Processing method for recovering solvent in lithium difluorophosphate synthesis process, and preparation method of lithium difluorophosphate

Abstract

The present invention relates to a method for treating a recovered solvent in a lithium difluorophosphate synthesis process and a method for preparing lithium difluorophosphate, belonging to the technical field of lithium difluorophosphate preparation. The treatment method of the present invention is characterized by comprising the following steps: mixing phosphorus pentafluoride into a recovered solvent and then reacting; the amount of phosphorus pentafluoride mixed into the recovered solvent is 4.5 to 6.5 times the mass of insoluble matter in the recovered solvent; and the recovered solvent is a solvent recovered after solid-liquid separation following the reaction of lithium hexafluorophosphate and organosilicon oxide in a poor organic solvent for lithium difluorophosphate to generate lithium difluorophosphate. The treatment method of the present invention is simple to operate, and when the recovered solvent is recycled after treatment, the content of insoluble matter in the synthesized lithium difluorophosphate can be reduced, thereby improving the recycling efficiency of the solvent.

Description

Technical Field

[0001] The invention relates to a method for processing a recovered solvent in a lithium difluorophosphate synthesis process and a method for preparing lithium difluorophosphate, belonging to the technical field of lithium difluorophosphate preparation. Background Art

[0002] Lithium batteries are a type of clean energy that is highly safe and pollution-free. Lithium-ion batteries can be used in new energy vehicles, electronic products and other fields. In recent years, the new energy vehicle industry has developed rapidly, especially during the period when government subsidy policies were released. The new energy vehicle industry has grown rapidly, especially the large-scale application of power batteries and energy storage batteries, which has favorably driven the development of the lithium battery industry, making lithium batteries an expanding global industry.

[0003] In recent years, lithium difluorophosphate (LDP), a highly effective functional additive, has been widely used in the electrolytes of lithium-ion secondary batteries. LDP forms a low-impedance interface film on the positive and negative electrodes of lithium-ion batteries, inhibiting side reactions between the electrodes and the electrolyte and improving the battery's cycle life.

[0004] Lithium difluorophosphate, with the molecular formula LiPO₂F₂, is a white powdery solid with a melting point of 340°C. When exposed to air, it readily absorbs moisture and becomes acidic. Lithium difluorophosphate is primarily used as an electrolyte additive for lithium batteries. Studies have shown that adding a small amount of lithium difluorophosphate to a lithium hexafluorophosphate electrolyte system can significantly improve the battery's high- and low-temperature cycling performance.

[0005] Currently, the mainstream method for preparing lithium difluorophosphate is to react lithium hexafluorophosphate with lithium carbonate to produce lithium difluorophosphate, lithium fluoride, and carbon dioxide. This process suffers from high raw material costs, complex processes, high energy consumption, difficulty in product separation and purification, and low yield, making it unsuitable for industrial implementation.

[0006] Compared with the above-mentioned prior art, the method for preparing lithium difluorophosphate by reacting lithium hexafluorophosphate and organic silicon oxide has the characteristics of simple process, high reaction efficiency and high product yield. For example, the Chinese invention patent application publication number CN109867269A discloses a method for preparing lithium difluorophosphate, which uses lithium hexafluorophosphate and tris(trimethylsilyl)phosphite to synthesize lithium difluorophosphate in a solvent. The method has a simple process, high reaction efficiency and a product yield of more than 89%. However, the recycling of the solvent during the reaction will lead to an excessively high insoluble matter content in the finished product (20,000 to 30,000 ppm), which seriously affects the purity of the product. Summary of the Invention

[0007] The present invention aims to provide a method for treating a recovered solvent in a lithium difluorophosphate synthesis process, so as to solve the problem of excessively high insoluble matter content in lithium difluorophosphate prepared with lithium hexafluorophosphate and organosilicon oxide as reactants during solvent recycling.

[0008] Another object of the present invention is to provide a method for preparing lithium difluorophosphate.

