Preparation method of liquid lithium hexafluorophosphate

Abstract

The invention relates to a preparation method of liquid lithium hexafluorophosphate, which comprises the following steps: in a reactor, taking a non-aqueous organic solvent as a dispersing agent, taking simple substance phosphorus, phosphorus oxide (not containing hydrogen) or phosphorus halide as a phosphorus source, taking lithium halide as a lithium source, carrying out one-pot fluorination reaction on excessive F2-containing gas at 5-20 DEG C for 50-350 minutes, and carrying out flash evaporation to remove the solvent after the reaction is finished, so as to obtain a lithium hexafluorophosphate solid; and dissolving the solid product in an ester organic solvent, filtering, and removing impurities from resin to obtain the liquid lithium hexafluorophosphate. The method has the advantages of simple process flow, low cost, high fluorination efficiency, high product yield, high purity and the like.

Description

Technical Field

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

[0002] Under the background of "dual carbon", the market space for new energy industries such as power batteries and energy storage is vast, and there is a huge demand for upstream lithium battery electrolyte materials. Lithium hexafluorophosphate is the most important electrolyte lithium salt in the current lithium battery electrolyte because of its high conductivity, moderate ion migration number and dissociation constant, good antioxidant properties, and strong aluminum foil passivation ability, which can match various positive and negative electrode materials.

[0003] Lithium hexafluorophosphate mainly has two forms: crystal and liquid. At present, the preparation methods of crystalline lithium hexafluorophosphate mainly include gas-solid method, hydrofluoric acid solvent method and ion exchange method. Among them, the hydrogen fluoride solvent method has a simple process and high product purity, and is the mainstream process in the industry; liquid lithium hexafluorophosphate is mainly obtained by salting phosphorus pentafluoride gas with lithium fluoride in an organic solvent. This method has the advantages of low cost of large-scale production, but has the disadvantages of long process flow and cumbersome process. For example, CN1711214A discloses a method for preparing fluorine-containing lithium compounds, which is to contact LiF with element M and / or fluoride of element M in the presence of fluorine gas for 1-500 hours, and the temperature is 100°C or higher and 1000°C or lower; M is selected from elements B, P, As, Sb, Bi, V, Nb and Ta. Although this method can successfully synthesize lithium hexafluorophosphate, it has defects such as too high reaction temperature (300°C) and too long reaction time (10.5h) (see Table 1 of the specification), which greatly increases the production cost and is not suitable for large-scale production.

[0004] Driven by technological innovation and market competition, there is an urgent need to develop a liquid lithium hexafluorophosphate production process with a simple process flow, green and clean, and low cost. Based on this, this application was developed. Summary of the invention

[0005] The present invention aims to overcome the technical defects of the existing fluorine gas fluorination method such as low reaction efficiency and low product purity, and provide a method for preparing liquid lithium hexafluorophosphate. The method has the advantages of simple process flow, low cost, high fluorination efficiency, high product yield and high purity.

[0006] To achieve the above object, the present invention adopts the following technical solution: A method for preparing liquid lithium hexafluorophosphate comprises the following steps: in a reactor, using a non-aqueous organic solvent as a dispersant, elemental phosphorus, phosphorus oxide (containing no hydrogen), or phosphorus halide as a phosphorus source, and lithium halide as a lithium source, and performing a one-pot fluorination reaction with an excess amount of F2-containing gas at 5-20°C and 150-250kPa for 50-350min; after the reaction, the solvent is removed by flash evaporation to obtain solid lithium hexafluorophosphate; and dissolving the solid product in an ester organic solvent, filtering, and removing impurities with a resin to obtain liquid lithium hexafluorophosphate.

[0007] Preferably, the fluorination reactor is a tubular reactor; the mass fraction of the raw materials used is greater than or equal to 99.9%, wherein the solid raw materials are high-purity anhydrous micron-sized powders. The phosphorus source includes but is not limited to white phosphorus, red phosphorus, phosphorus pentoxide, phosphorus oxychloride, phosphorus trichloride, etc. The lithium source includes but is not limited to lithium fluoride, lithium chloride, etc.

[0008] Specifically, the F2-containing gas used in the present invention is composed of 1-100% by mass of fluorine gas and 0-99% by mass of inert gas. Further, the inert gas can be preferably selected as nitrogen. Further, the F2-containing gas is preferably composed of a mixture of 5-30% by volume of fluorine gas and 95-70% by volume of nitrogen, that is, a F2 / N2 mixed gas with a volume percentage of 5-30% is preferred. Further, in order to improve the reaction efficiency, a F2 / N2 mixed gas with a volume percentage of 15-30% is preferred, and the flow rate is 500-1000ml / min.

