The invention relates to an electrochemical cell including: at least a pair of current collector plates that are placed in parallel to each other, flat electrodes containing aqueous electrolyte printed on opposing faces of said current collectors, such that a peripheral region is defined on each of said faces of said current collectors, which region is not covered by said electrode, and a separating medium interposed between said electrodes, the geometric form and size of said separating medium being identical to the form and size of said current collector plates, said separating medium having a central region permeable to said electrolyte, surrounded by a peripheral masked region which is non-permeable to said electrolyte, such that the permeable region of said separating medium coincide with the electrodes printed on the opposing faces of said current collectors, with respect to position, geometric form and size; wherein the pores in the peripheral region of the separating medium are impregnated with a suitable sealant, and wherein one or more layers of adhesives are deposited on said sealant in said peripheral region.