Robust Anode‐Free Sodium Batteries with Durably Sodophilic Interfaces by Suppressing Sodium‐Alloy Transformation

Abstract Anode‐free sodium batteries (AFSBs) are a desirable choice for high‐energy‐density and low‐cost battery systems. However, the rapid capacity decline resulting from irreversible sodium plating and stripping remains a big challenge for AFSBs. Herein, a copper‐dominated Cu 2 Sb composite coating employing a co‐sputtering strategy is designed to improve the sodophilicity of copper foils. The Cu 2 Sb coating can construct a durably sodophilic and stable interface by suppressing the alloying transition of the sodophilic phase and alleviating the volumetric deformation of the coating. This stable alloy interface can greatly enhance sodium nucleation and improve ion transport at the interface by forming homogeneous NaF‐rich solid electrolyte interphase (SEI) film. Ultimately, the AFSB assembled using this unique substrate with a highly loaded Na 3 V 2 (PO 4 ) 3 (NVP) cathode (≈10 mg cm −2 ) can cycle 600 cycles deliver a discharge capacity of 75.4 mAh g −1 with a capacity retention of 74.2%, which is much higher than those of the untreated one or antimony coating one (<30% after 200 cycles). This co‐sputtering strategy provides new insights into the design of sodophilic coatings with sodium‐alloying ability and can be extended to the optimization of zinc‐metal batteries.