GB2039132A

GB2039132A - Sodium sulphur battery seal

Info

Publication number: GB2039132A
Application number: GB7937795A
Authority: GB
Original assignee: Ford Motor Co Ltd; Ford Motor Co
Current assignee: Ford Motor Co Ltd; Ford Motor Co
Priority date: 1978-11-01
Filing date: 1979-10-31
Publication date: 1980-07-30
Also published as: CA1123904A; US4192911A

Description

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GB2 039 132A

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SPECIFICATION Sodium sulfur battery seal

5 This invention is directed to a seal for a sodium sulfur battery in which a flexible diaphragm sealing elements respectively engage opposite sides of a ceramic component of the battery which separates an anode compart-" 10 ment from a cathode compartment of the battery.

While I am aware of the disclosures contained in many patents in the sodium sulfur battery area, I am unaware of any prior art 15 which shows or suggests a seal for a sodium sulfur battery such as disclosed in this application. U.S. patent 4,024,321 does use a spring element 18 in order to affect some sealing in a sodium sulfur battery, but that 20 sealing is brought about by an axial spring action of the spring element 18.

In general, I developed the sealing structure disclosed in this specification in order to develop a seal for a sodium sulfur battery which 25 was simple in construction and efficient in operation. I principally desired to develop a seal which could be contained within the diameter of the outer can member of the battery. In such a manner, a plurality of 30 batteries may be positioned more closely to one another in forming a large battery for a power load balancing application. I also desired to develop a seal which could be made from relatively inexpensive materials and be 35 made in a manner such that an effective seal is easily generated upon assembly of the structure disclosed in the specification.

SUMMARY OF THE INVENTION 40 This invention relates to a seal for a sodium sulfur battery and, more particularly, to an improved seal for using flexible diaphragm seals against a ceramic member of the battery which acts as a separator between the bat-45 tery's anodic compartment and its cathodic ; compartment. The flexible diaphragm seal of this invention will allow the ceramic member to be out of phase on location with its associated container, will allow for misalignment on 50 cold assembly, will allow for movement of cell components when the cell is going through freeze thaw cycles, and will allow for the difference in component growth when heated.

The seal of this invention may be made 55 against a very smooth surfaced ceramic member. In the case where a smooth ceramic member is used, the improved seal includes the following structure. An outer metal can member of circular cross section is used 60 which has an open end. A ring-shaped flexible diaphragm seal is provided which has an inner circumferential edge and an outer circumferential edge, which outer circumferential edge is bonded in a gas tight relationship to 65 the open end of the outer can member. The ring-shaped flexible diaphragm seal has a "U" shaped cross section between its circumferential edges to provide resiliency thereto. The inner circumferential edge of the ring-70 shaped flexible diaphragm seal is in interference fit with a smooth outer facing surface of a ring-shaped ceramic member which also has a smooth, inner facing surface. The interference fit between the smooth outer facing 75 surface of the ring-shaped ceramic member and the inner circumferential edge of the ring-shaped flexible diaphragm seal provides a gas tight seal therebetween. An outer diameter of a disc-shaped inner flexible diaphragm seal 80 having a curved cross section is in interference fit with the smooth, inner facing surface of the ring-shaped ceramic member to provide a gas tight seal therebetween. In such a manner, a gas tight seal is provided on both 85 sides of a ceramic member which is used to separate the compartments of a sodium sulfur battery. The ceramic member may be the electrolyte of the battery.

In an alternate construction, the ring-shaped 90 ceramic member is left in its "as sintered" state, namely, a state in which the outer facing surface and inner facing surface thereof are rough, rather than a smooth condition which is brought about by grinding of a 95 sintered ceramic material. In the situation where the ceramic member is left in its "as sintered" condition, a thin coating of a soft metal is formed on both the inner facing surface and the outer facing surface of the 100 ring-shaped ceramic member to define a smooth surface on both the inner facing surface and the outer facing surface thereof. The metal coating, when engaged by the interference fit of the aforementioned flexible dia-105 phragm seal and disc-shaped inner flexible diaphragm seal, provides the means whereby a gas tight seal is formed between the mentioned components.

110 BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention, itself, however, both as to its organi-115 zation and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in conjunction with the accompa-120 nying drawings wherein like characters indicate like parts throughout tht, several figures, and in which:

Figure 1 is an elevation view, in cross section, of a sodium sulfur battery sealed by a 125 seal of my invention;

Figure 2 is a top view of the sodium sulfur battery of Fig. 1; and

Figure 3 is an exploded view of one corner of the battery of Fig. 1 showing the sealing 130 structure in larger dimension.

