Page 321 - Handbook of Battery Materials

11.1 General Principles 291

U 30s
(V)
9.6

9.4

9.2

9.0

2
50 100 150 200 (mΩ cm )
Polyethylene Electrical Resistance
Separators of Separator Material
Figure 11.5 Cold crank voltage as a function of separator
electrical resistance. Reprinted from W. B¨ ohnstedt, Automo-
tive lead/acid battery separators: a global overview. J. Power
Sources, 1996, 59, 45–50, with kind permission from Elsevier
Science S.A., Lausanne [3].

a 12 V battery, the voltage drop due to the separator resistance amounts to ∼0.15 V;
Figure 11.5 shows this correlation.
The dependence of separator electrical resistance on porosity for the selected SLI
battery separator (0.25 mm backweb thickness) and the practical approximation
2
T P = 1 can be seen in Figure 11.6.
Other characterizing separator properties are either application-related or
product-specific; they will therefore be discussed with the individual separator
types.

11.1.3
Battery and Battery Separator Markets

There are no indications, or only vague ones, of the size of the various battery
separator markets in the literature [3]. A rough estimate can be deduced from
the sales figures for battery systems by a rule of thumb: the sales value of
separators is roughly 2–5% of the sales for the battery producers. Even the data
for battery markets are not uniformly gathered, however, and contain considerable
uncertainties.
The total sales value for battery systems worldwide in 1997 may amount to US
$25.5 billion and the sales value for battery separators correspondingly to US $600
million; Table 11.1 gives an estimate of the work battery market, split according to
the different battery systems.
From this – albeit rather rough – overview, the proportions become clear: around
45% of all battery sales worldwide and thus also separator sales worldwide are in
lead–acid batteries and a further 13% in the rechargeable alkaline battery sector.