Electrolyte tank of a redox flow battery having a pipe assembly

Abstract

In order to detect leakages of an electrolyte in a redox flow battery at an early stage and also without a corresponding leakage sensor system and in order to interrupt a siphon effect which is produced, it is proposed that a pipe assembly (50) is arranged in the electrolyte tank (13a, 13b), which pipe assembly comprises at least two pipes (51, 52, 61, 62) of different lengths, wherein each of the at least two pipes (51, 52, 61, 62) has a first axial end (51-1, 52-1, 61-1, 62-1) and a second axial end (51-2, 52-2, 61-2, 62-2), which are connected to one another in each case by a flow volume (53, 54, 63, 64), wherein the first axial ends (51-1, 52-1, 61-1, 62-1) are open and end in the electrolyte tank (13a, 13b) at different depths (T1, T2, T3, T4), wherein the second ends (51-2, 52-2, 61-2, 62-2), opposite the first axial ends (51-1, 52-1, 61-1, 62-1), of the at least two pipes (51, 52, 61, 62) open into a mixing volume (56) in a connection pipe (55), wherein the flow volumes (53, 54, 63, 64) of the at least two pipes (51, 52, 61, 62) are connected to one another via the mixing volume (56) and wherein the mixing volume (56) is located above the fill level (LVa, LVb) of the electrolyte (15a, 15b) when the electrolyte tank (13a, 13b) is used.

Description

[0001] Electrolyte tank of a redox flow battery with a pipe arrangement

[0002] The present invention relates to an electrolyte tank for an electrolyte of a redox flow battery, wherein a pipe arrangement for supplying electrolytes to the electrolyte tank or for removing electrolytes from the electrolyte tank is arranged on the electrolyte tank, and wherein, when using the electrolyte tank, the electrolyte tank contains an electrolyte of the redox flow battery at a certain fill level.

[0003] The present invention relates to redox flow batteries. A redox flow battery is an electrochemical energy storage device for energy storage on an electrochemical basis and typically consists of electrolyte tanks for storing positive and negative electrolytes, as well as pumps and lines for circulating the electrolytes through one or more cell stacks, each comprising a number of individual cells. The individual cells of the cell stack are each formed by a positive half-cell and a negative half-cell arranged side by side, with the positive and negative half-cells of an individual cell being separated from each other by a semipermeable membrane, typically an ion exchange membrane. The semipermeable membrane is, for example, a cation and / or anion exchange membrane, e.g., based on a sulfonated fluoropolymer such as polytetrafluoroethylene (PTFE).The positive half-cell contains a positive electrode within a frame, through which the positive electrolyte flows. The negative half-cell contains a negative electrode within a frame, through which the negative electrolyte flows. The positive and negative electrolytes are circulated separately through the half-cells. The positive and negative electrodes are usually made of porous graphite felts through which the electrolyte flows. Electrode plates, such as bipolar plates, are arranged between adjacent cells of the cell stack to act as current collectors; these are usually made of a composite material of carbon and plastic.On the axial outer surfaces of the individual cells of the cell stack, located on the outermost surfaces, are current collectors on the electrode plates. These collectors provide an external electrical contact, allowing an electrical voltage to be drawn across the entire cell stack (discharging the redox flow battery) or applied to the cell stack (charging the redox flow battery). The cell stack is terminated on each axial outer surface by an end plate, which holds the cell stack together.

[0004] The electrolyte of a redox flow battery is a liquid and essentially comprises an electrochemical redox couple consisting of a first redox element and a second redox element, each in the form of a redox-active element or ion, or combinations of redox-active elements and / or ions with different electrical charges (oxidation states). A multitude of redox-active elements or ions, or combinations thereof, can be used as redox couples in a redox flow battery. The redox elements of a redox couple are typically dissolved in the electrolyte liquid. The electrolyte liquid is usually an aqueous acid, such as aqueous sulfuric acid. Redox flow batteries with a wide variety of redox couple combinations are known. Some non-exhaustive examples of known combinations of redox couples are: 2+ / V 3+ vs. VO2+ / VC>2 + (in a vanadium redox flow battery), V 2+ / V 3+ vs. Br7CIBr2, Br2 / Br vs. S / S 2 ', Br / Br2 vs. Zn 2+ / Zn, Ce 4+ / Ce 3+ vs. V 2+ / V 3+ , Fe 3+ / Fe 2+ vs. Br2 / Br, Fe 3+ / Fe 2+ vs. Cr^ / Cr 2 *, Mn 2+ / Mn 3+ vs. Br2 / Br, Fe 3+ / Fe 2+ vs. Ti 2+ / TiO 2+ and others. The redox elements can be contained in the electrolyte in various chemical compounds, for example in the form of sulfates, such as vanadium sulfate, or chlorides, such as vanadium chloride. The vanadium-based redox flow battery is the most widely used, which is why the invention will be described below, but without limiting the generality, using a vanadium redox flow battery as an example.

[0005] In a vanadium-based redox flow battery, the positive electrolyte in the charged state consists of a redox couple in the form of vanadium with an oxidation number of +4 (also known as V). lv or V 4+ (designated) and vanadium with an oxidation number of +5 (also known as V) v or V 5+ The negative electrolyte, in its charged state, consists of a redox couple in the form of vanadium with an oxidation number of +2 (also known as V" or V). 2+ (designated) and vanadium with an oxidation number of +3 (also known as V) IH or V 3+ (designated) - meaning that the negative electrolyte has a more negative electrochemical potential than the positive electrolyte.

[0006] When a redox flow battery is operating, electrical energy is either delivered to a load or absorbed from an energy source. In the example of a vanadium-based redox flow battery, the well-known chemical reaction (redox reaction) 2H₂ takes place. ++ VÜ2 + + V 2+ <-> VO 2+ + V 3+ + H2O during charging / discharging in a single cell of the redox flow battery. During the charging process, the reaction is triggered by an external current or voltage source, which applies an electrical voltage to a single cell (or the entire cell stack).

