For decades, researchers and technologists have regarded batteries and
capacitors as two distinct energy storage devices: batteries, known for
storing more energy but releasing it slowly; and capacitors, which quickly
discharge energy in smaller spurts. But an international team of
researchers, including co-author
Yury Gogotsi, PhD, Distinguished University and Bach professor of Materials Science and
Engineering, now suggests that these mechanisms exist on a smooth spectrum,
and that trying to categorize a device as one or the other could be
hampering progress in the field.
Yury Gogotsi, PhD
What happens in-between classic batteries and supercapacitors has been a
controversial topic for a long time,” Gogotsi says. “So-called
‘pseudocapacitors’ and hybrid energy storage devices have been studied for
at least 30 years, but some scientists have attempted to reject
pseudocapacitance completely, claiming that there are only these two extreme
cases and everything else is a superposition of two mechanisms acting in
parallel.”
The authors point out that in many of these hybrid devices, ions are nearly
absorbed between layers of electrode materials. In others, where porous
nanomaterials in electrodes have been designed to maximize the full chemical
intake, or adsorption, of ions, researchers have seen much faster energy
discharges, likely due to the persistence of the electrolyte substance
preventing the ions from fully intercalating.
Both instances fall outside of the traditional binary definition, but their
properties are proving to be a valuable combination when it comes to
powering new technology.
“We expect that understanding the ion desolvation and its role in
determining the energy storage mechanism will allow us to reach the point
when we combine high energy and high power in a single energy storage
device,” Gogotsi said. “Think of batteries charging within a few minutes –
you plug in your cell phone, unplug it a few minutes later, and can use it
at least for a few hours. With 2D materials, like MXenes or graphenes, we
can make flexible batteries for flexible and wearable electronics that can
charge quickly and be used for a long time on a single charge.”