Mechanistic Insight on the Solid Electrolyte Interphase (SEI) Formed By a Superconcentrated [Li][TFSI] in Acetonitrile Electrolyte Near Lithium Metal

Abstract

Superconcentrated salt solutions are promising alternatives to conventional electrolytes in Li-ion batteries because of their enhanced redox stability and tendency to form a stable and rigid solid electrolyte interphase (SEI). Herein, we performed density functional theory-based molecular dynamics (DFT-MD) simulations to understand the initial electrode reactions between the Li metal and superconcentrated electrolyte solution of Li bis(trifluoromethanesulfonyl)imide ([Li][TFSI]) in acetonitrile (AN). We thoroughly analyzed the structure and composition of the SEI formed near the Li metal. We show that reductive decomposition of the TFSI anions contributes majorly in the initial SEI formation and the AN molecules are relatively stable against the redox processes occurring near the Li metal. The atomized C, O, F, and S atoms contributed by the TFSI anions forms the stable inorganic layer leading to highly structured and inhomogeneous SEI. The AN molecules and undissociated N–SO2–CF3 fragments are mostly aligned away from the Li layers. Figure 1