1,4-DIOXANE SLOVATE OF LITHIUM DIFLUOROBIS(OXALATO)PHOSPHATE, METHOD FOR PREPARING THE SAME, AND ELECTROLYTE COMPOSITION COMPRISING THE SAME

Abstract

A 1,4-dioxane solvate of lithium difluoro bis(oxalato)phosphate, a method for preparing the same, and an electrolyte composition containing the same are disclosed. The 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate has excellent crystallinity and filterability, so that a compound with high purity can be obtained in high yield. Further, since it has excellent stability against moisture, its distribution and storage are easy and the stability of the composition containing 1,4-dioxane solvate of lithium difluoro bis(oxalato)phosphate can be greatly improved.

Claims

1. A 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate.

2. The solvate according to claim 1, wherein the lithium difluorobis(oxalato)phosphate is represented by the following formula (I): ##STR00003##

3. The solvate according to claim 1, wherein the solvate is a crystalline form.

4. The solvate according to claim 3, wherein the solvate is a crystalline form showing an X-ray powder diffraction (XRPD) pattern characterized by peaks having I/I.sub.o values of at least 10% (I is the intensity of each peak; I.sub.o is the intensity of the highest peak) at diffraction angles (2θ) of 9.7±0.2, 9.9±0.2, 15.4±0.2, 15.7±0.2, 16.9±0.2, 17.5±0.2, 17.9±0.2, 19.6±0.2, 19.8±0.2, 20.3±0.2, 21.3±0.2, 23.4±0.2, 23.8±0.2, 24.6±0.2, 24.9±0.2, 26.4±0.2, and 41.4±0.2.

5. The solvate according to claim 1, wherein the solvate has a purity of 99.5% or more.

6. A method for preparing a 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate comprising: (i) adding 1,4-dioxane to a solution of lithium difluorobis(oxalato)phosphate dissolved in a non-aqueous solvent, followed by stirring; and (ii) filtering a solid produced in step (i).

7. The method according to claim 6, wherein the lithium difluorobis(oxalato) phosphate is prepared by adding methyltrichlorosilane (MeSiCl.sub.3) or silicon tetrachloride (SiCl.sub.4) to lithium hexafluorophosphate (LiPF.sub.6) and oxalic acid to react.

8. The method according to claim 6, wherein the concentration of the lithium difluorobis(oxalato)phosphate solution in step (i) is 5 to 50% (w/v).

9. The method according to claim 6, wherein the addition amount of 1,4-dioxane to the lithium difluorobis(oxalato)phosphate solution in step (i) is 1:0.5 to 1:8.0 by weight.

10. The method according to claim 6, wherein the stirring in step (i) is performed for 1 to 30 hours.

11. The method according to claim 6, wherein the stirring in step (i) is performed at 0 to 60° C.

12. The method according to claim 6, wherein a drying is performed after the filtering in step (ii).

13. An electrolyte composition for a secondary battery comprising a 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate according to claim 1, a non-aqueous solvent, and a lithium salt.

14. An electrolyte composition for a secondary battery comprising a 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate according to claim 2, a non-aqueous solvent, and a lithium salt.

15. An electrolyte composition for a secondary battery comprising a 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate according to claim 3, a non-aqueous solvent, and a lithium salt.

16. An electrolyte composition for a secondary battery comprising a 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate according to claim 4, a non-aqueous solvent, and a lithium salt.

17. An electrolyte composition for a secondary battery comprising a 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate according to claim 5, a non-aqueous solvent, and a lithium salt.

Description

BRIEF DESCRIPTION OF FIGURES

[0043] FIG. 1 is a result of .sup.1H NMR analysis of the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate.

[0044] FIG. 2 is a result of .sup.13C NMR analysis of the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate.

[0045] FIG. 3 is a result of .sup.19F NMR analysis of the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate.

[0046] FIG. 4 is a result of .sup.31P NMR analysis of the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate.

[0047] FIG. 5 is a result of .sup.13C NMR analysis of the lithium difluorobis(oxalato)phosphate.

[0048] FIG. 6 is an X-ray powder diffraction pattern of the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate in a crystalline form.

[0049] FIG. 7 is a thermogravimetric analysis diagram of the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate.

