Iodine Weakened Phosphorus‐Sodium Interaction Enables Near‐Complete Reversible Sodium‐Ion Storage

Abstract Red phosphorus (RP) anodes exhibit a high theoretical specific capacity for sodium (Na)‐ion storage; however, their practical application is hindered by insufficient Coulombic efficiency, primarily due to substantial sodium trapping within the crystalline Na 3 P. Guided by dual descriptors of electronegativity difference and atomic radius ratio, an innovative iodine (I)‐mediated alloying strategy is proposed that achieves near‐complete reversibility in sodiation and de‐sodiation reactions. Through iodine doping, the resultant lattice distortion and electron delocalization induce the formation of a low‐crystallinity I─P─Na phase upon sodiation, as opposed to the conventional high‐crystallinity Na 3 P. This structural modification significantly weakens Na─P bonding interactions and enhances Na + dealloying kinetics. Consequently, the iodine‐modified Na─P alloy demonstrates a substantially reduced de‐sodiation energy barrier, delivering an ultrahigh initial Coulombic efficiency of 98.3% and a high reversible capacity of 1786 mAh g −1 , alongside an exceptional cyclic Coulombic efficiency of 99.9%. These results demonstrate the critical role of heteroatom‐doped weak‐bonding alloys in improving the electrochemical reversibility of phosphorus‐based anodes, offering a promising pathway for advancing high‐performance sodium‐ion batteries.