WO2008039416A1

WO2008039416A1 - Dendrite-resistant separator for alkaline storage batteries

Info

Publication number: WO2008039416A1
Application number: PCT/US2007/020601
Authority: WO
Inventors: George W. Adamson; Hieu M. Duong; Huawen Li; Ladan E. Vajdi
Original assignee: Zpower Inc.
Priority date: 2006-09-25
Filing date: 2007-09-24
Publication date: 2008-04-03

Abstract

A dendrite-resistant separator layer for use in alkaline zinc-silver oxide storage batteries comprises a coating of a cross-linked polyvinyl alcohol polymer filled with zirconium oxide powder. The separator layer may be free-standing or be applied to a substrate, and can optionally comprise additives such as a conductivity enhancer, a surfactant, or a plasticizer.

Description

DENDRITE-RESISTANT SEPARA TOR FOR ALKALINE STORA GE BA TTERIES

CLAIM OF PRIORITY

[0001] The present application claims priority to U.S. provisional patent application serial no. 60/826,863, which was filed September 25, 2006 and is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention is concerned with electrical storage batteries, and in particular, it is concerned with separators for alkaline storage batteries.

BACKGROUND OF THE INVENTION

[0003] An electrical storage battery comprises one electrochemical cell or a plurality of electrochemical cells of the same type, the latter typically being connected in series to provide a higher voltage or in parallel to provide a higher charge capacity than provided by a single cell. An electrochemical cell comprises an electrolyte interposed between and in contact with an anode and a cathode. For a storage battery, the anode comprises an active material that is readily oxidized, and the cathode comprises an active material that is readily reduced. During battery discharge, the anode active material is oxidized and the cathode active material is reduced, so that electrons flow from the anode through an external load to the cathode, and ions flow through the electrolyte between the electrodes. [0004] Many electrochemical cells used for electrical storage applications also include a separator between the anode and the cathode is required to prevent reactants and reaction products present at one electrode from reacting and/or interfering with reactions at the other electrode. An exception is the common lead acid sulfate battery for which the reactants and reaction products for both electrodes are insoluble lead metal or lead oxides and sulfates. To be effective, a battery separator must be electronically insulating, and remain so during the life of the battery, to avoid battery self-discharge via internal shorting between the electrodes, hi addition, a battery separator must be both an effective electrolyte transport barrier and a sufficiently good ionic conductor to avoid excessive separator resistance that substantially lowers the discharge voltage.

[0005] Electrical storage batteries are classified as either "primary" or "secondary" batteries. Primary batteries involve at least one irreversible electrode reaction and cannot be recharged with useful charge efficiency by applying a reverse voltage. Secondary batteries involve relatively reversible electrode reactions and can be recharged with acceptable loss of charge capacity over numerous charge-discharge cycles. Separator requirements for secondary batteries tend to be more demanding since the separator must survive repeated charge- discharge cycles. [0006] For secondary batteries comprising a highly oxidative cathode, a highly reducing anode, and an alkaline electrolyte, separator requirements are particularly stringent. The separator must be chemically stable in strongly alkaline solution, resist oxidation in contact with the highly oxidizing cathode, and resist reduction in contact with the highly reducing anode. Since ions, especially metal oxide ions, from the cathode can be somewhat soluble in alkaline solutions and tend to be chemically reduced to metal on separator surfaces, the separator must also inhibit transport and/or chemical reduction of metal ions. Otherwise, a buildup of metal deposits within separator pores may increase the separator resistance in the ^"k short term and ultimately lead to shorting failure due to formation of a continuous metal path through the separator. In addition, because of the strong tendency of anodes to form dendrites during charging, the separator must suppress dendritic growth and/or resist dendrite penetration to avoid failure due to formation of a dendritic short between the electrodes. A related issue with anodes is shape change, in which the central part of the electrode tends to thicken during charge-discharge cycling. The causes of shape change are complicated and not well-understood but apparently involve differentials in the current distribution and solution mass transport along the electrode surface. The separator preferably mitigates zinc electrode shape change by exhibiting uniform and stable ionic conductivity and ionic transport properties.

