A kind of preparation method of sodium difluorophosphate

Abstract

The present invention relates to a method for preparing sodium difluorophosphate, comprising the following steps: 1) reacting sodium fluoride, phosphorus pentoxide and hydrogen fluoride gas in a reaction vessel with supercritical carbon dioxide fluid as a dispersion medium; or reacting sodium hydrogen fluoride and phosphorus pentoxide in a reaction vessel with supercritical carbon dioxide fluid as a dispersion medium; 2) the generated sodium difluorophosphate is insoluble in the supercritical carbon dioxide fluid, and after the reaction is completed, the supercritical carbon dioxide fluid is discharged from the reaction vessel to obtain sodium difluorophosphate solid. The purity of the sodium difluorophosphate generated by the reaction is detected to be above 99%, and the yield is above 89%. The method for preparing sodium difluorophosphate provided by the present invention is simple to operate, has high reaction efficiency, high utilization rate of reaction raw material elements, high purification efficiency, and is green and environmentally friendly, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention relates to a preparation method of sodium difluorophosphate and belongs to the technical field of battery electrolyte. Background Art

[0002] Since the advent of lithium-ion batteries, they have not only been widely used in portable electronic devices, but also have been increasingly valued in power batteries and large-scale energy storage systems. However, the scarcity and uneven geographical distribution of lithium resources have limited the development of lithium-ion batteries to a certain extent. Therefore, it is inevitable to find a substitute for lithium. Since sodium and lithium have similar physical and chemical properties, are abundant in the earth's crust and are inexpensive, sodium-ion batteries are also energy storage batteries with great development potential.

[0003] The working principle and structure of sodium-ion batteries are highly similar to those of lithium-ion batteries. Their energy density is close to or exceeds that of lithium iron phosphate batteries, and their low-temperature performance, cycle performance, and fast charge and discharge performance are better than those of lithium-ion batteries. At the same time, the global sodium resources are abundant, cheaper, and more environmentally friendly. Therefore, sodium-ion batteries are very promising as an alternative technology to lithium-ion batteries. Due to the severe limitations of lithium resources in the future, sodium-ion batteries will be more widely used in the energy storage and electric vehicle markets. Overall, the prospects for sodium-ion batteries as energy storage batteries are still very promising. Therefore, it is necessary to develop new battery electrolytes and electrolyte additives for the development and development of sodium-ion batteries.

[0004] Sodium difluorophosphate, with the molecular formula of NaPO2F2, is a white powdery solid. It is used in the field of sodium ion batteries. As an electrolyte additive, it can reduce impedance and improve the battery's cycle performance and high-temperature storage performance. At present, there are two main methods for preparing sodium difluorophosphate. One is the solid phase method: specifically, sodium fluoride and phosphorus pentoxide solid are heated in a sealed tank. This method has simple reaction components, but the yield of the target product sodium difluorophosphate is low, only 10-20%, and the reaction conditions are difficult to control, and the energy consumption is relatively high; the other is the direct reaction method: specifically, difluorophosphoric acid is used to directly react with oxygen-containing sodium salt to generate sodium difluorophosphate. This method has a higher yield of sodium difluorophosphate than the solid phase method, but difluorophosphoric acid is unstable and highly toxic, and has high requirements for production equipment, and produces more industrial wastewater, which is not conducive to environmental protection. Summary of the invention

[0005] The invention aims to provide a method for preparing sodium difluorophosphate, so as to solve the problems of low yield, low utilization rate of raw materials, complicated purification steps and long production time in the prior art for preparing sodium difluorophosphate.

[0006] In order to achieve the above object, the technical scheme of a method for preparing sodium difluorophosphate in the present invention is:

[0007] A method for preparing sodium difluorophosphate comprises the following steps:

[0008] 1) reacting sodium fluoride, phosphorus pentoxide and hydrogen fluoride gas in a reaction vessel with supercritical carbon dioxide fluid as a dispersion medium; or reacting sodium hydrogen fluoride and phosphorus pentoxide in a reaction vessel with supercritical carbon dioxide fluid as a dispersion medium;

[0009] 2) The generated sodium difluorophosphate is insoluble in supercritical carbon dioxide fluid. After the reaction is completed, the supercritical carbon dioxide fluid is discharged from the reaction container to obtain sodium difluorophosphate solid.

