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Healable Cathode Could Unlock Potential of Solid-state Lithium-sulfur Batteries

May 27, 2024

The University of California San Diego, in collaboration with chemists from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, has developed a new cathode material for solid-state lithium-sulfur batteries.

This material is structurally healable and highly conductive, overcoming the limitations of current cathodes. The research team utilized three beamlines at the National Synchrotron Light Source II (NSLS-II) and electron microscopes at the Center for Functional Nanomaterials, both DOE Office of Science user facilities, to characterize a sulfur iodide cathode material that significantly enhances the cyclability of a solid-state lithium-sulfur battery.

Solid-state lithium-sulfur batteries, composed of a solid electrolyte, a lithium metal anode, and a sulfur cathode, are a promising alternative to current lithium-ion batteries due to their increased energy density and lower costs. They have the potential to store up to twice as much energy per kilogram as conventional lithium-ion batteries, potentially doubling the range of electric vehicles without increasing the battery pack’s weight.

However, the development of these batteries has been hindered by the inherent characteristics of sulfur cathodes. Sulfur is a poor electron conductor and sulfur cathodes experience significant expansion and contraction during charging and discharging, leading to structural damage and decreased contact with the solid electrolyte.

To address these issues, the research team developed a new cathode material: a crystal composed of sulfur and iodine. This drastically increased the cathode material’s electrical conductivity by 11 orders of magnitude, making it 100 billion times more conductive than crystals made of sulfur alone. The new crystal material also possesses a low melting point of 65 degrees Celsius (149 degrees Fahrenheit), allowing the cathode to be easily re-melted after the battery is charged to repair the damaged interfaces from cycling.

The researchers constructed a test battery using the new cathode material and subjected it to repeated charge and discharge cycles. The battery remained stable for over 400 cycles while retaining 87 percent of its capacity.

The team is now working to further advance the solid-state lithium-sulfur battery technology by improving cell engineering designs and scaling up the cell format.

“This sulfur-iodide cathode presents a unique concept for managing some of the main impediments to commercialization of Li-S batteries,” said study co-senior author Shyue Ping Ong, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering.

“The low melting point of our new cathode material makes repairing the interfaces possible, a long sought-after solution for these batteries,” said study co-first author Jianbin Zhou, a former nanoengineering postdoctoral researcher from Liu’s research group.