Disassociating Lithium Salts in Deep Eutectic Solvents and Inhibiting Aluminum Corrosion for Low-Temperature Lithium-Metal Batteries

Low-temperature lithium-ion (Li-ion) batteries necessitate high-disassociation Li salts in low melting point solvents to favor transport kinetics. While lithium bis(fluorosulfonyl)imide (LiFSI) is being developed for low-temperature electrolytes due to its weakly coordinated anion that enables a high dissociation constant, the deep eutectic solvents (DESs) benefit electrolyte mobility. Such salt and solvent combination is expected to address challenges of freezing electrolytes, low charge carriers, and sluggish ion transport across interfaces encountered under subzero temperature conditions. However, LiFSI corrodes the aluminum (Al) foil and disconnects electron pathways between the active material and the Al current collector, endangering battery stability at high voltages. Herein, the strongly coordinated anion (nitride, NO₃^-) is introduced into the DESs by high-dielectric-constant dimethyl sulfoxide (DMSO) to inhibit Al corrosion. The Al anodic voltage in Li||Al cells is extended to 4.6 V (vs Li⁺/Li). This rational-designed electrolyte enables the cell with an impressive low-temperature performance even at a high areal loading of 4.5 mAh cm^-2. The cell equipped with this electrolyte can be cycled over 200 cycles at −20 °C with inconspicuous capacity degradation. This work adopts disassociating Li salts in DESs and inhibiting Al corrosion, which is expected to enrich the fundamentals of mediating Li⁺ transport and Al corrosion to promote low-temperature Li-metal battery performances.