Electronic behavior and impedance analysis of microcrystalline LiFePO4

Abstract

We report on the structure, DC electrical conductivity, dielectric, and impedance spectroscopic characterization of microcrystalline LiFePO4 cathode material. Frequency variation of the dielectric constant (epsilon') exhibits the dispersion that can be modeled with a modified Debye's function, which considers the possibility of more than one ion contributing to the relaxation. At a constant frequency, the dielectric constant value increases with increasing temperature. At 100 kHz, the measured values of epsilon' at 433 and 473 K are 4.6 and 5.7, respectively. The real (Z') and imaginary part (ZaEuro(3)) of impedance as a function of frequency at different temperatures indicate the existence of relaxation processes and their distribution in LiFePO4. Cole-Cole plots at different temperatures indicate that the conductivity is predominantly due to the intrinsic bulk grains. Temperature variation of DC electrical conductivity (sigma (dc)) (273-573 K) follows the Arrhenius relationship. Activation energy (E (a)) calculated from the ln sigma (dc) versus 1000/T plot is 0.44 eV, which indicates the predominant electronic conduction mechanism in LiFePO4. The AC conductivity increases with increasing frequency and temperature.