Lead-Acid Storage Batteries |
DOE-HDBK-1084-95 |
OPERATON AND CONSTRUCTION |
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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 (H2SO4). The negative electrode of a fully charged battery is composed of sponge lead (Pb) and the positive electrode is composed of lead dioxide (PbO2).
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 (SO42-) are driven back into the electrolyte solution to form sulfuric acid. The reactions involved in the cell follow.
At the positive electrode
PbO |
2 |
+ 3H+ + HSO - |
+ 2e- Discharge |
PbSO + 2H O (1.685 V). |
(2) |
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Charge |
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At the negative electrode |
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Pb + HSO |
- Discharge |
PbSO + H+ |
+ 2e- |
(0.356 V). |
(3) |
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4 |
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Charge |
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For the overall cell |
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PbO |
2 |
+ Pb + 2H SO |
Discharge 2PbSO + 2H O |
(2.041 V). |
(4) |
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4 |
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Charge
Therefore the maximum open-circuit voltage that can be developed by a single lead-acid cell is 2.041 V.
Rev. 0 |
Page 13 |
Batteries |