Patent Application
20160301077
This invention is concerned with new electrodes and alkaline electrochemical cells that use these electrodes, such as batteries.
Many traditional electrochemical cells, such as those found in batteries, use electrodes that are formed from an active material and a binder that are combined to create a paste or gel that is applied to a current collector, such as a mesh current collector. The current collector (e.g., a conductive mesh) aggregates charge from the active material.
In cells configured as described above, the binder has several functions: 1. to distribute the electrode active materials so that they are electrically connected with each other, 2. to bond the electrode active materials to their respective current collectors, and 3. to coat and protect the electrode active materials from direct contact with the electrolyte.
A binder suited for use in an electrochemical cell such as a battery should at least perform these three functions. Traditional binders such as PTFE and CMC present manufacturing problems or have physical properties that limit the efficiency of electrochemical cells, and thus, limiting the utility, cycle life, or shelf life of batteries.
For instance, PTFE possesses poor solubility in most solvents, so the ability to manufacture a uniform mixture of active material and PTFE is difficult, and typically requires the use of surfactants to make a PTFE suspension for uniform distribution of electrode active materials and binder material. However, surfactants promote undesired side effects on a battery performance. Other efforts to create a uniform mixture of active material and binder included creating water-based PTFE suspensions, which impairs subsequent electrode coating processes, and scale-ability for battery manufacturing. Another traditional binder is CMC, which has favorable gelling properties; however it is a very poor binding agent for strong oxidizing active materials such as metal oxides (e.g., AgO, Ag2O3, and/or Ag2O). CMC also has a tendency to generate gas during battery cycling and storage that may be caused by the poor coating property of CMC on the active materials.
Therefore, the present invention provides improved electrodes that are free of one or more of the abovementioned problems suffered by traditional binders.
The present invention provides novel electrodes comprising one or more electrode active materials and a binder material, wherein the binder material comprises PVDF or a copolymer thereof.
Another aspect of the present invention provides novel electrochemical cells, such as those used in batteries, that comprise an alkaline electrolyte, an anode, and a cathode, wherein the anode comprises a first binder material and a first active material, and the cathode comprises a second binder material and a second active material, and either the first binder material, the second binder material, or both comprises PVDF or a copolymer thereof.
A third aspect of the present invention provides a method of producing an electrode for use in an alkaline battery comprising providing a binder material and providing an electrode active material, wherein the binder material comprises PVDF or a copolymer thereof.
A fourth aspect of the present invention provides a method of producing an alkaline electrochemical cell comprising providing an alkaline electrolyte, providing an anode, and providing a cathode, wherein the anode comprises a first binder material and a first active material, and the cathode comprises a second binder material and a second active material, and either the first binder material, the second binder material, or both comprises PVDF or a copolymer thereof.
The present invention provides novel electrodes comprising an active material and a binder material. These electrodes are useful in electrochemical cells such as those used in alkaline batteries.
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. For secondary batteries of the present invention, a battery anode is designated as the positive electrode during discharge, and as the negative electrode during charge.
The term “alkaline battery” refers to a primary battery or a secondary battery, wherein the primary or secondary battery comprises an alkaline electrolyte.
As used herein, an “electrolyte” refers to a substance that behaves as an electrically conductive medium. For example, the electrolyte facilitates the mobilization of electrons and cations in the cell. Electrolytes include mixtures of materials such as aqueous solutions of alkaline agents. Some electrolytes also comprise additives such as buffers. For example, an electrolyte comprises a buffer comprising a borate or a phosphate. Exemplary electrolytes include, without limitation aqueous KOH, aqueous NaOH, or the liquid mixture of KOH in a polymer.
As used herein, “alkaline agent” refers to a base or ionic salt of an alkali metal (e.g., an aqueous hydroxide of an alkali metal). Furthermore, an alkaline agent forms hydroxide ions when dissolved in water or other polar solvents. Exemplary alkaline electrolytes include without limitation LiOH, NaOH, KOH, CsOH, RbOH, or combinations thereof.
A “cycle” refers to a single charge and discharge of a battery.
For convenience, the polymer name “polyvinylidene fluoride” and its corresponding initials “PVDF” is used interchangeably as adjectives to distinguish polymers, solutions for preparing polymers, and polymer coatings. Use of these names and initials in no way implies the absence of other constituents. These adjectives also encompass substituted and co-polymerized polymers. A substituted polymer denotes one for which a substituent group, a methyl group, for example, replaces a hydrogen on the polymer backbone.
As used herein, “Ah” refers to Ampere (Amp) Hour and is a scientific unit for the capacity of a battery or electrochemical cell. A derivative unit, “mAh” represents a milliamp hour and is 1/1000 of an Ah.
As used herein, “maximum voltage” or “rated voltage” refers to the maximum voltage an electrochemical cell can be charged without interfering with the cell's intended utility. For example, in several zinc-silver electrochemical cells that are useful in portable electronic devices, the maximum voltage is less than about 3.0 V (e.g., less than about 2.8 V, less than about 2.5 V, about 2.3 V or less, or about 2.0 V). In other batteries, such as lithium ion batteries that are useful in portable electronic devices, the maximum voltage is less than about 15.0 V (e.g., less than about 13.0 V, or about 12.6 V or less). The maximum voltage for a battery can vary depending on the number of charge cycles constituting the battery's useful life, the shelf-life of the battery, the power demands of the battery, the configuration of the electrodes in the battery, and the amount of active materials used in the battery.
