A process for the preparation of hexafluorophosphate

Abstract

The application relates to a preparation method of a hexafluorophosphate, and belongs to the field of battery electrolytes. The preparation method comprises the following steps: carrying out an electrolysis reaction on anhydrous HF, phosphorus powder and an alkali metal fluoride salt to generate the hexafluorophosphate. The weak fluorine is electrolyzed from the anhydrous HF, and then the weak fluorine, the phosphorus powder and the alkali metal fluoride salt are reacted to directly synthesize the hexafluorophosphate by one-pot method, so that the yield is higher and the operation is simple. Compared with the reaction of fluorine gas and elemental phosphorus, the reaction of the weak fluorine obtained by the electrolysis method and the phosphorus powder is more moderate, easy to control and high in safety.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a hexafluorophosphate, and belongs to the field of battery electrolytes. BACKGROUND

[0002] Lithium ion batteries, as a rapidly developing energy storage device, are widely used in 3C fields and power battery fields due to high energy density and excellent cycle performance. However, the service life and capacity of power batteries continue to decline in recent years, which limits the development of power batteries to some extent.

[0003] Lithium hexafluorophosphate (LiPF6) is used as an electrolyte of a lithium ion battery, and is mainly used in the fields of lithium ion power batteries, lithium ion energy storage batteries and other daily batteries, and has become one of the irreplaceable electrolytes of lithium ion batteries. At present, the synthesis of lithium hexafluorophosphate mainly adopts a hydrogen fluoride solvent method, that is, lithium fluoride dissolved in hydrogen fluoride is reacted with phosphorus pentafluoride to generate lithium hexafluorophosphate.

[0004] There are mainly three methods for preparing phosphorus pentafluoride: (1) red phosphorus is directly reacted with fluorine gas; (2) hexafluorophosphoric acid and water are generated by reacting diphosphorus pentoxide or concentrated phosphoric acid with anhydrous hydrogen fluoride, and then phosphorus pentafluoride gas is obtained by dehydrating oleum; (3) phosphorus pentafluoride or hexafluorophosphoric acid is obtained by reacting phosphorus pentachloride with anhydrous hydrogen fluoride. Among them, the reaction of red phosphorus with fluorine gas to prepare phosphorus pentafluoride is violent, difficult to control, poor in safety, and the elemental phosphorus is easy to sublimate, cannot be fully utilized, and is easy to block the pipeline. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of a hexafluorophosphate, which solves the problems of violent reaction, difficult control and poor safety in the preparation of phosphorus pentafluoride in the prior art.

[0006] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0007] A preparation method of a hexafluorophosphate, comprising the following steps: electrolyzing anhydrous HF, phosphorus powder and alkali metal fluoride salt to generate a hexafluorophosphate.

[0008] In the present application, weak fluorine is electrolyzed from anhydrous HF, and then the weak fluorine, phosphorus powder and alkali metal fluoride salt are reacted to directly synthesize a hexafluorophosphate by one-pot method, which is high in yield and simple in operation. Compared with the reaction of fluorine gas and elemental phosphorus, the reaction of weak fluorine obtained by electrolysis and phosphorus powder is more gentle, easy to control and high in safety.

[0009] In order to facilitate the electrolysis of weak fluorine from anhydrous HF and improve the reaction efficiency, preferably, the molar ratio of the anhydrous HF, phosphorus powder and alkali metal fluoride salt is (15-25):(1-1.05):(1-1.05).

[0010] In order to improve the synthesis efficiency of hexafluorophosphate, preferably, the reaction is that fluorine atoms are electrolyzed from anhydrous HF at low voltage, the fluorine atoms, phosphorus powder and alkali metal fluoride are reacted in an anhydrous hydrogen fluoride solvent which is not electrolyzed, to obtain hexafluorophosphate. The fluorine atoms are weak fluorine with weak activity.

[0011] Preferably, the temperature of the electrolysis reaction is 15-30℃, and the voltage is 10-15V. At the reaction temperature, both the synthesis of hexafluorophosphate and the prevention of phosphorus powder from sublimation can be ensured, so as to avoid the blockage of the pipeline and make the phosphorus powder fully utilized. The voltage can make the anhydrous HF partially electrolyzed, so that the reaction can proceed normally. The temperature of the electrolysis reaction is further preferably 15-25℃.

[0012] Preferably, the alkali metal fluoride is one of lithium fluoride and sodium fluoride. The two alkali metal fluorides are commonly used raw materials for the synthesis of electrolytes.

[0013] Preferably, the electrolysis reaction includes first removing water, and then reacting at the high voltage of 10-15V. The reaction is carried out in a protective atmosphere, such as nitrogen.

[0014] Preferably, the voltage for removing water is 5-7V.

[0015] In order to improve the purity of hexafluorophosphate, preferably, crystallization, solid-liquid separation and drying are carried out after the electrolysis reaction.

