Preparation method of high-purity sodium hexafluorophosphate

Abstract

The invention relates to the technical field of sodium hexafluorophosphate production, and particularly discloses a preparation method of high-purity sodium hexafluorophosphate. Comprising six steps of reaction liquid preparation, preliminary reaction, high-temperature reaction, low-temperature reaction, filtering and washing, drying and the like, ammonium hexafluorophosphate and a vacuum-dried sodium source are respectively put into a tetrahydrofuran (THF) solvent, then an ammonium hexafluorophosphate-THF solution is slowly added into a sodium source-THF suspension drop by drop, the sodium source-THF suspension reacts with the ammonium hexafluorophosphate-THF suspension, and the ammonium hexafluorophosphate-THF suspension is obtained. And white powdery sodium hexafluorophosphate is generated under the control of a high-temperature reflux reaction and a low-temperature reaction, so that the technical problem that the risk of preparation safety is relatively high due to the fact that hydrogen fluoride liquid with strong corrosivity is used when the sodium hexafluorophosphate is prepared in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the technical field of sodium hexafluorophosphate production, in particular to a method for preparing high-purity sodium hexafluorophosphate. Background Art

[0002] In recent years, sodium-ion batteries have become a research hotspot for the next generation of rechargeable batteries due to the natural abundance of sodium and similar working principles to lithium-ion batteries. Sodium deposits are evenly distributed around the world, so they are less susceptible to geographical and market price fluctuations and are much cheaper than lithium. Although the inherently lower energy density is the main disadvantage of sodium batteries, low battery costs dominate for large-scale or stationary storage applications. Given the low abundance and relatively high cost of lithium, it is foreseeable that the development of sodium batteries for grid storage will be crucial to relieve the pressure on lithium batteries.

[0003] Electrolyte is indispensable in sodium batteries because it undertakes the function of transferring Na+ between cathode and anode, and can form an electrode-electrolyte interface, inhibiting the reaction at the interface, thereby affecting the working voltage window and cycle performance. Sodium electrolyte salts need to meet the following requirements: high solubility, good thermal stability, wide electrochemical window, no side reactions with positive and negative electrode materials and separators, good compatibility, low cost, environmental protection and pollution-free. Sodium hexafluorophosphate (NaPF6), as the most important sodium salt of sodium battery electrolyte, has the advantages of high conductivity, good ion migration number, strong electrochemical stability, and antioxidant properties. At the same time, its hexafluorophosphate anion can decompose to form SEI components such as LiF / NaF, fluorophosphate and fluorinated organic matter, promote the formation of appropriate SEI film, prevent the corrosion of the positive electrode current collector at high potential, and effectively passivate the positive electrode aluminum foil, which makes NaPF6 match various positive and negative electrode materials. Its preparation method and quality requirements are also constantly improving. At present, there are few studies on the synthesis of sodium hexafluorophosphate in China, and most of the synthesis methods involve the use of hydrofluoric acid. For example, Chinese Patent Publication No. CN108946769A relates to a method for preparing sodium hexafluorophosphate, which includes passing phosphorus pentafluoride gas into a sodium fluoride-hydrogen fluoride solution for reaction to obtain a sodium hexafluorophosphate solution, and crystallizing and drying the sodium hexafluorophosphate under stirring conditions. However, the hydrogen fluoride liquid used in this method is highly corrosive and has major safety issues. In this regard, a synthesis method that does not use hydrogen fluoride is disclosed in the prior art, such as Patent Publication No.: A method for preparing hexafluorophosphate is disclosed in a patent document of CN115304048A, which utilizes ammonium hexafluorophosphate and a material containing metal elements to react together to prepare a method for hexafluorophosphate, which includes sodium hexafluorophosphate.

[0004] Although the above patent can prepare hexafluorophosphate, metallic sodium is extremely active. When it is directly added to an ammonium hexafluorophosphate solution, the reaction is violent and difficult to control, which leads to a high technical problem of the safety risk of the preparation. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing high-purity sodium hexafluorophosphate, so as to solve the technical problem that in the prior art mentioned above, metallic sodium is used in the preparation of sodium hexafluorophosphate, and metallic sodium is extremely active. When it is directly added to an ammonium hexafluorophosphate solution for reaction, the reaction is violent, which makes the risk of preparation safety high.

