A preparation method for co-producing lithium difluorophosphate and lithium hexafluorophosphate

Abstract

The present invention provides a preparation method for co-producing lithium difluorophosphate and lithium hexafluorophosphate, which comprises the following steps: 1) Dissolve lithium phosphate in a carbonate solvent to obtain a lithium phosphate solution, and adjust the temperature of the solution to 5-10 °C; 2) Introduce phosphorus pentafluoride gas into the aforementioned lithium phosphate solution and gradually carry out a reaction to generate lithium difluorophosphate and lithium fluoride. The lithium fluoride continues to react with phosphorus pentafluoride to generate lithium hexafluorophosphate. Finally, the molar ratio of lithium phosphate to phosphorus pentafluoride is 1:2 ± 0.1, and a solution of lithium difluorophosphate and lithium hexafluorophosphate is obtained. Among them, lithium hexafluorophosphate dissolves in the carbonate solution to form a lithium hexafluorophosphate solution, and lithium difluorophosphate is slightly soluble in the carbonate and precipitates in the form of crystals to form a turbid solution; 3) Separate the lithium hexafluorophosphate solution and the lithium difluorophosphate turbid solution. The crystalline lithium difluorophosphate is dried to obtain the finished product, and the concentration of the liquid-phase lithium hexafluorophosphate can be directly adjusted and then enter the electrolyte system.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical product preparation, and particularly relates to a preparation method for co-producing lithium difluorophosphate and lithium hexafluorophosphate. Background Art

[0002] As a prior patent application: CN202211453030.9, a preparation method for co-producing lithium difluorophosphate and lithium hexafluorophosphate, is a partial priority patent of the present invention.

[0003] Lithium hexafluorophosphate, LiPF6, CAS: 21324 - 40 - 3, is mainly used as an electrolyte for lithium-ion battery electrolytes. Lithium hexafluorophosphate has the most advantages in terms of conductivity, safety, and environmental friendliness in organic solvents, and has become the lithium salt electrolyte with the widest application range at present.

[0004] Lithium difluorophosphate, LiPO2F2, CAS: 24389 - 25 - 1, is mainly used as an additive for lithium-ion battery electrolytes to improve the cycle life and enhance the performance of lithium-ion batteries.

[0005] Currently, for the preparation of lithium hexafluorophosphate, the common method is to dissolve lithium fluoride in anhydrous hydrogen fluoride and introduce phosphorus pentafluoride gas. After synthesis, it is crystallized, dried, etc. The operation of anhydrous hydrogen fluoride as a solvent is highly dangerous, the extraction process is troublesome, and there are problems such as waste of energy and materials when redissolving the crystallized solid for use in electrolytes. Some materials mention using lithium carbonate and phosphorus pentafluoride to react to prepare lithium hexafluorophosphate. In this system, the carbonate group (CO32-) will be replaced, and the phosphorus in phosphorus pentafluoride enters the system in the pentavalent (P5+) form. The reaction to generate lithium hexafluorophosphate lacks the presence of negative fluoride (F-), so the route is not feasible. When using lithium phosphate as a raw material, first lithium phosphate reacts with phosphorus pentafluoride to generate lithium difluorophosphate and lithium fluoride, and the lithium fluoride provides negative fluoride (F-) to continue reacting with phosphorus pentafluoride to generate lithium hexafluorophosphate, which conforms to the synthesis mechanism of lithium hexafluorophosphate.

[0006] There is a patent mentioning using phosphorus oxides as raw materials to prepare lithium hexafluorophosphate. The principle is to prepare phosphorus pentafluoride from phosphorus oxides and then react with fluorine-containing lithium salts to prepare fluorine-containing phosphates. The present invention directly prepares phosphates using oxygen-containing phosphates, and the preparation process is shorter, so the cost is lower. Summary of the Invention

[0007] The main object of the present invention is to provide a preparation method for co-producing lithium difluorophosphate and lithium hexafluorophosphate, with simple raw materials, capable of simultaneously producing two lithium salts, and also capable of controlling the addition amount of phosphorus pentafluoride to produce lithium difluorophosphate and lithium fluoride.

