Polymer composite film and preparation method thereof, and lithium ion battery

In order to solve the problem of poor heat stability of the polymer composite film in the prior art, the invention provides a polymer composite film which comprises a porous diaphragm and a fiber layer positioned on the diaphragm surface, wherein the fiber layer material contains polyetherimide. The invention also provides a preparation method of the polymer composite film and a lithium ion battery using the polymer composite film. The polymer composite film provided by the invention has favorable heat stability.