During the second gradient of the slope region, sodium ions insert between the graphene layers to reach intralayer defect sites and defect sites within pore walls, producing an increase in interlayer spacing. This mechanism describes the sodium insertion required to reach defect sites, or "defectassisted intercalation", which is distinct from the conventional intercalation mechanism. The two sequential storage mechanisms that occur during the slope region are corroborated by the observed interlayer spacing shift, expansion of C-C bonds, ∆𝜌(𝑟) 𝑏𝑟𝑜𝑎𝑑 , and DFT calculations which indicate sodium adsorption and insertion in the layers. Within the plateau region, sodium ions simultaneously intercalate between graphene layers and fill the pores with the formation of metallic sodium clusters in the pores. The ratio between pore filling and intercalation, as well as which pores are preferentially filled, depends on the specific HC microstructure. At higher pyrolysis temperatures, larger pores are available and preferentially fill through the formation of larger sodium clusters. For these HC microstructures, pore filling is the dominant sodium storage mechanism when compared with intercalation.