Facile fabrication of microporous polypropylene membrane separator for lithium-ion batteries

Microporous polypropylene (PP) membranes are fabricated by melt mixing and are employed as a separator for lithium-ion batteries. Microporous PP having different porosities and pore sizes are prepared by mixing it with different types of rubbers (Natural Rubber (NR), Styrene Butadiene Rubber (SBR), and Acrylonitrile Butadiene Rubber (NBR)). SEM analysis reveals the formation of co-continuous morphology of PP by the extraction of rubber phase from the blend. The size shape and distribution of pores obtained with different rubber gives an insight into the nature of the interaction of these materials and PP. Mechanical studies reveal that tensile strength and elongation at break depends on the pore size and pore density. Physical properties such as electrolyte uptake, wettability, and porosity of the membranes are also measured and NR etched PP shows better porosity (62%), wettability and electrolyte uptake (140%) than SBR and NBR etched PP. The ionic conductivity of NR etched PP was measured as a function of temperature and shows a conductivity greater than the celgard separator. Finally, a 2032 type of coin cell composed of Li/LiFePO4 was assembled and the cycling performance was analyzed at different C-rates. Cycling studies prove that the performance of the new membranes was superior to the celgard separator.