JPH0410712B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention describes the use of super acidic bases such as LiPF ₆ .
This invention relates to a method for producing a solute for a non-aqueous electrolyte consisting of a lithium salt of (acid anion).

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.

In addition, the LiPF ₆ mentioned above is a typical one known as a lithium salt of a so-called super acidic base.
Many other solutes for nonaqueous electrolytes made of lithium salts similar to those described above include LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiAlCl _{4 ,} and the like. If these various lithium salts are synthesized using the same method as LiPF ₆ mentioned above and acidic impurities such as hydrogen fluoride or hydrogen chloride are mixed in, it will cause the same decomposition and adverse effects on the organic solvent as described above. As a result, battery performance tends to deteriorate.

However, conventionally, when using lithium salts of super acidic bases, such as LiPF ₆ as a representative example, as solutes for non-aqueous electrolytes, the water and volatile impurities contained in them have been removed by vacuum drying. However, almost no treatment is performed to remove the aforementioned acidic impurities.

In view of the above circumstances, the inventors initially solved the acidic impurities by a method in which a lithium salt of a super acidic base containing acidic impurities was dissolved exothermically in an organic solvent such as dimethoxyethane, and then cooled and recrystallized. However, since the lithium salt to be recrystallized is solvated, acidic impurities remain in the incorporated solvent molecules, and the intended purpose of removing acidic impurities cannot be fully achieved. Nakatsuta.

This invention was discovered as a result of further studies from the above viewpoint, and its gist is that in producing a solute for a non-aqueous electrolyte consisting of a lithium salt of a super acidic base, sodium A method for producing a solute for a nonaqueous electrolyte, characterized by obtaining a lithium salt of a superacidic base by dissolving a salt or a potassium salt in an organic solvent and ion-exchanging it with a lithium ion type cation exchange resin. It is in.

That is, in this invention, the method of directly synthesizing the lithium salt of a superacidic base by the method described above inevitably introduces acidic impurities, and it is not easy to remove these impurities. A potassium salt is synthesized and then ion-exchanged with a lithium ion type cation exchange resin. According to this method, the sodium salt or potassium salt is sufficiently treated with alkali during the manufacturing process. Since it is a lithium salt, almost no acidic impurities remain, and therefore the lithium salt obtained by ion-exchanging it also contains very little acidic impurities.

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

In this invention, a typical lithium salt of a superacidic base is LiPF ₆ , but other examples include LiBF ₄ , LiSbF ₆ , LiAsF ₆ and LiAlCl ₄ as described above. In addition to these, those known as lithium salts of superacidic bases, which are susceptible to adverse effects such as decomposition due to contamination with acidic impurities, are also included in the target substances of the present invention, as described above.

In this invention, first, a potassium salt or a sodium salt of a superacidic base corresponding to the above-mentioned lithium salt is obtained. This method is arbitrary as long as the manufacturing process includes a sufficient alkali treatment step. For example, the following method is effective for KPF ₆ or NaPF ₆ . That is, potassium chloride or sodium chloride and phosphorus pentachloride are fluorinated in liquid hydrogen fluoride and heated on an oil bath to drive off the hydrogen fluoride. After that, in the case of using potassium chloride, the crude salt is dissolved in warm water, potassium hydroxide solution is added until it becomes alkaline with phenolphthalein, the precipitate is removed, and then the salt is cooled in an ice bath. For those using sodium chloride, dissolve the crude salt in methanol, add a methanol solution of sodium hydroxide until it becomes alkaline with phenolphthalein, centrifuge the precipitate, concentrate, and precipitate crystals under reduced pressure. According to
Obtain pure KPF ₆ or NaPF ₆ respectively.

Next, the above potassium salt or sodium salt is dried under reduced pressure to remove water and other impurities as necessary, then dissolved in an appropriate organic solvent, and passed through a lithium ion type cation exchange resin. ion exchange between potassium or sodium ions and lithium ions (column method), or ion exchange by immersing a lithium ion type cation exchange resin in an organic solvent in which potassium or sodium salts are dissolved. Let them do it (Batsuchi method).

Examples of the above organic solvents include 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 1,2-diethoxyethane, 2-methyltetrahydrofuran, propylene carbonate, and γ, which are commonly used for non-aqueous electrolytes. −
A solvent having a polar group such as an ether bond or an ester bond in its molecule, such as butyrolactone, and having a high dielectric constant is preferred, but other solvents may be used. The concentration of potassium salt or sodium salt in the organic solvent is usually about 1 to 30% by weight.

Lithium ion type cation exchange resin is produced by stirring a general sodium ion type cation exchange resin in an organic solvent containing a high concentration of lithium ions, such as lithium chloride, or by stirring it into a sodium ion type ion exchange resin. It can be easily obtained by passing an organic solvent containing lithium ions through it to cause ion exchange between sodium ions and lithium ions. The organic solvent used in the above process is one that can dissolve lithium ions at a high concentration, for example, about 10 to 30% by weight. Those exemplified as solvents can be used in the same manner.

The organic solvent solution of the lithium salt of a superacidic base obtained by ion exchange in the above method can be used as it is as a non-aqueous electrolyte after being dehydrated if necessary. In addition, the lithium salt alone is obtained by once removing the organic solvent under reduced pressure,
This may be redissolved in a predetermined organic solvent to form a non-aqueous electrolyte.

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

Example 1 A lithium ion type cation exchange resin was obtained by slowly passing 1,3-dioxolane in which 15% by weight of lithium chloride was dissolved into a column of a commercially available sodium ion type cation exchange resin.

Next, commercially available NaPF ₆ from which most of the acidic impurities have been removed through an alkali treatment process was added to 18 ml of 1,3-dioxolane as an organic solvent.
This was passed through the lithium ion type cation exchange resin described above to obtain 1,3-dioxolane in which pure LiPF ₆ containing no acidic impurities was dissolved.

Using this as an electrolyte, a lithium battery as shown in the figure was produced by a conventional method. In the figure, 1 is a cathode made of lithium as an active material, 2 is an anode made of FeS ₂ , MnO ₂ or TiS ₂ as an active material, 3 is a separator made of nonwoven fabric such as polypropylene, and 4 is a cathode made of lithium as an active material.
is a gasket interposed between the anode can 5 and the cathode terminal plate 6.

The results of examining the battery capacity and internal resistance over time when this battery was stored at 60°C were as follows. For comparison, the experiments were carried out except that LiPF ₆ (containing acidic impurities), which was directly synthesized by dissolving LiF in anhydrous hydrogen fluoride and blowing gaseous PF ₅ into it, was used as the solute for the non-aqueous electrolyte. Regarding the lithium battery produced in the same manner as in Example 1, test results similar to those described above are also listed.

Example product Comparative example product Deterioration rate of battery capacity 1%/month 4%/month Rate of increase in internal resistance 50%/month 60%/month As is clear from the above results, this invention method improves battery performance. It can be seen that the highly purified lithium salt of a superacidic base that contributes to improvement can be produced 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 a lithium salt of a super acid anion, the sodium salt or potassium salt of the base is dissolved in an organic solvent, and lithium ions are dissolved in the solute. A method for producing a solute for a non-aqueous electrolyte, characterized by obtaining a lithium salt of a super acidic base by ion exchange with a type of cation exchange resin. 2 The lithium salt of superacid base is LiPF ₆ ,
The method for producing a solute for a non-aqueous electrolyte according to claim 1, wherein the solute is selected from LiBF ₄ , LiSbF ₆ , LiAsF ₆ and LiAlCl ₄ .