A preparation method of lithium difluorophosphate

Abstract

The present invention relates to a method for preparing lithium difluorophosphate, comprising the steps of heating lithium hexafluorophosphate and an excess of hexamethyldisiloxane at 50-55°C to react and produce lithium difluorophosphate. This method utilizes a one-pot salt formation and purification process, resulting in a simple and easy-to-control reaction system, no side reactions, and effectively preventing the entry of other impurities into the system. The product is highly pure, facilitating industrial large-scale production. Experiments have shown that the yield of the product obtained by the present invention can reach over 96.2%, and the purity can reach over 99.9%.

Description

Technical Field

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

[0002] In recent years, lithium-ion batteries have been widely used in various sectors of society, such as consumer electronics, smart wearables, electric mobility, and power storage. As one of the four key materials in lithium-ion battery manufacturing, lithium-ion battery electrolyte is involved in key national development areas such as new energy, lithium batteries, and new materials. In recent years, with the development of new energy vehicles and the continuous improvement of electric vehicle technology, the market demand for large lithium batteries has gradually been released, significantly increasing the demand for lithium-ion batteries.

[0003] Currently, lithium hexafluorophosphate (LFP) is the primary electrolyte material in lithium-ion battery electrolytes. However, LFP is sensitive to water and exhibits poor thermal stability. Lithium difluorophosphate (LDP) can be used as an electrolyte additive in lithium-ion batteries. Adding LDP to LFP electrolyte systems can reduce electrode polarization, significantly improve the battery's room-temperature and high-temperature cycling stability, and high-temperature storage performance. It can also reduce the battery's internal resistance and form a protective film on the battery's positive electrode, significantly enhancing the battery's cycling performance. This technology has high industrial value.

[0004] Chinese patent application CN 116281934 A discloses a method for preparing lithium difluorophosphate, which involves dissolving lithium hexafluorophosphate in dimethyl carbonate and reacting it with aluminum oxide. This method requires filtration, redissolution, recrystallization, and drying to obtain the lithium difluorophosphate product. This process is cumbersome and involves complex separation and purification steps. Chinese patent application CN 107226463B discloses a combined method for preparing lithium difluorophosphate and lithium tetrafluoroborate, which involves reacting lithium hexafluorophosphate, lithium carbonate, and boron trifluoride in an organic solvent system to produce lithium difluorophosphate salt. However, this method suffers from the following issues: the reaction gases readily react with the organic solvent to produce byproducts, and the method requires two concentration, separation, and purification steps, resulting in a complex process and a high risk of product deterioration. Chinese patent application CN115353087A discloses a method for producing lithium difluorophosphate. DMC and lithium hexafluorophosphate are mixed into a lithium hexafluorophosphate solution, and hexamethyldisiloxane is added dropwise to react and generate lithium difluorophosphate. The method includes filtering, deacidification, recrystallization, filtering, and drying to obtain the product lithium difluorophosphate. However, the process is complex and difficult to control, and is prone to introducing more solvent residues. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing lithium difluorophosphate, which is used to solve the problem in the prior art that the reaction is complex and difficult to control.

[0006] A method for preparing lithium difluorophosphate comprises the following steps:

[0007] Lithium hexafluorophosphate and excess hexamethyldisiloxane are heated to react at 50-55° C. to prepare lithium difluorophosphate.

[0008] The beneficial effects of the above technical solution are as follows: the present invention uses hexamethyldisiloxane as a solvent, without introducing other solvents, and mixes it with solid particulate lithium hexafluorophosphate to obtain high-purity lithium difluorophosphate. The method adopts a one-pot salt formation and purification process, with hexamethyldisiloxane serving as both the raw material and the solvent. Excess hexamethyldisiloxane solvent is used to ensure the complete reaction of the lithium hexafluorophosphate. The reaction system of the present invention is simple and easy to control, has no side reactions, effectively avoids the possibility of other impurities entering the system, and achieves high product purity and yield.

[0009] This method is simple and practical, has mild reaction conditions, and can reuse raw materials, resulting in lower costs and higher efficiency. The waste gas generated during the reaction is easy to treat, and the resulting product has higher purity, which is conducive to industrial large-scale production. Experiments have found that the yield of the product obtained by the present invention can reach over 92.8% and the purity can reach over 91.3%. After using ultrasonic treatment, the yield of the product obtained by the present invention can reach over 96.2% and the purity can reach over 99.9%.

[0010] The reaction process of the preparation method of the present invention is schematically shown as follows:

[0011] LiPF6+2(SiMe3)2O→LiPO2F2+4SiMe3F; the SiMe3F is a gas.

