HK1071231B - Flexible thin printed battery - Google Patents

Description

FIELD OF THE INVENTION

This invention relates to a flexible thin battery. More specifically, this invention relates to a flexible thin printed battery wherein one or more of the electrodes are printed onto a flexible substrate using a printable ink, and to devices powered by such batteries.

BACKGROUND OF THE INVENTION

Flexible planar thin batteries utilizing lithium-based chemistries are known wherein the electrodes are formulated by the deposition of an active material film onto a substrate using various deposition techniques such as pulsed laser deposition, spin coating and sputtering. These techniques tend to require relatively costly and complex equipment and do not lend themselves to a high throughput inexpensive manufacturing process. Further, many devices requiring a power supply, such as novelty packaging and greeting cards augmented with audio and/or visual outputs, are manufactured on high speed web-based printing lines. Lithium-based technologies are not an attractive power source for such low cost per unit applications. The ability to produce both the device and the power supply in a single process presents opportunities for cost savings. There is therefore a need to develop an inexpensive electrochemical power supply that can be produced in a web-based process by stenciling, screen printing or other thick film application processes. As used herein, "print" and "printing" and "printable" refer to any such thick film application process whereby the layer produced is between 10 and 250 µm thick and includes both stenciling and screen printing processes.

US-A-5,652,042 discloses flexible zinc/carbon batteries with printed electrodes and gelled electrolyte.

It is therefore an object of the invention to provide a printable zinc ink that can be printed directly onto a nonconductive substrate without the need for a distinct anode current collector.

It is a further object of the invention to provide a printable zinc ink that can be printed directly onto a flexible nonconductive polymer substrate without the need for a distinct anode current collector.

It is a further object of the invention to provide an electrochemical cell with a printed anode, a printed cathode current collector, a printed cathode and a printed separator/electrolyte.

It is a further object of the invention to provide an electrochemical cell with a printed zinc anode, a printed manganese dioxide cathode and a printed metallic cathode current collector in an electrolyte comprising zinc chloride.

It is a further object of the invention to provide an electrochemical cell with a printed zinc anode, a printed manganese dioxide cathode and a printed metallic cathode current collector in an electrolyte comprising zinc acetate.

It is a further object of the invention to provide an electrochemical cell with an anode printed onto a first flexible polymer substrate, a cathode current collector printed onto a second flexible polymer substrate, a cathode printed directly onto the printed cathode current collector, wherein said first and second flexible polymer substrates are subsequently joined together to form a battery housing or package.

It is a further object of the invention to provide an electrochemical cell with an anode and a cathode current collector both printed directly onto a first piece of nonconductive substrate material in a coplanar arrangement, a printed cathode printed directly onto the cathode current collector and where a second piece of substrate material is subsequently joined with the first together to form a battery housing or package.

It is a further object of the invention to provide a carbon zinc electrochemical cell with at least one electrode printed onto a nonconductive substrate and a printable gelled polymer electrolyte that also functions as a separator.

It is a further object of the invention to provide an electrochemical cell with at least one electrode printed onto a nonconductive substrate, where said substrate forms a flexible battery housing or package and current flows between the interior of said package and the exterior of said package using discontinuous tabs in order to assure electrochemical compatibility between the external tab and the internal cell chemistry, to allow for a more robust external tab development and to reduce the potential for electrolyte leakage through the package or housing seal.

It is a further object of the invention to provide a printable gelled zinc chloride electrolyte that is particularly suitable for use in cells having printed co-planar electrodes.

It is a further object of the within invention to provide a device powered by such a printed flexible battery and having one or more printed components.

SUMMARY OF THE INVENTION

The present invention relates to a carbon zinc battery comprising a zinc anode printed directly onto a first section of a flexible non-conductive substrate material, a sealed housing, and a gelled electrolyte comprising zinc chloride, water and a gelling agent, wherein said anode and said gelled electrolyte are contained within said housing, characterized in that the zinc anode is obtainable by directly printing an aqueous anode formulation comprising zinc, zinc acetate and polyvinylpyrrolidone having a molecular weight of 2.0 to 4.0 million onto said first section of the flexible non-conductive substrate material.

Preferred embodiments are apparent from the dependent claims.

A thin, flexible printed battery is provided comprising at least one printed electrode that can be a printed anode or a printed cathode assembly and an electrolyte contained within a sealed housing or package and further comprising external contacts or tabs to provide current from the battery to the battery powered device. The electrode assembly can incorporate either a coplanar or a cofacial electrode arrangement.

The external contacts for the battery preferably have a first terminal end external to the battery package and a second terminal end positioned within the seal area of the battery package. Such an external contact will be referred to herein as discontinuous in the seal area of the housing or package. Current travels between the electrode and the external contact by way of a distinct interval current collector having a terminal end also positioned within the seal area of the battery pack. The internal current collector can be a material distinct from the electrode or can alternately comprise a portion of the electrode itself where the electrode is sufficiently conductive.

The anode comprises a zinc ink printed directly onto a nonconductive substrate and is sufficiently conductive so as to eliminate the need for a distinct anode current collector. The cathode assembly comprises a printed cathode current collector and a cathode printed directly onto the printed cathode collector. The cathode current collector in a carbon zinc cell comprises a conductive carbon ink printed directly onto the nonconductive substrate, or, alternatively, silver ink particles printed onto the substrate and then coated with a conductive carbon film. The electrolyte is chosen based on the electrode materials utilized, and can be an aqueous zinc chloride solution, or a Leclanche electrolyte.

The nonconductive substrate for the anode ink and the cathode current collector is a flexible nonconductive polymer material that can be joined together to form a battery package or housing. Various aspects of the printed battery of the within invention can be utilized in alternate cell chemistries without departing from the scope of the within invention.

