Composite foil as well as preparation method and application thereof

The invention discloses a composite foil as well as a preparation method and application thereof. The composite foil comprises a metal simple substance layer and metal alloy layers which are tightly attached to the two opposite surfaces of the metal simple substance layer. Wherein the metal alloy layer is made of Cu-X alloy, and X is selected from at least one of metal elements with the activity larger than that of Cu. The porous composite foil prepared by taking the composite foil as a precursor material and combining with a corresponding dealloying process can solve the problem that the existing two-dimensional foil cannot cope with the infinite volume expansion of the lithium metal battery, and meanwhile, the existence of the porous structure can effectively inhibit the phenomenon of lithium dendrite growth of the lithium metal battery.