Li-ion Intercalation, Rectification, and Solid Electrolyte Interphase in Molecular Tunnel Junctions

This paper describes Li-ion intercalation into pyrenyl terminated self-assembled monolayer (SAM) on gold, inspired from graphite anode in Li-ion battery, and its effect on tunneling performance in molecular junction incorporating the SAM. As the concentration of Li-ion precursor ([LiPF₆]) increased from 0 to 10^-2 M, rectification ratio increased up to ~10². Further experiments revealed that the intercalation-induced changes in orientation of PYR group and in the HOMO energy level accounts for the enhanced rectification. Treatment of high concentrations of LiPF6 (from 10^-2 to 100 M) yielded considerable solid electrolyte interphase (SEI), mainly composed of LiF, on the surface of SAM, resulting in disappearance of rectification. It was attributed to renormalization of the HOMO level back to that of the intact SAM, caused by the SEI layer. Our work demonstrates interplay between Li-ion intercalation, SEI, and tunneling in molecular junction, benefiting the research of molecular electronics as well as SAM-based battery.

https://pubs.acs.org/doi/10.1021/acs.nanolett.2c01669