Redox flow battery and method for manufacturing a redox flow battery

Abstract

Redox flow battery (1) comprising a number of stacked frames (10, 11, 12) made of plastic, planar electrodes (7) and membranes (6), wherein each electrode (7) is supported by a relief-like rake-shaped structure (16, 17) of a frame (10, 11, 12) and passages (18) for electrolyte solution are formed within the rake shape from one side (US) of the frame (10, 11, 12) to its opposite side (OS), and wherein several mutually parallel, strip-shaped seals (27, 30), namely firstly a seal (27) on the membrane (6) and secondly a seal (30) on the electrode (7), extend in the transverse direction of the rake-shaped structure (16, 17), i.e. orthogonally to a plurality of teeth (24, 25) which form the rake-shaped structure (16, 17), wherein the aforementioned relief-like rake-shaped structure (16) is formed by a frame (11) of the first type, with an additional second type of frame (12) existing,wherein the frame (12) of the second type also describes a relief-like rake-shaped structure (17), and the different frames (11, 12) are stacked alternately on top of each other, wherein the frames (11) of the first type form a fluid channel (21, 22, 23) alternating between the frame sides (US, OS) and the frames (12) of the second type form a fluid channel (28) running continuously on the same side (US) of the frame (12), and wherein, in a top view of one side (OS, US) of the frames (10, 11, 12), a circumference of the membranes (6) is arranged within a circumference of the electrodes (7) and a circumference of the electrodes (7) is arranged within a circumference of the frames (10, 11, 12), such that the alternately stacked frames (10, 11, 12) are in direct contact with each other.

Description

[0001] The invention relates to a redox flow battery comprising a number of frames arranged in a stacked form. The invention further relates to a method for manufacturing such a redox flow battery.

[0002] EP 3 545 566 B1 and US 2020 0 075 969 A1, which originates from the same patent family, describe a possible design for the frame of an electrochemical redox flow cell. The frame forms supply and discharge channels for an electrochemical fluid. The shape of the channels described in EP 3 545 566 B1 aims to reduce shunting. Furthermore, the channels are designed to achieve a homogeneous distribution of the electrochemical fluids.

[0003] A redox flow system described in US 2015 / 0125768 A1 comprises various frame and insert elements, which are assigned to half-cells of the electrochemical system, i.e., the redox flow system. The redox flow system according to US 2015 / 0125768 A1 has a stacked structure, with seals, particularly in the form of O-ring seals, located at various points within the stack.

[0004] The use of O-ring seals in stacked arrangements of electrochemical cells is also known from documents WO 01 / 03224 A1 and JP 2000260460 A.

[0005] German patent application DE 10 2019 209 583 A1 proposes the use of sealing elements of different manufacturing types in an electrochemical system, in particular a redox flow system. Among other things, DE 10 2019 209 583 A1 addresses the production of sealing elements using injection molding or dispensing processes.

[0006] The formation of sealing elements on a flow plate of a redox flow stack is also addressed in CN 210489738 U, which concerns a vanadium redox flow battery.

[0007] Possibilities for the mechanical connection of an electrode with a sealing frame of an electrode module for a redox flow battery are described in detail in DE 10 2013 009 629 A1.

[0008] DE 102 16 306 A1 discloses a bipolar plate, generally referred to as a contact plate, for electrochemical cells. The contact plate is made of a graphite-thermoplastic composite material and structured in the form of channels.

[0009] A flow battery system described in CN 102751525 A comprises, among other things, a flow frame, a conductive plate, a porous electrode, and a separator, wherein the porous electrode is inserted into a cavity provided by the flow frame. Inlets and outlets for electrolyte are formed by the flow frame. Connections between the inlets and outlets and the porous electrode are established via various channels.

[0010] US patent 2020 0 075 984 A1 discloses a redox flow cell stack with an intermediate frame for receiving an intermediate plate which is inserted between two electrochemical cells.

[0011] The invention is based on the objective of further developing redox flow batteries compared to the aforementioned prior art, particularly with regard to manufacturing and sealing technology.

[0012] This problem is solved according to the invention by a redox flow battery with the features of claim 1. Likewise, the problem is solved by a method for producing a redox flow battery according to claim 5. The embodiments and advantages of the invention explained below in connection with the manufacturing method also apply mutatis mutandis to the device, i.e., the redox flow battery, and vice versa.

