In situ growth of triazine-based β-ketoenamine COFs on carbon nanotubes for durable sodium-ion battery anodes

Covalent organic frameworks (COFs) are crystalline porous polymers with tunable structures, high surface area, and excellent chemical stability, making them promising electrode materials for the development of rechargeable lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). However, pristine COFs often suffer from poor electrical conductivity and limited redox site accessibility, restricting their overall electrochemical performance. To overcome these limitations, we have synthesized a redox-active triazine-based β-ketoenamine COF integrated with carbon nanotubes (COF@CNT) via in situ Schiff base condensation. This COF@CNT composite exhibits strong π-π interactions, promoting uniform COF growth on CNTs, enhancing electrical conductivity, and increasing accessible redox sites. Electrochemical measurements demonstrate a fivefold increase in capacity relative to the pristine COF, delivering a reversible capacity of 250 mAh g^-1 at 0.05 A g^-1. The composite exhibits excellent long-term cycling durability over 1000 consecutive cycles, comprising 500 cycles at 0.5 A g^-1 with a capacity retention of 73%, followed by an additional 500 cycles at 1 A g^-1 with a high capacity retention of 94%, while maintaining minimal capacity decay and excellent rate capability. Mechanistic studies indicated a mixed contribution from surface-controlled and diffusion-controlled Na⁺ storage processes. This work demonstrates that the COF@CNT composite effectively addresses conductivity and stability challenges, presenting a promising alternative for developing durable, high-performance SIB anodes.