Our study indicates that during the plateau region, there is simultaneous sodium intercalation and pore filling, with the relative contribution of these mechanisms depending on the HC microstructure. At lower pyrolysis temperatures, the combination of larger interlayer spacing, lower volume fraction of pores, and smaller pore volumes results in Na intercalation being the dominant storage mechanism. A larger contribution from intercalation is consistent with fewer pores filling during the plateau, as we previously reported. Furthermore, smaller sodium clusters formed at lower pyrolysis temperatures are consistent with the preferential filling of smaller pores. At higher pyrolysis temperatures, smaller interlayer spacing and larger volume fraction and pore volumes make it more difficult for sodium ions to intercalate. This produces a higher fraction of sodium stored in closed pores as metallic clusters, consistent with the Na-Na correlations in ∆𝜌(𝑟) 𝑏𝑟𝑜𝑎𝑑 as well as our previous findings from XAS and operando SAXS experiments.