In the Mn oxide system, we find that comparing values of the site preference index (SPI) across ion-site pairs can predict the preferred ion for a given site and the preferred site for a given ion. The site preference index is a measure of how close a cation's BV sum is to its formal charge, with lower values signifying a more favorable occupation. The results of this inexpensive calculation for 𝛼-MnO 2 (Fig. ) show why K + prefers the 8-coordinated 2b site, whereas Na + and Ca 2+ prefer the 4-coordinated 2a site and Li + , Zn 2+ , Mg 2+ and Al 3+ occupy the smaller 5-coordinated 8h site. They also reveal why, for example, in the 2a site, Na + is preferred relative to Ca 2+ (reflected in their respective insertion voltages) despite its slightly larger ionic radius. The ordering of site preference index values for different ions in the same site rationalize the ordering of the insertion voltages of these cations at low capacity (Fig. ). The trend from lower to higher index values going from Li + to Zn 2+ to Mg 2+ to Al 3+ in the 8h site explains the opposite trend (from higher to lower) in insertion voltages of these ions. At higher capacities, Jahn-Teller distortions and ioninduced structural relaxations, which BV theory does not capture, can complicate the predictive power of this approach. Nevertheless, its success, particularly at low capacities, highlights the electrostatic interactions between cation and site that determine the energy of non-protonic cation insertion into MnO 2 in the dilute limit.