Page 339 - Handbook of Battery Materials

11.2 Separators for Lead–Acid Storage Batteries 309

in order to enable production of microporous pocketing material resistant to
penetration (Grace GmbH (unpublished results)) [66]. In practice, PVC separators
prove themselves in starter batteries in climatically warmer areas, where the battery
life is, however, noticeably reduced because of increased corrosion rates at elevated
temperature and vibration due to the road condition. The failure modes are similar
for all leaf separator versions: shedding of positive active mass fills the mud room at
the bottom of the container and leads to bottom shorts there, unless – which is the
normal case – the grids of the positive electrodes are totally corroded beforehand.
In many countries starter batteries are almost 100% recycled; PVC separators
can cause some problems here [67]. A prior separation of PVC from other battery
components, which is quite tedious, would be desirable, because a PVC content
decreases the recycling purity of the container polypropylene and makes further
processing of this plastic more difficult. Also, any chlorine compounds liberated
can form environmentally hazardous products with other substances; the usual
remedy is to install costly filter stations, with the residues representing possibly
toxic wastes requiring special disposal methods.
Sintered PVC separators are frequently produced only for captive consumption;
beyond that there are specialized producers for these separators [64, 67, 68] and
for equipment for their production [64]. The data compiled in Table 11.6 comprise
only premium products of independent producers.

11.2.2.2.2 Cellulosic Separators Cellulosic separators, the closest relatives to
the wood veneer, surprisingly have retained some of its properties, which differ-
entiates these separators from purely synthetic ones: primarily a positive effect
in reducing the water loss in starter batteries [39, 69–71]. This impact tends to
decrease as the antimony content in the alloys is lowered, but it still represents an
advantage over other leaf separators, unless a microporous pocket is required by
the alloy anyway.
A voluminous, highly porous, special paper of cotton linters, or other pre-
mium α-cellulose fibers is passed through an immersion bath of aqueous
phenol–formaldehyde resin solution and dried. A different process combines the
production of the paper directly with its impregnation. Common to both processes

Table 11.6 Sintered PVC separators.

Brand name Backweb Electrical Porosity (%) Pore size Supplier
thickness resistance a (average) (µm)
(mm)

Accuma PVC 0.20–0.30 170 30 30 Accuma S.p.A.
[68]
ICS LR type 0.30 170 37 <25 ICS S.p.A. [69]
Jungfer LJF 0.25–0.30 170 33 <30 Jungfer GmbH
& Co. KG [64]

a
Electrical resistance of a separator of 1.3 mm overall thickness.