Patent ID: 9172075
Filing Date: 2015-10-27
Classification: H01M,Y02E,Y02P,Y10T

Abstract:
1. A method of making a thin polymeric separator having an open porous structure that, when placed between and in facial contact with a positive electrode and a negative electrode in an electrochemical cell and filled with an electrolyte solution, permits the flow of ions in the cell from one electrode through the separator to the other electrode, each electrode having a shape in plan view and an electrical contact, the method comprising: a) forming a polymer-containing film having a non-uniform thickness across its width, the film comprising a polymer and a polymer solvent in which the polymer is soluble; b) selectively densifying the polymer-containing film by changing the thickness of the film by different amounts across its width so that the polymer-containing film has a non-uniform polymer concentration across its width; c) subjecting the film to a solvent exchange process in which the polymer solvent of the film is at least partially replaced with a non-solvent in which the polymer is not soluble, wherein the polymer of the polymer-containing film is precipitated to form a porous structure in the film, the porous structure comprising the precipitated polymer and having a porosity that varies across the width of the film; and d) obtaining the thin polymeric separator from the film in a shape complementary to the shapes of the positive and negative electrodes such that the porous structure includes pores that are sized and can be arranged in the cell to permit higher ionic current flow through the separator at locations removed from the electrical contacts on the electrodes so as to more uniformly distribute ionic current flow through the separator over the whole facial area of the separator.