Process for the preparation of anhydrous hexafluorophosphoric acid and high purity liquid salt thereof

Abstract

The application provides a preparation method of anhydrous hexafluorophosphoric acid and a high-purity liquid salt thereof, and belongs to the technical field of secondary batteries. The anhydrous hexafluorophosphoric acid is obtained by the following steps: reacting a phosphorus-containing compound with anhydrous hydrogen fluoride to generate an aqueous solution of hexafluorophosphoric acid, removing water by using an organic solvent, crystallizing, and sweating to purify; and the high-purity liquid hexafluorophosphate salt is obtained by the following steps: reacting the high-purity anhydrous hexafluorophosphoric acid with an alkali metal source uniformly dispersed in an organic solvent, and removing impurities. The preparation method of the anhydrous hexafluorophosphoric acid is simple and efficient, the product has a low water content, is not easy to hydrolyze to generate byproducts, and has a purity of no less than 99.9%, the high-purity liquid hexafluorophosphate salt is prepared by using the anhydrous hexafluorophosphoric acid, the preparation step of the hexafluorophosphate salt crystal is omitted, the high-purity hexafluorophosphate salt liquid is directly obtained, and the method is more economical.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a preparation method of anhydrous hexafluorophosphoric acid and a high-purity liquid salt thereof. BACKGROUND

[0002] Hexafluorophosphate (MPF6, M = Li, Na, K, etc.) is an important electrolyte salt for various secondary battery systems. Lithium hexafluorophosphate can form a stable SEI film on the carbon negative electrode, effectively passivate the aluminum current collector, have a wide electrochemical window, and have high conductivity in non-aqueous solvents, and is the most important electrolyte salt for lithium-ion batteries. Although lithium-ion batteries have been widely used, the lithium resources on the earth are very limited and have high cost. The research and development of sodium-ion batteries and their main salt sodium hexafluorophosphate, which have similar working mechanisms as lithium-ion batteries, have also become one of the current hotspots. In addition, potassium hexafluorophosphate can be used to prepare other hexafluorophosphate salts, and the preparation method thereof is also of great concern.

[0003] Currently, there are mainly two kinds of mainstream preparation processes for liquid hexafluorophosphate: one is to use anhydrous hydrogen fluoride as a solvent, and to react phosphorus pentafluoride with alkali metal fluoride (MF, M = Li, Na, K, etc.) to obtain a crystal product through crystallization, filtration and drying. The crystal product is dissolved in a carbonate solvent to obtain a liquid hexafluorophosphate salt. The second is to react hexafluorophosphoric acid (HPF6) with MF in a carbonate solvent to obtain a liquid lithium salt product after removing water.

[0004] From the perspective of preparing a liquid hexafluorophosphate salt, the second process can omit the preparation step of hexafluorophosphate crystals and is more economical. However, the second process has the disadvantage that the hexafluorophosphoric acid contains water, and the obtained hexafluorophosphate salt product is prone to hydrolysis to produce by-products such as anhydrous hydrogen fluoride (HF), alkali metal fluoride (MF), phosphorus oxyfluoride (POF3) 、 diphosphoric acid (HPO2F2), monofluorophosphoric acid (H2PO3F), etc. The adverse effects of HF on the battery include: 1) it can catalyze the polymerization of organic solvents in the electrolyte, leading to an increase in the viscosity of the organic electrolyte and a decrease in the conductivity; 2) it can consume Li + ions during the charging and discharging process of the lithium battery, and the increase in the content of lithium fluoride (LiF) in the SEI film composition can increase the interfacial impedance of the electrode, thereby increasing the internal resistance of the battery; 3) it can react with the SEI film and damage the SEI film; and 4) it can dissolve the positive electrode material, causing the capacity of the positive electrode material to decay; and MF can deposit on the negative electrode surface and affect the quality of the SEI film; POF 3、 HPO2F2, H2PO3F, etc. can further release HF when they come into contact with water, thereby affecting the charging and discharging performance and safety of the lithium battery. The hydrolysis by-products greatly limit the large-scale application thereof.

[0005] Therefore, water removal in hexafluorophosphoric acid and control of water generation in the process of preparing liquid salt by hexafluorophosphoric acid method are urgent problems to be solved in the industry. SUMMARY

[0006] To solve the above problems, one object of the present application is to provide a preparation method of anhydrous hexafluorophosphoric acid, and the obtained HPF6 has a purity of more than 99.9%, and high-purity anhydrous hexafluorophosphoric acid can be obtained.