[0010] The beneficial effect of the above technical scheme is that the present invention uses supercritical carbon dioxide fluid (SCO2) as a reaction solvent, utilizes its dispersibility, makes sodium fluoride or sodium hydrogen fluoride and phosphorus pentoxide solid uniformly dispersed in the supercritical fluid, reacts more thoroughly, significantly improves the efficiency of the reaction, and significantly improves the yield. The generated sodium difluorophosphate is insoluble in the supercritical carbon dioxide fluid, and the byproduct water can be removed by the supercritical carbon dioxide fluid after the reaction is completed, and the obtained sodium difluorophosphate solid product has high purity.

[0011] Specifically, the use of carbon dioxide (CO2) supercritical fluid is beneficial to protect sodium difluorophosphate from hydrolysis, and the fluid can carry away excess reactant hydrogen fluoride and reaction byproduct water, further improving the purity of the sodium difluorophosphate product.

[0012] As a further improvement, in step 1), the sodium fluoride and phosphorus pentoxide are dispersed in a supercritical carbon dioxide fluid, and hydrogen fluoride gas is introduced to carry out a fluorination reaction.

[0013] The beneficial effect of the above technical solution is that: the present invention firstly evenly disperses sodium fluoride and phosphorus pentoxide solids in supercritical carbon dioxide fluid, and then introduces hydrogen fluoride gas to carry out fluorination reaction, so that the overall reaction is more thorough and the raw material utilization rate is high.

[0014] More specifically, the entire reaction is carried out in a closed reaction vessel. After the reaction is completed, the CO2 supercritical fluid is discharged from the closed reaction vessel to remove the fluid, and new supercritical carbon dioxide fluid is continuously introduced into the reaction vessel. The new fluid helps to ensure that the original pressure in the reactor is maintained, thereby reducing the water content in the sodium difluorophosphate, and the new fluid takes away the moisture and HF on the solid surface, further improving the purity of the sodium difluorophosphate.

[0015] As a further improvement, the molar mass ratio of hydrogen fluoride, sodium fluoride and phosphorus pentoxide is (2.2-2.4):(2-2.05):1.

[0016] The beneficial effect of the above technical solution is that the amount of HF is excessive relative to sodium fluoride and phosphorus pentoxide during the reaction, which helps to further ensure the yield of sodium difluorophosphate, and the excess HF will be taken out by the CO2 supercritical fluid. After gas-liquid separation, the unreacted HF can continue to participate in a new round of preparation of sodium difluorophosphate, without causing a waste of cost.

[0017] As a further improvement, the molar mass ratio of sodium bifluoride to phosphorus pentoxide is (2-2.05):1.

[0018] As a further improvement, the reaction temperature is 30-40° C. and the pressure is 10-30 MPa.

[0019] Those skilled in the art will understand that when SCO2 is used as a solvent, the required conditions are: the reaction environment is maintained above the critical temperature (31.1°C) and critical pressure (7.9MPa) of CO2. Preferably, the reaction temperature is 30-40°C and the pressure is 10-30MPa. Further, the reaction temperature is 35-40°C and the pressure is 10-20MPa.

[0020] As a further improvement, the preparation method includes reducing the pressure and cooling the discharged supercritical carbon dioxide fluid to obtain liquid water, gaseous hydrogen fluoride and gaseous carbon dioxide.

[0021] The beneficial effect of the above technical solution is that after the reaction is completed, the supercritical carbon dioxide fluid is discharged from the reaction system, the CO2 supercritical fluid is converted into a gaseous state by reducing pressure and cooling, and the by-product water is separated and collected, laying the foundation for the subsequent separation of unreacted hydrogen fluoride.

[0022] As a further improvement, the decompression is to reduce the pressure of the fluid to 0-1 MPa, and the cooling is to reduce the temperature of the fluid to 0-30°C.

[0023] As a further improvement, the gaseous hydrogen fluoride and gaseous carbon dioxide are cooled to obtain liquid hydrogen fluoride and gaseous carbon dioxide.

