Treatment methods for ceramics and associated compositions

Abstract

Methods for removing or suppressing formation of surface deposits of metal carbonate upon a sintered ceramic may take place by excluding conditions that may promote metal carbonate formation. Such methods may comprise: providing a sintered ceramic having a surface deposit of metal carbonate present upon at least one of a first face or a second face of the sintered ceramic; heating the sintered ceramic at a first temperature in a first environment comprising an inert gas, a sub-atmospheric pressure, or both, wherein the first temperature is effective to remove at least a portion of the surface deposit of metal carbonate from the sintered ceramic; and cooling the sintered ceramic in a second environment comprising an inert gas, a sub-atmospheric pressure, or both to a second temperature of 100°C or below. Sintered ceramics may comprise a first surface comprising lithium lanthanum zirconium oxide with specified surface atomic ratios and / or surface roughness.

Description

Attorney Docket No. SP24-323 PCTTREATMENT METHODS FOR CERAMICS AND ASSOCIATED COMPOSITIONSCROSS-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 / 727,259, filed on December 3, 2024, the content of which is relied upon and incorporated herein by reference in its entirety.FIELD

[0002] The present disclosure generally relates to ceramics and methods for production thereof, and more specifically, thin ceramics lacking or having decreased amounts of a surface carbonate and methods for production thereof.BACKGROUND

[0003] Although lithium-ion batteries have revolutionized many aspects of daily activities, there remain significant concerns about this type of energy-storage medium. Conventional lithium-ion batteries utilize a liquid or gel-polymer electrolyte and an ion-permeable polymer-based separator between the anode and cathode. While technological advancements have been made in conventional lithium-ion batteries, such energy-storage media continue to suffer from various issues such as, for example, limited capacity density and energy density, as well as safety concerns, all of which may pose implementation challenges, especially for large-scale commercial applications.

[0004] Thus, there remains a need in the art for improved battery technologies. The present disclosure is directed to this need as well as other important goals.SUMMARY

[0005] In some aspects, the present disclosure provides sintered ceramics comprising: a first surface comprising lithium lanthanum zirconium oxide (LLZO). At least one of the following conditions is met: Condition a) the first surface of the sintered ceramic has a surface atomic ratio of fithium: lanthanum within +5% of 7:3, and a surface atomic ratio of lithium: zirconium within +5% of 7:2, each surface atomic ratio being measured by X-ray photoelectron spectroscopy (XPS) at a depth within 20 nm of the first surface; or Condition b) an average surface roughness (Sa) of the sintered ceramic, as determined by scanning laser confocal microscopy and measured as a height relative to a geometrically flat surface, rangesAttorney Docket No. SP24-323 PCT from 0.2 mm to 0.35 mm, and a surface area of the sintered ceramic, measured as an average developed interfacial area ratio (Sdr) relative to the geometrically flat surface, increases from 40% to 90% relative to the geometrically flat surface.

[0006] In some or other aspects, the present disclosure provides methods for removing at least a portion of a surface carbonate from a sintered ceramic. The methods comprise: providing a sintered ceramic, a surface deposit of metal carbonate being present upon at least one of a first face or a second face of the sintered ceramic; heating the sintered ceramic at a first temperature in a first environment comprising an inert gas, a sub-atmospheric pressure, or both, wherein the first temperature is effective to remove at least a portion of the surface deposit of metal carbonate from the sintered ceramic; and cooling the sintered ceramic in a second environment comprising an inert gas, a sub-atmospheric pressure, or both to a second temperature of 100°C or below.

[0007] In still other aspects, the present disclosure provides sintering methods that minimize or preclude formation of a surface carbonate upon a sintered ceramic. The methods comprise: sintering a green ceramic at a sintering temperature in a first environment comprising an inert gas, a sub-atmospheric pressure, or both, thereby forming a sintered ceramic; and without exposing the sintered ceramic to conditions effective to form a surface deposit of a metal carbonate on the sintered ceramic, cooling the sintered ceramic in a second environment comprising an inert gas, a sub-atmospheric pressure, or both to a second temperature of 100°C or below.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following figures are included to illustrate certain aspects of the disclosure, and should not be viewed as exclusive configurations. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

[0009] FIGS. 1 and 2 show cycling data for cells having a cathode side constructed with different orientations of LLZO obtained from heat treatment.

[0010] FIG. 3 is a Nyquist plot of interfacial resistance for cells having a cathode side constructed with different orientations of LLZO obtained from heat treatment. Interfacial resistance for a cell constructed with acid-etched LLZO is also shown.

[0011] FIG. 4 shows cycling data for a cell having LLZO treated with a 4-minute acid-etch in 1 M HC1.

[0012] FIG. 5 is an SEM image of heat-treated LLZO that is then cooled in vacuum.Attorney Docket No. SP24-323 PCT

[0013] FIG. 6 is an SEM image of LLZO treated for 4 minutes with 1 M HC1.

[0014] FIGS. 7 and 8 are bar graphs showing, respectively, variations in average surface roughness (Sa) and surface area, evaluated as an average developed interfacial area ratio (Sdr), for LLZO treated under various conditions to remove lithium carbonate.DETAILED DESCRIPTION

[0015] The present disclosure generally relates to ceramics and methods for production thereof, and more specifically, thin ceramics lacking or having decreased amounts of a surface carbonate and methods for production thereof.

[0016] There are issues associated with conventional lithium-ion batteries. Solid-state lithium batteries having a lithium metal anode represent an attractive alternative to lithium- ion batteries. Whereas lithium-ion batteries utilize a liquid or gel-polymer electrolyte for conveying lithium ions across an ion-permeable polymer-based separator from the anode electrode to the cathode electrode and back again, solid-state lithium batteries utilize a solid electrolyte, typically a solid oxide electrolyte, as the conduction medium between the cathode and the anode. In addition to offering higher energy density values, the solid oxide electrolyte alleviates many of the safety concerns associated with the liquid or gel-polymer electrolytes of lithium-ion batteries. The solid oxide electrolyte may abut the cathode and the anode as a thin structure, thereby providing a short conduction pathway between the two.

[0017] Lithium lanthanum zirconium oxide (LLZO), also referred to as lithium garnet, is one type of solid oxide electrolyte material that has been explored for use in solid-state lithium batteries. A difficulty with LLZO, however, is the ready formation of surface deposits of lithium carbonate upon exposure of this material to even trace amounts of moist air, especially at high temperatures upon cool-down from sintering. Even prolonged exposure of LLZO to ambient air having ordinary relative humidity levels at or near room temperature may lead to formation of lithium carbonate deposits. The lithium carbonate deposits may result in insufficient contact between the cathode and the anode in a solid-state battery, thereby leading to high interfacial resistance, low current density, and large polarization values. Even more significantly, inhomogeneous lithium carbonate deposition may result in variations in the local current density upon the solid oxide electrolyte. If the local current density exceeds a critical current density, lithium dendrite formation may occur during repeated cycles of charging and discharging, which may eventually lead to shorting.

[0018] Techniques for removing surface deposits of lithium carbonate from LLZO are known, but remain problematic. Known approaches for removing lithium carbonate involveAttorney Docket No. SP24-323 PCT polishing or acid-etching to remove the lithium carbonate through mechanical action or chemical dissolution, respectively. Both approaches run the risk of damaging LLZO and other solid-oxide electrolytes having a thin structure, such as ceramic ribbons. Such damage may increase the failure rate of solid-state batteries due to shorting. Due to the fragility of LLZO and other solid oxide electrolytes having a thin structure, such as LLZO ribbons, polishing is typically limited to relatively thick structures, such as pellets or other monolithic bodies of LLZO and other solid oxides.

[0019] Acid-etching of LLZO having a thin structure presents a different set of issues, among which include removal of LLZO from grain boundaries, additional thinning of the LLZO thin structure, and production of excessive porosity and surface irregularities that may again result in lithium dendrite formation as a consequence of an irregular current density. Similar changes may occur in other solid oxide electrolytes. Additionally, acid-etching may protonate the surface of LLZO or other solid oxide electrolytes. Protonated LLZO is sometimes more prone to lithium dendrite formation than is pristine LLZO itself, even absent other modifications that may encourage formation of lithium dendrites.

[0020] A further difficulty posed by lithium carbonate formation and removal by conventional techniques is that of lithium deficiency. During lithium carbonate formation, lithium ions diffuse to the surface of the LLZO under the influence of high temperatures and react with carbon dioxide to produce the lithium carbonate upon the surface. Even if they are successful in removing the lithium carbonate deposits, mechanical or chemical processes lead to permanent loss of lithium ions from the solid oxide electrolyte, either as residue solids or dissolved lithium ions, thereby producing a lithium-deficient complex oxide that is less conductive compared to pristine LLZO. Accordingly, a number of challenges remain to be resolved for effective utilization of LLZO and similar solid oxide electrolytes in solid-state batteries.

[0021] The present disclosure provides sintered ceramics and methods for production thereof that, in some aspects, address the foregoing needs and provide related advantages as well. In contrast to conventional mechanical and chemical methods for removing lithium carbonate deposits from the surface of LLZO and other solid oxide electrolytes, the present disclosure provides various treatment processes, including thermal processes (e.g., thermal treatments or heat treatment methods) for at least partially removing lithium carbonate from the surface of LLZO and / or preventing or lessening the formation of lithium carbonate upon the surface of LLZO in the first place. The processes described herein may be conducted such that minimal exposure to carbon dioxide and water takes place during cool-downAttorney Docket No. SP24-323 PCT following the thermal process, either following sintering or a separate thermal treatment, thereby limiting the opportunity for lithium carbonate to form or re-form. Although particularly beneficial for treating LLZO, the methods disclosed herein may be beneficial for any solid oxide electrolyte in which formation of a surface carbonate is problematic.

[0022] The treatments herein, including thermal treatment of LLZO and similar solid oxide electrolytes, offer several distinct advantages compared to other techniques for removing lithium carbonate or other metal carbonate deposits and / or preventing carbonate formation in the first place. Aside from performance benefits (e.g., decreased surface resistance) achieved simply by removing the lithium carbonate, the treatments of the present disclosure may be conducted without chemically altering the surface of the LLZO (e.g., through protonation in the case of acid-etching) or thinning of the LLZO, altering the surface morphology of the LLZO through grain modification or removal, or introducing excessive porosity to the LLZO, any or all of which may lead to an increased risk of lithium dendrite formation and shorting, as well as decreased mechanical strength. Additionally, the treatments herein avoid generation of spent acids as a hazardous waste stream.

[0023] Whereas polishing and acid-etching permanently remove lithium ions from the LLZO, either as lithium carbonate residue solids or dissolved lithium ions, respectively, and leave behind lithium-deficient LLZO, thermal treatment according to the disclosure herein instead decomposes the carbonate and leaves the lithium ions behind upon the LLZO. Once liberated from the carbonate, the lithium ions may diffuse back to the interior of the LLZO under the heating conditions and restore or maintain the complex oxide at or near an ideal stoichiometry (e.g., LiyLasZnOn).

[0024] Treatments according to the present disclosure may be conducted at various stages for producing and manipulating LLZO and similar solid oxide electrolytes having a thin structure, depending on whether existing lithium carbonate deposits need to be removed from the LLZO or if suppression of lithium carbonate formation following sintering needs to take place. The latter may prevent lithium carbonate formation from occurring in the first place. Thus, the treatments disclosed herein may be conducted after production of a sintered ceramic or in conjunction with (coupled to) sintering methods for forming a sintered ceramic. Moreover, the treatments disclosed herein are compatible with continuous sintering processes for producing LLZO and similar solid oxide electrolytes having a thin structure on a large scale, such as in the form of spoolable lengths of ribbon ceramic materials. Additional details regarding how heat treatment may be employed at various stages of production and manipulation of solid oxide electrolytes having a thin structure are described hereinbelow.Attorney Docket No. SP24-323 PCT

[0025] Although the description herein is primarily directed to LLZO, it is to be appreciated that the methods described herein may also be applicable to other types of solid oxide electrolytes having a thin structure and susceptible to formation of a carbonate upon their surface. As non-limiting examples, the treatments of the present disclosure may also be applicable to ionic conductors such as b-alumina, NASICON (Nai+X, Zr2SixP3-xOi2, 0<x<3), and sulfide-based sodium-ion conductors.

