CA1172692A - Electrochemical cell - Google Patents
Electrochemical cellInfo
- Publication number
- CA1172692A CA1172692A CA000417350A CA417350A CA1172692A CA 1172692 A CA1172692 A CA 1172692A CA 000417350 A CA000417350 A CA 000417350A CA 417350 A CA417350 A CA 417350A CA 1172692 A CA1172692 A CA 1172692A
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- CA
- Canada
- Prior art keywords
- electrolyte
- cell
- sodium
- ions
- active cathode
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Classifications
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- 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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- Secondary Cells (AREA)
Abstract
ABSTRACT
An electrochemical cell is provided with a molten sodium anode and a molten sodium aluminium halide salt electrolyte. The cathode comprises FeCl2, NiCl2, CoCl2 or CrCl2 as active cathode substance dispersed in an electronically conductive electro-lyte-permeable matrix which is impregnated by the electrolyte. Between the anode and the electrolyte, and isolating them from each other, is a solid conductor of sodium ions or a micromolecular sieve which contains sodium sorbed therein. The proportions of sodium and aluminium ions in the electrolyte are selected so that the solubility of the active cathode substance in the electrolyte is at or near its minimum.
An electrochemical cell is provided with a molten sodium anode and a molten sodium aluminium halide salt electrolyte. The cathode comprises FeCl2, NiCl2, CoCl2 or CrCl2 as active cathode substance dispersed in an electronically conductive electro-lyte-permeable matrix which is impregnated by the electrolyte. Between the anode and the electrolyte, and isolating them from each other, is a solid conductor of sodium ions or a micromolecular sieve which contains sodium sorbed therein. The proportions of sodium and aluminium ions in the electrolyte are selected so that the solubility of the active cathode substance in the electrolyte is at or near its minimum.
Description
~ 17~6~2 T~IS INVENTION relates to an electrochemical cell.
In particular, it relates to a rechargeable electrochemical cell suitable for secondary use.
According to the invention, an electrochemical cell comprises a sodium anode which is molten at the operating temperature of the cell, a sodium aluminium halide molten salt electrolyte which is also molten at the operating temperature of the cell, a cathode which i5 impregnated by the electrolyte and which comprises, as the electrochemically active cathode substance of the cell, a transition metal chloride selected from the group consisting in FeC12, NiC12, CoC12 and CrC12 dispersed in an electrolyte-permeable matrix which is electronically conductive, and, between the anode and the electrolyte and isolating the anode from the electrolyte, a solid conductor of sodium ions or a micromolecular sieve which contains sodium sorbed therein, the proportions of sodium ions ~ and aluminium ions in the electrolyte being selected so that ; ~ ~ the solubility of the active cathode substance in the molten ~ eleckrolyte is at or near its minimum.
.
~ 1~2692 By 'isolating' is meant that any ionic sodium or metallic sodium moving from the anode to the electrolyte or vice versa, has to pass through the internal crystal structure of the solid conductor or through the microporous interior of the carrier, as the case may be.
The electrolyte is conveniently a sodium aluminium chloride molten salt electrolyte, which can, depending on the proportions of sodium and aluminiumr have a melting point of the order of 15QC or less, and wherein, also depending on its composition, the active cathode substance can be virtually insoluble. This electrolyte may contain a minor proportion of up to, say, lO~ by mass and usually less, o~ a dopant such as an alkali metal halide other than sodium chloride, by means of which its melting point is reduced. The dopant may thus comprise an alkali metal fluoride, but the proportions of the constituents o~ the electrolyte should be selected such that the solubility of the active cathode substance in the electrolyte ~ is kept to a minimum.
: ~:
The Applicant has found that the minimum solubility o~ the active cathode substances in the sodium aluminium chloride electrolytes (which may be doped as described above), occurs when the molar ratio of the alkali metal halide to the aluminium halide is about l:l. In other words, the relative quantities of said alkali metal ions, aluminium ions and halide ` ~ ~72~2 ions should conform substantially with the stoichiometric product:
M Al X4 wherein M represents alkali metal cations; and X represents halide anions.
Such electrolytes are among those described in the Applicant's United States Patent 4 287 271.
