JP7476226B2 - Printable lithium battery - Google Patents

Description

RELATED APPLICATIONS The following applications claim priority to U.S. Patent Application No. 16/573,587, filed September 17, 2019, which claims priority to U.S. Provisional Application No. 62/874,269, filed July 15, 2019, U.S. Provisional Application No. 62/864,739, filed June 21, 2019, and International Application Nos. PCT/US19/23376, PCT/US19/23383, and PCT/US19/23390, filed March 21, 2019. This application claims priority to U.S. Patent Application Nos. 16/359,707, 16/359,725, and 16/359,733, filed March 20, 2019, which in turn claims priority to U.S. Provisional Application Nos. 62/646,521, filed March 22, 2018, and 62/691,819, filed June 29, 2018, the disclosures of each of which are incorporated by reference in their entirety.

The present invention relates to a battery that uses a printable lithium composition.

Lithium and lithium-ion secondary batteries, or rechargeable batteries, are used in certain applications such as mobile phones, camcorders, laptop computers, and more recently in higher power applications such as electric and hybrid electric vehicles. In these applications, it is preferable for the secondary battery to have as high a specific capacity as possible, while still providing safe operating conditions and good cyclability so that the high specific capacity is maintained on subsequent recharge and discharge cycles.

Secondary batteries come in a variety of configurations, but each configuration includes a positive electrode (i.e., cathode), a negative electrode (i.e., anode), a separator that separates the cathode and anode, and an electrolyte that is in electrochemical communication with the cathode and anode. In the case of a lithium secondary battery, lithium ions are transferred from the anode to the cathode through the electrolyte when the secondary battery is being discharged, i.e., used in its particular application. During the discharge process, electrons are withdrawn from the anode and transferred to the cathode through an external circuit. During charging or recharging of the secondary battery, lithium ions are transferred from the cathode to the anode through the electrolyte.

A new lithium-ion cell or battery is initially in a discharged state. During the first charge of a lithium-ion cell, lithium migrates from the cathode material to the anode active material. The lithium that migrates from the cathode to the anode reacts with the electrolyte material at the surface of the graphite anode, forming a passive film on the anode. The passive film formed on the graphite anode is the solid electrolyte interface (SEI). During subsequent discharges, the lithium consumed by the formation of the SEI is not transferred back to the cathode. This results in a lithium-ion cell with a lower capacity than the initial charge capacity because some of the lithium was consumed by the formation of the SEI. The capacity of the lithium-ion cell is reduced when the available lithium is partially consumed in the first cycle. This phenomenon is called irreversible capacity and is known to consume about 10% to more than 20% of the capacity of a lithium-ion cell. Thus, after the initial charge of a lithium-ion cell, the lithium-ion cell loses about 10% to more than 20% of its capacity.

One solution is to prelithiate the anode using stabilized lithium metal powder. For example, lithium powder can be stabilized by passivating the metal powder surface with carbon dioxide, as described in U.S. Pat. Nos. 5,567,474, 5,776,369 and 5,976,403, the entire disclosures of which are incorporated herein by reference. Lithium metal powder passivated with _CO2 can only be used in air with low moisture levels for a limited period of time before the lithium metal content is reduced due to the reaction of lithium metal with air. Another solution is to apply a coating such as fluorine, wax, phosphorus or polymer to the lithium metal powder, as described, for example, in U.S. Pat. Nos. 7,588,623, 8,021,496, 8,377,236 and U.S. Patent Application Publication No. 2017/0149052.

However, there is still a need for solid-state batteries with lithiated or prelithiated components to increase energy density and improve safety and manufacturability.

To this end, the present invention provides a solid-state battery having one or more components that are prelithiated, i.e., lithiated with a printable lithium composition. Solid-state batteries that include the printable lithium composition have increased energy density, improved safety, and improved manufacturability.

In one embodiment, the battery may include a cathode and a composite anode. The composite anode may include a lithium metal anode and at least one interfacial layer between the lithium metal anode and the solid electrolyte. For example, the lithium metal anode and/or interfacial layer may be formed from a printable lithium composition composed of lithium metal powder, a polymer binder compatible with the lithium metal powder, a rheology modifier compatible with the lithium metal powder, and a solvent compatible with the lithium metal powder and the polymer binder. The interfacial layer may be added to the surface of the solid electrolyte to improve the uniformity of its surface and optimize the contact between the surface of the lithium metal anode and the surface of the solid electrolyte, resulting in better battery performance. In another embodiment, the anode may be formed from a printable lithium formulation and act as an interfacial layer.

In another embodiment, the lithium metal anode and/or interfacial layer may be comprised of a foil or film formed from a printable lithium composition comprising a lithium metal powder, a polymeric binder compatible with the lithium metal powder, and a rheology modifier compatible with the lithium metal powder and the polymeric binder, the rheology modifier providing a three-dimensional support structure that prevents degradation of the foil or film and improves durability of the foil or film when coated with the printable lithium composition.

In some embodiments, the cathode can be a composite of a non-lithiated cathode material and printable Li metal. For example, a sulfur cathode can be pre-lithiated with printable Li, and this composite cathode can be paired with a non-lithiated or pre-lithiated anode in a solid-state battery.

FIG. 1 is a schematic diagram of a solid-state battery according to one embodiment of the present invention.

13 is a temperature and pressure profile for reactivity testing of SLMP/styrene butadiene/toluene printable lithium compositions.

1 is a plot showing the cycling performance of a pouch cell with a thin lithium film derived from printable lithium versus a commercially available lithium thin foil as the anode.

1 is a plot showing the cycling voltage of a solid-state coin battery having a LiFePO ₄ (LFP) cathode, a Li ₁₀ GeP ₂ S ₁₂ (LGPS) solid electrolyte, and an anode comprising a printable lithium composition.

1 is a plot showing charge and discharge capacity versus cycle number at 70° C. for one embodiment.

These and other aspects of the invention will now be described in more detail with reference to the descriptions and methods provided herein. It is understood that the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

The terms used in the description of the invention herein are for the purpose of describing particular embodiments only and are not intended to be limiting of the invention. When used in the description of the embodiments of the invention and in the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Also, as used herein, "and/or" denotes and includes any and all possible combinations of one or more of the associated listed items.

