WO2011008744A1

WO2011008744A1 - Lithium based inks and electrodes, batteries made therefrom, and methods of manufacture thereof

Info

Publication number: WO2011008744A1
Application number: PCT/US2010/041811
Authority: WO
Inventors: Murali Sethumadhavan
Original assignee: Rogers Corporation
Priority date: 2009-07-14
Filing date: 2010-07-13
Publication date: 2011-01-20

Abstract

A lithium based ink, comprising a lithium based powder comprising a lithium metal powder and an additional metal powder; a high-temperature polymer binder; and a solvent.

Description

LITHIUM BASED INKS AND ELECTRODES, BATTERIES MADE

THEREFROM, AND METHODS OF MANUFACTURE THEREOF

BACKGROUND

[0001] This invention generally relates to lithium based inks and electrodes, methods for the manufacture of the lithium based inks and electrodes, and batteries formed therefrom, including primary and secondary lithium batteries.

[0002] A number of advanced battery technologies have recently been developed to service many energy-related applications ranging from vehicles to consumer electronics, such as metal hydride (e.g., Ni-MH), nickel-cadmium (Ni-Cd), lithium batteries with liquid electrolytes and recently, lithium batteries with polymer electrolytes.

Lithium primary and secondary batteries are an important component in this developing technology. Some efforts have been made to develop lithium deposition methods based on sprays or vapor deposition, but these methods can involve toxic solvents or expensive equipment. Also important is the ability to control the interface between the electrolyte and the lithium electrode, particularly when the electrolyte is a solid and to control dendrite growth for secondary batteries.

[0003] Several methods exist for producing lithium battery anodes from lithium powders. For example, in some methods, a lithium powder anode can be made from an emulsified lithium powder in inorganic or hydrocarbon oil. In another method, lithium slurries can be used to produce the anode. In this case, lithium metal powder and a host material are mixed with a no-aqueous liquid such as THF and a binder, and formed into a slurry. However, the slurries are typically not formulated to be applied by printing, but rather casting or spin coating. In still other methods, the lithium metal powder can be formed into an ink, wherein the ink is formulated to be printed onto substrates using a variety of printing techniques, including screen printing, offset litho printing, gravure printing, flexographic printing, pad printing, ink jet printing, and the like. Such printing techniques allow for high speed, high volume production of printed substrates (e.g., anodes).

[0004] The material properties of lithium powder, however, can present challenges in the manufacturing process. In particular, lithium metal powders can be difficult to work with, particularly when ultra thin layers of lithium are desirable. Moreover, due to inefficiencies in the process and settling of the lithium powder in the inks, much more lithium powder is used than is necessary in order to produce an effective anode. A perceived need exists to improve the processability of lithium materials for use in batteries for a wide variety of applications, and furthermore to reduce the amount of expensive lithium metal powder needed to produce an anode. Further, it would be desirable to form a lithium based ink formulation that can provide a higher charger capacity battery than currently available. Still further, it would be desirable to form a lithium ink based anode with the same or better charge capacity of current batteries using less lithium metal powder, therefore, lowering the cost of manufacturing the batteries.

SUMMARY OF INVENTION

[0005] The above-described drawbacks and disadvantages are alleviated by a lithium based ink comprising a lithium based powder comprising a lithium metal powder and an additional metal powder; a high-temperature polymer binder; and a solvent.

[0006] Also described is an anode comprising an anode current collector, and an electrode layer disposed on the anode current collector, the electrode layer comprising a lithium based powder comprising a lithium metal powder and an additional metal powder, and a high-temperature polymer binder.

[0007] A method of printing an anode for a lithium battery is described, comprising formulating a lithium based ink comprising a lithium metal powder and an additional metal powder; a high-temperature polymer binder; and a solvent; and printing the ink on a current collector.

[0008] Also described are anodes and batteries comprising the lithium based ink composition, and their methods of manufacture.

[0009] The invention is further illustrated by the following drawings, detailed description, and examples.

BRIEF DESCRIPTION OF DRAWINGS

[0010] Referring now to the exemplary drawings wherein like elements are numbered alike in the figure:

[0011] FIGURE 1 illustrates a cross-sectional view of an exemplary embodiment of a lithium battery.

DETAILED DESCRIPTION

[0012] Lithium metal powder based inks, anodes made from the inks, and primary and secondary lithium metal batteries made from the anodes are provided herein. As used herein, an "ink" includes any coating formulation that can form a thin film (or, depending on the coating technique, pattern) upon application to a substrate. The lithium powder based inks include a lithium metal powder, one or more additional (non-lithium) metal powders, a solvent and a binder, and optionally an electronically conductive material and/or a lithium salt. In particular, the invention provides a lithium based ink for use in printing an electrode for a lithium battery, the ink comprising lithium metal powder, one or more additional metal powders, a high temperature polymer binder, and a solvent. In general, compositions are formulated to function as sophisticated ink formulations rather than mere slurry

compositions. For example, the ink spreading properties and viscosity can be carefully controlled, together with particle shape, particle size distribution, and average particle size. Primary and secondary lithium batteries based on the lithium based ink disclosed herein have properties equal to or superior to current lithium batteries, and in some cases, are

manufactured with less lithium metal.

