Dr.G.S.

KALYANASUNDARAM
MEMORIAL SCHOOL
CHEMISTRY INVESTIGATORY PROJECT
SESSION - 2023-2024

TOPIC: CHEMICAL REACTION IN

SECONDARY CELL

NAME :
ROLL NO :
CLASS & SECTION :XII-E
SUBJECT :CHEMISTRY
SUBJECT CODE :043
 INDEX

• BATTERY

• BATTERY TYPES

• SECONDARY CELL

• IMPORTANT SECONDARY BATTERIES

• A LEAD-ACID BATTERY

• CHEMICAL REACTION FOR DISCHARGING

• LEAD ACID BATTERY CHARGING

• NICKEL–CADMIUM BATTERY

• A FULLY CHARGED NI–CD CELL CONTAINS

• APPLICATIONS
BATTERY
• A Battery is a device consisting of one or more electrical cells that convert
chemical energy into electrical energy. Every battery is basically a galvanic
cell where redox reactions take place between two electrodes which act as
the source of the chemical energy.

BATTERY TYPES
Batteries can be broadly divided into two major types.

• Primary Cell / Primary battery

• Secondary Cell / Secondary battery
SECONDARY CELL
• A rechargeable battery, storage battery, or secondary cell (formally a
type of energy accumulator), is a type of electrical battery which can be
charged, discharged into a load, and recharged many times, as opposed
to a disposable or primary battery, which is supplied fully charged and
discarded after use.
• It is composed of one or more electrochemical cells.

• Rechargeable batteries are produced in many different shapes and sizes,

ranging from button cells to megawatt systems connected to stabilize an
electrical distribution network.

• Several different combinations of electrode materials and electrolytes

are used, including lead–acid, zinc–air, nickel–cadmium (NiCd), nickel–
metal hydride (NiMH), lithium-ion (Li-ion), lithium iron phosphate
(LiFePO4), and lithium-ion polymer (Li-ion polymer).

• Rechargeable batteries typically initially cost more than disposable

batteries but have a much lower total cost of ownership and
environmental impact, as they can be recharged inexpensively many
times before they need replacing.

• Some rechargeable battery types are available in the same sizes and
voltages as disposable types, and can be used interchangeably with
them.

• Billions of dollars in research are being invested around the world for
improving batteries and industry also focuses on building better batteries

• Some characteristics of rechargeable battery are given below:

1. In rechargeable batteries, energy is induced by applying an

external source to the chemical substances.
2. The chemical reaction that occurs in them is reversible.
3. Internal resistance is comparatively low.
4. They have a high self-discharge rate comparatively.
5. They have a bulky and complex design.
6. They have high resell value.
IMPORTANT SECONDARY BATTERIES
1. Lead storage battery
2. Nickel-Cadmiam battery

What is a LEAD-ACID BATTERY?

• The Lead-acid battery is one of the oldest types of rechargeable batteries.
These batteries were invented in the year 1859 by the French physicist
Gaston Plante.

• Despite having a small energy-to-volume ratio and a very low energy-to-

weight ratio, its ability to supply high surge contents reveals that the cells
have a relatively large power-to-weight ratio.
 • Lead-acid batteries can be classified as secondary batteries. The chemical
reactions that occur in secondary cells are reversible. The reactants that
generate an electric current in these batteries (via chemical reactions) can
be regenerated by passing a current through the battery (recharging).

• The chemical process of extracting current from a secondary battery

(forward reaction) is called discharging. The method of regenerating active
material is called charging.

Sealed Lead Acid Battery

• The sealed lead-acid battery consists of six cells mounted side by side in a
single case. The cells are coupled together, and each 2.0V cell adds up to
the overall 12.0V capacity of the battery.

• Despite being relatively heavy, lead-acid batteries are still preferred over
other lightweight options owing to their ability to deliver large surges of
electricity (which is required to start a cold engine in an automobile)

• A completely charged lead-acid battery is made up of a stack of alternating

lead oxide electrodes, isolated from each other by layers of porous
separators.

• All these parts are placed in a concentrated solution of sulfuric acid.

Intercell connectors connect the positive end of one cell to the negative
end of the next cell hence the six cells are in series.

CHEMICAL REACTION FOR DISCHARGING

When the battery is discharged, it acts as a galvanic cell and the following chemical
reaction occurs.

Negative:

➢ Pb(s) + HSO4– + H2O(l) –> 2e– + PbSO4(s) + H3O+(aq) (oxidation )

Positive:

➢ PbO2(s) + HSO4–(aq) + 3H3O+(aq) + 2e– –> PbSO4(s) + 5H2O(l)

(reduction)
 • Lead sulfate is formed at both electrodes. Two electrons are also transferred in the
complete reaction. The lead-acid battery is packed in a thick rubber or plastic case
to prevent leakage of the corrosive sulphuric acid.