[0007] In order to satisfy the numerous and often conflicting separator requirements for zinc- silver oxide batteries, a separator stack comprised of a plurality of separator layers that perform specific functions is needed. The key required functions are resistance to electrochemical oxidation and silver ion transport from the cathode, and resistance to electrochemical reduction and dendrite penetration from the anode. [0008] Cellophane is an effective separator developed for alkaline batteries; however, this separator material decomposes chemically in alkaline electrolytes, which limits the useful life of the battery. Cellophane is also subject to chemical oxidation by soluble silver ions and electrochemical oxidation in contact with silver electrodes. Furthermore, cellophane exhibits low mechanical strength and poor resistance to penetration by dendrites. [0009] To solve some of the problems caused by the cellophane separators, new separator materials have been developed.

SUMMARY OF THE INVENTION

[0010] The invention provides separators for use in an alkaline battery (e.g., a zinc-silver oxide alkaline battery) comprising an alkaline electrolyte, an anode, and a cathode, wherein the separator comprises a cross-linked polyvinyl alcohol polymer and a zirconium oxide powder. The separators of the present invention can optionally comprise additives such as a conductivity enhancer, a surfactant, a plasticizer, or the like.

[0011] Advantageously, the separators comprising a cross-linked polyvinyl alcohol polymer and a zirconium oxide powder exhibit a resistance to dendrite formation caused by the migration of cathode and anode metals into the separator. Separators comprising a cross- linked polyvinyl alcohol polymer, a zirconium oxide powder, and a conductivity enhancer formation are resistant to dendrite formation but also exhibits high ionic conductivity which is beneficial for battery discharge performance.

[0012] Another aspect of the present invention provides batteries that are formed from an anode comprising zinc, a cathode comprising silver oxide, an electrolyte, and a separator comprising a cross-linked polyvinyl alcohol polymer and a zirconium oxide powder. [0013] Another aspect of the present invention provides methods of forming a separator comprising providing a mixture of a polyvinyl precursor polymer, a cross-linking agent, and zirconium oxide powder. In some embodiments, the mixture also comprises additives such as a surfactant, a conductivity enhancer, a plasticizer, or the like. [0014] In several embodiments, the mean molecular weight of the polyvinyl precursor polymer is greater than about 5000 amu. In other embodiments, the precursor polymer is at least about 80% hydrolyzed. Some precursor polymers further comprise vinyl acetate, ethylene, vinyl butyral, or any combination thereof.

[0015] Further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description.

DETAILED DESCRIPTION

[0016] The present invention provides separators useful in alkaline storage batteries, wherein the separator comprises a cross-linked polyvinyl alcohol polymer and zirconium oxide powder. The present invention also provides batteries comprising this novel separator and methods of forming such separators.

[0017] It is noted that separators of the present invention reduce the formation of dendrites in zinc-silver oxide batteries under normal operating conditions, i.e., when the batteries are stored and used in temperatures from about -20° C to about 70° C, and are not overcharged or charged above their rated capacity. [0018] I. DEFINITIONS

[0019] The term "battery" encompasses electrical storage devices comprising one electrochemical cell or a plurality of electrochemical cells. A "secondary battery" is rechargeable, whereas a "primary battery" is not rechargeable. [0020] A "battery anode" is designated as the positive electrode during battery discharge, and as the negative electrode during battery charge.

[0021] Both the polymer name "polyvinyl alcohol" and its corresponding initials (PVA) are used interchangeably as adjectives to designate polymer types, solutions for preparing polymers, and polymer coatings. Use of these adjectives in no way implies the absence of other constituents.

[0022] The symbol M denotes molar concentration.

