Sodium difluorophosphate as well as preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion battery electrolytes, in particular to sodium difluorophosphate and a preparation method and application thereof.The preparation method comprises the following steps that sodium hexafluorophosphate and oxide react in a non-aqueous solvent, solid-liquid separation is conducted on a product obtained after the reaction is finished, then reduced pressure distillation is conducted on filtrate, and sodium difluorophosphate is obtained; the preparation method comprises the following steps: adding sodium difluorophosphate into a reaction kettle, carrying out suction filtration after carrying out cold shock by using a non-aqueous solvent, filtering out mother liquor, washing the product by using absolute ether, and drying the obtained product to obtain white powdery sodium difluorophosphate. According to the preparation method of the sodium difluorophosphate, the reaction process is one-step reaction, the reaction does not need toxic gases such as HF, the preparation process is convenient, rapid and easy to operate, more inorganic salts can be dissolved by selecting the polar solvent, so that the reaction is more sufficient, byproducts are easy to separate, impurities are prevented from being introduced, the product purity is higher, and the method is suitable for industrial production. And the liquid product obtained after the one-step reaction can be used as the electrolyte of the sodium-ion battery after being processed, so that a direction is provided for the application of the sodium-ion battery.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion battery electrolyte, in particular to sodium difluorophosphate and a preparation method and application thereof. Background Art

[0002] At present, the emerging industry of electrochemical energy storage as renewable energy is developing rapidly like "mushrooms after rain". Among them, lithium-ion batteries have been widely used in power vehicles, 3C digital, energy storage and other fields due to their advantages of high energy density, good cycle performance, high operating voltage and long service life. With the rapid growth of market demand, the scale of lithium battery manufacturing has increased sharply. The problem that follows is that the price of lithium carbonate, the core raw material of the battery, has once soared, causing the cost of the entire battery manufacturing industry to surge. As alkali metal elements of the same main group, sodium and lithium have certain similarities in chemical properties. At the same time, sodium has a large reserve in the earth's crust, with obvious cost advantages and a safer supply chain in the future. In addition, the existing lithium-ion battery material production equipment and battery assembly production lines are fully suitable for the production of sodium-ion batteries, with broad industrialization prospects, significant economic advantages, and great significance for energy strategic deployment.

[0003] Similar to lithium-ion batteries, the main components of sodium battery electrolytes also include electrolyte salts, organic solvents and additives. However, the additives commonly used in lithium-ion battery electrolytes are not very effective in sodium batteries, especially in terms of high and low temperature performance. It has been reported that lithium difluorophosphate (molecular formula LiPO2F2) can significantly improve the high and low temperature cycle performance of lithium batteries. However, there are few reports on the synthesis method of sodium difluorophosphate.

[0004] At present, the reported methods for preparing sodium difluorophosphate are mainly divided into two categories. One is the solid phase method: it refers to the preparation method of mixing sodium fluoride and phosphorus pentoxide solids in a sealed tube and heating them. However, the yield of sodium difluorophosphate prepared by this method is low, the energy consumption is high, and the reaction is difficult to control; the other is the direct reaction method: it refers to the preparation of sodium difluorophosphate by direct reaction of sodium difluorophosphate and sodium carbonate. However, this method has the characteristics of difluorophosphoric acid being unstable, highly toxic, expensive, and difficult to obtain high-purity raw materials, which is not conducive to industrial production.

[0005] Chinese patent CN115947351A discloses a method for co-producing sodium hexafluorophosphate and sodium difluorophosphate. However, the process first requires anhydrous hydrofluoric acid to react with phosphorus, then generate phosphorus oxyfluoride with fuming sulfuric acid, and then generate sodium difluorophosphate by reacting phosphorus oxyfluoride with a sodium source and silicon oxide. The whole process is complicated and cumbersome, and dangerous hydrofluoric acid and fuming sulfuric acid are used as raw materials. The whole process is not environmentally friendly. Chinese patent CN116101996A discloses a method for synthesizing sodium difluorophosphate: phosphorus pentoxide is reacted with hydrofluoric acid to generate sodium difluorophosphate and monofluorophosphate, and then difluorophosphate and monofluorophosphate are separated by purification. The selectivity of sodium difluorophosphate in this method is low, and a relatively complex purification operation is required to obtain sodium difluorophosphate suitable for battery use. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a method for preparing sodium difluorophosphate. The reaction process is a one-step reaction, and no toxic gases such as HF are required for the reaction. The preparation process is convenient, fast and easy to operate. Polar solvents are selected to dissolve more inorganic salts to make the reaction more complete, and by-products are easily separated to avoid the introduction of impurities, so that the product purity is higher. The method has low requirements on equipment, thereby reducing costs and obtaining high-purity sodium difluorophosphate.

