DE2638484A1 - ELECTROCHEMICAL CELL - Google Patents

Description

Patent attorneys Dipl.-Ing. RWeickmann,

Dipl.-Ing. H. Wh [ckmann, Dipl.-Phys. Dr. K. Fincke SPMT Dipl.-Ing. RA Weickmann, Dipl.-Chem. B. Huber

8 MUNICH 86, DEN

POST BOX'860 820

MÖHLSTRASSE 22, CALL NUMBER 98 39 21/22

CHLORIDE SILENT POWER LIMITED, London SW1W OAU / England 52 Grosvenor Gardens

Electrochemical cell

The invention relates to an electrochemical cell which has a solid electrolyte in tubular form which separates a liquid alkali metal, which forms an anode, from a liquid cathodic reactant or participant. Such cells operate at an elevated temperature, typically at a temperature above 200 ⁰ C. A sodium-sulfur cell which normally operates between 300 and 35O ° C, but which can operate 270-400 ⁰ C, is a familiar example a cell that has a solid electrolyte.

The electrolyte material is a material through which ions of the alkali metal can migrate. A number of them solid electrolyte materials are known; in the case of sodium-sulfur cells, it is common practice to use a ß-alumina ceramic material to use. Similar to other known solid electrolytes, this material has only one

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limited mechanical strength, and one of the main possibilities one cell failure is the rupture of the electrolyte tube. Apart from the loss of the cell due to a battery the rupture of a pipe there is also the possibility of the risk of destruction of surrounding equipment or systems or the harm to personnel in the event of an electrolyte breakage, when there is sudden mixing of a large amount of liquid alkali metal with the cathodic reactant.

The present invention relates to increasing the resistance of the tubular electrolyte material to a break due to hoop stress or stress. The linear expansion coefficient of ß-aluminum oxide is about 7 x 10 "K", and the difference in thermal expansion, e.g. between a solid, central cathode current absorber, which has a relatively high coefficient of thermal expansion, and the electrolyte tube, leads to that the electrolyte is exposed to circumferential voltage loads when a cold cell is heated to its operating temperature will. A central cathode is preferred in a sodium-sulfur cell, but the same or similar difficulties occur when a solid, central anode is used. The electrolyte will also put loads in the area exposed to the seal, both due to the compressive forces exerted by the seal and due to the differential movement between the sealing components caused by changes in cell temperature will.

In accordance with the present invention, in a cell having a tubular housing, there is a tube of solid electrolyte material contains, which separates the alkali metal from a cathodic reactant, a compression or. Restraint device (hereinafter collectively referred to as "compression device")

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the electrolyte tube is provided around that has such a coefficient of thermal expansion has an increasing inward pressure on the electrolyte tube as the temperature increases. With this structure, the "electrolyte tube in the Operating temperature can be put under compression. The increasing pressure as the temperature rises reduces the possibility of that the pipe bursts under circumferential stress or stress. The compression device can initially be preloaded biased so that it exerts an inward pressure at room temperature.

The compressing device, in its simplest form, may be a device such as a wire around the tube have, or which has a lower coefficient of thermal expansion than that of the pipe. However, it often is advantageous to take advantage of the fact that there is necessarily an outer housing around the pipe, and consequently is in one embodiment of the invention in the annular area between the housing and the electrolyte tube a material is provided which is either in powder form or is shaped to be under pressure is deformable in radial directions, the material having a higher coefficient of thermal expansion than the material of the housing, so that when the temperature of the cell increases, pressure in of this material on the electrolyte tube Radial direction is exercised. This material therefore exerts a pressure that corresponds to the circumferential stress or load on the electrolyte tube opposed, and this pressure increases as the temperature rises. The cell can initially be constructed so that the electrolyte is biased or loaded at room temperature.

