Patent Application
20070051631
This application is the U.S. National Stage of International Application No. PCT/EP2004/000785, filed Apr. 15, 2004 and claims the benefit thereof. The International Application claims the benefits of German application No. 10323883.2, filed May 26, 2003, both applications are incorporated by reference herein in their entirety.
The invention relates to an electrochemical battery, especially a fuel cell battery or electrolytic cell battery comprising several electrolytic electrode units, a number of cooling cards for respectively cooling at least one the electrolytic electrode units and at least one pressure chamber which can be impinged by a pressure independently of the media supply of the electrolytic electrode units for creating a contact pressure between components of the electrochemical battery that adjoin the pressure chamber. This type of electrochemical battery is for example known from EP 0 591 800 B1.
EP 0 591 800 B1 discloses a fuel cell battery, which features in each case two interconnected plates arranged in parallel to each other and forming an intermediate cavity between two electrolytic electrode units arranged in parallel to each other and each consisting of an anode, a Polymer Electrolyte Membrane (PEM) and a cathode. Between the plates and the electrodes of the two adjacent electrolytic electrode units are embodied gas or fluid spaces for introducing operating media such as hydrogen or oxygen to the electrolytic electrode units.
One way in which the cavity between the two plates arranged in parallel to each other can be used is to feed in or to extract the cooling medium. In this case the two plates form a cooling card for cooling the two electrolytic electrode units. Instead of being used for inserting and removing the cooling medium, the cavity can also be used as a pressurized chamber for setting up a pressure pad which exerts pressure on the adjacent components and thereby creates a contact pressure between these adjacent components, to guarantee a good current flow between these two components for example. On the other hand such a pressure pad can be used as an element for compensate for tolerances in the dimensions of the adjacent components. However, when the cooling card is used as a pressure pad the cooling of the fuel cell block is reduced.
A battery known from DE 27 29 640 C3 consisting of a number of electrochemical cells, especially fuel elements, features electrolytic electrode units arranged in parallel to each other, between which contact elements are arranged for tapping off power. These contact elements feature a cavity for feeding in a pressurized medium and are thus embodied as pressure pads for pressing together the overall arrangement. This enables an even contact pressure to be created between adjacent components and thereby for example the current flow between these components improved. No cooling of the electrolytic electrode units is provided here.
Cooling cards are additionally generally known, from WO 02/50953A2 for example. A cooling card disclosed in this application is embodied as a composite printed circuit board with two plates which form a cavity between them. This cavity features inlet and outlet channels and has cooling water or also heating water flowing through it during the operation of the fuel cells.
The object of the invention is to develop an electrochemical battery of the type mentioned at the start that combines a simple and compact structure stands and outstandingly good cooling of the electrolytic electrode units and good contact pressure between adjoining components.
In accordance with the invention this object is achieved by the claims. Advantageous embodiments of the invention are the object of the dependent claims.
An electrochemical battery In this case is taken to mean a fuel cell battery as well as a battery comprising electrolytic cells.
In accordance with the invention the at least one pressure chamber is adjacent to at least one of the cooling cards and is at least partly delimited by this cooling card. A cooling card in this case is taken to mean any type of welded plate or plate formed in any other way which forms a cavity for a cooling medium. For example it includes double plates which lie on top of one another and are joined together along their edges to seal against each other. The cooling cards can include openings for accepting and emitting cooling media. To reduce the transfer resistance to adjacent components a cooling card can be provided additionally with a contact plate and/or contact foil on its surface.
The invention thus departs from the path previously followed of forming a pressure pad by applying pressure to the cavity of a cooling card. Instead a cooling card is used for forming a pressure chamber located outside the cooling card. The cooling card can thus continue to be supplied with the cooling medium and enable electrolytic electrode units to be cooled, while a contact pressure between adjacent parts can be created by the pressure area. The use of cooling cards to construct the pressure chamber makes the battery stand out by virtue of its small number of different parts and also a simple and compact construction.
If the cooling card is directly adjacent to an electrolytic electrode unit and is in contact with this unit electrically, it serves to draw current from this electrolytic electrode unit as well as to cool it. As well as the current collector element which contacts the electrolytic electrode unit, in this case the cooling card, making flat contact with the unit, the transfer resistance between the electrolytic electrode unit and the current collector element is also of significance. As a rule the transfer resistance drops as the contact pressure increases. Unless even contact pressure is exerted on the surface of the electrolytic electrode unit, cross currents occur from areas with high transfer resistance to areas with low transfer resistance. These types of cross currents flowing through poorly conducting materials such as carbon paper, catalyzer layers, carbon-plastic composites or poorly conducting sheet metal causes a voltage drop and thereby loss of efficiency. With the aid of the pressure chamber an even pressure can now be applied to the entire cooling card, an even contact pressure created between the cooling card and the electrolytic electrode unit and cross currents on the surface of the electrolytic electrode unit avoided.