[0013] The one or more additional metal powders help to reduce the amount of lithium metal powder required in the ink. As used herein, the term "additional metal powder" is used to generally refer to a second metal powder in the ink other than the lithium metal powder. Exemplary additional metal powders are described in greater detail below. The reduction in lithium metal powder improves the processability of the ink during the printing processes, while reducing the manufacturing cost of the anode. Moreover, the additional metal powder enhances the charge capacity of the final battery when compared to lithium powder inks alone. The lithium based powder that includes the additional metals provides flexibility to lithium battery design. In one embodiment, it can be desirable to increase the charge capacity by utilizing the same amount of lithium powder as would be used without the additional powder, together with the additional metal powder. In another embodiment, it can be desirable to produce a less expensive battery having the same charge capacity by reducing the amount of lithium powder present in the lithium based ink.

[0014] Useful additional (i.e., non-lithium) metal powder for the lithium based ink formulation include, without limitation, copper, nickel, stainless steel, gold, silver, aluminum, zinc, tin, lead, transition metals, and alloys comprising at least one of the foregoing. There are no particular limitations regarding the shape or texture of the powder particles. The additional metal powder can be generally finely divided powders, desirably having an average particle size of less than or equal to about 500 micrometers; specifically less than or equal to about 100 micrometers; more specifically less than or equal to about 50 micrometers. In some embodiments the average particle size of the additional metal powder is less than or equal to about 20 micrometers, in other embodiments the average particle size of the additional metal powder is less than or equal to about 10 micrometers, and in still other embodiments the average particle size of the additional metal powder is less than or equal to about 1 micrometers. For example, additional metal powders having an average particle size from about 1 to 100 micrometers can be used. The lithium based ink can comprise the lithium metal powder and an additional metal powder or a plurality of additional metal powders. Two or more additional metal powders can be mixed to form alloys and other mixtures that can then be mixed with the lithium powder. When two or more additional metal powders are present in the lithium based ink, the average particle size of the two powders can be the same or different. Likewise, the average particle size of the lithium metal powder and the additional metal powder(s) can be the same or different.

[0015] The lithium metal powders used in the production of the lithium based inks can be generally finely divided lithium metal powders, desirably having an average particle size of less than or equal to about 500 micrometers; specifically less than or equal to about 100 micrometers; more specifically less than or equal to about 50 micrometers. In some embodiments the average particle size of the additional metal powder is less than or equal to about 20 micrometers, in other embodiments the average particle size of the additional metal powder is less than or equal to about 10 micrometers, and in still other embodiments the average particle size of the additional metal powder is less than or equal to about 1 micrometers. For example, additional metal powders having an average particle size from about 1 to 100 micrometers can be used.

[0016] Nanoscale lithium metal powders can also be used to formulate the lithium based inks provided herein. As used herein a "nanoscale" lithium metal powder is a lithium metal powder having an average particle size of less than or equal to about 1 micrometer. In one embodiment, nanoscale lithium metal powders have an average particle size of less than or equal to about 500 nanometers; specifically less than or equal to about 100 nanometers; more specifically less than or equal to about 70 nanometers; still more specifically less than or equal to about 50 nanometers, and even more specifically less than or equal to about 20 nanometers. For example, the lithium metal powders can have an average particle size from about 10 to 1,000 nanometers. The nanoparticles can be highly uniform in size and possess a high level of purity.

[0017] The relative amounts of the various components that make up the inks can vary depending on a variety of factors, including the viscosity requirements of the chosen printing method and conductivity requirements of the intended application, materials cost, processability of the ink, and the like. The viscosity of the ink formulations can be tailored to a chosen printing technique by changing the nature and amount of binder and/or solvent in the formulation, while the conductivity of the ink formulations can be tailored for a selected application by changing the nature and amount of conductive materials or additional metal powder and the size of the conductive or additional metal powder particles in the ink formulations.

