The HC microstructure ultimately determines the total capacity and the relative capacities of the slope (with its different gradients) and plateau regions. The distinct features of the potential-capacity curve signify that multiple processes are needed to describe sodium storage along a single charge/discharge cycle. It has been established that sodium is incorporated into HC through three main processes: i) adsorption to defect sites at the surface of graphene layers, in graphitic layers, and pore walls, ii) intercalation between graphene layers, and iii) filling of nanopores. Several studies using Raman spectroscopy and DFT calculations have correlated the slope capacity with the concentration of defects in graphene sheets, attributing the capacity in the slope region to sodium adsorption in defect sites, such as monovacancies, divacancies, and oxygen heteroatoms. In contrast, using Raman spectroscopy and X-ray diffraction, other studies propose that sodium intercalation between graphene layers is the dominant storage mechanism within the slope region. More complex mechanisms have also been proposed. Reddy et al., using in situ Raman and DFT, suggested a four-stage sequential mechanism: during the slope region, sodium ions first adsorb onto the active surface sites, then insert and adsorb onto intralayer defect sites before intercalating to fill the interlayers and, finally, filling the pores during the plateau region. Morikawa et al., using ex situ wide-and small-angle Xray scattering (SAXS), proposed a mechanism where sodium ions adsorb during the slope region, then intercalate at the end of the slope region and during the plateau region, and after the maximum intercalation capacity has been reached, sodium fills the pores at the end of the plateau region. More recently, using DFT, X-ray diffraction and electrochemical measurements, Li et al. proposed a two-stage sequential mechanism where sodium ions adsorb in a range of defect sites, such as monovacancies, divacancies, and oxygen heteroatoms during the slope region, and then sodium fill the pores and form quasi-metallic clusters during the plateau region. However, the specific storage mechanisms corresponding to distinct capacity regions, as well as the sequence and details of the diffusion and storage steps remain under debate. Further advancing HC anodes requires generalizable storage mechanisms for each voltage regime that can account for the range of HC microstructures encountered from different precursors (e.g., glucose, lignin, coconut shells, and synthetic resins) and synthesis conditions.