JPH0410711B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a solute for a non-aqueous electrolyte comprising LiPF ₆ .

For batteries that use lithium as the cathode active material,
As the electrolytic solution, a non-aqueous electrolytic solution is used, which is obtained by dissolving an appropriate solute, that is, an electrolyte for imparting ionic conductivity, in an organic solvent. Typical examples of the above solutes in this type of electrolyte are
LiPF ₆ is known. LiPF ₆ is generally produced by dissolving LiF in anhydrous hydrogen fluoride and adding gaseous PF ₅ to this.
It is made by injecting and reacting,
LiPF ₆ produced by this method usually contains acidic impurities such as hydrogen fluoride and HPOxFy in the crystal particles.

When such LiPF ₆ is dissolved in an organic solvent to make a non-aqueous electrolyte, the liquid becomes acidic, which accelerates the decomposition of LiPF ₆ , and the PF ₅ produced by this decomposition is likely to form a Lewis base. It attacks organic solvents such as 1,3-dioxolane and easily decomposes or polymerizes the solvents. For this reason,
This results in an increase in internal resistance and a decrease in battery capacity during storage after battery assembly.

However, when using this type of crude LiPF ₆ as a solute for nonaqueous electrolytes, conventionally, the water and volatile impurities contained in it have been removed by vacuum drying, but the acidic impurities mentioned above have been removed by vacuum drying. There is almost no removal process.

In view of the above circumstances, the inventors initially
Attempts were made to remove acidic impurities by exothermically dissolving LiPF ₆ in an organic solvent such as dimethoxyethane, followed by cooling and recrystallization, but since the recrystallized LiPF ₆ was solvated. As a result, acidic impurities remained in the incorporated solvent molecules, and the intended purpose of removing acidic impurities could not be sufficiently achieved. Of course, LiPF ₆ of relatively high purity can be obtained by repeating the recrystallization process many times, but in this case, the yield will be extremely low and the efficiency of the manufacturing process will be greatly impaired.

This invention was discovered as a result of further studies from the above viewpoint, and its gist is that when producing a solute for a non-aqueous electrolyte consisting of LiPF ₆ , LiPF ₆ containing acidic impurities is After exothermic dissolution in a solvent, a processing agent consisting of a Li compound or amines that can form a salt or a complex compound with the above acidic impurities is added to neutralize it.
The present invention provides a method for producing a solute for a non-aqueous electrolyte, which comprises filtering LiPF ₆ that has been cooled and recrystallized.

That is, in this invention, when crude LiPF ₆ is recrystallized in an organic solvent, a specific processing agent that reacts with acidic impurities is added to neutralize the crude LiPF ₆ . According to this, if the neutralization reaction product is insoluble in an organic solvent, it can be filtered out together with the excess processing agent (surplus not dissolved in the organic solvent), and the neutralization reaction product soluble in an organic solvent can be filtered out. In this case, it was recrystallized by cooling.
When LiPF ₆ is collected by filtration, the above-mentioned reactants can be left in the filtrate and removed.

LiPF ₆ obtained in this way has a very low content of acidic impurities by performing the above operations, that is, dissolution in an organic solvent, neutralization treatment, and recrystallization, only once. Therefore, unlike the simple recrystallization method described above, there is no particular need to repeat the same operation many times, and this extremely reduces the yield of LiPF ₆ , which also greatly reduces the production efficiency. Not at all. Of course, it is possible to increase the removal rate of acidic impurities by repeating the operation within a range that does not impair the above characteristics.

As described above, according to the present invention, it is possible to obtain highly pure LiPF ₆ with few acidic impurities, so when it is dissolved in an organic solvent to form a non-aqueous electrolyte, the decomposition of LiPF ₆ over time can be suppressed. Furthermore, the possibility of inducing decomposition or polymerization of the organic solvent is avoided, and extremely good results can be obtained in terms of aging characteristics of battery capacity and internal resistance after battery assembly.

LiPF ₆ containing acidic impurities applied to this invention
As mentioned above, LiF contains impurities such as hydrogen fluoride and HPOxFy, which are obtained by dissolving LiF in anhydrous hydrogen fluoride and blowing gaseous PF ₅ into it. ₆ , it may be obtained by other manufacturing methods.

In this invention, the above crude LiPF ₆ is first dissolved in an organic solvent. This organic solvent may be non-polar or one with polar groups as long as it can dissolve LiPF ₆ , but if solubility is important, it is recommended to use non-aqueous electrolyte Commonly used as 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 1,2-diethoxyethane, 2-methyltetrahydrofuran, propylene carbonate, γ-
It is preferable to use a material with a high dielectric constant, such as butyrolactone, which has a polar group such as an ether bond or an ester bond in its molecule.

Among these, 1,2-dimethoxyethane, 1,2
- It is also preferable to use materials such as diethoxyethane and propylene carbonate, which, when a portion of LiPF ₆ decomposes before neutralization, coordinate with the decomposition product PF ₅ to create a chemically stable state. It is. Of course, as long as the neutralization treatment is carried out as soon as possible to suppress the above decomposition, and as long as appropriate additives are used to achieve a chemically stable state, 1.3
- Polar solvents that are inherently prone to decomposition or polymerization due to the presence of PF ₅ such as dioxolane can also be used as preferred solvents.

