DE102014104601A1 - Electrochemical cell, in particular for a redox flow battery, and method of production - Google Patents

Abstract

An electrochemical cell, in particular for a redox flow battery, has a plastic cell wall (14) which encloses a cavity which is separated by an ion-conducting membrane (11) into two half-cells (16, 18), each one a first and a second end (12, 13), at which fluid connections (40) are provided for the passage of an electrolyte, wherein the two half-cells (16, 18) each have planar electrodes (20, 22) extending between the first and extend the second end parallel to the membrane (11), wherein the electrodes of porous graphite, in particular one or more layers (21) of graphite paper, wherein the fluid ports (40) at the first and second ends (12, 13) of each half-cell (16, 18) are formed for direct flow with electrolyte along the extension direction of the respective electrode (20, 22).

Description

The invention relates to an electrochemical cell, in particular for a redox flow battery, with a cell wall made of plastic, which encloses a cavity, which is separated by an ion-conductive membrane into two half-cells, each having a first and a second end, where Fluid connections are provided to flow through with an electrolyte, wherein the two half-cells each have planar electrodes which extend parallel to the membrane between the first and the second end, and wherein the electrodes are made of porous graphite.

The invention further relates to a composite of such electrochemical cells and a method for producing such a cell.

Such a composite of electrochemical cells for a redox flow battery is out of the WO 2011/075135 A1 known.

For serial connection of the individual cells with each other bipolar plates are provided here. In the bipolar plates coherent flow fields are formed by partially closing individual, interconnected channels, via which the respective positively charged electrolyte (anolyte) or the negatively charged electrolyte (catholyte) in the respective half-cell is added or removed.

Such an arrangement is very complex and increases the total resistance of the cell network.

Against this background, the invention has for its object to provide an electrochemical cell and a composite of electrochemical cells, which are given a simple and inexpensive construction and the highest possible performance.

Furthermore, a method for producing such a cell is to be specified.

This object is achieved by an electrochemical cell, in particular for a redox flow battery, with a cell wall made of plastic, which encloses a cavity which is separated by an ion-conducting membrane into two half-cells, each having a first and a second end in which fluid connections are provided for the passage through an electrolyte, wherein the two half-cells each have planar electrodes which extend parallel to the membrane between the first and the second end, wherein the electrodes are made of porous graphite, in particular one or more layers of graphite paper , and wherein the fluid ports are formed at the first and second ends of each half-cell for direct flow of electrolyte along the extending direction of the respective electrode.

The object of the invention is completely solved in this way.

It has been shown that an immediate flow through the electrodes made of porous graphite is readily possible. In this way, additional flow fields can be dispensed with, which simplifies the structure and reduces the total resistance of the cell.

In a further embodiment of the invention, the electrodes are each in contact with current collector plates.

In this case, the current collector plates may consist of a metal which is not resistant to the electrolyte, in particular of copper, and may be protected in each case by an acid-resistant protective layer against the electrolyte. Alternatively, the current collector plates may also be made of a material that is resistant to the electrolyte, such as graphite or gold. Or the current collector plates are coated approximately with a gold layer.

According to a further embodiment of the invention, the protective layer consists of graphite or a conductive plastic and is preferably formed plate-shaped.

In this way, a current collector plate made of a non-resistant metal, such as copper, can be completely protected against the electrolyte.

According to a further embodiment of the invention, the individual layers of the cell, consisting at least of the membrane, the first and second electrode and optionally current collector plates and plate-shaped protective layers, at least peripherally sealed to the plastic of the cell wall.

In this way, a compact cell structure and an intensive contact between the respective electrolytes and the electrodes are ensured.

Preferably, in this case the individual layers of the cell are pressed together tightly.

In this way, there is a particularly intense interaction between the electrolyte, the electrodes and the membrane.

According to a further embodiment of the invention, the individual layers of the cell are at least peripherally connected to each other by a plastic laminate or joined together by a plastic injection molding.

In this way, a simple production is possible.

According to a further embodiment of the invention, at least one electrode is in contact with a bipolar plate which is designed for the serial connection of the relevant half cell to a half cell of an adjacent cell.

This is a first possibility for serial interconnection of adjacent cells.

In this case, the bipolar plate is preferably made of graphite or copper, which is each provided on the electrode side with an acid-resistant protective layer.

