Page 345 - Handbook of Battery Materials

11.2 Separators for Lead–Acid Storage Batteries 315

U
[v]
14.8

DIN 43 539–02 Cold
Charge : 5 h (14.8 V)
(April 1983) ) Crank
12.5 Disharge: 2 h (5 I 20
Test
40° ± 2 °C 65 h open circuit stand
−18 °C
40° ± 2 °C
20 40 60 80 100 120 140 160 t [h]
168
U
[v]
14.8

DIN 43 539–02 E Charge : 2.5 h (14.8 V) Cold
(February 1983) Disharge: 0.5 h (10 I 20 ) Crank
12.5
50° ± 2 °C 67 h open circuit stand Test
−18 °C
50° ± 2 °C
20 40 60 80 100 120 140 160 t [h]
168

Figure 11.20 DIN standards: weekly cycling regimes.

as specially developed polyethylene separators (e.g., DARAMIC V [75]) are able
to decrease the water consumption significantly. The electrochemical processes
involved are rather complex, and a detailed description is beyond the scope of this
chapter. Briefly, the basic principle behind the reduction of water loss by separators
is their continuous release of specific organic molecules, for example, aromatic
aldehydes, which are selectively adsorbed at antimonial sites of the negative
electrode, inhibiting there the catalytic effect of antimony on hydrogen evolution
and thus lowering the water consumption [69, 70]. The current trend toward
low-antimony or lead–calcium alloys – primarily for productivity reasons – reduces
the importance of these effects; nevertheless, they remain decisive in many
instances.
The above comparative evaluation of starter battery separators refers to moderate
◦
ambient temperatures: the standard battery tests are performed at 40 or 50 C.
What happens, however, on going to significantly higher temperatures, such as 60
◦
or 75 C? This question cannot be answered without considering the alloys used:
batteries with antimonial alloys show a water consumption that rises steeply with
increasing temperature [40], leaving as the only possibilities for such applications
either the hybrid construction, that is, positive electrode with low-antimony alloy,
negative electrode lead–calcium, or even both electrodes lead–calcium.
Because of the increased shedding with these alloys, pure leaf separation is hardly
suitable. Separations with supporting glass mats or fleeces as well as microfiber
glass mats provide technical advantages, but are expensive and can be justified only