Methods of making cross-ply microporous membrane battery separator, and the battery separators made thereby

Abstract

Continuous seamless cross-plied battery separators are formed by bringing at least two anisotropic with respect to mechanical strength (e.g. uniaxially oriented), microporous plies into adhering face contact such that the uniaxial orientation of one microporous ply is angularly biased relative to the other microporous ply (e.g., between 20.degree. to 90.degree.). This biased relationship between the microporous plies is most preferably achieved by spirally or helically slitting a tubular microporous membrane. The plies are adhered to one another with adhesive and/or by means of heat and pressure. The cross-plied battery separators of this invention exhibit increased puncture strength without significant decrease in permeability. As a result, the battery separators of this invention are especially useful in battery cell configurations whereby the battery separator is sandwiched between anode and cathode sheets to form a composite battery cell structure which is then rolled or folded to be placed in a battery cell can.

Dependencies are inferred from the claim text.