[0023] It is noted that batteries and battery electrodes are denoted with respect to the active materials in the fully-charged state. For example, a zinc-silver oxide battery comprises a zinc anode and a silver oxide cathode. However, more than one species is present at a battery electrode under most conditions; a zinc electrode generally comprises zinc metal and zinc oxide (except when fully charged), and a silver oxide electrode usually comprises silver oxide

(AgO and/or Ag₂O) and silver metal (except when fully discharged).

[0024] The term "oxide" applied to alkaline batteries and alkaline battery electrodes encompasses corresponding "hydroxide" species, which are typically present, at least under some conditions.

[0025] Battery separators may be configured in a variety of ways. For example, a separator for a rectangular battery electrode may be in the form of a sheet or film comparable in size or slightly larger than the electrode, and may simply be placed on the electrode or may be sealed around the edges. The edges of the separator may be sealed to the electrode, an electrode current collector, a battery case, or another separator sheet or film on the backside of the electrode via an adhesive sealant, a gasket, or fusion (heat sealing) of the separator or another material. The separator may also be in the form of a sheet or film wrapped and folded around the electrode to form a single layer (front and back), an overlapping layer, or multiple layers.

For a cylindrical battery, the separator may be spirally wound with the electrodes in a jellyroll configuration. Typically, the separator is included in an electrode stack comprising a plurality of separator layers. The separator of this invention may be incorporated in a battery in any suitable configuration.

[0026] II. SEPARATORS AND BATTERIES

[0027] The present invention provides a separator for use in a zinc-silver oxide storage battery, comprising a cross-linked polyvinyl alcohol polymer, a cross-linking agent, and a zirconium oxide powder.

[0028] In several embodiments, the cross-linked polyvinyl alcohol polymer is a copolymer.

For example, the cross-linked PVA polymer is a copolymer comprising a first monomer, PVA, and a second monomer. In some instances, the PVA polymer is a copolymer comprising at least 60 mole percent of PVA and a second monomer. In other examples, the second monomer comprises vinyl acetate, ethylene, vinyl butyral, or any combination thereof.

[0029] Separators of the present invention also comprise a cross-linking agent in a sufficient quantity as to render the separator substantially insoluble in water. In several embodiments, the cross-linking agent used in the separators of the present invention comprises a monoaldehyde (e.g., formaldehyde or glyoxilic acid); aliphatic, furyl or aryl dialdehydes (e.g., glutaraldehyde, 2,6 furyldialdehyde or terephthaldehyde); dicarboxylic acids (e.g., oxalic acid or succinic acid); polyisocyanates; methylolmelamine; copolymers of styrene and maleic anhydride; germaic acid and its salts; boron compounds (e.g., boron oxide, boric acid or its salts; or metabolic acid or its salts); or salts of copper, zinc, aluminum or titanium. For example, the cross-linking agent comprises boric acid.

[0030] Separators of the present invention also comprise zirconium oxide powder. In several embodiments, the separator comprises from about 1 wt % to about 99 wt % (e.g., from about 2 wt % to about 98 wt %, from about 20 wt % to about 60 wt %, or from about 30 wt % to about 50 wt %).

[0031] Separators of the present invention also comprise a reduced ionic conductivity. For example, in several embodiments, the separator comprises an ionic resistance of less than about 20 mΩ/cm², (e.g., less than about 10 mΩ/cm², less than about 5 mΩ/cm², or less than about 4mΩ/cm²).

