Page 349 - Handbook of Battery Materials

11.2 Separators for Lead–Acid Storage Batteries 319

Finally, one development results from returning to a basic idea from the dawn
of the lead–acid battery, wherein the functions of support for the positive active
material and of the separator are combined into one component: the gauntlet
separator [83], consisting of a coarsely porous, flexible support structure coated
with microporous polyethylene material for separation. The future has to show
whether this approach will be able to meet all demands.
Characteristic data for polyethylene separators in comparison with competing
systems are discussed later in this section (Table 11.11).

11.2.3.1.2 Rubber Separators A thin layer of a mix of natural rubber, sulfur,
precipitated silica, water, and some additives, such as carbon black and vulcanizing
agents, is extruded on a paper support belt, calendered, and vulcanized as a roll
◦
in an autoclave under elevated pressure and temperature (≈180 C). A modified
process extrudes and calenders a ribbed profile and crosslinks the rubber separator
by irradiation.
Rubber separators have a relatively low porosity (∼50–55%) and thus high acid
displacement and electrical resistance. Furthermore, they are brittle and for this
reason difficult to handle in larger sizes. In order to balance this disadvantage, an
adjustment to a lower degree of crosslinking has been attempted; the result was a
corresponding increase in susceptibility to oxidative attack.

Table 11.11 Separators for lead–acid traction batteries.

Polyethylene Rubber Phenol–formaldehyde– Microporous
separators separators resorcinol separators PVC
separators

Supplier Daramic, Inc. Amerace [86] Daramic, Inc. [60, 61] AMER-SILs a
[60, 61] a [86]
Brand name DARAMIC Ace-Sil DARAK 5000 AMEK-SIL
Industrial CL Standard
Backweb 0.6 0.8 0.6 0.5
thickness (mm)
Pore size 0.1 0.2 0.5 0.5
(average) (µm)
Acid displacement 320 450 235 250
3
–2
(cm m )
Electrical resistance 280 240 120 200
2
(m cm )
Initial capacity b + 0 ++ ++
Handling properties b ++ 0 + +
Water consumption b + ++ 0 0
a Polyethylene industrial separators are also available from ENTEK International [62].
b
Ranking: ++, very good; +, good; 0, acceptable; –, poor.