A preparation method of lithium difluorophosphate

Abstract

The present invention relates to the field of lithium battery additive synthesis technology, specifically discloses a kind of preparation method of lithium difluorophosphate. The inventive method includes the following steps: (1) under a closed inert gas environment, lithium fluoride solid and phosphoric acid cyclic anhydride are added to an organic solvent and uniformly dispersed, and the control system temperature is 10 DEG C ~ 60 DEG C, then slowly added to the system. Fluorination reagent, finish, then continue to be incubated, and the total reaction time is 3 ~ 4h; (2) the reaction mass of step (1) is concentrated, and after cooling and crystallization, lithium difluorophosphate is filtered and dried to obtain lithium difluorophosphate, and the purity of lithium difluorophosphate reaches more than 99.5%; wherein, the lithium fluoride in step (1) is replaced with sodium fluoride or potassium fluoride, and final step (2) obtains sodium difluorophosphate or potassium difluorophosphate respectively, and its purity reaches more than 99.5%. The present invention has low reaction energy consumption, high element utilization rate and is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery additive synthesis, and in particular to a method for preparing lithium difluorophosphate. Background Art

[0002] Lithium-ion batteries have higher specific capacity and discharge voltage than traditional lead-acid batteries and alkaline batteries, and are less polluting to the environment. In the development of lithium salt additive products, traditional lithium hexafluorophosphate as an electrolyte can no longer meet the requirements of lithium-ion batteries for use under special environmental conditions. However, lithium difluorophosphate as an electrolyte additive can effectively improve the high cycle performance and high and low temperature storage performance of lithium-ion batteries, significantly improving their cycle stability at -15°C, and forming a more stable SEI film under high temperature conditions. The formed SEI film can effectively prevent the electrolyte from corroding the electrodes and current collectors, giving lithium-ion batteries better high and low temperature performance. Therefore, lithium difluorophosphate, as a new type of lithium salt additive, is not only of great significance to the use and development of lithium batteries, but also has great commercial value as an industrial product.

[0003] Currently, there are many methods for producing lithium difluorophosphate. For example, lithium difluorophosphate is prepared by reacting lithium hexafluorophosphate with siloxane. This method is difficult to produce, and the byproduct is a fluorosilane, which is highly toxic. The production process is dangerous and very unfavorable.

[0004] For example, CN113148971A discloses a method for reacting POCl3 with anhydrous triphosphate in an organic solvent. This method has a low yield and low product purity. Furthermore, the phosphates used (such as Na3PO4 and K3PO4) can cause excessive levels of other metal ions (sodium and potassium) in the product besides lithium, making it unsuitable for use in lithium battery electrolytes and unsuitable for industrial production.

[0005] For example, CN106882782A discloses a method of reacting POF3 with P2O5 and lithium-containing inorganic salts (LiF, LiOH, Li2CO3) in an organic solvent. The POF3 used in this reaction is a gas and has high activity, which is inconvenient to store and transport. The reaction is a pressurized reaction, with high equipment requirements. The moisture content of the reaction system needs to be less than 1ppm. The reaction conditions are harsh and industrialization is difficult to achieve.

[0006] For example, CN112897494A discloses a synthesis process for lithium difluorophosphate, in which a phosphorus oxide compound, lithium fluoride, and phosphorus pentafluoride are reacted in anhydrous hydrogen fluoride to synthesize lithium difluorophosphate. The P2O5 therein easily reacts with water to form phosphate. Moreover, when the phosphorus oxide compound is polyphosphoric acid or metaphosphoric acid (see Examples 6 and 7), the reaction byproduct is phosphoric acid, and the element utilization rate is low. At the same time, the phosphate is difficult to handle in subsequent processing. The residual phosphate will corrode the lithium battery separator material and the aluminum coating material, thereby causing a battery short circuit and a fire. Therefore, the lithium difluorophosphate is not suitable for use in lithium battery electrolytes.

