. FIG. 7 shows an exemplary channel shape. FIG. 8 shows the Nyquist plot of RFB using carbon felt and electrodes with a flow field in 1 M NaCl in the frequency range from 1 mHz to 1 MHz. Figure 9 shows the Bode plot of RFB using carbon felt in 1M NaCl in the frequency range from 1 mHz to 1 MHz. FIG. 10 shows the Bode plot of RFB using electrodes with flow fields in 1M NaCl in the frequency range from 1 mHz to 1 MHz. Figure 11 shows the rate test of RFB in a cell with an open circuit voltage of 0.95 V. The IR-corrected discharge voltage and IR-corrected power density are shown for the cell using carbon felt and the cell using electrodes with a flow field. FIG. 12 shows a block diagram of an exemplary redox battery cell stack. [Detailed explanation]

[0126] In the following description, for purposes of explanation and not limitation, specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent to those skilled in the art that the present disclosure may be practiced in other embodiments that depart from these specific details.

[0127] Exemplary embodiments of the redox battery single cells described herein allow for a wide range of redox species to be used in the redox electrolyte. By providing a first electrode with a flow field, higher currents, current densities (e.g., up to 10 A / cm) can be provided by the single cell or stack comprising the cell. 2 ), and therefore power density, can be achieved.

[0128] Furthermore, by including the first flow field at the first electrode, the additional carbon felt commonly used in the prior art to distribute the electrolyte containing the redox active species can be omitted.

[0129] In addition to the structural simplification of the system (by avoiding additional carbon felt or equivalent components for electrolyte distribution), the inclusion of flow fields at the electrodes significantly reduces the pumping capacity required for electrolyte circulation and therefore reduces the overall power consumption of the cell.

[0130] FIG. 1 shows an exemplary redox battery (100) having electrodes (101), where a first electrode (101a) includes a flow field and a membrane (102) is disposed between the first electrode (101a) and a second electrode (101b). In the exemplary redox battery unit cell shown in FIG. 1, the flow field of the first electrode (101a) is coupled to a first storage tank (103), such as an anode electrolysis tank, and the second electrode (101b) is coupled to a second storage tank (104), such as a cathode electrolysis tank. Current collectors (105) are coupled to the first electrode (101a), i.e., first current collector (105a), and the second electrode (101b), i.e., second current collector (105b). First pumps (106a) and second pumps (106b) are configured to supply anode and cathode electrolysis to the associated electrodes, respectively.

[0131] 2 shows a further exemplary redox battery (200) in which the second electrode (201b) is an air electrode. That is, the part of the redox battery unit cell that can be coupled to the negative electrode electrolysis tank (203) is the same as the redox battery unit cell (100) shown in FIG. 1 (consisting of a pump (206) and a membrane (202)), but the second electrode is an air electrode (201b) with a fluid in contact with the second solid electrode (201b) (this is not shown as a separate feature in FIG. 2 because it is part of the second electrode (201b)). That is, charge transferred from the first electrode side to the second electrode (201b) via ions can be further transferred by electrochemical reactions such as oxygen:

number

[0132] 3-6 illustrate flow field configurations such as those described above, including single serpentine, multiple serpentine, mixed serpentine (FIGS. 3A-3C), parallel, discontinuous (FIGS. 4A, 4B), pin-type, cross-type (FIGS. 5A, 5B), fractal finger-like alternating, asymmetric channel, and mesh-type (FIGS. 6A-6C), according to some exemplary embodiments as described herein. In selected configurations, the direction of electrolyte or fluid flow into and out of the flow field is indicated by arrows.

[0133] FIG. 7 illustrates selected channel shapes, including rectangular, triangular, and semicircular, according to some exemplary embodiments as described herein.

[0134] 8 shows a Nyquist plot of a single redox battery cell according to the present disclosure (first electrode with a flow field) compared to a single redox battery cell without a flow field but with an electrode having carbon felt for electrolyte distribution in 1 M NaCl in the frequency range of 1 mHz to 1 MHz. While the shapes of the two plots are generally similar, the single redox battery cell according to the present disclosure (indicated by the triangular measurement points) shows an overall reduced ohmic resistance compared to the single redox battery cell with carbon felt (indicated by the circular measurement points).

[0135] Figure 9 shows a Bode plot of a single redox battery cell with electrodes without a flow field in 1M NaCl but with carbon felt for electrolyte distribution, over the frequency range of 1 mHz to 1 MHz. In the Bode plot, frequency is plotted on the vertical axis, and electrical phase shift and absolute impedance are plotted on the horizontal axis. In Figure 9, the circular measurement points for the carbon felt system represent log(|Z|) vs. log(frequency) data, and the square measurement points represent phase(Z) vs. log(frequency) data.

[0136] 10 shows a Bode plot of a single redox battery cell (first electrode with flow field) according to the present disclosure in 1 M NaCl over the frequency range of 1 mHz to 1 MHz. In FIG. 10, the circular measurement points represent data for log(|Z|) vs. log(frequency), and the square measurement points represent data for phase(Z) vs. log(frequency) for the flow field system according to the present disclosure.

