Pyrochlore to garnet transition enabled by open-air plasma treatment for lithium lanthanum zirconium oxide solid-state electrolytes

Abstract

Synthesizing a garnet-type lithium lanthanum zirconate includes combining a lithium component and a doped pyrochlore to yield a mixture and plasma processing the mixture under ambient conditions to yield the garnet-type lithium lanthanum zirconate.

Description

Attorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dPYROCHLORE TO GARNET TRANSITION ENABLED BY OPEN-AIR PLASMA TREATMENT FOR LITHIUM LANTHANUM ZIRCONIUM OXIDE SOLID-STATE ELECTROLYTES CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U. S. Patent Application No. 63 / 741,594 filed on January 3, 2025, which is incorporated by reference herein in its entirety.STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under TI-2234636 awarded by the National Science Foundation. The government has certain rights in the invention.TECHNICAL FIELD

[0003] This invention relates to the use of an open-air plasma processing method for the preparation of lithium-ion battery materials.BACKGROUND

[0004] Garnet-type lithium lanthanum zirconate (e.g., Li7La3Zr2O12) materials are lithium-ion conducting solid-state electrolytes that can be used in solid-state batteries.Garnet-type lithium lanthanum zirconate can be prepared via solid-state reactions from component reagents (e.g., Li2CO3, ZrO2, La2O3) that involve synthesis at high temperatures (>900°C) for long durations (e.g., usually in excess of 8 hours). Extrinsic dopants in garnet-type lithium lanthanum zirconate (e.g., Al, Ta, Ga, or Nb) are included to stabilize the highly conducting cubic phase of garnet-type lithium lanthanum zirconate. Subsequent to the synthesis, high temperature sintering (>1100°C, typically in excess of 6 hours) is used for densification of the garnet-type lithium lanthanum zirconate powders to form a ceramic. As a result of the high temperatures and long reaction times for synthesis and sintering, the materials are susceptible to lithium loss, which results in formation of poorly conducting phases.SUMMARY

[0005] This disclosure describes the use of an open-air plasma processing method for preparing lithium-ion battery materials. The plasma process enables rapid conversion of reagentsAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dinto the desired target product using a combination of heat and reactive species. In addition, an external shroud made of a machinable, high-temperature metal (e.g., stainless steel) enables injection of externally supplied compressed gas into the region surrounding the plasma. The compressed gas can be oxidizing, reducing, or inert. The compressed gas allows for displacement of the ambient air molecules and enables the use of an inert shroud gas (e.g., nitrogen). The shroud gas can be used to cool the sample back to room temperature after the plasma treatment or to keep the sample in an inert atmosphere after the plasma treatment. Using an open-air plasma processing method, pyrochlore-type precursors based on lithium lanthanum zirconate can be reacted with a lithium compound to form a lithium-ion conducting solid-state electrolyte (e.g., a garnet-type lithium lanthanum zirconate).

[0006] In a first general aspect, synthesizing a garnet-type lithium lanthanum zirconate includes combining a lithium component and a doped pyrochlore to yield a mixture and plasma processing the mixture under ambient conditions to yield the garnet-type lithium lanthanum zirconate.

[0007] Implementations of the first general aspect may include one or more of the following features.

[0008] In some cases, combining includes ball-milling. In some implementations, the lithium component includes lithium hydroxide. The doped pyrochlore can include a dopant. The dopant can include aluminum, tantalum, gallium, niobium, antimony, or any combination thereof. In some cases, the garnet-type lithium lanthanum zirconate is in the form of a film. The doped pyrochlore can include La2.4Zr2MaOβ, where 0.2 < a < 0.4, 7.9 < < 8.2 and M includes aluminum, gallium, or a combination thereof. The garnet-type lithium lanthanum zirconate can include Li7-3xMxLa3Zr2O12, where 0.2 < x < 0.4 and M includes aluminum, gallium, or a combination thereof. The doped pyrochlore can include La2.4ZraMbOc, where 0.8 < a < 1.44, 0.16 < b < 0.8, 6.88 < c < 12, and M includes niobium, tantalum, antimony, or a combination thereof. The garnet-type lithium lanthanum zirconate can include Li7-yLa3Zr2-yMyO12, where 0.2 <y < 1.0 and M includes niobium, tantalum, antimony, or a combination thereof.

[0009] Plasma processing the mixture under ambient conditions can include exposing the mixture to an open-air plasma. In certain implementations, the plasma processing includes a treatment time up to 10 minutes. In some cases, the plasma processing includes a treatment time in a range of 2 minutes to 8 minutes. The plasma processing can include adjusting a distanceAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dbetween a nozzle of a plasma generator and a surface of the mixture to a length between 1 mm and 10 mm. In certain cases, the plasma processing includes a plasma cycle time in a range of 10% to 100%. The plasma processing can include generating an open-air plasma. The plasma processing can occur in the absence of radiant heat provided by an oven. The plasma processing can occur at atmospheric pressure. A temperature of the mixture during the plasma processing is typically in a range of 500°C to 1100°C.

[0010] Some implementations of the first general aspect further include compressing the mixture before plasma processing. Compressing the mixture can include cold pressing. In some cases, compressing the mixture yields a pellet. A mass of the pellet is typically between 50 mg and 100 mg. A thickness of the pellet is typically between 0.5 mm and 1mm.

