Formation of artificial solid electrolyte interphase by grafting for improving Li-ion intercalation and preventing exfoliation of graphite

Various grafting methods for surface modification of graphite powder are reported. p-Carboxylic benzene diazonium salt has been grafted on graphite powder using different grafting methods namely electrochemical grafting, in situ grafting aqueous, in situ grafting non-aqueous, and spontaneous grafting. Each grafting method results in a different loading of the surface organic layer, which is quantified by X-ray photoelectron spectroscopy. Grafted graphite powders exhibit controlled solid electrolyte interphase (SEI) morphology, Li-ion intercalation, and averted exfoliation. Grafted graphite powders were further modified by transformation of the terminal functional group of the grafted surface layer by chemical or electrochemical treatments. This step tunes the reactivity of grafted material towards non-aqueous electrolyte, which is reflected in modified electrochemical properties like formation of SEI, overall Li-ion intercalation/deintercalation kinetics, cyclability, practical specific charge, and eventual exfoliation of graphite. The morphology of the grafted samples is retained after electrochemical cycling as well as after functional group transformation steps. The morphology of the SEI is also seen to be similar to that of the grafted layer in all the cases. These methods offer a pathway for tuning SEI properties and preventing exfoliation of graphite in propylene carbonate based electrolyte.