[0006] In order to solve the above problems, the technical solution adopted by the present invention is as follows: a method for preparing high-purity sodium hexafluorophosphate, comprising the following steps:

[0007] S1: preparing a reaction solution: dissolving ammonium hexafluorophosphate in THF solvent to obtain an ammonium hexafluorophosphate-THF solution, and adding a vacuum-dried sodium source into the THF solvent to form a sodium source-THF suspension;

[0008] S2: Preliminary reaction: drop the ammonium hexafluorophosphate-THF solution into the sodium source-THF suspension for a preliminary reaction, the preliminary reaction time is 1 to 2 hours;

[0009] S3: High temperature reaction: The mixed reaction liquid after the preliminary reaction is subjected to a high temperature reaction by heating and reflux, and the heating and reflux reaction time is 5-8h;

[0010] S4: Low temperature reaction: After the heating reflux in S3 is completed, the reaction solution is cooled to 40-60°C for low temperature reaction, and the reaction is stirred for 10-20h;

[0011] S5: Filtration and washing: Filter the reaction solution after the reaction in S4, and wash it with water after filtration;

[0012] S6: Drying: vacuum evaporation and concentration of the solid particles washed in S4, and drying to obtain a white powdery sodium hexafluorophosphate product;

[0013] The steps S1 and S2 need to be carried out in an inert protective atmosphere, and the sodium source is metallic sodium.

[0014] The beneficial effects of this embodiment are:

[0015] 1. In the prior art, most of the processes for preparing sodium hexafluorophosphate are to react phosphorus pentafluoride with sodium fluoride-hydrogen fluoride solution. However, hydrofluoric acid is a highly corrosive liquid, and the risk of safety in preparation is high. At the same time, the equipment used must have strong corrosion resistance. It is necessary to set a corrosion-resistant lining such as fluororubber on the inner layer of the equipment, and the equipment needs to be maintained regularly to avoid damage to the lining and corrosion of the equipment by hydrofluoric acid. In the present application, a different process route is prepared, ammonium hexafluorophosphate is reacted with a sodium source, and tetrahydrofuran is used as a solvent, so that the whole process does not involve highly corrosive solvents and reaction liquids, which reduces the risk of safety in preparation and reduces the corrosion of the equipment, thereby extending the service life of the equipment and reducing maintenance costs.

[0016] 2. In this application, tetrahydrofuran is selected as the solvent to avoid the use of solvents containing water, which will not react violently with the sodium source - metallic sodium, making the reaction controllable and safe.

[0017] 3. The density of the solvent tetrahydrofuran is 0.89, while the density of metallic sodium is 0.968. Compared with other solvents, metallic sodium can sink into tetrahydrofuran instead of floating on the surface of the solvent. In the process of sinking to the bottom, the two are in contact and mixed, and the mixing is more complete. It is difficult to mix by stirring when floating on the surface, but sinking into the solvent can be mixed evenly with a simple stirrer. Therefore, during preparation, violent reactions of metallic sodium powder on the surface and in local areas can be avoided.

[0018] 4. In the preparation method of the present application, the process of using metallic sodium is carried out in an inert protective atmosphere. Therefore, the metallic sodium powder is not easily exposed to the air, and the metallic sodium powder is sunk in tetrahydrofuran and will not be exposed to the gas during the reaction. Even if a small amount of air enters the environment, it is difficult to come into contact with metallic sodium, so that the sodium source of the present application will not be oxidized by the air, and the reaction process is highly controllable and safe.

[0019] 5. In the present application, the ammonium hexafluorophosphate-THF solution is added dropwise to the sodium source-THF suspension for preliminary reaction. Compared with the reaction in which the sodium source-THF suspension is added to the ammonium hexafluorophosphate-THF solution, this method is to add the solution dropwise to the suspension, so the suspension can be in a stirring state and is evenly dispersed. The ammonium hexafluorophosphate-THF is a solution, and both are homogeneous before contact. Therefore, they can react quickly after contact, and there will be no problem of uneven reaction. The sodium hexafluorophosphate produced has good consistency.

[0020] 6. The present application divides the reaction into three stages, namely, a preliminary reaction, a high-temperature reaction stage, and a low-temperature reaction stage. The preliminary reaction is used to make the two mixed in a homogeneous phase, and the metal powder in the suspension and the ammonium hexafluorophosphate are mutually adsorbed to obtain a better mixing effect. The high-temperature reflux reaction is used to promote the rapid reaction, provide an inductive driving force, and make the yield high. The final low-temperature reaction aging is used to increase the yield while giving the sodium hexafluorophosphate crystal growth time. Since the solvent is tetrahydrofuran, it is easy to separate from the sodium hexafluorophosphate in the later stage. Therefore, compared with other solvents, the produced sodium hexafluorophosphate will not wrap the solvent, so its purity is higher. Since the reaction is divided into three stages, namely, a preliminary reaction, a high-temperature reaction stage, and a low-temperature reaction, the temperature change curve of the reaction is used to control the growth rate and time of the crystal. Therefore, the crystal structure formed is blocky and has good structural properties.

[0021] Furthermore, the sodium source in S1 is powdered metallic sodium.

[0022] Furthermore, the inert protective atmosphere is nitrogen.

[0023] Furthermore, the detergent in S5 is pentane.

[0024] Furthermore, the heating reflux reaction time in S3 is 5 hours.

[0025] Furthermore, the initial reaction time of S2 is 1 h.

[0026] Furthermore, the reaction temperature in S4 is 55° C. and the stirring time is 10 h.

[0027] Furthermore, the vacuum evaporation concentration temperature in S6 is 30-40°C, and the drying temperature is 110-130°C.

[0028] Furthermore, in S6, the vacuum evaporation concentration temperature is 40°C and the drying temperature is 120°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart is prepared for the present invention;

[0030] Figure 2 This is the F-NMR (471 MHz) spectrum of Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The following is further described in detail by specific embodiments: "scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following range can be fully expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] Implementation example Figures 1-2 As shown:

[0033] Experimental Example 1

[0034] Under room temperature, 16.4 g (100 mol) of ammonium hexafluorophosphate was fully dissolved in THF solvent (tetrahydrofuran) under nitrogen atmosphere. In addition, 4.6 g (200 mmol) of powdered metallic sodium after vacuum drying was added to THF solvent. Subsequently, the ammonium hexafluorophosphate solution was slowly added dropwise to the THF solution containing sodium for a preliminary reaction and stirred for 1 hour. The reaction solution was then heated to reflux for 6 hours for a high-temperature reaction, cooled to 40°C, and stirred for 16 hours for a low-temperature reaction. After the low-temperature reaction was completed, the reaction solution was filtered, 2.5 equivalents of pentane were added for washing, vacuum evaporated and concentrated at 40°C, and vacuum dried at 120°C for 24 hours to obtain sodium hexafluorophosphate (yield 81%).

[0035] Experimental Example 2

[0036] Under room temperature, 16.4 g (100 mol) of ammonium hexafluorophosphate was fully dissolved in THF solvent under nitrogen atmosphere. In addition, 4.6 g (200 mol) of metallic sodium after vacuum drying was added to THF solvent. Subsequently, the ammonium hexafluorophosphate solution was slowly added dropwise to the THF solution containing sodium for preliminary reaction. Stir for 2 h. Then, the reaction solution was heated to reflux for 6 hours for high temperature reaction, cooled to 45 ° C, stirred for 16 h, and after the low temperature reaction was completed, the reaction solution was filtered, 2.5 equivalents of pentane were added for washing, vacuum evaporated and concentrated at 40 ° C, and vacuum dried at 120 ° C for 24 h to obtain sodium hexafluorophosphate (yield 85%).

[0037] Experimental Example 3

[0038] Under room temperature, 16.4 g (100 mol) of ammonium hexafluorophosphate was fully dissolved in THF solvent under nitrogen atmosphere. In addition, 4.6 g (200 mol) of metallic sodium after vacuum drying was added to THF solvent. Subsequently, the ammonium hexafluorophosphate solution was slowly added dropwise to the THF solution containing sodium for preliminary reaction and stirred for 1 hour. The reaction solution was then heated to reflux for 6 hours for high temperature reaction, cooled to 50°C, and stirred for 16 hours. The product precipitated, and after the low temperature reaction was completed, the reaction solution was filtered, 2.5 equivalents of pentane were added for washing, vacuum evaporated and concentrated at 40°C, and vacuum dried at 120°C for 24 hours to obtain sodium hexafluorophosphate (yield 92%).

[0039] Experimental Example 4

[0040] Under room temperature, 16.4 g (100 mol) of ammonium hexafluorophosphate was fully dissolved in THF solvent under nitrogen atmosphere. In addition, 4.6 g (200 mol) of metallic sodium after vacuum drying was added to THF solvent. Subsequently, the ammonium hexafluorophosphate solution was slowly added to the surface of the sodium suspended in the THF solution for preliminary reaction and stirred for 2 h. The reaction solution was then heated to reflux for 6 hours for high temperature reaction, cooled to 60 ° C, and stirred for 16 h. The product precipitated. After the low temperature reaction was completed, the reaction solution was filtered, 2.5 equivalents of pentane were added for washing, vacuum evaporated and concentrated at 40 ° C, and dried for 24 h to obtain sodium hexafluorophosphate (yield 86%).

[0041] Comparative Example 1

[0042] Under room temperature, 16.4 g (100 mol) of ammonium hexafluorophosphate was fully dissolved in THF solvent under nitrogen atmosphere. In addition, 4.6 g (200 mol) of metallic sodium after vacuum drying was added to THF solvent. Subsequently, the ammonium hexafluorophosphate solution was slowly added dropwise to the surface of the sodium suspended in the THF solution for preliminary reaction and stirred for 1 hour. The reaction solution was then heated to reflux for 6 hours for high temperature reaction. After cooling to room temperature, the reaction solution was directly filtered, 2.5 equivalents of pentane were added for washing, vacuum evaporated and concentrated at 40°C, and dried for 24 hours to obtain sodium hexafluorophosphate (yield 70%).

