The disclosure describes a method for the preparation of metallic alloys containing an alkali or alkali-earth metal, such as lithium, and a host metal, such as aluminum. Initially, an active organic solution of the alkali or the alkali-earth metal is prepared, and a source of the alkali or alkali-earth metal which are both brought together with one another. On the other hand, a metallic structure containing the host metal is prepared, the metallic structure is brought together with the organic solution which is kept in touch with the source of metal until there is formed an alloy of the host metal and of the alkali or alkali-earth metal with the metallic structure, and the alloy possesses an activity which is determined by that of the organic solution. The organic solution then acts as transfer agent of the alkali or alkali-earth metal towards the host metallic structure. To prepare a negative electrode, the alloy is brought together with an electrolyte, such as a thin polymeric film. The disclosure also describes the electrodes as well as the electrochemical generators produced by using these electrodes. Considerably improved properties of cycling are obtained.