A preparation method of sodium difluorophosphate

Abstract

The invention relates to the field of fine chemicals, and in particular to a method for preparing sodium difluorophosphate. The method adopts sodium carbonate, difluorophosphoric acid, a solvent, and a desiccant, and carries out reaction, filtration, and purification to obtain the sodium difluorophosphate. In the method, the difluorophosphoric acid is firstly purified by adsorption with a silsesquioxane adsorption resin, and the purity after purification is as high as 99.5%. The desiccant uses a NaA molecular sieve, and the NaA molecular sieve is prepared by adopting SiO2, Al2O3, sodium hydroxide, deionization, aging, microwave nucleation, and crystallization. The NaA molecular sieve prepared by the method has good performance and a large static water absorption capacity. The method for preparing the sodium difluorophosphate of the invention has a simple process, low equipment investment, low reaction temperature, easy separation, and high product purity.

Description

Technical Field

[0001] The present invention relates to the field of fine chemicals, in particular to a method for preparing sodium difluorophosphate. Background Art

[0002] In recent years, the rapid development of smart devices such as mobile phones and tablets has led to a rapid increase in the market share of small lithium batteries. Furthermore, with the increasing sophistication of electric vehicle technology, market demand for large lithium batteries is also gradually increasing. The lithium battery market is expected to maintain its growth trend in the coming years. Most lithium batteries are secondary batteries, which suffer from technical difficulties such as poor stability, low-temperature resistance, and poor cycling characteristics. Lithium difluorophosphate as an electrolyte can effectively address these shortcomings.

[0003] Because sodium difluorophosphate has similar chemical properties to lithium difluorophosphate, it is expected to become an ideal electrolyte additive.

[0004] CN202180016949.9: relates to the synthesis and evaluation of difluorophosphate additives for use in energy storage devices. The difluorophosphate additive can be selected from the group consisting of lithium difluorophosphate (LFO), sodium difluorophosphate (NaFO), ammonium difluorophosphate (AFO), tetramethylammonium difluorophosphate (MAFO), potassium difluorophosphate (KFO), and combinations thereof. In some cases, the difluorophosphate additive is not lithium difluorophosphate (LFO).

[0005] CN202110947056.8: Provided is an electrolyte for a lithium-ion battery and a formation method thereof, the electrolyte comprising: a mixture of a cyclic carbonate and a chain carbonate in a volume ratio of 3-4:1 as an organic solvent, an electrolyte salt, and an additive, the additive being vinylene carbonate, sodium difluorophosphate, methyl vinyl sulfone and 1-methyl-2-piperidone; wherein the mass ratio of the above four additives is vinylene carbonate: sodium difluorophosphate: methyl vinyl sulfone: 1-methyl-2-piperidone = 20-22: 1-1.2: 16-20: 8-10; and further, a formation method using the electrolyte is provided, comprising: charging the battery after injection with a constant current to a predetermined voltage, then charging with a constant voltage at a predetermined voltage, heating and aging for a predetermined time, and then cycling the battery with a constant current between the charge cut-off voltage and the discharge cut-off voltage for several times. Due to the synergistic effect between the additives, the electrolyte of the present invention can limit the growth of the internal resistance of the battery while improving the battery cycle performance, thereby improving the rate performance.

[0006] CN202111501459.6: A wide-temperature sodium ion battery electrolyte is disclosed, comprising an organic solvent, a sodium salt and a functional additive; the functional additive comprises one or more of tris(trimethylsilyl)phosphate, N,N-dimethyltrifluoroacetamide, fluoroethylene carbonate, vinyl sulfate, and sodium difluorophosphate. The beneficial effects of the present invention are as follows: tris(trimethylsilyl)phosphate is used in the functional additive, which can be adsorbed on the surface of the material in preference to the solvent at high temperature, and catalytically decomposes on the surface of the excess ion at high potential to generate a higher concentration of organic decomposition products, thereby preventing the continuous oxidative decomposition of the electrolyte and the dissolution of transition metal ions caused by the corrosion of the material by HF in the electrolyte, reducing the interfacial impedance and thus improving the high-temperature cycle performance of the battery; using N,N-dimethyltrifluoroacetamide in the functional additive can provide better oxidative stability protection for the positive electrode material at low temperatures, and can improve the capacity retention rate at low temperatures.

