Lithium hexafluorophosphate and a process for its preparation

Abstract

The application belongs to the field of new energy, and discloses a preparation process of lithium hexafluorophosphate, which comprises the following steps: step 1: lithium fluoride and phosphorus pentachloride are reacted in an organic solvent to obtain a first mixture; and step 2: a fluorination reagent is added into the first mixture to obtain lithium hexafluorophosphate; the fluorination reagent is one or more of potassium fluoride, ammonium fluoride, calcium fluoride, potassium bifluoride and ammonium bifluoride. The process can obtain lithium hexafluorophosphate by a solvent method, and the yield is not less than 88%. Meanwhile, the application also discloses lithium hexafluorophosphate obtained based on the process.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of new energy, and particularly relates to lithium hexafluorophosphate and a preparation process thereof. BACKGROUND

[0002] A lithium ion battery mainly comprises four parts of a positive electrode, a negative electrode, an electrolyte and a diaphragm. The electrolyte bears the function of transporting and conducting lithium ions between the positive and negative electrodes of the battery, and is called the "blood" of the lithium ion battery. The purity of the electrolyte plays a crucial role in the shelf time and service life, internal resistance and power characteristics, charging and discharging efficiency, temperature range for use and safety performance of the lithium ion battery. The most widely used electrolyte in the lithium ion battery is lithium hexafluorophosphate (LiPF6), which has the advantages of high conductivity, large anion radius, difficulty in association and good electrochemical performance, and can form a SEI film on the surface of the electrode material to inhibit the corrosion of the current collector.

[0003] At present, the mainstream method for preparing lithium hexafluorophosphate at home and abroad is a hydrogen fluoride solvent method. For example, CN101570327A and CN114804060A report that anhydrous hydrogen fluoride and phosphorus pentachloride are reacted to produce phosphorus pentafluoride mixed gas, and then the phosphorus pentafluoride mixed gas is introduced into a lithium fluoride hydrogen fluoride solution to obtain lithium hexafluorophosphate. CN101723346B and CN102951620A use phosphorus pentachloride and anhydrous hydrogen fluoride to react to obtain a mixed solution of lithium hexafluorophosphate and anhydrous hydrogen fluoride; an anhydrous hydrogen fluoride solution of lithium fluoride is prepared; and then the anhydrous hydrogen fluoride solution of lithium fluoride is added to the mixed solution of lithium hexafluorophosphate and anhydrous hydrogen fluoride to obtain a lithium hexafluorophosphate solution. CN104211029B and CN114865091A report that lithium hexafluorophosphate solution is prepared by directly adding phosphorus pentachloride to an anhydrous hydrogen fluoride solution containing lithium fluoride.

[0004] In the above hydrogen fluoride solvent method, hydrogen fluoride is used as a solvent to dissolve lithium fluoride, avoiding poor gas-solid and solid-solid reaction effects; and hydrogen fluoride is used as a fluorinating agent to fluorinate phosphorus pentachloride into phosphorus pentafluoride, avoiding the use of phosphorus pentafluoride as a raw material which has strong toxicity and corrosion. Although the hydrogen fluoride solvent method has the above advantages, it also has the following disadvantages: 1. The use of hydrogen fluoride as a raw material requires high equipment and has safety hazards; 2. LiPF6·HF complex is easily generated, which is difficult to separate and purify, and affects the product quality; and 3. The production cost is high.

[0005] In order to avoid the use of hydrogen fluoride, a few existing technologies also disclose schemes without using hydrogen fluoride, for example:

[0006] CN1224405A discloses a method for preparing LiPF6, in which LiF is reacted with PCl5 or POC13 at a reaction temperature of-20 to 300 DEG C under normal pressure for a reaction time of 0.1 to 10 hours to form LiPF6.

[0007] The reaction equation is:

[0008] a) PCl5+ 6LiF→ 5LiCl + LiPF6

[0009] b) 4POCl3+ 18LiF→ 12LiCl + Li3PO4+ 3LiPF6.

[0010] The patent also states: "preferably using diethyl ether as solvent, because LiPF6 is particularly easy to dissolve in diethyl ether". According to the data recorded in the patent examples, only when using diethyl ether as the solvent, the yield is more than 95% (specifically 95.7%), and when using propylene carbonate (86.1%) and dichloromethane (83%) as the solvent, the yield is not more than 90%. It shows that the scheme has high requirements for the type of solvent, and the most suitable is the ether solvent, and when the carbonate solvent commonly used as the electrolyte solvent is used in the reaction, it will lead to a decrease in yield. Although the use of diethyl ether in the scheme can obtain a higher yield, a patent (CN1224405A) also proposes that solvents such as diethyl ether are easy to produce peroxide and contain complex impurities, which reduces the quality of the product and also increases the difficulty of purification.