When referring to a polymer, the term “Mn” is used interchangeably with “mean molecular weight”.
As used herein, an “anode” is an electrode through which (positive) electric current flows into a polarized electrical device. In a battery or galvanic cell, the anode is the negative electrode from which electrons flow during the discharging phase in the battery. The anode is also the electrode that undergoes chemical oxidation during the discharging phase. However, in secondary, or rechargeable, cells, the anode is the electrode that undergoes chemical reduction during the cell's charging phase. Anodes are formed from electrically conductive or semiconductive materials, e.g., metals, metal oxides, metal alloys, metal composites, semiconductors, or the like. Common anode materials include Si, Sn, Al, Ti, Mg, Fe, Bi, Zn, Sb, Ni, Pb, Li, Zr, Hg, Cd, Cu, LiC6, mischmetals, alloys thereof, oxides thereof, or composites thereof.
Anodes may have many configurations. For example, an anode may be configured from a conductive mesh or grid that is coated with one or more anode materials. In another example, an anode may be a solid sheet or bar of anode material.
As used herein, a “cathode” is an electrode from which (positive) electric current flows out of a polarized electrical device. In a battery or galvanic cell, the cathode is the positive electrode into which electrons flow during the discharging phase in the battery. The cathode is also the electrode that undergoes chemical reduction during the discharging phase. However, in secondary or rechargeable cells, the cathode is the electrode that undergoes chemical oxidation during the cell's charging phase. Cathodes are formed from electrically conductive or semiconductive materials, e.g., metals, metal oxides, metal alloys, metal composites, semiconductors, or the like. Common cathode materials include AgO, Ag2O, Ag2O3, HgO, Hg2O, CuO, CdO, NiOOH, Pb2O4, PbO2, LiFePO4, Li3V2(PO4)3, V6O13, V2O5, Fe3O4, Fe2O3, MnO2, LiCoO2, LiNiO2, LiMn2O4, or composites thereof.
Cathodes may also have many configurations. For example, a cathode may be configured from a conductive mesh that is coated with one or more cathode materials. In another example, a cathode may be a solid sheet or bar of cathode material.
As used herein, an “electronic device” is any device that is powered by electricity. For example, and electronic device can include a portable computer, a portable music player, a cellular phone, a portable video player, or any device that combines the operational features thereof.
As used herein, “cycle life” is the maximum number of times a secondary battery can be charged and discharged.
The symbol “M” denotes molar concentration.
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 an anode comprising zinc and a cathode comprising silver oxide. Nonetheless, more than one species is present at a battery electrode under most conditions. For example, a zinc electrode generally comprises zinc metal and zinc oxide (except when fully charged), and a silver oxide electrode usually comprises a silver oxide (AgO, Ag2O, and/or Ag2O3) and silver metal (except when fully discharged).
The term “oxide” applied to alkaline batteries and alkaline battery electrodes encompasses corresponding “hydroxide” species, which are typically present, at least under some conditions.
As used herein “substantially stable” refers to a compound or component that remains substantially chemically unchanged in the presence of an alkaline electrolyte (e.g., potassium hydroxide) and/or in the presence of an oxidizing agent (e.g., silver ions present in the cathode or dissolved in the electrolyte).
As used herein, the terms “first” and/or “second” do not refer to order or denote relative positions in space or time, but these terms are used to distinguish between two different elements or components. For example, a first separator does not necessarily proceed a second separator in time or space; however, the first separator is not the second separator and vice versa. Although it is possible for a first separator to proceed a second separator in space or time, it is equally possible that a second separator proceeds a first separator in space or time.
One aspect of the present invention provides electrodes for use in electrochemical cells having a strong alkaline environment such as those found in alkaline batteries. Such electrodes comprise a binder material and an active material, wherein the binder material comprises PVDF or a PVDF copolymer.
Electrodes of the present invention can comprise any suitable active material such as a metal oxide (e.g., AgO, Ag2O, Ag2O3, or the like), and metal alloys such as Ni—Zn alloys.
In one embodiment the electrode active material comprises at least one metal or metal oxide. In several embodiments, the electrode is a cathode and the active material is one selected from AgO, Ag2O3, Ag2O, HgO, Hg2O, CuO, CdO, NiOOH, Pb2O4, PbO2, LiFePO4, Li3V2(PO4)3, V6O13, V2O5, Fe3O4, Fe2O3, MnO2, LiCoO2, LiNiO2, LiMn2O4, or composites thereof. For example, the electrode is a cathode having an active material comprising AgO or Ag2O3. In another embodiment, the electrode is an anode and the active material is one selected from Si, Sn, Al, Ti, Mg, Fe, Bi, Zn, Sb, Ni, Pb, Li, Zr, Hg, Cd, Cu, LiC6, mischmetals, alloys thereof, oxides thereof, or composites thereof. Anodes of the present invention can also comprise inactive compounds such as ceramics (e.g., ITO, TiN or TiNOx). For example, the electrode is an anode having an active material comprising Zn or ZnO.
