Lithium-ion batteries are widely used in electronic devices due to their high energy density and long cycle life. However, the use of flammable organic solvents in electrolytes leads to frequent safety problems. Therefore, ensuring the safety of lithium-ion batteries has become an essential and urgent research topic. In this study, vinyl tris(2-methoxyethoxy)silane (VTMS) and triethyl phosphite (TEPi), serving as flame retardant additives, were employed to systematically explore the synergistic flame retardant effect and elucidate the underlying mechanism between them. Additionally, an assessment was conducted to examine the impact of their incorporation on the performance of the battery. The results indicate that the introduction of a combination of VTMS and TEPi led to the formation of a uniform and compact char layer under elevated temperatures, in contrast to the use of either additive alone. Incorporating 5 wt% of VTMS and TEPi enhances the thermal stability of the LiCoO₂ electrode, resulting in discharge capacity exceeding 145 mA h g⁻¹ for Li|LiFePO₄ and 315 mA h g⁻¹ for Li|natural graphite half cells, respectively, at a current density of 0.5C. Moreover, their utilization facilitates the generation of the solid electrolyte interphase (SEI) film. This study offers a novel perspective for investigating flame-retardant electrolytes in lithium-ion batteries.