Lithium garnet ribbon with low linear shrinkage after sintering and method of making same

Abstract

Disclosed herein are embodiments of a method in which a continuous green tape is fired in a furnace to form a ceramic ribbon of sintered lithium garnet. The continuous green tape includes particles of lithium garnet that are coated with a passivation layer or that have been tape-cast in a dry atmosphere. The continuous green tape has a length, a width, and a thickness. The width is greater than the thickness, and the length is greater than the width. The continuous green tape has a linear shrinkage of less than or equal to 25% after firing to form the ceramic ribbon.

Description

LITHIUM GARNET RIBBON WITH LOW LINEAR SHRINKAGE AFTER SINTERING AND METHOD OF MAKING SAMECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application No. 63 / 546,863 filed November 1, 2023, the content of which is incorporated herein by reference in its entirety.BACKGROUND

[0002] The disclosure relates to a lithium garnet material, and more particularly to methods to decrease the amount of linear shrinkage of a lithium garnet ribbon during sintering.

[0003] Lithium-ion battery cells typically include a cathode, an anode, and a permeable separation membrane disposed therebetween. A liquid electrolyte fills the volume in the cell, soaking the electrodes and separation membrane. Lithium ions, which are intercalated in the electrodes, move between the electrodes through the electrolyte during charging and discharging. Such lithium-ion battery cells may experience short circuits because of lithium dendrite formation through the permeable separation membrane, and the liquid electrolyte is generally volatile, which can lead to flammability issues. In contrast to such lithium-ion battery cells, solid-state batteries are considered more reliable and safer. In addition, solid-state batteries have higher energy density because of their smaller construction.SUMMARY

[0004] According to a first aspect, embodiments of the present disclosure relate to a method. In the method, a continuous green tape is fired in a furnace to form a ceramic ribbon of sintered lithium garnet. The continuous green tape comprises particles of lithium garnet that are coated with a passivation layer. The continuous green tape comprises a length, a width, and a thickness. The width is greater than the thickness, and the length is greater than the width. The continuous green tape has a linear shrinkage of less than or equal to 25% after firing to form the ceramic ribbon.

[0005] According to a second aspect, embodiments of the present disclosure relate to a method. In the method, particles of lithium garnet powder are calcined to remove lithium carbonate from outer surfaces of the particles. The calcined particles of lithium garnet are added to a slurry. The slurry is tape cast in a dry atmosphere to form a continuous green tape, and the continuous green tape is fired to form a ceramic ribbon of sintered lithium garnet. The continuous green tape comprises a length, a width, and a thickness. The width is greater thanthe thickness, and the length is greater than the width. The continuous green tape has a linear shrinkage of less than or equal to 25% after firing to form the ceramic ribbon.

[0006] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0007] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment s), and together with the description serve to explain principles and operation of the various embodiments. In the drawings:

[0009] FIG. 1 is a schematic representation of a solid-state battery cell including a solid electrolyte formed form a low-shrink lithium garnet ribbon, according to one or more exemplary embodiments;

[0010] FIG. 2 is a process flow diagram of a method for forming a continuous ribbon substrate of lithium garnet from pristine lithium garnet particles that were tape-cast in a dry atmosphere, according to an exemplary embodiment;

[0011] FIG. 3 is an illustrated process flow diagram of a method of forming a continuous ribbon substrate of lithium garnet from lithium garnet particles passivated through powder atomic layer deposition, according to one or more exemplary embodiments;

[0012] FIG. 4 is a scanning electron microscope (SEM) image of a cross-section of the ribbon of sintered lithium garnet, according to one or more exemplary embodiments;

[0013] FIGS. 5 and 6 depict X-ray diffraction (XRD) patterns for a pellet having an atomic layer deposition (ALD) coating according to one or more embodiments of the present disclosure and an uncoated pellet, respectively;

[0014] FIG. 7 provides a comparison of XRD patterns for the ALD coated pellet and the uncoated pellet of FIGS. 5 and 6 after sintering;

[0015] FIG. 8 is an SEM image of a top surface of the ALD coated pellet of FIG. 5 after sintering, according to one or more embodiments of the present disclosure;

[0016] FIG. 9 is an SEM image of a top surface of the uncoated pellet of FIG. 6 after sintering;

[0017] FIG. 10 is a graph of the lithium-ion concentration in solution over time for the ALD coated pellet of FIG. 5 and for the uncoated pellet of FIG. 6; and

[0018] FIG. 11 provides a comparison of a top surface of an uncoated, acid cleaned sintered pellet and an ALD coated sintered pellet immediately after treatment and after exposure to ambient air.DETAILED DESCRIPTION

[0019] Reference will now be made in detail to various embodiments of methods for reducing linear shrinkage of a green tape of lithium garnet when sintering to form a ceramic ribbon, examples of which are illustrated in the accompanying drawings. As will be discussed more fully below, lithium garnet is a promising material for solid state battery technology, but lithium garnet is highly reactive with moisture and carbon dioxide in ambient air. This reactivity makes processing lithium garnet difficult, particularly processing in a continuous, roll-to-roll manner. Because of the reactivity, the surface of the lithium garnet protonates and carbonates, increasing the volume of the lithium garnet. When in the form of particles, the increased volume makes achieving full density of sintered parts difficult and may lead to warpage of the green tape during sintering. According to embodiments of the present disclosure, the particles of lithium garnet are prevented from reacting with ambient air. In one method, pristine particles of lithium garnet are added to a slurry and tape cast in a dry atmosphere substantially free of volatiles, and in another method, the particles of lithium garnet are passivated with a thin, conformal coating applied through a powder atomic layer deposition process. Both of these methods reduce the linear shrinkage experienced by a green tape during sintering to 25% or less. These and other aspects and advantages of the disclosed methods of reducing linear shrinkage of a green tape during sintering will be described more fully below. The embodiments discussed herein are presented by way of illustration and not limitation.

