WO2024002386A1

WO2024002386A1 - Preparation method for lithium difluorophosphate and product obtained therefrom

Info

Publication number: WO2024002386A1
Application number: PCT/CN2023/111383
Authority: WO
Inventors: 于鑫; 贾国文; 朱振涛; 李超; 丁建涛; 王德勇; 耿其琛; 李宏亮
Original assignee: 山东海科创新研究院有限公司
Priority date: 2022-10-18
Filing date: 2023-08-07
Publication date: 2024-01-04
Also published as: CN115477297A; CN115477297B

Abstract

Provided in the present application are a preparation method for lithium difluorophosphate and a product obtained therefrom, which belong to the technical field of preparation of lithium battery additives. The preparation method for lithium difluorophosphate comprises the following steps: 1) mixing ammonium fluoride, phosphorus pentoxide and a polar aprotic organic system, and heating same to 80-90ºC for a reaction so as to obtain ammonium difluorophosphate, wherein the polar aprotic organic system is a mixed solution of N,N-dimethylformamide and acetonitrile; and 2) mixing the ammonium difluorophosphate and anhydrous lithium hydroxide with an organic solvent, and reacting same to obtain lithium difluorophosphate, wherein the organic solvent is ethylene glycol dimethyl ether, dimethyl carbonate or ethyl acetate. The preparation method for lithium difluorophosphate provided in the present application has high product purity and yield and involves stable reactions.

Description

Preparation method of lithium difluorophosphate and products obtained therefrom

This application requires the priority of the Chinese patent application submitted to the China Patent Office on October 18, 2022, with the application number 202211272875.8 and the application name "A preparation method of lithium difluorophosphate and the resulting product", and its entire content is approved by This reference is incorporated into this application.

Technical field

The present application belongs to the technical field of lithium battery additive preparation, and in particular relates to a preparation method of lithium difluorophosphate and the resulting product.

Background technique

Lithium difluorophosphate was initially used to construct a solid electrolyte interface film on graphite anodes to solve the problems of poor rate performance and cycle stability of high-loading graphite anodes. Experiments have shown that a small amount of lithium difluorophosphate can promote the formation of the SEI film on the graphite negative electrode, and the film-forming effect is significantly better than that of vinylene carbonate. At the same time, when lithium difluorophosphate is added alone, the SEI film is produced due to the decomposition of lithium difluorophosphate. The high resistance material lithium fluoride content is too high, which affects the battery's discharge performance at high rates, so it performs best when used together with vinylene carbonate. At the same time, adding lithium difluorophosphate to ternary/graphite batteries can significantly improve the low-temperature performance of the battery, and the cycle stability of the battery added with lithium difluorophosphate is significantly better. This is because at low temperatures, the lithium fluoride component in the SEI film is beneficial to reducing the membrane resistance.

The synthesis of traditional lithium salt additives is usually related to lithium hexafluorophosphate, especially the synthesis of lithium difluorophosphate, which is generated by the reaction of lithium hexafluorophosphate and lithium carbonate or lithium hexafluorophosphate and siloxane. Due to the high price of lithium hexafluorophosphate, the cost of lithium salt additives remains high. Moreover, the existing preparation methods of lithium difluorophosphate generally have low yields and many by-products. In particular, the acid value and the content of lithium phosphate, lithium metaphosphate and lithium monofluorophosphate are high, which have a great impact on the performance of the electrolyte. , resulting in the application scope of lithium difluorophosphate being still limited and difficult to popularize. Patent CN 111717906 A. Potassium fluoride and phosphorus pentoxide are placed in a solid-phase reactor and heated at a constant temperature of 150°C for 12 hours to obtain KPF ₂ O ₂ , which is then mixed with LiClO ₄ to undergo a series of reactions to obtain lithium difluorophosphate. The disadvantage of this method is that there are too many side reactions in the pressure-resistant solid-phase reactor, which may produce phosphorus pentafluoride. The reaction process is complicated and the equipment requirements are relatively high.

Contents of the invention

To address at least one shortcoming in the prior art, this application provides a method for preparing lithium difluorophosphate and the resulting product.

The first aspect of this application provides a method for preparing lithium difluorophosphate, which includes the following steps:

1) Mix ammonium fluoride, phosphorus pentoxide and a polar aprotic organic system, raise the temperature to 80-90°C, and react to obtain ammonium difluorophosphate;

The polar aprotic organic system is a mixed solution of N,N-dimethylformamide and acetonitrile;

2) Mix the ammonium difluorophosphate and anhydrous lithium hydroxide with an organic solvent and react to obtain lithium difluorophosphate; the organic solvent is ethylene glycol dimethyl ether, dimethyl carbonate or ethyl acetate.

