WO2019061802A1 - Method for preparing lithium difluorophosphate - Google Patents

Abstract

A method for preparing lithium difluorophosphate comprises the steps of: (1) preparing phosphoryl fluoride by using phosphoryl chloride and a fluorinating reagent in a polar organic solvent; (2) adding lithium hydroxide to a polar organic solvent, The phosphorus oxyfluoride reaction is carried out under stirring; (3) after completion of the reaction, a lithium difluorophosphate solution is obtained by filtration, and after concentration, a weakly polar organic solvent is added for recrystallization, and the crystallized product is dried under reduced pressure to obtain a product. The method has the advantages that the raw materials are easy to obtain, the cost is low, the production process is simple, the dangerous unit operation involving high temperature and high pressure is not involved, the product is easy to be separated and purified, and the by-product hydrogen fluoride is added to the alkali metal carbonate aqueous solution to be used as a raw material for preparing the fluorination reagent.

Description

Preparation method of lithium difluorophosphate Technical field

The invention relates to the technical field of compound preparation, in particular to a preparation method of lithium difluorophosphate.

Background technique

As a new type of lithium ion battery electrolyte additive, lithium difluorophosphate improves the structural composition of the interface film by forming a stable passivation film, which is beneficial to reducing the internal resistance of the battery and improving the service life of the battery. The preparation process of lithium difluorophosphate mainly comprises: 1) hydrolysis of lithium hexafluorophosphate to form a mixture of lithium difluorophosphate and lithium hexafluorophosphate, and reaction of lithium hexafluorophosphate and Si-O-Si compound, both of which are difficult to prepare high-purity lithium difluorophosphate 2) the reaction of difluorophosphoric anhydride with lithium fluoride or lithium oxide, the raw material of difluorophosphoric anhydride is relatively rare, and the toxicity is large, and the industrialization cost is high; 3) the reaction of trifluorophosphorus with lithium phosphate or lithium fluoride, The former is required to react at high temperature and high pressure due to low lithium phosphate activity, the latter forms a mixture of lithium difluorophosphate and lithium hexafluorophosphate; 4) the reaction between phosphorus pentafluoride and lithium phosphate, the product is a mixture of lithium hexafluorophosphate and lithium difluorophosphate; 5) Lithium dihydrogen phosphate and hydrogen fluoride react under high temperature and high pressure, water is formed during the reaction, which easily leads to the hydrolysis of lithium difluorophosphate to produce impurities; 6) phosphoric anhydride and lithium fluoride react to form lithium difluorophosphate and lithium phosphate, solid The solid reaction is difficult to carry out completely, and the phosphoric anhydride mixed in the product is not easily removed.

Summary of the invention

It is an object of the present invention to provide a method for preparing high-purity lithium difluorophosphate required for a lithium ion battery.

In order to solve the above technical problems, the present invention provides a method for preparing lithium difluorophosphate, comprising the following steps:

(1) phosphorus oxychloride and a fluorinating reagent are used to prepare phosphoryl fluoride in a polar organic solvent;

(2) lithium hydroxide is added to a polar organic solvent, and a phosphorus oxyfluoride reaction is introduced under stirring;

(3) After completion of the reaction, a lithium difluorophosphate solution is obtained by filtration, and after concentration, a weakly polar organic solvent is added for recrystallization, and the crystallized product is dried under reduced pressure to give a product.

Preferably, the polar organic solvent described in the step (1) is acetonitrile, acetone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, butyl acetate, diethyl ether and methylate. One or more of the group tert-butyl ether.

Preferably, the fluorinating agent described in the step (1) is one of sodium fluoride, potassium fluoride, zinc fluoride, cesium trifluoride, and hydrogen fluoride.

More preferably, the fluorinating agent described in the step (1) is potassium fluoride and sodium fluoride.

Preferably, the stoichiometric molar ratio of the phosphoryl chloride and the fluorinating reagent described in the step (1) is 1:1.1 to 1:5, and the reaction The temperature is 25 to 80 °C.

Preferably, the stoichiometric molar ratio of the phosphoryl chloride and the fluorinating reagent described in the step (1) is 1:1.5 to 1:4.

Preferably, the polar organic solvent described in the step (2) is dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, acetonitrile, One or more of propionitrile, acetone, tetrahydrofuran, diethyl ether, methyl tert-butyl ether, dipropyl ether, dibutyl ether, ethylene glycol dimethyl ether.

Preferably, the reaction temperature in the step (2) is -5 to 60 °C.

Preferably, the weakly polar solvent described in the step (3) is one or more of dichloromethane, chloroform, n-hexane, cyclohexane, toluene, xylene, chlorobenzene or fluorobenzene.

Preferably, the temperature under reduced pressure drying in the step (3) is 60 to 120 °C.

The preparation method of the invention has simple process and low cost, and can obtain high-purity lithium difluorophosphate target product.

Detailed ways

The embodiments of the present invention are described below by way of specific examples, and those skilled in the art can readily understand other advantages and effects of the present invention from the disclosure of the present disclosure. One or more of the method steps mentioned in the present invention are not exclusive of other method steps that may be present before or after the combination step, or other method steps may be inserted between the steps explicitly mentioned, unless otherwise stated.

Example 1:

POCl ₃ + KF → POF ₃ + KCl

POF ₃ +LiOH→LiPO ₂ F ₂ +HF

76.67 g (0.5 mol) of phosphorus oxychloride was added to a 1000 mL reaction flask, and 100 mL of diethyl carbonate was added as a solvent, and 121.8 g (2.1 mol) of potassium fluoride was added thereto, and the reaction was stirred at a temperature of 60 ° C.