[0018] With regard to the composition of the lithium based powder (i.e., the mixture of lithium metal powder and additional metal powder), the relative amounts will depend on a variety of the same or similar factors as the ink formulation as a whole. In one embodiment, the additional metal powder will be present in the lithium based powder in an amount of about 1 to about 99 weight percent (wt%); specifically about 10 to about 80 wt%, more specifically about 20 to about 70 wt%, even more specifically about 30 to about 60 wt%, and still more specifically about 40 to about 50 wt%, based on the total weight of the lithium based powder. In another embodiment, the lithium based powder will include about 55 to about 95 wt% lithium metal powder and about 5 to about 45 wt% additional metal powder; specifically about 65 to about 85 wt% lithium metal powder and about 15 to about 35 wt% additional metal powder; and more specifically about 75 wt% lithium metal powder and about 25 wt% additional metal powder, based on the total weight of the lithium based powder. In still another embodiment, the lithium based powder will include about 55 to about 95 wt% additional metal powder and about 5 to about 45 wt% lithium metal powder; specifically about 65 to about 85 wt% additional metal powder and about 15 to about 35 wt% lithium metal powder; and more specifically about 75 wt% additional metal powder and about 25 wt% lithium metal powder, based on the total weight of the lithium based powder.

[0019] In one embodiment, as will be described in greater detail below, the lithium based ink formulation contains from about 20 to 50 wt% lithium based powder and from about 10 to 30 wt% polymer binder. In other embodiments, the lithium based ink includes from about 30 to 45 wt% lithium based powder, from about 15 to 20 wt% polymer binder, from about 20 to 30 wt% conductive material and from about 15 to 20 wt% lithium salt. However, the lithium powder based ink formulations provided herein are not limited to those having components present in amounts falling within these ranges.

[0020] The lithium based inks further include at least one polymer binder. The binder forms a film in which the lithium based powder is embedded once the ink has dried. Blends of polymers can be used. Exemplary polymer binders for use in some of the inks provided herein include, but are not limited to, polyvinylidene fluoride, polyethylene oxide, polyethylene, polypropylene, polytetrafluoroethylene, polyacrylates and mixtures and copolymers thereof. Other binders include a polyimide, polyamide, polyphenylene oxide, polyarylate, polyamide-imide, polyester-imide, polyester-amide-imide, polybenzimidazole, polybenzoxazoles, polysulfone, polyether sulfone, polysulfonamide, poly(quinoxaline), poly(para-phenylene), poly(arylene ether), including one substituted with a pyridyl group, poly(aryl ether sulfone), polyepoxide or a combination thereof. The binders can be crosslinkable (if substituted with crosslinkable groups) or a high temperature polymer, provided that it has sufficient solubility in the solvent used.

[0021] High temperature polymers having high glass transition temperatures can be specifically mentioned or use as binders in the ink formulations. High temperature polymers are a class of polymers typically used in the fabrication of articles which can be subjected to high temperatures (e.g. 400° C. -500° C, or greater). Special processing equipment can be needed to handle these high temperature polymers in normal processing because of the high glass transition. These materials are characterized by high glass transition temperatures and, when crystalline, melting points, are generally resistant to many solvents unless the polymer structure is modified to improve solubility. Exemplary polymer binders, including high temperature polymers, have functional groups capable of complexing with lithium salts and participating in ionic conduction. Exemplary high temperature polymers include, without limitation, polyimides, polyamides, polyphenylene oxides, polyarylates, polyamide-imides (PAI), polyester-imides, polyester- amide-imides, polybenzimidazoles (PBIs) and

poly(benzoxazoles). Polysulfones, polyether sulfones, polysulfonamides, poly(quinoxaline) (PPQ), poly(para-phenylenes) , poly(aryl ethers) (PAE-2s) substituted with a pyridyl group, poly(aryl ether sulfones) and polyepoxides can also be used. In some cases the high temperature polymers can be functionalized or modified to make them suitable for use in lithium metal batteries, as one of skill in the art would understand. Blends of polymers can be used including blends comprising the high temperature polymer and also a different type of polymer to the extent the application allows.

[0022] In some embodiments, the high temperature polymer is a polyimide that is substantially soluble in the solvent used to formulate the lithium based ink. The polyimides can be pre-imidized and are desirably provided as amorphous, thermoplastic polyimide powders. Exemplary polyimides are commercially available. These include MATRIMID 5218 and 9725 commercially available from Ciba-Geigy; ULTEM 1000 and 2000 commercially available from General Electric; and LaRC-CPl, LaRC-CP2 and LaRC-SI all of which are available from Imitec, Inc., Schenectady, N. Y. Some lithium based ink formulations will include one or more polyimides having a repeat unit weight per imide ring of no more than about 350.

[0023] In addition to polyimides, other generally glassy amorphous polymers can be used including, for example, high glass transition temperature polymers (e.g., Tg greater than 150° C; specifically Tg greater than 180° C; more specifically Tg greater than 200° C; still more specifically Tg greater than 250° C; and even more specifically Tg greater than 350° C). In general, the polymer can have polar groups which can complex with lithium salts and participate in ionic conduction. In some instances it is desirable to employ polymers having a Tg in the lower Tg range because they are easier to process.

