Preparation method of sodium hexafluorophosphate and sodium ion battery electrolyte

Abstract

The invention provides a preparation method of sodium hexafluorophosphate and a sodium-ion battery electrolyte in order to solve the problems that reaction conditions are harsh and chlorine-containing impurities are introduced when phosphorus pentachloride and hydrofluoride are used for preparing sodium hexafluorophosphate in the prior art. The preparation method comprises the following operation steps: synthesis of sodium hexafluorophosphate: introducing phosphorus pentafluoride gas into a hydrogen fluoride solution of sodium hydrogenfluoride, and reacting to obtain the hydrogen fluoride solution of sodium hexafluorophosphate; and solvent removal: distilling the hydrogen fluoride solution of sodium hexafluorophosphate to remove hydrogen fluoride and unreacted phosphorus pentafluoride to obtain sodium hexafluorophosphate. The preparation method provided by the invention can effectively reduce side reactions of the system, avoid introduction of impurities, and effectively improve the yield and purity of sodium hexafluorophosphate.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and specifically relates to a preparation method of sodium hexafluorophosphate and an electrolyte for sodium-ion batteries. Background Art

[0002] In the 21st century, lithium batteries are applied in many fields such as mobile phones, computers, wearable devices, electric vehicles, two-wheeled bicycles, power tools, street lamps, etc.

[0003] In contrast, sodium is widely sourced, abundant in reserves, and the sodium reserve is 420 times that of lithium, with a price much lower than that of lithium. In recent years, with the crazy rise in lithium prices, sodium-ion batteries are expected to receive wide attention for their cost 30 - 50% lower than that of lithium-ion batteries, especially in the fields of energy storage, hybrid power, and replacing lead-acid batteries, where sodium-ion batteries have attractive application prospects.

[0004] As a key material for sodium-ion batteries, sodium salts are the main factors determining the ionic conductivity and stability of the electrolyte. Among them, sodium hexafluorophosphate is widely used. In the existing preparation methods of sodium hexafluorophosphate, as described in Patent CN202210584178.X, phosphorus pentachloride reacts with hydrogen fluoride salts in a carbonate solvent to prepare sodium hexafluorophosphate. This preparation method has certain defects, mainly including: the applicable temperature window of the reaction is small, with little reaction occurring at too low temperatures, and serious side reactions occurring above 60°C. At the same time, this reaction needs to be carried out under negative pressure to remove the reaction products, and the reaction between phosphorus pentachloride and hydrogen fluoride salts is exothermic, easily causing local high temperatures, resulting in the decomposition of the generated sodium hexafluorophosphate. Moreover, using carbonate as the solvent causes side reactions between phosphorus pentachloride and the solvent at high temperatures, affecting the product purity. In addition, the chlorine-containing products generated by the reaction, such as hydrogen chloride, are difficult to completely remove, introducing chlorine-containing impurities into sodium hexafluorophosphate and affecting the battery performance. Summary of the Invention

[0005] Aiming at the problems of harsh reaction conditions and introduction of chlorine-containing impurities in the existing preparation of sodium hexafluorophosphate using phosphorus pentachloride and hydrogen fluoride salts, the present invention provides a preparation method of sodium hexafluorophosphate and an electrolyte for sodium-ion batteries.

[0006] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0007] On the one hand, the present invention provides a preparation method of sodium hexafluorophosphate, including the following operating steps:

[0008] Synthesis of sodium hexafluorophosphate: Pass phosphorus pentafluoride gas into a hydrogen fluoride solution of sodium hydrogen fluoride to obtain a hydrogen fluoride solution of sodium hexafluorophosphate;

[0009] Removing the solvent: The hydrogen fluoride solution of sodium hexafluorophosphate is distilled to remove hydrogen fluoride and unreacted phosphorus pentafluoride, obtaining sodium hexafluorophosphate.

[0010] Optionally, in the synthesis operation of sodium hexafluorophosphate, the reaction temperature is -20°C to 20°C.

[0011] Optionally, in the synthesis operation of sodium hexafluorophosphate, the molar amount of phosphorus pentafluoride gas introduced is 1 to 1.2 times the molar amount of sodium hydrogen fluoride.

[0012] Optionally, the synthesis operation of sodium hexafluorophosphate is carried out in a protective atmosphere.

[0013] Optionally, in the hydrogen fluoride solution of sodium hydrogen fluoride, the mass percentage content of sodium hydrogen fluoride is 10% to 50%.

[0014] Optionally, in the synthesis operation of sodium hexafluorophosphate, the feeding rate of phosphorus pentafluoride gas is 3 to 3000 L / min. After the phosphorus pentafluoride gas is completely introduced, the reaction continues for 0 to 10 h.