[0007] The design and function of a redox flow battery are well known, for example from WO 2018 / 087270 A1 or WO 2014 / 1331702 A1. For the operation of the redox flow battery, the electrolytes must be circulated through the cell stack, specifically through the individual cells of the cell stack, in an electrolyte circuit. The following problems arise in connection with the electrolyte circuit in redox flow batteries.

[0008] Due to insufficient or no electrolyte mixing in the electrolyte tank, electrolyte stratification can occur (electrolyte layers with different charge states within the tank). For example, electrolyte returned to the surface of the tank often forms a layer above the electrolyte already present. Because of insufficient electrolyte mixing, a certain proportion of the electrolyte is not circulated through the cell stacks and subsequently charged or discharged, due to the predetermined electrolyte extraction point. This dead volume of electrolyte reduces the usable battery capacity. Furthermore, this lack of electrolyte mixing can also lead to errors in monitoring the electrolyte's charge and discharge state, which can disrupt the operation of the redox flow battery.

[0009] Furthermore, unwanted leaks can occur in the electrolyte circuit, resulting in electrolyte escaping and being lost. This can lead to various problems. Firstly, the electrolyte's chemistry is often problematic (e.g., corrosive, toxic, etc.) and must not be released into the environment. Therefore, containment trays must be provided to collect any escaping electrolyte. These trays require space, especially if they need to be designed to hold the entire electrolyte volume. Separate containment trays for the cell stacks and electrolyte tanks may also be required.

[0010] If the cell stacks in the redox flow battery are positioned above the fluid level in the electrolyte tank, the leakage volume encompasses the volume of the fluid connections and the cell stacks up to the level of the leakage point on the damaged cell stack. This necessitates the appropriate design of the stack containment trays.

[0011] If, however, the cell stacks are partially positioned below the fluid level in the electrolyte tank, it must be taken into account that a siphon effect will occur if electrolyte leaks from a cell stack below the fluid level in the electrolyte tank. In the case of this existing fluid connection, despite the electrolyte pump being switched off, the electrolyte tank would be emptied to the level of the leak due to the siphon effect, which can lead to very large leakage volumes. With small (continuous) leaks along the electrolyte fluid path, air can be continuously drawn in if the leak point is located above the electrolyte level in the electrolyte tanks. The main problem here is the reaction of the oxygen in the air with the respective electrolyte, causing it to oxidize and lose capacity. This can also result in membrane or...

[0012] Electrode surfaces can be blocked by gas bubbles accumulating in individual cells, reducing stack efficiency, increasing cell resistance, and / or lowering cell voltage. With consistent charging cycles, this fault can lead to overloading or material fatigue of stack components such as the electrode plate, electrode material, and membrane. Overloading the electrode plates between half-cells can cause additional internal leakage, resulting in increased self-discharge and efficiency loss. Overloading the membrane can also lead to increased self-discharge and efficiency loss due to increased crossover (unwanted flow from one half-cell to the other within a single cell). Such leaks can potentially cause different electrolyte levels between the positive and negative tanks, further reducing battery capacity.

[0013] However, if an electrode plate directly adjacent to the metallic current collector is overloaded, electrolyte escapes from the stack. Due to its predetermined location, this type of leakage can be detected by sensors, thus interrupting the electrolyte circulation.

[0014] It is already known to incorporate leakage sensors into redox flow batteries to detect leaks. Leakage detection is typically achieved using leakage wires, which deflect upon contact with the conductive electrolyte and trigger the redox flow battery's safety circuit, thus interrupting, for example, the electrolyte circulation. However, the practical application of leakage sensors is spatially limited to paths along pre-defined weak points in the fluid circuit. If leaks occur in areas of the fluid path further away from the leakage sensors, the leak will be detected later or not at all, especially with small leakage volumes, because the escaping electrolyte may not even reach the sensors. Therefore, such leakage sensors are only of limited use or only applicable to specific types of faults.

[0015] This creates a need to detect electrolyte leaks in a redox flow battery early and even without dedicated leakage sensors. In the case of the siphon effect, there is an additional need to reliably and quickly interrupt the resulting siphon effect after the pump stops, so that in the event of damage, only a small and defined volume of electrolyte is lost, thus requiring only a small collection tray. Furthermore, it would be particularly advantageous to require only a limited, preferably constant, volume for the collection tray, independent of the electrolyte tank volume, which does not need to be rescaled for each application. There is also a need to achieve good electrolyte mixing within the electrolyte tanks.

[0016] This is achieved by the pipe arrangement comprising at least two pipes of different lengths, each of the at least two pipes having a first axial end and a second axial end, each connected to the other by a flow volume of the respective pipe, the first axial ends of the at least two pipes being open and ending at different depths in the electrolyte tank due to their different lengths, the depths being below the electrolyte level when using the electrolyte tank, the second ends of the at least two pipes opposite the first axial ends of the at least two pipes opening into a mixing volume, the mixing volume being provided in a connecting pipe, the flow volumes of the at least two pipes being connected to the other via the mixing volume, and the mixing volume being above the electrolyte level when using the electrolyte tank.The different axial lengths of the tubes improve electrolyte mixing in the electrolyte tank because electrolyte is always drawn from or supplied to different depths. On the other hand, the shorter (shortest) tube also interrupts the siphon effect, as gas is drawn from the gas space of the electrolyte tank when the first axial end of the shorter (shortest) tube is exposed, thus interrupting the siphon effect. This also limits and predetermines the amount of electrolyte that can be lost through the siphon effect. Finally, the tube arrangement also enables leak detection because gas in the electrolyte alters the operating parameters of the redox flow battery, which can be evaluated for leak detection without the need for additional leak sensors.

[0017] If the shorter of the at least two tubes has an additional slot-shaped recess in the region of its first axial end, extending at least partially in the axial direction of the shorter tube, and if this slot-shaped recess is located below the electrolyte level when the electrolyte tank is used, early leak detection can be provided. The slot-shaped recess allows a small amount of gas to enter the electrolyte at an early stage, which can be detected by changes in the operating data of the redox flow battery. This allows for early intervention in the event of a potential leak, before more significant damage or leakage occurs.

