TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Battery: The separator has a melt down temperature of greater than or equal to 160 degrees C.    TECHNOLOGY FOCUS - POLYMERS - Preferred Membrane: The membrane has a capacity recovery ratio of greater than or equal to 73%; machine direction (MD) 105 degrees C heat shrinkage of less than or equal to 3.5% and transverse direction (TD) 105 degrees C heat shrinkage of less than or equal to 5%; an electrolytic solution absorption speed of greater than or equal to 3.5; a thickness variation after heat compression of less than or equal to 10%; air permeability after heat compression of greater than or equal to 600 seconds/100 cm3; and a maximum shrinkage in the molten state of less than or equal to 25%. The membrane comprises (wt.%): the first polyethylene (20-80), where the first polyethylene resin has weight average molecular weight (Mw) of 2x 105 to 9x 105 and molecular weight distribution (MWD) of 3-50; polypropylene (5-60) having Mw of 6x 105 to 4x 106, MWD of 3-30, a heat of fusion of greater than or equal to 90 J/g; and second polyethylene (0-40), where the second polyethylene has Mw of 1x 106 to 5x 106, MWD of 3-30, a heat of fusion of greater than or equal to 90 J/g. Preferred Process: The process further involves: removing at least a portion of the solvent or diluent from the cooled extrudate to form a membrane; orienting the membrane to a magnification of about 1.1-2.5 fold in at least one direction; and heat-setting the membrane to form the microporous membrane. The step of orienting the cooled extrudate in at least a first direction utilizes a roll-type stretching machine or a tenter-type stretching machine. The step of further orienting the cooled extrudate in at least a second direction utilizes a tenter-type stretching machine. Preferred Composition: The polyolefin composition comprises a high density polyethylene (at least about 30 wt.%) and polypropylene (at least about 30 wt.%); and further comprises an ultra high molecular weight polyethylene (at least about 20 wt.%). The polyolefin composition comprises (wt.%): first polyethylene resin (at least 20), where the first polyethylene has Mw of 2x 105 to 9x 105 and MWD of 3-50; polypropylene (5-60) having Mw of 6x 105 to 4x 106, MWD of 3-30 and heat of fusion of greater than or equal to 90 J/g; and a second polyethylene (0-40) having Mw of 1x 106 to 5x 106 and MWD of 3-30. The polyethylene comprises a first polyethylene having Mw of less than 1x 106 and a second polyethylene having Mw of greater than or equal to 1x 106. The polypropylene has Mw of greater than or equal to 1x 104 and a heat of fusion of greater than or equal to 90 J/g. WIDER DISCLOSURE - Also disclosed is system for producing microporous polyolefin membrane.    EXAMPLE - A polyolefin composition (99.8 parts by mass) comprising ultra-high-molecular-weight polyethylene (UHMWPE) (20 mass.%) having weight average molecular weight (Mw) of 1.9x 106, molecular weight distribution (MWD) of 5.09, a melting point (Tm) of 135 degrees C, and a crystal dispersion temperature (Tcd) of 100 degrees C, high-density polyethylene (HDPE) (50 mass.%) having Mw of 5.6x 105 and MWD of 4.05, Tm of 135 degrees C, and Tcd of 100 degrees C, and a polypropylene (PP) (30 mass.%) having Mw of 6.6x 105, MWD of 11.4, and a heat of fusion of 103.3, and tetrakis (methylene-3 -(3,5-ditertiary-butyl-4-hydroxyphenyl)-propionate) methane as an antioxidant was dry-blended. The polyolefin composition had MWD of 8.6, Tm of 135 degrees C, and Tcd of 100 degrees C. The resultant mixture (30 parts by mass) was charged into a strong-blending double-screw extruder, and liquid paraffin (70 parts by mass) was supplied to the double-screw extruder via a side feeder. Melt-blending was conducted at 210 degrees C to prepare a first polyolefin solution. The polyolefin solution was supplied from its double-screw extruder to a monolayer-sheet-forming T-die at 210 degrees C, to form an extrudate. The extrudate was cooled while passing through cooling rolls controlled at 15 degrees C, to form a gel-like sheet. Using a first tenter-stretching machine, the gel-like sheet was biaxially stretched at 100 degrees C, to 2 fold in both machine and transverse directions. Using a second tenter-stretching machine, the gel-like sheet was again biaxially stretched, this time at 120 degrees C, to 2.5, fold in both machine and transverse directions. The stretched gel-like sheet was fixed to an aluminum frame, and immersed in a bath of methylene chloride controlled at 25 degrees C to remove the liquid paraffin. The resulting membrane was air-cooled at room temperature. The dried membrane was re-stretched by a batch-stretching machine to a magnification of 1.4 fold in a transverse direction at 125 degrees C. The re-stretched membrane, which remained fixed to the batch-stretching machine, was heat-set at 125 degrees C for 10 minutes to produce a microporous polyolefin membrane. The microporous polyolefin membrane was evaluated for melt down temperature and thickness fluctuations, and the result was found to be 163 degrees C and 0.52 respectively.