Page 318 - Handbook of Battery Materials

288 11 Separators

Figure 11.1 Microfiber glass fleece
separator (SEM).

30 mm
Figure 11.2 Sintered PVC separator
(SEM).

30 mm

Figure 11.3 Phenol–formaldehyde
resin–resorcinol separator (SEM).

1 mm

and 11.4 show microporous separators. It should be noted that the latter figures
have a 50-fold larger magnification!
The path taken by an ion from one electrode to the other will not be a straight
one, as it has to evade the solid structures by making detours. The ratio of the mean
actual path in comparison with the direct distance is called the tortuosity factor T.
For plastic bodies consisting essentially of spherical, interconnected particles with
voids in between, with a porosity of about 60%, this value is roughly 1.3; for higher
porosities it decreases to approach a value of 1.0 at very high porosities.