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CHAPTER I
Introduction
1. 1 Battery
An electrical battery is one or more electrochemical cells that convert stored
chemical energy into electrical energy by means of redox reactions.
1. 2 History of batteries
1748 – Benjamin Franklin first coined the term "battery" to describe an array of
charged glass plates.
1780 – Luigi Galvani was dissecting a frog affixed to a brass hook. When he
touched its leg with his iron scalpel, the leg twitched. Galvani believed the energy
that drove this contraction came from the leg itself, and called it "animal
electricity".
1800 – Volta invented the first true battery which came to be known as
the Voltaic Pile. It consisted of pairs of copper and zinc discs piled on top of each
other, separated by a layer of cloth or cardboard soaked in brine (i.e. the
electrolyte).
1836 – John Frederic Daniell invented the Daniell cell, which consisted of a
copper pot filled with a copper sulphate solution, in which was immersed an
unglazed earthenware container filled with sulphuric acid and a zinc electrode.
1844 – William Robert Grove invented Grove cell. It consisted of a zinc anode
dipped in sulfuric acid and a platinum cathode dipped in nitric acid, separated by
porous earthenware. The Grove cell provided a high current and nearly twice the
voltage of the Daniell cell.
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1859 – Gaston Plante invented the lead–acid battery, the first ever battery that
could be recharged by passing a reverse current through it. A lead acid cell
consists of a lead anode and a lead dioxide cathode immersed in sulphuric acid.
1866 – Georges Leclanche invented a battery that consisted of a zinc anode and
a manganese dioxide cathode wrapped in a porous material, dipped in a jar
of ammonium chloride solution. The manganese dioxide cathode had a little
carbon mixed into it as well, which improved electrolyte conductivity and
absorption.
1881 – Carl Gassner invented the first commercially successful dry cell battery
(zinc–carbon cell).
1899 – Waldemar Jungner invented the nickel–cadmium battery.
1901 – Thomas Alva Edison invented the alkaline storage battery.
1903 – Jungner invented the nickel–iron battery.
1970 – Lithium battery
1989 – Nickel/Metal hydride battery.
1980 – An American chemist John B. Goodenough led a research team at Sony
that would produce the lithium ion battery, a rechargeable and more stable version
of the lithium battery; the first ones were sold in 1991.
1996 – lithium ion polymer battery.
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1. 3 Categories and types of batteries
Batteries are classified into two broad categories.
Primary batteries irreversibly (within limits of practicality) transform chemical
energy to electrical energy. When the initial supply of reactants is exhausted,
energy cannot be readily restored to the battery by electrical means.
eg. Zinc–carbon batteries, Alkaline batteries
Secondary batteries can be recharged; that is, they can have their chemical
reactions reversed by supplying electrical energy to the cell, restoring their
original composition.
eg. Lead–acid batteries, Lithium ion batteries
1. 4 Battery cell types
There are many general types of electrochemical cells, according to chemical
processes applied and designs chosen. The variation includes galvanic cells, electrolytic
cells, fuel cells, flow cells and voltaic piles.
1. 4. 1 Wet cell
A wet cell battery has a liquid electrolyte. Other name is flooded cell, since the
liquid covers all internal parts, or vented cell, since gases produced during operation can
escape to the air. Wet cells may be primary cells (non–rechargeable) or secondary cells
(rechargeable). eg. Leclanche cell.
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1. 4. 2 Dry cell
A dry cell has the electrolyte immobilized as a paste, with only enough moisture
in the paste to allow current to flow. Compared to a wet cell, the battery can be operated
in any random position, and will not spill its electrolyte if inverted. eg. Zinc–carbon
battery.
1. 4. 3 Molten salt battery
A molten salt battery is a primary or secondary battery that uses a molten salt as
its electrolyte. eg. ZEBRA batteries (Na–NiCl2 battery).
1. 4. 4 Reserve battery
A reserve battery can be stored for a long period of time and is activated when its
internal parts (usually electrolyte) are assembled. For example, a battery for an electronic
fuze might be activated by the impact of firing a gun, breaking a capsule of electrolyte to
activate the battery and power the fuze's circuits. eg. Water–activated battery.
1. 5 Components of cell
Anode or negative electrode
Cathode or positive electrode
Electrolyte
Separator
Current collector
1. 5. 1 Anode
The electrode at which the oxidation occurs is called the anode. The charge on the
anode is negative.
