A process for the preparation of a difluorophosphate salt

Abstract

In order to overcome the problems of the existing preparation of lithium difluorophosphate, such as difficult control of reaction process, long process, low conversion rate and great difficulty in product purification, the present application provides a preparation method of lithium difluorophosphate, comprising the following operation steps: reacting hexafluorophosphate with carbon dioxide to obtain a reaction product containing lithium difluorophosphate under the catalysis of a fluorination reaction catalyst, and purifying to obtain lithium difluorophosphate. The preparation method of lithium difluorophosphate provided by the present application uses a fluorination reaction catalyst to promote the reaction of hexafluorophosphate and carbon dioxide, and at the same time guides the reaction to generate lithium difluorophosphate, thereby improving the reaction rate and conversion rate.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a method for preparing difluorophosphate. Background Technology

[0002] Difluorophosphate is primarily used as an additive in secondary battery electrolytes. Research data shows that adding difluorophosphate to secondary batteries can significantly improve their high-temperature cycle performance and high-temperature storage performance. Simultaneously, it can form a stable solid electrolyte interface film on the positive electrode surface, and by adjusting the composition of this interface film, the battery's safety, cycle performance, and lifespan can be improved.

[0003] Currently, the publicly disclosed methods for preparing lithium difluorophosphate mainly include:

[0004] 1. Synthesis using lithium hexafluorophosphate and silicon dioxide as raw materials has the disadvantage of slow reaction, long cycle, and difficulty in industrial application.

[0005] 2. Lithium difluorophosphate is synthesized using lithium hexafluorophosphate and lithium carbonate as raw materials and ultrapure water as a catalyst. This reaction has many side reactions, and the product contains impurities such as lithium monofluorophosphate, making purification difficult.

[0006] 3. Lithium difluorophosphate can be synthesized by reacting lithium hexafluorophosphate with siloxane-containing compounds, but the conversion rate of this method is currently low.

[0007] In summary, existing methods for preparing lithium difluorophosphate suffer from problems such as difficulty in controlling the reaction process, long process flow, low conversion rate, and difficulty in product purification, resulting in low purity of the obtained lithium difluorophosphate, which is difficult to meet the application requirements of battery-grade materials. Summary of the Invention

[0008] To address the problems of uncontrollable reaction process, long process, low conversion rate, and difficult product purification in existing lithium difluorophosphate preparation methods, this invention provides a method for preparing difluorophosphate.

[0009] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0010] This invention provides a method for preparing difluorophosphate, comprising the following steps:

[0011] Hexafluorophosphate was reacted with carbon dioxide under the catalysis of a fluorination catalyst to obtain a reaction product containing difluorophosphate, which was then purified to obtain difluorophosphate.

[0012] Optionally, the hexafluorophosphate includes lithium hexafluorophosphate and / or sodium hexafluorophosphate, and correspondingly, the obtained difluorophosphate includes lithium difluorophosphate and / or sodium difluorophosphate.

[0013] Optionally, the amount of carbon dioxide is 2.5 to 5 times that of the hexafluorophosphate.

[0014] Optionally, the fluorination reaction catalyst includes at least one of antimony trifluoride, boron trifluoride, aluminum trifluoride, bismuth trifluoride, antimony tetrafluoride, sulfuryl fluoride, sulfur tetrafluoride, phosphorus fluoride, phosphorus pentafluoride, antimony pentafluoride, triethylamine-HF complex, tripropylamine-HF complex, tetrabutylammonium fluoride, pyridine-HF complex, or equivalents, wherein the equivalents include at least one of precursors, complex salts, hydrates, solvent complexes, and hydrogen halide complexes, and the amount of the fluorination reaction catalyst added is 0.01% to 10% of the total mass of the reaction system.

[0015] Optionally, the reaction temperature of hexafluorophosphate with carbon dioxide is 115℃~150℃, and the reaction time is 12h~24h.

[0016] Optionally, the reaction of hexafluorophosphate with carbon dioxide can be carried out in an organic polar solvent.

[0017] Optionally, the organic polar solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, chloroform, ethyl formate, methyl tert-butyl ether, diethyl carbonate, propylene carbonate, ethyl isopropyl carbonate, ethylene carbonate, methyl isobutyl ketone, diethylene glycol dimethyl ether, isopropyl acetone, butyl acetate, cyclohexanone, methyl cyclohexanone, amyl acetate, sec-butyl acetate, isobutyl acetate, and butyl butyrate.

