Lilliwyte Societe Anonyme

South African Inventions Development Corporation

Programme 3 Patent Holdings

Roy C Galloway

Roger J Bones

David A Teagle

Johan Coetzer

Michael L Wright

Patrick T Moseley

Steven D Brooker

A method of making a cathode for a high temperature rechargeable electrochemical cell comprises impregnating a mixture, in granular form, of an alkali metal halide and a substance comprising a transition metal selected from the group consisting of iron, nickel, cobalt, chromium, manganese, and mixtures thereof, with an alkali metal aluminium halide molten salt electrolyte. The impregnated mixture is subjected to at least one charge cycle in a high temperature electrochemical cell in which the impregnated mixture forms the cathode and is located in a cathode compartment of the cell. The cathode compartment is separated from an anode compartment by a solid electrolyte separator. Alkali metal forms in the anode compartment during the charge cycle.

Electrochemical cell

The invention provides a method of protecting an electrochemical cell which has a molten sodium anode, a chloride-ion containing sodium aluminum halide molten salt electrolyte, an iron-containing cathode in contact with the electrolyte and a solid conductor of sodium ions which separates the anode from the electrolyte, from the adverse effects of overcharging. The method comprises operating the cell, to prevent oxidation of iron to FeCl.sub.3 in the cathode, by connecting it in parallel with a protective cell having an open circuit charging plateau at a voltage less than the open circuit voltage of the Fe/FeCl.sub.3 //Na plateau of the cell being protected, and greater than the open circuit voltage, in its fully charged state, of the cell being protected. The invention also provides a cell of this type protected in this fashion, a battery including one or more such protected cells, and a cathode for such cells.

The invention provides a cathode for an electrochemical cell, an electrochemical cell including the cathode, and a method of resisting a progressive drop in the capacity of the cathode with repeated charge/discharge cycling thereof. The invention involves doping the electrolyte, which is a sodium aluminium halide molten salt electrolyte containing chloride ions, and/or the active cathode substance, which is a nickel containing substance with a minor proportion of a chalcogen so that the chalcogen is dispersed therein.

The invention provides an electronically conductive tectosilicate which has, trapped within and forming part of its framework structure at the molecular or atomic level, colloidal particles of one or more electronically conducted species, which act to render the tectosilicate electronically conductive. The invention further provides a method of making such electronically conductive tectosilicate, wherein, for example, a zeolite is precipitated from the solution which has an electronically conductive species such as colloidal graphite in suspension therein, so that the colloidal particles of the electronically conductive species are trapped within and form part of the framework structure of the precipitate at the atomic or molecular level. The invention also extends to electronically conductive artifacts, such as electrodes for electrochemical cells, which are made from the electronically conductive tectosilicate by compacting the artifact from particles of the tectosilicate.

Method of making an electronically conductive tectosilicate, and such

An electrochemical cell is provided with a molten sodium anode and a molten sodium aluminium halide salt electrolyte. The cathode comprises FeCl.sub.2, NiCl.sub.2, CoCl.sub.2 or CrCl.sub.2 as active cathode substance dispersed in an electronically conductive electrolyte-permeable matrix which is impregnated by the electrolyte. Between the anode and the electrolyte, and isolating them from each other, is a solid conductor of sodium ions or a micromolecular sieve which contains sodium sorbed therein. The proportions of sodium and aluminium ions in the electrolyte are selected so that the solubility of the active cathode substance in the electrolyte is at or near its minimum.

The invention provides a method of making a cathode for an electrochemical cell which involves incorporating sodium chloride in dispersed form into an electrolyte permeable matrix and impregnating the matrix with a suitable sodium aluminum halide molten salt electrolyte. The matrix is formed from a transition metal selected from at least one member of the group consisting of Fe, Ni, Co, Cr and Mn, and the intermediate refractory hard metal compounds of said transition metals with at least one non-metal selected from the group consisting of carbon, silicon, boron, nitrogen and phosphorus.

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Pretoria, South Africa

Roy C Galloway