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• Double heteroatom (B and N) doped carbon nanofibers (BNC NFs) were constructed. • GITT method was used to investigate the storage mechanism of Na. • The 5BNC NFs (5 wt% boric acid) exhibited the highest electrochemical performance. A double heteroatom doping strategy is proposed to synthesize boron- and nitrogen-doped heteroatom carbon nanofibers (BNC NFs) as anode materials for sodium-ion batteries (SIBs). The specific capacity and rate performance of the BNC NF anode are higher than those of the NC NF anode. Particularly, the composite containing 5 wt% boric acid provides the highest reversible capacity of 249 mAh g−1 at a current density of 0.02 A g−1 and excellent cyclic stability of 144 mAh g−1 at 2 A g−1 after 3000 cycles. The excellent cyclic performance of the BNC NFs can be attributed to the defect-rich nanostructure derived by optimally doping boron under annealing, which is conducive to accelerating ion transport and introducing additional Na-ion storage active sites. The excellent capacity and long cycle stability of the full cell SIBs comprising the optimized BNC NFs anode and Na 3 V 2 (PO 4) 3 cathode suggest the promising potential of B-doped C NFs as anodes for rechargeable Na-ion batteries. The BNC NFs with double heteroatom (B and N) doped structure is realized as superior anode for sodium ion batteries providing excellent Na+ storage capacity and long-term cycling performance. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel 2 × 2 tunnel-structured K 1.28 Ti 8 O 16 @N-doped carbon nanofibers are prepared. • The electrode exhibits excellent long cycle performance. 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 K 1.28 Ti 8 O 16 @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 K 1.28 Ti 8 O 16 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. [Display omitted] [ABSTRACT FROM AUTHOR]

A highly performance binder-free and freestanding cathode for Li-O 2 battery (LOB) receives much attention to solve the major obstacles including sluggish oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) kinetics, unstable cathode, and irrational architecture design. Herein, we develop an effectively electrospinning to embed the oxygen vacancy-containing Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) particles into carbon nanofibers (BSCF@C nanofibers) towards the self-assembly cathode with high ORR and OER performance. Predictably, the BSCF@C nanofibers successfully prevent the BSCF particles from aggregation, facilitate O 2 adsorption and diffusion, enhance the electron transfer, accelerate the Li 2 O 2 nucleation/decomposition, and enhance the stability of cathode. Different from the conventional cathode, the LOBs with the BSCF@C nanofibers cathode perform an outstanding electrochemical performance, which providing a high discharge specific capacity of 11976 mAh g−1 and ultralong cycling stability of 98 times at the current density of 400 mA g−1. Notably, this work opens up an opportunity for the perovskite oxides with high crystallization temperature for high-performance energy storage systems at ambient temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

The exploration of sodium ion batteries (SIBs) cathodes with high voltage and high performance has stimulated the research on the honeycomb-layered oxides. However, their performance are severely restricted by the slow ion intercalation kinetics and inferior high rate capability. Herein, 1D nanofibers with controlled morphology and crystallinity have been constructed for the honeycomb-layered Na 3 Ni 2 BiO 6 and Na 3 Ni 2 SbO 6. The formation mechanisms of the nanofibers are probed. The significant effects of the porosity and particle crystallinity on ion transport kinetics and electrochemical properties of the oxide nanofibers are studied. Notably, the highly porous structure and low particle crystallinity are highly effective on promoting fast ion transport and improving high rate properties. Surprisingly, both modified nanofibers with uniform porous structure and low-crystallized nanoparticles achieve the better rate capability and faster ion transport capability than the reference samples. Moreover, the excellent sodium storage performance and stable high-rate cycling properties further demonstrate the high efficiency of 1D porous architecture on reversible sodium intercalation. Image 1 [ABSTRACT FROM AUTHOR]