Research team aims to further enhance the potential of lithium-sulfur batteries
Researchers from Vanderbilt University and the University of Maryland have introduced a new cell chemistry that could significantly increase the energy density of lithium-sulfur batteries. By incorporating chlorine, this approach enables additional electron transfer at higher voltages.
Graphic: Vanderbilt University
Lithium-sulfur batteries have long been considered a promising alternative to conventional lithium-ion cells, as sulfur is abundant and can store significantly more charge per unit weight. However, making them durable and practical has proven difficult so far.
In a study published in the journal “Nature Energy,” a team from the U.S. universities Vanderbilt University and University of Maryland describes a new approach in which sulfur participates in an additional energy-storing reaction. The result is a sulfur-based battery that operates at a higher average voltage and can store more charge.
Prototype of lithium-sulfur battery capable of storing 1,700 watt-hours of energy
In conventional systems, each sulfur atom exchanges two electrons, but the novel system incorporates chlorine to transfer a third electron. In laboratory tests, this increased sulfur’s storage capacity by about 58 percent and raised the average operating voltage from around 2.05 volts to 2.54 volts. Thanks to the combined improved charge storage capacity and higher voltage, one kilogram of sulfur in the experimental cell was able to store more than 1,700 watt-hours of energy.
To ensure reversibility, the researchers used molecular simulations to design an electrolyte. This electrolyte keeps chlorine reactive while preventing the resulting sulfur-chlorine product from dissolving and migrating to the lithium-metal anode.
78 Percent Capacity After 100 Charge Cycles
Various spectroscopy techniques confirmed that sulfur repeatedly moved through the new state during charging and discharging processes. A fabricated pouch cell retained 78 percent of its initial capacity after 100 charging cycles.
However, much work remains before commercial use is possible, as the prototype uses a lithium-metal anode and larger amounts of electrolyte. Considering all key battery components—not just the electrodes alone—scientists estimate that this approach could achieve a gravimetric energy density of 477 Wh/kg. This would represent roughly 37 percent higher than that of comparable conventional lithium-sulfur systems.
"The traditional perspective on lithium-sulfur batteries leaves part of the sulfur’s redox capacity unutilized," said De-en Jiang, professor of Chemical Engineering and Chemistry at Vanderbilt University and co-corresponding author of the study. "We wanted to find out if we could expand sulfur’s redox capability and use it to store more energy."
