Unveiling ionic diffusion in MgNiMnO₄ cathode material for Mg-ion batteries via combined computational and experimental studies

A major challenge in the field of rechargeable Mg batteries is the development of high voltage/high capacity cathode materials. Naturally, a first step in a general search of cathode materials for Mg batteries should be following the plethora of cathode materials relevant to Li-ion batteries. Indeed, several compounds that were thoroughly studied in connection to Li-ion batteries were found to interact reversibly with Mg ions, as well. The functionality of metal ion batteries relies on an efficient ionic transport within the electrodes’ active mass. In this study, we examined the extreme case of the MgNiMnO₄ material, using a combination of computational and experimental techniques. The scientific question being raised in this study was whether Mg ions can be extracted electrochemically from this compound. The experiments provided a negative answer and calculations based on density functional theory (DFT) + U showed that indeed Mg ions diffusion in this material is energetically unfavorable. It was confirmed again how computational work can be very useful in predicting barriers for ionic diffusion in hosts and hence, can save much of tedious experimental works. [Figure not available: see fulltext.]