When used herein to indicate a measurable value, such as the amount of a compound, dosage, time, temperature, and the like, the term "about" is intended to include variables of 20%, 10%, 5%, 1%, 0.5% or even 0.1% of the specified amount. Unless otherwise defined, all terms, including technical and scientific terms, used in the description have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

As used herein, the terms "comprise," "comprises," "comprising," "include," "includes," and "including" specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

As used herein, the term "consisting essentially of" (and grammatical variations thereof) as applied to the compositions and methods of the present invention means that the composition/method may include additional components so long as the additional components do not substantially alter the composition/method. The term "substantially alter" as applied to a composition/method indicates an increase or decrease in the efficacy of the composition/method by at least about 20% or more.

All patents, patent applications and publications referred to herein are hereby incorporated by reference in their entirety. In the event of a conflict in terminology, the present specification controls.

1, in accordance with one embodiment of the present invention, a solid-state battery 10 is provided that includes an anode 12, a cathode 14, and a solid-state electrolyte 16. The solid-state battery may further include an anode current collector 20 and a cathode current collector 22. In one embodiment, the printable lithium composition may be applied or deposited onto the current collector, electrode, and/or solid-state electrolyte of a solid-state battery. For example, the printable lithium composition may be used to form monolithic lithium metal anodes of various thicknesses and widths for use in solid-state batteries, including the solid-state batteries described in U.S. Pat. Nos. 8,252,438 and 9,893,379, which are incorporated herein by reference in their entireties. In yet another embodiment, the printable lithium composition may be applied or deposited to form a solid-state electrolyte for a solid-state battery, including a combination of the printable lithium composition and a polymeric or ceramic material to form the solid-state electrolyte. The printable lithium composition includes lithium metal powder, one or more polymeric binders, one or more rheology modifiers, and may further include a solvent or co-solvent.

The printable lithium composition may be applied to a current collector, electrode, or solid electrolyte in a variety of ways, including extrusion, coating, printing, painting, dipping, and spraying, as disclosed in U.S. Patent Application Publication No. 16/359,725, and incorporated herein by reference in its entirety. For example, an anode may be lithiated or prelithiated by printing the printable lithium composition onto the anode or current collector, which can form a lithium thin film of controlled thickness and width, or by coating the anode with the printable lithium composition.

The surface of a typical solid electrolyte may be rough depending on the choice of solid electrolyte, and therefore good contact may not be formed between the solid electrolyte and the lithium (foil) anode, resulting in a suboptimal interface and poor battery performance. In one embodiment, the printable lithium composition is used to prelithiate the solid electrolyte to modify the solid electrolyte surface and thus form an interface layer with improved adhesion to the lithium anode. In another embodiment, the interface layer may comprise a foil or film formed from the printable lithium composition. The printable lithium composition forming the interface layer may be applied to various types of solid electrolytes, including polymer, glass and ceramic electrolytes. Having a modified solid electrolyte surface optimizes the contact between the solid electrolyte and the lithium anode, improves the interface between the solid electrolyte and the lithium anode, and results in better battery performance by reducing the impedance rise caused by loss of contact between the lithium and the electrolyte due to the increase in volume of lithium during cycling.

Another example of a solid-state secondary battery may include a cathode capable of electrochemically absorbing and releasing lithium, an anode capable of electrochemically absorbing and releasing lithium, the anode including an active material layer including an active material, the active material layer being supported on a current collector, and a non-aqueous electrolyte, as described in U.S. Pat. No. 7,914,930, the entirety of which is incorporated herein by reference. The method includes reacting lithium with the active material of the anode by contacting a printable lithium composition with a surface of the active material layer of the anode, and then combining the anode with the cathode to form an electrode assembly.

As disclosed in U.S. Patent Application Publication No. 16/359,707, which is incorporated herein by reference in its entirety, the printable lithium composition includes lithium metal powder, a polymer binder, a rheology modifier, and may further include a solvent. The polymer binder may be compatible with the lithium metal powder. The rheology modifier may be compatible with the lithium metal powder and the polymer binder. The solvent may be compatible with the lithium metal powder and the polymer binder.

The lithium metal powder may be in the form of a finely divided powder. The lithium metal powder typically has an average particle size of less than about 80 microns, often less than about 40 microns, and sometimes less than about 20 microns. The lithium metal powder may be a low pyrophoric stabilized lithium metal powder (SLMP®) available from FMC Lithium Corp. The lithium metal powder may also include a substantially continuous layer or coating of fluorine, wax, phosphorus, or polymer or combinations thereof (as disclosed in U.S. Pat. Nos. 5,567,474, 5,776,369, and 5,976,403). The lithium metal powder has a significantly reduced reactivity with moisture and air.

The lithium metal powder may be alloyed with a metal. The lithium metal powder may be alloyed with, for example, an element from Groups I to VIII. Examples of suitable elements from Group IB may include silver or gold. Examples of suitable elements from Group IIB may include zinc, cadmium, or mercury. Examples of suitable elements from Group IIA of the periodic table may include beryllium, magnesium, calcium, strontium, barium, and radium. Examples of Group IIIA elements that may be used in the present invention may include boron, aluminum, gallium, indium, or thallium. Examples of Group IVA elements that may be used in the present invention may include carbon, silicon, germanium, tin, or lead. Examples of Group VA elements that may be used in the present invention may include nitrogen, phosphorus, or bismuth. Examples of suitable elements from Group VIIIB may include palladium or platinum.