[0032] The separators of the present invention can optionally comprise any suitable additives such as a conductivity enhancer, a surfactant, a plasticizer, or the like. [0033] In some embodiments, the separator further comprises a conductivity enhancer. For example, the separator comprises a cross-linked polyvinyl alcohol polymer, a zirconium oxide powder, and a conductivity enhancer. The conductivity enhancer comprises a copolymer of polyvinyl alcohol and a hydroxyl-conducting polymer. Suitable hydroxyl- conducting polymers have functional groups that facilitate migration of hydroxyl ions. In some examples, the hydroxyl-conducting polymer comprises polyacrylate, polylactone, polysulfonate, polycarboxylate, polysulfate, polysarconate, polyamide, polyamidosulfonate, or any combination thereof. A solution containing a copolymer of a polyvinyl alcohol and a polylactone is sold commercially under the trade name Vytek^® polymer by Celanese, Inc. In several examples, the separator comprises from about 1 wt % to about 10 wt % of conductivity enhancer. [0034] In other embodiments, the separator further comprises a surfactant. For example, the separator comprises a cross-linked polyvinyl alcohol polymer, a zirconium oxide powder, and a surfactant. The surfactant comprises one or more surfactants selected from an anionic surfactant, a cationic surfactant, a nonionic surfactant, an ampholytic surfactant, an amphoteric surfactant, and a zwitterionic surfactant. Such surfactants are commercially available. In several examples, the separator comprises from about 0.01 wt % to about 1 wt % of surfactant.

[0035] In several embodiments, the separator further comprises a plasticizer. For example, the separator comprises a cross-linked polyvinyl alcohol polymer, a zirconium oxide powder, and a plasticizer. The plasticizer comprises one or more plasticizers selected from glycerin, low-molecular- weight polyethylene glycols, aminoalcohols, polypropylene glycols, 1 ,3 pentanediol branched analogs, 1 ,3 pentanediol, and/or water. For example, the plasticizer comprises greater than about 1 wt % of glycerin, low-molecular-weight polyethylene glycols, aminoalcohols, polypropylene glycols, 1 ,3 pentanediol branched analogs, 1 ,3 pentanediol, or any combination thereof, and less than 99 wt % of water. In other examples, the plasticizer comprises from about 1 wt % to about 10 wt % of glycerin, low-molecular- weight polyethylene glycols, aminoalcohols, polypropylene glycols, 1 ,3 pentanediol branched analogs, 1,3 pentanediol, or any combination thereof, and from about 99 wt % to about 90 wt % of water.

[0036] Separators of the present invention can be a free-standing separator or they can optionally further comprise a substrate. In several embodiments, the separator comprises a cross-linked polyvinyl alcohol polymer, a zirconium oxide powder, and a porous or nonporous substrate. For example, the substrate can be a porous substrate. In some instances, the substrate is a porous substrate that comprises a woven or non-woven material. [0037] Another aspect of the present invention provides a dendrite-resistant separator comprising a cross-linked polyvinyl alcohol polymer, a cross-linking agent, and a zirconium oxide powder. Such separators can optionally comprise additives such as a conductivity enhancer, a surfactant, a plasticizer, a substrate, or any combination thereof as described above, and in any amounts described above.

[0038] Another aspect of the present invention provides a battery that comprises an anode comprising zinc, a cathode comprising silver oxide, an electrolyte, and a separator, wherein the separator comprises a cross-linked polyvinyl alcohol polymer, a cross-linking agent, and a zirconium oxide powder. [0039] In several embodiments, the cross-linked polyvinyl alcohol polymer is a copolymer comprising a first monomer consisting essentially of polyvinyl alcohol, and a second monomer, and the copolymer comprises at least 60 mole percent of the polyvinyl alcohol. In some examples, the second monomer comprises vinyl acetate, ethylene, vinyl butyral, or any combination thereof. In other examples, the cross-linked polyvinyl alcohol polymer is cross- linked with a cross-linking agent selected from a monoaldehyde, a dialdehyde, a dicarboxylic acid, a polyisocyanate, a methylolmelamine, a copolymer of styrene, a copolymer of maleic anhydride, germaic acid, a salt of germaic acid, a compound of boron, copper, zinc, aluminum or titanium, or any combination thereof. In several embodiments, the cross-linking agent comprises boric acid.

[0040] In other embodiments, the separator of the present battery further comprises a conductivity enhancer comprising a copolymer of polyvinyl alcohol and a hydroxyl- conducting polymer. In some examples, the hydroxyl-conducting polymer comprises polyacrylate, polylactone, polysulfonate, polycarboxylate, polysulfate, polysarconate, polyamide, or polyamidosulfonate, or combination thereof.

