US 20030008210A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2003/0008210 A1 Licht (43) Pub. Date: Jan. 9, 2003

(54) SILVER MAGANESE SALT CATHODES FOR (30) Foreign Application Priority Data ALKALINE BATTERIES Feb. 20, 2001 (IL) ...... 141527

(75) Inventor: Stuart Licht, Haifa (IL) Publication Classi?cation

Correspondence Address; (51) Int. Cl.7 ...... H01M 4/54; H01M 4/50; BROWDY AND NEIMARK, P.L.L.C. H01M 4/24; H01M 10/26; 624 NINTH STREET, NW H01M 10/32 SUITE 300 (52) US. Cl...... 429/219; 429/224; 429/207 WASHINGTON, DC 20001-5303 (US) (57) ABSTRACT (73) Assignee; CHEMERGY, Energy Technologies, An electric storage alkaline battery comprising an electri Technion City (IL) cally neutral alkaline ionic conductor, an anode and a cathode, Whereby electric storage is accomplished via elec (21) Appl, No; 10/076,268 trochemical reduction of the cathode and oxidation of the anode, Whereby said cathode includes electrochemically (22) Filed: May 13, 2002 active silver (per)manganate materials.

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SILVER MAGANESE SALT CATHODES FOR 1371]. In principle, this silver (per)manganate, AgMnO4, ALKALINE BATTERIES represent a substantial cathodic charge source for electrochemical storage, but [0001] The present invention relates to electric storage high rate charge transfer has been ine?icient. Independent of Whether batteries. More particularly, the invention relates to a novel AgMnO4 is described as silver permanganate, Ag(I)Mn(VII)O4, or silver alkaline electric storage battery With a cathode formed from peroximanganate, Ag(II)Mn(VI)O4, or as a mixed intermediate valence, Where Omanganese compound. a higher cathodic charge capacity than other permanganate or manganate salts. In addition to the manganese reduction, AgMnO4 permits the alkaline BACKGROUND OF THE INVENTION reduction, as Ag(I) (or if Ag(MnO4)2 had been used as Ag(II)) in the same [0002] MnO2 is the common active cathode material in potential domain, and exempli?ed by the silver oxide reductions: primary alkaline batteries. As an alternative to MnO2, a variety of permanganate compounds have been considered for cathode materials due to their high oxidation state Which, in principle permits signi?cant storage and release of elec [0009] Hence, independent of the Ag(I)/Mn(VII) or trical charge. HoWever, as described by J. Epstein and C. C. Ag(II)/Mn(VI) starting point, the alkaline cathodic reduction Liang, US. Pat. No. 3,799,959 (Oct. 12, 1971), most per AgMnO4 is consistent With an overall 5 electron reduction to manganates salts are overly soluble in alkaline solution and Ag(0) and Mn(III) at thermodynamically potential, this solubility can be destructive to the battery performance. E§0.35V vs SHE, for example as: In addition, most permanganate salts do not discharge effec tively in the solid phase, although as described by S. Licht E;0.35v vs SHE (7) and C. Marsh, US. Pat. No. 5,549,991, (Aug. 27, 1996), in [0010] It is an object of the present invention to provide an the solution phase they can support high currents. additive to the cathode in alkaline batteries Which provides a practical storage capacity greater than the capacity knoWn [0003] Compared to the manganese dioxide alkaline cath for conventional cathode materials. A novel electrochemi ode reaction, both manganates and permanganates can have cally active solid cathode is demonstrated using silver a signi?cantly higher faradaic capacity and higher cathodic permanganate. potential. The thermodynamic potential for the le- perman ganate to manganate reduction in aqueous alkaline media is: BRIEF DESCRIPTION OF THE INVENTION [0011] The invention relates to an electrical storage cell, [0004] and manganate also can exhibit a direct discharge so-called alkaline battery, comprising tWo half-cells Which to manganese dioxide, summariZed as the 2e“ reduction: are in electrochemical contact With one another through an electrically neutral alkaline ionic conductor, Wherein one of said half-cells comprises an anode and the other half-cell [0005] and alternately permanganate also can exhibit a comprises a cathode, Whereby electrical storage is accom direct discharge to manganese