| PATENT ASSIGNEE'S COUNTRY | Israel |
| UPDATE | 03.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 07.03.00 |
| PATENT TITLE |
Iron-based storage battery |
| PATENT ABSTRACT |
An electric storage battery having a solid phase Fe(VI) salt cathode. The anode may be any of a large variety of conventional anode materials capable of being oxidized. The cathode and anode are located in separate half-cells which are in electrochemcial contact trough an electrically neutral ionic conductor. Optionally means may be provided for impeding the transfer of chemically reactive species between the two half-cells. Also optionally gas separator means may be provided for preventing the build-up of oxygen, hydrogen and other gases. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 05.05.98 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT REFERENCES CITED |
Goff, H. et al., "Studies on the Mechanism of Isotopic Oxygen Exchange and Reduction of Ferrate (VI) Ion (FeO.sub.4.sup.2-).sup.1, " J. Amer. Chem. Soc., 93:23, Nov. 17, 1971, pp. 6058-6065. Gump, J. et al., "Preparation and Analysis of Barium Ferrate (VI)," Anal. Chem., 26, 1954, p. 1957. Thompson, G. et al., "Preparation and Purification of Potassium Ferrate. VI," J. Amer. Chem. Soc. 73, Mar. 1951, pp. 1379-1381. Schreyer, J. et al., "Stability of the Ferrate (VI) Ion in Aqueous Solution," Anal. Chem. 23, 1951, pp. 1312-1314 |
| PATENT CLAIMS |
I claim: 1. A storage battery, comprising two half-cells which are in electrochemical contact with one another through an electrically neutral ionic conductor, wherein one of said half-cells comprises an anode and the other half-cell comprises a cathode in form of a solid-phase Fe(VI) salt in an amount of at least 1% of the half-cell weight, whereby electrical discharge of charge is accomplished via electrochemical charge insertion to or from a valence of iron salt less than Fe(VI). 2. The battery according to claim 1, wherein said Fe(VI) salt includes a cation, selected from the group consisting of the alkali metal cations, ammonium H.sup.- alkali earth metal cations, transition metal cations, and cations of groups III, IV and V of the periodic table. 3. The battery according to claim 1, wherein said anode includes a metal capable of being oxidized. 4. The battery according to claim 3, wherein said metal is selected from the group consisting of zinc, lithium, magnesium, calcium, aluminium, cadmium, lead, iron, copper, cobalt, nickel, chromium, titanium, gallium, iridium, manganese, silver, cadmium, barium tungsten, molybdenum, sodium, potassium, rubidium and cesium. 5. The battery according to claim 1, wherein said anode includes hydrogen capable of being oxidized. 6. The battery according to claim 1, wherein said anode includes an inorganic salt capable of being oxidized. 7. The battery according to claim 1, wherein said anode includes an organic compound capable of being oxidized, selected from the group consisting of aromatic and non-aromatic compounds. 8. The battery according to claim 1, wherein said electrically neutral ionic conductor is an aqueous solution. 9. The battery according to claim 1, wherein said electrically neutral ionic conductor is a non-aqueous solution. 10. The battery according to claim 1, wherein said electrically neutral ionic conductor is a conductive polymer. 11. The battery according to claim 1, wherein said electrically neutral ionic conductor is a molten salt. 12. The battery according to claim 1, wherein said electrically neutral ionic conductor is a solid ionic conductor. 13. The battery according to claim 8, wherein said solution contains hydroxide ions. 14. The battery according to claim 8, wherein said solution contains dissolved Fe(VI) salt. 15. The battery according to claim 1, further characterized in that said Fe(VI) salt is in contact with a conductive material. 16. The battery according to claim 15, wherein said conductive material is selected from the group of graphite, carbon black and metals. 17. The battery according to claim 15, wherein conductive material comprises a mixed pressed powder. 18. The battery according to claim 15, wherein said conductive material comprises a planar surface or a wire. 19. The battery according to claim 15, wherein said conductive material comprises a porous substrate or grid. 20. The battery according to claim 1 further comprising means to impede transfer of chemically reactive species between said two half-cells. 