Study of pore morphology and anisotropic evolution with thermal excursion of UHMWPE film

Porous polyolefin films are commonly used as separators in the battery industry. The thermal response of this separator membrane is critical to battery performance, particularly with regard to battery safety. Two commercial separator films (Teklon and Asahi) were studied in this Thesis. The major component of these films is ultra high molecular weight polyethylene (UHMWPE). As the temperature of the films rises above the softening point, pores collapse and ion transport ceases leading to a current shutdown. Pore morphology evolution with temperature plays very important roles in the shutdown behavior.;Ultra small angle scattering (USAXS) was used to characterize pore evolution in near the softening temperature. Pore anisotropy on different length scales was measured by anisotropic ultra small angle scattering (AUSAXS). SEM images were also reported that were consistent with the USAXS analysis.;The study is divided into two sections: in situ conditioning and ex situ conditioning. The in situ study covers experiments on polyelectrolyte-saturated samples thermally conditioned in the x-ray instrument. The ex situ study focused on films conditioned external to the USAXS camera and studied at room temperature in the dry state. (Abstract shortened by UMI.).