Influence of the microstructure and its stability on the electrochemical properties of EMD produced from a range of precursors

Abstract

The influence of the microstructure and the stable crystal structure on the electrochemical properties of the electrolytic manganese dioxide (EMD) produced from manganese cake (EMDMC), low-grade manganese ore (EMDLMO), and synthetic manganese sulfate solutions (EMDSMS) is reported. X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry/differential thermal analysis, field emission scanning electron microscopy (FESEM), and chemical analyses were used to determine the structural and chemical characteristics of the EMD samples. The charge-discharge profile was studied in 9 M KOH using a galvanostatic charge-discharge unit. All the samples were found to contain predominantly gamma-phase MnO2, which is electrochemically active for energy storage applications. FESEM images show that preparation method significantly influences surface morphology, shape, and size of the EMD particles. In almost all cases, nanoparticles were obtained, with spindle-shaped nanoparticles for EMDMC, platy nanoparticles in the case of EMDLMO, and anisotropic growth of tetra-branched star-like nanoparticles of EMDSMS. These nanoparticles arrange themselves in a near net-like fashion, resulting in porosity of the flakes of EMD during electrochemical deposition. Thermal studies showed loss of structural water and formation of lower manganese oxides. The EMDMC showed superior discharge capacity of similar to 280 mAh g(-1) as compared to EMDLMO (275 mAh g(-1)) and EMDSMS (245 mAh g(-1)).