Tokyo
Scientists Unveil Solid-State Battery Breakthrough
- Tokyo University of Science researchers
have improved the response speed of solid-state batteries by two
orders of magnitude.
- Researchers used a novel technique to
investigate and modulate electric double layer dynamics.
- These findings can lead to the
commercialization of all-solid-state batteries with diverse
applications, particularly electric vehicles.
Tokyo University of Science researchers demonstrated unprecedented
control of response speed by over two orders of magnitude in a solid
state battery. This is a major steppingstone towards realization
of commercial all-solid-state batteries.
Solid-state battery‘s high surface resistance causes these
batteries to have low output, limiting their applications. The
researchers have employed a novel technique to investigate and
modulate electric double layer dynamics at the solid/solid electrolyte
interface. The achievement is carrier modulation and improved
switching response speed control in these batteries.
The reporting paper detailing their technique was published in Volume
31 of Materials Today Physics.
The search for clean energy and carbon neutrality, all-solid-state
lithium-ion batteries (ASS-LIBs) offers considerable promise. ASS-LIBs
are expected to be used in a wide range of applications including
electric vehicles (EVs). However, commercial application of these
batteries is currently facing a bottleneck – their output is reduced
owing to their high surface resistance. Moreover, the exact mechanism
of this surface resistance has been so far, unknown. Researchers have
alluded it to a phenomenon called the “electric double layer” (or EDL)
effect seen in colloidal substances (which are microscopic dispersions
of one kind of particle in another substance).
The EDL effect occurs when colloidal particles gain negative electric
charge by adsorbing the negatively charged ions of the dispersion
medium on their surface.
Dr. Tohru Higuchi, Associate Professor at Tokyo University of Science
(TUS) explained, “This occurs at the solid/solid electrolyte
interface, posing a problem in all-solid-state lithium batteries.”
Dr. Higuchi, along with colleagues Dr. Makoto Takayanagi from TUS, and
Dr. Takashi Tsuchiya and Dr. Kazuya Terabe from National Institute for
Materials Science in Japan, have devised a novel technique to
quantitatively evaluate the EDL effect at the solid/solid electrolyte
interface.
The researchers employed an all-solid-state hydrogen-terminated
diamond (H-diamond)-based EDL transistor (EDLT) to conduct Hall
measurements and pulse response measurements that determined EDL
charging characteristics. By inserting a nanometer-thick lithium
niobate or lithium phosphate interlayer between the H-diamond and
lithium solid electrolyte, the team could investigate the electrical
response of the EDL effect at the interface between these two layers.
The electrolyte’s composition did, indeed, influence the EDL effect in
a small region around the electrode interface. The EDL effect was
reduced when a certain electrolyte was introduced as an interlayer
between the electrode/solid electrolyte interface. EDL capacitance for
the lithium phosphate/H-diamond interface was much higher compared to
the lithium niobate/H-diamond interface.
The team’s article also explains how they improved the switching
response time for charging ASS-EDLs. Dr. Higuchi noted, “The EDL has
been shown to influence switching properties, so we considered that
the switching response time for charging ASS-EDLs could be greatly
improved by controlling the capacitance of the EDL. We used the
non-ion-permeable property of diamond in the electron layer of the
field-effect transistor and combined it with various lithium
conductors.”
The interlayer accelerated and decelerated the EDL charging speed. The
electrical response time of the EDLT was highly variable – it ranged
from about 60 milliseconds (low speed switching for lithium
phosphate/H-diamond interface) to about 230 microseconds (high speed
switching for lithium niobate/H-diamond interface). The team, however,
exhibited control over the EDL charging speed for over two orders of
magnitude.
To summarize, the researchers were able to achieve carrier modulation
in all-solid-state devices and improved their charging
characteristics. “These results from our research on the lithium-ion
conductive layer are important for improving the interface resistance
and may lead to the realization of all solid-state batteries with
excellent charge-discharge characteristics in the future,” noted Dr.
Higuchi.
All in so far this is a major steppingstone towards controlling the
interface resistance of ASS-LIBs that catalyzes their feasibility for
many applications. It will also help design better
solid-electrolyte-based devices, a class of gadgets which also
includes neuromorphic devices.
***
The solid-state design has some very attractive characteristics. For
now the architecture design isn’t cooperating. It sounds like this
team has revealed that the electrodes cover themselves thus
restricting the flow and in turn the power.
It does seem now that the problems and challenges are getting defined
thanks to this team’s efforts. Once defined and explained the
solutions can be worked out.
Solid-state might not be imminent, but now one has lots more confident
they are inevitable.
By Brian Westenhaus via New Energy and Fuel