[0020] Solid state batteries are considered a promising technology for secondary batteries with high capacity and high energy density for such applications as electric vehicles, consumer electronics, and energy storage, amongst other possibilities. Solid state batteries are expected to provide higher performance and higher safety at lower cost compared to conventional wet electrolyte lithium-ion batteries. FIG. 1 schematically depicts a solid-state battery (SSB) cell10 according to one or more exemplary embodiments. The SSB cell 10 includes a cathode 12, an anode 14, and a solid electrolyte 16. The solid electrolyte 16 is disposed between the cathode 12 and the anode 14. In one or more embodiments, the cathode 12 is comprised of a lithium- based oxide (such as lithium nickel cobalt aluminum oxide or lithium cobalt oxide), lithium- based phosphates (such as lithium iron phosphate), or vanadium oxide, for example. In one or more embodiments, the anode 14 is comprised of carbon, a titanate, a lithium alloy, or lithium metal. In one or more embodiments, the solid electrolyte 16 is comprised of a lithium garnet, such as lithium lanthanum zirconium oxide (LLZO) garnet having the formula of, e.g., Li?La3Zr20i2. LLZO garnet is considered a promising electrolyte for solid-state batteries because it has a high Li-ion conductivity (10‘4to 10'5Scm'1), a high Young’s modulus (150 GPa), and a wide electrochemical window (> 5 V vs. Li+ / Li), and compatibility with lithium metal.

[0021] In one or more embodiments, the SSB cell 10 also includes a cathode current collector 18 and an anode current collector 20. In one or more embodiments, the current collectors 18, 20 are comprised of aluminum, copper, nickel, titanium, or stainless steel, among other possibilities. In one or more embodiments, the current collectors 18, 20 are foil, meshed foils, foams, or carbon coated foils, amongst other possibilities.

[0022] The cathode 12, anode 14, solid electrolyte 16, and current collectors 18, 20 of the SSB cell 10 may be contained in a housing 22 (such as a pouch) having a positive lead 24 and a negative lead 26 in electrical communication with the cathode 12 and anode 14, respectively. In the embodiment shown in FIG. 1, the SSB cell 10 includes a single cathode 12, a single anode 14, and a single solid electrolyte 16, but in one or more other embodiments, the SSB cell 10 includes a single or a plurality of cathodes 16, a single or a plurality of anodes 14, and a single or a plurality of solid electrolytes 16, in particular in a stacked arrangement with alternating electrode (cathode 12 or anode 14) and solid electrolyte 16. A plurality of SSB cells 10 may be connected to form a battery, and multiple batteries may be connected to form a module, which can, in turn, be assembled into a battery pack. The battery pack can then be used as a power source for, e.g., an electric vehicle.

[0023] Continuous, roll-to-toll processes for the production of ribbon ceramics are advantageous because of the high throughput and ability to use such ribbons for downstream continuous, roll-to-roll processes. Because the solid electrolyte 16 of the SSB cell 10 is a ceramic material, it may be advantageous to produce the solid electrolyte 16 as a ribbon ceramic. However, lithium garnet is highly reactive with water and carbon dioxide in air,resulting in garnet protonation and surface carbonation (formation of H-LLZO and I^CCh). When lithium garnet particles are cast in a green tape, the reaction of the lithium garnet particles with air can cause debonding of the garnet particles with the polymer binder, embrittling the green tape and leading to the formation of cracks in the green tape. Additionally, the protonation and carbonation of the particle surface increases the volume and decreases the density of the lithium garnet particles. The increased volume is provided by volatile compounds that decompose during sintering, causing linear shrinkage of sintered ceramic ribbon relative to the green tape. A high linear shrinkage results in undesirable warpage of the sintered ribbon of lithium garnet.

[0024] Embodiments of the present disclosure relate to methods of reducing linear shrinkage of green tape during sintering. As will be described in detail below, a continuous substrate (i.e., strip or ribbon) of lithium garnet that is formed by (1) sintering a green tape produced from pristine lithium garnet particles tape-cast in a dry atmosphere or (2) sintering a green tape produced from lithium garnet particles passivated with a coating layer applied via powder atomic layer deposition (PALD). Both of the disclosed methods prevent the protonation and formation of lithium carbonate on the surface of the lithium garnet particles, which allows the continuous substrate of lithium garnet to be sintered to a higher density (i.e., lower porosity) and with less linear shrinkage.

[0025] Regarding the first method, FIG. 2 provides a process flow diagram of a method 100 of forming a ribbon of sintered lithium garnet. In one or more embodiments, a first step 101 of the method 100 involves obtaining pristine lithium garnet particles. As used herein, “pristine” refers to lithium garnet particles comprising at least 90 wt%, at least 92 wt% or at least 95 wt% of lithium garnet phase. Other phases may also be present in the pristine lithium garnet depending on the specific composition. For example, in LLZO lithium garnet, such other phase may include La2O3, La2Zr2O?, and Li2ZrO3, among other possibilities. Optionally, dopant elements may substitute at least one of Li, La, or Zr in LLZO, which may introduce still other minor phases. For example, the lithium garnet can comprise at least one of: (i) Li7-3aLa3Zr2LaOi2, with L = Al, Ga or Fe and 0<a<0.33; (ii) LiyLas-bZ^MbOn, with M = Bi, Ca, or Y and 0<b<l; (iii) Li7-cLa3(Zr2-cNc)Oi2, with N = In, Si, Ge, Sn, V, W, Te, Nb, or Ta and 0<c<l; (iv) Li7-xLa3(Zr2-xMx)Oi2, with M = In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg, Ca, or combinations thereof and 0<x<l, or a combination thereof. The lithium garnet compositions described herein are merely exemplary, and other lithium garnet compositions may also be used.

[0026] In one or more embodiments, the pristine lithium garnet particles are obtained by milling an ingot of lithium garnet. The ingot of lithium garnet may be produced by a solid- state reaction of oxide, hydroxide, and / or carbonate powders. For example, an ingot of tantalum-doped LLZO can be produced by mixing stoichiometric amounts of lithium carbonate (Li2COs), lanthanum oxide (La2Os), zirconium oxide (ZrCh), and tantalum oxide (Ta2Os) powders, calcining at a temperature of 950 °C for 5 hours, and heating to a temperature of 1200 °C for 5 hours. The ingot can then be milled to produce particles of lithium garnet having a median particle size (D50) in a range from 0.1 pm to 2 pm.