[0012] In order to ensure the purity of the prepared lithium difluorophosphate and avoid the generation of impurities, preferably, the purity of the hexamethyldisiloxane and lithium hexafluorophosphate is ≥99.9%, and the moisture content is ≤10 ppm.

[0013] In order to improve raw material utilization and reaction efficiency, preferably, the heating reaction is carried out under ultrasonic conditions.

[0014] In order to further improve the raw material utilization and reaction efficiency, preferably, the ultrasonic frequency is 30 to 40 kHz.

[0015] In order to ensure that lithium hexafluorophosphate reacts completely without producing other substances, preferably, the mass ratio of lithium hexafluorophosphate to hexamethyldisiloxane is (0.9-1.1): (3.1-3.5).

[0016] More preferably, the mass ratio of lithium hexafluorophosphate to hexamethyldisiloxane is 1:(3.1-3.5).

[0017] In order to fully react and utilize lithium hexafluorophosphate and hexamethyldisiloxane and improve the utilization rate of raw materials, preferably, the heating reaction time is 3 to 6 hours.

[0018] In order to obtain high-purity lithium difluorophosphate, preferably, solid-liquid separation is performed after the heating reaction, the solid is purged with an inert gas, and then dried.

[0019] In order to effectively remove the residual solvent and gas, preferably, the purge time is 20 to 30 minutes.

[0020] In order to further remove the residual solvent and gas and improve the purity of lithium difluorophosphate, preferably, the drying is vacuum drying at a temperature of 145-150°C.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] (1) The process of the present invention is simple and practical, the reaction system is clean, and the possibility of other impurities entering the system is effectively avoided, thereby obtaining high-quality lithium difluorophosphate.

[0023] (2) The reaction conditions of the present invention are mild, the post-reaction treatment is simple, and there is no need for subsequent complex processes such as concentration and crystallization. The synthesis is carried out in a one-step method, the reaction is rapid and thorough, and the yield is high.

[0024] (3) The present invention realizes the solvent-free preparation of lithium difluorophosphate, wherein hexamethyldisiloxane is both a raw material and a solvent, and the raw material can be reused after recovery, which saves costs and is suitable for industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The NMR phosphorus spectrum of lithium difluorophosphate prepared by the preparation method of lithium difluorophosphate in Example 1;

[0026] Figure 2 This is the nuclear magnetic fluorine spectrum of lithium difluorophosphate prepared by the preparation method of lithium difluorophosphate in Example 1. DETAILED DESCRIPTION

[0027] The methods for preparing lithium difluorophosphate in the prior art have complex reactions that are difficult to control, insufficient product purity, and low product yield. The present invention provides a method for preparing lithium difluorophosphate, comprising the following steps:

[0028] Lithium hexafluorophosphate and excess hexamethyldisiloxane are heated to react at 50-55° C. to prepare lithium difluorophosphate.

[0029] The technical concept of the present invention is as follows: the present invention uses hexamethyldisiloxane as a solvent, does not introduce other solvents, mixes with lithium hexafluorophosphate, and undergoes a heating reaction to obtain high-purity lithium difluorophosphate. The method adopts a one-pot salt formation and purification process, the reaction system is simple and easy to control, there are no side reactions, the possibility of other impurities entering the system is effectively avoided, and the product purity is high. The present invention realizes the solvent-free preparation of lithium difluorophosphate, wherein hexamethyldisiloxane is both a raw material and a solvent. The process of the present method is simple and practical, the reaction conditions are mild, and the raw materials can be reused, the cost is lower, the efficiency is higher, the waste gas generated in the reaction is easy to handle, and the purity of the obtained product is higher, which is conducive to industrial large-scale production. Experiments have found that the yield of the product obtained by the present invention can reach more than 92.8%, and the purity can reach more than 91.3%. After ultrasonic treatment, the yield of the product obtained by the present invention can reach more than 96.2%, and the purity can reach more than 99.9%.

[0030] Specifically, a method for preparing lithium difluorophosphate comprises the following steps:

[0031] (1) Maintaining an anhydrous dry environment, without adding any additional solvent, add fully dried lithium hexafluorophosphate and hexamethyldisiloxane into a container and stir thoroughly to mix;

[0032] (2) stirring the mixed solution under heating conditions to obtain a mixed solution of lithium difluorophosphate and hexamethyldisiloxane;

[0033] (3) High-quality lithium difluorophosphate is obtained in one step through positive pressure filtration, inert gas purging, and drying.

[0034] Preferably, step (1) is specifically to add qualified hexamethyldisiloxane and fully dried lithium hexafluorophosphate into a reaction bottle and stir them thoroughly.

