The role of carbonate and sulfite additives in propylene carbonate-based electrolytes on the formation of SEI layers at graphitic Li-ion battery anodes

Density functional theory (DFT) was used to investigate the effect of electrolyte additives such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl ethylene sulfite (VES), and ethylene sulfite (ES) in propylene carbonate (PC)-based Li-ion battery electrolytes on SEI formation at graphitic anodes. The higher desolvation energy of PC limits Li⁺ intercalation into graphite compared to solvated Li⁺ in EC. Li⁺(PC) ₃ clusters are found to be unstable with graphite intercalation compounds and become structurally deformed, preventing decomposition mechanisms and associated SEI formation in favor of co-intercalation that leads to exfoliation. DFT calculations demonstrate that the reduction decomposition of PC and electrolyte additives is such that the first electron reduction energies scale as ES > VES > VEC >PC. The second electron reduction follows ES > VES > VEC > VC > PC. The reactivity of the additives under consideration follows ES > VES > VEC > VC. The data demonstrate the supportive role of certain additives, particularly sulfites, in PC-based electrolytes for SEI film formation and stable cycling at graphitic carbon-based Li-ion battery anodes without exfoliation or degradation of the anode structure.