[0011] The prior art also discloses a scheme for preparing lithium hexafluorophosphate under a pressurized environment, for example: CN103213963B discloses a process method for directly preparing liquid lithium hexafluorophosphate (LiPF6), in the presence of a stabilizer and a catalyst, the pressure is controlled at 0.1-0.3Mpa, and the phosphorus pentachloride is directly prepared in the solvent with lithium fluoride to directly prepare liquid lithium hexafluorophosphate. Although this method can prepare lithium hexafluorophosphate with high yield, the purification is also more troublesome.

[0012] Therefore, it is urgent to find a preparation method of lithium hexafluorophosphate which can react under normal pressure, is easy to purify, and the yield is not affected by the type of solvent. SUMMARY

[0013] In view of the deficiencies of the prior art, the purpose of the present application is to provide a preparation process of lithium hexafluorophosphate, which can obtain lithium hexafluorophosphate by solvent method under normal pressure, the yield is not affected by the type of solvent, and the post-processing step is simple.

[0014] Meanwhile, the present application also discloses lithium hexafluorophosphate obtained based on the process.

[0015] In order to achieve the purpose of the present application, the following technical scheme is adopted: a preparation process of lithium hexafluorophosphate, comprising the following steps:

[0016] Step 1: lithium fluoride and phosphorus pentachloride are reacted in an organic solvent to obtain a first mixture;

[0017] Step 2: adding fluorination reagent to the first mixture to obtain lithium hexafluorophosphate;

[0018] The fluorination reagent is one or more of potassium fluoride, ammonium fluoride, calcium fluoride, potassium bifluoride, and ammonium bifluoride.

[0019] The possible chemical reaction of Step 1 is:

[0020] LiF + PCl5→ LiPFCl5

[0021] The possible chemical reaction of Step 2 (using potassium fluoride as an example) is:

[0022] LiPFCl5 + 5KF→ LiPF6 + 5KCl

[0023] The principle of the reaction is that a salt with stronger fluorination ability (such as potassium fluoride in the above equation) is used as the fluorination reagent to react in the reaction system. The fluorination reagent is insoluble in the organic solvent. The reaction is carried out by solid-liquid reaction to obtain a salt with no fluorination ability (such as potassium chloride in the above equation), which can be precipitated from the solution and separated easily.

[0024] Through the above method, the applicant surprisingly found that the yield can be increased to more than 89%, more preferably, to more than 95%, and more preferably, to more than 98%.

[0025] The chloride in the final product of the application exists in the form of precipitation in the solution, so the unreacted fluorination reagent and chloride can be removed by filtration, and the remaining solution containing lithium hexafluorophosphate can be directly sold, which can significantly reduce the cost required for purification and precipitation in the traditional method.

[0026] In the above preparation process of lithium hexafluorophosphate, the molar ratio of lithium fluoride, phosphorus pentachloride, and fluorination reagent is 1-7:1:0.5-7.5.

[0027] Preferably, the molar ratio of lithium fluoride, phosphorus pentachloride, and fluorination reagent is 1.01-4:1:2.5-6.5.

[0028] Generally, exceeding the above ratio will affect whether the reaction is completely carried out, but will not affect whether the reaction can be carried out. For example, excessive or insufficient lithium fluoride and phosphorus pentachloride will only result in the remaining of a certain component; insufficient use of the fluorination reagent will only result in incomplete fluorination and excessive impurities, and excessive use of the fluorination reagent will only result in excessive and waste of the fluorination reagent. The above ratio range is a more preferred range for industrial production.

[0029] In some embodiments of the present application, the molar ratio of lithium fluoride to phosphorus pentachloride can be 1.01:1, 1.5:1, 1.03:1, 2:1, 3:1, 4:1, 5:1, 6:1, 6.5:1, or 7:1.

[0030] In some embodiments of the present application, the molar ratio of phosphorus pentachloride to fluorination reagent is 1:5.1, 1:5.5, 1:6, 1:6.5, 1:7, or 1:7.5.

[0031] In the above preparation process of lithium hexafluorophosphate, the mass ratio of the organic solvent to lithium fluoride is 20-30:1. In step 1, the organic solvent should not be too much, and too much organic solvent is not conducive to the rapid progress of the first step conversion;

[0032] In some embodiments of the present application, the mass ratio of the organic solvent to lithium fluoride is 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, or 30:1.

