Lower defect concentrations in HC produced at high pyrolysis temperatures result in the smaller slope capacities observed in the potential-capacity curves. The observed increase in average interlayer spacing during the slope region has previously been attributed to conventional intercalation, characterized by reversible insertion of ions into the interlayer sites of a host lattice. However, we propose that sodium ions must first insert between the graphene layers to access intralayer defect sites, leading to an increase in interlayer spacing. Finally, we suggest that sodium adsorption at the surface defect sites is most likely to be irreversible, causing capacity losses during initial cycles. This is evidenced by the decrease in the slope capacity region during the second sodiation, the reduction in high voltage storage sites, the absence of two gradients in the slope region, and favorable sodium-ion adsorption energies.