[0008] The present invention adopts the following technical scheme: A preparation method for co-producing lithium difluorophosphate and lithium hexafluorophosphate, comprising the following steps:

[0009] 1) Dissolve lithium phosphate in a carbonate ester to obtain a lithium phosphate solution, and adjust the temperature of the solution to 5 - 10 °C;

[0010] 2) Pass phosphorus pentafluoride gas into the above-mentioned lithium phosphate solution to carry out the reaction step by step, generating lithium difluorophosphate and lithium fluoride. Lithium fluoride continues to react with phosphorus pentafluoride to generate lithium hexafluorophosphate. Finally, the molar ratio of lithium phosphate to phosphorus pentafluoride is 1:2 ± 0.1, obtaining lithium difluorophosphate and lithium hexafluorophosphate. Lithium hexafluorophosphate dissolves in the carbonate ester solution to form a lithium hexafluorophosphate solution, and lithium difluorophosphate is slightly soluble in the carbonate ester and precipitates in the form of crystals to form a turbid solution;

[0011] 3) Perform solid-liquid separation on the reacted lithium hexafluorophosphate and lithium difluorophosphate solution to obtain lithium difluorophosphate crystals and a lithium hexafluorophosphate solution; the liquid-phase lithium hexafluorophosphate can directly enter the electrolyte system after adjusting the concentration;

[0012] 4) The lithium difluorophosphate crystals are dried to obtain lithium difluorophosphate products;

[0013] 5) Adjust the concentration of the liquid-phase lithium hexafluorophosphate to 40 ± 0.1%.

[0014] As a further preference, in step 1), the solvent is dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, etc.

[0015] As a further preference, in step 1), the concentration of lithium phosphate in the solution is 20 - 25% (Wt%).

[0016] As a further preference, in step 2), the feeding rate of phosphorus pentafluoride is 10 - 15 L / min.

[0017] As a further preference, in step 4), the solid-liquid separation is centrifugal separation.

[0018] The beneficial effects of the present invention are as follows: The present invention uses lithium phosphate as the raw material. Compared with the traditional method of using lithium fluoride as the raw material to produce lithium hexafluorophosphate, the raw material cost is low, and lithium difluorophosphate can be produced as a by-product, with higher production efficiency.

[0019] As an optimized option, trifluoromethanesulfonyl carbonate can be added to the solvent, and its preparation method is as follows:

[0020] The preparation method of adding trifluoromethanesulfonyl carbonate to the solvent is as follows:

[0021] By weight, add 42 - 60 parts of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 50 - 100 parts of allyl diglycol dicarbonate, 200 - 600 parts of DMF, and 2 - 6 parts of ethylenediamine, stir at 50 - 60 °C for 30 - 80 minutes, and distill off DMF to obtain trifluoromethanesulfonyl carbonate-containing;

[0022] The addition amount is 0.5 - 3% of the mass percentage of the solvent.

[0023] The lithium hexafluorophosphate solution product can directly enter the electrolyte system, avoiding the processes of crystallization of lithium hexafluorophosphate and redissolution after entering the electrolyte, reducing the energy consumption, material consumption and labor consumption of low-temperature crystallization during the salt formation process, and being beneficial to cost reduction and efficiency increase in the industrial process.

[0024] Trifluoromethanesulfonyl carbonate, as an organic solvent, is used in the reaction for co-producing lithium hexafluorophosphate from lithium difluorophosphate, and has advantages such as high efficiency and high purity.

[0025] The fluorine atoms of the trifluoromethyl group in trifluoromethanesulfonyl carbonate are arranged in a cis configuration, which is the same as the arrangement order of the fluorine atoms in hexafluorophosphoric acid. Therefore, the two have affinity. At the same time, due to the trans arrangement of the remaining two fluorine atoms of the difluorophosphate group substituted by oxygen atoms, they are repulsive, which can increase the solubility of lithium hexafluorophosphate and reduce the solubility of lithium difluorophosphate, changing from slightly soluble to insoluble. The solubility curves of lithium hexafluorophosphate and lithium difluorophosphate in carbonate after adding trifluoromethanesulfonyl carbonate are as Figure 2 , Figure 3 shown.

[0026] Trifluoromethanesulfonyl carbonate can be used as an electrolyte additive to form a hybrid electrolyte by mixing an organic carbonate solvent with lithium bis(trifluoromethanesulfonyl)imide. The battery with this electrolyte can reduce the impedance at low temperature, and at the same time increase the capacity retention rate at low temperature, and can improve the charge-discharge rate in terms of charge-discharge performance.

