The invention discloses a composite
current collector and a preparation method thereof, a
magnesium ion battery and an electric device. The composite
current collector comprises a conductive composite base film, a three-dimensional porous conductive layer located on the conductive composite base film, and a first modified layer located on at least part of the surface of the three-dimensional porous conductive layer on the conductive composite base film, the conductive composite base film comprises a
polymer base film and a first
magnesium-loving
metal, a groove is formed in the surface of the
polymer base film, and the first
magnesium-loving
metal is located in the groove; the three-dimensional porous conductive layer is located on the side, away from the
polymer base film, of the first magnesium-loving
metal and comprises at least two
layers of
alloy layers arranged in a laminated mode, each
alloy layer comprises
copper and second magnesium-loving metal, and the content of the second magnesium-loving metal in the multiple
alloy layers is gradually decreased from the side close to the conductive composite base film to the side away from the conductive composite base film; the first modified layer includes a
covalent organic framework material. The composite
current collector can improve the deposition of magnesium ions, inhibit the growth of dendrites, reduce the
side reaction of an interface, and improve the
cycling stability of the
magnesium ion battery.