JP3257774B2 - Method for treating organic electrolyte containing lithium hexafluorophosphate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the treatment of lithium hexafluorophosphate in an organic electrolyte containing lithium hexafluorophosphate, which is currently used in large quantities for lithium ion batteries and lithium batteries. And also
The present invention relates to a technology for industrially reusing these compounds by separating hexafluorophosphate and lithium fluoride recovered by this treatment.

[0002]

2. Description of the Related Art As electrolytes for lithium ion secondary batteries and lithium secondary batteries, cyclic esters such as ethylene carbonate and propylene carbonate, and chain carbonates such as diethyl carbonate and dimethyl carbonate are mainly used. A solution obtained by dissolving lithium hexafluorophosphate as a solute in a mixed solvent combining the above is usually used. In order to treat these unnecessary organic electrolytes, they are usually incinerated in many cases, but the lithium hexafluorophosphate contained significantly consumes the furnace materials of the incinerator. In this electrolyte, hexafluorophosphate anion is relatively stable, and a general method for fixing hexafluorophosphate anion dissolved in an aqueous solution as a sparingly soluble salt, for example, The method of adding salts having large cations such as quaternary ammonium salts and quaternary phosphonium salts and recovering them as hexafluorophosphates with low solubility is difficult because these salts are easily soluble in organic solvents. Difficult to recover except when diluted. After dissolving in a large amount of water, it is hydrolyzed under strong acid conditions to make phosphoric acid and hydrofluoric acid, and calcium salts such as slaked lime can be added and fixed as calcium fluoride and phosphate apatite. The problem that it cannot be processed remains.

[0003]

In recent years, with the miniaturization and portability of various electronic devices, the demand for small, lightweight, and high energy density secondary batteries has been rapidly growing. A typical example is a lithium ion secondary battery. As the electrolytic solution, lithium hexafluorophosphate was dissolved as a solute in a mixed solvent of cyclic esters represented by ethylene carbonate and propylene carbonate, and chain carbonates represented by diethyl carbonate and dimethyl carbonate. Things are usually used. With the increase in demand for lithium ion secondary batteries and lithium secondary batteries that will be commercialized in the near future, treatment of electrolyte solutions containing lithium hexafluorophosphate no longer required,
Further, treatment of the electrolyte containing lithium hexafluorophosphate contained in the discarded lithium battery and lithium ion battery becomes a serious problem. Furthermore, no effective treatment for this problem has yet been established. An object of the present invention is to provide a method for effectively fixing lithium hexafluorophosphate in an organic electrolyte containing lithium hexafluorophosphate used for lithium batteries. . Another object of the present invention is to provide a technique capable of industrially reusing a compound recovered by this treatment.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, by adding a certain organic solvent to an organic electrolyte containing lithium hexafluorophosphate, Fix the lithium hexafluorophosphate in the electrolyte as potassium hexafluorophosphate or ammonium hexafluorophosphate by adding a fluoride salt such as potassium fluoride or ammonium fluoride. I found what I could do. In addition, lithium, which is a counter cation, can be fixed as lithium fluoride, and a technique of reusing the hexafluorophosphate and lithium fluoride recovered by filtration to further reuse the lithium fluoride has been found, thereby completing the present invention. Reached.

That is, in the present invention, treatment of an electrolyte containing lithium hexafluorophosphate which is no longer required, and
Regarding the treatment of the electrolytic solution containing lithium hexafluorophosphate contained in the discarded lithium battery and lithium ion battery, the number of carbon atoms represented by the general formula (A) C _n H _{2n + 1} OH── (A) n is a primary, secondary or tertiary alcohol having 2 to 5, for example, a series of alcohols represented by 2-propanol (primary, secondary and tertiary alcohols having 2 to 5 carbon atoms) By diluting or washing the electrolytic solution with a solvent containing
The liquid property of the electrolyte is changed to cause a smooth reaction between lithium hexafluorophosphate and potassium fluoride or ammonium fluoride in the electrolyte, and an additive (potassium fluoride or ammonium fluoride) and a product are formed. (Lithium fluoride and potassium hexafluorophosphate or ammonium hexafluorophosphate) were both found to be present as solids. These solids could be easily separated by a general filtration method, and most of the hexafluorophosphate anions were fixed in the solids.

