THEORY

The main method of generating electricity through chemical action is
through the use of cells or batteries.

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When two dissimilar substances, usually metals or metallic materials,
are immersed into a solution that produces a greater chemical action on one than
the other, an electrical potential difference is created. If a conductor is
connected between them, electrons will flow to equalize the charges. The
arrangement is a simple voltaic cell, where the two metallic substances are
electrodes and the solution is the electrolyte.

Electrochemistry is the branch of
physical chemistry that reviews the connection between electricity, as a
quantifiable and quantitative phenomenon, and identifiable chemical change,
with either electricity considered a result of a specific substance change or
the other way around. Electric
charges moving between electrodes and an electrolyte or ionic species in a
solution are part of these reactions. Therefore, the communication between
electrical energy and chemical change is shown in electrochemistry.

At the point when electrolysis, a chemical reaction caused by remotely
provided current, or if a battery, which is an electric current created by
impulsive chemical reaction response, it is called an electrochemical response.

As a rule, electrochemistry
portrays the overall reactions when singular redox responses are isolated yet
associated by an external electric circuit and an interceding electrolyte.

One of the common ways of
electricity generation via chemical means of generating electricity through
chemical action is using cells or batteries. At the point when two different
substances, normally metals or metallic materials, are drenched into a solution
that delivers a more prominent chemical action on one than the other, an
electrical potential difference is made. In the event that a conductor is
connected between them, electrons will stream to equalise the charges. The
course of action is a basic voltaic cell, where the two metallic substances are
electrodes and the solution is the electrolyte.

Next, we are going to explore the
components of cells, of which there are two main types: primary and secondary
cells.

 

COMPONENTS OF A BATTERY

In a battery, the anode is the negative electrode from which electrons
flow out towards the external part of the circuit. Internally the positively
charged cations are flowing away from the anode (even though it is negative and
therefore would be expected to attract them, this is due to electrode potential
relative to the electrolyte solution being different for the anode and cathode
metal/electrolyte systems); but, external to the cell in the circuit, electrons
are being pushed out through the negative contact and thus through the circuit
by the voltage potential as would be expected.

A cathode is the electrode from which a conventional current exits a
polarized electrical device. A conventional current shows the direction in
which positive electric charges move. Electrons have a negative electrical
charge, so the movement of electrons is opposite to that of the conventional
current flow. In a battery or galvanic cell, the cathode is the positive
terminal since that is where the current flows out of the device. This outward
current is carried internally by positive ions moving from the electrolyte to
the positive cathode (chemical energy is responsible for this
“uphill” motion). It is continued externally by electrons moving into
the battery which comprises of positive current flowing outwards.

When electrodes are placed in an electrolyte and a voltage is supplied,
the electrolyte will conduct electricity. Lone electrons normally cannot pass
through the electrolyte; instead, a chemical reaction occurs at the cathode,
providing electrons to the electrolyte. Another reaction occurs at the anode,
consuming electrons from the electrolyte. As a result, a negative charge cloud
develops in the electrolyte around the cathode, and a positive charge develops
around the anode. The ions in the electrolyte neutralize these charges,
enabling the electrons to keep flowing and the reactions to continue.

PRIMARY CELL

A primary cell is a cell which the chemical action erodes one of the
electrodes, usually anode. When it happens, either the electrode, or sometimes
electrolyte, has to be substituted. Examples of primary cells include Leclanche
cell and alkaline cell.

SECONDARY CELL

A secondary cell is a cell which the chemical action switches the
electrodes and the electrolyte as the cell sends current. They can be restored
through discharging, where electric current is forced through the cell in the
alternate direction. Batteries of vehicles, such as cars and aircraft, are
commonly known to be of the secondary cell variation. Examples of secondary
cells include lead-acid cell, nickel-cadmium cell, nickel metal hydride cell
and lithium ion cell.

 

TYPES OF CELLS & ITS
MECHANISMS

PRIMARY CELLS

LECLANCHE CELL

Electricity is produced in a Leclanché cell when zinc atoms on the
surface of the anode oxidizes. They lose valence electrons to become positively
charged ions. As the zinc ions move away from the anode, their electrons stay
on its surface. The anode now becomes more negatively charged than the cathode.
When the cells connected in an external electrical circuit, the excess
electrons on the zinc anode will flow through the circuit to the carbon rod,
forming an electric current.

When the electrons enter the cathode (Carbon rod), they react with
manganese dioxide (MnO2) and water (H2O) to produce manganese oxide (Mn2O3) and
negatively charged hydroxide ions. A secondary reaction is produced in which
the negative hydroxide ions react with positive ammonium ions in the ammonium
chloride electrolyte to produce molecules of ammonia and water.