[0009] Specifically, to ensure complete fluorination, the first and second feed liquids are introduced into the reactor at the same time, the flow rate is set to 100-500 g / min, and the feeding is completed at the same time. After the calculated amount of the first and second feed liquids are added, the collected reaction liquid is added to the reactor for a cyclic fluorination reaction until the calculated amount of fluorine-containing gas is added.

[0010] Furthermore, the molar ratio of lithium, phosphorus and fluorine in the raw material can be 1:1:6-7.

[0011] Specifically, the non-aqueous organic solvent can be selected from one or a combination of two or more perfluoroalkanes with a boiling point of -5°C to 30°C. Furthermore, the non-aqueous organic solvent is inert when exposed to fluorine gas; the fluorination temperature is lower than the boiling point of the non-aqueous organic solvent under the fluorination pressure. Preferably, the non-aqueous organic solvent includes but is not limited to perfluorobutane, perfluoropentane, etc.

[0012] Specifically, the raw material addition method is: under nitrogen protection, the solid / liquid phosphorus-containing raw material is uniformly dispersed in a non-aqueous organic solvent to form a first feed liquid, and the lithium halide is uniformly dispersed in a non-aqueous organic solvent to form a second feed liquid; further, the solid content of the first feed liquid and the second feed liquid is 5% to 20%. Specifically, the first feed liquid, the second feed liquid, and the F2-containing gas are simultaneously introduced into a tubular reactor for fluorination reaction.

[0013] Specifically, the tail gas containing F2 or Cl2 in the reaction process can be absorbed by alkali solution. Preferably, the alkali solution uses sodium hydroxide solution, that is, sodium hydroxide solution is selected as the tail gas absorption liquid. The tail gas absorption liquid is filtered, and the filter residue is washed with pure water and dried to obtain a high-purity sodium fluoride by-product; when the tail gas is F2 or F2+O2, the filtrate is supplemented with sodium hydroxide and pure water and then recycled as the tail gas absorption liquid; when the tail gas is F2+Cl2 or F2+Cl2+O2, the filtrate is a sodium hypochlorite solution.

[0014] Specifically, the ester organic solvent can be a carbonate solvent; preferably, the ester organic solvent can be selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, etc.; further, the main content of the ester organic solvent is greater than or equal to 99.95%, and the water content is less than 5ppm.

[0015] Specifically, the resin may be an ion exchange resin. Preferably, the ion exchange resin is an alkaline ion exchange resin for removing trace H in liquid hexafluorophosphate. + 、F - , Cl - Further, the alkaline ion exchange resin is selected from one or a mixture of two or more of styrene resins, styrene divinyl benzene resins and acrylic resins.

[0016] The preparation method of liquid lithium hexafluorophosphate of the present invention involves the following chemical reactions: Elemental phosphorus as raw material: 2P+6F2+2LiX=2LiPF6+X2 (X=F,Cl) Phosphorus oxide (without hydrogen) as raw material: 2P2O5+12F2+4LiX=4LiPF6+2X2+5O2 (X=F,Cl) 2POCl3+6F2+2LiX=2LiPF6+4X2+O2 (X=F,Cl) Phosphorus halide as raw material: 2PCl3+5F2+2LiX=2LiPF6+3X2 (X=F,Cl) Compared with the prior art, the present invention has the following beneficial effects: The method for preparing liquid lithium hexafluorophosphate of the present invention solves the technical defects of the existing fluorine gas fluorination method, such as low reaction efficiency and low product purity. The method of the present invention has the advantages of simple process flow, green and clean, low cost, etc. At the same time, the method is used to prepare liquid lithium hexafluorophosphate with high fluorination efficiency, high product yield (yield of more than 98%) and high purity. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

[0018] In the following examples, the mass fraction of the raw materials used is greater than or equal to 99.9%, wherein the solid raw materials are high-purity anhydrous micron-sized powders. All the raw materials used are common commercial products that can be directly purchased.

