Engineers at Purdue University have found a way to increase the life of lithium-sulfur batteries which has the added benefit of being a way to recycle plastic bags.

Lithium-sulfur batteries have been seen as the next generation of batteries to replace the current lithium ion batteeries. Lithium-sulfur batteries are cheaper and more energy-dense than lithium ion batteries but those developed so far don’t last as long – only being usable for about 100 charging cycles.

The Purdue researchers have shown that putting sulfur-soaked plastic in a microwave transforms the material into the ideal substance for increasing the life span of the forthcoming batteries to more than 200 charging-discharging cycles.

A phenomenon called the polysulfide shuttling effect limits how long a battery can last between charges. When a current is applied, lithium ions migrate to the sulfur and a chemical reaction takes place to produce lithium sulfide. The byproduct of this reaction, polysulfide, tends to cross back over to the lithium side and prevent the migration of lithium ions to sulfur. This decreases the charge capacity of a battery as well as their life span.

The easiest way to block polysulfide is to place a physical barrier between the lithium and the sulfur.

Transparent plastic bags, which comprise a big portion of plastic waste, are made from low-density polyethylene. This yields carbon when combined with sulfonated groups.

The researchers soaked plastic bags in a sulfur-containing solvent and put them in a microwave to provide the quick boost in temperature. The heat promoted the sulfonation and carbonization of the plastic and induced a higher density of pores for catching polysulfide. The low-density polyethylene plastic could then be made into a carbon scaffold to provide the barrier between the lithium and sulfur halves of a coin cell battery.

The researchers are now working on fabricating larger batteries using this concept.