[0018] The present invention is explained in more detail below with reference to Figures 1 to 11, which show exemplary, schematic, and non-limiting advantageous embodiments of the invention.

[0019] Fig. 1 shows the basic operating principle of a redox flow battery,

[0020] Fig. 2 shows a redox flow battery with a cell stack,

[0021] Fig. 3 shows a structure of a cell stack of a redox flow battery,

[0022] Fig. 4 shows an embodiment of a redox flow battery with multiple cell stacks,

[0023] Fig. 5 shows an embodiment of a pipe arrangement according to the invention for supplying or removing electrolytes,

[0024] Fig. 6 shows a detailed view of the pipe arrangement.

[0025] Fig. 7 shows a further embodiment of a pipe arrangement according to the invention for supplying or removing electrolytes, Fig. 8 shows a detailed view of the pipe arrangement,

[0026] Fig. 9 shows a further embodiment of a pipe arrangement according to the invention for supplying or removing electrolytes, Fig. 10 shows a pipe arrangement with a slot-shaped recess and Fig. 11 shows examples of different slot-shaped recesses.

[0027] For a better understanding of the invention, the structure and function of a redox flow battery 1 will be briefly explained below with reference to Figs. 1 to 4.

[0028] Fig. 1 shows a schematic diagram of a redox flow battery 1 using a single cell 2 of a cell stack 10 to illustrate the well-known operating principle of a redox flow battery 1. For clarity and illustration, Fig. 1 shows only a single cell 2 of a cell stack 10 of a redox flow battery 1, where a cell stack 10 will typically comprise a plurality of single cells 2 arranged side by side in the cell stack 10.

[0029] A single cell 2 consists of two half-cells 2a, 2b, which form a positive reaction chamber 3a and a negative reaction chamber 3b, wherein the two half-cells 2a, 2b, or the positive reaction chamber 3a and the negative reaction chamber 3b, are separated by a semipermeable, in particular ion-selective, membrane 4. The reaction chambers 3a, 3b are formed, for example, in recesses 6a, 6b of frames 5a, 5b. A cell electrode 7a, 7b is arranged in each of the frames 6a, 6b, or in the reaction chambers 3a, 3b, or in the recesses 6a, 6b, and is in contact with the respective electrolyte 15a, 15b located in the half-cell 2a, 2b. The recesses 6a, 6b and, if applicable, the cell electrodes 7a, 7b of a single cell 2 arranged therein are permeated by electrolytes 15a, 15b with different electrical charges or different redox potentials (positive and negative electrolyte).Each of the electrolytes 15a, 15b contains a redox couple with specific, time-varying concentrations (depending on the state of charge) of redox elements. The semipermeable, in particular ion-selective, membrane 4 can, for example, be made of sultate-modified polytetrafluoroethylene (PTFE), trade name Nation™, and allows ions to equalize the charge between the positive reaction chamber 3a and the negative reaction chamber 3b (or between the electrolytes 15a, 15b contained therein). Current connections 11, 12 are also provided on a cell stack 10 of a redox flow battery 1 to tap off an electrical cell stack voltage Vz applied to the cell stack 10 via a load 14 (discharging the redox flow battery 1) or to apply an electrical cell stack voltage Vz to the cell stack 10 (charging the redox flow battery 1).

[0030] An electrical load 14 can have any shape. Based on the electrical voltage, current, or power requirements of the electrical load 14, a cell stack 10 can be configured in a redox flow battery 1 to provide the necessary electrical voltage and / or current. Redox flow batteries 1 are often used as stationary energy storage systems, for example, as emergency power systems for industrial plants, storage systems for renewable energy (photovoltaics, wind power), and similar applications. Consequently, depending on the application, a person skilled in the art can design or select a cell stack 10, or a parallel and / or series connection of several cell stacks 10, or cell strings consisting of several cell stacks 10, and redox pairs in a redox flow battery 1.

[0031] The electrolytes 15a, 15b are stored in electrolyte tanks 13a, 13b and are circulated from there through the cell stack 10, specifically through each half-cell 2a, 2b of a single cell 2 of the cell stack 10, by means of electrolyte pumps 9a, 9b. For this purpose, a supply line 16a, 16b and a discharge line 17a, 17b are provided for each electrolyte 15a, 15b, which are connected via electrolyte connections 22a, 22b, 23a, 23b to associated electrolyte channels 18a, 18b, 19a, 19b (see Fig. 3) in the cell stack 10.

[0032] In a cell stack 10 with several adjacent individual cells 2, an electrode plate 8, like a bipolar plate, is arranged between each pair of adjacent individual cells 2 (Fig. 3). At the outer ends of the cell stack 10, a current connection 11, 12 can be made on the outer electrode plates 8 or on the outer half-cells 2a, 2b (or cell electrodes 7a, 7b) of the cell stack 10, which can be electrically contacted from the outside.

[0033] The typical structure of a cell stack 10 of a redox flow battery 1 is explained in more detail with reference to Figs. 2 and Fig. 3.

[0034] A cell stack 10 of a redox flow battery 1 comprises at least one single cell 2, typically a plurality of single cells 2, each of which is in turn formed from two frames 5a, 5b of half-cells 2a, 2b. A frame 5a, 5b is preferably made of a plastic, such as an elastomer, e.g., a polyolefinic thermoplastic elastomer (TPE or TPO), such as Santoprene®, or a thermoplastic vulcanize (TPV), particularly by injection molding. In the stack direction R (in the direction in which the single cells 2a, 2b are arranged side by side) between two frames 5a, 5b of a single cell 2, a semipermeable membrane 4, typically an ion exchange membrane (either a cation or anion exchange membrane, e.g., Nation®), is arranged in the cell stack 10.The membrane 4 separates the reaction chambers 3a, 3b, recesses 6a, 6b of the half-cells 2a, 2b of a single cell 2, the cell electrodes 7a, 7b arranged therein, and the electrolytes 15a, 15b contained therein. Between two single cells 2 adjacent in the stack direction R, an electrode plate 8, e.g., a bipolar plate, is arranged in the cell stack 10. The electrode plate 8 is inserted, as shown in Fig. 3, into mutually facing recesses 32 in the frames 5a, 5b. The frames 5a, 5b have central recesses 6a, 6b extending through the stack direction R, each forming a reaction chamber 3a, 3b, in which cell electrodes 7a, 7b, e.g., carbon fiber mats, are arranged, as shown in Fig. 3.

