‘Holy grail’ battery life tech could end smartphone woes (Wired UK)


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For years now we’ve watched smartphones get progressively in
every way — in terms of camera skills, screen resolution and raw
power. And yet there is one respect in which it feels they have
never really improved: battery life.

Fortunately the days of day-long battery life may be numbered as
material scientists and engineers from Stanford University reveal
that they have found a way to boost battery life by up to three
times. The key to their success lies in the creation of a pure
lithium anode — something that battery designers have been trying
to achieve for decades.

The breakthrough would allow for the development of the first
true lithium battery. At present only battery electrolytes contain
lithium, but having a lithium anode — the bit that discharges
electrons — will have a significant impact on the overall battery
life of electronics.

“Of all the materials that one might use in an anode, lithium
has the greatest potential. Some call it the Holy Grail,” said Professor Yi Cui, the lead researcher on the project.
Lithium is extremely lightweight and has an extremely high energy
density, which makes it much more efficient to put inside
batteries. “In practical terms, if we can improve the capacity of
batteries to, say, four times today’s, that would be exciting. You
might be able to have cell phone with double or triple the battery
life.”

The batteries could also have a huge impact on other devices,
including electric vehicles.

Researchers have been trying and failing for years to create a
lithium anode. Despite being ideal for making lighter, smaller and
more powerful batteries it poses many engineering challenges. The
main problem is that lithium expands when charging. This is true of
all anode materials, including graphite and silicon, to an extent,
but lithium’s expansion, is apparently “virtually unlimited”,
forcing its outer surface to crack. The effect of this is that
lithium ions escape and grow into hair-like tendrils that short
circuit the battery.

The second issue is that lithium reacts very powerfully with
battery electrolytes, causing them to be used up very quickly,
reducing battery life. The heat produced when they come into
contact means that they can sometimes cause fire, or even an
explosion.

To overcome these issues, the Stanford research team have built
a protective layer of nanospheres — connected carbon domes — over
the lithium anode. Like a flexible honeycomb, the nanosphere layer
is 5,000 times thinner than a human hair. It is both chemically
stable and mechanically strong, so will stop the lithium from
expanding when it charges.

The modified lithium anodes have proved very promising when
performing in early battery efficiency cycle tests, and the
research has been published in a study in the journal Nature Nanotechnology.

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28 July 2014 | 5:07 pm – Source: wired.co.uk

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