MXPA99010170A - An iron-based storage battery - Google Patents

Abstract

An electric storage battery having a solid phase Fe(VI) or Fe(V) or Fe(IV) 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 electrochemical contact through 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.

Description

A FERCILE BASE ACCUMULATOR The present invention relates to electric accumulators. More particularly, the invention relates to a new electric accumulator with ferric salt as a cathode. BACKGROUND OF THE INVENTION There is a current need to provide new improved electric accumulators, which are low cost, have a high energy density and are environmentally acceptable. Among the main types of accumulators are those in which the cathodes (the positive electrodes) are based on any of Pb02, HgO, Mn02 and NiOOH which are known to have a theoretical capacity in the range of 224 to 308 Ah / g . However, these cathode materials are considered hazardous or environmentally unfavorable. In the very recent US Patent. No. 5,429,894, iron-silver (iron in its zero-valence state) was suggested as an accumulator anode (negative). Ferric salts in the valence state +2 and +3 were also suggested in the past, as an accumulator cathode as described, for example, in the U.S. Patent. 4,675,256 and the U.S. Patent. 4,795,685.

At first glance, iron-containing salts in the valence state +6, hereinafter called Fe (VI), which are capable of achieving multiple electron reduction, would be able to provide a greater storage capacity of the cathode. However, the decomposition with reduction of iron to a less oxidized form (that is, to a lower valence state) occurs very rapidly, the stability of saline solutions with Fe (VI) being only of the order of a few hours at temperature environment (Anal. Chem. 23, 1312-4, 1951). Fe (VI) salts can be made by chemical oxidation, as reported by G. Thompson (J. Amer. Chem. Soc. 73, 1379, 1951), or by precipitation from another Fe (VI) salt, 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 about the chemistry of Fe (VI) salts. . The decomposition of a 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 Fe04"2 as in K2Fe04, is unstable in neutral aqueous solutions and decomposes to a proportion f according to the following equation: 2Fe042 + 3H20? 2Fe00H + 3/202 + 40H "The product resulting in this decomposition, FE (III) OOH, is environmentally more favorable than any of Pb02, HgO, Mn02 and NiOOH, but has a lower electrochemical storage capacity. present invention provide a new type of accumulator which is cheap, highly stable, has a large storage capacity, a high voltage and is environmentally friendly BRIEF DESCRIPTION OF THE INVENTION The invention relates to an electrical storage cell, called an accumulator, comprising two half cells which are in electrochemical contact with each other through an electrically neutral ion conductor, wherein one of the half cells comprises an anode and the other half cell comprises a cathode in the form of a salt of Fe (VI ) in solid phase in an amount of at least 1% of the weight of the half cell, whereby electrical storage is carried out through the reduction Electrochemical ion at a ferric salt valence lower than Fe (VI). The high valence state +6 of the iron in the salt provides the advantage of a large storage capacity and high voltage and the ferric salts provide an environmental advantage over most of the toxic materials used for electrical electrochemical storage. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a schematic illustration of an Fe (VI) accumulator according to the invention and; Figures 2 to 5 graphically illustrate performance aspects of various accumulators according to the invention as described in the Examples. DETAILED DESCRIPTION OF THE INVENTION The new accumulator according to the present invention is based on a half cell of Fe (VI) (hereinafter occasionally referred to as "super iron") serving as a cathode, in contact with a half cell of anode through an electrically neutral ion conductor. The discharge in this accumulator is based on the reduction of the salt of Fe (VI) to the state of valence +3. The salt of Fe (VI), for example, M2Fe04 where M is an alkali or ammonium cation, can be prepared by the oxidation of iron. Several methods of chemical oxidation have been suggested, but among the methods that produce salts of Fe (VI) of the highest purity is the one reported by G. Thompson.

