TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The membrane comprises 74-99 (preferably 90-97) wt.% first polyethylene having an Mw of less than or equal to 5x 105; 1-5 (preferably 2-5) wt.% second polyethylene having an Mw of greater than 5x 105; and 0-25 (preferably 5-10) wt.% polypropylene having an Mw of 3x 105 to 1.5x 106 and a heat of fusion of greater than 80 J/g. Preferred Parameter: The membrane has a melt down temperature of greater than or equal to 170 degrees C, an electrolytic solution absorption speed of 4.1-10, and a pore size distribution curve having at least two peaks, where 25-60% of the membrane's differential pore volume is associated with pores having diameters of greater than or equal to 100 nm. The membrane's differential pore volume curve exhibits a first area associated with pores having diameters of 10-1000 nm and a second area associated with pores having diameters of 200-1000 nm. The second area is 25-60% of the first area. Preferred Method: Between steps (D) and (E), the stretched extrudate is heat-set at a temperature of the stretching temperature plus minus 5 degrees C; is contacted with a heated roller at a temperature of from Tcd of the polyolefin composition to the m.pt. plus 10 degrees C of the polyolefin composition; and is then contacted with a hot solvent. Between steps (E) and (F), the membrane is heat-set at a temperature of the stretching temperature plus minus 5 degrees C, and the heat-set membrane is crosslinked by ionizing radiation rays including alpha -rays, beta -rays, gamma -rays and/or electron beams. After step (G), the heat-set microporous membrane is made more hydrophilic by monomer-grafting treatment, surfactant treatment, and/or corona-discharging treatment; and is then surface-coated with porous polypropylene, porous fluororesin, porous polyimide, and/or porous polyphenylene sulfide. The membrane-forming solvent is a liquid at room temperature. EXAMPLE - Dry-blended were 100 pts.wt. polyolefin composition comprising 2% ultra-high molecular weight polyethylene resin having a weight-average molecular weight (Mw) of 0.7x 106 and a molecular weight distribution (Mw/Mn) of 8, and 97.8% high density polyethylene resin having a Mw of 3x 105 and Mw/Mn of 8.6; and 0.2 pts.wt. tetrakis(methylene-3-(3,5-ditert.-butyl-4-hydroxyphenyl)-propionate) methane as an antioxidant. The polyethylene in the resultant polyolefin solution had a m.pt. of 135 degrees C and crystal dispersion temperature of 100 degrees C. The polyolefin solution (40 pts.wt.) was charged into a strong-blending double-screw extruder having an inner diameter of 58 mm and a length to diameter ratio of 42. Liquid paraffin (60 pts.wt., 50 cSt at 40 degrees C) was supplied to the double-screw extruder via a side feeder. Melt-blending was conducted at 210 degrees C and 200 rpm to prepare a polyethylene solution, which was then extruded from a T-die mounted to the double screw extruder. The extrudate was cooled while passing through cooling rolls controlled at 40 degrees C to form a gel-like sheet. Using a tenter-stretching machine, the gel-like sheet was simultaneously biaxially stretched at 118.5 degrees C to 5 fold in both longitudinal and transverse directions. The stretched gel-like sheet was fixed to an aluminum frame of 20 cm by 20 cm, immersed in a bath of methylene chloride controlled at 25 degrees C to remove the liquid paraffin with vibration of 100 rpm for 3 minutes, and dried by an air flow at room temperature. The dried membrane was re-stretched by a batch-stretching machine to a magnification of 1.5 fold in a transverse direction at 129 degrees C. The re-stretched membrane, which remained fixed to the batch-stretching machine, was heat-set at 129 degrees C for 30 seconds to produce a microporous polyethylene membrane.