[0043] Comparative Example 2

[0044] At room temperature, 16.4 g (100 mol) of ammonium hexafluorophosphate was fully dissolved in THF solvent under nitrogen atmosphere. In addition, 4.6 g (200 mol) of metallic sodium after vacuum drying was added to THF solvent. Subsequently, the ammonium hexafluorophosphate solution was slowly added dropwise to the THF solution containing sodium for a preliminary reaction. Stir for 1 hour. Then the reaction solution was heated to 50°C and stirred for 16 hours for low-temperature reaction. After the low-temperature reaction was completed, the reaction solution was filtered, 2.5 equivalents of pentane were added for washing, vacuum evaporated and concentrated at 40°C, and vacuum dried at 120°C for 24 hours to obtain sodium hexafluorophosphate (yield 72%).

[0045] Comparative Example 3

[0046] Under room temperature, 16.4 g (100 mol) of ammonium hexafluorophosphate was fully dissolved in THF solvent under nitrogen atmosphere. In addition, 4.6 g (200 mol) of metallic sodium after vacuum drying was added to THF solvent. Subsequently, the THF solution containing sodium was directly poured into the ammonium hexafluorophosphate solution, stirred for 10 min, and then the reaction solution was heated to reflux for 1 h for high temperature reaction, cooled to 50 ° C, stirred for 16 h, and after the low temperature reaction was completed, the reaction solution was filtered, 2.5 equivalents of pentane were added for washing, vacuum evaporated and concentrated at 40 ° C, and vacuum dried at 120 ° C for 24 h to obtain sodium hexafluorophosphate (yield 76%).

[0047] The data is as follows:

[0048]

[0049]

[0050] From the above data, it can be seen that if the high-temperature reflux reaction is directly used, and then the temperature is cooled to room temperature and filtered, washed and dried directly, the yield of sodium hexafluorophosphate is low. If the high-temperature reflux reaction is deleted and the low-temperature reaction of 40-60 degrees is directly carried out, the yield of sodium hexafluorophosphate is also low. The mixing process in the initial reaction process is also indispensable. After deleting it,

[0051] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing high-purity sodium hexafluorophosphate, characterized in that: The following steps are involved: S1: preparing a reaction solution: dissolving ammonium hexafluorophosphate in THF solvent to obtain an ammonium hexafluorophosphate-THF solution, and adding a vacuum-dried sodium source into the THF solvent to form a sodium source-THF suspension; S2: Preliminary reaction: drop the ammonium hexafluorophosphate-THF solution into the sodium source-THF suspension for a preliminary reaction, the preliminary reaction time is 1 to 2 hours; S3: High temperature reaction: The mixed reaction liquid after the preliminary reaction is subjected to a high temperature reaction by heating and reflux, and the heating and reflux reaction time is 5-8h; S4: Low temperature reaction: After the heating reflux in S3 is completed, the reaction solution is cooled to 40-60°C for low temperature reaction, and the reaction is stirred for 10-20h; S5: Filtration and washing: Filter the reaction solution after the reaction in S4, and wash it with water after filtration; S6: Drying: vacuum evaporation and concentration of the solid particles washed in S4, and drying to obtain a white powdery sodium hexafluorophosphate product; The steps S1 and S2 need to be carried out in an inert protective atmosphere, and the sodium source is metallic sodium.

2. The method for preparing high-purity sodium hexafluorophosphate according to claim 1, characterized in that: The sodium source in S1 is powdered metallic sodium.

3. The method for preparing high-purity sodium hexafluorophosphate according to claim 1, characterized in that: The inert protective atmosphere is nitrogen.

4. The method for preparing high-purity sodium hexafluorophosphate according to claim 1, characterized in that: The detergent in S5 is pentane.

5. The method for preparing high-purity sodium hexafluorophosphate according to claim 1, characterized in that: The heating reflux reaction time in S3 is 6 hours.

6. The method for preparing high-purity sodium hexafluorophosphate according to claim 1, characterized in that: The initial reaction time of S2 is 1 h.

7. The method for preparing high-purity sodium hexafluorophosphate according to claim 1, characterized in that: The reaction temperature in S4 is 50° C. and the stirring time is 16 h.

8. The method for preparing high-purity sodium hexafluorophosphate according to claim 1, characterized in that: The vacuum evaporation concentration temperature in S6 is 30-40°C, and the drying temperature is 110-130°C.

9. The method for preparing high-purity sodium hexafluorophosphate according to claim 5, characterized in that: In the S6, the vacuum evaporation concentration temperature is 40°C, and the drying temperature is 120°C.

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