[0018] Optionally, the reaction is carried out in a protective gas, and the reaction system is pressurized to 5-7 MPa.

[0019] Optionally, the purification operation is as follows: the reaction product is cooled to crystallize out crude difluorophosphate, filtered, and then recrystallized using an organic polar solvent to obtain difluorophosphate.

[0020] Optionally, during the reaction, the generated gas is collected and cooled to liquefy and separate the carbonyl fluoride.

[0021] According to the preparation method of difluorophosphate provided by the present invention, hexafluorophosphate is used as a reactant to react with carbon dioxide. The reactant carbon dioxide is a gas, and the carbonyl fluoride produced is also a gas. Therefore, this reaction system can easily separate unreacted reactant gases or product gases, reducing the difficulty of purifying the generated difluorophosphate and improving the purity of the obtained difluorophosphate. It should be noted that under normal conditions, the reaction rate of hexafluorophosphate with carbon dioxide is extremely low. Through extensive experiments, the inventors discovered that using a fluorination catalyst can significantly increase the reaction rate of hexafluorophosphate and carbon dioxide, while simultaneously guiding the reaction towards the formation of difluorophosphate, thus improving the reaction rate and conversion rate. Compared with existing preparation methods, the preparation method provided by the present invention has the characteristics of fewer side reactions, a shorter reaction process, and a higher reaction conversion rate. This also contributes to improving the purity of difluorophosphate, meeting the requirements of battery-grade applications, and reducing the difficulty of large-scale production of difluorophosphate, thus facilitating the mass production of difluorophosphate. Detailed Implementation

[0022] To make the technical problems solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0023] This invention provides a method for preparing difluorophosphate, comprising the following steps:

[0024] Hexafluorophosphate was reacted with carbon dioxide under the catalysis of a fluorination catalyst to obtain a reaction product containing difluorophosphate, which was then purified to obtain difluorophosphate.

[0025] The method for preparing difluorophosphate uses hexafluorophosphate as a reactant to react with carbon dioxide. Carbon dioxide is a gas, and the carbonyl fluoride produced is also a gas. This reaction system allows for easy separation of unreacted reactant gases or product gases, reducing the difficulty of purifying the resulting difluorophosphate and improving its purity. It should be noted that under normal conditions, the reaction rate between hexafluorophosphate and carbon dioxide is extremely low. Through extensive experimentation, the inventors discovered that using a fluorination catalyst can significantly increase the reaction rate between hexafluorophosphate and carbon dioxide, while simultaneously guiding the reaction towards the formation of difluorophosphate, thus improving the reaction rate and conversion rate. Compared to existing preparation methods, the method provided by this invention features fewer side reactions, a shorter reaction process, and a higher conversion rate. This also contributes to improving the purity of difluorophosphate, meeting the requirements for battery-grade applications, and reducing the difficulty of large-scale production of difluorophosphate, facilitating its mass production.

[0026] In some embodiments, the hexafluorophosphate includes lithium hexafluorophosphate and / or sodium hexafluorophosphate, and correspondingly, the resulting difluorophosphate includes lithium difluorophosphate and / or sodium difluorophosphate.

[0027] The chemical equation for the reaction in the preparation of lithium difluorophosphate is:

[0028] LiPF6 + 2CO2 = LiPO2F2 + 2COF2↑

[0029] The chemical equation for the reaction in the preparation of sodium difluorophosphate is:

[0030] NaPF6 + 2CO2 = NaPO2F2 + 2COF2↑

[0031] In some embodiments, the amount of carbon dioxide is 2.5 to 5 times that of hexafluorophosphate.

[0032] As shown in the above reaction equations, the amount of carbon dioxide added should be at least twice the equivalent of the hexafluorophosphate to ensure complete reaction and conversion of the hexafluorophosphate. In practice, to ensure sufficient reaction of the hexafluorophosphate and avoid residual hexafluorophosphate in the reaction products, the amount of carbon dioxide added can be appropriately increased. When the amount of carbon dioxide added is insufficient, unreacted hexafluorophosphate is likely to remain in the reaction system; while when the amount of carbon dioxide added is too high, although it is beneficial to the complete conversion of hexafluorophosphate, the material cost of the consumed carbon dioxide is relatively high.

