DE102016122284A1 - Redox flow battery for storing electrical energy with hollow-fiber membranes - Google Patents

Abstract

The invention relates to a redox flow battery (RFB) for storing electrical energy. The object of the invention to find a new type of tubular redox flow cells (RFCs) for energy storage, the dimensionable and powerful with a simple structure for high power densities Redox flow batteries (RFBs) are combined, is achieved according to the invention by at least the first polarity-specific half-cell is composed of a plurality of hollow fibers, wherein the membrane of the first half-cell from the total area of hollow fiber membranes of the plurality of hollow fibers is formed, at least the Hollow fibers of the first half-cell surrounding chamber filled with the liquid-permeable structure and a solvent containing at least one lead salt and at least partially bounded by a parallel to the hollow fibers of the first half-cell aligned support structure, and the second polarity-specific half-cell, the other flows through electrolyte is formed either by the liquid-permeable structure surrounding the hollow fibers of the first half-cell, or as a further number of hollow fibers, which are the same structure to the hollow fibers of the first half-cell and arranged within the liquid-permeable structure surrounding the hollow fibers of the first half-cell, is trained.

Description

The invention relates to a redox flow battery (RFB) for storing electrical energy, comprising at least one redox flow cell (RFC) as a reaction cell with chambers for the formation of polarity-specific half-cells for catholyte and anolyte, which are separated by at least one membrane and each having an electrolyte reservoir in connection, wherein a first and a second of the polarity-specific half-cells each with an electrolyte of at least one redox-active component, at least partially dissolved in substance or in a solvent and present therein conductive salts, flowed through and the electrolytes, catholyte and Anolyte, each with a pumping device are circulated and the membrane is provided as an interface for the suppression of mixing or electrochemical reactions of the redox-active components with each other and for efficient charge carrier exchange between the half-cells.

For large-scale storage of energy in the prior art alkaline secondary batteries are known, of which in particular the tubular constructed representatives should be mentioned, because they bring the best conditions for a technologically simple enlargement of the electrochemically active surfaces.

So is in the WO 2011/161072 A1 describes a device using alkali metal and sulfur as active materials in two separate, stacked tubular containers connected by means of a cation-only solid electrolyte. The active materials may be stored as liquids in external containers and supplied to the cells as needed. The two electrode spaces of the cells are separated by a solid electrolyte (in the form of a concentric ion-conducting ceramic electrolyte tube) of alumina.

Another sodium-sulfur secondary battery is in the US 2013/0288153 A1 disclosed. Here, an ion-conductive ceramic membrane of long TiO ₂ nanowires is provided which is capable of selectively transporting sodium ions between the anode and cathode solutions at comparatively low temperatures (<75 ° C).

Another alkaline secondary battery is in the WO 2015/035427 A1 described as a sodium-halogen battery, wherein tubular cells are separated by an ion-conducting ceramic membrane. At the negative electrode, liquid (s) of sodium (compounds) are generated by oxidation and metallic sodium is formed upon charging, and at least one reduction reaction involving a liquid halogen is carried out on the positive electrode, with the sodium ions traversing the electrolyte membrane, respectively. The two redox partners can be supplied to the cell as liquids from external storage containers.

A disadvantage of these prior art alkaline secondary batteries is that in each case an ion-conducting membrane is used and operated at elevated temperatures (often above 290 ° C, since the alkali metal used - usually sodium - must remain liquid). Lower temperatures lead to power drops because of the greatly increased internal resistance.

From the DE 10 2007 034 700 A1 is a redox flow battery based on a vanadium redox cell with a proton permeable membrane known, wherein the membrane is formed as a hollow profile having a plurality of first electrodes and a first electrolyte inside and outside a second electrolyte and a plurality of second Having electrodes. The hollow-profile membranes are preferably made as a textile fabric, such as non-woven, micro or hollow fibers, zirconium, titanium or silicon oxide or use citric acid in conjunction with nanoparticles of silicon, magnesium or their oxides. Furthermore, polymeric materials for the membrane hollow sections are mentioned, such as gelatin, polyvinyl alcohol, polyester, PTFE or PEEK, sulfonated tetrafluoroethylene and Nafion ^® .

The hollow profiles are arranged in parallel in a plane and incorporated into a self-supporting rectangular or annular frame, so that the parallel inner first electrodes are led out to the outer periphery of the frame to the outside. The electrodes arranged on the outside on the hollow profiles can, if appropriate combined, also be tapped on the outer frame.

Furthermore, in the WO 2015/007382 A1 Carbon nanotube micro-hollow fibers or carbon nanotube compositions, which mention, inter alia, the use in chemical energy converters and a so-called membrane electrode assembly (MEA) in tubular form to eliminate the known inadequate power and energy densities of redox flow Batteries or Fuel cell is proposed. The tubular structure has, at less than 2 mm in diameter, three major layers: a positive electrode and a negative electrode with a diaphragm interposed therebetween around an electrode. With such an MEA, higher power densities, lower manufacturing costs, and lower parasitic losses are achievable, however, the required ruggedness and stability can not be realized for commercial secondary batteries.

In the WO 2015/074764 A1 For example, all-vanadium RFB (aV-RFB) and oxygen-vanadium RFB (OV-RFB) are described as both flat and tubular cell arrays, each with three layers, positive and negative electrodes, and an intervening one ion-conducting membrane, are formed. The ion-conducting membrane, which is tubular, separates the two half-cells from the geometric structure into an outer space of the first half-cell of the battery with a bifunctional porous oxygen electrode and an interior of the second half-cell with two electrodes, wherein the bifunctionality of the positive electrode means that this both the oxygen evolution and the oxygen reduction takes place by means of suitable catalysts and the negative half cell has a fixed electrode with flow channel and a semi-solid electrode with carbon particles in the anolyte of acid-forming vanadium (II), (III) solution. As a result, the commercial production is much more difficult or costly.

The invention has for its object to find a new type of tubular redox flow cells (RFCs) for energy storage, which can be dimensioned with a simple structure of a few basic components for high power densities and robust and powerful redox flow batteries (RFBs) combined are.

According to the invention, the object of a redox flow battery (RFB) for storing electrical energy containing at least one redox flow cell (RFC) as a reaction cell with chambers for the formation of polarity-specific half-cells for catholyte and anolyte separated by at least one membrane and are each in contact with an electrolyte reservoir, wherein a first and a second of the polarity-specific half-cells each with an electrolyte of at least one redox-active component, at least partially dissolved in substance or in a solvent and dissolved therein conductive salts, flowed through and the electrolytes, Katholyt and anolyte, each with a pumping device are recirculated and the membrane is provided as an interface for suppressing mixing or electrochemical reactions of the redox-active components with each other and for efficient charge carrier exchange between the half-cells, achieved by Weni First, the first polarity-specific half-cell is composed of a plurality of hollow fibers, wherein the membrane of the first half cell is formed as an interface of a total area of hollow fiber membranes of the plurality of hollow fibers, each internally provided with an electrolyte-permeable electrode, flows through one of the electrolytes and on both sides Hollow fiber ends are connected to the electrolyte reservoir that the at least the hollow fibers surrounding the first half-cell filled with a liquid-permeable structure and a solvent containing at least one conducting salt and at least partially bounded by a parallel to the hollow fibers oriented support structure and that the second polarity-specific half cell, the from the other of the electrolytes flows through and is connected to the electrolyte reservoir of the second half-cell, either by the surrounding the hollow fibers of the first half-cell chamber with the f Lüssigkeitsdurchlässigen structure is formed as an electrode, or is formed by a further number of hollow fibers, which are structured equal to the hollow fibers of the first half-cell, internally equipped with a porous electrode and disposed within the hollow fibers surrounding the first half-cell chamber, wherein in the liquid-permeable Structure is provided with a conductive salt added solvent for electrical connection between hollow fiber membranes of the first and second half-cells.

Advantageously, the hollow-fiber membranes are designed as ion-selective membranes and act as interfaces on the principle of a lonentypauschlusses. In a preferred alternative variant, the hollow-fiber membranes are designed as size-exclusion membranes and act as boundary surfaces according to the principle of molecular size exclusion.

It proves to be particularly expedient that the hollow fibers of the first half-cell and the hollow fibers of the second half-cell are present in parallel planes as alternately and seamlessly arranged single-layer hollow fiber layers.

The directions of the hollow fibers of the hollow fiber layers of the first half-cell and the second half-cell are offset by an angle α with 0 ° <α <90 ° to each other. In an expedient variant, the hollow fibers of the first half-cell and the second half-cell are crossed at an angle α = 90 ° arranged to each other. In a further preferred variant, the hollow fibers of the first half-cell and the second half-cell may be arranged parallel to each other.

A preferred embodiment of the invention is that the liquid-permeable structure in the chamber surrounding the hollow fibers of the first and second half-cells by the cavities between the hollow fibers of the first and second half-cells and parallel to the hollow fibers of the first or second half-cell closely bounding the chamber Support structures is formed.

In a first embodiment, the chamber surrounding at least the hollow fibers of the first half cell has a circular or elliptical cross section and a cylinder jacket-shaped support structure oriented parallel to the hollow fiber membranes of the first half cell. Alternatively, however, the surrounding chamber may also have an n-cornered cross-section with n> 2 and rectangular-shaped support structures.

In the interior of the hollow-fiber membranes of the first half-cell and possibly the second half-cell, the porous electrodes are expediently formed by an electrically conductive, liquid-permeable filling material and electrically conductive current collectors are introduced into the filling material.

When the porous electrode of the second half cell is formed by an electrically conductive, liquid-permeable structure in the spaces outside the hollow fiber membranes of the first half cell, the current collectors of the second half cell are inserted in the liquid-permeable structure or each hollow fiber membrane of the first half cell is outside with a porous structure and at least a continuously connected, electrically conductive strip coated as a current collector, which is contacted at the end to an electrically conductive framework or housing.

In another embodiment, the porous electrode of the second half-cell is formed as a liquid-permeable structure of electrically conductive material in spaces outside the hollow fiber membranes of the first half-cell, wherein current collector with electrical contact to an electrically conductive support structure of the hollow fibers surrounding the first half-cell chamber in the liquid-permeable structure einbracht or the liquid-permeable structure is contacted as an electrode at attachment points or by applying or pressing on the at least partially electrically conductive support structure of the surrounding chamber.