Electrodes of the present invention comprise at least about 70 wt % of active material. For instance an electrode comprises at least 75 wt % (e.g., at least 80 wt %, at least 90 wt %, or at least 95 wt %) of active material. For example, a cathode comprises up to at least 90 wt % of the active material (e.g., AgO or Ag2O3).
Electrodes of the present invention also comprise binder material that includes PVDF or a PVDF copolymer. For example, the electrode comprises a PVDF copolymer consisting essentially of PVDF-co-HFP. Electrodes can comprise from about 1.5 wt % to about 10 wt % (e.g., from about 1.5 wt % to about 7 wt %) of binder material. Any of the abovementioned anodes or cathodes can comprise this binder material in the amounts described. In several embodiments, binder materials are substantially free of surfactants, i.e., having less than 0.5 wt % (e.g., less than 0.3 wt % or less than 0.25 wt %) of surfactant.
Electrodes of the present invention can comprise optional additives such as Bi2O3 in an amount of up to about 3 wt %.
Electrodes such as cathodes can comprise active materials that are coated or doped with other additives. One example provides a cathode comprising AgO that is doped with from about 0.5 wt % to about 10 wt % Pb. In another example, the cathode comprises AgO that is doped with from about 0.5 wt % to about 10 wt % Pb and coated with from about 0.5 wt % to about 5 wt % Pb.
A. Electrodes
Another aspect of the present invention provides electrochemical cells comprising an alkaline electrolyte, a cathode, and an anode; wherein the cathode comprises a first active material and a first binder material; the anode comprises a second active material and a second binder material; and the first binder material, the second binder material, or both comprises PVDF or PVDF copolymer.
In several embodiments, the cathode comprises at least 90 wt % of the first active material. For example, the cathode comprises at least 90 wt % of an active material selected from AgO, Ag2O, Ag2O3, HgO, Hg2O, CuO, CdO, NiOOH, Pb2O4, PbO2, LiFePO4, Li3V2(PO4)3, V6O13, V2O5, Fe3O4, Fe2O3, MnO2, LiCoO2, LiNiO2, LiMn2O4, or composites thereof.
In several examples, the active material of the cathode comprises AgO or Ag2O3.
In several embodiments, a cathode comprises up to about 10 wt % (e.g., up to about 6 wt %) of a binder material. For instance, the cathode comprises up to about 10 wt % of a binder that comprises PVDF or PVDF copolymer. In other examples, the binder material comprises a PVDF copolymer such as PVDF-co-HFP copolymer. In several embodiments, the PVDF-co-HFP copolymer has a mean molecular weight of less than about 600,000 amu (e.g., less than about 500,000 amu, or about 400,000 amu).
In alternative embodiments, an anode useful in the present electrochemical cells comprises at least 90 wt % of the second active material. For instance, an anode comprises at least about 90 wt % of an active material selected from Si, Sn, Al, Ti, Mg, Fe, Bi, Zn, Sb, Ni, Pb, Li, Zr, Hg, Cd, Cu, LiC6, mischmetals, alloys thereof, oxides thereof, or composites thereof. In several examples, the anode comprises an active material comprising Zn or ZnO.
In several embodiments, the anode comprises up to 10 wt % of a binder material. For instance, the anode comprises up to 6 wt % of a binder material. In several examples, the anode comprises binder material comprises up to 10 wt % of a binder material comprising PVDF or PVDF copolymer. For instance, the binder material comprises a PVDF copolymer such as PVDF-co-HFP copolymer. In other examples, the PVDF-co-HFP copolymer has a mean molecular weight of less than about 600,000 amu (e.g., less than about 500,000 amu, or about 400,000 amu).
B. Separator
Electrochemical cells of the present invention additionally comprise a separator that is separates the anode from the cathode.
Separators of the present invention can comprise a film having a single layer or a plurality of layers, wherein the plurality of layers may comprise a single polymer (or copolymer) or more than one polymer (or copolymer).
In several embodiments, the separators comprise a unitary structure formed from at least two strata. The separator can include strata wherein each layer comprises the same material, or each layer comprises a different layer, or the strata are layered to provide layers of the same material and at least on layer of another material. In several embodiments, one stratum comprises an oxidation resistant material, and the remaining stratum comprises a dendrite resistant material. In other embodiments, at least one stratum comprises an oxidation-resistant material, or at least one stratum comprises a dendrite-resistant material. The unitary structure is formed when the material comprising one stratum (e.g., an oxidation-resistant material) is coextruded with the material comprising another stratum (e.g., a dendrite resistant material or oxidation-resistant material). In several embodiments, the unitary separator is formed from the coextrusion of oxidation-resistant material with dendrite-resistant material.
In several embodiments, the oxidation-resistant material comprises a polyether polymer mixture and the dendrite resistant material comprises a PVA polymer mixture.
