Preparation method of lithium difluorophosphate

Abstract

The invention provides a preparation method of lithium difluorophosphate, and belongs to the technical field of lithium battery electrolytes.The method comprises the step that lithium phosphate, lithium metaphosphate and phosphorus pentafluoride react in supercritical carbon dioxide to obtain the lithium difluorophosphate, and the specific reaction equation comprises Li3PO4 + 2LiPO3 + 2PF5 = 5LiPO2F2. The method has the advantages of being high in reaction conversion rate, free of by-products, environmentally friendly, simple in process and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery electrolytes, and particularly relates to a preparation method of lithium difluorophosphate. Background Art

[0002] Lithium difluorophosphate is an important electrolyte additive, which can undergo redox reactions on the electrode surface to form a stable and dense protective film to protect the electrode, thereby improving the cycle performance of the battery and extending its service life, and has good development prospects.

[0003] Currently, the research on the preparation method of lithium difluorophosphate has become a hot topic. The method of reacting lithium hexafluorophosphate and lithium carbonate in an organic solvent is widely used, but this method has high costs and requires filtering of by-products. For example, the Chinese patent application with publication date of June 8, 2018 and publication number of CN108128764A uses lithium hexafluorophosphate and lithium carbonate as raw materials and ultrapure water as a catalyst to prepare lithium difluorophosphate, with high costs and many by-products; the Chinese patent with announcement date of June 16, 2020 and announcement number of CN107720717B prepares lithium difluorophosphate by contacting difluorophosphoric acid with lithium hydroxide or lithium carbonate in a non-aqueous solvent. Although this method has a simple process, a large amount of water is produced as a reaction by-product, causing product deterioration, and the added water remover will generate new impurities and requires purification; the Chinese patent with announcement date of September 13, 2024 and announcement number of CN116332150B disperses lithium borate and lithium metaborate in a supercritical carbon dioxide solvent, introduces phosphorus pentafluoride for reaction to obtain a mixture containing lithium difluorophosphate and lithium tetrafluoroborate, and then obtains lithium tetrafluoroborate through extraction and separation. This process requires extraction and separation, increasing production time and costs. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of lithium difluorophosphate to solve the technical problems of many by-products, complex process and high costs in the prior art.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is: A preparation method of lithium difluorophosphate, which includes reacting lithium phosphate, lithium metaphosphate and phosphorus pentafluoride in supercritical carbon dioxide to obtain lithium difluorophosphate.

[0006] The present invention belongs to a pioneering invention. The present invention provides a preparation method of lithium difluorophosphate. The reactant phosphorus pentafluoride gas in this method has high activity and high reaction conversion rate; lithium difluorophosphate is synthesized by a one-step method without by-products; this method has a simple process, is suitable for large-scale industrial production, and the gas can be recycled, which is green and environmentally friendly.

[0007] Preferably, the reaction temperature is 40 - 80 °C and the reaction pressure is 8 - 25 MPa.

[0008] Further preferably, the reaction time is 1 to 4 h.

[0009] Further preferably, the molar ratio of phosphorus pentafluoride to lithium phosphate is 2.1 to 2.3:1.

[0010] Preferably, the molar ratio of lithium phosphate to lithium metaphosphate is 1:2.

[0011] Preferably, after the reaction, the temperature and pressure are reduced. The temperature for reducing the temperature and pressure is 15 to 30 °C, and the pressure is normal pressure.

[0012] Further preferably, the reaction is carried out under stirring conditions. Description of the Drawings

[0013] Figure 1 19F NMR spectrum of Example 1 of the present invention; Figure 2 31P NMR spectrum of Example 1 of the present invention. Detailed Description

[0014] The present invention provides a method for preparing lithium difluorophosphate. Lithium phosphate and lithium metaphosphate are placed in supercritical carbon dioxide and reacted with phosphorus pentafluoride to prepare lithium difluorophosphate with high purity and good yield. The reaction principle is shown in Chemical Equation (1). This method has the advantages of simple process, high reaction conversion rate, no by-products, and environmental friendliness.

[0015] Li 3 PO 4 +2LiPO 3 +2PF 5 =5LiPO 2 F 2 (1) The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0016] I. Specific Embodiment of a Method for Preparing Lithium Difluorophosphate of the Present Invention Example 1 This example is a method for preparing lithium difluorophosphate, which includes the following steps: 11.6 g of lithium phosphate (0.1 mol) and 17.2 g of lithium metaphosphate (0.2 mol) were added to a reaction kettle, carbon dioxide was introduced, the temperature was raised (50 °C) and the pressure was increased (10 MPa) to the supercritical state, stirring was started to fully mix the materials, 26.46 g (0.21 mol) of phosphorus pentafluoride was introduced into the reaction kettle, and the reaction was carried out under stirring at 100 r / min for 2 h while maintaining the temperature and pressure; after the reaction was completed, the temperature was reduced (20 °C) and the pressure was reduced (normal pressure) to obtain lithium difluorophosphate, with a purity of 99.85% and a yield of 93.8%.