Another advantageous embodiment of the invention consists in that the porous electrode of the second half-cell is coated as a liquid-permeable structure on the outside of each hollow fiber membrane of the first half-cell and provided with at least one continuous electrically conductive strip as a current collector, wherein the current collector in electrical contact with an electrically conductive Support structure of the hollow fibers surrounding the first half-cell chamber or to another electrically conductive framework stand.

In an alternative variant of this, in the hollow fibers of the first half-cell and in the hollow fibers of the second half-cell, the porous electrodes are each applied to the inner sides of the hollow-fiber membranes as a porous layer and ends of the hollow-fiber membranes are slipped onto electrically conductive tubes or clamping sleeves as current collectors.

In a third variant, in which both half-cells are formed by hollow fibers, in the hollow fibers of the first half-cell and in the hollow fibers of the second half-cell, respectively, the electrically conductive current collectors are at the same time formed as electrodes in the interior of the hollow-fiber membranes, while being rectilinearly aligned or spirally wound and wound each led to the outside.

The invention is based on the fundamental idea that the use of tubular membranes (hollow fiber membranes), instead of individual flat membranes as used in all currently commercially available RFBs, can significantly increase the electrochemically important membrane surface per cell volume and thus the electrical performance of an RFB, at the same time size and cell weight are significantly reduced. However, at present the construction of known solutions for tubular RFBs always suffers from the fact that production-consuming electrodes and / or membrane coatings are required. Furthermore, the unavoidable replacement of redox-active substances between the half-cells (so-called "cross-contamination" or "cross-over"), which is additionally favored in tubular RFBs by the larger contact area between the electrolyte and the membrane, limits the lifetime of RFBS.

The invention solves these problems by forming inner and / or outer volumes of a plurality of identical hollow fibers as electrolyte flow paths and electrodes of the RFCs, wherein the hollow fibers are inserted as tubular membranes in a surrounding chamber having a porous liquid-permeable or electrolyte-permeable structure, either is designed as an electrode of the second half-cell or as a salt bridge to the likewise formed from hollow fibers second half-cell. In this case, the hollow-fiber membranes are preferably formed from different materials blocking the redox-active components, for example from plastics in the form of polymers (for example polyethersulfone) and other organic compounds, such as, for example, As cellulose, regenerated cellulose (RC) and other derivatives, or made of a ceramic.

In principle, all conceivable types of membranes can be used in the RFC according to the invention. In this context, the boundary surface of the respective half-cells with separated electrolytes according to the invention is understood to be a planar structure which is characterized in principle by the two minimum requirements, on the one hand ensuring efficient charge equalization through the transfer of charge carriers between the half-cells of an RFC and, on the other hand, at the same time Transition of the decisive for energy storage redox-active substances of the two electrolytes in the other half-cell precludes or completely suppressed electrochemical reactions of the redox-active substances of the two half-cells with each other across the membrane ideally. According to these provisos, particular preference is given to membranes which operate on the principle of ion-type exclusion or on the principle of size exclusion. But also fabrics made of other materials, which do not bring the last-mentioned properties are here conceivable as an interface separating the half-cells, as long as they fulfill the above-described function in their minimum requirements. Although the term "membrane" is limiting in terms of the above functions, for the sake of simplicity, and since it is also the preferred variant, it will be referred to hereinafter only as a "membrane" from this device.

In the case of a membrane that operates on the principle of size exclusion, the size exclusion is achieved by using redox-active macromolecules (eg, oligomers and polymers) and appropriately selected porous membranes whose pore size distribution is such that molecules of a certain geometric size ( ie from a certain hydrodynamic volume) or molar mass with high probability (> 90%) are retained. This is usually measured by the molecular weight of the macromolecule and an upper barrier to the pore size of the membrane, the so-called Molecular Weight Cut-Off (MWCO). As a result, macromolecular redox-active substances are retained with a molecular weight greater than the MWCO, while the smaller ions of the conductive salt can pass through the membrane for charge compensation. For this purpose, membranes with MWCOs of at least 0.4 kDa, more preferably between 1 kDa and 10 kDa, are used. But even larger MWCOs are conceivable in principle. The inventive choice of materials for the redox-active macromolecules and the macrotubular membranes is basically arbitrary and limited only by the fact that the materials must be chemically compatible with each other and not enter into unwanted chemical reactions with each other, so no decomposition, dissolution or otherwise dysfunctional change in the membrane material or the electrolyte occurs.

By membranes which operate on the ion-exclusion principle, it is meant those membranes which selectively selectively liberate ions. This ion type exclusion is achieved by electrically insulating, porous membrane materials, which are characterized in that they contain ionic groups and therefore keep electrically charged ions of the same charge from the passage, while ions of opposite charge can pass through the membrane, insofar as these ions in size at the same time do not exceed the small pore size of the membrane. A distinction is therefore made between anion- and cation-conducting membranes. A major representative of cation-conducting membranes are Nafion® membranes.

But also other types of membranes, which meet the above minimum requirements, are conceivable. Such an example is represented here by such ceramics, which are also generally referred to as solid electrolyte and whose conductivity is realized - possibly at elevated temperature - by thermally mobilized ions in the solid state structure of the ceramic (eg Na ₂ O, MgO, NaAl ₁₁ O ₁₇ , etc.).

Thus, in particular all those membrane and electrolyte materials whose usefulness is already known from the prior art for conventional flat-type RFCs can also profit from the additional, material-independent advantages of an RFC according to the invention with hollow-fiber membranes.

An electrically conductive porous layer may be applied as electrode (or part of the electrode) to a hollow-fiber membrane at least in order to assemble a half-cell therefrom by means of a multiplicity of hydrodynamically and electrically parallel-operated hollow fibers. Instead of or in addition to the coating, an electrically conductive, liquid-permeable structure (porous solid, bulk material, fiber fabric or fleece, yarn or the like) may also be introduced as an electrode into the hollow fiber. In this way, either only one of the half-cells or both half-cells can be constructed.

In a first case, the first half-cell, as described above, constructed and the second half-cell by an electrically conductive, liquid-permeable structure (porous solid, bed, fiber fabric or nonwoven or the like) is formed, in which the hollow fibers of the first half-cell - preferably as a plurality of parallel strands - are embedded, wherein the liquid-permeable structure or preferably arranged in parallel hollow fibers are each used as an electrode equipped with electrolyte flow path for each one of the half-cells. As "current collector" for the electrodes in the interior of the hollow fiber (s) can each be introduced an electrically conductive wire or rod or the fiber end grafted onto an electrically conductive tube, wherein the individual current collector are electrically connected in parallel. As a "current collector" for the outer electrode, at least one electrically conductive wire, rod, strip or plate can be introduced into the liquid-permeable structure or electrically conductive plates or an electrically conductive plate on at least one outer surface of the liquid-permeable structure parallel to the hollow fibers Cylinder shell (if the tubular overall shape is selected) are attached, which also represent a stabilizing carrier of the entire hollow fiber RFB.

In a second case, when both half-cells are formed of hollow fibers with internally rough or porous electrodes, the hollow fibers through which different electrolytes flow (either catholyte or anolyte), which are preferably traversed by wire or rod-shaped current collectors and are combined separately according to half-cell membership, are at least layered in parallel and stacked, wherein intermediate or surrounding cavities are preferably impregnated or flowed through with an electrically conductive salt solution, but may also be filled by an ion-conducting solid or an ionic liquid. The hollow fibers of different half-cells are preferably arranged individually alternately adjacent or in alternating layers. For the arrangement preferably a parallel arrangement in the respective basic geometry of the RFC "densest cylinder pack" or half-cell alternately stacked hollow fiber layers are conceivable, each having a rotation by an angle α with 0 <α ≤ 90 °.

The object of the invention is realized not only by the mere use of hollow fibers, but especially by novel arrangements of such hollow fibers as membranes in a membrane geometry adapted cell design and / or a novel mode of such hollow fiber cells.

The optional use of a salt bridge also provides a novel mode of operation for RFBs, which in particular allows both half-cells of a tubular RFB to be constructed and operated in the same way. A salt bridge according to the invention is understood to be an ion conductor which permits efficient exchange of ions between the half-cells and is preferably in the form of a liquid with dissolved inorganic or organic salts, but can also be an ion-conducting solid, an ion-conducting gel or an ionic liquid. Moreover, the resulting double membrane (each half cell brings a hollow fiber membrane with) the undesirable, but not completely suppressible replacement of the redox-active substances between the two half-cells (also called "cross-contamination" or "cross-over") additionally reduced or - practical seen - even almost completely suppressed. In addition, the damage of a membrane no longer leads to an involuntary mixing of the two electrolytes, as long as at least two hollow fibers of different half-cells are not damaged. One or more defective hollow-fiber membranes of a half-cell likewise do not immediately lead to failure of the functioning of the battery, but in the worst case only to a loss of performance.

With the hollow fiber RFB (HFRFB) according to the invention, it is possible to realize a new type of tubular RFBs for energy storage, which can be dimensioned and configured in a simple manner from a few basic components for high power densities as desired and highly variable. In particular, a uniform production of the half-cells without complicated porous electrodes is possible, with external flat pantographs at the same time provide the required mechanical stability of parallel and tight embedded in a liquid-permeable structure tubular half-cells and the basic structure allows a simple, different packaging of batteries of any power size. In addition, the invention allows the efficient operation of a salt bridge RFB, which provides for significantly increased reliability and lifetime of such a battery.