[0024] The solvents used in the lithium based inks can be typically anhydrous, aprotic polar organic solvents which are sufficiently chemically stable toward lithium metal, and capable of solvating, the lithium powders, polymeric binders and any conductive materials or lithium salts. Exemplary polar solvents include, without limitation, gamma-butyrolactone (GBL), tetrahydrofuran (THF) and propylene carbonate (PC), with GBL being preferred for printing applications. Other exemplary solvents include dioxane, 1,3-dioxolane, 1,2- dimethyloxyethane and dimethylsulfoxide.

[0025] Electronically conductive materials can also be added to the lithium based inks in order to enhance their conductivity for a given application. Carbonaceous materials, such as carbon powder or carbon nano-tubes, can be used to increase the conductivity of the inks. In addition, lithium salts can be added to the inks. Exemplary lithium salts include, without limitation, LiPF₆, lithium perfluoro sulfonate salts, LiTFSi, LiCl, LiBr, LiI, LiBOB, LiClO₄, LiBF₄, LiAsF₆, and LiCF₃SO₃.

[0026] An alternative to the highly active lithium based powder mixture of both the lithium metal powder and the additional non-lithium metal powder includes a substitute intercalation carbon to absorb lithium that came from another source. For example, the formulation can contain (i) a fine carbon such as mesocarbon microbeads (MCMB) 6-10 or 6- 25 manufactured by Osaka Gas Chemical Co. Ltd., (ii) a conductivity enhancing carbon such as Super P from TimCal Graphite & Carbon Co. or carbon nanotubes, (iii) a binder polymer, (iv) a lithium salt, and (v) a solvent such as GBL or mixtures of solvents. This mixture would be capable of being printed and dried to provide a lithium active anode. The amounts of each of the components can be adjusted to provide an effective lithium based ink formulation (e.g., viscosity, solids content) for a particular application, substrate, and printing method. For example, binder polymers, lithium salts, and solvents described herein can be used including, in particular, high temperature polymers such as polyimides and soluble polyimides. [0027] Application techniques for the inks include both conventional coating techniques and printing techniques. For example, the inks can be coated onto a surface, such as a current collector by vapor deposition, dip coating, spin coating and brush coating.

However, in an exemplary embodiment, the lithium based inks are formulated to be printed onto a surface. Application of the lithium based inks using printing methodologies is particularly advantageous because such methodologies allow for high speed, high volume application of the lithium based inks to underlying substrates, such as metal current collectors. This is particularly advantageous in the manufacture of lithium metal batteries because it is simpler and faster than more conventional production techniques where lithium metal foils are laminated to anode current collectors. Moreover, printing the inks eliminates the need for more complicated and expensive coating techniques, such as vapor deposition. In addition, by printing the inks onto a surface, such as a current collector, better interfaces can be produced and the need to spray a lithium composition is eliminated, reducing waste and environmental concerns. Many printing application also make it possible to deposit very thin layers of the inks. This reduces cost and makes thinner electronic components possible. For example, depending upon the particle size of the lithium and additional powders used to formulate the lithium based inks, layers of the ink having an average layer thickness of less than or equal to about 40 micrometers can be printed. In one embodiment, the layers of ink have an average layer thickness of less than or equal to about 30 micrometers; specifically less than or equal to about 20 micrometers; and more specifically less than or equal to about 10 micrometers.

[0028] The lithium based inks can be printed onto a substrate using a variety of printing methods, including screen printing, offset litho printing, gravure printing, flexographic printing, pad printing, ink-jet printing, and the like.

[0029] Screen printing uses a screen coated with a light sensitive emulsion or film, which blocks the holes in the screen. An image to be printed is supplied to the film. The imaged screen is then exposed to ultra-violet light followed by the washing away of any light sensitive emulsion that has not been hardened by the ultra-violet light. This leaves an open stencil which corresponds to the image that was supplied on the film. The screen is fitted on a press and the substrate to be printed is placed in position under the screen while ink is placed on top of the screen. A blade is pulled across the top of the screen, pushing the ink through the mesh onto the substrate to be printed. In one embodiment, the lithium based ink formulations for screen printing have viscosities of about 0.5 to about 50 Pa-sec; and more specifically about 1 to about 30 Pa-sec at 25° C. Using a screen printing process, a layer of lithium based ink having an average thickness of less than or equal to about 30 micrometers, specifically less than or equal to about 15 micrometers can be printed onto a substrate, provided the ink is prepared from a lithium and additional metal powders having a sufficiently small particle size.