[0033] In the above preparation process of lithium hexafluorophosphate, the step 1 is carried out at normal temperature and pressure, and the reaction time is 2-4h. In some embodiments of the present application, the reaction time is 2h, 3h, or 4h; the above normal temperature of the present application means that the reaction temperature does not need to be specifically controlled, such as 10-40℃, which can be 10℃, 20℃, 25℃, 30℃, or 40℃.

[0034] It should be noted that the present application does not exclude the operation at higher temperature and greater pressure, and the reaction can be carried out at normal temperature and pressure, which is one of the features of the present application. Generally, pressure operation is feasible, such as 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, or 0.5MPa; the reaction temperature can be controlled in a higher temperature range such as 40℃, 50℃, 60℃, 70℃, or 80℃.

[0035] In the above preparation process of lithium hexafluorophosphate, the reaction temperature of step 2 is 70-100℃, and the reaction time is 6-10h. In step 2, the fluorination reagent is added to the first mixture together with the organic solvent; the weight of the organic solvent used in step 2 is 2.5-5 times the weight of the fluorination reagent.

[0036] In actual experiment process, we found that if the temperature is too low, the fluorination is not complete, and if the temperature is too high, not only the energy consumption is too large, the solvent is boiled, but also unexpected side reactions may occur. Based on the selection of mature process, it is recommended that the reaction be carried out within the above temperature range.

[0037] In some embodiments of the present application, the reaction time is not too short to make the lithium hexafluorophosphate of the present application, but the preferred reaction time can make the yield of lithium hexafluorophosphate as high as possible; in some embodiments of the present application, the reaction time is 6h, 7h, 8h, 9h or 10h.

[0038] In the above preparation process of lithium hexafluorophosphate, the organic solvent is one or more of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, vinyl carbonate and propylene carbonate.

[0039] The present application is not limited to the above organic solvents, such as the ether described in the prior art or other organic solvents can obtain the product of the present application, but based on the characteristics of these solvents are not stable, the present application in the actual industrial production and will not choose to use; but does not exclude the organic solvent of the present application can contain as above non-preferred organic solvents.

[0040] At the same time, based on the final product of the present application is in the form of solution to be sold, so in general, it is suggested that the customer's requirements for the customer's battery product solvent combination.

[0041] Based on the above analysis can be seen, in the process control of the present application, the proportion of substances, the type and amount of solvent, reaction temperature and time, etc. within the foreseeable reasonable range of the skilled in the art can get better results, and will not affect the reaction can be carried out.

[0042] The optimization, change and combination of the process parameters of the present application should be considered within the scope of the present application.

[0043] Finally, the present application also discloses the lithium hexafluorophosphate obtained by the preparation process described above.

[0044] Compared with the prior art, the present application has the following beneficial effects:

[0045] (1) the present application does not use anhydrous hydrogen fluoride, simple operation, high safety, high yield;

[0046] (2) using electrolyte commonly used organic solvents, can directly obtain lithium hexafluorophosphate for sale;

[0047] (3) without using phosphorus pentafluoride as raw material, also no need to prepare phosphorus pentafluoride, reduce the security risks, but also avoid the influence of the impurity of phosphorus pentafluoride on the quality of lithium hexafluorophosphate;

[0048] (4) can be reacted under normal pressure, low requirements for reaction equipment, while saving energy consumption;

[0049] (5) Solvent type does not have a key impact on yield, and common solvents can achieve high yield;

[0050] (6) The product is easy to separate and purify, has high quality, and is suitable for industrial production.

[0051] The principle is that under normal temperature and pressure, lithium fluoride and phosphorus pentafluoride can only quickly perform the chemical reaction shown in step 1, and lithium fluoride needs a longer time, a greater pressure, or a catalyst (such as CN103213963B) to further fluorinate LiPFCl5 to obtain lithium hexafluorophosphate. In particular, in the case of low raw material concentration after the reaction, the reaction from LiPFCl5 to lithium hexafluorophosphate needs more time and is more difficult to completely react. In step 2, a fluorinating agent stronger than lithium fluoride is used to promote the forward progress of the fluorination reaction, thereby shortening the reaction time, avoiding harsh reaction conditions, and achieving a high yield in a short reaction time. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 The nuclear magnetic resonance (F-NMR) spectrum of the product of Example 1;

[0053] Figure 2 The nuclear magnetic resonance (P-NMR) spectrum of the product of Example 1. DETAILED DESCRIPTION

[0054] The technical solutions of the present application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as a specific limitation on the present application.