The polymer binder is selected to be compatible with the lithium metal powder. "Comparative with" or "compatibility" conveys that the polymer binder will not react violently with the lithium metal powder creating a safety hazard. The lithium metal powder and the polymer binder react to form a lithium-polymer complex, which should be stable at various temperatures. It is recognized that the amount (concentration) of lithium and polymer binder contributes to stability and reactivity. The polymer binder may have a molecular weight of about 1,000 to about 8,000,000, and often has a molecular weight of 2,000,000 to 5,000,000. Suitable polymeric binders may include one or more of poly(ethylene oxide), polystyrene, polyisobutylene, natural rubber, butadiene rubber, styrene-butadiene rubber, polyisoprene rubber, butyl rubber, hydrogenated nitrile butadiene rubber, epichlorohydrin rubber, acrylate rubber, silicone rubber, nitrile rubber, polyacrylic acid, polyvinylidene chloride, polyvinyl acetate, ethylene propylene diene termonomer, ethylene vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene terpolymer, polybutene. The binder may be a wax.

The rheology modifier is selected to be compatible with the lithium metal powder and the polymer binder. The rheology modifier provides rheological properties such as viscosity. The rheology modifier may also be multifunctional and provide electrical conductivity, improved capacity and/or improved stability/safety depending on the selection of the rheology modifier. To this end, the rheology modifier may be a combination of two or more compounds to provide different or additional properties. Examples of rheology modifiers may include one or more of carbon black, carbon nanotubes, graphene, silicon nanotubes, graphite, hard carbon and mixtures, fumed silica, titanium dioxide, zirconium dioxide and other Group IIA, IIIA, IVB, VB and VIA elements/compounds and mixtures or blends thereof.

Solvents that are compatible with lithium may include acyclic hydrocarbons, cyclic hydrocarbons, aromatic hydrocarbons, symmetric ethers, asymmetric ethers, cyclic ethers, alkanes, sulfones, mineral oils and mixtures, blends or co-solvents thereof. Examples of suitable acyclic and cyclic hydrocarbons include n-hexane, n-heptane, cyclohexane, and the like. Examples of suitable aromatic hydrocarbons include toluene, ethylbenzene, xylene, isopropylbenzene (cumene), and the like. Examples of suitable symmetric, asymmetric and cyclic ethers include di-n-butyl ether, methyl t-butyl ether, tetrahydrofuran, glyme, and the like. Commercially available synthetic isoparaffinic hydrocarbon solvents with adjusted boiling ranges, such as Shell Sol® (Shell Chemicals) and Isopar® (Exxon), are also suitable.

The polymer binder and solvent are selected to be compatible with each other and with the lithium metal powder. In general, the binder or solvent should be non-reactive with the lithium metal powder, or should be present in an amount such that any reaction is kept to a minimum and violent reactions are avoided. The binder and solvent should be compatible with each other at the temperatures at which the printable lithium composition is made and used. Preferably, the solvent (or co-solvent) is sufficiently volatile to evaporate readily from the printable lithium composition (e.g., in slurry form) to dry the printable lithium composition (slurry) after application.

The components of the printable lithium composition may be mixed together as a slurry or paste to provide a high concentration of solids. Thus, the slurry/paste may be in the form of a concentrate where not all of the solvent is added prior to the time of deposition or application. In one embodiment, the lithium metal powder should be uniformly suspended in the solvent such that upon application or deposition, a substantially uniform distribution of lithium metal powder is deposited or applied. The dry lithium powder may be dispersed, such as by vigorous agitation or stirring to apply high shear forces.

In another embodiment, a mixture of polymer binders, rheology modifiers, coating agents and other possible additives for lithium metal powder may be formed and introduced to contact the lithium droplets during dispersion at a temperature above the lithium melting point or at a lower temperature after cooling of the lithium dispersion, as described in U.S. Pat. No. 7,588,623, the disclosure of which is incorporated by reference in its entirety. The lithium metal thus modified may be introduced in dry powder form or in solution form in a selected solvent. It is understood that using a combination of various process parameters, specific coating and lithium powder properties for specific applications may be achieved.

Conventional prelithiation surface treatments require compositions with very low binder content and very high lithium, see, for example, U.S. Patent No. 9,649,688, the disclosure of which is incorporated by reference in its entirety. However, embodiments of printable lithium compositions according to the present invention can accommodate higher binder ratios, including up to 20 percent on a dry basis. Various properties of the printable lithium composition, such as viscosity and flow, can be modified by increasing the binder and modifier content up to 50% on a dry basis without losing the electrochemical activity of the lithium. Increasing the binder content facilitates the loading and flow of the printable lithium composition during printing. The printable lithium composition can include about 50% to about 98% by weight of lithium metal powder and about 2% to about 50% by weight of polymeric binder and rheology modifier on a dry weight basis. In one embodiment, the printable lithium composition includes about 60% to about 90% by weight of lithium metal powder and about 10% to about 40% by weight of polymeric binder and rheology modifier. In another embodiment, the printable lithium composition comprises about 75% to about 85% by weight of lithium metal powder and about 15% to about 30% by weight of a polymer binder and a rheology modifier.

An important aspect of the printable lithium composition is the rheological stability of the suspension. Because lithium metal has a low density of 0.534 g/cc, it is difficult to prevent separation of the lithium powder from the solvent suspension. By selecting the loading of lithium metal powder, the type and amount of polymer binder and conventional modifiers, the viscosity and rheology can be adjusted to produce a stable suspension of the present invention. Preferred embodiments do not exhibit separation beyond 90 days. This can be achieved by designing the composition with a zero shear viscosity in the range of 1×10 ⁴ cps to 1×10 ⁷ cps, which keeps the lithium in suspension, especially during storage. When shear is applied, the suspension viscosity decreases to a level suitable for use in printing or coating applications.

The resulting printable lithium composition may preferably have a viscosity of about 20 to about 20,000 cps, sometimes a viscosity of about 100 to 2,000 cps, and often a viscosity of about 700 to about 1,100 cps at 10 s ^-1 . At such viscosities, the printable lithium composition is a flowable suspension or gel. The printable lithium composition preferably has a long shelf life at room temperature and is stable against metallic lithium loss at temperatures up to 60°C, often up to 120°C, and occasionally up to 180°C. The printable lithium composition may separate somewhat over time, but can be returned to a suspension by gentle agitation and/or application of heat.