[0041] In some embodiments, the separator of the present invention further comprises a plasticizer. In other examples, the plasticizer comprises glycerin, a low-molecular-weight polyethylene glycol, an aminoalcohol, a polypropylene glycols, a 1,3 pentanediol branched analog, 1 ,3 pentanediol, or combinations thereof, and/or water.

[0042] In alternative embodiments, the separator of the present battery further comprises a porous substrate. In some examples, the substrate comprises a woven material or a nonwoven material.

[0043] In several embodiments, the separator of the present battery further comprises a surfactant. For example, the surfactant comprises an anionic surfactant, a cationic surfactant, a nonionic surfactant, an ampholytic surfactant, an amphoteric surfactant, or a zwitterionic surfactant, or combinations thereof.

[0044] In some embodiments, the separator of the present battery comprises from about 2 wt % to about 98 wt % of zirconium oxide.

[0045] In some embodiments, the separator of the present battery comprises an ionic resistance of less than about 20 mΩ/cm2.

[0046] Other separators useful in batteries of the present invention include those described above.

[0047] III. METHODS

[0048] Another aspect of the present invention provides methods of forming separators comprising providing a mixture comprising a polyvinyl precursor polymer, a cross-linking agent, and zirconium oxide powder and at least partially curing the mixture to form a separator.

[0049] In some embodiments, the PVA precursor polymer has a mean molecular weight of greater than about 5000 amu. In other examples, the PVA precursor polymer is at least partially hydrolyzed (e.g., at least about 70 % hydrolyzed, at least about 75 % hydrolyzed, or at least about 80 % hydrolyzed). In some examples, the PVA precursor polymer has a mean molecular weight greater than about 5000 amu and is at least 80 % hydrolyzed.

[0050] In some instances, when the cross-linked PVA polymer comprises a copolymer, the polyvinyl alcohol precursor comprises a first monomer, i.e., PVA, and a second monomer.

For example, the PVA precursor polymer comprises at least 60 mole percent of PVA and a second monomer comprising vinyl acetate, ethylene, vinyl butyral, or any combination thereof.

[0051] In several embodiments, the mixture comprises an amount of cross-linking agent sufficient to render the separator substantially insoluble in water. In some instances the cross-linking agent comprises a monoaldehyde (e.g., formaldehyde or glyoxilic acid); aliphatic, furyl or aryl dialdehydes (e.g., glutaraldehyde, 2,6 furyldialdehyde or terephthaldehyde); dicarboxylic acids (e.g., oxalic acid or succinic acid); polyisocyanates; methylolmelamine; copolymers of styrene and maleic anhydride; germaic acid and its salts; boron compounds (e.g., boron oxide, boric acid or its salts; or metaboric acid or its salts); or salts of copper, zinc, aluminum or titanium. For example, the cross-linking agent comprises boric acid.

[0052] The mixture also comprises zirconium oxide powder. In several embodiments, the separator comprises from about 1 wt % to about 99 wt % (e.g., from about 2 wt % to about 98 wt %) of zirconium oxide powder.

[0053] Other additives can be combined with the mixture to form separators of the present invention, such as conductivity enhancers, surfactants, and plasticizers.

[0054] In one embodiment, the mixture further comprises a conductivity enhancer comprising a copolymer of polyvinyl alcohol and a hydroxyl-conducting polymer. Suitable hydroxyl-conducting polymers have functional groups that facilitate migration of hydroxyl ions, hi some examples, the hydroxyl-conducting polymer comprises polyacrylate, polylactone, polysulfonate, polycarboxylate, polysulfate, polysarconate, polyamide, polyamidosulfonate, or any combination thereof. In other examples, the mixture comprises from about 1 wt % to about 10 wt % of conductivity enhancer.

