Planar-Confined Atomic Sn Anode via D-P Orbital Coupling for Durable Sodium-Ion Storage

Anode materials for sodium-ion batteries (SIBs) usually face a fundamental trade-off between high specific capacity and long-term cycling stability, primarily due to severe structural degradation induced by substantial Na⁺ accommodation. Here, we report a d-p orbital coupling strategy to chemically confine atomic Sn within the interlayers of an NbS₂ host, forming a NbSnS₂ architecture characterized by orbital coupling between Nb 4d_z² and Sn 5p states. This coupling markedly enhances electron density along the z direction, effectively suppressing Sn migration during repeated sodiation and desodiation to preserve the lattice integrity. Moreover, delocalized electrons in the Sn 5p_x/5p_y orbitals screen electrostatic interactions with Na⁺, facilitating smooth ion diffusion. Consequently, the NbSnS₂ anode delivers a specific capacity of 490 mAh g^-1 at 0.44 C with an initial Coulombic efficiency of 93.1%, together with remarkable high-rate performance, retaining 340 mAh g^-1 over 850 cycles at 11 C with nearly 100% capacity retention. In-situ and ex-situ analyses confirm the structural recovery of crystalline NbSnS₂ after cycling, validating a quasi-topological intercalation mechanism. This work establishes an orbital coupling-induced atomic confinement paradigm for the rational design of high-capacity and durable anode materials for advanced SIBs.