A method for preparing lithium hexafluorophosphate

Abstract

This invention provides a method for preparing lithium hexafluorophosphate. The method comprises the following steps: Step 1, adding molecular sieves to acetonitrile solvent, shaking well, and allowing to stand; Step 2, filtering the settled mixture to obtain treated acetonitrile solvent, and regenerating the filtered molecular sieve for reuse; Step 3, preparing a mixture of dried potassium hexafluorophosphate and the treated acetonitrile solvent in a container; Step 4, stirring the solution in the container, adding lithium hydride while stirring, and simultaneously introducing ammonia gas to catalyze the reaction until completion; Step 5, filtering the reactants from Step 4, performing vacuum distillation on the filtrate to recover some solvent, and then cooling to crystallize, obtaining a complex of lithium hexafluorophosphate and acetonitrile; Step 6, filtering the complex from Step 5 and vacuum drying to obtain lithium hexafluorophosphate. This method provides a green process for preparing lithium hexafluorophosphate that is safe, economical, and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of lithium hexafluorophosphate preparation technology, and specifically relates to a method for preparing lithium hexafluorophosphate. Background Technology

[0002] Lithium hexafluorophosphate (LiPF6), as a novel electrolyte material for lithium-ion batteries, has attracted widespread attention since the mid-20th century due to its superior specific energy and energy density. Its synthesis is challenging, and industrialization was not achieved until 1996 by Morita Chemical Co., Ltd. of Japan. With the rapid increase in demand for lithium batteries from industries such as portable electronics, electric vehicles, and electric bicycles, the demand for lithium hexafluorophosphate has been steadily rising, and it is currently one of the most widely used lithium salts in commercial lithium-ion batteries.

[0003] The mainstream preparation methods for lithium hexafluorophosphate can be divided into dry and wet methods based on the different raw materials. The dry method involves treating lithium fluoride (LiF) with anhydrous hydrogen fluoride (HF) to form porous lithium fluoride, which is then reacted with phosphorus pentafluoride (PF5) gas to obtain the product. The wet method involves dissolving lithium salts in anhydrous hydrogen fluoride, introducing phosphorus pentafluoride gas to react, and generating lithium hexafluorophosphate. Another wet method involves mixing a phosphorus source and lithium salt in anhydrous hydrogen fluoride to prepare lithium hexafluorophosphate. With further research, an organic solvent method has emerged, using organic solvents commonly used in lithium-ion battery electrolytes, such as propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC), as solvents. Catalysts or solubilizers are added to prepare liquid lithium hexafluorophosphate, or the raw materials required for lithium hexafluorophosphate preparation are dissolved in organic solvents with good solubility and dispersibility for reaction. Such organic solvents can be selected from one or more of anhydrous acetonitrile, carbonates, ethylene glycol dimethyl ether, anhydrous diethyl ether, pyridine, and tetrahydrofuran.

[0004] In industrial production, dry processes, due to their inherent limitations, are insufficient to produce economical products. The reaction between phosphorus pentafluoride gas and solid lithium fluoride results in a low conversion rate of lithium fluoride, leading to the dominance of wet processes. The wet process involves dissolving lithium fluoride in ten times its volume of anhydrous hydrogen fluoride to achieve a uniform reaction between phosphorus pentafluoride and lithium fluoride. While this allows for industrial-scale production, the introduction of hydrogen fluoride leads to significant adsorption in the product, making removal difficult and affecting product quality. Furthermore, it requires substantial equipment investment, reduces safety, and demands stringent process conditions, necessitating cryogenic conditions and resulting in high overall energy consumption.