It is noted that separators useful in electrochemical cells can be configured in any suitable way such that the separator is substantially inert in the presence of the anode, cathode and electrolyte of the electrochemical cell. 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 jelly-roll configuration. Typically, the separator is included in an electrode stack comprising a plurality of separators. The oxidation-resistant separator of the invention may be incorporated in a battery in any suitable configuration.
1. Polyether Polymer Material
In several embodiments of the present invention the oxidation-resistant stratum of the separator comprises a polyether polymer material that is coextruded with a dendrite-resistant material. The polyether material can comprise polyethylene oxide (PEO) or polypropylene oxide (PPO), or a copolymer or a mixture thereof. The polyether material may also be copolymerized or mixed with one or more other polymer materials, polyethylene, polypropylene and/or polytetrafluoroethylene (PTFE), for example. In some embodiments, the PE material is capable of forming a free-standing polyether film when extruded alone, or can form a free standing film when coextruded with a dendrite-resistant material. Furthermore, the polyether material is substantially inert in the alkaline battery electrolyte and in the presence of silver ions.
In alternative embodiments, the oxidation resistant material comprises a PE mixture that optionally includes zirconium oxide powder. Without intending to be limited by theory, it is theorized that the zirconium oxide powder inhibits silver ion transport by forming a surface complex with silver ions. The term “zirconium oxide” encompasses any oxide of zirconium, including zirconium dioxide and yttria-stabilized zirconium oxide. The zirconium oxide powder is dispersed throughout the PE material so as to provide a substantially uniform silver complexation and a uniform barrier to transport of silver ions. In several embodiments, the average particle size of the zirconium oxide powder is in the range from about 1 nm to about 5000 nm, e.g., from about 5 nm to about 100 nm.
In other embodiments, the oxidation-resistant material further comprises an optional conductivity enhancer. The conductivity enhancer can comprise an inorganic compound, potassium titanate, for example, or an organic material. Titanates of other alkali metals than potassium may be used. Suitable organic conductivity enhancing materials include organic sulfonates and carboxylates. Such organic compounds of sulfonic and carboxylic acids, which may be used singly or in combination, comprise a wide range of polymer materials that may include salts formed with a wide variety of electropositive cations, K+, Na+, Li+, Pb+2, Ag+, NH4+, Ba+2, Sr+2, Mg+2, Ca+2 or anilinium, for example. These compounds also include commercial perfluorinated sulfonic acid polymer materials, Nafion® and Flemion®, for example. The conductivity enhancer may include a sulfonate or carboxylate copolymer, with polyvinyl alcohol, for example, or a polymer having a 2-acrylamido-2-methyl propanyl as a functional group. A combination of one or more conductivity enhancing materials can be used.
Oxidation-resistant material that is coextruded to form a separator of the present invention can comprise from about 5 wt % to about 95 wt % (e.g., from about 20 wt % to about 60 wt %, or from about 30 wt % to about 50 wt %) of zirconium oxide and/or conductivity enhancer.
Oxidation-resistant materials can also comprise additives such as surfactants that improve dispersion of the zirconium oxide powder by preventing agglomeration of small particles. Any suitable surfactant may be used, including one or more anionic, cationic, non-ionic, ampholytic, amphoteric and zwitterionic surfactants, and mixtures thereof. In one embodiment, the separator comprises an anionic surfactant. For example, the separator comprises an anionic surfactant, and the anionic surfactant comprises a salt of sulfate, a salt of sulfonate, a salt of carboxylate, or a salt of sarcosinate. One useful surfactant comprises p-(1,1,3,3-tetramethylbutyl)-phenyl ether, which is commercially available under the trade name Triton X-100 from Rohm and Haas.
In several embodiments, the oxidation-resistant material comprises from about 0.01 wt % to about 1 wt % of surfactant.
2. Polyvinyl Polymer Material
In several embodiments of the present invention the dendrite-resistant stratum of the separator comprises a polyvinyl polymer material that is coextruded with the oxidation-resistant material. In several embodiments, the PVA material comprises a cross-linked polyvinyl alcohol polymer and a cross-linking agent.
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.
PVA material useful in 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 metaboric acid or its salts); or salts of copper, zinc, aluminum or titanium. For example, the cross-linking agent comprises boric acid.
In another embodiment, the PVA material optionally comprises zirconium oxide powder. In several embodiments, the PVA material 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 %).
In many embodiments, the dendrite-resistant strata of the separator of the present invention comprises 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 4 mΩ/cm2).
The PVA material that forms the dendrite-resistant stratum of the separator of the present invention can optionally comprise any suitable additives such as a conductivity enhancer, a surfactant, a plasticizer, or the like.
In some embodiments, the PVA material further comprises a conductivity enhancer. For example, the PVA material 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.
In other embodiments, the PVA material 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 PVA material comprises from about 0.01 wt % to about 1 wt % of surfactant.
In several embodiments, the dendrite-resistant stratum further comprises a plasticizer. For example, the dendrite-resistant stratum 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.
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.
3. Optional Substrate
In alternative embodiments, the separator of the present battery further comprises a substrate on which polymer materials (e.g., oxidation-resistant material and/or dendrite-reistant material) are coextruded. In some examples, the separate polymer materials are coextruded onto a single surface of the substrate. In other examples, the polymer materials are coextruded onto opposing surfaces of the substrate such that at least two strata forming the separator are separated by the substrate.
