Electrode‐Electrolyte Interface Regulation Enables Large‐Capacity Gel‐State Na Metal Batteries with Appealing Cycling Stability

Abstract Gel‐state Na metal batteries (NMBs) are promising candidates for the large‐scale energy storage due to the merits of low cost, abundant sodium resources, and high energy density. However, the long‐term lifespan and safety of NMBs with large capacity are limited by unstable electrode‐electrolyte interface. Herein, the electrode‐electrolyte interfaces are regulated by the mechanically robust GPE coupled with the artificial NaBr/Na x Sn y layer on Na anode, enabling the symmetric cells with a long‐term cycling lifespan of over 2500 h at 0.5 mA cm −2 , along with an ultralong cycle life of ca. 4700 h at 0.2 mA cm −2 under −20 °C. With an area capacity of ca. 0.9 mAh cm −2 based on Na 3 V 2 (PO 4 ) 3 , the SnBr 2 ‐Na|GPE|Na 3 V 2 (PO 4 ) 3 full cells exhibit a capacity retention of 96.6% after 1100 cycles, resulting from high ionic conductivity (3.7 mS cm −1 ) of GPE and stable inorganic NaBr/Na x Sn y layer on Na surface. This work provides a new insight for the development of NMBs with high safety and large capacity.