Better batteries from waste sulfur

April 16, 2013

A University of Arizona-led research team has discovered a simple process for making a new lightweight plastic (left) from waste sulfur (right) (credit: Jared Griebel/Pyun lab, University of Arizona department of chemistry and biochemistry)

A new chemical process can transform waste sulfur into a lightweight plastic that may improve batteries for electric cars, reports a University of Arizona-led team.

The new plastic also has other potential uses, including optical uses.

The team has successfully used the new plastic to make lithium-sulfur batteries.

Next-generation lithium-sulfur, or Li-S, batteries based on the plastic will be better for electric and hybrid cars and for military uses because they are more efficient, lighter and cheaper than those currently used, said lead researcher Jeffrey Pyun, a UA associate professor of chemistry and biochemistry.

The “garbage of transportation”

The team’s discovery could provide a new use for the sulfur left over when oil and natural gas are refined into cleaner-burning fuels.

Although there are some industrial uses for sulfur, the amount generated from refining fossil fuels far outstrips the current need for the element. Some oil refineries, such as those in Ft. McMurray in Alberta, are accumulating yellow mountains of waste sulfur.

About one-half pound of sulfur is left over for every 19 gallons of gasoline produced from fossil fuels, calculated co-author Jared Griebel, a UA chemistry and biochemistry doctoral candidate.

Better Li-S batteries

Sulfur poses technical challenges. It doesn’t easily form the stable long chains of molecules, known as polymers, needed make a moldable plastic, and most materials don’t dissolve in sulfur.

But Pyun and his colleagues tried something new: transforming liquid sulfur into a useful copolymer that eventually could be produced easily on an industrial scale.

They’ve dubbed their process “inverse vulcanization” because it requires mostly sulfur with a small amount of a “DIB” additive. Vulcanization is the chemical process that makes rubber more durable by adding a small amount of sulfur to rubber.

The new plastic has electrochemical properties superior to those of the elemental sulfur now used in Li-S batteries, the researchers report. The team’s batteries exhibited high specific capacity (823 mAh/g at 100 cycles) and enhanced capacity retention.

The new plastic performs better in batteries than elemental sulfur, Pyun said, because batteries with cathodes made of elemental sulfur can be used and recharged only a limited number of times before they fail.

Several companies have expressed interest in the new plastic and the new battery design, Pyun said.

The team’s next step is comparing properties of the new plastic to existing plastics and exploring other practical applications such as photonics for the new plastic.

The researchers have filed an international patent for their new chemical process and for the new polymeric electrode materials for Li-S batteries.

The National Research Foundation of Korea; the Korean Ministry of Education, Science and Technology, the American Chemical Society; and the University of Arizona funded the research.