In some embodiments of the first aspect of the application, N,N-dimethylformamide in the polar aprotic organic system is 4% to 10% in terms of mass percentage.

In some embodiments of the first aspect of the application, the molar ratio of ammonium fluoride to phosphorus pentoxide in step 1) is (3.3~3.5):1; the mass ratio of ammonium fluoride to the polar aprotic organic system 9:150～250.

In some embodiments of the first aspect of the present application, in step 1), a gradient heating method is used to raise the temperature to 80-90°C for reaction, and the rate of the gradient heating is 2.5-3.5°C/min; the reaction time is 4~6h.

In some embodiments of the first aspect of the application, after the reaction in step 1) is completed, a purification step is also included; the purification includes the following steps;

(1) Perform suction filtration of the reaction product obtained after the reaction is completed to obtain a filter cake;

(2) Mix the filter cake with ethanol, and filter the mixture to obtain a filtrate;

(3) Rotary evaporate the filtrate to obtain purified ammonium difluorophosphate.

In some embodiments of the first aspect of the application, the molar ratio of ammonium difluorophosphate and anhydrous lithium hydroxide in step 2) is 1: (1.03~1.08).

In some embodiments of the first aspect of the present application, the reaction temperature in step 2) is 25-30°C, and the reaction time is 1-3 hours.

In some embodiments of the first aspect of the present application, in step 2), stirring is performed during the reaction, and the stirring speed is 500 to 1000 rpm.

In some embodiments of the first aspect of the present application, after the reaction in step 2) is completed, it also includes The product is subjected to suction filtration and rotary evaporation in sequence. The temperature of the rotary evaporation is 35 to 40°C; the vacuum degree during the rotary evaporation is -0.1 to -0.2Mpa.

The second aspect of the present application provides lithium difluorophosphate prepared by any of the above methods. The acid value of the lithium difluorophosphate is 8 to 10 ppm and the purity is above 99.5%.

Compared with the existing technology, the advantages and positive effects of this application are:

(1) The preparation method of lithium difluorophosphate provided in at least one embodiment of the present application uses ammonium fluoride and phosphorus pentoxide as raw materials, uses a liquid phase method to first synthesize ammonium difluorophosphate, and then borrows ammonium difluorophosphate and Lithium hydroxide reacts to synthesize lithium difluorophosphate. This process does not require special equipment or high synthesis temperatures to synthesize lithium difluorophosphate, and the reaction raw materials are low in cost and easy to obtain. The synthesized lithium difluorophosphate has high purity, low cost, simple operation and fewer side reactions.

(2) The preparation method of lithium difluorophosphate provided in at least one embodiment of the present application is simple, the reaction is stable, the reaction raw materials are low in cost and easy to obtain, and the prepared product has high purity and high yield.

Description of drawings

Figure 1 shows the XRD characterization pattern of standard lithium difluorophosphate;

Figure 2 is the XRD characterization pattern of lithium difluorophosphate in Example 1;

Figure 3 is the XRD characterization pattern of lithium difluorophosphate in Comparative Example 4;

Figure 4 is a ¹⁹ F NMR spectrum of lithium difluorophosphate in Example 1;

Figure 5 is a ¹⁹ F NMR spectrum of lithium difluorophosphate in Comparative Example 4.

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

1) Mix ammonium fluoride, phosphorus pentoxide and polar aprotic organic system, and heat it to 80~90°C. Carry out reaction to obtain ammonium difluorophosphate;

In the above embodiments, ammonium fluoride, phosphorus pentoxide and a polar aprotic organic system are mixed, the temperature is raised to 80-90°C, and the reaction proceeds to obtain ammonium difluorophosphate.

In some embodiments, the polar aprotic organic system is a mixed solution of N,N-dimethylformamide and acetonitrile; in terms of mass percentage, the N,N- Dimethylformamide is 4% to 10%, optionally 5%.

In some embodiments, the molar ratio of ammonium fluoride to phosphorus pentoxide is (3.3~3.5):1; the mass ratio of ammonium fluoride to polar aprotic organic system is 9:150~250 , optionally 9:200.

Polar aprotic solvents will affect solute molecules and produce a solvation effect. In a weakly acidic environment (phosphorus pentoxide and ammonium fluoride are weakly acidic in the liquid phase mixed system), it is beneficial to use aprotic solvents. Phosphorus pentoxide and ammonium fluoride undergo a single-molecule nucleophilic substitution reaction to increase the reaction rate. At the same time, N,N-dimethylformamide acts as a connecting bridge between the liquid phase and the solid phase in the system, playing the role of a "catalyst". Promote the continuation of the reaction. Compared with using acetonitrile alone, phosphorus pentoxide and ammonium fluoride are more soluble in an aprotic mixed system, and the product purity and yield will be improved. It can be understood that in this application, the polar aprotic organic system formed by N,N-dimethylformamide and acetonitrile is the key operation of this application, and a conventional single solvent such as N,N-dimethylformamide is used. It is difficult to synthesize the required ammonium difluorophosphate using formamide/ethylene glycol dimethyl ether/dimethyl carbonate/ethyl acetate/methanol.

