Abstract
The dual effect of in-situ addition of anionic surfactants, sodium octyl sulfate (SOS), sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfate (STS) on the microstructure and electrochemical properties of electrolytic manganese dioxide (EMD) produced from waste low grade manganese residue is discussed. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), BET-surface area studies, thermogravimetry-differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FTIR) were used to determine the structure and chemistry of the EMD. All EMD samples were found to contain predominantly γ-phase MnO2, which is electrochemically active for energy storage applications. FESEM images showed that needle, rod and flower shaped nano-particles with a porous surface and platy nano-particles were obtained in the case of EMD deposited with and without surfactant respectively. Thermal studies showed loss of structural water and formation of lower manganese oxides indicating high stability of the EMD samples. The cyclic voltammetry and charge – discharge characteristics implied the presence of surfactants enhances the energy storage within the MnO2 structure. Addition of the surfactant at its optimum concentration greatly increased the EMD surface area, which in turn improved the cycle life of the EMD cathode. EMD obtained in the presence of 25, 50, 25 ppm of SOS, SDS, and STS respectively showed an improved cycle life relative to the EMD obtained in the absence of surfactant. EMD obtained without surfactant showed a capacity fade of 20 mAh g−1 within 15 discharge-charge cycles, while surfactant modified samples showed stable cyclic behavior of capacity 95 mAh g−1 even after 15 cycles.
Highlights
Global demand for new energy materials and energy storage devices is increasing rapidly and in parallel with the quest for alternative energy resources
The surfactant free bath yields Electrolytic manganese dioxide (EMD) with a current efficiency (CE) of 94% and energy consumption of 1.640 kWh kg−1, and with the introduction of surfactant the CE increases to a maximum level before decreasing on addition of excess of surfactant
It is worth noting that during EMD deposition at high temperature, hydrogen gas liberated at the cathode carries acidic mist to the air, which is hazardous to health and may cause damage to the environment, at an industrial scale of EMD production.[32]
Summary
Global demand for new energy materials and energy storage devices is increasing rapidly and in parallel with the quest for alternative energy resources. Manganese dioxide, used as the active material in Zn-MnO2 batteries, can be prepared both by chemical synthesis (chemical manganese dioxide, CMD) or electrochemical deposition (electrodeposited manganese dioxide, EMD) methods. Adequate primary Mn resources are available from which manganese dioxide can be produced, but the rapidly growing demand for manganese/manganese oxide has made it increasingly important to develop processes for economic recovery of manganese from low-grade manganese ores and other sources.[5] In order to fulfill the escalating demand of EMD for its application in rechargeable batteries and super capacitors, production of EMD from secondary resources is of great importance. Due to the rising demand for EMD, continual efforts are underway to find alternative sources from which EMD can be produced with better electrochemical performance
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