DESCRIPTION OF THE DRAWINGS

• FIGURE 1A is an electrochemical cell according to the within invention.
• FIGURE 1B is a cross sectional view of FIGURE 1A as indicated.
• FIGURE 2 is an electrochemical cell with cell contacts according to an embodiment of the within invention.
• FIGURE 3 is an electrochemical cell with cell contacts according to an alternate embodiment of the within invention.
• FIGURE 4 is an electrochemical cell with cell contacts according to another alternate embodiment of the within invention.
• FIGURE 5 is an electrochemical cell with cell contacts according to another alternate embodiment of the within invention.
• FIGURE 6A is an electrochemical cell with cell contacts according to another alternate embodiment of the within invention.
• FIGURE 6B is an electrochemical cell with cell contacts according to another alternate embodiment of the within invention.
• FIGURE 6C is an electrochemical cell with cell contacts according to another alternate embodiment of the within invention. FIGURE 7 is a printed anode and zinc mesh tab according to the within invention.
• FIGURE 8 is a printed cathode current collector and tab according to the within invention.
• FIGURE 9 is a co-planar printed anode and cathode according to the within invention.
• FIGURE 10 is the printed circuitry for a sound card device powered by a printed cell according to the within invention.
• FIGURE 11 is the final circuit for a sound card device powered by a printed cell according to the within invention.
• FIGURE 12 is a plot of required cathode area and discharge efficiency as a function of the weight percent of graphite for an aqueous based cathode ink at a given cathode thickness.
• FIGURE 13 is a plot of required cathode area and discharge efficiency as a function of the weight percent of graphite for a non-aqueous based cathode ink for the same cathode thickness.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Components of the thin flexible printed battery 1 of the within invention include a printed anode 3, a printed cathode 5, a cathode current collector 7, a separator 9 and an aqueous electrolyte contained within a flexible thin battery package, housing or enclosure 11. See Fig. 1A and Fig. 1B.

THE ANODE

We have discovered that an effective, conductive, aqueous zinc ink can be formulated and printed directly onto the surface of a nonconductive substrate without the necessity of first printing an anode current collector or otherwise supplying a conductive substrate to function as a discrete anode current collector. As used herein, the term "aqueous" means that water is utilized as at least one solvent in the anode ink formulation. We have discovered that the presence of excess zinc +2 cations enables a low resistance, high conductivity printable zinc ink. In a carbon zinc cell of the within invention, that is a cell using an electrolyte comprising zinc chloride, the source of excess zinc +2 cations is an aqueous solution of zinc acetate (Zn(OOCCH₃)•2H₂O) such as is available from, for example, Fisher Scientific, product designation Z20. While not wanting to be bound by theory, it is believed that the source of excess zinc +2 cations changes the conformation and aggregation of the polymer binder used in the ink formulation so that the polymer is less likely to form an insulating layer on the zinc particles, thereby improving the zinc particle to particle contact. In such a carbon zinc embodiment of the within invention, a polyvinylpyrrolidone (PVP) binder is used, preferably with a molecular weight of 2.2 to 2.8 million. Zinc nitrates and zinc sulfates are not appropriate sources for excess zinc cations since they are strong oxidants and will oxidize the zinc. Zinc chloride and other zinc halides are not appropriate sources of excess zinc cations in such a zinc ink formulation for use in a zinc chloride electrolyte since the PVP binder will not dissolve so as to form a uniform dispersion in a zinc chloride solution. Zinc acetate is therefore used as source of excess zinc cations in the zinc ink formulation for use in a zinc chloride electrolyte since the PVP binder does form a uniform dispersion in a zinc acetate solution.

The zinc powder of the zinc anode ink is commercially available from such sources as Big River Zinc, Union Miniere or Noranda, and is preferably alloyed with from 500 to 1600 ppm lead. Alternatively, the zinc is BIA zinc (a bismuth, indium and aluminum alloy) commercially available from zinc suppliers such as Noranda. The zinc anode ink of the within invention uses very fine zinc powder, or dust. The zinc dust preferably has a Microtrac particle size d(50) value of from 10 to 60 µm and is dimensioned such that the powder will pass through a 53µm (270 mesh) sieve (USA standard). As a rule of thumb, the d(50) value should not exceed one half of the desired ink layer thickness. Thus, if a desired ink layer thickness is 50 µm, the d(50) value of the powder component should in general not exceed 25 µm.

Other components of the preferred zinc ink in the carbon zinc electrochemical cell embodiment of the within invention include an appropriate binder that is compatible with the cell chemistry, including the cell electrolyte. In the carbon zinc embodiment of the within invention, an aqueous solution of polyvinylpyrrolidone (PVP) having a molecular weight of 2.0 to 4.0 million is utilized in conjunction with a source of excess zinc +2 ions, such as zinc acetate, as disclosed above. PVP is soluble in a zinc acetate solution but not in traditional carbon zinc electrolytes such as zinc chloride and ammonium chloride. PVP is commercially available from ISP Technologies, Inc. Wayne, New Jersey, product designation PVP-K120.

One concern with a PVP binder in an aqueous solution is that the resulting ink may result in high surface tension, high polarity and fast drying, particularly in a low humidity environment, as well as the generation of hydrogen gas resulting from the zinc corrosion reaction with water. We have discovered that a co-solvent system employing an aprotic solvent miscible with water and having a higher boiling point than water will result in the reduction of the surface tension of the ink, a decrease in the polarity of the ink, a decrease in the ink drying rate and a decrease in gassing. The preferred co-solvent in the zinc acetate based zinc ink described herein is N-methyl pyrrolidone (NMP), available from Honeywell Burdick & Jackson, Muskegon, Michigan, catalog number 304-1. NMP is soluble in an aqueous solution of zinc acetate.

In addition to a binder and solvent system, the zinc ink of the within invention can further include other cell additives to produce beneficial performance attributes. For example, the relatively fine particle size of the zinc employed in the zinc ink of the within invention results in increased gassing. A surfactant known to reduce gassing in alkaline cells has both a phosphate group and polyethylene oxide and/or polypropylene oxide chains. Such a surfactant is available commercially under the Union Carbide tradename Triton QS-44. We have discovered that surfactants of this type are even more beneficial in controlling gassing in acidic electrolytes such as LeClanche or zinc chloride electrolytes. As used herein, a "LeClanche electrolyte" is an electrolyte containing both zinc chloride and ammonium chloride.

