JPS5953216B2 - Synthesis method of anhydrous lithium borofluoride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION With the development of electronics, the development of batteries with high energy density and density is progressing, and in particular, lithium batteries using metal lithium, which has an extremely base electrode potential, as the negative electrode are attracting attention.

Since lithium reacts violently with water in these lithium batteries, it is necessary to use a non-aqueous electrolyte as the electrolyte, and conventionally organic/inorganic solvents and solutes suitable for this purpose have been used.

Among these solutes, lithium perchlorate (LiC1O, ), lithium borofluoride (LiBF0)
, lithium aluminum chloride (LiAlCl, ), potassium phosphorus fluoride (KPF0), sodium phosphorus fluoride,
(NaPF.

)O and other anhydrous Lewis acid salt compounds have been found to be useful. However, the most important thing to keep in mind when manufacturing such a solute is that impurities in the electrolyte will have a significant effect on the performance of the battery.

In other words, the secret to improving battery performance is to synthesize a solute with high quality and low residual water content, and this is considered to be a prerequisite for battery production.

The present invention relates to a method for synthesizing anhydrous lithium borofluoride, which is said to have particularly good properties among the several types of solvents mentioned above.

Two known methods for synthesizing lithium borofluoride have been reported: a wet method and an ether method.

(A) In the wet method, a hydrated salt is generated according to the following formula.

2HBF4aq-soln・+Li2C03→LiBF
4.H2O+C02 hydrate salt LiBF, .H.

During heating, O melts at 102°C before dehydration, and it is necessary to raise the temperature to about 200°C for dehydration, but LiBF4→L
Decomposition of iF+BF3 occurs, which not only reduces purity but also leaves water behind, making it unusable for lithium batteries. (B
) In the ether method, BF3・(C2H5)20+LiF→LiBF4+(C
2H5) 20 An anhydrous salt can be obtained by the reaction of a complex of boron trifluoride and methyl ether or ethyl ether with lithium fluoride, but since lithium fluoride and lithium borofluoride are poorly soluble in ether. However, there are drawbacks such as difficulty in obtaining high-quality products that are satisfactory for use in lithium batteries, and the use of dangerous ether.

As described above, when using lithium borofluoride for lithium batteries, it is not possible to obtain a product of satisfactory quality using known methods.

As a result of various studies, the inventors of the present invention have found that fluorocarbons can be dissolved in non-aqueous solvents. A synthesis method that uses one or more non-aqueous solvents having the following characteristics as part or all of the solvent when producing anhydrous lithium borofluoride by reacting lithium pentatsuride and boron trifluoride. invented.

11. Dissolve the produced lithium borofluoride. 2. Make a complex with boron trifluoride.

3. It is liquid over a wide temperature range.

Solvents that meet the above conditions include methyl acetate, ethyl monoacetate, dimethoxyethane, propylene carbonate, γ
-Butyrolactone, tetrahydrofuran (C4H8O
) could be found.

First, regarding the solubility of lithium borofluoride, it showed a large solubility as illustrated below. For comparison, the case of ethyl ether is approximately 1.7 wt% LiBF
4/Sat. sOln (25°C).

The solvents that form complexes with boron trifluoride are as follows. Solvents methyl acetate, ethyl acetate, making a 1:1m01BF3/MOI solvent complex.
Propylene carbonate, γ-butyrolactone, tetrahydrofuran 1:l and 2:1m01BF3/MO
Solvent dimethoxyethane that forms the solvent complex It is also clear from the following table of melting points and boiling points that these solvents are liquid over a wide temperature range.

To obtain crystals of anhydrous lithium borofluoride, boron trifluoride and lithium fluoride are reacted in a solvent in which lithium borofluoride has a high solubility to form a solution, and after removing insoluble materials, boron trifluoride is further added. The solubility of lithium borofluoride can be easily obtained by absorbing part or all of the solvent into a boron trifluoride complex, or by concentrating the solvent as it is.

The boron trifluoride complex is liquid depending on the temperature conditions, and the lithium borofluoride crystals can be easily isolated and the remaining solvent and the complex can be reused.

At this time, once the lithium borofluoride is dissolved,
By filtering, unreacted lithium fluoride and impurities in the lithium fluoride, such as lithium carbonate (Li2CO3) and lithium oxide (Li2O), can be removed, and high quality and good crystals can be obtained.

This series of operations is facilitated by the fact that the solvent is liquid over a wide temperature range.

