Batteries
M.Cricchio, A.Pafundi (*) A.Boyali (*) - Linguistic Mediator: G.Galdo (*) |
(*) Istituto Alfano I - (**) Istanbul Technical University |
Summary
In HEV and HSV vehicles the storing system is highly important. In this
section we will learn what a battery is, classification of batteries,
what a battery is used for, how to choose the appropriate battery, what
the Li-Ion battery is, what the charge regulator is and the importance
of charge regulators in a battery system.
What is a Battery?
All electric circuits
must have a source of energy. Circuits in your home get their energy from
power plants that generate electricity. Circuits in flashlights, cell
phones, and portable radios get their energy from batteries. In science
and technology, a battery is a device that stores energy and makes it
available in an electrical form
Classification of Batteries
Batteries can be roughly divided into physical
and chemical batteries. Batteries of a chemical type which can be repeatedly
charged are called rechargeable batteries. There are various types of
rechargeable batteries like the lead-acid batteries used in automobiles
and the smaller sized nickel cadmium rechargeable batteries. There are
also nickel metal hydride and lithium ion rechargeable batteries.
Choosing The Appropriate Battery
In HEV and HSV vehicles the storing system
is highly important. In fact, the storage system - stores the produced
energy - distributes energy while driving Batteries store energy. They
are also called secondary generators. There are too many different kinds
of batteries. Choosing the right battery for the right application is
very important. For example, in an electrical car, we have some significant
criterias such as:
- Rechargeable or not : In an electrical
car we must choose rechargeable batteries if we don’t want to change
all the pack for every cycle..
- Weight: Weight is an important design
factor. It is very important to choose lighter batteries in an electrical
car.
- Energy Density: This specification
relates energy storage capacity to weight, so using high density batteries
will be more effective in an electric car.
- Cycle Life: It is a criterion for
rechargable batteries and tells us how many times we can recharge the
battery. Using high cycle life batteries will reduce the battery cost.
- Voltage Capability: Some battery
kinds are not able to give high voltage. So we must calculate if the
battery pack can reach the required voltage or not.
- Security: Related to natural conditions
(temperature, humidity, shorting the battery etc.) some kinds of batteries
may explode and cause danger. We should consider the environmental conditions
also while choosing the battery system.
- Memory Effect: The memory effect is a condition of rechargeable Nickel
Cadmium and Nickel Metal Hydride batteries in which it their charge
holding capacity decreases with time.
Present performance data of different batteries is presented in the table
given below.
System |
Voltage |
Energy |
Autodiscarging |
Number of Cycles |
Comments |
Pb-Acid |
2.05 |
35-40 |
4 |
300-500 |
Low cost |
Ni-Cd |
1.2 |
40-60 |
10-20 |
1000-1500 |
Memory effect |
Ni-MeH |
1.2 |
60 |
30 |
300-500 |
Low memory effect |
Li-ion |
3.6 |
115 |
5-10 |
500-1000 |
No memory effect |
Zn-aria |
1.2 |
145 |
5 |
- |
- |
Data from: C.A. MATTIA - Termodinamica Chimica 2005 – Università
degli Studi di Salerno
Li-ion Battery
Having great performances, Li-ions batteries have superb storing systems
performance. They are still expensive because of the high cost of the
materials (catalysts) necessary to speed up the electrochemical reactions
inside the battery.
They are
- Fully efficient in conversion.
- Easy to work with and
- Have high specific energy.
|
Structure
of a Li-Ion Battery |
A Li-ion battery consists of
- A spiral structure,
- rolled up thin plates
- Lithium oxide on a carbon conductive polymer characterized by small
hollows
- A cathode that contains lithium in the reticular structure material
(generally oxides)
- Micro hollows
They have high energy to weight ratio, and there is no memory effect.
|
Carbon–Li
cell working scheme |
The negative electrode is based on the natural graphite highly crystalline
structure with small quantities (23%) of alloy materials that form ~100
micron layers on a thin copper plate or copper net. The positive electrode
is based on LiMn2-xMnxO4 (with x~0,05) and is supported on 100 -150 micron
layers of aluminium plate or net. Between the cathode and the anode is
a separating layer of fibreglass or microporous polyethylene soaked in
a not watery solution, for example LiClO4 in ethylenecarbonate/dimethylcarbonate.
The electrode separating kit is rolled up and inserted in a cylindrical
container. The solution is added into the inert atmosphere to avoid the
contamination due to the atmospheric humidity that would deteriorate the
graphite. It consists of a charging process and successive setting of
a passive film on the graphite to ensure further battery cycles. During
this phase CO2 is emitted and is sealed only at the end of the charging
process. Graphite Intercalation Compound (GIC) anodes have been used to
substitute for the graphite. KC8 electrodes release potassium originating
“expanded graphite” during the first charge. In the following cycles works
like the natural one obtaining resulting in quicker kinetics.
Li-polymer Batteries
A Li-polymer battery is very different from the Li-ion one. The electrolyte
is a solid conductive polymer with the advantage that the battery is completely
dry instead of being being kept in an organic solution.
Charge Regulators
In most applications, we use rechargeable
batteries. Thus charge-discharge characteristics are very important for
security and efficiency of the battery system. Due to this point, we need
some devices which charge batteries appropriately depending on the their
charge characteristics and which prevent overcharging - discharging of
the system. We call these devices “charge regulators”. There are several
kinds of charge regulators with different properties. Some charge regulators
first determine the kind of battery which they will charge. After that,
they use the appropriate charging algorithm for that kind of battery.
So, these kinds of charge regulators are able to charge more than one
type of battery. We should consider the voltage and current limits of
charge regulators while choosing them.
References
Douglas R. Carol, 2003, “The Winning Solarcar”, 1.Edition
Links
http://www.energoclub.it/accumulatori-elettrochimici-batterie.htm
http://www.area.fi.cnr.it/r&f/n4/pistoia.htm
http://www.unicam.it
http://www.fi.cnr.it
http://www.cpo.com/pdf/Physics%20First/EBook/PFC%20U5.pdf
http://www.batteryuniversity.com/partone-3.htm
http://www.speedace.info/lithium_ion_electric_car.htm
http://www.greencarcongress.com/2005/11/a123systems_lau.html
http://www.solarnavigator.net/batteries.htm
http://www.electricitystorage.org
http://www.e-mobile.ch/pdf/2005/Subat_WP5-006.pdf
Top - Previous Module
- Next Module |