Investigation of charge storage mechanisms is of great importance in developing new electrochemical energy storage materials. Here we study the intercalation mechanisms, electrochemical strains and cyclic stability of defective 2-D nanosheet δ-MnO2 electrodes using a combination of high energy X-ray scattering and X-ray spectroscopy. MnO2 nanosheets have a peculiar Mn3+ defect, one that is displaced from the plane of the nanosheet to form a “surface Frenkel” defect. The quantity of sodium ions intercalated correlates with the surface Mn3+ Frenkel defect density as determined by gravimetric and X-ray pair distribution function (PDF) analysis. Electrochemical strain manifests as contractions of the Mn-O bond lengths with increasing charge state, and the data shows that the in-plane Mn-Mn coordination also increases while the surface displaced Mn concentration decreases. This result indicates that the surface coordinated Mn3+ may be extracted from and re-inserted into the plane of the nanosheet during charge/discharge cycling. EXAFS studies of K and Rb intercalation show that there is significant disorder in the local environments around these cations, but do not definitively identify the intercalation sites.