To keep up with our advancing mobile technology, energy storage devices have been subject to material shrinking in the design process, which has left them vulnerable to short circuiting—as in recent cases with Samsung's Galaxy Note devices—which, when compounded with the presence of a flammable electrolyte liquid, can create an explosive situation.
So instead of a flammable electrolyte solution, the device designed by Vibha Kalra, a professor in Drexel University's College of Engineering, and her team, used a thick ion-rich gel electrolyte absorbed in a freestanding mat of porous carbon nanofibers to produce a liquid-free device.
The group recently published its new design for a "solvent-free solid-state supercapacitor" in the American Chemical Society journal Applied Materials and Interfaces.
"We have completely eliminated the component that can catch fire in these devices," Kalra said. "And, in doing so, we have also created an electrode that could enable energy storage devices to become lighter and better."
Not only is the group's supercapacitor solvent-free, but the compact design is also more durable and its energy storage capacity and charge-discharge lifespan are better than comparable devices currently being used. It is also able to operate at temperatures as high as 300 C, which means it would make mobile devices much more durable and less likely to become a fire hazard due to abuse.
"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 said. "The open-pore electrode is also free of binding agents that act as insulators and diminish performance."
The key to producing this durable device is a fiber-like electrode framework that the team created using a process called electrospinning. The process deposits a carbon precursor polymer solution in the form of a fibrous mat by extruding it through a rotating electric field.
The ionogel is then absorbed in the carbon fiber mat to create a complete electrode-electrolyte network. Its excellent performance characteristics are tied to this unique way of combining electrode and electrolyte solutions so that they are making contact over a larger surface area.
The mat also eliminates the need for many of the scaffolding materials that are essential parts of forming the physical electrode, but don't play a role in the energy storage process and contribute a good bit to the device's overall weight.
"State of the art electrodes are composed of fine powders that need to be blended with binding agents and made into a slurry, which is then applied into the device. These binders add dead weight to the device, as they are not conductive materials, and they actually hinder its performance," Kalra said. "Our electrodes are freestanding, thus eliminating the need for binders, whose processing can account for as much as 20 percent of the cost of manufacturing an electrode."
The next step for Kalra's group will be applying this technique to the production of solid-state batteries as well as exploring its application for smart fabrics.
For more cutting-edge electronics research, check out the First Biocompatible Ion Current Battery.