The present invention will be described more specifically. As an electrolyte for lithium ion secondary batteries and lithium secondary batteries, aprotic solvents, ethylene carbonate, propylene carbonate, diethyl carbonate,
A mixture in which lithium hexafluorophosphate is dissolved as a solute in a mixed solvent such as dimethyl carbonate, 1,2-diethoxyethane, dimethyl sulfoxide, sulfolane, γ-butyl lactone, and tetrahydrofuran is mainly used. Although the type and combination of solvents vary considerably depending on the battery manufacturer, conditions such as sufficient dissolution of lithium hexafluorophosphate, stable retention of lithium hexafluorophosphate, and high electrical conductivity are required. Therefore, there is not much difference in basic characteristics and liquid properties of the electrolytic solution.
Therefore, the present invention can be applied to all electrolyte solutions containing lithium hexafluorophosphate regardless of the type of the solvent.

In the present invention, typical examples of the electrolyte containing lithium hexafluorophosphate include 50 wt% -ethylene carbonate-50 wt% -diethyl carbonate,
And 50 wt% -propylene carbonate-50w
Various studies were conducted on two types of electrolyte solutions prepared by dissolving lithium hexafluorophosphate in t% -diethyl carbonate to prepare a 11.5 wt% solution. First, sodium hydroxide, potassium hydroxide, ammonia, potassium fluoride,
An attempt was made to fix the hexafluorophosphate anion by adding an inorganic compound such as sodium fluoride or ammonium fluoride, but none of them was successful. Thus, a method was attempted in which the liquid property of the electrolytic solution was changed by adding another organic solvent, and an inorganic salt was added to fix the hexafluorophosphate anion. As a result, methylene chloride and a series of alcohols (ethanol, 1-propyl alcohol, 2-propyl alcohol, 1-butanol, 2-butanol, t-butanol and octanol) are used in industrially used solvents. An effect was seen when used. Further, an effect was obtained when ammonium fluoride and an alkali metal fluoride such as sodium fluoride, potassium fluoride, cesium fluoride, and rubidium fluoride were used as the inorganic salts.

[0008] As a screening experiment, 11.5 w
A mixed solution of ethylene carbonate and diethyl carbonate containing t % lithium hexafluorophosphate (weight ratio 1:
1) 50 g, 50 g of organic solvent and 4 g of potassium fluoride
After placing in a 00 ml Teflon bottle and stirring with a magnetic stirrer at 20 ° C. for 2 hours, the solid content was separated by filtration, and the fluorine content in the filtrate was analyzed to remove lithium hexafluorophosphate (hereinafter referred to as “removal rate”). Simply referred to as removal rate). Table 1 shows some of the results.

[0009]

[Table 1]

[0010] Although methylene chloride has a high removal rate, it is difficult to use it as a solvent in the future due to problems of wastewater regulation and destruction of the ozone layer. Among the alcohols, no effect was observed for alcohols having a molecular weight larger than methanol and hexanol. Regarding the relationship between the amount of the solvent and the removal rate, the removal rate increases as the amount of the solvent increases. 50 g of a mixed solution of ethylene carbonate and diethyl carbonate (1: 1 by weight) containing 11.5 wt % lithium hexafluorophosphate and 4 g of potassium fluoride were fixed, and the amount of 2-propyl alcohol as a solvent was changed. After stirring with a magnetic stirrer at 20 ° C. for 2 hours, the solid content was filtered off. Table 2 shows the removal rate in the filtrate after filtration.
Shown in

[0011]

[Table 2]