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Characteristics
Efficiency as a reducing agent.
High coulombic output (Ah/g)
Good conductivity.
Stability
Example
Metals
1. 5. 2 Cathode
The electrode at which reduction occurs is termed the cathode. The charge on the
cathode is positive.
Characteristics
Good oxidizing agent.
Must stable when contact with electrolyte.
To achieve high performance.
Should be conductive.
Example
Metallic oxides
1. 5. 3 Electrolyte
The ionic conductor–which provides the medium for transfer of charge, as ions,
inside the cell between the anode and cathode.
Characteristics
Good ionic conductivity
Low viscosity and high dielectric constant
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Non reactivity with electrode materials
Example
Sulphuric acid, LiPF6 in 1: 1 (Ethylene carbonate and diethylene carbonate)
1. 5. 4 Separator
An ion permeable and electronically non conductive, spacer or material which
prevents electronic contact between electrodes of opposite polarity in the same cell.
Characteristics
Chemical stability.
Low thickness.
Mechanical strength.
High porosity & permeability.
Examples
Polypropylene, Glass, Non–Woven glass.
1. 5. 5 Current collector
An inert member of high electrical conductivity used to conduct current from or to
an electrode during discharge or charge.
Characteristics
Excellent bulk electrical conductivity.
Minimal thickness / weight.
Excellent surface conductivity.
Examples
Aluminium foil, Copper foil and Nickel mesh.
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1. 6 Operating principle of cell
1. 6. 1 Discharge
The operation of a cell during discharge is shown schematically in Fig. 1. 1a.
When the cell is connected to an external load, electrons flow from the anode, which is
oxidized, through the external load to the cathode, where the electrons are accepted and
the cathode material is reduced. The electric circuit is completed in the electrolyte by the
flow of anions (negative ions) and cations (positive ions) to the anode and cathode,
respectively.
1. 6. 2 Charge
During the recharge of a rechargeable or storage cell, the current flow is reversed
and oxidation takes place at the positive electrode and reduction at the negative electrode,
as shown in Fig. 1. 1b. As the anode is, by definition, the electrode at which oxidation
occurs and the cathode, the one where reduction takes place, the positive electrode is now
the anode and the negative the cathode.
1. 7 Lithium batteries
Lithium batteries1 were first proposed by M. S. Whittingham at Binghamton
University, at Exxon, in the 1970s. Whittingham used titanium (II) sulfide as the cathode
and lithium metal as the anode. The reversible intercalation in graphite and intercalation
into cathodic oxides was also already discovered2 in the 1970s by J.O. Besenhard at TU
Munich. He also proposed the application as high energy density lithium cells. In 1979,
John Goodenough demonstrated a rechargeable3 cell with high cell voltage in the 4V
range using lithium cobalt oxide (LiCoO2) as the positive electrode and lithium metal as
the negative electrode. This innovation provided the positive electrode material which
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made lithium ion batteries (LIBs) possible. LiCoO2 is a stable positive electrode material
which acts as a donor of lithium ions, which means that it can be used with a negative
electrode material other than lithium metal. In 1985, Akira Yoshino4 assembled a
prototype cell using carbonaceous material into which lithium ions could be inserted as
the anode, and as the cathode lithium cobalt oxide (LiCoO2), which is stable in air. By
using an anode material without metallic lithium, safety was dramatically improved over
batteries which used lithium metal. The use of lithium cobalt oxide (LiCoO2) enabled
industrial–scale production to be achieved easily. This was the birth of the current
lithium–ion battery. In 1991, Sony and Asahi Kasei released the first commercial
lithium–ion battery.
1. 8 Advantages of lithium–ion battery
•
High voltage
Lithium cells have voltages up to about 4V, depending on the cathode
material, compared with 1.5V for most other primary system. High open circuit
voltage in comparison to aqueous batteries (such as lead acid, nickel–metal hydride
and nickel–cadmium). This is beneficial because it increases the amount of power
that can be transferred at a lower current.
•
High energy density and power density
The energy density (100–250 Wh/Kg) and power density (250 Wh/L) of
lithium cell is 2–4 or more times better than that of conventional batteries (Lead acid,
zinc anode and Ni/MH batteries).
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•
Operation over a wide temperature range
Many of the lithium cells will perform over a temperature range from –40 to
70°C.