[0009] In order to achieve the above purpose, the technical solution adopted by the treatment method for recovering the solvent in the lithium difluorophosphate synthesis process of the present invention is:

[0010] A method for treating a recovered solvent in a lithium difluorophosphate synthesis process comprises the following steps: mixing phosphorus pentafluoride into the recovered solvent and then reacting; the amount of phosphorus pentafluoride mixed into the recovered solvent is 4.5 to 6.5 times the mass of insoluble matter in the recovered solvent; and the recovered solvent is a solvent obtained by reacting lithium hexafluorophosphate and organosilicon oxide in a poor organic solvent for lithium difluorophosphate to generate lithium difluorophosphate, followed by solid-liquid separation.

[0011] The present invention provides a method for treating a recovered solvent in a lithium difluorophosphate synthesis process. The method is simple to operate, and when the treated recovered solvent is recycled, the content of insoluble matter in the synthesized lithium difluorophosphate can be reduced, thereby improving the recycling efficiency of the solvent. The recovered solvent treated by the method is used in the preparation of lithium difluorophosphate, and the insoluble matter content in the obtained lithium difluorophosphate can be reduced to below 1000 ppm.

[0012] It is understood that the poor organic solvent is a good solvent for lithium hexafluorophosphate and organosilicon oxide. The poor organic solvent can be a solvent recovered from lithium hexafluorophosphate and organosilicon oxide as reactants to prepare difluorophosphoric acid, or it can be a fresh poor organic solvent. Furthermore, the mixing is to add a phosphorus pentafluoride solution to the recovered solvent; the solvent of the phosphorus pentafluoride solution is a poor organic solvent for lithium difluorophosphate; and the poor organic solvent is a carbonate solvent. The carbonate solvent is preferably a cyclic carbonate and / or a chain carbonate, for example, the cyclic carbonate is preferably ethylene carbonate, and the chain carbonate is preferably dimethyl carbonate and / or ethyl methyl carbonate. In the phosphorus pentafluoride solution, the mass of phosphorus pentafluoride is 9% to 50% of the mass of the solvent, for example, 15% to 50%, or for example, 20% to 33.3%, preferably 15% to 30%, for example, 20% to 30%. Preferably, the amount of phosphorus pentafluoride solution added is 4.9 to 6.1 times, for example, 5.5 to 6 times, the amount of insoluble matter in the recovery solvent.

[0013] Furthermore, the reaction in which phosphorus pentafluoride is mixed into the recovered solvent is carried out under stirring conditions, and the stirring speed is 100 r / min to 300 r / min. Furthermore, the stirring speed is 200 r / min to 250 r / min, for example, 250 r / min.

[0014] Furthermore, the phosphorus pentafluoride solution is added to the recovery solvent by dropwise addition, and the recovery solvent is stirred during the dropwise addition of the phosphorus pentafluoride solution. The dropwise addition speed is 20 mL / min to 60 mL / min.

[0015] Furthermore, the reaction temperature for mixing phosphorus pentafluoride in the recovery solvent is 30-60° C., for example, 30-50° C. Furthermore, the reaction temperature for mixing phosphorus pentafluoride in the recovery solvent is 40-50° C., for example, 45° C.

[0016] Furthermore, the reaction time of adding phosphorus pentafluoride to the recovery solvent is not less than 1 hour, for example, the reaction time is 1 to 5 hours. Preferably, the reaction time of adding phosphorus pentafluoride to the recovery solvent is not less than 2 hours, for example, the reaction time is 2 hours, 3 hours, 4 hours or 5 hours. Furthermore, the reaction time of adding phosphorus pentafluoride to the recovery solvent is 2 to 3 hours.

[0017] In order to prevent phosphorus pentafluoride from decomposing when it comes into contact with water and to improve the utilization rate of phosphorus pentafluoride, the reaction in which phosphorus pentafluoride is mixed into the recovery solvent is carried out under anhydrous conditions, for example, under closed conditions.