If the amount of the solvent with respect to the electrolyte containing lithium hexafluorophosphate is 0.5 times or less, there is almost no effect, and using a large amount is economically disadvantageous.
Therefore, it is preferable to use 0.5 to 40 times the amount of the solvent with respect to the electrolyte containing lithium hexafluorophosphate. In the case of the treatment of the electrolyte containing lithium hexafluorophosphate which is no longer required, a relatively small amount of solvent is used, and
Regarding the treatment of the lithium hexafluorophosphate-containing electrolytic solution contained in the discarded lithium battery and lithium ion battery, it is preferable to use a larger solvent in order to wash out with such a solvent. The solvent used may be any of the above-described series of alcohols as the main component, and the presence of impurities is not limited at all unless the lithium hexafluorophosphate or the electrolytic solution is decomposed. The solvent used in this treatment can be recovered by distillation from the filtrate and reused, or a waste liquid containing these alcohols discharged in another process can also be used. A mixed solvent of these alcohols may be used.

As inorganic salts, effects were observed on alkali metal fluorides such as sodium fluoride, potassium fluoride, cesium fluoride and rubidium fluoride, and ammonium fluoride. In particular, when cesium fluoride and rubidium fluoride were used, an effect exceeding the removal rate shown in Table 1 was observed, but these compounds are not suitable for this purpose because they are very expensive. On the other hand, sodium fluoride is very inexpensive, but its removal rate is lower than that of potassium fluoride and ammonium fluoride, and the generated sodium hexafluorophosphate is unstable in the atmosphere including moisture. There is. For these reasons, it is optimal to use a drug based on potassium fluoride or ammonium fluoride. This addition amount is sufficient if the reaction proceeds smoothly, from 1.0 to 2.0 equivalents to lithium hexafluorophosphate contained in the electrolytic solution. There is no. Potassium fluoride or ammonium fluoride can be used in the form of either a solid or a concentrated aqueous solution. However, when used in the form of an aqueous solution, the removal rate is reduced, so that it is preferably used in the form of a solid.

The solvent and potassium fluoride or ammonium fluoride may be added to the electrolyte containing lithium hexafluorophosphate in any order, provided that these three components are at least mixed. After the treatment, lithium hexafluorophosphate becomes a hardly soluble solid (lithium fluoride and potassium hexafluorophosphate, or lithium fluoride and ammonium hexafluorophosphate), and unreacted potassium fluoride or fluoride. It can be easily separated by filtration with ammonium. In the treatment of an electrolytic solution having a high dilution ratio with a solvent, it is effective to pass the diluted solution through a column filled with potassium fluoride or ammonium fluoride. By adjusting the flow rate, the hexafluorophosphate anion can be completely immobilized. The solid obtained by filtration is a mixture of lithium fluoride, potassium hexafluorophosphate and potassium fluoride, or a mixture of lithium fluoride, ammonium hexafluorophosphate and ammonium fluoride.
Each of the components could be recovered as a high-purity compound by treating with an aqueous system.

The separation method will be described in detail with reference to lithium fluoride, potassium hexafluorophosphate and potassium fluoride as examples. After the solid matter (lithium fluoride, potassium hexafluorophosphate and potassium fluoride) collected by filtration is dried and dissolved in hot water, only lithium fluoride having a low solubility exists as a solid matter. The slurry solution was subjected to hot filtration and washing with water, whereby high-purity lithium fluoride could be recovered. Instead of dissolving in hot water, a method of heating by adding water to the solid collected by filtration may be adopted. On the other hand, potassium hexafluorophosphate and potassium fluoride remain in the filtrate obtained by hot filtration. However, the difference in solubility between potassium hexafluorophosphate and potassium fluoride near room temperature is large. Only potassium phosphate precipitated as crystals and could be recovered by filtration. This purity was 98% or more, and was sufficiently reusable as industrial potassium hexafluorophosphate.