[0007] A second object of the present application is to provide a preparation method of high-purity liquid hexafluorophosphate salt using the anhydrous hexafluorophosphoric acid.

[0008] To achieve the above objects, the technical scheme of the preparation method of anhydrous hexafluorophosphoric acid of the present application is as follows:

[0009] A preparation method of anhydrous hexafluorophosphoric acid, comprising the following steps:

[0010] S1: reacting a phosphorus-containing compound and anhydrous hydrogen fluoride to generate an aqueous solution of hexafluorophosphoric acid;

[0011] S2: removing water from the aqueous solution of hexafluorophosphoric acid in step S1 by physical water removal using an organic solvent, crystallization, and sweating purification to obtain high-purity anhydrous hexafluorophosphoric acid.

[0012] The preparation method of anhydrous hexafluorophosphoric acid provided by the present application has a simple process, low water content of the product, and is not easy to hydrolyze to generate by-products, and the purity of HPF6 is ≥99.9%.

[0013] To further improve the reaction efficiency, preferably, the phosphorus-containing compound in step S1 is selected from one or more of polyphosphoric acid, concentrated phosphoric acid, and metaphosphoric acid.

[0014] To further improve the raw material utilization rate and improve the reaction rate, and make the preparation process more efficient, preferably, the phosphorus-containing compound and anhydrous hydrogen fluoride in step S1 are reacted in a micro-channel reactor, and the molar ratio of phosphorus in the phosphorus-containing compound to anhydrous hydrogen fluoride is 1:(6-7); to make the phosphorus-containing compound and anhydrous hydrogen fluoride react completely, and the purity of the hexafluorophosphoric acid generated by the reaction is higher, preferably, the reaction temperature in step S1 is -20-5°C.

[0015] To increase the flowability of the phosphorus-containing compound and improve the contact between the phosphorus-containing compound and hydrogen fluoride, preferably, the phosphorus-containing compound is heated to 50-75°C before being added to the micro-channel reactor.

[0016] The physical water removal is to remove water in the system by thin film evaporation under negative pressure using the water carrying capacity of the organic solvent to achieve the purpose of removing water in the system. To improve the water removal capacity, preferably, the physical water removal in step S2 is to remove water in the reaction system by thin film evaporation under negative pressure using an organic solvent.

[0017] In order to make the thin film evaporation more complete, the thin film evaporation temperature is 15-25℃, and the negative pressure range used is-0.05MPa to-0.1MPa.

[0018] In order to further improve the water removal capacity and make the purity of hexafluorophosphoric acid higher and the water content less, preferably, the thin film evaporation step of the organic solvent is repeated more than twice, the mass ratio of the organic solvent to the aqueous solution of hexafluorophosphoric acid in each thin film evaporation is 1-1.5:1, and in each thin film evaporation before the last thin film evaporation, the negative pressure evaporation is performed until the total mass of the system is reduced by 30%-50%. The last thin film evaporation obtains anhydrous hexafluorophosphoric acid. Since different solvents have different water-carrying capacities, the solvent with strong water-carrying capacity can achieve the purpose of complete water removal by repeating the thin film evaporation step twice, and the solvent with poor water-carrying capacity may need 3 or more than 3 water-carrying operations.

[0019] In order to slow down the hydrolysis of hexafluorophosphoric acid in the heating evaporation process, preferably, the organic solvent is selected from one or two of low-boiling halogenated alkanes or ethers; the organic solvent is selected from one or more of dichloromethane, dichloroethane, carbon tetrachloride, diethyl ether, petroleum ether, isopropyl ether, ethylene glycol dimethyl ether. More preferably, the organic solvent is selected from dichloromethane or diethyl ether, both of which are low-boiling compounds, which can reduce energy consumption and shorten the evaporation time during thin film evaporation.

[0020] In order to improve the crystallization rate of anhydrous HPF6, the crystallization temperature in step S2 is-10-0℃.

[0021] In order to efficiently remove impurities in anhydrous HPF6, the heating rate of sweating purification in step S2 is 0.1-0.5℃ / h.

[0022] The purity of the anhydrous hexafluorophosphoric acid obtained in step S2 is ≥99.9%.

