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• 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=

Lead-Acid Battery

• Nominal voltage = 2v• The positive plate is made of lead peroxide

(PbO2) while the negative plate is made of sponge lead (Pb).

• PbO2 + Pb + 2H2SO4 2PbSO4 + 2H2O

Lead-Acid Battery

• Variation of cell capacity with discharge rate:

Lead-Acid Battery

• Variation of cell capacity with discharge rate:

Lead-Acid Battery

• Variation of cell capacity with temperature:

Lead-Acid Battery

• Cycle life of the lead-acid battery:

Nickel-Cadmium Battery

• positive electrode-a nickel plate packed with nickel oxide, a negative electrode-made of cadmium, and an electrode –potassium hydroxide in water.

• 2Ni(OOH)+ Cd +2H2O 2Ni(OH)2 + Cd(OH)2

Nickel-Cadmium Battery

• Capacity dependence on temperature:

Nickel-Cadmium Battery

• 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.