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

Abstract

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.

Keywords

• X-ray diffraction
• FESEM
• Dielectric
• Impedance
• Electric modulus