JPS6041772A - Manufacture of spiral electrode - Google Patents

Abstract

PURPOSE:To prevent any internal short circuits and increase the effect of a separator by making a spiral electrode in such a manner as to cause the direction of the longer axis of the minute holes of a microporous resin film to coincide with the direction of the wrapping. CONSTITUTION:After a microporous polypropylene film 1 and a nonwoven polypropylene fabric are placed upon each other to make a separator 2, this is formed into a sack-like shape in such a manner as to locate the microporous polypropylene film 1 outside of the sack-like shape and to cause the direction of the longer axis of the minute holes to coincide with the direction of the length of the sack-like separator 2. Next, for instance, a positive plate 3 formed by packing a current-collecting stainless-steel net 4 with titanium disulfide used as a positive active material is inserted into the sack-like separator 2. Then, the thus obtained body and a negative plate 5 formed by pressing and fixing lithium to a stainless-steel current collector net are placed upon each other. After that, this is wrapped around a current-collecting pipe 6 a having a lid 7 to make a spiral electrode.

Description

[Detailed Description of the Invention] This invention relates to an improvement in the manufacturing method of a spiral electrode using a film as a separator, and aims to prevent internal short circuits in batteries and short circuits during charging when used in secondary batteries. .

A spiral electrode is generally made by stacking a positive electrode plate and a negative electrode plate and winding them in a spiral shape with a separator interposed between the positive electrode plate and the negative electrode plate. In order to prevent internal short circuits due to peeling of the positive electrode mixture powder from the positive electrode plate, the energization is carried out by forming a separator into a bag, placing the positive electrode plate inside the bag, and placing the positive electrode plate and negative electrode together with the positive electrode plate covered with the separator. The plates are overlapped.

By the way, in a battery using an organic electrolyte-based electrolyte, a resin film having a large number of directional micropores, called a microporous resin film, is used as a component of the separator, and the body on the positive electrode side due to the reaction. Resin films with a large number of directional micropores (hereinafter referred to as microporous resin films) are often used because they have good liquid retention properties and rarely cause deterioration of battery characteristics even when JrJ increases. It is used as a separator by laminating a nonwoven fabric such as a polypropylene nonwoven fabric or a polyethylene nonwoven fabric, or by laminating microporous resin films together. Particularly preferred is a stack of a microporous polypropylene film and a polypropylene nonwoven fabric, and the microporous polypropylene film is generally arranged so as to face the negative electrode.

However, when a spiral electrode is fabricated using a separator using such a microporous resin film and a battery is assembled, internal short circuits often occur. Particularly when used in secondary batteries, internal short circuits occur significantly during charging.

The present inventors have conducted various studies to investigate the cause of such internal short circuits and find measures to prevent them. As a result, we have found that such internal short circuits occur when the long axis direction of the micropores of the microporous resin film is spiral. If the winding is perpendicular to the direction of winding, the width of the pores will expand when the pores are wound, especially in secondary batteries, when lithium is deposited during charging. Since the microporous resin film has a dendritic shape, as the width of the micropores increases, it becomes easier for lithium to penetrate the separator, which increases the occurrence of internal short circuits. When creating a spiral electrode by arranging it in the same direction as the winding direction, the micropores extend in the length direction but the width becomes narrower, which not only prevents internal short circuits but also improves the separator effect. This led to the completion of the present invention.

The microporous resin film used as a separator in the present invention is a film formed by extrusion molding of a synthetic resin such as polyethylene, polypropylene, or nylon to have a large number of micropores, and the diameter of the micropores is, for example, in the longitudinal direction. is 0.02 to 0.2 pm, and the shortening direction is 0.
．． 01 to 0.05 μm. A typical commercially available example of such a microporous resin film is a polypropylene film commercially available from Polyplastics Co., Ltd. under the trade name "Duraguard". Preferred.

Next, embodiments of the present invention will be described with reference to the drawings.

Example 1 FIG. 1 is a plan view schematically showing a microporous polypropylene film used in this example, and in this microporous polypropylene film 1, micropores 1a are formed with directionality. .

