Dry Process of Fe-Li-ion Battery Separator The dry process can be subdivided into a uniaxial stretching process and a biaxial stretching process. The dry uniaxial stretching process is to prepare a high-oriented polypropylene or polyethylene film with low crystallinity by producing hard elastic fibers, and obtain a film with high crystallinity during high temperature annealing. The film is first stretched at low temperature to form micro-defects, and then at high temperature, the defects are pulled apart to form