Zinc ferrite nanorods coated with polydopamine-derived carbon for high-rate lithium ion batteries

Zinc ferrite (ZnFe2O4) nanorods are synthesized using a facile and scalable method, i.e., decomposition of oxalate precursors which are obtained through a polyvinyl alcohol-assisted aqueous precipitation reaction. The ZnFe2O4 nanorods are further coated with carbon by self-polymerization of dopamine on the surfaces of the ZnFe2O4 nanorods followed by carbonization. The carbon layer on the ZnFe2O4 nanorods is homogeneous with the thickness of 3 to 5 nm. The polydopamine-derived carbon coating greatly improves the electrochemical performances of the ZnFe2O4 nanorods, especially rate capability and cycling stability. When galvanostatic diacharging/charging at 0.5 and 2 A/g, the ZnFe2O4/carbon nanorod anode can deliver reversible capacities of 805 and 504 mAh/g, respectively, whereas the ZnFe2O4 nanorod anode only delivers the capacities of 616 and 154 mAh/g, respectively. Besides, the ZnFe2O4/carbon nanorod anode shows excellent cycling stability; no obvious capacity fading is observed at the current density of 1 A/g for 100 cycles. The improved electrochemical performances could be attributed to the enhanced electron conductivity of the ZnFe2O4 nanorods with the carbon layer, which is confirmed by electrochemical impedance spectroscopy measurements and scanning electron microscopic studies of the cycled electrodes.