dioxide, summariZed as the plished via electrochemical reduction of the cathode and 3e- reduction: oxidation of the anode. The cathode contains an electro chemically active silver manganate, or silver permanganate [0006] In addition, the MnO2 product can undergo a fur compound, or oxidiZed silver and manganate or permanga ther 1e- reduction, as utiliZed in the conventional commer nate material. cial alkaline (Zn anode/MnO2 cathode) cell: BRIEF DESCRIPTION OF THE FIGURES [0012] FIG. 1 is a diagrammatic illustration of the silver [0007] Manganate salts, being in the less oxidiZed man (per)manganate material cathode battery according to the ganese valence state of Mn(VI), Will store less charge in principle, than the permanganates. This loWer valence state invention; and Would also suggest that they Would be considered to be less [0013] FIGS. 2 to 8: illustrate graphically performance of chemically active. In principal, as described by equations 2 various battery aspects according to the invention as and 4, permanganate salts can undergo a total of a 4e described in the Examples. alkaline cathodic reduction, and by equations 3 and 4 manganate salts can undergo a total of a 3e- alkaline DETAILED DESCRIPTION OF THE cathodic reduction. Yet the manganate and permanganate INVENTION salts have not replaced the Widely used commercial alkaline MnO2 cathode due to a general perception that these salts are [0014] The novel battery according to the present inven too soluble (creating a tendency to react and decompose the tion is based on the addition of an electrochemically active anode), and that they exhibit only inef?cient, and/or loW silver manganate material or silver permanganate material to current density, charge transfer. form a cathode in an alkaline battery, as silver (permanga nate and hydroxide. In one embodiment the hydroxide is in [0008] The absorbance spectra and Xray diffraction of the form of a salt solid. In a preferred embodiment the solid AgMnO4 has been characteriZed P. Doyle, I. Kirkpatrick, hydroxide comprises at least 1% of the Weight of the cathode Spectrochimica Acta, 24A (1968) 1495]. AgMnO4 is not a mass. In other embodiments, the solid hydroxide comprises traditional Mn(VII) permanganate salt and the manganese at least 5% or 25% of the Weight of the cathode mass. In a evidently exists in a valence state betWeen VI and VII, While preferred embodiment the silver (per)manganate is in the the silver exists in a valence state betWeen I and II [L. F. form of AgMnO4, or in an alternate embodiment is in the Mehne, B. B. Wayland, J. Inorg. Nucl. Chem., 37 (1975) form of Ag(MnO 4)2, or in an alternate preferred embodiment US 2003/0008210 A1 Jan. 9, 2003

is formed from the mixture of silver salt, and a (per)man [0019] The electrically neutral alkaline ionic conductor ganate salt other than silver (per)manganate. In this alternate utiliZed in the battery according to the present invention, preferred embodiment, said silver salt is AgO, or in alternate comprises a medium that can support current density during embodiments, said silver salt is AgNO3, a silver halide, battery discharge in an alkaline medium. A typical repre Ag2O, AgOH, Ag2O2, or Ag(OH)2. In this alternate pre sentative ionic conductor is an aqueous solution preferably ferred embodiment said (per)manganate salt other than containing a high concentration of a hydroxide such as silver is a manganate salt such as BaMnO4, MgMnO4, KOH. In other typical embodiments, the electrically neutral CaMnO4, SrMnO4, K2MnO4, Na2MnO4, Li2MnO4, ionic conductor comprises a high concentration of NaOH. Rb2MnO4, Cs2MnO4, ammonium manganate, or a tetra alkyl ammonium manganate, and in another alternate [0020] An electric storage battery according to the inven tion may be rechargeable by application of a voltage in embodiment is a permanganate salt such as KMnO4, excess of the voltage as measured Without resistive load, of NaMnO4, LiMnO4, RbMnO4, CsMnO4, ammonium per the discharged or partially discharged cell. manganate, or a tetra alkyl ammonium permanganate. [0021] According to another embodiment of the invention, [0015] The phrase “theoretical charge capacity” refers to means are provided to impede