DE3238533A1 - Sodium solid-state galvanic cell - Google Patents

Abstract

The compounds BiCl3, BiBr3 and BiI3 are suitable as readily dischargeable cathode substances for a solid-state galvanic cell having a negative Na electrode and a solid-state electrolyte with specific Na<+> ion conductivity, for example a mixed crystal of the quaternary system Na2O-ZrO2-P2O5-SiO2. The solid-state electrolyte can be produced by sintering techniques as a compound body having a compact section and a highly porous section whose pores can be impregnated with the readily melting halides to produce a particularly intimate contact between the cathode and electrolyte.

Description

TEXT MISSING conductivity can be put aside.

The invention is based on the object for solid-state cells with negative Na-electrode and Na-ion-conducting solid electrolyte new cathode substances to make usable with good discharge and high Coulomb yield.

The object is achieved according to the invention in that the active material of the positive electrode is selected from the compounds BiCl3, 8i Br3, 8iJ3.

These substances are used with particular advantage in a cell, which has already been described in the earlier German patent application P 31 29 679.3 and their essential feature is that they are made in one piece by sintering is formed by solid electrolyte material and in addition to a dense, d. H. pore-free section has at least one highly porous section for the introduction of fusible electrode active material is provided. A Such compound bodies can be produced by adding bulk powder of the solid electrolyte material, one or two of which are mixed with a filler, but one filler-free is, carefully layered on top of each other and sintered at 0 temperatures above 1200 C. In this way, after the thermal decomposition of the filler, a complete Cell structure including the associated cathode and anode compartments in Form of self-supporting, highly porous sintered structures without phase boundaries merge into the massive solid electrolyte section in between.

The introduction of the substances according to the invention into the cathode compartment and if necessary. The sodium in the anode compartment is done by soaking in a vacuum. It is important that the pores of the framework are well protected from the active substance are wetted and that, furthermore, the vapor pressure of the active cathode substance is not Reached values at which the danger an attack on the sodium anode and thus a discharge of the cell via the gas phase occurs.

Of the bismuthologides to be used according to the invention, melts 8ich3 at 2320C, Bi 9r3 at 2180C and 8iJ3 at 408 ° C.

With the impregnation of these compounds in the framework structure achieves a particularly intimate amalgamation between active mass and electrolyte, which is a prerequisite for the cathode to be able to be discharged well. These preferably The measure of the invention provides almost the ideal conditions in the solid-state cell as they are in conventional liquid cells, where the liquid electrolyte all cavities of the solid electrodes, apart from closed pores, to be filled and thereby opens up a maximum electrode surface for the supply of electricity. A similar degree of mutual, two-dimensional contact would be through mere mixing the solids cannot be realized because in this case the electrochemical conversion inevitably on the discrete geometric contact surfaces of the affine particles would remain limited.

As has also been shown, the cathode substances according to the invention become without the solid-state electrolyte matrix which conducts Na + ions in the cathode compartment, only a small amount Coulomb yield achieved.

According to the invention, the molten cathode material before The porous ion guide structure is filled with a very fine-grained electron-conducting structure Substance (graphite or soot) are added to this way in the cathode compartment to incorporate an additional electron-conducting matrix into the cell. This measure is not necessary in principle, but lowers the internal resistance of the Cell considerably.

If no electron-conducting material is added, then with increasing Discharge depth of the electron-conducting part in the cathode compartment from the one in the implementation the cathode material metal (Bi) is taken over. the The addition amount of the electron conductive material can be 0 to 50% by volume, preferably 0 to 5 uol. %.

In the case of compound bodies with only one porous framework section, this can Na metal melted directly onto the opposite side of the densely sintered section while the porous section is reserved for the cathode material.

The figure shows a discharge curve for a Na / Si according to the invention Br3 element shown with a porous solid electrolyte matrix in the cathode compartment. The discharge took place with a constant current load of 15 uA / cm2. Remarkable is the favorable, flat voltage curve depending on the withdrawn capacity. The achieved mass yield of approx. 10 mAh corresponded to 33% of theory, based on the amount of Bi Br3 used.

an attack on the sodium anode and thus a discharge of the Cell arises through the gas phase.

Of the bismuthologides to be used according to the invention, melts BiC13 at 2320 #, Bi Br3 at 213 OC and Bi # 3 at 4080C.

With the impregnation of these compounds in the framework structure achieves a particularly intimate amalgamation between active mass and electrolyte, which is a prerequisite for the cathode to be able to be discharged well. These preferably The measure of the invention provides almost the ideal conditions in the solid-state cell as they are in conventional liquid cells, where the liquid electrolyte all cavities of the solid electrodes, apart from closed pores, to be filled and thereby opens up a maximum electrode surface for the supply of electricity. A similar degree of mutual, two-dimensional contact would be through mere mixing the solids cannot be realized because in this case the electrochemical conversion inevitably on the discrete geometric contact surfaces of the affine particles would remain limited.

As has also been shown, the cathode substances according to the invention become without the solid-state electrolyte matrix which conducts Na + ions in the cathode compartment, only a small amount Coulomb yield achieved.

According to the invention, the molten cathode material before The porous ion guide structure is filled with a very fine-grained electron-conducting structure Substance (graphite or soot) are added to this way in the cathode compartment to incorporate an additional electron-conducting matrix into the cell. This measure is not necessary in principle, but lowers the internal resistance of the Cell considerably.

If no electron-conducting material is added, then with increasing Discharge depth of the electron-conducting part in the cathode compartment from the one in the implementation the cathode material

Claims (4)

Claims 1. Galvanic element with a sodium ion-conductive Solid state electrolytes, a solid sodium negative electrode and a positive one Electrode, characterized in that the active material is the positive electrode is selected from the connections BiCl3, Bi Br3, BiJ3. 2. Galvanic element according to claim 1, characterized in that the active material of the positive electrode in one of the solid electrolyte sterisl formed porous sintered structure is arranged. 3. Galvanic element according to claim 1 or 2, characterized in that that the active material of the positive electrode added electron-conducting material is. 4. Galvanic element according to claim 3, characterized in that the additional amount of electron-conducting material 0 to TEXT MISSING