[0023] The technical scheme of the preparation method of the high-purity liquid hexafluorophosphoric acid salt of the present application is:

[0024] A preparation method of high-purity liquid hexafluorophosphoric acid salt using the anhydrous hexafluorophosphoric acid, the specific method comprising: under the protection of an inert atmosphere, a salt reaction is formed between an anhydrous high-purity alkali metal source and the high-purity anhydrous hexafluorophosphoric acid in an organic solvent, and after impurity removal, a high-purity liquid hexafluorophosphoric acid salt is obtained.

[0025] The preparation method of the high-purity liquid hexafluorophosphoric acid salt provided by the present application uses the anhydrous hexafluorophosphoric acid, the alkali metal source is selected freely, the method is simple and easy to implement, the preparation step of hexafluorophosphoric acid salt crystals is omitted, high-purity hexafluorophosphoric acid salt liquid is directly obtained, raw material loss is reduced, it is more economical, and it has potential for large-scale industrial production.

[0026] To make the salt formation reaction more complete and reduce the loss of raw materials, preferably, the salt formation reaction is first to disperse the anhydrous alkali metal source in an organic solvent, and then the high-purity anhydrous hexafluorophosphoric acid is added to carry out the salt formation reaction.

[0027] To improve the purity of the product and reduce the generation of by-products, preferably, the salt formation reaction is first incubated at -5-5℃ for 1-2h, and then warmed to 5-25℃ for 3-6h.

[0028] To improve the dispersibility of the raw materials in the solvent, preferably, the organic solvent is a carbonate solvent; more preferably, the organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and ethylene carbonate.

[0029] To prevent the introduction of water molecules, the hydrolysis of hexafluorophosphoric acid to generate by-products, and the influence on the purity of hexafluorophosphate, preferably, the organic solvent is dehydrated in advance using high-purity inert gas or molecular sieve, more preferably, the high-purity inert gas is nitrogen or argon, and the molecular sieve is conventional 4A or 5A molecular sieve, so that the water content of the non-polar solvent after dehydration is <5ppm.

[0030] To make the resulting liquid hexafluorophosphate have higher purity and the introduced impurities be easier to remove, preferably, the alkali metal source is selected from one of high-purity alkali metal element, alkali metal chloride, alkali metal phosphate, and alkali metal fluoride.

[0031] To improve the purity of the liquid hexafluorophosphate and remove impurities in the system, preferably, the impurity removal includes membrane filtration to remove solid by-products, and / or low-temperature negative pressure flash evaporation to remove volatile impurities that can be dissolved in the salt solution, and ion exchange resin deep impurity removal. More preferably, the membrane filtration is a two-stage membrane filtration to remove solid by-products, and the ion exchange resin is a selective ion exchange resin. More preferably, the ion exchange resin is a basic ion exchange resin to remove trace amounts of HF, HPF6, HCl and other impurities in the liquid hexafluorophosphate. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 NMR F spectrum of the aqueous hexafluorophosphoric acid solution prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0033] A method for preparing anhydrous hexafluorophosphoric acid, comprising the following steps:

[0034] S1: reacting a phosphorus-containing compound and anhydrous hydrogen fluoride to generate an aqueous hexafluorophosphoric acid solution;

[0035] S2: after physical dehydration, crystallization, and sweating purification of the aqueous hexafluorophosphoric acid solution in step S1 using an organic solvent, high-purity anhydrous hexafluorophosphoric acid is obtained.

[0036] In the specific embodiment, when the phosphorus-containing compound is polyphosphoric acid, the reaction equation of polyphosphoric acid (H n+2 P n O 3n+1 ) with anhydrous hydrogen fluoride in step S1 is as follows:

[0037] H n+2 P n O 3n+1 + 6nHF→nHPF6+ (3n+1)H2O

[0038] When the phosphorus-containing compound is concentrated phosphoric acid, the reaction equation of concentrated phosphoric acid (H3PO4) with anhydrous hydrogen fluoride in step S1 is as follows:

[0039] H3PO4+ 6HF→HPF6+ 4H2O

[0040] When the phosphorus-containing compound is metaphosphoric acid, the reaction equation of metaphosphoric acid [(HPO3) n , n = 3 or 4] with anhydrous hydrogen fluoride in step S1 is as follows:

[0041] (HPO3) n + 6nHF→nHPF6+ 3nH2O n = 3 or 4

[0042] In the specific embodiment, the microreactor pipe size in step S1 is 100-1000 microns, the material is silicon carbide, and a peristaltic pump is used.

