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

Abstract

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.