Laura Merrill

Chemical and Biomolecular Engineering

Faculty Advisor: Dr. Jennifer Schaefer

The Role of Morphology and Electrochemical Interface on the Electrodeposition/Dissolution Efficiency of Magnesium Batteries

The environmental impact of fossil fuels, including difficulties with CO2 capture, has led to the development of hybrid and electric vehicles. Rechargeable batteries are an integral part to the success of these technologies, and lithium-ion batteries are dominating the field of electrochemical energy storage. Despite the decrease in fossil fuel usage, electric vehicles are not necessarily environmentally friendly nor sustainable for the long-run given the current state-of-art of battery technologies. Lithium-ion batteries rely on materials that are not readily abundant nor easily recyclable. The majority of lithium reserves are contained in seawater and brine; exacting lithium from seawater is energy intensive and the projected amount needed would rely on improvement of current  technologies. Recycling lithium would lower the demand of raw materials, but there is currently only one commercial lithium recycling site in the United States. Common Li-ion intercalation cathodes contain materials such as cobalt. However the world’s main supplier, the Democratic Republic of the Congo, has faced many health and environmental problems since the rise of electronic devices, due to unsafe working conditions and water contamination. To mitigate these environmental risks, alternatives to intercalation electrodes and lithium-based batteries are under development. Magnesium metal is of interest for use as an anode material due to its large volumetric capacity (3833 mAh/cm3 versus 2026 mAh/cm3 for lithium) and widespread abundance. Magnesium can be recovered from a wide range of resources and is considered to be “virtually unlimited” by the US Geological Society. Because of magnesium’s abundance and widespread use, it is readily recyclable. However, magnesium metal cannot be used in place of lithium in an analogous battery system. Magnesium metal anodes are very sensitive and form a passivating layer in the presence of common salts, solvents, and trace impurities (water), which renders the battery nonrechargeable. Common electrolytes that enable highly reversible magnesium electrodeposition (charge, deposition; discharge, dissolution) use highly flammable compounds such as THF and Grignard reagents. Research efforts have focused on developing electrolytes with increased thermal stability and decreased corrosiveness in order to lead to the eventual application of magnesium batteries; despite these efforts, the magnesium deposition efficiencies are often compromised (< 80 %). My research project addresses the electrolyte/anode interface and altering the electrolyte chemistry to study the effect on battery operation. The emphasis of my research is on developing electrolytes that can maintain high electrochemical performance (measured by parameters such as electrochemical stability and electrodeposition/dissolution efficiency), while focusing on changing the corrosiveness and thermal properties of the electrolyte to make it more suitable for practical application. Recently, we demonstrated that a solvent mixture of butyl sulfone and THF can significantly increase the thermal stability of an electrolyte while maintaining efficiencies above 90 %. However, the deposition quality and interfacial chemistry between the solvent and the substrate are hypothesized to impact the efficiency of magnesium electrodeposition/dissolution. Furthermore, due to the reactivity of the magnesium surface, the library of solvents that can be used with high efficiency is limited. Therefore, we are also pursuing work on engineering an interphase on the magnesium anode that prevent decomposition on the electrode surface thus leading to increased efficiencies.