JPS5856463B2 - Manufacturing method of non-aqueous electrolyte battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a battery using a negative electrode having a light metal such as lithium as an active material, a positive electrode mixture comprising manganese dioxide as an active material, a conductive material, and a binder, and a non-aqueous electrolyte. The present invention relates to a method for producing the positive electrode mixture.

In recent years, lithium batteries that use lithium for the negative electrode and nonaqueous organic electrolytes for the electrolyte have attracted attention as high-energy density batteries.

Typical positive electrode active materials for lithium batteries include fluorinated graphite and manganese dioxide, both of which are in practical use.

When manganese dioxide is used as the positive electrode active material of this type of non-aqueous electrolyte battery, it is necessary to remove crystal water in manganese dioxide, and the crystal structure of manganese dioxide is γ- rather than γ-type.
Since the β type or β type has excellent discharge performance, 25
Heat treatment is performed at a temperature of 0 to 450°C.

This heat-treated manganese dioxide is mixed with a conductive material and a binder, and the bottom is shaped to match the shape of each battery to form positive electrode mixture pellets.Then, the pellets are heated in air or under reduced pressure to remove adhering water before battery assembly. and then dry the negative electrode lithium.
A battery was constructed by combining a separator and an electrolyte solution in which lithium perchlorate or lithium borofluoride was dissolved in an organic solvent such as propylene carbonate or dimethoxyethane.

Batteries constructed in this way generate a large amount of gas during storage, which causes expansion of the battery and increases internal impedance during storage, resulting in a significant deterioration in discharge performance after storage. There were drawbacks.

As a result of investigating the cause of this gas generation, the present inventors found that in the coexistence of a small amount of water remaining in the electrolyte or mixture, the active oxygen adsorbed on manganese dioxide is activated by the organic solvent in the electrolyte.
For example, it was found that it acts on propylene carbonate, decomposing the organic solvent and generating carbon dioxide gas.

This active oxygen is easier to remove as manganese dioxide is heated to a higher temperature, but conversely, the manganese dioxide that has released the adsorbed active oxygen has the property that the higher the temperature, the easier it is to adsorb active oxygen. .

For this reason, even if manganese dioxide or positive electrode mixture has been heat-treated under reduced pressure or in an inert gas, it may not be exposed to air at high temperatures, or heated in air to dry the mixture after molding. Then, the active oxygen that has been removed is adsorbed again on the surface of manganese dioxide, and batteries using such manganese dioxide are subject to expansion and storage deterioration due to gas generation.

The present invention improves the method for producing a positive electrode mixture, removes active oxygen in manganese dioxide, which is the main cause of gas generation, and provides a battery that does not undergo battery expansion or storage deterioration.

That is, the present invention applies a conductive material such as acetylene black, and a binder such as polytetrafluoroethylene, 4
The method is characterized by heating and drying a positive electrode mixture of ethylene heptafluoride and propylene hexafluoride copolymer under reduced pressure or in an inert gas atmosphere, and then cooling it under reduced pressure or in an inert gas atmosphere. do.

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

Manganese dioxide obtained by heat-treating γ-type manganese dioxide at a temperature of 350° C. for 4 hours under reduced pressure of 50 vItHg or less is used.

The heat treatment conditions for converting γ-type manganese dioxide into γ-β type or β type are: temperature 250-450°C, time 2
~8 hours is appropriate, and the atmosphere in this case is air,
It does not matter whether it is under reduced pressure or in an inert gas.

A positive electrode mixture of 100 parts by weight of the above heat-treated manganese dioxide, 4 parts by weight of acetylene black, and a dispersion of polytetrafluoroethylene corresponding to 5 parts by weight of resin was prepared into a material with a diameter of 177 g and a thickness of 1.1 μ. Pressure mold into a disc shape.

Next, this molding mixture is heated and dried at a temperature of 150 to 320°C under a reduced pressure of 50 vtt Hg or less, and then naturally cooled under the same reduced pressure. After the mixture temperature has decreased to 50°C or less, it is released into the atmosphere. Take it out.

This drying process removes the active oxygen adsorbed on the manganese dioxide along with the moisture in the mixture.

A suitable drying temperature is 150 to 320°C.

