The future of energy - Batteries included?

2013-02-06 11:19:58

The search for better ways of storing electricity is hotting up

Feb 2nd 2013 | LEMONT, ILLINOIS |From the print edition

KRIS PUPEK, an industrial chemist at Argonne National Laboratory in Lemont,

near Chicago, waves a tube of white powder in the air emphatically. A mere

pinch of the contents is sufficient for his analytical colleagues to work out

if it has the potential to be the next whizzy material in battery research. But

Dr Pupek does not deal in pinches. His job is to find out whether potential can

be turned into practice in other words, whether something that has the right

properties can be made cheaply, and in bulk. If it can, it is passed on to

industry for testing. The hope is that at least one of the tubes will start a

revolution.

Batteries are a hugely important technology. Modern life would be impossible

without them. But many engineers find them disappointing and feel that they

could be better still. Produce the right battery at the right price, these

engineers think, and you could make the internal-combustion engine redundant

and usher in a world in which free fuel, in the form of wind and solar energy,

was the norm. That really would be a revolution.

It is, however, a revolution that people have been awaiting a long time. And

the longer they wait, the more the doubters wonder if it will ever happen. The

Joint Centre for Energy Storage Research (JCESR), at which Dr Pupek and his

colleagues work, hopes to prove the doubters wrong. It has drawn together the

best brains in energy research from America s national laboratories and

universities, along with a group of interested companies. It has money, too. It

has just received a grant of $120m from the country s Department of Energy. The

aim, snappily expressed, is to make batteries five times more powerful and five

times cheaper in five years.

Think positive

Most batteries, from the ancient, lumbering lead-acid monsters used to start

cars, to the sleek, tiny lithium cells that power everything from e-book

readers to watches, have three essential components: two electrodes (an anode

and a cathode) and a medium called an electrolyte that allows positively

charged ions to move between the electrodes, balancing the flow of negatively

charged electrons that form the battery s useful current. The skill of creating

new types of battery is to tinker with the materials of these three components

in ways that make things better and cheaper. Dr Pupek s white powders are among

those materials.

To discover more of them, Argonne will make use of a rapidly growing

encyclopedia of substances created by Gerbrand Ceder of the Massachusetts

Institute of Technology. Dr Ceder runs the Materials Project, which aims to be

the Google of material properties . It allows researchers to speed up the way

they search for things with specific properties. Argonne will use the Materials

Project as a reference library in its search for better electrodes, and also

hopes to add to it.

The first test of any combination of substances that comes out of the Materials

Project, or anywhere else, will be to beat the most successful

electricity-storage device to emerge over the past 20 years: the lithium-ion

battery. Such batteries are now ubiquitous. Most famously, they power many of

the electric and hybrid-electric cars that are starting to appear on the roads.

More infamously, they have a tendency to overheat and burn. Two recent fires on

board Boeing s new 787 Dreamliners may have been caused by such batteries or

their control systems. Improving on lithium-ion would be a feather in the cap

of any laboratory.

George Crabtree, JCESR s newly appointed director, thinks such improvements

will be needed soon. He reckons that most of the gains in performance to be had

from lithium-ion batteries have already been achieved, making the batteries

ripe for replacement. Jeff Chamberlain, his deputy, is more bullish about the

existing technology. He says it may still be possible to double the amount of

energy a lithium-ion battery of given weight can store, and also reduce its

cost by 30-40%.

This illustrates the uncertainty about whether lithium-ion technology, if

pushed to its limits, can make electric vehicles truly competitive with those

run by internal-combustion engines, let alone better. McKinsey, a business

consultancy, reckons that lithium-ion batteries might be competitive by 2020

but, as the chart below shows, there is still a lot of work to do. Moreover,

pretenders to lithium-ion s throne are already emerging.

The leader is probably the lithium-air battery, in which metallic lithium is

oxidised at the anode and reduced at the cathode. In essence, it uses

atmospheric oxygen as the electrolyte. This reduces its weight and means its

energy density is theoretically enormous. That is important. One objection to

electric cars is that petrol packs six times more joules of energy into a

kilogram than a battery can manage. Bringing that ratio down would make

electric vehicles more attractive.

The lithium-air approach has consequently generated a lot of hype. It has

problems, though, which will take years of research to resolve. Lithium-air

batteries are hard to recharge and extremely temperamental. The chemical

reaction which powers them is not far removed from spontaneous combustion.

Lithium-air batteries are thus highly inflammable and require heavy safety

systems to stop them catching fire.

Luckily, the researchers at JCESR have other irons in the fire. One is the

multivalent-ion battery. A lithium atom has but a single electron available for

chemical reactions. A magnesium atom, by contrast, has two such valence

electrons, and an aluminium atom three.

Theoretically, says Dr Chamberlain, this means it might be possible get two or

three times as much energy out of a magnesium or aluminium battery. Though

these metals are not as light as lithium (nor as electropositive, to use a

piece of chemical jargon that is pertinent to the argument), their extra

valence electrons increase the amount of energy they can store, thus pushing

them forward in the competition with petrol. They are also cheaper than

lithium. And safer. Their ions, however, are harder to move around inside a

battery, which is why they have not been used much in the past, and this is

where new materials will need to be sought out.

The second transformation, besides electric cars, that better batteries might

bring about is what is known as grid-scale storage. If this could be done

cheaply enough it would revolutionise the economics of wind and solar energy by

making the main problem with such sources that the sun does not always shine

and the wind does not always blow irrelevant. To this end, Argonne s

researchers are working on what are known as flow batteries.

Go with the flow

In a conventional battery the electrolyte is contained within the cell and

serves to transport ions between the electrodes. The battery s charge is held

as chemical potential energy in those electrodes. In a flow battery the charge

is held in the electrolyte itself, which is stored in a tank and then pumped

through the cell to the place where the electrochemical reactions occur.

Unlike batteries based on cells, flow batteries can be made very large indeed,

so they can store vast amounts of energy. Hence the idea of using them to

collect surplus power from wind turbines and solar panels and squirrel it away

for use later. But their water-based electrolytes limit their potential,

because of water s tendency to decompose by electrolysis. That restricts the

voltage at which they can operate. Replacing their aqueous electrolytes with

organic ones would overcome this limitation, and Argonne s researchers are

endeavouring to do so.

A battery-driven world, then, would electrify parts of the economy, such as

transport, that have been recalcitrant, and would encourage the shift from

costly (and polluting) fossil fuels to fuels such as sunlight that cost

nothing. As a manifesto for a revolution, that takes some beating. The question

is, will the revolutionaries win, or will the ancien r gime prevail?