Page 344 - Handbook of Battery Materials

314 11 Separators

Table 11.10 Comparative evaluation of starter battery separators.

Polyethylene Sintered Cellulosic Cellulosic/glass Glass fiber
pocket PVC separators mix separators leaf
separators separators separators

Backweb thickness 0.25 0.30 0.55 0.50 0.70
(mm)
Pore size (average) (µm) 0.1 15 25 22 27
Acid displacement 120 210 170 140 110
–2
3
(cm m )
Electrical resistance 60 160 140 100 65
2
(m cm )
Test results (DIN 43
539-02)
(PbSb I.6/PbSb 1.6)
Cold crank voltage (V) 9.40 9.20 9.25 9.30 9.35
Cycle life test (weeks) >10 >10 >10 >10 >10
Accelerated cycle life >10 5 6 6 7
test (weeks)
(DIN 43 539 E-1980)
Water consumption a 2–4 4 2 2 4
–1
(g Ah )
a 504 h overcharge with 14.4 V at 40 C.
◦
to be underestimated, since it often presents the only way of meeting the acceptance
criteria of high-performance batteries reliably.
The life expectancy of a starter battery, according to DIN 43 539–02, is not affected
by the separator. Experience has shown that all batteries with modern standard
separators in cycle life tests not only last the required 5 weeks of cycling, but mostly
10 weeks or more. The cause of failure is typically positive grid corrosion – in good
agreement with practice [49]. This fact supports this standard, which is supposed
to reflect reality, but on an accelerated time scale.
A modification of the test conditions (DIN 43 539-02 E) did prove to show more
about the effect of the separator on battery life expectancy. In Figure 11.20 the
weekly cycling regimes of these two standards are compared. DIN 43 539-02 E,
requiring more discharges at a higher temperature, has been shown to uncover
significant differences between the individual types of separators. Macroporous
separators with average pore sizes of 10–30 µm like PVC, cellulosic, or glass
separators, just meet the required cycle life. Microporous pocket separators with
pore sizes distinctly below 1 µm prevent not only penetration through the separator,
but also – because of the pocket – bottom or side shorts, and this to such an extent
that even under these aggravated test conditions the separator does not limit the
cycle life duration.
Surprisingly the water consumption of a starter battery, provided that it contains
antimonial alloys, is affected by the separator. Some cellulosic separators as well