GB1562498A

GB1562498A - Electric batteries

Info

Publication number: GB1562498A
Application number: GB53225/75A
Authority: GB
Original assignee: UK Secretary of State for Industry
Current assignee: UK Secretary of State for Industry
Priority date: 1975-12-30
Filing date: 1975-12-30
Publication date: 1980-03-12
Also published as: DE2658392A1; DE2658392C2

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRIC BATTERIES (71) I, SECRETARY OF STATE FOR IN DUSTRY in Her Britannic Majesty's Government of the United Kingdom of Great Britain and Northern Ireland, London, a Body Corporate, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to electric cells of the kind for use with a liquid anode, a liquid cathode, a solid electrolyte, and an electrode means, and is an improvement in or modification of the invention claimed in Claim 1 of co-pending specification 1508805.

Claim 1 of co-pending specification 1508805 describes an electric cell comprising a solid electrolyte which on one side thereof bounds at least in part a compartment for a liquid anode and on the other side thereof bounds at least in part a compartment for a liquid cathode impregnated in a conductive felt, an electrically insulating support means supporting the solid electrolyte, an electrode means extending along the liquid cathode compartment, and a spacing means comprising a material having a relatively high electrical resistance and occupying a region of the liquid cathode compartment between a portion of the solid electrolyte and a portion of the electrode means so as to keep the conductive felt away from said region, whereby said region is arranged to be substantially free from the electro-chemical reactions that occur elsewhere in the liquid cathode compartment during operation of the cell so as to protect the cell from the adverse effects that could otherwise occur from electrochemical reactions at the region.

The present invention describes a modification or improvement of the invention described in Claim 1 of co-pending specification 1508805, and provides an electric cell comprising a solid electrolyte of tubular form which on the outside thereof bounds at least in part a compartment containing a liquid anode and in the space inside the solid electrolyte provides at least in part a compartment containing a liquid cathode, and electrical insulating material in the liquid cathode compartment adjacent to a portion of the solid electrolyte through which portion current intensification might otherwise occur during recharge of the cell, whereby said electrical insulating material inhibits said current intensification.

The portion of the solid electrolyte may be at one end of the solid electrolyte, and supported at said outside of the solid electrolyte by a ceramic member and joined to said ceramic member by glass sealing means, the electrical insulating material being arranged to extend along the solid electrolyte from said one end of the solid electrolyte to a position beyond that extremity of the glass sealing means remote from said one end of the solid electrolyte.

Desirably, the electrical insulating material comprises a member of plug-like form comprising ceramic material.

The invention will now be further described by way of example only with reference to the drawing filed with the Provisional Specification, the single figure of which shows a sectional representation of an electric cell of tubular form for use with liquid sodium and liquid sulphur, and adapted for operation with its longitudinal axis horizontal.

Referring now to the drawing, the electric cell is shown in median section and is of circular form in section; and it comprises a beta-alumina solid electrolyte 2 of blindended tubular form disposed within a stainless steel flanged casing 3 to define a compartment 4 therebetween for liquid sodium. A compartment 5 for liquid sulphur impregnated in an electron conductor in the form of a graphite felt 6 is provided inside the tubular solid electrolyte 2, a suitable distributed voidage being left within the graphite felt 6 to allow for expansion caused by the formation of sodium polysulphides when the electric cell discharges. The solid electrolyte 2 is joined at its open end by glass sealing means 7 to an alpha-alumina support flange 8. A flanged stainless steel wicking tube 9 is disposed concentrically about the solid electrolyte 2 so as to define a capillary space 10 for liquid sodium to constrain liquid sodium to flow over the surface of the solid electrolyte 2.

Inlet holes 11 extending along the base of the wicking tube 9 allow flow of liquid sodium from the liquid sodium compartment 4 to the capillary space 10.

An electrode means in the form of a rod of graphite provides a current collector 12 and extends centrally along the length of the liquid sulphur compartment 5. A spacing means in the form of a flanged alpha-alumina insulating spacer 13 has a spigot portion 14 which is a close fit inside the solid electrolyte 2. The spacer 13 provides a relatively high electrical resistance region bounding the solid electrolyte 2 extending from the open end of the solid electrolyte 2 to at least lcm beyond the extremity of the glass sealing means 7 masking the other side of the solid electrolyte 2 to protect that portion of the solid electrolyte 2 bounded by the glass sealing means 7.

A flange 15 of the spacer 13 bears against the support flange 8 and also provides an elongated path to inhibit the flow of electrons therearound. A stainless steel end cap 18 closes the liquid sulphur compartment 5, having a circular recess 16 in which the flange 15 locates, and a threaded spigot 19 which locates in a threaded hole 20 in the current collector 12. A spigot on the outside face of the end cap 18 provides a positive terminal 21, and a stainless steel spigot 17 welded to the casing 3 provides a negative terminal 17.

