Heterojunctions Based on (Co, Fe)Se₂ Nanostructures on Carbon Nanotubes for Rapid Ion Diffusion in Sodium-Ion Batteries

The development of anode materials with a high rate capability and cycle stability remains a significant challenge for sodium-ion batteries. In this study, a CNT@(Co, Fe)Se 2 heterojunction nanocomposite (HNC) was fabricated by in situ coating of (Co, Fe)Se 2 onto the surface of highly conductive CNTs, forming a heterojunction, using a convenient one-step solid-phase method. The synergistic effect of the heterostructure and selenium vacancies enhances charge and Na + ion conductivity, while the 3D porous framework of CNTs provides a pathway for charge transfer and Na + ion diffusion, resulting in the high specific capacity, excellent rate capability, and good cycle stability of the prepared CNT@(Co, Fe)Se 2 HNC. A reversible specific capacity of over 513 mAh g –1 was achieved after 250 cycles at 0.1 A g –1 . More than 87.55% of the specific capacity was retained as the current density increased from 0.1 to 3 A g –1 . After 1500 cycles at 5 A g –1, the CNT@(Co, Fe)Se 2 HNC maintained a high reversible specific capacity of 272.4 mAh g –1 with a high capacity retention of 98% and a constant Coulombic efficiency of 100%. The assembled Na 3 V 2 (PO 4 ) 3 //CNT@(Co, Fe)Se 2 full-cell battery exhibited a high anode-specific capacity of 420 mAh g –1 at 0.1 A g –1, with capacity retention exceeding 65.5% as the current density increased 50 times.