•
Flat discharge characteristics
A flat discharge curve is typical for many lithium cells.
•
No memory effect
•
Superior shelf life
Self–discharge rate of approximately 5–10% per month, compared to over 30%
per month in common nickel metal hydride batteries, approximately 1.25% per month for
low self–discharge Ni–MH batteries and 10% per month in nickel–cadmium batteries.
1. 9 Electrochemistry of lithium–ion Battery
During charge, the positive material is oxidized and the negative material is
reduced. In this process, lithium ions are de–intercalated from the positive material and
intercalated into the negative material. (Intercalated – a reaction where lithium ions are
reversibly removed or inserted into a host without a significant structural change to the
host) The reverse process is present during a discharge cycle. The operation of a Lithium
ion cell is shown schematically in Fig. 1. 2.
The positive electrode half–reaction is
Charge
Li1–xCoO2 + xLi+ + xe–
LiCoO2
Discharge
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The negative electrode half–reaction is
Charge
+
–
xLi + xe
+ 6C
LixC6
Discharge
The over all electrode reaction is
Discharge
CoO2 + LiC6
LiCoO2 + C6
Charge
1. 10 Classification of lithium batteries
Lithium batteries are classified into two broad categories.
Lithium battery
Li primary battery
Soluble
cathode
cells
Solid
cathode
cells
Li secondary battery
Solid
electrolyte
cells
Lithium
ion battery
Lithium ion
polymer
battery
1. 10. 1 Classification of lithium primary battery
Lithium primary cells classified on the basis of electrolyte used or cathode
material.
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a. Soluble–cathode cells
These use liquid or gaseous cathode materials that dissolve in the electrolyte or
the electrolyte solvent. Their operation depends on the formation of a passive layer on the
lithium anode resulting from a reaction between the lithium and the cathode material.
This prevents further chemical reaction (self– discharge) between anode and cathode or
reduces it to a very low rate. These cells are manufactured in many different
configurations and designs (such as high and low rate) and with a very wide range of
capacities. They are generally fabricated in cylindrical configuration in the smaller sizes,
upto about 35 Ah, using a bobbin construction for the low–rate cells and a spirally wound
(jelly–roll) structure for the high–rate designs. Prismatic containers, having flat parallel
plates, are generally used for the larger cells upto 10,000 Ah in size. Flator‘‘pancake–
shaped’’ configurations have also been designed. These soluble cathode lithium cells are
used for low to high discharge rates. The high–rate designs, using large electrode surface
areas, are noted for their high power density and are capable of delivering the highest
current densities of any active primary cell.
Eg. Li/SO2Cl2 cells
b. Solid–cathode cells
The second type of lithium anode primary cells uses solid rather than soluble
gaseous or liquid materials for the cathode. With these solid cathode materials, the cells
have the advantage of not being pressurized or necessarily requiring a hermetic–type seal,
but they do not have the high–rate capability of the soluble–cathode systems. They are
designed, generally, for low–to medium–rate applications such as memory backup,
security devices, portable electronic equipment, photographic equipment, watches,
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calculators and small lights. Button, flat, and cylindrical–shaped cells are available in
low–rate and the moderate–rate jelly–roll configurations. Eg. Li/V2O5 cell.
c. Solid–electrolyte cells
The third type of lithium anode primary batteries uses solid rather than liquid for
electrolytes. The solid electrolyte is formed in situ as the discharge product of the cell
reaction. However, the viscous liquid phase impart a plasticity to the cathode which
makes these solid state cells better able to adapt to volumetric changes during cell
discharge. These cells are noted for their extremely long storage life, in excess of 20
years, but are capable of only low–rate discharge in the micro ampere range. They are
used in applications such as memory backup, cardiac pacemakers, and similar equipment
where current requirements are low but long life is critical.