[0027] In one or more embodiments, the pristine lithium garnet particles are obtained by calcining previously-formed lithium garnet particles. For example, lithium garnet particles may be passivated with shells of lithium carbonate and lithium / proton exchanged garnet as described in U.S. Publication No. 2022 / 0384841 (“PASSIVATED LLZO PARTICLES AND TAPE CASTING OF LLZO FILMS,” filed May 28, 2021, and published on December 1, 2022), the entire contents of which are incorporated herein by reference thereto. Such passivated particles are then able to be stored in ambient air without concern for further reaction of the lithium garnet with water and carbon dioxide in the air. When forming a sintered ceramic ribbon of lithium garnet, the passivated lithium garnet particles can be converted to pristine garnet particles by calcining the passivated lithium garnet particles at a temperature of 800 °C for 2 hours. In one or more embodiments, calcining of the passivated lithium garnet particles is performed in an inert atmosphere (e.g., in an argon atmosphere).

[0028] After obtaining the pristine lithium garnet particles in the first step 101, a second step 102 of the method is to add the pristine lithium garnet particles to a slurry. In one or more embodiments, the slurry comprises a dispersant, a binder, and a solvent. In one or more embodiments, the slurry may further comprise a plasticizer.

[0029] In the slurry, the dispersant facilitates suspension of the pristine lithium garnet particles. The dispersant may also function as a wetting agent or a deflocculant in the slurry. In one or more embodiments the dispersant is a fatty acid, an ester, a terpineol, an alkyl sulphonate, an alkyl acryl sulphonate, a lignin sulphonate, or an amine functional molecule or polymer, amongst other possibilities. In one or more particular embodiments, the dispersant comprises a polyglycol polyester modified polyalkylene imine having an amine value of 48 mg KOH / g. An example of a commercially available dispersant suitable for use in the slurry is Disperbyk 2155 (BYK-Chemie GmbH, Wesel, Germany). Other dispersants may also be used to form the slurry.

[0030] In one or more embodiments, the solvent comprises an alkyl propionate, such as n-butyl propionate and / or n-propyl propionate.

[0031] In one or more embodiments, the organic binder comprises a synthetic resin, polymer, or copolymer, such as an acrylic resin, a carbon dioxide-based polymer, a polyvinyl butyral, a polyvinyl alcohol, a polyurethane, a methyl cellulose, a polystyrene, a styrene acrylate copolymer, or a dextrin, amongst other possibilities. In one or more particular embodiments, the binder comprises an iso-butyl methacrylate / n-butyl methacrylate resin. An example of a commercially available binder suitable for use in the slurry is Elvacite® 2046 (Mitsubishi Chemical America, Charlotte, NC).

[0032] In one or more embodiments, the slurry may further contain a plasticizer. The plasticizer can be used to increase green tape plasticity and decrease friction during handling and manufacture. Additionally, the plasticizer makes the green tape softer and more flexible. The plasticizer of the slurry can be a polar or nonpolar chemical or polymer, such as a phthalate, a phosphate, a carboxylic acid ester, an epoxidized fatty acid ester, a polymeric polyester, a modified polymer, a liquid rubber, or a paraffinic, aromatic, or naphthenic petroleum oil, among other possibilities. An example of a commercially available plasticizer suitable for use in the slurry is PL029 (Polymer Innovations, Inc., Vista, CA).

[0033] In one or more embodiments, the slurry comprises, per 100 parts of pristine lithium garnet, dispersant in an amount in a range from 2 to 4 parts and organic binder in an amount in a range from 15 to 20 parts of the organic binder. In one or more embodiments in which the slurry further comprises plasticizer, the plasticizer is present in an amount in a range from 4 to 6 parts per hundred of pristine lithium garnet, and in one or more such embodiments, the total amount of plasticizer and dispersant is present in an amount in a range from 6 to 10 parts per hundred of pristine lithium garnet.

[0034] In one or more embodiments, the method 100 includes a third step 103 of tape-casting the slurry in a dry atmosphere to form a green tape. In one or more embodiments, the green tape has a length, a width, and a thickness. The length is the longest dimension of the green tape, and the thickness is the shortest dimension of the green tape. In one or more embodiments, the width of the green tape is greater than the thickness, and the length of the green tape is greater than the width. In one or more embodiments, the green tape has any suitable thickness, such as a thickness in a range from 10 pm to 300 pm, in a range from 25 pm to 150 pm, in particular in a range from 40 pm to 130 pm. In one or more embodiments, the green tape has any suitable width, such as a width in a range from 1 cm to 100 cm, in particular in a range from 1 cm to 50 cm. in one or more embodiments, the green tape has any suitablelength, such as a length in a range from 10 cm to 100 m. Because the green tape is so much longer than wide and thick, the green tape may be described as “continuous,” especially in the context of roll-to-roll processing as described herein.

[0035] The reaction of lithium garnet with air starts with the reaction of lithium garnet with water in the air, and thus, the atmosphere is dry and substantially free of water. If reaction with water is avoided, then the garnet will not react with carbon dioxide at tape-casting temperatures. That is, garnet will react with carbon dioxide without water at temperatures of several hundreds of degrees, but tape-casting takes place at temperatures well below that. Nonetheless, in one or more embodiments, the atmosphere may also be free of carbon dioxide.

[0036] In one or more embodiments, a “dry” atmosphere is one in which the dew point is - 40 °C or less. In one or more embodiments, the dry atmosphere comprises 200 ppm of water or less, in particular 150 ppm of water or less, and most particularly 128 ppm of water or less. Further, in one or more embodiments, the atmosphere is substantially free of carbon dioxide. In one or more embodiments, the atmosphere comprises 50 ppm of carbon dioxide or less, in particular 10 ppm of carbon dioxide or less, and most particularly 5 ppm of carbon dioxide or less. In one or more embodiments, the atmosphere during tape casting comprises one or more such gases as N2, Ar, O2, and combinations thereof. In one or more embodiments, tape-cast green tape is dried in a dry atmosphere. During drying, the solvent evaporates and / or drains from the green tape, leaving the green tape containing the pristine lithium garnet particles, the dispersant, the binder, and the plasticizer (if included).

