Re*Move: A better battery to push EVs?

Up until now, car batteries have been a bit like films. Bear with me. There's an old film adage, which goes "quick, cheap, or good - pick two". You can have a good film on the cheap, but it won't happen quickly. Or you can makes something quick and cheaply - but no one will want to watch it.

With car batteries, the equivalents of quick, cheap and good are "range, charge time and cost". Except at the moment, it's more like 'pick one' than the film world's 'pick two'. As Top Gear reported when they conducted something of a hatchet job on the Tesla Roadster, currently lithium-ions cost the earth, on a standard US plug will take 8-16 hours to charge up a battery, which when hammered round a track, last for only about 50 miles.

Yet with any immature technology - and in the great scheme of things, lithium-ions are very young - come quantum leaps in performance improvement over time. As scientists and engineers experiment with battery chemistry, we often hear of new developments claiming to be the battery world's 'eureka' moment. So it's tempting to greet new announcements with scepticism, but the latest battery news genuinely appears to offer hope - not least because it comes from the brains at MIT...

The issue with ions

Lithium-ions get hot (felt the back of your phone or laptop when you've taxed it recently?). In extreme cases they overheat, and there have been various fire-related scare stories. The best ones in cars right now, even when hooked up to a special wall-socket convertor, take a couple of hours to charge. That's an issue for Joe Blogs who can currently fill a car in five minutes, with enough fuel to do 600km. This latter point, particularly, appears to represent one of the biggest hurdles to widescale electric vehicle adoption. But the MIT team discovered that by creating what they term a "beltway" to guide the ions as they pass through micro "tunnels" in the battery material, the movement of ions could occur much more quickly, ultimately meaning that the battery could be charged faster. Much faster. 30 times faster.

They also used lithium iron phosphate chemistry, instead of the lithium cobalt employed in current lithium-ion units. The phosphate units apparently don't suffer from overheating issues in the way the cobalt ones can. Completing the good news is the fact that lithium iron phosphate is cheaper than lithium cobalt. The technology has largely been ignored up until now because it's capable of holding less charge per given weight of material than the lithium cobalt in lithium ions (in other word's it's less energy dense). This causes problems, as reducing battery pack size and weight is a critical issue for automotive applications. However, the MIT team seem to think that using phosphate chemistry overcomes that issue too, because it doesn't lose its capacity to charge over time, in the way lithium cobalt does. Therefore, less 'redundant capacity' needs to be built into the battery in the first instance, allowing the unit to be smaller (and presumably weigh less).

We've had false starts before, but MIT have a habit of making breakthroughs - and already have relationships with big battery and car firms alike. So although we'd hesitate to say this could be the true breakthrough the world's been searching for in connection with lithium batteries, it does look highly promising. Fingers crossed.

Thanks to Sarah and Vinay for the tip-offs.

Posted by Joseph Simpson on 12th March 2009