Structural Characterization and Electrochemical Performance of Spinel Oxide Cathodes for High Voltage Mg-Ion Batteries

Abstract

Non-aqueous Mg-ion batteries are a class of next generation batteries that promise high energy densities as an alternative to Li-ion batteries. Materials discovery and development is therefore required to fulfill this promise. MgCrMnO4 solid-solution oxide spinel with suitable redox voltages and facile Mg2+ mobility has been identified as a promising candidate for practical, high voltage cathodes in Mg-ion batteries. Here, we discuss the development of this solid-solution spinel oxide class as a cathode material, novel synthesis methods of these oxide spinels, as well as their electrochemical performance. Mg-Cr-Mn spinel oxides with varying Cr and Mn content were synthesized via conventional sol-gel methods, urea co-precipitation, and layered double hydroxide precursors. High-resolution synchrotron XRD and solid-state nuclear magnetic resonance (NMR) spectroscopy characterization along with electron microscopy indicated that different synthetic routes resulted in structural and morphological differences. This in turn lead to differences in electrochemical performance: overpotentials on charge or discharge, reversibility, and deliverable capacity. Electrochemical results in Mg-ion full cells indicate improved performance (lower overpotentials, higher reversibility, and increased capacity) for MgCrxMn2-xO4 cathodes synthesized via urea co-precipitation. To the best of our knowledge, full cells testing these Mg-Cr-Mn spinel oxide cathodes have not been previously reported.