Page 333 - Handbook of Battery Materials

11.2 Separators for Lead–Acid Storage Batteries 303

+ 8%

Figure 11.11 Grid comparison: conventional vs pocket con-
struction. (Courtesy: VARTA Batterie AG.) Reprinted from W.
B¨ohnstedt, Automotive lead/acid battery separators: a global
overview, J. Power Sources, 1996, 59, 45–50, with kind per-
mission from Elsevier Science S.A., Lausanne [3].

[40, 49–51]. Here it has usually been the case of an atypical application, for
example, a power supply in seasonal use on a boat or long-term deep discharges re-
sulting in penetration shorts from the solution phase. Under extreme temperature
conditions, as in the famous Las Vegas taxicab service, the battery life is severely
reduced, but again the predominant failure modes are corrosion or worn-out pos-
itive electrodes and expander deterioration. One has to concede that under such
extreme conditions the separators also approach their limits of stability [40] and
less oxidation-stable versions can begin to shorten the battery life. The prevailing
cost pressure has led to increasing use of thinner backweb, for example, 150 µm,
in order to reduce raw material costs; this calls for a thorough evaluation of the
limitations mentioned above [41].
In this connection the remaining oil in the separator plays an important role. At
first glance, to increase the porosity a total extraction of the oil would be expedient,
but certain oil components have been shown to exert a protective action on the
polyethylene. Oil content and its distribution, as well as selection of the oil, thus
gain particular significance [41, 52–54].