Process for preparing doped lithium lanthanum zirconium oxide

Abstract

A process for preparing doped-lithium lanthanum zirconium oxide (doped-LLZO) is described herein. The method involves dry doping of a co-precipitated lanthanum zirconium oxide (LZO) precursor. Dry doping is a process in which a dry powdered dopant is ground and mixed with a pre-prepared co-precipitated LZO precursor and a lithium salt to provide a LLZO precursor composition, which is subsequently calcined to form a doped-LLZO. The process described herein comprises calcining a dry, powdered (e.g., micron, sub-micron or nano-powdered) mixture of a co-precipitated LZO precursor, a dopant salt or oxide, and a lithium salt under an oxygen-containing atmosphere at a temperature in the range of about 500 to about 1100° C., and recovering the doped-LLZO after calcining.

Claims

1. A process for preparing a doped lithium lanthanum zirconium oxide (doped-LLZO) comprising the sequential steps of: (a) calcining a dry, powdered mixture of a co-precipitated lanthanum zirconium oxide (LZO) precursor, a dopant, and a lithium salt in an oxygen-containing atmosphere at a temperature in the range of about 500 to about 1100° C.; and (b) recovering the doped-LLZO; wherein the co-precipitated LZO precursor comprises a mixture of lanthanum oxide and/or lanthanum hydroxide in combination with zirconium oxide and/or zirconium hydroxide, in which the La and Zr are present in a La:Zr elemental ratio of about 3:2, and the La and Zr are uniformly mixed at the atomic level; the dopant is a salt or oxide of a dopant ion, X, wherein X is not a Li, La Zr, or O ion, X cations replace a portion of Li, La, and/or Zr in the formula Li.sub.7La.sub.3Zr.sub.2O.sub.12, and X anions replace a portion of O anion in the formula Li.sub.7La.sub.3Zr.sub.2O.sub.12; and the lithium salt and the dopant are mixed with the LZO precursor in amounts selected to achieve a target Li:La:Zr:X ratio in the doped-LLZO.

2. The process of claim 1, wherein X comprises at least one ion selected from the group consisting of an alkaline earth metal cation, a transition metal cation, a lanthanide cation, an actinide cation, a main group metal cation, a metalloid cation, and a non-metal anion.

3. The process of claim 1, wherein the X comprises at least one cation selected from the group consisting of Al.sup.3+, Ta.sup.5+, Ga.sup.3+, Nb.sup.4+, Y.sup.3+, Fe.sup.3+, W.sup.6+, Te.sup.6+, Ba.sup.2+, Ce.sup.4+, Ti.sup.4+, B.sup.3+, and Sb.sup.5+.

4. The process of claim 1, wherein X comprises Al.sup.3+.

5. The process of claim 1, wherein X replaces about 0.15 to about 45 mole percent (mol %) of the Li in the formula Li.sub.7La.sub.3Zr.sub.2O.sub.12.

6. The process of claim 5, wherein X comprises at least one cation selected from the group consisting of B.sup.3+, Al.sup.3+, In.sup.3+, Si.sup.4+, Sr.sup.2+, Ge.sup.4+, Ga.sup.3+, Zn.sup.2+, Fe.sup.3+and Be.sup.3+.

7. The process of claim 1, wherein X replaces about 0.3 to about 50 mol % of La in the formula Li.sub.7La.sub.3Zr.sub.2O.sub.12.

8. The process of claim 7, wherein X comprises at least one cation selected from Ca.sup.2+, Sr.sup.2+, Mg.sup.2+, Rb.sup.+, Ba.sup.2+, Y.sup.2+, Bi.sup.3+, Ac.sup.3+, Ag.sup.1+, and a lanthanide cation having a 3+ oxidation state.

9. The process of claim 1, wherein X replaces about 0.5 to about 50 mol % of Zr in the formula Li.sub.7La.sub.3Zr.sub.2O.sub.12.

10. The process of claim 9, wherein X comprises at least one cation selected from the group consisting of Sc.sup.3+, Cr.sup.3+, Ni.sup.2+, Cu.sup.2+, Cd.sup.2+, Au.sup.3+, In.sup.3+, Tl.sup.3+, Eu.sup.2+, a metal cation having a 4+ oxidation state, a metalloid cation having a 4+ oxidation state, a metal cation having a 5+ oxidation state, and metalloid cation having a 5+ oxidation state.

