Asymmetric ultracapcitors combine the benefits of ultracaps—very high discharge rates and cycle life—with those of batteries—high energy densities and low self-discharge rates—to create a device that has significantly lower self discharge and much higher energy density than ultracapacitors, and significantly higher discharge rates and recharge cycles compared to batteries.

Most batteries that contain nickel oxyhydroxide use metallic nickel as a mechanical support and a current collector, said chemistry professor Bahne Cornilsen, who suggested replacing the nickel with carbon foam as a means to reduce the weight and cost of the storage device.

It’s lighter and cheaper, so we thought maybe we could use it as a scaffold, filling its holes with nickel oxyhydroxide. The carbon foam we are using has 72 percent porosity. That means 72 percent of its volume is empty space, so there’s plenty of room for the nickel oxyhydroxide. The carbon foam could also be made of renewable biomass, and that’s attractive.

—Tony Rogers, associate professor of chemical engineering

So far the team has achieved more than 127,000 cycles in their testing.

“Being lighter would give it a real advantage in handheld power tools and consumer electronics,” said Rogers. Hybrid electric vehicles are another potential market, since an asymmetric capacitor can charge and discharge more rapidly than a normal battery, making it useful for regenerative braking.

The group has applied for a patent on their new technology. Chemical engineering professor Michael Mullins is also a member of the research team. Graduate students contributing to the project are PhD graduate Matthew Chye and PhD student Wen Nee Yeo of the chemical engineering department and MS student Padmanaban Sasthan Kuttipillai and PhD student Jinjin Wang of the chemistry department.

The research is funded by the US Department of Energy,the Michigan Universities Commercialization Initiative, the Michigan Tech Research Excellence Fund and the Michigan Space Grant Consortium.