[0035] Through the recesses 6a, 6b in the frames 5a, 5b, the electrically differently charged electrolytes 15a, 15b are pumped through the respective half-cells 2a, 2b, whereby the cell electrode 7a, 7b of each half-cell 2a, 2b of a single cell 2 is permeated by an electrolyte 15a, 15b with a different electrical charge. The electrolytes 15a, 15b are supplied and discharged externally via electrolyte connections 22a, 22b, 23a, 23b and are then distributed internally via an electrolyte channel system with electrolyte channels 18a, 18b, 19a, 19b provided in the frames 5a, 5b. The electrolyte connections 22a, 22b, 23a, 23b are provided, for example, on an end plate 24 of the cell stack 10, as shown in Fig. 3, whereby other arrangements of the electrolyte connections 22a, 22b, 23a, 23b, for example on an end frame 20, are also possible.

[0036] The cell stack 10 can be terminated at both axial ends in the stack direction R by an end frame 20. An electrically conductive current collector 21 is arranged in the end frame 20, for example, in a recess on one end face of the end frame 20, and is connected to an externally extending electrical current connection 11, 12. In the illustrated embodiment, the current collector 21 rests against the last electrode plate 8 of the last individual cell 2 to establish an electrical contact. However, the current collector 21 or a current connection 11, 12 could also be designed differently. Likewise, the end frame 20 could be omitted from the cell stack 10.

[0037] In the illustrated embodiment, the cell stack 10 is arranged between two rigid end plates 24 and pressed together by clamping means 25. The clamping means 25 are, for example, designed with through bolts 26, nuts 27, washers 28, and springs 29, as shown in Fig. 2. However, the cell stack 10 can also be held together in other ways; in particular, the clamping means 25 can be designed differently. The two end plates 24 can also be arranged between two pressure plates 30, which are pressed together by the clamping means 25, as shown in Fig. 2. To prevent the frames 5a, 5b from settling due to the clamping force of the clamping means 25, a spacer 31 can also be provided between the end plates 24.

[0038] The present invention is not limited to a specific embodiment of a half-cell 2a, 2b, a single cell 2, a cell stack 10, or the redox flow battery 1. Likewise, the invention is not limited to a specific electrolyte 15a, 15b, or to specific redox elements in the electrolytes 15a, 15b. The above descriptions of a redox flow battery 1 serve only to illustrate the invention.

[0039] From the above description and the basic operating principle, it is also obvious that there is a positive electrolyte 15a and a negative electrolyte 15b, as well as, related to this, a positive half-cell 2a and a negative half-cell 2b of a single cell 2, and a positive electrolyte circuit with a positive electrolyte pump 9a and a negative electrolyte circuit with a negative electrolyte pump 9b.

[0040] A redox flow battery 1 can also comprise several cell stacks 10, as explained with reference to Fig. 4. In the embodiment shown in Fig. 4, two cell strings 40 are provided, each cell string 40 comprising a plurality of cell stacks 10, for example, as described above. However, a redox flow battery 1 can, of course, also have only one cell string 40. The cell stacks 10 in a cell string 40 can be electrically connected in series via the current terminals 11, 12 of the cell stacks 10 (not shown in Fig. 4 for clarity). However, other electrical connections of the cell stacks 10 in a cell string 40 are also possible, such as a parallel connection or a combination of series and parallel connections. In the embodiment shown in Fig. 4, the cell strings 40 are electrically connected in parallel (not shown in Fig. 4 for clarity).However, other electrical configurations of the cell strings 40 are also possible, such as a series connection or a combination of series and parallel connections. Such an electrical configuration of cell strings 40 can also be referred to as a single battery 41. A redox flow battery 1 can comprise several such single batteries 41, which in turn can be electrically interconnected by a series or parallel connection, or a combination of series and parallel connections. In this way, a redox flow battery 1 with the desired electrical output voltage and the desired electrical power can be realized.

[0041] Each cell stack 10 is supplied with a positive electrolyte 15a and a negative electrolyte 15b. For this purpose, an electrolyte tank 13a is provided for the positive electrolyte 15a and an electrolyte tank 13b for the negative electrolyte 15b. The positive electrolyte 15a is circulated through the cell stack 10 in the positive electrolyte circuit with a positive flow rate by a positive electrolyte pump 9a, and the negative electrolyte 15b is circulated in the negative electrolyte circuit with a negative flow rate by a negative electrolyte pump 9b, wherein the positive and negative flow rates are preferably approximately equal.

[0042] In the case of multiple individual batteries 41 of the redox flow battery 1, an electrolyte tank 13a for the positive electrolyte 15a and an electrolyte tank 13b for the negative electrolyte 15b, as well as a positive electrolyte pump 9a and a negative electrolyte pump 9b, can be provided for each individual battery 41. Thus, the individual batteries 41 would be electrically connected to each other, but would have separate electrolyte circuits.

[0043] In the minimum configuration, the redox flow battery 1 comprises at least one cell stack 10 consisting of a plurality of individual cells 2, wherein each individual cell 2 comprises a positive half-cell 2a with a positive cell electrode 7a and a negative half-cell 2b with a negative cell electrode 7b, wherein the positive half-cell 2a is supplied with the positive electrolyte 15a during operation of the redox flow battery 1 and the negative half-cell 2b is supplied with the negative electrolyte 15b during operation of the redox flow battery 1.

[0044] For example, a control unit 42 of the redox flow battery 1 controls the

[0045] Electrolyte pumps 9a, 9b are used to circulate the respective electrolyte 15a, 15b. The control unit 42 can also record operating data of the redox flow battery 1, for example by means of suitable sensors such as voltage or current sensors.