In one embodiment, the printable lithium composition comprises, on a solution basis, about 5 to 50 percent lithium metal powder, about 0.1 to 20 percent polymer binder, about 0.1 to 30 percent rheology modifier, and about 50 to 95 percent solvent. In one embodiment, the printable lithium composition comprises, on a solution basis, about 15 to 25 percent lithium metal powder, about 0.3 to 0.6 percent polymer binder with a molecular weight of 4,700,000, about 0.5 to 0.9 percent rheology modifier, and about 75 to 85 percent solvent. Typically, the printable lithium composition is applied or deposited to a thickness of about 50 microns to 200 microns before pressing. After pressing, the thickness can be reduced to about 1 to 50 microns. Examples of pressing techniques are described, for example, in U.S. Patent Nos. 3,721,113 and 6,232,014, which are incorporated herein by reference in their entireties.

Another aspect of the invention relates to a solid-state battery in which the current collector, electrode and/or solid electrolyte of the solid-state battery may comprise a substrate coated with a printable lithium composition, as described in U.S. Provisional Application No. 62/864,739 and U.S. Patent Application No. (Attorney Docket No. 073396.1263, filed concurrently herewith), both of which are incorporated herein by reference in their entirety. The printable lithium composition includes a lithium metal powder, a polymer binder compatible with the lithium metal powder, and a rheology modifier compatible with the lithium metal powder and the polymer binder, the rheology modifier being dispersible in the composition and providing a three-dimensional support structure to prevent degradation and improve the durability of the anode when made with the printable lithium composition.

In one embodiment, the rheology modifier is carbon-based. For example, the rheology modifier may be comprised of carbon nanotubes to provide structure for the coated electrode. In another embodiment, carbon black may be added as a rheology modifier. Without wishing to be limited by theory, it is believed that the carbon-based rheology modifier may also provide a conductive network between the lithium particles after pressing, effectively increasing the surface area during device operation, reducing surface current density, and providing a path for lithium ions to deposit in the bulk, not just on the surface of the foil as occurs with normal lithium foils. Other examples of suitable rheology modifiers may include non-carbon-based materials, including titanium oxide and silicon oxide. For example, silicon structures such as nanotubes or nanoparticles may be added as rheology modifiers to provide three-dimensional structure and/or additional capacity. The rheology modifier may also increase the durability of the layer (i.e., coating, foil or film) formed from the printable lithium composition by preventing mechanical degradation, allowing for faster charging.

In one embodiment, the printable lithium composition may be applied to a substrate, such as an energy storage device substrate. Examples may include current collectors, anodes, cathodes, and electrolytes. Examples of electrolytes may include solid electrolytes, polymer electrolytes, glass electrolytes, and ceramic electrolytes. In one example, the printable lithium composition may be applied or deposited to prelithiate an anode or cathode. The prelithiated anode or cathode may be incorporated into an energy storage device, such as a capacitor or battery. In another example, the substrate may be a lithium anode. For example, the lithium anode may be a flat lithium metal anode, or a lithium-carbon anode, such as an amine-functionalized lithium-carbon film, as described in Niu et al. [Nature Nanotechnology, Vol. 14, pgs. 594-201 (2019); DOI: 10.1038/s41565-019-0427-9], which is incorporated herein by reference in its entirety.

The printable lithium composition can be applied or deposited to form a solid electrolyte for a solid-state battery, including combinations of the printable lithium composition with a polymeric material, a glass material, or a ceramic material to form a solid electrolyte or a composite solid electrolyte. For example, the printable lithium composition and a polymeric material may be co-extruded to create a solid electrolyte film, optionally including other active electrolyte materials.

In another embodiment, the substrate comprises an electrode coated with the printable lithium composition and may further include a protective layer between the lithium layer and the electrolyte, such as the protective layer described in U.S. Pat. No. 6,214,061, which is incorporated herein by reference in its entirety. The protective layer may be a glassy or amorphous material capable of conducting lithium ions and suitable for preventing contact between the lithium surface and the electrolyte. Examples of suitable protective layers include lithium silicate, lithium borate, lithium aluminate, lithium phosphate, lithium phosphorus oxynitride, lithium silicosulfide, lithium borosulfide, lithium aminosulfide, and lithium phosphosulfide. The protective layer may be applied onto the electrode surface by a physical or chemical deposition process. The printable lithium composition may be applied onto the protective layer as a coating, foil, or film. In one embodiment, the protective layer may separate the lithium layer and the electrolyte, and the electrolyte may be composed of a substrate coated with the printable lithium composition. The formulation may be a vitreous or amorphous material capable of conducting lithium ions and suitable for preventing contact between the lithium surface and the electrolyte during charge/discharge cycles, as described by Li et al. [Joule, Vol. 3, No. 7, pgs. 1637-1646 (2019), DOI: 10.1016/j.joule.2019.05.022], the entire contents of which are incorporated herein by reference, may be used.

An embodiment may include a battery having a scalable three-dimensional (3D) lithium metal anode, such as that disclosed by Liu et al. [Energy Storage Materials, Vol. 16, pgs. 505-511 (2019), DOI: 10.1016/j.ensm. 2018.09.021], which is incorporated herein by reference in its entirety, and the cathode, electrolyte, 3D lithium metal anode, or combinations thereof, may each include a substrate coated with a printable lithium composition.

Another embodiment may include a battery having a cathode, electrolyte, and a lithium anode modified with ZnI2 as disclosed by Kolensikov et al. [Journal of the Electrochemical Society, vol. 166, no. 8, pages A1400-A1407 (2019), DOI: 10.1149/2.0401908jes], which is incorporated herein by reference in its entirety. The lithium anode may be prepared by applying a printable lithium composition onto a copper foil and modified by contacting _the foil with _ZnI2 in a tetrahydrofuran (THF) solution.

In another embodiment, the substrate may include a silicon-nanotube anode as described in Forney et al. [Nanoletters, Vol. 13, no. 9, pages 4158-4163 (2013), DOI: 10.1021/nl40176d], incorporated herein by reference. For example, the silicon nanotube anode may further include a lithium layer, such as a coating, foil, or film formed from a printable lithium composition.

