Electric cars are very much
welcomed in Norway and they are a common sight on the roads of the
Scandinavian country – so much so that electric cars topped the list of new
vehicle registrations for the second time. This poses a stark contrast to the
situation in Germany, where electric vehicles claim only a small portion of
the market. Of the 43 million cars on the roads in Germany, only a mere 8000
are electric powered.
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The main factors discouraging
motorists in Germany from switching to electric vehicles are the high
investments cost, their short driving ranges and the lack of charging
stations. Another major obstacle en route to the mass acceptance of electric
cars is the charging time involved. The minutes involved in refueling
conventional cars are so many folds shorter that it makes the situation
almost incomparable.
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However, the charging durations
could be dramatically shortened with the inclusion of supercapacitors. These
alternative energy storage devices are fast charging and can therefore better
support the use of economical energy in electric cars. Taking traditional
gasoline-powered vehicles for instance, the action of braking converts the
kinetic energy into heat which is dissipated and unused. Per contra,
generators on electric vehicles are able to tap into the kinetic energy by
converting it into electricity for further usage. This electricity often
comes in jolts and requires storage devices that can withstand high amount of
energy input within a short period of time. In this example, supercapacitors
with their capability in capturing and storing this converted energy in an
instant fits in the picture wholly.
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Unlike batteries that offer
limited charging/discharging rates, supercapacitors require only seconds to
charge and can feed the electric power back into the air-conditioning
systems, defogger, radio, etc. as required.
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Rapid energy storage devices are
distinguished by their energy and power density characteristics – in other
words, the amount of electrical energy the device can deliver with respect to
its mass and within a given period of time.
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Supercapacitors are known to
possess high power density, whereby large amounts of electrical energy can be
provided or captured within short durations, albeit at a short-coming of low
energy density. The amount of energy in which supercapacitors are able to
store is generally about 10% that of electrochemical batteries (when the two
devices of same weight are being compared).
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This is precisely where the
challenge lies and what the ElectroGraph project is attempting to address.
ElectroGraph is a project supported by the EU and its consortium consists of
ten partners from both research institutes and industries. One of the main
tasks of this project is to develop new types of supercapacitors with significantly
improved energy storage capacities.
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As the project is approaches its
closing phase in June, the project coordinator at Fraunhofer Institute for
Manufacturing Engineering and Automation IPA in Stuttgart, Carsten Glanz
explained the concept and approach taken en route to its successful
conclusion: “during the storage process, the electrical energy is stored as
charged particles attached on the electrode material.” “So to store more
energy efficiently, we designed light weight electrodes with larger, usable
surfaces.”
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Graphene
electrodes significantly improve energy efficiency
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In numerous tests, the researcher
and his team investigated the nano-material graphene, whose extremely high
specific surface area of up to 2,600 m2/g and high electrical conductivity
practically cries out for use as an electrode material. It consists of an
ultrathin monolayer lattice made of carbon atoms. When used as an electrode
material, it greatly increases the surface area with the same amount of
material. From this aspect, graphene is showing its potential in replacing
activated carbon – the material that has been used in commercial
supercapacitors to date – which has a specific surface area between 1000 and
1800 m2/g.
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“The space between the electrodes
is filled with a liquid electrolyte,” revealed Glanz. “We use ionic liquids
for this purpose. Graphene-based electrodes together with ionic liquid
electrolytes present an ideal material combination where we can operate at
higher voltages.”
By
arranging the graphene layers in a manner that there is a gap between the
individual layers, the researchers were able to establish a manufacturing
method that efficiently uses the intrinsic surface area available of this
nano-material. This prevents the individual graphene layers from restacking
into graphite, which would reduce the storage surface and consequently the
amount of energy storage capacity.
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“Our
electrodes have already surpassed commercially available one by 75 percent
in terms of storage capacity,” emphasizes the engineer. “I imagine that the
cars of the future will have a battery connected to many capacitors spread
throughout the vehicle, which will take over energy supply during
high-power demand phases during acceleration for example and ramming up of
the air-conditioning system. These capacitors will ease the burden on the
battery and cover voltage peaks when starting the car. As a result, the
size of massive batteries can be reduced.”
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Source: Fraunhofer Gesellschaft,&
nanowerk
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