JPH0639334B2 - Production method of β-manganese dioxide - Google Patents

Description

The present invention relates to a method for producing β-manganese dioxide used in lithium manganese batteries (Li-MnO ₂ batteries), solid electrolytic capacitors, various catalysts, etc., and particularly to a method for producing high-purity β-manganese dioxide. It is a thing.

Manganese dioxide (Mn
O ₂ ), α-manganese dioxide (α-MnO ₂ ), β-manganese dioxide (β-MnO ₂ ), γ
-Manganese dioxide (γ-MnO ₂ ) and the like are known, and, for example, manganese dioxide used as a positive electrode active material of a Li-MnO ₂ battery is conventionally obtained by electrolytic oxidation of manganese sulfate or manganese chloride from an acidic bath. Γ-MnO ₂ such as chemically synthesized manganese dioxide obtained by adding an alkaline solution of permanganate to a boiling solution of electrolytic manganese dioxide or neutral manganese sulfate is used.

By the way, γ-Mn obtained by the above-mentioned electrolytic oxidation or chemical synthesis
O ₂ is known to contain a considerable amount of water, and is also said to have a stoichiometric deviation. That is, when the electrolytic manganese dioxide or the chemically synthesized manganese dioxide is MnOx, it is said that x = 1.95 instead of x = 2.0. The deviation from x = 2.0 is considered to be due to the presence of manganese trioxide (Mn ₂ O ₃ ).

In this way, γ-MnO ₂ contains Mn
_Since it contains ₂ O ₃ , various defects have been problems in using this γ-MnO ₂ .

For example, in a Li-MnO ₂ battery, since metallic lithium is used as the negative electrode active material, it is extremely disliked by water.If water is present in the γ-MnO ₂ , the water reacts with the metal lithium. Corrosion of the battery canister or leakage will occur, resulting in poor storage characteristics. Further, since Mn ₂ O ₃ which is an impurity of γ-MnO ₂ is not an active material in a Li-MnO ₂ battery, the amount of γ-MnO _{2 that} can be used when this Mn ₂ O ₃ is mixed is considerably reduced and the battery is considerably reduced. The life of the battery is shortened, the electric resistance of the battery is increased, and the battery performance is significantly deteriorated. Alternatively, when the γ-MnO ₂ is used in a solid electrolytic capacitor, the withstand voltage due to the water content in the γ-MnO ₂ ,
Problems such as leakage current and changes over time occur, and impurities such as Mn
₂ O ₃ causes problems in increase of electric resistance, reliability of breakdown voltage, frequency characteristics, and the like. Furthermore, even when γ-MnO ₂ is used as a catalyst, the presence of Mn ₂ O ₃ is not preferable.

Therefore, conventionally, the above-mentioned γ-MnO ₂ is heat-treated under the condition of about 350 to 450 ° C. to remove the contained water before use. However, it is difficult to completely remove the above moisture even by such heat treatment, and the present inventors analyzed the composition by thermal analysis of the product obtained by heat treating electrolytic manganese dioxide at 350 to 450 ° C. The water content is 1.2 to 1.8% by weight, and the impurities considered to be Mn ₂ O ₃ are 7
It was found to be present at -18% by weight. Further, from the viewpoint of removing the water content, it is preferable that the heat treatment temperature is not higher and the treatment is performed for a long time, but in this case, decomposition of γ-MnO ₂ into Mn ₂ O ₃ is started and impurities are started. The amount of mixed in will increase.

Therefore, the thermodynamically stable β-
MnO ₂ is attracting attention. As a method for producing this β-MnO ₂ ,
Usually, a method of thermally decomposing manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O) is performed. For example, in the manufacturing process of a solid electrolytic capacitor, tantalum Ta or aluminum A is used.
A metal oxide film is formed on the valve metal, such as boric acid, ammonium borate, ammonium phosphate, etc., by an anodic oxidation method, and manganese nitrate is further dipped on it or sprayed by spraying. And the like, and thermally decomposed to form a β-MnO ₂ layer.

However, even in β-MnO ₂ obtained by thermal decomposition of manganese nitrate as described above, mixing of Mn ₂ O ₃ is not avoided and not only the quality of β-MnO ₂ is deteriorated, but also manganese nitrate as a raw material Since the price is high, it is difficult to supply in large quantities at a low price.

Furthermore, it is possible to heat-process γ-MnO ₂ such as electrolytic manganese dioxide or chemically synthesized manganese dioxide at a high temperature to cause a phase transition to β-MnO ₂ , but in this case also, the heat treatment temperature is high. Therefore, β-MnO ₂ thus generated is further decomposed and oxygen is released to generate impurities such as Mn ₂ O ₃ , which is not practical.