Substrates useful in these novel separators can comprise any suitable material that is substantially inert in an alkaline electrochemical cell. In several embodiments, the substrate is a woven or non-woven sheet. In other embodiments, the substrate is a non-woven sheet. Exemplary substrates that are commercially available include Solupor and Scimat, which are available from DSM Solutech Co. and SciMat, Ltd., respectively.
Electrochemical cells of the present invention can optionally comprise a separator layer comprising a PEO layer and a PVA layer. One such separator can be formed from solutions having substantially equivalent compositions used to prepare a bi-functional separator having individual separator layers. Polyvinyl alcohol layers were deposited from a 10 wt % PVA solution. The PEO solution comprised 87 to 97 wt % water, 2 to 6 wt % polyethylene oxide, 2 to 6 wt % yttria-stabilized zirconium oxide (filler), 0.2 to 1.5 wt % potassium titanate (conductivity enhancer), and 0.08 to 0.2 wt % Triton X-100 (surfactant). Conventional dispersing techniques were used to provide a uniform dispersion of the filler. The bi-functional separator was prepared by co-extrusion of the PVA and PEO solutions from a two-layer slot-die unit, and drying at 280° C. The individual separator layers were prepared using conventional film casting techniques.
In other embodiments, a separator is formed by coating a Solupor film with two layers of PEO material, wherein each layer of PEO material coats an opposing side of the Solupor film.
In another embodiment, the separator comprises a unitary structure comprising two layers of a PEO material that were coextruded to form a free standing separator.
C. Electrolytes
Electrochemical cells of the present invention comprise an alkaline electrolyte. In several embodiments, the electrolyte comprises NaOH or KOH. For instance, the electrolyte can comprise aqueous NaOH or KOH, or NaOH or KOH mixtures with liquids substantially free of water, such as liquid polymers. Exemplary alkaline polymer electrolytes include, without limitation, 90 wt % PEG-200 and 10 wt % KOH, 50 wt % PEG-200 and 50 wt % KOH; PEG-dimethyl ether that is saturated with KOH; PEG-dimethyl ether and 33 wt % KOH; PEG-dimethyl ether and 11 wt % KOH; and PEG-dimethyl ether (mean molecular weight of 500 amu) and 33 wt % KOH, that is further diluted to 11 wt % KOH with PEG-dimethyl ether having a mean molecular weight of 200 amu.
Exemplary electrolytes include aqueous metal-hydroxides such as NaOH and/or KOH. Other exemplary electrolytes include mixtures of a metal hydroxide and a polymer that is liquid at a range of operating and/or storage temperatures for the electrochemical cell into which it employed.
In other embodiments, the electrolyte is an aqueous mixture of NaOH or KOH having a concentration of at least 4 M (e.g., at least 8 M).
Polymers useful for formulating an electrolyte of the present invention are also at least substantially miscible with an alkaline agent. In one embodiment, the polymer is at least substantially miscible with the alkaline agent over a range of temperatures that at least includes the operating and storage temperatures of the electrochemical device in which the mixture is used. For example, the polymer is at least substantially miscible, e.g., substantially miscible with the alkaline agent at a temperature of at least −40° C. In other examples, the polymer is liquid at a temperature of at least −30° C. (e.g., at least −20° C., at least −10° C., or from about −40° C. to about 70° C.). In another embodiment, the polymer is at least substantially miscible with the alkaline agent at a temperature from about −20° C. to about 60° C. For example, the polymer is at least substantially miscible with the alkaline agent at a temperature of from about −10° C. to about 60° C.
In several embodiments, the polymer can combine with the alkaline agent at a temperature in the range of temperatures of the operation of the electrochemical device in which is it stored to form a solution.
In one embodiment, the electrolyte comprises a polymer of formula (I):
wherein each of R1, R2, R3, and R4 is independently (V1-Q1-V2-Q2-V3-Q3)n, each of V1, V2, and V3, is independently a bond or —O—, each of Q1, Q2, and Q3, is independently a bond, hydrogen, or a C1-4 linear unsubstituted alkyl, n is 1-5, and p is a positive integer of sufficient value such that the polymer of formula (I) has a total molecular weight of less than 10,000 amu (e.g., less than about 5000 amu, less than about 3000 amu, from about 50 amu to about 2000 amu, or from about 100 amu to about 1000 amu) and an alkaline agent.
In several embodiments, the polymer is straight or branched. For example, the polymer is straight. In other embodiments, R1 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, each of V1, Q1, V2, Q2, and V3 is a bond, and Q3 is hydrogen. In some embodiments, R4 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, each of V1, Q1, V2, Q2, and V3, is a bond, and Q3 is hydrogen. In other embodiments, both of R1 and R4 are (V1-Q1-V2-Q2-V3-Q3)n, each n is 1, each of V1, Q1, V2, Q2, and V3 is a bond, and each Q3 is hydrogen.
