CoSe2 nanodots embedded in N-doped dual-carbon nanospheres for boosting sodium-ion storage

Cobalt diselenide (CoSe2) is regarded as a rising star as anode materials for sodium-ion batteries (SIBs) due to fast sodium diffusion kinetics, and high theoretic capacity. Nonetheless, the intrinsic conversion reaction mechanism inevitably causes large volume variation accompanying the insertion of sodium ion, resulting in poor cycling stability. Furthermore, its low electronic conductivity always raises unsatisfactory rate capability. In this work, we design CoSe2 nanodots embedded in N-doped dual-carbon nanospheres (CoSe2/NC@NCSs) via a hard template assisted one-step selenization strategy as potential anode for SIBs. The unique hollow dual-carbon spheres as conductive matrix can provide fast electron transfer path for CoSe2 nanodots. Meanwhile, dual-carbon spheres with inner void acts as protective barrier for confining CoSe2 nanodots during sodiation/desodiation. Benefit from the synergetic merits of hollow dual-carbon spheres and CoSe2 nanodots, our CoSe2/NC@NCSs electrode exhibits competitive electrochemical performance with a reversible capacity of 386 mAh g−1 (0.2 A g−1), and an inspiring cyclability (148 mAh g−1 at 2 A g−1) over 800 cycles. A CoSe2/NC@NCSs//AC device was fabricated and exhibits stable cyclability at 1 A g−1 over 450 cycles, manifesting the great potential for sodium-ion hybrid capacitors. Our work paves a new route for the electrode design strategy for SIBs.