[0005] The preparation of lithium hexafluorophosphate using organic solvents is currently a research hotspot in China. One method involves reacting lithium fluoride with phosphorus pentafluoride in an organic solvent. However, the organic solvent reacts with phosphorus pentafluoride gas, producing colored impurities that affect the quality of the finished lithium hexafluorophosphate and the final lithium battery. Using a fluorinated organic solvent that does not react with phosphorus pentafluoride gas would increase production costs. Another method uses lithium chloride and potassium hexafluorophosphate as raw materials, reacting them in an organic solvent in the presence of a catalyst to synthesize lithium hexafluorophosphate. While this method avoids the use of toxic gases such as hydrogen fluoride, improving safety, it results in a low yield, yielding only an organic solution of lithium hexafluorophosphate. Yet another method involves a displacement reaction between lithium chloride and hexafluorophosphate in an organic solvent. However, lithium chloride has low solubility in organic solvents, leading to a large amount of solvent used, increased evaporation, and consequently, increased energy consumption. Furthermore, it introduces chloride ions into the finished product, affecting the performance of subsequent batteries. Summary of the Invention

[0006] Based on this, the present invention provides a method for preparing lithium hexafluorophosphate, which aims to provide a green process for preparing lithium hexafluorophosphate that does not use hydrogen fluoride, can be carried out under mild conditions, and integrates safety, economy and environmental protection.

[0007] This invention provides a method for preparing lithium hexafluorophosphate, comprising the following steps:

[0008] Step 1: Add molecular sieves to acetonitrile solvent, shake well and let stand to remove water from acetonitrile solvent;

[0009] Step 2: Filter the mixture after it has been allowed to stand to obtain the treated acetonitrile solvent. The filtered molecular sieve is then regenerated and reused in Step 1.

[0010] Step 3: Prepare a solution by mixing the dried potassium hexafluorophosphate with the treated acetonitrile solvent and place it in a container;

[0011] Step 4: Stir the solution in the container, add lithium hydride while stirring, and simultaneously introduce ammonia gas to catalyze the reaction until it is complete.

[0012] Step 5: Filter the reactants from Step 4, distill the filtrate under reduced pressure, recover part of the solvent, and then cool to crystallize, to obtain a complex of lithium hexafluorophosphate and acetonitrile.

[0013] Step 6: Filter the complex of lithium hexafluorophosphate and acetonitrile from step 5 and dry it under vacuum to obtain lithium hexafluorophosphate;

[0014] In this process, the acetonitrile from the vacuum distillation in step five and the vacuum drying in step six is ​​recovered and reused in step one.

[0015] In addition, the filter material from step six is ​​returned to step five for vacuum distillation and cooling crystallization.

[0016] Furthermore, the dried potassium hexafluorophosphate is mixed with the treated acetonitrile solvent to prepare an acetonitrile solution containing 15% to 20% potassium hexafluorophosphate.

[0017] Furthermore, lithium hydride is added under stirring, with a molar ratio of lithium hexafluorophosphate to lithium hydride of 1:1.05 to 3.

[0018] Furthermore, in the step of adding molecular sieve to acetonitrile solvent, shaking well and letting stand, the acetonitrile solvent with added molecular sieve is first shaken well and then left to stand for 24 hours, and then shaken once every 2 hours.

[0019] Furthermore, in the step of adding lithium hydride under stirring and simultaneously introducing ammonia gas to carry out the catalytic reaction until the reaction is completed, the ammonia gas flow rate is 1L / min to 5L / min, and the reaction time is 8h to 12h.

[0020] Furthermore, the drying method for potassium hexafluorophosphate is as follows: place the potassium hexafluorophosphate to be dried in a microwave drying device, control the power at 300W to 500W, and dry for 1 to 2 hours, with intermittent heating to avoid local overheating.

[0021] Furthermore, in the step of regenerating the filtered molecular sieve, the filtered molecular sieve is put into the microwave drying equipment and placed in a different area from the potassium hexafluorophosphate to be dried. The molecular sieve is microwave-heated for 0.5h to 2h to regenerate the molecular sieve.

[0022] Furthermore, before regenerating the filtered molecular sieve, the filtered molecular sieve and the potassium hexafluorophosphate to be dried are sealed together in a drying container to perform preliminary drying of the potassium hexafluorophosphate.

