In Situ Growth of Covalent Organic Frameworks on Carbon Nanotubes for High-Performance Potassium-Ion Batteries.

Redox-active covalent organic frameworks (COFs) have been demonstrated as promising organic electrodes in many electrochemical devices. However, their inherently low conductivity significantly hinders the full utilization of their internal redox-active sites. To address this issue, a simple solvothermal method is used to in situ polymerize 2,4,6-triformylphloroglucinol (TP) and p-phenylenediamine (PA) on the surface of carbon nanotubes (CNTs), generating a nanocable-like COF-based nanocomposite, TpPa-COF@CNT nanocables, which contain abundant β-ketoenamine groups. By combining the high specific surface area and dense active sites of COFs with the superior conductivity of CNTs, the TpPa-COF@CNT nanocables as the anode in potassium-ion batteries displayed excellent performance. The reason is that the isomerization between the enolic and keto forms reinforces the stability of molecular architecture, while the transformation of active sites from C=N to C=O improves the K adsorption capability. Notably, the TpPa-COF@CNT nanocable anode exhibits a high reversible capacity of 446.1 mAh g at 0.1 A g and maintains 282.5 mAh g even after 2000 cycles at a higher current density of 2.0 A g. Additionally, a full battery assembled with 3,4,9,10-Perylenetetracarboxylic dianhydride heat-treated at 450 °C as the cathode retains a reversible capacity of 273.6 mAh g after 200 cycles at 0.1 A g.