[0007] In summary, the existing preparation methods of lithium difluorophosphate have low product quality, complex processes, high reaction energy consumption, and low element utilization, which are very unfavorable for the industrialization and promotion of lithium difluorophosphate. Summary of the Invention

[0008] Based on the problems existing in the prior art, the present invention aims to provide a method for preparing lithium difluorophosphate with excellent product purity, simple process, low reaction energy consumption, high element utilization rate and suitable for industrial production.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] A method for preparing difluorophosphate comprises the following steps:

[0011] (1) In a closed inert gas environment, solid lithium fluoride and cyclic phosphoric acid anhydride are added to an organic solvent and uniformly dispersed, the system temperature is controlled at -10°C to 60°C, and then the fluorination reagent is slowly added to the system. After the addition is completed, the system is kept warm. The total reaction time is 3 to 4 hours; the total reaction time includes the addition time of the fluorination reagent and the holding time;

[0012] (2) The reaction material of step (1) is concentrated, cooled and crystallized, filtered and dried to obtain lithium difluorophosphate, wherein the purity of lithium difluorophosphate reaches more than 99.5%.

[0013] Furthermore, in step (1):

[0014] The lithium fluoride can be replaced by sodium fluoride or potassium fluoride, and the final step (2) is to obtain sodium difluorophosphate or potassium difluorophosphate, respectively, with a purity of more than 99.5%.

[0015] The structural formula of the phosphoric acid cyclic anhydride is as follows:

[0016] Here, R1 is an alkyl group having 1 to 4 carbon atoms.

[0017] The phosphoric acid cyclic anhydride is preferably 1-propyl phosphoric acid cyclic anhydride.

[0018] The organic solvent is any one of benzene, pyridine, ether, and carbonate, preferably any one of toluene, o-xylene, tetrahydrofuran, ethylene glycol dimethyl ether, ethyl methyl carbonate, diethyl carbonate, pyridine, ethylene glycol diethyl ether, and dimethyl carbonate, and most preferably pyridine.

[0019] The molar ratio of the lithium fluoride to the phosphoric acid cyclic anhydride is 3: 1. The concentration of the phosphoric acid cyclic anhydride in the system is 0.5-1.2 mol / L, preferably 0.7-1.0 mol / L.

[0020] The fluorination agent is hydrogen fluoride gas or a hydrogen fluoride pyridine complex (preferably a 70 wt % hydrogen fluoride pyridine solution).

[0021] The ratio of the amount of hydrogen fluoride to the amount of phosphoric acid cyclic anhydride in the fluorination reagent is 3:1.

[0022] Preferably, the system temperature is controlled at 20-40°C; more preferably, the system temperature is controlled at 20-30°C, and most preferably, the system temperature is controlled at 25±2°C; then the fluorination reagent is slowly added to the system over 2.5-3 hours, and then the temperature is kept warm for 0.5-1 hour.

[0023] Furthermore, in step (2): the reaction material of step (1) is concentrated, the concentration temperature is not more than 60° C., and the mass of the residue is concentrated to 2.5-2.7 times the mass of the theoretical product. After cooling to 5-10° C. for crystallization, it is filtered and dried to obtain lithium difluorophosphate.

[0024] In the present invention, preferably, lithium fluoride is used as the fluoride salt, 1-propyl phosphoric acid cyclic anhydride is used as the phosphoric acid cyclic anhydride, and hydrogen fluoride gas is used as the fluorination agent for the reaction. The reaction principle is:

[0025]

[0026] During the entire process of the above preparation method, the solution moisture content is less than 100 ppm and the solution is protected by an inert gas.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] (1) The raw materials for the reaction are readily available, the market supply and demand for the product is stable, and the solvent required for the reaction is also a relatively common solvent. Therefore, the process can be simple, the reaction does not produce toxic or harmful gases, the reaction has low requirements on the reaction equipment, and the production of lithium difluorophosphate with high product quality can be achieved.

[0029] (2) The purity of the lithium difluorophosphate produced by the present invention can reach over 99.5%, fully meeting the requirements for electrolyte preparation. Furthermore, the reaction yield is high, and the resulting solid particles have good dispersibility, which facilitates the promotion of lithium difluorophosphate as a new type of lithium salt additive with high and low temperature performance. It has significant commercial, social, and economic value.

