Fe₃O₄ Hollow Nanospheres Grown In Situ in Three-Dimensional Honeycomb Macroporous Carbon Boost Long-Life and High-Rate Lithium Ion Storage

A composite of Fe₃O₄ and carbon is constructed by a one-step calcination method with polystyrene spheres as template, polyvinyl pyrrolidone as assembling agent, and Fe(NO₃)₃ as Fe source. Material characterization demonstrates that Fe₃O₄ hollow nanospheres 10–16 nm in diameter are closely grown in situ inside three-dimensional honeycomb macroporous carbon with a pore diameter of about 200 nm. The composite material exhibits high specific capacity, delivering an average discharge capacity of 1618 mA h g⁻¹ at 0.1 A g⁻¹. The long-term cycling performance is excellent, achieving discharge capacity of 770 mA h g⁻¹ at 1 A g⁻¹ after 1000 cycles and 429 mA h g⁻¹ at 5 A g⁻¹ after 200 cycles. Even at 10 A g⁻¹, the rate capability is outstanding. Kinetics analyses reveal predominant capacitive behavior and low reaction impedance in electrochemical reaction. The excellent performance mainly benefits from the beneficial structural effects of Fe₃O₄ hollow nanospheres and honeycomb macroporous carbon. Fe₃O₄ hollow nanospheres@three-dimensional honeycomb macroporous carbon is a superior anode material for lithium-ion batteries.