[0046] The present invention relates to an electrolyte tank 13a, 13b for an electrolyte 15a, 15b of a redox flow battery 1. A pipe arrangement 50 for supplying an electrolyte 15a, 15b to the electrolyte tank 13a, 13b or for removing an electrolyte 15a, 15b from the electrolyte tank 13a, 13b is arranged on the electrolyte tank 13a, 13b, as shown in Fig. 5. Typically, an electrolyte tank 13a, 13b is equipped with a pipe arrangement 50 for supplying an electrolyte 15a, 15b to the electrolyte tank 13a, 13b and a pipe arrangement 50 for removing an electrolyte 15a, 15b from the electrolyte tank 13a, 13b. Electrolyte 15a, 15b can be pumped from an electrolyte tank 13a, 13b to the cell stack 10 and pumped back from the cell stack 10 to the same electrolyte tank 13a, 13b (as also shown in Fig. 1 or Fig. 4).In an electrolyte tank 13a, 13b, during operation of the redox flow battery 1, an electrolyte 15a, 15b of the redox flow battery is contained at a specific fill level LVa, LVb (indicated by dashed lines in Fig. 5). Above the fill level LVa, LVb, a gas space 59a, 59b is provided during operation of the redox flow battery 1, containing a gas, preferably an inert gas such as nitrogen. Due to the redox reaction, a gas mixture, such as a mixture of nitrogen and hydrogen, may also be present.

[0047] A supply line 16a, 16b or a discharge line 17a, 17b for circulating the electrolyte 15a, 15b through the cell stack 10, as shown for example in Fig. 1 or Fig. 4, can be connected to the pipe arrangement 50.

[0048] The pipe arrangement 50 comprises at least two pipes 51, 52 of different axial lengths. The pipes 51, 52 can have any cross-section, preferably a circular cross-section. Each of the at least two pipes 51, 52 has a first axial end 51-1, 52-1 and a second axial end 51-2, 52-2 (not visible in Fig. 5), which are each connected to each other by a flow volume 53, 54 (not visible in Fig. 5). This allows electrolyte 15a, 15b to flow from the respective first axial end 51-1, 52-1 via the flow volume 53, 54 to the respective second axial end 51-2, 52-2, or vice versa. The flow cross-section of the flow volumes 53, 54 is also fundamentally arbitrary and is preferably circular.

[0049] The first axial ends 51-1, 52-1 of the at least two tubes 51, 52 are open and terminate in the electrolyte tank 13a, 13b at different depths T1, T2 due to their different axial lengths. Depths T1, T2 are measured from the bottom of the electrolyte tank 13a, 13b. Because of the open first axial end 51-1, 52-1, the respective flow volume 53, 54 is connected to the electrolyte 15a, 15b in the electrolyte tank 13a, 13b when the electrolyte tank 13a, 13b is in use, i.e., during operation of the redox flow battery 1. The deeper the first axial end 51-1, 52-1 lies, the closer it is to the bottom of the respective electrolyte tank 13a, 13b. When using the electrolyte tank 13a, 13b, i.e. in operation, at least in normal operation, of the redox flow battery 1, the depths T1 , T2 are below the respective fill level LVa, LVb of the electrolyte 15, 15b in the electrolyte tank 13a, 13b.

[0050] Unless otherwise stated, terms such as "above" and "below" refer to vertical directions, where "above" denotes a position that is higher in terms of vertical direction than a certain other position and "below" denotes a position that is lower in terms of vertical direction than a certain other position.

[0051] The pipe arrangement 50 also includes a connecting pipe 55. A supply line 16a, 16b or a discharge line 17a, 17b is connected to the connecting pipe 55, for example via a suitable pipe connection 57. The connecting pipe 55 can also have any cross-section and flow cross-section, although it is preferably designed with a circular cross-section and flow cross-section.

[0052] A mixing volume 56 is provided in the connecting pipe 55. During operation of the redox flow battery 1, the electrolyte 15sa, 15b flows through the mixing volume 56. The second ends 51-2, 52-2 of the at least two tubes 51, 52 open into the mixing volume 56. This means that electrolyte 15a, 15b flows from the electrolyte tank 13a, 13b through the flow volumes 53, 54 of the tubes 51, 52 into the mixing volume 56b (when drawn from the electrolyte tank 13a, 13b via the tube arrangement 50) or that electrolyte 15a, 15b is distributed via the mixing volume 56 to the at least two tubes 51, 52 and flows through their flow volumes 53, 54 into the electrolyte tank 13a, 13b (when supplied to the electrolyte tank 13a, 13b via the tube arrangement 50). The flow volumes 53, 54 of the at least two pipes 51, 52 are thus connected to each other via the mixing volume 56.When using the electrolyte tank 13a, 13b, i.e. in operation of the redox flow battery 1, the mixing volume 56 is above the fill level LVa, LVb of the respective electrolyte 15a, 15b in the associated electrolyte tank 13a, 13b.

[0053] The mixing volume 56 is advantageously located outside the respective electrolyte tank 13a, 13b, preferably above the respective electrolyte tank 13a, 13b. A mounting flange 58 can be provided on the pipe assembly 50 to attach the pipe assembly 50 to the electrolyte tank 13a, 13b, for example by means of mounting screws.

[0054] With reference to Fig. 6, a first embodiment of the pipe arrangement 50 according to the invention is described in an electrolyte tank 13a, 13b.

[0055] In this embodiment, the longer pipe 51 of the at least two pipes has a smaller flow cross-section than the shorter pipe 52 of the at least two pipes. This allows the longer pipe 51 to be inserted into the shorter pipe 52 with its second end 52-1 and an axial insertion length L. In the region of the axial insertion length L, an axial flow channel S is thus formed between a radial outer surface AF of the longer pipe 51 (inner pipe) and a radial inner surface IF of the shorter pipe 52 (outer pipe), which also opens into the mixing volume 56. In an advantageous embodiment, the shorter pipe 52 transitions into the connecting pipe 55 with its second axial end 52-2 (as shown in Fig. 6), for example, in the region of the mixing volume 56.

