Preparation method of lithium difluorophosphate

Abstract

The invention belongs to the technical field of lithium ion battery additives, and provides a preparation method of lithium difluorophosphate, which comprises the following steps: mixing lithium carbonate, a silicon-oxygen compound and a solvent, and introducing phosphorus oxyfluoride to obtain the lithium difluorophosphate through one-step synthesis. According to the process, the lithium difluorophosphate is prepared by adopting a one-step method, the process flow is simple and easy to implement, the reaction condition is mild, the reaction is rapid and thorough, and the lithium difluorophosphate product with high yield and purity can be efficiently obtained. In addition, another technical characteristic of the invention is that a silicon-oxygen compound is used as one of the raw materials. The silicon-oxygen compound is added, so that a lithium by-product lithium fluoride generated by reaction of phosphorus oxyfluoride and a lithium source lithium carbonate which is low in price and easy to obtain can be continuously converted into a target product lithium difluorophosphate, complete utilization of lithium atoms is realized, a lithium difluorophosphate product with the purity of 99.5% or above can be efficiently obtained, the highest yield can reach 99%, and higher economic benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery additives, and in particular to a method for preparing lithium difluorophosphate. Background Art

[0002] Lithium difluorophosphate is a lithium-ion battery electrolyte additive that can form a low-impedance SEI film on the positive and negative electrode surfaces of lithium-ion batteries, inhibiting side reactions between the electrodes and the electrolyte, thereby improving the battery's cycle stability and rate performance at high and low temperatures. With the increasing application of lithium difluorophosphate, its preparation research has also received more and more attention.

[0003] The mainstream lithium difluorophosphate process mainly includes difluorophosphate method, lithium hexafluorophosphate method and other methods. Among them, the difluorophosphate method and the lithium hexafluorophosphate method are unstable and easily decomposed due to the raw materials difluorophosphate and lithium hexafluorophosphate, resulting in the reaction being difficult to control, many by-products, and difficult product purification and separation. Chinese patent application CN111224164A uses phosphorus pentafluoride and hydrocarbon disiloxane compounds to synthesize difluorophosphate siloxane compound intermediates, and then the intermediates react with lithium fluoride to obtain anhydrous lithium difluorophosphate. The lithium source used in this method is lithium fluoride, which is more expensive than lithium hydroxide and lithium carbonate, and the reaction time is longer. Chinese patent application CN113636533A discloses the use of phosphorus trifluoride to react with lithium carbonate to obtain lithium difluorophosphate. This method will generate another lithium by-product lithium fluoride, which has low atomic utilization of lithium atoms and reduces economic benefits. Chinese patent application CN108033435A discloses a process for producing difluorophosphate by reacting a phosphorus compound POF3 with lithium hydroxide. However, this method easily generates hydrogen fluoride, which causes the free acid content in the obtained lithium difluorophosphate product to easily exceed the standard, affecting the subsequent performance of lithium-ion battery electrolyte.

[0004] In summary, the current preparation process of lithium difluorophosphate still has disadvantages such as high raw material cost, low reaction atom utilization rate, many side reactions and low purity. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing lithium difluorophosphate.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing lithium difluorophosphate, comprising the following steps:

[0008] After lithium carbonate, silicon oxide and solvent are mixed, phosphorus oxytrifluoride is introduced to synthesize lithium difluorophosphate in one step.

[0009] Preferably, the silicon oxide compound is silicon dioxide or siloxane;

[0010] The siloxane is linear siloxane or cyclic siloxane.

[0011] Preferably, the solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, acetonitrile, propionitrile, acetone, tetrahydrofuran, diethyl ether, methyl tert-butyl ether, ethylene glycol dimethyl ether, propyl ether and butyl ether.

[0012] Preferably, the mass ratio of the lithium carbonate to the solvent is 1:30-50.