[0035] Preferably, the container in step (1) is connected to a bubbler and a tail gas absorption bottle filled with alkali solution; the bubbler is used to observe the reaction situation, and the tail gas absorption bottle filled with alkali solution is used to absorb the SiMe3F gas generated by the reaction.

[0036] Preferably, the inert gas for purging is nitrogen.

[0037] The implementation process of the present invention is described in detail below with reference to specific examples; the purity of hexamethyldisiloxane and lithium hexafluorophosphate used in the examples is ≥99.9%, and the moisture content is ≤10ppm;

[0038] 1. Specific Examples of the Preparation Method of Lithium Difluorophosphate of the Present Invention

[0039] Example 1

[0040] The preparation method of lithium difluorophosphate of this embodiment comprises the following steps:

[0041] (1) Take a 500ml three-necked flask, add 76g of lithium hexafluorophosphate and 236g of hexamethyldisiloxane, and stir thoroughly to mix;

[0042] (2) The mixture was placed in a 50°C oil bath and stirred under ultrasonic conditions at 30 kHz until a large amount of white solid appeared. Stirring was stopped after the reaction lasted for 3.5 hours.

[0043] (3) After the reaction was completed, positive pressure filtration was immediately performed, and the filter cake was blown with nitrogen for 30 minutes, and then vacuum dried at 150° C. to obtain 52.9 g of lithium difluorophosphate.

[0044] The NMR phosphorus spectrum and NMR fluorine spectrum of lithium difluorophosphate prepared by the above-mentioned preparation method of lithium difluorophosphate are shown as follows: Figure 1 and Figure 2 The two figures together illustrate that the lithium difluorophosphate produced by the above-mentioned lithium difluorophosphate preparation method has high purity and does not contain other impurities.

[0045] Example 2

[0046] The preparation method of lithium difluorophosphate of this embodiment comprises the following steps:

[0047] (1) Take a 500ml three-necked flask, add 60g of lithium hexafluorophosphate and 209g of hexamethyldisiloxane, and stir thoroughly;

[0048] (2) The mixture was placed in an oil bath at 55°C and stirred under ultrasonic conditions at 40kHz until a large amount of white solid appeared. The stirring was stopped after the reaction lasted for 3 hours.

[0049] (3) After the reaction was completed, positive pressure filtration was immediately performed, and the filter cake was blown with nitrogen for 30 minutes, and then vacuum dried at 150° C. to obtain 41.0 g of lithium difluorophosphate.

[0050] Example 3

[0051] The preparation method of lithium difluorophosphate of this embodiment comprises the following steps:

[0052] (1) Take a 500ml three-necked flask, add 76g of lithium hexafluorophosphate and 236g of hexamethyldisiloxane, and stir thoroughly;

[0053] (2) The mixture was placed in an oil bath at 50°C and stirred under ultrasonic conditions at 30kHz until a large amount of white solid appeared. Stirring was stopped after 6 hours of reaction.

[0054] (3) After the reaction was completed, positive pressure filtration was immediately performed, and the filter cake was blown with nitrogen for 30 minutes, and then vacuum dried at 150° C. to obtain 52.3 g of lithium difluorophosphate.

[0055] Example 4: The difference from Example 1 is that ultrasound is not used:

[0056] The preparation method of lithium difluorophosphate of this embodiment comprises the following steps:

[0057] (1) Take a 500ml three-necked flask, add 76g of lithium hexafluorophosphate and 236g of hexamethyldisiloxane, and stir thoroughly to mix;

[0058] (2) Place the above mixture in a 50°C oil bath and stir until a large amount of white solid appears. Stop stirring after 3.5 hours.

[0059] (3) After the reaction was completed, positive pressure filtration was immediately performed, and the filter cake was blown with nitrogen for 30 minutes, and then vacuum dried at 150° C. to obtain 50.1 g of lithium difluorophosphate.

[0060] In the technical solution of the present invention, a mass ratio of lithium hexafluorophosphate in the range of 0.9 to 1.1 can ensure that the lithium hexafluorophosphate reacts completely without producing other substances; a vacuum drying temperature in the range of 145 to 150° C. can effectively remove residual solvents and gases, thereby improving the purity of lithium difluorophosphate.

[0061] 2. Comparative Example

[0062] Comparative Example 1: The difference from Example 1 is that ultrasound is not used and the heating reaction temperature is 35°C:

[0063] The preparation method of lithium difluorophosphate in this comparative example comprises the following steps:

[0064] (1) Take a 500ml three-necked flask, add 76g of lithium hexafluorophosphate and 236g of hexamethyldisiloxane, and stir thoroughly;

[0065] (2) Place the above mixture in a 35°C oil bath and stir until a large amount of white solid appears. Stop stirring after 7 hours of reaction.

