Centering equity and the community in Transportation by Richard Ezike
Battery technology for electric cars
1. Battery technology for electric cars
by Jeremy Horne, Ph.D.
Before exploring what may lie in store for battery technology in electric vehicles,
both all-electric and hybrids, we should review what makes up a battery in the first
place. At that point we can begin understand the potentials and limitations of
electron storage as a source of energy for propelling ourselves down the road.
A battery simply is device that stores electrical charges based on the chemistry
used in the materials making it up. The difference in electrical potential (the number
of electrons in one substance) between two substances determines how much
electricity there is. Place your tongue between two coins made of different metals,
such as one made from copper and the other aluminum, and allow the two coins to
touch. You will feel a slight tingle and an acid taste. This is a simple battery, and
what you feel are electrons flowing from the nickel to the penny. Two metals,
commonly immersed in an acidic liquid will act as attraction points, or electrodes,
for charged particles, negative or positive. When a device or electrical resistance
connects the two electrodes current, or electrons, flow. The Table of Periodic
Elements is the basis for calculating electrical potential in materials. The principle of
detecting current is rather ancient.
About the year of 1936 in the village of Khuyut Rabbou'a, near Baghdad, Iraq was
discovered a three piece set of objects consisting of a clay pot with a stopper, a
coiled up sheet of cooper inside, and an iron rod that fit in the middle of the roll. In
1938, these artifacts came to the attention of Wilhelm König, the German director
of the National Museum of Iraq, they being housed right in the same museum! They
have assumed the appellation of “Baghdad battery”. König thought that the artifacts
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2. dated to the Parthian period (between 250 BCE and 224 CE), and that date hasn't
been substantially challenged since [1]. While the assemblage could theoretically be
used in conjunction with an electrolyte to for copper plating or to get a tingling
sensation as in medical therapy or religious ceremonies, the actual ability to do has
shown to be marginal. Nevertheless, it is intriguing to consider that this may have
been the first battery.
Alessandro Volta in 1792 invented a device, an electrochemical cell (called a “pile”)
that could store charges, and in 1800 he placed a number of these in series to make
what could truly be called the first battery, a means of storing electricity using the
chemical properties of materials. The word “pile” means battery in Europe. It can be
argued, however, that the Leyden jar, invented independently by German cleric
Ewald Georg von Kleist on 11 October 1745 and by Dutch scientist Pieter van
Musschenbroek of Leiden (Leyden) in 1745–1746 was the first battery, inasmuch as
it, too could store charges. It has been known since classical Greek times that
stroking an amber rod with cloth will produce sparks, and electrostatic generators
were built to do this mechanically. In fact, "elektron"(ηλεκτρον) is Greek for amber,
and one easily can discern the word being the root word for our present day
“electricity”. Even at the beginning of the 20th century Leyden jars were used
extensively in early wireless telegraphy (spark transmitter) and in equipment for
medical therapy. Now, capacitors are used.
Electrostatic generators were created in the 18th century, often consisting a large
wheel against which were placed soft substances, such as cloth, to “scrape”
electrons off the wheel. By allowing this current from the generator to the Leyden
jar, electrons would flow to electric plates to main until drawn off by coming into
contact with an object. Today, this principle is known as capacitance, and one need
only open up just about any electronic device to see the characteristic barrel-shaped
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3. objects that store electricity and marked often in microfarads (µf). Typically, they
are made of aluminum sheets interleaved with an insulator and coiled to result in
the drum-like shape. There have been numerous designs for the Leyden jar, with
most being constructed of a metallic foil coating both the inner and out part of a
bottle's wall, with the two pieces never touching each other. A conductor, such as a
chain, leads from the center of an insulated cap to the bottom of the jar and
touches the inner foil. The exiting chain has a contact point to which is touched the
discharge point of the electrostatic generator. The outer foil is grounded. When the
outer and inner foil meet, there is a spark, hence electricity.
Water filled Leyden jar (left) and 1914 physics book drawing (right) [2]
Battery construction and operation
There are two battery types, primary, or disposable, and secondary, or
rechargeable. The first are ubiquitous in unsophisticated devices like flashlights,
used one time, and are less expensive per battery. The second is the focal point of
our interest, as they can be used numerous times after recharges, but they are
considerably more costly. Numerous constructions and materials exist, nickel-metal
hydride battery being used in most electric cars in 2009 [3], but, for our discussion,
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4. we consider the lithium-ion battery, as the former are being phased out. They are
the same type of batteries used in laptop computers, cordless tools, and many
electronic devices.
The basic operation occurs in discharge by ionized lithium flowing from the anode
(positive terminal made from lithium embedded in carbon-based materials, usually
graphite) to the electrolyte (composed of lithium salts in organic solvents) through a
plastic separator (a micro porous membrane) and then to the cathode (negative
terminal made of lithium metal oxide or phosphate). Concurrently, the anode
releases electrons to an electric circuit connected to the battery and is oxidized.
Upon re-charging, the process is reversed, with the lithium ions traveling from the
cathode to the anode via the separator and electrolyte. The electrolyte can be
liquid, a gel, or solid polymer, with the greatest ease of ion flow being in the liquid
then the gel, and lastly, the polymer.