[0024] The beneficial effect of the above technical solution is that the obtained gaseous hydrogen fluoride and carbon dioxide are further cooled to below the boiling point of hydrogen fluoride (19°C), hydrogen fluoride (HF) is liquefied, liquid HF and gaseous CO2 are obtained, and the gas and liquid are separated. After the reaction is completed, the unreacted product is reused, which can reduce the production cost of sodium difluorophosphate and is green and environmentally friendly.

[0025] As a further improvement, the cooling is to lower the temperature to below the boiling point of hydrogen fluoride.

[0026] The beneficial effect of the above technical solution is that lowering the temperature to below the boiling point of hydrogen fluoride facilitates the separation of carbon dioxide and HF, which is beneficial to the reuse of HF that does not participate in the reaction.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The raw material selection of the preparation method of sodium difluorophosphate of the present invention proposes two schemes, scheme one: sodium fluoride, phosphorus pentoxide solid and HF gas are used as raw materials, SCO2 is used as a reaction solvent, and its gas dispersibility is used to make sodium fluoride and phosphorus pentoxide solid uniformly dispersed in a supercritical fluid, and the fluorinating agent HF is more fully in contact with it, and the reaction is more thorough, and the yield is higher; scheme two: sodium bifluoride and phosphorus pentoxide solid are used, and SCO2 is used as a reaction solvent, and its gas dispersibility is used to make sodium bifluoride and phosphorus pentoxide solid uniformly dispersed in a supercritical fluid for reaction. The byproduct water of the two schemes can be removed by fluid to obtain sodium difluorophosphate solid, and the product purity is high, and there is no need for subsequent complex purification and separation (such as: filtration, etc.) process, the operation steps are simplified, and the preparation time is shortened. In addition, the cost of sodium fluoride or sodium bifluoride, phosphorus pentoxide and HF used in the present invention is low, the element utilization rate of the reaction raw materials in the reaction process is high, and the byproduct is only water, and no other byproducts of the main elements of the reaction raw materials are wasted. At the same time, in the present invention, excess HF or HF decomposed by thermal decomposition of sodium bifluoride is taken out by SCO2, and after gas-liquid separation, the unreacted HF is reused, which can reduce the production cost of sodium difluorophosphate and is green and environmentally friendly. DETAILED DESCRIPTION

[0029] The preparation method of sodium difluorophosphate of the present invention comprises the following steps:

[0030] 1) reacting sodium fluoride, phosphorus pentoxide and hydrogen fluoride gas in a reaction vessel with supercritical carbon dioxide fluid as a dispersion medium; or reacting sodium hydrogen fluoride and phosphorus pentoxide in a reaction vessel with supercritical carbon dioxide fluid as a dispersion medium;

[0031] 2) The generated sodium difluorophosphate is insoluble in supercritical carbon dioxide fluid. After the reaction is completed, the supercritical carbon dioxide fluid is discharged from the reaction container to obtain sodium difluorophosphate solid.

[0032] The reaction principle is:

[0033] 2NaF+2HF+P2O5→2NaPO2F2+H2O or 2NaHF2+P2O5→2NaPO2F2+H2O.

[0034] Specifically, the preparation method comprises the following steps:

[0035] 1) Sodium fluoride and phosphorus pentoxide are added to a reactor, carbon dioxide gas is introduced, the temperature and pressure are increased to a supercritical state, stirring is started to fully mix the materials to obtain a dispersed system, excess HF gas is introduced into the reactor through a high-pressure pump, and the reaction is carried out under heat preservation and pressure under stirring conditions; or sodium hydrogen fluoride and phosphorus pentoxide are added to a reactor, carbon dioxide gas is introduced, the temperature and pressure are increased to a supercritical state, and the reaction is carried out under heat preservation and pressure under stirring conditions; the reaction temperature is 35-40°C, the pressure is 10-20MPa, and the reaction time is 1.5-3h. After the reaction is completed, stirring is stopped, the solid is at the bottom layer, and the upper layer fluid is pumped into the separation kettle through a pipeline, and the reactor continuously introduces new fluid to take away the surface moisture of the solid and excess HF into the separation kettle, which also has the effect of purification, and then the valves of the reactor and the separation kettle are disconnected, and the reactor is cooled to room temperature and pressure to collect the product.