[0055] Example 1

[0056] (1) At room temperature, 524 g of methyl ethyl carbonate, 26.2 g of lithium fluoride (1.01 mol), and 208.2 g of phosphorus pentachloride (1 mol) were added to a dry reaction kettle, and stirred for 2 h to obtain a first reaction solution;

[0057] (2) A methyl ethyl carbonate solution containing dispersed potassium fluoride was added to the first reaction solution, the total weight of the methyl ethyl carbonate solution was 1200 g, containing 319 g of potassium fluoride (5.5 mol), and the temperature was raised to 70°C under stirring, and reacted for 9 h;

[0058] (3) After the reaction was completed, the temperature was lowered to room temperature, and the filter was washed with methyl ethyl carbonate three times, each time 30 g; the filtrate was combined and concentrated under reduced pressure until crystals were precipitated, the concentration was stopped, the temperature was lowered to 0-5°C, and the crystals were precipitated under stirring for 1 h; the filter cake was dried to obtain lithium hexafluorophosphate product (the sample was sent for inspection, and the nuclear magnetic spectrum can be seen Figure 1 and Figure 2), yield 98.5%, purity 99.95%, moisture 18ppm, free acid 72ppm.

[0059] Example 2

[0060] (1) Add 688 g of ethyl methyl carbonate, 27.5 g (1.06 mol) of lithium fluoride, and 208.2 g (1 mol) of phosphorus pentachloride to a dry reaction kettle at room temperature, and stir for 3 h to obtain a first reaction solution;

[0061] (2) Adding a solution of ethyl methyl carbonate dispersed with potassium fluoride to the first reaction solution, wherein the total weight of the ethyl methyl carbonate solution is 1400 g and contains 377.5 g (6.5 mol) of potassium fluoride, stirring and heating to 85° C., and keeping the temperature to react for 8 h;

[0062] (3) After the reaction is completed, the mixture is cooled to room temperature, allowed to stand, filtered, and washed three times with 30 g of ethyl methyl carbonate each time; the filtrates are combined, concentrated under reduced pressure until crystals precipitate, the concentration is stopped, the temperature is lowered to 0-5°C, and stirred for crystallization for 1 hour; filtered, and the filter cake is dried to obtain lithium hexafluorophosphate product with a yield of 98.6%, a purity of 99.97%, 16 ppm of moisture, and 68 ppm of free acid.

[0063] Example 3

[0064] (1) Add 855 g of ethyl methyl carbonate, 28.5 g (1.1 mol) of lithium fluoride, and 208.2 g (1 mol) of phosphorus pentachloride to a dry reaction kettle at room temperature, and stir for 4 h to obtain a first reaction solution;

[0065] (2) Adding a solution of ethyl methyl carbonate dispersed with potassium fluoride to the first reaction solution, wherein the total weight of the ethyl methyl carbonate solution is 1600 g and contains 435 g (7.5 mol) of potassium fluoride, stirring and heating to 100° C., and keeping the temperature to react for 6 h;

[0066] (3) After the reaction is completed, the mixture is cooled to room temperature, allowed to stand, filtered, and washed three times with 30 g of ethyl methyl carbonate each time; the filtrates are combined, concentrated under reduced pressure until crystals precipitate, the concentration is stopped, the temperature is lowered to 0-5°C, and stirred for crystallization for 1 hour; filtered, and the filter cake is dried to obtain lithium hexafluorophosphate product with a yield of 98.8%, a purity of 99.97%, 12 ppm of water, and 66 ppm of free acid.

[0067] Example 4

[0068] (1) Add 688 g of ethyl methyl carbonate, 27.5 g (1.06 mol) of lithium fluoride, and 208.2 g (1 mol) of phosphorus pentachloride to a dry reaction kettle at room temperature, and stir for 3 h to obtain a first reaction solution;

[0069] (2) To the first reaction solution, add the methyl ethyl carbonate solution dispersed with ammonium fluoride, the total weight of the methyl ethyl carbonate solution is 1000g, containing 203g (5.5mol) of ammonium fluoride, stir to warm up to 80℃, and keep the temperature for 8h;

[0070] (3) After the reaction is completed, cool down to room temperature, stand for filtration, and wash the filter cake with methyl ethyl carbonate for three times, each time with 30g; combine the filtrate, concentrate under reduced pressure until crystals are precipitated, stop the concentration, cool down to 0-5℃, and stir for 1h for crystal precipitation; filter, and dry the filter cake to obtain the lithium hexafluorophosphate product, with a yield of 98.5%, a purity of 99.96%, moisture of 17ppm, and free acid of 70ppm.

