Engineering Chemistry Module 1. These slides are prepared according to VTU syllabus.

1. Dr Swastika Das

2.  Battery is a device consisting of a series of
galvanic cells connected in series or in
parallel, which can generate power.
 Convert stored chemical energy into electrical
energy
 Reaction between chemicals take place
 BATTERIES represent a silent form of energy
producing chemical devices, which generate
electricity on demand

3.  The rapidity with which energy resources and
oil fields are consumed at present and in the
future will depend on the rapidity with which
regions of the world industrialize, the rate of
population growth, the ultimate level of
human desires to possess material goods and
the effort that is made to accelerate
production.
 The growing concern with managing the
costs of military, space crafts, portable
electronics, implantable medical devices,
communication technology etc.
 Batteries are portable sources of electricity.

5.  Anode , Cathode, electrolyte, separator,
container.
 Anode – Negative terminal –oxidation occurs
(lose electrons)
 Cathode – Positive terminal –reduction occurs
(gain electrons)
 Electrolyte:
-is an ion-conducting medium which
conducts ions between the electrodes so that
the above reactions can take place
– Current to flow out of the battery to
perform work .

7.  Three types: Primary, Secondary and Reserve.
 Primary cell: Single use, reactions are
irreversible, used when long period of
storage are needed, once completely
discharged there is no further electrical use.
Example : Dry cell, Zn-MnO2, Li-MnO2 batteries

9.  Lead-Acid Battery
 Nickel-Cadmium Battery (Ni-Cd)
 Nickel-Iron Battery (Ni-Fe)
 Nickel-Metal hydride Battery (Ni-MH)
 Lithium-Ion battery (C-LiMxOy)

12.  A third battery category is commonly referred to as
the reserve cell. What differentiates the reserve cell from
primary and secondary cells in the fact that a key component
of the cell is separated from the remaining components, until
just prior to activation. The component most often isolated is
the electrolyte. This battery structure is commonly observed
in thermal batteries, whereby the electrolyte remains inactive
in a solid state until the melting point of the electrolyte is
reached, allowing for ionic conduction, thus activating the
battery. Reserve batteries effectively eliminate the possibility
of self-discharge and minimize chemical deterioration. Most
reserve batteries are used only once and then discarded.
Reserve batteries are used in timing, temperature and
pressure sensitive detonation devices in missiles, torpedoes,
and other weapon systems.

14.  Reserve cells are typically classified into the following 4 categories.
 Water activated batteries.
 Electrolyte activated batteries. ( Mg-Ag with magnesium water
electrolyte)
 Gas activated batteries.
 Heat activated batteries.

16.  Unlimited shelf life
 High power for short period of time
 Better Performance
 Various design options.

17. Construction :
The NiMH cell consists of three main elements:
Cathode: The active material at Cathode of the NiMH battery is nickel
oxy hydroxide ( NiOOH). The cathode is made up of highly
porous sintered nickel plates into which NiOOH is pasted.
The nickel oxide - hydroxide electrode only exchanges a proton in the
charge-discharge reaction, and this results in a very small change in
size, resulting in a high level of mechanical stability, and this in turn
results in a longer cycle life.
In view of the environmental fears about Nickel Cadmium batteries and
cells, Nickel Metal Hydride technology has taken over.
Nickel Metal Hydride, NiMH batteries and cells have a very similar level of
performance - similar voltage and charge characteristics. As such they are
virtually a direct replacement, although there are a few differences as can
be imagined.

18.  Anode: The active material for the negative
electrode is actually hydrogen. However it is not
physically possible to use hydrogen directly and
therefore the hydrogen is stored in the NiMH cell as
a metal hydride which also serves as the negative
electrode. As a point of interest, the metal hydrides
used in NiMH cells can normally hold between 1%
and 2% hydrogen by weight.
 The anode is made up of the highly porous nickel
wire gauge into which the active hydrogen storage
alloy is pasted. Two types of metal alloys are used:
(i) Alloy of Lanthanum and Nickel
(ii) Alloy of Titanium and Zirconium.