In a sodium-sulfur cell, the structure is preferably such that the cathodic reactant _9, ie the sulfur-containing material, - is within the electrolyte tube,

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while the sodium is around the outside of the electrolyte tube. Such a structure enables the use of a metallic housing which contains the sodium. It is then possible to use a relatively little expanding housing, for example a little expanding iron-nickel alloy or a ferritic stainless steel. Other low expansion metals and alloys suitable for the case and resistant to attack by sodium include cobalt (α = 14 x 10 "K ~) and some of its alloys, nickel (α = 13 x 10" K ~) ) and some of its alloys, niobium (α = 7 x 10 "Κ"") and some of its alloys, molybdenum (cc = 6 χ 10 ~ ⁶ K" ¹ ) and zircon (α = 6 χ 10 ~ ⁶ K " ¹ ) and some of its alloys, certain iron-nickel-cobalt alloys and simple carbon steel (α = 11 χ 10 K), which is or are protected against attack by sodium by means of a suitable surface coating, if such The symbol α denotes the coefficient of thermal expansion above and also in the following text. In this case, the material within the annular area around the electrolyte tube can comprise one or more elements of a relatively rapidly expanding alloy, e.g. stainless steel, the is disposed around the electrolyte tube, each member being deformable in the radial direction. Other materials with a high coefficient of thermal expansion include aluminum (α = 23 x 10 "K") and its alloys, copper (α = 17 x 10 "K") and some of its alloys. In addition, some of the materials mentioned above for The casing specified can be used in conjunction with a cell casing which has a very low coefficient of thermal expansion.Aluminum and copper are both resistant to attack by liquid sodium.

In an advantageous embodiment of a structure, an annular element made of stainless steel is provided,

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which is essentially a corrugated, corrugated, corrugated or corrugated shape (hereinafter collectively referred to as "corrugated" or "undulating") has, the corrugations, corrugations, ribs or grooves (summarized below referred to as "corrugations") extend back and forth across the annular region between the electrolyte tube and the housing. Such an element can be identical or similar in shape to a cuff, and from this It is therefore appropriate to refer to the element as a cuff. It should be noted, however, that the shape of the element is not critical as long as it allows deformation in the radial direction, with expansion when heated causes pressure to be exerted in the radial direction and to deform the element when or where it is it is necessary that the element adapts itself to the available space.

If a sleeve made of sheet material is used, the material can be perforated so that the flow of the alkali metal is facilitated.

Preferably, a cuff, if it is made of foils or Plate material is formed so shaped that it is, for example forms two or more rows of substantially cylindrical parts so that they can easily achieve the required Stress or stress due to the radial pressure supplies. In some cases it can be advantageous to use the ring-shaped To form an element from an arrangement of cylinders, which has separate cylinders or consists of such cylinders, those in the annular area around the electrolyte tube are packed around.

If a powder is used, it is possible to use any material that will withstand the conditions and one

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has a suitable coefficient of thermal expansion. As explained above, in a sodium-sulfur cell it is preferred to provide the sodium in the annular area around the outside of the electrolyte tube, and consequently must Be inert to liquid sodium and have a coefficient of thermal expansion greater than that of the material Housing of the cell is. The use of a powder has the advantage that the assembly of the cell is made easier. It It is also possible to pack the annular space with a suitable powder so that the electrolyte is preloaded or loaded at room temperature. - is tensioned. The powder helps wick the liquid sodium material, ensuring that that the wide surface of the electrolyte tube is kept wetted by liquid sodium. The powder also acts as a limiting agent for sodium flow in the event of a catastrophic electrolyte failure. The packed powder moreover, it helps to prevent or prevent leakage of the seal and degrades the packing the stress-bending stresses caused by the compressive forces of a seal at the end of the electrolyte tube will.

Suitable materials to be used as such powders include or are powdered metal of the materials suggested above for a cuff. It is also possible to use non-metallic materials, ceramic or vitreous or vitreous or glass-like materials "as powders that expand greatly in a cell to be used with low expansion. The alkali or alkaline earth halides can be suitable; for example united Calcium fluoride has a high coefficient of thermal expansion (19 x 10 K) and a high modulus of elasticity with chemical resistance to liquids Sodium.

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Both powder, as they have been described above, as well as the cuff mentioned carries or holds that Electrolyte tube inside the cell, which is beneficial in a cell which is used in application cases in which it provides propulsion power on vehicles, in which cases the electrolyte is due to acceleration or deceleration is charged.