Once the zinc ink has been formulated, it can then be screen printed or stenciled directly onto a flexible polymer substrate. The zinc ink of the within invention has sufficient conductivity so as to obviate the need for a distinct anode current collector to be printed or otherwise placed into contact with the anode formed from the zinc ink of the within invention. The anode formed from the zinc ink of the within invention maintains conductivity during the discharge even though the zinc is being consumed. The anode tab that forms the negative terminal external to the cell housing is directly connected with the zinc ink of the within invention, rather than being in electrical contact with a distinct anode collector.

The preferred substrate material is a flexible nonconductive polymer material that will be used to house the battery in a flexible package. Such a material is available as a laminate from Pharma Center Shelbyville, product designation 95014, with an ethylene acrylic acid heat sealable layer that forms the interior surface of the package. One of skill in the art will appreciate that the anode ink and the cathode current collector ink can also be printed directly onto other nonconductive materials that may or may not be flexible and may or may not form the battery package or housing. The surface upon which the anode ink and the cathode collector ink are applied will be the surface that ultimately is positioned within the battery package or housing. Such surfaces, in addition to providing a heat sealable surface can alternatively supply a pressure sealing surface, an epoxy sealing surface or other means of joining material together. Laminates which are constructed of a metal foil surrounded by a protective polymer on the outer side or surface and a heat or pressure sealable polyethylene or polypropylene on the opposing inner side are commonly available. Such laminates can be obtained from, for example, Pharma Center Shelbyville, Inc. of Shelbyville, Kentucky under the product designation 95014, Dai Nippon Printing Co., Ltd. of Tokyo, Japan under the product designation D-EL40E, and also, Sumitomo Electric Industries, Ltd. of Tokyo, Japan under the product designation L-NY-Al-TRPP-L. Alternatively, a laminate with an ethylene methacrylic or polyethylene methacrylic acid heat-sealable layer is made by Ludlow Coated Products of Homer, Louisiana. The appropriate laminate and associated sealing layer will be selected on the basis of, among other factors, the type of electrolyte to be used, as is known in the art. The impervious metallic foil layer can be any variety of metals such as, for example, aluminum, nickel, copper and stainless steel. The protective polymer layer is preferably a polyester or nylon, but other polymeric materials such as a polypropylene or a polyethylene could also be employed in this layer.

In the case of screen printing, it will be important to determine the optimum mesh opening for good printability of the ink, as is known in the art. Factors to consider include the particle size of the zinc, the ink viscosity and other flow properties under shear and the required thickness of the ink necessary to achieve sufficient capacity.

THE CATHODE ASSEMBLY

The cathode assembly of a carbon zinc cell according to the within invention (current collector and electrolytic manganese dioxide, or EMD, active material) is printed onto a flexible substrate to which the cathode current collector ink will adhere with minimal or no cracking, preferably onto the sealable surface of a flexible packaging material that will be used to house the battery. Such a flexible battery housing laminate material is available for example from Pharma Center Shelbyville, product designation number 95014, as described above.

First, a current collector is deposited onto the flexible polymer using a stencil, a screen or other suitable printing apparatus. The sealing surface of the laminate material is used as the printing surface, i.e. that surface of the material that will end up being positioned within the battery package or housing. The cathode current collector ink is preferably an ink formulated from materials sufficient to transfer electrons generated in the reduction of the cathode during discharge. The appropriate cathode current collector material will be selected based on the materials utilized in the cell, to maximize current transfer while minimizing undesirable reactions with other cell component materials, as is known in the art. In a carbon zinc cell according to the within invention using an EMD cathode, the cathode current collector is preferably a carbon ink such as is available from Acheson Colloids under product designation PF407C. Still more preferably, the carbon ink utilizes a solvent system devoid of functional alcohol units to prevent unintended reduction of the manganese dioxide cathode material, and to avoid extended curing periods. Such an ink is commercially available from Acheson Colloids under product designation PM 024, and avoids extended curing periods of the ink in a vacuum environment. The printed collector is then subjected to suitable curing to assure adequate drying and solvent evaporation

Cells having screen printed cathode collectors of various thicknesses using PF407C ink were evaluated to determine the minimum collector thicknesses for a given application. The cells had stenciled EMD cathodes and screen printed zinc anodes of 112 to 125 µm (dry), achieved with multiple screen passes. The cathode collectors were dried at 50°C under a 26.7 Pa (2 Torr) vacuum for 16 hours. The cells were then discharged under the test protocols described below for 100 cycles, and the cells still had a closed circuit voltage of greater than .9 volts. The results for a co-planar electrode assembly are presented in Table I and for a co-facial electrode assembly are presented in Table II: TABLE I (co-planar electrodes)

100 cycles (1 cycle = 6 sec. at 2 mA and 60 sec. off)	12 µm
100 cycles (1 cycle = 16 sec. at 8 mA and 60 sec. off)	70 µm

TABLE II (co-facial electrodes):

100 cycles (1 cycle = 6 sec. at 2 mA and 60 sec. off)	6-8 µm
100 cycles (1 cycle =16 sec. at 8 mA and 60 sec. off)	24-30 µm

The resistance of these collectors and their resulting performance are a function of the drying conditions utilized.

As noted above, carbon inks with high boiling point alcohol solvents require undesirable drying protocols to remove the solvent. A carbon ink has been developed for use as a cathode current collector in a zinc chloride or a Leclanche electrolyte that has acceptable conductivity without a complicated drying regimen. The current collector ink wet formulation comprises 8 to 10 weight percent of a styrene-ethylene - butylene-styrene (SEBS) block copolymer such as Kraton G1650 as is commercially available from Shell, 34 to 38 weight percent graphite such as KS6 available from Timcal America, product designation Timrex LB 1099, and the remainder being toluene or trichloroethylene solvent. Conductivity can be enhanced by the addition of carbon black in low (<5 weight percent) amounts. Other block co-polymers in the Kraton line are also suitable as binders for this ink, including styrene-butadiene -styrene materials.

Cells using this cathode current collector ink were evaluated. A 0.0762 mm (003 inch) leaded zinc foil was used as the anode. The cathode collector and the cathode were both stenciled. The cathode dry formulation was 90 weight percent manganese dioxide, 2 weight percent Carbopol 940 and 8 weight percent KS6 graphite. The current collector wet ink formulation was 10 weight percent Kraton G1650, 34 weight percent graphite and 56 weight percent toluene. The dry thickness of the collector was between 100 and 125 microns. The cells were discharged for 100 cycles, where a cycle is defined as an 8 mA current for 16 second followed by a 60 second rest. The cell voltage remained above .9 volts.

