"Ion highway" electrodes drive development of batteries that charge in seconds

"Ion highway" electrodes drive development of batteries that charge in seconds
An electrode made of the 2D material MXene could lead to batteries that charge in a matter of seconds
An electrode made of the 2D material MXene could lead to batteries that charge in a matter of seconds
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An electrode made of the 2D material MXene could lead to batteries that charge in a matter of seconds
An electrode made of the 2D material MXene could lead to batteries that charge in a matter of seconds

Supercapacitors can charge and release energy much faster than batteries, but they can't store as much. Now a team at Drexel University has used the two-dimensional material MXene to develop a new type of electrode, combining the capacitance of a regular battery with the speed of a supercapacitor, which could lead to devices that recharge in a matter of seconds.

The anxiety of a slowly-charging battery is something we're all familiar with, so it's not surprising that engineers are working on the issue. We've already seen teams tackle the problem using nanodots to improve electrode capacitance and electrolyte performance, and flexible supercapacitors with better charge times and lifespan. The Drexel team's first step towards striking a better balance between speed and storage, was to make the new electrodes out of MXene, a 2D material that's highly conductive.

"This paper refutes the widely accepted dogma that chemical charge storage, used in batteries and pseudocapacitors, is always much slower than physical storage used in electrical double-layer capacitors, also known as supercapacitors," says Yury Gogotsi, lead researcher on the team. "We demonstrate charging of thin MXene electrodes in tens of milliseconds. This is enabled by very high electronic conductivity of MXene. This paves the way to development of ultrafast energy storage devices than can be charged and discharged within seconds, but store much more energy than conventional supercapacitors."

The structure of the electrodes is just as important as the material. To store a charge, ions are held in ports called redox active sites, so the more of these ports there are, the more energy the battery can store. Not only does the new electrode pack in more redox active sites, but it's "macroporous", meaning it has plenty of small openings to allow more ions to reach the ports at the same time.

"In traditional batteries and supercapacitors, ions have a tortuous path toward charge storage ports, which not only slows down everything, but it also creates a situation where very few ions actually reach their destination at fast charging rates," says Maria Lukatskaya, first author of the paper. "The ideal electrode architecture would be something like ions moving to the ports via multi-lane, high-speed 'highways,' instead of taking single-lane roads. Our macroporous electrode design achieves this goal, which allows for rapid charging — on the order of a few seconds or less."

The research was published in the journal Nature Energy.

Source: Drexel University

So does this tech truly solve both the energy density and power density issues? Does it do so within reasonable space and weight constraints? More importantly, is it durable to allow a high charge/discharge cycle lifetime? And most importantly, is it cost effective and manufacturable? So many promising concepts appear, only to fade away without delivering on that promise!
When supercapacitors become the norm the world changes over night and a new epoch endures--the "Electrocopene". The age of the Jetsons is near.
Bruce H. Anderson
Moving upstream, one needs to consider what kind of conductors are necessary to deliver the kind of current for fast-charging anything.
Bruce is right: Imagine a laptop battery of 50Wh or so, charging in 5s. The charging power would be 36kW - if the charging process is 100% efficient. Existing power supplies are of the 100W size, and draw about 1 A, so they'd have to be 360x bigger and draw 360 A. That'll work...
Moving to a reasonable charging efficiency, say 90%, the heat dissipation at 36kW would be 3600W - enough to heat the battery to unsafe levels very quickly, and to almost certainly melt some components.
Now, imagine all that for a car-sized battery, e.g. 50kWh... Hilarity ensues. :)
And I thought that batteries had capacity measured in Watt Hours and capacitors had capacitance measured in Farads. You learn something new every day!
Ralf Biernacki
@ physics: You're basically spot-on. There is one workaround, the same used for long-distance power transmission: step up the voltage. If you charge at 120 V instead of 12 V, you will only have 36 A of charging current, a more reasonable proposition. The battery would have to be designed to reconfigure itself so that its cells are charged in series, and discharged mostly in parallel. It is still beyond the capacity of most household power supplies, and while I think that charging efficiency for this design can be brought to, say, 98%, there would still be a lot of heat generated. So I don't think 5s is realistic, either. 50s is more like it---that's not bad. And for car batteries the situation still looks hopeless, even with dedicated hi-current, hi-voltage charging stations, because of the heat issue.
Ralf Biernacki
@ Basil: that's because capacitors work at a broad range of voltages, and their energy capacity is proportional to voltage squared. Batteries (including the one described in the article) work at a nearly constant voltage, because that voltage is the electrochemical potential of their electrodes. If you keep voltage constant, capacity in farads is proportional to watt hours.