[0007] However, the yield of sodium difluorophosphate prepared by the above patents and prior art is only 10-20%, and more by-products are produced. Summary of the Invention

[0008] In view of the above-mentioned deficiencies in the prior art, in order to improve the yield and purity of sodium difluorophosphate products, the present invention provides a method for preparing sodium difluorophosphate.

[0009] The technical solutions of the present invention are as follows:

[0010] The first aspect of the present invention provides a method for preparing sodium difluorophosphate:

[0011] By weight, 120-140 parts of sodium carbonate, 200-220 parts of difluorophosphoric acid, 1000-1200 parts of solvent, and 20-30 parts of desiccant are added to a sealed polytetrafluoroethylene crystallization kettle, nitrogen is introduced, the temperature is raised to 40-60°C, and the mixture is stirred for 1-3 hours. After the reaction is completed, the mixture is filtered and purified to obtain sodium difluorophosphate. The reaction equation is as follows:

[0012]

[0013] In some embodiments, the solvent is selected from one or more of dimethyl sulfoxide, ethylene glycol dimethyl ether, 1,3-dioxolane, and polyethylene glycol dimethyl ether.

[0014] In some embodiments, the desiccant is selected from one or more of a silica gel desiccant and a molecular sieve desiccant.

[0015] In some embodiments, the molecular sieve desiccant is selected from NaA molecular sieve.

[0016] In a second aspect of the present invention, a method for preparing NaA molecular sieve is provided:

[0017] According to weight, 20-40 parts of SiO2 and 15-20 parts of Al2O3, 12-18 parts of sodium hydroxide, and 65-80 parts of deionized water are weighed as raw materials, vigorously stirred at room temperature, and aged for 1-4 hours to obtain a uniform synthetic liquid, and then the synthetic liquid is charged into a reactor and placed in a microwave oven for low-power nucleation and high-power crystallization. The obtained product is washed with 100-200 parts of deionized water until neutral, and dried to obtain NaA molecular sieve.

[0018] In some embodiments, the nucleation power is 200-300 W, and the time is 10-20 min.

[0019] In some embodiments, the crystallization power is 600-800 W, and the time is 30-60 min.

[0020] In some embodiments, the drying temperature is 40-50° C. and the drying time is 5-8 hours.

[0021] In some embodiments, the difluorophosphoric acid is first purified by adsorption on a silsesquioxane adsorption resin by:

[0022] S1: Amination reaction: Add 100-150 parts by weight of macroporous chloromethyl polystyrene balls, 50-100 parts of hexamethylenetetramine, and 500-1000 parts of water to a stirred tank, heat to 60-70°C for reaction, keep warm for 3-6 hours, filter, and vacuum dry to obtain a primary amino resin:

[0023] S2: By weight, 500-1000 parts of toluene, 46-100 parts of primary amino resin, 0.2-2.5 parts of 1,1-diaminoferrocene, and 1-4 parts of triethanolamine are added to a reaction kettle, nitrogen is introduced, and the mixture is stirred at 60-70°C for 2-5 hours. Then, 10-20 parts of acrylic silsesquioxane are added, the mixture is stirred at 60-70°C for 1-3 hours, filtered, washed with water until neutral, and dried to obtain the silsesquioxane adsorption resin.

[0024] In some embodiments, the silsesquioxane adsorption resin is filled in the adsorption column, and the filling amount is 30-40% of the volume percentage of the adsorption column.

[0025] In some embodiments, the difluorophosphoric acid flows through the adsorption column at a rate of 1-30 BV / h.