[0013] Preferably, the molar ratio of phosphorus oxyfluoride, lithium carbonate and silicon oxide is 2:1-1.05:0.5-1.

[0014] Preferably, the one-step synthesis is carried out at a temperature of 0 to 80° C. and for a time of 4 to 8 hours.

[0015] The present invention provides a method for preparing lithium difluorophosphate, comprising the following steps: mixing lithium carbonate, silicon oxide compounds and a solvent, and then introducing phosphorus oxyfluoride to synthesize lithium difluorophosphate in one step. The process of the present invention adopts a one-step method to prepare lithium difluorophosphate, the process flow is simple and easy to implement, the reaction conditions are mild, the reaction is rapid and thorough, and a lithium difluorophosphate product with high yield and purity can be obtained efficiently. In addition, another technical feature of the present invention is the use of silicon oxide compounds as one of the raw materials. The addition of silicon oxide compounds can make the lithium byproduct lithium fluoride produced by the reaction of phosphorus oxyfluoride with cheap and easily available lithium source lithium carbonate continuously converted into the target product lithium difluorophosphate, realize the full utilization of lithium atoms, and efficiently obtain a lithium difluorophosphate product with a purity of more than 99.5%, and the yield can be as high as 99%. At the same time, no other lithium byproducts are generated in the reaction except the target lithium product lithium difluorophosphate, which has higher economic benefits. DETAILED DESCRIPTION

[0016] The present invention provides a method for preparing lithium difluorophosphate, comprising the following steps:

[0017] After lithium carbonate, silicon oxide and solvent are mixed, phosphorus oxytrifluoride is introduced to synthesize lithium difluorophosphate in one step.

[0018] In the present invention, the silicon oxide compound is silicon dioxide or siloxane.

[0019] In the present invention, the siloxane is linear siloxane or cyclic siloxane.

[0020] In the present invention, the solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, acetonitrile, propionitrile, acetone, tetrahydrofuran, diethyl ether, methyl tert-butyl ether, ethylene glycol dimethyl ether, propyl ether and butyl ether.

[0021] In the present invention, the mass ratio of the lithium carbonate to the solvent is preferably 1:30-50, more preferably 1:35-45, and even more preferably 1:38-42.

[0022] In the present invention, the molar ratio of phosphorus oxyfluoride, lithium carbonate and silicon oxide is preferably 2:1-1.05:0.5-1, more preferably 2:1.01-1.04:0.6-0.9, and more preferably 2:1.02-1.03:0.7-0.8.

[0023] In the present invention, the introduction rate of phosphorus oxyfluoride is preferably 0.05 to 0.5 L / min, more preferably 0.1 to 0.4 L / min, and even more preferably 0.1 to 0.2 L / min.

[0024] In the present invention, the temperature of the one-step synthesis is preferably 0-80°C, more preferably 10-70°C, more preferably 20-60°C; the time is preferably 4-8h, more preferably 4.5-7.5h, more preferably 5-7h; the one-step synthesis is carried out in a protective atmosphere.

[0025] In the present invention, after the one-step synthesis is completed, the lithium difluorophosphate is purified; the system obtained by the reaction is subjected to solid-liquid separation; the filtrate is concentrated and then an organic solvent is added for crystallization; the obtained crystals are filtered and dried to obtain lithium difluorophosphate.

[0026] In the present invention, the concentration method is reduced pressure concentration, and the concentration temperature is preferably 45 to 85° C., more preferably 50 to 80° C., and more preferably 60 to 70° C.; the concentration pressure is preferably -0.09 to -0.1 MPa.

[0027] In the present invention, the organic solvent used for purification is one or more of dichloromethane, chloroform, toluene, xylene, trimethylbenzene, chlorobenzene, fluorobenzene, n-hexane and cyclohexane.

[0028] In the present invention, the drying temperature is preferably 60 to 100° C., more preferably 70 to 90° C., and more preferably 80 to 90° C.; the drying time is preferably 1 to 10 h, more preferably 2 to 8 h, and more preferably 4 to 6 h.