11. The process of claim 1, wherein X replaces about 0.8 to 33 mol % of O in the formula Li.sub.7La.sub.3Zr.sub.2O.sub.12.

12. The process of claim 11, wherein X is selected from the group consisting of F.sup.−, Cl.sup.−, Br.sup.−, a non-metal anion having a 1-oxidation state, and a non-metal anion having a 2-oxidation state.

13. The process of claim 1, wherein the lithium salt comprises at least one salt selected from the group consisting of lithium hydroxide, lithium carbonate, lithium acetate, lithium sulfide, lithium fluoride, and lithium chloride.

14. The process of claim 13, wherein the lithium salt is present in an amount that provides up to a 20 mol % excess of Li beyond what is required for the target ratio of Li:La:Zr:X.

15. The process of claim 1, wherein the co-precipitated LZO precursor comprises La(OH).sub.3 and ZrO.sub.2.

16. The process of claim 1, wherein the dopant comprises aluminum tris-acetylacetonate (Al(acac).sub.3).

17. The process of claim 1, wherein the dopant comprises an oxide of X.

18. The process of claim 1, wherein the dopant comprises a salt of X.

19. The process of claim 18, wherein the salt of X comprises at least one anion selected from the group consisting of hydroxide, carbonate, an organic carboxylate, nitrate, sulfide, fluoride, and chloride.

20. The process of claim 1, wherein X comprises two or more dopant ions.

21. The process of claim 1, further comprising grinding and mixing together the co-precipitated LZO precursor, the dopant, and the lithium salt to form the dry powdered mixture, prior to step (a).

22. The process of claim 21, further comprising preparing the co-precipitated LZO precursor prior to the grinding and mixing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 provides flow diagram illustrating one embodiment of the methods described herein.

(2) FIG. 2 provides an X-ray diffraction (XRD) pattern for co-precipitated LZO precursor, with reference patterns for La(OH).sub.3 and ZrO.sub.2 components shown below the LZO precursor plot.

(3) FIG. 3 provides an XRD pattern for an aluminum doped-LLZO (Li.sub.6.25La.sub.3Zr.sub.2Al.sub.0.25O.sub.12) prepared by the method described herein, with reference peaks for the target cubic-LLZO phase as well as minor side product LaAlO.sub.3 and Li.sub.0.5La.sub.2Al.sub.0.5O.sub.2 phases shown below the doped-LLZO plot.

DETAILED DESCRIPTION

(4) As described herein, dry doping of co-precipitated LZO precursor provides a new and effective process for preparing doped-LLZO. The methods described herein are versatile and robust, affording doped-LLZO with a highly uniform distribution of Li, La, Zr and dopant elements. These methods also allow incorporation of a wide variety of dopant species and even multiple dopant species.

(5) In one embodiment, a process for preparing doped-LLZO comprises calcining a dry, powdered mixture of a co-precipitated LZO precursor, a dopant, and a lithium salt in an oxygen-containing atmosphere at a temperature in the range of about 500 to about 1100° C., and recovering the doped-LLZO; wherein the co-precipitated LZO precursor comprises a mixture of lanthanum hydroxide in combination with zirconium oxide and/or zirconium hydroxide, prepared by co-precipitation, in which the La and Zr are present in a La:Zr elemental ratio of about 3:2, and the La and Zr are uniformly mixed at the atomic level; the dopant is a salt or oxide of a dopant ion, X, and the lithium salt and the dopant are mixed with the LZO precursor in amounts selected to achieve a target Li:La:Zr:X ratio in the doped-LLZO.

(6) The lithium salt can be any lithium salt that will decompose and become incorporated into the doped-LLZO during calcining. Typically, a sight excess of the lithium salt is utilized (e.g., 1 to 20 mol % excess, such as a 2 mol % excess, a 3 mol % excess, a 5 mol % excess, a 10 mol % excess, or a 15 mol % excess). The dopant salts are selected from the group consisting of hydroxides, carbonates, organic carboxylates (e.g., acetate, oxalate, acetylacetonate (acac), and the like), nitrates, sulfides, fluorides and chlorides.

