Lithium (Li) metal anodes are considered one of the most promising anodes for high-performance batteries with ultra-high specific energy density. However, uncontrolled dendrite growth and the unsuitability of common systems for high voltage hinder the development of Li metal batteries with long cycle life. Herein, we report a rationally designed artificial solid electrolyte interphase (SEI) for Li metal anodes, incorporating LiNO₃ and lithium difluoro(oxalato)borate (LiDFOB) as additives within a porous poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) polymer skeleton (referred to as PNF). LiNO₃ and LiDFOB can release and synergistically react at the electrode surface, leading to the in situ generation of a homogeneously distributed inorganic/organic SEI during the electrochemical process. This SEI improves homogeneity, ionic conductivity and mechanical stability, contributing to the suppression of electrolyte side reactions and Li dendrite growth. Moreover, a uniform CEI with high Li⁺ conductivity can be constructed on the NCM811 particles, further enhancing the structural integrity of the NCM811 cathode. As a result, the artificial SEI layer on Li metal anodes enables stable cycling of Li–Cu half cells in an ester-based electrolyte and Li–LiNi_0.8Mn_0.1Co_0.1O₂ full cell even at a high voltage of 4.5 V. This work provides new insights into designing homogeneous SEIs for Li metal batteries.