Lead-Acid Storage Batteries
DOE-HDBK-1084-95
OPERATON AND CONSTRUCTION
Rev. 0
Page 13
Batteries
OPERATION AND CONSTRUCTION
The following paragraphs describe the general operation and construction of lead-acid
batteries.
Lead-Acid Battery Active Materials
The active materials in a battery are those that participate in the electrochemical
charge/discharge reaction. These materials include the electrolyte and the positive and
negative electrodes. As mentioned earlier, the electrolyte in a lead-acid battery is a dilute
solution of sulfuric acid (H SO ). The negative electrode of a fully charged battery is
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4
composed of sponge lead (Pb) and the positive electrode is composed of lead dioxide (PbO ).
2
Electrochemistry of the Lead-Acid Cell
All lead-acid batteries operate on the same fundamental reactions. As the battery discharges,
the active materials in the electrodes (lead dioxide in the positive electrode and sponge lead in
the negative electrode) react with sulfuric acid in the electrolyte to form lead sulfate and
water. On recharge, the lead sulfate on both electrodes converts back to lead dioxide
(positive) and sponge lead (negative), and the sulfate ions (SO ) are driven back into the
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2-
electrolyte solution to form sulfuric acid. The reactions involved in the cell follow.
At the positive electrode
PbO + 3H + HSO + 2e
PbSO + 2H O (1.685 V).
(2)
2
4
4
2
+
-
- Discharge
$
%
Charge
At the negative electrode
Pb + HSO
PbSO + H + 2e (0.356 V).
(3)
4
4
- Discharge
+
-
$
%
Charge
For the overall cell
PbO + Pb + 2H SO
2PbSO + 2H O (2.041 V).
(4)
2
2
4
4
2
Discharge
$
%
Charge
Therefore the maximum open-circuit voltage that can be developed by a single lead-acid cell is
2.041 V.