In some embodiments, a gradient heating method is used to raise the temperature to 80-90°C for the reaction. The rate of the gradient heating is 2.5-3.5°C/min; the reaction time is 4-6 hours. Phosphorus pentoxide and ammonium fluoride are synthesized through solid-phase grinding in a glove box at room temperature to synthesize ammonium difluorophosphate, but the yield and purity are very low. During the reaction process, phosphorus pentoxide and ammonium fluoride come into contact with each other through grinding. A large amount of white smoke emits a large amount of heat, and then the temperature drops to room temperature to form hard agglomerates. It shows that in an anhydrous and anaerobic environment, phosphorus pentoxide and ammonium fluoride have strong activity when they come into contact with each other, and the reaction is violent. In the above embodiments, gradient heating is used to control the reaction temperature, which can prevent the production of other by-products due to local high temperatures.

After mixing ammonium fluoride salt and phosphorus pentoxide, when the temperature is raised to start the reaction, the temperature in the system will quickly soar to about 200°C. The product ammonium difluorophosphate will decompose into ammonium phosphate, causing irreversible damage and reaction. Can not control. In this application, ammonium fluoride, phosphorus pentoxide and polar aprotic organic systems are mixed. The entire reaction system exists in the liquid phase organic solvent. The intermolecular contact and collision of the reactants will be more complete than in the solid phase method. , the reaction is more thorough, and the temperature control in the liquid phase system is more accurate and uniform, so the corresponding organic by-products should be less, and the intermediate product ammonium difluorophosphate has high purity, which is conducive to the synthesis of lithium difluorophosphate through the associated reaction with lithium hydroxide High purity. At the same time, the use of a specific polar aprotic organic system can promote the forward reaction and increase the yield of ammonium difluorophosphate, thereby further improving the yield and purity of lithium difluorophosphate.

In some embodiments, after the reaction is completed, a purification step is also included; the purification includes the following steps;

In some embodiments, during the rotary evaporation, the temperature of the rotary evaporation water bath is preferably controlled to be 35-40°C; the vacuum degree during the rotary evaporation is -0.1--0.2Mpa, more preferably -0.15Mpa.

After obtaining ammonium difluorophosphate, the present application mixes the ammonium difluorophosphate and anhydrous lithium hydroxide with an organic solvent to react to obtain lithium difluorophosphate; the organic solvent is ethylene glycol dimethyl ether, dimethyl carbonate. Methyl ester or ethyl acetate, optionally glycol dimethyl ether.

In some embodiments, the molar ratio of ammonium difluorophosphate and anhydrous lithium hydroxide is 1: (1.03-1.08).

In some embodiments, the reaction temperature is 25-30°C and the reaction time is 1-3 hours.

In some embodiments, stirring is performed during the reaction, and the stirring speed is 500 to 1000 rpm.

In some embodiments, the organic solvent is ethylene glycol dimethyl ether.

In some embodiments, after the reaction is completed, the reaction product is further subjected to suction filtration and rotary evaporation in sequence. In some embodiments, the temperature of the rotary evaporation is 35-40°C; the degree of vacuum during the rotary evaporation is -0.1～-0.2Mpa, optionally -0.15Mpa. The chemical reaction formula for preparing lithium difluorophosphate in this application is as follows:

LiOH+NH ₄ PO ₂ F ₂ =LiPO ₂ F ₂ +NH ₃ ↑+H ₂ O

In order to further illustrate the present application, the technical solutions provided by the present application are described in detail below with reference to specific examples, but they should not be understood as limiting the protection scope of the present application.

The sources of raw materials in the examples are as follows: ammonium fluoride is a commercially available product from Xilong Chemical with a purity of 96%, phosphorus pentoxide is a commercially available product with a McLean purity of 99.99%, and N,N-dimethylformamide is a commercially available product. The commercially available product Maclean has a purity of 99.8%, the anhydrous acetonitrile is a commercially available product Maclean with a purity of 99.9%, and the ethanol is a commercially available product Aladdin analytical purity 99.5%.

