Crystalline structure and electrical conductivity of nickel substituted spinel lithium manganese oxide

Spinel LiMn2O4 is an important Li-ion battery cathode material due to its high-capacity, low toxicity and low cost. The substitution of Ni is a solution to overcome the limitation of the material including Jahn-Teller distortion and dissolution of Mn in electrolytes. In this work, the effects of Ni substitution on the structure and electrical conductivity characteristics of LiNixMn2-xO4 (x = 0, 0.05, 0.1, 0.2) that were synthesized by solid state reaction and sol-gel methods were investigated. X-ray diffraction (XRD) analyses revealed that the Ni substitution decreased the lattice constant and Mn-O distance, but increased the Li-O bond length and 8a tetrahedral volume. Although the Rietveld refinement results showed that the crystalline structure parameters of LiNixMn2-xO4 changed linearly by Ni substitution content which favoured the transportation of lithium ion, the relation of Ni content and electrical conductivities was non-linear. By electrochemical impedance spectroscopy (EIS) analyses, minimum peaks of the electronic and ionic conductivities at the substitution level of 0.05 were observed. The EIS analyses also revealed that the conduction behavior of the materials have dominated by the ionic conductivity, which was several orders higher than the electronic conductivity.