[0030] (3) The present invention uses readily available 1-propylphosphonic acid cyclic anhydride and lithium fluoride as raw materials, conducts a fluorination reaction with hydrogen fluoride at room temperature, and employs a solvothermal method to rapidly and efficiently prepare lithium difluorophosphate with high purity (greater than 99.5%) and yield (greater than 95%). This method significantly improves reaction time and efficiency, greatly facilitating industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the ion chromatogram of lithium difluorophosphate prepared in Example 3. DETAILED DESCRIPTION

[0032] The applicant further describes the technical solution of the present invention in conjunction with specific embodiments below, but the scope of protection requested by the claims of the present invention is not limited to these embodiments.

[0033] The inert gas environment described in the following examples and comparative examples is a nitrogen environment.

[0034] Example 1 A method for preparing lithium difluorophosphate comprises the following steps:

[0035] (1) At room temperature (25°C), under an inert gas atmosphere, 988 ml of pyridine was added to a 2 L 316 stainless steel reaction bottle (hereinafter referred to as the "reaction bottle"), followed by the addition of 77.82 g (3.00 mol) of lithium fluoride (electronic grade, the same below) and 318.8 g (1.00 mol) of 1-propylphosphoric acid cyclic anhydride, and the reaction materials were evenly dispersed using magnetic stirring;

[0036] (2) Seal the reaction bottle containing the reaction raw materials and place it in a low-temperature coolant circulation pump;

[0037] (3) Cool the reaction flask in step (2) to -10°C using cold ethanol, then introduce 60.03 g of hydrogen fluoride gas for 2.5-3 hours;

[0038] (4) After ventilation, the reaction was kept at -10°C for 1 h;

[0039] (5) The reaction flask containing the reaction material of step (4) was placed in an oil bath, and the temperature was slowly raised to 35-40° C. for concentration. After concentration until the mass of the residue was 2.5 times the mass of the theoretical product, the temperature was lowered to 10° C. for crystallization. The material was filtered, and the wet solid of the filter cake was dried at a drying temperature of 105° C. for 24 h to finally obtain 291.4 g of lithium difluorophosphate solid, with a yield of 90.02% and a product purity of 99.53%.

[0040] The lithium difluorophosphate solid product obtained in step (5) is placed in a container, and then the container is shaken. The product has good fluidity in the container, indicating that the product has good dispersibility.

[0041] Example 2 A method for preparing lithium difluorophosphate comprises the following steps:

[0042] (1) At room temperature (25°C), under an inert atmosphere, add 988 ml of pyridine to a 2 L 316 stainless steel reaction flask, then add 77.82 g of lithium fluoride and 318.8 g of 1-propylphosphoric acid cyclic anhydride, and use magnetic stirring to evenly disperse the reaction materials;

[0043] (2) Seal the reaction bottle containing the reaction raw materials;

[0044] (3) 60.03 g of hydrogen fluoride gas was introduced into the reaction flask in step (2) for 2.5-3 h;

[0045] (4) After ventilation, continue the reaction at room temperature for 1 h;

[0046] (5) The reaction flask containing the reaction material of step (4) was placed in an oil bath, heated to 35-40°C for concentration, and concentrated until the mass of the residue was 2.5 times the mass of the theoretical product. The temperature was then lowered to 10°C for crystallization, the material was filtered, and the wet solid of the filter cake was dried at a drying temperature of 105°C for 24 hours to finally obtain 307.5 g of lithium difluorophosphate solid, with a yield of 95% and a product purity of 99.73%.

[0047] The lithium difluorophosphate solid product obtained in step (5) is placed in a container, and then the container is shaken. The product has good fluidity in the container, indicating that the product has good dispersibility.

[0048] Example 3 A method for preparing lithium difluorophosphate comprises the following steps:

[0049] (1) At room temperature (25°C), under an inert atmosphere, add 988 ml of pyridine to a 2 L 316 stainless steel reaction flask, then add 77.82 g of lithium fluoride and 318.8 g of 1-propylphosphoric acid cyclic anhydride, and use magnetic stirring to evenly disperse the reaction materials;

[0050] (2) Seal the reaction bottle containing the reaction raw materials and place it in an oil bath;

[0051] (3) Heat the reaction flask in step (2) to 40°C in an oil bath, then introduce 60.03 g of hydrogen fluoride gas for 2.5-3 hours;

[0052] (4) After ventilation, keep the reaction at 40°C for 1 hour;

[0053] (5) The reaction flask containing the reaction material of step (4) was concentrated at 35-40° C. until the mass of the residue was 2.5 times the mass of the theoretical product, and then the temperature was lowered to 10° C. for crystallization. The material was filtered, and the wet solid of the filter cake was dried at a drying temperature of 105° C. for 24 h to finally obtain 297.8 g of lithium difluorophosphate solid, with a yield of 92% and a product purity of 99.60%.