[0011] Some implementations of the first general aspect further include flowing a gas proximate to the nozzle of the plasma generator and the garnet-type lithium lanthanum zirconate after the plasma processing, thereby cooling the garnet-type lithium lanthanum zirconate. The gas can include dry air, dry oxygen, nitrogen, or argon.

[0012] In a second general aspect, synthesizing a garnet-type lithium lanthanum zirconate cathode composite includes combining a cathode material with the mixture of the first general aspect to yield a second mixture, compressing the second mixture to yield a compressed mixture, and plasma processing the compressed mixture under ambient conditions to yield the garnet-type lithium lanthanum zirconate cathode composite.

[0013] Implementations of the second general aspect may include one or more of the following features.

[0014] The cathode material can include LiCoO2or LiNi0.5Mn0.3Co0.2O2.

[0015] A third general aspect includes the garnet-type lithium lanthanum zirconate cathode composite of the second general aspect.

[0016] In a fourth general aspect, synthesizing a garnet-type lithium lanthanum zirconate fdm includes depositing a thin fdm including the mixture of the first general aspect on a substrate and plasma processing the thin film under ambient conditions to yield the garnet-type lithium lanthanum zirconate film.

[0017] Implementations of the fourth general aspect may include one or more of the following features.Attorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-d

[0018] The mixture can be in the form of a suspension. In some cases, the mixture includes a polymer binder. The polymer binder can include polyvinylpyrrolidone or carboxymethyl cellulose. A thickness of the garnet-type lithium lanthanum zirconate film is typically between 1 μm and 500 μm.

[0019] The details of one or more embodiments of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1A is a flow chart showing operations in a process for synthesizing a garnet-type lithium lanthanum zirconate. FIG. IB shows a schematic diagram of an example setup for the plasma pyrochlore-to-garnet reaction.

[0021] FIG. 2 shows an X-ray diffraction pattern of a pellet after pyrochlore-to-garnet process using 60% plasma cycle time, a 5 mm nozzle distance, and a 5 minute treatment time.

[0022] FIG. 3 shows a temperature profile measured with a thermocouple for a plasma pyrochlore-to-garnet process applied to a thin film.

[0023] FIG. 4 shows a surface profilometry scan of a thin film after being subjected to a plasma pyrochlore-to-garnet process.

[0024] FIG. 5 shows an X-ray diffraction pattern of a thin film deposited on silicon after being subjected to the plasma pyrochlore-to-garnet process.

[0025] FIG. 6 shows an X-ray diffraction pattern of a pellet including a mixture of Ta5+-doped pyrochlore La2.4Zr1.12Ta0.48O7.04, lithium hydroxide, and LiCoO2after being subjected to the plasma pyrochlore-to-garnet process.

[0026] FIG. 7 shows an X-ray diffraction pattern of a pellet including a mixture of Ta5+-doped pyrochlore La2.4Zr1.12Ta0.48O7.04, lithium hydroxide, and LiNixMnyCozO2after being subjected to the plasma pyrochlore-to-garnet process.

[0027] FIG. 8A shows a schematic of a pellet covered from the plasma reactive species with a washer. FIG. 8B shows a schematic of a pellet exposed to plasma heating and plasma reactive species. FIG. 8C shows a schematic of a pellet heated on a hotplate.Attorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-d

[0028] FIG. 9 shows the X-ray diffraction patterns of the three test pellets after undergoing the treatments illustrated in FIGS. 8A-8C, compared with reference patterns for Ta-doped cubic lithium lanthanum zirconate, La2Zr2O7(pyrochlore), and Li2CO3.

[0029] FIG. 10 shows the Raman spectra of the three test pellets after undergoing the treatments illustrated in FIGS. 8A-8C.

[0030] FIG. 11 shows the X-ray diffraction patterns of the pellet samples A, B, C, and D.DETAILED DESCRIPTION

[0031] This disclosure describes the use of an open-air plasma treatment method for the conversion of pyrochlore precursors to lithium lanthanum zirconate. The open-air plasma treatment occurs under ambient conditions. As used herein, “ambient” conditions generally refer to a state characterized by an atmospheric pressure of approximately 1 atm and a temperature in a range of 18°C to 25°C. As described herein, “pyrochlore” generally refers to a metal oxide with a general formula of A2B2O7, where A represents an 8-fold coordinated metal, such as lanthanum, and B represents a 6-fold coordinated metal, such as zirconium. The A site cation generally has an oxidation state of +2 or +3, and the B site cation has a corresponding oxidation state of +5 or +4. Therefore, for a typical A2B2O7 compound, the metal cations have a total valence state of +14, which is balanced by 7 lattice O2−anions. A doped pyrochlore generally refers to a pyrochlore with extrinsic dopants, such as an aliovalent dopant for the B site cation. It can also refer to a pyrochlore that does not adopt the A2B2O7 stoichiometry but exhibits an excess of the A site cation or partial replacement of the B site cation with an extrinsic dopant. As described herein, a “garnet” or “garnet-type” oxide generally refers to compounds based on the Li7La3Zr2O12, which can exhibit a tetragonal structure without doping or a cubic structure with the aid of aliovalent doping. For cases where the dopant occupies the lithium site, the garnet-type lithium lanthanum zirconate compound can be written as Li7-3xMxLa3Zr2O12, where M = Al, Ga and 0.2 < x < 0.4. The doped pyrochlore compound used for these cases can be written as La2.4Zr2MaOβ, where M = Al, Ga and 0.2 < a < 0.4 and 7.9 < < 8.2. When the dopant substitutes the zirconium site, the garnet-type lithium lanthanum zirconate compound can be written as Li7-yLa3Zr2-yMyO12, where M = Nb, Ta, Sb and 0.2 <y < 1.0. The doped pyrochlore compound used for these cases can be written as La2.4ZraMbOc, where M = Nb, Ta, Sb and 0.8 < a < 1.44, 0.16 < b < 0.8, and 6.88 < c < 7.2. Cubic lithium lanthanum zirconate is used as aAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dlithium-ion conducting solid electrolyte due at least in part to its higher ionic conductivity of around 1 mS / cm, which is 2-3 orders of magnitude higher than that of a tetragonal lithium lanthanum zirconate.

