Recently, various electrolyte additives are used to reduce the negative impact on high voltage performance of the nickel-rich cathode (LiNixCoyMn1-x-yO2) (x >= 0.6). In this work, a selected additive, methyl diphenylphosphonate (MDPO), is applied to Li/LiNi0.8Co0.1Mn0.1O2(NCM811) half cells operating at high work voltages of 2.8-4.5 V. The electrochemical tests show that MDPO effectively widen the electrochemical window up to 5.0 V and stabilize the Coulombic efficiency, obtaining excellent capacity retention and low interface impedance. Different with the traditional additives, herein, our research confirms that the MDPO is a non-sacrificial additive which just tightly physical immobilized on the surface of NCM811 and stabilize the cathode/electrolyte interface, due to the fact that it doesn't oxidize within the whole working voltage range. This interface-regulating mechanism is further verified by post-test analysis and the first principle calculation. Furthermore, the MDPO also contributes to the thermal stability of the cells at high temperatures, which effectively increases the endothermic reaction onset temperature and shortens the self-quenching time of the electrolyte. This work provides a novel avenue for the design and screening of different electrolyte additives in the future study.