New Lithium-Ion Batteries That Work Well in Scorching Heat and Extreme Cold

Engineers at the University of California, San Diego (UCSD) have created new lithium-ion batteries that function well in both freezing cold and blistering hot conditions while retaining a high energy density. The researchers achieved this accomplishment by designing an electrolyte that is not only adaptable and stable throughout a wide temperature range, but also compatible with a high-energy anode and cathode.

The temperature-resilient batteries are reported in an article published in the journal Proceedings of the National Academy of Sciences the week of July 4th (PNAS).

This technology's batteries might allow electric vehicles in cold locations to drive further on a single charge. According to Zheng Chen, a professor of nanoengineering at UCSD Jacobs School of Engineering and senior author of the paper, they might also lessen the requirement for cooling systems to protect the cars' battery packs from overheating in hot areas.

“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,” Chen, a faculty member of the UCSD Sustainable Power and Energy Center, stated. “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.”

Guorui Cai

At -40 and 50 °C (-40 and 122 °F), the proof-of-concept batteries preserved 87.5 percent and 115.9 percent of their energy capacity, respectively. They also showed high Coulombic efficiencies of 98.2 percent and 98.7 percent at these temperatures, indicating that the batteries can withstand more charge and discharge cycles before failing.

Because of their unique electrolyte, Chen and colleagues' batteries are both cold and heat tolerant. It is composed of a dibutyl ether liquid solution combined with a lithium salt. Dibutyl ether molecules bond poorly to lithium ions, which is a unique property. In other words, while the battery operates, the electrolyte molecules easily release lithium ions. In a recent investigation, the researchers revealed that this weak chemical connection increases battery efficiency at sub-zero temperatures. Furthermore, dibutyl ether can withstand high temperatures since it remains liquid at high temperatures (it has a boiling point of 141 °C, or 286 °F).

Stabilizing lithium-sulfur chemistries

This electrolyte is also unique in that it is compatible with a lithium-sulfur battery, a type of rechargeable battery having a lithium anode and a sulfur cathode. Because they offer better energy densities and cheaper prices, lithium-sulfur batteries are a crucial component of next-generation battery technologies. They can store up to twice as much energy per kilogram as today's lithium-ion batteries, thereby doubling the range of electric cars without increasing the battery pack's weight. Furthermore, sulfur is more prevalent and easier to obtain than cobalt, which is utilized in standard lithium-ion battery cathodes.

However, there are issues with lithium-sulfur batteries. The cathode and anode are both extremely reactive. Sulfur cathodes are so reactive that they disintegrate while the battery is running. This problem worsens in hot weather. Furthermore, lithium metal anodes are prone to producing needle-like formations known as dendrites, which can puncture components of the battery and cause a short-circuit. As a result, lithium-sulfur batteries have a limited lifespan of tens of cycles.

“If you want a battery with high energy density, you typically need to use very harsh, complicated chemistry,” Chen explained. “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 itself—trying to do this through a wide temperature range is even more challenging.”

The UCSD research team's dibutyl ether electrolyte eliminates these problems at both high and low temperatures. They discovered that the batteries they examined had significantly longer cycle lifetimes than a normal lithium-sulfur battery. "Our electrolyte improves both the cathode and anode sides while also delivering good conductivity and interfacial stability," Chen explained.

The scientists also improved the stability of the sulfur cathode by grafting it to a polymer. This inhibits further sulfur dissolution into the electrolyte.

The next stages will be to scale up the battery chemistry, optimize it to perform at even greater temperatures, and increase cycle life even more.

Reference: “Solvent selection criteria for temperature-resilient lithium-sulfur batteries.” Co-authors include Guorui Cai, John Holoubek, Mingqian Li, Hongpeng Gao, Yijie Yin, Sicen Yu, Haodong Liu, Tod A. Pascal and Ping Liu, all at UC San Diego. Proceedings of the National Academy of Sciences.

This work was supported by an Early Career Faculty grant from NASA’s Space Technology Research Grants Program (ECF 80NSSC18K1512), the National Science Foundation through the UC San Diego Materials Research Science and Engineering Center (MRSEC, grant DMR-2011924), and the Office of Vehicle Technologies of the U.S. Department of Energy through the Advanced Battery Materials Research Program (Battery500 Consortium, contract DE-EE0007764). This work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI) at UC San Diego, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (grant ECCS-1542148).

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