Release Subtitle: Scientists at Okayama University use a new technique to reveal how dendrites form in rechargeable batteries
Release Summary Text:
Lithium-ion batteries are used in various electronic devices. But, they
also come with potential hazards, particularly if the battery is damaged
or overcharged. This usually occurs because, in its overcharged state,
spiky structures called “lithium dendrites” get deposited in the
battery. Now, scientists at Okayama University use a technique called
“operando nuclear magnetic resonance” to track the precise mechanism of
dendrite formation. They also extend their experiments to sodium-ion
batteries, making their practical application easier.
Full text of release:
Lithium-ion batteries (LIBs) are a common type of rechargeable
batteries. Their versatile nature and numerous applications in all sorts
of electronic devices—from mobile phones to cars—makes them seem too
good to be true. And perhaps they are: recently, there has been an
increase in the number of fire-related incidents associated with LIBs,
especially during charging, causing serious concerns over their safety.
Scientists now know that these incidents can be due to the use of a
broken or unauthorized charger. Often, improper use of these chargers
and overcharging can lead to the formation of spiky structures on the
negative electrode of the battery, called “lithium (Li) dendrites,”
which penetrate through the barrier between the negative and positive
electrodes and cause a short circuit. Thus, looking at exactly how
dendrite formation occurs is crucial to improving the safety of LIBs.
Scientists at Okayama University, led by Associate Professor Kazuma
Gotoh, recently took a step in this direction, in a new study published
in Journal of Materials Chemistry A. They delved into finding the
precise mechanism of dendrite formation in LIBs, in an effort to
overcome their limitations and make their practical application easier.
Dr Gotoh explains, “We wanted to analyze the formation of metal
dendrites in secondary (rechargeable) batteries and contribute to
improve the safety of batteries.”
Previous studies that tried to understand the process of Li dendrite
formation were successful to some extent: they revealed that when the
battery is in an overcharged state, dendrite formation occurs in the
“overlithiation” phase of the battery cycle. But, these experiments were
performed ex situ (outside the actual electrochemical environment), and
thus the exact time of onset of dendrite formation was not found. In
their new study, Dr Gotoh and his team decided to overcome this
limitation. They figured that by applying “operando” methods (which
replicate the electrochemical environment) to an analytical technique
called “nuclear magnetic resonance” (NMR), they can accurately track the
Li atoms in the inner structure of materials, which is not possible
when using ex situ methods.
Using this technique, the team had previously succeeded in observing the
overcharged states of two types of negative electrodes—graphite and
hard carbon electrodes—in the overlithiation phase of an LIB. In the new
study, they took this to the next level by observing the state of these
electrodes during the lithiation and delithiation process (the “charge
and discharge” cycle of the battery). Their NMR analysis helped them to
track the precise onset time of dendrite formation and Li deposition in
the overcharged battery, for both the graphite and hard carbon
electrodes. In graphite, they found the Li dendrites form soon after the
“fully lithiated” phase of the electrode occurs. In the hard carbon
electrode—in contrast—they observed that dendrites form only after
“quasimetallic” Li clusters occur in the pores of hard carbon. Thus, the
scientists deduced that when the battery is overcharged, the
quasimetallic Li cluster formation acts as a buffer for the formation of
Li dendrites in hard carbon electrodes. They even applied the same
analysis to another type of rechargeable battery, called sodium-ion
battery (NIB), and found similar results. Dr Gotoh explains, “We found
that some carbon materials having inner pores (such as amorphous carbon)
have a buffer effect for the deposition of Li and Na dendrites during
overcharging of batteries. This knowledge will play an important role in
ensuring the safety of LIBs and NIBs.”
By revealing the intricacies of the dendrite formation mechanisms in
LIBs and NIBs, Dr Gotoh and his team provide useful insight into their
safety. In fact, the scientists are optimistic that their findings can
be applied to other types of rechargeable batteries in the future. Dr
Gotoh concludes, “Our findings can be applied not only to LIBs and NIBs
but also to next-generation secondary batteries such as all solid-state
batteries. This is an important step in making their practical
application easier.”
With the findings of this new study, we can hope that we possibly are
one step closer to realizing our dream of truly sustainable energy
resources.
Release URL: https://www.eurekalert.org/pub_releases/2020-08/ou-nmp081920.php
Reference:
Title of original paper: Mechanisms for overcharging of carbon
electrodes in lithium-ion/sodium-ion batteries analysed by operando
solid-state NMR
Journal: Journal of Materials Chemistry A
DOI: http://dx.doi.org/10.1039/D0TA04005C
Contact Person: Kazuma Gotoh
E-mail: kgotoh(a)okayama-u.ac.jp
URL: http://chem.okayama-u.ac.jp/~solid/index_e.html
For inquiries, please contact us by replacing (a) with the @ mark.
https://www.okayama-u.ac.jp/eng/research_highlights/index_id111.html
https://sdgs.okayama-u.ac.jp/en/
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