19.  Electrolyte: The two electrodes are
seperated by a polypropylene seperator which
absorbs the electrolyte. The electrolyte in the
NiMH cell is an aqueous solution of
potassium hydroxide, KOH, which has a very
high conductivity. It is found that the
electrolyte concentration remains almost
constant over the charge / discharge cycle.
 Cell Representation :
MH/ KOH (5M)/ NiOOH, Ni(OH)2

21.  Anode: MH +OH- ---- M+H2O+ e-
 Cathode: NiOOH+H2O+ e- --- Ni(OH)2 +OH-
----------------------------------------
Net Reaction: MH +NiOOH ⇌ M+ Ni(OH)2
From the above reactions , it is evident that the concentration of
the electrolyte remains invariant i.e. doesn’t change. The cell
delivers a voltage of 1.25 V to 1.35 V.

22.  Environmental impact: NiMH battery technology has
overtaken NiCd because of their lower environmental impact. While
the use of toxic cadmium is removed from the NiMH cells the mining
and processing of the other metals used poses some environmental
threats. Fortunately when the NiMH batteries reach end of life, most
of the nickel can be recovered with relative ease.
 High capacity ,
 high energy density,
 longer time between charges,
 rapid recharge capability.
 High cycle life.
Self discharge : One disadvantage of the NiMH cell is that it has a
high rate of self-discharge. They can lose up to 3% of its charge per
week of storage.

23.  Ni- MH batteries were developed to meet
the increase energy demand by modern
electronic gadgets like cell phones, CD
players, laptops and other portable
consumer electronic applications where
high specific energy is required.

26. Lithium ion batteries provide improved levels of capacity combined with
reliable operation when compared to other forms of cell and battery
technology including Nickel Cadmium, Ni-Cd and Nickel Metal Hydride,
NiMH.
As a result of their characteristics, Lithium Ion, or Li-ion batteries have
become the battery technology of choice in a variety of areas. Li-ion
batteries are used almost exclusively in mobile phones, laptops, e-
readers and many other electronic gadgets. In addition to this, Li-ion
technology is also used being used for power applications - everything
from the smallest electronic gadgets, through mobile phones, laptops,
etc to power tools and there are even lithium ion car batteries for
powering electric cars.
The idea for lithium ion battery technology was first proposed in the
1970s by M Whittingham who used titanium sulphide for the cathode and
lithium metal for the anode. Although the cell produced power, it could
be unstable as lithium whiskers from the anode grew into the electrolyte
and eventually touched the cathode.

27.  Storing electrical energy in batteries is a key factor in solving the
world's energy supply. The element lithium is useful in batteries
since it willingly releases electrons. In 1980 John Goodenough
developed a lithium battery with a cathode of cobalt oxide, which,
at a molecular level, has spaces that can house lithium ions. This
cathode gave a higher voltage than earlier batteries.
Goodenough's contributions were crucial for the development of
lithium-ion batteries, which are used in for example mobile
phones and electric cars.
John Goodenough was born to American
parents in Jena, Germany on 25 July 1922.
After studying mathematics at Yale
University, he served during the Second
World War as a meteorologist in the US
Army. He then studied at the University of
Chicago, receiving a doctorate in physics
there in 1952. He subsequently worked at
the Massachusetts Institute of Technology
and Oxford University in Great Britain.
Since 1986 he has been a professor at the
University of Texas at Austin.

28.  In lithium-ion (Li-ion) batteries, energy storage and release is
provided by the movement of lithium ions from the positive to the
negative electrode back and forth via the electrolyte. In this
technology, the positive electrode acts as the initial lithium source
and the negative electrode as the host for lithium. Several
chemistries are gathered under the name of Li-ion batteries, as the
result of decades of selection and optimization close to perfection of
positive and negative active materials. Lithiated metal oxides or
phosphates are the most common material used as present positive
materials. Graphite, but also graphite/silicon or lithiated titanium
oxides are used as negative materials.
 With actual materials and cell designs, Li-ion technology is expected to reach an
energy limit in the next coming years. Nevertheless, very recent discoveries of new
families of disruptive active materials should unlock present limits. These
innovative compounds can store more lithium in positive and negative electrodes
and will allow for the first time to combine energy and power. In addition, with
these new compounds, the scarcity and criticality of raw materials are also taken
into account.

