Microwaving recycled plastic boosts lithium sulfur battery

May 10, 2018 // By Nick Flaherty
Researchers in the US have microwaved recycled plastics to boost the lifetime of lithium sulfur batteries.

Engineers at Purdue University put ink-free plastic soaked in a solvent containing sulfur into a microwave, and used that as a carbon scaffold for a lithium sulfur battery cell.

Lithium-sulfur batteries are cheaper and more energy-dense at 2600 Wh/kg than lithium ion cells but struggle with limited lifetime of around 100 cycles. The process, published in ACS Applied Materials and Interfaces, shows that putting sulfur-soaked plastic in a microwave, including transparent plastic bags, transforms the material into the ideal substance for increasing the lifespan of the forthcoming batteries to more than 200 cycles.

"No matter how many times you recycle plastic, that plastic stays on the earth," said Vilas Pol, associate professor in Purdue's School of Chemical Engineering. "We've been thinking of ways to get rid of it for a long time, and this is a way to at least add value."

Low-density polyethylene plastic, which is used for packaging and comprises a big portion of plastic waste, helps address the polysulfide shuttling effect that limits how long a battery can last between charges. When a current is applied to the cell, lithium ions migrate to the sulfur and a chemical reaction takes place to produce lithium sulfide. The byproduct of this reaction, polysulfide, tend 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 lifespan.

"The easiest way to block polysulfide is to place a physical barrier between lithium and sulfur," said Patrick Kim, a Purdue postdoc research associate in chemical engineering.

Previous studies had attempted making this barrier out of biomass, such as banana peels and pistachio shells, because the pores in biomass-derived carbon had the potential to catch polysulfide. Instead, the researchers looked at how plastic might be incorporated into a carbon scaffold to suppress polysulfide shuttling in a battery. 

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