[0043] In the specific embodiment, the phosphorus-containing compound and anhydrous hydrogen fluoride are simultaneously added to the microchannel reactor in step S1, the addition speed of the phosphorus-containing compound is 25-50 g / min, and the addition speed of anhydrous hydrogen fluoride is 40-60 g / min. The reaction in the microchannel reactor is relatively rapid, and the raw materials leave the reactor soon after the addition is completed. The residence time of the raw materials in the microchannel reactor is expressed by the raw material addition time, and the residence time is 150-200 s.

[0044] In the specific embodiment, the gas phase obtained after the thin film evaporation of the organic solvent in step S2 contains water and the organic solvent, and anhydrous organic solvent can be obtained by condensation, acid removal, distillation or rectification, and can be recycled.

[0045] In the specific embodiment, when the organic solvent in step S2 is diethyl ether, the mass fraction of diethyl ether is 1-2%.

[0046] In the specific embodiment, the purity and water content of HPF6 are tested after the completion of the reaction and after the sweating purification, and the sweating fraction with a purity of ≥99.9% after the sweating purification is high-purity anhydrous HPF6.

[0047] The application discloses a preparation method of high-purity liquid hexafluorophosphate by using the anhydrous hexafluorophosphoric acid, and specifically comprises the following steps: under the protection of inert atmosphere, an anhydrous high-purity alkali metal source is reacted with the high-purity anhydrous hexafluorophosphoric acid in an organic solvent to form a salt, and after impurity removal, high-purity liquid hexafluorophosphate is obtained.

[0048] The anhydrous alkali metal source and the anhydrous hexafluorophosphoric acid are reacted to form a salt in the organic solvent, when the alkali metal source is an alkali metal element, the reaction equation is as follows:

[0049] 2HPF6+2M→2MPF6+H2↑ (M=Li, Na, K, etc.);

[0050] When the alkali metal source is an alkali metal chloride, the reaction equation is as follows:

[0051] HPF6+MCl→MPF6+HCl↑ (M=Li, Na, K, etc.);

[0052] When the alkali metal source is an alkali metal fluoride, the reaction equation is as follows:

[0053] HPF6+MF→MPF6+HF↑ (M=Li, Na, K, etc.);

[0054] When the alkali metal source is an alkali metal phosphate, the reaction equation is as follows:

[0055] 2HPF6+M3PO4→2MPF6+MH2PO4 (M=Li, Na, K, etc.).

[0056] In the specific embodiment, the inert atmosphere is nitrogen.

[0057] In the specific embodiment, the mass ratio of the organic solvent to the high-purity anhydrous hexafluorophosphoric acid is 2.4-3:1.

[0058] The embodiments of the application are further described below in combination with specific examples. In the following examples, the chemical reagents are all commercially available conventional goods unless otherwise specified.

[0059] I. Specific examples of the preparation method of the anhydrous hexafluorophosphoric acid

[0060] Example 1

[0061] The preparation method of the anhydrous hexafluorophosphoric acid in the example comprises the following steps:

[0062] S1: the temperature of a micro-channel reactor is set to be -20 DEG C, a peristaltic pump is used to add 100g of polyphosphoric acid (H6P4O 13), 142.01 g of anhydrous hydrogen fluoride was added into the micro-channel reactor at a speed of 40 g / min and 56.81 g / min respectively, to obtain 242.01 g of aqueous solution of hexafluorophosphoric acid;

[0063] S2: The obtained aqueous solution of hexafluorophosphoric acid was transferred to a water removal kettle, 242.01 g of ether was added each time, and the system was thin film evaporated under the conditions of 15℃ and -0.1 MPa negative pressure to remove water, so that the total mass of the system remained 42%, and the above water removal step was repeated for 3 times to obtain 172.78 g of anhydrous HPF6 liquid, which was crystallized at -10℃, and sweating was carried out at a heating rate of 0.1℃ / h to obtain 165.87 g of anhydrous HPF6 liquid with a purity of ≥99.9%.