transfer of chemically reac the calculated charge capacity of that cathode material in tive species, or prevent electric contract betWeen the anode accord With the knoWn number of faradays (moles electrons) and cathode. Said means includes, but is not limited to a stored per mole of that material. The theoretical charge non-conductive separator con?gured With open channels, a capacity is calculated through equation 8 and Where n is the membrane, a ceramic frit, grids or pores or agar solution; number of discharge electrons, F is the Faraday’s constant= such means being so positioned as to separate said half cells 26.801 Amp hour per mol, and FW is the formula Weight: from each other. Theoretical charge capacity=n>

Theoretical charge capacity of several known cathode materials. EXAMPLE 1 determined With equation 2 [0024] Salts Which are less soluble are preferred as FW Charge capacity cathodic materials. In Water the solubility of AgMnO4 is cathode material cathode name n kg/mole Amp hour/kg relatively loW (60 millimolar); eight fold less soluble than MnO2 manganese dioxide 1 86.9 308 KMnO4, 10 to 100 times less than lithium, sodium, ammo NiOOH nickel oxyhydroxide 1 91.7 289 nium, calcium, strontium and barium permanganates. In the HgO mercury oxide 2 216.6 247 storage cell, loW solubility, or insolubility is preferred to Ag2O silver oxide 2 231.7 231 minimiZe parasitic cathode/anode interactions. An experi AgO silver peroxide 2 123.9 433 ment Was carried out, the object being to demonstrate the AgMnO4 silver(I) manganate 5 226.8 591 Ag(MnO4)2 silver permanganate 10 345.7 775 loW solubility of silver manganate in potassium hydroxide solutions of concentrations similar to those used in alkaline batteries. As measured in FIG. 2, the solubility of silver US 2003/0008210 A1 Jan. 9, 2003

permanganate is very loW compared to that of the other matrix that this Fe(VI) salt provides. The cathode reduction permanganate. As measured in FIG. 2, the solubility of is supported by a conductive matrix provided through inclu silver permanganate is very loW compared to that of most sion of graphite in the cathode mix. FIG. 5, probes the manganate salts, and is similar to the loW solubility of experimental 4e- (for KMnO4) or 5e- (for AgMnO4), ef? potassium manganate salt. ciency, determined by comparison of the measured cumu lative discharge ampere hours, as a fraction of the intrinsic EXAMPLE 2 charge determined from the mass of the salt. The Percent Storage Capacity is determined by the measured cumulative [0025] An experiment Was carried out, the object being to ampere hours, compared to the theoretical capacity. In this demonstrate that the silver manganate, prepared as a cathode ?gure utiliZation of higher Weight fraction (employing 32 mix under the same conditions as the common permanga Weight percent, rather than 9 Weight percent) graphite nate salt, KMnO4, discharges to a substantially higher frac greatly improves the percent storage capacity of the KMnO4, tion of it’s theoretical cathodic charge, particularly When a and Without being limited to any theory, reductive charge hydroxide salt is added. Salts that can discharge to a higher transfer appears to be signi?cantly effected by an insuf?cient percentage of their theoretical cathodic charge, are preferred conductive matrix. This is not the case for the AgMnO4 as alkaline cathodic salts. cathode Which is already conductive, and as seen in FIG. 5, [0026] Cells are prepared With identical Zinc anodes and added graphite results only in a marginal improvement in separators, as removed from commercialAAAalkaline cells. storage ef?ciency. Silver, in addition, to being an excellent Cell potential and energy capacity of alkaline AAA cells metallic conductor, sustains effective conductances of it’s Were measured during discharge at a constant load rate of cations through it’s oxides. As the AgMnO4/KOH dis 759. Cells contain either 3.4 g KMnO4, or 4.6 g AgMnO4 charges, the concentration of reduced silver groWs and in the 9 Weight percent graphite mix, and 9 Weight percent provides a groWing conductive matrix to increasingly facili 13.5 molar KOH electrolyte. In addition to these cells, those tate the