[0027] The reaction equation of the present invention is as follows:

[0028] (1) Li3PO4 + PF5 → 2LiPO2F2 + LiF

[0029] (2) LiF + PF5 → LiPF6

[0030] Or

[0031] Li3PO4 + 2PF5 → 2LiPO2F2 + LiPF6 Brief Description of the Drawings

[0032] Figure 1 is the process flow chart for co-producing lithium hexafluorophosphate from lithium difluorophosphate.

[0033] Figure 2 is the solubility of lithium hexafluorophosphate in carbonate solution before and after adding trifluoromethanesulfonyl carbonate.

[0034] Figure 3 is the solubility of lithium difluorophosphate in carbonate solution before and after adding trifluoromethanesulfonyl carbonate.

[0035] Figure 4 It is the battery impedance at -10°C in Example 8.

[0036] Figure 5 It is the capacity retention rate at -20°C in Example 8.

[0037] Figure 6 It is the graph of the discharge rate performance of Example 8.

[0038] Figure 7 It is the graph of the charge rate performance of Example 8. Detailed implementation manners

[0039] To better understand the above technical solutions, the technical solutions of this application will be described in detail through specific examples below. It should be understood that the specific examples of this application and the specific features therein are detailed descriptions of the technical solutions of this application, rather than limitations on the technical solutions of this application. Without conflict, the technical features in the embodiments of this application and the embodiments can be combined with each other. It should be understood that the term "and / or" used herein includes any and all combinations of one or more of the listed related items.

[0040] The following provides a more detailed description of this application through examples. These examples are only descriptions of the best implementation manners of this application and do not limit the scope of this application in any way.

[0041] Example 1

[0042] A preparation method for co-producing lithium difluorophosphate and lithium hexafluorophosphate includes the following steps:

[0043] 1) Dissolve 200 g of lithium phosphate in 800 g of dimethyl carbonate to obtain a 20% lithium phosphate solution, and adjust the temperature of the solution to 5°C;

[0044] 2) Introduce 435.2 g of phosphorus pentafluoride gas into the aforementioned lithium phosphate solution at room temperature, and react to obtain lithium difluorophosphate and lithium hexafluorophosphate. Among them, lithium difluorophosphate precipitates in crystal form and is suspended in the dimethyl carbonate solution, and lithium hexafluorophosphate is dissolved in the dimethyl carbonate solution;

[0045] 3) Centrifuge the above solution to obtain lithium difluorophosphate crystals and a lithium hexafluorophosphate solution;

[0046] 4) Dry the lithium difluorophosphate crystals to obtain lithium difluorophosphate (365.2 g) finished products;

[0047] 5) Sampling analysis shows that a total of 262 g of lithium hexafluorophosphate is generated. Heat and evaporate 393.5 g of dimethyl carbonate from the separated lithium hexafluorophosphate solution, and adjust the concentration of the lithium hexafluorophosphate solution to 40%.

[0048] Example 2

[0049] A preparation method of lithium difluorophosphate co-producing lithium hexafluorophosphate, comprising the following steps:

[0050] 1) Dissolve 260 g of lithium phosphate in 921.8 g of ethyl methyl carbonate to obtain a 22% lithium phosphate solution, and adjust the temperature of the solution to 8 °C;

[0051] 2) Introduce 565.8 g of phosphorus pentafluoride gas into the aforementioned lithium phosphate solution at room temperature, and react to obtain lithium difluorophosphate and lithium hexafluorophosphate. Among them, lithium difluorophosphate precipitates in the form of crystals and is suspended in the ethyl methyl carbonate solution, and lithium hexafluorophosphate is dissolved in the ethyl methyl carbonate solution;

[0052] 3) Centrifuge the above solution to obtain lithium difluorophosphate crystals and a lithium hexafluorophosphate solution;

[0053] 4) Dry the lithium difluorophosphate crystals to obtain lithium difluorophosphate (474.8 g) finished product;

[0054] 5) Sampling analysis shows that a total of 340.3 g of lithium hexafluorophosphate is generated. Heat and evaporate 413.5 g of ethyl methyl carbonate from the separated lithium hexafluorophosphate solution, and adjust the concentration of the lithium hexafluorophosphate solution to 40.1%.

