Due to the uprising demand of energy storage in consumer electronics and electric vehicles, tremendous effort and interest have been drawn into the development of novel electrolyte additive blends in lithium-ion batteries (LIBs). However, the applications of LIBs have several critical limitations, including elevated temperature performance, calendar life performance, and safety. The solid electrolyte interface (SEI), generated from the electrolyte reduction on the anode surface during the first few cycles, is believe to be one of the key players improving LIBs thermal stability. Various attempts to screen ultimate electrolyte additive blends and produce robust SEI layer for better cyclability in lithium-ion batteries operations at elevated temperature have been widely reported. The graphite/LiNi_1/3Co_1/3Mn_1/3O₂ coin cells containing electrolytes with and without 1, 3-propane sultone (PS) and vinylene carbonate (VC) have been prepared and investigated. The electrochemical performance of the cells is correlated with ex-situ surface analysis of the electrodes conducted by FTIR and XPS, and in-situ gas analysis by on-line electrochemical mass spectrometry (OEMS). The results suggest that incorporation of both PS and VC results in improved capacity retention upon cycling at 55 °C and lower impedance. Ex-situ surface analysis and OEMS confirm that incorporation of PS and VC alter the reduction reactions on the anode inhibiting ethylene generation and changing the structure of the solid electrolyte interface (SEI).  Incorporation of VC results in CO₂ evolution, formation of poly(VC), and inhibition of ethylene generation.  Incorporation of PS results in generation of lithium alkylsulfonate (RSO₂Li) and inhibition of ethylene generation.  The combination of PS and VC reduces the ethylene gassing during formation by more than 60 %.