[0056] It would of course be possible to insert more than two pipes 51, 52 into one another in the pipe arrangement 50. The pipes have different axial lengths, but their second axial ends all open into the mixing volume 56. The outermost pipe is the shortest, and the flow cross-sections of the pipes decrease with increasing axial length. An axial flow channel S forms between each pair of radially adjacent pipes, which opens into the mixing volume 56. Due to the different axial lengths of the pipes, the resulting flow channels are also typically of different lengths.

[0057] The following describes the operation of the pipe arrangement 50 in the electrolyte tank 13a, 13b.

[0058] In normal operation of the redox flow battery 1, the first axial ends 51-1, 52-1 of the at least two tubes 51, 52 are below the fill level LVa, LVb of the respective electrolyte 15a, 15b in the electrolyte tank 13a, 13b. When electrolyte 15a, 15b is pumped from the electrolyte tank 13a, 13b by the tube arrangement 50, electrolyte 15a, 15b is drawn in via the second axial end 51-2 of the longer tube 51. Likewise, electrolyte 15a, 15b is drawn in via the first axial end 52-1 of the shorter tube 52. Specifically, it is drawn in via the flow channel S formed between the tubes 51, 52. This draws electrolyte 15a, 15b from electrolyte tanks 13a, 13b at different depths T1, T2. This promotes electrolyte mixing by counteracting any potential electrolyte stratification in electrolyte tanks 13a, 13b.Likewise, the two electrolyte streams from different depths T1, T2 converge in the electrolyte tank 13a, 13b within the mixing volume 56 and are mixed, which also promotes electrolyte mixing. When electrolyte 15a, 15b is pumped into the electrolyte tank 13a, 13b via the pipe arrangement 50, the electrolyte 15a, 15b emerges from the pipes 51, 52 at different depths T1, T2, creating a flow within the electrolyte volume of the electrolyte tank 13a, 13b that results in improved electrolyte mixing.

[0059] This effect can be optimized by designing the flow cross-sections of the pipes 51, 52 and their axial lengths (or their depths T1, T2). It is advantageous if less electrolyte 15a, 15b is pumped from or into the upper layers of the electrolyte tank 13a, 13b.

[0060] If a leak occurs in the electrolyte circuit of the redox flow battery 1, resulting in the loss of electrolyte 15a, 15b outside the electrolyte tank 13a, 13b, the electrolyte level LVa, LVb in the respective electrolyte tank 13a, 13b decreases. If the electrolyte level LVa, LVb falls below the first axial end 52-1 of the shorter (shortest) tube 52, the first axial end 52-1 of the shorter (shortest) tube 52 is exposed (indicated by a dashed line in Fig. 6) and gas is drawn in from the gas space 59a, 59b in the electrolyte tank 13a, 13b via the shorter (shortest) tube 52. The aspirated gas interrupts a developing siphon effect, which, despite the electrolyte pumps 9a, 9b being switched off, could lead to the emptying of the electrolyte tank 13a, 13b. Here, too, the flow cross-section of the flow channel S can be designed and dimensioned so that enough gas is aspirated to reliably interrupt the siphon effect.

[0061] As is known, such a siphon effect can occur if at least one cell stack 10 or an electrolyte line connected to the electrolyte tank 13a, 13b in the redox flow battery 1 is positioned partially below the fluid level in the electrolyte tank 13a, 13b. Due to the siphon effect, even if the electrolyte pump 9a, 9b is switched off, the electrolyte tank 13a, 13b would be emptied down to the level of the leakage point. This can lead to very large leaks, which are prevented by the pipe arrangement 50.

[0062] However, the aspiration of gas can also be used to detect a leak in an electrolyte circuit, even independently of any sensors that may be present for leak detection. When gas is aspirated, it reaches the cell stack 10, specifically the individual cells 2 of the cell stack 10, and the gas bubbles adhere, at least temporarily, to the cell electrode 7a, 7b and / or the semipermeable, particularly ion-selective, membrane 4 between the half-cells 2a, 2b of the individual cell 2. This results in an abrupt change in the operating data of the cell stack 10 or an individual cell 2, be it a decrease in cell efficiency, an increase in electrical cell resistance, a drop in cell voltage, or a drop in cell current. Similarly, a fluctuation in the pump pressure or the pumping capacity of the electrolyte pump 9a, 9b can occur.Such operating data are typically recorded and available in a redox flow battery 1, for example in a control unit 42 of the redox flow battery 1. This operating data can be evaluated to detect a drop in the fill level LA, LB of the electrolyte 15a, 15b in the electrolyte tank 13a, 13b in which the pipe arrangement 50 is located. The evaluation can be carried out, for example, by comparison with predefined limit values. This allows a leak to be detected, even without dedicated leakage sensors, and the electrolyte pumps 9a, 9b can be stopped to prevent further leakage. The pipe arrangement 50 also interrupts any siphon effect that may develop.

[0063] A further embodiment of the pipe arrangement 50 according to the invention is shown in Figs. 7 and 8. In this embodiment, the at least two pipes 51, 52 are not nested inside one another, but arranged side by side. An embodiment with more than two pipes 51, 52, 61, 62, with different axial lengths, is shown, such that their first axial ends 51-1, 52-1, 61-1, 62-1 terminate at different depths T1, T2, T3, T4 in the electrolyte tank 13a, 13b. The respective opposing second axial ends 51-2, 52-2, 61-2, 62-2 open back into the mixing volume 56 in the connecting pipe 55.

[0064] The effect and function of this design is the same as that of the pipe arrangement 50 according to Fig. 6. The shortest of the pipes 51, 52, 61, 62 again ensures the siphon interruption and enables leak detection.

[0065] Fig. 9 shows another possible embodiment of the pipe arrangement 50 according to the invention.