[0015] Optionally, in the solvent removal operation, the method of vacuum distillation is adopted, the treatment temperature is 20 to 80°C, and the pressure is -0.06 to -0.1 MPa.

[0016] Optionally, the phosphorus pentafluoride gas is prepared by the following method:

[0017] Phosphorus pentoxide and anhydrous hydrogen fluoride are mixed and introduced into a reaction kettle, where the mass ratio of phosphorus pentoxide to hydrogen fluoride is 1:(2.6 - 2.9), the reaction temperature is 0 to 30°C, the reaction time is 2 to 6 h, the reaction pressure is 0.1 to 0.5 Mpa. After the reaction, fuming sulfuric acid is added to the kettle, and then the reaction kettle is heated to 120°C to 200°C to obtain a mixed gas of phosphorus pentafluoride and hydrogen fluoride. The mixed gas is separated by rectification, controlling the feeding temperature at 5°C to 35°C and the top pressure at 0.06 to 0.50 MPa to obtain phosphorus pentafluoride gas.

[0018] On the other hand, the present invention provides a sodium-ion battery electrolyte, including a non-aqueous organic solvent and sodium hexafluorophosphate, and the sodium hexafluorophosphate is prepared by the preparation method as described above.

[0019] According to the preparation method of sodium hexafluorophosphate provided by the present invention, phosphorus pentafluoride gas and sodium hydrogen fluoride are used as reactants. Phosphorus pentafluoride can directly react with sodium hydrogen fluoride to generate sodium hexafluorophosphate and hydrogen fluoride, and this reaction has a low dependence on temperature. Even under the condition of -20°C, the reaction can still proceed, which is conducive to carrying out the reaction in a low-temperature environment. The low-temperature reaction further improves the stability of the generated sodium hexafluorophosphate, avoiding decomposition at high temperatures. The by-products generated by this reaction are relatively single, only including hydrogen fluoride. Hydrogen fluoride has a low boiling point and can be removed by distillation, effectively avoiding the introduction of chlorine-containing impurities, and having a high yield and product purity. At the same time, hydrogen fluoride is used as the reaction system solution. As one of the reaction products, hydrogen fluoride as a solvent will not introduce new impurities or cause other side reactions to occur, and is removed by distillation together with the generated hydrogen fluoride in the later stage of the preparation process, reducing the production difficulty, and the separated hydrogen fluoride can be reused. Part of the hydrogen fluoride generated by the reaction can be used for the synthesis of raw material phosphorus pentafluoride, thereby realizing the co-production of sodium hexafluorophosphate and phosphorus pentafluoride and the recycling of by-products. Detailed implementation mode

[0020] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0021] An embodiment of the present invention provides a preparation method of sodium hexafluorophosphate, including the following operation steps:

[0022] Synthesis of sodium hexafluorophosphate: Introduce phosphorus pentafluoride gas into the hydrogen fluoride solution of sodium hydrogen fluoride, and react to obtain the hydrogen fluoride solution of sodium hexafluorophosphate;

[0023] Removing the solvent: Distill the hydrogen fluoride solution of sodium hexafluorophosphate to remove hydrogen fluoride and unreacted phosphorus pentafluoride to obtain sodium hexafluorophosphate.

[0024] Using phosphorus pentafluoride gas and sodium hydrogen fluoride as reactants, phosphorus pentafluoride can directly react with sodium hydrogen fluoride to form sodium hexafluorophosphate and hydrogen fluoride. This reaction has a low dependence on temperature and can still proceed even under the condition of -20°C, which is conducive to carrying out the reaction in a low-temperature environment. The low-temperature reaction further improves the stability of the generated sodium hexafluorophosphate, avoiding decomposition at high temperatures. The by-products generated by this reaction are relatively single, only including hydrogen fluoride. Hydrogen fluoride has a low boiling point and can be removed by distillation, effectively avoiding the introduction of chlorine-containing impurities, and has a high yield and product purity. At the same time, hydrogen fluoride is used as the reaction system solution. As one of the reaction products, hydrogen fluoride as the solvent will not introduce new impurities or cause other side reactions to occur, and is distilled off together with the generated hydrogen fluoride in the later stage of the preparation process, reducing the production difficulty, and the separated hydrogen fluoride can be reused. Part of the hydrogen fluoride generated by the reaction can be used for the synthesis of raw material phosphorus pentafluoride, thus realizing the co-production of sodium hexafluorophosphate and phosphorus pentafluoride and achieving the recycling of by-products.