As stated above, in another structure, the reinforcement of the electrolyte tube against an increase the circumferential tension or stress caused by heating be that one provides rings or bands or a winding of material around the electrolyte tube, the Material has a lower coefficient of expansion than the electrolyte material. Advantageously, such a Reinforcement achieved by wrapping one or more wires around the electrolyte tube. With this arrangement leads a different heat movement that occurs between the ambient temperature and the cell operating temperature, that the electrolyte is brought under compression, as in the other embodiments, so that he in this way is effectively reinforced against any stress circumferential load. A very suitable material that around the electrolyte tube may be wound in a sodium-sulfur cell, comprises or is carbon fiber material. Oriented carbon fibers, those obtained by graphitizing an organic fiber serving as a precursor, e.g. Polyacrylonitrile, contract along the fiber axis when their temperature is increased / in other words, this means that the coefficient of thermal expansion is negative. Such materials also have a high modulus of elasticity. Such wires or fibers can be used in a sodium-sulfur cell, the Has a central sodium electrode as the carbon fiber material is used in the cathodic reactant can. In a cell with the sodium around the outside

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of the electrolyte tube is provided around, a wire can be made Nickel-iron alloy or nickel-iron-cobalt alloy with low expansion or it can be carbon fibers or filaments of glass of suitable composition which have a suitable low coefficient of thermal expansion and are chemically resistant to sodium, to be wrapped around the electrolyte tube for its reinforcement.

In another construction, a perforated sheet or thin sheet of low expansion material is around wrapped the electrolyte tube around; provided that the coefficient of expansion of the film or plate material is lower than that of the electrolyte tube, the tube will be below Compression set when the temperature rises so that it is possible in this way to have the required compressive load is produced or developed at the operating temperature. In a sodium-sulfur cell where the If sodium is provided around the outside of the electrolyte tube, this perforated foil or thin plate can be arranged in this way be that it acts as a wick keeping the outer surface of the tube covered with sodium.

The invention will be described below with reference to some of those shown in principle in the figures of the drawing preferred embodiments explained in more detail; namely, FIGS. 1 to 5 show a schematic representation of cross sections through various embodiments of a sodium-sulfur cell.

Reference is first made to FIG. 1, in which a sodium-sulfur cell is shown schematically, which has an electrolyte tube 10 made of ß-aluminum oxide, which is coaxial is arranged within a cylindrical housing 11, which in turn, for example, from a low Expanding iron-nickel alloy or a corresponding ferritic stainless steel is. This spe-

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zial cell has the cathodic reactant, the Comprises sulfur and the polysulfide materials "formed when the cell is discharged" within the Electrolyte tube 10. To achieve an electronic line to the cathode is a central graphite current collector rod 13 with a graphite or carbon felt 14, which extends between the current collector rod and the electrolyte tube, intended. The annular area between the electrolyte tube 10 and the housing 11 is filled with sodium, which is liquid at the operating temperature of the cell. To reduce the hoop stress or stress in the electrolyte tube When the cell is heated, in the arrangement of FIG. 1 a sleeve 18 is provided which is made of stainless steel is. This sleeve is essentially a corrugated sheet or thin plate, the corrugations being transverse over the ring-shaped area between the electrolyte tube and the housing stretch back and forth. Fig. 1 shows a simple embodiment of the cuff in which the corrugations in have a substantial sinusoidal shape. The material must be sufficient in comparison with the expansion coefficient of the housing 11 have high coefficients of expansion in such a way that the pressure on the electrolyte tube increases when the temperature increases. The shape of the collar allows for deformation in the radial direction, and as a result causes it a different thermal expansion an increase in the pressure on the electrolyte tube. The size of this print differs from that The coefficient of expansion of the material and the relationship between the radial pressure and the deformation are determined, where the latter relationship depends on the shape and thickness of the material.

Fig. 2 shows a modification of the arrangement of FIG. 1, in which the shape of the sleeve is such that the various adjacent corrugations are brought into contact, thereby creating any tendency to completely overbend a corrugation during compression can be avoided.

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It can be seen that the sleeve of FIG. 1 is very similar to a series of cylindrical elements, and it is possible, as shown in FIG Housing 11 are arranged.

