A method for preparing lithium hexafluorophosphate

Abstract

The invention discloses a method for preparing lithium hexafluorophosphate, which comprises mixing a pentavalent phosphorus oxide compound with a pyridine solution of hydrogen fluoride for fluorination reaction to obtain pyridine hexafluorophosphate; pyridine hexafluorophosphate undergoes a lithiation reaction in an organic solvent, dehydrates phosphorus pentoxide, and filters to obtain an organic solution containing lithium hexafluorophosphate; the organic solution can prepare a lithium hexafluorophosphate solid product, or use an electrolyte solvent to obtain a lithium hexafluorophosphate liquid product. At the same time, the invention also relates to a method for mixing an excess fluorination agent and a dehydrated phosphorus pentoxide precipitate for secondary fluorination reaction, thereby realizing the recycling of hydrogen fluoride, pyridine and phosphorus element. The invention does not use highly corrosive hydrogen fluoride or hydrofluoric acid, does not produce phosphorus pentafluoride, and has high product purity, high raw material utilization rate, low pollution, low equipment investment, and high safety.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a method for preparing lithium hexafluorophosphate. Background Art

[0002] Compared with traditional batteries, lithium-ion batteries have advantages such as larger capacity, higher average output voltage, better cycle performance and conductivity, and have become the most widely used energy storage device today. They are widely used in electronics, information, computers, military, aerospace, power vehicles, electric vehicles and other fields.

[0003] Lithium hexafluorophosphate is one of the most commonly used electrolytes in the current lithium-ion battery field. Lithium hexafluorophosphate is called Lithium hexafluorophosphate in English. Its structural formula is LiPF6. It is a white crystal or powder with a relative density of 1.5. It is easy to absorb moisture and decompose when exposed to water or humid air. In particular, it decomposes rapidly in the air due to the action of water vapor, releasing PF5 and producing white smoke. It has a corrosive effect on the eyes, skin, and especially the lungs; it is unstable when heated; it is easily soluble in water, and is also soluble in organic solvents such as methanol, ethanol, acetone, and carbonates. As an electrolyte, it has the following advantages: ① It can form a SEI film in the electrode, especially in the carbon negative electrode; ② It can effectively passivate the positive electrode current collector, thereby effectively preventing its dissolution; ③ It has good electrochemical stability, and the electrochemical window is 5.1V, which is more suitable for the manufacturing requirements of lithium-ion batteries; ④ It has a large solubility in organic carbonate solvents and a relatively high conductivity; ⑤ It is environmentally friendly.

[0004] There are many preparation methods reported for lithium hexafluorophosphate, including gas-solid reaction method, HF solvent method, organic solvent method, ion exchange method, etc. At present, the HF solvent method is widely used in industrial preparation of lithium hexafluorophosphate.

[0005] The HF solvent method has different process routes, but all of them use phosphorus pentafluoride and lithium fluoride as raw materials, anhydrous hydrogen fluoride as solvent for reaction, and then freeze crystallize at low temperature after the reaction to separate lithium hexafluorophosphate. The reaction process uses anhydrous HF as a carrier, which requires a very low temperature environment. HF is used as a solvent in large excess, and there must be an HF removal process after the reaction is completed. Anhydrous HF and phosphorus pentafluoride are highly corrosive, toxic and harmful, and can corrode equipment. They place high demands on equipment corrosion protection and production environment, and the equipment investment is high. Otherwise, any leakage during the reaction will cause great harm to the environment and personnel. Lithium hexafluorophosphate products are sensitive to moisture, so it is extremely important to ensure anhydrous operation. Strict sealing is required not only during the reaction process, but also during the product transfer process. The above factors increase the HF solvent production cost of lithium hexafluorophosphate.

[0006] The gas-solid reaction method is the earliest preparation process of lithium hexafluorophosphate. In 1950, American scientist JH Simmons used PF5 gas and LiF to directly react in a nickel container under high temperature and high pressure conditions to produce lithium hexafluorophosphate. The equation is: PF5 (gas) + LiF (solid) = LiPF6 (solid). The specific process is to treat LiF with anhydrous HF to form porous LiF, and then introduce PF5 gas to react with porous LiF to obtain LiPF6. Since the generated lithium hexafluorophosphate completely covers the LiF solid particles, it prevents the further reaction from proceeding. Therefore, the lithium hexafluorophosphate product obtained by this method has low purity and low yield, making it difficult to achieve large-scale production.

