CA1298347C - Electrochemical cell - Google Patents
Electrochemical cellInfo
- Publication number
- CA1298347C CA1298347C CA000584816A CA584816A CA1298347C CA 1298347 C CA1298347 C CA 1298347C CA 000584816 A CA000584816 A CA 000584816A CA 584816 A CA584816 A CA 584816A CA 1298347 C CA1298347 C CA 1298347C
- Authority
- CA
- Canada
- Prior art keywords
- cell
- anode
- separator
- compartment
- metal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/36—Accumulators not provided for in groups H01M10/05-H01M10/34
- H01M10/39—Accumulators not provided for in groups H01M10/05-H01M10/34 working at high temperature
- H01M10/3909—Sodium-sulfur cells
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/36—Accumulators not provided for in groups H01M10/05-H01M10/34
- H01M10/39—Accumulators not provided for in groups H01M10/05-H01M10/34 working at high temperature
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Secondary Cells (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The invention provides a rechargeable high temperature electrochemical power storage cell having a molten alkali metal anode separated from a cathode by a separator. The separator divides the cell into an anode compartment which contains said alkali metal and a cathode compartment which contains a cathode. The separator permits the anode alkali metal to pass therethrough during discharge of the cell from the anode compartment to the cathode compartment into which it is released in ionic form for reaction with the cathode. The cell has an operative attitude in which it is upright, in which operative attitude the separator extends at an angle to the horizontal so that the level of the surface of anode metal in the anode compartment to which the separator is exposed, drops during discharge of the cell and rises during charging of the cell. The anode compartment has a lower portion and an upper portion which has a greater horizontal cross-section than the horizontal cross-section of the lower portion, and the lower portion is entirely filled with anode metal in the fully discharged state of the cell.
The invention provides a rechargeable high temperature electrochemical power storage cell having a molten alkali metal anode separated from a cathode by a separator. The separator divides the cell into an anode compartment which contains said alkali metal and a cathode compartment which contains a cathode. The separator permits the anode alkali metal to pass therethrough during discharge of the cell from the anode compartment to the cathode compartment into which it is released in ionic form for reaction with the cathode. The cell has an operative attitude in which it is upright, in which operative attitude the separator extends at an angle to the horizontal so that the level of the surface of anode metal in the anode compartment to which the separator is exposed, drops during discharge of the cell and rises during charging of the cell. The anode compartment has a lower portion and an upper portion which has a greater horizontal cross-section than the horizontal cross-section of the lower portion, and the lower portion is entirely filled with anode metal in the fully discharged state of the cell.
Description
- 129~3347 THIS INVENTION relates to an electrochemical cell. ~lore particularly the invention relates to a rechargeable high temperature electrochemical power storage cell of the type having a molten alkali metal anode separated from a cathode by a separator.
According to the invention there is provided a rechargeable high temperature electrochemical power storage cell having a molten al~ali metal anode separated from a cathode by a separator, the separator dividing the cell into an anode compartment which contains said alXali metal and a cathode compartment which contains a cathode, and the separator penmitting the anode alXali metal to pass therethrough during discharge of the cell from the anode compartment to the cathode cc)mpartment into which it is released in ionic form for reaction with the cathode, the cell having an opeTative attitude in which it is upright, in which operative attitude the separator extends at an angle to the horizontal so that the level of the surface of anode metal in the anode compartment to which the separator is exposed, drops during discharge of the cell and rises during charging of the cell, the anode compartment having a lower portion and an upper portion which has a greater horizontal cross-section than the horizontal cross-section of the lc)wer portion, and the lower portion being entirely filled with anode.~.etal in the fully discharged state of the cell.
The separator may be a solid electrolyte conductor of ions of the anode .metal, the separator being in the form of a cylindrical tube which is closed at one end.and open at the other and has a hollow interior, the separator tube being arranged in the interior of a cell.housing so that, in said operative attitude of the cell, the closed end of the tube is lowermost and the open end of the tube is uppermost, the ~298347 interior of the tube forming an electrode compartment and the tube being spaced from the housing so that a space is defined between the tube and the housing which forms another electrode compartment. In this type of construction, when the anode compartment is in the interior of the tube, it will normally be of circular or annular cross-section, and when it is outside the tube, it will normally be of annular cross-section. For the horizontal annular cross-section of the lower portion of the anode compartment to be less than that of the upper portion, it follows that, in this type of cell, the lower portion will have a smaller horizontal, eg radial, dimension than that of the upper portion. Thus, when the anode compartment is annular, the amlulus of the upper portion will be thicker than that of the lower portion.
