Effect of annealing temperatures on optical and electrochemical behavior of spinel LiMn₂O₄ as cathode materials for lithium-ion batteries applications

In the present work, spinel LiMn₂O₄ cathode porous material in nanostructure is synthesized via sol–gel method for rechargeable batteries applications at different annealing temperatures (350, 550, 750 °C). The annealing temperature effect on their structural, optical, and electrochemical properties was investigated. X-ray diffraction (XRD) patterns exhibit that all the synthesized samples revealed a pure cubic spinel structure (Fd \(\stackrel{-}{3}\) m space group). The crystallite size (17 to 36 nm) and lattice parameters (8.23 to 8.28 Å) found to be increasing with annealing temperature. The increase of bond lengths of the Mn-O bonds with temperature reveals these bonds are quite weak and hence the stability of structure will also decrease. Scanning electron microscope (SEM) reveals the development of porous in the prepared fragile structures. The FTIR spectrum verifies the presence of characteristic bend of LiMn₂O₄nanostructures in the prepared samples. Optical absorption and Tauc's plot studies illustrate that as the annealing temperature increased; the optical energy bandgap is also increased from 3.49 to 3.89 eV for LiMn₂O₄ nanostructures. The CV studies show that the cathodic and anodic peak appears at less potential difference for LiMn₂O₄ nanostructures at 350 °C as compared to higher temperatures, signifying that the reversibility of LiMn₂O₄ (350 °C) is much superior to that of other samples annealed at the higher temperature.