The cell is clamped together, using Grafoil gaskets 24 fitted between the flanged casing 3, the flanged wicking tube 9, the support flange 8, and the end cap 18, by a low alloy steel outer clamping sleeve 22 edge-welded to a low alloy steel end ring 23. An alpha-alumina collar 25 disposed between the end cap 18 and the current collector 12 electrically insulates them from one another.

In operation, when the electric cell discharges through an external circuit (not shown) the liquid sodium in contact with the solid electrolyte 2 is ionised with the release of electrons and forms the corresponding positive sodium ions. The electrons leave the cell through the negative terminal 17 to the external circuit, whilst the sodium ions are conducted through the solid electrolyte 2 to the liquid sulphur. The electrons from the external circuit are eventually conducted by the current collector 12 and graphite felt 6 to the liquid sulphur thereby forming sodium polysulphides with the sodium ions. That portion of the solid electrolyte 2 spaced by the spacer 13 from the graphite felt 6 and current collector 12 is substantially free from electrochemical reactions and thereby protects the glass seal 7 provided between the solid electrolyte 2 and the support flange 8 from the destructive effect of these reactions.

During recharge of the cell a current is provided to feed electrons through the negative terminal 17 to the liquid sodium, the other lead of the charging current being connected to the positive terminal 21. The flange 15 of the spacer 13 reduces the likelihood of a short circuit path between the end cap 18 and the solid electrolyte 2. The polysulphides in contact with the graphite felt 6 and the solid electrolyte 2 dissociate, and the sodium ions released flow through the solid electrolyte 2 to form sodium atoms with the electrons at the other side of the solid electrolyte 2.

Because of the insulated region provided by the spacer 13, substantially no electrochemical reactions take place at the adjacent surface of the solid electrolyte 2 and relatively few sodium ions flow therethrough, thereby avoiding problems from current intensification in the solid electrolyte 2.

Current intensification can arise during recharge when the edge of that part of the surface of the solid electrolyte 2 in the liquid sulphur compartment 5 at which electrochemical reactions occur with the polysulphides is near to or extends beyond the corresponding edge of the surface of the solid electrolyte 2 in the liquid sodium compartment 4 at which ionic reactions forming sodium atoms from the combination of sodium ions and electrons occur. An example is shown in the Figure, in which a portion of the solid electrolyte 2 having sulphur on one side is masked on the sodium side by the glass seal 7 used to join the solid electrolyte 2 to the support flange 8. If it were not for the spacer 13, current intensification would arise during recharge because the sodium ions flowing in the solid electrolyte 2 would converge and, therefore, increase in concentration in flowing towards a portion of the solid electrolyte 2 not masked by the glass seal 7 and could lead to breakdown of the solid electrolyte 2. Such a situation might be introduced elsewhere in the solid electrolyte, for example, at positions where the liquid anode surface of the solid electrolyte is masked in any manner, or the solid electrolyte is joined by a butt joint to a non-ionic conducting component.

Although the invention has been described in relation to the use of a spacing means to provide a region substantially free from electrochemical reactions at one end of the liquid cathode compartment, naturally a spacing means may be adapted in shape and arranged to provide similar regions elsewhere, for example, so as to smooth out the flow of sodium ions through the solid electrolyte at other local areas subject to current intensification during recharge of the cell.

Although the electrode means has been described as made of graphite, it may be made from some other carbonaceous material, and may be of composite construction, for example reinforced with a metal, such as stainless steel, to provide structural strength and reduce electrical resistance, the carbonaceous material providing a corrosion resistant outer conductive layer for such a composite electrode means. Alternatively, the electrode means may be provided by a metal suitably protected against the corrosive effects of the electrochemical reactions, for example, as described in co-pending application No.

48656/76 (11850) and corresponding United States Patent No. 4117209 in which an electrode means in the form of a cathode current collector is formed of an aluminium substrate or core on which is an interstrate layer of nickel-chromium alloy covered by a coating of conductive titanium oxide or other electronically conductive oxide intrinsically inert to the cathodic reactant. Both the interstrate layer and the titanium oxide layer are applied by plasma spraying. The interstrate layer may comprise a Nichrome (Registered Trade Mark) alloy (e.g. 80% Ni, 20% Cr by weight) or some other nickel chromium alloy containing at least 10% by weight of nickel and at least 10% by weight of chromium, the combined nickel and chromium being at least 50% by weight of the total and the balance being mainly iron and/or cobalt. The titanium oxide may be doped with 1 % by weight of niobium, or tantalum doping may be used, and a further conductive layer e.g. a vapour-deposited carbon layer, may be put over the conductive oxide layer. The electrode means may also be of hollow form, for example, as described in co-pending specification 1517536.

The invention may be incorporated in electric cells designed for operation in an alternative orientation to that shown in the drawing, for example, a vertical orientation.

It will be appreciated that alternative forms of spacing means may be used to space a portion of the solid electrolyte from the liquid cathode.

The insulating spacer 13 may be made of an alternative insulating material provided that it will withstand the environment within the liquid cathode compartment, or may be of composite construction (e.g. metal/ceramic) provided that the ceramic is arranged as an electrically insulating layer at the outer surface of the spacer.