[0026] In the description below, a sintered ceramic may be produced by a sintering process that takes place at high temperatures. The sintered ceramic may comprise or consist of LLZO, for example. Following the sintering process, lithium carbonate deposits may form upon at least one face of the sintered ceramic as the sintered ceramic cools down from the high temperatures of the sintering process, during which time the sintered ceramic remains at a temperature of several hundred degrees and is still very reactive toward even trace amounts of carbon dioxide and water. In some aspects of the present disclosure, a sintering process may be coupled to one or more protocols for suppressing formation of lithium carbonate deposits during cooling of the sintered ceramic. Specifically, the sintered ceramic obtained from the sintering process may be manipulated in a manner such that the sintered ceramic is exposed to conditions that avoid or are at least less likely to promote formation of lithium carbonate during cooling. Such conditions during cooling may include, but are not limited to, exposing the sintered ceramic to an inert gas during cooling, wherein the inert gas is carefully scrubbed to remove as much carbon dioxide and water as reasonably possible, maintaining the sintered ceramic at a sub-atmospheric pressure (at least a partial vacuum), or a combination thereof. Sufficiently rapid cooling may also aid in limiting or preventing carbonate formation, particularly in combination with one or more of the foregoing conditions. An optional diffusion barrier may additionally be utilized during cooling to physically block water and carbon dioxide from accessing at least one face of the sintered ceramic, thereby limiting the ability of the lithium or other atoms to react.

[0027] Alternately, the sintered ceramic may have been previously produced by a sintering process, but the sintered ceramic has been subsequently exposed to conditions that may form lithium carbonate deposits upon the LLZO or lithium carbonate deposits are present upon the LLZO. In the case of a sintered ceramic having or potentially having lithium carbonate deposits thereon, a heat treatment separate from the sintering process may be performed. The separate heat treatment may be conducted at a temperature sufficient to remove the lithium carbonate deposits from the sintered ceramic, typically at a temperature below the sintering temperature, again with the sintered ceramic being exposed to conditions during cooling thatAttorney Docket No. SP24-323 PCT avoid or are at least less likely to promote deposition of lithium carbonate. The conditions may be similar to those utilized following a sintering process to discourage formation of lithium carbonate upon the LLZO during cooling. Again, a diffusion barrier may optionally be employed during at least the cooling process as well.

[0028] Numerous variations are possible in the methods of the present disclosure, depending on whether heating / sintering and cooling utilize the same type of environment or different environments (e.g., inert gas, sub-atmospheric pressure, or a combination thereof). Additional description of various aspects of the present disclosure is provided hereinbelow.

[0029] In various aspects, sintering processes for producing LLZO and similar solid oxide electrolytes may take place in an environment comprising an inert gas, a sub-atmospheric pressure, or any combination thereof. Suitable inert gases may include, but are not limited to, nitrogen (N2), noble gases (He, Ne, Ar, Kr, Xe, or any combination thereof), or any combination thereof. When used, the inert gas may be static or flowing during the sintering process.

[0030] A pressure of the inert gas may be within +10% of atmospheric pressure during sintering. At sea level, atmospheric pressure is considered to be LOlxlO5Pa (760 torr or 1 atmosphere). In various aspects, an inert gas pressure during sintering may be 1.1 IxlO5Pa or less (836 torr or less, or 1.1 atmosphere or less), 1.07xl05Pa or less (798 torr or less, or 1.05 atmosphere or less), LOlxlO5Pa or less (760 torr or less, or 1 atmosphere or less), 9.62xl04Pa or less (722 torr or less, or 0.95 atmosphere or less), 9.12xl04Pa or more (684 torr or more, or 0.9 atmosphere or more), 1.07xl05Pa or more (798 torr or more, or 1.05 atmosphere or more), LOlxlO5Pa or more (760 torr or more, or 1 atmosphere or more), or 1.07xl05Pa or more (798 torr or more, or 1.05 atmosphere or more), or any range formed therefrom. In non-limiting aspects, the inert gas pressure during sintering may range from Pl to P2, wherein Pl and P2 are, independently, 9.12xl04Pa (684 torr or 0.9 atmosphere), 9.62xl04Pa (722 torr or 0.95 atmosphere), LOlxlO5Pa (760 torr or 1 atmosphere), 1.07xl05Pa (798 torr or 1.05 atmosphere), or L l lxlO5Pa (836 torr or 1.1 atmosphere), and P1<P2. In particular aspects, the inert gas pressure during sintering may range from 9.62xl04Pa (722 torr or 0.95 atmosphere) to LOlxlO5Pa (760 torr or 1 atmosphere), or LOlxlO5Pa (760 torr or 1 atmosphere) to 1.07xl05Pa (798 torr or 1.05 atmosphere). In some aspects, the pressure of the inert gas during sintering may be LOlxlO5Pa (760 torr or 1 atmosphere).

[0031] Alternately, the sintering process may take place at a sub-atmospheric pressure. As used herein, the term “sub-atmospheric pressure” refers to any pressure that is more than 10% below atmospheric pressure at sea level. As such, a sub-atmospheric pressure is 9.1xl04PaAttorney Docket No. SP24-323 PCT or less (684 torr or less or 0.9 atmosphere or less). More typically, suitable sub-atmospheric pressures during sintering include 1.33xl04Pa or less (100 torr or less, or 0.13 atmosphere or less), 1.20xl04Pa or less (90 torr or less, or 0.12 atmosphere or less), 1.07xl04Pa or less (80 torr, or less or 0.11 atmosphere or less), 9.33x103Pa or less (70 torr or less, or 0.092 atmosphere or less), 8.00xl03Pa or less (60 torr or less, or 0.079 atmosphere or less), 6.67xl03Pa or less (50 torr or less, or 0.066 atmosphere or less), 5.33xl03Pa or less (40 torr or less, or 0.053 atmosphere or less), 4.00xl03Pa or less (30 torr or less, or 0.039 atmosphere or less), 2.67xl03Pa or less (20 torr or less, or 0.026 atmosphere or less), 1 ,33xl03Pa or less (10 torr or less, or 0.013 atmosphere or less), 133 Pa or less (1 torr or less, or 0.0013 atmosphere or less), 13 Pa or more (0.1 torr or more, or 0.00013 atmosphere or more), 133 Pa or more (1 torr or more, or 0.0013 atmosphere or more), 1.33xl03Pa or more (10 torr or more, or 0.013 atmosphere or more), 2.67xl03Pa or more (20 torr or more, or 0.026 atmosphere or more), 4.00xl03Pa or more (30 torr or more, or 0.039 atmosphere or more), 5.33xl03Pa or more (40 torr or more, or 0.053 atmosphere or more), 6.67xl03Pa or more (50 torr or more, or 0.066 atmosphere or more), 8.00xl03Pa or more (60 torr or more, or 0.079 atmosphere or more), 9.33xl03Pa or more (70 torr or more, or 0.092 atmosphere or more), 1 ,07xl04Pa or more (80 torr or more, or 0.11 atmosphere or more), or 1 ,20xl04Pa or more (90 torr or more, or 0.12 atmosphere or more), or any range formed therefrom. In nonlimiting examples, the sub-atmospheric pressure during sintering may range from P3 to P4, wherein P3 and P4 are, independently, 13 Pa (0.1 torr or 0.00013 atmosphere), 133 Pa (1 torr or 0.0013 atmosphere), 1.33xl03Pa (10 torr or 0.013 atmosphere), 2.67xl03Pa (20 torr or 0.026 atmosphere), 4.00xl03Pa (30 torr or 0.039 atmosphere), 5.33xl03Pa (40 torr or 0.053 atmosphere), 6.67xl03Pa (50 torr or 0.066 atmosphere), 8.00xl03Pa (60 torr or 0.079 atmosphere), 9.33xl03Pa (70 torr or 0.092 atmosphere), 1.07xl04Pa (80 torr or 0.11 atmosphere), 1.20xl04Pa (90 torr or 0.12 atmosphere), or 1.33xl04Pa (100 torr or 0.13 atmosphere), and P3<P4. In some examples, the sub-atmospheric pressure during sintering may be 4.00xl03Pa or less (30 torr or less, or 0.039 atmosphere or less) or 2.67xl03Pa or less (20 torr or less, or 0.026 atmosphere or less), such as within a range of 1.33xl03Pa (10 torr or 0.013 atmosphere) to 2.67xl03Pa (20 torr or 0.026 atmosphere), 1.33xl03Pa (10 torr or 0.013 atmosphere) to 4.00xl03Pa (30 torr or 0.039 atmosphere), or 2.67xl03Pa (20 torr or 0.026 atmosphere) to 4.00xl03Pa (30 torr or 0.039 atmosphere).

[0032] Sintering processes for LLZO and similar solid oxide electrolytes may take place or have taken place at a sintering temperature of 900°C or more, 910°C or more, 920°C or more, 930°C or more, 940°C or more, 950°C or more, 960°C or more, 970°C or more, 980°C orAttorney Docket No. SP24-323 PCT more, 990°C or more, 1000°C or more, 1010°C or more, 1020°C or more, 1030°C or more, 1040°C or more, 1050°C or more, 1060°C or more, 1070°C or more, 1080°C or more, 1090°C or more, 1100°C or more, 1110°C or more, 1120°C or more, 1130°C or more, 1140°C or more, 1150°C or less, 1140°C or less, 1130°C or less, 1120°C or less, 1110°C or less, 1100°C or less, 1090°C or less, 1080°C or less, 1070°C or less, 1060°C or less, 1050°C or less, 1040°C or less, 1030°C or less, 1020°C or less, 1010°C or less, 1000°C or less, 990°C or less, 980°C or less, 970°C or less, 960°C or less, 950°C or less, 940°C or less, 930°C or less, 920°C or less, 910°C or less, or any range formed therefrom. In non-limiting aspects, the sintering temperature may range from T1 to T2, wherein T1 and T2 are, independently, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1090°C, or 1100°C, and T1<T2. In some aspects, the sintering temperature may range from 1000°C to 1100°C, 1000°C to 1050°C, 1050°C to 1100°C, 1070°C to 1100°C, or 1100°C to 1150°C.

[0033] The sintering process to produce the sintered ceramic may be a batch sintering process or a continuous sintering process. A continuous sintering process may produce the sintered ceramic as a ribbon ceramic or similar elongated ceramic material. A ribbon ceramic refers to a ceramic material having a length much greater than its width and a width much greater than its thickness. In non-limiting examples, continuous sintering processes may comprise reel-to-reel processes comprising tape casting and sintering to produce such ribbon ceramics. In such reel-to-reel processes, a support material may be discharged from a first (payout) reel and subsequently have a ceramic precursor cast thereon. The resulting green (precursor) ceramic material is continuously conveyed through suitable sintering conditions to form a ribbon ceramic after burn-off of the support material under the sintering conditions or after separation of the support material prior to the green ceramic entering the sintering conditions. The ribbon ceramic is then wound upon a second (take-up) reel, from which the ribbon ceramic may be discharged and cut to size for utilization in a part. Alternately, the ribbon ceramic may be stored on the second reel for later use of the ribbon ceramic. The length of the ribbon ceramic loaded upon the second reel is not considered to be particularly limited and may include minimum spoolable lengths of at least 20 cm (0.66 ft), at least 50 cm (1.64 ft), at least 100 cm (3.28 ft), at least 250 cm (8.2 feet), at least 500 cm (16.4 ft), at least 1000 cm (32.8 ft), at least 2500 cm (82 ft), at least 5000 cm (164 ft), at least 10000 cm (328 feet), at least 25000 cm (820 feet), or any range formed therefrom. Spoolable lengths of ribbon ceramic may include maximum lengths of about 50000 cm (1640 feet), 100000 cm (3280 feet), 150000 cm (4920 feet) or 200000 cm (6560 feet). Any of the foregoingAttorney Docket No. SP24-323 PCT minimum and maximum spoolable lengths may be combined in any manner to form any range.

[0034] Configurations utilizing reel-to-reel processes in association with removing lithium carbonate deposits or suppressing deposition of lithium carbonate upon LLZO and similar solid oxide electrolytes following reel-to-reel sintering processes are discussed in further detail below.

