Research into lithium-air batteries that have the same energy density as gasoline and with potential use in tractor trailers, is actively being investigated by Risø DTU, the National Laboratory for Sustainable Energy of the Technical University of Denmark. The research aims to remove the Achilles' heel of the electric car which is the limited energy density of today's batteries, which will only sustain short drives.

For electric cars to become the consumers' preferred mode of transport, the battery capacity must be significantly increased. The energy density in today's batteries is almost two orders lower than that of fossil fuels. This means that a battery pack containing energy corresponding to 50 litres of petrol, would weigh between 1.5 and 2 tonnes.

The most promising electric car batteries are based on the metal lithium (Li). Lithium is a soft, silver-white metal and is the lightest of all metals. It is extremely reactive and corrodes quickly in a humid atmosphere. It is typically stored under kerosene to avoid contact with oxygen and water. The lightness is one of the strengths of lithium. Traditional car batteries are based on lead (Pb), which is one of the heaviest metals in existence. To reduce the weight of batteries, lithium is the way to go.

Lithium is naturally occurring with approx. 65 g per tonne in top soil and approx. 0.1 g per tonne of water and can be extracted from soil as well as water, but if the lithium content is small, the extraction is costly.

Lithium is also used in anti-depressants, ceramics, glass, aluminium production, lubricants and synthetic rubber. The world's lithium reserves are found in countries such as Chile, China, Australia, Russia, Argentina, the USA, Zimbabwe and Bolivia. Lately, large deposits have been found in Afghanistan - so large that the USA has dubbed the country 'the Saudi Arabia of lithium'. In Bolivia, lithium is found in large quantities under Salar de Uyuni - the world's largest salt lake. Last year, Bolivia's president Morales announced that the country is going to invest $967 million in extracting lithium from the dried-out salt lake that covers more than 10,000 square kilometres and contains more than a quarter of the world's total lithium deposits.

The fight over the world's lithium resources will intensify in the future, but the upside is that the lithium part of batteries can be recycled, so when the batteries are worn out, the lithium can be extracted and form part of a new battery.

Li-air batteries are a promising opportunity in the long term. "If we succeed in developing this technology, we are facing the ultimate break-through for electric cars, because in practice, the energy density of Li-air batteries will be comparable to that of petrol and diesel, if you take into account that a combustion engine only has an efficiency of around 30 per cent," says Tejs Vegge, senior scientist in the Materials Research Division of Risø DTU. This makes battery powered trucks possible.