Preparation method of lithium difluorophosphate

Abstract

The invention discloses a preparation method of lithium difluorophosphate, which is prepared by taking lithium metaphosphate as a phosphorus source and hydrogen fluoride as a fluorinating reagent and then separating to obtain a product, and mainly comprises the following steps: dispersing lithium metaphosphate in a supercritical carbon dioxide solvent, and introducing hydrogen fluoride to fully react to obtain lithium difluorophosphate and water; and after the reaction is finished, discharging the supercritical carbon dioxide fluid, and carrying out cooling and depressurization separation to obtain the lithium difluorophosphate. The preparation method disclosed by the invention is simple to operate, efficient in reaction, convenient to separate, green and environment-friendly.

Description

TECHNICAL FIELD

[0001] The application relates to the field of lithium battery electrolyte, in particular to a preparation method of lithium difluorophosphate. BACKGROUND

[0002] Lithium difluorophosphate is an important lithium battery electrolyte additive, which can generate a stable and dense protective film on the electrode surface to protect the electrode, thereby effectively improving the cycle performance of the battery and prolonging the service life.

[0003] Patent CN116768184A discloses a method, in which lithium hexafluorophosphate reacts with silicon tetrachloride, and then lithium difluorophosphate tetrachloride is obtained by degassing and impurity removal, and then calcium oxide is added to obtain lithium difluorophosphate. The method introduces many elements, has many by-products, and needs multiple separation and purification steps, and the operation is relatively complex; patent CN115535994B discloses a method, in which phosphorus pentoxide and hydrogen fluoride are reacted, and then the reaction system and a lithium source are mixed and reacted in a non-aqueous solvent. The method needs multiple reactions, the operation is relatively complex, and there are many by-products, which affect the yield.

[0004] Therefore, the application provides a preparation method of lithium difluorophosphate, which is simple in operation, efficient in reaction, convenient in separation, and green and environment-friendly. SUMMARY

[0005] Therefore, the application provides a preparation method of lithium difluorophosphate, which is simple in operation, efficient in reaction, convenient in separation, and green and environment-friendly.

[0006] In order to achieve the above purpose, the application adopts the following technical scheme: The application provides a preparation method of lithium difluorophosphate, which comprises the following steps: (1) dispersing lithium metaphosphate in supercritical carbon dioxide solvent, and introducing hydrogen fluoride gas to sufficiently react to obtain lithium difluorophosphate and water; (2) after the reaction is completed, discharging the supercritical carbon dioxide fluid, and separating lithium difluorophosphate by reducing the temperature and pressure.

[0007] Further, in step (1), the molar ratio of the reaction lithium metaphosphate and hydrogen fluoride is 1: (2-2.5).

[0008] Further, in step (1), the reaction temperature is 35-100 DEG C, the pressure is 7.5-30 MPa, and the reaction time is 0.5-5 h.

[0009] Further, in step (2), the pressure is reduced to normal pressure after the reaction, and the temperature is reduced to 15-30 DEG C.

[0010] Preferably, in step (1), the molar ratio of lithium metaphosphate and hydrogen fluoride is 1: (2-2.3) Preferably, in step (1), the reaction temperature is 40-90℃, the pressure is 8-20 MPa, and the reaction time is 1-3 h.

[0011] Further, in step (1), the reaction is carried out under stirring.

[0012] The reaction principle of the present application is: LiPO3+2HF=LiPO2F2+H2O.

[0013] The present application has the following technical advantages: First, the lithium difluorophosphate is synthesized by one-step method, which is simple in operation and efficient in fluorination reaction. Second, supercritical carbon dioxide is used as the reaction solvent, which does not have the problem of deterioration caused by fluorination compared with the existing ester and ether solvents, and the method for separating by-products is simple and green. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is the fluorine spectrum of lithium difluorophosphate; Figure 2 is the phosphorus spectrum of lithium difluorophosphate. DETAILED DESCRIPTION

[0015] The present application provides a preparation method of lithium difluorophosphate, and those skilled in the art can refer to the content herein to appropriately improve the process parameters. It should be particularly pointed out that all similar substitutions and changes are obvious to those skilled in the art and belong to the scope of protection of the present application. The method and application of the present application have been described by preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0016] The present application provides a preparation method of lithium difluorophosphate, comprising the following steps: (1) dispersing lithium metaphosphate in supercritical carbon dioxide solvent, and introducing hydrogen fluoride to react sufficiently to obtain lithium difluorophosphate and water; (2) after the reaction is completed, discharging the supercritical carbon dioxide fluid, and separating lithium difluorophosphate by reducing temperature and pressure.

[0017] In step (1) of the present application, the molar ratio of lithium metaphosphate and hydrogen fluoride is preferably 1:2-2.5, and more preferably 1:2-2.3; the specific parameters of heating and pressurization are: temperature 35-100℃, pressure 7.5-30 MPa; preferably, the temperature is 40-90℃, the pressure is 8-20 MPa; and the reaction time is 0.5-5 h, and more preferably 1-3 h.

[0018] The step (2) of the present application is preferably: after the reaction of step (1) is completed, the supercritical carbon dioxide fluid is discharged to take away the byproduct water; the reaction system is cooled and depressurized to obtain lithium difluorophosphate; the depressurization is specifically to reduce the pressure to normal pressure; and the cooling is specifically to reduce the temperature to 15-30°C.