In accordance with an advantageous embodiment of the invention the pressure chamber is arranged between two of the cooling cards and at least partly delimited by these two cooling cards. With a stack arrangement of alternating electrolytic electrode units and cooling plates in the electrochemical battery the pressure chamber can thus be obtained in a simple manner by removing an electrolytic electrode unit from the stack arrangement between two cooling cards and using the empty space thus produced as a pressure chamber.
In accordance with a further advantageous embodiment of the invention the pressure chamber is arranged between one of the cooling cards and a pole plate and at least partly delimited by the cooling card and the pole plate. A pole plate in this case is taken to mean a plate which terminates a cell stack which is used for collecting current. Here too components already present in the battery are thus used for forming the pressure chamber and a more simple construction of the battery is thereby guaranteed.
To make it possible for current to flow through the pressure chamber a current transfer part is arranged within the pressure chamber, preferably adjoining the at least one cooling card. If the medium provided for creating internal pressure in the pressure chamber differs from the media with which the electrolytic electrode unit is operated, corrosive effects on the electrically conducting elements arranged within the pressure chamber for connection of two cooling cards or for connection of a cooling card with a pole plate can in principle be excluded.
Since the distances between the borders of the pressure chamber can change when pressure is applied, the current transfer part should make it possible to compensate for these distances. This is possible by the current transfer part being embodied as a spring element.
Within a block of cells stacked to form a battery a current flows in the normal case in an overall normal manner to the individual generally plate-shaped cells. The current transferred from cell to cell should in this case flow on the shortest possible path to keep the power dissipation low. Advantageously the spring element therefore features at least one sheet with a number of spring tongues bent outwards from the plane of the sheet. Via the spring tongues the current can flow on relatively short paths from one the two cooling plates at least partly delimiting the pressure chamber or between the cooling plate and pole plate delimiting the pressure chamber.
The spring tongues preferably enclose form acute angle with an adjacent cooling card in each case and thus make it possible to compensate for the gap within a wide area in the battery by comparison with the thicknesses of the flat components of the electrolytic electrode units and also an electrical connection divided up into a plurality of individual current paths between adjacent electrolytic electrode units or between an electrolytic electrode unit and a pole plate.
Preferably the at least one cooling card features a contact plate on its side facing the pressure chamber for reducing the transfer resistance to the current transfer part.
In accordance with a preferred development the contact plate features a conductive layer applied to a base layer, with the specific electrical conductivity of the conductive layer exceeding the specific electrical conductivity of the base layer The current collected on the surface of the cooling card and passed on to a further cooling card or a pole plate is typically not drawn off over the entire surface but only at individual points or areas of the cooling card. The conductive layer on the cooling card minimizes cross currents caused by poorly conducting materials and concentrates them into the material that conducts well, namely the conducting layer, so that at most a small power dissipation occurs.
The conductive layer is preferably applied in the form of an electrical coating or a foil to the basic layer. In each case is good electrical contact between the conductive layer and the at least slightly flexible base layer is established.
The thickness of the conductive layer, especially in the case in which it is embodied as an electrically created coating, is preferably less than the thickness of the base layer, in which case, because of the higher specific conductivity of the conductive layer, its absolute electrical conductivity can be greater than the absolute electrical conductivity of the base layer. In each case the contact plate, especially in the form of a combination of base layer and conductive layer, is far more conductive than the adjoining cooling card.
Within a cell stack of a battery it is sufficient to arrange a pressure chamber or a pressure pad consisting of two cooling cards and an intermediate pressure chamber between just a part of the individual cells or electrolytic electrode units. Typically the number of the electrolytic electrode units within the battery amounts to at least double the number of pressure pads, typically being ten times this number for example. The dimensions of the battery are thus at least not significantly increased by the pressure pads.
The advantage of invention lies especially in the fact that a pressure pad is created within a cell stack of an electrochemical battery which serves both as a geometrical compensation element, and also as a cooling element. Through spring elements arranged in the corrosion-protected pressure chamber a low-loss current conductance between adjacent electrolytic electrode units or between an electrolytic electrode unit and a pole plate is possible.
An exemplary embodiment of the invention is explained in more detail below with reference to a drawing.
a-c show cross-sectional views of an exemplary embodiment of a cooling card and of a contact plate respectively, and
a-b show especially advantageous embodiments of a spring element.
Parts which correspond to each other are shown by the same reference symbols in all the Figures.
