Composite current collector, preparation method thereof and battery

The invention discloses a composite current collector, a preparation method thereof and a battery. The composite current collector comprises a polymer film, and a transition layer and a conductive layer are sequentially arranged on the surface of at least one side of the polymer film; the transition layer is of a multi-layer structure; the crack growth interval r (%) of the composite current collector meets the following conditions: r is more than b and less than e, b-2 is more than 0 and less than or equal to 10, e-b is more than 15, b is a starting point of crack nucleation of the composite current collector, and e is a deformation end point of complete fracture of the composite current collector. According to the invention, the transition layer with a multi-layer structure is added in the composite current collector, so that the layers of the composite current collector have an extension heterogeneous characteristic, under the action of a mechanical external force, the transition layer firstly generates cr