Ultralow-Temperature Carboxylate Electrolyte for High-Voltage Lithium Metal Batteries.

Carbonate-based electrolytes possess high oxidative stability and solvation ability to Li in Li metal batteries (LMBs). However, they face significant challenges under cryogenic temperatures, including the sluggish reaction kinetics, uneven Li deposition, and severe interfacial side reactions, especially under the elevated cutoff voltages. Carboxylates usually have lower viscosity and freezing points. However, they still face low oxidative stability and poor film-forming ability. Herein, we designed an ultralow-temperature electrolyte by using a gamma-butyrolactone (GBL) and isobutyronitrile (iBN) mixed electrolyte to be used in high-voltage LMBs. The result demonstrated that the participation of iBN in the Li solvation structure could greatly improve the ion transfer kinetics and oxidation stability of the electrolyte through the interaction of C≡N with transition metal on the cathode. Combined with the lithium nitrate (LiNO) additive, the tame electrolyte exhibits high interfacial stability at a temperature range of -60 to -20 °C by forming dense and highly ionic conductive interfacial films. The assembled Li||LiNiCoMnO cell delivered a capacity of 88.8 mAh g and retained a 77.2% capacity retention after 450 cycles under -40 °C and a 4.5 V cutoff voltage. Even if the temperature decreased to -50 °C, it could still express a capacity of 89.7 mAh g with a 99% capacity retention for 50 cycles, surpassing most of the works involving carbonate-based electrolytes. Therefore, combining the superiorities of carboxylate and nitrile solvents provides a promising electrolyte design insight for the ultralow-temperature LMBs.