As the separator tube will usually (because of the way in which such tubes are typically made) be of constant diameter, different horizontal cross-sections for said upper and lower portions may be provided by having the casing circular in cross-section and by having the casing change in diameter (when the anode compartment is outside the tube);,or by placing an insert in the lower portion of the anode compartment (eg a tubular insert when the anode compartment is outside the tube, or a cylindrical or tubular insert when the anode compartment is inside the tube), with the insert concentric with the tube and radially spaced therefrom. Instead, the insert may be in powder or granular form.
In a particular embodiment, the separator tube may accordingly have a constant diameter, the interior of the tube forming the cathode compartment, the housing being of circular cross-section, and the tube being arranged concentrically therein and the space between the tube and housing forming an annular anode compartment.
When the anode compartment is annular in horizontal cross-section, the thickness of the annulus is preferably as low as practicable, eg about 0,1 - 0,2 mm for practical purposes. Similarly, the lower portion of the anode compartment should have an upper end which is as high as practicable, and the ~ower portion should extend upwardly to an upper end which is at least as high as the midpoint of the separator in a vertical direction. Accordingly, in a particular embodiment of the invention, the thickness of the lower portion of the annulus of the anode compartment is preferably at most 0,2 mm, the lower portion of the anode compartment having, when the cell is in its said operative attitude, an upper end which is at a level not lower than the level of the midpoint of the length of the separator tube.
Preferably the volume of the upper portion of the anode compartment is selected such that said upper portion is substantially full of anode metal when the cell is fully charged, and substantially empty when the cell is fully discharged, but with the lower portion remaining full at all times. In other words, the volume of the upper portion of the anode compartment may be related to the capacity of the cell such that the upper portion is substantially full of anode metal when the cell is fully charged, and so that, when the cell is fully discharged with the cell in its operative attitude, the level of anode metal in the anode compartment is at the top of the lower portion of the anode compartment, so that said lower portion is substantially full of anode metal when the cell is in said fully discharged state.
To promote wetting of the full surface of the separator e.Yposed to theanode compartment, said surface may be lined with a wicking material in said upper portion. Thus, the surface of the separator which is exposed to the anode compartment may be lined with wicking material for wicking the metal of the anode, the wicking material extending downwardly into contact with the anode metal in all states of charge of the cell when the cell is in its operative attitude. Such wicking material may be selected from the group consisting of a metal gauze, a metal powder held against the separator by a porous metal screen, a sintered porous metal liner and a felt liner. Naturally, other types of wicking material may instead be suitable.
In principle the wicking height should be kept as lo~- as possible so that, from this point of view, the upper portion of the anode compartment should be wide and shallow. However, from the point of view of volumetric energy density in a battery of close packed cells, it is desirable to have cells of substantially constant outer diameters, and without spaces therebetween. Thus, when the anode compartment is outside the separator tube, it follows that a deep upper ~298.~7 portion is desirable, only slightly wider than the lower portion. In practice there will be a trade-off between these contradictory requirements, in selecting the depth and width of said upper portion, to provide it with the necessary volume.
Typically, the separator will be a ceramic conductor of alkali metal ions, eg a conductor of sodium ions such as nasicon or beta-alumina, preferably beta"-alumina, but the invention applies also in principle to other types of separator, such as a micromolecular sieve, eg a tectosilicate such as a zeolite, containing the alkali metal of the anode sorbed in the microporous interior thereof, which would typically have channels, windows and pores of a size of not more than 50 Angstrom units and typically less than 20 Angstrom units. In each case, the advantage mentioned above of reducing wicking right to a minimum would in principle be achieved.
In such cells the alkali metal is typically sodium and the cathode may thus, for example, contain sulphur or sodium sulphides/polysulphides, the cell being a sodium/sulphur cell; or the cathode could, for example, be in the form of an electronically conductive electrolyte-permeable matrix impregnated with liquid electrolyte, the liquid electrolyte being an alkali metal aluminium halide molten salt electrolyte such as sodium aluminium chloride, preferably a 1:1 equimolar mix of alkali metal halide and aluminium halide. In this embodiment of the invention, the matrix may be formed from at least one member of the group comprising Fe, Ni, Co, Cr and Mn and compounds of said transition metals, with at least one non-metal of the group comprising carbon, silicon, boron, nitrogen and phosphorous.
