| Summary: | There has been significant interest in beyond lithium-ion batteries to accelerate the transition into a net-zero society. Of these, sodium-ion batteries are the most mature ‘rocking chair’ technology, but there are still concerns hindering its scale-up and commercialization, such as the chemical stability of the solid-electrolyte interphase (SEI). In this thesis, fluoroethylene carbonate, propane sultone, enflurane and tetraglyme were used as additives, to create different SEIs, which improved the electrochemical and chemical properties of the battery, compared to the plain system. During cycling the additives were reduced and incorporated in the SEI, managing to improve the cycling capacity, suppress gas evolution and facilitate charge transfer of the cell. The non-sacrificial character of tetraglyme, in contrast to the other additives, coupled with its non-flammability, offers the possibility of a battery with steady, long-term cycling behaviour and improved safety.
Magnesium-ion batteries have attracted a lot of attention due to their high theoretical gravimetric and volumetric energy density but are still at an early stage, with the main obstacle being the compatibility of the Mg negative electrode with the electrolyte solution. In this thesis, I show that Mg cycling is possible in the presence of an interphase layer, which possesses a critical role in achieving stable Mg cycling behaviour. Furthermore, the chemical and structural changes that occur on the electrode surface have been described during the electrochemical conditioning process and cross-sectional analysis of the Mg deposits revealed their internal structure. Finally, symmetrical Mg cells showed small charge/discharge overpotentials, but the interphase stability is still an issue during long-term cycling.
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