In Situ X-ray Photoelectron Spectroscopy Study of Lithium Interaction with Graphene and Nitrogen-Doped Graphene Films Produced by Chemical Vapor Deposition

It is commonly accepted that the presence of nitrogen atoms in a graphene lattice improves many properties of carbon materials and particularly enhances their electrochemical capacity in Li ion batteries. Here, we present model experiments for revealing the difference in interaction of lithium with N-doped and N-free graphene samples by monitoring the changes in their electronic states after the deposition of Li vapors. Graphene and N-doped graphene films have been grown by chemical vapor deposition on copper substrates using methane and acetonitrile as precursors. The electronic structure of the films transferred onto SiO2/Si substrates was examined by X-ray photoelectron spectroscopy (XPS) before and after deposition of lithium from a Li evaporation source under vacuum conditions. A comparison between two graphene samples using in situ XPS measurements has detected a higher accumulation of lithium on the N-doped graphene, which implies its high prospects in energy storage applications. Analysis of the XPS core-level binding energy shifts showed that charge density donated by lithium is localized near the nitrogen defects, especially around the nitrogen atoms directly substituting for carbon atoms.