[0013] The redox flow battery comprises a number of stacked plastic frames, flat electrodes, and membranes. Each electrode is supported by a relief-like, rake-shaped structure within the frame. This rake-shaped structure provides passages for electrolyte solution to flow from one side of the frame to the opposite side. Several parallel, strip-shaped seals—one at the membrane and one at the electrode—run transversely to the rake-shaped structure, i.e., orthogonally to the numerous teeth that form the relief-like, rake-shaped structure.

[0014] A relief-like structure is understood to be a three-dimensional structure that stands out from a completely or at least substantially closed surface. The term "relief" is used here in the same way as in connection with works of art or terrain features. In this case, the openings through which the electrolyte solution can flow represent deviations from the otherwise closed shape of the surface on which the relief is located. The reverse side of the so-called relief, which describes a tooth structure, can be either completely flat or also three-dimensionally structured.

[0015] The electrodes, which are supported by the frame, can be made of sheet metal, carbon-based materials, or mixtures of carbon-based materials and plastics, for example. In typical designs, the membranes are films with a thickness of less than 1 mm.

[0016] According to the invention, the frames are made of plastic, in particular in the form of injection-molded parts, wherein frames of the first type and differing frames of the second type exist, and the different frame types are arranged alternately in a stacked form. Each frame type has a rake-like structure. The various relief-like rake-like structures can extend to an interior space enclosed by the frames, i.e., the active field of the redox flow cell, and are located on the surface of the frames facing away from the membrane.

[0017] The seal intended for sealing the membrane can intersect the rake-like structure of the second type of frame – viewed from above. Simultaneously, the seal intended for sealing the electrode can be positioned outside the rake-like structure of the first type of frame – viewed from inside the frame.

[0018] Strip-shaped gaskets with a flat profile are particularly suitable as seals. Instead of gaskets with rectangular or round cross-sectional contours, gaskets with more complex shapes can also be used. It is also possible to injection-mold gaskets onto components of the redox flow cell stack, especially frames. Dispensing of gaskets is also possible. The gaskets for the membranes and the gaskets for the electrodes are collectively referred to as internal gaskets. Additional external gaskets seal the electrolyte space from the stack's environment.

[0019] In every design, the fact that the electrode has a significantly higher stiffness compared to the membrane is exploited. This makes it possible to support the electrode only section by section at the sealing point in the stack structure. Simultaneously, flow-through surfaces can be provided. According to the invention, the frames of the first type form a fluid channel that alternates between the frame sides, while the frames of the second type form a fluid channel that runs continuously on the same side of the frame. The supporting areas of the different frame types, designed as relief-like teeth, are advantageously positioned directly above one another to minimize deformations within the stack.

[0020] The teeth formed by the frame section (at least one of the teeth) are not necessarily aligned exactly orthogonally to the frame's edge. Rather, angled teeth are just as conceivable as teeth with varying widths along their length, so that, for example, the spaces between the teeth widen in the direction of fluid flow, i.e., along the tooth's length. Curved teeth or teeth with serpentine shapes are also possible. Furthermore, teeth can be interrupted along their length, meaning they can exist as individual, separate protrusions. The transition between a tooth and the outer area of ​​the frame, further away from the active field, can be completely flat, resulting in a seamless, flush connection of each tooth to the outer frame. Alternatively, the individual teeth can be raised like islands from the adjacent section of the frame.The latter option is particularly suitable when the frame is manufactured using injection molding.

[0021] Analogous to the shape of the teeth, numerous design variations are also possible for the shape of the strip-shaped seals. For example, when viewed from above the frames, one or all of the seals can have a curved or serpentine shape. In all cases, the main direction of extension of the seals, again viewed from above the stacked components of the redox flow battery, is not parallel to the main direction of extension of the teeth.

