Process for the preparation of battery grade sodium metaphosphate and sodium hexafluorophosphate

Abstract

In order to solve the technical problems that the production process of sodium hexafluorophosphate is complex and the production equipment is required to be high, the application provides a preparation method of battery grade sodium metaphosphate and sodium hexafluorophosphate. The application is characterized in that: high-purity sodium hydroxide is used for impurity removal, and the subsequent concentration crystallization and special gradient temperature drying process are cooperated, so that the obtained sodium metaphosphate has iron less than 1 ppm, calcium and magnesium less than 5 ppm, and potassium less than 10 ppm, which can meet the technical index requirements of battery grade sodium metaphosphate. On this basis, the battery grade sodium metaphosphate is used as a raw material to react with hydrofluoric acid to prepare a sodium hexafluorophosphate synthesis solution, and then the synthesis solution is filtered, high-speed centrifuged, negative pressure dried and vacuum packaged, so as to obtain battery grade sodium hexafluorophosphate. The application omits the step of configuring sodium hexafluorophosphate in the traditional preparation process, so that the production process is simplified and safer, and the production equipment is required to be low.

Description

Technical Field

[0001] This invention relates to a method for preparing sodium hexafluorophosphate, and more particularly to a method for preparing sodium hexafluorophosphate with impurity content that meets the requirements of battery technology and is suitable for mass production. Background Technology

[0002] Sodium hexafluorophosphate is a commonly used electrolyte that serves as a catalyst, acid catalyst, and dehydrating agent in chemical experiments and industrial production. It is also widely used in batteries, electrolytes, surfactants, and other fields. Furthermore, sodium hexafluorophosphate can be used in organic synthesis, high-temperature lubricants, and analytical chemistry.

[0003] Currently, sodium hexafluorophosphate (Sodium hexafluorophosphate) is mainly used in the production of energy storage batteries to replace some of the lithium hexafluorophosphate (LiPF6) electrolytes. Its significantly lower price compared to LiPF6 and the readily available availability of sodium ions have made it popular in the battery industry. Sodium hexafluorophosphate is currently produced using a process similar to that of lithium hexafluorophosphate. The traditional method involves modifying the equipment used for lithium hexafluorophosphate production to achieve the same results. However, this process is complex and requires sophisticated equipment. Summary of the Invention

[0004] To address the technical challenges of complex production processes and demanding equipment requirements for sodium hexafluorophosphate, this invention provides a method for preparing battery-grade sodium hexafluorophosphate.

[0005] While studying the preparation method of battery-grade sodium hexafluorophosphate, this invention also developed a preparation method of battery-grade sodium metaphosphate.

[0006] The technical solution of this invention is:

[0007] A method for preparing battery-grade sodium metaphosphate, characterized by the following steps:

[0008] Step 1.1 Dilute the electronic-grade phosphoric acid with ultrapure water to a phosphoric acid solution with a mass fraction of 35-45%;

[0009] Step 1.2 Add a high-purity sodium hydroxide solution with a mass fraction of 18-22% to the phosphoric acid solution and adjust the pH value to 1-2 to obtain a sodium dihydrogen phosphate synthesis solution; the high-purity sodium hydroxide solution contains less than 1 ppm of iron and less than 5 ppm of magnesium and calcium; the mass ratio of high-purity sodium hydroxide solution to phosphoric acid solution is 1:1.2-1.3; the pH value is adjusted to 1-2 in this step to help the impurity metal ions dissolve fully, so as to improve the purity of the sodium dihydrogen phosphate crystals obtained subsequently.

[0010] Step 2: Preparation of sodium dihydrogen phosphate crystals

[0011] Step 2.1 The sodium dihydrogen phosphate synthesis solution is heated and stirred to concentrate it. Heating is stopped after crystallization.

[0012] Step 2.2 Cooling and crystallization: Cool to 45-50℃ to ensure that impurity ions are fully dissolved in the solution. Keep warm for 2-3 hours to allow sodium dihydrogen phosphate to fully precipitate. After a large amount of crystals appear, take out the crystals, centrifuge and wash with water appropriately. Control the iron content to be less than 1 ppm, the calcium and magnesium content to be less than 5 ppm, and the potassium content to be less than 10 ppm to obtain sodium dihydrogen phosphate crystals.