[0007] In order to achieve the above purpose, the technical solutions provided are as follows:

[0008] A preparation method of sodium difluorophosphate, characterized in that it comprises the following steps: adding sodium hexafluorophosphate and an oxide to a non-aqueous solvent in the air and stirring for reaction, cooling the temperature after the reaction is completed, performing solid-liquid separation on the product obtained by the reaction, filtering out a small amount of insoluble matter, and then decompressing and distilling the filtrate until it becomes viscous after stirring, cold shocking with a non-aqueous solvent, and then filtering by suction, so that the product gradually precipitates in the form of white granular solids, filtering out the mother liquor, washing the product with anhydrous ether, and drying the obtained product to obtain white powdery sodium difluorophosphate.

[0009] Preferably, the molar ratio of the sodium hexafluorophosphate to the oxide is (1-2):1.

[0010] Preferably, the reaction temperature is 50-80° C., and the reaction time is 60-120 min.

[0011] Preferably, the oxide is one of boron trioxide, aluminum trioxide, iron trioxide, phosphorus pentoxide and magnesium oxide.

[0012] Preferably, the non-aqueous solvent is: the non-aqueous solvent is any one or more combinations of diethyl ether, isopropyl ether, ethylene glycol dimethyl ether, and tetrahydrofuran.

[0013] Preferably, the ratio of the sodium hexafluorophosphate to the non-aqueous solvent is 1 mol:400-1000 mL.

[0014] Preferably, the drying conditions are: drying at 90-150° C. and a vacuum degree of 10 KPa for 5-8 hours.

[0015] The reaction chemical formula is as follows:

[0016] 2M2O3+3NaPF6→3NaPO2F2+4MF3

[0017] Wherein: M is one of B, Al and Fe.

[0018] The present invention also provides sodium difluorophosphate, which is prepared by the above preparation method, wherein the purity of the sodium difluorophosphate is ≥99.5%.

[0019] The present invention also provides a non-aqueous electrolyte battery, which comprises a positive electrode, a negative electrode and an electrolyte comprising the above-mentioned sodium difluorophosphate.

[0020] The application of the above sodium difluorophosphate in the preparation of non-aqueous electrolyte batteries.

[0021] The beneficial effects of the present invention are:

[0022] 1. The non-aqueous solvent in which the sodium salt is dissolved in the present invention is a polar solvent. Increasing the polarity of the solvent has a greater impact on the solute, can reduce the energy of the transition state, reduce the activation energy of the reaction, and has a certain solubility for inorganic salts, so that the sodium salt is more soluble in the non-aqueous solvent for sufficient reaction.

[0023] 2. In the preparation method of sodium difluorophosphate provided by the present invention, the reaction process is a one-step reaction, the reaction does not require the use of toxic gases such as HF, the preparation process is convenient, fast, and easy to operate, the selection of polar solvents can dissolve more inorganic salts to make the reaction more complete, the by-products are easy to separate, the introduction of impurities is avoided, and the product purity is higher; the equipment requirements are low, thereby reducing costs and obtaining high-purity sodium difluorophosphate.

[0024] 3. In the present invention, the added solvent can be used together with sodium difluorophosphate as an electrolyte for sodium ion batteries.

[0025] 4. The reaction of the present invention is carried out in air rather than in an inert gas, which saves costs and is simpler and easier to implement. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] At room temperature, in the air, add 44.9g (0.3mol) of NaPF6 solid to 150mL of dry dimethyl carbonate, slowly add 11.6g (0.17mol) of diboron trioxide with a solid feeder while stirring, then heat the reaction in an oil bath pot to 70°C and stir for 1 hour, then filter while hot to remove insoluble impurities. After the filtrate is concentrated under reduced pressure to remove most of the solution, add 110mL of anhydrous ether, place it in an ice water bath, cool and crystallize for about 10 minutes, and when no more crystals are precipitated, filter under reduced pressure to obtain white crystals, and dry the obtained white crystals in a vacuum drying oven with a vacuum degree of 10Kpa, set the temperature to 110 degrees Celsius, and dry for four hours to obtain white powdery sodium difluorophosphate with a purity of 99.5%.

