Li-Metal Anode in a Conventional Li-Ion Battery Electrolyte: Solid Electrolyte Interphase Formation using Ab Initio Molecular Dynamics

Abstract

Ab initio molecular dynamics simulations were performed for Li + conducting electrolytes based on 1M lithium hexafluorophosphate (Li + PF 6 − ) in ethylene carbonate (EC)-ethylmethyl carbonate (EMC) (3:7wt) with 5 wt% vinylene carbonate (VC) in contact with Li-metal (electrode), finding a variety of products due to dissociations of all electrolyte components. The formed solid electrolyte interphase from electrolyte degradation arranges in an outer layer composed of denser materials (sitting over the anode surface) such as Li 2 (CH 2 O) 2 from EC, Li 2 CO 3 , Li 2 C 2 H 2 and Li 2 CO 2 from VC, and Li 2 C 3 H 5 O 2 and LiCH 3 O from EMC dissociations. Then follows an inner layer made of Li-binary compounds, Li 3 CO, Li 2 O and Li 3 C from EC, Li 2 O, Li 2 C 2 and LiH from VC, and LiF and Li 3 P from PF 6 − dissociations. We calculated electron affinities of electrolyte molecules during their decomposition using a polarizable continuum model to consider solvent effects molecules degradation. PF 6 − has the highest first and second electron affinities, despite explicit Coulomb repulsion, which eventually dissociates the molecule right after capturing an electron from the metal-anode; therefore, PF 6 − is also the fastest to dissociate. EMC has the lowest first and second electron affinities, thus it is the least prone to accept electrons and the least likely to dissociate at the Li-metal interface.