Researchers have moved one step closer to creating solid-state batteries from lithium and sulfur a practical reality. A team led by engineers on the University of California San Diego developed a brand new cathode material for solid-state lithium-sulfur batteries that’s electrically conductive and structurally healable — features that overcome the constraints of those batteries’ current cathodes.
The work was published within the journal Nature on March 6.
Solid-state lithium-sulfur batteries are a sort of rechargeable battery consisting of a solid electrolyte, an anode product of lithium metal and a cathode product of sulfur. These batteries hold promise as a superior alternative to current lithium-ion batteries as they provide increased energy density and lower costs. They’ve the potential to store as much as twice as much energy per kilogram as conventional lithium-ion batteries — in other words, they may double the range of electrical vehicles without increasing the battery pack’s weight. Moreover, the usage of abundant, easily sourced materials makes them an economically viable and environmentally friendlier selection.
Nevertheless, the event of lithium-sulfur solid-state batteries has been historically tormented by the inherent characteristics of sulfur cathodes. Not only is sulfur a poor electron conductor, but sulfur cathodes also experience significant expansion and contraction during charging and discharging, resulting in structural damage and decreased contact with the solid electrolyte. These issues collectively diminish the cathode’s ability to transfer charge, compromising the general performance and longevity of the solid-state battery.
To beat these challenges, a team led by researchers on the UC San Diego Sustainable Power and Energy Center developed a brand new cathode material: a crystal composed of sulfur and iodine. By inserting iodine molecules into the crystalline sulfur structure, the researchers drastically increased the cathode material’s electrical conductivity by 11 orders of magnitude, making it 100 billion times more conductive than crystals product of sulfur alone.
“We’re very excited in regards to the discovery of this recent material,” said study co-senior creator Ping Liu, a professor of nanoengineering and director of the Sustainable Power and Energy Center at UC San Diego. “The drastic increase in electrical conductivity in sulfur is a surprise and scientifically very interesting.”
Furthermore, the brand new crystal material possesses a low melting point of 65 degrees Celsius (149 degrees Fahrenheit), which is lower than the temperature of a hot mug of coffee. Which means the cathode will be easily re-melted after the battery is charged to repair the damaged interfaces from cycling. That is a crucial feature to handle the cumulative damage that happens on the solid-solid interface between the cathode and electrolyte during repeated charging and discharging.
“This sulfur-iodide cathode presents a novel concept for managing among the predominant impediments to commercialization of Li-S batteries,” said study co-senior creator Shyue Ping Ong, a professor of nanoengineering on the UC San Diego Jacobs School of Engineering. “Iodine disrupts the intermolecular bonds holding sulfur molecules together by just the suitable amount to lower its melting point to the Goldilocks zone — above room temperature yet low enough for the cathode to be periodically re-healed via melting.”
“The low melting point of our recent cathode material makes repairing the interfaces possible, an extended sought-after solution for these batteries,” said study co-first creator Jianbin Zhou, a former nanoengineering postdoctoral researcher from Liu’s research group. “This recent material is an enabling solution for future high energy density solid-state batteries.”
To validate the effectiveness of the brand new cathode material, the researchers constructed a test battery and subjected it to repeated charge and discharge cycles. The battery remained stable for over 400 cycles while retaining 87 percent of its capability.
“This discovery has the potential to unravel certainly one of the most important challenges to the introduction of solid-state lithium-sulfur batteries by dramatically increasing the useful lifetime of a battery,” said study co-author Christopher Brooks, chief scientist at Honda Research Institute USA, Inc. “The power for a battery to self-heal just by raising the temperature could significantly extend the full battery life cycle, creating a possible pathway toward real-world application of solid-state batteries.”
The team is working to further advance the solid-state lithium-sulfur battery technology by improving cell engineering designs and scaling up the cell format.
“While much stays to be done to deliver a viable solid state battery, our work is a big step,” said Liu. “This work was made possible because of great collaborations between our teams at UC San Diego and our research partners at national labs, academia and industry.”
This work was supported partially by the U.S. Department of Energy (DOE) Advanced Research Projects Agency-Energy (DE-AR0000781), the U.S. DOE Office of Science (DEAC02-05-CH11231).
Disclosures: Ping Liu and Jianbin Zhou report a U.S. provisional patent application filed on February 13, 2023, Serial No. _63/484,659, based on this work.