[0054] The lithium difluorophosphate solid product obtained in step (5) is placed in a container, and then the container is shaken. The product has good fluidity in the container, indicating that the product has good dispersibility.

[0055] Example 4 A method for preparing lithium difluorophosphate comprises the following steps:

[0056] (1) At room temperature (25°C), under an inert atmosphere, add 1115.6 ml of pyridine to a 2 L 316 stainless steel reaction flask, then add 125.96 g (3.00 mol) of sodium fluoride and 318.8 g (1.00 mol) of 1-propylphosphoric acid cyclic anhydride, and use magnetic stirring to evenly disperse the reaction materials;

[0057] (2) Seal the reaction bottle containing the reaction raw materials;

[0058] (3) 60.03 g of hydrogen fluoride gas was introduced into the reaction flask in step (2) for 2.5-3 h;

[0059] (4) After ventilation, continue the reaction at room temperature for 1 h;

[0060] (5) The reaction flask containing the reaction material of step (4) was placed in an oil bath, heated to 35-40°C for concentration, and concentrated until the mass of the residue was 2.5 times the mass of the theoretical product, then cooled to 10°C for crystallization, the material was filtered, and the wet solid of the filter cake was dried at a drying temperature of 105°C for 24 hours to finally obtain 355.1 g of sodium difluorophosphate solid, with a yield of 95.5% and a product purity of 99.69%.

[0061] The sodium difluorophosphate solid product obtained in step (5) is placed in a container, and then the container is shaken. The product has good fluidity in the container, indicating that the product has good dispersibility.

[0062] Example 5 A method for preparing lithium difluorophosphate comprises the following steps:

[0063] (1) At room temperature (25°C) and under an inert atmosphere, add 1260.5 ml of pyridine to a 2 L 316 stainless steel reaction flask, then add 174.3 g (3.00 mol) of potassium fluoride and 318.8 g (1.00 mol) of 1-propylphosphoric acid cyclic anhydride, and use magnetic stirring to evenly disperse the reaction materials.

[0064] (2) Seal the reaction bottle containing the reaction raw materials;

[0065] (3) 60.03 g of hydrogen fluoride gas was introduced into the reaction flask in step (2) for 2.5-3 h;

[0066] (4) After ventilation, continue the reaction at room temperature for 1 h;

[0067] (5) The reaction flask containing the reaction material of step (4) was placed in an oil bath, heated to 35-40° C. for concentration, and concentrated until the mass of the residue was 2.5 times the mass of the theoretical product, then cooled to 10° C. for crystallization, the material was filtered, and the filter cake wet solid was dried at a drying temperature of 105° C. for 24 h to finally obtain 403.4 g of potassium difluorophosphate solid, with a yield of 96.0% and a product purity of 99.65%.

[0068] The potassium difluorophosphate solid product obtained in step (5) is placed in a container, and then the container is shaken. The product has good fluidity in the container, indicating that the product has good dispersibility.

[0069] Example 6 A method for preparing lithium difluorophosphate comprises the following steps:

[0070] (1) At room temperature (25°C), under an inert atmosphere, add 988 ml of pyridine to a 2 L 316 stainless steel reaction flask, then add 77.82 g of lithium fluoride and 318.8 g of 1-propylphosphoric acid cyclic anhydride, and use magnetic stirring to evenly disperse the reaction materials;

[0071] (2) Seal the reaction bottle containing the reaction raw materials and place it in a hot oil pan;

[0072] (3) Heat the reaction flask in step (2) to 60°C in an oil bath, then introduce 60.03 g of hydrogen fluoride gas for 2.5-3 hours;

[0073] (4) After ventilation, keep the reaction at 60°C for 1 hour;

[0074] (5) The reaction flask containing the reaction material of step (4) was concentrated at 55-60° C. until the mass of the residue was 2.5 times the mass of the theoretical product, and then the temperature was lowered to 10° C. for crystallization. The material was filtered, and the wet solid of the filter cake was dried at a drying temperature of 105° C. for 24 h to finally obtain 296.1 g of lithium difluorophosphate solid, with a yield of 91.5% and a product purity of 99.59%.