[0055] Example 3

[0056] A preparation method of lithium difluorophosphate co-producing lithium hexafluorophosphate, comprising the following steps:

[0057] 1) Dissolve 320 g of lithium phosphate in 1041.7 g of diethyl carbonate to obtain a 23.5% lithium phosphate solution, and adjust the temperature of the solution to 10 °C;

[0058] 2) Introduce 696.4 g of phosphorus pentafluoride gas into the aforementioned lithium phosphate solution at room temperature, and react to obtain lithium difluorophosphate and lithium hexafluorophosphate. Among them, lithium difluorophosphate precipitates in the form of crystals and is suspended in the diethyl carbonate solution, and lithium hexafluorophosphate is dissolved in the diethyl carbonate solution;

[0059] 3) Centrifuge the above solution to obtain lithium difluorophosphate crystals and a lithium hexafluorophosphate solution;

[0060] 4) Dry the lithium difluorophosphate crystals to obtain lithium difluorophosphate (584.1 g) finished product;

[0061] 5) Sampling analysis shows that a total of 419.1 g of lithium hexafluorophosphate is generated. Heat and evaporate 410.4 g of diethyl carbonate from the separated lithium hexafluorophosphate solution, and adjust the concentration of the lithium hexafluorophosphate solution to 39.9%.

[0062] Example 4

[0063] A preparation method for co-producing lithium difluorophosphate and lithium hexafluorophosphate, comprising the following steps:

[0064] 1) Dissolve 390 g of lithium phosphate in 1170 g of dimethyl carbonate to obtain a 25% lithium phosphate solution, and adjust the temperature of the solution to 9 °C;

[0065] 2) At room temperature, introduce 848.7 g of phosphorus pentafluoride gas into the aforementioned lithium phosphate solution, and react to obtain lithium difluorophosphate and lithium hexafluorophosphate, wherein lithium difluorophosphate precipitates in crystal form and is suspended in the dimethyl carbonate solution, and lithium hexafluorophosphate is dissolved in the dimethyl carbonate solution;

[0066] 3) Centrifuge the above solution to obtain lithium difluorophosphate crystals and a lithium hexafluorophosphate solution;

[0067] 4) Dry the lithium difluorophosphate crystals to obtain the finished product of lithium difluorophosphate (712.0 g);

[0068] 5) Sampling analysis shows that a total of 511.0 g of lithium hexafluorophosphate is generated. Heat and evaporate 403.5 g of dimethyl carbonate from the separated lithium hexafluorophosphate solution, and adjust the concentration of the lithium hexafluorophosphate solution to 40.0%.

[0069] Example 5

[0070] In the technical solution of Example 1, trifluoromethanesulfonyl carbonate is added to the solvent, and its preparation method is as follows:

[0071] By weight, mix 42 parts of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 50 parts of allyl diglycol dicarbonate, 200 parts of DMF, and 2 parts of ethylenediamine, stir at 50 °C for 30 minutes, and distill off DMF to obtain trifluoromethanesulfonyl carbonate;

[0072] The addition amount is 0.5% of the solvent mass percentage.

[0073] The rest is the same as in Example 1.

[0074] Sampling analysis shows that a total of 262.2 g and 372.1 g of lithium hexafluorophosphate are generated.

[0075] Example 6

[0076] In the technical solution of Example 2, trifluoromethanesulfonyl carbonate is added to the solvent, and its preparation method is as follows:

[0077] The preparation method of adding trifluoromethanesulfonyl carbonate to the solvent is as follows:

[0078] By weight, 48 parts of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 70 parts of allyl diglycol dicarbonate, 300 parts of DMF, and 4 parts of ethylenediamine were stirred at 58 °C for 50 minutes, and then the DMF was distilled off to obtain trifluoromethanesulfonyl carbonate;

[0079] The addition amount is 0.8% of the mass percentage of the solvent.

[0080] The rest is the same as in Example 2.

[0081] Sampling and analysis showed that a total of 340.9 g and 483.9 g of lithium hexafluorophosphate were generated.

[0082] Example 7

[0083] In the technical solution of Example 4, trifluoromethanesulfonyl carbonate was added to the solvent, and its preparation method was as follows:

[0084] By weight, 60 parts of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 100 parts of allyl diglycol dicarbonate, 600 parts of DMF, and 6 parts of ethylenediamine were stirred at 60 °C for 80 minutes, and then the DMF was distilled off to obtain trifluoromethanesulfonyl carbonate;

[0085] The addition amount is 3% of the mass percentage of the solvent.

[0086] The rest is the same as in Example 4.