[0023] Furthermore, the acetonitrile solvent can be replaced with any one of ethyl acetate, pyridine, low alkyl ethers, nitrile, ketone, alcohol, amide, carbonate, or tetrahydrofuran.

[0024] Compared with the prior art, implementing the present invention has the following beneficial effects:

[0025] 1. Potassium hexafluorophosphate, the raw material in this invention, is easier to prepare than other hexafluorophosphates, and has stable chemical properties, without introducing other impurities due to decomposition;

[0026] 2. The process of this invention is simple to operate and the reaction process is mild, avoiding the use of a large number of cryogenic equipment, and has a significant effect on reducing energy consumption;

[0027] 3. The process in this invention does not use hydrogen fluoride, thus avoiding the formation of molecular adducts between lithium hexafluorophosphate and hydrogen fluoride during the reaction, and greatly reducing the energy consumption for removing hydrogen fluoride.

[0028] 4. In this invention, the conversion rate of potassium hexafluorophosphate reaches over 90%, and the byproducts are hydrogen and potassium hydroxide, while the catalyst is ammonia, all of which can be recycled. Attached Figure Description

[0029] Figure 1 The present invention provides a process flow diagram for the preparation of lithium hexafluorophosphate.

[0030] The following detailed embodiments will be further described in conjunction with the above-mentioned accompanying drawings. Detailed Implementation

[0031] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of the invention are illustrated in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] Please see Figure 1 The present invention provides a process flow diagram for preparing lithium hexafluorophosphate, wherein the preparation method specifically includes the following steps:

[0034] Step 1: Add molecular sieves to acetonitrile solvent, shake well and let stand to remove moisture from the acetonitrile solvent.

[0035] Molecular sieves are porous materials with uniform pore sizes, typically composed of silicates or aluminosilicates, possessing a high-density pore structure that can selectively adsorb molecules of certain sizes. In this embodiment of the invention, the acetonitrile solvent added to the molecular sieve is first shaken well and allowed to stand for 24 hours, then shaken every 2 hours thereafter to remove trace amounts of moisture from the acetonitrile solvent.

[0036] In other embodiments of the present invention, the organic solvent, in addition to acetonitrile as described herein, also includes ethyl acetate, other low-alkyl ethers, nitriles, ketones, amides, carbonates, tetrahydrofuran, pyridine, and other aprotic solvents. The acetonitrile solvent can be replaced with any one of ethyl acetate, pyridine, low-alkyl ethers, nitriles, ketones, alcohols, amides, carbonates, and tetrahydrofuran.

[0037] Step 2: Filter the mixture after it has been allowed to stand to obtain the treated acetonitrile solvent. The filtered molecular sieve is then regenerated and reused in Step 1.

[0038] It should be noted that the filtered molecular sieve is put into the microwave drying equipment and placed in a different area from the potassium hexafluorophosphate to be dried. The molecular sieve is microwave-heated for 0.5h to 2h to regenerate it. For example, the microwave-heated molecular sieve can be microwave-heated for 0.5h, 1h, 1.5h, 2h, etc., but is not limited to these. In addition, the temperature of the molecular sieve during the microwave drying process is usually controlled between 100℃ and 200℃.

[0039] In other embodiments of the present invention, before regenerating the filtered molecular sieve, the filtered molecular sieve and the potassium hexafluorophosphate to be dried are sealed together in a drying container. The purpose is to reuse the filtered molecular sieve and give full play to its remaining water absorption capacity to pre-dry the potassium hexafluorophosphate. Then, the potassium hexafluorophosphate and the molecular sieve are placed together in a microwave drying device for microwave heating. On the one hand, since the potassium hexafluorophosphate has been pre-dried, the drying efficiency in the microwave drying device can be improved. On the other hand, the molecular sieve that has fully absorbed water can be regenerated at the same time, which greatly optimizes the production process and meets the actual production requirements.