However, in other embodiments, R1 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, each of V1, Q1, V2, Q2, and V3 is a bond, and Q3 is —CH3, —CH2CH3, —CH2CH2CH3, or H. For example, R1 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, each of V1, Q1, V2, Q2, and V3 is a bond, and Q3 is —CH3 or H.
In another example, R1 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, one of Q1 or Q2 is —CH2—, —CH2CH2—, or —CH2CH2CH2—; V1 and V2 are each a bond; V3 is —O—, and Q3 is H.
In several other examples R4 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, each of V1, Q1, V2, Q2, is a bond, and V3 is —O— or a bond, and Q3 is hydrogen, —CH3, —CH2CH3, or —CH2CH2CH3. For example, R4 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, each of V1, Q1, V2, Q2, and V3 is a bond, and Q3 is —H, —CH3, —CH2CH3, or —CH2CH2CH3.
In another embodiment, R1 is (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, each of V1, Q1, V2, Q2, and V3 is a bond, and Q3 is —CH3, and R4 is (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, each of V1, Q1, V2, Q2, is a bond, and V3 is —O—, and Q3 is —H.
In some embodiments, R2 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, each of V1, Q1, V2, Q2, and V3 is a bond, and Q3 is —CH3, —CH2CH3, —CH2CH2CH3, or H. In other embodiments, R2 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, one of V1, Q1, V2, Q2, and V3 is —O—, and Q3 is —H.
In some embodiments, R3 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, each of V1, Q1, V2, Q2, and V3 is a bond, and Q3 is —CH3, —CH2CH3, —CH2CH2CH3, or H. In other embodiments, R3 is independently (V1-Q1-V2-Q2-V3-Q3)n, wherein n is 1, one of V1, Q1, V2, Q2, and V3 is —O—, and Q3 is —H.
In some embodiments, one of R1 or R4 is an alkyl group and the other is hydrogen. In other examples one of R1 and R4 is attached to the backbone of another polymer and the other is hydrogen
In some embodiments, the polymer comprises a polyethylene oxide. In other examples, the polymer comprises a polyethylene oxide selected from polyethylene glycol, polypropylene glycol, polybutylene glycol, alkyl-polyethylene glycol, alkyl-polypropylene glycol, alkyl-polybutylene glycol, and any combination thereof.
In another embodiment, the polymer is a polyethylene oxide having a mean molecular weight of less than 10,000 amu (e.g., less than 5000 amu, or from about 100 amu to about 1000 amu). In other embodiments, the polymer comprises polyethylene glycol.
Alkaline agents useful in the electrolyte of the present invention are capable of producing hydroxyl ions when mixed with an aqueous or polar solvent such as water and/or a liquid polymer.
In some embodiments, the alkaline agent comprises LiOH, NaOH, KOH, CsOH, RbOH, or combinations thereof. For example, the alkaline agent comprises LiOH, NaOH, KOH, or combinations thereof. In another example, the alkaline agent comprises KOH.
In several exemplary embodiments, the electrolyte of the present invention comprises a liquid polymer of formula (I) and an alkaline agent comprising LiOH, NaOH, KOH, CsOH, RbOH, or combinations thereof. In other exemplary embodiments, the electrolyte comprises a liquid polymer comprising a polyethylene oxide; and an alkaline agent comprising LiOH, NaOH, KOH, CsOH, RbOH, or combinations thereof. For example, the electrolyte comprises a polymer comprising a polyethylene oxide and an alkaline agent comprising KOH.
In several exemplary embodiments, the electrolyte of the present invention comprises more than about 1 wt % of alkaline agent (e.g., more than about 5 wt % of alkaline agent, or from about 5 wt % to about 76 wt % of alkaline agent). In one example, the electrolyte comprises a liquid polymer comprising a polyethylene oxide and 3 wt % or more (e.g., 4 wt % or more, from about 4 wt % to about 33 wt %, or from about 5 wt % to about 15 wt %) of an alkaline agent. For instance, the electrolyte comprises polyethylene oxide and 5 wt % or more of KOH. In another example, the electrolyte consists essentially of a polyethylene oxide having a molecular weight or mean molecular weight from about 100 amu to about 1000 amu and 5 wt % or more of KOH.
Electrolytes of the present invention can be substantially free of water. In several embodiments, the electrolyte comprises water in an amount of about 60 wt % or less (e.g., about 50 wt % or less, about 40 wt % or less, about 30 wt % or less, about 25 wt % or less, about 20 wt % or less, or about 10 wt % or less).
Exemplary alkaline polymer electrolytes include, without limitation, 90 wt % PEG-200 and 10 wt % KOH, 50 wt % PEG-200 and 50 wt % KOH; PEG-dimethyl ether that is saturated with KOH; PEG-dimethyl ether and 33 wt % KOH; PEG-dimethyl ether and 11 wt % KOH; and PEG-dimethyl ether (mean molecular weight of 500 amu) and 33 wt % KOH, that is further diluted to 11 wt % KOH with PEG-dimethyl ether having a mean molecular weight of 200 amu.
