Winterproof lithium-ion battery works at minus 80 degrees

A solution to the seemingly contradictory requirements for a high energy density battery operating at very low temperatures has been announced. The work is still a long way from mass production, but suggests that a major obstacle to electrifying aviation may not be as insurmountable as many have thought, along with a host of other potential applications.

Lithium-ion batteries have conquered most of the world, but are running into trouble at the poles. As temperatures drop, they charge more slowly and store less energy. Their reduced storage capacity in cold weather is an often-cited reason for people to avoid electric cars, although famously cold Norway seems undisturbed. Even though the problems are exaggerated in regular cold temperatures, things get worse in the kind of temperatures most of us hope never to encounter.

Restrictions on winter use in Antarctica aren’t really a problem for the global energy transition, but the altitude at which jets fly is also getting very cold. In addition to the challenge of making batteries light enough for large-scale aircraft, keeping them warm is a hassle that aerospace engineers don’t want to deal with. Now it looks like they might not have to.

The reason lithium-ion batteries are so cold-averse is that it is thought that even more important properties, such as high energy density and fast charging capability, can only be achieved over a narrow operating temperature range. Because most batteries also need to operate in the kind of temperatures people live in, this means performance must be sacrificed as temperatures drop.

The problem lies in batteries’ electrolytes, but a team led by Professor Xiulin Fan of Zhejiang University claims that an electrolyte made using “tiny solvents with low solvation energy” can do it all.

Existing electrolytes are good at conducting lithium ions and interacting with graphite anodes at temperatures around 25°C (77°F), but deteriorate in both as temperatures drop. High concentration electrolytes and other alternatives prevent freezing at the anode interface, but only because they are more viscous and therefore carry fewer charges, reducing performance under normal conditions.

The team examined the performance of a range of solvents and found that three small solvents can form Li+ transport channels that allow rapid ion movement. Two of these do not meet the other basic requirements for battery electrolytes, but fluoroacetonitrile appears to meet all the necessary criteria. The fact that the acronym (FAN) is the same as the names of two team members is probably just a happy coincidence.

Demonstration FAN electrolyte batteries exhibit excellent ionic conductivity at room temperature, the team claims, and also charge and discharge well from -80°C to 60°C (-112° to 140°F). At -70°C (-94°F), FAN’s performance beat some alternatives by a factor of about 10,000 times.

These batteries maintained their performance for 3,000 cycles at 6°C (43°F).

According to the South China Morning Post, Fan told Chinese-language site Science Times that the battery “can be charged in 10 minutes to reach 80 percent of charging capacity.”

The secret lies in the formation of two layers around the lithium ions, known as shells, both of which are smaller and more transportable than those in dilute carbonate electrolytes.

Lithium-ion batteries dominate the existing battery market largely because they are so light for the energy they can store. That makes them invaluable for laptops and mobile phones, and now also for electric cars. The additional research that came with their dominance, plus the economies of scale in production, means they are also currently the dominant technology for the fast-growing stationary battery market. However, when it comes to large batteries that draw energy from solar panels during the day and use them at night, many other technologies using cheaper materials are hot on the heels of lithium-ion.

Fan’s team claims that their technology is “generalizable and can be extended to other metal ion battery electrolytes,” which will be good news for grid operators in colder regions looking for ways to balance energy generation in winter.

The work has been published in Nature.

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