NOVELTY - The micro-porous polyolefin membrane useful as separators for a lithium ion battery, comprises a first polyethylene (80-90 wt.%) having molecular weights (Mw) of 2.5x 105 to 6x 105, polypropylene (5-15 wt.%) having molecular weights of 3x 105 to 1.5x 106, and a second polyethylene (1-5 wt.%) having molecular weights of greater than or equal to 7x 105. The membrane has an electrolytic solution absorption speed of 4.3-6, a pore size distribution curve with two peaks, and a melt down temperature of greater than or equal to 170 degrees C. The polypropylene has a heat of fusion of greater than or equal to 80 J/g.    USE - The micro-porous polyolefin membrane is useful as separators for a lithium ion battery, which is useful as a power source for an electric vehicle or hybrid electric vehicle (all claimed).    ADVANTAGE - The micro-porous polyolefin membrane has improved permeability, particle-blocking properties, mechanical strength, desirable electrolytic solution absorption characteristics, compression and heat shrinkage resistance, suitable dimensional stability, shutdown and meltdown properties, desired pin puncture strength, tensile rupture strength, tensile rupture elongation, and enhanced cyclability while retaining its high safety performance.    DETAILED DESCRIPTION - The micro-porous polyolefin membrane useful as separators for a lithium ion battery, comprises a first polyethylene (80-90 wt.%) having molecular weights (Mw) of 2.5x 105 to 6x 105, polypropylene (5-15 wt.%) having molecular weights of 3x 105 to 1.5x 106, and a second polyethylene (1-5 wt.%) having molecular weights of greater than or equal to 7x 105. The membrane has an electrolytic solution absorption speed of 4.3-6, a pore size distribution curve with two peaks, and a melt down temperature of greater than or equal to 170 degrees C. The polypropylene has a heat of fusion of greater than or equal to 80 J/g. The membrane 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 in the range of 25-60% of the first area. INDEPENDENT CLAIMS are included for:    (1) a method for manufacturing a micro-porous membrane; and    (2) a lithium ion battery.