SEPARATOR, PREPARATION METHOD, SECONDARY BATTERY, AND ELECTRIC DEVICE

A separator, a preparation method, a secondary battery, and an electric device. The separator includes a first porous base film, where the first porous base film is polyolefin, and a viscosity-average molecular weight of the first porous base film is greater than or equal to 1,200,000 g/mol, such that the separator has higher puncture strength; a degree of branching of the first porous base film is less than or equal to 5%.