Structural, impedance, dielectric and modulus analysis of LiNi1-x-y-0.02Mg0.02CoxZnyO2 cathode materials for lithium-ion batteries

Mg, Co and Zn co-substituted layer-structured cathode materials LiNiCoxZnyMg0.02O2 (x = y = 0.0, 0.02 and 0.04) were prepared by a solid-state reaction method. The materials were systematically characterized by X-ray diffraction (XRD), field effect scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), and electrical impedance spectroscopy (EIS) techniques. XRD analyses revealed the formation of a rhombohedral structure in the prepared materials with a typical α-NaFeO2 layered structure within R3¯m space group. The grain size was determined by FESEM in the range from 3.19 to 3.85 μm for all materials synthesized. The site of the local cation (Li-O) and of the transition metal cations (M-O) in the materials were identified by FT-IR. The complex impedance and modulus studies suggested the presence of a non-Debye type of multiple relaxations in these materials. The dielectric constant was found to increase with increasing Co and Zn concentrations. The ac conductivity studies revealed a typical negative temperature coefficient of resistance (NTCR) behavior, and the conductivity values varied from 1.58 × 10−5 to 8.46 × 10−6 S cm−1. The activation energy determined from the Arrhenius plots at 50 Hz was in the range of 0.23-0.78 eV.