The invention relates to an electrochemical element (1) comprising: a) a container (2) comprising an opening allowing the introduction of at least one electrochemical beam (7); and b) a closing part (3) for closing said container, comprising: i) at least one flat inner surface (4a, 4b, 4c) which is oriented towards the inside of the container and can be directly electrically connected to a current collector (6), ii) at least one flat outer surface (5a, 5b, 5c) which is oriented towards the outside of the container and can act as a terminal of the electrochemical element, and iii) at least one wall (8a, 8b, 8c) connecting said at least one flat inner surface to said at least one flat outer surface, said wall forming an angle of between 70 and 120° in relation to one of the two flat surfaces. The closing part of the container allows heat dissipation to be improved in the direction of the longitudinal axis of the element.