Of the various concerns that people have regarding electric cars, one of the most often-heard is the worry that their batteries won't work in cold winter weather. That may not be an issue in the semi-near future, however – scientists at the University of California, San Diego have created a new type of electrolyte that allows lithium batteries to work with "excellent performance" at temperatures as low as -60 ºC (-76 ºF). By contrast, traditional lithium-ion batteries tend to conk out at around -20 ºC (-4 ºF).

Instead of the usual liquid organic solvents, the new electrolyte is composed of pressurized liquefied fluoromethane gas. Its low viscosity allows for high ion mobility and thus high conductivity, even in extremely cold temperatures that would freeze conventional liquid electrolytes. That said, batteries using the gas still retain high performance while at room temperature.

The new electrolyte also has a natural shutdown mechanism that prevents "thermal runaway," a situation in which a series of chemical chain reactions cause a battery to overheat and catch fire. At high temperatures, the liquified gas loses its ability to dissolve salts, which causes the battery to lose conductivity and stop working. Once it's cooled down, however, it starts working again.

Additionally, regular liquid electrolytes negatively react with lithium metal battery anodes over time, diminishing the number of charge/discharge cycles that the battery can go through – this reportedly isn't a problem with the gas electrolyte. Additionally, it doesn't cause the formation of dendrites, which are needle-like lithium deposits which form on battery electrodes, and that can cause the battery to short-circuit.

UC San Diego researchers Yangyuchen Yang (left) and Cyrus Rustomji(Credit: David Baillot/UC San Diego Jacobs School of Engineering)

The scientists have also developed an electrolyte for use in electrochemical capacitors, made from liquefied difluoromethane gas. It allows them to run at temperatures as low as -80 ºC (-112 ºF), whereas their current low-temperature limit sits at -40 ºC (-40 ºF).

Ultimately, it is hoped that batteries and capacitors using such electrolytes could operate at temperatures as low as -100 ºC (-148 ºF), allowing for their use in space probes exploring outer planets like Jupiter and Saturn.

The research was led by Prof. Shirley Meng and postdoctoral researcher Cyrus Rustomji. It is described in a paper that was published this Thursday in the journal Science.

Source: UC San Diego

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