[0137] Additionally, the Bode plots for the two systems generally show similar trends. However, as discussed above with respect to the Nyquist plots, the overall resistance of the carbon felt system is greater than that of the flow field system of the present disclosure. The logarithmic resistance of the flow field system is more than halved, especially at low frequencies. While not wishing to be bound by theory, it is hypothesized that the differences between the Nyquist and Bode plots are due to additional resistance and / or capacitance within the redox battery unit cells that include the carbon felt. For example, the transport characteristics of carbon felt, as commonly used in the prior art, are known to be an important parameter because transport resistance can create significant parasitic power losses depending on the configuration of the redox battery unit cells.

[0138] Figure 11 shows the results of a rate test of the RFB for a cell with an open circuit voltage of 0.95 V. The IR-corrected voltage for the carbon felt system is shown as the circular data points. The IR-corrected voltage for the flow field system is shown as the diamond data points. The IR-corrected power density for the carbon felt system is shown as the square data points. The IR-corrected power density for the flow field system is shown as the triangle data points. Figure 11 shows that the flow field system provides a surprisingly increased discharge voltage and a surprisingly increased power density compared to the carbon felt system.

[0139] Figure 12 illustrates an exemplary redox battery cell stack 200. The exemplary stack illustrated in Figure 12 includes one redox battery cell and current collectors 110 electrically coupled to opposing sides of the redox battery cell.

[0140] It will be understood that the present disclosure has been described with reference to exemplary embodiments that may vary in many respects, and therefore the invention is limited only by the scope of the following claims. [Brief explanation of the drawings]

[0141] [Figure 1] 1 is a flowchart of a method for selecting a target palladium membrane according to an example of the present invention. [Figure 2] 1 shows an exemplary redox battery single cell coupled to a single electrolyte storage tank for supplying electrolyte for a single electrolyte. [Figure 3A] 1 shows an exemplary single serpentine structure. [Figure 3B] 1 shows an exemplary multi-serpentine structure. [Figure 3C] 1 illustrates an exemplary mixed serpentine structure. [Figure 4A] 1 shows an exemplary parallel structure. [Figure 4B] 1 illustrates an exemplary discontinuous structure. [Figure 5A] 1 illustrates an exemplary pin-type structure. [Figure 5B] 1 shows an exemplary cross-shaped structure. [Figure 6A] 1 shows an exemplary interdigitated structure. [Figure 6B] 1 illustrates an exemplary configuration with an asymmetric flow field. [Figure 6C] 1 illustrates an exemplary mesh structure. [Figure 7] 1 illustrates an exemplary flow field shape. [Figure 8] 1 shows Nyquist plots of RFB using carbon felt and electrodes with flow fields in 1 M NaCl in the frequency range from 1 mHz to 1 MHz. [Figure 9]1 shows a Bode plot of RFB using carbon felt in 1M NaCl in the frequency range from 1 mHz to 1 MHz. [Figure 10] 1 shows a Bode plot of RFB using electrodes with a flow field in 1M NaCl in the frequency range from 1 mHz to 1 MHz. [Figure 11] 1 shows a rate test of the RFB in a cell with an open circuit voltage of 0.95 V. 1 shows the IR-corrected discharge voltage and IR-corrected power density for a cell using carbon felt and a cell using electrodes with a flow field. [Figure 12] FIG. 1 shows a block diagram of an exemplary redox battery cell stack.

Claims

1. A first electrode; a second electrode disposed spaced apart from the first electrode; a membrane disposed between the first electrode and the second electrode; The first electrode comprises a first flow field.

2. 10. The single redox battery cell of claim 1, wherein the second electrode comprises a second flow field.

3. The redox battery unit cell according to claim 1 or 2, wherein the first electrode and / or the second electrode have an all-solid-state structure.

4. 4. The redox battery unit cell of claim 1, wherein the first flow field forms an integral part of the first electrode.

5. 5. The single redox battery cell of claim 1, wherein the second flow field forms an integral part of the second electrode.

6. 6. The single redox battery cell of claim 1, wherein the first flow field and the second flow field are substantially symmetrical with respect to the membrane disposed between the first electrode and the second electrode.

7. 7. The single 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 graphite, aluminum, carbon-coated aluminum, copper, and carbon-coated copper.

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

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

10. The membrane comprises: one or more inorganic membranes, optionally metal, ceramic or zeolite membranes, or 10. A single redox battery cell according to any one of claims 1 to 9, comprising one or more organic membranes, optionally synthetic or natural polymer membranes.

11. 10. A single 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. 12. A single 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 in the range of 5 Å to 100 Å, preferably in the range of 10 Å to 50 Å.

13. the first flow field comprises one or more first inlets coupled to a first storage tank and / or one or more first outlets coupled to the first storage tank; 13. The redox battery single cell according to claim 1, wherein one or more of the first inlets of the first flow field are preferably positioned substantially opposite a corresponding one of the one or more first outlets of the first flow field.

14. In combination with claim 2, the second flow field comprises one or more second inlets coupled to a second storage tank and / or one or more second outlets coupled to the second storage tank; 14. The redox battery single cell according to claim 1, wherein one or more of the second inlets of the second flow field are preferably positioned substantially opposite a corresponding one of the one or more second outlets of the second flow field.