[0022] The redox flow battery can generally be manufactured in the following steps: - Production of a plurality of frames of the first type, each of which has a relief-like rake-shaped structure on at least one side of its inner edge, wherein at least one passage is formed within the rake-shaped structure from one side of the frame to its opposite side, - Production of a plurality of frames of the second type, which are at least approximately identical to the frames of the first type and also each have a relief-like rake-shaped structure on at least one side of their inner edge, wherein the frames of the second type are free of openings in the area of ​​their rake-shaped structure, - Provision of a number of membranes and planar electrodes, - Attaching a first, inner, strip-shaped seal to the frame of the second type, wherein the seal is located on the surface of the frame which is opposite the relief-like, rake-shaped structured surface, and wherein the seal runs in the transverse direction of the rake-shaped structure, - Attaching a second, outer strip-shaped seal to the frame of the first type, wherein the seal is located on the same side of the frame on which the relief-like, rake-shaped structured surface of the first frame is located, and wherein the seal - viewed from the inside of the frame - is arranged further outwards than the opening and runs in the transverse direction of the rake-shaped structure, i.e. parallel to the seal on the frame of the second type - assuming an identical arrangement of the two frames, - Assembly of frame, electrode and membrane such that the membrane is arranged in a sealed manner between the different frames by means of the seal attached to the second type of frame and the electrode is partially supported by the relief-like rake-shaped structure of the first type of frame and sealed by the second strip-shaped seal, wherein in a top view of one side of the frames a circumference of the membranes is arranged within a circumference of the electrodes and a circumference of the electrodes is arranged within a circumference of the frames, such that the alternately stacked frames are arranged in direct contact with each other.

[0023] The application of the various strip-shaped seals mentioned in the fourth and fifth steps can, if these seals are not sprayed on, also take place in the last step, i.e. during the assembly of the frame, electrode and membrane.

[0024] In any case, the offset between the membrane seals and the electrode seals at the transition to the active field of the redox flow cell allows for a particularly low half-cell height while simultaneously ensuring low-resistance electrolyte flow. Typical designs also include port seals at the electrolyte solution inlets and outlets. Seals can be combined into molded gaskets at defined sealing levels, which, for example, can act as combined seals, sealing both the ports and the outer seal. Similarly, the electrode sealing can be combined with the port sealing and / or the outer seal using a single molded gasket.

[0025] The advantage of the invention lies particularly in the fact that the assembly-friendly design of a redox flow stack eliminates the need for gluing or welding processes. The sectional support of the electrode, provided by the relief-like, rake-shaped structure, facilitates fluid flow at the transition to the active field of the redox flow cell while simultaneously fulfilling all mechanical and sealing requirements. The latter requirements are reliably met by the offset membrane and electrode sealing lines.

[0026] In a top view of one side of the frames, a circumference of the membranes is arranged within a circumference of the electrodes and a circumference of the electrodes is arranged within a circumference of the frames, such that the alternately stacked frames are in direct contact with each other.

[0027] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 Components of a redox flow battery in perspective view, Fig. 2 one after removal of the top component from Fig. 1. Present stacked arrangement of redox flow components, Fig. 3 the stacked arrangement according Fig. 1 in perspective view from below, Fig. 4 a section of the cell stack formed by the redox flow battery in a cutaway perspective view, Fig. 5 a detail of the cell stack in a section view, Fig. 6. Partially shows a first frame section of the cell stack, Fig. 7. A second frame part of the cell stack is shown in part.

[0028] Unless otherwise stated, the following explanations apply to all embodiments. Corresponding or essentially equivalent parts are marked with the same reference numeral in all figures.

[0029] A redox flow battery, designated as 1, comprises a cell stack 2, also referred to as a stack, as its core component. Means for conveying electrolyte solutions are not shown in the figures. Different electrolyte currents through the cell stack 2 are designated EA and EB. For the basic function of the redox flow battery 1, reference is made to the prior art cited at the beginning.

[0030] The cell stack 2 comprises a multitude of electrochemical cells 3, i.e., redox flow cells, each redox flow cell 3 being composed of two half-cells 4, 5 separated by a membrane 6. Each electrode is designated 7, and a partially visible fleece is designated 8. The total height of each cell 3, designated HZ, is divided almost equally between the thickness of the first half-cell 4 and the thickness of the second half-cell 5. In the figures, the designations US for the bottom of the stack 2 and OS for its top are used. The designations US and OS do not indicate the actual installation position of the cell stack 2.

[0031] The cell stack 2 comprises a multitude of plastic frames 10, which, among other things, form ports 9 for the supply and discharge of electrolyte solutions. Each frame 10 is composed of a first frame part 11 and a second frame part 12. The electrolyte solutions flow through a distribution structure 13, which includes meanders 14 that minimize shunt currents. The active fields of the electrochemical cells 3 are designated 15.