(J. Amr. Chem. Soc. 73, 1379, 1951). By this method, Fe (VI) salts are obtained through the reaction of a hydrochloride and hypochlorite solution (such as NaOH and NaOCl) with a salt of Fe (III), such as Fe (N03) 3, as illustrated below: 2Fe (0H) 3 + 3C10"+ 40H"? 2Fe04 ~ 2 + 3C1"+ 5H20 (1) and the resulting Fe (VI) salt (such as K2Fe04) is recovered by precipitation from a less soluble solution (such as concentrated KOH) and then cleaned and dried. Additional typical salts of Fe (VI) are Mx (Fe04) and where xyy are integers and M is a cation of the group of alkaline alkali 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 K2Fe04, Na2Fe04, Li2Fe04, Cs2Fe04 / Rb2Fe04, H2Fe04, (NH4) 2Fe04, (N (C4H9) 4) 2Fe04, BeFe04, MgFe04, CaFe04, SrFe04 , BaFe04, Hg2Fe04, HgFe04, Cu2Fe04, CuFe04, ZnFe04, Ag2Fe04, AsFe04, Fe03, FeFe04, Fe2 (Fe04) 3, CrFe04, MnFe04, NiFe04, CoFe04, Al2 (Fe04) 3, In2 (Fe04) 3, Ga2 (Fe04) ) 3, SnFe0, PbFe04, Sn (Fe04) 2, Pb (Fe04) 2. Various methods of Fe (VI) synthesis have been suggested that include precipitation from another Fe (VI) salt, but the method that produced between the Fe (VI) salts of higher purity is the method reported by J. Gump et al. (Anal, Chem. 26, 1957, 1954). By this method, Fe (VI) salts can be obtained through the reaction of an existing Fe (VI) salt (such as K2Fe04) with a soluble salt (such as BaCl2 or BaN03) to precipitate another Fe salt. (VI) (such as BaFe04). Without being committed to any theory, based on the reduction of three electrons of these materials as expressed in the equation: Fe042 ~ + 3H20 + 3e ~? FeOOH + 50H "(2) electrical storage capacity is high as represented by a few of the materials in Table 1.

Table 1 Storage capacity of the cathode of various salts of Fß (VI) Salt of Fe (VI Weight of the Capacity of Formula G / mol load Li2Fe04 133.8 601 Amp hour / kg Na2Fe04 165.9 485 Amp hour / kg K2Fe04 198.0 406 Amp hour / kg Cs2Fe04 385.6 206 Amp hour / kg Ag2Fe04 335.6 236 Amp hour / kg MgFe04 144.1 558 Amp hour / kg CaFe04 159.9 505 Amp hour / kg SrFe04 207.5 387 Amp hour / kg BaFe0 257.2 313 Amp hour / kg The Fe (VI) salt whose preparation is exemplified by, but not limited to any chemical oxidation of Fe (III) or precipitation of another Fe (VI) salt is contacted 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 compressed 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 flat conductive surface, a cable, a porous conductive substrate or a conductive grid. The anode of the accumulator can be selected from the known list of metals capable of oxidation, typical examples being zinc, lithium; common accumulator anodes such as cadmium, lead and iron; high capacity metals such as: 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 other typical constituents capable of oxidation, examples include, but are not limited to hydrogen, (including but not limited to metal hydrides), inorganic salts and organic components including aromatic and non-aromatic compounds. The electrically neutral ion conductor used in the accumulator according to the present invention comprises a means that can support the current density during the discharge of the accumulator. A typical representative ionic conductor is an aqueous solution preferably containing a high concentration of a hydroxide such as KOH. In other typical modalities, the electrically neutral ionic conductor comprises common ionic conductive materials used in accumulators which include, but are not limited to, an aqueous solution, a non-aqueous solution, a conductive polymer, a solid ion conductor and a molten salt. In a preferred embodiment of the invention, the cell includes gas separating means such as a vent or a void space to prevent oxygen, hydrogen and other gas formation in the cell. According to another embodiment of the invention, the means are provided to prevent the transfer of chemically reactive species or to prevent electrical contact between the anode and the Fe (VI) salt cathode. The media 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; said means being arranged to separate the half cells from each other.

