Conductive Clay -- the Future of Energy Storage?

A new material that behaves like clay could be the future of supercapacitors and batteries that are easy to produce, last longer, and charge faster than what's currently on the market, Drexel University researchers said.

Called MXene clay, the material -- which is two-dimensional and comprised of three layers of titanium and two layers of carbon that's five atoms thick -- was developed by a team of researchers in Drexel's Department of Materials Science and Engineering led by Distinguished Professor Michel Barsoum.

Barsoum and his team discovered MXene while working on research funded by the Department of Energy to use a titanium-based, layered ceramic material called a MAX phase as an electrode for a supercapacitor. Specifically, doctoral student Michael Ghidiu, while applying a chemical etching process to remove aluminum from the MAX phase, wanted to swap out the process' typical use of hydrofluoric acid, which is toxic and unpleasant to work with, Barsoum told Design News, in an interview.

Ghidiu instead used a fluoride salt and hydrochloric acid, which are nontoxic and thus much safer to work with than hydrofluoric acid, to reduce the MAX phase to a pile of black particles, which he then washed in water. When Ghidiu did that, the material became clay-like and was something "that did not exist before," Barsoum told us.

"Our initial intention was to get rid of hydrofluoric acid, and what we got was something that behaved like clay," he said. "Now all of a sudden we have this new material; it's cheap, you can roll it, mold it, do anything you want with it."

When the team used the material as one of the electrodes in a supercapacitor, the storage numbers were "eye-popping," Barsoum said, at 900 farods per centimeter cubed -- or about two to three times the charge storage of the best carbon-based supercapacitor currently available commercially.

Barsoum and his team published a paper on their research in the journal Nature. While the paper focuses on MXene's use in supercapacitors, it also can be used as an electrode in batteries, and could potentially provide a storage advantage over materials used in lithium-ion batteries on the market, he said.

"We don't want to confine it to supercap at this point," Barsoum said, although so far, the storage results of the material's use as an electrode in lithium batteries is not as good as a commercial Sony battery. However, the team is working to confirm some capacity performance results that are better than commercial lithium batteries, he said.

MXene also has a number of production advantages over current battery materials in that it is inexpensive and non-toxic. From a production point of view, we do everything in water," Barsoum said. "It's plentiful, cheap, and environmentally benign. So this is a big advantage."

The team will continue to work with the material to achieve better energy-storage results in supercapacitors and batteries, he added.

Watch MXene in action:

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