Conformal Fe₃O₄ Sheath on Aligned Carbon Nanotube Scaffolds as High-Performance Anodes for Lithium Ion Batteries

A uniform Fe₃O₄ sheath is magnetron sputtered onto aligned carbon nanotube (CNT) scaffolds that are directly drawn from CNT arrays. The Fe₃O₄–CNT composite electrode, with the size of Fe₃O₄ confined to 5–7 nm, exhibits a high reversible capacity over 800 mAh g^–1 based on the total electrode mass, remarkable capacity retention, as well as high rate capability. The excellent performance is attributable to the superior electrical conductivity of CNTs, the uniform loading of Fe₃O₄ sheath, and the structural retention of the composite anode on cycling. As Fe₃O₄ is inexpensive and environmentally friendly, and the synthesis of Fe₃O₄–CNT is free of chemical wastes, this composite anode material holds considerable promise for high-performance lithium ion batteries