An electrical accumulator according to the invention can be rechargeable by applying a voltage in excess of the voltage as measured without resistive load, of the discharged or partially discharged cell. DETAILED DESCRIPTION OF FIGURE 1 Figure 1 schematically illustrates an electrochemical cell 10 based on a half cell of Fe (VI), an electrically neutral ion conductor and an anode. The cell contains an electrically neutral ion conductor 22, such as a concentrated aqueous solution of KOH, in contact with a cathode of Fe (VI) 14 in the form of a compressed agglomerate containing powdered graphite and solid K2Fe04- The reduction of Fe ions (VI) as in the form of anions Fe0 2", is achieved through the available electrons of the electrode 14. The anode electrode 12, such as in the metal form is also in contact with the electrically neutral ionic conductor 22 The electrons are released in the oxidation of the anode Optionally, the cell can contain a selective membrane of ion 20 as a separator, to minimize the non-electrochemical interaction between the cathode and the anode.

The invention will be illustrated hereinafter 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. Example 1 An experiment was carried out in order to increase the half-life of the Fe (VI) chemical species beyond 100 hours, in order to be available for electrochemical reduction. The decomposition ratio was characterized using a visible absorption spectrum of Fe0 2"in highly alkaline aqueous solution, which exhibits a well-defined maximum at 505 nm, an absorption support at 570 nm and two minimums at 390 nm and 675 nm. The molar absorptivity measured at 505 nm was 1040 molar "1 cm" 1 and remained constant up to 200 minimolar solutions of K2Fe0 The absorptivity at 505 nm of 2 millimolar K2Fe04 was substantially the same in a solution of lithium hydroxide or sodium hydroxide salts up to 15 molar or potassium hydroxide The electrolytes that were studied for the decomposition ratio of Fe0 2"contained various concentrations up to the saturation of LiOH, NaOH, KOH and CsOH at 4 ° C, 22 ° C and 40 ° C. The decomposition ratio of Fe042"was measured to be directly proportional to the Fe042 concentration first" according to the equation: d [Fe02"] / dt = kf [Fe042"] (3) which produces the half-life (tx / 2) for 50% of Fe042"to decompose resulting in: t? / 2 = 0.693 / kf (4) For this reason, at 22 ° C in a 5 molar LiOH solution, Fe042"is consumed 50 times faster at 100 millimolar compared to a Fe0 2 ~ 2 millimolar solution and both solutions have a half-life of 34 hours expressed as shown in the following table: Kf = 5.7 x 10"6 s" 1 (5) The stability of Fe (VI) in other solutions is shown in Table 2.

