Covalent-Organic-Framework-Based Li–CO₂ Batteries

Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials constructed from designer molecular building blocks that are linked and extended periodically via covalent bonds. Their high stability, open channels, and ease of functionalization suggest that they can function as a useful cathode material in reversible lithium batteries. Here, a COF constructed from hydrazone/hydrazide-containing molecular units, which shows good CO₂ sequestration properties, is reported. The COF is hybridized to Ru-nanoparticle-coated carbon nanotubes, and the composite is found to function as highly efficient cathode in a Li–CO₂ battery. The robust 1D channels in the COF serve as CO₂ ^– and lithium-ion-diffusion channels and improve the kinetics of electrochemical reactions. The COF-based Li–CO₂ battery exhibits an ultrahigh capacity of 27 348 mAh g⁻¹ at a current density of 200 mA g⁻¹, and a low cut-off overpotential of 1.24 V within a limiting capacity of 1000 mAh g⁻¹. The rate performance of the battery is improved considerably with the use of the COF at the cathode, where the battery shows a slow decay of discharge voltage from a current density of 0.1 to 4 A g⁻¹. The COF-based battery runs for 200 cycles when discharged/charged at a high current density of 1 A g⁻¹.