Example 1

Weigh 9.17g of ammonium fluoride, 10g of phosphorus pentoxide, and 200g of N,N-dimethylformamide-anhydrous acetonitrile (the mass proportion of N,N-dimethylformamide is 5%, and the remaining 95% is anhydrous acetonitrile) water, acetonitrile), add the above raw materials into a three-necked flask (in the three-necked flask, connect the mechanical stirring directly above, and the other two ports are connected to the thermometer sleeve and condenser tube respectively). Place the three-necked flask in an oil bath heating pot, and gradually heat up the temperature from room temperature to 85°C at a heating rate of 3°C/min. After reaching 85°C, react at a constant temperature for 5 hours.

After the reaction is completed, the reaction product is suction-filtered using a sand core suction filtration device, and the filtrate is separated from the filter cake. The filter cake was purified with 300 mL of ethanol, and the magnetic stirring speed was 600 rpm for 1 hour. The above materials are suction filtered using a sand core funnel, and the filtrate is separated from the filter cake. The filtrate was transferred to a rotary evaporator bottle for rotary evaporation treatment (rotor evaporation temperature was 35°C, vacuum degree was -0.15Mpa) to obtain 8.756g of ammonium difluorophosphate.

In a glove box (anhydrous and oxygen-free), react the ammonium difluorophosphate obtained above with 1.87g of anhydrous lithium hydroxide in 300 mL of ethylene glycol dimethyl ether solution (use a magnetic stirrer to stir during the reaction, Rotation speed: 1000rpm)2h. After the reaction is completed, the reaction product is filtered with a sand core funnel, the filtrate is separated from the filter cake, and the filtrate is transferred to a rotary evaporator bottle for rotary evaporation (the rotary evaporation temperature is 38°C, and the vacuum degree is -0.15Mpa), 7.92g of lithium difluorophosphate was obtained.

The prepared lithium difluorophosphate was characterized by XRD, as shown in Figure 2, and compared with the standard lithium difluorophosphate characterization chart (specifically shown in Figure 1). It can be seen that the prepared product is lithium difluorophosphate. .

The prepared lithium difluorophosphate was subjected to nuclear magnetic characterization (BRUKER AVANCE III 400 superconducting nuclear magnetic resonance spectrometer (NMR)), as shown in Figure 4.

Example 2

Weigh 8.908g of ammonium fluoride, 10g of phosphorus pentoxide, and 200g of N,N-dimethylformamide-anhydrous acetonitrile (the mass proportion of N,N-dimethylformamide is 5%, and the remaining 95% is anhydrous acetonitrile) water, acetonitrile), add the above raw materials into a three-necked flask (in the three-necked flask, connect the mechanical stirring directly above, and the other two ports are connected to the thermometer sleeve and condenser tube respectively). Place the three-necked flask in an oil bath heating pot and gradually heat it from room temperature to 85°C at a heating rate of 3°C/min. After reaching 85°C, the reaction is carried out at a constant temperature for 5 hours.

After the reaction is completed, the reaction product is suction-filtered using a sand core suction filtration device, and the filtrate is separated from the filter cake. The filter cake was purified with 300 mL of ethanol, and the magnetic stirring speed was 600 rpm for 1 hour. The above materials are suction filtered using a sand core funnel, and the filtrate is separated from the filter cake. The filtrate was transferred to a rotary evaporator bottle for rotary evaporation treatment (rotor evaporation temperature was 40°C, vacuum degree was -0.15Mpa) to obtain 7.863g of ammonium difluorophosphate.

In a glove box (anhydrous and oxygen-free), react the ammonium difluorophosphate obtained above with 1.679g of anhydrous lithium hydroxide in 300 mL of ethylene glycol dimethyl ether solution (use a magnetic stirrer to stir during the reaction, Rotation speed: 1000rpm)2h. After the reaction is completed, the reaction product is suction filtered using a sand core funnel, the filtrate is separated from the filter cake, and the filtrate is transferred to a rotary evaporator bottle for rotary evaporation (rotary evaporation temperature is 38°C; vacuum degree is -0.15Mpa) to obtain the second product. Lithium fluorophosphate 6.802g.

Example 3

Weigh 8.908g of ammonium fluoride, 10g of phosphorus pentoxide, and 240g of N,N-dimethylformamide-anhydrous acetonitrile (the mass proportion of N,N-dimethylformamide is 10%, and the remaining 90% is anhydrous acetonitrile) water, acetonitrile), add the above raw materials into a three-necked flask (in the three-necked flask, connect the mechanical stirring directly above, and the other two ports are connected to the thermometer sleeve and condenser tube respectively). Place the three-necked flask in an oil bath heating pot and gradually heat up the temperature from room temperature to 80°C at a heating rate of 3.5°C/min. After reaching 80°C, react at a constant temperature for 6 hours.

