The effect of 2,3-epoxypropyl methanesulfonate (OMS) as an electrolyte additive for lithium ion batteries (graphite/NCM) has been investigated. Incorporation of OMS improves the discharge capacity retention by 8% and increases the coulombic efficiency by 2% compared to cells containing standard electrolyte for cells cycled at 55 °C. Electrochemical measurements suggest that OMS reacts on the surface of the graphite anode modifying the solid electrolyte interphase (SEI). X-ray photoelectron spectroscopy (XPS) has been conducted to investigate the surface chemistry of electrodes cycled with OMS. Surface analysis suggests that lithium alkylsulfonates, the decomposition products of OMS, play a critical role in enhancing the SEI thermal stability and improving capacity retention.