[0013] Step 3: Preparation of battery-grade sodium metaphosphate

[0014] Step 3.1 Dry the sodium dihydrogen phosphate crystals in a gradient:

[0015] The sodium dihydrogen phosphate crystals are dried at 200-250℃ for 2-3 hours, crushed, and then dried at 550-600℃ for 2-3 hours, with the moisture content controlled to be less than 0.05%, to obtain sodium metaphosphate lumps.

[0016] Step 3.2: Crush the sodium metaphosphate lumps and pass them through a sieve with a mesh size of at least 200 mesh to obtain battery-grade sodium metaphosphate with very fine particle size. If this battery-grade sodium metaphosphate is subsequently used as a raw material to prepare battery-grade sodium hexafluorophosphate, its fine particle size facilitates rapid dissolution and complete reaction, while also preventing excessively large particles from scratching the PTFE reactor and introducing new mechanical impurities.

[0017] Furthermore, the high-purity sodium hydroxide in step 1.2 above is obtained by the following method: dissolving high-purity sodium hydroxide in ultrapure water, with a mass ratio of sodium hydroxide to ultrapure water of 1:3.6-4.4. After complete dissolution, mechanical impurities and precipitated impurities such as calcium hydroxide and magnesium hydroxide are filtered out using a filter cartridge with a precision of at least 1 micrometer. The iron content in the intermediate control solution is less than 1 ppm, and the magnesium and calcium contents are both less than 5 ppm, resulting in a high-purity sodium hydroxide solution with a mass fraction of 18-22%.

[0018] Further, in step 1.1 above, the electronic-grade phosphoric acid is diluted to a phosphoric acid solution with a mass fraction of 40%; in step 1.2 above, a high-purity sodium hydroxide solution with a mass fraction of 20% is added to the phosphoric acid solution.

[0019] Further, in step 2.1 above, the sodium dihydrogen phosphate synthesis solution is heated to 110-115°C and stirred and concentrated until the solution specific gravity is 1.55-1.6.

[0020] Furthermore, in step 2.2 above, the centrifugation speed is 1000-1500 rpm, the centrifugation time is 20-30 minutes, and an appropriate amount of hot water at 80℃ or above is added for washing. High-speed centrifugation in this step helps to fully remove dissolved impurities, and washing with hot water at 80℃ or above can better remove most of the free acid and some potassium ions.

[0021] Furthermore, in step 3.1 above, the sodium dihydrogen phosphate crystals are dried in a PTFE dish at 200-250°C for 2-3 hours, then crushed and dried in a quartz dish at 550-600°C for 2-3 hours. Using a PTFE dish to hold the sodium dihydrogen phosphate crystals during the first-gradient drying process prevents them from sticking to the container after dehydration and becoming difficult to remove.

[0022] The present invention also provides a battery-grade sodium metaphosphate, which is special in that it is prepared by the above-described method for preparing battery-grade sodium metaphosphate.

[0023] This invention also provides a method for preparing battery-grade sodium hexafluorophosphate, characterized by the following steps:

[0024] Step 1: Preparation of sodium hexafluorophosphate synthesis solution

[0025] Sodium hexafluorophosphate synthesis solution is prepared by reacting 85-90% hydrofluoric acid with the above-mentioned battery-grade sodium metaphosphate; wherein the hydrofluoric acid is in excess by 50-100%, the reaction temperature is controlled below 10℃, and the reaction is stirred for 3-5 hours.

[0026] Step 2: Preparation of sodium hexafluorophosphate crystals

[0027] The sodium hexafluorophosphate synthesis solution was filtered and centrifuged at high speed to obtain sodium hexafluorophosphate crystals;

[0028] Step 3: Preparation of battery-grade sodium hexafluorophosphate crystals

[0029] The sodium hexafluorophosphate crystals were placed in a vacuum chamber and dried for 3-5 hours at 100-180°C and 0.45-0.55 kg negative pressure. The moisture content was controlled to be less than 50 ppm, calcium, magnesium and potassium to be less than 10 ppm, and iron to be less than 1 ppm. The mixture was then vacuum packaged to obtain battery-grade sodium hexafluorophosphate.

[0030] Further, step one specifically involves: adding 85-90% hydrofluoric acid by mass to the fully enclosed PFA reactor through the feed port, cooling with brine, and controlling the temperature to be below -5℃; then slowly adding the battery-grade sodium metaphosphate to the fully enclosed PFA reactor at a rate of 1-2 kg / min through the feed port, controlling the temperature to be below 0℃, with an excess of 50-100% hydrofluoric acid; after the addition is completed, maintaining the temperature below 10℃, stirring and reacting for 3-5 hours to obtain a sodium hexafluorophosphate synthesis solution.