It follows, in general, that usually the separator will be a solid electrolyte conductor of sodium ions, the anode metal being molten sodium, there however being a reasonably wide choice, as indicated above, of active cathode material, electrolyte in the cathode compartment, catholyte in the cathode compartment, or the like.
The invention will now be described, by way of exam~le, with reference to the accompanying diagrammatic drawings, in which, 129834'7 FI~lJRE 1 shows a sectional side elevation of a cell in accordance with the invention;
FIGURE 2 shows a similar view of another cell according to the invention;
FIGURE 3 shows a detail on an enlàrged scale of the wicks of the cells; and FIGURE 4 shows a variation of the detail of Figure 3.
In the drawings, reference numeral 10 generally designates an electrochemical cell in accordance with the invention. The cell 10 has a molten sodium active anode material 12, a sodium aluminium chloride molten salt electrolyte 14, and a cathode 16 which is immersed in the electrolyte 14 and which in its discharged state comprises an electrolyte-permeable porous iron matrix which is electronically conductive and contains FeC12 in dispersed form therein as its charged active cathode substance. Instead, the matrix could for example be of porous nickel containing NiCl2 in dispersed form as its charged active cathode substance. The matrix of the cathode 16 is saturated with the electrolyte 14 and has sufficient finely divided N æ 1 dispersed therein to ensure that, in all states of charge of the active cathode substance, the electrolyte 14 is an equimolar mix of NaCl and AlCl3, ie stoichiometrically exact NaAlC14.
The cell 10 has a ~ild steel outer housing or casing 18 having a base 20 for supporting it in an upright attitude, as shown. The casing 18 is sealed to an alpha-alumina insulating ring 22. An open-ended beta"-alumina separator tube 24 is located concentrically within the casing 18, the lower end of the tube 24 being closed and the upper or open end of the tube 24 being glass-welded to the alpha-alumina ring 22 in sealing fashion. The open end of the tube 24 is closed by a closure disc 26 of mild steel, sealed to the alpha-alumina ring 22. An anode terminal post 28 is welded to the casing 18, and a cathode terminal post 30 passes through a sealed central opening in the disc 26, downwardly into the electrolyte 14. The lower portion of the post 30 is embedded in and in electronic contact with the matrix of the cathode 16. The matrix acts as a cathode current collector. There is an inert gas space 32 above the electrolyte 14, and an inert gas space 34 above the sodium 12.
The space between the casing 18 and tube 24, occupied by the sodium 12,foTms an anode compartment, and the interior of the tube 24 forms a cathode compartment. These compartments are separated from each other by the separator tube 24, and by the sealing of the tube 24, casing 18 and disc 26 to the alpha-alumina ring 22.
The overall charge/discharge reaction of the cell can be represen~ed bythe reaction:
discharge 2Na + FeC12 ~ 2NaCl + Fe charge Accordingly, sodium passes from the cathode compartment to the anode compartment during charging, through the separator 24; and it passes in the opposite direction during discharging. During discharging, the volume of the Fe/FeC12 active cathode substance increases, with a rise in the level of electrolyte 14 in the cathode compartment and a corresponding drop in the level of molten sodium active anode substance 12 in the anode compartment; and, upon charging, there is an rise in the level of active molten sodium anode substance 12 in the anode compartment, with a corresponding drop in the level of molten electrolyte 14, arising from a decrease in the volume of the Fe/FeCl2 active cathode substance.
With particular reference to Figure 1, it will be noted that the housing 18 is necked-in at 36 so that the anode compartment defined between the tube 24 and the casing 18 has a lower portion 38 and an upper portion 40, the upper portion being of a greater horizontal cross-section than that of the lower portion. In other words, the annular space between the tube 24 and casing 18 in the upper portion 40 of Figure l, is of substantially greater width, as sho~n by A, than that of the lower portion 38, shown by B.
