Biomorphic batteries could provide 72 times more energy for robots


Date:
August 19, 2020
Source:
University of Michigan
Summary:
Like biological fat reserves store energy in animals, a new
rechargeable zinc battery integrates into the structure of a robot
to provide much more energy, researchers have shown.



FULL STORY ==========================================================================
Like biological fat reserves store energy in animals, a new rechargeable
zinc battery integrates into the structure of a robot to provide much
more energy, a team led by the University of Michigan has shown.


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This approach to increasing capacity will be particularly important as
robots shrink to the microscale and below -- scales at which current stand-alone batteries are too big and inefficient.

"Robot designs are restricted by the need for batteries that often occupy
20% or more of the available space inside a robot, or account for a
similar proportion of the robot's weight," said Nicholas Kotov, the Joseph
B. and Florence V. Cejka Professor of Engineering, who led the research.

Applications for mobile robots are exploding, from delivery drones and
bike- lane take-out bots to robotic nurses and warehouse robots. On the
micro side, researchers are exploring swarm robots that can self-assemble
into larger devices. Multifunctional structural batteries can potentially
free up space and reduce weight, but until now they could only supplement
the main battery.

"No other structural battery reported is comparable, in terms of energy density, to today's state-of-the-art advanced lithium batteries. We
improved our prior version of structural zinc batteries on 10 different measures, some of which are 100 times better, to make it happen,"
Kotov said.

The combination of energy density and inexpensive materials means that
the battery may already double the range of delivery robots, he said.



========================================================================== "This is not the limit, however. We estimate that robots could have 72
times more power capacity if their exteriors were replaced with zinc
batteries, compared to having a single lithium ion battery," said
Mingqiang Wang, first author and recently a visiting researcher to
Kotov's lab.

The new battery works by passing hydroxide ions between a zinc electrode
and the air side through an electrolyte membrane. That membrane is partly
a network of aramid nanofibers -- the carbon-based fibers found in Kevlar
vests -- and a new water-based polymer gel. The gel helps shuttle the
hydroxide ions between the electrodes.

Made with cheap, abundant and largely nontoxic materials, the battery
is more environmentally friendly than those currently in use. The gel
and aramid nanofibers will not catch fire if the battery is damaged,
unlike the flammable electrolyte in lithium ion batteries. The aramid nanofibers could be upcycled from retired body armor.

To demonstrate their batteries, the researchers experimented with
regular-sized and miniaturized toy robots in the shape of a worm and
a scorpion. The team replaced their original batteries with zinc-air
cells. They wired the cells into the motors and wrapped them around the outsides of the creepy crawlers.

"Batteries that can do double duty -- to store charge and protect the
robot's 'organs' -- replicate the multifunctionality of fat tissues
serving to store energy in living creatures," said Ahmet Emre, a doctoral student in biomedical engineering in Kotov's lab.



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The downside of zinc batteries is that they maintain high capacity for
about 100 cycles, rather than the 500 or more that we expect from the
lithium ion batteries in our smartphones. This is because the zinc
metal forms spikes that eventually pierce the membrane between the
electrodes. The strong aramid nanofiber network between the electrodes
is the key to the relatively long cycle life for a zinc battery. And the inexpensive and recyclable materials make the batteries easy to replace.

Beyond the advantages of the battery's chemistry, Kotov says that the
design could enable a shift from a single battery to distributed energy storage, using graph theory approach developed at U-M.

"We don't have a single sac of fat, which would be bulky and require
a lot of costly energy transfer," Kotov said. "Distributed energy
storage, which is the biological way, is the way to go for highly
efficient biomorphic devices." A paper on this research is to be
published in Science Robotics, titled, "Biomorphic structural batteries
for robotics." This research is funded by the Department of Defense,
the National Science Foundation and the Air Force Office of Scientific Research. Battery testing took place at the U-M Energy Institute. Kotov
is also a professor of chemical engineering, materials science and
engineering and macromolecular science and engineering. Wang is a
postdoctoral researcher at Harbin Institute of Technology in China.

The University of Michigan has applied for patent protection and is
seeking commercial partners to bring the technology to market.


========================================================================== Story Source: Materials provided by University_of_Michigan. Note:
Content may be edited for style and length.


========================================================================== Related Multimedia:
* YouTube_video:_Structural,_rechargeable_zinc_battery ==========================================================================


Link to news story: https://www.sciencedaily.com/releases/2020/08/200819144111.htm

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