JP4405006B2 - Method for producing low moisture lithium hexafluorophosphate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for efficiently producing low-moisture lithium hexafluorophosphate useful as an organic synthesis reaction catalyst, including an electrolyte for a lithium secondary battery.
[0002]
[Prior art and problems to be solved by the invention]
Various methods for producing lithium hexafluorophosphate have been proposed.
However, a problem common to all the production methods is a problem of water mixing into the product due to the circulating use of the filtrate. That is, in any of the manufacturing methods, the reaction raw material lithium fluoride is newly dissolved in the filtrate after the lithium hexafluorophosphate is filtered and separated, and the batch reaction is continued repeatedly. The moisture in the filtrate gradually increases due to the moisture content of phosphorus pentachloride and lithium fluoride, the moisture mixed from the outside air during operation, etc. As a result, the moisture in the product lithium hexafluorophosphate gradually increases. There is a problem.
When lithium hexafluorophosphate is used as an electrolyte for a lithium battery, the electrolyte itself is hydrolyzed by the moisture contained therein, and the resulting hydrogen fluoride or oxyfluorophosphate compound degrades the battery performance. The water content of the lithium phosphate must be reduced as much as possible.
[0003]
Conventionally, as a method for reducing the water content of lithium hexafluorophosphate, lithium hexafluorophosphate crystals are dissolved in an oxygen-containing organic solvent having a boiling point of 100 ° C. or higher, and the oxygen-containing organic in this solution is dissolved. There is a method (Japanese Patent Laid-Open No. 61-254216) for removing water by distilling off all the solvent by distillation.
However, in this method, a large amount of solvent must be distilled and removed each time, and contamination due to impurity concentration in the solvent is a concern.
Other methods include fluorine treatment of lithium hexafluorophosphate crystals in an inert gas (Japanese Patent Publication No. 4-16406), or recrystallization of lithium hexafluorophosphate crystals into a solvent inert to fluorine. After dissolution, there is a method of fluorine treatment (Japanese Patent Publication No. 4-16407).
However, in these treatment methods, it is necessary to treat once isolated lithium hexafluorophosphate crystals with a separate apparatus, which is complicated and time-consuming to operate, and is not an industrially practical method. .
[0004]
Accordingly, the object of the present invention is to produce a low moisture lithium hexafluorophosphate that eliminates the disadvantages of the conventional methods described above, that is, to efficiently produce a low moisture hexafluorophosphate without requiring a special post-treatment. The object is to provide a method capable of producing lithium.
[0005]
[Means for Solving the Problems]
As a result of intensive investigations to achieve the above object, the inventors of the present invention have prepared the first reaction when producing lithium hexafluorophosphate using an anhydrous hydrogen fluoride solution of lithium fluoride and phosphorus pentafluoride. Lithium hexafluorophosphate with low water content can be produced easily and extremely efficiently by fluorinating an anhydrous hydrogen fluoride solution of lithium fluoride and a solution obtained by dissolving lithium fluoride in a circulating crystal filtrate. I found out.
The present invention has been made on the basis of the above knowledge, and an anhydrous hydrogen fluoride solution of lithium fluoride or a solution obtained by dissolving lithium fluoride in a filtrate that is circulated and used in the production process of lithium hexafluorophosphate, Then, phosphorus pentafluoride is added to the solution, and the lithium fluoride in the solution is reacted with phosphorus pentafluoride. The first invention is provided).
Moreover, the present invention adds phosphorus pentafluoride to an anhydrous hydrogen fluoride solution of lithium fluoride, or a solution in which lithium fluoride is dissolved in a filtrate that is circulated and used in the production process of lithium hexafluorophosphate, A method for producing low-moisture lithium hexafluorophosphate (hereinafter referred to as second invention), characterized in that after reacting lithium fluoride and phosphorus pentafluoride in the solution, the reaction solution is fluorinated. It is to provide.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the manufacturing method of the low moisture lithium hexafluorophosphate of this invention is explained in full detail.
First, the first invention will be described.
