DSM ASSIGNMENT submitted by

G.SRI SAI SAMHIHTA

212219007
Materials Science & Engineering (MSE)

SELECTION OF ELECTRODE MATERIAL FOR BATTERIES IN ELECTRIC

VEHICLE (TESLA ELECTRIC CAR)

1. INTRODUCTION:
WORKING OF AN ELECTRIC CAR :
Electric Car works on induction motor by using rechargeable batteries. The main parts of the
electric car are induction motor, invertor and battery power source. The battery source gives DC
power and invertor converts it to AC power source which is fed to induction motor and thus it
rotates. Induction motor contains two main parts stator and rotor. A three phase power supply is
given to stator which gives four pole magnetic fields. This rotating magnetic field induces on
rotor parts which makes it turn. In Induction motor, rotor always lags behind rotational magnetic
field. The speed depends on the ac power supply .so we can control the speed easily by varying
the frequency of current. Induction motor has wide range of speed whereas normal combustion
engine has limited range of speed so a transmission must be connected to engine to connect it to
drive wheel. Whereas induction motor can be directly connected to drive wheel. This is the main
advantage of Induction motor. For induction motor to work we need power supply which is
obtained from battery source.

Figure 1.Important parts of an electric vehicle

 Figure 2.Difference between IC Engine and Induction Motor

ADVANTAGES OF ELECTRIC VEHICLE:

 No fuel, no emissions
No petrol or diesel is needed in a f ully electric vehicle. So no emission of gases
 Less Running costs
 Low maintenance
 Performance
Electric cars are lighter, and – as all of their power is generated from a standing start .

These are certain drawbacks and portions where the electric car technology has to be improved.
1) Driving range
The range of the distance the electric vehicle travels is less compared to normal fossil fuelled
vehicles. Many of the electric cars can travel 70 – 100 miles, and even more, with only one trip
to the charging point.

2) Recharge time
Charging electric vehicles does take longer. Estimates show that 80% of EV charges take place
on a slow charge at home over night, which is sufficient for most purposes. Unfortunately, there
is no five minute recharge for electric cars just yet.

3) Battery life
The batteries currently in use in EVs do have a limited life expectancy, need to be replaced
every 3 – 10 years depending on the make and model.
These are the certain drawbacks where they have to be improved. Most important part is the
battery by varying the battery properties the above mentioned limitations can be overcome. The
only way of varying the battery properties is by altering the materials used in the battery. So the
selection of material for anode and cathode plays a vital role in overcoming these limitations.

2.BATTERY:
A typical battery consists of two or more electrochemical cells joined together. The battery
converts stored chemical energy into electric energy. A single battery cell is made of a negative
electrode and a positive electrode which are connected by an electrolyte. The chemical reaction
between the electrodes and electrolyte generates electricity. Rechargeable batteries can reverse
the chemical reaction by reversing the current. This way the battery can be recharged. The kind
of material used for the electrodes and electrolyte determines the battery specifications.
We have different kinds of rechargeable batteries like:
LEAD ACID-BATTERY
Ni-Cd BATTERY
NICKEL METAL HYDRIDE
LITHIUM ION BATTERY
Among all these rechargeable batteries most of the electric vehicles uses Lithium ion batteries
only. The following will give some of the properties for each of these batteries and will give
brief idea on why only Lithium ion batteries are used.

2.1. LEAD ACID BATTERY

Fig 3. Lead acid battery schematic diagram

Specific energy is low compared to the other battery technologies. A typical Pb/A battery for an EV has a
specific energy of around 35 Wh/kg and a specific power of 250 W/kg .The number of life cycles that can
be achieved by a Pb/A battery is 100 cycles for a normal car battery

2.2.NICKEL CADMIUM

Figure 4.Nickel Cadmium battery

 Relatively low energy density — compared with newer systems.