[0026] Reaction mechanism:

[0027] An addition reaction occurs between the primary amino resin, acrylic silsesquioxane, and 1,1-diaminoferrocene, and functional groups such as silsesquioxane and ferrocene are loaded onto the surface of the carbazole-based adsorption resin. The adsorption resin forms a complex with metal impurities in difluorophosphoric acid, thereby improving the purity of the difluorophosphoric acid and obtaining high-purity sodium difluorophosphate.

[0028] Technical effects:

[0029] The preparation method of sodium difluorophosphate of the present invention has the following significant effects compared with the prior art:

[0030] 1. In the present invention, difluorophosphoric acid is first purified by adsorption with silsesquioxane adsorption resin, and the purity after purification is as high as 99.5%;

[0031] 2. The NaA molecular sieve prepared by the present invention has good performance and large static water absorption capacity;

[0032] 3. The preparation method of sodium difluorophosphate of the present invention has simple process, low equipment investment, low reaction temperature, easy separation and high product purity. DETAILED DESCRIPTION

[0033] The present invention provides a polymer electrolyte, a preparation method thereof, and a secondary battery. To make the objectives, technical solutions, and effects of the present invention more clear and explicit, the present invention is further described below in detail. 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.

[0034] Example 1

[0035] A preparation method of sodium difluorophosphate, the operating steps of which are:

[0036] 120g of sodium carbonate, 200g of difluorophosphoric acid, 1000g of solvent, and 20g of desiccant were added to a sealed polytetrafluoroethylene crystallization kettle, nitrogen was introduced, the temperature was raised to 40°C, and the mixture was stirred for 1h. After the reaction was completed, sodium difluorophosphate was obtained by filtration and purification. The reaction equation is as follows:

[0037]

[0038] The solvent is dimethyl sulfoxide.

[0039] The desiccant is NaA molecular sieve, and the preparation method is:

[0040] Weigh 20g SiO2, 15g Al2O3, 12g sodium hydroxide, and 65g deionized water as raw materials, stir vigorously at room temperature, and age for 1h to obtain a uniform synthetic liquid. Then, the synthetic liquid is charged into a reactor and placed in a microwave oven for low-power nucleation and high-power crystallization. The obtained product is deionized with 100g water, washed with water until neutral, and dried to obtain NaA molecular sieve.

[0041] The nucleation power is 200W and the time is 10 minutes.

[0042] The crystallization power is 600W and the time is 30 minutes.

[0043] The drying temperature is 40° C. and the drying time is 5 hours.

[0044] The difluorophosphoric acid is first purified by adsorption with a silsesquioxane adsorption resin by the following method:

[0045] S1: Amination reaction: Add 100g macroporous chloromethyl polystyrene balls, 50g hexamethylenetetramine, and 500g water into a stirred tank, heat to 60°C for reaction, keep warm for 3h, filter, and vacuum dry to obtain a primary amino resin:

[0046] S2: 500 g of toluene, 46 g of primary amino resin, 0.2 g of 1,1-diaminoferrocene, and 1 g of triethanolamine were added to a reactor, nitrogen was introduced, and the mixture was stirred at 60° C. for 2 hours. Then, 10 g of acrylic silsesquioxane was added, and the mixture was stirred at 60° C. for 1 hour. The mixture was filtered, washed with water until neutral, and dried to obtain the silsesquioxane adsorption resin.

[0047] The silsesquioxane adsorption resin is filled in the adsorption column, and the filling amount is 30% of the volume percentage of the adsorption column.

[0048] The difluorophosphoric acid flows through the adsorption column at a speed of 1 BV / h.

[0049] Example 2

[0050] A preparation method of sodium difluorophosphate, the operating steps of which are:

[0051] 125g of sodium carbonate, 205g of difluorophosphoric acid, 1050g of solvent, and 24g of desiccant were added to a sealed polytetrafluoroethylene crystallization kettle, nitrogen was introduced, the temperature was raised to 45°C, and the mixture was stirred for 2h. After the reaction was completed, sodium difluorophosphate was obtained by filtration and purification. The reaction equation is as follows:

[0052]

[0053] The solvent is ethylene glycol dimethyl ether.