[0071] Example 5

[0072] (1) At room temperature, add 650g of methyl ethyl carbonate, 27.5g of lithium fluoride (1.06mol), and 208.2g of phosphorus pentachloride (1mol) into a dry reaction kettle, and stir for 3h to obtain a first reaction solution;

[0073] (2) To the first reaction solution, add the methyl ethyl carbonate solution dispersed with calcium fluoride, the total weight of the methyl ethyl carbonate solution is 1800g, containing 430g (5.5mol) of calcium fluoride, stir to warm up to 80℃, and keep the temperature for 8h;

[0074] (3) After the reaction is completed, cool down to room temperature, stand for filtration, and wash the filter cake with methyl ethyl carbonate for three times, each time with 30g; combine the filtrate, concentrate under reduced pressure until crystals are precipitated, stop the concentration, cool down to 0-5℃, and stir for 1h for crystal precipitation; filter, and dry the filter cake to obtain the lithium hexafluorophosphate product, with a yield of 98.8%, a purity of 99.98%, moisture of 15ppm, and free acid of 64ppm.

[0075] Example 6

[0076] (1) At room temperature, add 700g of methyl ethyl carbonate, 27.5g of lithium fluoride (1.06mol), and 208.2g of phosphorus pentachloride (1mol) into a dry reaction kettle, and stir for 3h to obtain a first reaction solution;

[0077] (2) To the first reaction solution, add the methyl ethyl carbonate solution dispersed with potassium bifluoride, the total weight of the methyl ethyl carbonate solution is 2000g, containing 547g (7mol) of potassium bifluoride, stir to warm up to 80℃, and keep the temperature for 8h;

[0078] (3) After the reaction is completed, cool down to room temperature, stand for filtration, and wash the filter cake with methyl ethyl carbonate for three times, each time with 30g; combine the filtrate, concentrate under reduced pressure until crystals are precipitated, stop the concentration, cool down to 0-5℃, and stir for 1h for crystal precipitation; filter, and dry the filter cake to obtain the lithium hexafluorophosphate product, with a yield of 98.8%, a purity of 99.97%, moisture of 16ppm, and free acid of 68ppm.

[0079] Example 7

[0080] The procedure was similar to Example 1 except that the fluorinating agent was a mixture of potassium fluoride and potassium bifluoride with a total molar amount of 5.5 mol and a molar ratio of potassium fluoride to potassium bifluoride of 1:1.

[0081] After the reaction was completed, the reaction mixture was cooled to room temperature, filtered, and washed with 30 g of ethyl methyl carbonate three times. The filtrate was combined and concentrated under reduced pressure until crystals were precipitated. The concentration was stopped and the mixture was cooled to 0-5°C and stirred for 1 h to crystallize. The mixture was filtered and the filter cake was dried to obtain the lithium hexafluorophosphate product with a yield of 98.2%, a purity of 99.95%, a moisture content of 17 ppm, and a free acid content of 63 ppm.

[0082] Example 8

[0083] The procedure was similar to Example 1 except that the fluorinating agent was a mixture of potassium fluoride and calcium fluoride with a total molar amount of 5.5 mol and a molar ratio of potassium fluoride to calcium fluoride of 1:1.

[0084] After the reaction was completed, the reaction mixture was cooled to room temperature, filtered, and washed with 30 g of ethyl methyl carbonate three times. The filtrate was combined and concentrated under reduced pressure until crystals were precipitated. The concentration was stopped and the mixture was cooled to 0-5°C and stirred for 1 h to crystallize. The mixture was filtered and the filter cake was dried to obtain the lithium hexafluorophosphate product with a yield of 98.2%, a purity of 99.95%, a moisture content of 17 ppm, and a free acid content of 63 ppm.

[0085] Example 9

[0086] The procedure was similar to Example 1 except that the organic solvent was replaced by dimethyl carbonate.

[0087] The reaction resulted in a yield of 98.9%, a purity of 99.96%, a moisture content of 14 ppm, and a free acid content of 53 ppm.

[0088] Example 10

[0089] The procedure was similar to Example 1 except that the organic solvent was replaced by diethyl carbonate.

[0090] The reaction resulted in a yield of 98.5%, a purity of 99.97%, a moisture content of 19 ppm, and a free acid content of 57 ppm.

[0091] During the implementation of the project, we tested the use of methyl acetate, ethyl acetate, ethylene carbonate, and propylene carbonate as the solvent instead of ethyl methyl carbonate. The results were similar to the case where ethyl methyl carbonate was used as the solvent with similar process parameters. In general, we found that the yield was not less than 95%. Similarly, the combination of the above solvents also achieved satisfactory yield.

