Spin-polarized DFT calculations were conducted using the Vienna Ab-initio Simulation Package (VASP) to evaluate sodium adsorption behavior in pristine and defected graphene/graphite models, as proxies of hard carbon electrodes with various types of local defects. The carbon electrode surfaces were modeled as both monolayer and bilayer graphene sheets. For simulating bulk-like intercalation, the graphite model was employed. Semi-local Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional, and a PAW representation of the wavefunction with a kinetic energy cutoff of 450 eV was used in all simulations. The Brillouin integration was performed using a 3x4x1 𝚪-centered Monkhorst-Pack grid. To capture the long-range dispersion forces between the graphene layers, an empirical DFT-D3 (BJ) energy correction was added and the simulation cells were fully relaxed to reach the energy and force thresholds of 10 -6 eV and 10 -5 eV/Å.