JP2732371B2 - Method for manufacturing spiral electrode for lithium secondary battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an improvement in a method for manufacturing a spiral electrode for a lithium secondary battery using a resin film having a number of directional fine holes as a separator. Another object of the present invention is to prevent the occurrence of an internal short circuit during battery assembly and the occurrence of an internal short circuit due to dendritic lithium during charging. 2. Description of the Related Art A spiral electrode is generally formed by laminating 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 the spirally. And usually, in order to prevent internal short circuit due to peeling of the positive electrode mixture powder from the positive electrode plate, the separator is made into a bag shape, the positive electrode plate is put therein, and the positive electrode plate is covered with the separator with the positive electrode plate. The negative electrode plate is overlaid. 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 is used as a constituent material of the separator. A resin film having a large number of micropores having this directionality (hereinafter, referred to as a microporous resin film) is preferably used because it has good liquid retention properties and does not cause a decrease in battery characteristics even when the volume of the resin increases. ) And a non-woven fabric such as a polypropylene non-woven fabric or a polyethylene non-woven fabric, or a micro-porous resin film is 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 manufactured using a separator using such a microporous resin film and a battery is assembled, occurrence of an internal short circuit is often recognized. In particular, when used in a secondary battery, the occurrence of an internal short circuit during charging is remarkable. The present inventors have conducted various studies to find out the cause of such an internal short-circuit and to find countermeasures to prevent the internal short-circuit. When the long axis direction of the micropores of the porous resin film is arranged in a direction perpendicular to the winding direction when spirally wound, it is caused by the widening of the micropores when spirally wound, particularly, In a secondary battery, lithium that is deposited during charging is in a dendritic form, so if the width of the micropores is widened, lithium tends to penetrate through the separator, so that an internal short circuit occurs more frequently. When a spiral electrode is fabricated by arranging the micropores in such a way that the major axis direction of the micropores is the same as the winding direction when spirally wound, the micropores extend in the length direction but become narrower because the width becomes narrower. To prevent short circuit Naturally, the inventors have found that the separator effect is further improved, and have completed the present invention. [0006] The microporous resin film used for the separator in the present invention is a film formed by extruding a synthetic resin such as polyethylene, polypropylene, nylon or the like 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. 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 "Duragard", and is particularly preferably used in the present invention. Can be 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. In this microporous polypropylene film 1, micropores 1a are formed with a direction. ing. [0009] The separator 2 was formed by laminating the microporous polypropylene film 1 and a polypropylene nonwoven fabric as described above, and formed into a rectangular bag shape. At that time, the microporous polypropylene film 1 was placed outside and the major axis direction of the micropores 1a was arranged in the same direction as the length direction of the bag-like separator 2 to form a bag. As shown in FIG. 2, a positive electrode plate 3 containing titanium disulfide as a positive electrode active material and held by a current collector network 4 made of stainless steel is put in the bag-shaped separator 2, and lithium is added to stainless steel. A negative electrode plate 5 is formed by press-fitting the negative electrode plate 5 with a positive electrode plate 3 covered with the separator 2 and spirally wound around a current collecting pipe 6 with a lid 7 as a core. Was formed. In this spiral electrode, the microporous polypropylene film 1 is arranged so that the major axis direction of the micropores 1a is in the same direction as the length direction of the bag-like separator 2, so that it is spirally wound. And the major axis direction of the fine holes is the same direction. The spiral electrode manufactured as described above is placed in a cylindrical battery case, and the volume ratio of 1,3-dioxolane to 1,2-dimethoxyethane is 70: 3 as an electrolytic solution.
Using a mixed solvent of LiB (C ₆ H ₅ ) ₄ dissolved in 0.6 mol / liter in a mixed solvent of No. 0, a hermetic seal was used 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 major axis direction of the micropores was perpendicular 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 and the battery of Comparative Example 1 manufactured as described above were discharged at a constant current of 1.0 mA and discharged at 1.5 V.
The charge / discharge was performed between the charge and the charge of 2.7 V, and the relationship between the number of cycles and the charge / discharge ratio was examined. The result is shown in FIG. The charge / discharge ratio is as shown in the following equation. The ratio between the amount of discharged electricity and the amount of charged electricity 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 as compared with the battery of Comparative Example 1, and had excellent charge / discharge characteristics. The charge / discharge ratio of the battery of Comparative Example 1 is high because the micropores of the microporous polypropylene film are opened when spirally wound, and dendritic lithium branches penetrate to the positive electrode side from there, and the inside of the battery. Probably due to short circuit. The reason why the battery of Example 1 has excellent charge / discharge characteristics is considered to be that the micropores of the microporous polypropylene film did not open and the occurrence of internal short circuit due to dendritic electrodeposited lithium could be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view schematically showing a microporous polypropylene film. FIG. 2 is a partially sectional perspective view schematically showing a state at the time of manufacturing a spiral electrode. 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 according to an example of the present invention and a battery using a spiral electrode manufactured by a conventional method. [Description of Signs] 1 Microporous polypropylene film 1a Micropore 2 Separator

Claims (1)

(57) [Claims] In manufacturing a spiral electrode for a lithium secondary battery, which is used by laminating a resin film having a number of directional pores and a nonwoven fabric for use as a separator, the resin film is interposed between the positive electrode plate and the negative electrode plate and the negative electrode plate is disposed between the separator. Lithium is interposed so as to be in contact with, and the resin film is arranged so that the major axis direction of the fine holes is in the same direction as the spiral direction when spirally wound, and spirally wound. A method for manufacturing a spiral electrode for a secondary battery.