[0018] The technical solution adopted in the preparation method of lithium difluorophosphate of the present invention is:

[0019] A method for preparing lithium difluorophosphate comprises the following steps:

[0020] 1) lithium hexafluorophosphate and organosilicon oxide as reactants react in a poor organic solvent for lithium difluorophosphate to generate lithium difluorophosphate, and then separate the solid and liquid to obtain lithium difluorophosphate solid, and collect the liquid after solid-liquid separation to obtain a recovered solvent;

[0021] 2) mixing phosphorus pentafluoride into the obtained recovery solvent and reacting the mixture to obtain a treated recovery solvent; the amount of phosphorus pentafluoride mixed into the recovery solvent is 4.5 to 6.5 times the amount of insoluble matter in the recovery solvent;

[0022] 3) returning the treated recovered solvent obtained in step 2) to step 1) as a poor organic solvent, and repeating steps 1) and 2).

[0023] The method for preparing lithium difluorophosphate of the present invention is simple to operate, can improve the recycling efficiency of poor organic solvents for lithium difluorophosphate, and can reduce the content of insoluble matter in the synthesized lithium difluorophosphate, thereby improving the purity of the lithium difluorophosphate and achieving high economic efficiency. The method for preparing lithium difluorophosphate of the present invention can achieve an insoluble matter content of less than 1000 ppm in the lithium difluorophosphate obtained by recycling poor organic solvents for lithium difluorophosphate.

[0024] Furthermore, in step 1), the reaction temperature is 30° C. to 90° C., and the reaction time is 6 to 15 hours. For example, the reaction temperature is 60° C., and the reaction time is 6 hours. Furthermore, the organosilicon oxide is a polymethylsiloxane, for example, dimethyldisiloxane and / or tetramethyldisiloxane.

[0025] Furthermore, in step 2), the mixing is performed by adding a phosphorus pentafluoride solution to a poor recovery solvent; the solvent of the phosphorus pentafluoride solution is a poor organic solvent for lithium difluorophosphate; and the poor organic solvent is a carbonate solvent. In the phosphorus pentafluoride solution, the mass of phosphorus pentafluoride is 9% to 50% of the mass of the poor solvent, for example, 15% to 50%, or 20% to 33.3%, preferably 15% to 30%, for example, 20% to 30%. Furthermore, the amount of phosphorus pentafluoride added is 4.9 to 6.1 times, for example, 5.5 to 6 times, the mass of insoluble matter in the recovery solvent.

[0026] Furthermore, in step 2), the reaction is carried out under stirring conditions, and the stirring speed is 100 r / min to 300 r / min. Furthermore, the stirring speed is 200 r / min to 250 r / min, for example, 250 r / min.

[0027] Furthermore, the phosphorus pentafluoride solution is added to the recovery solvent by dropwise addition, and the recovery poor solvent is stirred during the dropwise addition of the phosphorus pentafluoride solution. The dropwise addition speed is 30 mL / min to 60 mL / min.

[0028] Furthermore, in step 2), the reaction temperature is 30-60° C., for example, 30-50° C. Further, in step 2), the reaction temperature is 40-50° C., for example, 45° C.

[0029] Furthermore, in step 2), the reaction time is not less than 1 hour. For example, the reaction time is 1 to 5 hours. Preferably, in step 2), the reaction time is not less than 2 hours, for example, the reaction time is 2 hours, 3 hours, 4 hours or 5 hours. Furthermore, in step 2), the reaction time is 2 to 3 hours.

