PURPOSE: A high capacity energy storage device is provided to store large capacity energy by enabling voltage increase by a series combination and to improve productivity and assembility by facilitating the connection and the separation of a cartridge due to the specific pattern from an open rack. CONSTITUTION: A high capacity energy storage device includes a unit including a plurality of trays in which cells are mounted; a cartridge having a plural rows and layers of the units coupled with each other; and a rack having plural rows and layers of the cartridges coupled with each other. The cartridge includes first and second busbars for increasing pressure, longitudinally connecting the electrodes of the units in series; a third busbar for increasing pressure, horizontally connecting the electrodes of the units to each other in series; and a fourth busbar for insulating the space of the units, which is overlapped on the bottom of the third busbar. [Reference numerals] (AA) 1 line; (BB) 2 line; (CC) 3 line; (DD) 4 line; (EE) 5 line; (FF) 6 line; (GG) 7 line