[0037] In a fourth step 104 of the method 100, the tape-cast green tape is fired in a furnace at a temperature in a range from 950 °C to 1300 °C to sinter the green tape to form the ribbon of lithium garnet. In one or more embodiments, the tape-cast green tape is sintered as it passes continuously through a furnace heated to the sintering temperature. In one or more embodiments, the temperature in the furnace is not controlled to provide temperature ramping and cooling cycles. As a result of sintering according to the present disclosure, the green tape exhibits linear shrinkage of less than or equal to 25%. By “linear shrinkage,” it is meant that, as a result of sintering, the green tape shrinks 25% or less across its width or across its length. In one or more embodiments, total shrinkage of the green tape may be higher than 25% (e.g., when considering green tape area to sintered ceramic area), but shrinkage across one linear dimension is 25% or less.

[0038] Regarding the second method, a passivation layer on the lithium garnet particles applied through powder atomic layer deposition (PALD) provides the particles and resultant green tapewith long-term stability in air. FIG. 3 provides an illustrated flow diagram of steps of a method 300 for passivating lithium garnet particles 310. As discussed above, the lithium garnet particles may be comprised of any of a variety of lithium garnet compositions, including with and without dopants.

[0039] In a first step 301 of the method 300, the lithium garnet particles 310 are coated with a passivation layer 312 via a PALD process, in particular a plasma-assisted PALD process. In one or more embodiments, any lithium carbonate on the surface of the particles is removed or transformed into lithium compounds through plasma treatment. In one or more embodiments, the plasma treatment is performed using an inert gas and a treatment gas. In one or more embodiments, the inert gas is at least one of argon (Ar), helium (He), or neon (Ne). In one or more embodiments, the treatment gas does not include a hydroxyl (OH ), such as water. In one or more embodiments, the treatment gas includes fluorine (F), oxygen (O), hydrogen (H), nitrogen (N), or chlorine (Cl), for example. Suitable gases that may be used as the treatment gas include oxygen gas (O2), ozone (O3), ammonia (NH3), sulfur hexafluoride (SFe), or nitrogen trifluoride (NF3). In one or more embodiments, the treatment gas is provided at a flow rate of 1 seem to 50 seem, in particular about 30 seem. In one or more embodiments, the inert gas is provided at a flow rate of 1 seem to 50 seem, in particular about 15 seem. In one or more embodiments, the plasma treatment is performed at an RF power in a range of 50 W to 300 W, in particular about 200 W. In one or more embodiments, the plasma treatment is performed at a temperature in a range from 50 °C to 450 °C, in particular 150 °C to 350 °C.

[0040] In one or more other embodiments, volatile compounds are removed from the lithium garnet particles through heating alone or through a combination of heating and plasma treatment. In one or more embodiments, the volatile compounds are removed through heating the lithium garnet particles at a temperature in a range from 700 °C to 900 °C. Heating the particles to this temperature will cause the removal of all chemisorbed and physiosorbed water and carbon dioxide and will decompose any protonated garnet and lithium carbonate on the surface. In one or more other embodiments, the volatile compounds are removed through heating the lithium garnet particles to a temperature of at least 600 °C followed by plasma treating as discussed above. The heating will cause removal of chemisorbed and physiosorbed water and carbon dioxide and will decompose any protonated garnet, further removing water. The plasma treatment will remove any remaining lithium carbonate or transform it to lithium oxide compounds. In still one or more other embodiments, the lithium garnet particles are heated to a temperature of at least 400 °C to remove physiosorbed water and carbon dioxide,and the lithium garnet particles are plasma treated- to remove any remain lithium carbonate or transform it into lithium oxide compounds.

[0041] After the lithium garnet particles are plasma and / or heat treated, the lithium garnet particles 310 are passivated through PALD. In one or more embodiments, PALD provides a passivation layer 312 conformally surrounding the particles as shown in FIG. 3. The passivation layers 312 allow the lithium garnet substrate 100 to be handled and stored in air without formation of lithium carbonate on the surface of the lithium garnet substrate 100. In one or more embodiments, the passivation layer 312 has a thickness in a range from 1 nm to 20 nm, in particular in a range from 2 nm to 10 nm.

[0042] In one or more embodiments, the passivation layer 312 comprises an oxide, a nitride, a fluoride, an oxynitride, or an oxyfluoride. In one or more embodiments, the passivation layer 312 comprises AI2O3, SislS , SiCL, AIF3, LiF, LiAlCL, Li2O, Ga2Ch, LiGaCL, MgO, La2O3, Y2O3, ZnO, ZrCL, or SnCL.

[0043] In one or more embodiments, the temperature during PALD is in a range from room temperature (about 23 °C) to 350 °C, in particular from 150 °C to 350 °C. In one or more embodiments, PALD is conducted at an RF power in a range from 1 W to 300 W, in particular about 300 W.

[0044] In one or more embodiments, the PALD process involves alternatingly introducing precursors into a PALD chamber, allowing each precursor to react with the lithium garnet particles 310. Alternatively, the PALD process involves introducing the lithium garnet particles 310 into separate or sequential chambers each containing a precursor to allow the lithium garnet particles 310 to react with each precursor. The plasma treatment activates the surface of the particles for reaction with the precursor to form a first reaction layer. The precursor is evacuated from the chamber, and a second precursor may then be introduced to the PALD chamber to react with the first reaction layer. Alternatively, the particles are moved from one PALD chamber containing the first precursor to another PALD chamber containing the second precursor. For example, to form an AI2O3 passivation layer, the first precursor may contain aluminum, and the second precursor may contain oxygen. The precursors are selected such that the desired element (e.g., Al or O) reacts with the surfaces of the lithium garnet particles 310 or with the first reaction layer. In this way, atomic layers of the passivation material are built up through alternatingly reaction with the precursors. Depending on the type of passivation layer 312, one precursor may be sufficient to provide the desired passivationmaterial, but in one or more other embodiments, two, three, or more precursors may be used to prepare the desired passivation material.