[0055] In other embodiments, the mixture further comprises a surfactant. The surfactant may be one of many sold commercially as surfactants or dispersion agents. Suitable surfactants include anionic, cationic, nonionic, ampholytic, amphoteric or zwitterionic surfactants, and mixtures thereof. In some examples, the mixture comprises from about 0.01 wt % to about 1 wt % of surfactant.

[0056] In alternative embodiments, the mixture further comprises a plasticizer. The plasticizer can facilitate removal of a separator layer from a casting tray or mold. For example, the mixture comprises a plasticizer comprising glycerin, low-molecular-weight polyethylene glycols, aminoalcohols, polypropylene glycols, 1,3 pentanediol branched analogs, 1,3 pentanediol, or any combination thereof and/or water. In other examples, the conductivity enhancer comprises greater than 1 wt % of glycerin, low-molecular-weight polyethylene glycols, aminoalcohols, polypropylene glycols, 1 ,3 pentanediol branched analogs, 1 ,3 pentanediol, or any combination thereof, and less than 99 wt % water. In some examples, the conductivity enhancer comprises from about 1 wt % to about 10 wt % of glycerin, low-molecular- weight polyethylene glycols, aminoalcohols, polypropylene glycols, 1 ,3 pentanediol branched analogs, 1 ,3 pentanediol, or any combination thereof, and from about 99 wt % to about 90 wt % of water.

[0057] The mixture can be cast as a free-standing film, or it can be applied to a substrate. [0058] In one embodiment, the mixture is applied to a substrate. For example, the mixture is applied to the substrate by painting, spraying, dipping, or co-extruding the substrate with the mixture. Any combination of these is also suitable for applying the mixture to a substrate. [0059] Other application techniques include without limitation, manual painting, roller painting, spraying, or co-extrusion onto a conveyor belt.

[0060] The method of the present invention also comprises at least partially curing the mixture. The mixtures of the present invention can be cured using any suitable technique such as exposure to electromagnetic radiation (e.g., UV or X-Ray), heating, air drying, or any combination thereof.

[0061] In some embodiments, the separator formed using the abovementioned methods is a dendrite-resistant separator.

[0062] The dendrite-resistance of the separator comprising PVA material, a cross-linking agent, and zirconium oxide powder, and any optional additives, as described above, can be demonstrated comparatively against a separator that comprises a cross-linked PVA material and is substantially free of zirconium oxide powder (e.g., the separator comprises less than 1 wt % of zirconium oxide powder (e.g., less than 0.5 wt % of zirconium oxide powder)) using standard testing methods such as those described in "Study to Investigate and Improve the Zinc Electrode for Spacecraft Electrochemical Cells", James McBreen, August 1967 Accession Number N67-38923, Page 6, hereby incorporated in its entirety by reference. [0063] EXAMPLE

[0064] A mixture according to the invention was prepared by adding 1.8 g of zirconium oxide, 40.0 g of 5% Vytek^® 2012 polymer solution, and 0.006 g of sodium salt of dodecylbenzenesulfonic acid to 60.0 g of 5% aqueous solution of polyvinyl alcohol (Dupont). The mixture was stirred until uniform in appearance, and 1.2 g of 5% solution of boric acid was added as cross-linking agent. This mixture was stirred, placed on a casting tray and dried overnight. The resulting separator layer exhibited an ionic resistance below the detection limit of the measurement apparatus (4 mΩ/cm²), whereas a PVA film of comparable thickness but without additives exhibited a high ionic resistance (20 mΩ/cm²). The separator layer of the invention was also found to be more resistant to silver and zinc ion migration than a PVA film without additives.

OTHER EMBODIMENTS

[0065] The embodiments of the present invention have been illustrated and described above. Modifications and additional embodiments, however, will undoubtedly be apparent to those skilled in the art. Furthermore, equivalent elements may be substituted for those illustrated and described herein, parts or connections might be reversed or otherwise interchanged, and certain features of the invention may be utilized independently of other features. Consequently, the exemplary embodiments should be considered illustrative, rather than inclusive, while the appended claims are more indicative of the full scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A separator for use in a zinc-silver oxide storage battery, comprising a cross-linked polyvinyl alcohol polymer and a zirconium oxide powder.

