Molecular Understanding of Ion Intercalation Processes in Rechargeable Aluminum-Carbon Batteries

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One of the great challenges facing the Nation is to develop novel technologies that transform how renewable sourced energy can be sustainably and economically stored on a massive scale. Rechargeable batteries, which store energy electrochemically, have revolutionized consumer electronics. For greater scale applications including electric vehicles and grid-scale storage of renewable energy sources, substantial improvements are required for the performance properties of energy density, lifetime, and cost. Aluminum metal is a potentially ideal battery electrode material because it is earth abundant, non-flammable, non-toxic, low cost, and can store more charge per unit volume than other common metals. Recently, research on rechargeable batteries composed of aluminum metal and carbon electrodes has been published. However, mechanistic aspects of how the battery stores charge within the carbon electrodes are poorly understood. This project seeks to elucidate the fundamental processes underpinning how the carbon electrodes store and release ions and energy, particularly at the molecular level. These scientific insights will be used to design and synthesize novel carbon electrodes that will result in rechargeable aluminum-carbon batteries with improved energy storage properties. For educational outreach, high school and undergraduate students will collaborate with university researchers and receive advanced training on electrochemical systems. This research will be disseminated to a broader audience by high school demonstrations and on the City University of New York (CUNY) TV station, which is publically broadcast across New York City. The overarching objectives of this project are to understand ion intercalation processes in rechargeable aluminum-carbon batteries at the molecular level, and to use these insights to design new carbon electrode structures with improved energy storage properties. Aluminum-graphite batteries using ionic liquid electrolytes will first be studied to reveal insights into the chemical and structural changes that occur within the battery electrolyte and electrode materials as a function of state-of-charge and cycle number. The molecular-level environments, ion speciation and dynamics, and structures of intercalated carbon electrodes will be characterized by multi-dimensional nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), electron microscopy, and other techniques. These properties will be correlated with bulk electrochemical properties and device performance, yielding new multi-scale understanding. Alternative non-corrosive electrolyte systems will be investigated, which will enable studies of how mixtures of different ionic and solvent species participate and/or affect the intercalation processes. Lastly, novel carbon electrodes based on graphene and carbon nanotubes will be synthesized and tested in aluminum-carbon batteries. In particular, the role of local carbon structures and the effects of disorder on bulk electrochemical properties will be understood and controlled to yield improved electrode materials. Answers to the fundamental scientific questions posed in this work will enable researchers to better understand whether aluminum-carbon batteries could become practical energy storage systems.