uni'wissen 01-2012_ENG

wants to see on the streets by 2020 have hit the pavement. The electric motor itself is not the problem. It is regarded as technically mature. Hardly another machine – and certainly not the combustion engine – can hold a candle to it as far as energy efficiency is concerned. Whereas diesel engines convert a maximum of 50 percent of the energy fed to them into the acceleration of the car, and gasoline engines even less, electric motors can achieve up to 99 percent. Outside of reducing their weight, there is hardly anything left for engineers to improve on electric motors. Current Batteries Are Too Heavy The weak point is energy storage. “In order to power a car for 500 kilometers without being recharged, a battery built according to current technology would have to weigh 800 or 900 kilo grams,” says Krossing. “Much too heavy.” That would be 0.5 megajoules of energy per kilogram of battery. By way of comparison, a kilogram of gasoline contains around 43 megajoules of energy. It will thus be necessary to develop bat teries with much higher storage capacities in order to meet the needs of drivers. Low energy capacity is not the only problem with the batteries. The materials they are made of also need to be able to hold up under extreme conditions. After all, a car needs to run even in the middle of winter or on a hot summer day. The electrolyte fluid is particularly sensitive. If temper atures drop below minus 20 degrees Celsius, the electrolyte cannot form any crystals and the battery will not deliver any power. If the electrolyte is too hot, on the other hand, the salts dissolve in the solution and trigger further irreversible chem ical processes. This ruins the battery and must therefore be avoided at all costs. The Problem is the Price This is where Krossing’s research comes in. “This isn’t an academic problem but a technical problem,” he says. “There are electrolytes that withstand the extreme temperatures. For exam ple, we built a battery and left it in an oven for a week at 80 degrees Celsius. When we took it back out, it functioned perfectly.” The problem is not whether it is possible to build such batteries, but how expensive they are. “Our battery salts cost 500 euros per kilogram. That is alright for conducting research.” The electrolyte salts used in production lithium-ion batteries for flashlights, mobile telephones, or laptop computers currently cost around 30 euros per kilogram. “That’s what we’re aiming at.” The electrolytes will also play an important role in the necessary reduction of weight. Better electrolytes hold a higher charge without causing the battery to self-discharge. This means that “In order to power a car for 500 kilometers without being recharged, a battery built according to current technology would have to weigh 800 or 900 kilograms” Technically mature: Small-scale lithium- ion batteries are already mass produced for devices like mobile phones. Photo: WoGi/Fotolia 33

uni'wissen 01-2012_ENG

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