[0035] The sintered ceramic may be a thin ceramic, such as a ribbon ceramic, having a thickness of 5 mm or more, 10 mm or more, 15 mm or more, 20 mm or more, 25 mm or more, 30 mm or more, 40 mm or more, 50 mm or more, 60 mm or more, 70 mm or more, 80 mm or more, 90 mm or more, 100 mm or more, 120 mm or more, 140 mm or more, 160 mm or more, 180 mm or more, 200 mm or more, 220 mm or more, 240 mm or more, 260 mm or more, 280 mm or more, 300 mm or less, 280 mm or less, 260 mm or less, 240 mm or less, 220 mm or less, 200 mm or less, 180 mm or less, 160 mm or less, 140 mm or less, 120 mm or less, 100 mm or less, 90 mm or less, 80 mm or less, 70 mm or less, 60 mm or less, 50 mm or less, 40 mm or less, 30 mm or less, 25 mm or less, 20 mm or less, 15 mm or less, or 10 mm or less, or any range formed therefrom. In non-limiting aspects, the sintered ceramic may have a thickness ranging from W1 to W2, wherein W1 and W2 are, independently, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 120 mm, 140 mm, 160 mm, 180 mm, 200 mm, 220 mm, 240 mm, 260 mm, 280 mm, or 300 mm, and W1<W2. In some aspects, the thickness of the sintered ceramic may range from 25 mm to 75 mm, 20 mm to 50 mm, 30 mm to 60 mm, or 10 mm to 40 mm. Any sintered ceramic disclosed herein, including a ribbon ceramic, may have any of the foregoing thicknesses.

[0036] As indicated elsewhere herein, depending on the stage of production at which a heat treatment is performed and / or how cooling takes place thereafter, the heat treatment methods of the present disclosure may remove an existing lithium carbonate deposit from the surface of LLZO, and / or the cooling methods may prevent or limit formation of lithium carbonate deposits upon LLZO, or any combination thereof.

[0037] Heat treatment methods for removing an existing or suspected lithium carbonate deposit from the surface of a sintered ceramic, such as LLZO, for example, may take place following a sintering process. The heat treatment methods for removing an existing or suspected lithium carbonate deposit may be decoupled from the sintering process itself. The heat treatment may be conducted upon the sintered ceramic alone or upon a part already having the sintered ceramic emplaced therein. The part may comprise at least a portion of aAttorney Docket No. SP24-323 PCT solid-state battery, for instance. Alternately, the heat treatment may be conducted upon a ribbon ceramic that is transported via a reel-to-reel process through zones devoted to heating and cooling the ribbon ceramic.

[0038] Such methods may comprise: providing a sintered ceramic having a surface deposit of metal carbonate or a suspected deposit of metal carbonate (e.g., lithium carbonate in the case of the sintered ceramic comprising or consisting of LLZO) that is present upon at least one of a first face or a second face of the sintered ceramic; heating the sintered ceramic at a first temperature in a first environment comprising an inert gas, a sub-atmospheric pressure, or both, the first temperature being effective to remove at least a portion of the surface deposit of metal carbonate from the sintered ceramic; and cooling the sintered ceramic in a second environment comprising an inert gas, a sub-atmospheric pressure, or both to a second temperature of 100°C or below.

[0039] The second temperature may be a temperature at which the sintered ceramic is easily handled and / or leads to limited reactivity of the sintered ceramic with ambient atmosphere at or below the second temperature. Depending on the length of time the sintered ceramic needs to be exposed to ambient atmosphere or other conditions, as well as the amount of carbon dioxide and water present therein, the second temperature may be selected appropriately. In non-limiting aspects, the second temperature may be 100° or below, 90°C or below, 80°C or below, 70°C or below, 60°C or below, 50°C or below, 40°C or below, 30°C or below, 20°C or below, 10°C or below, 0°C or below, -10°C or above, 0°C or above, 10°C or above, 20°C or above, 30°C or above, 40°C or above, 50°C or above, 60°C or above, 70°C or above, 80°C or above, or 90°C or above, or any range formed therefrom. In some aspects, the second temperature may range from Cl to C2, wherein Cl and C2 are, independently,-10°C, 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C, and C1<C2. In some examples, the second temperature may range from 20°C to 40°C, 20°C to 30°C, 20°C to 25°C, or 25°C to 30°C.

[0040] Once removal of lithium carbonate is deemed complete, heating at the first temperature may be discontinued, and the sintered ceramic then begins to cool under the conditions of the second environment until the second temperature is reached. Depending on the type of atmosphere present during cooling, cooling may occur at an ambient rate or active cooling may be used to achieve a more rapid cooling rate. Active cooling may be conducted at any cooling rate that avoids imparting excess thermal shock to the sintered ceramic. Because the sintered ceramic and parts formed therefrom may differ in configuration andAttorney Docket No. SP24-323 PCT thickness, for example, different cooling rates may be suitable for various heat treatment scenarios. In non-limiting aspects, the cooling rate may be 10°C / minute or more, 25°C / minute or more, 50°C / minute or more, 100°C / minute or more, 150°C / minute or more, 200°C / minute or more, 250°C / minute or more, 300°C / minute or more, 400°C / minute or more, 500°C / minute or more, 600°C / minute or less, 500°C / minute or less, 400°C / minute or less, 300°C / minute or less, 250°C / minute or less, 200°C / minute or less, 150°C / minute or less, 100°C / minute or less, 50°C / minute or less, or 25°C / minute or less, or any range formed therefrom. In some aspects, the cooling rate may range from R1 to R2, wherein R1 and R2 are, independently, 10°C / minute, 25°C / minute, 50°C / minute, 100°C / minute, 150°C / minute, 200°C / minute, 250°C / minute, 300°C / minute, 400°C / minute, or 500°C / minute, and where R1<R2. In some examples, the cooling rate may range from 10°C / minute to 50°C / minute, 10°C / minute to 25°C / minute, 25°C / minute to 50°C / minute, 50°C / minute to 100°C / minute, 100°C / minute to 250°C / minute, 150°C / minute to 250°C / minute, or 150°C / minute to 200°C / minute.

[0041] When present, the inert gas and the conditions associated with the inert gas may be the same or different in the first environment and the second environment. Similarly, when present, the sub-atmospheric pressure may be the same or different in the first environment and the second environment. A combination of inert gas and sub-atmospheric pressure (e.g., an inert gas at a pressure below atmospheric pressure) may also be employed in the first environment, second environment, or both, and in some aspects, such combinations may be the same or different in the first and second environments. As non-limiting examples, different inert gases and / or inert gas pressures may be utilized in the first and second environments.

[0042] The sintered ceramic, from which a lithium carbonate deposit or similar metal carbonate deposit is to be removed, may be present in a part that is heated under the first environment having the first temperature. Thus, in addition to the sintered ceramic, the part may also undergo heating and cooling in the course of removing the lithium carbonate deposit from the sintered ceramic. The part may comprise at least a portion of a solid-state battery, for example. For instance, the sintered ceramic may be disposed as a thin separator upon either the cathode or anode, which may then be heated to promote removal of lithium carbonate or a similar metal carbonate. The sintered ceramic may have been cut to a desired size from a ribbon ceramic before being incorporated in the part, for example.

[0043] Heating the sintered ceramic at the first temperature may take place in a first environment that does not encourage further formation of lithium carbonate. In non-limitingAttorney Docket No. SP24-323 PCT examples, the first environment may comprise or consist essentially of an inert gas, a sub- atmospheric pressure, or both (an environment having both a sub-atmospheric pressure and containing an inert gas, / .< ., a sub-atmospheric pressure of inert gas). When the first environment includes an inert gas, a sub-atmospheric pressure, or both, the first temperature may be sufficient to degrade the carbonate, thereby removing at least a portion or even all of the lithium carbonate from the surface of the sintered ceramic, but without undesirably removing lithium ions therefrom.

[0044] The first temperature that is effective for removing lithium carbonate from the sintered ceramic may be 700°C or more, 710°C or more, 720°C or more, 730°C or more, 740°C or more, 750°C or more, 760°C or more, 770°C or more, 780°C or more, 790°C or more, 800°C or more, 810°C or more, 820°C or more, 830°C or more, 840°C or more, 850°C or more, 860°C or more, 870°C or more, 880°C or more, 890°C or more, 900°C or less,890°C or less, 880°C or less, 870°C or less, 860°C or less, 850°C or less, 840°C or less,830°C or less, 820°C or less, 810°C or less, 800°C or less, 790°C or less, 780°C or less,770°C or less, 760°C or less, 750°C or less, 740°C or less, 730°C or less, 720°C or less, or710°C or less, or any range formed therefrom. In non-limiting aspects, the first temperature may range from T3 to T4, wherein T3 and T4 are, independently, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, or 900°C, and where T3<T4. In some aspects, the first temperature may range from 700°C to 800°C, 700°C to 750°C, 750°C to 800°C, 780°C to 820°C, 820°C to 840°C, or 840°C to 860°C. In some examples, the first temperature may be below the sintering temperature used to produce the sintered ceramic.

[0045] Heating at the first temperature may be conducted for a sufficient time to remove all or at least a portion of the lithium carbonate deposit from the surface of the sintered ceramic. The heating time for promoting sufficient removal of the lithium carbonate may vary depending upon the first temperature used, as well as the pressure of the first environment. In general, lower temperatures may require longer heating times to promote effective removal of the lithium carbonate. The heating time may be 1 minute or more, 5 minutes or more, 10 minutes or more, 20 minutes or more, 30 minutes or more, 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, 5 hours or more, 6 hours or less, 5 hours or less, 4 hours or less, 3 hours or less, 2 hours or less, 1 hour or less, 30 minutes or less, 20 minutes or less, 10 minutes or less, or 5 minutes or less. In non-limiting aspects, the heating time may range from Hl to H2, wherein Hl and H2 are, independently, 1 minute, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6Attorney Docket No. SP24-323 PCT hours, and where H1<H2. In some aspects, the heating time may range from 10 minutes to 2 hours, 10 minutes to 30 minutes, 30 minutes to 1 hour, or 1 hour to 2 hours. In some cases, lower temperatures within the foregoing ranges may be favorable, particularly when the first environment comprises a sub-atmospheric pressure. Excessively high first temperatures combined with a sub-atmospheric pressure may promote unwanted sublimation and / or decomposition of the LLZO or other sintered ceramics under extended heating times in some cases.

[0046] Like a sintering process, heating at the first temperature may take place in a first environment comprising, consisting of, or consisting essentially of an inert gas. Suitable inert gases may include, but are not limited to, nitrogen (N2), noble gases (He, Ne, Ar, Kr, Xe, or any combination thereof), or any combination thereof.

[0047] According to one or more aspects, the inert gas may be present in the first environment at a pressure within +10% of atmospheric pressure. Such pressures may be similar to the inert gas pressures employed during sintering. Accordingly, the inert gas may have a pressure of l.l lxlO5Pa or less (836 torr or less, or 1.1 atmosphere or less), 1.07xl05Pa or less (798 torr or less, or 1.05 atmosphere or less), l.OlxlO5Pa or less (760 torr or less, or 1 atmosphere or less), 9.62xl04Pa or less (722 torr or less, or 0.95 atmosphere or less), 9.12xl04Pa or more (684 torr or more, or 0.9 atmosphere or more), 1.07xl05Pa or more (798 torr or more, or 1.05 atmosphere or more), l.OlxlO5Pa or more (760 torr or more, or 1 atmosphere or more), or 1.07xl05Pa or more (798 torr or more, or 1.05 atmosphere or more), or any range formed therefrom. In non-limiting aspects, the pressure of the inert gas while heating at the first temperature may range from P5 to P6, wherein P5 and P6 are, independently, 9.12xl04Pa (684 torr or 0.9 atmosphere), 9.62xl04Pa (722 torr or 0.95 atmosphere), l.OlxlO5Pa (760 torr or 1 atmosphere), 1.07xl05Pa (798 torr or 1.05 atmosphere), or 1.1 IxlO5Pa (836 torr or 1.1 atmosphere), and P5<P6. In particular aspects, the pressure of the inert gas while heating at the first temperature may range from 9.62xl04Pa (722 torr or 0.95 atmosphere) to l.OlxlO5Pa (760 torr or 1 atmosphere), or l.OlxlO5Pa (760 torr or 1 atmosphere) to 1.07xl05Pa (798 torr or 1.05 atmosphere). In some aspects, the pressure of the inert gas while heating at the first temperature may be approximately l.OlxlO5Pa (760 torr or 1 atmosphere).