[0029] The preparation method provided by the present invention has a reaction principle as follows (taking silicon dioxide as an example):

[0030] 4POF3+2Li2CO3+SiO2→4LiPO2F2+2CO2↑+SiF4↑

[0031] One equivalent of phosphorus oxyfluoride reacts with lithium carbonate to obtain one equivalent of lithium difluorophosphate and one equivalent of lithium fluoride. At the same time, one equivalent of phosphorus oxyfluoride reacts with a silicon-oxygen compound containing active oxygen to generate one equivalent of a difluorophosphate siloxane compound intermediate. One equivalent of the intermediate can react with one equivalent of lithium fluoride generated above to generate one equivalent of lithium difluorophosphate. Thus, one equivalent of lithium carbonate raw material can obtain two equivalents of the target lithium product lithium difluorophosphate. Other byproducts of the reaction are gases, and the solubility of lithium difluorophosphate in organic solvents is greater than that of lithium carbonate. Therefore, lithium difluorophosphate can be separated by a simple filtration method, and high-purity lithium difluorophosphate can be obtained by crystallization.

[0032] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0033] Example 1

[0034] A method for preparing lithium difluorophosphate comprises the following specific steps:

[0035] In an argon atmosphere, 22.2g of lithium carbonate, 9.0g of silicon dioxide and 900g of ethyl acetate were added to a dry reaction bottle equipped with magnetic stirring, condensation reflux and tail gas absorption, and then 62.4g of phosphorus oxytrifluoride was introduced. The gas flow rate of phosphorus oxytrifluoride was controlled to 0.1L / min, and the reaction was stirred at 40°C for 6 hours. The molar ratio of phosphorus oxytrifluoride, lithium carbonate and silicon oxide was 2:1:0.5. The reaction solution was cooled to room temperature and filtered. The filter residue was a small amount of unreacted lithium carbonate and silicon oxide, which could be reused. The lithium difluorophosphate filtrate was concentrated to 1 / 3 of the original volume at 60°C and -0.1MPa under reduced pressure, and then dichloromethane was added for crystallization. After filtering the precipitated solid, the solid was vacuum dried at 90°C for 5h to obtain 57.6g of lithium difluorophosphate, with a target product yield of 89.0% and a purity of 99.7%.

[0036] Example 2

[0037] In an argon atmosphere, 22.2g of lithium carbonate, 18.0g of silicon dioxide and 900g of ethyl acetate were added to a dry reaction bottle equipped with magnetic stirring, condensation reflux and tail gas absorption, and then 62.4g of phosphorus oxytrifluoride was introduced. The gas flow rate of phosphorus oxytrifluoride was controlled to 0.1L / min, and the reaction was stirred at 40°C for 5 hours. The molar ratio of phosphorus oxytrifluoride, lithium carbonate and silicon oxide compound was 2:1:1. The reaction solution was cooled to room temperature and filtered. The filter residue was a small amount of unreacted lithium carbonate and silicon oxide compound, which could be reused. The lithium difluorophosphate filtrate was concentrated to 1 / 3 of the original volume at 60°C and -0.1MPa under reduced pressure, and then dichloromethane was added for crystallization. After filtering the precipitated solid, the solid was vacuum dried at 90°C for 5h to obtain 61.2g of lithium difluorophosphate, with a target product yield of 94.6% and a purity of 99.7%.