Table 2 Solubility of Fe (VI). S in mM, decomposition ratio kf v t: stability time for 0 .01 liters (10 ml) of a molar solution (M) in contact with 0 .05 ka (50 o.) M, .FeO-. is either pred: ii or by means of the equation (5) Solution Temp S. mM Kf s "1 Fw * Stability (M? Fe04L (di) M LiOH 22 ° C 940 5.7xl0"6 133. 8 90 5 M NaOH 22 ° C 1410 1.8xl0" 5 165. 9 14 5 M KOH 22 ° C 72 2.4xl0"5 198. 1 170 5 M CsOH 22 ° C 33.7 1. IxlO-5 385. 6 4 10 M NaOH 22 ° C 490 1.2xl0"5 165. 9 55 10 M KOH 22 ° C 19 6.2xl0" 6 198. 1 240 10 M CsOH 22 ° C 9.2 6.3xl0 ~ 4 385. 6 26 10 M KOH 40 ° C 37.5 2. lxlO "5 198. 1 370 10 M KOH 4 ° C 8 2. Ixl0" d 198. 1 17400 15 M NaOH 22 ° C 146 5xl0"6 165. 9 480 13 M KOH 22 ° C 2.9 4.6xl0"6 198. 1 21900 KOH satu 22 ° C 1.7 2. lxlO" 7 198. 1 820000 * Fw - Weight of the formula. As it can be noticed, in LiOH, NaOH, KOH or 5 M CsOH the decomposition rate increases until the column of alkali hydroxides is moved downwards, at 22 ° C it is equal to tx / 2 being only 10 minutes in the CsOH solution 5 M. However, at higher concentrations of hydroxide, Fe042"is more stable in KOH than in NaOH; consequently electrolyte solutions of 10 M NaOH and KOH have t? / 2 of 16 and 31 hours respectively and 15 M NaOH and 13 M KOH have t? / 2 38 and 42 hours respectively. It was found that the reaction ratio kf are three times higher at 40 ° C and three times lower at 4 ° C. At 22 ° C a saturated solution of KOH (about 14 molar), the decomposition ratio is lower, being kf 2.1xl0 ~ 7s ~ 1 with a solution that has a half-life of 920 hours, more than a hundred times improvement over stability in a 5 molar KOH solution. The absolute decomposition ratio of Fe042 ~ is further minimized by several orders of magnitude in determining and using the electrolytes that limit their solubility to decrease d [Fe0 2 ~] / dt. For this purpose, as summarized in Table 2, for the NaOH and KOH electrolytes, the solubilities of Fe (VI) were measured. At 22 ° C, in a solution of 5 molar NaOH the solubility of Fe042"is about 1.4 moles, whereas in a saturated solution of KOH it is only Fe042" 0.0017 molar. Except for a concentrated (almost saturated) solution of 5 molar LiOH at 22 ° C, with a millimolar (S) solubility of Fe0 2 ~, S = 940, generally the solubility (s) decreased with an increase in Alkali cation mass. Consequently, for a solution of 5 molar NaOH, KOH and CsOH, S was 1410, 72 and 33.7 respectively. Similarly, for a solution of 10 molar KOH, 13 molar and saturated KOH, S was 19, 2.9 and 1.7 respectively. Solubility decreases with a decrease in temperature and at 60oC, 40oC and 4oC for a saturated KOH solution, S = 4.3, 2.9 and 1.2 respectively. These effects of high alkali cation mass, low temperature and high hydroxide concentration appear to be cumulative at 4 ° C in a 15 mol CsOH solution, Fe042"is highly insoluble, and a further improvement in Fe042 stability" is achieved use an excess of solid Fe (VI) in contact with a solution of Fe (VI) of low solubility. The prolonged results over several weeks on the decomposition of the solution are shown in Figure 2. Consequently, in a solution - 1 ( saturated with KOH that contains an excess of solid KOH, a solution with an initial concentration of 1.7 millimolar K2Fe04 lost only 0.3 • millimolar of Fe (VI) active in 100 hours. In a second experiment, a six-fold excess of K2Fe0 was added beyond the saturation point to a saturated solution of KOH. As shown in Figure 2, after one month the solution contains a constant concentration of Fe042" dissolved. These results provide a • trajectory to prepare stable concentrations of Fe (VI). This is shown schematically in the inset of Figure 2. The electrolyte is based on a concentrated hydroxide solution, which