Synergistic Regulation of Polyselenide Dissolution and Na‐Ion Diffusion of Se‐Vacancy‐Rich Bismuth Selenide toward Ultrafast and Durable Sodium‐Ion Batteries

Abstract Metal selenides (MSes) have great potential as candidate anode materials in high‐specific‐energy sodium‐ion batteries (SIBs) but are plagued by rapid capacity degradation and slow kinetics. Here, it is reveal that the Bi₂Se₃ anode discharge process involves multiple‐types of sodium polyselenides (Na‐pSe_x) which suffer from terrible dissolution and shuttling properties. Based on these observations, a nanoflower‐like composite of dual carbon‐confined Bi₂Se_3−x crystallites is designed via facile defect chemistry. The robust dual N‐doped carbon layer suppresses the precipitation and aggregation of Bi₂Se₃, significantly alleviating the dissolution and shuttle effect of Na‐pSe_x. Theoretical calculations indicate that the pyridine/pyrrole nitrogen sites exhibit strong van der Waals resistance and chemisorption properties against Na₂Se₄ and Na₂Se₂. Furthermore, the abundant Se vacancies improve the inherent conductivity of Bi₂Se₃, reduce the diffusion barrier of Na⁺, and accelerate the reaction kinetics. Consequently, the resulting Bi₂Se_3−x@DNC electrode exhibits extraordinary durability (over 2000 cycles at 10.0 A g⁻¹) and high‐rate capability (354.4 mAh g⁻¹ at 75.0 A g⁻¹), propelling the battery performance to new heights. Encouragingly, the assembled hybrid capacitor displays competitive rate performance and an ultra‐long lifespan exceeding 40 000 cycles, making the Bi₂Se_3−x@DNC electrode a promising candidate for SIBs.