[0031] Further, step two specifically involves: passing the sodium hexafluorophosphate synthesis solution obtained in step one through a pipeline into a PTFE filter for filtration, and then centrifuging at a speed of 2000-5000 rpm for at least 30 minutes to obtain sodium hexafluorophosphate crystals.

[0032] The present invention also provides a battery-grade sodium hexafluorophosphate, which is special in that it is prepared by the above-described method for preparing battery-grade sodium hexafluorophosphate.

[0033] The present invention also provides an energy storage battery, which is special in that it is produced using the above-mentioned battery-grade sodium hexafluorophosphate.

[0034] The beneficial effects of this invention are:

[0035] 1. Sodium metaphosphate prepared by traditional methods has excessively high impurity content, which cannot meet the mass production requirements of battery-grade sodium metaphosphate. However, this invention uses high-purity sodium hydroxide for impurity removal, combined with subsequent concentration crystallization and a special gradient temperature drying process, to finally obtain sodium metaphosphate with iron content less than 1 ppm, calcium and magnesium content less than 5 ppm, and potassium content less than 10 ppm, which can meet the technical specifications of battery-grade sodium metaphosphate.

[0036] 2. In the process of preparing sodium metaphosphate, the phosphoric acid solution used in this invention has a mass fraction of 35-45%, which can provide sufficient mother liquor for the subsequent concentration and crystallization steps to remove potassium ions. In addition, after the crystals are concentrated, heating is stopped and the temperature is cooled to 45-50°C. Within this temperature range, the potassium content in the sodium dihydrogen phosphate crystals is low, which can remove potassium ions as much as possible and provide support for the subsequent preparation of high-purity battery-grade sodium metaphosphate.

[0037] 3. Compared with the traditional preparation process of sodium hexafluorophosphate, the present invention eliminates the step of preparing hexafluorophosphate, which is required in the traditional preparation process, thus simplifying the production process and making it safer; since hexafluorophosphate is not required, the present invention has lower requirements for production equipment.

[0038] 4. In preparing sodium hexafluorophosphate, this invention avoids the preparation of hexafluorophosphate, thus reducing unsafe factors in the production process. Attached Figure Description

[0039] Figure 1 This is the XRD pattern of sodium metaphosphate prepared according to the present invention.

[0040] Figure 2 This is the XRD pattern of sodium hexafluorophosphate prepared according to the present invention.

[0041] Figure 3 These are the detection data of sodium metaphosphate prepared by this invention.

[0042] Figure 4 These are the test data for sodium hexafluorophosphate prepared according to this invention. Detailed Implementation

[0043] The concept of this invention is:

[0044] Considering the fundamental differences in properties between sodium hexafluorophosphate and lithium hexafluorophosphate, sodium hexafluorophosphate exhibits stronger resistance to hydrolysis under sufficient acid conditions and allows for the presence of small amounts of water in the reaction system. Therefore, its preparation process can be greatly simplified, reducing the requirements for production equipment and thus lowering its production costs.

[0045] The reaction equation involved in this invention is:

[0046] NaOH+H3PO4===NaH2PO4+H2O

[0047] NaH2PO4 === NaPO3 + H2O

[0048] NaPO3 + 6HF === NaPF6 + 3H2O

[0049] The present invention will be further described in detail below through examples.

[0050] Example 1:

[0051] This embodiment prepares battery-grade sodium metaphosphate through the following steps, and further prepares battery-grade sodium hexafluorophosphate using the battery-grade sodium metaphosphate:

[0052] Step 1: Refining sodium hydroxide

[0053] 640 kg of ultrapure water and 160 kg of high-purity sodium hydroxide were added to the reactor. After complete dissolution, the solution was filtered through a 1-micron filter cartridge. The iron content was controlled to be less than 1 ppm and the magnesium and calcium content to be less than 5 ppm, resulting in a 20% high-purity sodium hydroxide solution.

[0054] Step 2: Preparation of sodium dihydrogen phosphate synthesis solution

[0055] Step 2.1 Add 480 kg of electronic-grade phosphoric acid with a mass fraction of 85% to an enamel-lined reactor, and add 500 kg of ultrapure water to obtain a phosphoric acid solution with a mass fraction of approximately 40%.

