TECHNOLOGY FOCUS - POLYMERS - Preferred Membrane: The microporous membrane has electrolytic solution absorption speed of 4.6-6. The microporous membrane comprises (wt.%): polyethylene (75-99, preferably 80-95) having Mw of less than or equal to 7x 105; polyethylene (less than 1) having Mw of greater than 7x 105; and polypropylene (1-25, preferably 5-20) having a heat of fusion greater than or equal to 80 J/g and Mw of 3x 105 to 1.5x 106. The membrane has a pore size distribution curve having at least two peaks. In the membrane, 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 microporous 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, and where the second area is 25-60% of the first area. The membrane has a shut down temperature of less than or equal to 140 degrees C. Preferred Method: The method further involves heat-setting treatment step (4i) between steps (4) and (5) where the stretched extrudate is heat-set at a temperature of the stretching temperature plus minus 5 degrees C; heat roll treatment step (4ii) following step (4i) and before step (5) where the stretched extrudate contacts a heated roller at temperature from the crystal dispersion temperature of the polyolefin composition to the melting point +10 degrees C of the polyolefin composition; hot solvent treatment step (4iii) following step (4ii) and before step (5) where the stretched extrudate is contacted with a hot solvent; heat-setting treatment step (5i) conducted between the steps (5) and (6) where the stretched extrudate is heat-set at a temperature of the stretching temperature plus minus 5 degrees C; cross-linking step (5ii) following step (5i) and before step (6) where the heat-set membrane is cross-linked by ionizing radiation rays selected from at least one alpha -rays, beta -rays, gamma -rays, and electron beams; hydrophilizing treatment step (7i) following step (7) where the heat-set microporous membrane is made more hydrophilic by at least one monomer-grafting treatment, surfactant treatment, and corona-discharging treatment; surface-coating treatment step (8) following step (7) where the heat-set microporous membrane is coated with at least one porous polypropylene, porous fluororesin, porous polyimide, or porous polyphenylene sulfide. The polyolefin composition further comprises polypropylene (0-25) having heat of fusion greater than or equal to 80 J/g and Mw of 3x 105 to 1.5x 106. The diluent is a liquid at room temperature. EXAMPLE - Dry-blended comprising mixture of polyolefin composition (100 parts by mass (pbm)) of high density polyethylene (HDPE) resin (95%) having a weight-average molecular weight (Mw) of 3.5x 105 and Mw/number-average molecular weight (Mn) of 13.5, and polypropylene resin (5%) having Mw of 5.3x 105, and Mw/Mn of 1-100; and final polyolefin solution (0.2 pbm) of tetrakis(methylene-3-(3,5-ditertiary-butyl-4-hydroxyphenyl)-propionate) methane as an antioxidant, where the polyethylene had a melting point of 135 degrees C, and a crystal dispersion temperature of 100 degrees C. The resultant mixture (40 pbm) was charged into a extruder, and liquid paraffin (60 pbm) was supplied to the extruder. Melt-blending was conducted at 210 degrees C and 200 revolution per minute (rpm) to prepare a polyethylene solution. This polyethylene solution was extruded from the extruder. The extrudate was cooled, to form a gel-like sheet. The gel-like sheet was 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, 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 to a magnification of 1.5 fold in a transverse direction at 129 degrees C. The re-stretched membrane was heat-set at 129 degrees C for 30 seconds to produce a microporous polyethylene membrane.