SYNTHESIS OF NANOSTRUCTURED ZIRCONIUM PHOSPHATE

Abstract

A process produces zirconium phosphate by flame spray pyrolysis. A solution of at least one zirconium compound, an organic phosphate and a solvent with less than 10% by weight water is subjected to flame spray pyrolysis. Zirconium phosphate obtainable by this process finds application in batteries to encapsulate lithium mixed oxide particles.

Claims

1. A pyrogenically prepared zirconium phosphate of general formula ZrP.sub.2O.sub.7, wherein the pyrogenically prepared zirconium phosphate is in a form of aggregated primary particles, has a BET surface area, DIN 9277:2014, of 5 m.sup.2/g-100 m.sup.2/g, has a numerical mean particle diameter of d.sub.50=0.03 m-2 m, as determined by static light scattering (SLS), and has a tamped density, DIN ISO 787-11:1995; of 20 g/L-200 g/L.

2. A process for producing the pyrogenically prepared zirconium phosphate according to claim 1 by flame spray pyrolysis, the process comprising: subjecting to flame spray pyrolsis a solution comprising at least one zirconium carboxylate, wherein the at least one zirconium carboxylate contains 5 to 20 carbon atoms, an organic phosphate, and a solvent containing less than 10% by weight water.

3. The process according to claim 2, wherein the at least one zirconium carboxylate is a carboxylate selected from the group consisting of linear, branched or cyclic 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) of zirconium, and mixtures thereof.

4. The process according to claim 2, wherein the organic phosphate is selected from the group consisting of esters of phosphonic acid (H.sub.3PO.sub.3), orthophosphoric acid (H.sub.3PO.sub.4), metaphosphoric acid (HPO.sub.3), pyrophosphoric acid (H.sub.4P.sub.2O.sub.7), polyphosphoric acids, and mixtures thereof.

5. The process according to claim 2, wherein the organic phosphate is selected from the group consisting of alkyl ester, aryl ester, mixed alkyl/aryl esters, and mixtures thereof.

6. The process according to claim 2, wherein the organic phosphate is an alkyl ester having alkyl groups with 1 to 10 carbon atoms.

7. The process according to claim 2, wherein the solvent is selected from the group consisting of linear or cyclic, saturated or unsaturated, aliphatic or aromatic hydrocarbons, esters of carboxylic acids, ethers, alcohols, carboxylic acids, and the mixtures thereof.

8. The process according to claim 2, further comprising: thermally treating of the pyrogenically prepared zirconium phosphate, produced by flame spray pyrolysis, at a temperature of 600 C.-1300 C.

9. The process according to claim 8, further comprising milling of the thermally treated pyrogenically prepared zirconium phosphate.

10. A component of a solid-state electrolyte, comprising the pyrogenically prepared zirconium phosphate according to claim 1 as an additive in liquid, or gel electrolyte or as a constituent of an electrode of a lithium ion battery.

11. An electrode for a lithium ion battery comprising the pyrogenically prepared zirconium phosphate according to claim 1.

12. An electrolyte for a lithium ion battery comprising the pyrogenically prepared zirconium phosphate according to claim 1.

13. A lithium ion battery comprising the pyrogenically prepared zirconium phosphate according to claim 1.

14. The lithium ion battery according to claim 13, comprising a liquid or gel electrolyte.

15. The lithium ion battery according to claim 14, wherein the lithium ion battery is a solid-state battery.

16. An additive in liquid or gel electrolyte comprising the pyrogenically prepared zirconium phosphate according to claim 1.

17. A constituent of an electrode of a lithium ion battery comprising the pyrogenically prepared zirconium phosphate according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0089] FIG. 1 is a TEM image of zirconium phosphate particles prepared as described in example 1.

[0090] FIG. 2 shows XRD patterns of zirconium phosphates prepared as described in example 1.

[0091] FIG. 3 is a TEM image of zirconium phosphate particles prepared as described in example 1.

[0092] FIG. 4-2 and comparative examples 1-2.

[0093] FIG. 4 shows SEM images of NMC dry coated with fumed zirconium phosphate particles [0094] a) backscattered electrons (BSE) image, [0095] b) EDX mapping of Zr, [0096] c) high resolution SEM image.

[0097] FIG. 5 shows the cycling performance of uncoated NMC and NMC dry coated with fumed zirconium phosphate particles in lithium ion batteries with liquid electrolyte.

EXAMPLES

Example 1

[0098] 2,97 kg of a solution containing 1337 g of a commercial solution (Octa Solingen Zirconium 18), containing 18,01 wt. % Zr in the form of zirconium ethyl hexanoate and 982 g of a commercial solution (Alfa Aesar), containing 16.66 wt. % Phosphorous in the form of triethyl phosphate were mixed, resulting in a clear solution. This solution corresponds to a composition of ZrP.sub.2O.sub.7.

[0099] An aerosol of 1.25 kg/h of this solution and 5 Nm.sup.3/h of air was formed via a two-component nozzle and sprayed into a tubular reaction with a burning flame. The burning gases of the flame consist of 4.3 Nm.sup.3/h hydrogen and 25 Nm.sup.3/h of air. Additionally, 15 Nm.sup.3/h secondary air was used. After the reactor the reaction gases were cooled down and filtered.