[0025] In some embodiments, in the synthesis operation of the sodium hexafluorophosphate, the reaction temperature is -20°C to 20°C.

[0026] In the preparation method of this sodium hexafluorophosphate, a lower reaction temperature is adopted, aiming to inhibit the occurrence of side reactions and the thermal decomposition of the generated sodium hexafluorophosphate, thereby being conducive to improving the yield and purity of sodium hexafluorophosphate.

[0027] In some embodiments, in the synthesis operation of the sodium hexafluorophosphate, the molar amount of the introduced phosphorus pentafluoride gas is 1 to 1.2 times the molar amount of sodium hydrogen fluoride.

[0028] In a specific embodiment, in the synthesis operation of the sodium hexafluorophosphate, the molar amount of the introduced phosphorus pentafluoride gas can be 1 time, 1.02 times, 1.05 times, 1.08 times, 1.1 times, 1.15 times or 1.2 times the molar amount of sodium hydrogen fluoride.

[0029] In this preparation method, the reaction between the phosphorus pentafluoride gas and the sodium hydrogen fluoride is relatively easy to carry out. Therefore, using an equivalent amount of phosphorus pentafluoride gas can achieve the reaction with most of the sodium hydrogen fluoride. In some cases, since it is difficult to remove sodium hydrogen fluoride from the system by distillation, if there is residual sodium hydrogen fluoride in this reaction, it will cause impurities of sodium hydrogen fluoride to remain in the finally obtained sodium hexafluorophosphate. Therefore, in a preferred embodiment, more than 1-fold equivalent of phosphorus pentafluoride gas is used to react with sodium hydrogen fluoride to prepare sodium hexafluorophosphate to ensure the full reaction of sodium hydrogen fluoride; in a more preferred embodiment, the introduced amount of phosphorus pentafluoride gas is less than 1.2-fold equivalent. When the introduced amount of phosphorus pentafluoride gas exceeds 1.2-fold equivalent, there is no obvious improvement in the product yield and purity, but it will correspondingly increase the raw material cost and the subsequent separation difficulty.

[0030] In some embodiments, the synthesis operation of sodium hexafluorophosphate is carried out in a protective atmosphere.

[0031] The protective atmosphere is used to prevent oxygen and carbon dioxide in the air from dissolving in the system and causing side reactions. The protective atmosphere is selected from gases that do not participate in the reaction, such as nitrogen or inert gases.

[0032] In some embodiments, in the hydrofluoric acid solution of sodium hydrogen fluoride, the mass percentage content of sodium hydrogen fluoride is 10% - 50%.

[0033] Theoretically, the phosphorus pentafluoride gas can react with the hydrofluoric acid solution of sodium hydrogen fluoride at any mass concentration. However, based on considerations of production economy, the mass percentage content of sodium hydrogen fluoride can be limited within the above range to reduce the usage amount of hydrofluoric acid and the energy consumption for subsequent distillation to remove the solvent.

[0034] In some embodiments, in the synthesis operation of sodium hexafluorophosphate, the feeding rate of phosphorus pentafluoride gas is 3 - 3000 L / min. After the phosphorus pentafluoride gas is completely fed, the reaction continues for 0 - 10 h.

[0035] If the feeding rate of phosphorus pentafluoride gas is low, it will affect the production efficiency; if the feeding rate of phosphorus pentafluoride gas is high, it is easy to cause the reaction to be too violent, resulting in local overheating problems, and the phosphorus pentafluoride gas volatilizes without reaction, affecting the purity of the reaction product.

[0036] In some embodiments, in the solvent removal operation, the method of vacuum distillation is adopted, the treatment temperature is 20 - 80 °C, and the pressure is -0.06 - -0.1 MPa.

[0037] The boiling points of the generated hydrogen fluoride and the unreacted phosphorus pentafluoride are both relatively low, and distillation can be carried out at a relatively low temperature, thereby avoiding the decomposition of sodium hexafluorophosphate at high temperatures. At the same time, the boiling point of hydrogen fluoride can be further reduced by the method of vacuum distillation, thereby reducing the distillation temperature required and realizing the protection of sodium hexafluorophosphate.