[0056] Step 2.2 Add the purified high-purity sodium hydroxide solution from Step 1 to the phosphoric acid solution obtained in Step 2.1, and adjust the pH value to 1-2 to obtain sodium dihydrogen phosphate synthesis solution;

[0057] Step 3: Preparation of sodium dihydrogen phosphate crystals

[0058] Step 3.1 The sodium dihydrogen phosphate synthesis solution obtained in Step 2.2 is heated and stirred to concentrate. The temperature is raised to 110°C and the stirring speed is 70 rpm. The solution is concentrated until the specific gravity is 1.55-1.6 and a small amount of crystals appear. Then the heating is stopped.

[0059] Step 3.2 Cooling and crystallization: Cool to 47°C and keep warm for 3 hours. After a large amount of crystals appear, take out the crystals and put them into a centrifuge. Centrifuge at 1500 rpm for 30 minutes. During the process, add an appropriate amount of water above 80°C to wash the crystals. Control the iron content to be less than 1 ppm, calcium to be less than 5 ppm, magnesium to be less than 5 ppm, and potassium to be less than 10 ppm to obtain sodium dihydrogen phosphate crystals.

[0060] Step 4: Preparation of battery-grade sodium metaphosphate

[0061] Step 4.1 Place the sodium dihydrogen phosphate crystals obtained in Step 3.2 into a PTFE dish and dry at 250°C for 3 hours. After crushing, add them to a quartz dish and dry at 570°C for 3 hours. Control the moisture content to be less than 0.05% to obtain sodium metaphosphate blocks.

[0062] Step 4.2: Crush the sodium metaphosphate lumps obtained in Step 4.1 and pass them through a 200-mesh sieve to obtain sodium metaphosphate. Its qualitative diagram is shown below. Figure 1 Detection data such as Figure 3 .

[0063] Step 5: Synthesize battery-grade sodium hexafluorophosphate

[0064] Step 5.1 In a fully enclosed PFA reactor, first add 85% hydrofluoric acid by mass through the feed port, then cool with brine to control the temperature below -5℃. Next, slowly add the battery-grade sodium metaphosphate obtained in step 4.2 through the feed port at a rate of 1-2 kg / min, controlling the temperature below 0℃. The hydrofluoric acid is in 100% excess. After the addition is complete, keep the temperature below 10℃ and stir the reaction for 4 hours to obtain sodium hexafluorophosphate synthesis solution.

[0065] Step 5.2 The sodium hexafluorophosphate synthesis solution obtained in step 5.1 is piped into a PTFE filter for filtration, and then centrifuged at 5000 rpm for 30 minutes to obtain sodium hexafluorophosphate crystals;

[0066] Step 5.3: Place the sodium hexafluorophosphate crystals obtained in Step 5.2 into a vacuum drying oven and dry them at 180℃ under a negative pressure of 0.5 kg for 4 hours. Maintain the moisture content at less than 50 ppm, calcium, magnesium, and potassium at less than 10 ppm, and iron at less than 1 ppm. Vacuum package the product to obtain the target product. The product is identified as sodium hexafluorophosphate by XRD. Figure 1 As shown. The detection data for the sodium hexafluorophosphate prepared in this embodiment are as follows. Figure 4 As shown.

[0067] Example 2:

[0068] This embodiment prepares battery-grade sodium metaphosphate through the following steps, and further prepares battery-grade sodium hexafluorophosphate using the battery-grade sodium metaphosphate:

[0069] Step 1: Refining sodium hydroxide

[0070] 640 kg of ultrapure water and 140 kg of high-purity sodium hydroxide were added to the reactor. After complete dissolution, the solution was filtered through a 1-micron filter cartridge. The iron content was controlled to be less than 1 ppm and the magnesium and calcium content to be less than 5 ppm, resulting in a high-purity sodium hydroxide solution with a mass fraction of approximately 18%.

[0071] Step 2: Preparation of sodium dihydrogen phosphate synthesis solution

[0072] Step 2.1 Add 480 kg of electronic-grade phosphoric acid with a mass fraction of 85% to an enamel-lined reactor, and add 685 kg of ultrapure water to obtain a phosphoric acid solution with a mass fraction of approximately 35%.

