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Energy usage has increased substantially in recent years with an estimated global energy production predicted to reach 28 TW by 2050. Currently, approximately 85% of energy is generated from the combustion of fossil fuels such as coal, petroleum products and natural gas, which are neither sustainable nor eco-friendly. Renewable sources such as solar, wind and hydrothermal are alternatives to replace the current non-renewable primary energy source. This renewable energy dominated future leads to a world where energy storage systems need to be efficient to sustain the heavy loads because of increasing energy demands. Currently any renewable energy source must be paired with an energy storage device such as, a capacitor, battery, flywheel, pumped hydro or compressed air, to utilize both the energy produced and to increase the efficiency of the device. As renewable energy devices become more powerful and efficient, so must the energy storage device paired to it. Thin-film MnO2 deposits have exhibited properties that are highly desirable for use as ultracapacitors, due to its exceptional performance, high abundance, cheap production costs and non-toxicity. In this work the layered MnO2 thin-films were produced using a duty cycle method in which a constant potential is pulsed throughout the duration of the electrodeposition, this allowed for both the number and duration of pulses and rests to be varied which has ultimately enabled studying the effect of those factors on the performance of the MnO2 thin-films. The performance of the MnO2 thin-films were then analysed by sweeping the potential between 0.2-0.8 V vs SCE in a solution of 0.5 M K2SO4 for 250 times to observe cycling efficiency and morphological changes after cycles.

This work reports the ϒ-MnO2, and β-MnO2 single wall carbon nanotube (SWCNT) nanocomposite cathode material synthesised successfully by chemical method for lithium-ion batteries. The electrochemical properties galvanostatic charge-discharge, cycle ability, rate performance and cyclic voltammetry were greatly enhanced by using the (SWCNT) composite cathode as a comparison to the pristine ϒ-MnO2, and β-MnO2. As a consequence, the modified (SWCNT) composite cathode material exhibits superior initial discharge capacity 255 mAh g-1 at 0.1C with coulombic efficiency of 99.22% and 118 mAh g-1 at 1C with a capacity retention (coulombic efficiency) of 95.5% (99.9%) after 100 cycles in the potential window of 2.0-4.5V (vs Li/Li+). In comparison pristine β-MnO2 exhibit only 169 mAh g-1 at 0.1C, corresponding to lower initial coulombic efficiency of 97% and 73 mAh g-1 at 1C with capacity retention (coulombic efficiency) of 71.4% (92%) after 100 cycles. The significant improvement in the de-/lithiation kinetic can be accredited to the enhancement in apparent lithium ion diffusion coefficient and electronic conductivity making it more applicable in high power commercialization.

As a population the reliance on portable electronics and rapid development in electric vehicles in order to combat global warming has caused researchers to search for materials that exhibit excellent energy storage properties. Thin film manganese dioxide deposits have been observed to exhibit excellent behaviour and have become a popular research material for electrochemical capacitors and batteries. In this project a method was developed in which the mass change for a thin film of manganese dioxide during electrochemical experiments could be observed. Manganese dioxide was electrodeposited onto a platinum EQCM electrode allowing for the mass change throughout the deposition process to be recorded providing a better understanding of the electrodeposition mechanism. Once the manganese dioxide was prepared the EQCM was used as a working electrode throughout further electrochemical testing which included cyclic voltammetry (CV), step potential electrochemical spectroscopy (SPECS), and electrochemical impedance spectroscopy (EIS) while recording the mass change throughout each test. Cyclic voltammetry was conducted with a 25 mV/s sweep in 0.5 M K2SO4 from 0-0.8V vs SCE for 250 cycles. By doing this the capacitive performance of the material was determined, and by recording the mass change throughout the experiment it was possible to determine if there were faradaic, non-faradaic process occurring on the surface of the electrode affecting the charge storage mechanism and to observe sample stability throughout cycling. SPECS and EIS immediately followed the cycling which allowed for the observation of the maximum charge storage capability of the material and the mechanism in which the material stores charge. The impedance data allows for the analysis of the charge transfer mechanism and the various interfacial resistance and capacitance at the electrode-electrolyte interface. This combination of techniques has allowed for significantly greater understanding of the processes that the electrode materials are undergoing throughout the experiments and can be used as a powerful tool in various aspects of electrochemical analysis.

As a population the reliance on portable electronics and rapid development in electric vehicles in order to combat global warming has caused researchers to search for materials that exhibit excellent energy storage properties. Thin film MnO2 deposits have been observed to exhibit these properties and has become a popular research material for capacitors and batteries. In this project a method was developed in which the mass change for a thin film of MnO2 during electrochemical experiments could be observed. It was conducted by depositing MnO2 onto a platinum quartz crystal, by doing this it allowed for the mass change throughout the deposition process to be recorded providing a better understanding of the deposition mechanism. Once the MnO2 was deposited the EQCM was used as a working electrode throughout further electrochemical testing which included cyclic voltammetry (CV), step potential electrochemical spectroscopy (SPECS), and electrochemical impedance spectroscopy (EIS) while recording the mass change throughout each test. Cyclic voltammetry was conducted with a 25mV sweep from 0 - 0.8V for 250 cycles. By doing this the capacitive performance of the material was determined, however, by recording the mass change throughout the experiment it was possible to determine if there were faradaic, non-faradaic process occurring on the surface of the electrode affecting the charge storage mechanism and to observe sample stability throughout cycling. SPECS and EIS immediately followed the cycling which allowed for the observation of the maximum charge storage capability of the material and the mechanism in which the material stores energy. The impedance data allows for the analysis of the charge transfer mechanism and the various interfacial resistance and capacitance at the electrode-electrolyte interface. This technique has allowed for significantly greater understanding of the processes that the electrode materials are undergoing throughout the experiments and can be used as a powerful tool in various aspects of electrochemical analysis. Figure 1