[0045] In the paragraphs below, an example passivation material is provided along with example precursors that can be used to generate the desired passivation layer 312 on the lithium garnet particles 310.

[0046] In one or more embodiments, the passivation layer comprises AI2O3. In such embodiments, the Al precursor may be trimethyl aluminum (TMA), and the O precursor may be ozone (O3) or oxygen gas (O2).

[0047] In one or more embodiments, the passivation layer comprises Sis In such embodiments, the Si precursor may be bis(diethylamino)silane (BDEAS), bis(t- butylamino)silane (BTBAS), or Orthrus® (available from Air Liquide A.S., Paris, France), and the N precursor is ammonia (NH3) or a mixture of ammonia and nitrogen gas (N2).

[0048] In one or more embodiments, the passivation layer comprises SiCh. In such embodiments, the Si precursor may be BDEAS, BTBAS, or Orthrus®, and the O precursor may be O2 or O3.

[0049] In one or more embodiments, the passivation layer comprises LiF. In such embodiments, the Li precursor may be lithium bis(trimethylsilyl)amide (LiN(SiMe3)2), lithium tert-butoxide (LiOt-Bu), or lithium tetramethyl heptadionate (LiTMHD), and the F precursor may be sulfur hexafluoride (SFe) or nitrogen trifluoride (NF3).

[0050] In one or more embodiments, the passivation layer comprises LiAlCL. In such embodiments, the Li precursor may be LiN(SiMe3)2, LiOt-Bu, or LiTMHD, the Al precursor may be TMA, and the O precursor may be O2 or O3.

[0051] In one or more embodiments, the passivation layer comprises Li2O. In such embodiments, the Li precursor may be LiN(SiMe3)2, LiOt-Bu, or LiTMHD, and the O precursor may be O2 or O3.

[0052] In one or more embodiments, the passivation layer comprises LiAlCL. In such embodiments, the Li precursor may be LiN(SiMe3)2, LiOt-Bu, or LiTMHD, the Al precursor may be TMA, and the O precursor may be O2 or O3.

[0053] In one or more embodiments, the passivation layer comprises Ga2C>3. In such embodiments, the Ga precursor may be trimethyl gallium (TMG) or dimethyl gallium isopropoxide (DMGIP), and the O precursor may be O2 or O3.

[0054] In one or more embodiments the passivation layer comprises LiGaCL. In such embodiments, the Li precursor may be LiN(SiMe3)2, LiOt-Bu, or LiTMHD, the Ga precursor may be TMG or DMGIP, and the O precursor may be O2 or O3.

[0055] In one or more embodiments, the passivation layer comprises MgO. In such embodiments, the Mg precursor may be bis(ethylcyclopentadienyl)magnesium [(EtCp)2Mg], Mg(thd)2(EtOH)2, or Mg2(thd)4, and the O precursor may be O2 or O3.

[0056] In one or more embodiments, the passivation layer comprises La2O3. In such embodiments, the La precursor may be tris(N,N’-diisopropylformamidinato)lanthanum (La(iPr2-fmd)3), tris(tetramethylcyclopentadienyl) lanthanum(III) ((tMeCp)2La), or LANA, and the O precursor may be O2 or O3.

[0057] In one or more embodiments, the passivation layer comprises Y2O3. In such embodiments, the Y precursor may be yttrium tris-(N,N'-diisopropylacetamidinate) [Y(iPr2amd)3], Y(thd)s, Y(thd)3(bipy), or Y(thd)3(phen), and the O precursor may be O2 or O3.

[0058] In one or more embodiments, the passivation layer comprises is ZnO. In such embodiments, the Zn precursor may be diethyl zinc (DEZ), zinc acetate (Zn(CH3COO)2), dimethylzinc (Zn(CH3)2, DMZn), and the O precursor may be O2 or O3.

[0059] In one or more embodiments, the passivation layer comprises ZrCL. In such embodiments, the Zr precursor may be Zr(NMe2), TDMA-Zr, ZrL, or ZrCL, and the O precursor may be O2 or O3.

[0060] In one or more embodiments, the passivation layer comprises SnCL. In such embodiments, the Sn precursor may be SnCL or tetrakis(dimethylamido)tin [TDMASn], and the O precursor may be O2 or O3.

[0061] The foregoing examples of oxides, nitrides, and fluorides for forming the passivation layer 312 are merely exemplary, and other materials may be used as the passivation layer 312 so long as those materials are stable in air, bond to lithium garnet particles, and do not or do not substantially diminish the electrochemical performance of the SSB cell into which the lithium garnet ribbon is incorporated as an electrolyte.

[0062] The plasma treatment may remove lithium carbonate from the surface of the lithium garnet particles. The plasma treatment may also transform the lithium carbonate into lithium compounds on the surface of the particles. In one or more embodiments, the compounds may comprise Li-F, Li-O, Li-O-F, Li-F-O-C, Li-N, Li-N-O, or Li-N-O-C compounds. During PALD, the lithium compounds are further reacted to form lithium metal compounds. In one or more embodiments, the compounds may comprise Li-M -F, Li-M -O, Li-M -O-F, Li-M-F-O- C, Li-M-N, Li-M-N-0, or Li-M-N-O-C compounds. Further, during PALD, the passivation layer 312 may be formed over the lithium metal compounds.

[0063] In a second step 302 of the method 300, the lithium garnet particles 310 having the passivation layer 312 are incorporated into a slurry 314. The composition of the slurry is substantially the same as described above with the exception that the PALD coated particles are substituted for the pristine lithium garnet particles.