[0019] Example 1 The temperature of the first solid-liquid mixer was set to -10°C, and 31g of white phosphorus powder was evenly dispersed in 589g of perfluorobutane to form a first feed liquid with a solid content of 5%; the temperature of the second solid-liquid mixer was set to -10°C, and 26g of lithium fluoride was dispersed in 494g of perfluorobutane to form a second feed liquid with a solid content of 5%; the tubular reactor system was replaced with nitrogen, the fluorine gas flowmeter was turned on, the flow rate was set to 500ml / min, and 15% fluorine-nitrogen mixed gas (volume percentage, the same below) was introduced, and the first and second feed liquids (i.e., the first feed liquid, the second feed liquid, and the F2-containing gas were simultaneously introduced into the tubular reactor for fluorination reaction) were added respectively, and the reaction was carried out at 250kPa and 5°C for 340min. After the cyclic reaction was completed, the nitrogen purged system was pressurized into the flash evaporator, the pressure was reduced and the temperature was raised to room temperature, and the gas overflowing from the flash evaporator was condensed and collected to obtain perfluorobutane for recycling. The solid was purged with nitrogen to obtain 150.60 g of lithium hexafluorophosphate powder with a yield of 99.08%. The lithium hexafluorophosphate solid powder was dissolved in a high-purity low-water dimethyl carbonate solvent, filtered, and removed by a styrene-based alkaline ion exchange resin to obtain a high-purity liquid lithium hexafluorophosphate solution.

[0020] Example 2 The temperature of the first solid-liquid mixer was set to -10°C, and 31g of white phosphorus powder was evenly dispersed in 279g of perfluorobutane to form a first feed liquid with a solid content of 10%; the temperature of the second solid-liquid mixer was set to -10°C, and 42.5g of lithium chloride was dispersed in 382.5g of perfluorobutane to form a second feed liquid with a solid content of 10%; the tubular reactor system was replaced with nitrogen, the fluorine gas flowmeter was turned on, the flow rate was set to 1000ml / min, and 15% fluorine-nitrogen mixed gas was introduced, and the first and second feed liquids were added respectively, and the reaction was carried out at 250kPa and 10°C for 198min. After the cyclic reaction was completed, the nitrogen purged system was pressed, the reaction liquid was pumped into the flash kettle, the pressure was reduced and the temperature was raised to room temperature, and the gas overflowed from the flash kettle was condensed and collected to obtain perfluorobutane for recycling. The solid was purged with nitrogen to obtain 150.26g of lithium hexafluorophosphate powder with a yield of 98.85%. The solid lithium hexafluorophosphate powder is dissolved in a high-purity low-water ethyl methyl carbonate solvent, and then filtered and decontaminated with a styrene divinylbenzene alkaline ion exchange resin to obtain a high-purity liquid lithium hexafluorophosphate solution.

[0021] Example 3 The temperature of the first solid-liquid mixer was set to 5°C, and 35.5g of phosphorus pentoxide powder was evenly dispersed in 319.5g of perfluoropentane to form a first feed liquid with a solid content of 10%; the temperature of the second solid-liquid mixer was set to 5°C, and 13g of lithium fluoride was dispersed in 117g of perfluoropentane to form a second feed liquid with a solid content of 10%; the tubular reactor system was replaced with nitrogen, the fluorine gas flowmeter was turned on, the flow rate was set to 500ml / min, and 20% fluorine-nitrogen mixed gas was introduced, and the first and second feed liquids were added respectively, and the reaction was carried out at 150kPa and 15°C for 204min. After the cyclic reaction was completed, the nitrogen purged system was pressed into the flash kettle, the temperature was reduced to 35°C, and the gas overflowed from the flash kettle was condensed and collected to obtain perfluoropentane for recycling. The solid was purged with nitrogen to obtain 75.12g of lithium hexafluorophosphate powder with a yield of 98.88%. The solid lithium hexafluorophosphate powder is dissolved in a high-purity low-water ethyl methyl carbonate solvent, and then filtered and impurized with an acrylic acid alkaline ion exchange resin to obtain a high-purity liquid lithium hexafluorophosphate solution.

[0022] Example 4 The temperature of the first solid-liquid mixer was set to 5°C, and 35.5g of phosphorus pentoxide powder was evenly dispersed in 142g of perfluoropentane to form a first feed liquid with a solid content of 20%; the temperature of the second solid-liquid mixer was set to 5°C, and 21.25g of lithium chloride was dispersed in 85g of perfluoropentane to form a second feed liquid with a solid content of 20%; the tubular reactor system was replaced with nitrogen, the fluorine gas flowmeter was turned on, the flow rate was set to 500ml / min, and 20% fluorine-nitrogen mixed gas was introduced, and the first and second feed liquids were added respectively, and the reaction was carried out at 150kPa and 15°C for 247min. After the cyclic reaction was completed, the nitrogen purged system was pressed, the reaction liquid was pumped into the flash kettle, the temperature was reduced to 35°C, and the gas overflowed from the flash kettle was condensed and collected to obtain perfluoropentane for recycling. The solid was purged with nitrogen to obtain 74.90g of lithium hexafluorophosphate powder with a yield of 98.55%. The solid lithium hexafluorophosphate powder is dissolved in a high-purity low-water ethyl methyl carbonate solvent, and then filtered and impurities are removed by a styrene-based alkaline ion exchange resin to obtain a high-purity liquid lithium hexafluorophosphate solution.

