Tech Briefs Magazine - April 2021 - 43

require for AA or AAA batteries, the supercapacitors could power
a two-volt watch for an hour and a half.
To make the stretchable supercapacitors, the team first grew
a carbon nanotube forest -- a patch of millions of nanotubes
just 15 nanometers in diameter and 20-30 micrometers tall -
on top of a silicon wafer. They then coated a thin layer of gold
nanofilm on top of the carbon nanotube forest. The gold layer
acts as a sort of electric collector, dropping the resistance of
the device an order of magnitude below previous versions,
which allows the device to charge and discharge much faster.
The carbon nanotube forest is then transferred to a prestretched elastomer substrate with the base gold-side-down.
The gel-filled electrode is then relaxed to allow the pre-strain
to release, causing it to shrink to a quarter of its original size.
This process crumples up the thin layer of gold and smashes
together the " trees " in the carbon nanotube forest. The super-

dense forest is then filled with a gel electrolyte that can trap
electrons on the surface of the nanotubes. When two of these
final electrodes are sandwiched close together, an applied voltage loads one side with electrons while the other is drained,
creating a charged super-stretchable supercapacitor.
Stretchable supercapacitors could power some devices on
their own or they could be combined with other components
to overcome engineering challenges; for example, supercapacitors can be charged in a matter of seconds and then slowly recharge a battery that acts as the primary source of energy
for a device. This approach has been used for regenerative
breaking in hybrid cars, where energy is generated faster than
it can be stored. Supercapacitors increase the efficiency of
the whole system.
For more information, contact Ken Kingery at ken.kingery@duke.
edu; 919-660-8414.

Polymer/Ceramic Composite as a Thin-Film Solid Electrolyte
This composite can be used in lithium metal batteries.
Oak Ridge National Laboratory, Oak Ridge, Tennessee

ithium metal may potentially increase the energy density in
rechargeable batteries beyond what is currently achieved by
commercial lithium-ion batteries. The key to improving density lies in developing a powerful, thin, solid electrolyte. Solid
polymer electrolytes are flexible and low-cost but have low conductivity while ceramic-based electrolytes offer better conductivity but are too brittle to process.
Researchers have developed a thin-film, highly conductive,
solid-state electrolyte made of a polymer and ceramic-based
composite for lithium metal batteries. The electrolyte's novel
design is a three-dimensional interconnected structure that
can provide mechanical robustness and high lithium ionic conductivity at room temperature.
The film was fabricated by first forming a doped-lithium aluminum titanium phosphate ceramic thin film with thickness of
~25 μm by aqueous spray coating, a scalable process. The film is

partially sintered to form a three-dimensionally interconnected
structure with a dense backbone. It is then backfilled with a crosslinkable poly(ethylene oxide) (PEO)-based polymer electrolyte.
For more information, contact Jennifer J. Burke at burkejj@
ornl.gov; 865-414-6835.

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The thin-film solid-state electrolyte's three-dimensionally interconnected
structure increased conductivity through the ceramic base. (Credit: Xi
Chen/Oak Ridge National Laboratory, U.S. Dept. of Energy)

Tech Briefs, April 2021

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Tech Briefs Magazine - April 2021

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