[0054] The desiccant is selected from NaA molecular sieve, and the preparation method is:

[0055] Weigh 25g SiO2, 16g Al2O3, 14g sodium hydroxide and 70g deionized water as raw materials, stir vigorously at room temperature and age for 2h to obtain a uniform synthetic liquid. Then, put the synthetic liquid into a reactor and place it in a microwave oven for low-power nucleation and high-power crystallization. The obtained product is deionized with 140g, washed with water until neutral, and dried to obtain NaA molecular sieve.

[0056] The nucleation power is 250W and the time is 15 minutes.

[0057] The crystallization power is 650W and the time is 40 minutes.

[0058] The drying temperature is 45° C. and the drying time is 6 hours.

[0059] The difluorophosphoric acid is first purified by adsorption with a silsesquioxane adsorption resin by the following method:

[0060] S1: Amination reaction: Add 110g of macroporous chloromethyl polystyrene balls, 60g of hexamethylenetetramine, and 600g of water to a stirred tank, heat to 65°C for reaction, keep warm for 4h, filter, and vacuum dry to obtain a primary amino resin:

[0061] S2: 600 g of toluene, 60 g of primary amino resin, 1 g of 1,1-diaminoferrocene, and 2 g of triethanolamine were added to a reactor, nitrogen was introduced, and the mixture was stirred at 65° C. for 3 hours. Then, 14 g of acrylic silsesquioxane was added, the mixture was stirred at 65° C. for 2 hours, filtered, washed with water until neutral, and dried to obtain the silsesquioxane adsorption resin.

[0062] The silsesquioxane adsorption resin is filled in the adsorption column, and the filling amount is 35% of the volume percentage of the adsorption column.

[0063] The difluorophosphoric acid flows through the adsorption column at a speed of 10 BV / h.

[0064] Example 3

[0065] A preparation method of sodium difluorophosphate, the operating steps of which are:

[0066] 135g of sodium carbonate, 215g of difluorophosphoric acid, 1150g of solvent, and 28g of desiccant were added to a sealed polytetrafluoroethylene crystallization kettle, nitrogen was introduced, the temperature was raised to 55°C, and the mixture was stirred for 2h. After the reaction was completed, sodium difluorophosphate was obtained by filtration and purification. The reaction equation is as follows:

[0067]

[0068] The solvent is 1,3-dioxolane.

[0069] The desiccant is selected from NaA molecular sieve, and the preparation method is:

[0070] Weigh 35g SiO2, 18g Al2O3, 16g sodium hydroxide, and 75g deionized water as raw materials, stir vigorously at room temperature, and age for 3h to obtain a uniform synthetic liquid. Then, the synthetic liquid is charged into a reactor and placed in a microwave oven for low-power nucleation and high-power crystallization. The obtained product is deionized with 180g, washed with water until neutral, and dried to obtain NaA molecular sieve.

[0071] The nucleation power is 250W and the time is 18 minutes.

[0072] The crystallization power is 750W and the time is 50 minutes.

[0073] The drying temperature is 45° C. and the drying time is 7 hours.

[0074] The difluorophosphoric acid is first purified by adsorption with a silsesquioxane adsorption resin by the following method:

[0075] S1: Amination reaction: Add 140g of macroporous chloromethyl polystyrene balls, 90g of hexamethylenetetramine, and 900g of water to a stirred tank, heat to 65°C for reaction, keep warm for 5h, filter, and vacuum dry to obtain a primary amino resin:

[0076] S2: 900 g of toluene, 90 g of primary amino resin, 2 g of 1,1-diaminoferrocene, and 3 g of triethanolamine were added to a reactor, nitrogen was introduced, and the mixture was stirred at 65° C. for 4 hours. Then, 18 g of acrylic silsesquioxane was added, and the mixture was stirred at 65° C. for 2 hours. The mixture was filtered, washed with water until neutral, and dried to obtain the silsesquioxane adsorption resin.

[0077] The silsesquioxane adsorption resin is filled in the adsorption column, and the filling amount is 35% of the volume percentage of the adsorption column.

[0078] The difluorophosphoric acid flows through the adsorption column at a speed of 20 BV / h.