A metallic current collector will be more conductive than a carbon current collector, but will react with the manganese dioxide in a zinc chloride electrolyte. We have discovered that by coating a conductive metal or metallic ink such as silver, silver ink or aluminum with a protective conductive carbon film, the benefits of a metallic current collector can be achieved without the disadvantages of reactivity in a zinc chloride or a Leclanche electrolyte. The protective carbon coating preferably consists of a mixture of graphite such as KS6 (20-25 weight percent), an SEBS block copolymer such as Kraton G1650 (15-18 weight percent) and toluene (56-62 weight percent). Alternatively, the protective conductive carbon coating formulation can utilize carbon black (5-10 weight percent) with Kraton G1650 (15-18 weight percent) and toluene (72-75 weight percent). Other block co-polymers in the Kraton line are also suitable as binders for this protective coating ink, including styrene-butadiene -styrene materials.

Cells were evaluated using anode current collectors and cathode current collectors of silver ink with a printed protective conductive carbon ink. A silver was applied to the sealing surface of the flexible laminate packaging material such as described above and was cured at 70°C for one to two hours to a thickness of around 30 to 40 µm. The protective coating ink formulation was 18 weight percent Kraton 1650, 22 weight percent KS6 and 60 weight percent toluene, and was stenciled onto the silver and cured to a thickness of about 100 to 120 µm. The entire exposed surface of the silver ink was covered. Zinc anode inks as described in Table III and electrolytic manganese dioxide cathode inks as described in Table IV were then stenciled onto these protected silver collectors. The cells were assembled with a resulting interfacial surface area of 39 millimeters X 37 millimeters using a suitable separator and a 28 weight percent ammonium chloride +12 weight percent zinc chloride electrolyte and the housing was heat sealed. TABLE III (ANODE DRY FORMULATIONS):

		BINDER (weight percent)
FORMULATION #1	99.0	1.0 methyl cellulose
FORMULATION #2	98.0	2.0 PVDF

TABLE III (ANODE DRY FORMULATIONS):

seived through a 53 µm (270 mesh) creen, 500 ppm leaded zinc

TABLE IV (CATHODE DRY FORMULATIONS):

	MnO2 (weight percent)	BINDER (weight percent)
FORMULATION #1	90	2.0 methyl cellulose	8.0
FORMULATION #2	90	2.0 Carbopol 940	8.0

TABLE IV (CATHODE DRY FORMULATIONS):

'KS6

The cells were cathode limited and had stable open circuit voltages as demonstrated in Table V below and discharged at 10 mA continuous to a cutoff voltage of .9 volts with about 35 to 40 percent cathode efficiency. TABLE V (STABILITY TESTS):

	OCV (volts) 1 day	OCV (volts) 32 days	OCV (volts) 62 days
Cell 1	1.750	1.681	1.665
Cell 2	1.755	1.674	1.650
Cell 3	1.766	1.673	1.653

Once an appropriate collector is printed onto the substrate, the cathode ink is then printed onto the printed current collector. The cathode ink formulation is a mixture of EMD, binder and conductor in an aqueous or a non-aqueous solvent. The EMD powder utilized will depend on the targeted electrode thickness, desired discharge efficiency and intended application for the cell. Non-milled EMD with a d(50) of around 40 microns is unsuitable for a printed cathode with a targeted thickness of 50 µm or less. EMD with a d(50) measurement of around 1 µm can be obtained by jet-milling the EMD. Such a process is available from, for example, Sturtevant, Inc. in Hanover Massachusetts.

However the relatively poor rate capability of jet-milled EMD can require an excessively large electrode area or thickness or both for a given application. We have discovered that for a given cathode ink formulation and thickness and a desired discharge current there is a relationship between the amount of graphite used in the ink formulation, the discharge efficiency of the electrode and the required electrode area. Thus, for example, if we were to target a 50 µm thick electrode using an aqueous cathode ink comprising jet-milled EMD and a PVP binder in a cell with a targeted discharge current of 8 mA, a graphite content of between 12 weight percent and 49 weight percent (dry formula) results in a printed cathode with an optimum area and discharge efficiency. Where concerns of electrode area dominate discharge efficiency concerns, a graphite content of from about 19 weight percent to 35 weight percent (dry formula) should be utilized. See Fig. 12 (data predicted by model developed from actual cells). The preferred conductive graphite is KS6 synthetic graphite as is available from Timcal America, product designation Timrex LB 1099. For the same cell thickness using a nonaqueous cathode ink formulation with a PVDF binder and the same targeted discharge current, a graphite content of from about 12 weight percent to 70 weight percent (dry formula) is preferred. Where concerns of electrode area dominate discharge efficiency concerns, a graphite content of from about 28 weight percent to about 49 weight percent should be utilized. See Fig. 13 (data predicted by model developed from actual cells).

A preferred nonaqueous wet cathode ink formulation is 1.0 to 2.0 weight percent PVDF, 4.0 to 45.0 weight percent graphite and 17.0 to 66.0 weight percent EMD and 28.0 to 37.0 weight percent NMP solvent. An even more preferred formulation is 1.0 to 2.0 weight percent PVDF, 12.0 to 31.0 weight percent graphite and 31.0 to 51.0 weight percent EMD and 34.0 to 35.0 weight percent NMP solvent. A preferred aqueous wet cathode ink formulation is 1.0 to 4.0 weight percent PVP, 6.0 to 25.0 weight percent graphite and 25.0 to 43.0 weight percent EMD, balanced with water. Even more preferred is 1.5 to 2.0 weight percent PVP, 11.0-16.0 weight percent graphite and 33.0 to 38.0 weight percent EMD, balanced with water.

The cathode ink is prepared by pre-dissolving the binder in water, grinding the solid components together (EMD and conductive additive) and adding the solids to the binder solution. The mixture is stirred and then is printed onto the existing current collector. The cathode is then cured at a slightly elevated temperature for a time sufficient to dry the ink and drive off the solvents.