Eg. Li/LiI/I2 (P2VP)
1. 10. 2 Classification of lithium secondary batteries
Lithium secondary cells classified on the basis of electrolyte used.
a. Lithium–ion battery
The three primary functional components of a lithium–ion battery are the anode,
cathode, and electrolyte. The anode of a conventional lithium–ion cell is made from
carbon, the cathode is a metal oxide, and the electrolyte is a lithium salt in an organic
solvent. The most commercial popular anode material is graphite. The cathode is
generally one of three materials: a layered oxide (such as lithium cobalt oxide), a
polyanion (such as lithium iron phosphate), or a spinel (such as lithium manganese
oxide). The electrolyte is typically a mixture of organic carbonates such as ethylene
carbonate or diethyl carbonate containing complexes of lithium ions. These non–aqueous
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electrolytes
generally
use
non–coordinating
anion
salts
such
as
lithium
hexafluorophosphate (LiPF6), lithium hexafluoroarsenate monohydrate (LiAsF6. H2O),
lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), and lithium triflate
(LiCF3SO3). Depending on materials choices, the voltage, capacity, life, and safety of a
lithium–ion battery can change dramatically.
b. Lithium–ion polymer battery
Lithium–ion polymer batteries, polymer lithium ion, or more commonly lithium
polymer batteries (abbreviated Li–poly, Li–Pol, LiPo, LIP, PLI or LiP) are rechargeable
batteries (secondary cell batteries). This battery consists of a carbon anode and Li+
insertion material cathode and solid polymer electrolyte, in which lithium ions swing
between the two electrodes. Lithium polymer batteries have the same basic chemistry as
lithium ion batteries. However, the polymer cells use a porous separator that, when
exposed to the electrolyte, turns to a gel because the gel isn't flammable, lithium polymer
batteries have a different architecture, with the anode and cathode developed as a plate
and stacked on top of each other. Polymer electrolytes/separators can be solid polymers
(e.g., polyethylene oxide) and LiPF6, or other conducting salts and SiO2, or other fillers
for better mechanical properties. Lithium polymer batteries do not need a metal shell the
way that lithium ion batteries do. In fact, the shell of lithium polymer batteries is often
plastic.
1. 11 Components of lithium ion cells
1. 11. 1 Anode
The anode is the electrode at which oxidation takes place and electrons are fed
into the external circuit. Different type of anode materials are used in currently used
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lithium ion batteries such as lithium metal, carbonaceous materials, Sn, SnO based
materials and Intermetallic alloys etc.,
Criteria
The potential of lithium insertion and deinsertion in the anode Vs Li must be as
low as possible.
The amount of lithium which can be accommodated by the anode material should
be as high as possible to achieve a high specific capacity.
The anode should endure repeated Li insertion and deinsertion without any
structural change to obtain long cycle life.
Examples. Li, graphite, metal and metal oxides.
1. 11. 2 Cathode
The cathode is the electrode at which reduction takes place and into which
electrons are fed from the external circuit. A guest spaced such as lithium can be inserted
interstitially into the host lattice and extracted during recharge with little or no structural
modification of the host. The intercalated compounds are classified as follows
LiMO2 based materials (M = Co, Ni, Mn)
LiMPO4 based materials (M = Fe, Co, Ni and Mn)
LiMn2O4 based materials
Criteria
The insertion compound LixMyXz (X – anion) should have a high lithium
chemical potential (µLi(c)) to maximize the cell voltage.
The insertion compound LixMyXz should allow an insertion/extraction of a
large amount of lithium, to maximize the cell capacity.
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The lithium insertion/extraction process should be reversible with no or
minimal changes in the host structure over the entire range x of lithium
insertion/extraction in order to provide a good cycle life for the cell.
The insertion compound should support mixed conduction. It should have
good electronic conductivity σe and lithium ion conductivity σLi to
minimize polarization losses during the discharge/charge process and
thereby to support a high current density and power density.
The insertion compound should be chemically stable without undergoing
any reaction with the electrolyte over the entire range, x of lithium
insertion/extraction.
Examples. LiCoO2, LiMn2O4, LiFePO4 etc.
1. 11. 3 Electrolyte
Electrolytes can be defined as to serve as the medium for the transfer of charges,
which are in the form of ions, between a pair of electrodes. The vast majority of the
electrolytes are electrolytic solution types that consists of salts dissolved in either water
(aqueous) or organic molecules (nonaqueous) and are in a liquid in the service
temperature range.
Criteria
It should be a good ionic conductor and electronic insulator
It should have wide electrochemical window
It should also be inert to other cell components
It should be robust against other various abuses, such as electrical, mechanical or
thermal ones.
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Its components should be environmentally friendly.
