Summary
Sodium-ion batteries are a cheaper, more abundant alternative to lithium-ion cells for large-scale energy storage, and transition-metal oxides like cobalt oxide are candidate anode materials because of their high theoretical capacity. Here the authors synthesise Co₃O₄ fibres by electrospinning followed by calcination in air at 600 °C, yielding fibres made of agglomerated rounded nanoparticles of polycrystalline Co₃O₄ spinel, and evaluate them as a sodium-ion battery anode. Ex-situ analysis of cycled electrodes reveals the conversion-reaction mechanism: after the first sodiation/desodiation cycle CoO forms, which explains the drop in cathodic specific capacity from 983 to 580 mAh/g. The high aspect-ratio fibre morphology underlies both the high initial capacity and slow capacity fading — 407 mAh/g is retained after 30 cycles.