Electrostatic spray deposition of porous Fe₂V₄O₁₃ films as electrodes for Li-ion batteries

Porous thin films composed of complex Fe/V oxides (crystalline Fe₂V₄O₁₃ and amorphous Fe₂V₄O_12.29) are prepared by electrostatic spray deposition technique. The crystalline Fe₂V₄O₁₃ thin film shows a high initial capacity of 409 mAh g^-1. The cyclic voltammetry analysis of a Fe₂V₄O₁₃/Li cell reveals that the crystalline Fe₂V₄O₁₃ undergoes an irreversible phase transition when the lower cut-off voltage is below 2.5 V. Compared with the crystalline Fe₂V₄O₁₃, the amorphous Fe₂V₄O_12.29 thin film delivers a lower initial capacity of 349.9 mAh g^-1 but exhibits better cycling performance in the voltage range of 1.0-4.0 V. After 50 cycles, its capacity can still reach around 200 mAh g^-1. X-ray photoelectron spectroscopy (XPS) reveals that the Fe₂V₄O_12.29 thin film contains ions of mixed valence states V⁵⁺/V⁴⁺ and Fe³⁺/Fe²⁺, resulting in better rate capability for Fe₂V₄O_12.29 than for Fe₂V₄O₁₃. These results indicate that the amorphous Fe/V-oxide film is a promising electrode material for high energy applications. (C) 2012 Elsevier B. V. All rights reserved.