[0064] Example 2

[0065] The preparation method of anhydrous hexafluorophosphoric acid in this embodiment comprises the following steps:

[0066] S1: The temperature of the micro-channel reactor was set to -10℃, and a peristaltic pump was used to add 100 g of polyphosphoric acid (H6P4O 13 ), 149.11 g of anhydrous hydrogen fluoride was added into the micro-channel reactor at a speed of 40 g / min and 59.64 g / min respectively, to obtain 249.11 g of aqueous solution of hexafluorophosphoric acid;

[0067] S2: The obtained aqueous solution of hexafluorophosphoric acid was transferred to a water removal kettle, 373.67 g of dichloromethane was added each time, and the system was thin film evaporated under the conditions of 15℃ and -0.1 MPa negative pressure to remove water, so that the total mass of the system remained 43%, and the above water removal step was repeated for 3 times to obtain 172.78 g of anhydrous HPF6 liquid, which was crystallized at 0℃, and sweating was carried out at a heating rate of 0.1℃ / h to obtain 167.6 g of anhydrous HPF6 liquid with a purity of ≥99.9%.

[0068] Example 3

[0069] The preparation method of anhydrous hexafluorophosphoric acid in this embodiment comprises the following steps:

[0070] S1: The temperature of the micro-channel reactor was set to 5℃, and a peristaltic pump was used to add 100 g of polyphosphoric acid (H6P4O 13 ), 149.11 g of anhydrous hydrogen fluoride was added into the micro-channel reactor at a speed of 40 g / min and 59.64 g / min respectively, to obtain 249.11 g of aqueous solution of hexafluorophosphoric acid;

[0071] S2: The above obtained aqueous solution of HPF6 was transferred to a water removal kettle, 256.21 g of diethyl ether was added each time, and thin film evaporation was carried out under the conditions of 25°C and -0.1 MPa negative pressure to remove water, so that the total mass of the system remained 40%. After repeating the above water removal step twice, 172.78 g of anhydrous HPF6 liquid was obtained. Crystallization was carried out at -5°C, and sweating was carried out at a heating rate of 0.5°C / h, so that 164.14 g of anhydrous HPF6 liquid with a purity of ≥99.9% was obtained.

[0072] Example 4

[0073] The preparation method of anhydrous hexafluorophosphoric acid in this example comprises the following steps:

[0074] S1: The temperature of the microreactor was set to -20°C, and 100 g of concentrated phosphoric acid (H3PO4) with a mass concentration of 90% preheated to 50°C and 119.39 g of anhydrous hydrogen fluoride were simultaneously added to the microchannel reactor at a speed of 40 g / min and 47.76 g / min, respectively, to obtain 219.39 g of an aqueous solution of HPF6;

[0075] S2: The above obtained aqueous solution of HPF6 was transferred to a water removal kettle, 219.39 g of diethyl ether was added each time, and thin film evaporation was carried out under the conditions of 15°C and -0.1 MPa negative pressure to remove water, so that the total mass of the system remained 45%. After repeating the above water removal step three times, 134.10 g of anhydrous HPF6 liquid was obtained. Crystallization was carried out at -10°C, and sweating was carried out at a heating rate of 0.1°C / h, so that 127.40 g of anhydrous HPF6 liquid with a purity of ≥99.9% was obtained.

[0076] Example 5

[0077] The preparation method of anhydrous hexafluorophosphoric acid in this example comprises the following steps:

[0078] S1: The temperature of the microreactor was set to -10°C, and 100 g of phosphorus acid (HPO3)3 preheated to 75°C and 175 g of anhydrous hydrogen fluoride were simultaneously added to the microchannel reactor at a speed of 30 g / min and 52.5 g / min, respectively, to obtain 275 g of an aqueous solution of HPF6;

[0079] S2: The above obtained aqueous solution of HPF6 was transferred to a water removal kettle, 412.5 g of dichloromethane was added each time, and thin film evaporation was carried out under the conditions of 25°C and -0.1 MPa negative pressure to remove water, so that the total mass of the system remained 30%. After repeating the above water removal step three times, 179.44 g of anhydrous HPF6 liquid was obtained. Crystallization was carried out at -5°C, and sweating was carried out at a heating rate of 0.5°C / h, so that 172.26 g of anhydrous HPF6 liquid with a purity of ≥99.9% was obtained.

[0080] II. Embodiment of the preparation method of high-purity liquid hexafluorophosphate salt of the present application

[0081] Example 6

[0082] The preparation method of high-purity liquid lithium hexafluorophosphate of the present embodiment comprises:

[0083] The 7.95 g of metal lithium particles are uniformly dispersed into 402.92 g of dimethyl carbonate, and the high-purity anhydrous HPF6 liquid prepared in Example 1 is slowly and uniformly added into the mixed system under the condition of -5 ℃, and the reaction is kept for 1 h, then the temperature is increased to 10 ℃, and the reaction is continued for 6 h. After the reaction is completed, the insoluble substances are removed by two-stage membrane filtration, and the filtrate is filtered through the basic ion exchange resin for deep impurity removal, thereby obtaining 575.6 g of liquid LiPF6.