According to a further embodiment of the invention, the fluid connections at the first and second ends for the distribution of electrolyte via a plurality of holes, preferably in the form of a row of holes or a perforated grid, open into the half-cells.

In this way, a uniform distribution of the electrolyte is ensured for the flow through the half-cells.

In accordance with a further embodiment of the invention, the fluid connections are formed on the current collector plates, on the peripheral cell walls or on bipolar plates.

Depending on the structure and arrangement of the individual components of the cell thus an advantageous electrolyte supply and removal can be ensured. In particular, edge-side supply or removal to or from the electrodes can also take place, or a supply perpendicular thereto, i. over the main surfaces.

According to a further embodiment of the invention, the electrodes are electrochemically activated with respect to the electrolyte, preferably hydrophilicized.

As a result, the efficiency of the cell is improved. This can, for example, according to a method according to the EP 2 626 936 A1 which is incorporated by reference in its entirety.

According to a further embodiment of the invention, each half-cell is divided between the first and the second end into a plurality of sections, and each section is provided with fluid connections for the supply and removal of electrolyte.

If the length of the cell to be flowed through by the electrolyte becomes too long and the hydraulic resistance thus becomes too great, a remedy can be provided in this way in order to ensure a sufficient, intensive flow of the cell over the entire length with electrolyte.

A composite of a plurality of serially interconnected cells of the type described above can be made either via bipolar plates between adjacent half cells or by external connections outside the cells in the case of use of current collector plates.

Alternatively, for serial connection between adjacent half-cells distributor plates may be arranged, at which fluid connections are provided for supplying electrolyte, wherein the collector plates in each case the two half-cells associated power collector plates are provided, which are electrically connected to each other within the distributor plates.

In this way, the fluid supply via the distributor plates can also be used simultaneously for the electrical connection of adjacent half cells.

Furthermore, according to the invention, a method is provided for producing a cell, in which an ion-conductive membrane and two flat, porous electrodes of graphite, in particular of at least one layer of graphite paper, are provided, wherein one of the electrodes is disposed on one side of the membrane and the Membrane is laminated with the electrodes at least edge to a membrane electrode assembly.

Subsequently, seals can be applied to the membrane electrode unit on the edge, to which further layers, in particular current collector plates, protective plates or bipolar plates, are applied.

According to an alternative embodiment of the method according to the invention, an ion-conductive membrane and planar, porous electrodes made of graphite, in particular from at least one layer of graphite paper, and possibly current collector plates and plate-shaped protective layers are placed in an injection mold and sprayed with plastic, such that the layers at least edge side with each other connected and sealed and are enclosed on the outside by a plastic wall.

Here, the individual layers of the cell can be firmly pressed together.

Subsequently, the cells can be provided with fluid lines, such that in each case a half cell of an anolyte and a half cell of a catholyte can be flowed through.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings. Show it:

1 a first embodiment of an electrochemical cell according to the invention in cross section;

2a) . 2 B) a perspective view of two plates, in each of which a half-cell is formed, which are then screwed together to obtain a test cell;

2c) to 2f) Views of the associated protective plates and current collector plates;

3 a cross section through a first composite consisting of two cells, wherein the cells are interconnected via a bipolar plate;

4 a second composite consisting of two cells, the cells being externally connected in series with each other;

5 a third composite in which adjacent cells are interconnected via distributor plates;

6 a further composite in which adjacent cells are interconnected via bipolar plates, wherein in addition the distribution channels for Anolytzu- and -abfuhr and for Katholytzu- and -abfuhr are shown; and

7 a schematic representation of a cell which is divided into individual sections, which are each supplied separately with electrolyte.

An electrochemical cell that is suitable for a redox flow battery is in 1 shown in cross-section and generally designated by the numeral 10.

