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IFET COLLEGE OF ENGINEERING
(An Autonomous Institution)
DEPARTMENT OF ECE & EEE
SUBJECT CODE: 23CH2202 YEAR/SEMESTER: I / II
SUBJECT: CHEMISTRY FOR ELECTRONICS ENGINEERS
UNIT-III MODULE
UNIT III– BATTERIES AND FUEL CELLS
SYLLABUS: Batteries – Classification of batteries – Primary battery (Zn – Ag2O), Secondary
battery used in electric vehicles (EV): lead acid battery- Nickel Cadmium (NICAD) battery-
Nickel metal hydride battery-Lithium ion battery,– principle, charging and discharging –
applications-fuel cell: (Polymer Electrolyte Membrane (PEM), Phosphoric Acid Fuel Cells
(PAFCs), Super capacitors– Principle and working.
3.1. INTRODUCTION
In electrochemical cells, the chemical energy is converted into electrical energy. The cell
potential is related to free energy change (ΔG). In an electrochemical cell, the system does work by
transferring electrical energy through an electric circuit. Thus G for a reaction is a measure of the
maximum useful work that can be obtained from a chemical reaction.
G=maximum useful work
But we know that
Maximum useful work= nFE
When a cell operates, work is done on the4 surroundings (flow of electricity)
ΔG=-nFE (or) ΔG<0
Decrease in free energy is indicated by (-) ve sign.
One of the main uses of the galvanic cells is the generation of portable electrical energy.
These cells are known as batteries.
3.1. BATTERIES (or) ENERGY STORAGE DEVICES
It is an arrangement of several electrochemical cells connected in series that can be used as a source
of direct electric current.
3.2.1 Terminologies commonly used in battery:
Cell - An electrochemical device composed of positive and negative plates and electrolyte, which is
capable of storing electrical energy. It is the basic ―building block‖ of a battery.
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Anode - During discharge, the negative electrode of the cell is the anode. During charge, that
reverses and the positive electrode of the cell is the anode.
Cathode- During discharge, the positive electrode of the cell is the cathode. During charge, that
reverses and the positive electrode of the cell is the cathode.
Battery - An electrochemical device used to store energy. The term is usually applied to a group of
two or more electric cells connected together electrically.
Battery Capacity - The electric output of a cell or battery on a service test delivered before the cell
reaches a specified final electrical condition and may be expressed in ampere-hours, watt- hours or
similar units.
Accumulator - A rechargeable battery or cell.
Charge - The conversion of electric energy, provided in the form of a current into chemical energy
within the cell or battery.
Charge Rate - The amount of current applied to battery during the charging process.
Discharge - The conversion of the chemical energy of the battery into electric energy.
Cycle - One sequence of charge and discharge.
Capacity - The capacity of a battery is a measure of the amount of energy that it can deliver in a
single discharge.
3.2.2 Requirements of a battery
A useful battery should fulfill the following requirements.
It should be light and compact for easy transport.
It should have long life both when it is being used and when it is not used.
The voltage of the battery should not vary appreciably during its use.
3.3 CLASSIFICATIONS OF BATTERIES
A battery is an arrangement of several electrochemical cells connected in series that can be used
as a source of direct electric current.
Primary Battery (or) Primary cells (or) Non-reversible Battery: In these cells, the electrode
and the electrode reactions cannot be reversed by passing an external electrical energy. The
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reactions occur only once and after use they become dead. Examples –(Zn – Ag2O).
Secondary Battery (or) Secondary cells (or) Reversible Battery: In these cells, the electrode
reactions can be reversed by passing an external electrical energy. Therefore, they can be
recharged by passing electric current and used again and again. These are also called storage cells
or accumulators.
Examples- Nickel – Cadmium cell, Lithium Ion Battery.
Flow battery (or) Fuel cells: Flow battery is otherwise called as fuel cells. In these cells, the
reactants, products and electrolytes are continuously passing through the cell. Here, chemical
energy gets converted into electrical energy.
Fuel + Oxygen → Oxidation products +Electricity
Examples - Polymer Electrolyte Membrane (PEM), Phosphoric Acid Fuel Cells (PAFCs)
3.4. IMPORTANT PRIMARY BATTERY
3.4.1 Primary battery (Zn – Ag2O)
A silver oxide battery uses silver(I) oxide as the positive electrode (cathode), zinc as the negative
electrode (anode), plus an alkaline electrolyte, usually sodium hydroxide (NaOH) or potassium
hydroxide (KOH). The silver is reduced at the cathode from Ag(I) to Ag, and the zinc is oxidized
from Zn to Zn(II).
Description:
. The cathode is generally composed of monovalent silver oxide with added graphite to improve
conductivity. The anode is zinc powder mixed with a gelling agent, which is then dissolved in the
alkaline electrolyte. The two are separated by a combination of layers of grafted plastic
membrane, treated cellophane and non-woven absorbent fibres. The top cup (negative terminal) is
made up of laminated layers of copper, tin, steel and nickel, and the bottom cup (positive
terminal) is nickel-plated steel. An insulating gasket prevents contact between the two.
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