Closed‐Pore Engineering Couples Sodium Confinement and Interfacial Stabilization for Dendrite‐Resistant Hard Carbon Anodes

ABSTRACT Hard carbon, a leading anode for sodium‐ion batteries (SIBs), suffers from nonuniform sodium deposition, which causes dendrite growth and compromises safety and cycle life. Here, we report a closed‐pore engineering strategy based on cobalt‐doped hard carbon (CoHC) that couples internal sodium‐cluster confinement with interfacial stabilization. Internally, the closed nanopores redirect sodium storage from surface accumulation to deep pore filling, thereby inhibiting the growth of quasi‐metallic sodium clusters and dendrite propagation. Externally, the closed‐pore architecture regulates interfacial chemistry, leading to a thin, uniform, inorganic‐rich solid–electrolyte interphase (SEI) with reduced charge‐transfer resistance. In situ electrochemical tests confirm stable interfaces and suppressed dendrite growth in both Na||CoHC half cells and CoHC||Na 3 V 2 (PO 4 ) 3 (NVP) full cells, whereas severe dendritic deposition occurs on pristine hard carbon (HC) under identical current density. The CoHC anode delivers superior cycling stability with a capacity retention of 95% after 500 cycles, significantly outperforming HC. This work paves the way for dendrite‐resistant, safer, and longer‐lasting sodium‐ion batteries.