[0007] The organic solvent method also uses phosphorus pentafluoride and lithium fluoride as raw materials to prepare lithium hexafluorophosphate. Commonly used organic solvents are ethers, low alkyl esters such as EC, DEC and DMC, and acetonitrile. The difficulty of the preparation process using ethers and acetonitrile as solvents is that lithium hexafluorophosphate forms a complex with the solvent and dissolves in the solvent, and it is very difficult to separate and precipitate lithium hexafluorophosphate. Low alkyl esters such as EC, DEC and DMC are commonly used electrolyte solvents for lithium-ion batteries and have good solubility for lithium hexafluorophosphate. This method of preparing lithium hexafluorophosphate has the advantages of easy reaction control and high yield. However, when preparing lithium hexafluorophosphate solid products, due to the good solubility of lithium hexafluorophosphate in low alkyl esters such as EC, DEC and DMC, crystallization is difficult, and PF5 may have side reactions with organic solvents, causing the solution color to darken.

[0008] The ion exchange method is a method of obtaining lithium hexafluorophosphate by subjecting hexafluorophosphate to an ion exchange reaction with a lithium-containing compound in an organic solvent. Since the sodium, potassium, and ammonium hexafluorophosphate have better thermal and hydrothermal stability and are easy to store and use, this method can reduce the corrosiveness of materials and equipment requirements, and facilitate production operations. However, the hexafluorophosphate raw material used in the reaction is not easy to prepare; its properties are similar to those of lithium hexafluorophosphate, and it is extremely difficult to completely remove it, which makes the purification of lithium hexafluorophosphate more difficult; in addition, the metal salt obtained after ion exchange is difficult to recycle and can only be treated separately.

[0009] It can be seen that although the HF solvent method has been widely adopted, its materials are highly corrosive and dangerous, and the equipment investment is high; the organic solvent method is prone to introduce impurities due to the high reactivity of PF5 and the reaction with the solvent; the ion exchange method is difficult to purify the product because hexafluorophosphate metal salt (ammonium salt) is difficult to obtain, and the related cations are not easy to recover and reuse. Summary of the invention

[0010] The purpose of the present invention is to solve the above problems and provide a method for preparing lithium hexafluorophosphate, which can avoid the problems of high corrosiveness, high danger and high equipment requirements caused by the use of HF as a raw material; it has the advantages of both the organic solvent method and the ion exchange method, but does not involve the production of PF5, will not cause side reactions of organic solvents, can quickly prepare hexafluorophosphate, and the cations can be recycled and reused.

[0011] The technical solution of the present invention is:

[0012] A method for preparing lithium hexafluorophosphate, characterized in that: a pentavalent phosphorus oxide compound is mixed with a pyridine solution of hydrogen fluoride for fluorination reaction to obtain pyridine hexafluorophosphate; pyridine hexafluorophosphate is subjected to a lithiation reaction in an organic solvent, phosphorus pentoxide is used to remove water, and an organic solution containing lithium hexafluorophosphate is obtained by filtration; the organic solution can be used to prepare a lithium hexafluorophosphate solid product, and an electrolyte solvent can also be used to obtain a lithium hexafluorophosphate liquid product.

[0013] Further: comprising the following steps:

[0014] Step 1: mixing a pentavalent phosphorus oxide with a pyridine solution of hydrogen fluoride, wherein the molar ratio of phosphorus element to hydrogen fluoride is 1:5-60, the reaction temperature is 0-60° C., and the reaction is stirred for 0.5-24 hours. After the reaction is completed, the mixture is filtered and dried at 40-80° C. to obtain pyridine hexafluorophosphate. The filtrate after filtration is a recyclable pyridine solution of hydrogen fluoride;

[0015] Step 2: adding the obtained pyridine hexafluorophosphate into an organic solvent, adding lithium carbonate or lithium hydroxide to carry out a lithiation reaction, wherein the molar feed ratio of pyridine hexafluorophosphate to lithium element is 1:0.8-1.5, and stirring the reaction at 0-60° C. for 0.5-24 hours;

[0016] Step 3: Take the reaction solution and determine the water content, add phosphorus pentoxide to the reaction solution, keep stirring at 0-60°C for 0.5-24h, cool to -20-10°C, filter to obtain an organic solution containing lithium hexafluorophosphate, and the filter residue is phosphorus-containing pyridinium salt;

[0017] Step 4: The organic solution of lithium hexafluorophosphate is evaporated and then crystallized to obtain a solid product of lithium hexafluorophosphate; if the organic solvent in the organic solution of lithium hexafluorophosphate is an electrolyte solvent, the solution can be directly used as a liquid product of lithium hexafluorophosphate.

