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Getting the chemistry right

The industry is serious about electric cars but there are many technical uncertainties about the battery technology, writes John Pullin

Hydrogen is No 1, helium next, and then…? A generation ago, you could be forgiven for not knowing that the third lightest element on the periodic table, and the lightest metal of all, is lithium. These days it’s on many lips and in many pockets.

Battery build: GM is spending $43 million to construct the first indigenous lithium-ion plant in the US

And it’s the subject of massive public and private investment in the automotive industry. A month or so ago, Nissan, with a little help from Gordon Brown, announced that it would build its first European plants to produce lithium-ion batteries for electric vehicles, with the “mother site” at Sunderland. Across the Atlantic, President Barack Obama’s latest budget handout to the US auto industry centred on building indigenous capability to make lithium-ion batteries.

Unconsidered lithium is suddenly big news and big bucks. Most major manufacturers have actual or planned hybrid vehicles; many plan full electric vehicles. All seem likely to rely on lithium-ion batteries.

The reason why lithium-ion is the chosen technology, says Tom Hazeldine, specialist consultant on transport fuels at AEA, is its high energy density. Packing a vehicle with enough electric power to give reasonable range using conventional lead-acid batteries would take up all the boot space and much of the back seat and would add prohibitive weight.

But power density is not the only issue, and “lithium-ion”, as a term, covers several different chemistries. Behind car companies’ announcements, there’s quite a bit of jockeying for position between different technologies. Ask Nissan what exactly it’s aiming to use in the Leaf, its newly-unveiled mainstream electric vehicle, or to produce at Sunderland, and you’re told it’ll be “advanced lithium-ion batteries”. Nothing too specific yet, then.

Mark Donaghy is global marketing chief for lithium-ion battery producer Valence, which has supplied batteries for commercial vehicles. He identifies eight separate issues that different chemistries have to balance: “There’s cost, energy density, weight, safety, raw material availability, environmental impact, charging rates and servicing,” he says. “There’s no such thing as a perfect battery,” he adds.

Until recently, most people’s experience of lithium-ion batteries was in mobile phones and laptop computers, where the flexibility, energy density and rechargeability virtually created the markets. But, says Hazeldine, simply scaling up the lithium cobalt oxide chemistry used in these devices to make a bigger battery for cars may not be the best option.

“This is probably the most expensive of the lithium-ion technologies, and cobalt is toxic, which goes against the aims for recycling,” he says. “Also there’s something of a safety issue in ‘thermal runaway’, which means that in phones and laptops they do occasionally catch fire.” This may not be much of a problem in small devices, but isn’t ideal in a car, particularly a hybrid with a fuel source close by.

Much development effort in recent years has gone into non-oxide Li-ion chemistry. Lithium iron phosphate is cheaper than the cobalt oxide, safer and less toxic, says Hazeldine. The downside is lower energy density. But the technology has been promising enough for arch-investor Warren Buffett to put serious money into BYD, a Chinese battery maker, in an attempt to turn it into a vehicle maker.

Valence patented a variant of this chemistry, a lithium iron magnesium phosphate, and has supplied a lot of batteries to power the Segway Personal Transporter. A further advantage of the iron phosphate formulations is that they stand more recharge cycles than the metal oxide batteries, says Donaghy. The company is now developing a lithium vanadium fluoro-phosphate material that packs more power density and does as well on recharging: it’s likely to be ready in a couple of years.

Recharging is an issue with a second aspect, though: the time taken to do it.

Present systems, where the lithium-based material is in the cathode, mostly require an overnight eight-hour recharge. Hazeldine says that work on a lithium titanate anode with a crystallised “spinel” surface, providing a greater surface area than a conventional smooth graphite anode, has been claimed to speed up charging to a matter of minutes, rather than hours.

Technical issues are not the whole story, though, and the eventual battery choice may well be determined by economics and politics. At present, lithium-based batteries add between £2,000 and £5,000 to the cost of a vehicle. Mass production may shave some off, but 80% of the cost is in raw materials. Involvement of big mining or oil corporations in lithium extraction might save a bit more.

But if battery vehicles turn out to be a long-running technology – and not just a temporary staging post in a transition from fossil fuels to a hydrogen future – then politics may well decide. Governments could subsidise battery production; new market models for battery sharing, taking the battery out of the capital cost of a vehicle, could change the economics.

Either way, we’re likely to hear a lot more about that obscure third element on the periodic table. Lithium has arrived.

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Getting the chemistry right

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Getting the chemistry right