[0040] Step 3: Prepare a mixture of dried potassium hexafluorophosphate and treated acetonitrile solvent, and place it in a container.

[0041] In this embodiment, dried potassium hexafluorophosphate is mixed with treated acetonitrile solvent to prepare an acetonitrile solution containing 15% to 20% potassium hexafluorophosphate. For example, dried potassium hexafluorophosphate is mixed with treated acetonitrile solvent to prepare an acetonitrile solution containing 15% potassium hexafluorophosphate, 16% potassium hexafluorophosphate, 17% potassium hexafluorophosphate, 18% potassium hexafluorophosphate, 19% potassium hexafluorophosphate, 20% potassium hexafluorophosphate, etc., but is not limited to these.

[0042] In addition, the drying method for potassium hexafluorophosphate is as follows: place the potassium hexafluorophosphate to be dried in a microwave drying device, control the power between 300W and 500W, and dry for 1 hour to 2 hours, with intermittent heating to avoid local overheating. Examples of control power include 300W, 350W, 400W, 450W, and 500W, but are not limited to these; examples of drying time include 1 hour, 1.5 hours, and 2 hours, but are not limited to these.

[0043] Step 4: Stir the solution in the container, add lithium hydride while stirring, and simultaneously introduce ammonia gas to catalyze the reaction until it is complete.

[0044] Specifically, lithium hydride is added under stirring conditions, with a molar ratio of lithium hexafluorophosphate to lithium hydride of 1:1.05 to 3. Examples of such ratios include 1:1.05, 1:1.25, 1:1.5, 1:1.75, 1:2, 1:2.25, 1:2.5, 1:2.75, and 1:3, but these are not limited to these examples.

[0045] In this embodiment, the flow rate of ammonia gas introduced is 1L / min to 5L / min, and the reaction time is 8h to 12h. For example, the flow rate of ammonia gas introduced is 1L / min, 2L / min, 3L / min, 4L / min and 5L / min, etc., but is not limited to these; the reaction time is 8h, 9h, 10h, 11h and 12h, etc., but is not limited to these.

[0046] Step 5: Filter the reactants from Step 4, distill the filtrate under reduced pressure, recover some of the solvent, and then cool to crystallize, obtaining a complex of lithium hexafluorophosphate and acetonitrile.

[0047] It should be noted that the complex of lithium hexafluorophosphate and acetonitrile is lithium hexafluorophosphate acetonitrile (Li(CH3CN)4PF6) solid.

[0048] Furthermore, potassium can be recovered during the filtration of the reactants in step four.

[0049] Step six: Filter the complex of lithium hexafluorophosphate and acetonitrile from step five and dry it under vacuum to obtain lithium hexafluorophosphate.

[0050] Specifically, the acetonitrile from the vacuum distillation in step five and the vacuum drying in step six is ​​recovered and reused in step one.

[0051] Furthermore, the filter material from step six is ​​returned to step five for vacuum distillation and cooling crystallization.

[0052] In summary, the embodiments of this invention provide a method for preparing lithium hexafluorophosphate. This method uses chemically stable potassium hexafluorophosphate and lithium hydride as raw materials, and carries out a catalytic reaction in an organic solvent to synthesize lithium hexafluorophosphate at room temperature and pressure. Specifically, it proposes a green process for preparing lithium hexafluorophosphate that does not use hydrogen fluoride, can be carried out under mild conditions, and integrates safety, economy, and environmental protection.

[0053] To facilitate understanding of the present invention, several embodiments are provided below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present invention will be more thorough and complete.

