Patent ID: 8486556
Filing Date: 2013-07-16
Classification: B29C,B29K,B32B,H01M,Y02E

Abstract:
1. A multi-layer microporous battery separator comprising: a high molecular weight polypropylene layer having a melt flow index (MFI) of <1.0 g/10 minutes; a polyethylene layer; a high molecular weight polypropylene layer having a melt flow index of <1.0 g/10 minutes; which forms a microporous battery separator by a dry stretch process, where said microporous battery separator has a porosity of ≦37% while maintaining a Gurley from 13 to 25 seconds, a thickness of ≦25 microns, said microporous battery separator exhibits an increase of 5% or more in mixed penetration strength compared to a tri-layer dry-stretched microporous battery separator of the same thickness and does not use said high molecular weight polypropylene, a net shrinkage of said microporous battery separator is less than 5% measured for 6 hours at 105° C., and an ionic resistance of said microporous battery separator is less than 2.5 ohms-cm made by a process for the preparation of a multi-layer microporous battery separator comprising the steps of: providing a polypropylene having a MFI≦1.0 measured at pellet before processing and a polyethylene; extruding said high molecular weight polypropylene to form a precursor polypropylene film; extruding said polyethylene to form a precursor polyethylene film; laminating said precursor polypropylene films to each side of said precursor polyethylene film to form a non-porous tri-layer precursor; annealing said non-porous tri-layer precursor; stretching said non-porous tri-layer precursor to form a stretched microporous tri-layer film; allowing a relaxation of said stretched microporous tri-layer film to form a microporous tri-layer film; and where net stretch of said microporous tri-layer film is less than 90%.