▎ 摘　　要

NOVELTY - Polymer film with high mechanical strength comprises 95-99 wt.% polyester and 1-5 wt.% additives, where the number average molecular weight of the polyester is 13000-20000 Da, the number of molecules of the polyester with a molecular weight ≮ 5000 Da is 0.5-5% of the total number of molecules of the polyester, and the molecular weight distribution index of the polyester is 1.6-2.4. USE - The polymer film is useful in composite current collector of battery. Can also useful in mobile phone, notebook computer, unmanned aerial vehicle, electric automobile and other consumption battery or power battery. ADVANTAGE - The method controls number average molecular weight of the polymer film raw material, improves mechanical strength of the polymer film in the MD direction, reduces membrane rupture rate, uses polymer film as a supporting membrane to manufacture a composite current collector with high mechanical strength, and promotes application of composite current collectors in batteries. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: manufacturing method of the polymer film, comprising sequentially performing first longitudinal stretching treatment, transverse stretching treatment and second longitudinal stretching treatment, where the process conditions for the first longitudinal stretching is as follows: the first longitudinal stretching ratio (3.0-4.0): 1, and first longitudinal stretching temperature is 80-120℃. The process condition of the transverse stretching is as follows: transverse stretching ratio (3.0-4.0): 1, and transverse stretching temperature is 90-140℃, and the process conditions of the second longitudinal stretching is as follows: the second longitudinal stretching ratio (1.1-1.3): 1, and second longitudinal stretching temperature is 80-120℃; composite film, comprising a supporting film and a metal-enriched layer, at least one surface of the supporting film is attached with the metal-enriched layer, where the supporting film comprises polymer film or polymer film; composite current collector; electrode sheet, comprising composite current collector, and an active material layer attached to at least one surface of the composite current collector; lithium secondary battery, comprising electrode sheet; and electronic device.