[0032] A doped pyrochlore that allows for the formation of lithium lanthanum zirconate upon reaction with a lithium compound (eg., lithium hydroxide, lithium carbonate, lithium oxide) serves as a precursor for cubic lithium lanthanum zirconate. In some examples, if lithium hydroxide is used as the lithium source, the lithium hydroxide melts at temperatures above its melting point of 462°C and decomposes into lithium oxide, which reacts with the doped pyrochlore to form a garnet phase, followed by densification of the garnet through grain coalescence. The combination of heat and reactive species from the plasma rapidly convert the precursors to the desired target phase. The plasma-based pyrochlore-to-garnet reaction accelerates throughput of the lithium lanthanum zirconate synthesis compared to a furnace-based pyrochlore-to-garnet reaction. The process can also be implemented in a roll-to-roll fashion to enable scalable processing of the materials. Open-air plasma technology is a tunable alternate heat source that is compatible with a range of materials and device structures. It offers advantages over radiofrequency or microwave plasmas at least in part because it has the potential to rapidly transform materials at a controllable temperature.

[0033] A combination of energy sources is generated from the open-air plasma system, which includes electrons and reactive species such as radicals, metastable species, and photons. These reactive species are produced in combination with convective heat to rapidly transfer energy to enable ultrafast conversion of pyrochlore precursors to lithium lanthanum zirconate. Thus, plasma treatment applied to precursor mixtures carries out the pyrochlore-to-garnet reaction more effectively than a thermal treatment alone. Such reductions in synthesis temperature and time are expected to have impacts on the large-scale manufacturability and costeffectiveness of the materials. Additionally, the open-air plasma can also be integrated in-line with the deposition of the lithium lanthanum zirconate precursors to enable continuous processing.

[0034] In one example, La2.4Zr1.12Ta0.48O7.04is used as a pyrochlore precursor to obtain the Ta-doped cubic lithium lanthanum zirconate with nominal composition of Li7-yLa3Zr2-yTayO12, y = 0.6 or Li6.4La3Zr1.4Ta0.6O12. This pyrochlore compound represents doping of the stoichiometric pyrochlore, La2Zr2O7, with excess lanthanum and substitution of tantalum for zirconium. The Ta-Attorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-ddoped pyrochlore La2.4Zr1.12Ta0.48O7.04is mixed with the lithium compound and subjected to a heat treatment to form dense Ta-doped cubic lithium lanthanum zirconate in a reactive sintering process. The plasma-based pyrochlore-to-garnet reaction is a reactive sintering process at least in part because the lithium lanthanum zirconate reaction and densification takes place in the same heat treatment.

[0035] La2.4Zr1.12Ta0.48O7.04is synthesized using molten salt or sol-gel methods to prepare the tantalum(Ta)-doped lithium lanthanum zirconate (Li6.4La3Zr1.4Ta0.6O12). Using the plasma treatment process, the Ta5+-doped pyrochlore is reactively sintered with lithium hydroxide. The ability to dope pyrochlores for use as precursors to a Ta-doped cubic lithium lanthanum zirconate compound is due at least in part to the nanocrystalline nature of the pyrochlore particles and the versatility of the pyrochlore structure. Extrinsic dopants in lithium lanthanum zirconate (e.g., Al, Ta, Ga, Nb) are included to stabilize the highly conducting cubic phase of lithium lanthanum zirconate.

[0036] The open-air plasma treatment can be used to prepare composites of Ta-doped cubic lithium lanthanum zirconate with cathode materials, such as LiCoO2or LiNixMnyCozO2. In this process, the open-air plasma treatment can be used to carry out co-sintering and densification of composites that contain mixtures of the cathode material, a lithium component (e.g., lithium hydroxide), and lithium lanthanum zirconate. In some examples, the precursors to the lithium lanthanum zirconate, such as doped pyrochlore and lithium hydroxide, are mixed with the cathode particles and reactively sintered using plasma-based pyrochlore-to-garnet process to form the cathode composites.

