Planting nitrogen-rich motif into porous aromatic frameworks to boost redox potential and multi-ion storage for wide-temperature sodium-organic batteries

Redox-active porous aromatic frameworks (PAFs) have emerged as hopeful candidates for sodium-ion batteries (SIBs) in view of their porous structures, chemical stability and tunable architectures. Herein, we successfully synthesized two redox-active PAFs (PAF-305 and PAF-306) with different nitrogen-containing motifs, and demonstrated their application as cathode materials for SIBs. Density functional theory (DFT) calculations reveal that nitrogen-rich PAF-305 exhibits a lower lowest unoccupied molecular orbital (LUMO) energy level (−3.35 eV) and a narrower energy gap (Eg) (2.40 eV) compared with nitrogen-poor PAF-306. As expected, PAF-305 displays outstanding electrochemical performance, comprising a high reversible capacity of 145.2 mAh g−1 at 0.05 A g−1 and satisfactory cycling stability with 92% capacity retention over 1000 cycles at 0.2 A g−1. Remarkably, PAF-305 maintains robust electrochemical properties across a wide temperature range (−20 °C to 50 °C). Through a combination of experimental characterizations and theoretical calculations, the sodium-ion storage mechanism of PAF-305 is elucidated. This study not only provides a promising strategy for exploring other redox-active organic units in the design of novel PAFs, but also expands the potential applications of PAFs in energy storage systems.