Lithium ion battery
As ever there's a big gap to be bridged between lab tests and industrial-scale application, but tests seem promising.
The latest lithium-ion batteries on the market are likely to extend the charge-to-charge life of phones and electric cars by as much as 40 percent, says TechXplore.
This leap forward, which comes after more than a decade of incremental improvements, is happening because developers replaced the battery's graphite anode with one made from silicon.
Research from Drexel University and Trinity College in Ireland now suggests that an even greater improvement could be in line if the silicon is fortified with a special type of material called MXene.
This adjustment could extend the life of Li-ion batteries as much as five times, the group recently reported in Nature Communications. It's possible because of the two-dimensional MXene material's ability to prevent the silicon anode from expanding to its breaking point during charging—a problem that's prevented its use for some time.
"Silicon anodes are projected to replace graphite anodes in Li-ion batteries with a huge impact on the amount of energy stored," said Yury Gogotsi, Ph.D., Distinguished University and Bach Professor in Drexel's College of Engineering and director of the A.J. Drexel Nanomaterials Institute in the Department of Materials Science and Engineering, who was a co-author of the research. "We've discovered adding MXene materials to the silicon anodes can stabilize them enough to actually be used in batteries."
In batteries, charge is held in electrodes—the cathode and anode—and delivered to our devices as ions travel from anode to cathode. The ions return to the anode when the battery is recharged. Battery life has steadily been increased by finding ways to improve the electrodes' ability to send and receive more ions.
Substituting silicon for graphite as the primary material in the Li-ion anode would improve its capacity for taking in ions because each silicon atom can accept up to four lithium ions, while in graphite anodes, six carbon atoms take in just one lithium. But as it charges, silicon also expands—as much as 300 percent—which can cause it to break and the battery to malfunction.
Most solutions to this problem have involved adding carbon materials and polymer binders to create a framework to contain the silicon. The process for doing it, according to Gogotsi, is complex and carbon contributes little to charge storage by the battery.
By contrast, the Drexel and Trinity group's method mixes silicon powder into a MXene solution to create a hybrid silicon-MXene anode. MXene nanosheets distribute randomly and form a continuous network while wrapping around the silicon particles, thus acting as conductive additive and binder at the same time. It's the MXene framework that also imposes order on ions as they arrive and prevents the anode from expanding.
"MXenes are the key to helping silicon reach its potential in batteries," Gogotsi said. "Because MXenes are two-dimensional materials, there is more room for the ions in the anode and they can move more quickly into it—thus improving both capacity and conductivity of the electrode. They also have excellent mechanical strength, so silicon-MXene anodes are also quite durable up to 450 microns thickness."
Full report here.
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