Wednesday, October 27, 2010

Materials Science: Use Your Electric Car's Bodywork as the Battery

From the Economist:

Making the bodywork

COMPARED with other electric vehicles, the Tesla Roadster is what you might call a hot rod. With an impressive range of 380km (236 miles) between charges, the two-seater sports car is capable of going from zero to 96kph in just 3.9 seconds. But as is so often the case, such performance comes at a cost. For a vehicle that weighs around 1,200kg (2,645 pounds) a whopping 450kg of that is taken up by the car’s batteries.

Although new battery technologies are emerging, their weight and size is likely to remain a drag on the development of electric and hybrid cars, forcing manufacturers to come up with new and inventive ways to shed weight and free up space. One solution which researchers are exploring is to build cars using a hybrid material: a carbon composite that is also capable of storing electrical energy. That way, car designers could combine structural form with electrical function.

Carbon composites are extremely strong and light. They are already used in products ranging from tennis racquets to aircraft wings. Some supercars are built with the material, but it is generally too expensive for mass-produced vehicles. With the additional ability to store energy, however, carbon composites could become a lot more attractive for the automotive industry, says Emile Greenhalgh of Imperial College, London, who is leading the research as part of a broader European Union project called STORAGE into incorporating different battery materials into the bodywork of a car. The work’s academic and industrial partners include the British Ministry of Defence, which is interested in extending the range of robotic drones, and Volvo, a carmaker.

Like traditional composites, Dr Greenhalgh’s material consists of woven sheets of carbon fibres which are made rigid using a cured resin. To enable this material to store electrical energy, two layers of woven fibres are made into a sandwich, separated by a thin layer of a glass-based insulating material. The resin within the carbon layers is laced with lithium ions, so that each layer acts like an electrode, causing the positively charged lithium ions to collect in one layer when a voltage is applied, and a current to flow when the sandwich is placed in a circuit. All this is encapsulated within further layers to ensure that it is electrically isolated.
Strictly speaking the composite behaves less like a battery than a capacitor, or rather a supercapacitor, says Dr Greenhalgh....MORE