WO2014000984A1

WO2014000984A1 - Electrical energy store

Info

Publication number: WO2014000984A1
Application number: PCT/EP2013/060482
Authority: WO
Inventors: Harald Landes; Carsten Schuh; Thomas Soller
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-06-29
Filing date: 2013-05-22
Publication date: 2014-01-03
Also published as: DE102012211322A1

Abstract

The invention relates to an electrical energy store comprising a storage cell (4), which in turn comprises an air electrode (6), which is connected to air channels in an air supply device (20), and a storage electrode (10), wherein the storage electrode (10) adjoins a storage structure (9), wherein electrical contacts rest on the storage electrode (10), characterized in that the contacts are in the form of an array of separate contact pins (12).

Description

description

The invention relates to an electrical energy store according to claim 1.

For storage of surplus electricity, which is generated, for example, in the generation of electricity by renewable energy sources or by power plants, which are operated in the range of optimum efficiency and for which there is no temporary demand in the grid, various technical alternatives are used. One of them is the rechargeable metal air battery (Rechargeable Oxide Battery, ROB). ROBs are usually operated at temperatures between 600 ° C and 900 ° C. Here, oxygen, which is supplied to a (positive) air electrode of the electric cell is converted into oxygen ions, transported by a solid electrolyte and brought to the opposite negative electrode (discharge) or transported from the negative electrode via the solid electrolyte to the air side (charging). At the negative electrode (depending on whether it is charged or discharged), a reduction or oxidation reaction takes place with a gaseous redox couple, whereby the oxygen taken up or released by the gaseous redox couple is converted by diffusion of the components of the redox couple to a porous redox couple , So gas-permeable and also oxidizable and reducible storage medium is transferred. Due to the high temperatures required for the transport of oxygen in the ceramic electrolyte for this process, the choice of materials for the cell materials used and the construction of the cell parts and the arrangement of the storage medium is very complex. In particular, the individual components suffer after several redox cycles, which are operated at the said operating temperatures. Furthermore, for economic use, it is always desirable to increase the storage density per storage cell or per unit volume of the energy store. It is therefore an object of the invention to provide an electrical energy store based on a ROB which, compared to the prior art, has a storage density which is improved with high mechanical stability.

The solution of the problem consists in an electrical energy storage device with a memory cell having the features of claim 1. Here, the memory cell of the electrical energy storage on an air electrode, which is in communication with air channels of an air supply device and it further comprises a storage electrode, wherein the two electrodes usually separated from each other by a solid electrolyte. A memory structure adjoins the storage electrode, electrical contacts being applied to the storage electrode. The invention is characterized in that the contacts are designed in the form of a field of separate contact pins. This array of separate pins reduces the total surface area of contactors while increasing the volume available to the active storage material, and thus the ratio of the volume of active storage material to the total volume of the electrical energy storage. Thus, the energy density, ie the amount of energy per unit volume of the electrical energy storage is increased. This also increases the power density per unit volume of the energy storage, which at the same time leads to a reduction in the cost per stored amount of energy or per stored power.

In an advantageous embodiment of the invention, it is expedient that the memory structure per memory cell is designed as a coherent component, which in turn has recesses through which the contact pins extend. When mounting the electrical energy storage thus the memory structure is inserted with their recesses on the pins. Alternatively, self-service Of course, smaller units of the memory structure can be cut in such a way that they can be arranged around the individual contacts, which would, however, mean a higher assembly outlay.

Furthermore, it may be expedient to arrange an additional contact network between the contact pins and the storage electrode, by means of which a better outflow of the electrons onto the contact pins can take place and by the deformability of which a mechanical relief of local pressure peaks is provided.

It has been found that the diameter of the contact pins is advantageously between 2 mm and 7 mm, more preferably between 3 mm and 4 mm. In this case, the cross-section of the contact pins can assume different expedient geometries. Here, in particular, a circular, but also an oval or rectangular or polygonal cross-section is expedient. The cross section of the contact pins is particularly relevant for the production of the contact pins per se and the recess of the memory structure.

The distance between the contact pins is preferably between 10 mm and 30 mm, more preferably between 17 mm and 21 mm. This distance of the pins is small enough that an undisturbed flow of electrons can be made through the contacts, but at the same time it is large enough to provide as much volume for the memory structure available.

In a further advantageous embodiment of the invention, the contact pins on rounded heads, which rest on the storage electrode. Such a rivet shape similar design may be useful to reduce the mechanical pressure load of the stack structure or the pressure load on the substantially consisting of a ceramic material electrode structure. In addition, due to this rounded head shape manufacturing tolerances the memory structure or the other stack components are compensated. Furthermore, a metal net located between the contact pins and the storage electrode (eg of nickel) helps to limit local pressure forces.

Furthermore, it is expedient to construct the electrical energy store from a plurality of different memory cells, which are combined in total in a stack. In this case, it is expedient to use an interconnector plate which contains air ducts on one side of the air and has contact pins on an opposite side, which is referred to as the memory side.

The current path in an energy store with a stack which in turn has interconnector plates preferably takes place as follows: First, the current passes through a volume material of a first interconnector plate, continues to flow via contact webs between the air channels of the first interconnector plate to which the air electrode abuts another station is the solid state electrolyte followed by the storage electrode. From here, the electrons flow along the current path into the contact pins of a second interconnector plate and finally into the bulk material of the second interconnector plate. Depending on how many stacks follow each other, the described current path is repeated several times to outer electrodes, the electrons are derived or introduced.

Further features and further advantageous embodiments of the invention are explained in more detail with reference to the following figures. These are merely exemplary embodiments that do not limit the scope of protection. Showing:

FIG. 1 shows a schematic representation of a cell of a rechargeable oxide battery, FIG. 2 is an exploded view of a stack viewed from above, FIG. 3 is an exploded view of the stack from FIG. 2 viewed from below,

4 shows a cross section through a memory cell with current path,

FIG. 5 shows a plan view of an interconnector plate on the memory side,

FIG. 6 shows a cross section of the interconnector plate from FIG. 5,

Figure 7 is a plan view of a memory structure and

FIG. 8 shows a cross section through the storage structure according to FIG. 7.

The mode of operation of a rechargeable oxide battery (ROB) will first of all be described schematically with reference to FIG. 1 insofar as this is necessary for the present description of the invention. A common structure of a ROB is that at a positive electrode 6, which is also referred to as an air electrode, a process gas, in particular air, is blown through a gas supply 20, wherein the

Discharging (circuit on the right side of the screen) the air is deprived of oxygen. The oxygen passes in the form of oxygen ions 0 ^{2 "} through a voltage applied to the positive electrode 6 solid electrolyte 7, to a negative

Electrode 10. This is connected via a gaseous redox pair, for example a hydrogen-steam mixture, to the porous storage medium in the channel structure. Would at the negative electrode 10, a dense layer of the active Storage material present, the charging capacity of the battery would be exhausted quickly.

For this reason, it is expedient to use a storage structure 9 of porous material on the negative electrode 10 as the energy storage medium, which contains a functionally effective oxidizable material as an active storage material, preferably in the form of iron and / or iron oxide. By means of a gaseous redox couple, for example H ₂ / H ₂ O, in the operating state of the battery, the oxygen ions transported by the solid electrolyte 7, after being discharged at the negative electrode in the form of water vapor through pore channels of the porous storage structure 9, which is the active Storage material includes transported. Depending on whether a discharge or charging process is present, the metal or the metal oxide (iron / iron oxide) is oxidized or reduced and the oxygen required for this is supplied by the gaseous redox couple H ₂ / H ₂ O or transported back to the solid electrolyte. This mechanism of

Oxygen transport via a redox couple is referred to as a shuttle mechanism.

The advantage of the iron as an oxidizable material, ie as an active storage material in the storage structure 9, is that it has approximately the same rest voltage of approximately 1 V in its oxidation process, such as the redox couple H ₂ / H ₂ O at a partial pressure ratio of 1, otherwise, there is an increased resistance to oxygen transport through the diffusing components of this redox couple.

The diffusion of the oxygen ions through the solid electrolyte 7 requires a high operating temperature of 600 to 900 ° C of the described ROB, but also for the optimal composition of the redox pair H ₂ / H ₂ 0 in equilibrium with the storage material, this temperature range is advantageous. Here, not only is the structure of the electrodes 6 and 10 and the electrolyte 7 a high thermal load out but also the memory structure 9, which comprises the active storage material.

An advantage of the ROB is that it can be extended almost modularly by its smallest unit, namely the memory cell. Thus, a small battery for stationary home use as well as a large-scale system for storing the energy of a

Power plant.

Several of the memory cells 4 described in FIG. 1 are combined to form a so-called stack 2. The structure of a stack 2 and the arrangement of the memory cells 4 in the stack 2 is illustrated by the exploded views in FIG. 2 and FIG. FIG. 2 shows the structure of a stack, which is viewed from above and is assembled in the order from bottom to top. The stack 2 initially comprises a bottom plate 24, which is optionally composed of a plurality of individual plates, which in turn have functional structures and depressions, for example, for air guidance. This composition of individual plates, which is not described here in detail, to the bottom plate 24, for example, by a brazing process.

The base plate 24 has an air supply 20 and an air discharge 22. As already described, 24 non-visible channels for the supply of air are integrated here by the composition of individual plates in the bottom plate. Furthermore, the bottom plate 24 centering pin 29, through which now more

Components of the stack 2 centered can be applied. The next layer is followed by an electrode-electrolyte unit 25, which comprises, in particular, the already described positive electrode 6, the solid state electrolyte 7 and the storage electrode 10. This is a self-supporting ceramic structure, to which the individual functional areas such as the electrodes or the solid electrolyte are applied in a thin-film process. As a further layer follows a seal 26, which consists for example of a slightly above the operating temperature melting glass frit, which then seals the individual plates of the stack 2 at the operating temperatures of the battery. The next following plate is a so-called inner connector plate 27, which has two functionally effective sides. On its lower side 34, which is visible in FIG. 3, the air supply channels (air ducts 18) (not shown here in detail) are located on the positive electrode 6 of FIG

Memory cell 4 boundaries. On the upper side (memory side 32) has the interconnector plate 27 (not shown in FIG. 2) contact pins 12 which penetrate the memory structure 9 and are introduced into this. The upper side of the interconnector plate 27 in FIG. 2 has the same

Structure on how the top of the base plate 24. Again, the contact pins 12 are provided for insertion into the storage medium 9. This side with the contact pins 12 is in each case facing the storage electrode 10 of the storage cell 4.

By way of example, FIG. 2 shows a further level of the sequence of electrode-electrolyte unit 25, seal 26 under a cover plate 28 for the overall construction of the stack 2. In principle, of course, a number of further levels of these components can follow, so that a stack usually has between 10 and more layers of memory cells 4. In FIG. 3, the same stack 2, which is described in FIG. 2, is shown in the opposite direction. In Figure 3, one looks from below on the base plate 24, it follows again the electrode-electrolyte unit 25 and the seal 26. The interconnector plate 27 is now also visible from below, in which case the view is directed to the air side 34, the Air electrode faces (air side 34). In this example, four separate areas on the air side 34 are shown on the interconnector plate a subdivision into four individual memory cells 4 per stack level correspond (this division into four memory cells is to be regarded as purely exemplary). The memory cell 4 is thus composed in this example of a quarter of the surface of the respective interconnector plate 27 and the base plate 24 and the cover plate 28 together. Furthermore, the respective cell 4 is formed by a sequence of the respective air side 34, seal 26, electrode-electrolyte unit 25 and again a quarter of the memory side 32 of the base plate 24 and the interconnector plate 27. In this case, the air side 34 is supplied with air by the process gas by means of a stack-internal air distribution device (also called a manifold), which is not shown in more detail here, and which encompasses several levels of the stack. The supply of the memory side with the gaseous redox couple takes place in this example in that the memory pages of the interconnector plates are open to the environment and the stack is in a container which is filled with water vapor / hydrogen mixture.

FIG. 4 shows a cross-section through a memory cell 4, by means of which a current path 14 of the current flowing through the stack is exemplarily illustrated by the dashed line 14. The cell 4, viewed from the top to the bottom, begins with an interconnector plate 27, which has contact webs 19 on its air side, through which in turn the air channels 18 are formed. On the surfaces of the contact webs 19 is applied to the electrode-electrolyte unit 25, the positive electrode (air electrode 6) the solid electrolyte 7 and the negative

Electrode, called storage electrode 10 includes. On the storage electrode 10 are in turn contact pins 12, through which the current is derived and further led to the bulk material 36 of the interconnector plate 27.

FIG. 5 shows the plan view of an interconnector plate 27, with the memory page 32 being looked at. The memory page 32 has the contact pins 12, the protrude from the interconnector plate 27, on. The contact pins 12 can be produced, for example, by milling out the material from the surface of the interconnector plate 27. In principle, however, it is also possible to achieve this by a method, for example by welding,

Apply surfacing or brazing. Also, a chemical or electrochemical selective etching of the material on the memory side 32 of the interconnector plate 27 may be appropriate.

FIG. 6 shows a cross section through the interconnector plate from FIG. 5.

