WO2003005476A1

WO2003005476A1 - Charging or discharging station for a redox flow battery

Info

Publication number: WO2003005476A1
Application number: PCT/AT2002/000145
Authority: WO
Inventors: Martha Maly-Schreiber; Adam Whitehead; Christoph Hagg
Original assignee: Funktionswerkstoffe Forschungs- U. Entwicklungs Gmbh
Priority date: 2001-07-02
Filing date: 2002-05-15
Publication date: 2003-01-16
Also published as: AT410268B8; ATA10142001A; AT410268B

Abstract

The invention relates to a charging or discharging station for a redox flow battery. Said station comprises a number of flow cells (1) which respectively consist of two half cells (3, 4) which are separated by a selectively ion-permeable membrane (2) and can be flown through by differently charged electrolyte liquids. An electrode (5, 6) is respectively arranged in each half cell (3, 4) and is connected in an electroconductive manner to the electrode of another cell (1) or to an external connection (+, -). In order to be able to adjust the charging or discharging current and voltage for the respective function, the electroconductive connection (15) of at least one of the electrodes (5, 6) can be carried out by means of interconnected switching elements (16) which enable at least individual groups of cells (1) to be the optionally connected in parallel or in series.

Description

The invention relates to a charging or discharging station for a redox flow-through battery, with a number of flow-through cells, each consisting of two half-cells that can be flowed through by differently charged electrolyte liquids and separated by means of a selectively ion-permeable membrane, in each of which an electrode is arranged, which is electrically connected to the electrode of another cell or to an external connection.

Arrangements of the type mentioned are known, for example, from DE 29 27 868 AI or also WO 00/57507 AI and use electro-chemical reduction and oxidation processes for storing and releasing electrical energy, which are essentially in the liquid phase using soluble salts of Metals that have different oxidation states run off. For example, chrome redox batteries, iron-titanium redox batteries or, more recently, vanadium redox batteries (VRB) are known, which have now reached technologically and structurally mature stages and are used in practical use, for example for temporary storage in photovoltaic systems. Redox batteries of this type have the serious advantage that the underlying electrochemical reactions take place completely in the solutions themselves, and thus no chemical compounds are deposited on or in the electrodes or are detached from them during charging or discharging. This makes it possible, for example, to charge the battery by simply and quickly replacing the otherwise charged electrolyte liquids, which also allows the use of batteries of this type in vehicles which, like the conventional filling stations, can also be charged at electrolyte filling stations. The storage capacity of such redox batteries can be influenced in the simplest way via the volume of the available electrolyte solutions, the available discharge voltage and output being easily influenced via the cell size and number of interconnected cells.

In order to reduce the system-related losses due to the necessary exchange of ions and electrons between the half cells or to the current arresters, According to DE 2927 868 already mentioned at the beginning, it is proposed to apply the anode and cathode as an electrolyte-permeable thin layer directly to opposite surfaces of the partially permeable, ion-selective membrane separating the two half cells and to contact them at many points on the surface facing away from the membrane by means of an electrically conductive lattice. This grid-shaped current conductor was then electrically conductively connected to the outside or to the closest electrode of an adjacent cell by means of end plates or bipolar separating inserts forming flow channels for the electrolyte. This resulted in a structurally simple manner in electrically series-connected cell assemblies through which the electrolyte fluids could flow essentially in parallel via channels and inflow and outflow openings.

Similar arrangements are known from WO 00/57507 mentioned in the introduction, in which the electrodes assigned to the half cells are not arranged on the central, ion-selective separation membrane but on the outer cell walls, so-called bipolar electrodes being used, in which between the two , Electrodes to be assigned to adjacent flow cells in the partition are themselves electrically conductive connections created by overlapping continuous electrically conductive fibers. In this way, too, there is an electrical series connection of a large number of flow cells which can be selected within wide limits, which makes it possible to select discharge voltages in a very simple manner.