[0007]
Fluorination of the above-mentioned anhydrous hydrogen fluoride solution of lithium fluoride or a solution obtained by dissolving lithium fluoride in a filtrate is performed using fluorine gas. The fluorination may be carried out by directly introducing fluorine gas into a reactor for producing lithium hexafluorophosphate, or may be carried out in a separate container from the reactor, After carrying out by separately providing a device for efficient contact, the treated solution may be returned to the reactor. The fluorine gas used for the fluorination is preferably recycled for cost and environmental considerations.
[0008]
The fluorination can be performed under normal pressure, under pressure, or under reduced pressure. The reaction temperature of the fluorination is desirably as high as possible under pressure in consideration of the reaction between moisture and fluorine. However, the upper limit temperature is 50 ° C. or less, preferably 30 ° C. in consideration of the pressure resistance of the apparatus. It is as follows. The lower limit temperature can be lowered to a temperature at which a solute such as lithium fluoride or lithium hexafluorophosphate does not precipitate, but it is desirable to set it to −20 ° C. or higher in view of the efficiency of fluorination. That is, the fluorination reaction temperature is preferably in the range of -20 to + 30 ° C.
Moreover, when performing the said fluorination under pressure, it is preferable to make the reactor internal pressure into the range of 10-20 kPa (G), and when performing the said fluorination under reduced pressure, the reactor internal pressure is -80- A range of −30 kPa (G) is preferable.
[0009]
The concentration of the fluorine gas used for the fluorination may be arbitrary. That is, even when 100% by volume of fluorine is used, or for dilution, inert gases (nitrogen, helium, argon, neon, etc.), carbon tetrafluoride, hexafluoroethane, nitrogen trifluoride, sulfur hexafluoride, etc. However, it is desirable to use a fluorine gas having a concentration of 10% by volume or more in view of efficiency.
The fluorination time required for the fluorination is usually several seconds to several hours although it depends on the concentration of the fluorine gas used. Considering the efficiency of fluorination, it is desirable to adjust the concentration of the fluorine gas so that the fluorination is completed in 1 minute to 1 hour.
[0010]
The reaction between lithium fluoride and phosphorus pentafluoride in the solution after fluorination can be carried out in the same manner as in the conventional method. Preferably, the solution is fluorinated at a temperature of −30 to 0 ° C. It is recommended to add phosphorus phosphide and react.
The solution preferably has an anhydrous hydrogen fluoride / lithium fluoride molar ratio of 10 to 35, and the amount of phosphorus pentafluoride added is 1 with respect to 1 mol of lithium fluoride in the solution. 0.0 to 1.1 mol is preferred.
[0011]
Acquisition of lithium hexafluorophosphate from the reaction solution can be performed by cooling the reaction solution to precipitate crystals of lithium hexafluorophosphate and heating and drying the crystals in an inert gas.
The lithium hexafluorophosphate obtained by the method of the present invention has a low moisture content of less than 10 ppm.
[0012]
Next, the second invention will be described.
The second invention is carried out in the same manner as the first invention except that the fluorination is performed after the reaction between lithium fluoride and phosphorus pentafluoride.
That is, the reaction between lithium fluoride in the solution before fluorination and phosphorus pentafluoride in the second invention is the same as the reaction between lithium fluoride in the solution after fluorination and phosphorus pentafluoride in the first invention. The reaction solution in the second invention may be fluorinated in the same manner as the solution fluorination in the first invention.
[0013]
【Example】
Examples of the present invention will be described below together with comparative examples, but the present invention is not limited to these examples. Example 4 is a reference example.