Therefore, the present invention has been proposed in order to eliminate the drawbacks of the above-mentioned conventional method, high-purity β-MnO ₂ using electrolytic manganese dioxide or chemically synthesized manganese dioxide that is inexpensive and easily available as a raw material. An object of the present invention is to provide a method for producing β-MnO ₂ capable of obtaining

The present inventors, as a result of earnest studies to achieve the above-mentioned object, previously heat-treated electrolytic manganese dioxide or chemically synthesized manganese dioxide at a high temperature to convert it into a mixture of β-MnO ₂ and Mn ₂ O _3. The present invention has been completed by further discovering that highly pure β-MnO ₂ can be obtained by adding nitric acid to this mixture and subjecting it to heat treatment, which is obtained by heat treating electrolytic manganese dioxide or chemically synthesized manganese dioxide. It is characterized in that nitric acid is added to a mixed product of β-manganese dioxide and manganese trioxide to perform heat treatment.

That is, in the present invention, γ-MnO ₂ such as electrolytic manganese dioxide or chemically synthesized manganese dioxide is prepared as a starting material, and this γ-MnO ₂ is first heat-treated at a temperature of 420 to 650 ° C.

The product of this heat treatment is a mixture of the above and γ-MnO β-MnO ₂ by phase transition _2, and Mn ₂ O ₃ produced by pyrolysis.

Then, β-MnO ₂ and Mn ₂ O ₃ produced by the above heat treatment
Nitric acid is added to the mixture and heated again to perform heat treatment.

The heat treatment temperature with the nitric acid is 170 to 500 ° C.
Is preferred. When the heat treatment temperature exceeds 500 ° C., β-MnO ₂ produced is further decomposed and is an impurity.
May produce Mn ₂ O ₃ . The amount of nitric acid added during the heat treatment is 1 per 1.00 g of the product (mixture of β-MnO ₂ and Mn ₂ O ₃ ) of the above γ-MnO ₂ heat treatment.
It is preferable that the value of 3 normal is 0.4 m or more, that is, 0.52 gram equivalent or more. If the amount of nitric acid added is less than 0.52 gram equivalent, oxidation is insufficient and Mn ₂ O ₃ which is an impurity
May remain.

The heat treatment to which nitric acid is added may be performed once, or may be repeated twice or more as necessary.

By the above production method, β-MnO ₂ with extremely high purity is produced. When this β-MnO ₂ was analyzed by thermal analysis, it was confirmed that the weight before thermal decomposition was in good agreement with the theoretical amount when β-MnO _{2 was} 100%, and that it contained almost no impurities or water. In addition, as a result of this thermal analysis, β-MnO ₂ obtained was 5
It has also been found that it is stable up to around 00 ° C., so that even if it contains some water, it is possible to almost completely remove this water by heat treatment at high temperature.

Thus, according to the present invention, it is possible to produce highly pure β-MnO ₂ containing almost no water or impurities from inexpensive γ-MnO ₂ such as electrolytic manganese dioxide or chemically synthesized manganese dioxide as a raw material. is there.

Hereinafter, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

Example 1 First, commercially available electrolytic manganese dioxide was heat-treated at 525 ° C. for 2 hours.

The diffraction X-ray spectrum of the electrolytic manganese dioxide is shown in FIG. 1, and the diffraction X-ray spectrum of the product obtained by the heat treatment is shown in FIG. From FIG. 1, the diffraction X-ray spectrum of the electrolytic manganese dioxide can be determined by ASTM (The Am
erican Society for Tezting Materials) Card 14-
It is found that it is γ-MnO ₂ having a poor crystallinity in agreement with 644. Further, from FIG. 2, the product obtained by the heat treatment is A
Β-MnO ₂ and AST matching STM card 24-735
It can be seen that it is a mixture with Mn ₂ O ₃ corresponding to M-card 10-69.

Then, β-MnO ₂ and Mn ₂ O, which are products of the above heat treatment,
50 g of the mixture with ₃ is placed in a porcelain crucible and concentrated nitric acid (1
(3N) 40 m was added and placed in an electric furnace. And
The temperature was raised to 280 ° C. at a rate of 12 ° C. per hour, and this temperature was maintained for 2 hours for heat treatment.

The diffraction X-ray spectrum of the obtained product is shown in FIG.
From FIG. 3, it can be seen that Mn ₂ O
_The diffraction peak based on ₃ disappeared, and the ASTM card 24-
It can be seen that β-MnO ₂ corresponding to 735 is produced in high purity.

Furthermore, the product obtained in this example was subjected to thermogravimetric analysis to examine its composition.

