JPH0845547A - Manufacture of spiral electrode for lithium secondary battery - Google Patents

Abstract

PURPOSE:To prevent the generation of an internal short circuit in a battery assembling time and a battery charging time, by providing a separator in a specific condition, and winding it in a spiral form, when a spiral electrode for lithium secondary battery in which the separator is formed by superposing a resin film having numerous pores which have an orienting property, and a nonwoven fabric, is obtained. CONSTITUTION:When a lithium secondary battery in which a resin film having numerous minute pores 1a which have an orienting property; and a nonwoven fabric; are superposed so as to form a separator 2, is obtained, the separator 2 is provided to make the resin film contact with a negative electrode plate 5 between a positive electrode 3 and the negative electrode 5, and to make its direction same as the winding direction of the longer axial direction of the minute pores 1a wound in a spiral form, and the separator 2 is wound in a spiral form.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method of manufacturing a spiral electrode for a lithium secondary battery, which uses a resin film having a large number of directional micropores as a separator, and prevents the occurrence of an internal short circuit during battery assembly. It is also intended to prevent the occurrence of an internal short circuit due to the dendritic lithium during charging.

[0002]

2. Description of the Related Art A spiral electrode is generally manufactured by stacking a positive electrode plate and a negative electrode plate in a state where a separator is interposed between the positive electrode plate and the negative electrode plate and winding them in a spiral shape. Then, usually in order to prevent an internal short circuit due to peeling of the positive electrode mixture powder from the positive electrode plate, the separator is formed into a bag shape, the positive electrode plate is put therein, and the positive electrode plate is covered with the positive electrode plate. The negative electrode plate is overlaid.

By the way, in a battery using an organic electrolyte-based electrolytic solution, a resin film having a large number of directional fine pores called a microporous resin film as a constituent material of the above-mentioned separator has a positive electrode side associated with the reaction. The resin film having a large number of directional micropores (hereinafter referred to as microporous resin film) Said) and a non-woven fabric such as polypropylene non-woven fabric or polyethylene non-woven fabric, or microporous resin films are superposed on each other and used as a separator. In particular, a laminate of a microporous polypropylene film and a polypropylene nonwoven fabric is preferably used, and the microporous polypropylene film is usually arranged so as to face the negative electrode.

[0004]

However, when a spiral electrode is produced using a separator using such a microporous resin film and a battery is assembled, an internal short circuit is often observed. Particularly when used in a secondary battery, the occurrence of internal short circuit during charging is remarkable.

[0005]

The inventors of the present invention have conducted various studies to find out the cause of such an internal short circuit and to find a preventive measure, and as a result, such an internal short circuit is caused by a microporous resin. If the long-axis direction of the micropores of the film is arranged in a direction perpendicular to the spiral winding direction, it is caused by the widening of the micropores when spirally wound, especially the secondary battery. In the case of lithium, the lithium electrodeposited during charging is dendritic, and if the width of the micropores is widened, lithium easily penetrates through the separator and internal short circuits often occur. When the spiral electrode is manufactured by arranging so that the major axis direction of the coil is the same as the spiral direction, the micropores extend in the length direction but become narrower in width, preventing internal short circuit. Not to mention Sepa It found that over data effect is further improved, and accomplished the present invention.

The microporous resin film used as the separator in the present invention is a film formed by extrusion molding a synthetic resin such as polyethylene, polypropylene or nylon so as to have a large number of micropores. For example, the major axis direction is 0.02 to 0.2 μm, and the minor axis direction is 0.01 to 0.05 μm. As a typical commercially available example of such a microporous resin film, there is a polypropylene film commercially available from Polyplastics Co., Ltd. under the trade name of "Duraguard", which is particularly preferably used in the present invention. To be

[0007]

Embodiments of the present invention will now 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. In this microporous polypropylene film 1, the micropores 1a are formed with directionality. ing.

The microporous polypropylene film 1 and the polypropylene non-woven fabric as described above were laminated to form a separator 2, which was formed into a rectangular bag shape. At that time, the microporous polypropylene film 1 was placed outside, and the micropores 1a were arranged so that the long axis direction thereof was the same direction as the length direction of the bag-shaped separator 2 to form a bag shape.

As shown in FIG. 2, a positive electrode plate 3 having titanium disulfide as a positive electrode active material and held by a stainless steel current collecting net 4 is placed in the bag-shaped separator 2, while lithium is used in stainless steel. A negative electrode plate 5 is formed by pressure-bonding to a current collector made of metal, and is superposed on the positive electrode plate 3 covered with the separator 2, and is spirally wound around a current collecting pipe 6 with a lid 7 as a core to form a spiral electrode. Was formed.

In this spiral electrode, since the microporous polypropylene film 1 is arranged so that the long axis direction of the micropores 1a is the same as the length direction of the bag-shaped separator 2, the microporous polypropylene film 1 is spirally wound. And the long axis direction of the fine holes are the same direction.

The spiral electrode manufactured as described above is placed in a cylindrical battery case, and the capacity ratio of 1,3-dioxolane and 1,2-dimethoxyethane as the electrolytic solution is 70: 3.
A battery in which LiB (C ₆ H ₅ ) ₄ was dissolved at 0.6 mol / liter in a mixed solvent of 0 was hermetically sealed to manufacture a battery.

Comparative Example 1 A spiral electrode was formed in the same manner as in Example 1 except that the microporous polypropylene film was arranged so that the long axis direction of the micropores was orthogonal to the winding direction when spirally wound. Thereafter, a battery was manufactured in the same manner as in Example 1.

The battery of Example 1 manufactured as described above and the battery of Comparative Example 1 were discharged at a constant current of 1.0 mA at 1.5 V.
~ Charging / discharging between 2.7V, the relationship between the number of cycles and charging / discharging ratio was investigated, and the result was shown in FIG. The charge / discharge ratio is as shown in the following equation. It is the ratio of the amount of electricity discharged and the amount of electricity charged in each cycle,
The closer the charge / discharge ratio is to 1, the better the charge / discharge characteristics.

As shown in FIG. 3, the battery of Example 1 had a charge / discharge ratio close to 1 and an excellent charge / discharge characteristic as compared with the battery of Comparative Example 1. In the battery of Comparative Example 1, the charge / discharge ratio is high because the micropores of the microporous polypropylene film are opened when spirally wound, and the dendritic lithium from the branch is penetrated to the positive electrode side to the inside. This is probably due to the occurrence of a short circuit. Further, it is considered that the battery of Example 1 has excellent charge / discharge characteristics because the micropores of the microporous polypropylene film were not opened and the occurrence of internal short circuit due to dendritic lithium was suppressed.

[Brief description 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 a state at the time of manufacturing a spiral electrode.

FIG. 3 is a diagram showing a relationship between a cycle number and a charge / discharge ratio of a battery using a spiral electrode manufactured according to an example of the present invention and a battery using a spiral electrode manufactured by a conventional method.

[Explanation of symbols]

 1 Microporous polypropylene film 1a Micropore 2 Separator

Claims (1)

[Claims] 1. In manufacturing a spiral electrode for a lithium secondary battery, which comprises using a non-woven fabric and a resin film having a large number of directional fine pores as a separator, the separator is placed between a positive electrode plate and a negative electrode plate. The resin film is interposed so as to be in contact with the negative electrode plate, and the resin film is wound so that the long axis direction of the fine holes is in the same direction as the spiral winding direction. A method of manufacturing a spiral electrode for a lithium secondary battery, which comprises: