New nanomaterial can allow electric vehicles to travel farther

WASHINGTON: Scientists have used a powdery nanomaterial to extend the lifespan of lithium-sulfur batteries which could increase the driving range of electric vehicles.

Researchers added the powder, a kind of nanomaterial called a metal organic framework, to the battery's cathode to capture problematic polysulfides that usually cause lithium-sulfur batteries to fail after a few charges.

"Lithium-sulfur batteries have the potential to power tomorrow's electric vehicles, but they need to last longer after each charge and be able to be repeatedly recharged," said materials chemist Jie Xiao of the US Department of Energy's Pacific Northwest National Laboratory (PNNL).

"Our metal organic framework may offer a new way to make that happen," Xiao said.

Today's electric vehicles are typically powered by lithium-ion batteries. But the chemistry of lithium-ion batteries limits how much energy they can store.

As a result, electric vehicle drivers are often anxious about how far they can go before needing to charge. One promising solution is the lithium-sulfur battery, which can hold as much as four times more energy per mass than lithium-ion batteries.

This would enable electric vehicles to drive farther on a single charge, as well as help store more renewable energy. The down side of lithium-sulfur batteries, however, is they have a much shorter lifespan because they can't currently be charged as many times as lithium-ion batteries.

Researchers worldwide are trying to improve materials for each battery component to increase the lifespan and mainstream use of lithium-sulfur batteries.

For this research, Xiao and her colleagues honed in on the cathode to stop polysulfides from moving through the electrolyte.

Many materials with tiny holes have been examined to physically trap polysulfides inside the cathode. Metal organic frameworks (MOF) are porous, but the added strength of PNNL's material is its ability to strongly attract the polysulfide molecules.

The framework's positively charged nickel centre tightly binds the polysulfide molecules to the cathodes.

The result is a coordinate covalent bond that, when combined with the framework's porous structure, causes the polysulfides to stay put.

During lab tests, a lithium-sulfur battery with PNNL's MOF cathode maintained 89 per cent of its initial power capacity after 100 charge-and discharge cycles.

The study describing the material was published in the American Chemical Society journal Nano Letters.