[0066] (3) After the reaction was completed, positive pressure filtration was immediately performed, and the filter cake was blown with nitrogen for 30 minutes, and then vacuum dried at 150° C. to obtain 45.9 g of lithium difluorophosphate.

[0067] Comparative Example 2: The difference from Example 1 is that the heating reaction temperature is 65°C:

[0068] The preparation method of lithium difluorophosphate in this comparative example comprises the following steps:

[0069] (1) Take a 500ml three-necked flask, add 76g of lithium hexafluorophosphate and 236g of hexamethyldisiloxane, and stir thoroughly to mix;

[0070] (2) The mixture was placed in an oil bath at 65°C and stirred under ultrasonic conditions at 30 kHz until a large amount of white solid appeared. Stirring was stopped after the reaction lasted for 3.5 h.

[0071] (3) After the reaction was completed, positive pressure filtration was immediately performed, and the filter cake was blown with nitrogen for 30 minutes, and then vacuum dried at 150° C. to obtain 44.4 g of lithium difluorophosphate.

[0072] 3. Experimental Examples

[0073] The purity and yield of lithium difluorophosphate prepared by the preparation methods of lithium difluorophosphate in Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 1:

[0074] Table 1 Purity and yield of lithium difluorophosphate prepared in Examples 1 to 4 and Comparative Examples 1 to 2

[0075] Performance parameters Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 purity 99.9％ 99.9％ 99.9％ 91.3％ 83.2％ 80.9％ Yield 98.0％ 96.2％ 96.8％ 92.8％ 85％ 82.3％

[0076] As shown in Table 1, in the preparation methods of lithium difluorophosphate of Examples 1 to 3, the purity of lithium difluorophosphate prepared using ultrasound can reach 99.9%, and the yield can reach more than 96.2%. In Example 4, ultrasound is not used, and the purity and yield of lithium difluorophosphate prepared by its preparation method of lithium difluorophosphate are lower than those of Example 1, namely 91.3% and 92.8%, respectively. In Comparative Example 1, the heating temperature is low and ultrasound is not used. The purity of lithium difluorophosphate prepared by its preparation method of lithium difluorophosphate is 83.2% and the yield is 85%. In Comparative Example 2, the heating temperature is high, and the purity and yield of lithium difluorophosphate prepared by its preparation method of lithium difluorophosphate are 80.9% and 82.3%, respectively.

[0077] In summary, the product yield obtained by the preparation method of lithium difluorophosphate of the present invention can reach more than 92.8%, and the purity can reach more than 91.3%; after using ultrasound, the yield and purity of the prepared product are better, the yield can reach more than 96.2%, and the purity can reach more than 99.9%. The present invention realizes the solvent-free preparation of lithium difluorophosphate without adding additional solvent, wherein hexamethyldisiloxane is both a raw material and a solvent, and lithium difluorophosphate is synthesized by a one-step method, realizing the recycling of raw materials. The process of the present invention is simple and practical, the reaction conditions are mild, the cost is lower, the efficiency is higher, the waste gas generated in the reaction is easy to treat, and the obtained product has a higher purity, which is conducive to industrial production.

[0078] The above is a detailed description of the embodiment process, but it does not limit the technical solution of the present invention. Ordinary technicians in this field should understand that any modifications, partial replacements and variations of the above embodiments can be made within the scope of the present invention, which should all be included in the required scope of the present invention.

Claims

1. A method for preparing lithium difluorophosphate, characterized in that: The following steps are involved: Lithium hexafluorophosphate and an excess of hexamethyldisiloxane are heated to react at 50-55° C. to prepare lithium difluorophosphate; the mass ratio of lithium hexafluorophosphate to hexamethyldisiloxane is (0.9-1.1):(3.1-3.5), and hexamethyldisiloxane serves as both a raw material and a solvent; the heating reaction is carried out under ultrasonic conditions.

2. The method for preparing lithium difluorophosphate according to claim 1, wherein The ultrasonic frequency is 30-40 kHz.

3. The method for preparing lithium difluorophosphate according to claim 1, wherein The mass ratio of the lithium hexafluorophosphate to hexamethyldisiloxane is 1:(3.1-3.5).

4. The method for preparing lithium difluorophosphate according to claim 2, wherein The heating reaction time is 3 to 6 hours.

5. The method for preparing lithium difluorophosphate according to claim 1, wherein After the heating reaction, solid-liquid separation is performed, the solid is purged with an inert gas, and then dried.

6. The method for preparing lithium difluorophosphate according to claim 5, wherein The drying is vacuum drying at a temperature of 145-150°C.

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