FIG. 4 is a graph showing the results of thermogravimetric analysis at a temperature rise of 10 ° C. per minute, where a is a thermal decomposition curve of commercially available electrolytic manganese dioxide, and b is the beginning of this example. Shows the thermal decomposition curve of the product obtained by the heat treatment of, and c shows the thermal decomposition curve of β-MnO ₂ obtained by the heat treatment with addition of nitric acid. In FIG. 4, the vertical axis represents the relative weight when the theoretical amount of MnO ₂ obtained by back-calculating from the amount of Mn ₂ O ₃ finally obtained is 100%.

From FIG. 4, it can be seen that the electrolytic manganese dioxide, which is the raw material of this example, greatly exceeds the theoretical amount before the temperature rises, remarkably decreases in weight as the temperature rises, and falls below the theoretical amount at 300 ° C. or higher. There is. It is considered that this is because the electrolytic manganese dioxide contains a large amount of water and gradually releases the water by heating, and also contains a substance such as Mn ₂ O ₃ as an impurity. In addition, in the product obtained by heat-treating this electrolytic manganese dioxide at 525 ° C., although the weight loss due to the release of water was not observed as shown by b in FIG. 4, the weight before thermal decomposition was MnO ₂ 100. %
It is significantly lower than that of the above case, and it can be seen that a considerable amount becomes Mn ₂ O ₃ and is a mixture of β-MnO ₂ and Mn ₂ O ₃ . On the other hand, the final product of this example obtained by the heat treatment with addition of nitric acid is as shown in FIG.
Since the weight before thermal decomposition (500 ° C or less) is in good agreement with the theoretical amount of MnO ₂ 100% and is extremely stable, it contains almost no impurities such as Mn ₂ O ₃ and water, and thermodynamically It turns out that is also very stable.

From the results of the above X-ray diffraction and thermogravimetric analysis, it is clear that highly pure β-MnO ₂ was obtained in this example.

A scanning electron micrograph of the product obtained in this example is shown in FIG. The line observed in white in FIG. 5 is a marker that serves as a reference for the length, and
It shows μm.

Example 2 A commercially available electrolytic manganese dioxide similar to that used in Example 1 was used.
It heat-processed at 5 degreeC for 2 hours.

The diffraction X-ray spectrum of the product obtained is shown in FIG.
As shown in FIG. 6, the product is ASTM card 24-73.
It can be seen that it is a mixture of β-MnO ₂ matching 5 and Mn ₂ O ₃ matching ASTM card 10-69.

Next, 50 g of the above mixture was placed in a porcelain crucible, 40 m of concentrated nitric acid (13 normal) was added, and the mixture was placed in an electric furnace and heated to 280 ° C. at a heating rate of 12 ° C. per hour for heat treatment.

Further, 40 m of concentrated nitric acid was added and the above heat treatment was performed again.

The diffraction X-ray spectrum of the obtained product is shown in FIG.
From FIG. 7, it can be seen that in the above product, the diffraction peak of Mn ₂ O ₃ disappeared and the product became a β-MnO ₂ single phase.

The thermal decomposition curves of the mixture obtained by the first heat treatment and the product finally obtained are shown by d and e in FIG. 8, respectively. From FIG. 8, it can be seen that nearly half the amount of the above mixture is Mn ₂ O _3, and the final product has a weight before pyrolysis of 100% of MnO _{2, which} is in agreement with the theoretical amount of water and water. It can be seen that it contains almost no impurities Mn ₂ O ₃ .

[Brief description of drawings]

1 to 5 show an embodiment to which the present invention is applied. FIG. 1 is a diffraction X-ray spectrum of electrolytic manganese dioxide as a raw material, and FIG. 2 is obtained by heat treatment of electrolytic manganese dioxide. X-ray spectrum of the product obtained,
FIG. 3 is a diffraction X-ray spectrum of the product obtained by the heat treatment with addition of nitric acid, and FIG. 4 is a graph showing the thermal decomposition curve of β-MnO ₂ obtained in comparison with the thermal decomposition curve of electrolytic manganese dioxide. FIG. 5 is a photograph showing the obtained β-MnO ₂ crystal. 6 to 8 show another embodiment of the present invention. FIG. 6 is a diffracted X-ray spectrum of a product obtained by heat treatment of electrolytic manganese dioxide as a raw material, and FIG. 7 is nitric acid. FIG. 8 is a graph showing the thermal decomposition curve of β-MnO ₂ obtained by the diffracted X-ray spectrum of the product obtained by the heat treatment with addition of.

Claims (1)

[Claims] 1. A method for producing β-manganese dioxide, which comprises adding nitric acid to a mixed product of β-manganese dioxide and manganese trioxide obtained by heat-treating electrolytic manganese dioxide or chemically synthesized manganese dioxide, and then heat-treating.