[0054] Example 1

[0055] This invention provides a method for preparing lithium hexafluorophosphate in Example 1. Specifically, acetonitrile is dehydrated using a molecular sieve, then dissolved in dried potassium hexafluorophosphate to prepare a solution containing 20% ​​potassium hexafluorophosphate. Solid lithium hydride is then added, with a molar ratio of lithium hexafluorophosphate to lithium hydride of 1:1.2. Ammonia gas is introduced at a flow rate of 2 L / min under stirring to catalyze the reaction for 8 hours. The mixture is filtered to remove insoluble matter, and the filtrate is distilled under reduced pressure at 65°C to recover a portion of the acetonitrile. The solution is cooled to crystallize, filtered, and the resulting solid lithium hexafluorophosphate (acetonitrile) is obtained. The filtrate is combined with the next batch and distilled under reduced pressure again. The solid lithium hexafluorophosphate is then vacuum dried to recover acetonitrile again, yielding the final product, solid lithium hexafluorophosphate. The lithium hexafluorophosphate prepared in Example 1 has a purity of 99.96%, a moisture content of 8 ppm, and a chloride ion content of 2 ppm.

[0056] Example 2

[0057] Example 2 of this invention also provides a method for preparing lithium hexafluorophosphate, the difference being that in Example 1, the molar ratio of lithium hexafluorophosphate to lithium hydride is 1:1.05. The lithium hexafluorophosphate prepared in Example 2 has a purity of 99.96%, a water content of 9 ppm, and a chloride ion content of 2 ppm.

[0058] Example 3

[0059] Example 3 of this invention also provides a method for preparing lithium hexafluorophosphate, the difference from Example 1 being that the molar ratio of lithium hexafluorophosphate to lithium hydride is 1:1.5. The lithium hexafluorophosphate prepared in Example 3 has a purity of 99.95%, a water content of 7 ppm, and a chloride ion content of 1 ppm.

[0060] Example 4

[0061] Example 4 of this invention also provides a method for preparing lithium hexafluorophosphate, the difference from Example 1 being that the molar ratio of lithium hexafluorophosphate to lithium hydride is 1:2. The lithium hexafluorophosphate prepared in Example 4 has a purity of 99.96%, a water content of 6 ppm, and a chloride ion content of 1 ppm.

[0062] Example 5

[0063] Example 5 of this invention also provides a method for preparing lithium hexafluorophosphate, the difference from Example 1 being that the molar ratio of lithium hexafluorophosphate to lithium hydride is 1:2.5. The lithium hexafluorophosphate prepared in Example 5 has a purity of 99.96%, a water content of 6 ppm, and a chloride ion content of 2 ppm.

[0064] Example 6

[0065] Example 6 of this invention also provides a method for preparing lithium hexafluorophosphate, the difference from Example 1 being that the molar ratio of lithium hexafluorophosphate to lithium hydride is 1:3. The lithium hexafluorophosphate prepared in Example 6 has a purity of 99.95%, a water content of 5 ppm, and a chloride ion content of 2 ppm.

[0066] Example 7

[0067] Example 7 of this invention also provides a method for preparing lithium hexafluorophosphate, the difference being that in Example 1, ammonia gas is introduced at a flow rate of 1 L / min under stirring. The lithium hexafluorophosphate prepared in Example 7 has a purity of 99.95%, a water content of 8 ppm, and a chloride ion content of 2 ppm.

[0068] Example 8

[0069] Example 8 of this invention also provides a method for preparing lithium hexafluorophosphate, the difference being that in Example 1, ammonia gas is introduced at a flow rate of 3 L / min under stirring. The lithium hexafluorophosphate prepared in Example 8 has a purity of 99.97%, a water content of 7 ppm, and a chloride ion content of 1 ppm.

[0070] Example 9

[0071] Example 9 of this invention also provides a method for preparing lithium hexafluorophosphate, the difference being that in Example 1, ammonia gas is introduced at a flow rate of 4 L / min under stirring. The lithium hexafluorophosphate prepared in Example 9 has a purity of 99.96%, a water content of 8 ppm, and a chloride ion content of 2 ppm.

