Effects of temperature and concentration of sulfuric acid on the electrodeposition of grainy electrolytic manganese dioxide

The effects of temperature and the concentration of sulfuric acid on the cell voltage, the anode current efficiency of electrodeposition and the particle size of grainy electrolytic manganese dioxide (EMD) were investigated. The structure, particle size and appearance of grainy EMD were determined by powder X-ray diffraction, laser particle size analysis and scanning electron micrograph measurements. As the concentration of sulfuric acid increases, both the cell voltage and the average anode current efficiency decrease. With the increase of electrolysis temperature in the range of 30-60°C, the cell voltage, average anode current efficiency and particle size decrease. The optimum temperature of 30°C and concentration of sulfuric acid of 2.5 mol/L for electrodeposition of the grainy EMD were obtained. XRD patterns show that the grainy EMD electrodeposited under the optimum conditions consists of γ-MnO₂ and has an orthorhombic lattice structure. According to the results of SEM, the grainy EMD has a spherical or sphere-like appearance and a narrow particle size distribution with an average size of about 7 μm. The grainy EMD is a promising cathode of rechargeable alkaline batteries for high energy density and a prospective precursor for production of the LiMn₂O₄ cathode of lithium ion batteries.