A method for preparing a tetra(fluorophosphoryl)imide alkali metal salt

Abstract

The application belongs to the technical field of fluorine chemical synthesis, and particularly relates to a preparation method of tetra (fluorophosphoryl) imide alkali metal salt, at least comprising the following steps: mixing phosphoryl chloride, alkyl primary amine and acid binding agent in an organic solvent, stirring and reacting, and filtering to remove byproducts; adding a fluorination reagent, stirring and reacting, and filtering to remove byproducts; adding alkyl secondary amine, stirring and reacting, washing with deionized water, and removing the organic solvent under reduced pressure; adding a polar solvent and an alkali metal compound, stirring and reacting, filtering, concentrating, adding a weakly polar organic solvent to perform recrystallization, and drying under reduced pressure to obtain a finished product. Compared with the prior art, the raw materials used in the application are easy to obtain and low in cost, the production process is simple, no dangerous unit operation of high temperature and high pressure is involved, the product is easy to separate and purify, three-waste emissions are small, the application is friendly to the environment, the operation steps are simple, the product is easy to separate and purify, the purity and yield are high, the application is suitable for industrial mass production, and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fluorine chemical synthesis, and particularly relates to a preparation method of alkali metal salt of tetra (fluorophosphoryl) imide, in particular to a preparation method of alkali metal salt (M[N(POF2)2], wherein M = Li, Na, K, Rb, Cs) of tetra (fluorophosphoryl) imide. BACKGROUND

[0002] The fluorophosphorylimide salt structure has stable chemical and electrochemical properties, and in particular lithium salt, sodium salt and quaternary ammonium salt, which have important industrial application values in the fields of high-performance non-aqueous electrolyte materials for clean energy devices such as secondary lithium batteries, secondary sodium batteries, supercapacitors and aluminum electrolytic capacitors, and new high-efficiency catalysts.

[0003] There are mainly three kinds of preparation methods of tetra (fluorophosphoryl) imide and its alkali metal salt in the prior art:

[0004] The first kind is to prepare lithium tetra (fluorophosphoryl) imide by reacting phosphorus oxyfluoride and lithium bis (trimethylsilyl) amide, but lithium bis (trimethylsilyl) amide has high cost and is not conducive to large-scale production and application.

[0005] The second kind is to prepare alkali metal salt of tetra (fluorophosphoryl) imide by reacting tetra (chlorophosphoryl) imide and alkali metal fluoride in nitromethane, but the reaction condition is harsh and there is a safety problem.

[0006] The third kind is to prepare tetra (fluorophosphoryl) imide by reacting tetra (chlorophosphoryl) imide with hydrogen fluoride under the action of a catalyst, and then further reacting with potassium carbonate to obtain potassium tetra (fluorophosphoryl) imide, and then further reacting with lithium perchlorate to obtain lithium tetra (fluorophosphoryl) imide. However, this method has the problems of high impurity content and low purity.

[0007] In summary, the methods for preparing tetra (fluorophosphoryl) imide and its alkali metal salt reported in the existing literature have the disadvantages of difficult purification and separation, low product purity and yield, and cannot meet the requirements of high purity and mass production of electrolyte materials. In addition, due to the harsh reaction condition, the use of a large amount of strong corrosive or toxic compounds, the existing synthesis method cannot meet the requirements of large-scale industrial production.

[0008] Therefore, the application aims to provide a preparation method of tetra (fluorophosphoryl) imide alkali metal salt, which has the characteristics of simple operation steps, easy separation and purification of products, high purity and yield, and suitability for industrial mass production, so as to overcome the disadvantages of the prior art, such as complicated operation, low yield, environmental pollution caused by toxic reagents, difficult operation of fluorine-containing gas reagents, complicated product separation operation, and difficult purification of products. The tetra (fluorophosphoryl) imide alkali metal salt synthesized by the method of the application can be used as an electrolyte salt of an electrochemical energy storage battery, preparation of a catalyst, and synthesis of a high-performance ionic liquid. SUMMARY

[0009] The application aims to provide a preparation method of tetra (fluorophosphoryl) imide alkali metal salt, which has the characteristics of simple operation steps, easy separation and purification of products, high purity and yield, and suitability for industrial mass production, so as to overcome the disadvantages of the prior art, such as complicated operation, low yield, environmental pollution caused by toxic reagents, difficult operation of fluorine-containing gas reagents, complicated product separation operation, and difficult purification of products. The tetra (fluorophosphoryl) imide alkali metal salt synthesized by the method of the application can be used as an electrolyte salt of an electrochemical energy storage battery, preparation of a catalyst, and synthesis of a high-performance ionic liquid.

