Organic–inorganic assembly engineering of core–double-shell VSe1.6/C@N–C⊂MoSe2 nanotubes for boosting Na+/K+ storage performance

Abstract

Core–shell structures with gradient components are considered as promising active materials for energy storage systems because of their prominent synergistic effects and enhanced reaction kinetics. In this work, gradient-structured VSe_1.6/C@N–C⊂MoSe₂ nanotubes, with VSe_1.6/C inner cores, and double shells of protecting N–C layers and an activated MoSe₂ outer shell, are prepared through a high-temperature selenization process of a tailored template, which are obtained from an organic–inorganic assembly process. As for the storage of the large-sized Na⁺/K⁺ ions, this ingenious structure of VSe_1.6/C@N–C⊂MoSe₂ nanotubes can markedly enhance the reaction kinetics and well balance the reaction activity and cycling stability, due to increased ion/electron diffusion channels from the MoSe₂ and N–C shells, abundant internal interfaces and gradient-component distribution. As a result, a capacity of 232.4 mA h g⁻¹ over 10 000 cycles can be retained at a current of 5.0 A g⁻¹, with a capacity retention of 86.8%. As for potassium ion batteries (PIBs), VSe_1.6/C@N–C⊂MoSe₂ nanotubes deliver a high and stable capacity of 180 mA h g⁻¹ at 1.0 A g⁻¹ for 5000 cycles with a capacity retention of 71.3%. Based on dQ/dV analysis and ex situ XRD results, the VSe_1.6/C@N–C⊂MoSe₂ anode has a hybrid mechanism of MoSe₂ (intercalation and conversion reactions) and VSe_1.6 (only intercalation reaction) and high reversibility for K⁺ storage. And combined with the component and structural superiorities, high cycling stability can be achieved for the VSe_1.6/C@N–C⊂MoSe₂ nanotubes in PIBs.