[0048] According to one or more aspects, heating the sintered ceramic at the first temperature may take place in a first environment comprising an elevated pressure that is at least 10% above atmospheric pressure. The elevated pressure may be provided by an inert gas or a combination thereof. The elevated pressure may be 1.1 IxlO5Pa or more (836 torr orAttorney Docket No. SP24-323 PCT more, or 1.1 atmosphere or more), 1.22xl05Pa or more (912 torr or more, or 1.2 atmosphere or more), 1.32xl05Pa or more (988 torr or more, or 1.3 atmosphere or more), 1.42xl05Pa or more (1064 torr or more, or 1.4 atmosphere or more), 1.52xl05Pa or more (1140 torr or more, or 1.5 atmosphere or more), 1.62xl05Pa or more (1216 torr or more, or 1.6 atmosphere or more), 1.72xl05Pa or more (1292 torr or more, or 1.7 atmosphere or more), 1.82xl05Pa or more (1368 torr or more, or 1.8 atmosphere or more), 1.92xl05Pa or more (1444 torr or more, or 1.9 atmosphere or more), or 2.03xl05Pa or less (1520 torr or less, or 2 atmosphere or less), 1.92xl05Pa or less (1444 torr or less, or 1.9 atmosphere or less), 1.82xl05Pa or less (1368 torr or less, or 1.8 atmosphere or less), 1.72xl05Pa or less (1292 torr or less, or 1.7 atmosphere or less), 1.62xl05Pa or less (1216 torr or less, or 1.6 atmosphere or less), 1.52xl05Pa or less (1140 torr or less, or 1.5 atmosphere or less), 1.42xl05Pa or less (1064 torr or less, or 1.4 atmosphere or less), 1.32xl05Pa or less (988 torr or less, or 1.3 atmosphere or less), 1.22xl05Pa or less (912 torr or less, or 1.2 atmosphere or less), or any range formed therefrom. In non-limiting aspects, the pressure of the inert gas while heating at the first temperature may range from P7 to P8, wherein P7 and P8 are, independently, 1.1 IxlO5Pa (836 torr, or 1.1 atmosphere), 1.22xl05Pa (912 torr, or 1.2 atmosphere), 1.32xl05Pa (988 torr, or 1.3 atmosphere), 1.42xl05Pa (1064 torr, or 1.4 atmosphere), 1.52xl05Pa (1140 torr, or 1.5 atmosphere), 1.62xl05Pa (1216 torr, or 1.6 atmosphere), 1.72xl05Pa (1292 torr, or 1.7 atmosphere), 1.82xl05Pa (1368 torr, or 1.8 atmosphere), 1.92xl05Pa (1444 torr, or 1.9 atmosphere), or 2.03xl05Pa (1520 torr, or 2 atmosphere), and where P7<P8. In some aspects, the pressure while heating at the first temperature may range from 1.22xl05Pa (912 torr, or 1.2 atmosphere) to 1.62xl05Pa (1216 torr, or 1.6 atmosphere), 1.22xl05Pa (912 torr, or 1.2 atmosphere) to 1.32xl05Pa (988 torr, or 1.3 atmosphere), 1.32xl05Pa (988 torr, or 1.3 atmosphere) tol.62xl05Pa (1216 torr, or 1.6 atmosphere), or 1.42xl05Pa (1064 torr, or 1.4 atmosphere) to 1.52xl05Pa (1140 torr, or 1.5 atmosphere).

[0049] According to one or more aspects, heating the sintered ceramic at the first temperature may take place in a first environment comprising a sub-atmospheric pressure that is at least 10% below atmospheric pressure. The sub-atmospheric pressure may be 9.12xl04Pa or less (684 torr, or less or 0.9 atmosphere or less), 8.1 IxlO4Pa or less (608 torr or less, or 0.8 atmosphere or less), 7.09 x 104Pa or less (532 torr or less, or 0.7 atmosphere or less), 6.08xl04Pa or less (456 torr or less, or 0.6 atmosphere or less), 5.07xl04Pa or less (380 torr or less, or 0.5 atmosphere of less), 4.05xl04Pa or less (304 torr or less, or 0.4 atmosphere or less), 4.05xl04Pa or more (304 torr or more, or 0.4 atmosphere or more), 5.07xl04Pa or more (380 torr or more, or 0.5 atmosphere of more), 6.08xl04Pa or more (456 torr or more,Attorney Docket No. SP24-323 PCT or 0.6 atmosphere or more), 7.09 x 104Pa or more (532 torr or more, or 0.7 atmosphere or more), or 8.1 IxlO4Pa or more (608 torr or more, or 0.8 atmosphere or more), or any range formed therefrom. More typically, suitable sub-atmospheric pressures while heating at the first temperature include a pressure of 1.33xl04Pa or less (100 torr or less, or 0.13 atmosphere or less), 1.20xl04Pa or less (90 torr or less, or 0.12 atmosphere or less), 1.07xl04Pa or less (80 torr or less, or 0.11 atmosphere or less), 9.33xl03Pa or less (70 torr or less, or 0.092 atmosphere or less), 8.00xl03Pa or less (60 torr or less, or 0.079 atmosphere or less), 6.67xl03Pa or less (50 torr or less, or 0.066 atmosphere or less), 5.33xl03Pa or less (40 torr or less, or 0.053 atmosphere or less), 4.00xl03Pa or less (30 torr or less, or 0.039 atmosphere or less), 2.67xl03Pa or less (20 torr or less, or 0.026 atmosphere or less), 1 ,33xl03Pa or less (10 torr or less, or 0.013 atmosphere or less), 133 Pa or less (1 torr or less, or 0.0013 atmosphere or less), 13 Pa or more (0.1 torr or more, or 0.00013 atmosphere or more), 133 Pa or more (1 torr or more, or 0.0013 atmosphere or more), 1.33xl03Pa or more (10 torr or more, or 0.013 atmosphere or more), 2.67xl03Pa or more (20 torr or more, or 0.026 atmosphere or more), 4.00xl03Pa or more (30 torr or more, or 0.039 atmosphere or more), 5.33xl03Pa or more (40 torr or more, or 0.053 atmosphere or more), 6.67xl03Pa or more (50 torr or more, or 0.066 atmosphere or more), 8.00xl03Pa or more (60 torr or more, or 0.079 atmosphere or more), 9.33xl03Pa or more (70 torr or more, or 0.092 atmosphere or more), 1 ,07xl04Pa or more (80 torr or more, or 0.11 atmosphere or more), or 1 ,20xl04Pa or more (90 torr or more, or 0.12 atmosphere or more), or any range formed therefrom. In nonlimiting aspects, the sub-atmospheric pressure while heating at the first temperature may range from P9 to P10, wherein P9 and P10 are, independently, 13 Pa (0.1 torr or 0.00013 atmosphere), 133 Pa (1 torr or 0.0013 atmosphere), 1.33xl03Pa (10 torr or 0.013 atmosphere), 2.67xl03Pa (20 torr or 0.026 atmosphere), 4.00xl03Pa (30 torr or 0.039 atmosphere), 5.33xl03Pa (40 torr or 0.053 atmosphere), 6.67xl03Pa (50 torr or 0.066 atmosphere), 8.00xl03Pa (60 torr or 0.079 atmosphere), 9.33xl03Pa (70 torr or 0.092 atmosphere), 1.07xl04Pa (80 torr or 0.11 atmosphere), 1.20xl04Pa (90 torr or 0.12 atmosphere), or 1.33xl04Pa (100 torr or 0.13 atmosphere), and where P9<P10. In some aspects, the sub-atmospheric pressure may be about 4.00xl03Pa or below (30 torr or below, or 0.039 atmosphere or below) or 2.67xl03Pa or below (20 torr or below, or 0.026 atmosphere or below), such as within a range of 1.33xl03Pa (10 torr or 0.013 atmosphere) to 2.67xl03Pa (20 torr or 0.026 atmosphere), 1.33xl03Pa (10 torr or 0.013 atmosphere) to 4.00xl03Pa (30 torr or 0.039, or 2.67xl03Pa (20 torr or 0.026 atmosphere) to 4.00xl03Pa (30 torr or 0.039 atmosphere).Attorney Docket No. SP24-323 PCT

[0050] It is envisioned that an inert gas may constitute substantially all of the residual pressure (partial pressure) in a first environment comprising a sub-atmospheric pressure. To achieve such a first environment, a vessel containing the sintered ceramic may undergo one or more cycles of purging with inert gas, evacuating the inert gas with a vacuum pump, followed by additional pumping until a desired sub-atmospheric pressure is reached. Alternately, inert gas may be provided to the first environment until a desired sub- atmospheric pressure of the inert gas is reached. Water and / or carbon dioxide may remain as negligible impurities after a sufficient number of pumping cycles. Any remaining water and / or carbon dioxide may represent those introduced via the inert gas. The desired sub- atmospheric pressure may be established before heating at the first temperature takes place. Once the desired sub-atmospheric pressure has been established, the vacuum pump may be isolated from the vessel in which the sub-atmospheric pressure is maintained (static vacuum) or continue to apply suction to the vessel in which the sub-atmospheric pressure is maintained (dynamic vacuum).

[0051] While heating at the first temperature and cooling to the second temperature, the sintered ceramic may be disposed upon a thermal mass. As used herein, the term “thermal mass” refers to a body having a mass much higher than that of the sintered ceramic disposed thereon, such as a mass of approximately 50-fold or more higher than that of the sintered ceramic. The sintered ceramic may be disposed upon the thermal mass alone or when incorporated within a part. Use of a thermal mass during heating may provide several benefits. Because the thermal mass directly contacts the sintered ceramic, the thermal mass may promote conveyance of thermal energy from the thermal mass into the sintered ceramic to promote heating thereof. The thermal mass may also be movable, should the sintered ceramic need to be moved to a different location for cooling (e.g., to a different vessel). Suitable thermal masses may include materials having high heat capacity values, such as metals, ceramics, and the like. Illustrative materials that may be present in a thermal mass include, but are not limited to, stainless steel, nickel, alumina, zirconia, graphite, GRAFOIL, and the like. Additionally, a base material of a thermal mass may be coated with metals such as platinum, gold, or other metals that are prohibitively expensive to utilize alone as a solid metal body.

[0052] To promote heating, an entire vessel containing the thermal mass may be heated at the first temperature or the thermal mass may be locally heated. Local heating of the thermal mass may be desirable to avoid the need for heating the entirety of the vessel in which heating to remove the metal carbonate takes place.Attorney Docket No. SP24-323 PCT

[0053] When heating takes place on a thermal mass, a first face of the sintered ceramic may contact the thermal mass during heating and cooling. In addition to providing the heat transfer benefits discussed above, the thermal mass may further serve as a diffusion barrier that limits access of water and / or carbon dioxide to the first face of the sintered ceramic, thereby lessening the likelihood of lithium carbonate re-forming on the first face of the sintered ceramic during cooling.

[0054] A diffusion barrier may also be present upon a second face of the sintered ceramic at least during cooling, wherein the second face is opposite the first face and the diffusion barrier upon the second face differs from the thermal mass. Suitable materials for such diffusion barriers include substances that are stable at the temperatures to which the sintered ceramic is heated prior to being cooled to the second temperature. Additional characteristics of suitable materials for a diffusion barrier may include, for example, at least partial impermeability to carbon dioxide and water over a range of temperatures and ready removability once the diffusion barrier is no longer needed. Suitable diffusion barrier materials may include, for example, alumina or zirconia thin ceramics that are applied to the second face prior to or during cooling. For example, the diffusion barrier may be applied to the second face of the sintered ceramic prior to heating at the first temperature or while heating at the first temperature. Alternately, the diffusion barrier may be applied to the second face of the sintered ceramic after heating is complete but before cooling takes place. In a roll-to-roll process, for example, the sintered ceramic may be discharged from a first roll and the diffusion barrier may be discharged from a second roll onto the sintered ceramic. If desired, the diffusion barrier may be removed from the sintered ceramic after sufficient cooling has taken place, and the diffusion barrier may be reused in a subsequent heating process.

[0055] When removing lithium carbonate from the sintered ceramic, heating at the first temperature and cooling to the second temperature may take place in a single vessel (chamber) or in multiple vessels (e.g., multiple chambers). A single vessel may be configured to heat the sintered ceramic at the first temperature in the presence of an inert gas and / or while maintaining a sub-atmospheric pressure, optionally with the sintered ceramic disposed upon a thermal mass. In some examples, heating of the sintered ceramic may take place in a vessel at the first temperature in the presence of an elevated pressure of inert gas (e.g., a pressure of at least 10% above atmospheric pressure). For example, in some aspects, the single vessel may be a vacuum oven, and / or a vacuum chamber containing a thermal mass that may be suitably heated. In some aspects, a first vessel may be used for heating theAttorney Docket No. SP24-323 PCT sintered ceramic at the first temperature in the presence of an inert gas or while maintaining a sub-atmospheric pressure, and after heating, the sintered ceramic may be transferred to a second vessel for cooling, wherein the second vessel may be configured to contain an inert gas or, more typically, to maintain a sub-atmospheric pressure.

