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How Super Capacitors May Super Charge Electric Car Use
Technology Briefing |
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TranscriptElectric cars are very popular in Norway; so much so that electric cars topped the list of new vehicle registrations for the second year in a row. However that's certainly not true in Germany or the United States, where electric vehicles claim only a very small portion of the market. For example, of the 43 million cars on the roads in Germany, a mere 8,000 are powered by electricity. The main factors discouraging motorists in Germany from switching to electric vehicles are their high upfront 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 many times shorter than for electrics. However, the charging durations could be dramatically shortened with the inclusion of super-capacitors based on innovative nano-materials. Why? The biggest factor is charge/discharge speed. For instance, consider traditional gasoline-powered vehicles: The action of braking converts the kinetic energy into heat, which is dissipated and unused. On the contrary, generators on electric vehicles are able to tap into this kinetic energy by converting it into electricity for further usage. However, since this electricity often comes in jolts, it requires storage devices that can withstand large energy inputs within a very short period of time. Supercapacitors are known to possess high power density, whereby large amounts of electrical energy can be provided or captured within short durations. However, they have a low energy density; that is, the amount of energy that super-capacitors are able to store is generally only about 10 percent of the amount stored in electrochemical batteries of the same weight. That's the challenge of the ElectroGraph project supported by the EU and a consortium of research institutes and industry groups. One of its main tasks is to develop new types of super-capacitors with significantly improved energy storage capacities. The ElectroGraph project did so by designing lightweight electrodes with larger usable surfaces. In numerous tests, the researchers investigated the nano-material graphene, which consists of an ultrathin mono-layer lattice made of carbon atoms; this gives it an extremely high specific surface area of up to 2,600 square meters per gram and high electrical conductivity. When used as an electrode material, it greatly increases the surface area per unit weight versus any other available material. As such, graphene has demonstrated its potential to replace activated carbon, the material that has been used in commercial super-capacitors so far. Graphene-based electrodes, together with ionic liquid electrolytes, present an ideal material combination that can operate at higher voltages. To do this, the researchers were able to establish a manufacturing method that prevents the individual graphene layers from restacking into graphite and reducing the amount of energy storage capacity. The graphene-based electrodes produced by the ElectroGraph project have already surpassed commercially available ones by 75 percent in terms of storage capacity. As we discussed in the most recent issue of our sister-publication, Trends, cars of the future may combine cost-effective flow batteries with state-of-the-art super-capacitors. This combination will store energy cheaply for optimal range, while effectively supplying power surges during high-demand phases like acceleration when ramping up the air-conditioning system. These capacitors will also ease the burden on the battery and cover voltage peaks when starting the car. As a result, the massive size of batteries can be reduced. |
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