[0023] Example 5 The temperature of the first solid-liquid mixer was set to -10°C, and 153.5g of phosphorus oxychloride powder was evenly dispersed in 1381.5g of perfluorobutane to form a first feed liquid with a concentration of 10%; the temperature of the second solid-liquid mixer was set to -10°C, and 26g of lithium fluoride was dispersed in 234g of perfluorobutane to form a second feed liquid with a concentration of 10%; the tubular reactor system was replaced with nitrogen, the fluorine gas flowmeter was turned on, the flow rate was set to 1000ml / min, 30% fluorine-nitrogen mixed gas was introduced, and the first and second feed liquids were added respectively, and the reaction was carried out at 250kPa and 10°C for 86min. After the cyclic reaction was completed, the nitrogen purged system was pressed, the reaction liquid was pumped into the flash kettle, the pressure was reduced and the temperature was raised to room temperature, and the gas overflowed from the flash kettle was condensed and collected to obtain perfluorobutane for recycling. The solid was purged with nitrogen to obtain 150.15g of lithium hexafluorophosphate powder with a yield of 98.78%. The solid lithium hexafluorophosphate powder is dissolved in a high-purity low-water dimethyl carbonate solvent, and then filtered and decontaminated with a styrene divinylbenzene alkaline ion exchange resin to obtain a high-purity liquid lithium hexafluorophosphate solution.

[0024] Example 6 The temperature of the first solid-liquid mixer was set to -10°C, and 153.5g of phosphorus oxychloride powder was evenly dispersed in 2916.5g of perfluorobutane at room temperature to form a first feed liquid with a concentration of 5%; the temperature of the second solid-liquid mixer was set to -10°C, and 42.5g of lithium chloride was dispersed in 807.5g of perfluorobutane to form a second feed liquid with a concentration of 5%; the tubular reactor system was replaced with nitrogen, the fluorine gas flowmeter was turned on, the flow rate was set to 1000ml / min, 20% fluorine-nitrogen mixed gas was introduced, and the first and second feed liquids were added respectively, and the reaction was carried out at 150kPa and 20°C for 256min. After the cyclic reaction was completed, the nitrogen purged system was pressed, the reaction liquid was pumped into the flash kettle, the pressure was reduced and the temperature was raised to room temperature, and the gas overflowed from the flash kettle was condensed and collected to obtain perfluorobutane for recycling. The solid was purged with nitrogen to obtain 150.21g of lithium hexafluorophosphate powder with a yield of 98.82%. The solid lithium hexafluorophosphate powder is dissolved in a high-purity low-water dimethyl carbonate solvent, and then filtered and impurities are removed by acrylic acid alkaline ion exchange resin to obtain a high-purity liquid lithium hexafluorophosphate solution.

[0025] Example 7 The temperature of the first solid-liquid mixer was set to 5°C, and 137.5g of phosphorus trichloride powder was evenly dispersed in 1237.5g of perfluoropentane to form a first feed liquid with a concentration of 10%; the temperature of the second solid-liquid mixer was set to 5°C, and 26g of lithium fluoride was dispersed in 234g of perfluoropentane to form a second feed liquid with a concentration of 10%; the tubular reactor system was replaced with nitrogen, the fluorine gas flowmeter was turned on, the flow rate was set to 1000ml / min, and 20% fluorine-nitrogen mixed gas was introduced, and the first and second feed liquids were added respectively at 150kPa and 20°C for 213min. After the cyclic reaction was completed, the nitrogen purged system was pressurized into the flash evaporator, the temperature was reduced to 35°C, and the gas overflowed from the flash evaporator was condensed and collected to obtain perfluoropentane for recycling. The solid was purged with nitrogen to obtain 149.82g of lithium hexafluorophosphate powder with a yield of 98.56%. The solid lithium hexafluorophosphate powder is dissolved in a high-purity low-water dimethyl carbonate solvent, and then filtered and decontaminated with a styrene-based alkaline ion exchange resin to obtain a high-purity liquid lithium hexafluorophosphate solution.