[0092] Example 11

[0093] (1) Add 724 g of methyl ethyl carbonate, 52.4 g of lithium fluoride (2 mol), and 208.2 g of phosphorus pentachloride (1 mol) into a dry reaction kettle at room temperature, and stir for 2 h to obtain a first reaction solution;

[0094] (2) Add a potassium fluoride-dispersed methyl ethyl carbonate solution into the first reaction solution, the total weight of the methyl ethyl carbonate solution is 1000 g, and the potassium fluoride-dispersed methyl ethyl carbonate solution contains 261.6 g of potassium fluoride (4.51 mol), stir to raise the temperature to 70°C, and keep the temperature for 9 h;

[0095] (3) After the reaction is completed, the temperature is lowered to room temperature, and the mixture is filtered and washed with methyl ethyl carbonate three times, each time with 30 g of methyl ethyl carbonate; the filtrates are combined, concentrated under reduced pressure until crystals are precipitated, the concentration is stopped, the temperature is lowered to 0-5°C, and the mixture is stirred for 1 h for crystal precipitation; the mixture is filtered, and the filter cake is dried to obtain the lithium hexafluorophosphate product, the yield is 96.4%, the purity is 99.91%, the water content is 14 ppm, and the free acid content is 71 ppm.

[0096] Example 12

[0097] (1) Add 824 g of methyl ethyl carbonate, 78.6 g of lithium fluoride (3 mol), and 208.2 g of phosphorus pentachloride (1 mol) into a dry reaction kettle at room temperature, and stir for 2 h to obtain a first reaction solution;

[0098] (2) Add a potassium fluoride-dispersed methyl ethyl carbonate solution into the first reaction solution, the total weight of the methyl ethyl carbonate solution is 900 g, and the potassium fluoride-dispersed methyl ethyl carbonate solution contains 203.6 g of potassium fluoride (3.51 mol), stir to raise the temperature to 70°C, and keep the temperature for 9 h;

[0099] (3) After the reaction is completed, the temperature is lowered to room temperature, and the mixture is filtered and washed with methyl ethyl carbonate three times, each time with 30 g of methyl ethyl carbonate; the filtrates are combined, concentrated under reduced pressure until crystals are precipitated, the concentration is stopped, the temperature is lowered to 0-5°C, and the mixture is stirred for 1 h for crystal precipitation; the mixture is filtered, and the filter cake is dried to obtain the lithium hexafluorophosphate product, the yield is 94.1%, the purity is 99.92%, the water content is 21 ppm, and the free acid content is 79 ppm.

[0100] Example 13

[0101] (1) Add 924 g of methyl ethyl carbonate, 104.8 g of lithium fluoride (4 mol), and 208.2 g of phosphorus pentachloride (1 mol) into a dry reaction kettle at room temperature, and stir for 2 h to obtain a first reaction solution;

[0102] (2) Add a potassium fluoride-dispersed methyl ethyl carbonate solution into the first reaction solution, the total weight of the methyl ethyl carbonate solution is 800 g, and the potassium fluoride-dispersed methyl ethyl carbonate solution contains 145.6 g of potassium fluoride (2.51 mol), stir to raise the temperature to 70°C, and keep the temperature for 9 h;

[0103] (3) After the reaction is completed, the temperature is lowered to room temperature, and the filtrate is filtered and washed with methyl ethyl carbonate three times, 30 g each time; the filtrate is combined and concentrated under reduced pressure until crystals are precipitated, the concentration is stopped, the temperature is lowered to 0-5°C, and the crystals are stirred for 1 h; the crystals are filtered and dried to obtain the lithium hexafluorophosphate product, with a yield of 91.6%, a purity of 99.87%, a moisture content of 25 ppm, and a free acid content of 67 ppm.

[0104] Example 14

[0105] (1) At room temperature, 1024 g of methyl ethyl carbonate, 131 g of lithium fluoride (5 mol), and 208.2 g of phosphorus pentachloride (1 mol) are added to a dry reaction kettle, and stirred for 2 h to obtain a first reaction solution;

[0106] (2) A methyl ethyl carbonate solution containing potassium fluoride is added to the first reaction solution, the total weight of the methyl ethyl carbonate solution is 700 g, and the potassium fluoride contains 87.6 g (1.5 mol); the temperature is raised to 70°C, and the reaction is maintained for 9 h;

[0107] (3) After the reaction is completed, the temperature is lowered to room temperature, and the filtrate is filtered and washed with methyl ethyl carbonate three times, 30 g each time; the filtrate is combined and concentrated under reduced pressure until crystals are precipitated, the concentration is stopped, the temperature is lowered to 0-5°C, and the crystals are stirred for 1 h; the crystals are filtered and dried to obtain the lithium hexafluorophosphate product, with a yield of 91.6%, a purity of 99.87%, a moisture content of 25 ppm, and a free acid content of 67 ppm.

