A "Flexible" Solvent Molecule Enabling High-Performance Lithium Metal Batteries.

Abstract

Localized high-concentration electrolytes (LHCEs) exhibit good performance in lithium metal batteries. However, understanding how the intermolecular interactions between solvents and diluents regulate the solvation structure and interfacial layer structure remains limited. Here, we reported an LHCE in which strong hydrogen bonding between diluents and solvents alters the conformation and polarity of "flexible" solvent molecules, thereby effectively regulating the solvation structure of Li+ ion and promoting the formation of robust electrode interfaces. The endpoint H of the "flexible" chain O-CH-CH3 of the 2,5-dimethyltetrahydrofuran (2,5-THF) solvent and the F of the benzotrifluoride (BTF) diluent form strong hydrogen bonds, which expand the bond angle of the 2,5-THF molecule. The expanded bond angle increases the steric hindrance of the 2,5-THF and decreases its polarity. This leads to an increase in the anion content within the solvation structure, which in turn enhances the performance of both the lithium anode and the sulfurized polyacrylonitrile (SPAN) cathode. As a result, the lithium anode shows a Coulombic efficiency (CE) of as high as 99.4%. The assembled Li||SPAN battery exhibits impressive stability with an average CE of 99.8% over 700 cycles. Moreover, the Li||SPAN pouch cell can be stably cycled with a high energy density of 301.4 Wh kg-1.