JPH07118318B2 - Method for producing active material for organic electrolyte battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an active material for an organic electrolyte battery.

2. Description of the Related Art Organic electrolyte batteries have higher discharge voltage and energy density than aqueous batteries, so that the demand for them has been expanding rapidly in recent years. Among them, batteries provided with manganese dioxide as a positive electrode active material are generally used in many cases because of inexpensive raw materials, high discharge voltage of 3 V, and low self-discharge.

On the other hand, an organic electrolyte battery using a lithium-cobalt composite oxide as the positive electrode active material is described by K. Mizushima et al.
It was first proposed by es.Bull., vol.15,783 (1980)). K. Mizushima et al. Reported that LiCoO ₂ was synthesized when lithium carbonate and cobalt carbonate were mixed and fired at 900 ° C. in air, and that this LiCoO ₂ was a 1M LiBF ₄ / PC (PC: propylene carbonate) electrolyte Among them, it showed excellent reversibility of charge and discharge, and it was clarified that a discharge voltage of more than 4V was obtained when lithium was used for the negative electrode.

However, since then, there have been few reports on organic electrolyte batteries using this LiCoO ₂ (lithium-cobalt composite oxide) as a positive electrode active material.

Then, the inventor tried to synthesize this lithium-cobalt composite oxide, and found that the discharge capacity was greatly affected by the raw material mixing ratio. That is, as shown in (1) of FIG. 1, the lithium-cobalt composite oxide obtained from the mixture of lithium carbonate and cobalt carbonate is
When the mixing ratio (atomic ratio) of cobalt and lithium was 1, the discharge capacity (lithium intercalation number) was the maximum. It was also found that the discharge capacity sharply decreased even when the mixing ratio of lithium to cobalt was less than 1 or exceeded 1.

From the above results, it can be said that strictly adjusting the mixing ratio of cobalt and lithium to 1: 1 is extremely important.
However, in order to perform such precise mixing, it is necessary to mix for a long period of time and use a combination of several mixing methods, which leads to an increase in the production cost of the battery. Further, in mass production, it is not easy to make the mixing ratio of the raw material powders uniform.

Therefore, there has been a demand for a new method for synthesizing an active material that does not cause a decrease in discharge capacity even if the composition has some non-uniform composition.

Means for Solving the Problems In the present invention, a cobalt compound and a lithium compound are mixed and thermally decomposed so that the atomic ratio of lithium to cobalt is 1 or more and 10 or less, and then water or an organic substance is used. It is characterized in that a lithium-cobalt composite oxide is synthesized by washing and then drying. Then, in order to further clarify the effect, it is desirable that the cleaning treatment is ultrasonic cleaning.

Action The inventor has examined the cause of the maximum discharge capacity when the mixed atomic ratio of cobalt to lithium (hereinafter referred to as Li / Co) is 1 when the raw materials are mixed. As a result, as described in detail in Examples below, the decrease in discharge capacity is
It was found that this is due to the inclusion of cobalt oxide or unreacted starting lithium compound as an impurity in the thermal decomposition product. Furthermore, although it is difficult to remove the cobalt oxide when the thermal decomposition product is subjected to cleaning treatment, it is possible to effectively remove the unreacted starting lithium compound, and the ultrasonic cleaning makes the impurities more effective. Lithium can be removed, and even if the washing treatment is performed, the charging / discharging voltage of the active material does not decrease and the discharge capacity does not decrease. Furthermore, if lithium is excessive, it is difficult to wash and remove the unreacted raw material. It was clarified that / Co ≦ 10 is desirable.

That is, the inventor conducted an original study to mix the raw materials at an excessive lithium mixing ratio (Li / Co is 1 or more and 10 or less), and then pyrolyzes the mixture to perform a cleaning treatment, resulting in a nonuniform composition during mixing. It was found for the first time that the influence of the above on the dispersion of the discharge capacity can be reduced.

Example Li / Co = 0.4, Li / Co = 1.
Mix in various ratios of 0 and Li / Co = 2.0 and 900 ℃ in air
It was pyrolyzed for 20 hours to synthesize a lithium-cobalt composite oxide.

As a result of X-ray diffraction analysis of this thermal decomposition product, Li / Co = 0.4
The thermal decomposition products of LiCoO ₂ include CoO and Co ₃ O ₄
It was confirmed that the diffraction peak was considered to be. Also, Li / Co
Only the diffraction peak of LiCoO ₂ was observed in the thermal decomposition product of 1.0. And the Li / Co = 2.0 thermal decomposition product contains Li
A diffraction peak of CoO _{2 and} a diffraction peak considered to be Li ₂ Co ₃ were observed.

From the above results, in (1) of FIG. 1, the discharge capacity is
It is considered that the cause of the maximum at Li / Co = 1.0 is due to the minimum amount of impurities contained in the thermal decomposition product when Li / Co = 1.0. That is, in the fired product with Li / Co <1.0, cobalt oxide was included as an impurity, and Li / Co>
It is considered that the fired product of 1.0 is caused by containing lithium carbonate as an impurity.