[0016] In order to remove impurities in the reaction product, preferably, the pore size of the filter plate for filtration is 700-800 mesh.

[0017] Preferably, the crystallization is evaporation crystallization, and the temperature of the evaporation crystallization is 30-40℃; the temperature of the drying is 60-80℃. The evaporation crystallization can remove unreacted excess anhydrous HF and reduce impurities in the product. Moreover, the evaporation crystallization uses a lower temperature, and after the evaporation is completed, the temperature is raised for drying, which can more thoroughly remove impurities and reduce the processing cost. DETAILED DESCRIPTION

[0018] The present application electrolyzes weak fluorine from anhydrous HF, and then reacts the weak fluorine, phosphorus powder and alkali metal fluoride in an anhydrous HF solvent which is not electrolyzed, to obtain hexafluorophosphate.

[0019] The reaction equation involved in the present application is: 10HF+2P+2MF=2MPF6+5H2

[0020] In the formula, M=Li or Na.

[0021] The preparation method of the hexafluorophosphate of the present application comprises the following steps: adding anhydrous HF, phosphorus powder and alkali metal fluoride into an electrolytic cell which is dried and replaced by nitrogen; then, the electrolytic cell is dehydrated until no gas is generated; after the dehydration is completed, the temperature is controlled at 15-30 DEG C and the voltage is controlled at 10-15 V for reaction, and the reaction is completed when the current of the electrolytic cell is substantially 0; after cooling, the reactants are filtered by a filter plate, and the obtained filtrate is evaporated, crystallized and dried to obtain the finished lithium hexafluorophosphate. The anode material in the electrolytic cell is Monel, and the cathode material is a nickel plate.

[0022] The technical solutions of the present application are further described below in combination with the specific embodiments.

[0023] Firstly, the specific embodiment of the preparation method of the hexafluorophosphate of the present application is as follows:

[0024] Embodiment 1

[0025] The preparation method of the lithium hexafluorophosphate of the present embodiment adopts the following steps:

[0026] (1) A 2L electrolytic cell is dried and replaced by nitrogen, and 300g of anhydrous HF, 31g of yellow phosphorus powder and 26g of lithium fluoride are added into the electrolytic cell under the protection of nitrogen;

[0027] (2) The voltage of the electrolytic cell is adjusted and controlled to 5V by a small constant-current transformer, and the reaction system is first electrolyzed and dehydrated until no oxygen is generated at the anode of the electrolytic cell, and the dehydration is completed;

[0028] (3) After the electrolytic cell is dehydrated, the reaction temperature is controlled to 15 DEG C by a low-temperature fluid, the electrolysis voltage is increased to 10V, and the current of the electrolytic cell is observed, and the reaction is completed when the current of the electrolytic cell is substantially 0; during the reaction, hydrogen is generated at the cathode, and after the reaction is completed, lithium fluoride is consumed and no electron transfer occurs, and the reaction is terminated;

[0029] (4) After the reaction, the electrolytic cell is cooled to 0 DEG C, and then filtered by a filter plate with a pore size of 700;

[0030] (5) The temperature of the crystallization tank is set to 40 DEG C, and the excess HF in the filtrate is evaporated to obtain crude lithium hexafluorophosphate; and the evaporated HF is condensed and collected for reuse;

[0031] (6) The crude lithium hexafluorophosphate is dried at a temperature of 70 DEG C to obtain 144.5g of finished lithium hexafluorophosphate with a purity of 99.94% and a yield of 95.1%.

[0032] Embodiment 2

[0033] The preparation method of the lithium hexafluorophosphate of the present embodiment adopts the following steps:

[0034] (1) Dry a 2L electrolytic cell and replace with nitrogen gas, and add 400g of anhydrous HF, 31g of yellow phosphorus powder, and 26g of lithium fluoride into the electrolytic cell under the protection of nitrogen gas;

[0035] (2) Adjust the voltage of the electrolytic cell to 7V through a small constant-current transformer to control the water removal of the reaction system, until no gas is generated at the anode of the electrolytic cell, and the water removal is completed;

[0036] (3) After the electrolytic cell is dehydrated, control the reaction temperature to be 20℃ through a low-temperature fluid, and increase the electrolysis voltage to 12V, and observe the electrolytic current, and when the electrolytic current is basically 0, the reaction is completed;

[0037] (4) After the reaction, cool the electrolytic cell to 5℃, and then filter through a filter plate with a pore size of 800, and transfer the obtained filtrate to a crystallization tank;

[0038] (5) Set the temperature of the crystallization tank to 35℃, evaporate the excess HF in the filtrate to obtain crude lithium hexafluorophosphate, and collect and reuse the evaporated HF;

[0039] (6) Dry the crude lithium hexafluorophosphate at a drying temperature of 60℃ to obtain 143.2g of finished lithium hexafluorophosphate with a purity of 99.92% and a yield of 94.2%.