The polymer binder is selected to be compatible with the lithium metal powder. "Compatible with" or "compatible" conveys that the polymer binder will not react violently with the lithium metal powder creating a safety hazard. The lithium metal powder and the polymer binder react to form a lithium-polymer complex, which should be stable at various temperatures. It is recognized that the amount (concentration) of lithium and polymer binder contributes to stability and reactivity. The polymer binder may have a molecular weight of about 1,000 to about 8,000,000, and often has a molecular weight of 2,000,000 to 5,000,000. Suitable polymeric binders may include one or more of poly(ethylene oxide), polystyrene, polyisobutylene, natural rubber, butadiene rubber, styrene-butadiene rubber, polyisoprene rubber, butyl rubber, hydrogenated nitrile butadiene rubber, epichlorohydrin rubber, acrylate rubber, silicone rubber, nitrile rubber, polyacrylic acid, polyvinylidene chloride, polyvinyl acetate, ethylene propylene diene termonomer, ethylene vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene terpolymer, polybutene. The binder may be a wax.

The rheology modifier is selected to be compatible with the lithium metal powder and the polymer binder and dispersible in the composition. A preferred embodiment of the printable lithium composition includes a carbon-based rheology modifier, such as carbon nanotubes. The use of carbon nanotubes can also provide a three-dimensional support structure and conductive network for the lithium anode when coated with the printable lithium composition, increasing its surface area. Another support structure may be as described by Cui et al. [Science Advances, Vol. 4, no. 7, page 5168, DOI: 10.1126/sciadv. aat 5168], which is incorporated herein by reference in its entirety, using hollow carbon spheres as stable hosts that prevent parasitic reactions and result in improved cycling behavior. Yet another support structure may be nanowires, as described in U.S. Pat. No. 10,090,512, which is incorporated herein by reference in its entirety. Other compatible carbon-based rheology modifiers include carbon black, graphene, graphite, hard carbon, and mixtures or blends thereof.

Additional rheology modifiers may be added to the composition to adjust properties such as viscosity and flow under shear conditions. The rheology modifier may also provide electrical conductivity, improved capacity and/or improved stability/safety, depending on the selection of the rheology modifier. To this end, the rheology modifier may be a combination of two or more compounds to provide different or additional properties. Examples of rheology modifiers may include one or more of silicon nanotubes, fumed silica, titanium dioxide, zirconium dioxide and other Group IIA, IIIA, IVB, VB and VIA elements/compounds and mixtures or blends thereof. Other additives for improving lithium ion conductivity may be used, such as electrochemical device electrolyte salts, such as lithium perchlorate ( _LiClO4 ), lithium hexafluorophosphate ( _LiPF6 ), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate ( _LiBF4 ), lithium nitrate ( _LiNO3 ), lithium bis(oxalato)borate (LiBOB), lithium trifluoromethanesulfonimide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

In another embodiment, a mixture of polymer binders, rheology modifiers, coating agents and other possible additives for lithium metal powder may be formed and introduced to contact the lithium droplets during dispersion at a temperature above the lithium melting point or at a lower temperature after cooling of the lithium dispersion, as described in U.S. Pat. No. 7,588,623, the disclosure of which is incorporated by reference in its entirety. The lithium metal thus modified may be introduced in dry powder form or in solution form in a selected solvent. It is understood that using a combination of various process parameters, specific coating and lithium powder properties for specific applications may be achieved.

The printable lithium composition may be in the form of a foil or film, as described in U.S. Provisional Application No. 62/864,739, which is incorporated herein by reference in its entirety. In one embodiment, a foil or film formed from the printable lithium composition may be applied to a substrate for use in one or more components in a battery. For example, the battery may include a cathode, an electrolyte, and an anode having a substrate coated with the printable lithium composition. The electrolyte may have a concentration of greater than 1 M, often greater than about 3 M, and sometimes greater than 5 M. Examples of suitable electrolytes include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate (LiBF ₄ ), lithium nitrate (LiNO ₃ ), lithium bis(oxalato)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium trifluoromethanesulfonimide (LiTFSI), and mixtures or blends thereof. An illustrative example is a battery having a cathode and an anode with a substrate coated with a printable lithium composition and a high-concentration electrolyte, where LiFSI is the primary salt of the high-concentration electrolyte. Another example is a battery having a cathode and an anode with a substrate coated with a printable lithium composition and a two-salt liquid electrolyte, as described in Weber et al. [Nature Energy, Vol. 4, pgs. 683-689 (2019), DOI: 10.1038/s41560-019-0428-9] and U.S. Patent Application Publication No. 2019/0036171, both of which are incorporated herein by reference. The two-salt liquid electrolyte may be composed of lithium difluoro(oxalato)borate (LiDFOB) and _LiBF4 and may have a concentration of about 1M. The two-salt electrolyte may provide improved initial capacity retention and improved cycling performance.

In one embodiment, the printable lithium composition is deposited or applied to an active anode material on a current collector, i.e., forming a prelithiated anode. Suitable active anode materials include graphite and other carbon-based materials, alloys such as tin/cobalt, tin/cobalt/carbon, silicon-carbon, various silicone/tin-based composite compounds, germanium-based composites, titanium-based composites, elemental silicon and germanium. The anode material can be a foil, mesh or foam. Application can be by spraying, extrusion, coating, printing, painting, dipping and spraying, as disclosed in co-pending U.S. Patent Application Publication No. 16/359,725, which is incorporated herein by reference in its entirety.

In one embodiment, the anode active material and the printable lithium composition are provided together and extruded onto a current collector (e.g., copper, nickel, etc.). For example, the anode active material and the printable lithium composition can be mixed and coextruded together. Examples of anode active materials include graphite, graphite-SiO, graphite-SnO, SiO, hard carbon, and other lithium ion battery and lithium ion capacitor anode materials. In another embodiment, the anode active material and the printable lithium composition are coextruded to form a layer of the printable lithium composition on the current collector. Deposition of the printable lithium composition, including the extrusion techniques described above, can include deposition in a wide variety of patterns (e.g., dots, stripes), thicknesses, widths, etc. For example, the printable lithium composition and the anode active material can be deposited as a series of stripes, as described in U.S. Publication No. 2014/0186519, which is incorporated herein by reference in its entirety. The stripes form a 3D structure that corresponds to the expansion of the anode active material during lithiation. For example, silicon can expand 300 to 400% during lithiation. Such swelling can potentially adversely affect the anode and its performance. By depositing printable lithium as stripes in the Y plane, in an alternating pattern between the stripes of the silicon anode, the silicon anode material can expand in the X plane, mitigating electrochemical polishing and loss of electrical contact of the particles. Thus, the printing method can provide a buffer against expansion. In another example of using a printable lithium formulation to form an anode, the lithium formulation can be co-extruded in layers with a cathode and a separator to produce a solid-state battery.

