MATH & TECHNOLOGY
Lithium-oxygen batteries get a boost
Redesign stores more energy, lasts longer than its predecessors
ATOM & COSMOS
Electrons hang 10
in new accelerator
In AWAKE experiment, the
particles surf protons’ waves
BY MARIA TEMMING
A new type of lithium-oxygen battery
could pack more energy and last longer
than its predecessors.
Lithium-oxygen batteries, which
are more energy-dense and made of
more sustainable materials than typical lithium-ion batteries, are promising
candidates for the next generation of
rechargeable batteries (SN: 1/21/17,
p. 22). But lithium-oxygen batteries aren’t
widely used because they die quickly.
By tweaking the building materials,
researchers have constructed a lithium-oxygen battery that can release nearly
100 percent of its stored charge and be
recharged at least 150 times. This battery,
described in the Aug. 24 Science, could
become a more reliable power source for
electric cars or other electronics.
Lithium-oxygen cells are made of
two electrodes, an anode and a cathode, separated by an electrolyte. When
BY EMILY CONOVER
Particle accelerator technology has
crested a new wave.
In a first, scientists have shown that
electrons can gain energy by surfing
waves kicked up by protons shot through
plasma. The technique might someday
help produce electron beams at higher
energies than now possible, to investigate subatomic particles’ inner workings.
Standard particle accelerators rely on
radio frequency cavities, metallic cham-
bers that create oscillating electromag-
netic fields to push particles along. With
the new demonstration, “we’re trying to
develop a new kind of accelerator tech-
the battery is powering a device, oxygen
molecules on the cathode combine with
lithium ions from the electrolyte to form
a solid compound called lithium peroxide.
That chemical reaction releases energy.
Recharging the battery breaks
apart the lithium peroxide,
returning oxygen and lithium
to their starting positions.
But forging lithium peroxide
generates unwanted chemical by-products, which wastes
energy. As a result, the battery
may be able to deliver only
about 80 percent of its stored
electric charge to the device it’s powering. These pesky chemicals also damage
the battery’s electrolyte and cathode, so
the battery often fails after only a few
dozen recharges, says Larry Curtiss, a
materials chemist at Argonne National
Laboratory in Lemont, Ill.
To build a better lithium-oxygen
nology,” says Allen Caldwell of the Max
Planck Institute for Physics in Munich.
Caldwell is a spokesperson for the
AWAKE collaboration, which reported
the results online August 29 in Nature.
At the particle physics lab CERN near
Geneva, the team sent beams of high-energy protons through plasma, a state
of matter in which electrons and positively charged atoms called ions mingle.
The protons set the plasma’s electrons
jiggling, creating waves that accelerated electrons that were injected into
the plasma. Injected electrons reached
energies of up to 2 billion electron volts.
Previously, scientists demonstrated
the potential of plasma accelerators by
speeding up electrons using waves set
off by a laser or a beam of electrons. But
proton beams can carry more energy, so
electrons accelerated by protons’ plasma
waves may be able to reach higher energies in a single burst of acceleration.
The new result doesn’t match the ener-
battery, chemist Linda Nazar of the
University of Waterloo in Canada and
colleagues replaced the typical organic
electrolyte for an inorganic molten salt,
and the standard carbon-based cathode
for a metal one.
In this battery, oxygen combines with
lithium to create lithium oxide. This
chemical reaction can store 50 percent
more energy than the lithium peroxide
reaction. And lithium oxide
doesn’t produce the chemical by-products that lithium
peroxide does. That allows
the new lithium-oxygen battery to release nearly all of its
stored charge and recharge
more times than lithium-oxygen cells that form lithium
The new battery has to be heated to at
least 150° Celsius to work. So there’s still
much work to be done before the battery
is used in vehicles. Changing the substance used for the battery’s electrolyte
may bring down its operating temperature, says Yang Shao-Horn, an energy
and materials researcher at MIT. s
gies produced in previous plasma accel-
erators. The study is a proof of principle
showing that proton beams can be used.
High-energy electrons are particularly
useful for particle physics because they
are elementary particles — they have no
smaller constituents. Protons, however,
are made up of a sea of quarks, resulting
in messier collisions. And because each
quark carries a small part of the pro-
ton’s total energy, only a fraction of that
energy goes into a collision. Electrons
put all their oomph into each smashup.
But electrons are hard to accelerate:
If put in an accelerator ring, they rapidly
bleed off energy. So AWAKE uses acceler-
ated protons to get electrons up to speed.
Some scientists had been skeptical that
plasma could be controlled enough for an
effort like AWAKE to work, says physi-
cist Wim Leemans of Lawrence Berkeley
National Laboratory in California. “This
is very rewarding to see that, yes, the
plasma technology has advanced.” s
energy a new kind
battery could store
compared with a