JPS62290073A - Organic electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To increase current efficiency in charge-discharge of a negative electrode and cycle life of a battery by using gamma-butyrolactone whose hydrogen in third or fourth position is snbstituted with chlorine or fluorine as a solvent of organic electrolyte. CONSTITUTION:gamma-butyrolactone whose hydrogen in third or fourth position is substituted with chlorine or fluorine is used as a solvent of organic electrolyte. When gamma-butyrolactone(BL) is used as a solvent, by substituting hydrogen in the C position with chlorine or fluorine, C-O bond is difficult to break because of strong electron attraction and current efficiency is increased. For example, 3-chloro-gamma-butyrolactone obtained by substituting hydrogen in third position with chlorine has structural formation shown in the formula I, 4-chloro-gamma- butyrolactone is shown in the formula ll, and 3-chloro-4 fluoro-gamma-butyrolactone is shown in the formula III.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention Industrial Field of Application The present invention relates to the improvement of organic electrolyte secondary batteries using lithium or the like in the negative electrode, and in particular to the improvement of organic electrolyte solvents. , which improves the current efficiency of charging and discharging the negative electrode.

Conventional Technology Organic electrolyte batteries that use alkali metals such as lithium as negative electrodes are expected to have higher energy density than conventional lead or nickel-cadmium storage batteries, and are being actively researched. As a typical example, lithium metal is used as the negative electrode, titanium disulfide (TiS2) is used as the positive electrode, and lithium perchlorate (LiCjl104) is used as the solute of the organic electrolyte.
Hexafluoroarsinate (LiAsF6), γ in the solvent
-Butyrolactone (BL) and 2-methyltetrahydrofuran (2-Me-THF) are used.

Problems to be Solved by the Invention In these batteries, the current efficiency of charging and discharging the negative electrode is 60 to 8.
It has not been put into practical use yet because it is as low as 0%.

Means for Solving the Problems The present invention is characterized by the use of γ-butyrolactone in which hydrogen at at least 3 or 4 positions is replaced with chlorine or fluorine, in place of the conventional organic electrolyte solvent.

Action Conventional propylene carbonate) (PC) and 2-Me-T
When the negative electrode lithium is charged in the organic electrolyte used as the HF'i solvent, part of the precipitated lithium reacts with the solvent because it is active lithium, and a 3... lithium salt is generated. For example, it has been reported that in PC, the precipitated lithium becomes lithium carbonate as shown in the following formula. It is believed that this solvent also reacts with lithium in the case of BL and 2-Me-THF.

Therefore, the current efficiency of the negative electrode (the amount of charge that can be discharged relative to the amount of charge required for charging) was as low as 60 to 80 inches.

The inventor thought that the C-00 bond would be broken by the reaction with Li in the case of BL as well, and by replacing the hydrogen at the C position with chlorine or fluorine, the strong electron-withdrawing properties of these , the C--O bond becomes difficult to break, which is thought to improve current efficiency. For example, 3-chloro-γ-butyrolactone in which position 3 is substituted with chlorine has a structure as shown in formula (1).

scH20,, (1) Similarly, the structure of 4-chloro-γ-butyrolactone (a)
Formula K, ifv:, 3-ri c + rho 470 rho The structure of γ-butyrolactone is shown in formula (3).

GHCjl　-OH,.

CH20 (2) \　C1 CH-〇HCJJ I (3) CH20 \. 1 Example Next, the present invention will be explained in detail.

Example 1 The current efficiency of negative electrode lithium was investigated in a beaker-type cell. A nickel plate measuring 2 cm x 2 cm was used as a negative electrode current collector, and a nickel ribbon was attached as a lead to this. Platinum was used as the counter electrode. Lithium was used as the reference electrode. Various organic electrolytes were placed in this cell, and after charging at 4 mA for 2 hours, the potential of the negative electrode at 4 mA was 1.5 m with respect to the reference electrode.
The battery was discharged until OV K, and charging and discharging were repeated in this manner. Current efficiency was calculated based on the amount of charge that was discharged relative to the amount of charge that was charged. For example, if the discharge is 1.5 hours, (1.5hrX 4mA)/(2hrX 4mA
)X100=76i%. This charge/discharge cycle was repeated 50 times to determine the average current efficiency. The larger this value is, the less the precipitated lithium has reacted with the solvent. All solutes were Li(JO4) at a concentration of 0.1 mol/l.
' was used. The results are shown in the table.

