One dimensional pea-shaped NiSe2 nanoparticles encapsulated in N-doped graphitic carbon fibers to boost redox reversibility in sodium-ion batteries

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.