(7) Preferably, the LZO precursor is prepared by co-precipitation of lanthanum hydroxide (La(OH).sub.3) and zirconium oxide (ZrO.sub.2) and/or zirconium hydroxide (Zr(OH).sub.4) from an aqueous solution of lanthanum and zirconium salts to form an intimately mixed LZO precursor composition.

(8) In some embodiments, the method further comprises preparing the powdered mixture by combining, grinding and mixing the co-precipitated LZO precursor, the dopant, and the lithium salt prior to calcining the powered mixture. The grinding and mixing can be performed, e.g., in a high energy ball mill, a planetary ball mill, a fluidized bed jet mill, a hammer mill, rolling mill, automated mortar and pestle, micronizing mill, or any other such equipment for preparing dry powdered materials. In some preferred embodiments, the grinding and mixing is performed using a planetary ball mill.

(9) In yet other embodiments, the method further comprises preparing the co-precipitated LZO precursor prior to the grinding and mixing. The LZO precursor is prepared by co-precipitating zirconium oxide and/or hydroxide with hydroxide from an aqueous solution of La and Zr salts in the appropriate La:Zr elemental ratio, e.g., by adding NaOH as the precipitating agent and to control the pH.

(10) In some embodiments of the methods described herein a single dopant is utilized, while in some other embodiments two or more dopant materials are utilized. The dopant element/ion can comprise any metal, metalloid, or non-metal element. In some embodiments the dopant element comprises a transition metal, a main group metal, a lanthanide, an actinide, an alkaline earth metal, a metalloid, a non-metal, or a combination of two or more of the foregoing.

(11) As described in S. Ramakumar et al. “Lithium garnets: synthesis, structure, Li.sup.+ conductivity, Li.sup.+ dynamics and applications, Prog. Mat. Sci. 2017, 88:325-411 (“Ramakumar”) which is incorporated herein by reference in its entirety, different cations tend to preferentially replace either Li, La, or Zr in LLZO (see e.g., the annotated periodic table provided on page 385 of Ramakumar. For example, B.sup.3+, Al.sup.3+, Ga.sup.3+, Zn.sup.2+, Fe.sup.3+and Be.sup.3+ tend to replace Li in Li.sub.7La.sub.3Zr.sub.2O.sub.12; Ca.sup.2+, Sr.sup.2+, Ba.sup.2+, Y.sup.2+, Bi.sup.3+, Ac.sup.3+, Ag.sup.1+, and lanthanides having a 3+ oxidation state tend to replace La in Li.sub.7La.sub.3Zr.sub.2O.sub.12; and Mg.sup.2+, Sc.sup.3+, Cr.sup.3+, Ni.sup.2+, Cu.sup.2+, Cd.sup.2+, Au.sup.3+, In.sup.3+, Tl.sup.3+, Eu.sup.2+, metal or metalloid elements having a 4+ oxidation state, and metal or metalloid elements having a 5+ oxidation state tend to replace Zr in Li.sub.7La.sub.3Zr.sub.2O.sub.12. Anions such as F.sup.1−, Cl.sup.1−, and S.sup.2− can replace oxygen.

(12) Methods for preparing co-precipitated LZO precursor have recently been examined in the literature, for example, as described in Ramakumar, referred to above, or in S. Cao et al., “Modeling, Preparation and Elemental Doping of Li.sub.7La.sub.3Zr.sub.2O.sub.12 Garnet-type Solid Electrolytes: A Review”, J Korean Ceramic Soc., 2019, 56:111-129, which is incorporated herein by reference in its entirety. See also S. Yang, et al., “Ionic Conductivity of Ga-Doped LLZO Prepared Using Couette-Taylor Reactor for All-Solid Lithium Batteries”, J. Ind. Eng. Chem., 2017, 56:422-427; D. Kim, et al., “Fabrication and Electrochemical Characteristics of NCM-Based All-Solid Lithium Batteries Using Nano-Grade Garnet Al-LLZO Powder”, J. Ind. Eng. Chem., 2019, 71:445-451; H. Kim, et al., “Method for Preparing Solid Electrolyte for All-Solid-State Lithium Secondary Battery” U.S. Patent Publication No. US2018/0248223 Al (Aug. 30, 2018); C. Shao, et al., “Structure and Ionic Conductivity of Cubic Li.sub.7La.sub.3Zr.sub.2O.sub.12 Solid Electrolyte Prepared by Chemical Co-Precipitation Method”, Solid State Ionics, 2016, 287:13-16; and R. Kun, et al., “Structural and Computational Assessment of the Influence of Wet-Chemical Processing of the Al-Substituted Cubic Li.sub.7La.sub.3Zr.sub.2O.sub.12”, ACS Appl. Mater. Interfaces, 2018, 10:37188-37197; each of which is incorporated herein by reference.

