Polyoxometalates are key materials for energy conversion and storage due to their unique chemical tunability and electrochemical reactivity. Herein, we report that functionalization of molecular vanadium oxides, polyoxovanadates, with redox-inert Ca2+ cations leads to a significant increase in their electron storage capabilities. The electrochemical performance of the Ca2+-functionalized dodecavanadate [Ca2V12O32Cl(DMF) 3]2− (={Ca2V12}) was thus compared with that of the precursor compound (H2NMe2)2 [V12O32Cl] 3− (={V12}). {Ca2V12} can store up to five electrons per cluster, while {V12} only shows one reversible redox transition. In initial studies, we demonstrated that {Ca2V12} can be used as an active material in lithium-ion cathodes. Our results show how redox-inert cations can be used as structural and electrostatic stabilizers, leading to major changes in the redox-chemistry of polyoxovanadates