Tuning the electrical and cycling performance of nickel manganese oxide hexagonal-shaped particles via preparation routes for lithium-ion batteries

Abstract

In this study, simple and effective solid-state and sol-gel routes are attempted to synthesize Nickel Manganese Oxide, NiMn2O4 (NMO). Structural, morphological, electrical, and electrochemical properties are investigated with calcination temperatures. XRD results confirm the highly crystalline cubic spinel structure with zero impurities for all samples, except NMOS_700, which indicates the presence of a slight NiMnO3 phase. SEM and TEM micrographs confirm the formation of hexagonal shape particles of size less than <0.5μm. At low calcination temperatures, grouped and uneven-shaped particles are observed with increased particle size. Electrical measurements depict the strong dependence of conductivities (σac and σdc) on grain size, grain boundary, and operating temperature. All the samples exhibit conductivities between 10-8 - 10-4 S/cm with the varied calcination temperature. Electrochemical performances are explored via Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV), and Galvanostatic Charge-Discharge (GCD) profiles. Sample NMOB_700 and NMOB_800 exhibit the initial discharging capacity of 1104 and 1188 mAh g-1 at 100 mA g-1 current density. All the samples exhibit above 98% columbic efficiency after two initial cycles and show the reversible nature of NiMn2O4 and excellent cyclability. The electrochemical results confirm that preparation methods and calcination temperature have a great impact on the grain properties of materials. Multiple oxidation states of Mn and Ni is also confirmed through the XPS study.