JP2882723B2 - Purification method of lithium hexafluorophosphate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying lithium hexafluorophosphate useful as an electrolyte for a lithium secondary battery and a catalyst for an organic synthesis reaction.

[0002]

2. Description of the Related Art Lithium hexafluorophosphate is a very unstable compound. For this reason, the quality is deteriorated due to hydrolysis by water or the like mixed into the system as an impurity from the manufacturing process or from storage and handling. In general, lithium fluoride and phosphoric acid oxyfluoride (MPO _x F _y ; M = Li, H; y = 6-2x) are impurities generated by hydrolysis of lithium hexafluorophosphate or the like.
And so on.

When lithium hexafluorophosphate containing such impurities is dissolved in an organic solvent and used as an electrolyte for a lithium battery, lithium fluoride is insoluble in the organic solvent and filtration of the electrolyte is necessary. Becomes In addition, the oxyfluorophosphate compound causes decomposition or polymerization of the organic solvent,
It is conceivable that the internal resistance of the battery increases and the capacity decreases.

[0004] As a method of removing such impurities,
A method of dissolving lithium hexafluorophosphate in an organic solvent and removing impurities with an ion-exchange resin
No. 774) or a method of performing a neutralization treatment in an organic solvent (Japanese Unexamined Patent Publication No.
No. 9-81870) or a method of reacting and removing a phosphoric acid oxyfluoride compound with fluorine gas (Japanese Patent Publication No. 4-16406,
Japanese Patent Publication No. 4-16407) is known. But,
These operations are complicated, and since the only way to remove lithium fluoride is to perform filtration, productivity is poor.

As described above, none of the conventional methods has been satisfactory.

[0006]

[Specific means for solving the problem]
As a result of intensive studies in view of the problems of the related art, the present invention has been achieved.

That is, the present invention relates to a method for purifying lithium hexafluorophosphate, which comprises contacting lithium hexafluorophosphate with a gas containing phosphorus pentafluoride.

[0008] Lithium hexafluorophosphate used in the present invention is a very unstable compound, and undergoes a decomposition reaction due to water and the like mixed into the system as impurities from the manufacturing process or from storage and handling. , Reduce its quality. Examples of impurities generated by this decomposition reaction include lithium fluoride and phosphoric acid oxyfluoride.

As a result of various studies by the present inventors, it was found that lithium fluoride and a phosphoric acid oxyfluoride compound were brought into contact by bringing a gas containing phosphorus pentafluoride into contact with lithium hexafluorophosphate having such impurities. At the same time, they found that they could be reduced.

The reason that these impurities can be removed by a gas containing phosphorus pentafluoride is that, in the case of lithium fluoride, the combination of lithium fluoride and phosphorus pentafluoride as shown in the following formula gives It is speculated that it will return to lithium phosphate. In the case of LiF + PF ₅ → LiPF ₆ oxyfluorophosphate compound, it is presumed that substitution of phosphorus oxyfluoride with phosphorus pentafluoride occurs. _{MPO x F y + PF 5 →} MPF 6 + PO x F y-1 ↑ (HPF 6 dissociates gasified) purification by the present invention is from 0.1 to 100 percent, preferably 1
This is performed by bringing 0 to 100% of phosphorus pentafluoride gas into contact with lithium hexafluorophosphate. A concentration of 0.1% or less is not preferable because the effect is small. The temperature is preferably 300 ° C. or lower in order to prevent the dissociation of lithium hexafluorophosphate due to heat. Atmospheric pressure is sufficient. Quantitatively,
What is necessary is just to contain phosphorus pentafluoride in an equivalent amount or more with respect to impurities. The gas mixed with phosphorus pentafluoride may be any gas that does not react with lithium hexafluorophosphate. However, if hydrogen fluoride is used as this gas, it is more effective than using 100% phosphorus pentafluoride gas. Is big.

[0011] Lithium hexafluorophosphate purified by the method of the present invention has a very high purity, and the impurity concentration of lithium fluoride and phosphoric acid oxyfluoride is 0 to 2%.
00 ppm.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 32 g of lithium fluoride is dissolved in 500 g of hydrofluoric anhydride. 155 g of phosphorus pentafluoride gas is blown into this solution,
Reacted with lithium fluoride. The resulting reaction solution was slowly cooled to −20 ° C. overnight to precipitate crystals of lithium hexafluorophosphate. This was separated by filtration and the attached hydrogen fluoride was removed under reduced pressure at room temperature. As a result, 65 g of lithium hexafluorophosphate crystals having a uniform particle size of about 1 mm were obtained. Its purity was 99% or more.

When the lithium hexafluorophosphate thus obtained was hydrolyzed, 500 ppm of hydrogen fluoride, 800 ppm of lithium fluoride and 1000 ppm of a phosphoric acid oxyfluoride compound were generated as impurities. 10 g of this lithium hexafluorophosphate was put into a processing apparatus made of SUS304, first heated to 160 ° C., and then 1 t
Vacuum drying was performed under reduced pressure of orr for 1 hour to remove hydrogen fluoride. Next, after cooling to room temperature and sealing in 100% phosphorus pentafluoride at atmospheric pressure for 12 hours, the phosphorus pentafluoride was evacuated and lithium hexafluorophosphate was taken out. The obtained lithium hexafluorophosphate contained 50 ppm or less of hydrogen fluoride, 100 ppm of lithium fluoride, and 50 ppm or less of the oxyfluorophosphate compound.

Example 2 As in Example 1, 500 ppm of hydrogen fluoride, 800 ppm of lithium fluoride and 1000 parts of a phosphoric acid oxyfluoride compound were used.
10 g of lithium hexafluorophosphate containing 3 ppm
After placing it in a processing device made of 04 and heating to 160 ° C,
Vacuum drying was performed under reduced pressure of 1 torr for 1 hour to remove hydrogen fluoride. Next, the mixture was cooled to room temperature and sealed in a 1: 1 mixture of phosphorus pentafluoride / hydrogen fluoride for 5 hours, and then these gases were removed at 90 ° C. under reduced pressure. Hydrogen fluoride, lithium fluoride and phosphoric acid oxyfluoride compound in the obtained lithium hexafluorophosphate were all 50 ppm or less.

[0016]

According to the present invention, high-purity lithium hexafluorophosphate having an impurity concentration of lithium fluoride, phosphorus oxyfluoride or the like lower than that of the conventional one can be obtained relatively easily.

Continuing on the front page (72) Inventor Hisakazu Ito 5253 Oki Ube, Oji, Ube City, Yamaguchi Prefecture Inside Central Glass Co., Ltd. Inside Ube Research Laboratory (72) Inventor Makoto Asegawa 5253 Oki Obe, Oji, Ube City, Yamaguchi Prefecture Central Glass Co., Ltd. (56) References JP-A-60-251109 (JP, A) JP-A-4-175216 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01B 25/455 H01M 6/16 H01M 10/40

Claims (1)

(57) [Claims] 1. A method for purifying lithium hexafluorophosphate, comprising contacting lithium hexafluorophosphate with a gas containing phosphorus pentafluoride.