• 1: eine schematische Prinzipdarstellung einer erfindungsgemäßen Hohlfaser-RFB mit einer Schnittdarstellung einer erfindungsgemäßen RFC;
• 2: eine schematische Darstellung einer ersten Ausführung der Erfindung als zylindrische Hohlfaser-RFB (HFRFB), bei der eine Anzahl von Hohlfasern als Hohlfasermembranen in eine elektrisch leitende, flüssigkeitsdurchlässige Struktur in Form eines Filzes aus Graphit eingebettet ist, wobei die Hohlfasern der ersten Halbzellen von einem ersten Elektrolyten und die flüssigkeitsdurchlässige Struktur der zweiten Halbzelle von einem zweiten Elektrolyten durchströmt sind;
• 3: eine schematische Darstellung einer zweiten Ausführung der Erfindung als quaderförmige HFRFB, bei der eine Anzahl von Hohlfasern als Hohlfasermembranen in eine elektrisch leitende, flüssigkeitsdurchlässige Struktur in Form einer Gewebe- oder Vliesstruktur aus Kohlenstoff eingebettet sind, wobei die Hohlfasern der ersten Halbzelle von einem ersten Elektrolyten und die flüssigkeitsdurchlässige Struktur der zweiten Halbzelle von einem zweiten Elektrolyten durchströmt sind;
• 4: eine schematische Darstellung einer dritten Ausführung der Erfindung als zylindrische HFRFB, bei der eine Anzahl von ersten tubulären Hohlfasermembranen und eine (gleiche) Anzahl von zweiten tubulären Hohlfasermembranen in eine flüssigkeitsdurchlässige Struktur in dichtester Zylinderpackung eingebracht sind, wobei die Hohlfasern der ersten Halbzelle von einem ersten Elektrolyten und die Hohlfasern der zweiten Halbzelle von einem zweiten Elektrolyten durchströmt sind und die flüssigkeitsdurchlässige Struktur, welche gänzlich durch die die Hohlfasern umgebenden Außenräume gebildet ist, mit einer Leitsalzlösung gefüllt ist;
• 5: eine schematische Darstellung einer vierten Ausführung der Erfindung als quaderförmige HFRFB, bei der eine Anzahl von ersten tubulären Hohlfasern und eine (gleiche) Anzahl von zweiten tubulären Hohlfasern in „dichtester Zylinderpackung“ in Hohlfaserschichten angeordnet sind, wobei die Hohlfasern der ersten Halbzelle und der zweiten Halbzelle abwechselnd von einem ersten und einem zweiten Elektrolyten durchströmt und die Hohlräume zwischen den Hohlfasern mit einer Leitsalzlösung gefüllt sind;
• 6a: eine Prinzipdarstellung einer ersten Variante, wie erfindungsgemäße Hohlfasern zu stapelbaren RFCs zusammengefügt sind, mit räumlich einfacher Verknüpfung einer ersten Halbzelle aus elektrisch und hydrodynamisch parallel miteinander verschalteten Hohlfasern mit drahtförmigen Stromabnehmern und einer zweiten Halbzelle aus umgebender flüssigkeitsdurchlässiger, elektrisch leitender Struktur;
• 6b: eine Prinzipdarstellung einer zweiten Variante, wie erfindungsgemäße Hohlfasern zu stapelbaren RFCs zusammengefügt sind, mit räumlich einfacher Verknüpfung einer ersten Halbzelle aus elektrisch und hydrodynamisch parallel miteinander verschalteten Hohlfasern mit drahtförmigen Stromabnehmern und einer zweiten Halbzelle aus umgebender flüssigkeitsdurchlässiger, elektrisch leitender Struktur;
• 7a: eine Prinzipdarstellung, wie erfindungsgemäße Hohlfasern zu stapelbaren RFCs zusammengefügt sind, mit räumlich anspruchsvoller Verknüpfung einer ersten Halbzelle aus elektrisch und hydrodynamisch parallel miteinander verschalteten Hohlfasern mit drahtförmigen Stromabnehmern und einer zweiten Halbzelle aus elektrisch und hydrodynamisch miteinander parallel verschalteten Hohlfasern mit drahtförmigen Stromabnehmern mit vollständig separater Elektrolytführung für die Hohlfasern der ersten und zweiten Halbzellen und Leitsalzlösung zwischen den Hohlfasern;
• 7b: eine Prinzipdarstellung, wie Hohlfasern zu stapelbaren, erfindungsgemäßen tubulären oder quaderförmigen RFCs zusammengefügt sind, mit räumlich einfacher Verknüpfung einer ersten Halbzelle aus elektrisch und hydrodynamisch parallel miteinander verschalteten Hohlfasern mit drahtförmigen Stromabnehmern und einer zweiten Halbzelle aus elektrisch und hydrodynamisch miteinander parallel verschalteten Hohlfasern mit drahtförmigen Stromabnehmern und mit großflächiger Kontaktierung und einer Salzbrücke zwischen den Hohlfasern der ersten und der zweiten Halbzelle, aber bei teilweisem Kontakt der Hohlfasermembranen zu beiden Elektrolyten;
• 8: eine Prinzipdarstellung einer RFB aus erfindungsgemäßen RFCs in einem vertikalen Stapel bei hydrodynamischer Parallelschaltung der RFCs und elektrischer Reihenschaltung durch direkte Kontaktierung an den Stapelflächen;
• 9: eine Prinzipdarstellung einer RFB aus erfindungsgemäßen RFCs in einem horizontalen Stapel bei hydrodynamischer Parallelschaltung der RFCs und elektrischer Reihenschaltung durch Verdrahtung an den Stirnflächen der einzelnen RFCs im Stapel;
• 10: eine Prinzipdarstellung einer RFB aus erfindungsgemäßen RFCs in mehreren vertikalen Stapeln bei hydrodynamischer Parallelschaltung der RFCs und elektrischer Reihenschaltung durch Verdrahtung der Stapel miteinander;
• 11: eine perspektivische Prinzipdarstellung der Anordnung der Hohlfasern in einer erfindungsgemäßen RFC mit Halbzellen aus jeweils schichtförmig angeordneten Hohlfasern, wobei abwechselnd Schichten von Hohlfasern je einer Halbzelle mit paralleler Ausrichtung der Hohlfasern gestapelt sind;
• 12: eine perspektivische Prinzipdarstellung der Anordnung der Hohlfasern in einer erfindungsgemäßen RFC mit Halbzellen aus jeweils schichtförmig angeordneten Hohlfasern, wobei abwechselnd Schichten von Hohlfasern je einer Halbzelle mit gekreuzter Ausrichtung der Hohlfasern gestapelt sind.

The invention will be explained in more detail with reference to embodiments and drawings. Showing:

• 1 : a schematic diagram of a hollow fiber RFB according to the invention with a sectional view of an RFC according to the invention;
• 2 : A schematic representation of a first embodiment of the invention as a hollow-fiber cylindrical RFB (HFRFB), in which a number of hollow fibers embedded as hollow fiber membranes in an electrically conductive, liquid-permeable structure in the form of a felt made of graphite, wherein the hollow fibers of the first half-cells of a first electrolyte and the liquid-permeable structure of the second half-cell are flowed through by a second electrolyte;
• 3 a schematic representation of a second embodiment of the invention as cuboid HFRFB, in which a number of hollow fibers are embedded as hollow fiber membranes in an electrically conductive, liquid-permeable structure in the form of a woven or non-woven structure made of carbon, wherein the hollow fibers of the first half-cell of a first electrolyte and the liquid-permeable structure of the second half cell is traversed by a second electrolyte;
• 4 FIG. 2 is a schematic representation of a third embodiment of the invention as a cylindrical HFRFB in which a number of first tubular hollow fiber membranes and a (equal) number of second tubular hollow fiber membranes are incorporated into a liquid pervious structure in close-packed cylindrical packing, wherein the hollow fibers of the first half cell are from a first Electrolytes and the hollow fibers of the second half-cell are flowed through by a second electrolyte and the liquid-permeable structure, which is formed entirely by the outer spaces surrounding the hollow fibers, is filled with a conductive salt solution;
• 5 FIG. 2 is a schematic representation of a fourth embodiment of the invention as a cuboid HFRFB in which a number of first tubular hollow fibers and a (same) number of second tubular hollow fibers are arranged in "densest-cylinder" layers in hollow fiber layers, wherein the hollow fibers of the first half-cell and the second Half-cell alternately flows through a first and a second electrolyte and the cavities between the hollow fibers are filled with a Leitsalzlösung;
• 6a FIG. 2: shows a schematic representation of a first variant of how hollow fibers according to the invention are joined together to form stackable RFCs with spatially simple connection of a first half cell of electrically and hydrodynamically connected parallel hollow fibers with wire-shaped current collectors and a second half cell of surrounding, liquid-permeable, electrically conductive structure;
• 6b FIG. 2: shows a schematic representation of a second variant of how hollow fibers according to the invention are joined together to form stackable RFCs with spatially simple connection of a first half cell of electrically and hydrodynamically connected parallel hollow fibers with wire-shaped current collectors and a second half cell of surrounding, liquid-permeable, electrically conductive structure;
• 7a : A schematic representation of how hollow fibers according to the invention are combined to form stackable RFCs, with spatially demanding linking of a first half cell of electrically and hydrodynamically parallel interconnected hollow fibers with wire-shaped current collectors and a second half cell of electrically and hydrodynamically interconnected parallel hollow fibers with wire-shaped current collectors with completely separate electrolyte guide for the hollow fibers of the first and second half cells and conductive salt solution between the hollow fibers;
• 7b : A schematic representation of how hollow fibers are stacked into stackable, tubular or cuboid RFCs according to the invention, with spatially simple connection of a first half cell of electrically and hydrodynamically parallel interconnected hollow fibers with wire-shaped current collectors and a second half cell of electrically and hydrodynamically interconnected parallel hollow fibers with wire-shaped current collectors and with large-area contacting and a salt bridge between the hollow fibers of the first and the second half-cell, but with partial contact of the hollow-fiber membranes to both electrolytes;
• 8th : A schematic diagram of an RFB from RFCs according to the invention in a vertical stack with hydrodynamic parallel connection of the RFCs and electrical series connection by direct contacting at the stacking surfaces;
• 9 : A schematic representation of an RFB from RFCs according to the invention in a horizontal stack with hydrodynamic parallel connection of the RFCs and electrical series connection by wiring at the end faces of the individual RFCs in the stack;
• 10 FIG. 2: a schematic representation of an RFB from RFCs according to the invention in a plurality of vertical stacks with hydrodynamic parallel connection of the RFCs and electrical series connection by wiring the stacks together; FIG.
• 11 : A perspective schematic representation of the arrangement of the hollow fibers in an RFC according to the invention with half-cells of each layered arranged hollow fibers, wherein alternately layers of hollow fibers are each a half-cell stacked with parallel alignment of the hollow fibers;
• 12 : A perspective schematic representation of the arrangement of the hollow fibers in an RFC according to the invention with half-cells of each layered arranged hollow fibers, wherein alternately layers of hollow fibers are each a half-cell with crossed alignment of the hollow fibers stacked.

