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Researchers at Virginia Tech’s (Blacksburg, Va., U.S.) College of Science are finding industrial uses for porous carbon fibers in electrochemical energy storage.

The carbon fibers, as recently reported by CW, have been developed by Guoliang “Greg” Liu, an assistant professor of chemistry and member of the Macromolecules Innovation Institute. His lab used block copolymers to create carbon fibers with mesopores uniformly scattered throughout, making them similar to a sponge.

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Liu’s in Nature Communications shows how these fibers can enable high energy density and high electron/ion charging rates, which are typically mutually exclusive in electrochemical energy storage devices. Liu’s long-term vision is to build exterior car shells out of porous carbon fibers that could store energy within the pores.

“This is the next step that will be relevant to industry,” Liu says. “We want to make an industrial-friendly process. Now industry should seriously look at carbon fiber not only as a structural material but also as an energy storage platform for cars, aircrafts and others.”

According to Liu, carbon fiber has been used for energy storage when coupled with pseudocapacitive materials such as manganese oxide (Mn02), which enable the fiber to store a large amount of energy. Liu studied the use of MnO2 in his research, soaking the carbon fibers in a solution of KMnO4 precursor. The precursor then reacted with the carbon, etching away a thin layer of carbon and anchoring onto the rest of the carbon, creating a thin coat of about 2 nanometers in thickness.

However, according to Liu, using MnO2 in this way can create the problem of slow charge-discharge rates. Too little MnO2 means the storage capacity is too low. Too much MnO2 creates too thick of a coat that is electrically insulating and slows down the transport of ions.

Liu’s porous carbon fibers reportedly have the ability to overcome this challenge. Tests in his lab showed high loading of MnO2 as well as sustained high charging and discharging rates. Liu’s lab loaded up to 7 mg/cm² of MnO2 before performance dropped. That’s reportedly double or nearly triple the amount of MnO2 that industry can currently utilize.

“We have achieved 84 percent of the theoretical limit of this material at a mass loading of 7 mg/cm²,” Liu says. “If you load 7 mg/cm² of other materials, you will not reach this.”

In the long term, Liu sees electric supercacitor cars replacing gasoline-powered vehicles. In the short term, he looks toward using carbon fiber parts to deliver energy in a short period to accelerate cars faster. Beyond the automotive industry, Liu envisions uses for his fiber in other transportation applications such as delivery drones. 

“If you want a drone to deliver products for Amazon, you want the drone to carry as much weight as possible, and you want the drone to be as lightweight as possible,” Liu says. “Carbon fiber-based drones can do both jobs. The carbon fibers are strong structural materials for carrying the goods, and they are energy storage materials to provide power for transportation.”

The first author of the most recent paper is Tianyu Liu, a postdoctoral associate in the Liu Lab. Also involved in the research were Zhengping Zhou and Yichen Guo, two former postdoctoral associates, and Dong Guo, a third-year doctoral student in the Department of Chemistry.