The organophosphorus compounds tris(trimethylsilyl) phosphite (TMSP) and vinylene carbonate (VC) have been considered for use as functional additives to improve the electrochemical performance of Li1.1Mn1.86Mg0.04O4 (LMO)/graphite full cells. Our investigation reveals that the combination of VC and TMSP as additives enhances the cycling properties and storage performance of full cells at 60°C. The unique functions of the TMSP additive in the VC electrolyte are investigated via ex situ X-ray photoelectron spectroscopy (XPS) and 19F nuclear magnetic resonance (NMR) measurements. The TMSP additive effectively eliminates trace water and hydrogen fluoride (HF) and produces a protective film on the LMO cathode that alleviates manganese dissolution at 60°C.