[0029] The synthesis reaction formula of the present embodiment is as follows:

[0030] 3NaPF6+2B2O3→3NaPO2F2+4BF3↑

[0031] Figure 1 The NaDFP obtained in Example 1 of the present invention 19 F NMR spectrum.

[0032] Example 2

[0033] At room temperature, in the air, add 15.19g (0.1mol) of NaPF6 solid to 100mL of dry dimethyl carbonate, slowly add 6.79g (0.067mol) of aluminum oxide with a solid feeder while stirring, then heat the reaction in an oil bath to 70°C and stir for 1 hour, then filter while hot to remove insoluble impurities. After the filtrate is concentrated under reduced pressure to remove most of the solution, add 110mL of anhydrous ether, place it in an ice-water bath, cool and crystallize for 10min, then filter to obtain white crystals, and dry the obtained product in a vacuum drying oven at 140°C and a vacuum degree of 10Kpa for 6 hours to obtain sodium difluorophosphate in white powder form.

[0034] The synthesis reaction formula of the present embodiment is as follows:

[0035] 2NaPF6+3Al2O3→3NaPO2F2+4AlF3

[0036] Example 3

[0037] At room temperature, in the air, add 134.4g (0.8mol) of NaPF6 solid to 300mL of dry dimethyl carbonate, slowly add 48 (0.5mol) of ferric oxide with a solid feeder while stirring, then heat the reaction in an oil bath pot to 70°C and stir for 1 hour, then filter while hot to remove insoluble impurities. After the filtrate is concentrated under reduced pressure to remove most of the solution, add 110mL of anhydrous ether, place it in an ice-water bath, cool and crystallize for 10min, then filter to obtain white crystals, and dry the obtained product in a vacuum drying oven at 140°C and a vacuum degree of 10Kpa for 6 hours to obtain white powdery sodium difluorophosphate.

[0038] The synthesis reaction formula of the present embodiment is as follows:

[0039] 2NaPF6+3Fe2O3→3NaPO2F2+4FeF3

[0040] By comparing Example 1, Example 2 and Example 3, the reaction byproduct in Example 1 is BF3 gas, which makes it easier to observe the reaction and is easy to separate, thus simplifying the experimental operation.

[0041] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for preparing sodium difluorophosphate, characterized in that, The method comprises the following steps: adding sodium hexafluorophosphate and oxide into a non-aqueous solvent in the air and stirring for reaction; cooling the mixture to room temperature after the reaction is completed; performing solid-liquid separation on the product obtained by the reaction; filtering off a small amount of insoluble matter; performing reduced pressure distillation on the filtrate until it becomes viscous after stirring; performing cold shock with a non-aqueous solvent; and performing suction filtration, wherein the product gradually precipitates in the form of white granular solid; filtering off the mother liquor; washing the product with anhydrous ether; and drying the obtained product to obtain white powdery sodium difluorophosphate.

2. A method for preparing sodium difluorophosphate according to claim 1, characterized in that: The molar ratio of the sodium hexafluorophosphate to the oxide is (1-2):

1.

3. A method for preparing sodium difluorophosphate according to claim 1, characterized in that: The reaction temperature is 50-80°C, and the reaction time is 60-120 minutes.

4. A method for preparing sodium difluorophosphate according to claim 1, characterized in that: The oxide is one of boron trioxide, aluminum trioxide, iron trioxide, phosphorus pentoxide and magnesium oxide.

5. A method for preparing sodium difluorophosphate according to claim 1, characterized in that: The non-aqueous solvent is any one or more of diethyl ether, isopropyl ether, ethylene glycol dimethyl ether and tetrahydrofuran.

6. A method for preparing sodium difluorophosphate according to claim 1, characterized in that: The ratio of the sodium hexafluorophosphate to the non-aqueous solvent is 1 mol:400-1000 mL.

7. A method for preparing sodium difluorophosphate according to claim 1, characterized in that: The drying conditions are: drying at 90-150° C. and a vacuum degree of 10 KPa for 5-8 hours.

8. Sodium difluorophosphate, which is prepared by the preparation method according to any one of claims 1 to 7, wherein: The purity of the sodium difluorophosphate is ≥99.5%. 9 . A non-aqueous electrolyte battery comprising a positive electrode, a negative electrode and an electrolyte comprising the sodium difluorophosphate according to claim 8 .

10. Use of the sodium difluorophosphate according to claim 8 in the preparation of non-aqueous electrolyte batteries.

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