Effects of Annealing Temperature on Microstructure and Electrochemical Properties of Perovskite-type Oxide LaFeO3 as Negative Electrode for Metal Hydride/Nickel(MH/Ni) Batteries

We reported the effects of annealing temperatures on microstructure and electrochemical properties of perovskite-type oxide LaFeO3 prepared by stearic acid combustion method. X-Ray diffraction(XRD) patterns show that the annealed LaFeO3 powder has orthorhombic structure. Scanning electron microscopy(SEM) and transmission electron microscopy(TEM) images show the presence of homogeneously dispersed, less aggregated, and small crystals(30-40 nm) at annealing temperatures of 500 and 600 degrees C. However, as the annealing temperature was increased to 700 and 800 degrees C, the crystals began to combine with each other and grew into further larger crystals(90-100 nm). The electrochemical performance of the annealed oxides was measured at 60 degrees C using chronopotentiometry, potentiodynamic polarization, and cyclic voltammetry. As the annealing temperature increased, the discharge capacity and anti-corrosion ability of the oxide electrode first increased and then decreased, reaching the optimum values at 600 degrees C, with a maximum discharge capacity of 563 mA h/g. The better electrochemical performance of LaFeO3 annealed at 600 degrees C could be ascribed to their smaller and more homogeneous crystals.