[0064] In a third step 303 of the method 300, the slurry is tape-cast into green tape 316. In contrast to the previous method, the tape-casting does not need to be performed in a dry atmosphere because the lithium garnet particles have been passivated through PALD. Additionally, the green tape 316 does not need to remain in a dry atmosphere while the solvent drains / evaporates out from the green tape 316.

[0065] In a fourth step 304 of the method 300, binder is burned out from the green tape 316. During binder burnout, the organic material is removed from the green tape 316 and the lithium garnet particles 310 having the passivation layers 312 undergo partial sintering. In one or more embodiments, the green tape is heated to a temperature in a range from 300 °C to 600 °C for a time of 0.5 minutes to 15 minutes during binder burn out in the fourth step 304.

[0066] In a fifth step 305 of the method 300, the green tape 316 is sintered to forming the ribbon 318 of lithium garnet. In one or more embodiments, the green tape is heated to a temperature in a range from 950 °C to 1300 °C for a time of 3 minutes to 60 minutes, in particular from 5 minutes to 20 minutes, to fuse the particles of lithium garnet into a dense ceramic. As can be seen in the fifth step 305 of the method 300, the material of the passivation layer 312 may be retained in interstices within the matrix of the fused lithium garnet particles of the ribbon 318.

[0067] Using the methods described herein, the linear shrinkage of a continuous ceramic substrate undergoing a transition from green tape to ribbon ceramic is 25% or less. The linear shrinkage for a continuous ceramic substrate can be estimate according to Equation 1, below:

[0068] where P is the green tape porosity, Wvis the wt% of volatiles in the garnet powder (which can be measured using thermogravimetric analysis (TGA)), p is the actual density of the garnet powder in green tape including all volatiles, po is the garnet density after removal of all volatiles, Vgf is the garnet powder volumetric solid loading in the green tape. The volumetric solid loading of the garnet powder can be calculated according to Equation 2, below:

[0069] where the volumes are calculated by the corresponding material mass divided by its density. In Equation 2, the Vadditive component may include such additives as lithium carbonate (Li2CO3), which is a sintering aid and functions to compensate for Li loss during garnet sintering. In Equation 2, the term Vgamet refers to the passivated powder used for the tape casting. In one or more other embodiments, Vgamet may refer to fully passivated garnet, partially passivated garnet, or garnet passivated by different methods (which may result in different compositions).

[0070] According to the present disclosure, the parameters of density p and wt% of volatiles are optimized to decrease the linear shrinkage. In particular, the pristine lithium garnet tapecast in the dry atmosphere does not protonate or carbonate to increase the volume of the particles (thereby decreasing density), and the lack of protonation and carbonation, limits the amount of volatiles evolved during sintering. For the PALD-coated particles, the passivation layer prevents the formation of the volatiles that decompose during sintering.

[0071] EXPERIMENTAL EXAMPLES

[0072] EXAMPLE 1

[0073] LLZO garnet powder doped with tantalum (Li6.5La3Zr1.5Tao.5O12) was prepared by solid state reaction of powders of Li2CO3, La2O3, ZrO2, and Ta2Os provided in stoichiometric amounts. The powders were mixed in a tubular mixer followed by ball milling. The powder was screened and added to a platinum crucible. The powder in the crucible was calcined in air to 950 °C for 5 hours and heated to 1200 °C for another 5 hours to provide an ingot of lithium garnet. Surface contamination of platinum from the crucible was removed, and the lithium garnet was jet milled into a powder with a median particle size (D50) of about 0.6 pm. The powder obtained was 95 wt% pure cubic garnet as shown in Table 1, below.Table 1. Composition of Pristine Lithium Garnet Powder

[0074] The garnet powder was mixed with lithium carbonate (U2CO3) to provide excess lithium. To ensure that all reaction products that may have formed in ambient air were removed, the powder was calcined again at 800 °C for 2 hours in an argon atmosphere. The pristine garnet powder was added immediately to a tape-casting slurry. The composition of the tape-casting slurry is provided in Table 2, below.Table 2. Slurry Compositions of Passivated Lithium Garnet

[0075] In the above slurry compositions, the Dispersant was Disperbyk-2155. Solvent 1 was n-propyl propionate, and Solvent 2 was n-butyl propionate. The Plasticizer was PL029, and the Binder was Elvacite® 2046.

[0076] The slurry was tape-cast in a dry, argon atmosphere. After drying, the green tape was cut into 4 cm by 4 cm squares, which were fired at 1075 °C for 3 minutes and then at 1160 °C for another 3 minutes. During firing, the squares were sandwiched between grafoils to keep the squares flat. After firing, the samples were measured, and the squares had shrunk to 3 cm by 3 cm. Thus, the linear shrinkage (shrinkage along one dimension) was 25%.

[0077] FIG. 4 provides a scanning electron microscope (SEM) image of a cross-section of the ribbon of sintered lithium garnet. As can be seen in FIG. 4, the sintered lithium garnet is dense with low porosity and small pores.

[0078] EXAMPLE 2

[0079] In order to simulate the effect of providing a PALD coating on lithium garnet powders, pellets of lithium garnet were coated with through a standard ALD process. In particular, green pellets were pre-formed in a 30 mm cylindrical die set using a hydraulic, uniaxial press with a force of 3000 lbs. The preforms were then cold isostatically pressed to a higher density at a pressure of 36.5 kpsi. The pressed pellets were sealed in aluminum vacuum bags prior to ALD coating. ALD coating plasma and precursors were introduced following an overnight vacuumpurging at 250 °C to allow complete outgassing. Samples were supported by stainless steel cones so that ALD coatings were conformally developed around the surfaces.

[0080] One ALD coated sample was exposed to air for aging along with an uncoated control sample. The XRD patterns for both the ALD coated sample and the uncoated sample after aging in air for 2 weeks are provided in FIGS. 5 and 6, respectively. From a comparison of the XRD patterns, it can be seen that the uncoated samples develop characteristic peaks for lithium carbonate and lanthanum hydroxide (FIG. 6), whereas the XRD pattern remains substantially unchanged for the ALD coated sample. The amount of Li2COs formed after two weeks for the uncoated sample was roughly 17 wt% according to the semi-quantitative XRD.