[0033] In some embodiments, the fluorination reaction catalyst includes at least one of antimony trifluoride, boron trifluoride, aluminum trifluoride, bismuth trifluoride, antimony tetrafluoride, thioyl fluoride, sulfur tetrafluoride, phosphorus fluoride, phosphorus pentafluoride, antimony pentafluoride, triethylamine-HF complex, tripropylamine-HF complex, tetrabutylammonium fluoride, pyridine-HF complex, or equivalents, wherein the equivalents include at least one of precursors, complex salts, hydrates, solvent complexes, and hydrogen halide complexes.

[0034] In some embodiments, the amount of the fluorination reaction catalyst added is 0.01% to 10% of the total mass of the reaction system.

[0035] In specific embodiments, the amount of the fluorination reaction catalyst added can be 0.1%, 1%, 3%, or 6% of the total mass of the reaction system.

[0036] The fluorination catalyst is a key catalyst for promoting the reaction between hexafluorophosphate and carbon dioxide. When the amount of the fluorination catalyst added is too low, the reaction rate of hexafluorophosphate with carbon dioxide is low; when the amount of the fluorination catalyst added is too high, the purification difficulty of the generated difluorophosphate will increase due to the solubility of the fluorination catalyst in organic polar solvents.

[0037] In some embodiments, the reaction temperature of hexafluorophosphate with carbon dioxide is 115°C to 150°C, and the reaction time is 12h to 24h.

[0038] Increasing the reaction temperature promotes the reaction between hexafluorophosphate and carbon dioxide. According to the reaction process measurements, the reaction is endothermic, requiring approximately 60 kJ of heat to react per mole of lithium hexafluorophosphate. Heating with an external heat source can ensure the reaction between hexafluorophosphate and carbon dioxide proceeds. If the reaction temperature is too low, the reaction rate between hexafluorophosphate and carbon dioxide will be affected; if the reaction temperature is too high, side reactions are likely to occur, which is detrimental to improving the yield and purity of difluorophosphate.

[0039] In some embodiments, the reaction of hexafluorophosphate with carbon dioxide is carried out in an organic polar solvent.

[0040] The hexafluorophosphate is readily soluble in organic polar solvents, which can fully disperse the hexafluorophosphate, thereby increasing the reaction contact area between the hexafluorophosphate and carbon dioxide gas, improving reaction efficiency and conversion rate. On the other hand, the selection of a suitable organic polar solvent can inhibit side reactions to a certain extent.

[0041] In some preferred embodiments, the organic polar solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, chloroform, ethyl formate, methyl tert-butyl ether, diethyl carbonate, propylene carbonate, ethyl isopropyl carbonate, ethylene carbonate, methyl isobutyl ketone, diethylene glycol dimethyl ether, isopropyl acetone, butyl acetate, cyclohexanone, methyl cyclohexanone, amyl acetate, sec-butyl acetate, isobutyl acetate, and butyl butyrate.

[0042] The above-mentioned organic polar solvents have high solubility for hexafluorophosphate and good stability, which can promote the forward reaction.

[0043] The moisture content of the organic polar solvent should be controlled to below 20 ppm.

[0044] In some embodiments, the reaction is carried out in a protective gas, and the reaction system is pressurized to 5-7 MPa.

[0045] Due to the inherent instability of hexafluorophosphate and difluorophosphate, placing the reaction in a protective gas atmosphere can effectively prevent the influence of water vapor and oxygen in the air on the reaction itself. At the same time, the water content of the organic polar solvent used must also be controlled.

[0046] The protective gas is selected from gases that do not participate in the reaction, such as nitrogen and argon.

[0047] In the reaction system of the present invention, the reaction between hexafluorophosphate and carbon dioxide can be promoted by appropriately increasing the pressure. Specifically, as the pressure increases, the reaction rate between hexafluorophosphate and carbon dioxide gradually increases. Therefore, increasing the pressure is beneficial for the reaction to proceed.

