Nanocrystalline ZnFe2O4 and Ag-doped ZnFe2O4 films used as new anode materials for Li-ion batteries

Nanocrystalline ZnFe2O4 and AgxZnFe2O4 (x = 0.16, 0.37, 0.50) thin films have been prepared by reactive pulsed laser deposition, and used as anode materials for Li-ion batteries for the first time. X-ray diffraction (XRD) and scanning electron microscopy measurements showed that the prepared films were composed of a nanocrystalline structure with the average particle size less than 100 nm. The initial reversible capacity of ZnFe2O4 and Ag0.37ZnFe2O4 film electrodes reached 556 and 700 mAh/g, respectively, at a current density of 10 muA cm(-2) between 0.01 and 3.0 V. The Ag0.37ZnFe2O4 film electrode exhibited better cyclability than ZnFe2O4 film electrode, and retained 91% of the reversible capacity up to 100 cycles. According to our results on cyclic voltammetry of Li/ZnFe2O4 cell coupled with ex situ photoelectron spectroscopy and XRD measurements of as-deposited and lithiated film electrodes, we suggest that the mechanism of ZnFe2O4 film reacted with lithium involves reduction of Zn2+ and Fe3+ to metallic Zn and Fe2+, accompanying the formation of Li-Zn alloy. The dramatically improved electrochemical performance of Ag0.37ZnFe2O4 film electrode might be related to the change of the reaction process after silver doping. (C) 2004 The Electrochemical Society.