High Voltage Flexible Sodium-Ion Battery Cathode Materials Based on 1D Covalent Organic Framework.

Covalent organic frameworks (COFs) have emerged as promising electrode materials for sodium-ion batteries (SIBs) due to their well-ordered porous structures that facilitate ion storage and transport. However, conventional 2D and 3D COFs often require post-processing, such as ball milling or carbon compositing, to enhance electrochemical performance. In this study, a 1D imine-linked COF, N,N,N',N'-Tetrakis(4-aminophenyl)-1,4-phenylenediamine-2,6-pyridinedicarboxaldehyde (TP-PDA), is synthesized via a one-step Schiff base reaction, achieving a fully conjugated and porous structure that enables efficient sodium-ion transport. TP-PDA is insoluble in organic electrolytes, ensuring stable cycling performance. The material exhibits a high average discharge potential of 3.1 V and delivers a discharge capacity of 124 mAh g at 3 A g after 1800 cycles, with a capacity retention exceeding 90%. In a full-cell configuration with a hard carbon anode, the battery maintains a stable capacity of 122 mAh g after 10 000 cycles at 1 A g without noticeable capacity degradation. Furthermore, the flexible pouch cell retains its electrochemical integrity under bending conditions, demonstrating its potential for flexible and wearable energy storage applications.