BEST MODE

[0050] The present invention is further illustrated by the following examples, which are not to be construed to limit the scope of the invention.

Example 1: Preparation of 1,4-dioxane Solvate of Lithium difluorobis(oxalato)phosphate

[0051] 26 g of lithium hexafluorophosphate (LiPF.sub.6) (0.171 mol), 30.8 g of anhydrous oxalic acid, and 174 g of ethyl methyl carbonate were added to a 500 ml three-neck double jacketed reactor with a magnetic stirrer, mixed and stirred. The molar ratio of lithium hexafluorophosphate and oxalic acid was 1:2. The reaction temperature was set to 40° C. to raise the internal temperature, and then 51.2 g of methyltrichlorosilane (MeSiCl.sub.3) was added dropwise over 1 hour. The molar ratio of lithium hexafluorophosphate and methyltrichlorosilane was 1:2. After completion of the addition, stirring was continued at 40° C. for an additional 2 hours to complete the reaction. After completion of the reaction, a transparent, colorless filtrate was obtained.

[0052] MeSiF.sub.3 and HCl gas, which were reaction by-products, were collected by first passing 500 g of water cooled to 10° C. or less, and then passing through a −50° C. low temperature trap.

[0053] After HCl gas and volatile materials were removed by degassing with a vacuum pump at room temperature for 2 hours, 322 g of 1,4-dioxane was added and stirred at room temperature for 10 hours. The resulting solid was filtered and dried under vacuum at 50° C. to obtain 73.1 g of the title compound as a white solid (yield: 100%).

[0054] As an internal standard, 3,5-difluorobenzonitrile was added and dissolved in acetonitrile-d.sub.3 to measure .sup.1H, .sup.13C, .sup.19F and .sup.31P NMR. The results are shown in FIGS. 1 to 4.

[0055] The structure can be confirmed in .sup.13C, .sup.19F and .sup.31P NMR of FIGS. 2, 3 and 4, and the molar ratio of 1,4-dioxane to LDFOP was calculated as 1:2.0 from the .sup.1H and .sup.19F NMR results of FIGS. 1 and 3.

[0056] The purity of the obtained solvate was measured with a nuclear magnetic resonance spectrometer (NMR spectrometer). As a result, it was confirmed that the purity was 99.5%.

Example 2: Preparation of 1,4-dioxane Solvate of Lithium difluorobis(oxalato)phosphate

[0057] 72.4 g (yield 99%, purity: 99.5%) of the title compound was obtained in the same manner as in Example 1, except that dimethyl carbonate was used instead of ethyl methyl carbonate as a solvent.

Example 3: Preparation of 1,4-dioxane Solvate of Lithium difluorobis(oxalato)phosphate

[0058] 72.3 g (yield 99%, purity: 99.5%) of the title compound was obtained in the same manner as in Example 1, except that diethyl carbonate was used instead of ethyl methyl carbonate as a solvent.

Comparative Example 1

[0059] The same method as in Example 1 was performed except that tetrahydrofuran was used instead of 1,4-dioxane, but no solid was produced.

Comparative Example 2

[0060] The same method as in Example 1 was performed except that 1,3-dioxane was used instead of 1,4-dioxane, but no solid was produced.

Comparative Example 3

[0061] The same method as in Example 1 was performed except that 2-methyl-1,3-dioxolane was used instead of 1,4-dioxane, but no solid was produced.

Comparative Example 4

[0062] The same method as in Example 1 was performed except that 4-methyl-1,3-dioxolane was used instead of 1,4-dioxane, but no solid was produced.

Comparative Example 5

[0063] The same method as in Example 1 was performed except that tetrahydropyran was used instead of 1,4-dioxane, but no solid was produced.

Comparative Example 6

[0064] The same method as in Example 1 was performed except that 2-methyltetrahydrofuran was used instead of 1,4-dioxane, but no solid was produced.

Comparative Example 7

[0065] The same method as in Example 1 was performed except that 1,3,5-trioxane was used instead of 1,4-dioxane, but no solid was produced.

