Two-dimensional copper-porphyrin covalent triazine framework for lithium-ion batteries

Robust covalent organic frameworks (COFs) with abundant redox-active sites have attracted intense attention for organic cathode materials due to the ordered structure and excellent stability. Herein, a two-dimensional (2D) crystalline copper-porphyrin covalent triazine framework (CuBCPP-CTF) was synthesized via polycondensation of 5,15-bis(4-cyanophenyl) porphyrin (H₂BCPP) and followed by post-copperization. The integration of copper-porphyrin moieties and triazine linkages provides two kinds of functional sites for outstanding Li⁺ and PF₆⁻ ions storage. Electrochemical studies reveal a high discharge capacity of 232 mAh·g⁻¹ at 200 mA·g⁻¹ and high mid-point voltage (2.77 V vs. Li⁺/Li), corresponding to an outstanding energy density of 601 Wh·kg⁻¹. Density functional theory calculations and ex-situ characterizations disclose the intrinsic bipolar redox mechanism of metalloporphyrin for both PF₆⁻ and Li⁺ accommodation and p-type triazine units for PF₆⁻ storage.