REACTION MECHANISMS AND INTERFACE CHARACTERISTICS OF ELECTRODE AND ELECTROLYTE MATERIALS FOR MAGNESIUM BATTERIES
Lee, Sang Bok
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Rechargeable magnesium (Mg) batteries are an emerging electrical energy storage technology proposed as an alternative to current Lithium-ion (Li-ion) batteries. Mg batteries have the potential to provide more energy than current Li-ion systems due to the high volumetric capacity and low reduction potential of Mg metal, in addition to higher abundance and cheaper cost of Mg compared to Li metal. However, there are many challenges regarding Mg battery chemistry and materials that must be resolved before they can be successfully commercialized. The work in this dissertation addresses a few of these challenges, including poor Mg2+ diffusion in MnO2 cathodes, interfacial limitations at the Mg anode and MnO2 cathode surfaces, and the development of solid-state electrolytes as an alternative to liquid electrolytes that passivate the Mg anode interface. These issues are investigated from a fundamental chemical and electrochemical standpoint to help improve future design of rechargeable Mg batteries. In the first study, the electrochemical reactions and charge storage mechanism of electrodeposited MnO2 cathodes in water-containing organic electrolyte are explored using X-ray photoelectron spectroscopy. These results demonstrate the key role that water plays in enabling the reversible insertion/extraction of Mg2+ from the MnO2. Second, a heterogeneous electrode structure, PEDOT/MnO2 coaxial nanowires, is utilized to study the effect of conductive polymer surface layers on the MnO2, specifically regarding the effect on the cathode’s cyclability and power performance as well as the overall charge storage mechanism. Additionally, to investigate the potential for anode protection on Mg metal, ALD Al2O3 is deposited on different Mg metal substrates to determine whether it can improve Mg deposition and stripping at the Mg anode and prevent electrolyte degradation on the Mg surface. While it does not demonstrate the ability to effectively protect the anode during cycling, the results herein can help inform further protection layer development. Finally, the catalytic ability of Mg2+ salts is reported for the ring-opening polymerization of 1,3-dioxolane, moving toward exploring this polymer’s potential to be utilized as a solid-state electrolyte. The findings here give fundamental insights into materials’ properties that can be further utilized to design Mg batteries with high-voltage cathodes.