(Invited) Correlating Electrolyte Structure with Interphasial Chemistry of Lithium Metal Anode

Abstract

Properties of the solid-electrolyte interphase (SEI) strongly effects the morphology, features and overall performance of the Lithium metal anode (LMA). It is well accepted but least understood that the formation mechanism of SEI is correlated with the electrolyte solvation structure. Here, synchrotron X-ray diffraction (XRD), pair distribution function (PDF) analysis, and molecular dynamic (MD) simulation are employed to obtain direct insight to the correlation between electrolyte solvation structure and interphasial chemistry. Systems of lithium bis(fluorosulfonyl)imide in propylene carbonate, dimethyl carbonate, and dimethoxyethane at both low (1M) and high (5 M) salt concentrations are studied. While solvents dominate in the solvation structure for low concentration electrolytes (LCE), a large number of anions enter the solvation shell in high concentration electrolytes (HCE). Quantification of crystalline phases in the bulk SEI reveal that while dendrites are the dominant phases for SEI of LCE, their formation is significantly suppressed in SEI of HCE. Highly nano-sized LiF, Li2O, and LiOH are dominant crystalline phases in SEI of HCE. The SEI of HCE is also very rich in oligomers resulting from anion decomposition. The small crystallites and amorphous oligomers promise fast Li ion conduction in the SEI and therefore a superior electrochemical performance of LMA.