[0010] In order to achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0011] A preparation method of tetra (fluorophosphoryl) imide alkali metal salt, at least comprising the following steps:

[0012] In the first step, phosphorus oxychloride, alkyl primary amine and acid binding agent are mixed in an organic solvent, stirred and reacted, the byproduct is removed by filtration, and an N-alkyl tetra (chlorophosphoryl) imine solution is obtained;

[0013] In the second step, a fluorination reagent is added to the N-alkyl tetra (chlorophosphoryl) imine solution obtained in the first step, stirred and reacted, and the byproduct is removed by filtration, so as to obtain an N-alkyl tetra (fluorophosphoryl) imine solution;

[0014] In the third step, alkyl secondary amine is added to the N-alkyl tetra (fluorophosphoryl) imine solution obtained in the second step, stirred and reacted, so as to obtain tetra (fluorophosphoryl) imine tertiary ammonium salt; after being washed with deionized water, the organic solvent is removed under reduced pressure to obtain tetra (fluorophosphoryl) imine tertiary ammonium salt product;

[0015] In the fourth step, a polar solvent and an alkali metal compound are added to the tetra (fluorophosphoryl) imine tertiary ammonium salt obtained in the third step, stirred and reacted, filtered, concentrated, and recrystallized in a weakly polar organic solvent to obtain tetra (fluorophosphoryl) imine alkali metal salt, which is dried under reduced pressure to obtain the finished product.

[0016] The general structure of tetra (fluorophosphoryl) imide alkali metal salt is as follows:

[0017]

[0018] Where: M + is Li, Na, K, Rb or Cs.

[0019] As an improvement to the preparation method of tetrakis(fluorophosphoryl)imide alkali metal salt of the present invention, the organic solvent described in the first step is at least one of acetonitrile, acetone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, butyl acetate, diethyl ether, methyl tert-butyl ether and ethylene glycol dimethyl ether.

[0020] As an improvement to the preparation method of tetrakis(fluorophosphoryl)imide alkali metal salt of the present invention, the alkyl primary amine in the first step is at least one of methylamine, ethylamine, propylamine, butylamine, isopropylamine, isobutylamine and sec-butylamine.

[0021] As an improvement to the preparation method of tetrakis(fluorophosphoryl)imide alkali metal salt of the present invention, the acid binding agent described in the first step is at least one of triethylamine, tripropylamine, tributylamine, diisopropylethylamine, methyldiethylamine, methyldipropylamine, ethyldipropylamine, methyldibutylamine and ethyldibutylamine.

[0022] As an improvement to the preparation method of tetrakis(fluorophosphoryl)imide alkali metal salt of the present invention, the reaction temperature in the first step is -10-50°C, the reaction environment is protected by inert gas, and the stoichiometric molar ratio of phosphoryl chloride, primary alkyl amine and acid binding agent is 2:1:2 to 2:1.5:3.

[0023] As an improvement to the preparation method of alkali metal tetrakis(fluorophosphoryl)imide of the present invention, the fluorination reagent in the second step is at least one of potassium fluoride, sodium fluoride, hydrogen fluoride, triethylammonium hydrogen fluoride, pyridinium hydrogen fluoride, and antimony trifluoride; the stoichiometric molar ratio of the N-alkyltetrakis(chlorophosphoryl)imide and the fluorination reagent in the second step is 1:4 to 1:6; the reaction temperature in the second step is 25-80°C, and the reaction environment is protected by an inert gas.

[0024] As an improvement to the preparation method of tetrakis(fluorophosphoryl)imide alkali metal salt of the present invention, the secondary alkyl amine described in the third step is at least one of dimethylamine, diethylamine, dipropylamine, dibutylamine, diisopropylamine, diisobutylamine, di-sec-butylamine, methylethylamine, methylpropylamine, methylisopropylamine, methylbutylamine, methylisobutylamine, methylsec-butylamine, ethylpropylamine, ethylisopropylamine, ethylbutylamine, ethylisobutylamine and ethylsec-butylamine.

