On Electrolyte-Dependent Formation of Solid Electrolyte Interphase Film in Lithium-Ion Batteries: Strong Sensitivity to Small Structural Difference of Electrolyte Molecules

The performance increase of the lithium-ion battery (LIB) is critical for effectively leveling the cyclic nature of renewable energy sources related to the global warming. The current LIB performance with liquid electrolytes, e.g., ethylene carbonate (EC) and propylene carbonate (PC), is strongly dependent on a stable solid electrolyte interphase (SEI) films on the electrode surfaces. However, such electrolyte-dependent SEI film formation still remains not-fully understood. To investigate its microscopic characteristics, we have performed the atomistic reaction simulations with the recently developed hybrid Monte Carlo (MC)/molecular dynamics (MD) reaction method, and have exposed for the first time the atomistic picture of the structure of the SEI films consistent with the experimental evidence and conjectures. It was also found that the dense EC-based SEI film can protect electrolyte from the reduction, providing the cavities which have sufficient size for passing of Li+ cations. In contrast, the PC-based one became sparser, and is reasonably expected not to protect the electrolyte from reductive decomposition due to the presence of methyl group of PC, which prevents the stable aggregation of reaction products. Finally, it was concluded that the SEI film formation is strongly sensitive to the small structural difference of electrolyte molecules at the microscopic level.