[0018] Furthermore, in step 1, the pentavalent phosphorus oxide compound may be phosphorus pentoxide, orthophosphoric acid, metaphosphoric acid, or a combination of two or three of the above three. The raw material is preferably of battery grade quality.

[0019] In step 1, the mass concentration of hydrogen fluoride in the pyridine solution of hydrogen fluoride is 5% to 70%, preferably 40% to 56%.

[0020] In step 1, the molar ratio of phosphorus element to hydrogen fluoride is preferably 1:6-12, the reaction temperature is preferably 0-20°C, the reaction time is preferably 2-4h, the drying temperature is preferably 40-50°C, the drying is preferably carried out under low pressure, the pressure is further preferably 1-1000Pa, and the drying time is 0.5-24h, preferably 3-8h.

[0021] In step 2, the organic solvent is selected from a non-protonic polar solvent, including esters, ketones, ethers, nitriles, amides, and sulfone solvents, and examples thereof include ethyl acetate, propyl acetate, butyl acetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and ethylene carbonate. Propylene carbonate, acetone, ethyl ether, n-propyl ether, isopropyl ether, methyl tert-butyl ether, acetonitrile, propionitrile, N,N-dimethylformamide, dimethyl sulfoxide, etc., and preferred solvents include propyl acetate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The solvent may be one, or a combination of two or more. For the sake of process simplification, a single solvent is preferred. The amount of solvent used is more than 0.5 times the weight of pyridine hexafluorophosphate, preferably 2 to 3 times. The solvent quality grade is preferably battery grade.

[0022] In step 2, the quality grade of lithium carbonate or lithium hydroxide is preferably battery grade, the feed is measured in lithium element, the molar feed ratio of pyridinium hexafluorophosphate to lithium element is preferably 1:1.0-1.1, the lithiation reaction temperature is preferably 20-40°C, and the reaction time is preferably 6-8h.

[0023] In step 3, the method for determining the water content of the reaction solution is not limited, as long as the water content can be accurately determined. The molar ratio of the added phosphorus pentoxide to the water in the reaction solution is 0.34 to 1:1, preferably 0.48 to 0.55:1.

[0024] In step 3, the temperature of the heat preservation and stirring is preferably 30 to 50°C, the time is preferably 3 to 6 hours, and the cooling temperature is preferably -5 to 5°C.

[0025] In step 3, a precision filter is preferably used for filtration, and the filter accuracy is 0.1 to 30 microns, preferably 0.2 to 2 microns. The filtration can be performed by pressurized filtration or reduced pressure filtration.

[0026] In step 4, when preparing lithium hexafluorophosphate solid from lithium hexafluorophosphate organic solution, the evaporation temperature is 40-100°C, preferably 60-70°C, and the pressure is 1-20000 Pa. After evaporation, the concentration of lithium hexafluorophosphate is close to the saturation concentration of the current solvent. The crystallization method can be cooling crystallization or dissolution crystallization.

[0027] The present invention also includes a technical scheme for recycling and reusing hydrogen fluoride, phosphorus and pyridine in a lithium hexafluorophosphate preparation process: pyridine hexafluorophosphate is obtained by filtering after fluorination reaction, and phosphorus-containing pyridine salt solid is first recovered by filtering after lithiation reaction; the filtrate is filtered after fluorination reaction, and the recovered hydrogen fluoride-containing pyridine solution is mixed with the phosphorus-containing pyridine salt solid obtained by filtering after lithiation reaction to carry out secondary fluorination reaction, and the degree of secondary fluorination is insufficient with the amount of hydrogen fluoride in the pyridine solution for recycling hydrogen fluoride, and hydrogen fluoride can be quantitatively supplemented until fluorination is complete, and pyridine hexafluorophosphate is obtained by filtering and drying for step 2 reaction; hydrogen fluoride in the filtrate after secondary fluorination is almost completely consumed, and the filtrate is dehydrated, deacidified, and purified to recover pyridine, and hydrogen fluoride pyridine solution is configured again. Thereby, the utilization rate of hydrogen fluoride and phosphorus elements is improved, pyridine recovery and reuse is achieved, and the discharge of three wastes is avoided.