Turning to Figure 2, the casing 18 has a substantially constantdiameter, but the same effect is obtained by providing an inert cylindrical insert 42 in the lower portion-of the casing 18, in contact with said casing 18 and spaced from the tube-24. The insert 42 may be of solid, hollow or particulate (powder) construction. Once again, the ~298.~4~
anode compartment has an upper portion 40 and a lower portion 38, the width A of the upper portion 40 being greater than the width B of the lower portion, said lower portion 38 being defined between the tube 24 and the insert 42.
In Figure 1 in solid lines the upper portion 40 of the casing is shown for a cell for use in a battery where good volumetric energy density and efficient close packing of cells is a consideration. The upper portion 40 thus has a relatively great depth and a relatively small value for A. In cells for use in situations where said density and close packing are not a consideration, the upper portion can have a lesser depth and a great value for A, as shown in broken lines in Figure 1 at 40.1.
In each upper portion 40, the outer surface of the tube 24 is lined by a wick 44. This wick 44 is shown in detail in Figures 3 and 4, where it is generally designated 44, and is shown in contact with part of the tube 24.
The wick 44 comprises an inner layer of finely porous material 46, an outer layer 48 of coarsely porous material, and an outermost gauze layer 50, which holds the layers 44 alld 46 in place up against each other and up against the tube 24.
~ !
The dimensions of the casing 18 (Figure 1) and the casing 18 together with the insert 42 (Figure 2) are selected so that in all states of charge of the cell the lower portion 38 of the anode compartment will always remain filled by sodium 12, and such that, when the cell is fully discharged, each upper portion 40 is substantially empty of sodium 12.
During charging of the cell, sodium will enter the anode compartment, and the level of sodium 12 therein will rise, reducing the volume of the gas space 34, and during discharging the sodium level will drop.
It is, however, desirable that the entire outer surface of the tube 24 be wetted by sodium in all states of charge, and for this reason the wick 44 is provided to wick molten sodi.um upwardly over the whole of the outer surface of the tube 24.
Wicking sodium upwardly against gravily is, however, difficult, and cannot easily be effected over substantial heights. It is for this reason that the cells 10 are provided with their upper portions 40 and lower portions 38, designed so that the lower portions 38 are filled with sodium at all times. This permits wicking of sodium upwardly to be required only in the upper portions 40, over relatively reduced heights, less than the full height of the tube 24. In this regard it is to be noted that the spacing B will be kept as low as possible, being of the order of 0,1 to 0,2 mm, and the lower portion 38 extends at least halfway up the tube 24.
With particular reference to Figures 3 and 4, it is contemplated that the layers 46 and 48 will remain saturated with sodium at all times, and that the gauze 50 will retain pools or droplets of sodium thereon, as indicated at 52, when exposed to the gas space 34. In this regard it should be noted that the materials of the wick should preferably be easily wettable by sodium, conveniently being transition metals such as iron, nickel, or the like. In its detailed construction, the wick 50 has a plurality of structures 54 which hold the pools or droplets 52 of sodium in place. These structures 54 may be bucket-shaped, dispersed in spaced relationship from one another over the outer surface of the outer layer 48; or they may be in the form of vertically spaced circumferentially extending gutter-like channels extending around said layer 48. Those of Figure 3 are shown to be of part-circular cross-section, and those of Figure 4 are shown to be of verti.cally elongated cross-section. Naturally, if desired, a less sophisticated gauze or mesh 50 may be used, eg of expanded metal diamond mesh construction, provided it fulfils the function of keeping droplets 52 of sodium in contact with said outer layer 48.
According to the invention there is provided a rechargeable high temperature electrochemical power storage cell having a molten al~ali metal anode separated from a cathode by a separator, the separator dividing the cell into an anode compartment which contains said alXali metal and a cathode compartment which contains a cathode, and the separator penmitting the anode alXali metal to pass therethrough during discharge of the cell from the anode compartment to the cathode cc)mpartment into which it is released in ionic form for reaction with the cathode, the cell having an opeTative attitude in which it is upright, in which operative attitude the separator extends at an angle to the horizontal so that the level of the surface of anode metal in the anode compartment to which the separator is exposed, drops during discharge of the cell and rises during charging of the cell, the anode compartment having a lower portion and an upper portion which has a greater horizontal cross-section than the horizontal cross-section of the lc)wer portion, and the lower portion being entirely filled with anode.~.etal in the fully discharged state of the cell.