[0037] Thin films of a Ta-doped cubic lithium lanthanum zirconate can be prepared using the plasma-based pyrochlore-to-garnet process. In this process, a lithium component (e.g., lithium hydroxide) and a doped pyrochlore is mixed to yield a mixture, and the mixture is deposited as a thin film on a substrate. The mixture can include a polymer binder (e.g., polyvinylpyrrolidone or carboxymethyl cellulose). The thin film undergoes plasma processing to yield the garnet-type lithium lanthanum zirconate film. In some cases, the mixture is in the form of a suspension. A thickness of the garnet-type lithium lanthanum zirconate film is between 1 pm and 500 pm (e.g., a thickness between 20 pm to 30 pm).

[0038] FIG. 1A is a flow chart showing operations in an example process 100 for synthesizing a garnet-type lithium lanthanum zirconate. In 102, a lithium component and a dopedAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dpyrochlore is combined to yield a mixture. In some implementations, the lithium component includes lithium hydroxide. The doped pyrochlore can include a dopant, and the dopant can include aluminum, tantalum, gallium, niobium, antimony, or any combination thereof. In some implementations, when M includes aluminum, gallium, or a combination thereof, the doped pyrochlore compound has a chemical formula La2.4Zr2MaOβ, where 0.2 < a < 0.4 and 7.9 < P < 8.2. In certain implementations, when M includes niobium, tantalum, antimony, or a combination thereof, the doped pyrochlore compound has a chemical formula La2.4ZraMbOc, where 0.8 < a < 1.44, 0.16 < b < 0.8, and 6.88 < c < 7.2. In some cases, combining the lithium component and the doped pyrochlore includes ball milling.

[0039] In 104, the mixture is plasma processed under ambient conditions to yield the garnettype lithium lanthanum zirconate. In some cases, when M includes aluminum, gallium, or a combination thereof, the garnet-type lithium lanthanum zirconate compound has a chemical formula Li7-3xMxLa3Zr2O12, where 0.2 < x < 0.4. In some implementations, when M includes niobium, tantalum, antimony, or a combination thereof, the garnet-type lithium lanthanum zirconate compound has a chemical formula Li7-yLa3Zr2-yMyO12, where 0.2 <y < 1.0. The garnet-type lithium lanthanum zirconate can be in the form of a fdm.

[0040] The plasma processing can occur at atmospheric pressure. In some implementations, plasma processing the mixture under ambient conditions includes exposing the mixture to an open-air plasma. In some cases, plasma processing includes a treatment time up to 10 minutes. In certain implementations, plasma processing includes a treatment time in a range of 2 minutes to 8 minutes. Plasma processing can include a plasma cycle time in a range of 10% to 100%.Plasma processing can include adjusting a distance between a nozzle of a plasma generator and a surface of the mixture to a length between 1 mm and 10 mm. In some cases, plasma processing includes generating an open-air plasma. In certain implementations, plasma processing occurs in the absence of radiant heat provided by an oven. A temperature of the mixture during the plasma processing can be in a range of 500°C to 1100°C.

[0041] Process 100 can further include compressing the mixture before plasma processing. In some cases, compressing the mixture includes cold pressing. Compressing the mixture can yield a pellet. The mass of the pellet can be between 50 mg and 100 mg and a thickness of the pellet can be between 0.5 mm and 1 mm. Process 100 can further include flowing a gas proximate to the nozzle of the plasma generator and the garnet-type lithium lanthanum zirconate after theAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dplasma processing, thereby cooling the garnet-type lithium lanthanum zirconate. The gas can include dry air, dry oxygen, nitrogen, or argon.EXAMPLES

[0042] FIG. IB shows a schematic diagram of an example setup used to carry out the plasma pyrochlore-to-garnet reaction. The open-air plasma treatment was carried out using a FG5001S – V1.10 Open-air® Plasma Generator from Plasmatreat GmbH, Steinhagen, Germany. The sample exposed to the plasma is a green pellet including particles of tantalum doped pyrochlore (La2.4Zr1.12Ta0.48O7.04) that are ball-milled with an excess of lithium hydroxide. The ball milled mixture is cold pressed to form a green pellet. In a typical experiment, the mass of the pellet is 80 mg and thickness is 0.8 mm after cold pressing. The green pellet was placed on a substrate and the plasma nozzle was situated a variable distance from the surface of the pellet. The plasma cycle time, nozzle distance from the top surface of the pellet, and treatment duration time were varied to convert the green pellet to lithium lanthanum zirconate. Plasma cycle time is described as a percentage of time when the plasma receives voltage divided by the total treatment time. For example, a plasma cycle time of 30% refers to the plasma operating from a voltage waveform that is at full power for 30% of the time and at zero power for 70% of the time. The presence of the shroud and the ability to flow compressed gas locally around the plasma nozzle was used to promote reactions with the plasma, control the gas environment, and / or reduce the temperature of the sample after the plasma treatment. In some reactions, a nitrogen shroud gas was delivered at a rate of 40 liters per minute for 2 minutes following the plasma treatment. A type K-thermocouple (not shown) was used to measure the approximate temperature of the sample at each condition.