[0028] The secondary fluorination reaction of adding hydrogen fluoride refers to adding a pyridine solution of hydrogen fluoride, and the concentration can be 20% to 70%, preferably 60% to 70%.

[0029] The amount of hydrogen fluoride added is calculated by subtracting the amount of hydrogen fluoride in the pyridine solution recovered from the amount of hydrogen fluoride required for fluoridation of phosphorus in the phosphorus-containing pyridine salt, so that the molar ratio of total hydrogen fluoride to phosphorus in the phosphorus-containing pyridine salt is 0.9-1.1:1, preferably 1-1.05:1.

[0030] During the secondary fluorination, the reaction temperature is 0 to 80°C, preferably 40 to 60°C; the reaction time is 2 to 18 hours, preferably 6 to 10 hours.

[0031] The drying temperature of the pyridinium hexafluorophosphate obtained by the secondary fluorination is preferably 40-50° C., and the drying is preferably carried out under low pressure, preferably 1-1000 Pa, and the drying time is 0.5-24 h, preferably 3-8 h.

[0032] The pyridine recovery technology scheme, pyridine dehydration, deacidification, and purification treatment methods adopt industrially known schemes, which can be listed as first alkali neutralization, then molecular sieve dehydration, and finally distillation purification; calcium oxide dehydration and deacidification, and then distillation purification; or first brine washing acid separation, then molecular sieve dehydration, and finally distillation purification.

[0033] The present invention has the following advantages:

[0034] (1) Using a pyridine solution of hydrogen fluoride as a fluorinating agent (also known as Olah's reagent) has the advantage of being a milder fluorinating agent with much lower corrosiveness than pure HF or hydrofluoric acid; at the same time, it effectively inhibits the volatilization of HF, which can be understood as high-boiling-point HF, so the probability of gaseous HF leakage, damage and pollution is greatly reduced; it is a liquid at room temperature and can be used as a solvent, which is also convenient for transportation, storage and metering during use. Therefore, the use of this fluorinating agent reduces equipment requirements, improves safety, and is easy to operate. In addition, the pyridine solution of hydrogen fluoride is prepared by pyridine and anhydrous HF, and the raw materials are easy to purify and impurities are not easily introduced.

[0035] (2) The process does not produce PF5, so it will not cause the solvent to deteriorate and introduce impurities; the preparation process has no strict environmental moisture requirements, and the introduction of moisture will not cause material hydrolysis and produce serious corrosiveness.

[0036] (3) By using electrolyte solvents such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc., liquid lithium salt products of lithium hexafluorophosphate can be directly prepared, eliminating the solid lithium hexafluorophosphate preparation process, with high yield, high purity, low moisture and acidity, and no chloride ions and insolubles; the liquid product is easy to store and transport.

[0037] (4) It can achieve efficient utilization of hydrogen fluoride and phosphorus, pyridine recovery and circulation, and avoid pollution. DETAILED DESCRIPTION

[0038] The following examples further describe the present invention in detail.

[0039] In the following examples, the reagents and raw materials used are of battery grade quality; all reactors and auxiliary equipment are made of tetrafluoroethylene or PFA; and the process is protected by nitrogen atmosphere.

[0040] Example 1

[0041] In a closed flask with stirring, add 142 g of phosphorus pentoxide, cool to 0°C, slowly drop 834 g of 43.2% hydrogen fluoride pyridine solution, and maintain the reaction temperature at 0-10°C. Continue stirring and reacting for 3 hours, filter to obtain a white solid, and dry at 50°C, 100 Pa for 3 hours to obtain 448 g of pyridinium hexafluorophosphate.