[0014]
[Example 1]
Charge 1600 g of anhydrous hydrogen fluoride (hereinafter abbreviated as HF) into a 3 liter stirrer and Hastelloy C reactor with cooling jacket, cool to −35 ° C., and dissolve 75 g of lithium fluoride in this while stirring. Then, an anhydrous hydrogen fluoride solution of lithium fluoride was prepared. The solution temperature was −19 ° C. Next, fluorine gas having a concentration of 50% by volume diluted with nitrogen was introduced into the reactor for 1 hour while stirring at a rate of 800 ml / min to dehydrate (fluorinate) the solution. Subsequently, 500 g of phosphorus pentafluoride was introduced into the reactor while stirring and reacted, and then the reaction solution was cooled to −50 ° C. to precipitate crystals. The crystals were filtered off and dried in a nitrogen stream at 50 ° C. to obtain 220 g of lithium hexafluorophosphate crystals having a diameter of 1 to 2 mm. The water content in the crystals was 3 ppm (the water content was measured by the Karl Fischer method. The same applies to the following examples and comparative examples).
[0015]
[Example 2]
HF was newly added to the “filtrate after filtering the crystals” in Example 1 to 1800 g, and 37 g of lithium fluoride was dissolved therein. Using this solution, under the same conditions as in Example 1, after dehydration by fluorination, 230 g of phosphorus pentafluoride was introduced to carry out the reaction, thereby obtaining 239 g of lithium hexafluorophosphate crystals. The moisture in the crystal was 4 ppm.
[0016]
Example 3
The same operation as in Example 2 was repeated 40 times. The moisture in the crystal of lithium hexafluorophosphate produced for the 40th time was 6 ppm.
[0017]
Example 4
1300 g of HF was charged into a 3 liter capacity stirrer and Hastelloy C reactor equipped with a cooling jacket, and 80 g of lithium fluoride was dissolved therein to prepare an anhydrous hydrogen fluoride solution of lithium fluoride. After the temperature of the solution was adjusted to −10 ° C., 500 g of phosphorus pentafluoride synthesized by the reaction of phosphorus pentachloride and HF was introduced and reacted in another Hastelloy C reactor. The temperature after completion of the reaction was 13 ° C. After cooling the reaction solution to 0 ° C., fluorine gas having a concentration of 100% by volume was introduced for 40 minutes while stirring at a rate of 300 ml / min to dehydrate (fluorinate) the reaction solution. Next, the reaction solution was cooled to −50 ° C. to precipitate crystals. The crystals were separated by filtration and dried in a nitrogen stream at 50 ° C. to obtain 188 g of lithium hexafluorophosphate crystals. The moisture in the crystal was 4 ppm.
[0018]
[Comparative Example 1]
Except that the dehydration (fluorination) operation was omitted, the same procedure as in Example 1 was performed to obtain 251 g of lithium hexafluorophosphate crystals. The lithium hexafluorophosphate crystal had a uniform particle size, but the water content in the crystal was 11 ppm.
[0019]
[Comparative Example 2]
Without performing dehydration (fluorination) operation, the reaction was performed 40 times by repeatedly using the “filtrate after filtering the crystals” of Comparative Example 1. The water content in the crystal of lithium hexafluorophosphate produced for the 40th time was 26 ppm.
[0020]
[Comparative Example 3]
Except that the dehydration (fluorination) operation was omitted, the same procedure as in Example 4 was performed to obtain 184 g of lithium hexafluorophosphate crystals. The water content in the crystals was 26 ppm.
[0021]
【The invention's effect】
According to the method for producing lithium hexafluorophosphate of the present invention, lithium hexafluorophosphate having a low water content can be efficiently produced without requiring a special post-treatment or the like.

Claims (3)

  Fluorinate a solution of lithium fluoride in anhydrous hydrogen fluoride or a solution in which lithium fluoride is circulated and used in the lithium hexafluorophosphate manufacturing process, and then add phosphorus pentafluoride to the above solution And a method for producing low-moisture lithium hexafluorophosphate, wherein lithium fluoride and phosphorus pentafluoride in the solution are reacted. Fluorinated method of low moisture lithium hexafluorophosphate of claim 1 Symbol placement carried out using a concentration of 10 to 100 volume% of the fluorine gas. The method for producing low-moisture lithium hexafluorophosphate according to claim 1 or 2 , wherein the fluorination temperature is in the range of -20 to + 30 ° C, and the fluorination time is in the range of 1 minute to 1 hour.