[0081] Sintering of the ALD coated and uncoated sample pellets was performed in an atmosphere-controlled tube furnace with rapid sintering capability. The samples were placed on a graphite crucible and transferred into the hot zone at a speed of 2 inches per minute. The tube furnace was kept at 1160 °C with argon flowing during the entire sintering cycle. The samples were held at the sintering position for 30 mins and transferred out for cooling again at a speed of 2 inches per minute. After sintering, the ALD coated and uncoated samples were visually distinguishable with the ALD coated samples appearing more translucent grey / pink in color and the uncoated samples appearing pale white with minimal coloration.

[0082] As can be seen in FIG. 7, XRD scans were conducted on the top surfaces of the sintered ALD coated and uncoated samples. The ALD coated sample preserved at least 90%, in particular at least 95%, and most particularly about 100% cubic LLZO phase upon sintering. In contrast, the uncoated sample maintained less than 90% cubic LLZO phase upon sintering, in particular only about 85% of cubic LLZO. Accordingly, the ALD passivation layer suppressed phase transformation during sintering.

[0083] FIGS. 8 and 9 are SEM images of the ALD coated sample and the uncoated sample, respectively. The ALD coated sample exhibits large grains (10-50 pm size) over the top sintered surface, whereas no such grains can be seen in the uncoated sample. The presence of the large grains in the ALD coated sample indicates that the densification and grain growth are much more pronounced as a result of the AI2O3 ALD coating. Platelet-shape phases were observed on the uncoated samples, which were confirmed to be La2Os according to the XRD and EDS results.

[0084] EXAMPLE 3

[0085] LLZO is known to undergo protonation in solvents with certain polarity, for example, water and alcohols, so that lattice Li is lost as Li+ ions diffuse into the solvents. Thus, water-based processing of lithium garnet has been largely hindered, blocking a potential pathway to a low-cost and environmentally friendly manufacturing process. To evaluate the effectiveness of ALD coating on improving the solvent stability of lithium garnet and study the possibility of ALD coating for future slurry preparation and continuous green tape manufacture, two green pellets with and without ALD coatings were prepared. Deionized water was used as the solvent because of its relatively high polarity compared to alcoholic solvents. The hydrolysis reaction between the lithium garnet and water was monitored with pH strips. Pellets were gently immersed in 50 mL of DI water in two glass beakers. Sampling by pH strips took place at 5 minutes, 20 minutes, and 120 mins after the pellets were immersed. Based on the color changes of the pH strips, the solution with the uncoated lithium garnet pellet turned immediately to basic, and the pH went up to 14 after 2 hrs because of the aggressive formation of LiOH. The pH strips for the solution with the ALD coated pellet exhibited much smaller color changed, and the increase of pH for that solution was much slower than the uncoated sample. Thus, the ALD coating provides protection of the pellet against hydrolysis.

[0086] Inductively coupled plasma - optical emission spectrometry (ICP-OES) was employed to quantify the Li+ content in the solutions that were sampled at 5 minutes, 20 minutes, and 120 minutes of water immersion. As can be seen in FIG. 10, the total Li+concentration in the solution was almost 15 times higher for the uncoated sample than the ALD coated sample after 2 hrs, which further demonstrates the effectiveness of ALD coating in promoting the solvent stability of lithium garnet.

[0087] Further, it was observed that the uncoated specimen was structurally dissociated in solution after 2 hrs of water immersion, while the ALD coated sample stayed intact, keeping its original shape.

[0088] EXAMPLE 4

[0089] Garnet sample surfaces were ALD coated with AI2O3 with thicknesses of 5 nm, 10 nm, and 20 nm. Oxygen plasma treatment was used to decompose the surface Li2COs and leave behind LiOx. The ALD deposition was conducted at 250 °C with tri-methyl Al (TMA) as the Al precursor. Oxygen gas (O2) plasma was used instead of H2O as the oxidant to avoid the hydroxide formation by the reaction of H2O with garnet.

[0090] The AI2O3 ALD coated surfaces were exposed to air, and the surface air passivation effect was compared with a 0.1M 5min acid treated garnet samples. Acid treatment is known to clean the Li2CO3 on the surface and form protonated LLZO (H-LLZO) on the surface, which also passivates garnet surface. FIG. 11 shows the acid-treated control sample’s surface morphology changed from right after acid treatment to 20 days after exposure in air. After 20days, a layer of Li2CO3 had formed on the garnet, and the Li2CO3 covers the garnet grains. FIG. 11 also shows the 10 nm AI2O3 ALD coated garnet surface that is right after the coating and after 40 days of exposure to air. There is no significant change of the surface morphology, indicating that the AI2O3 ALD coating played an effective role in protecting garnet from reacting with H2O and CO2 in air. Thus, a 10 nm ALD coating of AI2O3 is sufficient to protect garnet surface, including in powder form.

[0091] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that any particular order be inferred. In addition, as used herein, the article “a” is intended to include one or more than one component or element and is not intended to be construed as meaning only one.

[0092] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosed embodiments. Since modifications, combinations, sub-combinations, and variations of the disclosed embodiments incorporating the spirit and substance of the embodiments may occur to persons skilled in the art, the disclosed embodiments should be construed to include everything within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A method, comprising: firing a continuous green tape in a furnace to form a ceramic ribbon of sintered lithium garnet, the continuous green tape comprising particles of lithium garnet that are coated with a passivation layer; and wherein the continuous green tape comprises a length, a width, and a thickness, the width being greater than the thickness and the length being greater than the width, and wherein the continuous green tape has a linear shrinkage of less than or equal to 25% after firing to form the ceramic ribbon.

2. The method of claim 1, wherein the particles of lithium garnet comprise outer surfaces that are substantially free from lithium carbonate and wherein the passivation layer is disposed on the outer surfaces of the particles.

3. The method of claim 1 or claim 2, wherein the passivation layer comprises a thickness of 1 nm to 20 nm.

4. The method of any one of claims 1-3, wherein the lithium garnet comprises a lithium lanthanum zirconium oxide.

5. The method of claim 4, wherein the lithium garnet is doped with at least one of In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg, or Ca.

