Rapid synthesis of phase-junction CoSe2-based nanocomposites (O/C-CoSe2@NC) for enhanced sodium-ion storage

Abstract

Employing cobalt selenide (CoSe₂) as an anode material for sodium-ion batteries (SIBs) is severely hindered by its inherently low electronic conductivity and sluggish Na⁺ diffusion kinetics. Phase engineering is recognized as an effective strategy to enhance the intrinsic conductivity of CoSe₂ while simultaneously accelerating sodium-ion diffusion. In this study, we employed an ultrafast, solid-phase microwave selenization strategy method to achieve in situ encapsulation of unique cubic/orthorhombic-CoSe₂ phase-junction (O/C-CoSe₂) nanoparticles within a nitrogen-doped carbon matrix (O/C-CoSe₂@NC). The resultant O/C-CoSe₂@NC nanocomposite of phase junction interface structure configuration significantly reduces the diffusion energy barrier for Na⁺ ions and accelerates electrochemical reaction kinetics. A three-dimensional porous carbon framework derived from metal–organic frameworks (MOFs) not only substantially enhances the overall conductivity of the composite but also effectively mitigates volume expansion during the sodiation/desodiation process as a robust protective barrier. As anticipated, the O/C-CoSe₂@NC material exhibits outstanding rate performance (263.32 mAh g⁻¹ at 10 A g⁻¹) and ultra-long cycle life (294.84 mAh g⁻¹ after 1400 cycles at 5 A g⁻¹). When assembled into full cells (O/C-CoSe₂@NC//NVP@C), it retains a discharge capacity of 162.4 mAh g⁻¹ after 150 cycles at 0.5 A g⁻¹, demonstrating commercial viability. In situ X-ray diffraction (XRD), ex situ high resolution transmission electron microscopy (TEM), in situ electrochemical impedance spectroscopy (EIS) tests and theoretical calculations are selected to further investigate the sodium storage mechanism of the O/C-CoSe₂@NC and the potential factors contributing to its enhanced performance. Moreover, this ultrafast and green microwave synthesis technique can be extended to large-scale preparation of other metal selenide–carbon composites.