Dynamis lead-line Technical Manual - Page 3

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2. Reactions of Sealed Lead Acid Batteries

When the lead acid battery is discharging, the active materials of both the
positive and negative plates are reacted with sulfuric acid to form lead sulfate. After
discharge, the concentration of sulfuric acid in the electrolyte is decreased, and results
in the increase of the internal resistance of the battery.
On charging, the battery reactions are reversed, i.e., the lead sulfate of the
positive plate is converted to lead dioxide, and the lead sulfate of the negative plate is
converted to sponge lead, with the production of sulfuric acid and results in the
increase of electrolyte concentration.
Battery Charged
(+plate)
(- plate)
PbO
2
+
(lead dioxide)
As the charge nears completion little lead sulfate remains to convert to lead
dioxide or lead. The charging current begins to decompose water into oxygen and
hydrogen, i.e., the oxidation of water into oxygen at the surface of positive plate and
the reduction of proton into hydrogen at the surface of negative plate. For the
conventional flooded lead-acid battery, the evolved oxygen and hydrogen bubble to
the top of the electrolyte and escape to outside, and water loss is resulted. For the
valve regulated lead-acid battery, the evolved oxygen from the positive plate is easily
transported to the negative plate to be absorbed through the gas tunnel in the glass mat
separator with starved electrolyte. The absorbed oxygen depolarizes the negative plate
with the formation of lead sulfate, and no hydrogen is generated in this condition.
With very little gas evolution, the water loss of VRLA battery is minimized.
DYNAMIS Batterien GmbH
Tel. +49 7735 93669-0
(solution)
Pb
+
2H
SO
2
(lead)
(sulfuric acid)
Brühlstr. 15 D-78465 Dettingen / Konstanz
Fax +49 7735 93669-91
www.dynamis-batterien.de
Battery Discharged
(+plate)
PbSO
4
4
+
(lead sulphate)
(- plate)
(solution)
PbSO
2H
4
+
(lead sulphate)
(water)
04.12.2006
O
2
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