The high-voltage lithium metal battery (HVLMB) with the Ni-rich cathode is one of the most promising next-generation energy storage systems due to its significantly high energy density (>500 Wh kg⁻¹). Nevertheless, the real application of HVLMB is limited by the unstable electrode/electrolyte interface and the heterogeneous reaction of polycrystalline Ni-rich layered oxide ternary cathode. To overcome these challenges, an effective strategy is proposed utilizing a high-voltage bifunctional nitrile-borate molecule, tris(2-cyanoethyl) borate, as a film-forming additive and the robust single-crystal LiNi_0.88Co_0.09Mn_0.03O₂ (SC-NCM) cathode as a feasible alternative cathode: a high voltage stable protective film improves the electrode/electrolyte interface, and the outstanding chemo-mechanical of micro-sized particles effectively suppress the localized overutilization of active material. The TCEB derived CEI layer not only enlarges the electrochemical oxidation window of the electrolyte but also protects the cathode from notorious interfacial side reactions. With this strategy, the cycling stability of SC-NCM||Li-metal battery is significantly improved at an ultrahigh cut-off voltage of 4.7 V, exhibiting a high reversible capacity of 158.7 mAh g⁻¹ with the capacity retention of 80 % after 150 cycles at 1C. This work provides an effective way to improve the cycle stability for high-voltage SC-NCM||Li metal batteries with high-energy density through optimizing electrolytes and modifying the structure of the cathode.