We request 3 days on NIMROD to study the changes in the structure and mesostructure of the anode of a novel high energy-density Na-ion battery during the first charge/discharge cycle. The potential capacity of a Na-ion battery is currently limited by the choice of anode material. With graphite prohibited because, in contrast to lithium, sodium does not intercalate between the graphene layers, hard carbon, with a lower capacity, is one of the next best alternatives. Our principal objectives are to understand (i) the nature of sodium intercalation (given that sodium intercalation does not occur in graphite), (ii) the evolution of Na nanoparticles within the hard-carbon anode and (iii) the comparative rates of these two processes on charging and discharging. NIMROD is the ideal instrument to study these phenomena as (i) and (ii) occur at the atomic level and mesoscale respectively.