An Anion-Tuned Solid Electrolyte Interphase with Fast Ion Transfer Kinetics for Stable Lithium Anodes

The spatial distribution and transport characteristics of lithium ions (Li+) in the electrochemical interface region of a lithium anode in a lithium ion battery directly determine Li+ deposition behavior. The regulation of the Li+ solvation sheath on the solid electrolyte interphase (SEI) by electrolyte chemistry is key but challenging. Here, 1 m lithium trifluoroacetate (LiTFA) is induced to the electrolyte to regulate the Li+ solvation sheath, which significantly suppresses Li dendrite formation and enables a high Coulombic efficiency of 98.8% over 500 cycles. With its strong coordination between the carbonyl groups (C(sic)O) and Li+, TFA(-) modulates the environment of the Li+ solvation sheath and facilitates fast desolvation kinetics. In addition, due to relatively smaller lowest unoccupied molecular orbital energy than solvents, TFA(-) has a preferential reduction to produce a stable SEI with uniform distribution of LiF and Li2O. Such stable SEI effectively reduces the energy barrier for Li+ diffusion, contributing to low nucleation overpotential, fast ion transfer kinetics, and uniform Li+ deposition with high cycling stability. This work provides an alternative insight into the design of interface chemistry in terms of regulating anions in the Li+ solvation sheath. It is anticipated that this anion-tuned strategy will pave the way to construct stable SEIs for other battery systems.