Electrochemical characterization of amorphous LiFe(WO 4) 2 thin films as positive electrodes for rechargeable lithium batteries

Abstract

Amorphous LiFe(WO 4) 2 thin films have been fabricated by radio-frequency (R.F.) sputtering deposition at room temperature. The as-deposited and electrochemically cycled thin films are, respectively, characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectra techniques. An initial discharge capacity of 198 mAh/g in Li/LiFe(WO 4) 2 cells is obtained, and the electrochemical behavior is mostly preserved in the following cycling. These results identified the electrochemical reactivity of two redox couples, Fe 3+/Fe 2+ and W 6+/W x+ ( x = 4 or 5). The kinetic parameters and chemical diffusion coefficients of Li intercalation/deintercalation are estimated by cyclic voltammetry and alternate-current (AC) impedance measurements. All-solid-state thin film lithium batteries with Li/LiPON/LiFe(WO 4) 2 layers are fabricated and show high capacity of 104 μAh/cm 2 μm in the first discharge. As-deposited LiFe(WO 4) 2 thin film is expected to be a promising positive electrode material for future rechargeable thin film batteries due to its large volumetric rate capacity, low-temperature fabrication and good electrode/electrolyte interface.