[0032] The distribution structures 13 comprise a relief-like, rake-shaped structure 16 of the frame part 11 and a similarly relief-like, rake-shaped structure 17 of the second frame part 12. Insofar as the distribution structure 13 is formed by the second frame part 12, the electrolyte flow EB flows exclusively on the side of the frame part 12 arbitrarily designated US. In the first frame part 11, however, the electrolyte flow EA changes from the underside US of the frame part 11 to its upper side OS. For this purpose, passages 18 are provided in the first frame part 11. After the electrolyte flow EA has been directed from the underside US through the passage 18 to the upper side OS, the electrolyte solution flows between teeth 24, which form the rake-shaped structure 16. The length of the teeth 24, measured in the direction of flow of the electrolyte flow EA, is designated L24. The length L24 is a multiple of the height of teeth 24, designated H24.

[0033] By transferring the electrolyte current EA from the underside US to the upper side OS, the electrolyte current EA is introduced into the active field 15 in a volume region separated from the membrane 6. The teeth 24, between which the electrolyte current EA flows, simultaneously support the electrode 7. In an outer region, further away from the active field 15, the electrolyte current EA flows through a channel generally designated 20, which is bounded above by the first frame part 11 and below by the second frame part 12, whereby the directional designations "bottom" and "top" in this case also refer only to the orientations of the frames 10 chosen in the figures.

[0034] The section of channel 20 located upstream of orifice 18, which carries the electrolyte flow EA, is referred to as the outer channel section 21 and includes a constriction 23 immediately upstream of orifice 18. The section of channel 20 located downstream of orifice 18, in the direction of flow, is referred to as the inner channel section 22 and is formed by the spaces between teeth 24. Below teeth 24 is a flat, closed surface section 19, which rests on the membrane 6 and extends to the active field 15.

[0035] The rake-shaped structure 17 of the second frame part 12 comprises a plurality of teeth 25, whose length is specified as L25 and whose height as H25. Above the teeth 25, a groove 26 is located in the second frame part 12, which runs orthogonally to the teeth 25, i.e., transversely to the flow direction of the electrolyte current EB. A first seal 27 is inserted into the groove 26, which seals the membrane 6. A channel section 28 running within the second frame part 12, through which the electrolyte current EB flows, is located continuously on the underside US of the second frame part 12 and, like the inner channel section 22, opens into the active field 15 at a point raised from the membrane 6.

[0036] In the first frame section 11, on the side opposite the constriction 23, there is a groove 29 into which a second seal 30 is inserted, sealing the electrode 7. The second seal 30 is thus located further outwards than the first seal 27, viewed from the active field 15. Furthermore, there are seals 31 with which the ports 9 are sealed. An outer seal 32 is placed around all ports 9 and the active field 15; this seal 32 may be combined with the seals 31. The measuring terminals of the stack 2 present in the present case are designated 33 and are intended for measuring the individual voltage of the cells 3. Reference symbol list 1 Redox flow battery 2 cell stacks, Stack 3 electrochemical cell 4 half-cell 5 half-cell 6 Membran 7 electrode 8 fleece 9 Port 10 frames 11 first frame part 12 second frame part 13 Distribution structure 14 meanders 15 Active field 16 rake-shaped structure of the first frame part 17 rake-shaped structure of the second frame part 18 Passage in the first frame section 19 flat closed surface section below structure 16 20 channels 21 outer channel section in the first frame part 22 inner channel section in the first frame part 23 Constriction in the outer canal section 24 teeth of the rake-shaped structure of the first frame part 25 teeth of the rake-shaped structure of the second frame part 26 groove in the second frame part 27 first seal, sealing the membrane 28 Canal section in the second frame part 29 groove in the first frame part 30 second seal, sealing the electrode 31 Seal at the port 32 outer seal 33 Measuring connection EA Electrolyte current A EB Electrolyte current B H24 Height of tooth 24 H25 Height of tooth 25 HZ cell height L24 Length of tooth 24 L25 Length of tooth 25 US subpage OS top

