SHORT COMMUNICATION Unveiling ionic diffusion in MgNiMnO 4 cathode material for Mg-ion batteries via combined computational and experimental studies H. Shasha 1 & N. Yatom 1 & M. Prill 2 & J. Zaffran 1 & S. Biswas 1 & D. Aurbach 3 & M. Caspary Toroker 1,4 & Y. Ein-Eli 1,4 Received: 10 July 2019 /Revised: 10 September 2019 /Accepted: 10 September 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract 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 MgNiMnO 4 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. Keywords Ionic diffusion . Density functional theory . DFT + U . Mg-ion batteries . Transition metal oxides . Spinel structure Introduction The steady growth in world’ s population along with the on- going improvement in our life quality has led to a rapid in- crease in the demand for energy. The energetic demands place batteries, fuel cells, super capacitors, and other electrochemi- cal power sources in the forefront of the search for sustainable energy sources and storage systems. While Li-ion batteries have become increasingly predominant today, several issues, such as safety concerns, high cost, and limited charge-storage capacity have intrigued the scientific community to perform research on alternative systems. One of the most challenging, yet promising, avenues in mod- ern electrochemistry relates to the development of novel, high energy density systems based on multivalent metals, due to their ability to exchange high amount of charge per weight and vol- ume [1, 2]. Mg possesses several characteristics that place it as one of most promising anode materials for high energy density batteries. Its specific volumetric capacity reaches 3833 mAh/ cm 3 , almost twice than that of the Li metal, and it is highly advantageous for energy storage applications. Together with Mg high natural abundance in the Earth’ s crust, low price of ca $2/kg, [3] and very good safety characteristics (compared to most of other active metals), Mg represents an attractive alternative negative electrode for applications, in which cost and safety con- siderations are very important [1, 4]. Yet, magnesium-based sys- tems pose 3 significant challenges: 1. The incompatibility of Mg-metal anodes with most of possible/relevant non-aqueous electrolyte solutions due to the formation of passivating layers. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10008-019-04401-7) contains supplementary material, which is available to authorized users. * M. Caspary Toroker maytalc@tx.technion.ac.il * Y. Ein-Eli eineli@tx.technion.ac.il 1 Department of Materials Science and Engineering, Technion-Israel Institute of Technology, 3200003 Haifa, Israel 2 Institute of Energy and Climate Research (IEK-2), Forschungszentrum Jülich, 52425 Jülich, Germany 3 Department of Chemistry, Bar-Ilan University, 5290002 Ramat Gan, Israel 4 Grand Technion Energy Program, Technion - Israel Institute of Technology, 3200003 Haifa, Israel Journal of Solid State Electrochemistry https://doi.org/10.1007/s10008-019-04401-7