Role of additives in formation of solid-electrolyte interfaces on carbon electrodes and their effect on high-voltage stability

The in situ modification of a lithium hexafluorophosphate-based electrolyte using a molybdenum oxide catalyst and small amount of water (1 vol %) yields hydrolysis products such as mono-, di-, and alkylfluorophosphates. The electrochemical stability of ultrahigh-purity, high-surface-area carbon electrodes derived from polyfurfuryl alcohol was tested using the modified electrolyte. Favorable modification of the solid electrolyte interface (SEI) layer on the activated carbon electrode increased the cyclable electrochemical voltage window (4.8-1.2 V vs. Li/Li⁺). The chemical modification of the SEI layer induced by electrolyte additives was characterized by using X-ray photoelectron spectroscopy. Solid results: The formation of stable solid-electrolyte interfaces SEIs on high-surface-area activated carbon electrodes helps to extend their electrochemical voltage window, to 4.8 -1.2 V vs Li/Li⁺. SEI layers with higher inorganic contents are formed due to the presence of fluorophosphates-based additives in the electrolyte.