The search for the longer-lasting, faster-charging battery keeps going and going…
Inside a ground floor laboratory on a quiet corner of Drexel’s campus, Michael Ghidiu spreads out the raw ingredients for a substance dubbed “MXene clay.”
“This is what it looks like,” he says. “You can see that it goes from a lighter grey color as a powder, to black when it is hydrated.”
The 25-year-old graduate student smears some onto a water-permeable sheet, layering another on top. Picture a pie crust in between two layers of wax paper. Then using a rolling pin, or in this case, just the round surface of a bottle, Ghidiu flattens the clay out.
“Once it dries, you should be able to peel these apart. Then you have a film that looks like this,” he says, holding up a dime-size portion made earlier in the week.
It doesn’t look all that revolutionary, but the titanium-carbide material has the potential to reshape the world of energy storage. The substance is made up of wafer-like layers only one nanometer thick, providing surface area to hold power. It’s also conductive and water-friendly, which simplifies the manufacturing process, making it an attractive raw material to replace graphite in the next generation of lithium ion batteries.
“The material itself, these two-dimensional metal carbides that we call MXene, were discovered here in 2011,” says Drexel professor Michel Barsoum, who is advising Ghidiu’s Ph.D. work. “And the way we used to make them was with hydrofluoric acid, which is a nasty acid. So when Mike joined the group about a year and a half ago, he asked me why are we using HF. I said, ’cause it works.'”
“Well, he asked if he could try hydrochloric acid combined with a fluoride salt,” says Barsoum. The safer process worked, and unexpectedly produced MXene material with a clay-like consistency that can be rolled out like cookie dough and shaped into electrodes.
A FASTER REFUEL
A quick background on portable device power: today, there are batteries, which can hold a lot of energy but charge slowly, and then there are supercapacitors, or “supercaps,” which recharge quickly, but can’t hold as much juice.
“Now, what we are trying to do is something that I don’t think people thought was possible, which was to move supercaps into the realm of batteries,” says Barsoum.
If the clay can combine the best of both worlds, that means a power source that won’t degrade over time. Today, cell phone and laptop batteries have relatively short lifespans, because the daily charging and discharging breaks down the chemicals inside. Barsoum says its not a huge stumbling block, because they’re usually cheap to replace.
“But if you are going to make electric cars, the battery pack is on the order of $10,000,” he continues. “So there is no way you are going to buy a new pack for your car every two years at $10,000 a pop. So that is very big issue.”
Drexel’s clay has been put through 10,000 charge/recharge cycles, without showing any signs it weakens over time. It also fuels up lightening fast.
“By using supercapacitors instead of batteries, what we can do, we can charge [a] phone in several seconds,” says researcher Maria Lukatskaya, a 26-year old Drexel Ph.D. student.
As good as that sounds, don’t expect to find the clay in your next iPhone. The team still needs to increase how much charge it can hold. Right now, Barsoum says MXene is at 900 farads per cubic centimeter, the unit scientists use to measure capacity.
“This is not even first generation, this is zero generation,” he says. “If in a year, we don’t double this number, please come back and interview me cause then we really don’t know what we are doing.”
Twelve months may be a self-imposed milestone for Barsoum, but the industry’s timeline for new materials typically stretches out much longer.
“People want it done in 15 years. Typically, more like 25 to 30 years, so it is a slow process,” he says. “People have a very strong reluctance to use new materials.”
Whatever the long-term outcome for the clay, Barsoum says he’s thrilled his students—Michael and Maria—are able to savor such a major discovery so early in their careers. Their work appears in the prestigious journal Nature.
“There’s nothing that comes close to going to bed at night, knowing something…you are the only person in the history of mankind to know. Doesn’t get any better than that.”