Extreme Temperatures Are No Barrier for Novel Battery
Engineers at the University of California at San Diego have developed lithium-ion batteries that work well in very cold and hot temperatures, while providing a lot of energy. The researchers achieved this feat by developing an electrolyte that is not only versatile and robust over a wide range of temperatures, but is also compatible with a high-energy anode and cathode.
Temperature-resistant batteries are described in a paper published the week of July 4th Proceedings of the National Academy of Sciences (PNAS).
These batteries could allow electric vehicles in cold climates to travel farther on a single charge; they could also reduce the need for cooling systems to prevent vehicle batteries from overheating in warm climates, said Zheng Chen, a professor of nanoengineering at Jacobs School of Engineering at UC San Diego and lead author of the study.
“You need high-temperature operation in areas where the ambient temperature can reach three digits and the roads get even hotter. In electric vehicles, battery packs are usually underground, close to these hot roads.” , explained Chen, who is also a faculty member at the UC San Diego Center for Energy and Sustainable Energy. “In addition, the batteries are heated only because current passes during operation. If the batteries cannot tolerate this heating at high temperature, their performance will degrade rapidly.
In the tests, the concept test batteries retained 87.5% and 115.9% of their energy capacity at -40 and 50 C (-40 and 122 F), respectively. They also had high coulomb efficiencies of 98.2% and 98.7% at these temperatures, respectively, meaning batteries can experience more charging and discharging cycles before they stop working.
The batteries that Chen and his colleagues developed are both cold and heat tolerant thanks to their electrolyte. It is made from a liquid solution of dibutyl ether mixed with a lithium salt. A special feature of dibutyl ether is that its molecules bind weakly to lithium ions. In other words, electrolyte molecules can easily release lithium ions while the battery is running. This weak molecular interaction, researchers had discovered in a previous study, improves battery performance at sub-zero temperatures. In addition, dibutyl ether can easily absorb heat because it remains liquid at high temperatures (it has a boiling point of 141 C or 286 F).
Stabilization of lithium-sulfur chemistry
What also makes this electrolyte special is that it is compatible with a lithium sulfur battery, which is a type of rechargeable battery that has a lithium metal anode and a sulfur cathode. Lithium sulfur batteries are an essential part of next-generation battery technologies because they promise higher energy densities and lower costs. They can store up to twice as much energy per kilo as current lithium-ion batteries; this could double the range of electric vehicles without increasing the weight of the battery. In addition, sulfur is more abundant and less problematic at source than the cobalt used in traditional lithium-ion battery cathodes.
But there are problems with lithium and sulfur batteries. Both the cathode and the anode are super reactive. Sulfur cathodes are so reactive that they dissolve during battery operation. This problem gets worse at high temperatures. And lithium metal anodes are prone to forming needle-like structures called dendrites that can pierce parts of the battery, short-circuiting it. As a result, lithium sulfur batteries only last up to dozens of cycles.
“If you want a battery with high power density, you usually have to use very hard and complicated chemistry,” Chen said. “High energy means more reactions are happening, which means less stability, more degradation. Making a high-energy battery that is stable is a difficult task in itself: trying to do it through a wide range of temperatures is even more difficult. “
The dibutyl ether electrolyte developed by the UC San Diego team avoids these problems, even at high and low temperatures. The batteries they tested had a much longer cycle life than a typical lithium sulfur battery. “Our electrolyte helps improve both the cathode side and the anode side while providing high conductivity and interfacial stability,” Chen said.
The team also designed the sulfur cathode to be more stable by grafting it to a polymer. This prevents more sulfur from dissolving in the electrolyte.
The next steps include increasing the chemistry of the battery, optimizing it to work at even higher temperatures, and further extending the life of the cycle.
Reference: Cai G, Holoubek J, Li M, Gao H, Yin Y, Yu S, et al. Solvent selection criteria for temperature-resistant lithium sulfur batteries. Proc. Natl. Acad. Science. 2022.
This article has been republished from the following materials. Note: The material may have been edited by duration and content. For more information, contact the source cited.