Effect of Ni and Fe substitution on the thermal, structural, vibrational spectroscopic and electrochemical properties of LiMn2O4 cathode material

Spinel LiMn2O4, Li1.025(Mn1.95Ni0.025Fe0.025)O4, and Li1.025(Mn1.9Ni0.025Fe0.05)O4 cathodes were synthesized by a two-step solid-state reaction method. The thermal, structural, vibrational spectra and electrochemical properties of these materials were characterized by using TGA-DTA, XRD, SEM, EDS, Fourier-FT-IR spectroscopy, Raman spectroscopy, and charge-discharge test. The TGA-DTA analysis confirmed that 800°C is the suitable temperature for synthesizing all the samples using Li2CO3, Fe2O3, MnO2, and NiO precursors. The XRD analysis revealed the formation of a single-phase cubic spinel structure with Fd3¯m space group. Two distinct strong absorption peaks were identified by FT-IR analysis in the wavenumber regions of 512 to 621 cm−1. Enhancement of the discharge specific capacity due to Ni and Fe substitution into LiMn2O4 was observed. Among all samples, Li1.025(Mn1.95Ni0.025Fe0.025)O4 exhibited excellent cyclic performance (97.4%) after 50 cycles.