Ambient temperature sodium-ion batteries are emerging as a new chemistry platform for energy storage technologies. Anodes that consist of carbon have been used for this application due to their highly stable and reversible Na cycling nature. In the search of new carbon materials with various microstructure morphologies, we have synthesized spherical carbon particles via an autogenic process. Na-23 MAS solid-state NMR characterization method as a function of the state of charge of carbon was used to determine that these spherical carbon anodes show pure, reversible Na intercalation into graphene regions: these materials are devoid of nanocavity or nanopore filling of Na. This feature and the spherical morphology create low reactivity behavior with the electrolyte which assists in the material's highly reversible (de)sodiation. Specific capacity is 40 mAhg(-1) at a high-rate of 10C (1.5 Ag-1) thus demonstrating that the graphene element in hard carbons contributes largely to the rate capability.(c) 2014 Published by Elsevier Ltd.