Na 2 S Presodiation Enables Long Cycling Anode‐Free Sodium Batteries via Rapid Spontaneous Reactions

Abstract Anode‐free sodium batteries (AFSBs) with high energy density and low‐cost suffer from low cycling capacity retention due to the limited amount of active sodium ions and their rapid consumption. To address this issue, this study demonstrates an air‐stable Al/C‐Na 2 S@Na 3 V 2 (PO 4 ) 3 sandwich‐structured cathode containing 37.8% extra active sodium ions, in which high‐sodium‐content sodium sulfide (Na 2 S) is utilized as a presodiation reagent to introduce additional active sodium ions via an industrially scalable spraying method. Benefiting from the rapid spontaneous reaction between Na 2 S x and Na 3−x V 2 (PO 4 ) 3 (NVP), the polysulfides are immobilized within the cathode and converted to S 8 at low voltage and without the assistance of catalysts. The Na 2 S@NVP electrodes can be stored and operated in a dry environment, compatible with existing electrode production processes. The integration of low‐cost zinc foil with high reversibility for sodium plating/stripping as anode current collector effectively reduces sodium loss. The fabricated Na 2 S@NVP||Zn AFSBs retain 70.8% NVP active site utilization after stable cycling over 300 cycles at 1C, highlighting its potential for large‐scale applications.