[0043] FIG. 2 shows the X-ray diffraction pattern obtained from an exemplary pellet after undergoing the plasma pyrochlore-to-garnet process. The plasma cycle time was 60%, nozzle distance was 5 mm, and treatment time was 5 minutes. The approximate temperature at this condition is 850°C. The X-ray diffraction pattern shows that the top face of the pellet (facing the plasma) has been converted into the cubic structure of tantalum doped lithium lanthanum zirconate with nominal composition of Li6.4La3Zr1.4Ta0.6O12. The X-ray diffraction pattern of the bottom face of the pellet (facing the substrate) also matched the reference pattern for cubic lithium lanthanum zirconate. There is a reflection (indicated with an asterisk) associated with theAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dpyrochlore structure, indicating a small quantity of unreacted precursor. This shows that the 5 minute plasma treatment time was sufficient to convert the pyrochlore and lithium hydroxide precursors to garnet using these conditions. Optical microscope images of the exemplary pellet described above, before and after undergoing the plasma pyrochlore-to-garnet process, show that the pellet remains intact after the exposure to the plasma and conversion to garnet.

[0044] Thin film formation: The open-air plasma treatment was carried out on thin films. An exemplary thin film including doped pyrochlores mixed with a lithium compound was prepared by using a doctor blade to coat a suspension onto a silicon wafer substrate. The suspension was prepared by mixing 1.5 g of tantalum doped pyrochlore with nominal composition of Li6.4La3Zr1.4Ta0.6O12and 0.36 g of lithium hydroxide (representing 25 wt% excess lithium hydroxide) into 7 mL of isopropyl alcohol using ball-milling for 60 minutes. After ball-milling, the isopropyl alcohol was removed by heating at 130°C. The dried mixture was mixed with 0.075 g (5 wt%) of polyvinylpyrrolidone and resuspended in 2.25 mL of ethanol. Carboxymethyl cellulose can be used as a binder. The doctor blade height was varied from 100 mm to 250 mm, the blade speed was varied from 15 mm / s to 45 mm / s, and the suspension volume was varied from 30 pL to 100 pL. After coating, the films were dried at 90°C. The conditions used for this exemplary film were 200 mm blade height, 45 mm / s blade speed, 30 pL suspension volume, and 90°C drying temperature. The plasma cycle time, nozzle distance from the top surface of the thin films, and treatment duration time were varied to convert the green pellet to lithium lanthanum zirconate.

[0045] FIG. 3 shows the temperature profile measured using a type K-thermocouple for the plasma treatment applied to the exemplary thin film with the following conditions: 100% plasma cycle time, 25 mm nozzle distance above the sample for 30 seconds, 5 mm nozzle distance for 5 minutes, and 18 liter per minute plasma ionization gas flow rate. The thin film was exposed to maximum temperature of about 952.6 ± 30.6°C for 5 minutes. Optical microscopy images of the exemplary thin film was taken before and after the plasma treatment. The images show that the surface morphology of the film was unchanged after exposure to the plasma and conversion to the garnet phase.

[0046] FIG. 4 shows the surface profilometry measurements for the exemplary thin film after the plasma treatment. A scratch was applied to the film to expose the surface and allow for theAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dthickness of the film to be measured when the profilometry probe was passed across the scratch. The results show that the thickness of the thin film is between 20 μm and 30 μm.

[0047] FIG. 5 shows the X-ray diffraction results of the exemplary thin film after the plasma treatment. The plasma treatment included plasma conditions of 100% plasma cycle time, a 25 mm nozzle distance for 30 seconds, and a 5 mm nozzle distance for 5 minutes The results show that most of the reflections match those expected for the cubic structure of Ta-doped cubic lithium lanthanum zirconate, with some minor reflections observed matching the pyrochlore structure, indicated with the asterisks. These findings indicate conversion of the reagents to the garnet-type phase after the 5 minute plasma pyrochlore-to-garnet reaction within the thin film.

[0048] Cathode composite formation: The open-air plasma treatment was used to carry out cathode composite formation and co-sintering in a pellet. To prepare the exemplary cathode composite pellet, Ta-doped pyrochlore La2.4Zr1.12Ta0.4sO7.04 was ball-milled with an excess of lithium hydroxide. This mixture was ball-milled with LiCoO2 powder and pressed into a pellet. The vol% of LiCoO2 in the pellet was 50 %. The pellet was exposed to the plasma using 100% plasma cycle time at a nozzle distance of 25 mm for 30 seconds, followed by 100% plasma cycle time at a nozzle distance of 9 mm for 5 minutes under 18 liter per minute plasma ionization gas flow rate. FIG. 6 shows the X-ray diffraction results of the exemplary LiCoO2cathode composite pellet after the plasma treatment. The results show that the Ta-doped pyrochlore precursor was transformed to Ta-doped cubic lithium lanthanum zirconate with the cubic garnet structure and that the LiCoO2structure was retained after the plasma treatment. There are small amounts of lithium carbonate as impurity phase and minimal unreacted pyrochlore.

[0049] A dark field optical microscopy image of the top and bottom face of the exemplary LiCoO2cathode composite pellet was taken after the plasma treatment. The images show that the LiCoO2cathode composite pellet remains intact after the exposure to the plasma and conversion of the Ta-doped pyrochlore precursor and lithium hydroxide to garnet.

