In this work, tris(2-(thiophen-2-yl) ethyl) phosphate is designed, synthesized and applied as a functional electrolyte additive for lithium ion batteries with high-voltage LiCoO2 cathode. The tris(2-(thiophen-2-yl) ethyl) phosphate contains both of thiophen group and phosphorus element. The thiophen group forms a thinner electron conductive cathode electrolyte interphase to increase the thermal stability of LiCoO2 to de-active the catalytic and oxidative sites. In addition, the phosphorus element enhances the interfacial lithium ion conductivities by forming LiPxOyFz. Therefore, the thiophen group and phosphorus element in tris(2-(thiophen-2-yl) ethyl) phosphate work synergistically to optimize the electronic and ionic conductivity of cathode electrolyte interphase in high-voltage lithium ion batteries. As a result, when the batteries are cycled in the electrolyte with 0.1 wt% tris(2-(thiophen-2-yl) ethyl) phosphate, the Li//LiCoO2 half cells perform high thermal stability and deliver an excellent rate capability of 140 mAh g−1 at 5 C, and the graphite//LiCoO2 full cells present a significantly improved discharge capacity and stability of 139.9 mAh g−1 at 130 cycles with a high capacity retention of 90.72%.