Preparation method and application of monofluorophosphoric acid mixed anhydride

Abstract

The invention provides a preparation method and application of monofluorophosphoric acid mixed anhydride. The preparation method of the monofluorophosphoric acid mixed anhydride comprises the following steps: adding sodium monofluorophosphate into a first organic solvent, cooling to-10 to 0 DEG C, dropwise adding trimethylchlorosilane, gradually heating to room temperature, stirring for reaction, filtering a reactant after the reaction is completed, and carrying out reduced pressure distillation to obtain an intermediate; and adding a lithium salt and the intermediate into a second organic solvent, stirring and mixing, reacting at normal temperature, filtering, and carrying out reduced pressure distillation. The preparation method is simple and high in yield, is very helpful for improving the performance of the secondary battery, and can be used as a secondary battery electrolyte additive with excellent performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage devices, in particular to a synthesis of a secondary battery electrolyte material, and more particularly to a preparation method of a monofluorophosphoric mixed anhydride and application thereof. BACKGROUND

[0002] Monofluorophosphoric compounds are a class of electrolyte additives in secondary battery electrolyte, although they are not as widely used as difluorophosphoric compounds or polyfluorophosphoric compounds, they have their own characteristics and application performance. Common monofluorophosphoric compounds include lithium monofluorophosphate (LiPO3F) and monofluorophosphate ester compounds. On the one hand, monofluorophosphoric compounds (such as lithium monofluorophosphate LiPO3F) have a solid electrolyte interface film (SEI / CEI film) formed on the electrode surface, which is significantly weaker than difluorophosphoric compounds or polyfluorophosphoric compounds. On the other hand, monofluorophosphoric compounds have low solubility in non-aqueous solvents, which may limit their effective concentration in the battery electrolyte, making it difficult to play an interface optimization role.

[0003] Monofluorophosphoric mixed anhydride compounds are acyl-modified monofluorophosphoric compounds. There are few reports on monofluorophosphoric mixed anhydride compounds and their preparation methods, and it is necessary to study acyl-modified compounds of monofluorophosphoric compounds in order to expand the application range of monofluorophosphoric compounds. SUMMARY

[0004] Based on the above problems, the purpose of the present application is to provide a preparation method of a monofluorophosphoric mixed anhydride and application thereof, which has a simple preparation method and high yield. In addition, it is very helpful to improve the performance of secondary batteries and can be used as a secondary battery electrolyte additive with excellent performance. To achieve the above-mentioned purpose, the first aspect of the present application provides a preparation method of a monofluorophosphoric mixed anhydride, comprising the following steps: (1) adding sodium monofluorophosphate into a first organic solvent, cooling to -10~0℃, then adding trimethylchlorosilane dropwise and gradually warming to room temperature, then stirring to react, and after the reaction is completed, filtering and distilling under reduced pressure to obtain an intermediate; (2) adding a lithium salt and the intermediate into a second organic solvent, stirring and mixing, then reacting at room temperature, and then filtering and distilling under reduced pressure.

[0005] The structural formula of the monofluorophosphoric mixed anhydride of the present application is shown as Formula I, wherein R1 and R2 are each independently acetyl, trifluoroacetyl, trifluoromethylsulfinyl, trifluoromethylsulfonyl, methylsulfinyl or methylsulfonyl.

[0006]

[0007] Formula I The monofluorophosphoric mixed anhydride of the present application is prepared by reacting inexpensive sodium monofluorophosphate and trimethylchlorosilane (TMSCl) to generate the intermediate bis(trimethylsilyl) monofluorophosphate, which is then reacted with a lithium salt to generate the monofluorophosphoric mixed anhydride. The byproduct lithium trimethylsilanolate (boiling point 40℃) formed in the reaction has a low boiling point and is easily removed, and after removal, it can well promote the reaction, so the yield is high. This preparation method is relatively friendly, compared with some monofluorophosphoric compounds which are difficult to synthesize, have low yield and complex byproduct treatment, it has the advantages of relatively simple process, higher yield and lower production cost, which is conducive to large-scale production and application, and reduces the overall manufacturing cost of the battery.

[0008] As a technical solution of the present application, the first organic solvent and the second organic solvent are each independently selected from tetrahydrofuran, dichloromethane, chloroform or dioxane.

[0009] As a technical solution of the present application, the molar ratio of the sodium monofluorophosphate to the trimethylchlorosilane is 1:2.0-2.5.

