Microporous membrane of polyethylene-based composite material and preparation method thereof

A membrane, consisting of polyethylene and a modifying agent, wherein:

• the modifying agent is distributed in the polyethylene, accounts for 10-25 wt. % of the membrane and is a rubber selected from polyisobutylene (PIB), ethylene-propylene methylene copolymer (EPM), or a mixture thereof, the rubber having a dynamic viscosity of between 50 and 2000 Pa·s at 100° C. and a weight average molecular weight of between 90,000 and 250,000;
• pores on one side of the membrane are smaller in size than pores on the other side;
• and
• the membrane has a latent heat of fusion of between 150 and 195 J/g, a fusion point of between 133 and 145° C., an average pore size of between 80 and 300 nm, a porosity of between 40 and 75%, an initial Gurley value of between 30 s/100 cc and 400 s/100 cc, a thickness of between 20 and 50 μm, a longitudinal tensile strength of exceeding 70 MPa, and a transversal elongation at break of exceeding 100%.