[0084] Example 7

[0085] The preparation method of high-purity liquid lithium hexafluorophosphate of the present embodiment comprises:

[0086] The 49.27 g of high-purity anhydrous lithium chloride is uniformly dispersed into 407.14 g of methyl ethyl carbonate, and the high-purity anhydrous HPF6 liquid prepared in Example 2 is slowly and uniformly added into the system under the condition of 0 ℃, and the reaction is kept for 1 h, then the temperature is increased to 20 ℃, and the reaction is continued for 5 h. After the reaction is completed, the temperature is decreased to 5 ℃, and the hydrogen chloride dissolved in the system is removed by negative pressure flash evaporation, then the insoluble substances are removed by two-stage membrane filtration, and the filtrate is filtered through the basic ion exchange resin for deep impurity removal, thereby obtaining 580 g of liquid LiPF6.

[0087] Example 8

[0088] The preparation method of high-purity liquid sodium hexafluorophosphate of the present embodiment comprises:

[0089] The 92.19 g of high-purity anhydrous sodium phosphate is uniformly dispersed into 440.7 g of methyl ethyl carbonate, and the high-purity anhydrous HPF6 liquid prepared in Example 3 is slowly and uniformly added into the system under the condition of 5 ℃, and the reaction is kept for 1 h, then the temperature is increased to 25 ℃, and the reaction is continued for 3 h. After the reaction is completed, the by-product sodium dihydrogen phosphate is removed by two-stage membrane filtration, and the filtrate is filtered through the basic ion exchange resin for deep impurity removal, thereby obtaining 629 g of liquid NaPF6.

[0090] Example 9

[0091] The preparation method of high-purity liquid potassium hexafluorophosphate of the present embodiment comprises:

[0092] The 65.89 g of high purity potassium fluoride powder was uniformly dispersed in 487.76 g of dimethyl carbonate, and the high purity anhydrous HPF6 liquid prepared in Example 1 was slowly and uniformly added into the mixed system at -5°C, and the reaction was kept for 1 h, then the temperature was increased to 5°C and the reaction was continued for 6 h. After the reaction was completed, the hydrogen fluoride dissolved in the system was removed by flash evaporation under negative pressure, then the insoluble substances were removed by two-stage membrane filtration, and the filtrate was filtered through an alkaline ion exchange resin for deep impurity removal, thereby obtaining 575.6 g of liquid KPF6.

[0093] Example 10

[0094] The preparation method of the high purity liquid lithium hexafluorophosphate of the present example comprises:

[0095] The 7.95 g of metallic lithium particles was uniformly dispersed in 497.61 g of dimethyl carbonate, and the high purity anhydrous HPF6 liquid prepared in Example 4 was slowly and uniformly added into the mixed system at -5°C, and the reaction was kept for 1 h, then the temperature was increased to 15°C and the reaction was continued for 6 h. After the reaction was completed, the insoluble substances were removed by two-stage membrane filtration, and the filtrate was filtered through an alkaline ion exchange resin for deep impurity removal, thereby obtaining 670.29 g of liquid LiPF6.

[0096] Example 11

[0097] The preparation method of the high purity liquid lithium hexafluorophosphate of the present example comprises:

[0098] The 49.27 g of high purity anhydrous lithium chloride was uniformly dispersed in 502.80 g of methyl ethyl carbonate, and the high purity anhydrous HPF6 liquid prepared in Example 5 was slowly and uniformly added into the system at 0°C, and the reaction was kept for 1 h, then the temperature was increased to 25°C and the reaction was continued for 3 h. After the reaction was completed, the temperature was decreased to 5°C, the hydrogen chloride dissolved in the system was removed by flash evaporation under negative pressure, then the insoluble substances were removed by two-stage membrane filtration, and the filtrate was filtered through an alkaline ion exchange resin for deep impurity removal, thereby obtaining 677.29 g of liquid LiPF6.

