Abstract: In recent years, sodium-ion batteries (SIBs) have emerged as a promising technology for energy storage systems (ESSs) because of the abundance and affordability of sodium. Recently, metal selenides have been studied as promising high-performance conversion-type anode materials in SIBs. Among them, nickel selenide (NiSe₂) has received considerable attention due to its high theoretical capacity of 495 mAh g^-1 and conductivity. However, it still suffers from poor cycling stability because of the low electrochemical reactivity, large volume expansion, and structural instability during cycles. To address these challenges, NiSe₂ nanoparticles encapsulated in N-doped graphitic carbon fibers (NiSe₂@NGCF) were synthesized by using ZIF-8 as a template. NiSe₂@NGCF showed a high discharge capacity of 558.3 mAh g^-1 with a fading rate of 0.14% per cycle after 200 cycles at 0.5 A g^-1 in 0.01-3.0 V. At a very high current density of 5 A g^-1, the capacity still displayed excellent long-term cycle life with a discharge capacity of 406.1 mAh g^-1 with a fading rate of 0.016% per cycle after 3000 cycles. The mechanism of the excellent electrochemical performance of NiSe₂@NGCF was thoroughly investigated by ex-situ XRD, TEM, and SEM analyses. Furthermore, NiSe₂@NGCF//Na₃V₂(PO₄)₃ full-cell also delivered an excellent reversible capacity of 378.7 mAh g^-1 at 0.1 A g^-1 after 50 cycles, demonstrating its potential for practical application in SIBs.

Key words: Sodium-ion batteries, Anode materials, Nickel selenide, N-doped graphitic carbon fibers, One-dimensional electrode