In immobilizing the hexafluorophosphate anion, an agent mainly composed of ammonium fluoride can be used instead of potassium fluoride. In the case of using a drug containing ammonium fluoride as a main component, high-purity lithium fluoride can be recovered by the same principle as that of using a drug containing potassium fluoride as a main component. Only ammonium hexafluorophosphate precipitates as crystals of ammonium fluoride phosphate and ammonium fluoride upon cooling, and can be collected by filtration. Almost no difference was observed in the removal rates when potassium fluoride and ammonium fluoride were used. However, a comparison was made between the subsequent process, in which lithium fluoride, potassium hexafluorophosphate and potassium fluoride were separated, and the case in which lithium fluoride, ammonium hexafluorophosphate and ammonium fluoride were separated. Since the recovery operation is easier because the solubility of potassium hexafluorophosphate in water is smaller than the solubility of ammonium hexafluorophosphate, potassium fluoride is mainly used rather than using an agent mainly containing ammonium fluoride. It is more advantageous to use a drug as a component.

[0017]

Next, the present invention will be further described with reference to specific examples. (Example 1) A stirrer was provided with 2000 g of a mixed solvent of ethylene carbonate and diethyl carbonate (1: 1 by weight) containing 11.5 wt% of lithium hexafluorophosphate, 2000 g of 2-propanol, and 160 g of potassium fluoride. Into a 5000 ml polyethylene reactor and treated for 2 hours. After treatment, as a result of filtration to remove solids,
The hexafluorophosphate ion concentration (in terms of lithium hexafluorophosphate) in the solution was reduced to 1.18%. The removal rate of lithium hexafluorophosphate was 80%.

Example 2 2000 g of a mixed solvent of propylene carbonate and diethyl carbonate (1: 1 by weight) containing 11.5 wt % of lithium hexafluorophosphate, 2-propanol 20
00g and 160g of potassium fluoride were added with a stirrer 5
It was placed in a 000 ml polyethylene reactor and treated for 2 hours. After the treatment, the solid matter was removed by filtration. As a result, the concentration of hexafluorophosphate ion (in terms of lithium hexafluorophosphate) in the liquid was reduced to 1.02%. The removal rate of lithium hexafluorophosphate was 82%.

Example 3 Ethylene carbonate containing 11.5 wt % of lithium hexafluorophosphate and diethyl carbonate (weight ratio 1:
1) 1000 g of the mixed solvent and 2-propanol 2000
g and 80 g of potassium fluoride in a 5000
The mixture was placed in a ml polyethylene reactor and treated for 2 hours. After the treatment, the solid matter was removed by filtration. As a result, the concentration of hexafluorophosphate ions (in terms of lithium hexafluorophosphate) in the liquid was reduced to 0.31%. The removal rate of lithium hexafluorophosphate was 92%.

Example 4 Ethylene carbonate containing 11.5 wt % of lithium hexafluorophosphate and diethyl carbonate (weight ratio 1:
1) 333 g of mixed solvent and 3000 g of 2-propanol
And 27.6 g of potassium fluoride in a 500 equipped with a stirrer.
The mixture was placed in a 0 ml polyethylene reactor and treated for 2 hours.
After the treatment, the solid matter was removed by filtration. As a result, the concentration of the hexafluorophosphate ion (in terms of lithium hexafluorophosphate) in the liquid was reduced to 0.01% or less. The removal rate of lithium hexafluorophosphate was 99% or more.

Example 5 Ethylene carbonate containing 11.5 wt % of lithium hexafluorophosphate and diethyl carbonate (weight ratio 1:
1) 333 g of mixed solvent and 6000 g of 2-propanol
Was passed through a column filled with 50 g of potassium fluoride at a rate of 10 ml / min. The concentration of the hexafluorophosphate ion (in terms of lithium hexafluorophosphate) in the solution passed through the column was reduced to 0.01% or less.

Example 6 Ethylene carbonate containing 11.5 wt % of lithium hexafluorophosphate and diethyl carbonate (weight ratio 1:
1) 1000 g of the mixed solvent and 2-propanol 2000
g of ammonium fluoride and 51 g of ammonium fluoride with a stirrer.
It was placed in a 00 ml polyethylene container and treated for 2 hours.
After the treatment, the solid matter was removed by filtration. As a result, the concentration of hexafluorophosphate ion (in terms of lithium hexafluorophosphate) in the liquid was reduced to 0.47%. The removal rate of lithium hexafluorophosphate was 88%.