manganese reduction. In the more ef?cient KOH indicated as 32% graphite cathodes, contains 2.3 g KMnO4, activated AgMnO4 discharge, distinct voltage plateaus are and 2.8 g AgMnO4 in the respective cathode mixes. The observed in FIG. 5 at 1.7 and 1.5 volts, equivalent to sodium permanganate mix also includes solid NaOH to approximately one third and tWo thirds of the discharge. avoid an overly Wet mixture, as Well as 32 Wt % graphite (2.1 Each of these potential steps is presumably a mixed potential g of NaMnO4.H2O and NaOH in a 9:1 Weight ratio). related to portions of the overall 5 electron transfer. [0027] Permanganates and manganese salts represent a [0030] FIG. 5 shoWs that silver manganate, prepared as a substantial source of cathodic charge, but discharge ineffec cathode mix under the same conditions as the common tively in traditional alkaline batteries. As summariZed in permanganate salts, KMnO4, discharges to a substantially FIG. 3, a cathode consisting of KMnO4 alone, or AgMnO4 higher fraction of it’s theoretical cathodic charge. Under alone, or KMnO4 and KOH together, discharge ineffectively these conditions, and as seen in the ?gure middle, a cathode in a conventional AAA cell con?guration. In the same cell comprised of only KMnO4, exhibits less than half of the con?guration the pure AgMnO4 cathode discharges less capacity of the AgFeO4 cathode. effectively, than a pure manganate or pure potassium per [0031] FIGS. 6 and 7 demonstrate that for the high rate manganate cathode. HoWever, a cathode of AgMnO4 and discharge domains, accomplished by discharging the cells KOH together discharges effectively to a high discharge over a constant 2.89 load, the KOH activated AgMnO4 capacity of 2.0 Wh. Evidently the intimate mixture of these cathode discharges more effectively than the pure AgMnO4, reaction products are substantially more electrochemical or other manganate or permanganate cathodes alone. This active than silver permanganate alone. ?gures also demonstrates that mixtures of other manganate [0028] A cathode Which discharges to a high total energy, or permanganate cathodes With AgO discharges in a manner is preferred. FIG. 4, presents the higher discharge energy similar to the hydroxide activated AgMnO4 cathodes. This measured for the silver manganate cathode, compared to a is also demonstrate for the loW rate di charge domain, in KMnO4 cathode under the same conditions. The ?gure sum FIG. 8. mariZes the measured discharge of NaMnO4, or KMnO4 EXAMPLE 3 compared to the AgMnO4 cathode alkaline AAA cells. Despite the loWer intrinsic Mn(VIQIV) capacity of the [0032] An experiment Was carried out, the object being to silver manganate salt, this salt’s cathode approaches 1.0 Wh, demonstrate that the silver permanganate cathode can also yielding a higher discharge capacity than the sodium or be used in combination With other cathode salts. AgMnO4 potassium permanganate cathode cells. As is evident in the mixed With a Fe(VI) salt cathode discharges effectively as an ?gure, the measured discharge capacity is higher, despite the alkaline cathode. FIG. 2, also includes the discharge of loWer intrinsic 4e- capacities, for the heavier alkali cation alkaline cells With a mixed cathode Which includes the permanganates compared to the lighter alkali permangan Fe(VI) salt, BaFeO4, and silver permanganate, and it is ates. The measured capacity of sodium, and potassium evident that the mixed AgMnO4/Fe(VI) cathode can also permanganate cathodes is ~0.45 Wh and 0.8 Wh. The attain a high discharge capacity of 2.0 Wh. sodium permanganate discharge required a higher fraction EXAMPLE 4 (32 Weight percent) of graphite to generate a discharge. [0033] In an alternate con?guration Ag(MnO4)2 can also [0029] Compared to the AgMnO4 cell, the pure KMnO4 be used as an alkaline cathode. We ?nd by spectral analysis cathode cell in FIG. 2, exhibits a lesser, but signi?cant, that Ag(MnO4)2 is formed by the mixture of AgMnO4 and improvement With KOH addition. In the presence of KOH, oxidiZing agent, or the mixture of a permanganate salt other this enhanced Mn(VII) charge transfer indicated for KMnO4 than AgMnO4, a silver salt, other than AgMnO4, and an containing KOH, is attributed to the improved conductive oxidiZing agent. US 2003/0008210 A1 Jan. 9, 2003