The arrangement for storing electrical energy consists in a basic structure - as in 1 as a redox flow cell (RFC 1 ) - from two adjacent half-cells, with different electrolytes 5 respectively. 6 are flowed through and through a plurality of tubular membranes in the form of hollow fibers 2 respectively. 3 are separated. 1 shows a two-level cut through the RFC 1 with their inclusion in a very stylized redox flow battery (RFB 9 ). The cutting planes are chosen so that one plane has multiple hollow fibers 2 . 3 axially intersects and the other plane orthogonal to several hollow fibers 2 and 3 shows radially cut.

A variety of hollow fibers 2 . 3 from hollow fiber membranes 21 respectively. 31 is filled or coated with an inner liquid-permeable, electrically conductive material, as the electrolyte-flowed electrode 22 respectively. 32 and with an electrically conductive current collector 23 respectively. 33 inside hollow fiber membrane 21 respectively. 31 and electrode 22 respectively. 32 is trained.

The hollow fiber membranes 21 . 31 can be formed by a wide variety of materials, such as plastics in the form of polymers and their derivatives, eg. Polyethylene (PE), polyurethane (PU), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVAL), polyacrylonitrile (PAN), polysulfone (PSU), polyethersulfone (PES ), Polyesters, e.g. As polyethylene terephthalate (PET), modified polyethersulfone (mPES), polyamides (PA), in particular polyamides, such as PA 6 , PA 6.6 (nylon), PA 6.10, PA 6.12, PA 11, PA 12, silicone polyamides, silicone carbonate, silicone sulfone, silicone propylene; Polyimides (PI), polytetrafluoroethylene (PTFE); from polypiperazineamide in the form of thin film membranes or cellulose acetate support layer and polyamide filter cover; from organic substances such as cellulose and derivatives thereof, e.g. Regenerated cellulose (RC), cellulose ethers, cellulose esters, e.g. Cellulose nitrate, cellulose acetate (CA), cellulose triacetate (CTA), or a ceramic (eg Al ₂ O ₃ , ZrO ₂ , TiO ₂ , Al ₂ O ₃ + TiO ₂ , BaO + TiO ₂ , Zr ₃ (PO ₄ ) ₄ , SiO ₂ , Na ₂ O, MgO, NaAl ₁₁ O ₁₇ , etc.) and based on the principle of ion-type exclusion or preferably based on the principle of molecular size exclusion.

Membranes according to the principle of ion-type exclusion consist of ion-conducting materials, preferably of sulfonated polymers and derivatives thereof, but also polymers with other ionic substituents, such as. NH ₃ ⁺ , NRH ₂ ⁺ , NR ₂ H ⁺ , NR ₃ ⁺ , PR ₃ ⁺ , SR ₂ ⁺ , COO ^- , PO ₃ ^2- , PO ₃ H ^- , C ₆ H ₄ O ^- , etc., wherein the polymers may correspond to those of the aforementioned list. Fluorinated polymers are particularly suitable because of their increased chemical resistance.

Examples of membranes according to the principle of size exclusion are a Regeneratzellulosemembran (RC) with a MWCO of 1 kDa in an electrolyte of water with sodium chloride as the conductive salt and each one in the electrolyte for the respective half-cell dissolved polymer (molecular weights greater than 1 kDa) as redox-active substance ; a Regeneratzellulosemembran with a MWCO of 5 kDa in an electrolyte of propylene carbonate and with tetrabutylammonium hexafluorophosphate as conductive salt and each one in the electrolyte for each half-cell dissolved polymer (molecular weight greater than 5 kDa) as redox-active substance; a Polyethersulfonmembran having a MWCO of 3 kDa in water with potassium chloride as the conductive salt, each with a dissolved in the electrolyte for the respective half-cell polymer (molecular weight greater than 3 kDa) as redox-active substance, etc. Here, the size exclusion membranes are each selected so that the MWCO of the membrane is below the value for the number average molecular weight of the redox-active macromolecule used.

An example of a tubular RFC based on the ion-type exclusion principle 1 For example, a variety of hollow fiber membranes of Nafion® in an electrolyte of sulfuric acid with vanadium pentoxide as the redox-active substance would be an important material construction known from commercial flat-panel RFBs. Outside are the hollow fibers 2 from a liquid-permeable structure 4 enclosed, which is formed as any extruded cylindrical or prismatic, wherein the outer surfaces along the strand direction with an electrically conductive support structure 41 (at least as a cage-like Housing) are coated or made entirely of it. The support structure 41 but may also consist of non-conductive material when electrically conductive pantograph 43 directly into the liquid-permeable structure 4 are inserted (not in 1 drawn).

In the liquid-permeable structure 4 is the entire variety of hollow fibers 2 and 3 in direct and parallel ordered (in 5 and 11 shown) or arranged in layers crossed manner (only in 12 shown), wherein the liquid-permeable structure 4 with one of the electrolytes 5 . 6 soaked or instead of the electrolyte 6 the hollow fibers 2 . 3 surrounding space is completely filled with a liquid or solid ion conductor.

The electrodes 22 . 32 respectively. 42 , where the electrochemical processes take place, can by various approaches in the interior and in the outer space of the hollow fibers 2 . 3 be arranged. In this case, the interiors or the outer spaces of the hollow fibers of a half-cell ( 2 or 3 ) in each case electrically and hydrodynamically in parallel with each other. The sum of the cross-sectional areas or the volumes of the two half-cells is preferably to be chosen so that they are the same size. However, it may due to different properties (viscosity, energy density, etc.) of the two electrolytes 5 . 6 Under certain circumstances, it may also be advantageous to choose different cross-sectional areas or half-cell volumes or at least to design the volume throughput in both half-cells differently with the aim of optimizing the performance. Through the use of hollow fiber membranes 21 . 31 Instead of flat membranes, in particular diffusion paths and the ion current paths which are usually associated with comparatively high ohmic resistances are shortened, which leads to an effective reduction of the internal resistance and the electrochemical overvoltages in the system and thus to an increase in the power per cell volume of an RFC 1 leads.

The possible number of hollow fibers 2 . 3 in an RFC 1 is unlimited in principle. Their exact choice depends essentially on the cell geometry and, above all, on the desired membrane area, which is one of the main factors limiting the RFC's electrical power 1 is why the dimensioning of the hollow fiber membranes 21 . 31 and the external dimensions of the RFC 1 mainly aimed at this size. From the very high variability in the choice of number, inner and outer diameter, z. B. between 1 .mu.m and 10 mm, preferably 100 .mu.m to 1 mm, length, for example 1 mm to 1 m, preferably 1 cm to 20 cm, geometric arrangement and choice of the membrane material (see above) of the hollow fiber membranes 21 . 31 results in an enormous variety of meaningful different design options of such a redox flow battery 9 , hereinafter also referred to as hollow fiber redox flow battery (HFRFB).

In the design of an RFC 1 Two aspects are mainly crucial. The first point concerns the cell geometry and thus the flow or flow around the porous electrodes 22 . 32 respectively. 42 with the respective electrolyte 5 respectively. 6 , This point is particularly dependent on the choice of the geometric dimensions of the hollow fibers 2 respectively. 3 , their number, as well as geometric arrangement and their appropriate gap-free embedding in an elastically conformable, yielding or crack-free with the hollow fibers 2 . 3 pierceable liquid permeable structure 4 and their introduction into a support structure 41 (eg a housing). The mechanical stabilization of the hollow fibers 2 . 3 as well as the separation of the flow paths in an RFC 1 for in the electrolyte circuit 51 the first half-cell and in the electrolyte circuit 61 The second half cell may be achieved by attaching or pouring the hollow fiber membrane ends into a stabilizing, sealing matrix (eg of silicone or a synthetic resin, such as epoxy resin), as shown in FIG 6a . 6b and 7a . 7b is shown.

The second point concerns the condition of the electrodes, at their interface with the electrolyte 5 respectively. 6 the electrochemical reactions take place, as well as the electrical contacting of the electrodes 22 . 32 . 42 ,

It should be noted that these two problems may, but not necessarily, be solved separately. Since this results in various possible combinations of cell geometry and electrode design, these two aspects are considered separately below.

Example 1: Tubular cell with a half-cell of a plurality of hollow fibers

In 2 is an axial section through a tubular RFC 1 without the further periphery of an RFB 9 (only in 1 , and Figs. 8-10), in which the polarity-specific first half-cell is made up of the entirety of the interiors of a multiplicity of hollow fibers 2 and the oppositely poled second half cell from a total of one around the hollow fibers 2 and liquid-permeable structure therebetween 4 be formed.

In the tubular RFC 1 are the hollow fiber membranes 21 modified polyethersulfone (mPES) in this example (eg Spectrum Labs company, inner diameter 1 mm, size exclusion with MWCO 3 kDa) with a packing density of 0.60 in the surrounding electrically conductive, liquid-permeable structure 4 embedded, which in this case as a porous electrode 42 is formed in the form of a felt made of graphite and as a cylindrical or cylindrical rolled strand material. The electrode 42 is in a macrotubular graphite tube as a support structure 41 arranged with an inner diameter of 8.8 cm and a length of 10 cm, the support structure 41 at the same time as a pantograph 43 provided the second half-cell and with a power connection 8th (only in 1 such as 8th to 10 drawn) is connected.

In the first half cell, each of the hollow fiber membranes is 21 with a carbon fiber braid as the electrolyte-permeable porous electrode 22 and a centrally inserted into the mesh electrically conductive pantograph 23 , preferably in the form of a nickel wire (or silver wire), which may also be coated with carbon. All are pantographs 23 the first half-cell of the RFC 1 united together in an electrical parallel connection and via an electrical load (battery discharge) or a power connection 8th (Voltage source for battery charging, only in 1 shown) with the pantograph 43 the second half-cell connected to a closed circuit (electrolyte circuits 51 . 61 only in 1 drawn). The porous electrode 22 is with a first redox-active polymer, for example in the form of a viologen polymer (molar mass, M _n = 31 kDa) after Janoshka et al. [in: Nature 2015, 527, 78-81 ] may be dissolved in aqueous sodium chloride solution, as the electrolyte 5 flows through and by means of a pump 53 in the electrolyte circuit 51 into the electrolyte reservoir 52 pumped and stored there.

