JPH09232008A - Regenerating method for nonaqueous electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recycle deteriorated nonaqueous electrolyte. SOLUTION: When deteriorated nonaqueous electrolyte is recycled by activated carbon, the activated carbon is added in form of powder or particle by 100g or more in relation to one liter of nonaqueous electrolyte. The nonaqueous electrolyte is stirred after addition, it is left for the required time, and the deterioration causing material in electrolyte is adsorbed by the activated carbon. The deteriorating causing material can be removed from the electrolyte by filtering the electrolyte and removing the activated carbon after leaving, and regeneration of deteriorated electrolyte can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte used in various batteries such as a lithium secondary battery, and more particularly to a method for regenerating a deteriorated electrolyte.

[0002]

2. Description of the Related Art Non-aqueous electrolytes used in various batteries such as lithium secondary batteries are used for testing or research of batteries, and are stored in containers for a long period of time or in a high temperature environment. When placed underneath, it may discolor or deteriorate. These discolorations and alterations are caused by the inclusion of moisture in the air in the electrolyte,
It is considered that the cause is that a large amount of a substance such as hydrogen fluoride (HF) formed by decomposition of a salt or a polymer of a solvent such as propylene carbonate or polypropylene is generated. The non-aqueous electrolyte solution deteriorates by impairing the original ability of the electrolyte solution due to the production of a large amount of such salt decomposition products and solvent polymerization products. Most of the deteriorated electrolyte was discarded without being reused elsewhere.

[0003]

However, since the non-aqueous electrolyte solution is a very expensive and valuable material, it has been desired to reuse it after deterioration.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method of regenerating a deteriorated non-aqueous electrolytic solution. is there.

[0005]

In order to achieve the above object, in the method for regenerating a non-aqueous electrolyte according to the present invention,
Activated carbon is added to the deteriorated non-aqueous electrolyte, the non-aqueous electrolyte is stirred, and then the non-aqueous electrolyte is left for a required time,
Then, the non-aqueous electrolyte solution is filtered to remove the activated carbon. According to this method, the cause of deterioration such as HF contained in the deteriorated non-aqueous electrolyte can be adsorbed on the activated carbon and removed. As a result, the capacity of the deteriorated non-aqueous electrolyte can be restored, and the electrolyte can be used again as an electrolyte. Therefore, even if the non-aqueous electrolyte is deteriorated, it can be reused without discarding it.

[0006] Preferably, the non-aqueous electrolyte solution is repeatedly stirred or left standing until the HF amount of the deteriorated non-aqueous electrolyte solution becomes 40 ppm or less. In this way, if the HF content of the non-aqueous electrolyte solution becomes 40 ppm or less,
The ability as an electrolytic solution can be restored to a level comparable to that before deterioration and can be regenerated so that it can be sufficiently used as an electrolytic solution.

Further, preferably, if 100 g or more of the activated carbon is added to 1 liter of the non-aqueous electrolyte solution, the deterioration-causing substances can be sufficiently removed.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A method for regenerating a non-aqueous electrolyte solution according to the present invention will be described below with reference to the accompanying drawings. The non-aqueous electrolyte solution according to the present invention is used, for example, in various batteries such as a lithium secondary battery.

This non-aqueous electrolytic solution is obtained by dissolving an electrolyte in an organic solvent, and the organic solvent used here is, for example, propylene carbonate (abbreviation: P
C, the same hereinafter), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylene carbonate (EC), 1,2-dimethoxyethane (DME), γ-
Butyrolactone (γ-BL), tetrahydrofuran (T
HF), 2-methyltetrahydrofuran (2-MeTH
F), diethyl ether (DEE), sulfolane (S
L) and the like, single solvents or mixed solvents thereof. Further, as the electrolyte, for example, LiPF ₆ , Li
ClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO
There are ₃ etc.

