The
batteries successfully powered a flexible display system equipped with a microcontroller
and Bluetooth modules. Here too the battery performed better than commercially
available Li coin cells. Courtesy: University of California San Diego.
A team of
researchers has developed a flexible, rechargeable silver oxide-zinc battery
with a five to 10 times greater areal energy density than state of the art. The
battery also is easier to manufacture; while most flexible batteries need to be
manufactured in sterile conditions, under vacuum, this one can be screen
printed in normal lab conditions. The device can be used in flexible,
stretchable electronics for wearables as well as soft robotics.
The team,
made up of researchers at the University of California San Diego and
California-based company ZPower, details their findings in the Dec. 7 issue of
the journal Joule.
“Our
batteries can be designed around electronics, instead of electronics needed to
be designed around batteries,†said Lu Yin, one of the paper’s co-first authors
and a Ph.D. student in the research group of UC San Diego’s nanoengineering
Professor Joseph Wang.
The areal
capacity for this innovative battery is 50 milliamps per square centimeter at
room temperature — this is 10-20 times greater than the areal capacity of a
typical Lithium ion battery. So for the same surface area, the battery
described in Joule can provide 5 to 10 times more power.
“This kind of areal capacity has never been obtained before,†Yinsaid. “And our manufacturing method is affordable and scalable.â€
The
areal capacity for this innovative battery is 50 milliamps per square
centimeter at room temperature — this is 10-20 times greater than the areal
capacity of a typical Lithium ion battery. So for the same surface area, the
battery described in Joule can provide 5 to 10 times more power. Courtesy:
University of California San Diego.
The new
battery has higher capacity than any of the flexible batteries currently
available on the market. That’s because the battery has a much lower impedance
— the resistance of an electric circuit or device to alternative current. The
lower the impedance, the better the battery performance against high current
discharge.
“As the 5G
and Internet of Things (IoT) market grows rapidly, this battery that
outperforms commercial products in high current wireless devices will likely be
a main contender as the next-generation power source for consumer electronics,â€
said Jonathan Scharf the paper’s co-first author and a Ph.D. candidate in the
research group of UC San Diego’s nanoengineering Professor Ying Shirley Meng.
The
batteries successfully powered a flexible display system equipped with a
microcontroller and Bluetooth modules. Here too the battery performed better
than commercially available Li coin cells.
The
printed battery cells were recharged for more than 80 cycles, without showing
any major signs of capacity loss. The cells also remained functional in spite
of repeated bending and twisting.
“Our core
focus was to improve both battery performance and the manufacturing process,â€
said Ying Shirley Meng, director of the UC San Diego Institute for Materials
Discovery and Design and one of the paper’s corresponding authors.
To create
the battery, the researchers used a proprietary cathode design and chemistry
from ZPower. Wang and his team contributed their expertise in printable,
stretchable sensors and stretchable batteries. Meng and her colleagues provided
their expertise in advanced characterization for electrochemical energy storage
systems and characterized each iteration of the battery prototype until it
reached peak performance.
The recipe
to better performance
The
battery’s exceptional energy density is due to its silver oxide-zinc,
(AgO-Zn)chemistry. Most commercial flexible batteries use a Ag2O-Zn chemistry.
As a result, they usually have limited cycle life and have low capacity. This
limits their use to low-power, disposable electronics.
AgO is
traditionally considered unstable. But ZPower’s AgO cathode material relies on
a proprietary lead oxide coating to improve AgO’s electrochemical stability and
conductivity.
As an
added benefit, the AgO-Zn chemistry is responsible for the battery’s low
impedance. The battery’s printed current collectors also have excellent
conductivity, which also helps achieve lower impedance.
Improved
manufacturing
But AgO
had never been used in a screen-printed battery before, because it is highly
oxidative and chemically degrades quickly. By testing various solvents and
binders, researchers in Wang’s lab at UC San Diego were able to find an ink
formulation that makes AgO viable for printing. As a result, the battery can be
printed in only a few seconds once the inks are prepared. It is dry and ready
to use in just minutes. The battery could also be printed in a roll-to-roll
process, which would increase the speed and make manufacturing scalable.
The batteries
are printed onto a polymer film that is chemically stable, elastic, and has a
high melting point (about 200 degrees C or 400 degrees Fahrenheit) that can be
heat sealed. Current collectors, the zinc anode, the AgO cathode and their
corresponding separators each constitute a stacked screen-printed layer.
The team
is already at work on the next generation of the battery, aiming for cheaper,
faster charging devices with even lower impedance that would be used in 5G
devices and soft robotics that require high power and customizable and flexible
form factors.