Patent ID: 8455140

Claim:
A method of making and using a porous polymer separator layer that may function as all or part of a separator for use in an electrochemical battery cell of a secondary liquid-electrolyte battery, the method comprising: (a) forming a film from a polymer solution that comprises a polymer material dissolved in a polymer solvent, the film having a cross-section with a non-uniform thickness; and (b) precipitating the polymer material present in the film into a porous polymer separator layer, the porous polymer separator layer having a cross-section that comprises a first edge and a second edge opposite the first edge, each of the first and second edges of the cross-section having a height that defines a thickness of the porous polymer separator layer at the first and second edges, respectively, and wherein the height of the first edge is greater than the height of the second edge such that the porous polymer separator layer has a thickness at the cross-section that decreases from the first edge to the second edge, the porous polymer separator layer further having a porosity in the range of about 30% to about 90% that is distributed evenly throughout the separator layer.