[0056] In some aspects, a sintered ceramic being held stationary may be heated and cooled under a sub-atmospheric pressure, typically with heating and cooling taking place in a single vessel. The heating and cooling may occur in a batchwise manner. The single vessel in which heating and cooling take place may be continuously evacuated with a vacuum pump, for example, during heating and cooling. The sub-atmospheric pressure during heating and the sub-atmosphere pressure during cooling may be the same or different. Once the desired sub-atmospheric pressure has been established in the single vessel, the vacuum pump may be isolated from the single vessel in which the sub-atmospheric pressure is maintained (static vacuum) or continue to apply suction to the single vessel in which the sub-atmospheric pressure is maintained (dynamic vacuum). Optionally, the sintered ceramic may be housed in a vacuum vessel that is portable after being cooled, such that the sintered ceramic may be easily transported to a desired location for further manipulation. Any of the cooling rates specified herein may be utilized.

[0057] In some aspects, a sintered ceramic being held stationary may be heated in the presence of an inert gas and cooled under a sub-atmospheric pressure. The heating and cooling may occur in a batchwise manner. The inert gas may be maintained within +10% of atmospheric pressure during heating, or the inert gas may be maintained at an elevated pressure, including the elevated pressures discussed above. Optionally, a diffusion barrier may overlay an exposed face of the sintered ceramic, wherein the diffusion barrier may be applied to the sintered ceramic before or during heating, such that the diffusion barrier is present once cooling begins. Heating and cooling may take place in a single vessel, or heating and cooling may take place in separate vessels. Once the desired sub-atmospheric pressure has been established, the vacuum pump may be isolated from the vessel in which the sub-atmospheric pressure is maintained (static vacuum) or continue to apply suction to the vessel in which the sub-atmospheric pressure is maintained (dynamic vacuum).

[0058] The sintered ceramic may be held stationary during heating and cooling, or the sintered ceramic may be moving when undergoing heating and cooling. A part containing a piece of ribbon ceramic, for example, may be held stationary while being heated and cooled in a first vessel, or held stationary while being heated in a first vessel and cooled in a second vessel, as described in more detail elsewhere herein. Continuous heat treatment processes areAttorney Docket No. SP24-323 PCT compatible with movement of the sintered ceramic during heating and cooling. A ribbon ceramic, for example, may be transported (conveyed from a first reel to a second reel) while being heated and cooled.

[0059] In some aspects, heating of a ribbon ceramic may take place under a sub- atmospheric pressure, and cooling of the ribbon ceramic may also take place under a sub- atmospheric pressure. Heating and cooling of the ribbon ceramic may take place in a single vessel. A reel-to-reel system may be incorporated within the single vessel for conveying the ribbon ceramic from a first reel to a second reel while being heated and cooled. Cooling may take place by ambient heat loss to the surrounding environment, or cooling may take place actively by providing a cooling stream comprising an inert gas at a lower temperature than the ceramic ribbon and / or by the ribbon ceramic maintaining contact with an actively cooled surface before being received on the second reel. Rapid cooling by active cooling may be desirable to lessen the reactivity of the sintered ceramic toward carbon dioxide and water. Any of the cooling rates specified herein may be utilized.

[0060] In some aspects, heating of a ribbon ceramic may take place in the presence of an inert gas, and cooling of the ribbon ceramic may also take place in the presence of an inert gas. Heating and cooling of the ribbon ceramic in the presence of the inert gas may take place in a single vessel. A reel-to-reel system may be incorporated within the single vessel for conveying the ribbon ceramic from a first reel to a second reel while being heated and cooled. Optionally, a diffusion barrier may be applied to the ribbon ceramic before cooling. For example, the diffusion barrier may be applied to the ribbon ceramic after the sintering process originally used to produce the ribbon ceramic, or the diffusion barrier may be introduced to the ribbon ceramic during the reel-to-reel process conveying the ribbon ceramic from the first reel to the second reel during heating to remove the metal carbonate, such that the diffusion barrier remains present during cooling. Cooling may take place by ambient heat loss to the surrounding environment, or cooling may take place actively by providing a cooling stream comprising an inert gas at a lower temperature than the ceramic ribbon and / or by the ribbon ceramic maintaining contact with an actively cooled surface before being received on the second reel. Any of the cooling rates specified herein may be utilized.

[0061] In some examples, heating at the first temperature to remove metal carbonates may take place in a first environment comprising a sub-atmospheric pressure, and cooling to the second temperature may take place in a second environment also comprising a sub- atmospheric pressure. The sub-atmospheric pressure of the first and second environments may be the same or different ( / .< ., have different pressures). In some aspects, the first andAttorney Docket No. SP24-323 PCT second environments may have the same or substantially the same sub-atmospheric pressure, and heating and cooling may take place in a single vessel (chamber) at the sub-atmospheric pressure(s). In some examples, a ribbon ceramic may be conveyed from a first (payout) reel to a second (take-up) reel, each housed within the single vessel at the sub-atmospheric pressure, with the ribbon ceramic being heated at the first temperature during transit to the second reel. The ribbon ceramic on the second reel may then be cooled under the sub- atmospheric pressure to preclude re-formation of lithium carbonate. Alternately, the ribbon ceramic may be cooled to the second temperature in the single vessel at the sub-atmospheric pressure before being wound upon the second reel.

[0062] In any aspect described herein, the second environment may contain a low concentration of carbon dioxide and / or water to avoid formation of lithium carbonate as the sintered ceramic cools to the second temperature. In non-limiting examples, cooling the sintered ceramic to the second temperature may take place in a second environment having a water content of 30 parts per billion (ppb) or less, 25 ppb or less, 20 ppb or less, 15 ppb or less, 10 ppb or less, 9 ppb or less, 8 ppb or less, 7 ppb or less, 6 ppb or less, 5 ppb or less, 4 ppb or less, or 3 ppb or less, or any range formed therefrom, such as a water content within a range of 3 ppb to 5 ppb, 5 ppb to 8 ppb, 7 ppb to 15 ppb, or 10 ppb to 20 ppb. In some or other non-limiting examples, cooling the sintered ceramic may take place in a second environment having a carbon dioxide content of 10 parts per million (ppm) or less, 9 ppm or less, 8 ppm or less, 7 ppm or less, 6 ppm or less, 5 ppm or less, 4 ppm or less, 3 ppm or less, 2 ppm or less, or 1 ppm or less, or any range formed therefrom, such as a water content within a range of 1 ppm to 5 ppm, 2 ppm to 6 ppm, 1 ppm to 3 ppm, or 3 ppm to 7 ppm.

[0063] Techniques for achieving water and carbon dioxide contents within the foregoing ranges are well known, for example, by passing a stream of the inert gas through a desiccant, a carbon dioxide adsorber, or any combination thereof. Examples include, for instance, amines, metal hydroxides (e.g., lithium hydroxide, sodium hydroxide, or potassium hydroxide), zeolites, molecular sieves, membranes, cryogenic cold fingers, and the like. Electrochemical methods for consuming water and / or carbon dioxide may also be used to decrease residual amounts of these substances.

[0064] Methods of the present disclosure may also be coupled to a sintering process in order to prevent or minimize formation of metal carbonate deposits upon the surface of the solid oxide electrolyte as cool-down from the sintering process takes place. As with the above description directed to removing an existing or suspected deposit of metal oxide, methods coupled to a sintering process may utilize an environment comprising an inert gas, aAttorney Docket No. SP24-323 PCT sub-atmospheric pressure, or both during cooling to decrease the risk of forming metal oxide upon the surface of the solid oxide electrolyte.

[0065] Such methods may comprise: sintering a green ceramic at a sintering temperature in a first environment comprising an inert gas, a sub-atmospheric pressure, or both, thereby forming a sintered ceramic; and without exposing the sintered ceramic to conditions effective to form a surface deposit of metal carbonate on the sintered ceramic, cooling the sintered ceramic in a second environment comprising an inert gas, a sub-atmospheric pressure, or both to a second temperature of 100°C or below. In various aspects, the sintered ceramic material may comprise LLZO.

[0066] General conditions for conducting a sintering process are described in more detail elsewhere herein. In more specific examples, the sintering process may have a sintering temperature ranging from 950°C to 1150°C. The sintering process may take place in a first environment comprising an inert gas, a sub-atmospheric pressure, or both, as also described in more detail elsewhere herein.

[0067] The second temperature may be a temperature at which the sintered ceramic is easily handled and / or also leads to limited reactivity of the sintered ceramic with ambient atmosphere at or below the second temperature. Depending on the length of time the sintered ceramic needs to be exposed to ambient atmosphere or other conditions after cool-down, as well as the amount of carbon dioxide and water present therein, the second temperature may be selected appropriately. In non-limiting aspects, the second temperature may be 100° or below, 90°C or below, 80°C or below, 70°C or below, 60°C or below, 50°C or below, 40°C or below, 30°C or below, 20°C or below, 10°C or below, 0°C or below, -10°C or above, 0°C or above, 10°C or above, 20°C or above, 30°C or above, 40°C or above, 50°C or above, 60°C or above, 70°C or above, 80°C or above, or 90°C or above, or any range formed therefrom. In some aspects, the second temperature may range from Cl to C2, wherein Cl and C2 are, independently, -10°C, 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C, and C1<C2. In some examples, the second temperature may range from 20°C to 40°C, 20°C to 30°C, 20°C to 25°C, or 25°C to 30°C.

[0068] Cooling the sintered ceramic may take place without exposing sintered ceramic to ambient air or other conditions that may promote carbonate formation at or below the sintering temperature until it is desired to do so. The term “ambient air” refers to atmospheric air, as well as the amounts of moisture contained therein. To protect the sintered ceramic from ambient air following sintering, cooling of the sintered ceramic obtained fromAttorney Docket No. SP24-323 PCT the sintering process may take place in a second environment comprising an inert gas, a sub- atmospheric pressure, or both.

[0069] The first environment of the sintering process and the second environment during cooling may be the same or different. In some examples, the first environment and the second environment may each comprise an inert gas, or the first environment and the second environment may each comprise a sub-atmospheric pressure. When an inert gas is used in the second environment, the inert gas may have a higher pressure in the second environment than in the first environment and / or the inert gas may have been more rigorously purified to remove carbon dioxide and / or water therefrom in the second environment but not necessarily in the first environment. In some aspects, when an inert gas is used in the second environment, the inert gas may have a higher pressure in the first environment than in the second environment and / or the inert gas may have been more rigorously purified to remove carbon dioxide and / or water therefrom in the first environment than in the second environment.

[0070] To limit the risk of forming metal carbonate, the second environment may have a lower concentration of water and carbon dioxide than does the first environment. For example, the second environment may have a water content of 30 parts per billion (ppb) or less, 25 ppb or less, 20 ppb or less, 15 ppb or less, 10 ppb or less, 9 ppb or less, 8 ppb or less, 7 ppb or less, 6 ppb or less, 5 ppb or less, 4 ppb or less, 3 ppb or less, 2 ppb or less, 1 ppb or less, 0 ppb, or any range formed therefrom, such as a water content within a range of 0 ppb to 10 ppb, 0 ppb to 5 ppb, 1 ppb to 5 ppb, 2 ppb to 6 ppb, 1 ppb to 3 ppb, or 3 ppb to 7 ppb. In some or other non-limiting examples, cooling the sintered ceramic may take place in a second environment having a carbon dioxide content of 10 parts per million (ppm) or less, 9 ppm or less, 8 ppm or less, 7 ppm or less, 6 ppm or less, 5 ppm or less, 4 ppm or less, 3 ppm or less, 2 ppm or less, or 1 ppm or less, or any range formed therefrom, such as a water content within a range of 1 ppm to 5 ppm, 2 ppm to 6 ppm, 1 ppm to 3 ppm, or 3 ppm to 7 ppm. Illustrative techniques for achieving the foregoing carbon dioxide and water concentrations in an inert gas are provided elsewhere herein.

[0071] To accomplish the foregoing, the sintering process and cooling may take place in a single vessel. When sintering and cooling take place in a single vessel, the first environment may be exchanged for the second environment without exposing the sintered ceramic to ambient air, or the first environment and the second environment may be equivalent to one another and not in need of exchange.Attorney Docket No. SP24-323 PCT

[0072] In some examples, a continuous sintering process may be conducted in a single vessel. The continuous sintering process may comprise reel-to-reel tape casting and sintering to produce a ribbon ceramic, for example. As discussed above, a precursor of the ribbon ceramic may be provided from a first reel and undergo heating at the sintering temperature, and the resulting ribbon ceramic may be wound onto a second reel after or while being cooled. Optionally, a diffusion barrier may be applied during or after tape casting or during sintering, such that the diffusion barrier is present upon the sintered ceramic during cooling. Suitable diffusion barriers may include, for example, alumina or zirconia ribbon ceramics that overlay one or more faces of the ribbon ceramic to limit access of carbon dioxide and water thereto. In other examples, discontinuous diffusion barriers may travel at the same rate as the ribbon ceramic and provide protection against oxygen and carbon dioxide until the ribbon ceramic has cooled sufficiently. For example, a discontinuous diffusion barrier may be on a rotating loop that approaches the surface of the ribbon ceramic during cooling so as to limit access of carbon dioxide and water thereto.