1. A battery comprising tWo half-cells Which are in an 16. The battery according to claim 14 Whereby said electrochemical contact With one another through an elec manganate salt is a BaMnO4. trically neutral alkaline ionic conductor, Wherein one of said 17. The battery according to claim 14 Whereby said half-cells comprises an anode and the other half-cell com manganate salt is MgMnO4, CaMnO4, SrMnO4, K2MnO4, prises a cathode, Whereby electrical discharge is accom Na2MnO4, Li2MnO4, Rb2MnO4, Cs2MnO4, ammonium plished via reduction of the cathode and oxidation of the manganate, or a tetra alkyl ammonium manganate. anode, and Whereby said cathode includes silver (per)man 18. The battery according to claim 4 Whereby said (per ganate salt and hydroxide. )manganate salt other than silver is a permanganate salt. 2. The battery according to claim 1 Whereby said silver 19. The battery according to claim 18 Whereby said (per)manganate is in the form of AgMnO4. permanganate salt is a KMnO4. 3. The battery according to claim 1 Whereby said silver 20. The battery according to claim 18 Whereby said (per)manganate is in the form of Ag(MnO4)2. permanganate salt is NaMnO4, LiMnO4, RbMnO4, 4. The battery according to claim 1 Whereby said silver CsMnO4, ammonium permanganate, or a tetra alkyl ammo (per)manganate is formed from the mixture of silver salt, nium permanganate. and a (per)manganate salt other than silver (per)manganate. 21. The battery according to claim 4 Whereby said mixture 5. The battery according to claim 4 Whereby said silver also includes an oxidiZing agent. salt is AgNO3, or AgNO2 22. The battery according to claim 7 Whereby said oxi 6. The battery according to claim 4 Whereby said silver diZing agent is a hypochlorite salt. salt is a silver halide, silver halate, silver perhalate, or silver 23. The battery according to claim 7 Whereby said oxi halite. diZing agent is a peroxydisulfate salt. 7. The battery according to claim 4 Whereby said silver 24. The battery according to claim 1 Whereby said silver salt contains carbon, from the salt list of silver acetate, silver permanganate comprises at least 1% of the Weight of the carbonate, silver fulimate, silver lactate, silver acetylide, silver levunilate, silver oxalate, silver palimate, silver cyan cathode mass. ate, silver thiocyanate, silver benZoate, silver propionate, 25. The battery according to claim 1 Whereby said silver silver salicyate, silver stearate or silver tartrate. permanganate comprises at least 5% of the Weight of the 8. The battery according to claim 4 Whereby said silver cathode mass. salt is chosen from the list of silver tetraborate, silver sulfate, 26. The battery according to claim 1 Whereby said silver silver thiosulfate, silver dithionate, silver selenate, silver permanganate comprises at least 25% of the Weight of the selinide, silver telluride, silver tungstate, silver aZide, silver cathode mass. phosphate, silver orthophosphate or silver pyrophosphate. 27. The battery according to claim 1 Whereby said 9. The battery according to claim 4 Whereby said silver hydroxide comprises a solid salt. salt is a silver oxide. 28. The battery according to claim 1 Whereby said 10. The battery according to claim 6 Whereby said silver hydroxide salt is potassium hydroxide. oxide, is Ag2O or AgOH. 29. The battery according to claim 27 Whereby said 11. The battery according to claim 4 Whereby said silver hydroxide salt comprises at least 1% of the Weight of the salt is a silver peroxide. cathode mass. 12. The battery according to claim 4 Whereby said silver 30. The battery according to claim 27 Whereby said peroxide is AgO hydroxide salt comprises at least 5% of the Weight of the 13. The battery according to claim 12 Whereby said silver cathode mass. peroxide is Ag2O2 or Ag(OH)2. 31. The battery according to claim 27 Whereby said 14. The battery according to claim 4 Whereby said (per hydroxide salt comprises at least 25% of the Weight of the )manganate salt other than silver is a manganate salt. cathode mass. 15. The battery according to claim 14 Whereby said manganate salt is a K2MnO4.