In this way, the proportions of the constituents can be selected so that the melting point of the electrolyte at atmospheric pressure is below 140C. Minor proportions of dopants may be tolerated in the electrolyte, e.g. substances which will ionize in the molten electrolyte to provide ions which affect the electrolytic action of the electrolyte or, as mentioned above, substances which reduce its melting point, but their nature and quantity should be insu~ficient to alter ~; the essential character of the electrolyte as a sodium aluminium chloride electrolyte, wherein the M Al X4 product is maintained~ ~
~:
~o ~hen the cell contains a solid conductor of sodium ions, said solid conductor may be beta-alumina or nasicon.
:::
Instead, when the cell contains a micromolecular sieve this carrier can be regarded as a conductor of sodium metal and/or sodium ions, depending on the mechanism whereby a 1726~2 sodium is transported therethrough.
By 'micromolecular sieve is meant a molecular sieve having interconnected cavities and/or channels in its interior and windows and/or pores in its surface leading to said 5 cavities and channels, the windows, pores, cavities and/or channels having a size of not more than 50 Angstroms and preferably less than 20 Angstroms.
Suitable micromolecular sieves are mineral micromole~
cular sieves, ie inorganic lattice or framework structures such as tectosilicates, eg the zeolites 13X, 3A, 4~ or the like, although certain essentially organic micromolecular sieves such as clathrates may, in certain circumstances, be suitable.
The active cathode substance should preferably be evenly dispersed throughout the matrix; and it may be in finely divided particulate form and/or it may adhere as fine particles ar a thin layer to the matrix, preferably so that there are no large particles or thick layers of active cathode substance present, and preferably so that none of the active cathode substance is spaced physically from the material of the matrix, which acts as a current collector, by an excessive spacing, eg in large cavities in the matrix. In other words, the active cathode substance preEerably should be close to or adherent to the material of the matrix, and should be as thinly spread as possible, consistent with the porosity of the matrix and the :
1 ~2~2 quantity of cathode substance required to be present. Large particles or thick layers of active cathode substance will not prevent the cell from working, but will merely be inefficient, a proportion of the active cathode substance remote from the cathode material amounting merely to dead weight.
As the electrochemically active cathode substance, FeCl (ferrous chloride) is attractive, for reasons of availability and cost, and because it can be substantially insoluble in a sodium aluminium chloride electrolyte in which the molar ratio of sodium chloride to aluminium chloride is The matrix of the ~athode in turn can be any suitable electronically conductive subs-tance capable of oroviding access to the cathode substance of the sodium ions of the electrolyte.
Carbon in the form of graphite may ~e used, or a porous matrix of the transition metal itself can be used. Suitable solid artifacts for use as cathodes can ~e made from graphite or the metal, for use in the cathodes, as described hereunder.
The transition metal chlorides of the cathodes of the present invention can be obtained from the metals in question or from compounds of the metals in question which can be treated to yield the desired chloride, eg refractory compounds of the transition metal, or other chlorides -thereof. In each case, the oxida-tion state of the metal in the metal chloride in the cathode should be as low as possible, and the presence of higher chlorides of the metal should be avoided, so that solubility of cathode material in -the electrolyte melt is avoided as far as is practicable.
Thus, a sintered artifact can be made o~ the transition metal in question, in a manner similar to that used for the construction of porous iron electrodes. This can then be chlorinated electrochemically, or chemically by reaction with chlorine gas, or with chlorine gas diluted by a suitable diluent.
When electrochemical chlorination is being employed, : the cathode so formed can be removed to the cell where it is to be used, or .i~ it is chlorinated in situ, the original composition o~ the electrolyte should be selected, or the electrolyte should be modiEied a~ter chlorination, so that the electrochemically active cathode substance is substantially insoluble therein~
:
If chemical chlorination has been used, subsequent heating under vacuum can be employed to sublime off unwanted volatiles, such as any FeC13 obtained in making an FeC12/Fe cathode artifact. According to this method of manufacture, the resultant cathode is the desired transition metal chloride in ` ~ 17 2~9 2 question, finely dispersed through a porous matrix of the transition metal, which is an electronic conductor and can be electrochemically active, depending on the cell environment, and can thus ~urther enhance cell capacity.
