Cathode Atomic Structures and Their Electrolyte Interfaces in Lithium-sulfur Batteries

Lithium-sulfur batteries (LSBs) are a promising alternative to conventional battery technologies due to their high theoretical energy density. However, the insulating nature of sulfur and the polysulfide shuttle effect present practical challenges to achieving this. This study employs molecular dynamics simulations with a ReaxFF reactive force field to investigate the structure of LSB cathode-electrolyte interfaces, with cathode materials made from different sized graphene flakes and elemental sulfur (S8). Smaller graphene flakes were seen to bond more with the sulfur, while structures with larger graphene flakes featured fewer C-S bonds and more long-chain sulfur species. Observing the interface between the cathode and an organic electrolyte revealed that cathode structures with larger graphene flakes could orientate to shield the long-chain sulfur and lithium polysulfide species from interacting with and dissolving into the electrolyte. Additional simulations were performed to investigate cathode materials with regions of crystalline alpha-S8. However, it was found that the ReaxFF force field used for LSB systems cannot effectively model crystalline sulfur under constant pressure conditions. Further development of reactive force fields for simulation of graphene flake and sulfur electrodes in the presence of electrolyte are therefore required to explore the full range of likely structures using these methods. Cathode structures with different sized graphene flakes were modelled alongside electrolyte with lithium using ReaxFF. Flake size and the resulting cathode structure was found to affect polysulfide shuttle.image