JPH03291850A - Manufacture of sheet electrode - Google Patents

Abstract

PURPOSE:To prevent burning accidents during heat treatment by giving heat treatment to a sheet in-process product made up with electrode active material, binder. solvent and a current collector while providing a cavity between sheet layers using a preset method. CONSTITUTION:Polyvinylbutyral and phthalic acid butyl are added to active material with manganese dioxide as main element, dissolved and kneaded with alcohol and formed in a sheet shape integrally with a current collector. The in-process product 1 of such a sheet electrode is given heat treatment for 48 hours or so at 50-300 deg.C while separating one layer from the other to decompose polyvunylbutyral and phthalic acid butyral. A cavity between layers is formed by pile-winding on a stainless corrugated belt 2 of thickness 0.1-0.2mm or wind ing in a corrugated shape between fixed rollers 14a, 14b in sequence. The cavity allows heat to be dissipated during the heat treatment and the in-process product 1 to be completed without being subjected to burning.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of manufacturing a sheet-like electrode used, for example, as a positive electrode of a spiral-shaped lithium battery.

<Prior art> For example, in a spiral type lithium-manganese battery using a non-aqueous electrolyte, a power generation element consisting of an electrode group consisting of a sheet-shaped positive electrode and a negative electrode wound into a roll with a separator in between is placed in a battery can. It has a storage structure.

When producing the above-mentioned positive electrode, a procedure such as that described in Japanese Patent Application No. 1-112931 filed by the applicant of the present invention is adopted. That is, to an active material made of manganese dioxide mixed with a conductive agent such as graphite or acetylene black, polyvinyl butyral as a binder, dibutyl phthalate as a plasticizer, and alcohol as a solvent are added and kneaded. This mixture is integrally formed into a sheet-like electrode together with a current collector by extrusion molding. Polyvinyl butyral, dibutyl phthalate, and the like are used to impart rubber-like elasticity to the mixture by kneading it with alcohol, so that it can be easily formed into a sheet by extrusion molding or the like.

In order to decompose these binders, plasticizers, alcohols, etc., the sheet electrode 1 is wound into a roll via an interlayer belt 15 made of glass fiber coated with Teflon, for example, as shown in FIG. A method is adopted in which the material is heat-treated at a predetermined decomposition temperature in a drying oven, then press-rolled to a predetermined thickness, and cut into pieces to form the above-mentioned positive electrode.

<Problems to be Solved by the Invention> However, when performing heat treatment as described above, the phenomenon that the sheet-like electrode burns frequently occurs, making it difficult to obtain electrodes with stable performance at a high yield. There was a problem that.

According to the research of the present inventor, this is because the sheet-like electrode and the interlayer belt are heat-treated in close contact with each other, so that the heat generated by the exothermic reaction during the decomposition of the binder during the heat treatment is effectively transferred to the outside. It was found that this was because heat could not be dissipated and the temperature of the sheet electrode rose to the combustion temperature.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a sheet-like electrode that allows heat treatment at a predetermined decomposition temperature without burning the sheet-like electrode.

Means for Solving the Problems> That is, the method for producing a sheet-like electrode according to the present invention comprises adding polyvinyl butyral as a binder, dibutyl phthalate as a plasticizer, and a solvent to an active material containing manganese dioxide as a main component. A sheet-like electrode obtained by integrally molding a mixture with a current collector by extrusion molding and kneading with alcohol added thereto is wound through a wavy interlayer belt in which uneven grooves are sequentially formed in the winding direction. The gist of this method is to rotate it and heat treat it in this state.

Instead of performing the heat treatment while being wound around the wavy interlayer belt as described above, the heat treatment may be performed while the sheet electrodes are spaced apart in a wavy manner without contacting each other.

In the case of separating the electrodes in a wavy manner as described above, for example, a method may be used in which the sheet electrodes are sequentially wound in a wavy manner between a plurality of pairs of fixed support rollers provided facing each other at appropriate intervals.