[0030] In offset litho printing, generally, images are supplied to printing plates, which are dampened by ink which adheres to the image area. The image is then transferred to a rubber blanket, and from the rubber blanket to a substrate. In one embodiment, viscosities for lithium based inks for use in offset litho printing are from about 10 to about 100 Pas at 20° C; specifically from about 30 to about 80 Pas at 20° C. Offset litho printing is capable of providing very thin layers of ink. In fact the layer thickness of the printed ink can be limited by the particle size of the lithium based powders. For example, if the lithium and additional metal powder have small enough particle sizes, the lithium based inks can be applied in layers having an average thickness of about 0.5 to about 2 micrometers.

[0031] Gravure printing uses, generally, a cylinder onto which an image has been engraved with cells. To print, the cells are filled with ink and the substrate to be printed is passed between the printing cylinder and an impression roller. The lithium based inks used with gravure printing typically have viscosities much lower than those used with screen or offset litho printing. For example, some gravure printing inks will have a viscosity from about 0.01 to about 0.5 Pa-sec at 25° C, specifically from about 0.05 to about 0.2 Pa-sec at 25° C. Like offset litho printing, gravure printing is capable of printing very thin layers of lithium ink. For example, depending on the size of the lithium and additional metal powders used, gravure printing can be used to print lithium based ink in layers having an average thickness of about 0.8 to about 8 micrometers.

[0032] In flexographic printing, a screened roller is generally used to apply a thin layer of relatively fluid ink to the surface of a flexible printing plate. A rotating plate roller is then used to bring the inked surface of the printing plate into contact with a web to be printed and an impression roller presses the web against the plate to effect the transfer of the ink. In one embodiment, the lithium based ink formulations for flexographic printing have viscosities similar to those used for gravure printing, specifically from about 0.01 to about 0.7 Pa-sec; and more specifically about 0.05 to about 0.5 Pa-sec at 25° C. Depending on the size of the lithium and additional metal powders used to formulate the inks, flexographic printing can be used to produce ink layers with an average thickness from about 0.5 to about 5 micrometers; specifically from about 0.8 to about 2.5 micrometers. [0033] In pad printing an image to be transferred generally is etched into a printing plate known as a cliche. The cliche is initially flooded with ink and then cleaned to leave ink only in the image area. A silicon transfer pad is then positioned over the cliche and pressed onto it to transfer the ink. The pad is lifted away from the cliche and the ink is allowed to partially dry, rendering it tackier and more viscous. The pad is then pressed onto a substrate where the ink is deposited. Lithium based ink formulations for pad printing will have viscosities similar to those of the screen printing ink formulations.

[0034] InkJet printers generally use a series of nozzles to spray drops of ink directly on the paper. InkJet printers are typically used with inks having viscosities of about 0.001 to about 0.05 Pa-sec at 25° C. and can produce ink layers having an average thickness of about 0.1 to about 30 micrometers; specifically about 0.3 to about 20 micrometers.

[0035] The lithium based inks can be provided in a number of different formulations to be used with different printing processes for different applications. Two of the primary considerations when choosing a formulation are the viscosity and conductivity of the ink. As noted above, the viscosity requirements of an ink can vary dramatically based on the printing technique to be used. Viscosity will depend, at least in part, on the amount of solvent and polymer binder present in the composition. In particular it will depend on the ratio of lithium metal powder and additional metal powder in the lithium based powder, and the ratio of the lithium based powder to the conductive material and binder in the composition. Another consideration, that can be taken together with viscosity considerations, is the conductivity requirements for a given application.

[0036] One application for which the lithium based inks provided herein are useful is in the production of electrodes, such as anodes for lithium metal batteries. Such anodes can be fabricated with the lithium based inks provided herein by printing the ink onto the surface of an anode current collector. The anode current collector is an electrically conductive member made from a metal, such as aluminum, copper, nickel, iron or stainless steel. The current collector can be a foil or a grid.

[0037] The anodes provided herein can be incorporated into both primary and secondary lithium metal batteries. Although different battery constructions are possible, each battery will include at least one anode, at least one cathode and an electrolyte in

electrochemical communication with each anode and each cathode. Such batteries represent an improvement over more conventional lithium metal only based batteries because the lithium metal powder in combination with the additional metal powder tend to be manufactured more easily and cheaply, and in some cases provide a battery with a greater charge capacity.

[0038] One or more anodes in the battery are composed of a current collector with an electrode layer of lithium metal powder in a polymer binder, disposed thereon. The anodes can be formed by printing a lithium based ink, of the type described above, onto the current collector and allowing the ink to substantially dry.

[0039] The electrolyte can be any suitable electrolyte for use in a lithium metal battery, many of which are known and commercially available. Exemplary electrolytes include liquid electrolytes, solid polymer electrolytes and polymer matrix electrolytes (PMEs). In order to provide ionic conductivity to the anode, the electrolytes include at least one lithium salt. Lithium salts that can be used in the electrolytes include, but are not limited to, LiCl, LiBr, LiI, LiClO₄, LiBF₄, LiAsF₆, Li(CH₃CO₂), Li(CF₃SO₃), Li(CF₃SO₂)₂N, Li(CF₃SO₂)₃C, Li(CF₃CO₂), Li(B(C₆H₅)₄), Li(SCN), and Li(NO₃). LiPF₆ and LiTFSi are particularly well- suited for use in the electrolytes.