6-7 In the table, the types of solvents used in the present invention are shown in the following abbreviations. 3-chloro-γ-butyrolactone is obtained by replacing hydrogen at position 3 with chlorine, but the latter γ-butyrolactone is abbreviated to 3-chloro. Similarly, all later γ−
Abbreviated for butyrolactone.

From this, it can be seen that the current efficiency of charging and discharging is increased by replacing hydrogen at the 3rd or 4th position with chlorine or fluorine. Also, the degree of substitution is 3 and 4.
The best results were those in which both were replaced with chlorine and fluorine, and those in which both were fluorinated and chlorinated were found to be good.

Example 2 A lithium disk having a diameter of 17.61 Wfi and a thickness of 0.5 mm was used as a negative electrode. The theoretical filling capacity at this time is 247mA
It is h. For the positive electrode, 0.4 g of a mixture of 10 parts by weight of TiO2, 10 parts by weight of acetylene black as a conductive agent, and 10 parts by weight of poly 47-fluorinated ethylene as a binder was added.
A compression molded disc having a diameter of 17.5ffljX was used. The theoretical filling capacity at this time was 80 mAh.

A flat battery was prototyped from these positive and negative electrodes.

The structure of this battery is shown in FIG. In FIG. 1, 1 is a battery case, 2 is a sealing plate, 3 is a negative electrode lithium, 4 is a separator, 5 is a positive electrode, and 6 is a gas foot.

This battery was repeatedly charged and discharged at a constant current of 2 m. Discharging occurs when the battery voltage reaches 1.2V, and charging occurs when the battery voltage reaches 2.8V.
Each was stopped when reaching v.

1 mole/7 for solute in organic electrolyte! L engineering AsF6'?
:Using. The amount of organic electrolyte in each battery was 200 μl. The 3-chloro-4- of the present invention is added to the solvent of the organic electrolyte.
Batteries using chloro-γ-butyrolactone, 3-chloro-γ-butyrolactone, 4-chloro-γ-butyrolactone, 3-fluoro-γ-butyrolactone, and 4-fluoro-γ-butyrolactone are A, B, C, D, respectively. E, conventional B L and 2-Me-THF batteries were respectively F
, G. In FIG. 2, the amount of electricity discharged in each cycle of these batteries is plotted. This shows that the cycle characteristics of the battery are improved by using the γ-butyrolactone of the present invention in which hydrogen at the position Ii4 is replaced with chlorine or fluorine. This is because the current efficiency of charging and discharging the negative electrode has improved.

The above has described an example in which lithium was used as the negative electrode. However, when a lithium-aluminum 9,-2 alloy or an alloy of lead, tin, bismuth, cadmium, etc. is used as the negative electrode, lithium is contained in the negative electrode by charging. The solvent of the present invention also had a great effect on electrodes that occlude lithium and release the occluded lithium upon discharge.

Regarding the positive electrode, only the case of TiO2 is shown, but
The solvent of the present invention has a great effect on the negative electrode, and even if other active materials are used for the positive electrode, the charging and discharging efficiency of the negative electrode of the battery is improved, and the cycle characteristics of the battery are accordingly improved.

Effects of the Invention As described above, according to the present invention, the current efficiency of charging and discharging the negative electrode is improved, and the cycle characteristics of the battery are improved.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view of a battery used in an example of the present invention;
The figure is a diagram showing a comparison of cycle characteristics of batteries using each solvent. 3... Negative electrode, 4... Separator, 5...
...Positive electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person3-
1st class 2nd figure Ikuru Chichi

Claims (1)

[Claims] 1. An organic electrolyte secondary battery comprising a negative electrode, a positive electrode, and an organic electrolyte, characterized in that γ-butyrolactone in which hydrogen at at least the 3rd or 4th position is replaced with chlorine or fluorine is used as a solvent for the organic electrolyte.