Unlocking Mg2+ storage in imine-functionalized CNTs@COF hybrids: role of in situ coatings in enhancing magnesium battery performance

Abstract

Magnesium batteries exhibit promising prospects owing to their high theoretical volumetric capacity, abundant natural reserves, and superior safety. However, their practical applications are hindered by the sluggish diffusion kinetics of Mg²⁺ in conventional cathode materials. This study innovatively proposes a strategy for the epitaxial growth of imine-linked covalent organic frameworks on the surface of carbon nanotubes (CNTs@COF), thereby effectively balancing electrode conductivity and the density of active sites through precise control of the COF layer thickness. This composite material not only facilitates the efficient diffusion of Mg²⁺ via axially aligned COF channels and continuous charge transport networks but also enhances electrical conductivity through the incorporation of CNTs, significantly improving the energy storage performance, cycling stability, and utilization efficiency of active sites in magnesium batteries. Furthermore, the Mg²⁺ storage mechanism in CNTs@COF is hypothesized to involve the storage of six electrons per CN bond within each COF unit. As a result, CNTs@COF exhibits superior discharge capacity, rate capabilities, and cycling performance (e.g., 191.7 mAh g⁻¹ at 20 mA g⁻¹ after 200 cycles and 107.6 mAh g⁻¹ at 500 mA g⁻¹ after 3000 cycles). The synthetic approach paves the way for constructing high-performance multivalent battery systems, bridging the gap from molecular design to macroscopic electrochemical performance.