Heterointerface-engineered CoSe2-NiSe2@carbon nanofibers via spatial nanoconfinement for high-performance sodium-ion batteries

Heterointerface engineering has emerged as a promising strategy to enhance the sluggish reaction kinetics and structural instability of conversion-type anode materials for sodium-ion batteries. Herein, a built-in electric field-enhanced CoSe 2 -NiSe 2 heterojunction embedded in flexible nitrogen-doped carbon nanofibers (CoSe 2 -NiSe 2 @CNFs) is constructed via electrospinning and selenization route. The heterointerface induces charge redistribution and accelerates ion diffusion, while the conductive and elastic CNF network effectively accommodates volume changes and maintains structural integrity. As a result, the CoSe 2 -NiSe 2 @CNFs anode achieves a high reversible capacity of 413.8 mAh g −1 at 0.2 A g −1 after 100 cycles and exhibits remarkable long-term cyclability, retaining 309.7 mAh g −1 after 1000 cycles at 1 A g −1 . The reversible conversion mechanism and interfacial stability are systematically validated through ex situ experimental measurements and DFT calculations, which confirm enhanced Na + adsorption and optimized ion transport kinetics at the heterointerface. Moreover, paired with a Na 3 V 2 (PO 4 ) 3 cathode in a full cell, it demonstrates stable cycling performance with low polarization. This work provides an integrated interface-confinement design strategy toward high-rate and a highly fatigue-resistant electrode with exceptional cycling stability.