PSI researcher Claire Villevieille, head of the Battery Materials Group, at the instrument for X-ray diffraction.
Paul Scherrer Institut / Markus Fischer
Lithium-sulphur batteries can theoretically deliver significantly more energy than modern lithium-ion batteries, but today’s prototypes lose capacity significantly after only a few charging cycles. In collaboration with Grenoble Alpes University in France, materials researchers at the Paul Scherrer Institute (PSI) in Switzerland have used an-X-ray-based procedure to make visible the way internal processes in the lithium-sulphur batteries lead to capacity loss. The researchers showed that when quartz powder is added to the liquid component of the battery, it can slow down the loss. Its use as an additive in the liquid component of the battery increases the available energy and curbs the capacity loss that sets in over time according to the researchers.
Other researchers had previously already determined that quartz powder interacts with the materials in lithium-sulphur batteries. The PSI researchers have now quantified the benefit of quartz powder. With this additive, a lithium-sulphur battery’s performance is improved by 25 to 30 percent, says PSI researcher Claire Villevieille, co-author of the study: “We simply added the quartz powder to the electrolyte – that is, the liquid component of the battery – like adding washing powder to the laundry.”
Coulombic efficiency rises from around 80 to 90 percent
The researchers found that quartz powder binds unwanted rogue polysulphides that pass into the battery’s liquid component during the operation of the lithium-sulphur battery, the same way as soap binds dirt. This increases and preserves the charging capacity because the battery interior stays clean and functional for a longer time, and the reversibility of the discharging process improves according to the researchers. “We call this the Coulombic efficiency”, explains Villevieille. It should increase from around 80 to 90 percent. By comparison, the Coulombic efficiency of a conventional lithium-ion battery is more than 99.9 percent.
Quartz powder works like a laundry detergent
The positive effect of quartz was revealed when the PSI researchers, together with a colleague at Grenoble Alpes University, examined the chemical processes within the battery using a method known as operando X-ray diffraction. To make the polysulphides visible, the researchers dipped glass fibres into the electrolyte. Unexpectedly, they found that the glass fibres reduced the unwanted accumulation of sulphides. The researchers inferred that since glass consists mainly of quartz, it was natural to begin using quartz powder as a type of cleaning agent in the batteries.
Inexpensive and straightforward
The researchers acknowledge that there are, in principle, other approaches by which polysulphides can be prevented from dissolving and limiting the battery function: But these were either very complicated or very expensive or both, especially when the method needs to be implemented on an industrial scale. Quartz, in contrast, is inexpensive and simple to add to the electrolyte.