The ideal separator that suits all purposes does not exist.
This is because different battery applications require diverse
combinations of properties. There are a range of properties,
however, that are considered generally desirable for most
applications:
acceptable tensile strength (0.875–1.75 kN m1) and
elongation (0.5–10%) for processing;
high porosity (95% uncompressed) to allow for effective
acid filling and oxygen-transport;
serve as an electronic insulator, but when partially saturated
display low ionic resistivity (50–70 mO cm2);
readily wettable by sulfuric acid over the life of the
battery;
minimal shrinkage on wetting, sustain a high level of
applied pressure at the positive-plate, and conform to the
surface of the plates at the required level of force;
resistance to attack by battery strength acid at high
temperatures (80–120 8C) and by oxidation at high potentials;
high chemical purity, i.e., must not release metal or
organic impurities, such as transition metals or chloride
species;
have a pore-size distribution (1–20 mm) which provides a
sufficient supply of acid to the plates at the desired rate,
but presents no risk of dendritic growth;