[0100] The resulting white powder had a BET surface area of 36 m.sup.2/g and a tamped density of 65 g/l. The TEM image of the particles is shown in FIG. 1 and the XRD analysis (FIG. 2) showed, that the major phase of the product was the cubic phase of zirconium phosphate. FIG. 3 shows the aggregate size distribution of this material after 30 min of ultrasonic treatment.

Example 2

Dry Coating of Zirconium Phosphate (ZPO) on CAM

[0101] The commercial NMC 7 1.5 1.5-powder (Linyi Gelon LIB Co., Type PLB-H7) with a BET surface area of 0.30-0.60 m.sup.2/g, medium diameter d50=10,62 m (via laser scattering), was mixed with the respective amount (1.0 wt. %) of ZPO-powder (according to example 1) in a high intensity laboratory mixer (SOMAKON mixer MP-GL with 0.5 L mixing unit) at first for 1 min at 500 rpm to homogeneously mix the two powders. Afterwards the mixing intensity was increased to 2000 rpm for 5 min to achieve the dry coating of the NMC particles by ZPO.

[0102] Coated NMC particles are achieved with a ZPO-coating layer thickness of 20-200 nm. FIG. 4 shows SEM-images of NMC dry coated by ZPO. Comparison of the back-scatter electron image (a) and the EDX-mapping of Zr (b) of NMC dry coated by fumed ZPO reveals that a fully and homogeneous coverage around all cathode particles by ZPO was found. No larger ZPO agglomerates were detected, showing that the dispersion of nanostructured fumed ZPO was successful. Additionally, no free unattached ZPO-particles next to the cathode particles were found, indicating the strong adhesion between coating and substrate. The high-resolution SEM image (c) shows a homogeneous distribution of ZPO with a high degree of surface coverage of the CAM.

Example 3

Electrochemical Tests

[0103] Electrodes for electrochemical measurements were prepared by blending 90 wt. % NMC with 5 wt. % PVDF (Solef PVDF 5130) as a binder and 5 wt. % SUPER C65 (IMERYS) as a conductive additive under inert gas atmosphere. N-Methyl-2-pyrrolidone (NMP) was used as the solvent. The slurry was casted on aluminum foil and dried for 20 min on 120 C. heating plate in air. Afterward, the electrode sheet was dried in a vacuum furnace at 120 C. for 2 h. The area-related cathode loading is adjusted to 2,00,1 mAh cm.sup.2. Circular electrodes with a diameter of 12 mm were punched out, calendered to achieve an electrode density of 3.0 g cm.sup.3, and dried again in a vacuum furnace at 120 C. for 12 h to remove any residual water and NMP. For the cycling tests the cells were assembled as CR2032 type coin cells (MTI Corporation) in an argon-filled glovebox (GLOVEBOX SYSTEMTECHNIK GmbH). Lithium metal (ROCKWOOD LITHIUM GmbH) is used as the anode material. Celgard 2500 was used as the separator. 35 L of a solution of 1 molar LiPF6 in ethylene carbonate and ethyl methyl carbonate (50:50 wt./wt.; SIGMA-ALDRICH) was used as electrolyte. The cells were locked with a crimper (MTI). For electrochemical evaluations galvanostatic cycling was performed between 3.0 and 4.3 V vs Li.sup.+/Li at 25 C. For the calculation of the capacities and the specific currents, only the mass of the active material was considered and a theoretical capacity of 180 mAh/g of NMC 7 1.5 1.5 is supposed. For the coin half-cells during cycling, the C-rate was increased every four cycles, starting from 0.1/0.1 (Charge/Discharge) to 0.2/0.2, 0.5/0.5, 1.0/1.0 and 1.0/2.0 C. Afterward, the cell was cycled at 1/1 C for long term stability test.

[0104] FIG. 5 shows the influence of the received ZPO coating layer on the cycling performance. The performance of NMC coated by fumed ZPO is compared against the uncoated NMC. From the graph data, it can be intuitively concluded that the fumed ZPO coating improves the performance and cycle life of NMC significantly. The NMC coated by fumed ZPO shows an improved rate capability and long-term cycling stability.

Measurement of LiOH and Li.sub.2CO.sub.3 Content

[0105] 2 g of the cathode material powder and 30 mL deionized water were placed into a 100 mL titration beaker and stirred for 10 minutes at room temperature. The remaining solids were filtered off and the filter was rinsed with 20 mL of deionized water. All the liquids were collected in a 100 mL titration beaker. The LiOH and Li.sub.2CO.sub.3 contents were determined by titration with hydrochloric acid (c(HCl)=0.1 mol/L) using Tris(hydroxymethyl)aminomethane (TRIS) as standard. Therefore the beaker was put on the manual titration stand (Excellence Titrator T7 with the 20 mL Burette DV1020 and the Electrode DGi111-SC from Mettler Toledo) and titration was started.

[0106] For the material of Example 1 0,05 wt. % of LiOH and 0.265 wt. % of Li.sub.2CO.sub.3 were detected by titration. In comparison, 0,168 wt. % of LiOH and 0.511 wt. % of Li.sub.2CO.sub.3 were detected by titration on the uncoated NMC.

[0107] As can be seen from the examples the inventive zirconium phosphate (ZPO) is well suited to be used advantageously as a constituent of an electrode. Besides improved performance and cycle life it has also been shown that the inventive material is capable of reducing the LiOH/Li.sub.2CO.sub.3 content thus emphasizing the lithium ion scavenging ability of the inventive zirconium phosphate.