Fig. 4 shows a further embodiment of the structure, in which a powder material 20 is packed in the annular region between the electrolyte tube 10 and the outer casing 11 is selected so that its coefficient of thermal expansion is sufficiently large in comparison with that of the outer Housing is such that it is ensured that when the temperature rises, pressure is exerted on the electrolyte tube will.

Fig. 5 shows another structure in which a wire 22 is wound around the electrolyte tube 10. This wire has a smaller coefficient of expansion than the material of the electrolyte tube so that the tube is placed under compression as the temperature rises. In the case of a cell, which, as shown, has a central cathode, the wire may be made of low elongation iron-nickel or Iron-nickel-cobalt alloy, or from threads of a suitable glass or from threads of oriented Carbon fiber material. This arrangement which uses a wire tightly wrapped around the electrolyte tube can also be used with a cell that has a central anode and where the cathodic reactant, i.e., the sulfur-containing material, is provided in the annular area between the electrolyte tube and the housing is. In this latter case, the wire must be made of a material that meets the conditions of the cathodic region resists; advantageously material is made of or applied with oriented carbon fibers. The wire can be attached as a spiral around the electrolyte tube, wherein

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the spiral extends the length of the tube, or the wire can be provided as a series of rings running longitudinally the length of the pipe are spaced so that the compressive load in the circumferential direction in the pipe is substantially - is applied uniformly over the entire pipe. Each end of the wire can be attached, e.g., to the other end of the wire or to a different turn on the wire or the wire, in such a way that ensured becomes that the rings or the coil remain tight or tight around the ceramic tube.

In another construction, perforated metal is a foil or thin plate around the electrolyte tube at room temperature wrapped around, the metal being selected so that it has a coefficient of expansion less than that of the electrolyte tube, so that when the cell is brought to normal operating temperature, the electrolyte is subjected to compressive stress.

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Claims (27)

