Engineers at the University of California San Diego have developed a lithium-sulfur battery that performs well in extremes of cold and hot temperatures.
The researchers’ electrolyte was used in a lithium-sulfur battery in which the cathode consists of sulfur grafted to the conductor polymer sulfurised polyacrylonitrile (SPAN).
In tests, the proof-of-concept batteries retained 87.5% and 115.9% of their energy capacity at -40 to 50oC (-40 to 122oF), respectively; they also had high Coulombic efficiencies of 98.2% and 98.7%, respectively.
The electrolyte is made of a liquid solution of dibutyl ether— whose molecules bind weakly to lithium ions and have a boiling point of 141oC, or 286oF— mixed with a lithium salt.
This means the electrolyte molecules can easily let go of lithium ions as the battery runs, which improves battery performance at sub-zero temperatures, the researchers discovered in a previous study.
The research was published in the peer-reviewed multidisciplinary scientific journal Proceedings of the National Academy of Sciences (PNAS).
Zheng Chen, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering and senior author of the study, said: “You need high temperature operation in areas where the ambient temperature can reach the triple digits and the roads get even hotter.
“In electric vehicles, the battery packs are typically under the floor, close to these hot roads.
“Also, batteries warm up just from having a current run through during operation. If the batteries cannot tolerate this warmup at high temperature, their performance will quickly degrade.”
The dibutyl ether electrolyte developed by the UC San Diego team allowed much longer cycling lives than a typical lithium-sulfur battery.
Chen said the electrolyte helped improve both the cathode side and anode side while providing high conductivity and interfacial stability.
The team also engineered the sulfur cathode to be more stable by grafting it to a polymer to prevent more sulfur from dissolving into the electrolyte.
Next steps include scaling up the battery chemistry, optimising it to work at even higher temperatures and further extending cycle life.
Image: Guorui Cai, a nanoengineering postdoctoral researcher at UC San Diego, prepares a battery pouch cell for testing at subfreezing temperature. Photos by David Baillot/UC San Diego Jacobs School of Engineering