Redox flow batteries are based on the principle that two electrolytes flow through the half cells of an electrochemical cell, changing their oxidation state on the surface of the electrodes. The emitted or absorbed in the half-cell reactions electrons perform work via an external circuit. The circuit is closed by the ion-conductive membrane, which ensures the charge balance between the two half-cells. The electrolyte solution for each of the two half-cells is stored in tanks and, if necessary, supplied to a central reaction unit in the charging or discharging process by means of pumps. The tank size determines the energy content of the battery, the charge / discharge unit determines the performance of the battery. During the charging and discharging process, the valence of the ions of the respective salt is changed. Vanadium redox flow batteries are currently being developed. The redox couple used in such a vanadium redox flow battery is V / V, that is, for the electrolytic solution, the same element is used in both the cathodic half-cell and the anodic half-cell. The electrolyte solutions consist essentially of dilute sulfuric acid with dissolved vanadium salts in different oxidation states.

In the 1 shown electrochemical cell is preferably provided for a vanadium redox flow battery.

The cell 10 consists of a first half cell 16 and a second half cell 18 passing through an ion-conductive membrane 11 are separated from each other. On each side of the membrane 11 is an electrode 20 respectively. 22 provided, which consists of porous graphite and preferably from one to five layers of about 0.4 mm thick graphite paper. In 1 are the individual layers by the numeral 21 indicated. From the central membrane 11 and the two-sided electrodes 20 . 22 on both sides of the membrane 11 is laminated with a suitable plastic, preferably polypropylene or polyethylene, a membrane-graphite paper unit (MEA), as indicated by numeral 32 is indicated. The edge wall 14 of the MEA 32 comes with seals 38 provided to make a close contact with the adjacent elements 34 . 36 which are distributor plates in the present case 34 . 36 is. These distributor plates 34 . 36 are directly on the two outer surfaces of the MEA 32 put on and with the MEA 32 screwed or glued. Alternatively, they may also be potted, fused, overmoulded or encased.

Immediately adjacent to each electrode 20 . 22 is on the side of an associated distributor plate 34 first a protective plate 24 respectively. 26 made of graphite, which covers almost the entire electrode surface. The protective plates 24 . 26 serve to protect a copper plate in contact therewith 28 respectively. 30 which serves as a current collector plate against the electrolyte, which is a sulfuric acid solution.

On the opposite side of each distributor plate 34 . 36 In turn, a corresponding protective plate made of graphite and thus located in contact with copper plate is provided. The two current collector plates 28 . 30 each distributor plate 34 . 36 are internal through an electrical connection 42 connected with each other. Thus, the distribution plates 34 . 36 be used for serial interconnection of adjacent half-cells with each other.

In each distributor plate 34 . 36 are additional fluid channels 40 provided, which serve for the supply and removal of electrolytes and for direct introduction into the adjacent electrode layer or for direct removal from the adjacent electrode layer.

Based on 2a) to 2f) subsequently becomes a test cell 10 made up of two half-cells 16 . 18 was prepared, described in more detail.

In 2 are two half cells 16 . 18 shown, which are made of polypropylene. Every half cell 16 . 18 has a housing made of polypropylene 14 in, in the middle of a depression 44 is provided in the on the two ends of the half cell 16 . 18 each a sequence of holes 46 out through an internal distribution channel inside the housing 14 with an external hose connection 40 are connected.

In the middle of the case 14 is a depression 48 for receiving an associated protective plate 24a . 26a according to 2c) . 2d) and above a current collector plate 28a . 30a according to 2e) . 2f) intended. There is also a central hole 50 provided over which the relevant current collector plate made of copper can be electrically connected. After the respective protective plates and the current collector plates in the associated recesses 44 . 48 are inserted, then several layers of graphite paper are inserted and the second half-cell 18 on the first half cell 16 put on and both half cells 16 . 18 then by screws passing through the associated screw holes 47 be inserted, bolted together.

In 3 is a first embodiment of a composite, which is made by series connection of several cells, shown in cross section and in total with numeral 60 designated. In this composite 60 it is only the series connection of two cells 64 . 66 , It is understood that usually a larger number of cells is connected in series with each other.

In the present case is a central bipolar plate 62 provided by means of which adjacent half-cells 16 . 18 are connected directly in series with each other. On both sides of the bipolar plate 62 is each an electrode 20 arranged, followed by a membrane 11 , This is followed in each case by another electrode 22 at. In each case a current collector plate is in contact 28 . 30 made of copper, passing through the cell wall 12 led out to the outside.