[0075] The lithium difluorophosphate solid product obtained in step (5) is placed in a container, and then the container is shaken. The product has good fluidity in the container, indicating that the product has good dispersibility.

[0076] Example 7 A method for preparing lithium difluorophosphate comprises the following steps:

[0077] (1) At room temperature (25°C), under an inert atmosphere, add 988 ml of pyridine to a 2 L 316 stainless steel reaction flask, then add 77.82 g of lithium fluoride and 318.8 g of 1-propylphosphoric acid cyclic anhydride, and use magnetic stirring to evenly disperse the reaction materials;

[0078] (2) Seal the reaction bottle containing the reaction raw materials;

[0079] (3) adding 85.75 g of 70 wt % hydrogen fluoride pyridine solution to the reaction flask in step (2) dropwise for 2.5-3 h;

[0080] (4) After the addition was complete, the reaction was continued at room temperature for 1 h;

[0081] (5) The reaction flask containing the reaction material of step (4) was placed in an oil bath, heated to 35-40° C. for concentration, and concentrated until the mass of the residue was 2.5 times the mass of the theoretical product. The temperature was then lowered to 10° C. for crystallization, the material was filtered, and the wet solid of the filter cake was dried at a drying temperature of 105° C. for 24 h to finally obtain 294.9 g of lithium difluorophosphate solid, with a yield of 91.1% and a product purity of 99.53%.

[0082] The lithium difluorophosphate solid product obtained in step (5) is placed in a container, and then the container is shaken. The product has good fluidity in the container, indicating that the product has good dispersibility.

[0083] Comparative Example 1 A method for preparing lithium difluorophosphate comprises the following steps:

[0084] (1) At room temperature (25°C), under an inert atmosphere, add 988 ml of pyridine to a 2 L 316 stainless steel reaction flask, then add 76.5 g (2.95 mol) of lithium fluoride and 318.8 g (1.00 mol) of 1-propylphosphoric acid cyclic anhydride, and stir the reaction materials uniformly using a magnetic stirrer;

[0085] (2) Seal the reaction bottle containing the reaction raw materials;

[0086] (3) 60.03 g of hydrogen fluoride gas was introduced into the reaction flask in step (2) for 2.5-3 h;

[0087] (4) After ventilation, continue the reaction at room temperature for 1 h;

[0088] (5) The reaction flask containing the reaction material of step (4) was placed in an oil bath, heated to 35-40°C for concentration, and concentrated until the mass of the residue was 2.5 times the mass of the theoretical product. The temperature was then lowered to 10°C for crystallization, the material was filtered, and the wet solid of the filter cake was dried at a drying temperature of 105°C for 24 hours to finally obtain 294.6 g of lithium difluorophosphate solid, with a yield of 92.5% and a product purity of 98.9%.

[0089] Comparison of Example 2 with Comparative Example 1 shows that when the molar ratio of lithium fluoride to 1-propyl phosphoric acid cyclic anhydride is less than 3, the raw material 1-propyl phosphoric acid cyclic anhydride cannot react completely, thereby affecting the purity of the product.

[0090] Comparative Example 2 A method for preparing lithium difluorophosphate comprises the following steps:

[0091] (1) At room temperature (25°C), under an inert atmosphere, add 988 ml of pyridine to a 2 L 316 stainless steel reaction flask, then add 103.76 g (4 mol) of lithium fluoride and 318.8 g of 1-propylphosphoric acid cyclic anhydride, and use magnetic stirring to evenly disperse the reaction materials;

[0092] (2) Seal the reaction bottle containing the reaction raw materials;

[0093] (3) 60.03 g of hydrogen fluoride gas was introduced into the reaction flask in step (2) for 2.5-3 h;

[0094] (4) After ventilation, continue the reaction at room temperature for 1 h;

[0095] (5) The reaction flask containing the reaction material of step (4) was placed in an oil bath, heated to 35-40°C for concentration, and concentrated until the mass of the residue was 2.5 times the mass of the theoretical product. The temperature was then lowered to 10°C for crystallization, the material was filtered, and the wet solid of the filter cake was dried at a drying temperature of 105°C for 24 hours to finally obtain 324.1 g of lithium difluorophosphate solid with a product purity of 92%.