Classification
Electrolytes can be roughly divided into three groups as follows
Liquid electrolytes eg. LiPF6 in 1: 1 (EC: DEC)
Solid polymer electrolyte eg. LiClO4 – PEO
Gel polymer electrolyte eg. PVDF – HFP
1. 11. 4 Separators
A separator is a porous membrane placed between electrodes of opposite polarity,
permeable to ionic flow but preventing electrical contact of the electrodes.
Criteria
Electronic insulator
Minimal electrolyte (ionic) resistance
Mechanical and dimensional stability
Sufficient physical strength to allow easy handling
Chemical resistance to degradation by electrolyte, impurities and electrode
reactants and products
Effective in preventing migration of particles or colloidal or soluble species
between the two electrodes
Readily wetted by electrolyte
Uniform in thickness and other properties
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Classification
Separators for batteries can be divided into different types, depending on their
physical and chemical characteristics. They can be molded, woven, non–oven,
microporous, bonded, papers, or laminates.
Eg. Polypropylene, cellulose, nonwoven fabric and celgard etc.
1. 11. 5 Current collectors
A structural part of a complicated electrode assembly. Its primary purpose is to
conduct the electricity between the actual working (reacting) parts of the electrode and
the terminals. Current collectors must be electrochemically stable when in contact with
the cell component during the potential operation window of an electrode. In lithium
batteries Al can be used as current collector for positive electrode and Cu foil for
negative electrode. The rough surface of substrate enhanced the adhesive force between
an active material and a current collector. Therefore, surface roughness of substrate is an
important factor to improve the cycleability of Li–ion cell.
a. Aluminium foil
For high voltage5 (>3.5 V Vs Li/Li+) LIBs, Al is the material of choice. It is used
extensively with lithiated transition metal oxides upto 5V Vs. Li/Li+. In air and aqueous
solutions, Al can be protected by a thin and dense oxide passive layer, Al2O3. Its low
price and good electrical conductivity due to a high purity of Al metal expand the
potential application for lithium batteries.
b. Copper foil
Almost all commercial, rechargeable lithium batteries use carbonaceous materials
applied to a copper foil substrate as the negative electrode. As lithium ions, which are
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released from the positive electrodes, are intercalated to the carbonaceous negative
electrode materials, the resulting potential6 reaches between 0.25 and 0.01 V Vs. Li/Li+.
In this state, the negative electrode materials, the Cu current collector, and the electrolyte
are electrochemically reduced. Cu metal surface is likely to reduce the electrolyte at the
potential 3 V Vs. Li/Li+, generating the cathodic current beecause of this, Cu metal is
stable at a lower narrow potential range and is generally acceptable for negative electrode
current collectors.
1. 12 Applications of lithium primary and secondary batteries
Lithium primary and secondary batteries are widely used in consumer, industrial,
medical, automotive and military devices.
General usage
Lithium–ion batteries can be used both in devices that need recharging, such as
cell phones, and in products whose batteries are difficult, expensive or impossible to
recharge or replace, such as cardiac pacemakers.
Portable electronics
In portable electronics, batteries needs to be recharged many times, and the
lithium–ion battery can handle hundreds of recharges. Products that use the lithium–ion
battery include iPods, cell phones, PCs, laptops, watches and digital cameras.
Medical applications
Implantable electronic devices cannot be recharged or replaced without great
expense, so the batteries used need to be small and able to last for years. Implantable
products that use lithium–ion batteries include cardiac pacemakers, cardiac defibrillators,
neuro stimulators and drug infusion systems.
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Military applications
The lithium–ion battery's long life and light weight make it the battery used in
many military functions, including providing power for the computers in missiles.
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1. 13 References
1. M. S. Whittingham, Science 192 (1976) 1126.
2. R. Schallhorn, R. Kuhlmann, J. O. Besenhard, Mater. Res. Bull. 11 (1976) 83.
3. USPTO search for inventions by "Goodenough, John".
4. US 4668595, Yoshino; Akira, "Secondary Battery", issued 10 May 1985, assigned
to Asahi Kasei.
5. S. T. Myung, Y. Hitoshi, Y. K. Sun, J. Mater. Chem. 21 (2011) 9891.
6. K. L. Lee, J. Y. Jung, S. W. Lee, H. S. Moon, J. W. Park, J. Power Sources 129
(2004) 270.
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Fig. 1. 1 Operation of cell a) Discharge b) Charge
Fig. 1. 2 Lithium – ion battery – operating principle (source: www.marklines.com)
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