[0066] In the embodiment shown in Fig. 9, the longer pipe 51 again has a smaller flow cross-section than the shorter pipe 52. The longer pipe 51 is inserted into the shorter pipe 52 at its second end 51-2 and with an axial insertion length L, so that an axial flow channel S is formed in the region of the axial insertion length between an outer surface AF of the longer pipe 51 and an inner surface IF of the shorter pipe 52. The axial flow channel S is connected to the flow volume 53 of the longer pipe 51 via at least one opening 60 in the outer shell of the radially inner longer pipe 51. The flow volume 54 of the shorter pipe 52 is connected to the mixing volume 56 of the connecting pipe 55. Thus, the flow volume 53 of the longer pipe 51 is also connected to the mixing volume 56 in the connecting pipe 55 via the at least one opening 60. The mixing volume 56 is therefore above the opening 60.When the electrolyte tank 13a, 13b is used, i.e., during operation of the redox flow battery 1, at least one opening 60 is located above the electrolyte level LVa, LVb in the electrolyte tank 13a, 13b. The second axial end 52-2 of the shorter tube 52 is closed above the at least one opening 60. In an advantageous embodiment, the longer tube 51 transitions into the connecting tube 55 at its second axial end 51-2. In this embodiment, more than two tubes 51, 52 can, of course, be provided, with all radially inner tubes having an opening 60.

[0067] If electrolyte 15a, 15b is pumped from the electrolyte tank 13a, 13b via this pipe arrangement 50, electrolyte 15a, 15b is also drawn in through the opening 60 via the flow channel S (as indicated by the arrows in Fig. 9). However, if the fill level LVa, LVb falls below the first axial end 52-1 of the shorter pipe 52 (Fig. 9, right), gas is drawn in through the opening 60 from the gas space of the electrolyte tank 13a, 13b, thus interrupting any siphon effect that may develop.

[0068] From the above explanations, it is evident that the depth T2 of the shorter (shortest) tube 52 in the electrolyte tank 13a, 13b should be as close as possible to the normal fill level LVa, LVb of the respective electrolyte 15a, 15b in the electrolyte tank 13a, 13b. This minimizes electrolyte 15a, 15b loss via siphoning. Natural fluctuations in the fill level LVa, LVb of the respective electrolyte 15a, 15b should be taken into account. For example, during operation of the redox flow battery 1, due to the chemical properties of the ion exchange membrane 4 in the individual cells 2, water from the electrolyte 15a, 15b may migrate more readily into the positive or negative half-cell 2a, 2b, which can change the fill level LVa, LVb of the respective electrolyte 15a, 15b.

[0069] The pipe arrangement 50 can also be equipped with an early leak detection system, as described below with reference to Fig. 10 and Fig. 11.

[0070] For early leak detection, a slot-shaped recess 65 is provided in the outer shell of the shorter (shortest) tube 52 of the tube arrangement 50, which is also used for the siphon interruption, in the region of the first axial end 52-1. Preferably, the slot-shaped recess 65 extends to the first axial end 52-1 of the shorter (shortest) tube 52. Electrolyte 13a, 13b can flow from outside the tube 52 into the flow channel 54 of the tube 52 via the slot-shaped recess 65. The slot-shaped recess 65 extends at least partially in the axial direction of the shorter (shortest) tube 52. During operation, at least during normal operation, of the redox flow battery 1, the slot-shaped recess 65 lies below the fill level LVa, LVb of the electrolyte tank 13a, 13b in which the tube arrangement 50 is located. Such a slot-shaped recess 65 can be used in any of the described embodiments of the tube arrangement 50.

[0071] The effect of the slot-shaped recess 65 is explained below.

[0072] In normal operation of the redox flow battery 1, the slot-shaped recess 65 lies below the fill level LVa, LVb of the electrolyte tank 13a, 13b in which the pipe assembly 50 is located. Thus, electrolyte 15a, 15b is easily drawn in (when electrolyte 15a, 15b is withdrawn) or discharged (when electrolyte 15a, 15b is supplied) via the slot-shaped recess 65. If the fill level LVa, LVb of the electrolyte 15a, 15b drops, the upper part of the slot-shaped recess 65 will eventually be exposed before the first axial end 52-1 of the shorter (shortest) pipe 52 is exposed. This allows a small amount of gas to be drawn from the gas space 59a, 59b in the electrolyte tank 13a, 13b through the exposed slot-shaped recess 65, thereby introducing a small amount of gas into the electrolyte 15a, 15b. This small amount of gas reaches the cell stack 10, specifically the individual cells 2 of the cell stack 10.The gas bubbles adhere, at least temporarily, to the cell electrode 7a, 7b and / or the semipermeable, in particular ion-selective, membrane 4 between the half-cells 2a, 2b of the single cell 2. This leads to an abrupt change in the operating data of the cell stack 10 or a single cell 2, be it a decrease in cell efficiency, an increase in electrical cell resistance, a drop in cell voltage, or a drop in cell current. Similarly, a fluctuation in the pump pressure or pumping capacity of the electrolyte pump 9a, 9b can occur. Such operating data are typically recorded and available in a redox flow battery 1, for example, in a control unit 42 of the redox flow battery 1. The operating data can thus be evaluated to detect a drop in the fill level LVa, LVb of the electrolyte 15a, 15b in the electrolyte tank 13a, 13b in which the pipe arrangement 50 is located.The evaluation can be carried out, for example, by comparison with predefined limit values. This allows a leak to be detected early, even without dedicated leakage sensors, and the electrolyte pumps 9a and 9b can be stopped to prevent further leakage. The pipe arrangement 50 also interrupts any siphon effect that may develop.

[0073] The shape of the slot-shaped recess 65 can influence early leak detection. Advantageously, the slot-shaped recess 65 is designed such that initially a small opening area is exposed, and the opening area increases as the fill level LVa, LVb decreases. Figure 11 shows examples of possible configurations of the slot-shaped recess 65 with increasing opening area. The increasing opening area allows more gas to enter the electrolyte 15a, 15b as the fill level LVa, LVb in the electrolyte tank 13a, 13b, in which the pipe arrangement 50 is located, decreases. The increasing amount of gas entering the electrolyte alters the operating parameters of the redox flow battery 1, which can be evaluated, for example, in the control unit 42.This allows an early warning to be given in the event of small amounts of gas, for example to a control center, maintenance can be triggered and / or the control unit 40 can change the operating mode of the redox flow battery 1.

