WO2021228526A1 - Cell stack with heatable end plate - Google Patents

Abstract

The present invention relates to a cell stack (1), in particular a fuel cell stack. The cell stack (1) comprises several individual cells (4) which are mounted between two end plates (2, 3). At least one heat channel (15) is integrated into at least one of the end plates (2, 3).

Description

description

Title:

Cell stack with heatable end plate

The present invention relates to a cell stack with a heatable end plate.

State of the art

In fuel cell systems, the oxidizing agent oxygen from the ambient air is generally used to react in the fuel cell - in the individual cells - with hydrogen to form water and thus to deliver electrical power through electrochemical conversion.

From US5789091 A a fuel cell stack is known in which a large number of individual cells are clamped between two end plates by means of tensioning straps.

A fuel cell stack is known from WO19081866 A1 in which a large number of individual cells are clamped between two end plates, a heating plate being arranged on one of the end plates.

Due to the tensioning forces required, the end plates are usually very stable and thus also made comparatively massive, so that they have a very large heat capacity compared to the relatively thin individual cells, especially if the end plates are made of metal.

The object of the present invention is to improve the thermal management of the cell stack, in particular for a cold start load case. Disclosure of the invention

For this purpose, the cell stack comprises a plurality of individual cells, the individual cells being arranged between two end plates. At least one heat channel is integrated in at least one of the end plates. At least one heating channel is preferably integrated in each of the two end plates. The cell stack is advantageously designed as a fuel cell stack; however, the cell stack can also be designed, for example, as a battery cell stack or as an electrolysis cell stack.

In this context, a heat channel is to be understood in particular as a channel which contains a heat transfer fluid or a heating medium and which is guided essentially within the cell stack, that is to say has no connection to, for example, an external heat exchanger.

The end plate can be heated comparatively quickly through the heat channel, in particular in the case of a cold start of the cell stack, and the end plate is therefore designed to be heatable. The comparatively large heat capacity of the end plate, which slows down the heating of the neighboring individual cells and virtually represents a cold pole for them, can thus be counteracted.

The at least one heat channel can be completely integrated into the end plate. However, it can also be formed between the end plate and a current collecting plate. The current collecting plate limits the heat channel in the direction of the individual cells, preferably by means of a flat surface. The current collecting plate also serves as a current tap - for example via a current collector formed on the current collecting plate - for the entire cell stack. In this design, the functions of current consumption and heat channel limitation are therefore combined in the current collecting plate. The production of the heat channels can be carried out comparatively easily, for example by milling into the end plate, the milled heat channel then being covered with the current collecting plate. In advantageous developments, a heating cartridge is also integrated in the end plate. The heating cartridge is thermally coupled to the at least one heating channel. As a result, the heat channel or the walls of the heat channel, which are formed on the end plate, can be supplied with heat energy.

The heating cartridge converts electrical energy into thermal energy. In the event of maintenance, the heating cartridge is much easier to replace than, for example, a heating foil inserted between the individual cells and the end plate. If you want to replace a heating foil, the tension in the cell stack must be released, so that components of the individual cells - for example polymer electrolyte membranes and gas diffusion layers - can no longer be reused. The heating cartridge, on the other hand, can be used in an easily accessible place and exchanged while maintaining the tension in the cell stack. The heat channels, in turn, can also be routed to places that are difficult to access.

At least one fluid channel is preferably formed in the end plate. The at least one heat channel is formed adjacent to the fluid channel. As a result, when a heated heating medium flows through it, for example, the heat channel is able to heat the fluid channel - and thus also the fluid flowing through the fluid channel. The end plate preferably has six fluid channels, each with an inlet and an outlet for the fuel, for the oxidizing agent and for a cooling medium. In preferred developments, the cooling medium and heating medium can be identical, in particular if the at least one heat channel is fluidically connected to a cooling circuit of the cell stack. Depending on the ambient temperature and the temperature of the cell stack, the heating medium / cooling medium then has a heating or cooling effect on the cell stack or the other fluids flowing therein.

In advantageous embodiments, the at least one heating channel is filled with a heating medium or a heating fluid. As a result, heat can advantageously be transported via convection, particularly advantageously via forced convection. The end plate is heated even faster. In preferred developments, at least portions of the heating medium undergo a phase transition during a cold start phase of the cell stack, for example in a temperature window between -40 ° C and 100 ° C. Particularly preferably, the heating medium runs through a phase change from vapor to liquid, as a result of which it can give off an amount of latent heat to the end plate. The latent heat of a phase transition is usually very large, so that a corresponding heating effect due to condensation of the heating medium on the walls of the heating channel is particularly large.

