Reversible Graphite Anode Cycling with PC-Based Electrolytes Enabled by Added Sulfur Trioxide Complexes

Pyridine sulfur trioxide (PyrSO 3 ), trimethyl amine sulfur trioxide (Me 3 NSO 3 ), and triethyl amine sulfur trioxide (Et 3 NSO 3 ) complexes have been investigated as electrolyte additives for lithium ion batteries. Incorporation of 0.5 to 2.0% of the SO 3 complexes into a PC/EMC (1:1 v/v) 1 M LiPF 6 baseline electrolyte affords reversible cycling of graphite anodes confirming generation of a stable Solid Electrolyte Interphase (SEI). Good cycling performance is observed for graphite/LiNi 0.5 Mn 1.5 O 4 cells cycled to high potential (4.8 V vs Li) containing PC based electrolyte with added SO 3 complexes. Ex-situ surface analysis via X-ray Photoelectron Spectroscopy (XPS) of the anodes reveals SO 3 complex reduction on the surface of the graphite anode generates a sulfur-based SEI containing sulfites, sulfide, and sulfate species. The presence of the sulfur containing species is likely critical for the stability of the SEI. Ex-situ XPS analyses of the LiNi 0.5 Mn 1.5 O 4 cathodes suggest that reaction of Me 3 NSO 3 or Et 3 NSO 3 complexes at high potential result in the generation of a stable passivation layer which affords good capacity retention and coulombic efficiency.