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DESCRIPTION OF A PREFERRED EMBODIMENT

The general principle of operation of a so-5 dium sulfur battery is well known to those skilled in the art, as is evidenced by the great number of patents which have issued in this area. Therefore, no discussion will be undertaken herein of the theory and operation of 10 such a battery.

Those skilled in the art know that it is necessary to seal the anodic compartment of the battery from the cathodic compartment of the battery so that the battery may carry out 15 its intended function. Many different types of seals have been developed as is evidenced by the number of patents which have issued in this area. However, I am unaware of any sealing structure like or similar to the structure 20 to be disclosed herein.

Also, for the sake of simplicity, only the general components of a sodium sulfur battery are shown in the drawings. Many of the particular components that are used in order 25 to achieve operability of the battery are not shown in the drawings as these components are not necessary to teach to one skilled in the art the seal construction of this application. Reference is now made to the drawings. 30 In Fig. 1, there is seen a hermetically sealed alkali metal battery, generally designated by the numeral 10. This battery includes a ceramic ring 12 which has an inner surface 14 and an outer surface 16. In the 35 case of the preferred embodiment, the ceramic material is formed from a materia! such as alpha alumina of high purity, such as 99.8%. Also in accordance with the teachings of a preferred embodiment of this invention, 40 the inner surface 14 and the outer surface 16 of the ceramic ring 12 are ground by a suitable grinding device, such as a diamond wheel, in order to achieve a smooth continuous flat surface thereon.

45 An inner casing 18 of a solid alkaline ion-conductive material is in the form of a closed end tube. This casing is used as a reaction zone separator and will permit the transfer of ions of an anodic reactant therethrough to a 50 cathodic reactant. The casing 18 is bonded by a glass seal, not shown, at its open end to a bottom surface of the ceramic ring 12.

An outer metal can member 20 of circular cross section is also provided. This can mem-55 ber has an open end 22. A ring-shaped flexible diaphragm seal 24 has an inner circumferential edge 26 and an outer circumferential edge 28, which outer circumferential edge 28 is bonded in an gas tight relationship to the 60 open end 22 of the outer can member 20, as is best seen in Fig. 3. The bonding together of these members may be effected by means of an electron beam welding operation.

In accordance with the teachings of a pref-65 erred embodiment of this invention, the outer metal can member 20 is formed of a material such as 430 stainless steel, which is a high chrome containing stainless steel. The interior surface of the outer can member 20 may also have a chrome coating thereover. In a like manner, in accordance with the preferred teachings of this invention, the ring-shaped flexible diaphragm seal 24 is also formed of 430 stainless steel and has a thickness of " about .010 to 0.20 inch.

The ring-shaped flexible diaphragm seal 24 has a generally "U" shaped cross section between its circumferential edges 26 and 28. This shape is readily apparent by viewing Fig. 3. The purpose of this shape is to provide resiliency to the ring-shaped flexible diaphragm seal 24.

The inner circumferential edge 26 of the flexible diaphragm seal 24 is of a diameter slightly less than the diameter of the outer facing surface 16 of the ceramic ring 12. As previously mentioned, this outer facing surface 16 is smooth. In such a manner, the inner circumferential edge 26 of the flexible diaphragm 24 forms an interference fit with the smooth, outer facing surface 16 of the ring-shaped ceramic member 1 2 to provide a gas tight seal therebetween.

A disc-shaped inner flexible diaphragm seal 30, formed of 430 stainless steel, has a curved cross section. This inner flexible seal has an outer circumferential edge 32 which has a diameter slightly greater in diameter than the diameter of the smooth, inner facing surface 14 of the ring-shaped ceramic member 12. In this manner, the outer circumferential edge 32 of the inner flexible diaphragm seal 30 forms an interference fit with the smooth, inner facing surface 14 of the ceramic ring 12 to provide a gas tight seal therebetween. A filler tube 34, associated with seal 30, is shown in its open condition providing a passageway to fill the electrode compartment defined in the interior of the inner casing 18.

As above described, the seals between two compartments of a sodium sulfur battery are formed in a relatively easy and simple manner, and in a manner in which the seals are formed within the diameter of an outer metal can 20. As discussed in this preferred embodiment, the seals are made across an alpha alumina ceramic ring. They may as well be made directly to the inner casing 18 which serves as the electrolyte of the battery.

In order to reduce the cost of the battery structure, it is preferable to use the ceramic ring in an as fired condition. By this, I mean that the ceramic ring is used as it is manufactured after the sintering thereof. In such a case, the inner surface 14 and outer surface 16 thereof are rough in nature. As was noted above, in order to make the inner surface 14 and outer surface 16 smooth, it is necessary to grind the same with a device such as a

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diamond grinding wheel. Such an operation is, or course, expensive.