The current flow thus passes over the one contact plate 28 through the membrane 11 , the bipolar plate 62 , the more membrane 11 and the other contact plate 30 , In contrast, the electrolyte according to the arrows 68 respectively. 69 at the edge of the half cells 16 . 18 introduced and extends substantially along the extension direction through the porous electrodes 20 . 22 ,

In 4 is another interconnection of a network consisting of two cells 64a . 66a represented and in total with the numeral 60a designated. The cells 64a . 66a are here as completely closed, from the cell wall 14 formed surrounded cells. There is no bipolar plate provided, instead the current collector plates 28 . 30 two adjacent half cells through the cell wall 14 led out to the outside and outside by means of a connection 70 , about using a rivet 72 , electrically connected.

In 5 is again a series connection of a network 60b using distribution plates 34 . 36 . 74 shown. The distributor plates 34 . 36 . 74 correspond to the previously based on 1 described distributor plates. Each distributor plate 34 . 36 . 74 has fluid connections 76 . 78 . 80 . 82 (See the distributor plate shown separately 74 ' ), which are formed for the supply of electrolyte directly into the region of an adjacent electrode or for the discharge of electrolyte from the electrode, as in the arrows 80 . 82 is indicated. The electrical interconnection of the adjacent cells via the distribution plates 34 . 36 . 74 each by an electrical connection between the opposing current collector plates 28 . 30 on the outsides of a respective distributor plate 34 . 36 . 74 , In this way, the respective outer distributor plate of the composite 60b the positive pole or the negative pole ready (cf. 83 . 84 ).

6 shows a composite 60c consisting of several serially interconnected cells using interposed bipolar plates 62 for serial connection.

Additionally are in 6 suitable distributor 85 . 86 for the supply of catholyte or anolyte laterally into the respective electrodes 22 respectively. 20 shown, as well as on the opposite side corresponding distribution lines 87 . 88 for the removal of the catholyte or anolyte from the electrodes 22 . 20 ,

To complete a redox flow battery, in addition, the corresponding container for receiving the catholyte and the anolyte and appropriate pumping devices should be added, as well as an external circuit through which the connection between the positive pole 83 and the negative pole 84 is closed.

In 7 is additionally shown schematically as a cell 10a between their two ends 12 . 13 into a series of sections 90 can be divided transversely. If the distance to be overcome for the particular electrolyte is too great due to the electrode in question, an excessively large pressure drop can be counteracted in this way and each section can be counteracted 90 be equipped with its own supply or discharge for the electrolyte in question.

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• WO 2011/075135 A1 [0003]
• EP 2626936 A1 [0029]

Claims (20)

