Nanomaterial-packed cathode extends range of EV lithium-sulfur batteries

April 17, 2014 // By Paul Buckley
Researchers at the USA's Department of Energy Pacific Northwest National Laboratory have developed a metal organic framework that can be added to an electric vehicle battery's cathode to capture polysulfides that cause lithium-sulfur batteries to fail after a few charges.

Adding the powdery nanomaterial could help EVs to travel farther by extending the mileage range of lithium-sulfur batteries.

"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 Department of Energy's Pacific Northwest National Laboratory. "Our metal organic framework may offer a new way to make that happen."

Small batteries are shown being tested at PNNL

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.

The lithium-sulfur battery's main obstacles are unwanted side reactions that cut the battery's life short. The undesirable action starts on the battery's sulfur-containing cathode, which slowly disintegrates and forms molecules called polysulfides that dissolve into the liquid electrolyte. Some of the sulfur - an essential part of the battery's chemical reactions - never returns to the cathode. As a result, the cathode has less material to keep the reactions going and the battery quickly dies.

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