Wednesday, August 30, 2023

EV Batteries and PFAS

Yoo, Dong‐Joo, Liu, Qian, Cohen, Orion, Kim, Minkyu, Persson, Kristin A., and Zhang, Zhengcheng. Rational Design of Fluorinated Electrolytes for Low Temperature Lithium‐Ion Batteries. Germany: N. p., 2023. Web. doi:10.1002/aenm.202204182.

Lithium-ion batteries are used widely in portable electronics because of their long operation time, life span, and relatively simple manufacturing process. Lithium-ion batteries operate best at moderate temperatures.  Lithium-ion batteries have also been adopted for electric vehicle use. Lithium-ion batteries are rechargeable, lightweight, and capable of higher energy density than most other available battery types.

They are smaller than the batteries used to start gas-powered vehicles’ internal combustion engines. Of course, as well as starting the car, batteries in electric vehicles keep it moving, and they run the vehicle’s other systems like air conditioning, entertainment, and driver assistance systems.

When lithium-ion batteries are exposed to cold temperatures, their storage capacity –how much energy they can store between charges – drops to approximately 77% at around −5 °F. As the temperature falls, the storage capacity continues to fall. This happens because the ethylene carbonate used as the electrolyte solidifies at about -4 °F.

Now, however, with the spread of electric vehicles, the performance of the lithium-ion batteries at low temperatures has become an issue due to the vast performance difference depending on regions and seasons. To have the entire local transportation fleet knocked out during a polar vortex could be disastrous.

Low temperature performance is one of the most challenging aspects of lithium-ion batteries and EV adoption itself. The lithium-ion batteries used in most battery electric vehicles suffer reduced charging efficiency, significant capacity loss, and accelerated aging in low temperatures. This has a negative effect on electric vehicles’ driving range in cold climates and winter.

The batteries in the electric vehicle also power all the other systems.  Heating the cabin area of the vehicle requires significant amounts of power in cold climates (as does cooling the cabin in hot climates). Testing has shown that, because of this, electric vehicles’ range is reduced to approximately 45% when the external temperature is 5 °F or lower and recharging the batteries is slower.

The authors of the above cited study searched for a solvent that would stay liquid at low temperatures yet still form the crucil SEI barrier over the anode. They have found that replacing the left handed  terminal methyl groups of the ethyl acetate with a  trifluoromethyl group produced the desired effect.

In laboratory tests the ethyl acetate trifluoromethyl was found to be as stable in its energy storage capacity over 400 recharging cycles at  5 °F as the battery containing ethyl acetate was at room temperature. While this solves the problem of EV batteries in winter weather, it potentially adds another PFAS (a forever chemical) to wide spread use. Are we destroying ourselves and planet to reduce greenhouse gasses. The researchers have applied for a patent. You can read the research at the link above.

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