In the second half cell, the graphite felt becomes a porous outer electrode 42 with the second electrolyte 6 consisting of a second redox-active polymer, which, for example, in the form of a TEMPO polymer (molar mass, M _n = 20 kDa) according to [ Janoschka et al., Nature 2015, 527, 78-81 ] dissolved in aqueous sodium chloride solution, flows through and into a second electrolyte circuit 61 with an electrolyte reservoir 62 and a pump 63 involved. This is the tubular RFC 1 to an RFB 9 completes and can with other tubular RFCs 1 stacked into a cell stack or directly as an RFB 9 be used from a single cell.

Also useful may be hollow fiber membranes 21 be used from ceramic materials. The use of such membranes can increase the chemical resistance of an RFC 1 greatly increase compared to organic solvents. So it is possible to have an RFC 1 with electrolytes 5 . 6 based on organic solvents, such as. As acetonitrile, propylene carbonate, dimethyl sulfoxide, etc. to operate.

Two surfaces in planar RFC 1 have to be completely sealed off when using tubular (tubular) RFCs 1 in a HFRFB. If you want to increase the absolute performance of the latter, you can simply its diameter and the number of hollow fibers 2 increase or with much less effort the RFC 1 extend axially.

When making a longer tubular RFC 1 There is little additional effort because tubular components can be manufactured by continuous processes, such as extrusion in almost any length. The necessary area of seal remains constant with a change in the tube length, since only the strand ends must be sealed, which is an advantage over a planar RFC 1 or a conventional flat-panel RFC.

A computational estimate of exemplary, meaningful dimensioning possibilities of this variant of the RFC 1 is given in Table 1. Here, membrane areas of 5 cm ² to 1 m ² for an RFC 1 what's usual for RFC 1 from laboratory scale to commercially available systems. The membrane surface is assumed because it decisively defines the ohmic internal resistance of a cell and at the same time determines its cell size. Especially with RFCs with flat membranes, the membrane area is equal to the minimum size, which is an RFC 1 occupies its base. With HFRFBs, the variety of dimensioning options is much higher with the same membrane area.

The membrane areas listed in the table and resulting cell dimensions are therefore expressly not limiting, but are to be understood as a few examples of the enormous variety of realizable with hollow fiber membranes Zelldimensionierungen. Because of the compact Construction of hollow fiber cells is here in particular a much larger, meaningful membrane surface conceivable, as listed or realized for conventional RFCs with flat membrane so far.

The mathematical estimation of the dimensioning of a hollow fiber cell according to this embodiment is made by calculating how many parallel aligned hollow fibers 2 . 3 a reasonable number and with a uniform diameter (eg, 0.5 mm or 1 mm) are needed to reach the given membrane area at a given cell length. The requirement of equal volumes for both half-cells results in the computationally necessary cell length and the computationally necessary cell diameter. It is crucial for the choice of the cell length that the pressure drop to maintain the electrolyte flow increases with increasing cell length and thus the energy efficiency of the RFC 1 is reduced. However, this can easily be compensated in an HFRFB due to the high membrane area-cell volume ratio by increasing the cell diameter while reducing / limiting the cell length, while still retaining the advantage of more compact design over conventional RFCs with flat membranes of the same membrane area. Furthermore, for the estimates listed, the diameter of the cylindrical current collector inside the fiber is assumed to be 250 μm, although thicker or thinner variants are also conceivable here. The concrete choice depends on the current carrying capacity of the material, the desired overall surface and last but not least on the production costs. Tab. 1: Exemplary embodiment 1 (round cell with hollow fibers): 10000 0.1 0.12 3200 9.94 8.72 0.05 0.07 6400 9.94 6.58 Membrane area [cm ² ] Diameter hollow fiber (inside) Diameter hollow fiber (outside) Number of hollow fibers (N) Cell length (L) Cell diameter * (D _{1: 1} ) [cm] [cm] [1] [cm] [cm] 5 0.1 0.12 3 5.3 0.38 0.05 0.07 6 5.3 0.20 100 0.1 0.12 32 9.94 0.87 0.05 0.07 64 9.94 0.66 1000 0.1 0.12 320 9.94 2.76 0.05 0.07 640 9.94 2.08 10000 0.1 0.12 3200 9.94 8.72 0.05 0.07 6400 9.94 6.58 * Half-cells of equal size are preferred, so this column shows the total diameter of the cell, which results mathematically at a ratio of 1: 1 of the half-cell volumes.

While flat polymer membranes (not shown) are also variable in size and do not constrain the scaling of a planar cell, they provide, as previously indicated, a significantly smaller membrane area per cell volume.

For this purpose too, a table of the dimensioning possibilities (for comparison with the exemplary embodiments according to the invention) is given below. Tab. 2: Conventional flat cells with flat membrane (square plan) Membrane area [cm ² ] Half cell thickness [cm] Edge length [cm] Cross-sectional area [cm ² ] Theoretical power * [W] 5 0.4 2.24 5 0.28 100 0.5 10.00 100 5.6 1000 0.5 31.62 1000 56 10000 0.5 100.00 10000 560 * Assumption: vanadium RFB, ie voltage: 1.4 V, assumed average current density: 40 mA / cm ²

Example 2: Flat Cell with Hollow Fiber Membranes

Despite the above-mentioned disadvantages of planar RFCs of a flat membrane RFB are alternative to the tubular RFC 1 according to 2 also planar RFCs 1 using hollow-fiber membranes 21 are equipped, interesting. The design of such a planar RFC 1 is in 3 shown.

The planar RFC 1 has a base of defined geometry and freely selectable dimensions (eg as listed in Tab. The base may in principle be a polygon (eg triangular, rectangular, trapezoidal, hexagonal, etc.), but is preferably rectangular, as in the embodiment according to FIG 3 shown. The hollow fibers 2 from cellulose triacetate (inside diameter 0.5 mm, size exclusion membrane with MWCO 1 kDa) are in the volume of the planar RFC 1 arranged in parallel or layered crossed. In this case, the entirety of the hollow fibers form 2 one hand and one the hollow fibers 2 contiguous surrounding electrically conductive, liquid permeable structure 4 as a porous electrode 42 in the form of a carbon fabric or nonwoven structure, on the other hand, the two separate half-cells. This variant is in 3 shown in the hollow fibers 2 orthogonal to the rectangular base or top surface of a prism-shaped strand of the fabric or nonwoven structure as a porous electrode 42 and are arranged parallel to each other and to the flat side surfaces. Optionally, in this type of RFC 1 the hollow fibers 2 are combined and laminated to lamellar composites, wherein at least individual hollow fiber layers 72 . 73 can also be alternately offset by an angle α with 0 ° ≤α≤90 °, preferably by an angle α = 90 ° to each other can be rotated (see Figs. 11, 12). The electrolyte flow takes place on the one hand through the interior of the hollow fibers 2 (Electrolyte 5 through the first half-cell) and, second, in the porous electrode 42 (Electrolyte 6 in the second half cell). It is irrelevant whether electrolyte 5 for example, a viologen polymer dissolved in water (e.g. Janoschka et al., Nature 2015, 527, 78-81 ] with molar mass, M _n = 19 kDa) and potassium chloride dissolved therein, and electrolyte 6 containing, for example, a TEMPO polymer (for example, [ Janoschka et al., Nature 2015, 527, 78-81 ] with molar mass M _n = 10 kDa) can also be dissolved in aqueous potassium chloride solution, the two half-cells in the same direction or in opposite directions to each other or - if this allows the respective geometry (eg., With shown rectangular base) - flow perpendicular to each other. Here is the sum of the cross-sectional areas of the electrodes 22 in the hollow fiber membranes 21 to the perfused cross-sectional area of the liquid-permeable structure 4 (= porous electrode 42 ) to separate electrolyte circuits 51 respectively. 61 at the same volume throughput, each with an electrolyte reservoir 52 respectively. 62 for the electrolytes 5 respectively. 6 at the same pumping power for the pumps 53 and 63 to reach.

However, it may due to different electrolyte properties (viscosity, energy density, etc.) of the electrolytes 5 and 6 may also be advantageous under certain circumstances to choose different cross-sectional areas and / or to adjust the volume throughput by different pumping levels. As an arithmetic estimate for some exemplary dimensions of this embodiment of the hollow fiber cells according to the invention, the following Table 3 is added. In this case, a rectangular base area with edge lengths a, b is assumed whose ratio to one another is 1: 2. Other aspect ratios are also conceivable, for example an aspect ratio of 1: 1 (ie square footprint) representing a maximum surface area given the circumference of the rectangle. However, off-square aspect ratios have the advantage of cell stacks. The choice of the aspect ratio of 1: 2 for subsequent estimates is thus an example of the computationally infinite possibilities, which is a compromise between surface area and advantageous stackability of the RFC 1 represents.

The estimation of the sizing of a hollow fiber cell according to this embodiment is made by calculating how many parallel aligned hollow fibers of a reasonable number and of uniform diameter (eg 0.5 mm or 1 mm) are required to satisfy the given Reach membrane surface. Under the requirement of equal volumes for both half-cells, this results in the computationally necessary cell length and edge length a. The cell or edge length (depending on whether the flow in the second half-cell parallel or perpendicular to the hollow fibers) is ultimately limited by the fact that the pressure drop to maintain the electrolyte flow increases with increasing cell length and the energy efficiency of the RFC 1 reduced. However, this can be easily compensated in a hollow fiber RFB by the high membrane area-to-cell volume ratio by increasing the cell surface area while reducing / limiting the cell length, while still maintaining the advantage of more compact design compared to flat cells with flat membranes of the same membrane area. Furthermore, for the estimates listed, the diameter of the cylindrical current collector inside the fiber is assumed to be 250 μm, although thicker or thinner variants are also conceivable here. The concrete choice depends on the current carrying capacity of the material, the desired overall surface and last but not least on the production costs. Tab. 3: Exemplary embodiment 2 (cell with rectangular layout and with hollow fibers): Membrane area [cm ² ] Diameter hollow fiber (inside) Diameter hollow fiber (outside) Number of hollow fibers (N) Cell length (L) Edge length * (a _{1: 1} ) [cm] [cm] [1] [cm] [cm] 5 0.1 0.12 16 0.99 0.39 0.05 0.07 32 0.99 0.29 100 0.1 0.12 64 4.97 0.77 0.05 0.07 128 4.97 0.58 1000 0.1 0.12 320 9.95 1.73 0.05 0.07 640 9.95 1.30 10000 0.1 0.12 3200 9.95 5.47 0.05 0.07 6400 9.95 4.13 * Half-cells of equal size are preferred, so this column shows the total cell edge lengths, which are mathematically determined at a ratio of 1: 1 of the half-cell volumes.

