Synthesis and electrochemical properties of dual doped spinels LiNi x Al y Mn 2 − x − y O 4 via facile novel chelated sol–gel method as possible cathode material for lithium rechargeable batteries

LiMn2O4 and LiNixAlyMn2−x−yO4 (x = 0.50; y = 0.05–0.50) powders have been synthesized via facile sol–gel method using Behenic acid as active chelating agent. The synthesized samples are subjected to physical characterizations such as thermo gravimetric analysis (TG/DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and electrochemical studies viz., galvanostatic cycling properties, electrochemical impedance spectroscopy (EIS) and differential capacity curves (dQ/dE). Finger print XRD patterns of LiMn2O4 and LiNixAlyMn2−x−yO4 fortify the high degree of crystallinity with better phase purity. FESEM images of the undoped pristine spinel illustrate uniform spherical grains surface morphology with an average particle size of 0.5 µm while Ni doped particles depict the spherical grains growth (50 nm) with ice-cube surface morphology. TEM images of the spinel LiMn2O4 shows the uniform spherical morphology with particle size of (100 nm) while low level of Al–doping spinel (LiNi0.5Al0.05Mn1.45O4) displaying cloudy particles with agglomerated particles of (50 nm). The LiMn2O4 samples calcined at 850 °C deliver the discharge capacity of 130 mAh/g in the first cycle corresponds to 94% columbic efficiency with capacity fade of 1.5 mAh/g/cycle over the investigated 10 cycles. Among all four dopant compositions investigated, LiNi0.5Al0.05Mn1.45O4 delivers the maximum discharge capacity of 126 mAh/g during the first cycle and shows the stable cycling performance with low capacity fade of 1 mAh/g/cycle (capacity retention of 92%) over the investigated 10 cycles. Electrochemical impedance studies of spinel LiMn2O4 and LiNi0.5Al0.05Mn1.45O4 depict the high and low real polarization of 1562 and 1100 Ω.