[0072] Example 10

[0073] Example 10 of this invention also provides a method for preparing lithium hexafluorophosphate. The difference from Example 1 is that ammonia gas is introduced at a flow rate of 5 L / min under stirring. The lithium hexafluorophosphate prepared in Example 10 has a purity of 99.96%, a water content of 8 ppm, and a chloride ion content of 1 ppm.

[0074] Example 11

[0075] Example 11 of this invention also provides a method for preparing lithium hexafluorophosphate, the difference from Example 1 being that a catalytic reaction is performed and the reaction time is 10 hours. The lithium hexafluorophosphate prepared in Example 11 has a purity of 99.96%, a water content of 7 ppm, and a chloride ion content of 2 ppm.

[0076] Example 12

[0077] Example 12 of this invention also provides a method for preparing lithium hexafluorophosphate, the difference from Example 1 being that a catalytic reaction is performed and the reaction time is 12 hours. The lithium hexafluorophosphate prepared in Example 12 has a purity of 99.97%, a water content of 9 ppm, and a chloride ion content of 2 ppm.

[0078] Example 13

[0079] Example 13 of this invention also provides a method for preparing lithium hexafluorophosphate. The difference from Example 1 is that, after removing moisture with a molecular sieve, acetonitrile is dissolved in dried potassium hexafluorophosphate to prepare a solution containing 15% potassium hexafluorophosphate. The lithium hexafluorophosphate prepared in Example 13 has a purity of 99.96%, a moisture content of 7 ppm, and a chloride ion content of 2 ppm.

[0080] Example 14

[0081] Example 14 of this invention also provides a method for preparing lithium hexafluorophosphate. The difference from Example 1 is that, after removing moisture with a molecular sieve, acetonitrile is dissolved in dried potassium hexafluorophosphate to prepare a solution containing 18% potassium hexafluorophosphate. The lithium hexafluorophosphate prepared in Example 14 has a purity of 99.97%, a moisture content of 8 ppm, and a chloride ion content of 1 ppm.

[0082] Comparative Example 1

[0083] Comparative Example 1 of this invention also provides a method for preparing lithium hexafluorophosphate. The difference from Example 1 is that lithium hydride is added under stirring, and the molar ratio of lithium hexafluorophosphate to lithium hydride is 1:1. The lithium hexafluorophosphate prepared in Comparative Example 1 has a purity of 99.85%, a water content of 13 ppm, and a chloride ion content of 3 ppm.

[0084] Comparative Example 2

[0085] Comparative Example 2 of this invention also provides a method for preparing lithium hexafluorophosphate. The difference from Example 1 is that lithium hydride is added under stirring, and the molar ratio of lithium hexafluorophosphate to lithium hydride is 1:3.2. The lithium hexafluorophosphate prepared in Comparative Example 2 has a purity of 99.84%, a water content of 10 ppm, and a chloride ion content of 4 ppm.

[0086] Comparative Example 3

[0087] Comparative Example 3 of this invention also provides a method for preparing lithium hexafluorophosphate. The difference from Example 1 is that, after removing moisture with a molecular sieve, acetonitrile is dissolved in dried potassium hexafluorophosphate to prepare a solution containing 10% potassium hexafluorophosphate. The lithium hexafluorophosphate prepared in Comparative Example 3 has a purity of 99.86%, a water content of 10 ppm, and a chloride ion content of 3 ppm.

[0088] Comparative Example 4

[0089] Comparative Example 4 of this invention also provides a method for preparing lithium hexafluorophosphate. The difference from Example 1 is that, after removing moisture with a molecular sieve, acetonitrile is dissolved in dried potassium hexafluorophosphate to prepare a solution containing 25% potassium hexafluorophosphate. The lithium hexafluorophosphate prepared in Comparative Example 4 has a purity of 99.83%, a water content of 12 ppm, and a chloride ion content of 4 ppm.