contains a cation that inhibits decomposition, such as K +. The solution is not only saturated with K2Fe0, but also contains an excess of solid K2Fe04. The generalized system uses mass (m) of Fe salt (VI) with weight of the formula (FW) in contact with a volume of a solution (V). The dissolution of such mass provides a constant saturated concentration (S) of Fe (VI). The required stable time (testabie) necessary for the concentration of Fe (VI) to be found below S is represented by the formula: testable = m FW "1 V" 1 kf (5) Using the measured values of S and kf, Table 2 presents the predicted average life of a system containing 0.05 kg (50 g) of Mg2Fe04 in contact with 0.01 liter (10 ml) of the respective alkaline hydroxide. A saturated KOH is an attractive electrolyte, which minimizes both the solubility and the loss ratio of K2Fe0. When decomposition occurs, the excess of solid K2Fe04 dissolves providing a source of constant regulator to maintain a corresponding saturated solution with a predicted half-life of K2Fe0 of more than 1,000 years. The release of the cathode materials into the environment would result in a dilution of the hydroxide, which would improve the dissolution of Fe0 2"and rapid degeneration to a harmless FeOOH according to equation (1). an experiment to determine the ability to reach a high voltage and the theoretical reduction capacity of three electrons in the discharge of salts of Fe (VI) in solutions as expressed in the equation.This was examined by means of a galvanostatic reduction of Fe (VI) dissolved in a 13.5 molar solution of potassium hydroxide Figure 3 shows the evolution time of the potential, during the reduction of Fe (VI), in an initial cinitial concentration = 2.5 millimolar of K2Fe0, in volume V = 0.5 ml of a solution of 13.5 molar KOH was reduced to a current density J = 0.100 mA / cm2, and a subsequent continuous reduction to J = 0.010 mA / cm2, at a Pt electrode with a surface area, A = 1 0 cm2 The integration of the transferred charge, q = tJ A / F (where F is the Faraday constant and t being the time) produces the relative oxidation state = q / (Vcinitial) compared to the Fe (III) product charge. As shown in Figure 3, solid curve 1 illustrates the oxidation state of the starting material which approaches Fe (VI) according to the equation and produces the +6 valence state of the iron. After the termination of the three-electron transfer, the negative change in potential as illustrated in Figure 3 is consistent with the initial Fe (VI) depletion and the subsequent evolution of hydrogen. A half cathode cell - with a more positive redox pair will result in a higher voltage accumulator and the half cell of Fe (VI) will have a high positive redox potential. At the end of the discharge in Figure 3 after 1, of the 3 electrons per Iron, a solution containing the average Fe (V) has been transferred, for example as in the form of Fe04. "Stop the discharge in the Figure 3 after 2, of the 3 electrons per Iron, a solution containing the average Fe (IV) has been transferred, for example as in the form of Fe03"Respectively, in these last two cases, the recommencement of the reduction results in the discharge of an accumulator of Fe (V) or Fe (VI) .The redox potentials measured in a platinum electrode, of 2 millimolar, 20 millimolar, 60 millimolar and 100 millimolar K2Fe0 in various sodium hydroxide solutions show that they are positive, increase with Fe (VI) concentration and decrease with hydroxide concentration In general, this redox potential varies from E (15 molar NaOH) , K2Fe04 2 millimolar) = o.5 V to E (5 molar NaOH, K2Fe04 100 millimolar) = 0.7 V, measured in volts against the standard hydrogen electrode and were similar values in KOH solutions.

