Engineers have developed new high-energy lithium-ion batteries that perform well in frigid and sweltering temperatures.
Engineers at the University of California San Diego (UCSD) have developed new lithium-ion batteries that perform well in freezing temperatures and scorching hot temperatures, while still packing a lot of energy. According to the researchers, this feat was achieved by developing an electrolyte that is not only versatile and robust over a wide temperature range, but also compatible with a high-energy anode and cathode.
The temperature-resistant batteries are described in a paper published the week of July 4 in the journal Proceedings of the National Academy of Sciences (PNAS).
Batteries based on this technology could enable electric vehicles in cold climates to travel farther on a single charge. They may also reduce the need for cooling systems to prevent the vehicles’ batteries from overheating in hot climates, said Zheng Chen, a professor of nanoengineering at the UCSD Jacobs School of Engineering and senior author of the study.
“You have to work at high temperatures in areas where the ambient temperature can reach triple digits and the roads get even hotter. In electric vehicles, the battery packs are usually located under the floor, close to these hot roads,” explained Chen, who is also a faculty member of the UCSD Sustainable Power and Energy Center. current flows through it. If the batteries cannot tolerate this warming at high temperature, their performance will deteriorate rapidly.”
Study lead author Guorui Cai, a postdoctoral researcher in nanoengineering at UC San Diego, is preparing a battery pouch for testing in freezing temperatures. Credit: David Baillot/UC San Diego Jacobs School of Engineering
In tests, the proof-of-concept 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 efficiency of 98.2% and 98.7% respectively at these temperatures, meaning the batteries can go through more charge and discharge cycles before they stop working.
The batteries Chen and colleagues have developed are both cold and heat tolerant thanks to their unique electrolyte. It is made from a liquid solution of dibutyl ether mixed with a lithium salt. A special feature of dibutyl ether is that the molecules bind weakly to lithium ions. In other words, the electrolyte molecules can easily release lithium ions while the battery is working. This weak molecular interaction, the researchers found in a previous study, improves battery performance in freezing temperatures. In addition, dibutyl ether can easily absorb the heat because it remains liquid at high temperatures (it has a boiling point of 141°C or 286°F).
High temperature performance of battery pouches tested in an oven heated to 50°C. Credit: David Baillot/UC San Diego Jacobs School of Engineering
Stabilizing lithium-sulfur chemistries
What is also special about this electrolyte is that it is compatible with a lithium-sulfur battery, 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 as they promise higher energy densities and lower costs. They can store up to twice as much energy per kilogram as current lithium-ion batteries – this could double the range of electric vehicles without increasing the weight of the battery pack. Also, sulfur is more abundant and less problematic to obtain than the cobalt used in traditional lithium-ion battery cathodes.
But there are problems with lithium-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 puncture parts of the battery, causing it to short-circuit. As a result, lithium-sulfur batteries only last up to tens of cycles.
Zheng Chen, professor of nanoengineering at UC San Diego. Credit: David Baillot/UC San Diego Jacobs School of Engineering
“If you want a high-energy-density battery, you usually have to use a very hard, complicated chemistry,” Chen says. “High energy means more reactions take place, which means less stability, more degradation. Making a high-energy battery that’s stable is a difficult task in itself — it’s even more challenging to do this over a wide temperature range.”
The dibutyl ether electrolyte developed by the UCSD research team prevents these problems even at high and low temperatures. The batteries they tested had a much longer lifespan than a typical lithium-sulfur battery. “Our electrolyte helps improve both the cathode side and the anode side while ensuring high conductivity and interfacial stability,” Chen said.
The team also developed the sulfur cathode to be more stable by grafting it onto a polymer. This prevents more sulfur from dissolving in the electrolyte.
The next steps include scaling up the battery chemistry, optimizing it to operate at even higher temperatures, and further extending its life.
Reference: “Solvent Selection Criteria for Temperature Resistant 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 from 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 from the US 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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