Interfacial Engineering of a Bi/SnS Heterojunction with a Built-in Electric Field toward High-Capacity Sodium-Ion Storage

Tin sulfide exhibits promise as a high-capacity anode for sodium-ion batteries but suffers from substantial volume expansion and sluggish kinetics. We constructed a hydrangea-like Bi/SnS heterojunction to address these challenges. Theoretical calculations reveal that the work function difference between metallic Bi and semiconducting SnS drives electron transfer from Bi to SnS, generating a built-in electric field (BIEF) at the interface. This field significantly enhances charge transfer kinetics while reducing the Na⁺ diffusion barrier to 0.12 eV and buffering volume variations. Consequently, the Bi/SnS anode demonstrates exceptional performance with an initial Coulombic efficiency of 92%, delivering 901 mAh g^-1 at 0.1 A g^-1 and maintaining 400 mAh g^-1 at 20 A g^-1. It exhibits remarkable cycling stability with 79.21% capacity retention after 3000 cycles at 10 A g^-1, providing fundamental insights for heterointerface engineering in energy storage applications.