Lithiation of Silicon Nanoclusters

In this paper, we investigate the lithiation of pristine amorphous silicon nanoclusters with diameters from 0.8 to 1.4 nm using first-principles molecular dynamics. It is found that this process occurs in two stages. In the first one, Li atoms accumulate at the surface of the nanocluster. A transfer of electrons from Li to the Si atoms takes place, which is accompanied by moderate structural changes. At a given Li coverage threshold that is related to the nanoparticle size, it becomes energetically favorable for any additional Li atoms to penetrate into the nanoparticle. Our results suggest that the driving force for this transition is the increasing electrostatic repulsion between positively charged surface Li ions. Beyond the threshold a second lithiation stage starts where the nanocluster is progressively filled with Li atoms. This leads to significant structural changes, but no sign of fracture is observed during the first lithiation cycle, suggesting that the amorphous silicon cluster remains intact at this size.