Page 328 - Handbook of Battery Materials

298 11 Separators

are necessary to ensure the oxygen transport [23–25]. A number of producers of
specialized papers started to manufacture and develop these microfiber glass mats
further. Fibers below 1 µm in diameter are expensive, and due to their shortness
(∼1 mm) contribute little to the tensile strength. Binder may be omitted, however,
to achieve good wettability; the addition of longer glass fibers of large diameter is
required to improve the processability of such separators. A microfiber content of
20–30% has proven sufficient largely to optimize the desired characteristics [26].
The market for sealed stationary batteries has greatly increased since 1980, both by
the growth of the PC market as well as by the decentralization of emergency power
supplies and telephone exchanges, even though this conversion has not remained
undisputed [27]. Table 11.3 gives an estimate of the present situation; these figures
also include small consumer lead–acid batteries, which are constructed similarly.
More than 60% of all stationary batteries are currently being produced in the sealed
version, with the total market growing by roughly 5–10% annually.

11.2.1.3.2 Traction Battery Separators Electric road vehicles have been reduced
to insignificance, as mentioned already, by vehicles with combustion engines. An-
other electric vehicle – the electrically driven submarine – presented a continuous
challenge to lead–acid battery separator development since the 1930s and 1940s.
The wood veneers originally used in electric vehicles proved too difficult to handle,
especially if tall cells had to be manufactured. Therefore much intense effort took
place to develop the first plastic separators. In this respect the microporous hard
rubber separator, still available today in a more advanced version, and a microp-
orous PVC separator (Porvic I) merit special mention [28]. For the latter, a molten
blend of PVC, plasticizer, and starch was rolled into a flat product. In a lengthy
process the starch was subsequently leached out, leaving voids interconnected
through holes in their walls. This resulted in an extremely high porosity (levels of
up to 85% were reported), but due to a high tortuosity factor of about 1.7 there was
also a relatively high electrical resistance.

Table 11.3 World lead–acid stationary and consumer battery
production I997 (million watt-hour, estimate).

Polyethylene Phenol– PVC Rubber Microfiber Total
separators formaldehyde– separators separators glass mat
resorcinol separators
separators

USA–Canada 620 3.50 60 120 3900 5050
Europe 210 1520 510 180 2350 4770
Asia–Pacific 150 50 420 410 2600 3630
Latin America 80 40 120 140 100 480
Total (million Wh) 1060 1960 1110 850 8950 13 930
(%) 7.6 14.1 8.0 6.1 64.2 100.0