PREPARATION OF NANOSTRUCTURED MIXED LITHIUM ZIRCONIUM OXIDES BY MEANS OF SPRAY PYROLYSIS

Abstract

A process may produce mixed oxides including lithium, zirconium, and optionally at least one other than Li and Zr metal, by flame spray pyrolysis. Mixed oxides are obtainable by such a process. Such mixed oxides may be used in lithium ion batteries.

Claims

1. A process for producing a mixed oxide comprising lithium, zirconium and optionally at least one other than Li and Zr metal, by flame spray pyrolysis, the process comprising: flame spray pyrolyzing at least one solution of metal precursors, comprising (i) a lithium carboxylate and/or a zirconium carboxylate, the carboxylates comprising 5 to 20 carbon atoms; and (ii) a solvent mixture comprising an alcohol and a carboxylic acid comprising 5 to 20 carbon atoms, the solvent mixture comprising less than 10 wt. % water, and a molar ratio of the alcohol to the carboxylic acid being in a range of from 1:20 to 20:1.

2. The process of claim 1, wherein the spray flame pyrolyzing comprises: (a) atomizing at least one solution of metal precursors to afford an aerosol with an atomizer gas; (b) bringing the aerosol to reaction in a reaction space of a reactor with a flame obtained by ignition of a mixture of fuel gas and an oxygen-comprising gas to obtain a reaction stream; (c) cooling the reaction stream to obtain a solid metal is cooled; and (d) removing the solid metal oxide from the reaction stream.

3. The process of claim 1, wherein the mixed oxide is a compound of a general formula
Li.sub.aZr.sub.bM.sub.cO.sub.0.5a+2b+d   (I), wherein 1.5≤a≤15, 0.5≤b≤3.0, 0≤c≤5, d=0.5c for M=Na or K Na, K; d=c for M═Be, Mg, Ca, Sr, Ba, Zn, Co, Ni, Cu, or Mn, d=1.5c for M═B, Al, Ga, In, Fe, Sc, Y, or La, d=2c for M═Ti, Zr, Hf, Ce, Si, Ge, Sn, or Pb, d=2.5c for M═V, Nb, or Ta, and d=3c for M═Mo or W.

4. The process of claim 1, wherein the mixed oxide has a BET surface area in a range of from 0.1 to 100 m.sup.2/g.

5. The process of claim 1, whererin the lithium and zirconium carboxylates, independently of each other, comprise pentanoate (C5), hexanoate (C6), heptanoate (C7), octanoate (C8), nonanoate (C9), decanoate (D10), undecanoate (C11), dodecanoate (C12), tridecanoate (C13), tetradecanoate (C14), pentadecanoate (C15), hexadecanoate (C16), heprtadecanoate (C17), octadecanoate (C18), nonadecanoate (C19), icosanoate (C20), or a mixture of two or more of any of these, of lithium and/or zirconium, each carboxyl ate being independently linear, branched, or cyclic.

6. The process of claim 1, wherein the alcohol is selected from the group consisting of methanol, ethanol, n-propanol, iso propanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, n-hexanol, cyclohexanol, n octanol, 2-ethylhexanol, n-decanol, neodecanol, and a mixture thereof.

7. The process of claim 1, wherein the solution of metal precursors comprises a chelating agent selected from the group consisting of a diamine, 1,3-dicarbonyl compound, and a mixture of two or more of any of these.

8. The process of claim 1, wherein the mixed oxide has a numerical d.sub.50 mean particle diameter in a range of from 0.05 to 2 μm, as determined by static light scattering (SLS).

9. The process of claim 1, wherein the mixed oxide has a tamped density in a range of from 20 to 1000 g/L.

10. The process of claim 1, further comprising: thermally treating the mixed oxide produced by flame spray pyrolysis.

11. The process of claim 10, wherein the thermally treating is carried out at a temperature in a range of from 600 to 1300° C.

12. The process of claim 1, further comprising: milling the mixed oxide produced by flame spray pyrolysis.

13. The process of claim 12, wherein the milling is ball milling.

14. A mixed oxide, comprising: lithium; zirconium, and optionally at least one other than Li and Zr metal, wherein the mixed oxide is in the form of aggregated primary particles, wherein the mixed oxide has a BET surface area in a range of from 15 to 50 m.sup.2/g, wherein the mixed oxide has a d.sub.50 numerical mean particle diameter in a range of from 0.1 to 2 μm, as determined by static light scattering (SLS), and wherein the mixed oxide has a tamped density in a range of from 30 to 150 g/L.