Instead, a refractory compound of the transition metal in question, such as a carbide thereof, can be mixed with a small quantity of a carbon-forming binder, eg phenol formaldehyde resin. The resulting mix is then pressed into electrode shape and the resin can be cracked in a vacuum at temperatures in excess o~ 600C, the temperature being selected to pyrolyse the binder to conductive carbon and to degrade the carbide to the metal and graphite. Thus, in the case of iron, Fe3C can be degraded to alpha iron and graphite. The resulting electrode is a ~ine dispersion of alpha iron and carbon which can be chlorinated by the method described above, the matrix comprising any conductive iron or graphite remaining after the chlorination.
Still further, the chloride itself can be finely divided and mixed with a suitable conducting medium for the matrix, such as graphite, and the cathode pressed as an artifact from the mixture.
In each case, prior to assembling the cell, the cathode must be loaded with the electrolyte with which it is to 1 ~726~32 _9_ be used, and this can be effected by vacuum impregnation followed by pressurization, to promote complete penetration o the electrolyte into the artifact.
Test cells were made in accordance with the inuen-tion, assembled under an argon atmosphere. In each case,beta alumina separated the sodi~m anode from the electrolyte, and to ensure good wetting in use of the beta alumina by the molten sodium, the beta alumina and sodium were preheated to 400C and cooled under argon. The cathode was then placed in position and suficient molten electrolyte was added under argon, the electrolyte comprising an equimolar mix of sodium chloride and aluminium chloride. The anode and cathode were arranged to have suitable current collectors in contact therewith, and the beta alumina was arranged so that it form-ed a continuous barrier between the electrolyte and sodium.
Test cells of this nature were used in the follow-ing examples as illustrated in the accompanying drawings, in which:
Figure 1 shows a Tafel Plot at the start of discharge of a cell for Example 1, voltage versus current being shown, and the current being shown logarithmically;
Figure 2 shows, for the cell of Example 1, a plot of voltage against capacity for the 12th charge/discharge cycle of the cell of Example 1 whose Tafel Plot is shown in Figure l;
and Figure 3 shows a plot, similar to Figure 2, of voltage against capacity for the cell described in Example 2.
,,, ~ ~72692 9a-A 5 g disc-shaped sintered iron electrode having a diameter of 30 mm and a thickness of 3 mm was chlorinated chemically by reaction with chlorine gas and heated under vacuum to sublime off volatile FeC13. From the uptake of chlorine, the discharge capacity was calculated ~o be approximately O,6 Amp hr. It : .
.
;
~-,-. .
i 172~;~2 should be noted that experimental capacity was found to be in good agreement with calculated capacity.
It was found that the charge-dtscharge process could represented as fallows:
2Na+ + (Fe2~Cl-) conductin~ +2e discharge, (Fe~ conducting ~2Na+C1~
charge -2e matrix In the electrolyte melt Na+ is the charge-carrying species.
Reduction and oxidation of the iron takes place at the conducting matrix, with which the iron makes electronic contact. Charge transfer was found to be rapid and the cathode was found to tolerate high current densities, in excess of 150 mAcm 2, with little cell polarisation. Figure 1 shows a Tafel Plot at the start of discharge of voltage vs current for the cell, current being shown logarithmically. The ohmic internal resistance-free plot shows the absence of polarisation up to current densities in excess of 150 mAcm 2, at a tempeFature of 180C.
Figure 2 shows the twelfth charge-discharge cycle, ie:
Charge: 2,38 V - 2,60 V, 5 hour rate Discharge: 2,28 V - 1,96 V, 5 hour rate ; 20 Capacity: 740 J g 1 ~excluding electrolyte) Coulombic efficiency: 100%
Temperature: 230C
Current Density: 50 mA/cm Open Cîrcuit Vol-tage (O.C.V.~: 2,35 V.