Example 3. Tube cell with hollow fibers for both half cells

As a modified variant of that in Example 1 ( 2 ) described tubular RFC 1 is in particular an arrangement densest packed, aligned parallel to each other hollow-fiber membranes 21 and 31 , which consist in this embodiment of Nafion® (inner diameter 2 mm, ion exclusion: cation-conductive), another useful and advantageous embodiment of the invention, as in 4 is shown. The hollow fibers 2 the first half cell and the hollow fibers 3 the second half cell are in hollow fiber layers 71 , which are stylized in two of the plurality of layers as their mid-planes, alternately arranged. The spaces between the hollow fibers 2 and 3 the individual hollow fiber layers 71 be there (possibly also by using hollow fiber membranes 21 . 31 different geometric dimensions) and minimizes the densest packing of hollow fiber membranes 21 . 31 realized in the given, cylindrical basic geometry. At least half of the totality of the hollow fiber membranes arranged in this way 21 and 31 (ie the hollow fibers 2 the first half cell) is filled with electrolyte 5 flows through and a maximum of half the totality of the thus arranged hollow fiber membranes 21 and 31 (namely the hollow fibers 3 the second half-cell) with electrolyte 6 , Both electrolytes 5 . 6 can - due to the use of a hollow fiber-shaped cation-conducting membrane - in contrast to previous embodiments, also consist of low molecular weight substances as a redox couple. As one of the most important representatives for flat membrane based RFBs 9 This can also be done, for example, in this embodiment of the RFC according to the invention 1 an electrolyte of vanadium pentoxide dissolved in aqueous sulfuric acid. The flow directions in each half cell or for each of the hollow fibers 2 or 3 separately selectable. The remaining spaces between the hollow fibers 2 and 3 be as liquid-permeable structure 4 with a dormant or (by other pumps, not drawn) circulated pure conductive salt solution of aqueous sulfuric acid completely filled, the salt bridge 7 in each case between the two through the hollow fibers 2 and 3 designed half-cells acts. The solvent and the dissolved salt correspond to the solvent of the electrolyte 5 and 6 and one as an auxiliary electrolyte in the electrolyte 5 and 6 used conductive salt. As a result, the circuit between the half-cells is closed.

As the distances between adjacent hollow fiber membranes 21 . 31 in this type of RFC 1 are minimal, result in the average minimum ion current paths, which lead the ions of the auxiliary electrolyte over a maximum average distance, the sum of double membrane thickness and double fiber radius of the hollow fibers 2 and 3 equivalent. This new mode of operation and the associated cell configuration of a tubular RFC with hollow-fiber membranes results in a production-related advantage over the other exemplary embodiments presented and other tubular RFCs known from the prior art, since with a suitable choice of material for electrodes 22 . 32 and pantographs 23 . 33 the two half-cells can be constructed and manufactured completely the same. The different half-cells are characterized as such only by the different filling, electrolyte 5 or electrolyte 6 , out. Electrolyte supply and current collection can be implemented separately for both half cells, but each in an identical manner, which is naturally not the case with other hollow fiber cells, if a half cell through the interiors and the other through the outer spaces of the individual hollow fibers 2 is realized. In particular, the electrolyte and electrolyte discharge can be designed so that in each case on the inlet or outlet side, the ends of the hollow fibers 2 one half cell extended and embedded in a separate matrix and the ends of the hollow fibers 3 directly lead to a laterally outgoing channel, as for example in 7a and 7b drawn in a sectional view. The two different electrolytes 5 respectively. 6 flow out of or into two separate channels / chambers, from which they in corresponding other areas of a cell stack or in the electrolyte reservoir 52 respectively. 62 can be directed.

Furthermore, there is for each RFC 1 and any RFC known in the art has a small but finite probability of transition from redox-active molecules of a first half-cell to a second half-cell, thereby causing unavoidable cross-contamination of the electrolytes 5 . 6 Both half-cells, which is a limiting factor for the life of any known in the art RFB, where all-vanadium RFBs here due to the regenerability of the electrolytes 5 . 6 occupy a special position.

The risk of cross-contamination of both electrolytes 5 and 6 in the RFC according to the invention 1 is significantly reduced because the the hollow fiber membrane 21 . 31 Inadvertently passing redox-active molecules first into the salt bridge 7 go over there and then be present in a strong dilution, without a functional impairment occurs. Further, in mechanical failure, one of the hollow fiber membranes occurs 21 . 31 not immediately a mixture of the two electrolytes 5 and 6 a, as this at least two hollow fiber membranes 21 and 31 different half cells must be damaged. In the execution according to 7b This is high security compared to the execution according to 7a slightly reduced, because the hollow fiber membranes 21 or 31 in the area of the inlet and outlet channels 54 . 55 the hollow fibers 2 and the inlet and outlet channels 64 . 65 the hollow fibers 3 are not completely encapsulated and thereby each with two electrolytes 5 and 6 on different sides of the hollow fiber membranes 21 respectively. 31 get in touch. Through this constructive solution of the supply of electrolytes 5 . 6 However, it is possible to design the inlet and outlet channels 54 . 55 . 64 . 65 make it simpler and more uniform, what the production costs compared to the execution according to 7a reduced. In flat cells and in the other hollow fiber cells of the embodiments according to 2 and 3 However, it is always sufficient to damage the flat membrane or a hollow fiber membrane 21 or 31 , which in the case of most redox species leads to complete uselessness of both electrolytes 5 . 6 and a total failure of the RFB 9 can lead.

Possibilities for dimensioning the present version of the RFC 1 with hollow fibers 2 and 3 in the same way for each of the half-cells are listed in the following Table 4 as computational estimates. The estimation is largely based on the same assumptions and calculations as already described in Example 1. The only difference is the requirement of a densest cylinder packing of the hollow fibers 2 . 3 which, as described above, minimizes the hollow fiber spacings and gaps with the purpose of minimizing the internal resistance of the RFC 1 serves. This results in a maximum packing density for a given number of hollow fibers 2 . 3 with fixed membrane surface. Otherwise, the statements made in Example 1 on dimensions and pressure drops also apply to this embodiment. Tab. 4: Exemplary embodiment 3 (round cell with hollow fibers for each half cell): Membrane area [cm ² ] Diameter hollow fiber (inside) Diameter hollow fiber (outside) Number of hollow fibers (N) Cell length (L) Cell diameter * (D) [cm] [cm] [1] [cm] [cm] 5 0.1 0.12 3 5.3 0.29 0.05 0.07 6 5.3 0.20 100 0.1 0.12 32 9.94 0.77 0.05 0.07 64 9.94 0.61 1000 0.1 0.12 320 9.94 2.32 0.05 0.07 640 9.94 1.88 10000 0.1 0.12 3200 9.94 7.19 0.05 0.07 6400 9.94 5.84 * Here, the maximum possible packing density was assumed, which can be achieved for the given number of parallel hollow fibers in a cylindrical cell geometry.

Example 4. Flat cell with hollow fibers for both half cells

In 5 is as a modified variant of in 3 described planar RFC 1 with densely packed, parallel or perpendicular aligned (possibly interwoven) hollow fiber membranes 21 and 31 another useful embodiment of the invention shown as RFC 1 is formed with a rectangular plan and based on the same basic principle as Example 3. The spaces between the hollow fibers 2 and 3 , which here exemplified from regenerated cellulose (inner diameter 1 mm, size exclusion with MWCO 3 kDa) are also here (optionally also by using hollow fiber membranes 21 . 31 different geometric dimensions) minimized as possible. At least half of the totality of the hollow fiber membranes arranged in this way 21 . 31 (Hollow fibers 2 the first half cell) is filled with electrolyte 5 (eg a TEMPO polymer according to [ Winsberg et al., Adv. Mat. 2016, 28, 2238-2243 ] in water with equal parts of zinc and ammonium chloride) and a maximum of half of the totality of the hollow fiber membranes arranged in this way 21 . 31 (Hollow fibers 3 the second half cell) is filled with electrolyte 6 (eg after [ Winsberg et al., Adv. Mat. 2016, 28, 2238-2243 ] equal parts of zinc and ammonium chloride in water) flows through.

In this case, two hollow fibers are for the second half cell 3 less than hollow fibers 2 necessary for the first half cell. The exemplary selected, unequal hollow fiber number serves the purpose of equalizing the volume flow rate of the two half-cells with their different viscous electrolytes 5 . 6 while maintaining the same pumping levels. In addition, the hollow fibers 2 and 3 each layer alternately arranged in layers; by way of example in three hollow fiber layers 71 (Clarified by their parting planes), which lie in closest packing cylinder abut each other, wherein the flow directions in the hollow fibers 2 . 3 the two half-cells are again arbitrary in the same direction or in opposite directions selectable. The remaining spaces between the hollow fibers 2 and 3 are as in Example 3 with a quiescent or circulating electrolyte salt salt bridge 7 completely filled, which consists in this example of water and in equal parts dissolved zinc and ammonium chloride. As electrodes 22 in the hollow fibers 2 become porous carbon rods (1 mm) and as electrodes 32 in the hollow fibers 3 used in carbon yarn braided zinc wires, which in both cases at the same time as a current collector 23 and 33 are formed.

