In Search of the Flux Capacitor - Part 2

Continued from Part One

I GOT THE POWER

Jay Leno's voluminous garage suggests why. "I have a 1909 Baker Electric," boasts the coiffed comedian, who's as renowned for his car collection as his Woganesque humour. "That goes 110 miles on a single charge." What's more, it still works. "I have never done any maintenance," he insists, "other than maybe greasing the wheel hubs." To consumers reared on built-in obsolescence, to say nothing of the business plans depending on it, this can come as a shock. "You don't do anything," Leno repeats. "You plug it in, charge it and drive it. The motor is virtually maintenance-free." Apart from the Tesla, which makes similar boast about servicing, there are few cars in production or in the pipeline that can match the Baker's mileage, even if they could run it off the road. The Th!nk City, for example, due like half a dozen other mini EVs to hit U.S. tarmac by 2010, claims to get 124 miles per charge, though it would be less if you drove flat out at 60 mph.

Not much had changed in battery technology when the EV1 was launched. Its lead acid cells used 100-year-old science and although fairly effective they were heavy and far from ideal. The nickel-metal hydride (Ni-MH) replacements weren't particularly light either, but performance improved quite a bit and some Japanese cars still use something similar. Switching to lithium cells helped shrink mobile phones and the same principle delivers cars more power from less weight, although the Tesla Roadster's half-tonne bulk in the boot does have the advantage of generating more downforce, which comes in handy when navigating tight corners. The obstacle for many years was lithium's reactivity, which is why it can store so much energy. It's enough to "incinerate anybody in the car," warns Barrie Lawson of Axeon, a Dundee-based battery maker that's joined up with Allied Vehicles to launch electric taxis in London. "That's always been the great fear."

In the case of the Tesla, which has passed U.S. crash tests, there are 6,831 little cells to worry about, lined up in 11 separate sheets and grounded in a gloopy substance to keep them apart. Even if one blows it won't affect the others, the company says, so there's nothing to worry about when driving. Even if you crash, and a battery's broken up, an open circuit cuts its current instantly, says Barrie Lawson. Still, a spate of spontaneous laptop combustion spread panic among carmakers. Manufacturing safety checks have been tightened, and Toyota postponed plans to introduce new battery chemistry for the Prius. Lawson cautions against reading too much into this, stressing that the danger from electric parts dislodged in an accident would be "no worse than spilling a tank of petrol." Moreover, he says, "if someone came along today and proposed that you carry this highly inflammable stuff around just with a tank with a thin steel wall around it, they would say you were crazy."

Martin Eberhard concurs. "To me it's actually quite amazing that you can take a relatively small car, smack it into a truck at you know, 50 or 75 miles an hour and the gasoline tank doesn't just explode all over the place every time." Thankfully the same seems to be true for the Tesla, although rival carmakers still make scoffing noises about the number of volatile batteries joined together. In one sense they sort of have a point: the greater the number of cells, the harder it is to ensure that they hold a full charge without them automatically defaulting to the storage capacity of the weakest in the series, which weakens further every time you load it to below maximum. "We've got 72 cells in our battery pack," says Greg Starns, the head of software development at Frazer-Nash Research, another firm which plans to launch electric taxis in London this year. "And we're doing everything we can to make that fewer."

The problem is called equalisation and the solution a battery management system, or interface, which every EV needs to run effectively. The Tesla's was "a huge challenge", says Owen, though he claims it's no longer a concern – the car will load up from its wall-mounted three-phase charger in just three or four hours. Sceptics crunching these numbers say that it might take more than five times longer, at best, using a regular plug socket, but Tesla says an overnight charge is still doable. Nevertheless, this battery set up alone costs between $20-30,000, which is what American consumers are used to paying for a mid-range SUV. Put it in a heavier car, like Tesla's new Model S sedan (which may turn out to be a four-door hatchback if rumours are true), and performance would suffer. Even that vehicle, due in 2010, is expected to sell for somewhere above $60,000. A mass-market model at half that price is still just the stuff of Tesla fantasy, although it's talked about as next on the to do list.

"It all comes back to the battery," says Bill Reinert, of Toyota's U.S. Advanced Technology Group. "If you want to run longer and further on electric power alone, it means a bigger battery, it means charging a battery more fully and discharging it more completely. And it means provisions for cooling or ventilation in order to give the batteries longer life." That means choosing what you want and what you're willing to give up, in terms of space, weight and convenience as well as price. Glyn Owen expects batteries to go like microchips, though his EV version of Moore's law is a more conservative 10-year forecast of doubled power and halved size. "There's room for at least another doubling of capacity," agrees Martin Eberhard, who still holds a chunk of Tesla stock, if not management responsibility for talking up the company's prospects. Barrie Lawson isn't convinced. "There's nothing going to come along and make the battery half the size in the near future," he says. "There's no huge breakthroughs on the horizon that will make a big impact on the chemistry but there are many variations on the chemistry to optimise the battery performance."

It's a question of "flavours of lithium", to use Lawson's favoured phrase. Crudely simplified, batteries use lithium in its ionic form (which means stripping the atoms of an electron to make them positive). When the cell's fully charged, these ions congregate around its anode, which is usually made of graphite. During use, ions migrate within the battery to the other electrode, the cathode, and negatively charged electrons pass between the two via an external circuit that drives the motor. Electrodes are where it gets interesting.

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