The ceramic ring 12 may be used in an "as sintered" condition if the inner surface 14 5 and outer surface 16 are coated with a thin coating of a soft metalal, not shown. Such a metal coating may be, for example, an aluminum metal coating applied by a plasma spray operation. A preferred aluminum for such a 10 spray operation is one having a high purity, such as an 1100 aluminum. In general, a metal coating of about 0.015 inches is sufficient to provide a smooth surface against which an interference fit may be made by the ring-15 shaped flexible diaphragm seal 24 and the disc-shaped inner flexible diaphragm seal 30 at their respective inner circumferential edge 26 and outer circumferential edge 32.

In general, I may say the savings resulting 20 in not grinding the ceramic ring 12 and using it in its as sintered condition more than covers the cost of applying the smooth coating to the inner surface 14 and outer surface 16 of the ceramic ring 12 in such a plasma spray 25 operation.

Once again, if one desires, they may use the seal directly to the ceramic material which forms the electrolyte of the battery, and may apply the coating thereto if the electrolyte is 30 in an as sintered condition.

While particular embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art, that various changes and modifications may be 35 made without departing from the invention, and it is intended to cover in the appended claims, all such modifications and equivalents as fall within the true spirit and scope of this invention.

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Claims

1. In a sodium sulfur battery an improved seal for sealing against a ceramic member which acts as a separator between an anode 45 compartment and a cathode compartment, which improved seal includes the following structure:

an outer metal can member of circular cross section having an open end; 50 a ring-shaped flexible diaphragm seal having an inner circumferential edge and an outer circumferential edge, said flexible diaphragm seal having a generally "U" shaped cross section between its circumferential edges to 55 provide resiliency thereto, said outer circumferential edge of said flexible diaphragm being bonded in a gas tight relationship to said open end of said outer can member;

a ring-shaped ceramic member having a 60 smooth, inner facing surface and a smooth, outer facing surface, said inner circumferential edge of said flexible diaphragm seal being slightly less in diameter than the diameter of said outer facing surface of said ring-shaped 65 ceramic member whereby said inner circumferential edge of said flexible diaphragm forms an interference fit with said smooth, outer facing surface of said ring-shaped ceramic member to provide a gas tight seal there-70 between; and a disc-shaped inner flexible diaphragm seal having a curved cross section and an outer diameter slightly greater in diameter than the diameter of said smooth, inner facing surface 75 of said ring-shaped ceramic member whereby said outer circumferential edge of said inner flexible diaphragm forms an interference fit with said smooth, inner facing surface of said ring-shaped ceramic member to provide a gas 80 tight seal therebetween.

2. The seal of Claim 1, wherein said ring-shaped ceramic member is the electrolyte of the battery.

3. In a sodium sulfur battery an improved 85 seal for sealing against a ceramic member which acts as a separator between an anode compartment and a cathode compartment, which improved seal includes the following structure:

90 an outer metal can member of circular cross section having an open end;

a ring-shaped flexible diaphragm seal having an inner circumferential edge and an outer circumferential edge, said flexible diaphragm 95 seal having a generally "U" shaped cross section between its circumferential edges to provide resiliency thereto, said outer circumferential edge of said flexible diaphragm seal being bonded in a gas tight relationship to 100 said open end of said outer can member;

an as sintered ring-shaped ceramic member having an inner facing surface and an outer facing surface;

a thin coating of a soft metal formed on 105 both said inner facing surface and said outer facing surface of said ring-shaped ceramic member to define a smooth surface on both said inner facing surface and said outer facing surface of said ring-shaped ceramic member, 110 said inner circumferential edge of said flexible diaphragm seal being slightly less in diameter than the diameter of said coated, facing surface of said ring-shaped ceramic member whereby said inner circumferential edge of 115 said flexible diaphragm forms an interference fit with said coated, outer facing surface of said ring-shaped ceramic member to provide a gas tight seal therebetween; and a disc-shaped inner flexible diaphragm seal 1 20 having a curved cross section and an outer diameter slightly greater in diameter than the diameter of said coated, inner facing surface of said ring-shaped ceramic member whereby said outer circumferential edge of said inner 125 flexible diaphragm seal forms an interference fit with said coated, inner facing surface of said ring-shaped ceramic member to provide a gas tight seal therebetween.

4. The seal of Claim 3, wherein said ce-

1 30 ramie member is the electrolyte of the battery.

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Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd.—1980.

Published at The Patent Office, 25 Southampton Buildings,

London, WC2A 1AY, from which copies may be obtained.