p/n-Type Polyimide Covalent Organic Frameworks for High-Performance Cathodes in Sodium-Ion Batteries

Covalent organic frameworks (COFs) are viewed as promising organic electrode materials for metal-ion batteries due to their structural diversity and tailoring capabilities. In this work, firstly using the monomers N,N,N',N'-tetrakis(4-aminophenyl)-1,4-phenylenediamine (TPDA) and terephthaldehyde (TA), p-type phenylenediamine-based imine-linked TPDA-TA-COF is synthesized. To construct a bipolar redox-active, porous and highly crystalline polyimide-linked COF, i.e., TPDA-NDI-COF, n-type 1,4,5,8-naphthalene tetracarboxylic dianhydride (NDA) molecules are incorporated into p-type TPDA-TA-COF structure via postsynthetic linker exchange method. This tailored COF demonstrated a wide potential window (1.03.6 V vs Na⁺/Na) with dual redox-active centers, positioning it as a favorable cathode material for sodium-ion batteries (SIBs). Owing to the inheritance of multiple redox functionalities, TPDA-NDI-COF can deliver a specific capacity of 67 mAh g^-1 at 0.05 A g^-1, which is double the capacity of TPDA-TA-COF (28 mAh g^-1). The incorporation of carbon nanotube (CNT) into the TPDA-NDI-COF matrix resulted in an enhancement of specific capacity to 120 mAh g^-1 at 0.02 A g^-1. TPDA-NDI-50%CNT demonstrated robust cyclic stability and retained a capacity of 92 mAh g^-1 even after 10 000 cycles at 1.0 A g^-1. Furthermore, the COF cathode exhibited an average discharge voltage of 2.1 V, surpassing the performance of most reported COF as a host material.