[0042] 448g of pyridinium hexafluorophosphate was added to a flask containing 1000g of dimethyl carbonate, and 48g of anhydrous lithium hydroxide was added. The mixture was heated to 30°C with stirring and reacted for 6h. The reaction water content was measured to be 2.41%. 142g of phosphorus pentoxide was weighed and added to the solution in 10 times, and the temperature was raised to 40°C and stirred for 4h. The reaction solution was cooled to 0°C and filtered with a precision filter with an accuracy of 1 micron to obtain 1285g of a colorless and transparent solution. The content of lithium hexafluorophosphate in the solution was measured to be 23.2%, and the yield was 98.1%. Further analysis showed that the solution had a water content of 3.2ppm, an acidity (HF meter) of 5.6ppm, chloride ions were not detected, sulfate ions were not detected, insoluble matter had been removed and not measured, sodium ions were 2.4ppm, and the remaining metal cations were all less than 1ppm. The liquid lithium hexafluorophosphate solution can be easily transferred into a storage tank for storage and used for electrolyte configuration.

[0043] Example 2

[0044] In a closed PFA flask with stirring, add 196g of orthophosphoric acid, cool to 0°C, slowly drop 763g of 50.3% hydrogen fluoride pyridine solution, and maintain the reaction temperature at 10-20°C. Continue stirring the reaction for 2h, filter to obtain a white solid, and dry at 50°C, 1000Pa for 8h to obtain 441g of pyridinium hexafluorophosphate.

[0045] 441g of pyridinium hexafluorophosphate was added to a flask containing 900g of diethyl carbonate, and 74g of anhydrous lithium carbonate was added. The mixture was heated to 30°C with stirring and reacted for 8h. The reaction water content was measured to be 1.32%. 71.5g of phosphorus pentoxide was weighed and added to the solution in 6 portions, and stirred at 30°C for 6h. The reaction solution was cooled to -5°C and filtered with a precision filter with an accuracy of 0.5 microns to obtain 1167g of a colorless and transparent solution. The content of lithium hexafluorophosphate in the solution was measured to be 25.5%, and the yield was 97.9%. Further analysis showed that the solution had a water content of 1.5ppm, an acidity (HF meter) of 3.6ppm, chloride ions were not detected, sulfate ions were not detected, insoluble matter had been removed and not measured, sodium ions were 2.6ppm, and the remaining metal cations were all less than 1ppm.

[0046] Example 3

[0047] The preparation method of pyridinium hexafluorophosphate is the same as that of Example 1.

[0048] Add 447g of pyridinium hexafluorophosphate to a flask containing 1200g of propyl acetate, add 75g of anhydrous lithium carbonate, heat to 20°C with stirring, and react for 8h. Samples were taken and the reaction water content was 1.09%. Take 72g of phosphorus pentoxide and add it to the solution in 6 times, keep it warm and stir it at 20°C for 6h. Cool the reaction solution to -5°C, filter it under pressure with a precision filter with an accuracy of 0.22 microns, and obtain 1500g of colorless and transparent solution. The solution was concentrated at 60°C and 15000Pa to a total of 490g with a mass concentration of 60% lithium hexafluorophosphate and a yield of 96.7%. Divide the lithium hexafluorophosphate concentrate into two batches of 245g each.

[0049] One batch was cooled and crystallized: cooled to -30℃, filtered, and dried at 60℃ and 1000Pa to obtain 97g of lithium hexafluorophosphate crystals. The water content was 6.5ppm, the acidity (HF meter) was 14.3ppm, the chloride ion was not detected, the sulfate ion was not detected, the insoluble matter was 13.3ppm, the sodium ion was 4.2ppm, the potassium ion was 1.4ppm, and the other metal cations were all less than 1ppm. The main content of lithium hexafluorophosphate was >99.99%.

[0050] Another batch of concentrated solution was added with 500g of anhydrous dichloromethane for dissolution and crystallization, filtered, and dried at 60°C and 1000Pa to obtain 69g of lithium hexafluorophosphate crystals. The water content was 7.9ppm, the acidity (HF meter) was 11.2ppm, the chloride ion was not detected, the sulfate ion was not detected, the insoluble matter was 19.3ppm, the sodium ion was 7.2ppm, the potassium ion was 2.4ppm, and the other metal cations were all less than 1ppm, and the main content of lithium hexafluorophosphate was >99.99%.

[0051] Example 4: Recovery and Reuse of Hydrogen Fluoride and Phosphorus

[0052] Secondary fluorination reaction: 520g of the filtrate recovered after the fluorination reaction in Example 1, i.e., the hydrogen fluoride pyridine solution, was measured to have a residual hydrogen fluoride content of 22.7%; in Example 1, 336g of phosphorus-containing pyridine salt was recovered by filtration after the lithiation reaction. The recovered hydrogen fluoride pyridine solution was added dropwise to the reactor containing the recovered phosphorus-containing pyridine salt, and 175g of 70% hydrogen fluoride pyridine solution was added dropwise. The reaction temperature was controlled at 30-40°C. After the addition was completed, the mixture was stirred at 40°C for 8h. A white solid was obtained after filtration. The solid was dried at 50°C and 500Pa for 5h to obtain 443g of hexafluorophosphate pyridine salt.