29. A lithium ion battery has four main constituents:
 Anode: Anode material is not purely lithium
due to the high reactivity of lithium. The
anode is made up of graphite which can store
and exchange lithium ions. This type of
graphite compounds are called as
intercalation compounds. The guest
molecules can be I2, K+ , or Li + .
 Intercalation means the reversible inclusion
of a molecule or ion into compounds with
layered structure.
 Example: Graphite has layered structure.

30.  Cathode: This is the positive electrode and it
is typically made from a lithium based metal
oxide of some form. There are several
different lithium ion battery technologies, so
the exact format will change from one type to
the next.
 The metal oxides used in cathode are:
LiCoO2, LiNiO2 , LiMn2O4. Out of these three,
LiCoO2 has the best performance but it is
toxic and expensive. LiNiO2 is stable but Ni
ions may disorder. LiMn2O4 is comparatively
the best and it does not cause environmental
pollution.

32.  Electrolyte: The electrolyte is the placed between the
two electrodes within the cell. Since Li ion reacts
violently with water, therefore a non aqueous
electrolyte must be used in Lithium ion battery. The
electrolyte is LiPF6 dissolved in a mixture of ethylene
carbonate and diethyl carbonate. It is often a mixture
of organic carbonates such as ethylene carbonate,
diethyl carbonate,.
 Separator: In order to prevent the two electrodes
touching a separator is placed between the anode
and cathode. This absorbs the electrolyte, and
enables the passage of ions, but prevents the direct
contact of the two electrodes within the lithium in
cell.

33.  Anode : LixC6 --- xLi+ +xe- +6C
 Cathode : xLi+ +xe- +LiMn2O4-- LixMn2O4
 -------------------------------------------------------------
LixC6 +LiMn2O4 ⇌ LixMn2O4 +6C
 During discharge Li+ ions dissociate from an anode
and migrate towards cathode through the
electrolyte.
 During charging, lithium from cathode material is
ionized and move towards the anode.
 At the same time, electrons travel through the
external circuits.

34.  High energy density because of light weight
of Lithium.
 High cycle life ( 500- 1000)
 Doesn’t self discharge
 High capacity
 long shelf life
 High voltage > 4Volts
 It can work for a wide range of temperature
-700C to 400C.

35.  Overcharging or overheating or short
circuiting results in fire or explosions.
 For safe long lasting product, specific safety
issues must be taken into consideration while
discharging the battery.
 Applications:
 Used in cell phones and other electronic
gadgets.

36.  Generally, entropy is defined as a measure of randomness
or disorder of a system. This concept was introduced by a
German physicist named Rudolf Clausius in the year 1850.
 From a thermodynamics viewpoint of entropy, we do not
consider the microscopic details of a system. Instead,
entropy is used to describe the behaviour of a system in
terms of thermodynamic properties such as temperature,
pressure, entropy, and heat capacity. This thermodynamic
description took into consideration the state of
equilibrium of the systems.
 Entropy is a measure of the molecular disorder.
Entropy order: gas>liquid>solids

37.  It is a thermodynamic function.
 It is a state function. It depends on the state of the system
and not the path that is followed.
 It is represented by S but in the standard state, it is
represented by S°.
 It’s SI unit is J/Kmol.
 It’s CGS unit is cal/Kmol.
 Entropy is an extensive property which means that it
scales with the size or extent of a system.
 Note: The greater disorder will be seen in an isolated
system, hence entropy also increases. When chemical
reactions take place if reactants break into more number
of products, entropy also gets increased. A system at
higher temperatures has greater randomness than a
system at a lower temperature. From these examples, it is
clear that entropy increases with a decrease in regularity.

38.  In physics and physical chemistry, free energy refers to the
amount of internal energy of a thermodynamic system that is
available to perform work. There are different forms of
thermodynamic free energy:
 Gibbs free energy is the energy that may be converted into work
in a system that is at constant temperature and pressure.
The equation for Gibbs free energy is:
G = H – TS
where G is Gibbs free energy, H is enthalpy, T is temperature,
and S is entropy.
 Helmholtz free energy is energy that may be converted into work
at constant temperature and volume.
 The equation for Helmholtz free energy is:
 A = U – TS
 where A is the Helmholtz free energy, U is the internal energy of
the system, T is the absolute temperature (Kelvin) and S is the
entropy of the system.