FIG 1 shows sections in a simplified cross sectional diagram of an electrochemical battery 1 in the form of a fuel cell battery or a fuel cell block also referred to for short as a fuel cell or fuel cell stack. The battery 1 comprises a first pole plate 2, a second pole plate not shown, arranged at a distance from the first plate and parallel to it, as well as a number of electrolytic electrode units 3 arranged between these plates. Between two of the electrolytic electrode units 3, which are also referred to as membrane-electrolytic electrode units (ME) and comprise carbon papers, catalyzer layers and membranes of the fuel cell 1, as well as between an outside electrolytic electrode unit 3 and the adjacent pole plate 2 a cooling card 4 is arranged. The cooling cards 4 also used as bipolar plates are formed from thin metal sheets which can be easily deformed because of the material strength and geometrical structure and adapt to differences in height of the adjacent components, i.e. the membrane-electrolytic electrode units 3 including gas chambers not shown in any greater detail or the pole plates 2.
in the section of the battery 1 shown in
The distance between the opposite contact plates 7 of the cooling cards 4 in the pressure pad 5 thus varies, this distance being a function of the tolerances of the components which are arranged between two pressure pads 5, the spring characteristics of these components, provided they can be deformed by pressure and the level of the pressure which the medium in the pressure pad 5 exerts. The cooling cards 4 collect electrical current from the electrolytic electrode units 3 over their surface.
For transfer of the current through the geometrically variable pressure chamber 6 a spring element 8 shown in more detail in
The contact plate 7 can consist entirely of a material with high electrical conductivity, such as gold for example. A more cost-effective solution is possible in accordance with
Three exemplary embodiments of cooling cards 4 and contact plates 7 interacting with them, which are each suitable for an arrangement in accordance with
The cooling card 4 shown in
In the exemplary embodiment in accordance with
The exemplary embodiment shown in
a and 5b show two especially advantageous embodiments of a current transfer part embodied as a spring element. The spring element is embodied as a contact spring sheet 21 and features a metal sheet 22 with spring tongues 23 protruding from the plane of the sheet 28, with two spring tongues 23a, 23b being arranged and formed in each case such that is a force is exerted on the tongue tips 25 in a direction perpendicular to the plane of the sheet 28 the bending moments M created by each of the spring tongues in the plane of the sheet 28 at least partly cancel each other out.
Through the at least part mutual cancelation of the bending moments created in the sheet plane 28 a twisting of the connecting post 32 between the two spring tongues 23a, 23b can be largely avoided and the connecting post can be kept small in this way. This enables a large number of spring tongues to be arranged in the plane of the sheet, so that a high number of contacts of the contact spring sheet and as a result short paths for as loss-free as possible current conduction through the battery are made possible. In addition smaller connecting posts lead to an improvement in the spring characteristics of the contact spring sheet.
At the same time, as a result of the reduced bending moments, bending tensions on the foot points 27a,27b of the spring tongues 23a, 23b can be reduced and thus plastic and irreversible deformations avoided. This means that-the height to which the spring tongues can be bent and thereby also the spring path of the contact spring sheet 21 are increased.
To this end the two spring tongues 23a, 23b have a symmetrical arrangement and/or form around the axis in relation to an axis 24 running at right angles to the plane of the sheet 28. Preferably the spring tongues 23a, 23b are each in the form of an arc. In the embodiment in accordance with
If the contact spring tongue 21 is pressed together between two components, the tips 25 of the spring tongues 23a, 23b glide over the surface of the component on which they are lying. To prevent them sticking there as a result of possibly their own sharp edges or on intended surface structures of the component to be contacted, the tips of the tongues 25 are bent over.
Preferably the current transfer part is enclosed by a frame, especially a frame of which the external form and/or external dimensions are identical with those of an electrolyte or membrane component of the battery. In this case the frame can be used to bring a dimensional tuning between sealing elements which seal the membrane to the same proportions. The pressure chamber can be created in a simple way by replacing an electrolytic electrode unit in a cell stack by a current transfer part enclosed by a frame such as for example a contact spring sheet 21. The frame can be made from a preferably elastic material for this purpose. If the adjoining components feature an elastic sealing material on their contact surfaces, the frame can also be hard. Preferably the frame is then made of a metal, e.g. in the form of a metal foil.
To increase the spring path the spring element can also a sheet with spring tongues bent outwards on both sides of the sheet from the plane of the sheet. Alternatively for increasing the spring path two contact spring sheets can be laid against each other.
| Number | Date | Country | Kind |
|---|---|---|---|
| 103 23 883.2 | May 2003 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE04/00785 | 4/15/2004 | WO | 11/9/2006 |