[0050] The open-air plasma treatment was also used to carry out LiNixMnyCozO2cathode composite pellet formation and co-sintering. To prepare the exemplary cathode composite pellet, Ta-doped pyrochlore La2.4Zr1.12Ta0.48O7.04was ball-milled with an excess of lithium hydroxide. This mixture was ball-milled with LiNixMnyCozO2 powder with a composition of LiNi0.5Mn0.3Co0.2O2. The vol% of LiNi0.5Mn0.3Co0.2O2in the pellet was 50 %. The pellet was exposed to the following plasma treatment: 100% plasma cycle time, 25 mm nozzle distanceAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dabove the sample for 30 seconds, 5 mm nozzle distance for 5 minutes, and 18 liter per min plasma ionization gas flow rate.

[0051] FIG. 7 shows the X-ray diffraction results of the exemplary LiNi0.5Mn0.3Co0.2O2 cathode composite pellet after the plasma treatment. The results show that the Ta-doped pyrochlore precursor was transformed to the garnet structure and that the LiNi0.5Mn0.3Co0.2O2 structure was retained after the plasma treatment.

[0052] The role of the plasma in the plasma pyrochlore-to-garnet process was assessed. Pellets were prepared containing a mixture of a doped pyrochlore precursor, lithium hydroxide, and carboxymethyl cellulose binder. To isolate the effect of the plasma, a pellet was covered with a metal washer so that direct plasma contact was prevented while thermal energy (heat) from the plasma could still be transferred to the pellet, as shown in FIG. 8A. For comparison, a pellet was subjected to direct plasma heating without the cover, as shown in FIG. 8B. Another pellet was thermally heated using a standard hot plate, as shown in FIG. 8C. The approximate temperatures were measured for each pellet following a 20 minute warmup time and a 20 minute plasma treatment time. For the pellet heated on the hotplate, the temperature was measured after a 120 minute warmup time and a 20 minute hold time. The temperature measurements indicate that the three different pellets were subjected to a similar temperature, ranging between 270°C and 280°C (e.g., 270°C, 275°C, 280°C).

[0053] FIG. 9 shows the X-ray diffraction patterns of each pellet after the treatments. The X-ray diffraction patterns for the pellet heated on the hot plate and with the cover preventing direct plasma exposure were similar, with reflections being assigned to the pyrochlore phase. The pellet heated on the hot plate also showed reflections from lithium carbonate, which is likely the result of the reaction of lithium hydroxide with atmospheric water and carbon dioxide. Negligible reflections from the garnet phase were identified in these pellets.

[0054] The uncovered pellet that had direct exposure to the plasma shows a conversion of the pyrochlore precursor to the garnet phase. This suggested that the reactive species in the plasma plays a role in catalyzing the formation of the garnet phase. FIG. 10 shows the Raman spectra of the three pellets. The Raman spectra for the uncovered pellet that had direct plasma exposure shows modes attributed to the garnet phase at 110 cm'1, 670 cm'1, and 760 cm'1and the pyrochlore phase at 195 cm'1. The Raman spectra of the covered pellet and the pellet heated on the hotplate showed modes from the pyrochlore phase, such as the broad band at 330 cm'1. TheAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dresults indicate that direct plasma exposure plays a role in garnet phase formation at approximately 270°C, whereas heating at a similar temperature without plasma exposure does not result in substantial garnet formation from the pyrochlore and lithium hydroxide reagents.

[0055] The effect of various parameters, such as plasma cycling time, reaction time, and nozzle distance were assessed. Table 1 shows pellet samples A, B, C, and D with corresponding assessment conditions. FIG. 11 shows X-ray diffraction measurements taken after each pellet was subjected to the assigned plasma treatment conditions.Table 1. Assessment conditions for pellet samples A, B, C, and D.Pellet Plasma Time (minutes) Nozzle Phase pure? Mechanical Cycling Time Distance Stability A 100% 7 3 mm Yes Brittle B 25% 5 3 mm No Flakey C 45% 5 3 mm Yes IntactD 60% 5 5 mm Yes Intact

[0056] Pellet A showed signs of overtreatment. The X-ray diffraction measurements of Pellet A show high amounts of impurity from lithium lanthanum zirconate degradation. Analysis of Pellet B following treatment suggested that the reaction was incomplete. For example, the X-ray analysis measurement of Pellet B indicated that the mixture was not phase pure, showing peaks that can be attributed at least in part to the unreacted pyrochlore precursors. The surface of Pellet B also appeared to be flakey, suggesting incomplete sintering. Pellets C and D exhibited the high structural integrity and showed negligible impurity peaks in the X-ray diffraction spectra. These measurements suggest that a treatment time of 5 minutes, a plasma cycle time ranging from 45% to 60 %, and a nozzle distance between 3 mm to 5 mm establish conditions that allow for the conversion reaction to reach completion.EMBODIMENTS

[0057] Although the disclosed inventive concepts include those defined in the attached claims, it should be understood that the inventive concepts can also be defined in accordance with the following embodiments.

[0058] Embodiment 1 is the method of synthesizing a garnet-type lithium lanthanum zirconate, the method including: combining a lithium component and a doped pyrochlore to yieldAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-da mixture; and plasma processing the mixture under ambient conditions to yield the garnet-type lithium lanthanum zirconate.

[0059] Embodiment 2 is the method of embodiment 1, further including compressing the mixture before plasma processing.

[0060] Embodiment 3 is the method of any one of embodiments 1-2, wherein the doped pyrochlore includes a dopant, and the dopant includes aluminum, tantalum, gallium, niobium, antimony, or any combination thereof.

