LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811), a Ni-rich layered oxide, is a promising cathode material for high-energy density lithium-ion batteries (LIBs). However, its structural instability, caused by adverse phase transitions and continuous oxygen release, as well as deteriorated interfacial stability due to excessive electrolyte oxidative decomposition, limits its widespread application. To address these issues, a new concept is proposed that surface targeted precise functionalization (STPF) of the NCM811 cathode using a synergistic slurry additive (SSA) approach. This approach involves coating the NCM811 particle surface with 3-aminopropyl dimethoxy methyl silane (3-ADMS), followed by the precise deposition of ascorbic acid via an acid-base interaction. The slurry additives induce the formation of an ultra-thin spinel surface layer and a stable cathode–electrolyte interface (CEI), which enhances the electrochemical kinetics and inhibits crack propagation. The STPF strategy implemented by the SSA approach significantly improves the cyclic stability and rate performance of the NCM811 cathode in both half-cell and full-cell configurations. This work establishes a promising strategy to enhance the structural stability and electrochemical performance of nickel-rich cathodes and provides a feasible route to promote practical applications of high-energy density lithium-ion battery technology.