[0040] Batteries that use a liquid electrolyte include a separator film disposed between each anode and each cathode. In this construction, the separator films are typically porous organic polymer films saturated with the lithium salt electrolyte solution. Any separator film known to those skilled in the art can be used as a barrier between each anode and cathode layer. The separator film is typically a freestanding film comprised of an organic polymer, such as polypropylene, polyethylene or polyvinylidene fluoride, and is generally saturated with a liquid lithium electrolyte solution. Examples of such films include, but are not limited to, Kynar-FLEX from Atochem North America; and CELGARD 3401 from Celgard, Inc.

[0041] Solid polymer electrolytes can be generally gel type electrolytes, which trap solvent and salt in the pores of the polymer to provide a medium for ionic conduction. The polymer electrolytes generally can function as separators between anodes and cathodes and as electrolytes. Polymer electrolytes can be made from such polymers as polyethylene oxide (PEO), polyether based polymers and other polymers, which are configured as gels, including polyacrylonitrile (PAN), polymethylmethacrylate (PMMA) and polyvinylidine fluoride (PVDF).

[0042] In some embodiments of the batteries provided herein, the electrolyte is a polymer matrix electrolyte. In these PMEs, a solvent is integrated with the polymer and a lithium salt in a homogeneous and substantially optically clear matrix. As a result the PMEs are substantially free of non-absorbed solvent or identifiable pores. Unlike conventional gel polymers where the polymer only provides mechanical support, the polymer, salt and solvent that make up the PME all participate in ionic conduction. In one exemplary embodiment, the PME includes a polyimide, at least one lithium salt in a concentration of at least 0.5 moles of lithium per mole of imide ring provided by the polyimide and at least one solvent, all intermixed. The PME is generally homogeneous as evidenced by its high level of optical clarity. As used herein, when the PME is referred to as being substantially optically clear. The phrase "substantially optically clear" regarding the PME refers to the PME being at least 90% clear (transmissive), preferably at least 95%, and most preferably being at least 99% clear as measured by a standard turbidity measurement, transmitting through a normalized 1 mil film using 540 nm light.

[0043] The lithium salt is desirably present in an amount between 0.5 and 2.0 moles Li per mole of imide ring provided by the polyimide, or 1.2 and 2.0 moles Li per mole of imide ring provided by the polyimide. Exemplary lithium salts for use with PMEs include LiCl, LiBr, LiI, LiBOB, LiClO₄, LiBF₄, LiAsF₆, LiPF₆, LiTFSi, LiCF₃SO₃, and

LiN(CF₃SOs)₂.

[0044] A repeat unit weight per imide ring of the polyimide can be no more than 350, no more than 300, or no more than 250. The polyimide is preferably soluble at 25° C. in at least one solvent selected from the group consisting of N-methylpyrrolidinone (NMP), dimethylacetamide (DMAc) and dimethylformamide (DMF).

[0045] In one embodiment, the ionic conductivity of the PME at 25° C. is at least 1x10-4 S/cm; and specifically at least 3x10-4 S/cm. T he PME desirably provides at least one infrared absorption between about 1630 and 1690 cm-1, even though neither the salt nor the polyimide provide any absorption peaks in this range. Solvent can be included in the PME to improve conductivity and other properties. For example, solvent content of the PME can be about 15 wt. % to about 40 wt. % for applications wherein high discharge rates or lower temperatures are needed. Solvent content of about 10 wt. % or less can be used for other applications. For polyimide systems, it can be difficult to remove all solvent.

[0046] The cathodes used to construct the batteries can be any cathode material suitable for use with lithium metal batteries, many of which are known. For example, the cathode can comprise a polymer binder, an intercalation material, and an electrochemically active material. The electrochemically active material is desirably a metal oxide, such as MnO₂ or a lithium metal oxide, such as a lithium vanadium oxide (Lix VyOz), a lithium transition metal oxide (e. g. LiMn₂O₄), LiCoO₂, LiNiO₂, Li₄TIsOi₂, LiVxOy, a metal sulfide (e.g. TiS₂) and LiFePO₄. When the anode and the electrolyte and/or the cathode each include a polyimide, they can all include the same or different polyimides. Exemplary intercalation materials include, but are not limited to, carbon black and graphite.

[0047] In one embodiment, the cathode comprises a cathode current collector having an electrode layer disposed thereon, wherein the electrode layer includes an amorphous, thermoplastic polyimide, an electronic conductive filler and a metal oxide.