After the reaction is completed, the reaction product is suction-filtered using a sand core suction filtration device, and the filtrate is separated from the filter cake. The filter cake was purified with 300 mL of ethanol, and the magnetic stirring speed was 600 rpm for 1 hour. The above materials are suction filtered using a sand core funnel, and the filtrate is separated from the filter cake. The filtrate was transferred to a rotary evaporation bottle for rotary evaporation treatment (rotor evaporation temperature was 40°C, vacuum degree was -0.15Mpa) to obtain 7.631g of ammonium difluorophosphate.

In a glove box (anhydrous and oxygen-free), react the ammonium difluorophosphate obtained above with 1.679g of anhydrous lithium hydroxide in 300 mL of dimethyl carbonate solution (a magnetic stirrer is used for stirring during the reaction, and the rotation speed is 1000 rpm )3h. After the reaction is completed, the reaction product is suction filtered using a sand core funnel, the filtrate is separated from the filter cake, and the filtrate is transferred to a rotary evaporator bottle for rotary evaporation (rotary evaporation temperature is 38°C; vacuum degree is -0.15Mpa) to obtain the second product. Lithium fluorophosphate 6.785g.

Example 4

Weigh 8.908g of ammonium fluoride, 10g of phosphorus pentoxide, and 200g of N,N-dimethylformamide-anhydrous acetonitrile (the mass proportion of N,N-dimethylformamide is 10%, and the remaining 90% is anhydrous acetonitrile) water, acetonitrile), add the above raw materials into a three-necked flask (in the three-necked flask, connect the mechanical stirring directly above, and the other two ports are connected to the thermometer sleeve and condenser tube respectively). Place the three-necked flask in an oil bath heating pot, and gradually heat up the temperature from room temperature to 90°C at a heating rate of 2.5°C/min. After reaching 90°C, react at a constant temperature for 4 hours.

After the reaction is completed, the reaction product is suction-filtered using a sand core suction filtration device, and the filtrate is separated from the filter cake. The filter cake was purified with 300 mL of ethanol, and the magnetic stirring speed was 600 rpm for 1 hour. The above materials are suction filtered using a sand core funnel, and the filtrate is separated from the filter cake. The filtrate was transferred to a rotary evaporator bottle for rotary evaporation treatment (rotor evaporation temperature was 40°C, vacuum degree was -0.15Mpa) to obtain 7.313g of ammonium difluorophosphate.

In a glove box (anhydrous and oxygen-free), react the ammonium difluorophosphate obtained above with 1.679g of anhydrous lithium hydroxide in 300 mL of ethylene glycol dimethyl ether solution (use a magnetic stirrer to stir during the reaction, Rotation speed: 1000rpm)3h. After the reaction is completed, the reaction product is suction filtered using a sand core funnel, the filtrate is separated from the filter cake, and the filtrate is transferred to a rotary evaporator bottle for rotary evaporation (rotary evaporation temperature is 38°C; vacuum degree is -0.15Mpa) to obtain the second product. Lithium fluorophosphate 6.565g.

Comparative example 1

The difference from Example 1 is that when preparing ammonium difluorophosphate, only anhydrous acetonitrile was added and N,N-dimethylformamide was not added. Other operating steps are exactly the same as in Example 1, and the specific process is as follows:

Weigh 9.17g of ammonium fluoride, 10g of phosphorus pentoxide, and 200g of anhydrous acetonitrile, and add the above raw materials into a three-necked flask (in the three-necked flask, a mechanical stirrer is connected directly above it, and the other two ports are connected to the thermometer sleeve and condenser tube respectively) . Place the three-necked flask in an oil bath heating pot and gradually heat it from room temperature to 85°C at a heating rate of 3°C/min. After reaching 85°C, the reaction is carried out at a constant temperature for 5 hours.

After the reaction is completed, the reaction product is suction-filtered using a sand core suction filtration device, and the filtrate is separated from the filter cake. The filter cake was purified with 300 mL of ethanol, and the magnetic stirring speed was 600 rpm for 1 hour. The above materials are suction filtered using a sand core funnel, and the filtrate is separated from the filter cake. The filtrate was transferred to a rotary evaporator bottle for rotary evaporation treatment (rotor evaporation temperature was 35°C, vacuum degree was -0.15Mpa) to obtain 5.897g of ammonium difluorophosphate.

In a glove box (anhydrous and oxygen-free), react the ammonium difluorophosphate obtained above with 1.259g of anhydrous lithium hydroxide in 300 mL of ethylene glycol dimethyl ether solution (use a magnetic stirrer to stir during the reaction, Rotation speed: 1000rpm)2h. After the reaction is completed, the reaction product is filtered with a sand core funnel, the filtrate is separated from the filter cake, and the filtrate is transferred to a rotary evaporator bottle for rotary evaporation (rotary evaporation temperature is 38°C, vacuum degree is -0.15Mpa) to obtain the second product. Lithium fluorophosphate 4.972g.