ALKALINE CELL

A cylindrical cell is contained in a drawn stainless steel can, which is
the cathode connection. The positive electrode mixture is a compressed paste of
manganese dioxide with carbon powder added for increased conductivity. The
paste may be pressed into the can or deposited as pre-molded rings. The hollow
centre of the cathode is lined with a separator, which prevents contact of the
electrode materials and short-circuiting of the cell. The separator is made of
a non-woven layer of cellulose or a synthetic polymer. The separator must
conduct ions and remain stable in the highly alkaline electrolyte solution.

The negative electrode is composed of a dispersion of zinc powder in a
gel containing the potassium hydroxide electrolyte. The zinc powder provides
more surface area for chemical reactions to take place, compared to a metal
can. This lowers the internal resistance of the cell. To prevent gassing of the
cell at the end of its life, more manganese dioxide is used than required to
react with all the zinc. Also, plastic-made gasket is usually added to increase
leakage resistance.

Aluminium foil is wrapped as the final process of battery manufacturing,
as a decoration as well as providing superior protection for the battery
compared to a cardboard wrapper. In an alkaline
battery, the negative electrode is zinc, the positive electrode is manganese
dioxide and the electrolyte are potassium hydroxide. Only the zinc and
manganese dioxide are used up during discharging process. The alkaline
electrolyte of potassium hydroxide remains, as there are equal amounts of OH?
consumed and produced.

 

SECONDARY CELLS

LEAD-ACID CELL

Rechargeable Small Sealed Lead Acid (SSLA) batteries are valve-regulated
lead acid batteries (VRLA batteries). They do not require regular addition of
water as compared to primary cells, and they vent less gas than flooded (wet)
lead-acid batteries. Hence, they are often referred to as “maintenance free”
batteries, as it does not require much maintenance
to maintain it. The reduced venting is an advantage as they can be used
in confined or poorly ventilated spaces.

There are two types of VRLA batteries:

1.   Absorbed
glass mat (AGM) battery

2.  Gel
battery (“Gel Cell”)

An absorbed glass mat battery has the electrolyte absorbed in a
fibre-glass mat separator while a gel cell has the electrolyte mixed with
silica dust to form an stablised gel.

NICKEL CADMIUM BATTERIES

A rechargeable Nickel Cadmium battery in the charged state consist of
nickel hydroxide (NiOOH) in the anode and cadmium (Cd) in the cathode.  Potassium hydroxide (KOH) is normally used
for the electrolyte. Due to their low internal resistance and the very good
current conducting properties, NiCad batteries can supply extremely high
currents and they have the ability to recharge rapidly. In addition, these
cells are capable of sustaining extremely low temperatures (-20°C). The
selection of the separator (nylon or polypropylene) and the electrolyte (KOH,
LiOH, NaOH) affect the voltage conditions in the case of a high current
discharge, the service life and the overcharging capability. Nickel Cadmium
cells generally offer a long service life thereby ensuring a high degree of
economy. For this reason, cells require a safety valve. In the case of misuse,
a very high-pressure may arise quickly.

NICKEL METAL HYDRIDE BATTERIES

A Nickel Metal Hydride Battery is a rechargeable NiMH battery which
consist of nickel hydroxide (NiOOH) in the cathode and a hydrogen storing metal
alloy (MH) in the anode. Potassium hydroxide (KOH) acts as the electrolyte in
this battery setup.  Compared to NiCad
batteries, Nickel Metal Hydride batteries tend to have a much higher energy
density per volume and weight.

LITHIUM ION BATTERIES

Lithium ion battery is a rechargeable battery where the negative
electrode (anode) and positive electrode (cathode) materials where reaction for
the lithium ion (Li+) takes place. Lithium ions move from the anode and is
attracted to cathode during discharge and are form into the cathode. The ions
reverse direction during charging.  Since
lithium ions are form into the cathode materials during charge or discharge,
there is no free lithium metal within a lithium-ion cell.

Commercially, lithium ion cells have a voltage range of approximately
3.0V to 4.2V. The electrolyte used is composed of an organic solvent and
dissolved lithium salt. This provides a medium for the lithium ion to move. In
a lithium ion cell, alternating layers of anode and cathode are separated by a
separator which is a porous film.

 

 

 

 

 

APPLICATIONS

PRIMARY CELLS

LECLANCHE CELL

The electromotive force (EMF) produced by a Leclanche cell is around 1.4
volts, with a resistance of several ohms where a porous pot is used. It is
often used in telegraphy and signalling, where infrequent current is needed and
it is advisable that a battery should require maintenance.

