The present invention relates to a metal-ion accumulator (A), comprising a stack of elementary electrochemical cells, each comprising a cathode (2), an anode (3), and a separator (1) impregnated with electrolyte intercalated between the anode and the cathode, each anode and cathode consisting of a substrate (2S, 3S) formed from a metal foil comprising a central portion (22, 32) supporting, on at least one of its main faces, a layer of active metal ion insertion material, the porosity of the layers of active material of the electrodes of one of the given polarities (anode or cathode) having at least two different values in the stack, the highest porosity being that of at least one electrode of said polarity, arranged between the center and the ends of the stack.