Spatial Confinement Induced by Bimetallic Phosphides Heterostructure Toward Stable Sodium Storage Materials

Tin phosphide (Sn 4 P 3 ) has emerged as a promising anode material for sodium‐ion batteries (SIBs) owing to its high theoretical capacity and favorable redox potential. However, unstable Sn 0 intermediates and Sn 0 /Na 3 P interfaces formed upon (de)sodiation severely compromise its reversibility and stability. Herein, heterostructure configurations of Sn 4 P 3 /MP x (M = Mn, Fe, Cu, etc.) enclosed inside conductive graphene sheets (G) have been proposed and fabricated. The in situ formed M 0 intermediates during sodiation exhibit strong adsorption energies on Sn 0 , which offer enhanced spatial confinement to mitigate particle agglomeration and volumetric expansion of Sn 0 . The bimetallic phosphide heterostructures further promote charge transfer and ion diffusion kinetics by establishing built‐in electric fields and optimized Na + migration pathways. As a result, Sn 4 P 3 /MP x @G anodes exhibit superb sodium storage performance. Especially, the optimized Sn 4 P 3 /CuP 2 @G can deliver a high initial Coulombic efficiency of 90.9%, high cyclic Coulombic efficiencies (>99.5%), and ultralong cycleability (3500 cycles with 429.5 mAh g −1 at 1 A g −1 ). When paired with a Na 3 V 2 (PO 4 ) 3 cathode, the full cell combines a high energy density of 213.6 Wh kg −1 and an excellent capacity retention of 98% after 500 cycles. This work elucidates the (de)sodiation mechanisms of bimetallic phosphides and offers new insights into the development of advanced SIBs.