15. A mixed oxide, comprising: lithium; zirconium; and optionally at least one other than Li and Zr metal, wherein the mixed oxide is in the form of aggregated primary particles, wherein the mixed oxide has a BET surface area of less than 10 m.sup.2/g, wherein the mixed oxide has a d.sub.50 numerical mean particle diameter in a range of from 1 to 50 μm, as determined by static light scattering (SLS), and wherein the mixed oxide has a tamped density in a range of from 400 to 1000 g/L.

16. A solid-state electrolyte or electrode of a lithium ion battery, comprising: the mixed oxide of claim 14 as an additive in liquid, gel electrolyte, or a constituent of the electrode of a lithium ion battery.

17. A lithium ion battery, comprising: the mixed oxide of claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0120] FIGS. 1A and 1B are TEM images of Li—La—Zr—Al mixed oxide particles prepared as described in comparative example 1.

[0121] FIGS. 2A and 2B are TEM images of Li—La—Zr—Al mixed oxide (LLZO) particles prepared as described in comparative example 2.

[0122] FIG. 3A and 3B are TEM images of inventive Li—La—Zr—Al mixed oxide (LLZO) particles prepared as described in example 1.

[0123] FIG. 4 shows XRD patterns of the inventive Li—La—Zr—Al mixed oxide (LLZO) prepared as described in examples 1-3.

[0124] FIG. 5 shows SEM-EDX mapping image of La (white) on LLZO-coated NMC prepared using LLZO prepared as described in example 1.

[0125] FIG. 6 shows SEM-EDX mapping image of La (white) on LLZO-coated NMC prepared using LLZO prepared as described in comparative example 1.

[0126] FIG. 7 shows the statistical analyses of the area distribution of La in the SEM-EDX mapping images of LLZO-coated NMC prepared using LLZO prepared as described in comparative example 1 and example 1.

[0127] FIG. 8 shows the results of the initial impedance tests of all-solid-state Li metal batteries with LLZO prepared as described in examples 2 and 3 and without LLZO (PEO), measured by electrochemical impedance spectroscopy (EIS).

[0128] FIG. 9 shows the results of the initial formation between 3.0V and 4.3V at 60° C. and 0.1C of all-solid-state Li metal batteries with LLZO prepared as described in examples 2 and 3 and without LLZO (PEO).

EXAMPLES

[0129] Commercial mixed lithium nickel manganese cobalt oxide powder NMC (7-1.5-1.5) (Type PLB-H7) with a BET surface area of 0.30-0.60 m.sup.2/g, a medium particle diameter d.sub.50=10.6±2 μm (determined by static laser scattering method), was supplied by Linyi Gelon LIB Co.

[0130] Commercial polyethylene oxide (PEO, from Sigma-Aldrich) with an average molecular weight of 4*10.sup.5 g/mol was used for the electrolyte formulation. PEO was used as received. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) from Kishida with a purity >99% (battery grade) was used as received in the glove box.

[0131] Commercial lithium deposited Cu foil was purchased from Honjo Metal, the thickness of the copper layer is 10 μm and the thickness of lithium layer is 20 μm.

Comparative Example 1

[0132] (Li—La—Zr—Al Mixed Oxide from Aqueous Nitrate Precursors)

[0133] 18.63 kg of an aqueous solution containing 1142 g LiNO.sub.3, 2839 g La(NO.sub.3).sub.3*6H.sub.2O, 1670 g Zr(NO.sub.3).sub.4 (metal content: 24 wt %) and 212 g Al(NO.sub.3).sub.3*9H.sub.2O was prepared under constant stirring until a clear solution was obtained. This solution corresponds to a composition Li.sub.7.54La.sub.3Zr.sub.2Al.sub.0.26O.sub.12.66.

[0134] An aerosol was formed of 2.5 kg/h of this solution and 15 Nm.sup.3/h of air via a two-component nozzle and sprayed into a tubular reaction with a burning flame. The burning gases of the flame consist of 20 Nm.sup.3/h hydrogen and 75 Nm.sup.3/h of air, resulting in a control temperature at the measurement point one meter below the spray nozzle of 900° C. Additionally, 25 Nm.sup.3/h of secondary air was used. After the reactor the reaction gases were cooled down and filtered.