The separator may be a solid electrolyte conductor of ions of the anode .metal, the separator being in the form of a cylindrical tube which is closed at one end.and open at the other and has a hollow interior, the separator tube being arranged in the interior of a cell.housing so that, in said operative attitude of the cell, the closed end of the tube is lowermost and the open end of the tube is uppermost, the ~298347 interior of the tube forming an electrode compartment and the tube being spaced from the housing so that a space is defined between the tube and the housing which forms another electrode compartment. In this type of construction, when the anode compartment is in the interior of the tube, it will normally be of circular or annular cross-section, and when it is outside the tube, it will normally be of annular cross-section. For the horizontal annular cross-section of the lower portion of the anode compartment to be less than that of the upper portion, it follows that, in this type of cell, the lower portion will have a smaller horizontal, eg radial, dimension than that of the upper portion. Thus, when the anode compartment is annular, the amlulus of the upper portion will be thicker than that of the lower portion.
As the separator tube will usually (because of the way in which such tubes are typically made) be of constant diameter, different horizontal cross-sections for said upper and lower portions may be provided by having the casing circular in cross-section and by having the casing change in diameter (when the anode compartment is outside the tube);,or by placing an insert in the lower portion of the anode compartment (eg a tubular insert when the anode compartment is outside the tube, or a cylindrical or tubular insert when the anode compartment is inside the tube), with the insert concentric with the tube and radially spaced therefrom. Instead, the insert may be in powder or granular form.
In a particular embodiment, the separator tube may accordingly have a constant diameter, the interior of the tube forming the cathode compartment, the housing being of circular cross-section, and the tube being arranged concentrically therein and the space between the tube and housing forming an annular anode compartment.
When the anode compartment is annular in horizontal cross-section, the thickness of the annulus is preferably as low as practicable, eg about 0,1 - 0,2 mm for practical purposes. Similarly, the lower portion of the anode compartment should have an upper end which is as high as practicable, and the ~ower portion should extend upwardly to an upper end which is at least as high as the midpoint of the separator in a vertical direction. Accordingly, in a particular embodiment of the invention, the thickness of the lower portion of the annulus of the anode compartment is preferably at most 0,2 mm, the lower portion of the anode compartment having, when the cell is in its said operative attitude, an upper end which is at a level not lower than the level of the midpoint of the length of the separator tube.
Preferably the volume of the upper portion of the anode compartment is selected such that said upper portion is substantially full of anode metal when the cell is fully charged, and substantially empty when the cell is fully discharged, but with the lower portion remaining full at all times. In other words, the volume of the upper portion of the anode compartment may be related to the capacity of the cell such that the upper portion is substantially full of anode metal when the cell is fully charged, and so that, when the cell is fully discharged with the cell in its operative attitude, the level of anode metal in the anode compartment is at the top of the lower portion of the anode compartment, so that said lower portion is substantially full of anode metal when the cell is in said fully discharged state.
To promote wetting of the full surface of the separator e.Yposed to theanode compartment, said surface may be lined with a wicking material in said upper portion. Thus, the surface of the separator which is exposed to the anode compartment may be lined with wicking material for wicking the metal of the anode, the wicking material extending downwardly into contact with the anode metal in all states of charge of the cell when the cell is in its operative attitude. Such wicking material may be selected from the group consisting of a metal gauze, a metal powder held against the separator by a porous metal screen, a sintered porous metal liner and a felt liner. Naturally, other types of wicking material may instead be suitable.
In principle the wicking height should be kept as lo~- as possible so that, from this point of view, the upper portion of the anode compartment should be wide and shallow. However, from the point of view of volumetric energy density in a battery of close packed cells, it is desirable to have cells of substantially constant outer diameters, and without spaces therebetween. Thus, when the anode compartment is outside the separator tube, it follows that a deep upper ~298.~7 portion is desirable, only slightly wider than the lower portion. In practice there will be a trade-off between these contradictory requirements, in selecting the depth and width of said upper portion, to provide it with the necessary volume.
Typically, the separator will be a ceramic conductor of alkali metal ions, eg a conductor of sodium ions such as nasicon or beta-alumina, preferably beta"-alumina, but the invention applies also in principle to other types of separator, such as a micromolecular sieve, eg a tectosilicate such as a zeolite, containing the alkali metal of the anode sorbed in the microporous interior thereof, which would typically have channels, windows and pores of a size of not more than 50 Angstrom units and typically less than 20 Angstrom units. In each case, the advantage mentioned above of reducing wicking right to a minimum would in principle be achieved.