[0038] Example 3

[0039] In an argon atmosphere, 22.2g of lithium carbonate, 48.7g of hexamethyldisiloxane and 900g of ethyl acetate were added to a dry reaction bottle equipped with magnetic stirring, condensation reflux and tail gas absorption, and then 62.4g of phosphorus oxytrifluoride was introduced. The gas flow rate of phosphorus oxytrifluoride was controlled to 0.1L / min, and the reaction was carried out at 40°C for 5 hours. The molar ratio of phosphorus oxytrifluoride, lithium carbonate and silicon oxide compound was 2:1:1. The reaction solution was cooled to room temperature and filtered. The filter residue was part of the unreacted lithium carbonate and silicon oxide compound, which could be reused. The lithium difluorophosphate filtrate was concentrated to 1 / 3 of the original volume at 60°C and -0.1MPa under reduced pressure, and then dichloromethane was added for crystallization. After filtering the precipitated solid, the solid was vacuum dried at 90°C for 5h to obtain 64.2g of lithium difluorophosphate, with a yield of 99.2% and a purity of 99.5%.

[0040] Comparative Example 1

[0041] Compared with Example 1, this comparative example does not add silicon oxide compounds, and only uses lithium carbonate and phosphorus oxyfluoride as reaction raw materials. The specific steps are as follows:

[0042] In an argon atmosphere, 22.2g of lithium carbonate and 900g of ethyl acetate were added to a dry reaction bottle equipped with magnetic stirring, condensation reflux and tail gas absorption, followed by the introduction of 62.4g of phosphorus oxyfluoride, the gas flow rate of phosphorus oxyfluoride was controlled to 0.1L / min, and the reaction was stirred at 40°C for 6 hours. The molar ratio of phosphorus oxyfluoride to lithium carbonate is 2:1. The reaction solution was cooled to room temperature and filtered. The filter residue was a small amount of unreacted lithium carbonate and silicon oxide compounds, which can be reused. The lithium difluorophosphate filtrate was concentrated to 1 / 3 of the original volume at 60°C and -0.1MPa under reduced pressure, and dichloromethane was added for crystallization. After filtering the precipitated solid, the solid was vacuum dried at 90°C for 5h to obtain 27.5g of lithium difluorophosphate and 6.6g of lithium fluoride.

[0043] By comparing the results of Example 1 with Comparative Example 1, it can be seen that under the same conditions, Example 1 with the addition of silicon oxide compounds can obtain 57.6g of lithium difluorophosphate product, while Comparative Example 1 without the addition of silicon oxide compounds only obtains 27.5g of the target lithium product. The method of the present invention uses phosphorus oxyfluoride, lithium carbonate and silicon oxide compounds as reaction raw materials, and obtains the target lithium product lithium difluorophosphate by a one-step method under solvent conditions. Compared with the case where no silicon oxide compound is added in Comparative Example 1, all lithium atoms in lithium carbonate are converted into the target product, and no other lithium byproducts are generated, thereby improving the comprehensive utilization rate of lithium atoms and the yield of the target product, and having higher economic benefits.

[0044] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing lithium difluorophosphate, characterized in that: It includes the following steps: After lithium carbonate, silicon oxide and solvent are mixed, phosphorus oxytrifluoride is introduced to synthesize lithium difluorophosphate in one step.

2. The method for preparing lithium difluorophosphate according to claim 1, characterized in that: The silicon-oxygen compound is silicon dioxide or siloxane; The siloxane is linear siloxane or cyclic siloxane.

3. The method for preparing lithium difluorophosphate according to claim 1 or 2, characterized in that: The solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, acetonitrile, propionitrile, acetone, tetrahydrofuran, diethyl ether, methyl tert-butyl ether, ethylene glycol dimethyl ether, propyl ether and butyl ether.

4. The method for preparing lithium difluorophosphate according to claim 1, characterized in that: The mass ratio of the lithium carbonate to the solvent is 1:30-50.

5. The method for preparing lithium difluorophosphate according to claim 1, 2 or 4, characterized in that: The molar ratio of phosphorus oxyfluoride, lithium carbonate and silicon oxide is 2:1-1.05:0.5-1.

6. The method for preparing lithium difluorophosphate according to claim 5, characterized in that: The temperature of the one-step synthesis is 0-80°C and the time is 4-8h.