1 I~2~2 EXAMPL~ 2 5 g of Fe3C (having a 325 mesh average particle size obtained from Cerac Inc.) together with 0,5 g phenol formaldehyde binder (obtained from Polyresin Products (Pty) Limited) were intimately mixed and then pressed in a uniaxial press (about 34 500 kPa) into a pellet which was heated under argon for a period and at a temperature (eg about 3 hours at 1000C) sufficient to effect breakdown of the Fe3C to alpha iron and graphite. The only identifia~le crystalline products found were indeed alpha iron and graphite. The artifact was then chlorinated, as described with reference to Example 1, and the chlorine uptake gave an estimated capacity of 0,5 Amp hr, based on the calculated quantity of 1ron chloride present. As in Example 1, the experimental capacity was found to ~e in good agreement ~ith the calculated capacity.
. .
: Figure 3 shows the eleventh charge-discharge cycle of this cell, i.e.:
; ~' Charge: 2,64 - 2,90 V, 5 hour rate Discharge: 2,05 - 1,70 V, 5 hour rate ~;~ 20 Capacity: 540 J g 1 (excluding electrolyte) Coulombic efficienc~: 100%
Temperature: 230C
Current Density: 50 mA/cm Open Circuit Voltage (O.C.V.): 2,35 V.
l 172fi92 The present invention shows striking advantages, particularly as regards current density and the absence of any high internal resistance caused by polarization at high current densities, when compared with similar cells where the electro-chemically active cathode material is soluble in the electrolyte.In the case of the latter, concentration polarization takes place and high internal resistances are encountered, so that only low curren-t densities can be tolerated, rendering these cells unsuitable for high power applications such as automotive propulsion.
In particular, it relates to a rechargeable electrochemical cell suitable for secondary use.
According to the invention, an electrochemical cell comprises a sodium anode which is molten at the operating temperature of the cell, a sodium aluminium halide molten salt electrolyte which is also molten at the operating temperature of the cell, a cathode which i5 impregnated by the electrolyte and which comprises, as the electrochemically active cathode substance of the cell, a transition metal chloride selected from the group consisting in FeC12, NiC12, CoC12 and CrC12 dispersed in an electrolyte-permeable matrix which is electronically conductive, and, between the anode and the electrolyte and isolating the anode from the electrolyte, a solid conductor of sodium ions or a micromolecular sieve which contains sodium sorbed therein, the proportions of sodium ions ~ and aluminium ions in the electrolyte being selected so that ; ~ ~ the solubility of the active cathode substance in the molten ~ eleckrolyte is at or near its minimum.
.
~ 1~2692 By 'isolating' is meant that any ionic sodium or metallic sodium moving from the anode to the electrolyte or vice versa, has to pass through the internal crystal structure of the solid conductor or through the microporous interior of the carrier, as the case may be.
The electrolyte is conveniently a sodium aluminium chloride molten salt electrolyte, which can, depending on the proportions of sodium and aluminiumr have a melting point of the order of 15QC or less, and wherein, also depending on its composition, the active cathode substance can be virtually insoluble. This electrolyte may contain a minor proportion of up to, say, lO~ by mass and usually less, o~ a dopant such as an alkali metal halide other than sodium chloride, by means of which its melting point is reduced. The dopant may thus comprise an alkali metal fluoride, but the proportions of the constituents o~ the electrolyte should be selected such that the solubility of the active cathode substance in the electrolyte ~ is kept to a minimum.
: ~:
The Applicant has found that the minimum solubility o~ the active cathode substances in the sodium aluminium chloride electrolytes (which may be doped as described above), occurs when the molar ratio of the alkali metal halide to the aluminium halide is about l:l. In other words, the relative quantities of said alkali metal ions, aluminium ions and halide ` ~ ~72~2 ions should conform substantially with the stoichiometric product:
M Al X4 wherein M represents alkali metal cations; and X represents halide anions.
Such electrolytes are among those described in the Applicant's United States Patent 4 287 271.
In this way, the proportions of the constituents can be selected so that the melting point of the electrolyte at atmospheric pressure is below 140C. Minor proportions of dopants may be tolerated in the electrolyte, e.g. substances which will ionize in the molten electrolyte to provide ions which affect the electrolytic action of the electrolyte or, as mentioned above, substances which reduce its melting point, but their nature and quantity should be insu~ficient to alter ~; the essential character of the electrolyte as a sodium aluminium chloride electrolyte, wherein the M Al X4 product is maintained~ ~
~:
~o ~hen the cell contains a solid conductor of sodium ions, said solid conductor may be beta-alumina or nasicon.