(13) Preferably, the LZO precursor is prepared by co-precipitation. The lanthanum and zirconium salts for co-precipitation preferably are selected from the group consisting of carbonates, nitrates, and sulfates. Additionally, ammonium hydroxide is typically used as a complexing agent while sodium hydroxide is present to control the pH and act as a precipitating agent. Once the LZO precursor is collected, it must be washed to remove salt-based by-products and dried to afford the final powdered form of the LZO precursor.

(14) FIG. 1 provides a flow diagram illustrating one embodiment of the methods described herein. In FIG. 1, co-precipitated LZO is prepared at step 102. The co-precipitated LZO from step 102 is ground and mixed together with a lithium salt and a dopant at step 104 to form a dry, powdered mixture. The dry powdered mixture from step 104 is then calcined in step 106 at a temperature in the range of about 500 to 1100° C. in an oxygen-containing atmosphere (e.g., air, or O.sub.2), e.g., for a period of time of about 1 hour to about 12 hours. Finally, the doped-LLZO is recovered in step 108. Optionally the doped LLZO can be further ground in Step 110.

(15) The following non-limiting examples are provided to illustrate certain aspects and features of the methods described herein.

EXAMPLE 1

(16) Co-precipitated LZO precursor was prepared by dissolving La(NO.sub.3).sub.3 and Zr(SO.sub.4).sub.2 salts in deionized water to produce an aqueous transition metal solution so that the molar ratio of La:Zr was about 3:2. Separate aqueous solutions containing NH.sub.4OH and NaOH were prepared. The molar concentration of a hydroxide solution:transition metal solution was about 2:1. The transition metal and NH.sub.4OH solutions were simultaneously fed into a Taylor vortex reactor by a pump set at a selected pumping rate, e.g., mL/min, to chelate with the transition metal ions, and achieve an approximate 4 hour residence time. Meanwhile, the sodium hydroxide was pumped to maintain a pH of 11 using a PID controller. The rotation speed of the Taylor vortex reactor was set to 800 RPM to mix the solutions and resulting precipitate within the reactor while the temperature of the reactor was set to 50° C. The LZO precursor slurry was collected from the overflow outlet of the reactor, washed with deionized water to remove salt-based by-products, and dried under vacuum.

(17) The co-precipitated LZO was examined by XRD. An XRD pattern of the LZO precursor is shown in FIG. 2, with the predicted peaks for the lanthanum hydroxide and zirconium oxide components shown below the XRD plot of the precursor. As is evident in FIG. 2, the actual spectrum agrees well with the predicted peak distribution. In addition, energy-dispersive X-ray spectroscopy (EDS) mapping was performed on the co-precipitated LZO precursor, which showed that La, Zr, and O were substantially uniformly spatially distributed in the LZO precursor material.

EXAMPLE 2

(18) A dry powdered mixture of co-precipitated LZO precursor from Example 1, Al(acac).sub.3 as the dopant, and lithium hydroxide was prepared by grinding in a mortar and pestle.

EXAMPLE 3

(19) A doped-LLZO of formula Li.sub.0.25La.sub.3Zr.sub.2Al.sub.0.25O.sub.12 was prepared from the mixture of Example 2 by calcining at about 900° C. for about 6 hours under an atmosphere of flowing oxygen.

(20) The doped-LLZO of formula Li.sub.0.25La.sub.3Zr.sub.2Al.sub.0.25O.sub.12 was examined by XRD. Based on the XRD pattern shown in FIG. 3, the peaks observed in the doped-LLZO agree well with the predicted peak distribution for cubic Li.sub.0.25La.sub.3Zr.sub.2Al.sub.0.25O.sub.12, with minor impurities of side product LaAlO.sub.3 and Li.sub.0.5La.sub.2Al.sub.0.5O.sub.2 phases (see the predicted peak distributions below the spectrum).

(21) All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

(22) The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

(23) Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.