JPS6120489B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing manganese dioxide, which is used as a positive electrode active material in a battery that uses a light metal such as lithium as a negative electrode active material and uses a non-aqueous electrolyte.

In general, manganese dioxide used as a positive electrode active material for non-aqueous batteries is obtained by electrolysis and made into a differentiated powder, and further, in order to remove the water content,
We use materials that have undergone appropriate heat treatment. There is a close relationship between this heat treatment temperature, the electrochemical activity of manganese dioxide, and battery storage performance, and the higher the treatment temperature, the less deterioration in discharge performance associated with battery storage. Remarkable. However, as the treatment temperature increases, the high rate discharge characteristics of the battery deteriorates, and the internal resistance of the battery increases significantly during storage.

The following reasons can be considered as these causes.
In other words, when manganese dioxide is heat-treated, the amount of water contained in the crystals decreases, but at the same time, the surface area of the manganese dioxide particles also decreases significantly, resulting in a decrease in high-rate discharge characteristics while improving high-temperature storage performance. It is thought that this is accompanied by Furthermore, manganese dioxide is decomposed by the reaction of 2MnO ₂ →Mn ₂ O ₃ + 1/2O ₂ when heated, and this reaction is thought to partially occur at temperatures of 300 to 400°C.
It is considered that electrochemically inactive manganese sesquioxide Mn ₂ O ₃ is generated on the surface of the manganese dioxide particles. In particular, in batteries using manganese dioxide treated at temperatures of 400 to 450°C, the decrease in high-rate discharge characteristics and the increase in battery internal impedance with storage are largely due to the formation of Mn ₂ O ₃ mentioned above. Conceivable.

The present invention dissolves Mn ₂ O ₃ generated on the surface of manganese dioxide particles by heat treating electrolytic manganese dioxide and then performing acid treatment with an acid that dissolves Mn ₂ O ₃ and does not cause a disproportionation reaction. The object of the present invention is to provide manganese dioxide having excellent properties such as high rate discharge characteristics, positive electrode utilization rate, and storage performance.

Mn ₂ O ₃ can be easily removed by treating heat-treated manganese dioxide with hydrochloric acid, hydrofluoric acid, hydrochloric acid, etc. It can also be removed with sulfuric acid, but in this case MnO ₂ is removed by a disproportionation reaction.
was produced, and this MnO ₂ had a crystal structure different from that of heat-treated manganese dioxide and had properties unsuitable as an active material for non-aqueous batteries. Hydrochloric acid, hydrofluoric acid,
When hydrochloric acid is used, MnO ₂ is dissolved together with Mn ₂ O ₃ , but this does not pose a particular problem since only the particle surface layer is dissolved.

The present invention will be explained below with reference to Examples.

Electrolytic manganese dioxide at 200℃, 250℃, 300℃
℃, 350℃, 400℃, and 450℃ for 8 hours each in a glass board.The heat-treated manganese dioxide was immersed in 1N hydrochloric acid and heated at 20℃.
Treat for 1 to 2 hours. After filtration, it was thoroughly washed with water to remove hydrochloric acid, and then dried at 80°C.

A battery was manufactured using the manganese dioxide as described below. A mixture of 100 parts by weight of manganese dioxide, 8 parts by weight of acetylene black as a conductive material, and 6 parts by weight of fluororesin is pressure molded, and the volume
The positive electrode was 150mAh. For the negative electrode, a rolled lithium plate cut into predetermined dimensions was used. The electrolytic solution used was a mixture of propylene carbonate and dimethoxyethane in a volume ratio of 1:1 in which 1.0 mole of lithium perchlorate was dissolved.
A battery using manganese dioxide according to the present invention is designated as A. For comparison, a battery B was manufactured in the same manner using manganese dioxide by the conventional method, which was subjected to the same heat treatment as described above but without acid treatment.

Figure 1 shows the change in battery internal resistance when the manganese dioxide heat treatment temperature and the battery were stored at 60°C for one month. Immediately after battery manufacture, there is almost no difference between batteries A and B, but
After storage, the increase in internal resistance of battery A is small, and a significant difference is observed especially when the heat treatment temperature is 300° C. or higher. The increase in internal resistance at a heat treatment temperature of 300℃ or lower is mainly due to residual moisture in manganese dioxide, and at a heat treatment temperature of 300℃ or higher, it is thought to be due to manganese dioxide decomposition products. It can be explained that the higher the value, the greater the effect of acid treatment.

FIG. 2 shows the 500Ω constant resistance discharge characteristics of batteries A and B immediately after manufacture and after storage at 60°C for one month when the heat treatment temperature was 450°C. As is clear from the figure, both immediately after manufacture and after storage, battery A using acid-treated manganese dioxide has a higher flat voltage of about 50 mV and a utilization rate of about 10% higher, showing that the acid treatment has a greater effect. I understand that.

The same effect as described above could be obtained by using hydrofluoric acid or hydrochloric acid in addition to hydrochloric acid to remove Mn ₂ O ₃ . In acid treatment, Mn ₂ O ₃ is dissolved and
Any acid that does not cause a disproportionation reaction can be used.

If the heat treatment temperature is about 500℃, the decomposition of manganese dioxide will be significant, which is inappropriate.
Moisture removal becomes insufficient at temperatures around ℃. From the above, a suitable treatment temperature is 300 to 450°C; in this temperature range, moisture can be removed sufficiently and the acid treatment effect is also large.

As described above, the present invention improves the positive electrode utilization rate, high rate discharge characteristics, and improves the positive electrode utilization rate and high rate discharge characteristics by removing oxygen-deficient compounds such as Mn ₂ O ₃ generated on the surface of manganese dioxide particles by heat treatment using acid treatment. The object of the present invention is to easily provide manganese dioxide for non-aqueous batteries that has excellent properties in terms of storage performance.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between the heat treatment temperature of manganese dioxide and the internal resistance of the battery depending on storage, and FIG. 2 shows the 500Ω constant resistance discharge characteristics of the battery immediately after manufacture and after storage.

Claims (1)

[Claims] 1. After heat-treating electrolytic manganese dioxide,
A method for producing manganese dioxide for non-aqueous batteries, characterized by performing acid treatment with an acid that dissolves Mn ₂ O ₃ and does not cause a disproportionation reaction. 2. The method for producing manganese dioxide for nonaqueous batteries according to claim 1, wherein the heat treatment temperature is 300 to 450°C. 3. The method for producing manganese dioxide for nonaqueous batteries according to claim 1 or 2, wherein the acid is selected from the group consisting of hydrochloric acid, hydrofluoric acid, and hydrobromic acid.