Environmental Engineering Reference
In-Depth Information
5.3.2 Main Characteristics of Different Types of Batteries
5.3.2.1 Lead-acid Batteries
The lead batteries had their industrial beginning with the first experiments of
Plantè on storage batteries in 1859 [
14
]. Since then many other type of storage
batteries have been studied and tested, but lead-acid batteries have been the most
largely developed and represent the type of battery most widely used in the past
century.
A lead-acid battery is constituted by a spongy lead anode, a porous lead dioxide
cathode and an electrolyte based on a aqueous solution of H
2
SO
4
(about 2.3 M).
During the discharge phase, when current is drawn, both electrodes react with the
electrolyte to form surface lead sulfate, according to the following semi-reactions [
15
]:
at Pb anode (negative terminal)
Pb
þ
SO
2
4
!
PbSO
4
þ
2e
ð
5
:
4
Þ
where the generation of electrons due to lead oxidation allows the occurring of an
electric current through an external circuit
at PbO
2
cathode (positive terminal)
PbO
2
þ
4H
þ
!
Pb
4
þ
þ
2H
2
O
ð
i
Þ
ð
5
:
5
Þ
Pb
4
þ
þ
2e
!
Pb
2
þ
ð
ii
Þ
ð
5
:
6
Þ
Pb
2
þ
þ
SO
2
4
!
PbSO
4
ð
iii
Þ
ð
5
:
7
Þ
where the hydrogen from sulfuric acid reacts with oxygen of lead dioxide to form
water, while the lead is reduced by the electrons coming from the external circuit
to a form suitable to react with the sulfate ion.
Then the overall electrochemical process involved in the voltage production by
a lead-acid battery is:
Pb
þ
PbO
2
þ
2H
2
SO
4
!
2PbSO
4
þ
2H
2
O
ð
5
:
8
Þ
to which an open circuit voltage is 2.1 V at room temperature is associated. The
reversed reaction is of course involved in the charge process, when the lead sulfate
is broken down, lead oxide is deposited on the positive electrode and lead is
deposited on the negative electrode.
Different types of lead-acid batteries have been developed as energy sources
for many power applications, like traction and backup or standby power systems.
The flooded lead-acid batteries have an excess or flooded electrolyte and they
were the largest used at the beginning of the last century for many applications.
Valve-regulated lead-acid (VRLA) batteries were developed as an alternative to
the flooded lead-acid batteries, in order to maintain levels of distilled water and
prevent drying of cells, which means safe operation for battery packs in electric
