JPH05279003A - Production of lithium hexafluorophosphate - Google Patents

Abstract

PURPOSE:To inexpensively produce high-purity lithium hexafluorophosphate to be used as an electrolyte for a lithium cell without forming lithium oxyfluoride as the source of an acidic substance, without using phosphorus pentafluoride and with a simple process. CONSTITUTION:Phosphorus pentachloride is allowed to react with hydrogen fluoride, the generated gaseous mixture of phosphorus pentafluoride and hydrogen chloride is passed through a trap cooled by dry ice-acetone and cooled to -40 to -84 deg.C, and phosphorus oxyfluoride is separated and removed. The gas is then introduced into hydrogen fluoride dissolving lithium fluoride to produce lithium hexafluorophosphate.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing high-purity lithium hexafluorophosphate.

[0002]

2. Description of the Related Art Lithium hexafluorophosphate is an important substance as an electrolyte for lithium batteries. At present, lithium perchlorate, which is used in large amounts in lithium batteries, has been pointed out to be dangerous, and the development of safer electrolytes has been urgently needed. Lithium hexafluorophosphate has extremely high safety and excellent physical properties, and is regarded as an indispensable substance especially for lithium secondary batteries.

This lithium hexafluorophosphate is conventionally produced by dissolving lithium chloride in hydrogen fluoride and adding phosphorus pentachloride to it [Fluorine Chemistry Vol. 1 (195
0)]. In this method, phosphorus pentachloride having a strong hygroscopic property is directly charged into hydrogen fluoride, so that the water contained in phosphorus pentachloride and the water absorbed from the air at the time of charging enter the product. Lithium oxyfluoride such as LiPOF ₄ , which is easily hydrolyzed, is mixed and mixed, and even if it is used as an electrolyte of a lithium battery, it is hydrolyzed by a trace amount of water in the electrolytic solution to generate an acidic substance, which damages the electrolytic solution , Cannot be used as an electrolyte in lithium batteries.

It is also produced by the reaction of lithium fluoride with phosphorus pentafluoride (eg US Pat. No. 3,60).
7,020, JP 64-72901). Although this method has little adverse effect due to the mixing of water as described above, phosphorus pentafluoride is a gas and requires a cylinder for handling. In addition, the manufacturing method of phosphorus pentafluoride is complicated. For example, Japanese Patent Publication Sho 49
According to No. 33277, calcium fluoride is reacted with phosphoric acid and sulfuric anhydride at a high temperature, and the product is separated and purified to produce phosphorus pentafluoride. Further, according to Japanese Examined Patent Publication No. 50-13760, phosphoric acid pentafluoride is produced by reacting a solution of phosphoric acid hexafluoride with sulfuric anhydride. Therefore, phosphorus pentafluoride becomes expensive, and the fact that expensive phosphorus pentafluoride must be used makes lithium hexafluorophosphate expensive.

The present invention solves the problem in the prior art of producing lithium oxyfluoride, which is unfavorable as the electrolyte of a lithium battery, which causes the generation of acidic substances by mixing water into the reaction system and is expensive. It is an object of the present invention to provide a method for inexpensively producing high-purity lithium hexafluorophosphate by a simple process that does not use phosphorus pentafluoride, which is difficult to handle.

[0006]

In order to achieve the above object, in the present invention, the gas generated by the reaction of phosphorus pentachloride and hydrogen fluoride is cooled to -40 to -84 ° C to remove phosphorus oxyfluoride. After that, lithium fluoride is introduced into dissolved hydrogen fluoride.

The method of the present invention will be described more specifically as follows.
Phosphorus pentachloride and hydrogen fluoride are reacted, and the resulting mixed gas of phosphorus pentafluoride and hydrogen chloride is passed through, for example, dry ice-acetone or a trap cooled with liquid nitrogen.
After cooling to 40 to −84 ° C. to remove phosphorus oxyfluoride, lithium hexafluorophosphate is produced by introducing it into hydrogen fluoride in which lithium fluoride is dissolved in advance.