2. The separator of claim 1, wherein the cross-linked polyvinyl alcohol polymer is a copolymer comprising a first monomer consisting essentially of polyvinyl alcohol, and a second monomer, wherein the copolymer comprises at least 60 mole percent of the polyvinyl alcohol.

3. The separator of claim 2, wherein the second monomer comprises vinyl acetate, ethylene, vinyl butyral, or any combination thereof.

4. The separator of claim 1 , wherein the cross-linked polyvinyl alcohol polymer is cross- linked with a cross-linking agent selected from a monoaldehyde, a dialdehyde, a dicarboxylic acid, a polyisocyanate, a methylolmelamine, a copolymer of styrene, a copolymer of maleic anhydride, germaic acid, a salt of germaic acid, a compound of boron, copper, zinc, aluminum or titanium, or combinations thereof.

5. The separator of claim 4, wherein the cross-linking agent comprises boric acid.

6. The separator of claim 1, further comprising a conductivity enhancer comprising a copolymer of polyvinyl alcohol and a hydroxyl-conducting polymer.

7. The separator of claim 6, wherein the hydroxyl-conducting polymer comprises polyacrylate, polylactone, polysulfonate, polycarboxylate, polysulfate, polysarconate, polyamide, or polyamidosulfonate, or combinations thereof.

8. The separator of claim 1 , further comprising a plasticizer.

9. The separator of claim 8, wherein the plasticizer comprises glycerin, a low-molecular- weight polyethylene glycol, an aminoalcohol, a polypropylene glycols, a 1,3 pentanediol branched analog, 1 ,3 pentanediol, or combinations thereof, and/or water.

10. The separator of claim 1 , further comprising a porous substrate.

1 1. The separator of claim 10, wherein the substrate comprises a woven material or a nonwoven material.

12. The separator of claim 1, further comprising a surfactant.

13. The separator of claim 12, wherein the surfactant comprises an anionic surfactant, a cationic surfactant, a nonionic surfactant, an ampholytic surfactant, an amphoteric surfactant, or a zwitterionic surfactant, or combinations thereof.

14. The separator of claim 1 , wherein the separator comprises from about 2 wt % to about 98 wt % of zirconium oxide.

15. The separator of claim 1 , wherein the separator comprises an ionic resistance of less than about 20 mΩ/cm².

16. A battery comprising an anode comprising zinc; a cathode comprising silver oxide; an electrolyte; and a separator comprising a cross-linked polyvinyl alcohol polymer, a cross- linking agent, and a zirconium oxide powder.

17. The battery of claim 16, wherein the cross-linked polyvinyl alcohol polymer is a copolymer comprising a first monomer consisting essentially of polyvinyl alcohol, and a second monomer, and the copolymer comprises at least 60 mole percent of the polyvinyl alcohol.

18. The battery of claim 17, wherein the second monomer comprises vinyl acetate, ethylene, vinyl butyral, or any combination thereof.

19. The battery of claim 16, wherein the cross-linked polyvinyl alcohol polymer is cross- linked with a cross-linking agent selected from a monoaldehyde, a dialdehyde, a dicarboxylic acid, a polyisocyanate, a methylolmelamine, a copolymer of styrene, a copolymer of maleic anhydride, germaic acid, a salt of germaic acid, a compound of boron, copper, zinc, aluminum or titanium, or any combination thereof.

20. The battery of claim 19, wherein the cross-linking agent comprises boric acid.

21. The battery of claim 16, wherein the separator further comprises a conductivity enhancer comprising a copolymer of polyvinyl alcohol and a hydroxyl-conducting polymer.

22. The battery of claim 21 , wherein the hydroxyl-conducting polymer comprises polyacrylate, polylactone, polysulfonate, polycarboxylate, polysulfate, polysarconate, polyamide, or polyamidosulfonate, or combination thereof.

