N-Doped Carbon Nanofibers Encapsulating CoO@Co <sub>9</sub>S <sub>8</sub> Nanoparticles: Preparation from Thiacalixarene-Supported Co <sub>32</sub> Cluster Precursors by Electrospinning and Application for Superior Li-Ion Storage

Abstract

Thiacalixarene-supported Co32nanoclusters as precursors encapsulated in polyacrylonitrile nanofibers (Co32@PAN-NFs) by electrospinning has been utilized to fabricate N-doped CoO@Co9S8 carbon nanofibers (CoO@Co9S8@CNFs) for superior Li-ion storage. The S-riching Co32 clusters capped by organic sheets afforded the well dispersed cobalt oxide/sulfide nanoparticles embedded in carbon nanofiber composites by direct calcination. The N-doped CoO@Co9S8 @CNFs nanocomposite has been utilized as anode materials for lithium ion battery with the reversible capabilities being of 1051.8, 967.6, 894.7, 782.7, 669.5 and 525.4 mAh·g-1 at 0.1, 0.2, 0.5, 1, 2 and 3 A·g-1, respectively. The CoO@Co9S8 @CNFs also showed a relatively high stable capacity of 551.7 mAh·g-1 at the current density of 1 A·g-1 after 200 cycles of rate experiments. The as-obtained N-doped CoO@Co9S8 @CNFs nanocomposites exhibited superior reversible capacity, rate performance, coulomb efficiency (74.5% vs 63.9%) and cyclic stability comparing with CoO@Co9 S8@C derived from simple annealing of Co32 templates.