[0073] In some examples, continuous sintering and cooling may both take place under an inert gas. A pressure of the inert gas during cooling may be higher than an inert gas pressure during sintering or vice versa. A higher inert gas pressure during cooling may limit the ability of carbon dioxide and water to access the cooling location where they may react with the surface of the ribbon ceramic. Optionally, the inert gas provided during cooling may have been further purified to remove carbon dioxide and / or water therefrom. Cooling may take place by ambient heat loss to the surrounding environment, or cooling may take place actively by providing a cooling stream comprising an inert gas at a lower temperature than the ceramic ribbon and / or by the ribbon ceramic maintaining contact with an actively cooled surface before being received on the second reel. Rapid cooling by active cooling may be desirable to lessen the reactivity of the sintered ceramic toward carbon dioxide and water. Any of the cooling rates specified herein may be utilized.

[0074] In some examples, continuous sintering and cooling both take place under a sub- atmospheric pressure. Cooling may take place by ambient heat loss to the surrounding environment, or cooling may take place actively by providing a cooling stream comprising an inert gas at a lower temperature than the ceramic ribbon and / or by the ribbon ceramic maintaining contact with an actively cooled surface before being received on the second reel. Any of the cooling rates specified herein may be utilized.

[0075] LLZO and other sintered ceramics having a thin structure may be produced to minimize or eliminate carbonate formation (e.g., lithium carbonate) upon at least a firstAttorney Docket No. SP24-323 PCT surface thereof. For example, LLZO may be produced to be free or substantially free of lithium carbonate upon at least a first surface of the sintered ceramic. Other sintered ceramics processed in a similar manner may likewise be free or substantially free of a metal carbonate upon a surface thereof.

[0076] In some aspects, the first surface of the sintered ceramic may contain 5 mol% or less metal carbonate, 4 mol% or less metal carbonate, 3 mol% or less metal carbonate, 2 mol% or less metal carbonate, 1 mol% or less metal carbonate, 0.8 mol% or less metal carbonate, 0.6 mol% or less metal carbonate, 0.4 mol% or less metal carbonate, 0.2 mol% or less metal carbonate, 0.08 mol% or less metal carbonate, 0.06 mol% or less metal carbonate, 0.04 mol% or less metal carbonate, 0.02 mol% or less metal carbonate, or 0 mol% metal carbonate, or any range formed therefrom. The foregoing values may be measured by X-ray photoelectron spectroscopy (XPS) and may be obtained from the relative peak intensities obtained from surface interrogation of the sintered ceramic. For surface percentages of metal oxide measured by XPS, the amount of metal oxide is measured at a depth within 20 nm of the first surface. In non-limiting examples, the metal carbonate may be present at a mol% ranging from Ml to M2, wherein Ml and M2 may be, independently, 5 mol%, 4 mol%, 3 mol%, 2 mol%, 1 mol%, 0.9 mol%, 0.8 mol%, 0.7 mol%, 0.6 mol%, 0.5 mol%, 0.4 mol%, 0.3 mol%, 0.2 mol%, 0.1 mol%, 0.09 mol%, 0.08 mol%, 0.07 mol%, 0.06 mol%, 0.05 mol%, 0.04 mol%, 0.03 mol%, 0.02 mol%, 0.01 mol%, or >0 mol%, and M1<M2. In some examples, the mol% of metal carbonate may range from 0 to 0.5 mol%, 0 mol% to 1 mol%, 0.1 mol% to 1 mol%, 0.5 mol% to 2 mol%, or 1 mol% to 5 mol%.

[0077] In the case of LLZO, the first surface of the sintered ceramic may contain 5 mol% or less lithium carbonate, 4 mol% or less lithium carbonate, 3 mol% or less lithium carbonate, 2 mol% or less lithium carbonate, 1 mol% or less lithium carbonate, 0.8 mol% or less lithium carbonate, 0.6 mol% or less lithium carbonate, 0.4 mol% or less lithium carbonate, 0.2 mol% or less lithium carbonate, 0.08 mol% or less lithium carbonate, 0.06 mol% or less lithium carbonate, 0.04 mol% or less lithium carbonate, 0.02 mol% or less lithium carbonate, or 0 mol% lithium carbonate, or any range formed therefrom. The foregoing values are measured by X-ray photoelectron spectroscopy (XPS) at a depth within 20 nm of the first surface. In non-limiting examples, the lithium carbonate may be present at a mol% ranging from LI to L2, wherein LI and L2 may be, independently, 5 mol%, 4 mol%, 3 mol%, 2, mol% 1 mol%, 0.9 mol%, 0.8 mol%, 0.7 mol%, 0.6 mol%, 0.5 mol%, 0.4 mol%, 0.3 mol%, 0.2 mol%, 0.1 mol%, 0.09 mol%, 0.08 mol%, 0.07 mol%, 0.06 mol%, 0.05 mol%, 0.04 mol%, 0.03 mol%, 0.02 mol%, 0.01 mol%, or >0 mol%, and L1<L2. In some examples, the mol% of lithiumAttorney Docket No. SP24-323 PCT carbonate may range from 0 mol% to 0.5 mol%, 0 mol% to 1 mol%, 0.1 mol% to 1 mol%, 0.5 mol% to 2 mol%, or 1 mol% to 5 mol%.

[0078] By conducting heating and cooling to minimize or remove lithium carbonate upon a surface thereof, LLZO may be produced with an ideal or near-ideal stoichiometry (e.g., LiyLasZnOn), since lithium ions are not permanently removed from the LLZO, as they are when processing a sintered ceramic by polishing or acid-etching. Other ceramics that may become deficient in at least one atom when polished or acid-etched may similarly be produced with an ideal or near-ideal stoichiometry when processed by the heat treatments disclosed herein. LLZO of the present disclosure, in contrast, may be distinguished from that modified by alternative techniques for removing lithium carbonate deposits. For example, other types of LLZO, such as those that are lithium-deficient and potentially produced by alternative techniques, will have a lower overall amount of lithium and therefore have altered atomic ratios of lithiumdanthanum and lithium: zirconium upon the first surface of the sintered ceramic. The term “atomic ratio” refers to a molar ratio of a first atom to a second atom, irrespective of any other atoms with which the first atom and / or the second atom may be bonded. The foregoing atomic ratios may be measured by XPS at a depth within 20 nm of the first surface. LLZO of the present disclosure may have a surface atomic ratio of lithiumdanthanum within +5% of 7:3 and a surface atomic ratio of lithium: zirconium within +5% of 7:2. In some aspects, the surface atomic ratio of lithium: lanthanum is no greater than 7:3 and the surface atomic ratio of lithium: zirconium is no greater than 7:2. If surface atomic ratio of lithiumdanthanum is no greater than 7:3 and the surface atomic ratio of lithium: zirconium is no greater than 7:2, this means that the LLZO is not lithium-deficient relative to pristine LLZO. For purposes of the foregoing, the surface atomic ratio refers to the measured atomic ratio at a depth within 20 nm from the first surface of the sintered ceramic.

[0079] Average surface area and average surface roughness are additional characteristics that together may distinguish LLZO of the present disclosure from that resulting from alternative techniques for removing lithium carbonate. Average surface roughness (Sa) and average surface area, measured as the average developed interfacial area ratio (Sdr), may be measured by scanning laser confocal microscopy or, alternately, by atomic force microscopy or interferometry. The term “average developed interfacial area ratio (Sdr)” refers to the ratio of measured surface area to geometric surface area, where the geometric surface area is the area of a geometrically flat geometric shape. That is, Sdr represents the percentage ofAttorney Docket No. SP24-323 PCT additional surface area that is contributed by texture as compared to an ideal plane the size of the measurement region.

[0080] The average surface roughness (Sa) represents the average peak height measured in a sample of the LLZO or other sintered ceramic, as measured relative to a geometrically flat surface, and is given in units of length. The average surface roughness may be 0.20 mm or more, 0.21 mm or more, 0.22 mm or more, 0.23 mm or more, 0.24 mm or more, 0.25 mm or more, 0.26 mm or more, 0.27 mm or more, 0.28 mm or more, 0.29 mm or more, 0.30 mm or more, 0.31 mm or more, 0.32 mm or more, 0.33 mm or more, 0.34 mm or more, 0.35 mm or less, 0.34 mm or less, 0.33 mm or less, 0.32 mm or less, 0.31 mm or less, 0.30 mm or less, 0.29 mm or less, 0.28 mm or less, 0.27 mm or less, 0.26 mm or less, 0.25 mm or less, 0.24 mm or less, 0.23 mm or less, 0.22 mm or less, or 0.21 mm or less, or any range formed therefrom. In some aspects, the average surface roughness may range from R1 to R2, wherein R1 and R2 are, independently, 0.20 mm, 0.21 mm, 0.22 mm, 0.23 mm, 0.24 mm, 0.25 mm, 0.26 mm, 0.27 mm, 0.28 mm, 0.29 mm, 0.30 mm, 0.31 mm, 0.32 mm, 0.33 mm, 0.34 mm, or 0.35 mm, and R1<R2. In some examples, the average surface roughness may range from 0.2 mm to 0.35 mm.

[0081] The average surface area, measured as the average developed interfacial area ratio (Sdr) relative to a geometrically flat surface, is given as a unitless ratio. The average surface area, evaluated as a Sdr value, may range from R3 to R4, wherein R3 and R4 are, independently, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, or 90, and R3<R4. In some aspects, the surface area, evaluated as a Sdr value, may range from 40 to 90. The foregoing represent the increase in surface area relative to the geometrically flat surface.

[0082] In various aspects, the surface of LLZO of the present disclosure may be nonprotonated or substantially non-protonated. The protonation state of the LLZO may be evaluated by measuring the lattice parameter obtained from X-ray powder diffraction, for example.

[0083] When viewed through a suitable imaging technique, grains of the sintered ceramic (e.g., LLZO) of the present disclosure continue to resemble as-produced ceramic from sintering and are distinguished by smooth external surfaces that are well-packed with one another. Acid-etching, in contrast, produces grains of sintered ceramic (e.g., LLZO) that are faceted and have sharp edges, and the grains are not as close-packed due to widened grainAttorney Docket No. SP24-323 PCT boundaries, thereby leading to increased porosity relative to as-produced LLZO. The differences in morphology may be observed in the SEM images of FIGS. 5 and 6.

[0084] The LLZO or other sintered ceramics of the present disclosure may be incorporated in a solid-state battery as a separator between a cathode and an anode. The solid-state battery may be a solid-state lithium battery, for instance. The sintered ceramic may exhibit a decreased incidence of shorting and low interfacial impedance values relative to sintered ceramics having metal oxide removed by alternative techniques. For example, the solid-state battery may have a shorting rate of 30% or less when charging or discharging the solid-state battery and / or the solid-state battery may have an interfacial resistance of about 75 Q cm2or less.

[0085] Various aspects are contemplated herein, several of which are set forth in the paragraphs below. It is explicitly contemplated that any aspect or portion thereof can be combined to form a combination. The phrase “any other aspect herein” means any numbered aspect herein, or any aspect or aspects disclosed elsewhere herein.

[0086] Aspects disclosed herein include the following:

[0087] Aspect 1. A sintered ceramic comprising: a first surface comprising lithium lanthanum zirconium oxide (LLZO); wherein at least one of the following conditions is met:Condition a) the first surface of the sintered ceramic has a surface atomic ratio of lithiumdanthanum within +5% of 7:3, and a surface atomic ratio of lithium: zirconium within +5% of 7:2, each surface atomic ratio being measured by X-ray photoelectron spectroscopy (XPS) at a depth within 20 nm of the first surface; orCondition b) an average surface roughness (Sa) of the sintered ceramic, as determined by scanning laser confocal microscopy and measured as a height relative to a geometrically flat surface, ranges from 0.2 mm to 0.35 mm, and a surface area of the sintered ceramic, measured as an average developed interfacial area ratio (Sdr) relative to the geometrically flat surface, increases from 40% to 90% relative to the geometrically flat surface.

[0088] Aspect 2. The sintered ceramic of aspect 1, any preceding aspect, or any other aspect herein, wherein the first surface of the sintered ceramic contains 5 mol% or less lithium carbonate at a depth within 20 nm of the first surface.