Comparative Example 8: Preparation of Lithium difluorobis(oxalato)phosphate in a Solid Form

[0066] 26 g of lithium hexafluorophosphate (LiPF.sub.6) (0.171 mol), 30.8 g of anhydrous oxalic acid, and 174 g of ethyl methyl carbonate were added to a 500 ml three-neck double jacketed reactor with a magnetic stirrer, mixed and stirred. The molar ratio of lithium hexafluorophosphate and oxalic acid was 1:2. The reaction temperature was set to 40° C. to raise the internal temperature, and then 51.2 g of methyltrichlorosilane (MeSiCl.sub.3) was added dropwise over 1 hour. The molar ratio of lithium hexafluorophosphate and methyltrichlorosilane was 1:2. After completion of the addition, stirring was continued at 40° C. for an additional 2 hours to complete the reaction. After completion of the reaction, a transparent, colorless filtrate was obtained.

[0067] MeSiF.sub.3 and HCl gas, which were reaction by-products, were collected by first passing 500 g of water cooled to 10° C. or less, and then passing through a −50° C. low temperature trap.

[0068] After HCl gas and volatile materials were removed by degassing with a vacuum pump at room temperature for 2 hours, 322 g of methylene chloride (MC) was added, stirred at room temperature for 10 hours, and filtered to obtain 27.5 g of the title compound as a white solid (yield: 64%).

[0069] Lithium difluorobis(oxalato)phosphate in a solid form was confirmed by .sup.13C NMR (FIG. 5).

Experimental Example 1: XRD Analysis

[0070] X-ray powder diffraction analysis (XRD) of the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate prepared in Example 1 was performed, and the results are shown in FIG. 6.

[0071] FIG. 6 showed that the compound prepared in Example 1 was a crystalline form. The characteristic peaks shown in the XRD of FIG. 6 are shown in Table 1 below, where ‘2θ’ denotes a diffraction angle, and ‘I/I.sub.0’ denotes the relative intensity of the peak.

TABLE-US-00001 TABLE 1 2θ I/I.sub.0 (%) 9.7 21 9.9 19 15.4 27 15.7 43 16.9 21 17.5 49 17.9 29 19.6 35 19.8 53 20.3 100 21.3 66 23.4 15 23.8 17 24.6 25 24.9 23 26.4 26 41.4 10

Experimental Example 2: Thermogravimetric Analysis (TGA)

[0072] Thermogravimetric analysis (TGA) was performed on the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate prepared in Example 1.

[0073] Thermogravimetric analysis (TGA) was performed using a STA 409 PC/PG from NETZSCH. About 20 mg of a sample was placed in a platinum pan to prepare a sample required for the TGA experiment. It was heated to 25-800° C. under nitrogen at a rate of 10° C./min. The results of thermogravimetric analysis are shown in FIG. 7.

Experimental Example 3: Hygroscopicity Test

[0074] The hygroscopicity of each of the compounds prepared in Example 1 and Comparative example 8 was evaluated by the Karl Fischer Titration method.

[0075] Specifically, the hygroscopicity was measured by exposing 100 g of the sample to constant moisture at room temperature, weighing 0.2 g of the sample, and titrating the change in moisture of the solid by a coulometric method. The results are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Moisture gain (ppm) 0 day 0.5 day 1 day 2 days 7 days Example 1 0 88 166 321 866 Comparative 0 893 1711 2343 4521 example 8

[0076] Table 2 shows that the hygroscopicity of the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate prepared in Example 1 is lower than that of the lithium difluorobis (oxalato)phosphate in a solid form prepared in Comparative Example 8.

Experimental Example 4: Test of Impurity Content

[0077] 3.1 g of the compound prepared in Example 1 was dissolved in 10 g of ethyl methyl carbonate to prepare a sample, and 2.0 g of the compound prepared in Comparative example 8 was dissolved in 10 g of ethyl methyl carbonate to prepare a sample. Then, the moisture content in each sample, acidity and chlorine (Cl) content were measured.

[0078] The results are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Example 1 Comparative example 8 Moisture (ppm) 10.2 23.1 Acidity (ppm) 24 46 Cl content (ppm) N/D 688

[0079] Table 3 shows that the moisture content, acidity and chlorine (Cl) content of the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate prepared in Example 1 are lower than those of the lithium difluorobis(oxalato)phosphate in a solid form prepared in Comparative example 8. In particular, it was confirmed that chlorine (Cl) was not detected in the 1,4-dioxane solvate of lithium difluorobis(oxalato)phosphate prepared in Example 1.