TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The cathode comprises a current collector, and a cathodic active material layer on the current collector capable of absorbing and discharging lithium ions.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The diluent is at least one aliphatic, alicyclic or aromatic hydrocarbon, mineral oil distillate, and phthalates, having a viscosity of 30-500 cSt when measured at a temperature of 25 degrees C. The electrolyte comprises lithium salts in an organic solvent.    TECHNOLOGY FOCUS - POLYMERS - Preferred Membrane: The first polyolefin is polyethylene and where the membrane comprises polyethylene (1-20 wt.%). The microporous membrane further comprises a second polyethylene having an weight average molecular weight (Mw) of greater than 1 x 106 and/or a third polyethylene having Mw of less than or equal to 1 x 106 and a T80 of greater than 132 degrees C. Preferred Method: The extruding of step (a) is conducted in a temperature of 140-250 degrees C. The polymer in the polymer-diluent mixture is 5-50 wt.%, based on the weight of the mixture. The method further involves stretching the membrane in at least one planar direction following step (c); subjecting the membrane to a thermal treatment following step (c). The stretching of step (c) is conducted biaxially to a magnification factor in the range of 9-fold to 49-fold in area, while exposing the extrudate to a temperature of 90-125 degrees C. The method further involves removing any remaining volatile species from the membrane after step (c). The membrane is exposed to 70-135 degrees C during membrane stretching following step (c). Preferred Components: The first polyolefin (A1) has Mw of 1x 104-4x 105; and has low melting peak (Tm) of 120-126 degrees C. The first polyolefin has an Mw of 1 x 105, a T80-T25 of less than or equal to 15 degrees C, and where the first polyolefin is present in the membrane in an amount of 10-30 wt.%, based on the weight of the membrane. EXAMPLE - A polyethylene mixture (100 parts by mass (pbm)) comprising ultra-high molecular weight polyethylene (UHMWPE) (18 mass%) having an weight average molecular weight (Mw) of 1.95 x 106; high density polyethylene (HDPE) (74 mass%) having Mw of 5.6 x 105, a low melting peak (Tm) of 134.9 degrees C, and a temperature (T80) at which the crystal-melting calorie Delta Hm measured by melting distribution (DSC) at temperature-elevating speed of 10 degrees C/minute reached 80% of total Delta Hm of 135.1 degrees C; and a polyethylene (8 mass%) having Mw of 3.8 x 104, a temperature (T25) at which the crystal-melting calorie Delta Hm measured by DSC at temperature-elevating speed of 10 degrees C/minute reached 25% of total Delta Hm of 114.6 degrees C, T80 of 125.9 degrees C, and Tm of 126.1 degrees C were dry-blended with tetrakis (methylene-3-(3,5-ditertiary-butyl-4-hydroxyphenyl)-propionate) methane (0.5 pbm). The resultant mixture (25 pbm) was charged into a strong-blending, double-screw extruder and liquid paraffin (75 pbm) was supplied to the double-screw extruder. The polyethylene solution was supplied from the double-screw extruder and extruded in a 1 mm-thick sheet shape. The extrudate was cooled by a cooling roll controlled at 50 degrees C to form a gel-like sheet. The gel-like sheet was simultaneously biaxially stretched by a batch-type stretching machine to 5-fold in both longitudinal direction (MD) and transverse direction (TD) while exposing the extrudate to a temperature of 115 degrees C. The stretched sheet was then fixed to an aluminum frame plate of 20 cm x 20 cm and immersed in a washing bath of methylene chloride controlled at 25 degrees C, and washed while swaying at 100 rotation per minutes (rpm) for 3 minutes to remove the liquid paraffin. The washed membrane was air-dried at room temperature. The dried membrane was then fixed to a tenter and heat-set at 115 degrees C for 10 minutes to produce a microporous membrane (test) having average thickness of 16 mu m; normalized air permeability of 218 seconds/100cm3/20 mu m; heat shrinkage MD/TD (%) of 7.5/7.5; normalized pin puncture strength of 345 g/20 mu m; and shutdown temperature of 129.8 degrees C. A comparative microporous polyethylene membrane was produced in the same manner as the test membrane except using first polyethylene having Mw of 7.5x 105, T25 of 100.5 degrees C, T80 of 116.6 degrees C, and Tm of 117.3 degrees C. The obtained comparative membrane had average thickness of 21.5 mu m; normalized air permeability of 481 seconds/100cm3/20 mu m; heat shrinkage MD/TD (%) of 7.6/7.9; normalized pin puncture strength of 220 g/20 mu m; and shutdown temperature of 131.6 degrees C.