TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The kaolin clay further comprises calcined kaolin (5-20 wt.%). The kaolin clay is present in an amount of 20-80 wt.%, and the separator is not subject to shutdown, regardless of temperature.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The polyolefin further comprises an ulthira high molecular weight polyethylene (UHMWPE) having a minimum average molecular weight of 1x 106; is a mixture of UHMWPE having a minimum average molecular weight of 1x 106 and a polypropylene (PP) having a melt index of less than or equal to 2, and where the weight ratio of UHMWPE to PP is greater than or equal to 50%; or a mixture of UHMWPE (10-50 wt.%) having a minimum average molecular weight of 1 million and a high density polyethylene (40-70 wt.%) having an average an average molecular weight of 300000-800000. The microporous membrane has a melt integrity of greater than or equal to 150 degrees C. EXAMPLE - A dry-blend consisting of UHMW polyethylene (50 wt.%) having molecular weight of 1x 106, kaolin (50 wt.%) with density of 2.6 was prepared. The mixture was fed into an extruder. The dry blend mixture was melt-kneaded in the extruder while feeding liquid paraffin (60 wt.%) making a solution. The above solution was extruded from a film die into the form of a sheet. Using a two-roll casting roll, the gel sheet was subsequently cooled down producing a 2-4 mil thick gel sheet. The liquid paraffin in the gel sheet was extracted by solvent and dried. The dried microporous sheet was subsequently stretched in both directions at 125 degrees C for 100% and also heat set at 120 degrees C, producing a 25 mu thick microporous membrane. The produced thick microporous membrane was tested for air permeability (Gurley number), shutdown and melt integrity, shrinkage, tensile strength, and puncture resistance. The Gurley number was less than 10 seconds, the sample did not shut down, had a melt integrity more than 190 degrees C, shrinkage of less than 5%, tensile strength of less than 2% offset, and puncture resistance of more than 400 g. The Gurley number prior to stretching of 2-4 mil (50-200 mu ) thick material was measured and it was less than 200 seconds.