SEPARATOR AND ELECTROLYTE

For co-facial electrode assemblies, a separator is necessary to electrically isolate the electrodes while still enabling the flow of ions, as is known in the art. The separator can be a paper separator, a gelled separator or a printed separator. In a carbon zinc embodiment of the within invention using an electrode assembly with a co-facial arrangement, a coated kraft paper separator can be utilized as a separator. As an example, a suitable separator base paper is available commercially from Munksjo #300542 (57 g/m²) and is preferably coated to a level of 20 grams per square meter (gsm) (dry) with a mixture having a dry coating composition of starch (preferably 83.6 weight percent, commercially available from, for example, Roquette LAB2469), gel (preferably 7.9 weight percent, commercially available from, for example, Courtaulds B1209), PVP (preferably 2.1 weight percent), and surfactant additive (preferably 1.4 weight percent ethyl tallow amine known commercially as Crodamet) and water (5.0 weight percent). Appropriate coated kraft paper separators are described, for example, in EP 0832502 B1 , WO 96/38869 , WO 98/07204 , US Pat. No. 6221532 and WO 99/35700 . Other suitable separator materials can be used in cells according to the within invention without departing from the scope of the within invention.

For a carbon zinc cell embodiment according to the within invention, the electrolyte is preferably an aqueous solution of zinc chloride, as is known in the art. Additives to prevent or reduce gassing and to encourage other performance attributes can be used, such as cetyltrimethylammonium bromide (available commercially as Cetrimide) and lead chloride. Cetyltrimethylammonium bromide is available from Aldrich, product number 855820. Cetrimide can also be introduced into the cell in a variety of ways, such as in the electrode ink formulations or as a component of a separate coating printed or otherwise applied to an electrode or separator paper surface.

We have further discovered an alternative gelled electrolyte for use in a carbon zinc printed cell of the within invention that is particularly beneficial in reducing the internal resistance of cells having coplanar electrodes. We have discovered that the addition of nonionic or anionic derivatives with natural guar gum to an aqueous zinc chloride solution produces such a gelled electrolyte. The preferred additive is Galactasol A4 available commercially from Aqualon Company in Wilmington Delaware.

Cells were made using 0.0762 mm (003 inch) thick X 6 millimeter wide zinc foil (500 ppm lead) anodes and printed cathodes in a co-planar construction to compare their performance in a standard zinc chloride electrolyte versus the gelled Galactasol electrolyte. The cathode collector in all four cells was the Acheson PF407C carbon ink. The cathode dry formulation by weight was 2 percent PVP, 28 percent KS6 and 70 percent jet-milled Chemetals EMD. The gelled electrolyte cells used a mixture of 6 weight percent Galactasol in a 28 weight percent zinc chloride solution. The gelled electrolyte was made by gradually adding a 6 weight percent Galactasol solution to a 28 weight percent zinc chloride solution contained in a beaker. The solution was stirred with a magnet bar and then the gelled electrolyte was left at room temperature overnight to let the trapped air escape. The control cells used a coated kraft separator paper soaked in a 28 weight percent zinc chloride solution. The cells were subjected to a cycled discharge regimen where a cycle was defined as a discharge at 2 mA for six seconds and 0 mA for 60 seconds, and were discharged until they reached a cutoff voltage of .9 volts. Table VI further describes the cell inputs and performance data. TABLE VI:

Cell	Cathode thickness (µm)	Cathode weight (gm)	Cathode input (mAh)	Electrolyte	Electrolyte weight (gm)	Cycles	Utilisation
1	78	.147	28.71	Gelled	.65	6260	73%
2	116	.175	34.18	Gelled	.65	7290	71%
3 control	115	.135	26.37	Liquid	.60	3680	47%
4 control	113	.178	34.76	Liquid	.60	5010	48%

The gelled electrolyte cells performed significantly better during this test.

CELL CONTACTS

Cell contacts present a design challenge for a number of reasons. It is desirable to be able to select the external contact materials without regard to the potential for unfavorable reactions between the external contacts and the materials utilized within the cell (such as electrolyte). Constraints imposed by the internal cell environment can interfere with the development of external tabs with the desired strength and current carrying properties. Further, leakage of electrolyte can be a problem with cells using aqueous electrolytes and metal structures for carrying current from the electrode to the external cell terminal. This leakage is a result at least in part of the propensity of electrolyte to travel, or "creep" along the metal surface of a current carrying structure that extends from the interior of the cell housing or package and through the sealed cell perimeter out to the external cell environment. We have discovered that an advantageous cell design employs a "discontinuous" current carrying system. As used herein, a "discontinuous" current carrying system exists where two distinct structures are employed for the purpose of carrying current between an electrode and the external cell terminal. One structure, referred to herein as a current collector, extends from the interior of the cell into the seal area and has a terminal end within the seal area or at the seal outer perimeter. A second external structure, referred to herein as the external terminal, extends from the external environment into the seal area, or contacts a conductive adhesive or epoxy that is positioned within the seal area. A conductive bridge, formed of direct contact between the two structures, or a conductive adhesive or epoxy that extends between the two structures, provides a pathway for current flow within the seal perimeter area. In this way, the cells of the within invention do not have a single metallic pathway for electrolyte creepage. The "seal area" as used herein includes the area of the cell packaging or housing material that is joined together using a pressure seal or heat seal or epoxy or other means of joining two sections together.

In one embodiment depicted in Fig. 2, the current collector 13 for an electrode extends into the seal area 15, while a second metallic external terminal 17 extends into the sealing area and contacts the current collector 13 within the sealing area. In this embodiment, electrical conductivity for current flow is provided by the physical contact between the internal current collector and the external terminal. In a second embodiment depicted in Fig. 3, the current collector 13 and the external terminal 17 are not in physical contact. Electrical conductivity is provided by an electrically conductive adhesive or epoxy 19 located at least in part within the seal area 15 and bridging the two structures. In a third embodiment depicted in Fig. 4, the conductive adhesive or epoxy 19 extends to the area external to the cell and forms the external cell contact. In Fig. 5, the adhesive or epoxy 19 extends to the area external to the cell and contacts an external metallic tab or terminal 21. Figures 6A-6C illustrate further alternate embodiments of the external cell contact or terminal 17. In these embodiments, at least one of the external contacts has an increased surface area external to the cell packaging or housing. We have found that increasing the external contact surface area improves the discharge efficiency of the cell.

