GB2162680A

GB2162680A - Electrochemical generator of the sodium-sulfur type

Info

Publication number: GB2162680A
Application number: GB08519042A
Authority: GB
Inventors: Raymond Vic
Original assignee: Compagnie Generale dElectricite SA
Current assignee: Alcatel Lucent SAS
Priority date: 1984-07-30
Filing date: 1985-07-29
Publication date: 1986-02-05
Also published as: GB8519042D0; DE3526661A1; FR2568413A1; FR2568413B1

Abstract

Sodium-sulfur type electrochemical generator has a sodium reservoir consisting of a cylinder (1) of beta or beta double prime alumina, closed at both ends by two discs of alpha alumina (5, 6). This reservoir is immersed inside a metal positive reservoir in the form of a cylinder (15) the ends whereof are connected to the two alpha alumina discs by metal annular connecting members (16, 17) which can be deformed. <IMAGE>

Description

SPECIFICATION Electrochemical generator of the sodium-sulfur type This invention relates to an electrochemical generator of the sodium-sulfur type.

The presently known generators basically comprise: -a metal positive reservoir containing a positive electrode of which the active material, liquid at the temperature of operation, is formed of sulfur and of its alkaline salts; -a solid electrolyte tube closed at the bottom, made of beta or of beta double prime alumina, separating said positive electrode from the negative electrode, which is liquid at the temperature of operation and which is constituted by sodium; said tube placed inside said positive reservoir in a manner such that its external face bathes in said positive active material; -and a support or insulating ceramic to maintain said tube of electrolyte inside said positive reservoir, said support and tube being connected by a glass seal.

The present invention is directed to providing a generator structure which is simpler than the known structure, while being more resistant to shocks and vibrations.

The invention thus provides an electrochemical generator of the sodium-sulfur type which comprises: -a metal positive reservoir containing a positive electrode the active material of which, liquid at the temperature of operation, consists of sulfur and its alkaline salts; -and a solid electrolyte tube of beta or of beta double prime alumina within said positive reservoir and which separates said positive active material from the negative electrode of which the active material, liquid at the temperature of operation, is sodium, characterized by the fact that said solid electrolyte is constituted by a hollow cylinder of beta or beta double prime alumina the two ends of which respectively are closed by two sealed discs of alpha alumina, and that said positive reservoir consists of a metal cylinder the bottom and top edges of which are respectively welded to two metal annular connecting parts also sealingly welded to said alpha alumina discs, said metal, annular connecting parts being shaped to permit elastic deformations of the connection.

The annular connecting parts make it possible to compensate for differences in expansion between the cylinder of beta or beta double prime alumina and the metal positive reservoir, especially in case of complete cooling of the entire generator.

According to a first embodiment, the internal walls of said cylinder of beta or beta double prime alumina are lined with metallic wicks; these wicks are for example in the form of a sintered sponge of iron or nickel.

According to another embodiment, said cylinder contains a metal bottle, perforated at its lower part, the external diameter of which is slightly smaller than the internal diameter of said cylinder, and incompletely filled with sodium placed under pressure.

Other features and advantages of the invention will appear in the course of the following description of embodiments illustrated in the attached drawing, given as an illustration only and which is not limitative.

Figures 1 and 2 respectively show schematic, partial sectional view of two embodiments of the sodium-sulfur generator according to the invention.

In Figure 1 there has been designated by 1 a cylinder of beta double prime alumina open at both ends. It is closed at its upper end by a disc 5 of alpha alumina and at its lower end by 3 disc 6 of alpha alumina. The tightness of the connections is obtained by glass seals 7 and 8. The reservoir thus formed is meant to receive sodium 2 which is liquid at generator operating temperature.

Disc 6 comprises a center bore in which there is fastened a filling tube 10 for sodium and which also serves as a negative terminal for the generator. This tubing is joined at the lower face of disc 6 by means of a metal connecting collar 11 sealingly welded along the entire periphery 14 of tubing 10 and sealed along a ring 12 by thermocompression on disc 6.

The internal wall and bottom of the sodium reservoir are lined with wicks 3 and 4 constituted by a layer of sintered metal, a sponge of nickel or iron for example, having a porosity ranging between 50% and 95%.

The wicks serve to distribute the sodium and collect the current; they are connected to terminal 10.

The tube 1 of beta double prime alumina is thus traversed by homogenous current densities; in case of accidental breaking of the tube in the course of operation, the speed of penetration of the sodium into the positive compartment is limited.

The metal positive reservoir, which serves as a case for the generator and as a positive terminal, consists of a cylinder of chromized mild steel 15 tightly connected with discs 5 and 6 respectively by means of two metal annular members 16 and 17, also made of chromized mild steel. Said annular members are welded around the periphery 18 and 19 of the two ends of cylinder 15. In addition, they are bonded by thermocompression to the periphery 21 and 22 of the external faces of discs 5 and 6.

