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. (C) 2017 Elsevier B.V. All rights reserved.