[0108] Example 15

[0109] (1) At room temperature, 1224 g of methyl ethyl carbonate, 157.2 g of lithium fluoride (6 mol), and 208.2 g of phosphorus pentachloride (1 mol) are added to a dry reaction kettle, and stirred for 2 h to obtain a first reaction solution;

[0110] (2) A methyl ethyl carbonate solution containing potassium fluoride is added to the first reaction solution, the total weight of the methyl ethyl carbonate solution is 500 g, and the potassium fluoride contains 29.6 g (0.51 mol); the temperature is raised to 70°C, and the reaction is maintained for 9 h;

[0111] (3) After the reaction is completed, the temperature is lowered to room temperature, and the filtrate is filtered and washed with methyl ethyl carbonate three times, 30 g each time; the filtrate is combined and concentrated under reduced pressure until crystals are precipitated, the concentration is stopped, the temperature is lowered to 0-5°C, and the crystals are stirred for 1 h; the crystals are filtered and dried to obtain the lithium hexafluorophosphate product, with a yield of 91.6%, a purity of 99.87%, a moisture content of 25 ppm, and a free acid content of 67 ppm.

[0112] Example 16

[0113] The procedure of Example 1 is generally followed, except that in step 3, after the reaction is completed, the temperature is lowered to room temperature, and the filtrate is filtered and washed with methyl ethyl carbonate three times, 30 g each time; the filtrate is combined, and the entire reaction process is completed.

[0114] The electrolyte of the present embodiment is diluted or concentrated according to the needs of the customer, so that the content of lithium hexafluorophosphate is adjusted to be in the range of 8-25wt%.

[0115] It should be noted that the operations performed in Example 16 can still be applied to Examples 1-15; in actual production and sales, according to the different needs of customers, we will choose the organic solvent required by the customer as the continuous phase of the reaction in Step 1 and Step 2;

[0116] As a common commercial formula of electrolyte, various types of additives can also be added before leaving the factory on the basis of the above examples, such as additives for improving the high-temperature resistance of electrolyte / battery, additives for improving the low-temperature resistance of electrolyte / battery, additives for improving the cycle performance of battery, additives for reducing the impedance of battery, etc.

[0117] Comparative Example 1

[0118] (1) At room temperature, 1724g of ethyl methyl carbonate, 169.3g of lithium fluoride (6.51mol), and 208.2g of phosphorus pentachloride (1mol) were added to a dry reaction kettle, and stirred for 2h to obtain a first reaction solution;

[0119] (2) Stirring was carried out to raise the temperature to 70°C, and the reaction was carried out for 9h;

[0120] (3) After the reaction was completed, the temperature was lowered to room temperature, and the filter cake was dried to obtain lithium hexafluorophosphate product, with a yield of 84.3%, a purity of 99.91%, a moisture content of 19ppm, and a free acid content of 75ppm.

[0121] Comparative Example 2

[0122] (1) At room temperature, 524g of ethyl methyl carbonate, 26.2g of lithium fluoride (1.01mol), and 208.2g of phosphorus pentachloride (1mol) were added to a dry reaction kettle, and stirred for 2h to obtain a first reaction solution;

[0123] (2) A lithium fluoride-dispersed ethyl methyl carbonate solution was added to the first reaction solution, the total weight of the ethyl methyl carbonate solution was 1200g, containing 143g of lithium fluoride (5.5mol), and stirring was carried out to raise the temperature to 70°C, and the reaction was carried out for 9h;

[0124] (3) After the reaction is completed, it is cooled to room temperature, filtered and washed with methyl ethyl carbonate three times, each time 30 g; the filtrate is combined and concentrated under reduced pressure until crystals are precipitated, the concentration is stopped, cooled to 0-5°C and stirred for 1 h to precipitate crystals; filtered and the filter cake is dried to obtain the lithium hexafluorophosphate product, with a yield of 87.6%, a purity of 99.91%, moisture of 20 ppm and free acid of 70 ppm.

[0125] It should be noted that the conversion rates of all examples and comparative examples of the present application are calculated based on phosphorus pentachloride.

[0126] Result analysis:

[0127] 1. As can be seen from Examples 1-6, under different process parameter conditions, the method of the present application can achieve a high yield.