Although the amount of the organic solvent used is not particularly limited, it is desirable to keep it to the minimum necessary so that recrystallization can be performed in high yield by cooling. For solvents with polar groups such as those exemplified above and which cause coordination bonds, the amount is usually 3 times or more by mole relative to LiPF ₆ .
Preferably, the amount is 5 times or more by mole.

When crude LiPF ₆ is dissolved in such an organic solvent, it generally generates heat due to the heat of dissolution and reaches 60 to 70℃, so after that, neutralization treatment with Li compounds or amines is performed while maintaining the above temperature by external heating. Let's do it. A neutralization treatment time of about 2 to 4 hours is usually sufficient.

Li compounds or amines for neutralization treatment are
It may be added to the organic solvent at the same time as LiPF ₆ , or it may be added after the above temperature has been reached. Preferably, they are added at the same time, so that partial decomposition of LiPF ₆ that may occur before addition can be prevented as much as possible.

Such Li compounds or amines are
Acidic impurities contained in LiPF ₆ , especially those that can form salts or complex compounds with hydrogen fluoride, are fine, and whether or not they are soluble in organic solvents is not an essential issue, but in general, even a very small amount Compounds that are soluble are preferably used. A typical example is as a Li compound.
LiF, LiO, Li ₂ CO ₃ and the like, and amines such as triethylamine and N-N-N'-N'-tetramethylethylenediamine. The amount used should be sufficient to remove acidic impurities;
The amount is about 1 to 20 parts by weight per 100 parts by weight of LiPF ₆ .

After the above neutralization treatment, the reaction solution is filtered while maintaining the temperature to remove excess processing agents such as Li compounds and reaction products dispersed and suspended in the reaction solution. Then, when the filtrate is cooled to near room temperature, the
Since LiPF ₆ crystals precipitate, the desired purified LiPF ₆ can be obtained by filtering the crystals. If it is desired to further reduce the content of acidic impurities in this purified LiPF ₆ , the above operation can be repeated.

The LiPF ₆ thus obtained contains almost no acidic impurities, but is solvated by the organic solvent used, so by appropriately selecting the temperature conditions for drying under normal pressure or under reduced pressure, The above-mentioned solvent can be completely removed or the number of solvated moles can be reduced, and it can be used as a solute for a non-aqueous electrolyte. As the organic solvent used at this time, it is preferable to use a conventionally used organic solvent, that is, one having a polar group such as an ether bond or an ester bond in the molecule and having a high dielectric constant, as exemplified as a preferable solvent for purification. Ru.

Note that if the organic solvent used during purification can be used as is as an organic solvent for non-aqueous electrolytes, it can be used in the same manner as above without going through the above-mentioned operation for removing or reducing the solvent. can.

EXAMPLES Below, examples of the present invention will be described in more detail.

Example 1. 100g of crude LiPF ₆ containing acidic impurities was dissolved in 700ml of 2-dimethoxyethane, and further
10 g of Li ₂ CO ₃ was added. Due to the exothermic reaction, the liquid temperature increases
After reaching 60 to 70°C, the temperature was maintained by external heating and the reaction was continued for about 2 hours. During this reaction, a portion of Li ₂ CO ₃ remained undissolved and was dispersed in suspension in the liquid.

After the above neutralization reaction, the suspended matter was separated and removed by filtration while maintaining the temperature of the solution, and then the filtrate was cooled.
LiPF ₆ was crystallized. This precipitate was collected by filtration,
Further, the solvated 1,2-dimethoxyethane was removed by drying under reduced pressure.

The purified LiPF ₆ obtained in this way; 45.6 g was
A non-aqueous electrolyte was prepared by dissolving it in 200 ml of 1,3-dioxolane, and using this electrolyte, a lithium battery as shown was fabricated by a conventional method. In the figure, 1
is a cathode with lithium as the active material, 2 is FeS ₂ ,
An anode using MnO ₂ or TiS ₂ as an active material, 3 a separator made of a nonwoven fabric such as polypropylene, and 4 a gasket interposed between the anode can 5 and the cathode terminal plate 6.

The results of examining the changes in battery capacity over time when this battery was stored at room temperature and the changes over time in internal resistance when stored at 60°C were as follows. For comparison, the crude LiPF ₆ used in the example
Test results similar to those described above are also listed for a battery produced in the same manner as in the example except that the solute was used as the solute for the non-aqueous electrolyte.

Example product Comparative example product Deterioration rate of battery capacity 0.5%/month 3%/month Increase rate of internal resistance 0.1Ω/month 0.5Ω/month As is clear from the above results, according to the method of the invention, the battery characteristics High purity LiPF ₆ contributes to improvement
It can be seen that it can be manufactured easily.

[Brief explanation of drawings]

The drawing is a cross-sectional view showing an example of a lithium battery manufactured using the solute for non-aqueous electrolyte obtained by the method of the present invention.

Claims (1)

[Claims] 1. In producing a solute for a non-aqueous electrolyte consisting of LiPF ₆ , LiPF ₆ containing acidic impurities is exothermically dissolved in an organic solvent, and at the same time, a Li compound or amine that can form a salt or a complex compound with the above acidic impurities is added. 1. A method for producing a solute for a non-aqueous electrolyte, which comprises neutralizing LiPF ₆ by adding a treatment agent consisting of the following, followed by cooling and recrystallizing LiPF 6.