Preparation method and application of double-layer polymer diaphragm

The invention discloses a preparation method and application of a double-layer polymer diaphragm, and particularly, the preparation method comprises the following steps: introducing a polyolefin raw material into an extrusion system to obtain an extruded diaphragm, annealing the extruded diaphragm to obtain a single-layer diaphragm, and superposing a plurality of single-layer diaphragms to form a multi-layer composite layer, according to the laminating method, a double-layer membrane group is formed in a manner that non-laminating roller surfaces of two single-layer membranes are laminated according to a laminating roller surface and a non-laminating roller surface which are formed during extrusion, and then the double-layer membrane group is laminated to form a multi-layer composite layer. The invention also discloses the double-layer polymer diaphragm prepared by the method and application of the method and the diaphragm in the field of lithium ion batteries. According to the preparation method, the strippi