Next, the inventor tried to remove impurities contained in the fired product by a cleaning treatment. That is, the fired product was ultrasonically washed with purified water, dried and then subjected to X-ray diffraction analysis. The results are shown in Table 1. In the table, ASTM
Also shown are the X-ray diffraction data of LiCoO ₂ shown in No. 16-427 of the card and the X-ray diffraction data of the lithium-cobalt composite oxide (Li / Co = 2.0) which has not been washed.

In the case where Li / Co = 0.4 was washed, the diffraction peaks, which are considered to be those of cobalt oxides (Co ₃ O ₄ , CoO), were observed in the same manner as before washing, but Li / Co = 1.0 and Li In the case where /Co=2.0 was washed, the diffraction peak considered to be lithium carbonate (Li ₂ Co ₃ ) disappeared. Further, in all cases, the diffraction peak, which is considered to be due to LiCoO ₂ , did not change before and after washing.

Next, the thermal decomposition products of Li / Co = 0.4, Li / Co = 1.0 and Li / Co = 2.0 were washed with running water and ultrasonically washed.
After hot air drying at 120 ° C for 6 hours, add Teflon dispersion and 5wt% acetylene black and mix,
It was wrapped with a nickel wire mesh and mixed to form an electrode. And 1M LiC
1mA / cm in lO ₄ / PC-DME (DME: dimethoxyethane) electrolyte
Charged and discharged at ² . FIG. 1 (2) shows the results when washed with running water, and (3) shows the results when ultrasonically washed. Li
The thermal decomposition product of /Co=0.4 showed no change in discharge capacity before and after washing, while the thermal decomposition product of Li / Co = 2.0 increased the discharge capacity by washing with running water. Then, in the case of ultrasonic cleaning, the discharge capacity was further improved as compared with that in running water cleaning, and the discharge capacity became equal to that of the thermal decomposition product of Li / Co = 1.0.

Here, with respect to the thermal decomposition product of Li / Co = 2.0, changes in the particle structure due to washing were observed with an electron microscope. The electron micrograph is shown in FIG. In the figure, (A) is an unwashed product, (B) is a product washed with running water, and (C) is a product subjected to ultrasonic cleaning. From the figure, it was found that the fine crystals adhering to the surface of the active material were slightly removed by washing with running water, and were further completely removed by ultrasonic cleaning.

When the thermal decomposition product of Li / Co> 1.0 is washed with water,
Although the cause of the increase in discharge capacity is not clear, it is considered from the above results that the residual lithium carbonate dissolves well in water and can be removed by a washing treatment. In fact, the same effect was obtained by washing with an organic solvent that dissolves the remaining lithium carbonate and lithium oxide well. Moreover, since the impurities such as CoO and Co ₂ O ₃ are insoluble in water even if the burned material with Li / Co <1.0 cannot be removed even by the cleaning treatment, the discharge capacity remains smaller than that with Li / Co = 1.0. It is believed that there is.

Instead of cobalt carbonate or lithium carbonate
An experiment was conducted in which the respective metals, oxides, hydroxides, nitrates, halides or oxalates were mixed, thermally decomposed and then ultrasonically cleaned. A part of this result is shown in FIG. In the figure, the case where lithium oxide and cobalt nitrate are mixed is shown in (4), the case where lithium chloride and cobalt hydroxide are combined is shown in (5), and the case where lithium oxalate and metallic cobalt are mixed is shown. Is shown in (6). Also in these cases, the thermal decomposition products of Li / Co> 1.0 that were ultrasonically cleaned with water or organic matter had a discharge capacity of Li
It became the same as when /Co=1.0. Also, from the figure, Li / Co
It can be seen that when is 10 or more, the discharge capacity is rapidly decreasing. It is considered that this is because the cleaning effect is reduced when the amount of lithium is excessive. Therefore, it can be said that Li / Co ≦ 10 is desirable.

EFFECTS OF THE INVENTION As described above, the active material manufacturing method of the present invention does not require a precise raw material mixing step, and therefore an active material for organic electrolyte batteries having excellent discharge performance can be manufactured inexpensively and in large quantities. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of the raw material mixture ratio on the discharge capacity. 2 (A) to (C) show unwashed,
It is the figure (electron micrograph) which showed the particle structure of the thermal decomposition product at the time of running water washing and ultrasonic washing. FIG. 3 is a diagram showing the influence of the raw material mixing ratio on the discharge capacity of the thermal decomposition product after the cleaning treatment when various raw materials are used.

Claims (1)

[Claims] 1. A cobalt compound and a lithium compound are mixed so that the atomic ratio of lithium to cobalt is from 1 to 10 and thermally decomposed, and then washed with water or an organic substance and dried. A method for producing an active material for an organic electrolyte battery, which comprises synthesizing a lithium-cobalt composite oxide.