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Materials

Ionic liquid gel gives supercapacitors a boost

Encasing the charge-conducting material in methyl cellulose yields gelled electrolyte for charge-storage devices

by Mitch Jacoby
October 2, 2017 | APPEARED IN VOLUME 95, ISSUE 39

Credit: ACS Appl. Mater. Interfaces
Carbon nanofibers a few hundred nanometers wide (left) coated with an ionic liquid electrolyte gel (center) serve as electrodes in long-lasting supercapacitors (right, zoomed-out cross section shows two electrodes on either side of a separator).

A simple method for confining an ionic liquid in a methyl cellulose matrix yields a porous, gel-like material that may be useful for fabricating supercapacitors, according to a new study (ACS Appl. Mater. Interfaces 2017,DOI: 10.1021/acsami.7b07479). Supercapacitors are rechargeable electrostatic energy storage devices that are widely used in electric vehicles, medical devices, and consumer electronics. Unlike batteries, which store a relatively large electrical charge and deliver energy slowly, supercapacitors deliver limited quantities of electrical energy in rapid bursts. Broadening the voltage window over which supercapacitors operate could help expand their range of applications. For that reason, researchers have tried replacing the aqueous electrolytes typically used in these devices with nonaqueous substitutes such as ionic liquids. But ionic liquids often cause leakage and corrosion problems. So a team led by Vibha Kalra of Drexel University and Parameswara Rao Chinnam of Temple University devised a method to bypass those problems. The team prepared an ionic liquid solution containing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and a small amount of methyl cellulose. Then they used that solution, which entraps the ionic liquid in a durable polymeric matrix, as a gelled electrolyte to coat highly porous carbon nanofiber mesh electrodes. From that material, the team made high-performing supercapacitors that retained more than 95% of their initial capacitance, even after 20,000 charging cycles.

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