(669a) Crystalline Molybdenum & Manganese Compounds As Cathode Materials for Rechargeable Aluminum Batteries

Aluminum metal is an ideal electrode material for rechargeable batteries because it is low cost, inherently safe, the most abundant metal in the earth’s crust, and has the highest volumetric capacity of any common metal electrode. However, few cathode materials have been successfully paired with aluminum metal anodes in a rechargeable battery, in part due to the challenges associated with the high charge density of trivalent aluminum cations and the highly reactive nature of the chloroaluminate-containing ionic liquids commonly used as electrolytes. Here, investigations of crystalline molybdenum and manganese compounds will be presented as potential cathode materials for rechargeable aluminum metal batteries. Molecular-scale understanding of their charge storage mechanisms will be discussed, revealed by a combination of multi-dimensional solid-state magic-angle-spinning (MAS) NMR spectroscopy, X-ray diffraction, electron microscopy, and electrochemical methods. Intrinsic challenges will be discussed associated with the intercalation and solid-state diffusion of trivalent aluminum-ions. Side reactions between the composite cathodes and the chloroaluminate-containing ionic liquid electrolytes will also be discussed, including potential conversion strategies. The results and analyses contribute to the fundamental scientific understanding necessary to design new cathode materials for rechargeable aluminum metal batteries with improved cycle lifetimes, rate capabilities, and energy densities.