Chloride Silent Power, Ltd.

The Electricity Council

Graham Robinson

Ivor Wynn Jones

Thomas Lewis Bird

Roger J Bones

Peter J Bindin

Michael P Brennan

John Molyneux

Geoffrey J May

Lyndon James Miles

Trevor Leslie Markin

Michael McNamee

Raymond O Ansell

Keith Taylor Scott

Sodium sulphur cells are commonly connected in parallel. It is a problem with such arrangements that if one cell sustains a short circuit failure, the parallel connected cells discharge through it. In an embodiment disclosed, a switch series connected to a cell or series of cells, goes open circuit should current in excess of a predetermined value and consequently associated with the failure of a cell, flow through the switch. The switch comprises a conducting rod separated into two portions and placed within a beta alumina tube containing sodium: the level of the sodium determines whether an electrical circuit is completed between the portions rendering the switch 'on'. Sodium, contained within an outer conducting tube, also surrounds the inner beta alumina tube, there being an electrical connection from the outer tube, via a resistor, to one portion of the rod. Should a current flow in a direction through the switch corresponding to discharge through a failed series connected cell, the arrangement is such that sodium within the inner tube is at a higher potential than sodium outside the inner tube. Accordingly, sodium cations flow out of the inner tube resulting in the lowering of the sodium level until the switch turns off, thus preventing further discharge through the failed cell.

Alkali metal switch device

A cathode structure for a sodium sulphur cell is formed of a stack of elements of carbon fibre material or predominantly of carbon fibre material, each element being punched out of a sheet of the material having fibres randomly oriented in planes parallel to the plane of the sheet. For a cylindrical cell, the elements are of annular form with a central aperture.

Cathode electrode structures for sodium sulphur cells and their

In a sodium sulphur cell, the cathode current collector in the sulphur/polysulphide cathodic reactant comprises an impermeable tube, e.g. a carbon or graphite tube which is inert to the cathodic reactant and contains a solid metal core, e.g. an aluminium core, and a deformable electronic conductor, e.g. graphite felt, as a conducting interface between the impermeable tube and the core. In a preferred construction, the current collector is axially located within a cylindrical electrolyte tube, the space between the electrolyte tube and impermeable tube containing the sulphur/polysulphides and a graphite felt. The outer surface of the impermeable tube in this case has grooves or recesses to form a sulphur reservoir.

Sodium sulphur cells

In a sodium sulphur cell having a cathodic region containing sulphur/polysulphides forming a cathodic reactant between a solid electrolyte and a cathode current collector, the electronically conductive matrix containing the cathode reactant is formed of a porous metal structure, preferably metal fibres, coated with graphite or carbon to form an electronically conductive protective coating.

Cathode structure for sodium sulphur cells

In a sodium sulphur cell having a porous matrix forming an electronic conductor in the cathodic region and extending between the surface of the solid electrolyte and a cathode current collector, this matrix is a composite comprising a first material formed of graphite or carbon of a material coated with graphite or carbon, which first material is intimately mixed with a second material, such as alumina fibres, which is more easily wetted by the polysulphides than is the first material.

In a sodium-sulphur cell having a solid electrolyte separating sodium from a cathodic region containing sulphur/polysulphides in a graphite felt, a cathode current collector is formed of an aluminium substrate on which is an interstrate layer of nickel-chromium alloy covered by a coating of titanium oxide or other electronically conductive oxide intrinsically inert to the cathodic reactant.

Electrochemical cells

In a sodium sulphur cell, the cathode current collector in the sulphur/polysulphide cathodic reactant comprises a carbon or graphite tube containing a solid metal, e.g. aluminum, core and a liquid metal, e.g. tin or a tin-lead alloy, as a conducting interface between the carbon or graphite tube and the core. In a preferred construction, the current collector is axially located within a cylindrical electrolyte tube, the space between the electrolyte tube and graphite tube containing the sulphur/polysulphides and a graphite felt. The outer surface of the graphite tube in this case may have grooves or recesses to form a sulphur reservoir.

In a sodium sulphur cell, the cathode current collector in the sulphur/polysulphide cathodic reactant comprises a carbon or graphite tube containing a solid metal, e.g. aluminum, core and a deformable electronic conductor, e.g. graphite felt, as a conducting interface between the carbon or graphite tube and the core. In a preferred construction, the current collector is axially located within a cylindrical electrolyte tube, the space between the electrolyte tube and graphite tube containing the sulphur/polysulphides and a graphite felt. The outer surface of the graphite tube in this case may have grooves or recesses to form a sulphur reservoir.

In a sodium-sulphur cell having a solid electrolyte and a cathode current collector with a porous conductive matrix, e.g. carbon or graphite felt, in the region between the electrolyte and the current collector, the matrix is formed of a plurality of discrete elements with electronically conductive material, e.g. graphite foil, between the elements extending across the region between the current collector and the electrolyte to increase the conductivity across that region.

Sodium-sulphur cells

In a sodium sulphur cell, the cathode current collector in the sulphur/polysulphide cathodic reactant comprises a carbon or graphite tube containing a solid metal, e.g. aluminium, core and a liquid metal, e.g. tin or a tin-lead alloy, as a conducting interface between the carbon or graphite tube and the core. In a preferred construction, the current collector is axially located within a cylindrical electrolyte tube, the space between the electrolyte tube and graphite tube containing the sulphur/polysulphides and a graphite felt. The outer surface of the graphite tube in this case may have grooves or recesses to form a sulphur reservoir.

In an electrochemical cell, such as a sodium-sulphur cell, having a liquid metal electrode and a solid electrolyte, the solid electrolyte is an upright tube with a closed end and a reservoir is provided above the top of the electrolyte tube to accommodate the increased volume of the cathodic reactant as the cell discharges whereby the whole surface of the electrolyte can be in contact with the cathodic reactant despite the increase in volume of the cathodic reactant in the cathodic compartment.

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Chester, United Kingdom

Graham Robinson