Carbon Nanotubes Coupled Bipolar Covalent Organic Frameworks With Nitrogen-Enriched Redox-Active Sites for High-Performance Lithium-Organic Batteries.

Abstract

Covalent organic frameworks (COFs) are frequently explored as attractive electrode materials for next-generation sustainable lithium-ion batteries. Unfortunately, such metal-free electrode materials suffer from low practical capacities and poor rate capabilities, due to low intrinsic conductivity, limited redox-active sites, and insufficient electrochemical utilization. Herein, integrating conductive carbon nanotubes (CNTs) with bipolar-type COFs enriched by multi-electron redox-active sites is rationally crafted by in situ Schiff base condensation to fabricate robust core-shell hierarchical heterostructures (CNT@COF). Remarkably, the as-fabricated CNT@COF cathode delivers a large reversible capacity (253.1 mAh g^-1 at 0.2 A g^-1), high rate capability (161.6 mA h g^-1 at 5 A g^-1), and excellent cycling stability (retaining 76.6% of initial capacity at 5 A g^-1 over 1000 cycles), because of the fast ion/electron transport and high utilization of active groups. Accordingly, both spectroscopy techniques and theoretical calculations are employed to reveal the redox reaction mechanisms of COF moieties and the reversible conversion of bipolar-type nitrogen-containing active centers (imine, triazine, and triphenylamine) against with PF₆ ^-/Li⁺ is rationalized clearly. This work crafts an unusual strategy to address common issues for organic polymer electrodes by macromolecular engineering to unlock the barrier of high-capacity and high-rate storage in powerful batteries.