NOVELTY - An electrochemical cell (100) comprises an electrode (120) containing a current collector (112), and positive and negative active material layers (121, 122), a current collector extension part (123) located between the layers; a hollow core; an electrolyte isolation barrier wall; a case; and an electrolyte injection port. Several first electrolyte injection holes are formed in the current collector extension part at predetermined intervals, and second electrolyte injection holes corresponding to the first injection holes are formed in a sidewall of core.    USE - As an electrochemical cell useful in industrial and vehicle application fields requiring several tens of several hundreds of volts, and can be applied to ultracapacitor such as electric double layer capacitor, and to other electric energy storage devices such as lead acid battery, nickel metal hydride (NiMH) battery, nickel cadmium (NiCd) battery, a lithium ion battery, and aluminum electrolytic capacitor.    ADVANTAGE - The electrochemical cell has a simple electric connection structure for equalizing voltages of unit cells, and improved reliability and productivity. The quasi-bipolar electrochemical cell is simple, reliable, easy-to-manufacture, productive, and easy-to-install. In the electrochemical cell, a predetermined amount of electrolyte can be easily injected into each unit cell of electrochemical cells connected in series from the outside of the electrochemical cells, and a less pressure is applied to the electrolyte isolation barrier wall because the pressure levels inside the unit cells can be uniformly maintained, so that the electrolyte isolation barrier wall can be easily constructed and electrolyte can be isolated more effectively by the electrolyte isolation barrier wall. Only one safety vent can be disposed at the electrolyte injection port formed at the side surface of the case instead of disposing several safety vents at the side surface of the case, so that the electrochemical cell can have a simple structure and the number of holes formed in the case can be reduced to minimize electrolyte leakage. In the electrochemical cell, the bead can be formed in the case in which an electrode assembly is accommodated to isolate electrolyte easily and prevent current leakage and corrosion. In the cell, safety vent having a membrane capable of transmitting gas can be used to seal an electrolyte injection part, and thus the electrochemical cell cam have a slim shape. The electrolyte injection holes corresponding to unit cells can be formed in the core to easily inject electrolyte into the unit cells and improve electrolyte isolation efficiency. The wire holes can be formed in the core, and wires can be connected to the quasi-bipolar electrode to equalize voltages of unit cells and improve the reliability of the electrochemical cell. The wire strips can be disposed on the core to easily assemble the electrochemical cell using a conductive adhesive. The electric connection structure for voltage equalization of unit cells can be simplified by attaching a conductive sheet to an electrode assembly. The metal sheet having high heat conductivity can be attached to a current collector of the quasi-bipolar electrode to dissipate heat efficiently. The current collectors of quasi- bipolar electrodes can have an integrated strip shape to easily assemble the electrochemical cell. The case can be formed by connecting metal tubes using insulation sealing parts so as to simplify an electric connection structure for voltage equalization. The electrodes can be integrated to easily wind the electrodes around the core.    DETAILED DESCRIPTION - An electrochemical cell (100) comprises an electrode (120) containing a current collector (112), and positive and negative active material layers (121, 122) disposed at both sides of the current collector and spaced apart from each other with a current collector extension part is located between the active material layers; a hollow core; an electrolyte isolation barrier wall disposed at the current collector extension part of the electrode; a case accommodating an electrode assembly formed by winding electrode around the core; and an electrolyte injection port disposed in a side surface of the case and connected to an inside area of the core. A polarity of the electrode is used as an opposite polarity in a neighboring cell. Several first electrolyte injection holes are formed in the current collector extension part of the electrode at predetermined intervals, and second electrolyte injection holes corresponding to the first electrolyte injection holes are formed in a sidewall of the core. The electrolyte isolation barrier wall is formed of a conductive material. The first electrolyte injection holes are formed in the current collector extension part at both sides of the electrolyte isolation barrier wall. The electrochemical cell further comprises a safety vent at the electrolyte injection port disposed in the side surface of the case, a connection part through which an electric connection to the electrode from an outside of the electrochemical cell is allowed, a conductive line, and a strip attached to a position at which the electrolyte isolation barrier wall is disposed. The safety vent comprises a membrane capable of transmitting gas. The case is formed by winding a sheet including an adhesive around the electrode assembly after forming the electrolyte isolation barrier wall on an outer side of the electrode assembly. The adhesive is a heat adhesion sheet. The electrode assembly accommodated in the case is inserted in a reinforcement tube.    DESCRIPTION OF DRAWING(S) - The figure shows a perspective view of the electrodes of the electrochemical cell having a quasi-bipolar structure.    Electrochemical cell (100)    Mono polar electrode (110)    Current collector (112)    Quasi-bipolar electrode (120)    Positive and negative active material layers (121, 122)    Current collector extension part (123)