WHAT I CLAIM IS: 1. An electric cell comprising a solid electrolyte of tubular form which on the outside thereof bounds at least in part a compartment containing a liquid anode and in the space inside the solid electrolyte provides at least in part a compartment containing a liquid cathode, and electrical insulating material in the liquid cathode compartment adjacent to a portion of the solid electrolyte through which portion current intensification might otherwise occur during recharge of the cell, whereby said electrical insulating material inhibits said current intensification.

2. An electric cell as claimed in Claim 1, wherein said portion of the solid electrolyte is at one end of the solid electrolyte and is supported at said outside of the solid electrolyte by a ceramic member and joined to said ceramic member by glass sealing means, and the electrical insulating material is arranged to extend along the solid electrolyte from said one end of the solid electrolyte to a position beyond that extremity of the glass sealing means remote from said one end of the solid electrolyte.

3. An electric cell as claimed in Claim 1 or Claim 2, wherein the electrical insulating material comprises a member of plug-like form comprising ceramic material.

4. An electric cell as claimed in Claim 3, wherein the plug-like member has a shape to provide an elongate path around the periphery thereof so as to inhibit the flow of electrons therearound.

5. An electric cell as claimed in Claim 3 or Claim 4, wherein the plug-like member is of composite construction.

6. An electric cell as claimed in any one of the preceding claims, wherein the liquid anode comprises liquid sodium, and the liquid cathode comprises liquid sulphur.

7. An electric cell substantially as hereinbefore described with reference to the drawing filed with the Provisional Specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

made from some other carbonaceous material, and may be of composite construction, for example reinforced with a metal, such as stainless steel, to provide structural strength and reduce electrical resistance, the carbonaceous material providing a corrosion resistant outer conductive layer for such a composite electrode means. Alternatively, the electrode means may be provided by a metal suitably protected against the corrosive effects of the electrochemical reactions, for example, as described in co-pending application No.

48656/76 (11850) and corresponding United States Patent No. 4117209 in which an electrode means in the form of a cathode current collector is formed of an aluminium substrate or core on which is an interstrate layer of nickel-chromium alloy covered by a coating of conductive titanium oxide or other electronically conductive oxide intrinsically inert to the cathodic reactant. Both the interstrate layer and the titanium oxide layer are applied by plasma spraying. The interstrate layer may comprise a Nichrome (Registered Trade Mark) alloy (e.g. 80% Ni, 20% Cr by weight) or some other nickel chromium alloy containing at least 10% by weight of nickel and at least 10% by weight of chromium, the combined nickel and chromium being at least 50% by weight of the total and the balance being mainly iron and/or cobalt. The titanium oxide may be doped with 1 % by weight of niobium, or tantalum doping may be used, and a further conductive layer e.g. a vapour-deposited carbon layer, may be put over the conductive oxide layer. The electrode means may also be of hollow form, for example, as described in co-pending specification 1517536.

The invention may be incorporated in electric cells designed for operation in an alternative orientation to that shown in the drawing, for example, a vertical orientation.

It will be appreciated that alternative forms of spacing means may be used to space a portion of the solid electrolyte from the liquid cathode.

The insulating spacer 13 may be made of an alternative insulating material provided that it will withstand the environment within the liquid cathode compartment, or may be of composite construction (e.g. metal/ceramic) provided that the ceramic is arranged as an electrically insulating layer at the outer surface of the spacer.

WHAT I CLAIM IS: 1. An electric cell comprising a solid electrolyte of tubular form which on the outside thereof bounds at least in part a compartment containing a liquid anode and in the space inside the solid electrolyte provides at least in part a compartment containing a liquid cathode, and electrical insulating material in the liquid cathode compartment adjacent to a portion of the solid electrolyte through which portion current intensification might otherwise occur during recharge of the cell, whereby said electrical insulating material inhibits said current intensification.
2. An electric cell as claimed in Claim 1, wherein said portion of the solid electrolyte is at one end of the solid electrolyte and is supported at said outside of the solid electrolyte by a ceramic member and joined to said ceramic member by glass sealing means, and the electrical insulating material is arranged to extend along the solid electrolyte from said one end of the solid electrolyte to a position beyond that extremity of the glass sealing means remote from said one end of the solid electrolyte.
3. An electric cell as claimed in Claim 1 or Claim 2, wherein the electrical insulating material comprises a member of plug-like form comprising ceramic material.
4. An electric cell as claimed in Claim 3, wherein the plug-like member has a shape to provide an elongate path around the periphery thereof so as to inhibit the flow of electrons therearound.
5. An electric cell as claimed in Claim 3 or Claim 4, wherein the plug-like member is of composite construction.
6. An electric cell as claimed in any one of the preceding claims, wherein the liquid anode comprises liquid sodium, and the liquid cathode comprises liquid sulphur.
7. An electric cell substantially as hereinbefore described with reference to the drawing filed with the Provisional Specification.