[0048] In a specific embodiment, a dehydrated organic polar solvent is placed in a reactor under protective gas conditions. The gas in the reactor is replaced three times with a protective gas containing less than 10 ppm of water. The reactor and the organic polar solvent in it are cooled to 10°C or below. Hexafluorophosphate is added and stirred to dissolve. Then, a fluorination reaction catalyst is added. The reactor is heated to 115°C to 150°C, and then carbon dioxide gas is introduced to carry out the reaction.

[0049] In some embodiments, the purification operation is as follows: the reaction product is cooled to crystallize the crude difluorophosphate, filtered, and then recrystallized using an organic polar solvent to obtain difluorophosphate.

[0050] The purity of the difluorophosphate can be effectively improved by cooling crystallization and recrystallization.

[0051] In some embodiments, during the reaction, the gas generated is collected and cooled to liquefy and separate the carbonyl fluoride contained therein.

[0052] Since the boiling points of the carbonyl fluoride produced in the reaction are significantly different from those of carbon dioxide gas, the carbonyl fluoride can be fully separated from the carbon dioxide gas by simple cooling. Carbonyl fluoride itself is an important chemical raw material. The method for preparing difluorophosphate provided by this invention can achieve the co-production of difluorophosphate and carbonyl fluoride, and the separated carbon dioxide gas can be used as a reaction raw material, thereby realizing the reuse of materials.

[0053] The present invention will be further illustrated by the following examples.

[0054] Example 1

[0055] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0056] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0057] Example 2

[0058] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0059] 1500 ml of propylene carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and propylene carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of propylene carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0060] Example 3

[0061] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0062] 1500 ml of methyl isobutyl ketone (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and methyl isobutyl ketone were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was then recrystallized again with an equal amount of methyl isobutyl ketone, and the crystals were vacuum dried to obtain pure lithium difluorophosphate.

[0063] Example 4

[0064] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0065] 1500 ml of propylene carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and propylene carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 140°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was then recrystallized again with an equal amount of propylene carbonate, and the crystals were vacuum dried to obtain pure lithium difluorophosphate.

[0066] Example 5

[0067] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0068] 1500 ml of propylene carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and propylene carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 150°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was then recrystallized again with an equal amount of propylene carbonate, and the crystals were vacuum dried to obtain pure lithium difluorophosphate.

[0069] Example 6

[0070] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0071] 1500 ml of propylene carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and propylene carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 132 g (3 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of propylene carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0072] Example 7

[0073] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0074] 1500 ml of propylene carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and propylene carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 220 g (5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was then recrystallized again with an equal amount of propylene carbonate, and the crystals were vacuum dried to obtain pure lithium difluorophosphate.

[0075] Example 8

[0076] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0077] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 7 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0078] Example 9

[0079] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0080] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 0.15 g (0.1%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was then recrystallized again with an equal amount of diethyl carbonate, and the crystals were vacuum dried to obtain pure lithium difluorophosphate.

[0081] Example 10

[0082] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0083] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 1.53 g (1%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0084] Example 11

[0085] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0086] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 9.2 g (6%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0087] Example 12

[0088] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0089] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of aluminum trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0090] Example 13

[0091] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0092] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of bismuth trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0093] Example 14

[0094] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0095] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 80°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0096] Example 15

[0097] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0098] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 180°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0099] Example 16

[0100] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0101] Add 1500 ml of toluene (moisture content <20 ppm) to the reactor. After purging the reactor three times with inert gas, cool the reactor and toluene to -5°C. Then add 151.9 g (1 mol) of lithium hexafluorophosphate and stir until dissolved. Add 4.6 g (3%) of antimony trifluoride catalyst. Heat the reactor to 120°C and introduce 110 g (2.5 mol) of carbon dioxide gas, adjusting the pressure to 5 MPa. React for 12 h. Transfer the reactor to a glove box and cool to 5°C. Separate the liquid and solid phases by filtration. Take the solid phase and recrystallize it again with an equal amount of toluene. Then dry the crystals under vacuum to obtain pure lithium difluorophosphate.