[0048] One procedure for producing the cathode includes forming a slurry of an electrochemically active material, a polymer binder and an intercalation material in a solvent. The slurry is then coated or printed onto a cathode current collector, such as a aluminum or nickel foil, and the solvent is allowed to evaporate.

[0049] Fabrication of batteries using the lithium based electrodes can be carried out with known methods as well with methods as described herein. One or more batteries can be fabricated quickly and efficiently using printing technologies wherein a lithium metal powder based anode, a polymer electrolyte and a cathode are all printed using screen printing or other printing techniques.

[0050] The lithium based inks provided herein make it possible to fabricate a battery in which all three components are printed. For example, a printed lithium battery can be produced by printing a slurry of an electrochemically active material, such as a lithium metal oxide, a polymer binder, such as a polyimide and an intercalation material, such as graphite in an appropriate solvent onto a metal foil or mesh current collector and allowed to dry to provide a cathode. A polymer electrolyte can then be printed over the printed cathode by printing a solution of a polymer binder, such as a polyimide, a lithium salt and an appropriate solvent onto the cathode. The electrolyte is allowed to dry to remove solvent with an effective amount of solvent retained for conductivity purposes, such as, for example, 5 to 50 weight % versus polyimide plus salt. At this point the overcoated cathode has become both the cathode and the membrane separator. The anode can be either printed directly onto the printed polymer electrolyte or onto a metal current collector, which is then placed over the printed polymer electrolyte. PMEs are well-suited for use in printed lithium batteries because, unlike conventional polymer electrolytes, they do not include free solvents or gel which might interfere with the printing process or the quality of the final printed layers.

[0051] Of course, it is not necessary that the anode, cathode and electrolyte be printed. One or more these components can be cast or otherwise processed. In one exemplary fabrication process a separator is cast from a solution as a free-standing film. The separator is then sandwiched between a cathode, which can be printed or cast onto a current collector, and an anode, which can be printed or cast onto a current collector. The layers are then laminated together under heat and pressure. If the cell is based on a polymer electrolyte, the separator also serves as the electrolyte. If the cell is based on a liquid electrolyte, the liquid electrolyte is introduced into the system to provide electrochemical communication between the anode and cathode.

[0052] FIG. 1 shows a battery which, if desired, can be made in accordance with the process outlined in herein. The battery includes a copper anode current collector 600, a printed lithium based anode 602, a printed PME 604, a printed cathode 606 and an aluminum cathode current collector 608. The anode and cathode current collectors 600, 608 are sealed around the perimeter of the battery with a polyester sealant frame 610.

[0053] The lithium metal batteries provided herein can be used to power electronic devices that use ultrathin, flexible batteries. Although these devices have proven useful in a broad range of applications, their penetration into some markets has been stalled by size and cost considerations. Frequently, it is the size and cost of production of the battery that powers these devices that prove to be the limiting factors. As discussed above, the lithium based inks provided herein, allow for the high speed, high volume production of printed lithium powder anodes and lithium metal batteries. The batteries so produced have the potential to be thinner and less costly to produce than lithium metal batteries made by more conventional techniques and containing solely lithium metal powder.

[0054] Examples of applications that can be powered by the present batteries include, but are not limited to, sensors, medical applications, military applications, security

applications, music, audio and broadcast applications, computing applications, financial transaction applications, transportation applications and measuring and metering applications. Specific examples of sensors include tracking and identification sensors (e.g., Smart Cards, radiofrequency identification (RFID) tags, biometric sensors and friend or foe identification detectors). These sensors are useful in homeland security applications where they can be used to track and/or identify baggage and passengers and to authenticate documents such as passports and visas. Other sensor devices include emergency, security and environment sensors (e.g., fire alarms, smoke detectors, motion detectors, chemical sensors, temperature sensors, time-temperature indicators, humidity sensors and acoustic seismic sensors). These sensors can take the form of microelectromechanical sensors (i.e., "Smart Dust" sensors). Specific examples of medical devices include external wearable medical devices (e.g., ambulatory infusion pumps), telemetry systems, blood analyzers, bone growth stimulators, Holter monitors, pulse oximeters, external pacemakers and defibrillators. Specific examples of military devices include communications devices (e.g., wireless transmitters), thermal imaging devices, night vision devices, surveillance devices, undersea mines, military radios, guidance and positioning system, search and rescue transponders, radar jammers, respiratory protection suits and sonobuoys. Music, audio and broadcast devices include wireless microphones, transmitters and amplifiers. Specific examples of computing devices include computer clocks and memory backup devices. Specific examples of financial transaction applications include both secure transaction devices (e.g., Smart credit and debit cards) and non-secure transaction devices (e.g., gift and loyalty cards). It should be understood that this list of possible applications is not intended to be exhaustive.

