Battery separators with variable porosity

摘要

A porous polymer battery separator includes variable porosity along its length and can increase the uniformity of the current density within electrochemical battery cells that may normally experience higher current density and higher temperatures near their terminal ends than they do near their opposite ends. By disposing a variable porosity separator between the electrodes of an electrochemical cell such that its terminal end has a lower porosity than its opposite end, the transport of ions through the separator can be more restricted in normally high current regions and less restricted in normally low current regions, thereby increasing the overall uniformity of current density within the cell. The separators may be produced by a dry-stretching process or by a wet process. These processes may include forming a polymer-containing film, producing a uniform distribution of pore sites within the film, and reforming the polymer-containing film to a uniform thickness.

主权项

1. A method of making a polymeric separator having an open porous structure that, when placed between and in facial contact with a positive electrode and a negative electrode of an electrochemical cell 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 and an electrical contact, the polymeric separator having a terminal end for placement near the electrical contact of each electrode in the cell and an opposite end for placement away from the electrical contact of each electrode in the cell, the porous structure including pores sized and arranged so that one or both of a porosity or an average pore size is higher at the opposite end of the separator than at the terminal end of the separator, the method comprising:
a) forming a polymer-containing film having a thickness across its width that gradually increases from a first end to a second end; b) producing a uniform distribution of pore sites throughout the polymer-containing film; c) reforming the polymer-containing film to a uniform thickness, thereby introducing the open porous structure to the film; and d) obtaining the polymeric separator from the film in a shape complementary to the shapes of the positive and negative electrodes, wherein the separator is obtained from the film so that the terminal end and the opposite end of the separator are spaced apart in the widthwise direction of the film from which the separator is obtained, the terminal end of the separator corresponding to the first end of the polymer-containing film formed in step a) and the opposite end of the separator corresponding to the second end of the polymer-containing film formed in step a).