In one embodiment, the anode may be prelithiated using a printable lithium composition, as described in U.S. Pat. No. 9,837,659, which is incorporated herein by reference in its entirety. For example, the method includes disposing a layer of the printable lithium composition adjacent to a surface of a pre-manufactured/pre-formed anode. The pre-manufactured electrode includes an electroactive material. In one variation, the printable lithium composition may be applied to a carrier/substrate via a deposition process. The carrier substrate on which the layer of the printable lithium composition may be disposed may be selected from the group consisting of, by way of non-limiting example, a polymer film (e.g., polystyrene, polyethylene, polyethylene oxide, polyester, polypropylene, polypolytetrafluoroethylene), a ceramic film, a copper foil, a nickel foil, or a metal foam. Heat may then be applied to the printable lithium composition layer on the substrate or pre-formed anode. The printable lithium composition layer on the substrate or pre-formed anode may be further compressed together under pressure. The heat and optional pressure facilitate the migration of lithium to the surface of the substrate or anode. When transferred to a prefabricated anode, pressure and heat can cause mechanical lithiation, especially if the prefabricated anode contains graphite. In this way, lithium is transferred to the electrode and incorporated into the active material for favorable thermodynamics.

In further embodiments, at least a portion of the printable lithium composition can be provided to the anode active material prior to the battery formation process. That is, the anode can include a partially lithium-loaded silicon-based active material, as described in U.S. Patent Application Publication No. 2018/0269471, which is incorporated herein by reference, where the partially loaded active material has a selected degree of lithium loading, such as by intercalation/alloying.

Some embodiments of the battery may utilize a composite cathode. For example, the battery may include a sulfur cathode as described in U.S. Pat. Nos. 9,882,238 and 9,917,303, which are incorporated herein by reference in their entireties.

In one embodiment, the printable lithium composition may be incorporated into a three-dimensional electrode structure, as described in U.S. Patent Application Publication No. 2018/0013126, which is incorporated herein by reference in its entirety. For example, the printable lithium composition may be incorporated into a three-dimensional porous anode, a porous current collector, or a porous polymer or ceramic membrane, and the printable lithium composition may be deposited therein. The printable lithium composition may be incorporated into a solid electrolyte, which may be combined with or applied to a lithium metal anode to form a composite anode. The solid electrolyte may be applied as one or more interfacial ion-conducting electrolyte layers or interfaces to the lithium metal anode. An example is described in U.S. Patent No. 8,182,943, which is incorporated herein by reference in its entirety.

In another embodiment, the printable lithium composition may be incorporated into a three-dimensional electrode structure, as described in U.S. Patent Application Publication No. 2018/0013126, which is incorporated by reference in its entirety. The three-dimensional electrode may be a permeable composite material comprised of a support defining pores and an alkali metal deposit on the support, the alkali metal being deposited using the printable lithium composition. The three-dimensional electrode may have a porosity of about 1 vol.% to about 95 vol.% and a mean flow pore size ranging from about 1 nm to about 300 μm.

Another embodiment of the battery may include a composite anode formed using a pulsed electron beam, as described in U.S. Pat. No. 10,047,432, the entirety of which is incorporated herein by reference. For example, a pulsed electron beam may be used as a virtual cathode deposition (VCD) process applied to the anode material, where a three-dimensional porous anode structure is created using the electron beam. The three-dimensional structure formed from the pulsed electron beam may be a carbon allotrope (CALIB) for lithium-ion batteries. The CALIB structure may be co-deposited with lithium using a printable lithium composition to form a carbon polymorph.

In some embodiments, an electrode prelithiated with the printable lithium composition can be assembled into a cell with an electrode preloaded with lithium. A separator can be placed between each electrode. A current can be passed between the electrodes. For example, an anode prelithiated with the printable lithium composition of the present invention can be formed into a secondary battery, such as described in U.S. Pat. No. 6,706,447, which is incorporated by reference in its entirety.

The cathode is formed of an active material that is typically combined with a carbonaceous material and a binder polymer. The active material used in the cathode is preferably a material that can be lithiated. Preferably, non-lithiated materials, such as MnO ₂ , V ₂ O ₅ , MoS ₂ , metal fluorides or mixtures thereof, sulfur and sulfur composites, can be used as active materials. However, lithiated materials, such as LiMn ₂ O ₄ and LiMO ₂ , where M is Ni, Co or Mn, that can be further lithiated, can also be used. Non-lithiated active materials are preferred because of the wider selection of cathode materials in this configuration that can provide higher specific capacity, lower cost, and increased energy and power compared to conventional secondary batteries that include lithiated active materials.

Example 1
10 g of styrene butadiene rubber liquid (S-SBR Europrene Sol R 72613) is dissolved in 90 g of toluene (99% anhydrous, Sigma Aldrich) by stirring for 12 hours at 21° C. 6 g of a 10 wt % SBR (polymer binder) in toluene (solvent) solution is combined with 0.1 g of carbon black (Timcal Super P) (rheology modifier) and 16 g of toluene and dispersed in a Thinky ARE 250 planetary mixer at 2000 rpm for 6 minutes. 9.3 g of stabilized lithium metal powder (SLMP®, FMC Lithium Corp.) with a polymer coating of 20 to 200 nm and a d50 of 20 μm is added to this suspension and dispersed in a Thinky mixer at 1000 rpm for 3 minutes. The printable lithium is then filtered through a 180 μm opening stainless steel mesh. The printable lithium suspension is then coated onto a copper current collector with a wet thickness of 2 mils (about 50 μm) by doctor blade. Figure 3 is a plot showing the cycling performance of a pouch cell with a 20 micron lithium thin film from the printable lithium versus a commercial 50 micron lithium foil as the anode.