Comparative example 2

The difference from Example 1 is that when preparing ammonium difluorophosphate, only N,N-dimethylformamide was added, and anhydrous acetonitrile was not added. Other operating steps are exactly the same as in Example 1, and the specific process is as follows:

Weigh 9.17g of ammonium fluoride, 10g of phosphorus pentoxide, and 200g of N,N-dimethylformamide, and add the above raw materials into a three-necked flask (in the three-necked flask, connect mechanical stirring directly above it, and the other two ports are connected to thermometers. casing and condenser tube). Place the three-necked flask in an oil bath heating pot and gradually heat it from room temperature to 85°C at a heating rate of 3°C/min. After reaching 85°C, the reaction is carried out at a constant temperature for 5 hours.

After the reaction is completed, the reaction product is suction-filtered using a sand core suction filtration device, and the filtrate is separated from the filter cake. The filter cake was purified with 300 mL of ethanol, and the magnetic stirring speed was 600 rpm for 1 hour. The above materials are suction filtered using a sand core funnel, and the filtrate is separated from the filter cake. The filtrate was transferred to a rotary evaporator bottle for rotary evaporation treatment (rotor evaporation temperature was 35°C, vacuum degree was -0.15Mpa) to obtain 1.051g of ammonium difluorophosphate.

In a glove box (anhydrous and oxygen-free), react the ammonium difluorophosphate and anhydrous lithium hydroxide obtained above in 300 mL of ethylene glycol dimethyl ether solution (use a magnetic stirrer to stir during the reaction, the speed 1000rpm)2h. After the reaction is completed, the reaction product is suction filtered using a sand core funnel, and the filtrate Separate from the filter cake, transfer the filtrate to a rotary evaporator bottle for rotary evaporation (rotor evaporation temperature is 38°C, vacuum degree is -0.15Mpa) to obtain 0.802g of lithium difluorophosphate.

Comparative example 3

The difference from Example 1 is that when preparing ammonium difluorophosphate, the addition ratio of N,N-dimethylformamide and anhydrous acetonitrile in the polar aprotic organic system is different. Other operating steps are exactly the same as in Example 1, and the specific process is as follows:

Weigh 9.17g of ammonium fluoride, 10g of phosphorus pentoxide, and 200g of N,N-dimethylformamide-anhydrous acetonitrile (the mass proportion of N,N-dimethylformamide is 50%, and the remaining 50% is anhydrous acetonitrile) water, acetonitrile), add the above raw materials into a three-necked flask (in the three-necked flask, connect the mechanical stirring directly above, and the other two ports are connected to the thermometer sleeve and condenser tube respectively). Place the three-necked flask in an oil bath heating pot and gradually heat it from room temperature to 85°C at a heating rate of 3°C/min. After reaching 85°C, the reaction is carried out at a constant temperature for 5 hours.

After the reaction is completed, the reaction product is suction-filtered using a sand core suction filtration device, and the filtrate is separated from the filter cake. The filter cake was purified with 300 mL of ethanol, and the magnetic stirring speed was 600 rpm for 1 hour. The above materials are suction filtered using a sand core funnel, and the filtrate is separated from the filter cake. The filtrate was transferred to a rotary evaporation bottle for rotary evaporation treatment (rotor evaporation temperature was 35°C, vacuum degree was -0.15Mpa) to obtain 5.012g of ammonium difluorophosphate.

In a glove box (anhydrous and oxygen-free), react the ammonium difluorophosphate and anhydrous lithium hydroxide obtained above in 300 mL of ethylene glycol dimethyl ether solution (use a magnetic stirrer to stir during the reaction, and the speed 1000rpm)2h. After the reaction is completed, the reaction product is filtered with a sand core funnel, the filtrate is separated from the filter cake, and the filtrate is transferred to a rotary evaporator bottle for rotary evaporation (rotary evaporation temperature is 38°C, vacuum degree is -0.15Mpa) to obtain the second product. Lithium fluorophosphate 4.227g.

Comparative example 4

Weigh 9.17g of ammonium fluoride and 10g of phosphorus pentoxide, and mix evenly with a double-center mixer (speed 500rpm, time 10min). Repeat three times. After each mixing, the materials are ground and pulverized with a copper bowl. After mixing evenly, transfer the materials to the polytetrafluoroethylene reaction device, connect the corresponding temperature sensor and exhaust gas absorption device; then transfer the customized reaction device to the heating mantle, heat to 200°C, and maintain a constant temperature for 2 hours.