Example 3 As summarized in Table 3, the steady-state current densities observed at 22 ° C are low, less than 100 μA / cm2 for the 2mM reduction (Fe042"thousand imolar) .This can be improved six times by the use of a highly porous Ni substrate in surface area, although the resulting current density of 0.4 mA / cm2 remains too low for many accumulator applications.These current densities are dramatically improved through the formation of a K2Fe04 tablet solid, containing 30% by weight of micro particulate graphite (2μm powder) to improve conductivity It is argued that a hundred times increase in current occurs, as shown in Table 3, in the comparison of flat electrocatalysts with the solid K2Fe04 / carbon electrode, with current densities of 10 mA / cm2 and higher.The capacity of the solid K2Fe04 tablet and the voltage are low without added graphite and improves lower current densities, J. As shown in the Table 3, the addition of up to 10% graphite, by weight, further improves both the capacity and the voltage of the cathode reduction of Fe (VI during discharge) Table 3 Maximum steady state cathodic current density and polarization losses for the reduction of Fe (VI) in various electrodes and various solutions at 22 ° C. Fe (VI) referred to K1FeQi: C re f er a tio n gra phito Electrode Solution Polarization Current Losses Maximum mA crrf MV cm2 mA "1 2m Fe (VI) Ni plane 13 .5M KQH 700 0.07 2trM Fe (VI) Pt plane 13 .5M KOH 500 0.06 Neither porous 2nM Fe (VI) 60 pores / inch 13.5M KOH 150 0.4 100% Fe (VE) in 50 mg disc 13.5M KOH 120 0.5 95% Fe (VD, 5% C in 50 pg- disc 13.5M KDH 60 90% Fe (VI), 10% C in 50 mg disc 13.5M KDH 30 70% Fe (VI) 30% C in 50 mg disc 13.5M KOH 20 10 70% Fe (VI), 30% C in 50 mg disc 10M KOH 15 20 Example 4 This example illustrates the use of zinc metal anodes and that during discharge with these anodes a high fraction of the electrical storage capacity of the Fe (VI) super iron salts is achieved as K2Fe0 (with a storage capacity of 406 Ah / kg, Table 1) and other listed salts in Table 1 as SrFe04, Ag2Fe04, CaFe0 and BaFe04. The super iron cathode can be combined with a zinc anode to form a super iron / zinc accumulator. In alkaline solutions, zinc oxidation is: Zn + 20H "-> ZnO + H20 + 2e" (6) Combined with equation 2, this describes a discharge of the super iron-zinc accumulator, as described below: 2Fe042"+ 3Zn + 3H20 -» 3ZnO + 2Fe00H + 40H "(7) The accumulators of super iron-zinc, for example, are based on the salt of Fe (VI) K2Fe0, have a higher theoretical specific energy than aqueous accumulators conventional (alkaline, metal hydride, lead or Ni / Cd), of: 1.8 Volt x 271 Ah / kg = 490 Wh / kg (8) Super iron / zinc accumulators, consisting of flat zinc and salt electrodes / μcarbon of K2Fe04 solids separated by 10 or 13.5 M KOH were discharged at 22 ° C. The accumulator had an open circuit measured voltage of 1.7 to 1.8 V. The excess zinc was used to produce a cell with a limited capacity of Fe042"and determines the coulombic efficiency of the reduction of three electronsec. 2. This efficiency was determined experimentally by comparing the coulombs generated during the discharge to the theoretical faradic equivalents available in the mass of K2Fe04, SrFe0, Ag2Fe04, CaFe04 or BaFe04. As seen in Figure 4, at a low current density discharge of 0.6 mA / cm2, more than 85% of the 3e "theoretical by Fe042" is achieved. It is measured beyond 65% efficiency at 3.5 mA / cm2. Similar shocks are measured when the electrodes are separated by 10 M KOH. The cells are also discharged well with small volumes of aqueous solution. As illustrated in Figure 4, the Ag2Fe04 / Zinc accumulator exhibits a second lower voltage plate which leads to a prolonged discharge behavior. Without committing to any theory, this is related to the discharge of Fe (VI) and Ag (I) according to: Ag2Fe04 + 3H20 + 5 e '? FeOOH + 2Ag + 50H (9) A measured comparison of a super iron / zinc accumulator compared to a conventional alkaline battery is illustrated in Figure 5. Therefore, a conventional alkaline button configuration cell is discharged under a constant load of 3000 ohm and the specific energy determined as the cell potential multiplied by the current over time and divided by the mass. The 0.399g mass of the cell was composed of 0.139g of Zn, electrolyte and separator, as well as 0.260g of Mn02 containing cathode. In the super iron / zinc accumulator a second conventional cell is opened and the Mn02 containing cathode is replaced by 0.180 g of Fe (VI) cathode comprising 90% mass of K2Fe04 and 10% graphite. As illustrated in Figure 5, under the same discharge load regime of 3000 ohm, the super iron cell provides a storage capacity of approximately 250 W / kg, about 160% increase compared to that of the alkaline battery conventional.