[0019] In order to further illustrate the present application, the following embodiments are used to describe in detail the preparation method of lithium difluorophosphate for battery electrolyte provided by the present application.

[0020] The present application does not have special restrictions on the sources of all raw materials, which are commercially available.

[0021] Example 1 A preparation method of lithium difluorophosphate, the process is as follows: 43 g of lithium metaphosphate (0.5 mol) is added to a reaction kettle, carbon dioxide gas is introduced, and the temperature is increased (70°C) and the pressure is increased (12 MPa) to a supercritical state, and the stirring is started to mix the materials fully, 22 g (1.1 mol) of hydrogen fluoride gas is introduced into the reaction kettle, and the reaction is carried out under stirring, temperature and pressure for 2 h; after the reaction is completed, the stirring is stopped, the fluid is discharged into a separation kettle, and the product is washed with carbon dioxide fluid twice, each time for 10 minutes, and after washing, the separation kettle is cooled (20°C) and depressurized (normal pressure) to obtain dry lithium difluorophosphate 49.45 g, and the fluorine spectrum and phosphorus spectrum of lithium difluorophosphate are shown in Figure 1 and Figure 2 LiPO2F2: white solid. 19 F NMR (376 MHz, DMSO- d 6 ): δ =-79.60 (d, J =942 Hz) ppm. 31 P NMR (162 MHz, DMSO- d 6 ): δ =-16.30 (t, J =944 Hz) ppm. By NMR data, compared with standard samples, the structure of the compound is confirmed to be the target product LiPO2F2. The purity is 99.6%, and the yield is 91.2%.

[0022] Example 2 A preparation method of lithium difluorophosphate, the process is as follows: Put 43g lithium metaphosphate (0.5mol) into the reaction kettle, and pass carbon dioxide gas, and increase the temperature (90℃) and pressure (20MPa) to the supercritical state, and open the stirring to mix the materials, and pass 23g (1.15mol) hydrogen fluoride gas into the reaction kettle, and keep the temperature and pressure under stirring for 3h; after the reaction is completed, stop the stirring, and pour the fluid into the separation kettle, and pass the carbon dioxide fluid to wash the product twice, each time for 10min, and after washing, reduce the temperature (20℃) and pressure (normal pressure) of the separation kettle to obtain dry lithium difluorophosphate 50.17g, with a purity of 99.89% and a yield of 92.8%.

[0023] Example 3 A method for preparing lithium difluorophosphate, the process being as follows: put 43g lithium metaphosphate (0.5mol) into the reaction kettle, and pass carbon dioxide, and increase the temperature (50℃) and pressure (8MPa) to the supercritical state, and open the stirring to mix the materials, and pass 23g (1.15mol) hydrogen fluoride gas into the reaction kettle, and keep the temperature and pressure under stirring for 3h; after the reaction is completed, stop the stirring, and pour the fluid into the separation kettle, and pass the carbon dioxide fluid to wash the product twice, each time for 10min, and after washing, reduce the temperature (20℃) and pressure (normal pressure) of the separation kettle to obtain dry lithium difluorophosphate 49.39g, with a purity of 99.5% and a yield of 91%. Comparative Example 1 A method for preparing lithium difluorophosphate, the process being as follows: Put 43g lithium metaphosphate (0.5mol) into the reaction kettle, and pass carbon dioxide gas, and increase the temperature (50℃) and pressure (8MPa) to the supercritical state, and open the stirring to mix the materials, and pass 19g (0.95mol) hydrogen fluoride gas into the reaction kettle, and keep the temperature and pressure under stirring for 3h; after the reaction is completed, stop the stirring, and pour the fluid into the separation kettle, and pass the carbon dioxide fluid to wash the product twice, each time for 10min, and after washing, reduce the temperature (20℃) and pressure (normal pressure) of the reaction separation kettle to obtain lithium difluorophosphate 48.4g, with a purity of 90.3% and a yield of 85.2%.

[0024] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the scope of the present application.

Claims

1. A method for preparing lithium difluorophosphate, characterized in that: The process is as follows: lithium metaphosphate is dispersed in a supercritical carbon dioxide solvent, and hydrogen fluoride gas is introduced to react; after the reaction is completed, the supercritical carbon dioxide fluid is discharged, and the temperature and pressure are reduced to separate and obtain lithium difluorophosphate.

2. The method for preparing lithium difluorophosphate according to claim 1, wherein The molar ratio of the lithium metaphosphate to hydrogen fluoride is 1:(2-2.5).

3. The method for preparing lithium difluorophosphate according to claim 1, wherein The reaction temperature is 35° C. to 100° C., the pressure is 7.5 MPa to 30 MPa, and the reaction time is 0.5 to 5 h.

4. The method for preparing lithium difluorophosphate according to claim 1, wherein: The temperature reduction and pressure reduction refer to reducing the pressure to normal pressure and the temperature to 15°C to 30°C.

5. The method for preparing lithium difluorophosphate according to claim 3, wherein: The reaction temperature is 40° C. to 90° C., the pressure is 8 MPa to 20 MPa, and the reaction time is 1 to 3 hours.

6. The method for preparing lithium difluorophosphate according to claim 2, wherein: The molar ratio of the lithium metaphosphate to hydrogen fluoride is 1:(2-2.3).

7. The method for preparing lithium difluorophosphate according to claim 1, wherein: The reaction is carried out under stirring conditions.

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