Claims

Redox flow battery (1) comprising a number of stacked frames (10, 11, 12) made of plastic, planar electrodes (7) and membranes (6), wherein each electrode (7) is supported by a relief-like rake-shaped structure (16, 17) of a frame (10, 11, 12) and passages (18) for electrolyte solution are formed within the rake shape from one side (US) of the frame (10, 11, 12) to its opposite side (OS), and wherein several mutually parallel, strip-shaped seals (27, 30), namely firstly a seal (27) on the membrane (6) and secondly a seal (30) on the electrode (7), extend in the transverse direction of the rake-shaped structure (16, 17), i.e. orthogonally to a plurality of teeth (24, 25) which form the rake-shaped structure (16, 17), wherein the aforementioned relief-like rake-shaped structure (16) is formed by a frame (11) of the first type, with an additional second type of frame (12) existing,wherein the frame (12) of the second type also describes a relief-like rake-shaped structure (17), and the different frames (11, 12) are stacked alternately on top of each other, wherein the frames (11) of the first type form a fluid channel (21, 22, 23) alternating between the frame sides (US, OS) and the frames (12) of the second type form a fluid channel (28) running continuously on the same side (US) of the frame (12), and wherein, in a top view of one side (OS, US) of the frames (10, 11, 12), a circumference of the membranes (6) is arranged within a circumference of the electrodes (7) and a circumference of the electrodes (7) is arranged within a circumference of the frames (10, 11, 12), such that the alternately stacked frames (10, 11, 12) are in direct contact with each other. Redox flow battery (1) according to claim 1 , characterized in that the various relief-like rake-shaped structures (16, 17) extend to an interior space (15) circumscribed by the frames (11, 12) and are each located on the surface (OS, US) of the frames (11, 12) facing away from the membrane (6). Redox flow battery (1) according to claim 2 , characterized in that the seal (27) provided for sealing the membrane (6) crosses the rake-shaped structure (17) of the frame (12) of the second type - in top view of the frame (12). Redox flow battery (1) according to claim 2 or 3, characterized in that the seal (30) provided for sealing the electrode (7) - viewed from the inside of the frame (11) - is arranged outside the rake-shaped structure (16) of the frame (11) of the first type. A method for manufacturing a redox flow battery (1) according to any one of claims 1 to 4, comprising the following steps: - manufacturing a plurality of frames (11) of the first type, each of which has a relief-like rake-shaped structure (16) on at least one side of its inner edge, wherein at least one opening (18) is formed within the rake-shaped structure (16) from one side (US) of the frame (11) to its opposite side (OS), - manufacturing a plurality of frames (12) of the second type, which are at least approximately congruent with the frames (11) of the first type and also each have a relief-like rake-shaped structure (17) on at least one side of their inner edge, wherein the frames (12) of the second type are free of openings in the region of their rake-shaped structure (17), - providing a number of membranes (6) and planar electrodes (7), - attaching a first, inner, strip-shaped seal (27) to the frame (12) of the second type.wherein the seal (27) is located on the surface (OS) of the frame (12) opposite the relief-like, rake-shaped structured surface (US), and wherein the seal (27) extends transversely to the rake-shaped structure (17),- attaching a second, outer, strip-shaped seal (30) to the frame (11) of the first type, wherein the seal (30) is located on the same side (OS) of the frame (11) on which the relief-like, rake-shaped structured surface of the first frame (11) is also located, and wherein the seal (30) – viewed from the inside (15) of the frame (11) – is arranged further outwards than the opening (18) and extends transversely to the rake-shaped structure (16), i.e., parallel to the seal (27) on the frame (27) of the second type – assuming an identical arrangement of the two frames (11, 12),- assembly of frame (11, 12), electrode (7) and membrane (6) such,that the membrane (6) is arranged in a sealed manner between the different frames (11, 12) by means of the seal (27) attached to the frame (12) of the second type, and the electrode (7) is partially supported by the relief-like rake-shaped structure (16) of the frame (11) of the first type and sealed by the second strip-shaped seal (30), wherein, in a top view of one side (OS, US) of the frames (10, 11, 12), a circumference of the membranes (6) is arranged within a circumference of the electrodes (7) and a circumference of the electrodes (7) is arranged within a circumference of the frames (10, 11, 12), such that the alternately stacked frames (10, 11, 12) are arranged in direct contact with each other. Method according to claim 5, characterized in that the frames (11, 12) are manufactured using the plastic injection molding process. Method according to claim 5 or 6, characterized in that at least one of the strip-shaped seals (27, 30) is manufactured by injection molding.

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