NOVELTY - The storage unit (1) has an electrode film arrangement arranged in a metallic cell housing (3). A cell cover (6) closes the housing. A filling opening (6.1) is provided in the cell cover for filling an electrochemical substance i.e. electrolyte. The housing has a tab-shaped extension (3.1) bent toward a top surface of the cell cover. The extension sealingly covers the filling opening, and is connected with the cell cover in force-fit, form-fit and/or material fit manner. A venting opening is integrated into the extension and opens when exceeding a predetermined value of inner pressure.    USE - Electrochemical energy storage unit i.e. lithium ion cell, for use as a component of a battery of an electric car, a hybrid vehicle or a fuel cell operated vehicle. Can also be used for a medical device.    ADVANTAGE - The tab-shaped extension of the cell housing sealingly covers the filling opening, and is connected with the cell cover in the force-fit, form-fit and/or material fit manner such that a need for a separate supplementary component for closing the filling opening is avoided, thus minimizing assembly effort and reducing manufacturing cost of the energy storage unit. The venting opening is integrated into the extension and opens when exceeding the predetermined value of the inner pressure such that risk of an exothermic chain reaction in cell chemistry and/or explosion of the energy storage unit are reduced.    DETAILED DESCRIPTION - The electrode film arrangement is provided in form of an electrode film coil. An INDEPENDENT CLAIM is also included for a method for closing a filling opening provided in a cell cover of an electrochemical energy storage unit.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic perspective view of an enlarged section of an energy storage unit before closing a filling opening.    Electrochemical energy storage unit (1)    Metallic cell housing (3)    Tab-shaped extension of metallic cell housing (3.1)    Cell cover (6)    Filling opening (6.1)