To understand the storage mechanisms during sodiation, ex situ XPDF measurements were tances have been measured with differential PDF and predicted with DFT. For r > ~8 Å, deviations in ∆𝜌(𝑟) 𝑏𝑟𝑜𝑎𝑑 from the predicted Na-C insertion model may be caused by correlations from neighboring Na-Na atoms, the presence of defects such as monovacancies and divacancies, which will alter the relative intensities of the peaks, and C-C correlations that are broader in real space (e.g. disorder in the carbon matrix). However, the simple models for the broad component provide a reasonable match to the experimental data, indicating that a range of structures are present during sodium storage in the slope region, consistent with the literature. To account for the sharp C-C correlations that appear during cycling and are present in Similar C-C expansion values have been reported following sodium insertion in HC and potassium intercalated in graphite. The trend in C-C expansion within the slope region has been rationalized by sodium adsorption at intralayer graphene defect sites. Raman spectroscopy and X-ray diffraction studies indicate that the transfer of charge-compensating electrons to π* antibonding orbitals in graphite layers that accompanies alkaline metal adsorption results in weakening and expansion of the C-C bond. HC-2000 exhibits smaller C-C expansion compared to the lower temperature HCs. This can be rationalized by HC-2000 having the lowest overall defect concentration which results in lower sodium adsorption and thus less transfer of electrons to the carbon. Instead, more electrons transfer to the sodium, which is consistent with our previous XAS data that shows a reduced sodium oxidation state. Within the plateau region, the C-C bond Using DFT calculations, we further elucidate how surface defects alter sodium incorporation energies. At the atomistic scale, surface adsorption at the atop, bridge and hollow sites of pristine graphene are energetically unfavorable (Figure (a), Figure ). We find that sodium adsorption at each of these sites is energetically similar: 0.67, 0.63 and 0.71 eV at the atop/bridge/hollow sites, respectively. However, in the presence of monovacancies or divacancies, the sodium adsorption energies are substantially lowered, -0.99 eV and -0.55 eV, respectively, indicating that interactions between sodium and defected carbon are most favored. This observation, consistent with previous work, underscores the importance of defects in facilitating sodium adsorption. In addition, DFT calculations reveal how intralayer defects, specifically monovacancies, alter sodium incorporation energies in expanded d002 graphite. As shown in Figure (b), the presence of intralayer defect sites makes sodium intercalation more favorable. We define this as the "defect-assisted intercalation" mechanism, in which intercalated sodium ions are coordinated by intralayer defect sites, consistent with previous characterization of defect environments. This mechanism differs from conventional intercalation due to the significantly stronger electrostatic coordination provided by the charge-deficient carbon at defect sites (Figure )). Our DFT results demonstrate that the minimum favorable post-intercalation d002 spacing for defect-assisted intercalation is ~3.6 Å, compared to ~4.2 Å for conventional intercalation. This highlights how defects play a pivotal role in lowering the energy barrier for sodium incorporation, thereby enhancing intercalation in defected carbon structures.