[0036] Supercritical carbon dioxide, water, and unreacted hydrogen fluoride are in the separation kettle. Open the pressure relief valve and cooling circulating water to reduce the temperature and pressure to 19-30°C and 0.1Mpa. Carbon dioxide becomes gaseous and HF is gaseous. Liquid water is discharged from the separation kettle from the bottom. The separation kettle is then cooled to <19°C to convert hydrogen fluoride into liquid, which is then discharged and collected.

[0037] 1. Specific embodiment of a method for preparing sodium difluorophosphate

[0038] Example 1

[0039] The preparation method of the sodium difluorophosphate of the present embodiment adopts the following steps:

[0040] After the reaction-extraction system is replaced with high-purity CO2 gas for multiple times, 42g sodium fluoride and 71g phosphorus pentoxide are added to the reactor, carbon dioxide gas is introduced to increase the temperature and pressure to 40°C and 10MPa, and stirring is started to fully mix the materials for 0.8h; 24g HF gas is introduced into the reactor through a high-pressure pump, and the reaction is carried out for 2h under stirring conditions at a temperature and pressure of 40°C and 10MPa; after the reaction is completed, stirring is stopped, the solid is at the bottom, the upper fluid is pumped into the separation kettle through a pipeline, and the reactor is continuously introduced with new fluid to take away the surface moisture of the solid and the excess HF into the separation kettle, which also plays a purification effect, and then the reactor and the separation kettle valve are disconnected, and the reactor is cooled to room temperature and pressure to collect the product. 119.3g of sodium difluorophosphate with a purity of 99.8% is obtained in the reactor, and the yield is 96%.

[0041] The fluid is pumped into the separation kettle, the pressure relief valve and the cooling circulating water are opened, the temperature and pressure are reduced to 30°C and 0.1MPa, the water is discharged, and the temperature is then reduced to 5°C and 0.1MPa to liquefy the hydrogen fluoride, and the hydrogen fluoride liquid is discharged and collected.

[0042] Example 2

[0043] The preparation method of the sodium difluorophosphate of the present embodiment adopts the following steps:

[0044] After the reaction-extraction system is replaced with high-purity CO2 gas for multiple times, 42g sodium fluoride and 71g phosphorus pentoxide are added to the reactor, carbon dioxide gas is introduced to increase the temperature and pressure to 35°C and 20MPa, and stirring is started to fully mix the materials for 0.5h; 22g HF gas is introduced into the reactor through a high-pressure pump, and the reaction is kept at a temperature and pressure of 35°C and 20MPa under stirring conditions for 1.1h; after the reaction is completed, stirring is stopped, the solid is at the bottom, the upper fluid is pumped into the separation kettle through a pipeline, and the reactor is continuously introduced with new fluid to take away the surface moisture of the solid and the excess HF into the separation kettle, which also plays a purification effect, and then the reactor and the separation kettle valve are disconnected, and the reactor is cooled to room temperature and pressure to collect the product. 121.1g of sodium difluorophosphate with a purity of 99.91% is obtained in the reactor, and the yield is 97.57%.

[0045] The fluid is pumped into the separation kettle, the pressure relief valve and the cooling circulating water are opened, the temperature and pressure are reduced to 30°C and 0.09MPa, the water is discharged, and then the temperature is reduced to 0°C and 0.05MPa to liquefy the hydrogen fluoride, and the hydrogen fluoride liquid is discharged and collected.

[0046] Example 3

[0047] The preparation method of the sodium difluorophosphate of the present embodiment adopts the following steps:

[0048] After the reaction-extraction system is replaced with high-purity CO2 gas for multiple times, 62g sodium bifluoride and 71g phosphorus pentoxide are added to the reactor, carbon dioxide gas is introduced to increase the temperature and pressure to 35°C and 20MPa, stirring is started to fully mix the materials and react for a total of 2h; after the reaction is completed, stirring is stopped, the solid is at the bottom, the upper fluid is pumped into the separation kettle through the pipeline, and the reactor is continuously introduced with new fluid to take away the surface moisture of the solid and HF (the hydrogen fluoride is a trace amount of hydrogen fluoride that is decomposed by sodium bifluoride and does not participate in the reaction) into the separation kettle, which also plays a purification effect, and then the reactor and the separation kettle valve are disconnected, and the reactor is cooled to normal temperature and pressure to collect the product. 112.2g of sodium difluorophosphate with a purity of 99.1% is obtained in the reactor, and the yield is 89.67%.