[0099] Example 12

[0100] The preparation method of the high purity liquid sodium hexafluorophosphate of the present example comprises:

[0101] The 92.19 g of high purity anhydrous sodium phosphate was uniformly dispersed in 492.42 g of methyl ethyl carbonate, and the high purity anhydrous HPF6 liquid prepared in Example 4 was slowly and uniformly added into the system at 5°C, and the reaction was kept for 1 h, then the temperature was increased to 20°C and the reaction was continued for 4 h. After the reaction was completed, the by-product sodium dihydrogen phosphate was removed by two-stage membrane filtration, and the filtrate was filtered through an alkaline ion exchange resin for deep impurity removal, thereby obtaining 681.29 g of liquid NaPF6.

[0102] Example 13

[0103] The preparation method of the high-purity liquid potassium hexafluorophosphate of the present embodiment comprises:

[0104] 65.89 g of high-purity potassium fluoride powder is uniformly dispersed into 497.61 g of dimethyl carbonate, and the high-purity anhydrous HPF6 liquid prepared in Example 5 is slowly and uniformly added into the mixed system at-5℃, and the reaction is kept for 1 h, and then the temperature is increased to 10℃ and the reaction is continued for 6 h. After the reaction is completed, the hydrogen fluoride dissolved in the system is removed by negative pressure flash evaporation, and then the insoluble substances are removed by two-stage membrane filtration, and the filtrate is filtered through an alkaline ion exchange resin for deep impurity removal, to obtain 706.65 g of liquid KPF6.

[0105] III. Experimental Examples

[0106] Experimental Example 1

[0107] The nuclear magnetic qualitative test is performed on the aqueous solution of hexafluorophosphoric acid prepared in Example 1, and the test results are shown in Figure 1 Figure 1 The measured nuclear magnetic F spectrum proves that the preparation method provided by the present application has obtained hexafluorophosphoric acid.

[0108] Experimental Example 2

[0109] In this experimental example, the moisture, HF, HPO2F 2、 H2PO3F content in the hexafluorophosphoric acid is tested by a volumetric method moisture tester, an ion activity meter, and ion chromatography, and the moisture content, acidity, and single metal ion content of the liquid salt of hexafluorophosphoric acid are tested by a coulometric moisture tester, an acid-base titration method, and an ICP-OES method.

[0110] The test results of the moisture, hexafluorophosphoric acid, and impurity contents in the aqueous solution of hexafluorophosphoric acid obtained in the S1 step of Examples 1-5 are shown in Table 1.

[0111] Table 1 Moisture, hexafluorophosphoric acid, and impurity contents in the aqueous solution of hexafluorophosphoric acid

[0112]

[0113]

[0114] After the multiple thin film evaporation water removal steps in the S2 step of Examples 1-5 of the present embodiment, anhydrous HPF6 liquid is obtained. A comparative example is set up to perform a thin film evaporation water removal once, to compare the effects of multiple thin film evaporation water removal. The preparation method of the anhydrous HPF6 liquid of the comparative example comprises: S1: setting the temperature of the microchannel reactor to-20℃, and using a peristaltic pump to add 100 g of polyphosphoric acid (H6P4O 13 ​), 142.01 g of anhydrous hydrogen fluoride was added into the micro-channel reactor at a speed of 40 g / min and 56.81 g / min, respectively, to react, and 242.01 g of aqueous solution of hexafluorophosphoric acid was obtained; S2: the aqueous solution of hexafluorophosphoric acid obtained above was transferred into a water removal kettle, 242.01 g of ether was added, and water was removed by thin film evaporation under the conditions of 15℃ and negative pressure-0.1 MPa, so that the total mass of the system was left with 42%, and 203.28 g of anhydrous HPF6 liquid was obtained.

[0115] The test results of the moisture content and the content of hexafluorophosphoric acid and impurities in the anhydrous HPF6 liquid obtained in the S2 step of Examples 1-5 and Comparative Examples are shown in Table 2.

[0116] Table 2 Moisture content and content of hexafluorophosphoric acid and impurities in anhydrous HPF6 liquid

[0117] Moisture (%) HPF6 (%) HF (%) HPO2F2 (%) H2PO3F (%) Example 1 0.0029 99.965 0.0198 0.0089 0.0034 Example 2 0.0022 99.972 0.017 0.0060 0.0028 Example 3 0.0026 99.971 0.0196 0.0054 0.0014 Example 4 0.0019 99.975 0.016 0.0051 0.0020 Example 5 0.0021 99.972 0.017 0.0061 0.0028 Comparative Example 4.67 - - - -

[0118] The preparation method of anhydrous hexafluorophosphoric acid provided by the application has high moisture removal rate, low impurity content, and the prepared anhydrous hexafluorophosphoric acid has a purity of up to 99.9% or more, a moisture content of less than 0.003% or less, and hexafluorophosphoric acid is not easy to hydrolyze to produce by-products, which is conducive to the further preparation of hexafluorophosphate products.

