A prolonged January cold snap in Chicago left owners of electric vehicles struggling to keep a charge. With reduced driving ranges and charging times taking longer than usual, the performance limitations of lithium-ion batteries in the cold were evident. A new study led by Xiulin Fan of Zhejiang University finds that using a unique organic solvent in the electrolyte of lithium-ion batteries holds promise for faster charging times and improved low-temperature performance.

Conventional lithium-ion batteries use carbonate solvents, which produce two known types of ion transport, as shown in figure panels a and b. During vehicular transport, a lithium cation is carried by a shell made up of the solvent molecules surrounding it. Structural transport occurs when cations hop between solvent molecules. Various factors, including salt concentration and solvent type, determine which transport mechanism occurs, and both can happen simultaneously in the same battery.

Until now, (a) vehicular transport and (b) structural transport were the two known mechanisms of cation conduction in lithium-ion batteries. A solvent with unique properties has revealed (c) a third mechanism that uses ligand channels to produce ultrafast charging, which is effective even at very low temperatures. (Adapted from D. Lu et al., Nature 627, 101, 2024.)

Until now, (a) vehicular transport and (b) structural transport were the two known mechanisms of cation conduction in lithium-ion batteries. A solvent with unique properties has revealed (c) a third mechanism that uses ligand channels to produce ultrafast charging, which is effective even at very low temperatures. (Adapted from D. Lu et al., Nature 627, 101, 2024.)

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Fan and colleagues evaluated the known properties of dozens of solvents. They looked for a solvent with a specific combination of qualities that could promote faster charging and long-term performance: small molecule size, a low lithium-ion transport energy barrier, and low reactivity with electrodes. They landed on fluoroacetonitrile (FAN). With its particular combination of properties, FAN could facilitate a previously untapped mechanism of lithium-ion transport that drastically speeds up conduction.

The new ion-transport mechanism, as understood through molecular-dynamics simulations and confirmed by observations, is facilitated by the formation of two layers of solvent sheaths around lithium ions, shown in figure panel c. Solvent molecules in the outer sheath pull lithium ions from the inner sheath and form fast-conducting channels known as ligand channels. The researchers found that because of its small size and low lithium-ion transport energy barrier, the FAN-based electrolyte was able to activate ion transport through ligand channels.

Charging an electric vehicle at the Mt Hood Skibowl EV station. (Courtesy of the Oregon Department of Transportation/CC BY 2.0 DEED.)

Charging an electric vehicle at the Mt Hood Skibowl EV station. (Courtesy of the Oregon Department of Transportation/CC BY 2.0 DEED.)

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The FAN-based electrolyte produced ionic conductivity that was four times as high as that achieved by typical carbonate-based electrolytes at 25 °C. Further, at −70 °C, it produced ionic conductivity comparable with the room-temperature performance of conventional solvents. And it was more than twice as high as the conductivity exhibited by state-of-the-art liquefied-gas electrolytes at the same low temperature. That higher ionic conductivity could translate into faster charging times, longer running times, and better performance at low temperatures. Battery design and performance depend on many interacting factors, so more work will be needed to integrate the new solvent into commercially available batteries. But the findings offer hope for a future where electric vehicle drivers won’t be left out in the cold. (D. Lu et al., Nature 627, 101, 2024.)

A version of this story was originally published online on 8 March 2024.

1.
D.
Lu
,
R.
Li
,
M. M.
Rahman
,
P.
Yu
,
L.
Lv
,
S.
Yang
,
Y.
Huang
,
C.
Sun
,
S.
Zhang
,
H.
Zhang
,
J.
Zhang
,
X.
Xiao
,
T.
Deng
,
L.
Fan
,
L.
Chen
,
J.
Wang
,
E.
Hu
,
C.
Wang
,
X.
Fan
,
Nature
627
,
101
(
2024
).