[0049] The fluid is pumped into the separation kettle, the pressure relief valve and the cooling circulating water are opened, the temperature and pressure are reduced to 30°C and 0.08MPa, the water is discharged, and the temperature is then reduced to 5°C and 0.06MPa to liquefy the hydrogen fluoride, and the hydrogen fluoride liquid is discharged and collected.

[0050] 2. Comparison

[0051] Comparative Example 1

[0052] The preparation method of the sodium difluorophosphate of this comparative example adopts the following steps:

[0053] 42g of sodium fluoride, 71g of phosphorus pentoxide and 1000g of dichloroethane were added to a tetrafluoroethylene reaction kettle, protected by nitrogen, stirred and heated to 35°C, 26g of HF gas was introduced into the reactor, and the reaction was carried out for 3.5h. After the reaction was completed, nitrogen was purged, the reaction liquid was filtered, and the filter cake was dried at 95°C to obtain 112.7g of sodium difluorophosphate with a purity of 93.6% and a yield of 85.1%.

[0054] 3. Experimental Examples

[0055] This experimental example tests the sodium difluorophosphate products prepared in Examples 1 to 3 and Comparative Example 1. The test results of the products of each Example and Comparative Example are shown in Table 1. The reaction product is tested by ion chromatography and nuclear magnetic resonance, and the purity is obtained by comprehensive calculation.

[0056] Table 1 Test results of sodium difluorophosphate products prepared in Examples 1 to 3 and Comparative Example 1

[0057] purity(%) Yield (%) Moisture (ppm) Free acid (ppm) Chloride ion (ppm) Sulfate (ppm) Example 1 99.8 96 62 50 0.9 0.6 Example 2 99.91 97.57 18 25 0.4 0.2 Example 3 99.1 89.67 35 32 1.1 0.9 Comparative Example 1 93.6 85.1 620 1856 6.8 0.9

[0058] In summary, the sodium difluorophosphate product prepared by the method of the present invention has high purity and low impurity content, and can meet the application requirements of sodium battery electrolyte salt or additive.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The patent protection scope of the present invention shall be based on the claims. All equivalent structural changes made using the contents of the specification of the present invention should also be included in the protection scope of the present invention.

Claims

1. A method for preparing sodium difluorophosphate, characterized in that: The following steps are involved: 1) reacting sodium fluoride, phosphorus pentoxide and hydrogen fluoride gas in a reaction vessel with supercritical carbon dioxide fluid as a dispersion medium; the molar mass ratio of hydrogen fluoride, sodium fluoride and phosphorus pentoxide is (2.2-2.4):(2-2.05):1; 2) The generated sodium difluorophosphate is insoluble in supercritical carbon dioxide fluid. After the reaction is completed, the supercritical carbon dioxide fluid is discharged from the reaction container to obtain sodium difluorophosphate solid.

2. The preparation method of sodium difluorophosphate according to claim 1, wherein: In step 1), the sodium fluoride and phosphorus pentoxide are dispersed in a supercritical carbon dioxide fluid, and hydrogen fluoride gas is introduced to carry out a fluorination reaction.

3. The preparation method of sodium difluorophosphate according to claim 1, wherein: The reaction temperature is 30-40°C and the pressure is 10-30MPa.

4. The preparation method of sodium difluorophosphate according to claim 1, wherein: The preparation method comprises reducing the pressure and cooling the discharged supercritical carbon dioxide fluid to obtain liquid water, gaseous hydrogen fluoride and gaseous carbon dioxide.

5. The preparation method of sodium difluorophosphate according to claim 4, wherein: The decompression is to reduce the pressure of the fluid to 0-1 MPa, and the cooling is to reduce the temperature of the fluid to 0-30°C.

6. The preparation method of sodium difluorophosphate according to claim 4, characterized in that: The gaseous hydrogen fluoride and gaseous carbon dioxide are cooled to obtain liquid hydrogen fluoride and gaseous carbon dioxide.

7. The preparation method of sodium difluorophosphate according to claim 6, wherein: The temperature reduction is to reduce the temperature to below the boiling point of hydrogen fluoride.