Storage element

Abstract

A storage element for a solid-electrolyte battery is provided, having a main body which is composed of a porous matrix of sintered ceramic particles, and also having a redox system which is composed of a first metal and/or at least one oxide of the first metal, wherein a basic composition of the storage element comprises at least one further oxide from the group comprising Y2O3, MgO, Gd2O3, WO3, ZnO, MnO which is suitable for forming an oxidic mixed phase with the first metal and/or the at least one oxide of the first metal.

Claims

1. A storage element for a solid electrolyte battery, comprising a main element composed of a porous matrix of sintered ceramic particles and a redox system composed of a first metal and/or at least one oxide of the first metal, wherein a base composition of the storage element comprises at least one further oxide from the group consisting of Y.sub.2O.sub.3, MgO, Gd.sub.2O.sub.3, WO.sub.3, ZnO, and MnO which is suitable for forming an oxidic mixed phase with the first metal and/or the at least one oxide of the first metal, and wherein the at least one further oxide and/or the oxidic mixed phase are/is distributed inhomogeneously in the main element of the storage element.

2. The storage element as claimed in claim 1, wherein the first metal and/or the at least one oxide of the first metal is embedded in the form of particles in the matrix of the main element.

3. The storage element as claimed in claim 2, wherein the at least one further oxide is embedded in the form of particles of the at least one further oxide and/or the oxidic mixed phase in the matrix of the main element.

4. The storage element as claimed in claim 2, wherein the particles of the first metal and/or the at least one oxide of the first metal make up a proportion by volume of more than 50% by volume of the main element.

5. The storage element as claimed in claim 3, wherein the particles of the at least one further oxide and/or the oxidic mixed phase make up a proportion by volume of less than 50% by volume of the main element.

6. The storage element as claimed in claim 2, wherein the main element has a proportion of pores of less than 50% by volume.

7. The storage element as claimed in claim 1, wherein the first metal and/or the at least one oxide of the first metal is embedded in the form of particles which additionally contain at least one further oxide and/or the oxidic mixed phase in the matrix of the main element.

8. The storage element as claimed in claim 7, wherein the particles which additionally contain the at least one further oxide and/or the oxidic mixed phase make up a proportion by volume of more than 50% by volume of the main element.

9. The storage element as claimed in claim 7, wherein the main element has a proportion of pores of less than 50% by volume.

10. The storage element as claimed in claim 1, wherein the ceramic matrix comprises an oxidic compound of at least one main group metal and/or transition group metal, wherein the oxidic compound consists of a (Y,Sc,Zr)O.sub.2, (Gd,Ce)O.sub.2, Al.sub.2O.sub.3, MgO, TiO.sub.2 or (La,Sr,Ca,Ce)(Fe,Ti,Cr,Ga,Co)O.sub.3-based material.

11. The storage element as claimed in claim 1, wherein the at least one further oxide and/or the oxidic mixed phase forms a support skeleton in the form of a microstructure penetrating all through, within the main element.

12. A storage element for a solid electrolyte battery, comprising a main element composed of a porous matrix of sintered ceramic particles, the ceramic matrix comprising an oxidic compound of at least one main group metal and/or transition group metal, and a redox system composed of a first metal and/or at least one oxide of the first metal, wherein a base composition of the storage element comprises at least one further oxide from the group consisting of Y.sub.2O.sub.3, MgO, Gd.sub.2O.sub.3, WO.sub.3, ZnO, and MnO which is suitable for forming an oxidic mixed phase with the first metal and/or the at least one oxide of the first metal, and wherein the at least one further oxide and/or the oxidic mixed phase is/are arranged in the form of barrier layers in the main element, between which layers which are at least predominantly free of the at least one further oxide and/or the oxidic mixed phase are located.

13. The storage element as claimed in claim 12, wherein the at least one further oxide and/or the oxidic mixed phase forms a support skeleton.

14. The storage element as claimed in claim 12, wherein the particles of the first metal and/or the at least one oxide of the first metal make up a proportion by volume of more than 50% by volume of the main element.

15. The storage element as claimed in claim 12, wherein the at least one further oxide is embedded in the form of particles of the at least one further oxide and/or the oxidic mixed phase in the matrix of the main element, and wherein the particles of the at least one further oxide and/or the oxidic mixed phase make up a proportion by volume of less than 50% by volume of the main element.

Description

DETAILED DESCRIPTION OF INVENTION

(1) Embodiments are illustrated below with the aid of working examples.

(2) To achieve efficient energy storage, new types of rechargeable solid electrolyte batteries having ceramic main elements derived from a solid oxide fuel cell, for example a zirconium dioxide electrolyte layer, and also oxide ceramics as cathode and anode are being developed at present. Metal/metal oxide pairs such as Fe/Fe.sub.xO.sub.y or Ni/NiO preferably serve as central redox elements for this purpose. There is the fundamental problem of very effectively exploiting the theoretical storage capacities and achieving largely constant discharging characteristics in potentiostatic or galvanostatic operation. The long-term stability also has to be ensured both under charging-discharging cycling and in standby operation.

(3) Known storage materials display distinct degradation of the store over time in charging-discharging cycles, which is attributable to separation of iron from the matrix material, for example zirconium oxide. The demixing of the storage structure is attributable to migration of the cationic iron in the direction of the oxygen source during the oxidation process and leads to disadvantageous sintering or agglomerate formation of the storage material and thus to a continuous decrease in the storage capacity.

(4) In order to overcome this problem, iron diffusion in the direction of the oxygen source is prevented by binding the iron to a complex iron compound. The use of Y.sub.3Fe.sub.5O.sub.12, Fe.sub.xMg.sub.1-xO, Gd.sub.3Fe.sub.5O.sub.12, Fe.sub.2WO.sub.6, (Zn,Fe.sup.2+)WO.sub.4, (Zn,Mn.sup.2+,Fe.sup.2+) (Fe.sup.3+,Mn.sup.3+).sub.2O.sub.4 is particularly advantageous for this purpose.

(5) Two variants of binding the iron are possible here.

(6) The storage element can, in one variant, comprise the redox-active storage material S, i.e. iron/iron oxide, a ceramic matrix material M and an oxide compound O which can react with the storage material S to form one of the abovementioned complex oxide phases and is configured as a skeleton structure. During the discharging process, i.e. during the course of the oxidation process, mass flow of the storage material S occurring in the direction of the oxygen gradient is countered by the oxide of iron reacting with the oxide compounds O to form a new phase and thus being bound to the skeleton structure.

(7) The storage structure in this case comprises a redox-active storage material S having a proportion by volume X.sub.S of more than 50% by volume, an oxide compound having a proportion by volume x.sub.O of less than 50% by volume, a proportion of pores x.sub.P of less than 50% by volume and optionally one or more ceramic matrix materials M having a proportion by volume of x.sub.m=100-x.sub.S-x.sub.O-x.sub.P.

(8) In the case of an iron-based store, S is one or more optionally doped oxide-dispersion-strengthened iron oxides such as FeO, Fe.sub.3O.sub.4, Fe.sub.2O.sub.3 and/or metallic iron. As oxide compound, use is made of either one of the abovementioned compositions, which may likewise be doped or ODS-modified, or individual oxides from among the compounds listed, for example Y.sub.2O.sub.3, MgO, Gd.sub.2O.sub.3, WO.sub.3, ZnO or MnO. As ceramic matrix material, it is possible to employ all oxidic compounds of the main group metals and transition group metals, in particular (Y,Sc,Zr)O.sub.2, (Gd,Ce)O.sub.2, Al.sub.2O.sub.3, MgOTiO.sub.2 and (La,Sr,Ca,Ce)(Fe,Ti,Cr,Ga,Co)O.sub.3-based materials

(9) As an alternative thereto, the redox-active storage material S.sub.O can be present not as iron oxide and/or metallic iron in the storage element but instead as fundamental constituent of an iron-rich oxide compound of the abovementioned type. Here too, no iron diffusion in the direction of the oxygen source occurs during the discharging process since the iron remains attached to the oxide compound. A further advantage of this variant is that a higher volumetric iron content than in binary iron oxides can sometimes be achieved.

(10) In this case, the storage structure comprises the redox-active storage material S.sub.O, having a proportion by volume x.sub.S of more than 0% by volume, a proportion of pores x.sub.P of less than 50% by volume and optionally one or more ceramic matrix materials M having a proportion by volume x.sub.M=100-x.sub.SO-x.sub.P. In the specific case of an iron-based store, S.sub.O is one of the following compounds: Y.sub.3Fe.sub.5O.sub.12, Fe.sub.xMg.sub.1-xO, Fe.sub.2O.sub.3+Gd.sub.3Fe.sub.5O.sub.12, Fe.sub.2O.sub.3+Fe.sub.2WO.sub.6, (Zn,Fe.sup.2+)WO.sub.4, (Zn,Mn.sup.2+,Fe.sup.2+)(Fe.sup.3+, Mn.sup.3+).sub.2O.sub.4. Here too, compounds suitable for the ceramic matrix materials are all oxidic compounds of the main group metals and the transition group metals, in particular likewise the abovementioned materials groups.

(11) In both the working examples described, the necessary iron compounds can be prepared by conventional mixed oxide routes, but also by precursor processes, wet-chemical processes and PVD/CVD processes.

(12) The constituents S, O and M or S.sub.O and M can be present either isotropically or in aligned or gradated form in the storage structure. Multilayer structures in which barrier layers composed of the oxide compound O are incorporated, or else structures in which the oxide compound O and/or the ceramic matrix M form a support skeleton, are particularly advantageous.

(13) Further processing of these materials to form the storage element can conceivably be carried out via all conventional ceramic processes, for example pressing, screen printing, tape casting, slip casting, spray processes, electrophoretic deposition and the like. A thermal after-treatment by means of sintering can also be carried out using the materials mentioned.

(14) In the examples mentioned, the main cause of store degradation, namely the migration of the redox-active species in the direction of the oxide source caused by the discharging process and the associated loss of specific surface area by the driven sintering of the storage particles is countered by binding of the iron to the oxide composition during charging. The composites described can have a variety of structural forms, for example as powder mixture, multilayer structures and/or skeleton structures and the like, and allow reproducible, flexible and inexpensive mass production of the storage medium. Apart from the iron/iron oxide-based stores described, it goes without saying that the working examples can be applied to various metal storage materials, oxidic binding partners and ceramic matrices. In addition, higher volumetric than in the binary compounds can advantageously be realized.