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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

 

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