Civil Engineering Reference
In-Depth Information
TABLE 10-1
Average Cell Voltage During Discharge in Various Rechargeable Batteries
Electrochemistry
Cell Voltage
Remark
Lead-acid
2.0
Least cost technology
Nickel-cadmium
1.2
Exhibits memory effect
Nickel-metal hydride
1.2
Temperature sensitive
Lithium-ion
3.4
Safe, contains no metallic lithium
Lithium-polymer
3.0
Contains metallic lithium
Zinc-air
1.2
Requires good air management to limit self-discharge
rate
FIGURE 10-2
Specific energy and energy density of various electrochemistries.
10.2.1
Lead-Acid
This is the most common type of rechargeable battery used today because
of its maturity and high performance over cost ratio, even though it has the
least energy density by weight and volume. In the lead-acid battery under
discharge, water and lead sulfate are formed, the water dilutes the sulfuric
acid electrolyte, and the specific gravity of the electrolyte decreases with the
decreasing state of charge. The recharging reverses the reaction in the lead
and lead dioxide is formed at the negative and positive plates, respectively,
restoring the battery into its originally charged state.
The lead-acid battery comes in various versions. The shallow-cycle version
is used in automobiles where a short burst of energy is drawn from the
battery when needed. The deep-cycle version, on the other hand, is suitable
for repeated full charge and discharge cycles. Most energy storage applica-
tions require deep-cycle batteries. The lead-acid battery is also available in