In such cells the alkali metal is typically sodium and the cathode may thus, for example, contain sulphur or sodium sulphides/polysulphides, the cell being a sodium/sulphur cell; or the cathode could, for example, be in the form of an electronically conductive electrolyte-permeable matrix impregnated with liquid electrolyte, the liquid electrolyte being an alkali metal aluminium halide molten salt electrolyte such as sodium aluminium chloride, preferably a 1:1 equimolar mix of alkali metal halide and aluminium halide. In this embodiment of the invention, the matrix may be formed from at least one member of the group comprising Fe, Ni, Co, Cr and Mn and compounds of said transition metals, with at least one non-metal of the group comprising carbon, silicon, boron, nitrogen and phosphorous.
It follows, in general, that usually the separator will be a solid electrolyte conductor of sodium ions, the anode metal being molten sodium, there however being a reasonably wide choice, as indicated above, of active cathode material, electrolyte in the cathode compartment, catholyte in the cathode compartment, or the like.
The invention will now be described, by way of exam~le, with reference to the accompanying diagrammatic drawings, in which, 129834'7 FI~lJRE 1 shows a sectional side elevation of a cell in accordance with the invention;
FIGURE 2 shows a similar view of another cell according to the invention;
FIGURE 3 shows a detail on an enlàrged scale of the wicks of the cells; and FIGURE 4 shows a variation of the detail of Figure 3.
In the drawings, reference numeral 10 generally designates an electrochemical cell in accordance with the invention. The cell 10 has a molten sodium active anode material 12, a sodium aluminium chloride molten salt electrolyte 14, and a cathode 16 which is immersed in the electrolyte 14 and which in its discharged state comprises an electrolyte-permeable porous iron matrix which is electronically conductive and contains FeC12 in dispersed form therein as its charged active cathode substance. Instead, the matrix could for example be of porous nickel containing NiCl2 in dispersed form as its charged active cathode substance. The matrix of the cathode 16 is saturated with the electrolyte 14 and has sufficient finely divided N æ 1 dispersed therein to ensure that, in all states of charge of the active cathode substance, the electrolyte 14 is an equimolar mix of NaCl and AlCl3, ie stoichiometrically exact NaAlC14.
The cell 10 has a ~ild steel outer housing or casing 18 having a base 20 for supporting it in an upright attitude, as shown. The casing 18 is sealed to an alpha-alumina insulating ring 22. An open-ended beta"-alumina separator tube 24 is located concentrically within the casing 18, the lower end of the tube 24 being closed and the upper or open end of the tube 24 being glass-welded to the alpha-alumina ring 22 in sealing fashion. The open end of the tube 24 is closed by a closure disc 26 of mild steel, sealed to the alpha-alumina ring 22. An anode terminal post 28 is welded to the casing 18, and a cathode terminal post 30 passes through a sealed central opening in the disc 26, downwardly into the electrolyte 14. The lower portion of the post 30 is embedded in and in electronic contact with the matrix of the cathode 16. The matrix acts as a cathode current collector. There is an inert gas space 32 above the electrolyte 14, and an inert gas space 34 above the sodium 12.
The space between the casing 18 and tube 24, occupied by the sodium 12,foTms an anode compartment, and the interior of the tube 24 forms a cathode compartment. These compartments are separated from each other by the separator tube 24, and by the sealing of the tube 24, casing 18 and disc 26 to the alpha-alumina ring 22.
The overall charge/discharge reaction of the cell can be represen~ed bythe reaction:
discharge 2Na + FeC12 ~ 2NaCl + Fe charge Accordingly, sodium passes from the cathode compartment to the anode compartment during charging, through the separator 24; and it passes in the opposite direction during discharging. During discharging, the volume of the Fe/FeC12 active cathode substance increases, with a rise in the level of electrolyte 14 in the cathode compartment and a corresponding drop in the level of molten sodium active anode substance 12 in the anode compartment; and, upon charging, there is an rise in the level of active molten sodium anode substance 12 in the anode compartment, with a corresponding drop in the level of molten electrolyte 14, arising from a decrease in the volume of the Fe/FeCl2 active cathode substance.
