Novel ternary fluorinated electrolyte's enhanced interfacial kinetics enables ultra-low temperature performance of lithium-ion batteries

Abstract

The exploration of new territories in space and the Arctic have highlighted a growing demand for energy storage solutions that can withstand extremely low temperatures (LTs). The current lithium-ion batteries are not suitable for such conditions without significant heating or thermal protection, as the electrolyte can freeze and the desolvation energy barrier for the Li-ion is high. To address this issue, a new type of ternary fluorinated electrolyte has been developed, which has an extremely low freezing point (FP) and enhanced charge transfer kinetics compared to the standard commercial electrolyte (COM). The F-FFN electrolyte showed superior performance and was comprised of a single lithium salt, lithium bis(fluorosulfonyl)amide (LiFSI), dissolved in a three-solvent mixture of a highly polar fluoroethylene carbonate (FEC), intermediately polar methyl (2,2,2-trifluoroethyl) carbonate (FEMC), and weakly polar nonaflurobutyl methyl ether (NONA) (FP = −135 °C). This specific solvent mixture was chosen to take advantage of the differences in dielectric constants between the three solvents, with NONA serving as a non-polar diluent to decrease the freezing point and charge transfer activation energy (E_a,CT). The optimized F-FFN electrolyte retained 61% of its room temperature (RT) capacity at −50 °C with a low E_a,CT of 55.71 kJ mol⁻¹ compared to COM, which retained only 25% of its RT capacity at −25 °C. Excellent LT performance for F-FFN electrolyte in a Li‖LiFePO₄ cell is attributed to the tailored solvation shell incorporating a higher fraction of lithium salt anions compared to T-FFN, which had more unassociated anions. The cathode electrolyte interface (CEI) of the F-FFN electrolyte features a higher fraction of LiF and Li₂CO₃, which helps to allow for a superior subzero temperature performance over the T-FFN and COM electrolytes organic polymer and carboxyl based CEIs.