JP2898163B2 - Stabilized lithium hexafluorophosphate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to stabilized lithium hexafluorophosphate useful as an electrolyte for a lithium secondary battery or 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.

[0003] Various purification methods have been proposed for removing impurities generated by such decomposition, but a method for fundamentally suppressing this decomposition has not yet been found.

[0004]

[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 provides a stabilized lithium hexafluorophosphate characterized by having a lithium fluoride layer surface. Lithium hexafluorophosphate used in the present invention is a very unstable compound, and the following hydrolysis reaction is caused by water mixed into the system as an impurity from the manufacturing process or from storage and handling. Wake up and reduce quality. LiPF ₆ + xH ₂ O → LiPO _X F _(6-2X) + 2 × HF (1) LiPO _X F _(6-2X) , HF generated by this decomposition reaction
It is known that impurities such as have a significant effect on battery performance when used as an electrolyte for lithium batteries, which is a use of lithium hexafluorophosphate.

As a result of various studies, the present inventors have made a conventional pure hexafluorophosphate by forming a composition in which the surface of lithium hexafluorophosphate is deliberately made into a lithium fluoride layer at the production stage. It has been found that hydrolysis resistance and self-decomposition resistance can be made better than lithium.

Conventionally, it was thought that the hydrolysis reaction proceeds simply by the mechanism as shown in equation (1). However, as a result of investigation, it is estimated that the hydrolysis proceeds by the following two-stage reaction mechanism. You. _{LiPF 6 → LiF + PF 5 (} 2) as the reason for the _{PF 5 + xH 2 O → PO} X F (5-2X) + 2xHF (3) stabilization by lithium fluoride layer is simply physical surface protection rather, due to the unusually high lithium fluoride concentration in the surface, (2) dissociation equilibrium is disturbed, and the reverse reaction proceeds, presumed occurrence of hydrolysable PF ₅ is sometimes referred suppressed Is done.

[0008] lithium fluoride order to this stabilization, 0.01-0.5%, preferably against lithium hexafluorophosphate PF ₅ gas to possible ingress surface, 0.
It needs to be present in an amount of 02 to 0.1 wt%.

At 0.01 wt% or less, there is no stabilizing effect, and at 0.5 wt% or more, there is an effect, but when lithium hexafluorophosphate is dissolved in a solvent, a large amount of LiF remains as an undissolved component and is filtered. Operation is required, which is complicated.

[0010] Lithium hexafluorophosphate stabilized by such a method hardly decomposed even when handled in air having a dew point of -20 ° C, but it did not have a lithium fluoride layer. The concentration of HF, one of the impurities generated by decomposition, is 400 ppm.
Increased.

As a specific means for forming a crystal surface of lithium hexafluorophosphate into a lithium fluoride layer, there is a method of subjecting the crystal to heat treatment, decomposing only the surface, and converting the crystal to lithium fluoride. However, the method is not particularly limited.

[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 hydrofluoric acid was removed under reduced pressure. Thereby, 1mm
65 g of lithium hexafluorophosphate crystals of uniform particle size
was gotten. Its purity is 99.9% or more,
Hydrofluoric acid as an impurity was 50 ppm, and lithium fluoride was 50 ppm or less.

This lithium hexafluorophosphate is SUS30
4 and heated to 160 ° C.
Heat treatment was performed for 1 hour under reduced pressure of torr. The concentration of hydrofluoric acid in the obtained lithium hexafluorophosphate is 50 ppm,
Lithium fluoride was 900 ppm (0.09 wt%). In addition, when PF ₅ gas was introduced into the surface of the crystal after this treatment, the fact that lithium fluoride was reduced to 50 ppm or less confirmed that this lithium fluoride was present on the surface layer through which PF ₅ gas could enter. did it.

After the treatment, lithium hexafluorophosphate is added to -20.
When left in air having a dew point of 5 ° C. for 5 hours, no increase in hydrofluoric acid was observed. Example 2 In the same manner as in Example 1, the synthesized lithium hexafluorophosphate was put into a SUS304 processing apparatus, and heated at 40 ° C.
For 24 hours at 5 L / min. Nitrogen gas was passed through the apparatus at a flow rate of. As a result, the hydrofluoric acid concentration of the impurity becomes 50 p.
pm, the concentration of lithium fluoride on the surface is 400 ppm (0.
(0.4 wt%) of lithium hexafluorophosphate.

After the treatment, lithium hexafluorophosphate is added to -20.
When left in air having a dew point of ° C. for 5 hours, the hydrofluoric acid concentration became 100 ppm. Example 3 Lithium hexafluorophosphate synthesized in the same manner as in Example 1 was placed in a SUS304 processing apparatus and heated at 40 ° C.
For 12 hours at 5 L / min. Nitrogen gas was passed through the apparatus at a flow rate of. As a result, the hydrofluoric acid concentration of the impurity becomes 50 p.
pm, the concentration of lithium fluoride on the surface is 200 ppm (0.
02 wt%) of lithium hexafluorophosphate.

After the treatment, lithium hexafluorophosphate is added to -20.
When left in air having a dew point of ° C. for 5 hours, the hydrofluoric acid concentration became 200 ppm. Comparative Example 1 Lithium hexafluorophosphate was synthesized in the same manner as in Example 1. It has a purity of 99.9% or more, a hydrofluoric acid concentration of impurities of 50 ppm, and a lithium fluoride concentration of 5 ppm.
It was 0 ppm or less.

When this unstabilized lithium hexafluorophosphate was left in air having a dew point of -20 ° C. for 5 hours, the hydrofluoric acid concentration increased to 700 ppm.

[0019]

The stabilized lithium hexafluorophosphate of the present invention is easier to handle than the conventional lithium hexafluorophosphate, and decomposes hydrofluoric acid and the like, which are considered harmful when used for lithium secondary batteries and the like. The generation of products is extremely low.

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Hisakazu Ito 5253 Oki Obe, Oji, Ube City, Yamaguchi Prefecture Inside Central Glass Co., Ltd. Inside Ube Laboratory, Glass Co., Ltd. (72) Inventor Makoto Asegawa, 5253 Oki Ube, Oji, Ube City, Yamaguchi Prefecture Central Glass Co., Ltd. Ube Research Laboratories, Inc. (56) References JP-A-4-175216 (JP, A) JP-A-60-251109 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01B 25 / 455 H01M 6/18

Claims (1)

(57) [Claims] 1. A stabilized lithium hexafluorophosphate having a lithium fluoride layer surface.