Effect of pH values on structural, optical, electrical and electrochemical properties of spinel LiMn2O4 cathode materials

Abstract

In the present work, we have synthesized the spinel LiMn 2 O 4 cathode materials via a sol-gel method at 750 °C for 8 h under optimal conditions at different pH values (3, 6 and 9) and studied the effect of different pH values on the structural, optical, electrical and electrochemical properties. X-ray diffraction (XRD) analysis identified the synthesized materials as crystallized in the cubic spinel structure (Fd3m) with slight decrease in the lattice parameters. SEM exhibits the formation of a spongy and fragile network structure in the synthesized samples. An enhancement in the optical energy band ( E g ) leads to the blue shift in the synthesized samples with reduced crystallite size. Cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) investigations show that the LiMn 2 O 4 nanostructures synthesized at pH 9 exhibit the long-term cycle constancy and a superior electrochemical reproducibility as compared to those synthesized at pH values of 3 and 6. The results revealed that pH plays a significant role in tuning the structural, optical and electrochemical properties of the LiMn 2 O 4 cathode material, which is considered a promising substitute of cathode materials for the novel lithium-ion battery applications. • Spinel LiMn 2 O 4 cathode materials were successfully synthesized via sol-gel method. • A significant enhancement in optical band gap has been observed with the increase of pH values. • LiMn 2 O 4 nanostructures synthesized at pH 9 exhibit long-term cycle constancy and superior electrochemical reproducibility. • Investigation revealed that pH values play a significant role in tuning the optical and electrochemical properties.