Example 2
10 g of ethylene propylene diene terpolymer (EPDM) (Dow Nordel IP 4725P) with a molecular weight of 135,000 is dissolved in 90 g of p-xylene (anhydrous 99%, Sigma Aldrich) by stirring for 12 hours at 21° C. 6 g of a 10 wt % EPDM (polymer binder) p-xylene (solvent) solution is combined with 0.1 g of TiO2 (Evonik Industries) (rheology modifier) and 16 g of toluene and dispersed in a Thinky ARE 250 planetary mixer at 2000 rpm for 6 minutes. 9.3 g of stabilized lithium metal powder (SLMP®, Corp.) with a polymer coating of 20 to 200 nm and a d50 of 20 μm is added to this suspension and dispersed in a Thinky mixer at 1000 rpm for 3 minutes. The printable lithium is then filtered through a 180 μm opening stainless steel mesh. The printable lithium composition is then coated onto a copper current collector with a wet thickness of 2 mils (about 50 μm) by doctor blade.

Example 3
1.5 g of PIB with a molecular weight of 1.27 M is dissolved in 85 g of toluene by stirring at 21° C. for 12 hours. Then, 1.5 g of carbon nanotubes are added to the solution and stirred continuously for about 1 hour to form a uniform suspension. 30 g of stabilized lithium metal powder (SLMP®, FMC Lithium Corp.) with a polymer coating of 20 to 200 nm and a d50 of 20 μm is added to the suspension and dispersed in a Thinky mixer at 1000 rpm for 3 minutes. The printable lithium suspension is then filtered through a 180 μm opening stainless steel mesh. The printable lithium composition is then printed onto a copper current collector with a wet thickness of 2 mils (about 50 μm) and a dry thickness of about 25 μm before lamination.

Shelf Life Stability The printable lithium components should be selected to ensure chemical stability for long shelf life at room temperature and stability at higher temperatures for shorter periods such as during shipping and drying processes. The stability of the printable lithium composition was tested using calorimetry. 1.5 g of SLMP was added to a Hastelloy ARC bomb sample container with a volume of 10 ml. 2.4 g of 4% SBR binder solution was added to the container. The container was equipped with a 24 Ω resistive heater and thermocouple to monitor and control the temperature of the sample. The bomb sample device was loaded into a 350 ml containment container with insulation. A Fauske Industries Advance Reactive Screening Systems Tool calorimeter was used to evaluate the compatibility of the printable lithium solution during a constant rate temperature ramp to 190° C. The temperature ramp rate was 2° C./min and the sample temperature was held at 190° C. for 60 minutes. The test was performed under 200 psi argon pressure to prevent solvent boiling. Figure 2 shows the temperature and pressure profile of the reactivity test of the SLMP/styrene butadiene/toluene printable lithium composition.

Printing Performance
The quality of a printable lithium composition in terms of printability is measured by flow consistency, which directly affects several factors, such as the ability of the composition to control the amount of lithium added to a substrate or electrode surface. A useful way to measure flow is flow conductance, which is a measure of the amount added per square centimeter that is related to the factors that control the amount of addition, namely the pressure during extrusion and the speed of the printer head. Flow conductance can be most simply thought of as the inverse of the resistance to flow.

This display allows comparisons between prints at variable pressures and speeds, and can alert you to the non-linear relationship between flow and pressure due to changes in flow conductance. These are important for scaling printable lithium loadings up or down depending on the needs of the anode or cathode. An ideal printable lithium composition would behave linearly with changes in extrusion pressure.

To test the printability, the printable lithium composition is filtered through a 180 μm opening stainless steel mesh and added to a Nordson EFD 10 ml syringe. The syringe is loaded into a Nordson EFD HP4x syringe dispenser and attached to a slot-die printhead. The slot-die printhead is equipped with a 100 μm to 300 μm thick shim with channel openings designed to deliver the desired printable lithium composition loading. The slot-die head is mounted on a Loctite 300 series robot. The printhead speed is set at 200 mm/s and the printing pressure is 20 to 200 psi argon depending on the shim and channel design. The printing length is 14 cm. In an example printing trial experiment, the printable lithium composition was printed 30 times from a single syringe with dispenser settings ranging from 80 psi to 200 psi. In this printing trial, the average flow conductance was 0.14

with a standard deviation of 0.02. While this printable composition does not behave perfectly linearly, the composition flow rate response to changes in dispenser pressure is predictable, allowing one of skill in the art to fine-tune the lithium loading to a desired level. Thus, at fixed dispenser pressure conditions, the lithium loading can be controlled with a high degree of consistency. For example,

For lithium metal prints, the coefficient of variation is approximately 5%.

Electrochemical Testing The effectiveness of prelithiation of the printable lithium composition can be evaluated by printing the required amount of printable lithium on the surface of a fabricated electrode. The amount of prelithiated lithium is determined by testing the anode material in a half-cell format and calculating the lithium required to compensate for first cycle losses due to SEI formation or other side reactions. To calculate the required amount of printable lithium, the capacity of the composition as lithium metal must be known, which for the composition used as an example is about 3600 mAh/g on a dry lithium basis.

The prelithiation effect is tested using a graphite-SiO/NCA pouch cell. The graphite-SiO anode sheet formulation is: artificial graphite (90.06%) + SiO (4.74%) + carbon black (1.4%) + SBR/CMC (3.8%). The capacity loading of the electrode is 3.59 mAh/ ^cm2 with a first cycle CE (coulombic efficiency) of 87%. Printable lithium is applied to the graphite-SiO anode at 0.15 mg/ ^cm2 lithium metal. The electrode is dried at 80°C for 100 minutes and then laminated with a roller gap of about 75% of the thickness of the electrode. A 7 cm x 7 cm electrode is die-cut from the printable lithiated anode sheet. The positive electrode formulation is: NCA (96%) + carbon black (2%) + PVdF (2%). The positive electrode is 6.8 cm x 6.8 cm with a capacity loading of 3.37 mAh/ ^cm2 . The NCA cathode has a first cycle CE of 90%. The anode to cathode capacity ratio is 1.06 with a baseline first cycle CE of 77% for all cells. Single layer pouch cells are assembled and 1M _LiPF6 /EC+DEC (1:1) is used as the electrolyte. The cells are preconditioned at 21°C for 12 hours and then a formation cycle is performed at 40°C. The formation protocol is 0.1C charge to 4.2V, constant voltage to 0.01C and 0.1C discharge to 2.8V. The described tests demonstrated a first cycle CE of 89%.

