NOVELTY - The battery has a battery case (23) accommodating an electrode assembly (10) and including an outer coating layer (25) and a piezoelectric element layer (26) formed on an inner surface of the outer coating layer. A protection circuit module (30) is mounted outside the battery case and electrically connected to the electrode assembly. A voltage storage is provided to the protection circuit module. The piezoelectric element layer converts absorbed vibration into voltage and stores the voltage in the voltage storage such that the battery is self-charged for occasion demands.    USE - Self-charged secondary battery.    ADVANTAGE - The battery allows the piezoelectric element layer to be formed as package material of the battery, so that the battery can be self-charged using the voltage generated in the piezoelectric element layer according to the vibration generated in an electronic device by movement of the electronic device. The battery allows a sealing portion to be folded toward sides of the battery case so as to reduce volume of the battery when the battery is packaged in an outer casing. The battery allows an insulation tape to prevent a short circuit between the battery case and electrode tabs. The battery allows the protection layer to prevent an electrolyte and the piezoelectric element layer from reacting with each other, thus improving stability of the battery.    DETAILED DESCRIPTION - The piezoelectric element layer is made of a piezoelectric film layer. The battery utilizes a piezoelectric material layer made of ceramic and polymer, which is polyvinylidene fluoride (PVDF). The piezoelectric material layer is made of powder. The battery utilizes a protection layer, which is made of a cast polypropylene film. The outer coating layer is made of an oriented nylon film. The piezoelectric element layer is made of a ceramic piezoelectric layer, which is a zinc-oxide-based layer. The piezoelectric material layer is made by laminating a set of sheets.    DESCRIPTION OF DRAWING(S) - The drawing shows an exploded perspective view of a secondary battery.    Electrode assembly (10)    Battery case (23)    Outer coating layer (25)    Piezoelectric element layer (26)    Protection circuit module (30)