Researchers in the U.S. have developed a new lithium-sulfur battery chemistry that allows sulfur to participate in an additional energy-storing reaction, potentially increasing how much energy these experimental batteries can hold.

The team from Vanderbilt University and the University of Maryland used chlorine to enable sulfur atoms to exchange a third electron during charging and discharging. 

Laboratory tests showed the approach increased sulfur’s charge-storage capacity by about 58 percent while raising the average operating voltage from roughly 2.05 volts to 2.54 volts.

The findings could help researchers extract more energy from sulfur, an abundant and relatively inexpensive material already being explored as an alternative to cathode materials used in lithium-ion batteries.

Lithium-sulfur batteries have attracted attention because sulfur can store considerably more charge by weight than materials commonly used in lithium-ion cathodes. However, conventional lithium-sulfur chemistry operates at a relatively low voltage.

“The traditional way of thinking about lithium-sulfur batteries leaves some of sulfur’s redox power untapped. We wanted to see whether we could expand sulfur’s redox capability and use it to store more energy,” said De-en Jiang, the H. Eugene McBrayer Professor of Chemical Engineering and Professor of Chemistry at Vanderbilt University. 

In conventional lithium-sulfur batteries, each sulfur atom exchanges two electrons as the battery charges and discharges. The researchers introduced chlorine to extend this process, enabling sulfur to exchange a third electron.

The additional reaction occurs at a higher voltage. Together, the increased charge capacity and voltage enabled one kilogram of sulfur to store more than 1,700 watt-hours of energy in the experimental cell.

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