The printable Li anode is tested in a coin-type solid-state battery. The lithium anode electrode printed in Example 3 is dried at 110°C for 2 minutes in a drying room (RH<1% at 21°C) and cut into 12 mm disks. The cathode electrode is fabricated by pressing 6.6 mg of a powder mixture composed of LiFePO4 (LFP):Li10GeP2S12 (LGPS) = 7:3 wt% using a dry pellet die press (MTI Corp., EQ-Die-12D-B). The applied pressure is 50,000 psi. Then, 99.6 mg of LGPS powder is spread on the cathode electrode. This powder is then pressed with the same pressure (50,000 psi) into a solid electrolyte film. The Li anode is then placed on top of the solid electrolyte film and pressed using a pressure of 25,000 psi. The all-solid-state battery is then tested by cycling between 2.8 V and 3.8 V in a pressure-controlled (up to 20 MPa) split coin cell (MTI Corp., part number: EQ-PSC) at 70° C. at a current density of C/10. FIG. 4A shows the cycle voltage of a coin-type all-solid-state battery with an LFP cathode, LGPS solid electrolyte, and printable Li as the anode. FIG. 4A shows an all-solid-state battery with a typical LFP charge voltage plateau of 3.5 V and a discharge voltage plateau of about 3.4 V. FIG. 4B shows the charge and discharge capacity versus cycle number for the all-solid-state battery cycled at 70° C. The all-solid-state battery cycled well for the first 12 cycles.

Although the present technique is illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those skilled in the art that other embodiments and examples may perform similar functions and/or achieve similar results. All such equivalent embodiments and examples are within the spirit and scope of the present technique.

Claims (7)

1. A battery comprising a cathode and a composite anode, the composite anode comprising:
Lithium metal anode,
a solid electrolyte; and at least one interfacial layer between a surface of the lithium metal anode and a surface of the solid electrolyte, the at least one interfacial layer being in the form of a film or foil having a thickness of 1 to 50 micrometers formed from a printable lithium composition consisting of, on a dry weight basis, 50 wt % to 98 wt % lithium metal powder, 2 wt % to 50 wt % polymer binder , a rheology modifier , and a solvent ;
the polymer binder is one or more of poly(ethylene oxide), polystyrene, polyisobutylene, natural rubber, butadiene rubber, styrene-butadiene rubber, polyisoprene rubber, butyl rubber, hydrogenated nitrile butadiene rubber, epichlorohydrin rubber, acrylate rubber, silicone rubber, nitrile rubber, polyacrylic acid, polyvinylidene chloride, polyvinyl acetate, ethylene propylene diene termonomer, ethylene vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene terpolymer, and polybutene;
the rheology modifier is one or more of carbon black, carbon nanotubes, graphene, silicon nanotubes, graphite, hard carbon, and mixtures or blends thereof, or fumed silica, titanium dioxide, zirconium dioxide, and other Group IIA, IIIA, IVB, VB, and VIA elements/compounds, and mixtures or blends thereof ;
The solvent is an acyclic hydrocarbon, a cyclic hydrocarbon, an aromatic hydrocarbon, a symmetrical ether, an asymmetrical ether, a cyclic ether, an alkane, a sulfone, a mineral oil, and mixtures, blends or co-solvents thereof;
battery. The battery of claim 1, wherein the lithium metal anode is a lithium metal anode formed by coating a substrate with the printable lithium composition. The battery of claim 2, wherein the printable lithium composition forming the lithium metal anode comprises, by solution weight, 5 wt% to 50 wt% of the lithium metal powder, 0.1 wt% to 20 wt% of the polymer binder, 0.1 wt% to 30 wt% of the rheology modifier, and 50 wt% to 95 wt% of the solvent. The battery of claim 1, wherein the lithium metal anode is a three-dimensional anode. The battery of claim 2, wherein the substrate is flat. The battery of claim 2, wherein the substrate has a three-dimensional porous structure. A battery,
Cathode,
an anode formed from a printable lithium composition consisting of lithium metal powder , a polymer binder , a rheology modifier , and a solvent ; and at least one interfacial layer applied to the anode to form a composite anode;
the at least one interfacial layer is formed from a printable lithium composition consisting of 50% to 98% by weight lithium metal powder and 2% to 50% by weight polymer binder on a dry weight basis, and is in the form of a film or foil having a thickness of 1 to 50 micrometers;
the polymer binder is one or more of poly(ethylene oxide), polystyrene, polyisobutylene, natural rubber, butadiene rubber, styrene-butadiene rubber, polyisoprene rubber, butyl rubber, hydrogenated nitrile butadiene rubber, epichlorohydrin rubber, acrylate rubber, silicone rubber, nitrile rubber, polyacrylic acid, polyvinylidene chloride, polyvinyl acetate, ethylene propylene diene termonomer, ethylene vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene terpolymer, and polybutene;
the rheology modifier is one or more of carbon black, carbon nanotubes, graphene, silicon nanotubes, graphite, hard carbon, and mixtures or blends thereof, or fumed silica, titanium dioxide, zirconium dioxide, and other Group IIA, IIIA, IVB, VB, and VIA elements/compounds, and mixtures or blends thereof ;
The solvent is an acyclic hydrocarbon, a cyclic hydrocarbon, an aromatic hydrocarbon, a symmetrical ether, an asymmetrical ether, a cyclic ether, an alkane, a sulfone, a mineral oil, and mixtures, blends or co-solvents thereof;
battery.

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