In this example, the spaces between the hollow fibers 2 and 3 the two half-cells and the voltage applied to the outer hollow fiber layers support structures 41 in the form of two non-conducting plane-parallel plates with a non-conductive liquid-permeable structure 4 filled out of a cured porous foam and thus the hollow fibers 2 and 3 between the plates of the support structure 41 fixed. Here is the salt solution of the salt bridge 7 present within the pores of the porous foam. The circuit between the half-cells is characterized in the same manner as previously closed by the filled electrolyte solution, at the same time a positive fixation of the stacked layers of alternately arranged hollow fibers 2 and 3 is guaranteed within and between the layers. Exemplary dimensions of the RFC 1 The present design are in turn in Tab. 5 as calculated Estimates stated. The estimate is based on the assumption that the hollow fibers 2 . 3 arranged in layers and the respective layers are packed as close as possible and in addition the rectangle has an aspect ratio of 1: 2. This does not necessarily correspond to the mathematically closest packing of cylinders in a given rectangle. The latter, however, is not mathematically known for any rectangle and therefore has to be determined on a case-by-case basis. In addition, the packing in hollow fiber layers in most cases results anyway the smallest mean distance of hollow fibers 2 . 3 in a given rectangle. Therefore, the dimensions given in Tab. 5 are to be understood as meaningful, exemplary estimation, but not as the only sensible arrangement of the given hollow fiber number in a rectangular cell geometry. Apart from that, the statements made in Example 2 apply to the dimensions of a rectangular RFC 1 and pressure drops during operation of such an RFC 1 also for this embodiment 3 to. Tab. 5: Embodiment 4 (RFC with rectangular layout and hollow fibers for each half-cell): Membrane area [cm ² ] Diameter hollow fiber (inside) Through hollow fiber (outside) r number of hollow fibers (N) Cell length (L) Edge length a Edge length b [cm] [cm] [1] [cm] [cm] [cm] 5 0.1 0.12 15 1.06 0.33 0.66 0.05 0.07 28 1.14 0.26 0.53 100 0.1 0.12 60 5.31 0.63 1.26 0.05 0.07 135 4.72 0.54 1.09 1000 0.1 0.12 336 9.47 1.47 2.94 0.05 0.07 680 9.36 1.21 2.42 10000 0.1 0.12 3225 9.87 4.53 9.06 0.05 0.07 6405 9.94 3.69 7.39

Also in this embodiment of the invention results, analogous to the third embodiment, a production advantage over the presented embodiments 1 and 2 , as with a suitable choice of material for electrodes 22 . 32 and pantographs 23 . 33 the two half-cells can be constructed and manufactured completely the same. The different half cells differ only and solely by the different filling with electrolyte 5 respectively. 6 , Electrolyte supply and current collection can be implemented separately for both half cells, but each in an identical manner, which is naturally not the case with other hollow fiber cells, if the first half cell through the interior and the second through the outer spaces of the individual hollow fibers 2 is realized. In particular, the electrolyte and electrolyte discharge can be designed so that in each case on the inlet or outlet side, the hollow fibers 2 which extends a half cell and whose ends are embedded in a separate matrix and the hollow fibers 3 directly lead to a laterally outgoing channel, as for example in 7a and 7b drawn in a sectional view. An additional advantage also results for the mechanical fixation of the hollow fibers 2 . 3 and the assembly of the RFC 1 by the layered arrangement of the hollow fibers 2 . 3 in a cured, porous foam.

There is also the risk of cross-contamination of both electrolytes 5 and 6 as explained in detail for Example 3 and for the same reasons, clearly over a conventional flat membrane RFB or HFRFB according to the embodiments 1 and 2 reduced.

An additional explanatory schematic diagram and a further modification of the rectangular version of the RFC 1 according to 5 are schematic in 11 and 12 (without representation of the hollow fibers 2 . 3 surrounding chamber and support structure 41 ). Here are the representation of the arrangement of the hollow fibers 2 and 3 the different half-cells exclusively the layered hollow fibers 2 and 3 for the rectangular layout of the RFC 1 drawn. In each case, the hollow fibers 2 in a hollow fiber layer 72 and the hollow fibers 3 in another hollow fiber layer 73 arranged. Thus, the stacking of the individual hollow fibers 2 . 3 the different half-cells in alternating layer sequence possible. For that shows 11 the stacking of the different hollow fiber layers 72 . 73 in parallel orientation, which is also the closest to the stratification cylinder packing of the hollow fibers 2 and 3 allowed. In contrast, in 12 an alignment of the hollow fibers 2 and 3 proposed at an angle α = 90 °. As a result, the flow directions of the electrolytes 5 and 6 crossed to each other, creating the inlet and outlet channels 54 . 55 of the hollow fibers 2 the first half-cell and inlet and outlet channels 64 . 65 the hollow fibers 3 the second half cell (not in 11 and 12 at different side edges of the rectangular layout of the RFC 1 lie. This facilitates the supply of electrolytes 5 and 6 in otherwise similar compact, rectangular design of the RFC 1 , It should also be noted that the angle α between the orientations of the hollow fiber layers 72 . 73 is adjustable to any values between 0 ≤ α ≤ 90 °, without any such alignment of the hollow fiber layers 72 and 73 is explicitly drawn to each other.

The inventive arrangement for storing electrical energy allows easy production of an RFC 1 with hollow fiber membranes 21 . 31 Without the usual problems of electrode production, since these are formed by the electrolyte paths themselves and must be contacted only by additional current collector with good electrical conductivity.

The following explanations are intended to illustrate exemplary possibilities for the realization of electrodes 22 . 32 . 42 and pantographs 23 . 33 . 43 for the hollow fiber membranes 21 . 31 and can in principle be used for all previous embodiments which relate to HFRFB, ie can be combined with them or implemented in them.

It is an RFC according to the invention 1 produced. A first embodiment of the electrodes 22 . 32 respectively. 42 for an RFC 1 of this type are porous coatings. On the inside and the outside of the hollow fiber membranes 21 For this purpose, by suitable methods, such as, for example, vapor deposition, thermal spraying, dip coating and printing methods, in each case an electrically conductive porous layer is applied, which serves as a porous electrode 22 or at least as part of the electrode 22 serves. The choice of the coating method is in principle limited by the fact that the membrane or any support structures of the membrane is not dissolved or otherwise destroyed and the possible pore structure of the membrane may not be clogged or damaged. The material of the hollow fiber membrane 21 itself isolated the respective porous electrode 22 on the inside of the hollow fiber membrane 21 and the porous outer electrode 42 on the outside of the hollow fiber membrane 21 electrical from each other to exclude short circuits. The thus created small distance between the electrodes 22 and 42 , which is in the range of 10 microns to several hundred microns, ensures minimal diffusion paths of the ions, resulting in a reduction of the internal resistance of the RFC 1 leads compared to conventional RFCs with flat membranes. For RFCs according to the invention 1 in a variant with salt bridge 7 are configured (as in embodiments 3 and 4 exemplified), the described embodiment of the electrodes 22 also only on the inside and both for the hollow fiber membranes 21 a first half cell as well as the hollow fiber membranes 31 and the associated electrodes 32 done a second half-cell.

In addition, in a second embodiment of the electrodes 22 . 32 . 42 instead of or in addition to a membrane coating, the interior space and the exterior space of the hollow-fiber membranes 21 . 31 completely with liquid-permeable, electrically conductive structures as electrodes 22 . 32 . 42 fill out.

In RFCs 1 according to or similar to the embodiments 1 and 2 for which a first half cell passes through the hollow fibers 2 and a second half cell through which the hollow fibers 2 This is done by filling the hollow-fiber membranes 21 surrounding spaces with an electrically conductive, liquid-permeable structure 4 as a porous electrode 42 in the form of bulk solids (eg of irregular or regularly shaped small parts, such as globules, very small grains, etc. of carbon, aluminum, copper, zinc, nickel, silver, or other metals, alloys or conductive materials, as long as they are in the respective electrolytes 5 . 6 are electrochemically stable and do not undergo unwanted side reactions), felts, fabrics, knits, knits, nonwovens, papers, meshes or lattice-like structures, foams, fibers and / or yarns of carbon, carbon composites and / or metals (eg aluminum, copper , Zinc, nickel, silver, etc.) happen. Also alternately stacking thin porous electrode layers of the aforementioned or similar materials and layers of hollow fiber membranes 21 is conceivable. Inside the hollow fiber membranes 21 such RFC 1 can the porous electrode 22 then also be realized by liquid-permeable, electrically conductive structures, for which the previously for the hollow-fiber membranes 21 surrounding chamber described embodiments and materials come into question. In particular, however, in the interior of the hollow fiber membranes 21 also electrically conductive wires or rods with and without brush-like or otherwise porous coating, porous rods or strand-like structures (eg fibers, yarns, fabrics, etc.) of the above-mentioned materials as electrodes 22 be used. Furthermore, simple or additionally chemically or mechanically roughened wires, rods or other non-porous string-like structures can be used for this purpose.

For the interior of the hollow fiber membranes 31 as they are in RFCs 1 according to or similar to the embodiments 3 and 4 are realized apply to the electrodes 32 the same designs as above for the hollow fiber membranes 21 and the associated electrodes 22 were explained.

Further, the porous electrodes 22 . 32 instead of them, as previously described, on the hollow fiber membrane 21 . 31 to precipitate or in any way in the finished hollow fiber membrane 21 . 31 - be implemented by processes in which the membrane material on appropriately preformed liquid-permeable, electrically conductive structures 4 , as described above, is deposited.

As a pantograph 23 . 33 for the hollow fiber interior of the hollow fiber membranes 21 . 31 located electrodes 22 . 32 are electrically conductive rods (for example made of carbon, aluminum, copper, zinc, nickel, silver, etc.), which are preferably roughened or porous and in the case of porous electrodes 22 . 32 can be simply inserted into the porous electrode structure or woven directly in wick-like structures. For electrodes 22 and 32 , which are formed as a membrane coating, the current decrease by at least one in each case in the interior of the hollow fiber membranes 21 . 31 to the porous coating material of the electrodes 22 . 32 applied electrically conductive wire, rod, strip or similar strand-like shaped pantograph 23 . 33 which leads axially outward, or by slipping the (also coated) ends of the hollow fiber membranes 21 . 31 on electrically conductive tubes (not shown) take place. The latter can then be electrically connected in parallel to each other by wire or a second, electrically conductive framework. On additional pantographs 23 . 33 can be completely dispensed with in a further variant by the electrodes described above 22 . 32 also at the same time as a pantograph 23 . 33 summarized to the outside.

For external contacting of the inside of the hollow fibers 2 . 3 realized half cell (s) of an RFC 1 become the pantographs 23 . 33 the individual hollow fiber membranes 21 . 31 then extended to the outside and each to a common busbar 24 . 34 - ie electrically connected in parallel - attached, from which the current from the outside of the RFC 1 can be removed (see 6a to 7b ).

For a half cell passing through the hollow fibers 2 surrounding chamber is formed and its porous outer electrode 42 by an electrically conductive liquid-permeable structure described above 4 is formed, the current collection and external contacting for the RFC 1 by applying / pressing an electrically conductive pantograph 43 on / to the liquid-permeable structure 4 also by at least one of the support structures 41 or may be formed by parts thereof, as in 6a and 6b is drawn by way of example in a schematic diagram. Moreover, it is also possible in the porous outer electrode 42 at least one strand-like pantograph 43 For example, in the form of an electrically conductive wire, rod, another strand-like structure or a grid or a planar structure, and to the outside as an electrical contact of the RFC 1 train.