[0008]

Function: Phosphorus pentachloride and hydrogen fluoride react almost quantitatively at room temperature to produce a mixed gas of phosphorus pentafluoride and hydrogen chloride containing a small amount of impure components. Then, at this time, a part of phosphorus pentafluoride becomes phosphorus oxyfluoride such as POF ₃ due to the water content contained in phosphorus pentachloride. This substance, which is phosphorus oxyfluoride, has a boiling point of -39.4 ° C and a melting point of -39.8 ° C, a large difference from the boiling point of phosphorus pentafluoride of -84.8 ° C, and can be easily separated by cooling. A mixed gas of phosphorus pentafluoride and hydrogen chloride produced by reacting with hydrogen fluoride is cooled to -40 to -84 ° C to remove phosphorus oxyfluoride. Then, by introducing this gas into hydrogen fluoride in which lithium fluoride is dissolved, high-purity lithium hexafluorophosphate can be manufactured.

As described above, the present invention has found that phosphorus pentachloride and hydrogen fluoride react substantially quantitatively at room temperature to generate a mixed gas of phosphorus pentafluoride and hydrogen chloride, and At this time, a part of phosphorus pentafluoride becomes phosphorus oxyfluoride such as POF ₃ due to the water contained in phosphorus pentachloride, but this substance has a boiling point of -39.4 ° C and a melting point of -39.8 ° C. This is based on the fact that the difference in boiling point of phosphorus fluoride from -84.8 ° C is large and that it can be easily separated by cooling, and this newly found fact is utilized in the production of lithium hexafluorophosphate to produce acidic substances. Without producing lithium oxyfluoride, which causes
It is intended to inexpensively produce high-purity lithium hexafluorophosphate by a simple process that does not use phosphorus pentafluoride.

In the present invention, the cooling temperature of the gas produced by the reaction between phosphorus pentachloride and hydrogen fluoride is -40 to -84.
The reason why the temperature is set to ° C is as follows. That is, when the cooling temperature of this gas is higher than −40 ° C., impurities such as POF ₃ cannot be completely separated and reach the reaction vessel, for example, and the purity of lithium hexafluorophosphate obtained is too low. On the contrary, when the cooling temperature of the gas is lower than −84 ° C., phosphorus pentafluoride and hydrogen chloride, which are the main compositions of this gas, are condensed into something like a trap, which is not preferable. Because it will occur. -8 above gas
When the temperature is lower than 4 ° C, both phosphorus pentafluoride and hydrogen chloride are condensed because the boiling point of phosphorus pentafluoride is -84.8 ° C.
This is because the boiling point of hydrogen chloride is -84.9 ° C. Therefore,
The cooling temperature of the gas generated by the reaction of phosphorus pentachloride and hydrogen fluoride should be -40 to -84 ° C.

The object, structure and operation of the present invention are as described above, and preferred examples of the present invention will be described in detail below together with their operation and the like.

The production of lithium hexafluorophosphate must be carried out in a completely sealed container in order to avoid mixing of water.
Solid phosphorus pentachloride is directly charged into a container (hereinafter referred to as a reaction container) containing hydrogen fluoride in which lithium fluoride is dissolved, in addition to water entering the reaction system as described above. Phosphorus chloride absorbs water in the air and solidifies at the input port, or reacts with hydrogen fluoride gas in the reaction vessel at the input port, generating highly toxic phosphorus pentafluoride and hydrogen chloride gas and inputting. Undesirable phenomena such as gushing from the mouth occur.

In the case of the method of the present invention, it is not necessary to pay particular attention to the absorption of phosphorus pentachloride, but the container for reacting phosphorus pentachloride and hydrogen fluoride (hereinafter referred to as gasification container) is
It is a mere empty container until hydrogen fluoride is introduced, and it is easy to put phosphorus pentachloride in this container in a dry state. The hydrogen fluoride introduced into the gasification container may be either liquid or gas, and only gas flows from the gasification container to the reaction container, and both are easily sealed. Phosphorus pentachloride is placed in a container (gasification container) made of a corrosion-resistant material such as stainless steel and Hastelloy, and then sealed.

Hydrogen fluoride is introduced through a conduit attached to this vessel. In this case, hydrogen fluoride may be liquid or gaseous, but it is preferable to vaporize and blow it in order to reduce the water content in the hydrogen fluoride. The reaction starts at room temperature, but the temperature gradually rises due to the heat of reaction. There is no particular need to adjust the temperature, but in order to cool the produced gas efficiently, cool it or adjust the amount of hydrogen fluoride to 50 ° C.
Hold down to a certain degree. Gas is generated almost simultaneously with the introduction of hydrogen fluoride. This gas is a mixed gas of phosphorus pentafluoride and hydrogen chloride containing a small amount of impurities and unreacted hydrogen fluoride.