 Memory effect — the NiCd must periodically be exercised to prevent memory effect.
 Environmentally unfriendly — the NiCd contains toxic metals.
 Has relatively high self-discharge — needs recharging after storage.
2.3.NICKEL METAL HYDRIDE BATTERY:

Figure 5.Nickel Metal hydride battery

 Limited service life — if repeatedly deep cycled, especially at high load currents, the
performance starts to deteriorate after 200 to 300 cycles.
 Limited discharge current — although a NiMH battery is capable of delivering high
discharge currents.The NiMH generates more heat during charge and requires a longer
charge time than the NiCd.
 High maintenance — battery requires regular full discharge to prevent crystalline
formation.About 20 percent more expensive than NiCd

Figure 6 Graph showing different specific

energy densities for different batteries
As we can observe from the graph ,the specific energy density is very high for Lithium ion battery which
means they can store more amount of energy in given mass.It is also having less self-discharge compared
to other battery types. The Highest cell voltage of around 3.6 V can be achieved in Lithium ion Batteries.
The Cell voltages for other batteries lie well below the value of 2 V . By considering the above properties
most of the electric vehicle manufacturing companies choose Lithium ion battery even though it is having
certain disadvantages

2.4.LITHIUM ION BATTERIES :

Lithium ion batteries can be characterized as energy storage systems that rely on insertion reactions from
both electrodes where lithium ions act as the charge carrier.It consists of cathode and anode and liquid
electrolyte. Cathode is made of Lithium metal oxide and anode is made of porous conducting material.
Lithium ions travels from the cathode to anode .A separating membrane is used to allow lithium ions to
pass between the electrodes while preventing an internal short circuit .This arrangement is shown
conceptually in the Figure , with the transport aspects of the battery when operating as an energy source
(i.e., a galvanic device) illustrated—the electrons travel from the negative electrode to the positive
electrode while simultaneously the Li+ ions travel from the negative electrode through the electrolyte to
the positive electrode to maintain electro neutrality. When the system is operated in charge mode (i.e., as
an electrolytic device) the electron current and Li+ ion flow is reversed.
Some of the important properties of this Lithium ion battery
(1) very low density of lithium,
(2) very small radius of lithium, and
(3) very low reduction potential of lithium compared to any other element.

Figure 7.Schematic of Lithium ion battery

There are therefore many choices of materials for the positive and negative electrode materials,
the electrolyte, and the separator. The technological limitations of the various materials are
driven by their function, as detailed below. The electrolyte must offer the highest possible
lithium ion transport under use conditions. The batteries must operate in the general
environment, likely to extend from, e.g., −30 °C for a vehicle that has been parked for a period of
time in extreme cold, to +60 °C for a battery that has heated as a consequence of the combination
of environmental conditions and heat generated by charging

The cost of lithium ion batteries is very high. It is around 1000-2000 $/KWh whereas the cost of
lead acid batteries is 300$/kWh and for Ni-Cd it is around 350 $/KWh and even Lithium ion
battery cost is higher than Ni-Metal hydride. But the price will be reduced because of
combination of different materials used in this type of batteries, they can also used for other
applications after completion of certain number of cycles
As the market grows and production scales up,there will be reduction in costo
The following graph shows reduction of cost of lithium ion batteries over certain period of years.

Figure 11.Graph showing cost of lithium ion batteries vs year

Costs per kilowatt hour (kWh) declined substantially over the study period: “Industry-wide cost
estimates declined by approximately 14% annually between 2007 and 2014.The “learning rate,”
which is the cost reduction after a cumulative doubling of production, was between 6% and 9%.
This indicates that as manufacturing of electric vehicles increases in scale, vehicle-battery costs
per kilowatt hour will continue to drop.Estimates show that the inflection point for batteries is
approximately $150 per kilowatt hour, shown by the rose-colored band in the above graph:

Regardless of their advantages, the practical usage of Lithium ion batteries in the electric vehicle
still has numerous obstacles to overcome. The main drawbacks of lithium ion batteries include
their cost, requiring protection from overcharge/discharge, short circuit and abnormal
temperature behavior, limited current and voltage range and cyclic life problems. In order to
achieve all these properties we can vary the materials used for electrodes in Lithium ion
batteries. Each group of electrode material have their own advantages and limitations, thus
material selection plays a crucial role in applicability of the Lithium ion batter

3.SELECTION OF CATHODE MATERIAL FOR LITHIUM ION BATTERIES:

CATHODE MATERIAL:
The cathode is one of the important components of LIBs. The cathode material must have a
stable crystalline over wide ranges of composition because during the charging cycle, the
oxidation reaction leads to large compositional changes and therefore to unfavorable phase
changes.
Cathode materials can store energy through two different mechanism,
(1) intercalation and
(2) conversion reaction
Conversion electrodes undergo a solid-state redox reaction during lithiation/delithiation, in
which there is a change in the crystalline structure, accompanied by the breaking and
recombining chemical bonds, while the intercalation cathode materials act as a host for Li ions,
so that the ions can insert in or extract from the material reversibly. Metal halides such as FeF2 ,
CoFe, NiF2 are examples of conversion based cathode materials. Due to the high volume
expansion, poor electron conductivity and hysteresis issues, development of conversion based
cathode materials has faced a lot of challenges. So we choose transition metals as cathode
materials. Cathode materials are transition metal oxides due to their higher operating voltage and
the resulting higher energy storage capability
DATA ON AVAILABILITY:
We have following materials available for use of cathode ;(Lithium transition metal oxides)
Lithium Cobalt Oxide (LiCoO2)-
Lithium Nickel Oxide (LiNiO2)
Lithium Manganese Oxide (LiMn2O4)-LMO
Lithium Iron Phosphate (LiFePO4)-LFP
Lithium Nickel Manganese Cobalt Oxide (Li(NixMnyCo1−x−y)O2)-NMC
Lithium Nickel Cobalt Aluminum Oxide (Li(NixCoyAl1−x−y)O2) -NCA

DATA ON REQUIREMENT :
Output voltage
Specific energy capacity
Specific power.
Life span
Cost
Safety

3.1.Lithium Cobalt Oxide (LiCoO2)

Lithium Cobalt Oxide (LiCoO2) is very reactive and therefore suffers from poor thermal stability
and must be monitored during operation to ensure safe use. The limited availability of cobalt also
makes it more expensive and difficult to be a viable option for use in EVs.
The cathode reaction is represented as
LiCoO2= 1/2 Li+ + 1/2 e- + Li0.5CoO2

3.2.Lithium Nickel Oxide (LiNiO2)

LiNiO2 was recognized as a promising material for high voltage batteries (i.e., an approx. 4 V
vs. Li/Li+ electrode potential), because it is a lower cost material (it is Co free) and has a high
theoretical capacity of 250 Ah kg−1. The formation of a self-passivation layer at the surfaces
caused difficulties with its use. Because stoichiometric LiNiO2 requires great care in
manufacture, and is a somewhat less practical electrode material.

3.3.Lithium Manganese Oxide (LiMn2O4)

It gives lower internal resistance and good current handling. Low internal cell resistance enables
fast charging and high-current discharging. Li-manganese can be discharged at currents of 20–30
A with moderate heat buildup in an 18,650 package.This chemistry provides better thermal
stability than the lithium cobalt oxide battery but results in approximately 33% lower capacity
and a lower life span. .

3.4.Lithium Iron Phosphate (LiFePO4)

LiFePO4 (LFP) offers good electrochemical performance with low resistance, besides high
current rating and long cycle life. The phosphate helps to stabilize the electrode against
overcharging and provides a higher tolerance to heat which limits the breakdown of the material.
These batteries have a wide temperature range and can operate between +60 ◦C to −30 ◦C.
LiFePO4 has a higher self-discharge than other Li-ion batteries, which can cause balancing
issues with aging. Further, moisture seems to significantly limit the lifetime of the battery.

3.5.Lithium Nickel Manganese Cobalt Oxide (Li(NixMnyCo1−x−y)O2)

Lithium Nickel Manganese Cobalt Oxide (NMC) electrodes can be designed for high specific
energy or power with high density: Nickel is known for its high specific energy but poor
stability; manganese has the benefit of forming a spinel structure to achieve low internal
resistance but offers a low specific energy . Combining nickel and manganese enhances each
other’s strengths, making NMC the most successful Li-ion system and suitable for EV .