Another aspect of the present invention provides methods of manufacturing electrochemical cells comprising providing a cathode comprising AgO and a first binder material; providing an anode comprising Zn or ZnO and a second binder material; and providing an alkaline electrolyte, wherein the alkaline electrolyte comprises NaOH or KOH in a concentration of at least 8 M, the cathode comprises at least about 88 wt % of AgO, the anode comprises at least 88 wt % of Zn or ZnO, and either the first binder material, the second binder material, or both comprises PVDF or a PVDF copolymer.
In several examples, the active material of the cathode comprises AgO. In other examples, the AgO is doped with up to 10 wt % of Pb. In several examples, the AgO is doped with up to 5 wt % of Pb, or the AgO is doped with up to 5 wt % of Pb and is coated with up to 5 wt % Pb.
In several embodiments, the anode comprises up to 10 wt % of a binder material. For instance, the anode comprises up to 6 wt % of a binder material. In several examples, the anode comprises binder material comprises up to 10 wt % of a binder material comprising PVDF or PVDF copolymer. For instance, the binder material comprises a PVDF copolymer such as PVDF-co-HFP copolymer. In other examples, the PVDF-co-HFP copolymer has a mean molecular weight of less than about 600,000 amu (e.g., less than about 500,000 amu, or about 400,000 amu).
In the examples below, several exemplary electrodes (anodes and/or cathodes) of the present invention are described. Several of these exemplary electrodes are evaluated by incorporating them into test electrochemical cells of the present invention, which are described and evaluated below. It is noted that these test cells are intended to be non-limiting examples of electrochemical cells of the present invention.
Materials:
Processing Procedure:
This procedure was generally followed to produce anodes having formulations according to Table 1, below:
Each of the amounts presented in Table 1 are in units of wt %.
The charging profile as well as capacity evaluations for the abovementioned anodes are provided in
Materials:
Test Cathode Active Material
The test cathode active material used in test cells described below was PbAc coated AgO powder (PbAc: AgO=1.5:100, D.F. Goldsmith Chemical and Metal Corp.).
This cell was produced using the following components:
Cathode: Test Cathode Active Material with 1 wt % PTFE binder
Anode: Zn with 5 wt % PVDF binder
Electrolyte: (40 wt % conc.) aq. KOH
The electrodes were separately wrapped in a PEO film. The PEO film was formulated as follows:
Each of these ingredients were mixed and a sufficient amount of the resulting mixture was cast onto a 25 micron porous polyolefin substrate (i.e. Solupor, DSM Solutech) to give a PEO film having a dry thickness of about 40 microns.
A separator was situated between the electrodes. The separator included a free standing structure including two PVA-based layers that were each formulated from:
These ingredients were mixed and cast in a glass tray so that the final dry thickness is approximately 40 microns.
The separator was soaked in the KOH solution for 12 hours before being assembled into the cell. Charge current was C/10 for the first 2 charge cycles and reached 2.03 V. After the first 2 charge cycles, a constant voltage of 1.98V is maintained until the cell reached its rated capacity. Discharge density was maintained at C/10 for the first 2 charge cycles, and cutoff voltage was 1.1 V. For subsequent charge cycles, charge current was increased to C/7.5 until voltage reached 2.03 V, then a constant voltage at 1.98V is kept for charging until the cell reached to the rated capacity, and discharge density is kept at C/5, and the cutoff voltage is 1.1V. Note that C is the rated capacity of the cell based on the amounts of electrode and cathode materials.
The cell profiled in
Furthermore, the over potential of this cell is very low, which indicates that the impedance of this cell is also very low. The upper voltage during charge is ˜1.9V at C/10 current rate, which is much lower than the standard value of ˜1.94V. This behavior may relate to the excellent binding strength of the PVDF that would reduce the interface impedance between the active material and the current collector resulting a low overall cell impedance.
This cell was produced using the following materials:
Cathode: Test Cathode Active Material with 1 wt % PTFE binder
Anode: Zn with 3 wt % PVDF binder
Electrolyte: (32 wt % conc.) aq. KOH
The electrodes were separately wrapped in a PEO film formulated as described in Example 3. A separator was situated between the electrodes, which was formulated as described in Example 3. The separator was soaked in the KOH solution for 12 hours before being assembled into the cell. Charge current was C/10 for the first 2 charge cycles and reached 2.03 V. After the first 2 charge cycles, a constant voltage of 1.98V is maintained until the cell reached its rated capacity. Discharge density was maintained at C/10 for the first 2 charge cycles, and cutoff voltage was 1.1 V. For subsequent charge cycles, charge current was increased to C/7.5 until voltage reached 2.03 V, then a constant voltage at 1.98V is kept for charging until the cell reached to the rated capacity, and discharge density is kept at C/5, and the cutoff voltage is 1.1V.
Referring to
These cells were produced using the following materials:
Cathode: Test Cathode Active Material 1 wt % PTFE binder
Anode: Zn with 2 wt % PVDF binder
Electrolyte: (32 wt % conc.) aq. KOH
In cell nos. 3 and 4, profiled in
In cell no. 5, profiled in
The cell was charged and discharged as described in Examples 3 and 4, above.
