Critical Role of Surface Defects in the Controllable Deposition of Li₂S on Graphene: From Molecule to Crystallite

Uncontrollable electrochemical deposition of Li₂S has negative impacts on the electrochemical performance of lithium–sulfur batteries, but the relationship between the deposition and the surface defects is rarely reported. Herein, ab initio molecular dynamics (AIMD) and density functional theory (DFT) approaches are used to study the Li₂S deposition behaviors on pristine and defected graphene substrates, including pyridinic N (PDN) doped and single vacancy (SV), as well as the interfacial characteristics, in that such defects could improve the polarity of the graphene material, which plays a vital role in the cathode. The result shows that due to the constraint of molecular vibration, Li₂S molecules tend to form stable adsorption with PDN atoms and SV defects, followed by the nucleation of Li₂S clusters on these sites. Moreover, the clusters are more likely to grow near these sites following a spherical pattern, while a lamellar pattern is favorable on pristine graphene substrates. It is also discovered that PDN atoms and SV defects provide atomic-level pathways for the electronic transfer within the Li₂S–electrode interface, further improving the electrochemical performance of the Li–S battery. It is found for the first time that surface defects also have strong impacts on the deposition pattern of Li₂S and provide electronic pathways simultaneously. Our work demonstrated the interior relationship between the surface defects in carbon substrates and the stability of Li₂S precipitates, which is of high significance to understand the electrochemical kinetics and design Li–S battery with long cycle life.