[0055] Ranges disclosed herein are inclusive of the recited endpoint and are independently combinable. "Combination" is inclusive of blends, mixtures, alloys, reaction products, and the like. Also, "combinations comprising at least one of the foregoing" means that the list is inclusive of each element individually, as well as combinations of two or more elements of the list, and combinations of one or more elements of the list with non-list elements. The terms "first," "second," and so forth, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier "about" used in connection with a quantity is inclusive of the state value and has the meaning dictated by context, (e.g., includes the degree of error associated with measurement of the particular quantity). In addition, it is to be understood that the described elements can be combined in any suitable manner in the various embodiments.

[0056] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0057] While the invention has been described with reference to several embodiments thereof, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A lithium based ink, comprising

a lithium based powder comprising a lithium metal powder and an additional metal powder;

a polymer binder; and

a solvent.

2. The lithium of ink of Claim 1, wherein the additional metal powder comprises copper, nickel, stainless steel, gold, silver, aluminum, zinc, tin, lead, transition metals, or a combination comprising at least at least one of the foregoing.

3. The lithium ink of claims 1-2, wherein the polymer binder comprises a polyimide, polyamide, polyphenylene oxide, polyarylate, polyester-imide, polyester-amide - imide, poly(benzoxazole) , polysulfone, polyether sulfone, poly sulfonamide,

poly(quinoxaline), poly(para-phenylene), poly(aryl ether), poly(aryl ether) substituted with a pyridyl group, poly(aryl ether sulfone), polyepoxide, and combinations thereof.

4. The lithium ink of claims 1-3, wherein the high temperature polymer has a glass transition temperature of at least 150° C.

5. The lithium ink of claims 1-4, wherein the polyimide comprises a pre- imidized, amorphous, thermoplastic polyimide powder that is soluble in a polar solvent.

6. The lithium ink of claims 1-5, wherein the additional metal powder is present in the lithium based powder in an amount of about 1 to about 99 wt%; specifically about 10 to about 80 wt%, more specifically about 20 to about 70 wt%, even more specifically about 30 to about 60 wt%, and still more specifically about 40 to about 50 wt%, based on the total weight of the lithium based powder.

7. The lithium ink of claims 1-5, wherein the lithium based powder comprises about 55 to about 95 wt% lithium metal powder and about 5 to about 45 wt% additional metal powder; specifically about 65 to about 85 wt% lithium metal powder and about 15 to about 35 wt% additional metal powder; and more specifically about 75 wt% lithium metal powder and about 25 wt% additional metal powder, based on the total weight of the lithium based powder.

8. The lithium ink of claims 1-5, wherein the lithium based powder comprises about 55 to about 95 wt% additional metal powder and about 5 to about 45 wt% lithium metal powder; specifically about 65 to about 85 wt% additional metal powder and about 15 to about 35 wt% lithium metal powder; and more specifically about 75 wt% additional metal powder and about 25 wt% lithium metal powder, based on the total weight of the lithium based powder

9. The lithium ink of claims 1-8, wherein the lithium metal powder has an average particle size equal to that of the additional metal powder.

10. The lithium ink of claims 1-8, wherein the lithium metal powder has an average particle size different than that of the additional metal powder.

11. The lithium ink of claims 1-9, wherein the lithium metal powder and the additional metal powder have an average particle size less than or equal t about 50 micrometers.

12. An anode, comprising:

an anode current collector; and

an electrode layer disposed on the anode current collector, the electrode layer comprising a lithium based powder comprising a lithium metal powder and an additional metal powder, and a high-temperature polymer binder.

13. The anode of claim 12, wherein the electrode layer has an average thickness of less than or equal to 30 micrometers.

14. The anode of claims 12-13, wherein the additional metal powder comprises copper, nickel, stainless steel, gold, silver, aluminum, zinc, tin, lead, transition metals, or a combination comprising at least at least one of the foregoing.

15. A battery, comprising:

the anode of claim 12;

a cathode; and

an electrolyte in electrochemical communication with the cathode and the anode.

16. The battery of claim 15, wherein the electrolyte comprises a polyimide solid polymer electrolyte.

17. A lithium metal battery, comprising:

a cathode;

an anode comprising a printed electrode layer comprising a lithium based powder comprising a lithium metal powder and an additional metal powder, and a high- temperature polymer binder; and

a polymer electrolyte disposed between the cathode and the anode.

18. The lithium metal battery of claim 17, wherein the additional metal powder comprises copper, nickel, stainless steel, gold, silver, aluminum, zinc, tin, lead, transition metals, or a combination comprising at least at least one of the foregoing.

19. A method of printing an anode for a lithium battery, comprising: formulating an ink according to any of claims 1-11; and printing the ink on a current collector.

20. A anode made by the method of claim 19.