With particular reference to Figure 1, it will be noted that the housing 18 is necked-in at 36 so that the anode compartment defined between the tube 24 and the casing 18 has a lower portion 38 and an upper portion 40, the upper portion being of a greater horizontal cross-section than that of the lower portion. In other words, the annular space between the tube 24 and casing 18 in the upper portion 40 of Figure l, is of substantially greater width, as sho~n by A, than that of the lower portion 38, shown by B.
Turning to Figure 2, the casing 18 has a substantially constantdiameter, but the same effect is obtained by providing an inert cylindrical insert 42 in the lower portion-of the casing 18, in contact with said casing 18 and spaced from the tube-24. The insert 42 may be of solid, hollow or particulate (powder) construction. Once again, the ~298.~4~
anode compartment has an upper portion 40 and a lower portion 38, the width A of the upper portion 40 being greater than the width B of the lower portion, said lower portion 38 being defined between the tube 24 and the insert 42.
In Figure 1 in solid lines the upper portion 40 of the casing is shown for a cell for use in a battery where good volumetric energy density and efficient close packing of cells is a consideration. The upper portion 40 thus has a relatively great depth and a relatively small value for A. In cells for use in situations where said density and close packing are not a consideration, the upper portion can have a lesser depth and a great value for A, as shown in broken lines in Figure 1 at 40.1.
In each upper portion 40, the outer surface of the tube 24 is lined by a wick 44. This wick 44 is shown in detail in Figures 3 and 4, where it is generally designated 44, and is shown in contact with part of the tube 24.
The wick 44 comprises an inner layer of finely porous material 46, an outer layer 48 of coarsely porous material, and an outermost gauze layer 50, which holds the layers 44 alld 46 in place up against each other and up against the tube 24.
~ !
The dimensions of the casing 18 (Figure 1) and the casing 18 together with the insert 42 (Figure 2) are selected so that in all states of charge of the cell the lower portion 38 of the anode compartment will always remain filled by sodium 12, and such that, when the cell is fully discharged, each upper portion 40 is substantially empty of sodium 12.
During charging of the cell, sodium will enter the anode compartment, and the level of sodium 12 therein will rise, reducing the volume of the gas space 34, and during discharging the sodium level will drop.
It is, however, desirable that the entire outer surface of the tube 24 be wetted by sodium in all states of charge, and for this reason the wick 44 is provided to wick molten sodi.um upwardly over the whole of the outer surface of the tube 24.
Wicking sodium upwardly against gravily is, however, difficult, and cannot easily be effected over substantial heights. It is for this reason that the cells 10 are provided with their upper portions 40 and lower portions 38, designed so that the lower portions 38 are filled with sodium at all times. This permits wicking of sodium upwardly to be required only in the upper portions 40, over relatively reduced heights, less than the full height of the tube 24. In this regard it is to be noted that the spacing B will be kept as low as possible, being of the order of 0,1 to 0,2 mm, and the lower portion 38 extends at least halfway up the tube 24.
With particular reference to Figures 3 and 4, it is contemplated that the layers 46 and 48 will remain saturated with sodium at all times, and that the gauze 50 will retain pools or droplets of sodium thereon, as indicated at 52, when exposed to the gas space 34. In this regard it should be noted that the materials of the wick should preferably be easily wettable by sodium, conveniently being transition metals such as iron, nickel, or the like. In its detailed construction, the wick 50 has a plurality of structures 54 which hold the pools or droplets 52 of sodium in place. These structures 54 may be bucket-shaped, dispersed in spaced relationship from one another over the outer surface of the outer layer 48; or they may be in the form of vertically spaced circumferentially extending gutter-like channels extending around said layer 48. Those of Figure 3 are shown to be of part-circular cross-section, and those of Figure 4 are shown to be of verti.cally elongated cross-section. Naturally, if desired, a less sophisticated gauze or mesh 50 may be used, eg of expanded metal diamond mesh construction, provided it fulfils the function of keeping droplets 52 of sodium in contact with said outer layer 48.
Claims (8)
1. A rechargeable high temperature electrochemical power storage cell having a molten alkali metal anode separated from a cathode by a separator, the separator dividing the cell into an anode compartment which contains said alkali metal and a cathode compartment which contains a cathode, and the separator permitting the anode alkali metal to pass therethrough during discharge of the cell from the anode compartment to the cathode compartment into which it is released in ionic form for reaction with the cathode, the cell having an operative attitude in which it is upright, in which operative attitude the separator extends at an angle to the horizontal so that the level of the surface of anode metal in the anode compartment to the separator is exposed, drops during discharge of the cell and rises during charging of the cell, the anode compartment having a lower portion and an upper portion which has a greater horizontal cross-section than the horizontal cross-section of the lower portion, and the lower portion being entirely filled with anode metal in the fully discharged state of the cell.
