In situ growth of MOF-derived nitrogen-doped carbon nanotubes on hollow MXene spheres for K-ion storage

Abstract

Two-dimensional (2D) MXenes have the potential as electrode materials for energy storage owing to their unique structural properties and excellent electrochemical properties. Unfortunately, MXene nanosheets easily stack due to van der Waals forces, which degrade the electrochemical performance of MXene-based materials. Herein, the three-dimensional (3D) structure of hollow spheres constructed by 2D MXene nanosheets using a template method can effectively reduce the stacking of MXene nanosheets. However, electron conduction is hampered by the gaps between the MXene spheres. To enhance the conductivity between MXene spheres, sea urchin-like hollow MXene spheres coupled with metal organic frame (MOF)-derived nitrogen-doped carbon nanotubes (CoN-CNT@SMXene) were synthesized by in situ tip growth of nitrogen-doped carbon nanotubes with CoN-capped tips on the surface of MXene hollow spheres. The cross-linked nanotubes drastically enhanced the connections of the MXene hollow spheres and provided a superior electron and ion migration bridge. When applied as an anode in potassium-ion batteries (PIBs), CoN-CNT@SMXene performs much better than the bare MXene spheres in terms of capacity, current rate and cycle stability. The capacity still maintained 253 mA h g⁻¹ at 400 mA g⁻¹ for 1000 cycles. This study inspires the development of high-performance MXene-based materials in K-ion batteries.