FR2487130A1 - Electrochemical generator of the sodium-sulphur type - with corrugations in lower, container esp. near solid electrolyte to accommodation shrinkage and expansion - Google Patents

Abstract

Electrochemical generator operating at high temp. comprises a metal container contg. an anodic active material, liquid at the operating temp. and a second metal container contg. a cathodic active material also liq. at the operating temp. The containers are connected at their open ends by a seal which carries a solid electrolyte tube inside one of the containers opening into the other. Specifically, the container contg. the cathode material includes on at least part of its surface, deformations designed to absorb mechanical constraints occurring during operation of the cell. The cell is pref. a Na/S cell. Stresses, such as those occurring on cooling from the working temp. to ambient and reheating, can be accommodated.

Description

Sodium-sulfur electrochemical generator
The present invention relates to an electrochemical sodium-sulfur generator.

 It is known that such generators are constituted by a negative reservoir containing liquid sodium and by a positive reservoir containing sulfur impregnating a conductive material such as graphite fibers.

 These generally cylindrical tanks are sealed by their open ends on either side of an alpha alumina plate.

 In addition, a solid electrolyte tube made of sodium alumina beta is sealed by means of a glass at its open end in an opening in the alpha alumina plate.

 It is also known that such generators operate in a temperature range of between 300 and 3500C approximately.

 However, we realize that after the generator stops and during its cooling it occurs at the level of the components, mechanical stresses leading either to the breaking of the seal between the positive reservoir and the alpha alumina plate, or the fracture of the seal between the electrolyte tube and said alpha alumina plate, or the breakage of said alpha alumina plate.

In fact, the phenomena that cause these breaks are as follows:
When the generator is cooled from its operating temperature, ie 300 to 3500C. Up to room temperature, there is a contraction of the metal reservoir significantly greater than that of the electrolyte tube.

 This would not have an unfortunate effect if the electrolyte tube remained free relative to the reservoir (except, of course, the upper end of the tube sealed to the alpha alumina plate).

 However, at a temperature of the order of 250 to 2800C, crystallization occurs of the polysulphides which block the electrolyte tube with respect to the reservoir and in particular between the lower end of the electrolyte tube and the bottom of the reservoir.

From the combination of these two phenomena of different natures, that is to say on the one hand the blocking towards 2500C and on the other hand the
contraction between 2500C and room temperature, result from efforts, traction on the reservoir, compression on the electrolyte tube, shearing on the alpha alumina plate, traction on the tank / alpha alumina plate sealing and shear on the sealing of alpha alumina plate / electrolyte tube.

 The result of these opposing efforts is the breaking of the alpha alumina plate or the seals as previously mentioned.

 The present invention overcomes these drawbacks.

 The subject of the invention is therefore an electrochemical generator operating at high temperature comprising a metal tank containing an anodic active material which is liquid at operating temperature and a metal tank containing a cathodic active material which is liquid at operating temperature, said tanks being joined by their ends open by sealing means, said sealing means also carrying a solid electrolyte tube situated inside one of the reservoirs and opening into the other reservoir, characterized in that the reservoir containing the material cathodic active comprises on at least part of its surface deformations capable of absorbing mechanical stresses during the cooling of said generator.

Other characteristics and advantages of the invention emerge from the description which follows, given by way of purely illustrative but in no way limiting, with reference to the appended drawings in which
FIG. 1 represents a conventional sodium-sulfur electrochemical generator.

 FIG. 2 represents a first embodiment of an electrochemical generator according to the invention.

 FIG. 3 represents a second embodiment of an electrochemical generator according to the invention.

 FIG. 4 represents a third embodiment of an electrochemical generator according to the invention.

 FIG. 1 therefore shows a conventional generator comprising a negative reservoir 1 containing an anodic active material which is liquid at the operating temperature, in this case liquid sodium 2 and a positive reservoir 3 containing a cathodic active material which is also liquid at the operating temperature. , in this case sulfur 4 impregnating graphite fibers (not shown). These reservoirs are sealed with their ends open to an alpha 5 alumina plate, while an electrolyte tube 6 of sodium alumina beta is sealed by means of a glass 7 at its open end to the plate 5 and opens into the tank 1 while bathing in the sulfur contained in the positive tank 3.

 Of course, a reverse arrangement could be envisaged, that is to say that the sodium could be placed in the tank 3 which would then be the negative tank, while the sulfur 4 would be contained in the tank 1 and the tube. electrolyte 6, said reservoir then being the positive reservoir.

 The arrows F materialize the tensile stress exerted during cooling on the positive reservoir 3, while the arrows F ′ illustrate the compression force to which the electrolyte tube 6 is subjected, hence the fracture or fracture of the seals as previously indicated.

 In the embodiment according to the invention shown in FIG. 2, it can be seen that a large amplitude corrugation 10 of the wall has been created at the upper part of the positive reservoir 3 substantially at the level of the plate 5. In this way, the tensile force exerted during cooling on the reservoir 3 is absorbed, the corrugation 10 taking the position illustrated in 10 '.

 In the embodiment shown in FIG. 3, it can be seen that there have been formed on almost the entire wall of the positive reservoir 3, corrugations 11 of small amplitude, also absorbing the tensile force during cooling in taking the position materialized in 11 '.

 The advantage of such an arrangement lies in the fact that the polysulphides crystallized during cooling are kept at the level of the corrugations, which thus prevents any abrasion by friction on the electrolyte tube 6 and on the internal wall of the reservoir 3.

 With reference to FIG. 4, it can be seen that a ripple 10 of large amplitude has been formed at the upper part of the wall of the reservoir 3 as illustrated in FIG. 2, and on the remainder of the wall ripples of lower amplitude as illustrated in FIG. 3, the operating mode being that explained with reference to FIGS. 2 and 3.

 It is obvious that in the case where the sodium 2 is placed in the tank 3 and the sulfur 4 in the tank 1, the corrugations 10, 11 as shown in FIGS. 2, 3 and 4 would be formed on the wall of the tank 1 which would then be the positive tank.

 The sodium-sulfur generators according to the invention therefore allow repeated heating and cooling cycles without the slightest failure.

 They find advantageous applications in traction batteries for motor vehicles.

 Of course, the invention is in no way limited to the embodiments described and shown which have been given only by way of example.

 In particular, it is possible, without departing from the scope of the invention, to make detailed modifications, to change certain provisions or to replace certain means by equivalent means.

Claims (5)

1 / Electrochemical generator operating at high temperature comprising a metal reservoir containing an anodic active material liquid at operating temperature and a metal reservoir containing a cathodic active material liquid at operating temperature, said reservoirs being joined by their open ends by means for sealing, said sealing means also carrying a solid electrolyte tube situated inside one of the reservoirs and opening into the other reservoir, characterized in that the reservoir containing the cathodic active material comprises on at least part of its surface area of deformations capable of absorbing mechanical stresses during the cooling of said generator.  2 / Generator according to claim 1, characterized in that said deformations comprise a wide amplitude ripple formed on the wall of said tank at its upper part and substantially at said sealing means. 3 / Generator according to claim 1, characterized in that said deformations include undulations of small amplitude formed on its wall. 4 / generator according to claim 1, characterized in that said corrugations comprise on the one hand a ripple of large amplitude formed on the wall of said tank at its upper part, substantially at the level of said sealing means, and on the other hand small amplitude undulations made on the remaining part of the wall of said tank. 5 / Battery comprising at least one generator according to one of the preceding claims.