Amorphous TiO2 Ion transport bridges boosting sodiation kinetics of carbon-encapsulated bi nanofibers for fast-charging and long-cycle sodium storage

Flexible carbon buffering and rigid TiO 2 confinement stabilize Bi nanoparticles. • Amorphous TiO 2 with pseudocapacitive ion storage acts as an ion-transport bridge for fast Na + shuttling to Bi. • The as-prepared electrode exhibits excellent fast-charging capability and long-term cycling stability. Developing fast-charging sodium-ion batteries (SIBs) is highly desirable yet fundamentally challenging due to the sluggish Na + diffusion kinetics and severe structural degradation of electrode materials. Despite their high theoretical capacity, alloy-type Bi anodes suffer from severe volume expansion and inherently sluggish solid-state sodiation kinetics, which lead to limited rate capability. Herein, Bi/TiO 2 /C composite nanofibers (BTC) are fabricated via electrospinning and carbonization, achieving uniform embedding of Bi nanoparticles in an amorphous TiO 2 -decorated carbon nanofiber. The carbon framework provides flexible buffering and a conductive network. Amorphous TiO 2 not only acts as a rigid filler to further buffer the expansion and aggregation of Bi but also exhibits pseudocapacitive Na + storage behavior, allowing it to function as a local Na + reservoir and ion-transport bridge. This structure enables rapid Na + supply to adjacent Bi active sites, thereby accelerating the stepwise alloying reaction and maintaining fast reaction kinetics even at ultrahigh rates. This synergistic effect enables the BTC anode to deliver 226.16 mAh g -1 after 3000 cycles at 20 A g -1 , and the assembled Na 3 V 2 (PO 4 ) 3 @C (NVP@C)//BTC full cell maintains 207.72 mAh g -1 after 4000 cycles. This study offers an innovative strategy for structural regulation and performance optimization of anode materials for high-capacity fast-charging SIBs. A novel Bi/TiO 2 /C composite nanofiber anode is rationally designed via electrospinning and carbonization for fast-charging sodium storage. Amorphous TiO 2 serves dual roles as ion-transport bridges that enrich Na + and as dispersants that prevent Bi agglomeration, while the carbon matrix buffers volume expansion, thereby synergistically accelerating sodiation kinetics and enabling ultrahigh rate capability with long-term cycling stability. Download: Download high-res image (267KB) Download: Download full-size image