The anode and cathode external terminals or contacts are preferably printed onto a flexible nonconductive polymer substrate with a silver based conductive polymer ink such as Electrodag 479SS available from Acheson Colloids, Port Huron, Michigan. The cathode collector is then printed onto the external cathode contact so that the collector and the external contact overlap in at least the seal area of the cell package or container. In the same manner, the anode ink is printed onto the external anode contact so that the anode and the external contact overlap in at least the seal area of the cell package or container.

At least a portion of the seal area includes an adhesive or epoxy for joining together two surfaces of packaging material to form the cell package or housing. The adhesive can be activated by heat or pressure or other means as is known in the art. Alternatively, the seal area can compromise an epoxy that forms a seal by a polymerization reaction initiated chemically, thermally or using photoinitiation or encapsulation as is known in the art. Use of a two part conductive epoxy can accommodate delays in manufacturing by avoiding epoxy curing during the delay.

CELL ASSEMBLY AND PACKAGING

Initially, the external tabs for the electrodes are printed onto a flexible nonconductive polymer substrate that preferably forms the battery package. The zinc ink is formulated and applied directly to the substrate surface. The shape of the electrode is selected according to the cell design for the given application, as is known in the art. In a carbon zinc embodiment of the within invention, the zinc ink is printed onto the substrate using a silk screen, stencil or other suitable printing apparatus with a pattern that allows the ink to form an area that will interface with a cathode, and an area that will overlap a portion of the tab in the area that will be sealed to form the package. A suitable drying and/or curing protocol is engaged, depending on the ink formulation.

The ink for the cathode current collector is formulated and applied to a second section of flexible polymer substrate material, by stencil, screen or other suitable printing apparatus, followed by a suitable drying protocol. The second section of flexible polymer substrate material upon which the cathode current collector is printed may either be a section that allows for a co-planar arrangement between anode and cathode or a section that allows for a co-facial arrangement of anode and cathode. As used herein, "co-facial" electrodes share an interfacial area between a major anode surface and a major cathode surface. Co-facial electrodes are to be distinguished from "co-planar" electrodes, where a major anode assembly (anode + collector, if any) surface and a major cathode assembly (cathode + collector, if any) surface lie approximately in the same plane and are printed directly or indirectly onto a single piece of substrate material. The cathode current collector shape is selected so as to allow for sufficient contact with the cathode ink, and preferably also forms an area that will overlap a portion of the cathode tab in the seal area. The current collector ink is dried and then the cathode ink is printed onto the current collector and dried.

A separator is disposed between the anode and cathode in the case of electrodes in a co-facial arrangement. Electrolyte is introduced into the cell by way of separator paper soak up of free electrolyte or by way of a gel formulation that incorporates electrolyte or by way of electrode soak up of free electrolyte, or a combination thereof as is known in the art. The cell package or housing is then sealed together. In a preferred embodiment, the external contacts for the cell are discontinuous, as defined herein.

EXAMPLE 1: (all percents are by weight unless otherwise indicated)

Cells were made according to this example. The anode ink wet formulation was 9.6 percent zinc acetate dihydrate, 31.7 percent water, 1.3 percent PVP (molecular weight of 2.2 to 2.8 million) and 57.4 percent zinc dust. The zinc ink was made by first combining the zinc acetate dihydrate obtained from Aldrich Chemical Company with water to form an aqueous solution. PVP was added to the aqueous solution to make a viscous salt-polymer solution. Zinc dust added and the mixture was stirred until homogeneous. The zinc dust was leaded with .16 percent lead. The zinc dust had a Microtrac average volumetric particle size, or d(50) value of about 10 µm. The mixture was allowed to stand to achieve the appropriate thickness, about 90 to 120 minutes. An anode was then screen printed by hand. The anode substrate was the inner heat sealable surface of a flexible polymer and metal laminate packaging material available from Pharma Center Shelbyville, product number 95014. The laminate comprises an inner heat sealable ethylene acrylic acid layer, a layer of aluminum, and an outer protective polymer layer. Four to five wet passes over the screen resulted in an anode 39 millimeters X 37 millimeters with a thickness of about .087 millimeters. The anode was dried at 70°C for five minutes. An anode tab 23 made of 0.0508mm (002 inch) thick zinc mesh was adhesively attached to the substrate 25 for place holding until the anode ink 27 was printed onto the substrate, overlapping one end of the tab and thereby affixing it to the substrate. See Fig. 7, illustrating the zinc mesh external tab 23 and the anode ink 27, prior to trimming the part for assembly into a cell. Alternatively, the anode tab 23 could also be printed silver ink.

The cathode current collector ink was a carbon ink provided by Acheson Colloids, product number PF407C. The cathode collector 29 was stenciled onto the heat sealable surface of a discrete piece of the same laminate material 31 used for the anode substrate. The resulting collector that would contact the printed cathode was 40 millimeters X 38 millimeters with a thickness of about .052 millimeters. A tab extension 33 was stenciled using the same cathode collector ink and extending from the collector. See Fig. 8. The cathode collector and tab extension was cured at 50 °C for 16 hours under vacuum to drive off the solvents used in the ink.

The cathode ink wet formulation was 1.1 percent polyvinylpyrrolidone (PVP), 44.4 percent water, 15.5 percent graphite and 38.8 percent manganese dioxide. A binder solution was mixed by combining the PVP and the water. The dry solid graphite KS6 (Timcal America, product designation Timrex LB 1099) and EMD (available from Chemetals and jet-milled by Sturtevant so that the Microtrac d(50) value is less than 1 micron) were crushed together to insure good mixing and then were added to the binder solution. The mixture was stirred by hand until smooth and homogeneous. The cathode was then stenciled onto the cathode current collector to a size of 40 X 38 X .139 millimeters, and cured at 70°C for five to ten minutes.

