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Abstract A lack of suitable energy storage technologies is arguably the most significant impediment to a modern sustainable energy infrastructure. The storage of chemical energy, in the form of batteries, is a clear solution to the problem. But, modern battery technologies today fail to meet the required metrics for the full electric grid and / or the role of an electric vehicle. There are significent efforts by scientists and engineers in the follow up and study of chemicals to find batteries able, in theory, to outperform current technologies and avoid their safety issues and all shortcomings on it like Li-ion cells. For instance, magnesium ion batteries are thought to be a possible replacement to existing Li-based systems becouse of the high abundance of the elements (Mg is the fifth-most abundant metal on earth), which are non-toxic and do not degrade in air. Magnesium/sulfur (Mg/S) batteries represent a very promising technology for these applications because, in theory, they have a higher theoretical volumetric capacity than lithium/sulfur (Li/S) batteries (2062 vs 3832 mAh cm-3 ) because of the divalent nature of Mg2+ . Most importantly, magnesium does not form dendrites through deposition/stripping process, that is attributed to be the major cause for the safety issue in lithium ion battery and rechargeable lithium battery. However, there are two challenges obstructing the commercial application of the MgS battery, low electronic conductivity of sulfur (S) and formation of magnesium polysulfide species that dissolve into the electrolyte during cycling. Another challenge, the creation of a suitable electrolyte that does not interact with the magnesium anode causing non conducting passivation layers on the surface of Mg which prevents reversibility of the reaction. To address these issues, the following hypotheses are proposed for this study: 1. The sulfur (S) is mixed with the carbon (C) to form a cathode composite with high electronic conductivity. 2. Synthesis and characterisation of polyvinylidene fluoride/ magnesium trifloromethan sulfonate polymer electrolyte and evaluate its performance with MgS battery. 3. Synthesis and characterisation of halogen free electrolyte (HFE) with different concentration of succininitrile (HFE_SN) and evaluate its performance with MgS battery. 4. Introduction of DMSO on the optimised sample of HFE_SN as a trial to change the interfacial structure at the Mg anode surface and facilitates the transport of Mg-ions. The present thesis consists of 6 chapters Chapter 1 gives the overview of fossil fuels, energy storage systems, batteries as energy storage system, type of battery, history of battery, a secondary battery, magnesium rechargeable battery, next-generation batteries, magnesium/sulfur battery, halogen free electrolyte (HFE), and battery characteristics. Chapter 2 gives literature surveys for the previous works in this field. Chapter 3 contains the description of the materials used in this thesis and its physical and chemical properties as well as principles, instrumentations and analytical methods employed in the present study. The physicochemical techniques employed were scanning electron microscopy (SEM), X-ray diffractometer (XRD), energy dispersive Xray analysis (EDS), fourier transform infrared spectroscopy (FTIR), uv-visible absorption spectroscopy (UV), thermogravimetry analysis (TGA), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge-discharge. Part one of chapter 4, is an attempt of studying synthesis and characterisation of polyvinylidene fluoride/magnesium triflate polymer electrolyte for magnesium/sulfur battery application. Magnesium-ion conducting polymer electrolytes (PE) based on polyvinylidene fluoride (PVDF), tetraethylene glycol dimethyl ether (TEGDME) and SN with magnesium triflate (CF3SO3)2Mg salt was synthesised by solution casting method. Fourier-transform infrared spectroscopy (FTIR) shows a composite between the polymer and the (CF3SO3)2Mg salt forms. X-ray diffraction (XRD) data reveals that the broad reflections of the PVDF polymer are reduced with the addition of (CF3SO3)2Mg, with scanning electron microscopy (SEM) illustrating changes in the morphology. The ionic conductivity found to be 2.9x10-5 S cm-1 at room temperature (RT) and the ionic transfer number ݐశమ= 0.4 and 0.8 at RT and 55 oC, respectively. The assembled MgS prototype cell with this polymer electrolyte (PE) delivered very low initial charge and discharge capacity. Protection layer on the surface of Mg anode and dual electrolyte introduced to improve the electrochemical performances of MgS cell. Part two of chapter 4, is an attempt to studying the role of succinonitrile (SN) in optimizing the electrochemical performance of a halogen-free electrolyte (HFE_SN) that is based on magnesium nitrate (Mg(NO3)2), TEGDME and Mg(CF3SO3)2 with different concentration of SN. Introducing a small amount of SN increased the ionic conductivity values 2.8×10-5 S. cm-1 and ionic transference number ݐశమ= 0.8 and 0.9 at RT and 55 oC, respectively of HFE. Low content of SN results in electrolyte with low overpotential and high stable Mg stripping/plating. The MgS cell prototype with this electrolyte delivered a high initial discharge/charge capacity with concise cycle life. The concept of protecting the surface of Mg anode with organic and inorganic interface relatively increases the cycle life of the MgS cell. Part three of chapter 4, is an attempt to change the interfacial structure at the Mg anode surface and facilitate the transport of Mg-ions by introducing different concentrations of dimethyl sulfoxide (DMSO) on the optimized sample of HFE_SN (L1). The as-prepared electrolyte shows high conductivity (b= 4.48 ×10-5 , 6.52 ×10-5 and 9.41 ×10-5 S. cm-1 at 303, 323, and 343 K, respectively) and high ionic transference number ( ݐశమ = 0.91/0.94 at room temperature/55 ºC), for the matrix containing 0.75 ml of DMSO. Also, the cell with 0.75 ml of DMSO shows high oxidation stability, very low overpotential and steady Mg stripping/plating up to 100 h. Postmortem analysis of magnesium electrodes at different electrochemical states reveals the role of DMSO in [ improving Mg-ion passage through HFE by evolving the anode/electrolyte interface at the Mg surface improving Mg-ion passage through HFE by evolving the anode/electrolyte interface at the Mg surface. This electrolyte is expected to achieve excellent performance and good cycle stability when applied in the magnesium battery in future work. |