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A new manufacturing method for lithium-ion batteries could lead to smaller,
lighter batteries that can be charged in just seconds.
Batteries that discharge just as quickly would be useful for electric and
hybrid cars, where a quick jolt of charge is needed for acceleration.
The approach only requires simple changes to the production process of a
well-known material.
The new research is reported in the scientific journal Nature.
Because of the electronic punch that they pack, gram for gram, lithium-ion
batteries are the most common rechargeable batteries found in consumer
electronics, such as laptops.
However, they take a long time to charge; researchers have assumed until now
that there was a speed limit on the lithium ions and electrons that pass
through the batteries to form an electrochemical circuit.
Tiny holes
Gerbrand Ceder, at the Massachusetts Institute of Technology (MIT), US, and his
colleagues used a computer simulation to model the movements of ions and
electrons in a variant of the standard lithium material known as lithium iron
phosphate.
The simulation indicated that ions were moving at great speed.
"If transport of the lithium ions was so fast, something else had to be the
problem," Professor Ceder said.
That problem turned out to be the way ions passed through the material.
They pass through minuscule tunnels, whose entrances are present at the surface
of the material.
However, the team discovered that to get into these channels, the ions had to
be positioned directly in front of the tunnel entrances - if they were not,
they could not get through.
The solution, Ceder discovered, was to engineer the material such that it has a
so-called "beltway" that guides the ions towards the tunnel entrances.
Traffic management
A prototype battery made using the new technique could be charged in less than
20 seconds - in comparison to six minutes with an untreated sample of the
material.
Most commercial batteries use a material made up of lithium and cobalt, but
lithium iron phosphate does not suffer from overheating - something that has
affected laptop and mp3 player batteries in a number of incidents.
Even though it is cheap, lithium iron phosphate has until now received little
attention because lithium cobalt batteries can store slightly more charge for a
given weight.
However, the researchers found that their new material does not lose its
capacity to charge over time in the way that standard lithium ion batteries do.
That means that the excess material put into standard batteries to compensate
for this loss over time is not necessary, leading to smaller, lighter batteries
with phenomenal charging rates.
What is more, because there are relatively few changes to the standard
manufacturing process, Professor Ceder believes the new battery material could
make it to market within two to three years.