[0030] Furthermore, in step 2), the reaction is carried out under anhydrous conditions, for example, in a sealed environment. To prevent decomposition and deterioration of lithium hexafluorophosphate, the reaction of lithium hexafluorophosphate and organosilicon oxide in a poor organic solvent for lithium difluorophosphate in step 1) to produce lithium difluorophosphate also needs to be carried out under anhydrous conditions. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0032] Examples 1 to 8

[0033] The preparation method of lithium difluorophosphate of this embodiment comprises the following steps:

[0034] 1) Lithium difluorophosphate is prepared from lithium hexafluorophosphate and dimethyldisiloxane, the specific steps are as follows:

[0035] First, a three-necked flask is dried, and then 71g of lithium hexafluorophosphate is added to the three-necked flask under nitrogen protection. Then, 560g of ethylene carbonate (a poor organic solvent for lithium difluorophosphate) is added to the three-necked flask and dissolved with stirring at room temperature. After the lithium hexafluorophosphate is completely dissolved, 70g of dimethyldisiloxane is added to the three-necked flask, and the temperature is raised to 70°C under stirring. The reaction is continued for 6 hours, and the generated gas is passed into an alkaline solution for absorption. After the reaction, a lithium difluorophosphate synthesis liquid is obtained, which is filtered to obtain a lithium difluorophosphate solid, and the filtrate is recovered to obtain a recovered poor solvent; the content of insoluble matter in the recovered solvent is 0.8%; and the content of insoluble matter in the obtained lithium difluorophosphate solid is 25800ppm;

[0036] 2) In a dry room fume hood, weigh 400 g of fresh ethylene carbonate (DEC) into a clean, dry three-necked flask. While keeping it sealed, slowly introduce 99.5% pure phosphorus pentafluoride (PF5) gas into the flask. The gas inlet rate is slightly adjusted based on the intensity of the reaction to ensure complete absorption of the phosphorus pentafluoride and prevent excessive pressure from causing the stopper to break. After introducing a mass m1 of phosphorus pentafluoride gas, seal the flask and allow it to stand for 24 hours to obtain a phosphorus pentafluoride solution. The mass m1 for each example is shown in Table 1.

[0037] 3) In a fume hood in a dry room, 300 g (containing 2.4 g of insoluble matter) of the recovered poor solvent obtained in step 1) was weighed in a clean, dry three-necked flask. The recovered solvent was kept at a temperature of T in an oil bath, stirring was started and the stirring speed was set to v. A phosphorus pentafluoride solution having a mass of m2 was slowly added dropwise to the recovered poor solvent at a dropping rate of 20 mL / min. After the dropwise addition was completed, the temperature of the system was maintained at T and the stirring reaction was continued under closed conditions for a time of t to obtain a treated recovered solvent. The temperature T, mass m2, stirring speed v, and stirring reaction time t in each embodiment are specifically shown in Table 1.

[0038] 4) The treated recovered solvent obtained in step 3) is returned to step 1) as a poor organic solvent to repeat steps 1) to 3).

[0039] The insoluble matter content in the lithium difluorophosphate obtained in step 4) of Examples 1 to 8 was detected and analyzed respectively. The detection method comprises the following steps: dissolving the obtained lithium difluorophosphate solid in an ethyl acetate solution 12 times the mass of the sample, filtering the solution, drying the obtained insoluble matter, and weighing the solution. The insoluble matter content was determined based on the ratio of the amount of lithium difluorophosphate to the amount of undissolved material. The determination method for the insoluble matter content in the recovered solvent was the same as the finished product determination method, which was to dissolve the recovered solvent in ethyl acetate 12 times the mass of the recovered solvent, then filter the solution, dry the obtained solid, and weigh the solution, and then calculate the insoluble matter content in the recovered solvent. The test results of the insoluble matter content in the lithium difluorophosphate solid obtained when step 1) was repeated for the first time are shown in Table 1.

[0040] Table 1 Related condition parameters in Examples 1 to 8 and insoluble matter detection and analysis results of preparing lithium difluorophosphate solid in step 4)

[0041] Example <![CDATA[Mass m1, g]]> Speed v, r / min <![CDATA[Mass m2, g]]> Temperature T,℃ Time t,h Insoluble matter content, ppm 1 100 250 60 45 3 580 2 200 250 44 45 3 570 3 50 250 108 45 3 1680 4 100 100 65 45 3 1550 5 100 200 65 45 3 1190 6 100 250 60 30 3 960 7 100 250 60 45 1 2160 8 100 250 60 45 5 560

[0042] In step 1) of Example 1, the recovered solvent obtained after filtering the synthesis of lithium difluorophosphate from lithium hexafluorophosphate and dimethyldisiloxane in an ethylene carbonate solution was not treated but directly returned for use as a poor solvent for lithium difluorophosphate. The insoluble matter content in the finished product after multiple cycles is shown in Table 2.