After the reaction is completed, the reaction product is suction-filtered using a sand core suction filtration device, and the filtrate is separated from the filter cake. The filter cake was purified with 300 mL of ethanol, and the magnetic stirring speed was 600 rpm for 1 hour. Will go up The above materials are suction filtered using a sand core funnel, and the filtrate is separated from the filter cake. The filtrate was transferred to a rotary evaporator bottle for rotary evaporation treatment (rotor evaporation temperature was 35°C, vacuum degree was -0.15Mpa) to obtain 3.872g of ammonium difluorophosphate.

In a glove box (anhydrous and oxygen-free), react the ammonium difluorophosphate obtained above with 0.766g of anhydrous lithium hydroxide in 300 mL of ethylene glycol dimethyl ether solution (use a magnetic stirrer to stir during the reaction, Rotation speed: 1000rpm)2h. After the reaction is completed, the reaction product is filtered with a sand core funnel, the filtrate is separated from the filter cake, and the filtrate is transferred to a rotary evaporator bottle for rotary evaporation (rotary evaporation temperature is 38°C, vacuum degree is -0.15Mpa) to obtain the second product. Lithium fluorophosphate 2.976g.

The prepared lithium difluorophosphate was characterized by XRD, as shown in Figure 3. It can be seen from Figures 1 to 3 that although the LiPO ₂ F ₂ synthesized in Comparative Example 4 and the LiPO ₂ F ₂ standard material and the LiPO ₂ F ₂ product synthesized in Example 1 have the same main peak position and peak intensity, the peak intensity is basically the same. There are three small impurity peaks around the main peak of lithium difluorophosphate synthesized in Ratio 4, which shows that it is not as pure as the LiPO ₂ F ₂ synthesized in Example 1 and has a single structure.

The prepared lithium difluorophosphate was subjected to nuclear magnetic characterization (BRUKER AVANCE III 400 superconducting nuclear magnetic resonance spectrometer (NMR)), as shown in Figure 5. As can be seen from Figures 4 and 5, there are four absorption peaks in the ¹⁹ F NMR spectrum of LiPO ₂ F ₂ in Comparative Example 4, indicating that the fluorine element in the LiPO ₂ F ₂ product structure has two chemical environments. The type is not single, and there are other impurities; as can be seen from Figure 4, there are two absorption peaks in the ¹⁹ F NMR spectrum of LiPO ₂ F ₂ , and no other impurity peaks appear, indicating that the fluorine element in the LiPO ₂ F ₂ product structure is only A chemical environment free of other impurities. And the corresponding chemical shifts δ are -79.3658ppm and 81.0441ppm corresponding to the two fluorine atoms in LiPO ₂ F ₂ . Therefore, the LiPO ₂ F ₂ prepared in Example 1 has a single structure and high purity.

Comparative example 5

The difference from Example 1 is that when preparing ammonium difluorophosphate, only ethylene glycol dimethyl ether is added, and other operating steps are exactly the same as Example 1. The specific process is as follows:

Weigh 9.17g of ammonium fluoride, 10g of phosphorus pentoxide, and 200g of ethylene glycol dimethyl ether, and add the above raw materials into a three-necked flask (in the three-necked flask, connect mechanical stirring directly above it, and the other two ports are connected to the thermometer sleeve and condenser tube). Place the three-necked flask in an oil bath heating pot and gradually heat it from room temperature to 85°C at a heating rate of 3°C/min. After reaching 85°C, the reaction is carried out at a constant temperature for 5 hours.

After the reaction is completed, the reaction product is suction-filtered using a sand core suction filtration device, and the filtrate is separated from the filter cake. The filter cake was purified with 300 mL of ethanol, and the magnetic stirring speed was 600 rpm for 1 hour. The above materials are suction filtered using a sand core funnel, and the filtrate is separated from the filter cake. The filtrate was transferred to a rotary evaporation bottle for rotary evaporation treatment (rotor evaporation temperature was 35°C, vacuum degree was -0.15Mpa) to obtain 0.526g of ammonium difluorophosphate.

In a glove box (anhydrous and oxygen-free), react the ammonium difluorophosphate obtained above with 0.112g of anhydrous lithium hydroxide in 300 mL of ethylene glycol dimethyl ether solution (use a magnetic stirrer to stir during the reaction, Rotation speed: 1000rpm)2h. After the reaction is completed, the reaction product is filtered with a sand core funnel, the filtrate is separated from the filter cake, and the filtrate is transferred to a rotary evaporator bottle for rotary evaporation (rotary evaporation temperature is 38°C, vacuum degree is -0.15Mpa) to obtain the second product. Lithium fluorophosphate 0.302g.