[0079] Example 4

[0080] A preparation method of sodium difluorophosphate, the operating steps of which are:

[0081] 140g of sodium carbonate, 220g of difluorophosphoric acid, 1200g of solvent, and 30g of desiccant were added to a sealed polytetrafluoroethylene crystallization kettle, nitrogen was introduced, the temperature was raised to 60°C, and the mixture was stirred for 3h. After the reaction was completed, sodium difluorophosphate was obtained by filtration and purification. The reaction equation is as follows:

[0082]

[0083] The solvent is polyethylene glycol dimethyl ether.

[0084] The desiccant is selected from NaA molecular sieve, and the preparation method is:

[0085] Weigh 40g SiO2, 20g Al2O3, 18g sodium hydroxide and 80g deionized water as raw materials, stir vigorously at room temperature and age for 4h to obtain a uniform synthetic liquid, then put the synthetic liquid into a reactor and place it in a microwave oven for low-power nucleation and high-power crystallization. The obtained product is deionized with 200g water, washed with water until neutral, and dried to obtain NaA molecular sieve.

[0086] The nucleation power is 300W and the time is 20 minutes.

[0087] The crystallization power is 800W and the time is 60 minutes.

[0088] The drying temperature is 50° C. and the drying time is 8 hours.

[0089] The difluorophosphoric acid is first purified by adsorption with a silsesquioxane adsorption resin by the following method:

[0090] S1: Amination reaction: Add 150g macroporous chloromethyl polystyrene balls, 100g hexamethylenetetramine, and 1000g water into a stirred tank, heat to 70°C for reaction, keep warm for 6h, filter, and vacuum dry to obtain a primary amino resin:

[0091] S2: 1000 g of toluene, 100 g of primary amino resin, 2.5 g of 1,1-diaminoferrocene, and 4 g of triethanolamine were added to a reactor, nitrogen was introduced, and the mixture was stirred at 70° C. for 5 hours. Then, 20 g of acrylic silsesquioxane was added, and the mixture was stirred at 70° C. for 3 hours. The mixture was filtered, washed with water until neutral, and dried to obtain the silsesquioxane adsorption resin.

[0092] The silsesquioxane adsorption resin is filled in the adsorption column, and the filling amount is 40% of the volume percentage of the adsorption column.

[0093] The difluorophosphoric acid flows through the adsorption column at a speed of 30 BV / h.

[0094] Comparative Example 1

[0095] A preparation method of sodium difluorophosphate, the operating steps of which are:

[0096] 120g of sodium carbonate, 200g of difluorophosphoric acid, 1000g of solvent, and 20g of desiccant were added to a sealed polytetrafluoroethylene crystallization kettle, nitrogen was introduced, the temperature was raised to 40°C, and the mixture was stirred for 1h. After the reaction was completed, sodium difluorophosphate was obtained by filtration and purification. The reaction equation is as follows:

[0097]

[0098] The solvent is dimethyl sulfoxide.

[0099] The desiccant is NaA molecular sieve, and the preparation method is:

[0100] Weigh 20g SiO2, 15g Al2O3, 12g sodium hydroxide, and 65g deionized water as raw materials, stir vigorously at room temperature, and age for 1h to obtain a uniform synthetic liquid. Then, the synthetic liquid is charged into a reactor and placed in a microwave oven for low-power nucleation and high-power crystallization. The obtained product is deionized with 100g water, washed with water until neutral, and dried to obtain NaA molecular sieve.

[0101] The nucleation power is 200W and the time is 10 minutes.

[0102] The crystallization power is 600W and the time is 30 minutes.

[0103] The drying temperature is 40° C. and the drying time is 5 hours.

[0104] Comparative Example 2

[0105] A preparation method of sodium difluorophosphate, the operating steps of which are:

[0106] 120g of sodium carbonate, 200g of difluorophosphoric acid, 1000g of solvent, and 20g of desiccant were added to a sealed polytetrafluoroethylene crystallization kettle, nitrogen was introduced, the temperature was raised to 40°C, and the mixture was stirred for 1h. After the reaction was completed, sodium difluorophosphate was obtained by filtration and purification. The reaction equation is as follows:

[0107]

[0108] The solvent is dimethyl sulfoxide.

[0109] The desiccant is NaA molecular sieve, and the preparation method is:

[0110] Weigh 15g of Al2O3, 12g of sodium hydroxide, and 65g of deionized water as raw materials, stir vigorously at room temperature, and age for 1h to obtain a uniform synthetic liquid. Then, the synthetic liquid is charged into a reactor and placed in a microwave oven for low-power nucleation and high-power crystallization. The obtained product is deionized with 100g of water, washed with water until neutral, and dried to obtain NaA molecular sieve.

[0111] The nucleation power is 200W and the time is 10 minutes.

[0112] The crystallization power is 600W and the time is 30 minutes.

[0113] The drying temperature is 40° C. and the drying time is 5 hours.

[0114] The difluorophosphoric acid is first purified by adsorption with a silsesquioxane adsorption resin by the following method:

[0115] S1: Amination reaction: Add 100g macroporous chloromethyl polystyrene balls, 50g hexamethylenetetramine, and 500g water into a stirred tank, heat to 60°C for reaction, keep warm for 3h, filter, and vacuum dry to obtain a primary amino resin:

[0116] S2: 500 g of toluene, 46 g of primary amino resin, 0.2 g of 1,1-diaminoferrocene, and 1 g of triethanolamine were added to a reactor, nitrogen was introduced, and the mixture was stirred at 60° C. for 2 hours. Then, 10 g of acrylic silsesquioxane was added, and the mixture was stirred at 60° C. for 1 hour. The mixture was filtered, washed with water until neutral, and dried to obtain the silsesquioxane adsorption resin.

[0117] The silsesquioxane adsorption resin is filled in the adsorption column, and the filling amount is 30% of the volume percentage of the adsorption column.

[0118] The difluorophosphoric acid flows through the adsorption column at a speed of 1 BV / h.

[0119] Comparative Example 3

[0120] A preparation method of sodium difluorophosphate, the operating steps of which are:

[0121] 120g of sodium carbonate, 200g of difluorophosphoric acid, 1000g of solvent, and 20g of desiccant were added to a sealed polytetrafluoroethylene crystallization kettle, nitrogen was introduced, the temperature was raised to 40°C, and the mixture was stirred for 1h. After the reaction was completed, sodium difluorophosphate was obtained by filtration and purification. The reaction equation is as follows:

[0122]

[0123] The solvent is dimethyl sulfoxide.

[0124] The desiccant is NaA molecular sieve, and the preparation method is:

[0125] Weigh 20g SiO2, 12g sodium hydroxide, and 65g deionized water as raw materials, stir vigorously at room temperature, and age for 1h to obtain a uniform synthetic liquid. Then, the synthetic liquid is charged into a reactor and placed in a microwave oven for low-power nucleation and high-power crystallization. The obtained product is deionized with 100g water, washed with water until neutral, and dried to obtain NaA molecular sieve.

[0126] The nucleation power is 200W and the time is 10 minutes.

[0127] The crystallization power is 600W and the time is 30 minutes.

[0128] The drying temperature is 40° C. and the drying time is 5 hours.

[0129] The difluorophosphoric acid is first purified by adsorption with a silsesquioxane adsorption resin by the following method:

[0130] S1: Amination reaction: Add 100g macroporous chloromethyl polystyrene balls, 50g hexamethylenetetramine, and 500g water into a stirred tank, heat to 60°C for reaction, keep warm for 3h, filter, and vacuum dry to obtain a primary amino resin:

[0131] S2: 500 g of toluene, 46 g of primary amino resin, 0.2 g of 1,1-diaminoferrocene, and 1 g of triethanolamine were added to a reactor, nitrogen was introduced, and the mixture was stirred at 60° C. for 2 hours. Then, 10 g of acrylic silsesquioxane was added, and the mixture was stirred at 60° C. for 1 hour. The mixture was filtered, washed with water until neutral, and dried to obtain the silsesquioxane adsorption resin.