21. The battery according to claim 20, wherein said means is a non conductive separator configured with open channels, grids or pores. 22. The battery according to claim 1, wherein said electrically neutral ionic conductor contains a further solid solute or dissolved liquid for improving the stability of Fe(VI) and effectiveness of cell discharge. 23. The battery according to claim 22, wherein said further solid solute is selected from KOH and CsOH. 24. The battery according to claim 22, wherein said further solid solute is selected from LiOH and NaOH. 25. The battery according to claim 22, wherein said further dissolved liquid is an aqueous solution. 26. The battery of claim 20 in which said means to impede chemically reactive ion transfer comprises a membrane positioned to separate said half cells. 27. The battery according to claim 22, wherein said further dissolved liquid is a non-aqueous solution. 28. The battery according to claim 1, wherein said cell is rechargeable by application of a voltage in excess of the discharge cell open circuit potential. 29. The battery of claim 8, wherein said solution contains the concentration of tip to 5 molar hydroxide ions. 30. The battery of claim 8, wherein said solution contains the concentration from 5 to 10 molar hydroxide ions. 31. The battery of claim 8, wherein said solution contains the concentration from 10 molar to a solution saturated in hydroxide ions. 32. The battery according to claim 13, wherein the concentration of said Fe(VI) salt is at least 0.0001 molar. 33. The battery of claim 8, wherein the concentration of said Fe(VI) salt is above 0.0001 molar. 34. The battery of claim 8, wherein the concentration of said Fe(VI) ions is above 0.01 molar. 35. The battery of claim 8, wherein the concentration of said Fe(VI) ions is at or above 1 molar. 36. The battery according to claim 1 including a gas separator means for preventing the build-up of oxygen, hydrogen. |
| PATENT DESCRIPTION |
The present invention relates to electric storage batteries. More particularly, the invention relates to a novel electric storage battery with an iron salt as cathode. BACKGROUND OF THE INVENTION There is an ongoing need for providing novel improved electrical storage batteries, which are low-cost have a high-energy density and are environmentally acceptable. Among the main types of storage batteries are those in which the cathodes (the positive electrodes) are based on any of PbO.sub.2, HgO, MnO.sub.2 and NiOOH which are known to possess a theoretical capacity in the range of between 224 to 308 Ah/g. However, these cathode materials are considered as hazardous or environmentally unfriendly. In a very recent U.S. Pat. No. 5,429,894, iron-silver (iron in its zero valence state) was suggested as a battery anode (negative). Iron salts in the +2 and +3 valence state, were also suggested as a battery cathode in the past as described, for example, in U.S. Pat. No. 4,675,256 and U.S. Pat. No. 4,795,685. Prima facie, salts containing iron in the +6 valence state, hereafter called Fe(VI), which are capable of multiple electron reduction, would be capable to provide a higher cathode storage capacity. However, decomposition with reduction of the iron to a less oxidized form (i.e. to a lower valence state) occurs very rapidly, the stability of Fe(VI) salt solutions being only the order of a few hours at room temperature (Anal. Chem. 23, 1312-4, 1951). The Fe(VI) salts may be made by chemical oxidation, such as reported by G. Thompson (J. Amer. Chem, Soc. 73, 1379, 1951), or by precipitation from another Fe(VI) salt, such as reported by J. Gump et al. (Anal. Chem. 26, 1957, 1954). However, as mentioned in a later report by H. Goff et al (J. Amer. Chem, Soc. 93, 6058-6065, 1971), only little is known on the chemistry of Fe(VI) salts. The decomposition of an Fe(VI) salt to a salt in which the iron has a lower valence, results in a spontaneous loss of the electrochemical storage capacity. For example, the anion FeO.sub.4.sup.-2 such as in K.sub.2 FeO.sub.4, is unstable in neutral aqueous solutions and decomposes at a rate k.sub.f according to the following equation: 2FeO.sub.4.sup.2- +3H.sub.2 O.fwdarw.2FeOOH+3/20.sub.2 +4OH.sup.