The Amersil corrugated TGL400 separator with 78.5%
volume porosity has been tested in gel motive power cells
and compared to a competitor’s ribbed separator with 70%
porosity. The discharge was performed with 62.5 A at 6 h
rate to 1.70 Vpc (100% depth of discharge). The charge was
performed at 75 A until 1.08 charge factor with a cut-off
voltage of 2.33 Vpc.
Results of capacity and recharge times are shown on
Figs. 6 and 7. From beginning to 200 cycles, the capacity
of cells insulated with Amersil TGL is slightly higher or
comparable to the competition separator. After 250 cycles,
however, the capacity is 10% higher with the Amersil
corrugated separator, due to higher porosity and lower
electrical resistance (Fig. 6). A second test performed with
a 12 h standard BCI cycle-life test confirms these results on
capacity (Fig. 8).
Concerning recharge efficiency, Fig. 7 shows that, from
50 to 400 cycles, the time needed to fully recharge the cells
is longer for the competition separator than for TGL400.
More than the single effect of higher porosity and larger pore
size, the tortuosity of the Amersil separator helps slowing
the oxygen transfer in order to allow an easier recharge of the
negative plate before current is used for oxygen reduction.
Moreover, even though no detailed study has been performed
yet concerning compression in gelled-electrolyte
batteries, one can assume that compression is also an issue,
as gel VRLA may also suffer from poor contact between the
immobilised electrolyte and the plates, when battery is
ageing and gel is drying out due to water loss. In that case,
the springiness of the Amersil separator might be highly
beneficial to maintain plate–electrolyte contact. This important
aspect has to be further evaluated.