Film type battery

Abstract: In a film type battery comprising a generating element which is formed by laminating a negative active material, an electrolyte and a positive active material into a layer shape (1, 2, 3), terminal plates (5, 6) which are installed on and under the generating element and serve also as a current collector and a container, and a frame-shaped sealing material (4) which is installed on peripheral edges of the terminal plates, seals the generating element in between the both terminal plates and insulates one terminal plate from the other; the sealing material is improved. The sealing material is a multi-layer structure, in which a material having a small moisture permeability is used for an outside layer, and a material having a large resistance to leakage of an electrolyte is used for an inside layer.

Description: This invention relates to film type batteries e.g. for use in portable electric and battery powered equipment. In recent years, portable electric and battery powered equipment have become smaller. Demands to reduce the size and thickness of batteries have increased in proportion, especially demands for a film-type battery with high reliability and a thickness not more than 0.5 mm. Film-type batteries using light metal such as lithium for negative active material are available as thin as 0.1 mm, the thicknesses of the current collector and sealing portions becoming as small as tens of microns. Fig. 1 is a vertical sectional view showing a conventional film type battery having a negative active material layer 1, e.g. of metallic lithium, a positive active material layer 2 and an ion-conductive electrolyte layer 3 forming a generating element. A negative terminal plate 5 and a positive terminal plate 6 serve simultaneously as current collectors and as a container. These may be stainless steel or nickel plates having a thickness of 15 to 30 microns. A frame of sealing material 4, which seals the generating element in between the terminal plates 5, 6 and insulates the terminal plates from one another is installed between the peripheries of the terminal plates. The sealing material is denatured polypropylene resin, to which the plates are thermally bonded. When a film-type battery having the above construction has been put in service for a long period, there have been problems with battery performance being spoiled by electrolyte leaking from or moisture and oxygen leaking to the sealing portion. If moisture enters it reacts with metallic lithium forming the negative active material so that battery capacity is reduced. GB-2201031 describes a battery of the above-described construction in which the edge of the lower terminal plate is turned up and approaches close to the edge of the upper terminal plate to enclose the generating element. A composite rectangular-section frame of sealing material extends around between the opposed terminal plate edges. It has a main rectangular-section body of water-impermeable material, e.g. polyethylene or PVDC, and a thin internal solvent-resistant facing layer e.g. of polyester, nylon, PVDC or EVOH, to retain the electrolytes ether solvent. Its outer and upper faces carry a thin layer of another polymer e.g. EVA, to provide adhesion to the steel casing. The exemplified battery is 1.4 mm thick: not really a film-type battery. An aim of this invention is to provide a film-type battery which is excellent in long-term reliability. The present invention is defined in claim 1 and is a film-type battery using a frame of sealing material having an inside electrolyte-resistant layer of silicone rubber-type adhesive agent and an outside water-resistant layer of denatured polyolefin-type resin. A material formed by graft polymerising maleic anhydride to polypropylene resin can be used for the denatured polyolefin-type resin. In the drawings; Fig. 1 exemplifies a known construction, already described, Fig. 2 is a cross-sectional view of a battery exemplifying the invention, and Fig. 3 is a graph showing storage performance of the Fig. 2 battery relative to the known type. Fig. 2 is a sectional view showing a film-type battery embodying the invention. The basic components are numbered as in Fig. 1. Metallic lithium is used for the negative active material. The principal component of the positive active material is maganese dioxide. The battery has a battery capacity of 50 mAh and a thickness of 0.1 mm. The electrolyte layer 3 is composed of polypropylene non-woven fabric, and the non-woven fabric is impregnated with nonaqueous-solvent electrolyte prepared by dissolving lithium perchlorate in a solvent of propylene carbonate mixed with dimethoxy ethane. The terminal plates 5, 6 are stainless steel plates 15 µm thick. The sealing material 4 has a double-layer structure with an inside sealing material 47 and an outside sealing material 48, each 1.5 mm wide. The inside sealing material 47 is silicone rubber group adhesive agent and the outside sealing material 48 is of denatured polypropylene resin. The sealing material 4 is connected to the terminal plates 5, 6 at 190°C by means of thermal pressure bonding. This thermal pressure bonding is carried out under reduced pressure in order to remove air from the battery interior. For comparison, a film-type battery was prepared having the same structure except that the sealing material 4 was a single layer of denatured polypropylene resin 3 mm wide; that is, the same structure as in Fig. 1. It also had a battery capacity of 50 mAh and a thickness of 0.1 mm. The storage performances of the batteries were compared. Each was stored in an air-conditioned bath having a relative humidity of 90 to 95%, and the relation between days of storage and decrease in battery capacity was examined. The decrease in battery capacity was examined. The decrease in battery capacity was examined by discharging down to an end voltage of 2V at 25°C with a current of 0.5 mAh and by metering a duration time to measure a residual capacity. Five batteries were tested for each measuring stage, and mean values calculated. The results are shown in Fig. 3 where the abscissa denotes the days of storage day and the ordinate denotes residual capacity (%). As seen from Fig. 3, the decrease in battery capacity of the battery embodying the invention was very small and its storage performance excellent. The decrease in battery capacity of the battery of comparison example was large, and its electrolyte leaked after 60 days. In the battery of the embodiment, since the denatured polypropylene resin forming the component material of the outside sealing material 48 has a small moisture permeability, the ingress of moisture into the battery is restricted. Exhaustion of the metallic lithium serving as negative active material, caused by reaction with moisture, is thereby prevented. At the same time the silicone rubber-group adhesive agent forming the component material of the inside sealing material 47 has a large resistance to electrolyte, so that leakage of the electrolyte is also prevented. Consequently, the decrease in battery capacity is very small and long-term reliability is improved. The structure of the sealing material 4 is not limited to a double-layer structure. It may be a structure including three or more layers, provided that a layer of the olefin material having small moisture permeability is installed at the outside and a layer of the silicone material having a large resistance to the electrolyte is installed at the inside.

Claims: A film-type battery comprising a layer-form generating element comprising laminated layers of negative active material (1), electrolyte (3) and positive active material (2); negative and positive terminal plates (5,6) on the respective faces of the generating element, serving to contain the generating element and act as negative and positive current collectors, and having peripheries which extend beyond the generating element, and a frame (4) of sealing material disposed between the opposed peripheries of the terminal plates (5,6) to seal in the generating element and insulate the terminal plates (5,6) from one another, the frame having an outside water-resistant layer and an inside electrolyte-resistant layer, and wherein the inside layer (47) is of silicone rubber-type adhesive agent and the outside layer (48) is of denatured polyolefin-type resin. A battery according to claim 1 in which the outside layer (48) is of denatured polypropylene resin. A battery according to claim 1 or claim 2 in which said adhesive agent and polyolefin-type resin are bonded to the terminal plates (5,6) by thermal pressure bonding. A battery according to any one of the preceding claims in which the frame (4) of sealing material is a two-layer construction consisting of said inside and outside layers (47,48). A battery according to any one of the preceding claims in which the terminal plates (5,6) are stainless steel plates. A battery according to any one of the preceding claims which is not more than 0.5mm thick. A battery according to claim 6 which is 0.1mm thick.

Inventors: IZUCHI SYUICHI, KATO SHIRO, MURATA KAZUO, TAKEUCHI KENICHI, IZUCHI, SYUICHI, KATO, SHIRO, MURATA, KAZUO, TAKEUCHI, KENICHI, MURATA, KAZUO, C/O YUASA CORP.
Applicants: YUASA BATTERY CO LTD, YUASA CORPORATION
Application year: 1992
Main classification: H01M2
IPC codes: H01M2