Movement of charges in lithium ion battery [4]
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5. Energy usage varies with the type of vehicle, hybrid electric (HEV), plug-in hybrid
electric (PHEV), and straight electric (EV). HEVs use the battery for assisting the
motor, while the PHEVs start out with the battery being the sole source of power
and afterwards only as a power assist, and the latter is the only source of power. In
all cases, a lithium-ion battery is used. The first two require only a shallow cycle
(the battery not being fully charged) and the EV's a deep cycle (where you fully
charge and can drain without damage, marine batteries being an example).
Battery performance for electric vehicle types [5]
There are four parameters that have been used to assess the appropriate battery
for an application, these being energy/weight ratio, energy/volume ratio, power to
weight ratio, and the cost in watt-hours (in the U.S., that being the watt-hours per
dollar). While lead-acid produces more energy per dollar, it still is not suitable for
EVs because of its power per unit weight and energy per volume in watt-hours, as
the following chart illustrates.
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6. Energy/weig Energy/volu
Power/wei Energy/US
Battery ht me
ght $
Type Watt- watt-
watt/Kg watt-hr/$
hours/Kg hours/L
Lead-acid 30-40 60-75 180 4-10
NIckel-Zinc 60-70 170 900 2-3
Lithium-Ion 160 270 1800 3-5
Lithium-
130-200 300 to 2800 3-5
Polymer
Lead polymer batteries are used in hybrid vehicles. [6]
Two other values often are considered, the self-discharge rate, meaning charge
dissipation with age, and the cycle life of the batteries, or how many times the
batteries can undergo a deep or complete discharge and still be re-charged [7].
Problems associated with lithium ion batteries
In terms of efficiency energy per unit mass a lithium ion battery is much lower than
for other power sources, such as petroleum. Weight is a major problem, the metals
used to create the power being the major factor. Most of the weight of the vehicle is
the battery (average of 333 kg – 2009) [8] and motor, of course, most of the
energy expended in powering that vehicle is just to transport the battery itself! A
conventional mid-sized car, by contrast has the power train (v-6 engine – 181 kg -
and transmission) not even half the vehicle weight. Perhaps the most limiting factor
is the range; the average electric car is lucky be able to get 150 range [9]. That
range is extended only in hybrids, such as a gas/natural gas/electric car. There are
environmental costs, not the least of which is the energy to produce them, from the
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7. mining of the minerals, energy required in their manufacturing, and disposal.
Recycling is not easy, as there are not many usable components.
Lithium-ion batteries, while having good power density, have short cycle lives, with
the battery degrading with each recharge. Even sitting on a shelf the battery
degrades. Besides the cathode being somewhat toxic, there is a fire risk if the
battery is punctured or not charged properly. Lithium-ion batteries don't like cold
conditions, and in very cold places, inefficient heating devices have to be used just
to keep the battery going.
A central problem with lithium-ion batteries is their loss of capacity to store
electricity over time. A minor scandal has erupted over Apple's sale of the very
expensive iPods amounting to several hundreds of dollars with their failing a few
short years because of battery's inability to be recharged [10]. Laptops have the
same deficiency, and it is not inexpensive to replace this power source. Scientists
have investigated the problem and discovered that the lithium ions carrying the
electric charges were not only diminished but has accumulated on the anode, with a
lessened concentration of lithium, as opposed to new batteries. One cannot reverse
this problem and only can dispose of the battery. In addition, the nanostructures of
the battery coarsen over time [11].
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8. References (Subject is indicated by URL – accessed 7 October 2011)
[1] http://en.wikipedia.org/wiki/Baghdad_Battery
[2] http://en.wikipedia.org/wiki/Leyden_jar
[3] http://gigaom.com/cleantech/the-future-of-electric-vehicle-batteries-lithium-ion-china/
[4] Lithium-ion Batteries for Electric Vehicles: The U.S. Value Chain, p. 15,
https://docs.google.com/viewer?url=http://www.cggc.duke.edu/pdfs/Lithium-Ion_Batteries_10-5-
10.pdf&embedded=true&chrome=true
[5] Ibid., p. 12
[6] http://www.allaboutbatteries.com/electric_cars.html
[7] http://www.allaboutbatteries.com/electric_cars.html
[8] DOE - http://www.whitehouse.gov/files/documents/Battery-and-Electric-Vehicle-Report-FINAL.pdf
[9] http://www1.eere.energy.gov/vehiclesandfuels/avta/light_duty/fsev/fsev_batteries.html
[10] http://en.wikipedia.org/wiki/IPod_Mini
[11] http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
[12] http://www.whitehouse.gov/files/documents/Battery-and-Electric-Vehicle-Report-FINAL.pdf
[13] http://web.mit.edu/newsoffice/2011/flow-batteries-0606.html
[14] http://www.nrel.gov/vehiclesandfuels/energystorage/ultracapacitors.html
[15] http://www.nrel.gov/vehiclesandfuels/energystorage/ultracapacitors.html
[16] http://arpa-
e.energy.gov/ProgramsProjects/BEEST/TheAllElectronBatteryaquantumleapforwardi.aspx
[17] http://pubs.acs.org/cen/science/88/8847sci1.html, http://www.physorg.com/news176646131.html
[18] http://micro.magnet.fsu.edu/electromag/electricity/batteries/metalair.html
[19] http://www.ict.fraunhofer.de/EN/coreco/AE/Batt_tech/Bat_dev/index.jsp
Resources (Subject is indicated by URL – accessed 7 October 2011)
http://www.sweethaven02.com/ModElec/electrical01/Lesson0402.pdf
http://en.wikipedia.org/wiki/History_of_the_battery
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
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