Such a non-aqueous electrolyte solution is used in the test or research of batteries and the like, and when it is stored in a container or the like and stored for a long period of time or placed in a high temperature environment, the water content in the air is increased. Due to the incorporation of a large amount of a substance such as HF or the like formed by the decomposition of a salt or a polymer of a solvent such as propylene carbonate or polypropylene, a large amount of the substance may be discolored or deteriorated to deteriorate.

Table 1 below summarizes the states of the four types of non-aqueous electrolytes, Examples 1 to 4 before and after deterioration, in terms of color, water content and HF content. Here, Examples 1 to 4 are, respectively, a single solvent of PC, a mixed solvent of PC and DEC with a mixing ratio of 1: 1 and a mixed solvent of PC, DEC and DMC with a mixing ratio of 1: 1: 1.
For a mixed solvent of EC, PC and DEC having a mixing ratio of 1: 1: 1, LiPF ₆ as an electrolyte was 1 mol / mol, respectively.
Dissolved at a rate of 1 liter.

[0012]

[Table 1] From this Table 1, when the non-aqueous electrolyte solution deteriorates, it changes from colorless and transparent to dark brown or black and contains H
It can be seen that the F content and the water content are also increased as compared with those before the deterioration.

In the present invention, such deteriorated non-aqueous electrolyte is regenerated by using activated carbon. The activated carbon used here is mainly of plant type and mineral type, and in the plant type, coconut shell activated carbon made from palm shells is famous, in addition to this, general wood, sawdust, charcoal, ash. (Sawdust dry distillate), fruit shells such as walnut shells, fruit seeds (peaches, etc.), fruit shell charcoal, fruit seed charcoal, pulp production by-product, lignin, waste liquor, sugar waste (bacus), molasses, etc. In addition, in the mineral system, there are peat, grass peat, lignite, lignite, leek coal, anthracite, coke, coal tar, coal pitch, petroleum distillation residue, petroleum pitch and the like. In addition to these, there are seaweed and regenerated fibers (rayon) as natural materials, and phenol, saran, acrylic resin, etc. as synthetic materials.

Activated carbon made of these materials is used in the form of powder or particles and is added to the deteriorated non-aqueous electrolyte. After the addition, by stirring the non-aqueous electrolyte solution, the activated carbon is sufficiently mixed with the electrolyte solution. Furthermore, by allowing the non-aqueous electrolyte solution to stand for a required time, the cause of deterioration of the non-aqueous electrolyte solution is sufficiently adsorbed on the activated carbon. Here, in order to perform sufficient adsorption by the activated carbon, stirring and standing may be further repeated. After that, by filtering the non-aqueous electrolyte solution to remove the activated carbon, the cause of deterioration can be removed from the deteriorated non-aqueous electrolyte solution, and the non-aqueous electrolyte solution can be regenerated.

The test conducted to confirm the effect of the present invention will be described below. In this test, first, in order to know the performance limit against deterioration of the electrolytic solution, the relationship between the amount of HF contained in the non-aqueous electrolytic solution and the charge / discharge performance of the battery was examined. Here, based on the non-aqueous electrolyte having the same composition as in Example 2, the HF contents were 10 ppm, 20 ppm, 30 ppm and 40, respectively.
Seven types of electrolytic solutions were set to ppm, 50 ppm, 60 ppm, and 70 ppm, respectively, and spiral type lithium secondary batteries were assembled using these electrolytic solutions.

