Scientists develop new lithium battery: can work normally in high temperature and extreme cold environment

A team of engineers at the University of California, San Diego (UCSD) has developed a new type of lithium-ion battery that performs well in both extremely cold and extremely hot temperatures while still storing a lot of energy. The researchers say the reason for this is due to a newly developed electrolyte that is not only versatile and durable over a wide temperature range, but also compatible with high-energy anodes and cathodes.

The results, published July 4 in the Proceedings of the National Academy of Sciences (PNAS), could allow electric vehicles to travel farther even in cold climates. They could also reduce the need for cooling systems to prevent vehicle battery packs from overheating in hot climates, said Zheng Chen, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering and senior author of the study.

“If you need to drive in triple-digit (Fahrenheit) heat conditions, it’s a major challenge for car batteries,” Chen explained. “In electric vehicles, the battery pack is typically located in the chassis, closer to these hot roads. Additionally, the batteries heat up during operation due to the current passing through them. If the batteries can’t withstand this high temperature preheating, their performance will degrade rapidly.”

In testing, the proof-of-concept cells retained 87.5% and 115.9% of their energy capacity at -40°C and 50°C (-40 and 122°F), respectively. At those temperatures, they also had high coulombic efficiencies of 98.2% and 98.7%, respectively, meaning the cells could go through more charge and discharge cycles before they stopped working.

The battery developed by Chen and colleagues is both cold-resistant and heat-resistant thanks to its unique electrolyte. It is made of a liquid solution of dibutyl ether mixed with a lithium salt. One feature of dibutyl ether is that its molecules are weakly bound to lithium ions. In other words, when the battery is running, the electrolyte molecules easily release lithium ions. The researchers found in a previous study that this weak molecular interaction can improve the performance of the battery at sub-zero temperatures. In addition, dibutyl ether easily absorbs heat because it remains liquid at high temperatures (the boiling point is 141 °C or 286 °F).

Another special thing about this electrolyte is that it is compatible with lithium-sulfur batteries, a type of rechargeable battery whose anode is made of lithium metal and whose cathode is made of sulfur. Lithium-sulfur batteries are an important part of next-generation battery technology because they promise higher energy density and lower costs. They can store twice as much energy per kilogram as today's lithium-ion batteries - which could double the range of electric vehicles without increasing the weight of the battery pack. In addition, sulfur is more abundant and less problematic than the cobalt used in traditional lithium-ion battery cathodes.

But lithium-sulfur batteries have problems. Both the cathode and anode are super reactive. The sulfur cathodes are so reactive that they dissolve during the battery's operation. This problem gets worse at high temperatures. The lithium metal anodes tend to form needle-like structures called dendrites that can pierce parts of the battery, causing it to short-circuit. As a result, lithium-sulfur batteries only last for a few dozen cycles.

“If you want a battery with high energy density, you usually need to use very harsh, complex chemistries,” Chen said. “High energy means more reactions are happening, which means less stability and more degradation. Making stable, high-energy batteries is a difficult task in itself — trying to do it over a wide temperature range is even more challenging.”