LAUSR

The present study elucidates the role of surface oxygen functional groups on the electrochemical behavior of porous carbons when used as anodes for Li-ion batteries. To achieve this objective, a carbon xerogel (CX) obtained by pyrolysis of a resorcinol-formaldehyde gel was modified by different post-synthesis treatments in order to modulate its surface chemistry while maintaining its external surface constant. Various surface modifications were obtained by oxidation in air, in-situ polymerization of dopamine and, finally, by grafting of a polyethylene oxide layer on the polydopamine coating. While oxidation in air did not affect the pore texture of the CX, modifications by coating techniques substantially decreased the micropore fraction. Detailed electrochemical characterizations of the materials processed as electrodes were performed by capacitance measurements and galvanostatic cycling. Surface chemistry results, by X-ray photoelectron spectroscopy, show that the accessibility and the capacity increase when carbonyl (R-C=O) groups are formed on the CX, but not with oxides and hydroxyls. The amount of surface carbonyls, and in particular aldehyde (O=CH) groups, is found as the key parameter since it is directly correlated with the modified CX electrochemical behavior. Overall, the explored surface coatings tend to reduce the micropore volume and add mainly hydroxyl functional groups but hardly change the Li+ insertion/de-insertion capacities, while oxidation in air adds carbonyl groups, increasing the Li+ ions storage capacity thanks to an improved accessibility to the carbon network, which is not caused by any textural change.