Microporous polypropylene film I and Volip I cobylene nonwoven fabric as described in Section 1 were superimposed to form a separator 2, which was formed into a rectangular bag shape. At that time, the microporous polypropylene film 1 is placed on the outside, and the micropores 1a are
The bag-shaped separator 2 was arranged so that its long axis direction was the same as the length direction of the bag-shaped separator 2.

As shown in FIG. 2, inside this bag-shaped separator 2, titane disulfide is used as a positive electrode active material, and a stainless steel current collecting network 4 is placed inside the bag-shaped separator 2.
On the other hand, lithium was crimped onto a stainless steel current collector net to form a negative electrode plate 5, which was overlapped with the positive electrode plate 3 covered with the separator 2, and the lid 7 was closed. A spiral electrode was formed by winding the current collecting vibro in a spiral shape around the core.

In this a1-wound electrode, the microporous polypropylene film 1 is arranged so that the long axis direction of the micropores 1a is in the same direction as the length direction of the bag-shaped separator 2.
The direction of spiral winding and the long axis direction of the micropores are in the same direction.

The spiral electrode manufactured as described above was placed in a cylindrical battery case, and 1.3-dioxolane and 1.2
A battery was produced by hermetically sealing LiB(CsHs)4 dissolved in a mixed solvent having a volume ratio of 70:30 with -cymetogishetane at a concentration of 0.6 T nyl/p/8.

Comparative Example 1 A spiral electrode was formed in the same manner as in Example 1 by arranging a microporous Volip 11 pyrene film so that the long axis direction of the micropores was perpendicular to the direction of spiral winding. A battery was manufactured in the same manner as in Example (2).

- Battery of Example 1 and Comparative Example 1 manufactured as described in
1. (Discharge 1.5V to charge 2 at 1mA constant current)
．． The battery was charged between 7V and the relationship between the number of cycles and the charge/discharge ratio was plotted, and the results are shown in FIG.

Note that the charge/discharge ratio is the ratio of the amount of electricity charged (mAh), the amount of electricity discharged (mAh), and the amount of electricity charged and discharged in each cycle, as shown in the following formula. , the closer the charge-discharge ratio is to 1, the better the charge-discharge characteristics are.

As shown in FIG. 3, the battery of Example 1 had a charge/discharge ratio closer to 1 than the battery of Comparative Example 1, and its charge/discharge characteristics were deviated. The reason why the battery of Comparative Example 1 has a high charge-discharge ratio is that the fine pores in the microporous polypropylene film open up when it is spirally wound, and the dendritic electrodeposited lithium flows from there to the positive electrode side. This is thought to be due to the occurrence of an internal short circuit. Furthermore, the reason why the battery of Example 1 had excellent charge-discharge characteristics is thought to be because the microporous polypropylene film did not have micropores, which suppressed the occurrence of internal short circuits due to the dendritic electrodeposited lithium.

[Brief explanation of drawings]

FIG. 1 is a plan view schematically showing a microporous polypropylene film, FIG. 2 is a partial cross-sectional perspective view schematically showing the state during manufacture of a spiral electrode, and FIG. 3 is a plan view schematically showing a microporous polypropylene film. FIG. 3 is a diagram showing the relationship between the number of cycles and the charge/discharge ratio of a battery using a spiral electrode manufactured by a conventional method and a battery using a spiral electrode manufactured by a conventional method. 1...m 7L t'l polypropylene film, 1a
...Minor pores, 2...Separator patent issued by 19ii Hitachi Maxell Co., Ltd.

Claims (1)

[Claims] (1. In manufacturing a spiral electrode using a resin film having a large number of directional micropores as a separator, "1. The resin film is wound in a spiral shape with the long axis direction of the micropores ( A method for producing a spiral electrode characterized by winding it in a spiral shape by arranging it in the same direction as the winding direction when the electrode is wound. A method for manufacturing a spiral electrode according to claim 1 of H144, which is obtained by laminating a birene nonwoven fabric.