:::
Instead, when the cell contains a micromolecular sieve this carrier can be regarded as a conductor of sodium metal and/or sodium ions, depending on the mechanism whereby a 1726~2 sodium is transported therethrough.
By 'micromolecular sieve is meant a molecular sieve having interconnected cavities and/or channels in its interior and windows and/or pores in its surface leading to said 5 cavities and channels, the windows, pores, cavities and/or channels having a size of not more than 50 Angstroms and preferably less than 20 Angstroms.
Suitable micromolecular sieves are mineral micromole~
cular sieves, ie inorganic lattice or framework structures such as tectosilicates, eg the zeolites 13X, 3A, 4~ or the like, although certain essentially organic micromolecular sieves such as clathrates may, in certain circumstances, be suitable.
The active cathode substance should preferably be evenly dispersed throughout the matrix; and it may be in finely divided particulate form and/or it may adhere as fine particles ar a thin layer to the matrix, preferably so that there are no large particles or thick layers of active cathode substance present, and preferably so that none of the active cathode substance is spaced physically from the material of the matrix, which acts as a current collector, by an excessive spacing, eg in large cavities in the matrix. In other words, the active cathode substance preEerably should be close to or adherent to the material of the matrix, and should be as thinly spread as possible, consistent with the porosity of the matrix and the :
1 ~2~2 quantity of cathode substance required to be present. Large particles or thick layers of active cathode substance will not prevent the cell from working, but will merely be inefficient, a proportion of the active cathode substance remote from the cathode material amounting merely to dead weight.
As the electrochemically active cathode substance, FeCl (ferrous chloride) is attractive, for reasons of availability and cost, and because it can be substantially insoluble in a sodium aluminium chloride electrolyte in which the molar ratio of sodium chloride to aluminium chloride is The matrix of the ~athode in turn can be any suitable electronically conductive subs-tance capable of oroviding access to the cathode substance of the sodium ions of the electrolyte.
Carbon in the form of graphite may ~e used, or a porous matrix of the transition metal itself can be used. Suitable solid artifacts for use as cathodes can ~e made from graphite or the metal, for use in the cathodes, as described hereunder.
The transition metal chlorides of the cathodes of the present invention can be obtained from the metals in question or from compounds of the metals in question which can be treated to yield the desired chloride, eg refractory compounds of the transition metal, or other chlorides -thereof. In each case, the oxida-tion state of the metal in the metal chloride in the cathode should be as low as possible, and the presence of higher chlorides of the metal should be avoided, so that solubility of cathode material in -the electrolyte melt is avoided as far as is practicable.
Thus, a sintered artifact can be made o~ the transition metal in question, in a manner similar to that used for the construction of porous iron electrodes. This can then be chlorinated electrochemically, or chemically by reaction with chlorine gas, or with chlorine gas diluted by a suitable diluent.
When electrochemical chlorination is being employed, : the cathode so formed can be removed to the cell where it is to be used, or .i~ it is chlorinated in situ, the original composition o~ the electrolyte should be selected, or the electrolyte should be modiEied a~ter chlorination, so that the electrochemically active cathode substance is substantially insoluble therein~
:
If chemical chlorination has been used, subsequent heating under vacuum can be employed to sublime off unwanted volatiles, such as any FeC13 obtained in making an FeC12/Fe cathode artifact. According to this method of manufacture, the resultant cathode is the desired transition metal chloride in ` ~ 17 2~9 2 question, finely dispersed through a porous matrix of the transition metal, which is an electronic conductor and can be electrochemically active, depending on the cell environment, and can thus ~urther enhance cell capacity.
Instead, a refractory compound of the transition metal in question, such as a carbide thereof, can be mixed with a small quantity of a carbon-forming binder, eg phenol formaldehyde resin. The resulting mix is then pressed into electrode shape and the resin can be cracked in a vacuum at temperatures in excess o~ 600C, the temperature being selected to pyrolyse the binder to conductive carbon and to degrade the carbide to the metal and graphite. Thus, in the case of iron, Fe3C can be degraded to alpha iron and graphite. The resulting electrode is a ~ine dispersion of alpha iron and carbon which can be chlorinated by the method described above, the matrix comprising any conductive iron or graphite remaining after the chlorination.