[0061] Embodiment 4 is the method of any one of embodiments 1-3, wherein the lithium component includes lithium hydroxide.

[0062] Embodiment 5 is the method of any one of embodiments 1-4, wherein plasma processing the mixture under ambient conditions includes exposing the mixture to an open-air plasma.

[0063] Embodiment 6 is the method of any one of embodiments 1-5, wherein combining includes ball-milling.

[0064] Embodiment 7 is the method of any one of embodiments 2-6, wherein compressing the mixture includes cold pressing.

[0065] Embodiment 8 is the method of any one of embodiments 2-7, wherein compressing the mixture yields a pellet.

[0066] Embodiment 9 is the method of embodiment 8, wherein a mass of the pellet is between 50 mg and 100 mg.

[0067] Embodiment 10 is the method of embodiment 8, wherein a thickness of the pellet is between 0.5 mm and 1 mm.

[0068] Embodiment 11 is the method of any one of embodiments 1-10, wherein the plasma processing includes a treatment time up to 10 minutes.

[0069] Embodiment 12 is the method of embodiment 11, wherein the plasma processing includes a treatment time in a range of 2 minutes to 8 minutes.

[0070] Embodiment 13 is the method of any one of embodiments 1-12, wherein the plasma processing includes adjusting a distance between a nozzle of a plasma generator and a surface of the mixture to a length between 1 mm and 10 mm.

[0071] Embodiment 14 is the method of any one of embodiments 1-13, wherein the plasma processing includes a plasma cycle time in a range of 10% to 100%.Attorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-d

[0072] Embodiment 15 is the method of any one of embodiments 1-14, wherein the garnettype lithium lanthanum zirconate is in the form of a film.

[0073] Embodiment 16 is the method of any one of embodiments 1-15, wherein the plasma processing includes generating an open-air plasma.

[0074] Embodiment 17 is the method of any one of embodiments 1-16, wherein the plasma processing occurs in the absence of radiant heat provided by an oven.

[0075] Embodiment 18 is the method of any one of embodiments 1-17, wherein a temperature of the mixture during the plasma processing is in a range of 500°C to 1100°C.

[0076] Embodiment 19 is the method of any one of embodiments 1-18, wherein the plasma processing occurs at atmospheric pressure.

[0077] Embodiment 20 is the method of any one of embodiments 1-19, wherein the doped pyrochlore includes La2.4Zr2MaOβ, 0.2 < a < 0.4 and 7.9 < 0 < 8.2, and M includes aluminum, gallium, or a combination thereof.

[0078] Embodiment 21 is the method of any one of embodiments 1-20, wherein the garnettype lithium lanthanum zirconate includes Li7-3xMxLa3Zr2O12, 0.2 ≤ x ≤ 0.4, and M includes aluminum, gallium, or a combination thereof.

[0079] Embodiment 22 is the method of any one of embodiments 1-19, wherein the doped pyrochlore includes La2.4ZraMbOc, 0.8 ≤ a ≤ 1.44, 0.16 ≤ b ≤ 0.8, 6.88 ≤ c ≤ 7.2, and M includes niobium, tantalum, antimony, or a combination thereof.

[0080] Embodiment 23 is the method of any one of embodiments 1-19 and 22, wherein the garnet-type lithium lanthanum zirconate includes Li7-yLa3Zr2-yMyO12, 0.2 ≤ y ≤ 1.0, and M includes niobium, tantalum, antimony, or a combination thereof.

[0081] Embodiment 24 is the method of any one of embodiments 1-23, further including flowing a gas proximate to the nozzle of the plasma generator and the garnet-type lithium lanthanum zirconate after the plasma processing, thereby cooling the garnet-type lithium lanthanum zirconate.

[0082] Embodiment 25 is the method of embodiment 24, wherein the gas includes dry air, dry oxygen, nitrogen, or argon.

[0083] Embodiment 26 is a method of synthesizing a garnet-type lithium lanthanum zirconate cathode composite, the method including: combining a cathode material with the mixture of any one of embodiments 1-25 to yield a second mixture; compressing the secondAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dmixture to yield a compressed mixture; and plasma processing the compressed mixture under ambient conditions to yield the garnet-type lithium lanthanum zirconate cathode composite.

[0084] Embodiment 27 is the method of embodiment 26, wherein the cathode material includes LiCoO2or LiNi0.5Mn0.3Co0.2O2.

[0085] Embodiment 28 is the garnet-type lithium lanthanum zirconate composite of embodiments 26 or 27.

[0086] Embodiment 29 is a method of synthesizing a garnet-type lithium lanthanum zirconate film, the method including: depositing a thin film including the mixture of any one of embodiments 1-25 on a substrate; and plasma processing the thin film under ambient conditions to yield the garnet-type lithium lanthanum zirconate film.

[0087] Embodiment 30 is the method of embodiment 29, wherein the mixture is in the form of a suspension.

[0088] Embodiment 31 is the method of any one of embodiments 29-30, wherein the mixture includes a polymer binder.

[0089] Embodiment 32 is the method of embodiment 31, wherein the polymer binder includes polyvinylpyrrolidone or carboxymethyl cellulose.

[0090] Embodiment 33 is the method of any one of embodiments 29-32, wherein a thickness of the garnet-type lithium lanthanum zirconate film is between 1 μm and 500 μm.

