Facile thermochemical conversion of FeOOH nanorods to ZnFeO nanorods for high-rate lithium storage.

We successfully prepared ZnFeO nanorods (ZFO-NRs) by a simple thermochemical reaction of FeOOH nanorods with Zn(NO) to use as an anode material in lithium-ion batteries. The FeOOH nanorod shape was well maintained after conversion into ZFO-NR with the formation of porous structures. The nanorod structure and porous morphology facilitate Li transport, improve the reaction rates owing to the larger contact area with the electrolyte, and reduce the mechanical stress during lithiation/delithiation. The ZFO-NR electrode exhibited a reversible capacity of 725 mA h g at 1 A g and maintained a capacity of 668 mA h g at 2 A g; these capacities are much higher and more stable than those of ZFO nanoparticles prepared by a hydrothermal method (ZFO-HT) (216 and 117 mA h g at 1 and 2 A g, respectively). Although ZFO-NRs exhibited high, stable capacities at moderate current densities for charging and discharging, the capacity rapidly decreased under fast charging/discharging conditions (>4 A g). However, carbonized ZFO-NR (C/ZFO-NR) exhibited an improved reversible capacity and rate capability resulting from an increased conductivity compared with ZFO-NRs. The specific capacity of C/ZFO-NRs at 1 A g was 765 mA h g; notably, a capacity of 680 mA h g was maintained at 6 A g.