Electronic behavior and impedance analysis of microcrystalline LiFePO₄

We report on the structure, DC electrical conductivity, dielectric, and impedance spectroscopic characterization of microcrystalline LiFePO₄ cathode material. Frequency variation of the dielectric constant (ε′) 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 ε′ at 433 and 473 K are 4.6 and 5.7, respectively. The real (Z′) and imaginary part (Z″) 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 (σ _dc) (273–573 K) follows the Arrhenius relationship. Activation energy (E _a) calculated from the ln σ _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.