[0096] (6) At room temperature (25° C.), the 92% pure product obtained in step (5) was added to 971 g of ethylene glycol dimethyl ether and slowly dissolved. The material was filtered, and the filtrate was heated to 35-40° C. and concentrated. After the residue was concentrated to a mass 2.1 times that of the theoretical product, the temperature was lowered to 10° C. for crystallization. The material was filtered, and the wet solid of the filter cake was dried at 105° C. for 24 h to obtain 277.33 g of a solid product with a yield of 85.67% and a product purity of 99.78%.

[0097] Comparison of Example 2 with Comparative Example 1 shows that when the molar ratio of lithium fluoride to 1-propylphosphoric acid cyclic anhydride is greater than 3, the raw material lithium fluoride is excessive, and the resulting product purity does not meet the standard, requiring further impurity removal to obtain a high-purity product. However, the purification and impurity removal step affects the product yield.

Claims

1. A method for preparing difluorophosphate, characterized in that: The steps include: (1) In a closed inert gas environment, lithium fluoride solid and phosphoric acid cyclic anhydride are added to an organic solvent and uniformly dispersed, the concentration of phosphoric acid cyclic anhydride in the system is 0.5-1.2 mol / L, the system temperature is controlled to be -10°C to 60°C, and then the fluorination reagent is slowly added to the system. After the addition is completed, the system is kept warm, and the total reaction time is 3 to 4 hours; the organic solvent is any one of toluene, o-xylene, tetrahydrofuran, ethylene glycol dimethyl ether, ethyl methyl carbonate, diethyl carbonate, pyridine, ethylene glycol diethyl ether, and dimethyl carbonate; (2) concentrating the reaction material of step (1) at a temperature not exceeding 60° C. until the mass of the residue is 2.5-2.7 times the mass of the theoretical product, cooling to 5-10° C. for crystallization, filtering, and drying to obtain lithium difluorophosphate, wherein the purity of the lithium difluorophosphate reaches above 99.5%; The structural formula of the phosphoric acid cyclic anhydride is as follows: Wherein, R1 is an alkyl group having 1 to 4 carbon atoms; The fluorination agent is hydrogen fluoride gas or hydrogen fluoride pyridine complex; The molar ratio of the lithium fluoride to the phosphoric acid cyclic anhydride is 3:1, and the molar ratio of the hydrogen fluoride to the phosphoric acid cyclic anhydride in the fluorination reagent is 3:1; Alternatively, the lithium fluoride in step (1) is replaced by sodium fluoride or potassium fluoride, and finally in step (2) sodium difluorophosphate or potassium difluorophosphate is obtained, respectively, with a purity of more than 99.5%.

2. The preparation method according to claim 1, characterized in that The phosphoric acid cyclic anhydride is 1-propyl phosphoric acid cyclic anhydride.

3. The preparation method according to claim 1, characterized in that The concentration of phosphoric acid cyclic anhydride in the system is 0.7-1.0 mol / L.

4. The preparation method according to claim 1, characterized in that The hydrogen fluoride pyridine complex is a 70 wt% hydrogen fluoride pyridine solution.

5. The preparation method according to claim 1, characterized in that In step (1), the system temperature is controlled to be 20-40°C.

6. The preparation method according to claim 5, characterized in that In step (1), the system temperature is controlled to be 20-30°C.

7. The preparation method according to claim 6, characterized in that In step (1), the system temperature is controlled to be 25±2°C.

8. The preparation method according to claim 1, characterized in that In step (1), the fluorination reagent is slowly added to the system over a period of 2.5 to 3 hours, and the mixture is then kept warm for 0.5 to 1 hour.

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