Electrochemical cell, in particular for a redox flow battery, having a plastic cell wall ( 14 ) enclosing a cavity defined by an ion-conductive membrane ( 11 ) in two half cells ( 16 . 18 ), each having a first and a second end ( 12 . 13 ), at which fluid connections ( 40 . 76 . 78 . 80 . 82 . 85 . 86 ) are provided to flow through with an electrolyte, wherein the two half-cells ( 16 . 18 ) each flat electrodes ( 20 . 22 ) located between the first and second ends ( 12 . 13 ) parallel to the membrane ( 11 ), the electrodes ( 20 . 22 ) of porous graphite, in particular of one or more layers ( 21 ) of graphite paper, and wherein the fluid connections ( 40 . 76 . 78 . 80 . 82 . 85 . 86 ) at the first and second ends ( 12 . 13 ) of each half cell ( 16 . 18 ) for direct flow with electrolytes along the extension direction of the respective electrode ( 20 . 22 ) are formed. Cell according to Claim 1, in which the electrodes ( 20 . 22 ) each with current collectors ( 28 . 30 ), in particular in the form of current collector plates ( 28 . 30 ), stay in contact. Cell according to Claim 2, in which the current collectors ( 28 . 30 ) consist of a metal which is not resistant to the electrolyte, in particular of copper, and in each case by an acid-resistant protective layer ( 24 . 26 ) are protected from the electrolyte. Cell according to Claim 3, in which the protective layer ( 24 . 26 ) consists of graphite or a conductive plastic and is preferably plate-shaped. Cell according to one of the preceding claims, in which the individual layers of the cell consisting at least of the membrane ( 11 ), the first and second electrodes ( 20 . 22 ), and possibly current collectors ( 28 . 30 ) and plate-shaped protective layers ( 24 . 26 ), at least peripherally sealed with the plastic of the cell wall ( 14 ) are connected. A cell according to claim 5, wherein the individual layers of the cell ( 10 . 10a ) are pressed tightly together. A cell according to claim 5 or 6, wherein the individual layers of the cell ( 10 . 10a ) are at least peripherally connected to each other by a plastic laminate or are joined together by a plastic injection molding. Cell according to one of the preceding claims, in which at least one electrode ( 20 . 22 ) with a bipolar plate ( 62 ) connected to the serial interconnection of the relevant half cell ( 16 . 18 ) with a half-cell ( 16 . 18 ) of an adjacent cell ( 10 . 10a ) is trained. Cell according to Claim 8, in which the bipolar plate ( 62 ) consists of graphite, or consists of copper, which is each provided on the electrode side with an acid-resistant protective layer. Cell according to one of the preceding claims, in which the fluid connections ( 40 . 76 . 78 . 80 . 82 . 85 . 86 ) at the first and second ends ( 12 . 13 ) for distributing electrolyte through a plurality of holes ( 46 ), preferably in the form of a row of holes ( 46 ) or a perforated grid, into the half-cells ( 16 . 18 ). Cell according to one of the preceding claims, in which the fluid connections ( 40 . 76 . 78 . 80 . 82 . 85 . 86 ) at the current collectors ( 28 . 30 ), on the peripheral cell walls ( 12 ) or to bipolar plates ( 62 ) are formed. Cell according to one of the preceding claims, in which the electrodes ( 20 . 22 ) are electrochemically activated to the electrolytes, preferably are hydrophilicized. A cell according to any one of the preceding claims, wherein each half cell ( 16 . 18 ) between the first and second ends ( 12 . 13 ) into a plurality of sections ( 90 ) and each section ( 90 ) Has fluid connections for the supply and removal of electrolyte. Composite of a plurality of cells connected in series ( 10 . 10a ) according to one of the preceding claims, wherein the interconnection either via bipolar plates ( 62 ) between adjacent half cells or by external interconnections ( 70 ) outside the cells in the case of the use of current collectors ( 28 . 30 ) he follows. Composite of a plurality of cells connected in series ( 10 . 10a ) according to one of claims 1 to 13, in which between adjacent half-cells ( 16 . 18 ) Distribution plates ( 34 . 36 ) are arranged, at which fluid connections ( 40 ) are provided for electrolyte supply, wherein at the distributor plates ( 34 . 36 ) each of the two half-cells ( 16 . 18 ) associated current collectors ( 28 . 30 ) provided within the distributor plates ( 34 . 36 ) are electrically connected together. Method for producing a cell according to one of Claims 1 to 13, in which an ion-conducting membrane ( 11 ) and two flat, porous electrodes ( 20 . 22 ) are made of graphite, in particular of at least one layer of graphite paper, each one of the electrodes ( 20 . 22 ) on one side of the membrane ( 11 ) and the membrane ( 11 ) with the electrodes ( 20 . 22 ) at least peripherally to a membrane electrode unit ( 32 ) is laminated. The method of claim 16, wherein the membrane electrode assembly ( 32 ) edge seals ( 38 ) are applied to the other layers, in particular current collector ( 28 . 30 ), Protective plates ( 24 . 26 ) or bipolar plates ( 62 ). Method for producing a cell according to one of Claims 1 to 13, in which an ion-conducting membrane ( 11 ) and flat, porous electrodes ( 20 . 22 ) of graphite, in particular of at least one layer ( 21 ) of graphite paper, and possibly current collectors ( 28 . 30 ) and plate-like protective layers ( 24 . 26 ) are inserted into an injection mold, and are sprayed with plastic, such that the layers are at least peripherally connected to each other and sealed and the outside of a plastic wall ( 14 ) are enclosed. Method according to Claim 18, in which the individual layers ( 10 . 10a ) of the cell are firmly pressed together. Method according to one of Claims 16 to 19, in which the cell ( 10 . 10a ) subsequently with fluid lines ( 40 . 76 . 78 . 80 . 82 . 85 . 86 ), such that in each case one half-cell ( 16 . 18 ) of an anolyte and a half cell ( 16 . 18 ) can be flowed through by a catholyte.

Images