SECONDARY BATTERY

A piezoelectric element layer is further formed as a package material of a secondary battery, so that the secondary battery can be self-charged using a voltage generated in the piezoelectric element layer according to vibration generated in an electronic device and vibration generated by movement of the electronic device itself. The secondary battery includes a battery case that accommodates an electrode assembly, the battery case having an outer coating layer and a piezoelectric element layer formed on an inner surface of the outer coating layer, and a protection circuit module mounted to an outside of the battery case and electrically connected to the electrode assembly. In the secondary battery, a voltage storage is provided to the protection circuit module, and the piezoelectric element layer converts absorbed vibration into voltage and then stores the voltage in the voltage storage so that the secondary battery is self-charged as occasion demands.