Lilliwyte Societe Anonyme

Programme 3 Patent Holdings

South African Inventions Development Corporation

David A Teagle

Roger J Bones

Roy C Galloway

Johan Coetzer

Marion R Rance

Michael L Wright

James H Duncan

Steven D Brooker

Stephen D Brooker

Patrick T Moseley

An electrochemical cell 10 housing a cylindrical housing 12 and a solid electrolyte separator tube 24 located concentrically therein, dividing the housing into an electrode compartment in the tube and an electrode compartment outside the tube. The cell has a solid electrolyte holder 36, 74 located in the tube and containing active electrode material 54. One of the electrode compartments contains active anode material, the other containing active cathode material. The electrode material in the holder is in electronic contact with the electrode material 54 in the housing outside the tube.

Electrochemical cell

A laterally compressed envelope of solid electrolyte material is provided for use as an electrode holder in an electrochemical cell. It has two opposed major faces sealed together along at least part of the periphery of the envelope, each major face being provided by a sheet of said solid electrolyte material. Each sheet is provided on its inner surface with a plurality of ribs or corrugations extending alongside one another, each rib or corrugation of each said sheet crossing over a plurality of the ribs or corrugations of the other said sheet. The envelope has an internal volume, between the sheets, defined at least in part by grooves or valleys between the ribs or crests of the corrugations. Each part of said internal volume is in communication with each other part of said internal volume. The invention also provides a method of making the envelope, and an electrochemical cell in which the envelope forms an electrode holder.

Electrochemical cells

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.

A method of making a cathode suitable for an electrochemical cell of the type having a molten sodium anode, a beta'-alumina separator, and a cathode which comprises one or more transition metals selected from the group comprising Fe, Ni, Co, Cr and Mn. The method comprises heating a particulate starting material comprising at least one member of the group of transition metals in an oxidizing atmosphere to cause its particles to become at least partially oxidized, and to adhere together to form a unitary porous matrix. This matrix is then heated in a reducing atmosphere at least partially to reduce the oxide formed during the formation of the matrix, and the reduced matrix is then impregnated with a sodium aluminium chloride molten salt electrolyte. Sodium chloride in dispersed form is incorporated into the matrix, preferably by mixing sodium chloride in particulate form with the particulate transition metal starting material, before the heating in an oxidizing atmosphere to form the matrix.

Method of making a transition metal electrode

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.

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.

Growing community of inventors

Swindon, United Kingdom

David A Teagle