Energy storage with increased density is required for electronic devices, electric vehicles, and smart grids. Current lithium ion battery technology utilizes cathodes with high voltage and high capacity against a graphitic carbon anode, shuttling Li ions back and forth on charge and discharge in a non-aqueous electrolyte. Alternative strategies to increase energy density are under heavy investigation throughout chemistry, focusing on the beyond Li-ion space. Increasing the energy density at the cell level can be achieved by the use of pure metal anodes instead of carbon, however, dendritic growth from pure metal anodes is a major safety problem. Fortunately, some metals are known to strip and plate without such issues. Mg is one such metal that may also permit solid state intercalation. Here we will probe Mg diffusion in the solid state, typically thought to be too slow for batteries.