Supercapacitor Holds 74% Capacity After 40 Hammer Strikes

April 29, 2019 by Scott McMahan

Researchers at Washington University in St. Louis created a supercapacitor that can withstand a hammer striking it more than 40 times. The supercapacitor is also non-flammable, unlike lithium-ion batteries. The work is featured as the cover story of the April 23 edition of the journal Sustainable Energy and Fuels.

"Accidentally dropping electronics, such as a laptop or cellphone, is a common scenario that may lead to the failure of the device," said Julio D'Arcy, assistant professor of chemistry in Arts & Sciences. "In some cases, energy storage devices catch on fire due to impact-caused failure. The chance of impact damage will only increase as electronics become more flexible and worn on the human body."

Hongmin Wang, a chemistry Ph.D. candidate who works in D'Arcy's lab, led the work to create the new material.

The researchers controlled the formation of rust in the solution, to grow a micrometer-thick porous mat of conducting fibers attached to a soft, bendable layer of organic plastic resulting in an open-faced sandwich. (See the illustration above courtesy of D'Arcy laboratory / Washington University).

"This is the same mechanism that is responsible for the formation of rust on the surface of a wet piece of steel," D'Arcy said. "Here, we have carefully designed the nanostructure orientation so that a polymer film assembles parallel to a rusted surface. It produces an interwoven mat of polymer nanofibers with a textile-like structure that is flexible and ideal for storing energy in a supercapacitor."

They repeatedly bent the new material to different angles. They hammered it over and over, and they also tested it before and after an impact equivalent to a car collision at 30 mph. The same amount of impact would fracture other materials such as metal and carbon.

After the first hammer strike, the material retained 80 percent of its ability to store energy at peak efficiencies. Even after 40 repeated strikes, it was still at 74 percent energy storage capacity.

Specifically, they used template-less direct vapor synthesis to produce a mat of poly(3,4-ethylenedioxythiophene) (PEDOT) 1D nanostructures. According to the researchers, the nanofibers "weave" in situ into a micrometer-thick porous fibrillar mat.

The nanofibrillar PEDOT mat had a high conductivity (334Scm−1), capacitance (164F/g) and was stable after bending. It withstood an impact energy density of 125 kJ/m2 and continued storing 80% of its original capacity. Then after 40 strikes the energy storage capacity only went down another 6%.

Reference Material

Wang, H., Santino, L. M., Rubin, M., Diao, Y. , Lu, Y., and D'Arcy, J. Self-woven nanofibrillar PEDOT mats for impact-resistant supercapacitors, 18 January 2019, Sustainable Energy Fuels, 2019,3, 1154-1162