[0025] As an improvement of the preparation method of the alkali metal salt of tetra (fluorophosphoryl) imide, the stoichiometric molar ratio of the N-alkyl tetra (fluorophosphoryl) imide solution and the secondary alkyl amine in the third step is 1:1-1:2, and the reaction temperature in the third step is 25-80℃, and the reaction environment is inert gas protection.

[0026] As an improvement of the preparation method of the alkali metal salt of tetra (fluorophosphoryl) imide, the polar solvent in the fourth step is at least one of water, methanol, ethanol, propanol, isopropanol, butanol, acetonitrile, ethylene glycol dimethyl ether, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate and butyl acetate; the alkali metal compound in the fourth step is at least one of lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, lithium methoxide, sodium methoxide, potassium methoxide, lithium ethoxide, sodium ethoxide, potassium ethoxide, lithium propanol, sodium propanol, potassium propanol, lithium butanol, sodium butanol, potassium butanol, lithium amide, sodium amide and potassium amide; and the weak polar organic solvent is at least one of dichloromethane, dichloroethane, toluene, hexane, cyclohexane and petroleum ether.

[0027] As an improvement of the preparation method of the alkali metal salt of tetra (fluorophosphoryl) imide, the stoichiometric molar ratio of the tetrafluorophosphoryl imide tertiary ammonium salt and the alkali metal compound is 1:1-1:2, and the reaction temperature in the fourth step is 25-80℃, and the reaction environment is inert gas protection.

[0028] Compared with the prior art, the raw materials used in the present application are easy to obtain, low in cost and simple in production process, and no dangerous unit operation of high temperature and high pressure is involved. The product is easy to separate and purify, and the discharge of three wastes is less, which is friendly to the environment. Moreover, the present application has the characteristics of simple operation steps, easy separation and purification of products, high purity and yield, and is suitable for industrial mass production, so as to overcome the disadvantages of the prior art, such as complicated operation, low yield, environmental pollution caused by the use of toxic reagents, difficult operation caused by the use of fluorine-containing gas reagents, complicated product separation operation and difficult product purification. The alkali metal salt of tetra (fluorophosphoryl) imide synthesized by the method of the present application can be used as an electrolyte salt for electrochemical energy storage batteries, or for the preparation of catalysts, and the synthesis of high-performance ionic liquids. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present application more apparent and easy to understand, the specific embodiments of the present application are described in detail below.

[0030] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in other ways, which are different from those described herein, and similar modifications can be made by those skilled in the art without departing from the scope of the present application, so the present application is not limited to the specific embodiments disclosed below.

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the embodiments of the present application will be further described in detail below.

[0032] Example 1

[0033] The present embodiment provides a preparation method of lithium tetra (fluorophosphoryl) imide, comprising the following steps:

[0034] In the first step, 45 grams (1 mole) of ethylamine, 202 grams (2 moles) of triethylamine and 1000 mL of acetonitrile are added into a 2L reaction bottle under nitrogen protection, and the temperature is controlled at 0°C, and then 306 grams (2 moles) of phosphorus oxychloride is added dropwise. After the dropwise addition is completed, the reaction is stirred at 25°C for 24 hours, and then the insoluble substances are removed by filtration under reduced pressure to obtain a light brown yellow solution (N-ethyl tetra (chlorophosphoryl) imine solution) for the next reaction.

[0035] In the second step, 261 grams (4.5 moles) of potassium fluoride is added into the reaction solution obtained in the above step under magnetic stirring and nitrogen protection, and then the reaction is stirred at 60°C for 12 hours, and then the insoluble substances are removed by filtration to obtain a light brown yellow solution (N-ethyl tetra (fluorophosphoryl) imine solution) for the next reaction.

[0036] In the third step, 73 grams (1 mole) of diethylamine is added into the reaction solution obtained in the above step under magnetic stirring and nitrogen protection, and then the reaction is stirred at 25°C for 12 hours, and then the reaction solution is washed with deionized water, and then the organic solvent is removed under reduced pressure to obtain a light brown yellow viscous liquid (tetra (fluorophosphoryl) imine tertiary ammonium salt product) for the next reaction.

