Hierarchically nanoporous pyropolymer nanofibers for surface-induced sodium-ion storage

- Hierarchically nanoporous pyropolymer nanofibers (HN-PNFs) were fabricated.
- HN-PNFs have a high specific surface area of ∼3,950 m2 g−1 and numerous heteroatoms.
- HN-PNFs exhibit high capacities of ∼292 mAh g−1 and great rate/cycling performances.
- High energy (258 Wh kg−1) and high power (21,500 W kg−1) are achieved.

Surface-driven charge storage materials based on both electrochemical double layer (EDL) formation and pseudocapacitive behavior can deliver high energy and power capabilities with long-lasting cycling performance. On the other hand, the electrochemical performance is strongly dependent on the material properties, requiring sophisticated electrode design with a high active surface area and a large number of redox-active sites. In this study, hierarchically nanoporous pyropolymer nanofibers (HN-PNFs) were fabricated from electrospun polyacrylonitrile nanofibers by simple heating with KOH. The HN-PNFs have a hierarchically nanoporous structure and an exceptionally high specific surface area of 3,950.7 m2 g−1 as well as numerous redox-active heteroatoms (C/O and C/N ratio of 10.6 and 16.8, respectively). These unique material properties of HN-PNFs resulted in high reversible Na-ion capacity of ∼292 mAh g−1 as well as rapid kinetics and stable cycling performance in the cathodic potential range (1-4.5 V vs. Na+/Na). Furthermore, energy storage devices based on HN-PNFs showed a remarkably high specific energy of ∼258 Wh kg−1 at ∼245 W kg−1 as well as a high specific power of ∼21,500 W kg−1 at ∼78 Wh kg−1, with long and stable cycling behaviors over 2,000 cycles.

Hierarchically nanoporous pyropolymer nanofibers (HN-PNFs) fabricated from electrospun polyacrylonitrile nanofibers by simple heating with KOH exhibited high electrochemical performance for Na-ion storage.158