Abstract: An electrochemical generator comprising thin films including a positive electrode and its collector, and a sheet of a host metal intended to later on constitute a negative electrode, as well as an electrolyte which is conductive towards alkaline ions and also a source of alkali ions. The sheet of the host metal has voids whose quantity and arrangement are capable of locally absorbing any lateral expansion of the sheet of host metal and thereby substantially preventing all cumulative change in the plane of the sheet of host metal when there is an initial formation of alloy in the sheet between the host metal and an alkali metal which is brought about by the alkaline ions. A method of manufacturing such a generator is also described.