[0087] Sampling and analysis showed that a total of 419.6 g and 595.8 g of lithium hexafluorophosphate were generated.

[0088] Example 8

[0089] To test the changes in the low-temperature impedance, low-temperature capacity retention rate, and charge-discharge performance of the battery after adding lithium trifluoromethanesulfonate to form a hybrid electrolyte, in a 4.4V NCM622 / natural graphite battery system, the battery impedance was tested after adding trifluoromethanesulfonyl carbonate. The test data at -10 °C are shown in Table 8-1, and the test curve is shown in the appendix Figure 4 . The results showed that the battery impedance was lower than that of the basic electrolyte.

[0090] Table 8-1 Battery impedance data of the basic electrolyte and after adding trifluoromethanesulfonyl carbonate:

[0091]

[0092]

[0093] In a 4.4V NCM622 / natural graphite battery system, the capacity retention rate was tested after adding trifluoromethanesulfonyl carbonate. The test data at -20 °C are shown in Table 8-2, and the test curve is shown in the appendixFigure 5 . The results show that the capacity retention rate is higher than that of the basic electrolyte.

[0094] Table 8-2 Capacity retention rates of the basic electrolyte and the electrolyte with trifluoromethanesulfonyl carbonate added:

[0095]

[0096] In the 4.4V NCM622 / natural graphite battery system, the rate charge-discharge performance was tested after adding trifluoromethanesulfonyl carbonate. The test data are shown in Table 8-3, and the test curves are shown in the appendix Figure 6 、 7 . The results show that the rate charge-discharge performance is higher than that of the basic electrolyte.

[0097] Table 8-3 Rate charge-discharge performances of the basic electrolyte and the electrolyte with trifluoromethanesulfonyl carbonate added:

[0098]

[0099] In the above embodiments, lithium phosphate was used as an example for illustration. This raw material can be replaced with sodium phosphate to prepare sodium hexafluorophosphate and sodium difluorophosphate, and this sodium salt is also suitable for this patent.

[0100] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0101] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A preparation method for co-producing lithium difluorophosphate and lithium hexafluorophosphate, comprising the following steps: S1: Dissolve lithium phosphate in a carbonate solvent to obtain a lithium phosphate solution, and adjust the temperature of the lithium phosphate solution to 5-10 °C; S2: Introduce phosphorus pentafluoride gas into the above-mentioned lithium phosphate solution to gradually carry out a reaction to generate lithium difluorophosphate and lithium fluoride. Lithium fluoride continues to react with phosphorus pentafluoride to generate lithium hexafluorophosphate. Finally, the molar ratio of lithium phosphate to phosphorus pentafluoride is 1:2 ± 0.1 to obtain lithium difluorophosphate and lithium hexafluorophosphate. Lithium hexafluorophosphate dissolves in the carbonate solution to form a lithium hexafluorophosphate solution, and lithium difluorophosphate is slightly soluble in the carbonate and precipitates in the form of crystals to form a turbid solution; S3: Perform solid-liquid separation on the reacted lithium hexafluorophosphate and lithium difluorophosphate solution to obtain lithium difluorophosphate crystals and a lithium hexafluorophosphate solution; the concentration of the liquid-phase lithium hexafluorophosphate can be directly adjusted and then enter the electrolyte system; S4: The lithium difluorophosphate crystals are dried to obtain lithium difluorophosphate products; S5: Adjust the concentration of the liquid-phase lithium hexafluorophosphate to 40 ± 0.1 wt%; Trifluoromethanesulfonyl carbonate is added to the lithium phosphate solution, and its preparation method is as follows: By weight, add 4-11 parts of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 200-400 parts of allyl diglycol dicarbonate, and 10-16 parts of triethylamine, stir at 50-60 °C for 30-80 minutes, and distill off DMF to obtain trifluoromethanesulfonyl carbonate.

2. The preparation method of lithium hexafluorophosphate according to claim 1, wherein: The carbonate solvent includes dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

3. The preparation method of lithium hexafluorophosphate according to claim 1, characterized in that: The concentration of lithium phosphate in the lithium phosphate solution is 20-25% wt%.

4. The preparation method of lithium difluorophosphate and coproduction of lithium hexafluorophosphate according to claim 1 is characterized in that: The addition amount of the trifluoromethanesulfonyl carbonate is 0.5-3% of the mass percentage of the carbonate solvent.

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