In advantageous embodiments, the at least one heat channel is fluidically connected to a cooling circuit of the cell stack. At least one of the fluid channels is then preferably integrated into the cooling circuit. The cooling circuit can then function both as a cooling circuit and as a heating circuit - in particular during a cold start phase.

The individual cells are preferably clamped between the two end plates by means of at least one clamping device. Forces therefore act on the end plates which would cause an undesired appreciable deformation of the end plates if the end plates were not made correspondingly stiff. However, it is precisely this rigid design that means that the end plates act like cold poles on the neighboring individual cells in the event of a cold start. Accordingly, it is advantageous if heat channels are integrated into such end plates in order to accelerate the warming up of the end plates or the fluids flowing through them.

The invention additionally comprises a motor vehicle with the cell stack according to the invention designed as a fuel cell stack. The individual cells are therefore designed as fuel cells. The motor vehicle has the same advantages mentioned for the cell stack, in particular a rapid cold start phase, through which the motor vehicle can be quickly brought to its rated output. Furthermore, simple maintenance, in particular the easily accessible replacement of the heating cartridge, is an advantage for mobile applications such as a motor vehicle. Embodiments of the invention are shown in the drawings and explained in more detail in the description below. It shows:

FIG. 1 schematically shows a cell stack known from the prior art.

FIG. 2 schematically shows a further cell stack known from the prior art.

FIG. 3 shows a section through a cell stack according to the invention, only the essential areas being shown.

FIG. 4 shows section A-A of FIG. 3.

FIG. 1 shows schematically a cell stack 1 designed as a fuel cell stack, as is known from US5789091A. The fuel cell stack 1 has a plurality of individual cells 4 designed as fuel cells, which are clamped between two end plates 2, 3. The tensioning takes place by means of two tensioning devices 10 designed as tensioning straps, which extend tightly around the end plates 2, 3 and the individual cells 4, so that the fuel cell stack 1 is held and secured in its assembled state.

FIG. 2 schematically shows a cell stack 1 designed as a fuel cell stack, as is known from WO19081866 A1. This cell stack 1 is also designed as a fuel cell stack and has a plurality of individual cells 4 which are clamped between two end plates 2, 3. The clamping devices 10 are designed as tie rods or as screws. Between the end plates 2, 3 and the individual cells 4 there is arranged a current collecting plate 5, 6, which in turn each have a current collector 6a; the current collector of the upper current collecting plate 5 is covered due to the perspective view and is therefore not shown. The cell stack 1 of the embodiment in FIG. 2 also has a heating foil 20 which is attached to the upper end plate 2.

According to the invention, as an alternative to the heating film 20, at least one heat channel is now integrated into the end plate 2, 3.

For this purpose, FIG. 3 shows a section through a cell stack 1, only the essential areas being shown. In the detail of FIG. 3, only the upper end plate 2 can be seen, but an analogous design is also possible for the lower end plate 3.

Between the end plate 2 and the individual cells 4 connected in series, the current collecting plate 5 is arranged with the current collector 5a for current tapping. In the case of a metallic end plate 2, an electrical insulation film is also arranged between the current collecting plate 5 and the end plate 2. In the embodiment of FIG. 3, however, the end plate 2 preferably consists of an electrically non-conductive material, preferably of a polymer composite component, so that an insulation film is not required. The polymer composite component can definitely be reinforced with metal, so that it behaves as stiffly as possible under the forces of the clamping device 10 (not shown).

In the section of FIG. 3, two fluid channels 7 are shown. However, the cell stack 1 often has six fluid channels 7, each for supplying and removing the fuel - for example hydrogen - and the oxidizing agent - for example oxygen - and optionally for supplying and removing a cooling medium into the individual cells 4, which are shown in FIG Figure 3 are perpendicular to the cutting plane in the depth of the sketch and are therefore not visible. In the end plate 2, heat channels 15 are integrated, which, among other things, are also preferably arranged surrounding the fluid channels 7 or adjacent to them. As a result, one or more fluids flowing through the fluid channels 7 into the individual cells 4 can be heated in a targeted manner for a cold start phase of the cell stack 1. The individual cells 4 can accordingly be operated quickly at an optimal operating temperature. Furthermore, any ice crystals can be quickly thawed at ambient temperatures below 0 ° C. in the fluid channels 7 and further also in the individual cells 4. By heating via the heat channels 15, the wall temperature of at least some fluid channels 7 can also be increased in such a way that no ice crystals can form on the walls during a cold start.

