2.2. Characterization

Powder X–ray diffraction (XRD) measurements of the synthesized samples were performed using an X–ray diffractometer (D8A25, Bruker, USA) operated at 40 keV and 40 mA, using Cu Kα radiation. Microstructural investigation of the powders was performed via a scanning electron microscopy (SEM, JSM–7500F, JEOL, Japan) and a high–resolution transmission electron microscope (HR–TEM, JEM–2100Plus JEOL, Japan). The particle sizes of the powders were measured using a static light–scattering analyzer (Mastersizer 2000, Malvern Instruments Ltd., UK), resulting in a measurement range of 0.04–2000 μm. The density of the cathode was measured using gas pycnometry (AccuPyc II, ATA scientific pty ltd, Australia), a non–destructive technique that employs gas displacement, often helium, to measure the volume of a material. The local structure of the sample was studied by Raman spectroscopy (MRI) using a laser with a wavelength of 532 nm and a power of 100 mW. Chemical state and composition analyses were then performed by X–ray photoelectron spectroscopy (XPS) using a Physical Electronics instrument (PHI 5000 VersaProbe Ⅲ, ULVAC–PHI. Inc., Japan) with an Al X–ray source.