Structural stability and electrochemical properties of gadolinium-substituted LiGdxMn2-xO4 spinel as cathode materials for Li-ion rechargeable batteries

Gadolinium-substituted spinel LiGdxMn2-xO4 (x = 0.0 and 0.5) cathode crystals were synthesized by co-precipitation and dual calcination. Structural characterization using X-ray diffraction pattern revealed that gadolinium doping in LiMn2O4 resulted in the highly ordered cubic spinel structure with only slight increase in the average d-spacing and lattice parameters. X-ray photoelectron spectroscopic analysis indicated an increase in the average oxidation state of manganese in the Gd-doped material in comparison to its pristine spinel counterpart. Morphological characterization using field emission scanning electron microscopy and transmission electron microscopy revealed that gadolinium doping in LiMn2O4 resulted in a decrease of the average particle size. Electrochemical charge/discharge studies at various current rates showed that the LiGd0.5Mn1.5O4 spinel exhibited excellent and stable cycling stability in comparison to Gd-free LiMn2O4 spinel. Gd-substitution in LiMn2O4 brought structural stability via the expansion of LiO4 tetrahedra, contraction of MnO6 octahedra, and avoidance of the Jahn-Teller distortion effect, which translated in high-rate performance and less capacity fading. In addition Gd-doping was found via electrochemical AC impedance spectroscopy to lead to significant increase in electronic conductivity as evident by less charge transfer resistance than the pristine.