In the present invention, the amount of polyvinyl butyral added is about 2 to 15% by weight based on the active material (manganese dioxide, conductive agent, etc.), and the amount of dibutyl phthalate added is about 30 to 70% by weight based on the polyvinyl butyral. and
Further, alcohol (ethyl alcohol and other alcohols) may be used in an amount necessary to give the mixture the above-mentioned rubber-like elasticity. Further, as the binder, polyvinyl butyral may be prepared by adding alcohol such as ethanol to Teflon aqueous dispersion and emulsifying the binder by stirring and emulsifying the binder.

Further, the above heat treatment is preferably performed at a temperature of 300° C. or lower, and is usually performed at a predetermined temperature pattern in which the temperature is increased in steps. If the treatment temperature is higher than 300° C., there is a risk that an insulating oxide film may be formed on the surface of the transformation 1 of manganese dioxide or the current collector (made of stainless steel, etc.).

Furthermore, if the heat treatment is performed by increasing the temperature linearly to 300° C., even if the method of the present application is used, it will be difficult to prevent the mixture or electrode from burning due to the heat of oxidation reaction.

In addition, the heat treatment time is determined to be an appropriate time considering the size of the treatment tank, the thickness and capacity of the 5 mixture, and specifically,
For example, it may be done for about 48 hours. For example, the heat treatment time is 8
If the temperature is rapidly increased over time to shorten the thermal decomposition cycle, it becomes difficult to prevent the mixture or electrode from burning, as described above. Further, even if the heat treatment time is set to 96 hours, for example, and the thermal decomposition cycle is lengthened, the amount of thermal decomposition remains constant, so there is no point in using too long a heat treatment time.

<Function> If the sheet electrode is wound around the wavy interlayer belt and heat treated as described above, a space communicating with the outside will be formed on the electrode surface, and the heat generated by the exothermic reaction during the heat treatment will be dissipated. Heat can be dissipated quickly through this space, and as a result,
The rise in temperature of the electrode is minimized, and burning of the sheet electrode during the heat treatment process can be prevented.

On the other hand, by heat-treating the sheet-like electrodes in a state where they are spaced apart in a wavy manner as described above, heat dissipation is good because there is no coating such as an interlayer belt, and therefore the heat generated during heat treatment is quickly dissipated to the outside. , similarly to the above, burning of the sheet electrode can be prevented.

<Example> Examples will be described below.

Manganese dioxide 80% by weight, conductive agent 7% by weight.

Emulsion of Teflon aqueous dispersion (specific gravity 1.5,
Solid content 60% by weight) 3% by weight, polyvinyl butyral 6
．． An appropriate amount of alcohol was mixed with 5% by weight of dibutyl phthalate and 3.5% by weight of dibutyl phthalate, and the mixture was kneaded for 1 hour to obtain a mixture having rubber-like elasticity.

This mixture is put into an extrusion molding machine equipped with a crosshead, and within this crosshead, a porous current collector made of punched stainless steel metal and the mixture are integrally formed, that is, they are combined on both sides of the porous current collector. Sheet-like electrodes were prepared by pressing the respective agents.

A wavy interlayer belt 2 is stacked on this sheet electrode 1 as shown in FIG. 1(A), and this wavy interlayer belt 2
The material was wound into a roll shape through a roller to obtain a wound structure (product 1 of the present invention) having a diameter of 60 to 70 cm as shown in FIG. 1(B).

The wavy interlayer belt 2 has a width of 50 mm and a thickness of 0.1 to 0.
．． As shown in Fig. 2, convex grooves 2a and concave grooves 2b are sequentially formed in the winding direction R of stainless steel thin plates, titanium thin plates, nickel thin plates, etc. 3I
A material of approximately Im size was used. If the depth 11 is shallower than this, it will be difficult to properly dissipate heat, while if it is deeper than this, the length of the sheet-shaped electrode due to the winding diameter will be shortened, and the amount that can be heat-treated will be reduced. , processing efficiency is poor. Although the illustrated wavy interlayer belt 2 has an arcuate wavy shape,
In addition, for example, it may be formed into a wavy shape bent at an appropriate angle.