[0089] Aspect 3. The sintered ceramic of aspect 1 or aspect 2, any preceding aspect, or any other aspect herein, wherein Condition a) is met and the surface atomic ratio ofAttorney Docket No. SP24-323 PCT lithium:lanthanum is no greater than 7:3, and the surface atomic ratio of lithium :zirconium is no greater than 7:2.

[0090] Aspect 4. The sintered ceramic of any one of aspects 1-3, any preceding aspect, or any other aspect herein, wherein the first surface of the sintered ceramic is non-protonated.

[0091] Aspect 5. The sintered ceramic of any one of aspects 1-4, any preceding aspect, or any other aspect herein, wherein the sintered ceramic has a thickness ranging from 20 pm to 50 pm.

[0092] Aspect 6. A solid-state battery comprising a separator between a cathode and an anode, the separator comprising the sintered ceramic of any one of aspects 1-5.

[0093] Aspect 7. The solid-state battery of aspect 6, any preceding aspect, or any other aspect herein, wherein the solid-state battery has a shorting rate of 30% or less when charging and discharging the solid-state battery, as evaluated over at least 26 charge-discharge cycles, including at least 6 charge-discharge cycles at a 1 C rate.

[0094] Aspect 8. The solid-state battery of aspect 6 or aspect 7, any preceding aspect, or any other aspect herein, wherein the solid-state battery has an interfacial resistance of about 75 Q cm2or less.

[0095] Aspect 9. A method comprising: providing a sintered ceramic, a surface deposit of metal carbonate being present upon at least one of a first face or a second face of the sintered ceramic; heating the sintered ceramic at a first temperature in a first environment comprising an inert gas, a sub-atmospheric pressure, or both, wherein the first temperature is effective to remove at least a portion of the surface deposit of metal carbonate from the sintered ceramic; and cooling the sintered ceramic in a second environment comprising an inert gas, a sub-atmospheric pressure, or both to a second temperature of 100°C or below.

[0096] Aspect 10. The method of aspect 9, any preceding aspect, or any other aspect herein, wherein the sintered ceramic comprises LLZO and lithium carbonate is present as the surface deposit upon the sintered ceramic.

[0097] Aspect 11. The method of aspect 9 or aspect 10, any preceding aspect, or any other aspect herein, wherein heating the sintered ceramic takes place in a first chamber and cooling the sintered ceramic takes place in a second chamber.

[0098] Aspect 12. The method of aspect 9 or aspect 10, any preceding aspect, or any other aspect herein, wherein heating and cooling the sintered ceramic take place in a single chamber.Attorney Docket No. SP24-323 PCT

[0099] Aspect 13. The method of any one of aspects 9, 10, or 12, any preceding aspect, or any other aspect herein, wherein the sintered ceramic is held stationary during heating and cooling.

[0100] Aspect 14. The method of any one of aspects 9-13, any preceding aspect, or any other aspect herein, wherein the sintered ceramic is present in a part, and the part also undergoes heating and cooling.

[0101] Aspect 15. The method of any one of aspects 9-14, any preceding aspect, or any other aspect herein, wherein the first face of the sintered ceramic contacts a thermal mass while heating and cooling.

[0102] Aspect 16. The method of any one of aspects 9-15, any preceding aspect, or any other aspect herein, wherein the second face is opposite the first face, and a diffusion barrier is present upon the second face of the sintered ceramic at least while cooling the sintered ceramic and optionally while heating the sintered ceramic.

[0103] Aspect 17. The method of aspect 16, any preceding aspect, or any other aspect herein, further comprising: applying the diffusion barrier to the second face of the sintered ceramic prior to heating or while heating the sintered ceramic.

[0104] Aspect 18. The method of any one of aspects 9-17, any preceding aspect, or any other aspect herein, wherein the first environment and the second environment each comprise the sub-atmospheric pressure.

[0105] Aspect 19. The method of any one of aspects 9-17, any preceding aspect, or any other aspect herein, wherein the first environment comprises the inert gas, and the second environment comprises the sub-atmospheric pressure.

[0106] Aspect 20. The method of any one of aspects 9-17 or aspect 19, any preceding aspect, or any other aspect herein, wherein the inert gas is pressurized at least 10% above atmospheric pressure in the first environment.

[0107] Aspect 21. The method of any one of aspects 9, 10, or 12, any preceding aspect, or any other aspect herein, wherein the sintered ceramic is a ribbon ceramic, and the ribbon ceramic is conveyed from a first reel to a second reel while being heated and cooled.

[0108] Aspect 22. The method of aspect 21, any preceding aspect, or any other aspect herein, wherein the first environment comprises the sub-atmospheric pressure, and the second environment comprises the sub-atmospheric pressure.Attorney Docket No. SP24-323 PCT

[0109] Aspect 23. The method of aspect 21, any preceding aspect, or any other aspect herein, wherein the first environment comprises the inert gas, and the second environment comprises the inert gas.

[0110] Aspect 24. The method of aspect 23, any preceding aspect, or any other aspect herein, wherein the inert gas is pressurized at least 10% above atmospheric pressure in the first environment.

[0111] Aspect 25. The method of aspect 23 or aspect 24, any preceding aspect, or any other aspect herein, wherein a diffusion barrier is applied to at least one of the first face or the second face of the sintered ceramic prior to or during cooling.

[0112] Aspect 26. The method of any one of aspects 9-25, any preceding aspect, or any other aspect herein, wherein the first temperature is at least 750°C.

[0113] Aspect 27. The method of any one of aspects 9-26, any preceding aspect, or any other aspect herein, wherein the first temperature ranges from 750°C to 900°C.

[0114] Aspect 28. The method of any one of aspects 9-26, any preceding aspect, or any other aspect herein, wherein the first temperature ranges from 750°C to 800°C.

[0115] Aspect 29. The method of any one of aspects 9-28, any preceding aspect, or any other aspect herein, wherein the second environment comprises a water content of 10 parts per billion (ppb) or less and a carbon dioxide content of 10 parts per million (ppm) or less.

[0116] Aspect 30. The method of any one of aspects 9-29, any preceding aspect, or any other aspect herein, wherein the sintered ceramic has a thickness ranging from 20 pm to 50 pm.

[0117] Aspect 31. A method comprising: sintering a green ceramic at a sintering temperature in a first environment comprising an inert gas, a sub-atmospheric pressure, or both, thereby forming a sintered ceramic; and without exposing the sintered ceramic to conditions effective to form a surface deposit of a metal carbonate on the sintered ceramic, cooling the sintered ceramic in a second environment comprising an inert gas, a sub-atmospheric pressure, or both to a second temperature of 100°C or below.

[0118] Aspect 32. The method of aspect 31, any preceding aspect, or any other aspect herein, wherein the sintered ceramic comprises LLZO.

[0119] Aspect 33. The method of aspect 31 or aspect 32, any preceding aspect, or any other aspect herein, wherein the sintering temperature ranges from 950°C to 1100°C.Attorney Docket No. SP24-323 PCT

[0120] Aspect 34. The method of any one of aspects 31-33, any preceding aspect, or any other aspect herein, wherein the first environment and the second environment each comprise an inert gas, or the first environment and the second environment each comprise a sub- atmospheric pressure.

[0121] Aspect 35. The method of any one of aspects 31-34, any preceding aspect, or any other aspect herein, wherein the second environment has a lower concentration of water and carbon dioxide than does the first environment.

[0122] Aspect 36. The method of any one of aspects 31-35, any preceding aspect, or any other aspect herein, wherein sintering and cooling take place in a single chamber.

[0123] Aspect 37. The method of aspect 36, any preceding aspect, or any other aspect herein, wherein sintering the green ceramic takes place continuously and comprises reel-to- reel tape casting and sintering, and the sintered ceramic is a ribbon ceramic; wherein the ribbon ceramic is wound onto a reel while or after being cooled.

[0124] Aspect 38. The method of aspect 37, any preceding aspect, or any other aspect herein, wherein a diffusion barrier is applied during or after tape casting or during sintering the green ceramic, such that the diffusion barrier is present upon the sintered ceramic during cooling.

[0125] Aspect 39. The method of any one of aspects 31-38, any preceding aspect, or any other aspect herein, wherein the first and second environments comprise the inert gas; wherein the first environment comprises a first inert gas pressure, and the second environment comprises a second inert gas pressure higher than the first inert gas pressure.

[0126] Aspect 40. The method of any one of aspects 31-39, any preceding aspect, or any other aspect herein, wherein the first environment and the second environment both comprise the sub-atmospheric pressure.

[0127] Aspect 41. The method of any one of aspects 31-40, any preceding aspect, or any other aspect herein, wherein the second environment comprises a water content of 30 parts per billion (ppb) or less and a carbon dioxide content of 10 parts per million (ppm) or less.

[0128] Aspect 42. The method of any one of aspects 31-41, any preceding aspect, or any other aspect herein, wherein the sintered ceramic has a thickness ranging from 20 pm to 50 pm.

[0129] Aspect 43. The method of any one of aspects 31-42, any preceding aspect, or any other aspect herein, wherein the conditions effective to form the surface deposit of the metal carbonate on the sintered ceramic comprise ambient atmosphere.Attorney Docket No. SP24-323 PCT

[0130] To facilitate a better understanding of the present disclosure, the following examples are provided. In no way should the following examples be read to limit the scope of the disclosure.EXAMPLES

[0131] The LLZO used in these experiments was bi-layer Toshima ribbon ceramic with a polymeric binder fired on rhenium. The nominal thickness was 100 pm. Cells were constructed using a 2.5 mA hr / cm2nickel manganese cobalt oxide (NMC) cathode and lithium metal anode with 300 nm of tin evaporatively deposited on the LLZO of the ribbon ceramic. The tin improves cycling performance. A 3 -bar external stack pressure was applied to the cells. Electrochemical impedance spectroscopy (EIS) was conducted using a Gamry interface 1000 potentiostat prior to any cycling, with the cell resting at open circuit potential (typically 3.0-3.3 V). Cycling data was measured on an Arbin 64 channel cycler. The test sequence increases the charge rate (C-rate) from C / 12, C / 8, C / 3, C / 2, C / 1, while maintaining a discharge rate of C / 8.

[0132] Batch Heat Treatment to Remove Existing LiiCOs. Batch heat treatment of a LLZO-containing part was conducted at 850°C for 1 hour in an argon furnace. The argon had a dew point of -44°C (80 ppm H2O), with residual contents of oxygen and carbon dioxide being 40 ppm and 10 ppm respectively. The argon was maintained at atmospheric pressure throughout the heating process and at a continuous flow rate of 1-2 standard liters per minute (slpm) from a cryogenic argon source. While in the argon furnace, the part was heated on a large thermal mass comprising graphite and having a flexible GRAFOIL surface. The thermal mass had overall dimensions of 50 mm x 40 mm x 8 mm and a mass of 63 g. After heating was complete, the thermal mass and the LLZO-containing part were quickly transferred to a sealed container, which was then evacuated with a vacuum pump. Thereafter, the part was allowed to cool under a vacuum pressure of 28” Hg (9.48 x 105Pa, 711 torr) at a cooling rate of approximately 80°C to 100°C per minute.

[0133] After cool-down, the part was incorporated in a lithium metal battery cell with the downward-facing side during heating contacting the cathode. The LLZO exhibited an interfacial resistance of 37 Q cm2and an as-fired surface roughness of 0.27 mm, as determined by scanning laser confocal microscopy and measured relative to a geometrically flat surface (see FIG. 4 below, which exemplifies the surface roughness). When the opposite side of the LLZO (the upward-facing side during heating) contacted the cathode, the interfacial resistance was approximately 90 Q cm2. The higher interfacial resistance of theAttorney Docket No. SP24-323 PCT upward-facing side is believed to result from there being no diffusion barrier limiting access to the surface of the LLZO. The thermal mass contacting the downward-facing side of the LLZO, in contrast, serves as a de facto diffusion barrier during heating and leads to a lower interfacial resistance when the downward-facing side contacts the cathode in the lithium metal battery cell. When the cooling was conducted under inert gas instead of vacuum and the upward-facing side again contacted the cathode, the interfacial resistance increased still further to 146 Q cm2.