[0026] Example 8 The temperature of the second solid-liquid mixer was set to 5°C, and 137.5g of phosphorus trichloride powder was evenly dispersed in 550g of perfluoropentane to form a first feed liquid with a concentration of 20%; the temperature of the second solid-liquid mixer was set to 5°C, and 42.5g of lithium chloride was dispersed in 170g of perfluoropentane to form a second feed liquid with a concentration of 20%; the tubular reactor system was replaced with nitrogen, the fluorine gas flowmeter was turned on, the flow rate was set to 500ml / min, and 20% fluorine nitrogen mixed gas was introduced, and the first and second feed liquids were added respectively at 250kPa and 20°C for 298min. After the cyclic reaction was completed, the nitrogen purged system was pressurized into the flash kettle, the temperature was reduced to 35°C, and the gas overflowed from the flash kettle was condensed and collected to obtain perfluoropentane for recycling. The solid was purged with nitrogen to obtain 150.0g of lithium hexafluorophosphate powder with a yield of 98.68%. The solid lithium hexafluorophosphate powder is dissolved in a high-purity low-water dimethyl carbonate solvent, and then filtered and decontaminated with a styrene divinylbenzene alkaline ion exchange resin to obtain a high-purity liquid lithium hexafluorophosphate solution.

[0027] The tail gas containing F2 or Cl2 in the above reaction process is absorbed by alkali solution, and the alkali solution uses sodium hydroxide solution, that is, sodium hydroxide solution is selected as the tail gas absorption liquid. The tail gas absorption liquid is filtered, and the filter residue is washed with pure water and dried to obtain a high-purity sodium fluoride by-product; when the tail gas is F2 or F2+O2, the filtrate is supplemented with sodium hydroxide and pure water and then recycled as the tail gas absorption liquid; when the tail gas is F2+Cl2 or F2+Cl2+O2, the filtrate is a sodium hypochlorite solution.

Claims

1. A method for preparing liquid lithium hexafluorophosphate, characterized in that: In a reactor, a non-aqueous organic solvent is used as a dispersant, elemental phosphorus, phosphorus oxide, or phosphorus halide is used as a phosphorus source, and lithium halide is used as a lithium source. A fluorination reaction is carried out with an excess of F2-containing gas at 5-20°C for 50-350 minutes. After the reaction is completed, the solvent is flashed off to obtain a solid; the solid product is dissolved in an ester organic solvent, filtered, and subjected to resin decontamination to obtain the solid.

2. The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that: The reactor is a tubular reactor.

3. The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that: The F2-containing gas used is composed of 1-100% by mass of fluorine gas and 0-99% by mass of inert gas, and the inert gas is nitrogen.

4. The method for preparing liquid lithium hexafluorophosphate as claimed in claim 3, characterized in that: The F2-containing gas is composed of a mixture of 5-30% by volume of fluorine gas and 95-70% by volume of nitrogen.

5. The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that: The molar ratio of lithium, phosphorus and fluorine in the raw materials is 1:1:6-7.

6. The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that: The non-aqueous organic solvent is selected from one or a combination of two or more perfluoroalkanes having a boiling point of -5°C to 30°C.

7. The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that: The raw material adding method is: under nitrogen protection, the solid / liquid phosphorus-containing raw material is evenly dispersed in a non-aqueous organic solvent to form a first feed liquid, and the lithium halide is evenly dispersed in a non-aqueous organic solvent to form a second feed liquid; the solid content of the first feed liquid and the second feed liquid is 5% to 20%; the first feed liquid, the second feed liquid, and the F2-containing gas are simultaneously introduced into the reactor for fluorination reaction.

8. The method for preparing liquid lithium hexafluorophosphate as claimed in claim 1, characterized in that: The ester organic solvent is a carbonate solvent; the carbonate solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and ethylene carbonate.

9. The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that: The resin is an ion exchange resin, and the ion exchange resin is a basic ion exchange resin.

10. The method for preparing liquid lithium hexafluorophosphate according to claim 1, characterized in that: The tail gas containing F2 or Cl2 in the reaction process is absorbed by alkali liquid, and the alkali liquid uses sodium hydroxide solution; the tail gas absorption liquid is filtered, and the filter residue is washed with pure water and dried to obtain sodium fluoride by-product; when the tail gas is F2 or F2+O2, the filtrate is supplemented with sodium hydroxide and pure water and then recycled as the tail gas absorption liquid; when the tail gas is F2+Cl2 or F2+Cl2+O2, the filtrate is sodium hypochlorite solution.