[0128] Another feature of the present application is that the fluorinated salt can be directly separated by filtration, and the mixture of residual lithium hexafluorophosphate and organic solvent can be directly sold without treatment, effectively reducing the production cost. The reason is that in the organic solvent system, potassium chloride and other salts are more likely to precipitate in the organic system than lithium chloride; therefore, the potassium chloride and other products generated in the reaction can be basically removed by filtration to obtain high-purity lithium hexafluorophosphate.

[0129] 2. The inventors have also conducted a large number of experiments by replacing different solvents, and found that the type of solvent does not have a decisive impact on the final yield.

[0130] 3. The use of a specific fluorinating agent is the basis for the realization of the present application, as can be seen from Comparative Examples 1 and 2, using a method similar to the prior art, a high yield cannot be obtained in a common solvent system.

[0131] The two-step method of the present application for preparing lithium hexafluorophosphate has a yield that is 10-15% higher than that of Comparative Examples 1 and 2 (traditional technology), which can reduce the difficulty of product separation and improve the product purity.

[0132] The possible reason is that in the reaction process of lithium fluoride and phosphorus pentafluoride, lithium fluoride may be used as a fluorinating agent to fluorinate the intermediate product to obtain lithium hexafluorophosphate. However, due to the relatively low fluorination ability of lithium fluoride, in the case where the concentrations of lithium fluoride and phosphorus pentafluoride or the intermediate product are very low at the later stage of the reaction, without special treatment such as pressurization or addition of a catalyst, the reaction rate is significantly slower, and it is difficult to obtain a high yield in a short time. The intermediate product of step 1 is formed at a faster rate, and the present application takes advantage of this to fluorinate the intermediate product with other fluorinating agents with higher fluorination ability after the rapid formation of the intermediate product, thereby improving the efficiency of the fluorination reaction in step 2 and ensuring that the overall reaction achieves a high yield in a short time.

[0133] 4. As seen from Example 1, Example 11 to Example 15, with the total amount of lithium fluoride and fluorinating agent unchanged, the yield of lithium hexafluorophosphate in the product gradually increases with the increase of the fluorinating agent in Step 2. This shows that the addition of the selected fluorinating agent in the present application in Step 2 can accelerate the reaction, and within a certain range, the more the amount, the more obvious the effect on the conversion rate. Referring to Example 14 and Example 15, their conversion rate improvement ability has already been weak, and the reason is that, compared with more lithium fluoride and phosphorus pentachloride, due to the small amount of fluorinating agent, the reaction in Step 2 can only proceed to a certain extent, and the reaction system is still dominated by the reaction of lithium fluoride and phosphorus pentachloride.

[0134] Therefore, in order to obtain a high yield in a common organic solvent system, the selection of a suitable fluorinating agent and the timing of the addition of the fluorinating agent are the keys and cores of the present application.

[0135] The applicant declares that the process method of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, and it does not mean that the present application must rely on the above process steps to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the selected raw materials of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A process for preparing lithium hexafluorophosphate, characterized in that: The following steps are involved: Step 1: lithium fluoride and phosphorus pentachloride react in an organic solvent to obtain a first mixture; Step 2: adding a fluorination agent to the first mixture to react and obtain lithium hexafluorophosphate; the reaction temperature of step 2 is 70-100° C.; The organic solvent is one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, ethylene carbonate and propylene carbonate; The fluorination agent is one or more of potassium fluoride, ammonium fluoride, calcium fluoride, potassium bifluoride, and ammonium bifluoride.

2. The process for preparing lithium hexafluorophosphate according to claim 1, wherein: The molar ratio of the lithium fluoride, phosphorus pentachloride and fluorination agent is 1-7:1:0.5-7.

5.

3. The process for preparing lithium hexafluorophosphate according to claim 1, wherein: The molar ratio of the lithium fluoride, phosphorus pentachloride and fluorination agent is 1.01-4:1:2.5-6.

5.

4. The process for preparing lithium hexafluorophosphate according to claim 1, wherein: In step 1, the mass ratio of the organic solvent to lithium fluoride is 20-30:

1.

5. The process for preparing lithium hexafluorophosphate according to claim 1, wherein: The step 1 is carried out at room temperature and pressure for 2 to 4 hours.

6. The process for preparing lithium hexafluorophosphate according to claim 1, wherein: The reaction time of step 2 is 6 to 10 hours.

7. The process for preparing lithium hexafluorophosphate according to claim 1, characterized in that: In step 2, the fluorination agent is added to the first mixture together with the organic solvent; the weight of the organic solvent used in step 2 is 2.5-5 times the weight of the fluorination agent.

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