[0134] FIGS. 1 and 2 show cycling data for cells having the cathode side constructed with different orientations of LLZO obtained from heat treatment. FIG. 1 shows cycling data for a cell having the upward-facing side of the LLZO facing the cathode side and contacting the cathode, where the upward-facing side was not protected by a diffusion barrier. FIG. 2 shows cycling data for a cell having the downward-facing side of the LLZO facing the cathode side and contacting the cathode, where the downward-facing side is protected by the thermal mass as a de facto diffusion barrier. As shown in FIG. 1 (upward-facing side of the LLZO faces the cathode side), there was a high ohmic drop during initial charging and ohmic-dominated charging at 1 C (coulomb), as indicated by the shape and rapid rise to 4.2 V of the charging data. The corresponding data shown in FIG. 2 (downward-facing side of the LLZO faces the cathode side) demonstrated a smaller ohmic drop. This conclusion may be reached by evaluating the corresponding Nyquist plots of the interfacial resistance (FIG. 3). In the Nyquist plots, the smaller semicircular region before the rapid rises of each plot is characteristic of the sample having the downward-facing side contacting the cathode having the lower interfacial resistance.

[0135] For comparison, FIG. 4 shows cycling data for a cell having LLZO prepared with a 4-minute acid-etch in 1 M HC1. The corresponding Nyquist plot for acid etching is shown in FIG. 3.

[0136] Characterization of Batch Heated LLZO. Differences in appearance can be seen in LLZO that is heat-treated as above in comparison to acid-treated LLZO. FIG. 5 is an SEM image of heat-treated LLZO that is then cooled in vacuum. As shown, the LLZO particles remained well-consolidated and exhibited a rounded appearance. FIG. 6 is an SEM image of LLZO treated for 4 minutes with 1 M HC1. As shown, the LLZO particles treated with acid assumed a more faceted appearance and exhibited increased interparticle spacing, equating to increased porosity. The acid-treated samples also showed small amounts of residual lithium carbonate (dashed circles in FIG. 6). The amount of residual lithium carbonate increased with decreasing acid concentration, even at longer treatment times (data not shown).Attorney Docket No. SP24-323 PCT

[0137] FIGS. 7 and 8 are bar graphs showing, respectively, variations in average surface roughness (Sa) and surface area, evaluated as average developed interfacial area ratio (Sdr), for LLZO treated under various conditions to remove lithium carbonate. A heat-treated sample was prepared as above. A polished sample was prepared by manually polishing both sides of a 100 mm thick LLZO sample with a diamond abrasive film having 15 mm particles for 3-5 minutes per side, followed by further fine polishing with a 1 mm particle size diamond film for another 3-5 minutes per side. Acid treatment was conducted by contacting the LLZO with different concentrations of HC1 over variable contact times. The following acid-treatment conditions were used. 4 minutes / 1 M HC1, 5 minutes / 1 M HC1, 7 minutes / 0.5 M HC1, and 20 minutes / 0.1 M HC1. As shown, the acid-treated samples displayed increased surface area and surface roughness. Heat treatment results in lower values of surface area and roughness, though the values were not as low as those obtained by polishing. Although polishing resulted in the lowest surface area and surface roughness values, polishing was not compatible with thin LLZO samples due to the rigor of the polishing conditions and the fragility of LLZO having a thin structure.

[0138] The LLZO samples tested in FIGS. 7 and 8 were also incorporated in a solid-state lithium battery, and their performance was tested. Testing results are summarized in Table 1. Table 1

[0139] As shown, the shorting rate was much lower for the heat-treated samples. Heat treatment also afforded undetectable mass loss, unlike the other treatment methods.

[0140] The term “substantially” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. This term is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. Thus, for example, a composition that isAttorney Docket No. SP24-323 PCT“substantially free” of any specific component (e.g., AI2O3, MgO, or any other component) is one in which the component is not actively added or batched into the composition, but may be present in small amounts as a contaminant (e.g., less than 1000, 500, 400, 300, 200, or 100 ppm), or, if actively added or batched, is present in an amount less than 1 wt.% (e.g., or can be specified to be less than 0.5 wt.%, 0.1 wt.%, or 0.05 wt.%.), based on total amount of the composition (moles or mass for ppm, and mass for wt.%).

[0141] All documents described herein are incorporated by reference herein for purposes of all jurisdictions where such practice is allowed, including any priority documents and / or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific aspects, while forms of the disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited thereby. For example, the compositions described herein may be free of any component or composition not expressly recited or disclosed herein. Any method may lack any step not recited or disclosed herein. Likewise, the term “comprising” is considered synonymous with the term “including.” Whenever a method, composition, element, or group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with the transitional phrases “consisting essentially of,” “consisting of,” “selected from the group consisting of,” or “is” preceding the recitation of the composition, element, or elements and vice versa.

[0142] Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from a to b” or, equivalently, “from a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces.

[0143] One or more illustrative aspects are presented herein. Not all features of a physical implementation are described or shown in this application for the sake of clarity. It is understood that in the development of a physical aspect of the present disclosure, numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, business-related, government-related and other constraints, which vary by implementation and from time to time. While a developer's efforts might beAttorney Docket No. SP24-323 PCT time-consuming, such efforts would be, nevertheless, a routine undertaking for one of ordinary skill in the art and having benefit of this disclosure.

[0144] Therefore, the present disclosure is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular aspects disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to one having ordinary skill in the art and having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative aspects disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present disclosure. The aspects illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and / or any optional element disclosed herein.

Claims

Attorney Docket No. SP24-323 PCTWHAT IS CLAIMED IS:

1. A sintered ceramic comprising: a first surface comprising lithium lanthanum zirconium oxide (LLZO); wherein at least one of the following conditions is met:Condition a) the first surface of the sintered ceramic has a surface atomic ratio of lithiumdanthanum within +5% of 7:3, and a surface atomic ratio of lithium: zirconium within +5% of 7:2, each surface atomic ratio being measured by X-ray photoelectron spectroscopy (XPS) at a depth within 20 nm of the first surface; orCondition b) an average surface roughness (Sa) of the sintered ceramic, as determined by scanning laser confocal microscopy and measured as a height relative to a geometrically flat surface, ranges from 0.2 mm to 0.35 mm, and a surface area of the sintered ceramic, measured as an average developed interfacial area ratio (Sdr) relative to the geometrically flat surface, increases from 40% to 90% relative to the geometrically flat surface.

2. The sintered ceramic of claim 1, wherein the first surface of the sintered ceramic contains 5 mol% or less lithium carbonate at the depth within 20 nm of the first surface, as evaluated by XPS.

3. The sintered ceramic of claim 1 or claim 2, wherein Condition a) is met and the surface atomic ratio of lithiunrlanthanum is no greater than 7:3, and the surface atomic ratio of lithium: zirconium is no greater than 7:2.

4. The sintered ceramic of any one of claims 1-3, wherein the first surface of the sintered ceramic is non-protonated.

5. The sintered ceramic of any one of claims 1-4, wherein the sintered ceramic has a thickness ranging from 20 pm to 50 pm.

6. A solid-state battery comprising a separator between a cathode and an anode, the separator comprising the sintered ceramic of any one of claims 1-5.

7. The solid-state battery of claim 6, wherein the solid-state battery has a shorting rate of 30% or less when charging and discharging the solid-state battery, as evaluated overAttorney Docket No. SP24-323 PCT at least 26 charge-discharge cycles, including at least 6 charge-discharge cycles at a 1 C rate.

8. The solid-state battery of claim 6 or claim 7, wherein the solid-state battery has an interfacial resistance of about 75 (1cm2or less.

9. A method comprising: providing a sintered ceramic, a surface deposit of metal carbonate being present upon at least one of a first face or a second face of the sintered ceramic; heating the sintered ceramic at a first temperature in a first environment comprising an inert gas, a sub-atmospheric pressure, or both, wherein the first temperature is effective to remove at least a portion of the surface deposit of metal carbonate from the sintered ceramic; and cooling the sintered ceramic in a second environment comprising an inert gas, a sub-atmospheric pressure, or both to a second temperature of 100°C or below.

10. The method of claim 9, wherein the sintered ceramic comprises LLZO and lithium carbonate is present as the surface deposit upon the sintered ceramic.

11. The method of claim 9 or claim 10, wherein heating the sintered ceramic takes place in a first chamber and cooling the sintered ceramic takes place in a second chamber.

12. The method of claim 9 or claim 10, wherein heating and cooling the sintered ceramic take place in a single chamber.

13. The method of any one of claims 9, 10, or 12, wherein the sintered ceramic is held stationary during heating and cooling.

14. The method of any one of claims 9-13, wherein the sintered ceramic is present in a part, and the part also undergoes heating and cooling.

15. The method of any one of claims 9-14, wherein the first face of the sintered ceramic contacts a thermal mass while heating and cooling.

16. The method of any one of claims 9-15, wherein the second face is opposite the first face, and a diffusion barrier is present upon the second face of the sintered ceramic atAttorney Docket No. SP24-323 PCT least while cooling the sintered ceramic and optionally while heating the sintered ceramic.

17. The method of claim 16, further comprising: applying the diffusion barrier to the second face of the sintered ceramic prior to heating or while heating the sintered ceramic.

18. The method of any one of claims 9-17, wherein the first environment and the second environment each comprise the sub-atmospheric pressure.

19. The method of any one of claims 9-17, wherein the first environment comprises the inert gas, and the second environment comprises the sub-atmospheric pressure.

20. The method of any one of claims 9-17 or 19, wherein the inert gas is pressurized at least 10% above atmospheric pressure in the first environment.

21. The method of any one of claims 9, 10, or 12, wherein the sintered ceramic is a ribbon ceramic, and the ribbon ceramic is conveyed from a first reel to a second reel while being heated and cooled.

22. The method of claim 21, wherein the first environment comprises the sub-atmospheric pressure, and the second environment comprises the sub-atmospheric pressure.

23. The method of claim 21, wherein the first environment comprises the inert gas, and the second environment comprises the inert gas.

24. The method of claim 23, wherein the inert gas is pressurized at least 10% above atmospheric pressure in the first environment.

25. The method of claim 23 or claim 24, wherein a diffusion barrier is applied to at least one of the first face or the second face of the sintered ceramic prior to or during cooling.

26. The method of any one of claims 9-25, wherein the first temperature is at least 750°C.

27. The method of any one of claims 9-26, wherein the first temperature ranges from 750°C to 900°C.Attorney Docket No. SP24-323 PCT28. The method of any one of claims 9-26, wherein the first temperature ranges from 750°C to 800°C.

29. The method of any one of claims 9-28, wherein the second environment comprises a water content of 10 parts per billion (ppb) or less and a carbon dioxide content of 10 parts per million (ppm) or less.

30. The method of any one of claims 9-29, wherein the sintered ceramic has a thickness ranging from 20 pm to 50 pm.

31. A method comprising: sintering a green ceramic at a sintering temperature in a first environment comprising an inert gas, a sub-atmospheric pressure, or both, thereby forming a sintered ceramic; and without exposing the sintered ceramic to conditions effective to form a surface deposit of a metal carbonate on the sintered ceramic, cooling the sintered ceramic in a second environment comprising an inert gas, a sub-atmospheric pressure, or both to a second temperature of 100°C or below.

32. The method of claim 31, wherein the sintered ceramic comprises LLZO.

33. The method of claim 31 or claim 32, wherein the sintering temperature ranges from 950°C to 1100°C.

34. The method of any one of claims 31-33, wherein the first environment and the second environment each comprise an inert gas, or the first environment and the second environment each comprise a sub-atmospheric pressure.

35. The method of any one of claims 31-34, wherein the second environment has a lower concentration of water and carbon dioxide than does the first environment.

36. The method of any one of claims 31-35, wherein sintering and cooling take place in a single chamber.

37. The method of claim 36, wherein sintering the green ceramic takes place continuously and comprises reel-to-reel tape casting and sintering, and the sintered ceramic is aAttorney Docket No. SP24-323 PCT ribbon ceramic; wherein the ribbon ceramic is wound onto a reel while or after being cooled.

38. The method of claim 37, wherein a diffusion barrier is applied during or after tape casting or during sintering the green ceramic, such that the diffusion barrier is present upon the sintered ceramic during cooling.

39. The method of any one of claims 31-38, wherein the first and second environments comprise the inert gas; wherein the first environment comprises a first inert gas pressure, and the second environment comprises a second inert gas pressure higher than the first inert gas pressure.

40. The method of any one of claims 31-39, wherein the first environment and the second environment both comprise the sub-atmospheric pressure.

41. The method of any one of claims 31-40, wherein the second environment comprises a water content of 30 parts per billion (ppb) or less and a carbon dioxide content of 10 parts per million (ppm) or less.

42. The method of any one of claims 31-41, wherein the sintered ceramic has a thickness ranging from 20 pm to 50 pm.

43. The method of any one of claims 31-42, wherein the conditions effective to form the surface deposit of the metal carbonate on the sintered ceramic comprise ambient atmosphere.

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