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

Pyridine sulfur trioxide (PyrSO3), trimethyl amine sulfur trioxide (Me3NSO3), and triethyl amine sulfur trioxide (Et3NSO3) complexes have been investigated as electrolyte additives for lithium ion batteries. Incorporation of 0.5 to 2.0% of the SO3 complexes into a PC/EMC (1:1 v/v) 1 M LiPF6 baseline electrolyte affords reversible cycling of graphite anodes confirming generation of a stable Solid Electrolyte Interphase (SEI). Good cycling performance is observed for graphite/LiNi0.5Mn1.5O4 cells cycled to high potential (4.8 V vs Li) containing PC based electrolyte with added SO3 complexes. Ex-situ surface analysis via X-ray Photoelectron Spectroscopy (XPS) of the anodes reveals SO3 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 LiNi0.5Mn1.5O4 cathodes suggest that reaction of Me3NSO3 or Et3NSO3 complexes at high potential result in the generation of a stable passivation layer which affords good capacity retention and coulombic efficiency.