It should also be noted that it is irrelevant to the invention which concrete electrolytes and membrane materials are used in an HFRFB according to the invention. The advantages of the invention are mainly due to the variety of geometries, the increased membrane surface, possibly the use of readily available size exclusion membranes in hollow fiber form and the use of a salt bridge 7 , Thus, for an inventive HFRFB with their corresponding advantages over a flat membrane RFB, all membrane materials, electrolytes and redox pairs are available in each case, which can also be realized for flat membranes. For this reason, the electrolytes and membrane specifications listed above in the exemplary embodiments represent only more or less arbitrarily chosen examples whose functionality in RFCs with flat membranes has already been described in the literature (eg. J. Noack et al., Angew. Chem. Int. Ed. 2015, 54, 9776-9809 ; or J. Winsberg et al., Angew. Chem. Int. Ed. 2016, DOI: 10.1002 / anie.201604925R1 ) has been adequately demonstrated and, of course, suitable for use in an HFRFB.

Finally, it should be pointed out that the use of hollow fibers and the departure from the flat membrane cell geometries familiar from the prior art is not a disadvantage with regard to the design of cell stacks. Several RFCs according to the invention 1 can also be easily interconnected to cell stacks, as exemplified for cells with rectangular or circular base or top surface in Figs. 8-10 is shown. There are several RFCs 1 stacked vertically or horizontally arranged and hydrodynamically connected in parallel while being electrically connected in series. Thus, it is possible to build up cell stacks which provide the known advantages, such as, for example, the increase in the RFB power by increasing the nominal voltage and the option via battery management to dynamically add or disable individual RFCs or entire sub-stacks of an RFB depending on the power requirement.

LIST OF REFERENCE NUMBERS

1

Redox Flow Cell (RFC)

2

Hollow fiber (the first half cell)

21

Hollow fiber membrane (the first half cell)

22

(porous) electrode (the first half-cell)

23

(inner) current collector (the first half-cell)

24

(outer) busbar (the inner pantograph 23 )

3

Hollow fiber (the second half cell)

31

Hollow fiber membrane (the second half cell)

32

(porous) electrode (the second half-cell)

33

(inner) current collector (the second half-cell)

34

(outer) busbar (the inner pantograph)

4

liquid-permeable structure

41

Support structure (housing)

42

(porous) outer electrode

43

(outer) pantograph

5

Electrolyte (the first half-cell)

51

Electrolyte circuit (the first half-cell)

52

Electrolyte reservoir (the first half-cell)

53

Pump (the first half-cell)

54

Inlet channel (the hollow fiber 2 )

55

Outlet channel (the hollow fiber 2 )

6

Electrolyte (the second half-cell)

61

Electrolyte circuit (the second half-cell)

62

Electrolyte reservoir (the second half-cell)

63

Pump (the second half-cell)

64

Inlet channel (the hollow fiber 3 )

65

Outlet channel (the hollow fiber 3 )

7

salt bridge

71

Hollow fiber layer (with alternating hollow fibers 2 . 3 )

72

Hollow fiber layer (the first half cell)

73

Hollow fiber layer (the second half cell)

8th

power connection

9

Redox Flow Battery (RFB)

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2011/161072 A1 [0003]
• US 2013/0288153 A1 [0004]
• WO 2015/035427 A1 [0005]
• DE 102007034700 A1 [0007]
• WO 2015/007382 A1 [0009]
• WO 2015/074764 A1 [0010]

Cited non-patent literature

• Janoshka et al. [in: Nature 2015, 527, 78-81 [0052]
• Janoschka et al., Nature 2015, 527, 78-81 [0053, 0063]
• Winsberg et al., Adv. Mat. 2016, 28, 2238-2243 [0071]
• J. Noack et al., Angew. Chem. Int. Ed. 2015, 54, 9776-9809 [0087]
• J. Winsberg et al., Angew. Chem. Int. Ed. 2016, DOI: 10.1002 / anie.201604925R1 [0087]

Claims (16)

Redox flow battery for storing electrical energy, comprising at least one redox flow cell as a reaction cell with chambers for the formation of polarity-specific half-cells for catholyte and anolyte, which are separated by at least one membrane and each with an electrolyte reservoir (52, 62) , wherein a first and a second of the polarity-specific half-cells each with an electrolyte (5, 6) of at least one redox-active component, which is at least partially dissolved in substance or in a solvent and present therein dissolved conductive salts, flowed through and the electrolytes (5, 6) each with a pumping means (53, 63) are recirculated and the membrane is provided as an interface for suppressing mixing or electrochemical reactions of the redox-active components with each other and for efficient charge carrier exchange between the half-cells, characterized in that - at least the first polarity-specific half-cell is composed of a plurality of hollow fibers (2), wherein the membrane of the first half cell is formed as an interface of a total area of hollow fiber membranes (21) of the plurality of hollow fibers (2), each internally provided with an electrolyte-permeable electrode (22) one of the electrolytes (5, 6) flows through and is connected to the electrolyte reservoir (52) at hollow fiber ends on both sides, - the chamber surrounding at least the hollow fibers (2) of the first half cell is filled with a liquid-permeable structure (4) and a solvent containing at least one conducting salt and at least partially bounded by a parallel to the hollow fibers (2) aligned support structure (41) and - the second polarity-specific half-cell, which is flowed through by the other of the electrolytes (5, 6) and connected to the electrolyte reservoir (62) of the second half-cell , Either by the comb surrounding the hollow fibers (2) of the first half-cell r is formed with the liquid-permeable structure (4) as an electrode (42), or is formed by a further number of hollow fibers (3), which are structured identically to the hollow fibers (2) of the first half-cell, internally with a porous electrode (32 ) and within which the hollow fibers (2) of the first half-cell surrounding chamber are arranged, wherein in the liquid-permeable structure (4) with a conductive salt added solvent for electrical connection between hollow fiber membranes (21, 31) of the first and second half-cells is present. Arrangement according to Claim 1 , characterized in that the hollow fiber membranes (21, 31) are formed as ion-selective membranes and act as interfaces on the principle of an ion-type exclusion. Arrangement according to Claim 1 , characterized in that the hollow fiber membranes (21, 31) are designed as size exclusion membranes and act as interfaces according to the principle of molecular size exclusion. Arrangement according to one of Claims 1 to 3 , characterized in that the hollow fibers (2) of the first half-cell and the hollow fibers (3) of the second half-cell are alternately provided in parallel planes as a single-layered hollow fiber layers (72, 73) arranged without gaps. Arrangement according to Claim 4 , characterized in that the hollow fibers (2, 3) of the first and the second half-cell in adjacent hollow fiber layers (72, 73) are offset by an angle α with 0 ° <α <90 ° to each other. Arrangement according to Claim 4 , characterized in that the hollow fibers (2, 3) of the first and the second half-cell in adjacent hollow fiber layers (72, 73) are crossed at an angle α = 90 ° to each other. Arrangement according to Claim 4 , characterized in that the hollow fibers (2, 3) of the first half-cell and the second half-cell are arranged parallel to each other and gapless. Arrangement according to one of Claims 1 to 7 Characterized in that the liquid permeable structure (4) in which the hollow fibers (2, 3) of at least the first half cell surrounding chamber through spaces between the hollow fibers (2, 3) of at least the first half cell and to the hollow fibers (parallel 2, 3 ) the chamber is formed narrow limiting support structures (41). Arrangement according to one of Claims 1 to 8th , characterized in that the at least the hollow fibers (2) of the first half-cell surrounding chamber has a circular or elliptical cross-section and a parallel to the hollow fiber membranes (21) of the first half-cell aligned cylinder jacket-shaped support structure (41). Arrangement according to one of Claims 1 to 8th , characterized in that the at least the hollow fibers (2) of the first half-cell surrounding chamber has an n-angular cross-section with n> 2 and support structures (41) as a rectangular wall shape. Arrangement according to one of Claims 1 to 10 , characterized in that the porous electrodes (22, 32) in the interior of the hollow fiber membranes (21, 31) of the at least first half-cell formed by an electrically conductive, liquid-permeable filling material and provided with introduced into the filler electrically conductive pantographs (23, 33) , Arrangement according to one of Claims 1 - 3 and 9 - 11 , characterized in that the porous electrode (42) of the second half-cell is formed as a liquid-permeable structure (4) of electrically conductive material in spaces outside the hollow fiber membranes (21) of the first half-cell, wherein current collector (43) with electrical contact to an electrically conductive Support structure (41) of the hollow fibers (2) of the first half-cell surrounding chamber in the liquid-permeable structure (4) are introduced or the liquid-permeable structure (4) as an electrode (42) at attachment sites or by applying or pressing on the at least partially electrically conductive support structure (41) of the surrounding chamber is contacted. Arrangement according to one of Claims 1 - 3 and 9 - 11 characterized in that the porous electrode (42) of the second half cell as liquid permeable structure (4) is externally coated on each hollow fiber membrane (21) of the first half cell and provided with at least one continuous electrically conductive strip as current collector (43), the current collectors (43) are in electrical contact with an electrically conductive support structure (41) of the hollow fibers (2) surrounding the first half-cell chamber or to another electrically conductive framework. Arrangement according to one of Claims 1 to 11 , characterized in that in the hollow-fiber membranes (21) of the first half-cell and in the hollow-fiber membranes (31) of the second half-cell respectively an electrically conductive, liquid-permeable filling material as a porous electrodes (22, 32) inside the hollow-fiber membranes (21, 31) introduced space filling is and electrically conductive current collector (23, 33) are inserted into the filling material. Arrangement according to one of Claims 1 to 11 characterized in that in the hollow fibers (2, 3) of the first and second half cells, the porous electrodes (22, 32) are respectively applied to the inner sides of the hollow fiber membranes (21, 31) as a porous layer and ends of the hollow fiber membranes (21, 31 ) are placed on electrically conductive tubes or clamping sleeves as current collector (23, 33). Arrangement according to Claim 1 , characterized in that in the hollow fibers (2, 3 of the first and the second half-cell respectively electrically conductive current collector (23, 33) at the same time as electrodes (22, 32) in the interior of the hollow fiber membranes (21, 31) formed and rectilinear or spiral are wound up in a shaped form and are each guided outwards.

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