[0073] Step 2.2 Add the purified high-purity sodium hydroxide solution from Step 1 to the phosphoric acid solution obtained in Step 2.1, and adjust the pH value to 1-2 to obtain sodium dihydrogen phosphate synthesis solution;

[0074] Step 3: Preparation of sodium dihydrogen phosphate crystals

[0075] Step 3.1 The sodium dihydrogen phosphate synthesis solution obtained in Step 2.2 is heated and stirred to concentrate. The temperature is raised to 115°C and the stirring speed is 70 rpm. The solution is concentrated until the specific gravity is 1.58 and a small amount of crystals appear. Then the heating is stopped.

[0076] Step 3.2 Cooling and crystallization: Cool to 49℃ and keep warm for 3 hours. After a large amount of crystals appear, take out the crystals and put them into a centrifuge. Centrifuge at 1200 rpm for 30 minutes. During the process, add an appropriate amount of water above 80℃ to wash. Control the iron content to be less than 1 ppm, calcium to be less than 5 ppm, magnesium to be less than 5 ppm, and potassium to be less than 10 ppm to obtain sodium dihydrogen phosphate crystals.

[0077] Step 4: Preparation of battery-grade sodium metaphosphate

[0078] Step 4.1 Place the sodium dihydrogen phosphate crystals obtained in Step 3.2 into a PTFE dish and dry at 250°C for 3 hours. After crushing, add them to a quartz dish and dry at 600°C for 3 hours. Control the moisture content to be less than 0.05% to obtain sodium metaphosphate blocks.

[0079] Step 4.2: Crush the sodium metaphosphate lumps obtained in Step 4.1 and pass them through a 200-mesh sieve to obtain sodium metaphosphate. Its qualitative diagram is shown below. Figure 2 Detection data such as Figure 3 As shown.

[0080] Step 5: Synthesize battery-grade sodium hexafluorophosphate

[0081] Step 5.1 In a fully enclosed PFA reactor, first add 90% hydrofluoric acid by mass through the feed port, then cool with brine to control the temperature below -7℃. Next, slowly add the battery-grade sodium metaphosphate obtained in step 4.2 through the feed port at a rate of 1-2 kg / min, controlling the temperature below 0℃. Add 50% excess hydrofluoric acid. After the addition is complete, keep the temperature below 10℃ and stir the reaction for 4 hours to obtain sodium hexafluorophosphate synthesis solution.

[0082] Step 5.2 The sodium hexafluorophosphate synthesis solution obtained in Step 5.1 is piped into a PTFE filter for filtration, and then centrifuged at 3500 rpm for 30 minutes to obtain sodium hexafluorophosphate crystals;

[0083] Step 5.3: Place the sodium hexafluorophosphate crystals obtained in Step 5.2 into a vacuum drying oven and dry them at 150℃ and 0.45 kg negative pressure for 5 hours. Maintain the moisture content at less than 50 ppm, calcium, magnesium, and potassium at less than 10 ppm, and iron at less than 1 ppm. Vacuum package the product to obtain the target product. The product is identified as sodium hexafluorophosphate by XRD. Figure 1 As shown. The detection data for the sodium hexafluorophosphate prepared in this embodiment are as follows. Figure 4 As shown.

[0084] Example 3:

[0085] This embodiment prepares battery-grade sodium metaphosphate through the following steps, and further prepares battery-grade sodium hexafluorophosphate using the battery-grade sodium metaphosphate:

[0086] Step 1: Refining sodium hydroxide

[0087] 640 kg of ultrapure water and 180 kg of high-purity sodium hydroxide were added to the reactor. After complete dissolution, the solution was filtered through a 1-micron filter cartridge. The iron content was controlled to be less than 1 ppm and the magnesium and calcium content to be less than 5 ppm, resulting in a high-purity sodium hydroxide solution with a mass fraction of approximately 22%.

[0088] Step 2: Preparation of sodium dihydrogen phosphate synthesis solution

[0089] Step 2.1 Add 480 kg of electronic-grade phosphoric acid with a mass fraction of 85% to an enamel-lined reactor, and add 426 kg of ultrapure water to obtain a phosphoric acid solution with a mass fraction of approximately 45%.