[0038] In some embodiments, the phosphorus pentafluoride gas is prepared by the following method:

[0039] Phosphorus pentoxide and anhydrous hydrogen fluoride are mixed and introduced into a reaction kettle, where the mass ratio of phosphorus pentoxide to hydrogen fluoride is 1:(2.6 - 2.9), the reaction temperature is 0 - 30°C, the reaction time is 2 - 6 h, the reaction pressure is 0.1 - 0.5 Mpa. After the reaction, fuming sulfuric acid is added to the kettle, and then the reaction kettle is heated to 120°C - 200°C to obtain a mixed gas of phosphorus pentafluoride and hydrogen fluoride. The mixed gas is separated by distillation, controlling the feed temperature at 5°C - 35°C and the top pressure at 0.06 - 0.50 Mpa to obtain phosphorus pentafluoride gas.

[0040] Another embodiment of the present invention provides a sodium-ion battery electrolyte, including a non-aqueous organic solvent and sodium hexafluorophosphate, and the sodium hexafluorophosphate is prepared by the preparation method as described above.

[0041] In some embodiments, the non-aqueous organic solvent includes at least one of carbonates, carboxylates, and ethers;

[0042] Preferably, the carbonates include cyclic or chain carbonates with 3 - 5 carbon atoms. The cyclic carbonates include at least one of ethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, propylene carbonate, γ-butyrolactone, and butylene carbonate; the chain carbonates include at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate;

[0043] The carboxylates include carboxylates with 2 - 6 carbon atoms, and the carboxylates include at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and propyl propionate;

[0044] The ethers include cyclic ethers or chain ethers with 4 - 10 carbon atoms. The cyclic ethers include at least one of 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran; the chain ethers include at least one of dimethoxymethane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether;

[0045] Based on the mass of the electrolyte being 100%, the mass percentage content of the non-aqueous organic solvent is 70% - 95%.

[0046] The present invention is further illustrated by the following examples.

[0047] Example 1

[0048] This example is used to illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including the following operating steps:

[0049] At -10°C, in a nitrogen atmosphere, 300 g of sodium hydrogen fluoride is dissolved in 700 g of anhydrous hydrogen fluoride to prepare a 30% hydrogen fluoride solution of sodium hydrogen fluoride. The temperature is maintained at -10°C, and 1.0 equivalent of purified phosphorus pentafluoride gas is introduced. The feeding rate of phosphorus pentafluoride is 10 L / min. After the gas feeding is completed, the reaction continues for 2 h. The filter residue is filtered, and the filtrate is concentrated under reduced pressure to remove phosphorus pentafluoride and hydrogen fluoride. The distillation temperature is 30°C, and the pressure is -0.09 MPa to obtain pure sodium hexafluorophosphate.

[0050] Example 2

[0051] This example is used to illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including most of the operation steps in Example 1. The difference is that:

[0052] The feeding amount of phosphorus pentafluoride gas is 1.03 equivalents.

[0053] Example 3

[0054] This example is used to illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including most of the operation steps in Example 1. The difference is that:

[0055] The feeding amount of phosphorus pentafluoride gas is 1.05 equivalents.

[0056] Example 4

[0057] This example is used to illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including most of the operation steps in Example 1. The difference is that:

[0058] The feeding amount of phosphorus pentafluoride gas is 1.1 equivalents.

[0059] Example 5

[0060] This example is used to illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including most of the operation steps in Example 1. The difference is that:

[0061] The feeding amount of phosphorus pentafluoride gas is 1.2 equivalents.

[0062] Example 6

[0063] This example is used to illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including most of the operation steps in Example 1. The difference is that:

[0064] The temperature of the reaction system is maintained at 10°C.

[0065] Example 7

[0066] This example is used to illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including most of the operation steps in Example 6, and the differences are as follows:

[0067] The feeding amount of phosphorus pentafluoride gas is 1.03 times equivalent.

[0068] Example 8

[0069] This example is used to illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including most of the operation steps in Example 6, and the differences are as follows:

[0070] The feeding amount of phosphorus pentafluoride gas is 1.05 times equivalent.

[0071] Example 9

[0072] This example is used to illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including most of the operation steps in Example 6, and the differences are as follows:

[0073] The feeding amount of phosphorus pentafluoride gas is 1.1 times equivalent.

[0074] Example 10

[0075] This example is used to illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including most of the operation steps in Example 6, and the differences are as follows:

[0076] The feeding amount of phosphorus pentafluoride gas is 1.2 times equivalent.

[0077] Comparative Example 1

[0078] This comparative example is used to comparatively illustrate the preparation method of sodium hexafluorophosphate disclosed in the present invention, including most of the operation steps in Example 1, and the differences are as follows:

[0079] Phosphorus pentachloride powder is used to replace phosphorus pentafluoride gas;

[0080] The phosphorus pentachloride powder is equally divided into ten portions and added to the hydrofluoric acid solution of sodium hydrogen fluoride at intervals for reaction.