In all known arrangements of the type mentioned at the outset, the serial connection of the individual flow cells was always used to enable the described simple structure of the cell network or to ensure common output voltages that can be obtained without further losses, which however (as long as the same cell network alternately as charging and discharge station is used) has the disadvantage that the battery must also be charged serially. An attempt was made to counter this, for example in accordance with WO 89/05528, by having a separate battery system in each case Charging and discharging station (working together with the same electrolyte reservoir) are provided, with which the individual stations can then be better adapted to the charging or discharging function, which is done, for example, by varying the number and size of the individual cells, which are still connected in series.

In order to avoid the disadvantages of the known arrangements mentioned in the different requirements for loading and unloading stations, the present invention now takes a different approach. It is based on the consideration that the requirements for a charging station for redox flow batteries can usually be met much better and more simply by connecting the individual flow cells in parallel, while in most cases it is simpler and more advantageous for the discharge station for the electrical ones Series connection of the cells remain. In order to enable such a concept while maintaining a structurally simple structure of the cell network, it is proposed according to the present invention that the addressed electrically conductive connection of at least some of the electrodes via interposed switching elements, which selectively connect parallel or series electrical connection of at least individual groups of cells enable, runs, which enables a very advantageous influence on the characteristics of the battery or the adaptation to the respective use of the cell network (for charging or discharging). This allows the current and voltage to be adapted to the respective needs in the simplest way, both when charging and discharging the battery. The parallel connection of all individual cells results, for example, in a charge or discharge voltage corresponding to the individual cell with a correspondingly multiplied charge or discharge current - the groupwise or parallel connection which is possible in groups enables a wide variety of gradations to be made between maximum voltage and maximum current. Individual cells or even cell groups can be monitored very easily in the parallel connection, with which, for example, defective individual cells or cell groups can be recognized and taken into account. Local overloading of individual cells and thus dangerous gas development can occur This prevents them, which increases the lifespan and the security of the system.

In a further embodiment of the invention, it is provided that the switching elements have a switching position in which at least individual connections of the electrodes are open. With these opened connections, for example, the self-discharges via the electrolyte fluids which are otherwise inevitable when such redox flow-through batteries are in the idle state, since there is no longer an electrically conductive connection between the electrodes of different electrolyte spaces. In the previous arrangements, in order to avoid further self-discharge of the electrolyte fluids, it was always provided that the cell contents were shut off in an electrically insulating manner from the remaining electrolyte volume during standstill, so that this self-discharge was limited to the cell contents. When the battery was put back into operation, however, it was always necessary to replace the electrolyte fluids in the cells before normal function was restored. The described separation of the connections of the electrodes, which is possible by the invention, completely eliminates the problem in the simplest way and the battery can be used at any time without loss of self-discharge.

The invention is explained in more detail below with reference to the embodiments shown schematically in the drawing. 1 shows a redox flow-through battery according to the known prior art, and FIGS. 2 to 4 each show only the most essential components of a charging or discharging station for such a battery in an exemplary embodiment according to the present invention.

The redox flow battery according to FIG. 1 (for example a vanadium redox battery) has four flow cells 1, each of which consists of two half cells 3, 4 which can be flowed through by differently charged electrolyte liquids and separated by means of a selectively ion-permeable membrane 2. In each of the half cells 3, 4 there is in each case an electrode 5, 6 which is electrical in the manner explained in more detail below is conductively connected to the electrode 6, 5 of another cell or to an external connection (+ or - at the top in FIG. 1).

The electrolyte liquids (corresponding to the anode and cathode also referred to as aπolyte and catholyte) are stored in containers 7, 8 (the volume of which determines the storage capacity of the battery) and are fed via lines 9, 10 and pumps 11, if necessary, via the respective half cells 3 , 4 is circulated, the electrochemical reduction or oxidation processes which cause the storage or release of the electrical energy to take place (see, for example, the explanations in the aforementioned DE 29 27 868 A1). Apart from the outer electrodes 5, 6, which are connected to the outer connections + and - via connection lines 12, 13, the further electrodes 5, 6, respectively assigned to the half cells, are arranged on bipolar partition walls 14, with flow between the two adjoining one another Electrodes to be assigned to cells are created via the partition 14 even electrically conductive connections. This results in an electrical series connection of all (in the example four) flow cells 1, the total voltage between the connections + and - (lines 12 and 13) corresponding to the sum of the individual cell voltages, which in turn depends on the redox potential of the respective redox partner depend.