In the embodiment of FIG. 3, a heating cartridge 16 is also integrated into the end plate 2. The heating cartridge 16 is thermally coupled to the heating channels 15 so that thermal energy can be released from the heating cartridge 16 to the heating channels 15 and further through the walls 15a of the heating channels 15 to the end plate 2 and the fluid channels 7. To this end, the heating cartridge 16 preferably converts electrical energy into thermal energy, for example by means of electrical resistors.

The heat channels 15 are bordered by the associated walls 15 a of the end plate 2. The heat channels 15 are advantageously filled with a heating medium which has a high thermal conductivity. The heating medium is particularly preferably designed in such a way that an energy transport essentially only takes place in a specific temperature working window, that is to say the heat or temperature range. the energy transport can optionally be limited to a certain temperature working window by a phase transition of the heating medium. For example, by evaporation of the heating medium, a large amount of heat can be absorbed by the heating cartridge 16 in its vicinity via the adjacent walls 15a of the heat channels 15 and released at another location, preferably in the vicinity of the fluid channels 7, to the end plate 2 by condensation. Outside of the phase transition, the heat is then only transported via heat conduction.

The heat channels 15 can be designed as heat pipes, for example. The heat pipes or the associated walls 15a can be angled, straight, flat, round, designed as a separate part or integrated.

FIG. 4 shows the section AA of FIG. 3. The end plate 2 has six fluid channels 7, each with an inlet and outlet for the fuel, the oxidizing agent and the cooling medium. The heat channels 15 are adjacent to the fluid channels 7 formed in order to be able to heat the fluids - that is, fuel, oxidizing agent and cooling medium. Thus, not only the end plate 2 is heated, but also - at least in part - the fluids flowing through the fluid channels 7.

The high heat capacity of the end plates 2, 3 means that, when starting, in particular at low ambient temperatures, the end plates 2, 3 act like cold poles above all on the individual cells 4 arranged close to them. The outer individual cells 4 of the cell stack 1 thus reach operating temperature more slowly than the inner individual cells 4. The heating of the end plates 2, 3 and also the heating of the fluids flowing through the fluid channels 7 counteract this effect. In the ideal case, the heating of the end plates 2, 3 by means of the heating cartridges 16 and the heating channels 15 leads to rapid, uniform heating of the individual cells 4 that is homogeneous over the entire cell stack 1.

If, on the other hand, end plates 2, 3 made of plastic are used, then these end plates 2, 3 are again thermally well insulated, so that the end plate 2, 3, including its fluid channels 7, can be poorly heated in the event of a cold start. Here, too, end plates 2, 3 with corresponding heat channels 15 are advantageous, in particular if these are arranged adjacent to the fluid channels 7, so that the fluids flowing into the individual cells 4 can be preheated.

In general, the heat channels 15 can be formed completely in the end plate 2, 3, as shown for example in FIG. 3, or only partially limited by the end plate 2, 3 and partially by a further component such as the current collecting plate 5.

Claims

Expectations 1. Cell stack (1) with several individual cells (4), the individual cells (4) being arranged between two end plates (2, 3), characterized in that at least one heat channel (15) in at least one of the end plates (2, 3) is integrated. 2. Cell stack (1) according to claim 1, characterized in that a heating cartridge (16) is also integrated in the end plate (2, 3), the heating cartridge (16) being thermally coupled to the at least one heating channel (15). 3. Cell stack (1) according to claim 1 or 2, characterized in that at least one fluid channel (7) is formed in the end plate (2, 3), the at least one heat channel (15) being formed adjacent to the fluid channel (7). 4. cell stack (1) according to one of claims 1 to 3, characterized in that the at least one heat channel (15) is filled with a heating medium. 5. cell stack (1) according to claim 4, characterized in that at least portions of the heating medium undergo a phase transition during a cold start phase of the cell stack (1). 6. cell stack (1) according to any one of the preceding claims, characterized in that the at least one heat channel (15) is fluidically connected to a cooling circuit of the cell stack (1). 7. cell stack (1) according to any one of the preceding claims characterized in that the individual cells (4) are clamped between the two end plates (2, 3) by means of at least one clamping device (10). 8. cell stack (1) according to any one of the preceding claims, characterized in that the at least one heat channel (15) is formed between the end plate (2, 3) and a current collecting plate (5). 9. Motor vehicle with a cell stack designed as a fuel cell stack (1) according to one of the preceding claims.