Thus during discharging

1. Both the plates are transformed into lead sulfate (PbSO4).

2. Sulphuric acid is consumed and water is formed which reduces the specific gravity
of electrolyte from 1.28 to 1.18

3. The terminal voltage of each battery cell falls to 1.8V.

4. Chemical energy is converted into electrical energy which is delivered to load.

LEAD ACID BATTERY CHARGING

• The sulphuric acid existing in the lead discharge battery decomposes and needs to
be replaced. Sometimes, the plates change their structure by themselves.
Eventually, the battery becomes less efficient and should be charged or changed.

• When car batteries spend considerable durations of time in their discharged states,
the lead sulfate build-up may become extremely difficult to remove.

• This is the reason why lead-acid batteries must be charged as soon as possible (to
prevent the building up of lead sulfate). Charging of the lead batteries is usually
done by providing an external current source.

• A plug is inserted which is linked to the lead-acid battery and the chemical reaction
proceeds in the opposite direction.

• In cases where the sulphuric acid in the battery (or some other component of the
battery) has undergone decomposition, the charging process may become
inefficient. Therefore, it is advisable to check the battery periodically.
Thus during charging

1. The anode is transformed into lead peroxide (PbO2) and cathode into the
spongy lead (Pb).

2. Water is consumed and sulphuric acid is formed which increases the specific
gravity of electrolyte from 1.18 to 1.28.

3. The terminal voltage of each battery cell increases to 2.2 to 2.5V.

4. Electrical energy is converted into chemical energy which is stored in the cell.

What is NICKEL–CADMIUM BATTERY ?

• The nickel–cadmium battery (Ni–Cd battery or NiCad battery) is a type of
rechargeable battery using nickel oxide hydroxide and metallic cadmium as
electrodes.

• The abbreviation Ni–Cd is derived from the chemical symbols of nickel (Ni) and
cadmium (Cd): the abbreviation NiCad is a registered trademark of SAFT
Corporation, although this brand name is commonly used to describe all Ni–Cd
batteries.

• Wet-cell nickel–cadmium batteries were invented in 1899. A Ni–Cd battery has a

terminal voltage during discharge of around 1.2 volts which decreases little until
nearly the end of discharge. The maximum electromotive force offered by a Ni–Cd
cell is 1.3 V
A FULLY CHARGED NI–CD CELL CONTAINS:
1. a nickel(III) oxide-hydroxide positive electrode plate
2. a cadmium negative electrode plate,a separator, and
3. an alkaline electrolyte (potassium hydroxide).

• Ni–Cd batteries usually have a metal case with a sealing plate equipped with
a self-sealing safety valve. The positive and negative electrode plates,
isolated from each other by the separator, are rolled in a spiral shape inside
the case.

• This is known as the jelly-roll design and allows a Ni–Cd cell to deliver a much
higher maximum current than an equivalent size alkaline cell. Alkaline cells
have a bobbin construction where the cell casing is filled with electrolyte and
contains a graphite rod which acts as the positive electrode.

• As a relatively small area of the electrode is in contact with the electrolyte

(as opposed to the jelly-roll design), the internal resistance for an equivalent
sized alkaline cell is higher which limits the maximum current that can be
delivered.

The chemical reactions at the cadmium electrode during discharge are

The reactions at the nickel oxide electrode are:

The net reaction during discharge is

• during recharge, the reactions go from right to left. The alkaline electrolyte
(commonly KOH) is not consumed in this reaction and therefore its specific
gravity, unlike in lead–acid batteries, is not a guide to its state of charge.

• When Jungner built the first Ni–Cd batteries, he used nickel oxide in the
positive electrode, and iron and cadmium materials in the negative. It was
not until later that pure cadmium metal and nickel hydroxide were used.

• Until about 1960, the chemical reaction was not completely understood.
There were several speculations as to the reaction products. The debate was
finally resolved by infrared spectroscopy, which revealed cadmium
hydroxide and nickel hydroxide.

• Another historically important variation on the basic Ni–Cd cell is the

addition of lithium hydroxide to the potassium hydroxide electrolyte. This
was believed to prolong the service life by making the cell more resistant to
electrical abuse.

• The Ni–Cd battery in its modern form is extremely resistant to electrical

abuse anyway, so this practice has been discontinued.
APPLICATIONS

• Sealed Ni–Cd cells may be used individually, or assembled into battery packs
containing two or more cells. Small cells are used for portable electronics and toys
(such as solar garden lights), often using cells manufactured in the same sizes as
primary cells.

• When Ni–Cd batteries are substituted for primary cells, the lower terminal voltage
and smaller ampere-hour capacity may reduce performance as compared to
primary cells.

• Miniature button cells are sometimes used in photographic equipment, hand-held

lamps (flashlight or torch), computer-memory standby, toys, and novelties.

• Specialty Ni–Cd batteries are used in cordless and wireless telephones, emergency
lighting, and other applications. With a relatively low internal resistance, they can
supply high surge currents.

• This makes them a favourable choice for remote-controlled electric model

airplanes, boats, and cars, as well as cordless power tools and camera flash units.

• Larger flooded cells are used for aircraft starting batteries, electric vehicles, and
standby power.