Here, the spiral type lithium secondary battery will be described in detail. This battery, as shown in FIG.
Inside the cylindrical negative electrode can 2, an electrode group 10 formed by spirally winding a polypropylene porous film separator 8 sandwiched between a positive electrode sheet 4 and a negative electrode sheet 6 is housed, and the negative electrode can 2 A positive electrode terminal plate 14 with a safety valve is sealed at the open end of the via a polypropylene insulating gasket 12. The positive electrode sheet 4 was prepared by mixing LiCoO _{2 as} a positive electrode active material, carbon powder as a conductive material, and an aqueous dispersion of PTFE as a binder at a weight ratio of 100: 10: 10, and kneading them in a paste form with water. A positive electrode mixture that has a thickness of 30
The aluminum foil with a thickness of μm is applied on both sides, dried, rolled, cut into a predetermined size, and formed into a band shape. A positive electrode lead plate 16 made of titanium is attached to the positive electrode sheet 4 by spot welding on the exposed aluminum foil surface by stripping a part of the positive electrode mixture perpendicular to the longitudinal direction of the sheet. Each positive electrode sheet 4 is coated with about 6.0 g of LiCoO ₂ .
The negative electrode sheet 6 is formed by applying a negative electrode carbon material to a copper metal foil, drying it, rolling it, cutting it into a predetermined size, and molding it into a strip shape. Then, in the negative electrode sheet 6,
A negative electrode lead plate 18 made of nickel is attached by spot welding to the surface of the copper metal foil which is exposed by stripping off a part of the negative electrode mixture perpendicularly to the longitudinal direction of the sheet. The positive electrode lead plate 16 extends from the upper end portion of the electrode group 10 and is connected to the lower surface of the positive electrode terminal plate 14 by spot welding, while the negative electrode lead plate 18 extends from the lower end portion of the electrode group 10. An insulating bottom plate 20 made of polypropylene interposed between the lower end surface of 10 and the inner bottom surface of the negative electrode can 4.
And is connected to the inner bottom surface of the negative electrode can 4 by spot welding. About 2.3 ml of the non-aqueous electrolyte was poured into the negative electrode can 4, and the battery was an AA battery (14.5 φm).
m × 50 mm).

Then, each of the assembled batteries was subjected to a cycle test in which charging / discharging was repeated with an upper limit voltage of 4.2 V and a lower limit voltage of 3.0 V and a current density of 1 mA / cm ² . The discharge capacity was measured for each cycle, and the horizontal axis represents the number of cycles and the vertical axis represents the discharge capacity, which is shown as a graph in FIG. From FIG. 2, it was confirmed that the discharge capacity of the electrolyte solution containing 50 ppm or more of HF was reduced by 100 cycles and sufficient performance could not be obtained. On the other hand, it was confirmed that when the HF content of the non-aqueous electrolyte solution was 40 ppm or less, stable charge / discharge cycle characteristics were obtained. From these, it was found that the upper limit value of the contained HF amount for the electrolyte to sufficiently exhibit its performance is 40 ppm.

Next, in order to know the adsorption capacity of activated carbon, the relationship between the amount of activated carbon added and the amount of HF contained in the electrolytic solution was investigated. Here, the deteriorated electrolyte solutions according to Examples 1 to 4 were used, and the activated carbon used was powdery coconut shell activated carbon having a particle size of about 20 μm. The amount of activated carbon added was set at every 20 g within the range of 0 to 200 g per liter of the electrolytic solution. After the activated carbon was added, the container of the electrolytic solution was shaken to stir the electrolytic solution inside, and then the container was shaken 3 or 4 times to allow the electrolytic solution to re-stir for 20 days. Then, the amount of HF of the electrolytic solution after each standing was measured, and the results of Examples 1 to 4 are shown in the graphs of FIGS. 3 to 6, respectively.

From these FIGS. 3 to 6, it was confirmed that the amount of HF decreased as the amount of activated carbon added increased. Then, from the above results, the upper limit of the amount of HF contained in the electrolytic solution is 4
Since it was 0 ppm, it was found that if the amount of activated carbon added was at least about 100 g per liter of the electrolytic solution, it was possible to sufficiently adsorb and remove deterioration-causing substances such as HF.