Performance Testing

The properties of the products prepared in Examples 1 to 4 and Comparative Examples 1 to 5 were tested. The specific test indicators were purity, moisture, acid value and yield. The specific results are shown in Table 1. The specific indicator test methods are as follows:

(1) Purity test: This experiment uses the external standard method of ion chromatography to conduct the purity test.

(2) Moisture test: Use a cassette furnace to heat the ammonium difluorophosphate sample to a certain temperature, use dry air to blow the evaporated water vapor into the Karl Fischer reagent in the reaction cup, and measure it using the Coulomb method.

(3) Acid value: Use a microburette, use bromothymol blue indicator, and titrate the free acid in the sample with sodium hydroxide standard titration solution.

(4) Yield: calculated based on the product results in the purity test and into the reaction equation.

Table 1 Performance test results

It can be seen from Table 1 that the methods provided in Examples 1-4 of the present application are better than those in Comparative Example 1 using acetonitrile alone. As a solvent, the yield is greatly improved. However, Comparative Example 2 uses N,N-dimethylformamide and Comparative Example 5 uses ethylene glycol dimethyl ether as a solvent. The yield of ammonium difluorophosphate is extremely low, resulting in the final The yield of lithium difluorophosphate is also lower. In Comparative Example 4, no solvent was added, and ammonium fluoride and phosphorus pentoxide were directly mixed for reaction. After white smoke was generated during the reaction, the system temperature soared to 200°C, which was extremely difficult to control. Therefore, along with the increase of the raw material ammonium fluoride, After decomposition, further phosphorus pentoxide reacts with moisture in the air at high temperatures to first generate a small amount of metaphosphoric acid, which is extremely toxic, and then quickly turns into phosphoric acid, so the reaction yield is low and the overall effect is poor. It can be concluded that the lithium difluorophosphate prepared by the method provided in Examples 1-4 of the present application has high purity, high yield, simple and easy operation, and is suitable for industrial production.

The above are only the preferred embodiments of the present application. It should be pointed out that for those of ordinary skill in the art, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications can also be made. should be regarded as the scope of protection of this application.

Claims

A method for preparing lithium difluorophosphate, which is characterized in that it includes the following steps:

1) Mix ammonium fluoride, phosphorus pentoxide and a polar aprotic organic system, raise the temperature to 80-90°C, and react to obtain ammonium difluorophosphate;

The polar aprotic organic system is a mixed solution of N,N-dimethylformamide and acetonitrile;

2) Mix the ammonium difluorophosphate and anhydrous lithium hydroxide with an organic solvent and react to obtain lithium difluorophosphate; the organic solvent is ethylene glycol dimethyl ether, dimethyl carbonate or ethyl acetate.
The preparation method according to claim 1, characterized in that, in terms of mass percentage, N,N-dimethylformamide in the polar aprotic organic system is 4% to 10%.
The preparation method according to claim 1, characterized in that the molar ratio of ammonium fluoride and phosphorus pentoxide in step 1) is (3.3~3.5):1; the mass of ammonium fluoride and polar aprotic organic system The ratio is 9:150~200.
The preparation method according to claim 1, characterized in that in step 1), a gradient heating method is used to raise the temperature to 80-90°C for reaction, and the rate of the gradient heating is 2.5-3.5°C/min; the reaction The time is 4 to 6 hours.
The preparation method according to claim 1, characterized in that, after the reaction in step 1) is completed, purification is also performed; the purification includes the following steps;

(1) Perform suction filtration of the reaction product obtained after the reaction is completed to obtain a filter cake;

(2) Mix the filter cake with ethanol, and filter the mixture to obtain a filtrate;

(3) Rotary evaporate the filtrate to obtain purified ammonium difluorophosphate.
The preparation method according to claim 1, characterized in that the molar ratio of ammonium difluorophosphate and anhydrous lithium hydroxide in step 2) is 1: (1.03~1.08).
The preparation method according to claim 1, characterized in that in step 2), the reaction temperature is 25-30°C and the reaction time is 1-3h.
The preparation method according to claim 1, characterized in that in step 2), stirring is performed during the reaction, and the stirring speed is 500 to 1000 rpm.
The preparation method according to claim 1, characterized in that, in step 2), the reaction is completed Finally, the reaction product is subjected to suction filtration and rotary evaporation in sequence. The temperature of the rotary evaporation is 35 to 45°C; the vacuum degree during the rotary evaporation is -0.1 to -0.2Mpa.
The lithium difluorophosphate prepared by the method of any one of claims 1 to 9 is characterized in that the acid value of the lithium difluorophosphate is 8 to 10 ppm and the purity is above 99.5%.