[0102] Example 17

[0103] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0104] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 66 g (1.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0105] Example 18

[0106] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0107] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 0.5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0108] Example 19

[0109] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0110] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 2 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0111] Example 20

[0112] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0113] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 23 g (15%) of antimony trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0114] Example 21

[0115] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0116] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of boron trifluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0117] Example 22

[0118] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0119] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of sulfuryl fluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0120] Example 23

[0121] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0122] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of tetrabutylammonium fluoride catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0123] Example 24

[0124] This embodiment illustrates a method for preparing difluorophosphate disclosed in this invention, including the following steps:

[0125] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. Next, 4.6 g (3%) of pyridine-HF complex catalyst was added. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain pure lithium difluorophosphate.

[0126] Comparative Example 1

[0127] This comparative example is used to illustrate the preparation method of difluorophosphate disclosed in this invention, which includes the following steps:

[0128] 1500 ml of diethyl carbonate (moisture content <20 ppm) was added to the reactor. After purging the reactor three times with inert gas, the reactor and diethyl carbonate were cooled to -5°C. Then, 151.9 g (1 mol) of lithium hexafluorophosphate was added and stirred until dissolved. The reactor was heated to 120°C, and 110 g (2.5 mol) of carbon dioxide gas was introduced, adjusting the pressure to 5 MPa. The reaction was carried out for 12 h. The reactor was then transferred to a glove box and cooled to 5°C. The liquid and solid phases were separated by filtration. The solid phase was recrystallized again with an equal amount of diethyl carbonate, and the crystals were then vacuum dried to obtain lithium difluorophosphate.

[0129] Performance testing

[0130] The liquid phase obtained after filtration was subjected to color and turbidity analysis. The purity and impurities of the prepared lithium difluorophosphate were detected, and the yield was calculated. The test results are recorded in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] As can be seen from the test results in Table 1, the preparation method provided by this invention can convert lithium hexafluorophosphate to lithium difluorophosphate in high yield. The gas pressure, reaction temperature, solvent selection, catalyst dosage, and catalyst type all affect the reaction results. The lithium difluorophosphate obtained by this method also has high purity. This preparation method is simple to operate and suitable for large-scale production.

[0135] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing difluorophosphate, characterized in that, The following steps are included: Hexafluorophosphate was reacted with carbon dioxide in an organic polar solvent under the catalysis of a fluorination catalyst to obtain a reaction product containing difluorophosphate. The reaction temperature of hexafluorophosphate with carbon dioxide was 115℃~150℃ and the reaction time was 12h~24h. Difluorophosphate was then purified. The hexafluorophosphate includes lithium hexafluorophosphate and / or sodium hexafluorophosphate, and correspondingly, the obtained difluorophosphate includes lithium difluorophosphate and / or sodium difluorophosphate. The amount of carbon dioxide is 2.5 to 5 times that of hexafluorophosphate; The fluorination reaction catalyst includes at least one of antimony trifluoride, boron trifluoride, aluminum trifluoride, bismuth trifluoride, antimony tetrafluoride, thioyl fluoride, antimony pentafluoride, triethylamine-HF complex, tripropylamine-HF complex, tetrabutylammonium fluoride, pyridine-HF complex, or equivalents, wherein the equivalents include at least one of complex salts, hydrates, and solvent complexes, and the amount of catalyst added is 0.01% to 10% of the total mass of the reaction system.

2. The method for preparing difluorophosphate according to claim 1, characterized in that, The organic polar solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, chloroform, ethyl formate, methyl tert-butyl ether, diethyl carbonate, propylene carbonate, ethyl isopropyl carbonate, ethylene carbonate, methyl isobutyl ketone, diethylene glycol dimethyl ether, isopropyl acetone, butyl acetate, cyclohexanone, methyl cyclohexanone, amyl acetate, sec-butyl acetate, isobutyl acetate, and butyl butyrate.

3. The method for preparing difluorophosphate according to claim 1, characterized in that, The reaction is carried out in a protective gas atmosphere, and the reaction system is pressurized to 5-7 MPa.

4. The method for preparing difluorophosphate according to claim 1, characterized in that, The purification process involves cooling the reaction product to allow crude difluorophosphate to crystallize out. After filtration, recrystallization is performed using an organic polar solvent to obtain difluorophosphate.

5. The method for preparing difluorophosphate according to claim 1, characterized in that, During the reaction, the generated gas is collected and cooled to liquefy and separate the carbonyl fluoride.

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