Conversion-Reaction-Enhanced BiOCl Anode via Cu Doping for High-Performance Sodium-Ion Batteries

BiOCl is regarded as a prospective anode material in sodium-ion batteries (SIBs), owing to its distinctive layered crystal structure and considerable theoretical capacity. Nevertheless, its real-world utilization is highly restricted by significant volume fluctuations during cycling and an unclear Na + storage mechanism. In this study, we report a Cu-doped BiOCl (Cu-BiOCl) anode for SIB applications. The systematic characterizations together with electrochemical investigations disclose that the Cu-BiOCl undergoes a conversion and alloying/dealloying mechanism during cycling. The metallic Bi serves as the primary active component for Na + storage, while the formed Na 3 OCl stimulates Na + migration. Furthermore, repetitive cycling induces a gradual transformation of metallic Bi into a nanoporous network, which not only promotes ion transport but also alleviates mechanical stress caused by volume variation. Most importantly, the incorporation of Cu introduces significant delocalization in the local environment and weakens bond strength validated by density functional theory calculations, which not only facilitates electron transfer but also lowers the energy barrier for Na + diffusion as well as bond dissociation during conversion reactions. Consequently, the Cu-BiOCl anode delivers high rate capability and superior cycling durability, giving an invertible capacity of 332.3 mAh g –1 at 10 A g –1 and an exceptional lifespan of 316.6 mAh g –1 at 10 A g –1 even after 5,000 cycles. When coupled with a Na 3 V 2 (PO 4 ) 3 cathode, the full cell employing the Cu-BiOCl anode discloses remarkable rate performance and outstanding cycling retention. This research provides significant insight into the rational design and engineering of advanced Bi-based anodes for grid-oriented sodium-ion energy storage systems.