[0043] Table 2 Insoluble matter content in finished products after multiple cycles

[0044] Solvent cycles / times Insoluble matter content of finished lithium difluorophosphate / ppm 0 660 1 2230 2 6480 3 8950 4 12300 5 15200

[0045] It can be seen from the above table that with the recycling of solvents, insoluble matter in the finished product will accumulate, causing the insoluble matter content of the finished product to increase.

[0046] As can be seen from the data in Table 1 and Table 2, the preparation method of lithium difluorophosphate of the present invention is simple to operate, the treatment of the solvent can be recycled and reused, the production cost is greatly reduced, and the resource value is maximized. At the same time, the content of insoluble matter in the lithium difluorophosphate product prepared when the solvent is recycled can be effectively reduced, meeting the requirements for use of electrolytes for lithium batteries.

[0047] In the embodiment of the treatment method for recovering the solvent in the lithium difluorophosphate synthesis process of the present invention, the treatment method is the same as steps 2) to 3) in Examples 1 to 8 and will not be repeated here.

Claims

1. A method for recovering solvent in a lithium difluorophosphate synthesis process, characterized in that: The following steps are involved: Phosphorus pentafluoride is mixed into a recovery solvent and then reacted at 30-60° C. for 2-3 hours. The amount of phosphorus pentafluoride mixed into the recovery solvent is 4.5-6.5 times the amount of insoluble matter in the recovery solvent. The recovery solvent is a solvent recovered after solid-liquid separation after lithium difluorophosphate is generated by reacting lithium hexafluorophosphate and organosilicon oxide as reactants in a poor organic solvent for lithium difluorophosphate.

2. The method for recovering solvent in the lithium difluorophosphate synthesis process according to claim 1, wherein: The mixing is to add phosphorus pentafluoride solution into the recovery solvent; the solvent of the phosphorus pentafluoride solution is a poor organic solvent of lithium difluorophosphate; and the poor organic solvent is a carbonate solvent.

3. The method for recovering solvent in the lithium difluorophosphate synthesis process according to claim 1 or 2, wherein: The reaction of mixing phosphorus pentafluoride into the recovered solvent is carried out under stirring conditions, and the stirring speed is 200r / min to 250r / min.

4. A method for preparing lithium difluorophosphate, characterized in that: The following steps are involved: 1) Lithium hexafluorophosphate and organosilicon oxide are reacted in a poor organic solvent for lithium difluorophosphate to generate lithium difluorophosphate, followed by solid-liquid separation to obtain lithium difluorophosphate solid, and the liquid after solid-liquid separation is collected to obtain a recovered solvent; 2) adding phosphorus pentafluoride to the recovered solvent and reacting the mixture at 30-60° C. for 2-3 hours to obtain a treated recovered solvent; the amount of phosphorus pentafluoride added to the recovered solvent is 4.5-6.5 times the amount of insoluble matter in the recovered solvent; 3) The treated recovered solvent obtained in step 2) is returned to step 1) as a poor organic solvent, and steps 1) and 2) are repeated.

5. The method for preparing lithium difluorophosphate according to claim 4, wherein: In step 1), the reaction temperature is 30° C. to 90° C., and the reaction time is 6 to 15 hours.

6. The method for preparing lithium difluorophosphate according to claim 4 or 5, characterized in that: In step 2), the mixing is to add phosphorus pentafluoride solution into the recovery solvent; the solvent of the phosphorus pentafluoride solution is a poor organic solvent for lithium difluorophosphate; and the poor organic solvent is a carbonate solvent.