### Experiment 8

```Experiment 8
Batteries
Types of Batteries
• 1) Primary (unrechargeable).
• Reaction irreversible.
• 2) Secondary (rechargeable).
• Reaction reversible.
How does a battery work?
• Positive Plate.
• Negative Plate.
• Acidic or alkaline electrolyte.
• All forms a cell.
Battery Terminology
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Nominal voltage: the nominal voltage of the cell is a fixed value.
Capacity (C): the total charge in Ah that can be drawn from a fully charged battery at a specific
discharge rate and electrolyte temperature (20°C) before a specific cut-off voltage is reached.
I5: current expressed as a fraction of the nominal battery capacity: I5=C5/5.
End-of-charge voltage: the voltage of a battery during charging at a specific constant current when
the battery has become completely charged.
End-of-discharge voltage: the voltage of a battery during discharging at a specific constant current
when the battery has become completely discharged.
Deep discharge: is when a battery is discharged beyond the end-of-discharge voltage, a lead-acid
battery is in a state of deep discharge when only 20% to 30% of its nominal capacity remains.
Overcharging: a phenomenon that occurs when excessive current is supplied to the battery at the
end of recharge. The excess current produces electrolysis of water in the electrolyte releasing
hydrogen and oxygen gases and hence losing water.
State of charge (SOC): it expresses the residual capacity of the battery as a percentage of the rated
battery capacity. The formula is as follows:
SOC=
• Nominal voltage = 2v
(PbO2) while the negative plate is made of
• PbO2 + Pb + 2H2SO4  2PbSO4 + 2H2O
• Variation of cell capacity with discharge rate:
• Variation of cell capacity with discharge rate:
• Variation of cell capacity with temperature:
• Cycle life of the lead-acid battery:
• positive electrode-a nickel plate packed with
nickel oxide, a negative electrode-made of
hydroxide in water.
• 2Ni(OOH)+ Cd +2H2O  2Ni(OH)2 + Cd(OH)2
• Capacity dependence on temperature:
• Cycle life of the battery:
Zinc-Carbon BATTERIES
• A zinc-carbon dry cell or battery with a
nominal cell voltage of 1.5 volts is packaged in
a zinc can that serves as both a container and
negative terminal while the positive terminal
is a carbon rod surrounded by a mixture of
manganese dioxide and carbon powder . The
electrolyte used is a paste of zinc chloride and
ammonium chloride dissolved in water.
Zinc-Carbon BATTERIES
• 2MnO2 + 2NH4Cl + Zn --> ZnCL2.2NH3 + H2O +
MN2O3
General Info
• All batteries suffer from self discharge up to
3% of original capacity.
• Handle batteries with care to prevent hazards.
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