High-performance sodium storage of nano-CoSe₂ at nitrogen doping carbon frameworks with carbon nanotube shuttles

CoSe₂ exhibits a high theoretical sodium storage capacity as an anode material for sodium-ion batteries (SIBs). However, it faces several challenges during electrochemical cycling, including the shuttle effect of sodium polyselenide, volume expansion, and poor electrical conductivity. To address these issues, this study proposes a novel approach to synthesize CoSe₂@NC/CNTs materials using cross-linked PMMA spheres as templates. The resulting structure demonstrates a hollow core-shell configuration comprising nitrogen-doped carbon nanotubes (N-CNTs) and dispersed CoSe₂ nanoparticles. This is confirmed through characterization techniques such as XRD, Raman spectroscopy, SEM imaging, and TEM analysis, which verify the successful preparation. Moreover, XPS and TG analyses reveal the presence of strong interfacial interactions within the structure. These unique structural features enable CoSe₂@NC/CNTs to exhibit exceptional sodium storage performance: remarkable stability (after 5000 cycles at 20 A·g⁻¹, the specific capacity only slightly decreases from 320 to 280 mAh·g⁻¹ with a minimal degradation rate of 0.8% per cycle) and practicality (the specific capacity of the full battery NTO||CoSe₂@NC/CNTs assembled with sodium nickel-iron-manganate oxide (NTO-NaNi_1/3Fe_1/3Mn_1/3O₂) remains at 323 mAh·g⁻¹ after 120 cycles at a high current intensity of 5 A·g⁻¹). Additionally, we elucidate the intrinsic reason behind the strong stability of CoSe₂@NC/CNTs through SEM and EDS analysis after cycling while also providing ex situ characterization to explain their sodium storage.