[0037] In the fourth step, the light brown yellow viscous liquid obtained in the above step is dissolved in ethanol, and then 42 grams (1 mole) of lithium hydroxide monohydrate is added at room temperature, and then the reaction is stirred for 12 hours, and then the solvent is removed under reduced pressure to obtain a light yellow solid, which is further dissolved in dimethyl carbonate, and then the insoluble substances are removed by filtration, and then the filtrate is concentrated under reduced pressure, and then dichloromethane is added for recrystallization, and then the filtrate is dried under reduced pressure to obtain 171 grams of white solid (lithium tetra (fluorophosphoryl) imide). The experiment shows that the yield of the present application is 90%, and the purity of the lithium tetra (fluorophosphoryl) imide is 99.95%, Cl <5ppm, SO4 2- <5ppm, K <1ppm, Mg <1ppm, Ca <1ppm, Fe <1ppm, Hg ND, Cr <1ppm.

[0038] The chemical reaction formula in the reaction process of the present embodiment is as follows:

[0039]

[0040] Example 2

[0041] The embodiment provides a preparation method of sodium tetrafluorophosphorimide, which comprises the following steps.

[0042] In the first step, 59 g (1 mol) of propylamine, 244 g (2 mol) of tripropylamine and 1000 mL of dimethyl carbonate are added into a 2 L reaction bottle under nitrogen protection and temperature control at 0 DEG C, and 306 g (2 mol) of phosphorus oxychloride is added dropwise. After the dropwise addition is completed, the reaction is stirred at 25 DEG C for 24 hours, and insoluble substances are removed by filtration under reduced pressure. A light brownish yellow solution (N-ethyl tetra(chlorophosphor)imide solution) is obtained and used in the next reaction.

[0043] In the second step, 261 g (4.5 mol) of potassium fluoride is added into the reaction solution obtained in the above step under magnetic stirring and nitrogen protection, and the reaction is stirred at 60 DEG C for 12 hours. After the reaction, insoluble substances are removed by filtration, and a light brownish yellow solution (N-ethyl tetra(fluorophosphor)imide solution) is obtained and used in the next reaction.

[0044] In the third step, 101 g (1 mol) of dipropylamine is added into the reaction solution obtained in the above step under magnetic stirring and nitrogen protection, and the reaction is stirred at 25 DEG C for 12 hours. After the reaction, the reaction solution is washed with deionized water, and organic solvents are removed under reduced pressure. A light brownish yellow viscous liquid (pure tetra(fluorophosphor)imide tertiary ammonium salt) is obtained and used in the next reaction.

[0045] In the fourth step, the light brownish yellow viscous liquid obtained in the above step is dissolved in water, 40 g (1 mol) of sodium hydroxide is added at room temperature, the reaction is stirred for 12 hours, and the solvent is removed under reduced pressure to obtain a light yellow solid. The light yellow solid is further dissolved in dimethyl carbonate, insoluble substances are removed by filtration, and dichloroethane is added after concentration under reduced pressure. The mixture is recrystallized, and the filter residue is dried under reduced pressure to obtain 182 g of white solid sodium tetra(fluorophosphor)imide. The yield is 88%, the purity of sodium tetra(fluorophosphor)imide is 99.95%, Cl is less than 5 ppm, SO42- is less than 5 ppm, K is less than 1 ppm, Mg is less than 1 ppm, Ca is less than 1 ppm, Fe is less than 1 ppm, Hg is ND, and Cr is less than 1 ppm.

[0046] The chemical reaction formula in the reaction process of the embodiment is as follows:

[0047]

[0048] Embodiment 3

[0049] The embodiment provides a preparation method of potassium tetrafluorophosphorimide, which comprises the following steps.

[0050] First step, under nitrogen protection, control temperature 0℃, 45 grams (1 mol) of ethylamine, 202 grams (2 mol) of triethylamine and 1000 mL of ethyl acetate were added to a 2L reaction bottle, and 306 grams (2 mol) of phosphorus oxychloride was added dropwise. After the dropwise addition was completed, the reaction was stirred at 25℃ for 24 hours, and the insoluble matter was removed by filtration under reduced pressure. A light brownish yellow solution (N-ethyl tetra (chlorophosphoryl) imine solution) was obtained for the next step reaction.

[0051] Second step, under magnetic stirring and nitrogen protection, 484 grams (4 mol) of triethylamine hydrogen fluoride was added to the above obtained reaction solution, and after stirring at 40℃ for 8 hours, the insoluble matter was removed by filtration to obtain a light brownish yellow solution (N-ethyl tetra (fluorophosphoryl) imine solution) for the next step reaction.