[0090] Comparative Example 5

[0091] Comparative Example 5 of this invention also provides a method for preparing lithium hexafluorophosphate. The difference from Example 1 is that ammonia gas is introduced at a flow rate of 0.5 L / min under stirring. The lithium hexafluorophosphate prepared in Comparative Example 5 has a purity of 99.82%, a water content of 12 ppm, and a chloride ion content of 2 ppm.

[0092] The purity, moisture content, and chloride ion content of the lithium hexafluorophosphate products from Examples 1 to 14 and Comparative Examples 1 to 5 of this invention were tested. The specific results are shown in the table below:

[0093]

[0094] As shown in the table above, the lithium hexafluorophosphate prepared by this invention has a purity of over 99.95%, a moisture content of less than 10 ppm, and a chloride ion content of less than 2 ppm.

[0095] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0096] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for preparing lithium hexafluorophosphate, characterized in that, Includes the following steps: Step 1: Add molecular sieves to acetonitrile solvent, shake well and let stand to remove water from acetonitrile solvent; Step 2: Filter the mixture after it has been allowed to stand to obtain the treated acetonitrile solvent. The filtered molecular sieve is then regenerated and reused in Step 1. Step 3: Prepare a solution by mixing the dried potassium hexafluorophosphate with the treated acetonitrile solvent and place it in a container; Step 4: Stir the solution in the container, add lithium hydride while stirring, and simultaneously introduce ammonia gas to catalyze the reaction until it is complete. Step 5: Filter the reactants from Step 4, distill the filtrate under reduced pressure, recover part of the solvent, and then cool to crystallize, to obtain a complex of lithium hexafluorophosphate and acetonitrile. Step 6: Filter the complex of lithium hexafluorophosphate and acetonitrile from step 5 and dry it under vacuum to obtain lithium hexafluorophosphate; In this process, the acetonitrile from the vacuum distillation in step five and the vacuum drying in step six is ​​recovered and reused in step one. In addition, the filter material from step six is ​​returned to step five for vacuum distillation and cooling crystallization; The dried potassium hexafluorophosphate was mixed with the treated acetonitrile solvent to prepare an acetonitrile solution containing 15% to 20% potassium hexafluorophosphate. Lithium hydride is added under stirring, with a molar ratio of lithium hexafluorophosphate to lithium hydride of 1:1.05 to 3; In the step of adding lithium hydride under stirring and simultaneously introducing ammonia gas to catalyze the reaction until the reaction is completed, the ammonia gas flow rate is 1L / min to 5L / min, and the reaction time is 8h to 12h.

2. The method for preparing lithium hexafluorophosphate according to claim 1, characterized in that, In the step of adding molecular sieve to acetonitrile solvent, shaking well and letting stand, the acetonitrile solvent with added molecular sieve is first shaken well and then left to stand for 24 hours, and then shaken once every 2 hours.

3. The method for preparing lithium hexafluorophosphate according to claim 2, characterized in that, The drying method for potassium hexafluorophosphate is as follows: place the potassium hexafluorophosphate to be dried in a microwave drying device, control the power at 300W to 500W, and dry for 1 to 2 hours, with intermittent heating to avoid local overheating.

4. The method for preparing lithium hexafluorophosphate according to claim 3, characterized in that, In the step of regenerating the filtered molecular sieve, the filtered molecular sieve is put into the microwave drying equipment and placed in a different area from the potassium hexafluorophosphate to be dried. The molecular sieve is microwave heated for 0.5h to 2h to regenerate the molecular sieve.

5. The method for preparing lithium hexafluorophosphate according to claim 4, characterized in that, Before regenerating the filtered molecular sieve, the filtered molecular sieve and the potassium hexafluorophosphate to be dried are sealed together in a drying container to perform preliminary drying of the potassium hexafluorophosphate.

6. The method for preparing lithium hexafluorophosphate according to claim 5, characterized in that, Replace the acetonitrile solvent with any one of ethyl acetate, pyridine, low alkyl ethers, ketones, alcohols, amides, carbonates, or tetrahydrofuran.

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