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

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

17. 16. The redox battery single cell of claim 15, wherein a diameter of a first one of the first inlets is different from a diameter of a second one of the first inlets, and / or a shape of a first one of the first inlets is different from a shape of a second one of the first inlets.

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

19. 19. The single redox battery cell according to claim 13, wherein the first flow field comprises a plurality of first outlets coupled to the first storage tank.

20. 20. The single redox battery cell of claim 14, wherein the second flow field comprises a plurality of second outlets coupled to the second storage tank.

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

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

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

24. 24. The redox battery single cell according to claim 19, wherein the inlet shape of a first inlet among the first inlets is different from the outlet shape of a first outlet among the first outlets.

25. 25. The redox battery single cell according to claim 20, wherein the inlet diameter of a first of the second inlets is different from the outlet diameter of a first of the second outlets.

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

27. 27. The single redox battery cell of claim 1, wherein the first flow field comprises one or more channels separated by ribs for supplying a first electrolyte to the first electrode.

28. 28. The single redox battery cell of claim 2, or the single redox battery cell of 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 supplying a second electrolyte to the second electrode.

29. 29. The single redox battery cell of claim 27 or 28, wherein the one or more channels form one or more of a single serpentine structure, a multiple serpentine structure, a mixed serpentine structure, a parallel structure, a discontinuous structure, a pin-type structure, a cross-type structure, an interdigitated structure, a fractal interdigitated structure, a structure with asymmetric channels, a mesh structure, or one or more combinations thereof.

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

31. 31. The single redox battery cell of claim 27, wherein the one or more channels provided in the first flow field exhibit, along at least a portion of the respective channel, a rectangular shape, a square shape, a parallelogram shape, a trapezoid shape, a triangular shape, or a semicircular shape.

32. 32. A redox battery cell as described in claim 28, or a redox battery cell as described in any one of claims 29 to 31 in combination with claim 28, wherein the one or more channels provided in the second flow field exhibit a rectangular shape, a quadrilateral shape, a parallelogram shape, a trapezoid shape, a triangular shape, or a semicircular shape along at least a portion of the respective channel.

33. 33. The redox battery single cell of claim 27, wherein the one or more channels provided in the first flow field comprise one or more first microchannels and / or one or more first vortex promoters.

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

35. 35. The redox battery single cell of claim 33 or 34, wherein the one or more first and / or second vortex promoters comprise one or more of the following: one or more droplet-shaped obstacles, one or more circular obstacles, one or more twisted tapes, one or more coil wires, one or more baffle shapes, one or more twisted tape coil wires, and one or more twisted tapes with one or more rods.

36. 36. The redox battery single cell of claim 27, wherein a ratio of an average rib width of ribs provided in the first flow field to an average channel width of channels provided 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.

37. 37. A redox battery cell as claimed in claim 28, or a redox battery cell as claimed in any one of claims 29 to 36 in combination with claim 28, wherein a ratio of an average rib width of ribs provided in the second flow field to an average channel width of channels provided 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.

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

39. the average channel width of the channels provided in the second flow field is in the range of 1.0 to 5.0 mm, preferably 2.0 to 4.0 mm; the average channel height of the channels provided in the second flow field is in the range of 0.1 to 2.0 mm, preferably 0.5 to 1.0 mm; and A redox battery single cell as described in claim 28, or a redox battery single cell as described in any one of claims 29 to 38 in combination with claim 28, wherein the average rib width of the ribs provided in the second flow field is in the range of 0.5 to 1.5 mm, preferably 0.75 to 1.25 mm.

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

41. 41. The single redox battery cell according to claim 13, wherein the first storage tank contains at least a first electrolyte solution having a pH value of pH=2 to pH=8, preferably pH=2 to pH=5, and more preferably pH=3.5 to pH=4.

5.

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

5.

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

44. 44. The single redox battery cell of claim 42, or the single redox battery cell of claim 43 in combination with claim 42, wherein the second electrolyte comprises a second buffer system.

45. 45. The single redox battery cell of claim 41, wherein the first and / or second electrolyte solution comprises polyatomic ions, preferably selected from the group consisting of vanadates, molybdates, tungstates, niobates, tantalates, manganates, ferrates, nickelates, and mixtures thereof, preferably at a concentration in the range of 0.1 M to 2.0 M.

46. The cell has a current of 0.1 A / cm ２ to 10 A / cm ２ , preferably 0.1 A / cm ２ to 5 A / cm ２ , more preferably 0.5 A / cm ２ to 2 A / cm ２ 46. ​​The single redox battery cell of claim 1, which provides a current density in the range of

47. 47. The redox battery cell of claim 1, wherein the second electrode comprises a fluid.

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

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

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

51. A redox battery cell stack comprising one or more redox battery cells according to any one of claims 1 to 50, The redox battery cell stack, wherein the stack further comprises one or more current collectors coupled to the first electrode and / or the second electrode of one or more redox batteries.

52. 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 storage tank to the first flow field of the first electrode.

53. 53. The redox battery cell stack of 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 storage tank to the second flow field of the second electrode.

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