[0090] Step 2.2 Add the purified high-purity sodium hydroxide solution from Step 1 to the phosphoric acid solution obtained in Step 2.1, and adjust the pH value to 1-2 to obtain sodium dihydrogen phosphate synthesis solution;

[0091] Step 3: Preparation of sodium dihydrogen phosphate crystals

[0092] Step 3.1 The sodium dihydrogen phosphate synthesis solution obtained in Step 2.2 is heated and stirred to concentrate. The temperature is raised to 112°C and the stirring speed is 65 rpm. The solution is concentrated until the specific gravity is 1.6 and a small amount of crystals appear. Then the heating is stopped.

[0093] Step 3.2 Cooling and crystallization: Cool to 45℃ and keep warm for 2 hours. After a large amount of crystals appear, take out the crystals and put them into a centrifuge. Centrifuge at 1000 rpm for 30 minutes. During the process, add an appropriate amount of water above 80℃ to wash. Control the iron content to be less than 1 ppm, calcium to be less than 5 ppm, magnesium to be less than 5 ppm, and potassium to be less than 10 ppm to obtain sodium dihydrogen phosphate crystals.

[0094] Step 4: Preparation of battery-grade sodium metaphosphate

[0095] Step 4.1 Place the sodium dihydrogen phosphate crystals obtained in Step 3.2 into a PTFE dish and dry at 200°C for 3 hours. After crushing, add them to a quartz dish and dry at 600°C for 3 hours. Control the moisture content to be less than 0.05% to obtain sodium metaphosphate blocks.

[0096] Step 4.2: Crush the sodium metaphosphate lumps obtained in Step 4.1 and pass them through a 200-mesh sieve to obtain sodium metaphosphate. Qualitative diagram as follows: Figure 2 Detection data such as Figure 3 .

[0097] Step 5: Synthesize battery-grade sodium hexafluorophosphate

[0098] Step 5.1 In a fully enclosed PFA reactor, first add hydrofluoric acid with a mass fraction of 87% through the feed port, cool it by passing brine, and control the temperature to be less than -7℃. Then, slowly add the battery-grade sodium metaphosphate obtained in step 4.2 through the feed port at a rate of 1-2 kg / min, control the temperature to be less than 0℃, and add 80% excess hydrofluoric acid. After the addition is completed, keep the temperature below 10℃ and stir the reaction for 4 hours to obtain sodium hexafluorophosphate synthesis solution.

[0099] Step 5.2 The sodium hexafluorophosphate synthesis solution obtained in Step 5.1 is piped into a PTFE filter for filtration, and then centrifuged at 2000 rpm for 40 minutes to obtain sodium hexafluorophosphate crystals;

[0100] Step 5.3: Place the sodium hexafluorophosphate crystals obtained in Step 5.2 into a vacuum drying oven and dry them at 100℃ and 0.55 kg negative pressure for 5 hours. Maintain the moisture content at less than 50 ppm, calcium, magnesium, and potassium at less than 10 ppm, and iron at less than 1 ppm. Vacuum package the product to obtain the target product. The product is identified as sodium hexafluorophosphate by XRD. Figure 1 As shown. The detection data is as follows. Figure 4As shown.

[0101] Example 4:

[0102] This embodiment prepares battery-grade sodium metaphosphate through the following steps, and further prepares battery-grade sodium hexafluorophosphate using the battery-grade sodium metaphosphate:

[0103] Step 1: Refining sodium hydroxide

[0104] 640 kg of ultrapure water and 150 kg of high-purity sodium hydroxide were added to the reactor. After complete dissolution, the solution was filtered through a 1-micron filter cartridge. The iron content was controlled to be less than 1 ppm and the magnesium and calcium content to be less than 5 ppm, resulting in a high-purity sodium hydroxide solution with a mass fraction of approximately 19%.

[0105] Step 2: Preparation of sodium dihydrogen phosphate synthesis solution

[0106] Step 2.1 Add 480 kg of electronic-grade phosphoric acid with a mass fraction of 85% to an enamel-lined reactor, and add 593 kg of ultrapure water to obtain a phosphoric acid solution with a mass fraction of approximately 38%.

[0107] Step 2.2 Add the purified high-purity sodium hydroxide solution from Step 1 to the phosphoric acid solution obtained in Step 2.1, and adjust the pH value to 1-2 to obtain sodium dihydrogen phosphate synthesis solution;

[0108] Step 3: Preparation of sodium dihydrogen phosphate crystals

[0109] Step 3.1 The sodium dihydrogen phosphate synthesis solution obtained in Step 2.2 is heated and stirred to concentrate. The temperature is raised to 112°C and the stirring speed is 65 rpm. The solution is concentrated to a specific gravity of 1.55. After a small amount of crystals appear, the heating is stopped.