Example 7 Ethylene carbonate containing 11.5 wt % of lithium hexafluorophosphate and diethyl carbonate (weight ratio 1:
1) 333 g of mixed solvent and 3000 g of 2-propanol
And 17.6 g of potassium fluoride in a 500 equipped with a stirrer.
The mixture was placed in a 0 ml polyethylene container and treated for 2 hours. After the treatment, the solid matter was removed by filtration. As a result, the concentration of the hexafluorophosphate ion (in terms of lithium hexafluorophosphate) in the liquid was reduced to 0.02%. The removal rate of lithium hexafluorophosphate was 98%.

(Example 8) In Examples 1 and 2, 150 g of a solid (lithium fluoride, potassium hexafluorophosphate and potassium fluoride) collected by filtration and drying was added to 50
Suspended in 0 g of water, heated to 90 ° C., and subjected to hot filtration-washing-drying to obtain lithium fluoride having a purity of 99.5% or more.
9.8 g were recovered. When the filtrate subjected to the hot filtration was cooled to room temperature, white crystals of potassium hexafluorophosphate were precipitated, and 75.6 g of potassium hexafluorophosphate having a purity of 98.5% was recovered by filtering and drying.

[0025]

According to the processing method of claims 1 to 5,
Regarding the treatment of lithium hexafluorophosphate in an organic electrolyte containing lithium hexafluorophosphate used for lithium ion batteries and lithium batteries, which is expected to be a major problem in the near future, In addition to providing a treatment method, this treatment allows industrially useful hexafluorophosphate and lithium fluoride to be recovered,
Reuse can be possible.

In particular, according to the processing method of the second aspect,
Lithium hexafluorophosphate in an organic electrolyte solution containing lithium hexafluorophosphate can be treated using an appropriate amount of a solvent.

According to the processing method of the third aspect,
Lithium hexafluorophosphate in an organic electrolytic solution containing lithium hexafluorophosphate can be treated using an appropriate amount of potassium fluoride or ammonium fluoride.

According to the processing method of the fourth aspect,
High-purity lithium fluoride can be effectively recovered.

According to the processing method of the fifth aspect,
High-purity potassium hexafluorophosphate or ammonium hexafluorophosphate can be effectively recovered.

Continuation of the front page (56) References JP-A-11-167936 (JP, A) JP-A-6-251805 (JP, A) JP-A-6-338352 (JP, A) JP-A-2-276163 (JP) (A) Special table Hei 9-506329 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 10/54 H01M 6/16 H01M 6/52 C01B 25/10

Claims (5)

(57) [Claims] 1. A defluorination treatment of the organic electrolyte containing a lithium ion battery and lithium hexafluorophosphate is used for a lithium battery, the general formula _{(A) C n H 2n +} 1 OH ...... (A ) By adding a solvent mainly composed of primary, secondary or tertiary alcohols having 2 to 5 carbon atoms n and a chemical mainly composed of potassium fluoride or ammonium fluoride. A method for treating an organic electrolytic solution, wherein lithium fluoride phosphate is converted into a hardly soluble solid and separated. 2. An alcohol having a content of 0.5 to 40 times the amount of an alcohol represented by the general formula (A) C _n H _{2n + 1} OH (A) with respect to an electrolyte containing lithium hexafluorophosphate. 2. The method for treating an organic electrolytic solution according to claim 1, wherein a solvent as a component is used. 3. The method according to claim 1, wherein an agent containing potassium fluoride or ammonium fluoride as a main component is used in an amount of 1.0 to 2.0 times the amount of lithium hexafluorophosphate contained in the electrolytic solution. The method for treating an organic electrolyte. 4. Separated solids are heated by adding water, or hot water is added to dissolve other than water-insoluble lithium fluoride, and then filtered to remove lithium fluoride. The method for treating an organic electrolytic solution according to claim 1, wherein the organic electrolyte solution is recovered. 5. The organic compound according to claim 4, wherein the recovered filtrate is cooled to precipitate crystals of potassium hexafluorophosphate or ammonium hexafluorophosphate, and recovered by filtration. Electrolyte treatment method.