A cold trap is provided between the gasification vessel and the reaction vessel to cool the mixed gas in order to remove phosphorus oxyfluoride among the impure components. The cold trap is attached to, for example, a mixed solution of dry ice-acetone in order to cool it to a melting point of POF ₃ of −39.8 ° C. or lower. A cooling temperature of -40 to -84 ° C is sufficient. A filling material may be placed in the trap in order to improve the separation of the gas and the component solidified by cooling. When the mixed gas is cooled to −40 to −84 ° C., white powder accumulates in this trap. When this powder is reacted with lithium fluoride in hydrogen fluoride, Li which shows strong acidity in aqueous solution
Generate POF ₄ . From this, the mixed gas is -40
It can be seen that the phosphorus oxyfluoride was easily separated by cooling to ~ -84 ° C.

Thus, the mixed gas of phosphorus pentafluoride and hydrogen chloride from which the impure components have been removed is introduced into a reaction vessel containing hydrogen fluoride in which lithium fluoride is dissolved. Trace amounts of impurities such as iron are not preferable for lithium hexafluorophosphate as a battery electrolyte. Therefore, the reaction vessel is preferably made of a fluororesin having excellent corrosion resistance. The reaction container is closed except for the inlet for introducing the mixed gas and the outlet for hydrogen chloride which does not participate in the reaction, and moisture does not enter from the outside.

Hydrogen fluoride is used in an amount of 5 to 50 parts with respect to 1 part of lithium fluoride. Lithium fluoride does not necessarily have to be completely dissolved in hydrogen fluoride and may be in a suspended state, but it is not preferable to settle at the bottom of the container. In order to avoid precipitation, the solubility should be within the range. On the other hand, if it is too dilute, a large amount of hydrogen fluoride must be distilled off in order to precipitate lithium hexafluorophosphate crystals, which is uneconomical. For that purpose, it is preferable to use 10 to 30 parts of hydrogen fluoride. Hydrogen fluoride usually contains about 10 ppm of water, but can be used as it is. If necessary, rectification can be carried out to further remove water.

The temperature of the reaction vessel must be kept below 19.5 ° C, which is the boiling point of hydrogen fluoride, but is preferably 0 to -10 ° C. At −20 ° C. or less, depending on the amount of hydrogen fluoride used, lithium hexafluorophosphate may crystallize during the reaction, and unreacted lithium fluoride may be contained, resulting in a reduction in the purity of the product.

Phosphorus pentachloride is 1.05 to 1.5 mol, preferably 1.1 to 1.2 mol, per mol of lithium fluoride.
This is because the water contained in phosphorus pentachloride is taken into consideration and unreacted lithium fluoride is prevented from remaining.

After completion of the reaction, nitrogen gas was passed through while keeping the temperature of the solution at 0 to 20 ° C. to distill off hydrogen fluoride,
After concentrating to 1/5, cool to 0-20 ° C. The formed crystals are filtered, and hydrogen fluoride is completely removed by passing nitrogen at 40 to 80 ° C. to obtain high-purity lithium hexafluorophosphate containing very few acidic substances produced by hydrolysis.

[0021]

EXAMPLES Examples of the present invention will be described below together with comparative examples.

Example 1 Into a 10 L fluororesin reaction vessel equipped with a gas inlet, a gas outlet and a stirrer was placed 5 kg of hydrogen fluoride having 250 g of lithium fluoride dissolved therein, and the mixture was cooled to -5 ° C. Hydrogen fluoride in a separately prepared container was vaporized and passed through a gasification container containing 2.4 kg of phosphorus pentachloride corresponding to 1.2 times mol. Then, the generated mixed gas of phosphorus pentafluoride and hydrogen chloride was cooled to −50 ° C. by a cold trap immersed in a dry ice-acetone bath, and then introduced through a gas blowing port. A small amount of white powder accumulated in the trap. After the phosphorus pentachloride has been completely consumed,
Nitrogen was passed through while maintaining the temperature at 0 ° C., and the liquid material was concentrated to 1/3.
The crystals that were kept overnight at -20 ° C were filtered and dried in a nitrogen stream at 50 ° C to give 962 g of crystals. This was 99.8% lithium hexafluorophosphate, 10 g of which was dissolved in a predetermined amount of water and titrated with 0.1N-NaOH using phenolphthalein as an indicator, the consumption was 1.1 ml.