Still further, the chloride itself can be finely divided and mixed with a suitable conducting medium for the matrix, such as graphite, and the cathode pressed as an artifact from the mixture.
In each case, prior to assembling the cell, the cathode must be loaded with the electrolyte with which it is to 1 ~726~32 _9_ be used, and this can be effected by vacuum impregnation followed by pressurization, to promote complete penetration o the electrolyte into the artifact.
Test cells were made in accordance with the inuen-tion, assembled under an argon atmosphere. In each case,beta alumina separated the sodi~m anode from the electrolyte, and to ensure good wetting in use of the beta alumina by the molten sodium, the beta alumina and sodium were preheated to 400C and cooled under argon. The cathode was then placed in position and suficient molten electrolyte was added under argon, the electrolyte comprising an equimolar mix of sodium chloride and aluminium chloride. The anode and cathode were arranged to have suitable current collectors in contact therewith, and the beta alumina was arranged so that it form-ed a continuous barrier between the electrolyte and sodium.
Test cells of this nature were used in the follow-ing examples as illustrated in the accompanying drawings, in which:
Figure 1 shows a Tafel Plot at the start of discharge of a cell for Example 1, voltage versus current being shown, and the current being shown logarithmically;
Figure 2 shows, for the cell of Example 1, a plot of voltage against capacity for the 12th charge/discharge cycle of the cell of Example 1 whose Tafel Plot is shown in Figure l;
and Figure 3 shows a plot, similar to Figure 2, of voltage against capacity for the cell described in Example 2.
,,, ~ ~72692 9a-A 5 g disc-shaped sintered iron electrode having a diameter of 30 mm and a thickness of 3 mm was chlorinated chemically by reaction with chlorine gas and heated under vacuum to sublime off volatile FeC13. From the uptake of chlorine, the discharge capacity was calculated ~o be approximately O,6 Amp hr. It : .
.
;
~-,-. .
i 172~;~2 should be noted that experimental capacity was found to be in good agreement with calculated capacity.
It was found that the charge-dtscharge process could represented as fallows:
2Na+ + (Fe2~Cl-) conductin~ +2e discharge, (Fe~ conducting ~2Na+C1~
charge -2e matrix In the electrolyte melt Na+ is the charge-carrying species.
Reduction and oxidation of the iron takes place at the conducting matrix, with which the iron makes electronic contact. Charge transfer was found to be rapid and the cathode was found to tolerate high current densities, in excess of 150 mAcm 2, with little cell polarisation. Figure 1 shows a Tafel Plot at the start of discharge of voltage vs current for the cell, current being shown logarithmically. The ohmic internal resistance-free plot shows the absence of polarisation up to current densities in excess of 150 mAcm 2, at a tempeFature of 180C.
Figure 2 shows the twelfth charge-discharge cycle, ie:
Charge: 2,38 V - 2,60 V, 5 hour rate Discharge: 2,28 V - 1,96 V, 5 hour rate ; 20 Capacity: 740 J g 1 ~excluding electrolyte) Coulombic efficiency: 100%
Temperature: 230C
Current Density: 50 mA/cm Open Cîrcuit Vol-tage (O.C.V.~: 2,35 V.
1 I~2~2 EXAMPL~ 2 5 g of Fe3C (having a 325 mesh average particle size obtained from Cerac Inc.) together with 0,5 g phenol formaldehyde binder (obtained from Polyresin Products (Pty) Limited) were intimately mixed and then pressed in a uniaxial press (about 34 500 kPa) into a pellet which was heated under argon for a period and at a temperature (eg about 3 hours at 1000C) sufficient to effect breakdown of the Fe3C to alpha iron and graphite. The only identifia~le crystalline products found were indeed alpha iron and graphite. The artifact was then chlorinated, as described with reference to Example 1, and the chlorine uptake gave an estimated capacity of 0,5 Amp hr, based on the calculated quantity of 1ron chloride present. As in Example 1, the experimental capacity was found to ~e in good agreement ~ith the calculated capacity.
. .