A coated kraft separator paper with a thickness of about 95 µm is used. The separator base paper is available from Munksjo #300542, and is coated at a level of 20 grams per square meter (gsm) with a mixture of starch (83.6 weight percent available from Roquette LAB2469), gel (7.9 weight percent available from Courtlands B1209), PVP (2.1 weight percent), surfactant (1.4 weight percent ethyl tallow amine known commercially as Crodamet) and water (5 weight percent). The paper was wetted with the cell electrolyte, a 28 percent by weight zinc chloride solution with 1000 ppm Cetrimide BP (cetyl trimethyl ammonium bromide, available from ABA Chemical Ltd., Cheshire, England) and 600 ppm lead chloride added to the solution. The electrolyte solution is filtered to remove solids prior to use. The electrode surfaces were also wetted with the electrolyte so that a total of between .7 and .8 grams of electrolyte was incorporated into the cell. The separator was placed onto either electrode and oriented such that the coated side of the separator faced the zinc anode. The electrode substrates were trimmed to an appropriate size and the cell was heat sealed around the perimeter, such that the electrode tabs extended beyond the heat seal to the exterior of the cell package. Since the packaging laminate, upon trimming, exposed an edge of the inner aluminum foil layer, a strip of polyethylene was wrapped around the anode tab to insure against shorting between the aluminum and the zinc ink.

Two of these cells were connected in series to a printed circuit and powered an LED and sound card application with a current drain of 8 mA. In addition, several of these cells were discharged for at least 100 cycles, where a cycle is defined as 8 mA for 16 seconds on and 0 mA (no drain) for 60 seconds.

EXAMPLE 2:

Co-planar electrode assembly cells were constructed according to this example. An anode was printed using the same anode ink formulation and substrate as in Example 1, and a 0.0508mm (002 inch) thick zinc mesh anode current collector as in Example 1 was affixed to the substrate in the same manner as in Example 1. The anode 34 was screen printed to a size of 50.4 millimeters X 6.8 millimeters with an average thickness of .109 millimeters. The cathode current collector and cathode were stenciled using the same formulation as in Example 1 onto the same substrate as the anode to form a co-planar electrode arrangement. The cathode current collector 35 was stenciled to a size of 40 millimeters X 27 millimeters X .036 millimeters, while the cathode ink 37 was stenciled onto the current collector with a thickness of .166 millimeters. See Fig. 9. The gap between the cathode and the anode was 2.0 millimeters. The electrode surfaces were wetted up with the same electrolyte as in Example 1, and the same separator paper as in Example 1 was introduced to provide an electrolyte soakup such that a total of .6 to .7 grams of electrolyte was introduced into the cell. The separator paper in this co-planar arrangement is sized to cover both the anode and the cathode.

The substrate was trimmed to the appropriate size and a second piece of the packaging material was placed over the first so that the heat sealable surfaces face each other, as in Example 1, and the two are sealed together around the cell perimeter, exposing the tabs for the anode and cathode to the external environment of the cell.

Two cells were connected in series to a printed circuit and powered a sound card application with a current drain of 2 mA. In addition, several cells were discharged for at least 100 cycles, where a cycle is defined as 2mA for 6 seconds on and 0 mA (no drain) for 60 seconds.

EXAMPLE 3:

Co-facial electrode assembly cells were constructed as follows. A zinc mesh anode was utilized in the cells of this example, consisting of a 0.127µm (005 inch) thick piece of zinc mesh available from Delkar Corporation. The mesh was cut to 39 millimeters X 37 millimeters and adhered to the same substrate material as in Examples 1 and 2. The anode current collector was formed from this zinc mesh also and adhered to the substrate in the same manner.

The cathode current collector for the cells of this example used the same carbon ink as in Example 1, and was stenciled as in Example 1 to a size of 40 millimeters X 38 millimeters with an average thickness of .052 millimeters on the same substrate material as in Example 1. The cathode ink was the same ink formulation as in Example 1, and was stenciled onto the collector as in Example 1 to an average thickness of .149 millimeters. The same separator material was used as in Example 1 and the same electrolyte as in Example 1 was introduced into the cell by wetting the cathode surface and the separator so as to introduce an average of .743 grams of electrolyte into the cell. The two substrates were then joined together by heat sealing.

Three cells were connected in series to a printed circuit and powered an electroluminescent display with a current drain of about 15 mA.

EXAMPLE 4: (ZINC CHLORIDE ELECTROLYTE CELLS WITH AN AQUEOUS ZINC INK CO-SOLVENT FORMULATION)

Cells were constructed utilizing an aqueous zinc ink formulation with a co-solvent system in accordance with the within invention. The cells had a printed zinc anode, a printed manganese dioxide cathode, a zinc chloride electrolyte and a coated kraft paper separator as described above. The electrolyte was a 28 weight percent zinc chloride solution to which 600 ppm lead chloride and 1000 ppm cetyltrimethylammoniium bromide (available from Aldrich) was added. This solution was filtered to remove solids prior to introduction into the cells. A co-solvent system comprising water and NMP was utilized with a PVP binder in the zinc ink formulation. The anode zinc ink general formulation was 8.6 grams Union Miniere zinc dust (1600 ppm lead) with a laser median diameter of 10.2 µm, .2 grams PVP K-120, 4.5 mL 1.4 molar zinc acetate aqueous solution and .5 mL NMP. The cathode ink general formulation was 7 grams Chemetals jet-milled EMD (d(50)<1µm, d(90)<3µm,

2.8 grams synthetic graphite KS6, .2 grams PVP K-120 and 10 mL water. The actual zinc and EMD inputs per cell are listed in Table VL The anode tab silver ink (Acheson Colloids, Electrodag 479SS, except where otherwise noted) and the cathode tab and current collector ink (Acheson Colloids, Electrodag PF407C) were printed onto the sealing surface of a metal laminated packaging material available from Pharma Center Shelbyville, product number 95014, and dried. The cathode ink and the anode ink as described above were printed onto the respective collectors and the cells were assembled into a co-facial arrangement and a separator was placed between the electrodes. The cells were trimmed, heat sealed along three sides, about .7 to .8 grams of the electrolyte was dispensed into the cell and the cell was sealed. The cells were discharged for 100 cycles and the results are presented in Table VII: TABLE VII:

0.2685	0.1505	Pass 8mA pulse test for 100 cycles @ 16sec. on/60 sec. off.
0.2891**	0.1575**	Pass 15mA pulse test for 100 cycles @ 16sec. on/60 sec. off.
0.3342**	0.1855**	Pass 15mA. pulse test for 100 cycles @ 16sec. on/60 sec. off.
*0.4371**	0.1820**	Pass 15mA pulse test for 100 cycles @ 16sec. on/60 sec. off.

