Shown is a sample
holder used to test samples of lithiated silicon to determine its
nano-mechanical
properties. The
device was used to develop a detailed nano-mechanical study of mechanical
degradation
processes in silicon thin films. (Credit: Rob Felt, Georgia Tech)
(September 24, 2015) A
detailed nano-mechanical study of mechanical degradation processes in silicon
structures containing varying levels of lithium ions offers good news for
researchers attempting to develop reliable next-generation rechargeable
batteries using silicon-based electrodes.
Anodes – the negative electrodes – based on silicon can
theoretically store up to ten times more lithium ions than conventional
graphite electrodes, making the material attractive for use in high-performance
lithium-ion batteries. However, the brittleness of the material has discouraged
efforts to use pure silicon in battery anodes, which must withstand dramatic
volume changes during charge and discharge cycles.
Using a combination of experimental and simulation
techniques, researchers from the Georgia Institute of Technology and three
other research organizations have reported surprisingly high damage tolerance
in electrochemically-lithiated silicon materials. The work suggests that
all-silicon anodes may be commercially viable if battery charge levels are kept
high enough to maintain the material in its ductile state.
Examining thin
film silicon
(Left to right)
Professor Ting Zhu and Assistant Professor Shuman Xia, both from
Georgia Tech’s
Woodruff School of Mechanical Engineering, show how a thin film electrode
made of amorphous
silicon was tested in a custom environmental indenter. To provide proper
environmental
control, samples containing lithiated silicon were tested with the device
inside
the glovebox shown
in the background. (Credit: Rob Felt, Georgia Tech)
Using the results of the studies, the researchers charted
the changing mechanical properties of the silicon structures as a function of
their lithium content. By suggesting a range of operating conditions under
which the silicon remains ductile, Xia hopes the work will cause battery
engineers to take a new look at all-silicon electrodes.
“Our work has fundamental and immediate implications for the
development of high-capacity lithium-based batteries, both from practical and
fundamental points of view,” he said. “Lithiated silicon can have a very high
damage tolerance beyond a threshold value of lithium concentration. This tells
us that silicon-based batteries could be made very durable if we carefully
control the depth of discharge.”