In order to take into account or enable different charging and discharging voltages and currents, it has already been proposed in such series arrangements of flow cells to provide individual tapping points on central electrodes 5 and 6, which also means the use of only a partial combination of the entire flow cells, for example for charging the electrolyte fluids with a lower voltage. Furthermore, it has also already been proposed to implement such arrangements with separately configurable charging and discharging stations, which likewise enables charging and discharging processes which can be optimized independently of one another.

According to the present invention, as schematically shown in FIGS. 2 to 4, it is now provided that the electrically conductive connection 15 at least some of the elec- trodes 5, 6 runs through interposed switching elements 16, which enable the optional electrical parallel (Fig. 3) or series connection (Fig. 2) at least individual groups of cells 1 or according to Fig. 4 can also have a switching position in which at least individual connections 15 of the electrodes 5, 6 are open at all.

According to FIG. 2, only the uppermost outer electrode 5 (corresponding to the left outer electrode 5 in FIG. 1) is connected to the positive connection, while correspondingly only the lowest outer electrode 6 (corresponding to the right outer electrode 6 in FIG. 1) is connected to the negative connection , The electrode pairs 5, 6 lying between them (here four) are connected via the switching elements 15, which, viewed electrically, results in the same series connection of the cell network as in FIG. 1. The separating membranes 2 are indicated here as dotted lines - the flow through the half cells through the two different electrolyte liquids is indicated by the arrows 17 and 18, respectively. 1, there are of course no direct electrically and ionically conductive connections between the adjacent electrodes 5, 6 (electrodes 5 and 6 are separated by an insulation layer) - as described, these connections are only made via the switching elements 16 shown here ,

According to FIG. 3, the switching elements 16 (which can be imagined in FIG. 2 as two switching bridges lying in parallel and rotatable by one end point each) are now switched so that each electrode 5 with the plus connection and each electrode 6 with the minus connection in Connection is established, with which an electrical parallel connection is realized and the total voltage corresponds to that of a single flow cell.

4, the switching elements 16 are in the open position, the individual electrodes 6, 7 being potential-free, which prevents the electrolyte liquids from self-discharging.

Apart from the synchronization of all switching elements 16 shown in FIGS. 2 to 4, this could also be switched so that, for example, two cells in series and these groups are then connected in parallel - a wide variety of combinations are possible in the entire cell network, which is largely free Influencing La discharge and discharge voltage and current enables. For example, open switching states according to FIG. 4 could also be provided for individual cells in the network if a faulty behavior of individual cells is detected via connected measuring devices (not shown here), which should remain switched off for safety reasons. Overall, the most diverse possibilities result from the interposed switching elements 16.

It is also clear to the person skilled in the art that the switching elements 16 or their attachment in the electrical connections 15 between the electrodes 5, 6 can be freely selected within wide limits - in particular, semiconductor switching elements, electronic switches such as IGBTs, Mosfets, electrical ones, for example Relays or transistors, are used and also controlled by an electronic feedback / control system. Apart from that, manually operated switches (cells are manually switched to parallel or serial operation) would also be possible.

claims:

Claims

claims:

1. Charging or discharging station for a redox flow-through battery, with a number of flow-through cells (1), each of which consists of two differently charged electrolyte liquids through which by means of a selectively ion-permeable membrane (2) separate half cells (3, 4) , in each of which an electrode (5, 6) is arranged, which is electrically conductively connected to the electrode (6, 5) of another cell 1 or to an external connection (+, -), characterized in that the electrically conductive Connection (15) of at least some of the electrodes (5, 6) via interposed switching elements (16), which allow the optional electrical parallel or series connection of at least individual groups of cells (1).

2. Loading or unloading station according to claim 1, characterized in that the switching elements (16) have a switching position in which at least individual connections (15) of the electrodes (5, 6) are open.