Drexel University researchers have made yet another breakthrough in energy storage technology, with a team publishing their design for a “solvent-free solid-state supercapacitor” in an American Chemical Society journal, Applied Materials & Interfaces.
The team consists of researchers from Drexel University and Temple University and is led by Vibha Kalra, associate professor of chemical engineering at Drexel’s College of Engineering. The team also includes Kalra’s doctoral assistant Sila Simotwo, and Stephanie L. Wunder and Parameswara Chinnam from Temple University.
The team’s design includes a fabric-like electrode that is durable and lighter than what is in current devices for electric energy storage, like batteries and supercapacitors. An important factor in this new design is that it is free of flammable solvents.
Normally, batteries rely on conductive, — and often flammable — liquid solutions to carry charge. In the case that these fluids leak, or a short-circuit occurs, there is an extreme risk for fires and explosions. Samsung recalled its Galaxy Note 7 in Sept. 2016 after reports that the phone could overheat and explode as a result of battery issues.
The team’s new design completely removes the flammable component of the device, instead replacing it with an inflammable substitute. The team used a carbon-nanofiber mat soaked in ion-rich gel as an electrode in the design.
“We have completely eliminated the component that can catch fire in these devices,” Kalra said in an interview with DrexelNow. “And, in doing so, we have also created an electrode that could enable energy storage devices to become lighter and better,” she continued.
Supercapacitors are similar to batteries in that they typically use a flammable electrolyte solution. But supercapacitors give strong bursts of short term power while batteries provide more long term energy.
Kalra’s team was able to make a more durable supercapacitor that does not contain flammable liquid. The energy storage capacity and charge-discharge lifespan are also improved. Since the supercapacitor can operate at up to 300 degrees Celsius, devices will be more durable and less of a fire hazard.
The fact that the electrolytes and electrolyte solution will be able to make contact over a larger surface area is part of the reason why this material will be able to enhance performance in devices.
“To allow industrially relevant electrode thickness and loading, we have developed a cloth-like electrode composed of nanofibers that provides a well-defined three-dimensional open pore structure for easy infusion of the solid electrolyte precursor.” Kalra told DrexelNow. “The open-pore electrode is also free of binding agents that act as insulators and diminish performance.”
The binding agent that is normally needed with the solvent adds weight and decreases the performance of a device since the binders act as insulators instead of conductors. Kalra and his team were able to completely avoid the need for binders.
“Our electrodes are synthesized directly as a freestanding non-woven mat of nanofibers eliminating the need for binders or slurry processing. … they are device-ready and are directly incorporated into the supercapacitor,” Kalra told IEEE Spectrum in an email.
The newly developed electrodes have an energy density of 65 watt-hours per kilogram and a capacitance of 153 Farad per gram. The capacitance fades by four percent over 20,000 charge-discharge cycles. However, the device that the Drexel team has made is not fully flexible.
“This work is currently underway and is the next step in our research. … As of now, the key advantage of this solid state device is elimination of flammable components,” Kalra told IEEE Spectrum.
According to theengineer.co.uk, “[The Drexel team’s] next goal is to construct and test solid-state batteries and explore whether the technology could be used in ‘smart fabrics.’”