Furthermore, if necessary, the wavy interlayer belt may of course be subjected to Teflon coating treatment.

In addition, a wound structure (comparative product) was prepared by similarly winding the mixture into a roll via a sheet-like interlayer belt in which both sides of glass fibers were coated with Teflon.

These were placed in an electric furnace, which is a drying furnace, and heat-treated by gradually increasing the temperature from 50 to 300°C over 48 hours using the temperature cycle shown in Figure 3. decomposed polyvinyl butyral and dibutyl phthalate. After that, it is rolled with a rolling roll or a press to form a sheet-like electrode with a predetermined thickness and density. Figure 4 shows a spiral type lithium battery using this sheet-like electrode cut into appropriate lengths as the positive electrode 3. The power generation elements 7 to 13 are respectively a porous current collector, a battery can, an insulating gasket, a terminal plate, a sealing plate, a bottom plate, and a lead plate.

On the other hand, as shown in FIGS. 5(A) and 5(B), a roller with a width t2 of 2000 mm is provided with a plurality of pairs of fixed rollers 14a and 14b supported facing each other at appropriate intervals at the upper and lower ends. Using a winding tool consisting of a stainless steel frame 14 with a height t3 of 1500 mm, the sheet-like electrode 1 is wrapped around these fixed rollers 14a, 1.
4b, and the sheet electrodes 1 are arranged in a wavy manner without contacting each other.
Inventive product 2) was prepared, and the same heat treatment as above was performed in this state. If the wrapping is carried out using a device equipped with a transport part using a cart or the like at the bottom of the framework 14, it can be transported into the electric furnace for heat treatment, or removed from the electric furnace after heat treatment. It makes moving work easier when transporting.

The rate of non-defective sheet electrodes after heat treatment for Inventive Products 1 and 2 and the comparative product explained above is as shown in the table below, and the comparative product burns at a high rate of 89%, resulting in defective products. In contrast, there was no combustion in product 1.2 of the present invention.

Table <Effects of the Invention> As described above, according to the method for producing a sheet-like electrode of the present invention, the heat generated by the exothermic reaction during heat treatment can be quickly dissipated, so that the sheet-like electrode cannot be burned. As a result, electrodes with stable performance can be obtained at a high yield.

[Brief explanation of drawings]

Figures 1 (^) and (B) are explanatory diagrams of the case where a sheet electrode is wound using a wavy interlayer belt, Figure 2 is an explanatory diagram of a wavy interlayer belt, and Figure 3 is an example of heat treatment. Graph, FIG. 4 is a cross-sectional view of a spiral-shaped lithium battery whose positive electrode is a sheet-shaped electrode heat-treated by the method of the example, and FIG. 5 (A).
5(B) is a perspective view of an example in which sheet electrodes are separated in a wavy manner by a winding device equipped with a fixed roller, and FIG. 5(B) is an explanatory diagram thereof;
FIG. 6 is an explanatory diagram of a conventional example. 1... Sheet-like electrode, 2... Wavy interlayer belt, 14
...framework, 14a, 14b...fixed rollers. Patent Applicant Fuji Electrochemical Co., Ltd. Agent Tomo Omata Figure 4 +2 Figure 5 (B)

Claims (1)

[Claims] 1. Extrusion of a mixture obtained by adding and kneading polyvinyl butyral as a binder, dibutyl phthalate as a plasticizer, and alcohol as a solvent to an active material whose main component is manganese dioxide. The sheet electrode is formed integrally with a current collector by molding, and this sheet electrode is heat-treated while being wound through a wavy interlayer belt in which uneven grooves are sequentially formed in the winding direction. Characteristic method for manufacturing sheet-like electrodes. 2. The sheet according to claim 1, characterized in that instead of winding the sheet through the wavy interlayer belt, the heat treatment is performed while the sheet electrodes are spaced apart in a wavy manner without contacting each other. A method for manufacturing a shaped electrode.