[0081] Performance Test

[0082] The prepared sodium hexafluorophosphate is subjected to purity test and yield calculation, and the test results are filled in Table 1.

[0083] Table 1

[0084]

[0085]

[0086] From the test results of Examples 1-5, it can be seen that when the reaction temperature is -10°C, as the molar ratio of sodium bifluoride to phosphorus pentafluoride increases, both the purity and yield of sodium hexafluorophosphate show an upward trend. When the molar ratio of sodium bifluoride to phosphorus pentafluoride is 1:1.05, it is a relatively optimal reaction condition.

[0087] From the test results of Examples 6-10, it can be seen that when the reaction temperature is 10°C, as the molar ratio of sodium bifluoride to phosphorus pentafluoride increases, both the purity and yield of sodium hexafluorophosphate show an upward trend. When the molar ratio of sodium bifluoride to phosphorus pentafluoride is 1:1.10, it is a relatively optimal reaction condition.

[0088] By comparing the test results of Example 3 and Example 8, it can be seen that with the same feed ratio, the higher the temperature, the lower the purity. The possible reason is that the higher the temperature, the more phosphorus pentafluoride volatilizes and is lost.

[0089] By comparing the test results of Example 1 and Comparative Example 1, it can be seen that compared with the preparation method using phosphorus pentachloride, the reaction of phosphorus pentafluoride with sodium bifluoride in the present invention can effectively improve the yield and purity of sodium hexafluorophosphate. The speculated reason is the reduction of side reactions.

[0090] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of sodium hexafluorophosphate, characterized in that, It includes the following operation steps: Synthesis of sodium hexafluorophosphate: Pass phosphorus pentafluoride gas into a hydrofluoric acid solution of sodium hydrogen fluoride, and react to obtain a hydrofluoric acid solution of sodium hexafluorophosphate; Removing the solvent: Distill the hydrofluoric acid solution of sodium hexafluorophosphate to remove hydrofluoric acid and unreacted phosphorus pentafluoride to obtain sodium hexafluorophosphate.

2. The preparation method of sodium hexafluorophosphate according to claim 1, wherein, In the synthesis operation of the sodium hexafluorophosphate, the reaction temperature is -20°C to 20°C.

3. The preparation method of sodium hexafluorophosphate according to claim 1, wherein In the synthesis operation of the sodium hexafluorophosphate, the molar amount of the introduced phosphorus pentafluoride gas is 1 to 1.2 times the molar amount of sodium hydrogen fluoride.

4. The preparation method of sodium hexafluorophosphate according to claim 1, characterized in that, The synthesis operation of the sodium hexafluorophosphate is carried out in a protective atmosphere.

5. The preparation method of sodium hexafluorophosphate according to claim 1, wherein, In the hydrofluoric acid solution of sodium hydrogen fluoride, the mass percentage content of sodium hydrogen fluoride is 10% to 50%.

6. The preparation method of sodium hexafluorophosphate according to claim 1, wherein, In the synthesis operation of the sodium hexafluorophosphate, the feeding rate of phosphorus pentafluoride gas is 3 to 3000 L / min. After the phosphorus pentafluoride gas is completely introduced, continue to react for 0 to 10 h.

7. The method for preparing sodium hexafluorophosphate according to claim 1, characterized in that, In the operation of removing the solvent, a reduced-pressure distillation method is adopted, the treatment temperature is 20 to 80°C, and the pressure is -0.06 to -0.1 MPa.

8. The method for preparing sodium hexafluorophosphate according to claim 1, characterized in that, The phosphorus pentafluoride gas is prepared by the following method: Mix phosphorus pentoxide and anhydrous hydrofluoric acid and introduce them into a reaction kettle, where the mass ratio of phosphorus pentoxide to hydrofluoric acid is 1:(2.6 to 2.9), the reaction temperature is 0 to 30°C, the reaction time is 2 to 6 h, the reaction pressure is 0.1 to 0.5 Mpa. After the reaction is completed, fuming sulfuric acid is added to the kettle, and then the reaction kettle is heated to 120°C to 200°C to obtain a mixed gas of phosphorus pentafluoride and hydrofluoric acid. The mixed gas is separated by rectification, controlling the feeding temperature at 5°C to 35°C and the top pressure at 0.06 to 0.50 MPa to obtain phosphorus pentafluoride gas.

9. A sodium-ion battery electrolyte, characterized in that, It includes a non-aqueous organic solvent and sodium hexafluorophosphate, and the sodium hexafluorophosphate is prepared by the preparation method described in any one of claims 1 to 8.

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