Construting stable 2 × 2 tunnel-structured K1.28Ti8O16@N-doped carbon nanofibers for ultralong cycling sodium-ion batteries

Sodium-ion batteries (SIBs) are one of the most potential candidates for large-scale energy storage due to the low cost and eco-friendliness, however, a stable and reversible anode is urgently developed. In this work, a novel 2 × 2 tunnel-structured K1.28Ti8O16@N-doped carbon nanofibers (KTO@N CNFs) anode is successfully synthesized via simple electrospinning and subsequent thermal treatment with urea acted as the additional convenient nitrogen source. In-situ X-ray diffraction (XRD) measurement confirms the intercalation reaction mechanism and robust structure during Na+insertion/extraction. This composite material exhibits a reversible capacity of 116.4 mAh g − 1 at a current density of 100 mA g − 1 after 1000 cycles. More impressively, even at a high current density of 1 A g − 1, the battery delivers capacity retention of 98.4 mAh g − 1 after 5000 cycles. The excellent electrochemical performance is attributed to the adequate 2 × 2 tunnel structure and the nano-confinement of N-doped nanofibers on K1.28Ti8O16 nanocrystals, which offers enough diffusion paths and enhance the ionic diffusion of sodium ions. This work provides a facile strategy to synthesis stable, reversible, and long-cycle anode for sodium-ion batteries.