In recent years, as portable electronic devices are made compact and the weight of them are reduced, it has been highly demanded for batteries which supply electric power to these electronic devices to decrease their size, thickness or weight irrespective of uses thereof such as driving means or backup means.
As a battery for satisfying such a demand, has been developed and put into practical use a nonaqueous electrolyte battery, what is called a lithium battery which includes a cathode and an anode having active materials capable of reversibly inserting and extracting lithium ions and a nonaqueous electrolyte and has such advantages as a high output and high energy density.
Especially, the lithium battery including a polymer electrolyte as the nonaqueous electrolyte has characteristics that the battery is excellent in its leak resistance and high in its safety. Further, since the lithium battery including the polymer electrolyte is light in its weight and may be thinned in this thickness, the configuration of the battery can be designed so as to meet the forms or size of various kinds of electronic devices. Therefore, this lithium battery has a feature that has not been seen in the conventional batteries.
For example, when a thin and flat plate type polymer electrolyte battery is produced, a battery element may be formed by providing a polymer electrolyte between a thin sheet type cathode and a thin sheet type anode and the battery element may be covered with a laminate film having an aluminum foil as a core material.
Nowadays, in order to make various types of electronic devices more compact, it has been necessary to efficiently employ the inner spaces of the electronic devices, and it has been especially demanded to use the inner spaces having curved surfaces as spaces for accommodating the batteries serving as the power sources of the electronic device.
However, for instance, as shown in FIG. 1, when a flat plate type polymer electrolyte battery 102 is attached to an inner space having a curved surface in a portable electronic device 101 such as a portable telephone or a PDA, useless spaces 103 are inconveniently generated between the casing of the electronic device 101 and the flat plate type polymer electrolyte battery 102 so that the inner space of the electronic device 101 cannot be efficiently used.
Thus, as a method for efficiently using these spaces 103, the flat plate type polymer electrolyte battery 102 may be curved so as to meet the form of the inner space of the electronic device 101.
However, since the flat plate type polymer electrolyte battery 102 has a flat plate type battery element including a thin sheet type cathode and a thin sheet type anode and a polymer electrolyte interposed therebetween, even when the flat plate type polymer electrolyte battery 102 is curved, a desired curved form cannot be held for a long time. Further, an electrode active material layer may be cracked or further may be separated from a current collector due to an external force when the flat plate type battery element is bent. Therefore, when the flat plate type polymer electrolyte battery 102 is bent, battery characteristics are disadvantageously extremely deteriorated.
For example, in Japanese Patent Application Laid-Open No. hei 11-307130, is disclosed a method for bending a flat plate type battery element by applying a thermocompression bonding process to the battery element (refer it to simply as a flat plate type battery element, hereinafter) having a cathode and an anode laminated through a polymer electrolyte using two rolls respectively having different diameter. According to this method, although the curved configuration of the battery element is maintained, a shearing stress by the rolls with different diameter is exerted on a part between an active material layer and a current collector, so that the resistance of a cell is undesirably increased, a short-circuit is apt to be generated at the end of a stacked electrode, and accordingly, a stable battery performance cannot be inconveniently obtained. Further, not only the curvature of a desired curved configuration can be extremely hardly obtained, but also the thickness of a cell is inconveniently greatly regulated.