[0132] The silsesquioxane adsorption resin is filled in the adsorption column, and the filling amount is 30% of the volume percentage of the adsorption column.

[0133] The difluorophosphoric acid flows through the adsorption column at a speed of 1 BV / h.

[0134] The product purity and yield in the above specific embodiment are calculated according to the following formula, and the results are shown in the following table:

[0135] 1. Purity: Purity of sodium difluorophosphate = mass of sodium difluorophosphate in the mixture / mass of the mixture × 100%;

[0136] 2. Yield: Yield of sodium difluorophosphate = actual amount of sodium difluorophosphate produced / theoretical amount of sodium difluorophosphate produced × 100%.

[0137]

[0138] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A preparation method of sodium difluorophosphate, comprising the following steps: By weight, 120-140 parts of sodium carbonate, 200-220 parts of difluorophosphoric acid, 1000-1200 parts of solvent, and 20-30 parts of desiccant are added to a sealed polytetrafluoroethylene crystallization kettle, nitrogen is introduced, the temperature is raised to 40-60°C, and the mixture is stirred for 1-3 hours. After the reaction is completed, the mixture is filtered and purified to obtain sodium difluorophosphate. The reaction equation is as follows: The difluorophosphoric acid is first purified by adsorption with a silsesquioxane adsorption resin by the following method: S1: Amination reaction: Add 100-150 parts by weight of macroporous chloromethyl polystyrene balls, 50-100 parts of hexamethylenetetramine, and 500-1000 parts of water to a stirred tank, heat to 60-70°C for reaction, keep warm for 3-6 hours, filter, and vacuum dry to obtain a primary amino resin: S2: Add 500-1000 parts of toluene, 46-100 parts of primary amino resin, 0.2-2.5 parts of 1,1-diaminoferrocene, and 1-4 parts of triethanolamine to a reaction kettle, introduce nitrogen, mix and stir at 60-70°C for 2-5 hours, then add 10-20 parts of acrylic silsesquioxane, mix and stir at 60-70°C for 1-3 hours, filter, wash with water until neutral, and dry to obtain the silsesquioxane adsorption resin; The silsesquioxane adsorption resin is filled in the adsorption column, and the filling amount is 30-40% of the volume percentage of the adsorption column.

2. a preparation method of sodium difluorophosphate according to claim 1, characterized in that: The solvent is selected from one or more of dimethyl sulfoxide, ethylene glycol dimethyl ether, 1,3-dioxolane, and polyethylene glycol dimethyl ether.

3. A method for preparing sodium difluorophosphate according to claim 1, wherein: The desiccant is selected from one or more of a silica gel desiccant and a molecular sieve desiccant.

4. A method for preparing sodium difluorophosphate according to claim 3, wherein: The molecular sieve desiccant is NaA molecular sieve, and the preparation method is as follows: According to weight, 20-40 parts of SiO2, 15-20 parts of Al2O3, 12-18 parts of sodium hydroxide, and 65-80 parts of deionized water are weighed as raw materials, vigorously stirred at room temperature, and aged for 1-4 hours to obtain a uniform synthetic liquid. The synthetic liquid is then charged into a reactor and placed in a microwave oven for low-power nucleation and high-power crystallization. The resulting product is washed with 100-200 parts of deionized water until neutral, and then dried to obtain NaA molecular sieve.

5. A method for preparing sodium difluorophosphate according to claim 4, wherein: The nucleation power is 200-300W, and the time is 10-20 minutes.

6. A method for preparing sodium difluorophosphate according to claim 4, wherein: The crystallization power is 600-800W, and the time is 30-60min.

7. A method for preparing sodium difluorophosphate according to claim 4, wherein: The drying temperature is 40-50° C. and the drying time is 5-8 hours.

8. A method for preparing sodium difluorophosphate according to claim 1, wherein: The speed at which the difluorophosphoric acid flows through the adsorption column is 1-30 BV / h.

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