Waterloo researchers step closer to energy dense Li-S rechargeable battery

Chemistry researchers at Waterloo University announced a breakthrough in making lithium-sulphur (Li-S) batteries a feasible and better alternative to the lithium cobalt oxide cathode currently used in lithium-ion cells.

Sulphur is not only a cheaper, lighter and more abundant material, the researchers say, but Li-S also possesses a significantly higher energy density, opening the possibility of powering electric vehicles three times further than current cells. Such a battery would also lower the cost (and weight) of the most expensive EV component.

While the superiority of Li-S has been known for years, it also has major challenges. It’s main drawback has been that a sulphur cathode exhausts itself after only a few recharge cycles. Typically, the sulphur dissolves into the electrolyte solution as it’s reduced by incoming electrons to form polysulphides.

However, Chemistry Professor Linda Nazar and her research team in the Faculty of Science at the University of Waterloo discovered that ultra-thin nanosheets of manganese dioxide (MnO2) maintains the rechargable sulphur cathode.

They found that the oxygenated surface of the MnO2 nanosheet chemically recycles the sulphides in a two-step process involving a surface-bound intermediate, polythiosulfate. The result is a high-performance cathode that can recharge more than 2000 cycles.

“Very few researchers study or even teach sulphur chemistry anymore,” said Nazar, who also holds the Canada Research Chair in Solid State Energy Materials.. “It’s ironic we had to look so far back in the literature to understand something that may so radically change our future.”

Postdoctoral research associate Xiao Liang, the lead author, and graduate students Connor Hart and Quan Pang also discovered that graphene oxide seems to work by a similar mechanism. They are currently investigating other oxides to find the best sulphur retaining material.
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