Claims / Ί. Electrochemical cell with a tube made of solid electrolyte material, which separates a liquid alkali metal from a cathodic reactant, characterized in that that one or more compression devices (18,19, 20,22) are provided around the electrolyte tube (10), which have such a coefficient of thermal expansion that they increase with increasing Temperature, exert increasing inward pressure on the electrolyte tube. 2. Electrochemical cell according to claim 1, characterized in that that the compression device or devices (18,19,20,22) are initially preloaded or are tensioned so that they exert an inward pressure at room temperature. 3 · Electrochemical cell according to claim 1 or 2, characterized characterized in that the compressing device or devices (18.19 »20.22) has a device or have, which extends completely around the tube (10) and has a coefficient of thermal expansion, which is smaller than that of the pipe. 4. Electrochemical cell according to claim 3, characterized in that that the compression device or devices has or have a wire (22) or is or are such a wire which extends around the electrolyte tube (10). 5- electrochemical cell according to claim 1 or 2, characterized characterized in that in the annular region which extends between an outer housing (11) which is provided around the tube (10) is, and the electrolyte tube extends, a material (18, 19,20) in powder form or in such a form that it is under 709 8 09/0874 Pressure is deformable in radial directions, is provided, this material having a higher coefficient of expansion than the material of the housing, so that when the temperature of the cell is increased, pressure in this material radial direction is exerted on the electrolyte tube. 6. Electrochemical cell according to one of claims 1 to 5, characterized in that it is used as a sodium-sulfur cell is formed and has a ß-aluminum oxide tube (10), which forms a solid electrolyte, the sulfur-containing separates cathodic reactant from liquid sodium, the compressing device (18,19,20,22) around the β-alumina tube is provided and has a coefficient of thermal expansion which is relative to that of the β-alumina is such that increasing inward pressure is exerted on the β-alumina tube as the temperature increases increases, thereby compressing the pipe at its operating temperature. 7. Electrochemical cell according to claim 6, characterized in that that the coefficient of thermal expansion of the compression device or compression devices (18,19, 20,22) is lower than that of ß-aluminum oxide. 8. Electrochemical cell according to claim 6 or 7, characterized characterized in that the cathodic reactant within the ElektrοIytrohrs (10) and the sodium in a housing (11) provided around the outside of the electrolyte tube wherein the housing is a tubular housing made of a metal having a relatively low coefficient of thermal expansion is formed, and wherein further the annular region between the housing and the electrolyte tube contains one or more elements (18,19,20) made of a material, which has a relatively high coefficient of thermal expansion, the difference being the coefficient of thermal expansion 709809/0874 of the housing and the elements are sufficiently large and the elements are radially deformable so that the elements when rising exert an inward pressure on the surface of the electrolyte tube depending on the temperature. 9. Electrochemical cell according to claim 8, characterized in that that the housing (11) made of a ferritic, stainless steel or an iron-nickel alloy with lower Expansion is formed. 10. Electrochemical cell according to claim 8, characterized in that that the housing (11) is made of cobalt or nickel or niobium or molybdenum or zirconium or from a Alloy containing any one or more of these materials and resistant to attack by molten sodium is resilient. 11. Electrochemical cell according to claim 8, characterized in that that the housing (11) is formed from an iron-nickel-cobalt alloy. 12. Electrochemical cell according to claim 8, characterized in that that the housing (11) is formed from a carbon steel, which has a surface coating for protection against attack by sodium. 13 · Electrochemical cell according to one of Claims 8 to 12, characterized in that the element (18, 19, 20) or each of the elements in the annular region is formed from a metal which is resistant to attack by sodium is chemically resistant. 14. Electrochemical cell according to one of claims 8 to 12, characterized in that the metal element (18 , 19, 20) or each metal element in the annular region is formed from aluminum or copper. 709809/0874 15. Electrochemical cell according to claim 13, characterized in that that the metal element (18,19,20) or each metal element in the annular region is made of an alloy made of aluminum or an alloy of 'copper that is resistant to attack by sodium. 16. Electrochemical cell according to one of claims 6 to 15 ,, characterized in that the element (18, 19, 20) or each of the elements in the annular region is an annular Element (18) which extends around the electrolyte tube (10) and has a corrugated shape with the corrugations across the annular area between the electrolyte tube and the housing (11) extend back and forth. 17 · Electrochemical cell according to claim 16, characterized in that that the element (18) or each of the elements formed from a metal foil or a thin plate of metal and is perforated to facilitate sodium flow. 18. Electrochemical cell according to claim 16 or 17, characterized in that the corrugations are shaped so that they form two or more rows of substantially cylindrical members, each row wrapping around the annular region extends around. 19. Electrochemical cell according to one of claims 6 to 15, characterized in that a plurality of said elements is provided, wherein the elements are cylinders (19) which are parallel to the axis of the electrolyte tube (10) in the extending annular area between the electrolyte tube and the housing (11). 20. Electrochemical cell according to one of claims 6 to 15, characterized in that said elements of a 709809/0874 Powder (20) or some other lumpy material in the annular area between the electrolyte tube (10) and the housing (11) are formed. 21. Electrochemical cell according to claim 20, characterized in that that the powder (20) or the lumpy material in the annular area between the housing (11) and the Electrolyte tube (10) is packed so that it biases the electrolyte into a compression state at room temperature. 22. Electrochemical cell according to claim 6, characterized in that that the compressing device or devices (22) rings, brackets, bands, strips, supports or the like. From a material with a lower coefficient of expansion than the coefficient of expansion of ß-aluminum oxide around the Electrolyte tube (10) encompassed or are encompassed along its length. 23. Electrochemical cell according to claim 6, characterized in that that the compression device or devices (22) is flexible material with a lower coefficient of thermal expansion as the coefficient of thermal expansion of the β-alumina includes or are, this being flexible material is wrapped around the electrolyte tube (10) along its length. 24. Electrochemical cell according to claim 22 or 23, characterized in that the compressing device or devices (22) comprises or comprises or .is or are metal wire. 25. Electrochemical cell according to claim 22 or 23, characterized characterized in that the compressing means (22) comprises carbon fiber material or is or are. 709803/0874 26. Electrochemical cell according to claim 22 or 23, characterized characterized in that the compressing means (22) are filaments of sodium resistant Glass, which has a lower coefficient of thermal expansion than the β-alumina electrolyte, includes or are. 27. Electrochemical cell according to claim 6, characterized in that that the compression device or devices (22) perforated metal foil or perforated metal sheet, wrapped around the electrolyte tube (10), comprised or is or are. 709809/0874 Blank page