EXAMPLE 2 5 kg of hydrogen fluoride in which 400 g of lithium fluoride was dissolved was placed in a 10 L fluororesin reaction vessel equipped with a gas inlet, a gas outlet and a stirrer and cooled to -5 ° C. The hydrogen fluoride in a separately prepared container was vaporized and passed through a gasification container containing 3.6 kg of phosphorus pentachloride, which corresponds to 1.1 times the molar amount. Then, the generated mixed gas of phosphorus pentafluoride and hydrogen chloride was cooled to -40 ° C by a cold trap immersed in a dry ice-acetone bath, and then introduced from a gas blowing port. A small amount of white powder accumulated in the trap. After the phosphorus pentachloride is completely consumed,
Nitrogen was passed through while maintaining the temperature at 0 ° C. to concentrate the liquid volume to 1/4.
The crystals that were kept overnight at -20 ° C were filtered and dried in a nitrogen stream at 50 ° C to give 962 g of crystals. This was 99.5% lithium hexafluorophosphate, and 10 g of it was subjected to a pruning experiment under the same conditions as in Example 1. As a result, the consumption was 1.2 ml.

Example 3 The same operation as in Example 1 was carried out except that the cold trap was cooled to −84 ° C. by using a cooling controller using liquid nitrogen. As a result, 952 g of crystals were obtained.
This is 99.8% lithium hexafluorophosphate, part 1
When 0 g was used to perform a trimming experiment under the same conditions as in Example 1, the consumption was 1.2 ml.

Comparative Example 1 Example except that a mixed gas of phosphorus pentafluoride and hydrogen chloride generated in a gasification vessel was directly introduced into a reaction vessel without passing through a cold trap immersed in a dry ice-acetone bath. The same operation as in 1 was performed to obtain 957 g of crystals. This was 98.9% lithium hexafluorophosphate, and when 10 g of it was subjected to a pruning experiment under the same conditions as in Example 1, the consumption was 18.5 ml, and the acidic substance produced by hydrolysis was
It was 15 times or more that of Example 1.

Comparative Example 2 5 kg of hydrogen fluoride having 250 g of lithium fluoride dissolved therein was placed in a 10 L fluororesin reaction vessel equipped with a gas blowing port, a gas outlet and a stirrer, and cooled to -5 ° C to obtain lithium fluoride. 2.4 kg of phosphorus pentachloride, which corresponds to 1.2 times the molar amount of, was directly added little by little. After the reaction, the same treatment as in Example 1 was performed, and as a result, insoluble impurities were mixed in fine gray water.
5 g of crystals were obtained. This was lithium hexafluorophosphate having a purity of 98.3%, and 10 g of lithium hexafluorophosphate was subjected to a pruning experiment under the same conditions as in Example 1. As a result, the consumption amount was 28.5 ml, and the acidic substance produced by hydrolysis was Was 24 times or more that of Example 1.

Comparative Example 3 The cold trap was cooled to −90 ° C. using a cooling control device using liquid nitrogen, and synthesis was attempted according to Example 1. However, most of the 5 fluorine generated in the gasifier was used. Since phosphorus oxide and hydrogen chloride were condensed in the cold trap, lithium hexafluorophosphate could not be synthesized.

[0028]

As is apparent from the above, according to the present invention, a simple process without producing lithium oxyfluoride, which causes an acidic substance, and without using phosphorus pentafluoride Thus, high-purity lithium hexafluorophosphate can be manufactured at low cost.

Claims (1)

[Claims] 1. A gas produced by the reaction of phosphorus pentachloride and hydrogen fluoride in hydrogen fluoride in which lithium fluoride is dissolved is cooled to -40 to -84 ° C. to remove phosphorus oxyfluoride, A method for producing lithium hexafluorophosphate, which comprises introducing.