[0053] Preparation of lithium hexafluorophosphate from secondary fluorinated pyridinium hexafluorophosphate: Add 443g of pyridinium hexafluorophosphate to a flask containing 1200g of isopropyl ether, add 50g of lithium hydroxide, heat to 40°C with stirring, and react for 7h. The reaction water content was measured to be 2.20%. Weigh 150g of phosphorus pentoxide and add it to the solution in 10 times, and stir for 4h. Cool the reaction solution to 0°C and filter it under pressure with a precision filter with an accuracy of 0.22 microns to obtain 1495g of a colorless and transparent solution. Concentrate the solution at 45°C and 20000Pa to a total of 519g of lithium hexafluorophosphate with a mass concentration of 58% and a yield of 97.5%. 1500g of toluene was added to the concentrated solution for dissolution and crystallization to obtain 245g of lithium hexafluorophosphate crystals. The water content was 4.2ppm, the acidity (HF) was 15.9ppm, chloride ions were not detected, sulfate ions were not detected, insoluble matter was 27.4ppm, sodium ions were 7.6ppm, potassium ions were 2.8ppm, and the remaining metal cations were all less than 1ppm. The main content of lithium hexafluorophosphate was >99.99%.

[0054] Example 5 Pyridine Recovery and Recycling

[0055] Pyridine recovery: add 20 g of sodium chloride to 580 g of the secondary fluorination filtrate under stirring, and after stirring, separate the solution into layers, and take the upper organic liquid as pyridine; add 100 g of 4A molecular sieve to the pyridine liquid and dry for 24 hours; take the liquid for distillation to obtain 355.7 g of pyridine, with a yield of 96.7%, a water content of 6.7 ppm, and a content of 99.9%.

[0056] Reconfiguration of the hydrogen fluoride pyridine solution: 300 g of the purified pyridine solution was recovered and cooled to 0°C in a reactor, and anhydrous HF gas was introduced into the reactor under stirring for absorption, and the temperature during HF absorption was controlled at 0-10°C. When the weight of the reactor increased by 405 g, the introduction of hydrogen fluoride was stopped, and stirring was maintained for 60 minutes. The hydrogen fluoride concentration in the hydrogen fluoride pyridine solution was sampled and analyzed to be 57.4%.

[0057] The recovered pyridine was subjected to a primary fluorination-secondary fluorination-recycling cycle for 3 times, wherein the primary fluorination experimental conditions were as described in Example 3, and lithium hexafluorophosphate was prepared by a dissolution crystallization method; and the secondary fluorination experimental conditions were as described in Example 4 to prepare secondary fluorinated lithium hexafluorophosphate. The results are shown in the following table:

[0058] It can be seen that the recycling and reuse of pyridine has no obvious effect on the quality of lithium hexafluorophosphate products; after multiple recycling, the single recovery rate is maintained at about 97%, achieving the recovery of most pyridine

[0059]

Claims

1. A method for preparing lithium hexafluorophosphate, characterized in that: A pentavalent phosphorus oxide compound is mixed with a pyridine solution of hydrogen fluoride for fluorination reaction to obtain pyridine hexafluorophosphate; pyridine hexafluorophosphate is subjected to a lithiation reaction in an organic solvent, phosphorus pentoxide is used to remove water, and an organic solution containing lithium hexafluorophosphate is obtained by filtration; the organic solution can be used to prepare a lithium hexafluorophosphate solid product, or an electrolyte solvent can be used to obtain a lithium hexafluorophosphate liquid product, which specifically includes the following steps: Step 1: mixing a pentavalent phosphorus oxide with a pyridine solution of hydrogen fluoride, wherein the molar ratio of phosphorus element to hydrogen fluoride is 1:5-60, the reaction temperature is 0-60° C., and the mixture is stirred for 0.5-24 hours. After the reaction is completed, the mixture is filtered and dried at 40-80° C. to obtain pyridine hexafluorophosphate; Step 2: adding the obtained pyridine hexafluorophosphate into an organic solvent, adding lithium carbonate or lithium hydroxide to carry out a lithiation reaction, wherein the molar feed ratio of pyridine hexafluorophosphate to lithium element is 1:0.8-1.5, and stirring the reaction at 0-60° C. for 0.5-24 hours; Step 3: Take the reaction solution and determine the water content, add phosphorus pentoxide to the reaction solution, keep stirring at 0-60°C for 0.5-24h, cool to -20-10°C, filter to obtain an organic solution containing lithium hexafluorophosphate, and the filter residue is phosphorus-containing pyridinium salt; Step 4: The organic solution of lithium hexafluorophosphate is evaporated and then crystallized to obtain a solid product of lithium hexafluorophosphate; if the organic solvent in the organic solution of lithium hexafluorophosphate is an electrolyte solvent, the solution can be directly used as a liquid product of lithium hexafluorophosphate.