[0110] Step 3.2 Cooling and crystallization: Cool to 50℃ and keep warm for 3 hours. After a large amount of crystals appear, take out the crystals and put them into a centrifuge. Centrifuge at 1400 rpm for 20 minutes. During the process, add an appropriate amount of water above 80℃ to wash. Control the iron content to be less than 1 ppm, calcium to be less than 5 ppm, magnesium to be less than 5 ppm, and potassium to be less than 10 ppm to obtain sodium dihydrogen phosphate crystals.

[0111] Step 4: Preparation of battery-grade sodium metaphosphate

[0112] Step 4.1 Place the sodium dihydrogen phosphate crystals obtained in Step 3.2 into a PTFE dish and dry at 230°C for 2 hours. After crushing, add them to a quartz dish and dry at 550°C for 3 hours. Control the moisture content to be less than 0.05% to obtain sodium metaphosphate blocks.

[0113] Step 4.2: Crush the sodium metaphosphate lumps obtained in Step 4.1 and pass them through a 200-mesh sieve to obtain sodium metaphosphate. Qualitative diagram as follows: Figure 2 Detection data such as Figure 3 .

[0114] Step 5: Synthesize battery-grade sodium hexafluorophosphate

[0115] Step 5.1 In a fully enclosed PFA reactor, first add 88% hydrofluoric acid by mass through the feed port, then cool with brine to control the temperature below -5℃. Next, slowly add the battery-grade sodium metaphosphate obtained in step 4.2 through the feed port at a rate of 1-2 kg / min, controlling the temperature below 0℃. The hydrofluoric acid is in 75% excess. After the addition is complete, keep the temperature below 10℃ and stir the reaction for 4 hours to obtain sodium hexafluorophosphate synthesis solution.

[0116] Step 5.2 The sodium hexafluorophosphate synthesis solution obtained in Step 5.1 is piped into a PTFE filter for filtration, and then centrifuged at 4500 rpm for 30 minutes to obtain sodium hexafluorophosphate crystals;

[0117] Step 5.3: Place the sodium hexafluorophosphate crystals obtained in Step 5.2 into a vacuum drying oven and dry them at 160℃ and 0.52 kg negative pressure for 5 hours. Maintain the moisture content at less than 50 ppm, calcium, magnesium, and potassium at less than 10 ppm, and iron at less than 1 ppm. Vacuum package the product to obtain the target product. The product is identified as sodium hexafluorophosphate by XRD. Figure 1 As shown. The detection data is as follows. Figure 4 As shown.

[0118] As can be seen from the above embodiments and their test data, the preparation method of battery-grade sodium metaphosphate and sodium hexafluorophosphate provided by the present invention is very stable, the obtained products have high repeatability, and the indicators meet the requirements.

Claims

1. A method for preparing battery-grade sodium hexafluorophosphate, characterized in that, Includes the following steps: Step 1: Preparation of sodium hexafluorophosphate synthesis solution Sodium hexafluorophosphate synthesis solution is prepared by reacting 85-90% hydrofluoric acid with battery-grade sodium metaphosphate; wherein the hydrofluoric acid is in 50-100% excess, the reaction temperature is controlled below 10℃, and the reaction is stirred for 3-5 hours. Step 2: Preparation of sodium hexafluorophosphate crystals The sodium hexafluorophosphate synthesis solution was filtered and centrifuged at high speed to obtain sodium hexafluorophosphate crystals; Step 3: Preparation of battery-grade sodium hexafluorophosphate crystals The sodium hexafluorophosphate crystals were placed in a vacuum chamber and dried for 3-5 hours at 100-180°C and 0.45-0.55 kg negative pressure. The moisture content was controlled to be less than 50 ppm, calcium, magnesium and potassium to be less than 10 ppm, and iron to be less than 1 ppm. The mixture was then vacuum packaged to obtain battery-grade sodium hexafluorophosphate.

2. The method for preparing battery-grade sodium hexafluorophosphate according to claim 1, characterized in that: Step one is as follows: Add hydrofluoric acid with a mass fraction of 85-90% into the fully enclosed PFA reactor through the feed port, cool with brine, and control the temperature to be less than -5℃; then slowly add the battery-grade sodium metaphosphate into the fully enclosed PFA reactor at a rate of 1-2 kg / min through the feed port, control the temperature to be less than 0℃, and add 50-100% excess hydrofluoric acid; after the addition is completed, keep the temperature below 10℃ and stir the reaction for 3-5 hours to obtain sodium hexafluorophosphate synthesis solution.