[0010] As a technical solution of the present application, the stirring time in step (I) is 18-72 h.

[0011] As a technical solution of the present application, the lithium salt is selected from lithium acetate, lithium trifluoroacetate, lithium trifluoromethylsulfinate, lithium trifluoromethylsulfonate, lithium methylsulfinate or lithium methylsulfonate.

[0012] As a technical solution of the present application, the molar ratio of the lithium salt to the intermediate is 1:2.

[0013] As a technical solution of the present application, the stirring time in step (II) is 12-72 h.

[0014] The second aspect of the present application provides the application of the monofluorophosphoric mixed anhydride prepared by the above-mentioned preparation method of the monofluorophosphoric mixed anhydride in a battery. The monofluorophosphoric mixed anhydride has high solubility in non-aqueous solvents and is helpful to improve the performance of secondary batteries, and can be used as a secondary battery electrolyte additive with excellent performance. DETAILED DESCRIPTION

[0015] The monofluorophosphoric mixed anhydride prepared by the preparation method of the present application has good compatibility and can be applied to electrolytes of various different systems, and can be used in different electrode materials (such as ternary materials, lithium iron phosphate, silicon-based negative electrodes, etc.) and battery systems (lithium ion batteries, sodium ion batteries, etc.) to improve the performance of secondary batteries in different application scenarios.

[0016] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0017] Example 1 This embodiment describes a method for preparing compound one, wherein R1 and R2 are both acetyl groups, and includes the following steps.

[0018] (a) 60 g of sodium monofluorophosphate was added to 1000 ml of tetrahydrofuran, and then the temperature was lowered to 0 °C. 105 g of TMSCl was added dropwise to the reaction flask. After the addition was complete, the temperature was gradually raised to room temperature, and the mixture was stirred for 16 h. After the reaction was completed, the mixture was filtered, and the filtrate was concentrated under vacuum to obtain a colorless liquid. The liquid was then distilled under reduced pressure to obtain 56.7 g of di(trimethylsilyl)monofluorophosphate, which was a colorless liquid with a yield of 48.0%. The di(trimethylsilyl)monofluorophosphate was detected by nuclear magnetic resonance and ESI. 1 H-NMR (400 MHz, DMSO, ppm): 0.18 (s, J=1.2Hz, 18H); 13 C-NMR (100MHz, deuterated DMSO, ppm): δ 4.7; 19 F-NMR (282 MHz, DMSO, ppm): -72.8(d). ESI-MS(m / s):245.1[M+H] + .

[0019] The reaction equation is shown below.

[0020]

[0021] (ii) 5.4 g of lithium acetate and 10 g of bis(trimethylsilyl) monofluorophosphate were added to 150 ml of anhydrous dichloromethane and stirred until homogeneous. Sodium acetate was insoluble. The mixture was then stirred at room temperature for 18 h. After the reaction was completed, a small amount of insoluble matter was filtered off, and the dichloromethane and the low-boiling-point byproduct lithium trimethylsilanolate (boiling point 40 °C) were evaporated under reduced pressure to obtain 7.10 g of compound one, with a yield of 94.2%. Compound one was subjected to NMR and ESI detection. 1 ¹H NMR (400MHz, deuterated DMSO, ppm): 2.14 (s, J=1.6Hz, 6H). 13 C-NMR (100MHz, deuterated DMSO, ppm): δ 20.1, 173.6. 19 F-NMR (282MHz, DMSO, ppm): -72.1(d). ESI-MS(m / s): 184.1 [M+H]+ .

[0022] The reaction equation is shown below.

[0023]

[0024] Compound 1 Example 2 This embodiment describes a method for preparing compound two, wherein R1 and R2 are both trifluoroacetyl groups, and includes the following steps.

[0025] (a) Same as step (a) in Example 1.

[0026] (ii) 9.83 g of lithium trifluoroacetate and 10 g of bis(trimethylsilyl) monofluorophosphate were added to 150 ml of anhydrous dichloromethane and stirred until homogeneous. Sodium trifluoroacetate was insoluble. The mixture was then stirred at room temperature for 24 h. After the reaction was completed, a small amount of insoluble matter was filtered off, and the dichloromethane and the low-boiling-point byproduct lithium trimethylsilanolate (boiling point 40 °C) were evaporated under reduced pressure to obtain 10.93 g of compound II, with a yield of 91.3%. Compound II was subjected to NMR and ESI detection. 13 C-NMR (100MHz, deuterated DMSO, ppm): δ115.1, 176.7; 19F-NMR (282 MHz, DMSO, ppm): -74.9 (s), -70.5 (d); ESI-MS (m / s): 292.9[M+H] + .