[0052] Third step, under magnetic stirring and nitrogen protection, 73 grams (1 mol) of diethylamine was added to the above obtained reaction solution, and after stirring at 25℃ for 12 hours, it was washed with deionized water and the organic solvent was removed under reduced pressure to obtain a light brownish yellow viscous liquid (tetra (fluorophosphoryl) imine tertiary ammonium salt pure product) for the next step reaction.

[0053] Fourth step, under magnetic stirring and nitrogen protection, the above obtained light brownish yellow viscous liquid was dissolved in methanol, 75.9 grams (0.55 mol) of potassium carbonate was added at room temperature, and the reaction was stirred for 10 hours. The solvent was removed under reduced pressure to obtain a light yellow solid, which was further dissolved in dimethyl carbonate, the insoluble matter was removed by filtration, and after concentration under reduced pressure, toluene was added for recrystallization. After filtration, the filter residue was dried under reduced pressure to obtain 205 grams of white solid, with a yield of 92%, and the purity of tetra (fluorophosphoryl) imine potassium was 99.95%, Cl <5 ppm, SO42-<5 ppm, K <1 ppm, Mg <1 ppm, Ca <1 ppm, Fe <1 ppm, Hg ND, Cr <1 ppm.

[0054] The chemical reaction formula during the reaction process of this example is as follows:

[0055]

[0056] Example 4

[0057] The example provides a preparation method of lithium tetra (fluorophosphoryl) imide, which comprises the following steps:

[0058] First step, under nitrogen protection, control temperature 10℃, 1.1 mol of butylamine, 2.1 mol of tributylamine and 1000 mL of acetone were added to a 2L reaction bottle, and 2 mol of phosphorus oxychloride was added dropwise. After the dropwise addition was completed, the reaction was stirred at 35℃ for 12 hours, and the insoluble matter was removed by filtration under reduced pressure to obtain a light brownish yellow solution (N-butyl tetra (chlorophosphoryl) imine solution) for the next step reaction.

[0059] Second step, under magnetic stirring and nitrogen protection, 5 mol of hydrogen fluoride pyridine was added to the above obtained reaction solution, and after stirring at 70°C for 8 hours, the insoluble matter was removed by filtration to obtain a light brown yellow solution (N-butyl tetra (fluorophosphoryl) imine solution) for the next step reaction.

[0060] Third step, under magnetic stirring and nitrogen protection, 1.1 mol of dibutylamine was added to the above obtained reaction solution, and after stirring at 50°C for 8 hours, deionized water was washed, and the organic solvent was removed under reduced pressure to obtain a light brown yellow viscous liquid (tetra (fluorophosphoryl) imine tertiary ammonium salt pure product) for the next step reaction.

[0061] Fourth step, under magnetic stirring and nitrogen protection, the above obtained light brown yellow viscous liquid was dissolved in butanol, 1.1 mol of lithium carbonate was added at room temperature, and stirred for 8 hours. The solvent was removed under reduced pressure to obtain a light yellow solid, which was further dissolved in diethyl carbonate, the insoluble matter was removed by filtration, and after concentration under reduced pressure, cyclohexane was added for recrystallization. After filtration, the filter residue was dried under reduced pressure to obtain a white solid (lithium tetra (fluorophosphoryl) imide).

[0062] Example 5

[0063] The present embodiment provides a preparation method of sodium tetra (fluorophosphoryl) imide, comprising the following steps:

[0064] First step, under nitrogen protection, control the temperature at 20°C, 1.2 mol of isopropylamine, 2.2 mol of methyl diethylamine and 1000 mL of diethyl carbonate were added to a 2L reaction bottle, and 2 mol of phosphorus oxychloride was added dropwise. After the dropwise addition was completed, the reaction was stirred at 15°C for 10 hours, and the insoluble matter was removed by filtration under reduced pressure. A light brown yellow solution (N-isopropyl tetra (chlorophosphoryl) imine solution) was obtained for the next step reaction.

[0065] Second step, under magnetic stirring and nitrogen protection, 4.8 mol of sodium fluoride was added to the above obtained reaction solution, and after stirring at 55°C for 8 hours, the insoluble matter was removed by filtration to obtain a light brown yellow solution (N-isopropyl tetra (fluorophosphoryl) imine solution) for the next step reaction.