In addition, when preparing a lithium borofluoride solution, such as an electrolyte for lithium batteries, it is necessary to first synthesize lithium borofluoride crystals, which are extremely deliquescent and difficult to handle.
Rather than dissolving in a solvent, as in the method of the present invention, a solvent,
Synthesizing the target product all at once by mixing boron trifluoride and lithium fluoride is thought to be preferable in terms of the number of operations and economical efficiency, since there is less contamination of water and impurities.

For applications such as batteries that require conductive non-aqueous solutions,
Generally, the following properties are required, and many of the target solvents of the present invention meet these properties.

Lithium borofluoride has high solubility in 8 solvents.

8 Chemically stable against electrodes and others.

O solution has ionic conductivity.

This is not a coincidence; as has been made clear by the present invention, when synthesizing anhydrous lithium borofluoride, there are problems such as the high solubility of lithium borofluoride in aprotic solvents and corrosion of the equipment as described above. This is probably due to the fact that there are fewer people.

In addition to the above-mentioned solvents, methanol, ethanol, sulfur dioxide, thionyl chloride (SOCl2), ethylene carbonate, methylpyrrolidone, etc. have similar properties and are difficult to procure as water-free solvents, and boron trifluoride Although there are some drawbacks such as the high solubility of lithium borofluoride in the complex, the high melting point of the boron trifluoride complex, and the fact that it is solid or gaseous at room temperature, it is possible to use these in some cases. You can also do it.

For example, if the melting point is high, a third substance with a low melting point can be added. The method for synthesizing anhydrous lithium borofluoride crystals and solutions according to the present invention has the following characteristics.

1 High purity lithium borofluoride can be synthesized.

2. Since a non-aqueous solvent is used, the most inconvenient generation and contamination of water can be avoided.

3 Product yield is high.

24 Once in a dissolved state, purification such as dehydration, removal of undissolved substances, and decolorization is easy. 5
Electrolytes for batteries can be directly synthesized.

Next, examples of the synthesis method according to the present invention will be shown.

Example A stirrer was set in a 15-liter glass three-loaf flask, and 2500 g of ethyl acetate after dehydration with anhydrous calcium chloride was added thereto and continuously stirred. While cooling the outside of the flask with water, 1750.1 g of boron trifluoride gas was added. was blown until it could no longer be dissolved and absorbed.

Next, 600 g of lithium fluoride was added, dissolved, and undissolved matter was filtered out, and then 850 g of boron trifluoride gas was blown into the solution while stirring and cooling with water until a precipitate crystallized.

The product was vacuum-dried at 90°C for 3 hours after suction filtration, and the purity was 9.
Lithium borofluoride 900 with 9.8% and moisture 0.01%
I got g.

Example 2 A stirrer was set in a 5-liter glass three-hole flask, and 1720 g of dimethoxyethane purified by distillation and 60 g of pulverized and thoroughly dried lithium fluoride were continuously stirred, and the outside of the flask was cooled with water. While doing so, 136 g of boron trifluoride gas was slowly inhaled.

The product is a 1M LiBF4 solution in dimethoxyethane,
It could be used as an electrolyte for lithium batteries, etc.

Example 3 A stirrer was set in a 5-liter three-bottle glass flask, and 1,900 g of propylene carbonate purified by distillation and 200 g of benzene were added, and 60 g of pulverized and thoroughly dried lithium fluoride were continuously stirred. While cooling the outside with water, 136 g of boron trifluoride gas was slowly blown in.

The product is 1M-LiBF4 propylene carbonate.
The benzene solution could be used as a low-viscosity electrolyte for lithium batteries, etc. Example 4 A stirrer was set in a 5-liter three-bottle glass flask, and 2150 g of distilled and purified γ-butyrolactone and 100 g of R-113 (CCl2CF2) and 60 g of pulverized and thoroughly dried lithium fluoride were added and stirred continuously. 136 g of boron trifluoride gas was slowly blown into the flask while stirring and cooling the outside of the flask with water.

Claims (1)

[Claims] 1. When producing anhydrous lithium borofluoride by reacting lithium fluoride and boron trifluoride in a non-aqueous solvent, methyl acetate dissolves the produced lithium borofluoride and forms a complex with boron trifluoride;
A method for synthesizing anhydrous lithium borofluoride, characterized in that ethyl acetate, dimethoxyethane, propylene carbonate, γ-butyrolactone or tetrahydrofuran is used as a solvent.