Researchers at Drexel University’s College of Engineering have taken a huge step toward the fastest smartphone charging yet. The team was led by Yury Gogotsi, PhD, distinguished professor at Drexel in the Department of Materials Science and Engineering.
The team created new electrode designs from MXene, a highly conductive, two-dimensional material. This new design could make energy storage technology like batteries just as fast as the supercapacitors that are often used to provide energy in emergency situations or to provide quick bursts of energy.
"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," Gogotsi said. "We demonstrate charging of thin MXene electrodes in tens of milliseconds. This is enabled by the very high electronic conductivity of MXene. This paves the way to the development of ultrafast energy storage devices than can be charged and discharged within seconds, but store much more energy than conventional supercapacitors."
Electrode design is the key to faster charging. Electrode materials offer ports for the charge to be stored. These ports are called “redox active sites” in electrochemistry and hold an electrical charge when each ion is delivered. Moreore ports means more more energy storage.
Patrice Simon, PhD, and Zifeng Lin, from Université Paul Sabatier in France, produced a hydrogel electrode design that has more redox active sites. This allows the electrode to store as much charge for its volume as a battery. This measure of capacity is called “volumetric performance” and is an important metric for judging the utility of energy storage devices.
To make the hydrogel electrode ports more attractive to ion traffic, the team designed electrode architectures with many small openings—called open macroporosity—to make the redox active sites in the MXene material readily accessible to ions.
"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," said Lukatskaya, the first author on the paper, who conducted the research as part of the A.J. Drexel Nanomaterials Institute. "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."
MXene's advantage as an electrode material is its conductivity. Materials that allow for the rapid flow of an electrical current, for example, aluminum and copper, are often used in electric cables. MXenes are conductive so the ions have a wide-open path to many storage ports, and can move quickly to meet electrons there.
Battery electrodes are the latest application for Mxene since its discovery by Drexel researchers in 2011. Since then reserchers have been testing Mxene in many applications from energy storage to electromagnetic radiation shielding and water filtering. The latest development is significant because it fixes a primary problem that hinders the expansion of the electric vehicle market as well as the mobile devices market.
The paper on this research was published in the journal Nature Energy.