[0066] Third step, under magnetic stirring and nitrogen protection, 1.2 mol of methyl ethylamine was added to the above obtained reaction solution, and after stirring at 35°C for 10 hours, deionized water was washed, and the organic solvent was removed under reduced pressure to obtain a light brown yellow viscous liquid (tetra (fluorophosphoryl) imine tertiary ammonium salt pure product) for the next step reaction.

[0067] The fourth step is to dissolve the above-obtained light brown viscous liquid in water under magnetic stirring and nitrogen protection, add 0.6 mol of sodium carbonate at room temperature, stir and react for 8 hours, remove the solvent under reduced pressure to obtain a light yellow solid, further dissolve it in ethyl acetate, filter to remove insoluble matter, concentrate under reduced pressure, add hexane for recrystallization, filter and dry the residue under reduced pressure to obtain a white solid sodium tetrakis(fluorophosphoryl)imide.

[0068] Example 6

[0069] This embodiment provides a method for preparing potassium tetrakis(fluorophosphoryl)imide, comprising the following steps:

[0070] In the first step, under nitrogen and at 30°C, 1.05 mol of isobutylamine, 2.15 mol of diisopropylethylamine, and 1000 mL of propyl acetate were added to a 2 L reaction flask. 2 mol of phosphorus oxychloride was then added dropwise. After the addition was complete, the reaction was stirred at 10°C for 15 hours. Insoluble matter was removed by filtration under reduced pressure. The resulting light brown solution (N-alkyltetrakis(chlorophosphoryl)imide solution) was used for the next reaction.

[0071] In the second step, 4.8 mol of antimony trifluoride was added to the reaction solution obtained above under magnetic stirring and nitrogen protection. After stirring at 45°C for 10 hours, the insoluble matter was removed by filtration to obtain a light brown solution (N-alkyltetrakis(fluorophosphoryl)imide solution) for the next reaction.

[0072] In the third step, 1.3 mol of diisopropylamine was added to the reaction solution obtained above under magnetic stirring and nitrogen protection. After stirring at 45°C for 6 hours, the mixture was washed with deionized water and the organic solvent was removed under reduced pressure to obtain a light brown viscous liquid (pure tertiary ammonium salt of tetrakis(fluorophosphoryl)imide) for the next reaction.

[0073] In the fourth step, the light brown viscous liquid obtained above was dissolved in propyl acetate under magnetic stirring and nitrogen protection, 1.2 mol of potassium hydroxide was added at room temperature, and the reaction was stirred for 9 hours. The solvent was removed under reduced pressure to obtain a light yellow solid, which was further dissolved in diethyl carbonate. The insoluble matter was removed by filtration, and after concentration under reduced pressure, cyclohexane was added for recrystallization. After filtration, the filter residue was dried under reduced pressure to obtain a white solid potassium tetrakis(fluorophosphoryl)imide.

[0074] The technical solution of the present invention has easy-to-obtain raw materials, low cost, simple production process, no dangerous unit operations involving high temperature and high pressure, and the product is easy to separate and purify.

[0075] Those skilled in the art can make various modifications and changes to the above embodiments according to the disclosure and teachings herein. Therefore, the application is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the application shall fall within the protection scope of the claims of the application. In addition, although some specific terms are used in the specification, these terms are only for convenience of description and do not constitute any limitation on the application.

Claims

1. A method for preparing an alkali metal salt of tetrakis(fluorophosphoryl)imide, characterized in that: At least the following steps are included: In the first step, phosphorus oxychloride, an alkyl primary amine, and an acid binding agent are mixed in an organic solvent, stirred for reaction, and by-products are removed by filtration to obtain an N-alkyltetrakis(chlorophosphoryl)imide solution; In the second step, a fluorination agent is added to the N-alkyltetrakis(chlorophosphoryl)imide solution obtained in the first step, the mixture is stirred for reaction, and the by-product is removed by filtration to obtain an N-alkyltetrakis(fluorophosphoryl)imide solution; In the third step, an alkyl secondary amine is added to the N-alkyltetra(fluorophosphoryl)imide solution obtained in the second step, and the mixture is stirred to react to obtain a tertiary ammonium salt of tetra(fluorophosphoryl)imide. After being thoroughly washed with deionized water, the organic solvent is removed under reduced pressure to obtain a pure tertiary ammonium salt of tetra(fluorophosphoryl)imide. In the fourth step, a polar solvent and an alkali metal compound are added to the tertiary ammonium salt of tetrakis(fluorophosphoryl)imide obtained in the third step, the mixture is stirred for reaction, filtered and concentrated, and a weakly polar organic solvent is added for recrystallization to obtain an alkali metal salt of tetrakis(fluorophosphoryl)imide, which is then dried under reduced pressure to obtain a finished product; The primary alkylamine in the first step is at least one of methylamine, ethylamine, propylamine, butylamine, isopropylamine, isobutylamine and sec-butylamine.