3.6 Lithium Nickel Cobalt Aluminum Oxide (Li(NixCoyAl1−x−y)O2)

It shares similarities with NMC by offering high specific energy and specific power (the rate at
which the battery can deliver energy), and a long life span. NCA is not as safe as the others listed
above and as such, require special safety monitoring measures to be employed for use in EVs.
They are also more costly to manufacture, limiting their viability for use in other applications .

Figure 9.Different potentialls for different

cathode materials.
 Figure 10.Comparision of different properties for different cathode materials.

Comparisons of different types of Li-ion batteries used in EVs from the following perspectives:
specific energy (capacity), specific power, safety, performance, life span, and cost.
As we compare all the properties ,one of the most important parameters is specific power .As we
can see from the above chart ,only Lithium Iron Phosphate (LiFePO4 ) has the highest specific
power .The next important property for the electrode is the specific energy capacity which is
highest for the Lithium Nickel Manganese Cobalt Oxide (NMC).The voltage output of the
Lithium Nickel Manganese Cobalt Oxide (NMC) and Lithium Nickel Cobalt aluminium oxide
(NCA) has the same output voltage of 3.8V.The Lithium Titanium oxide has good life span and
safer material compared to all other electrode materials for anode but the output voltage of
around 2.5V which is very very small which makes it a bad option for using this material as a
cathode material for the electric vehicles
 By comparing all the properties NMC is the only electrode material which is touching all the
sixth hexagon corners for all the properties equally (Cost,Lifespan,Safety,Specific power)
and it is having highest specific energy capacity and it is also having good output voltage
compared to other electrode material .So we can select this material as cathode material for
its use in Lithium ion battery.
4.ANODE MATERIALS:
The anode material acts as host for Lithium ions during charging and their movement to original
position during discharging. In order to select the material for anode it should be porous and
should have good conductivity based on this qualities we got the following materials

DATA ON AVAILABILITY
Carbon based electrodes (graphite ,carbon nanotubes and carbon nanofibres).(Based on
intercalation reaction).
Lithium Titanate (Li4Ti5O12)
Lithium Metal
Silicon (material based on alloy reactions)
Conversion Electrodes( electrodes based on conversion reactions).

DATA ON REQUIREMENT
High specific capacity
Low electrode potential (So that the difference between the positive and negative electrode
should be high ,as we selected cathode material having highe electrode potentail ,the anode
should have less electrode potential)
Low cost

4.1 Carbon Based Electrodes

Carbon usually synthetic graphite ,low average voltage and a relatively flat voltage rendering a
high overall cell voltage and high round trip energy efficiency . It is a very abundant, low cost
and non-toxic material. Regrettably, under some specific conditions, carbon reacts with
atmospheric oxygen, and in the case of a thermal runaway event, the electrode can catch fire
Increasing the surface area of the carbonaceous materials can provide more space for Li ions
accommodation between the layers and therefore higher attainable capacity. New carbon
materials such as carbon Nano fibers (CNF), carbon nanotubes (CNT) and graphene can also be
used .
4.2 Lithium Titanate (Li4Ti5O12)
Li-titanate (LTO) forms into a spinel structure.. It has zero volume change during lithiation,
leading to an extremely long operational lifetime for the electrode, coupled with the improved
safety owing to an extremely flat discharge and charge plateau at about 1.55 V vs. Li/Li+ . This
material has low electronic conductivity and the Li+ diffusion coefficient of this material can
result in poor performance at high power levels,

4.3 Lithium Metal:

The significant electrode capacity may decrease the mass of the negative electrode by an order of
magnitude, and possibly decrease the mass of the overall battery by about a third. Unfortunately,
Li metal electrodes in secondary batteries have proved challenging due to the growth of metallic
dendrites during Li plating/stripping, with short circuit caused by the dendrites leading to thermal
runaway and a risk of fire/explosion.

