They’ve done it again: The
battery barons of Stanford, led by Yi Cui, have created what those in
the industry call the “Holy Grail” of lithium-ion battery design. In
specific, they’ve finally worked out how to create a rugged lithium
electrode that can increase the capacity of a lithium-ion battery by
three to four times — as in, this lithium electrode, on its own, could
increase the battery life of your smartphone by three times, or
significantly reduce the size and cost of an electric car’s battery
pack.
A lithium-ion battery’s capacity (i.e. the amount of work it
can do before it runs out of juice) is mostly dictated by how many
lithium ions can be sucked up into the anode during charging. (For a
more details on lithium-ion battery chemistry, read our featured story about how they work.)
In almost all modern LIBs, the anode is made of graphite. Graphite is
cheap and long-lasting (it keeps its capacity over hundreds of
charge/discharge cycles), but its useful capacity is actually quite low
(about 350 mAh/g). Lithium is by far the best anode material with a
specific capacity that’s more than ten times that of graphite (3,860
mAh/g), but it degrades very quickly — and, perhaps more importantly, it
has a tendency to
violently explode when brought into contact
with the electrolyte. If these niggling issues could be rectified, a LIB
with much higher capacity could be built (not quite 10 times higher
though; there are lots of other factors at play that prevent theoretical
limits from being hit).
Now, a team at Stanford university, led by Yi Cui — the mastermind behind a huge number of battery breakthroughs
that we’ve written about on ExtremeTech — have found a way of creating
lithium anodes that keep their capacity over 150 charge/discharge
cycles… and don’t explode. [
doi:10.1038/nnano.2014.152 - "Interconnected hollow carbon nanospheres for stable lithium metal anodes"]

Lithium anodes crack and form dendrites — but not with Stanford’s new carbon nanosphere coating!
Similar to other recent battery breakthroughs,
nanotech is the key to Stanford’s new lithium electrode. One of the
main problems with lithium is that it expands dramatically when it
absorbs ions during charging, creating cracks in the metal. Lithium ions
then ooze out of these cracks, forming “mossy” metal deposits known as
dendrites. These dendrites very quickly lower the battery’s efficiency,
so that it’s fairly useless after just a handful of cycles. To prevent
these cracks and dendrites from forming, Stanford deposits a layer of
carbon nanospheres
on the surface of the lithium anode. As you can see in the photos,
these nanospheres create an interconnected series of domes that are
strong enough to maintain the lithium’s structural integrity, while
still allowing the electricity-carrying ions to pass back and forth.
This protective layer, which is about 20nm thick, also prevents the
lithium from reacting explosively with the electrolyte.

Some cool microscopic imagery of Stanford’s carbon nanospheres
All
told, in technical terms, this new lithium anode has a coulombic
(Faraday) efficiency of 99% after 150 cycles. Cui says this is short of
the 99.9% required for a commercially viable design, but “
while
we’re not quite to that 99.9 percent threshold, where we need to be,
we’re close and this is a significant improvement over any previous
design. With some additional engineering and new electrolytes, we
believe we can realize a practical and stable lithium metal anode that
could power the next generation of rechargeable batteries.”
In
real-world terms, this new lithium anode could triple or quadruple the
battery life of your smartphone or electric vehicle — or, alternatively,
make it so you can get away with a much smaller battery. For EVs, where the cost of the batteries is a major barrier to mass-market pricing and adoption, this could be a very serious breakthrough.