Novel Structural Motif To Promote Mg-Ion Mobility: Investigating ABO₄ Zircons as Magnesium Intercalation Cathodes

There is an increasing need for sustainable energy storagesolutionsas fossil fuels are replaced by renewable energy sources. Multivalentbatteries, specifically Mg batteries, are one energy storage technologythat researchers continue to develop with hopes to surpass the performanceof Li-ion batteries. However, the limited energy density and transportproperties of Mg cathodes remain critical challenges preventing therealization of high-performance multivalent batteries. In this work,ABO(4) zircon materials (A = Y, Eu and B = V, Cr) are computationallyand experimentally evaluated as Mg intercalation cathodes. Remarkablygood Mg-ion transport properties were predicted and Mg-ion intercalationwas experimentally verified in sol-gel synthesized zircon YVO4, EuVO4, and EuCrO4. Among them, EuVO4 exhibited the best electrochemical performance and demonstratedrepeated reversible cycling. While we believe that the one-dimensionaldiffusion channels and redox-active species tetragonal coordinationlimit the value of many zircons as high-performance cathodes, theirunique structural motif of overlapping polyhedra along the diffusionpathway appears instrumental for promoting good Mg-ion mobility. Themotif results in a favorable "6-5-4" change in coordinationthat avoids unfavorable sites with lower coordination along the diffusionpathway and a structural design metric for future Mg cathode development.