23. The battery of claim 16, wherein the separator further comprises a plasticizer.

24. The battery of claim 23, wherein the plasticizer comprises glycerin, a low-molecular- weight polyethylene glycol, an aminoalcohol, a polypropylene glycols, a 1,3 pentanediol branched analog, 1,3 pentanediol, or combinations thereof, and/or water.

25. The battery of claim 16, wherein the separator further comprises a porous substrate.

26. The battery of claim 25, wherein the substrate comprises a woven material or a nonwoven material.

27. The battery of claim 16, wherein the separator further comprises a surfactant.

28. The battery of claim 27, wherein the surfactant comprises an anionic surfactant, a cationic surfactant, a nonionic surfactant, an ampholytic surfactant, an amphoteric surfactant, or a zwitterionic surfactant, or combinations thereof.

29. The battery of claim 16, wherein the separator comprises from about 2 wt % to about 98 wt % of zirconium oxide.

30. The battery of claim 16, wherein the separator exhibits an ionic resistance of less than about 20 mΩ/cm².

31. A method of forming a separator for zinc-silver oxide storage batteries comprising providing a mixture that comprises a polyvinyl alcohol precursor polymer, a cross-linking agent, and zirconium oxide powder; and curing the mixture to form a separator.

32. The method of claim 31 , wherein the mean molecular weight of the polyvinyl alcohol precursor polymer is greater than 5000 amu.

33. The method of claim 32, wherein the polyvinyl alcohol precursor polymer is at least 80% hydrolyzed.

34. The method of claim 31 , wherein the mixture further comprises at least 60 mole percent polyvinyl alcohol.

35. The method of claim 31, wherein the mixture further comprises vinyl acetate, ethylene, vinyl butyral, or any combination thereof.

36. The method of claim 31 , wherein the cross-linking agent is selected from a monoaldehyde, a dialdehyde, a dicarboxylic acid, a polyisocyanate, a methylolmelamine, a copolymer of styrene, a copolymer of maleic anhydride, germaic acid, a salt of germaic acid, a compound of boron, copper, zinc, aluminum or titanium, or combinations thereof.

37. The method of claim 36, wherein the cross-linking agent comprises boronic acid.

38. The method of claim 31, wherein the mixture further comprises a conductivity enhancer comprising a copolymer of polyvinyl alcohol and a hydroxyl-conducting polymer.

39. The method of claim 38, wherein the hydroxyl-conducting polymer comprises polyacrylate, polylactone, polysulfonate, polycarboxylate, polysulfate, polysarconate, polyamide, or polyamidosulfonate, or combinations thereof.

40. The method of claim 31 , wherein the mixture further comprises a surfactant.

41. The method of claim 40, wherein the surfactant comprises an anionic surfactant, a cationic surfactant, a nonionic surfactant, an ampholytic surfactant, an amphoteric surfactant, or a zwitterionic surfactant, or combinations thereof.

42. The method of claim 31 , wherein the mixture further comprises a plasticizer.

43. The method of claim 42, wherein the plasticizer comprises glycerin, a low-molecular- weight polyethylene glycol, an aminoalcohol, a polypropylene glycols, a 1 ,3 pentanediol branched analog, 1 ,3 pentanediol, or combinations thereof, and/or water.

44. The method of claim 31 , further comprising applying the mixture to a porous substrate.

45. The method of claim 44, wherein the mixture is applied to the porous substrate by painting, dipping, spraying, co-extrusion, or any combination thereof.

46. The method of claim 45, wherein the porous substrate further comprises a woven material or a non- woven material.

47. The method of claim 31 , wherein the mixture is cured by air drying, heating, or exposure to electromagnetic radiation, or any combination thereof.

48. A separator for use in a zinc-silver oxide storage battery, the separator comprising a cross-linked polyvinyl alcohol polymer; a cross-linking agent; a zirconium oxide powder; a conductivity enhancer; a plasticizer; a surfactant; and a substrate.