[0119] The test results of the liquid hexafluorophosphate obtained in Examples 6-13 are shown in Table 3.

[0120] Table 3 Moisture content, acidity and content of single metal ion in liquid hexafluorophosphate

[0121]

[0122]

[0123] The metal impurity ions in the electrolyte solution have a lower reduction potential than lithium ions, and in the charging process, the content of metal impurity ions is small, which can avoid the metal impurity ions being embedded into the carbon negative electrode before lithium ions, reduce the position of lithium ion embedding, and further reduce the reversible capacity of the lithium ion battery, and the deposition of metal impurity ions can also cause the graphite electrode surface to be unable to form an effective passivation layer, which can damage the entire battery. The liquid hexafluorophosphate prepared by using the anhydrous hexafluorophosphoric acid described in the application has a moisture content of less than 10 ppm, an acidity of less than 20 ppm, and a single metal ion content of ≤3 ppm, which is very suitable for use as an electrolyte salt solution for secondary batteries.

Claims

1. A process for the preparation of anhydrous hexafluorophosphoric acid, characterized in that, The method comprises the following steps: S1: reacting polyphosphoric acid and anhydrous hydrogen fluoride to generate an aqueous solution of hexafluorophosphoric acid; S2: after the aqueous solution of hexafluorophosphoric acid in step S1 is physically dehydrated, crystallized and purified by sweating using an organic solvent, high-purity anhydrous hexafluorophosphoric acid is obtained; in step S2, the water in the reaction system is removed by thin film evaporation of the organic solvent under negative pressure.

2. The method for preparing anhydrous hexafluorophosphoric acid as described in claim 1, characterized in that, In step S1, the polyphosphoric acid and the anhydrous hydrogen fluoride are reacted in a microchannel reactor, and the molar ratio of phosphorus in the polyphosphoric acid to the anhydrous hydrogen fluoride is 1: (6-7).

3. The method for preparing anhydrous hexafluorophosphoric acid as described in claim 1, characterized in that, The reaction temperature in step S1 is -20-5℃.

4. The method for preparing anhydrous hexafluorophosphoric acid as described in claim 1, characterized in that, The crystallization temperature in step S2 is -10-0℃.

5. The method for preparing anhydrous hexafluorophosphoric acid as described in claim 4, characterized in that, The thin film evaporation temperature is 15-25℃, and the negative pressure range used is -0.05MPa to -0.1MPa.

6. The method for preparing anhydrous hexafluorophosphoric acid as described in claim 4, characterized in that, The thin film evaporation step of the organic solvent is repeated for more than 2 times, and in each thin film evaporation, the mass ratio of the organic solvent to the aqueous solution of hexafluorophosphoric acid is 1-1.5:1; in each thin film evaporation before the last thin film evaporation, the negative pressure evaporation is performed until the total mass of the system is reduced to 40%-50%; and the last thin film evaporation obtains anhydrous hexafluorophosphoric acid.

7. The method for preparing anhydrous hexafluorophosphoric acid as described in claim 4, characterized in that, The organic solvent is selected from one or both of halogenated alkanes or ethers.

8. The method for preparing anhydrous hexafluorophosphoric acid as described in claim 4, characterized in that, The organic solvent is selected from one or more of dichloromethane, dichloroethane, carbon tetrachloride, diethyl ether, petroleum ether, isopropyl ether, and glycol dimethyl ether.

9. The process for the preparation of anhydrous hexafluorophosphoric acid according to any one of claims 1 to 8, characterized in that, The anhydrous hexafluorophosphoric acid obtained in step S2 has a purity of ≥99.9%.

10. A process for the preparation of high purity liquid hexafluorophosphate salt using the anhydrous hexafluorophosphoric acid of claim 1, characterized in that, The specific method comprises: under the protection of an inert atmosphere, generating a salt reaction of an anhydrous high-purity alkali metal source and the high-purity anhydrous hexafluorophosphoric acid in an organic solvent, and after impurity removal, obtaining high-purity liquid hexafluorophosphate.

11. The method for preparing high-purity liquid hexafluorophosphate as described in claim 10, characterized in that, The salt formation reaction is first incubated at -5-5℃ for 1-2h, and then warmed to 5-25℃ for 3-6h.

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