Probing the electric double layer structure at nitrogen-doped graphite electrodes by constant-potential molecular dynamics simulations

Abstract

Electric double layer (EDL) is a critical topic in electrochemistry and largely determines the working performance of lithium batteries. However, atomic insights into the EDL structures on heteroatom-modified graphite anodes and EDL evolution with electrode potential are very lacking. Herein, a constant-potential molecular dynamics (CPMD) method is proposed to probe the EDL structure under working conditions, taking N-doped graphite electrodes and carbonate electrolytes as an example. An interface model was developed, incorporating the electrode potential and atom electronegativities. As a result, an insightful atomic scenario for the EDL structure under varied electrode potentials has been established, which unveils the important role of doping sites in regulating both the EDL structures and the following electrochemical reactions at the atomic level. Specifically, the negatively charged N atoms repel the anions and adsorb Li+ at high and low potentials, respectively. Such preferential adsorption suggests that N-doped graphite can promote Li+ desolvation and regulate the location of Li+ deposition. This CPMD method not only unveils the mysterious function of N-doping from the viewpoint of EDL at the atomic level but also applies to probe the interfacial structure on other complicated electrodes.