The Leclanché battery wet cell was the forerunner of the modern
zinc-carbon battery (a dry cell). The addition of zinc chloride to the
electrolyte paste actually increased the EMF to 1.5 volts. Later developments
provided ammonium chloride completely, giving the cell to endure more sustained
discharge without its internal resistance rising as quickly (the zinc chloride
cell).

 

SECONDARY CELLS

LEAD-ACID CELL

The lead-acid batteries are primarily used in the automobile industry.
It used to as starters, for lighting and ignition of the car.

The wet cell standby batteries are designed for deep discharge and are
mainly used as a backup power supply. Lead-acid batteries are used in powering
the emergency lighting and to power sump pumps in case of a power failure.

 

Traction (propulsion) batteries are used in golf carts and other
electric vehicles are powered by batteries. Large lead-acid batteries are used
to power the electric motors in conventional submarines when they are
underwater and also as a back-up power on nuclear submarines. Moreover,
electrolyte spillage does not occur in valve-regulated lead acid batteries.
This makes them practical in applications where spillage is not favoured such
as alarms and smaller computer systems, (particularly in uninterruptible power
supplies; UPS), powering electric scooters, electric wheelchairs, electrified
bicycles, micro hybrid vehicles, and motorcycles.

Lead-acid batteries were used to supply the filament (heater) voltage,
with 2 V common in early vacuum tube (valve) radio receivers.

Headlamps found in a miner’s headgear are usually powered by two or
three cells.

NICKEL CADMIUM BATTERIES

Closed Ni-Cad cells may be assembled into battery packs which has two or
more cells, or it may just be used individually. Smaller cells are normally
used in kid’s toys or other portable electrical devices, which often using the
cells that are like the sizing of primary cells. Performance will be reduced
when primary cells are substituted by Ni-Cad batteries because Ni-Cad batteries
have lower terminal voltage and smaller ampere-hour capacity.  Photographic equipment, flashlights, watches
and toys sometimes use miniature button cells.

Specialty Ni-Cad batteries is a favourable choice for camera flash
units, boats, cars and cordless power tools as they have low internal
resistance and can supply high surge currents. They are also used in emergency
lighting and cordless home telephones etc.

Larger flooded cells are used for standby power and also aircraft
starting batteries.

NICKEL METAL HYDRIDE BATTERIES

The primary use of the NiMH batteries is in electric plug-in vehicles
(i.e. General Motors EV1, First-generation Toyota RAV4 EV, Honda EV Plus, Ford
Ranger EV and Vectrix scooter) and hybrid vehicles (i.e. the Toyota Prius,
Honda Insight, Ford Escape Hybrid, Chevrolet Malibu Hybrid and Honda Civic
Hybrid). However, this is slowly being taken over by lithium ion batteries.

 

LITHIUM ION BATTERIES

Lithium-Ion batteries are lightweight and have a high energy density.
Due to this, it is used as the power source for a variety of devices. Such
devices include many of the latest mobile devices (i.e. smartphones,
tablets,laptops), power tools (i.e. cordless drills, saws and sanders) and
electric vehicles (i.e. electric cars, hybrid vehicles, electric bicycles,
personal transporters and advanced electric wheelchairs). In order to power
larger devices such as the electric vehicles multiple batteries in parallel
rather than a single unit as it is much more effective.

LIthium-Ion batteries are also used in telecommunication applications.
Secondary non-aqueous lithium batteries provide reliable backup power to load
equipment located in a network environment of a typical telecommunications
service provider

 

4. Advantages and
Disadvantages of Batteries 

There are several advantages of using batteries over other methods of
generating EMF. Firstly, batteries are able to be used in applications
requiring high current. They have high energy density and are able to be
charged and discharged easily. Moreover, they are more eco-friendly compared to
combustion of fossil fuel as the exhaust gas from the electrolysis is only
water vapour. Next, they are able to produce stable voltage, unlike friction
method which makes it good for practical applications. Lastly, they are more
portable and can store energy. However, using chemical means for power
generation also has its disadvantages.

This method is resistant to high temperatures and can vary the output of
the voltage produced and can also restrict applications in certain situations.
Using batteries needs regular maintenance. This makes it troublesome and
injuries can occur during maintenance check. An example could be acid running
into the eyes and eventually blinding the person.

Moreover batteries suffer from thermal runaway (especially so in NiCad
battery), a condition where they are not properly charged despite long hours of
charging. Possible explosions due to chemical reaction happening when gases are
released at electrodes. This is known as Polarization. Polarization in
batteries requires it to be regularly filled with electrolyte. Batteries have
internal resistance and are unable to produce large industrial amounts of
electricity unlike light, combustion methods.