Concentration Induced Modulation of Solvation Structure for High Performance Lithium Metal Battery by Regulating Energy Level of Lumo Orbital

Abstract

Nitrile electrolytes have attracted extensive attention for achieving high-voltage lithium metal batteries. However, the poor compatibility of nitrile electrolyte with Li anode remains a huge challenge owing to severe side reactions. Herein, changing concentration of LiTFSI in succinonitrile (SN) is proposed to improve interface compatibility by regulating the solvation structure. The higher coordination number (1.3) of TFSI- in high concentration electrolytes results in a LiF-rich SEI film, accounting for the superior performance of LiNi0.8Co0.1Mn0.1O2|Li cell with negligible capacity fade after 100 cycles at 0.5 C. Density functional theory (DFT) suggests that the solvation structure with a high coordination number of TFSI- towards Li+ leads to a reduced Lowest Unoccupied Molecular Orbital (LUMO) energy level, which promotes the decomposition of TFSI- to form LiF-rich film. Also, a reduced decomposition energy barrier of anion is demonstrated. This work provides an encouraging way to enhance interface stability via modulating the solvation structure achieved by regulating concentration.

Keywords: Succinonitrile, High-concentration, Solvation structure, LiF-rich film, Interface stability