: Figure 3 shows the eleventh charge-discharge cycle of this cell, i.e.:
; ~' Charge: 2,64 - 2,90 V, 5 hour rate Discharge: 2,05 - 1,70 V, 5 hour rate ~;~ 20 Capacity: 540 J g 1 (excluding electrolyte) Coulombic efficienc~: 100%
Temperature: 230C
Current Density: 50 mA/cm Open Circuit Voltage (O.C.V.): 2,35 V.
l 172fi92 The present invention shows striking advantages, particularly as regards current density and the absence of any high internal resistance caused by polarization at high current densities, when compared with similar cells where the electro-chemically active cathode material is soluble in the electrolyte.In the case of the latter, concentration polarization takes place and high internal resistances are encountered, so that only low curren-t densities can be tolerated, rendering these cells unsuitable for high power applications such as automotive propulsion.
Claims (12)
1. An electrochemical cell which comprises a sodium anode which is molten at the operating temperature of the cell, a sodium aluminium halide molten salt electrolyte which is also molten at the operating temperature of the cell, a cathode which is impregnated by the electrolyte and comprises, as the electrochemically active cathode substance of the cell, a transition metal chloride selected from the group consisting in FeCl2, NiCl2, CoCl2 and CrCl2 dispersed in an electrolyte-permeable matrix which is electronically conductive, and, between the anode and the electrolyte and isolating the anode from the electrolyte, a solid conductor of sodium ions or a micromolecular sieve which contains sodium sorbed therein, the proportions of sodium ions and aluminium ions in the electrolyte being selected so that the solubility of the active cathode substance in the molten electrolyte is at or near its minimum.
2. A cell as claimed in claim 1, in which the electrolyte is a sodium aluminium chloride molten salt electrolyte.
3. A cell as claimed in claim 2, in which the electrolyte contains less than 10% by mass of an alkali metal dopant whereby its melting point is reduced, the proportions of alkali metal and aluminium ions and the proportion and nature of the dopant being selected so that the electrolyte has a melting point of 150°C or less.
4. A cell as claimed in claim 2, in which the molar ratio of alkali metal halide to aluminium halide in the electrolyte is substantially 1:1, the relative quantities of the alkali metal ions, aluminium ions and halide ions conforming substantially with the stoichiometric product:
MAlX4 wherein: M represents the alkali metal cations; and X represents the halide anions.
MAlX4 wherein: M represents the alkali metal cations; and X represents the halide anions.
5. A cell as claimed in claim 1, in which the anode is isolated from the electrolyte by a solid conductor of sodium ions selected from the group consisting in beta-alumina or nasicon.
6. A cell as claimed in claim 1, in which the anode is isolated from the electrolyte by a micromolecular sieve selected from the group consisting in zeolite 13X, zeolite 3A
and zeolite 4A.
and zeolite 4A.
7. A cell as claimed in claim 1, in which the active cathode material is ferrous chloride (FeCl2).
8. A cell as claimed in claim 1, in which the active cathode substance is evenly dispersed throughout the matrix, in finely divided particulate form or in the form of a thin layer adhering to the material of the matrix.
9. A cell as claimed in claim 1, in which the matrix of the cathode comprises carbon or the transition metal of the active cathode substance.
10. A cell as claimed in claim 1, in which the cathode comprises an artifact formed from the transition metal of the active cathode substance or a refractory compound thereof, which metal or compound has been chemically or electrochemically treated to convert said transition metal or compound into the active cathode material.
11. A cell as claimed in claim 10, in which a refractory compound of the transition metal has been heated to degrade it to the metal, and then has been chlorinated chemically or electrochemically.
12. A cell as claimed in claim 1, in which the cathode comprises an artifact formed from an evenly dispersed finely divided mixture of the active cathode substance and a suitable conducting medium which forms the matrix.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8134373 | 1981-12-10 | ||
| GB8134373 | 1981-12-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1172692A true CA1172692A (en) | 1984-08-14 |
Family
ID=10525893
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000417350A Expired CA1172692A (en) | 1981-12-10 | 1982-12-09 | Electrochemical cell |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1172692A (en) |
-
1982
- 1982-12-09 CA CA000417350A patent/CA1172692A/en not_active Expired
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