3. The method for preparing battery-grade sodium hexafluorophosphate according to claim 2, characterized in that: Step two specifically involves: passing the sodium hexafluorophosphate synthesis solution obtained in step one through a pipeline into a PTFE filter for filtration, and then centrifuging at a speed of 2000-5000 rpm for at least 30 minutes to obtain sodium hexafluorophosphate crystals.

4. The method for preparing battery-grade sodium hexafluorophosphate according to any one of claims 1-3, characterized in that: The battery-grade sodium metaphosphate used in step one is prepared by the following method: Step 1: Preparation of sodium dihydrogen phosphate synthesis solution Step 1.1 Dilute the electronic-grade phosphoric acid with ultrapure water to a phosphoric acid solution with a mass fraction of 35-45%; Step 1.2 Add a high-purity sodium hydroxide solution with a mass fraction of 18-22% to the phosphoric acid solution and adjust the pH value to 1-2 to obtain a sodium dihydrogen phosphate synthesis solution; the high-purity sodium hydroxide solution contains less than 1 ppm of iron and less than 5 ppm of magnesium and calcium; the mass ratio of high-purity sodium hydroxide solution to phosphoric acid solution is 1:1.2-1.

3. Step 2: Preparation of sodium dihydrogen phosphate crystals Step 2.1 The sodium dihydrogen phosphate synthesis solution is heated and stirred to concentrate it. Heating is stopped after crystallization. Step 2.2 Cooling and crystallization: Cool down to 45-50℃ and keep warm for 2-3 hours. After a large amount of crystals appear, take out the crystals, centrifuge and wash with water appropriately. Control the iron content to be less than 1 ppm, the calcium and magnesium content to be less than 5 ppm, and the potassium content to be less than 10 ppm to obtain sodium dihydrogen phosphate crystals. Step 3: Preparation of battery-grade sodium metaphosphate Step 3.1 Dry the sodium dihydrogen phosphate crystals in a gradient: The sodium dihydrogen phosphate crystals are dried at 200-250℃ for 2-3 hours, crushed, and then dried at 550-600℃ for 2-3 hours, with the moisture content controlled to be less than 0.05%, to obtain sodium metaphosphate lumps. Step 3.2 Crush the sodium metaphosphate lumps and pass them through a sieve with a mesh size of at least 200 to obtain battery-grade sodium metaphosphate.

5. The method for preparing battery-grade sodium hexafluorophosphate according to claim 4, characterized in that: The high-purity sodium hydroxide in step 1.2 is obtained by the following method: dissolving high-purity sodium hydroxide in ultrapure water at a mass ratio of sodium hydroxide to ultrapure water of 1:3.6-4.

4. After complete dissolution, the solution is filtered with a filter cartridge with a precision of at least 1 micrometer. The iron content in the solution is less than 1 ppm, and the magnesium and calcium contents are both less than 5 ppm, resulting in a high-purity sodium hydroxide solution with a mass fraction of 18-22%.

6. The method for preparing battery-grade sodium hexafluorophosphate according to claim 5, characterized in that: In step 1.1, electronic-grade phosphoric acid is diluted to a phosphoric acid solution with a mass fraction of 40%; in step 1.2, a high-purity sodium hydroxide solution with a mass fraction of 20% is added to the phosphoric acid solution.

7. The method for preparing battery-grade sodium hexafluorophosphate according to claim 6, characterized in that: In step 2.1, the sodium dihydrogen phosphate synthesis solution is heated to 110-115°C and stirred and concentrated until the solution specific gravity is 1.55-1.

6.

8. The method for preparing battery-grade sodium hexafluorophosphate according to claim 7, characterized in that: In step 2.2, the centrifugation speed is 1000-1500 rpm, the centrifugation time is 20-30 minutes, and an appropriate amount of hot water at 80℃ or above is added for washing.

9. A battery-grade sodium hexafluorophosphate, characterized in that: It is prepared by the method described in any one of claims 1-8.

10. An energy storage battery, characterized in that: It is prepared using the battery-grade sodium hexafluorophosphate described in claim 9.

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