[0027] The reaction equation is shown below.

[0028]

[0029] Example 3 This embodiment describes a method for preparing compound three, wherein R1 and R2 are both trifluoromethyl sulfinyl groups, and the method includes the following steps.

[0030] (a) Same as step (a) in Example 1.

[0031] (ii) 11.47 g of lithium trifluoromethyl sulfinate and 10 g of bis(trimethylsilyl) monofluorophosphate were added to 150 ml of anhydrous dichloromethane and stirred until homogeneous. Lithium trifluoromethyl sulfinate was insoluble. The mixture was then stirred at room temperature for 20 h. After the reaction was completed, a small amount of insoluble matter was filtered off, and the dichloromethane and the low-boiling-point byproduct lithium trimethylsilanolate (boiling point 40 °C) were evaporated under reduced pressure to obtain 12.13 g of compound 3, with a yield of 89.2%. Compound 3 was subjected to NMR and ESI detection. 13 C-NMR (100MHz, deuterated DMSO, ppm): δ 153.1; 19F-NMR (282 MHz, DMSO, ppm): -78.4(t), -69.7(d);. ESI-MS (m / s):332.8[M+H] + .

[0032] The reaction equation is shown below.

[0033]

[0034] Example 4 This embodiment describes a method for preparing compound four, wherein R1 and R2 are both trifluoromethylsulfonyl groups, and the method includes the following steps.

[0035] (a) Same as step (a) in Example 1.

[0036] (ii) 12.78 g of lithium trifluoromethanesulfonate and 10 g of bis(trimethylsilyl)monofluorophosphate were added to 200 ml of tetrahydrofuran and stirred until homogeneous. Lithium trifluoromethanesulfonate was insoluble. The mixture was then stirred at room temperature for 25 h. After the reaction was completed, a small amount of insoluble matter was filtered off, and dichloromethane and the low-boiling-point byproduct lithium trimethylsilanolate (boiling point 40 °C) were evaporated under reduced pressure to obtain 13.08 g of compound four, with a yield of 87.7%. Compound four was subjected to NMR and ESI detection. 13 C-NMR (100MHz, deuterated DMSO, ppm): δ 123.6; 19 F-NMR (282 MHz, DMSO, ppm): -72.6, -66.3(d);. ESI-MS (m / s):364.9[M+H] + .

[0037] The reaction equation is shown below.

[0038]

[0039] Examples 1-4 illustrate some methods for preparing mixed monofluorophosphate anhydrides with high yields. Other unlisted mixed monofluorophosphate anhydrides can be prepared using the same methods. The compounds one through four prepared in Examples 1-4 are then applied to secondary batteries to verify their performance.

[0040] (1) Battery preparation LiNi cathode material 0.8 Co 0.1 Mn 0.1 Zr 0.03 O2, conductive agent SuperP, binder PVDF, and carbon nanotubes (CNTs) were mixed uniformly in a mass ratio of 96.5:1.5:1:1 to prepare a lithium-ion battery positive electrode slurry of a certain viscosity. This slurry was then coated onto aluminum foil used as a current collector, with a coating weight of 324 g / m².2 After drying at 85℃, the material is cold-pressed; then it is trimmed, cut into sheets, and slit. After slitting, it is dried at 8℃ for 4 hours under vacuum, and then the tabs are welded to produce a positive electrode sheet that meets the requirements.

[0041] Artificial graphite and silicon are mixed at a mass ratio of 90:10, and then mixed with conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) at a mass ratio of 95:1.5:1.0:2.5 to form a slurry. After being mixed evenly, the slurry is coated on both sides of copper foil, dried, and rolled to obtain a negative electrode sheet, thus producing a negative electrode sheet that meets the requirements.

[0042] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), butyl carbonate (BC), propylene carbonate (PC), and butyl acetate (BA) were mixed thoroughly in a mass ratio of 5:4:2:5:3 to obtain a mixed solvent of 87.0 g. This mixture was used as a non-aqueous organic solvent. Then, 1.0 g of each of compounds one through four were added to obtain mixed solutions. The mixed solutions were sealed and packaged, then frozen in a freezer (-4°C) for 2 hours. After removal, 12.0 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solutions in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After thorough mixing, the lithium-ion battery electrolyte was prepared.

