COVER FEATURE BATTERY HEALTH
& SAFETY
affect the battery’s cycle life through
surface passivation (SEI) on the
carbonaceous anode material, or
oxidation of the electrolyte that
results in the accumulation of
a resistive surface layer on the
cathodeactive- material.
Charging at a high speed can also
have an influence on battery wear,
but research has shown that it is the
constant voltage part, in the charging
process, that is the most damaging
to the battery.
These methods for predicting
battery health, however, miss many
important features that can indicate
the health of a battery.
A lot of research is now focused
on tracking the many processes that
happen within the battery and for
that to happen scientists are using
a variety of new techniques to probe
batteries in action.
Understanding degradation
A team of international scientists
have been looking at the dynamic
process that leads to battery
degradation in the electrodes of
lithium batteries and are using
neutron and X-ray tomography to
improve their understanding of the
processes that are involved.
The team, based at
Helmholtz-Zentrum Berlin and
University College London, are
using a mathematical method to
virtually unwind the electrodes
that are wound into the form of
a compact cylinder, to observe
the processes on the surfaces
of the electrodes.
According to Alessandro
Tengattini, an instrument
scientist at NeXT-Grenoble,
an imaging station at Institut
Laue-Langevin, “The research is
focused on basically two main
issues. We want to improve
levels of efficiency, so we can
develop longer lasting batteries
that can survive more recharging
cycles, and the other issue
that we are looking to address
is one of safety. There have been
a number of cases where lithiumbased
batteries have caught fire and
exploded or batteries have inflated.
Both pose a serious risk.
“We’re demanding more power
from our electronic devices, so
we need to understand the minor
fluctuations occurring inside the
batteries throughout their lifetime.
For example, in particular areas of
the battery you can see much higher
rates of depletion and it is possible to
observe areas of fracture and damage
to the battery, which can have a
significant impact on safety.
“While I wouldn’t say that current
methods of monitoring batteries
aren’t working, they are simply not
providing us with enough information.”
To better understand the structure
of the battery researchers have been
able to look at the electrode surfaces
during charging and discharging
by using a combination of two
complementary tomography methods.
Data is provided by HZB BER II
and Institut Laue-Langevin which
then employs X-ray tomography at
the European Synchrotron Radiation
Facility (ESRF) in Grenoble. There
the data is used to analyse the
microstructure of the electrodes
and detect any deformations and
discontinuities.
“Little research has been done
at this structural level, so by using
neutron tomography it is now possible
to directly observe the migration of
lithium ions to determine how the
distribution of the electrolyte in the
battery cell changes over time,”
explained Tengattini.
“This electro-unrolling technique
has enabled us to analyse the inside
of batteries, while they are in use,
to identify minuscule fluctuations to
almost the micrometre.”
The instrument at NeXT-Grenoble
allows for the simultaneous
acquisition of x-ray and neutron
tomography, developed in
collaboration between the Institut
Laue-Langevin and the Université
Grenoble-Alpes.
“It’s hard to analyse lithium with
x-rays because it is a light-weight
element, but in combination with
the high-flux neutrons provided at
the Institut Laue-Langevin we have
now started to learn more about the
electro-chemical and mechanical
properties that are at play while these
lithium-ion batteries are in use,” said
Tengattini.
When it comes to the lithiumion
battery its compact design
is usually achieved by winding
the thin sandwich of battery
electrodes into a cylindrical form
– that’s because the electrodes
need a large surface to facilitate
high capacity and rapid charging.
The mathematical method
that has been developed
enables physicists to virtually
unwind the battery electrodes -
because the cylindrical windings
of the battery are difficult to
examine quantitatively.
Only after mathematical
analysis and the virtual
unwinding can conclusions be
drawn about processes at the
individual sections of the winding.
The algorithm was originally
“While I wouldn’t
say that current
methods of
monitoring
batteries aren’t
working, they
are simply not
providing us
with enough
information.”
Alessandro
Tengattini
Below: 3D-Image of
a battery, virtually
cut with a computer
programme
www.newelectronics.co.uk 28 April 2020 11
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