[0091] Although this disclosure contains many specific embodiment details, these should not be construed as limitations on the scope of the subject matter or on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this disclosure in the context of separate embodiments can also be implemented, in combination, in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments, separately, or in any suitable sub-combination. Moreover, although previously described features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0092] Particular embodiments of the subject matter have been described. Other embodiments, alterations, and permutations of the described embodiments are within the scopeAttorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dof the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results.

[0093] Accordingly, the previously described example embodiments do not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure.

Claims

Attorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dWHAT IS CLAIMED IS:

1. A method of synthesizing a garnet-type lithium lanthanum zirconate, the method comprising:combining a lithium component and a doped pyrochlore to yield a mixture; and plasma processing the mixture under ambient conditions to yield the garnet-type lithium lanthanum zirconate.

2. The method of claim 1, further comprising compressing the mixture before plasma processing.

3. The method of claim 1, wherein the doped pyrochlore comprises a dopant, and the dopant comprises aluminum, tantalum, gallium, niobium, antimony, or any combination thereof.

4. The method of claim 1, wherein the lithium component comprises lithium hydroxide.

5. The method of claim 2, wherein plasma processing the mixture under ambient conditions comprises exposing the mixture to an open-air plasma.

6. The method of claim 1, wherein combining comprises ball-milling.

7. The method of claim 2, wherein compressing the mixture comprises cold pressing.

8. The method of claim 2, wherein compressing the mixture yields a pellet.

9. The method of claim 8, wherein a mass of the pellet is between 50 mg and 100 mg.

10. The method of claim 8, wherein a thickness of the pellet is between 0.5 mm and 1 mm.

11. The method of claim 1, wherein the plasma processing comprises a treatment time up to 10 minutes.Attorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-d12. The method of claim 11, wherein the plasma processing comprises a treatment time in a range of 2 minutes to 8 minutes.

13. The method of claim 1, wherein the plasma processing comprises adjusting a distance between a nozzle of a plasma generator and a surface of the mixture to a length between 1 mm and 10 mm.

14. The method of claim 1, wherein the plasma processing comprises a plasma cycle time in a range of 10% to 100%.

15. The method of claim 1, wherein the garnet-type lithium lanthanum zirconate is in the form of a film.

16. The method of claim 1, wherein the plasma processing comprises generating an open-air plasma.

17. The method of claim 1, wherein the plasma processing occurs in the absence of radiant heat provided by an oven.

18. The method of claim 1, wherein a temperature of the mixture during the plasma processing is in a range of 500°C to 1100°C.

19. The method of claim 1, wherein the plasma processing occurs at atmospheric pressure.

20. The method of claim 1, wherein:the doped pyrochlore comprises La2.4Zr2MaOβ, and 0.2 < a < 0.4 and 7.9 < 0 < 8.2; and M comprises aluminum, gallium, or a combination thereof.

21. The method of claim 1, wherein:Attorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-dthe garnet-type lithium lanthanum zirconate comprises Li7-3xMxLa3Zr2O12 and 0.2 ≤ x ≤ 0.4; andM comprises aluminum, gallium, or a combination thereof.

22. The method of claim 1, wherein:the doped pyrochlore comprises La2.4ZraMbOc, and 0.8 <a < 1.44, 0.16 < b < 0.8, 6.88 <c < 7 andM comprises niobium, tantalum, antimony, or a combination thereof.

23. The method of claim 1, wherein:the garnet-type lithium lanthanum zirconate comprises Li7-yLa3Zr2-yMyO12 and 0.2 ≤ y ≤ 1.0; andM comprises niobium, tantalum, antimony, or a combination thereof.

24. The method of claim 1, further comprising flowing a gas proximate to the nozzle of the plasma generator and the garnet-type lithium lanthanum zirconate after the plasma processing, thereby cooling the garnet-type lithium lanthanum zirconate.

25. The method of claim 24, wherein the gas comprises dry air, dry oxygen, nitrogen, or argon.

26. A method of synthesizing a garnet-type lithium lanthanum zirconate cathode composite, the method comprising:combining a cathode material with the mixture of claim 1 to yield a second mixture; compressing the second mixture to yield a compressed mixture; andplasma processing the compressed mixture under ambient conditions to yield the garnettype lithium lanthanum zirconate cathode composite.

27. The method of claim 26, wherein the cathode material comprises LiCoO2orLiNi0.5Mn0.3Co0.2O2.Attorney Docket No.: 22193-0392WO1 / M25-088PA-WOl-d28. The garnet-type lithium lanthanum zirconate cathode composite of claim 26.

29. A method of synthesizing a garnet-type lithium lanthanum zirconate film, the method comprising:depositing a thin film comprising the mixture of claim 1 on a substrate; andplasma processing the thin film under ambient conditions to yield the garnet-type lithium lanthanum zirconate film.

30. The method of claim 29, wherein the mixture is in the form of a suspension.

31. The method of claim 29, wherein the mixture comprises a polymer binder.

32. The method of claim 31, wherein the polymer binder comprises polyvinylpyrrolidone or carboxymethyl cellulose.

33. The method of claim 29, wherein a thickness of the garnet-type lithium lanthanum zirconate film is between 1 μm and 500 μm.

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