[0017] The NMR test results of the product obtained in this example are as follows Figure 1 and Figure 2 shown, confirming that the obtained product is lithium difluorophosphate.

[0018] Example 2 This example is a preparation method of lithium difluorophosphate, including the following steps: Add 11.6 g of lithium phosphate (0.1 mol) and 17.2 g of lithium metaphosphate (0.2 mol) into the reaction kettle, introduce carbon dioxide, raise the temperature (70 °C) and increase the pressure (20 MPa) to the supercritical state, turn on the stirrer to fully mix the materials, introduce 26.46 g (0.21 mol) of phosphorus pentafluoride into the reaction kettle, and keep the temperature and pressure constant for reaction for 2 h under the stirring condition of 100 r / min; after the reaction is completed, lower the temperature (20 °C) and reduce the pressure (atmospheric pressure) to obtain lithium difluorophosphate, with a purity of 99.9% and a yield of 95.2%.

[0019] The results of this example show that when the temperature and pressure of the reaction kettle are appropriately increased, the purity and yield of the prepared lithium difluorophosphate can be effectively improved.

[0020] Example 3 This example is a preparation method of lithium difluorophosphate, including the following steps: Add 11.6 g of lithium phosphate (0.1 mol) and 17.2 g of lithium metaphosphate (0.2 mol) into the reaction kettle, introduce carbon dioxide, raise the temperature (50 °C) and increase the pressure (10 MPa) to the supercritical state, turn on the stirrer to fully mix the materials, introduce 27.72 g (0.22 mol) of phosphorus pentafluoride into the reaction kettle, and keep the temperature and pressure constant for reaction for 4 h under the stirring condition of 100 r / min; after the reaction is completed, lower the temperature (20 °C) and reduce the pressure (atmospheric pressure) to obtain lithium difluorophosphate, with a purity of 99.88% and a yield of 94.3%.

[0021] The results of this example show that when the reaction amount of phosphorus pentafluoride is appropriately increased and the reaction time is increased, the purity and yield of the prepared lithium difluorophosphate can also be improved.

[0022] Comparative Example 1 Use 500 g of dimethyl carbonate as the base in a PFA reaction bottle, add 11.6 g of lithium phosphate (0.1 mol) and 17.2 g of lithium metaphosphate (0.2 mol), stir and mix, and raise the temperature to 50 °C. Slowly introduce 26.46 g (0.21 mol) of phosphorus pentafluoride gas at 50 °C and keep the temperature constant for reaction for 2 h. When the pressure no longer changes, replace with nitrogen, filter the reaction solution, concentrate the filtrate under reduced pressure, crystallize, filter, and dry to obtain lithium difluorophosphate, with a purity of 82.1% and a yield of 70.6%.

[0023] The results of this comparative example show that when supercritical carbon dioxide does not participate in the reaction of lithium phosphate, lithium metaphosphate and phosphorus pentafluoride, the purity and yield of the prepared lithium difluorophosphate both decrease significantly, and the technical effects of the present invention cannot be achieved.

[0024] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing lithium difluorophosphate, characterized in that: The method comprises the steps of reacting lithium phosphate, lithium metaphosphate and phosphorus pentafluoride in supercritical carbon dioxide to obtain lithium difluorophosphate.

2. The method for preparing lithium difluorophosphate according to claim 1, characterized in that: The reaction temperature is 40-80° C., and the reaction pressure is 8-25 MPa.

3. The method for preparing lithium difluorophosphate according to claim 2, characterized in that: The reaction time is 1 to 4 hours.

4. The method for preparing lithium difluorophosphate according to claim 1, characterized in that: The molar ratio of phosphorus pentafluoride to lithium phosphate is 2.1-2.3:

1.

5. The method for preparing lithium difluorophosphate according to claim 1, characterized in that: The molar ratio of the lithium phosphate to the lithium metaphosphate is 1:

2.

6. The method for preparing lithium difluorophosphate according to claim 1, characterized in that: After the reaction is completed, the temperature and pressure are reduced, the temperature of the temperature reduction and pressure reduction is 15-30° C., and the pressure is normal pressure.

7. The method for preparing lithium difluorophosphate according to any one of claims 1 to 3, characterized in that: The reaction is carried out under stirring conditions.

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