[0043] The positive electrode, negative electrode, and separator described above were stacked to form a lithium-ion battery with a thickness of 4.7 mm, a width of 55 mm, and a length of 60 mm. The battery was then vacuum-baked at 75°C for 10 hours and injected with the aforementioned lithium-ion battery electrolyte. After standing for 24 hours, the battery was charged to 4.45 V using a constant current of 0.1 C (180 mA), and then charged at a constant voltage of 4.45 V until the current dropped to 0.05 C (90 mA). It was then discharged to 3.0 V using 0.2 C (180 mA), and this charge-discharge cycle was repeated twice. Finally, the battery was charged to 3.8 V using 0.2 C (180 mA) to obtain lithium-ion batteries #1 to #4.

[0044] (2) Electrochemical performance tests were conducted on lithium-ion batteries 1#~4# under the following conditions, and the test results are shown in Table 1.

[0045] Room temperature cycle performance test: Under room temperature (25°C) conditions, the lithium-ion battery is charged and discharged once at 1.0C / 1.0C (battery discharge capacity is C0), with an upper limit voltage of 4.45V. Then, under room temperature conditions, it is charged and discharged for 500 cycles at 1.0C / 1.0C (battery discharge capacity is C1), and the capacity retention rate is calculated.

[0046] Capacity retention rate = (C1 / C0) × 100% High-temperature cycle performance test: Under high temperature (50°C) conditions, the lithium-ion battery is subjected to one 1.0C / 1.0C charge and discharge cycle (battery discharge capacity is C0), with an upper limit voltage of 4.45V. Then, under normal temperature conditions, it is subjected to 400 cycles of 1.0C / 1.0C charge and discharge (battery discharge capacity is C1), and the capacity retention rate is calculated.

[0047] Capacity retention rate = (C1 / C0) × 100% Table 1. Electrochemical performance test results of lithium-ion batteries #1 to #4

[0048] The results in Table 1 show that monofluorophosphate mixed anhydrides are beneficial for improving the high-temperature and room-temperature cycling performance of secondary batteries and can be used as a high-performance electrolyte additive for secondary batteries.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a mixed anhydride of monofluorophosphate, characterized in that, The structural formula is shown in Formula 1, wherein R1 and R2 are each independently an acetyl group, a trifluoroacetyl group, a trifluoromethylsulfinyl group, a trifluoromethylsulfinyl group, a methylsulfinyl group, or a methylsulfinyl group, and the following steps are included: (a) Sodium monofluorophosphate was added to the first organic solvent, and after cooling to -10~0℃, trimethylchlorosilane was added dropwise and the temperature was gradually raised to room temperature and stirred to carry out the reaction. After the reaction was completed, the reactants were filtered and distilled under reduced pressure to obtain the intermediate. (ii) The lithium salt and the intermediate are added to a second organic solvent, stirred and mixed, and then reacted at room temperature, followed by filtration and vacuum distillation. Formula 1.

2. The method for preparing monofluorophosphate mixed anhydrides according to claim 1, characterized in that, The first organic solvent and the second organic solvent are each independently selected from tetrahydrofuran, dichloromethane, trichloromethane or dioxane.

3. The method for preparing monofluorophosphate mixed anhydrides according to claim 1, characterized in that, The molar ratio of sodium monofluorophosphate to trimethylchlorosilane is 1:2.0~2.

5.

4. The method for preparing monofluorophosphate mixed anhydrides according to claim 1, characterized in that, The stirring time mentioned in step (1) is 18~72h.

5. The method for preparing monofluorophosphate mixed anhydrides according to claim 1, characterized in that, The lithium salt is selected from lithium acetate, lithium trifluoroacetate, lithium trifluoromethyl sulfinate, lithium trifluoromethyl sulfinate, lithium methyl sulfinate, or lithium methyl sulfonate.

6. The method for preparing monofluorophosphate mixed anhydrides according to claim 1, characterized in that, The molar ratio of the lithium salt to the intermediate is 1:

2.

7. The method for preparing monofluorophosphate mixed anhydrides according to claim 1, characterized in that, The stirring time in step (ii) is 12~72h.

8. The application of the monofluorophosphate mixed anhydride prepared by the method of any one of claims 1 to 7 in a battery.

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