Example 5 This example illustrates the use of cadmium metal anodes, with the half cell cathode Fe (VI) and the rechargeability of a super iron accumulator. The super iron / cadmium accumulators, consisting of flat cadmium electrode and solid / μ carbon K2Fe0 separated by 13.5 M KOH, were discharged at 22 ° C. The accumulator had an open-circuit measured voltage of 1.3 V and the constant current discharge was used to measure the storage capacity where the current i, multiplied by time and divided by the mass of K2Fe0 / provides the storage capacity of K2Fe0 measure = it / mass of K2Fe0. As seen in Table 4, at a current density discharge b ja of 0.4 mA / cm, a high storage capacity of 390 Amp hour / kg is obtained. A storage capacity was measured at 219 Amp hour / kg at 4 mA / cm2. Table 4 includes the discharge of 1 mA / cm2 repeated of super iron / cadmium accumulators during three loading / unloading cycles. The partial reduction of salts of Fe (VI) can cause, in addition to the salts of Fe (III), the formation of salts of Fe (V) and Fe (IV). Despite a lower capacity than the Fe (VI) half cell accumulator, these salts of Fe (V) and Fe (IV) can be used as super iron half cells to also provide a high capacity super iron accumulator. Table 4 Download and upload / download a cell containing % 2μm) and a cadmium anode in 13.5 M KOH at 22 ° C.