[0040] Example 3

[0041] The preparation method of lithium hexafluorophosphate in this example adopts the following steps:

[0042] (1) Dry a 2L electrolytic cell and replace with nitrogen gas, and add 400g of anhydrous HF, 31g of yellow phosphorus powder, and 26g of lithium fluoride into the electrolytic cell under the protection of nitrogen gas;

[0043] (2) Adjust the voltage of the electrolytic cell to 7V through a small constant-current transformer to control the water removal of the reaction system, until no gas is generated at the anode of the electrolytic cell, and the water removal is completed;

[0044] (3) After the electrolytic cell is dehydrated, control the reaction temperature to be 20℃ through a low-temperature fluid, and increase the electrolysis voltage to 12V, and observe the electrolytic current, and when the electrolytic current is basically 0, the reaction is completed;

[0045] (4) After the reaction, cool the electrolytic cell to 5℃, and then filter through a filter plate with a pore size of 800, and transfer the obtained filtrate to a crystallization tank;

[0046] (5) Set the temperature of the crystallization tank to 35℃, evaporate the excess HF in the filtrate to obtain crude lithium hexafluorophosphate, and collect and reuse the evaporated HF;

[0047] (6) The crude lithium hexafluorophosphate is dried at a drying temperature of 70°C to obtain 148.3 g of finished lithium hexafluorophosphate with a purity of 99.96% and a yield of 97.6%.

[0048] Example 4

[0049] The preparation method of sodium hexafluorophosphate in this example adopts the following steps:

[0050] (1) Dry and replace the 2L electrolytic cell with nitrogen, and then add 500g of anhydrous HF, 31g of yellow phosphorus powder, and 42g of sodium fluoride into the electrolytic cell under the protection of nitrogen;

[0051] (2) Adjust the voltage of the electrolytic cell to 5V through a small constant-current transformer to remove water from the reaction system until no gas is generated at the anode of the electrolytic cell, and the water removal is completed;

[0052] (3) After the electrolytic cell is dehydrated, control the reaction temperature to be 25°C through a low-temperature fluid, and increase the electrolysis voltage to 11V. Observe the current of the electrolytic cell, and when the current of the electrolytic cell is basically 0, the reaction is completed;

[0053] (4) After the reaction, cool the electrolytic cell to 5°C, and then filter through a filter plate with a pore size of 700μm. Transfer the obtained filtrate to a crystallization tank;

[0054] (5) Set the temperature of the crystallization tank to 40°C, evaporate the excess HF in the filtrate to obtain crude lithium hexafluorophosphate, and condense and collect the evaporated HF for reuse;

[0055] (6) Dry the crude lithium hexafluorophosphate at a drying temperature of 70°C to obtain 160.5g of finished sodium hexafluorophosphate with a purity of 99.91% and a yield of 95.5%.

Claims

1. A process for the preparation of hexafluorophosphate salts, characterized in that, The method comprises the following steps: The anhydrous HF, phosphorus powder and alkali metal fluoride salt are subjected to an electrolysis reaction to generate hexafluorophosphate; the electrolysis reaction is that the fluorine atoms are electrolyzed from the anhydrous HF, and the fluorine atoms, the phosphorus powder and the alkali metal fluoride salt are reacted in the anhydrous hydrogen fluoride solvent which is not subjected to electrolysis; the electrolysis reaction comprises the following steps: first, water is removed by electrolysis, and then the hexafluorophosphate is electrolyzed at 15-30 ℃ and 10-15 V.

2. The method for producing a hexafluorophosphate salt according to claim 1, characterized by, The molar ratio of the anhydrous HF, the phosphorus powder and the alkali metal fluoride salt is (15-25):(1-1.05):(1-1.05).

3. The method of preparing a hexafluorophosphate salt according to claim 1, characterized by, The temperature for electrolyzing the hexafluorophosphate is 15-25 ℃.

4. The process for the preparation of hexafluorophosphate salt according to any one of claims 1 to 3, characterized in that, The alkali metal fluoride salt is one of lithium fluoride and sodium fluoride.

5. The method of preparing a hexafluorophosphate salt according to claim 3, characterized by, The voltage for electrolyzing the hexafluorophosphate is 10-12 V.

6. The method of preparing a hexafluorophosphate salt according to claim 5, characterized in that, The voltage for removing water is 5-7 V.

7. The method of preparing a hexafluorophosphate salt according to any one of claims 1 to 3, characterized in that, The electrolysis reaction is followed by crystallization, solid-liquid separation and drying.

8. The method of preparing a hexafluorophosphate salt according to claim 7, characterized by, The crystallization is evaporation crystallization, and the temperature for the evaporation crystallization is 30-40 ℃; the temperature for the drying is 60-80 ℃.