TABLE VII:

*includes zinc for external contact tab; same printed zinc ink as was used for the anode **separator paper coating included cetyltrimethylammonium bromide available commercially as Cetrimide

EXAMPLE S: (SOUND CARD CIRCUIT)

A printed cell is assembled as follows: initially, a cathode collector is printed onto the sealing surface of a single sheet of a metal laminated packaging material available from Pharma Center Shelbyville, product number 95014, and dried. The cathode current collector is Electrodag PF-407C, a carbon polymer ink available from Acheson. The cathode collector is printed to a dry thickness of 36 µm X 27 millimeters X 40 millimeters. Next, silver external tabs for the anode and cathode are printed onto the sealing surface of the same sheet of metal laminate and dried. The cathode tab overlaps the cathode current collector ink already deposited onto the metal laminate surface. The silver ink is Acheson 479SS, and each tab has a dry dimension of 32.3 millimeters X 11.0 millimeters X 10.0 µm thick, and is separated from the other by 11 millimeters. An anode is printed on the same laminate sheet. The anode is a zinc ink with a wet composition of 57.35 weight percent Union Miniere zinc dust with a laser median diameter of 10 µm as reported by the manufacturer, 1.33 weight percent PVP, 31.74 weight percent water and 9.58 weight percent zinc acetate available from Aldrich as Zn(OOOCH₃)₂·2H₂O. The ink is made by first mixing the aqueous zinc acetate solution first, then dissolving the PVP into the solution, and finally adding the zinc dust and stirring until homogeneously mixed. The anode is printed onto the substrate material, overlapping the silver anode tab already deposited on the sealing surface of the metal laminate to a dry thickness of 100 µm X 6 millimeters X 38.6 millimeters. One of skill in the art will recognize that the order of printing can be changed, and the silver external tabs can be printed initially directly onto the sealing surface.without departing from the scope of the within invention.

The cathode manganese dioxide ink is then formulated. The wet formulation is 36.84 weight percent jet-milled Chemetals electrolytic manganese dioxide (EMD) with a d(50) particle size as determined with a treated Microtrac sample of less than 1 micron, 1.05 weight percent PVP, 14.74 weight percent KS6 and 47.37 weight percent water. The ink is made by pre-mixing the EMD with the KS6, pre-dissolving the PVP into the water, and then adding the powder mix into the polymer solution and stirring until a homogeneous mixture is obtained. The cathode is printed onto the current collector to a dry thickness of 190 microns X 28 millimeters X 40.6 millimeters and dried.

Coated kraft separator paper with a dry thickness of .089 to .114 millimeters X 40 millimeters X 43.6 millimeters is placed over the electrodes. The separator base paper is available from Munksjo #300542, and is coated at a level of 20 grams per square meter (gsm) with a mixture of starch (83.6 weight percent available from Roquette LAB2469), gel (7.9 weight percent available from Courtlands B1209), PVP (2.1 weight percent), surfactant (1.4 weight percent ethyl tallow amine known commercially as Crodamet) and water (5 weight percent). A second sheet of laminate packaging material is placed over the electrode assembly and the package is trimmed and heat sealed along three edges. Electrolyte in the amount of 0.6 grams is added to the package. The electrolyte is a 28 weight percent zinc chloride solution to which 600 ppm lead chloride and 1000 ppm cetyltrimethylammonium bromide are added. The final solution is then filtered to remove solids prior to use. After the electrolyte is added, the cell is heat sealed along the remaining edge and trimmed to the desired outer dimension.

0.254 mm A circuit 45 is screen printed to a thickness of 8-12 µm onto a 0.254 mm (010 inch) thick polyester film 47 available from Melinex #454 (see Fig. 12) using the Acheson silver ink (Electrodag 479SS) in a solvent of diethylene glycol monoethyl ether acetate and dried. A 200,000 ohm resistor 49 is printed to a thickness of 10 to 15 µm onto the circuit using Acheson carbon ink (Minico M 301401 RS) in a bisolvent of ethylene glycol monobutyl ether acetate and isophorene (see Fig. 10). A sound chip 51 available from Holtek (HT81R03) and a piezoelectric speaker 53 available from Star Micronics (QMB 105PX) are affixed to the circuit using silver epoxy available from Circuit Works (CW 2400). A switch is assembled using zinc foil on double stick tape and connected to the circuit. Two cells 55, 57 are connected to the circuit using the silver epoxy and the device is completed and ready for operation. See Fig. 11.

Claims (10)

1. A carbon zinc battery comprising a zinc anode printed directly onto a first section of a flexible non-conductive substrate material, a sealed housing, and a gelled electrolyte comprising zinc chloride, water and a gelling agent, wherein said anode and said gelled electrolyte are contained within said housing, characterized in that the zinc anode is obtainable by directly printing an aqueous anode formulation comprising zinc, zinc acetate and polyvinylpyrrolidone having a molecular weight of 2.0 to 4.0 million onto said first section of the flexible non-conductive substrate material.
2. The battery of claim 1, wherein said gelling agent comprises nonionic or anionic derivatives and natural guar gum.
3. The battery of claim 1, wherein said non-conductive substrate material is a polymer material.
4. The battery of claim 1, wherein said sealed housing is a sealed package.
5. The battery of claim 1, wherein said sealed housing comprises a flexible packaging material.
6. The battery of claim 1, further comprising a current collector and a seal area, wherein said sealed housing comprises a flexible non-conductive material, and said current collector extends through said seal area of said sealed housing.
7. The battery of claim 1, wherein said sealed housing is flexible and formed by said flexible non-conductive substrate.
8. The battery of claim 1, wherein the polyvinylpyrrolidone has a molecular weight of 2.2 to 2.80 million.
9. The battery of claim 1, wherein the aqueous anode formulation comprises a surfactant having a phosphate group and a polyethylene oxide and/or polypropylene oxide chain.
10. The battery of claim 1, wherein the electrolyte comprises cetyltrimethylammonium bromide and lead chloride.