[0135] The particle properties are shown in table 1, the TEM images of the particles are shown in FIG. 1A and 1B.

[0136] (Preparation of an NMC Powder Coated with Li—La—Zr—Al Mixed Oxide of Comparative Example 1)

[0137] The NMC-powder (99 g) was mixed with 1.0 g (1 wt %) of the fumed powder of the comparative example 1 in a high intensity laboratory mixer (Somakon mixer MP-GL with a 0.5 L mixing unit) at first for 1 min at 500 rpm (specific electrical power: 350W/kg NMC) to homogeneously mix the two powders. Afterwards the mixing intensity was increased to 2000 rpm (specific electrical power: 800 W/kg NMC, tip-speed of the mixing tool in the mixing unit: 10 m/s) and the mixing was continued for 5 min to achieve the dry coating of the NMC particles by the fumed powder of the comparative example 1.

Comparative Example 2

[0138] (Li—La—Zr—Al Mixed Oxide from Ethanolic Nitrate Precursors)

[0139] 18.3 kg of an ethanolic solution containing 779 g LiNO.sub.3, 1930 g La(NO.sub.3).sub.3*6H.sub.2O, 1139 g Zr(NO.sub.3).sub.4 (metal content: 24 wt %) and 146 g Al(NO.sub.3).sub.3*9H.sub.2O was prepared under constant stirring until a clear solution was obtained. This solution corresponds to a composition Li.sub.7.54La.sub.3Zr.sub.2Al.sub.0.26O.sub.12.66.

[0140] An aerosol was formed of 2.5 kg/h of this solution and 15 Nm.sup.3/h of air via a two-component nozzle and sprayed into a tubular reaction with a burning flame. The burning gases of the flame consist of 13.7 Nm.sup.3/h hydrogen and 75 Nm.sup.3/h of air, resulting in a control temperature at the measurement point one meter below the spray nozzle of 900° C. Additionally, 25 Nm.sup.3/h of secondary air was used. After the reactor the reaction gases were cooled down and filtered.

[0141] The particle properties are shown in table 1, the TEM images of the particles are shown in FIG. 2A and 2B.

Example 1

[0142] (Li—La—Zr—Al Mixed Oxide)

[0143] 1320 g of a commercial solution (Octa Solingen® Zirconium 12), containing 12 wt % Zr in the form of zirconium ethylhexanoate was mixed with 173 g of acetyl acetone. This solution was mixed under constant stirring with 2273 g of a commercial solution (Borchers® Deca Lithium 2), containing 2 wt % of Li in the form of lithium neodecanoate. A further solution, containing 1125 g La(NO.sub.3).sub.3*6H.sub.2O, 83.3 g Al(NO.sub.3).sub.3*9H.sub.2O, 2660 g ethanol and 2660 g ethylhexanoic acid (molar ratio ethanol:ethylhexanoic acid=3.1:1, water content in the solvent mixture: 2.7 wt %), was added under constant stirring until a clear solution was obtained. This solution corresponds to a composition Li.sub.7.54La.sub.3Zr.sub.2Al.sub.0.26O.sub.12.66.

[0144] An aerosol was formed of 2.5 kg/h stream of this solution and 15 Nm.sup.3/h stream of air via a two-component nozzle and sprayed into a tubular reaction with a burning flame. The burning gases of the flame consisted of 12.9 Nm.sup.3/h hydrogen and 75 Nm.sup.3/h of air, resulting in a control temperature at the measurement point one meter below the spray nozzle of 900° C. Additionally, 25 Nm.sup.3/h of secondary air was used. After the reactor the reaction gases were cooled down and filtered.

[0145] The particle properties are shown in Table 1, the TEM images of the particles are shown in FIG. 3A and 3B.

[0146] Preparation of an NMC Powder Coated with Li—La—Zr—Al Mixed Oxide of Example 1:

[0147] The NMC-powder (99 g) was mixed with 1.0 g (1 wt %) of the fumed powder of the example 1 in a high intensity laboratory mixer (Somakon mixer MP-GL with a 0.5 L mixing unit) at first for 1 min at 500 rpm (specific electrical power: 350 W/kg NMC) to homogeneously mix the two powders. Afterwards the mixing intensity was increased to 2000 rpm (specific electrical power: 800 W/kg NMC, tip-speed of the mixing tool in the mixing unit: 10 m/s) and the mixing was continued for 5 min to achieve the dry coating of the NMC particles by the fumed powder of the example 1.

