AbstractTo further understanding of the role of sodium in carbon cathode degradation in Hall–Héroult cells, potential‐energy surfaces and charge‐transfer curves are presented for finite‐size complexes of sodium intercalated between various polycyclic aromatic hydrocarbons. Calculations for lithium and potassium are included to highlight the disparate intercalation behaviour of the alkali metals in graphite intercalation compounds. Static energy barriers from DFT are used to compute macroscopic diffusion coefficients according to transition‐state theory. Comparing the calculated diffusion coefficient to experimental values from the literature sheds light on the role of lattice diffusion of sodium–graphite intercalation compounds in sodium intrusion in graphitic carbon cathodes.