2. The method according to claim 1, characterized in that: The pentavalent phosphorus oxide compound can be selected from phosphorus pentoxide, orthophosphoric acid or metaphosphoric acid, or a combination of two or three of the above three, and the raw material quality grade is battery grade; in the pyridine solution of hydrogen fluoride, the mass concentration of hydrogen fluoride is 5% to 70%, and the molar ratio of phosphorus element to hydrogen fluoride is preferably 1:6 to 12.

3. The method according to claim 1, characterized in that The fluorination reaction temperature is 0-20°C; the fluorination reaction time is 2-4h; the drying temperature is 40-50°C; the drying is carried out at a pressure less than atmospheric pressure, the pressure is 10-1000Pa, and the drying time is 0.5-24h.

4. The method according to claim 1, characterized in that: In the step 2, the organic solvent is a non-protonic polar solvent, the amount of the solvent is more than 0.5 times the weight of pyridine hexafluorophosphate, and the solvent quality grade is battery grade; the lithium carbonate or lithium hydroxide quality grade is battery grade; the feed is measured in lithium element, and the molar feed ratio of pyridine hexafluorophosphate to lithium element is 1:1.0-1.1; the lithiation reaction temperature is 20-40°C; and the lithiation reaction time is 6-8h.

5. The method according to claim 1, characterized in that In step 3, the molar ratio of the added phosphorus pentoxide to the water in the reaction solution is 0.34-1:1, the insulation stirring temperature is 30-50°C; the insulation stirring time is 3-6h; the cooling temperature is -5-5°C; and a precision filter is used for filtration, and the filter accuracy is 0.1-30 microns.

6. The method according to claim 1, characterized in that In the step 4, when preparing lithium hexafluorophosphate solid from lithium hexafluorophosphate organic solution, the evaporation temperature is 40-100° C. and the pressure is 1-20000 Pa.

7. The method according to claim 1, characterized in that After the fluorination reaction, pyridine hexafluorophosphate is obtained by filtration, and after the lithiation reaction, the phosphorus-containing pyridine salt solid is recovered by filtration; after the fluorination reaction, the filtrate is recovered, and the recovered hydrogen fluoride-containing pyridine solution is mixed with the phosphorus-containing pyridine salt solid obtained by filtration after the lithiation reaction to carry out a secondary fluorination reaction, and hydrogen fluoride is quantitatively supplemented until the fluorination is complete, and pyridine hexafluorophosphate is obtained by filtration and drying, and used for the reaction in step 2; after the secondary fluorination, the hydrogen fluoride in the filtrate is almost completely consumed, and the filtrate is dehydrated, deacidified, and purified to recover pyridine.

8. The method according to claim 7, characterized in that The secondary fluorination reaction of adding hydrogen fluoride refers to adding a pyridine solution of hydrogen fluoride with a concentration of 20% to 70%; after adding hydrogen fluoride, the molar ratio of total hydrogen fluoride to phosphorus in the phosphorus-containing pyridine salt is 0.9 to 1.1:1 during the secondary fluorination; during the secondary fluorination, the reaction temperature is 0 to 80°C and the reaction time is 2 to 18 hours.

9. The method according to claim 7, characterized in that The drying temperature of the pyridinium hexafluorophosphate obtained by the secondary fluorination is 40-50° C., and the drying is carried out under low pressure, the pressure is 1-1000 Pa, and the drying time is 0.5-24 hours.

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