- The resultant product in this decomposition: Fe(III)OOH, is environmentally more friendly than any of PbO.sub.2, HgO, MnO.sub.2 and NiOOH, but has a lower electrochemical storage capacity. It is an object of the present invention to provide a novel type of battery which is inexpensive, highly stable, possesses a high storage capacity, a high voltage and is environmentally friendly. BRIEF DESCRIPTION OF THE INVENTION The invention relates to an electrical storage cell, so-called battery, comprising two half-cells which are in electrochemical contact with one another through an electrically neutral ionic conductor, wherein one of said half-cells comprises an anode and the other half-cell comprises a cathode in form of a solid-phase Fe(VI) salt in an amount of at least 1% of the half-cell weight, whereby electrical storage is accomplished via electrochemical reduction to a valence of iron salt less than Fe(VI). The high +6 valence state of the iron in said salt provides the advantage of a high storage capacity and high voltage, and iron salts provide an environmental advantage over more toxic materials used for electrochemical electric storage. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a diagrammatic illustration of an Fe(VI) battery according to the invention; and FIGS. 2 to 5 illustrate graphically aspects of the performance of various batteries according to the invention as described in the Examples. DETAILED DESCRIPTION OF THE INVENTION The novel battery according to the present invention is based on an Fe(VI) (hereafter occasionally referred to as "super iron") half cell serving as cathode, in contact with an anode half cell through an electrically neutral ionic conductor. The discharge in this battery is based on the reduction of the Fe(VI) salt to the +3 valence state. The Fe(VI) salt, e.g. M.sub.2 FeO.sub.4 where M is an alkali cation or ammonium, may be prepared by oxidation of iron. Several chemical oxidation methods have been suggested, but among methods which yield Fe(VI) salts of highest purity is the one reported by G. Thompson (J. Amer. Chem. Soc, 73, 1379, 1951), By this method, Fe(VI) salts are obtained through the reaction of a solution of hydroxide and hypochlorite (such as NaOH and NaOCl with an Fe(III) salt, such as Fe(NO.sub.3).sub.3, as illustrated below: 2Fe(OH).sub.3 +3ClO.sup.- +4OH.sup..multidot. .fwdarw.2FeO.sub.4.sup.-3 +3Cl.sup.- +5H.sub.2 O (1) and the resulting Fe(VI) salt (such as K.sub.2 FeO.sub.4) is recovered by precipitation from a less soluble solution (such as concentrated KOH), and is then cleaned and dried. Further typical examples of Fe(VI) salts are M.sub.x((FeO.sub.4).sub.y where x and y are integers and M is a cation from the group of alkali earth metal cations, transition metal cations and cations of elements of groups III, IV and V of the periodic table, Examples thereof include, but are not limited to K.sub.2 FeO.sub.4, Na.sub.2 FeO.sub.4, Li.sub.2 FeO.sub.4, Cs.sub.2 FeO.sub.4, Rb.sub.2 FeO.sub.4, H.sub.2 FeO.sub.4, (NH.sub.4).sub.2 FeO.sub.4, (N(C.sub.4 H.sub.9).sub.4).sub.2 FeO.sub.4, BeFeO.sub.4, MgFeO.sub.4, CaFeO.sub.4, SrFeO.sub.4, BaFeO.sub.4, Hg.sub.2 FeO.sub.4, HgFeO.sub.4, Cu.sub.2 FeO.sub.4, CuFeO.sub.4, ZnFeO.sub.4, Ag.sub.2 FeO.sub.4, AsFeO.sub.4, FeO.sub.3, FeFeO.sub.4, Fe.sub.2 (FeO.sub.4).sub.3, CrFeO.sub.4, MnFeO.sub.4, NiFeO.sub.4, CoFeO.sub.4, Al.sub.2 (FeO.sub.4).sub.3, In.sub.2 (FeO.sub.4).sub.3, Ga.sub.2 (FeO.sub.4).sub.3, SnFeO.sub.4, PbFeO.sub.4, Sn(FeO.sub.4).sub.2, Pb(FeO.sub.4).sub.2. Several Fe(VI) syntheses methods which include precipitation from another Fe(VI) salt have been suggested, but the method which yields among the highest purity Fe(VI) salts is the method reported by J. Gump et al. (Anal. Chem. 26, 1957, 1954). By this method, Fe(VI) salts may be obtained through the reaction of an existing Fe(VI) salt (such as K.sub.2 FeO.sub.4) with a soluble salt (such BaCl.sub.2 or BaNO.sub.3) to precipitate another Fe(VI) salt (such as BaFeO.sub.4). Without being bound to any theory, based on the three-electron reduction of these materials as expressed in the equation: FeO.sub.4.sup.2- +3H.sub.2 O+3e.sup.- .fwdarw.FeOOH+5OH.sup.