Further, the performance of the battery using the regenerated electrolytic solution was examined. Here, activated carbon was added to the deteriorated electrolytes according to Examples 1 to 4 in a minimum amount, that is, 100 g per liter of the electrolyte, and after the addition, stirring of the electrolyte was performed in the same manner as described above. On the way, the container was shaken 3 or 4 times and left for 20 days while re-stirring the electrolytic solution, and then the activated carbon was removed by filtration to regenerate the electrolytic solution. In addition to the regenerated electrolytic solution, the electrolytic solution before deterioration was used as Comparative Example 1, and the deteriorated electrolytic solution was used as Comparative Example 2 to prepare Comparative Examples 1 and 2, respectively.
The spiral lithium secondary battery shown in was assembled. A charge / discharge cycle test was performed on each of the assembled batteries under the same conditions as in the above case, and the results are shown in Examples 1 to 4.
Each is shown in FIGS. 7 to 10.

From these FIGS. 7 to 10, Embodiments 1 to 4 are described.
With the regenerated electrolyte solution according to (1), the charge / discharge cycle characteristics comparable to those of Comparative Example 1 in the state before deterioration were obtained, and it was confirmed that the performance was sufficiently recovered by regeneration. .

[0022]

As described above in the embodiments of the invention, according to the method for regenerating a non-aqueous electrolyte according to the present invention, the deteriorated substance of the deteriorated non-aqueous electrolyte can be adsorbed and removed by activated carbon. As a result, the deteriorated non-aqueous electrolyte can be regenerated, and even if the non-aqueous electrolyte is deteriorated, it can be reused without discarding it.

By repeating stirring or leaving the non-aqueous electrolyte solution until the HF amount of the deteriorated non-aqueous electrolyte solution becomes 40 ppm or less, the performance as the electrolyte solution is comparable to that before deterioration. It can be recovered and regenerated so that it can be fully utilized as an electrolyte.

Furthermore, activated carbon is the non-aqueous electrolyte 1
If 100 g or more is added to the liter, the deterioration-causing substance can be sufficiently removed.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the internal structure of a spiral lithium secondary battery.

FIG. 2 shows the charge / discharge cycle characteristics of a battery based on the HF content of the electrolyte
It is the graph shown for every quantity.

FIG. 3 is a graph showing the relationship between the amount of activated carbon added to the electrolytic solution and the amount of contained HF after regeneration according to Example 1.

FIG. 4 is a graph showing the relationship between the amount of activated carbon added to the electrolytic solution according to Example 2 and the amount of contained HF after regeneration.

5 is a graph showing the relationship between the amount of activated carbon added to the electrolytic solution and the amount of contained HF after regeneration according to Example 3. FIG.

FIG. 6 is a graph showing the relationship between the amount of activated carbon added to the electrolytic solution and the amount of contained HF after regeneration according to Example 4.

7 is a graph showing charge / discharge cycle characteristics of the battery according to Example 1. FIG.

FIG. 8 is a graph showing charge / discharge cycle characteristics of the battery according to Example 2.

9 is a graph showing charge / discharge cycle characteristics of the battery according to Example 3. FIG.

FIG. 10 is a graph showing charge / discharge cycle characteristics of the battery according to Example 4.

[Explanation of symbols]

2 Negative electrode can 4 Positive electrode sheet 6 Negative electrode sheet 8 Separator 10 Electrode group 12 Gasket 14 Positive electrode terminal plate 16 Positive electrode lead plate 18 Negative electrode lead plate 20 Insulating bottom plate

Claims (3)

[Claims] 1. Activated carbon is added to a deteriorated non-aqueous electrolyte solution, the non-aqueous electrolyte solution is stirred, and the non-aqueous electrolyte solution is allowed to stand for a required period of time. Thereafter, the non-aqueous electrolyte solution is filtered to remove the activated carbon. A method for regenerating a non-aqueous electrolytic solution, which comprises removing the electrolytic solution. 2. The HF amount of the deteriorated non-aqueous electrolyte is 4
The method for regenerating a non-aqueous electrolytic solution according to claim 1, wherein the non-aqueous electrolytic solution is repeatedly stirred or left to stand until it becomes 0 ppm or less. 3. The method for regenerating a non-aqueous electrolytic solution according to claim 1, wherein 100 g or more of the activated carbon is added to 1 liter of the non-aqueous electrolytic solution.