Double‐Coordination Additives Induced High‐Entropy SEI for Stable Anode‐Less Sodium Metal Batteries

ABSTRACT Sodium‐ion batteries with abundant resources and cost‐effectiveness are promising candidates for energy storage. However, their insufficient energy density impedes deployment in energy‐intensive applications. Anode‐free configurations maximize energy density by eliminating the initial anode host, while facing critical challenges of irreversible sodium plating/stripping. Here, we present double‐coordination electrolyte additives‐benzimidazole (BZ) and zinc trifluoromethanesulfonate (ZF) to address these intrinsic limitations. The highly polar ZF pulls out the solvents in the primary solvation sheath for Na ⁺ diffusivity improving. Simultaneously, the ZF‐BZ complexes preferentially adsorb and decompose on the Cu foil surface, in situ forming a high‐entropy solid electrolyte interphase (ZnF _2, NaF, Na ₂ O, Na ₂ CO _3, and Na ₃ N). This ultrathin interphase (3.7 nm) features superior mechanical toughness and a lowered nucleation barrier, thereby facilitating rapid, uniform, and highly reversible sodium plating/stripping. Consequently, the Na||Cu cell using 1 m NaPF _6– diethylene glycol dimethyl–BZ/ZF electrolyte achieved an average Coulombic efficiency of 99.58% for 432 cycles at 3 mA cm ⁻² /3 mAh cm ⁻² and stable cycling stability for 800 h in Na||Na cell. The assembled anode‐less cell delivers a high energy‐density of 327.54 Wh kg ⁻¹ .