-(2) the electrical storage capacity is high as represented for a few of the materials in Table 1. TABLE 1 ______________________________________ Cathode storage capacity of several Fe(VI) salts Fe(VI) salt Formula Wt. G/mole Charge capacity ______________________________________ Li.sub.2 FeO.sub.4 133.8 601 Amp hour/kg Na.sub.2 FeO.sub.4 165.9 485 Amp hour/kg K.sub.2 FeO.sub.4 198.0 406 Amp hour/kg Cs.sub.2 FeO.sub.4 385.6 206 Amp hour/kg Ag.sub.2 FeO.sub.4 335.6 236 Amp hour/kg MgFeO.sub.4 144.1 558 Amp hour/kg CaFeO.sub.4 159.9 505 Amp hour/kg SrFeO.sub.4 207.5 387 Amp hour/kg BaFeO.sub.4 257.2 313 Amp hour/kg ______________________________________ The Fe(VI) salt whose preparation is exemplified by, but not limited to either chemical oxidation of Fe(III) or precipitation from another Fe(VI) salt is placed in contact with a conductive material, such as graphite, carbon black or a metal. These and other agents can be formed by mixing with Fe(VI) as a powder, and the powder can be pressed with these and other agents to improve mechanical strength. Rather than mixing with a conductive material, the Fe(VI) salt can be placed in direct contact with a conductive material. These conductive materials include but are not limited to a planar conductive surface, a wire, a porous conductive substrate or a conductive grid. The anode of the battery may be selected from the known list of metals capable of being oxidized, typical examples being zinc, lithium; common battery anodes such as cadmium, lead and iron; high capacity metals such: aluminum, magnesium, calcium; and other metals such as copper, cobalt, nickel, chromium, gallium, titanium, indium, manganese, silver, cadmium, barium, tungsten, molybdenum, sodium, potassium, rubidium and cesium. The anode may also be of other typical constituents capable of being oxidized, examples include, but are not limited to hydrogen, (including but not limited to metal hydrides), inorganic salts, and organic compounds including aromatic and non-aromatic compounds. The electrically neutral ionic conductor utilized in the battery according to the present invention, comprises a medium that can support current density during battery discharge. A typical representative ionic conductor is an aqueous solution preferably containing a high concentration of a hydroxide such as KOH. In other typical embodiments, the electrically neutral ionic conductor comprises common ionic conductor materials used in batteries which include, but are not limited to an aqueous solution, a non-aqueous solution, a conductive polymer, a solid ionic conductor and a molten salt. In a preferred embodiment of the invention, the cell includes gas separator means such as vent or a void space for preventing the build-up in the cell of oxygen, hydrogen and other gases. According to another embodiment of the invention, means are provided to impede transfer of chemically reactive species, or prevent electric contract between the anode and Fe(VI) salt cathode. Said means includes; but is not limited to a membrane, a ceramic frit, a non-conductive separator configured with open channels, grids or pores or agar solution; such means being so positioned as to separate said half cells from each other. An electric storage battery according to the invention may be rechargeable by application of a voltage in excess of the voltage as measured without resistive load, of the discharged or partially discharged cell. DETAILED DESCRIPTION OF FIG. 1 FIG. 1 illustrates schematically an electrochemical cell 10 based on an Fe(VI) half cell, an electrically neutral ionic conductor and an anode. The cell contains an electrically neutral ionic conductor 22, such as a concentrated aqueous solution of KOH, in contact with an Fe(VI) cathode 14 n form of a pressed pellet containing graphite powder and solid K.sub.2 FeO.sub.4. Reduction of Fe(VI) ions such as in the form of FeO.sub.4.sup.2- anions, is achieved via electrons available from the electrode 14. The anode electrode 12, such as in the form of metal is also in contact with the electrically neutral ionic conductor 22. Electrons are released in the oxidation of the anode. Optionally, the cell may contain an ion selective membrane 20 as a separator, for minimizing the non-electrochemical interaction between the cathode and the anode. The invention will be hereafter illustrated by the following Examples, it being understood that the Examples are presented only for a better understanding of the invention without implying any limitation thereof. |
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