Metal members 16 and 17 are bent to allow them to undergo a certain elastic deformation when they are subjected to stresses resulting from the differential expansion between the metal cylinder 15 and the beta double prime alumina cylinder 1 as a result of hot and cold cycling.

Cylinder 15 contains sulfur 30 introduced therein, as will be seen further on, in solid form in longitudinal portions of the cylinder.

The basic steps in manufacturing the generator according to the invention are as follows: --Begin by making the cylinder 1 of beta double prime alumina to the desired length.

--Fit disc 6 together with its terminal 10 to the cylinder 1 by means of glass seal 8.

--Inject nickel wicks 3 and 4 into cylinder 1.

--Presinter the nickel wicks 3 and 4 at about 750 C.

--Close the top of cylinder 1 by means of disc 5 and a glass seal 7. The temperature required to effect the glass seal, being on the order of 1,000 C, also completes the sintering of the nickel wicks 3 and 4.

--Attach annular members 16 and 17 by thermocompression to peripheral zones 21 and 22 respectively on alpha alumina discs 5 and 6.

--Place longitudinal portions 30 of solid sulfurbase electrode around cylinder 1.

--Install positive cylinder 15 and weld its top and bottom edges at 18 and 19 to the annular members 16 and 17.

--Inject sodium 2 through tubing 10.

--Close tubing 10.

As an indication, the physical dimensions of the generator according to the invention may be as follows: --The cylinder 1 of beta double prime alumina has an internal diameter of 34mm, an external diameter of 40mm and a length of 400mm.

--The cylinder 15 of chromized steel has an internal diameter of 55mm and a thickness of 0.5mm.

--The alpha alumina discs are 7 to 8mm thick.

--The sintered nickel wicks are approximately 2mm thick.

From the standpoint of electrical performance, a generator according to the invention calibrated at 175 Ah (300 Wh) provides charging and discharging current densities of approximately 57 mA,'cm2 and 80 mAicm2 respectively.

Figure 2 shows an alternative embodiment of the generator of Figure 1. Elements common to both figures bear like references.

In this embodiment, the sodium distribution wicks are replaced by a metallic bottle 20 with perforations 21 towards the bottom, having an external diameter slightly smaller than the interior diameter of the tube of beta double prime alumina 1. The top of bottle 20 comprises a neck 10 extending through disc 5. Said neck is sealingly connected to the disc by means of a collar 23 like collar 11 in Figure 1. The bottle 20 is incompletely filled with sodium which is pressurized (to a mximum of 1 bar) by means of an inert gas, so that the annular space 25 between the cylinder of beta double prime alumina 1 and bottle 20 will always be filled with sodium, regardless of the level of sodium in the bottle 20.

Of course, the present invention is not limited to the embodiments described in detail in the foregoing. In particular, alternative constructions for the positive reservoir and its connecting parts to the two alpha alumina plates closing the beta alumina cylinder will obviously occur to a person skilled in the art. Also, the reservoir need not have a circular cross section.

Claims

1. An electrochemical generator of the sodiumsulfur type comprising: -a metal positive reservoir containing a positive electrode the active material of which, liquid at the temperature of operation, consists of sulfur and its alkaline salts; -and a solid electrolyte tube of beta or of beta double prime alumina within said positive reservoir and which separates said positive active material from the negative electrode of which the active material, liquid at the temperature of operation, is sodium, characterized by the fact that said solid electrolyte is constituted by a hollow cylinder of beta or beta double prime alumina the two ends of which respectively are closed by two sealed discs of alpha alumina, and that said positive reservoir consists of a metal cylinder the bottom and top edges of which are respectively welded to two metal annular connecting parts also sealingly welded to said alpha alumina discs, said metal, annular connecting parts being shaped to permit elastic deformations of the connection.

2. An electrochemical generator according to Claim 1, wherein the inside walls of said beta alumina or beta double prime alumina cylinder are lined with metallic wicks.

3. An electrochemical generator according to Claim 1, wherein said beta alumina or beta double prime alumina cylinder contains a metal bottle with perforations near the bottom thereof and having an external diameter slightly smaller than the internal diameter of said cylinder and said bottle is incompletely filled with sodium under pressure.

4. An electrochemical generator according to Claims 1, 2 and 3, wherein one of said discs of alpha alumina comprises a bore hole through which sealingly passes a metal filling neck for filling the bottle with sodium, sealing being provided between said neck and said bore by a metal collar welded along the periphery of said neck and thermocompression bonded to the external face of the alpha alumina disc.

5. An electrochemical generator according to Claim 1, wherein said positive reservoir and said annular connecting parts are made of chromized mild steel.

6. An electrochemical generator according to Claim 2, wherein said metallic wicks consist of a sintered sponge of iron or nickel.

7. An electrochemical generator substantially as hereinbefore described with reference, to and as shown in, Figure 1 or Figure 2 of the drawings.