Each cycle 1 is prior to any recharge. Cycles 2 and 3 are subsequent to a recharge of 5 mA / cm2. Cycle 1 Discharge Capacity Current Storage -of__J2Fe04 measured 0.4 mA 390 Amp hour / kg 1. 0 mA 329 Amp hour / kg 1. 0 mA 329 Amp hour / kg 1. 0 mA 207 Amp hour / kg 1. 0 mA 195 Amp hour / kg 4. 0 mA 219 Amp hour / kg

Claims (38)

1. NOVELTY OF THE INVENTION Having described the present invention is considered as a novelty and therefore claimed as property described in the following claims: 1. An accumulator, comprising two half cells which are in electrochemical contact with each other through of an electrically neutral ionic conductor, wherein one of the half cells comprises an anode and the other half cell comprises a cathode in the form of a Fe (VI) salt in solid phase in an amount of at least 1% of the weight of the average cell, so electrical storage is done through electrochemical reduction for a valency of ferric salt less than Fe (VI).
2. 2. The accumulator according to claim 1 characterized in that the Fe (VI) salt includes a cation, selected from the group consisting of the alkali metal cations, alkaline earth metal cations of ammonium H +, transition metal cations and cations of Groups III, IV and V of the periodic table.
3. 3. The accumulator according to claim 1 or 2 characterized in that the anode includes a metal capable of oxidation.
4. The accumulator according to claim 3 characterized in that the metal is selected from the group consisting of zinc, lithium, magnesium, calcium, aluminum, cadmium, lead, iron, copper, cobalt, nickel, chromium, titanium, gallium, indium, manganese , silver, cadmium, barium, tungsten, molybdenum, sodium, potassium, rubidium and cesium.
5. 5. The accumulator according to claim 1 or 2 characterized in that the anode includes hydrogen capable of oxidation.
6. 6. The accumulator according to claim 1 or 2 characterized in that the anode includes an inorganic salt capable of oxidation.
7. 7. The accumulator according to the claim 1 or 2 characterized in that the anode includes an organic compound capable of oxidation, selected from the group consisting of aromatic and non-aromatic compounds.
8. 8. The accumulator according to the claim 1 or 2 characterized in that the electrically neutral ionic conductor is an aqueous solution.
9. 9. The accumulator according to claim 1 or 2 characterized in that the electrically neutral ionic conductor is a non-aqueous solution.
10. 10. The accumulator according to claim 1 or 2 characterized in that the electrically neutral ionic conductor is a conductive polymer.
11. The accumulator according to claim 1 or 2 characterized in that the electrically neutral ionic conductor is a molten salt.
12. 12. The accumulator according to claim 1 or 2 characterized in that the electrically neutral ion conductor is a solid ion conductor.
13. 13. The accumulator according to claim 8, characterized in that the solution contains hydroxide ions.
14. 14. The accumulator according to claim 8, characterized in that the solution contains dissolved Fe (VI) salt.
15. 15. The accumulator according to claim 1 or 2 characterized in that the Fe (VI) salt is in contact with a conductive material.
16. 16. The accumulator according to the claim 15 characterized in that the conductive material is selected from the group of graphite, carbon black and metals.
17. 17. The accumulator according to claim 15, characterized in that the conductive material comprises a mixed compressed powder.
18. 18. The accumulator according to claim 15, characterized in that the conductive material comprises a flat surface or a cable.
19. 19. The accumulator according to the claim 15 characterized in that the conductive material comprises a porous substrate or grid.
20. 20. The accumulator according to claim 1 or 2 characterized in that it comprises means for preventing the transfer of chemically reactive species between the two half cells.
21. 21. The accumulator according to claim 20 characterized in that the means is a nonconductive separator configured with open channels, grids or pores.
22. 22. The accumulator according to claim 1 or 2 characterized in that the electrically neutral ionic conductor contains an additional solid dissolved substance or a dissolved liquid to improve the stability of Fe (VI) and the efficiency of the discharge of the cell.
23. 23. The accumulator according to claim 22 characterized in that the additional solid dissolved substance is selected from KOH and CsOH.
24. 24. The accumulator according to claim 22 characterized in that the additional solid dissolved substance is selected from LiOH and NaOH.
25. 25. The accumulator according to claim 22, characterized in that the additional dissolved liquid is an aqueous solution.
26. 26. The accumulator according to claim 20, characterized in that the means for preventing the transfer of chemically reactive ion comprises a membrane placed to separate the cells half cells.
27. 27. The accumulator according to claim 22, characterized in that the additional dissolved liquid is a non-aqueous solution.
28. 28. The accumulator according to the claim 1 or 2 zadp characteristics because the cell is rechargeable by applying a voltage in excess of the open circuit potential of the discharge cell.
29. 29. The accumulator according to the claim 8 characterized in that the solution contains the concentration of molar hydroxide ions up to 5 molar.
30. 30. The accumulator according to claim 8 characterized in that the solution contains the concentration of 5 to 10 molar of hydroxide ions.
31. 31. The accumulator according to claim 8, characterized in that the solution contains the concentration of 10 molar for a solution saturated in hydroxide ions.
32. 32. The accumulator according to claim 13, characterized in that the concentration of the Fe (VI) salt is at least 0.0001 molar.
33. 33. The accumulator according to the claim 8 characterized in that the concentration of the Fe (VI) salt is above 0.0001 molar.
34. 34. The accumulator according to claim 8, characterized in that the concentration of the Fe (VI) ions is above 0.01 molar.
35. 35. The accumulator according to claim 8 characterized in that the concentration of Fe (VI) ions is or is above 1 molar.
36. 36. The accumulator according to claim 1 or 2 characterized in that it includes gas separating means to prevent the formation of oxygen, hydrogen and other gases.
37. 37. An accumulator comprising two half cells which are in electrochemical contact with one another through an electrically neutral ion conductor, wherein one of the half cells comprises an anode and the other half cell comprises at least 1% of the weight as a Fe (VI) salt, where the discharge in the electric storage cell is based on the reduction of the Fe (V) salt.
38. 38. An accumulator comprising two half cells which are in electrochemical contact with one another through an electrically neutral ion conductor, wherein one of the half cells comprises an anode and the other half cell comprises at least 1% of the weight as a Fe (IV) salt, where the discharge in the electrical storage cell is based on the reduction of the Fe (IV) salt.