Impedance characterisation of LiFePO4 ceramics

Pellets of LiFePO4, synthesised by solid state reaction, were sintered at two temperatures, 650 and 770 degrees C and their electrical properties measured by impedance spectroscopy over the temperature range 75 to 300 degrees C. Various equivalent circuits were tested to model the impedance data and a good fit to the bulk response obtained for a parallel combination of a resistance, R-1, capacitance, C-1, and constant phase element, CPE1. For pellets sintered at 650 degrees C, a second element, R-2-C-2-CPE2, was required, in series, to model an impedance attributed to a constriction resistance associated with the poorly sintered ceramic. At higher temperatures and low frequencies, evidence was obtained for a third impedance component attributed to a depletion layer associated with a Schottky barrier at the sample-electrode interface. (c) 2012 Published by Elsevier B.V.