JPS6225612B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating manganese dioxide, and its gist is that a member that absorbs microwaves and generates heat is brought into close contact with manganese dioxide, and that the water in the manganese dioxide is removed by irradiation with microwaves. The purpose is to selectively transform the crystal structure of manganese dioxide through heat generation, making it possible to create anhydrous or nearly anhydrous manganese dioxide that can be expected to improve battery performance as a positive electrode active material for non-aqueous electrolyte batteries. At the same time, we propose a method for selectively obtaining a desired crystal structure of manganese dioxide. Now, in recent years, light metals that are highly reactive with water, such as lithium and sodium, have been used as negative electrode active materials.
BACKGROUND ART Non-aqueous electrolyte batteries have been attracting attention as having high voltage and high energy density, and batteries using manganese dioxide, which is commonly used in conventional dry batteries, as a positive electrode active material have been put into practical use.
In this case, the manganese dioxide used in the non-aqueous electrolyte battery must be free of moisture as much as possible, unlike in the case of dry batteries. However, heat treatment methods have conventionally been applied to remove water, and it is thought that a change in crystal structure occurs at the same time as the removal of crystal water. It is generally known that manganese dioxide contains a large amount of crystallized water in addition to attached water, and when heat treated to remove this water, the structure of manganese dioxide depending on the treatment temperature was investigated using X-ray analysis. Then, at about 200°C, it exhibits a so-called γ-type crystal structure (γ-MnO ₂ ), and although the attached water has been removed, it still contains a large amount of crystal water. As the so-called γ-MnO ₂ gradually changes to β-type manganese dioxide (β-MnO ₂ ), the water of crystallization is gradually removed, and in the temperature range of about 250 to 350°C, it becomes the so-called γ-β type state. , furthermore from around 350℃
It is said that it becomes β-MnO ₂ in the temperature range of 450°C. It is said that decomposition of manganese dioxide begins at around 450℃. In this way, the transition of the crystal structure of manganese dioxide is thought to be influenced by the treatment temperature, and in heat treatment using an electric furnace, etc., the residual moisture content and the crystal structure are closely related, and the two should be controlled by separating them. It can be said that this is impossible. Therefore, the present inventors have conducted various experiments on dehydration methods for manganese dioxide, and have discovered that by irradiating manganese dioxide with microwaves, water can be removed to a large extent in a short period of time without causing a temperature rise. An experimental example is shown below. Put 100g of γ-type electrolytic manganese dioxide into a glass saucer, place it in the microwave, and heat it to 2450±.
A 50 MHz microwave was irradiated for 15 minutes. It was confirmed that the crystal structure of the electrolytic manganese dioxide treated in this manner was the same as before treatment, and the residual water content was 0.9%. As can be understood from this result, by irradiating manganese dioxide with microwaves, water can be removed to a large extent without causing an increase in the temperature of the entire manganese dioxide. Therefore, when manganese dioxide is irradiated with microwaves, if a member that absorbs microwaves and generates heat is placed in close contact with the manganese dioxide, the output of the microwave can be adjusted appropriately to reduce the heat generation temperature of the member at the same time as moisture removal. By controlling this, it is possible to greatly reduce the amount of residual water and obtain manganese dioxide having a desired crystal structure. The material that absorbs microwaves and generates heat may be ferrite, conductive rubber material, or a metal thin film with poor conductivity that is close to dielectric material. When placed alone in a microwave oven and irradiated for 5 minutes at an output of approximately 300 watts and a frequency of 2450±50 MHz, it was confirmed that the temperature of the ferrite saucer rose to 500°C. Therefore, it will be understood that the desired temperature, or in other words, the crystal structure of manganese dioxide, can be controlled to a desired value by appropriately adjusting the output power and irradiation time. Alternatively, the above member may be used as a saucer, or pieces of the member may be dispersed or formed into rod shapes and placed in manganese dioxide powder filled in a saucer made of a material that transmits microwaves such as glass. It is best to keep it in close contact with manganese dioxide. Examples of the present invention will be described in detail below. The table below shows the results when a ferrite saucer containing approximately 100 g of electrolytic manganese dioxide was placed in a microwave oven and irradiated with microwaves at an output of approximately 300 watts and a frequency of 2450 ± 50 MHz for a specified period of time.

【table】

[Table] The residual moisture content is determined by increasing the temperature of manganese dioxide after treatment and quantifying the moisture that comes out using a Karl Fischer.When the temperature is raised to 400℃, the residual moisture content is 0%.
It was calculated as The average of the center and surface areas is shown. The crystal structure was identified by X-ray diffraction (Fe tube), and those with a peak at 28° were designated as γ type, and those with a peak at 36° were designated as β type. Sampling was conducted from two locations: the center and the surface. According to the treatment method of the present invention, when manganese dioxide is irradiated with microwaves, water molecules in the polarized state of water (adhered water and crystal water) contained in manganese dioxide are excited and cause rotational movement. The frictional heat evaporates and instantly dehydrates the water. Unlike heat treatment in an electric furnace, for example, it is possible to remove a large amount of water without causing an extreme temperature rise, and it also reduces manganese dioxide. Manganese dioxide with a desired crystal structure can be obtained by controlling the heat generation temperature of the member by appropriately adjusting the output and time of the microwave due to the presence of a member that absorbs microwaves and generates heat in close contact with each other. Therefore, its industrial value is extremely great, especially as a method for treating manganese dioxide, which is applied as a positive electrode active material in non-aqueous electrolyte batteries, where the presence of moisture is a fatal problem.

Claims (1)

[Claims] 1. A member that absorbs microwaves and generates heat is brought into close contact with manganese dioxide, irradiated with microwaves to remove water in the manganese dioxide, and at the same time selectively transforms the crystal structure of the manganese dioxide by the heat generated by the member. Characteristic method of processing manganese dioxide.