The charge profiles illustrated in
These cells were produced using the following materials:
Cathode: Test Cathode Active Material with 5 wt % PVDF binder
Anode: Zn with 2 wt % PVDF-co-HFP binder
Electrolyte: (32 wt % conc.) aq. KOH
In cell 6, profiled in
In cells 7 and 8, profiled in
The cells were charged and discharged as described in Example 3 above.
The charge profiles illustrated in
It is noted that cells with different rated capacities (1.0 Ah, 5.6 Ah, 6.0 Ah), the rated charge capacity was obtained in one single CC step indicating excellent initial cell performance.
This cell was produced using the following materials:
Cathode: Test Cathode Active Material with 3 wt % PVDF binder
Anode: Zn with 2 wt % PVDF-co-HFP binder
Electrolyte: (32 wt % conc.) aq. KOH
In cell 9, the electrodes were separately wrapped in Solupor. The separator, as described in Example 3, was soaked in the KOH solution for 12 hours before being assembled into the cell. This cell was designed to have a rated capacity of about 5.6 Ah. The cells were charged and discharged as described in Examples 3 and 4 above.
Cell 10 was produced using the following materials:
Cathode: Test Cathode Active Material with 5% PVDF-co-HFP;
Anode: Zn with 2% PVDF-co-HFP
Electrolyte: (32 wt % conc.) aq. KOH
In cell 10, the electrodes were separately wrapped in Solupor. The separator, as used in cell no. 6 of Example 5, was soaked in the KOH solution for 12 hours before being assembled into the cell. The cell was charged and discharged as described in Example 3. Cell 10's charge profile is illustrated in
Cell 11 was produced using the following materials:
Cathode: Test Cathode Active Material with 3% PVDF-co-HFP;
Anode: Zn-10 (90.56%), ZnO (6.97%), Bi2O3 (0.47%) with 2% PVDF-co-HFP;
Electrolyte: (32 wt % conc.) aq. KOH
In cell 11, the electrodes were separately wrapped in Solupor. The separator, as described in Example 3, was soaked in the KOH solution for 12 hours before being assembled into the cell. The cell was charged and discharged as described in Example 3. Cell 11's charge profile is illustrated in
Cell 12 was produced using the following materials:
Cathode: Test Cathode Active Material with 2% PVDF-co-HFP
Anode: Zn-10 (90.56%), ZnO (6.97%), Bi2O3 (0.47%) with 2% PVDF-co-HFP
Electrolyte: (32 wt % conc.) aq. KOH
In cell 12, the electrodes were separately wrapped in Solupor. The separator, as described in Example 3, was soaked in the KOH solution for 12 hours before being assembled into the cell. The cell was charged and discharged as described in Example 3. Cell 12's charge profile is illustrated in
Cell 13 was produced using the following materials:
Cathode: Test Cathode Active Material with 1% PVDF-co-HFP
Anode: Zn-10 (90.56%), ZnO (6.97%), Bi2O3 (0.47%) with 2% PVDF-co-HFP
Electrolyte: (32 wt % conc.) aq. KOH
In cell 13, the electrodes were separately wrapped in Solupor. The separator included 4 layers ordered by thickness as Solupor-PVA-PVA-Solupor. To form this separator, PVA film was cast on a Solupor substrate as described in Examples 3 and 4. The resulting PVA film was layered onto another PVA film having a Solupor substrate to form the present separator. This separator was soaked in the KOH solution for 12 hours before being assembled into the cell. The cell was charged and discharged as described in Example 3. Cell 13's charge profile is illustrated in
Cell 14 was produced using the following materials:
Cathode: Test Cathode Active Material with 1 wt % PTFE binder
Anode: Zn with 2 wt % PVDF-co-HFP binder
Electrolyte: (32 wt % conc.) aq. KOH
In cell 14, the electrodes were separately wrapped in Solupor. The separator, as described in Example 3, was soaked in the KOH solution for 12 hours before being assembled into the cell. The cell was charged and discharged as described in Example 3. Cell 14's charge profile is illustrated in
Cell 15 was produced to have a rated capacity of 1.9 Ah using the following materials:
Cathode material: Test Cathode Active Material with 1% PTFE as binder
Anode material: Zn and 2 wt % PVDF as binder
Electrolyte: (32 wt % conc.) aq. KOH
In cell 15, the cathode was wrapped in Scimat film and the anode was wrapped in Solupor. The separator was formed to include 3 layers including 1 PEO-layer and 2 PVA layers. The PVA layers and the PEO layers were produced as described in Example 3. By thickness, the order of these layers was PEO-PVA-PVA. This separator was soaked in the KOH solution for 12 hours before being assembled into the cell. The cells was charged and discharged as described in Example 3. Cell 15's charge profile is illustrated in
All publications and patents referred to in this disclosure are incorporated herein by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Should the meaning of the terms in any of the patents or publications incorporated by reference conflict with the meaning of the terms used in this disclosure, the meaning of the terms in this disclosure are intended to be controlling. Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.
This PCT patent application claims priority to U.S. Provisional Patent Application Ser. No. 61/039,963, which was filed on Mar. 27, 2008 and is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61039963 | Mar 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12934283 | Jan 2011 | US |
| Child | 15097739 | US |
