Storage element for a solid electrolyte battery

Abstract

A storage element for a solid electrolyte battery is provided, having a main member including a porous ceramic matrix in which particles that are made of a first metal and/or a metal oxide and jointly form a redox couple are embedded. The storage element further includes particles made of another metal and/or an associated metal oxide, the other metal being electrochemically more noble than the first metal.

Claims

1. A storage element for a solid electrolyte battery, comprising: a main element composed of a porous ceramic matrix comprising first particles embedded therein, the first particles comprising at least one of particles of a first metal and particles of a first metal oxide of a redox pair, wherein the storage element comprises further particles comprising at least one of particles of a further metal and particles of an associated metal oxide, wherein the further metal is more chemically noble than the first metal, wherein the proportion by volume of the first particles is more than 50% by volume of the solids volume of the storage element, and wherein the storage element comprises alternating layers of ceramic matrix with embedded first particles and layers of the further particles.

2. The storage element as claimed in claim 1, wherein the further metal has a different diffusion velocity than the first metal in an alloy of the first metal and the further metal.

3. The storage element as claimed in claim 1, wherein the storage element has a pore volume of less than 50% by volume of its total volume.

4. The storage element as claimed claim 1, wherein the first metal is Fe.

5. The storage element as claimed claim 1, wherein the further metal is Ni.

6. The storage element as claimed claim 1, wherein the ceramic matrix is an oxidic ceramic.

7. The storage element as claimed in claim 1, wherein the ceramic matrix is selected from the group consisting of (Y,Sc,Zr)O.sub.2, (Gd,Ce)O.sub.2, Al.sub.sO.sub.3, MgO, TiO.sub.2, and (La,Sr,Ca,Ba,Ce)(Fe,Ti,Cr,Ga,Co,Mn)O.sub.3.

8. The storage element as claimed in claim 1, wherein the first metal is selected from the group consisting of nickel, copper, silver, gold, platinum, and palladium.

9. A storage element for a solid electrolyte battery, comprising: a main element comprising a porous ceramic matrix comprising first particles embedded therein, the first particles comprising at least one of particles of a first metal and particles of a first metal oxide of a redox pair; and further particles comprising particles of a further metal, wherein the further metal is more chemically noble than the first metal; wherein the storage element comprises alternating layers of the porous ceramic matrix with the first particles and layers of the further particles.

10. A storage element for a solid electrolyte battery, comprising: a main element comprising a porous ceramic matrix comprising discrete spherical first particles embedded therein, the discrete spherical first particles comprising at least one of discrete spherical particles of a first metal and discrete spherical particles of a first metal oxide of a redox pair; and further discrete spherical particles comprising particles of a further metal, wherein the further metal is more chemically noble than the first metal, wherein the storage element comprises alternating layers of the porous ceramic matrix with the discrete spherical first particles and layers of the further discrete spherical particles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention are illustrated below with the aid of the drawing, in which:

(2) FIG. 1 shows a schematic section through an example of a storage element according to an embodiment of the invention with homogeneous and isotropic particle distribution;

(3) FIG. 2 shows a schematic section through a further example of a storage element according to an embodiment of the invention having a layer structure; and

(4) FIG. 3 shows a schematic section through a further example of a storage element according to an embodiment of the invention having a skeleton-like microstructure.

DETAILED DESCRIPTION OF INVENTION

(5) A storage element denoted overall by 10 for a solid electrolyte battery comprises a ceramic matrix 12 in which a first class of particles 14 of a metal or an associated metal oxide and also a second class of particles 16 of a further metal and/or an associated metal oxide are embedded.

(6) During charging operation of a solid electrolyte battery having such a storage element 10, a solid electrolyte fuel cell assigned to the storage element 10 is operated in the electrolysis mode, with the metal oxide particles 14 being reduced to the corresponding metal by means of the reducing agent formed. In discharging operation, the metal particles 14 are oxidized to the corresponding oxide again by means of oxygen ions, with the liberated energy being able to be taken off as electricity.

(7) To ensure a high storage capacity and good charging and discharging kinetics, the particles 14 of the metal or metal oxide have to have a large active surface area. However, during the oxidation process, the metal atoms of the particles 14 tend to diffuse in the direction of the increasing oxygen ion gradient. This leads to demixing of the microstructure of the storage element 10, as a result of which the active surface area of the particles 14 is reduced and the storage capacity and charging and discharging kinetics are thus correspondingly impaired.

(8) To avoid this, particles 16 of another metal and/or an associated metal oxide are additionally embedded in the ceramic matrix 12. This can, as shown in FIG. 1, occur in the form of a homogeneous and isotropic distribution. When the metal oxides of the particles 14 are reduced to the corresponding metal, these metal atoms can alloy with the metal of the particles 16. It is important here that the atoms of the metal particle 16 have a lower diffusion velocity than the atoms of the metal particles 14 in the alloy formed. Furthermore, it has to be ensured that the metal of the particles 16 has to be chemically more noble than the metal of the particles 14, so that the particles 16 do not undergo any reaction during the oxidation-reduction cycle.

(9) In practice, it is therefore advisable to use iron and iron oxides for the particles 14 and nickel for the particles 16. The ceramic matrix 12 can be any oxidic ceramic of main group or transition group elements, as long as the ceramic is redox-inert and thermally stable enough under the electrochemical operating conditions to survive operating temperatures of about 900 C. In the simplest case, it is possible to use aluminum oxide, magnesium oxide, zirconium oxide or the like, but the use of more complex mixed oxides, for example yttrium, scandium, zirconium mixed oxides, gadolinium, cerium mixed oxides, complex mixed oxides having a first metallic component from the group consisting of lanthanum, strontium, calcium, barium, cerium and a second metallic component from the group consisting of iron, titanium, chromium, gadolinium, cobalt, manganese, is also possible.

(10) As an alternative to the homogeneous and isotropic distribution of the particles 14, 16 in the matrix 12, more complex structures are also possible. FIG. 2 shows an alternative embodiment of the storage element 10, in which the storage element 10 is made up of alternating layers 18, 20. The layers 18 are formed by a ceramic matrix 12 in which only particles 14 of the metal or metal oxide which participates in the redox process are embedded. In contrast, the layers 20 consist exclusively of particles 16 of the alloy former. The layers 20 here form a diffusion barrier for the atoms of the particles 14, so that, here too, diffusion is countered, or rehomogenization during charging operation is made possible. Rehomogenization can in all cases be controlled in a targeted manner by means of the charging conditions selected, in particular by the choice of temperature, time and current.

(11) Finally, FIG. 3 shows a further embodiment of a storage element 10 according to an embodiment of the invention, in which the particles 14 of the metal-metal oxide system which participates in the redox process are homogeneously distributed in the ceramic matrix 12. Within the matrix 12, a skeleton structure 22 of particles 16 of the alloy former is also provided. Here too, an efficient diffusion barrier or an assisting structure for rehomogenization is formed, but, in contrast to a layer structure as per FIG. 2, this has no preferential direction.

(12) The production of such structures can be carried out, depending on the microstructure of the storage element 10, using a number of ceramic production methods, for example pressing, extrusion, tape casting and subsequent stacking of the sheets and the like, so that reliable mass production is ensured.