NOVELTY - The device comprises: an electrode assembly; an electrode tap protruded from the electrode assembly, where the electrode tap includes a battery case for admitting the electrode assembly to an inner side; an electrode lead connected to the electrode tap; and a capsule containing an electrolyte in an inner portion, where the capsule is interposed between a projection hole for receiving the tap between the projection hole on one side opposite the battery case. The capsule is shifted to an upper side of the electrode assembly according to the pressure, and charges/discharges the electrolyte.    USE - The electrochemical device is useful in an electric vehicle, a cellular phone, a camcorder and in a notebook computer.    ADVANTAGE - The capsule is shifted to an upper side of the electrode assembly according to the pressure so as to charge/discharge the electrolyte, so that the rechargeable life cycle and the stability of the electrochemical device can be improved.    DETAILED DESCRIPTION - The electrochemical device comprises: an electrode assembly; an electrode tap protruded from the electrode assembly, where the electrode tap includes a battery case for admitting the electrode assembly to an inner side; an electrode lead connected to the electrode tap; and a capsule containing an electrolyte in an inner portion, where the capsule is interposed between a projection hole for receiving the electrode tap between the projection hole on one side opposite the battery case. The capsule is shifted to an upper side of the electrode assembly according to the pressure, and charges/discharges the electrolyte. The capsule overcharges the electrolyte with the temperature rise of the electrode assembly, where the capsule has a microporous surface through which the electrolyte is emitted, has an average particle diameter of 50 nm to 10 mu m, and further includes a performance improvement agent, where the performance improvement agent is a mixture of solid electrolyte interface formation additive, battery side reaction control additive, thermal stability improving additive and overcharging suppression additive.