Although temperatures below 150°C are sufficient for removing moisture,
Adsorbed active oxygen is not removed sufficiently.

Furthermore, if the drying temperature exceeds 320° C., the crystal structure of manganese dioxide will advance too much, the binder will decompose, and the shape of the mixture will become distorted, making it difficult to assemble the battery.

The drying time varies depending on the temperature, but 2 to 8 hours is appropriate.

The drying atmosphere is preferably an oxygen-free vacuum or an inert gas atmosphere such as argon or nitrogen, but a reduced pressure of 50rRXtHg or less is practically sufficient.

If the mixture heated and dried as described above is sufficiently cooled in the same atmosphere, active oxygen will not be adsorbed to manganese dioxide even if it is subsequently exposed to air.

Temperature of the mixture when taken out into the atmosphere after cooling 1. A temperature of at most 50°C is suitable; if exposed to an oxygen atmosphere at a temperature higher than this, active oxygen will be adsorbed to manganese dioxide again.

The thus dried and cooled positive electrode mixture is filled with negative electrode lithium,
and 1.0% in a solvent containing propylene carbonate and 1,2-dimethoxyethane mixed at a volume ratio of 5:2.
A coin-shaped lithium battery with a diameter of 23M and a thickness of 2.5U is constructed by combining electrolytes in which mol/l of lithium perchlorate is dissolved.

Since the active oxygen adsorbed to the manganese dioxide in the battery cell of the present invention produced as described above is removed and there is no re-adsorption, there is almost no gas generation as in the conventional case, and the performance after storage is also good. be.

Next, the effects of the present invention will be explained using specific examples.

Figure 1 & East The above positive electrode mixture was dried at various temperatures for 2 hours under a reduced pressure of 50 gHg or less, and then dried under the same reduced pressure for 2 hours.
(a) using a mixture cooled to 5°C and after drying,
When using a mixture that was immediately taken out into the air and cooled @b
), the relationship between the degree of expansion of the battery and the drying temperature when the battery was left at 60°C for 3 days is shown.

The degree of expansion was expressed as the difference between the thickness of the battery after expansion and the initial thickness.

Further, FIG. 2 shows the relationship between the internal impedance of the battery and the drying temperature of the mixture at 25° C. after the same battery as above was stored at 60° C. for one month.

These figures clearly show the effects of heating and cooling the mixture under reduced pressure.

The drying temperature is 150℃ or higher, especially if it is 200℃ or higher, the expansion and internal impedance of the battery will be small, but 320℃
The binder will decompose if it exceeds

Figure 3 shows a battery using a mixture that was dried at a temperature of 250°C for 2 hours under a reduced pressure of 501 rutt Hg or less, cooled to various temperatures in the same atmosphere, and then taken out into the atmosphere under the same conditions as above. The relationship between the degree of expansion of the battery and the cooling temperature is shown.

The figure shows that in the cooling process, it is appropriate to cool the mixture to below 50°C and then take it out into the atmosphere to avoid re-adsorption of active oxygen and to suppress expansion of the battery. .

In the above example, drying and cooling were performed under reduced pressure, but similar effects were obtained when processing was performed in an inert gas atmosphere such as argon or nitrogen.

As described above, according to the present invention, it is possible to obtain a nonaqueous electrolyte battery that does not expand due to gas generation and has good storage stability.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the mixture drying temperature and the degree of expansion of the battery when the mixture is heated and dried under reduced pressure and then cooled under reduced pressure or in the atmosphere. Figure 2 is also a diagram showing the relationship between the mixture drying temperature and the degree of expansion of the battery. FIG. 3 is a diagram showing the relationship between the temperature and the internal impedance after storage of the battery, and FIG. 3 is a diagram showing the relationship between the temperature after cooling the mixture in the cooling process and the degree of expansion of the battery.

Claims (1)

[Claims] 1 A positive electrode mixture consisting of γ-β type or β type manganese dioxide, a conductive material, and a binder is heated and dried at a temperature of 150 to 320°C under reduced pressure or in an inert gas atmosphere, and then dried under reduced pressure or in an inert gas atmosphere. A method for manufacturing a non-aqueous electrolyte battery, comprising a step of cooling to a temperature of 50° C. or lower in a gas atmosphere.