A new
"yolk-and-shell" nanoparticle could boost the capacity and power of
lithium-ion batteries.
The gray sphere at
center represents an aluminum nanoparticle, forming the "yolk."
The outer light-blue
layer represents a solid shell of titanium dioxide, and the space
in between the yolk
and shell allows the yolk to expand and contract without damaging the shell.
In the background is
an actual scanning electron microscope image of a collection of
these yolk-shell
nanoparticles. Image: Christine Daniloff/MIT
Aluminum could give a big boost to capacity and power of
lithium-ion batteries.
(August 6, 2015) One
big problem faced by electrodes in rechargeable batteries, as they go through
repeated cycles of charging and discharging, is that they must expand and
shrink during each cycle — sometimes doubling in volume, and then shrinking
back. This can lead to repeated shedding and reformation of its “skin” layer
that consumes lithium irreversibly, degrading the battery’s performance over
time.
Now a team of researchers at MIT and Tsinghua University in
China has found a novel way around that problem: creating an electrode made of
nanoparticles with a solid shell, and a “yolk” inside that can change size
again and again without affecting the shell. The innovation could drastically
improve cycle life, the team says, and provide a dramatic boost in the
battery’s capacity and power.
The new findings, which use aluminum as the key material for
the lithium-ion battery’s negative electrode, or anode, are reported in the
journal Nature Communications, in a paper by MIT professor Ju Li and six
others. The use of nanoparticles with an aluminum yolk and a titanium dioxide
shell has proven to be “the high-rate champion among high-capacity anodes,” the
team reports.
Most present lithium-ion batteries — the most widely used
form of rechargeable batteries — use anodes made of graphite, a form of carbon.
Graphite has a charge storage capacity of 0.35 ampere-hours per gram (Ah/g);
for many years, researchers have explored other options that would provide
greater energy storage for a given weight. Lithium metal, for example, can
store about 10 times as much energy per gram, but is extremely dangerous,
capable of short-circuiting or even catching fire. Silicon and tin have very
high capacity, but the capacity drops at high charging and discharging rates.