You've probably swapped batteries between remote controls and digital cameras, but how about between your laptop and a 120mph all-electric sports car? The £87,000 Tesla Roadster, the first motorway-legal production electric car on British roads, uses the very same lithium-ion cells as humble notebook computers.
The reason that identical batteries are found in such different devices is simple. Lithium-ion cells store the most energy for the lowest weight, and can be recharged hundreds of times without losing their capacity. If the Roadster used old-fashioned lead-acid technology, its batteries would weigh as much as an entire Toyota Prius.
But lithium-ion batteries are far from perfect. They are expensive – up to a third of the cost of the whole car – and there are safety issues, although the potential for these batteries to heat up is why car manufacturers rely on complex liquid-cooling systems. And while laptop batteries might contain just six or eight lithium-ion cells, the Tesla Roadster houses more than 6,800.
They also suffer in range and capacity. The Mitsubishi i-MiEV has a battery that stores the equivalent of half a gallon of petrol and takes seven hours to fully recharge.
However, quick chargers are coming soon, promising to take batteries from empty to 80% full in 15-30 minutes, and new technologies are on the horizon. "The only way that electric cars can become what people expect is if some radical innovation, like the ones we are funding, become real," says Vinod Khosla, a Silicon Valley venture capitalist. "We have two solid-state lithium-ion batteries with none of the liquid electrolytes that cause safety problems."
Other companies are looking further afield. Zinc-air batteries are theoretically much lighter and cheaper than lithium-ion cells, using oxygen from the air to oxidise zinc electrodes and create an electric current. Single-use zinc-air batteries have been around for years, and now Swiss company ReVolt claims to have cracked the problem of making them rechargeable – although only for tiny hearing-aid batteries so far.
Fuel cells are another potential power source. These electrochemical systems generate electricity cleanly from the reaction between oxygen and hydrogen, producing only water as a byproduct. However, fuel cells will only catch on once hydrogen fuelling stations are widespread .
"It's the wild west in energy storage right now," says JB Straubel, chief technical officer at Tesla Motors. "We can try to predict what will come in 10 years but it will likely be something from a completely different direction."
So although Tesla's next car, the Model S sedan, will ship with a lithium-ion battery, the company plans to let customers substitute other technologies as they become available. "People will be able to buy a new-generation battery 10 years after they bought the car," says Straubel. "It might have radically different capabilities – a 400-mile range or better power – and be cheaper than the initial pack."
Just don't expect to be able to put it into your laptop when you're done.
