A Cubic Mg2MnO4 Cathode for non-aqueous Magnesium Batteries

The feasibility of cubic Mg2MnO4 (c-Mg2MnO4) cathode for rechargeable magnesium batteries is scrutinized by both theoretical and experimental methods. To exploit the high valence state of Mn4+ upon magnesium insertion in c-Mg2MnO4, we substituted Mn3+ (0.645 angstrom) by the larger Mg2 + (0.72 angstrom) and studied a series of Mg1+yMn2-2y3+ Mn-y(4+) O-4 . The results prove that this Mg/Mn substitution results in a progressive increase of the unit cell parameter a due to the increasement in the average oxidation of Mn. We also distinguish the importance of having Mn(IV) in c-Mg2MnO4 vs. the known Mn(III) in tetragonal Mg2MnO4 (t-Mg2MnO4). The geometry optimization and energy calculations on the c-Mg2MnO4 system are carried out within the density functional theory (DFT) calculations indicating the Mg insertion occurs at 2.23 V with a volume expansion of ca. 8.7 %. Galvanostatic curves revealed a two-step profile with an average voltage of 2.1 V and 160 mA h g(-1) (0.5 Mg2+).

Automated summary

The feasibility of the cubic Mg2MnO4 cathode for rechargeable magnesium batteries is studied using both theoretical and experimental methods. By substituting Mn3+ with Mg2 +, the average oxidation of Mn increases, leading to a higher cell parameter a. The importance of Mn(IV) in c-Mg2MnO4 and the Mg insertion process are highlighted. Galvanostatic curves show a two-step profile with an average voltage of 2.1 V and a discharge capacity of 160 mA h g(-1).