(565b) Low Desolvation Energy Tailored Electrolyte for Enhanced Subzero Temperature Performance of Lithium-Ion Batteries

The exploration of new territories in space and the Arctic has 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 fluorinated electrolyte was designed on the basis of improving pre-existing fluorinated electrolytes to allow for both a lower freezing point (FP) and lower desolvation energy compared to the standard commercial electrolyte (COM). This work’s electrolyte is comprised of a single lithium salt, lithium bis(fluorosulfonyl)amide (LiFSI), dissolved in a four-solvent mixture of a highly polar fluoroethylene carbonate (FEC), intermediately polar methyl (2,2,2-trifluoroethyl) carbonate (FEMC), weakly polar nonaflurobutyl methyl ether (NONA) (FP= –135°C), and an additional solvent whose dielectric constant is slightly weaker than FEMC. This specific solvent mixture was chosen to allow for a greater incorporation of NONA, which serves as a nonpolar diluent to depress the freezing point and promote the incorporation of the salt anions into the solvation structure, by adding a fourth intermediately polar solvent like diethylene carbonate (DEC), ethyl methyl carbonate (EMC), or dibutyl carbonate (DBC). These three solvents were chosen due to their suitable freezing point and dielectric constants. The optimized F-FDFN electrolyte showed a superior ultralow temperature performance of 70% of its room temperature (RT) capacity at –50°C with a low desolvation energy of 60.1 kJ mol^-1 compared to COM, which retained only 25% of its RT capacity at –25°C. Excellent LT performance for F-FDFN electrolyte in a Li||LiFePO₄ cell is attributed to the tailored solvation shell incorporating a higher fraction of lithium salt anions compared to other prepared electrolytes, which had more unassociated anions.