6. The method of any one of claims 1-5, wherein the passivation layer comprises at least one of AI2O3, Si 3 N4, SiCh, AIF3, LiF, LiAlCh, Ga2C>3, LiGaCh, MgO, La2C>3, Y2O3, ZnO, ZrCh, or SnCh.

7. The method of any one of claims 1-6, wherein the particles comprise a median particle size (D50) in a range from 0.1 pm to 2 pm.

8. The method of any one of claims 1-7, wherein, prior to firing, the method further comprises: removing lithium carbonate from the particles of lithium garnet; and applying the passivation layer via powder atomic layer deposition.

9. The method of claim 8, wherein removing further comprises heating the particles of lithium garnet to a temperature in a range of 700 °C to 900 °C to remove chemisorbed and physiosorbed water and carbon dioxide and to decompose the lithium carbonate.

10. The method of claim 8, wherein removing further comprises heating the particles of lithium garnet to a temperature of at least 600 °C to remove chemisorbed and physiosorbed water and carbon dioxide and to decompose any protonated garnet to remove water followed by plasma treating to transform the lithium carbonate into lithium oxides.

11. The method of claim 8, wherein removing further comprises heating the particles of lithium garnet to a temperature of at least 400 °C to remove physiosorbed water and carbon dioxide and plasma treating to transform lithium carbonate into lithium oxides.

12. The method of claim 10 or claim 11, wherein the plasma treating further comprises transforming the lithium carbonate using radicals selected from a group consisting of oxygen, fluorine, hydrogen, nitrogen, chlorine radicals, and combinations thereof.

13. The method of any one of claims 1-12, wherein, prior to firing, the method further comprises: forming a slurry comprising the particles of lithium garnet coated with the passivation layer, an organic binder, and a solvent; and tape casting the slurry to form the continuous green tape.

14. The method of claim 13, wherein the organic binder comprises at least one of an acrylic, a carbon dioxide-based polymer, polyvinyl butyral, polyvinyl alcohol, polyurethane, methyl cellulose, polystyrene, styrene acrylate, or dextrin.

15. The method of claim 13 or claim 14, wherein the slurry further comprises a plasticizer.

16. The method of claim 15, wherein the plasticizer comprises at least one of a phthalate, a phosphate, a carboxylic acid ester, an epoxidized fatty acid ester, a polymeric polyester, a liquid rubber, or a paraffinic, aromatic, or naphthenic petroleum oil.

17. The method of any one of claims 13-16, wherein the slurry further comprises a dispersant.

18. The method of claim 17, wherein the dispersant comprises at least one of a fatty acid, an ester, a terpineol, an alkyl sulphate, an alkyl sulphonate, an alkyl acryl sulphonate, a lignin sulphonate, or an amine functional molecule.

19. The method of any one of claims 1-18, wherein the amount of lithium garnet in the ceramic ribbon of sintered lithium garnet is substantially similar to the amount of lithium garnet in the particles of lithium garnet, the particles of lithium garnet comprising at least 95 wt% lithium garnet.

20. The method of any one of claims 1-19, wherein the ceramic ribbon comprises material of the passivation layer between grains of sintered lithium garnet.

21. The method of any one of claims 1-20, wherein, prior to firing, the method further comprises unwinding the continuous green tape from a payoff reel.

22. The method of claim 21, wherein, after firing, the method further comprises winding the ceramic ribbon of sintered lithium garnet on a takeup reel.

23. A method, comprising: calcining particles of lithium garnet powder to remove lithium carbonate from outer surfaces of the particles; adding the calcined particles of lithium garnet to a slurry; tape casting the slurry in a dry atmosphere to form a continuous green tape; and firing the continuous green tape to form a ceramic ribbon of sintered lithium garnet; wherein the continuous green tape comprises a length, a width, and a thickness, the width being greater than the thickness and the length being greater than the width, and wherein the continuous green tape has a linear shrinkage of less than or equal to 25% after firing to form the ceramic ribbon.

24. The method of claim 23, wherein calcining further comprises heating the particles of lithium garnet to a temperature of at least 800 °C.

25. The method of claim 24, wherein heating comprises holding the particles of lithium garnet at the temperature for at least 1 hour.

26. The method of any one of claims 23-25, wherein the lithium garnet comprises a lithium lanthanum zirconium oxide.

27. The method of claim 26, wherein the lithium garnet is doped with at least one of In, Si, Ge, Sn, Sb, Sc, Ti, Hf, V, W, Te, Nb, Ta, Al, Ga, Fe, Bi, Y, Mg, or Ca.

28. The method of any one of claims 23-27, wherein the particles comprise a median particle size (D50) in a range from 0.1 pm to 2 pm.

29. The method of any one of claims 23-28, wherein the slurry comprises the particles of lithium garnet, a dispersant, an organic binder, and a solvent.

30. The method of claim 29, wherein the organic binder comprises at least one of an acrylic, a carbon dioxide-based polymer, polyvinyl butyral, polyvinyl alcohol, polyurethane, methyl cellulose, polystyrene, styrene acrylate, or dextrin.

31. The method of one of claims 23-30, wherein the slurry further comprises a plasticizer.

32. The method of claim 31, wherein the plasticizer comprises at least one of a phthalate, a phosphate, a carboxylic acid ester, an epoxidized fatty acid ester, a polymeric polyester, a liquid rubber, or a paraffinic, aromatic, or naphthenic petroleum oil.

33. The method of claim 29-32, wherein the dispersant comprises at least one of a fatty acid, an ester, a terpineol, an alkyl sulphate, an alkyl sulphonate, an alkyl acryl sulphonate, a lignin sulphonate, or an amine functional molecule.

34. The method of any one of claims 23-33, wherein the amount of lithium garnet in the ceramic ribbon of sintered lithium garnet is substantially similar to the amount of lithium garnet in the particles of lithium garnet, the particles of lithium garnet comprising at least 95 wt% lithium garnet.

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