[0074] The pipe arrangement 50 alone is also considered an independent invention. The pipe arrangement 50 comprises at least two pipes 51, 52 of different axial lengths. Each of the at least two pipes 51, 52 has a first axial end 51-1, 52-1 and a second axial end 51-2, 52-2, which are each connected to the other by a flow volume 53, 54 of the respective pipe 51, 52. The first axial ends 51-1, 52-1 of the at least two pipes 51, 52 are open. The second axial ends 51-2, 52-2 of the at least two pipes 51, 52, opposite the first axial ends 51-1, 52-1 of the at least two pipes 51, 52, open into a mixing volume in a connecting pipe 55 of the pipe arrangement 50. The flow volumes 53, 54 of the at least two pipes 51, 52 are connected to each other via the mixing volume 56. The pipe arrangement 50 can be configured as shown above with reference to Figures 5 to 11.

Claims

Patent claims 1. Electrolyte tank for an electrolyte (15a, 15b) of a redox flow battery (1), wherein a pipe arrangement (50) for supplying electrolytes (15a, 15b) to the electrolyte tank (13a, 13b) or for removing electrolytes (15a, 15b) from the electrolyte tank (13a, 13b) is arranged on the electrolyte tank (13a, 13b), and wherein, when the electrolyte tank (13a, 13b) is used, the electrolyte tank (13a, 13b) contains an electrolyte (15a, 15b) of the redox flow battery (1) at a specific fill level (LVa, LVb), characterized in that the pipe arrangement (50) comprises at least two pipes (51, 52, 61, 62) of different lengths, each of the at least two pipes (51 , 52, 61 , 62) has a first axial end (51-1, 52-1, 61-1, 62-1) and a second axial end (51-2, 52-2, 61-2, 62-2) which are each connected to each other by a flow volume (53, 54, 63, 64) such that the first axial ends (51-1 , 52-1 , 61-1, 62-1) of the at least two tubes (51 , 52, 61 ,62) are open and terminate in the electrolyte tank (13a, 13b) at different depths (T1, T2, T3, T4) due to their different lengths, wherein the depths (T1, T2, T3, T4) are below the fill level (LVa, LVb) of the electrolyte (15a, 15b) when using the electrolyte tank (13a, 13b), that the second ends (51-2, 52-2, 61-2, 62-2) of the at least two tubes (51, 52, 61, 62) opposite the first axial ends (51-1, 52-1, 61-1, 62-1) of the at least two tubes (50, 51, 61, 62) open into a mixing volume (56) and the mixing volume (56) opens into a connecting tube (55) it is provided that the flow volumes (53, 54, 63, 64) of the at least two tubes (51, 52, 61, 62) are connected to each other via the mixing volume (56) and that the mixing volume (56) is located above the fill level (LVa, LVb) of the electrolyte (15a, 15b) when using the electrolyte tank (13a, 13b).

2. Electrolyte tank according to claim 1, characterized in that the longer tube (51) of the at least two tubes (51, 52, 61, 62) has a smaller flow cross-section than the shorter tube (52, 61, 62) of the at least two tubes (51, 52, 61, 62), and that the longer tube (51) of the at least two tubes (51, 52, 61, 62) is inserted into the shorter tube (52, 61, 62) of the at least two tubes (51, 52, 61, 62) with its second end (51-2) and with an axial insertion length (L), such that an axial forms a flow channel (S) which opens into the mixing volume (56).

3. Electrolyte tank according to claim 2, characterized in that the shorter tube (52, 61, 62) of the at least two tubes (51, 52, 61, 62) transitions into the connecting tube (55) with its second axial end (52-2, 61-2, 62-2).

4. Electrolyte tank according to claim 1, characterized in that the longer tube (51) of the at least two tubes (51, 52, 61, 62) has a smaller flow cross-section than the shorter tube (52, 61, 62) of the at least two tubes (51, 52, 61, 62), and that the longer tube (51) of the at least two tubes (51, 52, 61, 62) is inserted into the shorter tube (52, 61, 62) of the at least two tubes (51, 52, 61, 62) with its second axial end (51-2) and with an axial insertion length (L), such that an axial flow cross-section is formed in the region of the axial insertion length (L) between an outer surface (AF) of the longer tube (51) and an inner surface (IF) of the shorter tube (52, 61, 62). flow channel (S) is formed, and that the axial flow channel (S) is connected to the flow volume (53) of the longer tube (51) via at least one opening (60) in the shell of the longer tube (51), wherein the at least one opening (60) is located above the fill level (LVa) when using the electrolyte tank (13a, 13b).LVb) of the electrolyte (15a, 15b) lies in the electrolyte tank (13a, 13b) and the second axial end (52-2, 61-2, 62-2) of the shorter tube (52, 61, 62) is closed above the at least one opening (60), so that the flow volumes (53, 54, 63, 64) of the at least two tubes (51, 52, 61, 62) are connected to the mixing volume (56).

5. Electrolyte tank according to claim 4, characterized in that the longer tube (51) of the at least two tubes (51, 52, 61, 62) transitions into the connecting tube (55) with its second axial end (51-2).

6. Electrolyte tank according to one of claims 1 to 5, characterized in that a slot-shaped recess (65) is provided in the jacket of the shorter tube (52, 61, 62) of the at least two tubes (51, 52, 61, 62) in the region of the first axial end (52-1, 61-1, 62-1), which extends at least partially in the axial direction of the shorter tube (52, 61, 62), wherein the slot-shaped recess (65) is located below the fill level (LVa, LVb) of the electrolyte (15a, 15b) in the electrolyte tank (13a, 13b) when the electrolyte tank (13a, 13b) is used.

7. Electrolyte tank according to claim 6, characterized in that the slot-shaped recess (65) extends to the first axial end (52-1 , 61-1 , 62-1) of the shorter tube (52, 61, 62) of the at least two tubes (51, 52, 61 , 62).

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