2. The method for preparing tetrakis(fluorophosphoryl)imide alkali metal salt according to claim 1, characterized in that: The organic solvent described in the first step is at least one of acetonitrile, acetone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, butyl acetate, diethyl ether, methyl tert-butyl ether and ethylene glycol dimethyl ether.

3. The method for preparing tetrakis(fluorophosphoryl)imide alkali metal salt according to claim 1, characterized in that: The acid binding agent described in the first step is at least one of triethylamine, tripropylamine, tributylamine, diisopropylethylamine, methyldiethylamine, methyldipropylamine, ethyldipropylamine, methyldibutylamine and ethyldibutylamine.

4. The method for preparing tetrakis(fluorophosphoryl)imide alkali metal salt according to claim 1, characterized in that: The reaction temperature in the first step is -10°C-50°C, the reaction environment is protected by inert gas, and the stoichiometric molar ratio of phosphorus oxychloride, alkyl primary amine and acid binding agent is 2:1:2 to 2:1.5:

3.

5. The method for preparing tetrakis(fluorophosphoryl)imide alkali metal salt according to claim 1, characterized in that: The fluorination agent in the second step is at least one of potassium fluoride, sodium fluoride, hydrogen fluoride, triethylammonium hydrogen fluoride, pyridinium hydrogen fluoride, and antimony trifluoride; the stoichiometric molar ratio of N-alkyltetrakis(chlorophosphoryl)imide to the fluorination agent in the second step is 1:4 to 1:6; the reaction temperature in the second step is 25-80°C, and the reaction environment is protected by inert gas.

6. The method for preparing tetrakis(fluorophosphoryl)imide alkali metal salt according to claim 1, characterized in that: The secondary alkyl amine described in the third step is at least one of dimethylamine, diethylamine, dipropylamine, dibutylamine, diisopropylamine, diisobutylamine, di-sec-butylamine, methylethylamine, methylpropylamine, methylisopropylamine, methylbutylamine, methylisobutylamine, methyl-sec-butylamine, ethylpropylamine, ethylisopropylamine, ethylbutylamine, ethylisobutylamine and ethyl-sec-butylamine.

7. The method for preparing tetrakis(fluorophosphoryl)imide alkali metal salt according to claim 1, characterized in that: The stoichiometric molar ratio of the N-alkyltetra(fluorophosphoryl)imide solution to the alkyl secondary amine in the third step is 1:1 to 1:2, and the reaction temperature in the third step is 25-80°C, and the reaction environment is protected by inert gas.

8. The method for preparing tetrakis(fluorophosphoryl)imide alkali metal salt according to claim 1, characterized in that: The polar solvent described in the fourth step is at least one of water, methanol, ethanol, propanol, isopropanol, butanol, acetonitrile, ethylene glycol dimethyl ether, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate and butyl acetate; the alkali metal compound described in the fourth step is at least one of lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, lithium methoxide, sodium methoxide, potassium methoxide, lithium ethoxide, sodium ethoxide, potassium ethoxide, lithium propoxide, sodium propoxide, potassium propoxide, lithium butoxide, sodium butoxide, potassium butoxide, lithium amide, sodium amide and potassium amide; and the weakly polar organic solvent is at least one of dichloromethane, dichloroethane, toluene, hexane, cyclohexane and petroleum ether.

9. The method for preparing tetrakis(fluorophosphoryl)imide alkali metal salt according to claim 1, characterized in that: The stoichiometric molar ratio of the tetrafluorophosphorylimide tertiary ammonium salt and the alkali metal compound is 1:1 to 1:2, and the reaction temperature in the fourth step is 25-80°C, and the reaction environment is protected by inert gas.

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