2. A cell as claimed in Claim 1, in which the separator is a solid electrolyte conductor of ions of the anode metal, the separator being in the form of a cylindrical tube which is closed at one end and open at the other and has a hollow interior, the separator tube being arranged in the interior of a cell housing so that, in said operative attitude of the cell, the closed end of the tube is lowermost and the open end of the tube is uppermost, the interior of the tube forming an electrode compartment and the tube being spaced from the housing so that a space is defined between the tube and the housing which forms another electrode compartment.
3. A cell as claimed in Claim 2, in which the separator tube has a constant diameter, the interior of the tube forming the cathode compartment, the housing being of circular cross-section, and the tube being arranged concentrically therein and the space between the tube and housing forming an annular anode compartment.
4. A cell as claimed in Claim 3, in which the radial thickness of the lower portion of the annulus of the anode compartment is at most 0,2 mm, the lower portion of the anode compartment having, when the cell is in its said operative attitude, an upper end which is at a level not lower than the level of the midpoint of the length of the separator.
5. A cell as claimed in Claim 1, in which the volume of the upper portion of the anode compartment is related to the capacity of the cell such that said upper portion is substantially full of anode metal when the cell is fully charged, and so that, when the cell is fully discharged with the cell in its operative attitude, the level of anode metal in the anode compartment is at the top of the lower portion of the anode compartment, so that said lower portion is substantially full of anode metal when the cell is in said fully discharged state.
6. A cell as claimed in Claim 1, in which the surface of the separator which is exposed to the anode compartment is lined with wicking material for wicking the metal of the anode, the wicking material extending downwardly into contact with the anode metal in all states of charge of the cell when the cell is in its operative attitude.
7. A cell as claimed in Claim 6, in which the wicking material is selected from the group consisting of a metal gauze, a metal powder held against the separator by a porous metal screen, a sintered porous metal liner, and a felt liner.
8. A cell as claimed in Claim 1, in which the separator is a solid electrolyte conductor of sodium ions, the anode metal being molten sodium.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8728395 | 1987-12-04 | ||
| GB878728395A GB8728395D0 (en) | 1987-12-04 | 1987-12-04 | Electrochemical cell |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1298347C true CA1298347C (en) | 1992-03-31 |
Family
ID=10628002
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000584816A Expired - Fee Related CA1298347C (en) | 1987-12-04 | 1988-12-02 | Electrochemical cell |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPH01194275A (en) |
| CA (1) | CA1298347C (en) |
| DE (1) | DE3840250A1 (en) |
| FR (1) | FR2624310A1 (en) |
| GB (1) | GB8728395D0 (en) |
| ZA (1) | ZA888743B (en) |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1513681A (en) * | 1974-02-15 | 1978-06-07 | Electricity Council | Sodium-sulphur cells |
| DE2529415A1 (en) * | 1974-07-03 | 1977-01-13 | Secretary Industry Brit | Electrical cell with liq. anode and cathode - and solid electrolyte employs glass insulating seals |
| GB1558186A (en) * | 1975-10-10 | 1979-12-19 | Chloride Silent Power Ltd | Alkali metal sulphur cells |
-
1987
- 1987-12-04 GB GB878728395A patent/GB8728395D0/en active Pending
-
1988
- 1988-11-22 ZA ZA888743A patent/ZA888743B/en unknown
- 1988-11-29 DE DE3840250A patent/DE3840250A1/en not_active Withdrawn
- 1988-12-01 JP JP63305117A patent/JPH01194275A/en active Pending
- 1988-12-02 CA CA000584816A patent/CA1298347C/en not_active Expired - Fee Related
- 1988-12-02 FR FR8815839A patent/FR2624310A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| GB8728395D0 (en) | 1988-01-13 |
| ZA888743B (en) | 1989-07-26 |
| DE3840250A1 (en) | 1989-06-15 |
| JPH01194275A (en) | 1989-08-04 |
| FR2624310A1 (en) | 1989-06-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |