EP2681343A2

EP2681343A2 - Method for the production of a porous element, and cell of a rechargeable oxide battery

Info

Publication number: EP2681343A2
Application number: EP12713692.7A
Authority: EP
Inventors: Ines Becker; Horst Greiner
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2011-04-27
Filing date: 2012-04-03
Publication date: 2014-01-08
Also published as: US9806327B2; WO2012146465A2; WO2012146465A3; US20140113201A1; DE102011017594A1

Abstract

The invention relates to a method for producing a porous element (2), comprising the following steps: - producing a powdery metal-ceramic composite material (4) comprising a metal matrix (6) and a ceramic portion (8) amounting to less than 25 percent by volume; - at least partially oxidizing the metal matrix (6) to obtain a metal oxide (10); - grinding the metal-ceramic composite material (4); - mixing the ground metal-ceramic composite material (4) with powdery ceramic supporting particles (12) to obtain a metal-ceramic/ceramic mixture (14); - shaping the metal-ceramic/ceramic mixture (14) into the porous element (2). The invention also relates to the preferable use of said porous element (2) as an energy storage medium in a battery.

Description

description

Method for producing a porous body and cell of a rechargeable oxide battery

To store surplus energy, such as when operating renewable energy sources, which can not be absorbed by the power grid, the so-called Rechargeable Oxide Batteries (ROB) provide a good way to safely store larger amounts of energy.

It is common to ROBs that an energy storage medium is needed to meet a variety of physical parameters. These include in particular a high number of charge and discharge cycles, it has been found that in particular the porosity of the storage medium as well as its mechanical stability are essential criteria. The ^¬ time be spent comparable powder beds or slurry or pre-sintered compacts of a metal oxide as a storage media. Although these storage media, it is possible to achieve a high loading of the cells with the energy storage medium, but the disadvantage is in all previously known embodiments of the storage medium, in particular, that at a higher number of discharge and charge cycles, the porosity decreases because of the Temperature stress the Me ^¬ tallpartikel sinter or merge with each other. As the number of cycles increases, therefore, there is an aging process of the energy storage unit, which forces the unit to be replaced soon.

The object of the invention is therefore to provide a method for producing a porous body, which serves as a storage medium for an energy storage unit. In any case, the object is to provide such an energy storage unit or a so-called cell of such a battery. The object is achieved in a method for producing a porous body according to claim 1, in a use of a porous body according to claim 10 and in a cell of a rechargeable oxide battery according to claim 11.

The method according to claim 1 for the production of a porous body in this case comprises the following steps:

First, a powdery Metallkeramikverbundwerk- represented fabric comprising both a metal matrix as well as egg ^¬ NEN ceramic part, wherein the volume fraction of Kera ^¬ Mika part is preferably less than 25%. This metal is ceramic composite diert now at least partially aufoxi-, so that the metal matrix is umgewan ^¬ punched to a metal oxide. According to strict terminology, this metal-ceramic composite material treated in this way would have to be referred to as ceramic composite material, since in the ideal case the entire metallic matrix is oxidized. Since in a proper application, as will be explained below, this func tional acting metal-ceramic composite material is cyclically oxidized and reduced, this material is referred to as Me ^¬ tallkeramikverbundwerkstoff further, it should be important for the Be spelling and for understanding, so is ex ^¬ plicitly the adjective placed before oxidized, is to recognize that it is in this process step to the oxidised th metal-ceramic composite material.

In a further process step, the oxidized Me ^¬ tallkeramikverbundwerkstoff optionally ground who ^¬ the, after which it is mixed with a powdery ceramic material, said powdered ceramic Materi ^¬ al hereinafter referred to as support particles, as this term describes its mode of action. The mixture thus obtained between the oxidized metal-ceramic composite material and the ceramic support particles will be referred to as a metal-ceramic / Ke ^¬ Ramik mixture. This mixture becomes shaping placed in a forming tool and the porous body is generated therefrom.

Compared to the prior art, is pressed in the previously pure metal, and from this, a porous body is prepared, the porous body of the invention differs as an energy store for a particular ROB in two Merkma ^¬ len. First, the metal which serves as the actual energy ^¬ memory, since it is cyclically oxidized and reduced, with a ceramic powder to a so-called ODS (Oxide Dis ^¬ persion Strengthened) reinforced. This ODS metal-ceramic composite already has a higher dimensional stability than is the case with a conventional metal particle. Such an ODS-cermet composite material is thus able to withstand many oxidation and reduction cycles mechanically without having to accept greater loss of strength. Furthermore, the density difference that exists between the metal and its oxide, which occurs cyclically in the oxidation and reduction processes, is also compensated to a considerable extent by the reinforcing ceramic component.

A second essential point of the porous body according to the invention, which is produced by the process according to the invention, is that the particles of the metal-ceramic composite material do not lie directly on top of each other, but that they are supported by ceramic support particles. The support particles also prevents sintering or fusion of the particles of the metal-ceramic composite material, since it is always possible to maintain a uniform porosity of the porous body over a large number of charging and discharging cycles.

In an advantageous embodiment of the invention, the metal matrix of the metal-ceramic composite material is iron or an iron alloy. Furthermore, the ceramic component consists in particular of an oxide ceramic z. B. in a very advantageous embodiment in a Zir konoxidkeramik, which may in particular be reinforced by yttrium or scandium doping again.

There are various possible and expedient methods for producing the powder-shaped metal-ceramic composite material; a method wherein the metal matrix, for example the iron powder, with the ceramic component, for example likewise a zirconium oxide ceramic, which may optionally be doped with scandium or yttrium , are alloyed together by the action of mechanical energy. Here, attritors or oscillating disk mills are especially suitable as equipment where the metal particles are repeatedly deformed micro ^¬ scopically by the action of mechanical energy, and the brittle ceramic particles constituting the ceramic content, be kneaded into the metal matrix. The term alloying is understood here that microscopic particles of the ceramic component to be enclosed by the Me ^¬ tallmatrix. It can come at the interfaces for the exchange of atoms of the individual material components, but it does not necessarily mean that this must be a chemical link between the materials. Rather, in the metal-ceramic composite material finely dispersed, the ceramic fraction is present in the larger metallic matrix grains.

In a preferred embodiment of the invention, the ceramic support particles, which are mixed with the metal-ceramic composite material, larger than the particles of the metal-ceramic composite material, which is always based on an average particle size, which results from a particle size distribution.

To produce a specific porosity of the porous body, it may also be expedient to add an additional filler, which is later removed, if appropriate by oxidation, from the porous body and selectively leaves pores. The particle size of the ceramic component in the metal-ceramic composite material is preferably in a range between 10 nm and 50 nm. Particularly small particles have proved to be good for a ^¬ Sonders reinforcement of the metal matrix. Since these particles are technically complex to produce and are optionally not produce inexpensive ge ^¬, it may also be desirable that the particle size of Keramikan ^¬ partly between 20 nm and 200 nm or between 20 nm and

500 nm. In this information, the particle size is always resorted to a broad particle size distribution, where there is also a significant number of particles in the peripheral areas of this distribution, which is why when specifying such distribution sizes is always assumed that 80% of the particles in the desired spectrum the particle size distribution are located.

These distribution assumptions also apply to the particle size distribution of the metal-ceramic composite, these particles are preferably larger by a factor of 10 to 100 than the ceramic component, which means that in an advantageous embodiment, at least 80% of the particles of the metal-ceramic composite material Size of 1 μπι and 50 μπι on ^¬ wise. The ceramic support particles should in turn preferably be larger by about one order of magnitude than the particles of the metal-ceramic composite material, it is expedient that a particle distribution of 80% of the ceramic support particles is preferably in a size between 10 μπι and 100 μπι.

Another aspect of the invention is a use of a porous body made by a method of the preceding claims as an energy storage medium in a rechargeable oxide battery (ROB).

Yet another part of the invention is a cell of a rechargeable oxide battery which is a positive electrode, a solid state electrolyte and at least one base plate for a negative electrode. The base plate for a negative electrode has recesses in which a porous body is disposed. The porous body is configured DER art in that it comprises on the one hand particles of a metal-ceramic composite material having a metal matrix and a ceramic portion and having the other hand, ceramic Stützpar ^¬ Tikel. The ceramic support particles act as already described for Erläu ^¬ esterification of the inventive method, in such a way that the particles of the metal-ceramic composite will not fuse together or sinter together so that a predetermined porosity of the porous body even after a plurality of Charging and discharging cycles of the cell is maintained.

Further embodiments of the invention and further features will be explained in more detail with reference to the following figures. These are merely exemplary Ausgestal tion forms of the invention, the no limitation of

Protection scope of the independent claims.

Showing:

Figure 1 is a schematic representation of a cell for a

ROB in loading and unloading condition,

FIG. 2 is an exploded view of the layered structure of a cell for a ROB;

Figure 3 is a schematic representation of a mixture of the

Metal matrix and ceramic component,

FIG. 4 shows the mixture from FIG. 3 after a mechanical alloy, with the metal-ceramic composite material now being produced,

Figure 5 of the oxidized metal-ceramic composite, Figure 6 of the metal-ceramic composite in oxidized

Mold mixed with ceramic support particles, Figure 7 is a schematic representation of the pressing method for

Pressing of the porous body,

Figure 8 is a schematic representation of the microstructure of the porous body.

Based on the figure 1, the operation of an ROB should be attributed ^¬ are roughly as far as this is necessary for the following description of the invention. A common structure, an ROB, is that at a positive electrode 20, a process gas, in particular air, is blown through an air inlet device 36, wherein oxygen is withdrawn from the air, in the form of oxygen ions through a solid electrolyte 22 to a negative electrode 26 passes. There it is discharged or charged, oxidized or reduced depending on the operating status. If now at the negative electrode of a solid layer to be oxidized or reducing material, frequently in the form of iron is used here vorlie ^¬ gene, the charging capacity of the battery would be quickly he ^¬ exhausted. For this reason, it is expedient to use a porous body 2 on the negative electrode as energy storage medium, which contains the functionally effective oxidizable Materi ^¬ al, ie in an appropriate form the iron.

A gaseous at operating condition of the battery redox couple, for example, H ₂ / H ₂ O, the oxygen through pores ^¬ channels of the porous body to the oxidizable material, ie the metal is present in the form of a metal-ceramic composite in the porous body present, transported. Depending ^¬ on whether a charging or discharging is present, the metal is tall or oxidized metal oxide or reduced, and the required for this oxygen through the gaseous redox couple H ₂ / H ₂ O supplied or to the solid electrolyte transported back (shuttle mechanism). The advantage of iron as the oxidizable material is ^¬ in that it comprises at its oxidation process is approximately the same Ru ^¬ hespannung of about IV as the redox couple H ₂ / H ₂ O. An object of the invention is to design this porous body in such a way that it is as mechanically stable as possible and can withstand mechanically even after a large number of charging and discharging cycles, which in turn mean oxidation or reduction of the energy storage medium.

FIG. 2 shows a somewhat more detailed structure of a cell, an ROB, in the form of an exploded view. The arrangement of the electrodes is shown in Figure 2 with respect to the figure 1 in reverse order, the positive electrode 20 is shown here above, which is designed in the form of a base plate 30 for the positive electrode 20. In this embodiment of the ROB, this supply device 36 and outlet device 38 for the process gas in particular air. In principle, however, it is also possible to operate an ROB in the closed state of the positive electrode, which will not be discussed further here in this example. On the base plate 30 of the positive electrode 20, a glass frame is arranged, on which in turn the solid electrolyte 22 is disposed, it is followed by another glass frame 32 and a contact grid 34, which is made for example of nickel forth ^¬ . Finally, now follows a base plate 24 of the nega ^¬ tive electrode 26, wherein the base plate 24 recesses 28, in which the porous body 2 is embedded, which is the energy storage medium of the cell 24 of the ROB.

For the preparation of the porous body 2, a suitable method is used, which is explained in more detail with reference to FIGS. 3 to 8. FIG. 3 shows a mixture which, on the one hand, comprises a metal matrix 6, this metal particle of the metal matrix 6 being iron particles. On the other hand, this mixture comprises a ceramic ^component 8, wherein a possible particle size distribution of the particles of the ceramic component 8 is preferably between 10 nm and 100 nm. The particles of the metal matrix 6 are preferably in

Range between 1 μπι and 50 μπι. The mixture is then placed in a device through which the metal particles 6 and the ceramic part 8 are mechanically alloyed. Here, in particular sondere suitable attritor in which, for example, Kera ^¬ mikkugeln the powder by mechanical action as often split and kneading, so that the ceramic powder be kneaded in the Me ^¬ tallmatrixpartikel 6 8 or alloyed. There is now so-called ODS material, which can be prepared in principle in other ways, but the method with the mechanical alloy has been found to be useful. The metal-ceramic composite material 4 thus obtained is oxidized in a next method step according to FIG. 5, the metal-ceramic composite material 4 now being present in oxidized form. Among other things, the oxidation process has the meaning that the metal-ceramic composite material is now more brittle and can be ground to a suitable particle size distribution by a grinding process, not illustrated here in the drawing. In particular μπι the size distribution between 1 and 50 μπι has arises as appropriate for the white ^¬ direct use of the metal-ceramic composite herausge-. If appropriate, this can be done by targeted sieving operations after the grinding process.

The powder thus obtained metal-ceramic composite material 4 in oxidized form is mixed with a further ceramic powder, wherein this is a powder of ceramic j ^¬'s supporting particles 12th FIG. 6 schematically shows the size comparison between the particles of the metal-ceramic composite material 4, which are usually between 1 μm and 50 μm, and the ceramic support particles 12. The ceramic support particles have in particular a particle size distribution between 10 μπι and 100 μπι. All data are broad ranges, and depending on the desired pore structure and absolute particle size, even narrower particle size distributions for all components described can be achieved by simple sieving techniques. In principle, it may also be advantageous to add fillers 16, which are burned out by the shaping of the porous body 2 is optionally, and ensure an even better poro ^¬ intensity. Furthermore, still follows according to FIG 7, a shape of the metal-ceramic / ceramic mixture 14 of Figure 6 to the porous body 2. As a molding method, in particular offer uniaxial pressing method, kaltiso- static pressing method (KIP) or hot isostatic pressing ^¬ process (HIP) at. It may also be expedient to sign the pressed porous body to a presintering process of about 800 ° C., so that the ceramic support particles 12 form first sintering necks with each other, whereby the strength of the porous body is increased. The porous Kör ^¬ per 2 is now inserted as described in Figure 2 in recesses 28 of the base plate 30 of the positive electrode 24, where it serves as an energy storage medium.

Claims

claims

1. A process for producing a porous body (2) comprises the following steps:

producing a powdered metal-ceramic composite material (4) comprising a metal matrix (6) and a ceramic component (8),

at least partially oxidizing the metal matrix (6) to form a metal oxide (10),

mixing the ground metal-ceramic composite material (4) with pulverulent ceramic support particles (12) to form a metal-ceramic / ceramic mixture (14),

- Shaping of the metal-ceramic / ceramic mixture (14) to the porous body (2).

2. The method according to claim 1, characterized in that the metal matrix (6) comprises iron or an iron alloy.

3. The method according to claim 1 or 2, characterized in that as a ceramic part (8) of the metal-ceramic composite material (4) a doped, in particular with yttrium or scandium doped zirconia ceramic is used.

4. The method according to any one of claims 1 to 3, characterized in that the metal matrix (6) and the ceramic part (8) are mixed in powder form and alloyed together by the action of mechanical energy.

5. The method according to any one of the preceding claims, characterized in that the ceramic support particles (12) which are mixed with the metal-ceramic composite material (4) have a larger average particle size than the Parti ^¬ angle of the metal-ceramic composite.

6. The method according to any one of the preceding claims, characterized in that the metal-ceramic / ceramic mixture (14) a filler (10) is added for later formation of pores (18).

7. The method according to any one of the preceding claims, characterized in that at least 80% of the particles of Kera ^¬ mikanteils (8) in the metal-ceramic composite body (4) has a size between 10 nm and 50 nm, preferably between 20 nm and

200 nm, and more preferably between 20 nm and 500 nm.

8. The method according to any one of the preceding claims, characterized in that at least 80% of the particles of the metal-ceramic composite material (4) has a size between 1 μπι and

50 μπι have.

9. The method according to any one of the preceding claims, characterized in that at least 80% of the particles of Kerami ^¬'s support particles (12) have a size between 10 μπι and 100 μπι.

10. Use of a porous body produced by a method according to one of claims 1 to 9 as Energiespei ^¬ chermedium in a rechargeable oxide battery.

A cell of a rechargeable oxide battery comprising a positive electrode (20), a solid state electrolyte (22) and a negative electrode base plate (24), the negative electrode base plate (24) having recesses (28 ), in which a porous body (2) is arranged, wherein the porous body (2) is designed such that it on the one hand particles of a metal-ceramic composite ^¬ material (4) with a metal matrix (6) and a ceramic component ( 8) and on the other hand has ceramic support particles (12).

12. A cell according to claim 11, characterized in that the particles of the metal-ceramic composite material (4) of the porous body (2) has a particle size distribution, after which min. at least 80% of the particles have a diameter between 1 μπι and 50 μπι.

13. Cell according to claim 11 or 12, characterized in that the ceramic support particles (12) have a particle size distribution, according to which at least 80% of the particles have a diameter between 10 μπι and 100 μπι.

14. A cell according to any one of claims 11 to 13, characterized in that a ceramic part (8) of the metal-ceramic composite material has a particle size, after which min ^¬ least 80% of the particles have a diameter between 10 nm and 500 nm.