Another 500 mL reaction flask was taken, 9.6 g (0.4 mol) of lithium hydroxide and 100 mL of anhydrous acetonitrile were added, and the mixture was magnetically stirred, and the phosphoryl fluoride prepared in the above step was passed at room temperature, and the reaction was stopped after 8 hours. Filtration under reduced pressure gave a clear filtrate, which was concentrated under reduced pressure and then toluene to afford crystals of lithium difluorophosphate. After drying at 80 ° C, 38.9 g of product was obtained.

Example 2:

POCl ₃ +NaF→POF ₃ +NaCl

POF ₃ +LiOH→LiPO ₂ F ₂ +HF

To a 1000 mL reaction flask, 76.67 g (0.5 mol) of phosphorus oxychloride was added, 100 mL of acetonitrile was added as a solvent, 88.2 g (2.1 mol) of sodium fluoride was added, and the reaction was stirred at 70 ° C.

Another 500 mL reaction flask was taken, 9.6 g (0.4 mol) of lithium hydroxide and 100 mL of anhydrous ethyl acetate were added, and magnetic stirring was carried out, and the phosphoryl fluoride prepared in the above step was passed at 0 ° C, and the reaction was stopped after 10 hours. Filtration under reduced pressure gave a clear filtrate. N-hexane was added to obtain lithium difluorophosphate crystals, and after drying at 80 ° C, 39.5 g of a product was obtained.

Example 3:

POCl ₃ +SbF ₃ →POF ₃ +SbCl ₃

POF ₃ +LiOH→LiPO ₂ F ₂ +HF

To a 1000 mL reaction flask, 76.67 g (0.5 mol) of phosphorus oxychloride was added, and 100 mL of propyl acetate was added as a solvent, and 375.9 g (2.1 mol) of ruthenium trifluoride was added thereto, and the mixture was stirred at 80 ° C to carry out a reaction.

Another 500 mL reaction flask was taken, 9.6 g (0.4 mol) of lithium hydroxide and 100 mL of anhydrous tetrahydrofuran were added, and the mixture was magnetically stirred, and the phosphoryl fluoride prepared in the above step was passed at 40 ° C, and the reaction was stopped after 8 hours. Filtration under reduced pressure gave a clear filtrate, which was concentrated under reduced pressure and then chlorobenzene to afford crystals of lithium difluorophosphate. After drying at 100 ° C, 37.4 g of product was obtained.

The technical scheme of the invention is easy to obtain, the cost is low, the production process is simple, the dangerous unit operation involving high temperature and high pressure is not involved, the product is easy to be separated and purified, and the generated hydrogen fluoride by-product is added to the alkali metal carbonate potassium carbonate aqueous solution to prepare the fluorination. Reagent raw materials.

The above is a preferred embodiment of the present invention, and it should be noted that those skilled in the art can also make several improvements and retouchings without departing from the principles of the present invention. It is the scope of protection of the present invention.

Claims (9)

A method for preparing lithium difluorophosphate, comprising the steps of: (1) phosphorus oxychloride and a fluorinating reagent are used to prepare phosphoryl fluoride in a polar organic solvent; (2) lithium hydroxide is added to a polar organic solvent, and a phosphorus oxyfluoride reaction is introduced under stirring; (3) After completion of the reaction, a lithium difluorophosphate solution is obtained by filtration, and after concentration, a weakly polar organic solvent is added for recrystallization, and the crystallized product is dried under reduced pressure to give a product. The method for preparing lithium difluorophosphate according to claim 1, wherein the polar organic solvent in the step (1) is acetonitrile, acetone, dimethyl carbonate, diethyl carbonate, and carbonic acid. One or more of ethyl ester, ethyl acetate, propyl acetate, butyl acetate, diethyl ether and methyl tert-butyl ether. The method for preparing lithium difluorophosphate according to claim 2, wherein the fluorinating reagent in the step (1) is sodium fluoride, potassium fluoride, zinc fluoride, antimony trifluoride, One of hydrogen fluoride. The method for preparing lithium difluorophosphate according to claim 3, wherein the stoichiometric molar ratio of the phosphoryl chloride and the fluorinating reagent in the step (1) is 1:1.1 to 1:5, and the reaction The temperature is 25 to 80 °C. The method for preparing lithium difluorophosphate according to claim 4, wherein the stoichiometric molar ratio of the phosphoryl chloride and the fluorinating reagent in the step (1) is 1:1.5 to 1:4. The method for preparing lithium difluorophosphate according to claim 1, wherein the polar organic solvent in the step (2) is dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, acetic acid. Ethyl ester, propyl acetate, butyl acetate, propyl propionate, acetonitrile, propionitrile, acetone, tetrahydrofuran, diethyl ether, methyl tert-butyl ether, propyl ether, dibutyl ether, ethylene glycol dimethyl ether Or several. The method for preparing lithium difluorophosphate according to claim 6, wherein the reaction temperature in the step (2) is -5 to 60 °C. The method for preparing lithium difluorophosphate according to claim 1, wherein the weakly polar solvent in the step (3) is dichloromethane, chloroform, n-hexane, cyclohexane or toluene. One or more of xylene, chlorobenzene, and fluorobenzene. The method for preparing lithium difluorophosphate according to claim 8, wherein the temperature under reduced pressure drying in the step (3) is 60 to 120 °C.