Conjugated polymeric molecules have been heralded as promising electrode materials for the next-generation energy-storage technologies owing to their chemical flexibility at the molecular level, environmental benefit, and cost advantage. However, before any practical implementation takes place, the low capacity, poor structural stability, and sluggish ion/electron diffusion kinetics remain the obstacles that have to be overcome. Here, we report the synthesis of a few-layered two-dimensional covalent organic framework trapped by carbon nanotubes as the anode of lithium-ion batteries. Remarkably, upon activation, this organic electrode delivers a large reversible capacity of 1536 mAh g⁻¹ and can sustain 500 cycles at 100 mA g⁻¹. Aided by theoretical calculations and electrochemical probing of the electrochemical behavior at different stages of cycling, the storage mechanism is revealed to be governed by 14-electron redox chemistry for a covalent organic framework monomer with one lithium ion per C=N group and six lithium ions per benzene ring. This work may pave the way to the development of high-capacity electrodes for organic rechargeable batteries.

Aiming to achieve metal–oxide-based electrodes for Li-ion batteries with enhanced energy density and cycling life, especially overcoming their negative volume expansion during cycling, more effort should be devoted to the exploration of the combination of morphology-controlled metal oxides with carbonaceous materials. In this work, we select dual/single-metallic organic frameworks immobilized on the surface of carbon nanotubes as the precursors to synthesize composites of ternary/single metal oxides with carbon nanotubes (ZnCo₂O₄@CNTs and ZnO@CNTs). The main product, ZnCo₂O₄@CNTs, consists of ultrafine ZnCo₂O₄ nanoparticles embedded deeply in the carbon nanotubes. The existence of small-size ternary metal oxides as well as the carbon nanotubes results in outstanding lithium-storage properties of the ZnCo₂O₄@CNT anode for lithium-ion batteries. It delivers an extremely high capacity (1507 mA h g⁻¹, 100 mA g⁻¹) after 200 cycles, which is larger than the theoretical value.