Example 2

[0148] (Calcined Li—La—Zr—Al Mixed Oxide)

[0149] The mixed oxide obtained in example 1 was calcined at 950° C. for 6h in a rotary kiln. The XRD analysis (FIG. 4) showed, that the major phase of the product was the cubic garnet structure.

Example 3

[0150] (Calcined and Ball Milled Li—La—Zr—Al Mixed Oxide)

[0151] The mixed oxide obtained in example 2 was further ball milled by ZrO.sub.2 balls with diameter of 0.5 mm in ethanol. The XRD analysis (FIG. 4) showed, that the major phase of the product was still the cubic garnet structure.

TABLE-US-00001 TABLE 1 Properties of the mixed oxides Tamped BET D10 D50 D90 density Example [m.sup.2/g] [μm] [μm] [μm] [g/L] Comparative 19 0.20 1.55 5.34 195 Example 1 Comparative 21 0.19 1.46 4.67 226 Example 2 Example 1 25 0.09 0.97 4.70 98 Example 2 <1 8.31 19.13 42.36 788 Example 3 10 0.41 0.93 5.78 680

[0152] Analysis of LLZO-Coated Mixed Lithium Transition Metal Oxides by SEM-EDX

[0153] FIG. 5 shows the SEM-EDX mapping of La (white) on LLZO-coated NMC prepared using fumed nano LLZO (Example 1), FIG. 6 shows the results of the analysis of NMC coated with fumed coarse LLZO (Comparative Example 1). The axes of FIGS. 5 and 6 show: x axis=diameter of particles; the lefty axis=volume in %, the right y axis=cumulative volume in %. NMC mixed oxide dry coated with fumed nano LLZO (Example 1), shows a full and homogeneous coverage of all NMC particles with LLZO (FIG. 5). No larger LLZO agglomerates were detected, showing a good dispersibility of nanostructured fumed nano LLZO. Additionally, no free unattached LLZO-particles next to the NMC particles were found, indicating the strong adhesion between coating and the substrate (NMC). In contrast, FIG. 6 shows that only the fine LLZO-particles of fumed coarse LLZO are attached to the surface of NMC particles. The larger LLZO-particles are non-dispersed and are therefore unattached, located next to the NMC particles. As a result, the NMC particles are not fully covered by zirconium oxide.

[0154] FIG. 7 shows the statistical analyses of example 1 and comparative example 1. The area distribution of La (white) μm.sup.2 in the SEM-EDX mapping is further analyzed by box normal plot and shows a clear difference of the dispersibility of La (white) between example 1 and comparative example 1.

[0155] Preparation of Hybrid Solid Electrolyte (HSE) Membrane

[0156] Mixing LLZO ceramic powder with polyethylene oxide (PEO) and LiTFSI resulted in solvent-free, hot pressing procedure, yielding flexible and freestanding membranes. Two sets of composite membranes with LLZO from example 2 and example 3 have been prepared according to Table 2. The HSE membrane of weighted LLZO was ground, milled with PEO and weighted LLZO to obtain a paste-like material, which was then annealed at 100° C. overnight, successively hot-pressed at 100° C. between Teflon substrates for a desired thickness about 110 μm.

TABLE-US-00002 TABLE 2 Recipe of hybrid solid electrolyte EO/Li PEO + LiTFSI (g) LLZO (g) LLZO wt % LLZO type 15 0.697 + 0.303 0.42 30% Example 2 15 0.697 + 0.303 0.42 30% Example 3

[0157] Assembly and Characterizations of All-Solid-State Lithium Metal Batteries

[0158] Three sets of all-solid-state NMC_HSE_Li metal batteries were assembled using (a) PEO without LLZO filler, (b) PEO using calcined LLZO (Example 2) filler and also (c) PEO using ball-milled LLZO (Example 3) filler. The initial impedance was analyzed by electrochemical impedance spectroscopy (EIS) and the results are shown in the FIG. 8. FIG. 9 shows the initial formation of these three cells between 3.0V and 4.3V at 60° C. and 0.1 C. The cell using LLZO from Example 3 showed the highest capacity of 140 mAh/g at 0.1 C discharge and the lowest impedance among three examples.