FIG. 7 shows a memory structure 9 with recesses 16. The recesses 16 are designed such that the memory structure 9 can be inserted directly into the memory side 32 of the interconnector plate 27 from FIG. 5 and the contact pins 12 run in the recesses 16. In this case, the contact pins 12 rest closely against the material of the memory structure 9, but there is a certain amount of play, so that the memory structure 9 can be pushed onto the contact pins 12 without tilting. It may be appropriate that the contact pins are slightly longer than the thickness of the storage disk, so that between the storage electrode and the storage disk or between the storage electrode and the

Full material of the interconnector plate remains a gap along which a lighter gas exchange of the gaseous Redoxpaa- res can take place along the stack level. FIG. 8 shows a cross section through the storage structure 9 from FIG.

A production of the storage structure can be effected, for example, by a uniaxial or isostatic pressing process of the storage material. A film casting process and an optional lamination of several films one above the other may also be expedient. Subsequently, in the green state or after sintering, the solidification of the Green body is used, the recesses 16 are introduced by drilling, punching, erosion, milling and laser, water or particle beam cutting. Likewise, it may be appropriate to the memory structure by near-net shape manufacturing such as by an extrusion process or by a

Injection molding already with the recess 16 represent.

It has been found to be expedient that the diameter of the contact pins between 2 mm and 7 mm, preferably between see 2 mm and 4 mm. Furthermore, the distance between the pins should be between 10 mm and 30 mm. Preferably, the distance should be between 17 mm and 21 mm. The arrangement of the contact pins 12 need not necessarily take place in regular Cartesian form, as shown by way of example in FIG. In this case, other arrangement patterns may be expedient.

The distance and the diameter of the contact pins 12 essentially result from the specific resistances which are to be found in the cell 4 along the current path 14 on the memory side. By contacting a critical resistance R _kr i _{t must} not be exceeded, the

one e.g. equal to 10% of the resistance of the ideally contacted electrode-electrolyte unit 25 can set. The contrario contribution of the contacting consists of 3 parts:

1. The effective resistance contribution caused by the passage of current through the interface between the contact pin and the storage electrode or the contact network placed thereon:

mean

R _K i the characteristic of this contact related to the actual contact surface

D is the diameter of the contact surface

L is the diameter of the electrode area supplied by this contact. 2. The effective resistance contribution caused by the voltage drop along the contact pin:

R ₂ = p _P h (L / D) ²

in which

_P p the resistivity of the pin material,

h means the length of the pin.

3. The effective resistance of Stromeinschnürung in the storage electrode or additionally covered by the contact network storage electrode:

R ₃ = γ RL ²

In which

γ «K [ln (L / D) - 3/4 + (D / L) ² (ln (L / D) + 1/4)]

R means the effective sheet resistance of the storage electrode, which, when the contact network rests only on the contact surfaces of the contact pins is given by p / d where

p the specific electronic resistance of the storage electrode

d means their thickness.

Limits for the design of L, D and h then result from each of the partial resistances remaining smaller than the critical resistance:

Ri <Rkrit,

R2 <Rkrit /

R3 <Rkrit /

R4 <Rkrit ·

Claims

claims

An electrical energy store having a storage cell (4) which in turn comprises an air electrode (6) in communication with air ducts (18) of an air supply device (20) and a storage electrode (10), the storage electrode (10) being connected to a storage structure (9) adjacent, wherein abut on the storage electrode (10) electrical contacts, characterized in that the contacts in the form of a field of separate contact pins (12) are configured.

2. Energy storage according to claim 1, characterized in that the memory structure (9) has recess (16) through which the contact pins (12) extend.

3. Energy storage according to claim 1 or 2, characterized in that between the contact pins (12) and the storage electrode (10) a contact network is arranged.

4. Energy store according to one of the preceding claims, characterized in that the diameter of the contact pins (12) is between 2 mm and 7 mm, preferably between 2 mm and 4 mm.

5. Energy store according to one of the preceding claims, characterized in that the contact pins (12) has a distance between 10 mm and 30 mm, preferably between 17 mm and 21 mm.

6. Energy store according to one of the preceding claims, characterized in that an interconnector plate (27) is provided, which on an air side (34) of the interconnector plate (27), the air ducts (18) are mounted and on the opposite side, a memory page (32 ), the contact pins (12) are arranged.

7. Energy storage according to claim 6, characterized in that a current path (14) passes through the following component components:

a bulk material (36) of a first interconnector plate (27),

- Contact webs (19) between the air channels (18) of the first interconnector plate (27),

the air electrode (6),

a solid electrolyte (7),

the contact pins (12 ') of a second interconnector plate (27'),

- The bulk material (36 ') of the second interconnector plate (27').

8. Energy store according to one of the preceding claims, characterized in that the contact pins (12) have rounded heads.