Molecular grafting on silicon anodes: artificial Solid-Electrolyte Interphase and surface stabilization

Silicon electrodes represent a great potential on increasing the energy density of Li-ion batteries, but stabilization during cycling is an important issue to be solved for enabling a reliable application. Such stabilization has been sought for by surface grafting of hydrogenated amorphous silicon (a-Si:H) electrodes. Grafting a molecular monolayer of carboxydecyl moieties (acid grafting) or poly(oxoethylene) (PEG) chains decreases the irreversible capacity and stabilizes the solid-electrolyte interphase (SEI) on a-Si:H. FTIR spectroscopy confirms a breathing behavior of the SEI layer at each step of charge/discharge through in-situ experiments, but also shows that acid grafting reduces this behavior to a large extent. In this way, acid grafting decreases the amount of charge irreversibly consumed for the formation of a spontaneous SEI and stabilizes the SEI along the electrochemical cycles.