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Long-lasting batteries
Research groups throughout the United
States and the world are dedicated to making
batteries last longer and hold more charge.
Research has been done on each of the
three battery components.
Yi Cui and his team at Stanford University
have turned to an anode made with silicon,
a close chemical relative of carbon. While
it takes six carbon atoms to hold onto one
lithium ion, one silicon atom holds onto four
lithium ions. This is a huge advantage for silicon and should increase the amount of energy
the battery can hold. However, silicon in a
battery swells when it absorbs Li+ during
charging, then shrinks during
use, as Li+ are drawn out
of the silicon. This expand-and-shrink cycle typically
causes the silicon to fracture
and be destroyed after only a
few cycles. To overcome this
issue, Cui’s team developed a
silicon nanowire electrode that
leaves room for thin “hairs” of
silicon to swell and shrink as
they absorb or release Li+. The
unique geometry allows the battery to cycle without damaging the silicon—
and unlocks the energy density benefits of
using silicon instead of carbon.
Mya Le Thai, a graduate student at the
University of California, Irvine, recently used
bundles of gold nanowire as a cathode. Since
nanowires are small, more surface area can be
achieved in a smaller volume. The nanowires
were coated with manganese(IV) oxide, which
gel, which prevents corrosion. Thai tested this
new cathode and found that it fully charges
and discharges up to 200,000 times without
damaging the metal, compared to the 5,000 to
7,000 charges a lithium-ion battery can with-
stand before dying.
Lithium-ion batteries have a non-aqueous
liquid electrolyte, such as ethylene carbonate, as well as lithium salts. The problem is
that this type of liquid restricts how fast Li+
can flow and limits the temperature range the
battery can function. For example, Apple says
its smartphone battery’s “comfort zone” is
between 0 °C (32 °F) and 35 °C (95 °F).
Yuki Kato and Ryoji Kanno, in collabora-
tion with Toyota, the Tokyo Institute of
Technology, and others, have
demonstrated potential solid
electrolytes as media for ion
transport. They have created
different crystalline structures
that include atoms of lithium,
silicon, phosphorus, sulfur, and
carbon through which ions
could “flow.” These crystals
are stable and they can hold
more charge and charge
faster than traditional liquid elec-
trolytes. The temperature range is –30 °C
(–22 °F) and
100 °C (212 °F)—a significantly wider range
than traditional liquid electrolytes.
These innovations have not hit the market
yet. One can only imagine how much better rechargeable batteries could be if these
improvements were combined. I, for one, look
forward to having a phone I can charge in
minutes, once per week. By that time, though,
that new phone will probably make my current
one seem like a Nokia 3220.
SELECTED REFERENCES
Schlesinger, H. The Battery. HarperCollins: New
York, 2010; pp. 85-122.
Service, R. How to Build a Better Battery through
Nanotechnology. Science Magazine, May 26,
2016: http://www.sciencemag.org/news/2016/05/
how-build-better-battery-through-nanotechnology
[accessed Sept 2017].
Apple battery Maximizing Performance.
http://www.apple.com/batteries/maximizingper-formance/ [accessed Sept 2017].
Fedor Kossakovski is a science writer who
lives in Boston, Mass. This is his first article in
ChemMatters.
tion reaction occurs at the anode, which
releases electrons. For each electron released
from the graphite anode, one lithium ion
moves from between the graphite through the
Li+-permeable membrane, into the cathode.
The electrons released during oxidation travel
through the external circuit and power your
phone, and they make it back to the cathode
to allow for LiCoO2 production.
Oxidation/Anode
LiC6 ➞ Li+ + C6(graphite)+ e–
Reduction/Cathode
CoO2 + Li+ + e– ➞ LiCoO2
When charging, the cathode material is oxidized, so lithium ions migrate from the cathode to the graphite in the anode. Li+ ions insert
between the planes and graphite is reduced.
“This is called a ‘rocking-chair’ battery system, because you rock the cations from one
side to the other and back,” Akridge said.
The actual function of modern lithium-ion
batteries does not differ much from the first
battery, which was produced in 1800. Since
Sony made the lithium-ion battery available
to the public in 1991, only its efficiency has
changed.
I realized that, although our hardware and
software have progressed to make our phones
much smarter, our batteries have barely kept
pace. Innovations in the battery industry are
rare. According to Akridge, “Batteries and
electronics evolved in two completely separate
ways. The evolution of batteries and
the evolution of electronics have
absolutely nothing to do with each
other. So, the question, ‘Why doesn’t one keep
up with the other?’ has no meaning.”
BATTERIES TOOK A LONG TIME TO MAKE THEIR WAY TO THE PUBLIC, probably because they were difficult to make and always required some wet
barrier such as Volta’s soaking paper. In the 1890s, the National Carbon
Company created the first dry-cell battery, a predecessor of
the modern AA battery and convenient enough to be used
by the public. Initially, dry-cell batteries were used only in novelty gad-
gets such as light-up ties. Eventually, the world caught on to their
usefulness, and more practical devices, such as flashlights,
portable electric clocks, and portable radios, began to appear.
The National Carbon Company supplied dry-cell batteries for
many of these devices and still exists today—as Energizer.
Batteries for Everyone!
www.acs.org/chemmatters 12 ChemMatters | DECEMBER 2017/JANUAR Y 2018