4.4 Silicon Based Electrodes

The lithium–silicon alloy has, in its fully lithiated composition, has higher specific capacity
compared to other conventional materials. The major issue with this electrode chemistry is the
significant volumetric change of the electrode material, where the transition between Si and
Li15Si4 causes a 280% volumetric change. Additional drawbacks of Si are a low Li+ diffusion
coefficient and high electrical resistivity

4.5 Conversion Electrodes

A different type of electrode material than the lithium intercalation metal oxide based electrodes
is the conversion electrode. In a conversion electrode, an actual chemical reaction takes place, as
opposed to the mere intercalation of the Li+ ions into the lattice of a host material. But specific
capacity much less than the silicon. Because of less specific capacity it is not recommended
compared to silicon as anode material.
 Figure 11.Graph Potential Vs Specific capacity for different electrode materials

Finally as we can see from the above graph and above mentioned properties ,
As we selected NMC as a cathode material inorder to have high electrode potential difference the
material for anode should have less electrode potentials ,So we cannot select Lithium Titanate
(Li4Ti5O12) and conversion electrodes as anode material as they are having 1.5V and 0.95V
respectively which can be depicted from above graph.
As we can see from the graph materials having highest capacity are Lithium Metal and Lithium
(Silicon) alloy .The use of Lithium metal has a chances of causing fire explosion which do not
make this material as a good choice for anode material. So even though the Silicon has
disadvantages like higher volume expansion and higher electrical resistivity, they can be
overcome. The use of Nanostructured Si, makes it accommodate volume expansion and using
heavily doped Si embedded in conductive matrices appears to lead to significantly improved
mechanical and electrical properties.
So we can select Silicon alloy as material for the anode in Lithium ion batteries for electric
vehicles.

5.ELECTROLYTE
The electrolyte is an essential part of the battery, providing ionic conductivity enabling Li+ ions
to shuttle between the two electrodes, while not being electronically conductive. The electrolyte
used varies based on the choice of electrode materials, but is typically composed of a mixture of
lithium salts (e.g., LiPF6) and an organic solvent (e.g., diethyl carbonate) to allow for ion
transfer.

6.BATTERY ARRANGEMENT IN ELECTRC VEHILE

 Figure 12.Image showing Battery pack and Induction motor

The battery pack gives DC power which is converted into AC power by using invertor. Battery
pack consists of 16 such modules constituting around 7000 cells.

Fig 13.Single module of battery

pack
 Fig 14. Inside the Single
module of battery pack

In each module numbers of cylindrical cells are arranged. These cylindrical cells are made of
Lithium ion battery which is connected in series and parallel. The glycol coolant is passed
through the inner tubes between the gaps .By using more number of small cells instead of big
cells, good amount of cooling is guaranteed. This minimizes thermal hotspots and increases the
life of battery pack.

Fig 15. Different Lithium ions

cells

Only cylindrical cells are preferred over other shapes because of the following
 They are easy to manufacture and are having good mechanical stability
 Good Positive thermal coefficient for safety
 Good cycling ability –good life spans
 When they are arranged on the surface they do not completely utilize the space but the gaps
between the cells can be used for cooling which increases life span.cylinderical cells donot
change in size while pouch and prismatic changes its size that means they undergo swelling
after sometime. They are also having good surface area.so that the cooling of the cell can be
done easily.
:

Fig 16. Lithium ion cylindrical

cell.

7.MANUFACTURING OF CYLINDRICAL CELLS :

Fig 17. Manufacturing of cell.

8.REFERENCES:

1) https://jufgnsm.ut.ac.ir/article_65962_e2ac924572aef78efb17de9faa5e4bbe.pdf
2) https://www.osti.gov/servlets/purl/1430487
3) file:///Users/rajkumar/Downloads/energies-12-01074.pdf
4) https://pubs.rsc.org/en/content/articlelanding/2017/cs/c6cs00875e#!divAbstract
5) https://www.researchgate.net/publication/327022861_Electrode_materials_for_lithium-
ion_batteries
6) https://www.sigmaaldrich.com/technical-documents/articles/material-matters/electrode-
materials-for-lithium-ion-batteries.html
7) https://www.researchgate.net/publication/294580055_Lithium-
ion_Batteries_for_Electric_Vehicles_the_US_Value_Chain
8) https://www.osti.gov/servlets/purl/1430487
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10)https://matmatch.com/blog/what-materials-are-behind-the-ev-battery-revolution/