The invention relates to an electrical energy storage assembly comprising an envelope and a capacitive element (30) contained in the envelope, said envelope comprising: at least one side wall (22); and two bottom walls (41) each located at an end of the side wall. Said storage assembly comprises at least one electroconductive intermediate connection part (50) to be arranged between the capacitive element and a bottom wall (41), in addition to a covering plate (51) for covering the end of the capacitive element (20), said covering plate (51) including at least one vent (53) for the passage of a fluid. The covering plate (51) is fixed to the capacitive element in such a way as to be in electrical contact therewith, and the intermediate connection part (50) is also fixed to the envelope in certain areas enabling a deformation of the bottom wall in relation to the intermediate connection part.